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You are an expert at summarizing long articles. Proceed to summarize the following text: 
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/325,623, filed on Apr. 21, 2016, the disclosure of which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
       [0002]    This invention pertains to detecting an obstruction of a passenger door in a transit vehicle. 
       SUMMARY OF THE INVENTION 
       [0003]    Briefly according to this invention, there is provided a method of detecting an obstruction of a passenger door on a public transit vehicle wherein the door operator is, for example, a brushed direct current electrical motor. The method comprises: repeatedly recording the profile of the motor current vs. door position as function, for example, of total motor rotations following initiation of an opening or closing of the door; based on the recorded profiles of motor current vs. door position establishing an acceptable increase in motor current for one or more discrete positions following initiation of opening or closing the door indicative of no obstruction; and comparing an instant current to the acceptable increase and indicating a potential door obstruction if the current exceeds the acceptable increase. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    Further features and other objects and advantages will become apparent from the following detailed description with reference to the drawings wherein: 
           [0005]      FIG. 1  shows the arrangement of an exemplary prior art transit door; 
           [0006]      FIG. 2  is a schematic diagram showing the features of the apparatus and circuitry for practicing this invention; 
           [0007]      FIGS. 3 and 4  are high level flow diagrams for the computer program used to implement this invention; and 
           [0008]      FIG. 5  is a chart showing motor current vs. door position. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0009]    Referring now to  FIG. 1 , there is shown the inside of a transit vehicle wall  10  with transit vehicle door panels  12 ,  13 . There are several well-known types of doors used in transit vehicles referred to as slide-glide doors, swing doors, parallel plug doors, and outside plug doors all generally used for bus applications. Also, well-known are slide-glide and bi-fold doors used on light rail trains. Common to all types of transit vehicle doors is a vertical shaft  14  journaled to the wall near an edge of the door panel when the door is closed. The shaft is connected to the door panel by one or more arm assemblies such that rotation of the shaft results in opening or closing of the door. A mechanical door operator  18  comprising a brushed DC motor is connected to rotate the shaft when a door open or close signal is provided. 
         [0010]    This invention is not limited to any particular type of transit door but, for purposes of explanation,  FIG. 1  illustrates a prior art double slide-glide door. Door panels  12 ,  13  have a pivotal connection at the top edge near the leading edge (when the door is opening) to an arm assembly  15 . The door panels are also hung from a follower  16  near the trailing edge of the door panel that slides in guide track  17  secured above the top edge of the door panel. When the shaft  14  is rotated to pull the door panel inward, the door glides to a position perpendicular to the door opening with the leading edge of the door pointing inwardly. Typically, mounted above the top edge of the door panel is a mechanical door operator  18  for driving connecting rods  19  which, in turn, drives cranks  20 , thus rotating the shaft  14 . 
         [0011]    Referring to  FIG. 2 , the door mechanism  30  comprises connecting rods, cranks, and a rotating door shaft, caused to move the door panel between open and closed position by a direct current brushed electric motor  31 . The output shaft of the electric motor is attached to a rotary encoder  32 . The rotary encoder outputs two square waves (A and B) that are 90 degrees out of phase. The encoder outputs a fixed number of pulse per rotation. As is well understood in the art, the A and B pulses, when input to a computer  33 , can be used by a decoder program  34  to determine the angle of rotation, and the rotational speed and direction of rotation. 
         [0012]    The motor  31  is a brushed DC motor. Its direction and speed is controlled by the DC current applied to the motor windings by a driver circuit  39 . The driver circuit is, in turn, controlled, for example, by a pulse width modulated (PMW) control program  35  of a computer  33 . 
         [0013]    The motor current applied to the motor is sensed and converted to a voltage signal at  36  that is digitized by the analog to digital input function  37  of the computer. The digitized current is stored in a computer memory  38  to build motor current profiles vs. door position following the opening or closing of the door. The digitized current may be stored for one or more discrete positions between opened and closed. The motor current profile may be continually adjusted, for example, by calculating an average of a prior established motor current profile (reference current draw value) and a real-time current draw value indicative of obstruction free operation. 
         [0014]    Motor torque is motor current or load related. Applied motor voltage determines speed. Motor rotational speed is self-adjusting until just enough current flows to meet torque requirements. If the load torque increases, the motor will slow enough so that the resulting back emf will allow the current to increase sufficiently to carry the load. Changing motor current is indicative of changing load torque. 
         [0015]    According to one embodiment of this invention, when the door is moved from open to close or close to open, the motor current data will be recorded in a table. This learned data represents the motor torque that is required at any point in the move operation. Due to speed changes or mechanical irregularities, the motor current may vary even when the door is unobstructed. Also, with various door types, as a result of changing mechanical advantage of the system due the linkages, the required torque can vary during door movement. Constant motor torque does not translate into constant door force and speed. 
         [0016]      FIG. 5  (solid line) shows a learned table in graph form of motor current vs. door position for a hypothetical door. The current rises from zero at a uniform rate as the door is moving to its targeted speed, remains constant for stretch of movement, and then drops off at a uniform rate as the speed is reduced approaching the final position. The motor current increases to 8 amps, levels off, and then decreases. Based on this table, a second table is created establishing the current limit for each position of the door. An offset current (acceptable limit or threshold) is added to the learned current for each position of the door to establish the current limit (dash-dot line). In  FIG. 5 , the initial offset is 3 amps and diminishes to 2 amps approaching the targeted speed. As the door nears the center position, the offset drops to 1 amp. The current limit is the current above which an obstruction is deemed to have been encountered. Thus, a smaller increase in motor current is needed to trigger an obstruction when the door is near the center position. A hypothetical motor current, in which an obstruction is detected, is illustrated in  FIG. 5  (dashed line). It is an advantage of this invention that the offset current can be varied during door movement and made appropriate to the particular type of door mechanism. It is also an advantage, according to this invention, that the offset current acceptable limit, or threshold, may be adjusted based on changing conditions or life of the door, the actuator, or the transit vehicle during usage or the last performed maintenance cycle. 
         [0017]    Referring now to  FIG. 3 , a flow diagram is shown for a computer program that controls learning the door motor current profile. After start  300 , the door motor current is recorded vs. door position as the door is opened and closed  301 . Then, obstruction current thresholds are entered considering door geometry  302 . The procedure is then complete  303 . 
         [0018]    Referring now to  FIG. 4 , a flow diagram is shown for a computer program for monitoring door motor current. If the door is being moved  400 , the door current at each door position is input  401 . At each position, the door motor current is compared with the obstruction current threshold for that position  402 . If the threshold is not exceeded, control loops back. However, if the threshold is exceeded, a door obstruction is deemed detected  403  and an output commands the door to be stopped by cutting off current to the door motor  404 . 
         [0019]    Having thus defined the invention in the detail and particularity required by the Patent Laws, what is desired protected by Letters Patent is set forth in the following claims.

Summary:
A method of detecting an obstruction of a passenger door on a public transit vehicle comprising the steps of: recording the profile of the actuator (motor) current vs. door position following initiation of an opening or closing of the door; based on the recorded profile of actuator current vs. door position acceptable increase in motor current for one or more discrete positions following initiation of opening or closing the door indicative of no obstruction; and comparing an instant current profile to the acceptable increase and indicating a potential door obstruction if the current exceeds the acceptable increase.