US2643741A - Elevator system having speed regulation and position control - Google Patents

Description

ESSELMAN ELEVATOR SYSTEM HAVING SPEED REGULATION 'ANDPOSI'IION CONTROL 7 Filed March 26, 1951 June 30, 1953 3 Sheets-Sheet 1 I mvzmbn Walter H.Esselmun.

WITNESSES: y 72 '5 ATTORNEY June 30, 1953 Filed March 26, 1951 Fig.2.

w. H. ESSELMAN ELEVATOR SYSTEM HAVING SPEED REGULATION AND posrrxou CONTROL 5 'sheets-Shet Fig.3.

. 5 2 498 5|B 49A I. SIB

Fig.4. E E U O 2 Field excitation 0 NA 75A :93A 7 WITNESSES: v INVENTOR Walter H.Esse|mo n. tfMma ATTO'RN EY Patented June 30,1953

ELEVATOR SYSTEM HAVING SPEED REGU- LATION AND POSITION CONTROL Walter I-l. Esselman, Pittsburgh, Pa., assignor t0 Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 26, 1951, Serial No. 217,635

This invention relates to systems for controlling the speed and position of moving bodies, and it has particular relation to elevator systems wherein the speed of an elevator car is regulated and the position of the elevator car is controlled.

Although the invention may be employed for the regulation of the speed and for the control of the position of various moving bodies, it is par- 'cularly desirable for the regulation of the speed and the control of the position of elevator cars. For this reason, the invention will be discussed particularly with reference to an elevator system.

In an elevator system an elevator car s mounted for movement with respect to a structure having a number of floors. When the elevator car is conditioned for a floor to floor run, it is'desirable that the elevator car operate at a regulated speed. Furthermore, the elevator car should land accurately at any floor at which a stop is to be made. In some cases, the elevator car is levelled in order to correct any failure of the elevator car platform to land or remain accurately at a desired floor.

In accordance with the invention, an elevator system is provided with a speed regulator coordi nated with a position control. If desired, the speed regulator or the position control may be employed independently of each other.

Speed regulation for an elevator car conveniently may be provided by comparing a voltage proportional to the speed of the elevator car'with a pattern or reference voltage. The difference between the two voltagesrepresents an error voltage which may be employed for controlling the energization of an elevator driving motor.

Theposition of the elevator car may be controlled by means of a pickup unit in the form of an impedance unit which cooperates with impedance control devices. One impedance control device is provided for each of the floors served by.

the elevator car and the impedance unit is mounted for movementwith respect to the impedance control devices in accordance with the movement of the elevator car relative to the associated floors. In a preferred embodiment of the invention, the pickup unit or impedance unit is mounted on the elevator car, whereas one of the impedance control devices is positioned adjacent each of the floors. served by the elevator car. 7

25 Claims. (Cl. 187 -29) magnitude of the displacement of the elevator car from a predetermined position relative to the floor is provided.

In a preferred embodiment of the invention, the impedance unit includes a pair of impedance elements having impedances dependent on the condition of fields associated with the impedance elements. Although the impedance elements may be selected from various types, such as capacitive reactances, they may be constructed conveniently as inductive reactances having magnetic fields which determine in part the impedance values of the elements. These impedance elements cooperate with the impedance control devices to provide impedance values Which vary oppositely in magnitude, respectively, as the elevator car moves away from a predetermined position. i

The invention contemplates the location of the impedance elements in two arms of a bridge circuit. The output of the bridge circuit is employed for controlling the energization of an electric motor employed for moving the elevator car. The output of the bridge circuit controls not only the direction of motion of the elevator car for levelling purposes, but it also controls the magnitude of the energization of the elevator car as a function of the displacement of the elevator car from a desired position.

It is, therefore, an object of the invention to provide an improved elevator system having coordinated speed regulation and position control of an elevator car.

It is a further object of the invention to provide an elevator system wherein a pickup unit is provided having an output which controls the'direction of movement of an elevator car and which controls the magnitude of the force available for moving the elevator car.

It is another object of the invention to provide a pair of impedance elements for controlling the position of a moving body wherein the impedance units are controlled through their fields for the purpose of providing outputs which vary oppositely in magnitude as the car moves away from. a predetermined position.

It is also an object of the invention to provide a bridge circuit wherein the impedance elements of the preceding paragraph are located in two arms of the bridge circuit.

Other objects of the invention will be apparent from the following description taken in conjunction with the accompanying drawings,

.. in which:

Figure 1 is a schematic view with parts broken 3 awa of an elevator system embodying the invention.

Fig. 1A is a schematic view of electromagnetic relays and switches employed in the system of Fig. 1. The contacts and coils of Figs. 1 and 1A are substantially in horizontal alignment,

Fig. 2 is a view in side elevation of animpedance unit and a control device suitable for the system of Fig. 1,

Fig. 3 is a view in front elevation with parts broken away of the apparatus shown in Fig. 2,

Fig. 4 is a graphical representation of electrical quantities and is employed in explaining the operation of the system illustrated in Fig. 1, and

Fig. 5 is a schematic view with parts broken away of an elevator system showing a modified form of invention, and

Fig. 5A is a schematic view of electromagnetic switches and relays in the system in Fig. 5. The various contacts and coils of Figs. 5 and 5A are substantially in horizontal alignment.

The following relays and switches are illustrated in Fig. 1:

D-Down switch UUp switch T--Transfer relay S-Stop relay BR,Brake relay RCar running relay The various switches and relays are shown in their deenergized conditions. A separate reference character is employed for each relay or switch or the operating coil for such relay or switch. In designating the contacts associated with the relay or switch, the reference character for the relay or switch is employed together with a suffix in the form of a numeral specific to each pair of contacts. For example, the symbol Ul represents the first pair of contacts of the up switch U. The symbol U3 represents the third pair of contacts for the up switch U. The contacts of the switches or relays may be front or make contacts which are closed when the relay coil is fully energized or the contacts may be back or break contacts which are open when the coil of the switch or relay is fully energized.

Referring to Fig. 1, it will be noted that a flexible rope or cable I has an elevator car 3 secured to one end thereof and a counterweight 5 secured to the remaining end of the rope. The rope passes around a sheave 1 which is secured to a shaft 9.

In order to rotate the sheave 1, an electric motor M may be coupled to the sheave in any suitable manner. In Fig. l, the armature of the motor M and the sheave 1 are secured to the common shaft 9 which also carries a brake drum l3. A brake shoe 13A is biased into braking engagement with the drum l3 by means of a spring I3B. The brake is released as a result of energization of a brake coil B which has an armature BA secured to the shoe I3A. Such electromagnetic brakes are well known in the elevator field.

To assist in the control of the motor M a voltage which is proportional to the rate of rotation of the shaft 9 is derived in any suitable manner. For example, a tachometer generator I5 has its armature secured to the shaft 9. This generator may be of the direct-current type and conveniently may have a field provided by permanent magnets. It will be understood that the voltage output of the generator I5 is proportional to the rate of rotation of the shaft 9. Such tachometer generators are well known in the art.

Various systems for energizing the motor M are available. For the purpose of illustration, it will be assumed that a variable voltage system is employed for operating the elevator car. In such a system a generator G has its armature connected in a loop circuit with the armature of the motor M through conductors I! and I9. It will be understood that the armature of the generator G is rotated at a substantially constant rate by suitable motor means such as an induction motor (not shown). The motor M may have a field winding MF which is energized from any suitable constant-voltage source of direct current.

The generator G has a self-excited field GFI which is connected across the armature terminals through an adjustable resistor rl and make contacts BR] of a brake relay BR.

In order to control the direction of rotation of the motor M, the generator G is provided with separate field excitation means. This field excitation means may be a single field winding and such a field Winding will be discussed with reference to Fig. 5. However, in Fig. 1, two field windings GFZ and GF3 are employed for this purpose. These field windings are energized to provide opposing field excitations for the generator G. Consequently, the resultant field excitation supplied by the field windings GF2 and GF3 is proportional to the difference between the magnetomotive forces developed by these two windings.

The field windings GFZ and GF3 are energized from a suitable source of alternating voltage represented by a transformer 2|. This transformer has a primary winding 23 which is energized from a source of constant alternating voltage. For example, the source may have a frequency of 60 cycles per second. The transformer 2| also has two similar secondary windings 25 and 21.

By inspection of Fig. 1, it will be observed that the generator field winding GFZ is energized from the secondary Winding 21 through a winding 29 and a full-wave rectifier 3|. In an analogous manner, the field winding GF3 is energized from the secondary winding 25 through a winding 33 and a full-wave rectifier 35. It will be understood that the rectifiers 3| and 35 are so poled relative to the field windings that the field windings GFZ and GF3 always act in opposition to each other.

When rectifiers are specified in Fig. 1, it is to be understood that filters may be employed, if desired, to eliminate ripple from the outputs of the rectifiers. It will be assumed, however, that filters are not required.

To reduce the control current required, the control of the field windings GF2 and GF3 may be exercised through a suitable amplifier which conveniently may be a magnetic amplifier. To this end, the windings 29 and 33 form parts of a balanced magnetic amplifier. Although the construction and operation of magnetic amplifiers is well known a brief discussion of the magnetic amplifier shown in Fig. 1 will be helpful.

The winding 29 has a core 29A which is constructed of soft magnetic material. This core also serves as a magnetic core for a biasing winding 29B and a control winding 290. In an analogous manner the winding 33 has a core 33A, a biasing winding 33B and a control winding 33C.

The biasing windings 29B and 33B are energized from a source of constant direct voltage represented by conductors LI and L2. These conductors are connected to a voltage divider represented by a resistor 1'2 having an adjustable tap34 associated therewith. The winding 33B is connected between the tap 34 and one terminal of the resistor T2. The winding 29B is connected between the tapv 34 and the remaining terminal of the resistor T2.

The control windings 29C and 330 may be energized to regulate the speed of the motor M or they may be energized to control the position of the car 3. The specific energization of these windings is determined by the break contacts TI and the make contacts T2 and T3 of a transfer relay T. With these contacts in the conditions illustrated in Fig. l, the windings 29C and 33C are connected to regulate the speed of the motor M. Such regulation is obtained by comparing the voltage output of the tachometer generator [5 with a pattern voltage derived from a voltage divider. This voltage divider is represented by a resistor R3 having an adjustable tap 3'! associated therewith.

The resistor R3 may be connected to a source of constant direct voltage represented by buses L3 and L4 through a reversing switch. The reversing switch comprises the make contacts UI and U2 of an up switch and the contacts DI and D2 of a down switch. When the elevator car is conditioned for up travel between two or more floors, the contacts UI and U2 are closed. When the elevator car is conditioned for floor to floor down travel, the make contacts DI and D2 are 5 closed to connect the resistor R3 across the buses L3 and L4. The polarities applied to the resistor R3 in the two cases are reversed.

The polarity of the output of the tachometer generator l5 depends on the direction of rotation of the shaft 9. The output voltage of the tachometer generator and the pattern voltage are connected in series opposition. Consequently, a difference or error voltage appears between the conductors 39 and 4|. Since the break contacts Tl are closed, the error voltage produces a current flowing in series through the control windings 33C and 29C.

The operation of the portion of the system of Fig. 1 which regulates the speed of the motor M now may be set forth. It will be assumed that the biasing windings 29B and 33B are energized to produce magnetomotive forces acting in the cores in the directions represented by the arrows 29D and 33D, respectively. Such magnetomotive forces result in the flow of some magnetic flux in the two cores.

Inasmuch as the field windings C-F2 and GF3 are connected to the secondary windings 25 and 21, some current flows through the two windings. However, the currents flowing in the two windings GFZ and GF3 are equal as long as no current flows through the control windings 29C and 330. Since the magnetomotive forces produced by the two field windings GFZ and GF3 act in opposition to each other, no field excitation from these two windings would be obtained under such conditions.

It will be assumed next that an error voltage appearing between the conductors 39 and 4| directs current through the windings 33C and 29C in series to produce magnetomotive forces acting in the cores 3 3A and 25A in the directions of the arrows 33E and 29E.

It will be noted that the magnetomotive forces represented by the arrows 33D and 33E act in the same direction with respect to the core 33A. Consequently, substantial magnetic flux flows through the magnetic core and increases, the admittance of the winding 33'. If sufficient mag- 6 netic flux flows to completely saturate the magnetic core, the winding 33 acts substantially as an air core winding. For this reason substantial current is permitted to flow through the winding 33 and through the field winding (3E3.

Referring next to the core 29A, it is clear that the magnetomotive forces represented by the arrows 29D and 29E act in opposition to each other about the core 29A. Consequently, relatively little magnetic flux fiows through the magnetic core 29A and the winding 29 consequently permits the flow therethrough of a relatively small current to the field winding GFZ. Since the field windings GF2 and GF3 act differentially on the generator G, it is clear that the field winding GFS controls the direction of the resultant excitation obtained from the two windings. The magnitude of such excitation of course depends on the magnitudes of the currents flowing through the control windings 33C and 29C.

If the error. voltage appearing between the conductors 39 and 4| were to reverse inpolarity, the magnetomotive forces produced by the windings 33C and 230 also would reverse. Such reversal would result in a larger excitation from the field winding GFZ than from the field winding GF3. Consequently, the field winding GFZ would control the direction of the excitation of the generator G. From this brief explanation it will be understood that the voltage output of the tachometer generator I5 is compared to the pattern voltage derived from the resistor R3. Any diiference between these voltages results in an error voltage which may be applied to the balanced magnetic amplifier to produce a resultant field excitation on the generator G which acts to decrease the difference between the voltage output of the tachometer generator and the pattern voltage.

When the transfer relay T is energized to open its break contacts TI and to close its make contacts T2 and T3, the system is conditioned to control the position of the elevator car 3. The system then may be employed for forcing the elevator car 3 into accurate registration with a floor at which it is to stop and it also may be employed for maintaining the elevator car in registration with such floor.

In order to control the position of the elevator car 3, a pickup unit 43 is mounted for movement in accordance with movement of the car with respect to position control devices 45. One of the position control devices is provided for each of the floors to be served by the elevator car. If the position control devices are mounted in the hoistway adjacent their respective floors, the pickup unit 43 may be mounted directly on the elevator car 3 for movement in a path adjacent to the position control devices.

In a preferred embodiment of the invention, the pickup unit comprises a pair of impedance elements 43A and 43B which are shown in the lower part of Fig. l. The impedance elements are shown on a somewhat larger scale in Figs. 2 and 3. It will be noted that the impedance element 43B includes a core constructed of soft magnetic material and the core has a notch therein which defines two pole faces 41B and 493. The notch leaves a neck of comparatively small cross section and a coil 51B is wound around this neck. It will be noted that the pole face 41B is considerably longer than the pole face 493 in the. direction of travel of the elevator car. Theimpedance element 43A is exactly similar to the, impedance element 433 but is reversed with respect thereto about a line transverse to the direction of travel of the elevator car. The corresponding pole faces and coil of the impedance element 43A are identified by the same reference characters except for replacement of the sufiix B by the sufiix A.

Each position control device 45 is in the form of a magnetic member or plate constructed of soft magnetic material. Each of the plates 45 extends parallel to the plane of the pole faces of the impedance elements and may have a width and length sufiicient to cover both of the impedance elements when the elevator car is positioned at the associated floor.

The impedances or the admittances of the coils HA and 51B are determined to a substantial extent by the position of the pickup unit with respect to each of the plates 45.

The coils IA and 5 IB are arranged in a bridge circuit having four arms. The arms contain, respectively, the coil 5IA, the coil 5|B, a secondary winding 52A of a transformer 52 and a secondary winding 52B of the transformer 52. The two secondary windings 52A and 52B are inductively coupled to a primary winding 520 which is energized from a source of constant alter nating voltage represented by conductors L5 and L6. The transformer 52 applies an alternating voltage across one diagonal of the bridge circuit or across the two secondary windings 52A and 52B.

The output from the bridge circuit is obtained from a terminal 54 located between the secondary windings 52A and 52B and a terminal 54A which is located between the coils 5lA and 5lB. Between these terminals a bridge output circuit is connected which includes in series the primary winding 51A of a transformer 51, a stopping relay S and the primary winding 59A of a transformer 59.

The transformer 51 has a secondary winding 5113 which is connected in a series circuit with a rectifier 6!, the secondary winding 63A of a transformer 63 and the control winding 33C. In a similar manner, the transformer 59 has a sec ondary winding 59B which is connected in a series circuit with a rectifier 65, the secondary winding 61A of a transformer 6'! and the control winding 29C. The primary windings of the transformers 63 and 67 are connected to the conductors L5 and L6.

The bridge circuit is employed for controlling the energizations of the field windings GFZ and GF3 in accordance with displacement of the elevator car from a predetermined position in registration with a fioor at which the elevator car is to stop. It will be understood that the energizations of the field windings GFZ and GF3 are controlled, respectively, in accordance with direct current supplied to the control windings 29C and 33C.

When the elevator car is positioned accurately at a floor at which it is to stop, the impedances of the coil 5|A and 5|B are equal and no current fiows through the primary windings 51A and 59A. Should the elevator car be displaced upwardly from its desired position in registration with the floor, the impedance of the coil 51A would be decreased. This is for the reason that the plate 45 now covers only part of the pole faces of the impedance element 43A and the reluctance of the magnetic path offered to magnetic fiux produced by current flowing in the coil 51A therefore is increased. As a result of such unbalance of the bridge circuit, an alter- 8 nating current flows through the primary windings 51A and 59A.

If the elevator car had been displaced downwardly from the desired position in registration with the floor, the bridge circuit would have been unbalanced in the opposite direction. Such unbalance would have resulted because of the decrease in impedance of the coil 5IB. The a1- ternating voltages across the primary windings 57A and 59A in the two cases would be in phase opposition. In other words, the phase of the output voltage of the bridge circuit reverses as the elevator car passes through its desired position in registration with a floor at which the elevator car is to stop.

When the secondary winding 51B is connected to the control winding 33C two alternating voltages control principally the amount of current supplied to the control winding. These are the voltages supplied by the secondary windings 51B and 63A. The alternating voltage supplied by the secondary winding 63A is a biasing or reference voltage and is poled to be in phase with the voltage across the secondary winding 513 When the elevator car is displaced downwardly from its desired position in registration with a floor at which it is to stop. Under these circumstances, a substantial current flows through the rectifier GI and the control winding 330. As will be shown later, the magnitude of this current increases with the displacement of the elevator car in a downward direction from its desired position. The energization oi the field winding GF3 varies in accordance with the current flowing through the control winding 33C.

When the secondary winding 59B is connected to the control winding 29C, two voltages control principally the current flowing through the control winding. These are the alternating voltages appearing across the secondary windings 59B and 61A. The two voltages are so poled that they are in phase agreement when the elevator car is above the desired position in registration with a fioor at which the elevator is to stop. Consequently, the current flowing through the control winding 29C and the current supplied to the field winding GF2 increases in accordance with the displacement of the elevator car 3 above a position in registration with a fioor at which it is to stop.

If the elevator car is below a floor at which it is to stop, the alternating voltages across the secondary windings 59B and 61A would be in phase opposition and a relatively small current would flow through the control winding 290. In a similar manner if the elevator car were above a position in registration with the floor at which it is to stop, the alternating voltages across the secondary windings 51B and 83A would be in phase opposition and relatively little current would flow through the control winding 33C.

The control exercised by the bridge circuit may be considered further in connection with Figs. 2 and 4. When the elevator car is in accurate registration with a floor, the impedance elements 43A and 43B are both covered by one of the plates 45, as shown in Fig. 2 Consequently, the coils 5|A and 51B exhibit a maximum impedance. This position of the car in Fig. 4 is represented by the axis Pi. ordinates in Fig. 4 represent displa ment of the elevator car from its position in registration. with the floor. Abscissas in Fig. 4 repre- Zeg; field excitation for the windings GE: and

As the elevator car moves downwardly from its desired position, the pole face 413 gradually leaves the associated plate 45. Consequently, the impedance of the coil 51B gradually decreases and the excitation of the field GFE, increases gradually as shown by the portion HA of the curve H. The shape of the portion HA depends to some extent on the shape of the pole face 41B. It may be substantially linear, as illustrated in Fig. 4, or it may have other curvatures as desired. When the pole face 41B has completely left the plate 45, the impedance of the coil 513 has its minimum value and the excitation of the field winding GF3 is a maximum, as shown by the portion MB of the curve H.

As the elevator car moves upwardly from the position represented in Fig. 2, the impedance of the coil 5IB remains unchanged. until the pole face 49B reaches the upper edge of the plate 55. During this period the field winding GF3 has its minimum excitation as shown by the portion l !C of the curve H. Upon continued upward movement of the elevator car, the pole face 493 leaves the plate 65 and the impedance of the coil 5K3 rapidly decreases. This results in a rapid increase in the excitation of the field winding G-F3, as shown by the portion l'lD of the curve H.

The effect of movement of the car on the impedance of the coil 51A may be shown in a similarmanner. If the car moves upwardly from the position corresponding to Fig. 2, the pole face il'A gradually leaves the plate 45 and the impedance of the coil 51A gradually decreases. This results in a gradual increase in the excitation of the field winding GFZ, as represented by the portion 13A of the curve 13. After the pole face 41A has left the plate 45, the coil 5 IA has its minimum impedance.

If the elevator car moves downwardly from the position corresponding toFig. 2, the impedance of the coil 5 IA remains constant until the associated pole face 49A (Fig. 3) reaches the lower edge of the plate 45. During this period the field winding GM has a minimum excitation as represented by the portion 13B of the curve '13.

Upon continued downward movement of the elevator car, the pole face 49A leaves the plate 45 and the impedance of the coil 52A rapidly decreases. This results in a rapid increase in the excitation of the field winding GFZ, as represented by the portion 13C of the curve f3.

It will be recalled that the field windings GP?! and GF3 of Fig. 1 act in opposition to each other. Consequently, the resultant field excitation is that represented by the curve 75 in Fig. 4. This curve represents the difference between the two curves II and 73. It will be noted that the resultant ex.- citation of the field windings GFZ and GF3 is zero when the elevator car is positioned accurately at the elevator floor. As the elevator car leaves its position of registration with the floor, the resultant excitation increases gradually in a direction dependent upon the direction of movement of the elevator car away from the floor. It will be assumed that this variation in excitation is linear, as represented by the portion 15A of the curve 15. If the elevator car moves sufliciently to carry the pickup unit 43 away from the plate :25, the resultant excitation provided by the two windings GFZ and GFES falls to zero, as shown by the portions 15B and 15C of the curve 15. By inspection of the portion 35A of the curve i5, it will be seen that the direction of the resultant excitation produced by the field windings GFZ and GF3 always is in a direction tending to urge the elevator car towards its desired position in registration with the floor.

Various control systems are known for elevator cars. For example, elevator cars may be arranged for automatic operation or for attendant operation. Although the circuits of theinvention may be employed for various types of conductors L3 and L l through make contacts BRZ' of a brake release relay. A discharge resistor R4 is connected across the brake coil for controlling the rate at which the brake is applied to stop the elevator car.

It is believed that a full understanding of the system of Fig. 1 will he facilitated by a discussion of typical operations of the system. It will be assumed first that the elevator car 3 is at the lower terminal, floor and that the car attendant desires to move the elevator car to the third The devices 79 represent conventional safety devices such as door contacts which must be closed before the elevator car can be started on a fioorto-fioor run.

The energization of the upswitch U results in closure of the make contacts U1 and U2 to connect the resistor R3 across the conductors L3 and L4 with proper polarity to initiate up travel of the elevator car.

Inasmuch as the elevator car is assumed to be at a standstill, the tachometer generator I5 has a zero output. voltage derived from the tap 31 and the resistor R3 is applied across the control windings 33C and 29C in series. It will be recalled that the magnetomotive forces resulting from such energizations of the coils 33C and 29C produce a substantial energization of the field Winding GFB and a relatively small energization of the field winding GFZ. The resultant field excitation from these windings consequently is in a direction to produce up motion of the elevator car.

The up switch U also closes its make contacts U3 to establish a holding circuit through the break contacts T4 of the transfer relay around the car switch CS. Opening of the break contacts U4 prevents energization of the down switch D. Closure of the make contacts U5 completes the following energizing circuit for the brake release relay BR:

L3U5T5 BRL4 The brake release relay BR. closes its make contacts BRA to complete an energizing circuit for the field winding GFI across the terminals of the generator armature. Consequently, the voltage of the generator G rapidly builds up to produce up travel of the elevator car.

The brake release relay BR also closes its make Consequently, the entire patterning across the conductors 39 and 4| decreases to decrease the current fiowing through the control windings 33C and 29C. The elevator car consequently approaches a stable running speed. If the running speed should be higher than the value called for by the pattern voltage, the direction of the currents flowing through the control windings 33C and 290 would reverse and the field winding GFZ would be energized to a de gree greater than that of the field winding GF'3. This would decrease the speed of the elevator car to the desired running value. In this way the speed of the elevator car is accurately regulated during a floor-to-floor run. As previously pointed out, the speed of the elevator car may be ad justed by manipulation of the tap 31.

The operation of the car switch also deenen gized the running relay R which opened make contacts Rl to prevent energization of the transformers 52, 63 and 61. In addition, the make contacts R2 opened to prevent energization of the transfer relay T.

After the elevator car has passed the second floor, the car attendant centers his car switch CS to energize the running relay R. Such cen tering of the car switch has no immediate effect on the energization of the up switch U, because of the holding circuit through the contacts U3 and U4.

The energization of the running relay R closes the make contacts R! to energize the primary windings of the transformers 52, E3 and 61. In addition, the make contacts R2 close but such closure has no immediate effect on the operation of the system.

As the elevator car nears the third fioor, the impedance element 43A finally reaches the plate 45 for the third floor and unbalances the bridge circuit sufficiently for the stopping relay S to pick up. The operation of the stopping relay S may be considered with reference to Fig. 4. The relay S may be designed to pick up when the bridge circuit has an output sufiicient to produce a resultant field excitation from the windings GFZ and GF3 which is represented in Fig. 4 by the dotted lines 93A and 933. For outputs of the bridge circuit below such values, the relay S is dropped out.

When the elevator car has reached with respect to the third floor, a point corresponding to the point 93C in Fig. 4, the relay S picks up to close its contacts SI. In closing, the contacts S! establish a holding circuit for the brake release relay BR. In addition, the make contacts S2 close to energize the transfer relay T through the closed make contacts R2.

The energization of the transfer relay T results in opening of the break contacts TI to interrupt the energization of the control windings 29C and 330 from the conductors 39 and 4|. In addition, the make contacts T2 and T3 close to energize the control windings 33C and 29C, respectively, from the transformers 51 and 59. Consequently, the field windings GFZ and GF3 are energized to produce the resultant excitation represented by the curve 15 in Fig. 4.

Opening of the break contacts T4 deenergizes the up switch U. The up switch U opens its make contacts UI and U2 to discontinue the energization of the resistor R3. Make contacts U3 open and break contacts U4 close but have no immediate eifect on the operation of the system.

The transfer relay T also opens its break con tacts T5. However, since the brake release relay continues to be energized through the contacts SI of the stop relay. The opening of the contacts T5 has no immediate effect on the operation of the system. The deenergization of the up switch U also opens the make contacts U5 but such opening also has no effect on the immediate operation of the system. I

The excitation of the field winding GF3 under the control of the bridge circuit S rapidly builds up to maintain the upward motion of the elevator car. As the elevator car continues to approach the third door, the resultant excitation of the field windings GF2 and GF3 follows the portion 15A of the curve 15 in Fig. 4. This means that the speed of the elevator car decreases .as it nears the third floor. When the output of the bridge circuit drops to a value below that corresponding to the dotted line 93a in Fig. 4, the stopping relay S drops out. The resultant opening of the make contacts SI deenergizes the brake release relay BR which opens its contacts BRI to deenergize the field winding GFi. The brake release relay also opens its make contacts BRZ to deenergize the brake coil B. Consequently, the brake is applied to stop the elevator car at the third floor. Inasmuch as the elevator car is travelling at an extremely slow speed at this time, a low value of discharge resistance represented by the resistor R4 may be employed to assure a soft braking action.

Should the elevator car drop below the third fioor for a distance sufficient to produce a substantial output from the bridge circuit, as rep S2 would reenergize the transfer relay T to recon nect the control windings 33C and 29C for energization from the transformers 5'! and 59. Consequently, the system again is conditioned for energization in accordance with the portion 15A of the curve 75 in Fig. 4 to return the elevator car to the third floor. When the elevator car is again adjacent the third fioor, the relay S drops out to stop the elevator car in the manner previously set forth.

It will be assumed next that the elevator car attendant desires to return to the lower terminal floor. In order to initiate such return, the elevator car attendant operates the car switch CS in a clockwise direction, as viewed in Fig. 1 to establish the following energizing circuit for the relay D:

The down switch D closes its contacts Di and D2 to energize the resistor R3 with proper polarity for down travel of the elevator car. Since the elevator car is stopped at the third floor, the tachometer generator l5 has no output and the entire pattern voltage is applied across the windings 33C and 29C in proper direction to produce down travel of the elevator car.

The down switch also opens its break contacts D3 to prevent energization of the up switch U and closes its make contacts D4 to establish a holding circuit through the break contacts T4 around the car switch.

The make contacts D5 close to energize the brake release relay through the closed break contacts T5 of the transfer relay. The brake release relay closes its make contacts BR! to connect the field winding GFI for energization and closes its make contacts BB2 to release the brake.

The deenergization of the running relay R resulting from the operation of the car switch opens the make contacts Rl to deenergize the transformers 52, 63 and 6?. Also the make contacts R2 open to prevent energization of the transfer relay T.

As the elevator car proceeds downwardly, the voltage of the tachometer generator l5 increases and the error voltage appearing between the conductors 39 and ll decreases. As previously pointed out, this error voltage assures good speed regulation and maintains the elevator car at a speed determined by the position of the tap 31.

After the elevator car has passed the second floor, the car attendant centers his car switch CS to energize the running relay R. The energization of the clown switch D is not afiected because of the holding circuit established through the contacts D4 and T4.

The running relay R closes its make contacts Rl to energize the primary windings of the transformers 52, 63 and 5?. Also the contacts R2 close to prepare the transfer relay T for subscquent energization.

' When the elevator car has reached a point at which the bridge circuit produces an output equal to that corresponding to the field excitation represented by the dotted line 9313 in Fig. 4, the stopping relay S is energized sufficiently to pick up. This relay closes its make contacts S! to establish a holding circuit for the brake I release relay BR. In addition, the contacts S2 close to energize the transfer relay T through the closed break contacts R2.

The transfer relay T opens its break contacts TI to interrupt the energization of the control windings 33C and 29C from the conductors 39 and 4!. Also the contacts T2 and T3 close to connect the control windings for energization "from the transformers 5'5 and The elevator car now is controlled in accordance with its displacement from the first floor and the resultant excitation of the field windings GFZ and GF3 corresponds to that represented by the curve E5 in Fig. 4.

The energization of the transfer relay also results in opening of the break contacts T lto deenergize the down switch D. The down switch opens its make contacts Di and D2 to deenergize the resistor R3. Closure of the break contacts D3 and opening of the make contacts D4 have no immediate efiect on the operation of the system. Opening of the break contacts T5 and opening of the make contacts D5 have no immediate effect on the operation of the system for the reason that a holding circuit therearound previously had been established through the contacts SI.

As the elevator car continues to approach the first floor, the output of the bridge circuit decreases until the stop relay S finally drops out. Such dropping of the stopping relay opens the make contacts S1 to deenergize the brake release relay BR. Also the contacts 82 open to deener gize the transfer relay T.

Should the elevator car fail to stop accurately at the first floor or should it move away from the first floor due to cable stretch or contraction, the stopping relay S again would be energized sufficiently to initiate a levelling operation of the elevator car It is believed that the levelling operation will be'clear from the preceding discussion.

In the embodiment of Fig. 5, the following relays and switches appear:

UXUp switch DXDown switch TX-Transfer relay DR-Door relay LRU-Up relay LRDlDown relay RX--Car running relay The up switch, the down switch and the transfer relay correspond to the up switch U, the down switch D and the transfer relay T of Fig. 1 but have somewhat different contact arrange ments. A number of the components of Fig. 1 are employed in Fig. 5 and are identified by the same reference characters. The generator GX of Fig. 5 corresponds to the generator G of Fig. 1 but has somewhat different field excitation circuits. It will be noted that the self-excited field Winding XFI of Fig. 5 corresponds to the field winding GFI of Fig. 1, but the connection of the former field winding is controlled by make contacts DXI and UK! of the down switch and the up switch respectively. The generator GX has a single control field winding XFZ which replaces the two field windings GFZ and GF3 of Fig. 1.

The field winding XF2 is energized through a grid-controlled rectifier which preferably is of the full-Wave type. Thus two thyratron tubes I01 and I83 are employed in the full-wave rectifier. Plate voltage for these tubes is supplied by a transformer I05 which has a primary winding Ii5A and two secondary windings I05B and 105C. The primary winding may be energized from a source of constant alternating voltage through a suitable phase shifter Ill]. The secondary windings [B5B and 1050 are connected in series across the anodes Ill IA and l 03A of the thyratron tubes. The cathodes "MC and H330 of the tubes each has a terminal connected to a common conductor H39. Suitable heating circuits (not illustrated) may be provided for the cathodes in a manner well understood in the art.

The field winding XFZ is connected between the conductor I09 and a terminal intermediate the secondary windings 66513 and W5C through a reversing switch. This reversing switch comprises contacts of the up switch UX and of the down switch DX. When the contacts UX2 and UX3 are closed, the field winding XFZ is connected with proper polarity to produce up travel of the elevator car. When the contacts DX2 and DX3 are closed, the field winding XF2 is connected with proper polarity to produce down travel of the elevator car. The full-wave rectifier is employed for energizing the field winding XFZ, both for regulating the speed of the elevator car and for controlling the position of the elevator car.

In order to regulate the speed of the elevator car, the thyratron tubes are provided with inputs proportional to an error voltage appearing between the conductors 39X and MX. This error voltage represents the difference between the output of the tachometer generator l5 and the pat tern voltage appearing between the tap 3'8 and the conductor L4.

The resistor R3 now is connected directly across the conductors L3 and L4. Since the tachometer generator l5 reverses its polarity in response to reversal in the direction of travel of the elevator car, the output voltage of the generator is connected in series with the pattern voltage through a reversing switch. This reversing switch includes the contacts UX4 and UX5 which are closed when the elevator car is conditioned for up travel. The reversing switch also includes the contacts DX I and DX5 which are closed when the elevator car is conditioned for down travel.

The conductor 39X is connected to the conductor I09 through break contacts TXI of the transfer relay. The conductor 4IX is connected to the control or grid electrodes IIIIG and 13G of the tubes through break contacts TX2 and TX3 of the transfer relay.

When the generator field winding XF'Z is to be energized through the thyratron tubes to regulate the speed of the elevator car, the grid electrodes IIIIG and 33G are both made positive with respect to their associated cathodes. The tubes then act as a full-wave rectifier to supply current to the field winding XFZ.

When the elevator car is to be controlled in accordance with its displacement from a pre determined position, the transfer relay TX is energized to open the break contacts TXI, TX2 and TX3 and disconnect the grid electrodes of the thyratron tubes from the conductors 39X and 4IX. In addition, the transfer relay closes its make contacts TX I, TX5 and TX5 to connect secondary windings II IA and IIIB of a transformer I I I, respectively, to provide input voltages for the tubes IBI and I113. The transformer III is energized from a bridge circuit which is similar to the bridge circuit of Fig. 1, except for the replacement of the primary windings 51A and 59A and the relay S of Fig. 1 by a single primary winding III C of the transformer III.

The transformer 52 and the transformer I85 may be energized from the same source of constant alternating voltage. However, in a preferred embodiment of the invention, the voltages are arranged to provide an output from the thyratron tubes which is dependent on the amplitude of the input thereto. To this end the voltage applied to the plate circuit of the thyratron tubes preferably leads or lags the voltage supplied by the transformer III to the thyratron tubes by a suitable angle, such as 60. The phase shifter I! may be adjusted to provide the desired phase relationship between the voltages.

It will be recalled that as the elevator car moves through a predetermined position at which it is registered with a floor at which it is to stop, the voltage applied to the output circuit of the bridge circuit reverses in phase. However, such reversal has no effect on the direction of the plate current obtained from the thyratron tubes. For this reason, an up relay LRU and a down relay LRD are provided to control the direction of movement of the elevator car as it is levelled into the proper position in registration with a floor at which it is to stop.

The up relay LRU is located in the plate circuit of a tube II3 which may be of any suitable type, such as a high vacuum triode or a thyratron. For the purpose of discussion, it will be assumed that the tube H3 is a thyratron tube. The down relay LED is located in the plate circuit of a similar tube II5. Alternating voltage is supplied for both plate circuits by means of a. transformer Ill which is energized from a suitable source of constant alternating voltage. It will be noted that the same instantaneous polarity is applied to both plates of the tubes I I3 and I I by the transformer H1.

The cathodes of the tubes H3 and H5 are both connected through a conductor I I9 to a terminal intermediate the two secondary windings iIIA and HIB. The conductor H9 is connected through a suitable source of biasing voltage, such as a battery I2I to the conductor I09. Conventional heating means (not shown) may be supplied for the cathodes of the tubes H3 and H5. The grid electrodes of the tubes H3 and H5 are connected, respectively, to conductors I23 and I25. It will be noted that the secondary winding I I IA is connected across the conductors I23 and I I9, whereas the secondary winding I I I3 is connected across the conductors H9 and I25.

If the elevator car is somewhat below the position which it should occupy in registration with the floor, the polarities supplied by the transformers III and Ill are such that the alternating inputs and outputs for the tube II3 are in phase. For this reason, substantial current will flow through the relay LRU and this relay will be energized sufliciently to pick up. At the same time the input and output voltages for the tube IIE will be in phase opposition and the relay LRD consequently remains deenergized. The relay LRU is effective for conditioning the system for up travel of the elevator car.

Should the elevator car be above the position it should occupy in registration with a floor, the input and output voltages for the tube I I 5 would be in phase agreement and sufficient plate current would flow to energize the relay LRD. At the same time the input and output voltages for the tube II3 would be in phase opposition and the relay LRU would remain deenergized. This conditions the elevator car for down travel.

It is believed that the operation of the system illustrated in Fig. 5 now may be considered. Let it be assumed first that the elevator car is positioned at the first or lower terminal floor, and that the car attendant desires to proceed to the third floor. The car switch CS is in its neutral position and the car running relay RX is deenergized. The car attendant first closes his hoistway and car doors to energize a door relay DR. Such a. relay is commonly provided and is connected in series with safety devices 19, such as door contacts, to assure closure of the doors before the car can be started on a floor to floor run. The door relay closes its contacts DRI when energized and opens its break contacts DB2. These contact changes have no immediate effect on the operation of the system.

The car attendant next rotates the car switch CS in a counterclockwise direction to establish the following energizing circuit for the running relay RX and the up direction switch UX:

The energized running relay RX opens its break contacts RXI to discontinue energization of the transformer 52. Also the break contacts RX2 open to interrupt deenergization of the transfer relay TX.

In response to deenergization of the transfer relay TX, the break contacts TXI, TX2 and TX3 close to connect the tubes IIJI and I03 for control by the error voltage appearing between the conductors 39X and MK. The contact TX4, TX5 and TXG are make contacts and open to disconnect the tubes IOI and I03 from the transformer III. The make contacts TX'I open but have no immediate effect on the operation of the system.

Since the up switch UK is now energized, it

17 closes its contacts UXI to connect the generator field winding XFI across the armature of the generator GX. The make contacts UX2 and UX3 close to connect the field winding XFZ to the tubes lcl and N33 for energization with proper polarity for up travel of the elevator car. The make contacts UX l and UXE close to connect the tachometer generator in series with the pattern voltage appearing across a portion of the resistor R3 with proper polarity to oppose the pattern voltage. The make contacts UXS close to energize the brake coil 13 and release the brake.

Inasmuch as the elevator car is at rest, the output of the tachometer generator I5 is zero and the entire pattern voltage is applied between the grid electrodes and cathodes of the tubes NH and H53. Consequently, substantial current flows through the field winding XFZ and the elevator car is accelerated in an up direction. As the elevator car accelerates the output voltage of the generator I5 increases to reduce the error voltage appearing between the conductors 38X and MX. Consequently, the elevator car approaches a definite speed which may be adjusted by adjustment of the tap 31.

When the car attendant believes that the ele vator car is sufficiently close to the third floor to land accurately at such floor, he centers the car switch CS. Such centering of the car switch deenergizes the running relay RX and the up switch UX.. The running relay RX closes its break contacts RXI to energize the transformer 52. In addition, the break. contacts RXZ close to prepare the transfer relay TX for subsequent energization.

Upon deenergize-tion, the up switch UX opens its make contacts UK! to interrupt the energization of the winding XFI. In addition, the contacts UX2 and X3 open to disconnect the field winding XF2 from the thyratron tubes I01 and N33. The contacts UX4 and UX open to disconnect the tachometer generator from the resistor R3. The contacts UXS open to deenergize the brake coil B. Consequently, the brake is applied to slow the elevator car for a landing at the third floor.

When the elevator car is within a short distance of the third fioor, the impedance element 13A is covered by a substantial part of the plate 45 and the impedance of the coil 5IA begins to increase. The resulting unbalance of the bridge produces an output from the transformer ill of proper phase to produce a flow of current through the up relay LRU. Consequently, the up relay closes its make contacts LRUI to energize the up switch UX.. The up switch operatesin the manner previously described.

In additiomthe up relay LRU closes its make contacts LRUZ to complete an energizing circuit for the transfer relay TX through the break contacts RXZ of the running relay. The transfer relay thereupon opens its break contacts TXI, TX2 and TX3 todisconnect the tubes [BI and I03 from the conductors 39X and X. In addition, the contacts TX4, TX5 and TXB close to connect the tubes [DI and N33 for reception of inputs from the transformer Hi. Finally the make contacts TX! close to establish a holding circuit around the contacts LRUZ.

The elevator car now is conditioned for up travel and the field XF2 is energized in accord= ance with the output of the transformer lli. Consequently, the elevator car continues to move upwardly until the output of the bridge circuit drops suiiiciently to premit the relay LRU to drop out.

Upon dropping out, the relay LRU opens its make contacts LRUI to deenergize the up switch UX. Such deenergization results in discontinuance of the excitation of the generator GK and application of the brake in the manner previously described. Since the elevator car is travelling slowly at this time, and since it is substantially in registration with the third floor, the application of the brake results in an accurate stopping of the elevator car at the third floor. In addition, the contacts LRUZ open but such opening has no immediate effect on the operation of the system.

Should the elevator car stop at a point somewhat above the third floor, the tubes H3 and I I5 would be energized from the transformer l l I with proper polarity to pick up the relay LED. The relay LRD thereupon would close its make contacts LED! to establish an energizing circuit for the down switch DX. The relay LRD also would close its make contacts LRD2 but such closure has no immediate effect on the operation of the system.

Upon being energized the down switch DX closes its contacts DX! to connect the generator field winding XFI across the terminals of the armature of the generator. In addition, contacts DXZ and DX3 close to connectthe field winding XFZ to the tubes [ill and I03 for energization with proper polarity for down travel of the elevator car. The field winding XF2 now is energized in accordance with the output of the transformer Ill.

Closure of the contacts DX4 and DX5 has no immediate effect on the operation of the system. However, the closing of the contacts DX6 energizes the brake coil to release the brake. The car now is conditioned for down travel and moves slowly toward the exact desired position in registration with the third floor. As it moves, the excitation of the generator field winding XF2 decreases. As a result of the decrease in the output of the transformer I l l, the relay LRD finally drops out. Upon dropping out, the relay opens its make contacts LRDI to deenergize the down switch DX. The down switch DX opens its contacts DXI to deenergize the field winding XFl. Also the contacts DX2 and DX3 open to deenergize the field windingXFZ.

The opening of the contacts DX4 and DX5 has no immediate eifect on the system. However, the opening of the make contacts DX6 deenergizes the brake coil B and reapplies the brake. Since the car is moved slowly'at this time and is accurately adjacent the third floor, a soft brake may be employed for stopping the elevator car accurately at the third floor.

' The car attendant now opens his car and hoistway doors and such opening results in deenergization of the door relay DR. The door relay opens its make contacts DR! but such opening has no immediate effect on the operation of the system. The door relay break contacts DB2 close to assure continued energization of thetransfer relay TX. Consequently, if the car should rise or drop slightly while its doors are open at the third fioor, one of the relays LRU or LRD would operate to initiate a return of the elevator car accurately into registration with the third fioor.

Let it be assumed that the car attendant desires to return to the lower terminal floor. He first closes the car and hoistway doors to energize the 19 door relay D-R. This relay closes its make con-- tacts DR! and opens its break contacts DB2.

The car attendant next rotates. the car switch CS in a clockwise; direction to establish. the following energizing circuit for. the running relay RX and the down switch. DX 1:

The running relay RX and the down switch DX now operates in the manner previously described.

It will be recalled that the opening of the break contacts RXZ results in deenergization of the transfer relay TX. Consequently, the generator field winding XFZ now is controlled in accordance with the error voltage appearing between the conductors 39X and AIX. Since the tachometer generator I has zero. voltage output while the elevator car stands at the third floor, the entire pattern voltage is applied to the. tubesv HH and I03 and the field winding XE'Z is energized with F proper polarity for down travel of the elevator car. The car consequently accelerates and as it accelerates the output of the. tachometer generator reduces the error voltage appearing between the conductors 59X and (UK. (The closure of the contacts DX4 and DXE assures connection of. the tachometer generator with proper polarity to oppose the pattern voltage.)

When the elevator car is sufiiciently close to the first floor for a landing operation, the car attendant centers his car switch C8 to. deenergize the running relay RX and the down switch .DX.

The running relay when deenergized operates as previously described to energize the transformer 52 and to prepare the transfer relay TX for subsequent energization. The down switch when deenergized operates as previously described.

As the elevator car continues its approach to.

the first floor, the impedance element 43B finally reaches a point at which a substantial portion thereof if covered by the plate 45 for the first fioor. The impedance of the coil 5|B' then starts to increase and the resultin unbalance of the bridge circuit produces an output from the transformer l l l. The output from the transformer l I I is of proper polarity to energize and pick up. the relay LRD. This relay operates as previously described to condition the elevator car for down travel under the control of the bridge circuit.

Consequently, the elevator car stops accurately at the first floor and the car attendant thereafter opens his doors to deenergize the. door relay DR.

Should the elevator car thereafter move away from the first floor because of cable stretch or contraction, the bridge circuit operates in, the manner previously described. to. return the ele vator car accurately in registration with the first floor.

Although the system has been described with reference to certain specific embodiments thereof, numerous modifications falling within the spirit and scope of the invention are possible.

I claim as my invention:

1. In an elevator system for a structure having a plurality of floors, an elevator car, motive means for moving the elevator car relative to the structure for serving the floors, electrical means for producing a first output which varies continuously as a function of the displacement of the elevator car in a first direction for a substantial distance from oneof said floors, said electrical means including means for producing a second output which varies continuously as a function of the displacement of the elevator car in a sec- 0nd direction for a. substantial distance from one of said floors, and means, for energizing said motive means in accordancewith the difference between, said outputs over said distances of displacement.

2. An elevator system as, claimed in claim 1, wherein the. electrical means comprises a pair of impedance elements movable with the e1evator. car, and a separate impedance control device associated with each of said floors, each of the impedance control devices being adjacent, but spaced from, the path of travel of the impedance elements, each of the, control devices havin a field established between the control device and the impedance elements when, adjacent thereto which is varied as a function of relative movement. therebetween.

3. An elevator system as claimed in claim wherein the impedance elements are reactance elements and connections for energizing the reactance elements by alternating current.

4. An elevator system as claimed in claim 2, wherein the impedance elements are electrcmagnets having airgaps, said impedance control devices each comprising a soft. magnetic plate positioned to bridge the airgaps of the impedance element to, an. extent dependent on the displacement. of the. car from a predetermined position.

5. In a position-responsive device, a plurality of spaced impedance-control devices, an impedance unit, means mounting the impedance unit for movement in, a path carryi g the imp n e unit successively adjacent each of the impedance-control devices, said impedance, unit comprising first and second impedance elements each having an impedance dependent on the displacement thereof relative to one of the impedancecontrol devices over a substantial range, the impedance or the first impedance element vars ns continuously in a predetermined pattern over a substantial range as the impedance moves for a substantial distance from a predetermined po sition in a first direction relative to one of the impedance-control devices, the impedance of the second impedance element varying continuously in substantially said predetermined pattern over a substantial range as, the impedance unit moves for a substantial distance from said predetermined position in a second direction which is opposite to the first direction. relative to said one of the impedance-control devices, and an sizing means responsive to. the difference b tween the. impedances 01 said impedance elements.

6. A. position-responsive device as claimed in claim 5, wherein the energizing means includes means for applying to each of said impedance elements an alternating energization to produce first and second outputs having magnitudes dependent respectively' on the impedances of said first and second impedance elements, rectifying means for each of said outputs, and translating means responsive to the difference between said rectified outputs.

7. A position-responsive device as claimed in claim 5, wherein the energizing means includes a pair of impedance devices connected in a series circuit, said impedance elements being connected in a series circuit, means for applying an alternating energization in parallel to said two series circuits, and output means responsive to the bridge voltage appearing between the connection for said impedance devices and the conction for said impedance elements.

8. A position-responsive device as claimed in claim '7, wherein said output means comprises first and second rectifier means connected for energization in accordance with said bridge voltage, a source of reference alternating voltage, and means connecting the source of reference voltage to said rectifier means, the two voltages applied to the first rectifier means being in phase agreement and the two voltages applied to the second rectifier means being in phase opposition for a first direction of movement of the impedance unit from the predetermined position, and the two voltages applied to the first rectifier means being in phase opposition and the two voltages applied to the second rectifier means being in phase agreement for a second direction of movement of the impedance unit from the predetermined position.

9. A position-responsive device as claimed in claim 8, wherein the energizing means comprises a dynamo-electric machine having field-excitation means, and connections for energizing the field-excitation means in accordance with the difference between the currents fiowing through said two rectifier means.

10. A position-responsive device as claimed in claim 9 in combination with means for producing an output dependent on the deviation of said machine from a predetermined speed pattern, and transfer means effective at a predetermined position of the impedance unit relative to one of the impedance-control devices for transferring the field. excitation means for energization in accordance with the last-named output.

11. In an elevator system for a structure hav= ing a plurality of floors, an elevator car, directcurrent motive means for moving the elevator car relative to the structure in a direction de pcndent on the polarity of an energisation supplied thereto, an electrical means for applying to the motive means an energization having a polarity dependent on the direction or displacement of the elevator car from a predetermined position and having a magnitude which varies continuously as a function of the magnitude of said displacement, said energization being poled to urgethe elevator car towards said predetermined position, said electrical means comprising a reference device and a pickup unit mounted for movement relative to the reference device in accordance with movement of the car.

12. An elevator system as claimed in claim 11, in combination with means for producing an output dependent on the deviation of the elevator car from a predetermined speed pattern, and means responsive to a predetermined departure of said elevator car from the predetermined position for replacing the first-named energization of the motive means by an energization de pendent on said output.

13. An elevator system as claimed in claim 12, wherein the last-named means includes transfer means responsive to the magnitude of said first-named energization, said transfer means being independent or said polarity.

14. An inductor assembly for an'elevator system comprising a magnetic member, and an electromagnet mounted for movement relative to the magnetic member, said electromagnet having a magnetic core configured with the magnetic member to provide an impedance for the electr-omagnet which first increases, then remcans substantially constant for a predetermined distance of travel and finally decreases at a rate different from said rate of increase as 22 the electromagnet passes the magnetic member.

15. An inductor assembly as claimed in claim 14 in combination with a rectifier, and connections for applying to the rectifier an alternating voltage controlled by said impedance.

16. An inductor assembl for an elevator sys tern comprising a magnetic member, and first and second similar electromagnets mounted for movement as a unit relative to the magnetic member through a path passing adjacent to the magnetic member, each of said electromagnets comprising a magnetic core configured with the magnetic member to provide an impedance which first increases and then decreases as the electromagnet passes the magnetic member, said electromagnets being reversed relative to each other about a line transverse to said path.

17. An inductor assembly as claimed in claim 16 in combination with first and second rectifiers, connections for applying to the first rectifier an alternating voltage controlled substantially by the impedance of the first electromagnet, con nections forapplying to the second rectifier an alternating voltage controlled substantially by the impedance of the second electromagnet, and means for obtaining an electrical quantity cor trolled by the difference between the outputs of said rectifiers.

18. In an elevator system for a structure having a plurality of floors, an elevator car, means including a motor for moving the elevator car elative to the structure for serving the floors, and motor control means including a positioning device, a bridge circuit having first and second impedance means in each of the arms of the bridge circuit, said impedance means having pedances dependent on the position of the posttioning device relative to the impedance means. and mounting means mounting the impedance means for movement relative to the positioning device in accordance with movement of the car relative to the structure, and means responsive to the variations in impedances of said arms for controlling the energization of the motor.

19. A system as claimed in claim 18, wherein said bridge circuit has input terminals and output terminals, said impedance means being reactive impedances having field-responsive im pcdance values and said positioning device comprising a field-controlling member positioned adjacent the path of travel of the reactive impedances for controlling the effective impedance values of said impedances.

20. A system as claimed in claim 19, wherein the impedance means are inductive impedances having magnetic fields when energized and the positioning device is a magnetic device for modiiying the magnetic fields of the impedance means.

21. In a motive system, a directional motor, and means for controlling the direction of rotation of the motor and the magnitude of energization thereof, said means comprising first and second impedance means, an impedancecontrol device, said impedance means being mounted for rotation relative to the impedancecontrol device in a path adjacent to the impedance-control device, said first impedance means having an impedance value which varies in magnitude in a predetermined direction as said impedance means travels relative towards a predetermined position relative to the impedance-control device, the second impedance means having an impedance value which varies in magnitude in a direction opposite to the predetermined direction as the impedance means 23 continues said travel beyond. said predetermined position, means for energizing the motor for op eration in a direction controlled by the sign or" the difference between said impedance values.

22. A system as claimed in claim 21, in combination with means for controlling the magnitude of the energization of the motor in accordance with the magnitude of the difference between said impedance values.

23. An elevator system for a structure having a plurality of floors, an elevator platform ll'lOLill'l'r ed for movement relative to the floors and. means for leveling the platform with one of the floors of the structure, said leveling means comprising means including a motor for moving the elevator platform relative to the one floor, a direction and speed control device for controlling movement of; the motor, a magnetically-sensitive impedance device mounted for movement with the platform, magnetizable means at said one floor cooperat" ing with said impedance device for altering the impedance of the impedance device as the platform moves, means responsive to a predetermined impedance of the impedance device for causing said direction and. speed control device to control the motor energiaation to produce movement of the platform towards the one floor, said last-named means being responsive to changes in impedance of said impedance device as the elevator platform moves for causing said direction and speed control device to continua1- ly reduce the speed of said motor as the elevator platform moves towards said one floor.

24. In a position responsive system, a structure, a body mounted for movement relative to the structure along a predetermined path, motive means for moving the body in either of opposite directions along the path in accordance with the polarity of an energization supplied thereto, and

control means for energizing the motive means to move the body and for stopping the body at spaced stations along said path, control means comprising a separate control device associated with the structure for each oi said etations, and a control unit including a pickup mounted for movement in accordance with movement of the body, said pickup when the body is at one of the stations being registered with the control device for such station, said control unit including means producing an energization for the motive means which changes in polarity as the pickup passes the control device associated with a station at which the body is to stop, and which increases in magnitude as a continuous function of the displacement of the pickup from the last-named control device for a substantial range of such displacement, the polarity of the last-named energization being selected to energize the motive means to move the towards the station at which it is to stop.

25. A position responsive system as claimed in claim 24 in combination with means producing an output dependent on the deviation of the body from a predetermined speed pattern, and transfer means responsive to a predetermined depar ture of the body from any of said stations for replacing the energization of the motive means derived from said control unit by an energization dependent on said output for regulating the speed of the motive means.

WALTER H. ESSELMAN.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,948,685 Stevens Feb. 27, 193 i

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