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# Rotary Calibration Method for Manipulator

IP.com Disclosure Number: IPCOM000053154D
Original Publication Date: 1981-Sep-01
Included in the Prior Art Database: 2005-Feb-12
Document File: 3 page(s) / 45K

IBM

## Related People

Szarek, JJ: AUTHOR

## Abstract

This article discusses a method of calibrating the rotary axis (yaw and roll) of a robotic manipulator. Two specific methods are described. The first uses a pair of spaced circular posts. The second uses a single square post.

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Rotary Calibration Method for Manipulator

This article discusses a method of calibrating the rotary axis (yaw and roll) of a robotic manipulator. Two specific methods are described. The first uses a pair of spaced circular posts. The second uses a single square post.

Referring to Fig. 1, the manipulator includes a gripper mechanism 10 which can be pivoted about a point 12. The gripper mechanism 10 includes parallel fingers 14 and 16. Finger 14 may have a light source 18, while finger 16 may have a photodetector 20. The source and detector are used to sense the presence of objects within the gripping range of the manipulator. The gripper 10 is secured to an arm 22 which initially will be assumed to be movable in the direction indicated by the double headed arrows; i.e., at right angles to the bisector of two circular posts 24 and 26 of known diameter d and known center- to-center spacing X.

The objective of the calibration process is to determine the value of the angle B between the post bisector and the gripper 10. The angle B is derived by measuring the total distance D over which the light beam path is blocked as the gripper moves across the posts and by using the known dimensions of the posts and the k own spacing between the posts. The distance D can be expressed as D = y + 2a (1) where y and a are defined in Fig. 1. Consideration of the geometry will show that y = x tan Theta = x (sin Theta over cos Theta) (2) a = d over 2 cos Theta (3) Substituting Equations (2) and (3) into Equation (1) will show that D = x sin Theta + d over cos Theta Since D, x and d are known quantities, the value of Theta can be calculated.

Equation (4) assumes that the manipulator arm 22 moves along a path perpendicular to the bisector of the posts 24 and 26. A more general case is illustrated in Fig. 2, where the arm 22 moves along a path a...