Yechao Liu

DSP/FPGA-based Controller Architecture for Flexible Joint Robot with Enhanced Impedance Performance

Some practical issues associated with enhancing the Cartesian impedance performance of flexible joint manipulator are investigated. A digital signal processing/field programmable gate array (DSP/FPGA) structure is proposed to realize the singular perturbation based impedance controller. To increase the bandwidth of torque control and minimize the joint torque ripple, boundary layer system and field-oriented control (FOC) are fully implemented in a FPGA of each joint. The kernel of the hardware system is a peripheral component interface (PCI)-based high speed floating-point DSP for the Cartesian level control, and FPGA for high speed (200 us cycle time) multipoint low-voltage differential signaling (M-LVDS) serial data bus communication between robot Cartesian level and joint level. Experimental results with a four-degree-of-freedom flexible-joint manipulator under constrained-motion task, demonstrate that the controller architecture can enhance the robot impedance performance effectively.

Biomimetic object impedance control for dual-arm cooperative 7-DOF manipulators

To mimic human behavior is an increasing trend for advanced robot control. In this paper, a novel biomimetic object impedance control strategy (BOI) is presented for dual-arm cooperative 7-DOF humanoid manipulators. A general impedance architecture comprising internal impedance control and object impedance control is adopted, which aims at conferring impedance behavior both in end-effector level and object level. Asymptotic stability and convergence of this controller are strictly derived from Lyapunov stability theory. Compared with conventional object impedance, the proposed controller can show different object impedance characteristics according to the external force applied on the object. It also can simultaneously minimize the energy cost of the adaptation process. Simulation and experimental results indicate that this controller exhibits explicit compliance behavior when the interaction with environment is weak and presents accumulation property of the stiffness and damping accordingly when the interaction is strong. This human-like characteristic enables the object/dual-arm system to deal with complex and unknown environmental disturbances. A novel biomimetic object impedance controller is proposed.Object/internal impedance are simultaneously achieved in a unified architecture.Stiffness and damping of the object impedance can be adapted accordingly.Agilely dealing with unknown interactions for object/dual-arm system is enabled.Strict stability analysis with simulation and experiments are given.

Cartesian path planning for base attitude adjustment of space robot

This paper presents a novel Cartesian path planning for space manipulator to achieve base (satellite) attitude adjustment and Cartesian task. The base attitude adjustment by the way of the movement of manipulator will save propellant compared with conventional attitude control system. A task-priority Reaction Null-space control method is applied to achieve the primary task to adjust attitude and secondary task to accomplish Cartesian task. Furthermore, The algorithm singularity is eliminated in the proposed algorithm compared with conventional Reaction Null-space algorithm and extended Jacobian algorithm. And the varied damping factors are introduced to avoid dynamics singularity. The simulation platform of the space robot control system based on Matlab/Simulink is built. The simulation results demonstrate the validity and feasibility of the proposed Cartesian path planning algorithm.

Adaptive hybrid position force control of dual-arm cooperative manipulators with uncertain dynamics and closed-chain kinematics

Abstract In this paper, a novel adaptive control for dual-arm cooperative manipulators is proposed to accomplish the hybrid position/force tracking in the presence of dynamic and closed-chain kinematic uncertainties. Self-convergent parameter estimation of the grasped objects centre of mass and contact force estimation are incorporated into this systematic scheme. Moreover, internal force and contact force tracking objectives are achieved simultaneously by incorporating into the position tracking formula with proper null-space projection and rotation transformation. Noisy force derivative signals are not required. This adaptive controller is mathematically derived based on Lyapunov stability analysis. Three sets of simulations corresponding to three different situations are presented to verify the effectiveness and superiority of the proposed controller.

Robust adaptive multi-task tracking control of redundant manipulators with dynamic and kinematic uncertainties and unknown disturbances

Abstract In this paper, a novel adaptive multi-priority controller for redundant manipulators is proposed to accomplish the multi-task tracking when kinematic/dynamic uncertainties and unknown disturbances exist. Prioritized redundancy resolution in kinematic level is incorporated into this passivity-based control framework. The kinematic and dynamic parameter adaptations are driven by both tracking error and prediction error. Moreover, the tracking information from both primary and subtasks are all utilized to accelerate the parameter estimation when the tasks are independent, whereas the inevitable tracking error of the subtasks due to algorithmic singularities is properly eliminated in the adaptation laws when the tasks are dependent. Potential ill-conditioned solution of the pseudoinverse is avoided using an improved singularity-robust inverse of the projected Jacobian. Along with the improvement of the multi-task tracking performance, smoothness of the commanded torques is still guaranteed for easy application. Measurements of the noisy joint acceleration and task velocity are avoided. The controller is mathematically derived based on Lyapunov stability analysis. Simulation results of the two cases are presented to verify the effectiveness and superiority of the proposed controller.

Hybrid impedance control of 7-DOF redundant manipulator with dual compliant surface

A control strategy based on the hybrid impedance control of 7-DOF manipulator is investigated to achieve force control and obstacle avoidance. And the redundancy resolution method is improved, the kinematic related function (arm angle) of manipulator is considered as the additional user-specified task, and a damping coefficients matrix is introduced, hence a singularity-robust inverse kinematics at acceleration level is proposed. The obstacle avoidance control of redundant manipulator is implemented in obstacle avoidance compliant surface. Furthermore, a virtual torque reacted on the additional compliant surface is introduced by artificial potential functions of obstacle, The control strategy based on the non-contact impedance control is adopted to deal with virtual contact. And a numerical simulation system based on Matlab/Simulink is built to verify the control strategy, the simulation results demonstrate the validity and feasibility of the proposed control strategy.

Adaptive object impedance control of dual-arm cooperative humanoid manipulators

A novel adaptive object impedance control strategy is presented for dual-arm cooperative humanoid manipulators. A general impedance scheme comprising internal impedance control and object impedance control is adopted, which aims at conferring a compliant behavior both in end-effector level and object lever. The adaptation law for the stiffness and damping of object impedance is derived from Lyapunov stability theory. In contrast with general object impedance, the proposed controller can exhibit different impedance characteristics according to the force exerted by environment on the object and can achieve minimizing the metabolic cost of the adaptation process. Simulation results show the object impedance controller exhibits explicit compliance behavior when the interaction with environment is weak and presents accumulation property of the stiffness and damping when the interaction is strong.

The electrical simulator for the space station manipulator under Linux/RTAI

This paper presents the development of the electrical simulator for the space station manipulator to support the design of the space manipulators controller and the data communication verification between the space station and the manipulator. The assembly of the space manipulator model consists of the joint controller model, the joint dynamics model and the serial manipulator model. Besides, the whole manipulator model and the other external devices related program are running under the real-time operating systems Linux/RTAI. The electrical simulator integrates telemetry interface, telecontrol interface and camera interface to response related command and exchange data with the space station. The performance testing of the simulator demonstrates that the latest developed electrical simulator meets practical application requirements.

Motion planning for redundant free-floating space robot with local optimization of reaction torque and joint torque simultaneously

This paper presents a novel way to derive the analytical expression of the reaction torque acted on the satellite bases centroid firstly. The reaction torque is acted as the optimization index to achieve the satellite base disturbance minimization in this paper. The null-space based solution and Lagrange multipliers based solution are utilized to solve the reaction torque plus joint torque minimization of redundant free-floating space robot. Besides, a special discretization strategy is utilized to obtain a low-level servo loops control laws which can also achieve reaction torque plus joint torque minimization. Thus this strategy can transform the acceleration level control scheme for multi-dynamics task optimization into the velocity level control scheme. A set of numerical experiments of a 7 DOF redundant free-floating space robot based on a simulation system under Matlab/Simulink verify the validity and feasibility of the proposed algorithm.

Robust adaptation based backlash and friction compensation for 3-DOF robotic head with dynamic uncertainties

In this paper, a novel robust adaptive controller is proposed to simultaneously cope with the unknown nonlinear backlash, friction and dynamic uncertainties in the 3-DOF robotic head system. Inverse backlash compensation with on-line backlash parameter estimation and model-based friction compensation with off-line Stribeck friction identification are incorporated into this robust adaptive scheme. By parametrically linearizing the system dynamic equation, dynamic uncertainties are estimated. This controller is mathematically derived by using Lyapunov stability analysis. Simulation results are presented to show the high tracking performance of the controller.