The quality of telepresence provided by a force-reflecting teleoperator is determined, for the most part, by the fidelity of the contact-force information fed back to the operator. These fed-back forces, however, also directly influence system stability, and in this paper we investigate the relationship between fidelity and stability with a view toward understanding how stability considerations impose fundamental limits on system performance. The key idea of our work is to draw an explicit distinction between the information conveyed by the force signal and the energy inherent in that signal. Using known physiological properties of the operator, we argue that there exists a natural partitioning between information and energy wherein information is conveyed at frequencies above roughly 30 Hz, while the energetic interaction between the slave and the environment takes place at frequencies below this. We embody this distinction in a two-channel framework that we claim provides insight into the design of force-reflecting systems. Using a 1-DOF model, we study the effect of various system characteristics, notably mass, stiffness, and damping properties, on performance and stability. This model is used to derive expressions for the maximum force-reflection ratio that guarantees stability against pure-stiffness environments and to investigate the role of various compensation elements, including local force control around the slave. Finally, a framework is developed for force-reflecting teleoperation that maximizes the force information conveyed to the operator, subject to the constraints imposed by stability considerations.

When the leg rods of a fully in-parallel manipulator are fixed in their lengths, it is usual that the device can be assembled in several distinct ways. Sometimes it happens that motion between such assemblies can take place such that the linkage is never at a special configuration; that is, a configuration where the moving-platform body acquires uncontrollable freedom relative to the base. The possibility of such motion has implications for control. Focusing on 3-3 devices, we present a geometric explanation of how these motions arise, and give a sufficient condition for their existence. For the 3-3 planar-motion device, we show that never-special assembly changing motions can be excluded by making platform and base triangles similar, and we conjecture that appropriate, perhaps identical, specialization for the octahedral manipulator has the same effect.

This paper describes the behavior of a commercial light detection and ranging (LiDAR) sensor in the presence of dust. This work is motivated by the need to develop perception systems that must operate where dust is present. This paper shows that the behavior of measurements from the sensor is systematic and predictable. LiDAR sensors exhibit four behaviors that are articulated and understood from the perspective of the shapeof-return signals from emitted light pulses. We subject the commercial sensor to a series of tests that measure the return pulses and show that they are consistent with theoretical predictions of behavior. Several important conclusions emerge: (i) where LiDAR measures dust, it does so to the leading edge of a dust cloud rather than as a random noise; (ii) dust starts to affect measurements when the atmospheric transmittance is less than 71%-74%, but this is quite variable with conditions; (iii) LiDAR is capable of ranging to a target in dust clouds with transmittance as low as 2% if the target is retroreflective and 6% if it is of low reflectivity; (iv) the effects of airborne particulates such as dust are less evident in the far field. The significance of this paper lies in providing insight into how better to use measurements from off-the-shelf LiDAR sensors in solving perception problems. C 2017 Wiley Periodicals, Inc.

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