Angular velocity sensor

An angular velocity sensor including a framelike vibrator supported on a fixed support portion via a pair of beams. The framelike vibrator is placed into an inertial state by being vibrated by a driving means, and a displacement of the framelike vibrator due to Coriolis force is detected. The fixed support portion is formed on a support substrate made of a material having a different coefficient of thermal expansion in the center of the framelike vibrator, and the beams are T-shaped and include a first beam portion for displacing the framelike vibrator by the driving means in the driving direction, and a second beam portion for displacing the framelike vibrator in the direction of generation of the Coriolis force.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an angular velocity sensor for use in a
 car navigation system, a camera shaking prevention device, a robot
 attitude control device, and the like.
 2. Description of the Related Art
 A conventional angular velocity sensor 40 will be described below with
 reference to FIGS. 7 and 8. Four anchor portions 42 are formed at the four
 corners of a support substrate 41 made of Pyrex glass. L-shaped beams 43
 are connected at one end to the anchor portions 42 and are connected at
 the other end to the four corners of a vibration weight 44, respectively.
 The vibration weight 44 serves as the load mass of the angular velocity
 sensor 40, and is allowed by the bending of the beams 43 to freely vibrate
 in the XY plane.
 Comb-shaped movable electrodes 44a and 44b are formed on end faces (in the
 X-axis direction) of the vibration weight 44, and movable electrodes 44c
 and 44d shaped like the character are formed on the other end faces (in
 the Y-axis direction).
 Fixed portions 45a to 45d are formed on the support substrate 41 between
 the adjoining anchor portions 42, respectively. A comb-shaped fixed
 electrode 46a formed on the inner side face of the fixed portion 45a is
 meshed with space therebetween with the movable electrode 44a to
 constitute a condenser 47a. A comb-shaped fixed electrode 46b formed on
 the inner side face of the fixed portion 45b is meshed with space
 therebetween with the movable electrode 44b to constitute a condenser 47b.
 Two F-shaped fixed electrodes 46c formed on the inner side face of the
 fixed portion 45c are meshed with space therebetween with the movable
 electrode 44c to constitute a condenser 47c. Furthermore, two F-shaped
 fixed electrodes 46d formed on the inner side face of the fixed portion
 45d are meshed with space therebetween with the movable electrode 44d to
 constitute a condenser 47d.
 A space 41a is formed under the beams 43, the vibration weight 44, the
 movable electrodes 44a to 44d, and the fixed electrodes 46a to 46d. In the
 angular velocity sensor 40, the elements, such as the anchor portions 42
 and the vibration weight 44, excluding the support substrate 41, are
 formed by working a silicon substrate. The four anchor portions 42 and the
 fixed portions 45a to 45d, which are made of silicon, are joined onto the
 support substrate 41 of Pyrex glass by anode coupling.
 Next, a description will be given of the operation of the angular velocity
 sensor 40. Since the angular velocity sensor 40 is operated with the
 anchor portions 42 connected to ground, the vibration weight 44 and the
 movable electrodes 44a to 44d are at ground potential.
 The vibration weight 44 is vibrated by electrostatic attractive force in
 the X-axis direction by applying AC voltages having a phase difference of
 180.degree., which are obtained by superimposing DC voltages, to the
 condenser 47a (between the anchor portion 42 and the fixed portion 45a)
 and the condenser 47b (between the anchor portion 42 and the fixed portion
 45b). When the angular velocity sensor 40 rotates about the Z-axis passing
 through the center of the vibration weight 44 while the vibration weight
 44 is thus vibrating, the vibration weight 44 receives a Coriolis force
 generated by the rotating force, and also vibrates in the Y-axis
 direction. The vibration components in the Yaxis direction are detected as
 capacitance changes by the condensers 47c and 47d, and these capacitance
 changes are converted into voltages and are differentially amplified,
 thereby determining the angular velocity.
 In the conventional angular velocity sensor 40, the four anchor portions 42
 made of a silicon material are joined to the four separate corners of the
 support substrate 41 made of a Pyrex glass material. The vibration weight
 44 similarly made of a silicon material is supported integrally with the
 anchor portions 42 via the four beams 43.
 Therefore, the difference in coefficient of thermal expansion between the
 support substrate 41 of Pyrex glass and the anchor portions 42 of silicon
 causes the joint portions therebetween to be warped. Because of this warp,
 the beams 43 connected to the vibration weight 44 receive compressive
 stress or tensile stress. The compressive stress and tensile stress become
 residual stress, which changes the vibration frequency of the vibration
 weight, and has an adverse effect on sensitivity of detection based on
 Coriolis force and the temperature characteristics of the mechanical
 resonant frequency of the vibration weight. For this reason, the detection
 sensitivity and the mechanical resonant frequency of the angular velocity
 sensor change substantially due to changes in temperature.
 SUMMARY OF THE INVENTION
 The present invention can solve the aforementioned problem associated with
 the conventional art and provides an angular velocity sensor with improved
 detection sensitivity and temperature characteristics of the mechanical
 resonant frequency.
 The angular velocity sensor comprises a framelike vibrator supported on a
 support portion via a pair of T-shaped beams, the support portion being
 disposed in the center of the framelike vibrator and being formed on a
 support substrate made of a material having a different coefficient of
 thermal expansion than the support portion. The T-shaped beams include a
 first beam portion structured and arranged for displacing the framelike
 vibrator in a first driving direction, and a second beam portion
 structured and arranged for displacing the framelike vibrator in a second
 direction orthogonal to the first direction in response to Coriolis force
 when the support portion is rotated about an axis extending in a third
 direction orthogonal to the first and second directions.
 According to the present invention, even when the fixed support portion and
 the support substrate are made of different materials and are different in
 coefficient of thermal expansion, since the framelike vibrator is
 supported by the single fixed support portion via the beams, tensile
 stress or compressive stress resulting from the difference in coefficient
 of thermal expansion is concentrated on the fixed support portion or is
 reduced, whereby residual stress on the beams decreases. Therefore, it is
 possible to prevent sensitivity of detection based on Coriolis force and
 the temperature characteristics of the mechanical resonant frequency of
 the vibration weight from being deteriorated due to the residual stress.
 Furthermore, temperature changes do not have a serious influence on the
 framelike vibrator because of the action of the pair of T-shaped beams
 composed of the first beam portion and the second beam portion that are
 placed orthogonal to each other.
 According to another aspect of the present invention, the angular velocity
 sensor comprises an inner framelike vibrator supported on a fixed support
 portion via a pair of inner beams and an outer framelike vibrator
 supported outside the inner framelike vibrator via at least a pair of
 outer beams. The fixed support portion is disposed in the center of the
 inner framelike vibrator and is formed on a support substrate made of a
 material having a different coefficient of thermal expansion in the center
 of the inner framelike vibrator than the support portion. The inner beams
 are structured and arranged to displace the inner framelike vibrator and
 the outer framelike vibrator in a first driving direction and the outer
 beams are structured and arranged to displace the outer framelike vibrator
 in a second direction orthogonal to the first direction in response to a
 Coriolis force when the support portion is rotated about an axis extending
 in a third direction orthogonal to the first and the second directions.
 According to this angular velocity sensor, the action of stress that the
 fixed support portion receives from the support substrate is similar to
 that first angular velocity sensor. That is, since the initial stress and
 stress resulting from temperature changes of the fixed support portion are
 reduced, the stress of the fixed support portion has little effect on the
 inner beams, the inner framelike vibrator, the outer beams, and the outer
 framelike vibrator.
 For the purpose of illustrating the invention, there is shown in the
 drawings several forms which are presently preferred, it being understood,
 however, that the invention is not limited to the precise arrangements and
 instrumentalities shown.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
 An angular velocity sensor according to an preferred embodiment of the
 present invention comprises a framelike vibrator supported on a fixed
 support portion via a pair of beams. The framelike vibrator is placed into
 an inertial state by being vibrated by a driving means, and a displacement
 of the framelike vibrator due to Coriolis force is detected. The fixed
 support portion is formed on a support substrate made of a material having
 a different coefficient of thermal expansion in the center of the
 framelike vibrator, and the beams are T-shaped and include a first beam
 portion for displacing the framelike vibrator by the driving means in the
 driving direction, and a second beam portion for displacing the framelike
 vibrator in the direction of generation of the Coriolis force.
 In this invention, the framelike vibrator is supported, at its center, on
 the support substrate, by a single fixed support portion, via a pair of
 T-shaped beams. The fixed support portion is joined or bonded to the
 support substrate made of a different material at one point in a heated
 atmosphere. Because of this joint or bonding in the presence of heat, when
 the temperature returns to normal temperature, tensile stress or
 compressive stress arises in the fixed support portion. These stresses
 possess temperature characteristics, and change, increase or decrease,
 with temperature. Since the fixed support portion is fixed on the support
 substrate at one point in the minimum area and in isolation, however, the
 stress (distortion), which the fixed support portion receives from the
 support substrate due to the temperature change, is not unevenly
 distributed, but is reduced. In this way, even when there is a difference
 in temperature coefficient between the support substrate and the fixed
 support portion, since the fixed support portion receives only a small
 stress from the support substrate, a pair of beams connected to the
 support substrate also receive a small stress from the initial stress and
 the stress varying with temperature of the support substrate. Therefore,
 the influence of the stress to be applied to the framelike vibrator via
 the pair of beams is reduced. Accordingly, it is possible to prevent
 sensitivity of detection based on Coriolis force and the temperature
 characteristics of the mechanical resonant frequency characteristics from
 being deteriorated due to residual stress and temperature changes of the
 fixed support portion.
 Furthermore, since the first beam portion connected to the support fixed
 portion and the second beam portion connected to the framelike vibrator
 are arranged orthogonal to each other in the pair of T-shaped beams, the
 second beam portion is not bent by the force acting from the direction of
 one of the intersecting axes, e.g., the driving force, whereas the first
 beam portion is bent to vibrate the framelike vibrator in the driving
 direction. In contrast, the first beam portion is not bent by the force
 acting from the direction of the other intersecting axis, e.g., Coriolis
 force, whereas the second beam portion is bent to displace the framelike
 vibrator in the direction of the Coriolis force. The difference in bending
 direction between the first beam portion and the second beam portion of
 the pair of T-shaped beams allows planar motion of the framelike vibrator.
 According to another preferred embodiment of the present invention, an
 inner framelike vibrator is supported on a fixed support portion via a
 pair of inner beams, an outer framelike vibrator is supported outside the
 inner framelike vibrator via at least a pair of outer beams. The inner
 framelike vibrator and the outer framelike vibrator are placed into an
 inertial state by being vibrated by a driving means in a fixed direction,
 and the displacement of the outer framelike vibrator based on Coriolis
 force is detected. The fixed support portion is formed on a support
 substrate made of a material having a different coefficient of thermal
 expansion in the center of the inner framelike vibrator. The inner beams
 displace the inner framelike vibrator and the outer framelike vibrator in
 the direction of driving by the driving means, and the outer beams
 displace the outer framelike vibrator in the direction of generation of
 the Coriolis force.
 According to the structure, the fixed support portion is joined or bonded
 to the support substrate made of a different material at one point. The
 stress that the fixed support portion receives from the support substrate
 acts in a manner similar to that according to the first preferred
 embodiment. That is, since the initial stress and the stress varying with
 temperature of the support substrate are reduced, the stress acting on the
 inner beams is small, and the stress imposed on the inner framelike
 vibrator connected to the inner beams also has little influence.
 Similarly, the stress that the outer framelike vibrator receives has
 little influence.
 The inner beam and the outer beam are arranged orthogonal to each other,
 correspond to the first beam portion and the second beam portion according
 to the first preferred embodiment, respectively, and serve almost similar
 functions. That is, while the outer beams are not bent by the force acting
 from the direction of one of the intersecting axes, e.g., driving force,
 the pair of inner beams are bent to vibrate the inner framelike vibrator
 and the outer framelike vibrator together in the driving direction. In
 contrast, while the inner beams are not bent by the force acting from the
 direction of the other intersecting axes, e.g., Coriolis force, the outer
 beams are bent to vibrate only the outer framelike vibrator in the
 direction of the Coriolis force without displacing the inner framelike
 vibrator. The bending of the inner beams and the outer beams in different
 directions allows planar motion of the outer framelike vibrator.
 Hereinafter, the preferred embodiments of the present invention are
 explained in more detail with reference to the drawings.
 An angular velocity sensor 1 according to the first preferred embodiment of
 the present invention will be described below with reference to FIGS. 1
 and 2. Numeral 1 denotes a support substrate that is formed by working a
 Pyrex glass substrate. On the upper surface of the support substrate 1,
 excluding the peripheral and center portions, a recessed portion la is
 formed to provide a free vibration space for movable sections, such as a
 framelike vibrator, which will be described later. Numeral 2 denotes a
 fixed support portion that is formed by working a silicon substrate, and
 that is formed on a projection at the center of the support substrate 1.
 From both side faces of the fixed support portion 2 in the Y-axis
 direction, first beam portions 3a and 4a extend in opposite directions
 along a straight line, namely, the Y-axis, and the leading ends thereof
 are perpendicularly connected to the centers of second beam portions 3b
 and 4b, respectively. Both ends of the second beam portions 3b and 4b are
 perpendicularly connected to the opposing inner side faces of a framelike
 vibrator 5, respectively. The first beam portion 3a and the second beam
 portion 3b constitute a T-shaped beam 3, and the first beam portion 4a and
 the second beam portion 4b constitute a T-shaped beam 4. The framelike
 vibrator 5 is supported by the fixed support portion 2 via the pair of
 T-shaped beams 3 and 4 so that it is capable of planar motion.
 Comb-shaped movable electrodes 5a and 5b are formed on both outer side
 faces of the framelike vibrator 5 in the extending direction of the second
 beam portions 3b and 4b (in the X-axis direction), respectively. T-shaped
 movable electrodes 5c and 5d are formed on both outer side faces in the
 extending direction of the first beam portions 3a and 4a (in the Y-axis
 direction), respectively.
 On the projecting peripheral portion of the support substrate 1, fixed
 portions 6a and 6b are formed at the positions facing the vibration
 electrodes 5a and 5b , and fixed portions 6c and 6d are formed at the
 positions facing the movable electrodes 5c and 5d, respectively. A
 comb-shaped fixed electrode 7a is formed on the inner side face of the
 fixed portion 6a so as to be meshed with space therebetween with the
 movable electrode 5a. A comb-shaped fixed electrode 7b is formed on the
 inner side face of the fixed portion 6b so as to be meshed with space
 therebetween with the movable electrode 5b . Two L-shaped fixed electrodes
 7c are formed on the inner side face of the fixed portion 6c so as to
 adjoin the movable electrode 5c with space therebetween. Furthermore, two
 L-shaped fixed electrodes 7d are formed on the inner side face of the
 fixed portion 6d so as to adjoin the movable electrode 5d with space
 therebetween.
 Movable sections including the pair of T-shaped beams 3 and 4, the
 framelike vibrator 5, and the movable electrodes 5a to 5d are formed
 integrally with the fixed support portion 2 by working a silicon
 substrate. The fixed portions 6a to 6d and the fixed electrodes 7a to 7d
 are also formed by working the same silicon substrate as the silicon
 substrate of which the fixed support portion 2 and the like are formed.
 Next, a description will be given of the operation of the angular velocity
 sensor 10. AC voltages having a phase difference of 180.degree. are
 applied between the movable electrode 5a and the fixed electrode 7a, and
 between the movable electrode 5b and the fixed electrode 7b, at the
 frequency that coincides with the mechanical resonant frequency of the
 movable sections including the framelike vibrator 5. Then, the framelike
 vibrator 5 is vibrated in the X-axis direction by the bending of the first
 beam portions 3a and 4a of the pair of T-shaped beams 3 and 4 (in this
 case, the second beam portions 3b and 4b are not bent). When the angular
 velocity sensor 10 rotates about the Z-axis passing through the center of
 the fixed support portion 2 while the framelike vibrator 5 is thus
 vibrating in an inertial state, the framelike vibrator 5 also vibrates in
 the Y-axis direction because of Coriolis force. The vibrations in the
 Y-axis direction are made possible by bending of the second beam portions
 3b and 4b of the pair of T-shaped beams 3 and 4. The capacitance produced
 between the fixed electrodes 7c and the movable electrode 5c and the
 capacitance produced between the fixed electrodes 7d and the movable
 electrode 5d change so that one of them increases and the other decreases.
 By subjecting these variable capacitances into conversion into voltages
 and differential amplification, the rotation angular velocity can be
 found.
 Next, an angular velocity sensor 20 according to a second embodiment of the
 present invention will be described with reference to FIGS. 3 and 4.
 Numeral 11 denotes a support substrate formed by working a Pyrex glass
 substrate, on which, excluding the peripheral portion and three center
 portions, a recessed portion 11a is formed to provide a free vibration
 space for movable sections including an inner framelike vibrator 12, an
 outer framelike vibrator 13, and the like.
 The inner framelike vibrator 12 is shaped like a rectangular frame composed
 of long bars 12a and 12b and short bars 12c and 12d. Inside the frame, a
 fixed support portion 16 and two fixed drive portions 17 and 18 are
 disposed. A pair of inner beams 19a and 19b are perpendicularly connected
 at one end to both side faces in the Y-axis direction of the fixed support
 portion 16 that is disposed at a projection in the center of the support
 substrate 11, and are perpendicularly connected at the other end to the
 centers of the opposing inner side faces of the long bars 12a and 12b of
 the inner framelike vibrator 12. The pair of inner beams 19a and 19b are
 placed in parallel with the short bars 12c and 12d along a straight line
 (Y-axis). The inner framelike vibrator 12 is supported via the pair of
 inner beams 19a and 19b so that it can vibrate in the X-axis direction.
 Driving poles 21 and 22 are connected to the inner side faces of the long
 bars 12a and 12b between the pair of inner beams 19a and 19b and the short
 bars 12c and 12d. On the outer side faces of the driving poles 21 and 22,
 movable comb electrodes 21a and 22a are formed, respectively. The movable
 comb electrodes 21a and 22a are meshed with space therebetween with fixed
 comb electrodes 17a and 18a formed in the fixed drive portions 17 and 18.
 The fixed drive portions 17 and 18 are formed on projections apart from
 the center of the support substrate 11.
 The outer framelike vibrator 13 is approximately similar in shape to the
 inner framelike vibrator 12, and is composed of long bars 13a and 13b and
 short bars 13c and 13d. Connecting portions 25a and 25b are provided at
 the centers of the outer side faces of the long bars 12a and 12b of the
 inner framelike vibrator 12, respectively. Two pairs of outer beams 26a
 and 26b, and 27a and 27b are connected at one end to the leading corners
 of the connecting portions 25a and 25b , and are connected at the other
 end to the short bars 13c and 13d in parallel with the long bars 13a and
 13b.
 H-shaped movable comb electrodes 23a and 24a are formed at the centers of
 the outer side faces of the long bars 13a and 13b of the outer framelike
 vibrator 13, and F-shaped movable comb electrodes 23b and 23c, and 24b and
 24c, are formed on both sides thereof.
 Furthermore, fixed detecting portions 28 and 29 are formed on the
 peripheral projecting portion in the Y-axis direction of the support
 substrate 11. T-shaped fixed electrodes 28a and 28b, and 29a and 29b are
 connected to the inner side faces of the fixed detecting portions 28 and
 29, respectively, and are meshed with space therebetween with the H-shaped
 and F-shaped movable comb electrodes 23a to 23c and 24a to 24c.
 The solid filled portions of the angular velocity sensor 20, such as the
 fixed support portion 16, represent fixed sections, and the lightly filled
 portions, such as the inner framelike vibrator 12 and the outer framelike
 vibrator 13, represent movable sections having an integral combined
 structure. The movable sections and the fixed sections are formed by
 working a silicon substrate. The movable sections are movably supported
 via the pair of inner beams 19a and 19b by the fixed support portion 16,
 connected to the support substrate 11, at the center of the inner
 framelike vibrator (outer framelike vibrator). Moreover, the inner
 framelike vibrator and the outer framelike vibrator are supported via the
 two pairs of outer beams 26a and 26b, and 27a and 27b, so that they can be
 displaced relative to each other.
 Next, the operation of the angular velocity sensor 20 will be described. AC
 voltages having a phase difference of 180.degree., which are obtained by
 superimposing DC voltages, are applied between the fixed comb electrode
 17a and the movable comb electrode 21a, and between the fixed comb
 electrode 18a and the movable comb electrode 22a. Then, the inner
 framelike vibrator 12 and the outer framelike vibrator 13 are vibrated in
 the X-axis direction due to bending of the pair of inner beams 19a and 19b
 (the two pairs of outer beams 26a and 26b, and 27a and 27b, are not bent).
 When the angular velocity sensor 20 rotates about the Z-axis passing
 through the center of the fixed support portion 16 while the inner
 framelike vibrator 12 and the outer framelike vibrator 13 are thus
 vibrating in an inertial state, Coriolis force in the Y-axis direction
 acts on the inner framelike vibrator 12 and the outer framelike vibrator
 13. The inner framelike vibrator 12 is not able to be displaced in the
 Y-axis direction, and only the outer framelike vibrator 13 vibrates in the
 Y-axis direction because of bending of the two pairs of outer beams 26a
 and 26b, and 27a and 27b. One of the capacitances generated between the
 movable comb electrodes 23a to 23c and the fixed comb electrodes 28a and
 28b, and between the movable comb electrodes 24a to 24c and the fixed comb
 electrodes 29a and 29b increases, whereas the other decreases. The
 rotation angular velocity is found by subjecting these increasing and
 decreasing capacitances to conversion into voltages and differential
 amplification.
 Next, an angular velocity sensor 30 according to a third embodiment of the
 present invention will be described with reference to FIGS. 5 and,6. In
 this angular velocity sensor 30, the single T-shaped fixed comb electrodes
 28a, 28b, 29a, and 29b in the angular velocity sensor 20 are changed to be
 double T-shaped and designated 28'a, 28'b, 29'a and 29'b, respectively,
 and the number of comb electrodes, such as the movable comb electrodes 21a
 and 22a and the fixed comb electrodes 17a and 18a, is increased, and in
 particular, portions 30a and 30b shown by two dot chain lines are added.
 Since other constituents are approximately similar to those of the angular
 velocity sensor 20, they are denoted by the same numerals, and a
 description thereof is omitted.
 Both ends of fixed detecting portions 28 and 29 are extended in the X-axis
 direction, and fixed comb electrodes 28c and 28d, and 29c and 29d, which
 are bent inward in the Y-axis direction, are provided at the leading ends
 thereof. The centers of short bars 13c and 13d of an outer framelike
 vibrator 13 are extended outward in the X-axis direction, and movable comb
 electrodes 23d and 23e and movable comb electrodes 24d and 24e are
 provided at the leading ends thereof so as to extend in both Y-axis
 directions and to be meshed with space therebetween with the fixed comb
 electrodes 28c and 28d and the fixed comb electrodes 29c and 29d. By
 adding the fixed comb electrodes and the movable comb electrodes in this
 way, it is possible to improve sensitivity in detecting the angular
 velocity based on Coriolis force. The operation of the angular velocity
 sensor 30 of this embodiment is similar to that of the angular velocity
 sensor 20 and, accordingly, a description thereof is omitted.
 While preferred embodiments of the invention have been disclosed, various
 modes of carrying out the principles disclosed herein are contemplated as
 being within the scope of the following claims. Therefore, it is
 understood that the scope of the invention is not to be limited except as
 otherwise set forth in the claims.