Inertial measurement unit, and electronic apparatus

Abstract

To provide an inertial measurement unit that easily measures an acceleration bias.SOLUTION: An inertial measurement unit comprises a housing 10 that is fixed to a fixation target surface 600 in a non-reversed posture or a reversed posture reversed by 180° from the non-reversed posture, and an acceleration sensor element 30 that is accommodated in the housing 10. The housing 10 has a first reference surface R1 in contact with the fixation target surface 600 in the non-reversed posture, and a second reference surface R2 in contact with the fixation target surface 600 in the reversed posture, and the first reference surface R1 and the second reference surface R2 are parallel to each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an inertial measurement unit and an electronic device. [Background technology]

[0002] Patent Document 1 describes a method for calculating a bias component included in the output value of an angular velocity sensor or an acceleration sensor, which is an inertial sensor. This calculation method uses an inversion mechanism to place the inertial sensor in a non-inverted position and an inverted position, and calculates the bias component based on the output value in each position. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-103542 Summary of the Invention [Problem to be solved by the invention]

[0004] In the conventional calculation method, the non-inverted position and the inverted position must be inverted by exactly 180 degrees, which requires a highly accurate inverting mechanism.In addition, when users calculate the bias component, it is difficult for them to prepare a highly accurate jig such as an inverting mechanism on their own, so the conventional calculation method had problems in terms of effectiveness. [Means for solving the problem]

[0005] An inertial measurement device according to one embodiment of the present application comprises a housing that is fixed to a fixed surface in a first attitude or a second attitude that is 180° inverted from the first attitude, and an acceleration sensor housed in the housing, wherein the housing has a first reference surface that contacts the fixed surface in the first attitude and a second reference surface that contacts the fixed surface in the second attitude, and the first reference surface and the second reference surface are parallel to each other.

[0006] An electronic device according to one aspect of the present application includes the inertial measurement unit described above. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 2 is a perspective view of the inertial measurement unit according to the first embodiment fixed in a non-inverted attitude. [Figure 2] FIG. 1 is a perspective view of an inertial measurement unit fixed in an inverted orientation. [Figure 3] Block diagram of an inertial measurement unit. [Figure 4A] FIG. 10 is an explanatory diagram showing output values ​​of the acceleration sensor element in a non-inverted attitude. [Figure 4B] FIG. 10 is an explanatory diagram showing the output value of the acceleration sensor element in an inverted posture. [Figure 5A] FIG. [Figure 5B] FIG. 2 is an explanatory diagram showing an inertial measurement unit fixed in a state where the first reference surface is in contact with a fixed surface. [Figure 6A] FIG. [Figure 6B] FIG. 2 is an explanatory diagram showing an inertial measurement unit fixed in a state where the second reference surface is in contact with a fixed surface. [Figure 7A] A table showing the relationship between acceleration bias and angle. [Figure 7B] A table showing the relationship between parallelism and angle. [Figure 8] FIG. 10 is a perspective view of an inertial measurement unit according to a second embodiment that is fixed in a non-inverted attitude. [Figure 9] FIG. 1 is a perspective view of an inertial measurement unit fixed in an inverted orientation. [Figure 10] FIG. 11 is a perspective view of an inertial measurement unit according to a third embodiment fixed in a non-inverted attitude. [Figure 11] FIG. 1 is a perspective view of an inertial measurement unit fixed in an inverted orientation. [Figure 12A] FIG. 10 is a side view of an inertial measurement unit according to a fourth embodiment fixed in a non-inverted attitude. [Figure 12B] FIG. 1 is a side view of an inertial measurement unit fixed in an inverted orientation. [Figure 13A] FIG. 10 is a side view showing another example of the inertial measurement unit according to the fourth embodiment fixed in a non-inverted attitude. [Figure 13B] FIG. 10 is a side view showing another example of an inertial measurement unit fixed in an inverted position. [Figure 14] FIG. 10 is a perspective view showing an example of an electronic device according to a fifth embodiment. [Figure 15] FIG. 13 is a perspective view showing another example of the electronic device according to the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] In each drawing, the dimensions of some components may be drawn to different scales to make the components easier to see. In each drawing, the X-axis, Y-axis, and Z-axis are perpendicular to one another. In the following description, "X-axis direction" refers to a direction parallel to the X-axis, "Y-axis direction" refers to a direction parallel to the Y-axis, and "Z-axis direction" refers to a direction parallel to the Z-axis. In the following description, the "plus side" refers to the tip side of the arrow direction of each of the X, Y, and Z axes, and the "minus side" refers to the end side of the arrow direction. In the following description, "planar view" refers to a view from the Z-axis direction relative to a plane that includes the X-axis and Y-axis.

[0009] 1. Embodiment 1 1.1.Inertial Measurement Unit 1 and 2 show a sensor unit 100 as an inertial measurement unit (IMU) according to a first embodiment. Fig. 1 is a perspective view of the sensor unit 100 in a non-inverted position and fixed to a fixed surface 600. Fig. 2 is a perspective view of the sensor unit 100 in an inverted position and fixed to a fixed surface 600.

[0010] In this embodiment, the sensor unit 100 is fixed to a fixed surface 600 of an electronic device such as a mobile device like a smartphone or a mobile object like an automobile, and is used to detect information such as vibration, tilt, and linear motion of the electronic device. In this embodiment, the sensor unit 100 includes an acceleration sensor element 30, and measures acceleration in a sensor coordinate system associated with the acceleration sensor element 30. In this embodiment, the acceleration sensor element 30 is an example of an acceleration sensor.

[0011] In this embodiment, the X-axis, Y-axis, and Z-axis indicate three-dimensional Cartesian coordinate axes of the sensor coordinate system of the acceleration sensor element 30. In the following description, the plane including the X-axis and Y-axis is assumed to be horizontal, and the Z-axis is assumed to be the direction of gravity.

[0012] 1, the sensor unit 100 is normally used in a non-inverted position fixed to a fixed surface 600. In this embodiment, the non-inverted position is an example of a first position. The value of the acceleration bias included in the output value of the acceleration sensor element 30 fluctuates due to changes in the temperature of the environment in which it is used, deterioration over time, etc. Therefore, in order to perform accurate detection, it is necessary to perform a calibration process periodically.

[0013] As shown in Fig. 2, the sensor unit 100 is fixed to the fixed surface 600 in an inverted posture during calibration. In the inverted posture, the sensor unit 100 measures the output value of the acceleration sensor element 30, calculates an acceleration bias value using a calculation method described below, and corrects the output value of the acceleration sensor element 30 using the calculated acceleration bias value. The inverted posture is a posture obtained by inverting the non-inverted posture by 180°. In this embodiment, the inverted posture is an example of the second posture.

[0014] 1.2. Structure of the Inertial Measurement Unit As shown in FIGS. 1 and 2, the sensor unit 100 includes a housing 10, and an acceleration sensor element 30 and a computing device 40 housed in the housing 10.

[0015] In this embodiment, the housing 10 is a rectangular parallelepiped with a square surface perpendicular to the Z axis, a side length of approximately 25 mm, and a thickness of approximately 10 mm. The shape and size of the housing 10 described above are merely examples. The housing 10 is a case that houses the acceleration sensor element 30, and is composed of a main body 11 and a lid 12.

[0016] The main body 11 has a storage section 13 inside, which is indicated by a broken line. The storage section 13 stores an acceleration sensor element 30, a computing device 40, and the like. The acceleration sensor element 30 detects acceleration in at least the Z-axis direction. The acceleration sensor element 30 may be a triaxial sensor that detects acceleration in each of the three axes X, Y, and Z, or may be a 6Dof (Degrees of Freedom) sensor that detects acceleration in the three axes and angular velocity in the three axes.

[0017] For example, a Si-MEMS (Micro Electro Mechanical Systems) sensor using silicon (Si) as the material can be used as the acceleration sensor element 30. The type of acceleration sensor element 30 can be selected depending on the application, and for example, if higher accuracy is required, a quartz acceleration sensor using a quartz oscillator can be used.

[0018] The arithmetic unit 40 is an integrated circuit device, such as a processor such as an MPU (Micro Processor Unit) or a CPU (Central Processing Unit). The arithmetic unit 40 receives the detection data output from the acceleration sensor element 30, performs various processes, and transmits the processed detection data to the outside via the connector 50.

[0019] The various processes performed by the calculation device 40 include sorting the detection data sent from the acceleration sensor element 30 by detection axis, calculating the average value of the detection data for each detection axis, performing temperature correction, zero point correction, alignment correction, etc. on each calculated average value or the received detection data, sensitivity adjustment processing, filter processing, calibration processing, and outputting the processed data from the connector 50.

[0020] The lid 12 is joined to the main body 11 via a packing (not shown) to seal the storage section 13. By appropriately selecting the type of packing to be used, the dustproofness and waterproofness of the storage section 13 can be made to have the desired performance.

[0021] Because the lid portion 12 and the main body portion 11 are joined via a packing, it is difficult to make the first surface 12a of the lid portion 12 flush with the second surface 11b of the main body portion 11. In other words, there is a high possibility that a step will be formed between the second surface 11b of the main body portion 11 and the first surface 12a of the lid portion 12. Therefore, when the sensor unit 100 is fixed to the fixing surface 600 in an inverted position, if the second surface 11b of the main body 11 and the first surface 12a of the lid 12 are fixed to the fixing surface 600 as the first reference surface R1, there is a risk that the direction of the detection axis of the acceleration sensor element 30 will deviate from the intended direction.

[0022] Therefore, in this embodiment, protrusions 21, 22, 23, and 24 are formed on the first surface 11a of the main body 11, and a first reference surface R1 is formed on each protrusion, and protrusions 25, 26, 27, and 28 are formed on the second surface 11b, and a second reference surface R2 is formed on each protrusion.

[0023] As shown in FIG. 2, the protrusions 21, 22, 23, and 24 are provided at the four corners of the first surface 11a of the main body 11, and protrude from the first surface 11a toward the positive side in the Z-axis direction. The protrusions 21, 22, 23, and 24 have reference surfaces 21a, 22a, 23a, and 24a, respectively, on the positive side in the Z axis direction.

[0024] In this embodiment, the reference surfaces 21a, 22a, 23a, and 24a are formed by polishing the positive sides of the protrusions 21, 22, 23, and 24 in the Z axis direction together. The reference surfaces 21a, 22a, 23a, and 24a form a first reference surface R1 indicated by a two-dot chain line. In this embodiment, the protrusion 21 is an example of a first protrusion, and the reference surface 21a is an example of a first surface. The protrusion 22 is an example of a second protrusion, and the reference surface 22a is an example of a second surface. The protrusion 23 is an example of a third protrusion, and the reference surface 23a is an example of a third surface.

[0025] As shown in FIG. 1, the protrusions 25, 26, 27, and 28 are provided at the four corners of the second surface 11b of the main body 11, and protrude from the second surface 11b toward the negative side in the Z-axis direction. In this embodiment, the protrusions 25, 26, 27, and 28 have reference surfaces 25a, 26a, 27a, and 28a, respectively, on the negative side in the Z axis direction.

[0026] In this embodiment, the reference surfaces 25a, 26a, 27a, and 28a are formed by polishing the negative Z-axis side of the protrusions 25, 26, 27, and 28 together. The reference surfaces 25a, 26a, 27a, and 28a form a second reference surface R2 indicated by a two-dot chain line. The second reference surface R2 and the first reference surface R1 are parallel to each other. In this embodiment, the protrusion 25 is an example of a fourth protrusion, and the reference surface 25a is an example of a fourth surface. The protrusion 26 is an example of a fifth protrusion, and the reference surface 26a is an example of a fifth surface. The protrusion 27 is an example of a sixth protrusion, and the reference surface 27a is an example of a sixth surface.

[0027] In this embodiment, in order to make the first reference surface R1 and the second reference surface R2 accurately parallel, the first reference surface R1 and the second reference surface R2 are each set to a predetermined parallelism P. The predetermined parallelism P will be described later.

[0028] In this embodiment, the first reference surface R1 is formed by polishing the protrusions 21, 22, 23, and 24. Therefore, the area to be polished can be made smaller than when the first reference surface R1 is formed by flattening the entire first surface 11a of the main body 11 by polishing or the like. Therefore, the first reference surface R1 can be easily set to the predetermined parallelism P.

[0029] Similarly, the second reference surface R2 is formed by polishing the protrusions 25, 26, 27, and 28. Therefore, the area to be polished can be made smaller than when the second reference surface R2 is formed by flattening the entire second surface 11b of the main body 11 by polishing or the like. Therefore, the second reference surface R2 can be easily set to the predetermined parallelism P.

[0030] 1, in the non-inverted posture, the sensor unit 100 is fixed to the fixed surface 600 by the screws 15 with the reference surfaces 21a of the protrusions 21, 22a of the protrusions 22, 23a of the protrusions 23, and 24a of the protrusions 24 in contact with the fixed surface 600. In other words, the sensor unit 100 is fixed to the fixed surface 600 by the screws 15 with the first reference surface R1 in contact with the fixed surface 600. The screw holes 14 are through holes that pass through the protrusions 21 and 25, the protrusions 22 and 26, the protrusions 23 and 27, and the protrusions 24 and 28.

[0031] 2, in the inverted posture, sensor unit 100 is fixed to fixed surface 600 by screws 15 with reference surfaces 25a of protrusions 25, 26a of protrusions 26, 27a of protrusions 27, and 28a of protrusions 28 in contact with fixed surface 600. In other words, sensor unit 100 is fixed to fixed surface 600 by screws 15 with second reference surface R2 in contact with fixed surface 600.

[0032] The connector 50 is provided on the side surface 11c of the main body 11. The connector 50 is electrically connected to the arithmetic device 40 and the acceleration sensor element 30. A connector of an electronic device that mounts the sensor unit 100 is connected to the connector 50, and the electronic device can acquire detection data of the acceleration sensor element 30 via the connector 50.

[0033] In this embodiment, the connector 50 is provided on the side surface 11c of the main body 11, so that the detection data of the acceleration sensor element 30 can be obtained via the connector 50 whether the sensor unit 100 is in a non-inverted or inverted position.

[0034] 1.3.Acceleration bias calculation method Fig. 3 is a block diagram of the sensor unit 100. Fig. 4A is a graph showing the relationship between the acceleration Z1 detected by the acceleration sensor element 30 and the true acceleration Z0 when the sensor unit 100 is in a non-inverted position, and Fig. 4B is a graph showing the relationship between the acceleration Z2 detected by the acceleration sensor element 30 and the true acceleration Z0 when the sensor unit 100 is in an inverted position.

[0035] As shown in FIG. 3, the arithmetic device 40 includes a drive detector 41, an ADC (Analog-Digital converter) 42, a calculator 43, a memory 44, and a corrector 45. The drive detection section 41 supplies the acceleration sensor element 30 with a drive voltage required for detecting acceleration, and detects acceleration based on a signal from the acceleration sensor element 30 . The ADC 42 quantizes the acceleration detected by the drive detection unit 41 and outputs the quantized acceleration.

[0036] The calculation unit 43 calculates the acceleration bias B included in the acceleration output by the ADC 42. As shown in FIG. 4A, when the sensor unit 100 is in a non-inverted position, if the acceleration detected by the drive detection unit 41 is Z1 and the true acceleration of the linear motion performed by the acceleration sensor element 30 is Z0, the acceleration Z1 and the acceleration Z0 have the relationship shown in the following equation (1). Z1 = AZ0 + Bp … (1) A is a coefficient, and Bp indicates the acceleration bias B in the non-inverted attitude.

[0037] As shown in FIG. 4B, when the sensor unit 100 is in the inverted posture, if the acceleration detected by the drive detection section 41 is Z2, the acceleration Z2 and the acceleration Z0 have the relationship of the following mathematical formula (2). Z2=-AZ0+Bn …(2) Bn indicates the acceleration bias B in the inverted attitude.

[0038] When the inverted posture is a posture that is exactly 180° inverted from the non-inverted posture, the acceleration bias Bp and the acceleration bias Bn are equal. Therefore, the acceleration bias B is calculated by the following formula (3). B=Bp=Bn=(Z1+Z2) / 2 …(3)

[0039] The storage unit 44 stores the calculated value of the acceleration bias B. The correction unit 45 acquires the acceleration output by the ADC 42, and corrects the acquired acceleration based on the acceleration bias B stored in the storage unit 44 using the following equation (4) to calculate the true acceleration Z0. Z0 = (Z1 - B) / A … (4)

[0040] 1.4. Parallelism of the first reference surface R1 and the second reference surface R2 5A to 7B, the parallelism P1 of the first reference surface R1 and the parallelism P2 of the second reference surface R2 will be described. In this embodiment, the parallelism P1 and the parallelism P2 are examples of the parallelism P.

[0041] FIG. 5A is an explanatory diagram of the first reference surface R1. FIG. 5B is an explanatory diagram showing the sensor unit 100 fixed in the non-inverted position with the first reference surface R1 in contact with the fixed surface 600. FIG. 6A is an explanatory diagram of the second reference surface R2. FIG. 6B is an explanatory diagram showing the sensor unit 100 fixed in the inverted position with the second reference surface R2 in contact with the fixed surface 600. FIG. 7A is a table showing the relationship between the acceleration bias Ba and the angle θ1 or the angle θ2, where the angle θ1 indicates the deviation angle between the first reference surface R1 and the datum plane A, and the angle θ2 indicates the deviation angle between the second reference surface R2 and the datum plane A. FIG. 7B is a table showing the relationship between the effective length L of the housing 10 and the parallelisms P1 and P2.

[0042] In order to accurately determine the acceleration bias B, the inverted attitude must be exactly 180° inverted with respect to the non-inverted attitude. For this reason, in this embodiment, the parallelism P1 of the first reference surface R1 that contacts the fixed surface 600 in the non-inverted posture and the parallelism P2 of the second reference surface R2 that contacts the fixed surface 600 in the inverted posture are each set to a predetermined value.

[0043] The predetermined values ​​of the parallelism P1 and P2 differ depending on the size of the housing 10 and the type of the acceleration sensor element 30. For example, if the housing 10 has a square surface perpendicular to the Z axis with a side length of approximately 25 mm and the acceleration sensor element 30 is a Si-MEMS sensor, it is preferable that the parallelism P1 and P2 be 0.2 mm or less. Also, if the square housing 10 has a side length of approximately 25 mm and the acceleration sensor element 30 is a quartz acceleration sensor, it is preferable that the parallelism P1 and P2 be 0.05 mm or less.

[0044] For example, if the housing 10 has a square surface perpendicular to the Z axis with a side length of approximately 50 mm and the acceleration sensor element 30 is a Si-MEMS sensor, it is preferable that the parallelism P1 and P2 be 0.4 mm or less. Also, if the square housing 10 has a side length of approximately 50 mm and the acceleration sensor element 30 is a quartz acceleration sensor, it is preferable that the parallelism P1 and P2 be 0.1 mm or less.

[0045] Thus, since the quartz acceleration sensor is more accurate than the Si-MEMS sensor, the parallelism P1 and P2 must be smaller. The values ​​of parallelism P1 and P2 depend on the length of one side of the surface of housing 10 that is perpendicular to the Z axis. The surface of housing 10 that is perpendicular to the Z axis is the surface that comes into contact with fixed surface 600.

[0046] 5A is a diagram schematically showing a first reference plane R1 and an angle θ1, which is a deviation angle between the first reference plane R1 and the datum plane A, when the predetermined parallelism P is parallelism P1. In FIG. 5A, the angle θ1 is drawn larger than the actual angle for ease of viewing.

[0047] When the parallelism P1 is 0.2 mm, the first reference plane R1 is parallel to the datum plane A and is located between the first plane S1 and the second plane S2 that are 0.2 mm apart in the Z-axis direction. In this case, the first reference surface R1 deviates from the datum plane A by a maximum angle θ1.

[0048] FIG. 5B shows the sensor unit 100 in the non-inverted position, fixed to the fixed surface 600 by the first reference surface R1 having a deviation angle of angle θ1. 5B, there is a deviation of an angle θ1 between the direction of the acceleration Zp detected by the acceleration sensor element 30 and the direction of the true acceleration Z. In this embodiment, the direction of the true acceleration Z is the direction of gravity.

[0049] An acceleration bias Ba is generated depending on the magnitude of this angle θ1. The acceleration bias Ba is included in the acceleration bias Bp described above and affects accuracy. Therefore, the acceleration bias Ba is required to be equal to or less than a required value depending on the type of acceleration sensor element 30.

[0050] For example, if the acceleration sensor element 30 is a Si-MEMS sensor, the acceleration bias Ba is preferably 8 mG or less. If the acceleration sensor element 30 is a quartz acceleration sensor that requires higher accuracy, the acceleration bias Ba is preferably 2 mG or less. The upper limit of the acceleration bias Ba is, for example, the initial error value specified in the specifications of the acceleration sensor element 30 or the sensor unit 100.

[0051] 7A, to set the acceleration bias Ba to 2 mG or less, the angle θ1 needs to be 0.114591° or less. To set the acceleration bias Ba to 8 mG or less, the angle θ1 needs to be 0.458356° or less.

[0052] The angle θ1 can be calculated from the following formula (5), where G is the gravitational acceleration. θ1=tan -1 (Ba / G) …(5)

[0053] If the length of one side of the housing 10 is the effective length L, the angle θ1 can also be calculated from the parallelism P1 and the effective length L using the following formula (6): The effective length L is the length of one side of the surface of the housing 10 that is perpendicular to the Z axis. θ1=tan -1 (P1 / L) …(6)

[0054] The acceleration bias Ba can be calculated from the following formula (7) based on formulas (5) and (6). Ba = G × P1 / L …(7)

[0055] As described above, the acceleration bias Ba is required to be equal to or less than a necessary value depending on the type of acceleration sensor element 30, and therefore the parallelism P1 is set to satisfy the following formula (8). Ba≧G×P1 / L …(8)

[0056] As shown in FIG. 7B, when the effective length L of the housing 10 is 25 mm and the required acceleration bias Ba is 2 mG, in other words, when the angle θ1 is 0.114591°, the parallelism P1 is set to 0.05 mm or less. As described above, when the acceleration sensor element 30 is a quartz acceleration sensor, the acceleration bias Ba is preferably 2 mG or less. Therefore, when the acceleration sensor element 30 mounted on the housing 10 is a quartz acceleration sensor, the parallelism P1 is set to 0.05 mm or less.

[0057] When the effective length L of the housing 10 is 25 mm and the required acceleration bias Ba is 8 mG, in other words, when the angle θ1 is 0.458356°, the parallelism P1 is set to 0.2 mm or less. As described above, when the acceleration sensor element 30 is a Si-MEMS sensor, the acceleration bias Ba is preferably 8 mG or less. Therefore, when the acceleration sensor element 30 mounted on the housing 10 is a Si-MEMS sensor, the parallelism P1 is set to 0.2 mm or less.

[0058] When the effective length L of the housing 10 is 50 mm and the required acceleration bias Ba is 2 mG, in other words, when the angle θ1 is 0.114591°, the parallelism P1 is set to 0.1 mm or less. As described above, when the acceleration sensor element 30 is a quartz acceleration sensor, the acceleration bias Ba is preferably 2 mG or less. Therefore, when the acceleration sensor element 30 mounted on the housing 10 is a quartz acceleration sensor, the parallelism P1 is set to 0.1 mm or less.

[0059] When the effective length L of the housing 10 is 50 mm and the required acceleration bias Ba is 8 mG, in other words, when the angle θ1 is 0.458356°, the parallelism P1 is set to 0.4 mm or less. As described above, when the acceleration sensor element 30 is a Si-MEMS sensor, the acceleration bias Ba is preferably 8 mG or less. Therefore, when the acceleration sensor element 30 mounted on the housing 10 is a Si-MEMS sensor, the parallelism P1 is set to 0.4 mm or less.

[0060] 6A is a diagram schematically showing the second reference plane R2 and the angle θ2, which is the deviation angle between the second reference plane R2 and the datum plane A, when the predetermined parallelism P is parallelism P2. In FIG. 6A, the angle θ2 is drawn larger than the actual angle for ease of viewing.

[0061] When the parallelism P2 is 0.2 mm, the second reference plane R2 is parallel to the datum plane A and is located between the first plane S1 and the second plane S2 that are 0.2 mm apart in the Z-axis direction. In this case, the second reference surface R2 is displaced from the datum plane A by a maximum angle θ2.

[0062] FIG. 6B shows the sensor unit 100 in the inverted posture, fixed to the fixed surface 600 by the second reference surface R2 having a deviation angle of angle θ2. As shown in FIG. 6B, a deviation of angle θ2 occurs between the direction of acceleration Zn detected by the acceleration sensor element 30 and the direction of true acceleration Z0.

[0063] The acceleration bias Ba is generated depending on the magnitude of this angle θ2. The acceleration bias Ba is included in the acceleration bias Bn described above and affects accuracy. Therefore, the acceleration bias Ba is required to be equal to or less than a required value depending on the type of acceleration sensor element 30, as described above.

[0064] In the above-described embodiment, as a suitable example of the first reference surface R1, the first reference surface R1 is constituted by the reference surfaces 21a, 22a, 23a, and 24a of the four protrusions 21, 22, 23, and 24 provided at the four corners of the first surface 11a of the main body portion 11.

[0065] However, the number of protrusions and reference surfaces that make up the first reference surface R1 is not limited to 4. As described in the embodiments described later, it may be 3, or even 5 or more. The first reference surface R1 may be configured by the reference surfaces of one or two protrusions provided so as to surround the center of the first surface 11a of the main body portion 11 in a plan view. Furthermore, the first reference surface R1 may be formed by the first surface 11a if the effort and cost required to flatten the first surface 11a is acceptable.

[0066] In the above-described embodiment, as a suitable example of the second reference surface R2, the second reference surface R2 is constituted by the reference surfaces 25a, 26a, 27a, and 28a of the four protrusions 25, 26, 27, and 28 provided at the four corners of the second surface 11b of the main body portion 11. However, the number of protrusions and reference surfaces that make up the second reference surface R2 is not limited to 4. As described in the embodiments described later, it may be 3, or even 5 or more. The second reference surface R2 may be configured by the reference surfaces of one or two protrusions provided so as to surround the center of the second surface 11b of the main body portion 11 in a plan view. Furthermore, the second reference surface R2 may be formed by the second surface 11b if the effort and cost required to flatten the second surface 11b is acceptable. In this case, it is preferable that the first surface 12a of the lid portion 12 does not protrude from the second surface 11b to the negative side in the Z-axis direction.

[0067] As described above, the sensor unit 100 serving as an inertial measurement device according to this embodiment has the following advantages. The sensor unit 100 of this embodiment comprises a housing 10 that is fixed to a fixed surface 600 in a non-inverted position as a first position or an inverted position as a second position that is 180° inverted from the non-inverted position, and an acceleration sensor element 30 that serves as an acceleration sensor housed in the housing 10, and the housing 10 has a first reference surface R1 that contacts the fixed surface 600 in the non-inverted position and a second reference surface R2 that contacts the fixed surface 600 in the inverted position, and the first reference surface R1 and the second reference surface R2 are parallel to each other.

[0068] As described above, in the sensor unit 100 of this embodiment, the housing 10 has the first reference surface R1 and the second reference surface R2 that are parallel to each other. Therefore, the sensor unit 100 of this embodiment can easily change the sensor unit 100 from a non-inverted position to an inverted position without using a highly accurate jig. Therefore, the sensor unit 100 of this embodiment can provide a sensor unit 100 that allows a user or the like to easily measure the acceleration bias B.

[0069] In the sensor unit 100 of this embodiment, the housing 10 has a main body 11 that houses the acceleration sensor element 30, a protrusion 21 that is provided on the main body 11 and serves as a first protrusion having a reference surface 21a that is a first surface that constitutes the first reference surface R1, a protrusion 22 that is provided on the main body 11 and serves as a second protrusion having a reference surface 22a that is a second surface that constitutes the first reference surface R1, and a protrusion 23 that is provided on the main body 11 and serves as a third protrusion having a reference surface 23a that is a third surface that constitutes the first reference surface R1.

[0070] In this way, in the sensor unit 100 of this embodiment, the first reference surface R1 is constituted by the reference surface 21a of the protrusion 21, the reference surface 22a of the protrusion 22, and the reference surface 23a of the protrusion . Therefore, in the sensor unit 100 of this embodiment, the first reference surface R1 can be more easily formed on the housing 10 than in the case where the first surface 11a of the main body 11 is used as the first reference surface R1.

[0071] In the sensor unit 100 of this embodiment, the housing 10 has a protrusion 25 as a fourth protrusion provided on the main body 11 and having a reference surface 25a as a fourth surface that constitutes the second reference surface R2, a protrusion 26 as a fifth protrusion provided on the main body 11 and having a reference surface 26a as a fifth surface that constitutes the second reference surface R2, and a protrusion 27 as a sixth protrusion provided on the main body 11 and having a reference surface 27a as a sixth surface that constitutes the second reference surface R2.

[0072] In this way, in the sensor unit 100 of this embodiment, the second reference surface R2 is constituted by the reference surface 25a of the protrusion 25, the reference surface 26a of the protrusion 26, and the reference surface 27a of the protrusion 27. Therefore, in the sensor unit 100 of this embodiment, the second reference surface R2 can be more easily formed on the housing 10 than when the second surface 11b of the main body 11 is used as the second reference surface R2.

[0073] The sensor unit 100 of this embodiment includes a connector 50 that is provided on the side surface 11c of the housing 10 and is electrically connected to an acceleration sensor element 30 that serves as an acceleration sensor. Therefore, the sensor unit 100 of this embodiment can use the connector 50 in both the non-inverted and inverted positions. Therefore, based on a configuration that can easily measure the acceleration bias B and easily maintain accuracy, highly accurate and reliable detection data processed by the computing device 40 can be output to the outside via the connector 50.

[0074] In the sensor unit 100 of this embodiment, the parallelism P1 and parallelism P2 as the parallelism P of the first reference surface R1 and the second reference surface R2 are 0.2 mm or less. Therefore, the sensor unit 100 of this embodiment can set the value of the acceleration bias Ba to a value equal to or less than the value required for the acceleration sensor element 30. Therefore, the sensor unit 100 of this embodiment can accurately measure the acceleration bias B.

[0075] In the sensor unit 100 of this embodiment, when the length of the first reference surface R1 is L mm, the gravitational acceleration is G, and the value of the acceleration bias Bp or the acceleration bias Bn included in the output value in the direction of gravitational acceleration of the acceleration sensor element 30 as an acceleration sensor is BmG, the parallelism P1 mm and the parallelism P2 mm as the parallelism P of the first reference surface R1 and the second reference surface R2, respectively, are G×P / L≦B Meet the following. Therefore, the sensor unit 100 of this embodiment can set the value of the acceleration bias Ba included in the acceleration bias Bp or the acceleration bias Bn to a value equal to or less than the value required for the acceleration sensor element 30. Therefore, the sensor unit 100 of this embodiment can accurately measure the acceleration bias B. Furthermore, the four protrusions 21, 22, 23, and 24 protrude to the positive side in the Z-axis direction, and the four protrusions 25, 26, 27, and 28 protrude to the negative side in the Z-axis direction. Therefore, each protrusion can be provided while maintaining the outer shape of the sensor unit 100 in the X and Y axes.

[0076] 2. Embodiment 2 8 and 9 show a sensor unit 200 as an inertial measurement device according to embodiment 2. Fig. 8 is a perspective view of the sensor unit 200 fixed to the fixed surface 600 in a non-inverted position. Fig. 9 is a perspective view of the sensor unit 200 fixed to the fixed surface 600 in an inverted position.

[0077] The second embodiment differs from the first embodiment in that the number of protrusions and reference surfaces that make up the first reference surface R1 and the second reference surface R2 is three, respectively. Note that the same components as those in the first embodiment are denoted by the same reference symbols, and their description will be omitted.

[0078] As shown in FIG. 8, the sensor unit 200 is normally used while being fixed to a fixed surface 600 in a non-inverted position. As shown in FIG. 9, the sensor unit 200 is fixed to the fixed surface 600 in an inverted position during the calibration process.

[0079] The sensor unit 200 has a housing 210, and an acceleration sensor element 30 and a computing device 40 (not shown) housed in the housing 210. In the second embodiment, the housing 210 is a rectangular parallelepiped with a rectangular surface perpendicular to the Z axis, the long side of the rectangle being approximately 50 mm, the short side being 25 mm, and the thickness being approximately 16 mm. The shape and size of the housing 210 described above are merely examples. In the second embodiment, the long side extends along the X axis direction, and the short side extends along the Y axis direction. Therefore, the above-mentioned effective length L for the angle deviation of the X axis from the Z axis is the length of the long side, and the above-mentioned effective length L for the angle deviation of the Y axis from the Z axis is the length of the short side. In order to satisfy Equation (8) for both the angle deviation of the X axis and the angle deviation of the Y axis, the above-mentioned effective length L may be the length of the short side. The housing 210 is a case for housing the acceleration sensor element 30 and is composed of a main body 211 and a lid 212 .

[0080] The main body 211 has a storage section inside, similar to that of the first embodiment. The storage section stores the acceleration sensor element 30 and the arithmetic unit 40, which are not shown. The lid portion 212 is joined to the second surface 211b of the main body portion 211 by screws 216 via a packing (not shown), thereby sealing the storage portion.

[0081] Because lid portion 212 and main body portion 211 are joined via a packing, it is difficult to make first surface 212a of lid portion 212 flush with main body portion 211. In other words, there is a high possibility that a step will be formed between main body portion 211 and first surface 212a of lid portion 212. Therefore, when the sensor unit 200 is fixed to the fixing surface 600 in an inverted position, if the sensor unit 200 is fixed to the fixing surface 600 using the main body 211 and the first surface 212a of the lid 212 as the reference plane, there is a risk that the direction of the detection axis of the acceleration sensor element 30 will deviate from the intended direction.

[0082] Therefore, in the second embodiment, protrusions 221, 222, and 223 are formed on the first surface 211a of the main body 211, and protrusions 224, 225, and 226 are formed on the second surface 211b, and a reference surface is formed on each protrusion.

[0083] As shown in FIG. 9, protrusions 221, 222, and 223 are provided at two of the four corners of first surface 211a of main body 211 and between the remaining two corners, and protrude from first surface 211a toward the positive side in the Z-axis direction. The protrusions 221, 222, and 223 have reference surfaces 221a, 222a, and 223a, respectively, on the positive side in the Z axis direction.

[0084] In the second embodiment, the reference surfaces 221a, 222a, and 223a are formed by polishing the positive sides of the protrusions 221, 222, and 223 in the Z axis direction together. The reference surfaces 221a, 222a, and 223a form a first reference surface R1 indicated by a two-dot chain line. In the second embodiment, the protrusion 221 is an example of a first protrusion, and the reference surface 221a is an example of a first surface. The protrusion 222 is an example of a second protrusion, and the reference surface 222a is an example of a second surface. The protrusion 223 is an example of a third protrusion, and the reference surface 223a is an example of a third surface.

[0085] As shown in FIG. 8, the protrusions 224, 225, and 226 are provided at two of the four corners of the second surface 211b of the main body 211 and between the remaining two corners, and protrude from the second surface 211b toward the negative Z-axis direction. In the second embodiment, the protrusions 224, 225, and 226 have reference surfaces 224a, 225a, and 226a, respectively, on the negative side in the Z axis direction.

[0086] In the second embodiment, the reference surfaces 224a, 225a, and 226a are formed by polishing the negative Z-axis sides of the protrusions 224, 225, and 226 together. The reference surfaces 224a, 225a, and 226a form a second reference surface R2 indicated by a two-dot chain line. The second reference surface R2 and the first reference surface R1 are parallel to each other. In the second embodiment, the protrusion 224 is an example of a fourth protrusion, and the reference surface 224a is an example of a fourth surface. The protrusion 225 is an example of a fifth protrusion, and the reference surface 225a is an example of a fifth surface. The protrusion 226 is an example of a sixth protrusion, and the reference surface 226a is an example of a sixth surface.

[0087] As described above, the first reference surface R1 and the second reference surface R2 are set to a predetermined parallelism P so that the first reference surface R1 and the second reference surface R2 are accurately parallel to each other. In the second embodiment, the first reference surface R1 is formed by polishing the protrusions 221, 222, and 223. Therefore, the area to be polished can be made smaller than when the first reference surface R1 is formed by flattening the entire first surface 211a of the main body 211 by polishing or the like. Therefore, the first reference surface R1 can be easily set to a predetermined parallelism P.

[0088] Similarly, the second reference surface R2 is formed by polishing the protrusions 224, 225, and 226. Therefore, the area to be polished can be made smaller than when the second reference surface R2 is formed by flattening the entire surface of the negative Z-axis side of the main body 211 and the first surface 212a of the lid 212 by polishing or the like. Therefore, the second reference surface R2 can be easily set to the predetermined parallelism P.

[0089] As shown in Figure 8, in the non-inverted position, the sensor unit 200 is fixed to the fixed surface 600 by screws (not shown) with the reference surface 221a of the protrusion 221, the reference surface 222a of the protrusion 222, and the reference surface 223a of the protrusion 223 in contact with the fixed surface 600. The screw holes 214 are through holes that penetrate between the protruding portions 221 and 224, between the protruding portions 222 and 225, and between the protruding portions 223 and 226.

[0090] As shown in Figure 9, the sensor unit 200 is fixed to the fixed surface 600 by screws (not shown) in an inverted position with the reference surface 224a of the protrusion 224, the reference surface 225a of the protrusion 225, and the reference surface 226a of the protrusion 226 in contact with the fixed surface 600.

[0091] The connector 250 is provided on the side surface 211c of the main body 211. The connector 250 is electrically connected to the arithmetic unit 40 and the acceleration sensor element 30. In the second embodiment, the connector 250 is provided on the side surface 211c of the main body 211, so that the detection data of the acceleration sensor element 30 can be acquired via the connector 250 whether the sensor unit 200 is in a non-inverted or inverted position.

[0092] 3. Embodiment 3 10 and 11 show a sensor unit 300 as an inertial measurement device according to embodiment 3. Fig. 10 is a perspective view of the sensor unit 300 fixed to a fixed surface 600 in a non-inverted position. Fig. 11 is a perspective view of the sensor unit 300 fixed to a fixed surface 600 in an inverted position.

[0093] The third embodiment differs from the first embodiment in that the number of protrusions and reference surfaces that make up the first reference surface R1 and the second reference surface R2 is three, and that the protrusions also protrude in the Y-axis direction from the side surfaces 311c and 311d of the housing 310. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and a description thereof will be omitted.

[0094] As shown in FIG. 10, the sensor unit 300 is normally used while being fixed to a fixed surface 600 in a non-inverted position. As shown in FIG. 11, the sensor unit 300 is fixed to the fixed surface 600 in an inverted position during the calibration process.

[0095] The sensor unit 300 has a housing 310. The housing 310 is a waterproof and dustproof case having high waterproof and dustproof properties, and the housing 310 has a storage section 313 inside, which stores the above-mentioned sensor unit 100. The storage section 313 may store the above-mentioned sensor unit 200 or the acceleration sensor element 30 and the arithmetic unit 40.

[0096] In the third embodiment, the housing 310 has a rectangular surface perpendicular to the Z axis, with the long side of the rectangle being approximately 60 mm, the short side being 50 mm, and the thickness being approximately 30 mm. The shape and size of the housing 310 described above are merely examples. In the third embodiment, the long side extends along the X axis direction, and the short side extends along the Y axis direction. Therefore, the above-mentioned effective length L is the length of the long side for the deviation angle of the X axis from the Z axis, and the above-mentioned effective length L is the length of the short side for the deviation angle of the Y axis from the Z axis. In order to satisfy Equation (8) for both the deviation angle of the X axis and the deviation angle of the Y axis, the above-mentioned effective length L may be the length of the short side. The housing 310 is a case for housing the acceleration sensor element 30 and is composed of a main body 311 and a lid 312 .

[0097] The housing 310 has a main body 311 and a cover 312 , and includes a storage section 313 inside the main body 311 . The lid portion 312 is joined to the main body portion 311 via a packing (not shown) to seal the storage portion 313 .

[0098] Because lid portion 312 and main body portion 311 are joined via a packing, it is difficult to make first surface 312a of lid portion 312 flush with second surface 311b of main body portion 311. In other words, there is a high possibility that a step will be formed between second surface 311b of main body portion 311 and first surface 312a of lid portion 312. Therefore, when the sensor unit 300 is fixed to the fixing surface 600 in an inverted position, if the second surface 311b of the main body 311 and the first surface 312a of the lid 312 are fixed to the fixing surface 600 as the second reference surface R2, there is a risk that the direction of the detection axis of the acceleration sensor element 30 mounted on the sensor unit 100 will deviate from the intended direction.

[0099] Therefore, in embodiment 3, protrusions 321 and 322 are provided on side surface 311c of main body 311, protruding to the positive side in the Z-axis direction and the negative side in the Y-axis direction, and protrusion 323 is provided on side surface 311d opposite side surface 311c, protruding to the positive side in the Z-axis direction and the positive side in the Y-axis direction. Reference surfaces are provided on each of protrusions 321, 322, and 323, and a first reference surface R1 is formed by each reference surface.

[0100] In embodiment 3, side surface 311c is provided with protrusions 324 and 325 that protrude to the negative Z-axis direction and the negative Y-axis direction, and side surface 311d is provided with protrusion 326 that protrudes to the negative Z-axis direction and the positive Y-axis direction. Reference surfaces are provided for each of protrusions 324, 325, and 326, and a second reference surface R2 is formed by these reference surfaces. On side surface 311c, protrusions 321 and 322 are provided on the first surface 311a side, and protrusions 324 and 325 are provided on the second surface 311b side. On side surface 311d, protrusion 323 is provided on the first surface 311a side, and protrusion 326 is provided on the second surface 311b side.

[0101] As shown in FIG. 11, the protrusions 321, 322, and 323 have reference surfaces 321a, 322a, and 323a, respectively, on the positive side in the Z-axis direction. In the third embodiment, the reference surfaces 321a, 322a, and 323a are formed by polishing the positive sides of the protrusions 321, 322, and 323 in the Z axis direction together.

[0102] Reference surfaces 321a, 322a, and 323a form a first reference surface R1 indicated by a dashed line. In embodiment 3, protrusion 321 is an example of a first protrusion, and reference surface 321a is an example of a first surface. Protrusion 322 is an example of a second protrusion, and reference surface 322a is an example of a second surface. Protrusion 323 is an example of a third protrusion, and reference surface 323a is an example of a third surface.

[0103] As shown in FIG. 10, the protrusions 324, 325, and 326 have reference surfaces 324a, 325a, and 326a, respectively, on the negative side in the Z axis direction. In the third embodiment, the reference surfaces 324a, 325a, and 326a are formed by polishing the negative Z-axis sides of the protrusions 324, 325, and 326 together.

[0104] The reference surfaces 324a, 325a, and 326a form a second reference surface R2 indicated by a dashed line. The second reference surface R2 and the first reference surface R1 are parallel to each other. In the third embodiment, the protrusion 324 is an example of a fourth protrusion, and the reference surface 324a is an example of a fourth surface. The protrusion 325 is an example of a fifth protrusion, and the reference surface 325a is an example of a fifth surface. The protrusion 326 is an example of a sixth protrusion, and the reference surface 326a is an example of a sixth surface.

[0105] As described above, the first reference surface R1 and the second reference surface R2 are set to a predetermined parallelism P so that the first reference surface R1 and the second reference surface R2 are accurately parallel to each other. In the third embodiment, the first reference surface R1 is formed by polishing the protrusions 321, 322, and 323. Therefore, the area to be polished can be made smaller than when the first reference surface R1 is formed by flattening the entire first surface 311a of the main body 311 by polishing or the like. Therefore, the first reference surface R1 can be easily set to the predetermined parallelism P.

[0106] Similarly, the second reference surface R2 is formed by polishing the protrusions 324, 325, and 326. Therefore, the area to be polished can be made smaller than when the second reference surface R2 is formed by flattening the entire second surface 311b of the main body 311 by polishing or the like. Therefore, the second reference surface R2 can be easily set to the predetermined parallelism P. Furthermore, protrusions 321, 322, 324, and 325 protrude toward the negative side in the Y-axis direction, and protrusions 323 and 326 protrude toward the positive side in the Y-axis direction. Therefore, each protrusion can be provided while ensuring a relatively large storage section 313 for storing sensor unit 100 and the like.

[0107] As shown in Figure 10, in the non-inverted position, the sensor unit 300 is fixed to the fixed surface 600 by screws (not shown) passed through each screw hole 314 of the protrusions 321, 322, and 323, with the reference surface 321a of the protrusion 321, the reference surface 322a of the protrusion 322, and the reference surface 323a of the protrusion 323 in contact with the fixed surface 600.

[0108] As shown in Figure 11, in an inverted position, sensor unit 300 is fixed to fixed surface 600 by screws (not shown) passed through each screw hole 314 of protrusions 324, 325, and 326, with reference surface 324a of protrusion 324, reference surface 325a of protrusion 325, and reference surface 326a of protrusion 326 in contact with fixed surface 600.

[0109] The connector 350 is provided on a side surface 311c of the main body 311. The connector 350 is electrically connected to the sensor unit 100. In embodiment 3, the connector 350 is provided on the side surface 311c of the main body 311, so that the detection data of the acceleration sensor element 30 of the sensor unit 100 can be obtained via the connector 350 whether the sensor unit 300 is in a non-inverted or inverted position.

[0110] As described above, the sensor unit 300 as an inertial measurement device of this embodiment has the following advantages in addition to the advantages of the above-described embodiments. In the sensor unit 300 of this embodiment, the protrusion 321 as a first protrusion protrudes from the main body 311 in the positive Z-axis direction as a first direction intersecting the first reference plane R1 and in the negative Y-axis direction as a second direction parallel to the first reference plane R1, the protrusion 322 as a second protrusion protrudes from the main body 311 in the positive Z-axis direction and the negative Y-axis direction, and the protrusion 323 as a third protrusion protrudes from the main body 311 in the positive Y-axis direction as a third direction opposite to the positive Z-axis direction and the negative Y-axis direction.

[0111] In this way, in the sensor unit 300 of this embodiment, the first reference surface R1 is constituted by the reference surface 321a of the protrusion 321, the reference surface 322a of the protrusion 322, and the reference surface 323a of the protrusion 323. Therefore, in the sensor unit 300 of this embodiment, the first reference surface R1 can be more easily formed on the housing 310 than in the case where the first surface 311a of the main body 311 is used as the first reference surface R1.

[0112] In the sensor unit 300 of this embodiment, the protrusion 324 as a fourth protrusion protrudes from the main body 311 to the negative side in the Z-axis direction as a fourth direction intersecting the second reference plane R2 and to the negative side in the Y-axis direction as a fifth direction parallel to the second reference plane R2, the protrusion 325 as a fifth protrusion protrudes to the negative side in the Z-axis direction and the negative side in the Y-axis direction, and the protrusion 326 as a sixth protrusion protrudes from the main body 311 to the positive side in the Y-axis direction as a sixth direction opposite to the negative side in the Z-axis direction and the negative side in the Y-axis direction.

[0113] In this way, in the sensor unit 300 of this embodiment, the second reference surface R2 is constituted by the reference surface 324a of the protrusion 324, the reference surface 325a of the protrusion 325, and the reference surface 326a of the protrusion 326. Therefore, in the sensor unit 300 of this embodiment, the second reference surface R2 can be formed more easily on the housing 310 than when the second surface 311b of the main body 311 is used as the second reference surface R2.

[0114] 4. Embodiment 4 12A to 13B show a sensor unit 400 as an inertial measurement device according to the fourth embodiment. Fig. 12A is a side view of sensor unit 400 fixed to fixation surface 600 in a non-inverted position. Fig. 12B is a side view of sensor unit 400 fixed to fixation surface 600 in an inverted position. Fig. 13A is a side view showing another example of sensor unit 400 fixed to fixation surface 610 in a non-inverted position. Fig. 13B is a side view showing another example of sensor unit 400 fixed to fixation surface 610 in an inverted position.

[0115] The fourth embodiment differs from the first embodiment in that the first reference surface R1 and the second reference surface R2 are provided on the same protruding portions, and that the protruding portions also protrude in the Y-axis direction from the side surfaces 411c and 411d of the housing 410. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and a description thereof will be omitted.

[0116] In embodiment 4, side surface 411c of main body 411 is provided with protrusions 421 and 422 that protrude to the positive side in the Z-axis direction and the negative side in the Y-axis direction, and side surface 311d opposite side surface 311c is provided with protrusions 423 and 424 that protrude to the positive side in the Z-axis direction and the positive side in the Y-axis direction, and the positive side in the Z-axis direction and the negative side in the Z-axis direction of each protrusion are respectively used as reference planes.

[0117] The protrusions 421, 422, 423, and 424 have reference surfaces 421a, 422a, 423a, and 424a, respectively, on the positive side in the Z axis direction. In the fourth embodiment, the reference surfaces 421a, 422a, 423a, and 424a form a first reference surface R1. In the fourth embodiment, the protrusion 421 is an example of a first protrusion, and the reference surface 421a is an example of a first surface. The protrusion 422 is an example of a second protrusion, and the reference surface 422a is an example of a second surface. The protrusion 423 is an example of a third protrusion, and the reference surface 423a is an example of a third surface.

[0118] The protrusions 421, 422, 423, and 424 have reference surfaces 421b, 422b, 423b, and 424b, respectively, on the negative side in the Z axis direction.

[0119] In the fourth embodiment, the reference surfaces 421b, 422b, 423b, and 424b constitute a second reference surface R2. In the fourth embodiment, the reference surface 421b is an example of a fourth surface. The reference surface 422b is an example of a fifth surface. The reference surface 423b is an example of a sixth surface.

[0120] 12A or 13A, sensor unit 400 is normally used in a non-inverted position, fixed to fixed surface 600 or fixed surface 610. In the non-inverted position, sensor unit 400 is fixed with reference surfaces 421a, 422a, 423a, and 424a in contact with fixed surface 600 or fixed surface 610.

[0121] 12B, during calibration, the sensor unit 400 is fixed to the fixed surface 610 in an inverted position. In the inverted position, the sensor unit 400 is fixed with the reference surfaces 421b, 422b, 423b, and 424b in contact with the fixed surface 600 via the spacers 460.

[0122] 13B, during calibration, sensor unit 400 is fixed to fixed surface 600 in an inverted position. In the inverted position, sensor unit 400 is fixed with reference surfaces 421b, 422b, 423b, and 424b in contact with fixed surface 610. Fixed surface 610 has a hole into which main body 411 of sensor unit 400 is inserted.

[0123] In the fourth embodiment, the housing 410 is a rectangular parallelepiped with a rectangular surface perpendicular to the Z axis, the long side of the rectangle being approximately 60 mm, the short side being 50 mm, and the thickness being approximately 30 mm. The shape and size of the housing 410 described above are merely examples. In the fourth embodiment, the long side extends along the X axis direction, and the short side extends along the Y axis direction. Therefore, the above-mentioned effective length L is the length of the long side for the deviation angle of the X axis from the Z axis, and the above-mentioned effective length L is the length of the short side for the deviation angle of the Y axis from the Z axis. In order to satisfy Equation (8) for both the deviation angle of the X axis and the deviation angle of the Y axis, the above-mentioned effective length L may be the length of the short side. The housing 410 is a case that houses the acceleration sensor element 30, and the housing 410 houses, for example, the sensor unit 100 described above.

[0124] As described above, the first reference surface R1 and the second reference surface R2 are set to a predetermined parallelism P so that the first reference surface R1 and the second reference surface R2 are accurately parallel to each other.

[0125] The connector 450 is provided on the side surface 411c of the main body 411. The connector 450 is electrically connected to the arithmetic unit 40 and the acceleration sensor element 30. In the fourth embodiment, the connector 450 is provided on the side surface 411c of the main body 411, so that the detection data of the acceleration sensor element 30 can be acquired via the connector 450 regardless of whether the sensor unit 400 is in the non-inverted or inverted position.

[0126] As described above, the sensor unit 400 serving as an inertial measurement device of this embodiment has the following advantages in addition to the advantages of the above-described embodiments. In the sensor unit 400 of this embodiment, the protrusion 421 as the first protrusion has a reference surface 421b as the fourth surface that constitutes the second reference surface R2, the protrusion 422 as the second protrusion has a reference surface 422b as the fifth surface that constitutes the second reference surface R2, and the protrusion 423 as the third protrusion has a reference surface 423b as the sixth surface that constitutes the second reference surface R2.

[0127] Thus, in the sensor unit 400 of this embodiment, the second reference surface R2 is constituted by the reference surface 421b of the protrusion 421, the reference surface 422b of the protrusion 422, the reference surface 423b of the protrusion 423, and the reference surface 424b of the protrusion 424. Therefore, the sensor unit 400 of this embodiment has a simpler structure than when the second reference surface R2 is formed on a different protrusion, and cost reduction and weight reduction can be achieved by reducing the amount of material.

[0128] 5. Embodiment 5 In the fifth embodiment, an electronic device including a sensor unit 100 as an inertial measurement device will be described. The above-described sensor units 200, 300, and 400 may be mounted on the electronic device. In the following, examples of electronic devices will be described, including a mobile device such as a smartphone and a mobile object such as an automobile.

[0129] 5.1. Mobile Device Overview FIG. 14 is a perspective view of a mobile device as an electronic device according to the fifth embodiment, showing the configuration of a smartphone 110 as an example of the mobile device.

[0130] The smartphone 110 is equipped with the sensor unit 100 . The inertial data of the sensor unit 100 is received by the control unit 111. The control unit 111 recognizes the attitude and behavior of the smartphone 110 from the received inertial data, and can change the image displayed on the display unit, sound an alarm or sound effect, or drive a vibration motor to vibrate the main body.

[0131] The sensor unit 100 may be mounted on a portable device other than the smartphone 110. For example, the sensor unit 100 may be mounted on a portable device such as a smartwatch, a portable activity tracker, a head mounted display (HMD), a mobile personal computer (PC), a tablet PC, a camera, or a personal digital assistant (PDA). This enables the portable device to recognize its posture and behavior using the inertial data from the sensor unit 100, and to change the displayed image, sound an alarm or sound effect, or drive a vibration motor to vibrate the main body.

[0132] In this manner, in the fifth embodiment, the sensor unit 100 is mounted on a portable device such as a smartphone 110 as an electronic device. Therefore, according to the fifth embodiment, the performance of the portable device equipped with the sensor unit 100 can be improved.

[0133] 5.2. Overview of Mobile Objects FIG. 15 is a perspective view of a moving body as an electronic device according to the fifth embodiment, showing the configuration of an automobile 130 as an example of the moving body.

[0134] The automobile 130 is equipped with the sensor unit 100 . The sensor unit 100 detects the attitude of the vehicle body 131 and transmits inertial data to the vehicle body attitude control device 132. The inertial data includes angular velocity and acceleration. When the vehicle body attitude control device 132, which controls the attitude of the vehicle body 131, receives the inertial data from the sensor unit 100, it detects the attitude of the vehicle body 131 based on the signal, and controls the hardness of the suspension or the brakes of each wheel 133 according to the detection results.

[0135] The inertial data from sensor unit 100 may also be utilized in ECUs (Electronic Control Units) such as keyless entry, immobilizers, car navigation systems, car air conditioners, anti-lock braking systems (ABS), airbags, TPMS (Tire Pressure Monitoring Systems), engine controls, inertial navigation control equipment for autonomous driving, and battery monitors for hybrid and electric vehicles.

[0136] The sensor unit 100 may be mounted on a moving body other than the automobile 130. Examples of other moving bodies include a bipedal robot, a train, an airplane, a ship, a radio-controlled airplane, a radio-controlled helicopter, a drone, agricultural machinery such as a tractor, and construction machinery. A moving body equipped with the sensor unit 100 can utilize the inertial data of the inertial measurement unit for attitude control and position measurement of the moving body.

[0137] In this manner, in the fifth embodiment, the sensor unit 100 is mounted on a moving body such as an automobile 130 as an electronic device. Therefore, according to the fifth embodiment, the performance of a moving object equipped with the sensor unit 100 can be improved.

[0138] Although the preferred embodiment has been described above, the present invention is not limited to the above embodiment. The configuration of each part of the present invention can be replaced with any configuration that exhibits the same function as the above embodiment, and any configuration can be added. [Explanation of symbols]

[0139] 10...housing, 11...main body, 11a...first surface, 11b...second surface, 11c...side surface, 12...lid, 12a...first surface, 13...storage section, 14...screw hole, 15...screw, 21...protrusion, 21a...reference surface, 22...protrusion, 22a...reference surface, 23...protrusion, 23a...reference surface, 24...protrusion, 24a...reference surface, 25...protrusion, 25a...reference surface, 26...protrusion, 26a...reference surface, 27...protrusion, 27a...reference surface, 28...protrusion, 28a...reference surface, 30...acceleration sensor element, 40...arithmetic unit, 41...drive detection unit, 42...ADC, 43...calculation unit, 44...storage unit, 4 5...correction unit, 50...connector, 100...sensor unit, 110...smartphone, 111...control unit, 130...automobile, 131...vehicle body, 132...vehicle body attitude control device, 133...wheel, 200...sensor unit, 210...casing, 211...main body, 211a...first surface, 211b...second surface, 211c...side, 212...lid, 212a...first surface, 214...screw hole, 216...screw, 221...protrusion, 221a...reference surface, 222...protrusion, 222a...reference surface, 223...protrusion, 223a...reference surface, 224...protrusion, 224a...reference surface, 225...protrusion portion, 225a...reference surface, 226...protrusion, 226a...reference surface, 250...connector, 300...sensor unit, 310...housing, 311...main body portion, 311a...first surface, 311b...second surface, 311c...side surface, 311d...side surface, 312...lid portion, 312a...first surface, 313...storage portion, 314...screw hole, 321...protrusion, 321a...reference surface, 322...protrusion, 322a...reference surface, 323...protrusion, 323a...reference surface, 324...protrusion, 324a...reference surface, 325...protrusion, 325a...reference surface, 326...protrusion, 326a...reference surface, 350...connector , 400...sensor unit, 410...housing, 411...main body, 411a...first surface, 411b...second surface, 411c...side surface, 421...protrusion, 421a, 421b...reference surface, 422...protrusion, 422a, 422b...reference surface, 423...protrusion, 423a, 423b...reference surface, 424...protrusion, 424a, 424b...reference surface, 450...connector, 460...spacer, 600, 610...fixed surface, P1, P2...parallelism, R1...first reference surface, R2...second reference surface, S1...first plane, S2...second plane, Z0, Z1, Z2...acceleration, A...datum plane.

Claims

1. a housing that is fixed to a fixed surface in a first position or a second position that is 180° inverted from the first position; an acceleration sensor housed in the housing, the housing has a first reference surface that contacts the fixed surface in the first attitude and a second reference surface that contacts the fixed surface in the second attitude, the first reference plane and the second reference plane are parallel to each other; Inertial measurement unit.

2. The housing includes: a main body that houses the acceleration sensor; a first protrusion provided on the main body portion and having a first surface that constitutes the first reference surface; a second protrusion provided on the main body portion and having a second surface that constitutes the first reference surface; a third protrusion provided on the main body portion and having a third surface that constitutes the first reference surface; 10. The inertial measurement unit of claim 1.

3. The housing includes: a fourth protrusion provided on the main body portion and having a fourth surface that constitutes the second reference surface; a fifth protrusion provided on the main body portion and having a fifth surface that constitutes the second reference surface; a sixth protrusion provided on the main body portion and having a sixth surface that constitutes the second reference surface; 3. The inertial measurement unit of claim 2.

4. the first protrusion protrudes from the main body in a first direction intersecting the first reference plane and in a second direction parallel to the first reference plane; the second protrusion protrudes from the main body in the first direction and the second direction; the third protrusion protrudes from the main body in a third direction opposite to the first direction and the second direction; 3. The inertial measurement unit of claim 2.

5. the fourth protrusion protrudes from the main body in a fourth direction intersecting the second reference plane and in a fifth direction parallel to the second reference plane; the fifth protrusion protrudes in the fourth direction and the fifth direction, the sixth protrusion protrudes from the main body in a sixth direction opposite to the fourth direction and the fifth direction; 4. The inertial measurement unit of claim 3.

6. the first protrusion has a fourth surface that constitutes the second reference surface, the second protrusion has a fifth surface that constitutes the second reference surface, the third protrusion has a sixth surface that constitutes the second reference surface; 5. The inertial measurement unit of claim 4.

7. a connector provided on a side surface of the housing and electrically connected to the acceleration sensor; 10. The inertial measurement unit of claim 1.

8. The parallelism of the first reference surface and the second reference surface is 0.2 mm or less.

10. The inertial measurement unit of claim 1.

9. When the length of the first reference surface is L mm, the gravitational acceleration is G, and the value of the acceleration bias included in the output value of the acceleration sensor in the direction of the gravitational acceleration is BmG, the parallelism P mm of each of the first reference surface and the second reference surface is G×P / L≦B fulfill, 10. The inertial measurement unit of claim 1.

10. An electronic device comprising the inertial measurement device according to any one of claims 1 to 9.

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