Gripping apparatus

Abstract

A main control device 40 of a gripping apparatus 1 moves claw parts 22 of a gripper 20 to an initial claw position where the opening width is between a maximum value and a minimum value depending on the type of a workpiece W to be gripped. When causing the gripper 20 to grip a workpiece, the main control device 40 causes the plurality of claw parts 22 to move from the initial claw position while causing the robot arm 12 to move the gripper 20 toward a workpiece W to cause the gripper 20 to grip the workpiece W.

Description

Gripping device

[0001] The technology disclosed in this specification relates to a gripping device having a gripping part capable of gripping a workpiece.

[0002] Patent Document 1 describes a gripping device having a gripping part capable of gripping a workpiece. In the gripping device, after moving the position of the gripping part from the reference position to the workpiece by the arm part, the workpiece can be gripped by adjusting the opening width of a plurality of claw parts in the gripping part. For example, the gripping device moves the gripping part for gripping the workpiece to a predetermined workpiece placement position, and then releases the gripping of the workpiece by the gripping part to complete the movement of the workpiece.

[0003] Japanese Patent Application Laid-Open No. 2018-144158

[0004] In order to improve productivity, it is desirable to shorten the time required for the gripping part to grip the workpiece in the gripping device. In particular, even in the process of sequentially gripping different types of workpieces, it is desirable to shorten the time required for the gripping part to grip the workpiece regardless of the difference in the workpiece shape. Therefore, there is room for improvement in shortening the time required for the gripping part to grip the workpiece.

[0005] An object of the present disclosure is to provide a gripping device capable of shortening the time required to grip a workpiece even when sequentially gripping different types of workpieces within one working process.

[0006] The gripping device according to the present disclosure includes a gripping part capable of gripping a workpiece by changing the positions of a plurality of claw parts, an arm part to which the gripping part is attached and whose position can be changed, and a control device. The control device moves the plurality of claw parts to an initial claw position where the opening width is between the maximum value and the minimum value according to the type of the workpiece to be gripped, and while moving the gripping part toward the workpiece to be gripped by the arm part, moves the plurality of claw parts from the initial claw position in the gripping part to grip the workpiece.

[0007] According to the above configuration, even when the gripping device sequentially grips different types of workpieces, the time required to grip the workpiece can be shortened.

[0008] This is a diagram illustrating the gripping device. This is a block diagram of the gripping device. This is a flowchart of the preparation procedure. This is a diagram illustrating the component information. This is a flowchart illustrating the procedure of processing performed by the main control device. This is a diagram illustrating point cloud data. This is a flowchart showing the process of S25 in Figure 5 in detail. This is a diagram illustrating the estimation of the gripping point. This is a timing chart related to workpiece removal. This is a flowchart illustrating the procedure for updating the initial jaw position.

[0009] (Outline of this embodiment) (1) The gripping device according to the present disclosure comprises a gripping unit capable of gripping a workpiece by changing the position of a plurality of claws, an arm unit to which the gripping unit is attached and capable of changing the position of the gripping unit, and a control device. The control device moves the plurality of claws to an initial claw position where the opening width is between the maximum and minimum values, according to the type of workpiece to be gripped, and moves the gripping unit toward the workpiece to be gripped by the arm unit, thereby moving the plurality of claws from the initial claw position to grip the workpiece.

[0010] In the gripping device with the above configuration, the time it takes to grip a workpiece can be shortened even when the shape of the workpiece varies greatly depending on the type, by moving multiple claws from their initial claw positions relative to the gripping unit according to the type of workpiece. Furthermore, by synchronizing the movement of the multiple claws from their initial claw positions with the period during which the arm moves the gripping unit toward the workpiece, the time it takes for the gripping unit to grip the workpiece can be shortened compared to when the movement of the gripping unit and the movement of the claws of the gripping unit are performed in separate periods.

[0011] (2) Depending on the type of workpiece, a gripping width is defined which indicates the opening width of multiple claws at multiple gripping points on which the gripping device can grip the workpiece, and the initial claw position may be a position corresponding to the multiple gripping widths defined for each type of workpiece. For example, in the case of workpieces stacked in bulk in a container, the orientation of each workpiece within the container may differ, so having multiple gripping points on the workpiece makes it possible to grip the workpiece regardless of its orientation within the container. In the above configuration, by setting the initial claw position to a value corresponding to the gripping width at multiple gripping points defined for each type of workpiece, the time required to grip the workpiece can be shortened even when the gripping point gripped by the gripping part differs depending on the orientation of the workpiece.

[0012] (3) The initial jaw position may be set to a position where the multiple jaw sections are opened to an average value of multiple gripping widths defined for the workpiece. This prevents the opening width of the jaw sections from becoming too large at the initial jaw position, even if the gripping widths at each gripping point of the workpiece differ significantly, and shortens the time required for the gripping section to grip the workpiece.

[0013] (4) The initial jaw position may be set so that the multiple jaws have an opening width corresponding to the gripping width at the gripping point with the highest priority among the multiple gripping points defined for the workpiece. For example, there may be a position that is given the highest priority as a gripping point for each workpiece. In the above configuration, by setting the opening width of the multiple jaws at the initial jaw position to a value corresponding to the gripping width at the gripping point with the highest priority, the time required to grip the workpiece can be minimized when the gripping part grips the gripping point with the highest priority.

[0014] (5) The initial jaw position may be set to a position where the multiple jaw sections are opened to a width corresponding to the median of multiple gripping widths defined for the workpiece. This prevents the opening width of the jaw sections from becoming too large at the initial jaw position, even when the gripping section grips one of the multiple gripping points defined for the workpiece, and shortens the time required for the gripping section to grip the workpiece.

[0015] (6) The control device may include a claw position update unit that records the gripping width at the gripping point when the gripping unit grips a workpiece, and updates the initial claw position based on the recorded past gripping width. As a result, as the number of times the workpiece is gripped increases, the initial claw position is updated to a value that is in line with the trend of the gripping point when the gripping unit grips the workpiece, thereby further shortening the time required for the gripping unit to grip the workpiece.

[0016] (7) The control device may be configured to include a warning unit that, when the gripping unit grips a workpiece to be gripped, compares the opening width of the multiple claws when the gripping unit actually grips the workpiece with a predetermined gripping width and issues a warning based on the comparison result. This makes it possible to warn the operator if the gripping width of the workpiece actually gripped by the gripping unit differs significantly from the assumed gripping width of the workpiece.

[0017] (8) The control device may be equipped with a measuring sensor for measuring the shape of the workpiece, and based on the measurement results from the measuring sensor, extract candidate gripping points, calculate a first movement time required to move the gripping unit to a candidate gripping point, calculate a second movement time required to move the multiple claws from the initial claw position to the gripping width at the candidate gripping point, and identify candidate gripping points where the second movement time is shorter than the first movement time as the object to be gripped. This makes it possible to select gripping points as objects to be gripped where the multiple claws can be moved from the initial claw position to the gripping width corresponding to the gripping point before the gripping unit is moved to the gripping point. As a result, the effect of shortening the time it takes for the gripping unit to grip the workpiece can be enhanced.

[0018] (Details of Embodiments of the Disclosure) The gripping devices according to the embodiments of this disclosure are described below. The gripping devices according to the embodiments are not limited to the configurations disclosed, but are shown in the claims and are intended to include all modifications in the meaning and scope equivalent to the claims.

[0019] (First Embodiment) The gripping device 1 shown in Figure 1 is a device that grips workpieces W such as bolts and cylindrical parts and moves them to a tray 3. The gripping device 1 mainly comprises a robot 10, a measuring sensor 30, and a main control device 40 (shown in Figure 2). As shown in Figure 1, a parts rack 4 and a workbench 5 are installed around the gripping device 1. The parts rack 4 has multiple shelves arranged in the height direction, and on each shelf are multiple containers 2 containing workpieces W. The containers 2 are rectangular boxes with an open top when viewed from above, and each container 2 contains workpieces W of the same type. A tray 3 is placed on the workbench 5. The tray 3 is a rectangular box with an open top when viewed from above, and its interior is divided into multiple parts storage compartments. The location on the workbench 5 where the tray 3 is placed is predetermined. The shapes of the containers 2 and trays 3 are not limited to the shapes described above and can be selected as appropriate. For example, tray 3 does not necessarily have to be divided into multiple component storage compartments.

[0020] The robot 10 constituting the gripping device 1 is an articulated robot and comprises a base 11, a robot arm 12, a gripper 20 which is an example of a gripping part, and a robot control device 25 (shown in Figure 2). The base 11 is a stand for fixing the robot 10 to the installation location and is fixed to the floor surface by anchor bolts or the like. One end of the robot arm 12 is fixed to the upper surface of the base 11. The robot arm 12 comprises seven link sections and six joint sections that connect each link section. Each joint section has a servo motor 15, as shown in Figure 2, and the relative angle between the link sections can be adjusted by controlling the rotation angle of the output shaft of each servo motor 15.

[0021] A gripper 20 is attached to the tip of the robot arm 12 via an adapter. The gripper 20 has a pair of claws 22 for gripping the workpiece W, and a gripper body 21 that slidably holds the pair of claws 22. The gripper body 21 houses a servo motor 23 (shown in Figure 2) and a displacement mechanism (not shown) that converts the rotation of the output shaft of the servo motor 23 into a sliding motion of the pair of claws 22. The gripper 20 can narrow its opening width by sliding the pair of claws 22 toward each other using the rotational drive of the servo motor 23. On the other hand, the gripper 20 can widen its opening width by sliding the pair of claws 22 toward each other using the rotational drive of the servo motor 23.

[0022] As shown in Figure 2, the robot control device 25 includes an arm motor driver 27 for adjusting the rotation angle and rotation speed of the servo motors 15 of the robot arm 12, and a gripping motor driver 26 for adjusting the rotation angle and rotation speed of the servo motors 23 of the gripper 20. Furthermore, the robot control device 25 can change the position of the tip of the robot arm 12, i.e., the position of the gripper 20, by controlling the rotation of each servo motor 23 of the robot arm 12 using the arm motor driver 27, based on commands output from the main control device 40. In addition, the robot control device 25 can change the opening width of the pair of claws 22 by controlling the rotation of the servo motors 23 using the gripping motor driver 26, based on commands output from the main control device 40.

[0023] A measuring sensor 30 for measuring the workpiece W is attached to the gripper body 21. In this embodiment, the measuring sensor 30 is a three-dimensional measuring sensor and can acquire three-dimensional point cloud data from the object, as shown in Figure 4, which will be described later. Here, the point cloud data is data that includes relative coordinates from a reference position on the measuring sensor 30. For example, a 3D camera, a three-dimensional laser measuring instrument, etc., can be used as the measuring sensor 30. The measuring sensor 30 is attached to the gripper body 21 with the imaging direction directed toward the tip of the claw portion 22 on the gripper 20 and the optical axis aligned with the direction in which the claw portion 22 extends. As a result, for example, by positioning the robot arm 12 so that the tips of the pair of claw portions 22 face the container 2, the measuring sensor 30 can place the container 2 containing the workpiece W within its measurement range.

[0024] The main control device 40 is a device that controls the robot 10 and the measurement sensor 30. The main control device 40 includes a calculation unit 41, memory 42, display unit 43, operation unit 44, input / output IF 45, image processing unit 46, etc. The calculation unit 41 includes a CPU and RAM (not shown). The memory 42 is a storage device having a non-volatile storage medium such as a hard disk. Various programs and data executed by the calculation unit 41 are stored in the memory 42. The display unit 43 is a device that displays text, images, etc., for example, a liquid crystal display. The operation unit 44 is a user interface that can receive instructions according to the operator's operation, and is an input device such as a physical key or touch panel. The input / output IF 45 is an interface for the calculation unit 41 to communicate with the robot control device 25 and the measurement sensor 30, etc. IF is an abbreviation for interface. The image processing unit 46 is an integrated circuit capable of performing known image processing on point cloud data acquired by the measurement sensor 30.

[0025] Although not shown in the diagram, the main control unit 40 is equipped with a communication interface for communicating with an external management device via a network. As will be described later, the main control unit 40 can acquire CAD information and other data from the management device via the communication interface.

[0026] In the gripping device 1 with the above configuration, the robot 10 can perform an retrieval operation in which it grasps workpieces W that are loosely stacked in a container 2 and moves the grasped workpieces W to a tray 3, according to a program stored in the memory 42. Prior to the robot 10's retrieval operation of workpieces W, the main control device 40 uses point cloud data acquired by the measurement sensor 30 to identify the position of the workpieces W to be grasped and the gripping point. The main control device 40 can then plan the posture of the robot arm 12 for grasping the identified gripping point. Furthermore, in the gripping device 1, each time the robot 10 performs an retrieval operation of workpieces W, the robot 10 is controlled to return to a reference position (sometimes called the home position). In this embodiment of the gripping device 1, the reference position may be set to the same position as the measurement position of the measurement sensor 30.

[0027] Furthermore, the gripping device 1 is capable of performing a pick-up operation to pick up workpieces of different types from the tray 3 within a single process. For example, the gripping device 1 can move workpiece WA, which is contained in container 2A, to tray 3 using the gripper 20, and then move workpiece WB, which is of a different type, which is contained in container 2B, to tray 3 using the gripper 20, and repeat this process. In other words, when one process is completed, different types of workpieces W will be placed in each component storage compartment of tray 3.

[0028] (Regarding preparation) Next, we will explain the preparations that are carried out prior to starting the workpiece removal operation of the gripping device 1. Figure 3 is a flowchart illustrating the preparations. In these preparations, information for each type of workpiece to be gripped is registered in the part information 100 recorded in the memory 42. For example, the registration of part information 100 carried out in the preparations is a process that is executed when the main control device 40 receives an operation from the operator on the operation unit 44.

[0029] In this embodiment, as an example, part information 100 is registered for each of the four workpiece types shown in Figure 4(a): workpiece WA, WB, WC, and WD. Workpiece WA is a bolt part, workpiece WB is a screw part, workpiece WC is a cylindrical pipe part, and workpiece WD is a connecting member.

[0030] As shown in Figure 3, in step 10, the main control device 40 registers the workpiece to be gripped as a part in the part information 100. Hereafter, step will also be referred to as "S". Specifically, the main control device 40 acquires CAD information containing information about the workpiece through communication with a management device (not shown), and registers the information contained in the CAD information into the corresponding items in the part information 100.

[0031] Figure 4(b) shows a portion of the part information 100. The part information 100 is a relational table that defines the relationship between each item and its registered value. In Figure 4(b), the items work type, gripping width, and initial jaw position are shown as an example. Hereafter, when referring to an item in the part information 100, it will be written as "item name," and when referring to the registered value of an item, it will be written as "item name registered value" to distinguish between the two. For example, using Figure 4(b) as an example, the item "work type" refers to an item in the part information 100, and the work type "WA" refers to the registered value registered in the item.

[0032] The item "Work Type" in part information 100 is an item where a value for identifying the type of work W is registered. In this embodiment, the work type "WA" is registered as the registered value for the item "Work Type" in part information 100A corresponding to work WA. In addition, the work type "WB" is registered in part information 100B corresponding to work WB, the work type "WC" is registered in part information 100C corresponding to work WC, and the work type "WD" is registered in part information 100D corresponding to work WC, as registered values ​​for the item "Work Type".

[0033] In S11, the main control device 40 accepts an operation from the operator and registers the value of the item "gripping width" included in the part information 100. The registered value of the item "gripping width" is a value that indicates the opening width of the pair of claws 22 required when the gripper 20 grips the gripping points of the workpiece W. The "gripping point" is a set of positions that the claws 22 contact when the gripper 20 grips the workpiece W, and is an arbitrarily determined position. Figure 4(c) is point cloud data of the workpiece WA detected by the measurement sensor 30. In the workpiece WA, two positions GP1 and GP2 are defined as gripping points, and gripping widths LG1 and LG2 are registered for each gripping point. For example, the gripping width LG is calculated by adding a margin value to the dimension between the relevant gripping points obtained from CAD. The margin value is a value that takes into account the part tolerance in the workpiece W. For example, in the case of workpiece WA, if the dimension of gripping point GP1 is φN, then "N + α", which is this dimension plus a margin value α, is registered as the gripping width at gripping point GP1.

[0034] When workpieces W are stacked loosely in container 2, the orientation of each workpiece W within container 2 will differ. Therefore, by defining multiple gripping points GP on each workpiece W, the gripper 20 can grip the workpiece W regardless of its orientation within container 2. The number of gripping points that the gripper 20 can grip may vary depending on the shape of the workpiece for each type of workpiece. For example, for workpiece WA, two gripping points GP1 and GP2 may be defined, and a gripping width corresponding to each gripping point GP1 and GP2 may be registered, while for workpiece WD, four gripping points may be defined, and a gripping width corresponding to each gripping point GP may be registered. The gripping points for each type of workpiece may be arbitrarily determined during pre-registration, or they may be determined as a result of known learning using a computer or the like.

[0035] In S12, the main control device 40 registers the value of the item "Initial Claw Position" in association with the registered value of the item "Work Type" in the part information 100. The item "Initial Claw Position" is an item in which the opening width of the pair of claws 22 is registered when the gripper 20 is waiting at the reference position.

[0036] The registered value for the item "Initial Claw Position" is registered as a value between the maximum value Lmax and the minimum value Lmin of the opening width of the pair of claw portions 22. In this embodiment, the main control device 40 calculates the average value of each registered value of the item "Gripping Width" associated with the item "Work Type" in the part information 100, and sets the calculated value as the registered value for the item "Initial Claw Position". For example, in part information 100A, two gripping widths "LG1" and "LG2" are registered in association with the work type "WA", so the average value of the two gripping widths "LG1" and "LG2" is registered as the registered value for the item "Initial Claw Position". Although not explained here, the main control device 40 also registers the values ​​of each part information 100B, 100C, and 100D for work types other than work type WA, such as WB, WC, and WD, through the processing in S10 to S12 as already described.

[0037] (Regarding the processing performed by the main control device) Next, we will explain the processing performed by the main control device 40 when a removal operation is performed on the workpiece W. This processing starts when the operator operates the main control device 40 to instruct a removal operation on the workpiece W. When the operator instructs a removal operation, they specify the number of trays 3 on which the workpiece W will be placed. The flow shown in Figure 5 shows the procedure for the processing performed by the main control device 40 when workpieces W of different workpiece types are placed on one tray 3. Therefore, if there are multiple trays 3 on which the workpiece W will be placed, the processing in Figure 5 will be repeated for the specified number of trays 3. Note that the memory 42 of the main control device 40 is assumed to already contain the registration values ​​of the part information 100 explained using Figure 4.

[0038] In S20, the main control device 40 determines whether or not all workpieces W of the specified workpiece types have been placed on the tray 3. At the start of the flow shown in Figure 5, since not all workpieces W of the specified workpiece types have been placed on the tray 3 (S20: NO), the main control device 40 proceeds to S21. In S21, the main control device 40 determines the workpiece type that will now be gripped by the gripper 20. The order in which the workpiece types are determined in S21 is executed according to the program recorded in the memory 42. First, the workpiece type "WA" corresponding to workpiece WA is determined to be the workpiece type that will now be gripped.

[0039] In S22, the main control device 40 refers to the part information 100 and moves the position of the pair of claws 22 in the gripper 20 to the initial claw position corresponding to the determined workpiece type. For example, in the part information shown in Figure 4(b), the initial claw position "Ps_A" is registered in association with the workpiece type "WA". Therefore, the main control device 40 outputs a command to the robot control device 25 so that the opening width of the pair of claws 22 becomes the value indicated by the initial claw position "Ps_A". As a result, the robot control device 25 controls the rotation of the servo motor 23 with the gripping motor driver 26 to move the pair of claws 22 to a position where their opening width becomes the value indicated by "Ps_A".

[0040] In S23, the main control device 40 uses the robot arm 12 to move the gripper 20 to a reference position corresponding to the workpiece type and acquires three-dimensional point cloud data (measurement data), which is the measurement result of the workpiece W by the measurement sensor 30. The memory 42 has in advance stored which container 2 on the parts rack 4 contains which workpiece W of which type.

[0041] In S24, the main control device 40 performs gripping position estimation to estimate point cloud data corresponding to workpieces W that can be gripped by the gripper 20 from the measured point cloud data. The image processing unit 46 of the main control device 40 refers to the registered value of the item "extraction information" associated with the workpiece type "WA" in the part information 100, and estimates point cloud data corresponding to workpieces W from the point cloud data acquired by the measurement sensor 30 by a well-known pattern matching using this registered value. In Figure 6, the set of point cloud data estimated to be workpieces W is enclosed by a dashed line, and for the sake of explanation, the point cloud data estimated to be workpieces W is labeled with the symbol "W". As shown in Figure 6, each workpiece W stacked loosely in the container 2 may have a different orientation, so the position of the point cloud data corresponding to workpieces W included in the measurement data also differs depending on the orientation of the workpieces W.

[0042] In S25, the main control device 40 performs a gripping plan to determine the workpiece W to be gripped and the gripping point. Figure 7 is a flowchart illustrating the detailed processing of the gripping plan performed by the main control device 40 in S25. In the following, the point cloud data corresponding to the workpiece W estimated in S24 will also be referred to as "workpiece point cloud data".

[0043] In S40, the main control device 40 determines that the series of processes described later in S41 to S46 has not been performed on all workpiece point cloud data (S40: NO), and proceeds to S41. In S41, the main control device 40 selects the workpiece point cloud data to be judged in S46, which will be described later.

[0044] In S42, the main control device 40 extracts all the point data indicating candidates for gripping points to be gripped by the gripper 20 from the selected workpiece point cloud data. Specifically, the image processing unit 46 of the main control device 40 estimates, as gripping points, the point data having an interval corresponding to the registered value of the item "gripping width" in the component information 100 among the point cloud data of two points included in the workpiece point cloud data. In addition to this, when the component information 100 registers feature information for specifying the gripping point, the image processing unit 46 may estimate the gripping point from the point cloud data by well-known template matching using this feature information of the gripping point. The main control device 40 extracts the point cloud data corresponding to the gripping points at all the "gripping widths" registered in the component information 100 for the same workpiece type.

[0045] In S43, the main control device 40 calculates the first movement time T1 required to move the gripper 20 from the reference position to the point data extracted as a candidate for the gripping point using the following (Equation 1). Note that the main control device 40 calculates the first movement time T1 for all the point data extracted as candidates for the gripping point. First movement time T1 = Gripper movement distance L1 / Gripper movement speed V1... (Equation 1)

[0046] The gripper moving distance L1 is the distance when the gripper 20 moves from the reference position P0 to the candidate for the gripping point. For example, in the present embodiment, as shown in FIG. 8(a), the main control device 40 calculates, on the relative coordinates, the straight-line distance from the reference position of the gripper 20 to the point data that is the candidate for the gripping point as the moving distance L1. In FIG. 8(a), the position between the pair of claw portions 22 is shown as the coordinates indicating the reference position P0 of the gripper 20, but the reference position P0 is not limited to this. Also, the point data used for calculating the gripper moving distance L1 among the two point data may be the point data closest to the reference position P0 among the two points, or the center point on the line segment connecting the two point data may be used. The gripper moving speed V1 is the moving speed when the gripper 20 moves to the gripping point. For example, the average value of the moving speed defined for the robot arm 12 can be used. In addition, when the moving speed of the robot arm 12 can be variably set by a program, the currently set moving speed of the robot arm 12 may be used as the gripper moving speed V1.

[0047] In S44, the main control device 40 calculates the second moving time T2 required to move the pair of claw portions 22 from the current initial claw position to the distance between the point data extracted as the candidate for the gripping point (that is, the gripping width obtained from the point data) using the following (Equation 2). Note that the main control device 40 calculates the second moving time T2 for all the point data extracted as the candidate for the gripping point. Second moving time T2 = Claw moving distance L2 / Claw moving speed V2... (Equation 2)

[0048] The claw moving distance L2 is the moving distance when the claw portion 22 of the gripper 20 moves from the initial claw position to the point data extracted as the candidate for the gripping point in S42. The claw moving speed V2 is the moving speed of the claw portion 22. For example, a moving speed predetermined for the gripper 20 may be used.

[0049] In S45, the main control device 40 registers point data where the calculated second movement time T2 is shorter than the first movement time T1 as point data indicating a candidate gripping point. In other words, the determination in S45 determines whether the pair of claws 22 can be moved from their initial position to an opening width that can grip the gripping point before the gripper 20 is moved from the reference position to the gripping point. If the second movement time T2 is the same as or shorter than the first movement time T1, the pair of claws 22 are already at an opening width that can grip the workpiece W before the gripper 20 is moved to the gripping point. Therefore, there is no delay time before the gripper 20 grips the workpiece W. On the other hand, if the second movement time T2 is longer than the first movement time T1, the pair of claws 22 continue to move even after the gripper 20 has been moved to the gripping point, so there is a delay time until the movement of the claws 22 stops. Therefore, point data like this is excluded from the list of potential gripping points.

[0050] In the example shown in Figure 8(a), the gripping points GP1_a and GP1_b extracted from the workpiece W1, which is close to the reference point, have a second movement time T2 that is longer than the first movement time T1 (T2 > T1), and are therefore excluded from the list of gripping point candidates (indicated by "×" in the figure). On the other hand, the gripping points GP7_a and GP7_b extracted from the workpiece W7, which is farther from the reference point, have a second movement time T2 that is shorter than the first movement time T1 (T2 < T1), and are therefore registered as gripping point candidates (indicated by "〇" in the figure).

[0051] In S46, the main control device 40 calculates the stability St for the registered point data indicating the gripping point. The stability St is an index indicating whether the gripper 20 can grip the gripping point stably. In this embodiment, the stability is calculated according to the distance from the center of gravity of the workpiece W to the gripping point and the contact area of ​​the pair of claws 22 at the gripping point. Specifically, the closer the gripping point is to the center of gravity of the workpiece W, the higher the stability St, and the further the gripping point is from the center of gravity of the workpiece W, the lower the stability St. The larger the contact area of ​​the gripping point with the claws 22, the higher the stability St, and the smaller the contact area of ​​the gripping point with the claws 22, the lower the stability St. The value of the stability St can be any value that allows for differences between different gripping points, for example, it can be a stepped evaluation with a certain range. When the main control device 40 finishes processing in S46, it returns to S40.

[0052] In S40, if the series of processes S41 to S46 has not been performed on all the workpiece point cloud data extracted from the point cloud data, the main control device 40 proceeds to S41 and selects new workpiece point cloud data. In other words, each of the processes S41 to S46 will be performed on the point cloud data corresponding to the new workpiece W.

[0053] Once this process is performed for all workpiece point cloud data (S40: YES), the main control device 40 proceeds to S47. In S47, the main control device 40 assigns a first rank to all point data registered as point data indicating candidate gripping points, according to the length of the first movement time T1. As a result of the processing in S47, the first rank R1 becomes higher for point data among the registered point data that indicate gripping points requiring a shorter movement time for the gripper 20.

[0054] In S48, the main control device 40 assigns a second rank to the registered point data according to its stability St. Through processing in S49, the second rank R2 becomes higher for the point data that indicates a gripping point with a high stability St when gripped by the gripper 20.

[0055] In S49, the main control device 40 identifies a gripping point from the registered point data where both the first rank R1 and the second rank R2 are high, and identifies the workpiece having the identified gripping point as the gripping target. In the example shown in Figure 8(b), among the gripping points for which point data has been registered, the gripping point GP4_b of workpiece W4 has the highest values ​​for both the first rank R1_4b and the second rank R2_4b, so the gripping point GP4_b is identified as the gripping point for this time (indicated by a circle in the figure). Then, workpiece W4, which includes this gripping point GP4_b, is identified as the gripping target. After completing the process in S49, the main control device 40 proceeds to S26 in Figure 5.

[0056] In S26, the main control device 40 performs an operation plan that includes the movement trajectory and posture of the robot arm 12 when moving the gripper 20 to the gripping point identified in the gripping plan in S25, as well as the position of the pair of claws 22 according to the opening width for gripping the workpiece W. In this embodiment, in the operation plan in S26, the position of the pair of claws 22 from the initial claw position to the position corresponding to the opening width of the pair of claws 22 for gripping the workpiece W (intermediate claw position, described later) is set, but instead, it is not necessary to set the gripping width in S26. Note that the operation plan is well known, so its explanation is omitted.

[0057] In S27, the main control device 40 controls the movement of the robot arm 12 to grip the gripping point of the workpiece W, according to the motion plan planned in S26, thereby moving the gripper 20 toward the workpiece W to be gripped. At this time, the main control device 40 transmits a claw movement command to move the pair of claws 22 from the opening width at the initial claw position to the opening width planned in S25. Here, the position of the pair of claws 22 after moving from the initial claw position is also referred to as the intermediate claw position. Since the pair of claws 22 are in the intermediate claw position, it becomes possible to insert the gripping point of the workpiece W between the pair of claws 22.

[0058] In S28, the main control device 40 outputs a gripping command to the robot control device 25 to initiate gripping of the workpiece W, causing the gripper 20 to grip the workpiece W. Upon receiving the gripping command, the robot control device 25 rotates the servo motor 23 using the gripping motor driver 26, moving the pair of claw portions 22 from the intermediate claw position to a position corresponding to the opening width for gripping the workpiece W.

[0059] In S29, the main control device 40 determines whether the opening width of the pair of claws 22 when the gripper 20 actually grips a workpiece is appropriate to the opening width assumed with respect to the gripping point of the workpiece W. For example, if the gripper 20 grips a workpiece W of a different type than the workpiece type specified in advance, the opening width of the pair of claws 22 will differ significantly from any of the registered values ​​of the "gripping width" item registered in the part information 100. Therefore, if the main control device 40 determines that S29 is incorrect (S29: NO), it proceeds to S30 and performs a warning process and discards the gripped workpiece W. In the warning process, the main control device 40 may display text or an image on the display unit 43 indicating that a workpiece W of a different type has been gripped. In addition, the display unit 43 may output a warning sound in the warning process. The main control device 40 then moves the gripper 20 to the discard position and discards the gripped workpiece W at the discard position. In this embodiment, the display unit 43 is an example of a warning unit.

[0060] When the main control device 40 determines that the opening width of the pair of claws 22 is appropriate (S29: YES), it proceeds to S31, where it moves the gripper 20 to the designated parts storage space in the tray 3 and places the workpiece W into the designated parts storage space.

[0061] Next, using Figure 9, we will explain the time progression from when the gripping device 1 removes the workpiece W from the container 2 until it is placed on the tray 3. Before time t1, the pair of claws 22 of the gripper 20 are in their initial claw position. Then, at time t1, a gripping command for the workpiece W is transmitted from the main control device 40 to the robot control device 25, causing the robot arm 12 to move the gripper 20 toward the gripping point of the specified workpiece W. In conjunction with the movement of the gripper 20 toward the gripping point, the pair of claws 22 move from their initial claw position to an intermediate claw position corresponding to the width of the gripping point.

[0062] At time t2, the pair of claws 22 have completed moving to the intermediate claw position. In this example, at time t3, which is later than time t2, the gripper 20 has completed moving to the gripping point. Then, after time t3, under the control of the robot control device 25, the pair of claws 22 move from the intermediate claw position, and at time t4, the gripper 20 has completed gripping the workpiece W. Subsequently, a command to move the workpiece W to the tray 3 is transmitted from the main control device 40 to the robot control device 25, causing the robot arm 12 to move the gripper 20 toward the tray 3.

[0063] At time t5, once the gripper 20 has completed moving to the tray 3, the robot control device 25 instructs the gripper 20 to release its grip on the workpiece W and move the pair of claws 22 back to their initial claw positions. Then, at time t6, once the gripper 20 has released its grip on the workpiece W, the main control device 40 sends a command to the robot control device 25 to return the gripper 20 to its reference position. Therefore, after time t6, the robot control device 25 uses the robot arm 12 to move the gripper 20 toward the reference position.

[0064] For example, consider a case where, after a gripping command for the workpiece W is transmitted from the main control device 40 to the robot control device 25, the opening width of the pair of claws 22 of the gripper 20 is changed from the maximum opening width. In this case, after the gripper 20 has completed moving to the gripping point (time t2 in the example of Figure 9), the robot control device 25 controls the pair of claws 22 to move from the maximum opening width to an intermediate claw position where gripping of the workpiece W can begin. In such a case, depending on the shape of the workpiece W, it is expected that the time required to move the position of the pair of claws 22 to the intermediate claw position where gripping of the workpiece W can begin may be long. Therefore, in the comparative example, depending on the type of workpiece, the time required from the transmission of the gripping command until the gripper 20 grips the workpiece W may be longer than the time shown in Figure 9 (the period from time t1 to t4).

[0065] In contrast, in this embodiment, the initial claw position of the pair of claws 22 is changed according to the type of workpiece. This shortens the time from when a gripping command is transmitted from the main control device 40 until the gripper 20 changes the pair of claws 22 from the initial claw position to the intermediate claw position and starts gripping the workpiece W. As a result, it is possible to suppress the time required for the gripper 20 to grip the workpiece W from becoming too long.

[0066] In the embodiment described above, the following effects can be achieved. By moving the positions of the multiple claw portions 22 to an initial claw position between the maximum and minimum values ​​of their opening width, depending on the type of workpiece to be gripped, the time required to move the claw portions 22 and grip the workpiece can be shortened, even when the shape of the workpiece differs greatly depending on the type of workpiece. Furthermore, by moving a pair of claw portions 22 from the initial claw position to an intermediate claw position in synchronization with the period during which the robot arm 12 moves the gripper 20 toward the workpiece W, the time required to grip the workpiece W can be shortened compared to when the movement of the gripper 20 and the movement of the claw portions 22 are performed in separate periods.

[0067] By setting the initial claw position of the claw portion 22 to a value corresponding to the gripping width at a plurality of gripping points determined for each type of workpiece, the time required to grip the workpiece W can be shortened even when the gripping point gripped by the gripper 20 differs depending on the orientation of the workpiece W inside the container 2.

[0068] By setting the initial claw position to a position where the opening width corresponds to the average value of multiple gripping widths defined for the workpiece W, it is possible to suppress the opening amount of the claw portion 22 at the initial claw position from becoming too large, regardless of which gripping point the gripper 20 grips.

[0069] The main control device 40 may be configured to compare the gripping width when the pair of claws 22 actually grip the workpiece W with a predetermined gripping width and issue a warning based on the comparison result. This makes it possible to warn the operator if the shape of the workpiece W that is actually gripped differs significantly from the expected shape of the workpiece W.

[0070] The main control device 40 identifies candidate gripping points to be gripped, where the second movement time T2 is shorter than the first movement time T1. This allows the gripper 20 to select a candidate gripping point from among multiple gripping points, where the pair of claws 22 can be moved from their initial claw position to an opening width sufficient to grip the gripping point before the gripper 20 is moved to the gripping point. This enhances the effect of shortening the time it takes for the gripper 20 to grip the workpiece.

[0071] (Second Embodiment) In the second embodiment, the configurations that differ from the first embodiment will be mainly described, and the same reference numerals will be used for the same components as in the first embodiment, and their descriptions will not be repeated. In this embodiment, compared to the first embodiment, the main control device 40 has a different configuration for updating the initial claw position registered in the component information 100.

[0072] Even after the registered value for the item "initial jaw position" is registered in the part information 100, there may be gripping points where the gripper 20 grips the workpiece W that are frequently used and gripping points that are not frequently used. Therefore, by updating the registered value for the item "initial jaw position" registered in the part information 100, taking into account the tendency of the gripper 20 to grip the workpiece W, it becomes possible to shorten the time required to grip the workpiece W in accordance with the tendency of the gripping points when the gripper 20 grips the workpiece W.

[0073] Figure 10 shows the process executed in S28 of Figure 5. In S50, the main control device 40 sends a gripping command for the workpiece W to the robot control device 25, causing the gripper 20 to grip the workpiece W.

[0074] In S51, the main control device 40 records the gripping width, which indicates the opening width of the pair of claws 22 when the gripper 20 grips the workpiece W, in the history information stored in the memory 42. The history information is information that records the gripping width values ​​when the gripper 20 gripped the gripping point of the workpiece W multiple times from the present to the past. The gripping width recorded in the history information in S51 is a value calculated by the image processing unit 46 in S25 using point data identified as candidate gripping points, and is different from the registered value of the item "gripping width" in the part information 100. The history information should record the gripping widths for multiple past times for each type of workpiece.

[0075] In S52, the main control device 40 updates the value of the item "initial jaw position" registered in the part information 100 using past gripping widths for the same workpiece type recorded in the history information. First, the main control device 40 extracts values ​​from multiple past gripping widths for the same workpiece type recorded in the history information from the value recorded this time, and calculates the average value of the extracted past gripping widths. Then, the main control device 40 registers the calculated average value as the updated initial jaw position in the item "initial jaw position" in the part information 100. As a result, each time the workpiece W is gripped by the gripper 20, the initial jaw position is updated taking into account the past gripping widths newly recorded in the history information.

[0076] In addition, the main control device 40 may calculate the updated initial claw position in S52 by multiplying the gripping width recorded in the history information by an effective ratio indicating the contribution to updating the initial claw position. For example, the main control device 40 can calculate the updated initial claw position using the following equation (Equation 3): Updated initial claw position = Initial claw position before update × (1 - α) + Current gripping width × α … (Equation 3) Note that "α" is an effective ratio and represents a value greater than 0 and less than 1. In this embodiment, the claw position update unit is realized by the processing performed by the main control device 40 in S51 and S52.

[0077] In the embodiment described above, the main control device 40 records the gripping width of the pair of claws 22 each time the gripper 20 grips the workpiece W, and updates the initial claw position based on the recorded past gripping widths. As a result, as the number of times the gripper 20 grips the workpiece W increases, the initial claw position is updated to match the tendency of the gripping point when the gripper 20 grips the workpiece W, thereby further reducing the time required for the gripper 20 to grip the workpiece W.

[0078] (Regarding the third embodiment) In the third embodiment, the configurations that differ from the first embodiment will be mainly described, and the same reference numerals will be used for the same components as in the first embodiment, and their descriptions will not be repeated. In this embodiment, the initial jaw position is set to a value determined by considering the priority of each gripping point among a plurality of gripping points defined for the workpiece.

[0079] For example, if there are multiple gripping points (gripping widths) that the gripper 20 can grip with respect to the workpiece W, the registered value of the item "initial claw position" in the part information 100 is calculated by multiplying each gripping width by a weighting coefficient indicating priority. The weighting coefficient indicating priority should be set so that the highest value is assigned to the gripping point (gripping width) with the highest priority, and the value of the weighting coefficient decreases as the priority decreases.

[0080] For example, if gripping widths LG_11, LG_12, LG_13, and LG_14 corresponding to four gripping points are registered in part information 100D for workpiece type WD, the initial claw position for workpiece type WD can be calculated using the following equation (Equation 4). In this example, the gripping width at the gripping point with the highest priority is assumed to be LG_11. Initial claw position = LG_11 × β1 + LG_12 × β2 + LG_13 × β3 + LG_14 × β4 + margin Note that β1 + β2 + β3 + β4 = 1 ... (Equation 4)

[0081] In the example above, by setting the weighting coefficient "β1" applied to the gripping width LG_11 to the highest value among the four weighting coefficients β1 to β4, the priority of the gripping point with gripping width LG_11 is given the highest priority. The values ​​of the other weighting coefficients β2, β3, and β4 should be determined according to a comparison of the priorities of the corresponding gripping points.

[0082] In the embodiment described above, the opening width of the multiple claw portions 22 at the initial claw position can be set to a value corresponding to the gripping width at the high-priority gripping point, thereby minimizing the time required to grip the workpiece when the gripper 20 grips the high-priority gripping point.

[0083] (Fourth Embodiment) In the fourth embodiment, the configurations that differ from the first embodiment will be mainly described, and the same reference numerals will be used for the same components as in the first embodiment, and their descriptions will not be repeated. In this embodiment, the initial claw position value is registered in the part information 100 as the median gripping width among a plurality of gripping points (gripping widths) defined for the workpiece type.

[0084] With the above configuration, by setting the initial claw position of the pair of claws 22 to an opening width corresponding to the median value of a plurality of gripping widths defined for the workpiece W, it is possible to suppress the opening amount of the pair of claws 22 from becoming too large regardless of the gripping point of the workpiece W, and to shorten the time required for the gripper 20 to grip the workpiece W.

[0085] (Regarding other embodiments) The technology disclosed herein is not limited to the embodiments described above, and the following embodiments, for example, are also included in the technical scope disclosed herein. The gripper 20 may have a shape comprising a pair of claw portions 22, or it may have a configuration comprising three or more claw portions. Furthermore, the gripper 20 may have a configuration in which the position of the claw portions 22 is changed by compressed air, in addition to a configuration in which the position of the claw portions 22 is changed by the rotation of the servo motor 23.

[0086] In the above embodiment, the workpiece W was measured by a measuring sensor 30 attached to the gripper 20, but instead, the measuring sensor 30 may be positioned above the robot 10. In this case as well, the point cloud data of the workpiece W measured by the measuring sensor 30 can be used to estimate the workpiece to be gripped and the gripping point.

[0087] In the above embodiment 1, the gripping device 1 was described using a 7-axis robot 10 as an example. However, the robot 10 may have a configuration of 8 or more axes or 6 or fewer axes, as long as it can change the position of the gripper 20. Furthermore, the robot 10 may be a horizontally articulated robot equipped with a gripper 20.

[0088] 10: Robot, 12: Robot arm, 20: Gripper, 22: Claw section, 25: Robot control device, 30: Measurement sensor, 40: Main control device, 100: Part information

Claims

1. A gripping device comprising: a gripping unit capable of gripping a workpiece by changing the position of multiple claws; an arm unit to which the gripping unit is attached and capable of changing the position of the gripping unit; and a control device, wherein the control device moves the multiple claws to an initial claw position where the opening width is between the maximum and minimum values, according to the type of workpiece to be gripped; and moves the multiple claws from the initial claw position while the arm unit moves the gripping unit toward the workpiece to be gripped, thereby gripping the workpiece with the gripping unit.

2. A gripping device according to claim 1, wherein the workpiece has a gripping width that indicates the opening width of the plurality of claws at a plurality of gripping points in which the gripping portion can grip the workpiece, according to the type of workpiece, and the initial claw position is a position corresponding to the plurality of gripping widths determined for each type of workpiece.

3. A gripping device according to claim 2, wherein the initial claw position is a position in which the plurality of claw portions are set to an opening width corresponding to the average value of a plurality of gripping widths determined with respect to the workpiece.

4. A gripping device according to claim 2, wherein the initial claw position is a position in which the plurality of claw portions are set to an opening width corresponding to the gripping width at the gripping point with the highest priority among the plurality of gripping points defined for the workpiece.

5. A gripping device according to claim 2, wherein the initial claw position is a position in which the plurality of claw portions are set to an opening width corresponding to the midpoint of a plurality of gripping widths defined with respect to the workpiece.

6. A gripping device according to any one of claims 2 to 5, wherein the control device includes a claw position updating unit that, when the gripping unit grips a workpiece, records the gripping width at the gripping point gripped by the gripping unit, and updates the initial claw position based on the recorded past gripping width.

7. A gripping device according to any one of claims 2 to 6, wherein the control device includes a warning unit that, when the gripping unit grips the workpiece, compares the opening width of the plurality of claws when the gripping unit grips the workpiece with a predetermined gripping width relative to the workpiece, and issues a warning based on the comparison result.

8. A gripping device according to any one of claims 1 to 7, comprising a measuring sensor for measuring the shape of a workpiece, wherein the control device extracts candidate gripping points from a plurality of gripping points based on the measurement results from the measuring sensor, calculates a first movement time required to move the gripping part to the candidate gripping point, calculates a second movement time required to move the plurality of claw parts from the initial claw position to the gripping width at the candidate gripping point, and identifies candidate gripping points for which the second movement time is shorter than the first movement time as objects to be gripped.

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