Patent Description:
Force sensors are used, for example, by robot arms and the like, and they detect a force (Fx, Fy, Fz) and a moment (Mx, My, Mz) with respect to three axes (x, y and z) orthogonal to each other (see, for example, Patent Literature <NUM>).

<CIT> discloses a force sensor which allows force detection in six directions.

The invention is defined by claim <NUM> and preferred embodiments are defined in claims <NUM>-<NUM>.

When the rigidity of the elastic body and strain body(, which may be combined together and referred to as a sensor body) is high and the amount of displacement among six axial directions is very small, the structure of the stopper needs to be processed at high accuracy, making it difficult to implement the stopper.

When the rigidity of the sensor body greatly differs from one axial direction to another, the designing of the stopper is complicated, making it difficult to implement the stopper.

On the other hand, when designing the sensor body without providing a stopper, it is difficult to increase the displacement of the elastic body and the strain body, and therefore a high sensor output cannot be obtained. As a result, the sensor thus obtained is vulnerable to an outer disturbance such as noise, and its measurement accuracy is low.

Embodiments of the present invention described herein aim to provide an elastic body with which a sufficient sensor output can be obtained and the measurement accuracy can be improved, and a force sensor using the same.

Mode for Carrying Out the Invention Hereinafter, the present embodiments will be described with reference to the drawings. In the drawings, the same members are denoted by the same reference symbols.

With reference to <FIG>, the configuration of a force sensor <NUM> according to an embodiment will be described.

The force sensor <NUM> is used, for example, in a robot arm or the like and detects the force (Fx, Fy, Fz) in X-, Y- and Z-axis directions and a torque (moment: Mx, My, Mz) around X, Y and Z axes.

As shown in <FIG> and <FIG>, the force sensor <NUM> comprises a cylindrical main body <NUM> and a cylindrical cover <NUM> covering the main body <NUM>. In the cover <NUM>, a mounting plate <NUM> is provided as a movable body operable on the main body <NUM>, and the mounting plate <NUM> is fixed to the cover <NUM> by a plurality of screws <NUM>. The cover <NUM> and the mounting plate <NUM> are provided to be operable on the main body <NUM>.

The main body <NUM> is fixed to, for example, a main portion of the robot arm (not shown). The mounting plate <NUM> is fixed to, for example, a hand portion of the robot arm.

Between the main body <NUM> and cover <NUM>, a ring-shaped sealing member <NUM> is provided. The sealing member <NUM> is formed of an elastic member, for example, a rubber or a foaming member, and seals the gap between the main body <NUM> and the cover <NUM> so as for the cover <NUM> to be operable on the main body <NUM>.

Between the main body <NUM> and the mounting plate <NUM>, an elastic body <NUM> is provided. The elastic body <NUM> is made of, for example, metal, and as will be described later, comprises one first structure <NUM>-<NUM>, a plurality of second structures <NUM>-<NUM>, a plurality of third structures <NUM>-<NUM> provided between the first structure <NUM>-<NUM> and the second structures <NUM>-<NUM>, and the like. The second structures <NUM>-<NUM> are arranged around the first structure <NUM>-<NUM> at equal intervals.

In this embodiment, the elastic body <NUM> comprises, for example, three second structures <NUM>-<NUM>. But, the number of second structures <NUM>-<NUM> is not limited to three, but may be three or more. When this embodiment is applied to some other device than the force sensor, for example, a torque sensor, the number of second structures <NUM>-<NUM> may be two.

As shown in <FIG>, the first structure <NUM>-<NUM> comprises six first elastic portions <NUM>-<NUM> therearound. The first elastic portions <NUM>-<NUM> are disposed around the first structure <NUM>-<NUM> and are each formed into a linear shape.

Each of the second structures <NUM>-<NUM> comprises two substantially U-shaped second elastic portions <NUM>-<NUM> and a relay potion <NUM>-<NUM> provided between the two second elastic portions <NUM>-<NUM> and on a straight line connecting these two second elastic portions <NUM>-<NUM> together.

Each of the third structures <NUM>-<NUM> is connected, by one end, to the first elastic portion <NUM>-<NUM> and is connected, by the other end, to the respective relay potion <NUM>-<NUM>. Two third structures <NUM>-<NUM> provided between the first structure <NUM>-<NUM> and one second structures <NUM>-<NUM> are placed parallel to each other.

The second structures <NUM>-<NUM> are fixed to the main body <NUM> by a plurality of screws <NUM>, and the first structure <NUM>-<NUM> is fixed to the mounting plate <NUM> by a plurality of screws <NUM> as shown in <FIG> and <FIG>.

As shown in <FIG> and <FIG>, a strain sensor <NUM> is provided between the first structure <NUM>-<NUM> and each relay potion <NUM>-<NUM>. More specifically, one end portion of the strain sensor <NUM> is fixed to the first structure <NUM>-<NUM> located between respective two first elastic portions <NUM>-<NUM> by a fixing plate <NUM> and a screw <NUM> inserted to a rear surface of the first elastic portion <NUM>-<NUM>, and the other end of the strain sensor <NUM> is fixed to a central portion of the respective relay potion <NUM>-<NUM> by a fixing plate <NUM> and a screw <NUM> inserted to a rear surface of the relay potion <NUM>-<NUM>. As will be described later, the strain sensor <NUM> comprises a metal-made strain body and a plurality of strain gauges disposed on a front surface of the strain body.

When the mounting plate <NUM> and the cover <NUM> operate on the main body <NUM> by an external force, the third structures <NUM>-<NUM>, the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM> are deformed. Accordingly, the strain bodies of strain sensors <NUM> are deformed, thus outputting electric signals from the respective strain gauges.

The strain gauges of the strain sensors <NUM> construct a bridge circuit, as will be described below, which detects the force (Fx, Fy, Fz) in the X, Y and Z-axis directions and the torque (moment: Mx, My, Mz) around the X, Y and Z-axes.

As shown in <FIG>, the main body <NUM> is provided with a plurality of stoppers <NUM> which protect the elastic bodies <NUM> from an external force. Each stopper <NUM> comprises a cylindrical stopper member <NUM>, a screw <NUM> as a fixing member and a plurality of openings 13a formed in the mounting plate <NUM>.

This embodiment illustrates the case which comprises three stoppers <NUM>. But, the number of stoppers <NUM> is not limited to three and may be three or more. The three stoppers <NUM> are each placed between respective adjacent structural bodies <NUM>-<NUM> of the three second structures <NUM>-<NUM>.

With the configuration that each stopper <NUM> is disposed between each adjacent pair of second structures <NUM>-<NUM>, it is possible to inhibit the diameter and outer dimensions of the elastic bodies <NUM> and the force sensor as a whole structure from increasing.

A plurality of projections 11a are provided on the surface of the main body <NUM>. Each of the projections 11a is located between each adjacent pair of second structures <NUM>-<NUM>.

As shown in <FIG>, each stopper member <NUM> is fixed to the respective projection 11a of the main body <NUM> while being inserted in the respective opening 13a of the mounting plate <NUM> by the respective screw <NUM>. The outer diameter of the stopper member <NUM> is set slightly less than the inner diameter of the opening 13a as will be described below. When the mounting plate <NUM> operates on the main body <NUM> so as to make the outer surface of the stopper member <NUM> abut on the inner surface of the opening 13a, the operation of the mounting plate <NUM> is stopped, thereby making it possible to prevent the elastic bodies <NUM> and the strain bodies of the strain sensors <NUM> from being damaged.

As shown in <FIG>, in a rear surface portion of the main body <NUM>, a printed board <NUM>, a plurality of flexible printed boards <NUM>, a rear cover <NUM>, a lead wire assembly <NUM> and a hollow tube <NUM> are provided. The printed board <NUM> comprises processing circuits (not shown) and the like, which supply power to a bridge circuit and process an output signal of the bridge circuit.

As shown in <FIG>, end portions of one side of the flexible printed boards <NUM> are disposed on an upper surface side of the main body <NUM>, and connected the strain sensors <NUM>, respectively. End portions of the other side of the flexible printed boards <NUM> are connected to the processing circuits and the like in the rear surface of the printed board <NUM>. The flexible printed boards <NUM> supply power to the strain gauges and supply signals from the strain gauges to the processing circuits.

The lead wire assembly <NUM> is connected to the printed board <NUM> to supply power to the processing circuits and transmit signals from the processing circuits. The rear cover <NUM> is fixed to the main body <NUM> by a plurality of screws and covers the printed board <NUM>.

An opening is made in the main body <NUM>, the cover <NUM>, the mounting plate <NUM>, the first structure <NUM>-<NUM> of the elastic bodies <NUM>, the printed board <NUM> and the central portion of the rear cover <NUM>, so as to communicate therethrough, and the hollow tube <NUM> is provided in the opening.

As shown in <FIG> and <FIG>, one end portion of the hollow tube <NUM> penetrates the rear cover <NUM>, the printed board <NUM> and the first structure <NUM>-<NUM>, and projects from the surface of the first structure <NUM>-<NUM>. A ring-like sealing member <NUM> is provided around the one end portion of the hollow tube <NUM>, which projects from the surface of the first structure <NUM>-<NUM>. The sealing member <NUM> is formed of, for example, a rubber or foam material, and it seals the gap between the opening of the mounting plate <NUM> and the one end portion of the hollow tube <NUM>. Thus, it is possible to prevent the entering of dust to the inner side of the mounting plate <NUM> from the outside of the cover <NUM>.

<FIG> shows the elastic body <NUM> and the strain sensor <NUM>. As described above, the elastic body <NUM> comprises one first structure <NUM>-<NUM>, three second structures <NUM>-<NUM>, a plurality of third structures <NUM>-<NUM>, six first elastic portions <NUM>-<NUM> provided in the first structure <NUM>-<NUM>, two second elastic portions <NUM>-<NUM> provided in each of the three second structures <NUM>-<NUM> and a relay potion <NUM>-<NUM> provided between each pair of the two second elastic portions <NUM>-<NUM>.

The second elastic portions <NUM>-<NUM> each are formed into a U-shape, and have a flexural or torsional rigidity lower than that of the second structures <NUM>-<NUM>. The first elastic portions <NUM>-<NUM> have a torsional rigidity equivalent to or lower than that of the second elastic portions <NUM>-<NUM>.

Each strain sensor <NUM> is provided between the first structure <NUM>-<NUM> located between the two respective first elastic portions <NUM>-<NUM> and the central portion of the respective relay potion <NUM>-<NUM>. Further, each strain sensor <NUM> is located between the two respective third structures <NUM>-<NUM> so as to be parallel to the two third structures <NUM>-<NUM>.

A thickness of each first elastic portion <NUM>-<NUM>, each second elastic portion <NUM>-<NUM> and each relay potion <NUM>-<NUM> is equal to a thickness of the first structure <NUM>-<NUM>, the second structures <NUM>-<NUM> and the third structures <NUM>-<NUM>, and a width W of the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM> is equal to a width of the third structures <NUM>-<NUM>. As lengths L1 and L2 of the U-shaped portion are longer and the width W of the U-shaped portion is more slender, the second elastic portions <NUM>-<NUM> are more flexible. Further, as their widths are less, the first elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM> are more flexible.

A thickness of a strain body 19a which constitutes the strain sensor <NUM> is less than those of the first structure <NUM>-<NUM>, the second structures <NUM>-<NUM>, the third structures <NUM>-<NUM>, the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM>, and a width of the strain body 19a is greater than those of the third structures <NUM>-<NUM>, the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM>. But the thicknesses and dimensions in width and their relationships in terms of size of the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM>, the relay potions <NUM>-<NUM> and the third structures <NUM>-<NUM>, can be changed as necessary.

The strain body 19a is thin rectangular as will be described later, and has a shape which has a large aspect ratio in its plane. Therefore, when the strain body 19a is a single unit, the strain body 19a has characteristics that its displacement is less with respect to the force in the Fx and Fy directions and the moment in the Mz direction, and its displacement is great with respect to the moment in the Mx and My directions and the force in the direction Fz due to the difference in moment of inertia of area.

On the other hand, when the amount of displacement of the elastic body <NUM> is excessively small, the structure of the stopper <NUM> is required to be processed at high accuracy. When the amount of displacement with respect to the force in the Fx and Fy directions and the moment in the Mz direction and the amount of displacement with respect to the moment in the Mx and My directions and the force in the Fz direction are large, the structure of the stopper <NUM> is complicated. Therefore, in order to constitute a high-precision force sensor of a simple structure, it is necessary that the difference in amount of displacement among the axes of the elastic body <NUM> should be small.

As to the elastic body <NUM> according to the present embodiment, the amount of displacement can be increased in a direction parallel to the X-Y plane (a plane containing the X-axis and Y-axis), and therefore even though the strain body 19a is only slightly displaced, it is possible to realize a large amount of displacement as a sensor body.

Further, the rigidity of the strain body 19a in the Z-axis direction is far less than the rigidity of the elastic body <NUM> in the Z-axis direction. Therefore, the rated load regarding the bending of the force sensor in the Z-axis direction cannot be applied to the single unit strain body 19a. Consequently, it is necessary to control the amount of displacement of the strain body 19a.

Therefore, the function required from the elastic body <NUM> is: (<NUM>) to have a large amount of displacement in the X-Y plane; and (<NUM>) to control the amount of displacement of the strain body 19a in reception of the load in the Z-axis direction.

<FIG> schematically shows the structure of the elastic body <NUM> according to the embodiment provided above.

The first structure <NUM>-<NUM> and the relay potion <NUM>-<NUM> are connected to each other by the first elastic portions <NUM>-<NUM> and the third structures <NUM>-<NUM> connected in series, and further connected by the strain body 19a.

The relay potion <NUM>-<NUM> and the second structure <NUM>-<NUM> are connected by the second elastic portions <NUM>-<NUM> provided therebetween.

Here, the first elastic portions <NUM>-<NUM> and the second elastic portions <NUM>-<NUM> have a function to increase the amount of displacement of the elastic body <NUM> with respect to the force in the Fx and Fy directions and the moment in the Mz direction, which will now be described more specifically.

As shown in <FIG>, when a force in the Fx and Fy directions is applied to the elastic body <NUM> and when a moment in the Mz direction is applied, the portion of the first elastic portion <NUM>-<NUM>, to which the respective third structure is connected, is deformed as indicated by an arrow. Thus, the amount of displacement of the second structures <NUM>-<NUM> with respect to the first structure <NUM>-<NUM> is increased. The strain body 19a is displaced as much depending on the width of the third structure <NUM>-<NUM>, the width of strain body 19a and the load, and here the amount of displacement of the strain body 19a is slight. That is, in the case of this embodiment, the amount of displacement of the second structure <NUM>-<NUM> with respect to the first structure <NUM>-<NUM> can be increased as compared to the amount of displacement of the strain body 19a.

As shown in <FIG>, when a force in the Fz direction is applied to the elastic body <NUM> and when the moment in the Mx and My direction is applied, the portion of the first elastic portion <NUM>-<NUM>, to which the third structure <NUM>-<NUM> is connected, is deformed as indicated an arrow. Thus, the amount of displacement of the third structure <NUM>-<NUM> in the thickness direction can be increased, and therefore the amount of displacement of the strain body 19a in the thickness direction can be increased. Consequently, the third structure <NUM>-<NUM> can be deformed into an approximately S-shape and the output voltage of the bridge circuit can be increased as will be described later.

<FIG> shows an example of deformation of the elastic body <NUM> according to this embodiment.

The first structure <NUM>-<NUM> includes the first elastic portion <NUM>-<NUM> which has a torsional rigidity equivalent to or less than that of the second elastic portion <NUM>-<NUM>. Therefore, when a force in, for example, the Fz direction is applied to the elastic body <NUM>, the first elastic portion <NUM>-<NUM> is deformed, thus deforming the second elastic portion <NUM>-<NUM>, and therefore the amount of lifting of the relay potion <NUM>-<NUM> is decreased. Thus, the third structure <NUM>-<NUM> is deformed into an approximately S-shape, and the strain body 19a provided between the first structure <NUM>-<NUM> and the relay potion <NUM>-<NUM> is deformed into an approximately S-shape.

<FIG> schematically shows deformation of the strain body 19a caused by the deformation of the elastic body <NUM> shown in <FIG>. On the surface of the strain body 19a, a plurality of strain gauges <NUM>-<NUM> are disposed as illustrated.

When the strain body 19a is deformed into an approximately S-shape by the deformation of the elastic body <NUM>, the strain gauges <NUM> and <NUM> provided on the surface of the strain body 19a are elongated, and the strain gauges <NUM> and <NUM> are compressed. As a result, the differences between the resistance value of the strain gauges <NUM> and <NUM> and the resistance value of the strain gauges <NUM> and <NUM> is increased, thus making it possible to increase the output voltage of the bridge circuit constituted by the strain gauges <NUM> to <NUM>. Therefore, the accuracy of the force sensor can be improved.

<FIG> shows a state of deformation of the elastic body <NUM> as a comparative example. This elastic body <NUM> is similar to the elastic body <NUM> of this embodiment, without the first elastic portion <NUM>-<NUM>. Without the first elastic portion <NUM>-<NUM>, when the force in, for example, the Fz direction is applied to the elastic body <NUM>, the second elastic portion <NUM>-<NUM>, which has a rigidity lower than that of the second structure <NUM>-<NUM>, is bent or twisted by deformation, and thus the third structure <NUM>-<NUM> is curved. Consequently, the relay potion <NUM>-<NUM> is lifted. Accordingly, the strain body 19a provided between the first structure <NUM>-<NUM> and the relay potion <NUM>-<NUM> is also curved.

<FIG> shows deformation of the strain body 19a caused by the deformation of the elastic body <NUM> shown in <FIG>. When the strain body 19a is curved by the curving of the elastic body <NUM>, the strain gauges <NUM> and <NUM> and the strain gauges <NUM> and <NUM> provided on the surface of the strain body 19a are all elongated. Therefore, the difference between the resistance value of the strain gauges <NUM> and <NUM> and the resistance value of the strain gauges <NUM> and <NUM> is small, and the output voltage of the bridge circuit constituted by the strain gauges <NUM> to <NUM> is also low. Therefore, it is difficult to improve the accuracy of the force sensor.

The second elastic portion <NUM>-<NUM> has a bending or torsional rigidity lower as compared to that of the second structure <NUM>-<NUM>. Therefore, when a force in the Fx and Fy directions is applied to the elastic body <NUM> and the moment in the Mz direction is applied thereto, the amount of displacement of the second structure <NUM>-<NUM> with respect to the first structure <NUM>-<NUM> can be increased despite that the strain body 19a provided between the first structure <NUM>-<NUM> and the relay potion <NUM>-<NUM> is displaced only by the amount controlled by the third structure <NUM>-<NUM>, which will be described later.

More specifically, the width of the U-shaped second elastic portion <NUM>-<NUM> is set narrow as compared to its thickness, thus creating a great difference in moment of inertia of area of the second elastic portion <NUM>-<NUM>. Therefore, the second elastic portion <NUM>-<NUM> has high rigidity to the force in the Fz direction and low rigidity to the moment in the Mz direction. When torsion is considered, the second elastic portion <NUM>-<NUM> has a flexibility equivalent to or higher than that assumed for simple bending to the force in the Fz direction. However, the second elastic portion <NUM>-<NUM> has a rigidity sufficient to the force in the Fz direction as compared to the moment in the Mz direction.

The third structure <NUM>-<NUM> is provided between the first elastic portion <NUM>-<NUM> and the relay potion <NUM>-<NUM> and disposed parallel to the strain sensor <NUM>. For this reason, when the force in the Fx and Fy directions and/or the moment in the Mz direction are applied to the elastic body <NUM>, the amount of displacement of the strain body 19a, which constitutes the strain sensor <NUM> in the thickness direction and the width direction, can be controlled.

More specifically, the thickness of the third structures <NUM>-<NUM> is greater than the thickness of strain body 19a, and the width of the third structure <NUM>-<NUM> is less than the width of the strain body 19a. Thus, with the third structure <NUM>-<NUM>, the amount of displacement of the strain body 19a having a different moment of inertia of area in the thickness direction and the width direction can be controlled.

The elastic body <NUM> of this embodiment comprises the first structure <NUM>-<NUM>, a plurality of second structures <NUM>-<NUM>, a plurality of first elastic portions <NUM>-<NUM> provided on the first structure <NUM>-<NUM>, second elastic portions <NUM>-<NUM> provided respectively in the second structures <NUM>-<NUM>, a relay potion <NUM>-<NUM> provided between two second elastic portions <NUM>-<NUM> and third structures <NUM>-<NUM> provided between the relay potion <NUM>-<NUM> and the first elastic portions <NUM>-<NUM>, and the rigidity of the second elastic portions <NUM>-<NUM> is lower than the rigidity of the second structures <NUM>-<NUM> and the rigidity of the first elastic portions <NUM>-<NUM> is less than or equal to the rigidity of the first structure <NUM>-<NUM>. With this structure, the rigidity of the entire elastic body <NUM> can be made lower as compared to that of the case where there are no first elastic portions <NUM>-<NUM> and second elastic portions <NUM>-<NUM>, the amount of displacement of the elastic body <NUM> to the force in the Fx and Fy directions, can be increased. Therefore, the amount of displacement of the elastic body <NUM> to the force in the Fx and Fy directions can be increased as compared to the slight deformation of the strain body 19a.

Further, the elastic body <NUM> of this embodiment comprises the first elastic portions <NUM>-<NUM>, the second elastic portions <NUM>-<NUM> and the relay potions <NUM>-<NUM>, and thus it can substantially equalize the amounts of displacement in the six axial directions. Moreover, as the force in the Fz direction is received, the deformation of the third structures <NUM>-<NUM> and the relay potions <NUM>-<NUM> can be inhibited, and the first elastic portions <NUM>-<NUM>, the third structures <NUM>-<NUM> and the relay potions <NUM>-<NUM> can be deformed into an approximately S-shape. Accordingly, the strain body 19a can be deformed into an S-shape, and therefore sufficient distortion can be imparted to the strain body 19a to the force in the Fz direction. Therefore, a high sensor output can be obtained, and a high-precision force sensor can be constructed.

Further, when the rigidity of the first elastic portions <NUM>-<NUM> is less than or equal to the rigidity of the second elastic portions <NUM>-<NUM>, large distortion can be imparted to the strain body 19a to the force in the Fz direction, and thus a further higher sensor output can be obtained. Note that, here the rigidity includes the axial rigidity, flexural rigidity, shearing rigidity and torsional rigidity.

Moreover, the elastic body <NUM> exhibits amounts of displacement in the six axial directions approximately equal to each other, and has a low rigidity as a whole. Therefore, with the stopper <NUM> of such a simple structure, the strain body 19a can be protected.

More specifically, in the case of a high-rigidity elastic body, the gap between the side surface of the stopper member <NUM> of the stopper <NUM> and the inner surface of the opening 13a of the mounting plate <NUM> needs to be set to, for example, <NUM>. Thus, it is difficult to process the device mechanically. However, when the rigidity of the entire elastic body <NUM> is low as in the present embodiment, the amount of displacement of the elastic body <NUM> at the rated load can be increased to, for example, <NUM> to <NUM>. Thus, the gap between the side surface of the stopper member <NUM> and the inner surface of the opening 13a of the mounting plate <NUM> can be widened, thereby making it easy to design the stopper <NUM> at the time of overloading and to process the stopper <NUM> mechanically.

Furthermore, at the time of overload, the displacement of the elastic body <NUM> and the strain body 19a can be inhibited by the high-rigidity stopper <NUM>, and therefore sufficient distortion can be imparted to the strain body 19a in a range of the rated load.

Thus, a high sensor output can be obtained. When there is no stopper <NUM>, it is necessary to set a rated load with which sufficient safety can be expected on the assumption of even the overloading. With this structure, sufficient distortion cannot be imparted to the strain body, and accordingly it is difficult to extract high sensor output.

<FIG> shows the first modified example of the elastic body <NUM>. The elastic body <NUM> shown in <FIG> is different from the elastic body <NUM> shown in <FIG> in that the relay potion <NUM>-<NUM> is fixed to the respective second structure <NUM>-<NUM>. That is, between the relay potion <NUM>-<NUM> and the respective second structure <NUM>-<NUM>, a connection section <NUM> is provided, and the relay potion <NUM>-<NUM> is fixed to the second structure <NUM>-<NUM> by the connection portion <NUM>.

The thickness of the connection portion <NUM> is equal to that of the second structure <NUM>-<NUM> and the relay potion <NUM>-<NUM>, and the width thereof is equal to the width of, for example, the third structure <NUM>-<NUM>.

Further, in this case, the first elastic portion <NUM>-<NUM> of the first structure <NUM>-<NUM> is excluded.

With the above-described structure, in the case where the torsional rigidity of a beam <NUM>-6a of the relay potion <NUM>-<NUM> shown in <FIG> is low as compared to the flexural-rigidity of the connection portion <NUM> and there is no first elastic portion <NUM>-<NUM> of the first structure <NUM>-<NUM>, when the third structure <NUM>-<NUM> is displaced by the force in the Fz direction, the surface of the relay potion <NUM>-<NUM> is held in an almost parallel position, although the height differs from the surface of the first structure <NUM>-<NUM> due to the connection portion <NUM>. Therefore, the strain body 19a can be deformed into an S-shape as shown in <FIG>, making it possible to increase the output voltage of the bridge circuit.

<FIG> shows the second modified example of the elastic body <NUM>. The elastic body <NUM> shown in <FIG> is different from the elastic body <NUM> shown in <FIG> in that the second elastic portion <NUM>-<NUM> is removed from the elastic body <NUM> shown in <FIG>. Further, the beam <NUM>-6a of the relay potion <NUM>-<NUM> may be removed.

With this structure, when the third structure <NUM>-<NUM> is displaced by the force in the Fz direction, the relay potion <NUM>-<NUM> is held in an almost parallel position, although height differs from that of the first structure <NUM>-<NUM> by the connection portion <NUM>. Therefore, with the second modified example as well, an advantage similar to that of the first modified example can be obtained.

<FIG> shows the third modified example of the elastic body <NUM>. In the elastic body <NUM> shown in <FIG>, <FIG> and <FIG>, the first elastic portions <NUM>-<NUM>, on which the third structures <NUM>-<NUM> are respectively provided, are provided on each respective third structure <NUM>-<NUM>.

In contrast, in the case of the third modified example shown in <FIG>, one first elastic portion <NUM>-<NUM> is provided for two third structures <NUM>-<NUM>. One end portion of the strain body 19a is provided in the respective first elastic portion <NUM>-<NUM> located between the two third structures <NUM>-<NUM>.

With the above-described structure as well, the third structures <NUM>-<NUM> are displaced by the force in the Fz direction, the strain body 19a can be deformed into an S-shape as shown in <FIG>, thereby making it possible to increase the output voltage of the bridge circuit.

Note that the number of the third structures provided in the first elastic portion <NUM>-<NUM> is not limited to two, but may be three or more.

<FIG> schematically shows the fourth modified example of the elastic body <NUM>, which does not fall within the scope of the claimed invention.

It suffices if the elastic body <NUM> can increase the amount of displacement of the elastic body <NUM> itself in the X-Y plane as compared to the amount of displacement of the strain body 19a, and control the amount of displacement of the strain body 19a when receiving the load in the Z-axis direction. Therefore, according to the embodiment, as shown in <FIG>, in the elastic body <NUM>, a plurality of second structures <NUM>-<NUM> are disposed around the first structure <NUM>-<NUM>, the third structures <NUM>-<NUM> are respectively placed between the first elastic portion <NUM>-<NUM> of the first structure <NUM>-<NUM> and the relay potion <NUM>-<NUM> of second structure <NUM>-<NUM> respectively, and each strain body 19a is placed between the respective first structure <NUM>-<NUM> and the respective relay potion <NUM>-<NUM>.

However, the structure is not limited to this, but as shown in <FIG>, a plurality of first structures <NUM>-<NUM> may be placed around a second structure <NUM>-<NUM>, the third structures <NUM>-<NUM> may be respectively placed between the relay potions <NUM>-<NUM> of the second structures <NUM>-<NUM> and the first elastic portions <NUM>-<NUM> of the first structures <NUM>-<NUM>, and each strain body 19a may be placed between the respective relay potion <NUM>-<NUM> and the respective first structure <NUM>-<NUM>.

With this structure as well, an advantage similar to that of this embodiment can be obtained.

Note that in this embodiment and each of the modified examples, the material and thickness of the first elastic portions <NUM>-<NUM> and second elastic portions <NUM>-<NUM> of the elastic body <NUM> are the same those of the third structures <NUM>-<NUM>, but they may be formed of different materials in different thicknesses.

In the case of the examples shown in <FIG> and <FIG>, the elastic body <NUM> comprises three second structures <NUM>-<NUM>. But, the three second structures <NUM>-<NUM> can be unified by changing the arrangement of the stopper <NUM>.

<FIG> shows a modified example of the elastic body <NUM> shown in <FIG>. In the fifth modified example, the second structure <NUM>-<NUM> has a ring shape, and a plurality of second elastic portions <NUM>-<NUM> and relay potions <NUM>-<NUM> are respectively provided in a plurality of locations of one second structure <NUM>-<NUM>. The rest of the structure is similar to that of <FIG>. In the case of this structure, a plurality of stoppers <NUM> may be disposed on, for example, an outer side of the elastic body <NUM>.

With the elastic body <NUM> having such a structure, an advantage similar to that of the elastic body of the structure shown in <FIG> can be obtained.

In the elastic body <NUM> shown in <FIG>, three second structures <NUM>-<NUM> can be made into one ring-shaped second structure <NUM>-<NUM> as shown in <FIG>. In this case as well, an advantage similar to that of the elastic body <NUM> shown in <FIG> can be obtained.

In the elastic body <NUM> shown in <FIG>, a plurality of first structures <NUM>-<NUM> can be made into one ring-shaped first structure <NUM>-<NUM> as shown in <FIG>. In this case as well, an advantage similar to that of the elastic body <NUM> shown in <FIG> can be obtained.

<FIG> shows an example of the strain sensor <NUM>. As described above, the strain sensor <NUM> is constituted by a strain body 19a and a plurality of strain gauges R1 to R8 provided on the surface of the strain body 19a. The strain body 19a is formed of metal and has a thickness less than its width. Therefore, the strain body 19a can be easily deformed in the thickness direction and not easily deformed in the width direction.

One end portion of the strain body 19a is provided in the first structure <NUM>-<NUM> and the other end portion is provided in the relay potion <NUM>-<NUM> of the respective second structure <NUM>-<NUM>. The strain gauges R1, R3, R5 and R8 are provided in the vicinity of the one end portion of the strain body 19a, the strain gauges R2, R4, R6, R7 are provided in the vicinity of the other end portion of the strain body 19a.

<FIG> shows an example of the bridge circuit which uses the strain gauges R1 to R8. The strain gauges R1, R2, R3 and R4 constitute a first bridge circuit BC1, and the strain gauges R5, R6, R7 and R8 constitute a second bridge circuit BC2.

In the first bridge circuit BC1, a series circuit of the strain gauge R2 and the strain gauge R1 and a series circuit of the strain gauge R4 and the strain gauge R3 are placed between a power source V and a ground GND. An output voltage Vout+ is output from a connection node between the strain gauge R2 and the strain gauge R1, and an output voltage Vout- is output from a connection node between the strain gauge R4 and the strain gauge R3. The output voltage Vout+ and the output voltage Vout- are supplied to an operational amplifier OP1, and the output voltage Vout is output from an output terminal of the operational amplifier OP1.

In the second bridge circuit BC2, a series circuit of the strain gauge R6 and the strain gauge R5 and a series circuit of the strain gauge R8 and the strain gauge R7 are placed between the power source V and the ground GND. An output voltage Vout+ is output from a connection node between the strain gauge R6 and the strain gauge R5, and an output voltage Vout- is output from a connection node of the strain gauge R8 and the strain gauge R7. The output voltage Vout+ and the output voltage Vout- are supplied to an operational amplifier OP2, and the output voltage Vout is output from an output terminal of an operational amplifier OP2.

As described above, the strain body 19a is deformed into an S-shape by the force of, for example, the Fz direction, and thus a high output voltage can be obtained from the first bridge circuit BC1 and the second bridge circuit BC2.

Note that the arrangement of the strain gauges R1 to R8 with respect to the strain body 19a and the structures of the bridge circuits BC1 and BC2 are not limited to this, but they can be modified.

The stopper <NUM> will be further described.

Generally, for the stopper, a cylindrical stopper member and a circular opening in which the stopper member is contained, are used. In the case of a stopper of this structure, a gap between a side surface of the stopper member and an inner surface of the opening is uniform in each of the axial directions. Therefore, when the rigidity of the elastic bodies provided on the strain body varies from one axis to another, a high load is applied at an operating point of the stopper in a shaft of high rigidity, thus making it difficult to reliably prevent breaking of the strain body.

<FIG> shows an example of the amount of displacement with respect to six axes of the sensor body (the elastic body <NUM> and the strain body 19a). As shown in <FIG>, when different safety factors are set for the amount of displacement of each of the six axes in the rating of the sensor body, the operable range of each axis will be different.

More specifically, the operable range of the sensor body in the Fx, Fy and Mz directions is smaller than the operable range of the sensor body in the Fz, Mx and My directions. In other words, the operable range of the strain body 19a in the width direction is smaller than the operable range of the strain body 19a in the thickness direction.

Thus, when the operable range differs from one axis to another in the sensor body, in the cylindrical stopper member and the circular opening, a high load is applied at an operating point of the stopper in a direction where the operable range is small, thus making it difficult to sufficiently protect the strain body.

<FIG>, <FIG> show the stopper member <NUM> according to this embodiment.

The stopper member <NUM> comprises, for example, a first portion 31a, a second portion 31b, a third the portion 31c, which are of different diameters, two projections 31d, an opening 31e in which a screw <NUM> is inserted, and a slit 31f.

The first portion 31a has a first diameter D1 and a diameter of the second portion 31b is less than the diameter of first portion 31a, and a diameter of the third portion 31c is less than the diameter of the second portion 31b. The two projections 31d are provided on the second portion 31b. These projections 31d are provided on respective sides of the second portion 31b to correspond to, for example, a direction (Fx, Fy, Mz directions) where the operable range of the elastic body <NUM> (the strain body 19a) is small. The surface of each of the projections 31d is curved along the inner surface of the opening 13a.

In <FIG>, L11 indicates an interval (distance) between the first portion 31a and the inner surface of the opening 13a of the mounting plate <NUM>. The interval L11 is, for example, an interval of the direction where the operable range of the elastic body <NUM> is large (Fz, Mx, My directions, that is, the thickness direction of the strain body 19a). Further, L12 indicates an interval between the projection 31d and the inner surface of the opening 13a. The interval L12 is, for example, an interval of the direction wherein the operable range of the elastic body <NUM> is small (Fx, Fy, Mz direction, that is, the width direction of the strain body 19a). The relationship between L11 and L12 is represented as L11 > L12.

More specifically, in the case of the example shown in <FIG>, L11 should preferably be, for example, <NUM>, and L12 be, for example, <NUM>.

That is, the interval L12 of the direction (Fx, Fy, Mz direction) where the strain body 19a is not easily deformed, is set narrower than the interval L11 of the direction (Fz, Mx, My direction) where it is easily deformed.

Note that a part corresponding to the interval L11 of the stopper member <NUM> is a first contact portion (CP1) in contact with the inner surface of the opening 13a, and a part corresponding to the interval L12 is a second contact portion (CP2) in contact with the inner surface of the opening 13a.

The third portion 31c is a part where a cylindrical jig (denoted by reference number <NUM> in <FIG>) is mounted so as to adjust the interval between the stopper member <NUM> and the opening 13a.

The slit 31f is provided in the third portion 31c. A center of the slit 31f is disposed at a position corresponding to the center of the linear line connecting the centers of the two projections 31d.

As shown in <FIG> and <FIG>, the slit 13d is provided at the position corresponding to the stopper <NUM> of the mounting plate <NUM>. The slit 13d is communicated to the opening 13a and is further made communicable to the slit 31f as well provided in the third portion 31c of the stopper member <NUM>.

<FIG> shows the stopper <NUM> in enlargement. The interval between the stopper member <NUM> and the opening 13a is adjusted using a jig <NUM>. The jig <NUM> comprises an insertion portion 80a, a key 80b and a knob 80c.

The insertion portion 80a is formed to be cylindrical, and the thickness of the cylinder is approximately equal to a distance between the side surface of the third portion 31c and the inner surface of the opening 13a. The distance between the side surface of the third portion 31c and the inner surface of the opening 13a is greater than the first interval L11.

The key 80b is provided in the insertion portion 80a, and placed along an axial center of the jig <NUM>. The key 80b has a shape approximately similar to a combined shape of the slit 31f of the stopper member <NUM> and the slit 13d of the mounting plate <NUM> on top of one another.

The knob 80c has, for example, a columnar shape, and comprises a hole 80d which penetrates the insertion portion 80a along its axial center. In the hole 80d, for example, a hexagon head wrench (not shown) is to be inserted to fix the stopper member <NUM>.

In order to adjust the interval between the stopper member <NUM> and the opening 13a, the respective screw <NUM> shown in <FIG> and <FIG> is loosened, and the jig <NUM> is inserted to the stopper <NUM>. More specifically, the insertion portion 80a of the jig <NUM> is inserted between the third portion 31c of the stopper member <NUM> and the opening 13a.

The thickness of the insertion portion 80a of the jig <NUM> is approximately equal to the distance between the side surface of the third portion 31c and the inner surface of the opening 13a. With this structure, the intervals L11 and L12 shown in <FIG> can be set by only inserting the insertion portion 80a to between the third portion 31c and the opening 13a.

Further, as the jig <NUM> is mounted to the stopper <NUM>, the key 80b of the jig <NUM> is inserted to the slit 31f of the stopper member <NUM> and the slit 13d of the amounting plate <NUM>. With this structure, the position of the projection 31d of the stopper member <NUM> can be set parallel to the X-Y plane.

While the jig <NUM> being mounted into the stopper <NUM>, a hexagon head wrench is inserted to the hole 80d to fasten the screw <NUM>, and thus the stopper member <NUM> is fixed to the main body <NUM> and thus the adjusting of the stopper member <NUM> is completed.

In the case where the stopper member <NUM> functions as a stopper, when the elastic body <NUM> is deformed into the direction (Fz, Mx, My direction) where the strain body 19a can be easily deformed, the first portion 31a of the stopper member <NUM> is brought into contact with the inner surface of the opening 13a, whereas the second portion 31b, the third portion 31c and the projection 31d are not brought into contact with the inner surface of the opening 13a.

When the elastic body <NUM> is deformed in the direction (Fx, Fy, Mz direction) where the strain body 19a cannot be easily deformed, the first portion 31a, the second portion 31b and the third portion 31c of the stopper member <NUM> are not brought into contact with the inner surface of the opening 13a, whereas the projection 31d is brought into contact with the inner surface of the opening 13a. Thus, the strain body 19a is protected.

According to the above-described structure, the second portion of the stopper member <NUM> comprises a pair of projections 31d in the direction where the operable range of the strain body 19a is small (Fx, Fy, Mz, the width direction of the strain body 19a), and the interval L12 between the inner surface of the opening 13a of the mounting plate <NUM> and the projection 31d is set less than the interval L11 between the first portion 31a of the stopper member <NUM> and the inner surface of the opening 13a of the mounting plate <NUM>. With this structure, in the direction where the operable range of the strain body 19a is small, it is possible to prevent the operating point of the stopper from being applied at a high load, thus making it possible to sufficiently protect the strain body 19a.

Further, the strain body 19a can be deformed sufficiently in the rated operable range, and therefore a high sensor output can be obtained. Therefore, a high-precision force sensor can be implemented.

Further, with use of the stopper <NUM> of this embodiment, it is possible to allow for non-uniformity of the rigidity among the six axial directions of the sensor body. When equalizing the rigidity values of the six axial directions of the sensor body, the size in shape of the elastic body <NUM> and the strain body 19a is generally increased. However, with use of the stopper <NUM> of this embodiment, it is possible to allow the non-uniformity of the rigidity among the six axial directions of the sensor body, and therefore the upsizing of the elastic body <NUM> and the strain body 19a can be prevented, thereby making it possible to implement a small-sized force sensor.

In the stopper member <NUM> discussed above, two projections 31d are provided in the second portion 31b, but the structure of the stopper <NUM> and the like is not limited to that of the example provided above.

<FIG> shows the first modified example of the stopper <NUM>. In the stopper <NUM> shown in <FIG>, a projection 31d is provided in the second portion 31b of the stopper member <NUM>. By contrast, in the first modified example, the second portion 31b of the stopper member <NUM> does not comprise a projection 31d, but it has a cylindrical shape and a pair of projections 13b are provided on an inner surface portion of the opening 13a, which corresponds to the second portion 31b.

More specifically, the pair of projections 13b are provided on each opposing surface of the opening 13a in the Fx, Fy and Mz directions, respectively. The projections 13b each comprise a flat surface, and the interval between the surface of the projection 13b and the surface of the second portion 31b is represented by L12. The reason why the projection 13b comprises a flat surface, is to avoid the projection 13b from being brought into contact with the second portion 31b of the stopper member <NUM> when the stopper member <NUM> moves in the Z-axis direction of the opening 13a.

<FIG> shows the second modified example of stopper <NUM>. In the second modified example, the shape of the opening 13a is circular as in the case of <FIG>, and the shape of the second portion 31b of the stopper member <NUM> is elliptical.

More specifically, a major axis of the ellipse is placed along the Fx, Fy and Mz directions, and an interval between one end portion and the other end portion of the major axis and the inner surface of the opening 13a is set as L12. Therefore, the major axis portion of the ellipse can carry out an operation similar to that of the projection 31d.

<FIG> shows the third modified example of the stopper <NUM>. In the second modified example shown in <FIG>, the shape of the second portion 31b of the stopper member <NUM> is elliptical. By contrast, in the third modified example, the shape of the second portion 31b of the stopper member <NUM> is circular, whereas the shape of a portion 13c of the opening 13a, which corresponds to the second portion 31b of the stopper member <NUM> is elliptical.

More specifically, in the portion 13c of the opening 13a, a minor axis of the ellipse is placed in the Fx, Fy and Mz directions, and an interval between the second portion 31b of the stopper member <NUM> and the inner surface of the portion 13c of the opening 13a is represented by L12.

According to the first to third modified examples, an advantage similar to that of the example shown in <FIG>, <FIG> can be obtained.

<FIG> and <FIG> show the fourth modified example of the stopper <NUM>, and they show only the stopper member <NUM>. The stopper member <NUM> shown in <FIG> includes a first portion 31a, a second portion 31b and a third portion 31c, and a pair of projections 31d are provided in the second portion 31b. Thus, in the case of the structure comprising a plurality of steps, high-precision processing can be performed easily. But, the second portion 31b is not necessarily essential.

As shown in <FIG> and <FIG>, in the fourth modified example, the stopper member <NUM> does not comprise a second portion 31b and a pair of projections 31d are provided in the first portion 31a.

With the stopper member <NUM> of the structure shown in <FIG> and <FIG>, a function and an effect similar to those of the stopper member <NUM> shown in <FIG> can be obtained.

<FIG> shows the fifth modified example of the stopper <NUM>. As in the fourth modified example, according to the fifth modified example, the stopper member <NUM> does not comprise a second portion 31b, and the first portion 31a does not comprise a pair of projections 31d and is cylindrical.

An inner surface portion of the opening 13a, which corresponds to the first portion 31a, comprises a pair of projections 13b. The pair of projections 13b are provided in each opposing surface of the opening 13a in the Fx, Fy and Mz directions, respectively, and the surface of the projection 13b is made flat. The interval between the surface of the projection 13b and the first portion 31a of the stopper member <NUM> is L12 and the interval between an inner surface portion of the opening 13a except for the projection 13b and the side surface of the first portion 31a is L11.

<FIG> shows the sixth modified example of the stopper <NUM>. As in the fourth modified example, according to the sixth modified example, the stopper member <NUM> does not comprise a second portion 31b, and also comprises a first portion 31a and a third portion 31c. The first portion 31a is elliptical. A major axis of the ellipse is placed in the Fx, Fy and Mz directions, and a minor axis of the ellipse is placed in the Fz, Mx and My directions.

The opening 13a is circular. In the first portion 31a, the interval between one end portion and the other end portion of the major axis of the ellipse and the inner surface of the opening 13a is L12 and the interval between one end portion and the other end portion of the minor axis of the ellipse and the inner surface of the opening 13a is L11.

<FIG> shows the seventh modified example of the stopper <NUM>. As in the case of the fourth modified example, according to the seventh modified example, the stopper member <NUM> does not comprise a second portion 31b, but comprises a first portion 31a and a third portion 31c. The first portion 31a and the third portion 31c are cylindrical.

A portion corresponding to the first portion 31a of the opening 13a is elliptical, and a minor axis of the ellipse is placed in the Fx, Fy and Mz directions, and a major axis of the ellipse is placed in the Fz, Mx and My directions. An interval between one end portion and the other end portion of the minor axis of the ellipse and the inner surface of the opening 13a is L12, and an interval between one end portion and the other end portion of the major axis of the ellipse and the inner surface of the opening 13a is L11.

A portion corresponding to the third portion 31c of the opening 13a is circular as indicated by a broken line. But, if the outer diameter of the insertion portion 80a of the jig <NUM> is elliptical, the entire opening 13a may be made elliptical.

According to the fifth to seventh modified examples, an advantage similar to that of the example shown in <FIG>, <FIG> can be obtained.

The stopper <NUM> described above comprises a cylindrical or partially elliptical stopper member <NUM> and a circular or elliptical opening 13a. But, the shapes of the stopper member <NUM> and the opening 13a are not limited to those of this example.

<FIG> show the eighth modified example of the stopper <NUM>. In the eighth modified example, the first portion 31a of the stopper member <NUM> is, for example, a square in which a length E1 of sides in the Fx, Fy and Mz directions and a length E2 of sides in the Fz, Mx and My directions are equal to each other.

The shape of the opening 13a portion corresponding to the first portion 31a is rectangular. Short sides of the rectangle are placed in the Fx, Fy and Mz directions, and long sides of the rectangle are placed in the Fz, Mx and My directions. An interval between a short side of the rectangle and the first portion 31a of the stopper member <NUM> is L11, and an interval between a long side of the rectangle and the first portion 31a of the stopper member <NUM> is L12.

In the opening 13a, the portion corresponding to the third portion 31c of the stopper member <NUM> is circular as indicated by a broken line. Therefore, the stopper member <NUM> can be positioned using the jig <NUM>.

<FIG> shows the ninth modified example of the stopper <NUM>. In the ninth modified example, the shape of the opening 13a, which corresponds to the first portion 31a of the stopper member <NUM> is a square. The first portion 31a of the stopper member <NUM> is rectangular, and a length E1 of a long side of the rectangle in the Fx, Fy and Mz directions is longer than a length E2 of a side in the Fz, Mx and My directions.

In the stopper member <NUM>, an interval between a short side of the rectangle and the inner surface of the opening 13a is L12, and an interval between a long side of the rectangle and the inner surface of the opening 13a is L11.

According to the eighth and ninth modified examples, an effect similar to those of the first to seventh modified examples can be obtained.

Claim 1:
A force sensor (<NUM>) characterized by comprising:
an elastic body (<NUM>), wherein the elastic body (<NUM>) comprises:
a first structure (<NUM>-<NUM>) including three or more first elastic portions (<NUM>-<NUM>) deformable in six axial directions;
three or more second structures (<NUM>-<NUM>) being arranged around the first structure at equal intervals, each second structure (<NUM>-<NUM>) including two second elastic portions (<NUM>-<NUM>) deformable in the six axial directions and a relay portion (<NUM>-<NUM>) connected between the two of second elastic portions (<NUM>-<NUM>), deformable in the six axial directions;
for each second structure (<NUM>-<NUM>) two third structures (<NUM>-<NUM>) are provided, each third structure (<NUM>-<NUM>) being connected between the respective relay portion (<NUM>-<NUM>) of the second structure (<NUM>-<NUM>) and respective one of the first elastic portions (<NUM>-<NUM>) of the first structure (<NUM>-<NUM>); and
for each second structure (<NUM>-<NUM>) a strain sensor (<NUM>) being connected between the first structure (<NUM>-<NUM>), located between the two respective first elastic portions (<NUM>-<NUM>), and the respective relay portion (<NUM>-<NUM>) wherein the strain sensor (<NUM>) is located between the two respective third structures (<NUM>-<NUM>) so as to be parallel to the two third structures (<NUM>-<NUM>).