Tetsuro Shibukawa

Design and control of a novel 4-DOFs parallel robot H4

This paper deals with the design and dynamic control simulation of a new type and dynamic control simulation of a new type of 4-DOFs parallel mechanism providing 3 translations and 1 rotation for high-speed handling and machining. This parallel mechanism is named as H4. A model-based dynamic control scheme is developed to improve the accuracy of the trajectory tracking. A simplified dynamic model is used for the H4 robot to decrease the cost of computation. A dynamic simulation is performed using ADAMS/sup TM/. In addition, the adept motion is used as a benchmark test to evaluate the effect of the dynamic control. The simulation results show that the dynamic control dramatically improves the trajectory tracking accuracy.

Study of Kinematic Calibration Method for Parallel Mechanism (3rd Report). Gravity Compensation and Kinematic Calibration Considering Gravity.

This paper presents the gravity compensation and kinematic calibration considering gravity for parallel mecha-nisms, which reduce position errors caused by elastic deformations of machine parts due to gravity. The influence on the elastic deformations to the positioning accuracy is analyzed using the model of force balance between gravity and the motor power. Then the inverse kinematics solution with gravity compensation is proposed, in which the kinematic parameters are updated gradually according to the traveling plate pose. This provides us a real time motion control with compensation not requiring extra compensation values. The kinematic calibration considering gravity is also proposed to identify kinamatic parameters with no load. In order to improve the positioning accuracy, the identified parameters are used with gravity compensation. These methods are applied on the parallel mechanism based milling machine, named HexaM, and the validity is verified by simulations and experiments.

Expanding the possibilities of position error compensation in CAM for PKM milling machines

PKM milling machines have promising advantages compared to SKM milling machines, such as a higher stiffness-to-mass ratio, enabling a better dynamic behaviour. Errors in the PKM driving chains cause position errors of the end effecter. Its parallel construction and non-uniform position error patterns make finding the error sources a challenging task. This paper presents the application and expansion of a position error reduction method. Measured and predicted error patterns, the latter generated by a kinematic model, are compared and the most likely error source is found. With this information, the NC code is systematically modified and the PKM machine can be adjusted.