Fluid handling – Inflatable article
Reexamination Certificate
1998-06-09
2001-03-20
Rivell, John (Department: 3753)
Fluid handling
Inflatable article
C137S596200, C251S129150, C251S129050, C005S713000
Reexamination Certificate
active
06202672
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates generally to a control valve system for air mattress or air cushion support surfaces and more specifically to a control valve system for air mattresses or support surfaces having a plurality of individually controllable chambers, for example, hospital beds.
Other cushion pressure control designs, which use one valve to isolate the cushion from a manifold, with either pressure or vacuum then applied to the manifold, cannot simultaneously increase the inflation of one cushion while exhausting from another. This means that adjusting the cushions in response to patient movement or changes in bed position takes longer, resulting in reduced comfort and possibly a less effective therapy. Also, this type of design cannot be used for the most effective type of patient rotation systems, which increase the pressure in one rotation cushion while simultaneously decreasing the pressure in another.
Other designs may use multiple valves with independent actuators to achieve the desired control conditions. This requires control wiring and space for each actuator. Also this does not insures that only one of the valves per pair is actuated at one time.
Bed cushions are typically inflated to pressures between ½ psi and 1 psi. At these low pressures, the size of the flow opening in the valve must be relatively large in order to pass an adequate volume of air to inflate or deflate the cushion in a reasonable amount of time.
Existing valves which have large flow openings either have very large actuators, or are “pilot operated.” A pilot operated valve uses a small actuator such as a solenoid to create a condition that causes a larger valve section to open. An example of this would be to use a solenoid to open a tiny valve which allows pressurized air to flow through into a chamber where it actuates a larger valve by pressing against a diaphragm. This type of pilot operated valve generally requires that the minimum air pressure be 3 psi or higher, in order to create enough force to actuate the larger valve. The types of pressurized air sources that are most desirable for hospital bed cushions (high flow low pressure blowers) do not generally create a high enough pressure to actuate a pilot operated valve unless the pilot device is very large.
Existing direct acting valves typically use electrical solenoids to operate a valve with a small opening. Since these valves are typically designed for higher pressures encountered in industrial and commercial applications, the valve openings are small.
The force acting against the operator for a direct acting valve is typically equal to the pressure the valve is sealing against multiplied by the cross sectional sealing area of the valve (F=P×A). In an industrial valve, this force might be 100 psi; if a valve had a cross sectional sealing area of 0.20 inches (a practical area for the flows and pressures required by a hospital bed), the force to be overcome by the actuator would be 20 lbs. However, in a hospital bed, the pressure would be on the order of 1 psi, for a total force of only 0.2 lbs.
Because it is impractical to consider using a solenoid developing 20 lbs. of force due to the physical size and high electrical power consumption in high pressure industrial applications, these valves are generally designed with flow openings (valve orifices) having a cross sectional area of on the order of 0.01 square inches. This size opening is too small for the flow rates required at the lower pressures found in a hospital bed system.
Another limitation of prior art valve control structures is the ability to provide proportional flow control.
The valve seat and valve disk can be designed to be either flat, round or with varying amounts of taper. With a flat valve seat, a small amount of movement from the actuator causes a significant increase in flow through the valve. This type of seat and disk design is most useful when it is desirable to inflate a cushion as quickly as possible, or when it is desirable to create a pressure “pulse” with the sudden opening of the valve to high flow conditions.
As the amount of taper is increased on the valve seat and disk, a smaller change in flow is created for a given movement of the actuator. This makes it possible to control the rate of flow through the valve by controlling the positioning of the actuator. This characteristic is particularly useful in “low air loss” cushions, where air is continuously exiting the cushion through a fixed or variable size orifice. A valve with proportioning characteristics can be actuated to where it just provides sufficient air flow to balance against the loss of air from the cushion. As an alternative, the proportioning valve can be used on the discharge side of the cushion to create a variable size orifice to control the rate of discharge from the cushion.
Another use for the proportional flow control characteristics is to control rotation of the patient on the air cushion support surface. Studies have shown that a slow rotation created by simultaneously inflating one cushion while deflating another cushion is preferable to rapid rotation.
When an on/off type of valve is used to inflate or deflate a cushion, the delay time between sensing that the desired pressure has been reached and the time the valve is closed can cause “overshoot” that requires additional correction and adjustment.
A proportional valve can be opened to a full flow position initially to achieve a high rate of flow, then as the desired pressure is approached, the valve can be changed to a partial flow position to reduce or eliminate the overshoot condition as the pressure sensor and bed controls detect the desired pressure being approached.
Proportional opening of valves will result in smoother initial inflation, avoiding pressure peaks or shock waves that may cause patient discomfort. Controlled proportional opening and closing of valves can also reduce the mechanical and air flow noise caused by valves which suddenly open and close.
In controlling the surface pressures of a multiple zone, bed conditions often arise that make it desirable that some cushions receive a higher rate of air flow than others. This may occur because one cushion has a higher volume than others, because the patient weight shifts from one cushion or set of cushions to another, or because of an operating mode change in the bed (for example, by going into a patient rotation mode).
With on/off valves, this can only be achieved by turning the valves on and off at different rates. Such a method of operation can cause uneven inflation, pressure surges, additional noise and longer response times to achieve the desired cushion inflation rates.
In some circumstances, it is desirable to inflate some zones (e.g., side bolsters, head supports, and rotational cushions) to significantly higher pressures than other zones. This is often accomplished by increasing the pressure levels in the pressure supply manifold to serve the requirements of these “hyperinflated zones”. With valve's having proportional control characteristics, it is possible to maintain accurate inflation control to the lower pressure zones by reducing the amount these valves open while the pressure manifold is in a hyperinflation state.
In other cases, the air supply may be limited for certain operational modes. For example, it may be desirable to inflate one or more cushion zones very quickly. If a less critical zone requires pressure at the same time, it may “rob” available air from the system, affecting the performance of the bed in meeting the requirements of the zone needing rapid inflation. Using a proportional valve allows the bed control system to restrict the opening of the less critical valves to allocate available air to the more critical locations.
This air apportioning capability can allow the use of small air sources, which require less electrical power, generate less noise and which occupy less space.
In the air cushion environment, an economic and effective actuator has not been found to p
Carruth W. Layne
Chambers Kenith W.
DeRidder Steven D.
Ellis Craig D.
McCormick Scott
Bose McKinney & Evans LLP
Hill-Rom Inc.
Rivell John
Schoenfeld Meredith H.
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