Design And Analysis Of A Novel Compliant Constant Torque Mechanism

Constant torque mechanism is a kind of mechanism that can realize constant torque output without using external sensors and actuators.It mainly utilizes the deformation of a compliant structure's flexibility to achieve the transfer and transformation of motion,force,and energy.The use of a compliant mechanism in designing a constant torque mechanism can effectively reduce friction,improve kinematic accuracy,help integral machining and reduce overall size.Therefore,a compliant constant torque mechanism based on the crank-slider linkage with springs is designed in this paper.The main work is as follows:Based on the position closed-loop vector equation of the crank-slider mechanism with additional spring,the singular points of its kinematic branch chain are identified.Based on the principle of virtual work,an analytical equation for the position change of the random mechanism with driving torque is constructed.The equation shows that the torque-position angle curve of the mechanism has four nonlinear stiffness characteristics: the bistable behaviour,the partial negative stiffness behavior,the partial zero-stiffness behaviour and the positive stiffness behaviour.The influence of spring stiffness on the non-linear stiffness characteristics is analyzed,and the mechanism of four kinds of nonlinear stiffness characteristics is obtained.The results show that when the mechanism moves from a non-singular point to a singular point in the kinematic branching chain and finally reaches another non-singular point,the four non-linear stiffness characteristics can be presented for different spring stiffness.Reasonable allocation of the stiffness of each additional spring can make the mechanism produce constant moment characteristics.Based on the design method of additional spring mechanism with non-linear stiffness,a compliant mechanism with the same non-linear stiffness is obtained by rigid body replacement synthesis method.The influence of structural parameters of flexible bar on the nonlinear stiffness characteristics of the flexible mechanism is analyzed.Based on the pseudo-rigid body model,the equivalent spring stiffness is obtained and the structural parameters of flexible members are reasonably arranged,and considering the manufacturing process,a new type of symmetrical compliant mechanism with constant torque characteristics is designed.The designed compliant constant torque mechanism is simulated and verified by experiments.The simulation results show that there will be a constant torque region in the compliant constant torque mechanism,and the calculated value coincides with the simulation value of ANSYS in the curve of the torque-position angle,and the error is not more than 5%.The correctness of the mathematical model established in this paper is verified.By comparing the experimental results with the simulation data and theoretical data,it is concluded that this method is feasible to design a compliant mechanism with constant moment characteristics by using the additional spring crank slider mechanism.Figure [61] table [3] reference [97].