Automatic stepwise load adjustment system for upper-body strength exercise

In this study, we designed and manufactured a fitness device that automatically provides exercise load by using multiple springs. To control the stiffness of the equivalent spring, a mechanism for automatically selecting the number of springs was designed. Using PID control, a hook was fixed to the correct position without a separate external sensor. The amount of deformation of the spring was measured in terms of the length that the user pulls, and the equivalent spring stiffness based on the number of selected springs was calculated such that the user's strength can be calculated.