In this paper we present an approach to estimating the contact state between a robot and its environment during task execution. Contact states are modeled by constraint equations parametrized by timedependent sensor data and time-independent object properties. At each sampling time, multiple model estimation is used to assess the most likely contact state. The assessment is performed by a hidden Markov model, which combines a measure of how well each set of constraint equations fits the sensor data with the probability of specific contact state transitions. The latter is embodied in a task-based contact state network. The approach is illustrated for a three-dimensional peg-in-hole insertion using a tabletop manipulator robot. Using only position sensing, the contact state sequence is successfully estimated without knowledge of nominal property values. Property estimates are obtained for the peg dimensions as well as the hole position and orientation.
This paper presents the design and testing of a multi-channel vibrotactile display composed of cylindrical handle with four embedded vibrating elements driven by piezoelectric beams. The experimental goal of the paper is to analyze the performance of the device during a teleoperated force controlled task. As a test bed, a teleoperator system composed of two PHANToM™ haptic devices is used to trace a rectangular path while the operator attempts to maintain a constant force at the remote manipulator's tip. Four sensory modalities are compared. The first is visual feedback alone. Then, visual feedback is combined with vibration, force feedback, and force feedback plus vibration. Comparisons among these four modes are presented in terms of mean force error. Results show that force feedback combined with vibration provide the best feedback for the task. They also indicate that the vibrotactile device provides a clear benefit in the intended application, by reducing the mean force errors by 35 percent when compared to visual feedback alone.
This paper presents the design and testing of a multi-channel vibrotactile display. It is composed of a cylindrical handle with four embedded vibrating elements driven by piezoelectric beams. Vibrations are transmitted to the hands through arrays of pins. The device was tested in sensory substitution for conveying force information during a teleoperated peg insertion. Results show that the device is effective in reducing peak forces during the insertion task.
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