Patent ID: 8712591

Claim:
A person-support apparatus comprising an inflatable support structure, a variable output pump in fluid communication with the inflatable support structure, wherein the variable output pump provides a flow of fluid to the inflatable support structure, and a controller coupled to the variable output pump, the controller including a circuit having an output for controlling the output of the pump, a processor in electrical communication with the circuit and operable to vary an output of the circuit, a memory device including instructions, that when executed by the processor, cause the processor to control the circuit to vary the output of the pump to maintain a constant flow from the pump, wherein the person-support apparatus further comprises a first sensor operable to sense a pressure in the inflatable support structure and to communicate a signal indicative of the pressure in the inflatable support structure to the processor, wherein the processor includes instructions that, when executed by the processor, control the output of the pump by using the time rate of change of pressure in the inflatable support structure to determine an error term, calculate an integral term of a proportion integral control based on the error term, calculate a proportional term of a proportional integral control based on the error term, adjust the gain of the integral term if the error term has a magnitude less than a threshold, and vary the output of the pump based on the proportional integral value.