This application claims benefit of priority to Japanese Patent Application No. 11-192224 filed Jul. 6, 1999, the entire content of which is incorporated by reference herein.
1. Field of the Invention
This invention relates to an active magnetic guide system guiding a movable unit such as an elevator cage.
2. Description of the Background
In general, an elevator cage is hung by wire cables and is driven by a hoisting machine along guide rails vertically fixed in a hoistway. The elevator cage may shake due to load imbalance or passenger motion, since the elevator cage is hung by wire cables. The shake is restrained by guiding the cage along guide rails.
Guide systems that include wheels rolling on guide rails and suspensions, are usually used for guiding the elevator cage along the guide rails. However, unwanted noise and vibration caused by irregularities in the rail such as warps and joints, are transferred to passengers in the cage via the wheels, spoiling the comfortable ride.
In order to resolve the above problem, various alternative approaches have been proposed, which are disclosed in Japanese patent publication (Kokai) No. 51-116548, Japanese patent publication (Kokai) No. 6-336383, and Japanese patent publication (Kokai) No. 7-187552. These references disclose an elevator cage provided with electromagnets operating attractive forces on guide rails made of iron, whereby the cage may be guided without contact with the guide rails.
Japanese patent publication (Kokai) No. 7-187552 discloses an electromagnet having a pair of coils wound on an E-shaped core, which guides an elevator cage by a magnetic force. According to this technology, the comfortable ride is provided, the number of components of an electromagnet unit is reduced, the structure is simplified, and the reliability is improved.
However, in the present guide systems for elevators as described above, there are some following problems.
If a guide system is designed so as to strictly trace the guide rails, the cage may shake in response to irregularities in the rail, as a result of which a comfortable ride may worsen. Accordingly, a guide system is designed to support the elevator cage with low rigidity. However, if the cage is supported by a guide system having low rigidity, the guide system requires a large stroke in order to permit a vibration of the cage, since an amplitude of a shake of the cage becomes larger in response to disturbance forces in the guiding direction. In order to control such large stroke by using magnetic force, a gap between an electromagnet and the guide rail should be large. However, if the gap is widened, the effective flux of the electromagnet reduces due to the increase of the magnetic resistance, as a result, a guiding force for the cage remarkably reduces in proportion to the squares of the flux.
According to a magnetic guide system composed of electromagnets, an attractive force operating on guide rails is inversely proportional to the about squares of the gap and is proportional to the about squares of an excitation current. In general, a linear control is widely employed with respect to an attractive force control for an electromagnet. In this case, even if the elevator-cage stops at an appropriate position, the electromagnet is excited in a predetermined excitation current for the following reasons.
Assume that an elevator cage stops at an appropriate position. Properly speaking, it may be thought that an excitation current is set to zero, because a guiding force is not needed. However, since an attractive force of an electromagnet is proportional to the squares of the excitation current, if the attractive force is made a linear approximation on the assumption that the excitation current is zero at a steady state, a coefficient term of an infinitesimal fluctuation of a gap, and a coefficient term of an infinitesimal fluctuation of an excitation current become zero. That is, where f is an attractive force of an electromagnet, x is a gap, i is an excitation current, partial differential terms of the attraction forces with regard to the gap x and the excitation current i, which are ∂f/∂x and ∂f/∂i, become zero. Consequently, it is difficult to design a linear control system.
Further, in order to obtain a satisfactory performance of the linear control system, the ∂f/∂x and the ∂f/∂i have a certain large value. The value is inversely proportional to the gap and is proportional to a magnetomotive force that at is the product of the excitation current and the number of turns of an electromagnet coil. Therefore, the ∂f/∂x and the ∂f/∂i are given appropriate values by increasing the excitation current or increasing the number of turns of the electromagnet coil. Accordingly, in case of a guide system composed of an electromagnet, in order to obtain a guide system having a satisfactory performance and a low rigidity, the electromagnet is excited with a large current in advance or an electromagnet coil having a large number of turns is used.
However, if the excitation current is made large, a cooling system is needed due to generation of heat. Further, if the number of turns of the electromagnet coil increases, the electromagnet become large in size and weight. According to a magnetic guide system composed of an electromagnet, as the magnetic guide system becomes larger, the weight gets heavier. This results in making an entire system of an elevator large, and increasing a cost.
As for a technology for restraining the generation of heat of the electromagnet coil, for example, as disclosed in Japanese patent publication (Kokai) No. 60-32581 and Japanese patent publication (Kokai) No. 61-102105, it is known that a magnetic guide system forms a common magnetic circuit made by an electromagnet and a permanent magnet at a gap between the magnetic guide system and a guide rail. The object of this technology is addressed to balance a gravitational force and an attractive force in the vertical direction of the magnetic guide system, operating on guide rail, since the technology is used for carrying articles with no contact with the guide rail. Finally, the magnetic guide system operates the attractive force on at least one guide rail in only one direction so as to support a weight of a supported material and to equalize a width of the magnetic guide system with the guide rail thereof. The supported material is guided along the guide rail by an allying force operating on the guide rail.
Generally speaking, since a weight of an elevator cage itself is supported by wire cables, it is not required that the guide rail be strong enough to receive more than a force for supporting a horizontal motion of the elevator cage. Therefore, the rigidity of the installation for the guide rails is not always high because of reducing an installation cost of the guide rails. According to an elevator having such feature, if a magnetic guide system operates an attractive force on guide rails in only one direction, the guide rails shift off the installed position. This gives rise to a difference in level at a joint of the guide rail and a deformation, thereby spoiling the comfortable ride.
Moreover, if a gap between the magnetic guide system and the guide rail is widened to reduce an attractive force operating on the guide rail, an allying force of an electromagnet reduces and the guidance by the allying force is hardly expected. In case the guidance by the allying force does not work well, an additional magnetic guide system is required. Consequently, the magnetic guide system becomes larger in size and weight, resulting in a large system for an elevator, and increasing its cost.
Accordingly, one object of this invention is to provide a magnetic guide system for an elevator, which improves a comfortable ride by restraining a shake of an elevator cage effectively.
Another object of the present invention is to provide a minimized and simplified magnetic guide system for an elevator.
Another object of the present invention is to provide a magnetic guide system for an elevator, which may not entail high cost.
The present invention provides a magnetic guide system for an elevator, including a movable unit configured to move along a guide rail, a magnet unit attached to the movable unit, having a plurality of electromagnets having magnetic poles facing the guide rail with a gap, at least two of the magnetic poles are disposed to operate attractive forces in opposite directions to each other on the guide rail, and a permanent magnet providing a magnetomotive force for guiding the movable unit, and forming a common magnetic circuit with one of the electromagnets at the gap, a sensor configured to detect a condition of the common magnetic circuit formed with the magnet unit and the guide rail, and a guide controller configured to control excitation currents to the electromagnets in response to an output of the sensor so as to stabilize the magnetic circuit.