Adjustable Stiffness CLSM and Its Application in a Gravity Off-Load System

Gravity offloading technology is crucial in scientific research and engineering, especially when simulating microgravity. Its core is active constant force control, which is a research hotspot in this field. Developing efficient low-stiffness mechanisms improves the force control accuracy of active constant force systems (ACFSs). This paper proposes a novel compliant low-stiffness mechanism (CLSM) that achieves quasi-linear characteristics by superimposing the linear positive stiffness of the tension spring and the negative stiffness of the V-shaped compliant beam. An efficient optimization design method for CLSM is proposed, simplifying the compliant mechanism design. The optimized CLSM can achieve quasi-linear low-stiffness output in a large displacement range with adjustable stiffness and load capacity. In addition, the optimized CLSM is characterized by high load-bearing capacity, low inertia, small volume, and low friction. A new lightweight and miniaturized ACFS based on CLSM is designed to meet the design requirements of the multicable gravity offloading system. The CLSM exhibits excellent dynamic characteristics of low inertia and friction, reducing the system’s internal disturbances while meeting the stiffness and load-bearing capacity requirements of ACFSs. The experimental prototype is established to test the ACFS. The results indicate that the control accuracy of ACFS with CLSM is significantly improved under dynamic excitation.