Systems, methods, and devices for fluidizing a fluidizable medium

1. A system for fluidizing a fluidizable medium, comprising:

a person support structure including a chamber containing a fluidizable medium and a plenum in fluid communication with the chamber,

a fluid supply in fluid communication with the plenum, the fluid supply having a variable fluid flow rate;

a sensor sensing the fluid pressure of the fluid in the plenum;

a controller electrically coupled to the sensor and the fluid supply, the controller varying the output of the fluid supply while measuring the fluid pressure within the plenum to achieve a desirable level of fluidization of the fluidizable medium by monitoring the pressure change as the fluid supply flow rate is increased and determining that an acceptable level of fluidization is achieved by detecting that the change in pressure as a function of the increase in fluid supply flow rate is indicative that the system has exceeded a fluidization threshold for the particular operating conditions and maintaining the flow rate of the fluid supply to exceed the fluidization threshold.

2. The system of claim 1 , wherein the desirable level of fluidization is proportional to a fluid flow rate of at least about 25 cubic feet per minute (CFM) through the fluidizable medium for a fluidizable medium depth of about 9inches.

3. The system of claim 1 , wherein the desirable level of fluidization is proportional to a fluid flow rate of between about 40 CFM and about 65 CFM through the fluidizable medium for a fluidizable medium depth of about 9 inches.

4. The system of claim 1 , wherein the desirable level of fluidization is determined as a function of a fluidization threshold of the fluidizable medium.

5. The system of claim 1 , wherein the desirable level of fluidization is proportional to a fluid flow rate of between about 25 CFM and about 35 CFM through the fluidizable medium for a fluidizable medium depth of about 9 inches.

6. The system of claim 1 , wherein the desirable level of fluidization is proportional to the rate of change of the fluid pressure within the plenum.

7. The system of claim 1 , wherein the controller controls the operation of the fluid supply as a function of the difference between the desirable level of fluidization and a level of fluidization of the fluidizable medium sensed by a second sensor that measures movement of the fluidizable medium.

8. The system of claim 1 , wherein the desirable level of fluidization includes the fluid flow rate through the fluidizable medium at about a fluidization threshold of the fluidizable medium increased by a predetermined amount.

9. The system of claim 1 , wherein the desirable level of fluidization includes the lesser of a first level of fluidization at a first time and a second level of fluidization at a second time so long as the lesser is greater than a fluidization threshold of the fluidizable medium.

10. The system of claim 1 , wherein the controller controls the fluid supply as a function of the difference between the pressure in the plenum at a fluidization threshold of the fluidizable medium and a pressure in the plenum at the desirable level of fluidization.

11. The system of claim 1 , wherein the desirable level of fluidization includes the lesser of a first level of fluidization at a first time and a second level of fluidization at a second time, if the lesser is less than a fluidization threshold of the fluidizable medium then the lesser is increased by a predetermined amount.

12. The system of claim 1 , wherein the controller increases a level of fluidization based on the pressure change as a function of the increase in fluid supply until a fluidization threshold is reached, and further increase the level of fluidization until an acceptable level of fluidization is achieved by detecting that the increase in pressure as a function of the increase in fluid supply has exceeded the fluidization threshold.

13. A system for fluidizing a fluidizable medium, comprising:

a person support structure including a chamber containing a fluidizable medium and a plenum in fluid communication with the chamber,

a fluid supply in fluid communication with the plenum, the fluid supply having a variable flow rate;

a sensor positioned within the plenum and sensing the fluid pressure of the fluid in the plenum;

a controller in electrical communication with the sensor and the fluid supply, the controller receiving a signal from the sensor indicative of the fluid pressure in the plenum and controlling the fluid supply to vary the flow rate of the fluid supply, the controller varying the flow rate of the fluid supply such that the rate of change in pressure within the plenum as the flow rate of the fluid supply is increased decreases to a first level that indicates that the flow rate of the fluid supply is sufficient to achieve a desirable level of fluidization of the fluidizable medium, the controller maintaining the flow rate of the fluid supply at the first level to maintain the desirable level of fluidization.

14. The system of claim 13 , wherein the desirable level of fluidization is determined as a function of a fluidization threshold of the fluidizable medium.

15. The system of claim 13 , wherein the desirable level of fluidization threshold is proportional to the rate of change of the fluid pressure within the plenum.

16. The system of claim 13 , wherein the desirable level of fluidization includes the fluid flow rate through the fluidizable medium at about a fluidization threshold of the fluidizable medium increased by a predetermined amount.

17. The system of claim 13 , wherein the desirable level of fluidization includes the lesser of a first level of fluidization at a first time and a second level of fluidization at a second time so long as the lesser is greater than a fluidization threshold of the fluidizable medium.

18. The system of claim 13 , wherein the desirable level of fluidization is proportional to increasing the pressure in the plenum by a predetermined amount above a fluidization threshold pressure.

19. The system of claim 13 , wherein the desirable level of fluidization includes the lesser of a first level of fluidization at a first time and a second level of fluidization at a second time, if the lesser is less than a fluidization threshold of the fluidizable medium then the lesser is increased by a predetermined amount.

20. The system of claim 13 , wherein the controller increases a level of fluidization based on the pressure change as a function of the increase in fluid supply until a fluidization threshold is reached, and further increases the level of fluidization until the desirable level of fluidization of the fluidizable medium is reached.