For safety purposes, cooperative robots are installed with an actuator composed of a low-power servo motor, a reduction gearbox, and a torque sensor. When cooperative robots make contact with humans or the environment, they must detect the contact force with a force sensor, a contact sensor, or a joint torque sensor. Equipping these sensors increases the cost and size of the application, but can be avoided under sufficient backdrivability of the actuator. To this end, we propose a method that maximizes the power transmission efficiency of the 3K planetary reduction gearbox and develop a prototype of the backdrivable reduction gearbox called the bilateral drive gear. For this maximization, the profile shift coefficients and the number of teeth are decided under some conditions. The forward-and backward-driving efficiencies of the prototype gearbox were 89.0% and 85.3%, respectively, and the reverse-drive starting torque was 0.020 N•m. The drive efficiency of the same gearbox with uncorrected teeth is 68.5%. The forward-driving efficiency was 20.5% higher than the nonoptimized one. We confirmed that prototype gearboxes with different gear ratios are easily backdrivable by hand.

This paper proposes a novel algorithm to locate a mobile terminal (MS) in a cellular system. The proposed algorithm is based signal strength measurements. It considers the fluctuation in received signal strength due to shadowing, and obtains probability density functions (pdf's) of the propagation distances. An overall pdf, obtained by combining the pdf's, is used to determine MS location. Results obtained from computer simulations and field experiments show that the proposed algorithm is more accurate than the conventional cell-based algorithm.

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In our previous paper [1], we simulated an accumulation-mode MOSFET with an epitaxial layer channel (epi-channel) that had a high channel mobility. In this paper, we experimentally show that channel mobility is enhanced by the epi-channel. On varying the thickness of the epi-channel, the channel mobility improved from a few cm2/Vs to 100 cm2/Vs. Finally, we show that the “Normally-off” accumulation MOSFET with a 720 V breakdown voltage has a low on-resistance (10.4 m1cm2) and that the 3 × 3 mm2 accumulation MOSFET operates over 10 A and its on-resistance is 19 m1cm2.

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