US3846604A

US3846604A - Overhead electrical switching device

Info

Publication number: US3846604A
Application number: US00368962A
Authority: US
Inventors: G Shallbetter
Original assignee: STATES ELECTRIC Mfg CO
Current assignee: STATES ELECTRIC Mfg CO
Priority date: 1973-06-11
Filing date: 1973-06-11
Publication date: 1974-11-05
Anticipated expiration: 1991-11-05

Abstract

An electrical switching device for use at remote locations such as room ceilings comprises a switch mounting plate having an electrical push button switch mounted thereto with an actuating plate confronting the push button and mounted for movement toward and away from the button, the actuating plate having guide rods projecting outwardly therefrom and extending within registering guide sockets in the switch mounting plate. Stops are provided at the end of the guide rods to contain the rods in the guide sockets, and coil springs are positioned about each guide rod between actuating plate and mounting plate to urge the actuating plate away from the mounting plate. The electrical switch device is mounted in a junction box within the room ceiling, and a cover plate mounted flush with the ceiling surface bears flushly against the actuating plate, the springs, guide rods and guide sockets cooperating to align the movable actuating plate parallel to the cover plate and parallel to the local surface of the ceiling. The switching device is actuated by an operator on the floor by depressing the actuating plate toward the mounting plate with a pole. The invention is particularly useful in buildings with movable wall partitions where it is necessary to control electric power flow to the wall partitions.

Description

United States Patent 1191 Shallbetter OVERHEAD ELECTRICAL SWITCHING DEVICE [75] Inventor: George H. Shallbetter, Minneapolis,

Minn.

[73] Assignee: States Electric Manufacturing Co.,

North Minneapolis, Minn.

[22] Filed: June 11, 1973 [21] Appl. No.: 368,962

[52] U.S. Cl 200/168 D, 174/48, 220/33 [51] Int. Cl. H0lh 9/02 [58] Field of Search ZOO/I53 T, 172 A, 86 R,

ZOO/86.5, DIG. 35, 168 D, 168 G, 166 H, 168 H, 3.3, 3.5, 3.6, 3.7; 174/66, 67, 48, 58

Primary Examiner-Robert K. Schaefer Assistant Examiner-William J. Smith Attorney, Agent, or FirmWilliamson, Bains & Moore 1451 Nov. 5, 1974 [57] ABSTRACT An electrical switching device for use at remote locations such as room ceilings comprises a switch mounting plate having an electrical push button switch mounted thereto with an actuating plate confronting the 'push button and mounted for movement toward and away from the button, the actuating plate having guide rods projecting outwardly therefrom and extending within registering guide sockets in the switch mounting plate. Stops are provided at the end of the guide rods to contain the rods in the guide sockets,

' and coil springs are positioned about each guide rod between actuating plate and mounting plate to urge the actuating plate away from the mounting plate. The electrical switch device is mounted in a junction box within the room ceiling, and a cover plate mounted flush with the ceiling surface bears flushly against the actuating plate, the springs, guide rods and guide sockets cooperating to align the movable actuating plate parallel to the cover plate and parallel to the local surface of the ceiling. The switching device is actuated by an operator on the floor by depressing the actuating plate toward the mounting plate with a pole. The invention is particularly useful in buildings with movable wall partitions where it is necessary to control electric power flow to the wall partitions.

5 Claims, 5 Drawing Figures IATENTEUN 5|974 sum NF 2 3.846.8(94

1 OVERHEAD ELECTRICAL SWITCHING DEVICE BACKGROUND OF THE INVENTION Many modern buildings such as schools and offices utilize movable wall partitions to subdivide their floor space. Typically the partitions are supported at their junction with the suspended ceiling by tongues extending therefrom into tracks or grooves on the ceiling, the tracks being formed in the framework of the suspended ceiling.

Frequently the wall partitions have standard electrical outlets therein, power being delivered to the partition through greenfield cable connected to junction boxes in the ceiling. As the movable partitions are installed or moved about to meet changing room use requirements it is necessary to have a switch to turn off electrical power flow from junction box to partition to provide safe working conditions during installation or moving. It is impractical to mount such switches on the movable partitions because it is desired to interrupt current flow before current reaches the partitions. It is also impractical to position switches on the floor since this has an undesirable effect on appearance and may require more elaborate protective structure to prevent breakage. The preferred position for such a switch from both aesthetic and economic viewpoints is on the ceiling where it is relatively accessible when needed but otherwise out of the way and out of reach of unauthorized persons.

Presently there are no commercially available switching devices for ceiling usage which are safe, reliable, or acceptable under standard electrical code requirements. Any such switching device used for ceiling installation must be aesthetically acceptable and compatible with suspended ceiling construction, easily operable from the floor below but substantially unbreakable if excessive operating pressure is applied to the switch by an operator on the floor below, and require minimal time to install. Since the lower surface of most suspended ceilings is not perfectly level, and in fact exhibits considerable local variation, the switch device should be self adjusting to the irregular surface of the ceiling.

BRIEF SUMMARY OF THE INVENTION The present invention relates to the field of electrical switching devices and comprises a switching device particularly well adapted for moon the suspended ceilings of buildings, such as schools and offices using movable wall partitions, to control electrical power flow to the wall partitions or to other points.

The electrical switching device invention is mounted within the suspended ceiling, the device being attached within a junction box positioned above the level of and attached to the framework of the suspended ceiling. A

switch mounting plate provided with a plurality of guide sockets therein is attached to a commercially available push button switch of the type which is operable between on and off conditionsby displacing the button a predetermined distance. An actuating plate confronts the button of the electrical switch and a plurality of guide rods are fixed to the surface of the actuating plate, their free ends extending through the guide sockets of the switch mounting plate. Stops positioned at the free ends of the guide rods contain the free ends within the guide sockets, permitting the actuating plate to move toward and away from the mounting plate as the guide rods slide through the guide sockets. Spring means are connected between the actuating plate and the mounting plate to urge the actuating plate away from the mounting plate to a rest position and yieldably retaining it there unless depressed toward the mounting plate by an operator.

The electrical switch and the described mounting plate and movably mounted actuating plate are positioned within the ceiling junction box, the actuating plate extending below the level of the facing of the suspended ceiling. A cover plate, painted to harmonize with the local ceiling panels, is mounted flushly against the facing of the suspended ceiling by screws engaging the junction box. The cover plate has a central aperture permitting access to the actuating plate; the spring means positioned between actuating and mounting plates urges the actuating plate flushly against the cover plate, assuring that the actuating plate is parallel to the cover plate. Since the cover plate is substantially parallel with and aligned to the local facing of the suspended ceiling, installation of the cover plate automatically aligns the actuating plate parallel to the cover plate and hence to the facing of the ceiling to achieve a neat but inconspicuous appearance. The mounting plate is provided with stops to prevent the actuating plate being overly depressed so as to damage the push button switch.

To operate the electrical switching device, an operator on the floor below the switch extends a pole through the access aperture of the cover plate and against the actuating plate to move the actuating plate from its normal rest position against the cover plate toward the mounting plate to actuating the push button switch, thereby opening or closing the switch.

The invention provides an apparatus which is easily installed since the actuating plate is self adjusting to the level of the ceiling facing when the cover plate is installed. Because the invention is provided with stops to limit the travel of the actuating plate toward the push button, the switch is protected from excessive compression and breakage is avoided, permitting the use of even relatively fragile, light weight switches. If desired a push button circuit breaker may be substituted for the electrical switch. As will be apparent hereafter, the invention is easily mounted to a modern suspended ceiling and meets all existing electrical code requirements. Since the cover plate and the actuating plate may be painted to match or harmonize with any existing suspended ceiling, a pleasing, aesthetic appearance always results. Still other advantages of the invention are that it is durable, compact, resistant to shock and rough handling, easy to manufacture and simple to assemble.

These and other objects and advantages of the invention will become apparent from the following description made with reference to the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the suspended ceiling and partition walls of a modern office building with an embodiment of the electrical switching device invention installed in the ceiling.

FIG. 2 is an exploded view showing an embodiment of the electrical switching device used with a junction box constructed for mounting to the framework of a suspended ceiling.

FIG. 3 is a side elevational view of an embodiment of the switching device invention mounted on an irregular ceiling showing alternative positions of the self adjustingactuating plate.

FIG. 4 is a side elevational view of an embodiment of the invention mounted on the ceiling and showing alternative positions of the movable actuating plate.

FIG. 5 is a top view of the mounting plate used with the invention.

MAIN DESCRIPTION Referring now to FIG. 1, an electrical switching device 10, embodying the invention is shown attached within an electrical junction box 12. The junction box 12 is welded to a mounting strap 14 arranged to be easily attached to commercially available frame members 16 which are part of the framework supporting panels 18 of the suspended ceiling. A cover plate 67 is mounted flush with the facing 23 of the ceiling.

Movable partition walls

19 and 20 are retained at their junctions with the ceiling by tongues 21 being inserted into tracks or grooves 22 formed in certain of the supporting frame members 17 of the suspended ceiling. A standard electrical outlet box 24 on partition wall 20 is electrically connected through greenfield cable 26 to a main junction power box 28 located in the joists of the ceiling. A powerline within greenfield cable 30 supplies-current to the box 28, and a cable 31 extends from box 28 to junction box 12 to permit power flow between

cables

30 and 26 to be switched on and off by the electrical switching device 10 located in box 12.

Referring now to FIG. 2, the junction box 12 is a commercially available steel box having mounting brackets 32 therein on opposite side walls welded to the sidewalls, the box also being provided with a plurality of removable knockouts at which electrical connectors may be attached to join electrical cables to the box. Plate mounting flanges 33 are tapped at bores 34 for attachment of a cover plate to be described hereafter.

The steel mounting strap 14 has an aperture 35 in its web 37 to permit access to the knockouts of box 12, the box being rigidly fixed to the strap 14 by welding or like means known to the art. The strap 14 is provided with sturdy, parallel spaced legs 36 oriented at right angles to the web 37. The free end of each leg 36 has a base 27 at a right angle to the leg and an upwardly turned tab 29 extendsfrom each base at a right angle thereto, the leg, base, and tab collectively forming an open top box channel 39 of a size adapted to fit conveniently and smoothly within the channel 40 of a commercially available suspended

ceiling frame member

16 or 17. The strap 14 along with box channel 39 comprises a means for mounting the junction box 12 to the framework of the suspended ceiling. Box channel mounting screws 41 are passed through frame member 16 and screwed into bores 42 of the tab 29 retaining the mounting strap 14 to the suspended ceiling framework. The box l2 is positioned such that the plate mounting flanges 33 lie near the facing 23 of the ceiling panel 18 but not projecting beyond the facing of the panel into the room.

The electrical switching device 10 utilizes a commercially available push button switch 45 having mounting tabs 46 thereon for attachment to switch mounting brackets 32 by means of switch screws 47. Wires 48 are connected to the terminals of the switch 45 and extend into the cable 31.

The switch 45 comprises a switch means usable with the invention, but it should be understood that any switch known or hereafter invented which utilizes a spring loaded depressable button to actuate the switch between on and off conditions is within the purview of the invention. The term switch means as used herein also includes a circuit breaker; in various situations it is desirable to use a circuit breaker in place of switch 45 to provide protection against current overload. It should also be understood that the term button as used herein is also intended to include any plunger or lever used to actuate a switch or breaker between on andoff conditions. The shown switch 45 utilizes the push button 49 which is movable in the directions of arrow 50, the button being depressed in the direction of the switch body 45 to actuate the switch and being spring loaded to be returned in the direction of mounting plate 53 when any applied pressure on the button 49 is removed.

The mounting plate 53 is formed of rigid metal such as steel and has a centrally located control aperture 54 through which push button 49 extends when the plate 53 is tightly secured to the front face of the switch 45 by mounting plate screws 55 which pass through bores in the mounting plate 53 and are threaded into the switch 45 utilizing the tapped holes in the switch 45 normally reserved for a commercially available switch cover plate.

The mounting plate 53 is provided with a plurality of guide sockets 56 positioned at the corners of the plate and passing through the plate. Although four such guide sockets are shown, it should be understood that a greater or lesser number could have been used although four such sockets are preferred. The longitudinal edges of the plate 53 are angled perpendicularly to the plate 53 to form flanged stops 57 and 58 for a function to be described hereafter.

A generally rectangular actuating plate 60 has an inner face 61 positioned to confront the button 49 I which extends through the control aperture 54 of mounting plate 53 toward the plate 60. The outer face 62 is substantially flat and is painted to resemble the color of the suspended ceiling facing 23. Compression studs 63 are rigidly imbedded in the plate 61, being forced through holes bored in the plate to receive the studs and extending perpendicularly to the plate and parallel to one another. The heads of the studs are substantially flush with the outer face of plate 60. The studs 63 are of a'diameter small enough to freely slide through the guide sockets 56 of mounting plate 53 and each stud has a hollow interior accessible from the free end 64 thereof and threaded to receive stud screws 65 therein. The stud screws 65 have a head diameter exceeding the diameter of the guide apertures 56 thereby serving as stops positioned at the free ends of the studs to contain the free ends of the studs within the guide sockets of the mounting plate 53. The compression studs 63 slide freely through the guide sockets 56 and serve as guide rods for moving the plate 62 from a rest position 68 where it flushly contacts the inner surface 66 of the cover plate 67, to a depressed position 69 (FIG. 3) wherein the push button 49 is depressed sufficiently to actuate the switch 45.

A plurality of coil springs 70 are positioned on the studs 63 between mounting plate 53 and actuating plate 60 to urge the actuating plate away from the mounting plate and toward its rest position 68 and yieldably retaining the actuating plate in the rest position 68 and permitting the plate 60 to be depressed by an operator. The shown plurality of coil springs 70 constitute a spring means usable with the invention, but it should be understood that other known springlike structures may be substituted for the shown springs 70 and are within the purview of the invention.

The actuating plate 61 is constructed with adequate width to assure that the inner face 61 strikes the flange stops 57 and 58 when depressed sufficiently. The stops 57 and 58 (FIG. 4) are positioned relative to button 49 to assure that the push button can be depressed sufficiently by actuating plate 60 to actuate the switch 45 before the actuating plate 60 encounters the

stops

57 and 58 at terminal position 72. It is desirable that the

stops

57 and 58 are encountered very shortly after the switch is adequately depressed for actuation to assure that the switch cannot be broken or damaged by excessive compression.

The lateral edges 73 and 74 of the plate 60 are provided with semicircular cutaways 75 to provide easy access of an assemblers screwdriver to the mounting plate screws 55, permitting easy attachment of the screws to the switch 45.

When the switch 45, mounting plate 53 and movably mounted actuating plate 60 have been mounted in the junction box 12, a cover plate 67 is attached to the plate mounting flanges 33 by cover screws 76. The cover plate 67 has an access aperture 78, and actuating plate 75 is urged flushly against cover plate 67 and retained in flush engagement by the cooperative action of the springs 70, guide rods 63 and guide sockets 56. The access aperture 78 is made of adequate size to permit an operator to insert a rod 79 (FIG. 1) therethrough to urge the actuating plate toward the switch 45 to operate the switch. A plastic or rubber tip 80 is placed on the rod end to protect the finish of the plate 60. A gasket 82 of relatively thin foamlike material is interposed between the outer surface 62 of actuating plate 60 and the cover plate 67 to prevent vibration and noise generation by the plates. Since numerous vibration producing apparatus is located within the ceilings of modern buildings, such as fans, loudspeakers and the like, it is important to avoid vibration of the metal components of the switching mechanism 10.

In operation, the junction box 12 with its strap 14 is installed in the ceiling of the building, the open box channels 39 being received within the channels 40 of the suspended ceiling frame members 17. Screws 41 are inserted through the members 17 and the channel 39 to retain the mounting strap 14 within the ceiling with the junction box 12 having its opening just above the facing 23 of the ceiling panels 18.

The wires 48 are connected to the terminals of the switch 45, and the electrical switching device is attached to the mounting brackets 32 of the junction box by switch screws 47, thus fixing the switching device 10 firmly within the junction box 12. It should be understood that the switching device 10 comprising the switch 45, the mounting plate 58 and the movably mounted actuating plate 60 are fully assembled as a unit when inserted in the box 12. After being thus mounted in the junction box 12, the actuating plate 60' projects through ceiling opening 85 and below the level of the facing 23 of ceiling panels 18.

Not infrequently, the facing defined by the ceiling panels 18 will not be parallel to the mounting plate 53 due to irregularities of the ceiling surface, but it is desirable that outer surface 62 of the actuating plate be aligned parallel to the facing of the local ceiling surrounding the junction box 12. To achieve this alignment, the cover plate 67 is installed over the ceiling panel 18, screws 76 securing the plate to the junction box 12. As the screws 76 are tightened and the plate 67 seats flushly against the facing of ceiling panels 18, the plate 67 urges the actuating plate 60 upwardly toward the mounting plate 53 aligning it parallel to the cover plate 67 and parallel to a predetermined plane such as that defined by the cover plate lying flushly against the local ceiling adjacent the opening 85 as shown in FIG. 3. As the actuating plate 60 moves toward the mounting plate 53, the guide rods 63 slide along the guide sockets 56 while the springs retain the plate 60 in flush engagement with the cover plate 67. The springs, guide sockets and guide rods cooperate to yieldably retain the actuating plate against the cover plate in parallel relation to the local ceiling surface in a rest position 68 shown in FIGS. 3 and 4.

When it is desired to actuate the switch 45, an operator uses a pole 79 having a soft tip thereon (FIG. 1), urging the tip through the access aperture 78 of the cover plate 67 and against actuating plate 60. The operator uses the pole 79 to exert upward pressure on the actuating plate 60 urging it from the rest position 68 to a depressed position 69 (FIG. 3) wherein the button 49 of the switch 45 is depressed sufficiently to actuate the switch between off and on positions. Occasionally the operator may inadvertently exert excessive pressure on plate 60 causing plate 60 to move to the terminal position 72 at which it encounters flanged stops 57 and 58 which prevent further travel of the actuating plate 60 and thereby protect the switch 45 and push button 49 from being broken. The reinforcement provided to strap 14 by turned edge 38 causes the strap to be resistant to bending or deformation caused by excessive upward force.

When the pressure is removed from the plate 60 by withdrawal of the rod 79, the coil springs 70 urge the plate 60 downwardly away from the mounting plate 53, the guide rods sliding smoothly through guide sockets 63 and directing the plate 60 back toward the cover plate 67.

Since the cover plate 67 and actuating plate 68 may be painted to resemble the ceiling paneling 18, these plates, which are the only parts of the device visible from below, are relatively inconspicuous and do not detract from the aesthetic appearance of the ceiling.

Accordingly the invention provides a highly reliable, compact, relatively inexpensive apparatus which can be easily positioned on the ceiling of a modern building or alternatively at other remote locations to control current flow to movable panel walls or the like at such times as necessary.

While the preferred embodiment of the present invention has been described, it should be understood that various changes, adaptations and modifications may be made therein without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is: 1. An overhead electrical switching device usable on a suspended ceiling having ceiling panels carried by frame members, the device positionable above an apera switch mounting plate having a plurality of guide sockets therein, said mounting plate attached to and within said junction box;

electrical switch means including a button, said switch means operable between on and off conditions by displacing said button a predetermined distance, said switch means being rigidly mounted to said switch mounting plate;

an actuating plate having an inner face positioned to confront said button of said electrical switch means and an outer substantially flat face;

a plurality of guide rods, each rod having an end fixed to said actuating plate and a free end, said free ends extending within said plurality of guide sockets of said mounting plate for sliding movement therethrough as said actuating plate moves relative to said mounting plate from a rest position wherein said button is not displaced said predetermined distance by said actuating plate, to a depressed position wherein said button is displaced said predetermined distance by said actuating plate to operate said switch means between on and off conditions;

a plurality of stops positioned at the free ends of a plurality of said guide rods to contain said free ends of said guide rods within said guide sockets in said mounting plate; and

spring means connected between said actuating plate and said mounting plate urging said actuating plate to said rest position and yieldably retaining said actuating plate in said rest position permitting said actuating plate to be depressed by an operator.

2. The overhead electrical switching device of claim 1 and further including a substantially flat cover plate having an access opening therein and mounted to said junction box below, parallel to, and against the plane of the adjacent ceiling surface, covering the aperture in the ceiling, said spring means cooperating with said plurality of guide rods and said guide sockets to yieldably urge said actuating plate toward said cover plate to align said actuating plate parallel to the plane of the ceiling and flush therewith for flush engagement against said cover plate thereby avoiding manual alignment of the switching device with the ceiling.

3. The overhead electrical switching device of claim 1 wherein said electrical switch means includes a circuit breaker to interrupt current flow when a predetermined current level is reached.

4. The overhead electrical switching device of claim 1 wherein said flat web of said strap is generally parallel to the ceiling and each said box channel includes a leg extending downwardly from said web at right angles to said web, said leg of said box channels further including a base extending from each said leg at a right angle and being generally parallel to the ceiling and a tab extending upwardly from said base and parallel to said leg.

5. An overhead electrical switching device positioned on a suspended ceiling having ceiling panels, above an aperture in the ceiling comprising:

a pair of parallel frame members usable for supporting the ceiling panels, each frame member having a longitudinal channel therealong;

a mounting strap including a rigid, generally flat web positionable above the ceiling, said web having a pair of box channels, a box channel extending from said web at opposite sides of said web, each box channel being inserted within and mounted to a said longitudinal channel of a said frame member to thereby retain said mounting strap to the frame members;

an electrical junction box fixed to said web of said mounting strap with its open side facing downwardly and confronting the aperture in the ceiling;

a switch mounting plate having a plurality of guide sockets therein, said mounting plate attached to and within said junction box;

electrical switch means including a button, said switch means operable between on and off conditions by displacing said button a predetermined distance, said switch means being mounted to said switch mounting plate;

plurality of stops positioned at the free ends of a plurality of said guide rods to contain said free ends of said guide rods within said guide sockets in said

Claims

1. An overhead electrical switching device usable on a suspended ceiling having ceiling panels carried by frame members, the device positionable above an aperture in the ceiling, comprising: a mounting strap including a rigid, generally flat web positionable above the ceiling panels, said web having a pair of box channels, a box channel extending from said web at opposite sides of said web, each said box channel being attachable to a frame member of the ceiling to thereby rigidly fix said strap to the frame members of the ceiling; an electrical junction box fixed to said web of said mounting strap with its open side facing downwardly and confronting the aperture in the ceiling; a switch mounting plate having a plurality of guide sockets therein, said mounting plate attached to and within said junction box; electrical switch means including a button, said switch means operable between on and off conditions by displacing said button a predetermined distance, said switch means being rigidly mounted to said switch mounting plate; an actuating plate having an inner face positioned to confront said button of said electrical switch means and an outer substantially flat face; a plurality of guide rods, each rod having an end fixed to said actuating plate and a free end, said free ends extending within said plurality of guide sockets of said mounting plate for sliding movement therethrough as said actuating plate moves relative to said mounting plate from a rest position wherein said button is not displaced said predetermined distance by said actuating plate, to a depressed position wherein said button is displaced said predetermined distance by said actuating plate to operate said switch means between on and off conditions; a plurality of stops Positioned at the free ends of a plurality of said guide rods to contain said free ends of said guide rods within said guide sockets in said mounting plate; and spring means connected between said actuating plate and said mounting plate urging said actuating plate to said rest position and yieldably retaining said actuating plate in said rest position permitting said actuating plate to be depressed by an operator.

5. An overhead electrical switching device positioned on a suspended ceiling having ceiling panels, above an aperture in the ceiling comprising: a pair of parallel frame members usable for supporting the ceiling panels, each frame member having a longitudinal channel therealong; a mounting strap including a rigid, generally flat web positionable above the ceiling, said web having a pair of box channels, a box channel extending from said web at opposite sides of said web, each box channel being inserted within and mounted to a said longitudinal channel of a said frame member to thereby retain said mounting strap to the frame members; an electrical junction box fixed to said web of said mounting strap with its open side facing downwardly and confronting the aperture in the ceiling; a switch mounting plate having a plurality of guide sockets therein, said mounting plate attached to and within said junction box; electrical switch means including a button, said switch means operable between on and off conditions by displacing said button a predetermined distance, said switch means being mounted to said switch mounting plate; an actuating plate having an inner face positioned to confront said button of said electrical switch means and an outer substantially flat face; a plurality of guide rods, each rod having an end fixed to said actuating plate and a free end, said free ends extending within said plurality of guide sockets of said mounting plate for sliding movement therethrough as said actuating plate moves relative to said mounting plate from a rest position wherein said button is not displaced said predetermined distance by said actuating plate, to a depressed position wherein said button is displaced said predetermined distance by said actuating plate to operate said switch means between on and off conditions; a plurality of stops positioned at the free ends of a plurality of said guide rods to contain said free ends of said guide rods within said guide sockets in said mounting plate; and spring means connected between said actuating plate and said mounting plate urging said actuating plate to said rest position and yieldably retaining said actuating plate in said rest position, permitting said actuating plate to be depressed by an operator.