US2117531A - Electromagnetic switching device - Google Patents

Description

May 17, 1938. R WOODLAND AL 2,117,531

ELECTROMAGNETIC SWITCHING DEVICE Filed Sept. 16. 1935 FIG.

l N VEN TORS CR. WOODLAND C. RHODES A TTORA'EY.

Patented May 17, 1938 UNITED STATES PATENT OFFICE ELECTROMAGNETIC SWITCHING DEVICE Application September In Great Britain 3 Claims.

The present invention relates to electromagnetic switching devices and is more particularly concerned with devices which are adapted to respond to momentary pulses of signalling current and thereby produce different circuit changes in accordance with the number of pulses received. One application of such an arrangement is in connection with systems for remote control over public supply mains and the chief object of the invention is to provide an improved switching device which will enable diflerent control operations for example, street lighting, shop window lighting and meter tariiT change to be effected over the same circuit. The system is arranged so that the switching devices for the various purposes will operate from certain number of pulses only and no others, the numbers chosen being difierent for each kind of control. Clearly if the signal pulses are all of the same kind and diiler only in number, then all switching devices will respond together, but it will be appreciated that only those which have the corresponding setting will be able to perform their circuit changing function in response to a particular train of impulses. In cases such as this where large numbers of switching devices are to be operated in synchronism, it is important that they shall not get out of step with each other, and it is a further object of the invention to provide that if this should occur the devices shall automatically correct themselves dur ing subsequent operations.

According to the invention an electromagnetic device for effecting switching operations in response to predetermined numbers of impulses of signalling current is arranged so that the impulses efiect the rotation of an operating member which returns to normal at the end of the train of impulses and thereupon operates a switching member to produce circuit changes if the impulse train comprises the predetermined number of impulses.

The invention will be better understood from the following description of one method of carrying it into effect, which should be taken in conjunction with the accompanying drawing comprising Figs. 1 and 2 which show side and front views respectively of an electromagnetic switching device according to the invention.

In the description which follows it is assumed that the switching device is to be operated in a local circuit under the control of a sensitive relay which responds to pulses of high frequency current superimposed on public supply mains in the manner described in the application of Philip 16, 1935, Serial No. 40,694 September 25, 1934 N. Roseby, Serial No, 4646, filed 2nd. February 1935. The invention however is not limited to this type of control and the device could also be operated directly either by pulses of the type considered or by pulses transmitted from the sending point in an independent circuit. The device illustrated is suitable for responding to pulses of alternating current at the supply frequency.

Referring to Fig. 1, the electromagnet which responds to the impulses comprises a spool l0 supported on one limb of a U-shaped laminated core member I l, the other limb of which lies behind the side plate l2 to which the armature is is pivoted. In order that the magnet shall respond reliably to alternating current, it is provided with what is known as a shaded pole formed by slitting the core adjacent to the armature and encircling one portion with a copper collar 24 as shown in the drawing. When the magnet is energized from the pulses it acts on a block of laminations riveted to the armature thereby causing the armature to be attracted and released in synchronism with the pulses. Pivoted to the free end of the armature is a spring loaded pawl 14 shown more clearly in Fig. 2 which serves to rotate the ratchet wheel 15 step by step against the return spring 15. Part of the return spring 16 which is approximately twice the length visible is accommodated in a hollowed out portion of the ratchet wheel 15. Ratchet wheel 15 is rigidly attached to ratchet wheel I1 and both revolve on a fixed shaft [8 supported in the arms of a U-shaped mounting bracket l9 secured to the base plate 20. A further arm of bracket 19 carrying an adjusting stop 39 for the armature M which will be described later is conveniently shown broken away in Fig. 2 to expose the driving mechanism. It will also be seen from this figure that the armature I3 is provided with a pair of short arms 3'! and 38 bent out at right angles on opposite sides, the one on the right 31 engaging with the armature restoring spring 2i and detent spring 22 shown in Fig. 1, while the one on the left 38 is forked and engages with the collared head of the air dash-pot 23. The function of the dash-pot is to retard the full release of the armature and so prevent the ratchet wheels returning to normal between pulses as will be described.

On the first attraction of the armature the ratchet wheels 15 and H are rotated one step and the detent spring 22 is lowered into engagement with the ratchet wheel ll so that the lug 25 on the spring 22 seats itself behind the appropriate tooth on the wheel. Simultaneously with this operation. the dash-pot 23 is depressed to the full. extent. Upon the de-energization of the magnet at the end of the first pulse, the armature releases quickly at first under the infiuence of the restoring spring 2i until its forked arm comes up against the head of the dash-pot plunger and thereafter further release is impeded by the drag of the dash-pot. By suitable adjustment it is arranged that the second and subsequent pulses are received before the armature has moved suffi-ciently far to lift the detent 25 on spring clear of the ratchet wheel i? and accordingly pulses are stored on the ratchet wheels which are advanced to a characteristic po sition.

At the end of the pulse train the armature has sufficient time to overcome the drag of the dash-pot and when it has fully released, the detent 25 on spring 22 is lifted clear of the ratchet wheel I? which thereupon restores to normal under the influence of the restoring spring l6. Pivoted to the ratchet wheel i1 is a wide detent 26 shown more clearly in Fig. 1 which bears against the face of cam 27 which is rigidly secured to the contact operating cam 28. Cam 2 is provided with notches around its face suitably spaced in accordance with the number and sequence of the impulses to which the device is to respond while cam 28 may be shaped as shown with a slow lift face suitable for com trolling the contact springs 29. Only one set of springs has been shown in the drawing but it will be understood that others may be provided in accordance with the control required.

The effect of the impulsing operation therefore is to advance ratchet wheel H to a predetermined position where the detent 26, which it carries, engages with a notch in the cam 21 and, upon release due to the withdrawal of detent 22, the two cams are rotated together to control the operation of the contact springs.

In a mixed system of the type suggested it may be arranged for example, that 2 and 3 impulses respectively will switch shop window lights on or off 4, 5, and 6 impulses will serve for the graduated control of street lights, that is, one lamp on, two lamps on, and both off while '7 and 8 impulses will control the meter tariff change at consumers premises.

The switching devices for the various control systems are therefore set by these impulses and although all devices respond simultaneously, only those which have the characteristic setting will be able to perform their circuit-changing functions. For this purpose the detent 26 is controlled from the double-armed swash plate 30 which is friction tight on the fixed shaft I8, being pressed against the side of the mounting bracket is by means of a fiat spring 3| secured to the bracket by the screws 32. During the forward stepping motion the swash plate Bil is pushed round by contacting with the upper edge (in the position shown) of the detent 26 and owing to the peculiar shape of the latter it is automatically tilted into engagement with the cam 21. Accordingly after the correct number of impulses have been received, the detent is tilted into a notch on the cam 21, and upon release the cams and swash plate are carried back to the normal position which is determined by the curved back of the detent coming up against a correspondingly curved face on the frame member ii If however, the number of impulses received is in excess of the number allocated for the system in which the particular switching device is located, the detent 26 is carried past the notch in the cam 2'! and upon release the rear edge leaves the swash plate and the front edge comes up against the other arm of the swash plate to drive it back to the normal position. It will be noticed however, that owing to the inclination of the other arm of the swash plate the detent becomes trapped and is prevented from entering the notch in the cam during the return movement.

If less than the predetermined number of impulses are received, the detent 26 will obviously fail to reach the notch in the cam 27! and the switch therefore restores without producing any change in the condition of the contact-controlling cam 28.

If at any time the switches should get out of step owing to the reception of a false set of pulses which operate some devices and not others it will be appreciated that the next set of pulses which applies to the devices of that switching system will bring them all into line. This feature is particularly important in the case of large networks since otherwise each individual switch may have to be visited and corrected.

Considering now the various operating details of the mechanism not yet dealt with, it will be seen that the normal position of the armature i 3 is regulated by the angle-shaped back stop 33 which is fastened to the front arm of the mounting bracket i9 and is capable of vertical adjustment thereon by the screw and slot shown in Fig. 2. The fully operated position of the armature is regulated by the pawl i i jamming against a front stop comprising an adjusting screw 39 threaded through the bracket member iii. The normal position angle of the spring-loaded pawl M is adjusted by bending the tongue 34, which is a part of the tail piece of pawl M and which rests against the underside of the armature, until the pawl 14 is directed towards a tooth on the ratchet wheel i5. In the normal position the cams 2'! and 28 are prevented from movement by the locking effect of the pawl 26 but in order to prevent their movement during the setting operation of the pawl, the moving spring of the contact pair 29 is provided with a notch as shown which is engaged by the tooth of cam 23 and introduces a slight locking effect, sufiicient to prevent the movement of the cams owing to vibration or the friction of the detent 26 moving over the operating face. The airdash-pot is' of the type employing a solid graphite plunger which is therefore self-lubricating and enjoys a long life.

The whole unit described is secured in a suitable manner to the mounting plate 35 preferably composed of insulating material of the synthetic resin type and is enclosed in a dust cover (not shown) of similar material. The electrical connections to be made external to the unit are led out to spring pins 36, the fixing for which passes through a hole in the mounting plate and is rigidly fastened thereto. Four such pins are pro vided to carry circuits for the operating coil and contact springs and these pins are adapted to register with sockets in a mounting frame and are suhiciently robust to hold the unit in its mounted position without the necessity for any other supporting brackets or attachments. Details of the mounting arrangements and dust cover are not shown in the drawing, but they follow the same general lines as in the case of the unit described in the application of Cecil R. Woodland, Serial No. 758,573, filed 21st December 1934.

We claim:

1. An electromagnetic circuit-closing device for effecting circuit changes, comprising a ratchet wheel, a spring, a detent carried by said wheel, a notched cam, means for rotating said wheel against the tension of said spring, and then releasing it, a friction element on said wheel, said element engaging said detent and causing it to engage a notch in said cam when the wheel is rotated a predetermined number of steps, said spring operating the wheel and cam together on release when the detent engages a notch, such element engaging said detent and holding it out of engagement with the notches of said cam when the wheel is rotated other than the predetermined number of steps, said spring returning said wheel to normal without operating the cam if the detent is moved past a notch by the wheel.

2. An electromagnetic device comprising switching springs, a cam for operating said springs having notches therein spaced at unequal intervals around the cam, a ratchet wheel, a magnet having means for rotating and releasing the wheel, a detent on the wheel moved thereby into position to engage a notch in the cam, a

spring for moving the wheel and cam through the medium of the detent when the wheel is released, said magnet responsive to a predetermined series of impulses to cause the cam to engage one notch and responsive to another predetermined series of impulses to engage a second notch, and a friction element between the cam and wheel having one part engaging the detent to cause it to engage a notch in the first instance and another part preventing the detent from engaging a notch in the other instance.

3. An electromagnetic switching device comprising a ratchet wheel, a magnet for rotating the wheel and releasing it, a detent carried backward and forward by the wheel, a notched cam adjacent the Wheel and having notches spaced at varying distances on its periphery engageable by said detent, a friction element associated with the detent, a pair of prongs on the element in the path of said detent, one prong of the element engaged by the detent on its forward movement to cause the detent to engage the periphery of the cam, and the other prong of said element engaged by the detent on its backward movement to prevent engagement of the detent with the periphery of the cam.

CECIL ROBERT WOODLAND. CECIL RHODES.

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