Force sensor

• US 6,530,283 B2
• Filed: 12/05/2000
• Issued: 03/11/2003
• Est. Priority Date: 12/13/1999
• Status: Active Grant

• Current Assignee: Wacoh Company
• Original Assignee: Nitta Corporation, Wacoh Company
• Inventors: Taniguchi, Nobumitsu, Okada, Kazuhiro, Morimoto, Hideo
• Primary Examiner(s): NOORI, MAX H
• Application Number:
  US09/730,429
• Publication Number:
  US 20010003326A1
• Time in Patent Office: 826 Days
• Field of Search: 737/80, 735/17.A, 738/620.43, 735/041.2, 735/143.4, 735/17.R, 735/141.8, 735/141.6, 324/661, 257/417, 361/785
• US Class Current: 73/780
• CPC Class Codes: G01L 5/165 using variations in capacitance
• CPC Class Codes: G01L 5/223 to joystick controls
• CPC Class Codes: H01H 13/70 having a plurality of operating members associated with different sets of contacts, e.g. keyboard mounting together a plurality of independent switches H02B
• CPC Class Codes: H01H 2205/024 Means to facilitate positioning
• CPC Class Codes: H01H 2215/012 Positioning of individual dome
• CPC Class Codes: H01H 2221/012 Joy stick type
• CPC Class Codes: H01H 2239/006 Containing a capacitive switch or usable as such
• CPC Class Codes: H01H 25/008 Operating part movable both angularly and rectilinearly, the rectilinear movement being perpendicular to the axis of angular movement
• CPC Class Codes: H01H 25/04 Operating part movable angularly in more than one plane, e.g. joystick
• CPC Class Codes: H03K 17/9625 using a force resistance transducer
• CPC Class Codes: H03K 17/975 using a capacitive movable element

Abstract

An intermediate displacement board (120) composed of a metal plate is arranged on a printed circuit board (110) having electrode patterns (E1-E7) and then a strain generative body (130) composed of silicon rubber is arranged on top thereof. Then, the arrangement is fixed to the printed circuit board (110) with attachments (140). Depressing a displacement portion (133) causes a connecting portion (132) to be deflected and an electrode (F0) to be brought into contact with the electrodes (E1, E2) to make them conductive, thereby allowing the pushbutton switch to be turned ON. Depressing further the displacement portion (133) causes an elastic deformation portion (134) to be elastically deformed and crushed and the intermediate displacement board (120) to be pushed downward. The capacitance of capacitors (C3-C7), which are constituted by the electrodes (E3-E7) and the intermediate displacement board (120), are varied according to the depression of the intermediate displacement board (120). By detecting the variation in capacitance, it becomes possible to detect three-dimensional components of an applied force.

Claims

1. A force sensor comprising:

a circuit board arranged at a position where an upper surface thereof is contained in an X-Y plane when an XYZ three-dimensional coordinate system is defined;

an acting body attached to the upper surface of said circuit board, said acting body having a displacement portion arranged above said circuit board and displaced when an external force is applied thereto, a securing portion fixed to said circuit board, and a connecting portion for connecting said displacement portion to said securing portion;

an elastic deformation body, formed on a lower, surface of said displacement portion and having elastic deformation properties;

a switch displacement electrode formed on a lower surface of said elastic deformation body;

a switch securing electrode formed on a position opposite to said switch displacement electrode on said circuit board; and

a capacitor adapted to produce a variation in capacitance caused by a displacement of said displacement portion;

wherein said connecting portion has flexibility so that when a force is applied to said displacement portion, a deflection is produced in said connecting portion, thereby causing a displacement in said displacement portion relative to said circuit board;

wherein when no force is applied to said displacement portion, said switch displacement electrode and said switch securing electrode are not kept in contact with each other, and when a force of a predetermined amount, including a component along a Z-axis of said coordinate system, is applied to said displacement portion, said switch displacement electrode and said switch securing electrode are brought into control with each other;

wherein when a further force, including a component along said taxis, is applied to said displacement portion, said elastic deformation body is elastically deformed, thereby allowing capacitance of amid capacitor to vary, with the contact state kept unchanged between said switch displacement electrode and said switch securing electrode; and

wherein said switch displacement electrode and said switch securing electrode form a switch which is closed when said displacement electrode is brought into contact with said securing electrode, whereafter when said elastically deformable body is elastically deformed, a change in capacitance of said capacitor is electrically detected to thereby recognize magnitude of a predetermined directional component of an applied force.

2. A force sensor according to claim 1:

wherein an acting body having a bowl-shaped portion is prepared and attached to the upper surface of the circuit board to be upside down, to use a portion corresponding to a bottom of the bowl as a displacement portion, to use a portion corresponding to a side of the bowl as a connecting portion, and to use a portion corresponding to a mouth of the bowl as a securing portion.

3. A force sensor according to claim 2:

wherein an intermediate displacement board is disposed between the circuit board and the acting body so that a part of the intermediate displacement board is secured to the circuit board as a displacement board securing portion and another part of the intermediate displacement board constitutes a displacement board displacement portion for generating a displacement caused by a displacement in the displacement portion or a deformation in the connecting portion; and

a capacitor securing electrode formed on the circuit board and a capacitor displacement electrode formed on said displacement board displacement portion constitute a capacitor.

4. A force sensor according to claim 3:

wherein a flexible plate having a bowl-shaped portion constitutes the intermediate displacement board, said intermediate displacement board being attached to the upper surface of the circuit board so as to arrange the bowl-shaped portion upside down, an open window being formed for allowing the elastic deformation body to penetrate therethrough on a portion corresponding to a bottom of the bowl, a portion surrounding the open window constituting the displacement board displacement portion, a portion corresponding to a mouth of the bowl constituting the displacement board securing portion, and the displacement portion or the connecting portion being brought into physical contact with the displacement board displacement portion to generate a displacement.

5. A force sensor according to claim 4:

wherein the intermediate displacement board is made of a metal material and the intermediate displacement board itself is used as a capacitor displacement electrode.

6. A force sensor according to claim 4:

wherein the intermediate displacement board is made of synthetic resin and a metal film formed on a lower surface thereof composes a capacitor displacement electrode.

7. A force sensor according to claim 6:

wherein a first additional switch electrode is formed on an upper surface of the intermediate displacement board and a second additional switch electrode is formed at a position opposite to said first additional switch electrode provided on a lower surface of the displacement portion so that both of said additional switch electrodes constituting an additional switch and a contact state between said first additional switch electrode and said second additional switch electrode is electrically detected, thereby enabling to provide additional information regarding an applied force.

8. A force sensor according to claim 7:

wherein when the Z-axis is defined at a center of the displacement portion, an additional switch is provided at a position located above a positive X-axis and another additional switch is provided at a position located above a negative X-axis, thereby enabling to provide information regarding an X-axis component of an applied force, based on a state of a pair of the additional switches.

9. A force sensor according to claim 8:

wherein an additional switch is further provided at a position located above a positive Y-axis and another additional switch is further provided at a position located above a negative Y-axis, thereby enabling to provide information regarding a Y-axis component of an applied force, based on a state of a pair of the further additional switches.

10. A force sensor according to claim 7:

wherein among a set of counter electrodes constituting the additional switch, one electrode is composed of a single electrode layer and the other electrode is composed of a pair of electrode layers, electrically independent of each other, and a conductive state between said pair of electrode layers is electrically detected, thereby enabling detection of a contact state of said counter electrodes.

11. A force sensor according to claim 1:

wherein a capacitor securing electrode formed on the upper surface of the circuit board and a capacitor displacement electrode formed on a lower surface of the displacement portion constitute a capacitor.

12. A force sensor according to claim 11:

wherein wiring is provided for making the capacitor displacement electrode and the switch displacement electrode conductive therebetween so that when the switch displacement electrode and the switch securing electrode are brought into contact with each other, capacitance between the switch securing electrode and the capacitor securing electrode is measured to detect a capacitance of the capacitor.

13. A force sensor according to claim 11:

wherein when the Z-axis is defined at a center of the displacement portion, a first capacitor is provided at a position located above a positive X-axis and a second capacitor is provided at a position located above a negative X-axis so as to determine direction and magnitude of an X-axis component of an applied force based on a difference in capacitance between a pair of said first and second capacitors.

14. A force sensor according to claim 13:

wherein a third capacitor is further provided at a position located above a positive Y-axis and a fourth capacitor is provided at a position located above a negative Y-axis so as to determine direction and magnitude of a Y-axis component of an applied force based on a difference in capacitance between a pair of said third and fourth capacitors.

15. A force sensor according to claim 11:

wherein a capacitor having an electrode formed to be generally symmetric with both the X- and Y-axes is provided so that a magnitude of a Z-axis component of an applied force can be determined based on capacitance of said capacitor.

16. A force sensor according to claim 11:

wherein two sets of capacitors including a signal input capacitor and a signal output capacitor are provided, respective capacitor securing electrodes of said two sets of capacitors are composed of separate electrodes electrically independent of each other and respective capacitor displacement electrodes of said two sets of capacitors are composed of a single common electrode electrically conductive with each other; and

periodic signal supply means for supplying a periodic signal to a capacitor securing electrode of said signal input capacitor and periodic signal detection means for detecting a periodic signal induced in a securing electrode of said signal output capacitor are provided so that a change in capacitance between said two sets of capacitors is obtained based on a magnitude of the periodic signal to be detected by means of said periodic signal detection means when the periodic signal of a predetermined magnitude is supplied by means of said periodic signal supply means.

17. A force sensor according to claim 11:

wherein an insulation film is formed on a surface of any one or both of a capacitor securing electrode and a capacitor displacement electrode.

18. A force sensor according to claim 1:

wherein the switch displacement electrode is composed of a single electrode layer and the switch securing electrode is composed of a pair of electrode layers electrically independent of each other, and a contact state of said pair of the electrode layers is electrically detected so as to detect a contact state between said switch displacement electrode and said switch securing electrode.

19. A force sensor according to claim 1:

wherein the elastic deformation portion is composed of a material having an elastic coefficient corresponding to detection sensitivity.

20. A force sensor according to claim 1:

wherein the elastic deformation portion is provided with a groove corresponding to detection sensitivity.

21. A force sensor according to claim 1:

wherein the acting body and the elastic deformation portion are composed of a strain generative body integrally formed of rubber.