Abstract:
A patient ventilator is connected with two stand-by switches wherein activation of both switches is required for stopping the ventilating function. The preferred stand-by switches are in the form of membrane switches in which a conductive dome is positioned and spaced between respective layers having electrical traces thereon cooperating with the dome for defining the switches. The application of manual pressure closes the spaces between the layers and activates both switches.

Description:
RELATED APPLICATIONS 
     Not applicable. 
     FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     MICROFICHE APPENDIX 
     Not applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of patient ventilators and membrane switches. More particularly, the invention is concerned with a patient ventilator connected to two stand-by switches wherein activation of both switches is required for stopping the ventilating function. The preferred stand-by switches are in the form of membrane switches in which a conductive dome is positioned and spaced between respective layers having electrical traces thereon cooperating with the dome for defining the switches. The application of manual pressure closes the spaces between the layers and activates both switches. 
     2. Description of the Prior Art 
     Patient ventilators assist or totally provide the respiratory function for a patient. If a single stand-by switch is used for stopping the ventilating function, there is a risk that a defect in the switch, such as a short circuit, could cause the ventilator to stop. The prior art solves this problem with a rotary switch mechanism having two stand-by switches in which activation of both switches is required for stopping the ventilating function. Those skilled in the art appreciate, however, that rotary switch mechanisms tend to be bulky and uneconomical, especially for the smaller sized home ventilators. 
     SUMMARY OF THE INVENTION 
     The present invention solves the prior art problems discussed above and provides a distinct advance in the state of the art. In particular, the ventilator and switch combination hereof provides a compact and economical arrangement. 
     In a preferred embodiment, a ventilator is connected to a membrane switch assembly having first and second membrane switches coupled with the ventilator for stopping the ventilating function thereof only upon activation of both of the switches. The assembly includes first and second membrane layers with an intermediate membrane layer therebetween. The layers are spaced and include circuit trace thereon cooperatively defining the switches in superposed relationship for activation of both switches in response to pressure closing the spaces between the layers. The preferred intermediate layer is in the form of a resilient, conductive dome positioned between the traces of the first and second layers. Pressure on the first layer causes the trace thereon to contact the top of the dome closing the first switch. This, in turn, collapses the dome into contact with the trace of a second layer thereby closing the second switch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic representation of a patient ventilator connected with two stand-by switches in the form of membrane switches; 
     FIG. 2 is an exploded view of the components of the preferred membrane switches of FIG. 1; and 
     FIG. 3 is a sectional view taken along line 3--3 of FIG. 2. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates preferred embodiment 10 in accordance with the present invention including ventilator 12 and membrane switch assembly 14. Ventilator 12 can be any type of ventilator such as hospital ventilator or a home care ventilator. Such ventilators are used for ventilating a patient by assisting the respiration or by providing the total respiratory function. 
     Membrane switch assembly 14 includes normally open, parallel connected, stand-by switches 16 and 18 electrically connected to ventilator 12 by line 20, common to both switches, and lines 22 and 24 for switches 16 and 18 respectively. In one example of use, ventilator 12 is controlled by a microprocessor with line 20 providing a positive supply voltage to switches 16, 18. Lines 22 and 24 provide input to the microprocessor and both must be closed to signal the stopping of the ventilating function. This may result in the ventilator placed in a pause mode or could signal power down of the ventilator. 
     FIGS. 2 and 3 further illustrate membrane switch assembly 14 which typically would include switches other than stand-by switches 16, 18 for controlling the various functions of the ventilator such as start, pressure adjustments and timing adjustments. As illustrated, assembly 14 includes a plurality of layers including graphic overlay 26, first switch layer 28, an intermediate switch layer in the nature of conductive dome 30, dome positioning layer 32, and second switch layer 34. As is conventional, layers 26, 28 and 32, 34 are composed of polyester, and adhesive is included between the various layers. Also, assembly 14 may include other layers as is conventional such as ESD grids, EMI planes, a clear window layer and so forth. Graphic overlay 26 includes graphic 36 printed thereon bearing the legend STAND-BY indicating the function of switches 16, 18. 
     First layer 28 includes connection tab 38 and circuit trace 40 on the lower or inboard side thereof as illustrated in FIG. 3. Circuit trace 40 includes trace portion 42 in the shape of a torus for engaging the top of dome 30 with linear portion of trace 40 being line 22 extending onto connection tab 38. 
     Resilient conductive dome 30 is composed of metal such as spring steel and includes dome section 44 and four, outwardly extending, electrical contacts 46, 48, 50 and 52. Upper surface 54 of dome section 44 and torus-shaped trace portion 42 of first layer 28 are spaced and define normally open, switch 16 therebetween. Contact between trace portion 42 and upper surface 54 result in closure of switch 16. 
     Second switch layer 34 includes electrical trace configured as contact pads 56, 58, 60 and 62 and trace portion 64 configured as common line 20 extending onto tab 66, and further includes circular trace portion 68 positioned centrally and electrically connected with trace portion 72 as line 24 extending onto tab 66 spaced from line 22. The lower surface 76 of dome section 44 and circular trace portion 68 are spaced and define normally open, switch 18 therebetween. 
     Dome contacts 46-52 are configured to register in electrical contact with pads 56-62 respectively. In this position, positioning layer 32 overlies second layer 34 with window 74 surrounding and locating dome 30 in the registration position relative to second layer 34. As best viewed in FIG. 3, torus-shaped trace portion 42, dome section 44 and circular trace portion 68 are in axial alignment. These components of assembly 14 are spaced so that switches 16, 18 are normally open. 
     In operation, the user applies pressure, that is, presses on graphic 36 of overlay 26. This action shifts first layer 28 downwardly and closes the space between torus-shaped trace portion 42 and upper surface 54 of dome section 44 to make electrical contact between these two components thereby closing switch 16. 
     The pressure on graphic 36 also causes torus-shaped trace portion 42 to collapse dome section 44 to close the space between lower surface 76 and circular trace portion 68. This results in electrical contact thereby closing switch 18. With both switches closed, signals are provided on both of lines 22 and 24 to ventilator 12 indicating that the ventilating function should cease. With the release of pressure on graphic 36, the layers of assembly 14 return to the spaced position and switches 16, 18 return to their respective open positions. The configuration of membrane switch assembly 14 in accordance with the present invention provides two superposed membrane switches, which has been unavailable in the prior art. 
     It will be appreciated that if either of switches 16 and 18 were to fail in the shorted condition, such would be insufficient to signal ventilator 12 to cease the ventilating function. It would still require pressing graphic 36 to close the other of the switches. In this way, the present invention provides reliable performance using the compactness and economies of membrane switches. Moreover, membrane switches are generally more resistant to adverse effects from environmental conditions such as moisture and dust as compared to the prior art mechanical switches. 
     Those skilled in the art will appreciate that the present invention encompasses many variations in the preferred embodiment described herein. Having thus described the preferred embodiment of the present invention, the following is claimed as new and desired to be secured by Letters Patent: