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
2002-05-16
2003-10-21
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
C198S330000, C198S572000
Reexamination Certificate
active
06634463
ABSTRACT:
FIELD OF INVENTION
The invention concerns a method and device to control the drive of a conveyor device in the form of an escalator or moving sidewalk, switchable between load operation and no-load operation. The conveyor device comprises a line voltage connection that delivers an essentially constant line frequency, an electric drive motor, especially in the form of an induction motor or synchronous motor, and a frequency changer.
BACKGROUND OF THE INVENTION
A typical conveyor device for personal conveyance in the form of an escalator or moving sidewalk includes a number of closely adjacent steps that are moved by means of a drive motor in the form of an endless belt in the desired direction of conveyance.
To reduce the power consumption and wear of such conveyor devices, a switch has been made to place such conveyor devices in transport movement only when needed, otherwise bringing them to a stop. For this purpose, a transport requirement signal device is provided, for example in the form of a foot mat, light barrier or manually operated switch arranged in front of the conveyor device in the direction of conveyance by means of which the presence of a requirement for transport can be established. If the transport requirement is present, for example, because a person has walked on the foot mat, the conveyor device is placed in forward movement for a predetermined time and switched off again when no further transport requirement has been established within a predetermined time.
To avoid peak loads during frequent engagement and disengagement of the conveyor device, it is known from WO 98/18711 not to switch the drive motor on and off abruptly but to have the speed of the drive motor rise or fall ramp-like during the switching processes. Induction motors are mostly used for such conveyor devices. Since the speed of an induction motor depends on the frequency of the ac power mains, which means constant speed of the induction motor when directly fed from an ac system with constant line frequency, a controllable frequency changer is used with which the line frequency fed to it can be controllably converted to an output frequency different from the line frequency.
The cost for a frequency changer that supplies the drive motor of an escalator or moving sidewalk indeed during load operation would be high, since the costs of the frequency changer rise enormously with the output power that the frequency changer must be able to deliver.
In order to keep the acquisition and operating costs low, WO 98/18711 proposes that the conveyor device only be driven with full transport speed in load operation, and only with reduced no-load speed in standby operation or no-load operation, during which no transport requirement exists, and that the drive motor only be fed from the frequency changer during no-load operation and switching processes, but directly from the line voltage source during load operation. This creates the possibility of laying out the frequency changer much smaller in terms of maximum power, which leads to a significant cost saving relative to a frequency changer whose maximum power is adapted to load operation of the conveyor belt. The conveyor device known from WO 98/18711 then converts to no-load operation, if no additional transport requirement is reported after executing a transport order, and is only shut down when no additional transport requirement is reported for a predetermined time after switching into no-load operation.
With the mentioned measures, a significant reduction of load peaks and abrupt speed changes of conveyor devices is achieved. However, unduly high transient currents can still occur during changing between line feed and frequency changer feed of the drive motor, because of deviations between the line frequency and the output frequency of the frequency changer and their phase positions at the time of switching between line feed and frequency changer feed of the drive motor and because of the actual voltage of the drive motor, which can lead to overloading of the frequency changer and to jerky movement changes of the conveyor device.
Such phenomena are overcome with a method disclosed in the republished previous German Patent Application 199 60 491.6 of the applicant and in which the line voltage and the frequency changer output voltage are compared to each other with respect to frequency and phase position and the frequency changer is controlled at an output frequency that has a predetermined frequency spacing from the line frequency. If a requirement for switching of the conveyor device from load operation to no-load operation or vice-versa is reported by means of a transport signal device, a switching control signal that triggers switching of the drive motor between frequency changer feed and line feed is generated at the time after signaling of this operational switching requirement, at which the output frequency of the frequency changer has both the predetermined frequency spacing relative to the line frequency and also a predetermined phase spacing between the frequency changer output frequency and the line frequency. By not issuing the switching control signal at the time at which the output frequency of the frequency changer agrees with the line frequency both in terms of frequency and phase, but in advance of the time at which the output frequency of the frequency changer has the predetermined frequency spacing relative to the line frequency and has also reached the predetermined phase spacing between the frequency changer output frequency and the line frequency, it is allowed that the switching devices used for switching between no-load operation and load operation, usually contactors, do not operate free of delay, on the one hand, and that, on the other hand, a currentless period is required between dropout of one contactor and pickup of the other contactor in order to avoid shorting of the line voltage through the frequency changer. There is a certain inherent delayed reaction between release of a switching control signal and dropout of the previously conducting contactor and finally pickup of the other contactor, which depends on the specific components of the specific conveyor device and is allowed for by the mentioned frequency spacing and the mentioned phase spacing.
The method described in German Patent Application 199 60 491.6 has proven itself well. However, there are cases in which one would want to get by with lower control costs and this should be achieved with the present invention.
SUMMARY OF THE INVENTION
The present invention concerns a method for control of the drive of a conveyor device, especially in the form of an escalator or moving sidewalk, switchable between load operation and no-load operation and having a drive motor and a frequency changer controllable at least with respect to the frequency and phase position of its output voltage, in which the drive motor in load operation is fed with a line voltage with an essentially constant line frequency and in no-load operation with the frequency changer output voltage, the phase difference between the phase position of the line voltage and the phase position of the frequency changer output voltage is determined, the phase position of the frequency changer output voltage is corrected according to the determined phase difference and is therefore brought essentially into agreement with the phase position of the line voltage, and switching is initiated as soon as this agreement is reached.
On the other hand, the invention concerns an electrical control device to control the drive of a conveyor device, especially in the form of an escalator or moving sidewalk, switchable between load operation and no-load operation and having a line voltage connection to supply a line voltage with essentially constant line frequency and a drive motor, having a frequency changer controllable at least with respect to frequency and phase position of its output voltage, a controllable switching device with a load operation switching state, in which the drive motor is coupled to the line voltage connecti
Blechschmidt Gunter
Kocur Michael B.
Mann Michael
Oesterle Robert
Spannhake Stefan
Otiscelecator Company
Salata Jonathan
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