For rigid body robot manipulators, the computed torque approach provides asymptotic stability for tracking control tasks. However, the state dependent matrices needed to complete the computed torque algorithm are normally unknown and possibly too complex for a real-time implementation. This paper proposes a simple controller with computed-torque-like structure enhanced by integral sliding mode, having pole-placement capability. For the reduction of the chattering effect generated by the sliding mode part, the integral sliding mode is posed as a perturbation estimator with quasi-continuous control action provided by an additional low-pass filter. The time-constant of the latter tunes the controller functionality between the perturbation compensation and a pure integral sliding mode control, as well as between chattering reduction and system robustness. A comparative simulation study between conventional sliding mode control, integral sliding mode control, and integral sliding mode in form of a perturbation estimator for a two-link robot arm validates the proposed design. copyright 2008 Taylor & Francis [accessed 2014 April 1st

The control of the evolution of the crystal size and shape distribution (CSSD) during crystallization processes is an important task in crystallization, as the final CSSD decisively influences the physical and solid state properties of crystalline material. This work utilizes sequential growth and dissolution cycles, which turn out to result in an essentially enlarged region of attainable crystal sizes and shapes. Using potassium dihydrogen phosphate as a model substance, such a cyclic crystallization process is realized in a batch scale and in a novel, fully automated, and controlled manner. To this end, a novel observer setup is presented, which is based on video microscopy, and facilitates the real-time monitoring of the evolution of the crystal size and shape distribution. Given this information, optimal strategies for the control of supersaturation profiles as well as CSSD are experimentally successfully implemented, proving a reliable and high-precision generic control scheme for crystal shape manipulation. The proposed theoretical and experimental research results are expected to be of use in targeted crystal size and shape manipulation in chemical and pharmaceutical industries.

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