The cLVSM: A Novel Compact Linear Variable Stiffness Mechanism Based on Circular Beams

Variable stiffness mechanisms (VSMs) are a class of compliant mechanisms that can adjust their intrinsic stiffness, which promises to be beneficial in applications needed to interact with the environment, such as collaborative robots, wearable robots, and polishing robots. This paper presents the design and optimization of a novel linear VSM, called cLVSM, to produce linear motion, conversely to the majority of VSMs designed to perform rotary motion. By changing the effective length of specially designed circular beams, the cLVSM is capable of continuous stiffness regulation from a minimum value to almost rigid. Different from the VSMs which need rotation-to-translation converting mechanisms for stiffness regulation, the stiffness of the proposed design is adjusted by directly rotating the beams without the use of additional mechanisms, which contributes to improving the structural compactness, and reducing the energy loss and error in transmission. Moreover, the beam rotation needed to regulate the stiffness is almost perpendicular to the beam deflection force, which helps to reduce the torque needed for stiffness regulation. The stiffness model of the proposed VSM is developed using the screw theory, and the design parameters are optimized using the genetic algorithm. The effectiveness of the mathematical model and the performance of the design are verified by simulation and experiments.