JP2005291745A - Inertial sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inertial sensor capable of being easily miniaturized with a simple structure. <P>SOLUTION: An acceleration sensor 1 includes a sensor body 3 and a detection means 5. The detection means comprises an elastic member 17, a magnetic field direction sensing element 19, and a magnetic field generating element 21. The elastic member is held to the sensor body in a cantilevered state. The magnetic field direction sensing element is a spin-valve type GMR element, and mounted on a movable part of the elastic member, and the magnetic field generating element is attached to the sensor body at a position opposite to the magnetic field direction sensing element. The sensor body includes a pair of left and right holding frames 7, 9 holding the elastic member, and a pair of upper and lower top plates 11, 13 holding the top plates 11, 13, and the holding frames and the top plates are composed of ceramics. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an inertial sensor.

  Conventionally, a mechanical structure type and a piezoelectric type are known as an acceleration sensor which is one of inertial sensors. An example of the mechanical structure type is disclosed in Japanese Patent Application Laid-Open No. 2002-365307. This sensor has an inertial body that moves by an inertial force, and senses acceleration by electrically capturing the movement of the inertial body to move the movable contact in accordance with the inertial force.

  An example of the piezoelectric type is disclosed in JP-A-6-273439. In this sensor, both ends of a bimorph type detection element are fixed. Further, the bimorph type detection element is divided into three parts, that is, a central part and both end parts, and the polarization directions of the central part and both end parts are set in reverse. Then, the acceleration is sensed by detecting a signal when the detection element is bent by the acceleration.

However, the above-described acceleration sensor of the mechanical structure type has a problem of causing wear and chattering of moving parts such as contacts, and generally has a complicated structure and is difficult to reduce in size. On the other hand, the piezoelectric type acceleration sensor has the following problems. That is, first, sensitivity is lowered due to deterioration of the polarization degree. Second, low-frequency impact signals and acceleration signals cannot be detected unless special measures such as attaching weights are taken. Third, the detection characteristics are affected by popcorn noise caused by the pyroelectric effect of the piezoelectric element. Fourthly, since the PZT piezoelectric ceramic is broken, it is difficult to take a large range. Fifth, there is a problem that a constant sustained displacement state cannot be detected only by obtaining a detection signal only at the moment when the displacement occurs.
JP 2002-365307 A JP-A-6-273439

  An object of the present invention is to provide an inertial sensor that has a simple structure and can be easily miniaturized.

  Another object of the present invention is to provide an inertial sensor that has a small number of parts and is easy to assemble.

  Yet another object of the present invention is to provide an inertial sensor that is resistant to wear and breakage.

  Still another object of the present invention is to provide an inertial sensor having a wide dynamic range.

  Still another object of the present invention is to provide an inertial sensor with high detection sensitivity.

  Still another object of the present invention is to provide an inertial sensor having little change with time.

  In order to solve the above-described problems, an inertial sensor according to the present invention is an inertial sensor including a sensor body and a detection unit, and the detection unit includes a support member, a magnetic field sensitive element, and a magnetic field generation element. The support member is held by the sensor body, one of the magnetic field sensitive element and the magnetic field generating element is attached to a movable part of the support member, and the other is attached to the sensor body. ing.

  Preferably, the support member is held in a cantilever state on the sensor body. The magnetic field sensitive element may be attached to the supporting member, and the magnetic field generating element may be attached to the sensor body, or the magnetic field generating element may be attached to the supporting member, and the magnetic field sensitive element may be It may be attached to the sensor body.

  According to such a configuration, only the support member and the magnetic field sensitive element or the magnetic field generating element integrated therewith are used as the movable parts, and detection can be performed with an extremely simple structure. Simplification and miniaturization can be achieved.

  Furthermore, since it does not involve contact with other parts of the movable part, damage due to wear or impact can be avoided. Furthermore, as the support member, it is not necessary to use a piezoelectric ceramic as in the prior art, and a member having sufficient elastic strength can be used, so that the dynamic range can be widened.

  Further, the magnetic field sensitive element is a spin valve type GMR element and captures a relative direction change of the magnetic field in a plane substantially parallel to the film surface or relative to the magnetic field in a plane substantially perpendicular to the film surface. It is also possible to capture various direction changes.

  According to this, since the detection characteristic of the magnetic field sensitive element depends on the direction of the external magnetic field and does not depend on the magnitude of the external magnetic field, there is an advantage that it does not exhibit a change with time due to a decrease in the holding power of the magnetic field generating element. Can be obtained.

  The support member may be arranged so as to respond to the excitation force in the orthogonal biaxial direction.

  According to such a configuration, it is possible to function as a biaxial sensor.

  The detection output of the magnetic field sensitive element may be taken out from both ends of the sensor body.

  According to such a configuration, the inertial sensor can be suitably attached to the substrate.

  The sensor main body includes a pair of left and right holding frames that sandwich the support member, and a pair of upper and lower top plates that sandwich the pair of holding frames, and the pair of holding frames and the pair of top plates are made of ceramic. It may be.

  According to this, since the acceleration sensor can be configured from an extremely small number of parts such as the support member, the holding frame, and the top plate, the structure is simplified, the size is reduced, the assembly is facilitated, and the manufacturing and assembly costs are reduced. Can be planned.

  Other features of the present invention and the operational effects thereof will be described in more detail by embodiments with reference to the accompanying drawings.

  Hereinafter, an embodiment in which the inertial sensor according to the present invention is implemented as an acceleration sensor will be described with reference to the accompanying drawings. In the drawings, the same reference numerals indicate the same or corresponding parts.

  FIG. 1 is an exploded perspective view of the acceleration sensor according to the present embodiment. The acceleration sensor 1 includes a sensor body 3 and detection means 5. The sensor body 3 further includes a pair of left and right holding frames 7 and 9, a pair of upper and lower top plates 11 and 13, and a spacer 15. The detection means 5 includes an elastic member (support member) 17, a magnetic field direction sensitive element (magnetic field sensitive element) 19, and a magnetic field generating element 21. In addition, the direction used for description shall be made into the X direction shown in FIG. 1 as the left-right direction, the Y direction as the front-back direction, and the Z direction as the up-down direction.

  The holding frames 7 and 9 constituting the sensor body 3 are U-shaped members in plan view, and are arranged in a state in which the concave surfaces face each other inward. The holding frames 7 and 9 are made of ceramic in the present embodiment. End electrodes 23 and 25 for taking out the detection output of the magnetic field direction sensitive element 19 are formed at both ends of the holding frames 7 and 9.

  The top plates 11 and 13 are flat plate-like members and are made of ceramic in the present embodiment. Concave portions 27 are formed on the lower surface of the upper top plate 11 and the upper surface of the lower top plate 13 so as not to hinder the operation of the elastic member 17. The top plates 11 and 13 are arranged in a state in which the concave portions 27 face each other. End electrodes 23 and 25 for taking out the detection output of the magnetic field direction sensitive element 19 are also formed at both ends of the top plates 11 and 13.

  The spacer 15 is a six-sided member interposed at the front end of the holding frames 7 and 9. The height of the spacer 15 is set to the same height as the holding frames 7 and 9 and the elastic member 17. The thickness of the spacer 15 is set to be equal to the thickness of the elastic member 17, and the longitudinal length of the spacer 15 is an end surface (hereinafter referred to as a front protruding end surface) 7 a protruding inward on the front side of the holding frames 7, 9. It is set to the same length as 9a. The spacer 15 is made of the same material as the holding frames 7 and 9.

  The elastic member 17 that constitutes the detection means 5 is a flat plate member that is formed in a strip shape, and extends the longest in the front-rear direction, and is formed with a thin thickness in the left-right direction. The elastic member 17 can be made of resin, ceramic, silicon, metal, or the like. When it is made of metal, it is used after being insulated. Further, the elastic member 17 is held in a state in which both side surfaces thereof are orthogonal to the inertia sensor mounting surface B (see FIG. 3).

  FIG. 2 is a perspective view of the holding frame and the detection means excluding the top plate, and FIGS. 3 and 4 are a front view and a plan view of the acceleration sensor, respectively. As shown in FIGS. 1 to 4, the elastic member 17 is sandwiched between a pair of left and right holding frames 7 and 9 in a cantilever state. Specifically, the rear end (and hence the fixed end) of the elastic member 17 is fixed by end surfaces (hereinafter referred to as rear protruding end surfaces) 7b and 9b protruding inward on the rear side of the holding frames 7 and 9. The On the other hand, a spacer 15 is sandwiched between the front projecting end faces 7a, 9a of the holding frames 7, 9.

  In a state where the elastic member 17 and the spacer 15 are sandwiched between the pair of holding frames 7 and 9, a swing space 29 is secured between the holding frames 7 and 9. The elastic member 17 extends in the front-rear direction within the swing space 29. The front end (free end) of the elastic member 17 terminates without reaching the spacer 15. In addition, the holding frames 7 and 9, the elastic member 17, and the spacer 15 constitute a hexahedron having no protruding portion in an assembled state.

  A magnetic field direction sensitive element 19 is attached to the movable portion of the elastic member 17, that is, in the present embodiment, in the vicinity of the free end. As the magnetic field direction sensitive element 19, a spin valve type GMR element is used. The magnetic field direction sensitive element 19 is affixed to the right side surface of the plate-like elastic member 17, and one output line T1 of the element 19 is the right side surface of the elastic member 17 as shown by a one-dot chain line in FIG. And is connected to the rear end electrode 25. Another output line T2 of the magnetic field direction sensitive element 19 is led to the left side surface of the elastic member 17 through a through hole provided in the elastic member 17 as shown by a two-dot chain line in FIG. Is extended along the inward concave surface of the left holding frame 7 and connected to the front end electrode 23. In each drawing, the magnetic field direction sensitive element 19 and the magnetic field generating element 21 are exaggerated in order to prioritize visibility and clarity of explanation.

  A magnetic field generating element 21 is attached to a position facing the magnetic field direction sensitive element 19 on the inward concave surface of the right holding frame 9. As the magnetic field generating element 21, a small magnet is used in the present embodiment. However, the present invention is not limited to this, and can be widely applied to any magnetized material such as a coating type magnetic material and a thin film type magnetic material. it can. The magnetic field generating element 21 and the magnetic field direction sensitive element 19 are arranged so as to be separated in a no-load state of inertia force.

  In the present embodiment, the front protruding end surfaces 7a and 9a and the rear protruding end surfaces 7b and 9b of the holding frames 7 and 9, the bottom surfaces of the inwardly concave surfaces of the holding frames 7 and 9, both the left and right side surfaces of the elastic member 17, and The left and right side surfaces of the spacer 15 are all formed and assembled so as to be parallel.

  The upper and lower surfaces of the holding frames 7 and 9, the elastic member 17, and the spacer 15 are covered with a pair of corresponding top plates 11 and 13. Above and below the swinging space 29 formed between the holding frames 7 and 9, an extra space defined by the concave portions 27 of the top plates 11 and 13 is widened.

  Here, resistance characteristics of the spin valve type GMR element as the magnetic field direction sensitive element 19 will be described with reference to FIGS. As shown in FIG. 5, the spin valve GMR element basically has a four-layer structure including a free rotation layer 19a, a Cu layer 19b, a pinned layer 19c, and an antiferromagnetic layer 19d. The magnetization direction P of the pinned layer is fixed by magnetic coupling with the antiferromagnetic layer 19d. On the other hand, when external magnetization that rotates in a plane parallel to the film surface of the magnetic field direction sensitive element 19 acts, the resistance characteristic is as shown in FIG. The horizontal axis is the angle θ1 formed by the external magnetization direction H and the pinned layer magnetization direction P, and the vertical axis is the resistance value change rate ΔR / R. On the other hand, when external magnetization that rotates in a plane perpendicular to the film surface of the magnetic field direction sensitive element 19 acts, the resistance characteristic is as shown in FIG. The horizontal axis is the angle θ2 formed by the external magnetization direction V and the pinned layer magnetization direction P, and the vertical axis is the resistance value change rate ΔR / R. Thus, the spin valve type GMR element can grasp the change in the magnetic field direction as the change in the resistance value.

  Next, the operation of the acceleration sensor 1 configured as described above will be described. The acceleration sensor 1 is attached to an acceleration detection target part in, for example, a hard disk drive or an optical disk drive incorporated in a portable electronic device. When no external force is applied to the acceleration detection target portion, that is, in a no-load state, the elastic member 17 extends straight in the front-rear direction as shown in FIG. It is maintained in parallel with the concave surfaces of the frames 7 and 9 at substantially equal intervals.

  Next, as shown in FIG. 8, when an external force F acts on the acceleration detection target part, the force also acts on the sensor body 3 of the acceleration sensor 1 fixed integrally to the acceleration detection target part. On the other hand, an inertial force I caused by an external force acts on the elastic member 17 supported in a cantilever state. The elastic member 17 swings with the inertial force I as shown in FIG. 8, for example, with the fixed end as a fulcrum. Thereby, the magnetic field direction sensitive element 19 fixed to the movable part of the elastic member 17 is displaced / inclined with respect to the magnetic field generating element 21.

  At this time, since the operation of the movable part of the elastic member 17 is a bending motion in the XY plane, the change in the direction of the magnetic field generated from the magnetic field generating element 21 is seen from the magnetic field direction sensitive element 19. This is understood as a phenomenon of rotation in a plane (XY plane) orthogonal to 19 film planes (YZ plane). Therefore, in the magnetic field direction sensitive element 19, a resistance value change corresponding to the change in the magnetic field direction as shown in FIG. 7 appears. This change in resistance value is taken out as a change in current value through the output lines T1 and T2 and the end electrodes 23 and 25 formed as thick film electrodes. And the acceleration resulting from external force is detectable from the change of an electric current value.

  As described above, in the present embodiment, acceleration can be detected with an extremely simple structure including only the elastic member 17 and the magnetic field direction sensitive element 19 integrated therewith as movable parts. The acceleration sensor 1 as a whole is also composed of an extremely small number of parts such as an elastic member 17 having a magnetic field direction sensitive element 19, holding frames 7 and 9 having a magnetic field generating element 21, and top plates 11 and 13. Simplification, miniaturization, ease of assembly, and cost reduction during manufacturing and assembly.

  In addition, since the movable part does not come into contact with other parts, damage due to wear or impact can be avoided. Furthermore, as an elastic member, it is not necessary to use a piezoelectric ceramic as in the prior art, and a member having sufficient elastic strength can be used, so that the dynamic range can be widened.

  In addition, since the magnetic field direction sensitive element is used as the detection means, sensing with good detection sensitivity can be maintained without causing the problem of deterioration of the degree of polarization unlike the piezoelectric element. Furthermore, since the change characteristic of the resistance value in the spin valve type GMR element depends on the direction of the external magnetic field and does not depend on the magnitude of the external magnetic field, it does not receive a change with time due to a decrease in the holding power of the magnetic field generating element. That's it.

  In addition, since the magnetic field direction sensitive element 19 is attached in the vicinity of the free end of the elastic member 17 in a cantilever state, acceleration can be detected at a position where the amplitude is large due to bending, and precise detection can be performed. Furthermore, even in a mode in which the magnetic field direction sensitive element 19 is attached to a movable part having a large amplitude, a detection output is obtained using the through holes, both side surfaces (both side parts) of the elastic member 17 and the inner surfaces of the holding frames 7 and 9. By taking it out, it is possible to output from both ends of the sensor body 3.

  Moreover, since it is a detection aspect which catches the magnetic field change by the relative displacement of the magnetic field direction sensitive element 19 and the magnetic field generating element 21, it can be used from a DC component. Furthermore, a smaller and lower profile can be adopted than the above-described configuration, and the needs of surface mount sensors that have been demanded in recent years can be met. In addition, since the holding frames 7 and 9 and the top plates 11 and 13 are made of ceramic, workability at the time of mass production can be improved when the holding frames 7 and 9 and the top plates 11 and 13 are formed in the above-described form.

  In the present embodiment, the magnetization direction of the pinned layer of the spin valve GMR element is set as indicated by symbol P in the partially enlarged perspective view E1 of FIG. Although the film surface (sensitive surface) is oriented parallel to the YZ plane, the following mode may be used instead. As shown in the partially enlarged perspective view E2 of FIG. 8, the magnetic field direction sensitive element 19 is arranged, and the pin layer magnetization direction P of the film surface (sensitive surface) of the magnetic field direction sensitive element 19 is oriented parallel to the XY plane. May be. In that case, the relative change of the external magnetic field is regarded as a phenomenon of rotating in a plane (XY plane) parallel to the sensitive surface (XY plane) of the magnetic field direction sensitive element 19. Therefore, in the magnetic field direction sensitive element 19, a resistance value change corresponding to the change in the magnetic field direction as shown in FIG. 6 appears.

  Next, another embodiment of the present invention will be described with reference to FIGS. This embodiment is the same as the above-described embodiment shown in FIGS. 1 to 5 except for the sensitive surface of the magnetic field direction sensitive element, the direction of the elastic member, and the accompanying structure. 9 and 10 correspond to FIG. 1 (the top plate is omitted) and FIG.

  The acceleration sensor 101 of the present embodiment includes an elastic member 117 that is inclined with respect to the height direction. The elastic member 117 is held so that the pair of left and right side surfaces 117a and 117b intersect with the inertia sensor mounting surface B (see FIG. 10) at an angle, that is, in a relationship that is neither parallel nor vertical. . A magnetic field direction sensitive element 19 is attached to the right side surface 117 b of the elastic member 117.

  The holding frames 107 and 109 that sandwich the elastic member 117 have front protruding end surfaces 107a and 109a and rear protruding end surfaces 107b and 109b extending in parallel with the side surfaces 117a and 117b of the elastic member 117. Like the elastic member 117, the spacer 115 sandwiched between the front projecting end surfaces 107a and 109a of the holding frames 107 and 109 has a pair of left and right side surfaces inclined with respect to the height direction. On the other hand, the inwardly concave surfaces of the holding frames 107 and 109 extend along the height direction.

  In this embodiment in which the elastic member is arranged so as to respond to the excitation force in the orthogonal biaxial direction as described above, in addition to the effects of the embodiment shown in FIGS. Can also be obtained. That is, since the elastic member 117 is simultaneously inclined with respect to the two surfaces of the XY plane and the YZ plane, the biaxial sensor capable of detecting the inertia force in the X direction and the inertia force in the Z direction. Can function as.

  Although the contents of the present invention have been specifically described with reference to the preferred embodiments, various modifications can be made by those skilled in the art based on the basic technical idea and teachings of the present invention. It is self-explanatory.

  For example, as the detection means, the magnetic field direction sensitive element may be fixed to a holding frame or the like, and the magnetic field generating element may be provided so as to move integrally with the elastic member. Further, the magnetic field direction sensing element and the magnetic field generating element are not limited to a mode in which only one set is provided, and a plurality of sets may be provided. In that case, you may provide in the one side of an elastic member, and you may distribute and provide in both sides. Further, the magnetic field direction sensitive element or the magnetic field generating element is not limited to the vicinity of the free end of the elastic member as long as it is a movable part, and may be provided in the vicinity of the central part in the longitudinal direction of the elastic member.

  Further, the support member to which the magnetic field direction sensitive element or the magnetic field generating element is attached may be a member that deforms in a very small range, and therefore, a member that is not generally called an elastic member can be used.

  In addition, it is preferable to ensure the magnetic shielding effect by covering the outside of the sensor body with a magnetic shield member or including a magnetic shield material in the sensor body. Further, the magnetic field direction sensitive element is not limited to a spin valve type as long as it is a GMR element, and a so-called TMR element that generates MR (Magnetic Resistance) using a tunnel current can also be used.

  Further, the spacer is not necessarily limited to being made of the same material as the holding frame or the like.

  Furthermore, this embodiment is not limited to use as an acceleration sensor, and can be widely implemented as an inertial sensor. Further, the inertia sensor here means a sensor that can detect a physical quantity that changes due to an inertia force, and examples thereof include an impact sensor, an angular velocity sensor, and an angular acceleration sensor.

It is a disassembled perspective view of the acceleration sensor which concerns on embodiment of this invention. FIG. 2 is a perspective view of a holding frame and a detection unit excluding a top plate with respect to the acceleration sensor of FIG. 1. It is a front view of the acceleration sensor of FIG. It is a top view except the top plate of the acceleration sensor of FIG. 1, Comprising: It is a figure which shows a no-load state. It is a figure which shows the structure of the spin valve type | mold GMR element as a magnetic field direction sensitive element. It is a figure which shows a resistance characteristic when external magnetization which rotates in the surface parallel to an element film surface acts in a spin valve type GMR element. It is a figure which shows a resistance characteristic when external magnetization which rotates in a surface perpendicular | vertical to an element film surface acts in a spin valve type GMR element. It is a figure of the state to which the external force was added regarding the plane of FIG. It is the disassembled perspective view which abbreviate | omitted the top plate regarding the acceleration sensor which concerns on another embodiment of this invention. It is a figure of the same aspect as FIG. 3 regarding the acceleration sensor of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,101 Acceleration sensor 3 Sensor main body 5 Detection means 7, 9, 107, 109 Holding frame 11, 13 Top plate 17, 117 Elastic member 19 Magnetic field direction sensitive element 21 Magnetic field generating element

Claims (8)

An inertial sensor including a sensor body and a detection means,
The detection means includes a support member, a magnetic field sensitive element, and a magnetic field generating element,
The support member is held by the sensor body,
One of the magnetic field sensitive element and the magnetic field generating element is attached to the support member, and the other is attached to the sensor body.
Inertial sensor. The inertial sensor according to claim 1,
The support member is held in a cantilever state on the sensor body.
Inertial sensor. The inertial sensor according to claim 1 or 2,
The magnetic field sensitive element is attached to the support member,
The magnetic field generating element is attached to the sensor body.
Inertial sensor. The inertial sensor according to claim 1 or 2,
The magnetic field generating element is attached to the support member,
The magnetic field sensitive element is attached to the sensor body,
Inertial sensor. The inertial sensor according to any one of claims 1 to 4,
The magnetic field sensitive element is a spin valve type GMR element and captures a relative direction change of the magnetic field in a plane substantially parallel to the film surface or a relative direction of the magnetic field in a plane substantially perpendicular to the film surface. Capture change,
Inertial sensor. The inertial sensor according to any one of claims 1 to 5,
The support member is disposed so as to respond to the excitation force in the orthogonal biaxial direction.
Inertial sensor. The inertial sensor according to any one of claims 1 to 6,
The detection output of the magnetic field sensitive element is taken out from both ends of the sensor body.
Inertial sensor. The inertial sensor according to any one of claims 1 to 7,
The sensor body includes a pair of left and right holding frames that sandwich the support member, and a pair of upper and lower top plates that sandwich the pair of holding frames,
The pair of holding frames and the pair of top plates are made of ceramic,
Inertial sensor.

Images