JP2011183513A - Apparatus and method of controlling gripper - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce consumption energy of an electric motor while keeping high gripping force so as to attain excellent durability. <P>SOLUTION: A CPU outputs, to a power supply unit, a first current instruction value I<SB>1</SB><SP>*</SP>for generating predetermined gripping force F<SB>a</SB>necessary for gripping an object to be gripped on a pair of fingers. The power supply unit supplies current of a first current value I<SB>1</SB>corresponding to the first current instruction value I<SB>1</SB><SP>*</SP>to the electric motor. In addition, the CPU reduces a current instruction to a second current instruction value I<SB>2</SB><SP>*</SP>with which the predetermined gripping force F<SB>a</SB>is kept based on the hysteresis characteristics of a gear reducer. The power supply unit supplies current of a second current value I<SB>2</SB>corresponding to the second current instruction value I<SB>2</SB><SP>*</SP>to the electric motor. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a gripping device control device and a gripping device control method applied to an industrial robot that performs automatic assembly.

  In recent years, there has been an increasing demand for automation for products having a small and complicated structure such as a camera, and there are many small parts used in these products, and there are a wide variety of parts. Such small parts need to be assembled in a narrow space at high speed and stably, and a gripping device has been proposed to cope with this (see Patent Document 1). The gripping device includes an electric motor, a cam member having a pair of semicircular cam grooves fixed to the output shaft of the electric motor, a pair of fingers having a drive pin that fits in the cam groove of the cam member, and a finger And a guide part for guiding.

JP 2000-233391 A

  However, in the gripping device, it is necessary to maintain the gripping force so that even if an external force is applied to the finger, the finger is not moved by the external force. Therefore, since it is necessary to supply a large current to the electric motor in order to maintain the gripping force, the power consumed by the electric motor becomes large, and the energy consumption will be increased if the gripping / assembling operation is repeated for a long time. There was a problem that (power consumption) becomes large. Moreover, if the energy consumption of the electric motor is large, the amount of heat generated by the electric motor also increases, which may reduce the durability of the gripping device.

  Accordingly, an object of the present invention is to provide a gripping device control device and a gripping device control method that reduce energy consumption of an electric motor and achieve high durability while maintaining a high gripping force. is there.

  The present invention grips an object to be grasped by opening / closing operation by an electric motor, a gear reducer that decelerates rotation of the output shaft of the electric motor, and a rotation / linear motion conversion mechanism provided on the output shaft of the gear reducer. In the control device for a gripping device having a pair of fingers, current supply means for supplying a current having a current value corresponding to the input current command value to the electric motor, and necessary for gripping the gripping object First current control means for outputting a first current command value for generating a predetermined gripping force to the pair of fingers to the current supply means, and a state in which the gripping object is gripped by the pair of fingers, A current command value to be output to the current supply means is smaller than the first current command value, and the pair of fingers with respect to the current supplied to the electric motor caused by the gear reducer Based on the hysteresis characteristic of the lifting force, is characterized in that and a second current control means for reducing said second current command value predetermined gripping force is maintained.

  The present invention also provides an object to be grasped by opening / closing operation by an electric motor, a gear reducer that decelerates rotation of the output shaft of the electric motor, and a rotation / linear motion conversion mechanism provided on the output shaft of the gear reducer. In a method for controlling a gripping device having a pair of fingers for gripping, the electric current of a first current value for generating a predetermined gripping force necessary for gripping the gripping object on the pair of fingers A first step of supplying to the motor; and a current supplied to the electric motor after causing the pair of fingers to generate the predetermined gripping force and gripping the gripping object in the first step. The predetermined gripping force is maintained based on a hysteresis characteristic of the gripping force of the pair of fingers with respect to the current supplied to the electric motor, which is smaller than the current value of 1 and caused by the gear reducer. That is characterized in that it comprises a second step of reducing the second current value.

  According to the present invention, when gripping an object to be gripped by a pair of fingers, the current supplied to the electric motor is reduced based on the hysteresis characteristics of the gear reducer while maintaining the gripping force. Energy consumption is reduced. Therefore, the amount of heat generated by the electric motor is reduced, and high durability can be realized.

It is a perspective view showing the outline of the grasping device and control device concerning a 1st embodiment of the present invention. It is explanatory drawing which shows schematic structure of a holding | gripping apparatus, (a) is sectional drawing of the holding | gripping apparatus which follows the IIa-IIa line | wire shown in FIG. 1, (b) is a perspective view of a gear reducer. It is a block diagram of a control apparatus. It is a figure which shows the hysteresis characteristic of the holding force of a pair of finger with respect to the electric current value of the electric current supplied to an electric motor. It is a flowchart which shows the control action by CPU of the control part of a control apparatus. It is a flowchart which shows control operation of CPU of the control part of the control apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between the electric current value supplied to the electric motor in 2nd Embodiment of this invention, and the output value of an encoder.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
FIG. 1 is a perspective view schematically showing a gripping device and a control device according to the first embodiment of the present invention. 2 is an explanatory view showing a schematic configuration of the gripping device, FIG. 2 (a) is a sectional view of the gripping device along the line IIa-IIa shown in FIG. 1, and FIG. 2 (b) is a diagram of the gear reducer. It is a perspective view. As shown in FIG. 1, the gripping device 1 and the control device 2 are connected by a cable 3, and the control device 2 supplies a current to the gripping device 1 through the cable 3. As shown in FIG. 2A, the gripping device 1 includes an electric motor 12 and a gear reducer 11 that reduces the rotation of the output shaft of the electric motor 12. An encoder 13 that detects the rotation angle (rotation position) of the output shaft of the electric motor 12 is provided on the side opposite to the side where the gear reducer 11 is disposed with respect to the electric motor 12. The electric motor 12, the gear reducer 11, and the encoder 13 are accommodated in the housing 10.

  The electric motor 12 is an AC servo motor. The gear reducer 11 is a planetary gear reducer in the first embodiment. The housing 10 is formed in a box shape, and one surface of the housing 10 is formed of a base member 9 formed with an opening 9a for projecting the output shaft 11a of the gear reducer 11 to the outside.

  The gripping device 1 includes a pair of (two) fingers 4, 4 disposed outside the housing 10, and a rack and pinion mechanism disposed between the gear reducer 11 and the pair of fingers 4, 4. And a rotation / linear motion conversion mechanism 5 constituted by: The rotation / linear motion converting mechanism 5 is provided on the output shaft 11 a of the gear reducer 11, and converts the rotational motion of the output shaft 11 a of the gear reducer 11 into the linear motion of the pair of fingers 4, 4 to convert the pair of fingers 4. , 4 are opened and closed. In the first embodiment, the gripping object W is a small part used in the production of a camera or the like, and in order to obtain a predetermined gripping force using a small electric motor 12 in order to reduce the size of the gripping device 1, A gear reducer 11 is provided. Each finger 4 is formed of a material having elastic characteristics such as stainless steel or iron, and when gripping the gripping object W, each finger 4 grips while being bent by this elasticity.

  As shown in FIG. 1, the rotation / linear motion conversion mechanism 5 has a pinion 6 fixed to the output shaft 11 a of the gear reducer 11. The rotation / linear motion conversion mechanism 5 is fixed to the bases of the pair of fingers 4, meshed with the pinion 6 with the pinion 6 interposed therebetween, and a pair of racks 7 and 7 that convert the rotational motion of the pinion 6 into linear motion. have. In other words, the pair of racks 7 and 7 are arranged opposite to each other with the pinion 6 sandwiched symmetrically about the axis of the output shaft 11a, and linearly move in opposite directions by the rotational movement of the pinion 6. Linear guides 8 are respectively arranged between the racks 7 and 7 and the base member 9. The linear guides 8 and 8 are fixed to the rack members 7 and 7 so that the racks 7 and 7 mesh with the pinion 6 and are fixed to the racks 7 and 7, and the rail portions 8 b and 8 b. And slider portions 8a and 8a that slide along. When the pinion 6 rotates with the rotation of the output shaft 11a of the gear reducer 11 due to the configuration of the rotation / linear motion conversion mechanism 5, the pair of racks 7 and 7 meshed with the pinion 6 are moved along the rail portions 8b and 8b. The pair of fingers 4 and 4 is opened and closed by linear movement in the opposite direction. In the first embodiment, the gripping object W can be gripped by the closing operation of the pair of fingers 4 and 4, and the gripping of the gripping object W can be released by the opening operation. In the first embodiment, since the rotation / linear motion conversion mechanism 5 is a rack and pinion mechanism, the pair of fingers 4 and 4 smoothly open and close, thereby saving power.

  The encoder 13 detects the rotation angle of the output shaft of the electric motor 12 and outputs the number of pulse signals corresponding to the rotation angle, but the rotation angle of the output shaft of the electric motor 12 and the opening and closing of the pair of fingers 4 and 4. There is a correspondence with the position. Therefore, the encoder 13 functions as detection means for detecting the opening / closing positions of the pair of fingers 4, 4 by detecting the rotation angle of the output shaft of the electric motor 12.

  The gear reducer 11 has an input shaft 24 connected to the output shaft of the electric motor 12 as shown in FIG. A sun gear 23 is fixed to the input shaft 24, and the three planetary gears 21, 21, 21 that mesh with the sun gear 23 are fixed to the exterior of the gear reducer 11 by rotating the sun gear 23. Revolving while meshing with the internal gear 22. These three planetary gears 21, 21, 21 are integrally connected to the output shaft 11a via a bearing, and the rotation of the electric motor 12 is reduced by these mechanisms and output to the output shaft 11a. The gear reducer 11 may be configured by combining a plurality of reduction mechanisms (for example, about two to three stages) according to a reduction ratio to be set.

FIG. 3 is a block diagram of the control device 2. The control device 2 includes the encoder 13 described above and a control unit 30 that receives the pulse signal P output from the encoder 13 and outputs a current command value I ^* . That is, information on the rotation angle of the electric motor 12, that is, the number of pulse signals P corresponding to the opening / closing positions of the pair of fingers 4, 4 is input to the control unit 30. Is detected. In addition, the control device 2 receives the current command value I ^* output from the control unit 30 and supplies a power of current value I corresponding to the current command value I ^* to the electric motor 12 as a power supply unit. Part 40 is provided. The control unit 30 includes a CPU 31, a ROM 32, and a RAM 33. The ROM 32 is a storage unit that stores in advance a control program for causing the CPU 31 to control the entire gripping device 1 and various information, and the CPU 31 operates based on the control program stored in the ROM 32. The ROM 32 as the storage means is a rewritable nonvolatile memory such as an EEPROM, but the storage means may be an HDD or the like instead of the ROM, and the storage medium is not particularly limited. The RAM 33 is a work area for temporarily storing calculation results of the CPU 31 and the like.

Here, when the object to be grasped W is grasped by the pair of fingers 4, 4, a load is applied to the gear reducer 11 having many meshed gears. When this load is applied to many gears of the gear reducer 11, distortion and friction are generated in each gear, and the relationship between the current value I of the current supplied to the electric motor 12 and the gripping force F by the pair of fingers 4, 4 is The hysteresis characteristic H is as shown in FIG. That is, the gripping force F by the pair of fingers 4 and 4 with respect to the current value I of the current supplied to the electric motor 12 due to the gear reducer 11 has a hysteresis characteristic H shown in FIG. Therefore, in the first embodiment, the CPU 31 controls the current command value I ^* output to the power supply unit 40 based on the hysteresis characteristic H, and thereby controls the current value I of the current supplied to the electric motor 12.

Hereinafter, the control operation of the CPU 31 based on the control program stored in the ROM 32 will be described with reference to FIG. 4 along the flowchart shown in FIG. First, the CPU 31 outputs, to the power supply unit 40, a _first current command value (gripping command) I ₁ ^* that causes the pair of fingers 4 and 4 to generate _a predetermined gripping force Fa necessary for gripping the gripping target object W. (First current control means). The first current command value I ₁ ^* power supply unit 40 which enter the supplies a first current value I ₁ of the current corresponding to the first current command value I ₁ ^* to the electric motor 12. That is, the first current having a current value _{I 1} for generating a predetermined gripping force _{F a} to the pair of fingers 4,4 are supplied to the electric motor 12 (S1-1). Accordingly, the grasped object W is gripped at a predetermined gripping force _{F a} by a pair of fingers 4, 4 (S1-2: In FIG. 4, the point A). The above steps S1-1 and S1-2 are the first step.

Then, CPU 31 is in a state where the grasped object W was gripped with a predetermined gripping force _{F a} to the pair of fingers 4,4, first current command value current command value ^{I *} to be output to the power supply unit 40 _{I 1} ^* Gradually lower from ^* . Thus, the power supply unit 40, the current value I of the current supplied to the electric motor 12, so that the gradually decreased from the first current value _{I 1} (S2-1). In this case, the hysteresis characteristic H due to reduction gear 11, the gripping force F of the pair of fingers 4,4, even lower the current value I is maintained at a predetermined gripping force F _a (point A-A ' while). Next, the CPU 31 sets the current command value I ^* output to the power supply unit 40 to be smaller than the first current command value I ₁ ^* and maintains the predetermined gripping force F _a based on the hysteresis characteristic H. It was reduced to the current command value I ₂ ^*, to stop the decrease of the current command value I ^*. In other words, the power supply unit 40, the current supplied to the electric motor 12, the first smaller than the current value I _1, and a second current value predetermined gripping force F _a on the basis of hysteresis characteristic H is maintained I ₂ Until the current value I is reduced (S2-2: point A ′ in FIG. 4). Thereby, the current command value I ^* becomes the second current command value I ₂ ^* , and the current value I of the current supplied to the electric motor 12 becomes the second current value I ₂ . The CPU 31 operating based on the control program in the above steps S2-1 and S2-2 functions as the second current control means, and these S2-1 and S2-2 correspond to the second step.

Here, the first current value I ₁ and the second current value I ₂ , that is, the first current command value I ₁ ^* and the second current command value I ₂ ^* are the components to be gripped (the gripping object W). Determined by experimentation according to The first current value I ₁ (first current command value I ₁ ^* ) is determined as a current value (current command value) that becomes _a predetermined gripping force Fa necessary for actually gripping the gripping target object W. . The second current value I ₂ (second current command value I ₂ ^* ) is determined based on the measurement result of the hysteresis characteristic H by experiment or the like. More specifically, the relationship between the first current command value I ₁ ^* and the second current command value I ₂ ^* is stored in advance in the ROM 32 serving as storage means. That is, the second current command value I ₂ ^* is a fixed value set using information on the hysteresis characteristic H measured in advance. Incidentally, the first relation between the current command value _I ^{1 *} and a second current command value _I ^{2 *,} the second current command value _I ^{2 *} is identified for the first current command value _I ^{1 *} What is necessary is just to be possible, for example, what is necessary is just to memorize | store beforehand in ROM32 as a computing equation, a table, etc. This storage operation to the ROM 32 need only be performed once before a series of assembly jobs are repeatedly executed. Further, if the object to be grasped W is specific and is not scheduled to be changed, the ROM 32 may not be able to rewrite the current command values I ₁ ^* and I ₂ ^* , and the current command value I ₁ ^* , I ₂ ^* may be stored.

In step S1-1, the CPU 31 reads the first current command value I ₁ ^* with reference to the ROM 32, gradually increases the read current command value I ₁ ^* to the read _first current command value I ₁ ^*, and outputs it to the power supply unit 40. . In steps S2-1 and S2-2, the ROM 32 is referred to, the second current command value I ₂ ^{* corresponding} to the first current command value I ₁ ^{* is} read from the ROM 32, and the read second current command is read out. The current command value is gradually decreased to the value I ₂ ^* and output to the power supply unit 40.

Above, in the first embodiment, when gripping the gripping target W by a pair of fingers 4,4, while maintaining the gripping force F to a predetermined gripping force F _a, based on the hysteresis characteristic H of the gear reducer 11 Thus, the current value I of the current supplied to the electric motor 12 is reduced by ΔI. Therefore, the power consumption of the electric motor 12 is reduced and the energy consumption (power consumption) of the electric motor 12 is reduced by the amount of reduction in the current value I of the current supplied to the electric motor 12 by ΔI (= I ₁ −I ₂ ). To do. Thereby, the calorific value of the electric motor 12 is also reduced, and the gripping device 1 can be made highly durable.

  Moreover, in this 1st Embodiment, in order to reduce the electric current value I of the electric current supplied to the electric motor 12, the lock mechanism which locks a pair of fingers 4 and 4 so that a pair of fingers 4 and 4 may not move is provided. There is no need and the structure is simple. Therefore, the gripping device 1 can be reduced in size.

[Second Embodiment]
In the first embodiment, the hysteresis characteristic W is measured in advance, and the second current command value I ₂ ^* is stored in the ROM 32 as the storage unit. However, in the second embodiment, the second current command value I ₂ ^* is stored. A case where the command value I ₂ ^* is automatically set will be described. The configuration of the gripping device is the same as that of the first embodiment, and the control device is the same as that of the first embodiment except that the control program stored in the ROM is different. Therefore, hereinafter, the configuration of the apparatus is the same as that in FIGS. 1 to 3 and will be described with the same reference numerals as those in the first embodiment.

  FIG. 6 is a flowchart showing the control operation of the CPU of the control unit of the control device according to the second embodiment of the present invention. FIG. 7 is a diagram showing the relationship between the current value of the current supplied to the electric motor and the output value of the encoder in the second embodiment of the present invention.

The CPU 31 operates based on a control program stored in the ROM 32. First, the CPU 31 outputs, to the power supply unit 40, a _first current command value (gripping command) I ₁ ^* that causes the pair of fingers 4 and 4 to generate _a predetermined gripping force Fa necessary for gripping the gripping target object W. (First current control means). The first current command value I ₁ ^* power supply unit 40 which enter the supplies a first current value I ₁ of the current corresponding to the first current command value I ₁ ^* to the electric motor 12. That is, the first current having a current value _{I 1} for generating a predetermined gripping force _{F a} to the pair of fingers 4,4 are supplied to the electric motor 12 (S1-1). Accordingly, the grasped object W is gripped at a predetermined gripping force _{F a} by a pair of fingers 4, 4 (S1-2: In FIG. 6, the point B). The above steps S1-1 and S1-2 are the first step. This point B corresponds to the point A in FIG.

Next, the CPU 31 gradually lowers the current command value I ^* output to the power supply unit 40 from the first current command value I ₁ ^{* in} a state where the pair of fingers 4 and 4 grips the gripping object W. Go. Thus, the power supply unit 40, the current value I of the current supplied to the electric motor 12, so that the gradually decreased from the first current value _{I 1} (S2-1). In this case, the hysteresis characteristic H due to reduction gear 11, the gripping force F of the pair of fingers 4,4, even lower the current value I is maintained at a predetermined gripping force F _a (point B-B ' while).

Here, the rotation angle of the output shaft of the electric motor 12, that is, the open / close position of the pair of fingers 4 and 4 is detected (S2-2 ': detection step), but the CPU 31 detects that the output value of the encoder 13 is a minute change ΔP. It is determined whether or not it has moved (S2-3 ′). That is, in this step S2-3 ′, the CPU 31 determines the open / close positions of the fingers 4 and 4 when the current of the first current value I ₁ corresponding to the first current command value I ₁ ^* is supplied to the electric motor 12. It is determined whether or not the fingers 4 and 4 are displaced in the opening direction by a predetermined amount as a reference. Here, in the detection step, the encoder 13 detects the open / closed positions of the pair of fingers 4 and 4, and a pulse is output as the detection result. Therefore, the CPU 31 obtains an output value (number of pulses) from the encoder 13 to determine step S2-3 ′. The detection operation by the encoder 13 is performed after step S2-1 in FIG. 6, but is always performed or at a predetermined sampling interval. Then, in the process of lowering the current, but the output value of the encoder 13 is monitored, when the result of determination in step S2-3 'is NO, the output value of the encoder 13 (number of pulses) is a value P _1, The pair of fingers 4, 4 remains stationary. Therefore, returning to step S2-1, the current value I is lowered.

Thus, CPU 31 can gradually decrease the current command value I ^* from the first current command value I ₁ ^*, gradually the current value of the current supplied to the electric motor 12 from the first current value I ₁ It is decreasing. Then, upon output values change small change amount ΔP of the encoder 13 (S2-3 ': YES), CPU31 has the current value I of the current supplied to the electric motor 12 and the second as a current value _{I 2} (S2- 4 ′), stopping the current reduction (S2-5 ′). At this time, it becomes a point B ″ in FIG. That is, the second current value I ₂ determined here is the minimum current value that can be held by the gripping force F in the hysteresis characteristic H in FIG.

Specifically, the CPU 31 uses the opening / closing positions of the fingers 4 and 4 when the current of the first current value I ₁ corresponding to the first current command value I ₁ ^* is supplied to the electric motor 12 as a reference position. Yes. Then, CPU 31 may continue to lower the current command value ^{I *} from the first current command value _I ^{1 *,} gradually lowering the current value I of the current supplied to the electric motor 12. Then, the CPU 31 uses the current command value I ^* output when the encoder 13 detects that the fingers 4 and 4 are displaced in the opening direction by a predetermined amount from the reference position as the second current command value I. ₂ ^* As shown, stop decreasing the current command value. Here, if the output value of the encoder 13 at the reference position of the fingers 4 and 4 is P ₁ , the predetermined amount of displacement of the fingers 4 and 4 is very small from the output value (number of pulses) P ₁ output from the encoder 13. This corresponds to the change amount ΔP. Thus, the power supply unit 40, while maintaining the pair of fingers 4,4 in a predetermined gripping force F _a, and the current supplied to the electric motor 12 is reduced to a second current value I _2. The CPU 31 that operates based on the control program in the above steps S2-1, S2-3 ′, S2-4 ′, and S2-5 ′ functions as the second current control means, and these steps become the second process. Correspond.

Here, the minute change amount ΔP in the output value of the encoder 13 is about several pulses, and the gripping force F at the fingers 4 and 4 hardly changes by the position change of about several pulses. For example, suppose that the reduction gear ratio of the gear reducer 11 is 1/100, and the encoder 13 is an encoder of 200 ppr. If it is used at 4 times, the detection resolution at the output shaft of the pinion 6 of the rotation / linear motion conversion mechanism 5 is 80000ppr. Assuming the pitch circle diameter Dp of the pinion 6, the resolution in the linear motion after converting the rotational motion into the linear motion is approximately Dp × π / 80000. Assuming that Dp is 10 mm, the resolution at the position after the linear motion conversion by the rack and pinion is about 0.0004 mm, and even if ΔP is 5 pulses, it becomes 0.002 mm. When gripping the object to be gripped W with the gripping force F = 10 N at the opening / closing position of the fingers 4, 4, the 5 pulses at the position of the encoder 13 are only about 0.002 mm at the fingers 4, 4, and the gripping force 10 N is Almost no change. Thus, the gripping force F for gripping the gripped object W by a pair of fingers 4,4 is maintained at a predetermined gripping force F _a. However, the number of pulses of ΔP varies depending on the gripping object W (part) to be gripped, the specifications of the gear reducer 11 and the encoder 13 included in the gripping device 1, and is not limited to the above numerical values.

As described above, in the second embodiment, it is not necessary to measure the hysteresis characteristic H in advance by looking at the minute change amount ΔP of the output value of the encoder 13, and the second current value I _{2 is} minimized. Can be set automatically. As a result, even if the gripping object W (component) to be gripped changes, it becomes possible to automatically minimize energy consumption (power consumption).

  In addition, although this invention was demonstrated based on the said embodiment, this invention is not limited to this. In the above embodiment, the gear reducer 11 is a planetary gear reducer. However, the present invention is not limited to this, and may be a wave gear reducer (so-called harmonic drive (registered trademark)). Since the above-described hysteresis characteristic occurs also in this wave gear reducer, the control in the above embodiment can be applied also to the wave gear reducer.

  Moreover, although the case where the rack-and-pinion mechanism is used as the rotation / linear motion conversion mechanism has been described in the above embodiment, the present invention is not limited to this, and it is sufficient that the rotation motion can be converted into a linear motion.

DESCRIPTION OF SYMBOLS 1 Grasping apparatus 2 Control apparatus 4 Finger 5 Rotation linear motion conversion mechanism 6 Pinion 7 Rack 11 Gear reducer 12 Electric motor 30 Control part 31 CPU (1st current control means, 2nd current control means)
32 ROM (storage means)

Claims (6)

An electric motor, a gear reducer that decelerates the rotation of the output shaft of the electric motor, and a pair of fingers that grips an object to be grasped by opening and closing operation by a rotation / linear motion conversion mechanism provided on the output shaft of the gear reducer In a control device of a gripping device having
Current supply means for supplying a current having a current value corresponding to the input current command value to the electric motor;
First current control means for outputting to the current supply means a first current command value for causing the pair of fingers to generate a predetermined gripping force necessary for gripping the gripping object;
The current command value output to the current supply means in a state where the gripping object is gripped by the pair of fingers is smaller than the first current command value and is caused by the gear reducer, Second current control means for reducing to a second current command value for maintaining the predetermined gripping force based on a hysteresis characteristic of the gripping force of the pair of fingers with respect to a current supplied to the electric motor. A control device for a gripping device. Storage means for storing in advance a relationship between the first current command value and the second current command value based on the measurement result of the hysteresis characteristic;
The second current control means reads out and outputs the second current command value corresponding to the first current command value output from the first current control means from the storage means. The control apparatus of the holding | grip apparatus of 1. Comprising detection means for detecting the opening and closing positions of the fingers;
When the second current control means outputs the second current command value, the current command value is gradually decreased from the first current command value, and a current corresponding to the first current command value is obtained. Current command value output when the detection means detects that the finger has been displaced in a predetermined predetermined opening direction with reference to the opening / closing position of the finger when a current of a value is supplied to the electric motor 2. The control device for a gripping device according to claim 1, wherein a decrease in the current command value is stopped with the second current command value as the second current command value. An electric motor, a gear reducer that decelerates the rotation of the output shaft of the electric motor, and a pair of fingers that grips an object to be grasped by opening and closing operation by a rotation / linear motion conversion mechanism provided on the output shaft of the gear reducer In a control method of a gripping device having
A first step of supplying, to the electric motor, a current having a first current value that causes the pair of fingers to generate a predetermined gripping force necessary to grip the gripping object;
After generating the predetermined gripping force on the pair of fingers in the first step and gripping the gripping object, a current supplied to the electric motor is smaller than the first current value, and A second step of reducing to a second current value at which the predetermined gripping force is maintained based on a hysteresis characteristic of the gripping force of the pair of fingers with respect to a current supplied to the electric motor caused by the gear reducer; A method of controlling a gripping device, comprising:   The method of controlling a gripping device according to claim 4, wherein the second current value is a fixed value set using information on the hysteresis characteristic measured in advance. A detection step of detecting the opening and closing position of the finger,
The second current value is a current value when the detection step detects that the finger has been displaced in a predetermined predetermined opening direction from the opening / closing position in the first step. The control method of the holding | gripping apparatus of Claim 4.

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