US 2979592 A
Description (OCR text may contain errors)
April 11, 1961 J. A. WATSON CAM OPERATED CONTACTORS 2 Sheets-Sheet 1 Filed Feb. 6, 1959 JOHN H/VJLEY HTT'OE /VEY' April 11, 1961 .1. A. WATSON 2,979,592
CAM OPERATED CONTACTORS Filed Feb. 6, 1959 2 Sheets-Sheet 2 A from/V T United States Patent CAM OPERATED CONTACTORS John Ansley Watson Rugby England, assignor to The British Thomson-Iiouston ilompany Limited, London, England, a British company Filed Feb. 6, 1959, Ser. No. 791,769 Claims priority, application Great Britain Feb. 7, 1958 4 Claims. (Cl. 200-153) This invention relates to cam operated contact arrangements, such as used in contactors of the kind having a movable contact acted upon in response to the cents to perform two movements, one for engaging anddisengaging a fixed contact, and one for causing a wiping action between the contacts while they engage each other.
Up to now the said two movements have been derived from a cam surface by means of one and the same actuating member, such as a cam roller associated with a spring. V
The invention aims at an improved construction WhlCh affords a separate and more accurate control of each one of the abovementioned two movements, and also permits use of a lower cam shaft torque than required for closing comparable contactors, of conventional construction, in which the biasing force to be overcome by the cam shaft torque is of considerable magnitude and much greater than necessary to overcome a spring force provided for the wiping operation. The present invention aims at reducing this counterforce, to reduce the maximum torque required from a cam shaft which is rotated for contact operation.
This is achieved according to the invention by deriving the said two movements through separate actuating members, which can be controlled by one and the same cam surface or by different cam surfaces rotated by a common cam shaft. In the latter case at least one of the cam surfaces can be made adjustable so that the angular spatial relationship of the elfective carn surfaces can be varied and the time relation of the two movements can be set for minimum torque requirement.
As will be seen it is possible to mount the two actuating members at the opposite ends of a common lever, or on individual levers.
The invention will be better understood and more details will become apparent from the following description referring to the accompanying drawings which illustrate by way of example preferred embodiments of the invention, and in which:
Fig. 1 is an elevation of one embodiment;
Fig. 2 is a side view in the direction of the arrow r of Fig. 1 to show an axial displacement of the two actuating members which comprise rollers; and
Fig. 3 shows in another embodiment the two actuating members carried on a common lever and biased by an additional spring means to eliminate back-lash in relation to the cam means.
Referring to Fig. 1 a contact 1 is electrically insulated and mounted on a fixed structure 2 using means known in the art. Another contact 3 shown in its open position is arranged to engage contact 1 when moved downwards and also to carry out a wiping movement substantially at right angles to the first movement. The contact 3 is mounted on a lever 4 pivoted at 5 to a lever 6 which carries an actuating roller 7 for co-operation with a cam surface (not shown). A compression spring 8 is arranged between the levers 4, 6 and it will be understood "ice that contact 3 will carry out a movement having a component at right angles'to the opening and closing movement, when the two contacts 1, 3 engages each other, and the roller 7 is movedin accordance with the shape of the cam surface thereby displacing lever 6 relative to lever 4 and compressing spring 8. The rotation of lever 4 under the force of spring 8 is limited by a stop 13.
Another actuating roller 9 is carried at the end of lever 10. The two levers 6, 10 are rotatable about a common pivot 11 and are secured together by a resilient member indicated at 12. This member can be of a known construction using a spring means for instance so as to allow for small resilient relative movement as required for neutralising slight errors in manufacture, and
also for a variable setting of the angular relationship between levers 6 and 10 which may be obtained by a conventional means, such as a pusher screw, and opposing spring (not-shown). For contact closure by the first movement, in onefof its two directions, the lever 6 is rowiththe fixed contact 1, and the final portion of the movement compresses the spring 8. Lever 10 connected to lever 6 by the member 12 moves in the same sense, a separate cam surface associated with roller 9 of lever 10 being shaped to permit said clockwise displacement of lever 10. This cam surface is' also shaped to rotate lever 10 counterclockwise as required for disengaging contact 3 from contact 1.
As can be seen from Fig. 2 each one of the levers 6 and 10 is bifurcated and comprises two side walls, one of which is bent so that the rollers 7 and 9 are olfset in the direction of the cam axis and the axis of the pivot 11. This axial displacement permits employment of coaxial but separate and differently shaped cam discs for cooperation with the two rollers 7 and 9. If desired the angular relationship of the two cam surfaces can be adjusted and the cams can be mounted with mutual overlap.
Since the cam surfaces when pressing against rollers 7, 9 cause rotation of the lever combinations 4, 6, 10 in the clockwise and counterclockwise directions, roller 7 can be used with advantage to control the contact closing movement, where as roller 9 controls the contact opening. The spring 8 which serves primarily for the wiping movement also produces contact pressure between 1 and 3. Thus a conventional spring (not shown) for contact pressure bias can be relieved, or may be completely dispensed with.
Fig. 3, in which similar parts are denoted by the same reference characters, shows an embodiment substantially similar to that of Figs. 1 and 2. However, a single lever 6a is employed in lieu of levers 6, 10 to carry the actuating rollers 7, 9, and instead of the resilient connecting member 12 of the first embodiment a biasing element 124, comprising for instance compression springs 14, 15, cooperates with a bracket 16 secured to the lever 6a and a stationary support 17 fastened to or forming part of the fixed structure 2, to eliminate back-lash between the rollers 7, 9 and their cam surfaces and also to maintain in a resilient fashion the angular position of lever 6a in relation to the fixed structure 2.
In one end position of the lever 6a the lower end of bracket 16 bears against the stationary support 17. It will also be seen that in this embodiment the spring arrangerhent 14, 15 biases the contact 3 to its open position, whereas the member 12 of the first embodiment biases the contact 3 to its closed position. The springs 14, 15 are positioned so as to afford a desired anti-back-lash effect without substantially increasing the load on the cam shaft. As the biasing element is formed by two springs 14, 15 pressing against the outer surfaces of parts 16, 17 and a rod 18 extends through the interiorof the coiled springs to press against outer spring caps .19, 20, the characteristic of the spring assembly can be made to be substantially linear so as to keep to a minimum the torque required from the operatingcam shaft.
' Other variations are possible without departure from the invention. Advantageously slight clearances to overcome manufacturing variations and be neutralized by member 12 or 12:: are provided between the rollers and their co-operating cam surfaces. For the same purpose a light spring can be mounted adjacent to roller 9 in such a manner that the back-lash is taken up when the contactor is open by lightly loading roller 9 onto its cam profile. When roller 7 is moved by its cam to close and wipe the contacts the light spring partially counterbalances the load thereby reducing the torque requirement.
What I claim is:
1. A cam operated electric contact arrangement having a fixed contact and a movable contact, a rocker carrying said movable contact, lever means carrying a first cam follower adapted for effecting contact-closing, and a second cam follower adapted for effecting contact-opening, said'lever means also carrying a pivot, said rocker being arranged to rotate about said pivot, and a compression spring disposed between confronting surfaces of said lever means and said rocker and arranged to bias said rocker away from said lever means to cause wiping between the two contact surfaces after said movable con tact has been pressed onto said stationary contact through the action of said first cam follower.
2. An arrangement as claimed in claim 1 wherein said lever means comprises a first lever carrying said first cam follower, a second lever carrying said second cam follower, a resilient member interconnecting the two levers and a stationary pivot for supporting the two levers.
3. An arrangement as claimed in claim 2 wherein each of the two levers comprises two side walls, one of the side walls of each lever being bent to enable offsetting of one cam follower relative to the other cam follower in the direction of the axis of the common pivot of the two levers.
4. An arrangement as claimed in claim 1 wherein said lever means comprises a unitary lever, with a resilient positioning means being provided to resiliently hold said lever in a predetermined position.
References Cited in the file of this patent UNITED STATES PATENTS