JP5430376B2 - Robot gripping device - Google Patents

Description

  The present invention relates to a robot gripping device for automatically assembling a workpiece.

  Conventionally, in the control of a robot that automatically assembles workpieces, a stress sensor is installed on the robot arm in order to detect a load applied to the robot arm. For example, a stress sensor using a piezoelectric element, a strain gauge, or the like has been used as the stress sensor.

  In addition, when a predetermined work is performed by holding a workpiece with a robot hand, there is one that detects the holding of the workpiece for the purpose of improving the certainty of the operation. A pressure sensor, a contact switch, a photoelectric switch or the like mounted on the hand is used to detect the grip of the workpiece. Some apparatuses provided with a camera for photographing a workpiece check the presence / absence of the workpiece, control the gripping, and the like. For example, Patent Document 1 discloses a device that acquires a visible image of a robot arm from a video camera image and controls the robot arm based on the acquired visible image. Patent Document 2 proposes a method using a gripping member that generates an optical fringe corresponding to a gripping force.

JP 04-352203 A JP 2008-197000 A

  In order to determine whether or not the hand has been held, it can be confirmed by the joint angle from an encoder or the like provided at the hand joint. However, when the workpiece is a thin sheet or a thin wire, the difference in joint angle, which is the encoder output of the joint, is small, and the reliability of grip detection is low. Further, as disclosed in Patent Document 2, in the configuration in which the optical fringes such as the photoelastic fringes are detected and gripped, the opposing surfaces 221a of the gripping members 202a and 202b, The sheet-like workpiece W is gripped by 221b. As shown in FIG. 8B, in the state before gripping, no optical fringes are generated due to gripping. When the thickness of the sheet-like workpiece W is extremely thin, it is difficult to detect the workpiece W, and it is difficult to directly determine whether or not the workpiece W is gripped from an image of the CCD camera. FIGS. 8C and 8D show optical fringes of the gripping member showing the difference between the presence and absence of a sheet-like workpiece under the same pressing force conditions. If the sheet-like workpiece is extremely thin, there is no difference in optical fringes, and it is difficult to detect whether or not the sheet-like workpiece is gripped. Similarly, it is difficult to detect whether or not a thin linear workpiece is gripped. Detection of such a thin work or a thin work becomes a problem.

  In an apparatus using a contact sensor or a pressure sensor in order to check whether or not a workpiece has been gripped by the hand, the contact sensor and the pressure sensor are mounted on the hand, so that the size of the apparatus increases. In addition, power supply to the contact sensor and pressure sensor and wiring for signal transmission / reception are required, and the apparatus becomes complicated.

  In addition, there is the following problem to confirm whether or not the work has slipped after gripping the work. An object such as transparent glass or a dark object is difficult to shoot with a camera, and slip cannot be detected by a change in an image. In order to detect a very small slip, a high-resolution camera is necessary and expensive.

  In the method of performing grip detection and slip detection using a contact sensor or a pressure sensor, two or more sensors are required, resulting in an increase in size and cost of the apparatus. In addition, since the contact sensor and the pressure sensor are detected in one direction, it is necessary to substantially match the detection direction of the sensor with the slip direction in order to detect slip, but it is not possible to match the detection direction with the workpiece slip direction. This will hinder the device configuration.

  An object of the present invention is to provide a robot gripping device that can accurately perform gripping detection of a workpiece with a simple configuration.

  In order to solve the above-described problems, a robot gripping apparatus according to the present invention includes a plurality of gripping members that can be opened and closed, an opening / closing means that opens and closes the plurality of gripping members, A contact pressing portion for gripping the workpiece disposed on a gripping member, and a workpiece that is disposed on at least one of the plurality of gripping members and that contacts the workpiece to detect the presence or absence of the workpiece. Presence / absence detection unit, means for detecting optical fringes due to distortion generated in each gripping member, control unit for controlling gripping force on the workpiece based on optical fringes due to distortion of the contact pressing unit, and workpiece presence / absence detection unit And a gripping confirmation unit for confirming gripping of the workpiece based on an optical fringe due to the distortion of the workpiece.

  Further, in a robot gripping apparatus for assembling a workpiece, a plurality of gripping members that can be freely opened and closed, an opening / closing means that opens and closes the plurality of gripping members, and a gripping device disposed on each gripping member. A contact pressing portion, a workpiece slip detection portion that is disposed on at least one of the plurality of gripping members and contacts the workpiece in order to detect slippage of the workpiece, and optical due to distortion generated in each gripping member A means for detecting fringes, a control unit for controlling a gripping force on the workpiece based on the optical fringes due to distortion of the contact pressing portion, and checking the slip of the workpieces based on optical fringes due to distortion of the workpiece slip detection unit And a workpiece slip confirmation portion.

  Further, in a robot gripping apparatus for assembling a workpiece, a plurality of gripping members that can be freely opened and closed, an opening / closing means that opens and closes the plurality of gripping members, and a gripping device disposed on each gripping member. A contact pressing portion, a workpiece position detecting portion that is disposed on at least one of the plurality of gripping members and contacts the workpiece to detect the position of the workpiece, and an optical component due to distortion generated in each gripping member A means for detecting fringes, a control unit for controlling gripping force on the workpiece based on optical fringes due to distortion of the contact pressing portion, and a gripping position of the workpieces based on optical fringes due to distortion of the workpiece position detection unit. And a gripping position confirmation unit to be confirmed.

  At least one gripping member is provided with a workpiece presence / absence detection unit, a workpiece slip detection unit, and a workpiece position detection unit separately from the contact pressing unit that grips the workpiece, thereby detecting optical fringes, Check slipping and workpiece gripping position. Without using a contact sensor or a pressure sensor, it is possible to perform a reliable gripping operation by performing gripping confirmation of the workpiece with optical fringes and controlling the gripping force of the contact pressing portion.

1 shows a robot gripping apparatus according to a first embodiment, where (a) is a perspective view and (b) is a side view. FIG. 1A and 1B illustrate the operation of the apparatus of FIG. 1, (a) is a perspective view showing a state before gripping a sheet-like workpiece, (b) is a front view thereof, and (c) is a front view showing a state of gripping the workpiece. FIG. 4D is a front view showing a state in which there is no work. FIG. 4A is a block diagram illustrating a configuration of a grip control unit according to the first embodiment, and FIG. FIG. 10 is a block diagram for explaining a configuration of a gripping control unit according to the second embodiment, and FIG. The operation of the robot gripping device according to the second embodiment will be described. (A) shows a state before gripping the workpiece, (b) shows a state where the workpiece is gripped, and (c) shows a state where the workpiece slips. It is a front view. FIG. 9A is a block diagram illustrating a configuration of a grip control unit according to the third embodiment, and FIG. The operation of the robot gripping device according to the third embodiment will be described. (A) is a state before gripping a workpiece, (b) is a state where the workpiece is gripped at a predetermined position, and (c) and (d) are It is a front view which shows the state which each workpiece | work position shifted | deviated. It is a figure explaining operation | movement of the conventional holding | gripping apparatus.

  FIG. 1 shows a robot gripping apparatus according to a first embodiment. This device is composed of a plurality of openable and closable gripping members 2a and 2b held in a casing 1, which move in the directions of arrows R, respectively, as shown in FIG. The workpiece W is gripped by contacting and pressing the workpiece W with pressure. The workpiece W is one part of a product that is gripped during assembly work by a robot arm or the like, for example.

  In this embodiment, the workpiece W is gripped by the two gripping members 2a and 2b, but may be configured by three or more gripping members. The gripping members 2a and 2b are connected to an actuator such as a drive motor which is an opening / closing means, and move in the direction of arrow R when the drive motor is driven. The gripping members 2a and 2b generate optical fringes according to distortion caused by a reaction force when gripping a workpiece.

  As shown in FIG. 3, the grip control unit 101 for opening and closing the grip members 2 a and 2 b includes an optical fringe acquisition unit 103 that acquires the optical fringes of the optical fringe generation unit 102 disposed on the grip members 2 a and 2 b. Connected.

  The optical fringe generator 102 is constituted by an optical elastic member created by disposing a member such as transparent glass or acrylic between two polarizing plates, for example. When an external force is applied to the optical elastic member, distortion corresponding to the stress occurs in the portion where the stress due to the reaction force is generated, and the molecular structure changes. Since the molecular structure changes, birefringence occurs when light is irradiated to the part where the distortion occurs. How birefringence depends on the magnitude of stress. Therefore, since the magnitude of the stress changes depending on the part of the member, when a load is applied to the optical elastic member, a plurality of birefringence occurs, and an optical fringe pattern is generated. Of the generated optical stripes, it can be considered that substantially the same stress is generated in the stripes of the same color. Therefore, the stress distribution can be calculated from the generated stripe pattern. Further, since the color of the optical fringe corresponds to the stress, the color of the optical fringe can be detected and the stress can be calculated. The optical fringe is information corresponding to the stress applied to the member, and the region where the density of the optical fringe is large indicates that the stress change is large. Optical fringes generated in the optical elastic member are called photoelastic fringes. The optical fringe generating unit 102 is configured by using such an optical elastic member for each of the gripping members 2a and 2b.

  The optical fringe generator 102 may generate optical interference fringes (Newton fringes) as optical fringes according to stress. Optical fringes can be generated by forming a minute gap combining a lens, a glass plate, and the like and irradiating light. Depending on the stress due to the reaction force, the width of the minute gap changes and the optical fringe also changes.

  Moreover, in order to apply to the material which does not permeate | transmit light, such as a metal, a photoelastic film | membrane can be stuck on the surface, and the optical fringe according to stress can be generated. In addition, any member may be used as long as it can generate optical fringes according to stress.

  The optical fringe acquisition unit 103 functions as a means for detecting optical fringes, detects the optical fringes generated by the optical fringe generation unit 102, and acquires optical fringe data. The optical fringe acquisition unit 103 uses a light detection sensor for visible light. As shown in FIG. 1A, the light detection sensor includes a light generation device 3 that generates light and a CCD sensor 4 that can detect visible light using a CCD element. Light generated from the light generator 3 passes through the gripping members 2 a and 2 b and is detected by the CCD sensor 4. In order to detect the optical fringes, it is necessary to align the wavelengths and directions of the light incident on the workpiece W and the transmitted light, so the polarizer 5 and the analyzer 6 are installed.

  The grip member 2a is connected to the links 7a and 8a, and the grip member 2b is connected to the links 7b and 8b. Although the gripping operation is performed in the rotation direction of the plurality of links, there is no problem even if the linear cylinder is combined and the gripping operation is performed in the linear direction. It is possible to grip in either direction.

  In addition, although the light detection accuracy is reduced, a general video camera can be used as the optical fringe acquisition unit 103.

  The gripping member driving unit 104 is a driving unit for driving the gripping members 2 a and 2 b to generate a gripping force, and the gripping force is controlled by the control unit 105. The gripping member driving unit 104 has a drive motor and a transmission motion mechanism, receives a control instruction from the outside, drives the drive motor, and moves the gripping members 2a and 2b. The links 7a, 7b, 8a, 8b control the gripping members 2a, 2b to arbitrary positions and postures. The housing 1 stores a drive control circuit and a robot arm interface. Further, it is used by connecting to a commercially available orthogonal robot or vertical articulated robot through a mechanical interface provided in the housing 1.

  The grip confirmation unit 106 confirms the gripping state of the workpiece W by the optical fringes generated in the optical fringe generation unit 102. As shown in FIGS. 1 and 2, the gripping members 2 a and 2 b that grip the sheet-like workpiece W have contact pressing portions 21 a and 21 b that touch the workpiece W and press and grip the workpiece W, respectively. At least one gripping member 2a among the plurality of gripping members has a workpiece presence / absence detection unit 22a that is a convex portion protruding toward the workpiece, and the remaining gripping members 2b do not interfere with the workpiece presence / absence detection unit 22a. It has the recessed part 22b facing a convex part. The workpiece presence / absence detector 22a is deformed by contact with the workpiece W to generate an optical fringe. FIG. 2C shows a state where the workpiece W is gripped, and FIG. 2D shows a state where there is no workpiece. As shown in FIG. 2D in advance, by recognizing an optical fringe without a workpiece, the difference in the gripping state is compared to detect whether or not the workpiece is gripped.

  The control unit 105 controls the grip member driving unit 104 based on the detection result of the optical fringe acquisition unit 103. The control unit 105 includes a CPU, a RAM in which a drive control program and a data analysis program are stored.

  When controlling the gripping member drive unit 104, first, the CPU reads a drive control program from the RAM. In accordance with the drive control program, a drive signal is transmitted to the gripping member drive unit 104 in order to achieve a predetermined operation (for example, gripping a workpiece).

  On the other hand, the CPU reads the data analysis program from the RAM. Then, the optical fringe data is analyzed by the data analysis program. As a result of the analysis, for example, when the gripping force of the gripping members 2a and 2b is larger than a preset allowable value, the drive signal transmitted to the gripping member driving unit 104 is stopped. Although there are other methods as described above for controlling the gripping member drive unit 104, other control methods will be described later.

  FIG. 3B is a flowchart showing the gripping operation in this embodiment. In step S <b> 1, the optical fringe acquisition unit 103 acquires data of optical fringes generated in the optical fringe generation unit 102. In step S2, the control unit 105 calculates a driving amount for driving the gripping members 2a and 2b, and determines whether or not the workpiece is gripped by using FIGS. 2C and 2D. The optical fringe pattern of the workpiece presence / absence detection unit 22a described will be examined. An optical fringe pattern that is not gripped or a gripped optical fringe pattern may be learned in advance. Depending on the gripping state, processing such as setting a predetermined error flag is performed. Further, when detecting the pattern shape, the state determination may be performed using only an image of a predetermined specific region in order to speed up the processing.

  In step S3, the control unit 105 determines whether or not to drive the grip members 2a and 2b, and changes the grip control. When an error flag that does not hold the workpiece is generated in step S2, a stop process is performed to end the holding operation. The end of the gripping operation is opening the gripping member or moving the gripping mechanism to a predetermined position. After the gripping operation is completed, a retry operation or message transmission to the host computer is performed. If there is no error flag, the process proceeds to step S4 to drive the gripping members 2a and 2b.

  In step S4, the control unit 105 transmits a driving instruction based on the driving amount calculated in step S2 to the gripping member driving unit 104, and causes the gripping member driving unit 104 to drive the gripping members 2a and 2b. Since the state of the gripping members 2a and 2b changes after driving, the process returns to step S1 again to acquire optical fringes. As described above, the gripping control based on the optical fringes can be performed by the processing from step S1 to step S4.

  In this embodiment, it is not necessary to provide a stress sensor or the like on the gripping members 2a and 2b in order to determine the gripping state. Therefore, the holding members 2a and 2b can be simplified. Moreover, since this apparatus can be constructed by using a member that generates optical fringes and a general video camera or the like, the cost for constructing the apparatus can be reduced as compared with an apparatus using a stress detection sensor or the like. . Furthermore, since it can be determined whether or not the workpiece is gripped by the optical fringes, a reliable gripping operation can be performed.

  In order to calculate the stress from the image data of the optical fringes, correspondence information indicating the correspondence between the stress and the pattern shape or color of the optical fringes is necessary. For example, a stress test using the gripping members 2a and 2b is performed, and correspondence information between the stress and the pattern shape or color of the optical fringes can be obtained from experimental data obtained from the test. Alternatively, the correspondence between the stress and the pattern shape or color of the optical fringes may be obtained by numerical calculation using a finite element method. As described above, it can be considered that almost the same stress is generated in the optical stripes of the same color. Therefore, the stress distribution can be obtained by drawing a stress line due to optical fringes by drawing a line in the same color region. If the stress distribution is used, the stress in the predetermined region can be calculated in detail, so that grip control based on the stress can be performed with higher accuracy.

  According to the present embodiment, the apparatus configuration can be simplified and the reliability can be improved as compared with a gripping apparatus using a contact switch, a photoelectric switch, or the like for checking whether or not the work is gripped.

  In this embodiment, in order to detect slipping of the gripped work and enable a reliable gripping work, a work slip confirmation unit 107 is added as shown in FIG. In addition, a workpiece slip detecting portion 23a which is a convex portion is formed on the gripping member 2a, and a concave portion 23b is formed on the gripping member 2b. The workpiece slip detection unit 23a is a convex portion having a slightly larger projection amount than the workpiece presence / absence detection unit 22a of the first embodiment, and the other configuration is the same as that of the first embodiment, and thus description thereof is omitted.

  FIG. 5A shows a state before the workpiece W is gripped, and optical fringes due to contact are not generated. FIG. 5B shows a state in which the workpiece W is gripped, and optical fringes similar to those in FIG. In FIG. 5 (c), the workpiece W slips in the downward direction in the figure, and the tip of the workpiece slip detection portion 23a is applied with a downward force in the figure by the frictional force of the workpiece W, and an optical fringe corresponding to this force is formed. It has occurred. Thus, when the work W slips, an optical fringe peculiar to the work slip detection unit 23a is generated, and the slip of the work W is detected from the optical fringe.

  FIG. 4B is a flowchart illustrating the gripping operation according to the second embodiment. The difference from the flowchart of the first embodiment is that step S15 is present after step S14. Steps S11 to S14 are the same as steps S1 to S4 of the first embodiment. In step S15, the workpiece slip detector 23a determines whether the workpiece W is slipping. When it is determined that the work W has slipped, the grip control is changed, such as the above-mentioned operation end operation. In this manner, the gripping of the workpiece W is detected, and the gripping control is performed according to the result, so that the gripping control can be surely performed.

  Appropriate work can be performed while comparing optical fringes generated on the gripping member during the work gripping work. In particular, it is effective for detecting a transparent object such as glass, which is difficult to detect with a camera, and slippage of minute movement.

  In this embodiment, the position of the workpiece after gripping is detected, so that gripping work can be surely performed. As shown in FIG. 6A, a gripping position confirmation unit 108 for confirming the gripping position of the workpiece W is provided. As shown in FIG. 7, the gripping member 2a has a workpiece position detection unit 24a composed of a plurality of convex portions. A recess 24b is formed in the gripping member 2b. Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  FIG. 7A shows a state before the workpiece W is gripped, and optical fringes due to the contact between the gripping members 2a and 2b and the workpiece W do not occur. FIG. 7B shows a state where the workpiece W is held at a predetermined holding position. FIG. 7C shows a state in which the position of the workpiece W is shifted downward in the drawing, and FIG. 7D shows a case in which the workpiece W is shifted further downward than in FIG. As shown in FIGS. 7B, 7C, and 7D, the optical fringes generated in the workpiece position detection units 24a are different, and the position of the workpiece W is detected based on the difference in the fringe patterns. The position of the workpiece W is detected from two or more optical fringe patterns. Although FIG. 7 illustrates the case where the workpiece W is displaced only in the downward direction in the figure, the workpiece position can be similarly detected even when the workpiece W is displaced in the upward direction.

  FIG. 6B is a flowchart illustrating the gripping operation according to the third embodiment. The difference from the flowchart of the first embodiment is that step S25 is provided after step S21. Steps S21 to S24 are the same as steps S1 to S4 of the first embodiment. In step S25, the grip position of the workpiece W is determined by the workpiece position detection unit 24a. When it is determined that the gripping position of the workpiece W is not a predetermined position, the gripping control is changed, such as the above-described work ending operation. As described above, it is possible to perform appropriate work while comparing and referring to the optical fringes generated in the gripping members 2a and 2b as needed.

DESCRIPTION OF SYMBOLS 1 Housing | casing 2a, 2b Holding member 3 Light generator 4 CCD sensor 5 Polarizer 6 Analyzer 21a, 21b Contact press part 22a Work presence detection part 22b, 23b, 24b Recessed part 23a Work slip detection part 24a Work position detection part 102 Optical Stripe generation unit 103 Optical fringe acquisition unit 104 Gripping member drive unit 105 Control unit 106 Gripping confirmation unit 107 Work slip confirmation unit 108 Gripping position confirmation unit

Claims (6)

In a robot gripping device that assembles workpieces,
A plurality of openable and closable gripping members;
Opening and closing means for opening and closing the plurality of gripping members;
A contact pressing portion disposed on each gripping member for gripping the workpiece;
A workpiece presence / absence detection unit disposed on at least one of the plurality of gripping members and contacting the workpiece to detect the presence / absence of the workpiece;
Means for detecting optical fringes due to distortion generated in each gripping member;
A control unit for controlling a gripping force on the workpiece based on optical fringes due to distortion of the contact pressing unit;
And a gripping confirmation unit that confirms gripping of the workpiece based on optical fringes due to distortion of the workpiece presence / absence detection unit. The workpiece presence / absence detection unit has a convex portion formed on at least one of the plurality of gripping members,
The robot gripping apparatus according to claim 1, wherein the remaining gripping member is formed with a concave portion facing the convex portion. In a robot gripping device that assembles workpieces,
A plurality of openable and closable gripping members;
Opening and closing means for opening and closing the plurality of gripping members;
A contact pressing portion disposed on each gripping member for gripping the workpiece;
A workpiece slip detector disposed on at least one of the plurality of gripping members and contacting the workpiece to detect slippage of the workpiece;
Means for detecting optical fringes due to distortion generated in each gripping member;
A control unit for controlling a gripping force on the workpiece based on optical fringes due to distortion of the contact pressing unit;
A gripping device for a robot, comprising: a work slip confirmation unit that confirms the slip of the work based on an optical fringe due to distortion of the work slip detection unit. The work slip detection part has a convex part formed on at least one of the plurality of gripping members,
The robot gripping device according to claim 3, wherein the remaining gripping member is formed with a concave portion facing the convex portion. In a robot gripping device that assembles workpieces,
A plurality of openable and closable gripping members;
Opening and closing means for opening and closing the plurality of gripping members;
A contact pressing portion disposed on each gripping member for gripping the workpiece;
A workpiece position detecting unit disposed on at least one of the plurality of gripping members and contacting the workpiece to detect the position of the workpiece;
Means for detecting optical fringes due to distortion generated in each gripping member;
A control unit for controlling a gripping force on the workpiece based on optical fringes due to distortion of the contact pressing unit;
A gripping device for a robot, comprising: a gripping position confirmation unit that confirms a gripping position of the workpiece based on an optical fringe due to distortion of the workpiece position detection unit. The workpiece position detection unit has a plurality of convex portions formed on at least one of the plurality of gripping members,
The robot gripping apparatus according to claim 5, wherein the remaining gripping members are formed with concave portions facing the plurality of convex portions.

Images