US1729874A - System of control - Google Patents

Description

M 1929- H. D. JAMES ET AL 1,729,874

SYSTEM OF CONTROL Filed March 1, 1925 2 Sheds-Sheet l WITNESSES:

INVENTORS 9 I c 2 Henvy D-James and 12 C Easel I ATTORNEY Oct. 1, 1929. H. D. JAMES ET AL 1,729,874

SYSTEM OF CONTROL Filed March 1, 1923 2 Sheets-Sheet 2 o 1 o R122. -0 2,5 0

a as 5R Fig.2.-

WITNESSES: INVENTORS Hem) D. James and W Hwvy C Nagel ATTORNEY Patented Oct. 1, 1929 UNITED STATES PATENT OFFICE HENRY D. JAMES, OF EDGEWOOD PARK, AND HARRY C. NAGEL, F \VILKINSBUBG, PENNSYLVANIA, ASSIGNORS TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA SYSTEM OF CONTROL Application filed March 1, 1923.

Our invention relates to rheostats for motor control systems and it has particular relation to rheostats as employed in connection. with shunt motors for starting or regulating the same. i

In the use of rheostats as usually constructed for connection in shunt motor field circuit-s and the like, the field excitation is initially made very high, by the traversal of fulhrating current through the field winding, followed by the introduction of gradually increasing resistance in the circuit to bring the motor up to the required speed. Rheostats of this type necessarily have the contact members thereof relatively large to properly carry the current without appreciable heating, and in some instances the contact blocks are larger atthe low resistance end of the rheostat, and gradually taper off in size as the resistance increases. In either instance, the total amount of copper required in the rheostat is relatively large and expensive.

One object of our invention is to provide a step-by-step rheostat in which the current will traverse two parallel paths until such time as a predetermined amount of resistance has been introduced into the circuit, and then will traverse a single series path when the current has been reduced to a moderate or relatively low value. By thus directing the current along two parallel resistance paths, and then a single series path, the resistors can be made of half the current-carrying capacity that would otherwise be required were the resistors connected wholly in series relation, and also a considerable saving in copper otherwise required in the contact resistor blocks may be effected.

Another object of our invention is to provide a rheostat whereby the field winding current, during operation of the rheostat, will be varied in fine gradations, thus producing a relatively smooth increase or decrease in the speed of the motor.

In the accompanying drawings,

Figure l is a semi-diagrammatic view of a rheostat embodying our invention, and

Fig. 2 is a partial schematic View of the same.

ends.

Serial No. 622,108.

As shown, the rheostat is provided with two distinct sets 1 and 2 of stationary con tact members or blocks, the set 1 comprising two concentrically related sections 3 and 4 of which a plurality of like and circumferentially spaced contact members 3 constitute the one section, and a plurality of similar contact members 1 radially spaced therefrom, constitute the other section. The set 2 also comprises two sections 5 and 6, consisting of contact members 5 and 6', respectively, which are similar in all respects to the corresponding sections of the set 1.

These sets are arranged in two circular paths about a common center, the contact members 3 and 6, respectively, of the two sets being arranged in the outer path, leavin equal spaces between their confronting The contact members 1 and 5 of the sets are similarly arranged in the inner path, except that contact members 4 are in staggered or alternate relation to contact members 3, and contact members 5 are in similar relation to contact members 6, for a purpose to be set forth. Concentric with the sets of contact members is arranged an annular contact member or ring 7, which serves as one terminal of the rheostat.

In the rheostat, there are three sets of resistors required, the one set 8, corresponding to contact members 3 and t, being connected at one end to the first contactmember 9 oi? section 3 and at its other end to intermediate contact member 10 of the same section. A second resistor 11, correspond ing to the upper portions of contact members 5 and 6, is connected at one end to the first contact member 12 of section 6, and at the other end to the intermediate contact member 13 of the same section. The resistors 8 and 11 are arranged in parallel re lation, one end of each being connected to the same terminal 14;, the other common connection being described later. The third or series resistor 15 is connected at one end to the last contact member 16 of section 3, by a tap 17,. (shown by dot and dash line) and at its other end to the resistor 11 of which it virtually is a. continuation.

The parallel resistors 8 and 11, are each divided at equidistant points into a plurality of lesser resistance units or substantially equal values, tie ends of successive units of the resistor 8 being alternately connected to successive contact members in sections 3 and 4. Similarly, the ends of successive units of resistor 11 are alternately connected to successive contact members of sections 5 and 6, between contact members 12 and 18. In the case or" resistor 15, equivalent resistance units are subdivided into parts of substantially equal resistance value, and the successive taps are connected in alternation to successive contact members of the sections 6, l, 3 and 5, as most clearly shown in Fig. 2.

The series resistor 15, considered in detail, is provided with the following alternate connections, a tap 21 to contact member 22 of section 6: a tap 23 (shown by dotted line in Fig. 1) to contact member 2% 01 section 4::

a tap 25 (shown by dot and dash line in Fig.

1) to contact member 26 of section 3, and a tap 27 to contact member 28 of section 5. in completing the internal connections, contact members 10 and 2 1 of sections a are connected to oneanot-her "y a tap 31 which, in turn, is connected to contact member 32 of section 3 by a tap 33.

Pivotally mounted on a centrally disposed post 34 is an'operating member or arm 35, of conducting material, provided near one end with brushes 36 and 37 for operating over the contact members of sections 3 and 4, respectively. A pair of similar brushes 38 and 39 are provided near the other end of the arm 35 for operating on the contact members of sections 6 and 5, respectively. The contact brushes 36 and 37 are illustrated as placed one-iiourth the width of a single contact block ahead of the other brushes 38 and 39 to afford relatively fine variations of re sistance, as hereinafter explained. The arm 35 is further provided with brushes Q0 and ll for operating over the annular contact member or ring 7, which constitutes one terminal of the rheostat.

In practice, a shunt field winding 42 is connected to the terminal 1e and the other terminal or contact ring 7 to the opposite side oi? tne excitation circuit, as is customary.

Such being the case, with the arm 35 positioned as shown, the initial circuit entends from the positive terminal of the source of energy, or dynamo-electric machine (not shown) through the field winding 42 to the junction post or terminal 1 where the circuit divides, one branch, including the first contact members 12 and 51 of sections 6 and 5, respectively, and brushes 33 and 39 to the arm 35, brush and contac-u ring 7 to the negative supply conductor 43. The other branch includes conductor 44, contact members 9 and 20 and brushes 36 and 37 of the arm and negative conductor l3 by way of brush &1 and contact ring 7.

In operation, when the arm 35 is moved in a clockwise direction, "for example, until brush 38 rests in the middle of the second contact member in sect-ion 6, the brush 39 then bridges the gap between the first two contact members of section 5. Without detailed tracing of circuits, it will be apparent that certain parallel paths are thus provided through the initial sections of each of the parallel-related resistors 3 and 11 to insert a relatively small amount of resistance in the field winding circuit, as. will be more clearly understood by inspection of Fig. 2.

By reason of the staggered arrangement of the contact members, 3 and 4, as well as 5' and 6, the variation in the eiiective resist-- ance values of the circuit is made very gradual. This result is caused by the progressive shifting of the active connections from one resistor tap to another, alternately by the brushes 38 and 39 in the one case, and by the brushes 36 and 37 in the other. I

Moreover, as mentioned above, the brushes and 39 are advanced in position with respectto the brushes 36 and 37, by a distance of one quarter that of the width of a single contact block. From this construction, it will be evident that the effect of the resistance variation, by means of brushes 38 and 39, will occur alternately with respect to the effect produced by the brushes 36 and 37. By this means a relatively fine variation of resistance -is produced by reason of the alternating action of the brushes 38 and 39 with respect to resistor 11, the similar action of brushes 36 and 37 with respect to resistor 8, and in addition thereto, the combined and relative action of the two sets of brushes.

As the arm 35 is advanced around toward the ends of the two parallel resistors 8 and 11, the action as described is repeated, whereby additional small resistance units are gradually inserted in circuit, as will be evident from an inspection of Fig. 2. By the time sufiicient resistance has been inserted in the field winding circuit, to reduce the current to a desirably low value and permit the use of the single series resistor 15 without danger of overheating, the said series resistor is gradually introduced into the circuit. This change becomes effective when the arm 35 is further advanced so that the brushes 38 and 39 thereof come into engagement with contactbloclrs 22 and 23, respectively, and the brushes 36 and 37 thereof come into engagementwith the contact members 32 and 24, respectively. At this time the first unit of the series resistor 15 is inserted in series relation with the other or parallel-related resistors 8 and 11.

As the arm 35 is further advanced, other units of the series resistor 15 are gradually introduced into circuit in accordance with the previously described method of operation. During the time that the single resistor 15 is being utilized, the entire resistors 8 and 11 are actively employed. This effect is ob tained by the permanent connection of the lower end of resistor 11 through conductor 23 to contact member 24, which, in turn, is connected to the lower end of resistor 8 (Fig. 2). By means of the use of the above-described quarter resistance units, taken with the staggered relation of the corresponding sets of contact members, a very line variation of current is effected during the latter part of the field-regulating period.

lVe have thus provided a rheostat embodying two parallel resistors to be traversed when the current value is high, and a single resistor when the current value is sutficiently low. In addition thereto, a very fine or gradual variation ot current is provided under all conditions, by reason of the peculiar relative posiions and connections of the various elements of the rheostat.

Vhile we have shown and described a prefer-red embodiment of our invention, change in, or substitution of various parts, their arrangement and cooperation, may be made within the scope of the invention set forth in the appended claims.

\Ve claim as our invention:

1. A rheostat comprising a plurality of contact members arranged in a circular path, a plurality of resistors disposed in parallelcircuit relation and connected alternately at intervals to said contact members, and a centrally disposed member adapted to operate over said contact members to alternately vary the effective resistance values of said resistors.

2. A rheostat comprising plural sets of contact members, each arranged in a circular path, a plurality of parallel resistors each having intermediate points corresponding to certain resistance values connected in alternation to certain of said contact members and another resistor in series with the parallel resistors and having intermediate points corresponding to small resistance values alternately connected to other of said contact members, and a member adapted to operate over the contact members to vary the effective resistance values of said resistors.

3. A rheostat comprising plural sets of contact members arranged in a circular path and in relatively staggered relation, a plurality of parallel-related resistors each connected to a plurality of said contact member sets, another resistor connected to other of said contact members and in series relation to the first-named resistors, and a movable arm adapted to operate over the contact members to vary the effective resistance values of said resistors.

4. In a rheostat, in combination, a plurality of resistors connected in parallel-circuit relation, a plurality of contact members disposed in staggered relation on opposite sides of the resistors, said contact members being electrically connected to the respective resistors, a single resistor connected in series-circuit relation with the parallel-connected resistors, staggered contact members electrically connected to the single resistor, and movable means for engaging the contact members for varying the effective length of the resistors.

5. In a rheostat, in combination, a plurality of resistors connected in parallel-circuit relat-ion, a double row of contact members disposed in staggered relation, said resistors being electrically connected at intervals and alternately to the contact members of the different rows, a single resistor connected in series-circuitrelationtotheparallel-connected resistors, said series-connected resistor being electrically connected at intervals and alternately to the contact members, and a rotatable contact member disposed to engage simultaneously the contact members connected to the parallel resistors to vary the eflective length of the resistors.

6. In a rheostat, in combination, a plurality of sets of contactmembers, said sets compris ing a plurality of concentrically disposed rows of spaced contact members, a resistor element electrically connected at predetermined intervals and alternately to the contact members of the different rows in a set, said resistors being connected in parallelcircuit relation, a single resistor connected in seriescircuit relation to the parallel-connected resistors, said resistor being alternately connected to the contact members of the different sets, and a movable contact member disposed to engage the contact member of each set to vary the effective length of both parallel resistors and the series resistor.

7. In a rheostat, in combination, a plurality of resistors connected in parallel-circuit relation, a plurality of sets of contact members symmetrically disposed about a common center, said sets comprising a plurality of rows of staggered contact members disposed in concentric relationship, the contact members of the rows of the sets being alternately connected at intervals to the resistors, a single resistor connected in series-circuit relation to the par a llel-connected resistors, said single resistor being alternately connected to the contact members of each set, and a movable-contact member having a plurality of arms disposed to engage the contact members of each set for concurrently varying the effective length of the resistors.

8. In a rheostat, in combination, a plu rality of resistors connected in parallel-circuit relation, a single resistor connected in series-circuit relation with the parallel-connected resistors, a plurality of sets of contact members electrically connected to the resistors, said sets comprising a plurality of concentrically disposed sections, the contact members in each section being staggered with respect to the contact members of the other section, and a rotatable member having arms engaging the contact members of each set for simultaneously varying the lengths of the resistors.

In testimony whereof, We have hereunto subscribed our names this 21st day of February, 1923.

HENRY D. JAMES. HARRY C. NAGEL.

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