CA1268055A - Centrifuge overspeed protection and imbalance detection system - Google Patents
Centrifuge overspeed protection and imbalance detection systemInfo
- Publication number
- CA1268055A CA1268055A CA000509849A CA509849A CA1268055A CA 1268055 A CA1268055 A CA 1268055A CA 000509849 A CA000509849 A CA 000509849A CA 509849 A CA509849 A CA 509849A CA 1268055 A CA1268055 A CA 1268055A
- Authority
- CA
- Canada
- Prior art keywords
- rotor
- frequency
- signal
- centrifuge
- speed
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/08—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors
- H02H7/093—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for dynamo-electric motors against increase beyond, or decrease below, a predetermined level of rotational speed
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
- B04B—CENTRIFUGES
- B04B13/00—Control arrangements specially designed for centrifuges; Programme control of centrifuges
- B04B13/003—Rotor identification systems
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B04—CENTRIFUGAL APPARATUS OR MACHINES FOR CARRYING-OUT PHYSICAL OR CHEMICAL PROCESSES
- B04B—CENTRIFUGES
- B04B9/00—Drives specially designed for centrifuges; Arrangement or disposition of transmission gearing; Suspending or balancing rotary bowls
- B04B9/14—Balancing rotary bowls ; Schrappers
- B04B9/146—Unbalance detection devices
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S388/00—Electricity: motor control systems
- Y10S388/907—Specific control circuit element or device
- Y10S388/912—Pulse or frequency counter
Abstract
CENTRIFUGE OVERSPEED PROTECTION
AND IMBALANCE DETECTION SYSTEM
Abstract A centrifuge overspeed protection and imbalance detection system is structured to provide a method for detecting rotor imbalance and rotor overspeed. The system has a single transducer to provide real-time data necessary to detect rotor imbalance and control motor speed.
Motor speed is controlled by synthesis of a drive frequency signal for driving the inverter motor control. The drive frequency signal may be inhibited to provide slow acceleration or deceleration, or to shut the motor off by providing a zero slip frequency. Motor control is responsive to a Rotor Identification circuit and operator programming, as well as a closed loop response to the real time tach signal.
Imbalance detection is provided by counting tach pulses in each of a plurality of intervals, detecting deviations in tach pulse rate and sounding an alarm when the irregularity of tach pulse signals exceeds the limits of a predetermined standard deviation.
AND IMBALANCE DETECTION SYSTEM
Abstract A centrifuge overspeed protection and imbalance detection system is structured to provide a method for detecting rotor imbalance and rotor overspeed. The system has a single transducer to provide real-time data necessary to detect rotor imbalance and control motor speed.
Motor speed is controlled by synthesis of a drive frequency signal for driving the inverter motor control. The drive frequency signal may be inhibited to provide slow acceleration or deceleration, or to shut the motor off by providing a zero slip frequency. Motor control is responsive to a Rotor Identification circuit and operator programming, as well as a closed loop response to the real time tach signal.
Imbalance detection is provided by counting tach pulses in each of a plurality of intervals, detecting deviations in tach pulse rate and sounding an alarm when the irregularity of tach pulse signals exceeds the limits of a predetermined standard deviation.
Description
~i8~:355 8D-438 Canada CE~TRIFUGE OVERSPEED PROTECTI02 A~D IMBALANCE DETECTIO~ SYSTEM
-Field of the Invention _ This invention relates to an automatic control system for regulating the operation of a centrifuge and, in particular, to a system for providing centrifuge overspeed protection and imbalance detection and a method for the system's implementation.
Background of the Invention Centrifuge operation presents a unique set of design criteria where precision control of the rotational operation of the cen-trifuge is required. The wide variety of biological and chemical experimental research which use centrifugation as their primary tool to achieve component separation and perform experimental assays places a requirement of versatility on the operational characteristics which must be built into the centrifuge.
m e centrifuge rotor is driven to extremely high rotational speeds in order to genera-te the centrifugal field required for biological research use.
The high rotational speeds of the rotor cause a severe build-up of kinetic energy, which if released, can lead to destructive explosion of the centrifuge and injury or damage to its surrounding environment as well as the human operator. Centrifuge rotors typically can fail if the rotor is run in excess of the speed designed for its safe operation. The slightest imbalance of the rotor or load which it carries can cause catastrophic failure.
~ le centrifuge apparatus has numerous rQtors which may be interchangeably used in conjunction with the same centrifuge motor and drive shaf-t in order that a : . .
..: ... :
- .':: : :
. . ,., :: .
BV~:~5 diversity of biological experimentation may be achieved. One standard of centrifuge design encompasses an induction motor and shaft which can accommodate the interchangeable rotors to be carried on the spindle of the motor shaft, each rotor having a different weight and strength of material and a different maximum safe speed above which the particular rotor should not be operated.
Also, even the slightest imbalance of the rotor or load which it carries may grow to larger imbalances and associated forces as the rotor speed and centrifugal field increases. Often, these imbalances do not arise until the rotor has achieved very high speeds. Strain and stress within the material of the rotor exhibiting a slight fracture at rest can cause the rotor to dismember at maximum speeds approaching 100,00~ revolutions per minute. The dynamic effect of any imbalancing forces cause complicated movement of the shaft upon which the rotor is suspended, such as dangerous whirls and ~yrations.
It is therefore clear that a versatile centrifugation system requires: (1) a maximum safe rotor speed be identified for each rotor; (2) the operational use and control of the rotor during centrifugation be monitored and controlled; and, (3) that any imbalance be detected. If possible, the use of a single sensor and transducer system would provide accuracy and asynchronous information which may be used to control the motor speed for all varieties of rotors.
One such system is disclosed in applicant's United States Patent No. 4,551,715, issued November 5, 1985, naming Durbin as inventor. In the disclosed specification, a method of rotor identification for each rotor and determination of rn/
, . ,~ ~. .
.. ,,, : , , .
~`805~
the rotor's maximum safe speed is presented which relies on a single magnetically sensitive transducer to provide the necessary rotor identification and maximum safe speed information in a straightforward and precise manner.
The disclosure of U.S. Patent No. 4,551,715 describes an improved signal processing circuit which allowed a tachometer signal and rotor identification signal to be generated from a single set of coding elements on the rotor.
The patent uses a circular array of magnetic coding elements on the rotor to provide the tachometer and rotor identification information. ~ Hall effect sensor is u~ed to detect the magnetic orientation of permanent magnets imbedded in the base of each interchangeable rotor. In the preferred embodiment of Durbin, six magnets spaced at equal intervals around the circumference of the rotor are positioned to direct a north-oriented or south-oriented magnetic field outward from the base of the rotor for detection by the Hall effect sensor. The Hall effect sensor detects a change in magnetic reluctance as the permanent magnet rotates past the fixed sensor and induces a voltage in the sensor. A series of sharply defined pulses are generated in the conduction pathway and amplified in the Durbin system. Thus the Durbin disclosure presents an embodiment which is able to identify a rotor on the basis of a single transducer accordiny to the combination and order in which north- and south-oriented magnets pass the Hall effect rotor. These same north and south pulses also produced a tach signal from which rotor speed can be identified. A central processing unit i5 used to compare rotor speed with rotor identification. Stored in the rn/
8D-438 Canada ~ 05S
central processing unit is an informa-tion listing identifying the maximum rated speed for each individual rotor. Once the rotor is identified on the basis of a coded pulse train generated by the north- and soutll-oriented magnets imbedded within the ro-tor, the central processing unit reads the maximum rating information stored within its memory and compared these readings with the actual speed. The central processing unit also is aware of what had been programmed at the human operator keyboard for the desired acceleration and speed. The central processing uni-t functions to prevent the rotor from being programmed or actually operated beyond its intended rating. The magnetic transducer detection system represented a significant improvement over optical sensing systems which were subject to interference from dirt and damage, as well as inadvertent customer abuse when the wrong optical rotor disc was affixed to a rotor rated for a lower speed.
Conventionally, motor control has been achieved in centrifuges by controlling the current or power to the induction motor which drives the rotor and shaft. Such current control may be disconnected or otherwise not be communicating with the centrifuge current bus. U.S.
Patent No. 4,286,203 to Ehret issuing August 25, 1981 to Beckman Ins-truments, Inc., the common assignee with this application, discloses a Slip Frequenc~ Control System for Variable S eed Induction Motors. This paten-ted - P
system controls rotor speed by maintaining a constant slip frequency regardless of motor speed. It is generally directed at normal operating conditions and drives the motor in response to an initial fixed frequency produced by relaxation oscillator 20. The system disclosed in the patent is not designed to respond to abnormal conditions such as rotor overspeed or imbalance.
-8D-438 Canada ~55 What is clearly needed to insure centrifuge safety and sample integrity is a method of controlling the speed of the induction motor of a centrifuge through use of the inEormation derived from the tach signal pulse train.
Additionally, it would be useful if imbalance detection could be effectuated to prevent imbalances which occur at high speeds from causing great destruction. The conventional art of centrifugation provides an electromechanical imbalance detector in the form of a microswitch which sits in proximity to the rotor shaft in order to detect whirling gyrations which may occur in the rotor shaft. The rotor shaft is fitted with a radially extending nub. A spring mounted microswitch adjacent to the nub of the spindle shaft makes contact if the shaft wobbles excessively. This causes the capacitor to be discharged and triggers a digital signal at the output of a monostable multivibratcr providing an active low pulse to the microprocessor. This detection system has worked fine at speeds below 30,00~ r.p.m., but unfortunately is not sufficiently responsive to detect imbalance during high speed rotation.
What is clearly needed is a sensor detection system which not only identifies individual rotors and their maximum safe speeds, but also controls their speed, monitors their speed, and detects rotor imbalance.
Summaxy of the Invention The present invention is a method and system for controlling and monitoring the speed of a centrifuge which rotates at ultrahigh speeds. Additionally, the method and system disclosed provides for the detection of ' . ,, ... .. .. .
8D-438 Canada ~ 5~
rotor imbalance and a means for sounding an alarm when the rotor speed or imbalance exceed predetermined value ranges.
In particular, a system for controlling and monitoring the rotational speed of a centrifuge ro-tor is disclosed. An electronic sensor detects the actual speed of the rotor asynchronously and on a real-time basis by driving a tach signal pulse train and providing this pulse train to the input of a phased lock loop frequency adder for combination with a computer derived slip frequency. During certain predetermined ranges, the frequency adder adds the slip frequency to the tach signal and derives a drive frequency which is sent to the Johnson counter of an inverter. The inverter in turn produces a three phase control signal for controlling the induction motor which drives the high speed centrifuge rotor. This closed loop system involves the creation of a slip frequency by converting the tach signal to a computer readable digital -format. Operator keyboard program and rotor identification circuit information are analyzed within the microprocessor o the central processing unit along with the converted tach signal information. These informational inputs to the central processing unit are combined to derive a slip frequency. The slip frequency is determined by passing a pulse train through a ~requency synthesizer which produces a frequency at the desired slip rate in accordanc~ with known formulations to maintain an optimal percentage of slip and yet accommodate operator keyboard program and Rotor Identification input. The slip frequency thus derived when added to the tach signal produces a drive frequency which controls the inver-t~r and the induction motor.
8D-438 Canada ~'~5~
During those periods in -the rotor acceleration cycle where it is not desirable to add the tach signal to a slip frequency, but simply generate a control signal directly from the computer, an override control signal is imparted to -the inverter to overtake and control the timing of the motor. This signal occurs generally during initial acceleration and final deceleration, as well as those circumstances where other safety problems are detected in the system, such as temperature exceeding predetermined limitations during rotor operation or rotor imbalance.
~ system for detecting rotor imbalance includes obtaining the tach signal pulse train derived from a sensor input and converting that signal to a CP~ readable foxmat. Various intervals of signals are counted to determine frequency and frequency deviations. If from one interval to another, tach signal frequency deviates substantially, a rotor imbalance is detected. Such irregular signals are an indicia-tion that the rotor has tilted away from the sensor, causing the Hall sensor to not detect all six magnets per revolution. In this manner, imbalance may be detected and an alarm override signal may be sent to the inver-ter to shut the motor down.
The invention also comprises a method for detecting high speed rotor imbalance and controlling and monitoring rotor speed. This method includes deriving a tach signal pulse train that corresponds to actual rotor speed;
converting the signal derived for analysis by a central processing means; comparing the actual signal with operator programmed acceleration instructions as well as information concerning the upper limits of acceleration from the Rotor Identification circuit; deriving from those sources of input a slip frequency which, when added .. . .
.~ .
: ~:
8D-438 Canada to the actual tach signal rotor frequency, produces a drive frequency for controlling the induction motor o~
the centrifuge motor. Additionally, a method is disclosed for detecting rotor imbalance by deriving a train of tach signal pulses; converting those pulses to a -format intelligible to a cen-tral unit; determining the frequency of pulses received during a variety of intervals; comparing the frequency derived at one time interval with the frequency derived at another time interval (with the expected frequency due to uniform acceleration accounted for) and producing a deviation frequency which corresponds to the difference in frequencies between the impulse; comparing the deviation frequency derived with a preset reference to determine whether the frequency deviation exceeds safe limits;
producing an override control signal to shut down the inverter and induction motor when preset limits are exceeded, thereby detecting rotor imbalance at high speeds.
Brief Description of the Drawin~s Figure 1 is a schematic-block diagram of a preferred embodiment of the centrifuge overspeed protection and imbalance detection system which is the sub~ect matter of this invention;
Figure 2A is a perspective view of the rotor showing one of the six magnets physically positioned at the base o-f the rotor in relation to the Hall Effect detector;
Figure 2B is a side view of the rotor operational mounted on a shaft, where the rotor base is slightly off its proper orientation indicative of rotor imbalance;
....
- . . . .
;. . . :- ~ . :
... ~ , . ..
. ., ,~ .
8D-438 Canada .~ 2 ~;~ 0 ~ 5 _g_ Figure 3 is a graphic representation of the relationship between slip frequency and rotor speed during the centrifuge operating cycle of the invention;
and, Figure 4 is a graphic xepresentation of rotor speed as a function of time during the centrifuge operating cycle in accordance with the invention.
Detailed Descri~ion of the P_eferred Embodiment With reference to Figure 1, there is disclosed a system by which information provided by -the tach signal pulse train may be utilized to control an induction motor and protect against overspeed and rotor imbalance.
me induction motor 12 has a spindle shaft 14 upon which an individually selected rotor 16 may be affixed. The underside plan view of the rotor 16 is represented by a flat circular surface having a plurality of magnets 20 imbedded therein. When driven by the induction motor 12, the rotor 16 revolves past the Hall effect sensor 18. The sensor 18 is able to detect changes in magnetic reluctance occurring when permanent magnets 20 pass the transducer surface of the ~all effect sensor 18. Figure 2A shows the flat circular base surface 82 of the rotor 16. m e permanent magnets 20 are embedded in the rotor base 82 and rotate past the Hall Effect sensor 18 as the rotor 16 turns.about its own axls .
The output tach pulse from the Hall effect sensox 13 (Figure 1) is conveyed through capacitor 22 in order to filter out unwanted D.C. noise, resulting in a waveform as shown at 24. As is apparent, waveform 24 compxises positive-going pulses representative of north-oriented magnets as well as negative-going pulses ~"_ , . ~, .: ,, : ,:. : ' :'' : :.:::.. ,:: . , - ::
8D-438 Canada -10- 1~8V55 representative of south ~agnets 20. This signal is then amplified by amplifier 26. ~le output of amplifier 26 is operatively fed to the inverting input of two separate operational amplifiers 28 and 30. ~le north signal first passes through inverter 32 so that the output at both operational amplifiers 28 and 30 will be signals of the same negative transition. South and north signals are distinguished by the Rotor Identifica~ion (I.D.) circuit 34 since within the Rotor Identification circuit 34 north and south pulses are counted separately. Additionally, the output signals from operational amplifiers 2~ and 30 are coupled to the input terminals of exclusive OR gate 36. Exclusive OR gate 36 triggers a pulse each time a north or a south signal is developed at either of its input terminals. The counters within Rotor Identification circuit 34 are triggered by the leading edge of the negative pulse produced at the output of exclusive OR gate 36. ~le output of exclusive OR gate 36 is tapped and the output pulse signal derived is coupled through the inverter gate 38, in order to produce the tach signal pulse train 40 as shown. This pulse train is the same pulse train produced and disclosed in the Durbin patent .
~ uniqu~e feature o~ this invention is the use of the pulse train shown at 40 to provide overspeed-protection and high speed imbalance information to the central processing unit (CPU) 42. In the conventional art, the central processing unit 42 controls the operation of the induction motor 12 by directly controlling the power inverter 50. Conventionally, the central processing unit 42 genera~ed a digital current command signal 68 which, when processed through a digital-to-analog converter ~4, produced an analog voltage which is capable of driving the power inverter 50 through Johnson counter 72. Current control may be used ;,~ i. . - --:,, ; ' :
8D-~38 Canada ~ 5S
to control the operation of the induction motor 12 by c~scading the voltage upward during acceleration and downward during deceleration while constantly maintaining the current at a level sufflcient to overcome the counter e.m.f. of the induction motor 12, driving -the mo-tor 12 up to an optimal and efficient operational mode. This ~orm of conventional current control of induction motor 12 has a disadvantage when it is the sole means of control. The current control line can be disrupted causing the current to rise. Loss of current control will result in driving the rotor to dastructive speeds or in the overheating and destruction of the induction motor. Even if the rotor identification circuit 3~ communicates to the CPU 42 that the rotor is rated below the speed that the current bus drives it, a severing of the current con-trol system may result in a rotor being driven overspeed and substantially damaging the centrifugation chamber. One reason this may occur is the fac-t that the digital current command signal system is designed to monitor actual current fed to the inverter 50 by means of an optical sensing system (not shown) which optically isolates the bus power supply from the digital current command signal. However, if for example -the current feedback phototransistor (which reads the "~ED" of the current bus) breaks down, the computer may continue to drive the digital current command signal upward in the absence of the actual current feedback, resulting in possible rotor destruction or induction motor 12 burnout.
The conven-tional art has heretofore taught the generation by the central processing unit of a fixed frequency reference which will serve as the basis of a synthesized frequency control system~ Such a fixed frequency signal may not accurately reflect operating conditions. A single fixed fre~uency signal, even when synthesized by the central processing unit, may lack the :.
. .
' . ~ ' ,, .
~D-438 Canada ~ 55 real time flexibility required to adapt the system to the wide range of interchangeable rotors which may be used by the human operator.
The invention provides a frequency drive signal controlling of the induction motor by means o~ a closed loop system which asynchronously monitors the actual tach signal and adjusts the control signal accordingly.
An improved motor control system by using a drive frequency control signal is provided in the preferred embodiment by simultaneously inputting the tach signal pulse train 40 into a pulse counter and tach signal converter 46 and a phase locked loop frequency adder 48. The frequency drive signal control system generally provides real time tach signal information to the cen-tral processing unit 42 which uses this information, as well as other informa-tion, to produce a drive frequency control signal. ~e tach signal pulse train 40 is imparted to the pulse counter and tach signal converter 46, which in the preferred embodiment is a programmable counter programmed to operate as a "Divide-by-N" counter. The pulse counter 46 may be a programmable interval timer manufactured by Intel Corporation of Santa Clara, California as Model 8253.
Bidirectional bus 52 provides a pathway for the pulse counter 46 to inform the central processing unit 42 as to the number of pulses counted during a pre-programmed time interval (N). Essen~ially, the pulse counter 46 converts the tach signal pulse train into at least two eight-bit digital words which the central processing unit 42 can store in its memory and use as a basis ~or ~ur-ther instructions. A crystal controlled clock 54 provides an extremely stable six megahertz frequency signal to the central processing unit and a timing signal o~ three megahertz (or approximately one hal~ that provided to the ' .: ,.. ,:~ ' :
;,; ,, ~ ~
~' 8D-43~ Canada -13- ~ 55 central processing unit 42) to the pulse counter 46, the frequency s~nthesizer 56, and the latch circuit 5~ Tach signals provided to the pulse counter 46 are additionally coupled to the flip-flop latch 58 for output to the frequency synthesizer 56 according to clock signal produced by the crystal controlled clock 54. Thus, tach signal rotor speed information is provided to the central processing unit 42 by the pulse counter 46 in the form of an eight-bit digital words. The tach signal 40 is also provided to the frequency synthesizer 56 as a conditioned signal through the latch 58 by way of the counter 46.
The pulse train is coupled to the synthesizer 56 in synchronization with the central processing unit 42 by the crystal controlled clock 54. The central processing unit 42 may subsequently send instructions along unidirectional bus 60 to the frequency synthesizer 56 to produce a slip frequency (fs) which is coupled to the frequency adder 48, a phase locked loop integrated circuit in the preferred embodiment. The frequency adder may be the CD40~6A COS/MO~ Integrated Circuit manufactured by RCA Solid State Division, RCA
Corporation, Somerville, N.J.08876. The frequency synthesizer 56 produces an output frequency, fs~ which is equal to the Erequency received from latch 58 divided by the "N" number provided by CPU 42. The frequency synthesizer 56 may be a "Divide-by-N" counter sold by Intel Corporation as a Model 8253 Programmable Interval Timer.
Induction motors require that there be some slip or difference between the drive speed provided by the inverter 50 and the actual speed which the rotor is able to run. (Actual speed is detected by this system as the tach signal pulse train 40.). For example, if an optimum operation of the induction motor 12 require that at a 10,000 revolutions per minute (RPM) drive speed, the .
.. :.~' ~ ' ''' -.
~ ~ , ., , . ' . ,'. ': .
8D-438 Canada ~2~0~, induction motor actually operates at 9800 revolutions per minute, then a slip frequency of 200 ~.P.M~ might be necessary to provide the torque to keep the induction motor running. As speed is increased, the percentage of slip must be maintained and the slip frequency must be increased. For smooth motor operation, slip Erequency should be kept at a relatively constant percentage of the drive control frequency driving the induction motor.
Thus, the ideal drive frequency is one which is increased by adding the actual tach signal frequency, derived from a tach signal pulse train such as 40 and adding that signal to a slip frequ~ncy (fs) 66 computed to maintain a fixed percen-ta~e but driving the induction motor :L2 at a Easter speed.
As a further example, assume -that the human operator, by use of the operator keyboard progra~ 62, has instructed the central processing unit 42 to accelerate the rotor in a linear fashion over the range of 1500 revolutions per minute up to 2,000 revolutions per minute. In order to carry out the opera-tor program instructions, the central processing unit must sense the actual rotor speed which it receives in a digital form from pulse counter 46. Once the central processing unit is informed that a speed of 1500 revolutions per minute has been achieved, it then executes the operator program by instructing the frequency synthesizer 56 to increase the slip frequency (fs) over a fixed period, so that the actual rotor frequency will increase from 1500 revolutions per minute to 2,000 revolutions per minute.
If, for 1500 revolutions per minute, the computer central processing unit 42 was ins-tructing the frequency synthesizer 56 to produce one pulse output for every three pulses input from latch 58 for a standard time interval, the new instruction would cause the Erequency synthesizer 56 to produce one a pulse for every four 8D-438 Canada 15 ~2'~
pulses which are latched from flip-flop in -the same standard time interval. The slip frequency would be increased 30% above the frequency needed to produce optimal slip at 1500 RPM, so that the new slip frequency produced to achieve 2000 RPM would represent a constant percentage of slip. In this manner the slip frequency may be changed to suit the pre-programmed requirements of the human operator.
In -the preferred embodiment, the drive frequency control system operates to initially accelerate the rotor to 5,000 revolutions per minute by ramping up both the drive current and the drive frequency with time in accordance to the pre-programmed instructions of the human operator. ~e system analyzes the tach signal 40 to ascertain the regularity of pulse rate before the rotor is allowed to accelerate as programmed up to 5,000 revolutions per minute. Once the rotor reaches an actual tach signal frequency indicating 5,000 revolutions per minute, the drive frequency signal 64 which is derived from the output of the phase locked 1GOP frequency adder 48 is the sum of the synthesized slip frequency 66 (fs) and the tach signal pulse train 40. The slip frequency selected is pre-programmed in the operating system for optimum electrical motor efficiency for the particular instantaneous speed achieved. The slip frequency is not uniform over the range of 5,000 revolutions per minute up to 100,000 revolutions per minute; however, the percen-tage slip is maintained as a constant percentage of actual speed to achieve greatest motor efficiency.
Control through operator keyboard program 62 is relinquished above the 5,000 revolutions per minute range. Additionally, the digital current command signal 68 varies motor current to maintain desired set speed ~le phase locked loop frequency adder 48 is used to provide a stable frequency which represents the sum of . :, -.. ~ . ~ .
..
. .
. . .
.
8D-438 Canada ~ ~ t~ 0~3 the tach signal plus the slip frequency, to achieve optimum motor torque over the entire range of motor operation. The inverter 50 is driven by the Johnson counter 72 to produce a -three-phase control signal 76 to control the induction motor 12 in a closed loop fashion.
During normal operation above 5,000 revolutions per minute, the drive frequency provided to the input of NOR gate 70 is imparted to Johnson counter 72 for driving the induction motor by generating a three-phase control signal 76. For speeds below 5,000 revolutions per minute, or during breaking deceleration, or in the event that an imbalance is detected or another alarm condition has been indicated to the central processing unit, the phase locked loop override control signal 74 triggers the output of ~OR gate 70 to disable the drive frequenc~ 64 and replace the drive frequency signal with a newly generated drive frequency for breaking or deceleration, or shutting down the system~ For example, the phase locked loop (P.P.L.) override signal 74 may cut off a first drive frequenCY output (fdrive) from the q Y
adder 48 and replace it with a frequency equal to the tach signal and a slip freqency of zero. When the tach signal equals the drive Erequency, the induction motor will coast and the system can shut down, even if the digital current command signal is unable to block the current to the induction motor. The override drive frequency signal (74) will cause the induction motor to coast to a safe stop, whether or not digital current command signal 68 reaches the Johnson counter 72. This PP~ override signal 74 provides a fail safe guard against loss of current command control.
As noted earlier, Figure 2A shows a perspective view of the rotor with the under side turned towards the viewer to illustrate the rotor body 16, the flat circular '-:
;.
:
8D-438 Canada -17- ~ S5 base 82, and t'ne magne-ts 20 imbedded equi-distant wi-thin the base 82. A Hall Effect sensor 18 is shown detecting the changes in magnetic flux and magnetic reluctance as the magnets 20 pass by the sensor 18. At speeds exceeding 30,000 R.P.M., in the event of rotor 16 imbalance, the sensor 18 will not detect the passage of all six magnets per revolution, and the output tach signal from sensor 18 will produce a tach signal 40 w]-ich deviates from expected frequency.
Figure 2B shows the condition o high-speed imbalance which may be present at speed.s in excess of 30,000 revolutions per minute. The Figure 2B is a pictoral representation of wha-t is believed to be the imbalance phenomena. The rotor 16 is slightly tilted off its horizontal axis 88, so that its side nearest the Hall EfEect de-tector 18 is turned away from the detector 18.
A gap 90 is created between the detector 18 and the rotor 16 when the rotor 16 and shaft 14 are tilted due to the imbalance. The detector is unable to de-tect a change in magnetic reluctance due to the passage of magnets ~0 over the detector 18, since a slight movement of the base 82 (Figure 2~) away from the detector 18 will render the detector 18 insensitive to the change in magnetic reluctance which would otherwise be detected. Thus, for each revolution while rotor imbalance is present, -the pulse train generated by the detector 18 as the rotor 16 revolves past the detector 18 is irregular and deviates from a reference pulse count stored in the CPU 42 of Figure 1. (The reference pulse count is stored as a number in the CPU 42 and corresponds to the count expected when the rotor 16 is properly balanced.~
Figure 3 is a graphic representation of the operational cycle of a centrifuge rotor for the entire range from zero to 100,000 revolutions per minute. Up to . ~ , '. ' .
. ~. . . ~ , ~, .: ~ :. , ' ' tjtj 8D-43U Canada a speed of 5,000 revolutions per minute, the rotor speed operation is not subject to the predictions of any mathematical equation. This initial area of operation is indicated in the shaded area on the graph in Figure 3 at 80. Beginning at 5,000 revolutions per minute and up to 100,000 revolutions, there is a linear relationship between slip frequency and rotor speed as indicated by the graph along sector 78. Above a range of 5,000 revolutions per minute, operator keyboard program is overridden and the computer automatically programs the optimal slip ~requency so that the rotor uniformly attains a speed of 100,000 revolutions per minute. As one will note, the linear slope of sector 78 is characteristic of a fixed percentage slip over the range o 5,000 revolutions per minute to 100,000 revolutions per minute, representative of a fixed percentage of rotor speed as the speed acceleration.
Referring to Figure 4, the relationship between rotor speed and time is indicated. Up to 5,000 revolutions per minute, the acceleration is gradual and nonlinear. Beginning at 5,000 revolutions per minute up to 100,000 revolutions, a rapid uni~orm acceleration takes place between time intervals Tl and T2. The segment of linear acceleration is indicated by reference character 84 of Figure 4.
The rotor imbalance detection system operates within the schematic structure of Figure 1~ A tach signal pulse train 40 is provided to the pulse counter and tach signal converter 46. The pulse count~r 46 generates an eight-bit digital signal which is representative of the tach signal frequency at the time the tach signal 40 is sampled for a preset period of time, such as a one second sampling period. The central processing unit records the Erequency of the tach signal .' '~
:`
8D-438 Canada ~2~8~5~
pulse provided by the pulse counter ~6 and stores this information within its memory registers ~not shown). The tach signal pulse train is sampled at a number of different intervals. For example, ten one-second intervals may be sampled and each sampling conducted ten seconds apart. The central processing unit 42 analyzes the data which it receives from the pulse counter 46 and determines whether each or any of the samplings indicate a fre~uency deviation or differential. (The CPU 42 has been programmed to include the constant acceleration of the rotor 16 for purposes of imbalance detection.) If ten samples are taken, each of the samples may be analyzed to determine whether there is a frequency devia-tion. Once the frequency deviation has been determined, -the central processing unit further analyæes the data to determine whether or not the deviation frequency so detected is a random occurrence or one which arises with great regularity~ The more regular the deviatiorl fre-quency, the more likely the central processing unit will determine that there is a cen-trifuge rotor imbalance.
Deviation frequency is the difference between expected signal and actual (imbalance indicating) frequency. For example, the number of frequency deviations and the amount of deviations, from an average frequency over the full range of the tach signals sampled could be matched by the computer against a mathematical statistical standard deviation curve. If the frequency deviation is ou-tside the predetermined range of standard statistical deviation (even after accounting for programmed cons-tant accelerations) as defined by the mathematical function stored within the computer, an alarm is sounded. In this manner, rotor frequency imbalance m~y be detected. This is an accurate means of detecting rotor imbalance, since an irregular or off-timed pulse or series of pulses within the tach signal pulse train ~0 indicates that as the magnets 20 revolve past the Hall Effect sensor 18, , . . .. .
'' . .. , ~ .. ..
~8~35~
8D-438 Canada the base plane 82 (Figure 2A) is slightly -tilted 50 that one or more magnets 20 do not produce tach signals as the rotor revolves about its axis. It is the missing tach signals that create the frequency deviation that the central processing unit 42 detects. Irregular tach pulse train signals indicate the existence oE rotor imbalance, since they deviate from the pulse train frequency expected if the rotor were in proper balance.
It should be noted that the preferred embodiment is merely illustrative of the centrifuge overspeed protection and imbalance detection system. The scope of the invention is not necessarily limited to the preferred embodiment. Many structural changes are possible and these changes are intended to be within the scope of this disclosure. For example, this system has many segments, such as the phase-locked loop and drive frequency inhibit gate which could be replaced by software commands and sub-routines within the CPU.
Consequently, the specific structural and functional details of the system disclosed are marely representative; they are deemed to afford the best embodiment for purposes of discloure and for providing support for the claims which define the scope of the present invention.
, .:
-Field of the Invention _ This invention relates to an automatic control system for regulating the operation of a centrifuge and, in particular, to a system for providing centrifuge overspeed protection and imbalance detection and a method for the system's implementation.
Background of the Invention Centrifuge operation presents a unique set of design criteria where precision control of the rotational operation of the cen-trifuge is required. The wide variety of biological and chemical experimental research which use centrifugation as their primary tool to achieve component separation and perform experimental assays places a requirement of versatility on the operational characteristics which must be built into the centrifuge.
m e centrifuge rotor is driven to extremely high rotational speeds in order to genera-te the centrifugal field required for biological research use.
The high rotational speeds of the rotor cause a severe build-up of kinetic energy, which if released, can lead to destructive explosion of the centrifuge and injury or damage to its surrounding environment as well as the human operator. Centrifuge rotors typically can fail if the rotor is run in excess of the speed designed for its safe operation. The slightest imbalance of the rotor or load which it carries can cause catastrophic failure.
~ le centrifuge apparatus has numerous rQtors which may be interchangeably used in conjunction with the same centrifuge motor and drive shaf-t in order that a : . .
..: ... :
- .':: : :
. . ,., :: .
BV~:~5 diversity of biological experimentation may be achieved. One standard of centrifuge design encompasses an induction motor and shaft which can accommodate the interchangeable rotors to be carried on the spindle of the motor shaft, each rotor having a different weight and strength of material and a different maximum safe speed above which the particular rotor should not be operated.
Also, even the slightest imbalance of the rotor or load which it carries may grow to larger imbalances and associated forces as the rotor speed and centrifugal field increases. Often, these imbalances do not arise until the rotor has achieved very high speeds. Strain and stress within the material of the rotor exhibiting a slight fracture at rest can cause the rotor to dismember at maximum speeds approaching 100,00~ revolutions per minute. The dynamic effect of any imbalancing forces cause complicated movement of the shaft upon which the rotor is suspended, such as dangerous whirls and ~yrations.
It is therefore clear that a versatile centrifugation system requires: (1) a maximum safe rotor speed be identified for each rotor; (2) the operational use and control of the rotor during centrifugation be monitored and controlled; and, (3) that any imbalance be detected. If possible, the use of a single sensor and transducer system would provide accuracy and asynchronous information which may be used to control the motor speed for all varieties of rotors.
One such system is disclosed in applicant's United States Patent No. 4,551,715, issued November 5, 1985, naming Durbin as inventor. In the disclosed specification, a method of rotor identification for each rotor and determination of rn/
, . ,~ ~. .
.. ,,, : , , .
~`805~
the rotor's maximum safe speed is presented which relies on a single magnetically sensitive transducer to provide the necessary rotor identification and maximum safe speed information in a straightforward and precise manner.
The disclosure of U.S. Patent No. 4,551,715 describes an improved signal processing circuit which allowed a tachometer signal and rotor identification signal to be generated from a single set of coding elements on the rotor.
The patent uses a circular array of magnetic coding elements on the rotor to provide the tachometer and rotor identification information. ~ Hall effect sensor is u~ed to detect the magnetic orientation of permanent magnets imbedded in the base of each interchangeable rotor. In the preferred embodiment of Durbin, six magnets spaced at equal intervals around the circumference of the rotor are positioned to direct a north-oriented or south-oriented magnetic field outward from the base of the rotor for detection by the Hall effect sensor. The Hall effect sensor detects a change in magnetic reluctance as the permanent magnet rotates past the fixed sensor and induces a voltage in the sensor. A series of sharply defined pulses are generated in the conduction pathway and amplified in the Durbin system. Thus the Durbin disclosure presents an embodiment which is able to identify a rotor on the basis of a single transducer accordiny to the combination and order in which north- and south-oriented magnets pass the Hall effect rotor. These same north and south pulses also produced a tach signal from which rotor speed can be identified. A central processing unit i5 used to compare rotor speed with rotor identification. Stored in the rn/
8D-438 Canada ~ 05S
central processing unit is an informa-tion listing identifying the maximum rated speed for each individual rotor. Once the rotor is identified on the basis of a coded pulse train generated by the north- and soutll-oriented magnets imbedded within the ro-tor, the central processing unit reads the maximum rating information stored within its memory and compared these readings with the actual speed. The central processing unit also is aware of what had been programmed at the human operator keyboard for the desired acceleration and speed. The central processing uni-t functions to prevent the rotor from being programmed or actually operated beyond its intended rating. The magnetic transducer detection system represented a significant improvement over optical sensing systems which were subject to interference from dirt and damage, as well as inadvertent customer abuse when the wrong optical rotor disc was affixed to a rotor rated for a lower speed.
Conventionally, motor control has been achieved in centrifuges by controlling the current or power to the induction motor which drives the rotor and shaft. Such current control may be disconnected or otherwise not be communicating with the centrifuge current bus. U.S.
Patent No. 4,286,203 to Ehret issuing August 25, 1981 to Beckman Ins-truments, Inc., the common assignee with this application, discloses a Slip Frequenc~ Control System for Variable S eed Induction Motors. This paten-ted - P
system controls rotor speed by maintaining a constant slip frequency regardless of motor speed. It is generally directed at normal operating conditions and drives the motor in response to an initial fixed frequency produced by relaxation oscillator 20. The system disclosed in the patent is not designed to respond to abnormal conditions such as rotor overspeed or imbalance.
-8D-438 Canada ~55 What is clearly needed to insure centrifuge safety and sample integrity is a method of controlling the speed of the induction motor of a centrifuge through use of the inEormation derived from the tach signal pulse train.
Additionally, it would be useful if imbalance detection could be effectuated to prevent imbalances which occur at high speeds from causing great destruction. The conventional art of centrifugation provides an electromechanical imbalance detector in the form of a microswitch which sits in proximity to the rotor shaft in order to detect whirling gyrations which may occur in the rotor shaft. The rotor shaft is fitted with a radially extending nub. A spring mounted microswitch adjacent to the nub of the spindle shaft makes contact if the shaft wobbles excessively. This causes the capacitor to be discharged and triggers a digital signal at the output of a monostable multivibratcr providing an active low pulse to the microprocessor. This detection system has worked fine at speeds below 30,00~ r.p.m., but unfortunately is not sufficiently responsive to detect imbalance during high speed rotation.
What is clearly needed is a sensor detection system which not only identifies individual rotors and their maximum safe speeds, but also controls their speed, monitors their speed, and detects rotor imbalance.
Summaxy of the Invention The present invention is a method and system for controlling and monitoring the speed of a centrifuge which rotates at ultrahigh speeds. Additionally, the method and system disclosed provides for the detection of ' . ,, ... .. .. .
8D-438 Canada ~ 5~
rotor imbalance and a means for sounding an alarm when the rotor speed or imbalance exceed predetermined value ranges.
In particular, a system for controlling and monitoring the rotational speed of a centrifuge ro-tor is disclosed. An electronic sensor detects the actual speed of the rotor asynchronously and on a real-time basis by driving a tach signal pulse train and providing this pulse train to the input of a phased lock loop frequency adder for combination with a computer derived slip frequency. During certain predetermined ranges, the frequency adder adds the slip frequency to the tach signal and derives a drive frequency which is sent to the Johnson counter of an inverter. The inverter in turn produces a three phase control signal for controlling the induction motor which drives the high speed centrifuge rotor. This closed loop system involves the creation of a slip frequency by converting the tach signal to a computer readable digital -format. Operator keyboard program and rotor identification circuit information are analyzed within the microprocessor o the central processing unit along with the converted tach signal information. These informational inputs to the central processing unit are combined to derive a slip frequency. The slip frequency is determined by passing a pulse train through a ~requency synthesizer which produces a frequency at the desired slip rate in accordanc~ with known formulations to maintain an optimal percentage of slip and yet accommodate operator keyboard program and Rotor Identification input. The slip frequency thus derived when added to the tach signal produces a drive frequency which controls the inver-t~r and the induction motor.
8D-438 Canada ~'~5~
During those periods in -the rotor acceleration cycle where it is not desirable to add the tach signal to a slip frequency, but simply generate a control signal directly from the computer, an override control signal is imparted to -the inverter to overtake and control the timing of the motor. This signal occurs generally during initial acceleration and final deceleration, as well as those circumstances where other safety problems are detected in the system, such as temperature exceeding predetermined limitations during rotor operation or rotor imbalance.
~ system for detecting rotor imbalance includes obtaining the tach signal pulse train derived from a sensor input and converting that signal to a CP~ readable foxmat. Various intervals of signals are counted to determine frequency and frequency deviations. If from one interval to another, tach signal frequency deviates substantially, a rotor imbalance is detected. Such irregular signals are an indicia-tion that the rotor has tilted away from the sensor, causing the Hall sensor to not detect all six magnets per revolution. In this manner, imbalance may be detected and an alarm override signal may be sent to the inver-ter to shut the motor down.
The invention also comprises a method for detecting high speed rotor imbalance and controlling and monitoring rotor speed. This method includes deriving a tach signal pulse train that corresponds to actual rotor speed;
converting the signal derived for analysis by a central processing means; comparing the actual signal with operator programmed acceleration instructions as well as information concerning the upper limits of acceleration from the Rotor Identification circuit; deriving from those sources of input a slip frequency which, when added .. . .
.~ .
: ~:
8D-438 Canada to the actual tach signal rotor frequency, produces a drive frequency for controlling the induction motor o~
the centrifuge motor. Additionally, a method is disclosed for detecting rotor imbalance by deriving a train of tach signal pulses; converting those pulses to a -format intelligible to a cen-tral unit; determining the frequency of pulses received during a variety of intervals; comparing the frequency derived at one time interval with the frequency derived at another time interval (with the expected frequency due to uniform acceleration accounted for) and producing a deviation frequency which corresponds to the difference in frequencies between the impulse; comparing the deviation frequency derived with a preset reference to determine whether the frequency deviation exceeds safe limits;
producing an override control signal to shut down the inverter and induction motor when preset limits are exceeded, thereby detecting rotor imbalance at high speeds.
Brief Description of the Drawin~s Figure 1 is a schematic-block diagram of a preferred embodiment of the centrifuge overspeed protection and imbalance detection system which is the sub~ect matter of this invention;
Figure 2A is a perspective view of the rotor showing one of the six magnets physically positioned at the base o-f the rotor in relation to the Hall Effect detector;
Figure 2B is a side view of the rotor operational mounted on a shaft, where the rotor base is slightly off its proper orientation indicative of rotor imbalance;
....
- . . . .
;. . . :- ~ . :
... ~ , . ..
. ., ,~ .
8D-438 Canada .~ 2 ~;~ 0 ~ 5 _g_ Figure 3 is a graphic representation of the relationship between slip frequency and rotor speed during the centrifuge operating cycle of the invention;
and, Figure 4 is a graphic xepresentation of rotor speed as a function of time during the centrifuge operating cycle in accordance with the invention.
Detailed Descri~ion of the P_eferred Embodiment With reference to Figure 1, there is disclosed a system by which information provided by -the tach signal pulse train may be utilized to control an induction motor and protect against overspeed and rotor imbalance.
me induction motor 12 has a spindle shaft 14 upon which an individually selected rotor 16 may be affixed. The underside plan view of the rotor 16 is represented by a flat circular surface having a plurality of magnets 20 imbedded therein. When driven by the induction motor 12, the rotor 16 revolves past the Hall effect sensor 18. The sensor 18 is able to detect changes in magnetic reluctance occurring when permanent magnets 20 pass the transducer surface of the ~all effect sensor 18. Figure 2A shows the flat circular base surface 82 of the rotor 16. m e permanent magnets 20 are embedded in the rotor base 82 and rotate past the Hall Effect sensor 18 as the rotor 16 turns.about its own axls .
The output tach pulse from the Hall effect sensox 13 (Figure 1) is conveyed through capacitor 22 in order to filter out unwanted D.C. noise, resulting in a waveform as shown at 24. As is apparent, waveform 24 compxises positive-going pulses representative of north-oriented magnets as well as negative-going pulses ~"_ , . ~, .: ,, : ,:. : ' :'' : :.:::.. ,:: . , - ::
8D-438 Canada -10- 1~8V55 representative of south ~agnets 20. This signal is then amplified by amplifier 26. ~le output of amplifier 26 is operatively fed to the inverting input of two separate operational amplifiers 28 and 30. ~le north signal first passes through inverter 32 so that the output at both operational amplifiers 28 and 30 will be signals of the same negative transition. South and north signals are distinguished by the Rotor Identifica~ion (I.D.) circuit 34 since within the Rotor Identification circuit 34 north and south pulses are counted separately. Additionally, the output signals from operational amplifiers 2~ and 30 are coupled to the input terminals of exclusive OR gate 36. Exclusive OR gate 36 triggers a pulse each time a north or a south signal is developed at either of its input terminals. The counters within Rotor Identification circuit 34 are triggered by the leading edge of the negative pulse produced at the output of exclusive OR gate 36. ~le output of exclusive OR gate 36 is tapped and the output pulse signal derived is coupled through the inverter gate 38, in order to produce the tach signal pulse train 40 as shown. This pulse train is the same pulse train produced and disclosed in the Durbin patent .
~ uniqu~e feature o~ this invention is the use of the pulse train shown at 40 to provide overspeed-protection and high speed imbalance information to the central processing unit (CPU) 42. In the conventional art, the central processing unit 42 controls the operation of the induction motor 12 by directly controlling the power inverter 50. Conventionally, the central processing unit 42 genera~ed a digital current command signal 68 which, when processed through a digital-to-analog converter ~4, produced an analog voltage which is capable of driving the power inverter 50 through Johnson counter 72. Current control may be used ;,~ i. . - --:,, ; ' :
8D-~38 Canada ~ 5S
to control the operation of the induction motor 12 by c~scading the voltage upward during acceleration and downward during deceleration while constantly maintaining the current at a level sufflcient to overcome the counter e.m.f. of the induction motor 12, driving -the mo-tor 12 up to an optimal and efficient operational mode. This ~orm of conventional current control of induction motor 12 has a disadvantage when it is the sole means of control. The current control line can be disrupted causing the current to rise. Loss of current control will result in driving the rotor to dastructive speeds or in the overheating and destruction of the induction motor. Even if the rotor identification circuit 3~ communicates to the CPU 42 that the rotor is rated below the speed that the current bus drives it, a severing of the current con-trol system may result in a rotor being driven overspeed and substantially damaging the centrifugation chamber. One reason this may occur is the fac-t that the digital current command signal system is designed to monitor actual current fed to the inverter 50 by means of an optical sensing system (not shown) which optically isolates the bus power supply from the digital current command signal. However, if for example -the current feedback phototransistor (which reads the "~ED" of the current bus) breaks down, the computer may continue to drive the digital current command signal upward in the absence of the actual current feedback, resulting in possible rotor destruction or induction motor 12 burnout.
The conven-tional art has heretofore taught the generation by the central processing unit of a fixed frequency reference which will serve as the basis of a synthesized frequency control system~ Such a fixed frequency signal may not accurately reflect operating conditions. A single fixed fre~uency signal, even when synthesized by the central processing unit, may lack the :.
. .
' . ~ ' ,, .
~D-438 Canada ~ 55 real time flexibility required to adapt the system to the wide range of interchangeable rotors which may be used by the human operator.
The invention provides a frequency drive signal controlling of the induction motor by means o~ a closed loop system which asynchronously monitors the actual tach signal and adjusts the control signal accordingly.
An improved motor control system by using a drive frequency control signal is provided in the preferred embodiment by simultaneously inputting the tach signal pulse train 40 into a pulse counter and tach signal converter 46 and a phase locked loop frequency adder 48. The frequency drive signal control system generally provides real time tach signal information to the cen-tral processing unit 42 which uses this information, as well as other informa-tion, to produce a drive frequency control signal. ~e tach signal pulse train 40 is imparted to the pulse counter and tach signal converter 46, which in the preferred embodiment is a programmable counter programmed to operate as a "Divide-by-N" counter. The pulse counter 46 may be a programmable interval timer manufactured by Intel Corporation of Santa Clara, California as Model 8253.
Bidirectional bus 52 provides a pathway for the pulse counter 46 to inform the central processing unit 42 as to the number of pulses counted during a pre-programmed time interval (N). Essen~ially, the pulse counter 46 converts the tach signal pulse train into at least two eight-bit digital words which the central processing unit 42 can store in its memory and use as a basis ~or ~ur-ther instructions. A crystal controlled clock 54 provides an extremely stable six megahertz frequency signal to the central processing unit and a timing signal o~ three megahertz (or approximately one hal~ that provided to the ' .: ,.. ,:~ ' :
;,; ,, ~ ~
~' 8D-43~ Canada -13- ~ 55 central processing unit 42) to the pulse counter 46, the frequency s~nthesizer 56, and the latch circuit 5~ Tach signals provided to the pulse counter 46 are additionally coupled to the flip-flop latch 58 for output to the frequency synthesizer 56 according to clock signal produced by the crystal controlled clock 54. Thus, tach signal rotor speed information is provided to the central processing unit 42 by the pulse counter 46 in the form of an eight-bit digital words. The tach signal 40 is also provided to the frequency synthesizer 56 as a conditioned signal through the latch 58 by way of the counter 46.
The pulse train is coupled to the synthesizer 56 in synchronization with the central processing unit 42 by the crystal controlled clock 54. The central processing unit 42 may subsequently send instructions along unidirectional bus 60 to the frequency synthesizer 56 to produce a slip frequency (fs) which is coupled to the frequency adder 48, a phase locked loop integrated circuit in the preferred embodiment. The frequency adder may be the CD40~6A COS/MO~ Integrated Circuit manufactured by RCA Solid State Division, RCA
Corporation, Somerville, N.J.08876. The frequency synthesizer 56 produces an output frequency, fs~ which is equal to the Erequency received from latch 58 divided by the "N" number provided by CPU 42. The frequency synthesizer 56 may be a "Divide-by-N" counter sold by Intel Corporation as a Model 8253 Programmable Interval Timer.
Induction motors require that there be some slip or difference between the drive speed provided by the inverter 50 and the actual speed which the rotor is able to run. (Actual speed is detected by this system as the tach signal pulse train 40.). For example, if an optimum operation of the induction motor 12 require that at a 10,000 revolutions per minute (RPM) drive speed, the .
.. :.~' ~ ' ''' -.
~ ~ , ., , . ' . ,'. ': .
8D-438 Canada ~2~0~, induction motor actually operates at 9800 revolutions per minute, then a slip frequency of 200 ~.P.M~ might be necessary to provide the torque to keep the induction motor running. As speed is increased, the percentage of slip must be maintained and the slip frequency must be increased. For smooth motor operation, slip Erequency should be kept at a relatively constant percentage of the drive control frequency driving the induction motor.
Thus, the ideal drive frequency is one which is increased by adding the actual tach signal frequency, derived from a tach signal pulse train such as 40 and adding that signal to a slip frequ~ncy (fs) 66 computed to maintain a fixed percen-ta~e but driving the induction motor :L2 at a Easter speed.
As a further example, assume -that the human operator, by use of the operator keyboard progra~ 62, has instructed the central processing unit 42 to accelerate the rotor in a linear fashion over the range of 1500 revolutions per minute up to 2,000 revolutions per minute. In order to carry out the opera-tor program instructions, the central processing unit must sense the actual rotor speed which it receives in a digital form from pulse counter 46. Once the central processing unit is informed that a speed of 1500 revolutions per minute has been achieved, it then executes the operator program by instructing the frequency synthesizer 56 to increase the slip frequency (fs) over a fixed period, so that the actual rotor frequency will increase from 1500 revolutions per minute to 2,000 revolutions per minute.
If, for 1500 revolutions per minute, the computer central processing unit 42 was ins-tructing the frequency synthesizer 56 to produce one pulse output for every three pulses input from latch 58 for a standard time interval, the new instruction would cause the Erequency synthesizer 56 to produce one a pulse for every four 8D-438 Canada 15 ~2'~
pulses which are latched from flip-flop in -the same standard time interval. The slip frequency would be increased 30% above the frequency needed to produce optimal slip at 1500 RPM, so that the new slip frequency produced to achieve 2000 RPM would represent a constant percentage of slip. In this manner the slip frequency may be changed to suit the pre-programmed requirements of the human operator.
In -the preferred embodiment, the drive frequency control system operates to initially accelerate the rotor to 5,000 revolutions per minute by ramping up both the drive current and the drive frequency with time in accordance to the pre-programmed instructions of the human operator. ~e system analyzes the tach signal 40 to ascertain the regularity of pulse rate before the rotor is allowed to accelerate as programmed up to 5,000 revolutions per minute. Once the rotor reaches an actual tach signal frequency indicating 5,000 revolutions per minute, the drive frequency signal 64 which is derived from the output of the phase locked 1GOP frequency adder 48 is the sum of the synthesized slip frequency 66 (fs) and the tach signal pulse train 40. The slip frequency selected is pre-programmed in the operating system for optimum electrical motor efficiency for the particular instantaneous speed achieved. The slip frequency is not uniform over the range of 5,000 revolutions per minute up to 100,000 revolutions per minute; however, the percen-tage slip is maintained as a constant percentage of actual speed to achieve greatest motor efficiency.
Control through operator keyboard program 62 is relinquished above the 5,000 revolutions per minute range. Additionally, the digital current command signal 68 varies motor current to maintain desired set speed ~le phase locked loop frequency adder 48 is used to provide a stable frequency which represents the sum of . :, -.. ~ . ~ .
..
. .
. . .
.
8D-438 Canada ~ ~ t~ 0~3 the tach signal plus the slip frequency, to achieve optimum motor torque over the entire range of motor operation. The inverter 50 is driven by the Johnson counter 72 to produce a -three-phase control signal 76 to control the induction motor 12 in a closed loop fashion.
During normal operation above 5,000 revolutions per minute, the drive frequency provided to the input of NOR gate 70 is imparted to Johnson counter 72 for driving the induction motor by generating a three-phase control signal 76. For speeds below 5,000 revolutions per minute, or during breaking deceleration, or in the event that an imbalance is detected or another alarm condition has been indicated to the central processing unit, the phase locked loop override control signal 74 triggers the output of ~OR gate 70 to disable the drive frequenc~ 64 and replace the drive frequency signal with a newly generated drive frequency for breaking or deceleration, or shutting down the system~ For example, the phase locked loop (P.P.L.) override signal 74 may cut off a first drive frequenCY output (fdrive) from the q Y
adder 48 and replace it with a frequency equal to the tach signal and a slip freqency of zero. When the tach signal equals the drive Erequency, the induction motor will coast and the system can shut down, even if the digital current command signal is unable to block the current to the induction motor. The override drive frequency signal (74) will cause the induction motor to coast to a safe stop, whether or not digital current command signal 68 reaches the Johnson counter 72. This PP~ override signal 74 provides a fail safe guard against loss of current command control.
As noted earlier, Figure 2A shows a perspective view of the rotor with the under side turned towards the viewer to illustrate the rotor body 16, the flat circular '-:
;.
:
8D-438 Canada -17- ~ S5 base 82, and t'ne magne-ts 20 imbedded equi-distant wi-thin the base 82. A Hall Effect sensor 18 is shown detecting the changes in magnetic flux and magnetic reluctance as the magnets 20 pass by the sensor 18. At speeds exceeding 30,000 R.P.M., in the event of rotor 16 imbalance, the sensor 18 will not detect the passage of all six magnets per revolution, and the output tach signal from sensor 18 will produce a tach signal 40 w]-ich deviates from expected frequency.
Figure 2B shows the condition o high-speed imbalance which may be present at speed.s in excess of 30,000 revolutions per minute. The Figure 2B is a pictoral representation of wha-t is believed to be the imbalance phenomena. The rotor 16 is slightly tilted off its horizontal axis 88, so that its side nearest the Hall EfEect de-tector 18 is turned away from the detector 18.
A gap 90 is created between the detector 18 and the rotor 16 when the rotor 16 and shaft 14 are tilted due to the imbalance. The detector is unable to de-tect a change in magnetic reluctance due to the passage of magnets ~0 over the detector 18, since a slight movement of the base 82 (Figure 2~) away from the detector 18 will render the detector 18 insensitive to the change in magnetic reluctance which would otherwise be detected. Thus, for each revolution while rotor imbalance is present, -the pulse train generated by the detector 18 as the rotor 16 revolves past the detector 18 is irregular and deviates from a reference pulse count stored in the CPU 42 of Figure 1. (The reference pulse count is stored as a number in the CPU 42 and corresponds to the count expected when the rotor 16 is properly balanced.~
Figure 3 is a graphic representation of the operational cycle of a centrifuge rotor for the entire range from zero to 100,000 revolutions per minute. Up to . ~ , '. ' .
. ~. . . ~ , ~, .: ~ :. , ' ' tjtj 8D-43U Canada a speed of 5,000 revolutions per minute, the rotor speed operation is not subject to the predictions of any mathematical equation. This initial area of operation is indicated in the shaded area on the graph in Figure 3 at 80. Beginning at 5,000 revolutions per minute and up to 100,000 revolutions, there is a linear relationship between slip frequency and rotor speed as indicated by the graph along sector 78. Above a range of 5,000 revolutions per minute, operator keyboard program is overridden and the computer automatically programs the optimal slip ~requency so that the rotor uniformly attains a speed of 100,000 revolutions per minute. As one will note, the linear slope of sector 78 is characteristic of a fixed percentage slip over the range o 5,000 revolutions per minute to 100,000 revolutions per minute, representative of a fixed percentage of rotor speed as the speed acceleration.
Referring to Figure 4, the relationship between rotor speed and time is indicated. Up to 5,000 revolutions per minute, the acceleration is gradual and nonlinear. Beginning at 5,000 revolutions per minute up to 100,000 revolutions, a rapid uni~orm acceleration takes place between time intervals Tl and T2. The segment of linear acceleration is indicated by reference character 84 of Figure 4.
The rotor imbalance detection system operates within the schematic structure of Figure 1~ A tach signal pulse train 40 is provided to the pulse counter and tach signal converter 46. The pulse count~r 46 generates an eight-bit digital signal which is representative of the tach signal frequency at the time the tach signal 40 is sampled for a preset period of time, such as a one second sampling period. The central processing unit records the Erequency of the tach signal .' '~
:`
8D-438 Canada ~2~8~5~
pulse provided by the pulse counter ~6 and stores this information within its memory registers ~not shown). The tach signal pulse train is sampled at a number of different intervals. For example, ten one-second intervals may be sampled and each sampling conducted ten seconds apart. The central processing unit 42 analyzes the data which it receives from the pulse counter 46 and determines whether each or any of the samplings indicate a fre~uency deviation or differential. (The CPU 42 has been programmed to include the constant acceleration of the rotor 16 for purposes of imbalance detection.) If ten samples are taken, each of the samples may be analyzed to determine whether there is a frequency devia-tion. Once the frequency deviation has been determined, -the central processing unit further analyæes the data to determine whether or not the deviation frequency so detected is a random occurrence or one which arises with great regularity~ The more regular the deviatiorl fre-quency, the more likely the central processing unit will determine that there is a cen-trifuge rotor imbalance.
Deviation frequency is the difference between expected signal and actual (imbalance indicating) frequency. For example, the number of frequency deviations and the amount of deviations, from an average frequency over the full range of the tach signals sampled could be matched by the computer against a mathematical statistical standard deviation curve. If the frequency deviation is ou-tside the predetermined range of standard statistical deviation (even after accounting for programmed cons-tant accelerations) as defined by the mathematical function stored within the computer, an alarm is sounded. In this manner, rotor frequency imbalance m~y be detected. This is an accurate means of detecting rotor imbalance, since an irregular or off-timed pulse or series of pulses within the tach signal pulse train ~0 indicates that as the magnets 20 revolve past the Hall Effect sensor 18, , . . .. .
'' . .. , ~ .. ..
~8~35~
8D-438 Canada the base plane 82 (Figure 2A) is slightly -tilted 50 that one or more magnets 20 do not produce tach signals as the rotor revolves about its axis. It is the missing tach signals that create the frequency deviation that the central processing unit 42 detects. Irregular tach pulse train signals indicate the existence oE rotor imbalance, since they deviate from the pulse train frequency expected if the rotor were in proper balance.
It should be noted that the preferred embodiment is merely illustrative of the centrifuge overspeed protection and imbalance detection system. The scope of the invention is not necessarily limited to the preferred embodiment. Many structural changes are possible and these changes are intended to be within the scope of this disclosure. For example, this system has many segments, such as the phase-locked loop and drive frequency inhibit gate which could be replaced by software commands and sub-routines within the CPU.
Consequently, the specific structural and functional details of the system disclosed are marely representative; they are deemed to afford the best embodiment for purposes of discloure and for providing support for the claims which define the scope of the present invention.
, .:
Claims (8)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for high speed centrifuge rotor imbalance detection, the steps of which comprising:
deriving a tach signal frequency which corresponds to the actual speed of a centrifuge rotor when said rotor is in balance and deviates therefrom when said rotor is out of balance;
determining the tach frequency signal derived for a plurality of discrete intervals;
calculating by means of a central processing unit any differences between the frequencies computed for each of the discrete intervals and deriving therefrom a deviation frequency signal;
measuring the deviation frequency signal derived against a predetermined standard, thereby detecting the presence of high speed rotor imbalance.
deriving a tach signal frequency which corresponds to the actual speed of a centrifuge rotor when said rotor is in balance and deviates therefrom when said rotor is out of balance;
determining the tach frequency signal derived for a plurality of discrete intervals;
calculating by means of a central processing unit any differences between the frequencies computed for each of the discrete intervals and deriving therefrom a deviation frequency signal;
measuring the deviation frequency signal derived against a predetermined standard, thereby detecting the presence of high speed rotor imbalance.
2. A system for the detection of high speed centrifuge rotor imbalance, comprising:
means for sensing true rotor speed when said rotor is in balance and generating a rotor tach signal having a frequency proportional thereto;
means for measuring the frequency of the rotor tack signal at a plurality of sampling intervals;
means for generating a dynamic reference frequency, said dynamic reference frequency being a reference frequency derived according to expected rotor operating conditions when the rotor is in proper balance;
said dynamic reference frequency changing with time as rotor speed and acceleration change;
comparing means for comparing the frequency of the rotor tach signal sampled at each of a plurality of intervals to the dynamic reference frequency and deriving a deviation frequency; and means for processing the deviation frequency and determining whether said deviation frequency exceeds a predetermined range, whereby centrifuge rotor imbalance is detected when said deviation frequency exceeds said predetermined range.
means for sensing true rotor speed when said rotor is in balance and generating a rotor tach signal having a frequency proportional thereto;
means for measuring the frequency of the rotor tack signal at a plurality of sampling intervals;
means for generating a dynamic reference frequency, said dynamic reference frequency being a reference frequency derived according to expected rotor operating conditions when the rotor is in proper balance;
said dynamic reference frequency changing with time as rotor speed and acceleration change;
comparing means for comparing the frequency of the rotor tach signal sampled at each of a plurality of intervals to the dynamic reference frequency and deriving a deviation frequency; and means for processing the deviation frequency and determining whether said deviation frequency exceeds a predetermined range, whereby centrifuge rotor imbalance is detected when said deviation frequency exceeds said predetermined range.
3. In determining irregularities in the operation of said centrifuge, the steps of which comprise:
deriving a tach signal during the operation of said centrifuge;
determining the frequency of said tach signal during a plurality of discrete intervals;
detecting any differences between any of the frequencies determined for each of the discrete intervals and an expected frequency; and comparing said detected difference against a known standard thereby detecting the existence of irregularity in the operation of said high speed centrifuge.
deriving a tach signal during the operation of said centrifuge;
determining the frequency of said tach signal during a plurality of discrete intervals;
detecting any differences between any of the frequencies determined for each of the discrete intervals and an expected frequency; and comparing said detected difference against a known standard thereby detecting the existence of irregularity in the operation of said high speed centrifuge.
4. In a centrifuge a system for the detection of rotor imbalance comprising:
signal generating means for generating an electrical signal having a frequency indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance; and means signalling the deviation of said frequency from an expected value by a predetermined amount.
signal generating means for generating an electrical signal having a frequency indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance; and means signalling the deviation of said frequency from an expected value by a predetermined amount.
5. The system according to claim 4 for the further detection of rotor overspeed comprising:
means comparing said frequency of said electrical signal against a frequency indicative of the maximum safe speed for said rotor and generating a signal indicating that said rotor has exceeded said maximum rotor speed.
means comparing said frequency of said electrical signal against a frequency indicative of the maximum safe speed for said rotor and generating a signal indicating that said rotor has exceeded said maximum rotor speed.
6. In a centrifuge a system for the detection of rotor imbalance comprising:
signal generating means for generating an electrical signal having a frequency indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance;
means for generating a reference signal having a frequency derived according to expected conditions when said rotor is in proper balance;
comparison means for comparing the frequency of said electrical signal from said signal generating means with the frequency of said reference signal; and deviation signal generating means for generating an output signal when the frequency of said electrical signal deviates from the frequency of said reference signal by a predetermined amount whereby centrifuge rotor imbalance is detected and signalled.
signal generating means for generating an electrical signal having a frequency indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance;
means for generating a reference signal having a frequency derived according to expected conditions when said rotor is in proper balance;
comparison means for comparing the frequency of said electrical signal from said signal generating means with the frequency of said reference signal; and deviation signal generating means for generating an output signal when the frequency of said electrical signal deviates from the frequency of said reference signal by a predetermined amount whereby centrifuge rotor imbalance is detected and signalled.
7. A system for the detection of centrifuge rotor over-speed and imbalance comprising:
signal generating means for generating an electrical signal having a characteristic indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance said electrical signal also having a characteristic identifying the particular rotor present;
means receiving said electrical signal and generating an output indicating the maximum speed for the identified rotor;
means for generating an output signal when said electrical signal indicates that the actual rotor speed has exceeded the maximum speed for said identified rotor;
means for measuring the speed indicating characteristic of said electrical signal at a plurality of sampling intervals;
means for generating a dynamic reference characteristic, said dynamic reference characteristic being a reference characteristic derived according to expected rotor, operating conditions when said rotor is in proper balance, said dynamic reference characteristic changing with time as rotor speed and acceleration change;
comparing means for comparing the characteristic of said electrical signal sampled at each of a plurality of intervals to the dynamic reference characteristic and deriving a deviation characteristic; and means for processing the deviation characteristic and determining whether said deviation characteristic exceeds a predetermined range and generating an output signal when said range is exceeded whereby centrifuge rotor imbalance is detected.
signal generating means for generating an electrical signal having a characteristic indicative of actual rotor speed when the centrifuge rotor is in balance and which deviates therefrom when said rotor is out of balance said electrical signal also having a characteristic identifying the particular rotor present;
means receiving said electrical signal and generating an output indicating the maximum speed for the identified rotor;
means for generating an output signal when said electrical signal indicates that the actual rotor speed has exceeded the maximum speed for said identified rotor;
means for measuring the speed indicating characteristic of said electrical signal at a plurality of sampling intervals;
means for generating a dynamic reference characteristic, said dynamic reference characteristic being a reference characteristic derived according to expected rotor, operating conditions when said rotor is in proper balance, said dynamic reference characteristic changing with time as rotor speed and acceleration change;
comparing means for comparing the characteristic of said electrical signal sampled at each of a plurality of intervals to the dynamic reference characteristic and deriving a deviation characteristic; and means for processing the deviation characteristic and determining whether said deviation characteristic exceeds a predetermined range and generating an output signal when said range is exceeded whereby centrifuge rotor imbalance is detected.
8. The system according to claim 7 wherein said signal characteristic is frequency.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US06/740,086 US4700117A (en) | 1985-05-31 | 1985-05-31 | Centrifuge overspeed protection and imbalance detection system |
| US740,086 | 1985-05-31 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1268055A true CA1268055A (en) | 1990-04-24 |
Family
ID=24974986
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000509849A Expired CA1268055A (en) | 1985-05-31 | 1986-05-23 | Centrifuge overspeed protection and imbalance detection system |
Country Status (2)
| Country | Link |
|---|---|
| US (1) | US4700117A (en) |
| CA (1) | CA1268055A (en) |
Families Citing this family (52)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4758825A (en) * | 1986-03-03 | 1988-07-19 | Sweany Ralph S | Shaft speed monitor |
| US5037371A (en) * | 1986-12-10 | 1991-08-06 | E. I. Du Pont De Nemours And Company | Rotor recognition system |
| US4827197A (en) * | 1987-05-22 | 1989-05-02 | Beckman Instruments, Inc. | Method and apparatus for overspeed protection for high speed centrifuges |
| US4827196A (en) * | 1987-12-03 | 1989-05-02 | E. I. Du Pont De Nemours And Company | Motor control arrangement |
| US4903191A (en) * | 1987-12-23 | 1990-02-20 | E. I. Du Pont De Nemours And Company | Centrifuge control system having dual processors |
| FR2625923B1 (en) * | 1988-01-18 | 1992-02-21 | Acutronic France Sa | AUTOMATIC BALANCING DEVICE OF A CENTRIFUGE IN OPERATION |
| US4857811A (en) * | 1988-03-31 | 1989-08-15 | E. I. Du Pont De Nemours And Company | Evacuation pump control for a centrifuge instrument |
| DE3818407A1 (en) * | 1988-05-31 | 1989-12-07 | Hermle Kg Berthold | DEVICE FOR CONTROLLING THE OPERATION OF A CENTRIFUGE |
| SU1704840A1 (en) * | 1988-07-18 | 1992-01-15 | Московское научно-производственное объединение "Биофизприбор" | Centrifuge checking device |
| US5066135A (en) * | 1988-08-09 | 1991-11-19 | Beckman Instruments, Inc. | Rotatable vortexing turntable |
| DE9013638U1 (en) * | 1990-09-28 | 1990-12-06 | Siemens Ag, 8000 Muenchen, De | |
| US5235864A (en) * | 1990-12-21 | 1993-08-17 | E. I. Du Pont De Nemours And Company | Centrifuge rotor identification system based on rotor velocity |
| US5221250A (en) * | 1991-01-07 | 1993-06-22 | Beckman Instruments, Inc. | Coding of maximum operating speed on centrifuge rotors and detection thereof |
| US5207634A (en) * | 1991-01-23 | 1993-05-04 | Biotope, Inc. | Self-balancing apparatus and method for a centrifuge device |
| US5338283A (en) * | 1992-10-09 | 1994-08-16 | E. I. Du Pont De Nemours And Company | Centrifuge rotor identification system |
| JP2514554B2 (en) * | 1992-12-28 | 1996-07-10 | 株式会社久保田製作所 | Centrifuge |
| DE4335119C2 (en) * | 1993-10-15 | 1997-11-20 | Eppendorf Geraetebau Gmbh | Laboratory centrifuge with unbalance shutdown |
| US5509881A (en) * | 1994-07-07 | 1996-04-23 | Beckman Instruments, Inc. | Centrifuge rotor identification and refrigeration control system based on windage |
| US5518493A (en) * | 1994-07-07 | 1996-05-21 | Beckman Instruments, Inc. | Automatic rotor identification based on a rotor-transmitted signal |
| US5905348A (en) * | 1995-06-06 | 1999-05-18 | Sl Montevideo Technology, Inc. | Powering and control of a brushless DC motor |
| JP3710001B2 (en) * | 1995-06-16 | 2005-10-26 | 日立工機株式会社 | centrifuge |
| US5649893A (en) * | 1996-05-22 | 1997-07-22 | Hitachi Koki Co., Ltd. | Centrifugal apparatus having series-implemented protection means |
| JP3533874B2 (en) * | 1996-10-18 | 2004-05-31 | 日立工機株式会社 | Centrifuge with overspeed protection device |
| US5800331A (en) * | 1997-10-01 | 1998-09-01 | Song; Jin Y. | Imbalance detection and rotor identification system |
| US6860845B1 (en) * | 1999-07-14 | 2005-03-01 | Neal J. Miller | System and process for separating multi phase mixtures using three phase centrifuge and fuzzy logic |
| DE10082534B4 (en) | 1999-09-03 | 2005-10-06 | Küster Automotive Door Systems GmbH | Method for controlling an electric motor driven adjusting device for vehicles, for example for windows and device for carrying out the method |
| JP3879360B2 (en) * | 2000-03-17 | 2007-02-14 | 日立工機株式会社 | Centrifuge |
| US6368265B1 (en) | 2000-04-11 | 2002-04-09 | Kendro Laboratory Products, L.P. | Method and system for energy management and overspeed protection of a centrifuge |
| US6507161B2 (en) * | 2000-04-14 | 2003-01-14 | The Western States Machine Company | Centrifuge motor control |
| US6635007B2 (en) * | 2000-07-17 | 2003-10-21 | Thermo Iec, Inc. | Method and apparatus for detecting and controlling imbalance conditions in a centrifuge system |
| US6350224B1 (en) | 2000-07-17 | 2002-02-26 | Westinghouse Savannah River Company, Llc | Centrifugal unbalance detection system |
| US7150858B2 (en) * | 2000-08-18 | 2006-12-19 | Arkray, Inc. | Centrifugal separator |
| JP3951582B2 (en) * | 2000-10-06 | 2007-08-01 | 日立工機株式会社 | centrifuge |
| US6589151B2 (en) * | 2001-04-27 | 2003-07-08 | Hitachi Koki Co., Ltd. | Centrifugal separator capable of reading a rotor identification signal under different rotor rotation conditions |
| JP3956646B2 (en) * | 2001-05-21 | 2007-08-08 | 日立工機株式会社 | Centrifuge |
| US7458928B2 (en) * | 2002-06-13 | 2008-12-02 | Kendro Laboratory Products, Lp | Centrifuge energy management system and method |
| DE10305067A1 (en) * | 2003-02-07 | 2004-08-19 | Fag Kugelfischer Ag | Method for determining and quantitatively evaluating an imbalance in a shaft-bearing system |
| US6943509B2 (en) * | 2003-07-09 | 2005-09-13 | Kendro Laboratory Products, Lp | Rotor speed control device and method |
| SE528701C2 (en) * | 2005-06-08 | 2007-01-30 | Alfa Laval Corp Ab | Centrifugal separator for purification of a gas |
| WO2007070448A2 (en) * | 2005-12-09 | 2007-06-21 | Pacific Centrifuge, Llc | Biofuel centrifuge |
| DE102009045822A1 (en) * | 2009-10-20 | 2011-04-28 | Robert Bosch Gmbh | Electronically commutated electric motor with calibrated motor torque constant |
| US8222760B2 (en) * | 2010-06-29 | 2012-07-17 | General Electric Company | Method for controlling a proximity sensor of a wind turbine |
| US8870733B2 (en) | 2010-11-19 | 2014-10-28 | Kensey Nash Corporation | Centrifuge |
| US8317672B2 (en) | 2010-11-19 | 2012-11-27 | Kensey Nash Corporation | Centrifuge method and apparatus |
| US8556794B2 (en) | 2010-11-19 | 2013-10-15 | Kensey Nash Corporation | Centrifuge |
| DE102011100044B4 (en) * | 2011-04-29 | 2017-10-05 | Thermo Electron Led Gmbh | Sensor arrangement for identifying a rotor and centrifuge used in a centrifuge |
| US9046050B2 (en) * | 2011-09-15 | 2015-06-02 | General Electric Company | Shaft imbalance detection system |
| KR102369602B1 (en) | 2014-01-31 | 2022-03-02 | 디에스엠 아이피 어셋츠 비.브이. | Adipose tissue centrifuge and method of use |
| DE102014116527B4 (en) * | 2014-11-12 | 2020-01-23 | Andreas Hettich Gmbh & Co. Kg | Centrifuge and method for detecting unbalance in the centrifuge |
| US9983087B2 (en) | 2014-12-10 | 2018-05-29 | General Electric Company | Methods and systems to determine rotor imbalance |
| US10227937B2 (en) | 2015-11-04 | 2019-03-12 | Ge Global Sourcing Llc | Methods and system for a turbocharger |
| DE102018101457A1 (en) | 2018-01-23 | 2019-07-25 | Eppendorf Ag | Method and device for monitoring the speed of an element |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1325536A (en) * | 1969-08-13 | 1973-08-01 | Mse Holdings Ltd | Centrifuges |
| US3746247A (en) * | 1970-12-23 | 1973-07-17 | Electro Nucleonics | Ultracentrifuge with rotor speed identification |
| JPS5783194A (en) * | 1980-11-10 | 1982-05-24 | Hitachi Ltd | Ac motor controlling device using pulse width modulation inverter |
| ATE17928T1 (en) * | 1981-12-24 | 1986-02-15 | Kontron Holding Ag | DEVICE FOR NON-CONTACT IMBALANCE MEASUREMENT. |
| GB8324912D0 (en) * | 1983-09-17 | 1983-10-19 | Fisons Plc | Magnetic device |
| US4551715A (en) * | 1984-04-30 | 1985-11-05 | Beckman Instruments, Inc. | Tachometer and rotor identification apparatus for centrifuges |
-
1985
- 1985-05-31 US US06/740,086 patent/US4700117A/en not_active Expired - Fee Related
-
1986
- 1986-05-23 CA CA000509849A patent/CA1268055A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| US4700117A (en) | 1987-10-13 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CA1268055A (en) | Centrifuge overspeed protection and imbalance detection system | |
| US4601696A (en) | Centrifuge provided with a rotor identification | |
| US5800331A (en) | Imbalance detection and rotor identification system | |
| US4827197A (en) | Method and apparatus for overspeed protection for high speed centrifuges | |
| US5383838A (en) | Tachometer and rotor identification system for centrifuges | |
| EP1419013A1 (en) | A method and system for energy management and overspeed protection of a centrifuge | |
| JPH114589A (en) | Measuring device of drag torque of rotating machine, monitoring system of movement of electric motor, and system for adjusting operation parameter of centrifugal separator with built-in measuring device | |
| KR100683503B1 (en) | Electrically driven potter's wheel | |
| EP0570391B1 (en) | Centrifuge rotor identification system based on rotor velocity | |
| EP0321920B1 (en) | Centrifuge control system having dual processors | |
| US6350224B1 (en) | Centrifugal unbalance detection system | |
| US5650578A (en) | Energy monitor for a centrifuge instrument | |
| WO1987000770A1 (en) | Overspeed protection signal override system for a centrifuge apparatus | |
| JPH0334279Y2 (en) | ||
| JPS5651668A (en) | Detecting method for abnormal rotational speed of rotator | |
| JPS56133617A (en) | Vibration monitoring method of rotary machine | |
| SU1034127A1 (en) | Method of checking disbalance of motor rotor | |
| CA1169483A (en) | Constant speed electric motor | |
| JPH04267956A (en) | Centrifuge | |
| JPH05104031A (en) | Abnormal vibration detector of centrifugal separator | |
| FR2387686A1 (en) | Fixing radial blades on rotary shaft of food chopping machine - with improved security and facility to adjust balance | |
| EP0428469A2 (en) | Digital speed controller for washing machine motors | |
| JPS5512215A (en) | Drive control process and system for turbine dynamo | |
| JPS5753262A (en) | Monitor for operation of centrifuge | |
| JPH04156965A (en) | Safety device for centrifugal separator |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |