US1768122A

US1768122A - Control system

Info

Publication number: US1768122A
Application number: US271953A
Authority: US
Inventors: Lee I Davis
Original assignee: Otis Elevator Co
Current assignee: Otis Elevator Co
Priority date: 1925-10-29
Filing date: 1928-04-21
Publication date: 1930-06-24
Anticipated expiration: 1947-06-24

Description

AJune 24, 1930. 4[ DAvls 1,768,122

- CONTROL SYSTEM f Original Filed Oct. 2.9, 1925 2 Sheets-Sheet l L Q m sNvEN'row VBY mm ATTORNEY June 24, 1930. L. 1. DAVIS 1,768,122`

1 CONTROL SYSTEM Original Filed Oct. 29, 1925 2 Sheets-Sheet 2 DIZO U55- L/37 U34 ARnATuQE VaLTAGE ARMA Tune VDL-maf Flo FIEL o VoLTA GE NVENTOR 'ATTORNEY Patented June 24, 1930 UNITED STATES PATENT OFFICE LEE I. Davis, or NEW YoEx, N. Y., AssmNort 'ro o'rrs ELEvA'roE. COMPANY, or

JERSEY CITY, NEW'JEESEY, A coRPoRATIoN or NEW JERSEY 'coNraoL SYSTEM Original application filed October 29,1925, Serial No. 65,612. Divided and this application filed April '21, 1928. Serial No. 271,953. y

The invention relates to control systems, and particularly to control systems for elevators.

This application is a division of application Serial No. 65,612, filed October 29, 1925.

In elevator control systems where the elevator motor is supplied with current vby a variable voltage generator, the ener'ator is required to operate over a wi e range of E. M. F. values varying from a maximum in one direction to a maximum in the other. Where self-levelling apparatus is employed, the generator is re uired to operate at low values of E. in bringing the car to a level with a desired landing. Due to the residual flux of the generator field, the E. M. F. values obtained for a given value of field current duringthe levelling operation vary considerably, depending on the previous magnetic state of the machine and whether the car is approaching the landing or returning to the landin after an overrun. Such variations in n. M. F. Values cause undesirable variations in the voperation of the car during the levelling period.`

One feature of the invention resides in energizing the field' Windin of a generator in such manner that the e ects of residual flux are minimized during periods vwhen a low voltage is desired.

Other features and advantages will become apparent vfrom the following description,l

taken in connection with the accompanying drawings wherein one embodiment of the invention is illustrated and in which:

Figure 1 is a diagram of an elevator control system;

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

Figures 3, 4 and 5 are hysteresis curves employed to illustrate the invention.

No attempt is made in Figure 1 to show the coils and'contacts of the various electromagnetic switches in their associated positions, a straight diagram being employed wherein the coils and contacts of the various switches are separated in such manner as to` render the circuits involved relatively simple. Alsov the parts of other switches and apparatus are separated in the interest of sim 1 ifying the diagram. For a clearer un erstanding of the inventiomthe stationary contacts' of the switchesl are illustrated incross section. It is to be understood that the system illustrated is chosen merely forfconvenience of description and that, although described in conjunction Ywith a car switch controlled system, the invention is equally applicable to other typesofelevator systems such as push button controlsystems and to other systems employing a work motor supplied withcurrent from thefgenerator yof a motor generator'set.

The motor generator sety comprlses a drivi,

ing motor 11, illustratedfor convenience of description as of the direct current type, and a variable voltage direct current generator 12. The armature of the driving motor is designated 13 and its field winding 14. -The armature ofthe generator is designated 15, itsseries field winding 16, its'separately excited field winding being divided into two

portions

17 and 18. The elevator motor is designated as a whole by the numeral 20, its armature being designated 21 and its fleld winding 22. An adjustable resistance 29 is arranged in shunt vto the generator series field Winding. Discharge resistances 23 and 24 are provided forl the

portions

17 and 18 respectively ofthe generator separately excited field winding. Discharge resistance 25 provided for the elevator motor field winding. A resistance 26 is provided for controlling the strength of the generator field and therefore the voltage applied to the elevator motor armature. 27 is the release coil forv the elevator motor electromagnetic brake. This coil is provided with

discharge resistances

28, 30 and 31 for controlling the application of the brake under different conditions of operation. 32 and 33 are the up slow speed contacts and the down slowrspeed contacts respectively of the levelling switch, the up and down fast speed levelling switch contacts being designated 34 and 35 respectively. 36 is the armature and 37 `is-the--field windi of the motor 38 for moving the rollers x(ithe levelling switchinto position to clear the levelling cams. and 41 are the direct current supply mains. 42 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 numeral 43. 44 is the safety switch in the car. The various safety, limit, stop and emergency switches and door and gate contacts are omitted in order to simplify the description.

The electromagnetic switches have been designated as follows:

A-Potential switch,

B-Up direct-ion switch,

C-Down direction switch,

D-Up slow speed levelling relay,

E-Down slow speed levelling relay,

F-Accelerating switch,

(ir-Maintaining relay,

H-Brake switch,

J-Protective relay,

K-AuXiliary protective relay,

L-Slow down switch,

M-Series field relay,

N-Series field switch,

G-Hard brake switch,

P-Levelling switch motor relay.

Throughout the description which follows, these letters, in addition to the usual reference numerals, will be applied to the parts of the above enumerated switches. For example, contacts B 66 are contacts on the up direction switch, while actuating coil A 45 is the coil that operates the potential switch. The electromagnetic switches are shown .in their deenergized positions.

Upon the closing of the knife switch 42, the driving motor 11, elevator motor field winding 22 and potential switch actuating coil A 45 are energized, the circuit for coil A 45 being by way of line 46 including protective relay contacts J 47, auxiliary protective relay contacts K 48 and safety switch 44. The driving motor starts in operation, bringing the generator 12 up to full speed. Starting means for the drivin motor are omitted to simplify the description. The potential switch, upon operation, causes the engagement of contacts A and A 51 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.

Assume that the system is designed for an installation of several floors and that the car is at rest at the first floor landing. In order to start the car in the up direction, the operator moves the car switch into position where its contact bar 52

bridges contacts

53, 54,' 55 and 56. Upon the contact bar 52 engaging contact 54, a circuit is completed for the actuating coil B 57 of the up direction switch and the actuating coil H 58 of the brake switch. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 60 through coils H 58 and B 57,

contacts

54 and 53 of the car switch, by way of line 61 through contacts C 62, line 63, switch 44, line 46, by way of line 89, to the right-hand blade of switch 42. The engagement of the contact bar and contact 55 prepares a circuit for the actuating coil F 83 of the accelerating switch. The engagement of the contact bar and contact 56 completes a circuit for the actuating coil P 59 of the levelling switch motor relay. This circuit may be traced from the lefthand blade of switch 42, by way of line 79 through contact A 50, by way of line 92 through coil P 59,

contacts

56 and 53 of the car switch, to the right-hand blade of switch 42 as above traced.

It is preferred to provide the direction switches with a mechanical interlock to pre- Vent their simultaneous operation. Such an interlock may be of the form of a walking beam pivotally mounted for engaging catches on the armatures of the direction switches. Upon operation of the up direction switch in response to the energization of its actuating coil B 57, contacts B 65 separate and contacts B 66, B 67 and B 68 engage. The separation of contacts B 65 breaks the circuit leading from the car switch down feed Contact 70, contacts B 65 and the corresponding down direction switch contacts C 62 serving as electrical interlocks. The engagement of contacts B 68 prepares the circuit for the up direction switch holding coil B 71 and the brake switch holding coil H 72. The engagement of contacts B 66 and B 67 completes a circuit for the generator separatelyI excited field winding. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50 and resistance 26, by way of line 7 3 through contacts B 66, by way of line 74 through field winding portion 17, actuating coil G 75 of the maintaining relay, slow-down switch contacts L 76, field winding portion 18, by way of line 89 through contacts B 67 and contacts A 51, to the right-hand blade of switch 42. Relay G does not operate at this time as insuicient current is supplied to its actuating coil.

The brake switch H operates simultaneously with the direction switch B. Switch H. upon operation. causes the separation of contacts H 77 and H 78 and the engagement of contacts H 80 and H 81. The separation of contacts H 77 disconnects the generator separately excited field winding from the generator armature. The purpose of contacts H 77 will be seen from later' description. The separation of contacts H 78 disconnects resistance 31 from across the brake release coil 27. Resistance 81 being of low ohmic value, its disconnection before contacts H 8O engage prevents excess power consumption from

mains

40 and 41. The engagement of contacts H 80 completes the circuit for the brake release coil 27. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 82 through coil 27 and contacts H 80, by way of line 89 through contacts A 51, to the right-hand 4blade of switch 42. The engagement of contacts H 81 completes the circuit for the accelerating switch actuating coil F 83. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 84 through contacts H 81, reactance 85 and coil F 83,

contacts

55 and 53 of the car switch, by way o1 11ne 61 through contacts C 62, line 63, switch 44, line 46, line 89, to the right-hand blade of switch 42.

The levelling switch motor relay, upon operation, causes the engagement of contacts P 93, completing the circuit for the levelling switch motor 38. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 94 through armature 36 and field winding 37 of motor 38 and contacts P 93, by way of'line 89 through contacts A 51, to the righthand blade of switch 42. The levelling switch motor acts to move the levelling switch operating rollers so as to clear the levelling cams during movement of the car. This operation will be explained later.

The brake release coil 27 being energized and current being supplied from the generator armature 15 to the elevator motor armature 21, due to the generator

field windlng portions

17 and 18 being energized, the elevator motor starts. The field winding portion 18 as now connected assists the field winding portion 17.

The accelerating switch F does not operate immediately the circuitfor its actuating coil F 83 is completed, its action being delayed by the reactance 85. Upon operation, switch F causes the separation of contacts F 8'( and the engagement of contacts F 88 and F 90. The separation of contacts F 87 removes t-ne short-circuit around the holding coil P 91 of the levelling switch motor relay. The engagement of contacts F 88 completes the circuit for holding coils B 71, P 91 and H 72. This circuit may be traced from the lefthand bladeof switch 42, by way of line 79 through contacts A 50, by way of line 95 through coil B 71 and contacts B 68, by way of line 96 through coils P 91 and H 72 and contacts F 88, by way of line 89 through contacts A 51, to the right-hand blade of switch 42. The purpose of the energization of these holding coils will be seen from later description. The engagement of contacts F 90 shortcircuits resistance 26, increasing the voltage comes up to full speed. Also sufficient current is now supplied to the coil G to cause the operation of the maintaining relay.

Thus contacts G 97 engage, by-passing accelerating switch contacts F 88. It is to be understood that several. accelerating switches may be employed to short-circuit successively sections of resistance 26, all but one, illustrated as short-circuiting the whole of the resistance, being omitted in order to simplify' the description.

The starting of the car in the down direction is accomplished in a similar manner and will be only briefly described. The operator moves the car switch into position where its contact bar 52

bridges contacts

70, 98, 100 and 101. Upon the engagement of the contact bar and contact 98, a circuit is completed for the down direction switch actuating coil C 102 and coil H 58 which circuit may be traced from the left-hand blade of switch 42, through coil H 58, as previously traced, by way of line 103 through coil C 102,

car switch contacts

98 and 70, by way of line 63 through contacts B 65, to the right-hand blade of switch 42 as previously traced. The engagement of the contact bar and contact 10() prepares a circuit for coil F 83 and the engagement of the contact bar and contact 101 completes a circuit for the coil P 59 by way of line 104. The down direction switch, upon operation, causes the separation of contacts C 62 and the engagement of contacts C 105,v C 106 and C 107, these contacts corresponding with up direction switch contacts B 65, B 66, B 67 and B 68 respectively. The holding coil of the down direction switch is designated C 64. The circuit for coil F 83 is completed by contacts H 81 as before. Further than this, the operation of starting the car in the downdirection is the same as described for starting it in the up direction.

Assume that the car is running in the up direction and that the operator centers the car switch between the second and third floors in orderto stop at the third Hoor landing. Upon the disengagement of the contact bar 52 and contact 56,'the circuit for the levelling switch motor relay actuating coil P 59 is broken. The relay remains in operated condition, however, due to its holding coil P 91. The disengagement of contact 55 and the contact bar breaks the circuit for the accelerating switch actuating coil F 83. The accelerating switch,ltherefore, drops out, causing the separation of contacts F 88 and F 90 and the engagement of contacts F 87. The separation of contacts F 88 is simply in perparation for the next starting operation, the circuit for coils B 71, P 91 and H 72 being maintained by contacts G 97. The separation of contacts F 90 removes the short circuit for resistance 26, decreasing the strength `of the generator

field winding portions

17 and 18. Thus the generator E. M. F. is decreased and the speed of the elevator motor is reduced. Discharge resistances 23 and 24 act to smooth out the retardation. The engagement of contacts F 87 short-circuits the holding coil P 91 of the levelling switch motor relay. The disengagement of contact 54 and contact bar 52 breaks the circuit for actuating coils B 57 and H 58. The up direction switch and brake switch are maintained ih operated condition, however, by their holding coils B 71 and H 72 respectively.

The levelling switch motor relay P, dropping out upon the short-circuiting of coil P 91, causes the separation of contacts P 93 to deenergize the levelling switch motor 38. In this manner the operating rollers of the levelling switch are extended for engagement by the .levelling cams. Referring briefly to Figure 2, the levelling switch motor is operatively connected to the levelling switch by means of an arm 108 on the motor shaft, a connecting link 110 and a lever 111. In the starting operation, the motor 38 being energized, arm 108 rotates, acting through link 110 and lever 111 to move the levelling switch as a whole about a pivot. In this manner the levelling

switch operating rollers

112 and 113 are moved into position where they do not engage the levelling

cams

114 and 115 during motion of the car, a stop being provided to determine the extent of the movement. It is to be understood that levelling cams are provided for each floor. The level- .ling switch is pivoted on a bracket 116 secured to the car frame. In the stopping operation, upon the deenergization of the levelling switch motor, a spring (not shown) moves the lever 111 and therefore the level'- ling switch back into the first described position with the

rollers

112 and 113 extended for engagement by the levelling cams. Each pair of levelling

contacts

32, 33, 34 and 35 comprises a. stationary contact and a movable contact operated by the engagement of its corresponding roller and levelling cam. The

fast speed contacts

34 and 35 are arranged to separate before their corresponding

slow speed contacts

32 and 33 in the levelling operation. Springs (not shown) are provided for causing the separation of the contacts of the pairs as the levelling operation is effected and stops are provided for determining the extent of movement of the rollers as they ride off the levelling cams.

t will be assumed that 'the up levelling switch operating roller 112 moves onto the vertical surface of up levelling cam 114 before relay G drops out. The engagement of up slow speed levelling contact-s 32 completes a circuit for actuating coils H 58 and B 57 and up slow speed levelling relay actuating coil I) 117. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 60 through coil H 58, coil B 57, contacts 32 and coil D 117, by way of line 89 through contacts A 51, to the right-hand blade of switch 42. The engagement of fast speed levelling contacts 34 by-passes resistance 118, the purpose of which will be explained below. The energization of coils H 58 and B 57 has no particular effect at this time as the up direction switch and brake switch are being maintained in operated condition by coils B 71 and H 72. Relay G, however, drops out as soon as the current flowing through its actuating coil drops to a predetermined value, the current being sustained by the action of field winding portion 17 and discharge resistance 23. As a result, contacts G 97 separate, deenergizing holding coils B 71 and H 72. The up direction switch and brake switch are then maintained operated by coils B 57 and H 58. Had the slow speed levelling contacts not been in engagement when the relay G dropped out, their subsequent engagement as roller 112 rode onto the vertical surface of the cam would cause the energization of coils H 58 and B 57.

As set forth above, actuating coil D 117 of the up slow speed levelling relay was energized upon the engagement of slow speed levelling contacts 32. This relay, upon operation, causes the engagement of contacts D 120, completing the circuit for coil L 121. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 122 through contacts D 120, up series field relay actuating coil M 123, up hard brake switch actuating coil O 124 and a portion 125 of reactance 126, by way of line 127 through coil L 121, line 128, by Way of line 89 through contacts A 51, to the right-hand blade of switch 42. The circuit comprising contacts L 130, down series field relay actuating'coil M 131, down hard brake switch actuating coil O 132 and the other portion 133 of reactance 126 are in parallel with coils M 123 and O 124 and reactance portion 125. The polarities of the coils of relay M and switch O and of the portions of the reactance 126 is such that the ampere turns in coils M 131 and O 132 and reactance portion'133 neutralize the ampere turns in coils M 123 and O 124 and reactancc portion 125 respectively so that the resultant ma gnetizing force for the magnetic circuits of the relay, switch and reactance is zero. Thus neither relay M nor switch O operates. The slow-down switch L, however, operates immediately, causing the separation of contacts L 76 and L 130 and the engagement of contacts L 134, L 135, L 136, L 137 and L 138. The separation of contacts L 76 disconnects

field winding portions

17 and 18, field winding portion 17 being connected to the

mains

40 and 41 by the engagement of contacts L 134 and field winding portion 18 being connected to the generator armature through resistance 140 by the engagement of contacts L 135. The polarity of the latter connection is such that the current supplied to the field winding portion 18 flows in such direction as to create a niagnetizing force which opposes the magnetizing force due to field winding portion 17. The effect of field winding portion 18 is reduced by resistance 140. The engagement of contacts L 138 completes a shortcircuit through fast speed levelling switch contacts 34 for an adjustable portion of resistance 26. These connections cause the elevator motor to run at a desired levelling speed as will be explained later in more detail. Resistances 23 and 24 act to smooth out the changes in generator E. M. F. due to these operations. The purpose of the engagement of contacts L 136 and L 137 will be explained later. It is to be noted that the separation of contacts L 76 also breaks the circuit for coil G 75. Thus had the current in coil G not dropped to a sufficiently low value to permit relay G to drop out, as might result from the late centering of the car switch, the disengagement of contacts L 76 in response to the engagement of up slow speed levelling contacts 32 insures the separation of contacts G 97 and the cons uent deenergization of holding coils B 71 and 72.

The separation of contacts L 130 breaks the parallel circuit around coils M 123 and O 124 and reactance rportion 126. Upon the separation of contacts L 130, the reactance reduces the current su plied to coils M 123 and O 124 to a value below that required to operate relay M and switch O and thereafter prevents the ra id building up of the current, thus slightly elaying the operation of the rela and switch. Switch O may be adjusted so that it operates almost immediately the current against starts to build up. Switch O, upon operation, causes the separation of contacts O 141 to break the circuit for resistance 3() irl parallel with the brake release coil 27. Relay M, upon operation, causes the engagement of contacts M 142 to complete the circuit for the series field switch actuating coil N 143. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 128 throu h coil N 143 and contacts M 142, by way o line 89 through contacts A 51, to the right-hand blade of switch 42. Switch N, upon operation, causes the separation of contacts N 144, breaking the circuit including resistance 29 in shunt to the generator series field winding 16. The generator series field coils are so wound' that, without the parallel resistance 29, they would have too great an effect for proper operation of the car. The desired compoun vg is obtained by employing the low resistance shunt. Upon separation of contacts N 144,v the strength of the series field is increased for the levelling operation so as to aid in obtaining the desired 'stopping operation. The short delay in the action of relay M, and therefore the switch N, upon the initiation of the levelling operation, is desirable in order that the current in the generator armature-elevator motor armature circuit may ad'ust itself to such a value that proper series eld strength during the levelling operation may be obtained.

As the car nears the third floor landing,

roller 112 rides offy the vertical surface onto the oblique surface of cam 114. This results in theseparation of up fast speed levelling contacts 34, removing the short-circuit around resistance 118. The generator E. M. F., therefore, is again lowered and the elevator motor runs at its slowest speed.

Shortly before the car reaches an exact level with the landing, the roller 112 rides off the oblique surface of cam 114, thereby separating the slow speed levelling contacts 32. The circuit for coils H 58, B 57 and D 117 is thus broken. Switch B drops out causing the separation of contacts B 68, B 67 and B 66 and the reengagement of contacts B 65. The reengagement of contacts B 65 and the separation of contacts B 68 are in preparation for the next starting operation. Contacts B 66 and B 67 will be referred to later. Up slow speed levelling relay D drops out, causing the separation of contacts D 120. Thus the circuit is broken for coils M 123, O 124 and L 121. Relay M and switch L drop out immediately but switch O is delayed in its action by the effect of reactance 126 and discharge resistance 145. It is to be noted that the discharge current for coil O 124 and the reactance passes through down coil O 132 in such direction as to cause coil O 132 to assist coil O 124 inmaintaining switch O in operated condition. Relay M, upon dropping out, causes the separation of contacts M 142, deenergizing series field switch actuating coil N 143. Switch N drops out to reconnect resistance 29 across the generator series field. Switch L, upon droppin out, causes the separation of contacts L 134, L 135, L 136, L 137 and L 138 and the engagement of contacts L 76 and L 130. The separation of contacts L 136, L 137 and L 138 and the engagement of contacts L 130 are in preparation for the next starting operation. Contacts L 134, L 135 and L 76 will be referred to later. Switch H drops out along with switch B and relay D, causing the separation of contacts H 81 and H 80 and the engagement of contacts H 78 and H 77. The separation of contacts H 81 is in preparation for the next starting operation. The separation of contacts H 8O breaks the circuit for the brake release coil 27, effecting the application of the brake. The engagement of contacts H 78 during this operation has no particular function.

The engagement of contacts H 77 along with the separtion of contacts B 66 and B 67 of the up direction switch and the separation of contacts L 134 and L 135 and the engagement of contacts L 7 6 of the slowedown switch disconnects field winding portion 17 from mains 40-41 and connects both

field winding portions

17 and 18 to the generator armature. The polarity of the latter connection is such that the generator sends current through the whole field winding in such direction as to oppose the flux which produces the generator E. M. F., thus tending t0 destroy the residual flux of the generator field. Thus, the brake being applied and the generator separatel excited eld winding being disconnected rom mains 40-41, the car is brought to rest level with the third fioor landing. Since the engagement of contacts O 141 is delayed, a hard application of the brake is obtained, assuring a positive stop at the landing.

In the event of an overrun, the operation of the switches is modified. Assuming in the above example that the car overruns the third fioor to the extent of causing the engagement of down slow Speed levelling contacts 33, a circuit is completed for coils H 58 and C 102 and actuating coil E 146 of the down slow speed levelling relay. This circuit may be traced through coil H 58 as previously traced, by way of line 103 through coil C 102, contacts 33 and coil E 146, by way of line 89 through contacts A 51, to the righthand blade of switch 42. The relay E, upon peration, causes the engagement of contacts 147, completing a circuit for down, coils M 131 and O 132 and coil L 121. This circuit may be traced from the left-hand blade of switch 42, by way of line 79 through contacts A 50, by way of line 148 through contacts E 147, coils M 131 and O 132 and reactance portion 133, by way of line 127 through coil L 121, to the right-hand blade of switch 42 as previously traced. Due to the fact that contacts L 130 are in engagement, up coils M 123 and O 124 are connected in parallel with down coils M 131 and() 132. Thus, as previously explained, the switch L operates immediately, causing the separation of contacts L 130 and L 76 and the engagement of contacts L 134, L 135, L 136, L 137 and L 138. Since contacts H 77 are separated and contacts C 105 and C 106 are in engagement due to the energization of coils H 58 and C 102 respectively, the separation of contacts L 76 and the engagement of contacts L 134 and L 135 cause the connection of field winding portion 17 to mains 40-41 and the connection of field winding portion 18 to the generator armature. As will be seen romlater description, such connections of the field winding portions cause the generationl of an E. M. F. which causes the elevator motor to be returned to the floor in the down direction and which E. M. F. is of a value very near to that generated with the car approaching the floor in the up direction. Variations in the generator E. M. F. for the levelling operations cause variations in the operation of the elevator motor. By causing the veneration of more uniform voltages for level ing, as by the above arrangement, such variations in the levelling operation are substantially eliminated.

Relay M and switch O do not operate immediately upon the engagement of contacts E 147 and the separation of contacts L 130. When approaching the floor in theup direction, the current flowing through reactance portion 125 caused a flux to be built up in the reactance in one direction. Upon the separation of contacts D 120, the current in the reactance and coil O 124 discharged into resistance 145 tending to maintain the flux built up and, as previously explained, switch O in operated condition.- Upon the engagement of contacts E 147 and the separation of contacts L 130 on the overrun, the current supplied to coils M 131 and O 132 must reverse the flux in the reactance, thus taking a longer time to build up to a value sufficient to cause the operation of relay M and switch O. Thus contacts N 144, depending for their separation upon the operation of relay M, remain closed temporarily to insure that the current in the generator armature-motor armature circuit has fallen to a low value. Since the current in the series field winding may be flowing in a direction such as to cause the generation of an E. M. F. which is of proper polarity for operating the car in the down direction, immediate increase in the strength of the series field might result in an overrun in the down direction. As the car returns to the floor, it is stopped by the separation of slow speed levelling contacts 33 in a manner similar to that described for approaching the floor.

If the overrun is great enough to cause the engagement of the down fast speed levelling contacts 35 as well as the down slow speed levelling contacts 33, resistance 118 is shortcircuited, increasing the generator voltage and causing the elevator motor to run at its fast levelling speed. Further than this, the operation on an overrun is as above described.

It is to be understood that the operator may control both the acceleration and retardation of the car by moving the car switch in steps. 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 65 which remain separated until the up direction switch drops out.

In variable voltage control systems of the type wherein the elevator motor is supplied with current from the generator' of a motor generator set, the generator is required to opvarying from a maximum yure illustrates the conditions when a small possibility of crate over a wide range of E. M. F. values, in one direction to a maximum in the other. When operating at low values of E. M. F., the armature voltage obtained for a given field current may vary over a wide range due to the varying effects of residual flux. This effect is very marked under levelling operatin conditions where low values of generated M. F. are employed. Such low values, of E. M. F. are usually obtained by permitting only a small amount of current to flow through the generator separately excited field winding so as to produce low values of flux. Thus the residual flux present forms a large percentage of the total flux and therefore affects the operation of the system very markedly. In order that the effects of residual flux may be clearly seen, reference may be had tothe assumed hysteresis curve shown in Figure 3. This figcurrent is supplied to the separately excited field winding of a separately excited generator, as during levellingoperation. It will be seen that, for a certain current value, represented by the magnet-izing force Mm, the E. M. F. of the generator may be any value between V1 and V3 depending on the previous magnetic state of the machine and whether the car is approaching the floor from one direction or is returning to the floor in this direction after an overrun from the opposite direction. V2 represents the minimum value of the generator E. M. F. for a magnetizing force Mm of equal but opposite value to magnetizing force Mm. Obviously, such large E.' M. F. variations might result in undesirable variations in operation under levelling conditions. These variations cannot be satisfactorily corrected by adjusting the amount ot resistance in series with the Separately excited field winding. For example, if the amount of resistance were decreased in order to raise the value of V3, the value of V1 also would be raised, resulting in an increasing tendency to run past the floor. Similarly, if the amount of resistance were increased in order to lower the value of V1, the value of V3 also. would be lowered, with the V3 being of too low a value to return the car to the floor after an overrun. Thus, if the values of V1 and V3 can be made nearly equal for levelling operating conditions, the system may be adjusted so as to obtain more uniform operation. This desired result may be attainedby connecting field winding portion 18 to the generator armature and energizing field winding portion 17.

For convenience of explaining the action of the

portions

17 and 18 of the field winding, as-- sume that the generator has been in operation with the portions connected across the mains in such mann-eras to assist each other and that, as a final step in reducing the generator E. M. F., both portions are disconnected from the mains and that portion 18 is connected to the generator armature and portion 17 left unenergized, the polarity of the connection between the generator armature and portion 18y being such that the generator sends current therethrough in a direction to oppose the flux which produces the generator E. M. F. The final values of the generator E. M. F. under such conditions are illustrated in Figure 4, In this figure, the line X-Y is the resistance line of the field and shows the relation hetween the voltage applied to the field winding and the number of ampere turns produced thereby. With the hysteresis curve, as before, in the first and third angles, the line X-Y for winding portion 18, in accordance with the polarity of connection assumed, is in the second and fourth angles. If both winding portions had been left disconnected, the gen erator E. M. F. would have assumed a value V@ or V9 depending on the previous polarity of the machine. These values would be due to the residual flux of the generator field. For convenience of further explanation, assume that the previous polarity of the generator corresponded with the polarity indicated by E. M. F. value Vgat the time that Winding portion 17 was disconnected and winding portion 18 was connected to the armature. It is to be understood that the value of the generator E. M. F. at the instant of the change of connections would be determined by the time constant of the field and therefore might be greater than V8. Assuming, however, that the generator E. M. F. was at a value V8 at the instant'f change, this E. M. F. applied to winding portion 18 would tend to cause this p portion to exert a magnetizing force of a value M52. Such magnetizing force, however, opposing the flux which produced the armature E. M. F., would cause a decreasein the value of the E. M. F. generated. A decreased E. M. F. would simply mean a decrease again in the value of the opposing inagnetizing force. As a result, a state of equilibrium would be reached where any tendency for a decrease in armature E. M. F. -Would result in a decrease in opposing magnetizing force with the consequent increase in armature E. M. F., i. e., once the armature E. M. F.

is reduced to a value V4, a decrease in value v would mean that the opposing magnetizing force would tend to assume a value Mba, for example, which would tend to increase the value of the armature E. M. F. The value V5 represents the armature E. M. F. with the state of equilibrium obtained after a previous armature E. M. F. of the other polarity.

According to the preferred arrangement, however, as previously explained, ield winding portion 17 is energized from the mains when portion 18 is connected to the generator armature. With the winding portions connected in this manner, conditions become as illustrated in Figure 5. In this figure, Mm

represents the magnetizing force created by winding portion 17 with the car moving in one direction while Mb represents the magnetizing force created by winding portion 18 for the state of equilibrium with the car approaching the floor in this direction and M61 represents the magnetizing force created by winding port-ion 18 for the state of equilibrium when the car is being returned to the floor in this direction after an overrun from the opposite direction. Graphicall the effect of the magnetizing force Mm1 o windin portion 17 is to shift the resistance line X for winding portion 18 to the right. When the car is approaching the floor in this direction, therefore, the final value of the armature E. M. F. is that due to the difference in the magnetizing forces of the winding portions, i. e., Mam-Mb, and is represented as V8. W'hen the car is returning to the floor in this direction after an overrun from the other direction, the nal value of the armature E. M. F. is that due to the difference in the magnetizing .forces of the winding (portions, i.e., Mml-Mbl, and is represente as VT. The armature E. M. F., therefore, lies between the values V8 and V1, which values, relatively speaking, are very nearly equal. Thus the possible range of variation 1s much smaller than when an undivided separately excited field winding is used as explained in connection with Figure 3. The increase in field current to obtain the desired magnetizing force Mm1 of the winding portion 17 for the voltages V6 and V1 is effected by the engagement of contacts L 138 in the system described. Any tendency for an increase in the armature E. M. F. under the above described conditions would result in an increase in the magnetizing force of the winding portion 18 and thus a decrease in the net magnetizing force, and vice versa.

p It is preferred to utilize the field winding portion 18 to assist the field winding 17 during car switch operation as described above. The arrangement of the field winding may be as indicated in Figure 2. Here the field coils for the north poles are grouped together to be used as winding portion 17 while the field coils for the south poles are grouped together to be used as winding portion 18. lVith the switch L in the position illustrated, these windings are connected so as to assist each other, providing alternate north and south poles. The direction of the current is indicated by arrows. The circuit for the field winding may be traced by way of line 74 through winding portion 17 constituting the N poles, through coil G 75, contacts L 76 and winding portion 18 constituting the S poles, to line 89. It is to be understood that the manner of winding is such as to obtain the desired polarity. lVith the winding of switch L energized by the levelling switch contacts, the switch is moved into its other position so as to disconnect winding portion 18 from the mains and to connect it to the generator armature with the proper polarity. The circuit for winding portion 17 may now be traced by way of line 74 through winding portion 17, by way of line 170 through contacts L 134, to line 89. The circuit for winding portion 18 may be traced from the lower armature terminal, line 171, a portion of line 89, by way of line 74 through winding portion 18, by way of line 172 through contacts L 135 and resistance 140, series field windings 16, to the upper armature terminal.

Lines

173 and 174 indicate the connection from the generator armature to the motor armature. The direction of the current in the generator armature-motor armature circuit when the motor is lifting a load is indicated by double arrows. It is to be understood that the manner of winding for the series field is such thatV the field due to the series winding assists that due to the separately excited field winding portions, when the motor is lifting a load. Thus, upon the operation of switch L to cause the engagement of its contacts L 134 and L 135 and the separation of its contacts L 76, the current supplied to the field winding portion 18 is reversed. This is true regardless of whether the elevator motor is lifting or lowering a load since the polarity of the generator armature does not change upon regeneration. The engagement of contacts L 138 results in an increase in magnetizing force due to the field winding portion 17 as previously explained. Resistance 140, connected in series with the field winding portion 18 when the latter is connected to the generator armature serves to reduce the amount of current supplied to this portion and therefore the magnetizing force produced thereby, the resistance determining the slope of the line X--Y and therefore the relative values of the armature E. M. F. Thus it will be seen that, with the above described arrangement, variations in operation during levelling caused by the effeet of the residual flux of the generator are substantially eliminated. It is to be understood that the above described arrangement is applicable to generators of other pole numbers, a four pole generator being chosen merely for convenience of description. Also it is to be understood that the coils of the field windlng might be grouped in other relations to effect the desired result.

The series field winding 16 acts to assist the separately excited field winding portions to obtain the desired conditions during operation. Under normal car switch operation, when these winding portions assist each other, the series field winding acts in the usual manner to compensate for varying load conditions. During levelling conditions, when the elevator motor is lifting a load, the effect of the series field winding is to aid in bringing the car to the fioor since the current flow in the series field winding is in such direction as to produce a magnetizing force which assists that due to field winding portion 17 and opposes that due to field winding portion 18. Conversely, when the elevator motor is lowering a load, the effect of the series field winding is to aid in causing the car to stop at the fioor since the current flow in the series field winding is in such direction as to produce a magnetizing force which 0pposes that due to field winding portion 17 and assists that due to field winding portion 18.

Referring again to Figure 1, in order to guard against an open circuit in field winding portion 18 during levelling, with the resultant increase in generator E. M. F. and therefore car speed when contacts L 138 are in engagement, the protective relay J may be employed. Along with the employment of relay J, contacts L 136 and L 137 are employed to connect resistance 15() to the generator armature. The protective relay actuating coil J 151 is connected between a` point on this resistance and the mid point of field winding portion 18. A bridge circuit is thus formed and is so balanced that under normal levelling operating conditions, no current flows through coil J 151. However, if an open circuit occurs in field winding -portion 18 itself or in the circuit for resistance 150, current fiows through coil J 151, causing the operation of the relay. The relay, upon operation, causes the separation of contacts J 47 inthe circuit for the actuating coil A 45 of the potential` switch. Relay J is preferably of the latched type to maintain contacts J 47 separated, once the relay is operated, until manually reset. Switch A, upon dropping out, causes the separation of contacts A 50 and A 51. Thus the main field windinor is disconnected from

mains

40 and 41 and the brake is applied, bringing the motor to a stop. Since half of field winding portion 18 is in each side of the bridge circuit, any transient voltages induced in the winding balance out and do not cause the operation of the protective relay J. However,

. if resistance 140 in one side of the bridge circuit is large, it may be desirable to divide it into halves, putting one-half in one side of the bridge circuit and the other' half in the other side. Suchy arrangement would result in a perfect balance and would insure that `relay J would not be operated under transient voltage conditions.

If desired, the auxiliary protective relay K, preferably of the same type as relay J so as to maintain its contacts K 48 separated until manually reset once the relay has operated, may be employed to protect against an accidental open circuit for the coil J 151 and against the accidental short circuit of resistance E26 during levelling operation which would result in an excessive voltage being applied to field winding portion 17. It is to be noted that the auxiliary protective relay is provided with two coils K 153 and K 154. Under normal car switch operating conditions, coil K-153 `is connected in series with coil J 151 across one-half of field winding portion 18 andrcoil K 154 across field winding portion 17. By means of the resistances 155 and 15G,.the currentsupplied to the coils ma be adjusted so that the ampere turns .o one coil neutralize those of the other. If the circuit yfor coil J. 151 should be accidentally opened, coil K 154 alone would be energized, causing the operation of the relay K. Relay K, upon operation, causes the separation of contacts K 48 in the circuit for the potential switch actuating coil A 45. Thusv the car is brought to a stop in the manner above described. During the levelling operation, coil K 153 is shortcircuited by contacts L 137 so that only coil K '154 is energized. Coil K 154 is designed, however, so as to causethe operation of the auxiliary protective relay K to effect the stopping of the car when an excessive voltage, such as would result from the short-circuiting of resistance 26, is applied to the coil. The coils of relay K are wound with a larger number of turns than coil J f 151 so that, under normal car switch operation, the current flowing through coils K 153 and J 151 does not cause` the operation of relay J.

It is to be noted that, vwhen the car is stopped by deenergizing theactuating coil of the potential switch or by the centering of the car switch at such time as to stop the car without the levelling zone, the switch O is not operated. Thuscontacts O 141 are in engagement, leaving resistance 80 in parallel with resistance 28, and, upon the engagement of contacts H 78, resistance 31 is connected in parallel with resistances 28 and 3() and a so-ft application of the brake is obtained.

As many changescould be made in the above arrangement and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all Inatter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative andv not in a limiting sense.

What is claimed is: 1. In combination, a generator having an armature and a field winding, a source of current, means for connecting the whole ofy said field'winding to said source, and means for reconnecting said field winding in such manner that one portion thereof is connected to said source and another portion thereof is connected to the armature 'of the generator.

2. In combination, a generator having an armature and a field winding, means for driving said generator, a source of current, means for connecting the whole of said Winding to said source, and means for changing the connections of said winding so as to have a portion thereof connected to said source with another portion connected to the generator armature.

3. In combination a generator having an armature and a field Winding, means for driving said generator, a source of current, means for connecting the Whole of said field winding to said source, means for reconnecting said field Winding in such manner that one portion thereof is connected to said source and the other portion thereof is connected to the generator armature, and means for reducing the voltage ap lied to said other ortion of the field winding below that of the generator armature.

4. In combination, a generator having an armature and a field Winding, means for driv ing said generator, a source of current, means for connecting the Whole of said field Winding to said source, means for changing the connections of said field Winding so as to have a portion thereof connected to said source with another portion connected to the armature ofthe generator, and means for reducing the voltage applied to said other p0rtion of the field Winding below that of the generator armature.

5. In combination, a generator having an armature and a field Winding, a source of current, means for connecting the whole of said field winding to said source, a resistance, and means for changing the connections of said field Winding' so as to have a ortion thereof connected to said source wit another portion connected in circuit with said resistance to the armature of the generator.

6. In combination, a generator having an armature and a field Winding, said field wind ing comprising a coil on each field pole, means for driving said generator, a source of current, and means for connecting certain of said coils to said source and the remainder of said coils to the armature of the generator, the manner of connecting said remaining coils being such thattheir magnetizing force opposes that of said certain coils.

7. In combination, a generator having an armature and a field Winding, said field winding comprising a plurality of coils, one on cach field pole, a source of current, means for connecting said coils to said source, and means for disconnecting alternate coils from said source and connecting them to the generator armature 8. In combination, a generator having an armature and a field winding, said field winding comprising a plurality of coils, one on each field pole, means for driving said generator, a source of current, means for connecting all of said coils to said source in such manner as to excite the alternate` poles for like polarities, and means for disconnecting the coils of alternate poles from said source 'and connecting them to the generator arr ture in such manner as to reverse the elicit ation of said alternate poles 9. In combination, a generator having an y armature and a field Winding, said field winding comprising a pluralityv of coils, one en each field pole, means for driving said gen erator, a source of current, means for connecting said coils to said source, means for disconnecting alternate coils from said source and connecting them to the generator armature, and means for reducing the volt-N a e applied to said alternate coils Iieloiv thai: o the Generator armature 10. Ion combination, a frenerator havin mi armature and a field Winding, said field 'a ing comprising a plurality of coils, on' each Held pole, means for driving said L erator, a source of current, means for c wg necting all of said coils to said source in such manner as to excite the alternate pole; foi,` like polarities, means for disconnecting the coils of alternate poles from said source anc. connecting them to the generator armat in such manner as to reverse their excitatic and means for reducing the voltage applic. to said coils of alternate poles below that ci: the generator armature.

l1. In combination, a Jenerator having armature and a field Win ing, means for d ing said generator, a source of current, mear for connecting the whole of-said field Winding` to said source so as to cause the generation of r. certain voltage, and means for decreasir" said voltage, said last included means com prising means for connecting a portion said Winding across said armature.

l2. In combination, a generator having a.;- armature and a field Winding, means for di.` ing said generator, a source of current, y sistance, means for connecting the field "rin, ing to said source in circuit with said resance to cause the generation of a certain flotay age, and means for decreasing said voltage` 1j, said last included means comprising meaW for connecting a portion of said winding said armature and for short-circuiting at leas*J a portion of said resistance.

13. In combination, a generator having f armature and a field Winding, means for d ing said generator, a source of current, a resistance, means for connecting the field wind ing to said source in circuit with said res' ance to cause the generation of a certain. vc. age, means for increasing said voltage, sa third named means comprising means for short-circuiting said resistance, and means for decreasing said voltage, said last "'Wucf means comprising means for conn` portion of said Winding to said armut means for short-circuiting :i portion of 'e resistance.

14. In combination, a Generator having an armature and a field Winding, said field Wind- 312e l said resistance, and means for ldecreasing sai voltage, said last included means' compris-` ing means for connectlng certain of said coils to said armature. and for shortc1rcu1t1ng a portion of said resistance.

15. In combination, a motor, a variable -voltage generator for supplying current to said motor, said generator having an armature and a field winding, a source of'current, means for causing the motor to run at a. certain speed, said means comprising means for connecting said field winding to said source, and means for causing the motor to run at a slower speed, said last included means comprising means for connecting a portion of said field winding to said armature.

16. In combination, 'a motor, a variable voltage generator for supplying current to said motor, saidenerator having an armature and a field winding, a source of current, means for causing the motor to run atacertain speed, said means comprising means for connecting said field win ing to said source, and means for causing the motor to run at a a, slower speed, said last included means coml prislng means for disconnecting av portion of said winding from said source and connecting it to the armature of the generator in such manner as to reverse the flow of current through said ortion.

17. In com ination, a motor, a variable voltage generator for supplying current to said motor, said enerator having an armature and a field winding, a source of current, .means for causing the motor to run at a certain speed, said means comprisingmeans for connecting said field winding to said source, means for causing said motor to run at a' slower speed, said second included means comprising means for disconnecting a portion of said wlnding from said source and connecting it to the armature of the generator, and means for reducing the voltage applied to said portion of the field winding below that of the generator armature.

18. In combination, a Generator havin an armature and a field winding, means for riving said generator, a sourcel of current, means for connecting one portion of said winding to saidvsource and another portion to the generator armature, and means operable upon the occurrence of an open circuit in said another portion of the winding to disconnect said one portion of said winding from said source.

19. In combination, a enerator havin an armature and a field win ing, means for riv-` ing said generator, a source of current, means for connecting the whole of said field winding to said source, a resistance, means for reconnecting said field winding in such manner that one portion thereof is connected to said source in circuit with said resistance so as to cause the application of a voltage of a. `A

certain value to said portion and another portion thereof isV connected to the generator armature, and means operable, upon an in crease in the voltage a plied to said one portion to a value higher han said certain value, to disconnect said one portion from said source.

In testimony whereof, I have signed my name to this specification.

LEE I; DAVIS.