The paper deals with the shaking force balancing of the DELTA robot. The DELTA robot has been developed by Prof. Reymond Clavel  as a three-degree-of-freedom parallel robot, dedicated to high-speed applications of lightweight objects in the microengineering, electronic, food and pharmaceutical industries. By adding a supplementary independent rotation, it has been transformed to a robot for pick-and-place applications. The basic idea behind the Delta robot design is the use of parallelograms. A parallelogram allows an output link to remain at a fixed orientation with respect to an input link. The use of three such parallelograms restrains completely the orientation of the mobile platform, which remains only with three purely translational degrees of freedom.

The main benefit of Delta robots is that the heavy motors are fixed on the frame, allowing the moving parts of the robot to be very light. In the modern design of Delta robots, the motion is being translated down through carbon fiber arms, where there is far less mass being moved.

It should be noted that the shaking force and shaking moment balancing of parallel robots is a complicated problem because it can only be achieved either by an unavoidable increase of the total mass of moving links or by a considerably more complicated design of the initial parallel mechanism . In the previous research, it has been shown that fully shaking force balancing of the DELTA robot can be achieved by adding three counter-masses with two additional links and the complete shaking moment balancing can be achieved by active actuation of three additional rotating links. It should be noted that the shaking force and shaking moment balancing of parallel robots is a complicated problem because it can only be achieved either by an unavoidable increase of the total mass of moving links or by a considerably more complicated design of the initial parallel mechanism.

In this paper, the balancing of the shaking force of the DELTA robot is carried out through the center of mass acceleration minimization. The trajectories of the total mass center of moving links are defined as a straight line between the initial and final positions of the end-effector. Then, the motion between these positions is parameterized with “bang-bang” motion profile. Such a motion generation allows the reduction of the maximal value of the center of mass acceleration and, consequently, leads to the reduction in the shaking force. A main advantage of this method is its simplicity and versatility. It is carried out without any modification of mass redistribution of the initial robot structure, i.e. without adding counterweights. In the case of changing trajectory or payload, it is just necessary to provide the initial and final coordinates of the platform, calculate the input parameters according to the proposed method and implemented in the robot control system. The efficiency of the suggested approach is illustrated by numerical simulations.


Shaking Force Balancing of the Delta Robot

Division / Sponsors: 
Design Engineering Division and Computers & Information In Engineering Division


Paper Proceedings: https://asmedigitalcollection.asme.org/IDETC-CIE/IDETC-CIE2020/volume/83907

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