CA1169677A - Vibrating beam rotation sensor - Google Patents
Vibrating beam rotation sensorInfo
- Publication number
- CA1169677A CA1169677A CA000396486A CA396486A CA1169677A CA 1169677 A CA1169677 A CA 1169677A CA 000396486 A CA000396486 A CA 000396486A CA 396486 A CA396486 A CA 396486A CA 1169677 A CA1169677 A CA 1169677A
- Authority
- CA
- Canada
- Prior art keywords
- support structure
- cantilever beam
- sensor
- rotation
- signal
- 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
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01C—MEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
- G01C19/00—Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
- G01C19/56—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces
- G01C19/5719—Turn-sensitive devices using vibrating masses, e.g. vibratory angular rate sensors based on Coriolis forces using planar vibrating masses driven in a translation vibration along an axis
Abstract
360-80-0290 : VIBRATING BEAM ROTATION SENSOR A rotation sensor having a vibrating cantilever beam is disclosed herein. The sensor comprises an integral signle crystal silicon cantilever beam and support structure, an oscillator circuit for generating an electrical signal vibrating the cantilever beam at or near its natural resonant frequency and a piezoresitive element formed at the base of the base of the vibrating beam. The piezoresistive element is only sensitive to the stresses induced in the beam due to the rotation of the beam about an axis parallel to its length.
Description
116g677.
VIBRATING BEAM ROTATION SENSOR
~ackground of the Invention Field of the Invention The invention is related to the field of rotation sensors and in particular to a vibrating beam rotation sensor.
Prior Art The use of a vibrating reed or cantilever beam to detect a rotational velocity is known in the art. ~.
Lyman is U.S. patent 2,513,340 discloses a resiliently mounted electrically driven tuning fork. The vibration of the fork produces periodic changes in its moment of inertia. The periodic changes in the tuning fork's moment of inertia produce periodic forces opposing angular rotation. An angular lag or displacement between the resiliently mounted tuning fork and its base is proportional to the angular or rotational acceleration while the amplitude of the periodic force ls proportional to the rotational velocity.
The concept of a single vibrating member is disclosed by Barnaby et al in U.S. patent 2,544,646. In his angular velocity measuring instrument, two serially connected reeds or cantilever beams are constrained to vibrate at right angles to each other. The first or lower beam is electrically stimulated to vibrate the upper beam. The moment of inertia of the upper beam will produce a periodically varying force resisting an angular displacement from its initial plane of vibration. This periodic force is proportional to the displacement.
Rotation of the lower beam will cause the upper beam to vibrate in a plane normal to vibration plane of the lower beam. The vibration amplitude of the upper beam is pro-portional to the angular velocity of rotation. In two of aarnaby's embodiments, the upper and lower beams are piezoelectric crystals.
Mumme in V.S. patent 3,842,681 expands Barnaby's vibrating beam concept to a two axis angular rate sensor.
In the sensor disclosed by Mumme, the lower vibrating reed is replaced by an oscillating rotary hub. Four cantilever beams are supported from the hub in a cruciform pattern normal to its oscillatory axis and are oscillated as rigid members. Coriolis forces generated by the oscillating cantilever beams oppose the rotation of sensor about one of the axes defined by the cruciform cantilever beam configuration and cause the beams defining the other axis to vibrate in a direction normal to the cruciform plane. The cantilever beams are made from a piezoelectric material which outputs a signal in response to their vibration normal to the cruciform plane.
Summary of the Invention The invention is rotation sensor having an elec-trically vibrated cantilevered silicon beam supported from an integral silicon support structure. A piezo-resistive element is diffused on the surface of the beam at its base end which is only responsive to the stresses produced by the rotation of the vibrating beam about an axis parallel to its length. In the preferred embodiment the oscillator circuit for generating the electrical signals stimulating the vibration of the cantilever beam and amplifer circuits converting the resistance changes of the piezoresistive element to electrical signals are formed on the surface of the silicon substrate using existing inteqrated circuit technology.
1189~7~
In accordance with one aspect o~ the present invention there is provided a rotation sensor comprising a single crystal support structure having an axis of rotation;
an integral cantilever beam supported from the support structure for vibration only in a predetermi.ned plane relative to the support structure and parallel to the axis of rotation, the cantilever beam having a base end attached to the support structure and a free end; means for vibrating the free end of the cantilever beam in the predetermined plane; and first sensor means for detecting traverse stresses at the base resisting rotation of the vibrating cantilever beam about the axis ~o generate a signal having a value corresponding to the rotational velocity of the support structure about the axis of rotation.
In accordance with a second aspect there is provided a method for sensing a rotation comprising the steps of vibrating a single crystal silicon cantilever beam in a predetermined plane relative to a support structure; and detecting the stress induced in the cantilever beam resisting the displacement of the vibrating beam from the predetermined plane due to the rotation of the support structure to generate a rate signal having a value proportional to the rate of rotation.
- 2a -csm/~
1 1~967~
One advantage of the invention is that the sensor has only two parts. Another advantage of the invention is that the piezoresistive elements and electronic circuits can be formed directly on the surfaces of the vibrating beam and the support structure respectively eliminatlng the need for ancillatory support electronics.
Another advantage of the invention is that the associated electronics can be formed directly on the silicon surfaces of the sensor using existing integrated circuit fabrication techniques making the sensor relatively lnexpensive to produce. Still another advantage of the sensor is that it is extremely small compared to compar-able prior art sensors. These and other advantages of the invention will become apparent from r~ading the specification in conjunction with the accompanying drawings.
Brief Discription of the Drawings Figure 1 is a top view of a first embodiment of the rotation velocity sensor.
Figure 2 is a cross sectional view of the embodiment shown in Figure 1.
Figure 3 is a cross sectional view of the sensor showing an alternate configuration for the base electrode.
Figure 4 is a top view of a second embodiment of the rotation velocity sensor having a feedback piezorestive element.
Figure 5 is a top view of a third embodiment of the rotation velocity sensor having the oscillator circuit and amplifier circuit formed directly on the surface of the silicon support structure.
Figure 6 is a block diagram of the rotation sensor in combination with a utilization device.
1 ~96~ 360-80-0290 Detailed Description of the_Invention A top and cross-sectional view of a first embodiment of the vibrating beam rotation sensor are shown or Fig-ures 1 and 2 respectively. The vibrating beam rota~ion sensor embodies a thin single crystal silicon can~ilever beam 10 suspended from an integral silicon support struc-ture 12. The silicon beam 10 may be fabricated using the techniques disclosed by M. F. Hribsek and R. W. Newcomb in the article "High Q Selective Filters Using Mechanical Resonance of Silicon Beams. IEEE Transactions on Circuits and Systems Vol CAS 25, No. 4 April 1978. The silicon support structure is fused to a base electrode 14. The base electrode 14 may be a metal substrate as shown in Figure 2 or may be a thin metalic electrode 14 disposed on the -upper surface of a silicon or glass substrate 16 facing the cantilever beam 10 as shown in Figure 3.
An osclllator 20 generates an alternating electrical potential difference between the base electrode 14 and a beam electrode 18 disposed along a surface of the cantilever beam 10. The beam electrode 18 may be disposed along the bottom of the beam 10 as shown in Figure 2, however it may alternatively be disposed along the top surface of beam 10. The fre~uency of the oscillator 20 corresponds to the resonant frequency of the cantilever beam so that the alternating electric field between electrodes 14 and 18 produces a periodic electrostatic force vibrating beam 10 at or near its natural resonant frequency.
The crystallographic axes of the integral single crystal silicon beam 10 and support structure 12 are selected such that the 001 axis is parallel to the length of the beam and the 110 axis is normal to the length of 1 l69677 the beam and parallel to the beam's top surface. The directions of the 001 and lI0 crystallographic axes are illustrated by arrows 26 and 28 respectively on Figure l.
Similarly, the 001 and llO crystallographic axes are illustrated by arrows 26 and 30 in Figure 2.
A p-type piezorestive element 22 is disposed at the base end of beam lO with its axis parallel to the llO
axis of the beam's crystalline structure. The piezoresistive element may be implanted or diffused into the silicon structure of the beam using methods well known in the art. The orientation of the silicon's crystallographic axes with respect to the beam and the orientation of piezorestive element are critical to the proper operation of the rotation sensor as will be discussed hereinafter.
The operation of the rotation sensor is as follows:
The oscillator circuit 20 produces an oscillating electrostatic field between the beam electrode 18 and the base electrode 14. The oscillating electrostatic field produces a perlodic electrostatic force on cantilevered beam 10 causing it to vibrate at or near its resonant freguency in a plane defined by the 001 and llO axes of the crystallographic structure of beam lO.
The primary stresses produced in the vicinity piezorestive element 22 due to the vibration of the beam are transverse to axis of the piezoresistive element 22.
The sensitivity of the piezoresistive element to this transverse stress is given by:
aR/R = ~ ~ +~ ~ + ~r' ~ ' where ~ R is the change in resistivity of the piezoresistive element;
R is the unstrained resistance of the piezoresistive element;
" 1 16967~
t and ~iY* are the piezoresistive coefficients longitudinal and transverse to the piezoresistive elements' axis and ~ ~ ~ and C~ are the corresponding stresses.
The values for ~1 and ~ for a p-type piezoresis-tive layer are given by O.N. Tufte et al, in the article"Silicon Diffused-Element Piezoresistive Diaphragms"
published in the Journal of Applied Physcis, Volume 33, November 11, pages 3322-3327, November 1961. The transverse piezoresistive coefficient, ~f, for a p-type element with this orientation i5 zero. The stresses along the 110 and 110 axes due to the simple vibration of the beam are vanishing small and can be ignored. The piezoresistive element 22 therefore is insensitive to the simple vibration of the beam in the plane defined by the 110 and 001 axes of the single crystal silicon beam.
As discussed with reference to the vibrating rota-20 tion sensors of the prior art, the law of conservation of angular momentum will tend to keep the beam 10 vibrating in it's initial plane of vibration unless acted on by a torque. Rotation of the substrate 12 about an axis 32 passing through the length of the beam 10 will produce a torque on beam 10, resulting in a stress along the 110 crystallographic axis. The piezoresistive element 22 located at the base of the beam will respond to this stress and produce a change ~R in its resistance value R.
The sensitivity of a p-type lightly doped silicon piezoresistive element for a longitudinal stress is R/R z ~ ~ 44 /2) ~
where ~44 has a value 138 x 10 12 cm2/dyne and ~ is the stress produced due to the moment of inertia of the ~ 16967~ 360-80-0290 vibrating beam resisting rotation. The factors ~ and as taught by O. N. Tufle et al are only possible second order components of a transverse stress produced by the twisting force. Therefore a rotation of the sensor about axis 32 passing through the length of beam 10 will pro-duce a change, ~ R, in the value of the piezoresistive element proportional to force produced by the vibrating beam lO resisting rotation. Because the force resisting rotation is proportional to the vibrating beam's moment of inertia, the change ~ R in the resistance of the piezo-resistive element 22 will fluctuate at a frequency corresponding to the frequency vibrating beam 10 and have a magnitude proportion to the rate at which the support structure is rotated.
A second embodiment of the vibrating beam rotation sensor is shown on Figures 4. This embodiment of the sensor is basically the same as shown on Figures 1 and 2 but includes a second piezoresistive element 34 disposed on the surface of the beam 10 having its length or axis parallel to the 001 crystallographic axis.
The piezoresistive element 34 is connected in series with a fixed resistance element 36 between a source of electrical power designated B+ and a common ground. The junction between fixed resistance element 36 and piezo-resistive element 34 is connected to an operationalamplifier 38. The output of amplifier 38 is connected to the beam electrode 18 and a phase detector 44.
The piezoresistive element 22 is connected in series with a second fixed resistance element 40 between the source of electrical power and a common ground. The junction between fixed resistance element 40 and piezoresistive element 22 is connected to the input of an operational amplier 42 having its output connected to the phase detector 44 and an output terminal 46. The phase detector 44 produces an output on terminal 48. As is ~ 16967~ 360-80-0290 known in the art, terminals 46 and 48 may be connected to a display or utilization device such as an automatic pilot for an aircraft or a guidance system for a missile.
The operation of the rotation sensor illustrated on Figure 4 is as follows: Piezoresistive element 34 in contrast to piezoresistive element 22 is sensitive to the vibration of beam 10, and its resistance will oscillate between a maximum and minumum values in synchroni~ation with the vibration of beam 10. The serially connected fixed resistance element 36 and piezoresistive element 34 form a voltage divider network generating an oscillating signal, at its junction, having a frequency corresponding to the resonant frequency of beam 10. This signal is amplified by operational amplifier 36 and the amplified signal is applied between base electrode 14 and beam electrode 18 producing an electrostatic force sustaining the vibration of beam 10. The combination of beam 10, piezoresistive element 34 and amplifier 38 function as conventional Hartley oscillator where the beam 10 is equivalent to a tuned circuit and piezoresistive element 34 provides the re~uired feedback signal. It is assumed that the operational amplifier 36 includes any necessary phase shift capabilities such that its amplified signal applied between electrodes 14 and 18 will have the proper phase for sustaining the vibration of beam 10.
Piezoresistive element 22, as described with refer-ence to Figures 1 and 2, is insensitive to the simple vibration of beam 10 but will change value in response to ; any stress generated when the support substate is rotated about axis of rotation 32. This change in resistance is converted to a voltage signal at the junction between fixed resistance element 40 and piezoresistive element 22. This voltage signal is amplified by operational amplifier 42 which functions as a buffer amplifier. The output of amplifier 42 is a signal having a value - ~169677 360-80-0290 indicative of the rate at which the support structure is being rotated and a phase with respect to the vibration of the beam 10 indicative of the direction in which the support structure is rotated. The phase of the output signals of amplifiers 38 and 42 are compared ln the phase detector 44 which outputs a first signal when the two signals are in phase indicating the support structure is being rotated in a fir~t direction and a second signal when the two signals are 180 degrees out of phase indicating the support structure is being rotated in the opposite direction.
Referring now to Figure 5, fixed resistance elements 36 and 40 may be diffused or implanted directly on the surface of the support structure 12 along with opera-tional amplifiers 38 and 42 using existing integratedcircuit technology. A power source, such as battery 50 delivers electrical power the integrated electronic circuits and piezoresistive elements via terminal 52.
~erminal 46 receives the output of amplifier 42 indi-cative of the rate at which the support substrate isrotating about the axes of rotation 32 and is equivalent to terminal 46 discussed with reference to Figure 4. The phase detector 44 may be a seperate entity as shown with respect to Figure 4 or may also be formed on the surface of the silicon support structure along with amplifier 38 and 42 as shown on Figure 5.
Referring now to Figure 6, there is shown a rotation sensor 60 of the type shown in Figure 5 in conjunction with a utilization device 64. Utilization device 64 may be an automatic pilot for an aircraft, a guidance system for a missile, or simply a display panel. The output signals on terminals 46 and 48 of rotation sensor 60 are the outputs of amplifier 42 and phase detector 44 as discussed relative to Figure 5. Terminals 46 and 48 are connected to a signal generator 62 which converts the ~ 16967~ 360-80-0290 amplitude of the signal output by amplifier 42 into a rotational velocity signal. This rotational velocity signal may be an analog signal, a frequency signal or a digital signal indicative of the sensed rotational velocity. The signal generator 62 also outputs a signal indicative of the rotational direction. The outputs of the signal generator 62 are received by the utilization device 64.
The rotational velocity signal generated by the signal generator 62 may also be received by an integrator 66 which integrates the rotational velocity signal with respect to time to generate an attitude or displacement signal indicative of the total rotational (angular) displacement of the sensor from a reference position.
The attitude signal may also be received and utilized by the utilization device.
The rotational velocity signal generated by the signal generator 62 may also be received by a differentiator 68 which dlfferentiates the rotational velocity signal with respect to time to generate a rotational (angular) acceleration signal indicative of the rotational acceleration of the sensor 60. The rotational acceleration signal may also be received and utilized by the utilization device 64.
It is not intended that the invention be limited to the exact configuration shown, materials or circuits discussed herein. It is submitted that one skilled in the art may make changes or modifications without departing from the spirit of the invention as disclosed or set forth in the appended claims.
VIBRATING BEAM ROTATION SENSOR
~ackground of the Invention Field of the Invention The invention is related to the field of rotation sensors and in particular to a vibrating beam rotation sensor.
Prior Art The use of a vibrating reed or cantilever beam to detect a rotational velocity is known in the art. ~.
Lyman is U.S. patent 2,513,340 discloses a resiliently mounted electrically driven tuning fork. The vibration of the fork produces periodic changes in its moment of inertia. The periodic changes in the tuning fork's moment of inertia produce periodic forces opposing angular rotation. An angular lag or displacement between the resiliently mounted tuning fork and its base is proportional to the angular or rotational acceleration while the amplitude of the periodic force ls proportional to the rotational velocity.
The concept of a single vibrating member is disclosed by Barnaby et al in U.S. patent 2,544,646. In his angular velocity measuring instrument, two serially connected reeds or cantilever beams are constrained to vibrate at right angles to each other. The first or lower beam is electrically stimulated to vibrate the upper beam. The moment of inertia of the upper beam will produce a periodically varying force resisting an angular displacement from its initial plane of vibration. This periodic force is proportional to the displacement.
Rotation of the lower beam will cause the upper beam to vibrate in a plane normal to vibration plane of the lower beam. The vibration amplitude of the upper beam is pro-portional to the angular velocity of rotation. In two of aarnaby's embodiments, the upper and lower beams are piezoelectric crystals.
Mumme in V.S. patent 3,842,681 expands Barnaby's vibrating beam concept to a two axis angular rate sensor.
In the sensor disclosed by Mumme, the lower vibrating reed is replaced by an oscillating rotary hub. Four cantilever beams are supported from the hub in a cruciform pattern normal to its oscillatory axis and are oscillated as rigid members. Coriolis forces generated by the oscillating cantilever beams oppose the rotation of sensor about one of the axes defined by the cruciform cantilever beam configuration and cause the beams defining the other axis to vibrate in a direction normal to the cruciform plane. The cantilever beams are made from a piezoelectric material which outputs a signal in response to their vibration normal to the cruciform plane.
Summary of the Invention The invention is rotation sensor having an elec-trically vibrated cantilevered silicon beam supported from an integral silicon support structure. A piezo-resistive element is diffused on the surface of the beam at its base end which is only responsive to the stresses produced by the rotation of the vibrating beam about an axis parallel to its length. In the preferred embodiment the oscillator circuit for generating the electrical signals stimulating the vibration of the cantilever beam and amplifer circuits converting the resistance changes of the piezoresistive element to electrical signals are formed on the surface of the silicon substrate using existing inteqrated circuit technology.
1189~7~
In accordance with one aspect o~ the present invention there is provided a rotation sensor comprising a single crystal support structure having an axis of rotation;
an integral cantilever beam supported from the support structure for vibration only in a predetermi.ned plane relative to the support structure and parallel to the axis of rotation, the cantilever beam having a base end attached to the support structure and a free end; means for vibrating the free end of the cantilever beam in the predetermined plane; and first sensor means for detecting traverse stresses at the base resisting rotation of the vibrating cantilever beam about the axis ~o generate a signal having a value corresponding to the rotational velocity of the support structure about the axis of rotation.
In accordance with a second aspect there is provided a method for sensing a rotation comprising the steps of vibrating a single crystal silicon cantilever beam in a predetermined plane relative to a support structure; and detecting the stress induced in the cantilever beam resisting the displacement of the vibrating beam from the predetermined plane due to the rotation of the support structure to generate a rate signal having a value proportional to the rate of rotation.
- 2a -csm/~
1 1~967~
One advantage of the invention is that the sensor has only two parts. Another advantage of the invention is that the piezoresistive elements and electronic circuits can be formed directly on the surfaces of the vibrating beam and the support structure respectively eliminatlng the need for ancillatory support electronics.
Another advantage of the invention is that the associated electronics can be formed directly on the silicon surfaces of the sensor using existing integrated circuit fabrication techniques making the sensor relatively lnexpensive to produce. Still another advantage of the sensor is that it is extremely small compared to compar-able prior art sensors. These and other advantages of the invention will become apparent from r~ading the specification in conjunction with the accompanying drawings.
Brief Discription of the Drawings Figure 1 is a top view of a first embodiment of the rotation velocity sensor.
Figure 2 is a cross sectional view of the embodiment shown in Figure 1.
Figure 3 is a cross sectional view of the sensor showing an alternate configuration for the base electrode.
Figure 4 is a top view of a second embodiment of the rotation velocity sensor having a feedback piezorestive element.
Figure 5 is a top view of a third embodiment of the rotation velocity sensor having the oscillator circuit and amplifier circuit formed directly on the surface of the silicon support structure.
Figure 6 is a block diagram of the rotation sensor in combination with a utilization device.
1 ~96~ 360-80-0290 Detailed Description of the_Invention A top and cross-sectional view of a first embodiment of the vibrating beam rotation sensor are shown or Fig-ures 1 and 2 respectively. The vibrating beam rota~ion sensor embodies a thin single crystal silicon can~ilever beam 10 suspended from an integral silicon support struc-ture 12. The silicon beam 10 may be fabricated using the techniques disclosed by M. F. Hribsek and R. W. Newcomb in the article "High Q Selective Filters Using Mechanical Resonance of Silicon Beams. IEEE Transactions on Circuits and Systems Vol CAS 25, No. 4 April 1978. The silicon support structure is fused to a base electrode 14. The base electrode 14 may be a metal substrate as shown in Figure 2 or may be a thin metalic electrode 14 disposed on the -upper surface of a silicon or glass substrate 16 facing the cantilever beam 10 as shown in Figure 3.
An osclllator 20 generates an alternating electrical potential difference between the base electrode 14 and a beam electrode 18 disposed along a surface of the cantilever beam 10. The beam electrode 18 may be disposed along the bottom of the beam 10 as shown in Figure 2, however it may alternatively be disposed along the top surface of beam 10. The fre~uency of the oscillator 20 corresponds to the resonant frequency of the cantilever beam so that the alternating electric field between electrodes 14 and 18 produces a periodic electrostatic force vibrating beam 10 at or near its natural resonant frequency.
The crystallographic axes of the integral single crystal silicon beam 10 and support structure 12 are selected such that the 001 axis is parallel to the length of the beam and the 110 axis is normal to the length of 1 l69677 the beam and parallel to the beam's top surface. The directions of the 001 and lI0 crystallographic axes are illustrated by arrows 26 and 28 respectively on Figure l.
Similarly, the 001 and llO crystallographic axes are illustrated by arrows 26 and 30 in Figure 2.
A p-type piezorestive element 22 is disposed at the base end of beam lO with its axis parallel to the llO
axis of the beam's crystalline structure. The piezoresistive element may be implanted or diffused into the silicon structure of the beam using methods well known in the art. The orientation of the silicon's crystallographic axes with respect to the beam and the orientation of piezorestive element are critical to the proper operation of the rotation sensor as will be discussed hereinafter.
The operation of the rotation sensor is as follows:
The oscillator circuit 20 produces an oscillating electrostatic field between the beam electrode 18 and the base electrode 14. The oscillating electrostatic field produces a perlodic electrostatic force on cantilevered beam 10 causing it to vibrate at or near its resonant freguency in a plane defined by the 001 and llO axes of the crystallographic structure of beam lO.
The primary stresses produced in the vicinity piezorestive element 22 due to the vibration of the beam are transverse to axis of the piezoresistive element 22.
The sensitivity of the piezoresistive element to this transverse stress is given by:
aR/R = ~ ~ +~ ~ + ~r' ~ ' where ~ R is the change in resistivity of the piezoresistive element;
R is the unstrained resistance of the piezoresistive element;
" 1 16967~
t and ~iY* are the piezoresistive coefficients longitudinal and transverse to the piezoresistive elements' axis and ~ ~ ~ and C~ are the corresponding stresses.
The values for ~1 and ~ for a p-type piezoresis-tive layer are given by O.N. Tufte et al, in the article"Silicon Diffused-Element Piezoresistive Diaphragms"
published in the Journal of Applied Physcis, Volume 33, November 11, pages 3322-3327, November 1961. The transverse piezoresistive coefficient, ~f, for a p-type element with this orientation i5 zero. The stresses along the 110 and 110 axes due to the simple vibration of the beam are vanishing small and can be ignored. The piezoresistive element 22 therefore is insensitive to the simple vibration of the beam in the plane defined by the 110 and 001 axes of the single crystal silicon beam.
As discussed with reference to the vibrating rota-20 tion sensors of the prior art, the law of conservation of angular momentum will tend to keep the beam 10 vibrating in it's initial plane of vibration unless acted on by a torque. Rotation of the substrate 12 about an axis 32 passing through the length of the beam 10 will produce a torque on beam 10, resulting in a stress along the 110 crystallographic axis. The piezoresistive element 22 located at the base of the beam will respond to this stress and produce a change ~R in its resistance value R.
The sensitivity of a p-type lightly doped silicon piezoresistive element for a longitudinal stress is R/R z ~ ~ 44 /2) ~
where ~44 has a value 138 x 10 12 cm2/dyne and ~ is the stress produced due to the moment of inertia of the ~ 16967~ 360-80-0290 vibrating beam resisting rotation. The factors ~ and as taught by O. N. Tufle et al are only possible second order components of a transverse stress produced by the twisting force. Therefore a rotation of the sensor about axis 32 passing through the length of beam 10 will pro-duce a change, ~ R, in the value of the piezoresistive element proportional to force produced by the vibrating beam lO resisting rotation. Because the force resisting rotation is proportional to the vibrating beam's moment of inertia, the change ~ R in the resistance of the piezo-resistive element 22 will fluctuate at a frequency corresponding to the frequency vibrating beam 10 and have a magnitude proportion to the rate at which the support structure is rotated.
A second embodiment of the vibrating beam rotation sensor is shown on Figures 4. This embodiment of the sensor is basically the same as shown on Figures 1 and 2 but includes a second piezoresistive element 34 disposed on the surface of the beam 10 having its length or axis parallel to the 001 crystallographic axis.
The piezoresistive element 34 is connected in series with a fixed resistance element 36 between a source of electrical power designated B+ and a common ground. The junction between fixed resistance element 36 and piezo-resistive element 34 is connected to an operationalamplifier 38. The output of amplifier 38 is connected to the beam electrode 18 and a phase detector 44.
The piezoresistive element 22 is connected in series with a second fixed resistance element 40 between the source of electrical power and a common ground. The junction between fixed resistance element 40 and piezoresistive element 22 is connected to the input of an operational amplier 42 having its output connected to the phase detector 44 and an output terminal 46. The phase detector 44 produces an output on terminal 48. As is ~ 16967~ 360-80-0290 known in the art, terminals 46 and 48 may be connected to a display or utilization device such as an automatic pilot for an aircraft or a guidance system for a missile.
The operation of the rotation sensor illustrated on Figure 4 is as follows: Piezoresistive element 34 in contrast to piezoresistive element 22 is sensitive to the vibration of beam 10, and its resistance will oscillate between a maximum and minumum values in synchroni~ation with the vibration of beam 10. The serially connected fixed resistance element 36 and piezoresistive element 34 form a voltage divider network generating an oscillating signal, at its junction, having a frequency corresponding to the resonant frequency of beam 10. This signal is amplified by operational amplifier 36 and the amplified signal is applied between base electrode 14 and beam electrode 18 producing an electrostatic force sustaining the vibration of beam 10. The combination of beam 10, piezoresistive element 34 and amplifier 38 function as conventional Hartley oscillator where the beam 10 is equivalent to a tuned circuit and piezoresistive element 34 provides the re~uired feedback signal. It is assumed that the operational amplifier 36 includes any necessary phase shift capabilities such that its amplified signal applied between electrodes 14 and 18 will have the proper phase for sustaining the vibration of beam 10.
Piezoresistive element 22, as described with refer-ence to Figures 1 and 2, is insensitive to the simple vibration of beam 10 but will change value in response to ; any stress generated when the support substate is rotated about axis of rotation 32. This change in resistance is converted to a voltage signal at the junction between fixed resistance element 40 and piezoresistive element 22. This voltage signal is amplified by operational amplifier 42 which functions as a buffer amplifier. The output of amplifier 42 is a signal having a value - ~169677 360-80-0290 indicative of the rate at which the support structure is being rotated and a phase with respect to the vibration of the beam 10 indicative of the direction in which the support structure is rotated. The phase of the output signals of amplifiers 38 and 42 are compared ln the phase detector 44 which outputs a first signal when the two signals are in phase indicating the support structure is being rotated in a fir~t direction and a second signal when the two signals are 180 degrees out of phase indicating the support structure is being rotated in the opposite direction.
Referring now to Figure 5, fixed resistance elements 36 and 40 may be diffused or implanted directly on the surface of the support structure 12 along with opera-tional amplifiers 38 and 42 using existing integratedcircuit technology. A power source, such as battery 50 delivers electrical power the integrated electronic circuits and piezoresistive elements via terminal 52.
~erminal 46 receives the output of amplifier 42 indi-cative of the rate at which the support substrate isrotating about the axes of rotation 32 and is equivalent to terminal 46 discussed with reference to Figure 4. The phase detector 44 may be a seperate entity as shown with respect to Figure 4 or may also be formed on the surface of the silicon support structure along with amplifier 38 and 42 as shown on Figure 5.
Referring now to Figure 6, there is shown a rotation sensor 60 of the type shown in Figure 5 in conjunction with a utilization device 64. Utilization device 64 may be an automatic pilot for an aircraft, a guidance system for a missile, or simply a display panel. The output signals on terminals 46 and 48 of rotation sensor 60 are the outputs of amplifier 42 and phase detector 44 as discussed relative to Figure 5. Terminals 46 and 48 are connected to a signal generator 62 which converts the ~ 16967~ 360-80-0290 amplitude of the signal output by amplifier 42 into a rotational velocity signal. This rotational velocity signal may be an analog signal, a frequency signal or a digital signal indicative of the sensed rotational velocity. The signal generator 62 also outputs a signal indicative of the rotational direction. The outputs of the signal generator 62 are received by the utilization device 64.
The rotational velocity signal generated by the signal generator 62 may also be received by an integrator 66 which integrates the rotational velocity signal with respect to time to generate an attitude or displacement signal indicative of the total rotational (angular) displacement of the sensor from a reference position.
The attitude signal may also be received and utilized by the utilization device.
The rotational velocity signal generated by the signal generator 62 may also be received by a differentiator 68 which dlfferentiates the rotational velocity signal with respect to time to generate a rotational (angular) acceleration signal indicative of the rotational acceleration of the sensor 60. The rotational acceleration signal may also be received and utilized by the utilization device 64.
It is not intended that the invention be limited to the exact configuration shown, materials or circuits discussed herein. It is submitted that one skilled in the art may make changes or modifications without departing from the spirit of the invention as disclosed or set forth in the appended claims.
Claims (43)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A rotation sensor comprising:
a single crystal support structure having an axis of rotation;
an integral cantilever beam supported from said support structure for vibration only in a predetermined plane relative to said support structure and parallel to said axis of rotation, said cantilever beam having a base end attached to said support structure and a free end;
means for vibrating the free end of said cantilever beam in said predetermined plane; and first sensor means for detecting traverse stresses at said base resisting rotation of said vibrating cantilever beam about said axis to generate a signal having a value corresponding to the rotational velocity of said support structure about said axis of rotation.
a single crystal support structure having an axis of rotation;
an integral cantilever beam supported from said support structure for vibration only in a predetermined plane relative to said support structure and parallel to said axis of rotation, said cantilever beam having a base end attached to said support structure and a free end;
means for vibrating the free end of said cantilever beam in said predetermined plane; and first sensor means for detecting traverse stresses at said base resisting rotation of said vibrating cantilever beam about said axis to generate a signal having a value corresponding to the rotational velocity of said support structure about said axis of rotation.
2. The rotation sensor of Claim 1 wherein said single crystal material is single crystal silicon.
3. The rotation sensor of Claim 1 wherein said single crystal silicon has a 001 crystallographic axis parallel to said axis of rotation and a 110 crystallographic axis normal to said 001 axis.
4. The rotation sensor of Claim 3 wherein said cantilever beam has a retangular configuration, said 110 crystallographic axis is parallel to one surface of said cantilever beam.
5. The rotation sensor of Claim 4 wherein said one surface is normal to the cantilever beams plane of vibration.
6. The rotation sensor of Claim 4 or 5 wherein said first sensor means is a p-type piezoresistive element formed on said one surface of said cantilever beam adjacent to said base end, said piezoresistive element having an axis parallel to said 110 crystallographic axis.
7. The rotation sensor of Claim 5 wherein said first sensor means comprises:
a p-type piezoresistive element formed in said one surface adjacent to said base end, said piezoresistive element having an axis parallel to said 1?0 crystallographic axis, and first amplifier circuit means formed in the surface of said support structure and connected to said piezore-sistive element for generating an output signal having a value indicative of the resistance value of said piezoresistive element.
a p-type piezoresistive element formed in said one surface adjacent to said base end, said piezoresistive element having an axis parallel to said 1?0 crystallographic axis, and first amplifier circuit means formed in the surface of said support structure and connected to said piezore-sistive element for generating an output signal having a value indicative of the resistance value of said piezoresistive element.
8. The rotation sensor of Claim 1 wherein said means for vibrating said cantilever beam comprises:
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said cantilever beam.
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said cantilever beam.
9. The rotation sensor of Claim 8 wherein said oscillator means comprises:
second sensor means for detecting the vibration of said cantilever beam to produce a signal having a frequency component corresponding to the vibration frequency of the cantilever beam; and amplifier means for amplifying the signal generated by said second sensor to generate said oscillating electric potential between said beam and fixed electrode.
second sensor means for detecting the vibration of said cantilever beam to produce a signal having a frequency component corresponding to the vibration frequency of the cantilever beam; and amplifier means for amplifying the signal generated by said second sensor to generate said oscillating electric potential between said beam and fixed electrode.
10. The rotation sensor of Claim 3 wherein said means for vibrating said cantilever beam comprises:
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode rigidly supported from said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam and fixed electrodes to produce an electrostatic force vibrating said cantilever beam.
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode rigidly supported from said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam and fixed electrodes to produce an electrostatic force vibrating said cantilever beam.
11. The rotation sensor of Claim 10 wherein said oscillator means comprises:
second sensor means for detecting the vibration of said cantilever beam to generate an output signal having a frequency corresponding to the vibrating frequency of the cantilever beams; and second amplifier means for amplifying said output signal to generate said oscillating electric potential.
second sensor means for detecting the vibration of said cantilever beam to generate an output signal having a frequency corresponding to the vibrating frequency of the cantilever beams; and second amplifier means for amplifying said output signal to generate said oscillating electric potential.
12. The rotation sensor of Claim 11 wherein said second sensor means is a second piezoresistive element formed on the surface of said cantilever beam adjacent to its base end and said amplifier is an integrated circuit formed on the surface of said support structure.
13. The rotation sensor of Claim 12 wherein said second piezoresistive element has its axis parallel to the 001 crystallographic axis of said integral structure.
14. The rotation sensor of Claim 7 wherein said means for vibrating said cantilever beam comprises:
a beam electrode disposed the surface of said cantilever beam opposite said one surface;
a fixed electrode regidly supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said beam.
a beam electrode disposed the surface of said cantilever beam opposite said one surface;
a fixed electrode regidly supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said beam.
15. The rotation sensor of Claim 14 wherein said oscillator means comprises:
a second piezoresistive element formed on the surface of said cantilever beam adjacent to its base end, said second piezoresistive having a resistance value oscillating in response to the vibration of said cantilever beam; and an integrated oscillator circuit formed on the surface of said support structure, said integrated oscil-lator circuit generating said oscillating electric potential between said beam electrode and said fixed electrode in response to the oscillating resistance value of said second piezoresistive element.
a second piezoresistive element formed on the surface of said cantilever beam adjacent to its base end, said second piezoresistive having a resistance value oscillating in response to the vibration of said cantilever beam; and an integrated oscillator circuit formed on the surface of said support structure, said integrated oscil-lator circuit generating said oscillating electric potential between said beam electrode and said fixed electrode in response to the oscillating resistance value of said second piezoresistive element.
16. The rotation sensor of Claim 1 further including phase detector means for detecting the phase relationship between said vibrating cantilever beam and the signal generated by said first sensor to generate a signal indicating the direction of rotation of said support structure.
17. The rotation sensor of Claims 1 or 16 further including integrator means for integrating the signal generated by said first sensor means to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position.
18. The rotation sensor of Claims 1 or 16 further including differentiator means for differentiating the signal generated by said first sensor to generate an acceleration signal indicative of the angular acceleration of said support structure.
19. The rotation sensor of Claims 1 or 16 further including:
integrator means for integrating the signal generated by said first sensor to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position and differentiator means for differentiating the signal generated by said first detector to generate an acceleration signal indicative of the angular acceleration of said support structure.
integrator means for integrating the signal generated by said first sensor to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position and differentiator means for differentiating the signal generated by said first detector to generate an acceleration signal indicative of the angular acceleration of said support structure.
20. The rotation sensor of Claim 14 further including phase detector means for detecting the phase relationship between said oscillator means and the output of said first amplifier circuit means to generate a signal indicating the direction of rotation of said support structure.
21.. The rotation sensor of Claims 11 or 20 further including integrator means for integrating the output of said first amplifier circuit means to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position.
22. The rotation sensor of Claims 14 or 20 further including differentiator means for differentiating the output of said first amplifier means to generate an acceleration signal indicative of the angular acceleration of said support structure.
23. The rotation sensor of Claims 14 or 20 further including:
integrator means for integrating the output of said first amplifier circuit means to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position; and differentiator means for differentiating the output of said first amplifier means to generate an acceleration signal indicative of the angular acceleration of said support structure.
integrator means for integrating the output of said first amplifier circuit means to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position; and differentiator means for differentiating the output of said first amplifier means to generate an acceleration signal indicative of the angular acceleration of said support structure.
24. A micromechanical angular rate sensor comprising:
an integral single crystal support structure and cantilever beam, said cantilever beam supported from said support structure parallel to an axis of rotation;
means for vibrating said cantilever beam in a plane parallel to said axis of rotation; and first sensor means for detecting the stresses at the base of said cantilever beam in a plane normal to said axis of rotation to generate a rate signal indicative of the rotation of said support structure about said axis of rotation.
an integral single crystal support structure and cantilever beam, said cantilever beam supported from said support structure parallel to an axis of rotation;
means for vibrating said cantilever beam in a plane parallel to said axis of rotation; and first sensor means for detecting the stresses at the base of said cantilever beam in a plane normal to said axis of rotation to generate a rate signal indicative of the rotation of said support structure about said axis of rotation.
25. The angular rate sensor of Claim 24 wherein said single crystal is single crystal silicon.
26. The angular rate sensor of Claim 25 wherein said single crystal silicon a 001 crystallographic axis parallel to said axis of rotation and a 1?0 crystallo-graphic axis normal to said 001 axis; and said sensor means is a p-type piezoresistive element formed on said cantilever beam adjacent to said support structure, said piezoresistive element having an axis parallel to said 1?0 crystallographic axis.
27. The angular rate sensor of Claim 26 further including first amplifier circuit means formed on the surface of said support structure. and connected to said piezoresistive element for generating an output signal having a value indicative of the resistance value of said piezoresistive element.
28. The angular rate sensor of Claim 26 wherein said means for vibrating said cantilever beam comprises:
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said cantilever beam.
a beam electrode disposed on a surface of said cantilever beam;
a fixed electrode supported by said support structure proximate said beam electrode; and oscillator means for generating an oscillating electric potential between said beam electrode and said fixed electrode to produce an electrostatic force vibrating said cantilever beam.
29. The angular rate sensor of Claim 28 wherein said oscillator means comprises:
second sensor means for detecting the vibration of said cantilever beam to generate an output signal having a frequency corresponding to the vibrating frequency of the cantilever beams; and second amplifier means for amplifying said output signal to generate said oscillating electric potential.
second sensor means for detecting the vibration of said cantilever beam to generate an output signal having a frequency corresponding to the vibrating frequency of the cantilever beams; and second amplifier means for amplifying said output signal to generate said oscillating electric potential.
30,. The angular rate sensor of Claim 29 wherein said second sensor means is a second piezoresistive element formed on the surface of said cantilever beam adjacent to said support structure and said amplifier is an integrated circuit formed on the surface of said support structure.
31. The angular rate sensor of Claim 29 further including phase detector means for detecting the phase relationship between the output signals of said first and second amplifiers to generate a direction signal indicating the direction the support structure is rotating with respect to axis.
32. The angular rate sensor of Claim 31 further including integrator means for integrating the output of said first amplifier with respect to time to generate a displacement signal indicative of the total angular displacement of said support structure from a predetermined position.
33. The angular rate sensor of Claim 31 or 32 further including a differentiator circuit for differentiating the output of said first amplifier with respect to time to generate a signal indicative of the angular acceleration of said support structure.
34. A method for sensing a rotation comprising the steps of:
vibrating a single crystal silicon cantilever beam in a predetermined plane relative to a support structure; and detecting the stress induced in said cantilever beam resisting the displacement of said vibrating beam from said predetermined plane due to the rotation of said support structure to generate a rate signal having a value proportional to the rate of rotation.
vibrating a single crystal silicon cantilever beam in a predetermined plane relative to a support structure; and detecting the stress induced in said cantilever beam resisting the displacement of said vibrating beam from said predetermined plane due to the rotation of said support structure to generate a rate signal having a value proportional to the rate of rotation.
35. The method of Claim 34 wherein the 001 crystallographic axis of said single crystal silicon is parallel to the length of said cantilever beam and said 1?0 crystallographic axis is normal to said beam, said step of vibrating vibrates said beam in a plane normal to said 1?0 crystallographic axis and said step of detecting includes detecting with a piezoresistive element formed on the surface of said cantilever beam with its length parallel to said 1?0 crystallographic axis to generate said rate signal having a value proportional to the stress induced in said cantilever beam due to a rotation about an axis parallel to said 001 crystallographic axis.
36. The method of Claim 35 wherein said step of detecting further includes converting the changes in the resistance value of said piezoresistive element due to said rotation to generate an electrical rate signal having a value proportional to the rate of rotation.
37. The method of Claim 36 wherein said step of vibrating comprises:
generating an oscillating electrical signal;
applying said oscillating signal between a fixed electrode and an electrode disposed on said cantilever beam to generate an electric field therebetween and produce an electrostatic force vibrating said beam.
generating an oscillating electrical signal;
applying said oscillating signal between a fixed electrode and an electrode disposed on said cantilever beam to generate an electric field therebetween and produce an electrostatic force vibrating said beam.
38. The method of Claim 37 wherein said step of generating an oscillating eiectrical signal generates an oscillating electric signal having a frequency corresponding to the resonant frequency of said cantilever beam.
39. The method of Claim 38 wherein said step of generating an oscillating field comprises the steps of:
detecting the vibration of said cantilever beam to generate an input signal having a frequency component corresponding to the vibrating frequency of said beam; and amplifying said input signal to generate said electrical signal.
detecting the vibration of said cantilever beam to generate an input signal having a frequency component corresponding to the vibrating frequency of said beam; and amplifying said input signal to generate said electrical signal.
40. The method of Claim 39 wherein said step of detecting the vibration frequency of said cantilever beam comprises the steps of:
detecting with a piezoresistive element formed on the surfaces of said beam the stresses induced in said beam due to its vibration.
detecting with a piezoresistive element formed on the surfaces of said beam the stresses induced in said beam due to its vibration.
41. The method of Claim 37 further including the step of comparing the phase of said electrical rate signal with said electrical signal to generate a phase signal indicative of the direction of rotation.
42. The method of Claim 40 further including the step of differentiating said rate signal to generate an angular acceleration signal.
43. The method of claims 40 or 41 further including the step of integrating said rate signal to generate a displacement signal indicative of the angle through which the vibrating cantilever beam was rotated.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US240,518 | 1981-03-04 | ||
| US06/240,518 US4381672A (en) | 1981-03-04 | 1981-03-04 | Vibrating beam rotation sensor |
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| Publication Number | Publication Date |
|---|---|
| CA1169677A true CA1169677A (en) | 1984-06-26 |
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ID=22906857
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000396486A Expired CA1169677A (en) | 1981-03-04 | 1982-02-17 | Vibrating beam rotation sensor |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4381672A (en) |
| EP (1) | EP0060185B1 (en) |
| JP (1) | JPS57160067A (en) |
| CA (1) | CA1169677A (en) |
| DE (1) | DE3267089D1 (en) |
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| US3992952A (en) * | 1974-12-20 | 1976-11-23 | The Singer Company | Control system for angular displacement sensor |
| JPS5925486B2 (en) * | 1977-11-15 | 1984-06-18 | シチズン時計株式会社 | piezoelectric vibrator container |
| US4264838A (en) * | 1979-10-01 | 1981-04-28 | Sperry Corporation | Force balanced piezoelectric vibratory rate sensor |
-
1981
- 1981-03-04 US US06/240,518 patent/US4381672A/en not_active Expired - Fee Related
-
1982
- 1982-02-17 CA CA000396486A patent/CA1169677A/en not_active Expired
- 1982-03-02 EP EP82400351A patent/EP0060185B1/en not_active Expired
- 1982-03-02 DE DE8282400351T patent/DE3267089D1/en not_active Expired
- 1982-03-04 JP JP3452382A patent/JPS57160067A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| DE3267089D1 (en) | 1985-12-05 |
| JPS57160067A (en) | 1982-10-02 |
| EP0060185B1 (en) | 1985-10-30 |
| US4381672A (en) | 1983-05-03 |
| EP0060185A1 (en) | 1982-09-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |