Conveyors: power-driven – Conveyor or accessory therefor specialized to convey people – By stairway having steps forming an endless member
Reexamination Certificate
2002-05-16
2004-08-31
Matecki, Kathy (Department: 3651)
Conveyors: power-driven
Conveyor or accessory therefor specialized to convey people
By stairway having steps forming an endless member
C198S324000, C198S322000
Reexamination Certificate
active
06782989
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a process and device for controlling the drive mechanism of a conveyor system in the form of an escalator or passenger conveyor which can be switched between load and no-load operation. The conveyor system comprises AC line voltage terminals, an electric drive motor, specifically, in the form of an induction motor or synchronous motor, and a frequency converter.
BACKGROUND OF THE INVENTION
A typical conveyor system for the transportation of passengers in the form of an escalator or passenger conveyor includes a plurality of closely adjacent running plates in the form of a continuous belt which are moved with the aid of the drive motor.
In order to reduce the power consumption and wear and tear on these types of conveyor systems, methods have been developed in which the conveyor movement of such conveyor systems is activated only when conveyance is required, while bringing the system to a stop otherwise. For this purpose, a device signaling the need for conveyance, for instance, in the form of a step mat which is arranged in the direction of conveyance in front of the conveyor system, an on/off photocell control device, or a manually operated switch, is provided, by means of which the presence of the need for conveyance can be determined. If a need for conveyance exists, for instance, because a passenger has stepped onto the step mat, the conveyor system is set in the conveyance motion for a predefined period of time and turned off again if no further need for conveyance has been detected within a predefined time period.
Preventing the abrupt turning on and off of the drive motor during frequent starting and stopping of the conveyor system to avoid peak loading by instead allowing the rotational speed of the drive motor to ramp up and ramp down is known in the prior art from WO 98/18711. Induction motors are predominantly used for these types of conveyor systems. Because the rotational speed of an induction motor, which depends on the frequency of the alternating voltage supplied to it, will be constant when it is directly supplied from an AC line with constant line frequency, an adjustable frequency converter is employed so that the line frequency supplied to it can be converted into a different output frequency.
The cost of a frequency converter which supplies the drive motor of an escalator or passenger conveyor under load is high because the cost of the frequency converter increases in direct proportion to the output power the frequency converter is capable of delivering.
In order to lower acquisition and operating costs, WO 98/18711 stipulates that the conveyor system be driven with full conveyance speed only under load but that in stand-by or in no-load operation, when no conveyance need exists, it is only driven at reduced, no-load speed, and that the drive motor will be supplied by the frequency converter only under no-load operation and changeover processes, while, however, under load, it will be supplied directly by the AC power line. This makes it possible to design the frequency converter with a much lower maximum power rating, which results in considerable cost savings compared to a frequency converter whose maximum power rating is matched to the load of the conveyor system. Then, if after carrying out a conveyance task, no further need for conveyance is indicated, the conveyor system known in the prior art from WO 98/18711 initially changes over to no-load operation and is not switched to stop until no new need for conveyance is indicated for a predefined time period after its changeover to no-load operation.
As a result of the measures mentioned, a considerable reduction of peak loads and abrupt changes in the speed of the conveyor systems is realized. However, while the drive motor alternates between being supplied power by the AC line and by the frequency converter, high transient currents may still occur; to be more specific, this is due to deviations between the line frequency and the output frequency of the frequency converter and their phase angles at the time of a changeover between power line and the frequency converter feeding of the drive motor and because of the induced voltage of the drive motor which can lead to overloading the frequency converter and to abrupt changes in the movement of the conveyor system.
Such manifestations have been overcome with a process which was disclosed in the subsequently published previous German Patent Application 199 60 491.6 of the applicant and in which the line voltage and the frequency converter output voltage are compared with respect to frequency and phase angle, and the frequency converter is controlled to an output frequency that exhibits a predefined frequency spacing from the line frequency. If a need for a changeover of the conveyor system from load to no-load operation or vice versa has been signaled by means of a conveyor signaling device, a changeover control signal which triggers the changeover of the power supplied to the drive motor by the frequency converter feeding and the power line is generated at that point in time after the need to switch operating modes has been signaled, at which point the output frequency of the frequency converter both exhibits the predefined frequency spacing with respect to the line frequency and a predefined phase spacing has been achieved between the output frequency of the frequency converter and the line frequency. By not emitting the changeover control signal at time when the output frequency of the frequency converter matches the line frequency, with respect to both frequency and phase, but instead, “with foresight,” emitting it at time when the output frequency of the frequency converter exhibits the predefined frequency spacing with respect to the line frequency and the predefined phase spacing between the output frequency of the frequency converter and the line frequency have been reached, consideration is given to the fact that switching devices, usually contactors, which are employed for the changeover between no-load and load operations, on the one hand, work without time lags and that, on the other hand, a zero-current period is required between the break of one contactor and the make of the other contactor, in order to avoid short-circuiting the network via the frequency converter. Between the emission of a changeover control signal and the break of the previously leading contactor, and, finally, the make of the other contactor, a certain inherent response time delay exists which depends on the specific components of the specific conveyor system and is given consideration through the aforementioned frequency spacing and the aforementioned phase spacing.
The process described in the German Patent Application 199 60 491.6 has proven to be successful. There are cases, however, in which fewer control expenditures are desired and this is to be realized with the present invention.
SUMMARY OF THE INVENTION
The present invention provides a process for controlling the drive mechanism of a conveyor system which can be switched between load and no-load operation, specifically, in the form of an escalator or passenger conveyor, exhibiting a drive motor and a variable frequency converter which, at least, is controllable with respect to the frequency of its output voltage, wherein, under load, the drive motor is supplied by the line voltage with an essentially constant line frequency, and at no-load, it is supplied with the output voltage of the variable frequency converter, the output variable frequency of the frequency converter, prior to a changeover from no-load to load operation or vice versa, is essentially brought to the line frequency with accurate phase by means of a PLL device, and this changeover is achieved as soon as this phase agreement occurs.
On the other hand, the invention provides electronic control device for controlling the drive mechanism of a conveyor system, specifically, in the form of an escalator or passenger conveyor, which can be switched between load and no-load operation and which comprises an A
Henkel Reinhard
Horbrugger Herbert
Spannhake Stefan
Matecki Kathy
Otis Elevator Company
Sharma Rashmi
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