A parallel robot with three translational degrees of freedom for machining operations
This paper proposes a new machine tool structure design for machining based on a Delta Robot architecture as object of study, known as Tsai's Manipulator, patented by Tsai in 1997. The new architecture employs only rotary joints instead of spherical ones as it is usual for Delta Robots. The rotary joints allow its mount under pretension to eliminate clearances or backlash, avoiding the use of expensive spherical joints. All the other mechanical parts are standard components, which makes the solution attractive in terms of cost. A simplified inverse kinematic solution over the one proposed by Tsai is presented, based on a practical approach. The simplified solution reduces the number of steps to solve the inverse kinematics without any loss of performance. In addition, a solution to deal with the coupled axis without parasitic motion is presented. To increase the accuracy and the stiffness of the robot, a special attention was given to the rotary joints using preload rotational ball bearing joints. The structure parts were manufactured mostly by laser cutting with almost no complementary machining processes. In order to evaluate the proposed solutions, a prototype was built and a dedicated control software was developed for this particular robot. Workpieces were milled with the robot to demonstrate its capability and the advantages regarding the proposed machine architecture.
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