Abstract
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 $\cdot$ 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.
Highlights
U NDER appropriate risk assessment, cooperative robots that can operate immediately next to workspaces without a safety fence are being actively developed in many fields [1]
Cooperative robots have an actuator composed of a low-power servo motor, a reduction gearbox, and a torque sensor
We developed prototype gearboxes with gear ratios between 1/48.7 and 1/378.5
Summary
U NDER appropriate risk assessment, cooperative robots that can operate immediately next to workspaces without a safety fence are being actively developed in many fields [1]. To improve the reverse driving performance of an actuator with speed reduction, researchers have developed a series elastic actuator (SEA) [15]–[18] and actuators with a built-in torque sensor [19]–[21]. The SEA includes a low-rigidity elastic element between the output of the speed reducer and the load, which measures the displacement under the load While this configuration realizes accurate torque control (i.e., good force control), it provides poor positioning accuracy. Both the SEA and built-in torque-sensing methods require additional elastic elements and sensors, which increase their cost Another type of actuator employing a low-ratio gearbox has been developed to reduce the rotor apparent inertia and to improve the actuator bandwidth by increasing the torque density of the actuator and decreasing the transmission ratio [22], [23].
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