Xianglong Wan

Experimental study on efficient use of singular configuration in pulling heavy objects with two-link robot arm.

This paper demonstrates that singular configuration of a two-link robot arm is advantageous in doing the task of pulling or lifting up a heavy object with small joint torques. As a result of numerical optimization, the initial configuration that minimizes the joint torques necessary for the task is close to the singular configuration where the arm is stretched out. The singular configuration has the dynamic feature that the joint angle vector can be accelerated in a certain direction almost independently of the mass of the object. Then, the joint torques can generate large kinetic energy efficiently at the singular configuration, and the energy can be utilized to pull or lift up the object. The experimental results show that the dynamic feature is practically useful, even when a feedback control is applied in order to make the object follow a planned trajectory.

Generation of large pulling force by a mobile manipulator through singular configuration

This paper deals with the optimal motion of a mobile manipulator for dragging a heavy object with the end effector. When the object is moved a certain distance, the torques that are consumed in the mobile manipulator during the motion are minimized by numerical optimization. In the optimized motion, the arm mounted on the mobile base passes through its singular configuration, and a large force to pull the object is generated simultaneously. A theoretical analysis is performed to explain the numerical results by using a simplified model of the mobile manipulator.

Advantage of singular configuration in pulling heavy object with a two-link mobile manipulator

In this paper, we reveal the advantage of singular configuration in pulling heavy objects with a two-link mobile manipulator. Unlike humans, the mobile manipulator can pull or drag the objects passing through its singular configuration where the manipulator is stretched out. The motion through singular configuration can generate, from the same amount of joint torques, much larger pulling force than the motion that avoids the configuration. Although the large force occurs only for a short period near the singular configuration, it can maximize the distance that the object is moved by the mobile manipulator under the condition that the consumption of joint torques is restricted. This advantage of singular configuration is verified by numerical simulations and theoretical analysis.

Landing Motion of a Legged Robot with Impact Force Reduction and Joint Torque Minimization

This paper deals with an optimal landing motion of a 4-link legged robot that minimizes the impact force at the contact point and the joint torques necessary during the motion. The cost function for optimization is given as the weighted sum of the one for impact force and the one for joint torques. While the configuration where the leg is bent is advantageous in reducing the impact force, the configuration that is close to a singular configuration is advantageous in minimizing the joint torques. It is shown by numerical optimization results with different weights for the cost function.

Dragging motion of a two-link mobile manipulator with large pull force through singular configuration: theoretical analysis and experimental verification

ABSTRACT This paper reveals the advantageous feature of singular configuration for a two-link mobile manipulator by theoretical analysis, numerical simulations and experiments. When a mobile manipulator drags a heavy object on a flat floor, a large pull force is required to overcome the friction force between the object and the floor. In the motion obtained by numerical optimization, unlike humans, a two-link mobile manipulator pulls the object with a large force by passing through singular configuration. We analyze theoretically the force applied to the object by the manipulator under several assumptions, and show that a large pull force can be generated near singular configuration from the energy stored in the manipulator. The feasibility of the motion obtained by numerical optimization is also shown by experimental results. GRAPHICAL ABSTRACT