Abstract:
A control system for a motorized freight elevator landing door in which all of the doors in a single line of a hoistway are controlled with one set of proximity sensors carried on the elevator car. The sensors signal a controller that operates electric motors for opening and closing the landing door where the car has stopped. The door operating motors are two speed units and the sensors and controller are arranged to operate the motors at high speed during most of the travel in opening or closing movement and at reduced speed at the end of movement. The controller applies power to the motor for a short period after the door is fully closed or open to stall the motors and thereby dampen any rebound motion.

Description:
BACKGROUND OF THE INVENTION 
   The invention relates to the control of motorized freight elevator doors. 
   PRIOR ART 
   Freight elevators, sometimes called cargo lifts or goods lifts are typically arranged with vertically sliding doors at their landings. Commonly, these doors are bi-parting panels or slide up to open panels. The landing doors can be motorized and various techniques are used by different manufacturers to control the opening and closing movement of a landing door. 
   For example, one system operates by applying a brake to the motor drive when the door is reaching the end of its travel in opening or closing movement. The positioning of the door is detected by switches or like devices mounted on the hoistway or shaft at the landing associated with each door. Such prior art systems, when being installed, require extensive wiring and numerous sensing devices in the shaft to detect the position of each landing door. The sensors can require careful adjustment and the motor drive controls can be troublesome when the sensors are not properly adjusted initially or eventually go out of adjustment through wear. 
   SUMMARY OF THE INVENTION 
   The invention provides a system for controlling the operation of motorized freight elevator landing doors. The system reduces the number of sensors needed to determine door position in a line of landings and eliminates the requirement of precise adjustment of any sensors and/or physical contact between the sensors and other components of the system. The system is further simplified by a door motor energization strategy that avoids critical timing or critical position sensing and reliably eliminates bouncing or rebounding of a door panel as it reaches full close or full open position. 
   As disclosed, the invention departs from a conventional practice where landing door position is detected by a plurality of sensors at each landing and, instead, locates the landing door position sensors on the elevator car. Thus, the same single set of sensors are used for all of the landings in a line served by the elevator car. This reduces installation cost and complexity and improves reliability. In the disclosed embodiment, the landing door position sensors are proximity switches or sensors arranged to detect the approach of a door as it nears its open or closed position. The signals from the proximity sensors are used by a controller to change a door motor speed from fast to slow near the end of opening or closing movement. The controller is arranged to continue to supply power to a door motor and allow it to stall for a short period after the door has come to a stop position to eliminate or suppress any tendency of the door to bounce when it engages an opposing surface at the limits of its motion. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic representation of a freight elevator car at a typical landing with a door, shown in an open position, and operated in accordance with the invention; 
       FIG. 2  is a view similar to  FIG. 1  with the door in a closed position; and 
       FIG. 3  is a schematic representation of a control circuit for motorized operation of the landing door. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIGS. 1 and 2 , a landing  10  is represented by a floor  11 . An opening  12  at the landing  10  to a shaft or hoistway  13  of an elevator car  14  is bridged by a lintel  16 . The opening  12  is closed or opened with a vertically sliding door  17  that, in the illustrated example, is a bi-parting style having an upper panel  18  and a lower panel  19 . The door panels  18 ,  19  are guided for vertical sliding movement by guide rails ( FIG. 3 ) adjacent both vertical edges of the panels in a known manner. The panels  18 ,  19  counterbalance one another through roller chains  26  trained over sheaves  27  lying above the vertical edges of the panels. Ends of the chains  26  are anchored to the upper panel  18  and lower panel  19  at points  23 ,  24 , respectively. The sheaves  27  are each rotationally power driven in either direction by an associated electric motor  28 . 
   The elevator car  14  includes a platform  29  and a ceiling  31  shown in  FIGS. 1 and 2  for reference purposes. A pair of sensing devices  36  and  37  in the form of non-contact proximity sensors or switches are rigidly mounted on the cab or car  14  preferably outside one of its vertical enclosure walls adjacent the vertical path of the landing door panels  18 ,  19 . One of the sensors  37  is located near the plane of the platform  29  and the other sensor  36  is mounted vertically above the first sensor near the mid-height of the car  14 . The proximity sensors  36 ,  37  are responsive to the near presence of an element  38  in the form of a vertically extending steel plate rigidly fixed on the lower door panel  19  proximal to a common imaginary vertical plane containing the sensors. The plate  38  can be adjusted vertically and horizontally towards and away from the sensors  36 ,  37  by loosening and tightening screws  39  received in slots  41 ,  42 , respectively, on a leg or flange  43  integral with the plate  38  and on a bracket  44  fixed on the lower door panel  19 . The screws  39  secure the plate  38  to the bracket  44  so that it is properly aligned relative to the proximity sensors  36 ,  37 . 
   With reference to  FIG. 3 , the proximity sensors  36 ,  37  communicate with a programmable logic controller  46  through lines  47 ,  48 , respectively. The controller  46  operates the door motors  28  through banks of relay contacts  51 ,  52 . The first relay contact bank  51  controls, the rotational direction of the motors  28  while the second bank of relay contacts  52  controls the speed of the motors. The operating coils of the relay contacts are indicated at O, C, DH and DL. These relay coils each have normally closed contacts identified by the same letters in series with other ones of the coils to avoid improper relay actuation. 
   Three-phase power is supplied to the controller  46  at lines  56 – 58 . The controller  46  through the banks of relay contacts  51 ,  52  supplies power to the landing door motors  28  which are two-speed reversible units, through appropriate combinations of three of five lines  61 – 65 . For simplicities sake, the lines  61 – 65  are only shown going to the motor  28  on the left in  FIG. 3 , but it will be understood that the motor  28  on the right is wired in parallel with the motor on the left. A zone switch  66 , when properly tripped, enables the operation of the motors  28 . 
   The motorized landing door system operates in the following manner. Assuming the door  17  is open as shown in  FIG. 1 , a signal such as results from a person pressing a close door button or calling for the car  14  from a landing different from where the car is, causes the controller  46  to energize the motors  28  in a high-speed door closing rotational direction through operation of the relays C, DH. The upper and lower panels  18  and  19  move towards each other in vertical translation at a fast rate. When the lower panel  19  approaches its closed position, the reference plate element  38  moves to a position where it is detected by the proximity sensor or switch  36 . This occurs, for example, about  8 ″ before the lower panel  19  reaches its fully closed position at a level where it contacts the lead edge surface of the upper panel  18 . The legend “SLOW DOWN TRAVEL” in  FIG. 2  illustrates the length or portion of the closing motion of the lower panel  19  during which the proximity sensor  36  senses that the panel is near its fully closed position. When the proximity sensor  36  first senses the proximity of the reference plate  38 , it signals the controller  46  through the line  47 . At this time, the controller  46  turns off the high speed relay DH and turns on the low speed relay DL to slow the door motors  28  down and avoid a high speed impact with the opposing lead surface of the upper door panel  18 . The controller  46 , moreover, is programmed to maintain the motors  28  energized with line power for a period long enough for them to stall when the door panels  18 ,  19  first close on each other and for a short period thereafter to damp out any potential bouncing or rebounding of the door panels. 
   The controller  46  opens the door panels  18 ,  19  by operating the motors  28  in a sequence similar to that described when closing the door panel. The controller  46 , through the relays O and DH causes the motors  28  to turn in a rotational direction to open the doors at high speed. When the lower panel  19  approaches a full open position, the proximity sensor  37  detects the presence of the lower edge area of the plate  38  and signals the controller  46  through the line  48  that the door is nearing its full open position. The controller  46  responds by energizing the relay DL to cause the motors  28  to operate at slow speed. This slow speed, as before in closing action, reduces impact forces when the door panels reach conventional open position stops. The controller  46  maintains electrical power to the motors  28  for a time period sufficient to ensure that after a door panel  18 ,  19  reaches a physical stop limiting opening movement, the motors are energized and are allowed to stall to damp any rebound or bouncing of the panels. 
   It will be understood that the described operation is performed at any landing in a line served by the elevator car  14 . The same proximity sensors  36 ,  37  on the car  14  work with plates or cams like the plate  38  provided on each landing door. The described system, thus, provides an advance over the art where the landing doors at each landing have their own dedicated separately mounted, wired and adjusted position sensors in the hoistway adjacent each landing. 
   Those skilled in the art will understand that the invention may be applied to single panel doors which, typically, open upwardly from a sill; in such a case, the proximity sensors or their equivalents that detect approach of the door to its fully open position is located near the car ceiling and the sensor detecting a nearly closed door position is located near the platform. Other types of position sensors can be substituted for the non-contact proximity sensors  36 ,  37  on the car  14  to determine that a landing door or panel is within a predetermined distance from a limit of its motion and to signal the controller of the same. These substitutes can include conventional limit switches or photodetectors, for example. A door panel can be operated in accordance with the invention by a single motor with appropriate mechanical drive, as is known in the art. 
   It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.