Design and Preliminary Evaluation of Two Tool Support Arm Exoskeletons for Gravity Compensation

We present two new arm exoskeletons based on a pantograph linkage. The exoskeletons can support a tool or load held in the hand of up to 9 kg. The pantograph linkage follows the geometry of a user’s upper arm and forearm, and supports the held mass with any arm orientation. The downward force of the load weight is supported by a fulcrum near the user’s shoulder and balanced by a countering downward force behind the user’s back. We present a Passive exoskeleton, which uses a gas spring mechanism to supply the downward force, and an Active exoskeleton that uses a motor. We analyze the forces produced by the gas spring mechanism as its geometry is varied, and explore different possible arrangements of the gas spring mechanism or motor relative to the pantograph linkage. We derive the equations governing the pantograph linkage, and simulate the forces resulting from the two exoskeletons. We conduct measurements of the forces produced by each exoskeleton, and compare them with the simulated forces.