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BACKGROUND OF THE INVENTION  
         [0001]    The invention relates in general to barrier movement operators and in particular to a jack shaft garage door operator having a sensing apparatus for preventing cable associated with a pull-up cable drum from becoming slack during the operation of the door and for providing a positive door locking system.  
           [0002]    One of the problems associated with jack shaft garage door operators is that while they are compact and may be conveniently used in garages which have little overhead room, they may present problems to the owners of the garage in that the cable may be payed out allowing the door to close under its own weight and if the door stalls or if the cable pay out drum rotates too far, the tension in the cable will drop and the cable may come off the drum necessitating a visit from a repairman. In addition, the jack shaft garage door operator does not provide any secure locking facility other than a lock at the bottom of the door, which may be tampered with by a burglar. If the door is not locked by some other means, the bottom lock may be forced or damaged and the door can be lifted open and the garage entered by an intruder.  
           [0003]    U.S. Pat. No. 3,785,809 discloses a door operator having a winch member built into a tilting door and movable with it. A cable is attached to a wall member supporting the door and another end of the cable is connected to an extensible arm.  
           [0004]    U.S. Pat. No. 2,185,828 discloses a catch for stopping a door from falling in the event that a sustaining cable or a counterbalance fails or breaks.  
           [0005]    U.S. Pat. No. 4,385,471 discloses a door including a stopping member having a clip connection  29  which engages a cable. If the cable breaks, as shown in FIG. 4, the arm  27  rotates outwardly bringing a cam dog  26  having a plurality of teeth  32  into locking engagement with a roller  13   a  to prevent the roller  13   a  from moving, thereby suspending the door in position.  
           [0006]    U.S. Pat. No. 4,520,591 to Calvagno discloses a system that is mechanically responsive to a break in a cable to prevent a door from falling.  
           [0007]    French Patent No. 2634-815-A includes an “antidrop” safety mechanism having a cam plate  21  on either side of the door equipped with a convex toothed edge to engage a bracket in case of door suspension failure. None of the aforementioned documents teach or disclose solutions for preventing a door from being opened or from stopping an operation of a garage door operator to cause it to reverse to take up cable which may have inadvertently been payed off a cable drum of a jack shaft door operator.  
           [0008]    What is needed is an improved barrier movement operator that avoids unwanted problems with the cable coming off the drum and provides security for the user.  
         SUMMARY OF THE INVENTION  
         [0009]    A jack shaft garage door operator is useful for opening and closing a movable barrier such as a garage door. The jack shaft garage door operator embodying the present invention includes a drive unit having an electric motor therein for driving a torsion shaft sometimes called a jack shaft. The jack shaft is mounted above a door opening and usually has coupled to it a spring, or the like, for providing a restoring force to the jack shaft to help raise the door and to support a portion of the weight of the door that is not supported by the L-shaped rails that a door usually rides in. A pull-up cable drum is connected to the jack shaft to be rotated thereby and has a multi-strand steel pull-up cable connected thereto that may be payed out to lower a door or wound up to raise the door. The pull-up cable is typically connected to a bottom portion of the door and, when wound up, will cause the door to rise along vertical portions of L-shaped rails. A cable tension sensing apparatus is mounted on a wall having a door opening. The cable tension sensing apparatus includes cable guide to retain the cable a substantially fixed distance from the wall and a spring driven cable follower which urges against the cable extending between the drum periphery and the cable guide. An alerting switch is connected to the cable follower and sends a signal indicating loss of cable tension when the cable follower moves beyond a predetermined distance. Additionally, the movement of the cable follower moves a door blocking arrangement to a position to block movement of the door when being raised without use of the motor.  
           [0010]    In the event that the cable is inadvertently payed out, for instance, by the door having reached the bottom of its travel and the operator continuing to run, the cable follower is allowed to move away from the wall by reduced tension (slack) in the cable and moves far enough that the alerting switch operates to generate a signal to which the operator responds by reversing the motor to raise the door. The garage door operator may otherwise be a conventional jack shaft garage door operator. The cable tension sensing apparatus prevents the cable from coming off the cable drum. In addition, a door stop for preventing the garage door from opening is attached to an upper panel of the garage door and, when in the closed position, is beneath the cable tension sensing apparatus when the door is pulled downwardly by full tension on the cable. When the cable follower moves as tension lessens in the cable, a sliding member is moved away from the wall above the door. If the door is attempted to be breached, for instance by an intruder attempting to lift the door, the cable becomes slack allowing the sliding member to come out from the wall so that it then engages compressionally a stop plate on the garage door thereby preventing further upward motion of the garage door.  
           [0011]    It is an aspect of the present invention to provide a jack shaft garage door operator having a cable tension sensor for providing door operator actions reversal to prevent cable paying off a cable drum.  
           [0012]    It is another aspect of the present invention to provide a jack shaft garage door operator having a door opening block adapted to engage a sliding member to prevent a door from being forced open.  
           [0013]    Other advantages of the invention will become obvious to one of ordinary skill in the art upon a perusal of the following specification and claims in light of the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a plan view of a portion of a garage having a garage door in a closed position with a jack shaft garage door operator associated therewith;  
         [0015]    [0015]FIG. 2 is a perspective view showing details of a portion of the jack shaft garage door operator shown in FIG. 1;  
         [0016]    [0016]FIG. 3 is a side view of a portion of the jack shaft garage door operator;  
         [0017]    [0017]FIG. 4 is a side view, showing a cable tensioning member of the jack shaft garage door operator positioned to take up slack in a pull-up cable;  
         [0018]    [0018]FIGS. 5 a - 5   b  is a circuit diagram showing portions of the electrical safety and control circuitry of the garage door opener;  
         [0019]    [0019]FIG. 6 is a perspective view of a frame used in the embodiment;  
         [0020]    [0020]FIG. 7 is a perspective view of a sliding member and door stop of the embodiment;  
         [0021]    [0021]FIG. 8 is a perspective view of a portion of the pivot member and tension sensor; and  
         [0022]    [0022]FIG. 9 is a perspective view of a tension sensor disabling apparatus. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0023]    Referring now to the drawings and especially to FIG. 1, a jack shaft garage door operator embodying the present invention and generally identified by numeral  10  is shown therein. The jack shaft garage door operator  10  is mounted on a garage wall  12  near a garage door opening which has associated with it a movable multiple panel garage door  16 .  
         [0024]    The jack shaft garage door operator  10  includes a drive unit  20  having a motor  25  (FIG. 5 b ) which is connected by a chain drive system  21  to a jack shaft  22 . The motor  25  of drive unit  20  is energized in a well known manner to rotate the jack shaft  22 . Cable drums  24  and  24 ′ are mounted on the jack shaft  22  to be turned and respective pull-up cables  26  and  26 ′ are wound around the cable drums  24  and  24 ′ to be pulled upwardly. A cable tension assembly shown at  28  is mounted on the wall  12  of the garage immediately above the door  16  adjacent the jack shaft  22 .  
         [0025]    The garage door  16  is a multiple paneled door consisting of a plurality of rectangular panels  40 ,  42 ,  44  and  46 . The panels  40  and  42  are connected by a plurality of hinges  50 . Panels  42  and  44  are connected by a plurality of hinges  52 . Panels  44  and  46  are connected by a plurality of hinges  54 . The door is carried on a plurality of rollers in a pair of L-shaped tracks  60 , when the door  16  is lowered, the jack shaft  22  is rotated to pay out the cables  26  and  26 ′ from the pull-up cable drums  24  and  24 ′.  
         [0026]    Drive unit  20  includes a controller  27  shown in detail in FIG. 5 a - 5   b  which responds to input signals to control the raising and lowering of door  16  by selectively stopping or energizing up and down rotation of motor  25 . Controller  27  responds to standard input signals in a known manner to raise and lower the door. Pushing a button  23  when the door is open or closed will cause a processor  31  of controller  27  to energize the motor  25  to move the door to the other state. Similarly, receipt of a properly encoded signal from a remote transmitter  29  (FIG. 1) at a receiver  33  will result in the processor  31  causing the door to open or close.  
         [0027]    The garage door operator includes infrared obstruction sensor apparatus comprising a transmitter  37  mounted on one side of the door and a receiver  35  mounted on the opposite side of the door. The transmitter  37  is aimed at the receiver  35  and transmits a recurring series of light pulses. The receiver  35  receives the light pulses and generates a series of electrical pulses on a conductor pair  39  connected to the controller  27 . It should be mentioned that the controller  27  also provides DC power to the transmitter  37  and receiver  35  via the conductor pair  39  to power their operation. Whenever the transmitted light beams from transmitter  37  to receiver  35  are blocked, the pulses on conductor  39  are terminated by receiver  35 . Processor  31  senses the stoppage of pulses and, when the door is traveling downward, the processor controls the motor  25  to stop and then to rotate to raise the door. Thus the door is kept from striking whatever is in the doorway blocking the light beam. The DC voltage which powers the operation of transmitter  37  is connected, in part, to transmitter  37  via a normally open contact  30  of a switch  32 . The closed state of contact  30  is maintained when tension is present in cable  26 . As is discussed later herein, when the tension in cable  26  decreases switch contact  30  opens and, the transmitter stops transmitting light pulses causing the pulses on conductors  39  to stop. As in the case of an optical obstruction, controller  31  responds to the stoppage of pulses on conductors  39  by raising the door when the door was traveling down.  
         [0028]    [0028]FIG. 2 is a perspective view of cable tension assembly  28  as mounted to wall  12  near cable drum  24 . Cable tension assembly  28  includes a cable guide roller  71  which is rotatably mounted to wall  12  in a roller frame  72 . Cable  26  passes between roller  71  and wall  12 . FIG. 3 is a plan view of the cable tension assembly as viewed outwardly from the center of the door  16 . As shown in FIG. 3, roller  71  is rotatably held by assembly  72  at a distance from wall  12  which is substantially equal to the distance between wall  12  and the perimeter  73  of drum  24 . Thus, the perimeter  73  of drum  24  and the roller  71  keep cable running substantially parallel to the surface of wall  12  when tension is present in the cable  26 .  
         [0029]    Roller holding assembly  72  is a portion of a frame  75  (FIG. 6) which supports portions of the tension assembly  28 . Frame  75  includes a portion  77  which is substantially normal to the surface of wall  12  and includes a slot  79  which is also normal to wall  12 . Cable tension assembly  28  also includes a sliding member  81  (FIG. 7), which is slidably connected to frame  75  at slot  79  by means of a nylon slide  85 . More specifically a pair of screws  86  secure nylon slide  85  to a front face of portion  77  by means of two holes  87  in sliding member  81 . After such attachment, sliding member  81  on one side of portion  77  and nylon slide  85  on the other are free to move normally to wall  12  while trapped in slot  79 . A doorstop  83  may also be attached to sliding member  81  to stop the raising of door  16  by means other than motor  25 .  
         [0030]    A cable tension sensing pivot member  91  is used to sense the tension in cable  26 . Pivot member  91  is slidably mounted to jack shaft  22  and is free to rotate about the longitudinal axis of jack shaft  22  as represented by accurate arrow  95  (FIG. 3). Pivot member  91  includes a cable sensor  97  which, after mounting pivot member  91 , is placed between cable  26  and wall  12 . Pivot member  91  includes a protrusion  98  which after assembly of the cable tension apparatus  28  is slidably inserted into a slot  82  of sliding member  81 . Rotational force is applied to pivot member  91  by a torsion spring  101  which is disposed between protrusion  98  and a tab  103  of frame  75 . By the operation of spring  101  the pivot member  91  is urged to rotate in a clockwise direction as shown in FIG. 3.  
         [0031]    It will be remembered that DC voltage is applied to the infrared transmitter  37  via the normally open contact  30  (FIG. 5 a ) of a switch  32 . In FIG. 2, switch  32  is shown mounted to frame  75  and with a switch lever  107  disposed between a shelf  109  of nylon sliding member  85  and wall  12 . When tension is present in cable  26  (FIG. 3) the cable tension follower  97  is urged against the force of spring  101  and maintained in a position shown in FIG. 3. In the “tensioned” position of FIG. 3 the switch lever  107  is held by sliding member  85  and switch contact  30  of switch  32  is kept in the closed state. Thus, when tension is present in cable  26  the infrared obstruction detection system operates in a normal, well known manner.  
         [0032]    Alternatively, FIG. 4 shows the situation when the cable is not under tension such as would occur if the door  16  became stuck when being lowered or the motor continued to run after reaching the down limit. Without the counter force of cable tension on cable guide  97 , spring  101  causes pivot member  91  to rotate clockwise to a position shown in FIG. 4. As pivot member  91  rotates, pin  98  moves within slot  82  causing sliding member  75  to move away from wall  12 . The movement of sliding member  75  raises the switch lever  107  until switch contact  30  of switch  32  assumes its normally open state. The opening of switch contact  30  removes DC voltage from transmitter  37  which results in controller  27  sensing the absence of pulses on conductor  39 . As described above, the controller  27  responds to the absence of pulses by controlling motor to raise door  16 . When motor  25  begins to turn the jack shaft  22  to raise the door, tension will be restored in cable  26  and the configuration shown in FIG. 3 will again be achieved.  
         [0033]    The raising of door  16  in response to a lack of cable tension occurs only when the door  16  is being lowered by motor  25 . When the door is in the lowered/closed state, processor  31  does not respond to the removal of cable tension by energizing motor  25  to raise the door. This occurs because processor  31  is programmed to perform a remedial opening of the door  16  only when the door is being closed under the control of controller  27 .  
         [0034]    Should someone, such as a burglar, attempt to raise a door  16 , which is in the closed state, the sliding member  81  and a door stop extension  83  provide protection. When the door is closed and an attempt to raise it is made, the cable  26  will go slack as shown in FIG. 4. The slack cable will result in sliding member  81  moving away from the wall  12 . Affixed to sliding member  81  is a door stop  83  which moves translationally along with sliding member  81 . A spacer block  111  (FIG. 1) is attached to the inside of the top panel  40  of the door  16  and strikes the door stop  83  which stops the door from further movement. Alternatively, when the door is being raised by the motor, tension is present in the cable and, as shown in FIG. 3, the door stop is retained near wall  12 . The block  111  will freely pass the door stop  83  when it is held near the wall  12 .  
         [0035]    Under certain conditions, such as the door spring  120  breaking or coming loose, the door  16  may be closed and tension is removed from the cable  26 . This might result in a blocked door as represented in FIG. 4. To prevent such, an emergency release control is provided whereby a person inside the garage can raise the door. The release control includes a release cable or rope  123  and handle  121  as represented in FIGS. 1 and 9. In FIG. 9 the cable tension assembly  28  has been simplified for ease of understanding. When the emergency release is present, the protrusion  98  is extended and is shown as  98 ′ in FIG. 9. Also the spring holding member  103 ′ is formed to more easily allow the rope or cable  123  to slide passed.  
         [0036]    The emergency release (FIG. 9) includes a cable or rope  123  connected to a user operated handle  121  at a free end and running up through guides  125  which are affixed to the wall  12 . The guides  125  retain the rope  123  in place and allow a 180° change in the rope&#39;s direction of movement. Rope  123  extends between the spring retainer  103 ′ and the wall  12  and passes over protrusion  98 ′ away from wall  12 . The rope  123  is then tied to an anchor  126 . When the door block is to be manually controlled, an operator pulls downwardly on handle  121  which tightens cable  123  and moves protrusion  98 ′ and sliding member  81  back toward the wall  12  freeing tube door  16  to be raised. Advantageously, rope  123  may also be attached to a clutch in opener  20  to release the motor  25  from the chain assembly  21  to ease the manual raising of the door.  
         [0037]    The preceding description is intended to be illustrative of the principles of the invention and modifications can be made to the embodiment and still be within the scope of the invention recited in the appended claims. For example, the torsion spring  120  of the preceding embodiment could be replaced by a counter weight. Further, the distance between the wall and cable tension assembly might be varied by the use of a shim to avoid the use of member  111  attached to door  16 .

Summary:
A cable tension sensing apparatus is mounted on a wall having a door opening. The jack shaft garage door operator includes a drive unit having an electric motor for driving a jack shaft mounted above a door opening. A pull-up cable drum is connected to the jack shaft and has a multi-strand steel pull-up cable that may be payed out to lower a door or wound up to raise the door. The cable tension sensing apparatus includes a cable guide to retain the cable a substantially fixed distance from the wall and a spring driven cable follower which urges against the cable extending between the drum periphery and the cable guide. An alerting switch is connected to the cable follower and sends a signal indicating loss of cable tension when the cable follower moves beyond a predetermined distance. Additionally, the movement of the cable follower moves a door blocking arrangement to a position to block movement of the door when being raised without use of the motor.