GB2225679A

GB2225679A - Elevator control apparatus employing electromagnetic brake

Info

Publication number: GB2225679A
Application number: GB8920968A
Authority: GB
Inventors: Masami Nomura
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1988-10-18
Filing date: 1989-09-15
Publication date: 1990-06-06
Anticipated expiration: 2009-09-15
Also published as: GB8920968D0; JPH02110090A; GB2225679B

Abstract

A brake 8 has a brake coil 14 which is deenergized to generate a braking force so as to brake an elevator cage 17, and is energized in response to a start command signal to release the braking force. To coordinate brake and motor operation, current sensing means 21 sense a change in current of said brake coil as based on a change in an inductance thereof after the current has reached a predetermined value, and deliver an actuating signal, when the braking force of said brake is released, to a drive circuit 5 which, when supplied with the actuating signal, feeds electric power to a motor 2 for driving the elevator cage 17. The actuating signal can be used to lower the voltage applied to the brake coil when the braking force of the brake is released (Figs 5 and 8). A fault finding circuit is actuated when a detection signal (6, Fig 2) indicating release of the brake is not obtained on lapse of a time delay provided by a counter (30). <IMAGE>

Description

ELEVATOR CONTROL APPARATUS Background of the Invention: This invention relates to an elevator control apparatus. More particularly, it consists in actuating an elevator control apparatus at the start of an elevator cage under the condition that an electromagnetic brake is reliably operating.

Fig. 9 is a schematic view showing the construction of a conventional elevator system. As shown in the figure, the elevator system comprises a common rotary shaft 1, on which a motor 2, a wheel tQ-be-braked 3 and a sheave 4 are mounted at suitable intervals.

The motor 2 is electrically connected with a motor drive circuit 5, which in turn is connected to a three-phase A.C. power source 7 through the contact 6a of an electromagnetic contactor (not shown). An electromagnetic brake 8 is constructed of a lining 9 which grasps and brakes the wheel to-be-braked 3, a plunger 10 which is attached to the lining 9, a compression spring 12 which is interposed between the plunger 10 and a base 11, a switch 13 which turns "on" or "off" in interlocking with the movement of the plunger 10, and a coil 14 which is wound round the plunger 10. Owing to the force of the spring 12, the electromagnetic brake 8 brakes the wheel to-be-braked 3 by means of the lining 9 through the plunger 10.When the coil 14 is energized by a brake control circuit 15, the plunger 10 is attracted overcoming the urging force of the spring 12, thereby to separate the lining 9 away from the wheel to-be-braked 3 and to release the braking of this wheel. ' Wound round the sheave 4 is a rope 16, one end of which has an elevator cage 17 coupled thereto and the other end of which has a counterweight 18 coupled thereto.

In starting the elevator cage 17, the aforementioned contact 6a and the contact 19a (in Fig. 10 to be referred. to below) of the brake control circuit 15 are closed, whereby the braking by the electromagnetic brake 8 is released, and electric power for generating a rotating torque is supplied from the power source 7 to the motor 2 by the motor drive circuit 5.

Fig. 10 is a circuit diagram of the brake control circuit 15 shown in Fig. 9. That contact 19a of the electromagnetic contactor (not shown) which is closed at the start of the elevator cage 17 but which is open during the stop thereof, the contact 13a of the aforementioned switch 13, and the aforementioned coil 14 are connected in series with one another across the plus (+) and minus (-) of a power source (not shown). The contact 13a is in a closed state in order to connect the coil 14 directly to the power source for the reason that, until the plunger 10 is attracted at the energization of the coil 14 of the electromagnetic brake 8, the coil 14 requires a great current for overcoming the urging force of the spring 12.Subsequently, once the plunger 10 has been attracted, the contact 13a falls into an open state because the attracted state of the plunger 10 can be maintained even with a decreased coil current. On this occasion, a current limiting resistor 20A connected in parallel with the contact 73a is operatively connected to the coil 14, whereby current to flow through this coil is decreased. A resistor 20B connected in parallel with the coil 14 is a coil protecting resistor by which electromagnetic energy having been stored in the coil 14 is absorbed when the coil current is cut off.

In starting the elevator cage 17, the electromagnetic contactor contact 19a is closed, and the coil 14 of the electromagnetic brake 8 is connected to the power source through the switch contact 13a as well as the electromagnetic contactor contact 19a. Thus, the coil 14 is energized to attract the plunger 10, so that. the lining 9 releases the braking of the wheel to-be-braked 3. The motor 2 begins to rotate, and the elevator cage 17 starts smoothly. Since, on this occasion, the contact 13a of the switch 13 interlocked with the plunger 10 opens, the coil current flows from the plus (+) of the power source to the minus (-) thereof via the electromagnetic contactor contact 19a, current limiting resistor 20A and coil 14, and the current to flow through the coil 14 is limited by the current limiting resistor 20A.As a result, the generation of heat by the coil 14 is suppressed, and the consumption of electric power in the coil 14 is also suppressed.

The prior-art elevator control apparatus is constructed and operated as stated above. Therefore, when the elevator cage is to be started, the motor sometimes generates the torque while the braking force of the brake is still acting. In this case, the moment the brake has been perfectly released to lose the braking force, the elevator cage is abruptly accelerated, to incur the problem that the riding quality of the cage is impaired. Moreover, since the switch contact of the brake control circuit is a mechanical contact, inferior touch is intrisically liable to occur, and inferior touch ascribable to the improper adjustment of the contact is also liable to occur. Therefore, the coil current is already limited during the attraction of the plunger. Accordingly, the motor might rotate with the plunger held unattracted, namely, with the lining and the wheel to-be-braked held in touch.In such a situation, the abnormal wear of the lining, etc. will arise, and the brake will fail to work, to cause a serious accident. These lead to the problems that the inspection of the switch contact is always required, and that the maintenance operation of the contact is laborious.

Summary of the Invention: This invention has been made in order to solve the problems mentioned above, and has for its object to provide an elevator control apparatus in which a motor is energized after acknowledging that current is flowing through a brake coil, thereby to smoothly perform a shift from the braking force of a brake to the torque of the motor, and in which the brake current is detected by deciding whether or not a plunger has actually operated, thereby to monitor the braking operation of the brake so as to prevent the burnout of the motor and the abnormal wear of the lining of the brake.

Brief Description of the Drawings: Fig. 1 is a schematic view of the whole construction of an elevator control apparatus according to this invention; Fig. 2 is a circuit connection diagram showing an embodiment of a start control circuit; Figs. 3A thru 3H are diagrams for explaining the operation of the embodiment in Fig. 2; Figs. 4A and 4B are diagrams of current characteristics each showing variation in the coil current of an electromagnetic brake; Fig. 5 is a circuit connection diagram showing an embodiment of a brake control circuit; Fig. 6 is a circuit connection diagram showing an embodiment of applied voltage-lowering means in Fig. 5; Figs. 7A thru 7E are diagrams for explaining the operation of the embodiment in Fig. 6; Fig. 8 is a circuit connection diagram showing another embodiment of the brake control circuit; ; Fig. 9 is a schematic view of the whole construction of a prior-art elevator control apparatus; and Fig. 10 is a circuit connection diagram of a brake control circuit in the prior-art apparatus.

Throughout the drawings, the same symbols indicate identical or equivalent portions.

Description of the Preferred Embodiments: In general, current i flowing through the coil of an electromagnetic brake and the terminal voltage E of the coil (constant in this case) are in the following relation:

where L denotes the inductance of the coil, and R the resistance thereof. The inductance L in Eq. (1) is constant until the plunger of the electromagnetic brake operates, so that the current i obtained from Eq. (1) is expressed by the following yell known equation:

The variation of this current i versus time t becomes as illustrated in Fig. 4A. On the other hand, when the plunger is attracted overcoming the urging force of the spring of the electromagnetic brake, the inductance L changes.That is, the following equation is obtained from Eq. (1):

Here, the differential term of the first term on the right side of Eq. (3) can be rewritten as follows:

where x denotes the dimension of the air gap of the plunger, and L(x) signifies that the inductance L is a function of the dimension x of the air gap.

Accordingly, dt is a speed at which the plunger dt d moves, while d L(x) is a quantity which expresses the change of the inductance L versus the change of the air gap and which becomes a minus value in this case. Consequently, in the case where the plunger is attracted, the variation of the current i becomes as illustrated in. Fig. 4B. More specifically, the current i increases according to Eq. (1) from point 0 to point I, and it decreases from the point I to point II in accordance with Eqs. (3) and (4) in the course in which the plunger is attracted. When the plunger has been fully attracted, the current i gradually increases from the point II in accordance with Eq. (1) which contains the inductance value in that state.

Accordingly, when the change of the current i depicted in Fig. 4B is detected, it can be sensed that the brake has been released.

Fig. 1 is a schematic view of the whole construction of an elevator control apparatus according to this invention, and Fig. 2 is a circuit connection diagram showing an embodiment of a start control circuit.

In Fig. 1, numeral 21 designates a current Sensor which: senses the current i of the circuit of a brake coil 14, and numeral 22 a D.C. power source. In Fig. 2, numeral 23 designates the output amplifier of the current sensor 21, numeral 24 a capacitor which is set so as to detect only the variation component of a voltage, and numeral 25 a signal amplifying transistor which constructs second current detection means together with the capacitor 24. Resistors 26 and 27 are set at optimal resistances so that the transistor 25 may be operated as an amplifier and may be rendered conductive when the output of the output amplifier 23 is not less than a voltage Vk illustrated in Fig. 3A (to be referred to later). Numeral 28 indicates an OR circuit, and numeral 29 an RST flip-flop circuit (hereinbelow, termed "F/F circuit").A counter 30 receives a RESET signal upon the closure of a start command contact 41 in Fig. 1 and counts clock pulses (C/P) since that time so as to deliver a high potential signal (hereinbelow, termed "H signal") when a predetermined value has been reached.

Thus, the counter 30 functions as timer means. An AND circuit 31 functions as a fault finding circuit.

An amplifying transistor 32 functions as first current detection means. Resistors 33, 34 and 35 are set-at optimal resistances so as to operate the transistor 32 when the output of the output amplifier 23 is not less than the voltage Vk. Numeral 36 denotes a NOT circuit, numeral 37 a one-shot multivibrator (hereinbelow, termed "OMV"), numeral 38 an OR circuit, and numeral 39 a NOT circuit. Symbol VB indicates a plus voltage source, and symbol -VB a minus voltage source. Letters a - h indicate the respective points of illustrated positions, the corresponding signals of which are shown in Figs. 3A - 3H. The embodiment constructed as described above operates as follows: When a contact 19a is closed in the same manner as stated in the prior-art example, the brake current i flows.This current i is sensed by the current sensor 21, and a signal shown in Fig. 3A is delivered to the output point a of the output amplifier 23.

As stated in conjunction with Figs. 4A and 4B, the signal corresponds to the case where a plunger 10 has been normally attracted.

More specifically, when the contact 19a is closed at a time to and the voltage of the point a reaches Vk at a time t1 the transistor 32 is rendered conductive, and its output at the point f having been the H signal till then becomes a low potential signal (hereinbelow, termed "L signal").

As a result, the output (point g) of the NOT circuit becomes the H signal as shown in Fig. 3G. Owing to this H signal, the OMV 37 generates the H signal for a short time interval (from the time t1 to a time t2) as shown in Fig. 3H. The H signal of the OMV 37 is directly applied to the set terminal S of the F/F circuit 29, and is applied to the clock terminal T thereof through the OR circuit 28. Thus, the H signal is provided from the terminal Q of the F/F circuit 29 as shown in Fig. 3C.

The voltage of the point a decreases for an interval from a time t3 to a time t4, the interval being the process of the attraction of the plunger 10. Meantime, the transistor 25 is nonconductive, so that the point b produces the H signal as shown in Fig. 3B. Owing to this H signal, the F/F circuit 29 is reset to produce the L signal at the point c. On the other hand, the counter 30 is timed for counting after the closure of the start command contact 41, and it is operated at a time t to produce the H signal at the point d. Since, however, the points c and d are not simultaneously supplied with the H signals, the output point e of the AND circuit 31 does not become the H signal. This signifies that a brake 8 is normal.

Meanwhile, an eiectromagnetic contactor 6 which actuates a motor drive circuit 5 so as to give the command of supplying a motor 2 with electric power for generating a rotating torque is energized for the first time when the point f has the L signal, that is, a start command has been issued, and besides, the point c has the L signal, that is, the attraction of the plunger 10 has been detected. In other words, the electromagnetic contactor 6 is energized after the output of the OR circuit -38 becomes the L signal and renders the output of the NOT circuit 39 the H signal. Owing to the energization, the motor drive circuit 5 is turned "on" through the contact 6a of the electromagnetic contactor 6, whereupon the motor 2 generates the rotating torque.

Thus, the motor 2 is driven at the same time that the brake 8 is released. Therefore, the motor 2 is not turned "on" with the brake 8 working, and the rotating torque is not generated later than the release of the brake 8, either.

Now, there will be described a case where no current flows through the brake coil 14 and a case where the plunger 10 does not operate normally.

First, in the case where no current flows through the brake coil 14, the signal of the point f remains the H signal, the output of the NOT circuit 39 remains the L signal, and the electromagnetic contactor 6 is not energized, so that an elevator cage 17 is prevented from starting. Besides, even when current flows, the signal of the point a continues to increase uniformly after the time t3 as indicated by a broken line in Fig. 3A in the case where the plunger 10 is not attracted. Therefore, the transistor 25 remains conductive, and the point b holds the L signal. Meanwhile, the F/F circuit 29 holds its set status for the reason that it has been set by the output of the OMV 37 to turn the point c into the H signal at the time t1 after which the point b still remains the L signal.Consequently, the point c remains the H signal even after the time t3 as indicated by a broken line in Fig. 3C.

When the output of the counter 30 becomes the H signal at the time t5, the output point e of the AND circuit 31 becomes the H signal as indicated by a broken line in Fig. 3E.

The bad condition of the brake 8 is known from the fact that the point e has become the H signal. On the basis of this signal, the elevator cage 17 is stopped, and the bad condition of the brake 8 is notified to a protective device (not shown), whereby any accident attendant upon the bad condition of the brake 8 can be prevented from occurring.

Moreover, since the point c does not become the L signal, the electromagnetic contactor 6 is not energized. Accordingly, when the brake 8 is not released, the motor 2 is not started, and hence, it does not burn out.

The above embodiment has been described as energizing the motor 2 after the release of the brake 8. In this case, the generation of the torque by the motor 2 involves some delay from'the point of time of the energization. When, in anticipation of the delay component, the motor 2 is energized at a proper timing which precedes the release of the brake 8, a period of time to be expended from the issue of the start command till the actual start of the elevator cage 17 can be-shortened, and besides, a shift from the braking force of the brake 8 to the torque of the motor 2 can be smoothly effected.

By way of example, in the circuit arrangement of Fig. 2, the electromagnetic contactor 6 is directly connected to the point g and is actuated by the conduction of the transistor 32 so as to energize the motor 2. Moreover, the time t1 at which the transistor 32 becomes conductive is adjusted so that, when the motor 2 is energized at the time t1 it may produce a torque just corresponding to a load at the time t4 at which the braking force becomes null. Thus, a prompt start can be attained in addition to a smooth start.

In the embodiment described above, the brake coil 14 is excited with direct current. However, the excitation of the brake coil 14 with alternating current can be similarly applied by sensing decrease in the excitation current which decreases as the plunger 10 is attracted. By way of example, the circuit arrangement shown in Fig. 2 can be diverted in such a way that the sensed result of the current sensor 21 is rectified and converted into direct current.

Fig. 5 is a circuit diagram showing an embodiment of a brake control circuit. In this brake control circuit 15, the contact 19a of an electromagnetic contact 19, the coil 14, and a semiconductor switching element, for example, the collector-emitter circuit of a power transistor 42 are connected in series across the plus (+) and minus (-) of a power source (not shown). A flywheel diode 43 is connected in parallel with the coil 14. This diode is used instead of the coil protecting resistor 20B in Fig. 10, and it improves the continuity of the coil current. The series circuit mentioned above is provided with the current sensor 21 which senses the current flowing through the coil 14.

Applied voltage-lowering means 44 is connected between the current sensor 21 and the base of the power transistor 42. This means 44 subjects the power transistor 42 to a pulse width control, thereby serving to limit the coil current and to lower the applied voltage of the coil 14.

Fig. 6 is a circuit diagram of the applied voltage-lowering means 44 shown in Fig. 5, and Pigs. 7A - 7E are waveform diagrams showing outputs at respective points a - e in Fig. 6. The applied voltage-lowering means 44 illustrated in Fig. 6 comprises a capacitor 45 which transmits only the variation component of the output point a (refer to Fig. 7A) of the current sensor 21 in Fig. 5, a transistor 46 which amplifies the variation component, the base bias resistor 47 and load resistor 48 of the transistor 46, an RST flip-flop 49 which provides the output of the point c (refer to Fig. 7C) corresponding to a variation at the output point b (refer to Fig. 7B) fo the transistor 46, a pulse oscillator 50 which delivers pulses of fixed pulse width (refer to Fig. 7D), a NAND gate 51, and an amplifier 52 which amplifies the output of the output point e (refer to Fig. 7E) of the NAND gate 51 and then delivers an output. The capacitor 45 is connected between the input terminal IT of the means 44 and the base of the transistor 46.

This transistor 46 has its emitter grounded, has its collector connected to a supply voltage +V through the load resistor 48, and has its base connected to the supply voltage +V through the base bias resistor 47. The RST flip-flop 49 has its input terminal T connected to the collector of the transistor 46, and has its output terminal Q connected to one input terminal of the NAND gate 51. The other input terminal of the NAND gate 51 is connected to the pulse oscillator 50, and the output terminal thereof is connected to the base of the power transistor 42 in Fig. 5 through the amplifier 52.

In operation, at the same time that, upon the entry of a cage start command, the motor 2 shown in Fig. 1 is connected to a three-phase power source 7 through the motor drive circuit 5, the electromagnetic contactor contact 19a shown in Fig. 5 is closed, and current begins to flow through the coil 14 (refer to Fig. 7A). At this point of time tot the output of the point c of the flipflop 49 in Fig. 6 is at a low level as seen from Fig. 7C. Accordingly, the output of the point e of the NAND gate 51 and the output of the amplifier 52, namely, the base input of the power transistor 42 become a high level, which renders the power transistor 42 conductive. As a result, the coil current increases as seen from Fig. 7A, and the attractive force of the plunger 10 overcomes the urging force of a spring 12, so that the plunger 10 moves. When the plunger 10 moves, the coil current changes abruptly as illustrated in Fig. 7A in the manner stated before, and hence, the output of the point b of the transistor 46 becomes a pulseshaped output as shown in Fig. 7B. When the pulseshaped output is impressed on the input terminal T of the flip-flop 49, this flip-flop 49 changes-over the output of the output point c from the low level to the high level and applies the high level output to one input terminal of the NAND gate 51. In consequence, the output of the point d of the pulse oscillator 50 having been applied to the other input terminal of the NAND gate 51 is validated, and the output of the point e of the NAND gate 51 becomes recurrent pulses of the high level and low level. These pulses are amplified by the amplifier 52, and are thereafter input to the base of the power transistor 42.Therefore, the power transistor 42 is repeatedly turned ON and OFF, whereby an average voltage to be applied to the coil 14 is lowered, and the current to flow through the coil 14 is limited.

Fig. 8 is a circuit diagram showing another embodiment of the brake control circuit. Likewise to the foregoing brake control circuit 15 in Fig. 5, the brake control circuit 15 of this embodiment employs the electromagnetic contactor contact 19a and the coil 14 which are connected in series across both the terminals of the power source.However, this embodiment differs from the foregoing embodiment in the point of replacing the power transistor 42 with a first rectifier circuit 53 which is constructed of a hybrid bridge including semiconductor switching elements, for example, thyristors and diodes, as well as a high-voltage A.C. power source HV which is connected on the input side of-the first rectifier circuit 53, and a second rectifier circuit 54 which is constructed of a bridge including semiconductor elements, for example, only diodes, as well. as a low-voltage A.C. power source LV which is connected on the input side of the second rectifier circuit 54. In addition, the applied voltage-lowering means 44 is connected between the current sensor 21 and the gates of the thyristors in the first rectifier circuit 53.

With the brake control circuit 15 Thus constructed, in starting the ëlevator cage 17, the applied voltagelowering means 44 ignites the thyristors in the first rectifier circuit 53, and the electromagnetic contactor contact 19a is closed. Then, a coil current flows through a series circuit which extends from the high-voltage A.C. power soruce NV via the first rectifier circuit 53, electromagnetic contactor contact 19a, coil 14 and fi-rst rectifier circuit 53 back to the high-voltage A.C. power source HV. Subsequently,.when the plunger 10 is attracted and the current sensor 21 senses the changes of the coil current, the applied voltage lowering means 44 extinguishes the thyristors.On this occasion, therefore, the decreased coil current flows through a series circuit which extends from the low-voltage A.C. power source LV, via the second rectifier circuit 54, electromagnetic contactor contact 19a, coil 14 and second rectifier circuit 54 back to the low-voltage A.C. power source LV, and the voltage to be applied to the coil 14 is lowered.

As described above in detail, according to this invention, the problems of inferior touch and improper adjustments ascribable to a mechanical contact are not involved at all, so that the elevator control apparatus of the invention is high in reliability and meritorious in cost. Moreover, since a so-called chopper system in which a semiconductor device is ON/OFF-controlled is adopted, a large installation space is not required and the problem of heat generation is not involved unlike a current limiting resistor, so that the apparatus can be reduced in size.

Claims

1. fin elevator control apparatus comprising: a brake in which a brake coil is deenergized, thereby to generate a braking force so as to brake an elevator cage, and said brake coil is energized in response to a start command signal, thereby to release the braking force; sensing means for sensing release of the brake and delivering an actuating signal when the braking force is released; and a drive circuit which, when supplied with the actuating signal feeds electric power for generating a rotating torque to a motor for driving said elevator cage.

2. Xn elevator control apparatus comprising: a brake in which a brake coil is deenergized, thereby to generate a braking force so as to brake an elevator cage, and said brake coil is energized in response to a start command signal, thereby to release the braking force; current sensing means for sensing change in a current of said brake coil as based on change in an inductance thereof after the current has reached a predetermined value, and deliuering an actuating signal, when the braking force of said brake is released; and a drive circuit which, when supplied with the actuating signal, feeds electric power for generating a rotating torque to a motor for driving said elevator cage.

3. fin elevator control apparatus according to Claim 2, wherein: said current sensing means is constructed of first, second and third current detection means; said first current detection means delivers a first detection signal when the current flowing through said brake coil has reached the predetermined value; said second current detection means delivers a second detection signal upon detecting the change of the current as based on the change of the inductance of said brake coil; and said third current detection means delivers the actuating signal when both the first and second detection signals are supplied thereto.

4. Rn elevator control apparatus according to Claim 3, wherein said first current detection means includes a transistor which receives the current flowing through said brake coil as an input of its control electrode and which is rendered conductive when the input has reached a predetermined value.

5. Rn elevator control apparatus according to Claim 3 or 4, wherein said second current detection means includes: a capacitor which receives the current flowing through said brake coil at one electrode thereof; a transistor whose control electrode is connected to the other electrode of said capacitor; and a flip-flop which delivers the second detection signal when said transistor is rendered conductive.

6. Rn elevator control apparatus according to Claim 3, 4 or 5, wherein said third current detection means includes: an OR gate which receives as one input thereof the output of said first current detection means and as the other input thereof the output of said second current detection means; and an inuerter which is connected to an output end of said OR gate.

7. Rn elevator control apparatus comprising: a brake in which a brake coil is deenergized, thereby to generate a braking force so as to brake an elevator cage, and said brake coil is energized in response to a start command signal, thereby to release the braking force; second current detection means for detecting change in a current of said brake as based on change in an inductance thereof, and delivering a second detection signal, when the braking force of said brake is released; and a fault finding circuit which is actuated when the second detection signal is not delivered upon lapse of a predetermined time interval after generation of the start command signal.

8. Rn elevator control apparatus according to Claim 7, wherein said fault finding circuit includes: timer means for counting a time interval after the generation of the start command signal, and deliuering a signal upon the lapse of the predetermined time intervals; and an AND gate which receives as one input thereof the ouput of said timer means and as the other input thereof the output of said second current detection means.

9. An elevator control apparatus according to Claim 7 or 8, wherein said second current detection means includes: a capacitor which receives the current flowing through said brake coil at one electrode thereof; a transistor whose control electrode is connected to the other electrode of said capacitor; and a flip-flop which delivers the second detection signal when said transistor is rendered conductive.

10. Rn elevator control apparatus comprising: a brake in which a brake coil is deenergized, thereby to generate a braking force so as to brake an elevator cage, and said brake coil is energized in response to a start command signal, thereby to release the braking force; and applied uoltage-control means for lowering a voltage to be applied to said brake coil, upon detecting change in a current of said brake coil as based on change in an inductance thereof, when the braking force of said brake is released.

11. fin elevator control apparatus according to Claim 10, wherein said applied voltage-control means includes: a transistor which is directly connected to said brake coil; and applied uoltage-lowering means having its output end connected to a control electrode of said transistor.

12. Rn elevator control apparatus according to Claim 11, wherein said applied uoltage-lowering means delivers a pulse signal upon sensing the change of the current of said brake coil as based on the change of the inductance thereof.

13. Rn elevator control apparatus according to Claim 11 or 12, wherein said applied uoltage-lowering means includes: fourth current detection means for delivering a fourth detection signal upon detecting the change of the current of said brake coil as based on the change of the inductance thereof; a pulse oscillator; and a gate which is enabled to pass an output of said pulse oscillator when the fourth detection signal is delivered.

14. Rn elevator control apparatus according to Claim 13, wherein said fourth current detection means includes: a capacitor which receives the current flowing through said brake coil at one electrode thereof; a transistor whose control electrode is connected to the other electrode of said capacitor; and a flip-flop which delivers the fourth detection signal when said transistor is rendered conductive.

15. fin elevator control apparatus substantially as described with reference to Figures 1 to 7 or Figure 8 of the accompanying drawings.