GB2437949A

GB2437949A - Electromagnetic retarder for passenger platform hoist

Info

Publication number: GB2437949A
Application number: GB0609233A
Authority: GB
Inventors: Michael Godwin
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-05-10
Filing date: 2006-05-10
Publication date: 2007-11-14
Also published as: WO2007129105A1; GB0609233D0

Abstract

The means of providing a passenger hoist for evacuation from any level in any building for example wheelchair persons and impaired mobility persons with or without carer is one form of this present invention that provides the essential component to safely control the speed of ascent or descent of a simple platform hoist. Attached to the platform or counterweight is the linear tuned electro-magnetic generator retarder which is guided in a stationary magnetic track alongside the platform or counterweight. Speed is 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 force that retards the platform or counterweight against the force of gravity created by the imbalance of a load comprising of a wheelchair person or impaired mobility person and carer etc.

Description

Passenger Platform Hoist

I. Field of Invention

The present invention relates generally to any type of roped and counterweighted hoist in it's simplest from e.g., hand powered and without any additional supply of energy to raise or lower a load carrying platform dependent only upon the bias of it's counter weighting. i.e., platform heavy and counterweight light DOWN travel, counterweight heavy platform light UP travel.

II. Description of the Prior Art

Typically such hoists are controlled manually by friction force and are restricted to light loads for materials and goods and are not considered safe enough passenger transportation, however 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 a simple platform hoist becomes a safe means of moving passengers from one level to another.

IlL Summary of Invention

The present invention is directed towards providing means of evacuating impaired mobility persons in wheelchairs from any level in a building safely to ground level in the event of an emergency.

In this 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 he less than the gross weight of the platform plus wheelchair person plus carer and hence when mechanically released the platform must descend under gravity causing the generator retarder(s) to move relative to the magnetic track(s). At the lowest level the platform being mechanically locked whilst any exit door is open and the carer having delivered the wheelchair person now returns to the platform closes the door and releases the detent. Being lighter than the counterweight the platform travels

I

upwards to any level selected and the carer now repeats the evacuation procedure until all wheelchair persons are sale at ground level. The present invention uses the potential energy [mgh} of either platform or counterweight whichever is heaviest to cause movement the resultant speed of which is uniquely controlled by the tuned linear electro-magnetic AC generator retarder attached to either platform or counterweight or both, moving relative to the magnetic track.

Brief Description of Drawings

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

Figure 2 Shows 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 the simple LCR series circuit that comprises the linear tuned generator retarder.

Figure 4 Shows a typical retarding force diagram as the frequency/speed of platform approaches resonance.

IV. Detailed Description of Preferred 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 preferred embodiment of the invention and are not intended to limit the invention thereto. The figures collectively and individually illustrate the application of a AC linear tuned electro-magnetic generator retarder to control a passenger platform hoist according to the present invention generally referenced 10 and its components.

As illustrated in Figure 1 a simple hoist 11 according to one embodiment of the invention is depicted. The platform 1 2 is shown about to travel upward with one person load and another view [b} about to travel downward with a wheelchair person load 13 and carer.

The fixed magnetic track 14 extends the full travel of the platform with the generator retarder 15 securely fixed to the platform guided between the permanent magnets.

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 with its speed controlled by the generator retarder 15.

The wheelchair person and carer exits at the bottom and the carer returns and steps on to the platform releases the detent 17 and duly ascends on the platform 12 being lighter than the counterweight 16 which descends from the top. The operation can be repeated until all wheelchair persons have been evacuated. The operational speed of the passenger hoist would be in the range of 0.2 -0.63 rn/s so that stopping at any intermediate floor in the UP direction can be almost instantaneous. 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 1 8 which is secured to the platform hoist consists of a coil which possesses inductance and a capacitor 19 which 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 must produce a current that flows round the series circuit Figure 3 passing through the coil of inductance L 23 and resistor R 24. Clearly any current flowing through the coil 23 in a magnetic field must according to Lenzs Law produce 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. The steepness 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 5 00mm section of linear tuned electro-magnetic generator/retarder.

Claims

VI. Claims 1) 1 claim a means of safely controlling the ascent or

descent speed of any simple hoist where any motion caused by the force of gravity due to any imbalance of the platform with respect to its counterweight is noiselessly controlled in its velocity by the action of an attached linear tuned AC electro-magnetic generatorretarder coupled via an air gap to a stationary magnetic track so ensuring that for varying loads a substantially constant velocity is safely maintained as determined by the Q value of the generator retarder series tuned circuit operating near resonance 2) A platform with velocity control as claimed in claim 1 that can serve many levels.

3) A platform with velocity control as claimed in c]aim 1 that uses the weight of the linear tuned generator(s) as part of the counterweight to offset the weight of any platform.