Fluid-based soft actuators are an attractive option for lightweight and human-safe robots. These actuators, combined with fluid pressure force feedback, are in principle a form of series-elastic actuation (SEA), in which nearly all driving-point (e.g. motor/gearbox) friction can be eliminated. Fiber-elastomer soft actuators offer unique low-friction and low-hysteresis mechanical properties which are particularly suited to force-control based on internal pressure force feedback, rather than traditional external force feedback using force/tactile sensing, since discontinuous (Coulomb) endpoint friction is unobservable to internal fluid pressure. However, compensation of endpoint smooth hysteresis through a model-based feedforward term is possible. We report on internal-pressure force feedback through a disturbance observer (DOB) and model-based feedforward compensation of endpoint friction and nonlinear hysteresis for a 2-DOF lightweight robotic gripper driven by rolling-diaphragm linear actuators coupled to direct-drive brushless motors, achieving an active low-frequency endpoint impedance range ("Z-width") of 50dB.

中文翻译：

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软机器人流体执行器的串联弹性力控制

基于流体的软执行器是轻巧且对人体安全的机器人的有吸引力的选择。这些致动器与流体压力力反馈相结合，原则上是串联弹性致动 (SEA) 的一种形式，其中几乎可以消除所有驱动点（例如电机/齿轮箱）摩擦。纤维弹性体软致动器提供独特的低摩擦和低滞后机械性能，特别适合基于内部压力反馈的力控制，而不是使用力/触觉传感的传统外部力反馈，因为不连续（库仑）端点摩擦无法观察到内部流体压力。然而，通过基于模型的前馈项补偿端点平滑滞后是可能的。