Dynamics and contouring control of a 3-DoF parallel kinematics machine

In machining applications, instead of tracking error (the difference between the actual position and the desired position), contouring error (the minimum distance from the actual position to the desired trajectory) characterizes product quality. In this paper, we propose a generalized moving task coordinate frames based contouring control for parallel kinematics machines, whose dynamics is in general coupled and strongly nonlinear. The Orthopod, a 3 degree-of-freedom purely translational parallel kinematics machine, is introduced as a control plant. The Lagrange-D’Alembert formulation is used to model the system dynamics. The developed dynamic model in Cartesian space is transformed and parametrized by tangential error, normal error, and binormal error in moving task coordinate frames. The contouring error is then approximated by the normal error and the binormal error, which is the projection of tracking error to the normal plane at the desired position. By employing the structural properties of the transformed dynamics, a special feedback linearization, the computed torque control is applied. It leads to a stabilization problem for a second-order linear time-invariant system. Coulumb plus viscous friction model is used to compensate friction effects. Friction parameters are identified by least-squares approach. For comparison purpose, the tracking error based computed torque control is also carried out. Experiments demonstrate that the proposed control scheme not only leads to improved contouring accuracy, but also produces smaller and smoother control input torques, which may contribute to smaller vibration.     

Spatial hybrid/parallel force control of a hexapod machine tool using structure-integrated force sensors and a commercial numerical control

Structure-integrated force measurement in hexapod structures or kinematics offers great potential for spatial process force control in six degrees of freedom. Although force control has been studied for many years, research questions remain unanswered, especially when regarding parallel kinematic machine tools with numerical control and integrated sensors. This contribution summarizes the technology of structure-integrated force sensing in hexapod machine tools and develops two approaches to use the measured signals for direct hybrid/parallel force control. For different use-cases, such as teach-in or synchronous force/position control with variable task frame, different approaches of set-point specification and injection of manipulated values are studied from a practical point of view. As a result of the work, the feasibility of the force control with structure-integrated sensors on a commercial CNC can be confirmed through appropriate experiments. Furthermore, the realized G-Code integration represents a practical solution for programming force-controlled machine tools in an easy and concise way from the NC programme.     

Interaction control of an industrial manipulator using LPV techniques

This paper presents the design and implementation of a hybrid force/motion control scheme on a six-degrees-of-freedom robotic manipulator employing a gain-scheduled linear parameter-varying (LPV) controller. A nonlinear dynamic model of the manipulator is obtained and the unknown parameters are estimated. The manipulator is decomposed into an inner and a wrist submodel, and a practical way is proposed to investigate the coupling between them. The motion control part of the hybrid controller which is the main focus of this paper is formed by a combination of an LPV controller and a model-based inverse dynamics controller for the inner submodel and the wrist joints, respectively. A quasi-LPV model with a reduced number of scheduling parameters is derived for the inner submodel, and a polytopic LPV gain-scheduled controller is synthesized in a two-degrees-of-freedom structure including feedback and feedforward parts, which is augmented by a friction compensation term. A PD controller with a feedforward path is designed to control the interaction force. The proposed hybrid force/motion scheme is implemented on the 6-DOF CRS A465 robotic manipulator to perform a writing task. Comparison of the results with those of a hybrid force/motion controller with a plain model-based inverse dynamics motion control and the same force control shows that the proposed controller improves the position tracking performance significantly.     

Precise position control of shape memory alloy actuator using inverse hysteresis model and model reference adaptive control system

Position control of Shape Memory Alloy (SMA) actuators has been a challenging topic during the last years due to their nonlinearities in the governing physical equations as well as their hysteresis behaviors. Using the inverse of phenomenological hysteresis model in order to compensate the input–output hysteresis behavior of these actuators shows the effectiveness of this approach. In this paper, in order to control the tip deflection of a large deformation flexible beam actuated by an SMA actuator wire, a feedforward–feedback controller is proposed. The feedforward part of the proposed control system, maps the beam deflection into SMA temperature, is based on the inverse of the generalized Prandtl–Ishlinskii model. An adaptive model reference temperature control system is cascaded to the inverse hysteresis model in order to estimate the SMA electrical current for tracking the reference signal. In addition, a closed-loop proportional–integral controller with position feedback is added to the feedforward controller to increase the accuracy as well as eliminate the steady state error in position control process. Experimental results indicate that the proposed controller has great accuracy in tracking some square wave signals. It is also experimentally shown that the suggested controller has precise tracking performance in presence of environmental disturbances.     

Adaptive robust control of fully-constrained cable driven parallel robots

In this paper, adaptive robust control (ARC) of fully-constrained cable driven parallel robots is studied in detail. Since kinematic and dynamic models of the robot are partly structurally unknown in practice, in this paper an adaptive robust sliding mode controller is proposed based on the adaptation of the upper bound of the uncertainties. This approach does not require pre-knowledge of the uncertainties upper bounds and linear regression form of kinematic and dynamic models. Moreover, to ensure that all cables remain in tension, proposed control algorithm benefit the internal force concept in its structure. The proposed controller not only keeps all cables under tension for the whole workspace of the robot, it is chattering-free, computationally simple and it does not require measurement of the end-effector acceleration. The stability of the closed-loop system with proposed control algorithm is analyzed through Lyapunov second method and it is shown that the tracking error will remain uniformly ultimately bounded (UUB). Finally, the effectiveness of the proposed control algorithm is examined through some experiments on a planar cable driven parallel robot and it is shown that the proposed controller is able to provide suitable tracking performance in practice.     

Tool-Center-Point control of the KAI manipulator using constrained QP optimization

The KAI manipulator is a four joint mobile manipulator, which will be used within the German road clearance package to investigate improvised explosive devices and ordnance from within an armored vehicle. To improve handling of the manipulator, a Tool-Center-Point (TCP) control is implemented. By using constrained quadratic optimization (cQP) it is possible to allow for the control of the manipulator within three different operating spaces. The QP is formulated to account for constraints in the joint angular rates and TCP velocities, as well as additional velocity constraints, e.g. on the movement of the center of mass of the manipulator. The proposed algorithm is able to handle redundant as well as non redundant manipulator kinematics. By using an efficient QP solver the algorithm can be used within a real-time trajectory generation scheme. The performance of the algorithm is demonstrated using simulation results and validated by measurements of the TCP control.     

关于压电致动器的动力学和致动作用力

从压电本构方程出发，将外加电信号处理为外界激励作用。在理论上给出了应用最广泛的矩形薄板压电致动器在激励作用下的动力学效应，同时给出了其致动作用力表达式，为以前的有关报道结果提供了严格的理论依据。根据结果不难具体分析这种压电致动器的动力学响应。     

Motion control algorithms based on the dynamic modelling of kinematically redundant hybrid parallel robots

This paper discusses the motion control problem of kinematically redundant hybrid parallel robots that were recently proposed. The kinematic and dynamic models are firstly reviewed. It is pointed out that the robot can be decomposed into two parts and that each part can be analysed independently. A new hybrid approach is proposed based on this property of the robot. This approach includes an adapted computed-torque control scheme for the legs that operates in the joint space as well as a compensation of the errors of the platform applied in the Cartesian space. The convergence of this proposed approach is also verified using the Lyapunov stability theory. Two example architectures of kinematically redundant robots are built and experiments are conducted. Finally, the results are compared and analysed in order to validate the improvements provided by the proposed control method. It is shown that the proposed control scheme significantly reduces the position error. Potential extensions of this work are also discussed.     

Quanta - A platform for rapid control and monitoring of heterogeneous rbots

Rapid prototyping, real-time control and monitoring of various events in robots are crucial requirements for research in the fields of modular and swarm robotics. A large quantities of resources (time, man power, infrastructure, etc.) are often invested in programming, interfacing the sensors, debugging the response to algorithms during prototyping and operational phases of a robot development cycle. The cost of developing an optimal infrastructure to efficiently address such control and monitoring requirements increases significantly in the presence of mobile robots. Though numerous solutions have been developed for minimizing the resources spent on hardware prototyping and algorithm validation in both static and mobile scenarios, it can be observed that researchers have either chosen methodologies that conflict with the power and infrastructure constraints of the research field or generated constrained solutions whose applications are restricted to the field itself. This paper develops a solution for addressing the challenges in controlling heterogeneous mobile robots. A platform named Quanta - a cost effective, energy efficient and high-speed wireless infrastructure is prototyped as a part of the research in the field of modular robotics. Quanta is capable of controlling and monitoring various events in/using a robot with the help of a light-weight communication protocol independent of the robot hardware architecture(s).     

基于CICS的中间业务平台设计与实现

CICS中间件为商业应用提供一个事务处理环境,适用于银行这样有大量突发联机事件的系统.提出一个基于CICS中间件的三层架构中间业务平台,屏蔽后端的不同硬件设备,同时保证了数据准确可靠的传送和事务的完整性.重点介绍了基于CICS的应用软件系统设计与实现过程,阐述了该系统的软件框架、功能模块和技术实现.     

InGaAs/InP界面控制对InGaAs薄膜电学和光学性质 的影响

研究了全固态源分子束外延(MBE)生长InGaAs/InP异质结界面扩散对InGaAs外延薄膜电学和光学性质的影响.通过X射线衍射、变温霍尔测试和变温光致发光等方法对InGaAs薄膜样品进行细致研究.发现在InGaAs/InP界面之间插入一层利用As_4生长的InGaAs过渡层,能够显著改善上层InGaAs(利用As_2生长)外延薄膜的电学性能,其低温迁移率显著提高.同时荧光峰反常蓝移动消失,光学性质有所改善.研究表明利用As_4生长InGaAs过渡层,可显著降低As在InP中反常扩散,获得陡峭的InGaAs/InP界面,从而提高InGaAs材料电学和光学性能.     

一种引入电流前馈的DC/DC数字控制算法的设计与实现

根据BUCK DC/DC变换器工作原理推导出以电感电流为变量的一种易于实现的数字控制策略。将该方法以电流前馈方式与带滞环PID控制方法相结合,形成一种电流前馈控制策略。并以Buck DC/DC为例进行仿真与实现。仿真和实验结果表明:该控制策略能够使Buck DC/DC具有良好的输入电压调整特性及开关误差校正能力,符合动态性能要求较高的数字控制应用。与常规控制方法相比,具有算法实现简单,响应速度快,电压过充小,整定参数少的优点。