JP4507578B2 - Angular velocity sensor - Google Patents

Description

The present invention relates to an angular velocity sensor, and more particularly, to an angular velocity sensor that hardly causes vibration leakage and that can provide high angular velocity detection accuracy .

  Conventionally, for example, a tuning fork vibrator as shown in FIG. 6 is used as a sensor element of an angular velocity sensor used for camera shake correction, vehicle posture detection, and the like (see, for example, Patent Document 1).

  The tuning fork vibrator 50 has a bimorph structure in which a pair of front and rear piezoelectric bodies 51 and 52 made of a polarized PZT ceramic material or the like are integrally joined, and a pair of left and right legs 56a and 56b are arranged in parallel from a root portion 55. The protrusion is formed. A pair of left and right drive electrodes 57a and 57b are formed at the center of one piezoelectric body 51, and detection electrodes 57c and 57d are formed on the left and right sides of the drive electrodes 57a and 57b, respectively. ˜57d are electrically separated by the cut groove 58.

  In the tuning fork vibrator 50, when a drive signal is applied from the outside to the drive electrodes 57a and 57b with the vicinity of the bottom surface of the root portion 55 fixed, a surface including both legs 56a and 56b (XZ in the figure). The two legs 56a and 56b vibrate so as to open and close in the X-axis direction in the figure (hereinafter, such vibration is referred to as in-plane vibration). In this state, when both the leg portions 56a and 56b are in in-plane vibration, an angular velocity with the longitudinal direction (the Z-axis direction in the figure) of these leg portions 56a and 56b as a rotation axis is added. Due to the Coriolis force generated in this manner, the legs 56a and 56b vibrate alternately back and forth in a direction (Y-axis direction in the figure) perpendicular to the plane including both legs 56a and 56b (hereinafter, such vibration is referred to as “vibration”). Called out-of-plane vibration). The angular velocity can be detected by taking out the output generated in the detection electrodes 57c and 57d according to the magnitude of the out-of-plane vibration.

Here, in the tuning fork vibrator 50 described above, the resonance frequency of the in-plane vibration of each leg 56a, 56b is f ₀ 1, the resonance frequency of the out-of-plane vibration is f ₀ 2, and the frequency of the drive signal applied from the outside is fd. If it is set in advance so that f ₀ 1≈fd and f ₀ 2≈fd, the in-plane vibration of the legs 56a and 56b will increase, and the out-of-plane vibration will occur due to the Coriolis force. Therefore, a sufficiently large detection output can be obtained.

JP 1998-111132 A

As described above, in the conventional tuning fork type vibrator 50, the resonance frequency f ₀ 2 of the out-of-plane vibration of each of the legs 56a and 56b is substantially matched with the frequency fd of the drive signal (that is, f ₀ 2≈fd). Therefore, a large detection output can be obtained because out-of-plane vibration is likely to occur due to the Coriolis force. However, if the out-of-plane vibration of both the leg portions 56a and 56b is large, a large torsional force is generated in the root portion 55 supporting the both leg portions 56a and 56b, and the vicinity of the bottom surface of the root portion 55 is unlikely to be a complete node. That is, vibration is leaked from the fixed portion, and the detection accuracy is deteriorated.

  As a countermeasure, as shown in FIG. 7, the dimension Lb of the root portion 55 along the longitudinal direction (Z-axis direction in the figure) of the leg portions 56a and 56b is changed to the dimension La of the root portion 55 shown in FIG. (Lb> La) can be considered. That is, if the root portion 55 is lengthened, the torsional force hardly reaches the vicinity of the bottom portion of the root portion 55, so that the influence of vibration leakage can be reduced.

  However, when the length Lb of the root portion 55 is increased in this way, the overall shape of the tuning fork vibrator increases accordingly, which is an obstacle to downsizing when used as an angular velocity sensor or the like.

  Note that the above-described vibration leakage problem occurs when large out-of-plane vibration is generated in the legs 56a and 56b due to Coriolis force, and the in-plane vibration generated in the legs 56a and 56b is bilaterally symmetric. Therefore, even if the root portion 55 is relatively short, it is difficult for force to be transmitted to the vicinity of the bottom portion, and therefore it can be said that vibration leakage does not easily occur.

  The present invention has been made to solve the above-described problem, and is a tuning fork vibrator that can reduce the influence of vibration leakage as much as possible and obtain high detection accuracy while being small in size as a whole. An object of the present invention is to provide a method for manufacturing the tuning fork vibrator and an angular velocity sensor using the tuning fork vibrator.

In order to achieve the above object, an angular velocity sensor according to the first aspect of the present invention comprises a parent tuning fork in which a pair of large legs project from a common root portion in parallel to form a parent tuning fork. Each of the large legs is formed with a pair of small legs that are opposed to each other at a predetermined interval in a direction orthogonal to the plane including both large legs and are shorter than the large legs. An angular velocity sensor comprising a sensor element composed of a tuning fork type vibrator configured as follows:
A front member having a main part of the pair of large legs, and a rear member having a main part of a pair of large legs formed in the same outer dimensions as the front member, The main parts of the large legs overlap each other, and there is a gap for forming a gap between the small legs of the child tuning fork between the main parts of the front and rear large legs. Combined,
The resonance frequency of the in-plane vibration and the out-of-plane vibration in the large leg portion of the parent tuning fork are different, and the resonance frequencies of the in-plane vibrations of the large leg portion of the parent tuning fork and the small leg portion of the child tuning fork are substantially the same. Is set,
The frequency of the drive signal for driving the sensor element is set so as to substantially coincide with the resonance frequency of the in-plane vibration of the large leg portion of the parent tuning fork. It is characterized in that the angular velocity is detected by the magnitude of the in-plane vibration in the small leg portion of the consonant tuning fork generated by the Coriolis force while causing internal vibration.

In the angular velocity sensor according to the first aspect of the invention, since the resonance frequencies of the in-plane vibration and the out-of-plane vibration of the large leg portion of the parent tuning fork are different, the out-of-plane vibration hardly occurs in the large leg portion. Therefore, it is difficult for a twisting force to be generated at the root portion. In addition, the vibration caused by the Coriolis force becomes in-plane vibration of the small leg portion of the consonant tuning fork, so that the vibration hardly reaches the root portion. In addition, since the small leg portion of the consonant tuning fork is shorter than the large leg portion of the parent tuning fork, the length of the root portion of the consonant tuning fork is substantially longer than the length of the root portion of the parent tuning fork. Vibration is less likely to reach the root of the tuning fork. Therefore, vibration leakage hardly occurs and high angular velocity detection accuracy can be obtained.

In addition, the angular velocity sensor of the present invention is set so that the resonance frequency of the in-plane vibration at the large leg portion of the parent tuning fork and the resonance frequency of the in-plane vibration at the small leg portion of the concentrator tuning fork both substantially match the drive frequency of the drive signal. In addition, since the in-plane vibration in the small leg portion of the consonant tuning fork due to the Coriolis force is increased, a sufficiently large detection output can be obtained.

Further, the angular velocity sensor according to the present invention includes a front member and a rear member in which the front and rear large leg constituent parts overlap each other, and a gap is formed between the front and rear large leg constituent parts. Therefore, it is possible to obtain a tuning fork vibrator having a required characteristic in which the parent tuning fork and the child tuning fork are integrated with a simple structure.

Furthermore, according to the angular velocity sensor according to the present invention, in the tuning fork type vibrator to be a sensor element, in-plane vibration occurs in the large leg portion of the parent tuning fork, but almost no out-of-plane vibration occurs, and due to Coriolis force. Since the in-plane vibration at the small leg portion of the consonant tuning fork increases, not only vibration leakage hardly occurs, but also a sufficiently large angular velocity detection output can be obtained. For this reason, it becomes possible to obtain an angular velocity sensor having high angular velocity detection accuracy.

FIG. 1 is a perspective view showing the overall configuration of a tuning fork vibrator according to an embodiment of the present invention.
The tuning fork vibrator 1 of this embodiment includes a front member 2 and a rear member 3 that are both formed in a tuning fork shape, and the two members 2 and 3 are overlapped and integrally joined with an adhesive or the like. It is configured. The front member 2 has a bimorph structure in which a pair of front and rear piezoelectric bodies 2a and 2b made of a polarized PZT ceramic material or the like are integrally joined, and a pair of left and right drive electrodes is provided at the center portion on one surface thereof. The detection electrodes 4c and 4d are formed on the left and right sides of the drive electrodes 4a and 4b, and the electrodes 4a to 4d are electrically separated by the cut grooves 5. Further, the rear member 3 is made of a ceramic material, and the left and right upper end portions thereof facing the front member 2 are notched in a stepped shape, whereby the gaps 3 a and 3 b are formed between the rear member 3 and the front member 2. Is formed.

  When viewed as a whole, the tuning fork vibrator 1 is configured such that a parent tuning fork 8 is configured by a pair of left and right large legs 10a and 10b projecting in parallel with each other at a predetermined interval from a common root portion 9. In addition, each large leg portion 10a, 10b of the parent tuning fork 8 has a predetermined gap 3a, 3b between each other in a direction (Y-axis direction in the drawing) orthogonal to the plane including both large leg portions 10a, 10b. A pair of small leg portions 13c, 13d, 14c, and 14d that are opposed to each other are formed. In this case, the length L22 in the longitudinal direction (Z-axis direction in the drawing) of each small leg portion 13c, 13d, 14c, 14d is shorter than the length L12 in the longitudinal direction of each large leg portion 10a, 10b. (L22 <L12) is set. As a result, consonant tuning forks 12a and 12b are individually configured in the large leg portions 10a and 10b.

  The large legs 10a, 10b of the parent tuning fork 8 vibrate in the plane along the XZ plane, and the small legs 13c, 13d and 14c, 14d of the consonant tuning forks 12a, 12b are in the plane along the YZ plane. Vibrate. In this case, the resonance frequency of the in-plane vibration of the large legs 10a and 10b of the parent tuning fork 8 and the resonance frequency of the in-plane vibration of the small legs 13c and 13d and 14c and 14d of the child tuning forks 12a and 12b are both externally applied. It is set so as to substantially match the drive frequency of the applied drive signal.

That is, the resonance frequency of the in-plane vibration at the large legs 10a and 10b of the parent tuning fork 8 is f ₀ 1, and the resonance frequency of the in-plane vibration at the small legs 13c and 13d and 14c and 14d of the child tuning forks 12a and 12b is f ₀ 3. When the frequency of the drive signal and fd, f ₀ 1 ≒ fd, is set to be f ₀ 3 ≒ fd. However, the resonance frequency f ₀ 2 of the out-of-plane vibration (vibration along the YZ plane) in the large legs 10a and 10b of the parent tuning fork 8 is greatly different from the frequency fd of the drive signal (that is, f ₀ 2 <<Fd, or f ₀ 2 >> fd). The resonance frequencies f ₀ 1 and f ₀ 3 of the in-plane vibrations of the parent tuning fork 8 and the child tuning forks 12a and 12b are the length L11 of the root portion 9 of the parent tuning fork 8 and the leg portions 10a and 10b. 13c, 13d, 14c, and 14d are set by appropriately selecting the length, width, thickness, and material.

  In order to detect the angular velocity by the tuning fork type vibrator 1 having the configuration shown in FIG. 1, for example, a detection circuit as shown in FIG. 2 is used.

In this detection circuit 20, a drive signal having a frequency fd output from the self-excited oscillation circuit 21 is applied to the drive electrodes 4 a and 4 b of the tuning fork vibrator 1 to cause both large legs 10 a and 10 b to vibrate in the plane. Let Then, when an angular velocity having a rotation axis in the longitudinal direction (the Z-axis direction in FIG. 1) of the large legs 10a and 10b is applied to the large legs 10a and 10b in the in-plane vibration, The accompanying Coriolis force is applied to both large legs 10a and 10b in a direction (Y-axis direction in the figure) perpendicular to the plane including both. At this time, as described above, the resonance frequency f ₀ 2 of the out-of-plane vibration (vibration along the YZ plane) in the large legs 10a and 10b of the parent tuning fork 8 is set to be significantly different from the frequency fd of the drive signal. Therefore, the large legs 10a and 10b of the parent tuning fork 8 do not vibrate out of plane. However, this Coriolis force is also applied to the small legs 13c, 13d and 14c, 14d of the consonant tuning forks 12a, 12b, and the resonance frequency f ₀ 3 of the in-plane vibration is the surface of the large legs 10a, 10b of the parent tuning fork 8. Since the resonance frequency f ₀ 1 of the internal vibration is substantially matched, the small legs 13c, 13d, 14c, and 14d of the consonant tuning forks 12a and 12b vibrate in-plane.

  The direction of the Coriolis force applied to the two small leg portions 13c, 13d, 14c, and 14d of the sub tuning forks 12a and 12b is the same direction. The direction of the Coriolis force applied to the two small legs 14c and 14d of the consonant tuning fork 12b is also the same. Nevertheless, the sub tuning forks 12a and 12b vibrate when opening and closing the tuning fork, although the structures of the base portions of the two small legs 13c and 13d or 14c and 14d are symmetrical, but the Coriolis force is applied. This is because it is asymmetric when viewed in relation to the direction.

  Here, when the sub tuning forks 12a and 12b vibrate in-plane, as shown in FIG. 3, two vibration modes are conceivable. First, as indicated by an arrow in FIG. 5A, when the pair of small leg portions 13c and 13d constituting one consonant tuning fork 12a is opened, the pair of small leg portions 14c constituting the other consonant tuning fork 12b. , 14d closes or vice versa (hereinafter referred to as the anti-phase vibration mode). Second, as shown by the arrows in FIG. 2B, when the pair of small leg portions 13c and 13d constituting one consonant tuning fork 12a is opened, the pair of small leg portions constituting the other consonant tuning fork 12b at the same time. This is a vibration mode in which 14c and 14d are also opened or vice versa (hereinafter referred to as a common-mode vibration mode). When the small leg portions 13c, 13d, 14c, and 14d of the sub tuning fork 12a and 12b vibrate in the in-phase vibration mode, the longitudinal direction (Z-axis direction in the figure) of the leg portion of the tuning fork vibrator 1 is set as the rotation axis. In this case, the rotation direction cannot be detected, and the rotation direction and the magnitude of the angular velocity can be detected only in the anti-phase vibration mode.

  Actually, the direction of the Coriolis force applied to each of the small leg portions 13c, 13d, 14c, 14d is reversed in the two sub tuning forks 12a, 12b. For example, when Coriolis force is applied to the child tuning fork 12a in the direction from the small legs 13c to 13d, Coriolis force is applied to the child tuning fork 12b in the direction from the small legs 14d to the small legs 14c. The small leg portion 13c on the side of the sub tuning fork 12a to which the Coriolis force is applied is made of a bimorph piezoelectric body, and the small leg portion 14d on the side of the sub tuning fork 12b to which the Coriolis force is applied is made of another ceramic material. Therefore, the physical characteristics of the two small leg portions 13c and 14d are slightly different, and there is a possibility that a difference in ease of vibration occurs due to the Coriolis force. As a result, when the two sub tuning forks 12a and 12b vibrate so that one small leg portion is opened, the other small leg portion vibrates so as to be closed. That is, it vibrates in the reverse phase vibration mode.

  Therefore, the output generated in the detection electrodes 4c and 4d according to the magnitude when the small legs 13c, 13d, 14c, and 14d of the sub tuning forks 12a and 12b vibrate in the in-plane vibration mode is individually I / V converted. The circuits 22c and 22d convert the signals into voltage signals, add these two outputs with the differential amplifier 23, and the differentially amplified output is synchronously detected with the synchronous detection circuit 24 and then amplified with the amplifier 25 and taken out. Further, the outputs of the respective I / V conversion circuits 22c and 22d are added by the wired OR circuit 26 and then input to the self-excited oscillation circuit 21, whereby the driving applied to the drive electrodes 4a and 4b of the tuning fork vibrator 1 is performed. A self-oscillating loop for obtaining a signal is formed.

Here, when attention is paid to the mutual vibration operation of the parent tuning fork 8 and the consonant tuning forks 12a and 12b of the tuning fork vibrator 1, first, for the parent tuning fork 8, the resonance frequency f ₀ of the in-plane vibration of the large legs 10a and 10b. Since 1 substantially matches the frequency fd of the drive signal (f ₀ 1≈fd), the large legs 10a and 10b vibrate in-plane, but the resonance frequency f _{0 of the} out-of-plane vibration of the large legs 10a and 10b. Since 2 is set to f ₀ 2 << fd or f ₀ 2 >> fd, out-of-plane vibration due to Coriolis force does not occur in the large leg portions 10a and 10b. For this reason, torsional force hardly acts on the root portion 9. On the other hand, Koonsa 12a, for 12b, Shoashi portion 13c, 13d, 14c, the resonance frequency f ₀ 3 of plane vibration of 14d is, f ₀ 3 ≒ fd So, the small leg portion 13c caused by the Coriolis force, 13d, 14c, The in-plane vibration of 14d is increased, and thus a sufficiently large detection output can be obtained.

  In addition, in this case, the small leg portions 13c, 13d, 14c, and 14d of the sub tuning forks 12a and 12b are caused to vibrate in-plane by the Coriolis force as described above, and therefore the root portion 9 is difficult to vibrate. Further, the small leg portions 13c, 13d, 14c, 14d of the consonant tuning forks 12a, 12b are shorter than the large leg portions 10a, 10b of the parent tuning fork 8 (L22 <L12). The length L21 of the portion is substantially longer than the length L11 of the root portion of the parent tuning fork 8 (L21> L11). From the above, even if the small legs 13c, 13d, 14c, 14d of the sub tuning forks 12a, 12b vibrate in the plane, the vibration is hardly transmitted to the root portion 9. Accordingly, the root portion 9 becomes a node close to an ideal, and vibration leakage from the conventional fixed portion does not occur, so that high angular velocity detection accuracy can be obtained.

  Next, a method for manufacturing the tuning fork vibrator 1 having the configuration shown in FIG. 1 will be described with reference to FIGS. 4 (a) to 4 (d).

  As shown in FIG. 4A, a bimorph structure rectangular piezoelectric substrate 41 formed by integrally joining a pair of upper and lower piezoelectric bodies 41a and 41b made of polarized PZT or the like, and substantially the same as this piezoelectric substrate 41 A ceramic substrate 42 made of a silicon material or the like having an outer dimension is prepared. In this case, the electrode 43 is previously formed on the piezoelectric substrate 41 over substantially the entire surface of the piezoelectric substrate 41, and the consonant tuning forks 12a and 12b are formed on the ceramic substrate 42 along a direction perpendicular to the longitudinal direction of the one surface side. A concave stepped portion 42a to be a gap 3a, 3b between the small leg portions 13c, 13d and 14c, 14d is formed.

  Then, as shown in FIG. 4B, the substrates 41 and 42 are bonded together with an adhesive or the like so that the electrode non-formation surface of the piezoelectric substrate 41 and the stepped portion 42a formation surface of the ceramic substrate 42 face each other. A body 44 is formed.

  Next, a predetermined portion (position indicated by a two-dot chain line in FIG. 4B) in the longitudinal direction of the joined body 44 is sequentially cut along a direction orthogonal to the longitudinal direction. Then, the cut block 45 as shown in FIG. 4C is obtained.

  Therefore, a plurality of pieces (for example, two pieces) of each cut block 45 are stacked in the thickness direction, and the portion to be the root portion 9 of the tuning fork type vibrator 1 is set downward. In this state, using a dicing saw or the like, a notch 46 to be a gap between the large legs 10a and 10b of the parent tuning fork 8 is predetermined along the longitudinal direction of the cutting block 45 as shown in FIG. Form with pitch.

  Thereafter, each of the overlapped cutting blocks 45 is disassembled and turned one by one sideways, and the notch grooves 5 for electrode separation are formed at a predetermined pitch along the short direction of the cutting blocks 45. A predetermined portion (a position indicated by a two-dot chain line in FIG. 4E) in the longitudinal direction of the cutting block 45 is sequentially cut along the short direction. As a result, a plurality (three in this example) of tuning fork vibrators 1 are obtained from one cut block 45.

  As described above, according to the method for manufacturing a tuning fork vibrator according to the present invention, a large number of tuning fork vibrators 1 can be manufactured at a time only by cutting and cutting. Therefore, the tuning fork vibrator 1 can be easily manufactured. And can be manufactured at low cost.

  In the above description of the manufacturing method, the concave step portions 42a to be the gaps 3a, 3b between the small legs 13c, 13d and 14c, 14d of the consonant tuning forks 12a, 12b are formed on the ceramic substrate 42. Instead, by separately attaching a separate ceramic material to be a convex portion on the surface of the flat ceramic substrate, the gaps 3a, 3b between the small legs 13c, 13d and 14c, 14d of the consonant tuning forks 12a, 12b are consequently obtained. It is also possible to form the stepped portion 42a to be.

  The tuning fork vibrator of the present invention is not limited to the one shown in FIG. 1, but may be one shown in FIGS. 5 (a) and 5 (b), for example.

  In other words, the tuning fork vibrator shown in FIG. 6A has a pair of driving electrodes 4a and a pair of electrodes arranged so as to sandwich the driving electrode 4a without providing a notch groove on one surface of the front member 2 of the bimorph structure. The detection electrodes 4c and 4d are patterned by screen printing or the like. The tuning fork vibrator shown in FIG. 2B is a ceramic material or the like between a bimorph structure front member 2 having electrodes 4a, 4c and 4d and a rear member 3 made of a ceramic material or the like having the same external dimensions. These are integrally joined with a spacer 6 made of Furthermore, the front member 2 or the rear member 3 does not necessarily have a bimorph structure, may have a unimorph structure, and may have a structure in which piezoelectric layers are laminated. Also in the tuning fork vibrator having each structure as described above, the same effects as the tuning fork vibrator 1 shown in FIG. 1 can be obtained.

  Although the present invention has been described with respect to the case where the tuning fork vibrator 1 is applied as an angular velocity sensor, the present invention is not limited to this, and it is necessary to obtain a detection output corresponding to the Coriolis force such as an acceleration sensor or an inertial sensor. It can be widely applied to a certain field.

It is a perspective view which shows the structure of the tuning fork type vibrator in the embodiment of the present invention. It is a circuit diagram which shows the detection circuit of the tuning fork type vibrator. It is a perspective view with which it uses for description of the vibration operation | movement of the tuning fork type vibrator. It is a perspective view with which it uses for description of the manufacturing process of the tuning fork type vibrator. It is a perspective view with which it uses for description of the manufacturing process of the tuning fork type vibrator. It is a perspective view with which it uses for description of the manufacturing process of the tuning fork type vibrator. It is a perspective view with which it uses for description of the manufacturing process of the tuning fork type vibrator. It is a perspective view with which it uses for description of the manufacturing process of the tuning fork type vibrator. It is a perspective view which shows the other structure of the tuning fork type vibrator of the present invention. It is a perspective view which shows the structure of the conventional tuning fork type vibrator. It is a perspective view which shows the structure of the other conventional tuning fork type vibrator.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tuning fork type vibrator 2 Front member 3 Back member 4a, 4b Drive electrode
4c, 4d Detection electrode 8 Parent tuning fork 9 Root portion 10a, 10b Large leg portion 12a, 12b Sub tuning fork 13c, 13d Small leg portion 14c, 14d Small leg portion 41 Piezoelectric substrate 42 Ceramic substrate 42a Stepped portion 43 Electrode 44 Combined body 45 Cut block 46 Notch

Claims (1)

A pair of large legs projecting in parallel from a common root is formed to form a parent tuning fork, and each large leg of the parent tuning fork has a direction perpendicular to the plane including both large legs. An angular velocity sensor comprising a sensor element composed of a tuning fork-type vibrator in which a pair of small legs that are opposed to each other at a predetermined interval and shorter than the large legs are formed to form a consonant tuning fork,
A front member having a main part of the pair of large legs, and a rear member having a main part of a pair of large legs formed in the same outer dimensions as the front member, The main parts of the large legs overlap each other, and there is a gap for forming a gap between the small legs of the child tuning fork between the main parts of the front and rear large legs. Combined,
The resonance frequency of the in-plane vibration and the out-of-plane vibration in the large leg portion of the parent tuning fork are different, and the resonance frequencies of the in-plane vibrations of the large leg portion of the parent tuning fork and the small leg portion of the child tuning fork are substantially the same. Is set,
The frequency of the drive signal for driving the sensor element is set so as to substantially coincide with the resonance frequency of the in-plane vibration of the large leg portion of the parent tuning fork. An angular velocity sensor configured to detect an angular velocity based on a magnitude of in-plane vibration in a small leg portion of a consonant tuning fork generated by Coriolis force while causing internal vibration.

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