METHOD OF OPTIMIZING THE WEIGHT OF A COUNTERWEIGHT OF AN ELEVATOR SYSTEM AND ELEVATOR SYSTEM WITH A COUNTERWEIGHT OF THAT KIND

Abstract

An elevator system includes a car with an empty weight MK, which car can move a rated load MLmax, a counterweight, which is coupled with the car by a support device so that it rises when the car lowers and lowers when the car rises, as well as a drive device which can apply a maximum traction force MFmax to the support means. According to the present invention the drive device is selected in such a manner that the maximum traction force MFmax is at least greater than half the rated load MLmax (MFmax>0.5×MLmax) and the weight MG of the counterweight is optimized in such a manner that it is substantially equal to the empty weight MK and the difference between the rated load MLmax of the car and the maximum traction force MFmax of the selected drive device (MG≈MK+(MLmax−MFmax)).

Description

DESCRIPTION OF THE DRAWINGS

The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:

FIG. 1 shows, schematically, the construction of an elevator system according to an embodiment of the present invention; and

FIG. 2 shows, schematically, the construction of a further elevator system according to an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description and appended drawings describe and illustrate various exemplary embodiments of the invention. The description and drawings serve to enable one skilled in the art to make and use the invention, and are not intended to limit the scope of the invention in any manner. In respect of the methods disclosed, the steps presented are exemplary in nature, and thus, the order of the steps is not necessary or critical.

The figures use the same reference numerals for comparable components.

An elevator system according to one embodiment of the present invention comprises, as schematically illustrated in FIG. 1, a car 1 with an empty weight MK, which car can raise or lower a load ML or hold it at a specific height. The load ML can correspond with a rated load MLmax.

A support means or device 2, which here is indicated as a single cable, is fastened to the car 1 by way of a floating roller 20. This cable is fixed at one end in a shaft region, is subsequently deflected over the floating roller 20, in the following loops around a drive pulley 30, is deflected at its other end over a counterweight floating roller 20.1 and again fixedly connected with the shaft.

A drive means or device 3 comprises a motor and a brake (in each instance not illustrated in detail), which can apply a lifting torque and holding torque to the drive pulley 30. This torque is converted in friction-locking manner to a traction force in the cable 2 looping around the drive pulley 30, so that the car 1 rises, lowers or is held at a height as a consequence of the lifting or holding torque.

The drive means 3 can, conditioned by its construction, apply the maximum static holding force MFmaxA by way of its brake, and the maximum dynamic time-extended lifting force MFmaxUD and maximum dynamic time-limited lifting force MFmaxUZ by way of its motor. In that case the static holding force able to be applied by the brake is, depending on the respective type of drive means, greater or smaller than the dynamic time-limited lifting force which the motor can apply for a short time. Due to the limited heat dissipation, this is in turn greater than the dynamic time-extended lifting force which the motor can deliver over a longer period of time.

As apparent from the schematic illustration of FIG. 1, a counterweight 4 is so coupled with the car 1 by way of the support means 2, which in the example of embodiment is identical with the driving means, that it rises when the car 1 lowers and lowers when the car 1 rises. By virtue of this balancing the traction force which the drive means 3 has to apply or transfer to the support means 2 reduces in known manner.

In the example of embodiment the elevator system outlined in FIG. 1 is designed as follows: Initially the empty weight MK of the car 1 and the rated load MLmax of the elevator system are determined. In the example of embodiment the empty car 1 weighs 1600 kg and the rated load may be estimated at 2,000 kg.

By virtue of the floating rollers 20, 20.1 these weights are halved in the following calculations, since the drive means has to apply only half the traction force by virtue of the block-and-tackle system (MK=800 kg; MLmax=1000 kg).

Four types of a drive product line are available as the possible drive means 3:

			maximum	maximum
		maximum	time-extended	time-limited
		holding force	lifting force	lifting force
	Type	MFmaxA	MFmaxUD	MFmaxUZ
	Type I	1250 kg	1250 kg	1500 kg
	Type II	1250 kg	1000 kg	1200 kg
	Type III	500 kg	750 kg	800 kg
	Type IV	500 kg	450 kg	600 kg

As is recognizable from the values in the second column, Types I and II or III and IV each have the same mechanical brake, but different drive motors. As is recognizable from the values in the fourth column, the lifting forces which the drive means 3 can apply for a short time exceed those available in time-extended operation.

Initially, in this example all above values are reduced by a factor 1.3 in order to take into consideration a safety factor equal to 1.3 (as previously explained) in the design. This factor takes into consideration, for example, friction influences, inertia forces, special requirements, etc. Subsequently, the smallest maximum traction force is ascertained for each drive means 3 from the holding force, time-extended force and time-limited force (underlined in the above table). This is compared with half the rated load MLmax/2=500 kg according to equation (3), since the drive means 3 would have to exert this half rated load even with a 50% balancing:

MFmax>0.5×MLmax>500 kg

Whereas Type III with MFmaxA/1.3 (=safety factor)=384 kg is still not sufficient, the drive means Type II with MFmaxUD/1.3=769 kg is that drive with the smallest sufficient traction force which fulfils the condition according to Equation (3) and is selected.

Since, however, this selected drive means 3 can elevator a load of 769 kg even in time-extended operation, whereas in the case of a balancing of 50% only 500 kg would be required, the weight MG of the counterweight 4 can be correspondingly reduced according to Equation (1) with consideration of the above-explained safety factor 1.3, wherein by virtue of the floating roller 20.1 at the counterweight side the weight of the counterweight is in turn doubled:

$\begin{array}{c}\mathrm{MG}/2=\mathrm{MK}+\left(\mathrm{ML}\max -\mathrm{MF}\max /1.3\right)\\ =800\mathrm{kg}+\left(1000\mathrm{kg}-769\mathrm{kg}\right)\\ =1031\mathrm{kg}\\ \mathrm{MG}=2\times 1031\mathrm{kg}\\ =2062\mathrm{kg}\end{array}$

Advantageously, the counterweight 4 is preferably selected to be somewhat greater in correspondence with one weight step, in the present case to, for example, 2075 kg.

The counterweight 4 is thus minimized relative to a conventional balancing of 50% at which the weight of the counterweight would be 2×(MK+MLmax/2)=2600 kg, wherein by contrast to a 30% balancing, as is known from the example of embodiment of U.S. Pat. No. 5,984,052, it is possible to operate with the same nominal speed profile at all loads, even at rated load. The traction force of the drive means 3 is therefore optimally utilized and at the same time the counterweight 4 is minimized or optimized.

In the example illustrated in FIG. 2 the car 1 is merely fastened by way of the one floating roller 20. The support means 2 is fixed at one end in the shaft region, is subsequently deflected over the floating roller 20, in the following loops around the drive pulley 30 and is fixedly connected at its other end with the counterweight 4. In this example the empty weight MK at the car side as well as the rated load MLmax are halved due to the floating roller 20 at the car side. The mass or weight of the counterweight 4 does not, however, have to be doubled again, since a floating roller is not used at the counterweight side. Calculation of the weight of the counterweight 4 is thus carried out as explained above, wherein merely, due to the absent roller 20.1, the weight of the counterweight 4 does not have to be doubled:

$\begin{array}{c}\mathrm{MG}=\mathrm{MK}+\left(\mathrm{ML}\max +\mathrm{MF}\max /1.3\right)\\ =800\mathrm{kg}+\left(1000\mathrm{kg}-769\mathrm{kg}\right)\\ =1031\mathrm{kg}\end{array}$

The counterweight 4 was preferably selected to be somewhat larger on the basis of the weight graduation, in the present case at, for example, 1050 kg. This example serves for clarification of the influence of the floating roller 20, 20.1, wherein it is to be noted that in this connection obviously the travel paths of the counterweight 4 and the car 1 result as different, which has to be taken into consideration in the design of the shaft.

Different procedures in the use of the formulae are possible, so that a number of the floating rollers 20, 20.1 can be taken into consideration in the weights of the car 1 and/or the counterweight 4 or the influence thereof can be taken into consideration in the holding force table. Equally, safety factors can be taken into consideration directly in the establishing of the holding forces or they can be taken into consideration in the establishing of the actual weight of the counterweight 4.

In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.

Claims

1. A method of optimizing a weight of a counterweight of an elevator system, the elevator system consisting of a car which has an empty weight (MK) and which can move a rated load (MLmax), a counterweight which has a weight (MG) and which is coupled with the car by a support means so that it rises when the car lowers and lowers when the car rises, and a drive means which can apply a maximum traction force (MFmax) to the support means, comprising the steps of: a. selecting the drive means from a plurality of drive means each with a different predetermined maximum traction force (MFmax), wherein the maximum traction force (MFmax) of the selected drive means is at least greater than half the rated load (MFmax>0.5×MLmax); andb. selecting the weight (MG) of the counterweight to be substantially equal to the empty weight (MK) and the difference between the rated load (MLmax) and the maximum traction force (MFmax) of the selected drive means (MG≈MK+(MLmax−MFmax)).

2. The method of optimizing the weight of the counterweight of an elevator system according to claim 1 wherein a smaller of a value of a static holding force (MFmaxA) by which the drive means holds the car at a height, a value of a dynamic time-extended lifting force (MFmaxUD) by which the drive means can lift the car over a longer period of time and a value of a dynamic time-limited lifting force (MFmaxUZ) by which the drive means can lift the car over a shorter time is the maximum traction force (MFmax) of each of the drive means of the plurality of drive means.

3. The method of optimizing the weight of the counterweight of an elevator system according to claim 1 wherein at least one of the weight of the counterweight and the empty weight of the car plus the rated load of the car is reduced in correspondence with a number of floating rollers around which the support means is deflected, or the maximum traction force of the selected drive means is increased in correspondence with the number of floating rollers around which the support means is deflected for said step b.

4. The method of optimizing the weight of the counterweight of an elevator system according to claim 1 wherein at least one of the empty weight of the car plus the rated load of the car and the weight of the counterweight is increased by a safety factor for consideration of the frictional and inertial forces occurring in operation, or the maximum traction force of the selected drive means is reduced by a safety factor for consideration of the frictional and inertial forces occurring in operation for said step b.

5. The method of optimizing the weight of the counterweight of an elevator system according to claim 4 wherein the safety factor is in a range of 1.1 to 2.0.

6. The method of optimizing the weight of the counterweight of an elevator system according to claim 4 wherein the safety factor is 1.3.

7. The method of optimizing the weight of the counterweight of an elevator system according to claim 1 including using at least one cable or belt as the support means, wherein the at least one cable or belt is coated with an elastomer material.

8. The method of optimizing the weight of the counterweight of an elevator system according to claim 7 wherein the elastomer is polyurethane material.

9. The method of optimizing the weight of the counterweight of an elevator system according to claim 1 including providing a motor and at least one drive pulley as the drive means for converting a drive output torque of the motor into a traction force on the support means.

10. The method of optimizing the weight of the counterweight of an elevator system according to claim 9 wherein the motor is a frequency-regulated electric motor.

11. The method of optimizing the weight of the counterweight of an elevator system according to claim 9 including providing a brake in the drive means which can apply a static holding moment to a drive pulley of the drive means.

12. The method of optimizing the weight of the counterweight of an elevator system according to claim 11 including selecting at least one of the motor and the brake from a plurality of motors and brakes each with a different predetermined holding or lifting moment.

13. An elevator system comprising: a car having an empty weight (MK) and which can move a rated load (MLmax);a counterweight having a weight (MG);a support means coupling said counterweight to said car so that said counterweight rises when said car lowers and lowers when said car rises; anda drive means which can apply a maximum traction force (MFmax) to said support means, the maximum traction force being at least greater than half the rated load (MLmax>0.5×MLmax), and the weight (MG) of said counterweight being substantially equal to the empty weight (MK) and a difference between the rated load (MLmax) of said car and the maximum traction force (MFmax) of said drive means (MG≈MK+(MLmax−MFmax)).