A barrier movement operator which uses an A.C. motor to move a barrier is disclosed herein. The operator senses a characteristic of barrier movement, such as motor rotation speed, to detect when the barrier contacts an obstruction. The motor and/or the circuitry for applying electrical power to the motor have been enhanced to improve the detectibility of contact with an obstruction.

[0001]     The present invention relates to barrier movement operators and particularly to barrier movement operators having improved characteristics for detecting obstructions to the movement of the barrier.  
         [0002]     Barrier movement operators generally comprise an electric motor coupled to a barrier and a controller which responds to user input signals to selectively energize the motor to move the barrier. The controller may also respond to additional input signals, such as those from photo-optic sensors sensing an opening over which the barrier moves, to control motor energization. For example, should a photo optic sensor detect an obstruction present in the barrier opening, the controller may respond by stopping and/or reversing motor energization to stop and/or reverse barrier movement. The controller may also respond to motor speed representing signals by controlling motor energization. Such may be used to stop and/or reverse the movement of a barrier when the motor speed, which represents the speed of movement of the barrier, falls below a predetermined amount as might occur if the barrier has contacted an obstruction to its movement.  
         [0003]     Detecting contact by the barrier with an obstacle by sensing the driving speed of the motor has certain inherent difficulties. The barrier, barrier guide system and the connection between the barrier and the motor all have momentum and all exhibit some amount of flexibility. When the leading edge of a barrier is slowed, it takes time for the inertia of the various parts to be overcome and for the slowing of the barrier to be reflected back to the motor via the flexible (springy) interconnection. Through proper design and construction techniques, such systems have been successfully achieved for response times and contact pressure thresholds to achieve safe operation. However, to achieve ever safer operation involving lower barrier contact forces and more rapid response times, new designs are needed.  
         [0004]     Motors for use with barrier movement operators are generally constructed or selected to operate efficiently and exhibit a motor rotation rate (motor speed) to torque characteristic represented in  FIG. 4 . The normal forces on the barrier generally allow the operating motor speed between the marks labeled A and B on  FIG. 4  resulting in a relatively flat slope of the speed versus torque characteristic. The “normal” motor having a characteristic as shown in  FIG. 4  exhibits a change of motor RPM of approximately 20 RPM per inch-pound of required motor torque. Improvements in obstruction contact times and reduction of obstruction contact forces is difficult with a motor having the characteristics of  FIG. 4  because the change of motor RPM is small for the normal range of obstruction forces. A need exists for a motor which operates with a torque to speed characteristic which is enhanced for rapid obstacle detection.  
         [0005]     Improvements in barrier contact obstacle detection may also be achieved by improvements in how sensed motor speed changes are interpreted. Existing barrier movement systems include obstacle detection functions which compare currently measured motor speed with an obstacle indicating threshold. The obstacle indicating threshold generally consists of an expected motor speed minus a constant which defines how much additional speed reduction represents an obstacle rather than a normal variation in operating speed. In some systems an average speed is assumed for the entire movement between open and closed positions and when motor speed falls below the normal speed minus a fixed threshold an obstacle is assumed. In other systems a speed history is determined for door movement by recording measured speeds at several (many) points along barrier travel. When the measured speed falls below the speed history for the same point in barrier travel minus a fixed threshold, an obstacle is assumed. Improvements are needed in obstacle detection to permit fine control of speed changes which indicate an obstruction. 
     
    
     DESCRIPTION OF DRAWING  
       [0006]      FIG. 1  shows a barrier movement system connected to a vertically moving garage door;  
         [0007]      FIG. 2  is a block diagram of the control apparatus for a barrier movement operator;  
         [0008]      FIG. 3  illustrates circuitry for detecting motor rotation speed;  
         [0009]      FIG. 4  is a graph of motor rotation speed versus required motor torque for existing induction A.C. motors;  
         [0010]      FIG. 5  is a graph of motor rotation speed versus required motor torque for enhanced A.C. induction motor operation;  
         [0011]      FIG. 6  is a diagram of a modified A.C. voltage which may be used to power A.C. motors;  
         [0012]      FIG. 7  is a graph representing motor speed and obstacle detection thresholds;  
         [0013]      FIGS. 8A  and B represent the stator and field windings of an A.C. induction motor;  
         [0014]      FIGS. 9A  and B represent the rotor of an A.C. induction motor; and  
         [0015]      FIG. 10  is a graph of motor torque versus motor current for normal and one enhanced induction A.C. motor. 
     
    
     DESCRIPTION  
       [0016]      FIG. 1  illustrates the use of a barrier movement operator  10  for vertically moving a garage door. It should be understood that a barrier movement operator as described and claimed herein may be used to move other types of barrier such as gates, window shutters and the like. Barrier movement operator  10  includes a head unit  12  mounted within a garage  14 . The head unit  12  is mounted to the ceiling of the garage  14  and includes a rail  18  extending therefrom with a releasable trolley  20  attached having an arm  22  extending to a multiple paneled garage door  24  positioned for movement along a pair of door rails  26  and  28 . The system includes a hand-held transmitter unit  30  adapted to send signals to an antenna  32  positioned on the head unit  12  and coupled to a receiver as will appear hereinafter. A switch module  39  is mounted on a wall of the garage. The switch module  39  is connected to the head unit by a pair os wires  39   a  and includes a command switch  39   b . An optical emitter  42  is connected via a power and signal line  44  to the head unit. An optical detector  46  is connected via a wire  48  to the head unit  12 .  
         [0017]     As shown in  FIG. 2 , the garage door operator  10 , which includes the head unit  12  has a controller  70  which includes the antenna  32 . The controller  70  includes a power supply  72  which receives alternating current from an alternating current source, such as  110  volt AC, at a pair of conductors  132  and  134 , and converts the alternating current into DC which is fed along a line  74  to a number of other elements in the controller  70 . The controller  70  includes and rf receiver  80  coupled via a line  82  to supply demodulated digital signals to a microcontroller  84 . The microcontroller  84  includes a non-volatile memory, which non-volatile memory stores set points and other customized digital data related to the operation of the control unit. An obstacle detector  90 , which comprises the infrared emitter  42  and detector  46  is coupled via a bus  92  (which comprises lines  44  and  48 ) to the microcontroller. The obstacle detector bus  92  includes lines  44  and  48 . The wall switch  39  is connected to supply signals to and is controlled by the microcontroller. The microcontroller, in response to switch closures, will send signals over a relay logic line  102  to a relay logic module  104  which connects power to an alternating current motor  106  having a power take-off shaft  108 . A tachometer  110  is connected to shaft  108  and provides a tachometer signal on a tachometer line  112  to the microcontroller  84 . The tachometer signal being indicative of the speed of rotation of the motor. The tachometer  110  may comprise an interrupter wheel represented at  115  ( FIG. 3 ) connected to rotate with the motor shaft  108 . A light source  128  and light receiver  127  detect rotation of the shaft by detecting successive passings of a plurality of light blocking apparatuses  117  and reporting to controller  84  via communication path  112 . Microcontroller  84  can then determine current motor speed by calculating the period between successive light blockages. It should be mentioned that other means for detecting rotation rate may also be employed such as a cup shaped interrupter with equally spaced apertures therethrough to successively block and pass light between source  128  and detector  127 . The signals on conductor  112  from tachometer  110  may also be used to identify the position of the barrier when used with a pass point arrangement or position detector shown at  120 , which operation is known in the art.  
         [0018]     The barrier movement operator of  FIG. 1  begins to move the barrier in response to a user pressing button  39 B of wall control  39  or pressing a transmit button of transmitter  30 . Generally, when movement begins the barrier is in the open or closed positions. When a command to move the barrier is received, the barrier driven toward the other limit. In the present embodiment the controller  10  tracks the position of the barrier in response to signals from tachometer  110  and formulates operations based on that sensed position. The controller also may respond to signals from optical detector  90  representing a possible obstruction by reversing the direction of a downwardly traveling barrier.  
         [0019]     The barrier movement operator of  FIG. 1  also responds to sensed information about the forces required to move the barrier to control further barrier movement. For example, as the barrier is moved, motor speed is continuously checked as an indication of the forces being required to move the barrier.  FIG. 4  is a graph of a normal motor showing motor rotation speed versus motor output torque. As the forces required to move the door increase the motor slows. The converse is also true. The predictable nature of speed change versus applied forces allows the motor speed to be used as an indication of such things as the barrier contacting an obstruction.  
         [0020]     Barrier movement operators have been constructed which respond to the motor speed falling below a fixed value by assuming that the barrier has contacted an obstruction and, accordingly, stop or reverse the travel of the barrier. More sophisticated systems have been designed which record measured motor speed at a number of barrier positions establish obstruction threshold histories for different barrier positions.  FIG. 7  illustrates one such thresholding system in which 6 thresholds labeled  50 ,  52 ,  54 ,  56 ,  58  and  60  are shown. It should be mentioned that in  FIG. 7  motor speed is represented by the period between successive light blockages from an interrupter wheel and as such higher on the graph of  FIG. 7  represents lower motor speed. During movement of the barrier, a number of different motor speeds are sensed as represented by the measured speed line. Zones of interest are then selected and a value representing the minimum speed in each zone is recorded. In  FIG. 7 , the minimum speed in a first zone is represented at  51 , a second at  53  and others at  55 ,  57 ,  59  and  61 . A predetermined speed difference value may then be subtracted from each minimum speed to establish the overall threshold for the zone. The references  50 ,  52 ,  54 ,  56 ,  58  and  60  represent the per zone thresholds. After the zone thresholds have been learned (or updated) whenever measured speed falls below the zone threshold an obstruction is assumed and the barrier is stopped or reversed.  
         [0021]     As shown in  FIG. 7  each minimum threshold is a fixed amount different from the minimum speed in the zone as represented by the couplets  50 - 51 ,  52 - 53 ,  54 - 55  and  56 - 57 . In the present embodiment, particular zones can be configured to be more sensitive than other zones. For example, the period (speed) difference between  57  and  56  is the same as the period (speed) difference between all other couplets toward the open representing left of the graph. Thus, all zones from  56 - 57  to the left are of substantially equal sensitivity. The zone represented by the couplet  58 - 59  is more sensitive because less speed difference between the measured minimum  59  and the threshold  58  exists than between the other couplet to the left. As can be seen in  FIG. 7  the most sensitive zone is near the closed position and advantageously is placed within 18 inches of the closed position.  
         [0022]     Other improvements to obstruction detection are made by the presently disclosed barrier movement system.  FIG. 4  represents the speed versus torque characteristic for a normal motor. As can be seen the slope of the line from A to B which represents a normal operating range, an increase of required torque of one ft. lb. results in a motor speed change of only about 12-13 RPM. This is a relatively small change to be rapidly detected, particularly in the real environment as represented by the measured speed line of  FIG. 7 .  FIG. 5  represents in the speed versus torque characteristic of a motor and its driving apparatus which is enhanced to improve motor speed change. The slope of the line between points A 1  and B 1  on  FIG. 5  results in a change of speed of approximately 47 to 48 RPM per inch-pound of torque thus making speed changes more easily detected.  
         [0023]     A characteristic as shown in  FIG. 5  can be achieved by producing a motor with the appropriate parameters.  FIGS. 8A and 8B  are views of a field winding/stator of an induction motor.  FIGS. 9A and 9B  represent the induction rotor of such a motor. The rotor of an AC induction motor includes a plurality of ferris metal rotor lamination formed together into a cylinder as represented at  62 . The rotor laminations have a plurality of regularly spaced apertures which are arranged to extend from one end of the rotor cylinder at an angle as represented by  64 . The apertures are filled with an electrically conductive non-ferris metal such as aluminum. Finally end rings  64  are formed at the ends of the diagonal conductive lines  64  from non-ferris electrical conductors to provide conductive paths between the diagonals  64 . Due to current induced by AC applied to the field coils, magnetic fields are produced in the rotor which cause rotation.  
         [0024]     Normally motors are designed to provide very low resistance in the cross paths  64  and the end rings  66  resulting in a characteristic as shown in  FIG. 4 . In the present embodiment, however, the resistances have been increased which results in an enhanced characteristic as shown in  FIG. 5 . In a preferred embodiment the resistance increase was produced by using smaller than normal amounts of non-ferris metal for conductors  64  and  66 . The results could also be achieved by fabricating the conductors  64  and  66  from non-ferris material having greater internal resistance.  
         [0025]     In the above discussion the enhanced characteristic ( FIG. 5 ) was achieved during motor fabrication or selection. Such can also be achieved by selective coupling of incoming AC power to the motor  106 . In  FIG. 2  incoming AC power is connected to conductor  132  and  134  which are in turn connected to a power control circuit  114 . An output of power control circuit  114  is used to power the motor. Power control circuit  114  selectively blocks portions of each cycle of the incoming sinusoidal AC wave form shown in  FIG. 6  to the motor  106  via relay logic  104 . The wave form of  FIG. 6  is achieved by a “light dimmer” circuit in power control which is preset to pass a predetermined percentage e.g., 60 percent of each sine wave cycle. Energization of an AC induction motor with a wave form shown in  FIG. 6  results in a characteristic as shown in  FIG. 5 . Greater control over the A.C. wave form applied to the motor  106  by using a power control circuit of the type described in U.S. patent application Ser. No. 10/622,214 filed 18 Jul. 2003 which is connected to microcontroller  84  via a control line  118 . Such greater control might include skipping entire cycles of applied A.C. Also the wave form of  FIG. 6  may be reproduced using high frequency e.g., 1KHZ duty cycle control.  
         [0026]     The preceding embodiment measured rotation speed of the motor to detect possible obstructions because motor speed represents present torque requirements of the motor. (See  FIGS. 4 and 5 ) The current drawn by an induction A.C. motor also represents the present torque requirements of the motor. As the force requirements increase so does the current applied to the motor. The motor current may be sensed by an optional current sensor  130  connected to the A.C. inputs of the relay logic  104 . ( FIG. 2 ) This relationship is shown in  FIG. 10  as  203  for a “normal” motor and  201  for a motor enhanced by the above described motor modifications and driving techniques. When motor current is sensed to detect possible obstructions, the enhanced characteristic  201  provides more rapid and certain obstruction detection.  
         [0027]     While there has been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended in the appended claims to cover all those changes and modifications which fall within the true spirit and scope of the present invention.