Robot control apparatus, and method and program for obtaining angle of joint of robot

A method of obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, wherein, in the 6-axis vertical articulated robot, the sixth axis of a sixth joint and a fifth axis of a fifth joint perpendicularly intersect each other, the fifth axis and a fourth axis of a fourth joint perpendicularly intersect each other, the fourth axis and a third axis of a third joint perpendicularly intersect each other, and there is a predetermined amount of offset between the sixth axis and the fourth axis, the method comprising:

• sequentially determining a point of interest;
• which is a point on a circumference of a circle having the predetermined amount of offset as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis, and the fifth axis and the plane which is orthogonal to the sixth axis;
• calculating a second intersection point which is an intersection point of the fourth axis and the third axis when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis;
• calculating an inner product value of a first vector directed from the second intersection point to the point of interest and a second vector directed from the point of interest to the first intersection point;
• and
• estimating that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis;
• wherein the sequentially determining the point of interest, the calculating the second intersection point, the calculating the inner product value of the first vector, and the estimating that the point of interest is the intersection point of the fifth axis and the fourth axis are all performed in real-time.

A non-transitory computer-readable medium containing a computer program that causes a computer to perform a method of obtaining an angle of each joint of a 6-axis vertical articulated robot when a position and a posture of an end effector attached on a sixth axis are given, wherein, in the 6-axis vertical articulated robot, the sixth axis of a sixth joint and a fifth axis of a fifth joint perpendicularly intersect each other, the fifth axis and a fourth axis of a fourth joint perpendicularly intersect each other, the fourth axis and a third axis of a third joint perpendicularly intersect each other, and there is a predetermined amount of offset between the sixth axis and the fourth axis, the method comprising:

• sequentially determining a point of interest, which is a point on a circumference of a circle having the predetermined amount of offset as a radius, around a first intersection point, on a plane which includes the first intersection point which is an intersection point of the sixth axis and the fifth axis and the plane which is orthogonal to the sixth axis;
• calculating a second intersection point which is an intersection point of the fourth axis and the third axis when it is assumed that the point of interest is an intersection point of the fifth axis and the fourth axis;
• calculating an inner product value of a first vector directed from the second intersection point to the point of interest and a second vector directed from the point of interest to the first intersection point;
• and
• estimating that the point of interest, when an absolute value of the inner product value is less than or equal to a predetermined threshold, is an intersection point of the fifth axis and the fourth axis;
• wherein the sequentially determining the point of interest, the calculating the second intersection point, the calculating the inner product value of the first vector, and the estimating that the point of interest is the intersection point of the fifth axis and the fourth axis are all performed in real-time.