A new mechanical design method of compliant actuators with non-linear stiffness with predefined deflection-torque profiles

Abstract Compliant actuators are able to perform the safe interaction between robotics and human or unstructured environment owing to their intrinsic compliant attribute. A compliant actuator with constant stiffness is easy to be designed but has some limitations in bandwidth. Compliant actuators with variable stiffness get better ability of environment adaption, but their mechanisms are almost complex and bulky. This paper proposed a new design methodology of compliant mechanisms whose stiffness matches the predefined a non-linear stiffness profile “small loads, low stiffness and large loads, high stiffness”, which is a common scenario of interaction in physical world. Owing to this idea, a compact compliant mechanism with predefined non-linear stiffness profile is proposed where a cantilever is used as basic elastic element with a special curve profile contacting with a roller. The new proposed actuator was adopted in compliant joints of rehabilitation robotic developed by ourselves. Meanwhile, three kinds of deflection-torque curves were implemented in simulation. At last, experimental and simulation results proved that the proposed method was effective to design the compliant mechanism to fulfill the predefined deflection-torque relationship of compliant non-linear stiffness actuators.