Design and Validation of a Novel Leaf Spring-Based Variable Stiffness Joint With Reconfigurability

Compliant joints can provide safer physical human-robot interaction. To effectively balance the response bandwidth and output impedance, variable stiffness joints have been studied by many researchers. Leaf spring-based variable stiffness joint (LSVSJ) has the advantages of easy construction and large stiffness range. This article presents the design and validation of a novel LSVSJ with reconfigurability (LSJR). Compared with most of the existing LSVSJ, this novel LSJR ensures the contact performance between the roller and the leaf spring, uses a novel effective length adjustment mechanism, and provides multiple stiffness ranges. The compliance of the LSJR is generated by leaf springs. The spring is bent by two rows of rollers integrated on an adjustable slider, where the distance between the rollers can be changed so as to achieve a tighter contact between the roller and the spring. The effective length of the spring can be adjusted by changing the position of the slider locating at the intersection between a straight rail and an arcuate rail. A reconfigurable number of leaf springs provide six different stiffness ranges (e.g., 138.55-396.08 N·m/rad for single leaf spring, and 384.56-1222.60 N·m/rad for a combination of three leaf springs). By integrating a high-resolution angle sensor, the LSJR can also measure the joint torque. Moreover, the hollow shaft structure of the joint is beneficial for passing cables through it. Experiments were performed to measure the stiffness of the LSJR under different configurations, validate its efficacy in unexpected collisions, and investigate its potential to be a one-degree-of-freedom torque sensor.