Design and experimental study of a passive power-source-free stiffness-self-adjustable mechanism

Passive variable stiffness joints have unique advantages over active variable stiffness joints and are currently eliciting increased attention.Existing passive variable stiffness joints rely mainly on sensors and special control algorithms,resulting in a bandwidth-limited response speed of the joint.We propose a new passive power-source-free stiffness-self-adjustable mechanism that can be used as the elbow joint of a robot arm.The new mechanism does not require special stiffness regulating motors or sensors and can realize large-range self-adaptive adjustment of stiffness in a purely mechanical manner.The variable stiffness mechanism can automatically adjust joint stiffness in accordance with the magnitude of the payload,and this adjustment is a successful imitation of the stiffness adjustment characteristics of the human elbow.The response speed is high because sensors and control algorithms are not needed.The variable stiffness principle is explained,and the design of the variable stiffness mechanism is analyzed.A prototype is fabricated,and the associated hardware is set up to validate the analytical stiffness model and design experimentally.

Design and Analysis of a 2-DOF Actuator with Variable Stiffness Based on Leaf Springs

Variable Stiffness Actuator(VSA)is the core mechanism to achieve physical human–robot interaction,which is an inevitable development trend in robotic.The existing variable stiffness actuators are basically single degree-of-freedom(DOF)rotating joints,which are achieving multi-DOF motion by cascades and resulting in complex robot body structures.In this paper,an integrated 2-DOF actuator with variable stiffness is proposed,which could be used for bionic wrist joints or shoulder joints.The 2-DOF motion is coupling in one universal joint,which is different from the way of single DOF actuators cascade.Based on the 2-DOF orthogonal motion generated by the spherical wrist parallel mechanism,the stiffness could be adjusted by varying the effective length of the springs,which is uniformly distributed in the variable stiffness unit.The variable stiffness principle,the model design,and theoretical analysis of the VSA are discussed in this work.The independence of adjusting the equilibrium position and stiffness of the actuator is validated by experiments.The results show that the measured actuator characteristics are sufficiently matched the theoretical values.In the future,VSA could be used in biped robot or robotic arm,ensuring the safety of human–robot interaction.