HOIST ASSEMBLY WITH ELECTROMAGNETIC GENERATOR

Field

The present invention relates generally to a hoist or hoist assembly, in particular to any type of roped and counterweighted hoist, for example a simple hoist such as a hand powered hoist which does not have an additional supply of energy to raise or lower a load carrying member or hoist platform, the hoist being dependent only upon the bias of its counter weighting, in which platform heavy/counterweight light produces down travel of the platform, and counterweight heavy/platform light produces up travel of the platform.

Background

Typically simple hoists are controlled manually by friction force and are restricted to light loads for materials and goods and are not considered safe enough for passenger transportation.

The present invention is made with this in mind.

Summary of Invention

According to an aspect of the invention, there is provided a hoist assembly comprising a platform, a counterweight and a generator retarder system which comprises a generator retarder and a magnetic track, the generator retarder system being connectable to the platform or counterweight so that the generator retarder is able to generate a retarding force as the generator retarder moves relative to the magnetic track to control the ascent or descent speed of the platform.

The generator retarder can be connected to the platform and the magnetic track can be fixed so that the platform and generator retarder can move relative to the track.

The generator retarder can comprise an LCR series circuit.

The speed can be controlled using the Q value of the generator retarder.

According to another aspect of the invention there is provided an exit system for a building comprising the hoist assembly.

According to another aspect of the invention there is provided a method of using a hoist assembly comprising a platform, a counterweight and a generator retarder system which comprises a generator retarder and a magnetic track, the method comprising: connecting the generator retarder system to the platform or counterweight; and controlling the ascent or descent speed of the platform by using the generator retarder to generate a retarding force as the generator retarder moves relative to the magnetic track.

According to another aspect of the invention there is provided a method of exiting a building using a hoist assembly comprising a platform, a counterweight and a generator retarder system which comprises a generator retarder and a magnetic track, the method comprising: moving onto the platform at a non-ground floor level of the building; and descending to ground level on the platform as the platform descends under the control of the generator retarder which generates a retarding force as the generator retarder moves relative to the magnetic track.

Accordingly, one or more embodiments can provide an improved hoist assembly.

One or more embodiments can safely control the speed of ascent or descent of a simple platform hoist.

One or more embodiments can provide means of evacuating impaired mobility persons in wheelchairs from any level in a building safely to ground level in the event of an emergency. By the attachment of a fail-safe electro-magnetic retarder using the principal of a tuned linear AC generator moving in a stationary magnetic track in one embodiment a simple platform hoist becomes a safe means of moving passengers from one level to another.

In one example a lightweight platform is loaded with a wheelchair person and carer and attached to it is a linear AC tuned generator retarder guided in a stationary magnetic track. The counterweight is roped to the platform and is of such a value to be less than the gross weight of the platform plus wheelchair person plus carer and hence when mechanically released the platform descends under gravity causing the generator retarder(s) to move relative to the magnetic track(s). At the lowest level the platform is mechanically locked whilst any exit door is open and the carer having delivered the wheelchair person can now return to the platform, close the door and release the lock/detent. Being lighter than the counterweight the platform travels upwards to any level selected and the carer can now repeat the evacuation procedure until all wheelchair persons are safe at ground level. One or more embodiments of the invention can use the potential energy [mgh] of either platform or counterweight whichever is heaviest to cause movement, the resultant speed of which can be uniquely controlled by the tuned linear electro-magnetic AC generator retarder which is attached to the platform, the counterweight or both, and which can move relative to the magnetic track to generate a retarding force.

Brief Description of the Drawings

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows an overall view of an embodiment of the invention showing a passenger hoist with the carer about to ascend [a] to collect another wheelchair and another view showing a wheelchair on the platform about to descend [b].

Figure 2 shows, for an embodiment of the invention, a fixed magnetic track complete with permanent magnets with a view of the linear tuned AC generator retarder situated between the permanent magnets and free to move up or down with the platform.

Figure 3 shows a simple LCR series circuit that comprises the linear tuned generator retarder of an embodiment of the invention.

Figure 4 shows a typical retarding force diagram as the frequency/speed of platform approaches resonance for an embodiment of the invention.

Detailed Description of Particular Embodiments

In the following description like reference characters, designate like or corresponding parts throughout several views. Also in the following description it is to be understood that such terms as forward rearward front back right left upwardly downwardly and the like words of convenience are not to be construed as limiting terms.

Referring now to the drawings in general illustrations are for the purpose of describing a particular embodiment of the invention and are not intended to limit the invention thereto. The figures collectively and individually illustrate the application of an AC linear tuned electro-magnetic generator retarder to control a passenger platform hoist according to an embodiment of the present invention generally referenced 10 and its components.

Figure 1 illustrates a simple hoist 11 in accordance with one embodiment of the invention. In view [a] the platform 12 is shown about to travel upward with a one person load and in the other view [b] the platform is shown about to travel downward with a wheelchair person load 13 and carer.

A fixed magnetic track 14 of permanent magnets extends the full travel of the platform with the generator retarder 15 securely fixed to the platform and guided to move between the permanent magnets. As the generator retarder 15 moves downwards relative to the track 14 it generates a retarding force that opposes the force of gravity created by the imbalance of a load comprising for example a wheelchair person or impaired mobility person and carer. For example the platform 13 at the top has a total weight of 400-kg including load and a counterweight of 200-kg. Clearly the platform 13 can only descend, and its speed is controlled by the generator retarder 15 through the retarding force that it generates as it moves down relative to the track 14.

At the bottom the platform is locked in position through a mechanical lock or detent 17.

The wheelchair person and carer exit at the bottom and the carer returns and steps on to the platform releases the detent 17. As the platform is now lighter than the counterweight 16, the carer ascends on the platform 12 and the counterweight 16 descends from the top. The operation can be repeated until all wheelchair persons have been evacuated. The operational speed of the passenger hoist assembly can typically be in the range of 0.2 - 0.63 m/s so that stopping at any intermediate floor in the up direction can be almost instantaneous. The generator retarder can be tuned to produce a retarding force which produces such an operational speed, by for example selecting appropriate components. For example, the speed can be controlled by the choice of inductance and capacitance elements of the series tuned circuit of the linear electro-magnetic generator retarder responsible for generating the retarding force. The components of the generator retarder are described in more detail below with reference to Figures 2-4. Other conventional fail-safe equipment can be added to the hoist to take care of rope breakage etc.

Figure 2 shows a more detailed typical layout of the permanent magnets 20 that are attached to the magnetic track via backing iron 21. The tuned generator retarder 18 which is secured to the platform hoist consists of a coil which possesses inductance (an inductor) 23 and a capacitor 19 which in this embodiment form the generator retarder series circuit shown in Figure 3, including the resistance R of the coil winding. By Faradays Laws of Inductance an EMF will be produced across the coil 18 when it moves up or down in the magnetic field emanating from the permanent magnets via an air gap 22.

This EMF alternates as the coil moves from one polarity to the opposite polarity of the permanent magnets and therefore alternately charges the capacitor 19 firstly with positive voltage and then with a negative voltage. This alternating potential produces a current that flows round the series circuit Figure 3 passing through the coil of inductance L 23 and resistor R 24. Any current flowing through the coil 23 in a magnetic field according to Lenz's Law produces a force that opposes its direction of motion. As the movement of the coil approaches the equivalent resonant frequency of

the L 23 and C 19 their AC resistance approaches zero leaving only the resistance R 24 to limit the current that produces the retarding force to oppose the force of gravity.

Figure 4 shows the build up of the retarder force output that opposes the force of gravity as the frequency/speed of the platform approaches resonance. This can be used to tune the generator retarder. The steepness 25 or Q value of the curve determines the regulation of the speed of the platform as the load increases to produce the maximum operating retarding force of 2000 Newtons for a 500mm section of linear tuned electro-magnetic generator/retarder.

Embodiments of the invention have been described by way of example only and are not intended to limit the scope of the invention. Variations and modifications of the described embodiments may be made within the scope of the invention. For example, the generator retarder can be positioned on the counterweight and a different circuit can be used to generate the retarding force.