# An Inverting-Tube Clutching Contractile Soft Pneumatic Actuator

## TL;DR

This paper introduces the InVACC, a soft pneumatic actuator with an integrated clutch that can contract significantly and support high loads, promising advancements in robotics and wearable haptics.

## Contribution

The paper presents a novel contracting soft pneumatic actuator combined with a soft clutch, enabling significant contraction and high load support in a simple, synergistic design.

## Key findings

- The InVAC can contract to one third of its length with constant force per pressure.
- The InVACC clutch can support up to 120 N before slipping.
- Hysteretic losses depend on actuation direction and rate.

## Abstract

This paper presents the simple synergistic combination of a novel contracting soft pneumatic actuator with a soft clutch (linear brake). The device is designated the Inverting-tube Vacuum ACtuator with Clutch (InVACC). The actuator alone (no clutch) is designated "InVAC" and uses vacuum pressure to invert a thin tube into a shorter section of reinforced flexible tubing. The inverting tube acts as rolling diaphragm and a flexible tendon. This allows the actuator to contract to one third of its extended length. The contractile-force-per-unit-pressure is approximately constant over the stroke. The theoretical maximum of this force is the product of the vacuum gauge pressure and half the interior cross-sectional area of the tube. The experimental evaluation revealed hysteretic losses that depend on the actuation direction and rate. With -81 kPa, the prototype produced 12.7 N of tension during extension and 7.5 N during retraction. The reinforced tubing of the InVAC was integrated with an inner collapsible "clutching" tube to create an InVACC. The clutch is engaged by applying a positive pressure between the reinforced tube and the clutching tube, which collapses the clutching tube onto the flexible tendon. With a pressure of 50 kPa, the InVACC clutch tested in this work was able to support a peak tensile load of 120 N before slipping. Though the fatigue life of the current prototypes is limited, improved fabrication methods for this novel actuator/clutch concept will enable new applications in robotics and wearable haptic systems.