Robot hand and control method for the robot hand

A robot hand is provided and includes a robot hand control unit that has at least three gripping fingers on a base and controls the robot hand, a plurality of drive mechanisms that brings the three gripping fingers independently close to or separate from each other, a plurality of drive control units that individually controls each of a plurality of drive sources of the plurality of drive mechanisms, and a distribution control unit that is disposed on the base and distributes an instruction value from the robot hand control unit to the plurality of drive control units associated with the plurality of gripping fingers. At least one of the gripping fingers includes an integrally formed drive source and drive control unit.

BACKGROUND

Field

The present disclosure relates to a robot hand and a control method for the robot hand.

Description of the Related Art

In recent years, assembly and processing of industrial products, such as cameras and printers, having small and complicated structures are being automated. Most of the parts used in such a kind of industrial products are small precision parts with various kinds of shapes.

In order to support gripping of such various kinds of parts, a robot hand that can realize various gripping forms adaptable to the parts having different shapes and dimensions is discussed (Japanese Patent Application Laid-Open No. 2017-164832). In Japanese Patent Application Laid-Open No. 2017-164832, the robot hand has three gripping fingers, and in order to realize various gripping forms, drive sources are disposed in all the three gripping fingers, respectively, to drive all the gripping fingers independently.

In order to accurately control the gripping fingers, generally a position detection mechanism such as an encoder is disposed in the drive source of each of the gripping fingers to enable performing feedback control. In Japanese Patent Application Laid-Open No. 2017-164832, however, the feedback control for the plurality of drive sources is executed by one control unit that controls the entire robot hand. Accordingly, control is concentrated in this control unit, and the control becomes complicated.

Further, the number of position detection mechanisms corresponding to the number of the drive sources is necessary to perform the feedback control on the drive sources, respectively. However, the structure of the robot hand becomes complicated if these position detection mechanisms are mounted. For example, the number of cables required for communication with the respective mechanisms increases. These cables are connected to the control unit installed outside a robot device, and are desirably connected so as to pass through a robot arm in order to prevent disconnection. However, since the number of the cables is large, it is difficult to accommodate the cables in the robot arm.

SUMMARY

Embodiments of the present disclosure are directed to a robot hand which is easily controllable and which allows easy routing of the cables even when the number of targets to be controlled increases.

According to an aspect of the present disclosure, a robot device includes a robot hand that has at least three finger portions on a base and grips a target object, and a robot hand control unit that controls the robot hand. Each of the three finger portions includes a plurality of drive mechanisms configured to bring the three finger portions close to or separate from each other independently, a position detection unit configured to detect positions of the three finger portions, and a plurality of drive control units configured to execute feedback control individually on each of a plurality of drive sources of the plurality of drive mechanisms, based on detection results from the position detection unit. The base having the three finger portions includes a distribution control unit configured to distribute a control value from the robot hand control unit to the plurality of drive control units associated with the three finger portions.

DESCRIPTION OF THE EMBODIMENTS

An exemplary embodiment is described below with reference to the accompanying drawings. The exemplary embodiment described below is only an example, and thus a person skilled in the art can appropriately change, for example, details of a configuration without departing from the scope of the embodiment.

FIG. 1illustrates a schematic configuration of a robot system100according to a first exemplary embodiment. InFIG. 1, the robot system100includes a robot arm main body200that is configured as an articulated robot, a robot hand main body300, a system control device400that controls the robot arm main body200and the robot hand main body300, and an external input device500. The robot system100further includes a robot arm control device600and a robot hand control device700that receive an instruction from the system control device400and control the robot arm main body200and the robot hand main body300, respectively.

The robot arm main body200according to the present exemplary embodiment is a six-axis articulated main body. The robot arm main body200includes a base210and six robot arm links201to206. The robot arm links201to206are respectively driven to be rotated about joint axes J1to J6as illustrated by the arrows.

As illustrated in the drawing, the base210and the robot arm link201of the robot arm main body200are connected to each other via a drive source, not illustrated. The robot arm link201has a movable range from an initial attitude to arrow directions around the joint axis J1.

The robot arm link201and the robot arm link202of the robot arm main body200are connected to each other via a drive source, not illustrated. The robot arm link202has a movable range from an initial attitude to arrow directions about the joint axis J2.

The robot arm link202and the robot arm link203of the robot arm main body200are connected via a drive source, not illustrated. The robot arm link203has a movable range from an initial attitude to arrow directions about the joint axis J3.

The robot arm link203and the robot arm link204of the robot arm main body200are connected to each other via a drive source, not illustrated. The robot arm link204has a movable range from an initial attitude to arrow directions about the joint axis J4.

The robot arm link204and the robot arm link205of the robot arm main body200are connected to each other via a drive source, not illustrated. The robot arm link205has a movable range from an initial attitude to arrow directions about the joint axis J5.

The robot arm link205and the robot arm link206of the robot arm main body200are connected via a drive source, not illustrated. The robot arm link206has a movable range from an initial attitude to arrow directions around the joint axis J6.

The robot hand main body300is attached to the robot arm link206at a tip of the robot arm main body200. The robot hand main body300is moved by the robot arm main body200to perform a gripping operation on a target object at any position. A detailed configuration of the robot hand main body300will be described below.

The system control device400controls the overall robot system100. The system control device400transmits an instruction to the robot arm control device600and the robot hand control device700, and the control devices control the robot arm main body200and the robot hand main body300, respectively. The robot hand main body300can be positioned at any three-dimensional position to grip the target object.

The external input device500is a teaching device that transmits data of a plurality of teaching points to the system control device400. The external input device500is used mainly when an operator specifies operations of the robot arm main body200and the robot hand main body300in an installation site of the robot system100.

FIGS. 2A to 2Cillustrate a schematic configuration of the robot hand main body300according to the first exemplary embodiment.FIGS. 2A and 2Bare perspective views of the robot hand main body300.FIG. 2Cis a diagram illustrating a state where a finger portion320is dismounted from a base340. The base340includes a motor345for turning, described below, a motor control unit341that controls the motor345, a distribution control unit350, a sensor operation substrate360, and turning drive shafts392and393.

As illustrated inFIGS. 2A and 2B, the robot hand main body300according to the present exemplary embodiment includes three finger portions310,320, and330mounted to the base340. The finger portions include contact portions381,382, and383, respectively, that come into contact with a target object.

The finger portions310,320, and330include motors315,325, and335, respectively, that bring the contact portions381,382, and383close to or separate from each other. The motors315,325, and335have encoders316,326, and336(FIG. 4), respectively, that measure rotation angles. The provision of the encoders allows positions of the contact portions to be precisely controlled.

The motors315,325, and335of the robot hand main body300bring the contact portions381,382, and383close to or separate from each other via the parallel link mechanisms10,20, and30. The parallel link mechanisms10,20, and30according to the present exemplary embodiment are configured by four-joint link mechanisms. This configuration can bring the contact portions381,382, and383close to or separate from each other while their attitudes are maintained in a parallel state. Any mechanisms other than the four-joint link mechanisms may be used as long as they can bring the contact portions381,382, and383close to or separate from each other while the attitudes are maintained in the parallel state.

The motors315,325, and335and the parallel link mechanisms10,20, and30are described as one example of a plurality of drive mechanisms that brings the three finger portions close to or separate from each other independently.

Further, in the present exemplary embodiment, the motor345is mounted to the base340so that the two finger portions320and330of the three finger portions can turn in directions of arrows a and b. The finger portions320and330are disposed detachably from the turning drive shafts392and393. The turning drive shafts392and393turn about axes O and O′, respectively. As a result, the finger portion320and the finger portion330can be turned in the directions of arrows a and b about the axes O and O′, respectively. The motor345rotates the turning drive shafts392and393through a gear mechanism, not illustrated. Note that the turning drive shafts392and393rotate in opposite directions in synchronization through the gear mechanism, not illustrated.

The motor345is provided with an encoder346(FIG. 4) that measures a rotational angle similarly to the motors315,325, and335of the finger portions, and thus turning positions of the finger portions320and330can be precisely controlled.

The above-described gear mechanism is one example of turning mechanism, and the motor345is one example of a turning drive source. The turning mechanism includes the turning drive shafts392and393.

Further, motor control units311,321,331, and341that control the motors315,325,335, and345, respectively, are mounted on the robot hand main body300according to the present exemplary embodiment. In particular the finger portions320and330to be driven to be turned are configured in such a manner that the motors325and335and the motor control units321and331that control the motors325and335, respectively, are provided integrally with each other. Accordingly, the motors325and335and the motor control units321and331can turn together with the finger portions320and330. That is, in the finger portions320and330, the motors325and335and the motor control units321and331are configured as a unit. The detailed configuration will be described below.

The motor control units311and341that control the motors315and345, respectively, are disposed on the base340. Further, the distribution control unit350that distributes communication and electric power to the motor control units is disposed on a surface opposite from the surface where the motor control units311and341are disposed (FIG. 2B). As a result, the motor control units311,321,331, and341can be connected collectively to the robot hand control device700. Details of the distribution control unit350will be described below.

Further, a force sensor361that detects an external force applied to a contact portion381is disposed on the contact portion381of the finger portion310. The finger portion310includes the sensor operation substrate360that converts a change in a voltage detected by the force sensor361into force information.

Further, a cable370that connects the motor control units311,321,331, and341, and the sensor operation substrate360to the system control device400is routed as illustrated inFIGS. 2A to 2C. Note that the cable370is used also for communication between the motors and the motor control units, and communication between the force sensor361and the sensor operation substrate360.

Herein, the finger portion310is not turned by the motor345. The provision of the force sensor361to the finger portion310can reduce a frequent operation of the force sensor361, and thus can reduce damage to the cable370of the force sensor361.

As illustrated inFIG. 2C, the finger portions320and330of the robot hand main body300according to the present exemplary embodiment of the present invention are detachable from the base340.FIG. 2Cillustrates a state where the finger portion320is detached from the base340as an example. A configuration of the finger portion320will be described below. Note that the finger portion330has a similar configuration.

As illustrated in the drawing, a fastening portion50is provided in the finger portion320to detachably fasten the finger portion320to the base340. The fastening portion50pinches the turning drive shaft392through a recessed groove54to attach the turning drive shaft392and the finger portion320. A protrusion51is provided on the turning drive shaft392, and a recess52is provided in an inner surface of the recessed groove54of the fastening portion50. When the turning drive shaft392is pinched by the fastening portion50, the protrusion51is fitted into the recess52, and the turning drive shaft392and the finger portion320are set in position.

Further, an internally threaded hole53is provided in the fastening portion50. A bolt, not illustrated, is inserted into the hole53to be fastened therein with the turning drive shaft392being pinched by the fastening portion50. As a result, an attachment state of the finger portion320and the turning drive shaft392is maintained.

Further, a bevel gear60is provided to an output shaft of the motor325that drives the parallel link mechanism20of the finger portion320so as to bend the a transmission path of the motive power at a right angle and to transmit motive power to an input shaft of a reduction gear70. An output shaft of the reduction gear70is connected to the parallel link mechanism20, and drive power of the motor325is transmitted to the parallel link mechanism20after being decelerated by the reduction gear70. The parallel link mechanism20is then driven to operate the contact portion382. At this time, the reduction gear70is preferably a wave reduction gear in order to reduce a backlash.

As described above, the bevel gear60is used to change the transmission path for the motive power of the motor325, and thus a space for mounting the motor control unit321in parallel to a vicinity of the motor325can be provided. As a result, the motor325and the motor control unit321can be integrally disposed in the finger portion320.

As described above, the motor325and the motor control unit321are provided in the finger portion320integrally as a unit so as to be detachable from the base340.

FIGS. 3A to 3Care top views illustrating an operation of the robot hand main body300according to the present exemplary embodiment.FIG. 3Aillustrates a state where a close/separate direction P of the contact portions382and383of the finger portions320and330is approximately vertical to an alternate long and short dash line C connecting the axis O and the axis O′. A close/separate direction of the contact portion381is indicated by an arrow S.FIG. 3Billustrates a state where an angle θ formed by the close/separate direction P and the alternate long and short dash line C is approximately 30°.FIG. 3Cillustrates a state where the close/separate direction P is approximately parallel with the alternate long and short dash line C.

The motor345inside the base340is driven to rotate the turning drive shafts392and393from the state inFIG. 3A. As a result, gripping forms inFIGS. 3B and 3Ccan be taken.

FIG. 3Billustrates a gripping form in which the turning drive shafts392and393are rotated from the state inFIG. 3Atoward the arrows a and b, respectively, and the close/separate direction P of the contact portions382and383and the alternate long and short dash line C form an angle of 30°.

FIG. 3Cillustrates a gripping form in which the turning drive shafts392and393are further driven fromFIG. 3Btoward the arrows a and b, respectively, and the close/separate direction P and the alternate long and short dash line C are substantially parallel to each other. At this time, stoppers80for limiting a turning range are provided to the base340so as to prevent the finger portions320and330from further turning toward the arrows a and b, respectively, and from interfering with the finger portion310.

Similarly, the stoppers80for limiting the turning range are provided to the base340so as to prevent, when the gripping form ofFIG. 3Cis returned to the gripping form ofFIG. 3A, the finger portion320and the finger portion330from turning excessively and interfering with each other.

As described above, various gripping forms are made possible by the motors315,325, and335that bring the contact portions381,382, and383of the finger portions310,320, and330close to or separate from each other, and the motor345that turns the finger portions320and330. The various gripping forms enables gripping of a variety of target objects.

FIG. 4is a block diagram illustrating details of a control system of the robot system100according to the present exemplary embodiment. As illustrated inFIG. 4, in the robot system100according to the present exemplary embodiment, the system control device400that controls the entire robot system transmits an instruction relating to an operation to the robot arm control device600and the robot hand control device700. The robot arm control device600and the robot hand control device700control the robot arm main body200and the robot hand main body300, respectively, based on the instruction from the system control device400. The control system of the robot hand main body300will be described in detail below, and description about details relating to the control of the robot arm main body200will be omitted.

InFIG. 4, the system control device400includes a microprocessor401having a read-only memory (ROM) (not illustrated) and a random access memory (RAM) (not illustrated). The ROM stores necessary data and a program according to various operations of the robot system100. The RAM is used as a working area of a central processing unit (CPU) (not illustrated). The system control device400is connected to the external input device500and the robot arm control device600via serial communication interfaces402and403, respectively. The system control device400is connected to the robot hand control device700via an input/output interface404.

A configuration similar to that described above is provided also to the robot arm control device600and the robot hand control device700. The robot arm control device600and the robot arm main body200are connected to each other by serial communication. A serial communication interface702of the robot hand control device700is connected to the robot hand main body300.

For example, a control area network (CAN) communication protocol is used for the communication between the robot hand control device700and the robot hand main body300. The respective control units are connected to each other by a CAN communication bus.

As illustrated in the drawing, the system control device400transmits the instruction relating to the operation of the robot hand main body300to the robot hand control device700. The instruction from the system control device400is a simple instruction value for specifying which target object is to be gripped.

The robot hand control device700receives the instruction from the system control device400, and performs an operation according to a type of target object to be gripped. The robot hand control device700collectively transmits control values of the motors315,325,335, and345to the distribution control unit350. At this time, the robot hand control device700determines the control values of the motors315,325,335, and345in consideration of the instruction received from the system control device400and a current state of the robot hand main body300.

The determined control values of the motors315,325,335, and345are transmitted to the motor control units311,321,331, and341via the distribution control unit350. The distribution control unit350distributes and transmits the corresponding control values to the motor control units311,321,331, and341.

The motor control units that receive the control values from the distribution control unit350, respectively, operate the motors to move the finger portions, and acquire information from the encoders316,326,336, and346provided to the motors, respectively. The motors are feedback controlled so that the finger portions310,320, and330come to positions according to the control values, respectively. The motor control units311,321, and331control the positions of the contact portions381,382, and383of the finger portions310,320, and330. The motor control unit341controls turning positions of the finger portions320and330.

At this time, the motor control units311,321,331, and341always transmit the current turning positions of the contact portions381,382, and383and the finger portions320and330to the robot hand control device700via the distribution control unit350. Further, if any of the motor control units311,321,331, and341does not perform the transmission, the motor control unit that does not perform the transmission is detected to be abnormal. Further, identifications (IDs) are allocated to the motor control units311,321,331, and341, and the IDs make determination of an abnormal part easy.

In this way, the robot hand control device700determines the control values of the motors, and determines whether the state of the robot hand main body300is normal or abnormal. If it is determined that the state is abnormal, the robot hand control device700transmits a stop instruction to the system control device400or the robot arm control device600.

In the present exemplary embodiment, the finger portion310has the triaxial force sensor361inside the contact portion381. The sensor operation substrate360disposed on the base340performs an operation on a detection value from the force sensor361to obtain a force value, and transmits the force value to the robot hand control device700via the distribution control unit350.

In the present exemplary embodiment, the detection value from the force sensor361is transmitted to the robot hand control device700. Alternatively, the detection value may be transmitted to the motor control units311,321, and331to execute feedback control by the force sensor361.

The finger portions310,320, and330grip a target object through control made by the motor control units311,321, and331. The gripping the target object is determined by the distribution control unit350based on the detection value from the force sensor361. An instruction value for the gripping detection is transmitted to the robot hand control device700.

On receiving the instruction value of the gripping detection, the robot hand control device700instructs the robot arm control device600to assemble the gripped target object, via the robot system control device400.

The robot arm control device600then controls the robot arm main body200to assemble the target object gripped by the robot hand main body300to another target object.

The motor control units311,321, and331are examples of a drive control unit, and the motor control unit341is an example of a turning control unit.

The robot hand control device700that controls the entire operation of the robot hand main body300only needs to determine the control values or control commands and control amounts of the motors315,325,335, and345. Thereafter, the motor control units311,321,331, and341mounted to the finger portions310,320, and330and the base340, respectively, executes the feedback control on the motors based on the values from the encoders316,326,336, and346. As a result, the robot hand control device700does not have to monitor the positions of the finger portions310,320, and330, and thus the entire operation of the robot hand main body300is easily controlled.

Further, since the motors315,325, and335and the motor control units311,321, and331are respectively disposed in the finger portions310,320, and330integrally, the communication cables between the motor control units311,321, and331and the motors315,325, and335can be accommodated in the finger portions310,320, and330. Further, since the distribution control unit350is also disposed on the base340, the cables370between the motor control units311,321,331, and341and the robot hand control device700can be unified by the distribution control unit350.

Therefore, the distribution control unit350enables the communication between the motor control units311,321,331, and341and the robot hand control device700by one cable. Accordingly, the cable routed from the robot hand control device700to the robot hand main body300can be easily accommodated inside the robot arm main body200.

Further, the finger portions320and330that are frequently driven by the turning operation are disposed detachably from the base340. In a case where a part of the finger portion is broken, maintenance work can be easily performed.

Further, in controlling the finger portions of the robot hand, there is a case where all the finger portions are desired to be driven in a synchronous manner in order to perform a wide variety of gripping. In the present exemplary embodiment, the distribution control unit350that distributes a control value from the robot hand control device700is disposed on the base340where all the finger portions310,320, and330are disposed.

As a result, lengths of the cables from the distribution control unit350to the motor control units311,321, and331of the finger portions can be set to be equivalent to each other. In this way, a delay in the synchronous driving caused by a difference in the cable lengths when synchronously driving the finger portions that are independently driven can be reduced.

In the robot hand main body300described above, the finger portions310,320, and330are independently driven. For this reason, in order to perform precise gripping, the driving of the motors315,325,335, and345needs to be accurate. Particularly if home positions for the driving of the motors315,325,335, and345are displaced, the finger portions310,320, and330are displaced and thus the precise gripping becomes difficult. Home position setting of the motors according to the present exemplary embodiment is described in detail below.

FIGS. 5A and 5Bare detailed diagrams of a mechanism that sets the home positions of the motors315,325, and335in the finger portions310,320, and330according to the present exemplary embodiment.FIG. 5Ais a perspective view of the gripping form illustrated inFIG. 3C, andFIG. 5Bis an enlarged view of an area A inFIG. 5A.FIG. 6is a flowchart illustrating the home position setting of the motors315,325, and335in the finger portions310,320, and330.

As illustrated inFIG. 5A, in the robot hand according to the present exemplary embodiment, when the home positions of the finger portions310,320, and330are set, the finger portions310,320, and330are separated from each other.

With reference toFIG. 5B, abutment portions90and91are provided to the finger portion320. The abutment portion91abuts against a link supporting portion21that supports the parallel link mechanism20, and the abutment portion90abuts against the stopper80described above. As a result, an abutment position between the abutment portion91and the link supporting portion21can be set as the home position of the motor325, and an abutment position between the abutment portion90and the stopper80can be set as the home position of the motor345that performs the turning driving.

The abutment portions90are disposed similarly in the finger portions310and330, respectively, and thus the home positions of the motors315and335provided to the finger portions310and330can be set. According to the present exemplary embodiment, the abutment portion91is provided to the finger portion320, but since the finger portions320and330turn synchronously by the motor345, even if the abutment portion91is provided to the finger portion330, the similar effect can be obtained.

FIG. 6illustrates a flow of the home position setting of the motors315,325, and335in the finger portions310,320, and330according to the present exemplary embodiment. When the robot hand control device700receives a command for starting the home position setting from the system control device400, the robot hand control device700transmits the command for starting the home position setting to the motor control units311,321, and331of the finger portions310,320, and330, and the flow starts.

In a case where the command for starting the home position setting is received, in step S101, the motor control units311,321,331, and341initialize parameters of the motors315,325,335, and345, respectively.

The processing proceeds to step S102, and the rotational directions of the motors315,325,335, and345are confirmed. Since Z phases of the motors cannot be searched if the abutment portions90and91abut against the stoppers80and the link supporting portions21, respectively, the movable directions of the motors are confirmed. The stoppers80and the link supporting portions21are members configuring the base340.

The processing proceeds to step S103, and a relationship between the Z phases and electric angles of the motors is obtained.

In step S104, the motors315,325,335, and345are driven until the abutment portions90provided to the finger portions310,320, and330and the abutment portion91provided to finger portion320abut against the link supporting portions21and the stoppers80, respectively.

When the motors315,325,335, and345are driven, in step S105, a determination is made whether current values of the motors are constant and variations of encoder values are within predetermined values. If Yes in step S105, the processing proceeds to step S106. If No in step S105, the processing returns to immediately before step S104, and the abutment of the abutment portions90and91is continued.

If Yes in step S105, the processing proceeds to step S106, and positions of the encoders316,326,336, and346at that time are set as the home positions of the motors315,325,335, and345that perform the close/separate operation of the contact portions381,382, and383and the turning operation of the finger portions310,320, and330.

In step S107, the finger portions310,320, and330are moved to predetermined positions that are the initial attitudes, and a signal that indicates completion of the home position setting is transmitted to the robot hand control device700. The flow of the home position setting is then ended.

According to the present exemplary embodiment, the command for starting the home position setting is transmitted simultaneously to the motor control units311,321,331, and341from the robot hand control device700, but the command may be individually transmitted to the motor control units311,321,331, and341.

Further, the home position of the motor345performing the turning of the finger portions320and330is preferably set after the home positions of the other motors315,325, and335are set. This enables all the finger portions310,320, and330to be located in a desired close/separate direction. Therefore, when the home position of the motor345is set, a danger of collision between the finger portions can be eliminated.

A processing procedure according to the present exemplary embodiment is, specifically, executed by the robot hand control device700. Therefore, the present invention includes a control program as software that realizes the above-described functions and a recording medium that records the program.

In the above exemplary embodiment, a case where microprocessors601,401, and701store the control program in a recording medium readable by a computer, but the present invention is not limited to this form. The control program for carrying out the present invention may be recorded in any recording medium as long as the recording medium is readable by a computer. For example, as the recording medium for supplying the control program, a hard disc drive (HDD), an external storage device, or a recording disc may be used.

Other Embodiments

The present disclosure is applicable to industrial robots.

This application claims the benefit of Japanese Patent Application No. 2017-239915, filed Dec. 14, 2017, which is hereby incorporated by reference herein in its entirety.