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.

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The actuators in robot joints are often equipped with reduction gears for increasing the power output. However, a high reduction ratio is required to decrease the backdrivability. In this paper, the backdrivability is improved by installing motor-and load-side encoders in the reduction gear. The proposed method comprises a backdrive assist control, feedforward friction compensation, and estimation and feedback of the load-side disturbance by using a multiencoder-based disturbance observer. The angular transmission error in the reduction gear is treated as a disturbance that affects the motor. This disturbance is estimated from the motor-and load-side angular accelerations, and provides feedback assistance to the backdrive. The effectiveness of the proposed method is verified through experiments.

This paper discusses solution for the singular configuration problem in wheel-legged mobile robot. First, we show the kinematic constraints of wheel-legged mobile robot. We describe the singular configuration problem at the inverse kinematics calculation. Next, we show a method using the redundancy in kinematic constraints to the acceleration level as solution of the singular configuration problem. Furthermore, we describe a new singular configuration problem that occurs in low speed wheeled locomotion. Finally, the damped least squares method is applied to solve the new singular configuration. In addition, we propose a design of a damping factor in the damped least squares method. The effectiveness of the solution is validated by three-dimensional simulation.

Wheel-legged mobile robots (i.e., robots that use leg and wheel mechanisms) have the potential for efficient movement in response to the environment. Singular configuration is an inevitable problem in wheel-legged mobile robots and must be solved to realize motion. This paper proposes a simplification of the motion generation method in the singular configuration of a wheel-legged mobile robot. The problem of inverse kinematic calculations in a wheellegged mobile robot is first modeled, and a solution method is proposed using an extension of the constraints to the acceleration level and the redundancy of the robot. The singular configuration problem in the low-speed region is then solved using the Levenberg-Marquardt method. A simple decision method using a weighted matrix for the damping factor is also proposed. The method is then verified using a three-dimensional simulation and an experiment.