Abstract:
A mercury switch which is actuated only on a specific movement of an individual by design of an internal cavity of the switch to control movement of a mercury ball into and out of engagement with two electrical contacts. The internal cavity has a truncated cone for receipt of the mercury ball, a surface of revolution sloping outward from the opening of the truncated cone and an interruption ramp in this surface of revolution to guide the mercury ball into the truncated cone for actuation of a switch when a critical angle of the switch has been exceeded.

Description:
This application claims priority from and the benefit of U.S. Provisional Application Ser. No. 60/466,433, filed on Apr. 30, 2003, hereby incorporated by reference in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates primarily to devices and methods for remote monitoring of bed-ridden patients to prevent injurious falls should the patient attempt to get out of bed. Devices of this type are seen in my prior U.S. Pat. Nos. 5,008,654 and 5,146,206, the subject matter of each of which is incorporated herein in its entirety by reference. However, the invention is generally related to any application where position and detection of a critical angle are required. 
   2. Discussion of the Related Art 
   The position activated mercury switch of this invention will be the primary component of the systems in my aforementioned patents. The system of the &#39;206 patent presently employs three mercury switches precisely mounted within the “PATIENT AMBULATION MOTION DETECTOR WITH MULTIPLE SWITCH MOTION DETECTION” so that it is known when an undesirable and dangerous body position has been achieved. The present invention replaces the three mercury switches with a single self-contained unit thereby reducing the cost of the detection component and provides ease of assembly, and overall reliability. 
   A separate patent is applied for this device because it is anticipated that this switch will have independent application in manufacturing processes and as a component of additional consumer products. Initially, however, its application will be associated with the referenced device as a replacement for the three strategically positioned mercury switches thus offering the advantages previously listed. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a mercury switch which is actuated only on a specific movement of an individual by design of an internal cavity of the switch to control movement of a mercury ball into and out of engagement with two electrical contacts. 
   This object is realized by forming an internal cavity having a truncated cone for receipt of the mercury ball, a surface of revolution sloping outward from the opening of the truncated cone and an interruption ramp in this surface of revolution to guide the mercury ball into the truncated cone for actuation of a switch when a critical angle of the switch has been exceeded. 
   These and other objects of the invention, as well as many of the intended advantages thereof, will become more readily apparent when reference is made to the following description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings are approximately four times the actual size of a switch configured for the referenced application. Other applications might require a larger or smaller size unit but the principles of operation would be the same and covered by this patent. 
       FIG. 1  is an exploded view of the component parts of the preferred Position Activated Mercury Switch of this invention. 
       FIG. 2  is a plan view with the closure removed from the switch showing the injection molded internal configuration with the mercury ball in the “ON” position. 
       FIG. 3  is a vertical cross-sectional view of the switch taken along lines  3 — 3  of  FIG. 2  with the mercury ball is in the “ON” position. 
       FIG. 4  is a cross-sectional view of the switch taken along lines  4 — 4  of  FIG. 2  with the mercury ball in the “ON” position. 
       FIGS. 5A–5D  are views similar to  FIG. 4  with the mercury ball in various positions obtained when used in a system such as discussed in my earlier patents. Four basic positions are shown:  FIG. 5A  shows the switch in the normal position (patient supine). The mercury ball is away from the contacts and the switch is “OFF”.  FIG. 5B  shows the switch in the “OFF” position with the patient lying face down.  FIG. 5C  shows the switch “OFF” with the patient in position for eating, taking medications, or other activity while seated.  FIG. 5D  shows the switch in the “ON” position as a result of the patient leaning forward as would be necessary to transition to the standing position. 
   

   Like reference characters refer to like parts throughout the several views of the drawings. 
   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In describing preferred embodiments of the invention illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. 
   Referring to  FIG. 1 , there is shown the components which make up the “Position Activated Mercury Switch” of this invention. The switch body  13  of the switch will be manufactured by injection molding both the internal and external configuration, the internal being the most important since its shape will determine the behavior of the mercury ball  15  as the switch body  13  is placed in an infinite number of positions. The mercury ball  15  is placed within the body and is free to move according to the dictates of gravity and the confinement of the internal configuration. 
   The size of the mercury ball will be determined by the switch size which, in turn, will be determined by the switch&#39;s application. When used to monitor a bed patient&#39;s position the switch would be about one fourth the size shown in the figures. The ball  15 , therefore, would be approximately three millimeters in diameter. In any event, the ball will be sized so that the contact probes  17  will be immersed in the liquid mercury deep enough to assure adequate electrical contact. 
   The electrical conductor assembly  14  will be inserted into the switch body  13  through the passageways provided by the molding process so that contact with the mercury ball  15  will complete a simple electrical circuit and activate an applicable external event, for example, an alarm to warn that the patient is attempting ambulation. 
   A closure  12  is provided to assure that the mercury ball  15  remains within the internal cavity regardless of the switch&#39;s position. During assembly, the mercury ball  15  is placed within the internal cavity and the closure  12  sealed with an appropriate bonding material. 
   A mounting flange  16  is shown as an internal part of the molded switch body  13 . Dependent on mounting requirements, the flange may be molded in any tangential plane to the body  13  of the switch. In certain applications, it may be desirable to eliminate the flange  16  altogether and mount the switch with an independent strap or clamp (not shown). 
     FIG. 2  is a plan view of the switch with the closure  12  removed so that the internal cavity can be viewed and its working surfaces can be explained. The internal cavity consists of three controlling surfaces:  18 -B, a truncated cone which directs the mercury ball  15 , shown in the “ON” position, to the electrical contacts (not visible);  18 -A, a surface of revolution sloping outward from the opening of  18 -B to control the position of the mercury ball  15  away from the electrical contact probes  17  when the switch position calls for the circuit to be broken, i.e., “OFF”; and  19 , an interruption to the surface  18 -A to provide a ramp to the conical surface  18 -B. The ramp&#39;s purpose is to direct the mercury ball  15  to the cavity  18 -B and the electrical contact probes  17 . The ramp  19  is placed in the plane of motion to be monitored, in this case, the plane of the patient leaning forward in an attempt to stand from a seated position at bedside. 
     FIG. 3  is a section ( 3 — 3 ) through  FIG. 2  and illustrates the shape of the internal cavity of the switch, the angle of slope of surface  18 -A, and the directional ramp  19 , into surface  18 -B. All other components are presented, in place, as they would be after final assembly. The mercury switch is in the “ON” position. 
     FIG. 4  is also a section ( 4 — 4 ) through  FIG. 2 . Here the difference in the directional ramp  19  and surface  18 -A are more clearly shown. All other items are the same. 
     FIG. 5  shows the four primary positions the switch will monitor. The combination of these positions are limitless. The location of the mercury ball  15  under the influence of gravity deals with these positions and only turns the switch “ON” when tilted forward as shown in  5 D. In all Figures, the double-lined side of the switch body is the side attached to the patient. 
     FIG. 5A  shows the patient (human figure) supine with the switch mounted on his/her upper body as indicated by the short line  20  in the chest area. The switch would be as shown; mercury ball  15  in the upper chamber and in the “OFF” condition. This would be the normal position for a bed-ridden patient. 
     FIG. 5B  indicates the switch condition if the patient is face-down or in any combination of  FIG. 5A  and  FIG. 5B . 
     FIG. 5C  shows the patient sitting up. The switch is still in the “OFF” condition, but the mercury ball  15  is in the “ready” position. Should the patient lean forward to the switch&#39;s critical angle, the alarm would be activated. The sitting position is important in that the patient must eat, take medicine, etc. Sensitivity to the allowable forward motion and avoidance of false alarms can be built into the system by proper design and angle of the directional ramp  19 . 
     FIG. 5D  shows the mercury switch in the “ON” (alarm) position. The critical angle has been exceeded. The mercury ball  15  has fallen into the cavity containing the electrical conductor assembly  14  and the alarm has been sounded. To turn the switch off, the switch (and patient) should be returned to the position of  FIG. 5A  or  5 B. The mercury ball  15  will then move out of contact with the electrical elements and the circuit will be broken. 
   The foregoing description should be considered as illustrative only of the principles of the invention. Since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and, accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.