ROBOT SYSTEM AND METHOD FOR CONTROLLING A ROBOT HAND

Abstract

Robot system (10), comprising: a robot hand (100) mounted on a distal end of a robot arm (15) to be moved by the robot arm (15) for holding an object (W), the robot hand (100) comprising: a base (103) mounted on the distal end of the robot arm (15); a first hand arm (101) mounted on the base (103) for reciprocating movement along a first axis and having a holding member (111), the first hand arm being configured to move the holding member (111) between a first distal position remote from the base (103) in a first direction and to a first proximal position closer to the base (103) than the first distal position, the holding member (111) comprising a plurality of grippers (117, 118) configured to open and close to grip the object (W); and a second hand arm (102) mounted on the base (103) for reciprocating movement along the first axis and having a counterweight (121), the second hand arm being adapted to move the counterweight (121) between a second distal position remote from the base (103) in a second direction opposite to the first direction and a second proximal position closer to the base (103) than the second distal position; and a controller (12) configured to control an operation of the robot hand (11), wherein the controller (12) controls the robot hand (100) such that the holding member (111) is moved from the first proximal position to the first distal position after the balance weight (121) is moved from the second proximal position to the second distal position.

Description

BACKGROUND OF THE INVENTION 1. Technical field

[0001] The invention relates to a robot system with a robot hand for holding and transporting an object and a method for controlling a robot hand. 2. State of the art

[0002] Industrial robots are known which have a robot hand which is provided with a linearly reciprocating holding component for holding an object, such as a workpiece (see, for example, Japanese patent publications JP 2002 - 172 569 A and JP 2006 - 16 144 A).

[0003] Furthermore, document US 6 210 097 B1 discloses a load robot comprising a loading section arranged on a robot body and a balancing device. The loading section has a loading plate that is movable toward a loading position spaced apart from the robot body. The balancing device moves in the opposite direction to the loading plate.

[0004] Furthermore, from document US 2011 / 0268549 A1 a palletizing robot is known which comprises a lifting frame, an end effector, an extendable mechanical arm and a balancing mechanism.

[0005] A conventional robot hand with a linearly reciprocating support member is mounted on a joint at the distal end of a robot arm, with a base of the robot hand serving as a bearing or support point. When the robot hand is required to hold an object located away from the joint, it moves the support member toward the object, holds it, and lifts it with the support member located away from the base.

[0006] A load moment acts on the frame and the joint, which depends on the distance between the holding component and the frame and the weight of the object. For a robot hand with a linearly reciprocating holding component, it is necessary to reduce the load moment acting on the base and the joint when the holding component lifts the object from a position relatively far from the base.

[0007] Furthermore, in such an arrangement with a linearly reciprocating support member, a load moment of inertia acts on the robot arm when conveying the object carried by the support member during operation. It is also desirable to reduce the load moment of inertia acting on the robot arm. SUMMARY OF THE INVENTION

[0008] According to the invention, a robot system according to claims 1 and 9 and a method for controlling a robot hand are provided.

[0009] According to one feature of the present invention, a robot arm is configured to hold and convey an article. The robot arm is provided with a base; a first hand arm mounted on the base, having a holding member configured to hold the article and capable of moving the holding member between a first distal position remote from the base in a first direction and a first proximal position closer to the base than the first distal position; and a second hand arm mounted on the base, including a counterweight, configured to move the counterweight between a second distal position remote from the base in a second direction opposite the first direction, to a second proximal position closer to the base than the second distal position.

[0010] The robot hand may further be provided with a first drive unit configured to drive the holding member for movement between the first distal position and the first proximal position; and with a second drive unit configured to drive the balance weight for movement between the second distal position and the second proximal position.

[0011] Furthermore, the robot hand can be provided with a coupling mechanism configured to couple a movement of the holding component by the first drive unit and a movement of the counterweight by the second drive unit. In this arrangement, the first drive unit and the second drive unit can have a common drive source.

[0012] Both the first drive unit and the second drive unit may comprise an air cylinder. Alternatively, the first drive unit and the second drive unit may also comprise a servo motor.

[0013] According to a further modification, the first drive unit or the second drive unit may comprise a servo motor and the other of the two drive units may then comprise an air cylinder.

[0014] According to another feature of the invention, a robot is provided with a robot hand having the above structure and with a robot arm on which the robot hand is mounted.

[0015] According to a further embodiment of the invention, a robot system is provided with the above-mentioned robot, and a controller is configured to control the robot. The robot system may further be provided with a load sensor configured to measure the weight of the object. A controller may control the movement of the counterweight by the second hand arm based on the weight of the object measured by the load sensor.

[0016] According to a further embodiment of the invention, a method for controlling the robot hand described above comprises the following steps: moving the balance weight from the second proximal position to the second distal position by means of the second hand arm; moving the holding member from the first proximal position to the first distal position by means of the first hand arm; and holding the object by driving the holding member.

[0017] The method may also comprise the following steps: measuring the weight of the object while holding it; calculating, based on the measured weight of the object, a target position at which the counterweight is to be arranged; and moving the counterweight with the second hand arm to the target position. BRIEF DESCRIPTION OF THE CHARACTERS

[0018] These and other objects, features and advantages of the invention will become more apparent from the following detailed description with reference to the figures. Fig. 1 is a schematic diagram of a robot system according to an embodiment of the invention; Fig. 2 is a perspective view of a robot hand according to an embodiment in a state in which the robot hand is extended; Fig. 3 is a perspective view of the robot hand according to Fig. 2 in a state where the robot hand is retracted; Fig. 4 is a diagram illustrating an example of the operation of a robot hand according to Fig. 2; Fig. 5 is a representation according to Fig. 1 to explain the function of the robot hand; Fig. 6 is a perspective view of a robot hand according to another embodiment, showing a state in which the robot hand is extended; Fig. 7 is a diagram showing an example of an operation of a robot hand according to Fig. 6; Fig. 8 is a perspective view of a robot hand according to another embodiment of the invention in a state where the robot hand is extended; Fig. 9 is a side view of a robot hand according to another embodiment in a state in which the robot hand is extended; and Fig. 10 is a representation corresponding Fig. 9 and shows a state in which the robot hand is Fig. 9 has been withdrawn. DESCRIPTION IN DETAIL

[0019] In the following, exemplary embodiments of the invention are described in detail with reference to the figures. First, the structure of a robot system 10 according to an exemplary embodiment is described with reference to Fig. 1. The robot system 10 includes a robot 11 configured to hold and convey an object W, such as a workpiece; and a controller 12 for controlling the robot 11. The robot 11 according to this embodiment is vertically articulated with a plurality of axes. Specifically, the robot 11 includes a robot arm 15 having a lower arm 13 mounted on a rotary base 17 and a front arm 14 mounted on the lower arm 13; and a robot hand 100 mounted on a joint 16 at the distal end of the robot arm 15.

[0020] Fig. Figure 2 shows the structure of a robot hand 100 according to this embodiment. The robot hand 100 has a base 103 mounted on the joint 16 of the front arm 14, a first hand arm 101 and a second hand arm 102 mounted on the base 103; a servo motor 104 configured to drive the first hand arm 101; and an air cylinder 105 configured to drive the second hand arm 102.

[0021] In Fig. In the state shown in Figure 2, the front arm 14 extends along a first axis A1. The base 103 is connected to the distal end of the front arm 14 via the joint 16, wherein the joint 16 has a first joint part 16a, a second joint part 16b, and a third joint part 16c, so that it is rotatable about the first axis A1, a second axis A2, and a third axis A3. The second axis A2 is orthogonal to the first axis A1 and rotates about the first axis A1. The third axis A3 is orthogonal to the second axis A2 and rotates about the second axis A2.

[0022] The base 103 is rotatable about the first axis A1 with respect to the front arm 14 by means of the first joint part 16a, which is arranged at one end of the front arm 14 in the direction of the first axis A1. The base 103 is rotatable about the second axis A2 with respect to the front arm 14 by means of the second joint part 16b, which is arranged in the direction of the first axis A1 on one side of the first joint part 16a. The base 103 is further rotatable about the third axis A3 with respect to the front arm 14 by means of the third joint part 16c, which is arranged in the direction of the third axis A3 on one side of the second joint part 16b.

[0023] A ball screw housing 106 extends from the base 103 in the positive direction of a fourth axis A4 (a direction which is Fig. 2 is marked by the arrow on the fourth axis A4) and is fixed to one side of the base 103 in the direction of the third axis. The fourth axis A4 rotates around the first axis A1, the second axis A2, and the third axis A3.

[0024] The ball screw housing 106 is hollow and box-shaped with a square cross-section, with the longitudinal axis oriented along the fourth axis A4. A ball screw (not shown) with a screw shaft extends along the fourth axis A4 and is housed in the interior of the ball screw housing 106. The end of the ball screw in the positive direction of the fourth axis A4 is connected to an output shaft (not shown) of the servo motor 104. An opening (not shown) extending along the fourth axis A4 is formed in an end surface 107 of the ball screw housing 106.

[0025] The first hand arm 101 includes: a connecting housing 108 mounted opposite the end face 107 of the ball screw housing 106; a motor housing 109 fixed on the side of the connecting housing 108 in the positive direction of the fourth axis A4; a shaft housing 110 extending from the connecting housing 108 in the negative direction of the fourth axis A4; and a support member 111 disposed on the side of the shaft housing 110 in the negative direction of the fourth axis A4. The connecting housing 108 is hollow and box-shaped and includes a connecting part (not shown) in its interior, the connecting part being connected to the ball screw housing 106.

[0026] The connecting part engages the screw spindle through the opening formed in the end surface 107 of the ball screw housing 106 and is supported by the ball screw housing 106 so as to be movable in the direction of the fourth axis A4. In this embodiment, rotational movement of the screw spindle is converted into movement of the connecting part housing 108 along the fourth axis A4. When the screw spindle is rotated about the fourth axis A4 in one direction, the connecting part engaged with the screw spindle is driven in the negative direction of the fourth axis A4. With this movement of the connecting part, the connecting part housing 108 is moved in the negative direction of the fourth axis A4.When the screw spindle is rotated in the opposite direction about the fourth axis A4, the connecting part is driven in the positive direction of the fourth axis A4, and as a result, the connecting part housing 108 is moved in the positive direction of the fourth axis A4. Thus, the connecting part housing 108 performs reciprocating movements along the fourth axis A4 as the screw spindle rotates.

[0027] The motor housing 109 is hollow and box-shaped and accommodates a motor (not shown) configured to drive the holding member 111 within its interior. The spindle housing 110 is hollow and box-shaped and accommodates a first shaft 112 and a second shaft 113 extending within its interior along the fourth axis A4. The ends of the two shafts 112, 113 in the positive direction of the fourth axis A4 are mechanically connected via a gear mechanism to the output shaft of the motor housed in the motor housing 109.

[0028] When the output shaft of the motor is rotated, the first shaft 112 and the second shaft 113 rotate around the fourth axis A4 in opposite directions due to the gear mechanism. The first shaft 112 and the second shaft 113 extend from their ends in the positive direction of the fourth axis and the negative direction of the fourth axis A4, respectively, pass through the interior of the connecting part housing 108 and the shaft housing 110, and extend outward in the negative direction of the fourth axis through a first through hole 115 and a second through hole 116 in the end surface 114 of the shaft housing 110.

[0029] The holding part 111 is mounted on the distal ends of the first shaft 112 and the second shaft 113. Specifically, the holding part 111 includes a first gripper 117 attached to the first shaft 112 and a second gripper 118 attached to the second shaft 113. The first gripper 117 and the second gripper 118 are each curved outward.

[0030] As described above, the shafts 112 and 113 are driven by the motor housed in the motor housing 109 and rotated in opposite directions. Accordingly, the tips of the grippers 117 and 118 can be moved toward each other and away from each other. According to this structure, the holding member 111 can grasp and hold the object W by means of the grippers 117 and 118, and can also release the object W.

[0031] In this embodiment, a load sensor 122 for measuring the weight of the object W is arranged between the holding part 111 and the shafts 112 and 113. The load sensor 122 obtains information regarding the weight of the object W according to a command from the controller 12 when the holding part 111 lifts the object W and transmits this information to the controller 12. The load sensor 122 will be described in more detail below.

[0032] The air cylinder 105 is mounted on an upper surface 119 of the ball screw housing 106 on the side of the base 103 facing the positive direction of the fourth axis A4. The air cylinder 105 includes a piston (not shown) driven by air pressure in the direction of the fourth axis A4. When the air pressure in the air cylinder 105 is increased by a compressor (not shown) arranged outside the device, the piston is driven in the positive direction of the fourth axis A4. On the other hand, when the air pressure in the air cylinder 105 is decreased by the compressor, the piston is driven in the negative direction of the fourth axis A4.

[0033] The second hand arm 102 has an arm plate 120 extending along the fourth axis A4 and a counterweight 121 attached to the arm plate 120. The arm plate 120 is designed to be movable along the fourth axis A4 on top of the air cylinder 105. The arm plate 120 is mechanically connected to the piston disposed in the air cylinder 105. As described above, the piston is reciprocated along the fourth axis A4 by the air pressure in the air cylinder 105. Therefore, the arm plate 120 also reciprocates along the fourth axis A4 along with the piston.

[0034] The counterweight 121 has a rectangular prismatic shape and a predetermined weight. The counterweight 121 is attached to the upper surface of the arm plate 120 at the end thereof in the positive direction of the fourth axis A4. The counterweight 221 moves back and forth along the fourth axis A4 together with the arm plate 120 by means of the air cylinder 105.

[0035] The Fig. The robot hand 100 shown in Figure 2 is configured in the extended state to hold the object W. In the extended state, the first hand arm 101 of the robot hand 100 brings the holding part 111 into a first distal position away from the base 103 in the positive direction of the fourth axis A4. In this state, the connecting part accommodated in the connecting part housing 108 is in a position close to the end of the screw spindle in the screw spindle housing 106 in the negative direction of the fourth axis A4.

[0036] As a result, the connecting part housing 108 is positioned relative to the ball screw housing 106 such that the end of the connecting part housing 108 in the negative direction of the fourth axis A4 is located near the end of the ball screw housing 106 in the negative direction of the fourth axis A4. When the connecting part housing 108 is positioned in this way, the holding part 111 attached to the shaft housing 110 in the negative direction of the fourth axis A4 is located in the first distal position away from the base 103 in the negative direction of the fourth axis A4.

[0037] On the other hand, in the extended state according to Fig. 2, the second hand arm 102 of the robot hand 100 moves the counterweight 121 to a second distal position in the positive direction of the fourth axis A4 away from the base 103. When the counterweight 121 is moved to the second distal position, the piston enclosed in the air cylinder 105 is driven by air pressure and brought to the end of the air cylinder 105 in a positive direction relative to the fourth axis A4.

[0038] As a result, the arm plate 120 is positioned relative to the air cylinder 105 such that the end of the arm plate 120 located in the negative direction of the fourth axis A4 is close to the end of the air cylinder 105 located in the positive direction of the fourth axis A4. When the arm plate 120 is positioned in this manner, the balance weight 121 attached to the end of the arm plate 120 located in the positive direction of the fourth axis A4 is disposed in the second distal position, which is farther away from the base 103 in the positive direction of the fourth axis A4.

[0039] Now, with reference to Fig. 3 the retracted state of the robot hand 100 is described. In the retracted state of the robot hand 100 according to Fig. 3, the first hand arm 101 of the robot hand 100 brings the holding part 111 into a first proximal position near the base 103. In this state, in which the holding part 111 is arranged in the first proximal position, the connecting part accommodated in the connecting part housing 108 is in a position near the end of the screw spindle in the ball drive housing 106 located in the positive direction of the fourth axis A4.

[0040] As a result, the connecting part housing 108 is positioned relative to the ball drive housing 106 such that the end of the connecting part housing 108 located in the positive direction of the fourth axis A4 is located near the end of the ball drive housing 106 located in the positive direction of the fourth axis A4. When the connecting part housing 108 is positioned in this way, the holding part 111 attached to the shaft housing is located in the first proximal position, which is closer to the base 103 than the first distal position. Therefore, in this embodiment, the first hand arm 101 is capable of moving the holding part 111 between the first distal position and the first proximal position, the latter being closer to the base 103 than the first distal position.

[0041] On the other hand, in Fig. 3, the second hand arm 102 of the robot hand 100 moves the balance weight 121 to a second proximal position near the base 103. In this state, the piston enclosed in the air cylinder 105 is arranged at the end of the air cylinder 105 located in the negative direction of the fourth axis A4.

[0042] As a result, the arm plate 120 is positioned relative to the air cylinder 105 such that the end of the arm plate 120 located in the negative direction of the fourth axis A4 is located near the end of the air cylinder 105 located in the negative direction of the fourth axis A4. When the arm plate 120 is positioned in this manner, the end of the arm plate 120 located in the positive direction of the fourth axis A4 is located in the second proximal position, which is closer to the base 103 than the second distal position. Thus, in this embodiment, the second hand arm 102 is capable of moving the balance weight 121 between the second distal position and the second proximal position, the latter being closer to the base 103 than the second distal position.

[0043] Now, the operation of the robot hand 100 according to this embodiment will be described with reference to Fig. 4. The Fig. The operating sequence described in Figure 4 starts when the controller 12 receives a command from a master controller or an operator to convey the object W.

[0044] When the controller 12 receives a command to convey the object W in step S1, the controller causes the robot arm 15 to move the robot hand 100 into a working position for holding the object W. To do this, the controller 12 reads a robot program previously stored in a memory in the controller 12. The controller 12 then moves the robot arm 15 according to the robot program so that the robot hand 100 comes to a position near the object W.

[0045] In step S2, the controller 12 moves the balance weight 121 (also referred to as a balance counterweight) to the second distal position. In doing so, the controller 12 controls the compressor so that the air pressure in the air cylinder 105 increases. As a result, the piston in the air cylinder 105 is driven in the positive direction of the fourth axis A4, and the arm plate 120 is also moved together with the piston in the positive direction of the fourth axis A4. As a result, the balance weight 121 is moved toward the second distal position. Thus, in this embodiment, the air cylinder 105 serves as a second drive unit configured to move the holding part 111 between the second distal position and the second proximal position.

[0046] In step S3, the controller 12 checks whether the balance weight 121 is located at the second distal position. For example, the controller 12 obtains data regarding a displacement of the arm plate 120 from a position sensor disposed in the second hand arm 101 to detect a displacement of the arm plate 120, and thereby determines whether the balance weight 121 is located at the second distal position. If the controller 12 determines "YES," the operation flow proceeds to step S4. On the other hand, if the controller determines "NO," the operation flow returns to step S2.

[0047] In step S4, the controller 12 moves the holding part 111 to the first distal position. In doing so, the controller 12 causes the servo motor 104 to rotate the lead screw of the ball drive in the ball drive housing 106. As described above, a rotational movement of the lead screw is converted into a movement of the connecting housing 108 along the fourth axis A4.

[0048] Through these actions, the shaft housing 110, the motor housing 109, and the shafts 112 and 113 attached to the connecting part housing 108 are moved together with the connecting part housing 108 in the negative direction of the fourth axis A4. As a result, the holding part 111 is moved toward the first distal position. Thus, in this embodiment, the servo motor 104 and the ball drive act as a first drive unit designed to move the holding part 111 between the first distal position and the first proximal position.

[0049] In step S5, the controller 12 checks whether the holding part 111 is in the first distal position. For example, the controller 112 determines that the holding part 111 is in the first distal position based on the number of rotations of the servo motor 104.

[0050] On the other hand, the controller 12 can obtain information regarding a displacement of the connecting part via a position sensor for detecting the displacement of the connecting part in the connecting part housing 108, and thus determine whether the holding part 111 is in the first distal position based on this information. If the controller 12 determines "YES," the operation flow proceeds to step S6. On the other hand, if the controller 12 determines "NO," the operation flow returns to step S4.

[0051] In step S6, the controller 12 checks whether the holding part 111 is holding the object W. The controller 12 then causes the robot arm 15 to move the holding part 111 to the position of the object W. The controller 12 then controls the motor arranged in the motor housing 109 to rotate the shafts 112 and 113 in opposite directions. When the shafts 112 and 113 rotate in this manner, the grippers 117 and 118 are moved toward each other and then hold the object W between them.

[0052] In step S7, the controller 12 checks whether the holding part 111 is holding the object W or not. For example, the controller 12 determines whether the holding part 111 is holding the object W based on information from the load sensor 122. If the controller 112 determines "YES," the operation flow proceeds to step S8. On the other hand, if the controller 12 determines "NO," the operation flow returns to step S6.

[0053] In step S8, the controller 12 moves the holding part 111 to the first proximal position. In doing so, the controller 12 controls the servo motor 104 to rotate the lead screw in the ball drive housing 106 in a direction opposite to the direction of step S4. As a result, the holding part 111 is moved toward the first proximal position.

[0054] In step S9, the controller 12 checks whether the holding part 111 is in the first proximal position or not. If the controller 12 determines "YES," the operation flow proceeds to step S10. On the other hand, if the controller 12 determines "NO," the operation flow returns to step S8.

[0055] In step S10, the controller 12 moves the counterweight 121 to the second proximal position. In doing so, the controller 12 controls the compressor to reduce the air pressure in the air cylinder 105. This drives the piston in the air cylinder 105 in the negative direction of the fourth axis A4. As a result, the counterweight 121 is moved toward the second proximal position.

[0056] In step S11, the controller 12 checks whether the balance weight 121 is in the second proximal position. If the controller 12 determines "YES," the operation flow proceeds to step S12. On the other hand, if the controller 12 determines "NO," the operation flow returns to step S10.

[0057] In step S12, the controller 12 actuates the robot arm 15 to move the robot hand 100 into a working position for releasing the object W. The controller 12 reads the previously stored robot program. The controller 12 then moves the robot arm 15 according to the robot program such that the robot hand 11 is brought into a position where the object W is to be released.

[0058] In step S13, the controller 12 controls the holding part 112 to release the object W. In doing so, the controller 12 first causes the robot arm 15 to move the holding part 111 to a position where the object W is to be placed. Then, the controller 12 rotates the motor housed in the motor housing 109 in a direction opposite to the direction in step S6. This operation moves the grippers 117 and 118 away from each other. As a result, the object W held by the grippers 117 and 118 is released from the holding part 111 and placed in a predetermined target position. Thus, the object W is conveyed to the desired target position.

[0059] In step S14, the controller 12 checks whether the holding part 111 has released the object W or not. For example, the controller 12 determines that the holding part 111 has released the object W based on information from the load sensor 122. If the controller 12 determines "YES," the operation flow proceeds to step S15. On the other hand, if the controller 12 determines "NO," the operation flow returns to step S13.

[0060] In step S15, the controller 12 moves the robot arm 15 to the home position. In doing so, the controller 12 moves the robot arm 15 to the home position before step S1. In step S16, the controller 12 checks whether it has received a subsequent command to convey another object. If the controller 12 determines "NO," the operation flow ends. If, on the other hand, the controller 12 determines "YES," the operation flow proceeds to step S1.

[0061] With the robot hand 100 of this embodiment, it is possible to reduce the load acting on the robot arm 15 when transporting an object W. This advantageous effect will be described below with reference to Fig. 5 described in more detail. Lifts according to Fig. 5 the robot hand 100 the object W with the holding part 111, the load moment M1 due to the weight of the object W acts on the joint 16 at the distal end of the robot arm 15 around the base 103, as shown by the arrow M1 in Fig. 5. The load moment M1 depends on the distance d1 between the center of gravity of the object W and the base 103 and the weight of the object W.

[0062] If the object W is heavy or located at a position far from the base 103, the load moment M1 at the joint 16 increases. As a result, the load acting on the robot arm 15 also increases.

[0063] Therefore, in this embodiment, the robot hand 100 is configured such that the balance weight 121 is disposed at the second distal position to reduce the load moment generated when holding the object W. The robot hand 100 first moves the balance weight 121 to the second distal position using the second hand arm 102, moves the holding part 111 to the first distal position using the first hand arm 101, and then holds the object with the holding part 111.

[0064] Then, the load moment M2 caused by the balance weight 121 acts on the joint 16, which is arranged at the distal end of the robot arm 15, around the base 103, as indicated by the arrow M2 in Fig. 5. The load moment M2 depends on the distance d2 between the center of gravity of the balance weight 121 and the base 103 and on the weight of the balance weight 121. Since the load moment M1 is reduced by the load moment M2, it is possible to hold a heavy object W or an object W at a large distance from the base 103 while keeping the load on the joint 16 and the robot arm 15 low.

[0065] As described above, in this embodiment, when the robot hand 100 holds the object W with the holding part 111, it first moves the balance weight 121 to the second distal position. Then, the robot hand 100 moves the holding part 111 to the first distal position, and thus the robot hand 100 is in the extended state. After holding and lifting the object W with the holding part 111, the robot hand 100 first moves the holding part 111 to the first proximal position. Then, the robot hand 100 moves the balance weight 121 to the second proximal position, so that the robot hand 100 is in the retracted state. By extending and retracting the robot hand in this order, it is possible to safely reduce the effect of the load moment M1 on the robot arm 15 when lifting the object W.In this embodiment, the robot hand 100 is capable of conveying the object W to a target position in the retracted state, with both the holding part 111 and the balance weight 121 disposed in the proximal positions. By conveying the object W in the retracted state of the robot hand 100 as described above, it is possible to reduce the load moment of inertia of the robot hand 100 and the object W during conveyance. Therefore, it is possible to convey the object W by the robot 11 at a correspondingly higher speed.

[0066] Furthermore, in this embodiment, since the robot hand 100 can transport the object W in the retracted state, it is possible to reduce the space that the robot hand 100 traverses when conveying the object W. Thus, it is possible to prevent a collision of the robot hand 100 with other objects when conveying the object W.

[0067] Since the load moment M1 due to the object W is reduced in this embodiment, it is also possible to hold the object W very stably. Vibrations of the robot hand 100 can thus be better avoided when conveying the object W. This also makes it possible to convey the object W to the desired position with high accuracy.

[0068] Now, with a view to Fig. 6, a robot hand 200 according to another embodiment is described. Components corresponding to the above embodiment are provided with the same reference numerals, so a repeated description can be omitted. The robot hand 200 has a base 103; a first hand arm 101; a second hand arm 102; a servo motor 104; and a second servo motor 204 configured to drive the second hand arm 102.

[0069] In this embodiment, the second hand arm 102 is driven by the servo motor 204 along the fourth axis A4. For this purpose, the robot hand 200 according to this embodiment has a second ball screw housing 206 on the side of the base 103 located in the positive direction of the fourth axis A4. The ball screw housing 206 is fixed to an upper surface of the first ball screw housing 106 and extends from the base 103 in the positive direction of the fourth axis A4.

[0070] The second ball screw housing 206 is a hollow, box-shaped member with a rectangular cross-section, with its longitudinal direction oriented along the fourth axis A4. A second ball screw with a second screw shaft (not shown) extends along the fourth axis A4 and is housed in the interior of the second ball screw housing 206. The end of the second screw shaft located in the positive direction of the fourth axis A4 is connected to an output shaft (not shown) of the servo motor 204.

[0071] In this embodiment, the arm plate 120 of the second hand arm 102 has a second connecting part (not shown) that is mechanically connected to the second ball screw housing 206. The second connecting part engages the second screw spindle and is supported by the second ball screw housing 206 so that it is movable along the fourth axis A4. Rotational movement of the second screw spindle is translated into movement of the arm plate 120 along the fourth axis A4, as in the first hand arm 101 described above.

[0072] Specifically, when the second screw spindle is rotated in one direction about the fourth axis A4, the connecting part engaged with the second screw spindle is driven in the positive direction of the fourth axis A4. With this movement of the second connecting part, the arm plate 120 is also moved in the positive direction of the fourth axis A4. When the second screw spindle is rotated in the other direction about the fourth axis A4, the second connecting part is driven in the negative direction of the fourth axis A4, and as a result, the arm plate 120 is moved in the negative direction of the fourth axis A4.

[0073] In this way, the arm plate 120 performs reciprocating movements along the fourth axis A4 when the second screw spindle is rotated. Thus, in this embodiment, the second servo motor 204 and the second ball screw serve as a second drive unit configured to move the balance weight 121 between the second distal position and the second proximal position.

[0074] Now the operational process at the Fig. 6 shown robot hand 200 with a view to Fig. 7. Since steps S1 to S9 and S12 to S16 are carried out according to Fig. 7 are the same as the corresponding steps according to Fig. 4, a repeated description can be omitted.

[0075] In the operation sequence of this embodiment, after step S7, the controller 12 measures the weight of the object W in step S21. The controller 12 receives information regarding the weight of the object W from the load sensor 122 and stores this information in a memory in the controller 12.

[0076] In step S22, the controller 12 calculates a position in which the counterweight 121 is to be arranged. This step S22 will now be described in more detail. In a production line, it may be necessary to convey objects W with different weights. In this case, the load moment M1 acting on the robot arm 15 can vary from object to object. In order to reduce the thus varying load moment M1 by the load moment M2 of the counterweight 121, it is necessary to control the distance d2 between the objects W.

[0077] Therefore, in this embodiment, the controller 12 measures the weight of the object W by means of the load sensor 122 in step S21, and in step S22, the controller 12 calculates the distance d2 by which the load moment M1 can be effectively reduced taking into account the weight of the object W. For example, the controller 12 calculates the distance d2 such that the equation: M1d1 2 ≈M2d2 2 is satisfied. Then, based on the calculation result regarding the distance d2, the controller 12 determines the displacement amount by which the second hand arm 102 is to be moved in the positive direction of the fourth A4.

[0078] In this embodiment, the robot hand 200 conveys the object W after arranging the holding part 111 in the first proximal position in step S9. In step S22, the controller 12 calculates the distance d2 at which the load moment M1 exerted by the object W on the robot arm 15 can be reduced when the holding part 111 is arranged in the first proximal position. After step S22, the controller 12 continues the process with step S8.

[0079] After step S9, in step S23, the controller 12 moves the balance weight 121 to the position calculated in step S22. Specifically, the controller 12 drives the second servo motor 204 according to the displacement of the second support arm 102 determined in step S22, thereby moving the arm plate 120 of the second hand arm 102 along the fourth axis A4.

[0080] In step S24, the controller 12 determines whether the counterweight 121 has been moved to the target position. For this purpose, the controller 12 obtains, for example, information regarding a displacement of the arm plate 120 from a position sensor arranged in the second hand arm 102 to detect a displacement of the arm plate 120 and thus determines whether the counterweight 121 is located in the target position. If the controller 12 determines "YES," the process proceeds to step S12. If, on the other hand, the controller 12 determines "NO," the process returns to step S2, and the loop of steps S23 to S24 is executed until the counterweight 121 is in the target position.

[0081] In this way, in this embodiment, the controller 12 controls the movement of the counterweight 121 based on the weight of the object W, which is measured by the load sensor 122. This makes it possible to reduce the load moment M1 acting on the robot arm 15 by the load moment M2 corresponding to the different load moments M1, even when the weights of the objects W to be conveyed differ from one another. This also makes it possible to use the robot hand 200 of this embodiment on a wider variety of production lines, since the robot hand 200 can convey a multitude of different objects.

[0082] In this embodiment, the drive units for driving the first hand arm 101 and the second hand arm 102 are formed by servo motors. This makes it possible to drive the first hand arm 101 and the second hand arm 102 at high speed. It is also possible to easily synchronize the operation of the first hand arm 101 and the second hand arm 102.

[0083] Now, a robot hand 300 according to a further embodiment will be described with reference to Fig. 8. The components corresponding to the above embodiments are provided with the same reference numerals, and a repeated description can be omitted in this respect. The rotary upper hand 300 has a base 103; a first hand arm 101; a second hand arm 102; an air cylinder 105; and an air cylinder 304 configured to drive the first hand arm 101.

[0084] In this embodiment, the first hand arm 101 is driven by the air cylinder 304 in the negative direction of the fourth axis A4. The air cylinder 304 is mounted on a block 306 extending from the base 103 in the positive direction of the fourth axis A4, on the motor housing 109 side in the positive direction of the fourth axis A4. The air cylinder 304 has a second piston (not shown) disposed within the air cylinder 304 and a cylinder shaft 304a attached to the second piston.

[0085] The cylinder shaft 304a extends from the air cylinder 304 in the negative direction of the fourth axis A4 and is attached to the end face of the motor housing 109 in the positive direction of the fourth axis A4. When the air pressure in the air cylinder 304 is increased by a compressor, the second piston is driven in the negative direction of the fourth axis A4. On the other hand, when the air pressure in the air cylinder 304 is decreased by the compressor, the second piston is driven in the positive direction of the fourth axis A4. The movement of the second piston is transmitted to the motor housing 109 via the cylinder shaft 304.

[0086] A connecting part housing 108 is supported on the block 306 so as to be movable along the fourth axis A4. When the motor housing 109 is driven by the air cylinder 304, the connecting part housing 108 and the shaft housing 110 are also moved integrally. In this way, the first hand arm 101 is moved by the air cylinder 304 along the fourth axis A4. Therefore, in this embodiment, the air cylinder 304 acts as a first drive unit configured to move a holding part 111 between the first distal position and the first proximal position.

[0087] In this embodiment, the drive units for the first hand arm 101 and the second hand arm 102 are formed by air cylinders. This enables the drive unit to be fixed at a relatively low cost.

[0088] Now, a robot hand 400 according to a further embodiment with reference to Fig. 9. Those components corresponding to those of the above embodiments are provided with the same reference numerals, so a repeated description is omitted. The rotary upper hand 400 has a base 103; a first hand arm 101; an air cylinder 304; a second hand arm 402 mounted on the base 103 so as to be movable along the fourth axis A4; and a coupling mechanism 403 configured to move the second hand arm 402 in conjunction with a movement of the first hand arm 101.

[0089] The second hand arm 402 has an arm plate 420 extending along the fourth axis A4; and a counterweight 121 attached to the arm plate 420. The arm plate 420 is mounted on a block 306 that is attached to the base 103 so as to be movable along the fourth axis A4. In this embodiment, an engagement part 412 is formed in the lower surface of the arm plate 420.

[0090] A connecting part housing 108 of the first hand arm 101 is supported on the block 306 so as to be movable along the fourth axis A4. An engagement part 411 is attached to the upper surface of the connecting part housing 108. The engagement part 411 is arranged on the block 306 and is moved together with the connecting part housing 108.

[0091] A gear 413 is arranged between the engaging part 412 of the arm plate 420 and the engaging part 411 which is fixed on the connecting part housing 108. The gear 413 is supported on the block 306 such that it is rotatable on the block 306 about an axis which is perpendicular to the plane of the drawing of the Fig. 9. The gear 413 is engaged with both the engaging part 412 of the arm plate 420 and the engaging part 411.

[0092] In this embodiment, a coupling mechanism 403 configured to link the first hand arm 101 and the second hand arm 402 is formed by the engaging part 412 of the arm plate 420, the engaging part 411, and the gear 413.

[0093] Now, the operation of the robot hand 400 according to this embodiment will be described with reference to Fig. 9 and Fig. 10. If the robot hand 400 is returned from the retracted state according to Fig. 10 into an extended state according to Fig. 9, the first hand arm 101 is moved in the negative direction of the fourth axis A4 by means of the air cylinder 304. With this movement, the engaging part 411 connected to the connecting part housing 108 is also moved integrally in the negative direction of the fourth axis A4.

[0094] Then, the gear 413 meshing with the engagement part 411 is viewed from the front side of Fig. 10 is rotated counterclockwise. When the gear 413 is rotated counterclockwise in this way, the engaging part 412 of the arm plate 420 is driven in the positive direction of the fourth axis A4.

[0095] As a result, the arm plate 420 and the balance weight 121 attached to the arm plate 420 are moved integrally in the positive direction of the fourth axis A4. In other words, in this embodiment, the gear 413 and the engaging part 412 engaged therewith function as a second drive unit configured to drive the second hand arm 402.

[0096] In this way, in this embodiment, the coupling mechanism 403 makes it possible to move the balance weight 121 by means of the air cylinder 304 along with a movement of the holding part 111. Due to this structure, it is possible to drive both the holding part 111 and the balance weight 121 with a single drive source by dividing the action of the drive source (in this case, the air cylinder 304) between the first hand arm and the second hand arm. With this structure, it is possible to avoid a costly power source with a complicated structure. Thus, the manufacturing cost of the robot hand 400 can also be reduced. In this way, it is also possible to reliably synchronize the holding part 111 and the balance weight 121 with each other in a simple manner.

[0097] In the above embodiments, the robot hand is brought into the extended state while the holding part is moved by the first hand arm in the negative direction of the fourth axis A4 and the balance weight is moved in the positive direction of the fourth axis A4, ie, in a direction opposite to the direction of movement of the holding part by the second hand arm.

[0098] With regard to reducing the moment exerted on the robot arm during transport of an object, the moment caused by the object is reduced by the movement of the counterweight at least in a direction opposite to the support member with respect to the base. Thus, the present invention is not limited to the above embodiments and can be implemented simply by moving the support member in the negative direction of the fourth axis A4 and the counterweight by any amount in the positive direction of the fourth axis A4 with respect to the base.

[0099] In the above embodiments, after holding the object by the holding member, the robot hand is retracted to move the object to a target position. However, it is also possible to move the object to the target position with the robot hand extended.

[0100] In the above embodiments, the load sensor provided for measuring the weight of the object is arranged between a shaft on which the support member is mounted and the support member. However, the invention is not limited to this. The load sensor can also be arranged, for example, on the base of the robot hand or on the robot arm.

[0101] For example, bending sensors can be arranged at multiple locations on the robot arm instead of a single load sensor, allowing the controller to detect the bending of the robot arm generated when the support member holds an object. This allows the controller to calculate the load torque on the robot arm based on the bending information transmitted by the bending sensors. With such a setup, the controller can receive bending information from the bending sensors at regular intervals and adjust the position of the counterweight in real time according to the load torque acting on the robot arm, which can constantly change.

[0102] With the robot hand described above, it is possible to reduce the load moment acting on the base and joint when conveying an object through the holding component by means of the counterweight. It is also possible to move both the holding component and the counterweight to proximal positions. This makes it possible to reduce the moment of inertia acting on the robot arm when holding and transporting an object with the holding component.

[0103] The invention has been explained above with reference to individual embodiments. However, these embodiments do not limit the invention defined in the claims. Furthermore, not all described combinations of features in the above embodiments need to be essential to the solution provided by the invention. It is clear to those skilled in the art that various modifications or improvements to the embodiments are possible. Such modifications or improvements are also included in the technical disclosure of the present invention as defined in the claims.

[0104] The order of execution of the method steps is not mandatory with respect to the claims, the description, and the figures unless an explicit restriction is stipulated. If the result of a previous method is used for a subsequent method, the terms "first" or "then" may not be necessary with respect to an operating sequence in the claims, the description, and the figures. A restriction in this sense does not apply, even if it is nevertheless a preferred, i.e., disclosed, embodiment.

Claims

[1] Robot system (10), comprising: a robot hand (100) mounted on a distal end of a robot arm (15) to be moved by the robot arm (15) for holding an object (W), the robot hand (100) comprising: a base (103) mounted on the distal end of the robot arm (15); a first hand arm (101) mounted on the base (103) for reciprocating movement along a first axis and having a holding member (111), the first hand arm being configured to move the holding member (111) between a first distal position remote from the base (103) in a first direction and to a first proximal position closer to the base (103) than the first distal position, the holding member (111) comprising a plurality of grippers (117, 118) configured to open and close to grip the object (W); and a second hand arm (102) mounted on the base (103) for reciprocating movement along the first axis and having a counterweight (121), the second hand arm being adapted to move the counterweight (121) between a second distal position remote from the base (103) in a second direction opposite to the first direction and to a second proximal position closer to the base (103) than the second distal position; and a controller (12) configured to control an operation of the robot hand (11), wherein the controller (12) controls the robot hand (100) such that the holding member (111) is moved from the first proximal position to the first distal position after the balance weight (121) is moved from the second proximal position to the second distal position. [2] Robot system according to claim 1, wherein the robot hand (100) further comprises: a first drive unit configured to move the holding member (111) between the first distal position and the first proximal position; and a second drive unit configured to move the balance weight (121) between the second distal position and the second proximal position. [3] Robot system according to claim 2, wherein the robot hand (100) further comprises: a coupling mechanism (403) configured to couple a movement of the holding member (111) by the first drive unit and a movement of the counterweight (121) by the second drive unit. [4] The robot system according to claim 3, wherein the first drive unit and the second drive unit have a common power source. [5] A robot system according to claim 2, wherein each of said first and second drive units comprises an air cylinder (105, 304). [6] Robot system according to claim 2, wherein both the first drive unit and the second drive unit comprise a servo motor (104, 204). [7] A robot system according to claim 2, wherein the first drive unit or the second drive unit comprises a servo motor (104) and the other drive unit comprises an air cylinder (105). [8] Robot system according to one of claims 1 to 7, further comprising: a robot arm (15) on which the robot hand (100) is mounted. [9] Robot system comprising: a robot (11) comprising: a robot hand (100) mounted on a distal end of a robot arm (15) to be moved by the robot arm (15) for holding an object (W), the robot hand (100) comprising: a base (103) mounted on the distal end of the robot arm (15); a first hand arm (101) mounted on the base (103) for reciprocating movement along a first axis and having a holding member (111), the first hand arm being configured to move the holding member (111) between a first distal position remote from the base (103) in a first direction and to a first proximal position closer to the base (103) than the first distal position, the holding member (111) comprising a plurality of grippers (117, 118) configured to open and close to grip the object (W); and a second hand arm (102) mounted on the base (103) for reciprocating movement along the first axis and having a counterweight (121), the second hand arm being adapted to move the counterweight (121) between a second distal position remote from the base (103) in a second direction opposite to the first direction and to a second proximal position closer to the base (103) than the second distal position; and a robot arm (15) on which the robot hand (100) is mounted; a controller (12) configured to control the robot (11); and a load sensor (122) configured to measure a weight of the object (W), wherein the controller (12) controls a movement of the counterweight (121) with the second hand arm (102) depending on the weight of the object (W) measured by the load sensor (122). [10] A method for controlling a robot hand (100) mounted on a distal end of a robot arm (15) to be moved by the robot arm (15), the robot hand (100) comprising: a base (103) mounted on the distal end of the robot arm (15); a first hand arm (101) mounted on the base (103) and having a holding member (111), the first hand arm being configured to move the holding member (111) between a first distal position away from the base (103) in a first direction and to a first proximal position closer to the base (103) than the first distal position, the holding member (111) comprising a plurality of grippers (117, 118) configured to open and close to grip the object (W); and a second hand arm (102) mounted on the base (103) and having a counterweight (121), the second hand arm being configured to move the counterweight (121) between a second distal position remote from the base (103) in a second direction opposite to the first direction and to a second proximal position closer to the base (103) than the second distal position, the method comprising the following steps: Moving the holding component (111) from the first proximal position to the first distal position by means of the first hand arm (101) after moving the counterweight (121) from the second proximal position to the second distal position by means of the second hand arm (102); and Holding the object (W) by actuating the holding component (111). [11] The method of claim 10, further comprising the steps of: Measuring the weight of the object (W) after grasping it; Calculating, on the basis of the measured weight of the object (W), a target position in which the counterweight (121) is to be arranged; and Moving the balance weight (121) to the target position using the second hand arm (102).

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