FR2551043A1 - CONTROL SYSTEM FOR A DRUM LIFTING APPARATUS - Google Patents

Abstract

DRUM LIFTING APPARATUS OF A TYPE WHICH INCLUDES A CAGE 13 ACTUATED BY A MOTOR 1 EXCITED ON A SINGLE PHASE DURING A DESCENT MANEUVER, AND WHICH INCLUDES MORE THAN 14 MEANS FOR DETECTING IF THE ROTATION SPEED OF THE MOTOR ROTATING UNDER THE ACTION OF THE OWN WEIGHT OF THE CAGE DURING A DESCENT MOVEMENT IS GREATER THAN A GIVEN VALUE AND MEANS 3, 4 OF CHANGING THE OPERATING MODE ALLOWING TO POWER THE MOTOR ON A SINGLE PHASE SIGNAL IS SENT BY MEANS OF DETECTION, THE MOTOR IS ONLY SUPPLIED ON A SINGLE PHASE AFTER ITS ROTATION SPEED EXCEEDS THE GIVEN VALUE, SO THAT THE MOTOR CAN CONTINUE TO TURN AND THE LIFTING APPARATUS TO DESCEND DESPITE THE RETENTION TORQUE GENERATED BY EXCITATION ON A PHASE.

Description

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  Control system for drum lifting device.

  The present invention relates to a control system for a drum lifting device, and more particularly to a system of this type capable of preventing a three-phase motor from reaching an equilibrium point where it no longer turns when the lifting device is operated for a downward movement and when the motor is energized in a single phase, this due to a

  torque acting between a rotor and a stator of the motor.

  Such a torque will hereinafter be called "holding torque".

  It has hitherto been proposed to excite the motor of a lifting device in a single phase, when

  maneuver down the cage carried by this device.

  A characteristic of the torque of a three-phase motor excited on a single phase is shown in FIG. 1 It can be seen that the direct or opposite direction of the torque depends on the direction of rotation of the motor. However, a holding torque is generated by the interaction of an alternating magnetic field of the stator with a current 20 of the rotor produced When the engine is turned in

  one or the other direction by exciting it on a phase.

  On the other hand, in a drum hoist, the motor is forced to turn in a certain direction by the force of gravity acting on the cage after the brakes are released. However, when the weight of the cage is low, it can it is relatively difficult to run the motor in the desired direction, even by combining the effect of the gravitational torque and that of the torque due to excitation in a single phase, this because of the friction on the

  engine bearings and associated transmission wheels and friction between the cage and the guide rails which are particularly high when starting the engine.

  The drum hoist can occasionally be used as a hoist for lifting and

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  descend building materials from a building before the elevator shaft is installed In this case, we usually attach a hook to one end of the main cable and a rope to the hook, 5 and an operator pulls the rope to make lower the hook However, for the reasons presented above, a very high force is necessary to pull the rope and bring down the cable when the motor is excited in a single phase This makes it impossible to use the lifting device for handling of these heavy materials An approach to this problem has been carried out, consisting in exciting the motor

  on a phase after pulling on the hook and the rope But this is not desirable because the maneuver becomes complicated.

  The present invention relates to a control system for a drum hoist, in which, when the hoist is maneuvered down, one phase power is supplied to the motor after a brake has been released. and after the rotational speed of the motor has become greater than a certain value, so that the motor can start to run against the holding torque. Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a diagram showing the torque characteristic of a motor excited on one phase; FIG. 2 is a circuit diagram showing an example of a control system for a drum lifting device according to the invention; FIG. 3 is a circuit diagram showing an example of a control circuit according to the invention; and

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  FIG. 4 is a circuit diagram showing an example of application of a drum lifting device according to the invention, for raising and lowering

luggages.

  FIG. 2 shows an embodiment of the control system for a drum lifting device

  according to the invention, o the number 1 designates a three-phase induction motor (hereinafter called "motor").

  The motor 1 is connected by a control system to a three-phase current source 2 The control system comprises a contactor 3 whose contacts 3 a, 3 b and 3 c are connected in series with the wires corresponding to the phases R, S and T respectively, and which connects the motor 1 with the three-phase source 2 Bilateral thyristors 15 4 a, 4 b are connected in series with the lines of the phases R and S, respectively The gate of the thyristor 4 a and the line of the phase R are connected together by contact Aa, normally open, of a relay A which will be described below The number 5 designates a rectifier, whose input contacts are connected by contacts 6 a and 6 b of a contactor 6 to the line of phase S on the one hand, at a point located between thyristor 4 b and contact 3 b, and at the line of phase T on the other hand, at a point located on the side of the source Contacts continuous outputs of rectifier 5 are connected by contacts 7 a and 7 b of a contactor 7

  at contacts 3b and 3c respectively, on the motor 1 side.

  The number 8 designates a drum coupled to the motor 1 The number 9 designates a braking means, disposed between the motor 1 and the drum 8 and comprising a solenoid 9 a capable of applying a braking force when activated The solenoid 9 a is connected by contact 10 a of a switch 10 to a direct current source 11 A cable 12 is wound on the drum 8, the free end of which is connected to a cage 13 The number 14 designates a sensor for speed

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  sensitive to the engine speed 1.

  FIG. 3 shows an embodiment of a control circuit of the control system, which controls the upward or downward movement of the drum hoist. The control circuit comprises an OR gate 20 receiving as inputs a signal UP control command and a DN control command signal The output of the OR gate 20 is connected to the base of a transistor 21 A circuit comprising in parallel 10 the contactor 3 and the switch 10 is connected in series between the collector of transistor 21 and an electrical source V The number 22 designates a comparator comparing a descent speed signal VT coming from a reference speed signal generator (not shown) with a speed signal VS coming from the speed detector 14 The comparator 22 output signal and the DN lowering control signal are applied to an AND gate 23, and the AND gate output signal 23 and the

  UP command are applied to an OR gate 24.

  The output of the OR gate 24 is connected to the base of a transistor 25 The relay A is mounted between the collector of the transistor 25 and the electrical source V.

  The operation according to this embodiment will be described below.

  When the drum lifting device must be maneuvered upwards at a given speed, the OR gates 20 and 24 are applied the up control signal UP, and cause the transistors 21 and 25 to be driven. The contactor 3, the switch 10 and relay A are thus activated and close, on the one hand, the contact Aa of relay A, which fully activates the thyristor 4 a and, on the other hand, close the contact 10 a, which activates the solenoid 9 thus loosens the braking means 9 Then, gradually increasing

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  the ignition angle of the thyristor 4 b until finally activating it completely, the speed of rotation of the meter Q 1 increases and it operates with three supply phases to raise the cage 13 During the deceleration of the cage when it is operated uphill, the contactor 3 is released and the contacts 3 a, 3 b and 3 c open while the contacts 6 a, 6 b and 7 a, 7 b close to provide an electrical voltage continues to motor 1 from rectifier 5, and 10 the ignition angle of thyristor 4 b is controlled so as to generate a variable braking torque, which causes motor 1 to decelerate when cage 13 arrives

on the desired floor.

  When the drum hoist is to be operated downward at a given speed, the

  thyristor 4 b is cut, and only thyristor 4 has driven.

  In this case, the brake is released at the start and after

  the motor 1 has reached a predetermined speed of rotation due to the weight of the cage, the thyristor 4 to 20 is on.

  More precisely, during a descent maneuver, when the descent control signal DN is generated, the OR gate 20 provides an output which makes the transistor 21 conductive. This actuates the contactor 25 3 and the switch 10 so as to close. contacts 3 a, 3 b, 3 c and 10 a Once contact 10 has closed, the solenoid 9 a is energized to release the brake 9 At this time, thyristor 4 a being non-conductive and the other thyristor 4 b being cut when the lifting device is maneuvered down at constant speed

  or accelerated, the motor is not electrically powered.

  Thus, when the brake is released, the motor 1 starts to rotate under the weight of the cage When the speed of rotation of the motor 1, that is to say the speed signal Vs supplied by the speed sensor 14, exceeds

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  the reference value VT, the comparator 22 delivers an output signal lHl The AND gate 23 is actuated by the signal C Hl and the descent control signal DN, and the signal leaving the AND gate 23 is supplied to the OR gate 24 then to transistor 25, making it conductive Relay A is then activated and its contact

  Aa closes, making thyristor 4 conductive.

  When thyristor 4 a is activated, motor 1 is energized on one phase and generates a corresponding torque. In this case, the excitation on one phase of the motor 1 being effective after it has started to rotate under the weight of the cage, its rotation can continue even in the presence of the holding torque, and the cage can descend. FIG. 4 shows an example of an application of a drum lifting device for lifting and lowering construction parts or materials, example in which the hook 15 is attached to the free end of the cable 12, another rope 16 being engaged in the hook 15 In FIG. 4, identical numbers are used to designate components

  identical corresponding to those of figure 2.

  In this embodiment, when the descent control signal is generated by a remote control interrupter, the contactor 3 and the switch 10 are actuated as in the case of FIG. 2, and when the contact 10a closes, the solenoid 9 a is energized to release the braking means 9 In this state, the cable 12 can be pulled by means of the cord 16 to turn the motor 1 When the speed of rotation of the motor 1 exceeds the reference value VT, relay A is actuated This makes thyristor 4 conductive, which excites the motor

  1 in a single phase, and thus the cable 12 can be easily unwound from the drum 8.

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  It will be noted that the speed detector and the means making it possible to switch to an operating mode on one phase of the motor during a descent maneuver are not limited to those described in this embodiment. According to the invention described above, the drum lifting device is designed in such a way that during a descent maneuver, a single-phase electrical supply is supplied to the motor 10 after the brake has been released and after the engine speed has exceeded a predetermined value Consequently, the engine does not lock when stopped even in the presence of the holding torque

  generated by the excitation on a phase, and the operation of the device downhill is ensured.

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Claims (7)

  1 Control system for a drum lifting device in which a three-phase motor (1) coupled to a drum (8) on which a cable (12) is wound, is supplied in a single phase when a cage (13) connected at a free end of the cable is maneuvered downwards, characterized in that it comprises a comparator (22) for comparing the speed of rotation (Vs) of said motor in the direction corresponding to the movement of the cage downwards, with a predefined reference value 10 completed (VT) and for generating a signal when the motor rotation speed exceeds the predetermined value, signal generating means (23, 24, 25, A) capable of generating a signal in response to the signal output of said comparator, and operating mode change means (3, 4) capable of triggering a power supply on a single phase of said motor in response to said signal from said generation means signal.   2 control system for a drum lifting apparatus according to claim 1, characterized in that it comprises a means for releasing (9a, 10a) of the brake (9) responding to an operating command (20, 21 ) allowing to release the brake (9) and   actuating a switch (3) to connect said motor 25 to an electrical power source (2).   3 control system for a drum lifting device according to claim 1, characterized in that the operating mode change means (3, 4) are actuated so as to provide an electrical excitation on three phases to said motor   when an ascent maneuver is ordered.   4 control system for drum lifting device according to claim 3, characterized in that it comprises control rectifier elements (5, 6, 7) connected to two of the phases of a source 9 2551 043   three-phase electric, and in that said operating mode change means can provide a complete commissioning command to one   said control rectifying elements.   5 control system for a drum lifting device according to claim 4, characterized in that said operating mode change means are capable of supplying said complete commissioning command to one of said control rectifier elements when a climb maneuver control signal is present and when said   signal generation means generates a signal.   6 control system for drum lifting device according to claim 4, characterized in that the cage (13) begins its movement by its own weight during a descent maneuver, while none of said control rectifying elements is not commissioned.   7 Control system for a drum lifting device according to claim 6, characterized in that said control rectifier elements, to which are not supplied signals for complete commissioning during a descent maneuver, are kept constantly cut.