FORCE SENSOR UNIT

Abstract

A force sensor unit having a simple structure to allow ready assembling and easy downsizing of the force sensor unit. The force sensor unit includes a cylindrical body, a substrate that blocks one end of the cylindrical body, a force sensor that is supported on the substrate, and a force transmission mechanism that is disposed in an internal space of the cylindrical body to transmit a force to the force sensor. The force transmission mechanism includes a contact member, a coil spring, and an operated member. These members are arranged in order in the internal space of the cylindrical body, and are not adhered to nor engaged with each other. The members except the substrate are simply fitted loosely in the internal space of the cylindrical body, thereby facilitating assembling of the force sensor unit and enabling downsizing of the force sensor unit.

Claims

1. A force sensor unit comprising: a cylindrical body; a blocking member that blocks one end of the cylindrical body; a force sensor supported on the blocking member; and a force transmission mechanism disposed in an internal space of the cylindrical body and operable to transmit a force to the force sensor, wherein: the cylindrical body is provided with a stopper at the other end of the cylindrical body, the stopper having an opening portion to communicate with the internal space of the cylindrical body and extending in a radially inward direction of the cylindrical body; the force transmission mechanism includes: a contact member that contacts a force receiving portion of the force sensor; an operated member including an operated portion exposed from the opening portion of the cylindrical body and an engaged portion to be engaged with the stopper; and an elastic member disposed between the contact member and the operated member; the contact member and the operated member each include a slide portion facing an inner wall surface of the cylindrical body, which surrounds the internal space of the cylindrical body, and capable of sliding in the internal space and shaped to allow the respective slide portions of the contact member and the operated member to slide along a centerline of the cylindrical body; a cross section of the internal space of the cylindrical body has a polygonal outline shape; the slide portion of the contact member is shaped to prevent the contact member from being rotated around the centerline of the cylindrical body by contacting the inner wall surface of the cylindrical body; the blocking member includes a substrate having a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor is mounted, and a back surface having a plurality of electrodes provided thereon and exposed externally from the cylindrical body; and an outline shape of the substrate is the same as or similar to the outline shape of the cross section of the outer peripheral surface of the cylindrical body.

2. A force sensor unit comprising: a cylindrical body; a blocking member that blocks one end of the cylindrical body; a force sensor supported on the blocking member; and a force transmission mechanism disposed in an internal space of the cylindrical body and operable to transmit a force to the force sensor, wherein: the cylindrical body is provided with a stopper at the other end of the cylindrical body, the stopper having an opening portion to communicate with the internal space of the cylindrical body and extending in a radially inward direction of the cylindrical body; the force transmission mechanism includes: a contact member that contacts a force receiving portion of the force sensor; an operated member including an operated portion exposed from the opening portion of the cylindrical body and an engaged portion to be engaged with the stopper; and an elastic member disposed between the contact member and the operated member; and the contact member and the operated member each include a slide portion facing an inner wall surface of the cylindrical body, which surrounds the internal space of the cylindrical body, and capable of sliding in the internal space and shaped to allow the respective slide portions of the contact member and the operated member to slide along a centerline of the cylindrical body.

3. The force sensor unit according to claim 2, wherein: a cross section of the internal space of the cylindrical body has a polygonal outline shape; and the slide portion of the contact member is shaped to prevent the contact member from being rotated around the centerline of the cylindrical body by contacting the inner wall surface of the cylindrical body.

4. The force sensor unit according to claim 2, wherein: a cross section of an outer peripheral surface of the cylindrical body has a polygonal outline shape; the blocking member includes a substrate having a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor is mounted, and a back surface having a plurality of electrodes provided thereon and exposed externally from the cylindrical body; and an outline shape of the substrate is the same as or similar to the outline shape of the cross section of the outer peripheral surface of the cylindrical body.

5. The force sensor unit according to claim 1, wherein the elastic member is formed of a coil spring.

6. The force sensor unit according to claim 1, wherein: the elastic member has an elastic constant that is defined to maximize a stroke of the operated member when a maximum allowable measurement force is applied to the force sensor.

7. The force sensor unit according to claim 1, wherein: the blocking member includes a substrate having a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor is mounted, and a back surface having a plurality of electrodes provided thereon and exposed externally from the cylindrical body; and the cylindrical body is metallic and includes two or more claw portions at the one end of the cylindrical body, the claw portions being bent in the radially inward direction to contact the back surface of the substrate.

8. The force sensor unit according to claim 7, wherein: an abutted portion is provided on the front surface of the substrate to abut onto an end face of the one end of the cylindrical body; and a plurality of recesses are formed in the back surface of the substrate to be engaged with the claw portions.

9. The force sensor unit according to claim 1, wherein the force receiving portion of the force sensor is a sphere.

10. The force sensor unit according to claim 3, wherein: a cross section of an outer peripheral surface of the cylindrical body has a polygonal outline shape; the blocking member includes a substrate having a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor is mounted, and a back surface having a plurality of electrodes provided thereon and exposed externally from the cylindrical body; and an outline shape of the substrate is the same as or similar to the outline shape of the cross section of the outer peripheral surface of the cylindrical body.

11. The force sensor unit according to claim 2, wherein the elastic member is formed of a coil spring.

12. The force sensor unit according to claim 2, wherein: the elastic member has an elastic constant that is defined to maximize a stroke of the operated member when a maximum allowable measurement force is applied to the force sensor.

13. The force sensor unit according to claim 3, wherein: the elastic member has an elastic constant that is defined to maximize a stroke of the operated member when a maximum allowable measurement force is applied to the force sensor.

14. The force sensor unit according to claim 4, wherein: the elastic member has an elastic constant that is defined to maximize a stroke of the operated member when a maximum allowable measurement force is applied to the force sensor.

15. The force sensor unit according to claim 5, wherein: the elastic member has an elastic constant that is defined to maximize a stroke of the operated member when a maximum allowable measurement force is applied to the force sensor.

16. The force sensor unit according to claim 2, wherein: the blocking member includes a substrate having a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor is mounted, and a back surface having a plurality of electrodes provided thereon and exposed externally from the cylindrical body; and the cylindrical body is metallic and includes two or more claw portions at the one end of the cylindrical body, the claw portions being bent in the radially inward direction to contact the back surface of the substrate.

17. The force sensor unit according to claim 16, wherein: an abutted portion is provided on the front surface of the substrate to abut onto an end face of the one end of the cylindrical body; and a plurality of recesses are formed in the back surface of the substrate to be engaged with the claw portions.

18. The force sensor unit according to claim 2, wherein the force receiving portion of the force sensor is a sphere.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0024] FIG. 1 is a perspective view illustrating an embodiment of a force sensor unit according to the present invention. In the figure, the cylindrical body is partially cut off.

[0025] FIGS. 2A and 2B are each a longitudinally cross sectional view of the embodiment of FIG. 1. FIG. 2A illustrates that the operated portion is situated in its initial position. FIG. 2B illustrates that the operated portion is pushed to its ultimate position.

[0026] FIG. 3 is a bottom plan view of the embodiment of FIG. 1.

[0027] FIG. 4 illustrates the force sensor unit of the embodiment of FIG. 1 in a disassembled state.

DESCRIPTION OF EMBODIMENT

[0028] Now, an embodiment of the present invention will be described below in detail with reference to the accompanying drawings. As illustrated in the figures, a force sensor unit of the present invention comprises a cylindrical body 10, a substrate 20 that blocks one end of the cylindrical body 10, a force sensor 30 supported on the substrate 20, and a force transmission mechanism disposed in an internal space of the cylindrical body 10 and operable to transmit a force to the force sensor 30. The transmission mechanism includes a contact member 40, a coil spring 50, and an operated member 60. The force sensor unit of the present embodiment is small-sized, having a total length of about 7 mm and a maximum outer diameter of about 4 mm. The force sensor 30 is cubic in shape with each side being about 2 mm. The maximum allowable width of mechanical displacement of a force sensor element is about 0.1 m or less.

[0029] The cylindrical body 10 is shaped in octagonal cylinder (column). Therefore, a cross section of the internal space of the cylindrical body 10 has an octagonal outline shape and a cross section of an outer peripheral surface of the cylindrical body 10 also has an octagonal shape. The cylindrical body 10 is metallic and is provided with two claw portions 12, 12 at one end thereof . The claw portions 12,12 are bent radially inward to contact a back surface of the substrate 20. At the other end of the cylindrical body 10, a circular opening portion 14 communicating with the internal space is provided in the vicinity of the center of the other end, and a ring-shaped stopper 16 extending radially inward of the cylindrical body 10 is provided in the vicinity of a periphery of the other end.

[0030] The substrate 20 has a front surface positioned on a side of the internal space of the cylindrical body, on which the force sensor 30 is mounted, and a back surface having four electrodes 22 provided thereon and exposed externally from the cylindrical body 10. The outline shape of the substrate 20 is octagonal, the same as the outline shape of the cross section of the outer peripheral surface of the cylindrical body 10. The octagonal outline shape of the substrate 20 makes it easy to fabricate multiple substrates 20, thereby facilitating manufacturing of the substrates 20. As a result, the price of the force sensor unit can be reduced. An abutted portion 24 is provided on the front surface of the substrate 20 to abut onto an end face of the one end of the cylindrical body 10. Two recesses 26, 26 are formed in the back surface of the substrate 20. The recesses 26, 26 are shaped complementarily with the two claw portions 12, 12 of the cylindrical body 10. The two claw portions 12, 12 are bent to be engaged in the recesses 26, 26.

[0031] The force sensor 30 is supported on the substrate 20. The force sensor 30 includes a pressure receiving portion 32, a case 34, and a force sensor element 36. The pressure receiving portion 32 is a sphere and is exposed from the top surface of the case 34. The case 34 is configured to restrict the movement of the pressure receiving portion 32. The force sensor element 36 is in contact with the pressure receiving portion 32 and is configured to be mechanically displaced when a force is applied from the pressure receiving portion 32. The mechanical displacement of the force sensor element 36 is converted into an electrical signal. The electrical signal is then output from electrodes 22 of the substrate 20.

[0032] The contact member 40 is in contact with the pressure receiving portion 32 of the force sensor 30 to transmit a force to the pressure receiving portion 32. The cross section of the contact member 40 is octagonal in shape as is substantially the same as that of the inner wall surface of the cylindrical body 10. The contact member 40 includes a slide portion 42 of which one end contacts the pressure receiving portion 32 of the force sensor 30 and a coil spring support portion 44 shaped in round column and projecting from the vicinity of the center of the other end of the slide portion 42. The side surface of the slide portion faces the inner wall surface of the cylindrical body 10 and is shaped to allow the slide portion 42 to slide along the center axis of the internal space of the cylindrical body 10.

[0033] The contact member 40 is prevented from being rotated by making the cross section of the contact member 40 and that of the inner wall surface of the cylindrical body 10 in an octagonal shape. Thus, it is possible to suppress variations in output from the force sensor 30 due to the rotation of the contact ember 40. In addition, the life of the force sensor 30 can be extended by preventing the pressure receiving portion 32 formed of a sphere from being rotated. Further, especially when the force sensor unit is small-sized, it is easier to manufacture the inner wall surface of the cylindrical body 10 and the slide portion that are shaped in an octagonal cylinder (column) including flat surfaces with high accuracy than in a round cylinder (column) of which the entire surface is curved. Thus, the contact member 40 can smoothly slide inside the cylindrical body 10, thereby preventing twisting and twirling of the contact member 40 from being caused.

[0034] The coil spring 50 is a compression spring and is disposed between the contact member 40 and the operated member 60 to work as a cushion, thereby suppressing variations in operating characteristics. Since the inside diameter of the coil spring 50 is substantially the same as that of the outside diameter of the coil spring support portion 44 of the contact member 40, the coil spring 50 is supported by the coil spring support portion 44 which has got into the coil spring 50. An elastic constant of the coil spring 50 is defined to maximize a stroke of the operated member 60 when a maximum allowable measurement force is applied to the force sensor 30.

[0035] The operated member 60 includes a slide portion 62, a round columnar operated portion 64, and an engaged portion 66. The cross section of the slide portion 62 is octagonal in shape as is substantially the same as the cross section of the inner wall surface of the cylindrical body 10 such that one end of the operated portion 60 is in contact with the coil spring 50 to slide along the centerline of the cylindrical body 10. The operated portion 64 projects from the vicinity of the center of the other end of the slide portion 62 and a leading portion of the operated portion 64 is exposed from an opening portion 14 of the cylindrical body 10 when the force sensor unit is assembled. The engaged portion 66 is formed of an end face of the other end of a portion of the slide portion 62 except a portion from which the operated portion 64 projects, and abuts against an inner surface of the stopper 16 of the cylindrical body 10 to be engaged with the stopper.

[0036] In the present embodiment, the contact member 40 and the operated member 60 are formed in substantially the same shape. In other embodiments, the shapes of the contact member and the operated member may be different.

[0037] Next, referring to FIG. 4, the assembling process of the force sensor unit of the present embodiment will be described below. When assembling the force sensor unit of the present embodiment, each member is inserted in order from an opening at one end of the cylindrical body 10. First, the operated member 60 is inserted such that the engaged portion 66 abuts on the stopper 16 of the cylindrical body 10 located at the other end to be engaged with the stopper 16; that a leading portion of the operated portion 64 is exposed from the opening portion 14 of the cylindrical body 10 located at the other end; and that the slide portion 62 of the operated member 60 faces the inner wall surface of the cylindrical body 10. Next, the coil spring 50 is inserted. Then, the contact member 40 is inserted such that the coil spring support portion 44 faces the coil spring 50; and that the slide portion 42 of the contact member 40 faces the inner wall surface of the cylindrical body 10. Finally, an opening at the one end of the cylindrical body 10 is blocked by the substrate 20 in such a manner that the force sensor 30 is disposed in the internal space of the cylindrical body 10. The abutted portion 24 of the substrate 20 abuts on an end face of the one end of the cylindrical body 10. At this moment, angle adjustment is performed such that an angle between two claw portions 12, 12 projecting from one end of the cylindrical body 10 with respect to the centerline should be consistent with an angle between two recesses 26, 26 of the substrate 20. The claw portions 12, 12 are radially bent by 90 degrees to respectively fit in the two recesses 26, 26. Thus, the opening at the one end of the cylindrical body 10 is blocked. The fitting of the claw portions 12, 12 and the recesses 26, 26 does not hinder implementation of the force sensor unit and can minimize the size of the force sensor unit as measured along the centerline.

[0038] The members arranged in order inside the internal space of the cylindrical body 10 are not adhered to nor engaged with each other. The members except the substrate 20 are simply fitted loosely in the internal space of the cylindrical body 10, thereby facilitating assembling of the force sensor unit.

[0039] In the present embodiment, the force sensor unit can readily be assembled through such a simple process that the members are inserted in order into the internal space of the cylindrical body 10 and finally one end of the cylindrical body 10 is blocked by the substrate 20.

[0040] The assembled force sensor unit according to the present embodiment is received in a stylus pen. The electrodes 22 located at one end are connected with electric wires (not illustrated) for external output. The operated portion 64 of the operated member 60 located at the other end is in contact with an end face of one end of an operating member 70. The other end of the operating member 70 is a leading point of the stylus pen (alternatively, the other end of the operating member 70 is connected to a leading point of the stylus pen). A force generated by an operator of the stylus pen when pressing the stylus pen onto a panel is transmitted to the force sensor unit. The operating member 70 is capable of sliding along the centerline of the force sensor unit so as to approach or get away from the force sensor. Specifically, the operating member 70 is inserted into a hollow pen holder in which the force sensor unit is fixedly situated.

[0041] Next, referring to FIGS. 2A and 2B, the actions of the force sensor unit of the present embodiment will be described below. FIG. 2A illustrates that the operated member 60 is situated in its initial position with no force being applied to the force sensor unit. Namely, a leading part of the operated portion 64 of the operated member 60 is exposed from an opening portion 14 of the cylindrical body 10 and the engaged portion 66 is engaged with the stopper 16 of the cylindrical body 10.

[0042] FIG. 2B illustrates that the maximum allowable measurement force is being applied to the force sensor unit as an operator strongly presses the leading point of a stylus pen onto a touch panel. At this moment, the operated member 60 is pushed by the operating member 70 to slide from the initial position to the ultimate position toward the force sensor 30 along the centerline of the cylindrical body 10 inside the internal space of the cylindrical body 10.

[0043] The operated portion 60 compresses the coil spring 50, which in turn pushes the contact member 40. The contact member 40 slides toward the force sensor 30 along the centerline of the internal space of the cylindrical body 10. The force is thus transmitted to the pressure receiving portion 32 of the force sensor 30.

[0044] Due to the buffer function of the coil spring 50, however, the width over which the contact member 40 slides is significantly shorter than the width over which the operated member 60 slides. The pressure receiving portion 32 contacting the contact member 40 is pushed by the contact member 40 to move, which causes mechanical displacement of the force sensor element 36. As a result, an electrical signal is output from the electrodes 22 according to the magnitude of the force applied to the operated portion 64 of the operated member 60.

[0045] In the above-mentioned state, the length and the elastic constant of the coil spring 50 have been adjusted such that the magnitude of the force by which the coil spring 50 presses the contact member 40 is substantially equal to the maximum allowable measurement force. Namely, the operated member 60 is capable of sliding within a stroke from the initial position illustrated in FIG. 2A to the position illustrated in FIG. 2B where the maximum allowable measurement force is applied. The stroke is designed so as to allow the force sensor 30 to produce a stable output with safety within the stroke.

[0046] Once the leading point of the stylus pen leaves the touch panel and the force applied to the operated portion 64 of the operated member 60 disappears, the force sensor element 36 is returned from the mechanical displacement, and the pressure receiving portion 32 is pushed by the force sensor element 36 to move. Then, the contact member 40 contacting the pressure receiving portion 36 slides away from the force sensor 30 and the coil spring 50 is stretched. The operated member 60 slides away from the force sensor 30 and the engaged portion 66 is engaged with the stopper 16 to return to its initial position illustrated in FIG. 2A.

[0047] In the force sensor unit of the present invention, the force transmission mechanism is constituted from the operated member 60, the coil spring 50 as the elastic member, and the contact member 40. The stroke within which the operated member 60 slides can be increased by interposing the coil spring 50 having a buffer function between the operated member 60 and the contact member 40.

[0048] High accuracy is required for the stability in output from the force sensor 30 and the safety to avoid an excessive force to be applied to the force sensor 30. As can be known from the foregoing, the required high accuracy is focused only on the coil spring 50. Especially for the small-sized force sensors, the range within which the mechanical displacement of the force sensor element 36 is caused stably and without damage risk is very narrow. The width over which the mechanical displacement of the force sensor element 36 is caused is limited by disposing the coil spring 50 in the middle to convert a large stroke externally applied into a narrow width. For this reason, the length and the elastic constant of the coil spring 50 is adjusted as accurately as possible.

[0049] In addition to the foregoing, as illustrated in FIG. 2B, an end face of one end of the operating member 70 abuts on an outer surface of the stopper 16 to stop there. This prevents the force sensor 30 from being damaged in case, for example, an accident such that a stylus pen falls down occurs to apply a strong impact to the force sensor 30 from the operating member 70.

INDUSTRIAL APPLICABILITY

[0050] According to the present invention, a force sensor unit has a simple structure to allow ready assembling and easy downsizing of the force sensor unit.

DESCRIPTION OF REFERENCE NUMERALS

[0051] 10 cylindrical body [0052] 12 claw portion [0053] 14 opening portion [0054] 16 stopper [0055] 20 substrate [0056] 22 electrode [0057] 24 abutted portion [0058] 26 recess [0059] 30 force sensor [0060] 32 pressure receiving portion [0061] 34 case [0062] 36 force sensor element [0063] 40 contact member [0064] 42 slide portion [0065] 44 coil spring support portion [0066] 50 coil spring [0067] 60 operated member [0068] 62 slide portion [0069] 64 operated portion [0070] 66 engaged portion [0071] 70 operating member