The estimation of dynamic parameters in mechanical systems constitutes an issue of crucial importance both for inverse dynamics based control strategies and dynamic simulation applications where high accuracy is required. The identification procedures can be classified in two main groups: indirect and direct procedures. The first ones act sequentially in several steps in each of them parameters of different nature (basically friction and inertial parameters) are identified by means of specifically designed experiments, while the direct procedures allow the identification of all parameters defining de dynamic model in a single stage. In this paper, the implementation and comparison of an indirect and a direct identification procedures on an industrial robot provided with an open control architecture is addressed.
Purpose -The purpose of this paper is to present the development and validation of a methodology which allows modeling and solving the inverse and direct dynamic problem in real time in robot manipulators. Design/methodology/approach -The robot dynamic equation is based on the Gibbs-Appell equation of motion, yielding a well-structured set of equations that can be computed in real time. This paper deals with the implementation and calculation of the inverse and direct dynamic problem in robots, with an application to the real-time control of a PUMA 560 industrial robot provided with an open control architecture based on an industrial personal computer. Findings -The experimental results show the validity of the dynamic model and that the proposed resolution method for the dynamic problem in real time is suitable for control purposes.Research limitations/implications -The accuracy of the applied friction model determines the accuracy of the identified overall model and consequently of the control. This is especially obvious in the case of the PUMA 560 robot, in which the presence of friction is remarkable in some of their joints. Hence, future work should focus on identifying a more precise friction model. The robot model could also be extended by incorporating rotor dynamics and could be applied for different robot configurations as parallel robots. Originality/value -Gibbs-Appell equations are used in order to develop the robotic manipulator dynamic model, instead of more usual dynamics formulations, due to several advantages that these exhibit. The obtained non-physical identified parameters are adapted in order to enable their use in a control algorithm.
This work deals with the real-time robot control implementation. In this paper, an algorithm for solving Inverse Dynamic Problem based on the Gibbs-Appell equations is proposed and verified. It is developed using mainly vectorial variables, and the equations are expressed in a recursive form, it has a computational complexity of O(n). This algorithm will be compared with one based on Newton-Euler equations of motion, formulated in a similar way, and using mainly vectors in
their recursive formulation. This algorithm was implemented in an industrial PUMA robot. For the robot control a new and open architecture based on PC had been implemented. The architecture used has two main advantages. First it provides a total open control architecture, and second it is not expensive. Because the controller is based on PC, any control technique can be programmed and implemented, and in this way the PUMA can work on high level tasks, such as automatic trajectory generation, task planning, control by artificial vision, etc.
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