Jan Swevers

Extended Bandwidth Zero Phase Error Tracking Control of Nonminimal Phase Systems

This paper describes a new feedforward algorithm for accurate tracking control of nonminimal phase systems. Accurate feedforward calculation involves a prefilter design using the inverse system model. Nonminimal phase systems cause problems with this prefilter design, because unstable zeros become unstable poles in the inverse model. The zero phase error tracking control algorithm (ZPETC) consists of a substitution scheme, which removes the unstable zeros

Modelling a pneumatic servo positioning system with friction

Treats the problem of modelling and identification of the various elements of a pneumatic servo positioning system with the aim of constructing a complete and effective model that can be used for simulation and accurate control of such systems. Particular attention is paid to two important elements that manifest a strong nonlinear behaviour, viz, air flow and friction. In the first instance, an empirical model connecting the pneumatic valves driving voltage, the pressures upstream and downstream, and the flow is hypothesised based on the nozzle formula. With this model, the flow function is then systematically identified. As regards friction, the Leuven model structure is used as basis for identification. Here, the two basic friction regimes, viz. presliding, with its hysteresis behaviour, and gross sliding are well exposed and their essential parameters identified.

Accurate Motion Controller Design Based on an Extended Pole Placement Method and a Disturbance Observer

Abstract The paper describes an innovative integrated design method for accurate tracking in motion control applications, in the presence of external disturbances like friction, cutting forces, etc. First, an extended pole placement method is developed to design feedforward controllers for applications with known future input commands, like in feeddrives for machine tools. It results in a noncausal reference model with a low-pass characteristic with selectable bandwidth and zero phase shift. A new feedback design approach, based on a state and disturbance observer is introduced. A loop transfer recovery procedure tunes the observer gains to compromise optimally between performance and robustness.

Generation of Periodic Trajectories for Optimal Robot Excitation

This paper describes the parameterization of robot excitation trajectories for optimal robot identification based on finite Fourier series. The coefficients of the Fourier series are optimized for minimal sensitivity of the identification to measurement disturbances, which is measured as the condition number of a regression matrix, taking into account motion constraints in joint and cartesian space. This approach allows obtaining small condition numbers with few coefficients for each joint, which simplifies the optimization problem significantly. The periodicity of the resulting trajectories and the fact that one has total control over theirfrequency content, are additional features of the presented parameterization approach. They allow further optimization of the excitation experiments through time domain data averaging and optimal selection of the excitation bandwidth, which both help the reduction of the disturbance level on the measurements, and therefore improve the identification accuracy.

Optimal Splines for Rigid Motion Systems: A Convex Programming Framework

This paper develops a general framework to synthesize optimal polynomial splines for rigid motion systems driven by cams or servomotors. This framework is based on numerical optimization, and has three main characteristics: (i) Spline knot locations are optimized through an indirect approach, based on providing a large number of fixed, uniformly distributed candidate knots; (ii) in order to efficiently solve the corresponding large-scale optimization problem to global optimality, only design objectives and constraints are allowed that result in convex programs; and (iii) one-norm regularization is used as an effective tool for selecting the better (that is, having fewer active knots) solution if many equally optimal solutions exist. The framework is developed and validated based on a double-dwell benchmark problem for which an analytical solution exists.

Linear Motor Ripple Compensation Using Position-Triggered Repetitive Control

Abstract A new linear motor ripple compensation method is proposed based on the repetitive control approach. Its implementation is much easier than the existing ripple compensation techniques. The repetitive control method is adapted to allow disturbances that are periodic in position rather than in time, and to allow periodic frequencies that can change sign. First experimental results demonstrate that the tracking error can be reduced by a factor of two.

A General and Numerically Efficient Framework to Design Sector-Type and Cylindrical Counterweights for Balancing of Planar Linkages

This paper extends previous work concerning convex reformulations of counterweight balancing by developing a general and numerically efficient design framework for counterweight balancing of arbitrarily complex planar linkages. At the numerical core of the framework is an iterative procedure, in which successively solving three convex optimization problems yields practical counterweight shapes in typically less than 1 CPU s. Several types of counterweights can be handled. The iterative procedure allows minimizing and/or constraining shaking force, shaking moment, driving torque, and bearing forces. Numerical experiments demonstrate the numerical superiority (in terms of computation time and balancing result) of the presented framework compared to existing approaches.

Counterweight Balancing for Vibration Reduction of Elastically Mounted Machine Frames: A Second-Order Cone Programming Approach

A moving linkage exerts fluctuating forces and moments on its supporting frame. One strategy to suppress the resulting frame vibration is to reduce the exciting forces and moments by adding counterweights to the linkage links. This paper develops a generic methodology to design such counterweights for planar linkages, based on formulating counterweight design as a second-order cone program. Second-order cone programs are convex, which implies that these nonlinear optimization problems have a global optimum that is guaranteed to be found in a numerically efficient manner. Two optimization criteria are considered: the frame vibration itself and the dynamic force transmitted to the machine floor. While the methodology is valid regardless of the complexity of the considered linkage, it is developed here for a literature benchmark consisting of a crank-rocker four-bar linkage supported by a rigid, elastically mounted frame with three degrees of freedom. For this particular benchmark, the second-order cone program slightly improves the previously known optimum. Moreover, numerical comparison with current state-of-the-art algorithms for nonlinear optimization shows that our approach results in a substantial reduction of the required computational time.

An Experimental Test Setup for Advanced Estimation and Control of an AirborneWind Energy System

This chapter gives a detailed description of a test setup developed at KU Leuven for the launch and recovery of unpropelled tethered airplanes. The airplanes are launched by bringing them up to flying speed while attached by a tether to the end of a rotating arm. In the development of the setup, particular care was taken to allow experimental validation of advanced estimation and control techniques such as moving horizon estimation and model predictive control. A detailed overview of the hardware, sensors and software used on this setup is given in this chapter. The applied estimation and control techniques are outlined in this chapter as well, and an analysis of the closed loop performance is given.

Optimal linear controller design for periodic inputs

Design Methodology for Controllers Facing Periodic Inputs.- Application to Feedforward Control.- Application to Estimated Disturbance Feedback Control.- Application to Repetitive Control.- Application to Feedback Control.- Experimental Validation on an Active Air Bearing Setup.- Conclusions.