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
Patent
1997-07-28
1999-04-20
Nappi, Robert E.
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
187391, B66B 106
Patent
active
058949100
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a procedure for regulating a velocity-controlled elevator drive in which an a.c. motor driving the elevator machinery is controlled by a frequency converter feeding the motor with a controlled frequency and voltage, said elevator drive being provided with devices detecting the load condition of the elevator.
An objective in the control of an elevator in a normal situation is to drive the elevator in such a way that, each time the elevator is operated, it will run through the distance between the starting floor and the target floor as fast as possible. Therefore, the elevator motor is generally so controlled that the acceleration, deceleration and speed of the elevator are in all circumstances as high as the machinery permits without causing inconvenience to passengers. For the control, it is required that the electric network supplying the elevator drive should produce sufficient power in all situations during elevator operation. In normal use, this is generally no problem.
When a disturbance occurs in the supply of power, the elevator will not work in the intended manner. To cope with power failures, elevators are provided with safety equipment enabling the elevator cars to be driven to landings. A longer break in the supply of electricity requires the connection of a reserve power system, which is generally designed to keep about one in four elevators available for use by passengers. In this case, the transport capacity of the elevators is dramatically reduced.
Disturbances may appear in the supply of electric energy even if no actual power failure occurs. The voltage in the electric supply network may fall below the nominal value or the frequency variations may exceed the allowed limits. In such cases, the protective devices used in the electric network and by the consumers of electricity are generally activated when certain preset limit values are reached. In elevator drives, such situations may occur in areas where the electricity distribution network is weak and also during construction when power is supplied by a temporary electricity supply system insufficient in capacity. When the voltage in the network falls, the load capacity of the network is generally reduced, so that a load of normal magnitude will cause an overload on the network, resulting in a further fall in the voltage, activation of protective equipment and break-off of power.
From patent specification U.S. Pat. No. 5,229,558, Kone Elevator GmbH, a solution is known in which the elevator is driven at a lower speed and/or acceleration when the supply voltage falls, correspondingly reducing the power requirement. However, this specification does not take the real power need of the elevator into account, but the transport capacity, i.e. the travelling speed of the elevator is reduced on-the basis of the condition of the electric network.
SUMMARY OF THE INVENTION
The object of the present invention is to achieve a new velocity-controlled elevator drive which works optimally when the network has a limited power supply capacity, e.g. during the use of a reserve power supply. A further object is to achieve a procedure for controlling the elevator motor that does not impose on the network a load exceeding the network tolerance but allows a maximal driving speed in different load situations. The procedure of the invention is characterized in that a power limit is input to the elevator machinery as a reference value and that the speed reference given to the frequency converter is determined on the basis of the power limit and the load condition.
According to an embodiment of the invention, the power limit is given as a relative value in relation to the nominal power of the elevator. According to another embodiment of the invention, the load condition is determined from the measurement signal of the load weighing device of the elevator. In a third embodiment of the invention, the power limit is determined according to the power supply capacity of the network.
With the invention, all
REFERENCES:
patent: 4399892 (1983-08-01), Watanabe
Ekholm Ralf
Lehtonen Timo
Suur-Askola Seppo
Kone OY
Nappi Robert E.
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