Gravity compensation for a bipedal humanoid robot

Abstract

Many research is nowadays done on humanoid robots. They can be very helpful in the future, for example in nursery homes to assist the nurses. The big advantages of humanoid robots is that they can operate in the human environment. At the Eindhoven University of Technology the robot TUlip is used as an experimental platform. TUlip is a bipedal humanoid robot with six actuators in each leg. When the robot is in double support phase the robot loses some degrees of freedom and becomes over actuated. The goal of this project is to design a feedforward gravity compensation algorithm which facilitates the feedback controllers of the robot joints and deals with the problem of over actuation. To obtain a feedforward algorithm which facilitates the feedback controllers of TUlip, calculations with the manipulator Jacobian are taken as a basis in designing the algorithm. When a certain force is desired on the tip of a robot manipulator the manipulator Jacobian can be used to calculate the required joint torques. In the case of the robot the torso is taken as a static basis with two robot manipulators as its legs. When a foot is in the support phase there are ground contact forces acting on this foot (the tip of the robot manipulator). These ground contact forces are estimated to determine the forces at the feet of the robot and these estimations are than used to calculate the required gravity compensation torques. The obtained algorithm is implemented in a Matlab, SimMechanics simulation model and simulations are performed with the robot in different static positions to verify if the obtained gravity compensation algorithm is helping the robot. From the simulation results it can be concluded that the obtained gravity compensation algorithm does not calculate satisfactory values. The reason for this is probably that the torso of the robot can not be taken as a static basis. Namely it is assumed that the forces guided through the torso from one leg to the other can be neglected. The forces guided through the torso are probably of significant matter that they can not be neglected. For the future it is recommended to investigate if it is possible to include the forces guided through the torso from one leg to the other. Another approach could be to leave some of the joints unactuated so that the robot is no longer over actuated