Abstract:
A door release system including a capacitive circuit that includes a touch bar, a microprocessor within the touch bar programmed with noise-discrimination software to sense touching of the bar, and at least one micro-switch within the bar to function as a back-up that picks up movement of the bar to release the latch should the capacitive circuit fail. Optionally, a sign illuminated by LEDs and an antimicrobial coating/treatment may be applied to the bar. The system is intended for use on magnetically locked doors. The addition of the micro-switches that are actuatable by continued movement on the touch bar after the bar is initially touched provides a redundant access function initiated by other than the capacitive effect of human touch, which is expected to simplify use and ease accessibility for personnel with prosthetics or who may otherwise have their hands occupied.

Description:
REFERENCE TO PRIOR APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application 61/244,047, filed Sep. 20, 2009. 
    
    
     TECHNICAL FIELD 
     The present invention relates to releasable door access control devices; more particularly, to such devices having redundant release sensing mechanisms; and most particularly, to a device having a release bar that includes a microprocessor-controlled capacitive circuit to sense touching of the bar or proximity of an object to the bar and one or more micro-switches as back-up that pick up any slight movement of the bar so as to release the door should the capacitive circuit release feature be unresponsive. 
     BACKGROUND OF THE INVENTION 
     A requirement of magnetically-locked exit doors is that the magnetic lock be deactivatable from within a building upon demand by a user desiring egress. A typical exit door is provided with a horizontal electromagnetic lock-deactivating bar mounted across the inner surface of the door and responsive in any of a wide variety of ways to pressure by a user. In the art, it is considered to be good design to provide two or more redundant deactivating systems to ensure that a door may be opened even if one of the systems malfunctions. 
     For example, U.S. Pat. No. 4,871,204 discloses a release system comprising a capacitive circuit, including a relay, that senses any touching of a fixed horizontal bar in a first user action, and a separate back-up micro-switch activatable circuit. The capacitive circuit relay, when engaged in response to the human touch sensor, includes means for opening the locking circuit for the electromagnetic lock. In the event of malfunction of the capacitance sensor system, egress can still be accomplished, in a second and separate user action. This is accomplished by pressing the push button switch, mounted on or near the bar, which activates the capacitive circuit relay. 
     A shortcoming of the disclosed system is that the capacitive sensor output signal can be corrupted by electronic noise, causing the door to become unlocked when not intended and potentially allowing ingress from the outside. A further shortcoming is that a second distinct user action is required to open the door if the capacitive sensor system fails. A user may not know of the push button switch, or a user may not remember the position of the push button switch or how the switch may be activated, especially in this system since the switch is concealed behind the push bar. 
     For another example, U.S. Pat. No. 5,969,440 discloses a release system comprising two electromechanical force transducer assemblies mounted within a moveable bar and responsive to translation of the bar. When a given amount of pressure is detected by either or both of the electromechanical force transducer assemblies, the door will be unlocked and can be subsequently opened. A back up switch is also located on the bar and will operate in a fail-safe manner (without power) to unlock the door in the event of a failure of one or both of the transducer assemblies upon detection of a greater amount of force being exerted upon the bar. 
     A shortcoming of the disclosed system is that activation of either or both of the transducers requires substantial force, for example, between 5 and 15 pounds of pressure, and operation of the back-up micro-switch requires not less than 15 pounds of pressure. The large force required to operate the back-up switch is needed to ensure that the pressure transducers come into play before the back-up switch is used. Forces in this high range may be beyond the capabilities of a user in a given situation. Further, the disclosed electromechanical force sensors use force sensing resistors whose sensitivity and output may change with aging of the sensors or of the associated actuating padding material. 
     In yet another example, U.S. Pat. No. 6,429,782 B2 discloses a door release system comprising a conductor forming part of a capacitor with variable capacitance dependent upon the proximity of a person, and a detector for sensing variation in the capacitance and for generating an output signal indicating proximity of the person relative to the conductor as the person&#39;s hand touches the release. The switch device further includes a mechanical switch arranged for actuation by a person gripping or pulling the door handle to additionally or alternatively indicate proximity of the person. The system includes an oscillator coupled to the conductor and a phase comparator. The variation in capacitance results in an associated change of frequency in the oscillator to produce a phase-modulated signal which is applied to the phase comparator to generate a signal representative of the change in frequency. 
     What is needed in the art is a door latch release system that includes a capacitive circuit including at least one capacitive sensor, a micro-processor programmed with noise-discrimination software to sense touching of the bar and a micro-switch, or switches, as back-up that picks up movement of the bar to release the door should the capacitive circuit be unresponsive. 
     It is a principal object of the present invention to increase the reliability of a door is release system by incorporating a back-up system that can redundantly release the door upon a natural and continued motion of the person opening the door. 
     It is a further object of the present invention to increase the reliability of a door release system by discriminating against spurious noise signals that can cause a capacitive switching system to open inadvertently or to be opened maliciously while also providing a back-up door release switch which is less sensitive to pounding on the exterior side of the door. 
     SUMMARY OF THE INVENTION 
     Briefly described, a door release system in accordance with the present invention includes a release bar, a capacitive circuit operatively connected to the bar, a micro-processor within the bar programmed with signal noise-discrimination software to sense actual touching of the bar and prevent spurious signals from causing non-intentional release of the door, and at least one micro-switch within the bar to function as a back-up that picks up movement of the bar to release the door should the capacitive circuit be unresponsive, for example, upon a failure of the capacitive circuit or if insufficient capacitance is added to the touch bar. The bar includes a primary mechanical switching actuation with reduced sensitivity to door vibrations in addition to an improved version of the capacitance-only touch sense function disclosed in U.S. Pat. No. 4,871,204, which is incorporated herein by reference. Optionally, an illuminated sign within the bar provides continuous identification of the door as an exit. Optionally an anti-microbial coating/treatment may be applied to the bar and end caps. 
     The system is intended for use on magnetically locked, non-fire rated doors. The addition of the mechanical switch actuation to the bar provides a new primary access function initiated by other than the capacitive human touch, which is expected to simplify use and ease accessibility for personnel with prosthetics or who may otherwise have their hands occupied (e.g. carrying boxes, manipulating carts, wheelchairs, etc.). In addition to capacitance-initiated touch sense function, mechanical movement of the bar is provided which is responsive to a lateral force as applied by any object (i.e. human hand pressure, hip, prosthesis, wheelchair, box, briefcase, etc.) to initiate activation of internal position detecting switches. The bar provides a release signal for as long as it senses capacitance from a human touch or by maintained mechanical switch actuation. The bar is fail safe (no power required) and a non-latching mechanical device. 
     The system allows re-securing of the door when the bar is released to allow the spring mechanism to return the bar to its original (at rest) position, thus disengaging the position detecting switches and when the human hand is totally disengaged from the bar. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  is an isometric view of a door release system in accordance with the present invention mounted on a door in a frame and an electromagnetic lock including an electromagnet on the door frame and an opposing striker plate or armature mounted on the door; 
         FIG. 2A  is an exploded isometric view an end portion of the door release system shown in  FIG. 1 , in accordance with the invention 
         FIG. 2B  is a cross-sectional view of an end portion of the door release system shown in  FIG. 1 , showing the system at rest in accordance with the invention; 
         FIG. 3  is a cross-sectional view like that shown in  FIG. 2B , showing the door release system in an activated position; 
         FIG. 4A-4P  are connecting segments of a schematic diagram of the electrical control circuit in accordance with the invention.  FIG. 4  shows the orientation of each segment shown in  FIGS. 4A-4P  to form the entire electrical control circuit diagram; 
         FIG. 5  is a schematic diagram of the micro-switch shown in  FIG. 4  in accordance with the invention; 
         FIG. 6  is a schematic diagram of an electrical circuit, used in association with the micro-switches, in accordance with the invention for filtering out electrical noise; and 
         FIG. 7  is a schematic diagram of a driver circuit for illuminating the LEDs shown in  FIG. 1  in accordance with the invention. 
       Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate currently preferred embodiments of the invention, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings,  FIG. 1  shows a door  12  and a door frame  14 . Secured to the door frame is an electromagnet  16  which, together with the striker plate or armature  18  on the door forms an electromagnetic lock. On the inside of the door and mounted thereon is a door release system  20  in accordance with the present invention, mounted to door  12  by insulating blocks  22  used to electrically isolate the bar assembly from the door ( FIGS. 2A ,  2 B and  3 ). In order to gain access to the interior of the secured area, inside door  12 , a coded input panel  26  ( FIG. 1 ) may be provided. 
     However, when egress from the secured area on the interior of the door  12  is desired, a person merely touches or pushes against system  20  and the result is to release the electromagnetic lock  16 ,  18 , so that the door  12  may be pushed open. 
     The precise method of de-energization of the electromagnetic lock  16 ,  18 , will be discussed in greater detail below. 
     Referring to  FIGS. 2A ,  2 B and  3 , an end  28  of system  20  is shown, mounted on insulating block  22  disposed on the inner surface of door  12 . The opposite end (not shown) of system  20  is substantially identical, permitting system  20  to be used without modification on either right-hinged (as shown in  FIG. 1 ) or left-hinged doors. Touch bar assembly  42  includes touch bar  44  and touch bar holder  40 . Actuator end cap  30  is attached to mounting bracket  32 . A return spring subassembly  34  having a spring  36  and a plunger  38  contained within a housing  39  is secured to mounting bracket  32  preferably with screws. Plunger  38  is positioned against a tab  41  on bar holder  40  which maintains location of touch bar assembly  42  against locating features  46  in mounting bracket  32 . Touch bar assembly  42  includes a sound deadening pad  48  attached to eliminate objectionable noise during movement of the bar assembly  42  in the mount bracket  32 . Touch bar assembly  42  is movable within end mounting bracket  32  in a plane orthogonal to door  12 , as shown in  FIG. 3 . A control PC board  50  and micro-switch  52  are disposed on rail features formed within mounting bracket  32 . Micro-switch  52  includes a leaf spring  54  abutting wall  55  of touch bar  44 . Touch bar  44  is part of a capacitive circuit as described below. At rest, bar  44  may be at a distance (A) from the surface of door  12 , for example, about 1.25 inches, as shown in  FIG. 2B . Actuator end cap  30  is attached to mount bracket  32  preferably with screws to protect return spring subassembly  34 , PC board  50 , mounting hardware and conductors from damage by carts, gurneys, etc. or from vandalism. 
     Note that a second pad  48  and micro-switch  52  (neither shown) are present at the opposite end of release system  20 , the second micro-switch  52  being connected effectively in series with the shown micro-switch  52 . Thus activation of either micro-switch  52  by itself serves to de-energize the electromagnetic lock. 
     Optionally, an illuminated sign  60  ( FIG. 1 ), reading for example “PUSH TO EXIT”, or other such messaging, may be formed in touch bar  44 , preferably comprising a plurality of LEDs and a multi-strand fiber-optic cable disposed behind a clear faceplate. 
     Also optionally, the user contact surfaces of touch bar assembly  42  may be coated with an anti-microbial coating (not shown) to prevent the spread of bacteria, for example, a powder coat containing silver ion as is known in the prior art. 
     In operation, as shown in  FIG. 3 , when touch bar assembly  42  is touched by a user, the capacitive circuit is energized to cause electromagnetic lock  16 , 18  ( FIG. 1 ) to be de-energized, permitting door  12  to be opened. However, if the capacitive circuit malfunctions, or if there is insufficient capacitance added by the touching, a continuing force  56  applied to touch bar assembly  42  in a continuous direction causes progressive translation of the touch bar toward the surface of door  12 . As touch bar  44  continues to move toward door  12 , leaf spring  54  moves away from the body of micro-switch  52 , thereby opening an electrical contact therein, which serves to open the electromagnetic lock circuit and deactivate the lock. After a limited travel of assembly  42 , for example, about 0.10 inch (opposed by return spring subassembly  34  and requiring a force of preferably only about 5 pounds), door  12  is released and pad  48  and touch bar assembly  42  are stopped by mounting bracket  32 . 
     Thus, in a single motion, a user can de-energize the lock and open the door via either the capacitive circuit or the micro-switch, unlike the prior art system disclosed in the incorporated reference wherein the capacitive circuit is activated in a first user motion, and a second user motion is required to find and flip or push the back-up switch. 
     Referring now to  FIGS. 4 ,  4 A- 4 P and  5 - 7 , a general control circuit for operation of system  20  is similar in overall concept to the control circuit disclosed in the incorporated U.S. Pat. No. 4,871,204, with significant improvements as noted below.  FIG. 4A-4P  are connecting segments of the electrical control circuit of the invention, and form the complete electrical control circuit when each segment is oriented as shown in  FIG. 4 . 
     Referring first to  FIG. 4I , touch bar  44  is schematically shown as feature  62 . Micro-switch  52  ( FIG. 4P ) by which the electromagnetic lock may be de-energized is also shown. Microprocessor  64  ( FIG. 4F ) generates a fixed square wave frequency of about 20 kilohertz which is voltage translated (5V to 9V) by transistor  66 . This provides the clock signal to pin  11  of flip-flop device  68  ( FIG. 4I ), and in turn generates a 10 kilohertz square wave at 50% duty cycle from pin  13  of flip-flop device  68  ( FIG. 4I ). The rising edge of this signal is shaped by capacitors  70  ( FIG. 4M) and 72  ( FIG. 4J ) and resistor  74  ( FIG. 4J ) before continuing to pin  5  of differential comparator  76  ( FIG. 4I ). Diode  78  ( FIG. 4J ) allows a fast discharge for the falling edge of this signal. The output at pin  13  of flip-flop device  68  ( FIG. 4I ) also is shaped by resistors  80  ( FIG. 4I) and 82  ( FIG. 4I ) and capacitor  84  ( FIG. 4I ) and, most importantly, human capacitance, such as a hand, that would touch bar  62  ( FIG. 4I ). Diode  86  ( FIG. 4I ) allows a fast discharge for the falling edge of this signal. As potentiometer  88  ( FIG. 4J ) is varied, the DC reference voltage applied to pin  6  of differential comparator  76  ( FIG. 4I ) will vary and in turn will produce a variable phase difference between the shaped input signal applied to pin  5  of differential comparator  76  ( FIG. 4I ) and the square wave output signal at pin  7  of differential comparator  76  ( FIG. 4I ). Likewise, as the capacitance on touch bar  62  ( FIG. 4I ) is changed the phase difference between the shaped input signal of pin  3  on differential comparator  90  ( FIG. 4E ) and the square wave output signal at pin  1  of differential comparator  90  ( FIG. 4E ) will change. In summary, in one case first differential comparator  76  (FIG.  4 I)has a fixed shaped rising input with a variable DC reference; and in the other case second differential comparator  90  ( FIG. 4E ) has a fixed DC reference, determined by resistors  92  ( FIG. 4E) and 94  ( FIG. 4E ) with a variable shaped rising input (due to the changing capacitance of touch bar  62 ) ( FIG. 4I ). In both cases, there exists a potential variable phase change between the input signal and output signal of the comparators. 
     Referring to flip flop device  96  ( FIG. 4F ), the state of the flip flop included in this circuit depends on a relative timing of the clock pulse applied to its pin  3  via differential comparator  76  ( FIG. 4I)and the  variable input applied to its pin  5 , via differential comparator  90  ( FIG. 4E ). Shaped square wave signals are also applied to touch bar  62  ( FIG. 4I ). Normally, the leading edge of the pulse applied to pin  5  of flip-flop device  96  ( FIG. 4F ) occurs prior to the arrival of the clock pulse at its pin  3 , so the flip flop in the device remains in its same state, with its pin  1  at a high potential. However, when the capacitance of the touch bar  62  ( FIG. 4I ) is significantly increased, as by the touching of an object such as a hand or package, the leading edge of the pulse applied to pin  5  of flip-flop device  96  ( FIG. 4F ) is delayed, so that it arrives subsequent to the clock pulse applied to its pin  3 . This changes the state of the flip flop so that the output at pin  1  of flip-flop device  96  ( FIG. 4F ) goes low, thereby turning off transistor  98  ( FIG. 4F ), and in turn initiates the first valid (bar touched) high pulse to the input (pin  3 ) of microprocessor  64  ( FIG. 4F ). 
     An important improvement of the present invention is the inclusion in the circuit after transistor  98  ( FIG. 4F ) of microprocessor  64  ( FIG. 4F ) which is programmed with intelligent electronic noise detection (discrimination) software as is known in the electronic arts. This improvement serves to filter out spurious electronic signals which are known to adversely affect prior art door release signals as are generated by circuitry in the incorporated reference. 
     Referring to  FIG. 5 , micro-switch  52 , which is normally closed, operates to open the circuit as described above. The full circuit supporting dual micro-switches  52   a  and  52   b  is shown in  FIG. 6 . It has been found in the prior art that rattling a locked door may cause a spurious mechanical noise signal which can cause micro-switches  52   a  and/or  52   b  to open. This circuitry provides the filtering out of short bursts of switch activation as might be experienced when someone is pounding on the door. Switches  52   a  and 52   b  are disposed near opposite ends of touch bar  44 / 62  and are selected and located to meet a safety requirement that less than a certain force, which may occur anywhere along the length of the touch bar  44 / 64 , is required to deactivate the circuit and unlock the door. First and second MOS-FET switches  104 ,  106  function as “smart” output switches for filtering out mechanical noise to which micro-switches  52   a  and  52   b  may be susceptible. MOS-FET switches  104 , 106  connect to the circuit shown in  FIG. 4  at junctions SW 1  NO,SW 1  NC,SW 1  COM ( 108 ) and SW 2 NO,SW 2 NC,SW 2 COM ( 110 ), respectively. Each of the MOS-FET switches  104 ,  106  shown in  FIG. 6  are referred to as a Dual N and P Channel Power MOS-FET. 
     Referring to the below referenced segments as shown in  FIG. 4 , the power supply circuit  112  ( FIG. 4A ) is conventional and includes an input at terminals  13 ,  14  which may be 12 volts to 24 volts DC. An output voltage of 9 volts is provided by power supply circuit  112  ( FIG. 4A ) for energization of the remainder of the data processing circuitry. Watch dog timer  114  ( FIG. 4C ) serves to guarantee that if microprocessor  64  ( FIG. 4F ) fails, the door will not open (unlock) by itself, but will then require physically pushing the bar to unlock. In that case, the capacitive operation/function of the bar is disabled. 
     Referring to  FIG. 7 , a driver circuit is shown for the plurality of LEDs  116  that illuminate the door sign  60  shown in  FIG. 1 . 
     In conclusion, it is to be understood that the foregoing detailed description and the accompanying drawings are illustrative of the principles of the invention. Various alternatives and variations may be employed without departing from the principles of the invention. Thus, by way of example and not of limitation, the touch bar  44  may be circular in configuration rather than rectangular; other electrical components may be employed to implement the function of the components shown in the circuits of  FIGS. 4A-4P  and  5  through  7 ; and a different electromagnetic lock may be employed other than that shown at  16 ,  18 . Also touch bar  44 , preferably formed of aluminum, might instead be formed of a high strength plastic with an inner conductive layer extending for a substantial portion of the area of the bar facing away from the door. Also, alternatively micro-switch  52  may be mounted on the outside of actuation bar  46  with leaf spring  54  bearing directly on the surface of door  12  or against mounting bracket  32 . Accordingly, the present invention is not limited precisely to the arrangements as shown and described hereinabove.