Elevator – industrial lift truck – or stationary lift for vehicle – Having specific load support drive-means or its control – Includes control for power source of drive-means
Reexamination Certificate
2000-05-03
2001-11-06
Salata, Jonathan (Department: 2837)
Elevator, industrial lift truck, or stationary lift for vehicle
Having specific load support drive-means or its control
Includes control for power source of drive-means
C187S288000
Reexamination Certificate
active
06311801
ABSTRACT:
TECHNICAL FIELD
This invention relates to an apparatus for controlling an electromagnetic brake of an elevator.
BACKGROUND ART
FIG. 6
is a schematic diagram showing a conventional elevator apparatus similar to the one disclosed in Japanese Patent Application Laid-open No. Hei 2-110090.
As illustrated, in the elevator apparatus, a drive motor
2
, a brake wheel
3
and a sheave
4
that constitute a hoisting machine are attached to a common rotational shaft
1
. The motor
2
is electrically connected to a motor control circuit
5
, and the motor control circuit
5
is connected through a contact
6
of an electromagnetic contactor to a three-phase power source
7
.
An electromagnetic brake
8
is made up of a plunger
10
attached to a lining
9
that effects the brake by clamping the brake wheel
3
, a spring
12
connected between the plunger
10
and a base
11
, a switch
13
opened/closed in association with the motion of the plunger
10
, and a brake coil
14
wound around the plunger
10
.
In the electromagnetic brake
8
, the plunger
10
is depressed by the force of the spring
12
, that is, the lining
9
attached to the plunger
10
is pressed onto the brake wheel
3
, thereby effecting the braking force. On the other hand, if the brake coil
14
is energized through a brake control circuit
15
that controls an electric current flowing in the brake coil
14
, the plunger
10
overcomes the force of the spring
12
, and is attracted, to thereby release the brake wheel
3
.
A rope
16
is hung over the sheave
4
, and one end of the rope
16
is connected to an elevator cage
17
, whereas the other end thereof is connected to a counterweight
18
.
FIG. 7
is a circuit diagram showing the conventional brake control circuits
15
shown in the block diagram of FIG.
6
.
In a brake control circuit
15
a
shown in
FIG. 7
, between a positive terminal (+) of a DC power source (not shown) and a negative terminal (−) thereof, a contact
19
of the electromagnetic contactor (not shown) which is closed at the time of the release of the electromagnetic brake
8
and is open at the time of the operation of the electromagnetic brake
8
, an electric current detector
22
, the brake coil
14
, and a semiconductor switch
20
are connected in series. Also, a flywheel diode
21
is connected in parallel with a serially connected assembly of the electric current detector
22
and the brake coil
14
. Connected to the base of the semiconductor switch
20
is a voltage-drop control circuit
23
to which the output of the electric current detector
22
is inputted to ON/OFF control the semiconductor switch
20
, i.e., to control the coil current through the pulse width control, thereby substantially dropping the voltage applied to the coil.
The brake control circuit
15
a
detects electric current flowing through the brake coil
14
by means of the electric current detector
22
, and controls the brake current using a chopper system in which ON/OFF control is carried out by the semiconductor switch
20
.
Also, in another brake control circuit , between a positive terminal (+) of a power source and a negative terminal (−) thereof, a contact similar to contact
19
shown in
FIG. 7
, a contact of the switch
13
shown in
FIG. 6
, and the brake coil
14
shown in
FIG. 6
are connected in series. Further, a resistor
24
is connected in parallel with the contact
13
a
of the switch
13
, and a resistor
25
is connected in parallel with the brake coil
14
.
In this case, since a large electric current is required to flow through the brake coil
14
to overcome the force of the spring
12
, so the plunger
10
is attracted, the contact
13
a
is in a closed state in which the brake coil
14
is directly connected to the power supply. However, it switches to an open state using such a characteristic that once the plunger
10
is attracted, the attracted state of the plunger
10
can be maintained even if the coil current is decreased.
Also, the resistor
24
connected in parallel to the contact
13
a
serves as a current limiting resistor that limits the current flowing the brake coil
14
when the plunger
10
is attracted and the contact
13
a
is open. The resistor
25
connected in parallel with the brake coil
14
serves as a coil protection resistor that absorbs the electromagnetic energy stored in the brake coil
14
when the coil current is interrupted. The brake current is controlled by the electromagnetic contactor
13
a
and the current limiting resistor.
In either of the above-mentioned types shown in FIG.
7
and described at the time of the brake attraction, the DC power source is directly connected to the brake coil
14
to cause a large current to flow therein. This generates a large energized magnetic force, thereby achieving the immediate brake release (pick-up). Once the brake is released, the voltage applied to both ends of the brake coil
14
is dropped by the action of the semiconductor switch
20
or the resistor
24
so as to limit the current flowing in the coil, thereby attracting and holding the brake. Consequently, it is possible to suppress the heat generation of the brake coil
14
as well as to reduce electric power consumption of the coil.
However, in the case where a only single system of the DC power source is provided as a control power source, and the power source cannot supply a required and sufficient high voltage for immediately releasing the electromagnetic brake, the conventional brake control circuit cannot release the brake immediately and, at worst, never releases the brake (plunger is not attracted), and therefore the elevator can not be driven.
In particular, since the recent tendency in elevators is also directed toward down-sizing and low electric-power consumption of the control apparatus, it is difficult to provide various control power sources using large-size commercially available transformers in accordance with needs as in a conventional fashion. Further, since the control voltage is made lower, the above-noted problem is unavoidable.
Further, the detailed description of the invention will be given below.
The control apparatus for an elevator is conventionally constructed of a large number of relays so as to be controlled by the relay-sequence. Therefore, the voltage used in the apparatus is relatively made high on assumption that the voltage enough to operate electromagnetic coils is to be supplied thereto. Further, since the hoisting machine is operated by the action of an electromagnetic coil, the brake of the hoisting machine has also been driven with the same voltage of the power source.
However, as the electronic technology for the control apparatus advances to replace the relay-sequence control with the computer control, its control voltage becomes low. Accordingly, if an electromagnetic coil for the low voltage is used, then the coil current at the time of attraction becomes relatively large, to thereby cause the voltage drop in a current supply line to the coil becomes large. Further, such a power source device as to have a large current capacity is required. In some cases, the attraction is liable to be difficult.
Furthermore, in the case where the voltage applied to the brake coil
14
is low, the flowing current is small and the attracting force is also low, thereby causing the motion slow and deteriorating the controllability. For this reason a separate power source remains to be provided for the brake coil. However, currently, since the most of the circuits are made electronic, it is required to eliminate the kinds of power sources.
The present invention has been made in view of the above, and therefore has an object of the present invention to provide a brake control apparatus for an elevator, which, in association with a tendency that the power source becomes lower in voltage, even if it is not provided with a power source having a high voltage that is necessary and sufficient at the time of the brake release, and even if it is provided with only one DC power source, can realize the brake release
Takagi Hiroyuki
Yamakawa Shigeki
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