JP4074840B2 - Force sensor - Google Patents

Description

  The present invention relates to a force sensor that can detect the direction and magnitude of a force.

As input parts for measuring instruments, control panels, portable information devices, and the like, there are sensors called force sensors or force sensors in addition to switches. Unlike a switch, this type of sensor can detect an intermediate force other than ON and OFF, so that finer control input is possible. In addition, since a force component in two or more directions can be detected by one sensor, there are advantages such as downsizing of the apparatus and reduction of restrictions on detection locations.
For large equipment, for example, a strain gauge is attached to a metal structure that supports the operating shaft, and the bending of the operating shaft is detected as a force, or the movement of the operating shaft supported by a spring is a potentiometer (variable resistor). Some of them are detected by an angle / position sensor. However, due to the downsizing and widespread use of devices, input components are required to be smaller and less expensive, and force sensors that utilize pressure-sensitive rubber and capacitance changes are often used.

FIG. 14A shows an example of a conventional configuration of a force sensor using such a change in capacitance. In the figure, 11 is a substrate, 12 is a fixed electrode, 13 is a movable electrode plate, 14 is a frame, Reference numeral 15 denotes an operation axis.
In this example, the fixed electrodes 12 are provided on the substrate 11 in total at a center of the circumference and at an interval of 90 ° on the circumference, and are provided on the substrate 11. The movable electrode plate 13 has a predetermined gap with the fixed electrodes 12. The peripheral edge is supported by the frame body 14 so as to face each other. The movable electrode plate 13 is flexible, and the operation shaft 15 is attached to the center of the upper surface of the movable electrode plate 13.

FIG. 14B shows an example of a state in which the operation shaft 15 of the force sensor having the above-described configuration is operated. When a force acts on the operation shaft 15 in the direction indicated by an arrow, for example, the operation shaft 15 is The inclination and the movable electrode plate 13 are bent and displaced as shown in the figure, whereby the distance from the fixed electrode 12 is changed and the capacitance is changed.
The capacitances at the five locations constituted by the five fixed electrodes 12 and the movable electrode plate 13 change according to the direction and magnitude of the force, and thus the direction and magnitude of the force are detected from the change in the capacitance. (See, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2001-27570

  By the way, in the force sensor configured as shown in FIG. 14, the axial direction of the operation shaft 15 is orthogonal to the plate surface of the substrate 11, that is, orthogonal to the axial direction of the operation shaft 15. Since the required number of the fixed electrodes 12 are arranged on the surface to be moved and the movable electrode plate 13 having a size facing the fixed electrodes 12 is supported by the frame body 14, for example, the operation shaft 15 is arranged on the side surface of the device. If the configuration in which the operation shaft 15 protrudes from the side surface is adopted, the substrate 11 is parallel to the side surface of the device, and therefore the size of the surface occupied by at least the fixed electrode 12 and the movable electrode plate 13 constituting the capacitance. As a result, the thickness (height) of the device is required, and accordingly, downsizing of the device is hindered.

Further, the wiring / component mounting board built in the device is generally arranged in parallel to the installation surface (horizontal plane) of the device, that is, is often arranged perpendicular to the side surface. Since such a device cannot be used as a substrate, a dedicated substrate parallel to the side surface of the device must be prepared for the substrate 11, which increases the cost.
In view of such a problem, the object of the present invention is not to require the thickness of the conventional device even when the operation shaft is arranged on the side surface of the device, so that the size of the device can be reduced, and An object of the present invention is to provide a force sensor that does not require a dedicated substrate parallel to the side surface.

According to the first aspect of the present invention, the operation shaft is configured by bundling a plurality of columnar bodies so as to be displaced from each other, and the capacitance is formed on the opposed surfaces of the columnar bodies so as to face each other. Electrodes configured to change their capacitances by shifting each other in the longitudinal direction are formed, the operation shaft is fixed at one end, the other end is a free end, and a force acts on the free end. In the force sensor that detects the direction and the magnitude of the force by the change in capacitance, the columnar bodies are displaced from each other, and the columnar bodies are displaced from each other. sandwiching the septum, on both sides of the partition wall, Keru set the electrodes to allow differential detection of a change in the electrostatic capacitance.

According to a second aspect of the present invention, in the first aspect of the present invention, the electrode is a comb-shaped electrode in which comb teeth are arranged in the longitudinal direction.
According to the invention of claim 3, in the invention of claim 1 , the columnar body has a quadrangular columnar shape, and the four columnar bodies are bundled so as to sandwich two orthogonal planes to constitute the operation shaft.

According to the present invention, the capacitance that changes in accordance with the direction and magnitude of the force acting on the operation shaft is configured inside the operation shaft, and the force is deflected by the operation shaft receiving the force. Can be detected by differential detection of capacitance change .
Therefore, unlike the conventional force sensor using the change in capacitance, it is not necessary to arrange the required number of electrodes for detecting capacitance on the surface orthogonal to the axial direction of the operation axis. The size in the direction perpendicular to the axial direction of the first and second axes can be greatly reduced, and an extremely small force sensor can be obtained.

  Therefore, for example, even when the operation shaft is arranged on the side surface of the device, the thickness of the device is not required, the device can be reduced in size, and the side surface of the device such as a conventional force sensor can be reduced. Since a parallel dedicated substrate is not required, the attachment can be performed easily and can be configured at low cost.

The best mode for carrying out the present invention will be described by way of example with reference to the drawings.
Figure 1 is prior to the present invention, which shows one study example of the force sensor discussed, the operating shaft 21 in this example is assumed to four pillars 22 is constituted by bundling a degree deviated from each other The FIG. 2A shows an outline of the appearance of the operation shaft 21, and FIG. 2B shows details of the four columnar bodies 22 constituting the operation shaft 21 separately. First, the configuration of the operation shaft 21 will be described with reference to FIG.
In this example, the four columnar bodies 22 have a quadrangular prism shape, and are bundled so as to sandwich two orthogonal surfaces to constitute the operation shaft 21. These columnar bodies 22 are made of resin, for example, and are made of an insulator.

As shown in FIG. 2B, comb-shaped electrodes 23 each having comb teeth 23 a arranged in the longitudinal direction are formed on two adjacent surfaces extending in the longitudinal direction of each columnar body 22. The part 23 b extends to the proximal end side of the columnar body 22. The comb electrode 23 is formed by, for example, printing of a conductive paste or vapor deposition of a metal film. Although not shown in the drawing, the surface of each comb-tooth electrode 23 is subjected to insulation treatment by resin coating or the like.
The comb-like electrodes 23 of the respective columnar bodies 22 are arranged on the mutually facing surfaces of the columnar bodies 22 by bundling the four columnar bodies 22, that is, located inside the operation shaft 21 and facing each other. The capacitance is constituted by 23. The electrostatic capacity is constituted by four sets of comb-tooth electrodes 23 at intervals of 90 °.

In this example, the comb-tooth electrodes 23 constituting the capacitance facing each other are arranged such that the positions of the comb-tooth 23a are shifted by half the width of the comb-tooth 23a in the longitudinal direction of the columnar body 22, and the connecting portion 23b. Are formed on the opposite sides of the overlapping portion of the comb teeth 23a.
The operation shaft 21 formed by bundling the columnar bodies 22 having the comb electrodes 23 as described above has one end (base end) as a fixed end and is housed in a case 24 as shown in FIG. 1A and fixedly supported. The other end is a free end.

The case 24 is made of, for example, resin, and in this example, the case 24 is provided with a capacitance-voltage conversion circuit. The connecting portion 23b of each comb electrode 23 is connected to this circuit, and the capacitance changes. Can be detected as a voltage change. In FIG. 1A, reference numeral 25 denotes a terminal, and in this example, it is partially hidden and cannot be seen, but has five terminals 25.
An operation portion 26 is attached to the free end of the operation shaft 21, and a sheath 27 is attached to the middle portion in the longitudinal direction of the operation shaft 21 in this example.
In this example, the operation portion 26 has a cylindrical shape, and the free end of the operation shaft 21 is inserted into a square hole 28 provided on one end face thereof and bonded and fixed as shown in FIG. 1B. In FIG. 1B, reference numeral 29 denotes an adhesive. As shown in the figure, the operation shaft 21 is bonded to the operation portion 26 at the periphery of the end portion, and there is a predetermined gap between the tip surface and the bottom surface of the square hole 28. Gaps (spaces) are provided.

For the adhesive 29, for example, a soft adhesive that does not harden such as a silicone-based adhesive is used, and the sheath 27 is also bonded by the same adhesive and is positioned at an intermediate position of the operation shaft 21. The four columnar bodies 22 are stably maintained in a bundled state by the sheath 27. The operation unit 26 and the sheath 27 are made of resin, for example.
Next, the operation of the force sensor having the above configuration will be described.
This force sensor detects a force in two orthogonal axes as shown by arrows in FIG. 3A. When a force is applied to the operation unit 26, the operation shaft 21 receives the force and is in the state shown in FIG. 3B. For example, as shown in FIG. 3C.

Each columnar body 22 is deflected and displaced from each other to the extent that it is displaced, that is, is allowed to be displaced, and in the state shown in FIG. 3C, the upper two columnar bodies 22 and the lower two columnar bodies 22 is displaced. Accordingly, the positions of the comb electrodes 23 formed on the opposing surfaces of the upper two columnar bodies 22 and the lower two columnar bodies 22 are relatively displaced in the longitudinal direction.
FIG. 4 shows an example of an initial state and a shifted state of a pair of comb-tooth electrodes 23 that constitute a capacitance opposite to each other. In FIG. 4, for example, the comb-tooth electrode 23-L is shown in FIG. When the comb electrode is formed on the upper surface of the lower columnar body 22 and the comb electrode 23-U is a comb electrode formed on the lower surface of the upper columnar body 22, the comb electrode 23- In the initial state (the state shown in FIG. 3B), L and 23-U are bent by the operation shaft 21 as shown in FIG. 3C from the state in which the comb teeth 23a overlap each other as shown in FIG. 4A. As shown in FIG. 4B, the position is relatively shifted, and the overlap of the comb teeth 23a is reduced. Therefore, in this case, the capacitance is reduced.

On the other hand, for example, when a force acts in the direction opposite to the arrow in FIG. 3C, the operation shaft 21 bends in the opposite direction, and in this case, the comb electrodes 23-L and 23-U are relatively displaced in the opposite direction to FIG. 4B. Thus, the overlapping state as shown in FIG. 4C occurs, and in this case, the capacitance increases.
Therefore, the direction and magnitude of the force acting on the operation unit 26 can be detected by detecting such a change in capacitance as a voltage change.
FIG. 5 shows the relationship between the direction in which the operating shaft 21 bends (the direction of bending) due to the force acting on the operating portion 26 and the change in the four capacitances formed by the four sets of comb-tooth electrodes 23. In FIG. 5A, C <b> 1 to C <b> 4 indicate capacitances configured by the comb electrodes 23 on the mutually opposing surfaces of the columnar body 22.

  FIG. 5B shows a normalized change in each of the capacitances C1 to C4 when the operation shaft 21 is bent by receiving an equivalent force in eight directions at 45 ° intervals as indicated by arrows in FIG. 5A. For example, when θ = 0 °, C1 and C3 do not change and are shown as 0.00. On the other hand, C2 and C4 change, and the change amount in this case is set to 1.00 as the maximum change amount. In addition, although the sign is reversed in C2 and C4, this changes, for example, the arrangement of the comb electrodes 23 opposed to each other in C2 and C4. This can be realized by adopting a configuration that shifts in the overlapping direction and shifts in the direction in which the comb teeth 23a are separated in C4. Note that the sign can be reversed on the circuit side.

As shown in FIG. 5B, each of the capacitances C1 to C4 changes according to the direction in which the operation shaft 21 bends, that is, according to the direction of the force acting on the operation unit 26. As shown, the direction and magnitude of the force can be detected even if the forces are in eight directions at 45 ° intervals.
As described above, in this example, the operation shaft 21 is composed of four columnar bodies 22 that are bundled so as to be displaced from each other. When the operation shaft 21 is deflected by receiving an external force, the columnar bodies 22 are displaced from each other. Accordingly, a total of four capacitances constituted by the comb-tooth electrodes 23 change on the opposing surfaces of the columnar body 22, and the direction and magnitude of the force applied by the change in the capacitance can be detected. It is possible.

Therefore, the operation shaft 21 has both input and detection functions, and the entire force sensor has the structure shown in FIG. 1A. That is, the operation shaft 21 is the same as the conventional force sensor shown in FIG. It is not necessary to arrange the required number of electrodes for capacitance detection on the plane orthogonal to the direction, and the area required (occupied) in the direction orthogonal to the axial direction of the operation axis can be greatly reduced. .
Therefore, for example, even when the operation shaft is arranged on the side surface of the device and the operation shaft protrudes from the side surface of the device, the thickness (height) of the device as required in the conventional force sensor is obtained. ) Is not necessary, and the height of the case (member) that supports the operation shaft is sufficient, which can greatly contribute to downsizing of the device.

In addition, the case that supports the operating shaft can be easily mounted on, for example, the board of the device itself, and does not require a dedicated board different from the board of the device as in the prior art, so that the installation becomes easier. Cost can be reduced.
In the configuration shown in FIG. 1A, the resin sheath 27 is attached to the middle portion of the operation shaft 21 in the longitudinal direction by a flexible adhesive. Instead of attachment, a sheath 27 'may be formed around the operating shaft 21 as shown in FIG. The sheath 27 ′ is formed using, for example, silicone rubber, and the axial length thereof may be increased as shown in FIG. 6 or may be provided over the entire length of the operation shaft 21. Can be selected.

On the other hand, FIG. 7 shows a configuration in which the rubber tube 31 is fitted around the operation shaft 21 in place of the attachment by bonding the sheath 27, and such a configuration can also be adopted. Note that the sheaths 27 and 27 ′ and the rubber tube 31 are not necessarily provided around the operation shaft 21 and may be omitted.
In the above-described example, the pitch and width of the comb teeth 23a are constant over the entire length of the comb-teeth electrode 23. By forming a capacitance with such a set of comb-teeth electrodes 23, the longitudinal direction of the columnar body 22 is achieved. However, the detection sensitivity is improved by increasing the number of the comb teeth 23a by narrowing the width of the comb teeth 23a, for example.

However, for example, if the deviation exceeds the width of the comb teeth 23a, the deviation amount and the capacitance change do not correspond to each other, and the detection accuracy is deteriorated.
FIG. 8B shows an example in which the shape of the comb electrode 23 is improved from these points. As shown in FIG. 8A, the deviation generated between the columnar bodies 22 when the operation shaft 21 is bent is shown. Since it is 0 at the fixed end of the operation shaft 21 and increases toward the free end, the width of the comb teeth 23a is narrowed on the fixed end side of the operation shaft 21 and fixed on the free end side in accordance with such a shift. Compared to the end side, the width of the comb teeth 23a is increased. By adopting such a shape, it is possible to obtain a comb-tooth electrode 23 'having excellent detection sensitivity and accuracy.

The electrodes formed on the opposing surfaces of the columnar bodies 22 are not limited to the comb-teeth electrodes as described above, and may be electrodes having a shape as shown in FIG. 9A, for example.
In this example, the two electrodes that are formed on the mutually opposing surfaces of the columnar body 22 and constitute the electrostatic capacitance are triangular electrodes 32 and 33. In the figure, 32a and 33a are the base ends of the columnar body 22 ( The extension part extended to the fixed end) side of the operation shaft 21 is shown.
The triangular electrodes 32 and 33 are opposed to each other in the state shown in FIG. 9B with the columnar bodies 22 being bundled. Accordingly, the overlapping areas change due to deviation from each other in the direction indicated by the arrow (longitudinal direction of the columnar body 22), whereby the capacitance changes, and the deviation can be detected. Instead of a complete triangle as in this example, for example, the hypotenuse of the triangle may be configured by a curve.

Next, an example will be described in which the operation shaft is not configured by bundling four columnar bodies as in the example described above, but by bundling three columnar bodies.
FIGS. 10A and 10B each show an outline of the appearance of an operation shaft configured by bundling three columnar bodies. In FIG. 10A, the columnar body 34 has a sectional fan shape, and the three columnar bodies 34 are bundled. Thus, a cylindrical operation shaft 35 is configured.
On the other hand, in FIG. 10B, the columnar body 36 has a triangular prism shape, and three columnar bodies 36 are bundled to form an operation shaft 37 having a regular triangular prism shape.

In any of the operation shafts 35 and 37, the comb-like electrodes 23 that constitute the capacitance are opposed to each other on the opposing surfaces of the columnar bodies 34 and 36, for example, like the operation shaft 21 shown in FIG. 2. The operation shafts 35 and 37 are formed to bend by receiving an external force and have three capacitances that change when the columnar bodies 34 and 36 are displaced from each other in the longitudinal direction.
FIG. 11 shows the relationship between the direction in which the operation axis bends and the change in the three capacitances in the force sensor having the operation axis composed of three columnar bodies as in FIG. In FIG. 11A, C <b> 1 to C <b> 3 indicate the capacitances configured on the opposing surfaces of the columnar body 34.

FIG. 11B shows the changes in the capacitances C1 to C3 when the operation shaft 35 is bent by receiving the same force in eight directions at 45 ° intervals as indicated by arrows in FIG. 11A, as in FIG. 5B. It is shown normalized.
Even when the operation shaft 35 is composed of the three columnar bodies 34 as described above, the capacitances C1 to C3 change in accordance with the direction in which the operation shaft 35 bends. Therefore, from the change in the capacitances C1 to C3. Similar to the force sensor shown in FIG. 1A, the direction and magnitude of the force acting on the operation unit 36 attached to the operation shaft 35 can be detected, and the direction of the force is not limited to four directions but eight directions. Can be detected.

Next, on the opposing surfaces of the columnar bodies, the change in capacitance formed by the electrodes (comb electrodes) facing each other is caused by the operation shaft receiving external force and the columnar bodies being displaced from each other. A configuration of an embodiment of the present invention capable of differential detection will be described.
12A differentially detects the four capacitances formed between the columnar bodies 22 with respect to the operation shaft 21 in which the four columnar bodies 22 having the quadrangular columnar shape shown in FIG. 2 are bundled. In this example, the operation shaft 41 is configured by bundling four columnar bodies 22 across a columnar body 42 having a cross-shaped cross section, that is, the opposing surfaces of the columnar bodies 22. A partition wall 43 constituted by the columnar bodies 42 is sandwiched between the two.

A columnar body 42 having a cross-shaped cross section made up of four partition walls 43 is configured as shown in FIG. 12B, and both surfaces of each partition wall 43 are electrostatically opposed to the comb-shaped electrodes 23 formed on the columnar body 22. Comb electrodes 44 constituting a capacitor are formed respectively.
These comb-teeth electrodes 44 form reference electrodes (ground electrodes). By adopting such a configuration, it is possible to differentially detect changes in capacitance. The columnar body 42 is made of, for example, a resin and is an insulator, and the surface of the comb-teeth electrode 44 is insulated by resin coating or the like. The four columnar bodies 22 and the columnar bodies 42 are They are bundled to the extent that they deviate from each other. The operation shaft 41 configured by the columnar bodies 22 and 42 is bent by receiving an external force, like the operation shaft 21.

Next, a description will be given of a force sensor configured not to detect forces acting in multiple axes such as four directions or eight directions as in the above-described force sensor, but to detect forces acting in one axis and two directions.
FIG. 13A shows an example of studying a force sensor configured to detect the direction and magnitude of the force in one axis and two directions. In this example, the operation shaft 51 is as shown in FIG. 13B. Two columnar bodies 52 having a quadrangular prism shape are bundled together, and electrostatic capacitances are formed on opposite surfaces of each other so as to be opposed to each other. An electrode (comb electrode) configured to change the capacitance is formed. Also in this example, as in FIG. 12, the capacitance change can be differentially detected by sandwiching the partition wall having electrodes formed on both surfaces between the two columnar bodies 52. It can also be used force sensor of good Una configuration of this depending on the application.

A is a perspective view showing an example of studying a force sensor, and B is a diagram for explaining a mounting structure of the operation unit. FIG. 2A is a perspective view showing an outline of an outer appearance of an operation shaft in FIG. 1, and FIG. 2B is a perspective view showing details of four columnar bodies constituting the operation shaft. The figure for demonstrating the state when the force and force which act on the operation part of the force sensor shown in FIG. 1 act. The figure which shows the state which the positional relationship of the initial state of the comb-tooth electrode which opposes mutually, and comprises an electrostatic capacitance, and the position shifted | deviated in the force sensor shown in FIG. The figure and table | surface for demonstrating the relationship between the direction in which an operating shaft bends, and the change of four electrostatic capacitances in the force sensor shown in FIG. The perspective view which shows the example which changed the structure of the sheath with respect to the force sensor shown in FIG. The perspective view which shows the example which replaced the sheath with the rubber tube with respect to the force sensor shown in FIG. The figure for demonstrating the example of a shape improvement of a comb-tooth electrode. The figure for demonstrating the other shape of the electrode which comprises an electrostatic capacitance. The perspective view which shows the example which comprised the operation axis | shaft with three columnar bodies, A is what made the columnar body the cross-sectional fan shape, B was what made the columnar body the cross-sectional triangle. FIG. 10B is a diagram and a table for explaining the relationship between the direction in which the operation axis bends and three capacitance changes in the force sensor having the operation axis shown in FIG. 10A. The figure for demonstrating the structure of the Example of this invention which enables the differential detection of an electrostatic capacitance. A is a perspective view showing an example of studying a force sensor having an operation shaft in which two columnar bodies are bundled, and B is a perspective view showing an outline of the appearance of the operation shaft. A is a sectional view showing a configuration of a conventional force sensor using a change in capacitance, and B is a diagram showing an example of an operation state thereof.

Claims (3)

The operation shaft is configured by bundling a plurality of columnar bodies so as to be displaced from each other,
Electrodes are formed on the opposing surfaces of the columnar bodies so as to oppose each other and are configured to change their capacitances by shifting from each other in the longitudinal direction of the columnar bodies. ,
One end of the operation shaft is fixed and the other end is a free end. The operation shaft is bent by a force acting on the free end, and the columnar bodies are displaced from each other to change the electrostatic capacity. in the force sensor that detect the direction and magnitude of the force by the change in capacitance,
A partition wall is sandwiched between the opposing surfaces of the columnar body,
A force sensor characterized in that electrodes capable of differential detection of the change in capacitance are provided on both surfaces of the partition wall. In the force sensor of claim 1 Symbol mounting,
The force sensor according to claim 1, wherein the electrode is a comb-teeth electrode in which comb teeth are arranged in the longitudinal direction. In the force sensor of claim 1 Symbol placement,
The columnar body has a quadrangular prism shape, and the columnar body is bundled so as to sandwich two orthogonal surfaces to constitute the operation shaft.

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