Calibration method of robot base frame by quaternion form

The accuracy pose of robot base frame with respect to the world frame needs to be calibrated under the task of multi-arm cooperation, identification of kinematics parameter and off-line program of robot. An accurately calibration method of robot base frame using quaternion form was proposed and applied. The kinematic model of robot was established by the product-of-exponential formula. 5 tool center points (TCPs), which were not coplanar, were measured with the external measuring device, and the corresponding robot joint configurations were also recorded. By considering the elements of rotational matrix corresponding to the base frame pose as the variables, a group of incompatible equations was set up, and the initial homogeneous matrix of the base frame pose was also obtained. However, due to the errors of measuring and truncation, the rotational matrix part of initial homogeneous matrix cannot satisfy the regulation of unit orthogonal matrix. Using the geometrical constraints of a quaternion, an objective equation by the form of penalty function was established, and the initial homogeneous matrix was orthogonalized. By a set of practical calibration experiments of robot, the validity of calibration method was verified, which improved the accuracy of the location of robot end.