Abstract:
An elevator system includes a car, configured to travel through a hoistway; a first stationary drive unit, con figured to be mounted in a hoistway, a first movable drive unit, configured to be functionally coupled to the car and to 
     Drive the first stationary drive unit, and a second movable drive unit, configured to be functionally coupled to the car and to the first stationary drive unit.

Description:
FIELD OF INVENTION 
       [0001]    The subject matter disclosed herein relates generally to the field of elevator systems, and more particularly, to a cargo lift for elevator systems. 
       BACKGROUND 
       [0002]    Construction, maintenance and service of elevators often requires that components be lifted along the hoistway for installation. For example, during installation of an elevator system, the drive machine and/or power transformer needs to be lifted to the top of the hoistway for installation. Similar loads may also need to be lifted during maintenance activities over the life of a building Existing construction techniques employ cranes to lift components up the hoistway. Cranes are expensive and require large amounts of space to operate. Elevator cars are also used for lifting one-piece loads, often referred to in the art as safe lifts. 
       BRIEF SUMMARY 
       [0003]    According to an exemplary embodiment, an elevator system includes a car, configured to travel through a hoistway; a first stationary drive unit, configured to be mounted in a hoistway, a first movable drive unit, configured to be functionally coupled to the car and to the first stationary drive unit, and a second movable drive unit, configured to be functionally coupled to the car and to the first stationary drive unit. 
         [0004]    According to another exemplary embodiment, a cargo lift for an elevator system, the cargo lift includes a car for travel in a hoistway; a first propulsion assembly, the first propulsion assembly including a first self-propelled drive unit, a stationary portion of the first self-propelled drive unit mounted in the hoistway and a moving portion of the first self-propelled drive unit mounted to the car; and a second propulsion assembly functionally coupled to the car, the second propulsion assembly including a second self-propelled drive unit, a moving portion of the second self-propelled drive unit functionally coupled to the car, the moving portion of the second self-propelled drive unit coacting with the stationary portion of the first self-propelled drive unit. 
         [0005]    According to another exemplary embodiment, a method for providing a cargo lift in an elevator system includes configuring a car for cargo lift, the configuring including: obtaining a first propulsion assembly, the first propulsion assembly including a first self-propelled drive unit, a stationary portion of the first self-propelled drive unit mounted in a hoistway and a moving portion of the first self-propelled drive unit mounted to the car; functionally coupling a second propulsion assembly to the car, the second propulsion assembly including a second self-propelled drive unit, a moving portion of the second self-propelled drive unit functionally coupled to the car, the moving portion of the second self-propelled drive unit coacting with the stationary portion of the first self-propelled drive unit; operating the car as a cargo lift; and configuring the car for passenger service. 
         [0006]    According to another exemplary embodiment, an elevator system includes a car, configured to travel through a hoistway; a first stationary drive unit, mounted in a hoistway; a second stationary drive unit, mounted in a hoistway; a first movable drive unit functionally coupled to the car and to the first stationary drive unit, and a second movable drive unit, functionally coupled to the car and to the first stationary drive unit; a third movable drive unit, unit, functionally coupled to the car and to the second stationary drive unit; and a fourth movable drive unit, functionally coupled to the car and to the second stationary drive unit. 
         [0007]    Other aspects, features, and techniques of embodiments of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Referring now to the drawings wherein like elements are numbered alike in the FIGURES: 
           [0009]      FIG. 1  depicts a self-propelled elevator cargo lift in an exemplary embodiment; 
           [0010]      FIG. 2  depicts a self-propelled elevator cargo lift in an exemplary embodiment; 
           [0011]      FIG. 3  is a top view of stator and magnetic screw in an exemplary embodiment; 
           [0012]      FIG. 4  depicts a self-propelled elevator cargo lift in an exemplary embodiment; 
           [0013]      FIG. 5  depicts a self-propelled elevator cargo lift in an exemplary embodiment; and 
           [0014]      FIG. 6  depicts a method of configuring an elevator car for cargo lift operations in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]      FIG. 1  depicts a cargo lift for an elevator system  10  in an exemplary embodiment. Elevator system  10  includes an elevator car  12  that travels in a hoistway  14 . Guide rails  16  are positioned in the hoistway  14  and serve to guide elevator car  12  along the hoistway. Multiple propulsion assemblies are used with elevator car  12  to impart motion to elevator car  12 . Shown in  FIG. 1 , a first propulsion assembly includes a pair of drive units  18 - 18 ′ and a second propulsion assembly includes a pair of drive units  19 - 19 ′. Using multiple pairs of drive units  18 - 18 ′ and  19 - 19 ′ enhances the load carrying capacity of the car  12  to serve lifting demands during construction, maintenance and service. Although two propulsion assemblies are shown, it is understood that more than two propulsion assemblies may be used. 
         [0016]    A controller  20  provides control signals to the propulsion assemblies to control motion of the car  12  (e.g., upwards or downwards) and to stop the car  12 . Controller  20  may be implemented using a general-purpose microprocessor executing a computer program stored on a storage medium to perform the operations described herein. Alternatively, controller  20  may be implemented in hardware (e.g., ASIC, FPGA) or in a combination of hardware/software. Controller  20  may also be part of an elevator control system. Power source  22  provides power to drive units  18 - 18 ′ and  19 - 19 ′ under the control of controller  20 . Power source  22  may be distributed along at least one rail in the hoistway  14  to power drive units  18 - 18 ′ and  19 - 19 ′ as car  12  travels. Alternatively, a power cable may be used to provide power to drive units  18 - 18 ′ and  19 - 19 ′. It is understood that other control elements (e.g., speed sensors, position sensor, accelerometers) may be in communication with controller  20  for controlling motion of car  12 . 
         [0017]      FIG. 2  depicts an elevator car  12  with a first propulsion assembly having a first pair of drive units  18 - 18 ′ and second propulsion assembly having a second pair of drive units  19 - 19 ′. Drive unit  18  includes a first portion in the form of a magnetic screw  30  having a magnetic element in the form of first permanent magnet  32  of a first polarity positioned along a non-linear (e.g., helical) path along a longitudinal axis of the magnetic screw  30 . The first portion (e.g., magnetic screw  30 ) is a moving portion, as it is connected to car  12  and travels with car  12 . A second magnetic element in the form of a second permanent magnet  34  of a second polarity (opposite the first polarity) is positioned along a non-linear (e.g., helical) path along a longitudinal axis of the magnetic screw  30 . The paths of the first permanent magnet  32  and second permanent magnet  34  do not intersect. 
         [0018]    A motor  36  (e.g., a spindle motor) is positioned at a first end of the magnetic screw  30  and rotates the magnetic screw  30  about its longitudinal axis in response to control signals from controller  20 . In an exemplary embodiment, the outer diameter of motor  36  is less than the outer diameter of magnetic screw  30  to allow the motor  36  to travel within a cavity in a stator. A brake  38  (e.g., a disk brake) is positioned at a second end of the magnetic screw  30  to apply a braking force in response to control signals from controller  20 . In an exemplary embodiment, the outer diameter of brake  38  is less than the outer diameter of magnetic screw  30  to allow the brake  38  to travel within a cavity in a stator. In an exemplary embodiment, brake  38  may be a disk brake. Further, brake  38  may be part of motor  36  in a single assembly. Drive unit  18  is coupled to the car  12  through supports, such as rotary and/or thrust bearings, for example. 
         [0019]    A drive unit  18 ′ may be positioned on an opposite side of car  12  as drive unit  18 . Components of the second drive unit  18 ′ are similar to those in the first drive unit  18  and labeled with similar reference numerals. Magnetic screw  30 ′ has a first permanent magnet  32 ′ of a first polarity positioned along a non-linear (e.g., helical) path along a longitudinal axis of the magnetic screw  30 ′. A second permanent magnet  34 ′ of a second polarity (opposite the first polarity) is positioned along a non-linear (e.g., helical) path along a longitudinal axis of the magnetic screw  30 ′. 
         [0020]    The pitch direction of the helical path of the first permanent magnet  32 ′ and the second permanent magnet  34 ′ is opposite that of the helical path of the first permanent magnet  32  and the second permanent magnet  34 . For example, the helical path of the first permanent magnet  32  and the second permanent magnet  34  may be counter clockwise whereas the helical path of the first permanent magnet  32 ′ and the second permanent magnet  34 ′ is clockwise. Further, motor  36 ′ rotates in a direction opposite to the direction of motor  36 . The opposite pitch and rotation direction of the magnetic screws  30  and  30 ′ balances rotational inertia forces on car  12  during acceleration.  FIG. 2  also depicts first portions of the second propulsion assembly having a second pair of drive units  19 - 19 ′. Drive units  19 - 19 ′ are constructed in a manner similar to drive units  18 - 18 ′ and similar elements are represented with similar reference numerals. 
         [0021]      FIG. 3  is a top view of a stator  17  and magnetic screw  30  in an exemplary embodiment. A similar stator may be positioned on each side of the hoistway. The stators  17  form a second, stationary portion of drive units  18 ,  18 ′,  19  and  19 ′, while magnetic screws  30  and  30 ′ form a first, moving portion of the drive units  18 ,  18 ′,  19  and  19 ′. Stator  17  may be formed as part of guide rail  16  or may be a separate element in the hoistway  14 . Stator  17  has a body  50  of generally rectangular cross section having a generally a circular cavity  52  in an interior of body  50 . Body  50  has an opening  54  leading to cavity  52 . Poles  56  extend inwardly into cavity  52  to magnetically coact with magnetic screw  30  to impart motion to the magnetic screw  30  and car  12 . The poles  56  preferably form a helical protrusion in the interior of the body  50 . 
         [0022]    Stator  17  may be formed using a variety of techniques. In one embodiment, stator  17  is made from a series of stacked plates of a ferrous material (e.g., steel or iron). In other embodiments, stator  17  may be formed from a corrugated metal pipe (e.g., steel or iron) having helical corrugations. The helical corrugations serve as the poles  56  on the interior of the pipe. An opening, similar to opening  54  in  FIG. 3 , may be machined in the pipe. In other embodiments, stator  16  may be formed by stamping poles  56  into a sheet of ferrous material (e.g., steel or iron) and then bending the sheet along its longitudinal axis to form stator  17 . 
         [0023]    When stator  17  is part of guide rail  16 , the outer surfaces of body  50  may be smooth and provide a guide surface for one or more guide rollers  60 . Guide rollers  60  may be coupled to the magnetic screw assembly  18  to center the magnetic screw  30  within stator  17 . Centering the magnetic screw  30  in stator  17  maintains an airgap between the magnetic screw  30  and poles  56 . A lubricant or other surface treatment may be applied to the outer surface of body  50  to promote smooth travel of the guide rollers  60 . 
         [0024]      FIG. 4  depicts a self-propelled elevator cargo lift in an exemplary embodiment. The cargo lift includes a car  12  fitted with a first propulsion assembly and a second propulsion assembly. The first propulsion assembly includes a pair of drive units  18 - 18 ′, on opposite sides of car  12 , and a second propulsion assembly includes a pair of drive units  19 - 19 ′, on opposite sides of car  12 . In the embodiment of  FIG. 4 , the drive units  18 ,  18 ′,  19  and  19 ′ are implemented using linear motors. Permanent magnets  74  define a first, moving portion of drive units  18 ,  18 ′,  19  and  19 ′ connected to, and traveling with, the car  12 . Stator windings  72  define a second, stationary portion of drive units  18 ,  18 ′,  19  and  19 ′ and may be formed on the guide rail  16  mounted in the hoistway  14 . Control signals from controller  20  to the pair of drive units  18 - 18 ′ and the pair of drive units  19 - 19 ′ impart motion to car  12 . 
         [0025]      FIG. 5  depicts a self-propelled elevator cargo lift in an exemplary embodiment. In  FIG. 5 , a first car  12  includes a first propulsion assembly having drive units  18  and  18 ′. A second car  12 ′ includes a second propulsion assembly having drive units  19  and  19 ′. First car  12  and second car  12 ′ are joined by a coupler  80  that physically connects cars  12  and  12 ′. Control signals from controller  20  to the pair of drive units  18 - 18 ′ and the pair of drive units  19 - 19 ′ impart motion to cars  12  and  12 ′. 
         [0026]    In the embodiments shown in  FIGS. 2-5 , each propulsion assembly includes a pair of drives units. It is understood that a single drive unit may be used in each propulsion assembly, as long as the propulsion assembly and guide system can handle moments caused by a system having a drive unit on a single side of the car. It is noted that the drive units  18 ,  18 ′,  19  and  19 ′ include two portions (e.g., moving and stationary) that coact to provide motion to the car  12 . For example, in  FIG. 4  a first, moving portion of drive unit  18  (i.e., permanent magnets  72 ) is coupled to the car  12  whereas a second, stationary portion of drive unit  18  (i.e., windings  72 ) is mounted in the hoistway. It is also noted that two drive units (e.g.,  18  and  19 ) may share and coact with a common stationary portion (e.g., stator  17 ). 
         [0027]      FIG. 6  depicts a method of configuring an elevator car for cargo lift operations in an exemplary embodiment. The process begins at  200  where a car is configured for cargo lift operations. This may entail securing a first propulsion assembly and second propulsion assembly to a car at  202 . Alternatively, this may entail coupling two cars to define a joined car, including a first car having a first propulsion assembly and a second car having a second propulsion assembly at  204 . At  206 , the car is used for cargo lift applications, such as lifting a drive machine or transformer to the top of the hoistway, of safe lift applications. It is understood that other cargo lift operations may be performed, including a variety of types of installation, maintenance and service. At  208 , the car is reconfigured for passenger service. This may entail removing the second propulsion assembly at  210  or decoupling the cars forming the joined car at  212 . 
         [0028]    Embodiments enable cargo lift operations by increasing car load through a serial connection of self-propelling pairs of drive units. Embodiments can be used as a cargo lift for transporting roped machines, which eliminates the need of using heavy duty cranes. Any kind self-propelling drive units may be used. 
         [0029]    Embodiments also provide a cargo lift earlier in the construction process. Once there is a minimal rail length installed in the hoistway, the system can be used to run and function as a working platform for all subsequent installation. There is no need to wait until the full rise and drive machine are in place to use the elevator. This allows other building construction trades to use the elevator(s) at a much earlier, lower rise stage. 
         [0030]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as being limited by the foregoing description, but is only limited by the scope of the appended claims.