US2846026A - Elevator control system - Google Patents

Description

Aug. 5, 1958 Filed Oct. 1, 1956 E. GOTT ET AL ELEVATOR CONTROL SYSTEM Fig4 3 Sheets-Sheet 2 VA as f/zvemors Aug. 5, 1958 E. GOTT ET AL ,0

' ELEVATOR CONTROL SYSTEM Filed Oct. 1, 1956 3 Sheets-Sheet 3 V Fig.9

United States PatentO ELEVATOR CONTROL SYSTEM Eric Gott and Bertil Ulfward, Johanneshov, Sweden, as-

signors to Allmiinna'Svenska Elektriska Aktiebolaget, Vasteras, Sweden, a corporation of Sweden Application October 1; 1956, Serial No. 613,135

Claims priority, application Sweden October 5, 1955 8' Claims. (Cl'. 187-49) This invention relates to an elevator control system having means for influencing the movement of an elevator car, and one object of the invention is to replace the normal control drum or to complete a simple control drum to give a very exact control of the stopping of the car. The most important range of application of the invention is for high speed elevators for substantial heights and for cases where the requirements for exact levelling are very important, but the inventionmay be utilized in all sorts of elevators or hoisting arrangements, such as mine hoists etc.

In elevator equipments as heretofore employed the acceleration, top speed and retardation of a car are determined solely by the properties of the hoisting machinery or by the qualities of eventually arranged speed regulators. In order to improve the exactness of the levelling, the hoisting machinery usually has been so arranged that the slow-down is performed in two steps, viz. first a retardation down to a low levelling speed and then a mechanical braking at the landing. The net error in the position of the car in relation to the landing floor has, however, always depended on the error in the means initiating the retardation and the mechanical braking. These means have hitherto usually been mechanically influenced by the movement of the car. Through the arrangement of these contact means in a sort of selector in the machine-house of the elevator, it was possible to obtain simple adjustment and control, but in order to ob tain reasonable dimensions it was necessary to model the movement of the car in a small scale, so that the adjustment has become critical and Wear has influenced the exactness of the levelling. The contact means in some cases have been placed in the elevator shaft, which gives good exactness, but the adjustment has-been ditlicult and dangerous to perform and very time-consuming.

The main object of the present invention is to provide an elevator control system making possible exact levelling and yet requiring only a small space.

A further object of the invention is to provide an elevator control system allowing easy and quick adjustment of the stopping of the elevator car.

A still further object is to provide an elevator control system in which the speed of the elevator car is controlled during the entire slow-down b'eforea landing, so that any prescribed variation of the speed during retardation may be obtained.

Also among the objects is the provision of an elevator control system automatically limiting the top speed of the car during travels between adjacent floors or otherwise to that value, which' in each separate case gives minimum travel time when prescribed limits of retardationand acceleration shall not be exceeded.

In accordance with this invention the elevator control system comprisesa magnetic memory in which a magnetisable material is arranged to move synchronously with the elevator car in relation to a pick-upmeans delivering a voltage dependent upon the time-derivative of the degree of. magnetization; in. the magnestisable material.

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2v passing the pick-up means to meansinfluencing the movement of the elevator car, the desired relation between the position and the movement of the car being stored in the magnetic memory.

A magnetic memory is distinguished from previously utilized arrangements, all of which may be designated as mechanical memories, primarily through the simplicity by which changes in the stored information may be performed and through the small volume needed for the storing of certain information. Through the utilization of a magnetic memory it, therefore, becomes possible to model the movement of the elevator car in a desired scale, which may be larger than 1:1, even at the largest possible elevator heights, and the desiredinformation can quickly and easily be imprinted in the memory after the erection of the entire elevator equipment.

When the movement of the car is modelled in a scale giving satisfactory exactness in the levelling, the larger part of the utilized magnetic memory will be vacant if only information about the initiation of the slow-down process is stored in the memory. In case the capacity of the'memory is utilized to a higher degree, the memory thus can contain much more information than that'which was conceivable in mechanical memories without any increase inthe space needed for the memory. Through the utilization of a magnetic memory it thus becomes possible, for example, to cause the memory to determine the speed of threw at every position during the slow-down process, whereby hitherto unattained traflic economy and exact levelling may be obtained while at the same time, the relay-equipment of the elevator may be simplified.

' The main disadvantages of the magnetic memory are that the information can be taken out only when the pickup means and the actual memory are moving in relation to each other, and that the output voltage from the pickup means usually must be amplified in a vacuum-tube amplifier. The vacuum-tube amplifier always introduces an" unsafe element, but it is always possible to arrange the control equipment in such a way that a fault in the amplifier only involves for instance a premature stop of the elevatorcar' or that the elevator car can move only at the levelling speed. The difficulty in that the magnetic memory cannot indicate the position of the car when it is standing still, can be solved e., g. through providing the elevator with a position indicator that is effective when the car is standing still as well as when it a way that the correct part of the memory may be se-' lectedindependently of the movement of the car, so that knowledge about the position of the car is not required.

The mode of operation of the invention and some of its advantages will be better understood from the following description with reference to the accompanying drawing, in which Fig.1 is a sketch of a normal elevator, Fig. 2 illustrates one form of the magnetic memory, Fig. 3' shows the speed and frequency characteristics of the magnetic memory, Figs. 4 and 7' show schematically two forms of elevator equipments utilizing arrangements according. to the invention, Figs. 5 and 8 show schematically the variations in the magnetization within different parts of the magnetic memory inthe arrangement according to Fig. 4 and Fig. 7, respectively, and Figspo and 9 finally show the speed ofthe elevator car as a functionof the time during a trip for an elevator according to Fig. 4 and Fig. 7, respectively. The designation numerals have the same meaning in all the figures.

In Fig. 1, I-V denote the five stories or landings being served by an elevatorcar which is carried by a cable 12 and is driven by a driving pulley 11, the driving machinery of which is not shown. The cable 12 has a counter-weight 13, and the position of the car in the shaft is indicated, by an arrangement 16, which via a sprocket 15 is influenced by an endless chain 14, which is connected to the car 10, and in the bottom of the elevator shaft passes round a sheave 17. The floor of the machine-room is designated by 19. The arrangement 16 may comprise an ordinary control drum of the mechanical type or an arrangement according to the present invention.

A common type of magnetic memory suitable for the present invention is shown in Fig. 2, in which 20 designates a cylindrical drum, the outer peripheral surface of which contains a magnetisable material, usually iron oxides or other iron compositions, which in fine-grained form is emulsified in a plastic. The drum 20 is provided with a shaft 21, which is journalled in a stand 22 and is connected to the sprocket 15, which is rotated by the chain 14 connected to the car. Immediately adjacent to the surface 20 are placed four pick-up devices 31, 32, 33, 34 the construction of which is well known in magnetic recording technics. The pick-up devices 31-34 are arranged on an arm 27 gliding on a rail 26 and having an internal screw thread engaging a screw 25. The screw is immovable in the axial direction but is rotatably journalled in the stand 22, and is rotated by a gear wheel 24 in engagement with a gear ring 23 on the drum 20. When the elevator car is moving, the chain 14 causes the drum 20 to rotate with its shaft 21, and at the same time the arm 27 is moved parallel to the drum 20, due to the rotation of the screw 25. The result is that each of the pick-up devices moves over a helicalline on the peripheral surface of the drum 20, and the different pickup devices are influenced by different parts of the said surface, so that they may pick up different information. Each pick-up device needs only a millimetre-Wide part of the drum 20, which means that the information to four pick-up devices for a story movement in a normal apartment house is contained in ten millimetre length of a drum having 350 mm. diameter when the modelling scale is 1:1.

The qualities of the magnetic memory are evident from Fig. 3 which shows the relation between the frequency f of the output alternating voltage from a pickup device and the amplitude e of the alternating voltage when the magnetization is changing sinusoidally with constant amplitude along the part of the memory influencing the pick-up device. The graphs 28, 29, correspond to diiferent speeds of the magnetisable material past the pick-up device, in that the graph 29 corresponds to a 50% higher and the graph 30 corresponds to a 10% higher speeds than the graph 28. It is evident from the graphs in Fig. 3 that if the period distance of the variations in the magnetization is increased with the play-off speed, so that the output frequency remains constant, even the output voltage will be constant as long as the speed exceeds a lower limit. This limit equals the speed where the period distance of the magnetization changes becomes so small that the pick-up device no longer is able to analyse the change, and corresponds usually to some kilohertz at 10 cm./sek. play-off speed. Conversely a given magnetization variation will give a frequency and an output voltage increasing with the playoff speed, so that the memory in this respect has the same properties as an alternating current tachometer-generator.

An example of the principal arrangement of an elevator according to the invention is shown in Fig. 4, in which the driving cable 12 of the car and the driving pulley 11 are shown. The driving pulley ll is connected to a driving motor 40 being part of a Ward-Leonard system comprising the field winding 41 of the motor, a generator 42 having a field winding 43 and a driving motor 44. The field winding 41 of the motor 40 is connected to a direct current source, and the field winding 43 of the generator 42 is connected to an automatic regulator 39, which in known manner is arranged to influence the speed of the motor 40 in such a way that the input voltage to the regulator 39 remains close to zero. The regulator 39 is thus in principle only an amplifier. The input voltage to the regulator 39 consists of the difference between the voltage from a tachometer-generator 45, sensing the speed of the car, and a reference voltage from a potentiometer 52. The potentiometer 52 is provided with two terminals 54 and 55, from which a ref erence voltage corresponding to top speed, respectively levelling speed can be taken out via a relay 71 having a changeover contact 73, 72, and it is connected to a stable direct current source having terminals 53 via contact parts 64, 65 and 69, 70 in two relays 61, 66, respectively. The relays 61 and 66 have for their purpose to give the car the correct direction of travel, in that tripping of the one relay corresponds to hoisting, while tripping of the other corresponds to lowering. The difference inthe direction of travel results from the fact that the polarity of the reference voltage is dependent on which of the relays 61, 62 is tripped, and the regulator 39 is arranged to deliver a field current, the polarity of which is determined by the polarity of the input voltage to the regulator. The elevator machinery is further provided with a mechanical brake 46, which is disengaged by a magnet coil 48, which, in series with a breaking contact 50 in a relay 51, is connected to terminals 49.

When the car moves from one floor to another, a contact chain is completed in the relay system of the elevator (not shown), and the terminals 49 and for instance the relay coil 61 will pass current. Thereby the mechanical brake 46 disengages, so that the car can move, and the potentiometer 52 is impressed with a voltage of a certain polarity. At the same time the relay coil 71 is connected to a voltage source via a contact part 62 in the relay 61 and a contact part 76 in a relay 74, so that the reference voltage corresponding to top speed from the terminal 54 of the potentiometer 52 is connected to the input circuit of the regulator 39 by the contact part 72 in the relay 71. As the car in the first instant is standing still, the tachometer-generator 45 gives no voltage, but the input voltage to the regulator 39 is still limited to a value smaller than the reference voltage by means of non-linear impedance means 57, 58, connected between the input terminals of the regulator 39. The current to the non-linear impedance means is limited by a resistor 56. Because of the relatively small input voltage to the regulator 39 in combination with the inertia in the control system, the car will be accelerated smoothly up to top speed, where the voltage from the tachometer-generator 45 becomes equal to the reference voltage. From then on the speed of the car will be constant, because errors in the speed are counteracted by the regulator 39.

The travel diagram of the car is shown in Fig. 6 in which the abscissae designate time t and the ordinate the speed v of the elevator. The movement of the car starts at time to, and at time t the car has obtained its top speed, which then is kept constant until time t when the slow-down to the desired landing shall begin. The moment for the commencement of the slow-down is determined by the position controller of the elevator, which comprises a magnetic memory 20 and a position indicator 82. The magnetic memory 20 is provided with three pick-up devices 31, 32, 33 and is driven by the chain 14 and the sprocket 15. The position indicator 82 is driven by the same chain 14 via a reduction gear 81, and it comprises a movable contact 83 which moves past fixed contacts 821-826 corresponding to thefloors served by the car. Each of the contacts 821-826 is connected to a corresponding contact 841-846 ina register 84 indicating which floors are selected. Usually the contacts 841-846 are contacts on relays which, by means of press buttons in the car or at the floors, are caused to trip to mark the selected floor.

In Fig. 4, the car is at floor I, which is indicated by the movable contact 83 making contact with the fixed contact 821 in. the position indicator 82, and the car must next stop at the landing IV, which is indicated by the contact 844 in the register 84 being closed. The car is accelerated up totop speed in the proper direction as previously explained and the contact 83 in the position indicator 82 moves towards the contact 824. When'this contact-is reached, a circuit is completedfrom the current source 79 through-relay coils 74 and 76 via contacts 844 and 824. Thereby the pickup device 31 is connected via. the contact 78 to an amplifier 35 connected to the relay coil 51, andtherelay 74. trips, so that the circuit from the current source 80 through relay 71 via the contact part 76 is broken; Instead, however, a circuit is completed from the amplifier 36 for the pick-up device 32 through the contact part 75 in relay 74'and the contact part63 in the relay 61 to the relay coil 71.

vA part of the magnetic memory 20 is shown in Fig. 5, in'which. the wavelines indicate the changes in-the magnetization state. The pick-up devices 31-32 are influenced by the informations 310330 and the magnetisable material 20 moves in the present case in the direction of the arrow.

:When the relays 77 and 74 trip, the pick-up device 31' is positioned between the signals 313 and 314, and the pick-up device 32 is influenced by the signal 324. The relay coil 51 is therefore unexcited, so that the mechanical. brake 46 remains disengaged and the signal 322, which is read oh by the pick-up device 32, causes relay 71 to remain excited after the switching. At the time t however, the signal 324 disappears, so that the relay 71 releases and the reference voltage in the input circuit. of the regulator 39 decreases to the value corresponding to levelling speed. The voltage from the tachometergenerator .45 will. thus dominate over the reference voltage so that the regulator 39 forces the car to retard. Because of the nonlinear impedance elements 57, 58 and the inertia in the control system, the retardation is smooth, and the movement changes. as indicated in. Fig. 6 by the graph 85. At the time t the elevator car attains the prescribed levelling, speed and continues with constant speed. At the time t however the pick-up device 31 becomes influenced by the signal 312, which causes the contact 50 on the relay 51 to release andthus causes the mechanical brake 46 to engage. At the same time the voltage is removed from the terminals 49 and from the relay 61. The car stops quickly andremains after. the time t at the desired landing. IV, because the brake 46 is engaged and the reference voltage to the regulator 39 is zero. The arrangements removing the voltage from the terminals. 49 and the relay 61 are for the sake of clearnessleft out on the drawing, but they may for instance. be contacts in at self-locking relay in: series with the breaking magnet 48.

From the above described operation of the arrangement according to Fig. 4 it will be seen that the exactness of the levelling is determined by-the magnetic memory 20, while theposition indicator 82 only indicates when the car comes within a certain range of a landing level. The position indicator 82 therefore may be made with small precision, and it will be understood that it may be substituted by anarrangement for counting the pulses 311, 312 from the magnetic memory, for instance a stepping selector, which is well known intelephone technics. It is further evident from the mode of operation that a tube failure in the amplifier 36, or at opposite travel direction the amplifier 37, would only cause the retardation to the levelling speed to be executed prematurely,.which is no serious fault. Of course even the engagement of the brake 46 may be determined by the time when a signal disappears in the same way as the change-over of the relay 72, and greater safety may thus be obtained.

In Fig. 4, the two pick-up devices 32 and 33 are provided each with one amplifier 36, 37, respectively, which of course is not necessary, as only one amplifier works at a time. It is also unnecessary to let the information 320 and 330 each take up one part of the memory, as they really contain the same signals. The two signals are only displaced in relation to each other a distance corresponding to the distance between the two points where the retardation shall begin for hoisting and for lowering, respectively. The same results may thus be obtained when the information 320 influences both the pick-up devices 32 and 33, but at the same time displace the-two pick-up devices mutually along the helical line carrying the information 320 a distance corresponding to the distance between theretardation points. In Fig. 4 there is only one pick-up device 31 for the signals for the engagement of the brake 46 in that the width of the signals 313, 314 etc. is supposed to be so small that it corresponds only to the reaction time of the brake 46, but it is of course possible to arrange one pick-up device for each direction of travel, if that is desirable.

The arrangement according to Fig. 4 works in principle in the same way as hitherto used arrangements with mechanical memories, and its advantages reside mainly in the compact construction which makes possible a large scale modelling and with great exactness. A presupposi tion for satisfactory exactness in the levelling is that the levelling. travel between the time t and L, is so long that possible errors in the top speed and retardation of the car can be compensated'through variations in the length of the levelling travel. At travel between adjacent floors where the travel time is so short that full speed cannot be attained, the levelling travel will become very' long, if special precautions are not taken. Through better utilization of the capacity of the magnetic memory, these disadvantages, may however, be avoided.

An example of such an. improved arrangement is shown in Fig. 7, where the driving machinery of the elevator inclusive with the regulator 39, the magnetic memory 20 and the position indicator S2 with appurtenant relay equiment of the elevator are the same as in Fig. 4. The most important differences from Fig. 4 are that the change of the travel direction, in Fig. 7, is obtainedthrough pole changing of the conductors connecting motor 40- andgenerator 42, instead of through pole changing of the reference voltage, and that a tachometer-generator is missing. Further, the magnetic memory is provided with four pick-up devices against the previous three. The starting of the elevator takes place as previously in that the terminals 49 and one of the directional relays 61 or 66 are impressed with voltage. At the same time the change-over contact 59 is changed so thatv the reference voltage from the potentiometer is connected in the input'circuit of the regulator 39. The change-over contact 59 may for instance be contact parts on. the relays 61 or 66, but for the sake of simplicity it has been drawn separately.

The voltage from the tachometer-generator (45) has in Fig. 7 been substituted by the rectified voltage from one of. the pick-up devices 32-34. The alternating voltage fromthe Working pick-up device is amplified in an amplifier 38, which may be a normal untuncd amplifier, and fed via. a capacitor 87 and a resistor 88 to a rectifier 89, which is loaded with a resistor 91 and a smoothing capacitor 90. When the elevator car is a great distance from theselected landing, the relay 74 is, as previously, unexcited and the pick-up device 33 is connected to the amplifier 38. As will be seen from Fig. 8, which schematically shows the magnetization state for part of the magnetisable material 20, the pick-up device 33 is infiuenced by a sinusoidally alternating excitation 330 and according to what previously has been said in connection with Fig. 3, the voltage across the resistor 91 will vary with the speed of the car 10 in the same way as the voltage from a tachometer-generator. If the capacity in the capacitor 87 is chosen in a certain way, it is even possible to obtain a quicker increase of the voltage across the resistor 91 than the speed near the normal working point. After the elevator has been started, the speed of the car will increase as described in conjunction with Fig. 4, in that the non-linear impedance 57 limits the control voltage on the regulator 39. When full speed is obtained, the speed will, as previously, be kept constant at such a value that the voltage on the input terminals of the regulator remains close to zero.

When the car approaches the desired landing, the pick-up device 31 becomes connected to the relay 51, and the relay 74 trips and changes the input of the amplifier 31 to the pick-up device 32 if the travel direction relay 66 is connected in. The change-over occurs after the points 313 and 323 on the part 310 respectively 320 of the magnetic memory have been passed, so that the relay 51 remains unexcited in the first instant and no change occurs in the input voltage to the amplifier 38. At the time t however, the distance between the crests of the magnetization in the magnetic memory part 320 begins to decrease the frequency from the pick-up device 32 thus tends to increase, and with the frequency even the voltage increases, so that the regulator 39 must decrease the speed of the car in order to retain the equilibrium between the reference voltage and the voltage across the resistor 91. Because the period distance of the magnetization changes is steadily decreasing, the car is consequently caused to retard in a certain way until a few millimeters from the landing, where the brake 46 is engaged because of the signals 314 through the pick-up device 31. From then on all relays are disconnected as described in conjunction with Fig. 4.

It will be evident that the top speed of the car will have very small influence on the levelling in the arrangement according to Fig. 7 since the speed at every point along the travel of the car is prescribed by the informations in the magnetic memory and no difiiculties when all arise at travelling between adjacent floors. It is even possible to obtain any wanted variation in the retardation through a suitable progress in the variation of the period distance in the magnetization changes in the memory. It is, of course, possible to control even the acceleration in the same way, if that is desirable.

The desired informations can easily be played into the memory after the elevator has been erected, for instance, by providing that the car is positioned in exact level with a landing and then is driven backwards while the wanted signals are played in from a model or the like. Such a registration process can be made quickly and easily in the machine house, and after control possible errors can quickly and easily be corrected.

The forms shown illustrate the execution of the invention only, and the scope of the invention is not limited to these or resembling forms. For instance the relay equipment of the elevator and the speed regulator may be varied within wide limits like the detail-construction of the magnetic memory.

We claim as our invention:

1. Means for controlling the movement of an elevator car, comprising a magnetic memory in which a magnetizable body is constrained to move past at least one magnetic pick-up serving as a reading head, in such a manner that the relative motion between the magnetic reading head and that part of the body passing said reading head is in fixed proportion to the movement of the elevator car, said body being magnetized to con.-

tain information about the movement of the car in such a manner that its residual magnetic flux, in different parts of the body, corresponds to a predetermined correlation between the movement of the elevator car and its position, said movement being controlled by means of the reading head delivering a control voltage which is proportional to the time derivative of the residual magnetic flux to which the reading headis exposed.

2. Means according to claim 1, for controlling the movement of an elevator car, in which the magnetizable body is in the form of a drum having a curved surface which is coated with a magnetic material and said material being magnetized along at least one helical path on said curved surface.

3. Means according to claim 1, for controlling the movement of an elevator car, comprising means for registering the approximate position of the car irrespective of whether or not the car is moving, said means being used to control the magnetic memory.

4. Means according to claim 1, for controlling the movement of an elevator car, in which a plurality of magnetic reading heads are exposed to the residual flux at difierent parts of the magnetizable body, some of said reading heads being used to control the movement of the elevator car in one direction of travel and the other heads being used when the car travels in the opposite direction.

5. Means according to claim 4, for controlling the movement of an elevator car, comprising means for registering the approximate position of the elevator car irrespective of whether or not the car is moving, said means, when the car is within a prescribed distance of the landing, engaging selectively those reading heads exposed to the residual flux in those parts of the magnetized body containing information about the cars approach to the various landings.

6. Means according to claim 5, for controlling the movement of an elevator car, in which the magnetic memory has an alternating voltage output which voltage is fed to an automatic speed regulator which is arranged to control the speed of the elevator car in such a manner that the frequency of the alternating output voltage remains constant.

7. Means according to claim 6, for controlling the movement of an elevator car comprising means whereby that part of the magnetizable body controlling the speed of the elevator car during its travel between selected landings contains a substantially sinusoidally varying residual magnetization whereas that part of the magnetizable body which controls the speed of the car during its approach to a landing contains a periodically varying residual magnetization, the period spacing of which decreases when the elevator car approaches a landing in such a manner that the output voltage from the reading head remains constant when the elevator car decelerates at a prescribed rate.

8. Means according to claim 7, for controlling the movement of an elevator car, comprising an amplifier having a constant gain within a certain frequency range, which amplifier is fed with the output voltage from the reading head exposed to the sinusoidal varying residual flux and which amplifier is arranged to feed its output voltage through a rectifier to a regulator arranged to control the speed of the elevator car in such a manner that the output voltage of said reading head remains constant.

References Cited in the file of this patent UNITED STATES PATENTS 2,474,861 Putt July 5, 1949

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