Patent Application
20090314584
Embodiments of the present invention relate, in general, to an apparatus for determining the load of an elevator and, more particularly, to an apparatus for automatically equalizing uneven tension of ropes of an elevator in combination with a load cell to determine elevator load.
When an elevator having a plurality of ropes for supporting a load is initially installed, or when ropes are exchanged, it may be difficult to precisely match the lengths of the ropes due to a variety of factors, such as the rigidity of the wire ropes and the misalignment of equipment providing tension to the ropes. Other factors causing a difference in length among the ropes may include the differential expansion rate of the ropes, a fault of a sheave material or rope material, an eccentric load applied to an elevator car, and/or combinations thereof. These factors, and others, may result in length differences between the ropes, which can have negative consequences. For instance, if a length difference exists between the ropes of an elevator system, the ropes may be subject to uneven tension because the load is unevenly applied to the ropes. Due to a variation in length among ropes, the ropes having relatively short lengths when compared to the others may be subject to over-tension such that the wires of those ropes are often rapidly worn. In addition, the ropes having relatively short lengths may be easily deformed or broken while causing early wear of sheave grooves and other components. Furthermore, an unbalanced load between the ropes may generate vibrations in longitudinal and transverse directions, which may be directly transferred to the elevator car, making passengers feel uneasy. The above-described situation may be similar to a situation involving a vehicle having an inferior wheel alignment, which can shorten the life span of related components including tires and can deteriorate steering performance and riding comfort.
The load of an elevator car may be measured with a load cell associated with a load weighing hitch plate or by associating a plurality of load cells with a plurality of suspension ropes to determine the cumulative load of the elevator car. The hitch plate system may be supported by a support frame suspended by traction cables or ropes. The hitch plate and load cell may often be coupled directly to the elevator car and connect the car to an upper crossbeam or yoke operatively connected with the hoist or traction cables or ropes. In this manner, the load of the car may be measured at a single point at the center of the elevator car.
Other load measuring systems may incorporate a load measurement device located at the dead end hitch. In such systems, the tension member terminations is mounted to a bracket, which is in turn mounted to a plate. The plate is attached to a guiderail to fix the tension members relative to the hoistway. An edge flange is attached to the plate opposite the guiderails and a strain gauge is attached to the flange. The load exerted by the car suspended by the tension members is transmitted by the plate to the edge flange which is designed such that the force applied to the edge plate by the hoisting ropes causes a large deformation in the edge flange. The strain in the edge flange may be measured by the strain gauge. In other systems, a load weighting device may be used (with a set of springs) to determine the car weight by measuring the compression of the springs.
An alternative configuration for monitoring the load of an elevator car may utilize multiple tension members associated with multiple load cells. A load weighing device for an elevator may be located at the termination of each tension member for suspending the elevator car. A typical system includes an elevator car and counterweight suspended by a tension member within a hoistway. Terminations are fixed to the end of the tension member, which are in turn attached to a structure such as a mounting plate or beam that is fixed relative to the hoistway. A load cell is fixed between a spring and a mounting plate such that the load cell measures the weight borne by the tension member. For elevators having multiple tension members, there may be a load cell for each tension member. The total load of the elevator car is then measured by adding each of the loads measured at each of the plurality of tension members.
Thus, having uneven tension between tension members of an elevator system may not only reduce the service life of the tension members and affect the quality of a passenger's ride, but also it may even jeopardize the safety of the lift operation. Therefore, it may be advantageous to provide an elevator load measurement system for an elevator system having a plurality of tension members that compensates for the differences in rope length of the tension members and accurately measures the load of an elevator car with a single load cell. It may also be advantageous to provide such an elevator load measurement system that works in real time. Furthermore, it may be advantageous to provide an elevator load measurement system that dampens any vibration energy in the tension members.
The accompanying drawings incorporated in and forming a part of the specification illustrate several aspects of the present invention, and together with the description serve to explain the principles of the invention; it being understood, however, that this invention is not limited to the precise arrangements shown. In the drawings, like reference numerals refer to like elements in the several views. In the drawings:
Versions described herein are configured to provide an apparatus for equalizing the tension between the ropes of an elevator in real time in combination with a load cell for monitoring the load of an elevator car. As used herein, the term “rope” will refer to any tension member suitable for use in the disclosed elevator system and apparatus, including but not limited to a rope, cable, chain, or other tension member or suspension means. In one version, the load of an elevator car having a plurality of ropes is automatically balanced while load is measured using a single load cell. The incorporation of a load cell with an autobalancing system permits an accurate measure of an elevator load to be taken while providing the benefits of having uniform rope lengths in the elevator system. Such a system may also account for and measure eccentric or uneven loads in an elevator system using only a single load cell. Thus, the number of load cells needed to take an accurate measure of an elevator system having multiple ropes may be reduced while at the same time the system may automatically adjust the lengths of the ropes to improve the useful life of the system and improve rider comfort. Furthermore, use of an aramid fiber rope, such as Kevlar®, may further improve the system by damping longitudinal and transverse vibrations that may cause rider discomfort.
Referring to
In the illustrated version, ropes (2) are associated with the compensating rope (30) via the rope coupling members (3), rods (40), and the upper sheave section (10). In this position, if a relative length difference occurs between ropes (2), or if there is an eccentric load in the elevator car (4), the compensating rope (30) is subject to uneven tension so that movement of the compensating rope (30) and rotation of sheaves (11), (21) may simultaneously occur, thereby compensating for the relative length difference or the uneven load. In one version, the relationship is such that even if a small amount of uneven tension occurs in the compensating rope (30), the sheaves (11), (21) will carry out a balancing action regardless of an amount of load applied to the compensating rope (30).
It will be appreciated that the upper sheave section (10) and lower sheave section (20) may be aligned in any suitable configuration such as a linear, circular or grouped pattern. Although not illustrated, it is also possible to align the movable sheaves (11) in two or three rows, or in a lozenge pattern, depending on an alignment of the fixed pulley sheaves (21).
Referring to
When suspended in such a manner, gravitational forces acting on the elevator car (4) will cause the tension on the compensation rope (30) to evenly disperse amongst the portions of the rope (T1-T8) between the upper sheave region (10) and lower sheave region (20). The equal distribution of the load results from the autobalancing of the system (1). A balancing of eccentric loads, in particular, may help to reduce the strain on elevator components and may improve rider comfort due to the minimization of transverse and longitudinal vibrations that can result from varying rope lengths. Vibrations may further be damped by the use of an aramid or para-aramid fiber rope, such as a material made from long molecular chains produced from PPTA (poly-paraphenylene terephthalamide) commonly known as Kevlar®, for the compensation rope (30). Ropes constructed from such materials have a natural damping effect that may further reduce vibration. The use of aramid ropes, such as a ¼″ Kevlar rope, may reduce the D/d ratio, which is the ratio between the sheave diameter and the rope diameter. A smaller D/d ratio may allow for the overall system (1) to be more compact. Additional damping features, such as springs, may be used, however the damping effects of aramid rope may be sufficient to eliminate additional damping components altogether. Although the illustrated system (1) is passive in that only gravitational forces are used to balance the elevator load, it will be appreciated that active systems, such as those incorporating a drive system or motor, may be utilized.
A load cell (35) may be positioned between one end of the compensation rope (30) and the elevator car (4). As illustrated in
For example, the uniformity of the autobalancing system (1) allows for an accurate load measurement to be taken with only a single load cell (35) at a terminus of the compensation rope (30). The load cell (35) can be associated with any suitable programmable processor to input the proper algorithm to ascertain load based upon the load cell (35) measurement and the number of sheaves and rope sections. Thus, only a single load cell (35) may be necessary to measure the load of the elevator car (4). Additionally, because the autobalancing system (1) will account for eccentric loads, the load measurements may be more accurate than systems that utilize springs or take measurements from only a single location. Improved accuracy in load monitoring may help the system function more effectively and efficiently in determining how to respond to hall calls, high traffic, and overloaded situations. By using this rope tension equalizer (8) the ride quality, rope life, sheave life, traction performance, and safety operation may be improved.
It will be appreciated that versions of the system (1) can be configured for use in high rise, mid rise, and low rise applications and can be used with any suspension means including wire rope, synthetic rope, a belt system, a chain system, and combinations thereof. It will also be appreciated that using a single load cell is not required and that numerous load cells may be used, such as for redundant monitoring, or for any other suitable purpose.
In summary, numerous benefits have been described which result from employing the concepts of the invention. The foregoing description of one or more embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed. Obvious modifications or variations are possible in light of the above teachings. The one or more embodiments were chosen and described in order to best illustrate the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto.
This application claims priority to and benefit of U.S. Provisional Application No. 61/073,911, filed on Jun. 19, 2008, which is herein incorporated by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61073911 | Jun 2008 | US |
