Jingfeng He

A Survey on Control of Parallel Manipulator

Based on extensive study on literatures of control of parallel manipulators and serial manipulators, control strategies such as computed torque control, PD+ control, PD with feedforward compensation, nonlinear adaptive control are classified into two categories: model-based control and performance-based control. Besides, as advanced control strategies, robust control and passivity-based control for the parallel manipulators are also introduced. Comparative study in view of computation burden and tracking performance are performed. It turned out that the physical structure properties of parallel manipulators’ dynamics are similar with that of serial ones, and this constitutes a common foundation for the two kinds of manipulators to develop together that control design of parallel manipulators can start with ever established control methods of serial manipulators.

Optimal design of a class of generalized symmetric gough-stewart parallel manipulators with dynamic isotropy and singularity-free workspace

In this paper, the definition of generalized symmetric Gough-Stewart parallel manipulators is presented. The concept of dynamic isotropy is proposed and the singular values of the bandwidth matrix are introduced to evaluate dynamic isotropy and solved analytically. Considering the payloads mass-geometry characteristics, the formulations for completely dynamic isotropy are derived in close form. It is proven that a generalized symmetric Gough-Stewart parallel manipulator is easer to achieve dynamic isotropy and applicable in engineering applications. An optimization procedure based on particle swarm optimization is proposed to obtain better dexterity and large singularity-free workspace, which guarantees the optimal solution and gives mechanically feasible realization.

Study on dynamic isotropy of a class of symmetric spatial parallel mechanisms with actuation redundancy

In this paper, we study dynamic isotropy using natural frequency analysis for a class of symmetric spatial parallel mechanisms (SSPMs) with 2p (p≥3) struts. This kind of dynamic isotropy has been defined as the square roots of the eigenvalues of the equivalent mass-spring systems formed via the interactions between rigid-body mechanical systems and their driving systems. Analytic expressions for these eigenvalues are then derived in the task space, which is linearly dependent on p. Furthermore, a general compliance center was found for all the SSPMs in which the parallel mechanisms are fully decoupled. Based on the dynamically decoupling, then, dynamic isotropy for the SSPM is discussed which shows that though taking the inertial parameters into consideration, the SSPM can not attain complete dynamic isotropy and the optimal dynamic isotropy index is the quartic root of two. At the end of the paper, to demonstrate these results, an example is given.

Model-based Control for 6-DOF Parallel Manipulator

A novel model-based controller for six-degree-of- freedom (DOF) parallel manipulator is proposed in this paper, in order to abatement the influence of platform load variety and compel the steady state errors converge to zero. In this paper, 6-DOF parallel manipulator is described as multi-rigid-body systems, the mathematical model of the 6-DOF parallel manipulator including dynamics based on Kane method and kinematics used closed-form solutions and Newton-Raphson method is built in generalized coordinate system. The model-based controller is presented with the feedback of cylinders positions of platform, desired trajectories and dynamics gravity as the input and the servovalve current as its output. The performance of the control scheme for 6-DOF parallel manipulator is analyzed. Simulation of the parallel manipulator with model-based controller is executed in MATLAB/Simulink, the simulation results indicate the model-based controller can reduce the influence of load variety of platform and eliminate steady state error of 6-DOF hydraulic driven parallel manipulator.

Modal control of a hydraulically driven redundant actuated fully parallel mechanism

In this paper, we consider the problem of modal-space control for the hydraulically driven fully parallel mechanism with actuation redundancy. Firstly, the mechanical-hydraulic interaction system is transformed into modal-space model. Then, independent modal decoupled systems for the redundant mechanism are obtained. According to the eigenvalue frequency characteristics, two types of modal systems – zero eigenvalue modal systems and nonzero ones – naturally result and these systems can be treated separately. For the nonzero eigenvalue modal systems, it is convenient to employ dynamic pressure feedback control to regulate damping. For the zero eigenvalue modal systems, we give a proof to show that they just lie in the null space of the Jacobian of the mechanism, then it is more appropriate to implement force control for this type of modal system. Some simulation results further explain the proposed modal-space control method.

Modeling and Key Technologies Study of Three-Stage Electro-Hydraulic Servo Valve

The modeling and study of three-stage electro-hydraulic servo valve are presented in this paper. According to its construction and principle, its model is built. The results of simulation and experimental test are consistent, which proves the validity of the model. Based on the study of the model, the performances of three-stage electro-hydraulic servo valve are mainly affected by pilot valve performance, spool and sleeve performance, position transducer performance and servo controller performance, which shows that there are four main key technologies. The study results have a guiding role for developing higher performance three-stage electro-hydraulic servo valve.

Optimal Design of an Orthogonal Generalized Parallel Manipulator Based on Swarm Particle Optimization Algorithm

Study of methods to design optimal Gough–Stewart parallel manipulator geometries meeting orthogonality is of high interest. The paper will design the Orthogonal Generalized Gough-Stewart Parallel Manipulator (OGGSPM) based on the composite hyperboloids. Moreover, Particle Swarm Optimization (PSO) algorithm is introduced to perform the structure optimization as the Jacobian matrix condition number is used as the evaluation index. As an example, two different optimization cases are presented.

Electro-hydraulic control system and frequency analysis for a hydraulically driven six-legged robot

This paper presents a methodical design of the electro-hydraulic control system for a large scale hydraulically driven six-legged robot, which can walk on rough terrain. Considering the widely varying load during the locomotion cycles, the electro-hydraulic control system should be capable of effectively handling widely varying load and possess high control bandwidth. To address these issues, a two-stage and distributed control architecture is presented. The co-simulation framework is fabricated by the interface technology integrating Simulink, AMESim and ADAMS, in order to build the total dynamics modeling. Subsequently, the design of power system and numerical evaluation of frequency analysis are implemented. Finally, verification tests were conducted in the outdoor environment to prove the effectiveness of the proposed design.

Design of a Maximally Regular Acceleration Sensor Based on Generalized Gough-Stewart Platforms

An analytical formulation and a new routine are presented to design a maximally regular acceleration sensor based on a generalized Gough-Stewart platform. The Jacobian matrix considering the measuring point is constructed symbolically and also acceleration mapping matrix done. Optimal indices and coupling evaluation are proposed to qualify performances of the sensor. Subsequently, the singular values of the acceleration Jacobian matrix are solved analytically to evaluate acceleration transmission. The conditions for the maximally regular acceleration are expressed in close-form. Based on the analytical formulation, an optimal design routine is put forward to determine a family of orthogonal and maximally regular acceleration sensor. With the aid of numerical examples, the acceleration-coupling is investigated and the results illustrate that the proposed design method is effective.

An Improved Study of Physically Based Fluid Simulation on GPU

A feasible routine for complex fluid simulation is presented, consisting of the pre-processing and runtime stage. The pre-processing stage generates all computation-aided textures, which speeds up the simulating and rendering at run-time stage. We improve the unreasonable processing in most previous methods and give a correct discretized solution of Poisson equation. To improve the computational accuracy, the residuals are calculated to adoptively control the Jacobian iterations based on ping-pong technique and reduction operation. The potential parallelism of GPU is harnessed by effectively organizing the data and taking advantages of 4-element parallelism of vector operations. The experiment reveals that the proposed routine creates visually convincing results with encouraging FPS and meets the requirements of real-time simulation.