Elevator with variable drag for car and counterweight

An elevator car and counterweight system is provided with a variable drag element. The variable drag element is controlled such that the lower of the counterweight and the car has a higher drag against further movement. In an embodiment which is particularly useful in a 2:1 roping system, the sheaves (54, 58) associated with the counterweight (56) and the car (60) receive a braking/drive motor (62, 64) to provide the variable drag. While the present invention provides the variable drag to compensate for vertical differences between the counterweight and car, the invention can also be utilized to hold the car at a particular floor. Further, this invention can be utilized to address a counterweight or car jump situation. Another disclosed drag element may be a magnetizable member (40, 33) guided along a guide rail (34, 36) for each of the car (32) and the counterweight (38). A control controls the magnetic force associated with the guide elements to hold the car or prevent counterweight jump.

BACKGROUND OF THE INVENTION

This application relates to an improvement to vary the drag associated with an elevator car and counterweight, particularly as each approach extreme ends of their travel range.

Elevators are typically provided with an elevator car that moves upwardly and downwardly within an elevator shaft. As is known, and as shown somewhat schematically inFIG. 1, the car12is balanced by a counterweight14. The two are connected by a rope16. Sheaves18and20guide the rope.

In the prior art, and particularly as the elevator car or counterweight reach extreme ends of travel, one of the two becomes lighter than the other. The hoist rope is more on one side and thus the hoist rope adds more weight to the lower of the hoist car and counterweight. This raises some complications and challenges in providing smooth travel for the car12. In particular, in very high rise applications, the provision of adequate counterweight balance forces at extreme positions of the counterweight or car becomes very challenging. Thus, compensating ropes22have sometimes been utilized. It would be desirable to eliminate the compensating ropes, such as rope22.

Other issues with regard to the control of movement of an elevator car and counterweight include a problem known as “releveling” in which the car may move slightly once stopped at a floor. Further, a condition known as “counterweight jump” or “car jump” can occur at the end of travel if the car or counterweight strikes a buffer in the pit. The other of the car or counterweight may continue in an upward direction due to stored inertia. The rope tension on the lower element may become low such that its rope can become slack resulting in slip at the traction sheave. As the counterweight subsequently drops, the rope will become taut again.

Thus, the present invention eliminates the need for compensating ropes, and provides smoother travel for the elevator particularly at extreme ranges of travel.

SUMMARY OF THE INVENTION

In one disclosed embodiment of this invention, a variable drag is associated with both the car and the counterweight. The drag is increased on the lighter of the two elements as they approach their extreme ends of travel. At the same time, the other element is driven. Thus, as the counterweight reaches lower points of travel, and conversely the car reaches higher points of travel, the car will become lighter relative to the counterweight, due to the hoist rope. The drag associated with the car will then be made to be higher than the drag associated with the counterweight. The counterweight rope portion is driven. In this way, the differences in weight can be addressed.

In an embodiment that is particularly useful in a 2:1 arrangement, the lower sheaves for the counterweight and car are provided with braking/drive motors. The braking motors thus provide the variable drag on one sheave such as described above while driving the other sheave.

A control monitors position and/or speed of the car and counterweight and controls the drag accordingly.

While the present invention is particularly useful to compensate for differences in weight between the counterweight and car during travel, the drag control elements can also be utilized to hold the car at a select position such as while it is stopped at a floor.

Another feature provided by this invention occurs if the car or counterweight strikes the buffer in the pit. The other of the car and counterweight will then continue in an upward direction due to stored inertia. In this event, the rope tension on the upwardly moving element becomes low such that the rope becomes briefly slack and may result in slip at the traction sheave, and perhaps jerk as the element subsequently drops and the rope again becomes taut. The present invention also allows the control feature of activating the drag control if such a strike is sensed. This reduces dynamic forces on the suspension ropes and the building.

In another embodiment that can be used in 1:1 elevator arrangements, a magnetically controlled element with a variable magnetic force is guided on the guide rails for the car and the counterweight. By controlling the magnetic force, the amount of drag on the car and the counterweight can be controlled relative to each other. While this embodiment may not eliminate compensating ropes, the “hold” and “strike” features mentioned above can be provided by this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2shows an embodiment50that is a 2:1 arrangement between the car60and the counterweight56. As is shown, with such an arrangement, the rope52passes over sheaves54and58associated with the counterweight56and car60, respectively. The sheaves54and58are provided with braking/drive motors62and64under the control of an elevator control such as, for example, control42shown inFIG. 3. The operation of the braking/drive motors62,64serves to provide a variable drag upon the roller sheaves54and58, to achieve the following control functions.

The control controls both motors62and64. In the illustrated position, the counterweight56is moving lower than the car60. With this movement, the counterweight56will reach a higher weight than the car60. In such a situation, the counterweight would not be acting to provide the counterweight benefit as adequately as if the car and counterweight were at more approximately equal vertical positions. This problem becomes particularly acute in very high rise applications. Thus, when the counterweight is below the car, the motor64is controlled to brake sheave54to compensate for the greater weight of counterweight56. At the same time, the other motor62brakes sheave58to compensate for the imbalance. Conversely, when the car is near the bottom of the path of travel, motor62will be controlled to brake sheave58, with sheave54being braked by motor64. Similarly, when the car or counterweight is at the bottom of the hoistway and it has to move upward, the motors62and64on the car and counterweight would drive the sheaves54and58, thereby equalizing the rope tension on car and counterweight. Such control can be utilized based upon position or speed of the counterweight56or car60. The control42(seeFIG. 3) is well within the ability of a worker in this art, and determining the amount of drag to compensate for the imbalance in height would also be well within the skill of a worker in this art. Moreover, information such as position and/or speed is already typically provided to a control for elevators, and thus the provision of the necessary inputs for control42to operate to control the motors62and64is within the skill of a worker in this art.

This embodiment thus allows a variable drag to be applied to either the counterweight or car to control imbalances in weight due to extreme differences in the vertical position of the counterweight and car. This provides benefits as would be appreciated within this art. Braking/drive motors62and64can also be utilized to hold the car at a desired location, and eliminate releveling. The variable drag can be utilized to hold the car at a floor. Thus, while stopped at a floor, the car may be held at an exact desired position.

Another feature provided by this invention occurs if the car or counterweight strikes the buffer in the pit. The other of the car and counterweight will then continue in an upward direction due to stored inertia. In this event, the rope tension on the upwardly moving element becomes low such that the rope becomes briefly slack and may result in slip at the traction sheave, and perhaps jerk as the element subsequently drops and the rope again becomes taut. The present invention also allows the control feature of activating the drag control if such a strike is sensed. This reduces dynamic forces on the suspension ropes and the building.

An elevator system30is illustrated inFIG. 3having a car32provided with a drag element33to be guided on guide rails34. As is known, cars are guided on guide rails in standard elevator systems. However, as will be explained in greater detail below, the drag element33is operated to control the amount of drag between the element and the guide rail. A similar guide rail36guides the counterweight38through a similar drag control member40.

While it is preferred to have a drag element associated with both the car and counterweight, it is possible that a single drag element associated with either the car or counterweight would achieve the control.

As shown inFIG. 4, in one embodiment, the rail36receives sides44of the drag control element40. These sides include magnetizable materials that can be controlled by an electric current to control the amount of magnetic force. In this way, the drag provided along the guide rails36and34by the elements33and40, respectively, can be varied and controlled.

The second embodiment shown inFIGS. 3 and 4will address the releveling and counterweight or car jump problem discussed above.