Transfer device and workpiece arrangement method

Abstract

To provide a transfer device capable of properly arranging a workpiece in a machine tool to prevent the occurrence of failure, and improving work efficiency by automation.SOLUTION: 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 it, while a 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. As a result, the state of the surface contact can be accurately grasped from the change in the resistance force, and the workpiece 90 can be carefully moved and correctly arranged with respect to the reference surface in the same manner as a manual operation, so that an arrangement failure of the workpiece can be avoided. Since the automation of the arrangement can be reasonably realized by transfer apparatus 1, it is not necessary to change the structure of machine tool 70, and it is possible to avoid complication and enlargement of machine tool 70 itself, and to suppress the cost related to introduction and use of machine tool 70.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a transfer device for placing a workpiece on a machine tool, and more particularly to a device for placing a workpiece in close contact with a reference surface in a workpiece fixing portion of the machine tool. [Background technology]

[0002] A surface grinder has 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 would place and fix the workpiece, such as a rectangular parallelepiped, in the appropriate position on the grinder table based on their experience, and then the workpiece was machined. In order to improve the efficiency of machining operations using such surface grinders, there is a demand for automation of the process of placing (setting) workpieces on the table, which has previously been done manually.

[0003] In recent years, various proposals have been made for automation techniques. For example, a table supporting the workpieces can be made rotatable, and multiple workpiece placement positions on the table can be set, with positions away from the grinding wheel used as the carry-in position for the unmachined workpiece and the carry-out position for the machined workpiece. When the table is rotated, the unmachined workpiece that was at the carry-in position reaches the machining position, and the machined workpiece that was at the machining position reaches the carry-out 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 carry-in position on the table by a predetermined transport means, and the machined workpiece can be carried out from the carry-out position on the table by a predetermined transport means. After machining of the workpiece is completed, the table is rotated, and the unmachined workpiece from the carry-in position is placed at the new machining position, and the machined workpiece is moved from the machining position to the carry-out 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 of such a conventional surface grinding machine is disclosed in Japanese Patent Laid-Open Publication No. 2-185357. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2-185357 Summary of the Invention [Problem to be solved by the invention]

[0006] The method exemplified in the above-mentioned patent document is a typical example of a conventional method for automating workpiece placement on a surface grinding machine. In the conventional surface grinders shown in the patent documents, 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, which results in a more complex structure, larger size, and higher costs compared to surface grinders with earlier types of tables.

[0007] Furthermore, according to the patent documents, 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 a skilled worker manually places the workpiece on the table. In particular, these methods have 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 manually pressing it against the table or jig, thereby positioning the workpiece in three axes and ensuring that the workpiece is tightly attached to 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 invention is disclosed 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. [Means for solving the problem]

[0010] The transfer device disclosed in the present invention 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 the force and / or moment 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 based on the change in the value of the resistance force acquired by the force sensor, it is determined whether the placement of the workpiece on the workpiece fixing part is normal or not.

[0011] According to the disclosure of the present invention, 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. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1(a) is a front view of a machine tool (grinding machine) to which a transfer device according to one embodiment of the present invention is applied, and FIG. 1(b) is a perspective view of the transfer device according to one embodiment of the present invention. [Figure 2] FIG. 2(a) is an explanatory diagram of the state in which the fingers of the hand section of a transfer device according to one embodiment of the present invention start to grip a workpiece, and FIG. 2(b) is an explanatory diagram of the state in which the fingers of the hand section of a transfer device according to one embodiment of the present invention grip a workpiece. [Figure 3] Figure 3(a) is an explanatory diagram of the surface contact state between a workpiece and a second reference surface by a transfer device according to one embodiment of the present invention, and Figure 3(b) is an explanatory diagram of the surface contact state between a workpiece and a first reference surface by a transfer device according to one embodiment of the present invention. [Figure 4] Figure 4(a) is an explanatory diagram of the state in which a transfer device according to one embodiment of the present invention starts to apply a transfer force to a workpiece in a direction approaching the third reference surface, and Figure 4(b) is an explanatory diagram of the state in which a transfer device according to one embodiment of the present invention makes surface contact with the third reference surface of the workpiece. [Figure 5] 10A and 10B are explanatory diagrams illustrating the change over time of resistance force in a workpiece placement process using a transfer device according to an embodiment of the present invention. [Figure 6] Figure 6(a) is an explanatory diagram of the state in which the fingers of the hand section of a transfer device according to one embodiment of the present invention start to release the grip of a workpiece, and Figure 6(b) is an explanatory diagram of the state in which the fingers of the hand section of a transfer device according to one embodiment of the present invention release the grip of a workpiece. [Figure 7] Figure 7(a) is an explanatory diagram of the state in which a transfer device according to one embodiment of the present invention starts to apply a transfer force to another workpiece in a direction approaching the first reference surface, and Figure 7(b) is an explanatory diagram of the state in which a transfer device according to one embodiment of the present invention makes surface contact with the first reference surface of the other workpiece. DETAILED DESCRIPTION OF THE INVENTION

[0013] A transfer device according to one embodiment of the present invention will be described below with reference to Figures 1 to 6. 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 positioning the workpiece, 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 fixed to the table top surface (the upper surface of the magnetic chuck 72). The side surface of the jig 73 that is perpendicular to the table top surface is a second reference surface 76, and the side surface of the jig 74 that is perpendicular to the table top surface is a 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.

[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, respectively. 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 includes 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). This 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. 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 portion.

[0020] The placement process, i.e., placement of the workpiece 90 on the workpiece fixing portion 71, is performed as a process in which the robot arm 10 applies a transport force to the workpiece 90 in a direction approaching the third reference surface 77 to move the workpiece 90 and bring the third surface 93 of the workpiece 90 into contact with the third reference surface 77. However, the premise is that 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 process.

[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 one 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 around 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 around 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 FIG. 4) is applied to the workpiece 90, to which the robot arm 10 applies a transport force in a direction that moves the workpiece 90 closer to the third reference plane 77. This resistance force is detected by the force sensor 20. The resistance force acquired by the force sensor 20 is a composite 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 comes into contact with 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 on the tip side of the robot arm 10 via the force sensor 20, and is capable of holding a workpiece 90. The hand portion 30 is provided so as 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 one pair of fingers 31 that can move in a direction perpendicular to the central axis direction of the force sensor 20 to grasp 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] In the hand unit 30, the finger units 31 are positioned relative to the workpiece 90 so that the center of gravity of the workpiece 90 is positioned in the direction of the central axis of the force sensor 20, and the workpiece 90 is gripped. It is desirable to adjust the contact position of the finger portion 31 against the side of the workpiece 90 so that the vertical center position of the finger portion 31 coincides with the vertical center position of the side of the workpiece 90, so that the finger portion 31 can grip the workpiece 90 stably, centered on 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 the detection of forces and moments by the force sensor 20, grasps 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 a 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 causing the third surface 93 of the workpiece 90 to contact 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 the first and second reference surfaces 75, 76 of the workpiece fixing portion 71 in surface contact with the first surface 91 and second surface 92 of the workpiece 90, respectively. At the same time, the control unit 40 applies a predetermined transport force from the robot arm 10 to the workpiece 90 in a direction that moves the workpiece 90 toward the third reference surface 77, thereby controlling the workpiece 90 to abut against the third reference surface 77.

[0031] The control unit 40 determines whether the placement of the workpiece 90 on the workpiece fixing portion 71 is normal or not based on the change in the value of the resistance force acquired by the force sensor 20 as the workpiece 90 moves when a transport force is applied to the workpiece 90. For example, when the resistance force acquired by the force sensor 20 undergoes the following changes, the control unit 40 determines that the workpiece 90 has been placed on the workpiece fixing unit 71 correctly.

[0032] First, the resistance force acquired by the force sensor 20 gradually increases in magnitude corresponding to the static friction force from the time the transport 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. Then, when the workpiece 90 starts to move, the resistance force acquired by the force sensor 20 corresponds to a kinetic friction force that is smaller than the maximum static friction force. However, as the workpiece 90, to which a transport 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 contacts the third reference surface 77, the resistance force acquired by the force sensor 20 increases rapidly in magnitude corresponding to the reaction force received from the third reference surface 77, and reaches a second peak value that is 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 obtained 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 an upper limit and a lower limit for the resistance force while the workpiece 90 is moving. The upper limit 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 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. The control unit 40 determines that the workpiece 90 is positioned correctly on the workpiece fixing portion 71 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 to move until it reaches the third reference plane 77.

[0035] In addition to this, 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 contacts the third reference surface 77. Then, if the control unit 40 detects a resistance force that reaches another upper limit value using the force sensor 20 during the elapsed time after the workpiece 90 is subjected to the transport force before it can reach the third reference surface 77, it determines that an abnormal state has occurred, in which the workpiece 90 has not been positioned properly on the workpiece fixing portion 71.

[0036] In addition, the control unit 40 pre-sets a threshold value of resistance force that corresponds to the reaction force received from the third reference surface 77 when the workpiece 90 reaches and contacts the third reference surface 77. Then, when the control unit 40 detects a resistance force equal to or greater than the threshold value via the force sensor 20 after the workpiece 90 has been moved by the application of a transport force and the time has elapsed for the workpiece 90 to reach the third reference plane 77, it 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 by the hand unit 30, and the robot arm 10 is moved to the space near each reference surface 75, 76, 77 on the workpiece fixing unit 71 of the machine tool 70.

[0038] At the very beginning of the carrying-in process, the workpiece 90 is held by the hand unit 30 in the following manner: 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 Figure 3), 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 taught to them in advance. The control related to this execution is based on a general robot control method that reproduces and executes the taught movements, and detailed explanation will be omitted.

[0041] Next, a process for placing a workpiece using the transfer device according to this embodiment will be described. As a premise, the transfer device 1 has previously executed the carry-in process. That is, the transfer device 1, while holding the workpiece 90 placed at a predetermined supply position with the hand unit 30, moves the robot arm 10 to move the workpiece 90 to the 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 the 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, a 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. 3(a)).

[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 upper 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. 3(b)). 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 step, first, a transfer 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 plane 77 (see FIG. 4(a)). In addition to this transport force, a pressing force is applied to the workpiece 90, which is a resultant force of a force in a direction approaching the first reference surface 75 and a force in a direction approaching the second reference surface 76. This force is for maintaining the surface contact state 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 part 71, and is applied continuously from the time the workpiece 90 comes into contact with the reference surfaces 75, 76. In addition, 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 state between the first surface 91 and 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. To the workpiece 90 to which the transport force is being applied, a resistance force (illustrated by the dashed arrow in FIG. 4(a)) consisting mainly of friction force is applied in the direction opposite to the direction of the transport force, and while the workpiece 90 is stationary, the resistance force increases. This resistance force can be acquired 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 may be cases where the friction between the workpiece 90 and each of the reference surfaces 75, 76 becomes extremely large due to, for example, the presence of sticky foreign matter between the workpiece 90 and each of the reference surfaces 75, 76. In such cases, the actual frictional force becomes excessively large relative to the applied transport force, and the workpiece 90 may remain stationary relative to each of the reference surfaces 75, 76 even if the transport force exceeds the original maximum static frictional force. At this time, the resistance force acquired by the force sensor 20 will indicate an excessively large value due to the friction force. If the resistance force acquired by the force sensor 20 is greater than the upper limit value of the resistance force set in advance (RF max1 ), the control unit 40 determines that the placement 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, it is possible to prevent machining defects from occurring. 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 ​​preset as the 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, foreign matter adhering to the reference surfaces 75, 76 or scratches on the reference surfaces 75, 76 may enter between the workpiece 90 and the reference surfaces 75, 76, and may affect the friction between the workpiece 90 and the reference surfaces 75, 76. If the effect of the foreign matter or scratches on the friction excessively increases the friction, the resistance force acquired by the force sensor 20 increases, and the upper limit 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 min2In either case, the placement of the workpiece 90 on the workpiece fixing part 71 is an undesirable situation that may adversely affect the machining accuracy, and therefore, it is important to clarify this situation by 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 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. 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 starts to be subjected to a transport force and a value corresponding to the maximum static friction force immediately before the workpiece 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 abuts against the third reference surface 77 of the workpiece fixing portion 71 (see FIG. 4(b)). When the workpiece 90 contacts 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 Figure 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 properly placed on the workpiece fixing unit 71. When the control unit 40 determines that the placement is proper 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 control unit 40 acquires a change in resistance force that exceeds a 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 determines that the resistance force is equal to or lower than the upper limit value (in FIG. 5, RF max1 If the force sensor 20 acquires 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 plane 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] In this case, the resistance force changes as follows: First, the resistance force gradually increases in magnitude corresponding to the static friction force from when the transfer force is applied to the workpiece 90 until the workpiece 90 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 is smaller than the first peak value and is equivalent to the kinetic friction force, 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 increases rapidly 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 FIG. 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. When 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 arranging the workpiece 90 on the workpiece fastening part 71 is completed, the workpiece releasing process is carried out next, in which the hand unit 30 releases the workpiece 90 from its hold. This workpiece releasing process is carried out in the following procedure.

[0058] First, the hand unit 30 applies a pressing force to the workpiece 90 against the first and second reference surfaces 75, 76, while moving the pair of fingers 31 of the hand unit 30 in directions away from each other, thereby releasing the grip of the workpiece 90 by the fingers 31 (see Figure 6). 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 hand unit 30, which has been separated from the workpiece 90, is moved to the initial position for the carry-in step for the next workpiece to be processed, and the workpiece releasing step is completed. However, the movement of the hand unit 30 away from the workpiece 90 is not limited to this. For example, if, after machining a 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. Also, if, after machining a workpiece, 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, 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, while acquiring 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, since 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 fastening part 71 is configured to have three reference surfaces 75, 76, and 77 that are perpendicular to one another for workpiece positioning, but this is not limited to this. For example, the workpiece fastening part may be configured to have only one reference surface, or the workpiece fastening part may be configured to have two reference surfaces. When the workpiece fastening part has only one reference surface, the workpiece is placed on the workpiece fastening part by applying a transport force to the workpiece while maintaining surface contact between the one reference surface of the workpiece fastening part and one surface of the workpiece, and the force sensor can acquire the resistance force acting on the workpiece in the direction opposite to the direction of the transport force. Even when the workpiece fixing part has two reference surfaces, the workpiece is placed on the workpiece fixing part by applying a transport force to the workpiece while maintaining surface contact between the two reference surfaces of the workpiece fixing part and the two corresponding surfaces of the workpiece.The force sensor can obtain the resistance force acting on the workpiece in the direction opposite to the direction of the transport 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 fixing 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, but 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 fixing portion 71, and then bring it into surface contact with the third reference surface 77, and then, as shown in Figure 7, apply a transfer force to the workpiece 95 in a direction that moves it closer to the first reference surface 75, which is the top surface of the table, to move the workpiece 95. In this case, too, the force sensor 20 acquires the resistance force (illustrated by the dashed arrow in Figure 7) 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, a determination is made as to whether the placement of the workpiece 95 on the workpiece fixing portion 71 is normal or not.

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

[0065] 1 Transfer device 10 Robotic Arm 20 Force sensor 30 Hand section 31 Finger section 40 Control Unit 70 Machine tools 71 Work fixing part (table) 72 Magnetic chuck 73, 74 Jig 75, 76, 77 Reference plane 90, 95 work 91, 92, 93 sides

Claims

1. A work transfer device that holds and moves a workpiece relative to a workpiece fixing section that fixes a workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing section, a force sensor capable of detecting a force and / or a moment acting on the workpiece; the workpiece fixing portion has a first reference surface, The workpiece is a solid having a first surface that is in contact with the first reference surface, As the arrangement of the workpiece on the workpiece fixing portion, a transfer force is applied to the workpiece to move it while maintaining a surface contact state between a first reference surface of the workpiece fixing portion and a first surface of the workpiece; the force sensor acquires a resistance force acting on the workpiece to which the transport force has been applied in a direction opposite to the direction of the transport force; and determining whether the workpiece is properly placed on the workpiece fixing portion based on a change in the value of the resistance force acquired by the force sensor. A transfer device characterized by:

2. 2. The transfer device of claim 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 a second reference surface of the workpiece fastening portion, The workpiece is placed on the workpiece fixing portion by applying a transfer force to the workpiece while maintaining a surface contact state between the first and second reference surfaces of the workpiece fixing portion and the first and second surfaces of the workpiece, respectively. A transfer device characterized by:

3. 3. The transfer device according to claim 2, the workpiece fixing portion has a third reference surface for workpiece positioning, which is arranged so as to be perpendicular to the first reference surface and the second reference surface; the workpiece has a third surface that contacts a third reference surface of the workpiece fixing portion, The workpiece is placed on the workpiece fixing portion by applying a transport force to the workpiece in a direction approaching the third reference surface while maintaining the first and second reference surfaces of the workpiece fixing portion and the first and second surfaces of the workpiece in surface contact with each other, thereby moving the workpiece. A transfer device characterized by:

4. 4. The transfer device according to claim 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 as the moved workpiece abuts against the third reference surface; The resistance force acquired by the force sensor is The magnitude of the force is gradually increased in accordance with the static friction force until the workpiece starts to move after the force is applied to it, a first peak value corresponding to a maximum static friction force is reached immediately before the workpiece starts to move, When the workpiece starts to move, the dynamic friction force is smaller than the maximum static friction force and falls within a certain fluctuation range regardless of the passage of time. When the workpiece reaches and abuts against the third reference surface, the magnitude of the reaction force increases rapidly in response to the reaction force received from the third reference surface, and becomes a second peak value that is greater than the first peak value. When the above changes occur, it is determined that the workpiece has been placed correctly on the workpiece fixing portion. A transfer device characterized by:

5. 4. The transfer device according to claim 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 as the moved workpiece abuts against the third reference surface; An upper limit value of the resistance force is set in advance, the upper limit value being equivalent to the reaction force received from the third reference surface when the workpiece reaches and abuts against the third reference surface, If the force sensor detects a resistance force that reaches the upper limit value during the time that has elapsed since the workpiece is subjected to a transport force and before the workpiece reaches the third reference plane, it is determined that the workpiece is not properly positioned on the workpiece fixing portion, which is an abnormal state. A transfer device characterized by:

6. 4. The transfer device according to claim 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 as the moved workpiece abuts against the third reference surface; A resistance threshold value corresponding to a reaction force received from the third reference surface when the workpiece reaches and contacts the third reference surface is set in advance; When the workpiece is moved by the application of a transport force and reaches the elapsed time when the workpiece can reach the third reference plane, if the force sensor detects a resistance force equal to or greater than the threshold value, it is determined that the workpiece has been properly placed on the workpiece fixing portion, and the movement of the workpiece is stopped. A transfer device characterized by:

7. 4. The transfer device according to claim 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 as the moved workpiece abuts against the third reference surface; Regarding the resistance force while the workpiece is moving, an upper limit value is set in advance, which is a magnitude between a value corresponding to the maximum static friction force immediately before the workpiece starts to move and a value corresponding 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, which is a magnitude between an initial value of the static friction force when the workpiece starts to be subjected to a transport force and the value corresponding to the maximum static friction force, If the resistance force acquired by the force sensor falls within a range from the lower limit value to the upper limit value during the elapsed time from when the workpiece starts to move until it does not reach the third reference plane, it is determined that the workpiece is properly placed on the workpiece fixing portion. A transfer device characterized by:

8. 2. The transfer device of claim 1, a robotic arm with multiple degrees of freedom; a hand unit provided at a tip end of the robot arm so as to be able to hold the workpiece; The force sensor is disposed between the tip of the robot arm and the hand unit. A transfer device characterized by:

9. 4. The transfer device according to claim 3, the machine tool is a grinding machine having a table as the workpiece fixing portion on which a workpiece to be ground can be fixed, one of the reference surfaces is the top surface of the table; The other two reference surfaces are surfaces that are perpendicular to the table top surface in one or more jigs fixed to the table top surface. A transfer device characterized by:

10. A workpiece placement method in which a predetermined transfer device holds and moves a workpiece to a workpiece fixing section that fixes the workpiece to be machined in a machine tool, and places the workpiece on the workpiece fixing section, The method includes at least a placement step of placing the work on the work fixing part by bringing the work into surface contact with a first reference surface for work positioning provided on the work fixing part by the transfer device, the transfer device has a force sensor capable of detecting a force and a moment acting on a workpiece being held, the workpiece is a solid body having a first surface that is in contact with a first reference surface of the workpiece fixing portion, In the placement step, the transfer device applies a transfer force to the workpiece to move the workpiece while maintaining a surface contact state between a first reference surface of the workpiece fixing portion and a first surface of the workpiece, and the force sensor acquires a resistance force applied to 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 workpiece is properly placed on the workpiece fixing portion based on a change in the value of the resistance force acquired by the force sensor in the placing step. A workpiece placement method.

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