METHOD OF DETERMINING REFERENCE POSITION OF INDUSTRIAL ROBOT

Abstract: In an industrial robot provided with a fixed base (1), a first arm (3) fixed pivotably to the fixed base (1), a second arm (4) fixed pivotably to a free end portion of the first arm (3), and a wrist (7) fixed to a free end portion of the second arm (4) and having a wrist base (8) and a movable flange (9), the determining of a reference position of the wrist (7) is done independently between itself and the second arm (4), the determining of reference positions of the first and second arms (3, 4) with respect to the fixed base (1) being done by a positioning jig (15) fixed to the fixed base (1). The reference position of one or a plurality of axes of an industrial robot including the axis of a free end portion of a wrist thereof is determined independently, so that such a positioning operation can be carried out with a tool kept attached to the free end portion of the wrist.

Description: Technical Field This invention relates to a reference position determination method for an industrial robot. Background Art Hitherto, reference position determination in an industrial robot is carried out as shown in FIG. 4. Namely, a fixed side jig 35 provided with a plurality of dial gauges (indicators) 32, 33 and 34 is attached to a fixed base 31 of the industrial robot to allow a movable side jig 37 attached to a wrist front end portion 36 of the industrial robot to be in contact with the dial gauges 32, 33 and 34 of the jig 35 to thereby carry out determination of reference position (e.g., Japanese Patent Publication No. 46716/1992). However, in accordance with the prior art, since determination of reference position is carried out in the state where the movable side jig 37 is attached to the wrist front end portion 36 of the industrial robot, there was the problem that tool must be detached from the wrist front end portion 36. In addition, since tool must be removed (detached), there was the problem that it is required to carry out positioning between the wrist front end portion 36 of the industrial robot and tool front end portion (working point) for a second time. The JP-A-6 031 661 describes a position calibrating device for an industrial robot according to the pre-characterising part of claim 1, which allows position calibration without removing a tool mounted to the wrist of the robot. For position calibrating a first calibrating jig can be mounted to one of several reference surfaces provided on a fixed part of the machine body and a second calibrating jig can be mounted to a jig mounting surface of the wrist separately from a tool mounting surface. Then the two calibrating jigs are brought into contact with each other for position calibrating of the robot. For using this calibrating device it is necessary to mount two different calibrating jigs to the wrist part and a fixed part of the robot. Further, this device does not provide any possibility for exactly calibrating the position of the movable wrist part in view to the arms of the robot. It is the object of the invention to provide an improved reference position determination method for an industrial robot, which allows an easy and more exact determination of the reference position. This object is fulfilled by a reference position determination device having the features disclosed in claim 1. Preferred embodiments are defined in the dependent subclaims. A reference position determination method for an industrial robot of this invention is such that, in an industrial robot comprising a fixed base, a first arm rotatably attached to the fixed base, a second arm rotatably attached to the front end portion of the first arm, and a wrist portion provided with a wrist base and a movable flange, attached to the front end portion of the second arm, determination of reference position of the wrist portion with respect to the second arm is carried out individually or independently between the wrist portion and the second arm, and determinations of reference positions of the first and second arms with respect to the fixed base are carried out by a positioning Jig attached to the fixed base. Moreover, positioning grooves caused to be in correspondence with each other when the movable flange is located at reference position with respect to the wrist base are respectively formed at the wrist base and the movable flange of the wrist portion; positioning grooves caused to be in correspondence with each other when the wrist base is located at reference position with respect to the second arm are respectively formed at the second arm and the wrist base; reference planes in X, Y and Z directions are formed on the surfaces in the X, Y and Z directions of the wrist base; a positioning jig is attached to the fixed base to form reference planes in the X, Y and Z directions corresponding to the reference planes in the X, Y and Z directions of the wrist base on the surfaces in the X, Y and Z directions of the positioning jig; positions of the respective positioning grooves of the wrist base and the movable flange are caused to be in correspondence with each other to carry out positioning of the movable base with respect to the wrist base; and the reference planes in the X, Y and Z directions of the wrist base are caused to be respectively tightly in contact with the reference planes in the X, Y and Z directions of the positioning jig to carry out determinations of reference positions of the first arm and the second arm with respect to the fixed base. Since the above-described means are used in the industrial robot to carry out determination of reference position of the movable flangle with respect to the wrist base of the wrist portion individually or independently, to carry out determination of reference position of the wrist base with respect to the second arm individually or independently, and to carry out determinations of reference positions of only the first arm and the second arm with respect to the fixed base by means of the positioning jig, there is no necessity of detaching tool from the wrist front end portion at the time of positioning. As described above, in accordance with this invention, since an approach is employed to individually or independently carry out determination of reference positions of one axis or plural axes including the front end axis of the wrist portion of the industrial robot, determination of reference position can be advantageously carried out in the state where tool is attached to the wrist front end portion. Brief Description of the Drawings FIG. 1 is a side view showing an embodiment in the case where this invention is applied to six-axis revolute joint type robot, wherein there is shown attitude of the robot when reference position of the industrial robot is determined. FIG. 2 shows the detail of the wrist portion in the embodiment of this invention, wherein FIG. 2(a) is a side view and FIG. 2(b) is a front view, FIG. 3 is an enlarged side view of the front end portion of a positioning jig which shows a second embodiment of this invention, and FIG. 4 is a side view showing a conventional reference position determination method. Best Mode for Carrying Out Invention A first embodiment of this invention will now be described with reference to the attached drawings. FIG. 1 is a side view showing the embodiment in the case where this invention is applied to the six-axis revolute joint type robot, and shows attitude of the robot when reference position of the industrial robot is determined. FIG. 2 shows the detail of the wrist portion, wherein FIG. 2(a) is a side view and FIG. 2(b) is a front view. In FIG. 1, reference numeral 1 denotes a fixed base, wherein a turning body portion 2 is rotatably provided within a horizontal plane surface at the upper portion. Reference numeral 3 denotes a first arm which is provided at the turning body portion 2 so that it can be fluctuated in upper and lower directions. Reference numeral 4 denotes a second arm which is provided at the front end portion of the first arm 3 so that it can be fluctuated in upper and lower directions. Reference numerals 5 and 6 denote a link for driving the second arm. Reference numeral 7 denotes a wrist portion provided at the front end portion of the second arm 4 so that twisting, flexing (bending) and rotation can be made, and is provided with a wrist base 8 and a movable flange 9, wherein reference planes 10, 11 and 12 in X, Y and Z directions are formed on the surfaces in the X, Y and Z directions of the wrist base 8. Reference numeral 13 denotes a positioning groove e.g., key groove, etc. formed at the second arm 4. Reference numeral 14 denotes a positioning groove such as key groove, etc. similar to the above, formed at the wrist base 8. These both positioning grooves 13, 14 are caused to be in correspondence with each other when the wrist base 8 is located at the reference position with respect to the second arm 4. Reference numeral 15 denotes a positioning jig which is composed of a body portion 16 and a positioning portion 17, wherein the body portion 16 is detachably attached to the fixed base 1. Moreover, at the positioning portion 17, reference planes 18, 19 and 20 in the X, Y and Z directions corresponding to the reference planes 10, 11 and 12 in the X, Y and Z directions of the wrist base 8 are formed on the surfaces in the X, Y and Z directions. Reference numeral 21 denotes a tool which is attached to the front end portion of the wrist portion 7, and is adapted so that attitude and position are controlled by twisting, flexing (bending) and rotation operations of the wrist portion 7. Reference numeral 22 denotes a positioning groove, e.g., key, groove, etc. formed at the wrist base 8, and reference numeral 23 denotes a positioning groove such as key groove similar to the above, formed at the movable flange 9. These both positioning grooves 22, 23 are caused to be in correspondence with each other when the movable flange 9 is located at the reference position with respect to the wrist base 8. The reference position determination method for industrial robot constituted in this way will now be described. Initially, determination of reference position with respect to the wrist base 8 of the movable flange 9 to which the tool 21 is attached, i.e., determination of reference position of the wrist front end axis for rotating the movable flange 9 is carried out by allowing the positioning groove 23 provided at the movable flange 9 to be in correspondence with the positioning groove 22 provided at the wrist base 8. Correspondence between these both positioning grooves is carried out by inserting a positioning piece 24, e.g., key, etc. so as to bridge over the both positioning grooves. Further, determination of reference position with respect to the second arm 4 of the wrist base 8, i.e., determination of reference position of the axis for carrying out flexing (bending) operation of the wrist portion 7 is carried out by allowing the positioning groove 14 provided at the wrist base 8 to be in correspondence with the positioning groove 13 provided at the second arm 4. Correspondence between these both positioning grooves 13, 14 is carried out by inserting a positioning piece 25, e.g., key, etc. so as to bridge over the both positioning grooves 13, 14. After the determination of reference position with respect to the second arm 4 of the wrist base 8 is completed, determinations of reference positions with respect to the fixed base 1 of the first arm 3 and the second arm 4, i.e., determinations of reference positions of respective axes for driving the both arms 3, 4 are carried out. The determinations of reference positions of the first arm 3 and the second arm 4 with respect to the fixed base 1 are carried out by allowing reference planes 10, 11, 12 in the X, Y, Z directions of the wrist base 8 to be respectively tightly in contact with the reference planes 18, 19, 20 in the X, Y, Z directions of the positioning jig. Since it is unnecessary to allow the front end portion of the wrist portion 7 to be in contact with the positioning jig 15, there is no necessity of detaching the tool 21 from the wrist portion 7 in the work for determining reference position of the robot. FIG. 3 is an enlarged side view of the front end portion of the positioning jig 15, i.e., the positioning portion 17 which shows the second embodiment. In the second embodiment, the positioning jig 15 is adapted so that the body portion 16 and the positioning portion 17 are constituted with separate members, and the positioning portion 17 is caused to undergo pressing and fixing onto the body portion 16 by an elastic body 26 such as coil spring, etc., whereby even in the case where the wrist portion 7 or the wrist base 8 collides with the positioning portion 17 by erroneous operation of the robot, impact can be absorbed. In this case, at both surfaces opposite to each other of the body portion 16 and the positioning portion 17, recessed portions 27 and 28 are respectively formed at two corresponding positions or more, and a ball 29 is inserted into these recessed portions 27, 28. Accordingly, even if the wrist base 8 collides with the positioning portion 17 of the positioning jig 15 so that position of the positioning portion 17 is shifted, when the wrist portion 7 is away from the positioning jig 15, it becomes possible to ensure precise reference position for a second time. Moreover, even in the case where position of the positioning portion 17 is greatly shifted, the recessed portions 27, 28 of the positioning portion 17 are returned to the position of the ball 29 to allow the ball 29 to fall within the recessed portion 27, thereby making it possible to easily return the positioning portion 17 to the reference position. In FIG. 3, reference numeral 30 denotes a bolt screwed into the body portion 16. While there is disclosed in the above-described embodiments the case where this invention is applied to the six-axis revolute joint type robot, this invention can be applied to robots of arbitrary number of axes type without being limited to the six-axis revolute joint type robot. It is to be noted that while the reference position determination method using the positioning groove and the positioning piece is used for determination of reference position of the wrist portion with respect to the second arm, such reference position determination method may be also used for determination of reference positions of the first and second arms with respect to the fixed base. Industrial Applicability This invention can be utilized, when applied to the industrial robot, in the field for providing a reference position determination method for an industrial robot which permits determination of reference position while attaching the tool at the wrist front end portion.

Claims: A reference position determination method for an industrial robot comprising a fixed base (1), a first arm (3) rotatably attached to the fixed base (1), a second arm (4) rotatably attached to the front end portion of the first arm (3), and a wrist portion (7) provided with a wrist base (8) and a movable flange (9), which is attached to the front end portion of the second arm (4), characterized by determining the reference position of the movable flange (9) with respect to the wrist base (8) by locking the movable flange (9) and the wrist base (8) with positioning means provided on said wrist base (8) and flange (9), determining the reference position of the wrist base (8) with respect to the second arm (4) by locking the wrist base (8) and the second arm (4) with positioning means provided on said wrist base (8) and the second arm (4), and determining the reference positions of the first (3) and second arm (4) with respect to the fixed base (1) by allowing reference planes (10, 11, 12) of the wrist portion (7) to be in contact with reference planes (18, 19, 20) of a positioning jig (15). A reference position determination method for an industrial robot as set forth in claim 1, characterized in that positioning grooves (22, 23) caused to be in correspondence with each other when the movable flange (9) is located at reference position with respect to the wrist base (8) are respectively formed at the wrist base (8) and the movable flange (9) of the wrist portion (7), positioning grooves (13, 14) caused to be in correspondence with each other when the wrist base (8) is located at reference position with respect to the second arm (4) are respectively formed at the second arm (4) and the wrist base (8), reference planes (10, 11, 12) in X, Y and Z directions are formed on the surfaces in the X, Y and Z directions of the wrist base (8), a positioning jig (15) is attached to the fixed base (1) to form reference planes (18, 19, 20) in the X, Y and Z directions corresponding to the reference surfaces (10, 11, 12) in the X, Y and Z directions of the wrist base (8) on the surfaces in X, Y and Z directions of the positioning jig (15), positions of the respective positioning grooves (22, 23) of the wrist base (8) and the movable flange (9) are caused to be in correspondence with each other to carry out positioning of the movable flange (9) with respect to the wrist base (8), and that the reference planes (10, 11, 12) in the X, Y and Z directions of the wrist base (8) are caused to be respectively tightly in contact with the reference planes (18, 19, 20) in the X, Y and Z directions of the positioning jig (15) to carry out determinations of reference positions of the first arm (3) and the second arm (4) with respect to the fixed base (1). A reference position determination method as set forth in claim 1 or 2, characterized in that the positioning jig (15) is constituted with a dig body (16) and a positioning piece (17), and the positioning piece (17) is caused to undergo pressing or fixing onto the dig body (16) by an elastic body (26) to absorb impact when the wrist base (8) collides with the positioning piece (17).

Inventors: NAKAKO TORU, TSUKUDA KOUJI, NAKAKO, TORU, TSUKUDA, KOUJI, NAKAKO, Toru, c/o K.K. Yaskawa Denki, TSUKUDA, Kouji, c/o K.K. Yaskawa Denki
Applicants: YASKAWA DENKI SEISAKUSHO KK, KABUSHIKI KAISHA YASKAWA DENKI
Application year: 1995
Main classification: B25J9
IPC codes: B25J19, B25J9