TW201940297A - Electric hand and method for grasping target object - Google Patents

Abstract

Provided is an electric hand (1) comprising: a rotary motor (10); a rotary motion member (40); a plurality of translational motion members (50); a guide part (30); and a torque sensor (20). The rotary motion member (40) is connected to a rotor (12) of the rotary motor (10). The translational motion members (50) move translationally in a tangential direction of a circumference centered on a rotation axis (AX) of the rotary motion member (40) accompanying the rotation of the rotary motion member (40). The guide part (30) guides the plurality of translational motion members (50) in directions of their translational motions. The torque sensor (20) detects torque occurring between the guide part (30) and the rotor (11) of the rotary motor (10).

Description

Electric hand and object holding method

The invention relates to a method for holding an electric hand and an object.

An electric hand is known that holds an object (workpiece) by opening and closing two fingers of an electric motor (for example, refer to Patent Document 1). This electric hand has a structure in which an electric motor, a screw, a nut, a pair of rocker arms, and a pair of fingers (holding portions) are sequentially connected. If the nut fitted to the screw rotationally driven by the electric motor reciprocates in the direction of the axis of the screw, a pair of rocker arms will swing, and a pair of fingers will approach each other to hold the object.
[Prior technical literature]
[Patent Literature]

[Patent Document 1] Japanese Patent Laid-Open No. 2016-112661

[Problems to be solved by the invention]

When the object is held by the electric hand while maintaining its shape, the output torque of the electric motor must be controlled so that the holding force of the electric hand becomes an appropriate value. However, in the electric hand disclosed in the aforementioned Patent Document 1, as a mechanism for holding an object, a complicated mechanism such as a link mechanism composed of a screw, a nut, a pair of swing arms, and a pair of fingers is assembled. If a complex mechanism as described above is interposed between the electric hand and the finger of the object to be held, the output torque of the electric motor is consumed by the action of the complex mechanism, and it is difficult to transfer the torque of the electric motor to the finger without damage . In addition, the relationship between the output torque and the holding power of the electric hand is greatly affected by the state of the mechanism.

In such a situation, even if the holding force of the electric hand is directly detected, it is difficult to control the output torque of the electric motor based on the detected value to hold the target object with an appropriate holding force. In addition, even if the output torque of the electric motor is detected and the electric motor is controlled based on the detected value, it is difficult to hold the target object with an appropriate holding force. With the electric hand disclosed in the aforementioned Patent Document 1, it is difficult to hold, for example, a softer person such as tofu in a state of maintaining a shape.

The present invention has been made in view of the above-mentioned actual circumstances, and an object thereof is to provide an electric hand and a method for holding an object that can hold the object with an appropriate holding force.
[Technical means to solve the problem]

In order to achieve the above object, the electric hand of the first aspect of the present invention includes:
Rotary motor
A rotary moving member connected to a rotor of the rotary motor;
A plurality of translational movement members, which accompany the rotation of the rotation movement member, perform translational movement in a tangential direction of the circumference centered on the rotation axis of the rotation movement member to hold the object;
A guide unit, which is under the force of the rotary motion member and the target object, maintains the plurality of translational motion members in a manner that does not perform a motion other than translational motion, and guides the plurality of translational motion members in the direction of its translational motion; And a torque sensor, which is disposed between the guide portion and the stator of the rotary motor, and detects only a torque having a linear relationship with the reaction force of the plurality of translational movement members holding the object.

In this case, the plurality of translational movement members may be rotationally symmetrically arranged with the rotation axis of the rotation movement member as a center.

A linear motion rail may be provided on the guide portion,
Blocks are respectively provided on the plurality of translational movement members, which are guided by the above-mentioned direct-moving rail; and claws, which approach or separate from the target object by translational movement.

Two of the blocks can be guided by the same linear motion rail.

A pinion may be provided on the end of the rotor that is not connected to the rotary motor in the rotary motion member.
A rack is provided on the translation movement member to mesh with the pinion.

A method for holding an object according to a second aspect of the present invention is to drive a rotor of a rotary motor to rotate a rotary moving member,
Along with the rotation of the rotary motion member, a plurality of translational motion members are translated in a tangential direction of a circle centered on the rotation axis of the rotary motion member to hold the object,
With the torque sensor provided between the guide and the stator of the rotary motor, only the torque having a linear relationship with the reaction force of the plurality of translational movement members holding the object is detected. The guide receives the force from the rotary motion member and the target object, and maintains the plurality of translational motion members in a manner that does not perform a motion other than translational motion, while guiding the plurality of translational motion members in the direction of their translational motion,
Based on the detected torque, the rotation of the rotary motor is adjusted, and the target object is held by the plurality of translational movement members.
[Effect of the invention]

According to the present invention, the rotor of the rotary motor is connected to the rotary motion member, and the plurality of translational motion members perform a translational movement by the rotation of the rotary motion member to hold the object. In addition, the torque sensor detects a torque generated between a guide that guides a plurality of translational motion members that receive the rotational force of the rotational motion member in the direction of translational motion and a stator of the rotary motor. If the plurality of translational moving members hold the target object, the opposing force of the holding force is applied from the target object to the translational moving member and transmitted to the rotationally moving member, the rotor and the stator of the rotary motor. This reaction force becomes a torque generated between the stator and the guide of the rotary motor, and is detected by a torque sensor.

With this configuration, the output torque of the rotary motor can be transmitted to the translational movement member without loss to hold the object, and the torque sensor can detect the guide portion as a reference and is equivalent to the translational movement member grip Torque of the counterforce of the holding force of the object. Thereby, a torque equivalent to the holding force of the object to be held can be detected, and the holding force can be accurately controlled based on the torque. As a result, the target object can be held with an appropriate holding force.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the whole figure, the same or equivalent components are marked with the same symbols.

As shown in FIGS. 1A, 1B, and 1C, a part of the electric hand 1 of this embodiment is covered by a cover 2. The stator 11 of the rotary motor 10 is exposed on the + z side of the housing 2. A pair of holding portions 3 protrude from the -z side of the cover 2. In the electric hand 1, the pair of gripping portions 3 grip the target object M and hold it with an appropriate gripping force. Here, the appropriate holding force is a force that exceeds the force of the static friction coefficient of the holding portion 3 and the target object M and the product of the target object M and can hold the target object M without deforming it. In this embodiment, the direction in which the grip portion 3 moves is the x-axis direction.

As shown in FIG. 2 as the AA section of FIG. 1B and FIG. 3 as the BB section of FIG. 1C, the electric hand 1 includes a rotary motor 10 as a driving source, a torque sensor 20 for detecting torque, The guide part 30 guided in the direction of the holding part 3 (FIG. 1A), the rotary motion member 40 performing a rotary motion, and one pair of translation motion members 50 performing a translational motion.

The rotary motor 10 includes a stator 11 and a rotor 12. The stator 11 has a rectangular parallelepiped casing, and the rotor 12 is rotatably held inside the casing. Moreover, the casing of the stator 11 may not be rectangular parallelepiped. The rotor 12 extends from the stator 11 in the −z direction. In FIGS. 2 and 3, the rotation axis AX is parallel to the z-axis direction. Electric power is supplied to the rotary motor 10 from the outside. The rotor 12 rotates around the rotation axis AX with respect to the stator 11 at a torque corresponding to the supplied electric power.

An end portion on the + z side of the torque sensor 20 is fastened and fixed to the stator 11 of the rotary motor 10 by bolts. On the other hand, the end portion on the -z side of the torque sensor 20 is fastened and fixed to the bottom plate 31 constituting the guide portion 30 by bolts. The torque sensor 20 detects a torque around the rotation axis AX generated between the stator 11 of the rotary motor 10 and the guide portion 30 (base plate 31).

The torque sensor 20 is provided with a cylindrical through hole 20 a having a rotation axis AX as a central axis. The rotor 12 of the rotary motor 10 is inserted into the through hole 20a in a rotatable state.

The guide portion 30 guides the translational movement member 50 (the holding portion 3 in FIG. 1A) along the direction of its translational movement, that is, the x-axis direction. In other words, the guide portion 30 restricts the movement of the translational movement member 50 in a direction other than the x-axis direction. The guide portion 30 includes a bottom plate 31, a housing 32, and a linear motion rail 33.

The bottom plate 31 is a flat plate-shaped member made of metal. The bottom plate 31 is connected to other members (for example, a bracket fixed to a building or the like) (not shown), and is a member that serves as a substrate of the guide portion 30. The base plate 31 is provided with a cylindrical through-hole 31 a having a rotation axis AX as a central axis. In a state where the through hole 31 a and the through hole 20 a of the torque sensor 20 are arranged coaxially, the bottom plate 31 is mounted on the torque sensor 20. The torque detected by the torque sensor 20 becomes the torque generated in the stator 11 of the rotary motor 10 with the base plate 31 as a reference.

The casing 32 is attached to the -z side surface of the bottom plate 31. An inner space 32 a is formed by the bottom plate 31 and the casing 32.

The linear motion rail 33 is mounted on the -z side surface of the casing 32. The linear motion rail 33 extends in the x-axis direction orthogonal to the rotation axis AX. As shown in FIG. 3, a groove portion 33 a on the side of the linear motion rail 33 is configured to engage with a pair of gripping portions 3 (translational movement member 50) to guide the groove portion 33 a to extend in the x-axis direction.

The rotary motion member 40 is connected to the rotor 12 of the rotary motor 10. The rotary motion member 40 includes a rotary body 41 and a pinion 42 (see FIG. 4). The rotating body 41 is a cylindrical member made of metal, is connected to the rotor 12 of the rotating motor 10, and extends in the direction of the rotation axis AX. The rotating body 41 enters the internal space 32 a of the housing 32 through the through hole 20 a of the torque sensor 20 and the through hole 31 a of the bottom plate 31.

A recessed portion 32b is provided on the housing 32 around the rotation axis AX, and a bearing 32c is inserted into the recessed portion 32b. The end portion on the -z side of the rotating body 41 is fitted into the bearing 32c. The rotating body 41 rotates around the rotation axis AX in accordance with the rotation of the rotor 12.

The pinion gear 42 is provided at an end portion of the rotor 12 to which the rotary motor 10 is not fixed, that is, an end portion of the rotary movement member 40 (rotating body 41) entering the internal space 32 a of the housing 32. As shown in FIG. 4, the pinion gear 42 is a circular gear that rotates around a rotation axis AX. Therefore, when the rotor 12 of the rotary motor 10 rotates, the rotary body 41 rotates and the pinion gear 42 rotates.

A pair of translational movement members 50 corresponds to a pair of holding portions 3 of FIG. 1. As shown in FIG. 4, the translational movement member 50 is disposed in a two-fold rotationally symmetrical manner with the rotation axis AX of the rotational movement member 40 as a center. The translational movement member 50 performs translational movement along the tangential direction of the circumference (the virtual circular arc C in FIG. 4) centered on the rotation axis AX of the rotational movement member 40 along with the rotation of the rotationally movement member 40.

The translation movement members 50 each include a translation body 51, a rack 52, a block 53, and a claw portion 54.

The translation body 51 is the body of the translational movement member 50 that performs translational movement in the x-axis direction. As shown in FIG. 3, through-holes 32 d are provided on both sides in the y-axis direction of the linear motion rail 33 in the housing 32. The translation body 51 protrudes from the internal space 32a of the housing 32 in the -z direction through the through hole 32d. The through-hole 32d uses the x-axis direction as a length direction so as not to hinder the movement of the translation body 51 in the x-axis direction.

More specifically, as shown in FIG. 4, the translation body 51 extends in the x-axis direction in the internal space 32 a of the housing 32, and bends in the −z direction from the end of the extended portion as shown in FIG. 3. It is folded, and protrudes to the outside of the housing 32 through the through hole 32d. As shown in FIG. 4, the end portion protruding to the outside of the housing 32 is a flat plate-shaped member parallel to the xy plane.

The rack 52 is a linear member that bites teeth in a straight direction. As shown in FIG. 4, the rack 52 is mounted on a portion of the translation body 51 that extends along the x-axis direction in the internal space 32 a of the housing 32. The rack gear 52 is engaged with the pinion gear 42, and the translation body 51 is moved in translation along the x-axis direction by the rotation of the pinion gear 42. More specifically, if the pinion gear 42 rotates, a pair of racks 52 are driven in the reverse direction, and a pair of translation bodies 51 approach or separate from each other.

The block 53 is connected to the + z side surface of the flat plate-shaped portion of the translation body 51 protruding to the outside of the casing 32. As shown in FIG. 3, the block 53 is fitted into the groove portion 33 a of the linear motion rail 33 and is connected to the linear motion rail 33 of the guide portion 30 so as to be slidable in the x-axis direction. The block 53 is guided by the linear motion rail 33 in the x-axis direction. If the translation body 51 performs translational movement in the x-axis direction, the block 53 also performs translational movement in the x-axis direction guided by the linear motion rail 33. In this embodiment, the two blocks 53 are guided by the same straight rail 33.

The claw portion 54 is provided at an end portion below the translation body 51. The claw portion 54 is disposed so as to face the other claw portion 54 in the x-axis direction. The pair of claw portions 54 approach or separate the target object M by translational movement.

The operation of the electric hand 1 of the present embodiment having the above-described configuration will be described. As shown in FIG. 5, when the electric hand 1 is actually used, the control device 60 of the rotary motor 10 and the driving device 70 of the rotary motor 10 must be controlled.

Here, the rotary motor 10 is a stepping motor. When the target object M is being held, the control device 60 outputs a pulse command to the driving device 70 while monitoring the sensor detection value of the torque sensor 20. The driving device 70 drives the rotary motor 10 according to the input pulse command.

For example, as shown in FIG. 6A, if the rotor 12 of the rotary motor 10 is rotationally driven at a torque T1 in accordance with a pulse command, the rotary moving member 40 (the pinion 42) is rotated. Along with the rotation of the rotational motion member 40, a pair of translational motion members 50 (rack rack 52) receives a force F1 from the rotational motion member 40 (pinion gear 42), and along the circumference centered on the rotation axis of the rotational motion member 40 (FIG. 4 The virtual arc C) translates in the tangential direction. The translational movement members 50 move in directions that approach each other.

As shown in FIG. 6B, when there is no target object M between the claw portions 54 of the pair of translational motion members 50, the translational motion member 50 performs translational motion without receiving a reaction force from the target object M. The torque sensor 20 detects a torque generated between the guide portion 30 and the stator 11 of the rotary motor 10. Here, the rotational movement member 40 receives a reaction force F1 'from the translation movement member 50. The torque detected by the torque sensor 20 becomes the reverse torque T1 ′ of the torque T1 of the stator 11 of the rotary motor 10 driving the rotor 12, the rotary motion member 40 and the translational motion member 50.

As shown in FIG. 7A, when the pair of claw portions 54 are in contact with the target object M, the pair of claw portions 54 receive a reaction force F2 ′ from the target object M, and the holding force thereof becomes F2 (F2> F1) larger than the force F1. If the object M is held by the holding force F2, as shown in FIG. 7B, the reaction force F2 'is transmitted from the translational movement member 50 to the rotation movement member 40, and the rotation movement member 40 receives the rotation motor 10 from the translational movement member 50. The torque T2 'of the rotor 12 is reversed.

As shown in FIG. 8A, the torque T2 ′ received by the rotary motion member 40 of the reaction force F2 ′ and opposite to the torque T is transmitted to the stator 11 of the rotary motor 10 via the rotary motion member 40 and the rotor 12 of the rotary motor 10. The bottom plate 31 of the guide portion 30 is fixed to an external member (not shown), and its position and posture are constant. Therefore, a torque T2 ′ is generated between the stator 11 of the rotary motor 10 and the guide portion 30 (the bottom plate 31). The torque sensor 20 detects this torque T2 '.

In the electric hand 1 of this embodiment, the rotary motion member 40 is inserted only between the rotary motor 10 and the translational motion member 50, and no complicated mechanism such as a link mechanism is provided. Therefore, the torque T2 'detected by the torque sensor 20 depends on the reaction force F2' of the holding force of the holding target object M. As shown in FIG. 8B, there is a linear relationship between the counterforce of the holding force and the torque T2 ′ detected by the torque sensor 20. For example, when the reaction force is F1 ', the torque detection value of the torque sensor 20 becomes T1', and when the reaction force is F2 ', the torque detection value of the torque sensor 20 becomes T2'.

When the torque of the control device 60 detected by the torque sensor 20 reaches T2 ', the control device 60 stops the rotation of the rotary motor 10 via the driving device 70. Thereby, the pair of gripping portions 3 grip the target object M while maintaining the gripping force F2. Accordingly, the electric hand 1 detects a torque having a linear relationship with the holding force of the target object M, and controls the torque to appropriately adjust the holding force.

Therefore, even when the target object M is a soft and easily flattened target object M, when the holding force for holding the target object M without being flattened is F2, the holding force for holding the target object M is also not. Since it becomes F2 or more, it can be held without squeezing the target object M.

In addition, the control device 60 may perform feedback control to control when holding the target object M. In this case, while the control device 60 monitors the sensor detection value of the torque sensor 20, performs feedback control with the holding force F2 as a target value, and outputs a pulse command to the driving device 70. The driving device 70 supplies driving power to the rotary motor 10 based on a pulse command. The rotary motor 10 rotates the rotor 12 and the rotary moving member 40 by the supplied driving power. Thereby, a pair of translational movement members 50 perform a translational movement, and a pair of claw portions 54 move in a direction approaching each other.

When the target object M is held by the pair of claws 54, the torque T2 ′ of the reaction force F2 ′ of the holding force F2 is detected by the torque sensor 20. While the control device 60 monitors the sensor detection value of the torque sensor 20, it outputs a pulse such that the holding force becomes F2 to the driving device 70, that is, the sensor detection value of the torque sensor 20 is maintained at T2 '. When instructed, the driving device 70 rotationally drives the rotary motor 10. Thereby, even if the target object M is soft and easy to be crushed, the target object M can be held by the non-squeezing holding force F2.

As described in detail above, according to the present embodiment, the rotor 12 of the rotary motor 10 is connected to the rotary motion member 40, and the plurality of translational motion members 50 that perform translational movements in accordance with the rotation of the rotary motion member 40 hold the object M . In addition, the torque sensor 20 detects a torque generated between the guide 30 that guides the plurality of translational motion members 50 that receive the rotational force of the rotational motion member 40 in the direction of the translational motion and the stator 11 of the rotary motor 10.

If the plurality of translational movement members 50 hold the target object M, the counter force F2 ′ of the holding force F2 is applied from the target object M to the translational movement member 50 and transmitted to the rotation movement member 40, the rotor 12 of the rotation motor 10, The stator 11. This reaction force F2 ′ is detected by the torque sensor 20 as a torque T2 ′ generated between the stator 11 and the guide portion 30 of the rotary motor 10.

With this configuration, the output torque of the rotary motor 10 can be transmitted to the translational movement member 50 without loss to hold the object M, and only the guide 30 can be detected as a reference and the object to be grasped with the translational movement member 50 can be detected. The reaction force F2 'of the holding force F2 of M has a linear torque T2'. Thereby, the holding force of the holding target object M can be detected, and the holding force can be accurately controlled based on the torque T2 '. As a result, the target object M can be held with an appropriate holding force.

According to this embodiment, the gripping force can be maintained at a value such as not squeezing the target object M even when the target object M is soft, such as tofu. As a result, the target object M can be held without being deformed.

Furthermore, in the above-mentioned embodiment, the translational movement member 50 is arranged in a double-rotational symmetry with the rotation axis AX of the rotation movement member 40 as the center, but the present invention is not limited thereto. As shown in FIG. 9A, the translational movement members 50 may be arranged in a triple rotation symmetry. In this case, as shown in FIG. 9B, the target object M is held by the three claw portions 54. The translational movement members 50 may also be arranged in four-fold rotational symmetry or more.

Further, in the above embodiment, the two blocks 53 are made to slide on one linear motion rail 33. Thereby, it is not necessary to provide the linear motion rail 33 for each block 53, and therefore, the electric hand 1 can be miniaturized.

Of course, two linear motion rails 33 may be provided, and the block 53 may be mounted on each linear motion rail 33 in a sliding manner. In addition, when three translational motion members 50 are arranged in a triple rotationally symmetrical manner as shown in FIG. 9A, the translational motion members 50 are respectively provided with linear motion rails 33.

Furthermore, in the above-mentioned embodiment, the pinion gear 42 is provided on the rotary motion member 40 and the rack 52 is provided on the translational motion member 50 to convert the rotary motion of the rotor 12 of the rotary motor 10 into the translational motion of the translational motion member 50. However, the present invention is not limited to this. For example, the grip portion 3 may be driven by another gear mechanism, such as a planetary gear mechanism. The grip portion 3 can also be driven by a cam method having a slot cam or a yoke cam. However, in the electric hand 1, a simpler mechanism that converts the rotational motion of the rotational force of the rotary motor into a linear motion of the holding target object M in one stage is preferable.

The type of the rotary motor 10 is not particularly limited. The rotary motor 10 may be an induction motor or a synchronous motor. The rotary motor 10 may be an AC motor or a DC motor. The rotary motor 10 may be a single-phase motor or a three-phase motor. In the above embodiment, the rotary motor 10 is a stepping motor. Therefore, the commands output to the rotary motor 10 are pulse commands, but the commands applied to the rotary motor 10 are voltage commands, current commands, and the like corresponding to the types of the rotary motor 10.

In addition, the bottom plate 31, the housing 32, and the linear motion rail 33 may be formed of an integral member.

The present invention can be implemented in various embodiments and modifications without departing from the broad spirit and scope of the invention. The above embodiments are used to explain the present invention and do not limit the scope of the present invention. That is, the scope of the present invention is shown by the scope of the patent application rather than the embodiment. Various modifications implemented within the scope of the patent application and the meaning of the equivalent invention are considered to be within the scope of the present invention.
[Industrial availability]

The invention can be applied to electric hands, especially electric hands that hold soft objects.

1‧‧‧ electric hand

2‧‧‧ Cover

3‧‧‧ holding section

10‧‧‧ Rotating Motor

11‧‧‧ stator

12‧‧‧ rotor

20‧‧‧Torque sensor

20a‧‧‧through hole

30‧‧‧Guide

31‧‧‧ floor

31a‧‧‧through hole

32‧‧‧ shell

32a‧‧‧Internal space

32b‧‧‧ recess

32c‧‧‧bearing

32d‧‧‧through hole

33‧‧‧Straight-moving rail

33a‧‧‧Slot

40‧‧‧ Rotating moving member

41‧‧‧Rotating body

42‧‧‧ pinion

50‧‧‧ translational movement component

51‧‧‧ pan body

52‧‧‧ Rack

53‧‧‧block

54‧‧‧Claw

60‧‧‧Control device

70‧‧‧Drive

AX‧‧‧Rotary axis

C‧‧‧Virtual Arc

M‧‧‧ Object

FIG. 1A is a perspective view showing an external appearance of an electric hand according to an embodiment of the present invention.

FIG. 1B is a side view of the electric hand of FIG. 1A.

FIG. 1C is a front view of the electric hand.

Fig. 2 is a sectional view taken along the line A-A of Fig. 1B showing the internal structure of the electric hand.

Fig. 3 is a sectional view taken along the line B-B of Fig. 1C showing the internal structure of the electric hand.

FIG. 4 is a plan view showing a portion where the rotational movement member and the translation movement member engage with each other.

FIG. 5 is a schematic diagram showing a control system of the electric hand of FIG. 1.

FIG. 6A is a schematic diagram showing the forces generated by the rotating movement member and the translation movement member in a state where the object is not held.

FIG. 6B is a schematic view showing a state of the claw portion when the target object is not held.

FIG. 7A is a schematic diagram showing a force applied to a claw portion while a target object is being held.

FIG. 7B is a schematic diagram showing the forces generated by the rotation movement member and the translation movement member in the state of holding the object.

FIG. 8A is a schematic diagram showing a torque detected by a torque sensor.

FIG. 8B is a graph showing the relationship between the reaction force of the holding force and the torque detected by the torque sensor.

FIG. 9A is a diagram showing a modification of the configuration of the translational movement member of the electric hand.

FIG. 9B is a diagram showing a state in which a target object is held.

Claims (6)

An electric hand having: Rotary motor A rotary moving member connected to a rotor of the rotary motor; A plurality of translational movement members, which accompany the rotation of the rotation movement member, perform translational movement in a tangential direction of the circumference centered on the rotation axis of the rotation movement member to hold the object; A guide unit, which is under the force of the rotary motion member and the target object, maintains the plurality of translational motion members in a manner that does not perform a motion other than translational motion, and guides the plurality of translational motion members in the direction of its translational motion; and The torque sensor is disposed between the guide portion and the stator of the rotary motor, and detects only a torque having a linear relationship with a reaction force of the plurality of translational movement members to hold the target object. The electric hand according to claim 1, wherein The plurality of translational movement members are arranged rotationally symmetrically around a rotation axis of the rotation movement member. The electric hand according to claim 1, wherein A linear motion rail is provided on the guiding part, The plurality of translational movement components are respectively provided with: A block, which is guided by the above-mentioned linear motion rail; and The claw portion approaches or separates from the target object by translational movement. The electric hand according to claim 3, wherein The two linear blocks are guided by the same linear motion rail. The electric hand according to any one of claims 1 to 4, wherein In the rotary motion member, a pinion is provided at an end portion of a rotor to which the rotary motor is not connected, A rack is provided on the translation movement member to mesh with the pinion. A method for holding an object, which drives a rotor of a rotary motor to rotate a rotary moving member, Along with the rotation of the rotary motion member, a plurality of translational motion members are translated in a tangential direction of a circle centered on the rotation axis of the rotary motion member to hold the object, With the torque sensor provided between the guide and the stator of the rotary motor, only the torque having a linear relationship with the reaction force of the plurality of translational movement members holding the object is detected. The guide receives the force from the rotary motion member and the target object, and maintains the plurality of translational motion members in a manner that does not perform a motion other than translational motion, while guiding the plurality of translational motion members in the direction of their translational motion, Based on the detected torque, the rotation of the rotary motor is adjusted, and the target object is held by the plurality of translational movement members.