On the Design of the Gravity Balancer Using Scotch Yoke Derivative Mechanism

Design of the gravity balancer prototypes based on the modified Scotch yoke type spring mechanism is presented. Followed by the brief description of the conceptual design and validation of the method, design of a one degree-of-freedom (dof) rotary system is proposed. In the 1st generation prototype model, the spring-gravity system is designed as a whole, while, in the 2nd generation model, the gravity balancer is designed as a modular unit for easy adjustment and simple replacement. The friction force due to the prismatic joints of a Scotch yoke derivative mechanism for the latter model has been greatly reduced by using a bushing bearing along with a guidance pole. As a consequence, by showing the equilibrium of the rotary system being sensitive to the fine-tuned position of the end-effector payload, the 2nd prototype model successfully demonstrates the gravity balancing capability of the entire system at all configurations within its range of motion. The issues related to the design of the one-dof gravity balancer are discussed, and the potential use of such balancers in the multiple-dof system is also proposed.