Wouter Hakvoort

Model-based iterative learning control applied to an industrial robot with elasticity

In this paper model-based iterative learning control (ILC) is applied to improve the tracking accuracy of an industrial robot with elasticity. The ILC algorithm iteratively updates the reference trajectory for the robot such that the predicted tracking error in the next iteration is minimised. The tracking error is predicted by a model of the closed-loop dynamics of the robot. The model includes the servo resonance frequency, the first resonance frequency caused by elasticity in the mechanism and the variation of both frequencies along the trajectory. Experimental results show that the tracking error of the robot can be reduced, even at frequencies beyond the first elastic resonance frequency.

ITERATIVE LEARNING CONTROL FOR IMPROVED END-EFFECTOR ACCURACY OF AN INDUSTRIAL ROBOT

Abstract In this paper Iterative Learning Control is used to improve the tracking accuracy of the end-effector of an industrial robot. The learning control algorithm is based on a straightforward robot model and an optimisation criterium. The algorithm is tested on an industrial robot, where the end-effector motion is measured relative to a weld seam using a seam tracking sensor based on optical triangulation. The experiments show that the tracking error can be reduced considerably in a few iterations.

Active vibration isolation control: Comparison of feedback and feedforward control strategies applied to Coriolis mass-flow meters

In this paper we describe the design, implementation and results of multi degree of freedom (DOF) active vibration control for a Coriolis mass-flow meter (CMFM). Without vibration control, environmental vibrational disturbances results in nanometre movement of the fluid-conveying tube which causes erroneous mass-flow measurements. In order to reduce the transmissibility from external vibrations to the internal tube displacement active vibration control is applied. A comparison of a feedback control strategy (adding virtual mass and skyhook damping) and an adaptive feedforward control strategy is made, taking into account the sensor noise levels. Theoretic results are validated with a multi-DOF experimental setup, showing up to 40dB reduction of the influence of external vibrations. The amount of reduction is limited by the sensor noise levels.

Vibration Isolation by an Actively Compliantly Mounted Sensor Applied to a Coriolis Mass-Flow Meter

In this paper, a vibration isolated design of a Coriolis mass-flow meter (CMFM) is proposed by introducing a compliant connection between the casing and the tube displacement sensors, with the objective to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of external vibrations. The transfer from external vibrations to the relative displacement measurement is analyzed and the design is optimized to minimize this transfer. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimized. The optimal tuning of the parameters is done actively by acceleration feedback. Based on simulation results, a prototype is built and validated. The validated design shows more than 24 dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.

Vibration isolation by compliant sensor mounting applied to a coriolis mass-flow meter

In this paper a vibration isolated design of the Coriolis Mass-Flow Meter (CMFM) is proposed, by introducing a compliant connection between the casing and the tube displacement sensors with the intention to obtain a relative displacement measurement of the fluid conveying tube, dependent on the tube actuation and mass-flow, but independent of casing excitations. Analyses are focussed on changing the transfer function of support excitations to the relative displacement measurement. The influence of external vibrations on a compliant sensor element and the tube are made equal by tuning the resonance frequency and damping of the compliant sensor element and therefore the influence on the relative displacement measurement is minimised. Based on simulation results, a prototype is built and validated. The validated design show a 20dB reduction of the influence of external vibrations on the mass-flow measurement value of a CMFM, without affecting the sensitivity for mass-flow.