JPS60257335A - Force sensor - Google Patents

Abstract

PURPOSE:To thin the thickness size of a sensor, to change performance by changing the thickness of a plate spring, and to improve a convenient property and an economical property by coupling a pair of plate springs in series and also at a relative angle of 90 deg., and placing radially its plural pieces. CONSTITUTION:Combined plate springs 14-17 are constituted as one body by coupling a pair of plate springs A, B whose section has been formed in the shape of a rectangle, respectively, in series in the longitudinal direction, and also so as to have a relative angle of 90 deg., and installed radially to the outside peripheral part of a holder 13. Each tip part of the plate springs 14-17 is supported so as to be freely slidable, and also freely rotatable by holding parts 18-21, respectively. Also, strain gauges S1-S8 are stuck to each plate spring A, B, respectively. In this state, forces of X, Y and Z directions and moment of the periphery of each axis of X, Y and Z can be derived easily by calculating an output of each strain gauge. In this way, a thin type sensor can be constituted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a force sensor, particularly a six-axis force sensor, used to detect forces and moments in arbitrary directions applied to a hand of a robot.

[Background of the invention]

In conventional robots, force sensors are attached to the hands.
There is little need to detect the axial force, and even if there is a need, the purpose is to detect the weight of the gripped part and the overload in that direction when pressed in one direction, so the first As shown in the figure, in most cases, a simple uniaxial (directional) force sensor 2A, such as a commercially available load cell, is attached to the robot arm 1.

However, in recent years, as robots have come to perform a wide variety of tasks, there is a need to detect force components in arbitrary directions applied to the robot arm 1 and control the robot's movements based on this detected value. The need for shaft sensors is increasing.

FIG. 2 shows a typical example of a conventional six-axis sensor.

In this sensor 2, a strain gauge 4α is attached to a plate spring 3 having a rectangular cross section, and the strain gauge 4α detects the strain of the plate spring 3 caused by a force or moment applied to the plate spring 6. If the cross section of the plate spring 6 is formed into a rectangular shape as shown in FIG. 2<b>, as can be seen from the difference in section modulus,
h) It is easy to deflect in response to the force in the input direction, but it is difficult to deflect in response to the force in the direction B, so it is effective for selectively detecting force in a specific direction, and the output signal of the female strain gauge It is well known that this simplifies the process.

For this reason, in general, a 6-axis force sensor has plate blades 5, 5.6 arranged so that their rectangular cross sections are perpendicular to the X-2 direction, as shown in FIG. 2 (α), and the plates are Ne5,
5.6, many of them are configured to detect force and moment components in the xryz directions.

This structure has the advantage that it is not only easy to design, but also easy to assemble.

When the force sensor is attached to the tip of a robot, the length of the leaf spring 6 affects the thickness of the force sensor. This has the disadvantage that the load torque acting on the hand increases. .

Therefore, this is a problem because the weight of the parts that the robot can grasp is reduced compared to the case where no force sensor is attached. This problem will be explained in detail with reference to FIG.

In FIG. 3, 1 is a four-bot arm, 7 is a wrist that is pivotally attached to the robot arm 1 via a wrist rotation shaft 8, and a cassette arm is attached to this wrist 7. 9 is a part held by the hand 7α of the wrist 7.

If the total weight acting on the center position of the gripping part 9 is W1, the distance between the wrist rotation axis 8 and the rain center of the gripping part 9 is L1, and the load torque acting on the wrist 7 is M, then this M is expressed as follows (1)
It is expressed by the formula.

M=WΦL (1) Therefore, when the force sensor 2A is attached, the allowable load torque of the wrist 7 of the p-borate is
It is desirable to make the thickness dimension of A, that is, the length dimension t of the leaf spring, as small as possible.

However, there is a problem in that t cannot be made extremely small due to limitations in detection ability.

[Purpose of the invention]

The present invention reduces the thickness of the above-mentioned perception sensor to approximately the width of the leaf spring, and also handles changes in detection performance by changing the thickness of the leaf spring, thereby achieving simplicity and economy. The purpose is to improve the

[Summary of the invention]

In order to achieve the above object, the present invention constitutes a combined leaf spring by combining and integrating a pair of leaf springs each having a cross section of 1Ej1 shape in series and having a relative angle of 90°. A strain gauge is attached to the pair of leaf springs.

This device is characterized in that a plurality of combination leaf springs are arranged radially and connected to each other, so that force and moment components in a plurality of directions can be detected.

[Embodiments of the invention]

゛Hereinafter, embodiments of the force sensor of the present invention will be described with reference to the drawings.

In FIGS. 4 and 5, 11 is a robot arm;
12 is a base attached to the robot arm 11, 13
is a holder attached to the center of the base 12, 14-1
Reference numeral 7 denotes a plurality of combination plates (four pieces symmetrically (cross-shaped) horizontally and vertically in the figure) attached radially to the outer periphery of the holder 13, and each of these combination plates 14 to 17 is
A pair of plates AlB each having a rectangular cross section are connected in series in the longitudinal direction and at a relative angle of 90° to form an integral structure. These combination plates 14
- 17 are slidably and rotatably supported by holding parts 18 - 21 consisting of ball bushes attached to a base 27 . Each of the leaf springs A and B of the combination leaf springs 14 to 17 is provided with strain gauges (Ss, S+), (S6.S2), and (S7).
*Ss ) and (Ss r Sa ) are attached, respectively. Further, a working hand or tool (not shown) is attached to the holder 16.

Next, the operation of this embodiment configured as described above will be explained.

Since a working hand or tool is attached to the tip of the holder j3, the combined leaf springs 14 to 17 are deflected by the reaction force exerted by the hand or tool. That is, as shown in Fig. 4, there is an X in the center of the force sensor.
, Y, and Z coordinates, the combined leaf spring 14. Each of the leaf springs A of i6 bends, but the leaf spring B, which is integrally connected to the leaf A, has a large section modulus in the X direction and is rigid, so it hardly bends.

i On the other hand, since the tips of the combination leaf springs 15.17 slide against the respective holding parts 19.21, the leaf springs A and B of the combination leaf springs 15, 17 do not deflect. Therefore, by detecting the output of each strain gauge Ss, Sy attached to each leaf spring A of the combination leaf springs i4, 16, the force in the X direction can be calculated from the sum of both detected values, so the signal It is possible to simplify the processing.

Similarly, due to the deflection of each leaf spring A of the combination leaf springs 15 and 17, the strain gauge s6 attached to each leaf spring A. The force in the Y direction can be calculated from the sum of the outputs of s, and the output of each strain gauge S1 to S4 of each combination leaf spring 14 to 17.

We can calculate the forces in two directions from the sum.

Furthermore, the moment around each axis of the XYZ axes) Mx.

Consider MySMz.

First, considering the moment Mx, each leaf spring B of the combination leaf springs 14 and 16 causes deflection, but the other plate spring A does not cause deflection because it has high rigidity. On the other hand, since the springs A and B of the combination leaf spring 1'5.17 rotate with respect to the holding part 19.21, they do not deflect, so each leaf spring B of the combination leaf springs 14 and 16 has a Twisted strain gauge S1. The moment Mx can be calculated only from the output of S3.

Moment My is the same as above, combination board & imitation 15.
Strain gauge s attached to each leaf spring B of 17
2 Concerned from the output of S4. Further, the moment) MZ can be determined from the outputs of the strain gauges S5 to Se attached to each of the leaf springs A of the combination leaf springs 14 to 17.

The above explanation can be summarized as shown in equation (2) below.

Fx O000tL OαOS+ Fy 00000 (L O(L 52pzh b b
b 0000 Ss Mx CO-C00000S4...(2) My O
1? Of? 0000 S5 Mz 0000 dd-(L-d S6SA8 However, α to d are force conversion coefficients of the strain gauge output.

As mentioned above, a pair of leaf springs each having a rectangular cross-section are connected in series in the longitudinal direction, and the four combined leaf springs are combined at an angle of 90 degrees, in the same plane. By arranging them in a cross shape, force calculation can be easily performed, and a force sensor that is thinner than a conventional six-axis force sensor can be constructed.

That is, as shown in FIG. 6, since the thickness l of the force sensor 2 becomes thinner, the distance L' between the wrist rotation axis 8 of the robot arm 11 and each center of the hand gripped item 9 is changed as shown in FIG. It can be made smaller than the conventional example shown. therefore,
According to this embodiment, assuming that the weight of the item held by the hand is the same, the load torque applied to the robot wrist can be reduced by a factor of L/L' compared to the conventional example.

On the other hand, if the output torque of the robot's wrist is constant,
It is possible to increase the weight of the hand-held item by a factor of L/L'.

Furthermore, according to this embodiment, when changing the maximum or minimum detection force of the sensor, arbitrary detection performance can be easily adjusted by changing only the plate thickness of the leaf spring without changing the external dimensions of the sensor body. This has the advantage that detection performance can be changed in a short time by pre-caulking only the plate springs.

In this embodiment, the base 12 of the sensor is attached to the robot arm 1, but the same effect can be obtained by attaching the holder 13 on the opposite side to the arm 1 and attaching a hand or tool to the base 12. . Furthermore, since the sensor body has a large space in the base 12, it is possible to incorporate an amplifier there. ,
The sensor can be used easily without preparing an external amplifier.

Another embodiment of the invention is shown in FIG. In this example, 3
The only difference is that the combination leaf springs 14 are attached radially to the outer periphery of a triangular holder 13 attached to the center of the base 12, and the other structures are the same. Since there is, I will omit the explanation.

With this configuration, it is possible not only to detect force in six axes, but also to reduce the number of strain gauges. On the other hand, the force calculation operation is complicated.

In addition, when the number of detection axes is four or less, it is possible to detect force by using a structure in which two combination plate springs 14 are symmetrically attached to a holder 13 attached to a base 12, as shown in FIG. It is.

〔Effect of the invention〕

As explained above, according to the present invention, by reducing the thickness of the force sensor to approximately the width of the leaf spring, it is possible to effectively utilize the transport capacity of the robot without reducing it. It is possible.

In addition, changes in detection performance can be handled by changing the thickness of the leaf spring without changing the external dimensions.
It can improve simplicity and economy.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of a conventional force sensor, Figure 2 (α) (/i
) is a perspective view of a conventional 6-axis force sensor and a sectional view of its leaf spring, FIG. 5 is an explanatory diagram of the operation of the conventional force sensor, and FIGS. 4 and 5 show an embodiment of the force sensor of the present invention. A perspective view and a plan view, FIG. 6 is an explanatory view of the operation of the same embodiment, and FIGS. 7 and 8 are plan views of other embodiments according to the present invention. A, B... Leaf spring, S1-S8... Strain gauge, 13... Holder, 14-17... Combination leaf spring, 18-21... Tip portion of combination leaf spring. Representative Patent Attorney Akio Takahashi Figure 1 Figure 2 (a) b (b) Figure 3 A Figure 4 Figure 5 Figure Otsu Rogo Figure γ

Claims (1)

[Claims] 1. A pair of leaf springs each having a rectangular cross section are connected in series and at a relative angle of 90° to form a combined leaf spring; A force sensor characterized in that a strain gauge is attached to each leaf spring, and a plurality of the combined leaf springs are arranged and connected radially to detect force and moment components in multiple directions. 2. Claim 1, characterized in that each base of the plurality of combination leaf springs is radially attached to a holder, and each tip of the combination leaf spring is supported slidably and rotatably. Force sensor as described in section.