Direct Learning for Parameter-Varying Feedforward Control: A Neural-Network Approach

The performance of a feedforward controller is primarily determined by the extent to which it can capture the relevant dynamics of a system. The aim of this paper is to develop an input-output linear parameter-varying (LPV) feedforward parameterization and a corresponding data-driven estimation method in which the dependency of the coefficients on the scheduling signal are learned by a neural network. The use of a neural network enables the parameterization to compensate a wide class of constant relative degree LPV systems. Efficient optimization of the neural-network-based controller is achieved through a Levenberg-Marquardt approach with analytic gradients and a pseudolinear approach generalizing Sanathanan-Koerner to the LPV case. The performance of the developed feedforward learning method is validated in a simulation study of an LPV system showing excellent performance.Comment: Final author version, accepted for publication at 62nd IEEE Conference on Decision and Control, Singapore, 202

Mechatronic design exploration for wide format printing systems

This work aims at increasing the performance of Wide Format Printing Systems (WFPS) via a mechatronic approach. With increasing performance is meant that one or more of the categories: productivity, print quality, reliability and/or cost of production, is improved without sacrificing one of the others. Although the main focus lies on WFPS, the methodology in this work can be extended to a wider class of printers or to other applications. Multi-printhead scanning inkjet configurations are considered where each printhead contains hundreds of nozzles. This work mainly concentrates on positioning of the 6 degrees of freedom of all printheads in time and space. Questions about what happens inside the nozzles will not be addressed. However, the macroscopic characteristics of the droplet formation process are taken into account, such as jet speed, jet timing and temporary nozzle congestion. A concept exploration is carried out, including a productivity analysis and a printing accuracy analysis focussing on mechanical design parameters. Both analyses are set up in a generic way such that they can be applied to other printer configurations or to a wider range of applications. Based on this analysis, two concepts are chosen to be investigated further. The first concept is active printhead alignment. Instead of putting all effort and cost in reduction of the manufacturing tolerances to obtain an accurate printhead alignment for higher productive WFPS, the misalignment of each printhead is measured and actively controlled. A low cost sensor, actuator, and alignment mechanism are developed to achieve this. An experimental setup is built to validate this concept. The concept has been shown to be feasible satisfying the accuracy specification of less than 10 µm. Moreover, this concept enables several extensions, such as (i) adding redundant printheads which take over printing for temporarily congested nozzles, (ii) staggering of printheads in paper transport direction or even distribute the printheads over multiple carriages which would be infeasible for fixed printheads due to thermal effects and parasitic dynamics. The second concept is a new carriage drive design for higher productive WFPS. A productivity increase can be achieved by increasing the amount of effectively printing nozzles and increasing the jet frequency. As a result, the carriage will be heavier due to the addition of printheads and the carriage speed will need to be increased due to the higher jet frequency. A doubling in mass and speed results in an actuator power increase by a factor of 16 for the case that the effective relative printing time is kept equal. Scaling of the drive in conventional WFPS is therefore expensive and energy inefficient. As an alternative, an energy buffering drive concept is developed which stores the kinetic energy of the carriage in a spring and returns this energy to the carriage in the opposite direction. This way, only a small additional carriage drive is required to overcome friction forces acting on the carriage while moving at a constant speed. To validate this concept, an experimental setup is built. The concept has been shown to be feasible. However, the prototype has to be engineered further to make it simpler such that it becomes cheaper in comparison with an equivalent conventional WFPS where the drive motor has been upscaled. The mechatronic design of both concepts focus on a much higher performance than conventional WFPS. The results are innovative designs which are easier scalable than conventional methods and enable new features which would not be possible by scaling conventional WFPS

MIMO FIR feedforward design for zero error tracking control

This paper discusses a multi-input multi-output (MIMO) finite impulse response (FIR) feedforward design. The design is intended for systems that have (non-)minimum phase zeros in the plant description. The zeros of the plant (either minimum or non-minimum phase) are used in the shaping of the reference signals whereas the poles of the plant are used in constructing feedforward forces. The FIR coefficients themselves are obtained from data-based optimizations which are the result of iterative machine measurements on an industrial wafer scanner. The resulting experimental results demonstrate the ability to obtain zero error tracking

Enhancing feedforward controller tuning via instrumental variables: with application to nanopositioning

\u3cp\u3eFeedforward control enables high performance of a motion system. Recently, algorithms have been proposed that eliminate bias errors in tuning the parameters of a feedforward controller. The aim of this paper is to develop a new algorithm that combines unbiased parameter estimates with optimal accuracy in terms of variance. A simulation study is presented to illustrate the poor accuracy properties of pre-existing algorithms compared to the proposed approach. Experimental results obtained on an industrial nanopositioning system confirm the practical relevance of the proposed method.\u3c/p\u3

Optimization aided Loop Shaping for Motion Systems

An approach is proposed which improves the quality and speed of manual loop shaping. Loop shaping is an iterative and creative controller design procedure where the control engineer uses frequency response function (FRF) data of the plant to shape the open loop response such that it satisfies stability, performance and robustness specifications. The advantage compared to automated controller design methods is that the control engineer can exploit all available a priori knowledge and expertise about the plant during the design process. As an assisting tool in manual loop shaping, we add a global optimization method, i.e. a genetic algorithm, where the objective function resembles as good as possible what the control engineer wants. As a result, the tuning process is substantially accelerated. The approach has been implemented in a Matlab-based control tuning tool showing good result