JP6616806B2 - Strain gauge and 3-axis force sensor - Google Patents

Description

  The present invention relates to a strain gauge and a three-axis force sensor including the same.

  A triaxial force sensor having a strain gauge is widely used in robots, game machines, various measuring instruments, and other devices. For example, Patent Documents 1 and 2 disclose an example of a triaxial force sensor including a strain gauge.

JP 2010-164495 A Japanese Patent No. 5008188

  In a triaxial force sensor having a strain gauge, the existence of a measurement error due to a change in ambient temperature is recognized, and suppression thereof is desired.

  In view of the above, an object of the present invention is to provide a strain gauge in which generation of measurement errors due to changes in ambient temperature is suppressed, and a three-axis force sensor including the strain gauge.

  The strain gauge according to the present invention is attached to a strain generating member that is distorted by receiving a load, detects a load acting in the first direction of the strain generating member by the first Wheatstone bridge circuit, and is orthogonal to the first direction of the strain generating member. The strain used for the detection by the second Wheatstone bridge circuit of the load acting in the second direction and the detection by the third Wheatstone bridge circuit of the load acting in the third direction orthogonal to the first and second directions of the strain generating member A gauge comprising a flexible base material and a circuit pattern formed on the base material, wherein the base material is attached to a strain generating region where strain is generated by receiving a load of the strain generating member. An area, a pair of insensitive areas arranged outside the strain generating area, and a connecting area that connects the sensitive area and the insensitive area, and the sensitive area and the insensitive area of the connecting area are connected. Direct to the direction The dimension of the orthogonal direction is smaller than the dimension of the sensitive region and the non-sensitive region in the orthogonal direction, and the circuit pattern includes two first strain-sensitive elements constituting the first Wheatstone bridge circuit and a second Wheatstone bridge circuit. Two second direction strain sensitive elements, two third direction strain sensitive elements constituting a third Wheatstone bridge circuit, and two first direction fixed resistance elements constituting a first Wheatstone bridge circuit; , Two second direction fixed resistance elements constituting the second Wheatstone bridge circuit, a first direction strain sensitive element, a second direction strain sensitive element, a third direction strain sensitive element, and a first direction The fixed resistance element and the second direction fixed resistance element are formed of the same material, and the first direction strain sensitive element, the second direction strain sensitive element, and the third direction strain The sensing element is formed in the sensing area, the first direction fixed resistance element and the second direction fixed resistance element are formed in the insensitive area, and the third direction strain sensing element is the first Wheatstone bridge. A circuit and a second Wheatstone bridge circuit are connected to form a third Wheatstone bridge circuit.

  A triaxial force sensor according to the present invention includes the above strain gauge, a plate-like strain generating member, and a load acting portion connected to the strain generating member.

  The triaxial force sensor according to the present invention further includes a peripheral wall standing upright in the third direction from the peripheral portion of the surface opposite to the surface to which the load acting portion of the strain generating member is connected, and the insensitive region is You may affix on the internal peripheral surface of a surrounding wall.

  In the strain gauge of the present invention and the three-axis force sensor including the strain gauge, occurrence of measurement errors due to changes in ambient temperature is suppressed.

It is sectional drawing of the electronic pen to which the triaxial force sensor which concerns on embodiment of this invention is applied. It is a perspective view of the 3 axis force sensor concerning the embodiment of the present invention. 3 is a cross-sectional view of the triaxial force sensor shown in FIG. 2 cut along a yz plane including an axis A. FIG. It is a figure which shows the wiring pattern of the strain gauge which concerns on embodiment of this invention. It is a circuit diagram corresponding to the wiring pattern of the strain gauge shown in FIG. It is explanatory drawing which shows the mode of a measurement in a triaxial force sensor.

<Embodiment>
Embodiments of the strain gauge and the triaxial force sensor according to the present invention will be described with reference to FIGS.

  As shown in FIG. 1, the electronic pen 200 includes tips 31 and 32, a triaxial force sensor 100, a holder 33, a body 34, and a front cap 35.

  The tip 31 is made of, for example, plastic and functions as a pen tip. The tip 32 is formed of, for example, SUS, and one end thereof is connected to the tip 31 and the other end is connected to the triaxial force sensor 100. As a result, an external load applied via the pen tip is measured by the triaxial force sensor 100.

  The holder 33 holds a PCB (Printed Circuit Board Assembly) on which various circuits are mounted in addition to a signal processing circuit and a power source necessary for the operation of the triaxial force sensor 100. The body 34 covers a part of the triaxial force sensor 100 and the holder 33, and the front cap 35 covers the remaining part of the triaxial force sensor 100 and the tip 32.

  Next, as shown in FIGS. 2 and 3, the triaxial force sensor 100 of the present embodiment includes a main body 10 that is rotationally symmetric about the axis A. The main body 10 includes a disc-shaped strain generating plate (plate-shaped strain generating member) 11 having an axis A as a rotation axis, and a load acting unit 12 that stands upright in the axial direction from the center of the surface 11a of the strain generating plate 11. And the peripheral wall 13 standing upright in the axial direction from the peripheral portion of the back surface 11b of the strain generating plate 11. Moreover, the load action part 12 is fitted to the tip 32 shown in FIG. The main body 10 is integrally formed of, for example, a synthetic resin material.

  In the following description, as shown in FIG. 2, two orthogonal radial directions of the strain generating plate 11 are defined as the x-axis (first direction) and the y-direction (second direction) of the triaxial force sensor 100 and the main body 10. To do. In addition, the direction of the axis A orthogonal to the x direction and the y direction is defined as the z direction (third direction) of the triaxial force sensor 100 and the main body 10.

  The strain generating plate 11 is a disc that is distorted by receiving an external load applied through the load acting portion 12. The strain in the strain generating plate 11 occurs on the front surface 11a and the back surface 11b (upper and lower surfaces orthogonal to the axis A in FIG. 2) of the strain generating plate 11, and does not occur on the peripheral wall 13 (the peripheral surface parallel to the axis A in FIG. 2). Or small enough to ignore. In this specification, like the surface 11a and the back surface 11b of the strain generating plate 11 in the present embodiment, a region that is distorted by an external load is referred to as a “strain generating region”. The diameter and thickness of the strain generating plate 11 are arbitrary.

  The load acting portion 12 moves in response to an external load and causes the strain generating plate 11 to be distorted. The load acting part 12 is provided on the surface 11 a of the strain plate 11 so that the central axis thereof coincides with the rotation axis (axis A) of the strain plate 11, that is, coaxially with the strain plate 11.

  The peripheral wall 13 stands upright from the back surface 11b along the outer periphery of the back surface 11b of the strain generating plate 11, and surrounds the back surface 11b. In addition, in FIG. 2, although illustrated about the case where the outer peripheral surface of the surrounding wall 13 is cylindrical, you may change the surrounding wall 13 as follows. That is, a planar portion intersecting (orthogonal) with the x axis may be formed on the outer peripheral surface of the peripheral wall 13 on one side or both sides of the peripheral wall 13 in the x axis direction. Alternatively, on one side or both sides of the peripheral wall 13 in the y-axis direction, a planar portion intersecting (orthogonal) with the y-axis may be formed on the outer peripheral surface of the peripheral wall 13.

  In particular, when a plane portion is provided only on one side of the peripheral wall 13 in the x-axis direction, the plane portion can be provided only on one side of the peripheral wall 13 in the y-axis direction. In this case, two flat portions are provided on the outer peripheral surface of the peripheral wall 13. Moreover, when providing a plane part on both sides of the peripheral wall 13 in the x-axis direction, the plane part can be provided on both sides of the peripheral wall 13 also in the y-axis direction. In this case, four plane portions are provided with respect to the outer peripheral surface of the peripheral wall 13.

  Thus, by providing a flat portion on the outer peripheral surface of the peripheral wall 13, the positioning of the main body 10 (that is, the three-axis force sensor 100) with respect to the holder 33 of the electronic pen 200 can be easily and reliably performed using the flat portion. It becomes possible to do. In addition, it is good also as positioning of the main-body part 10 with respect to the holder 33 is possible by providing an alignment mark with respect to the surrounding wall 13 which has a cylindrical outer peripheral surface like FIG.

  In the strain gauge 20 of the present embodiment, a part of the base material 21 (see FIG. 4) (sensitive area 21s) is attached to the back surface 11b of the strain generating plate 11, and the remaining parts (insensitive areas 21n1, 21n2) are peripheral walls. 13 is bent and attached to the inner peripheral surface.

FIG. 4 shows a state (development view) before the strain gauge 20 is attached to the strain-generating plate 11. As shown in FIG. 4, the strain gauge 20 includes a base material 21 and a circuit pattern CP printed on the surface of the base material 21. The substrate 21 has a sensitive area 21s and insensitive areas 21n1, 21n2 sandwiching the sensitive area 21s, and the circuit pattern CP has six strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z _2. And four fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ , eight terminals T _{1 to} T _8, and a wiring W connecting them. In the following description, the direction in which the insensitive areas 21n1 and 21n2 sandwich the sensitive area 21s is defined as the y direction (second direction), and the direction orthogonal to the y direction on the surface of the substrate 21 is defined as the x direction (first direction). ).

  The base material 21 is a flexible resin film, and includes a central circular sensitive area 21s, a pair of insensitive areas 21n1, 21n2 sandwiching the sensitive area 21s, and a sensitive area 21s and a pair of insensitive areas. It has a pair of connection area | region 21c1, 21c2 which connects 21n1, 21n2 respectively. As the resin film, it is desirable to use a flexible and highly flexible film that can be easily bent. As specific examples, polyester, polyimide, and the like can be used. It is also possible to form the sensitive area 21s, the insensitive areas 21n1, 21n2, and the coupling areas 21c1, 21c2 from different materials. However, these are made of the same material, and the temperature characteristics (resistance temperature coefficient) of the entire area are formed. Etc.) should be equal. In this case, the sensitive region 21s, the insensitive regions 21n1, 21n2, and the connecting regions 21c1, 21c2 are integrally cut out from the vicinity of the integrally formed material (for example, a sheet of polyester, polyimide, etc.). It is more desirable to form 21. Thereby, the temperature characteristics of each region can be made more uniform.

Since the sensitive area 21 s is an area that is attached to the back surface 11 b of the strain plate 11 of the main body 10, it has a diameter equal to or smaller than the back surface 11 b of the strain plate 11. On one surface of the sensitive area 21 s, strain sensitive elements (first direction strain sensitive elements) X ₁ and X ₂ with the center c sandwiched in the x direction are strain sensitive elements (second strains) sandwiched in the y direction. Directional strain sensitive elements) Y ₁ and Y ₂ are formed, and strain sensitive elements (third direction strain sensitive elements) Z ₁ and Z ₂ are formed along the outer periphery.

Each of the strain sensing elements X ₁ and X ₂ has an arc shape, and is formed to face the x direction with the circumferential direction along the outline of the load acting portion 12 indicated by a broken line in FIG. 4 as the width direction of the grid. Yes. Moreover, the sensitive elements X ₂ and strain sensitive elements X ₁ strain is formed equidistant from the center c, respectively.

Each of the strain sensitive elements Y ₁ and Y ₂ has an arc shape, and is formed so as to face the y direction with the circumferential direction along the outline of the load acting portion 12 as the width direction of the grid. In addition, the strain sensitive element Y ₁ and the strain sensitive element Y ₂ are formed at equidistant positions from the center c.

Each of the strain sensitive elements Z ₁ and Z ₂ has an arc shape, and is formed to face the x direction with the circumferential direction of the sensitive area 21 s as the width direction of the grid. The strain sensitive elements Z ₁ and Z ₂ are disposed on the side (outside) opposite to the center c of the strain sensitive elements X ₁ , X ₂ , Y ₁ , and Y ₂ .

  The pair of insensitive areas 21n1 and 21n2 sandwich the sensitive area 21s in the y direction, and each has a rectangular shape with the x direction as the long side direction and the y direction as the short side direction.

Fixed resistance elements (first direction fixed resistance elements) RX ₁ and RX ₂ extending in the x direction are formed side by side in the x direction at portions far from the sensitive area 21s on the surface of the insensitive area 21n1. Four terminals T ₁ , T ₂ , T ₃ , T ₄ arranged in the x direction are formed in a portion close to the sensitive area 21 s. That is, in the insensitive region 21n1, the fixed resistance elements RX ₁ and RX ₂ are disposed on the opposite side of the terminals T _{1 to} T ₄ from the sensitive region 21s.

Similarly, fixed resistance elements (second direction fixed resistance elements) RY ₁ and RY ₂ extending in the x direction are formed side by side in the x direction at portions far from the sensitive area 21s on the surface of the insensitive area 21n2. The four terminals T ₅ , T ₆ , T ₇ , and T ₈ arranged in the x direction are formed in a portion close to the sensitive area 21 s. That is, in the insensitive area 21n2, the fixed resistance elements RY ₁ and RY ₂ are arranged on the opposite side of the terminals T _{5 to} T ₈ from the sensitive area 21s.

  The connection regions 21c1 and 21c2 that connect the sensitive region 21s and the insensitive regions 21n1 and 21n2 are respectively in the x direction (orthogonal direction) orthogonal to the y direction in which the sensitive region 21s and the insensitive regions 21n1 and 21n2 are connected. The dimension (width) is smaller than the dimension (width) in the x direction of the sensitive area 21s and the insensitive areas 21n1, 21n2. Therefore, the base material 21 has a constricted shape in the connection regions 21c1 and 21c2.

As shown in FIGS. 4 and 5, the wiring W constitutes a first bridge circuit (first Wheatstone bridge circuit) BC1 by connecting the strain sensing elements X ₁ and X ₂ and the fixed resistance elements RX ₁ and RX _2. doing. Further, the terminal T ₁ is between the strain sensitive element X ₁ and the fixed resistance element RX ₁ , the terminal T ₂ is between the strain sensitive elements X ₁ and X ₂ , and between the fixed resistance elements RX ₁ and RX ₂ . to the terminal _{T 3,} the terminal _{T 4} is connected between the strain sensitive elements _{X 2} and the fixed resistance element RX _2.

Similarly, the wiring W constitutes a second bridge circuit (second Wheatstone bridge circuit) BC2 by connecting the strain sensitive elements Y ₁ and Y ₂ and the fixed resistance elements RY ₁ and RY ₂ . The terminal T ₈ is between the strain sensitive element Y ₁ and the fixed resistance element RY ₁ , the terminal T ₆ is between the strain sensitive elements Y ₁ and Y ₂ , and the terminal T is between the fixed resistance elements RY ₁ and RY _{2. 7,} the terminal _{T 5} is connected between the strain sensitive elements _{Y 2} and the fixed resistance element RY _2.

Is connected to the first bridge circuit BC1 between the one end of the strain sensitive elements Z ₁ and sensitive elements X ₁ strain and the fixed resistance element RX _1, the other end the strain sensitive elements Y ₁ and the fixed resistance element RY ₁ is connected to the second bridge circuit BC2. Similarly, the strain is connected to the first bridge circuit BC1 between the one end of the sensitive elements Z ₂ are the sensitive elements X ₂ strain and the fixed resistance element RX _2, the other end to the sensitive elements Y ₂ strain fixed It is connected to the second bridge circuit BC2 between the resistive element RY _2. As a result, the third bridge circuit (the third bridge circuit having the first bridge circuit BC1 and the second bridge circuit BC2 on the pair of opposite sides and the strain sensing elements Z ₁ and Z ₂ on the other pair of opposite sides, respectively. Wheatstone bridge circuit) BC3 is configured.

The strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ , fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ , and wiring W included in the circuit pattern CP are made of the same material. More preferably, it is formed by a nearby portion in one material. This material is, for example, copper, a copper alloy such as copper / nickel, or the like. The circuit pattern CP can be printed on the substrate 21 by photoetching, printing, vapor deposition, sputtering, or the like.

  As shown in FIG. 3, the strain gauge 20 is attached to the main body 10 so that the surface of the base material 21 opposite to the surface on which the circuit pattern CP is formed is in contact with the back surface 11 b of the strain generating plate 11. It has been.

Specifically, the sensitive region 21 s of the base material 21 has a strain generating plate such that the x direction and the y direction coincide with the x direction and the y direction of the main body 10 and the center c coincides with the axis A. 11 is attached to the back surface 11b. That is, the sensitive area 21 s is attached to the strain generating area where the strain is generated by receiving the load of the strain generating plate 11. Therefore, in a state where the sensitive area 21s of the base material 21 is attached to the strain generating plate 11, the strain sensitive elements X ₁ and X ₂ and the strain sensitive elements Y ₁ and Y ₂ are respectively in the x direction and y. It is arranged outside the load acting part 12 in the direction, in a region where the strain is relatively large.

The pair of insensitive areas 21 n 1 and 21 n 2 of the base material 21 are each bent and attached to the inner peripheral surface of the peripheral wall 13. That is, the insensitive areas 21n1 and 21n2 are disposed outside the strain generating area. Therefore, the terminals T ₁ , T ₂ , T ₃ , T ₄ formed in the insensitive area 21 n 1 and the terminals T ₅ , T ₆ , T ₇ , T ₈ formed in the insensitive area 21 n 2 are arranged on the radially inner side of the peripheral wall 13. It is facing and exposed.

  Next, usage and operation of the triaxial force sensor 100 and the strain gauge 20 of the present embodiment will be described.

When the triaxial force sensor 100 is used for the electronic pen 200, first, the load acting unit 12 is fitted to the pen tip (that is, the tip 32). Next, the terminals T _{1 to} T ₈ are connected to a signal processing circuit (not shown) using lead wires L _{1 to} L ₈ , respectively. The terminals T _{1 to} T ₈ and the lead wires L _{1 to} L ₈ can be joined by any method, for example, using solder or an anisotropic conductive film (ACF).

Terminals T ₁ and T ₅ are connected to a power source (not shown) by lead wires L ₁ and L ₅ , respectively. Terminals T ₂ , T ₃ , Terminals T ₆ , T ₇ , Terminals T ₄ , T ₈ are respectively connected to signals by lead wires L ₂ , L ₃ , lead wires L ₆ , L ₇ , lead wires L ₄ , L ₈ . It is connected to an arithmetic unit (not shown) in the signal processing circuit via an amplifier (not shown) in the processing circuit.

3 During operation of the force sensor 100, apply an input voltage Ei between the terminals T ₁ and the terminal T ₅ by the power source. The resistance value of each strain sensing element and the resistance value of each fixed resistance element constituting the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 have no deflection in the sensitive area 21s of the base material 21. In the state, the voltage is adjusted to be equal between the terminals T ₂ and T ₃ , the voltage is equal between the terminals T ₆ and T ₇ , and the voltage is equal between the terminals T ₄ and T ₈ .

Therefore, no distortion occurs in the strain-generating plate 11 as shown in FIG. 6 (a), in the absence of deflection sensitive region 21s, between the terminals _T 2, _{T 3,} between the terminals _T 6, _{T 7,} There is no potential difference between the terminals T ₄ and T ₈ , and the calculation unit does not calculate strain.

Next, as shown in FIG. 6B, when a load in the x direction is applied to the load acting portion 12, the load acting portion 12 receives the load and moves, causing the strain plate 11 to be distorted. At this time, the sensitive region 21s of the substrate 21 of the strain gauge 20 attached to Okoshiibitsuban 11 also strain-generating plate 11 and the flexure together, compressive strain in the strain sensitive elements X ₁ is, strain sensitive elements elongation strain is generated in the X _2.

As a result, the resistance values of the strain sensitive elements X ₁ and X ₂ change, and a potential difference is generated between the terminals T ₂ and T ₃ of the first bridge circuit BC1 including the strain sensitive elements X ₁ and X ₂ . Based on this potential difference, the calculation unit obtains the amount of strain generated in the strain plate 11 and obtains the magnitude of the load in the c direction acting on the load acting unit 12. At this time, the peripheral wall 13 is not distorted, and the resistance values of the fixed resistance elements RX ₁ and RX ₂ are constant.

  Even when a load in the y direction is applied to the load application unit 12, the magnitude of the load in the y direction that is applied in the same manner is obtained.

When a load in the z direction is applied to the load acting portion 12, the strain sensing plate X and the sensitive region 21 s of the base material 21 are curved so that the center protrudes, so that the strain sensitive elements X ₁ , X _2. , Y ₁ , Y ₂ , Z ₁ , and Z ₂ are all stretched and strain occurs. As a result, the combined resistance of the first bridge circuit BC1, the combined resistance of the second bridge circuit BC2, and the resistance values of the strain sensing elements Z ₁ and Z ₂ change, and the terminals T ₄ and T _{8 of} the third bridge circuit BC3 change. A potential difference occurs between them. Based on this potential difference, the calculation unit obtains the amount of strain generated in the strain plate 11 and obtains the magnitude of the load in the z direction acting on the load acting unit 12.

Here, the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 are printed on the substrate 21, and the strain sensitive elements X ₁ and X ₂ are printed. The significance of forming the same material as Y ₁ , Y ₂ , Z ₁ and Z ₂ will be described.

(1) By forming the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ in this way, the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are transformed into the strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z _2, and the same material and are formed at positions close to them. Here, the resistance temperature coefficient indicating the rate of change of the resistance value with respect to the temperature change is a physical property value that depends on the material. Therefore, in this embodiment, the resistance temperature coefficients of the all strain sensitive elements and all the fixed resistance elements are equal. Further, fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are formed on the base material 21, and in the vicinity of the strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ . Therefore, the change in the ambient temperature that affects all the strain-sensitive elements and all the fixed resistance elements is substantially the same. Therefore, when a change occurs in the ambient temperature, the resistance value of all strain sensing elements and the resistance value of all fixed resistance elements change at the same rate.

In the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3, when the balance of the resistance value changes between the resistance elements (strain sensitive element and fixed resistance element) included therein, the terminals Potential differences occur between T ₂ and T _3, between terminals T ₆ and T _{7, and} between terminals T ₄ and T ₈ , and strain is detected based on this. Therefore, when the balance between the resistance value of the strain sensing element and the resistance value of the fixed resistance element changes due to a change in the ambient temperature, a measurement error may occur due to the change in the balance. However, in this embodiment, when the ambient temperature changes, the resistance value of all strain sensing elements and the resistance value of all fixed resistance elements change at the same rate, so the ambient temperature has changed. Even in this case, the balance of resistance values between the elements does not change, and the occurrence of measurement errors is suppressed. Note that when the circuit pattern CP is formed, a strain sensitive element or the like is formed using a portion in the vicinity of a material (copper, copper alloy, or the like) prepared as an integral lump, so that the strain sensitive element X ₁ , X ₂ , Y ₁ , Y ₂ , Z ₁ , Z ₂ , fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ , wiring W can be made more uniform in temperature coefficient of resistance, resulting in better measurement errors Can be suppressed.

(2) As in the present embodiment, the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 are replaced with the insensitive areas 21n1 and 21n2 of the base 21. When the insensitive areas 21n1 and 21n2 are attached to a portion of the main body 10 where no distortion occurs (outside the strain generating area), the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are It can act as a dummy gauge for temperature compensation. Therefore, even when expansion or contraction occurs in the main body 10 including the strain generating plate 11 due to a change in the ambient temperature, the resistance values of the strain sensitive elements X ₁ , X ₂ , Y ₁ , Y ₂ due to the expansion or contraction. It is possible to suppress the occurrence of measurement errors by compensating for the change in.

(3) By forming the fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ on the base material 21 to form the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3, Each can be formed as a complete closed circuit on the substrate 21.

  In order to print the strain-sensitive element constituting the bridge circuit on the base material and to provide the fixed resistance element constituting the bridge circuit outside the base material, for example, in the signal processing circuit, in order to make the bridge circuit a closed circuit It is necessary to connect the strain-sensitive element on the substrate and the fixed resistance element of the signal processing unit with a lead wire or the like. In this case, the wiring on the base material and the lead wire are connected by joining the lead wire to the electrode provided on the base material, but this is a bridge when a joining resistance occurs at the joint between the electrode and the lead wire. Since it becomes a resistance in the circuit and causes a large strain detection error, the joining method is limited to solder joining that is so small that the joining resistance can be substantially ignored.

  However, in order to perform the soldering well, it is necessary to provide a relatively large electrode on the base material and to secure a pitch between the plurality of electrodes, so that the base material becomes large. In addition, in order to perform soldering satisfactorily, it is necessary to deposit solder with a certain thickness, which also hinders the downsizing of the triaxial force sensor.

On the other hand, in the present embodiment, the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 are each formed as a complete closed circuit on the substrate 21, and the terminals T _{1 to} T The connection between the base material 21 and the signal processing unit ₈ is merely a joint for connecting the first bridge circuit BC1, the second bridge circuit BC2, and the third bridge circuit BC3 to the power source and the calculation unit. Accordingly, in the present embodiment, generation of junction resistance at the junction between the terminal T ₁ through T ₈ and the lead wire L ₁ ~L ₈ is allowed, any bonding means other than solder bonding, for example, an anisotropic conductive film Bonding using can be employed. By using an anisotropic conductive film, the size of the electrodes, the pitch between the electrodes, and the thickness of the joint can all be reduced to about one-tenth of those in the case of solder joining. When it is desired to reduce the size of the sensor 100, bonding with an anisotropic conductive film is advantageous.

  The effects of the strain gauge 20 and the triaxial force sensor 100 of the present embodiment are as follows.

Since the strain gauge 20 forms the fixed resistance elements RX ₁ and RX _{2 of} the first bridge circuit BC1 and the fixed resistance elements RY ₁ and RY ₂ of the second bridge circuit BC2 on the base material 21, the above (2) The fixed resistance elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are formed of the same material as the strain sensitive elements X ₁ , X ₂ , Y ₁ , Y _2. Therefore, the effect (1) can be achieved.

In the strain gauge 20, in the sensitive region 21s, the strain sensitive elements _{X 1, X 2, Y 1} , Y 2, Z 1, only the _{Z 2} are formed, the terminal _T 1 through T ₈ and the fixed resistor The elements RX ₁ , RX ₂ , RY ₁ , RY ₂ are formed in the insensitive regions 21n1, 21n2. Therefore, the diameter (dimension) of the sensitive area 21 s can be reduced, and as a result, the strain plate 11 of the triaxial force sensor 100 can be reduced. The downsizing of the strain generating plate 11 leads to the downsizing of the triaxial force sensor 100, which is favorable.

In the strain gauge 20, since the terminal _T 1 through T ₈ is provided in the dead region 21N1,21n2, if necessary, without increasing the diameter of the sensitive area 21s, the size of the terminal _T 1 through T ₈ And the joining work with the lead wire or the like can be facilitated.

  Since the base material 21 of the strain gauge 20 includes the sensitive areas 21s and the insensitive areas 21n1 and 21n2 between the sensitive areas 21s and the insensitive areas 21n1 and 21n2, the coupling areas 21c1 and 21c2 are narrower than the sensitive areas 21n1 and 21n2. 21s and the insensitive regions 21n1 and 21n2 can be arranged in various modes without being restricted by the connection portions with the connecting regions 21c1 and 21c2.

  Since the three-axis force sensor 100 and the electronic pen 200 of the present embodiment include the strain gauge 20, the same effects as the effects of the strain gauge 20 can be achieved.

  As long as the characteristics of the present invention are maintained, the present invention is not limited to the above embodiments, and other forms conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention. .

10 Body 11 Strain plate (strain member)
DESCRIPTION OF SYMBOLS 12 Load action part 13 Perimeter wall 20 Strain gauge 21 Base material 21s Sensitive area | region 21c1, 21c2 Connection area | region 21n1, 21n2 Insensitive area | region 31, 32 Tip 33 Holder 34 Body 35 Front cap 100 Three-axis force sensor 200 Electronic pen BC1 1st bridge circuit (First Wheatstone bridge circuit)
BC2 Second bridge circuit (second Wheatstone bridge circuit)
BC3 Third bridge circuit (third Wheatstone bridge circuit)
RX ₁ , RX ₂ fixed resistance element (first direction fixed resistance element)
RY ₁ , RY ₂ fixed resistance element (second direction fixed resistance element)
T ₁ through T ₈ terminals _X 1, _{X 2} strain sensitive elements (first direction strain sensitive elements)
Y ₁ , Y ₂ strain sensitive element (second direction strain sensitive element)
Z ₁ , Z ₂ strain sensitive element (third direction strain sensitive element)

Claims (3)

Detection by a first Wheatstone bridge circuit of a load acting on the strain-generating member that is distorted by receiving a load and acting in the first direction of the strain-generating member, acting in a second direction orthogonal to the first direction of the strain-generating member A strain gauge used for detection by a second Wheatstone bridge circuit of a load to be applied and detection by a third Wheatstone bridge circuit of a load acting in a third direction orthogonal to the first and second directions of the strain-generating member,
A flexible substrate;
A circuit pattern formed on the substrate,
The base material is a sensitive area that is attached to a strain generating area where strain is generated by receiving a load of the strain generating member, a pair of insensitive areas disposed outside the strain generating area, the sensitive area, and the A connection region connecting the insensitive region,
The dimension in the orthogonal direction orthogonal to the direction in which the sensitive area and the insensitive area of the connected area are connected is smaller than the dimension in the orthogonal direction of the sensitive area and the insensitive area,
The circuit pattern includes two first direction strain sensitive elements constituting the first Wheatstone bridge circuit, two second direction strain sensitive elements constituting the second Wheatstone bridge circuit, and the third Wheatstone bridge. Two third direction strain sensitive elements constituting the circuit, two first direction fixed resistance elements constituting the first Wheatstone bridge circuit, and two second direction fixed resistances constituting the second Wheatstone bridge circuit An element,
The first direction strain sensitive element, the second direction strain sensitive element, the third direction strain sensitive element, the first direction fixed resistance element, and the second direction fixed resistance element are formed of the same material. And
The first direction strain sensitive element, the second direction strain sensitive element and the third direction strain sensitive element are formed in the sensitive region,
The first direction fixed resistance element and the second direction fixed resistance element are formed in the dead region,
The third direction strain sensing element is configured to connect the first Wheatstone bridge circuit and the second Wheatstone bridge circuit to form the third Wheatstone bridge circuit.
Strain gauge. A strain gauge according to claim 1;
The plate-like strain generating member;
A load acting portion connected to the strain generating member;
3-axis force sensor. A peripheral wall that stands upright in the third direction from the peripheral edge of the surface opposite to the surface to which the load acting portion of the strain generating member is connected;
The insensitive area is attached to the inner peripheral surface of the peripheral wall.
The triaxial force sensor according to claim 2.

Images