Abstract: A decubitis mat includes a plurality of individual cells (16 which are pressurized by air. A polymer sensor/vent structure (20) is mounted on the top surface of each cell and defines a plurality of polymer filled channels (28) and a vent valve (26) which is biased to a closed position. As a body resting on the mat heats the polymer, it undergoes a phase change an expands, causing biasing forces (30) which bias the vent valve to open, permitting air in the cell to be released providing air flow to the body.

Abstract: An actuator (A) includes a body (10) in which a plurality of chambers or bores (34) are defined. The bores are interconnected at an inner end by an elongated passage (30). A heater element (32) extends along the elongated passage. The elongated passage and the inner portion of each chamber or bore are filled with a polymeric material which expands and flows on heating, preferably undergoing a solid to liquid phase change. Extensible members (12), such as pistons, diaphragms, bellows, or the like, are mounted in the bores or wells. When the heater heats the polymeric material causing it to expand and flow, the extensible elements (12) extend under high force with limited travel. In one embodiment, the extension of the extensible members moves a thrust bearing (B) causing frictionally engageable plates (18, 22) of a friction member assembly (C) to engage.

Abstract: An operator selects an operating characteristic, such as a degree of extension or force of an extension member (66) of a thermal actuator (16), with an input circuit (10). The input control circuit generates a reference signal. A feedback circuit (18) monitors a characteristic of the thermal actuator such as a temperature of its internal polymer, extension of the extension member, force, or the like, and generates a corresponding feedback signal. An error circuit (12) compares the reference and feedback signals and generates an error signal in accordance therewith. A dither circuit (30) generates an oscillating dither signal that is superimposed on one of the control and feedback signals before comparison by the error circuit. A power conversion circuit (14) adjusts an amount of electrical power supplied to a heating element (54) of the thermal actuator in accordance with the error signal.