Cam Profile Generation for Cam-Spring Mechanism With Desired Torque

Commercial springs have linear characteristics. Nevertheless, in some cases, nonlinear behavior (e.g., nonlinear torque) is desired. To handle that, a cam-spring mechanism with a specified cam profile was proposed in our previous work. In this paper, to further study the cam profile generation, a new convenient design method is proposed. First, the model of cam-spring mechanism considering the friction force is analyzed. Based on this model, sorts of derivation processes are conducted for obtaining the expression of spring torque. When the friction coefficient is zero, the analytical solution of the equation (spring deformation) is derived. However, in practice, where the friction coefficient is not zero, an analytical solution is not available. Therefore, a numerical solution is sought. Then, with the obtained spring deformation, the cam profile and pitch curve are generated. Results of an experiment conducted to verify the new method show that the cam profile generated by the direct derivation method can precisely mimic the desired torque characteristics. In addition, the hysteresis induced by the friction force in the cam-spring mechanism is also studied. By increasing the spring stiffness, spring free length, and the cam eccentricity, the hysteresis in the cam-spring mechanism can be decreased.