Reverse pneumatic artificial muscles (rPAMs): Modeling, integration, and control

Abstract

Despite offering many advantages over traditional rigid actuators, soft pneumatic actuators suffer from a lack of comprehensive, computationally efficient models and precise embedded control schemes without bulky flow-control valves and extensive computer hardware. In this article, we consider an inexpensive and reliable soft linear actuator, called the reverse pneumatic artificial muscle (rPAM), which consists of silicone rubber that is radially constrained by symmetrical double-helix threading. We describe analytical and numerical static models of this actuator, and compare their performance against experimental results. To study the application of rPAMs to operate underlying kinematic linkage skeletons, we consider a single degree-of-freedom revolute joint that is driven antagonistically by two of these actuators. An analytical model is then derived, and its accuracy in predicting the static joint angle as a function of input pressures is presented. Using this analytical model, we perform dynamic characterization of this system. Finally, we propose a sliding-mode controller, and a sliding mode controller augmented by a feed-forward term to modulate miniature solenoid valves that control air flow to each actuator. Experiments show that both controllers function well, while the feed-forward term improves the performance of the controller following dynamic trajectories.

Soft Robotics: A Review of Recent Developments of Pneumatic Soft Actuators

“…This limited computation creates difficulty in avoidance of autonomous obstacles and movement Various soft robots with various actuation methods (a) Actuator with multi-material 3D printing [11]. (Open Access); (b) Soft linear actuator [12]. (Open Access); (c) Design for bidirectional bending [13].…”

“…Soft robots are controlled in low-level using pressure transducers which provides differences in actuator compliance, or volume control using strain sensors. Volume control is very effective in configuration control and assists setting a maximum safe displacement [1,4,7,12,32]. Valve sequencing control is controlling the body-segment actuator by pressurizing the actuator for a period by turning the valve on and off [10].…”

“…Due to the flexibility of the soft robots, they can manipulate their bodies, especially a gripper or finger [15,38], to grab objects of varying size and shape. Since the material of soft robotics is modeled after biological systems, soft robotics make for a very good option in the field of medical and wearable devices due to their flexibility and absorption factors, such as seen in recent reverse pneumatic artificial muscle technology [12,13,39] and manipulators for minimally invasive surgery [40].…”

Soft Hybrid Wave Spring Actuators

“…The existing pneumatic actuator used in this work is the reverse pneumatic artificial muscle (rPAM), a soft linear actuation concept inspired by biological anatomy, which we introduced in 2015 and have further analyzed . This actuator is called the rPAM because it operates on similar principles to the traditional PAM (also known as the McKibben actuator), only with a reversed direction of actuation (similar to the work of Gaylord et al).…”

“…Our approach utilizes these fiber‐reinforced elastomer tubes either in a prestrained state when driving a rigid kinematic skeleton, or as part of a soft bending continuum manipulator (a segment that bends gradually, and not at along a single axis). We have previously used rPAM actuators to drive rigid joints or as part of soft bending segments …”