US2957969A - Electrical switch units - Google Patents

Description

A. T. C. BURROWS ELECTRICAL SWITCH UNITS 2 Sheets-Sheet 1 Oct. 25, 1960 Filed March 19, 1958 Oct. 25, 1960 A. T. c. BURROWS ELECTRICAL SWITCH nuns 2 Sheets-Sheet 2 Filed March 19, 1958 United States Patent ELECTRICAL SWITCH UNITS Arthur Thomas Charles Burrows, Stevenage, England, assignor to Geo. W. King Limited, Stevenage, England, a British company Filed Mar. 19, 1958, Ser. No. 722,436 Claims priority, application Great Britain Mar. 22, 1957 4 Claims. (Cl. 200-164) This invention relates to electrical switch units and has as an object the provision of an improved switch unit of the push button type which is adapted particularly, although not exclusively, for controlling the operation of electric motors employed in hoists and other similar equipment.

According to the invention, a switch unit is provided which comprises fixed contacts of flat plate like form disposed in spaced relation in a common plane and movable contact means also of flat platelike form maintained in parallel relationship to said fixed contacts and movable into and out of engagement therewith along a path inclined to the plane thereof, the arrangement being such that said movable contact means will have a wiping action on the fixed contacts as they approach and are withdrawn from the latter.

In accordance with a further aspect of the invention, a switch unit may comprise fixed contacts, movable contact means movable into and out of engagement with said fixed contacts, a toggle linkage coupled to the movable contact means, a push button device and lever means interposed between said push button device and the toggle linkage and adapted on a predetermined movement of said device to actuate the toggle linkage thereby to cause the movable contact means to move rapidly into engagement with the fixed contacts, said linkage being eiTective to maintain substantially constant pressure between the contacts until the push button device is released.

In order that the said invention may be clearly understood and readily carried into effect the same will be hereinafter more fully described with reference to the accompanying drawings in which:

Figure 1 is a front elevational view of a push button switch assembly adapted to constitute a reversible controller for a reversible electric motor,

Figure 2 is a sectional view looking from the right of Figure 1.

It may be mentioned here that the controller illustrated in the drawings comprises two identical switch units which are disposed one above the other in a common casing, the mechanism of the unit in the lower half of the casing being merely inverted with respect to that in the upper. In order however to permit of satisfactory illustration of the construction, certain elements of the mechanism of the upper unit have been omitted from the lower and vice versa.

Referring now to the drawings, denotes a box like casing which is adapted to house the operative mechanisms of the two switch units. Mounted within each of the upper and lower parts of the casing are two pairs of fixed contacts such as are indicated at 11 and 12, such contacts being of flat plate-like form and being disposed in a common plane, there being means whereby current conductors such as are indicated at 13 and 14 can be attached thereto. Cooperating with the pairs of fixed contacts 11 and 12 of each switch unit is a pair of movable contacts or bridge pieces 15 which are carried in spaced parallel relationship by a carriage 16 ICC slidable back and forth along a pair of guide rods 17, the latter being fixedly mounted in spaced parallel relationship. As will be seen the axes of the guide rods 17 are inclined with respect to the plane of the fixed contacts so that as the movable contacts or bridge pieces 15 approach or are withdrawn from said fixed contacts they will have a wiping action on the latter.

The casing 10 is adapted to be closed by a cover plate 18 which is formed with two apertures through each of which a push button 19 is adapted to project, one such button being provided with respect to the uppermost switch unit and one with respect to the lower. Each push button incorporates a shoe or extension piece 20 adapted to slide in a guide way 21 formed in a supporting member or block 22 fixedly mounted within the casing. Pivotally connected at 23 to the shoe or extension piece 20 is one end of a link 24 the other end of which latter is pivotally connected to a lever 25 at a point intermediate the ends of the latter. This lever 25 which forms part of a dead center lever mechanism is pivotally connected at one end to a lug or bracket 26 fixedly mounted on or formed integrally with the casing 10. At its other end the lever 25 is provided with an inclined tongue or projection 27 having an aperture therein through which one end of a rod 28 is adapted to project, the other end of such rod being pivotally connected to a laterally projecting or offset portion 29 at one end of a substantially U-shaped lever 30 which also forms a part of the aforesaid dead center lever mechanism while additionally forming part of a toggle mechanism. Disposed around the aforesaid rod 28 is a coiled compression spring 31 which bears at one end against the tongue or projection 27 on the lever 25 and at the other against the laterally projecting or offset portion 29 at the base of the U-shaped lever 30. The outer ends of the limbs of the U-shaped lever 30 are pivotally connected to brackets or lugs one of which is indicated at 32 (Figure 2) formed integrally with or mounted on that side of the casing opposite that to which said lever 25 is connected. Pivotally connected to the lever 30 at aligned points intermediate the ends of the limbs thereof is a further U-shaped lever 33 which completes the aforesaid toggle mechanism, the outer ends of the limbs of said lever 33 being also pivotally connected to the carriage 16 on which the movable contacts or bridge pieces 15 are mounted.

As indicated above, the lever 25, the lever 30 and the interposed rod 28 and spring 31 constitute a dead center lever mechanism while the levers 30 and 33 constitute a toggle mechanism. The mechanism comprising the link 24 connecting the shoe or extension piece 20 to the lever 25 constitutes in eifect a toggle linkage.

The construction above described is such that on depression of one of the push buttons 19 the link 24 connected to the shoe or extension piece 20 will cause the lever 25 to move angularly thereby to compress the spring 31. Continued movement of the push button 19 will result in eventual actuation of the aforesaid dead center lever mechanism which will in turn be effective to operate the toggle mechanism thereby to impart movement to the slidable carriage 16 and hence movement of the movable contacts or bridge pieces 15 into engagement with the fixed contacts 11, 12. The arrangement is such that the mechanical advantage of the push button, link and lever mechanism will increase as the displacement of the push button from its inoperative position increases. When the carriage 16 is in its operative position the three hinges of the toggle mechanism indicated at A, B and C in Figure 2 will be nearly in a straight line so that the force exerted by the toggle mechanism to effect closure of the contacts will be suba stantially the maximum possible. It may be mentioned here that the center hinge B of the toggle mechanism will approach closely the dead center position but it will never go beyond such position.

The movable contacts or bridge pieces 16 will be held in place by spring means 36 which will deflect a predetermined amount when said member or bridge piece is in the closed position.

With switch units constructed in the manner indicated above, the velocities of engagement and disengagement of the contacts will be sufliciently high to prevent excessive arcing and even excessively slow operation of the push button will not cause abnormal arcing. Adequate pressure will be maintained between the contact surfaces during engagement and such pressure will remain substantially constant until the instant of. disengagement. Moreover the operating force required to actuate either push button will be so small that inching i.e. frequent pressing and release of the push button occurring during accurate placing of loads carried by pulley blocks and the like, may be eifected with ease.

Since the assembly shown in the drawings is designed to form a reversible controller for use with reversible electric motors it is necessary to incorporate means which, on operation of one push button 19 will be eifective to prevent operation of the second push button until the first is returned to its off position. In the embodiment illustrated, such means comprise a pivoted locking lever '34 of substantially T shape, that limb of the lever corresponding to the vertical limb of the T being pivotally connected at its outer or free end to a point 35 disposed in a plane intermediate the aforesaid shoes or extension pieces 20 on the respective push buttons 19. Those limbs of the lever 34 corresponding to the horizontal or cross member of the T will be disposed in a vertical plane (assuming that the switch units are disposed vertically one above the other as shown) and the arrangement will be such that on actuation of one push button 19 the end portion of the link 24 attached to the shoe or extension piece 20 or an abutment carried by the latter will cooperate with one edge of the vertical limb of the T-shaped lever 34 and will cause the latter to pivot so that one end of the cross or horizontal member of said lever will move into a position wherein it will engage and positively prevent movement of the carriage 16 of the second switch unit. As shown the limb of the lever 34 corresponding to the vertical limb of the T will preferably increase in width as it approaches the cross member so that the lateral edges of said limb will be inclined to the horizontal and thus in effect form cam or ramp surfaces which will result in angular movement of the lever on actuation of a push button. It will be appreciated that on movement of said lever 34 as a result of actuation of one push button 19 that edge of the vertical limb of the T opposite that contacted by the link 24 or abutment on the shoe or extension piece 20 of the actuated push button will be eifective to prevent movement of the second push button so that in effect two stops to eifect actuation of the latter will be provided.

It is to be understood that although a reversible con troller incorporating two switch units has been described and illustrated the invention is not limited thereto and that the use of a single unit is envisaged. In such a case however it will be appreciated that the pivoted locking lever 34 above referred to will be unnecessary and will be omitted.

It will be appreciated that for the control of reversible two speed motors four of the units above described may be coupled together such units being suitably interlocked.

If desired each unit of the kind indicated above may incorporate a second set of contacts with which the contact members or bridge pieces may cooperate when in their normally operative position thereby to provide electrical interlocking contacts for use, for example, during the plugging of electric motors.

In the case of electrically operated hoists it will be feasible to replace each of the usual limit switches by one of the units above described since such units are capable of breaking full load current.

I claim:

1. A reversible controller comprising two switch units each having otf and actuated conditions and each comprising fixed contacts, movable contact means, a carriage supporting the movable contact means for movement into and out of engagement with said fixed contacts, a toggle linkage coupled to the movable contact means, a push button device and spring biased lever means interposed between said push button device and the toggle linkage and adapted on a predetermined movement of said device to actuate the toggle linkage thereby to cause the movable contact means to move rapidly into en gagement with the fixed contacts, said linkage being effectivetto maintain substantially constant pressure between the contacts until the push button device is released; said units being superimposed one on the other, and means adapted on operation of one switch unit to be actuated positively to prevent operation of the second switch unit until such time as said one unit is returned to its 01f condition.

2. A reversible controller as in claim 1 in which the latter said means comprises a pivoted locking lever adapted on actuation of the push button device of one unit to be pivoted to move into the path of the carriage adapted to be actuated by the push button device of the second unit thereby positively to prevent movement of such carriage.

3. A reversible controller as in claim 2 wherein the locking lever includes a portion adapted on movement of said lever, due to the actuation of one push button to form a stop with respect to the second push button thereby to prevent depression of the latter.

4. An electric switch comprising fixed contacts of flat plate-like form disposed in spaced relationship in a common plane, movable contacts, a carriage supporting said movable contacts, fixed guides inclined at an angle to the plane of said fixed contacts, said carriage being slidable back and forth along said guides, a snap action toggle linkage coupled to the carriage, a push button device, and means interposed between said push button device and the toggle linkage and adapted on a predetermined movement of said device to actuate the toggle linkage thereby to cause the movable contacts to move rapidly into engagement with the fixed contacts, said linkage being effective to maintain substantially constant pressure between the contacts until the push button device is released; said means including a link pivoted to said push button device, a fixed bracket, a lever having one end pivotally coupled to said bracket, being centrally pivoted to said link and including, at its other end, a projection defining an aperture, a rod pivoted to said toggle linkage and extending through said aperture, and a spring encircling the rod and in compression between said toggle linkage and projection, said spring yieldably transmitting movements of said lever and projection to said toggle linkage.

References Cited in the file of this patent UNITED STATES PATENTS 1,357,726 Richter Nov. 2, 1920 1,502,785 Kerwin July 29, 1924 1,796,449 Getchell Mar. 17, 1931 2,248,387 Rosing, et al. July 8, 1941 2,550,623 Teruzzi Apr. 24, 1951 2,647,179 Martin July 28, 1953 FOREIGN PATENTS 828,752 Germany Jan. 21, 1952

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