US2307886A - Driving mechanism for selectors - Google Patents

Description

Jan. 12, 194.3. J. E. HANSSON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1937 '4 Sheets-Sheet l Fig.1 5

PI P2 HANSSON DRIVING ZIIECHANISM FOR SELEGTORS Griginal Filed Got. 14, 1957 4 Sheets-Sheet 2 Vmm 1 92/97 J. 4:. amym Jan. 12, 1943. .1. E. HANSSVON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1957 4 Sheets-Sheet 3 Fig.6

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J lgpsda'? Jan. 12, 1943. I J, E, HANSSON 2,307,886

DRIVING MECHANISM FOR SELECTORS Original Filed Oct. 14, 1937 4 Sheets-Sheet 4 INVENTOR,

ATTORN YS Patented Jan. 12, 1943 DRIVING MECHANISM FOR SELECTORS John Edvard Hansson, Stockholm, Sweden, as-

signor to Tclefonaktiebolaget L. M. Ericsson, Stockholm, Sweden, a company of Sweden 'Continuation of application Serial No. 169,054,

October 14, 1937.

4 Claims.

The present invention relates to a driving mechanism for selectors of the type used in remote control systems, particularly in telephone systems. Such selectors are driven either step by step by means of impulse controlled electromagnets or continuously by means of motors, each motor driving either a group of selectors or only an individual selector. Motor operation of selectors as distinguished from step-by-step operation is preferable in cases when the wiper velocities are high, because through such operation the chocks and resultant stresses in the selector material which occur in the step-wise operation are avoided. However, motor operation entails also certain inconveniences. With the ever increasing requirements which are put on the velocity of the wipers it has been found diiiicult reliably to effect testing on the bank contacts of the selectors and to bring the selector to a standstill. In selectors with indi vidual motor drive, one has also found it difficult to obtain in the necessarily very small motors the starting moments required for starting the selector and braking moments for centering the same.

The present invention has for its objects to eliminate said inconveniences and consists essentially therein that the selector is provided with a mechanism known per se for transmitting the movement of the motor shaft to the wipers, consisting for example of a pin Wheel and a rack, which mechanism is adapted to transform the substantially constant velocity of the motor shaft to a periodically changing velocity of the wiper. The invention also involves the advantage that the mean velocity of the wipers can be considerably increased beyond the limit determined by such functions of the selector as starting, contact testing and centering, because all or some of said functions can be brought to take place during the periods of lower velocity which fall between the velocity maxima. According to a preferred embodiment of the invention the transmission mechanism. is dimensioned in such a manner with respect to the distances between the bank contacts that the maxima of the wiper velocity fall between the testing positions of the wipers.

The invention will now be described more in detail having reference to the drawings accompanying this specification and forming part thereof, in which Figures 1 and 2 show a detail of an embodiment of the invention in side view and in plan view respectively This application May 4, 1940, Serial No. 333,411.

In Sweden October Figures 3 and 4 are diagrams showing the re lation between the space passed over by the selector wipers in Figures 1 and 2 and time;

Figure 5 is a corresponding diagram for the velocity as a function of the time.

Figure 6 is a corresponding diagram for the acceleration as a function of the time.

Figure '7 is a diagrammatic perspective view of a telephone switch having a motor driven mechanism constructed in accordance with the invention.

Referring to the drawings in detail, a motor M, Fig. 7, drives a shaft A provided at its end surface with pegs or pins Pi and P2 which are parallel with the axis of rotation of the shaft and are in engagement with teeth Ti, T2 and T3, Figs. 1. and 2 on a rack BK serving as a wiper holder. The axis of rotation of the shaft A is perpendicular to the wiper holder rack BK, so that a turning of the shaft A in the direction indicated by the arrow in Figure 1 will result in a lowering of the pin Pl into the space between the teeth TI and T2 and a raising of the pin P2, bringing the latter out of engagement with the teeth T2 and T3. The wiper holder rack is assumed to be so arranged on the selector, of which only a sliding surface S serving as a guide is shown in Fig. 1, that upon rotation of the shaft A the rack BK will be advanced longitudinally, the rack then moving between bank contacts. As shown in Figure '7, the bank contacts of the selector consists of parallel bare wires extending transversely of the racks, two of which are illustrated and designated as BK! and BK2. The rack BKI carries the line wipers LW, only one of which is visible on the drawings. the other being then located at the opposite side of the rack. The other rack BK2 carries the testing wiper TW. In testing the selector the motor shaft A will rotate in the direction indcated by the arrows.

The motor is included in a circuit I, having a normally closed contact ml and a normally open contact m2. The contact ml is controlled by a test relay TR included in the test circuit 2, which is controlled over the test wiper TW, the appertaining test wires W2 and contact n which are open, when the corresponding line is engaged, and closed, when the appertaining line is free.

The selector is started by the motor circuit 1 being closed at the contact m2. When the test wiper TW finds a disengaged line which, in the example shown in the drawing, is the last line of the contact bank, the test circuit is closed through the test relay TR, the test wiper TW, the

contact wire W2 and the appertaining contact 21.. The relay TR upon energizing opens the motor circuit whereby the racks come to rest exactly in the correct contact position, in which position both rods PI and P2 engage the teeth of the racks. The motor may be provided with known means for stopping the motor shaft at the moment of interruption of the motor-circuit. In Figure 3 two of said bank contacts are repre sented by the two hatched circles Wl and consecutive positions of the wiper carried by one of the racks are shown at Bl, B2, B3 and B4. The driving pins PI and P2 are represented in Figure 3 by the two uncompleted circles uppermost in the figure. Said figure is also intended to show that in the embodiment illustrated, the distance between the centres of the two adjacent contacts WI is equal to the distance between the centres of the driving pins. In other words, the pitch of the rack is equal to the pitch of the bank contacts. The same result can be obtained, of course, by means of a gearing ha ing some other suitable ratio of transmission. The pin wheel is provided with two diametrically opposed pins which means, as will be clear from the following, that the periods of maximum velocity of the wipers will occur between the testing positions thereof. If the shaft A is rotated at a uniform velocity in the direction indicated by the arrow in Figure 1, the pin Pl will perform the above mentioned movement downwards. Provided that the limiting surfaces of the teeth are parallel with the axis of the driving pins and are perpendicular to the direction of movement of the rack and that, furthermore, there is a certain play between the pin PI and the teeth Ti and T2, the rack will, to begin with, have no or only an insignificant movement. For this reason and because of the direction of application of the force between the pin PI and the tooth P2 there will be required only a very small starting moment for putting the shaft in motion. According as the angle of rotation of the shaft is increased the velocity at which the rack BK is displaced is also increased and said velocity will obtain its maximum for an angle of rotation of the shaft of 90. Thereafter the velocity of the rack will be decreased until the shaft has been rotated through 180 and the pin P! has taken the place of the pin P2. The above operation is repeated on continuing the rotation of the shaft in the same direction.

The above reasoning is illustrated through the diagrams in Figures 3 to 6. In Figure 3 the centre of rotation of the shaft A is designated C. In the starting position of the selector the wiper contact occupies its position BI testing on the left hand'bank contact Wi. The relation between the space V passed over by the wiper and the angle of rotation on of the shaft A is readily obtained in the manner shown in the figure. The mathematical expression for the corresponding curve is, if R. designates half the distance between the centres of the pins (see point M on the curve),

V=R (1cos a) The relation between the space V passed over by the wiper and the time t can be expressed for instance as V=f(t). If R=1 and if the angular velocity of the shaft A is constant and equal to w the following will be the relation between V and t:

VII

As will be clear from Figures 3 and 4 the space changes to begin with only slowly with the time. After the wiper contact has reached its position B2 and consequently is out of engagement with the left hand bank contact WI the space will increase almost proportionally to the time, and after the position B3 of the wiper has been reached it will increase more and more slowly. For comparison a straight line UN has been drawn which represents th relation between space and time for a toothed gearing. After the space between the adjacent contacts has been passed over by the wiper contact, the space-time curve for the next half revolution of the shaft can be obtained by displacing the coordinates parallelly with themselves until the origin 0 in Figure 4 coincides with the point M.

The wiper velocity as a function of the time will be readily obtained by deriving The wiper velocity is thus a sine function of the time (Figure 5). The Velocity is zero in the points 0 and L, i. e. at the moments of testing, and reaches its maximum between said points of time. By parallel displacement of the coordinates, so that the origin 0 coincides with the point L, the velocity curve for the next half revolution of the shaft A will be obtained. As will be clear from the velocity curve one will obtain for each step in a device according to the invention a low starting and braking velocity which results in a long testing time for the wiper. For the same reason the power required by the motor driving the shaft A on starting and during the testing of the wiper contact will be small while at the same time the motor power available is utilized in the best possible manner between the periods of testing.

The acceleration of the wiper is The acceleration of the shaft A (Figure 6) thus changes suddenly from a positive value (acceleration) to a negative value (retardation) (displacement of the origin to the point Q). Also the curve according to Figure 6 illustrates the properties of the driving arrangement previously referred to which make it suitable for selector operation. The acceleration passes for each period through zero, namely once continuously, when the velocity reaches its maximum value, and once suddenly, when the velocity is zero. On account of the play between driving pin and tooth surface previously referred to said latter zero value of the acceleration will remain for a short time resulting in that the driving moment which the driving motor is called upon to produce at the eginning of each period will be small.

A further advantage found in the driving arrangement according to the invention is that if the shaft is brought to a standstill in the position of the pin wheel shown in Figure 1 said wheel will lock the brush rack rendering impossible any transmission of inertia forces from the tooth rack to the motor. As will be clear from Figures 1 to 3 said locking occurs exactly in the contact positions. In operation with individual motors, the invention thus involves the advantage that the mass to be braked by the motor is small, since the mass of the rack need not be included therein. Said condition is of special importance when the motor is to be braked up and the selector centered through an electromagnetic braking field.

The invention is, of course, not limited to the embodiment shown but can be varied in many difierent ways without receding from the idea of the invention. To obtain the movement defined in the main claim one can thus use a rack with teeth having cycloidal limiting surfaces, the generatrices of which are parallel with the axis of the driving pins. One can also use maltese crosses, toothed gearings having cylinder locking, et cetera.

I claim:

1. In a telephone switch, a number of wipers, a rack cooperating with said wipers, a motor for rotation at a substantially constant speed, a movement transmission mechanism comprising a pin wheel for two diametrically opposed driving pins coacting with said rack to impart to the wipers a periodically varying speed, and field contacts so arranged with respect to said mechanism that the slower phase of the variable speed of the wipers coincides with the contact making phase of the movement.

2. A telephone switch as claimed in claim 1 in which the centre of the driving shaft is positioned between the surfaces through the tops and the roots of the teeth of the rack.

3. A telephone switch as claimed in claim 1 in which the distance between the centres of the driving pins is equal to the distance between the centres of the field contacts.

4. In a telephone switch a number of wipers, a rack cooperating with said wipers, a motor for rotation at a substantially constant speed, a movement transmission mechanism comprising a pin wheel for two diametrically opposed driving pins coacting with said rack to impart to the wipers a periodically varying speed, field contacts so arranged with respect to said mechanism that the slower phase of the variable speed of the wipers coincides with the contact making phase of the movement, and electrical testing means cooperating with said wipers to stop the movement of the switch in accurate position relatively to the field contacts.

JOHN EDVARD HANSSON.

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