Chunquan Xu

Intelligent compliant force/motion control of nonholonomic mobile manipulator working on the nonrigid surface

The task under consideration is to control a mobile manipulator for the class of nonrigid constrained motion. The working surface is deformable. The geometric and physical model of the surface is unknown and all contact force is nonlinear and difficult to model. To accomplish a task of this kind, we propose a force/motion fuzzy controller based on the philosophy of the parallel approach in two decoupled subspaces. In one subspace, we control the constant contact force normal to the surface and estimate the end-effector tool’s deformable depth of the surface; in the other, we keep the end-effector’s constant velocity parallel to the tangential plane of the surface and suppress the tangential force of the surface deformation. The nonholonomic mobile base is utilized to avoid the singularity. Stability is established and conditions for the control parameters are derived. Performance of the proposed controller is verified through computer simulations compared with the model-based control.

Motion Control of Golf Swing Robot Based on Target Dynamics

A new golf swing robot performing high-speed golf swings has been developed by the authors. This paper deals with the motion planning problem of the golf swing. A target dynamics based control scheme is proposed. This control scheme maps the robot to a harmonic oscillator (target dynamical system). Based on the target system, energy control is adopted to realize a specified hitting speed at a specified impact position in the swing. After the swing passed through the impact position, PD control and PD plus gravity, joint torque and coupling torque compensation control are adopted to smoothly slow down and stop the swing at a specified finish position. Simulation and experimental results show the effect of the proposed method

Motion Control of a Golf Swing Robot

In this paper we discuss our simulation and empirical study of a golf swing motion controller for a two-link golf swing robot. We distinguish two variants of the whole golf swing termed as hitting problem and stopping problem. For the hitting problem arising from backswing and downswing, we map the task into the output of a target dynamic system—a harmonic oscillator—under energy control. For the stopping problem that arises from follow-through, we propose a Proportional plus Gravity and Coupling Torque Compensation (PGCTC) feedback controller. Preliminary simulation study shows the proposed controllers solve the hitting problem and the stopping problem respectively. The controllers are implemented on a physical robot. Experimental results indicate the robot is able to perform desired golf swing-backswing, downswing, and follow-through. We also give a preliminary analysis on the proposed method to understand its merits and weaknesses.

Motion planning for a golf swing robot based on reverse time symmetry and PGCTC control

A new golf swing robot performing high-speed golf swings has been developed by the authors. This paper deals with the motion planning problem of the golf swing. At first, the reverse time symmetry and single pendulum inherences in manipulator dynamics are introduced. Then, by utilizing the first inherence, the Rest-to-Point motion planning problem for the backswing and downswing is transformed into a reverse time symmetric Point-to-Rest motion planning problem. Finally, based on the second inherence, a Proportional plus Gravity and Coupling Torque Compensation (PGCTC) control scheme is developed to solve both the reverse time symmetric Point-to-Rest motion planning problem for the backswing and downswing and the forward time Point-to-Rest problem for the follow-through. Simulation shows the effect of the proposed method.

Optimal Trajectory Generation for Manipulator with Strong Nonlinear Constraints and Multiple Boundary Conditions

Up to now, the research work about optimal trajectory generation mainly focuses on such motion planning with boundary conditions of specified initial and final configurations. Multiple boundary conditions are seldom taken into account. This paper explores the motion planning method for hyper dynamic manipulation with multiple boundary conditions of initial, final and middle configurations and strong nonlinear constraints derived from active torque limitation and joint stop, and B-spline based optimal torque trajectory generation method is proposed by authors. By transforming the torque limitation constraints into a series of linear limitations for the coefficients of B-spline, and by using SQP optimization algorithm, optimal solutions are obtained with high convergence. Numerical experiments show the proposed method has superior numerical stability and high optimization accuracy in dealing with the optimal motion planning problem with strong nonlinear constraints and multiple boundary conditions

Cooperative control of two mobile manipulators transporting objects on the slope

This paper reports our recent results on the motion control of cooperative transportation by two mobile manipulators following a reference trajectory on the slope. We propose a cooperative control algorithm which is divided into two steps. In the first step, the mobile manipulators regulate their postures to keep themselves away from falling using their redundant Degree-Of-Freedom. If the robots still cannot keep stable, then in the second step, both robots adjust their forces acting on the transported object to avoid falling. Simulation results are given to validate the proposed method.

Mechanism design and control of dynamically-coupled driving based manipulator

Usually the dynamic capability of conventional manipulators is limited by heavy structure. Different from those manipulators, human can do many hyper dynamic manipulations while in a smart structure by utilizing dynamically-coupled driving between body and arms. Aiming at improving the dynamic capability of a manipulator in a large extent, a basic concept and general method on the mechanism design and control of the manipulator is proposed, just to simulate the action of human utilizing the dynamically-coupled driving. Furthermore, using joint stop in a manipulator is enhancing the effect of dynamically-coupled driving. To show the feasibility of the proposal, a hyper dynamic manipulator has been fabricated and fundamental experiments have been carried out. Experimental results have shown the important role of the dynamically-coupled driving, to realize an efficient hyper dynamic manipulation while in a smart structure. This paper describes the developed prototype and experimental results.

SALSA-based motion optimization for robotic manipulators with strong nonlinear dynamic coupling

In this paper, the motion optimization for robotic manipulators is investigated by Support Area Level Set Algorithm (SALAS) through optimizing a high-dimensional nonlinear fitness function. The approach based on level set conception and the ability of Support Vector Machine(SVM) in distribution estimation integrates duel stages sampling strategies to avoid be converge in small search field too early and improve the rate of convergence to the potential solution. The simulations using two links robotic manipulators show satisfied results with SALSA.

Design for high dynamic performance robot based on dynamically coupled driving and joint stops

A new design approach is proposed for high dynamic performance robots, such as robots performing high-speed dynamic motions. This method is based on the utilization of dynamically coupled driving and joint stops. In the method, the dynamic performance index (DPI) formulated by the desired maximum motion specifications and the boundary conditions on initial/final configurations are combined to form a design index (DI) first. Then a dexterous mechanism consisting of very light actuators and links is initially designed under an assumption of utilizing dynamically coupled driving and joint stops. By increasing the load capabilities of the actuators step by step, an iterative process of searching for the solution of DI=0 with minimal torque needs is implemented to validate and improve the initial design. This process yields a robot that is lighter than conventional robots and capable of performing dynamic motions more efficiently by utilizing dynamically coupled driving and joint stops. Based on the method, a two-link golf swing robot performing high-speed swings is designed. Simulation results indicate the method can reduce the needs for the torque and power as compared with conventional design methods. The experiment clearly illustrates the merits of the method.

A new motion control method for golf swing robot hitting a ball

A new golf swing robot to simulate human motion has been developed. This paper deals with motion control of the robot for hitting a ball. For the case, it becomes important to control the motion of the robot after the impact, to avoid breaking a club. In this paper, a method for controlling the robot adaptable to various impact conditions is proposed. The motion state of the robot is estimated first by an extended Kalman filter, and a new reference trajectory is generated on-line according to the estimated state. The method has been implemented to the robot successfully