  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.
