US1771458A - Control system for elevators - Google Patents

Description

July 29, 1930. F, HYMA'NS 1,771,458

CONTROL SYSTEM FOR ELEVATORS Original Filed Jan. l2, 1926 2 Sheets-Sheet l F45 mmm'nl 47 I l l ma mi@ 'mw zw ,/97 G/sa- 226 P200 202 July 29, 1930. F; HYMANS 1,771,458

CONTROL SYSTEM FOR ELEVATORS` original 'med Jan. 12, 1926 2 sheets-sheet '2 Patented July 29,1930

UNITED STATES PATENT OFFICE FREDERICK HYMANS, Ol' YONXEBS, NEW YORK, ASSIGNOB TO OTIS ELEVATOB COI- PANY, OF JERSEY CITY, NEW JERSEY, A CORPORATIONv OF NEW JERSEY CONTROL SYSTEM FOR ELEVATORS Application med January l2, 1926,5er1a1 No. 80,763. vRenewed .Tune 21, 1929.

The invention relates to control s stems, and particularly to control systems orelevators.

In elevator systems in which the car is 5 brought to a stop automatically at a landing,

it is important that the speed of the car .during the stopping operation, be accurately controlled if good stops are to be made. This is particularly true in systems in which push button control is employed for causing the automatic slow-down as well as the final stop4v the elevator mot-0r to run at a suitable speed from which an accurate stop may be made. The time constant of the generator field during the slow down and stopping operations is an important factor, especially where a generator is used whose field has a large time constant.

Where power operated car gate and hatchway door mechanism is employed, or Where the gate and door are manually operated, it is desirable to effect the movement of the gate and door into open Aipositions by the time that the car has stopped at the floor. Such operation is advantageous particularly because of the amount of time which is saved. In high speed elevator systems, the time gained in making each stop is an important ,factor and, when the gain for a whole tripA is considered, it may be seen that the operat ing efficiency of the whole svstem is raised considerably. In such an arrangement, how ever, the speed of the car might be accidentally increased during the gate and door opening operation or While the gate and door are open with a passenger in the act of stepping into or out of the car.

One feature of the invention resides in arranging and 'connecting the generator" field windingsr so that, in stopping, the time rerapidlybrought to a proper value to cause quired for the generator field to adjust itself to the desired strengths is minimized.

Another feature is the minimizing of the possibility of occurrence of excessive speeds during the period when the hatchway door, and car gate when used, might be partially or wholly open.l

Other features and advantages will become apparent from the following description and appended claims.

The invention is particularly suitable for use in connection with self leveling elevator systems as in such systems it maybe necessary to reverse the direction of movement of the car `as well as to accelerate or retard it or to move it up or down in making alstop. While the invention is applicable to other elevator systems, principally those in which automatic stopping is employed, it will be described, by way` of illustration, as embodied in a system in which self leveling mechanism is provided.

In the drawings:

Figure l is a diagramof an elevator control system;

Figure 2 is a fragmental schematic view of a portion of the elevator system, illustrating particularly the manner in which the generator field windings are controlled during the leveling operation, and

Figure 3 is a portion of a diagram similar to Figure l showing a slightly different arrangement of the control system.

Referring to Figure 1, no attemptis made to show the coils and contacts of the various electromagnetic switches in their associated positions, a straight diagram being vemployed wherein the coils and contacts of the various switches are separated in such manner as to render the circuits involved relatively simple \Also the parts of other switches and apparatus are separated inthe interest of simplifying the diagram. For a clearer understanding of the invention, the stationary contacts of the switches are illus trated in cross section.

The motor generator set comprises a driving motor l1, illustrated for convenience of description as of the direct current type, and a variablewoltage direct current generator 12. The armature of the driving motorie designated 13 and its field winding 14. The armature of the generator is designated 15, its series field winding 16, its major separately excited field winding 17 and its minor separately excited field winding 18. The elevator motor is designated as a whole by the numeral 20, its armature being designated 21 and its field winding 22. An adjustable resistance 23 is arranged in shunt to the generator series field winding. Discharge resistances 24, 25 and 26 are provided for the generator major field, minor field and elevator motor field windings respectively. A resistance 27 is provided for controlling the strength of the generator field and therefore 'the voltage applied to the elevator motor armature during car switch operation. Another resistance 28 is provided for controlling the strength of the generator field during leveling operation. A resistance 29 controls the strength of the elevator motor field during different conditions of operation. 30 is the release coil for the elevator motor electromagnetic brake. This coil is provided with discharge resistanccs 31. 32 and 83 for controlling the application of the brake under different conditions of operation. 34 and 35 are the up slow speed contacts and the down slow speed contacts respectively of the leveling switch. the leveling switch up and down fast speed contacts being designated 36 and 37 respectively. 38 is the armature and 40 is the field winding of the motor 41 for moving the rollers of the leveling switch into position to clear the leveling cams. 42 is the armature and 43 is the field winding of the door control motor 44. 45 and 46 are the direct current supply mains. 47 is a double pole knife switch for connecting the system to the supply mains. In order to suit the type of diagram employed, the blades of this switch are shown separated. The car switch is designated as a whole by the nu-Y merel 48. 50 is the safety switch in the car. The series of door contacts are indicated by igle set of contacts 51. The gate contacts indicated as 52. The various safety, limit, stop and emergency switches are omitted in order to simplify the description.

rPhe electromagnetic switches have been designated as follows:

A-potential switch,

B--up main direction switch,

C--down main direction switch,

D-irst accelerating switch,

E--second accelerating switch,

F--series field switch,

G-series field relay,v

H-main brake and field switch,

J door control motor switch,

K-door control motor maintaining relay,

L-field control switch,

M -maintaining relay,

N-sequence relay,

O-accelerating relay,

P-hard brake switch,

R-leveling control relay,

LB-up leveling direction switch,

LC-down leveling direction switch,

LH--leveling brake and field switch,

LIL-fast speed leveling relay. Throughout the dcscriptionfwhich follows, these letters, in addition to the usual reference numerals, will be applied to the parts of the above enumerated switches. For eX- ample, contacts B 111 are contacts on the up main direction switch, while actuating coil A is the coil that operates the potential switch. The electromagnetic switches are shown in their deenergized posit-ions. Reactances are similarly designated by the character X.

Upon the closing of the knife switch 47, the driving motor 11, elevator motor field bwinding 22 and potential switch actuating coil A 53 are energized, the circuit for coil A 53 being through safety switch 50. The driving motor starts in operation, bringing the generator 12 up to full speed. The 'series field winding and starting means for the driving motor are omitted to simplify the description. With the elevator motor at rest, the current supplied to its field winding 22 is reduced by section 54 of resistance 29, providing what may be termed a standing field. The circuit for the elevator motor field winding may be traced from the left-hand blade of switch 47, line 55, by way of line 56 through field winding 22, resistance section 54 and second accelerating switch contacts E 57, line 58, to the right-hand blade of switch 47. It

is not desired to apply full line voltage to the field winding 22 when the elevator motor is not in operation because of increased power consumption. On the other hand, it is not desired toy have this field winding deenergized with the elevator motor at rest as a matter of safety and because of the time constant involved in building up. The potential switch, upon operation, causes the engagement of contacts A 60 and A 61, preparing the circuit for the generator separately excited field winding, the electromagnetic brake release coil and the control'circuits. The condition of the circuits so far described might be termed normal.

Referring brieliy to Figure 2, the car switch 48 comprises a set of u contacts 62, 63, 64, and 66 and a set of own contacts 67, 68,

. 69, and 71. A contact vsegment 72 for bridging the contacts of each vset is mounted ont e segmental support 73 of insulating material. A cam 74 is formed on the support above the pivot point 75. The cam is formed with a centrally disposed de ression 76 into which the operating roller 77 of the gate and door switch 78 extends with the car s switch in neutral or off position. The

switch 78 is pivoted at 80 sothat movement` of the car switch in either direction causes lUtl the engagement of the switch contacts. The car switch is operated by means of a control handle 8l'. It is preferred to provide centering springs (not shown) on the car switch to cause it to be returned to off position when released by the operator.

Referring back to Figure 1, assume that the systeniis designed for an installation of several floors and that the car is atrest at the first floor with the gate and door open. In the starting operation, the operator first gives the car switch a slight initial movement tov effect the closure of the' gate and door switch 78. For conveniencel of description, this switch is arranged to complete a circuit for the door control motor switch actuating coil v J 82. This circuit may be traced from the vao left-hand blade of switch 47, by way of line 55 through contacts A 60, .by way of line 83 Athrough coil J 82, resistance 84 and switch 78, line 85, switch 50, line 86, line 58, to the right-hand blade of switch 47 The gate control motor switch, upon operation, causes the engagement of contacts J 87, completing the circuit for the door control motor 44. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by way of line 88 `through contacts J 87, door control motor field winding 43 and armaturev 42, by way of line 58 through contacts A 61, to the right-hand blade of switch 47.

Referring again to Figure 2, mot-or 44 operates pneumatic gate and door operating mechanism, as for example through linkage 90, to move valve 91 for gate engine 92 to gate closedv position and to withdraw the retiring cam 93 from engagement with the roller provided on the end of the door engine valve lever 94. The lever 94 is operated b v a spring to move valve 95 for the door engi-ne 96 to door closed position. The gate and door engines operate through mechanism not shown to close the car gate 99 and hatchway door 109. It is to be understood that a door is provided in the hatchway for each landing.

Referring bac-k to Figure 1, if the-operator, after he has closed the gate and door, desires to open them. or if he desires to arrest their movement, lie lmay do so by releasing the car switch to return to oi position. This causes the opening of the gate and door switch 78 with the consequent deenergization of coil J 82 and the separation of contacts J 87.

- In this manner, the circuit for the motor 44 is broken. The spring 97 ,g shown in Figure 2, operates upon the deenergization of motor 44 to move valve 91 and, through cam 93 and .lever 94, valve. 95 into positions to cause.` fore the enggelnbp f s gmentw an (1,69,

the reverse operations of the engines 92 and 96 to open the gate and door. Obviously other forms of power operated gate and door mechanisms, such as electric in vlieu bf pneumatic, may be employed without departing from the spirit of the present invention brake and field switch and B 102 ofV theup 80' accelerating switches.

Assuming that the gate andtdoors `are closed, the gate contacts ,52 anddoor contacts 51 are in engagement. The operator may now move the carswitch to full operated position to start the carin "the up' di-y rection. It is to be noted thaty the gate and door switch 78 remains in closed positionwso long as the car switch ismovedfout of neutral position. Upon the engagement of contact segment 72 and contact 64, circuits are simultaneously completed for the oppositely Wound coils N 98and N 100v of-the s'equence relay, actuating coils R 2400i the leveling control relay, H 101 of the main main direction switch being in the circuit for coil N 100. The engagement of the contact segment and contacts 65 and 66 prepares circuits for the actuating coils ofthe The circuit for coil N 98 ofthe sequence relay may be traced from the' left-hand blade of switch 47, by'way of line 5 5 through contactsA 60, by way of line 103 through coil N 98 and resistance 104'c6ntaets 62 andI 64 of the car switch, by way, of line 105 through contacts C 106 of the down Amain direction switch, line 85, to the ri ht-liand blade of switch 47 as above trace' The circuit for coi'l N 100 may be traced from the left-hand blade of switch 47 by way ofline 55 through contacts A 60, by may of line 107 through door contacts 51, gate contacts 52, sequence relay contacts N 108 and coils'R 240,-,N 100,.

ibs

the relay.` If either coi'lis energized ahead of the other, or if either coil alone is energized, contacts N 108'separate, preventing the starting of the'car. If either the gate contacts 52 or any of the door` contacts 51' are separated at the time that car switch segment 72 engages contacts 64, coil N 98 alone is energized, resulting'l in the separation of contacts N 108. The separation'of contacts N 108 prevents the energilzation'of coil N 100, maintaining the sequencrela'y operated, and of coil B 102-preventing the operation'of the'I up.`riain`direction switch to effect the starting f 'the'car.' The 'gaas and door switch 78,',therore,is lcltfsfed"by the initialmovement ofthe car'switch 'so 'that the gate and door contactsmayvbe: closedhlb'e- Atact 64. However, if the carswitch lis moved into position where segment 2 conmet 64 before the, closatf ,theaooraad gate contacts, the sequence relay peratesto prevent the starting of the car. Thus it is its vprevent their simultaneous operation.

impossible to start the car on the door or gate contacts.

gate and door must be effected before the car switch is moved into full on position.

The leveling control relay R, upon operation, causes the separation of contacts R 241 in the circuit for theactuating coils of the leveling direction switches. The purpose of this arrangement will be described later.

It is preferred toprovide the main direc tion switches with a mechanical interlock to Such an interlock may be of the form of a walking beam pivotally mounted for engaging catches on the armatures of these switches. Upon operation of the up main direction switch in response to the energization of its actuating coil B 102, contacts B 110 separate and contacts B 111, B 112 and B 113 engage. The separation of contacts B 110 breaks the circuit leading from the car 'switch down feed contact 69, contacts B 110 and the corresponding down direction switch contacts C 106 serving as electrical interlocks as is well understood in the art. The engagement of contacts B 113 prepa-res the circuit for the up main direction switch holding coil B 115 and the main brake and field switch holding coil H 116. The engagement of contacts B111 and B 112 completes a circuit for the eneratorkmajor and minor separately excite field windings. This circuit may be traced from the left-hand blade of switch 47 by way of line 55 through contacts A 60, by way'of line 109 through resistance 27 and contacts B 111, by way of line -117 through field control switch contacts L 118, through the minor separately excited ield winding 18, by way ofline 120 through contacts L 121 and themajor se arately excited iield'winding 17 by way of line 219 through contacts B 112, b sway of lin'e 58 throug contacts A 61, to lle right-hand blade of switch 47. Y

The main brake and field switch H operates simultaneously with the: main direction switch B. Switch H, upon operation, causes the separation of contacts H 119, H1122 and H 123 and the engagement of contacts H124. H 125, H 126 and H 127. The separation of contacts H 119 disconnects the enerator separately excited field windings rom the generator armature. The purpose of this arrangement will be explained later. Contacts H 122 are in the circuit for the field control switch actuating coil L 128. The purpose of this arrangement also will be explained later.

The separation of contacts H 123 disconnects resistance `33 from across the brake release coil 30. Resistance 33 being of low ohmic value, its disconnection before contacts H 124 engage prevents excess power consumption from mains 45 and 46. The enga ement of contacts H 127 establishes a circuit for the door control motormaint'aining relay actuating coil K 130. This circuitmay be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by way of line `83 through coil J 82, by way 0f line 131 through up leveling direction switch contacts LB 132, down leveling direction switch contacts LC 133, contacts H 127 and coil K 130, line 85, to the right-hand blade of switch 47 as previously traced. The engagement of contacts H 125 further prepares the circuits for the actuating coils of the accelerating switches. The engagement of contacts H 126 short-circuits section 54 of the elevator motor field resistance 29, permittino the motor field to'build up to its full strengt The engagement of contacts H 124 completes the circuit for the brake `release coil 30. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by way of line 134 through contacts 135 operated by the brake, brake release coil 30 and contacts H 124, by way of line 58 through contacts A 61, to the right-hand blade of switch 47.

The door control motor maintaining relay coil K 130 in the circuit above traced is subject to the potential dro across resistance 84. The system is arrange so that the voltage thus applied to coil K 130 is suiicient to effect the operation of the relay. Contacts K 136 engage, upon the operation of the relay to by-passcontacts H 127. The purpose of this arrangement will be seen from later description. y

The brake release coil 30 beingy energized, the elevator motor eld being connected directly to the mains 45 and 46 and current being supplied from the generator armature 15 to the elevator motor armature 21, due to the energization of the generator ma'or and minor separately excited field windings, the elevator motor starts. The minor separately excited field winding as now connected assists the major se arately excited field winding.

As the bra e releases, the brake switch contacts 135 separate to insert cooling resistance this arrangement is to utilizefthe time con-v stant of the brake for timingfvthe acceleration 'ino -lever arms represent considerable mass to be set in motion. The circuit for coil D 141 completed by contacts O 140 may be traced from the left-hand blade of switch 47, by way of line through contacts A 60, by way of line 107 through the door contacts 51, gate contacts 52, and contacts N 108, by way of line 142 through contacts H 125, contacts O and coil D 141, contacts 65 and 64 of the car switch, to the right-hand blade of switch 47 as previously traced.

The operation of the first accelerating switch, in response to the energization of its actuating coil, causes the engagement of contacts D 143, D 144, D 145 and D 146. `The enga ment of contacts D k143 completes the circuit for the leveling switch motor 41. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by way of line 147 through contacts D 143, field winding 40 and armature 38 of motor 41, by way of line4 58 through contacts A 61, to the right-hand blade yof switch 47. The leveling switch motor acts, upon energization, to move the leveling switch operating rollers so as to clear the leveling cams during movement of the car.

This operation will be explained later. Thev engagement of contacts D 144 completes the circuit for holding coils B 115 and H 116. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by wa of line 148 through coil H 116 and contacts 144,I by way of line 150 through coil B 115 and contacts B 113, line 151, line 85, to the right-hand blade of switch 47 as previously traced. The purpose of the energization of these holding coils will be seen from later description. The engagement of contacts D 146 completes the circuit for the second accelerating switch actuatin coil E 152. This circuit maybe traced rom the left-hand blade of switch 47, by wa of line 55 through contacts A 60, by way ofy line 107 through door contacts 51, ate contacts 52 and contacts N 108, by way o line 142 through contacts H 125, by way of line 153 through contacts D 146, reactance X 154 and coil E 152, car switch contacts 66 and 64, to ther right-hand blade of switch 47 as previously traced. The engagementof contacts D 145 short-circuits section 155 of resistance'27, increasing the voltage applied to the generator field windings 17 and 18. Thus the generator E. M. F. is increased, increasing the speed of the motor.

The second. accelerating switch E does not operate immediately the circuit for its actubeing vlayed by the effect of reactance X 154. pon

ating coil is completed, its-'action deoperation, contacts E156 and E 57 separate and contacts E 157 and E 158 engage. The

separation of contacts E 156 removes the shunt circuit around a portion of resistance 160. The separation o contacts E 156 ybefore contacts E 158 engage prevents excess power consumption from mains 45 and 46. The engagement of contacts E 158 completes the circuit for thevfirst .accelerating switch holding coil D 161 and the maintaining relay actuating coil M 162. This circuit may be traced from the left-hand blade of switch 47,

by way of line 55 through contacts A 60, by way of line 151 through contacts E 158, reactance X 163, coil D 161 and coil M 162, line 85, to the right-hand bladel of switch 47 as previously traced. The maintaining relay contacts M 164 are thus caused to by-pass contacts D 144. The purpose of this larrangement will' be described later. The engagement of contacts E 157 short-circuits section 165 of resistance 27 to increase the voltage applied to the generator separately elgcted field windings 17 and 18. The E. M. F. of the generator, therefore, increases to its full value and the speed of the elevator motor increases. The separation of contacts E 57 removes the short circuit for section 167 of resistance 29 in the elevator motor field winding circuit, bringing the elevator motor up to fu l speed. y y

The starting of the car in the down direction is accom lished in a similar manner and will be only riefly described. The operator first moves the car switch into position to cause the closure of the gate and door and then into fullV on position where its contact segment 72 bridges contacts 67, 68, 69, 70 and 71. Thus-the circuit is completed for the down main direction switch actuating coil lC 168. This circuit may be traced from the left-hand blade of switch 47, through coil H 101 as previously traced, by way of line 170 through coil C 168, car switch contacts 68 and 69, by way of line 171 through contacts B 110, line 85, to the right-hand blade of switch 47 as previously traced.' The circuit for coil N 98 is by way of line 172.` The circuit for coil D 141 is by way of line 17 3.v

down direction is the same as described for.

starting it in the up direction.

Assume that the car is runnlng in the up direction and that the operator centers the los car switch between the second and third floors in order to stop at the third floor landing. Thus the contact segment 72 moves ofi contacts 66, 65, 64 and 63 and the circuits for the second accelerating switch actuating coil E 152, first accelerating switch actuating coil D v141. main brake and field switch actuating coil H 101, up main direction switch 'actuating coil B 102, levelingcontrol relay coil R 240 and sequence relay coils 1T 98 and N 100 are broken. The leveling control relay and the second acceleratingr switch drop out immediately. The first accelerating switch, main brake and lield switch and up main direction switch are maintained operated, however, by holding coils D 161, H 116 and B 115 respectively. The deenergization of coils N 98 and N 100 is in preparation 'for the next starting operation. It is to be noted that switch 78 is opened by the centering of the car switch. The circuit for coil J 82, however, is maintained through contacts H 127 and K 136 in parallel and coil K 130.

The Pleveling control relay, upon dropping out, causes the recngagement of contacts R 241. As previously stated, the purpose of Y this relay will be explained later.

The second accelerating switch, u on dropping out, causes the separation o contacts E 157 and E 158 and the reengagemerit of contacts E 57 and E 156. The separation of contacts E 157 reinserts section 165 of resistance 27 in series with the generator separately excited field windings to decrease the E. M. F. of the generator. The engagement of contacts E 57 short-circuits section 167 of resistance 29, .increasing the strength of the elevator motor field for the stopping operation. With the generator E. M. F. lowered and the strength of the elevator motor field increased, the speed of the elevator motor is decreased. The separation of contacts E 158 breaks the circuit for holding coil D 161 and coil M 162. The first accelerating switch D and maintaining relay M do not drop out immediately, however, their action being delayed by the effect of reactance X 163 in series with the coils and the discharge resistance 160 in parallel with the reactance and the coils. T he engagement of contacts E 156 to short-circuit a portion of resistance 160 is Vsa effective to prolong the time element of the switch and relay. The time element maybe adjusted to the desired value by changing the amount of the resistance portion short-circuited. Relay M is preferably adjusted to hold in at a smaller current value than the accelerating switch D. This may be readily accomplished due to the fact that the relay is much smaller and therefore lighter in construction than the accelerating switch and requires less current to hold in.

The rst accelerating switch, upon dropping out,vcauses the separation o contacts D 143, D 144, D 145 and D 146. The separation of contacts D 144 is in preparation for the next starting operation, contacts M 164 remaining in engagement to maintain holding coils H 116 and B 115 energized. The separation of contacts D 146 also is in preparation for the next starting operation, the circuit for coil E 152 having been broken by the movement of the car switch as above described. The separation of contacts D 145 removes the short circuit for section 155 of resistance 27, decreasing the strength of the generator field. Thus the generator E. M. F. is again decreased and the speed of the elevator motor' is reduced.

The separation of contacts D 143 deenergizes the leveling switch motor 41. In this manner the operating rollers of the leveling switch are extended for engagement bythe leveling cams. Referring brieily to Figure 27 the leveling switch motor is o eratively connected tothe leveling switch by means of an arm 180 on the motor shaft, a connecting link 181 and a lever 182. In the starting operation, the motor 41 being energized, arm

180 rotates, acting through link 181 and lever 182 to movethe leveling switch as a whole about a pivot. In this manner the leveling switch operating rollers 183 and 184 are moved into position where they do not engage the leveling cams 185 and 186 during motion of the car, a stop being provided to determine the extent of the movement. It is to be understood that leveling cams are provided for each floor. The leveling switch is pivoted on a bracket 187 secured to the car frame. In the stopping operation, upon the deenergiZation-of the leveling switch motor, a spring (not shown) moves the lever 182 and therefore the leveling switch back into the iirst described position with the rollers 183 and 184 extended for engagement by the leveling cams. Each pair of leveling switch contacts 34, 35, 36 and 37 comprises a stationary contact and a movable contact operated by the engagement of its corresponding roller and leveling cam. The fast speed contacts 36 and 37 are arranged to se arate before their corresponding slow spe contacts 34 and 35 in the leveling operation. Springs (not shown) are provided forcausing the separation of the contacts of the palrs as the leveling operation is effected and stops are provided for determining the extent of movement of the rollers as they ride Y off the leveling cams.

It will be assumed that the car has not reached the landing and that the up leveling switch operating roller 183 moves onto the vertical surface of up leveling cam 185 before relay M drops out. The engagement of leveling switch up slow speed contacts 34 completes acircuit for the up leveling direction switch actuating coil LB 188 and the leveling brake and field switch actuating coil LH 190. This circuit may be traced from the left-hand blade of switch 47, by way of line 55, through contacts A 60, line 191, leveling switch contacts 34, by way of line 192 through coil LB 188 and coil LH 190, by way of line 85 through levelin control relay contacts R 241, to the rightand blade of switch 47l as previously traced. The engagement ofthe leveling switch up fast speed contacts 36 completes the circuit for fast speed leveling relay actuating coil LF 193. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through `contacts A 60, line 191,l levelin switch contacts 34, line 194, leveling switc contacts 36,

by way of line 85 throuvh coil LF 193 and contacts R 241, to the Fight-hand blade of switch 47 as previously traced. It is to be noted that, dueto the fact that the circuit for coil LF 193 is through leveling switch vslow speed contacts 34, the circuit for coils LB 188 and LH 190 must be made in order that the circuit for coil LF 193 may be completed.. l

The up leveling direction switch LB, upon operation, causes the separation of contacts LB 132 andthe engagement of contacts LB 195 LB 196 and LB 197. Contacts LB 132 will be referred to later. The engagement of contacts LB 195 and LB 196 repares circuits for the generator se arate y excited field windings for the leve ing period. The engagement of contacts LB 197 completes the circuit for up series field relay actuating coil G 198 and u hard brake switch actuating coil P 200. his circuit may be traced from the left-hand blade of switch 47 by way of line through contacts A 60, by wa of line 201 through contacts LB 197, coil 198, coil P 200, and portion 202 of reactance X 203, line 204, b way of line 58 through contacts A 61, to t e ri ht-hand blade of switch 47.

The leve ing brake and field switch, o erating simultaneously with the up leve ing direction switch, causes the separation of contacts LH 205, LH 206 and LH 212 and the en agement of contacts LH 207, LH 208 and LH 210. Contacts LH 205 are in the circuit for resistance 33 across the brake release coil. Contacts LH 206v are in series with contacts H 119 in the circuit for connecting the generator separately excited field windings to the generator armature. Contacts LH 212 break the shunt circuit, comprising resistance 160, for coilsD 161 and M 162. Contacts LH 207 byass contacts H 124 in the circuit for the bra re release coil. 'Contacts LH 208 bypass contacts H 126 in the circuit for section 54 of 210 are in the circuit for the field controll the motor field resistance 29. Contacts LH Y The fast speed leveling relay, upon operation,` causes the engagement of contacts LF 213 and LF 214. The engagement of contacts LF 213 short-circuits resistance 28 employed to control the Strength of the generator field during leveling. The engagement of contacts LF 214 by-passes contacts LB 132, LC 133, H l

door operating mechanism due to the time required for the mechanism to start in operation. The circuit for the door controlmotor maintainin relay coil K 130, however, is broken by t 1e separationv of contacts LB 132.

The separation of contacts LH 212 to break the circuit for resistance 160'as above set forth causes relay M to drop lout and separate contacts M 164. As a resu'lt'the circuit for holding coils B and H 116 is broken, permittin the up main direction switch and main rake and field switch to drop out. Switch B, upon dropping out, causes the separation of contacts B 111,\B 112 and B 113 and the engagement of contacts B 110. The separation of contacts B 113%, and the enga ement of contacts B 110 is injpre aration or the next starting operation.- T e separation of contacts B '111 and B 112 breaks the circuit for the generator separately excited field windings. However, the windings are substantially immediately re-connected to the mains for the levelin operation by .the operation of switch as will be set forth below. The switch H, upon dropping out, causes the separation of contacts H 124, H 125, H 126 and H 127 and the en agement of contacts H 119, H 122 and 123.

llI

The separation of contacts H 125r and H 127 is in preparation for the next'starting operation. The separation of contacts H 124 and H 126 is without effect, the circuit for the brake release coil 30 being maintained by contacts LH 207 and section 54 of resistance 29 remaining short-circuited by contacts LH 208. The engagement of contacts H 119'and H 123 also is without effect as the circuit for reconnecting the generator separately excited field windings to the generator armature is maintainedbroken by contacts LH 206 and the shunt circuit for the brake release coil 30 comprising resistance 33 is maintained broken by contacts LH 205. The engagement .of contacts H 122,however, completes the circuit for the field control switch actuating coil L 128. This circuit may be traced from the left-hand blade of switch 47, by way of line 55 through contacts A 60, by way of line 215 through contacts H 122, contacts LH 210 and coil L 128, line 85, to the right-hand blade of switch 47 as previously traced.

The field control switch L, upon operation, causes the separation of contacts L 118 and L 121 and the engagement of contacts L 216 and L 217. The separation of contacts L 118 and L 121 and the engagement of contacts L 216 and L 217 reverses the connections for the generator minor separately excited field winding 18, the engagement of contacts L 216 and L 217 also reconnecting both generator separately excited ield windings -to the mains. rihe circuit for the generator iield windings may now be traced from the lefthand blade of switch 47, by way of line 55 through contacts A 60, contacts LF 213 shortcircuiting resistance 28, contacts LB 195, by way of line 120 through contacts L 217, minor iield winding 18, by way of line 218 through contacts L 216, major field winding 17, line 219, line 220, by way of line 58 through contacts LB 196 and contacts A 61, to the righthand blade of switchy 47. Itis to be noted that the circuit for the generator field windings through resistance 27 is now also broken .at contacts L 118. The polarity of these connections is such that the magnetizing force exerted by the major field winding is in the same direction as before. As regards the minor field winding, however, current now flows therein in such direction as to create a magnetizing force which opposes the magnetizing force due to the major field winding.

Discharge resistances 24 and 25 act to smooth out not only the changes in generator E. M. F. due to the reinsertion of resistance 27 in circuit with the separately excited field windings 17 and 18 in steps, but also the change due to the disconnection and reconnection of the field windings to the mains. 1t is to be understood that resistance 27 may be controlled in any number of steps, two being shown merely for convenience of description.

With contacts L 118 and L 121 separated and contacts L 216, L 217, LB 195, LB 196 and LF 213 in engagement, an E. M. F. is generated which causes the elevator motor to run at a suitable fast leveling speed, as will be seen from later description.

Relay G and switch P do not operate im' mediately their actuating coils are energized,

their action being delayed by reactance X 203. Switch P, however, is adjusted to operate almost immediately and, upon operation, causes the separation of contacts P 221, disconnecting resistance 32'from across the b rake release coil 30. Relay G, upon operation, causes the engagement of contacts G 222, completing the circuit for the series iield switch actuating coil F 223. This circuit may be traced from the left-hand blade of switch 47, by way oflline-55 through contacts A 60,

by way of line 224 through contacts G 222 and coil F 223, by way of line 58 through contacts A 61, to the right-hand blade of switch 47. Switch F, upon operation, causes the separation of contacts F 225, breaking the circuit including resistance 23 in shunt to the gen erator series field winding 16.' The generator series field is so wound that, without the parallel resistance 23, it would have too great an effect for proper operation of the car. The desired compounding is obtained by employing the low resistance shunt. Upon separation of contacts F 225` the strength of the series ield'is increased for the leveling operation so as to aid in bringing the motor to a stop. The short delay in the action of relay G, and therefore switch F, upon the initiation of the leveling operation, is desirable in order that the current in the generator armature-elevator motor armature circuit may adjust itself to such a value that proper series field strength during the leveling operation may be obtained.

As the car nears the third floor landing, roller 183 rides off the vertical surface onto the oblique surface of cam 185.v This results in the separation of leveling switch up fast speed contacts 36, deenergizing fast speed leveling relay coil LF 193. Relay LF, upon dropping out, causes the separation of contacts LF 213 and LF 214. The separation of contacts LF 213 removes the short circuit around resistance 28. The generator E. M. F. is thus lowered and the elevator motor runs at its slow leveling speed. The/separation of contacts LF 214 breaks the circuit for the door control motor switch coil J 82. Switch J, upon dropping out, causes the separation of contacts J 87 to deenergize the motor 44, thus effecting the automatic gate and door opening operation. The gate and door operating mechanism functions in the same manner as described for opening the gate and door in response to centering the car switch. In this manner the automatic gate and door opening operation is timed so that the gate and door open as the car stops at the landing. It is to be noted, however, that the automatic gate and door opening operation cannot take place until the leveling switch fast speed contacts separate.

Shortly before the car reaches the exact level with the landing, the roller183 rides off the oblique surface of cam 185, thereby separating the leveling switch up slow speed contacts 34. The circuit for coils LB 188 and LH 190 is thus broken. Switch LH drops out, causing the separation of contacts LH 207, LH 208 and LH 210 and the reengagement of contacts LH 205, LH 206 and LH 212.A

The engagement of contacts LH 212 is in preparation fory the next starting o eration. The separation of contacts LH`2O breaks the circuit for the brake release vcoilO effecting the application of the brake* The sepaisa ration of contacts LH 207 also breaks thecircuit for acceleratin relay coil O 138. The accelerating relay contacts O 140 in prepara-tion for the next starting operation. The separation of contacts LH 208 reinserts section 54 of resistance 29 in lseries with the elevator motor field winding, reducing the current therein to a standing field value. The separation of contacts LH 210 breaks the circuit for the field control switch coil'L 128, the switch dropping out in preparation for the next starting operation. It is to be noted that the separation of contacts L 216 and L 217 and the engagement of contacts L 118 and L 121 reconnects the generator separately excited field windings 17 and 18 for cumulative action. The reengagement of contacts LH 206 along with the 'windings in such manner as to engagement of contacts L 216 and L 217 reconnects the generator separately excited field windings to the generator armature. The polarity of this connection is such that the generator sends. current through the field (ppose the flux which produces the generator M. F., thus tending to destroy the residual flux of the generator field.

Up leveling direction switch LB, dropping out simultaneously with switch LH, causes the separation of contacts LB 195, LB 196 and LB 197 and the engagement of contactsLB 132. The engagement of contacts LB 132 is inpreparation for the next starting operation. The separation of contacts LB 195 and LB 196 disconnects the generator separately excited field windings from the mains, the windings being simultaneously reconnected to the generator armature by contacts LH 206, L 216 and L 217 as set forth above. The separation of contacts LB 197 breaksthe circuit for coils G 198 and P 200. The relay G drops out immediately, but the dropping out of switch P is delayed slightly due to the effect of the reactance X 203-and discharge resistance 226'. It is to be noted that the discharge current for'up coil P 200 and the reactance passes through down coil- P 227 in such direction as to cause coil P 227 to assist coil P 200 in maintaining switch P in operated condition. Re-

lay G, upon dropping out, causes the separation of contacts G 222 to deenergize coil F 223, switch F dropping out in turn to cause the engagement of contacts F 225. The engagement of contacts F 225 reconnects resistance 23 in parallel with the generator series field winding 16. Switch P, upon 'dropping out, causes the engagement of contacts P 221.

Thus the brake being applied and the generator separately excited field windings being disconnected from the mains, the car is brought to rest level withl the third floor landing. Since theengagement of contacts P 221 is delayed, the brake release coil 30 discharges only into resistance 31 of relatively high drops out, separating` vswitch 47 as previousl ohmic value and a hard application of the brake is obtained. In thismanner a sto at the landing is assured.y

lgith the sequence of operations as above described the car will be slowed down and sto ped level with the desired landing wit out sacrifice 'o'f smoothness. However, should the car switch be centered with the carl at a greater distance from the landing, the maintaining relay would hold in ,to effect through its contacts M 164, the retention of the main direction switch and main brake and field switch in operated condition. Should yrelay M drop out before the leveling switch contacts engage, the subsequent engagement of the leveling switch contacts as the leveling switch roller rides ontoy the cam would cause the o eration of switches LB and LH andl relay F to bring the car to a level with the floor. In the event 'that the car switch is centered late in the stop ing operation, as

for example when the leve ingswitch operating roller strikes the leveling cam upon the dropping out of the first accelerating switch D, the immediate separation of contacts LH 212 forces the dropping out ofthe main direcpositive tion switch and the main ggbrake and field connections for the field windings and thus slow down the elevator motor more rapidly. In lthis manner the tendency for the car to overrun the floor is reduced.

Should an overrun occur, however, the system is arranged so that the operation of the switches is modified. Assuming in the above example that the car overruns the third floor landin to the extent of causing the en agement o leveling switch down slow spee con-A tacts 35, a circult is completed for down leveling direction switch actuating coil LC 228 andcoil LH 190. This circuit may be traced from the left-hand blade of switch 47, by

-switch to permit the immediate change of the way of line 55 throughcontacts A 60, line 191, contacts 35, by way of line 230 through coil LC 228, by way of line 192 through coil LH 190, line 85, to the right-hand v.blade of traced. Contacts LH 205, LH 206 and L 212 are separated and contacts LH 207, LH 208 andLH 210 are engaged so'that the circuit for resistance 33 across the brake release coil is broken, the brake release coil is energized, resistance section 54 for the elevatormotor field windin is short circuited and the field control switc actuating coil L 128 is energized. l', Contacts LH 212 insure the dropping out ofthe main direction switch. With coil L 128 energized contacts L 118jand L 121 are separated and contacts L 216 and L 217 are in engagement. The switch LC operates to cause the separation of contacts LC 133 and the engagement of contacts LC 231, LC 232 and LC 233. The separation of contacts LC 133 is without particular e'ect M ih time. With to a low value.

tacts LH 206, L 118 and L 121 separated and contacts LC 231", LC 232, L 216 and L 217 in engagement, themajor and minor separately excited `eld windings are disconnected from the generator armature and are connected to the mains in such manner as to cause their magnetizing forces to oppose each other. Due to resistance 28 not bein short circuited, the desired voltage is a lie to the generator separately excited tie windings for slow speed leveling operation. Since the circuit for the enerator separately excited field windings 1s through the down leveling direction switch contacts, the flow of current through the windings is in a reversed direction from that during the levelin operation upon the car approaching the oor in the up direction and the car is caused to start in the down direction.

The engagement of contacts LC 233 coinpleted a clrcuit for the down series field relay actuating coil G 234 and the down hard brake switch actuatin coil P 227. This circuit may be traced rom the left-hand blade of switch 47, by way of line through contacts A 60, by way of line 235 through contacts LC 233, coil G 234, coil P 227 and portion 236 of reactance X 203, line 204, b way of line 58 through contacts A 61, to t e rightliand blade of switch 47. Relay G and switch P do not operate immediately upon the engagement of contacts LC 233. When approaching the oor in the up direction as described, the current tlowin through reactance portion 202 caused a ux to be built up in the reactance X 203 in one direction.

Upon the separation of contacts LB 197, the current in the reactance coil P 200 discharged into resistance 226 tending to maintain the ilux built up and, as previously explained, switch Pino erated condition. iUpon the engagement o contacts LC233 on the overrun, the current sup lied to coils G 234 and P 227 must reverse t e flux in the reactance, thus taking a longer time to build up to a value sufficient to cause the operation of relay G and switch P. Thus contacts F 225,

dependin for their operation upon the operation o relay G, remain closed temporarily to insure that the current in the generator armature-motor armature circuit has fallen Since the current in the series field winding may beflowing in a direction such Vas -to cause the generation of an E.M. Fi which is .of roper polarity for operatingthe. car in the l own direction, im mediateincrease in the strength ,of the scries field,'inight,resultv in -an overrun in the down direction.- Asthe car returns to the floor, it is sto ped by the separation of the leveling switc slow speed .contacts 35 in a mannerl similar tol that described for approachingthe floor in the up direction.

.If the overrun is great enough to cause the engagement of theleveling switch down fast speed contacts 37 as well as the leveling switch i cuit resistance 28, increasing the generator. voltage and causing the elevatorl motor to run at its fast leveling speed. Bela LF also causes the engagement of contacts F 214 to energize coil J 82 again in the event that it has become deenergized. Upon such an overrun, the automatic gate and door openin operation does not occur until contacts L 214 separate, as previously described. Further than this, the operation on an overrunI is as above described.

It is to be understood that the operator may control both the acceleration and retardation of the carfhy moving the car switch in steps. In the event that the operator starts the car from a floor by moving the car switch only so far as to engage one of the feed contacts, for example contact 64, the u main direction switch B and main brake an( vfield switch are operated to complete the circuit for the generator iield winding, by the engagement of contacts B 111 and contacts B 112, and to cause the release of the brake, by the engagement of contacts H 124. As the actuating coil of the first accelerating switch D is not energized, this switch does not operate and the leveling switch motor is not ener 'zed to move the levelin cams. The levei ever, operating along with switches B and H, causes the separation of contacts R 241 and thus prevents the cnergization of the down leveling switch actuating coil LC 228 as a result of the operation of 'the leveling switch during the upward movement of the car awa romthe floor. Contacts LC 231 and L 232, therefore, do not engage, preventin the establishing of a shunt circuit aroun the generator separately excited field winding. Should the operator suddenly move the car switch from one position into the other, for example from up into down position, injury to the system is prevented by contacts B which remain separated until the up direction switch drops out. It is to be noted that, when the car is suddenly reversed or sto ped be tween floors or stopped by opening t e safety switch 50. the switch P is not operated. Thus` contacts P 221 arc inengagement and a soft application of the brake is obtained.

The conditions under which` leveling operations have to takeplace are subject to constant variation. This is true even with a given load in the car. These conditions depend upon the position of the car .in the leveling zone at the time that the leveling operation begins.- Thus the car may have 'to be accelerated or retarded and it may have to move up or down. .Consistent results ,can b e obtained under such conditions b having the generator liel'd build up quic y to the deloo' lill

sredstrengths. This may be accomplished' by making the time constant of the separately excited generator field windings as small as ppssible andby causing the mutual induction tween the series and separate] excited field windings tovbe as little as possi le. The preferred arrangement for effecting these results has been described in connection with Figure 1. The arrangement of the field windings is schematically illustrated in Figure 2.

Referring to Fi ure 2, it is preferred to arrange the major eld winding 17 and minor field winding 18 as separate windings with the'coils constituting the minor field winding of a smaller number of turns than those of the major field winding, as indicated lby the small and large sized spools. The coils forming the major field winding are connected in series as are those forming the minor field winding. The coils are so wound as to provide poles of alternate polarity. With the switch L in deenergized position, as dur-v ing car switch operation, the current flows through the'colls on each ole 1n such d1rection as to have the minor eld winding assist the major field winding. Upon the car reaching the leveling zone, the switch L operates as previously described to separate contacts L 118 and L 121 and to effect the engagement of contacts L 216 and L 217. As a result, the direction of the fiow of current through the major field winding is unchanged but the flow of current through the minor field winding is reversed. The field flux is now produced by the difference ofthe ampere turns ofthe large P and small coils. This difference may be made such, by selection of the number of turns in the coils, that the desired E. M. F. for causing the elevator motor to run at the desired fast leveling speed is generated with the full volta-ge of the mains applied to the windings.

The desired slow leveling speed is obtained by means of the resistance 28 (see Figure 1).

In a generator provided with the usual series field. winding and separately excited field winding. the series field winding. due to.

t only is t e operation of the system rendered uncertain but the time required for the separately excited winding to overcome the effect of the mutual inductance adds to the time usually required to build the generator field up to its'desired strength. With the separately excited windings arranged as illustrated on the drawings, the effect of the opposing turns of the two coils on each field pole during leveling is that the coefficient of self inductance of the two coils and the coefficient ,of

.mutual inductance of the two coilswith the corresponding series field coil are the same as if eac pole were wound with a number of turns equal to the difference between the number of turns of the two coils. Thus the inductance is reduced, so that the nerator field will establish itself quickly during level' ing operation.

This arrangement for the control of the separately vexcited field windings minimizes the possibility of the elevator car moving at an excessive speed during the leveling period. The automatic opening of the gate and door during this period renders the feature of particular importance. In systems employing resistance in series with the elevator motor amature to control the speed of the motor during leveling, orv where the voltage a plied to the armature of the elevator motor uring leveling is controlled by means of resistance in series with the separately excited field winding of the generator which supplies power to the motor, there is always the possibility of all or a portion of such resistances becoming short-circuited or grounded, causing the speed f the elevator motor to increase. If mechanism were employed, as in the Ipresent system, to effect the automatic opening of the gate and door during the leveling period, the sudden increase in speed might occur while the gate and door were being opened, or after the gate and door were open when the leveling arrangement is slow in bringing the car to a level with the landing. In the resent system, the circuit for resistance 27 1s broken by the contacts on the main direction switches and field control switch contacts L 118. With such an arrangement,`it is impossible for the accidental short circuiting or grounding of resistance 27 during leveling and gate and door opening operation to cause an increase in the speed of the elevator car. An accidental short circuit of resistance 28 can do no more than cause the car to run at its fast leveling speed. I t is to be understood that contacts could be provided on the field control switch L to break the circuit for the gate motor maintaining relay coil K 130, instead of employing contacts LB 132 and LC 133, in order to insure that the gate and door would not open unless the connections for the field windings were changed.

Referring to Figure 3, only that portion of the control diagram which differs from the diagram of Figure 1 hasl been illustrated. In this diagram the leveling direction switch' contacts LB 195, LB 196, LC 231 and LC 232 are arranged Vfor by-passing main direction switch contacts B111, B112, C 175 and C 176 respectively. Resistance 28 is omitted and resistance 27 is employed to control the strength ofy the'generator field both during car switch and leveling operations. Additional contacts L 240 are arranged on the field control switch and contacts LH 241 on Sil lli

lill) the leveling brake and field switch. Contacts LH 241 areA arranged for short-circuiting an adjustable portion of resistance 27. Contacts LF 213, employed in Figure 1 to short circuit resistance 28, are arranged to short circuit the remainder of resistance 27. Contacts L 240 are employed -to prevent the completion of these short circuits until the main direction switch and main brake and field switch dropout. It is believed that the operation ofthe systemas thus arranged will be obvious from the description of the operation of the system of Figure 1. With such an arrangement.l the accidental short circuiting or grounding of resistance 27 while the gate and door are opening can have no greater effect than to cause the elevator motor to run at its fast leveling speed.

As many changes could be made inthe above arrangements and many apparently widely different embodiments of this invention could be made'without departing from the scope thereof, it is intended that all matter contained in t-he above description or shown in the accompanying drawin shall be interpreted as illustrative and'not in a limit ing sense. v

What is claimed is:

l. In combination, an elevator car, a hoisting motor therefor, a generator ifor supplying current to said motor, said generator having two field windin s, each of which comprises a plurality o series connected field coils, one for each field pole and the coils of one winding being of a smaller number of turns than those of the other, means for driving said generator, a source of current, means for causing the motor to raise or lower the car, said second'named means comprising means for connecting said windings in series relation to said source, and means for causing said motor to bring the car to a level with the desired landing regardless of' whether the car underruns or overruns the landing, said last named means comprising means for reconnecting said windings to said source in series relation -in such manner as to reverse the flow of current through one of said windings while causing the flow of current in the other winding to be in the same Adirection. as before.

2. In combination, anelevator car, a hoisting motor therefor, a generator for supplying current to said motor, said'generator having two field windings, a source of current,

,means for -causing the motor to run at a certainspeed, said means comprising means for connectingsaid .windings .to said. source, ,meanszfor causing the-motor to run at a slower speed, said second named -means compris- .ingmeans -for reversing ,the connections for one of said windings, a hatchway door,and means respopslivetothe operationl of the second named means for causin'gthe opening of said door.'A

3. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, said generator having a plurality of separately excited field windl lof' said mechanism during the operation of the second named means.

4. In combination, an elevator car, a hoisting motor therefor, a generator for supplying current to said motor, said generator having two field windings, one of said windings being of a smaller number of turns than the other, a source of current, means for causing said motor to run at a certain speed, said means comprising means for connecting said windingsv to the source in such manner that their magnetizing forces act': cumulatively, means for causing said 'inotor to run at a slower speed, said second named means comprising means forconnecting said windings to said source so as to cause their magnetizing forces to act in opposition, a car gate, a hatchway door, mechanism for causing the opening of said gate and door, and means for causing the operationof said mechanism during the operation of the second named means.

5. In combination; an elevator car; ahoisting motor therefor; a generator for supplying current to said motor, said generator having two separately excited field windings, one

being of a smaller number of turns than the other; a. source of current; means for causing the motor to run at a certain speed, said means comprising means for connecting said windings to said source in series relation so as to act cumulatively; means for bringing the car to a level with a desired landing in stopping, said second named means comprising means for reconnecting said windings to said source in series relation with the connections for but one of the-windings reversed to cause the motor to run at a fast leveling speed, a resistance, and meansfor causin the insertion of said resistance in circuit witg said windings as reconnected to cause the motor to run at a slow, leveling speed; a car gate; a hatcliway door; and means responsive to the means for causing the insertion of said resistance in circuit with said field windings for causing the opening of said gate and door.

6. In combination; an elevator car; a hoistmeans for starting said motor, said means com rising means for connecting said field win nngs tosaid source in series relation and in circuit with said resistance and, for thereafter short-circuiting the resistance to bring the motor up to full speed; means for bringing the car to a level with a desired landing in stopping, said second named means comprising means for disconnecting said Windings from said source and for reconnecting them in series relation with the connections for but one of the windings reversed to cause the motorto run at a fast leveling speed, a second resistance, and means for causing the insertion of said second resistance in clrcuit with said windings as reconnected to cause the motor to run at a slow leveling speed; a

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