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.     

Development of a parallel kinematic motion simulator platform

A six degrees-of-freedom (DOF) parallel kinematics machine (PKM) applicable to the motion simulation of hazardous chemicals transportation is developed in this paper. According to actual requirements of the motion simulation, a detailed analysis has been carried out including the issues of kinematics analysis and prototyping. Based on a full conceptual mechanical design, the kinematics analysis is performed, which is focused on inverse kinematics modeling, workspace determination, singularities analysis, etc. Moreover, a PKM prototype system is developed based on a series of aforementioned analysis. Finally, the preliminary experiments have been performed, which validate the effectiveness of the proposed system. While the primary goal of this research is aimed at simulating the motion of hazardous chemicals transportation, the concept and approach outlined can be extended to a variety of applications.     

Dynamic modeling and control of a 3-DOF Cartesian parallel manipulator

Dynamic modeling is the basic element for controller design of mechanisms. In this paper, an effective dynamic equation of a 3-DOF translational parallel manipulator for control purpose has been derived by the Lagrange-D’Alembert formulation. The structural properties of the derived dynamic equation were proved so that the vast control strategies developed for the serial counterparts can be easily extended for controlling the CPM (Cartesian parallel manipulator). The derived model also leads to decoupling dynamic characteristics, by which the complexity of the controller design can be significantly reduced. Based on this approach, a model-based computed torque method for positioning control of the CPM is illustrated. Both simulated and experimental results show that the model-based controller can achieve high positioning performance. Furthermore, it is shown that the coupling forces from other limbs play significant roles in the force components of the total dynamics of the CPM.     

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.     

Applications of VLSI technology in a massively parallel machine

NON-VON is a highly parallel non-von Neumann supercomputer presently under construction at Columbia University. The basis for NON-VON's significant cost/performance advantage lies in a highly unusual application of VLSI technology to the realization of massive computational parallelism. This paper outlines the manner in which the emerging technology of VLSI circuits is employed in NON-VON to achieve this advantage. Particular emphasis is given to novel aspects of the design, layout, and operation of the NON-VON processing element, eight of which are to be embedded within each integrated circuit chip.This research was supported in part by the Defense Advanced Research Projects Agency, under Contract N00039-84-C-0165, in part by the New York State Center for Advanced Technology in Computers and Information Systems at Columbia University, and in part by an IBM Faculty Development Award.     

Flexible joints control: A minimum-time feed-forward technique

The paper proposes a linear programming approach to the feed-forward minimum-time control of flexible joints. Taking into account both input and output constraints, the optimal bang–bang control is computed by discretizing a continuous-time joint model and by solving a sequence of linear programming feasibility problems. The resulting joint motion is a smooth rest-to-rest motion without oscillations. Theoretical analysis is presented and proof of convergence is given. Experimental results illustrate the proposed open-loop technique. Comparisons are made with inversion-based techniques.     

Operating conditions of OOK signal regenerator with feed-forward control

The optimum operating conditions for a signal regenerator employing a hybrid optical-electrical scheme for intensity-modulated signals are experimentally investigated. The scheme comprises an optical coupler, a photo-detector, and a Mach–Zehnder intensity modulator, and can suppress the intensity noise, accompanying extinction ratio degradation. It is shown that the operating conditions that achieve the lowest bit error rate (BER) after regeneration depend on the extinction ratio and the optical signal-to-noise ratio of the input signal. We also investigate the noise suppression effect under conditions that do not change the extinction ratio.     

Robust force control with a feed-forward inverse model controller for electro-hydraulic control loading systems of flight simulators

A hybrid control strategy for an electro-hydraulic control loading system (EHCLS) of a flight simulator in the presence of a control mechanism kinetic parameter perturbation is proposed to improve the force tracking accuracy and guarantee robust stability of the EHCLS system. A double-loop model of the EHCLS, including the control mechanism and the hydraulic mechanism, is established and analyzed from the force-displacement impedance perspective. A force closed-loop parameter model of the EHCLS is identified by a recursive-least-squares (RLS) algorithm and its inverse model is designed using a zero phase error compensation technology to expand the frequency bandwidth of the force closed-loop system of the EHCLS. A μ theory of robust control is employed to design a stable controller for enhancing robust stability of the EHCLS in the presence of uncertainties of the inner loop, the control mechanism and the high frequency disturbance force. Simulation and experimental results show that the proposed hybrid control approach can greatly improve the control performance of the EHCLS by expanding the frequency bandwidth of the force closed-loop system and enhancing stability of the EHCLS, which can decrease displacement output response error of the EHCLS from 10.34% to 3.1%.     

Local structurization kinematic decoupling of six-leg virtual-axis NC machine tool

Decoupling is always a difficult problem in the field of virtual-axis numerical control (NC) machine servocontrol. In this paper, the idea of local structurization method is combined with the theory of decoupling. A new decoupling method, local structurization decoupling method, is proposed first. Jacobian matrix is decomposed into two matrices-translation matrix and rotation matrix. So decoupling between parallel motion and rotation is implemented in a six-leg virtual-axis NC machine tool for small time intervals.     

Improvement of OOK signals with a polarization-independent feed-forward control circuit using an electro-absorption modulator

An optical-and-electrical hybrid scheme for improving on–off keying (OOK) signals is described. It is a feed-forward (FF) control circuit composed of an optical coupler, a photo-detector, and an electro-absorption (EA) modulator, which works to suppress “on” level fluctuations. Owing to the use of an EA modulator, the circuit operates irrespective of the polarization state of the input signal. In addition, the scheme can also improve the extinction ratio (ER) of OOK signals. Experiments were conducted to demonstrate the noise suppression and the ER improvement.     

An investigation of the kinematic control of a six-legged walking robot

A semi autonomous six-legged walking machine with hexagonal architecture that has been developed for research on gait control is described. The machine weighs 13 kg; each leg has three d.o.f. with closed-loop kinematics, actuated by D.C. electric drives. The kinematics is designed to achieve gravitational decoupling, which simplifies considerably the velocity control of the legs. The control architecture is decentralized, each leg being controlled by a separate microcontroller. A central computer coordinates the motion of the various legs (gait) and controls the attitude of the vehicle. The gait can be programmed arbitrarily.     

Experimental validation of the kinematic design of 3-PRS compliant parallel mechanisms

In this paper, a procedure for the kinematic design of a 3-PRS compliant parallel manipulator of 3 degree of freedom is proposed. First, under the assumption of small displacements, the solid body kinematics of the 3-PRS has been studied, performing a comprehensive analysis of the inverse and forward kinematic problem, and calculating the rotations that the revolute and spherical flexure joints must perform. Then, after defining some design requirements and therefore the necessary displacements to fulfill, a design process based on the finite element calculations has been stablished, giving the necessary guidelines to reach the optimal solution on a 3-PRS compliant mechanism. Also, a prototype has been tested, using a coordinate measuring machine to verify its dimensions and the resulting displacements in the end effector and the actuated joints. Finally, those measurements have been compared with the FEM and the rigid body kinematics predictions, contrasting the validity of those two modelling approaches for the kinematic design of compliant mechanisms.     

The control of a synchronous machine using optimal control theory

The selection of stabilizing signals to improve power system dynamic behavior is presented. Some results from modern control theory are used to show how such stabilizing signals may be derived systematically for a turboalternator model connected through a double circuit line to an infinite bus. The closed-loop performance of this nonlinear system model with the derived linear optimal controller is then evaluated for a wide range of input disturbances and operating conditions which include three-phase fault studies with autoreclosure.     

一种适用于0.8VCMOS助听器的电流模前馈增益控制系统

摘要：本文介绍了一种适用于助听器前端系统的电流模前馈增益控制系统。和传统自动增益控制系统相比,电流模前馈增益控制通过数字增益控制码来实现前端系统总谐波失真的显著降低。为了从麦克风微弱的输出信号中得到数字控制码, 本文提出了用电流模实现的整流电路和电流模状态控制电路.该设计基于0.13微米CMOS工艺. 测试表明芯片可工作于0.6V的电源电压.在电源电压为0.8V下, 输出摆幅500mVp-p的信号总谐波失真在0.06% (-64dB)以下, 且功耗控制在40uW以内.另外,系统的等效输入噪声达到4uVrms,最大增益保持在33dB.     

A current mode feed-forward gain control system for a 0.8 V CMOS hearing aid

A current mode feed-forward gain control（CMFGC）technique is presented,which is applied in the front-end system of a hearing aid chip.Compared with conventional automatic gain control（AGC）,CMFGC significantly improves the total harmonic distortion（THD）by digital gain control.To attain the digital gain control codes according to the extremely weak output signal from the microphone,a rectifier and a state controller implemented in current mode are proposed.A prototype chip has been designed based on a 0.13μm standard CMOS process.The measurement results show that the supply voltage can be as low as 0.6 V.And with the 0.8 V supply voltage,the THD is improved and below 0.06%（-64 dB）at the output level of 500 mV_p-p,yet the power consumption is limited to 40μW.In addition,the input referred noise is only 4μV_rmsand the maximum gain is maintained at 33 dB.     

A simple feed-forward control algorithm for fast dynamic gain profile control in a multiwavelength forward-pumped Raman fiber amplifier

We proposed and experimentally verified a very simple feed-forward dynamic gain profile control algorithm for a multiwavelength forward-pumped Raman fiber amplifier, using only the total input signal power as the feed signal.     

Demonstration of a feed-forward PMD compensation technique

We demonstrate a feed-forward technique, which characterizes first-order polarization-mode dispersion (PMD) and aligns it to a compensator. With appropriate components, the system could perform real-time compensation of first-order PMD with rapidly varying principal states of polarizations     

Combined kinematic and dynamic control of vehicle-manipulator systems

A vehicle-manipulator system (VMS) is a class of mobile robots characterised by their ability to carry or be a robotic arm and therefore also manipulate objects. The VMS class includes vehicles with a robotic manipulator, free-floating space robots, aerial manipulators and underwater vehicle-manipulator systems (UVMSs). All of these systems need a kinematic controller to solve the kinematic redundancy of the VMS and a dynamic controller to follow the reference given by the kinematic controller. In this paper, we propose a combined kinematic and dynamic control approach for VMSs. The approach uses the singularity-robust multiple task-priority (SRMTP) framework to generate a velocity reference combined with a dynamic velocity controller based on a robust sliding mode controller (SMC). Any SMC can be used as long as it can make the velocity vector converge to the velocity reference vector in finite time. This novel approach allows us to analyse the stability properties of the kinematic and dynamic subsystems together in the presence of model uncertainty. We show that the multiple set-point regulation tasks will converge asymptotically to zero without the strict requirement that the velocities are perfectly controlled. This novel approach thus avoids the assumption of perfect dynamic control that is common in kinematic stability analyses for robot manipulators. We present two examples of SMCs that can make the velocity vector converge to the velocity reference vector in finite time. We also demonstrate the applicability of the proposed approach through a simulation study of an articulated intervention-AUV (AIAUV), which is a type of UVMS, by conducting three simultaneous tasks. The results show that both SMC algorithms can make all the regulation tasks converge to their respective set-points. In the simulation study, we also include the results from two standard control methods, a proportional-integral-derivative (PID) controller and a feedback linearisation controller, and we use two different AIAUVs to illustrate the advantages and robustness achieved from using SMC.     

Nonlinear robust control of a vector-controlled synchronousreluctance machine

This paper presents the implementation of Slotine's approach of sliding mode control for position control of a vector-controlled synchronous reluctance machine. A comparison is undertaken between the performance of a fixed gain controller and two sliding mode controllers for both the regulator and servo cases. Invariant performance is obtained using Slotine's approach of sliding mode control compared to a fixed gain controller. Robustness to parameter variation is an important feature of this technique. This can be achieved through the control law design, assuming parameter variation bounds are known. These improvements are demonstrated for variations in the load inertia. Machine inductance ripple affects the quality of achievable position control. A state-space model for the machine to incorporate this effect yields drive simulation results that agree with presented experimental results