JPH03154794A - Detecting method of work holding state - Google Patents

Abstract

PURPOSE:To surely detect the holding state of a finger, by detecting the completion of the work holding in the case of no movement of a finger and detecting the work holding being not performed in the case where there is any movement. CONSTITUTION:Fingers 18a, 18b are moved to the position where a work is held according to the shape of the work. The fingers are driven further with a weak force so as to hold the work. The presence of the movement of the fingers 18a, 18b by this driving movement is detected by a rotary encoder 22. In this case, a control unit 28 recognizes the work being held in the case of no movement of the fingers 18a, 18b and decides the work being not held in the case where there is any movement.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a workpiece gripping state detection method for detecting a state in which a workpiece is clamped by fingers.

[Prior Art] Conventionally, a workpiece gripping state detection method for detecting a state in which a workpiece is clamped by fingers uses, for example, a limit switch, an optical fiber sensor, a proximity sensor, etc.
Based on the detection results from these switches and sensors, the gripping state of the workpiece by the fingers is detected.

[Problems to be Solved by the Invention] However, when such a detection method is applied to, for example, a general-purpose finger mounted on an NG machine tool, a problem arises. That is, this general-purpose finger has a single configuration,
It is configured to be able to grip various parts and is widely used. Here, depending on the arrangement position of a sensor or the like for detecting the gripping state of the workpiece by the fingers, there may be a case where the gripping state cannot be detected depending on the gripping state of the workpiece or the gripping position.

Specifically, as shown in FIG. 5A, when a cylindrical first workpiece b is gripped by the fingers a, a part of the first workpiece b faces the sensor C. With this shape, it becomes possible to detect the gripping state of the first workpiece b of almost any size through this sensor C. However, as shown in FIG. 5B, when a second workpiece d having a stepped portion is gripped by the finger a, the second workpiece d does not face the sensor C, so the sensor C is It becomes impossible to detect the gripping state through the grip.

As a result, it becomes necessary to specially prepare a finger equipped with a sensor for the second workpiece d. In other words, if the fingers themselves are configured, it is possible to grip workpieces of various shapes, but when trying to detect the gripping state, the scope of application is extremely narrowed and the applications are limited. Problems have been pointed out.

This invention was made in view of the above-mentioned problems, and an object of the invention is to be able to reliably grip a conventional finger without changing its configuration and without being equipped with a sensor. It is an object of the present invention to provide a workpiece gripping state detection method that can reliably detect the gripping state of fingers.

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the purpose, the workpiece gripping state detection method according to the present invention includes moving the fingers to a position where the workpiece is gripped according to the shape of the workpiece. a first step of moving; a second step of pushing and moving the fingers to further grip the workpiece with a weak force; and a third step of detecting whether or not the fingers have moved due to this second step; This third step is characterized by a fourth step of detecting completion of gripping the workpiece when there is no movement of the fingers, and detecting that gripping of the workpiece is not performed when there is movement of the fingers. .

[Embodiment] Hereinafter, the configuration of a finger device to which an embodiment of the work gripping state detection method according to the present invention is applied will be described in detail with reference to FIGS. 1 to 4 of the accompanying drawings.

As shown in FIG. 1, a finger device 10 to which an embodiment of the workpiece gripping state detection method is applied includes a main body 14 connected to an arm 12 of an NC machine tool (not shown). The main body 14 is formed of a casing with an open lower side, that is, it is made up of a horizontal piece 14a located on the upper side and left and right vertical pieces 14b and 14c that fall from both left and right ends of this horizontal piece 14a, respectively. It is configured.

A pair of guide rods 16a, 16't are arranged in a state in which both ends are fixed to these left and right vertical pieces 14b, 14c, respectively, and extend vertically parallel to each other and along the horizontal direction. has been done.

These upper and lower guide rods 16a and 16b allow the pair of finger members 18a to slide freely along the horizontal direction.
, 18b are supported. These finger members 18a
, 18b are formed to extend along the vertical direction.

Here, a reversible servo motor 2o as a drive source for driving the pair of finger members 18a and 18b to move away from and approach each other is mounted on the vertical piece 14c on the right side in the figure of the main body 14, as shown in the figure. The drive shaft is attached so that it rotates around a horizontal axis. A rotary encoder 22 for detecting the amount of rotation is attached to the servo motor 2o so that the amount of rotation can be accurately specified.

A feed screw 24 is integrally connected to a drive shaft (not shown) of the servo motor 20. Here, the feed screw 24 is composed of a normal threaded portion 24a located to the left in the figure from the center and a reverse threaded portion 24b located to the right. - On the other hand, the above-mentioned pair of finger members 18a
, 18b, the left finger member 18a has a screw hole portion 26a that is screwed into the normal thread portion 24a, and the right finger member 18b has a screw hole portion that screws into the reverse thread portion 24b. A portion 26b is formed respectively.

In this way, the left finger member 18a is connected to the forward threaded portion 24.
a, the right finger member 18b is also connected to the reverse threaded portion 24.
By screwing the feed screws 24 into the respective finger members 18a, the feed screws 24 are rotated clockwise.
, 18b are separated from each other, and the gripped workpiece is released. Further, by rotationally driving the feed screw 24 in the counterclockwise direction, both finger members 18
a% 18b will be close to each other, and the workpiece will be gripped between both finger members 18a and 18b.

Here, the servo motor 2o is connected to a control unit 28 of the NC machine tool, so that its rotational drive amount can be accurately controlled. Further, the rotary encoder 22 is also connected to this control unit 28 and outputs the detection result of the rotation amount of the servo motor 20 to it.

In the finger device 10 configured as described above, a method for detecting a workpiece gripping state, which is a feature of the present invention, will be described below.

First, when precision machining a workpiece W using this NC machine tool, the finger device 10 provided on this NC machine tool
are made to grip a workpiece W having a predetermined shape. For this reason, the finger device IO is set in advance so that both finger members 18a, 18b are separated by the maximum distance. From this maximum separation state, the control unit 28 inputs the external dimensions of the workpiece W to be machined (specifically, the external dimensions of the workpiece W to be gripped by both finger members 18a and 18b) via an input device (not shown). Enter. In response to this input, the control unit 28 sets the first target position of both finger members 18a, 18b to a position sufficient to grip the work W between them. The control unit 28 then activates the servo motor 20 to rotate the drive shaft of the servo motor 20 and therefore the feed screw 24 counterclockwise to both finger members 18 .
a and 18b are rotated by the number of rotations required to move them to the first target position.

Here, when driving this servo motor 20, the position gain is a large value, for example, the finger members 18a, 18
The motor torque required to move b by l mm is set to 2 kg-cm. - As a result, both finger members 18a and 18b are brought closer to each other, and as shown by solid lines in FIG. 2, the workpiece W is moved closer to both finger members 18a.
, 18b.

When the servo motor 20 set to such a large position gain rotates by the number of revolutions necessary to grip the workpiece W, that is, both finger members 8a.

When 18b is moved by a distance necessary to grip the workpiece W, both finger members 18a and 18b are brought to the first target position, and at this point, the drive of the servo motor 2o is stopped.

After the servo motor 20 stops driving, the position gain is a small value, for example, the finger member 18a.

The motor torque required to move 18b by 1 mm is set to 0.4 kg-am. This small position gain causes the servo motor 20 to rotate counterclockwise again.

Here, at the time when this position gain is changed to a small value, the target positions of both finger members 18a and 18b are changed from the first target position to the second target position set inside this (see FIG. (in which both finger members 18a and 18b are brought to the position shown by the dashed line).

That is, the second target position of both finger members 18a, 18b by the restarted servo motor 20 is set to a value slightly smaller than the external dimensions of the workpiece W described above, for example, 90% of the set external dimensions of the workpiece W. It is automatically set to the value.

As a result, when the workpiece W is not actually gripped by both finger members 18a and 18b, both finger members 18
a and 18b are moved closer together by the drive of the servo motor 20. This movement state is detected via the rotary encoder 22, and the detection result is sent to the control unit 28. Here, the control unit 28 includes both such finger members 18a.

Upon receiving a detection signal indicating that the finger member 18b has moved, it is recognized that the workpiece W is not actually gripped between the finger members 18a and 18b, and a predetermined warning operation is started.

On the other hand, if the rotary encoder 22 does not output a detection signal indicating that both finger members 18a, 18b have moved even after a predetermined period of time has elapsed even though the servo motor 20 has been started, the control unit 28 Finger member 18a.

It is recognized that the workpiece W is actually held between the positions 18b and 18b.

Then, the control unit 28 changes the target positions of the finger members 18a, 18b by the servo motor 20 from the second target position to the original first target position again. As a result, the output of the control signal that attempts to drive the servo motor 20 is stopped, and both finger members 18a, 18b
The starting state of the servo motor 20 is stopped while the workpiece W is not actually moved, in other words, the gripping state of the workpiece W is not released.

After this, the position gain by the servo motor 20 is returned to a large value of 2 kg-Cm, and the series of gripping operations is completed.

As described in detail above, according to this embodiment, when the workpiece W is gripped by the finger device 10, detection as to whether or not the workpiece W is actually gripped by the finger device IO is performed using a sensor as in the conventional method. Without using the finger members 18a, 18b, the finger members 18a, 18b are further pushed and moved so as to grip the workpiece W with a weak force, the presence or absence of movement of the finger members 18a, 18b is detected, and if there is no movement of the finger members 18a, 18b, the workpiece is This detects the completion of gripping the workpiece W, and detects that the workpiece W is not gripped if there is movement.

In particular, in this embodiment, both finger members 18a
, 18b to the first target position is set to be performed using a large value of position gain, so that positioning accuracy is maintained satisfactorily.

On the other hand, since the movement of both finger members 18a and 18b from the first target position to the second target position is set to be performed using a small value of position gain, this may cause damage to the workpiece W. There is no fear.

In this way, in this embodiment, without changing the configuration of the conventional finger device and by slightly changing the control procedure in the control unit 28, it is possible to operate the device shown in FIGS. 3A and 3B without using the sensor. As shown in the figure, the gripping states of workpieces W of various shapes can be reliably detected.

It goes without saying that this invention is not limited to the configuration of the one embodiment described above, and can be modified in various ways without departing from the gist of the invention.

For example, in the embodiment described above, both finger members 18a and 18b are moved to the first target position, and then both finger members 18a and 18b are moved to the first target position.

Although it has been explained that weakening the moving force of 18b is carried out by setting the position gain to a small value, the present invention is not limited to this, and for example, the structure may be configured as shown as a modified example in FIG. 4. Also good.

That is, in this modification, the servo motor 20 has
The first constant current device 3o is switchably connected to the second constant current device 34 via a changeover switch 32. Here, the first constant current device 30 is set to flow a strong current similar to when a large position gain of 2.0 kg-cm is achieved in the above-described embodiment, and the second constant current device 34 is A similar weak current is set to flow when a small position gain of 0.4 kg-cm is achieved.

In this way, in the above-mentioned embodiment, the magnitude of the gripping force by both finger members 18a and 18b is controlled by changing the position gain, whereas in the second modification, the magnitude of the gripping force by the finger members 18a and 18b is controlled directly. You may configure it so that it can be achieved by changing it yourself.

[Effects of the Invention] As described in detail above, the workpiece gripping state detection method according to the present invention includes a first step of moving the fingers to a position for gripping the workpiece according to the shape of the workpiece, and a first step of moving the fingers to a position where the workpiece is gripped. A second process in which the workpiece is further gripped and moved by force, a third process in which the presence or absence of movement of the finger is detected by this second process, and the movement of the finger in this third process. The present invention is characterized by comprising a fourth step of detecting completion of gripping the workpiece when there is no movement, and detecting that gripping of the workpiece is not performed when there is movement.

Therefore, according to this invention, it is possible to reliably detect the gripping state of a finger that can reliably grip a conventional finger without changing its configuration and without providing a sensor. A workpiece gripping state detection method will be provided.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing the configuration of a finger device in which an embodiment of the method for detecting a work gripping state according to the present invention is implemented; FIG. A front view showing the gripping position and the second target position: FIGS. 3A and 3B are front views showing the gripping states of workpieces of different shapes; FIG. 4 shows the configuration of a modification of this embodiment. FIGS. 5A and 5B are front views schematically showing a state in which a workpiece is gripped by a conventional finger device. In the figure, 10...finger device, 12...arm, 1
4...Main body, 14a...Horizontal side, 14b
; 14 c... Vertical side, 16a; 16b... Guide rod, 18a, 18b... Finger member, 2o
...Servo motor, 22...Port, -Tary encoder, 24-...Feed screw, 24a...Order thread portion, 24
b-... Reverse threaded part, 26a: 26b... Threaded hole part, 2
8... Control unit, 30... First constant power supply device,
32...switch, 34... second constant power supply device.

Claims (1)

[Claims] A first step of moving the fingers to a position to grip the workpiece according to the shape of the workpiece, and a second step of pushing and moving the fingers with a weak force so as to further grip the workpiece. , a third step of detecting the presence or absence of movement of the fingers in this second step, and a third step of detecting the completion of gripping the workpiece when there is no movement of the fingers, and detecting the completion of gripping the workpiece when there is movement of the fingers. and a fourth step of detecting that the workpiece gripping state is not being held.