Abstract:
An obstacle detection method and system for a barrier closure system comprising a sensor for measuring a predetermined parameter as it varies during a closure of a barrier. Memory stores the measured parameter to establish a first parameter profile and a threshold value associated therewith. A detection module compares a current value of the predetermined parameter to a corresponding barrier position of the first parameter profile and if the current value differs by more than a threshold value sets an obstacle detection state. Conveniently the profile is recalibrated to compensate for changes in the barrier closure system such as wear, and environmental conditions that may vary over time. Preferably the sensor includes a capacitance component.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to barrier closure systems and is particularly concerned with obstruction detection.  
       BACKGROUND OF THE INVENTION  
       [0002]     For automatic barriers such as gates or doors it is important to stop the gate motion when an obstruction is in the path of the gate. This issue has typically been addressed with mechanical contact sensors, for example as is commonly seen on elevator doors. Another approach is the use of beams, typically infrared, located next to the gate, or other non-contacting sensors, such as capacitance sensors taught in U.S. Pat. No. 5,337,039 and U.S. patent application 2003/0071727 published 17 Apr. 2003.  
         [0003]     For opposed sliding gates, that is one gate coming from each side of an opening and moving horizontally, it is desirable to have the gates come close together in the closed position and retract fully into the housing when in the open position. For a capacitance edge sensor this poses a problem because the capacitance between the housing in the open position and between the two sensors in the closed position can be much larger than the change caused by the presence of an obstruction, for example a hand.  
         [0004]     Previous attempts to address this issue have simply reduced the sensitivity and in some cases turned the safety device off when the gate was approaching the limits of its travel.  
       SUMMARY OF THE INVENTION  
       [0005]     An object of the present invention is to provide an improved gate closure system.  
         [0006]     In accordance with an aspect of the present invention there is provided an obstacle detection system for a barrier closure system comprising a sensor for measuring a predetermined parameter as it varies during a closure of a barrier, a memory for storing the measured parameter to establish a first parameter profile and a threshold value associated therewith and a detection module for comparing a current value of the predetermined value to a corresponding barrier position of the first parameter profile and if the current value differs by more than a threshold value, setting an obstacle detection state.  
         [0007]     In accordance with another aspect of the present invention there is provided a method of obstacle detection for a barrier closure system comprising the steps of: 
        1) sensing and storing a predetermined parameter as it varies during a closure of a barrier to establish a first parameter profile,     2) on subsequent closures, sensing the predetermined parameter and comparing a current value of the predetermined value to a corresponding barrier position of the first parameter profile, and     3) if the current value differs by more than a threshold value, setting an obstacle detection state.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The present invention will be further understood from the following detailed description with reference to the drawings in which:  
         [0012]      FIG. 1  illustrates a pair of turnstiles with sliding doors and including a sensor for detecting obstructions in accordance with an embodiment of the present invention;  
         [0013]      FIG. 2  illustrates a pair of turnstiles with angel wing doors or gates and including a sensor for detecting obstructions in accordance with an embodiment of the present invention;  
         [0014]      FIG. 3  illustrates in a perspective view detail of one turnstile of  FIG. 1 ;  
         [0015]      FIG. 4  graphically illustrates a capacitance profile for the sensor of  FIG. 1 ;  
         [0016]      FIG. 5  illustrates in a block diagram the gate closure system for the turnstile of  FIG. 1 ;  
         [0017]      FIG. 6  illustrates in a block diagram the signal and data flow for the system of  FIG. 5 ;  
         [0018]      FIG. 7  illustrates, in a flow chart, sensor and obstruction detection control logic for the system of  FIG. 5 ;  
         [0019]      FIG. 8  illustrates, in a flow chart, the step of acquiring a base profile of  FIG. 7 ;  
         [0020]      FIG. 9  illustrates, in a flow chart, the step of obstacle detection of  FIG. 7 ; and  
         [0021]      FIG. 10  illustrates, in a flow chart, the step of process detection algorithm of  FIG. 9 . 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]     Referring to  FIG. 1 , there is illustrated a pair of turnstiles with sliding doors including a sensor for detecting obstructions in accordance with an embodiment of the present invention. Each turnstile  10  includes a sliding gate  12  having an edge-mounted sensor  14 .  
         [0023]     Referring to  FIG. 2 , there is illustrated a pair of turnstiles with angel wing doors or gates including a sensor for detecting obstructions in accordance with an embodiment of the present invention. Each turnstile  20  includes a pivoting gate  22  having an edge-mounted sensor  24 .  
         [0024]     Referring to  FIG. 3 , there is illustrated in a perspective view detail of one turnstile of  FIG. 1 . The internal gate closure mechanism is shown with outer housing removed. A detailed section thereof  26  shows a portion of the sliding gate  12  with its edge-mounted sensor  14  connected via a coaxial cable  28  and a coax connector  30  to a sensor circuit card  32 .  
         [0025]     Referring to  FIG. 4 , there is graphically illustrated a capacitance profile for the sensor of  FIG. 1 . A base profile  40  is established by measuring capacitance during a plurality of door operations with out foreign objects present (no obstacles). Then during each subsequent operation, the capacitance profile is compared to the base profile  40 . When an obstacle is present, a shift in the capacitance profile occurs as shown in curve  42 . This shift is used by the obstacle detection system as described herein below.  
         [0026]     Referring to  FIG. 5 , there is illustrated in a block diagram the gate closure system for the turnstile of  FIG. 1 . The gate closure system  50  includes a motor control module  52 , motor and drive electronics  54  and sensor electronics  56 . Sensor electronics  56  uses a Motorola MC 33794 as the capacitance sensing electronics. This chip energizes the sensor  14  with a very stable 120 kHz signal and measures the drop across a resistor to determine the loading due to the sensor (and hence its capacitance). The sensor  14 , in the case of a non-metallic gate, can be almost any metallic strip. For example, an adhesive backed aluminum foil and a stainless steel strip about 1.5 cm wide in a plastic tube have both provided very good performance. It is important to insure the sensor remains firmly fixed to the gate to avoid unexpected changes in capacitance, i.e. changes not associated with the movement of the gate. The sensor electronics  56  are connected to the sensor  14  with a short length of coaxial cable  28 . At the electronics end  56  the cable shield is connected to the shield terminal of the MC 33974 and the center conductor to the E1 terminal (or E2 to E9 if they are selected). At the sensor end  14  the center conductor is connected to the metallic strip and the shield is left unconnected. This configuration ensures that the coax cable  28  is not sensitive. It is important to keep the coax cable  28  relatively short to avoid excess capacitive loading that would reduce system sensitivity. Lengths up to 1 meter have been found to be quite practical.  
         [0027]     As an alternative, a QT300 chip from Quantum Research Group could be used for the sensor electronics. This chip operates around 250 kHz and has a digital output as opposed to the analog output of the MC 33974. Either chip works quite well for this application. In fact almost any circuit that responds to capacitance changes can be used. For example, a relaxation oscillator could be used.  
         [0028]     Referring to  FIG. 6 , there is illustrated in a block diagram the signal and data flow for the system of  FIG. 5 .  FIG. 6  shows the motor control module  52  in further detail. The motor control module  52  includes a microprocessor  60 , having barrier  62  and sensor and obstruction detection  64  control logic, servo motor control logic  66  and analog input and filtering  68 .  
         [0029]     In an embodiment of the present invention, the problem of varying capacitance illustrated in  FIG. 4  is addressed by recording the capacitance as a function of position as the gate travels from the open to the closed position during a calibration run and then using this stored data to compare to the measured capacitance during operation. Any deviation from the stored pattern indicates an object in proximity to the sensor. This causes a signal to be sent to the motor control module to stop the gate moving or to reverse direction as desired.  
         [0030]     Once the gate is stopped due to a foreign object, the capacitance can continue to be monitored. If the object is removed, then gate motion can be resumed. If the object comes closer, the gate can be backed off to maintain a separation between the object and the gate.  
         [0031]     Environmental changes that occur slowly (for example, wear in the mechanism or a buildup of dirt) can be compensated for with an adaptive algorithm that records the capacitance versus position profile for each gate operation and adjusts the stored profile by a small fraction of the currently measured profile. If an obstruction is detected or a high dynamic response is seen on the capacitance readings during a move, the adaptive algorithm can be disabled, thereby ensuring that only the true gradual environmental changes are worked into the stored profile.  
         [0032]     A second variation of this technique records the capacitance as a function of time. For this implementation the system does not need a continuous reading of gate position but instead assumes that the gate moves with the same position vs. time profile each time it operates. The only information needed is the time the gate starts moving and the time it stops moving. This makes the system somewhat less sensitive because of variations of how the gate moves with time due to different loadings, machine wear etc., but these changes could be compensated for by an adaptive algorithm that learns the capacitance vs. time profile as the gate operates. The advantage of this second approach is that the sensor is less intimately connected to the gate mechanism and thus becomes easier to retrofit to existing systems.  
         [0033]     Referring to  FIG. 7 , there is illustrated, in a flow chart, operation of the sensor and obstruction detection control logic for the system of  FIG. 5 . The sensor and obstruction control logic begins operation with power up  70 , program initialization  71  and acquire base profile  72  steps. A decision block  73  determines if the barrier (gate or door) is starting to close, if No the process loops back and continues to query until a Yes occurs causing counters to initialize  74 , followed by obstacle detection  75  and a decision block  76  querying if movement of the barrier has ended. A Yes loops the process back to before decision block  73  while a No loops the process back prior to the obstacle detection  75 .  
         [0034]     Referring to  FIG. 8 , there is illustrated, in a flow chart, the step of acquiring a base profile of  FIG. 7 . The acquire profile step  72  of  FIG. 7  begins at a block  80 . Sensor readings are stored as the barrier is closed as represented by a capture readings on barrier close block  81 . A process and generate base profile block  82  creates an initial capacitance profile  40 . This profile is error checked  83  and if passed is followed by initializing thresholds  84  associated with the base profile  40 . If an error check fails an error handler block  85  is called. A return block  86  completes the acquire profile step  72 .  
         [0035]     Referring to  FIG. 9 , there is illustrated, in a flow chart, the step of obstacle detection of  FIG. 7 . The obstacle detection step  75  of  FIG. 7  begins at a block  90 . Current sensor readings and current position readings are obtained as represented by a block  91 . A process detection algorithm block  92  compares the current readings to the capacitance profile  40 . A decision block  93  determines if a trigger threshold is exceeded. If Yes, an announce obstruction detection block  94  is called. A return block  95  completes the obstacle detection step  75 .  
         [0036]     Referring to  FIG. 10 , there is illustrated, in a flow chart, the step of process detection algorithm of  FIG. 9 . The process detection algorithm step  92  of  FIG. 9  begins at a block  100 . Current sensor readings and current position readings are compared the current readings to the capacitance profile  40  as represented by a block  101 . A decision block  102  queries whether a trigger threshold is exceeded. A Yes leads to an increase triggerAccum block  103 . A No leads to a decrease triggerAccum block  104 . A return block  105  completes the process detection algorithm step  92 .  
         [0037]     Hence, one possible algorithm detects obstacles by looking at how fast the capacitance readings are moving away from the base profile. This is achieved by building a running deviance value, low pass filtered over the move. Each reading as it is received is weighted into the running deviance and then compared to that deviance. An ‘obstruction trigger count’ is adjusted according to the difference between the readings&#39; deviance from the base profile and the running deviance. The present scheme uses weighted increments and decrements to achieve a more accurate response to obstructions and at the same time to filter out transients.  
         [0000]     This technique serves  2  major purposes:  
         [0000]    
       
         
           
              (i) Base Profile Drift: By considering only how fast the readings are moving away from the profile any uniform drift in the actual profile (i.e. resultant of environment changes) are factored out.  
           
         
       
     
         [0039]     (ii) Increased Sensitivity and Early Detection: The capacitance readings are subject to a number of high frequency error sources. Any one reading has a potential error of +/−10 mV in the test setup employed. The technique used here is parameterized to trigger only on encountering relatively large number of successive reading differences. Early detection is still achieved as thresholds can be set near 2 mV with this approach.  
         [0040]     Note that the algorithm and mathematics can be implemented in a number of ways as is best suited for the performance of the particular microcontroller.  
         [0041]     Also note that this approach is and can be used in conjunction with a number of other thresholds schemes to produce an optimum response.  
         [0042]     The present invention is not restricted to dual opposed sliding gates and can be used with many different types of moving gates such as single gates, “angel wing gates”, lift gates, horizontal barrier arm gates and car park barrier arms.  
         [0043]     For simplicity of the description, embodiments of the present invention have been described with capacitance-based sensors. However the present invention is not restricted to capacitance-based sensors only but could apply to any non-contact sensor providing a signal that varies significantly with gate position and reacts to the presence of obstacles. Embodiments of the present invention can also include more than one type of sensor, for example IR beams may be combined with a capacitance sensor. Such a dual technology system could be used to provide redundancy for increased safety.  
         [0044]     Numerous modifications, variations and adaptations may be made to the particular embodiments of the invention described above without departing from the scope of the invention, which is defined in the claims.