Mechanical design and analysis of a novel variable stiffness actuator with symmetrical pivot adjustment

The safety of human-robot interaction is an essential requirement for designing collaborative robotics.Thus,this paper aims to design a novel variable stiffiiess actuator(VSA)that can provide safer physical human-robot interaction for collaborative robotics.VS A follows the idea of modular design,mainly including a variable stiffiiess module and a drive module.The variable stiffiiess module transmits the motion from the drive module in a roundabout maimer,making the modularization of VS A possible.As the key component of the variable stiffiiess module,a stiffness adjustment mechanism with a symmetrical structure is applied to change the positions of a pair of pivots in two levers linearly and simultaneously,which can eliminate the additional bending moment caused by the asymmetric structure.The design of the doubledeck grooves in the lever allows the pivot to move freely in the groove,avoiding the geometric constraint between the parts.Consequently,the VSA stiffiiess can change from zero to infinity as the pivot moves from one end of the groove to the other.To facilitate building a manipulator in the future,an expandable electrical system with a distributed structure is also proposed.Stiffiiess calibration and control experiments are performed to evaluate the physical performance of the designed VSA.Experiment results show that the VSA stiffiiess is close to the theoretical design stiffness.Furthermore,the VSA with a proportional-derivative feedback plus feedforward controller exhibits a fast response for stiffiiess regulation and a good performance for position tracking.