US2685348A - Elevator control system - Google Patents

Description

3, 1954 Y J. H. BORDEN 2,685,348

ELEVATOR CONTROL SYSTEM Filed Feb. 27, 1952 5 Sheets-Sheet 1 63 Snnentor JOSEPH H BORDE/V W w attorney g' 1954 J. H. BORDEN 2,685,348

ELEVATOR CONTROL SYSTEM Filed Feb. 27, 1952 5 Sheets-Sheet 2 ISnventor JOSEPH H BURDEN BB 9 W g 27 attorney? 2&85348 J. H. BURDEN ELEVATOR CONTROL SYSTEM Aug. 3, 1954 5 SheetsSheec 3 Filed Feb. 27, 1952 DEVICES Enucntot Aug. 3, 1954 J. H. BORDEN 2,685,348

ELEVATOR CONTROL SYSTEM Filed Feb. 2'7, 1952 5 Sheets-Sheet 4 46 mower/vs nay/05s =1 can/mm & 1 30 -27? 255 {m 237 t i a? 26/ 286 J F Znnenior Aug. 3, 1954 J. H. BORDEN 2,635,348

ELEVATOR CONTROL SYSTEM Filed Feb. 27, 1952 5 Sheets-Sheet 5 ELEVATOR POWER AND SIGNAL 3/? Bnventor 3/3 JOSEPH H BURDEN.

Patented Aug. 3, 1954 ELEVATOR CONTROL SYSTEM Joseph H. Borden, Toledo, Ohio, assignor to Haughton Elevator Company, Toledo, Ohio, a

corporation of Ohio Application February 27, 1952, Serial No. 273,593

Claims. 1

This invention relates to control systems for freight and passenger elevators and in particular to simplified controls for maintaining floor finding devices and speed controlling equipment in proper operational synchronism with an elevator car moving in a hatchway.

It has been common practice to drive a floor selecting device for an elevator by means of tapes or cables that are attached to the elevator car and that are Wound onto and attached to a drum or pulley geared to the selecting device. These tapes or cables are in addition to the cables that support the elevator car. Attempts have been made to eliminate the tape or cable drive for the floor selector and to drive the selector directly from the elevator drive motor. Such a control drive, when used with a traction drive, must make provision for the creepage that occurs between the elevator support cable and the motor drive pulley as the cable runs over the drive pulley. creepage, if not corrected, causes serious errors in the position of the floor selecting device mechanism. Complicated and expensive correcting devices have been employed to correct this creepage of the cables.

The principal object of this invention is to provide an improved creepage compensating mechanism that is simple, inexpensive and thoroughly reliable.

Another object is to provide a clutch mechanism in the drive between an elevator drive motor and a cooperating fiOOI selecting or other control mechanism to cooperate with means operatively connected to the floor selecting mechanism and adapted to slip the clutch mechanism when the car is leveled at a floor to synchronize the floor selecting mechanism with the elevator car and thus correct for creepage of the drive cables.

A still further object of the invention is to adapt an improved creepage correcting mechanism to an elevator control system employing a small constant speed reversible motor for driving a part of the floor selecting mechanism.

A still further object is to provide an electrically controlled clutch in the drive mechanism for an elevator control mechanism to cooperate with mechanical centering devices arranged so that when the clutch is released with the car level with a floor the centering devices accurately position the fioor selecting mechanism and thus correct for any accumulating creepage error.

More specific objects and advantages will be apparent from the following description of several embodiments of the invention.

According to the invention a slippable clutch is Suchincluded between a drive shaft of a traction type elevator drive motor and a floor selecting and controlling equipment and correcting means are provided for slipping the clutch in the event that the elevator car is level at a floor and the control mechanism has not assumed a precisely corresponding position. A traction type elevator is one in which the supporting cables for the car are carried over and frictionally driven by a drive pulley on the elevator drive motor shaft and then down the side of the hatchwa-y to a counterweight, the friction between the cables and the drive pulley being relied upon to transmit power from the drive pulley to the car. The slippable clutch may be either a spring loaded or magnetically actuated friction clutch adapted to slip in case of overload or upon release of the actuating means. The correcting means, which is energized only when the elevator motor is stopped with the car at a floor, is adapted to slip the clutch by the driving effort of an auxiliary motor or to release the clutch and permit a mechanical centering device or a detent to move the selecting mechanism into its proper position.

In normal operation of an elevator the support cable tends to creep one way or the other with respect to the elevator drive pulley depending upon the amount of load and direction of travel of the elevator. The amount of creepage is not large but must not be allowed to accumulate. Therefore, except under unusual emergency situations, it is not necessary to make large corrections.

The improved correcting devices may be substituted for more complicated arrangements such as are shown in United States Patent No. 1,943,114, issued January 9, 1934, or No. 2,052,432, issued December 1, 1936,

Improved correcting devices employing the invention are illustrated in the accompanying draw ings. In the drawings:

Figure I is a schematic representation of an elevator control system employing one form of the invention.

Figure II is a similar schematic figure employing a second form of the invention.

Figure III is an enlarged schematic illustration of an electrically actuated clutch used in the embodiment shown in Figure II.

Figures IV and V are simplified illustrations of a restoring or centering mechanism that cooperates with the electrically actuated clutch to center the control mechanism illustrated in Figure II.

Figure VI is a partially broken away side elevational view of a contacting mechanism serving as a rheostat control for the elevator drive motor.

Figure VII is a partially broken away plan view of the contacting mechanism.

Figure VIII is a vertical section of the contactin mechanism as seen from the line VIII-VIII of Figure VII.

Figure IX is a simplified wiring diagram showing onl enough of the control system to explain the operation of the creep-age correcting mechanism.

Figure X is a similar wiring diagram as modified to cooperate with the correcting mechanism shown in Figure II.

Figure XI is a simplified schematic illustration of another embodiment of the invention.

Figure XII is a simplified wiring diagram to show the electrical control for mechanism shown in Figure XI.

These specific figures and the accompanying description are merely to illustrate the invention and not to limit its scope.

In the simplified elevator control system shown in Figure I, an elevator car I is supported by a cable 2 trained over a drive pulley 3 and attached to a counterweight 4. The drive pulley 3 is mounted on an armature shaft 5 of a slow-speed direct-current elevator motor 6. A brake assembly 'i mounted adjacent the motor 6 is released when the motor is energized, and is spring set when the motor is ole-energized to prevent coasting of the elevator car i.

The elevator motor 6 is controlled according to signal transmitted from a floor selector mechanism 8 and a speed control rheostat assembly 9. The signals to initiate the starting and stopping of the drive motor 5 originate from the floor selector mechanism 8 as the operator or passengers register their calls, while the acceleration, deceleration, and constant speed running of the motor 6 is controlled by the rheostat 9.

In the control system illustrated in Figure I the floor selector mechanism 8 includes a carriage it that is supported and driven past banks of fixed contacts 5 I, each represented by a single contact, by a chain drive 52. The chain E2 is driven by a shaft 13, gearing l4 and a shaft connected to a reversible constant speed advance motor it. The advance motor i6 is preferably a slow-speed synchronous inductor motor having a full speed of approximately 75 revolutions per minute. This type of motor, which is manufactured by the General Electric Comp-any, is characterized b its extremely rapid acceleration and deceleration. The motor l6, which is driven by alternating current, reaches full speed within one cycle of the alternating current from the time it is energized and stop just as quickly when it is de-energized. The gear ratio through the gearing Hi and the chain drive l2 to the car riage it is such that the carriage ll] moves from one bank of contacts H to the next in the same time that the elevator car moves from one floor to the next when traveling at its normal running speed.

Conventional circuits such as are shown in the patents referred to are employed to energize the advance motor [6 when it is desired to operate the elevator from one floor to another. In addition, the fioor seelctor mechanism 8 includes a contact arrangement that continues to energize the advance motor 16 in one direction or the other until the carriage I0 is accurately centered with respect to the bank of contacts I! representing the floor at which the car is to be stopped.

The acceleration, running speed and deceleration of the elevator drive motor 6 is controlled by the rheostat assembly 9. The rheostat 9, driven through a differential gear assembly H, is jointly under the control of the advance motor 5 and the elevator drive motor 3. The advance motor l8 tends to drive the rheostat 8 in a direction to accelerate the elevator motor 5 in a direction to follow the advance motor Simultaneously the elevator motor 5, as it follows the advance motor it, tends to drive the rheostat 9 in a direction tending to reduc the speed of the elevator motor 6. When the speeds correspond the rheostat stops.

The diiferential gear assembly ll comprises a first input element or gear i8 connected to the shaft I5 driven by the advance motor 13, a second input gear i5 carried on a shaft 26 which is connected through friction clutch 2| to the armature shaft 5 of the elevator drive motor 6, a carrier 22 including gears 23 and 2s meshing with the input gears l8 and i9, and a carrier supported output gear 25 which through an idler 26 drives a gear 2? fixed on a shaft 23 of the rheostat assembly 9.

In this arrangement, the advance motor :5 opcrating in response to floor selector control circults drives the iioor selector carriage it towards the selected floor and at the same time, through the difierential gear mechanism ll turns the rheostat shaft in a direction to start and accelerate the elevator motor 6. The rheostat continues to turn until the speed of the shaft 29 connected to the elevator drive motor 5 corresponds to and is opposite in direction to the speed of the advance motor shaft it. When these speeds become equal the differential carrier 22 and the rheostat stops and the elevator drive motor runs at constant speed. At this time the elevator car l lags behind a position corresponding to the position of the floor selector carriage II] by an amount determined by the gear ratio and the movement of the rheostat 8 required to bring the elevator motor 6 up to speed. This lag is made generally proportional to the operating speed of the elevator and may be as great as twenty feet for an elevator operating at 899 feet per minute.

When the floor selector carrier I53 reaches the bank of contacts corresponding to the floor at which a stop is to be made the advance motor i6 is de-energized, instantly stops, and thereafter maintains the fioor selector mechanism in a position corresponding to that floor. At this instant of stopping of the advance motor it the elevator car I may be as much as two floors away from the floor at which it is to stop and is moving at full speed. The stoppage of the advance motor it stops the input gear !8 of the differential assembly i; so that the elevator drive motor 6, driving through the second input gear [9, rotates the differential carrier 2?. and with it the rheostat 9 toward the slow or zero speed setting. As the rheostat returns toward its center or zero speed setting the speed of the elevator drive motor 5 is correspondingly reduced. As the car approaches within a few feet of the floor at which it is to stop, leveling switches, mounted on the car and cooperating with inductor plates or cams in the hatchway, signal the exact position of the car and take over the control of the elevator motor 5 so as to bring the car I to a stop level with the floor regardless of any creepage that may have occurred between the support cable 2 and the pulley 3 or any stretch in the cable 2 because mounted in the carrier 53, a first input gear of load in the elevator car I. If it should happen because of creepage or stretch that the rheostat 9 does not return precisely to zero when the car is level at a floor auxiliary control circuits including a rotating contact arm 29 on the rheostat shaft 28 cooperating with fixed contacts 30 or 3! energize a correction motor 32 which through gearing 33 is connected to the input shaft 26 intermediate the clutch 2i and the second input gear is of the difierential. The motor 32, energized through one or the other of the contacts 39 or 35, develops suilicient torque to slip the clutch 2i and to drive the shaft 28 in a direction to return the rheostat assembly 9 to its center position. The required slipping of the clutch 2i corresponds to and corrects for the creepage and stretch of the cable 2 and thus maintains syn chronisrn between the car position and the control mechanism position.

Figure fl schematically illustrates another embodiment of the invention. In this embodiment mechanical means are employed for synchronizing the rheostat. As illustrated in Figure II an elevator car 34 is supported and driven by a cable 35 running over a grooved pulley 3B and connected to a counterweight 3'1. The pulley 35 is mounted on an armature shaft 38 of a slow-speed direct current elevator drive motor 39. A springset, electrically-released. brake mechanism 40 operatively attached to the armature shaft 38 holds the armature shaft against rotation when the drive motor 39 is de-energized. As in the preceding example, an advance motor 4! is connected through gearing 2 and a chain drive ll? to move a floor selector carriage M past a plurality of banks of contacts 45, each of which banks is represented by a single contact, corresponding to the floors served by the elevator car 34.

The speed of the elevator drive motor 39 is controlled by a rheostat assembly 46 including a moving arm that is mounted on and driven by a shaft operatively connected through an electrically actuated clutch 49 and gearing 53 to an output gear iii of a differential gear mechanism 52. The differential gear mechanism 52 comprises a carrier that is directly connected to the output gear i i, a pair of difierential gears 5t and 55 56 operatively connected to the armature shaft 38 of the drive motor, and a second input gear 5'! operatively connected through a shaft 53 to the advance motor 4!.

In Figures I and II the control mechanism is shown schematically and while the differential gear mechanism is shown as connected directly on the shafts of the elevator motors and advance motors it .s to be understood that in actual construction gearing or other mechanical drive means be interposed between the motor and the differential gear mechanism and that other forms of differential gear mechanism may be substituted 'for the bevel gear differential schematically illustrated in the figures.

In this example, as in the first, the advance motor ll is preferably a constant-speed reversible .motor having very rapid acceleration and deceleration characteristics. When it is desired to operate the elevator car 34 from one floor to another the advance motor Al is suitably energized and. it immediately drives the selector carriage 44 at constant speed towards that bank of contacts '45 which represents the selected floor at which the car is to stop. As the advance motor 4! is driving the selector carriage 44 it also, through the differential gear mechanism 52 and the now 6. energized clutch 49, rotates the arm 4'! of the rheostat assembly 46 so as to start and accelerate the elevator drive motor 39. As the elevator motor 39 accelerates it turns the connected differential input gear 56 oppositely to the advance motor driven input gear 5'! to reduce the speed and finally stop the motion of differential carrier 52 and the rheostat arm 4?. The rheostat arm 41 stops at a position such that the elevator motor 39 operates under the then applied load at its normal full speed. Any tendency of the elevator motor to run faster r slower results in movement of the differ ntial carrier 52 and rheostat arm-4'! in a direction to correct the motor speed.

Because or" the differential action and the movement required in th rheostat assembly 46 the elevator car 34 lags behind a position corresponding to the position or" the selector mechanism carriage 13 When the selector mechanism carriage reaches that one of the banks of contacts 45 representing the selected floor the advance motor 4| is immediately stopped thereby stopping the input gear 5i of the differential mechanism 52. The continuing rotation of the elevator drive motor 39 then drives the dirferential gear mechanism 52 and the rheostat arm :3? back to its center position thereby decelerating the elevator motor 39 the rheostat approaches its zero speed position. As in the preceding example leveling switches (not shown) on the car 34 and actuators in the hatchway control the final movement of the elevator drive motor 39 to stop the car 34 level with the selected door. If there is no stretching of the cable or creepage with respect to the pulley the rheostat arm 41 returns to its center position as the car is leveled with a floor.

While the actual position of the differential carrier 52 is immaterial, it is necessary that the rheostat arm ll be accurately returned to its center position each time the car 34 is leveled with a floor. In this embodiment the electrically actuated clutch 4:3 is released whenever the elevat-or car 38 stops and the leveling switches indicate that the car is level with the floor. As soon as the clutch t9 releases, a gravity operated centering mechanism immediatel returns the rheostat arm i! and shaft to their center positions. A simple mechanical return mechanism for this purpose comprises a pair of arms 60 and i i that are loosely journaled on and that extend radially in a downwardly inclined direction from the shaft The arms 653 and GI carry weights 62 and 63 on their lower ends. A driving mem her or collar es fixedly mounted on the shaft 48 has laterally extending lugs 65 and 55 which selectively engage the arms 68 6! depending upon the direction of rotation so as to lift the arm and its weight away from a stop 55?. When the clutch releases, the elevated one of the weighted arms 56 or 5i returns the shaft 48 to its centered position. In this embodiment the release of the electrically actuated clutch 49 and the mechanical centering action of the weighted arms and ii serves the same purpose as does the correction motor 32 and the friction clutch 35 shown in Figure I. In each example a old .h is included in one of the connections to differential gear mechanism. In each em bodimcnt the clutch is slipped each time the elevator car is leveled at a floor in an amount that compensates for the creepage that may have occurred between the elevator drive motor pulley and the car supporting cable.

In order to protect the control mechanism in cluding the rheostat assembly 9 or 46 from damage the clutches 2i or 9 are constructed to have limited torque transmitting capacity so that they may slip before suiiicient torque is transmitted to the rheostat or floor selecting mechanism to cause damage. In the embodiment shown in Figure I the torque transmitting capacity of the clutch 21 must be low enough so that the correction motor 32 can slip the clutch. In the embodiment shown in Figure II, the electrically actuated clutch (shown also in Figure III) comprises a magnet member 68 having a coil 6% arranged to attract an armature disk 16 with only sufficient force to reliably transmit the torque re quired. to lift the engaged one of the weighted arms 58 or Bl and to operate the rhecstat arm 4?. Should the rheostat jam with the elevator motor or the advance motor running the clutch slips before any parts are damaged. This just described slipping, which may occur at any time, is a safety precaution only and has nothing to do with the slip, occurring when the car is stopped at a floor, that corrects for creepage of the cables.

One of the problems involved in any elevator installation is to design the equipment for long life and simple maintenance. Since the rheostat assembly 9 or is as illustrated in Figures I and II is operated from center to nearly its complete range of movement in one direction or the other for every start and stop of the elevator the ordinary sliding contact rheostat such as is ordinarily used in the control of the direct current motors has too short a life to be satisfactory. According to this invention the rheostat assembly is constructed, as illustrated in Figures VI, VII and VIII, by substituting a plurality of cam operated switches for the usual sliding contacts. The cam operated switches short out various sections of a field control resistor employed with a generator driving the elevator motor. The improved rheostat assembly comprises a box-like frame having a continuous bottom plate I! and integrally formed upright end portions 12 and T3. The end portions l2 and it are connected together and braced by two pairs of longitudinally extending threaded rods ill, '55 and l5, II. The threaded rods are located along the sides of the assembly so as to leave a large free central space in the frame. A plurality of shallow U-shaped suoframes E3 are mounted on the threaded rods with the fiat bottom portion of each U-shaped frame extending parallel to and spaced from a plane through the pair of rods supporting that subframe. The flat bottom portion of the U-shape of the subframe it? comprises a small panel '59 of insulating material on which is mounted a plurality of pairs of stationary contact buttons 39. Each pair of contact buttons 86 are bridged by a movable contact bar 81 resiliently mounted on the end of an arm 82 pivotally,

mounted on an axle 33 carried in the subframe 18. A helical compression spring {is compressed between the arm 82 and the insulating panel 79 urges the arm away from the panel in order to separate the contact bar 8! from the contacts 86. Each of the arms 82 has a downwardly extending portion 35 carrying a roller 86 which coopcrates with a cam Bl adjustably mounted on a shaft 88 journaled in the end frame portions l2 and I3. The shaft 88 functionally corresponds to the shafts 28 and d8 of Figures I and II respectively.

Suitable gearing, such as gears 89, 9B and a chain sprocket Ell may be mounted on the end frame 13 and employed to connect the shaft 88 to the difierential mechanism. As indicated in Figure II the electrically actuated clutch 49, if used, is included between the shaft operating the contacts (the shaft 88) and the gearing such as the gears 89 and 80.

For convenience in wiring, the fixed contacts Si? each having a terminal stud 92 extending inwardly into a wiring space between the subframes I8 and above the path of the cams 8? on the shaft 88. A cover 533 fitting over the assembly of subframes l8 and the end frames l2 and I3 is attached to longitudinally extending angle irons bolted to the base 7 i.

In this preferred rheostat assembly the contacts 8t and contact bar 8! are used to short out resistors or sections of a resistor assembly in the motor speed control circuits. Some of the contacts may be used for other control functions in connection with the operation of the elevator drive motor.

The electrical controls for an elevator system, particularly of the automatic type, are quite complicated. Because the invention relates primarily to the mechanism for correcting the creepage the cables and improved means for controlling the elevator motor according to signals derived from the elevator motor, only those portions of the complete circuit which are directly relat d to the motor control are illustrated in the drawings. The circuits having to do with floor selection, registering of calls, operation of the elevator doors, and many other features have been omitted from these drawings.

Referrin now to Figure IX, which illustrates schematically the circuits associated with the mechanism schematically illustrated in Figure I, the elevator driving motor 6, shown near the bottom of the drawing, is connected through leads Hit and ill! to a direct-current generator I92 which is driven at a constant speed by an alternating current motor N33.

The elevator drive motor 5 has its field coil I04 connected directly to direct current supply leads m5 and IE5. While shown as directly connected, it is understood that control devices and safety devices may be included in this circuit to modify the operation of the motor. The generator I02 has a field coil Nil which is also energized from the power leads H15 and 858 according to the direction and speed at which the drive motor 6 is to run. In this arrangement the generator 492 is driven at constant speed by the alternating current motor 583 and the voltage appearing between the leads i053 and Edi, the output voltage of the generator, varies according to the current flow of the field coil l ti. Since the current flow in the field coil ifi of the motor 6 is constant the speed of the motor 5 varies directly as the voltage applied to its armature through the leads H18 and liil.

The direction of rotation of the elevator motor 5 is controlled by circuits represented by a singlepole double-throw switch its which, when it is in the position shown, permits current to flow through a lead 139, an operating coil HE and a lead i i to energize an up-direction control relay H2 and which, when it is thrown to its other position, permits current to flow through a lead H3, an operating coil li t and lead H5 to operate a down-direction control relay H5. The armatures of the relays H2 and H5 are preferably interlocked, as by a crosslinl; I ll cooperating with a fixed abutment 58, so that neither relay will operate unless the other is in its de-energized position.

The generator field coil I61 is energized for upward or downward car travel according to which one of the relays II2 or H6 is operated. Assuming that it is desired to move the car up wardly, the field coil IE1 is energized by current flowing through a circuit which may be traced from the power lead I through a first contact II9 of the up relay I12, through a lead I20, the generator field coil I01, a lead IZI, a second set of contacts I22 of the relay II2, a lead I23 and rheostat resistance I24 to the return power lead I06. If it is desired to operate the car in a down direction the direction control switch I03 is thrown to its other position to de-energize the up relay H2 and energize the down relay H6. The latter relay then closes its contacts I25 and I26 so that current may flow from the power lead I05, through the now closed contact I25, a jumper lead I21 to the lead I2I, the generator field coil I01, the return lead I20 from the field coil I01, the now closed contact I26, the lead I23 and the rheostat resistance I24. This circuit reverses the direction of current flow through the generator field coil I01 so as to reverse the direction of rotation of the elevator motor 6. In an actual control the up or down control relay H2 or II6 is not energized until the car is ready to move.

Because of certain dangers and risks from improper operation elevator control systems are equipped with numerous safety or protective devices all of which must be in operating order before the elevator can be operated in its regular manner. These protective devices have been grouped together and are indicated by the symbol labeled Protective evices shown in the upper portion of Figure IX. When these devices are all in order a circuit may be traced from a first alternating current power lead I28 through the now closed contacts of the protective devices and a lead I29 to an operatingcoil I30 of a safety relay I3I and then through a lead I32 to a second or return power lead I33. When the relay I3I is energized it closes its normally open contacts I34, I35, I36, I31 and I38; and opens its normally closed contacts I39 and I40.

When the elevator car is standing at a fioor, leveling switches and start control devices, represented by the symbol Leveling and Start Control in the upper right hand portion of the drawing, complete a circuit from the power lead I28 through a lead MI and an operating coil I42 of an advance motor stopping relay I43 and leads I44 and I45. As long as this circuit is maintained with the advance motor stopping relay I43 energ-ized contacts Hi6 and I41 are held open. When the car is ready to go a master switch I48 is closed and the start control releases the advance motor stopping relay I43 so that current flows from the power lead I28 through the now closed master switch I48 and contacts I41, a lead I49 and, for upward movement of the car, through a lead I53, contacts I5! of the up relay II2, contacts I36 or" the protective relay HI and an updirection field I52 of the advance motor I6, and a lead I53 to the return lead I33. For downward movement the circuit is through lead I54 connected to the lead I49, contacts I55 of the down relay IIS, contacts I36 and down field winding I58 of the advance motor I6, and then through a lead I51 to the return lead I33.

The advance motor I6 is a two-phase alternating-current motor employing a resistor-condenser circuit I58 connected between its input terminals so that both fields are energized whenever the motor is to run, the condenser furnishing the phase shift required between the current flowing in the two fields. Thus when the current flows through the lead I50 and contacts I5I and I35 the field coil I52 carries line current and the field coil I56 carries quadrature current so that the motor rotates in the up-direction. When the second field coil I56 is directly energized the first field carries quadrature current and the motor rotates in the opposite direction. The rotation of the advance motor I6 through its connection to the input shaft I5 of the diilerential gear carrier 22 rotates the rheostat assembly 9, schematically illustrated as a disk Ids and a series of contacts It, so as to progressively short out portions of the rheostat resistance I24 and thus increase the current flow in the generator field coil H31 and thereby, through the action of the generator I02, increase the speed of the elevator drive motor 6.

As will be recalled from Figure I, the advance motor I5 also drives a fioor selector carriage III which, as shown in Figure IX includes a bridging contactor IGI and a pair of spaced contacts I02 and I53. The bridging contactor I6I cooperates with a series of fixed contact points I54, I35, I66, I61, I68 and I69 representing various fioors that are served by the elevator. The contacts I04 and IE9, representing the terminal floors, are connected directly to the supply lead I23 while the intermediate contacts I to I68 inclusive are connected through car buttons I1 3, I1 I, H2 and I'I'EI to the power lead I23. The car buttons are the type which latch in place and are released either when the car reaches a terminal fioor or when it reverses before reaching a terminal floor.

The fioor selector mechanism also includes another set or" contacts I14 to I'It inclusive that cooperate with both the bridging contactor I6I and the spaced contactors I62 and I03.

When the advance motor It is started by closure of the contacts I41 of the advance motor stopping relay I43 a circuit is also completed from the then energized lead I49 through a branch lead I80, the contacts I45 of the relay I43, operating coil I8I of an advance motor relay I82 and a lead I83, the closed contacts I34 of the protective device relay I3I and a lead I84 connected to the return power lead I33. As long as this circuit is completed the advance motor control relay I82 holds its contacts I35, IEIfi and I81 open.

As the fioor selecting mechanism, driven by the advance motor I6, reaches a fioor contact for which one of the car buttons has been actuated a circuit is completed to stop the advance motor and cause it to center the selector mechanism carriage I0 with respect to the contacts representing that particular floor. The first circuit to be completed may be traced from the power line I28 through the depressed one of the car buttons I10 to I13 or the terminal contacts I34. or Its, the bridging contactor I' 'iI and the leading one or" the spaced contacts I62 and I63. If the car is proceeding upwardly the carriage is also proceeding upwardly so that the spaced contact I63 first meets the cooperating one of the contacts I14 to I19. Current then flows from the contact through a lead I83, now closed contacts I89 of the up relay H2, a lead IQI! and operating coil I9I of a stopping relay I92 and then through a lead I53 and a motor control contact I94 to the return lead $33. The motor control contact I54 is closed during such time as the rheostat assembly 9 calls for operall tion of the elevator motor 5. As soon as the stopping relay I92 is energized it closes its normally open contacts I 95 to complete a circuit from the lead I ill of the advance motor stopping relay Hi3 through a lead I95 to the return lead I 33. The relay i 33 thereupon opens its contacts Hi6 and It? thereby breaking the circuit from the power lead I28 to the advance motor It. When energized the stopping relay I92 also closed its other set of normally open contacts IQ? so that current may flow from the lead I93 energized through the fioor selector, through the now closed contacts E37 and a lead I98 to the lead its feeding the advance motor I6. The advance motor is energized through this circuit until it drives the floor selector mechanism carriage Ill far enough so that the leading contact 253 breaks connection with the corresponding one of the contacts I'M to H9 inclusive.

The opening of the contacts MG of the relay I43 de-energizes the advance motor control relay I82 so that it then closes its contacts I85 to I8? inclusive. The contacts itl connected between lead Its and 2% provide a bypass circuit from the supply lead I28 to the bridging contactor I6I so that the floor selector button may be released without removing power from the bridging contactor I6I.

The contacts I85 and H35 electrically connect the spaced apart contacts I82 and IE3 respectively to the advance motor control fields through lead 2M and 262. This latter circuit directly connecting the spaced apart contacts I62 and I63 to the advance motor It causes the advance motor to turn one way or the other to keep the spaced apart contacts I52 and IE3 accurately one on each side of and each spaced from the fixed contact representing the floor at which the elevator is to stop.

As the elevator approaches the floor and the rheostat 9 returns to its center position, the contact I94 opens and the circuit for the stopping relay I 82 is opened. The direct circuit to the advance motor is still maintained so that the motor controlled by contacts I82 and res actively resists any forces tending to drive the selector carriage away from its proper position.

As the elevator is approaching the selected floor, the leveling switches, through circuits not illustrated, take over the control of the elevator drive motor so as to accurately level the car with the selected floor. The leveling control, as the car approaches, closes a normally open set of contacts 263 to condition a circuit from the supply lead I28 through a lead 204, rheostat operated contacts or 3|, leads 285 or 2%, contacts It? or I38, correction motor control fields 201 or 298, contacts 2% operated by the elevator motor brake, and the now closed leveling control contacts 2&3 connected to the return lead I33. The brake contacts 299 are arranged to be closed as long as the spring-set brake mechanism 3' (Figure I) is de-energized and the brake is applied to the motor shaft 5. Therefore this circuit cannot be completed as long as the elevator motor can move.

In the event that slippage of the cable has occurred so that the rheostat assembly 5 does not return exactly to center position, one or the other of the cam actuated contacts 39 or 3! remains closed and the correction motor 32 is energized so that it drives the diiierential input shaft 29 and slips the clutch 2! until the opening of the closed one of the contacts 3fi or 3| indicates that 12 the rheostat has been returned to its center position.

The correction motor 32 is preferably a two phase motor and includes a condenser-resistor circuit lit to supply the quadrature current to that one of the fields 267 or 238 not directly energized through the cam operated contacts 36 or ill. it will be noted that the correction motor 32 can be operated only at such time as the elevator motor 6 is stopped and the leveling control indicates that the car is level with a floor.

This latter condition is important because the elevator may be stopped between floors in response to an emergency signal and the brake applied so that the contacts 2&9 are closed but with the floor selector mechanism out of register with any floor and the rheostat in position to call for high speed. Such an emergency stop occurs whenever any one of the protective devices is operated so that the protective relay I3I is released. Release of this relay opens the contacts I35 and IE6 of the circuits to the advance motor I5 and the contacts I37 and I38 controlling the correction motor 32 so that neither one of these motors may operate in its normal manner. The release of the protective relay I3I also closes its normaliy closed contacts. I39 and Mil so that current may flow from the power lead I28 through the lead eat, the closed one of the cam actuated contacts as or SI, leads 295 or 2% and the now closed contacts IE5; or Iii to the advance motor I8 which thereupon operates independently of any control of the door selecting mechanism 8 and runs in the direction required to bring the rheostat assembly 9 back to its mid or zero speed position with the contacts 38 and El both open. This action of the advance motor synchronizes the position of the floor selecting mechanism carriage I 0 and the elevator car I and thus elimihates the difference in position which normally occurs because of the lag of the elevator car position behind the corresponding floor selector carriage position. Auxiliary circuits (not shown) are provided so that an attendant may run the elevator .at slow speed with the protective relay l3! de-energized to bring the elevator car to a floor. The circuit including the cam operated contacts 355 or iii is maintained so that the advance motor I 5 responds to any movement of the rheostat assembly 9 and rotates in a direction so as to keep the rheostat at its center position. Such rotation drives the floor selector carriage ID at a speed and in a direction to keep it in step with the car. This type of control following an emergency stop is necessary because the elevator car may, for example, stop between the 4th and 5th fioors while the floor selector mechanism may then be located between the contacts representing the 2nd to 4th or 5th to 7th floors depending upon the direction of travel and the lag required between the car and selector mechanism positions for normal o eration. By causing the advance motor I 5 to return the rheostat assembly to zero following an emergency stop the selector mechanism is automatically properly positioned and is ready for regular operation without any further synchronizing operations. V

In this control system the correction motor 32 is energized only in the event that the elevator car is stopped level with a floor, as indicated by the leveling controls, at the same time that the elevator motor is de-energized and the brake applied. Under these conditions the correction motor circuit is completed and it operates through 13 the difierential to center the rheostat assembly.

Figure X illustrates the electric circuits which may be used in connection with the elevator system shown in Figure II. As shown in Figure X the elevator drive motor 39 has its armature electrically connected through heavy leads 2 and 212 to a generator .armature 213. The generator is driven at constant speed by an alternating current motor 2| 4. A field winding 215 of the elevator motor 33 is continually energized from direct current power leads 2l6 and 2|! by current flowing from the lead 218 through a branch lead 2H3, the field winding 215 and a second lead 219 connected to the power lead return 2H. Protective devices may be included in this circuit to protect the elevator system and its passengers in the event that this field circuit should fail and control of the elevator be lost.

The generator includes a generator field winding 22!] which is supplied with the electric current from the power leads 2 I6 and 2H. The current for the generator field is controlled according to the desired speed of operation of the elevator and is reversed to reverse the direction of operation. The circuit for supplying field current to the generator field 223 may be traced from the power supply lead 216 through a lead 22!, contacts 222 of an up relay 223, and a lead 224 connected to the generator field 220. From the field 22% the current fiows through a lead 225, contacts 226 of the relay 223, a lead 227, and part or all of a resistance 228 of the rheostat assembly 46 connected to the return lead 2". When it is desired to increase the speed of the elevator motor 39 the current flow through the generator field 220 is increased by shorting out successively larger portions of the rheostat resistance 228. The rheostat assembly 4% is shown as comprising a plurality of points or contacts 229 that are connected to the rheostat resistance 228 and which are connected together by a raised portion 230 of a rheostat disk 231 as the disk, which corresponds to the arm 41, rotates.

If it is desired to operate the elevator in a down direction the relay 223 is released and a down relay 232 is energized. When the relay 232 is energized it closes its contacts 233 and 234 so as to connect the generator field lead 224 to the lead 221 connected to the rheostat and to simultaneously connect the other generator field lead 225 to the supply voltage lead 22 I. This circuit connection reverses the flow of current in the generator field winding 22!! so that the motor 39 operates in the reverse direction.

The up and down relays 223 and 232 have operating coils 235 and 236 that are selectively energized through leads 23! and 238 from a single-pole double-throw switch 239 connected to the supply lead Zit. The single-pole doublethrow switch 239 is a simplified representation of conventional up and down control circuits.

The control circuits in this embodiment are substantially the same as those shown in Figure IX. As shown in this figure the protective devices associated with the control circuits for the elevator are grouped together and indicated by the symbol marked Protective Devices. When everything is in order for operation the Protective Devices complete a circuit from a first control power lead 240, through a lead 24!, an operating coil 242 or" a protective relay 243, and through a lead 244 to a return power lead 245.

The floor selecting mechanism, shown in the upper left hand portion of Figure X, includes 14 a bridging contact 246 and a pair of spaced contacts 241 and 248 that are carried on the carriage 44 illustrated schematically in Figure II. A plurality of car buttons 249 are arranged to control circuits from the power lead 240 to a series of contacts 250 to 255 inclusive that cooperate with the bridging contactor 245. There are no car buttons corresponding to the terminal fioor contacts 250 and 255 since the car must stop at these floors regardless if there is a car call for that fioor or not. The car buttons 249 are of the latching type that remain closed until the car reaches a terminal floor or reverses. The bridging contactor 245 serves to connect the contacts '25s to 255 selectively to a second series of contacts 256 to 25! inclusive that cooperate with the spaced contacts 241' and 248. These car buttons, contacts, the circuits therethrough, the bridging contactor 246, and the spaced contacts 241 and 248 of the movable carriage are employed in the stopping circuits for the advance motor 4|.

When everything is ready and the elevator is to move to another fioor a master switch 262 is closed to complete a circuit from the supply lead 249 through normally closed contacts 253 of an advance motor stopping relay 284, a lead 265 to contacts 286 of the down relay 232 and to contacts 2%! of the up relay 223. If it is desired that the car move upwardly the control circuits would have closed the single-pole doublethrow switch 239 to energize the up relay 223 so that the contacts 26'! will be closed. Also, since the protective devices are in order, the protective relay 243 will be energized and its contacts 263 and 259 will be closed while its contacts 210 and 211 are open. Thus, for movement in the up direction, the circuit from the master switch 262 is completed through the contacts 26! of the up relay 223, contacts 268 of the protective devices and a first field winding 269 or" the advance motor 4! the other lead of which is connected to the return lead 245. Quadrature current for a second phase winding 213 of the advance motor 41 is supplied through a condenserresistor circuit 274.

If it is desired to run the elevator in the down direction the circuit closes and the single-pole double-throw switch is thrown to its lower position to energize the down relay 232. This relay when energized closes its contacts 256 so that a circuit is completed from the master switch 262, through the contact 266, the contacts 259 of the protective relay, and the second field winding 273 of the advance motor. When running in the down direction the resistor condenser circuit 214 supplies quadrature current for the first field winding 222 of the advance motor 4|.

The master switch 222 is operated through circuits, not shown, when the leveling and start control is actuated and completes a circuit from the power lead 248, through operating coil 235 of the advanced motor stopping relay 264, and lead 226 to the start control.

This control, through operating rod also opens a set of contacts 258 included in the electrical circuit controlling the electrically actuated clutch 4:9. This circuit may be traced from the power lead 242, through a lead 272, the operation coil 3!; of the clutch 42, a lead 232, and contacts ZBI of the elevator brake to the return lead 245. The contacts 28!, in parallel with the leveling control contacts 275, are closed whenever the elevator motor brake is electrically energized so that the elevator is in condition to run. Thus the clutch coil 69 is energized at all time that the elevator is in condition to run as well as when the brake is set but the car is not level with a floor. The only time that both contacts M8 and EM are simultaneously opened is when the car is leveled with a floor so that the contacts are are open and the brake is set so that the contacts 285 are opened.

When the start control is operated to start the elevator it releases the advance motor stopping relay 264 to close its normally closed contacts 263 and a second set of normally closed contacts 282 so that current may fiow through an operating coil 283 or an advance motor relay through contacts 235 of the protective relay 253, and back to the power lead The relay 286, when energized, opens its contacts 235, 287 and 283.

The sequence of operations as the advance motor drives the selector carriage to the bank of contacts representing a selected floor may be followed and the control for the advance motor may be traced from the floor selecting mechanism through the various circuits and relays to the advance motor i i. Suppose the advance motor to be running to raise the carriage ii of Figure II and that the car button E is cooperating with the contact to be the next stop. As the carriage approaches, the bridging contactor 2:36 interconnects the leads 253 and 25% so that current may flow to the upper spaced contact 2 3?, through a lead 282i, now closed contacts 2% of the up relay 223, lead 294, operating coil 292 of a stopping relay 295i, and a contact 2% forming part of the rheostat assembly and which is closed during such time that the rheostat calls for rotation of the elevator motor. As soon as this circuit is completed the stopping relay closes its contacts 295 to complete a circuit to energize the relay 26! and thus open the contacts 282 and 263. This interrupts the flow of current directly from the power lead 2% to the advance motor ll. The advance motor, however, is still energized through the spaced contact Elli, leads 2853 and 253i, contacts 295 of the relay 283, and a lead :29? connected to the advance motor lead 255,. When the carriage moves far enough so that the contact 259 enters the space between the spaced contacts v2: and 2% the circuit to the advance motor ii and the relay is interrupted so that this relay opens and the advance motor stops. The operation of the stopping relay through circuits not shown, also operated the leveling control to re-energize he operating coil Elli of the relay 264 so that this relay is held energized when the relay 283 is released.

The opening of the contacts 282 of the relay 264 de-energized the relay 2% so that it closes its contact 288 to supply power through leads and 259 to the bridging contactor 2&6 and also to connect the spaced apart contacts "2 and 248 through its contacts 23% and 2t? to leads see and (till leading through the protective relay contacts 238 and 25?; to the advance motor ii. This last circuit energizes the advance motor directly should the carriage of the floor selecting mechanism move suc' that either of the contacts 2%? or 2M3 touch the intermediate fixed contact. Thus the advance motor holds the carriage centered with respect to the floor contacts. If the elevator is moving in the opposite direction contacts SE32 oi the down relay 232 are closed rather than the contacts 29% of the up relay and the lower spaced contact 26?; first meets the fixed contact 259 while the remainder of the circuit operates in the same manner.

If one of the protective devices or the operator should call for an emergency stop the elevator motor generator field circuit, is immediately opened, the protective relay is released, and the brake is set on the elevator motor. At such time the direct circuits to the advance motor 41 are also broken at contacts 258 and 269 while alternate circuits through protective relay contacts Zlil and 2H and one or the other of cam actuated switches 393 and ass is completed. The switches 303 and 3st are actuated by cams on the rheostat shaft is and are arranged so that one or other of the switches is closed as long as the rheostat is not in its neutral position. The advance motor therefore runs in a direction so as to turn the rheostat shaft ii; hack to its neutral position and in so doing drives the carriage (Figure II) including the bridging contactor are and spaced contacts 2 and it? to the position corresponding to the stopped position of the elevator car. Since the leveling devices were not actuated, a car not stopping at a floor, the circuit to the electromagnetic clutch it is not opened.

This circuit and the differential arrangement illustrated in Figure II, in a simple fashion, provides accurate rheossat operation for the speed control of an elevator motor during normal operation in running between and stopping at fioors as well as under abnormal conditions when an emergency stop has been made between iioors.

A slip-ping clutch cooperating with correcting devices may be applied to ot'l or types or elevator controls in addition to the type just described.

As shown in Figure XI, a slippacle friction clutch 355 is interposed between an armature shaft 386 of an elevator drive motor and a shaft Sill! which is connected through gearing 36% to drive a floor finding motor control mechanism 3m. A drive pulley Ell on the elevator motor shaft 3% carries a cable 3 i 2 from which an elevator car 3E3 and a counterweight 3 i4 are suspended, A correction motor Sid is connected through gearing 35% to the shaft extending between the clutch see the fioor finding gearing 399.

In this system the floor finding mechanism am includes a carriage 3!? that cooperates with contacts m to find the floors at which the car is to stop. This floor selecting mechanism is or" a conventional type that is usually driven by a tape or cable attached to the elevator car and not subject to creepage as are the car supporting cables. The floor finding mechanism controls the associated circuits and includes contact arrangements arranged so that the elevator motor is accelerated and decelerated according to a predetermined schedule a the floor finding carriage approaches a position corresponding to the selected floor. When the car is within a few feet of the fioor at which it is to stop, leveling controls including switches and actuators "nounted in the car and in the hatchway take over the final control of the motor to level the car at the selected floor. After the car has stopped at the floor a circuit illustrated in Figure XII is brought into play to energize the correction motor 315 which then drives the shaft and slipsthe clutch 395 until the fioor finding mechanism carriage 3|! is accurately centered on the contacts representing the selected floor. The correction motor, by slipping the clutch 3'85, synchronizes the position of the iioor finding mechanism with that of the elevator car each time the car stops at a floor and thus makes it unnecessary to provide a separate slip-free drive from the elevator car to the floor finding mechanism.

The correction motor is continually mechani- 17 cally connected to the shaft 303 and is driven by that shaft as the elevator is operated. However, the friction drag of the motor 3 I5 is not enough to slip the clutch 305 and interfere with the operation of the mechanism during travel between floors.

Figure XII illustrates those portions of the elevator control circuit which relate to the correction of position or synchronization of the floor finding mechanism with that of the car. In this circuit the elevator motor is shown as being driven by power and signal circuits 3 l S. The elevator car 3|3 includes leveling switches 320, connected through a suspended cable 32! to the control circuits 3l9, cooperating with inductor vanes or with actuators 322 spaced according to floors along the path of the elevator car. The floor selecting mechanism or floor finding mechanism includes along with other selector circuits a series of contacts 323 that are continually energized through a lead 324 and that cooperate with a pair of spaced apart contacts 325 and 326. These spaced apart contacts 325 and 326 are carried on the moving carriage 3|! of the fioor selecting mechanism and cooperate with the series of fixed contacts 323 representing the various floors. As long as the elevator is moving or stopped between floors the control circuit energizes a coil 32'! of a relay 328 by current flowing through leads 329. When the relay is energized it opens its contacts 330 and 33! which are connected between the spaced apart contacts 325 and 326 of the fioor finding mechanism and field coils 332 and 333 of the correction motor 3!5. If the elevator car is moving or stopped between floors, as may happen when an emergency stop is made, the relay is energized and the circuits to the correction motor 3 I5 are open at the contacts 333 and 33!.

When the elevator car is standing at a floor and the leveling control circuits indicate that the car is level with the floor the relay 328 is deenergized its contacts 330 and 33! are closed so that a circuit for the correction motor 3|5 may be completed from a supply lead 334 through the lead 324, through one of the contacts 323 to the spaced apart contact 325 in the event that the fioor selecting mechanism is positioned slightly below its correct position or to the Contact 326 in the event that the floor selecting carriage is too high. Assuming that the carriage i below its correct position current flows from the lead 324 through the contact 325, relay contacts 330, and the first field winding 332 of the correction motor to a return lead 335. Current also flows through a resistor-condenser circuit 335 to the second field coil 333 of the motor 3 I 5.

When the correction motor is energized it drives the shaft 308 and slips the clutch 305 until the floor selecting carriage is driven upwardly and the spaced apart contact 325 leaves the adjacent one of the fixed contacts 323. As soon as the circuit is broken the friction of the clutch 305 and the correction motor 3 I 5 causes the motor to stop quickly. In the event that the carriage is too high current flows from the leads 334 and 324, through the lower one of the spaced apart contacts 323 and through the relay contacts 33! and directly to the field coil 333 of the correction motor. This current flow in combination with quadrature current flowing through the condenser-resistor circuit 335 to the field coil 332 causes the correction motor 315 to drive the carriage downwardly until the spaced apart contacts 325 and 326 are on opposite sides of and out of con- 18 tact with the adjacent one of the fixed contacts 323.

The spaced apart contacts 325 and 326 each extend nearly but less than half of the distance between adjacent ones of the fixed contacts 323 representing the various floors served by the elevator. While the only lack of synchronism that may appear between the position of the elevator car and the position of the floor finder carriage occurs because of creepage or slippage of the elevator cable 3 !2 on the pulley 3| 1 the probable error in carriage position to be corrected by the correction motor 3l5 is a small percentage of the distance between the contacts 323. Therefore, it is improbable that the correction motor would drive the carriage to the wrong one of contacts 323 and thus introduce an error of one or more floors into the door finding equipment. Should such an error occur it may be corrected by run ning the elevator to one or the other of the terminal floors depending upon the direction of the error.

In this arrangement the correction motor 3!5, which may be a slow speed induction motor, in combination with the slippable clutch makes it possibl to eliminate the separate tape or cable drive ordinarily used with full control fioor finding mechanisms.

Various modifications in the control circuits and in the details of the structure of the clutches of the correction device may be made without departing from the scope of the invention.

Having described the invention, I claim:

1. In an elevator control, in combination, an elevator car that serves a plurality of floors, an electric elevator drive motor, a variable voltage generator electrically connected to the motor for driving the motor, said generator having a control field, a rheostat connected to control the flow of current in the control field, a floor selector mechanism, a reversible constant speed motor for driving the floor selector mechanism, differential gear mechanism having three elements which are operatively connected one to the constant speed motor, one to the elevator drive motor and one to the rheostat, a friction clutch interposed in on of the connections to the differential gear mechanism, and means for slipping the clutch to center the rheostat when the car is at rest at a floor.

2. In an elevator control, in combination, an elevator car that serves a plurality of floors, an electric elevator drive motor, a variable voltage generator electrically connected to the motor for driving the motor, said generator having a control field, a rheostat connected to control the current flow in the control field, a floor selector mechanism, a reversible constant speed motor for driving the floor selector mechanism, a difierential gear mechanism having a first element connected to the constant speed motor, a drive connection from a second element of the sliderential gear to the rheostat, a friction clutch connected to the elevator drive motor, a connection from the friction clutch to the third element of the differential, and means including a motor operatively connected to the third element of the differential for slipping the clutch to center the rheostat when the elevator car is at rest at a floor.

3. In an elevator control, in combination, an electric drive motor for hoisting an elevator car, a variable voltage generator electrically connected to the motor for driving the motor, a rheostat connected in series with the generator field for controlling its generated voltage, a floor selector mechanism adjacent the drive motor, a constant speed reversible motor .connected to the floor selector mechanism for driving th selector mechanism, an electrical control system responsive to an operators signals connected to the constant speed motor for driving the motor to position the selector mechanism in response to the signals, a differential gear mechanism having a pair of input connections and an output connection, one of said input connections being connected to the constant speed motor and the other of said inputs being connected to the elevator drive motor, a clutch having one portion connected to the output of the differential and another portion connected to the rheostat, means for releasing said clutch when the motors are at rest with the car at a floor, and means for centering the rheostat when the clutch is released.

4. In an elevator control system, in combination, an electric elevator drive motor, an elevator car, a friction drive between the elevator motor and the car, an elevator control mechanism having a part that moves according to movement of the car, a mechanical drive system from the elevator drive motor to the control mechanism part, a friction clutch included in said mechanical drive system, a second motor operatively connected to said drive system intermediate the clutch and the control mechanism, first signal means for indicating the condition of level of th car with respect to a floor served thereby, second signal means for indicating the position of the movable control mechanism part, and means responsive to said first and second signal means for energizing the second motor while the elevator motor is at rest to drive said control mechanism part to a position corresponding to the position of the car, thereby slipping the friction clutch in an amount to correct for the creepage in the friction drive between th elevator motor and the car.

5. In an elevator control system, in combination, an electric elevator drive motor, an elevator car, a friction driv between the elevator motor and the car, an elevator control mechanism having a part that is to be maintained in a predetermined relation to the position of the car, a mechanical drive system from th elevator drive motor to the control mechanism part, a friction clutch included in said drive system, a low speed synchronous motor geared to the drive system intermediate the friction clutch and the control mechanism part, signal means on the elevator car cooperating with said control mechanism for controlling the drive motor to stop the car level with a floor, said signal means also cooperating with the control mechanism to energize said low speed motor when the car is at rest to slip the clutch and synchronize the control mechanism with the elevator car position.

6. In an elevator control system, in combination, an electric elevator drive motor, an elevator .car, a variable voltage generator for driving the motor, a contactor mechanism for controlling the generator, a friction drive from the drive motor to the car, an elevator control mechanism having a part that moves according to the desired movement of the car, a reversible constant speed motor for moving said control mechanism part, a differential having an input shaft driven by said constant speed motor, a friction clutch elevator car that serves a plurality of floors, an

electric elevator drive motor equipped with a traction drive for driving said car, rotatable control means adapted to select the direction of rotation of said motor and control its speed, a floor selector mechanism comprising a plurality of fixed contacts and a movable carriage cooperating with the contacts, a reversible constant speed motor driving said carriage according to demands for elevator service, a difierential gear having three elements connected respectively to constant speed motor, the elevator drive motor, and the rotatable control means, a clutch in one of said differential gear connections, and means for slipping the clutch when the elevator car is at rest at a fioor to center said control means, whereby the effect or slippage in the traction drive is corrected.

8. In an elevator control, in combination, an elevator car that serves a plurality of floors, an electric elevator motor equipped with a traction drive for driving said car, floor selecting and motor control means, gearing including a clutch operatively connecting the elevator motor to the floor selecting control means, and means operative when the elevator is at rest for slipping the clutch in an amount proportional to the accumulated slippage of the traction drive since the last previous correction.

9. In an elevator control, in combination, an elevator car that serves a plurality of floors, an electric elevator motor equipped with a traction drive for driving the elevator car, floor selecting means having a member that is moved to positions corresponding to the floors to be served as the car is driven to such floors, gearing operatively connecting said elevator motor and the member of said floor selector, a clutch included in said gearing, means for indicating when the car is leveled with a floor, and means responsive to the leveling means and the floor selector means adapted to slip the clutch to correct for slippage of the traction drive.

10. In an elevator control, in combination, an elevator car that serves a plurality of floors, an electric elevator motor equipped with a traction drive for supporting and moving the elevator car, an elevator control system, a mechanical connection from the elevator motor to the control system for continuously indicating the instantaneous position of the elevator car, other means for indicating when a car is leveled at a fioor, a clutch included in said mechanical connection, and means responsive to said level indicating means for slipping said clutch to correct said go sition indication for slippage of the traction rive.

Name Date Santini Mar. 18, 1952 Number

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