ESCALATOR SERVICE SPEED CONTROL

COMMANDE DE VITESSE POUR ESCALIER MECANIQUE POUR FINS DE SERVICE

English Abstract

Escalator Service Speed Control
Abstract
Reduced running speeds are provided for
servicing an escalator by interposing a service unit
which is essentially a variable-frequency, variable-
voltage converter, between the AC source and the
escalator drive motor.
OT-541

Claims

CLAIMS:
1. A method of providing reduced running speed in an escalator
having an AC drive motor connected to a fixed frequency source
line, comprising the steps of:
temporarily connecting a portable, variable-frequency,
variable-voltage power converter to the drive motor instead of
the fixed frequency source;
wherein the frequency and voltage of the converter may be
adjusted to provide the reduced running speed.
2. The method of claim 1, wherein the step of connecting is
inserting plugs connected to the portable converter into
connectors fitted in the line for disconnecting the source from
the motor and connecting the converter thereto.
3. The method of claim 2, wherein the step of inserting plugs
is also for connecting the source to the converter.
4. A method of retrofitting an escalator for reduced running
speed and of providing said reduced running speed, said escalator
having an AC drive motor connected via a line to a fixed
frequency AC source, comprising:
providing connectors in the line,
wherein said connectors are receptacles for receiving plugs
for connecting a portable, variable-frequency, variable-voltage
power converter to the line so that the drive motor is connected
via the power converter to the AC source, replacing the direct
connection of the drive motor via the line to the AC source for
adjusting the frequency and voltage of the converter to
provide the reduced running speed.
5. An apparatus for servicing or maintaining an escalator
having an AC drive motor connected via a line to an AC power
source characterized in that:
connectors are provided in the line for temporarily
connecting the line to a portable variable-frequency and
variable-voltage power converter for making connections between
the AC power source and the converter as well as between the
converter and the AC drive motor and for disconnecting the
connection between the AC power source and the AC drive motor.

6. A method of servicing, i.e. overhauling or maintaining, an
escalator comprising an AC drive motor and motor drive means
connected to a fixed frequency power source, characterized by:
connecting a portable variable-frequency and
variable-voltage power converter to the drive motor;
disconnecting the motor drive means from the drive
motor: and
connecting the power source to power the power
converter and correspondingly varying the frequency and voltage
of the converter for setting the escalator speed when servicing
the escalator.
7. A method of servicing, i.e. overhauling or maintaining, an
escalator having an AC drive motor conneeted via a line to an AC
power source, characterized by:
providing on the escalator connectors in the line, such
that in connecting the line to another power source and making
connections to said other power source, the connection between
the AC power source and the drive motor can be removed
simultaneously;
connecting an external or portable variable-frequency
and variable-voltage power converter to the line via said
connector so that the drive motor is connected to the power
converter, and the power converter is connected to the AC power
source and powered by the latter, whereby the motor #peed is
controlled by the power converter, and
adjusting the frequency and voltage of the power
converter to correspondingly adjust the desired running speed.
8. A method of servicing an escalator having an AC drive
motor, and a motor drive, connected to a mixed frequency power
source, comprising the steps of:
connecting a portable variable-frequency, variable-
voltage power converter to the drive motor;
disconnecting the motor drive from the motor;
connecting the power source to power the power

converter; and
varying the frequency and voltage of the converter to
control escalator speed when servicing the escalator.
9. A method of servicing an escalator having an AC drive
motor connected via a line to an AC source, comprising the steps
of:
providing connectors in the line, a first connector
being such that in a simultaneous operation the connection
between the AC source and motor can be removed when
connecting an external variable-frequency, variable-
voltage power converter to the AC source via said first
connector,
a second connector being such that a connection is
established between the output of the converter and the drive
motor whereby the motor speed is controlled by the power
converter, replacing the direct connection of the drive motor via
the line to the AC source;
adjusting the frequency and voltage of the converter to
provided a desired running speed.
10. A connection device for retrofitting an escalator for
operability at a reduced running speed, said escalator having an
AC motor connected in a line to a fixed frequency AC source,
characterized by receptacles wherein a portable service unit
comprising a converter and adapted to be inserted by means of
plugs into the receptacles so that the AC source, the service
unit, and the AC motor are connected to each other in this order
for providing the reduced running speed.

Description

Description
Escalator Service Speed Control
Technical Field of the Invention
The invention relates to driving an escalator at
a reduced speed for maintenance and inspection.
Background of the Invention
It is known to drive an escalator at a reduced
"service" speed for inspection and maintenance~ In
one arrangement, the stator of the drive motor is
provided with two windings, one for normal, full
speed operation and one for service speed. Such
systems suffer from high starting currents, high
idling currents, and unfavorable overall efficiency.
Another arrangement is to provide an auxilary, small
motor to drive the escalator at a reduced cpeed.
This arrangement suffers from costly machanical
mounting and additional required maintenance.
Disclosure of the Invention
Therefore, it is an object of the invention to
provide a simple, inexpensive means for driving
e~calators at reduced speed.
According to the invention, a service unit
comprising a rectifier and a variable-frequency,
variable-voltage inverter (in combination designated
OT-541

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a converter), is interposed between the AC source and
the motor of an escalator. The voltage and frequency
outputs of the inverter are set so as to run the
escalator motor at a reduced speedO
S Other ob~ects, features and advantages of the
invention will become apparent in light of the
following description thereof~
Brief Description of the Drawing
The sole Figure contained herein is a schematic
block diagram of the invention.
Best Mode for Carrying Out the Invention
Variable-voltage, variable-fre~uency inverters
are readily available for controlling motor speeds~
An example is the LENZE TM 750_ series Gate Turnoff
(GTO) type inverters, which are available from Lenze
GmbH & Co, Aerzen 2, Hans-Lenz-Strasse 1 r FRG.
The Figure shows the service unit 10 of this
invention connected in the power line for an
asynchronous escalator motor 12. During normal
operation, an AC source 14 suplies power on a line 16
to the motor 12. (For descriptive ease, only one of
the three phase power lines is shown.)
Connec~ors 18 and 20 are fitted in the line 16
The connector 18 is of the interruptive (normally
closed) ~ype, so that when corresponding plugs 22 and
24 are inserted therein (as indicated by the dotted
lines~, the direct connection between the AC source
and the motor is replaced by a connectioll through the
service unit, so that all power to the motor flows
through the service unit.
.,

~3~32~
A rectifier 26 in the service unit first
converts the AC from the source to DC, and then
converts it back to AC in an inverter 22, whereupon
it is provided to the motor. An inverter, such as
the aforementioned LENZE 756, has a built-in
controller 30, which varies the frequency and voltaga
of the inventer output by use of pulse-width
modulation according to the setting of a set value
potentiometer 32. The variable-frequency, variable-
voltage output of the service unit ~ill affect themotor speed accordingly. The combination of a
rectifier and an inverter as shown is termed a
converter.
For servicing an escalator, a serviceman would
simply plug-in the service unit, w~ich has been
preset ~factory adjusted), or which can be field-
adjustable, to cause the motor to run at reduced
speed.
The advantages of a service unit as described
above are numerous~ Service speed can be adjusted to
any value, from approximately 5 percent to 100
percent of rated motor speed. Low starting currents
are required. Retrofitting existing escalators
simply requires installing appropriate connectors
therein (and disconnecting existing service speed
devices). There are no mechanical parts involved
and, perhaps the greatest advantage of all is that
only one service unit is required to service numerous
escalators, one at a time, or one for a single metro
station e.g.

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It should be understood that various
modifications may be made to the invention without
departing from the spirit and scope thereof.
What is claimed is:

Representative Drawing