US2265022A - Aerial passenger tramway - Google Patents

Description

Dec. 2, 1941. w E Z I AERIAL PASSENGER TRAMWAY Filed Feb. 18, 1939 2 Sheets-Sheet 1 if} 2' INVENTOR Wa/demar 1T fieflaz.

WITNESSES:

ATTORNEY Dec. 2, 1941, w L BENDZ 2,265,022

AERIAL PASSENGER TRAMWAY Filed Feb. 18, 1939 2 Sheeis-Sheet 2 WITNESSES: INVENTOR 7%M Wa Memar Z fieflaz.

ATTORNEY Patented Dec. 2, 1941 AERIAL PAS SEN GER TRAMWAY Waldemar I. Bendz, Arlington, Mass, assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application February 18, 1939, Serial No. 257,171

13 Claims.

This invention relates to tramway control systems, and is particularly directed to a system in which a car is moved through a predetermined path from one terminal position to a second terminal position, by means of a traction cable to which power is imparted through a motor driven sheave.

Because of the nature of the drive involving the transmission of power from the sheave to the traction rope, or cable, solely by the friction between the cable and the sheave, there may be a certain amount of slippage between the sheave and the traction rope. An indicator, that is provided to show the position of the traveling car, is usually also driven from a shaft that is mechanically connected to the sheave. Consequently, when slippage occurs between the sheave and the traction rope, the position of the indicator for the car will not correspond to, or be synchronous with, the position of the car and the indication given by the position indicator will therefore be false.

In the tramway system to which my present invention is applied, the passenger car travels along a supporting cable which is suspended between supports a considerable distance apart. Consequently, the car does not assume a definite position either vertically or horizontally within limits of position which are sufliciently close to permit the operation of a limit switch of the track type or so-called hatchway type. This is due to the fact that the vertical position of the car is variable, depending upon the load of the car and the sag of the cable, which may also be variable depending upon temperature as well as weight of the car and passengers. The horizontal position of the car is also variable due to wind and the unbalanced loading in the cars. Consequently, the usual form of limit switch of either of the types mentioned is not applicable to a drive of this type. While limit switches cannot be properly located to obtain the necessary number of slow-down points prior to a definite stop for the reasons as named above, it happens that the cars are carefully guided during the last few feet of travel so as to properly position the car for unloading of passengers.

In the present system, I employ a limit switch to be controlled by the car to aid in correcting the position of the indicator; and also employ the indicator, if desirable, to provide slow-down control for the main motor.

The primary object of my invention, therefore, is to provide a system that will automatically correct any deviation of the position indicator, when it deviates from a proper position corre sponding to the position of the car, because of slippage between the sheave and the traction rope.

In the accompanying drawings,

Figure 1 is a simple operating and control system arranged to operate in accordance with the principles of my invention;

Fig. 2 is a diagrammatic view showing the general disposition of the tramway system to which my invention has been applied: and

Fig. 3 is a simple operating and control system embodying a modification of my invention.

As shown in the diagram in Fig. 1 a main power motor I for the tramway system is arranged to be energized from a power circuit 2. The motor I drives a sheave 3 through appropriate reduction gearing 4. The sheave 3 is of the usual grooved pulley form and is arranged to drive a traction cable or rope 5 by friction. The traction cable 5, as illustrated in this application, operates substantially as an endless cable, in such manner that one portion 6 of the cable moves a tram car 1 in one direction, while an adjoining portion 8 of the cable will move a second tram car 9 in the opposite direction.

It will be understood, of course, that instead of an endless cable an equivalent system might be employed in which the two ends of the cable would be controlled to impart the proper direction of movement to reel in one end of the cable while paying out the other. Also, instead of an endless cable system on which two passenger cars are fastened, an equivalent system might be employed using only one car which is made to travel back and forth between two terminal po sitions. In either system the passenger car or cars may be replaced by a device or devices for carrying freight or other form of material.

Where two cars or devices are used, the system is a double reversible tramway. Where one car is used, the system is a single reversible tramway.

As shown in the drawings, the two tram cars will be alternately moved from one of their respective terminal positions to the other of their respective terminal positions. In order to provide the reversing movement to the cable, the motor I, which is shown as a shunt-wound direct current motor, is reversely energized by reversely connecting the field Winding II to the main power circuit 2 through either of two switches l2 0r Hi. The switches l2 and I3 are, in turn, selectively controlled by a controller switch [4 that is illustrated for simplicity as a single-pole double-throw switch. The armature circuit is i1- lustrated as passing through contact members on either switch l2 or l3 so the motor circuit will be opened, as both switches l2 and I3 are deenergized, when the master switch I4 is thrown to neutral position.

In order to slow down the main motor I as the tram cars l and 9 approach their respective terminal positions, the motor circuit is appropriately controlled to reduce the motor speed. In

practice, the system actually employed for that cuit when the motor is to be decelerated, and con-.

versely, to be shorted out of the armature circuit when the motor is to be accelerated from rest, in a manner and for a purpose that will be described below.

In order to indicate the respective positions of the tram cars 1 and 9, two position indicators l8 and I9 are provided. The position indicators are disposed upon threaded nuts 2| and 22 respectively mounted upon threaded lead screws 23 and 24, that are respectively driven by gears 25 and 26. a common driving gear 21 that is connected to the driven element 28 of a differential gear mechanism 29. The driving gear 3| of the differential mechanism 29 is connected through a suitable gear reduction 32 to the shaft 33 upon which the driving sheave 3 is connected.

In order to provide automatic or manual adjusting control of the position indicators i8 and I9, the differential mechanism 29 is provided with a driving gear 34 on the housing 35 of the differential mechanism 29. The housing 35 supports the two differential idler gears 35 and 31 that transmit motion from the driving gear 34 to the driven gear 28 of the diiierential mechanism.

In order to rotate the diiferential housing 35' by its gear 34, an auxiliary reversible motor 38 is provided that is disposed to rotate the housing '35 in either direction through a pinion 39, or to hold the housing 35 stationary to permit the differential operation of the differential mechanism.

When no slippage occurs between the driving sheave 3 and the traction rope or cable 5, the movement of the traction rope, and, consequent- 1y, of either tram car, will be attended by a corresponding proportional movement of the position indicators |8 and I9. The indicators will, therefore, occupy their respective terminal positions'when the tram cars are at their respective terminal positions.

Because of the slippage, however, that occurs between the driving sheave 3 and the traction rope 5, due to the tension in the'traction rope, which may be either positive or negative with respect to the torque of the driving sheave, the

position indicators will, more often than not, :not always be in a correct position corresponding to the position of the associated tram cars. In order to correct for such deviation of the position indicators from their proper positions due to cable slippage on the sheave, two limit switches 4| and 42 are provided and disposed adjacent the end or terminal'positions of the path of each of the tram cars 11 and'9, respectively, sothat the switches will be operated when the associated tram car moves to itsultimate posi tion at a selected-terminal. The limit switches 4| and 42, as controlled by their respectivetram cars 1 and 9, are employed to set up and control the circuit of the auxiliary motor 38 for the differential mechanism 29.

In order to complete the control of the auxiliary motor 33, two other auxiliary switches 43 and 44 are provided, and they are disposed at the ultimatepositions at selected terminal positions of the two indicators l8 and i9.

The gears 25 and 25 are driven by Thus, each tram car and its associated position indicator cooperate to control the auxiliary operation.

"Energy for the auxiliary motor 38 is shown as derived from a three-phase supply circuit 45. 'The motor '38 is also provided with a friction solenoid brake 46 of the conventional type, which is released when its operating coils 41 are energized and which is set by springs, for example, when its operating coils 41 are deenergized.

When no electric power is applied to the auxiliary motor 38, the brake 45 is set, and, through the gear connection betweenthe gear pinion 39 and the differential housing 35, locks the housing 35 against motion. While this condition exists, the differential acts as a straight one-to-one gear transmission to transmit rotation from the sheave shaft 33, through thegear reduction 32, to the driving gear 21 for the gears 25 and 26 to the lead screw gears 23 and '24.

When operation of the 'Jtransmisison is attended by no slippage between the sheave and the traction rope, each tram car will reach its terminal position at the same time as the corresponding position indicator reaches its terminal position. Under such condition no correction of the position indicators is required.

When conditions are such, however, that slippage does occur between the sheave and the traction rope, movement of the position indicatorswill not be proportional to and synchronous with the cable, and each position indicator will therefore not reach and occupy its correct relative position when its associated car reaches the terminal position. In order to correct for such deviation, the limit switch controlled by each car and the limit switch controlled by the associated position indicator are cooperatively connected, in series, to supply energy from the supply circuit 45 to the auxiliary motor 38, in the proper direction to rotate the housing of the differential mechanism, to operate the lead screws 23 and 24 ated car 1 when the car is in its terminal position.

The limit switch 42 for the car 9 is similar to limit switch 4|, and is provided with similar contact members 58 and 59 and a biasing spring 69 together with a control pivoted lever 6|, corresponding to the same elements on limit switch 4|.

A cooperating limit switch 43, that is controlled by the-position indicator l8 at one terminal position, is also a double contact switch provided with two contact switches 53 and 54 that are normally biased to closed position by a spring 55. An operating button 56 is provided to be engaged and depressed by a roller 51 on the position indicator l8 to open the circuits between the two contact switches 53 and 54.

A limit switch 44, controlled by the position indicator H3 at its other terminal position, is provided with contacts 63 and 64, a biasing spring 65 and an operating push button 66 similar to those provided for the limit switch 43.

The limit switch 43 is disposed to be operated by the position indicator |8 at the left-hand limit of its travel, and the limit switch 44 is located to be operated by the roller of the position indicator It! at the right-hand limit of its travel, at a position corresponding to the relative terminal or limit position of the position indicator l9. The operation of the two limit switches 43 and 44 by the position indicator |8 permits the position indicator l9 to be utilized for other control functions.

If no slippage has occurred between the sheave and the traction rope 5, while the car I has been raised from its lower terminal position to its upper terminal position, the position indicator l8 will move to, and be in, its proper relative terminal position to open limit switch 43 when car 1 reaches its upper terminal position to close the limit switch 4|. Thus, although the circuit for motor 38 will be set up at the limit switch 4|, it will be open at the limit switch 43 to keep the circuit open between the auxiliary motor 38 and its source of supply 45.

If, however, slippage has occurred between the sheave and the cable, due to an excessive loading of car 9, for example, so that the car 1 will reach its terminal position and close its limit switch 4| before position indicator |8 has been moved to its proper relative terminal position to open limit switch 43, limit switch 43 will still be closed when limit switch 4| is closed by movement of the car 1 to its upper terminal position. Indicator l8 will at that time occupy the dotted position A adjacent its proper relative terminal position above limit switch 43.

The energizing circuit is then closed from the supply source 45 through limit switch 43 of the position indicator 8, thence through limit switch 4| at car I, to the brake coils 41 and to the auxiliary motor 38. As shown, the third conductor of the supply circuit 45 is connected directly to the motor. Consequently, the brake coils are energized to release the brake and the auxiliary motor is energized to rotate the case or housing of the differential mechanism. Since the main motor is now stationary, the sheave shaft 33 and the transmission unit 32 will be held stationary, and the rotation of the differential mechanism case will rotate the lead screws 23 and 24 until the position indicator I8 is moved to its proper relative terminal position where it will engage and open the limit switch 43. The circuit to the auxiliary motor will thereupon be opened and. the brake restored to hold the auxiliary motor against further rotation.

When the main motor operation is reversed to lower the car "I, and to raise the car 9, the limit switch of car I will be opened, and, when car 9 reaches its upper terminal position, limit switch 42 will be closed. Limit switch 42 will cooperate with the position indicator switch 44 according to the position of the position indicator when the car 9 reaches its upper terminal position.

When the car 9 is in the proper terminal posi tion, the position indicator will open its limit switch 44, if no slippage has occurred. If slippage has occurred, the position indicator will move to position B when car 9 reaches top terminal position. Limit switch 44 will be closed and will cooperate with car limit switch 42 to complete the circuit from the auxiliary supply source 45 to the auxiliary motor 38 to energize 7 and release the brake 46, and to operate the case or housing 35 of the differential mechanism 29. The connections to the auxiliary motor are now reversed, however, with respect to the connections made through the other set of limit switches, and the direction of operation of the auxiliary motor 38 is now reversed. The lead screws are now operated to move the indicator I8 from position B to its proper limit position to open limit switch 44.

Assume, instead, that car 9 is excessively loaded as compared to car 1, thus causing slipping and that car 9 is raised from the full line position to the dotted line position, at the latter position closing limit switch 42. The indicator 8 will have overtravelled to the right of limit switch 44 to a position C (indicated in dotted lines). Therefore, since both limit switches 42 and 44 are closed, a circuit will be completed through motor 38 which will efiect a movement of the position indicator |8 to the right but which movement will be arrested by virtue of the fact that the threads of the lead screws 23 and 24 terminate just beyond the limit switches 43, 44 and just beyond switches and 86 at which positions are located biasing springs 9|, 92, 93 and 94 which urge the position indicator members in a direction toward the center of the lead screws. Therefore, as soon as the cars are moved in an opposite direction, that is, as soon as 'car 9 is moved from the dotted line position to the full line position, the position indicator 8 will be propelled to the left to approximately position. A at which time limit switch 4| will close and owing to the fact that limit switch 43 is also closed, a circuit to motor 38 will be completed thereby efiecting a correction of the position of indicator l8 (1. e., movement of indicator l8 to the left until it opens limit switch 43). In the event that instead of moving to a position A, the indicator again overtravels beyond the limit switch (this time, to the left of limit switch 43) no immediate correction will be aiforded and none will be had until the position indicator is stopped somewhere between limit switches A and 13. While this situation does permit inaccuracy of the position indicator, such inaccuracy is very small for one or a few round trips. The em.- bodiment illustrated in Fig. 3, which will be described hereinafter, completely eliminates the above-described errors.

In order to decelerate the motor to permit slow landing of the cars at the upper terminals, the armature circuit of the main motor is provided with the three resistors l5, l6 and I! previously referred to. These resistors are progressively short-circuited as the cars move away from terminal position and are progressively inserted into the armature circuit as the car approaches and gradually moves into its final terminal position at the loading terminal.

I show these resistors |5, I6 and H merely to illustrate a simple system for establishing a gradual deceleration of the motor. In actual practice a variable voltage direct current system is employed to control the motor speed, but its description would unnecessarily enlarge this description of the operation of that part of the system.

In order to control the insertion and removal of these resistors |5, H5 and H into and out of the motor circuit, three short-circuiting contactors H, 72 and 13 are employed for the respective resistors. The operating coils of the contactors ll, '12 and 13 are controlled by suitable interlocking switches, of which switches I4, I5

gressively open switches I3, I2 and II to deenergize the short-circuiting contactors and progressively and cumulatively insert the resistors II, I6 and I5 in the armature circuit of the motor.

Conversely, as the carsrnove away from the upper terminal position, the position indicator I9 will progressively reset the interlock switches to reenergize'the contactors 'I I, I2 and I3 to progressively short-circuit resistors I5, I6 and II,

.in sequence, to permit the motor speed to gradually increase.

As schematically illustrated, each of the interlock switches I4 to I9, inclusive, is provided with a suitable actuator 80, and a toggle, or overcenter, spring to hold the switch in the position to which it was last operated.

Each actuator 80, for the interlock switches I to I9 consists of an element provided with two arms 8| and 82 to be engaged by the roller 83 of the position indicator I9. When the roller engages the top arm BI, the switch is forced upwardly; when the roller engages the lower arm 82, the switch is forced downwardly. An overcenter toggle spring 85 is operated by the actuator 80 and serves to move the actuator and the switch to the extreme terminal positions of their path of movement, and to hold the switch in open or in closed position to which it has been moved.

When the toggle spring is moved by one arm of the actuator to move the actuator to its ex- H treme position in one direction, the other arm for controlling movement of the switch to the other direction, is moved into the path of the roller, to be engaged by the roller when the indicator reverses and moves back in the opposite direction. The roller 80 engages either arm of the actuator and moves the switch against the associated spring, to open or to close the circuits at the contacts of the switch.

When indicator I9 moves from its extreme left v position towards the right, switch I4 is operated to closed position, by the position indicator I9, to set up the circuits of all three operating coils of the contactors II, I2 and I3. The circuit for contactor II is completed .and contactor II operates to shunt resistor I5. As the position indicator I9 continues to move, however, it engages the lower arm of the actuator for switch I5, and moves switch I5 to closed position to close the circuit of th coil of contactor I2 and to set up the circuit for contactor I3. Contactors II and I2 will be held closed to short-circuit resistors I5 and I6.

As I the position indicator I9 progressively moves to the right, its roller will engage the lower arm of the actuator of switch I6 and will operate switch I6 to closed position to close the circuit of the coil of contactor I3. When switch I3 closes, it short circuits resistor II. The motor will then be energized with full voltage and accelerated to operating speed. The position indicator I9 ,will continue to move in accordance with the movement of the tram system.

As the position indicator, I9 approaches th other end of its path of travel, the switches 'II, I8 and I9 will be similarly operated in sequence, and their associated contacts will be opened to deenergize contactors I3, I2 and I I, sequentially, to progressively insert the resistors II, I6 and I5 .into the circuit of the motor armature.

As shown in Fig. 1, for the purpose of illustration, switch I9 is in closed position. That is the position switch I9 would occupy just before the roller of indicator I9 would engage the'upper arm of the actuator to move switch I9 to open position. It is also the position that switch I9 would occupy immediately upon reclosure, where the indicator I9 was started in operation from its extreme position, at the right, towards its terminal position at the left.

It will be observed that the actuatorsfor the switches are reversely arranged in the two terminal groups, so that motion of the indicator toward either terminal position will open the switches, and motion of the indicator from either terminal position will reclose the switches.

By means of such an arrangement, or its equivalent, the speed of the main drivinghmotor may be controlled according to the position of the car or carsof the system. i V

In addition, the proper relation between the cars or cars of the system and the position indicators is automatically established and maintained by the auxiliary motor, which corrects for any deviation during each cycle of operation.

Fig. 3 illustrates a modification of my invention in which there are two cars, IOI and I02, attached to an endless cable I93. The cable makes one or more turns around adriving sheave I64 and one of the cars is travelling up hill while the other car is travelling down. 'A driving motor I96 drives the sheave IG I through a suitable gear reduction I05.

The passenger cars travelup and down and are brought to a stop at passenger loading platforms at either end of the trip. An operator controls the movement of the cars and brings them to a proper stop at the loading platforms. This control of the car movement is manual under normal circumstances. However, in order to in corporate necessary safety features itis required that the passenger cars be brought to a normal stop at the proper position at each of the loading platforms regardless of the efficiency or physical alertness of the operator. In other words, if the operator becomes physically disabled or otherwise inattentive it is necessary to have the cars automatically stopped by the control in order to prevent an accident.

While there are several safety features incorporated in the control to bring the cars to a safe stop in case the operator fails to properly manipulate the control it is necessary to make this function automatic with respect tothe position of the cars. Because of the high speed of the cars it is highly desirableto have two or more points of automatic slow-down prior to reaching the final limit position of the cars.

A suitable gearing IE1 is interposed between the shaft of the drivingsheave and one member of a differential gear I08, another'member of the differential gear coupled to a screw I99 of the travelling nut limit-switch. The third member of the differentialgear I08 is directly coupled to 'a small reversing driving motor III equipped with a spring-setmagnetic-release friction brake I I2. Consequently, if the motor III remains stationary the differential gear will drive directly through between the gear reduction I01 and the screw of the travelling nut switch I09. A dog IIO can travel along the screw I09 and operate any of the various toggle type switch units such as II3-II4 or I23-I28. When the screw of the limit switch is properly aligned with respect to the position of the passenger cars the dog II travelling on the screw I09 should be at position A when the passenger cars are brought to a stop at the proper place at the loading platforms. At this position of the switch the dog should engage the switch II 4 so that the poles of the switches H8 are moved to their open position thereby disconnecting the motor III from the source of power I32-I33I34.

Two track type limit switches H9 and I20 are located so that the passenger car will close the contact members I2I of switch II9 when the car I02 is brought to its proper position at the loading platforms illustrated by the dotted lines. Likewise switch I20 closes contact members I22 when car IOI reaches the position illustrated by the solid lines.

Assume that car IOI is brought to a proper stop at the upper loading platform (illustrated by the full lines) and assume that dog H0 is in an incorrect position as shown due to slippage between the cables and sheaves. Switch I20 thereby closes contact members I22 and a circuit is then completed from the supply line I3I to lower contact members I 22, conductor I34, upper contact members II8, conductors I35, I36, thence to one terminal of motor III. Another circuit is also completed from supply line I33 to upper contact members I22, conductor I31, lower contact members IIB, conductors I38 and I44 to a second terminal of motor III. The third terminal is directly fed by conductor I32. Assume that due to slipping of the cable on the driving sheave the dog II 0 on the screw I09 stops at position C and, therefore, contact members II 8 are closed. The circuit is then established to energize the motor II I driving the control member of the differential gear I08. Since the sheave I04 is at standstill and the shaft driven by gearing I01 of the differential gear locks, rotation of the driving motor III will cause rotation of the screw I09. In this manner the screw will propel the dog IIO upwardly until switch I I4 opens contact members H8 in order to stop the driving motor. The screw has then been corrected to the proper position and has compensated for slip of the cable I03 with respect to the driving sheave I04.

Had the error been in the opposite direction the dog may have been moved too far by the screw and have assumed such position as illustrated by B. In this case the switch I I4 would close contact members II 1 and open contact members II8 thereby effecting a reversal of one of the incoming phase lines (I36-I34) and establishing a circuit to the driving motor I II in the reverse direction and the screw I09 would be driven in a direction as to propel the dog IIO downwardly. In other words, the final position of the dog IIO will be midway between the position AB as shown.

Correction at the opposite limit of travel is made in exactly the same way by operation of the switch II9 closing the contact members I2I when car I02 reaches the position illustrated by the dotted lines, completing the power circuit to switches H and H6. The procedure is exactly analogous to that outlined previously.

Switches I23 and I24 are incorporated as a part of the control equipment for driving the motor I06 and are the switches which control the final position limit and will cause the motor I06 to stop if the dog IIO engages either of.

switches I23 or I24. It is important to note that these latter switches must be operated by travel of the dog IIO beyond the position which operates the switches II3 and H4, previously discussed. Therefore, when the cars are stopped in their proper position by the operator manually operating the control, neither of the switches I 23 and I24 is engaged by the dog IIO. However, if the operator fails to shut ofi the power driving motor I06 the dog IIO will operate either switch I23 or I 24 which because of their series relationship with relay I43 will effect deenergization thereof and eifect stopping of the motor I06 and the cars will come to rest slightly beyond the travel which they normally assume. However, this diiferential in travel need only be a few feet and there would be no danger in such operation.

Switches I25, I26 and I21, I28 are used to slow down the operating speed of driving motor I06 prior to reaching the final limit position. There are only two such switches shown, but in actual practice this number may be four or more. The function of the control would be in case the operator failed to slow down the motor I06 by operation of the manual control master switch engagement of dog I I0 with switches I26, and I25 would deenergize relays MI and I42, successively, thus inserting resistances I39 and I40, successively in the main motor circuit thus slowing down the speed of motor I96 and finally stopping the motor when the dog I I0 reached the position B shown on the drawings that is after switch I 23 has been actuated. The operation would be similar if the limit of travel were in the opposite direction in which event switches I21 and I28 effect operation of relays MI and I42 respectively.

As shown in the drawings, the two tram cars will be alternately moved from one of their respective terminal positions to the other of their respective terminal positions. In order to provide the reversing movement to the cable the motor I06 which is shown as a shunt wound, direct current motor, is reversely energized by reversely connecting the field Winding I50 to the main power circuit through either of the two switches I5I or I52. The switches I5I and I52 are, in turn, selectively controlled by a controller switch I55 which is illustrated, for simplicity, as a single pole double throw switch. The armature circuit is illustrated as passing through contact members on either switch I5I or I52 so the motor circuit will be opened as both switches I SI and I52 are deenergized, when the master switch I55 is thrown to the neutral position.

In order to decelerate the main motor I06 as the tram cars IOI and I02 approach their respective terminal positions the motor circuit is appropriately controlled to reduce the motor speed. In practice, the system actually employed for that purpose is a variable voltage direct current system, but, for the sake of simplicity, I have illustrated a simple system in which the armature circuit is provided with two resistors I39 and I40 connected in series relationship and which are arranged to be progressively inserted into the armature circuit by deenergization of relays MI and I42, respectively.

Since it is necessary in most cases to provide a position indicator for indicating the position of the cars being operated, the equipment used' to: correct the screw of the travelling nut limit switch described above may also be used to correct the position of the indicator.

Referring to Figure 3, one method of accomplishing this would be to couple a gear reducer I29 of the proper ratio to the screw I09 of the travelling nut switch so as to operate a position indicator 130. The ratio of this gearing would be such that the full scale movement of the indicator would correspond to the movement of the cars for one trip. The position indicator may be directly coupled by some means of gearing illustrated or else it may be remotely operated by the conventional'type of synchcro-tie drive.

My invention is not limited to the details of the'system illustrated, since they may be modiiied to achieve the same result without departing from the invention asset forth in the appended claims.

V I claim as my invention:

1. In a tramway system, the combination with a driving motor, a sheave driven thereby, a traction rope drivenby the sheave to operate a car, and a position indicator also driven by the motor to indicate theposition of the car, of a differential mechanical connection between the motor and the position indicator to permit operation of the position indicator independently of the driving sheave to permit readjustment of the indicator relative to the sheave to compensate for slipping between the sheave and the traction rope and actuating means including the car itself for initiating said readjustment at terminal positions of said car.

2. A system as in claim 1, including an auxiliary motor that is provided to drive or to brake one element of the differential mechanical connection, and'switching means directly controlled by the car at a terminal position of its path of travel for controlling the operation and direction of rotation of the auxiliary motor.

3. In a tramway system, in which a motor-operated sheave drives a traction rope to move a car back and forth along a predetermined path, and also drives a travelling nut position indicator, means for automatically correcting the position of the indicatorfor slip between the traction rope and the sheave, said means comprising athreaded actuator for the travelling nut indi-i cator, a differential mechanical driving connection between the sheave and the threaded actuator for the indicator a motor for driving or for holding stationary one element of the differentialdriving connection, and a pair of limit switches, one located at each end of thepathof travel of the-car and in a position to be directly operated by the car at each end of its travel, for controlling a circuit to the motor for the differential to cause the motor to operate the actuator to shift the indicator, if necessary, to correct for slippage between the sheave and the traction rope.

4. In a tramway system, in which a motoroperated sheave drives a traction rope to move a car back and forth along a predetermined path-,andalso drives a travelling nut position indicator, means for automatically. correcting the position of the indicator for slip between the traction rope and the sheave, said means comprising; a threaded actuator for the travelling nut indicator, a 'differential'mechanical driving connection betweenthesheave and the threaded actuator for the'i'ndicatorjamotor-iordrivingpr ing said source through said limit switches in for holding stationary one'element: of: the differential driving; connection, and a; limit switch located at the endof the-path: of traveler. the:

car and in a position'to'be directly operated by the carat theend of; its travel, for: controlling: a circuit to the motor for the differential to: cause the motor to operate the actuatorr'to shiitf the indicator; if necessarmto' correct for: slippagebetweenthe sheave. and the traction rope,

and a limit switch operable-bythe position'imdicator for'opening' the circuit between the carresponding to car terminal position.

5. In a tramway system, in which a motoroperated sheave drives a. traction rope to move a car back and for-thalong: a" predetermined'i path; and also drives a travelling nut position indicator, means for automatically correcting the position of the indicator for slip between the traction rope-and the sheave; said: means 'com' prising a threaded actuator 'forthe travelling:

nut indicator, a differential mechanical driving ;connection between the'sheave and the threaded actuator'for the indicator, amotor for driving or for holding stationary one element of the dif ferential driving connection, a normally open limit switch'closable by the car atxterm'inalposi:

tion, a normally closed limit 1 switch operable by the position indicator atterrninal positionsfand" means connectingthe limit switches in series be tween a source of energy and the motor. for the;

differential;

6. In a tramway system, in which amotora operated sheave drives; a traction rope tofimove a 'car back and forth along ai'predetermined path, and also drives a travellingnut position indicator, means for automatically correcting A the position of'the indicator for slip between the 1 traction rope and the sheaveQsaid means comprising athreaded actuator for the vtravelling nut indicator, a differentia'l'mechanical driving conmotion between the sheave and the threaded j; actuator for the indicator, a motor for driving or for holding stationary one element of the:

differential driving connection, two normally open limit switches, each operable by car-associated means when the car is at corresponding" limit position'of its path of travel, two normally closed limit switches, each operable-by position-lindicator-associated means when theindicator" is at the corresponding limit positionof its path of travel, a source of energy, 'an'd means connectseries, respectively, to the motor'for the differthe sheave and the traction rope.

7. In atramway system, the combination with a driving motor, a sheavedriventhereby, a traction rope driven by the sheave to operate a car,

and a position 'indicator'als'o driven-by themotor' to indicate the position of the car, of a differential mechanical connection between 'themotor and the position indicator to permit'operationiot the position indicator independently of the driv..

irig sheave to permit readjustment of theindicator relative to the' sheave to compensate for slipping between the sheave and the traction rope,'and means theoperation of which is initiated by-the car, itself, when at its terminal 5 position for operating the differential connection "to readjust the indicator'relative to the' sheave to compensate for slippage between the rope and the sheave.

In a tramway system, the combination with a driving motor, a sheave driven thereby, a traction rope driven by the sheave to operate a car, and a position indicator also driven by the motor to indicate the position of the car, of a differential mechanical connection between the motor and the position indicator to permit operation of the position indicator independently of the driving sheave to permit readjustment of the indicator relative to the sheave to compensate for slipping between the sheave and the traction rope, and means the operation of which is initiated by the car itself when at its terminal position for operating the differential connection to readjust the indicator relative to the sheave to compensate for slippage between the rope and the sheave, a reversible means for operating the differential connection to readjust the indicator relative to the sheave to compensate for slippage between the rope and the sheave and switch means controlled by the position indicator and by the car to selectively energize the reversible means.

9. In a tramway system, the combination with a driving motor, a sheave driven thereby, a traction rope driven by the sheave to operate a car, and a position indicator also driven by the motor to indicate the position of the car, of a differential mechanical connection between the motor and the position indicator to permit opertion of the position indicator independently of the driving sheave to permit readjustment of the indicator relative to the sheave to compensate for slipping between the sheave and the traction rope, an auxiliary reversible motor operatively connected to drive one element of the differential mechanism other than that connected to the driving motor to operate the mechanism when the driving motor is stationary, and means including the car itself for energizing the auxiliary motor after the driving motor has moved the car to terminal position, and the driving motor is stationary.

10. In a tramway system, in combination, a car, a traction cable which has a portion thereof fastened to said car, a reversible driving motor, a sheave which is driven by said motor in one direction or another, depending upon the direction of rotation of said motor, to effect movement of said car in one direction or in an opposite direction; a mechanical differential gear system which is driven by said motor, a carpositicn indicator which is driven by said motor through said differential gear system, a second motor which also drives through said differential gear system for effecting adjustment of said indicator independently of said first-named driving motor, limit switch means which is adapted to be directly actuated by said car at the end of its travel for controlling said second motor and the position of said indicator to adjust for errors due to slippage between said sheave and said first driving motor.

11. In a tramway system, in combination, a car, a traction cable which has a portion thereof fastened to said car, a reversible driving motor, a sheave which is driven by said motor in one direction or another, depending upon the direction of rotation of said motor, to effect movement of said car in one direction or in an opposite direction; a mechanical differential gear system which is driven by said motor, a car-position indicator which is driven by said motor through said differential gear system, a second motor which also drives through said differential gear system for eifecting adjustment of said indicator independently of said firstnamed driving motor, a limit switch at the end of the path of travel of said car and which is adapted to be operated directly by said car to effect completion of a circuit through said second motor to effect movement of said indicator so to compensate for errors due to slippage between said sheave and said first driving motor, a longitudinally reciprocable switch actuating dog which is also driven through said mechanical differential gear system, switch means at the end of the nor ial travel of said dog which is actuated thereby for interrupting the circuit through said second motor to interrupt the corrective movement of said indicator.

12. In a tramway system, in combination, a car, a traction cable which has a portion thereof fastened to said car, a reversible driving motor, a sheave which is driven by said motor to effect movement of said car in one direction or an opposite direction; a mechanical differential gear system which is driven by said motor, a car-pcsition indicator which is driven by said .iotor through said differential gear system, a second motor which also drives through said differential gear system for effecting adjustment of said indicator independently of said first-named driving motor, a longitudinally reciprocable switch actuating dog which is also driven through said mechanical differential gear system, switch means beyond the end of the normal travel of said dog which is actuated thereby for effecting a slowing down, and upon further movement, a stopping of said first motor.

13. In a tramway system, in combination, a car, a traction cable which has a portion thereof fastened to said car, a reversible driving motor, a sheave which is driven by said motor to effect movement of said car in one direction or in an opposite direction; a mechanical differential gear system which is driven by said motor, a car-position indicator which is driven by said motor through said differential gear system, a second motor which also drives through said differential gear system for effecting adjustment of said indicator independently of said first-named drivin motor, a limit switch at the end of the path of travel of said car and which is adapted to be directly operated by said car to effect completion of a circuit through said second motor to effect movement of said indicator so as to compensate for errors due to slippage between said sheave and said first driving motor, a longitudinally reciprocable switch actuating dog which is also driven through said mechanical differential gear system, switch means at the end of the normal travel of said dog which is actuated thereby for interrupting the circuit through said second motor to interrupt the corrective movement of said indicator and a second switch means at the end of the normal travel of said dog, also actuated by said dog for slowing down the speed of said first motor and upon further travel of said dog, effecting stopping of said first motor.

WALDEMAR I. BENDZ.

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