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Summary form only given as follows. A mechanically passive device is described which, when controlled by an appropriate algorithm, restricts the user to move the tip of the device along a specified but arbitrary path. One advantage of such a device is safety from malfunctions of the controlling actuators. A novel approach for controlling such a device is presented, along with some results of the control algorithms that were implemented on the testbed device.
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Gomes et al. (2002) studied this question.