EP1375407A1

EP1375407A1 - Safety brake for hoisting device

Info

Publication number: EP1375407A1
Application number: EP03076987A
Authority: EP
Inventors: Jan Boere
Original assignee: LTF Liften BV
Current assignee: LTF Liften BV
Priority date: 2002-06-24
Filing date: 2003-06-24
Publication date: 2004-01-02
Also published as: NL1021599C2

Abstract

The present invention relates to a hoisting device for transporting objects, particularly goods, comprising:

a cage member (3) in which the objects for transporting can be placed, which cage member is displaceable in a shaft (5);
hoisting means (9) mounted on the cage member for hoisting and lowering the cage member in the shaft;
electric drive means (7) connectable to a power supply for driving the hoisting means;

the electric drive means comprising:

one or more electric motors;
one or more capacitors (13);
switch means (12) for connecting the electric motors to the supply voltage when sufficient supply voltage is available, and connecting at least one of the electric motors to at least one of the capacitors when insufficient supply voltage is available, for the purpose of counteracting the downward movement of the cage member.

Description

The present invention relates to a hoisting device for transporting objects, particularly goods. The invention also relates to a method for transporting objects.
Electric goods lifts of the non-counterweight type, i.e. of a type in which no counterweight is arranged on the lift cage to hold the goods lift in balance, are frequently applied for transporting goods. Two types can be distinguished here.
According to a first type the lift cage is displaced using a hydraulic system. A drawback of this type of goods lift is that, when goods of a high weight are placed in the lift cage, the lift cage moves slightly downward, which has the result that the floor of the lift cage is no longer at the same level as the floor.
According to a second type the lift cage is displaced mechanically by means of one or more chains or cables driven with an electric motor. For safety reasons this type of goods lift is usually provided with a brake. This brake has the function of braking the lift when the supply voltage of the lift drive is interrupted or at least falls below a predetermined minimum value. During normal use such a brake is deactivated, whereby the lift can be displaced up and downward in unimpeded manner. When the supply voltage is interrupted, such as for instance as a result of the voltage supplied by the electricity grid being cut off in the case of fire or when the main switch of the lift is switched off in respect of maintenance of the lift, the brake is automatically activated and will thus prevent the lift dropping downward at increasing speed.
In order to release people who are trapped in the lift cage or in order to gain access to goods in the lift cage it is necessary that others, for instance a lift engineer or a fireman, can allow the lift to drop in controlled manner into a so-called release zone of a stopping place at a lower level. This must also be possible if the supply voltage is cut off.
Certainly when people are trapped in the cage of the lift, it is too dangerous to deactivate the brake manually for a short time so as to allow the lift to drop downward. The uncontrolled downward movement of the lift cage occurring here, wherein the downward speed moreover increases sharply within a short time, is dangerous for people trapped in the lift cage or can damage goods stored in the lift cage.
It is the object of the present invention to provide an inherently safer hoisting device for transporting the objects, such as goods, people, animals and the like, wherein the above stated drawbacks of the prior art are obviated.
This object is achieved in a hoisting device for transporting objects, particularly goods, comprising:

a cage member in which the objects for transporting can be placed, which cage member is displaceable in a shaft;
hoisting means mounted on the cage member for hoisting and lowering the cage member in the shaft;
electric drive means connectable to a power supply for driving the hoisting means;

one or more electric motors;
one or more capacitors;
switch means for connecting the electric motors to the supply voltage when sufficient supply voltage is available, and connecting at least one of the electric motors to at least one of the capacitors when insufficient supply voltage is available, for the purpose of counteracting the downward movement of the cage member.

During normal operation the electric motor is energized with the supply voltage which is for instance supplied by the electricity grid. During normal operation the electric motors are thus connected to the power supply and not to the capacitors. When the hoisting device is out of operation, the electric motor is no longer energized but is however connected to one or more of the capacitors. At that moment the lift cage moving downward as a result of gravity drives the electric motor(s) of the drive via the chains or cables. The electric motor(s) then function as a type of "generator". The capacitors are charged by this generator action and at a given moment will begin to counteract the electric motor(s). The downward movement of the lift cage is braked as a result of this counteraction.
The counteraction depends on the rotation speed of the electric motor(s). Above a determined rotation speed the counteracting voltage increases exponentially, whereby the electric motor(s) and the lift cage connected thereto are braked to an increasing extent.
Although a braking function is brought about by connecting the electric motors to the capacitors, it is nevertheless recommended to provide separate braking means for braking the cage member in the shaft, wherein the braking means can be controlled so as to release the cage member when sufficient supply voltage is available and to brake the cage member when insufficient supply voltage or no supply voltage at all is available. The braking means are embodied such that the cage member is brought to a complete standstill when there is no supply voltage on the electric motors. In order to lower the lift cage in controlled manner for placing thereof at the same height as a stopping place at a lower level, the braking means, which are preferably operated manually, can be deactivated by an operative, whereafter the lift cage will displace downward relatively slowly and in controlled manner until it arrives at the correct height in the lift shaft.
In a preferred embodiment the capacities of the capacitors are so high that the lift cage of the hoisting device, at least in the case that too little supply voltage is available and, as the case arises, the braking means are deactivated, reaches a substantially constant downward speed.
The power supply preferably generates a three-phase alternating voltage, wherein at least one capacitor is used for each phase. In the case three-phase alternating voltage is used the capacitors are preferably delta-connected, wherein each of the phase terminals is connected to a corner of this delta connection. Such a connection is relatively simple and inexpensive.
According to a further preferred embodiment the switch is connected in series to the power supply for either connecting the electric motor to the power supply in the first position or connecting the electric motor to at least one capacitor in the second position. This ensures that the capacitors are never simultaneously connected to both the power supply and to the electric motors.
According to another aspect of the invention a method is provided for transporting objects, particularly goods, comprising of:

connecting the electric motor(s) of the hoisting device, preferably a hoisting device of the above described type, to the power supply when sufficient supply voltage is available for hoisting and lowering the cage member;
connecting the electric motor(s) to one or more capacitors for counteracting the descending movement of the cage member when insufficient supply voltage is available. A descent speed protection is hereby realized whereby the hoisting device becomes safer and the chance of damage to the contents of the lift cage is reduced.

The method preferably comprises of adjusting the descent speed of the cage member when insufficient supply voltage is available by modifying the capacitance of one or more capacitors. By adjusting the capacitance at which the electric motor is connected the degree of "counteraction" by the electric motor is also set. This degree of counteraction determines the speed at which the lift cage will displace downward under the influence of the force of gravity.
By modifying the capacitance of the capacitors an operative can adjust the speed of the lift cage as desired, this also depending on the weight of the goods situated in the lift cage at a given moment. In a specific preferred embodiment the capacitors therefore have a variable capacitance which, subject to the requirement, can be set directly by an operative such as an engineer from a position outside the lift cage. At a constant descent speed a relatively high capacitance is required when the lift is relatively heavily loaded. It is possible to suffice with a lower capacitance in the case of a less heavy lift load.
The method preferably also comprises of the above stated setting of the descent speed to a desired value. A (practically) constant descent speed can be realized by correct adjustment of the capacitance of capacitors.
Further advantages, features and details of the present invention will be elucidated on the basis of the description hereinbelow of a preferred embodiment thereof. Reference is made in the description to the annexed figures, in which:
Figure 1 shows a perspective view of a preferred embodiment of a hoisting device according to the invention;
Figure 2 shows a schematic circuit diagram for control of the hoisting device of figure 1.
Figure 1 shows a goods lift 1 for transporting goods in a lift shaft s from the ground floor b to a first floor v of a building, and vice versa. Goods lift 1 comprises a lift cage 2 arranged in lift shaft s and guidable along the walls thereof, which cage is provided with doors which can be opened 3. Lift shaft s is embodied as a concrete shaft in which, at the position of the lift doors, openings corresponding therewith (not shown) are arranged on the ground floor and on the first floor. Lift shaft s can however also be embodied in steel or the like. It is even conceivable to wholly dispense with a lift shaft and to guide the lift in a practically open construction.
The lift cage 2 shown in figure 1 is provided with a number of cage guides (not shown) with which the lift cage is guided along the shaft. The drive of the lift cage comprises an electric motor 7 which is arranged at the top of shaft s. The electric motor drives a shaft 8. The rotation of shaft 8 is converted by means of a toothed wheel into a vertically upward respectively downward movement of a chain 9. The chain is fixed to the top side of lift cage 2 so that the lift cage can be displaced in upward and downward direction using electric motor 7.
Figure 1 also shows that electric motor 7 comprises a brake 10 so that when the electric motor itself cuts out or the supply voltage is cut off the lift cage 2 is held at a fixed position. This brake can be operated manually, for instance by an engineer who has gained access to the top of the lift shaft.
Figure 2 shows the relevant part of the control of electric motor 7. Electric motor 7 (in the shown embodiment a second electric motor 7' is also provided) is a rotary current motor which is driven by a combination of three alternating currents L₁, L₂, L₃ (3 x 380 V) which have a relative phase difference of 120°. The rotating magnetic field occurring as a result hereof in electric motors 7 brings about rotation of a motor armature (not shown) which transmits its rotation to drive shaft 8. Conversely, when the drive shaft rotates as a result of a lift cage 2 displacing downward, the electric motor 7 fulfills the function of generator for generating the combination of three alternating voltages.
Input circuit 11 comprises three inputs for the three phase leads as well as a switch (main switch) with which the electric motors 7,7' can be switched on and off. Each of the three phase leads is connected to an electric motor 7' (or motors 7, 7'). When sufficient input voltage is available sufficient power can be provided with the electric motors to move the lift cage upward and downward. When the supply voltage decreases or is even interrupted completely, relay switches 12,12',12'' connect the three phases L₁, L₂, L₃ to a delta connection 13 of capacitors. A first capacitor C₁ is connected at nodes 15 and 16 to L₁ and L₂, a second capacitor C₂ is connected at nodes 16 and 17 to L₂ and L₃ and a third capacitor C₃ is connected at nodes 15 and 17 to L₁ and L₃.
If brake 10 is now released manually by an engineer, cage 2 of goods lift 1 will move downward of its own accord under the influence of the force of gravity. The downward "falling" cage 2 then drives the electric motor of the drive, which begins to operate as generator and thereby charges the capacitors until at a certain moment the capacitors begin to counteract the electric motors 7,7'. This counteraction depends on the rotation speed of the electric motor. Above a determined rotation speed the counteracting voltage increases exponentially, whereby electric motor 7,7', and thereby also lift cage 2 are braked increasingly harder.
With a correct choice of the capacitance of the capacitors it is possible to achieve in this manner that the cage of the goods lift maintains a controlled, constant, low downward speed when the brake is released by hand. This choice of capacitance can be such that the descent speed of the lift cage, which at a given moment will be constant, is realized when an average weight is arranged in lift cage 2. Embodiments can however also be envisaged in which the capacitance of the capacitors can be varied in situ by the engineer, so that the engineer has the option of adjusting the descent speed subject to the weight of the goods arranged in the lift cage.
The present invention is not limited to the above described preferred embodiment thereof; the rights sought are defined by the following claims, within the scope of which many modifications can be envisaged.

Claims

Hoisting device for transporting objects, particularly goods, comprising:

a cage member in which the objects for transporting can be placed, which cage member is displaceable in a shaft;

hoisting means mounted on the cage member for hoisting and lowering the cage member in the shaft;

electric drive means connectable to a power supply for driving the hoisting means;

the electric drive means comprising:

one or more electric motors;

one or more capacitors;

switch means for connecting the electric motors to the supply voltage when sufficient supply voltage is available, and connecting at least one of the electric motors to at least one of the capacitors when insufficient supply voltage is available, for the purpose of counteracting the downward movement of the cage member.
Hoisting device as claimed in claim 1, wherein the capacitance of the capacitors is chosen such that when there is insufficient or no supply voltage the speed of descent of the cage member is substantially constant.
Hoisting device as claimed in claim 1 or 2, wherein the power supply generates a three-phase alternating voltage, and at least one capacitor is used for each phase.
Device as claimed in any of the foregoing claims, comprising three delta-connected capacitors.
Hoisting device as claimed in any of the foregoing claims, wherein the switch is connected in series to the power supply for either connecting an electric motor to the power supply in a first position or connecting the electric motor to at least one capacitor in a second position.
Hoisting device as claimed in any of the foregoing claims, wherein the switch comprises a relay.
Hoisting device as claimed in any of the foregoing claims, comprising braking means for braking the cage member in the shaft, wherein the braking means can be controlled so as to release the cage member when sufficient supply voltage is available and to brake the cage member when insufficient supply voltage is available.
Hoisting device as claimed in claim 7, wherein the braking means comprise a switch for releasing the cage member when insufficient supply voltage is available.
Hoisting device as claimed in claim 8, wherein the switch is of the type which can be operated manually.
Hoisting device as claimed in any of the foregoing claims, which is of the non-counterweight type.
Hoisting device as claimed in any of the foregoing claims, wherein the capacitors have a variable capacitance.
Method for transporting objects, particularly goods, comprising of:

connecting the electric motor(s) of the hoisting device, preferably a hoisting device as claimed in any of the foregoing claims, to the power supply when sufficient supply voltage is available for hoisting and lowering the cage member;

connecting the electric motor(s) to one or more capacitors for counteracting the descending movement of the cage member when insufficient supply voltage is available.
Method as claimed in claim 12, comprising of adjusting the descent speed of the cage member when insufficient supply voltage is available by modifying the capacitance of one or more of the capacitors.
Method as claimed in claim 13, comprising of setting to a substantially constant descent speed.