Work holding device, work holding method, program, and control device

Abstract

To enable a work-piece to be re-held in a short time, when failing in holding the work-piece.SOLUTION: A work-piece holding device comprises: holding means that holds a work-piece one by one out of a plurality of work-pieces put in a three-dimensional space; information obtaining means that obtains three-dimensional information about the plurality of work-pieces; candidate calculating means that calculates a plurality of candidate holding points at the time when the holding means holds the work-pieces, on the basis of the three-dimensional information about the work-pieces; control means that selects one candidate holding point out of the plurality of calculated candidate holding points and controls the holding means so that the means holds the work-pieces, at the selected candidate holding point; and determining means that determines whether the work-piece is successfully held by control of the holding means by the control means. The control means, when it is determined that the work-piece is not successfully held, sets a predetermined range on the basis of the selected candidate holding point, and controls the holding means so that the work-piece is re-held at the other candidate holding point which is out of the predetermined range.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a work holding device for holding a work, a work holding method, a program, and a control device.

Background Art

[0002] There is known a work holding device that holds a work by holding means based on three-dimensional information of a plurality of stacked works (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, for example, depending on the loading position of the work or the attractive force due to magnetism when holding the work, there is a possibility of failure in holding the work. In that case, it is necessary to hold the work again, but it is conceivable that the arrangement of the work has changed, such as the work collapsing when the holding fails. Therefore, it becomes necessary to acquire the three-dimensional information of the work again, and it takes more time to re-hold the work.

[0005] The present invention has been made to solve such problems, and a main object thereof is to provide a work holding device, a work holding method, a program, and a control device capable of re-holding a work in a short time when the holding of the work fails.

Means for Solving the Problems

[0006] One aspect of the present invention for achieving the above object is holding means for holding one work at a time from a plurality of works placed in a three-dimensional space, Information acquisition means for acquiring three-dimensional information of the plurality of workpieces; Candidate calculation means for calculating a plurality of holding candidate points which are candidates for holding points of the workpiece when the holding means holds the workpiece, based on the three-dimensional information of the workpiece acquired by the information acquisition means; Control means for selecting one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation means, and controlling the holding means to hold the workpiece at the selected holding candidate point; Determination means for determining whether or not the holding of the workpiece has been successful by the control of the holding means by the control means; Comprising; When it is determined by the determination means that the holding of the workpiece has not been successful, the control means sets a predetermined range based on the selected holding candidate point, selects another holding candidate point outside the predetermined range, and controls the holding means to hold the workpiece again at the selected other holding candidate point. Workpiece holding device It is. In this aspect, when the determination means determines that the holding of the workpiece has not been successful when the holding means holds a plurality of workpieces simultaneously, When it is determined by the determination means that the holding of the workpiece has not been successful, the control means may control the holding means to release the workpiece, and then control the holding means to hold the workpiece again at the other holding candidate point. In this aspect, it further comprises weight detection means for detecting the weight of the workpiece when the holding means holds the workpiece, The determination means may determine whether or not the holding of the workpiece has been successful based on the weight of the workpiece detected by the weight detection means. In this aspect, the holding means may suck and hold the workpiece in a non-contact state. In this aspect, when it is determined by the determination means that the holding of the workpiece has not been successful, the control means sets a range within a predetermined distance from the selected holding candidate point as the predetermined range, The predetermined distance may be changed according to the number, weight, or size of the workpieces to be released. One aspect of the present invention for achieving the above object is a step of acquiring three-dimensional information of a plurality of workpieces placed in a three-dimensional space, a step of calculating a plurality of holding candidate points, which are candidates for holding points of the workpiece when the holding means holds the workpiece, based on the acquired three-dimensional information of the workpiece, a step of selecting one holding candidate point from the plurality of calculated holding candidate points and controlling the holding means to hold the workpiece at the selected holding candidate point, a step of determining whether the holding of the workpiece is successful by controlling the holding means, when it is determined that the holding of the workpiece is not successful, setting a predetermined range based on the selected holding candidate point, selecting another holding candidate point outside the predetermined range, and controlling the holding means to hold the workpiece again at the selected other holding candidate point, A workpiece holding method including may be used. One aspect of the present invention for achieving the above object is a process of acquiring three-dimensional information of a plurality of workpieces placed in a three-dimensional space, a process of calculating a plurality of holding candidate points, which are candidates for holding points of the workpiece when the holding means holds the workpiece, based on the acquired three-dimensional information of the workpiece, a process of selecting one holding candidate point from the plurality of calculated holding candidate points and controlling the holding means to hold the workpiece at the selected holding candidate point, a process of determining whether the holding of the workpiece is successful by controlling the holding means, when it is determined that the holding of the workpiece is not successful, setting a predetermined range based on the selected holding candidate point, selecting another holding candidate point outside the predetermined range, and controlling the holding means to hold the workpiece again at the selected other holding candidate point, A program for causing a computer to execute may be used. One aspect of the present invention for achieving the above object is as follows: Candidate calculation means for calculating a plurality of holding candidate points which are candidates for holding points of a workpiece when the holding means holds the workpiece based on three-dimensional information of a plurality of workpieces placed in a three-dimensional space; Control means for selecting one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation means and controlling the holding means to hold the workpiece at the selected holding candidate point; Judgment means for judging whether or not the holding of the workpiece has been successful by the control of the holding means by the control means; Comprising: When the control means is judged by the judgment means that the holding of the workpiece has not been successful, the control means sets a predetermined range based on the selected holding candidate point, selects another holding candidate point outside the predetermined range, and controls the holding means to hold the workpiece again at the selected other holding candidate point. It may be a control device. It may also be.

Effect of the Invention

[0007] According to the present invention, it is possible to provide a workpiece holding device, a workpiece holding method, a program, and a control device capable of re-holding a workpiece in a short time when the holding of the workpiece fails.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0009] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram showing a schematic system configuration of a work holding device according to the present embodiment. The work holding device 1 according to the present embodiment can hold and move one work at a time from a plurality of works arranged in a three-dimensional space. The plurality of works are parts such as those stacked in a box or on a flat plate. Note that the plurality of works include parts of any shape such as a planar shape or a three-dimensional shape.

[0010] The work holding device 1 according to the present embodiment includes a robot arm 2, a control device 3, and a three-dimensional vision sensor 4.

[0011] The robot arm 2 is a specific example of a holding means. The robot arm 2 is configured, for example, as a multi-joint arm having a plurality of links 21, joint portions (such as a wrist joint, an elbow joint, and a shoulder joint) 23 that rotatably connect the respective links 21, and an end effector 24 provided at its tip for holding a work.

[0012] Each joint portion 23 is provided with a rotation sensor such as an encoder for detecting rotation information of each joint portion 23, an actuator such as a servo motor for driving each joint portion 23, a force sensor for detecting the operating force of each joint portion 23, and the like. The force sensor is, for example, a torque sensor for detecting the torque of each joint portion 23. Each joint portion 23 is provided with a reduction mechanism or the like.

[0013] The end effector 24 attracts and holds the workpiece in a non-contact state by an attractive force such as a magnetic force or a pneumatic pressure. The end effector 24 is configured to, for example, electromagnetically adsorb the workpiece by generating a magnetic force and release the electromagnetically adsorbed workpiece by stopping the generation of the magnetic force.

[0014] The end effector 24 may be configured to grip the workpiece with fingers or the like. When the end effector 24 is configured to attract the workpiece by a magnetic force or the like, it is easy to hold a plurality of workpieces simultaneously, so that the holding failure described later is likely to occur, and thus the effects according to the present embodiment described later are greater.

[0015] A force sensor 5 is provided between the link tip side of the robot arm 2 and the end effector 24. The force sensor 5 is a specific example of a weight detection means. When the end effector 24 attracts and holds the workpiece, the weight of the workpiece is applied to the end effector 24. The force sensor 5 detects the weight of the workpiece.

[0016] The control device 3 performs various arithmetic processes and control processes on the robot arm 2. The control device 3 includes, for example, a processor 3a such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), an internal memory 3b such as a RAM (Random Access Memory) or a ROM (Read Only Memory), an HDD (Hard Disk Drive) or an S S D (Solid State Drive) and other storage devices 3c, an input / output I / F 3d for connecting peripheral devices such as a display, and a communication I / F 3e for communicating with devices outside the apparatus, and has a hardware configuration of a normal computer.

[0017] The three-dimensional vision sensor 4 is a specific example of information acquisition means. The three-dimensional vision sensor 4 acquires three-dimensional information of a plurality of workpieces. The three-dimensional information of the workpiece includes information such as the shape, position, and posture of each workpiece.

[0018] The three-dimensional vision sensor 4 is provided, for example, on the end effector 24 or the link 21 of the robot arm 2. The three-dimensional vision sensor 4 is composed of a camera, a laser sensor, etc. The three-dimensional vision sensor 4 outputs the acquired three-dimensional information of the workpiece to the control device 3.

[0019] FIG. 2 is a block diagram showing a schematic system configuration of the control device according to the present embodiment. The control device 3 according to the present embodiment includes a candidate calculation unit 31, a robot control unit 32, and a holding determination unit 33.

[0020] The candidate calculation unit 31 is a specific example of candidate calculation means. The candidate calculation unit 31 calculates a plurality of holding candidate points, which are candidates for the holding points (adsorption points) of the workpiece when the end effector 24 of the robot arm 2 holds the workpiece, based on the three-dimensional information of the workpiece acquired by the three-dimensional vision sensor 4.

[0021] For example, the candidate calculation unit 31 calculates depth information indicating the height position of each workpiece based on the three-dimensional information of the workpiece acquired by the three-dimensional vision sensor 4. The candidate calculation unit 31 detects the convex portions of each workpiece based on the calculated depth information of each workpiece. The candidate calculation unit may binarize the points with a height equal to or higher than a predetermined height as 1 and the points with a height less than the predetermined height as 0, and detect the points that become 1 as convex portions. The candidate calculation unit 31 detects, as holding candidate points, the convex portions having an end face area for adsorption by the end effector 24 equal to or greater than a threshold value from among the detected convex portions.

[0022] The candidate calculation unit 31 outputs the plurality of holding candidate points calculated as described above to the robot control unit 32.

[0023] The robot control unit 32 is a specific example of the control means. The robot control unit 32 controls the operation of the robot arm 2. The robot control unit 32 controls the actuators of each joint unit 23 based on, for example, the rotation information (such as the rotation angle) from the rotation sensors of each joint unit 23 and the operating force from the force sensors, thereby performing feedback control on the robot arm 2. In addition, the robot control unit 32 controls the adsorption and release of the workpiece by the end effector 24. Thereby, the robot control unit 32 can hold and move the workpiece by controlling the robot arm 2.

[0024] The robot control unit 32 selects one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation unit 31. For example, the robot control unit 32 selects the holding candidate point at the highest position from among the plurality of holding candidate points calculated by the candidate calculation unit 31. The robot control unit 32 may select the holding candidate point with the largest end face area of the convex portion from among the plurality of holding candidate points calculated by the candidate calculation unit 31. Note that the above method for selecting the holding candidate point is an example and is not limited thereto, and any selection method may be applied.

[0025] Based on the three-dimensional information of the workpiece acquired by the three-dimensional vision sensor 4, the robot control unit 32 controls the robot arm 2 so that the end effector 24 of the robot arm 2 holds the workpiece at the selected holding candidate point (hereinafter referred to as the selected holding candidate point).

[0026] The holding determination unit 33 is a specific example of the determination means. The holding determination unit 33 determines whether or not the holding of the workpiece has been successful by the control of the robot arm 2 by the robot control unit 32 described above.

[0027] The holding determination unit 33 determines that the holding of the workpiece has failed when the end effector 24 of the robot arm 2 approaches the workpiece (Fig. 3(a)) and the end effector 24 sucks and holds a plurality (for example, two) of workpieces simultaneously (Fig. 3(b)). Alternatively, the holding determination unit 33 determines that the holding of the workpiece has failed when the end effector 24 of the robot arm 2 holds zero workpieces, that is, when it cannot hold the workpiece. In particular, as described above, when sucking and holding a workpiece by a magnet or the like, it is likely that the failure of simultaneously holding a plurality of workpieces occurs, and it is necessary to surely determine this failure.

[0028] The holding determination unit 33 may determine whether the holding of the workpiece is successful based on the weight of the workpiece detected by the force sensor 5. The weight of the workpiece may be set in advance in the holding determination unit 33. The holding determination unit 33 determines that the holding of the workpiece has failed when the end effector 24 of the robot arm 2 sucks and holds a plurality of workpieces simultaneously (Fig. 3(b)) or when it is determined that zero workpieces are held based on the weight of the workpiece detected by the force sensor 5.

[0029] The holding determination unit 33 may determine whether the holding of the workpiece is successful based on an image of the workpiece captured by a camera. Note that it is more preferable that the holding determination unit 33 determines whether the holding of the workpiece is successful based on the weight of the workpiece detected by the force sensor 5 as described above. Thereby, the success of workpiece holding can be determined with high accuracy by simple processing.

[0030] The holding determination unit 33 outputs the determination result of the workpiece holding determined as described above to the robot control unit 32.

[0031] By the way, depending on, for example, the loading position of the workpiece or the suction force when holding the workpiece, there is a possibility of failure to hold the workpiece. In that case, it is necessary to hold the workpiece again. However, it is conceivable that the arrangement of the workpieces has changed, such as the workpieces stacked haphazardly collapsing when the holding fails. For this reason, it becomes necessary to acquire the three-dimensional information of the workpiece again, and more time is required for re-holding the workpiece.

[0032] On the other hand, in the present embodiment, when the holding determination unit 33 determines that the holding of the workpiece has failed, the robot control unit 32 sets a predetermined range based on the selected holding candidate point, selects another holding candidate point outside the predetermined range, and controls the robot arm 2 to hold the workpiece again at the selected other holding candidate point.

[0033] It is considered that the workpieces at other holding candidate points outside the predetermined range, which are located at positions away from the holding candidate point where the holding has failed, have not changed in arrangement due to the collapse of the workpieces caused by the holding failure. Therefore, the robot control unit 32 can control the robot arm 2 so that the end effector 24 of the robot arm 2 holds the workpiece at another holding candidate point outside the predetermined range based on the three-dimensional information of the workpiece already acquired by the three-dimensional vision sensor 4. As a result, since it is not necessary to acquire the three-dimensional information of the workpiece again, the workpiece can be re-held in a short time.

[0034] When the holding determination unit 33 determines that the holding of the workpiece has failed, the robot control unit 32 sets a predetermined range based on the selected holding candidate point. For example, as shown in FIG. 4, the robot control unit 32 sets the range within a predetermined distance from the selected holding candidate point X as the predetermined range (hatched portion) S. Here, the predetermined distance is set to an optimum value obtained experimentally based on the suction force of the end effector 24 or the like. The predetermined distance may be set in advance in the robot control unit 32.

[0035] When the workpiece is placed on an inclined surface, workpiece collapse due to holding failure is likely to occur in the inclined direction of the inclined surface. Therefore, the robot control unit 32 may set a predetermined range S based on the selected holding candidate point X in consideration of the inclined direction of this inclined surface. For example, as shown in FIG. 5, the robot control unit 32 may set an area that spreads from the selected holding candidate point X in the inclined direction of the inclined surface as the predetermined range S.

[0036] Also, as will be described later, when the end effector 24 of the robot arm 2 holds a plurality of workpieces simultaneously and the workpiece holding is not successful, the end effector 24 will release the plurality of workpieces it holds.

[0037] At this time, the robot control unit 32 may change the predetermined distance according to the number of workpieces to be released. It is considered that as the number of workpieces to be released increases, the range of collapse due to those workpieces expands. Therefore, the robot control unit 32 may increase the predetermined distance as the number of workpieces to be released increases. Thereby, the predetermined range S can be set with higher accuracy, and other holding candidate points outside the predetermined range that are surely not affected by collapse can be selected.

[0038] Similarly, the robot control unit 32 may change the predetermined distance according to the weight or size of the workpieces to be released. When the weight or size of the workpieces to be released increases, it is considered that the range of collapse due to those workpieces expands. Therefore, the robot control unit 32 may increase the predetermined distance as the weight or size of the workpieces to be released increases. Thereby, the predetermined range S can be set with higher accuracy, and other holding candidate points outside the predetermined range that are surely not affected by collapse can be selected.

[0039] As described above, when the end effector 24 of the robot arm 2 sucks and holds a plurality of workpieces simultaneously, the holding determination unit 33 determines that the workpiece holding is not successful. The robot control unit 32 controls the robot arm 2 so that the end effector 24 releases the plurality of workpieces according to the determination of the holding determination unit 33.

[0040] At this time, when the workpiece is placed on an inclined plane, the robot control unit 32 may control the robot arm 2 so that the end effector 24 releases the workpiece after offsetting the position of the end effector 24 in consideration of this inclined plane.

[0041] When the workpiece is placed on the inclined plane, it is assumed that the workpiece will shift along this inclined plane. Therefore, the robot control unit 32 may control the robot arm 2 so that the end effector 24 releases the workpiece after offsetting the position of the end effector 24 by the amount of shift of the workpiece due to this inclined plane.

[0042] When the robot control unit 32 offsets the position of the end effector 24 and determines that the offset position is within a predetermined range S, it controls the robot arm 2 so that the end effector 24 releases the workpiece. On the other hand, when the robot control unit 32 determines that the offset position is outside the predetermined range, it adjusts the offset position to be within the predetermined range S and then controls the robot arm 2 so that the end effector 24 releases the workpiece at the offset position.

[0043] By performing such control, the influence of load collapse due to workpiece release can be contained within a predetermined range S, and the influence of load collapse due to workpiece release outside the predetermined range can be suppressed. Therefore, the workpiece can be re-held at other holding candidate points outside the predetermined range where the influence of load collapse is more reliably absent.

[0044] As described above, after the end effector 24 releases the workpiece, the robot control unit 32 controls the robot arm 2 to re-hold the workpiece at other holding candidate points outside the predetermined range.

[0045] Here, for example, as shown in FIG. 4, when there are a plurality of other holding candidate points X1 outside the predetermined range S1, the robot control unit 32 selects, from among the plurality of other holding candidate points X1 outside the predetermined range S1, the other holding candidate point X1 that is farthest from the selected holding candidate point X, and controls the robot arm 2 to hold the workpiece again at the other holding candidate point X1. Thereby, the workpiece can be re-held at another holding candidate point outside the predetermined range where the influence of load collapse is smaller.

[0046] Subsequently, the workpiece holding method according to the present embodiment will be described. FIG. 6 is a flowchart showing the flow of the workpiece holding method according to the present embodiment. Note that the control process shown in FIG. 6 is repeatedly executed every predetermined time.

[0047] The three-dimensional vision sensor 4 acquires three-dimensional information of the workpiece and outputs it to the control device 3 (step S101).

[0048] Based on the three-dimensional information of the workpiece acquired by the three-dimensional vision sensor 4, the candidate calculation unit 31 of the control device 3 calculates a plurality of holding candidate points of the end effector 24 of the robot hand (step S102).

[0049] The robot control unit 32 selects one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation unit 31 (step S103). Based on the three-dimensional information of the workpiece acquired by the three-dimensional vision sensor 4, the robot control unit 32 controls the robot arm 2 so that the end effector 24 of the robot arm 2 holds the workpiece at the selected holding candidate point (step S104).

[0050] The holding determination unit 33 determines whether or not the workpiece has been successfully held by the control of the robot arm 2 by the robot control unit 32 described above (step S105).

[0051] When the robot control unit 32 determines that the workpiece cannot be held successfully by the holding determination unit 33 (NO in step S105), it sets a predetermined range based on the selected holding candidate points (step S106). The robot control unit 32 selects other holding candidate points outside the predetermined range (step S107). The robot control unit 32 controls the robot arm 2 to hold the workpiece again at the selected other holding candidate point (step S108).

[0052] On the other hand, when the robot control unit 32 determines that the workpiece has been held successfully by the holding determination unit 33 (YES in step S105), it ends this process.

[0053] As described above, when the workpiece holding device 1 according to the present embodiment determines that the workpiece cannot be held successfully, it sets a predetermined range based on the selected holding candidate points, selects other holding candidate points outside the predetermined range, and controls the robot arm 2 to hold the workpiece again at the selected other holding candidate point.

[0054] When the workpiece holding fails, the workpiece holding device 1 can control the robot arm 2 so that the end effector 24 of the robot arm 2 holds the workpiece at another holding candidate point outside the predetermined range based on the three-dimensional information of the workpiece already acquired by the three-dimensional vision sensor 4. As a result, it is not necessary to acquire the three-dimensional information of the workpiece again, so that the workpiece can be re-held in a short time.

[0055] The present invention can also be realized, for example, by causing a processor to execute a computer program for the process shown in FIG. 6.

[0056] The program can be stored using various types of non-transitory computer readable media and supplied to a computer. Non-transitory computer readable media include various types of tangible storage media. Examples of non-transitory computer readable media include magnetic recording media (such as flexible disks, magnetic tapes, hard disk drives), magneto-optical recording media (such as magneto-optical disks), CD-ROM (Read Only Memory), CD-R, CD-R / W, semiconductor memories (such as mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, RAM (random access memory)).

[0057] The program may also be supplied to the computer by various types of transitory computer readable media. Examples of transitory computer readable media include electrical signals, optical signals, and electromagnetic waves. The transitory computer readable media can supply the program to the computer via wired communication channels such as electric wires and optical fibers, or wireless communication channels.

[0058] Each part constituting the control unit according to each of the above-described embodiments can be realized not only by a program but also by dedicated hardware such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field-Programmable Gate Array) for a part or all of it.

Explanation of Reference Numerals

[0059] 1 Workholding device, 2 Robot arm, 3 Control device, 3a Processor, 3b Internal memory, 3c Storage device, 4 3D vision sensor, 5 Force sensor 21 Link, 23 Joint part, 24 End effector, 31 Candidate calculation unit, 32 Robot control unit, 33 Holding determination unit

Claims

1. holding means for holding one work at a time from among a plurality of works placed in a three-dimensional space; information acquisition means for acquiring three-dimensional information of the plurality of works; candidate calculation means for calculating a plurality of holding candidate points which are candidates for holding points of the work when the holding means holds the work, based on the three-dimensional information of the work acquired by the information acquisition means; control means for selecting one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation means, and controlling the holding means to hold the work at the selected holding candidate point; determination means for determining whether or not the holding of the work has been successful by the control of the holding means by the control means; comprising when the control means is determined by the determination means that the holding of the work has not been successful, the control means sets a range within a predetermined distance from the selected holding candidate point as a predetermined range, selects another holding candidate point outside the predetermined range, and controls the holding means to hold the work again at the selected other holding candidate point; when the holding means holds a plurality of works simultaneously, the determination means determines that the holding of the work has not been successful; when the control means is determined by the determination means that the holding of the work has not been successful, the control means controls the holding means to release the work within the predetermined range, and then controls the holding means to hold the work again at the other holding candidate point; the control means increases the predetermined distance as the number, weight, or size of the work to be released increases; Work holding device.

2. The work holding device according to claim 1, further comprising weight detection means for detecting the weight of the work when the holding means holds the work; the determination means determines whether or not the holding of the work has been successful based on the weight of the work detected by the weight detection means; Work holding device.

3. The work holding device according to claim 1, the holding means sucks and holds the work in a non-contact state by starting suction in a non-contact state and then adsorbing by coming into contact; Work holding device.

4. a step of acquiring three-dimensional information of a plurality of works placed in a three-dimensional space; a step of calculating a plurality of holding candidate points which are candidates for holding points of the work when the holding means holds the work, based on the acquired three-dimensional information of the work; Selecting one holding candidate point from among the plurality of calculated holding candidate points, and controlling the holding means to hold the workpiece at the selected holding candidate point; Determining whether the holding of the workpiece is successful under the control of the holding means; When it is determined that the holding of the workpiece has not been successful, setting a range within a predetermined distance from the selected holding candidate point as a predetermined range, selecting other holding candidate points outside the predetermined range, and controlling the holding means to hold the workpiece again at the selected other holding candidate points; including; When the holding means holds a plurality of workpieces simultaneously, determining that the holding of the workpiece has not been successful; When it is determined that the holding of the workpiece has not been successful, controlling the holding means to release the workpiece within the predetermined range, and then controlling the holding means to hold the workpiece again at the other holding candidate points; Increasing the predetermined distance as the number, weight, or size of the workpiece to be released increases; Workpiece holding method.

5. A process of acquiring three-dimensional information of a plurality of workpieces placed in a three-dimensional space; A process of calculating a plurality of holding candidate points that are candidates for holding points of the workpiece when the holding means holds the workpiece based on the acquired three-dimensional information of the workpiece; Selecting one holding candidate point from among the plurality of calculated holding candidate points, and controlling the holding means to hold the workpiece at the selected holding candidate point; A process of determining whether the holding of the workpiece is successful under the control of the holding means; When it is determined that the holding of the workpiece has not been successful, setting a range within a predetermined distance from the selected holding candidate point as a predetermined range, selecting other holding candidate points outside the predetermined range, and controlling the holding means to hold the workpiece again at the selected other holding candidate points; causing a computer to execute; When the holding means holds a plurality of workpieces simultaneously, determining that the holding of the workpiece has not been successful; When it is determined that the holding of the workpiece has not been successful, controlling the holding means to release the workpiece within the predetermined range, and then controlling the holding means to hold the workpiece again at the other holding candidate points; Increasing the predetermined distance as the number, weight, or size of the workpiece to be released increases; Program.

6. Candidate calculation means for calculating a plurality of holding candidate points, which are candidates for holding points of the workpiece when the holding means holds the workpiece, based on three-dimensional information of a plurality of workpieces placed in a three-dimensional space; Control means for selecting one holding candidate point from among the plurality of holding candidate points calculated by the candidate calculation means and controlling the holding means to hold the workpiece at the selected holding candidate point; Determination means for determining whether or not the holding of the workpiece has been successful by the control of the holding means by the control means; comprising: When the control means is determined by the determination means that the holding of the workpiece has not been successful, the control means sets a range within a predetermined distance from the selected holding candidate point as a predetermined range, selects another holding candidate point outside the predetermined range, and controls the holding means to hold the workpiece again at the selected other holding candidate point; When the holding means holds a plurality of workpieces at the same time, the determination means determines that the holding of the workpiece has not been successful; When the control means is determined by the determination means that the holding of the workpiece has not been successful, the control means controls the holding means to release the workpiece within the predetermined range, and then controls the holding means to hold the workpiece again at the other holding candidate point; The control means increases the predetermined distance as the number, weight, or size of the workpiece to be released increases; A control device.

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