A Dual-Mode Pneumatic Gravity Compensation Device

This study presents a novel dual-mode pneumatic gravity compensation device, which comprises a pneumatic cylinder, a rope–pulley system, and a gear mechanism. It employs a rope–pulley mechanism that allows the compensation force to depend solely on the load mass and remain independent of any joint rotation angle, thereby eliminating the need for complex control algorithms. The device operates in two modes—active and passive—adapting to varying operational conditions. In active mode, dynamic gravity compensation is achieved by regulating air pressure through an empirically calibrated constant pressure offset. In passive mode, a sealed vacuum chamber is created on one side of the cylinder, allowing atmospheric pressure alone to generate the required compensation force for a given load, without any external energy supply during operation. A prototype was constructed to validate the aforementioned principle. The results show that the device can maintain joint torque near zero, allowing the load to remain in a “0-gravity” suspended state. To demonstrate improved energy efficiency and performance in robotic systems, this study applies the gravity compensation device to a robotic arm and a floating backpack. The device enables the robotic arm to support loads beyond the motor's torque limit while reducing energy consumption in the joints. In addition, it offers power-off self-holding capabilities and simplifies the drag-teaching process. In the floating backpack application, the device effectively mitigates shoulder impact during exercise, reducing peak shoulder pressure by 59.7%.