METHOD OF CONTROLLING SEVEN-AXIS ARTICULATED ROBOT, CONTROL PROGRAM, AND ROBOT CONTROL DEVICE

• US 20130310973A1
• Filed: 12/21/2011
• Published: 11/21/2013
• Est. Priority Date: 12/28/2010
• Status: Active Grant

• Current Assignee: Kawasaki Jukogyo Kabushiki Kaisha
• Original Assignee: Kawasaki Jukogyo Kabushiki Kaisha
• Inventors: Kubota, Tetsuya, Tanaka, Hidenori, Ogata, Takamasa
• Granted Patent: US 9,120,223 B2
• Time in Patent Office: Days
• US Class Current: 700/245
• CPC Class Codes: B25J 9/046 Revolute coordinate type
• CPC Class Codes: B25J 9/06 characterised by multi-articulated arms
• CPC Class Codes: B25J 9/1607 Calculation of inertia, jacobian matrixes and inverses
• CPC Class Codes: B25J 9/1643 redundant control
• CPC Class Codes: G05B 2219/39018 Inverse calibration, find exact joint angles for given location in world space
• CPC Class Codes: G05B 2219/39414 7-DOF
• CPC Class Codes: G05B 2219/40344 Configuration index, control, limits of joint movement

Abstract

Provided is a method of controlling a seven-axis articulated robot including seven joints sequentially arranged from a proximal end of the robot to a distal end of the robot, the seven joints including rotational axes each causing a next joint to turn and rotational axes each causing a next joint to pivot, such that the rotational axes causing turning and the rotational axes causing pivoting are arranged alternately, the seven-axis articulated robot being configured such that rotational axes of three proximal end side joints of the robot do not intersect with each other at one point. The method includes performing inverse transformation using, as a constraint condition, such a joint angle of a middle joint among the three joints as to cause an assumed elbow angle to be constant in a case where a rotational axis of the middle joint is assumed as a shoulder.

Claims

1. A method of controlling a seven-axis articulated robot including seven joints sequentially arranged from a proximal end of the robot to a distal end of the robot, the seven joints including rotational axes each causing a next joint to turn and rotational axes each causing a next joint to pivot, such that the rotational axes causing turning and the rotational axes causing pivoting are arranged alternately, the seven-axis articulated robot being configured such that at least one of rotational axes of three proximal end side joints of the robot does not intersect with other rotational axes of the three proximal end side joints at one point,

the method comprising performing inverse transformation using, as a constraint condition, such a joint angle of a middle joint among the three joints as to cause an assumed elbow angle to be constant in a case where a rotational axis of the middle joint is assumed as a shoulder.

2. The method of controlling a seven-axis articulated robot according to claim 1, the method comprising:

calculating a first maximum value and a first minimum value, which are possible values of the joint angle of the middle joint and which are values to be taken from an initial state at a start of operation of the robot, by performing inverse transformation while setting a joint angle of a distal end side joint among the three joints to 0°

(a reference position) or 180°

(a maximum displacement position from the reference position); and

calculating, as an index indicating the assumed elbow angle, a ratio of the joint angle of the middle joint in the initial state within a range from the first maximum value to the first minimum value, wherein

such a joint angle of the middle joint as to cause the calculated ratio to be constant is used as the constraint condition.

3. The method of controlling a seven-axis articulated robot according to claim 2, wherein

a step of the constraint condition includes:

calculating a second maximum value and a second minimum value which are possible values of a current joint angle of the middle joint when the robot is in operation, by performing inverse transformation while setting the joint angle of the distal end side joint to 0°

(the reference position) or 180°

(the maximum displacement position from the reference position);

calculating a target value of the current joint angle of the middle joint when the robot is in operation, based on the calculated second maximum value, the calculated second minimum value, and the calculated ratio; and

applying the calculated target value to the joint angle of the middle joint, the joint angle being used as the constraint condition when performing the inverse transformation.

4. A control program of controlling a seven-axis articulated robot including seven joints sequentially arranged from a proximal end of the robot to a distal end of the robot, the seven joints including rotational axes each causing a next joint to turn and rotational axes each causing a next joint to pivot, such that the rotational axes causing turning and the rotational axes causing pivoting are arranged alternately, the seven-axis articulated robot being configured such that at least one of rotational axes of three proximal end side joints of the robot does not intersect with other rotational axes of the three proximal end side joints at one point,

the control program causing a computer to perform:

calculating a maximum value and a minimum value, which are possible values of a joint angle of the middle joint and which are values to be taken from an initial state at a start of operation of the robot, by performing inverse transformation while setting a joint angle of a distal end side joint among the three joints to 0°

(a reference position) or 180°

(a maximum displacement position from the reference position);

calculating, as an index indicating an assumed elbow angle in a case where a rotational axis of the middle joint is assumed as a shoulder, a ratio of the joint angle of the middle joint in the initial state within a range from the maximum value to the minimum value; and

performing inverse transformation using, as a constraint condition, such a joint angle of the middle joint as to cause the calculated ratio to be constant.

5. A robot control device configured to control a seven-axis articulated robot including seven joints sequentially arranged from a proximal end of the robot to a distal end of the robot, the seven joints including rotational axes each causing a next joint to turn and rotational axes each causing a next joint to pivot, such that the rotational axes causing turning and the rotational axes causing pivoting are arranged alternately, the seven-axis articulated robot being configured such that at least one of rotational axes of three proximal end side joints of the robot does not intersect with other rotational axes of the three proximal end side joints at one point,

the robot control device comprising:

a maximum and minimum value calculator configured to calculate a maximum value and a minimum value, which are possible values of a joint angle of the middle joint and which are values to be taken from an initial state at a start of operation of the robot, by performing inverse transformation while setting a joint angle of a distal end side joint among the three joints to 0°

(a reference position) or 180°

(a maximum displacement position from the reference position);

a ratio calculator configured to calculate, as an index indicating an assumed elbow angle in a case where a rotational axis of the middle joint is assumed as a shoulder, a ratio of the joint angle of the middle joint in the initial state within a range from the maximum value to the minimum value; and

an inverse transformation unit configured to perform inverse transformation using, as a constraint condition, such a joint angle of the middle joint as to cause the calculated ratio to be constant.