Torque control of the European robotic ARM (ERA)

As part of the European contribution to the International Space Station (ISS), the European Robotic Arm (ERA) is designed under contract from the European Space Agency. Among ERA's plus-points is that it helps to minimise joints output torque disturbances and vibrations during routine tasks. Noise created by usual drive assembly are often harmful and classical torque ripple peak to peak values of 20-40% of mean torque can typically be reached. The challenging project low ripple requirements allowed to develop a special electronics capable of introducing sophisticated currents in the motor phases. The present paper will first make a brief description of the mechanical part or Motor Unit, then, a detailed noise and perturbation analysis correlated to a torque compensation philosophy will be presented, illustrating the strategy to determine the digital tables storing the adequate phase current shapes. The next step will be the description of the Electronics Unit, outcome of a comprehensive thermal environmental and quite restrictive budget analysis. Protections philosophy, electrical and mechanical interfaces, mass and power budgets will be addressed. The on-going verification and qualification program will finally be addressed pointing out the very good torque ripple performances achieved after a full torque ripple calibration process.