Wim Symens

Gain-scheduling control of machine tools with varying structural flexibility

Abstract The high accelerations occurring in present-day machine tools are likely to excite the vibration modes of the machine structure. These structural eigenfrequencies are not constant but depend on the position of the tool in its workspace. High performance motion controllers should take into account these varying resonances. This paper discusses the gain-scheduling control approach for an experimental set-up containing a flexible beam of which the stiffness depends on its length. H ∞ -controllers are designed for several constant beam lengths and are linearly scheduled. Next to this ad-hoc scheduling, analytically scheduled controllers are synthesised. It is shown that the inherent conservatism in the design method limits the performance of the analytical approaches.

Identification of Interpolating Affine LPV Models for Mechatronic Systems with one Varying Parameter

This paper presents a technique to identify an affine parameter-dependent model based on a set of Linear- Time-Invariant (LTI) models that are identified in local operating points of the varying system. The systems under investigation are mechatronic systems in which the dynamic behaviour is depending on a single varying parameter. By fitting specific pole and zero loci on the poles and zeros of the local LTI models, an affine state-space model can be constructed. Since the resulting affine model is well conditioned and has a low complexity, it is suitable to be used for Linear- Parameter-Varying (LPV) control. The applicability of the presented technique is shown on an industrial pick-and-place machine with position-dependent dynamics.

A gain-scheduling-control technique for mechatronic systems with position-dependent dynamics

This paper presents a gain-scheduling-control technique for mechatronic systems with position dependent dynamics. The proposed method fits in the framework of traditional gain scheduling, where several controllers designed for fixed operating points are interpolated to construct a global gain-scheduling controller. A new interpolation approach is proposed starting from an affine interpolation between the poles, zeros and gains of the local controllers as a function of the varying parameter, resulting in a affine state-space representation. The presented method is applied on an industrial pick-and-place machine which has position-dependent dynamics. Experimental results show the benefit of the proposed method

Iso efficiency contour measurement results for variable speed drives

The efficiency of variable speed drives with induction motors and permanent magnet synchronous motors has received little attention so far in international standards. However the number of such applications is increasing rapidly and the potential energy savings are large. This paper is based on a measurement campaign of three collaborating research institutes and reports on the efficiency of motors up to 15 kW. The efficiency values are represented by means of iso efficiency contours. From these contours, the efficiency for IE1, IE2 and IE3 induction motors is compared with that of a permanent magnet machine for the entire torque - speed operation region. Also the impact of flux optimization with induction motors is analyzed. The required number of measurement points to construct accurate iso efficiency contours with minimum measurement effort is also discussed.

Badminton Playing Robot - a Multidisciplinary Test Case in Mechatronics

Abstract We present a Mechatronics design approach and related technologies for a badminton playing robot, as a first stage of a multi-year project. The robot is using non-modified shuttles and rackets, which are detected and localized using purely visual information. The robot subsystems are presented: mechanical design, visual detection of the shuttle, shuttle trajectory estimation and interception, actuation, control hardware and software. The paper demonstrates the multidisciplinary nature of the Mechatronics.

Parameter Sensitivity and Measurement Uncertainty Propagation in Torque-Estimation Algorithms for Induction Machines

This paper studies error propagation and parameter sensitivity based on a torque estimation model for induction machines. The model is based on the equation describing the interaction of rotor flux linkage and rotor currents. Contrary to classical schemes for induction motor control this is an open loop scheme, however, the model still requires different machine parameters. Therefore the parameters sensitivity of the model is performed. For validation, the model is implemented in the real-time environment dSPACE and a test induction machine is subjected to different combinations of speed and torque profiles. The identified model can be used to replace mechanical torque measurement devices or as a backup of a cheap torque sensor

Iso efficiency contours as a concept to characterize variable speed drive efficiency

Despite recent revisions and harmonization efforts of international motor efficiency standards which has lead to the revised IEC Std 60034-2-1 and the efficiency classification of IEC Std 60034-30, there remains a lacuna in the context of motor systems efficiency. Although IEC is preparing a “Guide for the selection and application of energy-efficient motors including variable-speed applications” labeled IEC Std 60034-31, to date, there is no internationally accepted test protocol that allows the determination of drive system efficiency at different load points. As the first in a set of three by a joint research project of three research institutes, this paper introduces iso efficiency contours as a useful tool in this context. The concept of these contours as well as their mutual interaction with system specifications and losses are discussed. A first testing protocol for all types of motor drives is proposed. The concept is illustrated by first results of an extensive testing campaign.

Robust and two-level (nonlinear) predictive control of switched dynamical systems with unknown references for optimal wet-clutch engagement

Modeling and control of clutch engagement has been recognized as a challenging control problem, due to nonlinear and time-varying dynamics, that is, switching between two discontinuous dynamic phases: the fill and the slip. Furthermore, the reference trajectories for obtaining an optimal clutch engagement are not a priori known and may require adaptation to varying operating conditions. Two (nonlinear) model predictive control strategies are proposed based on the partial or full (non)linear identification of these two phases. First, a local linear model of the fill phase is identified and a robust model predictive control is designed to account for the consequent uncertainty in the slip phase. Second, (non)linear models of both the fill and the slip phases are identified and a two-level (nonlinear) model predictive control controller is proposed, where two (nonlinear) model predictive control controllers are designed for the two phases tracking references generated and continuously adapted by high-level iterative learning controllers. The robust and two-level (nonlinear) model predictive controls are validated on a real clutch. The results obtained from the real setup show that the proposed control strategies lead to an optimal engagement of the wet-clutch system.

Calculating energy consumption of motor systems with varying load using iso efficiency contours

Increasing awareness of ecological problems forces machine manufacturers to design greener machines. This implies amongst other things the selection of the most efficient electric motor system for their specific application. On the other hand, machine building applications evolve more and more from constant speed and load characteristics to varying speed and load applications. Therefore, the motor system that is used evolves more and more from direct online (DOL) to motors fed by a variable speed drive (VSD). However, current efficiency standardization focuses on DOL applications, and can by consequence not offer assistance to the machine builder to select the most efficient motor-VSD combination for his particular varying load application. The goal of this paper is to present a methodology that allows to predict the energy consumption for a specific motor-VSD combination and a specific varying speed-load application, using the fairly new concept of iso efficiency contours. By comparing the predicted energy consumption for a number of selected combinations, the most efficient one is revealed.

Dynamic characterization of hysteresis elements in mechanical systems. I. Theoretical analysis

The pre-sliding–pre-rolling phase of friction behavior is dominated by rate-independent hysteresis. Many machine elements in common engineering use exhibit, therefore, the characteristic of “hysteresis springs,” for small displacements at least. Plain and rolling element bearings that are widely used in motion guidance of machine tools are typical examples. While the presence of a hysteresis element may mark the character of the resulting dynamics, little is to be found about this topic in the literature. The study of the nonlinear dynamics caused by such elements becomes imperative if we wish to achieve accurate control of such machines. In this Part I of the investigation, we examine a single-degree-of-freedom mass-hysteresis-spring system and show that, while the free response case is amenable to an exact solution, the more important case of forced response has no closed form solution and requires other methods of treatment. We consider harmonic-balance analysis methods (which are common analysis tools...