Image feature command generation of contour following tasks for SCARA robots employing Image-Based Visual Servoing—A PH-spline approach

Recently, visual servoing has been widely employed in industrial robots and has become an invaluable asset to enhance the functionality of the robot. However, the issue of image feature command generation in a visual servoing task receives little attention. In a contour following task that adopts Image-Based Visual Servoing (IBVS), it is crucial to perform motion planning on the desired image trajectory. Without proper motion planning, not only may the discrepancy between the target position and the current position on the image plane not converge, but also the flexibility of exploiting visual servoing for applications such as contour following will be limited. In order to cope with the aforementioned problem, this paper proposes a PH-spline based motion planning approach for systems that adopt IBVS. In particular, the exterior contour of an object is represented by a PH quantic spline. With proper acceleration/deceleration motion planning, a PH quantic spline interpolator is constructed to generate desired image feature commands so that IBVS can be applied to handle contour following problems of an object without a known geometric model. Furthermore, this paper also develops a depth estimation algorithm for the eye-to-hand camera structure, providing a convenient way to estimate the depth value that is essential in computing image Jacobian. Experimental results of several contour following tasks verify the effectiveness of the proposed approach.