US3786285A

US3786285A - Moment actuated transducer

Info

Publication number: US3786285A
Application number: US00313537A
Authority: US
Inventors: R Reibold
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-12-08
Filing date: 1972-12-08
Publication date: 1974-01-15
Anticipated expiration: 1991-01-15

Abstract

A moment-actuated transducer unit mounted to an elastic belt having Velcro-type fastener means for attaching the belt and transducer unit snugly around the chest or abdomen region of a subject''s body provides a highly sensitive and easily installed respiration transducer assembly. The output of the transducer unit can be connected directly to a high input impedance recorder or to a signal conditioning circuit which includes an unfiltered output and a high frequency filtered output wherein a regular high input impedance recorder can be selectively connected to either of such outputs.

Description

United States Patent [191. R eibold MOMENT ACTUATED TRANSDUCER [76] Inventor: Robert C. Reibold, 12062 Brookhaven Pk., Garden Grove, Calif. 92640 [22] Filed: Dec. 8, 1972 [21] Appl. No.: 313,537

Related US. Application Data [62] Division of Ser. No. 146,156, May 24, 1971.

[52] US. Cl 310/85, 310/86, 310/91 [51] Int. Cl l-l04r 17/00 [58] Field of Search 310/82, 8.3, 8.5,

[56] References Cited UNITED STATES PATENTS 3,546,497 12/1970 Craster 3l0/8.5 X 3,564,402 2/1971 Pittman 3/1966 Burkhalter et al 3l0/8.6

[ Jan. 15, 1974 Primary Examiner-Gerald Goldberg Assistant Examiner-Mark O. Budd Attorney- D. N. .leu, Walter .1. Jason and Donald L.

Royer [57] ABSTRACT A moment-actuated transducer unit mounted to an elastic belt having Velcro-type fastener means for attaching the belt and transducer unit snugly around the chest or abdomen region of a subjects body provides a highly sensitive and easily installed respiration transducer assembly. The output of the transducer unit can be connected directly to a high input impedance recorder or to a signal conditioning circuit which includes an unfiltered output and a high frequency filtered output wherein a regular high input impedance recorder can be selectively connected to either of such outputs.

3 Claims, 12 Drawing Figures Geil et al. 310/85 X PATENTEU 3.786285 SHEET 1 0F 2 [143/75 JAY/17 i "MOMENTACTUATED TRANSDUCER This is a division of application Set. No. l46,l56 filed May24, 1971.

BACKGROUND OF THE INVENTION My present invention relates generally to physiological measuring apparatus and, more particularly, to a means for obtaining accurate respiration data from human or other animal subjects either at rest or during intense activity thereof with negligible interference of their normal functions.

In the measurement'of respiration data, a thermistor face mask which encloses the nose and mouth areas of the subject is commonly used to measure the confined air temperature and its variation in order to determine respiration rate and volume. The thermistor mask is, however, encumbering to the wearer and relatively complex conditioning of the thermistor output signal is required to provide a useful signal which can be applied directly to an ordinary recorder. Of course, a face mask cannot be used on animals without greatly interfering withtheir normal activities.

Strain gage type transducers for sensing, stress changesdueto expansion orcontraction of the skin area to whichthey are affixedhave been employed to avoid the use of face masks. Such transducers are, however, cumbersome becauseof their (beam) size and they must normally be used in a bridge circuit. Further, the strain type transducer is relatively insensitive and also requires relatively complex signal conditioning before its output signal can be usefully applied to a regular recorder. L

An impedance pneumograph can be utilized to avoid the use of face masks. The pneumograph essentially measures the movements of the chest wall during respiration as changes in impedance between attached chest electrodes. It is, however, more troublesome to use because of the requirement for good electrical contacts with ,a subjects body. As in the preceding devices, it also requires relatively complex signal conditioning of its output 'signal'before it can be feasibly applied to an ordinary recorder.

SUMMARY or THE INVENTION Briefly, and in general terms, my invention is preferably accomplished by providing a highly sensitive and easily installed respiration transducer assembly including a moment-actuated transducer unit. mounted to an elastic belt having Velcro-type fastener means for attaching the belt and transducer unit snugly around the chest or abdomen portion of a subject's body, the output of the transducer unit being connectable directly to a high input impedance recorder or indirectly to a low input impedance recorder through a signal conditioning circuit (wherein such recorder is connected to the unfiltered output thereof).

'The transducer unit comprises a piezoelectric element including a thin piezoelectric crystal cemented to the front face of a thin metallic (beam) disc, a pair of parallel attachment (bending arm) loops affixed rigidly to the rear face of the metallic disc and protruding perpendicularly a predetermined distance before the front face thereof, a pair of electrical leads soldered respectively to the piezoelectric crystal and metallic disc, and a layer of resilient material encapsulating the piezoelectric element and inner portions of the attachment loops and electrical leads adjacent to the piezoelectric element. The elastic belt is connected to the exposed portions of the attachment loops and is used to support the transducer unit.

The signal conditioning circuit comprises an attenuator having an unfiltered output and a filtered output including a low pass filter having a cut-off frequency of about 0.2 hertz to reject higher frequency signals than the respiration signals, such as those caused by motion or vibration of the transducer unit when the subject is running. The conditioning circuit presents a high input impedance to the transducer unit and a low output impedance to a recorder or the low pass filter. A high or low input impedance recorder can be connected to the unfiltered output; however, a sufficiently high input impedance recorder which does not load the low pass filter should ordinarily be connected to the filtered output. The capacitance of the transducer unit and the shunting input impedance (resistance) of the conditioning circuit provides a relatively long time constant which permits the system to be self-balancing.

BRIEF DESCRIPTION OF THE DRAWINGS My invention will be more fully understood, and other features and advantages thereof will become apparent, from the description given below ofan exemplary embodiment of the invention. This description of the exemplary embodimentof the invention is to be taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a top plan view of a transducer assembly constructed in accordance with this invention and shown in' positionto be fastened about the lower chest or diaphragm area of a persons body;

FIG. 2 is a front elevational view of a piezoelectric element used in the construction of a transducer unit which is a component of the transducer assembly shown in FIG. 1; j t

FIG. 3 is a top plan view of the piezoelectric element shown in FIG. 2;

FIG. 4 is a side elevational view of an attachment loop used in the construction of the transducer unit component;

FIG. 5 is a top plan view of the attachment loop shown in FIG. 4;

FIG. 6 is a front elevational view of the transducer unit component prior to encapsulation thereof;

FIG. 7 is a top plan view of the unencapsulated transducer unit component shown in FIG. 6;

FIG. 8 is a front elevational view of the transducer unit component used in the transducer assembly of FIG. 1;

FIG. 9 is a top plan view of the transducer unit component shown in FIG. 8;

FIG. I0 is a circuit diagram of a signal conditioning circuit which is preferably used with the transducer assembly of FIG. 1;

FIG. 11 is a graph showing a curve of a respiration signal recorded by a recorder connected to the unfiltered output of the signal conditioning circuit of FIG. 10; and I FIG. 12 is another graph showing a curve of a respiration signal recorded by the recorder when connected to the filtered output of the signal conditioning circuit of FIG. 10.-

former coupling occurring when the toroidal magnetic core 17 is in an unsaturated condition. The amplitude of the signal that is transformer coupled to the same wire 21 is dependent upon the distance the magnet 18 is relative to the toroidal magnetic core 17.

Time delay means 22 is connected between the oscillating voltage source 12 and the switching circuit 13 to substantially parallel the signal path, passing through the toroidal magnetic core 17. The time delay means 22 preferably comprises a trigger circuit 23 and a series connected time delay circuit 24. The trigger circuit 23 may be a Schmitt trigger device, or may be any other suitable trigger device having a minimum threshold input level.

In operation, the oscillator drives the amplifier to such an extent to provide a sufficient output voltage across the primary winding formed by the drive line 19. This voltage is induced into the secondary winding formed by the sense line 21 when the toroidal magnetic core 17 is in an unsaturated condition. When the core is saturated the voltage decreases to zero and no output signal will be obtained.

The output of the oscillator circuit 12 also feeds the trigger circuit which produces a square wave output signal in phase with the sine wave. This is delivered to the delay circuit 24 to delay the positive pulses sufficient so that the positive edge occurs when voltage at the input of the flip-flop 14 is at its maximum. It will be understood that the delay function also can be accomplished by changing the trigger level of the trigger circuit 23.

The induced positive voltage in the secondary winding formed by the sense line 21 is sampled at the input terminal 14 of the flip-flop on positive edge of the clock. If the positive voltage is of sufficient magnitude the flip-flop will change to a logic one state and provide a feedback signal through a resistor 26. This feedback signal provides a bounceless output and an electrical hysteresis characteristic for the circuit. In the illustrated embodiment the signal delivered across the sense line 21 passes through a series resistor 27.

Referring now to FIG. 2 there is seen an alternate form of the solid state switch control circuit constructed in accordance with the principles of this inventionand is designated generally by reference numeral 30. Here a pulsating voltage source 31 is formed by a clock generator and is used to control the operation of a switching circuit 32. The switching circuit 32 is again shown as a flip-flop circuit similar to that disclosed with regard to FIG. 1. By utilizing the clock generator 31 the oscillator and Schmitt trigger configuration of FIG. 1 can be eliminated. The switching circuit 32 includes an input terminal 33 and a clock input terminal 34 which functions substantially in the same manner as disclosed above.

A toroidal magnetic core 36 is capable of being magnetically saturated and unsaturated as a result of movement of an associated permanent magnet 37. A drive wire 38 passes'through the toroidal magnetic core and has one end thereof coupled to an amplifier 39 and the other end thereof connected to a terminal point 40 located between a resistor 41 and a capacitor 42. A sense wire 43 also passes through the toroidal magnetic core and functions as the secondary winding of a transformer when the core is in the magnetically unsaturated condition. A delay line circuit path is provided by a delay circuit 46 which parallels the signal path provided through the toroidal magnetic core.

The flip-flop circuit 32 is provided with a feedback resistor 47 which functions in the same manner as the resistor 26 of FIG. 1. The amplifier 39 and time delay circuit 46 operate in synchronization with one another to provide input signals to the switching input terminal 33 and the clock input terminal 34. When the signal level at terminal 33 is of sufficient amplitude the flipflop will switch to its high state and when the signal level drops below a given level the flip-flop will automatically switch back to its low state.

For-a better understanding of the circuit of FIG. 2 reference is now made to FIG. 3 which is a more detailed showing of the circuit configuration. Here the clock circuit is illustrated by reference numeral 50 and comprises three invertor circuits 51, 52, and 53 connected in series with a capacitor 54 connected across the invertor 52. The time delay circuit is designated generally by reference numeral 55 and comprises a pair of series connected invertor circuits 56 and 57. The amplifier comprises a single transistor 58 and a resistor 59 having the emitter thereof connected to ground potential and collector thereof connected to the circuit point 40. The drive wire 38 is connected to the circuit point 40 and provides a current coupling output pulse when transistor 58 is rendered conductive to discharge capacitor 42.

While several specific embodiments are illustrated herein it will be understood that still other circuit configurations can be utilized without departing from the spirit and scope of the novel concepts disclosed and claimed herein.

The invention is claimed as follows:

1. A solid state switch control circuit, comprising in combination: an oscillating voltage source, a switching circuit having a switching input terminal, said switching circuit capable of being activated to a switched state when an input signal at said switching input terminal is above a predetermined voltage level, a closed magnetic core structure capable of being magnetically saturated and unsaturated in response to the application of a magnetic field, magnet means positioned adjacent said closed magnetic core structure for saturating and unsaturating said core, a drive wire connected to said oscillating voltage source and passing it through said closed magnetic core, structure a sense wire connected to said switching circuit and passing it through said closed magnetic core structure, said drive and sense wire providing a transformer coupling therebetween when said closed magnetic core structure is in an unsaturated state, and time delay means connected between said oscillating voltage source and said switching circuit and providing a parallel signal path to the signal path through said drive and sense wires, whereby actuation of said switching circuit will occur only when said closed magnetic core structure is sufficiently unsaturated and when a pulse is applied to said switching circuit through said time delay means.

2. The solid state switch control circuit according to claim 1, wherein said oscillating voltage source is an oscillator providing a sine wave, and said time delay means includes a trigger circuit connected in series with a delay circuit for providing a suitable time delay at a clock input of said switching circuit.

3. The solid state switch control circuit according to claim 2, further including amplifier means connected in filter 68 comprises series resistor R2 and shunt capacitor C2. The buffer stage 70 includes transistors Q1 and 02 wherein the base of the former transistor is connected to input terminal 62 by resistor R1 and the emitter is connected to the base of the latter transistor. The collectors of the transistors Q1 and Q2 are connected to a source 72 of positive voltage, and the emitter of the latter transistor is connected through series connected resistor R3 and potentiometer R4 to a source 74 of negative voltage. Series connected resistors R5 and R6 connect the source 72 to the base of the transistor Q1, and bias it and the transistor O2 to be normally always conducting. The emitter of transistor Q2 is connected to unfiltered output 76 by lead 78, and to filtered output 80 by the R2-C2 filter 68, as shown.-Potentiometer or rheostat R4 can be used to adjust the outputs 76 and 80 to zero or, if desired, to a positive or negative reference base.

In an illustrative and satisfactory embodiment of the signalconditioning circuit 60, the transistors Q1 and Q2 are each a 2N3391A transistor, resistors R1, R2, R3, R5 and R6 are respectively 100 megohms, S6 kilohms, l kilohm, 22 megohms and 22 megohms in value, potentiometer R4 is 10 kilohms in resistance, and capacitor C2 is microfarads (mfd.). in value, for example. The positive and

negative voltage sources

72 and 74 can be 5-volt batteries; however, where adjustment of the reference base need not be to zero, only one 5'-volt battery (72, for example) can be used (R4 connected to ground) and a reference base such as at 2.5 volts can be utilized.

In operation, the elastic belt 24 (FIG. 1) is fastened snugly (i.e., at a tactually established predetermined tension).around the chest or abdomen portion of a subject, and theelectrical leads 34 and 36 of the transducer unit 22 are connected to the input terminals 62 and 64of signal conditioning circuit 60 (FIG. 10) At least one oftheoutputs 76 or 80 is connected to a suitable recorder (not shown). Potentiometer R4 is then adjusted to produce a zero reference base. Inhalation by the subject ex'pands theibelt 24 and applies amoment to the. loops 28and 30 (bending arms) to cause a further central outward deflection of the metallic disc 58 (brass beam). .This also further deflects the piezoelectric crystal 56 cemented to the disc 58 and produces a positive output voltage from the outputs 76 and 80. Exhalation, of course, produces the opposite effect and a negative output voltage is produced from the outputs 76 and 80 when the deflection of the disc 58 is less than its initial, reference base, condition.

The attenuator 66 (FIG. 10) of the signal condition ing circuit 60 also presents a high input impedance to the transducer unit 22 and provides a low output impedance which generallymatches the input impedance of a low input impedance recorder that can be connected tothe unfiltered output 76. Of course, a regular high input impedance recorder can be connected to either the unfiltered output 76 or the filtered output 80. A sufficiently highinput impedance recorder (which does not load the resistor R2) should, however, be ordinarily connected to the filtered output 80.

The capacity (C1 of approximately 0.03 mfd.) of the transducer unit 22 shunted by the resistance (approximately 140 megohms) of the resistor R1 plus the input impedance of the buffer stage 70 provides a relatively long R-C time constant of about 5 seconds which. permits the system to be self-balancing, i.e., when the transducer unit 22 is deflected from its reference condition, an output voltage is generated therefrom which returns to zero by discharging through the resistor R1 and the buffer stage 70. This time constant can, of course, be varied by minor modification of the circuit components. The time constant should not be too short since the output voltage of the transducer unit 22 then would not follow the higher frequency respiration signal components accurately. On the other hand, an excessively long time constant would not allow any large transient voltage generated by the unit 22 (as from a sharp jolt) to be dissipated or decay with sufficient promptness.

FIG. 11 is a graph showing a curve S which was the respiration signal obtained from the unfiltered output 76 (output voltage v) and produced by a human subject running at approximately 6 m.p.h. on a treadmill. The respiration rate can be easily determined along the abscissa or time axis (time t) but the variation of respiration volume is somewhat obscured or confused by the superimposed, higher frequency, wavelets which are largely due to the bouncing and vibration of the transducer unit 22 caused by the running motions of the subject. In order to increase the accuracy and ease of determining both respiration rate and volume, the filtered output 80 can be used to drive the recorder.

FIG. 12 is a graph, similar to that of FIG. 11, showing a curve y which was the respiration signal obtained from the filtered output 80 and produced by the same running subject. It can be readily seen from an examination of the curves of S and y that both respiration rate and volume can be much more accurately and easily determined from the latter curve. The amplitude of the curve y, as measured from its reference base, is substantially devoid of the higher frequency and extaneous wavelets so that it clearly yields a far more accurate indication of instantaneous respiration volume of the subject. It may be noted that the curves of S and y, in FIGS. 11 and 12 are of consecutive signals produced by the same running subject, and are not the unfiltered and filtered forms'of an instantaneously identical signal. i

The respiration measuring system described above has served to obtain respiration data from human and animal subjects during intense activity thereof or at rest with negligible interference of their normal activity. The system is unencumbering to the subject and has extremely high sensitivity yet is of simple and inexpensive construction. It is self-balancing and particularly easy to install and operate to provide highly accurate and useful respiration data.

The system is capable of detecting and recording pressure changes of heart pulses when the transducer unit 22 is located on or near a surface artery. In determining pulse pressure and rate, for example, the transducer assembly 20 can be installed about the forehead of a person with the transducer unit 22 preferably positioned over a temple region of the persons head. Where the-transducer assembly 20 is suitably installed about the chest or abdomen of a person, the pulse rate can actually be noted from inspection of the unfiltered but not the filtered recorded curves of S and y (FIGS. 11 and 12). The pulse pressure signals appear as small prominences superimposed on the large peaks and valleys of the unfiltered respiration curve S for a person not engaged in intense activity, which activity would produce overriding and obscuring signals.

While an exemplary embodiment of this invention has been described above and shown in the accompanying drawings, it is to be understood that such embodiment is merely illustrative of, and not restrictive on, the broad invention and that I do-not desire to be limited in my invention to the details of construction or arrangement shown and described, for obvious modifications may occur to persons skilled in the art.

I claim:

1. In a transducer system of the class described, a transducer unit comprising:

a disc-like piezoelectric element including a deflectable planar beam, and a piezoelectric crystal bonded to a plane surface of said beam;

a pair of moment arms each including a normally lower and a normally upper end, said lower ends being affixed in a spaced relationship therebetween to said beam with said arms extending angularly a predetermined distance from said surface and intersecting at a substantial angle of at least about 45 degrees with respect thereto; and

means fastenable to force-generating support means and connecting with said arms at least near said upper ends thereof for supporting said element and providing a moment on said arms, said connecting means normally applying a force from said support means to said arms at least near said upper ends thereof in a direction generally parallel to said surface to provide said moment which bends said element and produces an output signal therefrom.

2. The invention as defined in claim 1 wherein said arms include a pair of loop-like arms each having a normally lower and a normally upper end portion and side portions joining said lower and upper end portions together in a closed loop, said lower end portions being affixed in a spaced parallel relationship with respect to each other to said beam and said side portions extending angularly a predetermined distance from said surface and intersecting at a substantial angle of at least about 60 with respect thereto, said connecting means includes an elastic belt attached at its ends to said upper end portions of said loops, and said support means includes a selected portion of a subject's body, said belt being fastened thereabout at a predetermined tension and applying a moment to said arms according to its instantaneous tension whereby said element is actuated with expansion and contraction of said belt by said body portion to produce a variable output signal from said element representative of the motions of said body portion.

3. The invention as defined in claim 2 wherein said side portions of said loops extend perpendicularly a predetermined distance from said surface, and said belt includes fastener means adjustable to secure said belt at a tactually established predetermined tension about said body portion.

Pb-wso UNITED STATES PATENT OFFICE Inventofls) v l l 569 CERTIFICATE OF CORRECTION "Patent No. '3 3 5 5 Dated Januar-Y 97 Robert V c. Reibold It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

e I Front; page, left column, Code "[76]" should read --[75]--;- and below the Inventor data, insert- [73] Assignee: McDonnell Douglas Corporation, corporation of,1 iary1and--$ line 35, "extaneous" should read --'-extraneous-.

, s ned and sealed this 3rd day of December 1974;

(SEAL) f Attest: I v

McCOY GIBSON JR. c. MARS-BALL DANN Attesting Officer Comisexoner of Patentsmg I UNITED STATES PATENT OFFICES r CERTIFICATE OF CORRECTION Patent No. 5 f -January l5, 197

Robert C. Reibold Inventor(s) It is certified that error eppears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Front; page, left column, Code "[76]" should read ----[75]---;"[

l and belowthe Inventor data, insert -[73] Assignee: McDonnell Douglas Corporation, a. corDorat-ion of Marylandw-fi 6,

1 line-35, "extaneous" should read -'-extra.neous--.

" Signed and sealed this 3rd day of December 1974.

(SEAL) Attest:

MCCOYMQGIBSON JR. 'c. MARS-IIIALL DANN Attesting Officer Comissloner oi facente

Claims

1. In a transducer system of the class described, a transducer unit comprising: a disc-like piezoelectric element including a deflectable planar beam, and a piezoelectric crystal bonded to a plane surface of said beam; a pair of moment arms each including a normally lower and a normally upper end, said lower ends being affixed in a spaced relationship therebetween to said beam with said arms extending angularly a predetermined distance from said surface and intersecting at a substantial angle of at least about 45 degrees with respect thereto; and means fastenable to force-generating support means and connecting with said arms at least near said upper ends thereof for supporting said element and providing a moment on said arms, said connecting means normally applying a force from said support means to said arms at least near said upper ends thereof in a direction generally parallel to said surface to provide said moment which bends said element and produces an output signal therefrom.

2. The invention as defined in claim 1 wherein said arms include a pair of loop-like arms each having a normally lower and a normally upper end portion and side portions joining said lower and upper end portions together in a closed loop, said lower end portions being affixed in a spaced parallel relationship with respect to each other to said beam and said side portions extending angularly a predetermined distance from said surface and intersecting at a substantial angle of at least about 60* with respect thereto, said connecting means includes an elastic belt attached at its ends to said upper end portions of said loops, and said support means includes a selected portion of a subject''s body, said belt being fastened thereabout at a predetermined tension and applying a moment to said arms according to its instantaneous tension whereby said element is actuated with expansion and contrAction of said belt by said body portion to produce a variable output signal from said element representative of the motions of said body portion.