JPH04164589A - Work holding device - Google Patents

Abstract

PURPOSE:To perform correct holding motion, holding state detecting motion, by setting holding position and holding force with the dimensional information and/or elastic information of a work. CONSTITUTION:A 1st target position setting means 28D which sets the 1st target position corresponding to the external shape of the work to be held of fingers 18a, 18b, and a 2nd target position setting means 28E setting the 2nd target position at the front part in the holding direction than this 1st target position, are provided. A driving means 20 moving this finger to the 2nd target position passing through the 1st target position is provided, a 1st holding force setting means 28F which sets the holding force of the work at the moving time from the 1st target position of the finger to the 2nd target position to a 1st holding force, and a 2nd holding force setting means 28G which sets the holding force of the work at the movement time to the 1st target position of the finger to the 2nd holding force different from the 1st holding force, are provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a workpiece gripping device that clamps a workpiece with fingers.

[Prior Art] Conventionally, a workpiece gripping state detection device for detecting the 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 NC 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. 7A, 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. 7B, 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.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to reliably maintain the gripping state of the conventional fingers without changing the configuration thereof and without providing a sensor. It is an object of the present invention to provide a workpiece gripping device that can detect a workpiece.

Another object of the present invention is to provide a workpiece gripping device that can reliably detect the gripping state of the fingers without using a sensor by equipping the finger drive control with a new function. It is.

Another object of the present invention is to increase the reliability of gripping the workpiece and to ensure safety when gripping the workpiece by appropriately changing the gripping force of the fingers on the workpiece according to the moving position of the workpiece. Another object of the present invention is to provide a gripping device.

A further object of the present invention is to provide a workpiece gripping device that can perform accurate gripping operations and gripping state detection operations based on dimensional information and/or elasticity information of the workpiece.

[Means for Solving the Problems] In order to solve the above-mentioned problems and achieve the purpose, a workpiece gripping device according to the present invention includes a pair of fingers that are provided so as to be able to move toward and away from each other, and a gripping mechanism of these fingers. The first step is to set a first target position according to the outer shape of the workpiece.
a target position setting means; a second target position setting means for setting a second target position forward of the first target position in the gripping direction;
a driving means for moving the finger through the first target position to a second target position; and a first gripping force that grips the workpiece when the finger moves from the first target position to the second target position. a first gripping force setting means for setting the
The present invention is characterized by comprising second gripping force setting means for setting the gripping force of the workpiece when the fingers are moved to the first target position to a second gripping force different from the first gripping force. .

Further, in the workpiece gripping device according to the present invention, gripping detection means performs an operation of detecting whether or not the workpiece is gripped by the fingers when the fingers move from the first target position to the second target position. It is further characterized by having the following.

Further, the workpiece gripping device according to the present invention is characterized in that the workpiece gripping device further includes warning signal output means for outputting a warning signal when the gripping detection means detects that the workpiece is not gripped.

Further, in the workpiece gripping device according to the present invention, the first target position setting means sets the first target position based on dimensional information of the workpiece to be gripped.

Further, in the workpiece gripping device according to the present invention, the second target position setting means sets the second target position based on elasticity information of the workpiece to be gripped.

Further, in the workpiece gripping device according to the present invention, when the elasticity of the workpiece to be gripped is small, the second target position setting means sets the second target position to a position close to the first target position. However, when the elasticity of the work to be gripped is high, the second target position is set at a position far from the first target position.

Further, in the workpiece gripping device according to the present invention, the first gripping force setting means sets the first gripping force weakly based on a small gripping gain.

Further, in the workpiece gripping device according to the present invention, the second gripping force setting means is characterized in that the second gripping force is set strongly based on a large gripping gain.

Further, in the workpiece gripping device according to the present invention, the first gripping force setting means sets the first gripping force weakly based on a small gripping gain during the gripping detection operation,
During the gripping operation, the first gripping force is set to be strong based on a large gripping gain.

Further, in the workpiece gripping device according to the present invention, the gripping detection means is provided with a reference value depending on the workpiece to be gripped, and the amount of movement of the fingers from the first target position to the second target position is determined by the reference value. It is characterized by detecting that the workpiece is not gripped when the gripping distance exceeds .

Further, in the workpiece gripping device according to the present invention, the gripping detection means may detect, when the amount of movement of the finger from the first target position to the second target position remains within the reference value even if the amount of movement of the finger from the first target position to the second target position exceeds the predetermined time. It is characterized by detecting that a workpiece is being gripped.

[Operation] In the workpiece gripping device configured as described above, after the fingers are once moved to the first target position sufficient to grip the workpiece to be gripped, the fingers are further moved to the first target position set forward in the gripping direction. It is driven to move toward the second target position. If the fingers move beyond a reference value specific to the workpiece to be gripped, it is recognized that the workpiece to be gripped does not actually exist, and an alarm signal is output. On the other hand, if the fingers move to the second target position only within a range that does not exceed the reference value even after the predetermined time has elapsed, it is determined that the fingers are actually gripping the workpiece at the first target position. After that, the workpiece gripping operation is continued.

[Embodiment] Hereinafter, the configuration of an embodiment of a work gripping device according to the present invention will be described in detail with reference to FIGS. 1 to 6 of the accompanying drawings.

As shown in FIG. 1, a workpiece gripping device 1 of this embodiment
0 includes a main body 14 that is connected to an arm 12 of an NC machine tool (not shown). This main body 14 is formed from a casing with an open bottom side. That is, this main body 14 is a horizontal piece 14a located on the upper side, and the left and right vertical pieces 14b, 1, which falls from the left and right ends of this horizontal 14a.
4c.

A pair of guide rods 16a, 16b are arranged vertically parallel to each other and extend horizontally, with both ends fixed to these left and right vertical pieces 14b, 14c, respectively.

A pair of finger members 18a, 18b for gripping a workpiece (not shown) is supported by these upper and lower guide rods 16a, 16b so as to be slidable in the horizontal direction. These finger members 18a, 18b are formed to extend along the up-down direction. Further, in this embodiment, the workpiece is both finger members 18a.
.

18b is set to be held in a pinched state by moving inward from both sides.

Here, a drive motor consisting of a reversible servo motor as a drive source for driving the pair of finger members 18a and 18b to move away from and approach each other is attached to the vertical piece 14c on the right side in the figure of the main body 14. 20 is attached so that it rotates around a horizontal axis on a drive shaft (not shown). A rotary encoder 22 for detecting the amount of rotation is attached to the drive motor 20 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 drive motor 20.

Here, this feed screw 24 has a normal threaded part 24a located to the left in the figure from the center, and a reverse threaded part 24a located to the right.
It is composed of b. The tip of the feed screw 24, that is, the left end in the figure, is rotatably supported by the left vertical piece 14b.

On the other hand, the above-mentioned pair of finger members 18a.

18b, the left finger member 18a has a threaded hole portion 26a that is screwed into the normal threaded portion 24a, and the right finger member 18b has a threaded hole portion that is threaded into the reverse threaded portion 24b. 26b are formed respectively. The feed screw 24 passes through the left and right finger members 18a, 18b with its forward threaded portion 24a and reverse threaded portion 24b screwed into corresponding screw holes 26a, 26b, 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, 18b.

Furthermore, origin sensors 30a and 30b are attached to the inner surfaces of both vertical pieces 14b and 14c, respectively. These origin sensors 30a and 30b receive an ON signal when the corresponding finger members 18a and 18b approach each other, that is,
It is set to output the origin arrival signal. In other words, in this embodiment, both finger members 18a,
The origin position is defined at the position where 18b is opened to the maximum extent.

Here, the drive motor 20 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 2.
8, and the detection result of the rotation amount of the drive motor 20 is output to this.

Next, with reference to FIG. 4, the configuration of the control system in this workpiece gripping device 10 will be explained.

That is, as shown in FIG. 4, the above-mentioned control unit 28 includes a workpiece size information memory 28A in which dimensional information IX of various workpieces is stored in advance, and elasticity information IX of various workpieces.
a workpiece elasticity information memory 28B that stores Y in advance;
Reference value information I for each workpiece in the gripping confirmation operation described later
Z is stored in advance (workpiece reference value information memory 28C).
It is equipped with Here, the dimension information IX of the workpiece is the gripped portion of the workpiece, that is, the finger member 18a.

18b is defined from the mutual separation distance at the parts of the workpiece that the images abut.

Further, this control unit 28 controls the fingers 18a,
A first target position setting section 28D for setting the first target position P1 when driving the movement of the workpiece 18b, the first target position PI from the first target position setting section 28D, and elasticity information from the workpiece elasticity information memory 28B. Based on IY, a second
The target setting section 28E is also provided.

Here, the above-mentioned reference value Z is used as a reference value when determining whether or not the workpiece to be gripped is actually gripped by the pair of finger members 18a and 18b. The distance between the first target position P1 and the second target position P2 (i.e., IP, -P2
+) is set at a predetermined ratio smaller distance depending on each workpiece.

Here, the first target position P1 includes both finger members 18a,
The gripper 18b is set at a position sufficient to lightly abut the gripped portion of the workpiece to be gripped. Also,
The second target position P2 is set based on the above-described first target position P, taking into consideration the elasticity of the workpiece to be gripped. Specifically, for example, when the elasticity is low, that is, the rigidity is high (when the amount of pushing deformation is small, the second target position P2 is set to On the other hand, when the elasticity is high, that is, when the rigidity is small and the amount of pushing deformation is large, the second finger position P2 is set at a position such that the position is 99% of the first target position P1. Part 1ga.

The position is set to be 80% of the separation distance of 18b.

Further, the control unit 28 controls the first target position P to the second target position P for the gripping detection operation based on the workpiece elasticity information IY from the workpiece elasticity information memory 28B described above.
2, and a first gripping gain setting section 28F for setting a smaller first gripping gain G in the movement toward the second target position Wpg from the first target position 51P for the gripping operation of the workpiece. Larger second grip gain G
It further includes a second grip gain setting section 28G for setting 2. In this embodiment, the first gripping gain G used for detecting the gripping state is set to an extremely weak value, for example, the torque Q when moving the finger members 18a, 18b by 1mm is set to 4 kgm, and the The second grip gain G2 used for gripping the workpiece is a relatively strong value, for example, a torque of 2.0 kgrn under similar conditions.
is set to .

Here, these first and second target position setting sections 28D,
28E, and first and second grip gain setting sections 28F, 28
G are both connected to a motor drive control unit 28H that controls specific drive control of the drive motor 20, and here, first and second target position information IP, , IP, and first and second grip gains are connected. Information IGI and IG2 are output. Furthermore, a current position detection unit 281 is connected to the rotary encoder 22 described above, which detects the current position P of the finger members 18a, 18b based on the rotation information IR of the drive shaft of the drive motor 20 from the rotary encoder 22. This current position detection section 28I is configured to output this current position information IP to a motor drive control section 28H and a grip detection section 28J, which will be described later.

This motor drive control section 28H has the above-mentioned first and second
Target position information IP,,IP! and the first and second grip gain information IG, , IG, and the finger member 18a from the current position detection unit 8 28I.

It is configured to output a drive signal to the motor driver 32 according to a predetermined procedure based on the current position information IP of the grip detection section 18b and grip confirmation information IOK, which will be described later, from the grip detection section 28J.

This motor drive control section 28H includes a counter 2.
8K is connected, and for this counter 28K,
It is configured so that the count signal C defined as the number of times of movement from the first target position P1 to the second target position P2 is set to eight. A movement signal generation section 28L is connected to this counter 28K, and when the count signal C reaches "2", a control signal S is sent to the movement signal generation section 28L. It is configured to output . Further, when the control signal S is outputted from the counter 28K, the movement signal generating section 28L outputs a movement start signal M to the movement mechanism 34 for moving and driving the arm 12 of the NC machine tool (not shown). It is configured to do so.

On the other hand, the above-mentioned grip detection section 28J is connected to a workpiece-specific reference value information memory 28C, a rotary encoder 22, a motor drive control section 28H, and a timer 28M. Then, the grip detection unit 28J, based on the reference value information IZ from the workpiece-specific reference value information memory 28C and the current position information IP from the rotary encoder 22,
It is configured to determine whether the finger members 18a, 18b are actually gripping the workpiece by determining the state of movement of the finger members 18a, 18b from the first target position P to the second target position P2. There is.

Specifically, this grip detection section 28J detects the first target position P,
If both finger members 18a and 18b move only within a reference value W within a predetermined time T toward the second target position P2, gripping of the workpiece is detected and gripping confirmation information I
When OK is output to the motor drive control unit 28H and both finger members 18a and 18b move from the first target position P toward the second target position P2 by more than the reference value W,
Detects that the workpiece is not gripped and displays non-gripping confirmation information I
It is configured to output NG to an alarm signal generating section 28N, which will be described later.

Here, since the gripping detection unit 28J detects the gripping of the workpiece based on no movement of both finger members 18a and 18b or movement within a predetermined range, the response of the mechanical part of the drive motor 20 is Delay, feed screw 24 and finger member 18a.

It becomes necessary to take into account the response delay when transmitting the driving force to 18b. Therefore, in this embodiment, timer 2
It is set so that the gripping confirmation of the workpiece is not executed until a predetermined time T, which is measured at 8M, has elapsed.

On the other hand, the above-mentioned alarm signal generating section 28N includes the grip detecting section 2
When receiving the output of the non-gripping confirmation information ING from 8J, it is configured to output an alarm signal A to the alarm device 36.

Here, in this embodiment, the alarm device 36 includes an alarm lamp and an alarm buzzer (not shown),
It is set to give both visual and auditory warnings when the workpiece is not gripped.

In the workpiece gripping device 10 configured as described above,
The workpiece gripping operation in the control unit 28 will be described below with reference to the flowcharts shown in FIGS. 5 and 6.

When precision machining a workpiece W using this NC machine tool, the workpiece gripping device provided on this NC machine tool! At 10,
A work W having a predetermined shape is held. For this reason, first, in step S10, the workpiece W to be held by the workpiece holding device 10 is specified. This specific operation includes information IX and IY about the dimension X and elasticity Y of the workpiece W, respectively. These workpiece size information and workpiece elasticity information are stored in a workpiece size information memory 28A and a workpiece elasticity information memory 28B, respectively.

Then, in step S12, based on the workpiece size information IX stored in the workpiece size information memory 28A,
In the first target position setting section 28D, the first target position P1
Set. Further, in step S14, the workpiece elasticity information IY stored in the workpiece elasticity information memory 28B
and the first target setting section 2 set in step SL2.
Based on the first target position information IP+ from 8D, the second
A second target position P2 is set in the target position setting section 28H.

Furthermore, in step S16, the first gripping gain setting section 28F sets the first gripping gain G based on the workpiece elasticity information IY stored in the workpiece elasticity information memory 28B.
Set 1. Then, in step S18, similarly to step S16, the second gripping gain G2 is set in the second gripping gain setting section 28G based on the workpiece elasticity information IY stored in the workpiece elasticity information memory 28B.

Furthermore, in step S20, it is determined whether or not the workpiece W to be gripped is actually gripped by the finger members 18a and 18b, based on the reference value information IZ stored in advance in the workpiece-specific reference value information memory 28C. Set the standard value 2. Then, in step S22, the count signal C to the counter 28 is reset to rOJ.

After that, in step S24, based on the rotation information IR from the rotary encoder 22, the current position detection unit 28
I, the current position P of the finger members 18a, 18b
, load. Then, in step S26, it is determined whether the current positions P of these finger members 18a, 18b are at the origin position. In this step S26, if it is determined No, that is, the finger member 18a,
18b does not turn on the origin sensors 30a and 30b, respectively, in step 328, the finger member 1
The drive motor 20 is controlled so that 8a and 18b reach the origin position, and the process proceeds to step S30. On the other hand, if it is determined YES in step S26, that is, if the finger members 18a and 18b turn on the origin sensors 30a and 30b, respectively, step S28 is skipped and the process jumps directly to step S30.

In this step S30, the first target setting section 28D
Read the first target position P, set in step S.
31, the second grip gain G2 is read from the second grip gain setting section 28G, and in step S32, the finger members 18a, 18b are moved toward the first target position P read in step S30. So that it moves with a thick second grip gain G2,
The drive motor 20 is driven and controlled. In detail, the drive motor 20 is started, and its drive shaft is therefore moved to the feed screw 2.
4 in the counterclockwise direction, both finger members 18a
, 18b move close to each other and are controlled to move toward the first target snow P1 so as to exhibit the second gripping gain.

Then, in step S34, based on the rotation information IR from the rotary encoder 22, the current position detection unit 28
I, the current position P of the finger members 18a, 18b
X is read, and in step S36, the finger member 18a.

18b has reached the first target position P.

If it is determined NO in this step S36,
That is, if it is determined that the finger members 18a, 18b have not yet reached the first target position P1, the process returns to step S32 described above and the subsequent steps are executed. On the other hand, if it is determined YES in step S36,
That is, the finger members 18a and 18b are at the first target position P1.
If it is determined that this has been reached, the process proceeds to step S38, where the driving of the drive motor 20 is stopped. As a result, the finger members 18a, 18b stop at the first target position P, as shown by solid lines in FIG. That is, both finger members 18a and 18b are stopped in a state in which they are lightly abutted on both end surfaces of the workpiece W, respectively.

From this state, the finger member 18a is further removed.

By moving 18b further inward, a gripping operation of the workpiece W is executed, but in this embodiment, prior to the actual gripping operation of the workpiece W, the workpiece W is attached to the finger member. 18a and 18b, and whether or not it is in a state where it can actually be gripped is determined by simply executing a control procedure without using a gripping sensor or the like.

That is, in step S40, the second target position setting section 2
Read the second target position P2 from 8E, and step S42
In step S44, a smaller first gripping gain G1 is read from the first gripping gain setting section 28F.
At this point, the reference value 2 of the work to be gripped is read from the workpiece reference value information memory 28G. Further, in step S46, the count value C of the counter 28 is incremented by "1", and in step S48
At this point, the timer 28M is started to measure time.

Then, in step S50, the finger member 18a
, 18b moves toward the second target position P2 read in step S40. Thereafter, in step S52, the current position detection unit 28I reads the current positions PK of the finger members 18a, 18b based on the rotation information IR from the rotary encoder 22, and in step S54, the first
The actual moving distance zx of the finger members 18a, 18b from the first target position ff1P is calculated from the difference in distance between the target position P1 and the current positions P of the finger members 18a, 18b read in step S52.

Thereafter, in step S56, the actual movement distance z8 of the finger members 18a, 18b is determined as the distance z8 in step S44.
It is determined whether or not it is smaller than the work reference value Z read in. That is, in step 856, an operation for confirming that the finger members 18a and 18b are gripping the workpiece is performed.

If it is determined No in this step S56, that is, the finger members 18a, 18b have moved significantly as shown by the dashed line in FIG. If it is determined that the workpiece-specific reference value is 2 or more, both finger members 18a
, 18b, and therefore, it is determined that the finger members 18a and 18b have exceeded the reference value 2 and are allowed to move from the first target position P1. In this way, it is determined whether the workpiece is not gripped, and as a result, in step S58, the grip detection section 28J sends the non-grip confirmation information ING to the alarm signal generation section 28N.

Then, in step S60, the alarm signal generator 28
Upon receiving this non-gripping confirmation information ING from N, an alarm signal A is outputted to the alarm device 36. As a result, upon receiving this alarm signal A, the alarm device 36 executes a predetermined alarm operation to notify the operator that the gripping device 10 has not performed a gripping operation on the workpiece. After this,
In step S62, finger members 18a, 18b
The drive motor 2o is drive-controlled so that the motor returns to the origin position P0, and the control unit 28 & il+ operation is completed.

On the other hand, if it is determined YES in step S56 mentioned above, that is, the finger member 18a.

If it is determined that the actual moving distance z8 of the finger member 18b from the first target position P is smaller than the reference value 2 specific to the workpiece, both finger members 18a.

Since the workpiece exists between the positions 18b and 18b, it is determined that the finger members 18a and 18b are only allowed to move from the first target position P1 within a range smaller than the reference value Z. However, as already mentioned above,
Since the actual moving distance Zx may be small due to a response delay, this response delay should be taken into consideration (In step S64, it is determined whether the elapsed time T of the timer 28M started in step 548 is longer than the allowable time T0. to judge.

If it is determined No in this step S64, that is, the elapsed time T from the start of the movement operation from the first target position P1 toward the second target position Pt is the allowable time T.

If it is determined that the
50, execute the following control procedure, and set the elapsed time T.
waits for the allowable time To to elapse. Here, if the actual moving distance Zx exceeds the reference value 2 while waiting for the elapsed time T to pass the allowable time T0, it is determined No in step S56, and the workpiece is W
It will be determined that the object is not grasped.

On the other hand, if YES is determined in this step S64, that is, the elapsed time T from the start of the movement operation from the first target position P1 toward the second target position P2 is the allowable time T. If it is determined that the workpiece W has been exceeded, it is determined that the workpiece W is to be gripped because the actual moving distance Zx has not exceeded the reference value 2 even after the allowable time T0 has been exceeded. As a result, in step S66, the grip confirmation information IOK is transmitted from the grip detection section 28J to the motor drive control section 2.
Output toward 8H. Then, in step S68, upon receiving the gripping confirmation information 10K, the driving of the drive motor 20 is stopped. Then, in step S70, the timer 28M is reset.

In the state in which gripping of the workpiece W is confirmed in this way, in the following control procedure, the finger members 18a,
The actual gripping operation of the workpiece W by 18b is performed.

That is, in step S72, the finger members 18a,
The drive motor 20 is controlled so that the drive motor 18b moves toward the first target position P1 described above. Then, in step S74, based on the rotation information IR from the rotary encoder 22, the current position detection section 28I detects the finger member 18a.

18b is read, and in step 876, the finger members 18a, 18b are moved to the first target position P,
Determine whether or not it has been reached.

If it is determined No in this step S76,
That is, if it is determined that the finger members 18a, 18b have not yet reached the first target position P1, the process returns to step S72 described above and the subsequent steps are executed. On the other hand, if it is determined YES in step S76,
That is, the finger members 18a and 18b are at the first target position P1.
If it is determined that this has been reached, the process proceeds to step S78, where the driving of the drive motor 20 is stopped. As a result, the finger members 18a and 18b return to the first target position P1 and stop.

After that, in step S80, the second gripping gain setting unit 28G sends the second
The grip gain G2 is read, and in step S82,
With this second gripping gain G2, the finger members 18a, 18
The drive motor 20 is driven and controlled so that the point b moves toward the second target position P2. In this way, the workpiece W is held at the second gripping gain G on both sides by both finger members 18a and 18b.
2 will result in a strong grip.

When the gripping operation is started in this manner, the counter value C is incremented by rlJ in step S84.

As a result, in combination with the increment operation in step 846 described above, this counter value C actually indicates "2".

Then, in step S86, the controller waits for an instruction to end the gripping operation, and when the end of the gripping operation is instructed, the driving of the drive motor 20 is stopped in step 588. Then, in step S90, the finger member 18a.

18b is the origin position P. The drive motor 20 is drive-controlled so as to move toward. After that, in step S92, based on the rotation information IR from the rotary encoder 22, the finger member 1 is
Read the current position P8 of 8a and 18b, and step S9
4, the finger members 18a and 18b are at the origin position P.
Determine whether the value has reached 0 or not.

If it is determined No in this step S94,
That is, the finger members 18a and 18b are still at the origin position P0.
If it is determined that this has not been achieved, the process returns to step S90 described above and the following steps are executed. On the other hand, if it is determined YES in step S94, that is, if it is determined that the finger members 18a, 18b have reached the origin position P0, the process proceeds to step S96, where the driving of the drive motor 20 is stopped. As a result, the finger members 18a, 18b stop while returning to the original position P0.

In this way, a series of control procedures related to the gripping operation of the workpiece W in the gripping device 10 is completed, and the control operation returns to the original state.

Next, referring to FIG. 6, a control procedure for outputting the movement signal M from the control unit 28 will be described.

That is, in the above-described series of control procedures related to the gripping operation of the workpiece W, when gripping of the workpiece W actually starts, with this actual start, the movement mechanism 34 of the arm 12 of the NC machine tool It is necessary to move the gripped workpiece W to a predetermined position (it is necessary to start the moving operation of the arm 12).

Therefore, in this embodiment, the movement signal M as a start signal for the movement operation of the arm 12 is used to count the number of times the movement operation from the first target position P1 to the second target position P2 is executed. The value C becomes "2", i.e. the first
The output is made in response to the actual start of the gripping operation defined as the second moving operation from the target position P1 to the second target position P2.

Specifically, as shown in FIG.
reads the count value C from the counter 28K in step 5100, and in step 5102,
It is determined whether this count value C has reached "2" or not. If it is determined No in this step 5102, that is, if the count value C has not reached "2" yet, the process returns to step 5100 and the count value C
Continue reading operation.

On the other hand, if it is determined YES in step 5102, that is, if it is determined that the count value C has become "2", the second target position P2 is moved from the first target position P1 to the second target position P2 for the purpose of grasping the workpiece W. Finger member 18a toward
, 18b has started to be moved, so in step 5104, a movement signal M is output to the movement mechanism 34, and this series of movement signal output procedures is completed.
Return to the original control procedure.

In this way, in this embodiment, there is no need to specifically output a control signal for outputting a movement signal M for starting the movement mechanism 34 (from the first target position P1 to the second target position P1). Count the number of movements towards position P2,
In response to this count value becoming "2", the movement signal M
I am trying to output . As a result, the finger member 18
a.

18b from the first target position P1 to the second target position P2 can be reliably identified by simply counting the number of times without determining whether the movement is a gripping detection operation or an actual gripping operation. It will be possible.

As described in detail above, according to this embodiment, when the workpiece gripping device 10 grips the workpiece W, detection of whether or not the workpiece W is actually gripped by the workpiece gripping device IO is performed as in the conventional method. Without using a sensor, the finger members 18a and 18b are pushed and moved to further grip the work W with a weak gripping force G, and the finger members 18a and 18b are moved so as to further grip the work W.
.

18b detects the presence or absence of substantial movement of the workpiece W according to its elasticity, detects gripping of the workpiece W when there is no movement of the finger members I8a and 18b, and detects the gripping of the workpiece W when there is movement.
is configured to detect that the grip is not being made.

In particular, in this embodiment, both finger members 18a
, 18b to the first target position P1 is set to be performed using the second gripping gain G2 having a large value, so that positioning accuracy is maintained satisfactorily. On the other hand, both finger members 18a and 18b are moved to the first target position P.

Since the setting is such that the second gripping gain G2 is smaller when moving the workpiece W from the second target position P2 to the second target position P2, there is no risk of the workpiece W being damaged due to the gripping confirmation operation of the workpiece W. be.

In this way, in this embodiment, the entire configuration of the conventional workpiece gripping device (without changing the control unit 28
By slightly changing the control procedure in , it becomes possible to reliably detect the gripping states of workpieces W of various shapes, as shown in FIG. 3A, without using a sensor.

Further, in this embodiment, the second target position P2 when performing the grip confirmation operation is changed in accordance with the elasticity information IY of the workpiece W to be gripped. Specifically, when the elasticity Y of the workpiece W is small, the second target position P2 is placed in the immediate vicinity of the first target position P1, and when the elasticity Y is large, the second target position P2 is placed far from the first target position P1. They are set respectively. In this way, since the second target position P2 is set according to the elasticity Y of the workpiece W to be gripped, under an appropriate gripping torque according to the elasticity Y of the workpiece W,
The drive motor 20 will be driven.

In addition, in this embodiment, the reference value Z when performing the grip confirmation operation is uniquely set for each work W to be gripped, and when the elasticity Y is small, the reference value 2 When the elasticity Y is small and the elasticity Y is large, the reference value Z is set large. As a result, if the elasticity Y is small (hard workpiece W), it is immediately determined whether or not the workpiece W is gripped, and if the elasticity Y is large and the workpiece W is soft, the elastic deformation is taken into account. It is determined whether or not the workpiece W is reliably gripped.

Furthermore, in this embodiment, even if the actual movement amount Z of the finger members 18a and 18b from the first target position P is smaller than the corresponding reference value Z, the gripping of the work W can be immediately performed. Rather than judging the state, taking into account the response delay of power transmission, even if a predetermined time T0 has elapsed since the start of movement for gripping structure a from the first target position P, the actual Gripping of the workpiece W is detected when the movement amount Z8 is smaller than the corresponding reference value Z. In this way, by considering the response delay of power transmission,
The gripping confirmation operation for the workpiece W will be executed reliably.

Further, in this embodiment, after the gripping of the workpiece W is detected, instead of continuing the gripping operation of the workpiece W from this detected position, the fingers are moved to the first target position P1. After returning the members 18a, 18b, the finger members 18a, 18b are moved from the first target position P1 toward the second target position P2 with a higher second gripping gain G2, so that the workpiece W can be moved. It is set to perform gripping. In this way,
In this embodiment, the actual gripping operation is started from the first target position P1 where both finger members 18a and 18b lightly contact both ends of the workpiece W.
The gripping force is gradually applied from the first target position P1, and damage to the workpiece W caused by the gripping operation is minimized.

This invention is not limited to the configuration of the one embodiment described above (it goes without saying that various modifications can be made without departing from the gist of the invention).

For example, in the above embodiment, as shown in FIG. 3A, the finger members 18a and 18b are moved close to each other to grip the workpiece W from the outside. The present invention is not limited to such a configuration, but as shown in a modified example in FIG. 3B, the finger members 18a and 18b may be moved apart from each other to extend the workpiece W from the inside. The same can be applied to the case where the grip is held in the same way.

[Effects of the Invention] As described in detail above, the workpiece gripping device according to the present invention includes a pair of fingers that are provided so as to be able to move toward and away from each other, and a first gripper of these fingers that corresponds to the outer shape of the workpiece to be gripped. a first target position setting means for setting a target position; a second target position setting means for setting a second target position forward of the first target position in the gripping direction;
a drive means for moving the workpiece through a target position to a second target position; and a first gripping unit that sets a gripping force of the workpiece to a first gripping force when the fingers move from the first target position to the second target position. force setting means; and said first force setting means of said finger.
The present invention is characterized by comprising second gripping force setting means for setting the gripping force of the workpiece during movement to the target position to a second gripping force different from the first gripping force.

Further, in the workpiece gripping device according to the present invention, gripping detection means performs an operation of detecting whether or not the workpiece is gripped by the fingers when the fingers move from the first target position to the second target position. It is further characterized by having the following.

Further, the workpiece gripping device according to the present invention is characterized in that the workpiece gripping device further includes warning signal output means for outputting a warning signal when the gripping detection means detects that the workpiece is not gripped.

Further, in the workpiece gripping device according to the present invention, the first target position setting means sets the first target position based on dimensional information of the workpiece to be gripped.

Further, in the workpiece gripping device according to the present invention, the second target position setting means sets the second target position based on elasticity information of the workpiece to be gripped.

Further, in the workpiece gripping device according to the present invention, when the elasticity of the workpiece to be gripped is small, the second target position setting means sets the second target position to a position close to the first target position. However, when the workpiece to be gripped has high elasticity, the second target position is set to a position far from the first target position.

Further, in the workpiece gripping device according to the present invention, the first gripping force setting means sets the first gripping force weakly based on a small gripping gain.

Further, in the workpiece gripping device according to the present invention, the second gripping force setting means is characterized in that the second gripping force is set strongly based on a large gripping gain.

Further, in the workpiece gripping device according to the present invention, the first gripping force setting means sets the first gripping force weakly based on a small gripping gain during the gripping detection operation,
During the gripping operation, the first gripping force is set to be strong based on a large gripping gain.

Further, in the workpiece gripping device according to the present invention, the gripping detection means is provided with a reference value depending on the workpiece to be gripped, and the amount of movement of the fingers from the first target position to the second target position is determined by the reference value. It is characterized by detecting that the workpiece is not gripped when the gripping distance exceeds .

Further, in the workpiece gripping device according to the present invention, the gripping detection means may detect, when the amount of movement of the finger from the first target position to the second target position is within the reference value even if the amount of movement of the finger from the first target position to the second target position exceeds the predetermined time. It is characterized by detecting that a workpiece is being gripped.

Therefore, according to the present invention, there is provided a workpiece gripping device that can reliably detect the gripping state of a conventional finger without changing its configuration and without being equipped with a sensor. become.

Further, according to the present invention, by equipping the finger drive control with a new function, the finger can be controlled without using a sensor.
A workpiece gripping device that can reliably detect the gripping state of the fingers will be provided.

Further, according to the present invention, by appropriately changing the gripping force of the fingers on the workpiece according to the movement position of the workpiece, the workpiece gripping bag can increase the certainty of gripping the workpiece and compensate for safety when gripping the workpiece. ! will be provided.

Further, according to the present invention, there is provided a workpiece gripping device that can perform accurate gripping operations and gripping state detection operations based on dimensional information and/or elasticity information of the workpiece.

[Brief explanation of the drawing]

FIG. 1 is a perspective view schematically showing the configuration of a workpiece gripping device in which an embodiment of the workpiece gripping device according to the present invention is implemented; FIG. 2 is a diagram showing the gripping of a workpiece W as a first target position by a finger member. FIG. 3A is a front view showing the gripping state of the workpiece; FIG. 3B is a modification of this embodiment in a manner different from the gripping state shown in FIG. 3A. A front view showing the gripping state of the workpiece; FIG. 4 is a block diagram showing the configuration of the control system of the workpiece gripping device of this embodiment; FIG. 5 is a control procedure for the workpiece gripping operation in the control system shown in FIG. 4. FIG. 6 is a flowchart showing a control procedure for outputting a movement signal; FIGS. 7A and 7B are front views schematically showing a state in which a workpiece is gripped by a conventional workpiece gripping device. In the figure, 10...work gripping device, 12...arm,
14...Body, 14a...Horizontal side, 14b; 14c
...Vertical side, 16a; 16b...Guide rod, 1
8a; 18b... Finger member, 20... Drive motor, 22... Rotary encoder, 24... Feed screw, 24a... Normal threaded portion, 24b... Reverse threaded portion, 2
6a; 26b...Screw hole portion, 28...Control unit, 28A...Workpiece dimension information memory, 28B...Workpiece elasticity information memory, 28C...Workpiece reference value information memory, 28D... First target position setting section, 28E...
- Second target position setting section, 28F... First gripping force setting section, 28G... Second grasping force setting section, 28H... Motor drive control section, 28I... Current position detection section, 28J.・
-Grip detection section, 28K...Counter, 28L...Movement signal generation section, 28M...Timer, 28N...Alarm signal generation section, 30a; 30b...Origin sensor, 3
2...Motor driver, 34...Movement mechanism, 36.
...It is an alarm device. □1 Length C, 7 - Figure 3A Figure 38 Figure 5 (E) Figure 6

Claims (11)

[Claims] (1) A pair of fingers that are provided so as to be able to move toward and away from each other; a first target position setting means for setting a first target position of these fingers according to the outer shape of the workpiece to be gripped; and the first target position. second target position setting means for setting a second target position further forward in the gripping direction; driving means for moving the finger through the first target position to a second target position; and driving means for moving the finger from the first target position to the second target position. a first gripping force setting means for setting the gripping force of the workpiece when moving to the second target position to a first gripping force; and the gripping force of the workpiece when the finger moves to the first target position; Said first
A workpiece gripping device comprising a second gripping force setting means for setting a second gripping force different from the gripping force. (2) The method further comprises gripping detection means for detecting whether or not the workpiece is gripped by the fingers when the fingers move from the first target position to the second target position. A workpiece gripping device according to claim 1. (3) The workpiece according to claim 2, further comprising warning signal output means for outputting a warning signal when the gripping detection means detects that the workpiece is not gripped. gripping device. (4) The workpiece gripping device according to claim 1, wherein the first target position setting means sets the first target position based on dimensional information of the workpiece to be gripped. (5) The workpiece gripping device according to claim 4, wherein the second target position setting means sets the second target position based on elasticity information of the workpiece to be gripped. (6) When the elasticity of the workpiece to be gripped is small, the second target position setting means sets the second target position to a position close to the first target position, and 6. The workpiece gripping device according to claim 5, wherein when the elasticity is high, the second target position is set to a position far from the first target position. (7) The workpiece gripping device according to claim 1, wherein the first gripping force setting means sets the first gripping force weakly based on a small gripping gain. (8) The workpiece gripping device according to claim 7, wherein the second gripping force setting means sets the second gripping force strongly based on a large gripping gain. (9) The first gripping force setting means sets the first gripping force weakly based on a small gripping gain during a gripping detection operation, and sets the first gripping force weakly based on a large gripping gain during a gripping operation. 2. The workpiece gripping device according to claim 1, wherein the gripping force is set to be strong. (10) The gripping detection means is provided with a reference value depending on the workpiece to be gripped, and when the amount of movement of the fingers from the first target position to the second target position exceeds the reference value, the gripping detection means detects the workpiece. 3. The workpiece gripping device according to claim 2, wherein the workpiece gripping device detects that the workpiece is not gripped. (11) The grip detecting means is configured to detect the grip even if the amount of movement of the finger from the first target position to the second target position exceeds a predetermined time.
11. The workpiece gripping device according to claim 10, wherein the workpiece gripping device detects that the workpiece is gripped when the value is within the reference value.