Hand and hand system

A hand includes a pair of finger members disposed separated by an interval and relatively movable in an interval direction, a finger drive unit that moves at least one of the finger members in the interval direction, a pair of holding pads that are provided on the respective finger members, and are supported to face each other and to be rotatable around an axis extending in the interval direction, and a pressing member that is provided to be movable in a direction intersecting a radial direction, at a position separated from the axis in the radial direction, and presses a surface of a workpiece held between the holding pads.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on Japanese Patent Application No. 2018-098192, the content of which is incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hand and a hand system.

BACKGROUND ART

A robot hand that includes paired main fingers and an auxiliary finger is well-known (for example, see PTL 1). The paired main fingers nip a workpiece as a working object from both sides to hold the workpiece, and the auxiliary finger comes into contact with the workpiece at a position different from positions of the main fingers. In the robot hand disclosed in PTL 1, the main fingers are rotated to be brought into close contact with a surface of the workpiece when the main fingers hold the workpiece.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

One aspect of the present invention provides a hand including: a pair of finger members disposed separated by an interval and relatively movable in an interval direction; a finger drive unit that moves at least one of the finger members in the interval direction; a pair of holding pads that are provided on the respective finger members, the pair of holding pads being supported to face each other and to be rotatable around an axis extending in the interval direction; and a pressing member that is provided to be movable in a direction intersecting a radial direction, at a position separated from the axis in the radial direction, the pressing member pressing a surface of a workpiece held between the holding pads.

Another aspect of the present invention provides a hand system including the above-described hand and a control unit. The hand includes a sensor that detects a rotation amount of at least one of the holding pads around the axis, and a pressing drive unit that moves the pressing member, and the control unit controls the pressing drive unit on a basis of the rotation amount detected by the sensor.

DESCRIPTION OF EMBODIMENTS

A hand50and a hand system100according to an embodiment of the present invention are described below with reference to drawings.

FIG. 1is a schematic diagram of the hand system100in which the hand50according to the present embodiment is mounted on a tip end of a robot10. The hand system100according to the present embodiment includes the hand50that can hold a workpiece W as a working object, the robot10that includes the hand50at the tip end and changes a position and an attitude of the hand50, and an imaging apparatus80that captures an image near the hand50.

The robot10is a vertical articulated robot including six joints. The robot10includes motors that rotate the respective joints around respective joint axes, and a control apparatus20that controls the motors.

Note that a coordinate system of XYZ axes illustrated inFIG. 1correspond to a coordinate system of XYZ axes illustrated in and afterFIG. 2.

As illustrated inFIG. 2toFIG. 4, the hand50includes a box base member51, a ball screw (finger drive unit)62that is supported inside the base member51so as to be rotatable around a longitudinal axis, and a finger motor (finger drive unit)53that rotates and drives the ball screw62. In the figures, reference numerals63and64denote bearing blocks that rotatably support the ball screw62.

Further, the hand50includes a fixed finger (finger member)55A fixed to the base member51, and a movable finger (finger member)55B that is supported so as to be movable in a direction along the longitudinal axis of the ball screw62by a linear guide66fixed to the base member51. The movable finger55B is fixed to an unillustrated nut of the ball screw62.

The fixed finger55A and the movable finger55B respectively include fixed-side holding pad (holding pad)54A and a movable-side holding pad (holding pad)54B that are supported so as to be rotatable around a rotation axis (axis) J7parallel to the longitudinal direction of the ball screw62. The fixed-side holding pad54A and the movable-side holding pad54B are disposed so as to face each other between the fixed finger55A and the movable finger55B. The fixed-side holding pad54A includes an encoder (sensor) EN that detects a rotation angle around the rotation axis J7of the fixed-side holding pad54to the fixed finger55A. Note that, in the following, the fixed finger55A and the movable finger55B are also collectively referred to as the “fingers55A and55B”, and the fixed-side holding pad54A and the movable-side holding pad54B are also collectively referred to as the “holding pads54A and54B”.

As illustrated inFIG. 4, the hand50includes a support member52, a pressing motor (pressing drive unit)57, and a ball screw spline58. The support member52extends from the base member51in a direction in which the finger55A and the finger55B extend from the base member51(negative direction in Z axis in figure). The pressing motor57is fixed to the support member52. The ball screw spline58linearly moves a shaft in a direction along the longitudinal axis with respect to the support member52by rotational driving force of the pressing motor57.

As illustrated inFIG. 4, a motor-side gear G1is fixed to a rotary shaft of the pressing motor57. The ball screw spline58includes a shaft and a nut engaging with the shaft. The nut is supported by a support member so as to be rotatable around a longitudinal axis of the shaft. A spline-side gear G2that engages with the motor-side gear G1is attached to the nut with the longitudinal axis of the shaft as a center axis.

Accordingly, when the pressing motor57is driven, the rotational driving force of the pressing motor57is transmitted to the nut of the ball screw spline58by the motor-side gear G1and the spline-side gear G2, and the shaft is moved in a direction along the longitudinal axis with respect to the nut. In the present embodiment, the longitudinal axis of the shaft of the ball screw spline58extends in parallel to a plane that is orthogonal to the rotation axis J7of the holding pads54A and54B at an intermediate position between the two fingers55A and55B, and is provided on side opposite to the base member51with the rotation axis J7in between.

As illustrated inFIG. 4, a cam follower59is supported so as to be rotatable around an axis J8parallel to the rotation axis J7, at tip end of the shaft of the ball screw spline58on the fingers55A and55B side.

The imaging apparatus80illustrated inFIG. 1acquires a captured image near the hand50. In other words, the imaging apparatus80is an apparatus that captures an image of the workpiece W held by the hand50. The captured image acquired by the imaging apparatus80is used for control performed by the control apparatus20described below.

FIG. 5is a block diagram of the hand system100. The control apparatus20includes a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), that are not illustrated inFIG. 5. When the CPU develops a program stored in the ROM to the RAM, the control apparatus20can execute various kinds of control with execution of functions of the program.

The control apparatus20includes a control unit22that controls a rotation amount of the finger motor53and a rotation amount of the pressing motor57, and a storage unit23that stores a three-dimensional model of the workpiece W, an operation program necessary to convey the workpiece W, etc.

The control unit22can detect the workpiece W in the captured image acquired by the imaging apparatus80with use of the three-dimensional model of the workpiece W stored in the storage unit23. When detecting the workpiece W in the captured image, the control unit22determines held positions of the workpiece W held by the respective holding pads54A and54B, based on the three-dimensional model of the workpiece W stored in the storage unit23and the attitude of the workpiece W in the captured image acquired by the imaging apparatus80.

The control unit22controls the motors corresponding to the respective joint axes of the robot10such that the holding pads54A and54B are located below the base member51and the held positions of the workpiece W are located on the rotation axis J7between the holding pads54A and54B.

After the held positions of the workpiece W are located on the rotation axis J7, the control unit22drives the finger motor53to move the movable finger55B toward the workpiece W, and controls the robot10to move the fixed finger55A toward the workpiece W. Accordingly, each of the holding pads54A and54B come close to the corresponding held position of the workpiece W while a relative distance between the fixed-side holding pad54A and the movable-side holding pad54B is reduced. As a result, the holding pads54A and54B come into contact with the respective held positions of the workpiece W, and can hold the workpiece W with sufficient surface pressure applied to the holding pads54A and54B in the rotation axis J7direction.

After the holding pads54A and54B hold the workpiece W, the control unit22drives the pressing motor57to move the cam follower59in a direction approaching the workpiece W along the longitudinal axis of the ball screw spline58.

After the cam follower59approaching the work piece W comes into contact with the workpiece W, the control unit22controls the robot10to raise the hand50and to lift the workpiece W, and causes the robot10to convey the workpiece W in a predetermined attitude. When the attitude of the workpiece W held by the holding pads54A and54B is changed through rotation around the rotation axis J7, the control unit22controls a movement of the ball screw spline58based on the rotation amount detected by the encoder EN and the operation program for conveyance of the workpiece W.

Action of the hand system100including the hand50according to the present embodiment is described along a flowchart of work conveyance processing illustrated inFIG. 6.

As illustrated inFIG. 6, the control unit22detects the workpiece W in the captured image acquired by the imaging apparatus80(step S1). When detecting the work piece W in the captured image (YES in step S1), the control unit22determines the held positions of the workpiece W, and controls the robot10and the hand50in order to cause the holding pads54A and54B to hold the workpiece W (step S2).

The control unit22moves the movable finger55B to cause the holding pads54A and54B to hold the respective held positions of the workpiece W (step S3). Thereafter, the control unit22moves the ball screw spline58to bring the cam follower59into contact with the workpiece W (step S4). After the cam follower59is brought into contact with the workpiece W, the control unit22controls the robot10and the hand50to lift the held workpiece W (step S5).

After the lifted workpiece W is rotated around the rotation axis J7, the control unit22controls the pressing motor57based on the rotation amount detected by the encoder EN. As a result, the shaft of the ball screw spline58is moved in the longitudinal axis direction to press the cam follower59against the workpiece W, which controls the attitude of the workpiece W (step S6). In the workpiece conveyance processing according to the present embodiment, the cam follower59presses the workpiece W such that the variation of the rotation amount detected after the workpiece W is held becomes zero. As a result, the attitude of the workpiece W before and after the holding pads54A and54B hold the workpiece W is maintained.

The control unit22conveys the workpiece W to a predetermined position (step S7) while maintaining the attitude of the held workpiece W, and the work conveyance processing then ends.

According to the hand50of the present embodiment, when the relative distance between the fixed finger55A and the movable finger55B is reduced while the workpiece W is disposed between the fixed finger55A and the movable finger55B, the workpiece W is held by the holding pads54A and54B. In a case where a centroid of the held workpiece W is not located at a position vertically below the rotation axis J7, a moment acts on the workpiece W in a direction in which the centroid of the workpiece W is moved to the position vertically below the rotation axis J7. As a result, the holding pads54A and54B is rotated together with the workpiece W around the rotation axis J7with respect to the fingers55A and55B. Therefore, it is unnecessary for the fingers55A and55B to receive the moment acting on the workpiece W, which makes it possible to downsize the fingers55A and55B while suppressing rigidity to receive the moment.

Further, according to the hand50of the present embodiment, the cam follower59coming into contact with the held workpiece W is rotatable around the axis J8that is parallel to the rotation axis J7. Accordingly, even if the ball screw spline58is moved with respect to the support member52and the contact position of the cam follower59and the workpiece W is changed, friction force occurred at the contact position can be reduced through rotation of the cam follower59around the axis J8. Accordingly, the attitude of the held workpiece W is easily changed, and the driving force of the pressing motor57to change the attitude of the workpiece W can be reduced.

Further, in the hand system100according to the present embodiment, the control unit22controls the pressing motor57based on the rotation amount detected by the encoder EN. Therefore, the control unit22can convey the workpiece W while maintaining the predetermined attitude of the workpiece W based on the attitude of the workpiece W before the holding pads54A and54B hold the workpiece W.

Further, in the hand system100according to the present embodiment, the control unit22causes the holding pads54A and54B to hold the respective held position of the workpiece W that have been determined based on the shape of the workpiece W detected in the captured image acquired by the imaging apparatus80. This determines the held positions at which the direction of the moment around the rotation axis J7applied to the workpiece W by force in the direction in which the ball screw spline58approaches the held workpiece W and the direction of the moment occurred around the rotation axis J7by the own weight of the workpiece W become reversed to each other. Accordingly, the cam follower59can generate the force in the direction to change the attitude of the workpiece W by the pressing force applied to the workpiece W.

Although the example of the hand50and the hand system100has been described in the above-described embodiment, the configuration of the hand50and the hand system100can be variously modified. The hand50according to the above-described embodiment includes only one ball screw spline58that presses the held workpiece W in the direction intersecting the rotation axis J7; however, the hand50may include two or more ball screw splines. For example, a longitudinal axis of a ball screw spline added in addition to the ball screw spline58according to the above-described embodiment may be disposed at a position on the base member51side of the rotation axis J7. In this case, the added ball screw spline moved along the longitudinal axis can apply, to the workpiece W, pressing force that generates a moment in a direction reverse to the direction of the moment around the rotation axis J7applied to the workpiece W by the ball screw spline58. As a result, the attitude of the held workpiece W is controlled irrespective of the held positions of the workpiece W held by the holding pads54A and54B.

In the above-described embodiment, the rotation amount is detected by the encoder EN. Alternatively, for example, a length measurement sensor provided on the support member52may detect a variation of a relative distance between the predetermined position of the held workpiece W and the length measurement sensor, to calculate the rotation amount of the workpiece W.

Although a servomotor is preferably used as the pressing motor57applying the rotational driving force to the ball screw spline58, a normal motor may be also used. Further, as a driving source to move the fingers55A and55B and the cam follower59along the respective longitudinal axes, a hydraulic cylinder may be used. The cam follower59is not an essential component, and the tip end of the ball screw spline58not including a rotation structure may come into contact with the held workpiece W.

Although the relative distance between the fingers55A and55B according to the above-described embodiment is linearly varied by the ball screw62, the fingers55A and55B can be variously modified within the scope of the well-known technology as long as the members are disposed separated by an interval so as to be relatively movable in the interval direction.

Although the ball screw spline58according to the above-described embodiment is a pressing member that is moved in parallel to the plane orthogonal to the rotation axis J7and is linearly moved along the longitudinal axis direction, it is sufficient for the ball screw spline58to move in the direction intersecting the rotation axis J7. For example, the ball screw spline58may be a pressing member that is pivoted around the rotation axis J7or around an axis parallel to the rotation axis J7, or a pressing member that is moved in an axis direction parallel to a plane not orthogonal to the rotation axis J7.

In the above-described embodiment, the held positions of the workpiece W are determined based on the workpiece W detected in the captured image acquired by the imaging apparatus80and the three-dimensional model of the workpiece W stored in the storage unit23; however, specification of the shape of the workpiece W with use of the captured image and determination of the held positions can be variously modified. For example, the three-dimensional model of the workpiece W may not be stored in the storage unit23, and the three-dimensional model and the held positions of the workpiece W may be specified based on the workpiece W detected in the captured image. Further, the hand system100may not include the imaging apparatus80.

As a result, the above-described embodiment leads to the following aspects.

One aspect of the present invention provides a hand including: a pair of finger members disposed separated by an interval and relatively movable in an interval direction; a finger drive unit that moves at least one of the finger members in the interval direction; a pair of holding pads that are provided on the respective finger members, the pair of holding pads being supported to face each other and to be rotatable around an axis extending in the interval direction; and a pressing member that is provided to be movable in a direction intersecting a radial direction, at a position separated from the axis in the radial direction, the pressing member pressing a surface of a workpiece held between the holding pads.

According to the present aspect, when the workpiece is disposed between the pair of finger members disposed separated by the interval and the finger members are relatively moved so as to come close to each other by operation of the finger drive unit, the pair of holding pads provided on the respective finger members are pressed against the surface of the workpiece from both sides, to hold the workpiece between the finger members.

When a centroid of the workpiece is not located at a position vertically below the axis of the holding pads, a rotational moment acts on the workpiece in a direction in which the centroid is moved to the position vertically below the axis, and the holding pads are rotated around the axis. Accordingly, it is unnecessary for the finger members to receive the moment acting on the workpiece, which makes it possible to downsize the finger members while suppressing the rigidity to receive the moment. Further, the pressing member presses the surface of the workpiece at the position separated from the axis, thereby adjusting the attitude of the workpiece around the axis.

In the above-described aspect, the pressing member may include a rod movable in the direction intersecting the radial direction, and a cam follower that is supported to be rotatable around an axis parallel to the axis at a tip end of the rod and is pressed against the surface of the workpiece.

With this configuration, the cam follower inside the pressing member comes into contact with the workpiece held by the holding pads. When the workpiece is rotated around the axis, the position where the workpiece and the cam follower are in contact with each other is changed in some cases. The cam follower is rotatable around the axis parallel to the axis as a rotation center of the workpiece. Therefore, even if the position where the workpiece and the cam follower are in contact with each other is changed, friction force is reduced and the contact position is accordingly smoothly changed. As a result, the attitude of the workpiece held by the holding pads is easily changed, and the force to change the attitude of the workpiece can be reduced.

Another aspect of the present invention provides a hand system including the above-described hand and a control unit. The hand includes a sensor that detects a rotation amount of at least one of the holding pads around the axis, and a pressing drive unit that moves the pressing member, and the control unit controls the pressing drive unit on a basis of the rotation amount detected by the sensor.

According to the present aspect, the change of the attitude before and after holding of the workpiece held by the holding pads is specified based on the rotation amount detected by the sensor. The pressing drive unit moves the pressing member based on the specified rotation amount, which enables the hand to hold the workpiece and to maintain the predetermined attitude of the workpiece based on the attitude of the workpiece before holding.

In the above-described aspect, the control unit may control the pressing drive unit to cause variation of the rotation amount detected by the sensor after the hand holds the workpiece, to become zero.

With this configuration, the hand system can move the workpiece in the attitude same as the attitude before holding of the workpiece.

In the above-described aspect, the hand system may further include an imaging apparatus that acquires a captured image at a vicinity of the holding pads, and the control unit may detect a shape of the workpiece in the captured image, and may cause the holding pads to hold respective positions of the workpiece at which the moved pressing member can press the workpiece, on the basis of the detected shape of the workpiece.

With this configuration, the workpiece is held by the holding pads in a state where the pressing member can press the workpiece, through specification of the shape of the workpiece. As a result, the workpiece is surely pressed by the pressing member, and the attitude of the workpiece can be changed by the pressing member.

The hand according to the present invention achieves an effect to prevent upsizing with a simple configuration.

REFERENCE SIGNS LIST