CROSS REFERENCE TO RELATED APPLICATION
 This application claims the benefit of U.S. provisional patent application Ser. No. 60/677,728, filed May 4, 2005, the advantages and disclosure of this application is hereby incorporated by reference.
FIELD OF THE INVENTION
 The present invention relates generally to a patient support apparatus and more particularly to a resonant frequency referencing percussion device of a vibrating patient support apparatus.
BACKGROUND OF THE INVENTION
 Patient support systems are well known in the art for providing therapy to a patient. A typical patient support apparatus comprises a mattress having a plurality of air bladders for supporting the patient against the bias of gravitational forces, a percussion device that alternates inflation and deflation of air bladders to provide percussion and vibration therapy to the patient, and a rotation device, usually positioned beneath the mattress, to rotate the patient from side to side. Percussion, vibration, and rotation therapy assist in reducing pulmonary problems and bed sores, respectively.
 One example of a rotation device in a mattress is shown in U.S. Pat. No. 5,611,096 to Bartlett et al. and incorporated herein by reference in its entirety. The rotation device of Bartlett et al. has two selectively inflatable and deflatable air bladders lying longitudinally beneath the mattress to provide rotation therapy to the patient for reducing bed sores. A controller including an operator input panel and display is used to control the rotation device. The input panel includes a plurality of raised buttons for advancing through and adjusting parameters associated with rotation functions.
 An example of a percussion or vibrating device in a mattress is shown in U.S. Patent Application Publication No. 2004/0193078 A1, to Flick et al. and incorporated herein by reference in its entirety. The percussion device of Flick et al. discloses a vibrating pad having a plurality of bladders that fill and deflate with the flow of air or fluid at a prescribed frequency controlled by a controller causing the above mattress or mattress cushion to vibrate. This vibration therapy is capable of reducing pulmonary problems such as the accumulation of secretions in the lungs.
 Unfortunately, controllers of known percussion devices do not sense or process displacement amplitude with displacement frequency of the vibrating media of the bladders. Hence, known percussion devices are not capable of detecting and/or utilizing natural resonant frequencies of the vibrating media. If the operating vibration frequency of known percussion devices is too distant from the natural resonant frequency, energy is wasted. If the operating vibration frequency is unintentionally at the natural resonant frequency, then damage or accelerated wear of the patient support apparatus may occur.
SUMMARY OF THE INVENTION
 A vibrating patient support apparatus has a resonant referencing percussion device preferably located internally to a cover of a mattress of the apparatus. The percussion device delivers a percussion or vibration at a controlled operating frequency that is preferably slightly less than a resonant frequency located internal to the mattress of the apparatus. With the various weight distributions of a patient, the device is capable of determining the ever shifting resonant frequency via signals received by the controller from a pressure sensor or accelerometer of the device. Because the operating frequency is slightly less than the natural resonating frequency, energy of the system is conserved. Because the operating frequency is not the controller calculated resonant frequency, wear on the device and potential damage is minimized.
 Preferably, the patient support apparatus includes a number of other devices for patient comfort and therapeutic treatment substantially located in a manageable and light weight mattress. All the devices are generally light weight with moving parts generally being bladders, thus relatively quiet when operating. For ease of manufacturing and cost, a substantial portion or all of the devices operate off of a common pump for preferably flowing pressurized air to an assortment of bladders. For instance, the percussion device preferably has bladders. Moreover, the apparatus preferably has a bladder operated rotation device for rotating a patient to minimize bed sores, a bladder operated firmness setting device for providing patient comfort, and an air loss control system for flowing air through the mattress to control temperature.
 Objects, features and advantages of the present invention include a patient support apparatus that has a relatively lightweight and manageable mattress having numerous devices for therapeutic treatment. Other advantages of the apparatus include a relatively simple and robust design that is inexpensive to manufacture, reduces wear and warranty costs and reduces energy consumption.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
 Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
 FIG. 1 is a perspective view of a patient support apparatus of the present invention positioned on a hospital bed frame;
 FIG. 2 is a cross-sectional view of the patient support apparatus taken along the line 2-2 in FIG. 1;
 FIG. 3 is a cross-sectional view of the patient support apparatus taken along the line 3-3 in FIG. 1;
 FIG. 4 is a schematic view of a control system of the patient support apparatus;
 FIG. 5 is a schematic view of an air flow system of the present invention;
 FIG. 6 is a schematic view of a resonant percussion device of the present invention;
 FIG. 7 is a partial enlarged cross section taken from the circle 7 of FIG. 3;
 FIG. 8 is a cross section similar in perspective to FIG. 7 and of a second embodiment of the patient support apparatus;
 FIG. 9 is a cross section similar in perspective to FIG. 7 and of a third embodiment of the patient support apparatus;
 FIG. 10 is a cross section similar in perspective to FIG. 7 and of a fourth embodiment of the patient support apparatus;
 FIG. 11 is a cross section similar in perspective to FIG. 7 and of a fifth embodiment of the patient support apparatus; and
 FIG. 12 is an amplitude versus frequency graph.
DETAILED DESCRIPTION OF THE INVENTION
 Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a vibrating patient support apparatus of the present invention is generally shown at 10.
 Referring to FIG. 1, the patient support apparatus 10 of the present invention is shown in combination with a mobile hospital bed frame 12. As illustrated, the hospital bed frame 12 typically includes a plurality of side rails 14 that can be lowered for patient transfer and raised to confine a patient. The hospital bed frame 12 can also include a plurality of adjustable sections including an adjustable head section 16 that is pivotally adjustable relative to a main body section 18 of the bed frame 12 to allow the patient to sit up while eating or visiting with family.
 Still referring to FIG. 1, the patient support apparatus 10 preferably comprises a generally self-contained mattress or pad assembly 20 having a patient support surface 22. The mattress 20 is referred to as being self-contained since a substantial portion of the working components of the mattress 20 that are used to carry out multiple functions, including a plurality of therapeutic functions, are enclosed by a cover 24 of the mattress 20. The cover 24 can be any conventional material including, but not limited to natural fibers, polymeric materials, or combinations thereof. The cover 24 is preferably a vapor permeable material to be used in conjunction with a low air loss mechanism 26 of the mattress 20 described below.
 Referring to FIG. 4, a controller 72 of the patient support apparatus 10 controls operation of a main pump 50 preferably located externally of the mattress 20. The main pump 50 supplies a controlled amount of pressurized air to multiple systems or devices of the mattress 20 that are generally located internally to the cover 24 of the mattress 20. These systems include; a low air loss device 82 having a low air loss control system 56 and the low air loss mechanism or perforated tubing 26, a firmness setting device 84 having a main valve system 58 and a main air bladder 36 (see FIG. 3), a percussion device 86 having a percussion control system 60 and a percussion mechanism 38, and a rotation device 88 having a rotation control system 62 and a rotation mechanism 40. The rotation mechanism 40 is preferably two air bladders 42 located beneath the percussion mechanism 38. The percussion mechanism 38 is preferably a plurality of air bladders 39 located beneath the main air bladder 36 of the mattress 20. The main air bladder 36, percussion mechanism 38, and rotation mechanism 40 are supported within the cover 24 of the mattress 20 by a base cushion 44 positioned within a perimeter of the frame 34. The base cushion 44 can be rigid or flexible and comprise an air bladder, or simply be constructed of conventional bedding materials such as foam, and the like.
 Preferably, a pendant 28 of the controller 72 is supported by a tower 30 coupled electrically to the mattress 20 and preferably supported structurally by the bed frame 12. The pendant 28 includes user interface 32 of the patient support apparatus 10 used to operate at least a portion of the functions of the mattress 20. The user interface 32 is preferably of a touch-screen display type that is well known to those skilled in the art for operator input, as well as output, based upon the particular software used to configure the user interface or touch-screen display 32. Here, the touch-screen display 32 has input and output capabilities. These features are shown in application Ser. No. 11/260,452, filed Oct. 27, 2005, hereby incorporated by reference.
 Referring to FIGS. 2-4, the mattress 20 has a generally peripheral frame 34 of a conventional bedding frame material. Such material can include, but is not limited to foam, polymeric materials, metal, gels, or combinations thereof. Generally disposed internally to the cover 24 of the mattress 20 is the main air bladder 36 of the firmness setting device 84, which is positioned within the perimeter of the frame 34 and immediately below an upper portion of the cover 24. The main air bladder 36 acts as the primary support for the patient and with a controlled flow of air into and out of the bladder 36 can be useful in controlling the temperature of the bedding material exposed to the patient.
 The percussion-vibration mechanism 38 of the percussion device 86 is positioned below the main air bladder 36, hereinafter referred to as the percussion mechanism 38. The percussion mechanism 38 provides both percussion and vibration therapy to the patient. The particular therapy being employed is dependent on the frequency or the number of beats per second generated by the percussion mechanism 38. For example, and not to be limited to these examples, the percussion therapy usually employs 1-7 beats per second (i.e. 1-7 hertz) and the vibration therapy employs 7 to 25 beats per second (i.e. 7-25 hertz). The percussion mechanism 38 may employ mechanical fingers or rollers to impart the percussion motion, but preferably comprises a pair of inflatable percussion bladders 39, best shown in FIG. 3, having fingerlike cells that oscillate between inflated and deflated states to provide the percussive movement required. Such a mechanism is illustrated in U.S. Patent Application Publication No. 2004/0193078 to Flick et al., previously referenced.
 Preferably, a rotation mechanism 40 of the rotation device 88 for rotation therapy is positioned below the percussion mechanism 38. The rotation mechanism 40 provides rotation therapy to the patient by rotating the patient from side to side. Along with percussion and percussion-vibration therapy, rotation therapy assists in reducing bed sores and pulmonary problems of the patient. The rotation mechanism 40 is preferably a pair of longitudinally positioned rotation bladders 42, shown in FIG. 3 and described in the '078 publication to Flick et al. The rotation bladders 42 are independently inflated and deflated to raise one side of the patient, lower the patient, and then raise the other side of the patient such that the patient experiences a side-to-side rotation that shifts pressures between the patient and the bladder 36 of the firmness setting device 84 of the mattress 20.
 Referring to FIGS. 3 and 4, the low air loss mechanism 26 of the mattress 20 used in conjunction with the encapsulating yet permeable cover 24 is preferably positioned inward of the cover 24. In operation, air is pumped from the low air loss mechanism 26 through the permeable cover 24 to reduce the temperature below the patient support surface 22 and decrease the chance of skin maceration that lowers the risk of bed sores. Preferably, the main pump 50 delivers pressurized air to the perforated tubing of the mechanism 26 disposed within the frame 34 and under the cover 24. The tubing is external to the main air bladder 36, the percussion mechanism 38, and the rotation mechanism 40.
 Referring specifically to FIG. 2, a first control unit 46 of a main control system 70 in the form of a rigid box and preferably not of the mattress 20 is shown adjacent to a foot end 48 of the mattress 20. The first control unit 46 encloses the main pump 50 and a power circuit board 52 of a main control system 70 for operating the main pump 50 and transferring power to the rest of the mattress components generally located in a second control unit 54. As shown, the first control unit 46 fits neatly below the foot end 48 of the mattress 20, but is not incorporated within the cover 24 of the mattress 20. Of course, other configurations with the first control unit 46 inside the cover 24 are also possible. Such configurations are illustrated in the '078 publication to Flick et al. In a preferred embodiment, the main pump 50 is used to inflate the main air bladder 36, the percussion bladders 39, and the rotation bladders 42, and to convey air to the perforated tube 26.
 The second control unit 54 of the main control system 70 in the form of a rigid box is shown beneath the cover 24 of the mattress 20 within the perimeter of the frame 34 (see FIG. 2). The second control unit 54 encloses the low air loss control system 56 for controlling the low air loss mechanism 26, the main valve system 58 for inflating and deflating the main air bladder 36, the percussion control system 60 for controlling the percussion mechanism 38, the rotation control system 62 for controlling the rotation mechanism 40, and a main circuit board 64 in operative communication with these systems and the power circuit board 52 of the first control unit 46. The second control unit 54 also preferably encloses a processor 74 and memory 78 of the controller 72 for controlling operation of these systems 56, 58, 60, 62 and the main pump 50. These systems 56, 58, 60, 62 may comprise motors, solenoid valves, and/or motor-controlled valves, as disclosed in the '078 publication. It should be appreciated that each of these separate control systems 56, 58, 60, 62 may also represent portions of a larger system. Those skilled in the art will now recognize that the systems employed for controlling operation of the loss air loss mechanism 26, main air bladder 36, percussion mechanism 38, and rotation mechanism 40 may assume a variety of configurations.
 Referring to FIG. 4, the main control system 70 of the patient support apparatus 10 is schematically illustrated. The main control system 70 includes the controller 72 which comprises the processor 74, the touch-screen display 32, a display driver 76 for driving the touch-screen display 32, the memory 78, and a communication interface 80. The controller 72, via communication interfaces 80, is also in operative communication with the low air loss control system 56, main valve system 58, percussion control system 60, rotation control system 62, and the main pump 50.
 Referring to FIG. 5, an air flow schematic of the patient support apparatus 10 is shown. The air flow schematic generally shows the movement of air through conduits from an air source 94 (preferably outside air at atmospheric pressure) via the main pump 50 to the second control unit 54 and more specifically, to the low air loss control system 56, the main valve system 58, the percussion control system 60, and the rotation control system 62. Each of these systems 56, 58, 60, 62 preferably comprises valve controls for operating their respective mechanisms, i.e., the perforated tube 26, the main air bladder 36, the percussion bladders 39, and the rotation bladders 42. Such valve controls are described in more detail in the previously referenced '078 publication to Flick et al. herein incorporated by reference. It should be appreciated that each of the separate control systems 56, 58, 60, 62 may be portions of a larger valve system, or the control systems 56, 58, 60, 62 may represent direct connections between the main pump 50 and the respective perforated tube 26 or bladders 36, 39, 42.
 With further regards to the percussion device 86 and more specific to the present invention, FIG. 6 illustrates the percussion device 86 having the previously described percussion control system 60 and the percussion mechanism 38. Referring to FIG. 7, the percussion mechanism 38 also has a resonating pad 100 located between the main bladder 36 and the percussion bladders 39, and a sensor 102 preferably being a pressure transducer located in preferably each percussion bladder 39 for sensing air pressure. Referring to FIG. 12, the resonating pad 100 is made of a resiliently flexible material having at least one known natural resonant frequency 104 that theoretically has a corresponding amplitude (displacement) that extends to infinity. The natural resonant frequency 104 is of the pad 100 when in an unloaded state (i.e. no patient weight) and as best illustrated by the solid amplitude vs. frequency curve 106 of FIG. 12.
 In operation, and assuming no patient load is placed upon the resonating pad 100 of mechanism 38, (see FIG. 12), the percussion device 68 inflates and deflates the plurality of bladders 39 at a baseline operating frequency 108 for optimal energy efficiency. In order to substantially reduce wear and potential damage of the device 86 via excessive vibration amplitude or displacement, the baseline operating frequency 108 is close to but is not at the resonant frequency 104 of the pad 100. Generally, the baseline operating frequency 108 of the percussion device 86 is slightly less than any chosen one of the at least one resonant frequencies 104. To optimize percussion therapy, the material and size of the resonating pad 100 is chosen with consideration made to the range of weight distributions of the patient that will tend to shift the amplitude vs. frequency curve 106. This shift or addition of compressive weight on the resonating pad 100 generally alters the resonating frequencies of the pad 100 and is best illustrated as the shifted curve 110 having shifted resonating frequencies 112 in FIG. 12.
 For ease of explanation, each bladder 39 has a pressure transducer 102, thus each bladder 39 can react to weight changes of the respective overhead portion of the patient. However, one skilled in the art would now know that a plurality of bladders 39 could be controlled by one pressure transducer 102. If, for instance possibly due to manufacturing cost, only one pressure transducer 102 is utilized, its optimal location would be toward the center of the mattress 22 or under the lungs of the patient since percussion therapy is primarily used for treatment of the lungs.
 In operation of the percussion device 86 with the weight of a patient on the mattress 22, the variable speed air pump 50 operates through the percussion control system 60 that preferably includes a double diaphragm valve system 99 for controlled inflation and deflation of the percussion bladders 39. The inflation of the percussion bladders 39 by the pump 50 is oscillated such that the pressure in the percussion bladders 39 is increased and decreased, thereby lifting and dropping the patient. The weight of the patient not only shifts the resonating frequency to curve 110 but also adds a biasing force against the percussion bladders 39 preferably distributed through the pad 100. This force correlates with a pressure increase in the percussion bladders 39. The pressure inside the percussion bladders 39 is continuously monitored by the pressure transducers 102 and communicated to the controller 72. As the speed of the pump 50 is changed, the pressure inside the percussion bladders 39 created by patient's potentially changing weight is monitored by the controller 72 to continually adjust for an optimal operating frequency 114 that correlates to a maximum pressure (pressure correlates to force divided by area, and area correlates to amplitude). The controller 72 then operates the pump 50 to achieve the optimal frequency 114 for percussion therapy for that particular patient.
 Referring to FIG. 8, a second embodiment of a mattress 22' is illustrated. In the second embodiment, the resonating pad 100 of the first embodiment is generally omitted. The percussion device 84' of the second embodiment operates similarly to the first embodiment except that the main air bladder 36' also functions as the resonating pad of the first embodiment, hence, it is the resonating frequency of the bladder 36' that is generally monitored indirectly by the pressure sensors 102'. As best illustrated in FIG. 9, a third embodiment of a mattress 22'' is illustrated that is similar to the second embodiment except that a main cushioning member 36'' of the mattress 22'' is not a bladder but a generally homogeneous and passive cushion preferably having a known natural resonating frequency.
 Referring to FIG. 10, a fourth embodiment of a mattress 22''' is illustrated wherein the sensors 102 of the first embodiment are generally replaced with accelerometers 102''' of the fourth embodiment. The accelerometers 102''' are positioned to measure displacement of a resonating pad 100''' that directly corresponds to amplitude of vibration and/or percussion. Referring to FIG. 11, a fifth embodiment of a mattress 22'''' is illustrated that is similar to the fourth embodiment except that a main cushioning member 36'''' of the mattress 22'''' is not a bladder but is a generally homogeneous and passive cushioning member 36'''' preferably having a known natural resonating frequency. In the fifth embodiment, the accelerometer 102'''' is preferably located in the cushioning member 36''''.
 While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention. For instance, the term mattress as applied to mattress 20 is not meant to be limited to a patient's bed, but may apply to any pad assembly that supports all or any portion of a patient against the bias of gravitational forces and whether or not the patient is intended to actual sleep upon the mattress or pad assembly.
 In light of the present invention, one skilled in the art would now realize that the bladder 36 may be a passive cushioning member thus generally eliminating the firmness setting device 84 altogether. Such a the cushioning member 36 could be a soft pad and/or made of a homogeneous material similar to the foam or gel of the frame 34. Moreover, the air pump 50 and associated conduits could be replaced with a temperature controlled fluid pump system or a central pump system capable of handling a plurality of beds.