Transfer device and workpiece arrangement method

Abstract

In a transfer device 1 holding a workpiece 90, the workpiece 90 is brought into surface contact with a first reference surface 75 of a workpiece fixing part 71, and then a transfer force is applied to the workpiece 90 to move, while resistance force applied in the opposite direction is acquired. Then, it is determined whether or not the arrangement state is appropriate with reference to the change state of the resistance force. Thus, the situation of the surface contact can be accurately grasped from the change in the resistance force, and the workpiece 90 can be correctly arranged by carefully moving the workpiece 90 to the reference surface as in manual work, and misarrangement of the workpiece can be avoided. The transfer device 1 being capable of realizing automation of the arrangement without difficulty eliminates the need for structural change in a machine tool 70, and can prevent complication and increase in size of the machine tool 70 itself, and can suppress cost related to introduction and use of the machine tool 70.

Description

Transfer device and workpiece placement method

[0001] The present disclosure relates to a transfer device that places a workpiece on a machine tool, and more particularly to a device that places a workpiece in close contact with a reference surface in a workpiece fixing portion of the machine tool.

[0002] Surface grinders have the advantage of being able to grind the outer surface of a workpiece to form a highly accurate flat surface. In precision machining of metal workpieces using a surface grinder, skilled technicians place and fix rectangular parallelepiped or other workpieces in the appropriate position on the grinder's table based on their experience. In order to improve the efficiency of such machining operations using surface grinders, there is a demand for automation of the process of placing (setting) workpieces on the table, which was previously done manually.

[0003] Various automation techniques have been proposed in recent years. For example, a rotatable table supporting the workpiece is used, and multiple workpiece placement positions on the table are set, with positions away from the grinding wheel used as the loading position for the unmachined workpiece and the unloading position for the machined workpiece. Then, when the table is rotated, the unmachined workpiece that was at the loading position reaches the machining position, and the machined workpiece that was at the machining position reaches the unloading position.

[0004] As a result, while the workpiece is being machined with the grinding wheel, the unmachined workpiece can be transported and placed at the loading position on the table by a predetermined transport means, and the machined workpiece can be unloaded from the unloading position on the table by a predetermined transport means. After the workpiece is machined, the table is rotated, and the unmachined workpiece from the loading position is placed at the new processing position, and the machined workpiece is moved from the processing position to the unloading position. In this way, the workpiece can be automatically attached to and detached from the table in parallel with the machining of the workpiece, and the setting of the workpiece on the table, which previously relied on manual labor, can be automated. An example of a method for automatically positioning and fixing a workpiece on the table in such a conventional surface grinder is disclosed in Japanese Patent Laid-Open Publication No. 2-185357.

[0005] Japanese Patent Publication No. 2-185357

[0006] A typical method for automating workpiece placement in a conventional surface grinder is the method exemplified in Patent Document 1. In the conventional surface grinder shown in Patent Document 1, the table on which the workpiece is fixed is replaced with an index table that rotates at a fixed angle and a rotary table on which the workpiece is fixed. As a result, the structure is more complex than surface grinders with earlier types of tables, and the size and cost are higher.

[0007] Furthermore, according to Patent Document 1, the work of placing a workpiece on a table is performed by a work loader or a robot. In this case, the workpiece is not placed on the table with the same care as when it is placed manually by a skilled worker. In particular, this technique has not yet been able to replace the placement work in which a worker abuts the workpiece against a table or a positioning jig on the table, and moves the workpiece while pressing it against the table or jig by hand, thereby positioning the workpiece in three axes and ensuring that the workpiece is in close contact with the table.

[0008] Therefore, when a workpiece is placed on the table, the placement process proceeds without going through the steps to determine whether the workpiece is in close contact with the table and correctly positioned, as accurately as an experienced worker would when performing manual work.If the workpiece is mistakenly moved to the machining process in an improperly positioned state, such as when the workpiece is not in close contact with the table, this could lead to problems such as poor machining.

[0009] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a transfer device and a workpiece placement method that can properly place a workpiece on a machine tool, prevent defects, and improve work efficiency through automation.

[0010] The transfer device disclosed herein is a work transfer device that holds and moves a workpiece relative to a workpiece fixing part that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing part, and is equipped with a force sensor that can detect forces and / or moments generated in the workpiece, wherein the workpiece fixing part has a first reference surface, and the workpiece is a three-dimensional object having a first surface that is in contact with the first reference surface, and the workpiece is placed on the workpiece fixing part by applying a transfer force to the workpiece while maintaining a surface contact state between the first reference surface of the workpiece fixing part and the first surface of the workpiece, and the force sensor acquires a resistance force that is applied to the workpiece to which the transfer force has been applied in a direction opposite to the direction of the transfer force, and determines whether the placement of the workpiece on the workpiece fixing part is normal or not based on the change in the value of the resistance force acquired by the force sensor.

[0011] According to the present disclosure, a transfer device holding a workpiece places the workpiece in surface contact with a first reference surface of a workpiece fixing portion, applies a transfer force to the workpiece to move it, and acquires the resistance force acting in the opposite direction. The change in the resistance force is then referenced to determine whether the placement state is appropriate. This allows the surface contact state to be accurately determined from the change in resistance force, and the workpiece can be carefully moved relative to the reference surface as if manually placed correctly, thereby avoiding incorrect workpiece placement. Furthermore, because the transfer device can easily automate placement, no structural changes to the machine tool are required, preventing the machine tool from becoming too complex or large, and reducing the costs associated with introducing and using the machine tool.

[0012] FIG. 1 is a front view of a machine tool (grinding machine) to which a transfer device according to an embodiment of the present disclosure is applied; FIG. 2 is a perspective view of a transfer device according to an embodiment of the present disclosure; FIG. 3 is an explanatory view of a state in which a workpiece is gripped by fingers of a hand unit in a transfer device according to an embodiment of the present disclosure; FIG. 4 is an explanatory view of a state in which a workpiece is gripped by fingers of a hand unit in a transfer device according to an embodiment of the present disclosure; FIG. 5 is an explanatory view of a state in which a workpiece is in surface contact with a second reference surface in a transfer device according to an embodiment of the present disclosure; FIG. 6 is an explanatory view of a state in which a workpiece is in surface contact with a first reference surface in a transfer device according to an embodiment of the present disclosure; FIG. 7 is an explanatory view of a state in which a transfer device according to an embodiment of the present disclosure starts applying a transfer force to a workpiece in a direction approaching a third reference surface; FIG. 8 is an explanatory view of a state in which a workpiece is in surface contact with a third reference surface in a transfer device according to an embodiment of the present disclosure; FIG. 9 is an explanatory view of a change in resistance force over time in a workpiece placement process by a transfer device according to an embodiment of the present disclosure; FIG. 10 is an explanatory view of a state in which a workpiece is released from grip by fingers of a hand unit in a transfer device according to an embodiment of the present disclosure; FIG. 11 is an explanatory view of a state in which a transfer device according to an embodiment of the present disclosure starts applying a transfer force to another workpiece in a direction approaching a first reference surface. 10 is an explanatory diagram illustrating a state in which a transfer device according to an embodiment of the present disclosure makes surface contact with a first reference surface of another workpiece. FIG.

[0013] 1A to 6B, a transfer device according to an embodiment of the present disclosure will be described. In this embodiment, an example of a device for placing a workpiece on a surface grinding machine as a machine tool will be described.

[0014] In each figure, the transfer device 1 of this embodiment holds and moves the workpiece 90 relative to a workpiece fixing portion 71 that fixes the workpiece 90 to be machined in a machine tool 70, and places the workpiece 90 on the workpiece fixing portion 71.

[0015] The machine tool 70 onto which the workpiece 90 is placed by the transfer device 1 is a surface grinder, and has a table as a workpiece fixing portion 71 on which the workpiece 90 to be ground can be fixed by a magnetic chuck 72 .

[0016] The workpiece fixing portion 71 has a first reference surface 75, a second reference surface 76, and a third reference surface 77 for workpiece positioning, which are arranged at right angles to each other. Of these, the first reference surface 75 is the upper surface of the table (the upper surface of the magnetic chuck 72). The workpiece fixing portion 71 also includes jigs 73 and 74 which are fixed to the upper surface of the table (the upper surface of the magnetic chuck 72). The side surface of the jig 73 which is perpendicular to the table upper surface is the second reference surface 76, and the side surface of the jig 74 which is perpendicular to the table upper surface is the third reference surface 77. It goes without saying that the second reference surface 76 of the jig 73 and the third reference surface 77 of the jig 74 form a right angle with each other.

[0017] The workpiece 90 placed on the machine tool 70 by the transfer device 1 is a solid having a surface to be machined and surfaces 91, 92, and 93 that contact the three reference surfaces 75, 76, and 77 of the workpiece fixing portion 71. Specifically, the workpiece 90 is a rectangular parallelepiped having a first surface 91, a second surface 92, and a third surface 93 that are perpendicular to one another. Of these, the first surface 91 contacts the first reference surface 75 of the workpiece fixing portion 71, the second surface 92 contacts the second reference surface 76, and the third surface 93 contacts the third reference surface 77.

[0018] Specifically, the transfer device 1 according to this embodiment is configured to include a robot arm 10, a force sensor 20, a hand unit 30, and a control unit 40. The robot arm 10 has multiple joints, and the position and orientation of the tip end where the hand unit 30 and the force sensor 20 are located can be adjusted with at least six degrees of freedom (three axial directions of the x-axis, y-axis, and z-axis, and three rotational directions around the x-axis, y-axis, and z-axis). The robot arm 10 is a known vertical articulated robot device with six or more degrees of freedom, and detailed description thereof will be omitted.

[0019] The robot arm 10 operates based on the control of the control unit 40, and executes a placement step in which the workpiece 90 held by the hand unit 30 at the tip end is placed on the workpiece fixing unit 71 of the machine tool 70. Note that the robot arm may be a device with fewer degrees of freedom, as long as it has the degrees of freedom necessary to place the workpiece on the workpiece fixing unit.

[0020] The placement step, i.e., placement of the workpiece 90 on the workpiece fixing portion 71, is performed as a step in which the robot arm 10 applies a transport force to the workpiece 90 in a direction that moves the workpiece 90 toward the third reference surface 77, thereby moving the workpiece 90 and bringing the third surface 93 of the workpiece 90 into contact with the third reference surface 77. However, as a premise, the robot arm 10 maintains a state in which the first surface 91 and the second surface 92 of the workpiece 90 are in surface contact with the first and second reference surfaces 75, 76 of the workpiece fixing portion 71, respectively, throughout the placement step.

[0021] In the placement process, the force such as the transport force that the robot arm 10 applies to the workpiece 90 is set to a magnitude that does not cause any problems to the workpiece 90 or the reference surfaces 75, 76, 77 even when the workpiece 90 is pressed against the reference surfaces 75, 76, 77, and the speed at which the workpiece 90 moves is set to be sufficient.

[0022] The force sensor 20 is interposed between the tip of the robot arm 10 and the hand unit 30, and is capable of detecting the force and moment acting on the workpiece 90 held by the hand unit 30. The force sensor 20 has an attachment mechanism for attaching to the tip of the robot arm 10 on one end face, and is attached to the tip of the robot arm 10 on this end face side. On the other hand, the force sensor 20 has an attachment mechanism for the hand unit 30 on the other end face opposite the one end face, and the hand unit 30 is attached to this other end face side.

[0023] The force sensor 20 is a six-axis force sensor that can detect forces in the directions of three orthogonal axes (x-axis, y-axis, z-axis) and moments about the three orthogonal axes that are applied to one end face side relative to the other end face side. The mechanism by which the force sensor 20 can detect forces in the directions of the three orthogonal axes and moments about the three orthogonal axes is similar to that of known force sensors (six-axis force sensors), and a detailed description thereof will be omitted.

[0024] In the placement process, a resistance force (illustrated by the dashed arrow in FIGS. 4A and 4B ) is applied to the workpiece 90 in the direction opposite to the direction of the transfer force applied by the robot arm 10, which moves the workpiece 90 toward the third reference surface 77. This resistance force is acquired by the force sensor 20. The resistance force acquired by the force sensor 20 is a resultant force including the frictional force caused by contact between the workpiece 90 and the first and second reference surfaces 75, 76, and the reaction force received from the third reference surface 77 when the moved workpiece 90 abuts against the third reference surface 77.

[0025] The hand unit 30 is attached to the other end face side of the force sensor 20, and is provided at the tip side of the robot arm 10 via the force sensor 20, so that it can hold a workpiece 90. The hand unit 30 is provided to protrude in a direction parallel to the central axis direction of the force sensor 20 (the extension direction of the tip of the robot arm 10), and has at least a pair of fingers 31 that can move in a direction perpendicular to the central axis direction of the force sensor 20 to grip a workpiece. The mechanism for gripping with the fingers 31 is similar to that of a known gripper-type robot hand, and a detailed description thereof will be omitted.

[0026] The hand unit 30 positions the fingers 31 relative to the workpiece 90 and grips the workpiece 90 so that the center of gravity of the workpiece 90 is aligned with the central axis of the force sensor 20. The contact position of the fingers 31 with the side surface of the workpiece 90 is preferably adjusted so that the vertical center position of the fingers 31 coincides with the vertical center position of the side surface of the workpiece 90, so that gripping by the fingers 31 is performed stably with the center position of the center of gravity of the workpiece 90.

[0027] The control unit 40 is connected to each actuator (not shown) in the robot arm 10 and the hand unit 30, and controls the operation of the robot arm 10 and the hand unit 30. The control unit 40 is also connected to the force sensor 20, receives signals output from the force sensor 20 in response to detection of forces and moments by the force sensor 20, determines the forces and moments from the signals, and uses them to control the robot arm 10 and the hand unit 30.

[0028] Prior to the placement step, the control unit 40 operates the robot arm 10 and adjusts the position and orientation of the workpiece 90 so that the second surface 92 of the workpiece 90 first comes into surface contact with the second reference surface 76 of the workpiece fastening part 71. Next, while maintaining the surface contact state between the second surface 92 and the second reference surface 76, the control unit 40 brings the first surface 91 of the workpiece 90 into surface contact with the first reference surface 75 of the workpiece fastening part 71.

[0029] Then, as control related to the placement process, the control unit 40 maintains the surface contact state between each surface 91, 92 of the workpiece 90 and each reference surface 75, 76 of the workpiece fixing portion 71, while ensuring that the third surface 93 of the workpiece 90 comes into contact with the third reference surface 77 of the workpiece fixing portion 71.

[0030] In detail, the control unit 40 controls the robot arm 10 to apply a predetermined pressing force to the workpiece 90 so as to maintain a state of surface contact between the first and second reference surfaces 75, 76 of the workpiece fixing unit 71 and the first surface 91 and second surface 92 of the workpiece 90, respectively. At the same time, the control unit 40 controls the robot arm 10 to apply a predetermined transport force to the workpiece 90 in a direction in which the workpiece 90 approaches the third reference surface 77, thereby moving the workpiece 90 and bringing the workpiece 90 into contact with the third reference surface 77.

[0031] The control unit 40 determines whether the workpiece 90 is correctly placed on the workpiece fixing unit 71 based on the change in the resistance value acquired by the force sensor 20 during the process in which a transport force is applied to the workpiece 90 and the workpiece 90 moves. For example, the control unit 40 determines that the workpiece 90 is correctly placed on the workpiece fixing unit 71 when the resistance acquired by the force sensor 20 changes as follows:

[0032] First, the resistance force acquired by the force sensor 20 gradually increases in magnitude corresponding to a static friction force from the time the workpiece 90 is subjected to the transfer force until it starts moving, and reaches a first peak value corresponding to the maximum static friction force just before the workpiece 90 starts moving. Then, once the workpiece 90 starts moving, the resistance force acquired by the force sensor 20 becomes equivalent to a kinetic friction force, which is smaller than the maximum static friction force. However, as the workpiece 90, to which the transfer force is applied, approaches the third reference surface 77, each of the surfaces 91 and 92 of the workpiece 90 tends to come into close contact with the respective contacting reference surfaces 75 and 76 due to ringing. Therefore, the kinetic friction force increases over time, and the resistance force tends to increase. Finally, when the workpiece reaches and abuts the third reference surface 77, the resistance force acquired by the force sensor 20 suddenly increases in magnitude corresponding to the reaction force from the third reference surface 77, reaching a second peak value greater than the first peak value.

[0033] When the workpiece 90 is placed correctly on the workpiece fixing portion 71, the change in the value of the resistance force acquired by the force sensor 20 is used as a criterion for determining whether the workpiece 90 has been placed correctly, based on past cases in which the resistance force has undergone the above-mentioned changes.

[0034] The control unit 40 also presets upper and lower limit values ​​for the resistance force while the workpiece 90 is moving. The upper limit value is a magnitude between a value corresponding to the maximum static friction force immediately before the workpiece 90 starts moving and a value corresponding to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and contacts the third reference surface 77. On the other hand, the lower limit value is a magnitude between the initial value of the static friction force when the workpiece 90 starts to be subjected to a transport force and a value corresponding to the maximum static friction force. If the resistance force acquired by the force sensor 20 falls within the range from the lower limit value to the upper limit value during the elapsed time from when the workpiece 90 starts moving until it does not reach the third reference surface 77, the control unit 40 determines that the workpiece 90 has been properly positioned on the workpiece fixing unit 71.

[0035] Separately, the control unit 40 pre-sets another upper limit value of the resistance force, which is equivalent to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and abuts against the third reference surface 77. Then, if the control unit 40 acquires a resistance force that reaches the other upper limit value with the force sensor 20 during the elapsed time from when the workpiece 90 is subjected to the transfer force until it reaches the third reference surface 77, the control unit 40 determines that the workpiece 90 has not been positioned properly on the workpiece fixing unit 71, indicating an abnormal state.

[0036] In addition, the control unit 40 presets a resistance threshold value that corresponds to the magnitude of the reaction force received from the third reference surface 77 when the workpiece 90 reaches and abuts against the third reference surface 77. Then, when the workpiece 90 is moved by the application of a transport force and the elapsed time has come when the workpiece 90 can reach the third reference surface 77, and the control unit 40 acquires a resistance force equal to or greater than the threshold value using the force sensor 20, the control unit 40 determines that the workpiece 90 has been properly placed on the workpiece fixing unit 71. In this case, the control unit 40 stops the movement of the workpiece 90.

[0037] Before the placement process, the transfer device 1 performs a loading process in which the workpiece 90 placed at a predetermined supply position is grasped and held with the hand unit 30, and the robot arm 10 is moved to a space near each reference surface 75, 76, 77 on the workpiece fixing unit 71 of the machine tool 70.

[0038] The holding of the workpiece 90 by the hand unit 30 at the very beginning of the carry-in process is performed as follows: First, the robot arm 10 is operated to adjust the position and orientation of the hand unit 30 so that the workpiece 90 placed at the supply position is positioned between the pair of fingers 31 of the hand unit 30.

[0039] Next, while maintaining the overall position of the hand unit 30, the pair of fingers 31 of the hand unit 30 are moved toward each other, and the workpiece 90 is grasped by the fingers 31 (see Figures 3A and 3B), completing the holding of the workpiece 90 by the hand unit 30.

[0040] In this loading process, the control unit 40 causes the robot arm 10 and the hand unit 30 to perform operations in accordance with a series of procedures that have been instructed in advance, and the control related to this execution is based on a general robot control method that reproduces and executes instructed movements, so detailed explanation will be omitted.

[0041] Next, a workpiece placement process using the transfer device according to this embodiment will be described. As a prerequisite, the transfer device 1 has previously executed a carry-in process. Specifically, the transfer device 1 moves the robot arm 10 while holding the workpiece 90 placed at a predetermined supply position with the hand unit 30, and moves the workpiece 90 to a space near each of the reference surfaces 75, 76, and 77 on the workpiece fixing unit 71 of the machine tool 70. At this stage, the hand unit 30 is positioned so that the workpiece 90 faces a second reference surface 76, which is the side surface of the jig 73 on the machine tool 70.

[0042] Furthermore, prior to the placement step, the transfer device 1 moves the robot arm 10 following the carry-in step to bring the workpiece 90 closer to the second reference surface 76 and bring a part of the second surface 92 of the workpiece 90 into contact with the second reference surface 76. By subsequently adjusting the position and orientation of the workpiece 90, part or all of the second surface 92 of the workpiece 90, excluding the portion to be machined, is brought into surface contact with the second reference surface 76 (see FIG. 3A ).

[0043] Furthermore, the transfer device 1 brings the first surface 91 of the workpiece 90 close to and into contact with the first reference surface 75 of the table top surface (the upper surface of the magnetic chuck 72) while maintaining the second surface 92 in surface contact with the second reference surface 76. As with the second surface 92 and the second reference surface 76, the first surface 91 of the workpiece 90 is also brought into surface contact with the first reference surface 75 over its entirety (see FIG. 3B ). With the first surface 91 and the second surface 92 thus in surface contact with the first reference surface 75 and the second reference surface 76, respectively, the workpiece 90 is positioned so that its third surface 93 faces the third reference surface 77 of the workpiece fixing portion 71 at a predetermined distance, and the workpiece comes to a standstill.

[0044] In the placement process, first, a transport force is applied from the robot arm 10 of the transfer device 1 to the stationary workpiece 90 in a direction that moves the workpiece 90 closer to the third reference surface 77 (see FIG. 4A ). In addition to this transport force, a pressing force is also applied to the workpiece 90, which is a resultant force of a force that moves the workpiece 90 closer to the first reference surface 75 and a force that moves the workpiece 90 closer to the second reference surface 76. This force is used to maintain surface contact between the first surface 91 and the second surface 92 of the workpiece 90 and the first and second reference surfaces 75, 76 of the workpiece fixing portion 71, and is continuously applied from the time the workpiece 90 comes into contact with the reference surfaces 75, 76. Furthermore, the transport force applied to the workpiece 90 is a force that is oriented parallel to the first and second reference surfaces 75, 76, and does not affect the surface contact between the first surface 91 and the second surface 92 of the workpiece 90 and the first and second reference surfaces 75, 76 of the workpiece fixing portion 71.

[0045] The workpiece 90 is in surface contact with the first and second reference surfaces 75, 76 of the workpiece fixing portion 71, and a pressing force is applied to these first and second reference surfaces 75, 76, causing friction between the workpiece 90 and the first and second reference surfaces 75, 76. The transport force applied to the workpiece 90 gradually increases from the start of application, but the workpiece 90 remains stationary for a while due to friction (static friction) between the workpiece 90 and the first and second reference surfaces 75, 76. A resistance force (illustrated by the dashed arrow in FIG. 4A ), mainly composed of friction, acts on the workpiece 90 in the direction opposite to the transport force, and the resistance force increases while the workpiece 90 is stationary. This resistance force can be detected by the force sensor 20.

[0046] When the transport force applied to the workpiece 90 exceeds the maximum static friction force between the workpiece 90 and each of the reference surfaces 75, 76, the workpiece 90 leaves the stationary state and starts to move. The force sensor 20 detects a state in which the resistance force gradually increases in response to the transport force and reaches a first peak value corresponding to the maximum static friction force (see FIG. 5).

[0047] On the other hand, there are cases where the friction between the workpiece 90 and each reference surface 75, 76 becomes extremely large due to the presence of a sticky foreign object between the workpiece 90 and each reference surface 75, 76. In such cases, the actual frictional force becomes excessively large relative to the applied transport force, and even if the transport force exceeds the original maximum static frictional force, the workpiece 90 may remain stationary relative to each reference surface 75, 76. In this case, the resistance force acquired by the force sensor 20 will indicate an excessively large value based on the frictional force. If the resistance force acquired by the force sensor 20 exceeds the preset upper limit of the resistance force (RF in FIG. 5), max1 ), the control unit 40 determines that the position of the workpiece 90 is abnormal. By being able to appropriately determine and deal with an obviously abnormal situation in which the workpiece 90 does not move even when force is applied to it, it is possible to prevent machining defects from occurring. Note that the upper limit of the resistance force here is set to a magnitude equivalent to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and abuts against the third reference surface 77.

[0048] Once the workpiece 90 starts to move, the resistance to the transport force also becomes smaller because the kinetic friction force as frictional resistance is smaller than the maximum static friction force. After the resistance force reaches a first peak value corresponding to the maximum static friction force when the workpiece 90 is stationary, the force sensor 20 acquires a resistance force corresponding to a kinetic friction force smaller than the maximum static friction force as the workpiece 90 starts to move (see FIG. 5).

[0049] If there are no particular problems while the workpiece 90 is moving and gradually approaching the third reference surface 77, the force sensor 20 acquires a resistance force corresponding to the dynamic friction force based on the friction between the workpiece 90 and each of the reference surfaces 75, 76. In this case, the resistance force acquired by the force sensor 20 falls within a range of values ​​that are preset as upper and lower limit values ​​of the resistance force while the workpiece 90 is moving, and the progress of the placement of the workpiece 90 is determined to be normal.

[0050] On the other hand, if the resistance force acquired by the force sensor 20 does not fall within the range defined by the upper and lower limit values ​​of the resistance force while the workpiece 90 is moving, the control unit 40 determines that the progress of the placement of the workpiece 90 is abnormal. As the workpiece 90 moves, it is quite possible that foreign matter adhering to the reference surfaces 75, 76 or scratches on the reference surfaces 75, 76 may get between the workpiece 90 and the reference surfaces 75, 76, affecting the friction between the workpiece 90 and the reference surfaces 75, 76. If the influence of the foreign matter, scratches, etc. on the friction excessively increases the friction, the resistance force acquired by the force sensor 20 increases, and the upper limit value of the resistance force while the workpiece 90 is moving (RF max2 On the other hand, if the influence of foreign matter, scratches, etc. on the friction excessively reduces the friction, the resistance force acquired by the force sensor 20 decreases, and the resistance force while the workpiece 90 is moving exceeds the lower limit value (RF min2 ) is below. In either case, since this is an undesirable situation that may adversely affect the machining accuracy when the workpiece 90 is placed on the workpiece fixing portion 71, it is important to identify this through abnormality determination in order to ensure accuracy. The upper limit of the resistance force while the workpiece 90 is moving is set to a magnitude between the value corresponding to the maximum static friction force immediately before the workpiece 90 starts moving and the value corresponding to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and abuts against the third reference surface 77. The lower limit of the resistance force while the workpiece 90 is moving is set to a magnitude between the initial value of the static friction force when the workpiece 90 begins to be subjected to a transport force and the value corresponding to the maximum static friction force immediately before the workpiece 90 starts moving.

[0051] As the workpiece 90 continues to move, the workpiece 90 approaches the third reference surface 77, and eventually the third surface 93 of the workpiece 90 comes into contact with the third reference surface 77 of the workpiece fastening portion 71 (see FIG. 4B ). When the workpiece 90 comes into contact with the third reference surface 77, the resistance force acquired by the force sensor 20 increases rapidly in magnitude corresponding to the reaction force that the workpiece 90 receives from the third reference surface 77, and reaches a second peak value that is greater than the first peak value (see FIG. 5 ).

[0052] The resistance force acquired as the second peak value by the force sensor 20 is equal to or exceeds a preset threshold value (TL RF ) or more, the control unit 40 determines that the workpiece 90 has been placed correctly on the workpiece fixing unit 71. When the control unit 40 determines that the placement is correct in this way, it stops the movement of the workpiece 90, thereby completing the placement process. The threshold value of the resistance force is set to a magnitude equivalent to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and abuts against the third reference surface 77.

[0053] The elapsed time is also taken into consideration when evaluating the resistance force acquired by the force sensor 20 when the moving workpiece 90 abuts against the third reference surface 77 of the workpiece fixing portion 71. The control unit 40 calculates in advance a predicted value for the time that will elapse until the workpiece 90 reaches the third reference surface 77, based on the speed at which the robot arm 10 moves the workpiece 90 and the initial distance between the workpiece 90 and the third reference surface 77. If the force sensor 20 acquires a change in the resistance force that exceeds the threshold value at a time close to this predicted value, the control unit 40 determines that the workpiece 90 has been positioned correctly. On the other hand, at a stage significantly earlier than the predicted value, the control unit 40 determines that the workpiece 90 has not yet reached the third reference surface 77, and does not compare the resistance force with the threshold value, but instead calculates that the resistance force is equal to or exceeds an upper limit value (RF in FIG. 5 ). max1 If the force sensor 20 detects a change in resistance force that exceeds this upper limit, the control unit 40 determines that an abnormal state has occurred, in which the workpiece 90 has not yet reached the third reference surface 77 and has not been positioned properly.

[0054] In addition, the control unit 40 can also determine that the workpiece 90 has been placed correctly on the workpiece fixing portion 71 if the resistance force acquired by the force sensor 20 undergoes a typical change based on a case in which the workpiece 90 has been placed correctly on the workpiece fixing portion 71.

[0055] The change in the resistance force in this case is as follows: Initially, the resistance force gradually increases in magnitude corresponding to static friction force from the time the transfer force is applied to the workpiece 90 until it starts to move, and reaches a first peak value corresponding to the maximum static friction force just before the workpiece 90 starts to move. After the workpiece 90 starts to move, the resistance force becomes a value corresponding to kinetic friction force, which is smaller than the first peak value, and remains within a certain fluctuation range regardless of the passage of time. Then, when the workpiece 90 reaches and abuts the third reference surface 77, the resistance force suddenly increases in magnitude corresponding to the reaction force received from the third reference surface 77, and reaches a second peak value greater than the first peak value.

[0056] By using this typical change in resistance force (see Figure 5) as a criterion for determining whether the workpiece 90 has been placed correctly, a more accurate evaluation can be made of the placement of the workpiece 90 on the workpiece fixing portion 71.

[0057] Next, the workpiece release process after the placement process will be described. After the process of bringing the surfaces 91, 92, and 93 of the workpiece 90 into contact with the reference surfaces 75, 76, and 77 of the workpiece fastening part 71 and properly placing the workpiece 90 on the workpiece fastening part 71 is completed, the workpiece release process is performed next, in which the hand unit 30 releases the workpiece 90 from its hold. This workpiece release process is performed according to the following procedure.

[0058] First, while the hand unit 30 applies a pressing force to the workpiece 90 against the first and second reference surfaces 75, 76, the pair of fingers 31 of the hand unit 30 are moved away from each other, thereby releasing the grip of the workpiece 90 by the fingers 31 (see FIGS. 6A and 6B ). Next, the robot arm 10 is operated to move the hand unit 30, and the entire hand unit 30 is moved away from the workpiece 90. At this time, it goes without saying that the hand unit 30 is moved so that each part of the hand unit 30 does not come into contact with the workpiece 90.

[0059] The workpiece releasing process is completed when the hand unit 30, which has been separated from the workpiece 90, is moved to the initial position for the carry-in process for the next workpiece to be machined. The movement of the hand unit 30, which has been separated from the workpiece 90, is not limited to this. For example, if, after machining the workpiece, it is necessary to change the position or orientation of the workpiece and further machine another surface of the workpiece, the hand unit may be retracted to a standby position ready to hold the machined workpiece. Furthermore, even if the transfer device also serves as a carry-out means for holding the machined workpiece and removing it from the workpiece fixing portion of the machine tool after machining, the hand unit may be retracted to a predetermined standby position ready to hold the machined workpiece.

[0060] In this way, the transfer device according to this embodiment places the workpiece 90 in surface contact with the first reference surface 75 of the workpiece fixing portion 71, applies a transfer force to the workpiece 90 to move it, and acquires the resistance force acting in the opposite direction. Then, referring to the change in the resistance force, it determines whether the placement state is appropriate. This allows the surface contact state to be accurately determined from the change in resistance force, and the workpiece 90 can be carefully moved relative to the reference surface 75 in a manner similar to manual work, allowing for correct placement, thereby avoiding improper placement of the workpiece 90. Furthermore, because the transfer device 1 can easily automate placement, there is no need to modify the structure of the machine tool, which avoids the machine tool itself becoming more complex and larger, thereby reducing the costs associated with introducing and using the machine tool.

[0061] Although the workpiece placement method according to this embodiment shows an example of application to the machine tool 70, which is a surface grinder, the present invention is not limited to this and may be applied to other machine tools. For example, the machine tool may be a machining center or a milling machine, and the present invention may be applied to the placement of workpieces on these.

[0062] Furthermore, in the workpiece placement method using the transfer device according to this embodiment, the workpiece fixing unit 71 is configured to have three reference surfaces 75, 76, and 77 that are perpendicular to each other for workpiece positioning. However, this is not limited to this. For example, the workpiece fixing unit may be configured to have only one reference surface or two reference surfaces. When the workpiece fixing unit has only one reference surface, a workpiece is placed on the workpiece fixing unit by applying a transfer force to the workpiece while maintaining surface contact between one reference surface of the workpiece fixing unit and one surface of the workpiece. The force sensor can acquire a resistance force acting on the workpiece in the direction opposite to the direction of the transfer force. When the workpiece fixing unit has two reference surfaces, a workpiece is placed on the workpiece fixing unit by maintaining surface contact between the two reference surfaces of the workpiece fixing unit and the two corresponding surfaces of the workpiece. The force sensor can acquire a resistance force acting on the workpiece in the direction opposite to the direction of the transfer force.

[0063] Furthermore, in the transfer device according to this embodiment, the workpiece 90 is brought into surface contact with the second reference surface 76 of the workpiece fastening portion 71, then brought into surface contact with the first reference surface 75, and then moved in a direction approaching the third reference surface 77. However, this is not limited to this. For example, the transfer device 1 can first bring the workpiece 95 into surface contact with the second reference surface 76 of the workpiece fastening portion 71, then bring it into surface contact with the third reference surface 77, and then, as shown in FIGS. 7A and 7B , apply a transport force to the workpiece 95 in a direction approaching the first reference surface 75, which is the table top, to move the workpiece 95. In this case, too, the force sensor 20 acquires a resistance force (illustrated by the dashed arrow in FIGS. 7A and 7B ) acting on the workpiece 95 in the direction opposite to the direction of the transport force, and based on the change in the value of this resistance force, it is determined whether the placement of the workpiece 95 on the workpiece fastening portion 71 is normal.

[0064] Furthermore, in the transfer device according to this embodiment, the control unit 40 determines that the placement of the workpiece 90 on the workpiece fixing unit 71 is abnormal rather than normal, and subsequent control processing is not specifically shown, but control may be performed as appropriate to avoid problems associated with the abnormal placement. For example, when the control unit determines that the placement state of the workpiece is abnormal, the control unit may perform control to stop the operation of the robot arm and to issue a predetermined notification to the operator indicating the abnormality.

[0065] The present disclosure includes the following aspects: (1) A work transfer device that holds and moves a workpiece relative to a workpiece fixing part that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing part, the transfer device comprising: a force sensor that can detect a force and / or a moment acting on the workpiece, the workpiece fixing part having a first reference plane, the workpiece being a solid having a first surface that is in contact with the first reference plane, the workpiece being placed on the workpiece fixing part by applying a transfer force to the workpiece while maintaining a surface contact state between the first reference plane of the workpiece fixing part and the first surface of the workpiece, the force sensor acquiring a resistance force that acts on the workpiece to which the transfer force has been applied in a direction opposite to the direction of the transfer force, and the transfer device determining whether or not the placement of the workpiece on the workpiece fixing part is normal based on a change in the value of the resistance force acquired by the force sensor. (2) In the transfer device described in (1), the workpiece fixing portion has a second reference surface for workpiece positioning that is arranged perpendicular to the first reference surface, the workpiece has a second surface that contacts the second reference surface of the workpiece fixing portion, and the workpiece is positioned on the workpiece fixing portion by applying a transfer force to the workpiece to move it while maintaining the first and second reference surfaces of the workpiece fixing portion in surface contact with the first surface and second surface of the workpiece, respectively. (3) In the transfer device described in (2), the workpiece fixing portion has a third reference surface for workpiece positioning that is arranged perpendicular to the first reference surface and the second reference surface, the workpiece has a third surface that contacts the third reference surface of the workpiece fixing portion, and the workpiece is positioned on the workpiece fixing portion by applying a transfer force to the workpiece in a direction that brings it closer to the third reference surface while maintaining the first and second reference surfaces of the workpiece fixing portion and the first surface and second surface of the workpiece in a surface contact state, respectively, to move the workpiece.(4) In the transfer device described in (3), the force sensor acquires as the resistance force a resultant force including a friction force caused by contact between the workpiece and the first and second reference surfaces, and a reaction force received from the third reference surface when the moved workpiece comes into contact with the third reference surface; and the resistance force acquired by the force sensor gradually increases in magnitude corresponding to a static friction force from the time when a transfer force is applied to the workpiece until it starts to move, reaches a first peak value corresponding to a maximum static friction force just before the workpiece starts to move, and when the workpiece starts to move, it becomes a state corresponding to a kinetic friction force smaller than the maximum static friction force and stays within a certain fluctuation range regardless of the passage of time, and when the workpiece reaches and comes into contact with the third reference surface, it suddenly increases in magnitude corresponding to a reaction force received from the third reference surface and reaches a second peak value greater than the first peak value. (5) In the transfer device described in (3), the force sensor acquires as the resistance force a resultant force including a frictional force caused by contact between the workpiece and the first and second reference surfaces and a reaction force received from the third reference surface when the moved workpiece abuts against the third reference surface, an upper limit value of the resistance force is set in advance, the magnitude of which corresponds to the reaction force received from the third reference surface when the workpiece reaches and abuts against the third reference surface, and when the force sensor acquires a resistance force that reaches the upper limit value within the elapsed time after the transfer force is applied to the workpiece before it reaches the third reference surface, the transfer device determines that the workpiece has not been positioned properly on the workpiece fixing portion, indicating an abnormal state.(6) In the transfer device described in (3), the force sensor acquires as the resistance force a resultant force including a frictional force caused by contact between the workpiece and the first and second reference surfaces and a reaction force received from the third reference surface when the moved workpiece abuts against the third reference surface, a resistance threshold value is set in advance that is equivalent to the reaction force received from the third reference surface when the workpiece reaches and abuts against the third reference surface, and when the force sensor acquires a resistance force equal to or greater than the threshold value after the workpiece has been moved with a transfer force applied and the time has elapsed for it to reach the third reference surface, the transfer device determines that the workpiece has been properly positioned on the workpiece fixing portion and stops the movement of the workpiece. (7) In the transfer device described in (3), the force sensor acquires, as the resistance force, a resultant force including a friction force caused by contact between the workpiece and the first and second reference surfaces, and a reaction force received from the third reference surface when the moved workpiece abuts against the third reference surface; an upper limit value is set in advance for the resistance force while the workpiece is moving, the upper limit value being a magnitude between a value equivalent to the maximum static friction force immediately before the workpiece starts moving and a value equivalent to the reaction force received from the third reference surface when the workpiece reaches and abuts against the third reference surface; and a lower limit value is set in advance, the upper limit value being a magnitude between the initial value of the static friction force when the transfer force begins to be applied to the workpiece and the value equivalent to the maximum static friction force; and if the resistance force acquired by the force sensor falls within the range from the lower limit value to the upper limit value during the elapsed time after the workpiece starts moving until it does not reach the third reference surface, the transfer device determines that the workpiece has been properly positioned on the workpiece fixing portion. (8) The transfer device described in (1) above, further comprising: a robot arm with multiple degrees of freedom; and a hand unit provided at the tip of the robot arm so as to be able to hold the workpiece; and the force sensor is interposed between the tip of the robot arm and the hand unit.(9) In the transfer device described in (3), the machine tool is a grinding machine having a table as the workpiece fixing part, on which a workpiece to be ground can be fixed, one of the reference surfaces is the upper surface of the table, and the other two of the reference surfaces are surfaces of one or more jigs fixed to the upper surface of the table that are perpendicular to the upper surface of the table. (10) A work placement method in which a predetermined transfer device holds and moves a workpiece relative to a workpiece fixing part that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing part, the method comprising at least a placement step in which the transfer device places the workpiece on the workpiece fixing part by bringing the workpiece into surface contact with a first reference surface for work positioning provided on the workpiece fixing part, the transfer device having a force sensor that can detect forces and moments acting on the workpiece it holds, the workpiece being a solid having a first surface that is in contact with the first reference surface of the workpiece fixing part, the placement step using the transfer device to apply a transfer force to the workpiece to move it while maintaining the first reference surface of the workpiece fixing part and the first surface of the work in surface contact, and the force sensor acquiring a resistance force that acts on the workpiece to which the transfer force has been applied in a direction opposite to the direction of the transfer force, and determining whether the placement of the workpiece on the workpiece fixing part is normal or not based on a change in the value of the resistance force acquired by the force sensor in the placement step.

[0066] This application is based on Japanese Patent Application No. 2024-124796 filed on July 31, 2024, the contents of which are incorporated herein by reference.

Claims

1. A work transfer device that holds and moves a workpiece relative to a workpiece fixing part that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing part, the transfer device being equipped with a force sensor that can detect forces and / or moments generated in the workpiece, the workpiece fixing part having a first reference surface, the workpiece being a solid having a first surface that is in contact with the first reference surface, the workpiece being placed on the workpiece fixing part by applying a transfer force to the workpiece while maintaining a surface contact state between the first reference surface of the workpiece fixing part and the first surface of the workpiece, the force sensor acquiring a resistance force that is applied to the workpiece to which the transfer force has been applied in a direction opposite to the direction of the transfer force, and the transfer device determining whether or not the placement of the workpiece on the workpiece fixing part is normal based on the change in the value of the resistance force acquired by the force sensor.

2. A transfer device as described in claim 1, wherein the work fixing portion has a second reference surface for positioning the work that is arranged at right angles to the first reference surface, and the work has a second surface that contacts the second reference surface of the work fixing portion, and the work is positioned on the work fixing portion by applying a transfer force to the work to move it while maintaining the first and second reference surfaces of the work fixing portion in surface contact with the first surface and second surface of the work, respectively.

3. A transfer device as described in claim 2, wherein the work fixing portion has a third reference surface for positioning the work that is arranged at right angles to the first reference surface and the second reference surface, and the work has a third surface that contacts the third reference surface of the work fixing portion, and the work is positioned on the work fixing portion by applying a transfer force to the work in a direction that brings it closer to the third reference surface while maintaining a surface contact state between the first and second reference surfaces of the work fixing portion and the first and second surfaces of the work, respectively, to move the work.

4. A transfer device according to claim 3, wherein the force sensor acquires as the resistance force a resultant force including a frictional force resulting from contact between the workpiece and the first and second reference surfaces, and a reaction force received from the third reference surface when the moved workpiece comes into contact with the third reference surface; and the resistance force acquired by the force sensor gradually increases in magnitude corresponding to a static frictional force after a transfer force is applied to the workpiece until it starts to move, reaches a first peak value corresponding to a maximum static frictional force just before the workpiece starts to move, and once the workpiece starts to move, reaches a state corresponding to a kinetic frictional force smaller than the maximum static frictional force and stays within a certain fluctuation range regardless of the passage of time, and once the workpiece reaches and comes into contact with the third reference surface, the resistance force rapidly increases in magnitude corresponding to a reaction force received from the third reference surface and reaches a second peak value greater than the first peak value.

5. A transfer device as described in claim 3, wherein the force sensor acquires as the resistance force a resultant force including a frictional force caused by contact between the workpiece and the first and second reference surfaces and a reaction force received from the third reference surface when the moved workpiece abuts against the third reference surface, and an upper limit value of the resistance force is set in advance, the magnitude of which corresponds to the reaction force received from the third reference surface when the workpiece reaches and abuts against the third reference surface, and when the force sensor acquires a resistance force that reaches the upper limit value within the elapsed time after the application of a transfer force until the workpiece reaches the third reference surface, the transfer device determines that the workpiece has not been positioned properly on the workpiece fixing portion, indicating an abnormal state.

6. A transfer device as described in claim 3, wherein the force sensor acquires as the resistance a resultant force including a frictional force caused by contact between the workpiece and the first and second reference surfaces and a reaction force received from the third reference surface when the moved workpiece comes into contact with the third reference surface, and a resistance threshold value is set in advance that is equivalent to the reaction force received from the third reference surface when the workpiece reaches and comes into contact with the third reference surface, and when the force sensor acquires a resistance force equal to or greater than the threshold value after the workpiece has been moved with a transfer force applied and the time has elapsed where it can reach the third reference surface, the transfer device determines that the workpiece has been properly positioned on the workpiece fixing portion and stops the movement of the workpiece.

7. A transfer device according to claim 3, wherein the force sensor acquires as the resistance force a resultant force including a frictional force caused by contact between the workpiece and the first and second reference surfaces and a reaction force received from the third reference surface when the moved workpiece comes into contact with the third reference surface; and with respect to the resistance force while the workpiece is moving, an upper limit value is set in advance which is a magnitude between a value equivalent to the maximum static friction force immediately before the workpiece starts moving and a value equivalent to the reaction force received from the third reference surface when the workpiece reaches and comes into contact with the third reference surface, and a lower limit value is set in advance which is a magnitude between the initial value of the static friction force when the transfer force begins to be applied to the workpiece and the value equivalent to the maximum static friction force; and a transfer device characterized in that if the resistance force acquired by the force sensor falls within the range from the lower limit value to the upper limit value during the elapsed time after the workpiece starts moving until it does not reach the third reference surface, it is determined that the workpiece has been properly positioned on the workpiece fixing portion.

8. A transfer device as described in claim 1, comprising a robot arm with multiple degrees of freedom and a hand unit provided at the tip of the robot arm so as to be able to hold the workpiece, and wherein the force sensor is interposed between the tip of the robot arm and the hand unit.

9. A transfer device as described in claim 3, wherein the machine tool is a grinding machine having a table as the workpiece fixing part, on which a workpiece to be ground can be fixed, one of the reference surfaces being the upper surface of the table, and the other two of the reference surfaces being surfaces of one or more jigs fixed to the upper surface of the table that are perpendicular to the upper surface of the table.

10. A work placement method in which a predetermined transfer device holds and moves a workpiece relative to a workpiece fixing part that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing part, the method comprising at least a placement step in which the transfer device places the workpiece on the workpiece fixing part by bringing the workpiece into surface contact with a first reference surface for work positioning provided on the workpiece fixing part, the transfer device having a force sensor that can detect forces and moments generated in the workpiece it holds, the workpiece being a solid having a first surface that is in contact with the first reference surface of the workpiece fixing part, the placement step using the transfer device to apply a transfer force to the workpiece to move it while maintaining a state of surface contact between the first reference surface of the workpiece fixing part and the first surface of the workpiece, and the force sensor acquiring a resistance force that acts on the workpiece to which the transfer force has been applied in a direction opposite to the direction of the transfer force, and the method comprising determining whether or not the placement of the workpiece on the workpiece fixing part is normal based on a change in the value of the resistance force acquired by the force sensor in the placement step.

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