Circuit control device

June 12, 1956

2,750,480

C. B. FREEMAN

CIRCUIT CONTROL DEVICE

Filed Jan. 29, 1953

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United States Patent Office _Patented ratentea June 1Z, lyob

2,750,480

CIRCUIT CONTROL DEVICE

Charles B. Freeman, Ferndale, Mich.

Application January 29,1953, Serial No. 334,064

Claims. (Cl. 200—168)

This invention relates to operator operable control devices or switches and especially to push button type circuit control devices for industrial purposes constructed to inhibit careless operation thereof, provide a maximum degree of resistance against damage and provide protection against electrical grounding for the operator. My invention further embraces apparatus for, and a method of making circuit control devices having the foregoing characteristics and at a reasonably low cost.

Circuit control devices are commonly employed in industry. Typical applications are for controlling hoists, wire drawing machines, and plating equipment. In many instances the control device is attached to one end of a flexible, so-called “walking” cable enabling the operator to manipulate the control device at some distance from the equipment. Moreover, the equipment controlled by the control device is often operable only so long as the operator maintains pressure upon the actuated push button of the control device.

In the past control devices of this type have had exposed operating buttons; their casings and other structure were readily attacked by acids and vapors and they were inherently dangerous to the operator from the standpoint of electrical grounding. Moreover, the control device when at the end of a free cable was oftentimes operable by impact thereof against a hard surface or object and its internal and exterior parts were readily damaged when this occurred.

The principal object of the present invention is to prevent the foregoing undesirable and dangerous effects from occurring and provide a circuit control device having a strong impact resisting structure, which also completely seals and protects the control mechanism against acid, water, oil, grease and salt spray and which substantially fully protects the operator from electrical grounding.

Another object is to provide a control device the operating elements of which may be comfortably actuated manually but which it will be difficult to unintentionally actuate, as by impact.

A specific object is to provide a control switch structure of convenient truncated cylindric shape for manual manipulation and operation which is protected by an enclosing layer of flexible, acid resisting and electrical insulating material, and in which the operating members are actuated against a predetermined resistance through a flexible membrane of such material.

A further object is to provide a circuit control device having all of the preceding characteristics, which is of practical design, easily assembled, substantially free of parts to loosen, and not prohibitive in cost to produce.

These and other objects and features of my invention including the novel details of construction, method of making, and combination of parts will be evident from the following description and the drawing illustrating my invention as applied to a control device having a plurality of push button operated switches.

In the drawing in which similar numerals designate corresponding parts of the structure, Figure 1 is an ele10 vational view partly in section of the control device of my invention;

Figure 2 is a sectional elevational view taken at 2—2 of Figure 1;

Figure 3 is a perspective view of the exterior of my control device;

Figure 4 is a perspective view of the switch mounting structure of my device, parts being broken away to show a switch unit;

Figure 5 is a diagrammatic view of a typical control circuit employing the control device of my invention; and

Figure 6 is a side elevational view of a fixture having dummy buttons for insertion in the casing of my control device when applying thereto the sealing coating layer which provides the membranes straddling the push buttons of my device.

Referring now to the drawing, 10 is an elongated, metallic tubular casing body or housing preferably of steel having a cylindrical wall 12 truncated by a flat side wall 14 within the perimetral circle of the cylinder. The size and stated shape of the casing is preferably chosen to enable easy gripping of the device by the operator and conformity of his fingers thereto. An integral end wall 16 of the casing is centrally apertured as at 18 for receiving a cable sealing and clamping assembly generally designated by the numeral 20. The end of the casing opposite the wall 16 is open when the casing is formed but is subsequently closed by a flat removable metallic disc or plate member 22 of truncated circular shape to fit within the truncated circular opening of the casing, this plate 22 constituting part of a switch unit generally referred to by the numeral 24.

The cable sealing assembly 20 comprises a tubular gland or bushing 26 having a threaded end 28 which projects through the aperture 18 of the casing 10 and receives a threaded clamp nut 30 by which a shoulder portion 32 of the bushing 26 larger than the aperture 18 is tightly drawn against the exterior side of the end wall 16. The bushing 26 has another threaded end 34 upon which is received a cable clamp nut 36. The bushing 26 has a circular bore 38 which is outwardly tapered at 39 for receiving a cylindrical packing or sealing grommet or ring 40 of rubber or other suitable insulating material. This ring is first assembled over an electrical cable 41 carrying the switch circuit wires when the cable is inserted through the bushing. After the cable is in proper position the gland nut 36 is drawn up forcing the ring 40 tightly against the tapered bore 39 of the bushing and against the outer cylindrical surface of the cable 41, to form a fluid and moisture seal therewith.

The switch unit 24 preferably comprises an elongated inverted U-shaped metallic member or channel 42 having a top wall 44 forming the base of the channel and side walls 46, 48, forming the legs thereof. One of the ends 50 of the channel 42 is suitably secured as by welding to the circular plate 22. The channel 42 is mounted centrally of the plate 22 and such that the inner face of the flat side wall 14 parallels and is coincident with the chordal edge 51 of the plate 22 and such that the lower edges 52, 54, of the side legs 46, 48, rest and may slide upon the inner surface of the cylindrical wall portion 12 of the casing 10 during assembly of the switch unit 24 into the casing. It will be understood that the edges 52, 54 of the channel not only guide the end plate 22 into position but enable the casing wall 12 to support the switch unit and take the reaction of any operating load imposed upon the switch unit.

In Figures 1 and 4 I have shown for purposes of illustration only, my control switch unit or device arranged to control two independent circuits. For this purpose I preferably employ conventional individual switches or switch assemblies 56, 58, preferably of the momentary

3,750,480 the opening 90 adjacent the open end of the casing it may be readily depressed and made .to move further into the casing to its correct position. This condition may be avoided by a slight rotation of the switch unit to misalign the buttons 86 and openings 90 until the unit 24 is substantially in its final position inwardly of the casing at which time the unit is rotated to realign the buttons and openings.

The control unit is completely sealed and protected against water, vapor, acid, grease, salt spray, and electrical grounding by an insulating layer 100 comprising flexible, non-porous, rubbery, plastic material preferably a synthetic resin such as a vinyl resin, resistant to these and similar substances, which layer 100 forms a continuous covering over the entire barrel of the casing 10, the exterior of the plate 22, the exterior of the end wall 16, and the flange portion 32 of the cable bushing 26.

The layer 100 is, moreover, securely bonded to the surfaces of these parts except over the buttons 86 where the layer MO provides the raised shaped membranes 102 conforming to the shape of the buttons 86 and bridging the openings 90 of the casing.

The layer 100 is of sufficient thickness, preferably about one sixteenth of an inch, to provide the unit with shock and impact resistance and sufficient flexural strength at the membranes M2 to prevent its cracking under repeated flexing of the membranes by operation of the buttons 86 through these membranes. It will be noted that since the buttons 86 are not bonded to the membranes 1.02 of the layer 100 the membrane may be freely flexed and it is possible to readily disassemble the switch unit and buttons from the casing.

A specific feature of my invention is the method I employ for obtaining the protective layer 100 and the flexible membranes 102 thereof. First, the bare casing 10 with a bushing 26 in position has its exterior surface coated, as by spraying or dipping, with a thin subprimer coating layer which will bond to the metal and which will provide a base to which may be bonded a subsequent main coating that will form an integral layer with the subprimer coating. A suitable subprimer coating I have successfully used is “Unichrome” primer 219PX which is a heat hardenable resin made by the United Chromium, Inc., Detroit, Mich. Before applying the primer coating the open end of the casing and the apertures 90 in the flat wall 14 may be suitably plugged and the outer threaded end 34 of the bushing 26 may be protected by suitable means which may also serve as a holder for the casing.during the coating operation. After the primer coating is applied it is dried and hardened by heating the coated casing for about 20 minutes or more at temperature of about 350 degrees F. to 385 degrees F.

Thereafter the plugs are removed and a dummy push button fixture 108 shown in Figure 6 is positioned within the casing 10. This dummy fixture comprises a plate 110, a pair of studs 112 secured to the plate 110 by screws 114 and a flat resilient L-shaped spring 116 also secured to the plate 110 by one of the screws 114. The studs contact single pole push type, two being shown. These switch assemblies which have suitable casings of insulation material are shown mounted in the channel 42 between the side legs 46, 48, as by suitable cross bolts or rivets 6.0. 5

As seen diagrammatically in Figure 1 each switch assembly includes a stationary contact 62 and a flexible circuit closing blade 64 normally spaced from the contact 62 and operable to make contact therewith for example to close the circuit by a push pin or operating plunger 10 65 suitably guided for axial movement in a bore -56 provided in the insulated body of the switch assembly.

The contact making blades 64 of the switches 56, 58, are connected to terminals 67, 68, respectively, served by the conductors, 70, 72, respectively of the cable 41 and 15 the stationary contacts 62 of these switches are connected to terminals 74, 76 respectively, served by the conductor 78 of the cable 41 which connects these terminals through a jumper 80.

The top wall 44 of the channel 42 as seen in Fig. 1 20 is pushed or pressed outwardly immediately above the switch operating plungers 65 to form raised and apertured conical protuberances 82 coaxial with the plungers 65 and which loosely journal the cylindrical shanks 84, of large cylindrical push buttons generally designated by the nu- 25 mera! 86 arranged above the plungers 65 and coaxial therewith. These push buttons are preferably made of a hard wood or suitable plastic insulating material such as a phenolic condensation product. Each push button .86 has a rounded or convex shaped head portion 88 re- 30 ceived in a circular opening 90 formed in the flat wall portion 14 of the casing 1® and has an annular shoulder forming portion 92 larger than the head portion 88 adapted to seat against the inner surface 93 of the wail portion 14. The annular portion 92 is undercut as at 35 94 adjacent the shank 84 of the button to form a seat for receiving a compression coil spring 96 the opposite end of which is received over the conical protuberance 82 of the channel.

The springs 96 maintain a constant bias against the 40 buttons 86 such that they are normally securely held with their annular portions 92 against the flat wall 14 of the casing 10. They also exert a bias against the switch unit 24 to maintain the edges 52, 54 of the channel 42 in contact with the cylindrical wall 12 of the casing 19. In the described position of the push button, as seen in ⁴⁰Figure 1, the shanks 84 thereof are spaced slightly from the outer ends of the switch plunger 66 in their circuit open condition to provide gaps 98 therebetween.

By preference the springs 96 are of sufficient strength so as to require considerable pressure effort on the part ⁵⁰of the switch operator to depress the buttons 86 and bring the switch blades 64 into contact with the switch contact 62 to close the switch circuit. This predetermined pressure effort is desirable in order to avoid unintentional operation of the switches during normal handling of the control device or by accidental bumping of the buttons against or by another object or by the weight of the unit should the control device rest upon a surface upon which it is supported by the buttons.

Assembly of the switch unit 24 and its operating but- θθ tons 86 in the casing 10 is readily effected by positioning the buttons 86 and their biasing springs 96 over the protuberances 82 respectively of the channel 42 as the latter is slid into the casing 10, the individual buttons being depressed sufficiently to permit the same to enter 65 the casing and the head portions 88 of the buttons bearing against the inner surface 93 of the casing wall 14 under the biasing action of the springs 96 which were compressed in depressing the buttons.

When the channel 42 is located in its final in-position, 70 the end plate 22 having then entered the casing opening, the buttons 86 will register with the openings 90 in the wall 14 and be snapped outwardly to the position shown in Figure 1 by the springs 96.

Should the first button to enter the casing snap into

112 are spaced apart the distance between the openings 90 of the casing 10 and are provided with button head and shoulder portions 118, 120 respectively corresponding to the head and shoulder portions 88 and 92 respectively of the buttons 86. When the dummy is positioned within the casing the spring 116 bears against the surface of the casing opposite the wall 14 and biases the plate 110 against such wall 14. When the studs are aligned with the apertures 90 the head portions thereof snap into position closing the apertures 90 and providing a projection above the outer flat surface of the casing wall 14 corresponding to that which would be made by the buttons 86.

The casing with the dummy fixture in position and serving as a holder, and with the cable opening 38 of the bushing 26 suitably plugged, is now preferably dipped 75 into a coating bath to within one quarter inch of fhe

2,750,480 open end of the casing. The bath preferably contains a material having the above defined properties and which will bond to and form an integral covering layer with the subprimer coating but which will not bond directly to the metal buttons of the dummy fixture. Preferably the bath will comprise a thermoplastic vinyl resin coating material such as produced by United Chromium Inc. of Detroit, Mich., under the name “Unichrome” 218X, this material providing a rubbery plastic layer when dried that will have all the properties set forth above. The casing is preferably held in the coating bath as aforesaid for a period between about two to five minutes until a thick layer of the coating material of about one-sixteenth inch thickness is formed over the primer coating on the casing and other parts to be covered. The coated casing is then removed from the bath and the composite resin layer heat dried at a temperature of about 365 degrees F. for a period of about 30 to 50 minutes.

It will be noted from Figure 1 that the composite layer 108 seals the joint between the bushing 26 and the casing wall 16 and forms a layer over the heads 118 of he dummy button portions of the fixture 108. Since the heads 118 were not coated with the primer coating the final coating layer will not bond thereto. Therefore the dummy fixture 108 may now be easily removed from the casing leaving a preformed thick flexible membrane 102 of the final coating layer extending across the peripherial portions of the apertures 90 of the casing.

In assembling the control device, the cable 41 with its sealing ring in position thereon may be drawn through the central aperture 38 of the bushing 26 and through the end opening of the casing and the three wire conductors 70, 72, 78 thereof connected to the terminals 67, 68, 74, and 76, as seen in Figure 1, of the switches 56 and 58. The cable is now pulled in the opposite direction and the switch unit 24 assembled in the casing 10 in the manner described above with the push buttons 86 seated in the pockets provided by the apertures 90 and membranes 102. In this operation the plate 22 is fitted into the end opening of the casing flush therewith and the plate 22 is either soldered or pinned as by pins 124 to the casing 10. If desired one or more stop pins 126 may be provided adjacent the open end of the casing 10 to provide a limit stop for the plate 22 during assembly.

The cable 41 is now clamped and sealed by the gland nut 36 which has preferably previously been treated on its outer surface with layers of the aforesaid primer and finish coatings. The nut preferably makes a pressure contact with the portion of the coating layer 100 covering the flange of the bushing 26.

Next, if the outer face of the end plate 22 has not previously been coated with the primer the end of the casing at the plate 22 which remains uncoated is dipped into a bath of the subprimer coating material described above, or sprayed therewith. This primer coating is then dried in the manner previously described and the newly primed portion is then dipped into the final vinyl coating bath to form with the primer a composite adherent coating layer 101 of the thickness of the layer 100 over the uncoated portion of the casing 10 at the end of the plate 22 and preferably laps the layer 100.

It will be understood that the layer 101 will readily amalgamate with the previously formed layer 100. The coating layer 101 is heat dried in the manner previously described to set this coating layer. If desired, the end plate 22 may be treated with the primer and final coatings before the switch unit is assembled in the casing and the thermoplastic layers 100, 101 thereafter amalgamated by a hot iron or similar instrument after the plate 22 is in position. The control unit is now completely sealed and ready for use.

By reason of the tubular construction and flat side on the casing the device readily conforms to the shape of the operator’s hands when gripped by the latter. When pres sure is applied in sufficient amount, by the fingers of the operator, or by his palm, to the membranes 102 the buttons 86 will be moved inwardly to actuate one or both of the switches 56, 58 as the case may be.

As seen in Figure 5, actuation of the switch 56 causes current to flow by way of the conductor 70 to the load A and when the switch 58 is actuated current flows by way of the conductor 72 to the load B. The current flows only so long as the buttons 86 are held depressed.

From the foregoing description of my invention it will be seen that I have provided a novel circuit control unit for industrial use in which the switch mechanism thereof is protected against moisture, vapor, acid etc. and which protects the operator against electrical grounding when the control unit is wet or dry and protects the switch mechanism of the unit against accidental operation.

It will be understood that various changes and modifications may be made in the specific structure of the control unit and in the manufacturing procedure described above without departing from the scope and spirit of my invention. For example, the control unit may be provided with a greater or lesser number of switches than that illustrated in Figure 1. Moreover, a plurality of switch mechanisms may be arranged in side by side relationship instead of end to end as illustrated. Furthermore the entire final coating 100 may be applied after the complete mechanism is assembled with the buttons 86 in place, the buttons 86 being then preferably formed of a material to which the coating layer 100 will not bond.