Patent Application
20090120728
This invention generally relates to elevator brakes and, more particularly to elevator machine brakes that include a load sensor for indicating a load on an elevator machine brake.
Elevator systems are widely known and used. Typical arrangements include an elevator cab that moves between landings in a building, for example, to transport passengers or cargo between different building levels. A motorized elevator machine moves a rope or belt assembly, which typically supports the weight of the cab, and moves the cab through a hoistway.
The elevator machine includes a machine shaft that is selectively rotationally driven by a motor. The machine shaft typically supports a sheave that rotates with the machine shaft. The ropes or belts are tracked through the sheave such that the elevator machine rotates the sheave in one direction to lower the cab and rotates the sheave in the opposite direction to raise the cab. The elevator machine also includes a brake that engages a disk or a flange that rotates with the machine shaft to hold the machine shaft and sheave stationary when the cab is at a selected landing.
Typical elevator systems include a controller that collects cab weight information and controls the elevator machine based upon the weight information. The controller typically receives the weight information from load-measuring devices installed in the floor of the car. Disadvantageously, floor-installed load-measuring devices often do not provide accurate enough weight information. When the weight in the cab is small, for example, floor-installed load-measuring devices may not accurately distinguish between the background weight of the cab and the small load. Also a load not centered in the cab will not give accurate weight information. Additional load-measuring devices may be used to increase the accuracy, however, the expense and maintenance of the elevator system increases with each additional device. Changes to the elevator such as counterweight loads or modifications to the car are not accounted for by the floor sensors.
Other elevator systems utilize the elevator brake to indicate the weight on the car. Typically, these systems utilize a load cell leveraged between the brake and the floor of the elevator machine room. The torque resulting from application of the brake results in a load on the load cell. Disadvantageously, these systems require a large amount of space in the elevator machine room, are inaccurate by the brake or machine weight added to the load cell amount, and may be expensive. Elevator brakes and load cells in this type of configuration may also cease to operate properly under high levels of torque, which may lead to undesirable conditions in the elevator system. One proposed solution includes making the load cells larger and more robust, however, this may lead to a loss of sensitivity in indicating the weight in the cab.
There is a need for a strong, compact, and sensitive system for providing elevator cab weight information. This invention addresses those needs and provides enhanced capabilities while avoiding the shortcomings and drawbacks of the prior art.
An exemplary elevator machine assembly useful in an elevator system includes a motor frame that supports a motor for selectively rotating a motor shaft. A brake selectively applies a braking force to resist rotation of the motor shaft. At least one load sensor resists movement of the brake relative to the motor frame. The load sensor provides an indication of a load that results from applying the braking force, which is indicative of the imbalance weight of an associated elevator cab in relation to a counterweight.
In another example, the elevator machine assembly includes a first member that resists movement of a braking member relative to a rigid member for a load between the braking member and the rigid member that is below a threshold operating load of the first member. A second member resists movement if the load exceeds the threshold operating load.
In one example, the first member is a load cell.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiments. The drawings that accompany the detailed description can be briefly described as follows.
The example shaft 28 includes a disk 34 within a brake 36. A brake-applying portion 38 of the brake 36 selectively applies a braking force to the disk 34 to resist rotation of the shaft 28. In one example, the controller 30 commands the brake-applying portion 38 to apply a braking force to hold the elevator cab 12 at a selected building landing 16 or to slow the movement of the elevator cab 12.
The motor frame 26 includes corresponding mounting bosses 44b that each support an opposite end of a corresponding load sensor 46. In the illustrated example, the load sensors 46 are secured to the mounting bosses 44a and 44b using fasteners, although other methods of attachment may alternatively be used.
Application of a braking force on the disk 34 results in a load between the brake 36 and the motor frame 26. The load is indicative of the difference in weight between the elevator cab 12 and the counterweight 22 (i.e. the weight of the cargo, passengers, etc. in the elevator cab 12). The difference in weight urges relative rotational movement (i.e., torque) about the axis 42 between the brake 36 and the motor frame 26. The load sensors 46 resist this movement and provide an indication of the load to the controller 30, for example.
These features may provide the benefits of detecting drag on the brake 36 and eliminating brake sensors (e.g. microswitches and proximity sensors) used in previously known assemblies. Drag on the brake 36 occurs if the brake-applying portion 38 fails to fully remove the braking force from the disk 34. In previously known assemblies, the brake sensors would detect whether the braking force was removed and provide feedback to the controller 30. The load sensors 46 replace this function by indicating the load between the brake 36 and the motor frame 26.
In the example shown, corresponding points on the load sensors 46 (for example, the points of attachment to the mounting boss 44a) are located approximately 180° circumferentially from each other with regard to the axis 42. In one example, this provides the advantage of a balanced resistance to movement about the shaft 28 and maintains or increases sensitivity in indicating the load.
The motor frame 26 and brake 36 include corresponding locking members 48a and 48b, respectively, that resist movement between the brake 36 and the motor frame 26 if the load exceeds a threshold operating load of the load sensors 46. One example threshold operating load is a load that would cause at least one of the load sensors 46 to detach from either of the mounting bosses 44a or 44b or to otherwise fail to continue resisting relative rotational movement between the brake and the motor housing. The locking members 48a and 48b are spaced apart a nominal distance such that the brake 36 can move relative to the motor frame 26 an amount corresponding to the nominal distance before the locking members 48a and 48b cooperate to resist movement. This feature allows the load sensors 46 to bear the load under normal circumstances and facilitates maintaining or increasing the sensitivity of the load sensors 46 by reducing or eliminating any load-absorbing interference between the locking members 48a and 48b when the load is below the threshold operating load.
In the example shown, the locking member 48b is a brake lock member that is positioned between two motor frame lock members 48a. If the load exceeds the threshold operating load of the load sensors 46, the brake 36 may approach a load limit of the load sensors. Upon rotating an amount corresponding to the nominal distance between the locking members 48a and 48b, the brake lock members 48b engage a corresponding one of the motor frame lock members 48a to resist further movement of the brake 36. This feature may provide the benefit of allowing use of smaller, less robust, and more accurate load sensors 46 compared to previously known assemblies because the load sensors 46 need not be designed to resist loads exceeding the threshold load.
The illustrated example includes a resilient cushion material 54 at least partially between the locking members 48a and 48b. The resilient cushion material 54 at least partially absorbs the load when the locking members 48a and 48b cooperate to resist the relative rotational movement between the brake 36 and motor frame 26. This feature may provide the benefit of reducing noise when the locking members cooperate.
The opening 61 and the portion of the motor frame 26 that receives the resistive member 60 include an inner diameter that allows easy rotational motion in relation to the outer diameter of the resistive member 60 such that the brake 36 is permitted to move a limited amount relative to the motor frame 26. When the brake 36 applies a braking force to the shaft 28, the resulting load between the brake 36 and the motor frame 26 urges the brake 36 to rotate relative to the motor frame 26. The rod and load sensor 46 provide a balancing of this load about the axis 42 to prevent large-scale radial movement (i.e., non-rotational) of the brake 36 relative to the motor frame 26 (but allowing rotational movement of the brake 36). The slight movement permits the load to transfer, or react, from the rod to the load sensor 46. Large-scale movement, which would otherwise prevent the load from transferring to the load sensor 46, is prevented. The rod therefore provides dual functions of stabilizing the brake 36 with respect to the acting load and transferring the load to the load sensor 46. The resistive member 60 may provide the advantage of a less expensive system compared to a system with a plurality of load sensors, shown in
If the load exceeds a threshold load of the compressive load sensors 46, the brake extension member 82 acts as the brake lock member 48 and cooperates with the motor from lock member 48a to resist further movement of the brake 36, as described above.
In the example shown, the brake 36 also includes a second brake extension member 84 located oppositely from the brake extension member 82. In the illustrated example, the second brake extension member 84 is associated with a resistive member 60. This resistive member could be replaced with a retaining member and a resilient material 86 could be used instead. The cushion material 86 includes a stiffness that is lower than the stiffness of the compressive load sensors 46 such that only a small fraction of the load is absorbed by the resilient cushion material 86. This example includes the benefit of increased sensitivity of the compressive load sensors 46 because only a minimal fraction of the load may be lost through absorption by the resilient cushion material 86 and the resistive member 60.
In one example, the elastic element 96 includes a known polymer material that changes the capacitance of the sensor element 94 when a dimension of the polymer material changes. In the example shown, the polymer material changes dimension (e.g. the dimension D) in response to a load between the brake 36 and motor frame 26 when the brake 36 applies a braking force. The load is transferred through the brake extension member 82 to compress the elastic element 96. In one example, the load compresses the polymer material and the sensing elements 94 provide an indication of a change in electrical capacitance resulting from the polymer material compression. The change in electrical capacitance corresponds to the compressed dimension D of the polymer material in a known manner. The dimension D corresponds to the load on the polymer material via stress versus strain analysis as is known, for example. The controller 30 receives the capacitance and determines the load between the brake 36 and motor frame 26 based upon a predetermined correspondence between electrical capacitance and the load.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US2005/006265 | 2/25/2005 | WO | 00 | 8/7/2007 |
