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
1999-02-10
2000-11-07
Salata, Jonathan
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
B66B 506
Patent
active
061422592
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a method for controlling a hydraulic elevator as generically defined by the preamble to claim 1, and to an apparatus for performing the method as generically defined by the preamble to claim 5.
Such controls are suitable for instance for operating an elevator system in which a car in an elevator shaft can approach various positions, such as different floors of a building. The drive of the car is effected by the cooperation of a reciprocating piston, connected to the car, and a reciprocating cylinder which is filled with a pressurized oil. The reciprocating cylinder communicates via a cylinder line with a pump that is driven by a motor. By rotation of the motor and the pump in one direction, pressurized oil can be fed from an oil tank to the reciprocating cylinder, thus moving the car in the upward direction. By rotation of the motor and the pump in the opposite direction, pressurized oil is fed from the reciprocating cylinder into the oil tank, thereby moving the car downward. Because of the weight of the car itself, the pressurized oil in the reciprocating cylinder and in the cylinder line is constantly at a certain pressure.
To control the motion, it is known for instance from U.S. Pat. No. 5,243,154 for a motor rigidly coupled to the pump to be controlled in terms of its direction of rotation and speed of rotation. It is also known to utilize the weight of the car and the resultant pressure in the downward motion in order to drive the pump. Because of the rigid coupling with the motor, the motor acts then as a generator, and the energy generated in the downward motion is either converted to heat or can be fed into the power supply network by a return feed unit. In addition, between the reciprocating cylinder and the pump a valve unit may be present, with which additional influence can be exerted on the flow of pressurized oil between the reciprocating cylinder and the pump.
In the pumps typically used for the aforementioned purpose, leakage is unavoidable.
Leakage is a function of the prevailing pressure. As a result, in upward motion the pump rpm has to be somewhat higher than it would have to be if there were no leakage. As a consequence, whenever the car is to be stopped at a certain position, the pump has to run at a certain rpm, so that it can pump a large enough quantity of pressurized oil to compensate precisely for this leakage. This is known for instance from U.S. Pat. No. 4,593,792.
From U.S. Pat. No. 5,212,951, a generic hydraulic elevator system is known in which the control of the motion of the car is accomplished by a variable-speed motor acting on the pump. With the aid of an electrically controlled check valve, the pressure on the side toward the pump is first adapted, before the onset of motion of the car, to the pressure that prevails on the side of the check valve toward the reciprocating cylinder. Only after this pressure adaptation does the check valve open, so that the motion of the car begins. With this provision, jerky motions on starting up are largely avoided.
From British Patent GB A 2 243 927, a hydraulic elevator system is known in which an electromagnetic control valve is present. Once again, the motion of the car does not begin until the pump pressure exceeds the reciprocating cylinder pressure. Only after this pressure adaptation does the control valve open the communication from the pump to the reciprocating cylinder.
In all these known versions with speed-regulated motors, there is the problem that the motors have a certain rpm elasticity, which is also known as slip. The least possible rpm with full torque and no operational disruption is a function of this slip. Below a thus-dictated limit rpm, the rotational behavior of the motor is unstable, which expresses itself in rpm fluctuations.
The object of the invention is to create an embodiment that takes account of these circumstances such that even at very low speeds, such as the transition to a stop, it makes jerkless travel possible. At the same time, the hydraulic elevator and its control sys
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Bisig Roland
Haussler Hubert
Moser Daniel
Veletovac Sead
Von Holzen Richard
Bucher-Guyer AG
Salata Jonathan
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