Research On Design And Control Of A Variable Stiffness Joint Actuator

Robots in the unstructured environment will inevitably make contact and collision with people or other things.Pure rigid joint drive has certain safety hazards.Variable stiffness and compliant actuation can effectively reduce human interaction collision damage,not only in the field of rehabilitation.It can provide a more comfortable state,and in the bionic field can effectively utilize the variable stiffness joint actuator flexible component energy storage characteristics to play a higher advantage.The variable stiffness joint actuator can not only meet the position requirements like the traditional rigid drive,but also adjust the output stiffness of the system.The environmental adaptability is more advantageous than the traditional rigid drive.In view of the current variable stiffness actuators,the limited range of adjustment,the slow response speed,the serious energy consumption and the heavy size of the structure,this paper proposes an effective arm length change based on the elliptical mechanism-like variable spring.Stiffness joint actuators and the following studies were carried out:Firstly,according to the specific application situation,the design index is determined,and the effective spring length of the variable spring is proposed to arrange the rotation axis and the force action point.Various layout schemes are proposed respectively.The comprehensive adjustment range is selected to make the structure compact and the most effective variable stiffness is selected.The scheme simplifies the leaf spring into a cantilever beam and establishes a mechanical model.The approximate variable stiffness characteristic is analyzed under small deformation conditions.The size optimization of the flexible component is optimized according to the technical target,and higher design precision is sought.The variable stiffness is based on the elliptical integral method.Large deformation analysis of mechanical models.Secondly,the three-dimensional model is built according to the dimensional parameters of the flexible component to carry out the overall structural design.The modular design mainly includes the stiffness adjustment mechanism,the main transmission mechanism and the stiffness transmission mechanism.The selection of related components was completed,and the finite element strength check was performed on the key components that were easily deformed by the load.The joints with variable stiffness were often subjected to impact loads,and the transient dynamic analysis of the output was performed.Again,the variable stiffness output approximation is seen as a transient fixed stiffness compliant drive that can be simplified to a transient elastic system.And establish its dynamic model to further improve the control system design.Considering that the output stiffness is a binary nonlinear relationship between the joint deflection angle and the effective arm length under large deformation conditions,the definition of the rotational stiffness requires differential operation.To ensure the differential is effective,the flexible torque and the output stiffness are approximate fitted.Stiffness for the planning of the dualmotor cooperative trajectory,as well as the selection and construction of the hardware system.Finally,the experimental platform was set up,and the proposed variable stiffness joint actuators were tested.The static stiffness identification,step tracking experiment and flexible hitting experiment were carried out,and the variable stiffness performance was evaluated objectively.