JP2005024310A - Inertia sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sensor for independently measuring angular velocities at the same time by using a piezoelectric vibration-type inertia sensor when exciting one sensor element to turn it centering around two axes orthogonal to its vibrating direction. <P>SOLUTION: When turning the sensor element centering around two axes orthogonal to an axis parallel to the vibrating direction with a vibration part of the sensor element unidirectionally excited, the sizes of Coriolis force generated by the respective turns are independently detected by this biaxial detection-type inertia sensor. Stretching vibration is used as a mode of excited vibration and bending vibration is used as a vibration mode when detecting Coriolis force. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
[Industrial application fields]
The present invention relates to an inertial sensor that measures simultaneously and independently the angular velocity when a single sensor element is excited and rotated about two axes orthogonal to the vibration direction.
[0002]
[Prior art]
A tuning fork type sensor element is shown in FIG. 5 as an example of an element used more than ever. This is because an excitation electrode is added to one of the two vibrating parts (2) of the tuning fork type sensor element, and an AC voltage is applied to this, so that the two branches are in a resonance state. Starts to vibrate in one direction. In this state, when rotation is applied about the second axis that is orthogonal to the first axis that is parallel to the vibration direction, the magnitude of the Coriolis force generated in the third axis direction that is further orthogonal is used as the amount of charge, and the vibration unit Detection is performed by a detection electrode provided on the other of the two branches.
[0003]
In this method, only one rotation axis (second axis) can be taken, and in order to measure the angular velocity rotating around a plurality of axes, sensors are required as many as the number of rotation axes in accordance with each axis. .
[0004]
These inertial sensors are called piezoelectric vibration type angular velocity sensors (PVG), and an object of mass m that vibrates with a velocity Vsin (t) in one axis direction is centered on a second axis orthogonal to the vibration direction. When a rotational motion is given with acceleration, a Coriolis force Fc is generated as one of inertia forces (apparent forces) appearing in the acceleration system. At this time, if the angular velocity is Ω,
Fc = 2mΩVsin (t) (1 set)
Can be expressed as From equation 1, it can be seen that the Coriolis force is proportional to the magnitude of the angular velocity.
[0005]
In addition, since the amount of charge generated in the piezoelectric sensor element is proportional to the mechanical strain generated according to the magnitude of the Coriolis force, the magnitude of the angular velocity is detected by a method that electrically measures the amount of charge. It becomes possible to do.
[0006]
These inertial sensors are mounted on robots, vehicles, airplanes, and the like, and are used for movement state grasping, posture control, moving object trajectory confirmation, image correction processing (camera shake sensor), and the like.
[0007]
In recent years, “hybridization” that combines multiple disparate sensors due to diversification of sensing information, and multiple sensor elements in one container due to space saving, and measurement corresponding to multiple action axes “Multi-axis integration” (Patent Documents 1 and 2) is performed.
[0008]
[Patent Document 1]
JP 07-092175 A [Patent Document 2]
Japanese Patent Laid-Open No. 2000-314744
[Problems to be solved by the invention]
Conventionally, improvement in measurement accuracy has been demanded, and the resolution of a single sensor has been developed with emphasis. However, in recent years, diversification of measurement information and further miniaturization have been demanded, and it is not limited to simply measuring a single physical quantity. For example, an accelerometer and an angular velocity sensor are combined, and the track of a moving object is calculated by arithmetic processing. Of small angular velocity sensors to support hybrid use of sensors, such as reading the current position and determining the current position, and use in small products and space-savings such as digital still cameras (DSC) and mobile terminals with cameras Is growing.
[0010]
In addition, when shooting with a hand held by a camera or the like, there are two axes that cause camera shake. Therefore, at present, two angular velocity sensors are mounted on one camera. This occupies a significant space, making it difficult to incorporate into a small general-purpose DSC or a portable terminal with a camera.
[0011]
[Means for Solving the Problems]
Now, DSCs, mobile terminals with cameras, and the like are becoming increasingly high in pixels, and are in the direction of improving image quality. Among them, image correction processing cannot be performed because the sensor cannot be incorporated, and the “blurring” of the image caused by camera shake causes the image quality to deteriorate significantly.
[0012]
An object of the present invention is to solve the problem of the angular velocity in which the angular velocity in two axes can be measured independently at the same time by using one sensor element in a container having a size equal to or smaller than that of a conventional camera shake sensor. It proposes a sensor that can be used for small and space-saving products.
[0013]
Therefore, the present invention provides a Coriolis generated by each rotation when rotating around two axes orthogonal to an axis parallel to the vibration direction in a state where the vibration part of the rectangular parallelepiped sensor element is excited in one direction. In a 2-axis detection type inertial sensor that detects the magnitude of force independently, stretching vibration is used as an excitation vibration mode, and flexural vibration is used as a vibration mode when detecting Coriolis force. It is an inertial sensor.
[0014]
Then, when the oscillating portion of the rectangular parallelepiped sensor element is excited in one direction, when rotating around two axes orthogonal to the axis parallel to the vibration direction, the magnitude of the Coriolis force generated by each rotation is large. In the two-axis detection type inertial sensor that detects each independently, the vibration frequency to be initially excited is F _E , and the natural frequency of the vibrating body in the direction related to the vibration mode induced by the Coriolis force generation, When F _f1 and F _f2 are set, respectively, F _f1 <F _E <F _f2 is satisfied.
[0015]
In addition, when the oscillating part of the rectangular parallelepiped sensor element is excited in one direction, when rotating around two axes orthogonal to the axis parallel to the vibration direction, the magnitude of the Coriolis force generated by each rotation is large. In the two-axis detection type inertial sensor that detects each independently, the vibration frequency to be initially excited is F _E , and the natural frequency of the vibrating body in the direction related to the vibration mode induced by the Coriolis force generation, When F _f1 and F _f2 respectively,
_{| F f1 -F E | / F} E _and, | F _f2 -F E | / value of _{F E} is by taking the range of 0.011 to 0.038, is excited to one of the sensor elements, the vibration direction When rotating around two axes perpendicular to the axis, it is possible to avoid the degeneration phenomenon of the two flexural vibration modes, and it is possible by setting the optimum sensitivity, and an inertial sensor that measures the angular velocity independently and simultaneously is obtained. be able to.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In each figure, the same numerals indicate the same objects. With respect to the angular velocity sensor according to the present invention, an example in which quartz that is a piezoelectric crystal is used as an element material will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a sensor element, in which 1 is a quartz crystal element, 2 is a support structure, 3 is an electrode for excitation vibration (excitation electrode), and 4 is a rotation axis 1 parallel to the X axis. An electrode (detection 1) for detecting the Coriolis force generated by the angular velocity (Ω1) when rotated about the center (Ω1), and 5 are the angular velocity (Ω2) when rotated about the rotation axis 2 parallel to the Z axis. The electrode (detection 2) for detecting the Coriolis force which generate | occur | produces is shown. Further, the orthogonal coordinate direction indicates the cutting direction of the crystal crystal. The shape of the sensor element is a rectangular parallelepiped.
[0017]
FIG. 2 shows the direction of excitation and the vibration mode induced by the generation of Coriolis force when the angular velocity is applied. Since drawing is complicated, each electrode is omitted. FIG. 3 shows the electrode arrangement at the sensor element cross-sectional position shown in FIG. 3A is an electrode arrangement of the AA cross section of FIG. 1, FIG. 3B is an electrode arrangement of the BB cross section of FIG. 1, and FIG. 3C is a CC line of FIG. The electrode arrangement of the cross section is shown. Each electrode has a two-terminal configuration and is connected to an external circuit via the surface of the support structure 2.
[0018]
In the sensor element, when an external excitation circuit (oscillation circuit) and the excitation electrode 3 are connected and an AC voltage is applied, the quartz crystal element 1 expands and contracts in the direction parallel to the Y axis, and longitudinal vibration is induced. The In this state, when an angular velocity Ω1 is applied around the rotation axis 1, a Coriolis force is generated, and bending vibration is induced along a plane parallel to the YZ plane.
[0019]
Further, when the angular velocity Ω2 is applied around the rotation axis 2, a Coriolis force is similarly generated, and bending vibration is induced along a plane parallel to the XY plane. Electric charges (piezoelectric effect) generated by the mechanical strain of the bending vibration are respectively induced in the electrodes of the detection 1 and the detection 2 and connected to a detection circuit outside via the surface of the support structure 2. These independent signals are amplified as AC signals in the detection circuit, then phase-compared and rectified with the excitation signal as means for determining the direction of rotation, and then converted into DC signals and output independently as sensor signals. Here, as an application, if two signals are fused together to perform arithmetic processing, it becomes possible to detect an angular velocity due to rotation of an arbitrary axis on a plane formed by the rotation axes 1 and 2.
[0020]
FIG. 4 shows the characteristic frequency of the vibrating body in the direction related to the vibration mode induced by the generation of Coriolis force, F _E , the vibration frequency that is initially excited for the element that is a feature of the present invention. when the _{F f1, F f2 respectively, | F f1 -F E | /} F E _and, | that range / _F value of _E is 0.011 from 0.038 is the optimum | F _f2 -F E It is a graph to show. If the ratio is outside the above range, for example 0.011 or less, a degeneracy phenomenon occurs, and if it exceeds 0.038, the sensitivity is significantly reduced. In the present embodiment, the X-axis direction or the Z-axis direction is fixed as the support point, but one end of the Y-axis may be fixed to simplify the support structure.
[0021]
【The invention's effect】
In the present invention, when rotation is applied to the sensor element in operation around the rotation axis in two directions, a total of three types of vibration modes are established for the sensor element: one longitudinal vibration and two orthogonal bending vibrations. Will do. The frequency of this bending vibration is dominant to the longitudinal vibration frequency that is the excitation vibration, but the two-axis frequencies (respective natural frequencies) at which the bending vibration is established are approximated on the sensor element structure (in terms of dimensions). Then, a malfunction that detects the vibration of the other axis occurs due to the degeneracy phenomenon of the mutual vibration mode. In the present invention, the two fundamental vibration frequencies of the sensor element can be separated vertically from the excitation frequency value to avoid the degeneration phenomenon of the vibration mode. By eliminating it, it is possible to measure with high accuracy and accuracy.
[0022]
The degree of detuning (frequency difference between the excitation vibration and each bending vibration) at this time is defined as F _E as the frequency of longitudinal vibration, F _f1 as one bending vibration frequency, and F _f2 as the other bending vibration frequency. When
F _f1 <F _E <F _f2 (2 formulas)
Under the conditions of
(F _E -F _f1 ) / F _E (3 formulas)
as well as,
(F _f2 -F _E ) / F _E (4 formulas)
Is set to be between 0.011 and 0.038, the Coriolis force can be efficiently converted into bending vibration.
[Brief description of the drawings]
FIG. 1 is an external view of a sensor element of the present invention.
FIG. 2 is a conceptual diagram showing a vibration mode when an angular velocity is applied to the sensor element of the present invention.
FIG. 3 is an electrode layout diagram at each vibration location (cross section) of FIG. 1;
A vibration frequency F _E which initially excitation of the present invention; FIG is a graph indicating the optimum area of the natural frequency F _f1, F _f2 direction of the vibrating body involved in the vibration mode induced by Coriolis force generated .
FIG. 5 is a plan view showing an example of a tuning fork type sensor element used in the prior art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sensor element main body 2 Support structure 3 Excitation (longitudinal vibration) electrode 4 Detection electrode 5 of bending vibration 1 Detection electrode of bending vibration 2

Claims (5)

When the oscillating part of the rectangular parallelepiped sensor element is excited in one direction, when rotating around two axes orthogonal to the axis parallel to the vibration direction, the magnitude of the Coriolis force generated by each rotation is calculated. In the two-axis detection type inertial sensor that detects each independently,
An inertial sensor characterized by using expansion and contraction vibration as a mode of excitation vibration and bending vibration as a vibration mode when detecting Coriolis force. The inertial sensor according to claim 1,
When the vibration frequency to be excited in the initial stage is F _E , and the natural frequencies of the vibrating body involved in the vibration mode induced by the Coriolis force generation are F _f1 and F _f2 , respectively.
F _f1 <F _E <F _f2
An inertial sensor characterized by In a state where the vibration part of the sensor element using the + X cut crystal in a rectangular parallelepiped is excited in one direction, the sensor element is rotated around two axes of the X axis and the Z axis perpendicular to the axis parallel to the Y axis vibration direction. In a two-axis detection type inertial sensor that independently detects the magnitude of the Coriolis force generated by each rotation,
An inertial sensor characterized by using expansion and contraction vibration as a mode of excitation vibration and bending vibration as a vibration mode when detecting Coriolis force. The inertial sensor according to claim 3, wherein
When the vibration frequency to be excited in the initial stage is F _E , and the natural frequencies of the vibrating body involved in the vibration mode induced by the Coriolis force generation are F _f1 and F _f2 , respectively.
F _f1 <F _E <F _f2
An inertial sensor characterized by The inertial sensor of claim 2 and claim 4,
_{| F f1 -F E | / F} E _and, | F _f2 -F E | / inertial sensor value of _{F E} is characterized by a 0.038 0.011.

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