Thermoplastic variable stiffness composites with embedded, networked sensing, actuation, and control

Abstract

We present a composite material consisting of a thermoplastic base material and embedded, networked sensing, actuation, and control to vary its stiffness locally based on computational logic. A polycaprolactone grid provides stiffness at room temperature. Each polycaprolactone element within the grid is equipped with a dedicated heating element, thermistor, and networked microcontroller that can drive the element to a desired temperature/stiffness. We present experimental results using a 4 × 1 grid that can assume different global conformations under the influence of gravity by simply changing the local stiffness of individual parts. We describe the composite structure and its manufacturing, the principles behind variable stiffness control using Joule heating, local sliding mode control of each polycaprolactone bar’s temperature and function, and limitations of the embedded multi-hop communication system. The function of the local temperature controller is evaluated experimentally.

Morphing Metal and Elastomer Bicontinuous Foams for Reversible Stiffness, Shape Memory, and Self‐Healing Soft Machines

“…[ 1,2 ] When touched, the sea cucumber can rapidly and reversibly increase the stiffness of its skin for protection. [ 3,4 ] Here, we present a synthetic composite material that demonstrates some of these abilities (i.e., stiffness variation and shape morphing) and incorporate this material into a soft robotic tentacle and morphing wing.Recent work on variable stiffness composites based on inducing phase changes in polymers [5][6][7][8][9] and metals [ 10,11 ] has begun to show promise in overcoming the usual tradeoff between shape adaptability and load-bearing capability. These synthetic materials are often layered composites [ 9 ] or contain soft microchannels fi lled with a low melting temperature material; [ 8,11 ] when the phase change material is molten, these composites deform easily.…”

Flexible Medical Devices: Review of Controllable Stiffness Solutions

“…An overtube for endoscopic applications based on LMPA is described in [36], using hot water to activate the change in stiffness. Numerous low melting point polymers are available with various transition temperatures [13,38]. The performances of such solutions will depend on the design, which could be optimized for obtaining very high performances [39].…”

“…The heat transmission can be performed by using a water flow [38,39], air [61], Joule losses [13,62] or magnetic induction [57]. Conducting polymers actuated with low voltages (<1 V) are used to develop a new catheter in [154].…”

“…Thermoplastics can be used for grippers with variable stiffness fingers [39] and for smart innovative robotic structures with enhanced properties [13]. A gripper made of small bags filled with MR fluids and coupled to a Kuka robot allows for pick and place operations of multiple objects (typically food) [70].…”

“…Variable stiffness solutions can be used in robotics for the development of a foot [9], in adaptive vibration damping [10], in bio-engineering for developing extracellular matrix [11], in architectural structures, in haptic interfaces or in robotics and grippers [12]. The change of stiffness can also be used for universal orthopedic casts, customized seatings and adaptive surfaces for aerodynamism properties [13].…”