A Continuously Variable Transmission System Designed for Human–Robot Interfaces
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Within a predefined limit, continuously variable transmission (CVT) systems can continuously vary the power transmission ratio. The transmission in CVTs is achieved via friction, belt or gear systems. If CVT designs can incorporate backdrivability, independent output position and impedance variation, shock absorbtion, and low mass and inertia, they can be employed in human–robot interfaces. Among various types of CVT designs, the two-cone drive CVT designs have a major drawback since the output torque and position cannot be changed independent of each other. The friction wheel used in this design does not have a holonomic motion capability and causes this inconvenience. In order to overcome this problem, a sphere is used in this work for the CVT design as the transmission element. In addition, it is stated in the literature that common CVT drive systems do not have the capability to be used in cyclic bidirectional motion. In the presented CVT design, a second sphere is added to the system with two springs from the lower part of the cones for pretension in order to solve the bidirectional transmission problem. In this paper, the working principle and conceptual design details of the novel two-cone CVT drive are presented. Experimental results showed that the novel CVT has the capacity to transmit bidirectional power with some accuracy. © 2021, Springer Nature Singapore Pte Ltd.