Electromechanical Door Holder-Closer

This invention relates in general to door operating devices and deals more particularly with improved door closing devices of the type which include hold-open mechanisms for automatic remote release in the event of emergency. Devices of the aforedescribed general type are extensively employed in schools, hospitals, public buildings and industrial establishments, wherein it is desirable that certain doors be maintained in at least partially open position during normal hours of operation, but close automatically upon occurrence of an emergency, as for example, a smoke or fire condition.

It is the general aim of the present invention to provide improved electromechanical devices of the aforedescribed general type which may be readily adjusted to desired hold-open position, and which may, if desired, include additional adjustment features to permit adjustment from one hold-open position to a lesser hold-open position by door movement. The devices of the present invention fail safe to assure door closure in the event of power interruption, for any reason, and permit an associated door to be manually closed from a hold-open position.

In accordance with the present invention, an apparatus for operating a door mounted for pivotal movement between open and closed positions includes a shaft which rotates when the door moves between its positions. The device further includes a clutch and means for coupling the clutch to the shaft for rotation therewith. A latching mechanism cooperable with the clutch in a latching position releasably retains the clutch to permit rotation of the shaft in only one direction in response to movement of the door toward one of its positions and to prevent rotation of the shaft in its opposite direction in response to a predetermined torque applied to the shaft. An electrically operated means is provided for releasably holding the latching means in its latching position.

FIG. 1 is a plan view of a device embodying the present invention, shown connected between a door and door frame, and shown in solid lines with the door closed and in broken lines with the door held in a partially open position by the device.

FIG. 2 is a plan view of the device of FIG. 1, shown with a portion of its cover broken away to reveal the structure therein.

FIG. 3 is a side elevational view of the device of FIG. 1 also shown with a portion of the cover broken away.

FIG. 4 is a somewhat enlarged plan view of the clutch mechanism of the apparatus of FIG. 1, parts thereof shown broken away.

FIG. 5 is a somewhat further enlarged fragmentary sectional view taken along the line 5--5 of FIG. 2.

FIG. 6 is a somewhat reduced fragmentary sectional view taken along the line 6--6 of FIG. 5.

FIG. 7 is generally similar to FIG. 6 but shows another embodiment of the invention.

FIG. 8 is a fragmentary plan view similar to FIG. 4 and shows another embodiment of the invention.

FIG. 9 is a fragmentary sectional view taken along the line 9--9 of FIG. 8.

FIG. 10 is a fragmentary sectional view taken along the line 10--10 of FIG. 9.

FIG. 11 is a fragmentary plan view similar to FIG. 4 and illustrates still another embodiment of the invention.

FIG. 12 is a sectional view taken along the line 12--12 of FIG. 11.

Turning now to the drawings, and referring first particularly to FIGS. 1-3, a device embodying the present invention and indicated generally by the reference numeral 10 is shown in FIG. 1 connected between a door 12 and its associated frame 14. As illustrated, the device is mounted on the top jamb of the door frame 14 and connected to the door 12 by a pair of arms 16 and 18 which comprise part of the illustrated device. However, other mounting and connecting arrangements may be employed, as will be evident from the following further description of the device.

The device 10 generally comprises a conventional door closer indicated generally at 20, which performs well known door closing and checking functions, and an attachment indicated generally at 22 cooperable with the door closer 20 to provide door hold-open and release functions hereinafter described. The attachment 22 includes a unidirectional or one-way engaging clutch 24 for mounting on the closer 20 and a mounting bracket or frame 69 which supports the closer 20, a latching mechanism comprising a liner system indicated generally by the numeral 26 cooperable with the clutch in a latching position, and an electrically operated holding and releasing mechanism designated generally at 28 for releasably retaining the lever system in its latched position.

Conventional door closers of various types may be used in practicing the invention, and, if desired, a closer may be manufactured as an integral part of the device, but preferably, and as shown, a Series 100 Door Closer, manufactured by P & F Corbin Division, Emhart Corporation, is employed. The door closer 20 has a casing 30 and a shaft or spindle 32 which is journalled therein and extends therethrough. The spindle has upper and lower end portions 34, 34 which respectively project above and below the casing. Each end portion has a substantially square cross-section as best shown in FIG. 6 for selective non-rotatable connection with the arm 16. The closer 20 is not handed, that is, it may be mounted to operate a door of either hand without modification and it is for this reason that two spindle end portions 34, 34 are provided for selective use. In the illustrated case, the arm 16 is non-rotatably connected to the spindle lower end portion 34 and causes the spindle to rotate when the door moves between its open and closed positions. A closer spring (not shown) contained in the left end of the casing 30, as it appears in FIG. 3, acts upon a horizontally disposed rack which drivingly engages a pinion (not shown) mounted on the spindle 32. The closer spring yieldably resists rotation of the spindle 32 in one direction or in a clockwise direction as viewed from above and as shown in FIG. 2. Hence, rotation of the arm 16 in a clockwise direction, as by opening the door 12, compresses or loads the closer compression spring to store energy therein for closing the door. A piston (not shown) associated with the aforementioned rack acts upon a quantity of hydraulic fluid or the like entrapped within the casing 30 to check or dampen movement of the door. The aforesaid closer may also be provided with means for adjusting the power of the closer spring and other means for adjusting the closing and latching speed of an associated door, all of which is well known to those skilled in the art.

Referring now to FIGS. 4-6, the clutch 24 is a one-way engaging or uni-directional ball clutch and comprises an inner part of clutch dial 36 which has a plurality of circumaxially spaced and radially outwardly opening ball receiving recesses 38, 38, each of which contains a ball 40. A generally cylindrical central aperture 42 in the dial receives an associated spindle end portion 34 therethrough, as best shown in FIG. 6, to permit angular movement of the spindle relative to the clutch. The dial is circumaxially surrounded by an outer part or locking ring 44 which has a plurality of radially inwardly opening ball receiving recesses or notches 46, 46 therein, the number of notches in the locking ring being substantially greater than the number of recesses in the dial. The dial 36, the balls 40, 40 and the locking ring 44 are retained in assembled relation between a pair of retaining rings 48, 48 riveted in assembly with the locking ring. The recesses 38, 38 and the notches 46, 46 are constructed and arranged to cooperate with the balls 40, 40 to permit free rotation of the clutch dial 36 is only one direction relative to the locking ring 44. Hence, the clutch is uni-directional or uni-rotational.

In accordance with the presently preferred embodiment of the invention, the locking ring 44 has 24 equally spaced ball receiving notches, whereas the dial 36 has three pairs of diametrically opposed ball receiving recesses. The relative spacing of the recesses is such that each time the dial is rotated in a clockwise direction from a locking position through an angle of five degrees relative to the locking ring 44, a pair of diametrically opposed balls 40, 40 are brought into alignment with an associated pair of diametrically opposed ball receiving notches 46, 46. As oriented in the drawings, the dial 36 is free to rotate in a clockwise direction relative to the locking ring 44, but locks in coupled engagement with the locking ring when rotated in a counterclockwise direction relative to the locking ring and through an angle not greater than five degrees from any previous dial position. A radially outwardly opening latch recess 50 is provided in the peripheral edge of the clutch 24 for a purpose hereinafter evident. It should be noted that the side walls of the recess diverge outwardly or toward the open end thereof to define cam surfaces 52, 52.

A pair of annular clutch linings or friction pads 54, 54 are respectively disposed above and below the clutch dial 36 in face-to-face relation therewith. The pads are made from asbestos cloth or like friction material and are retained in frictional engagement with the clutch dial 36 by a pair of bearing plates 56, 56. Each bearing plate has a square central aperture 58 and is received on the spindle upper end portion 34 in non-rotatable engagement therewith. The lower bearing plate 56 abuts an upwardly facing spindle shoulder 59 as best shown in FIG. 5. A cap 60 received on the upper end of the spindle 34 is retained by a fastener 62 which threadably engages the end portion 34. The cap is recessed for clearance with the upper end of the spindle and has a downwardly facing annular bearing surface 64 which engages the upper bearing plate. Frictional engagement between the friction pads 54, 54 and the clutch dial 36 may be adjusted by turning the threaded fastener 62 in one or an opposite direction relative to the spindle 32. It should also be noted that each friction pad 54 has an annular marginal portion 66 which is exposed outwardly beyond an associated bearing plate 56 and engages a chamfered surface 68 on an associated retaining ring 48. Thus, the pad marginal portions 66, 66 cooperate with the retaining ring surfaces 68, 68 to provide frictional connection between the dial 36 and locking ring 44 to yieldably resist relative rotation of the latter clutch parts.

The mounting bracket or frame 69 is preferably formed from sheet metal and has a generally vertically disposed rear mounting portion 70 provided with a plurality of mounting holes (not shown) for securing the device to a door or a door frame. A plurality of mounting tabs 72, 72 project forwardly from the mounting portion and receive fasteners which secure the closer 20 to the bracket 69. A generally horizontally disposed upper portion extends forwardly from the mounting portion 70 above the closer 20 and defines a horizontally disposed mounting surface 73 to support the latching mechanism 26 and the holding and releasing mechanism 28.

Considering now the latching mechanism 26, with particular reference to FIG. 2, this mechanism includes an elongated latching lever 74 and a generally L-shaped holding lever 76. The holding lever is pivotally secured near one end of the mounting surface 73 and near the left end of the bracket by a pivot stud 78 staked to the bracket 69. A tab 80 bent upwardly on the other end of the holding lever 76 carries an armature plate 82 hereinafter further described. The latching lever 74 is pivotally mounted on the frame rearwardly and to the right of the clutch 24 by a pivot stud 84 which passes through the end of the lever and is staked to the frame. The latching lever 74 extends generally tangentially of the clutch 24 and is connected to the holding lever by another pivot stud 86 which passes through a slot in the left end of the lever and is staked to the holding lever 76 intermediate its ends. The left end of the latching lever is slightly offset and spaced above the holding lever, the spacing therebetween being maintained by a spacing washer received on the pivot stud 86. A relatively light torsion spring 88 surrounds the washer and has one free end thereof in engagement with the tab 80 and its other free end in engagement with a spring retaining stump 90 staked to the frame. A resilient stop cushion 92 surrounds the base of the stump to provide a buffer for the holding lever. The latching lever 74 carries a latch pin 94 which is alignable with the latching recess 50 and movable with the lever 74 into and out of latching engagement with the clutch 24. In FIG. 2, the latching position of the latching lever 74 is shown in full lines and the releasing position of the lever is shown by broken lines.

The holding mechanism 28 generally comprises an electromagnet 96 which in an electrically energized condition cooperates in holding engagement with the armature plate 82. The electromagnet is preferably adapted for direct current operation and for this reason a rectifier 98 is also mounted on the frame. The rectifier and electromagnet are supported on a mounting tab bent upwardly from the bracket 69. The armature plate 82 preferably comprises a circular disc of magnetic material which has a threaded shank projecting centrally therefrom and through an aperture in the mounting tab 80 to receive a retaining nut. A compression spring 100 surrounds the shank between the tab and the plate to facilitate adjustment of the armature plate 82 relative to the electromagnet 96. The spring mounted arrangement of the armature plate also facilitates self-alignment between the armature plate and the electromagnet to assure efficient operation of the device.

When the device 10 is installed, the various parts thereof are preferably initially positioned as shown in full lines in FIG. 2, the door being in its closed position. The electromagnet 96 is normally energized and may be electrically connected to a suitable sensing device responsive to a predetermined ambient temperature or smoke condition. Initial adjustment of the device 10 is made by simply opening the door to a desired hold-open position while the electromagnet 96 is energized to retain the latching lever 74 in its latched position. As previously noted, the clutch 24 is arranged to permit free rotation of the dial 36 in a clockwise direction relative to the locking ring 44. The dial 36 is frictionally coupled to the spindle 32 as previously described whereas the locking ring 44 is restrained against rotation by engagement of the latch pin 94 and the latch recess 50. Thus, as the door is moved toward an open position, as shown in FIG. 1, the clutch dial 36 rotates in a clockwise direction with the spindle 32 and relative to the locking ring 44. The marginal portions 66, 66 which engage the chamfered surfaces 68, 68 on the retaining rings offer negligible frictional resistance to clockwise rotation of the spindle and clutch dial.

When the door 12 is released in a fully or partially open position, the action of the closer 20 tends to produce some slight retrograde movement of the door toward its closed position. However, as will be evident from the previous description of the clutch 24, the clutch dial 36 will lock in position relative to the locking ring 44 as the dial moves in a counterclockwise direction through an angle of not more than five degrees relative to the locking ring. In accordance with the presently preferred arrangement for installation, two degrees of clutch dial movement is approximately equal to one degree of door movement. Hence, the retrograde movement of the door after release and toward its closed position will not normally be greater than approximately two and one-half degrees. The frictional coupling between the spindle 32 and the dial 36 is adjusted so that torque required to move the spindle relative to the dial when the clutch is in its locked position is greater than the torque applied to the spindle by the door closer 20. Accordingly, the door will be held in its adjusted open position as long as the electromagnet 96 remains in an energized state.

When the electromagnet is de-energized, as by operation of an ambient temperature or smoke sensing device in circuit therewith, the armature plate 82 and holding lever 76 cease to hold the latching lever 74 in its latching position. Thereafter, the latch pin 94 is retained in the latch recess 50 only by the biasing force exerted on the lever 74 by the relatively light torsion spring 88. The torque exerted upon the spindle 32 by the door closer 20 is sufficient to cause the latch pin 94 to be cammed out of the recess 50 by engagement with an associated inclined cam surface 52. When the clutch 24 has rotated to a position wherein the latch recess 50 is out of alignment with the latch pin 94, the latter pin is retained in engagement with the peripheral surface of the clutch by the biasing force of the spring 88. The latching lever 74 is then in its released or broken line position as it appears in FIG. 2. It will be noted that when the latter lever is in its released position, the armature plate 82 is displaced a substantial distance from the electromagnet 96 and is beyond the influence thereof.

Referring now to FIG. 2 and assuming that the arm 16 moves through an angle of approximately 45.degree. to its broken line position indicated at 16a when the door is moved to its initial position of adjustment, it will be noted that the arm 16 has been displaced approximately 45.degree. relative to the latch recess 50. Thereafter, when the holding mechanism releases and the door closes, the arm 16 rotates in a counterclockwise direction to return to its normal or full line position in FIG. 2 and the latch recess 50 is displaced in a counterclockwise direction to the position indicated by broken lines at 50a. The next time the door is opened, the entire clutch 24 rotates in a clockwise direction with the spindle 32.

The latch pin 94 which is biased into engagement with the peripheral surface of the clutch 24 exerts a drag on the latter surface which tends to prevent the locking ring 44 from rotating in a clockwise direction with the spindle 32 and clutch dial 36. However, the frictional force exerted on the chamfered surfaces 68, 68 by the friction pad marginal portions 66, 66 is sufficient to resist the aforementioned drag. It will now be evident that the marginal portions 66, 66 function to retain the clutch in a predetermined position of adjustment. When the latch recess 50 is aligned with the latch pin 94, the pin is biased into the recess by the spring 88. If the electromagnet 96 is energized, the armature plate 82 will move into holding engagement therewith to maintain the door in hold-open position. Thus, once a particular hold-open position has been established, the door may be returned to that position of adjustment each time it is opened. A new position of adjustment may be established by further opening the door to a new position of adjustment beyond the previously established position.

The door may be adjusted from a fully open hold-back position or from any partially open hold-back position to a position of lesser opening by applying force to the door in the closing direction sufficient to overcome the frictional force which couples the clutch dial 36 to the spindle 32. Thus, the door 12 may be adjusted to an infinite number of hold-open positions by first moving it to a fully open position and then applying sufficient force in a closing direction to move it to any desired hold-open position.

It is sometimes required that a door be maintained in either a fully open or fully closed position, as for example, a corridor door or the like. In such instance, it is undesirable that the door be adjustable from one hold-open position to another hold-open position of lesser opening. A further embodiment of the invention is provided to meet the requirements of this situation. This further embodiment differs from the one previously described only in the manner in which the clutch is retained on the door closer spindle. Such a further embodiment is illustrated in FIG. 7 wherein a fragmentary portion of a clutch is shown and designated generally at 24a. The clutch 24a is provided with a non-circular aperture in its clutch disc 36a for receiving an associated spindle end portion 34a in non-rotatable engagement therein, substantially as shown. The clutch 24a is mounted on a spindle end portion such as indicated at 34a in the manner previously described; however, in this instance, the friction pads function only to overcome the drag exerted upon the locking and retaining ring assembly by the latch pin 94 in the manner aforedescribed and to prevent loss of clutch adjustment due to shock or vibration resulting from door movement. When the device of the present invention is provided with a clutch such as 24a the hold-open position of the door may be adjusted by simply opening the door while the latching mechanism is held in its latched position. Thereafter, the device may be further adjusted to other wider hold-open positions by further opening the door. However, when the door attains its fully open position, no further adjustment may be attained by door movement. Thereafter, each time the door is moved to its fully open position with the holding mechanism in its energized condition the door will be held in its fully open position. If a lesser hold-open position is desired after the device has been adjusted to its full hold-open position, the clutch must be removed from and repositioned on the spindle end portion 34a to permit further adjustment. It should be noted that it is always possible to close the door even when the device is in a hold-open position and held in the latter position by the holding mechanism. Since the clutch is connected in non-rotatable engagement with the spindle 32a and the locking ring 44a is in locked engagement with the clutch dial 36a when the door is moved toward its closed position, it will be evident that if a sufficient closing force is applied to the door, the latching pin carried by the latch lever will be cammed out of the latch recess in the clutch by an associated cam surface of the recess. Thus, one of the cam surfaces of the latch recess cooperates with the latch pin to override the latching and holding mechanisms. Thereafter, the door will move to its closed position under the normal action of the closer 20.

Referring now to FIGS. 8-10, another electromagnetic door holder-closer is illustrated which embodies the invention and includes an overrunning roller clutch designated 24b. The illustrated embodiment differs from the previous embodiment 10 only in the construction and arrangement of the clutch mechanism 24b, therefore, only the spindle of the closer is shown, the latter spindle being designated generally by the reference numeral 32b. The clutch 24b transmits torque load in one direction but overruns freely in the opposite direction and comprises a circular bearing plate 102, preferably centrally apertured for non-rotatable connection to the spindle end portion 34b. An annular thrust bearing 104 received on the spindle end portion 34b in rolling engagement with the bearing plate 102 supports an annular holding ring 106 which has a circular central aperture 107 to permit rotation of the holding ring relative to the spindle end portion 34b. As in the previously described embodiment, the holding ring or clutch part 106 has a latch recess 50b partially defined by cam surfaces 52b, 52b for cooperation with the latching mechanism (not shown) in a manner previously described. An annular friction pad 108 made from suitable clutch lining material is positioned in face-to-face engagement with the upper face of the holding ring 106 and coaxially surrounds the spindle 34b.

The clutch 24b further includes a generally cylindrical spindle shaft extension 110 which has an outwardly facing cylindrical bearing surface 112 and a non-circular central aperture 114 for non-rotatable connection with the spindle end portion 34b. A cylindrical clutch housing 116 retained on the spindle end portion by the shaft extension 110 has a cylindrical aperture 118 which receives the lower end portion of the shaft extension 110 therethrough. A unitary roller clutch unit 120 received in press fit engagement within a cylindrical recess in the clutch housing 116, as best shown in FIG. 8, comprises an overrunning roller clutch which includes a plurality of drive units or rollers 122, 122 arranged to wedge between the bearing surface 112 and inclined surfaces associated with its outer shell to transmit torque load in only one direction, as is well known in the clutch art. The clutch 120 has a plurality of springs 124, 124 which aid in positioning the rollers for instant clutch engagement or lockup. Preferably, and as shown, the clutch 120 comprises a drawn cup overrunning roller clutch of a type manufactured by The Torrington Company, Torrington, Conn. The clutch housing 116 is further supported for rotation with the holding ring 106 and relative to the spindle 32b and the spindle extension 110 by another thrust bearing 126 which surrounds the lower end portion of the spindle extension, as best shown in FIG. 9. The clutch 24b is retained in assembly with the spindle end portion 34b by a threaded fastener 62b and a washer 128. The fastener 62b is adjusted to vary frictional engagement between the friction pad 108 and the holding ring 106 and clutch housing 116.

When the device is installed on a door, such as the door 12 in FIG. 1, the electrically operated holding mechanism is energized, and the door is opened, the entire clutch assembly 24b turns as a unit in a clockwise direction with the spindle 32b until the latch pin associated with the latch mechanism enters the latch recess 50b. Thereafter, due to the overrunning feature of the roller clutch, further movement of the door in the opening direction causes the spindle extension 110 to rotate with the spindle 32b and in a clockwise direction relative to the clutch unit 120, the clutch housing 122, the friction pad 108 and the holding ring 106. The fastener 62b is adjusted to provide sufficient frictional coupling between the clutch housing 116 and the holding ring 106, through the friction pad 108 to overcome reactive torque of the door closer exerted in a counterclockwise direction by the closer spindle 32b acting upon the clutch housing 116 through the spindle extension 110 and the clutch unit 120. Thus, the door will be held open in any position to which it is opened while the electromagnetic associated with the latching mechanism remains in an energized condition to retain the latching mechanism in its latching position. As in the previously described embodiment shown in FIGS. 1-6, the door may be adjusted from any hold-open position to a lesser hold-open position by applying force to the door in the closing direction sufficient to overcome the frictional force which couples the clutch housing 116 to the holding ring 106 while the holding ring is retained in a fixed position by the latching mechanism. Thus, the door may be held in a fully open position or may be adjusted to any partially open condition desired by simply manipulating the door.

In FIGS. 11 and 12 there is shown still another embodiment of the invention particularly adapted for adjustment to hold a door in a single preselected hold-open position. Since the illustrated device differs from the device shown in FIGS. 1-6 only in the construction and arrangement of its clutch assembly 24c, only the closer spindle is shown and designated 32c. The clutch assembly 24c comprises a spindle stud 130 which has a non-circular central aperture 131 for non-rotatable connection with the spindle end portion 34c. It is retained in assembly with the spindle end portion by a fastener 62c and a washer 128c, as best shown in FIG. 12. The lower end portion of the spindle stud 130 is generally cylindrical and has a male thread thereon. The upper end portion of the stud 130 is threaded to receive an adjustment nut 132 and a lock nut 134 and has flats machined on its opposite sides to present a substantially non-circular cross section, as best shown in FIG. 11. A holding ring 106c is threaded onto the lower end portion of the spindle stud 130 and has a latch recess 50c formed therein and partially defined by cam surfaces 52c, 52c. The clutch 24c further includes a locking ring 136 which has a non-circular central aperture 138 for non-rotatable connection with the upper end portion of the spindle stud 130, as shown in FIG. 11, and is disposed on the spindle stud between the adjustment nut 132 and the holding ring 106c, as best shown in FIG. 12. An annular friction pad 140 made from suitable clutch lining material surrounds the spindle 32c and is positioned between opposing bearing surfaces on the holding ring 106c and the locking ring 136, as shown in FIG. 12. The clutch assembly 24c is handed, the hand of the clutch being determined by the hand of the threads on the holding ring and spindle stud, however, it may be made for doors of either hand.

In operation, the holding ring 106c is normally maintained in a fixed position relative to the closer casing by the latch mechanism (not shown) and its associated electrically operated holding mechanism (not shown). When an associated door, such as the door 12 (FIG. 1) is opened, rotation of the spindle 32c and its associated spindle stud 130 relative to the holding ring 106c, which is threaded onto the stud, causes the holding ring to move upward toward the locking ring 136 as the latter ring rotates with the spindle 32c and relative to the holding ring 106c. The upward movement of the holding ring 106c causes the locking ring 136 to move into abutting relation with the adjustment nut 132 thereabove. Thereafter, further rotation of the spindle stud 130 and the locking ring 136 causes a jamming relationship between the locking ring 136, the holding ring 106c, and the friction pad 106 positioned therebetween. If sufficient force is applied in opening the door to its hold-open position, the resulting frictional or jamming relationship between the rings will be sufficient to overcome the reactive force exerted in a closing direction by the door closer so that the door will be maintained in an open position. The door will remain in its predetermined hold-open position until either sufficient force is applied to the door in a closing direction to release the frictional coupling between the locking and holding rings or the latch mechanism is released, as by de-energizing the electromagnetic holding mechanism. After the door has been released from its predetermined hold-open position, it will close under the reactive force exerted by the closer mechanism. The predetermined hold-open position may be varied by loosening the lock nut 134 and moving the adjustment nut 132 toward or away from the locking ring 136, as required, to attain a desired hold-open position.

As in all of the previously described embodiments, one of the cam surfaces 52c, 52c is adapted to cooperate with the latch pin received in the recess 50c to cam it out of the recess in response to manual closing force applied to the door. Thus, means are provided to override the latching and holding mechanisms so that an associated door may be manually closed at all times.

As previously noted, the aforedescribed devices are usually connected in circuit with some type of sensing device for detecting an emergency situation, however, it should be understood that the devices of the present invention may be arranged to operate in response to any current interruption device as, for example, a simple electrical switch, to facilitate remote or local operation.