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This application is a continuation of application Ser. No. 08/443,178 filed May 17, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates, in general, to barrier operators and, in particular to a garage door operator including a system for detecting when an attempt is made to force open a closed garage door. 
     Several garage door operator systems are available on the market for maintaining a garage door either in a closed or open position. It is clear that the systems should be relatively easy to use and should be able to open the door relatively rapidly to allow quick and easy access to the garage. In addition, many systems are provided which include detectors, pressure detectors and the like that sense when the garage door is being brought down and the bottom edge of the door comes in contact with an obstacle prior to the door reaching the fully closed position. These systems are important because they prevent the garage door from closing on people, pets or small objects and, therefore, prevent personal injury and property damage. One of the drawbacks of such systems, however, is that for some such systems, when the door has been closed, if a lifting force is applied to the door, or instance by an unwanted intruder grabbing the handle of the door and attempting to raise it by jacking the door or the like, some systems through a force measurement routine, automatically cause the door to be opened, in order to prevent what the garage door operator senses might be potential harm. Of course, if the person operating the door is attempting to break and enter the garage for nefarious purposes and it is important that while the system prevents harm, the system also be provided such that the door cannot be forced open if the operator does not want it to be and if no persons or property are in danger. 
     A system available from the Stanley Company provides a garage door operator having upper travel limit and lower travel limit switches associated therewith. The switches may be set or moved so that the limits of travel may be changed. In the Stanley system, for instance, if the door has reached a nominal closed position and the operator has its down limit switch position changed, the door will actually dynamically track changes in the switch position and open or close according to switch commands. 
     Mechanical systems may be available that in effect, jam the door closed; however, once these systems are placed in effect, if a person not knowing that the door is down and effectively mechanically locked attempts to open the door the garage door operator then attempts to lift the door against the locking mechanism and the garage door operator may be inadvertently damaged thereby or, at the very least, not open the door because it is locked. 
     What is needed then is a system which provides a sensing modality for a garage door or other barrier operator which, while maintaining all safety features to prevent personal injury or property damage due to unwanted closing of the door, nevertheless senses when an intruder attempts to open the door and prevents the door from being opened by a positive drive force provided by the garage door operator motor. 
     SUMMARY OF THE INVENTION 
     The invention relates, in general, to a barrier system operator and, in particular, to a garage door operator which while having all safety features for preventing personal injury and property damage due to inadvertent closing of the garage door, nevertheless provides a positively actuated door closure system which prevents forcing the door once it has closed without having detected any objects underneath it. The system includes a barrier drive including an electric motor which may be connected to a belt, chain or screw drive. Means are provided for detecting motion of the movable barrier. These means may include a motor tachometer, upper and lower limit switches and the like. Means are also provided for detecting when a barrier command signal has been given to the barrier drive so that when a door has been commanded by a radio frequency control, the keypad control, indoor wired control or the like to open, the door may be automatically opened. The system also includes a storage device for storing the commanded state of the barrier drive which may be a microcontroller or a microprocessor in combination with a memory or some other integrated circuit device capable of storing digital or analog information. The commanded state is stored and is then compared in a comparator means with the position indicated by the barrier detection. In the event that the comparison of the barrier state signal and the barrier position signal indicates that the system already has been in a lowered position, usually for given time intervals, such as 27 seconds and attempt is made to raise the door causing unwanted motion of the door when there has been no up command given, an alarm signal is generated which may be passed through electronic and electromechanical logic to the door motor causing the door motor to provide thrust to the door to hold the door in the closed position. 
     In the alternative, the system may also provide a signal to operate a visual or audio alarm or to call over a telephonic or other wired system to a police department or to a security service to indicate that the system is being broken into. 
     It is a principal object of the present invention to provide a barrier operator for opening and closing a movable barrier which includes an electronic system for detecting when forced entry is being attempted on the carrier and for preventing the barrier from being opened. 
     Other objects of this 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 
     FIG. 1 is a perspective view of an apparatus comprising a garage door operator and embodying the present invention; 
     FIG. 2 is a block diagram of a portion of the head unit and associated controls of the apparatus shown in FIG. 1; 
     FIG. 3 is  FIGS. 3A-3C are a schematic diagram showing details of the circuit shown in FIG. 2; 
     FIG. 4 is a flow chart of a top level flow diagram for the apparatus embodying the present invention; 
     FIG. 5 is a flow diagram of an upper limit routine; 
     FIGS. 6A and 6B are a flow diagram controlling travel upward; 
     FIG. 7 is a flow diagram of a down limit routine; 
     FIGS. 8A and 8B are a flow chart of a downward or closing movement routine; 
     FIG. 9 is a flow chart of a barrier closed routine; and 
     FIG. 10 is a flow chart of an auto-reverse time delay routine. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings and especially to FIG. 1, more specifically a movable barrier door operator or garage door operator is generally shown therein and includes a head unit  12  mounted within a garage  14 . More specifically, 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. An external control pad  34  is positioned on the outside of the garage having a plurality of buttons thereon and disposed to communicate via radio frequency transmission with the antenna  32  of the head unit  12 . 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 . 
     The head unit  12  has a wired wall control panel  43  connected to it via a line or wire  43   a , as is shown in FIG.  2 . More specifically, the wall control panel  43  is connected to a charging circuit  70  and a discharging circuit  72  coupled via respective lines  74  and  76  to a wall control decoder  78 . The wall control decoder  78  decodes closures of a plurality of switches  80 ,  82  and  84  in the wall circuit. The wall control panel also includes a light emitting diode  86  connected by a resistor  88  to the line  43   a  and to ground. Switch  80  is the command switch, switch  82  is the work light switch and switch  84  is the vacation switch. Switch closures are decoded by the wall decoder  78  which sends signals along lines  90  and  92  to a motor control  94  coupled via motor control lines  96  to an electric motor  98  positioned within the head unit. A tachometer  100  receives a mechanical feed from the motor  98  and provides feedback signals on lines  102  to the motor controller. 
     The receiver unit also includes an antenna  110  coupled to receive radio frequency signals either from the fixed RF keypad  34  or the hand-held transmitter  30 . The RF signals are fed to a radio frequency receiver  112  where they are buffer amplified and supplied to a bandpass circuit  114  which outputs low frequency signals in the range of 1 Hz to 1 kHz. The low frequency signals are fed to an analog-to-digital converter  116  that sends digitized code signals to a radio controller  118 . The radio controller  118  is also connected to receive signals from a non-volatile memory  120  over a non-volatile memory bus  122  and to communicate via lines  124  and  126  with the motor controller  94 . A timer  128  is also provided, coupled via lines  130  with the radio controller, a line  132  with the motor controller and a line  134  with the wall control decoder  78 . A barrier travel limit detection device  190  includes an up limit detector  190   a  and a down limit detector  190   b  that sends signals to pins P 20  and P 21  of the microcontroller  282 (as depicted in FIG.  3 b). The obstacle detector comprising the emitter  42  and detector  46  send signals to pins P 03  and P 30  of the microcontroller  282 (as depicted in FIG. 3b) indicating when an obstacle is blocking the path of the door. 
     Referring now to FIG. 3, the system shown in FIG. 3 is shown therein with the antenna  110  coupled to a reactive divider network  250 , comprised of a pair of series connected inductances  252  and  254  and capacitors  256  and  258 , which supplies an RF signal to the buffer amplifier  112  having an NPN transistor  260  connected to receive the RF signal at its emitter  261 . The NPN transistor  260  has a capacitor  262  connected to it for power supply isolation. The buffer amplifier  112  provides a buffered radio frequency output signal on a lead  268 . The buffered RF signal is fed to an input  270  which forms part of a super-regenerative receiver  272  having an output at a line  274  coupled to the bandpass filter  114  which provides output to a comparator  278 . The bandpass filter  114  and analog-to-digital converter provide a digital level output signal at a lead  280  which is supplied to an input pin P 32  of an 8-bit Zilog microcontroller  282 . 
     The microcontroller  282  may have its mode of operation controlled by a programming or learning switch  300  positioned on the outside of the head unit  12  and coupled via a line  302  to the P 26  pin of the microcontroller  282 . The wired control panel  43  is connected via the lead  43   a  to input pins P 06  and P 07  The microcontroller  282  has a 4 MHz crystal  328  connected to it to provide clock signals. A force sensor  330  includes a bridge circuit having a potentiometer  332  for setting the up force and a potentiometer  334  for setting the down force, respectively connected to inverting terminals of a first comparator  336  and a second comparator  338 . The comparator  336  sends an up force signal over a line  339   a . The comparator  338  sends a down force signal over the line  339   b , respectively to pins P 04  and P 05  of the 8-bit microcontroller  282 . Although details of the operation of the microcontroller in conjunction with other portions of the circuit will be discussed hereinafter, it should be appreciated that the P 01  pin of the microcontroller is connected via a resistor  350  to a line  352  which is coupled to an NPN transistor  354  that controls a light relay  356  which may supply current via a lead  358  to a fight in the head unit or the like. Similarly, the pin P 000  feeds an output signal on a line  360  to a resistor  362  which biases a base of an NPN transistor  364  to cause the transistor  364  to conduct, drawing current through the coil of the relay an up relay  366  causing an up motor command to be sent over a line  90  to the motor  98 . Finally, the P 02  pin sends a signal through a line  370  to a resistor  372  via a line  374  to the base of an NPN transistor  376  connected to control current through a coil of a down control relay  378  which is coupled by one of the leads to the motor  98  to control motion of the motor  98 . 
     Electric power is received on a hot AC line  390  and a neutral line AC line  392  which are coupled to a transformer  393  at its primary winding  394 . The AC is stepped down at a secondary winding  395  and is full wave rectified by a full wave rectifier 3%. It may be appreciated that, in the alternative, a half wave rectifier may also be used. 
     A plurality of filter capacitors  398  receive the full wave rectified fluctuating voltage and remove some transients from the voltage supplying a voltage with reduced fluctuation to an input of a voltage regulator  400 . The voltage regulator  400  produces a 5-volt output signal available at a lead  402  for use in other portions of the circuit. 
     Referring now to FIG. 4, a top level routine is shown therein which is entered every two milliseconds upon at timing interrupt in a step  500 . The routine then enters a variety of other routines depending upon the value of a state number. When the state number is 2 an upper limit routine is entered in a step  502 . If the state number is 1, a traveling up routine is entered in a state  504 . If the state is 5, a down limit routine is entered in a step  506 . If the state is 4, a traveling down routine is entered in a step  508 . If the state is 6, a barrier halt or stopped in middle routine is entered in a step  510 . If the state is 0, an auto-reverse time delay routine is entered in a step  512 . When any of the aforementioned routines  502  through  512  are exited, a return step  514  is entered and other portions of code not pertinent to this invention are executed. 
     In the event that the state equals 2, the routine  502  is entered as may best be seen in FIG. 5 wherein the upper limit switch has indicated that the door has reached the upper end of its authorized travel, the motor is switched off and a watchdog timer is started in a step  514 . The work light command flag is set in step  516  to toggle the work light on. In a step  518 , a radio command or wall control command flag is tested for and, if set, the state is set to  4 . In a step  520 , the routine is exited and return is switched to the step  514 . In the event that the state has been set equal to  4 , in step  518  at the next 2 millisecond interval, control is transferred to the routine  508 . 
     In the event that the state has been set equal to 1, control is transferred to a barrier traveling up or a barrier opening routine shown in FIGS. 6A and 6B. In a step  522 , the work light is turned on and in the event that the light was off, a delay of 40 milliseconds is then provided to turn on the up motor output, the down motor output is turned off and the hold door closed flag is cleared. In a step  524 , after a start up delay of 1 second the rpm period of the tachometer is tested against the look up force and if the rpm period is too brief, a state is set to indicate that the door has stopped in mid travel. In a step  526 , a test is made to determine whether the one second timer has exceeded one second and whether the rpm period is below the set force limit indicating that the door has been halted in an unwanted manner. If it is not, control is transferred to a step  528  wherein the state variable is set to 6, following which the routine is exited in a step  530 . In the event that the decision in step  526  is positive, the up limit input is tested. If the voltage is low, it is increased. If it is high, the debounce is decreased. Control is then transferred to a test step  532  to test whether the limit debounce is greater than 24 milliseconds. If it is, the state is set equal to 2 in a step  534  and the routine is exited in a step  536 . If the limit debounce is less than 24 milliseconds, control is transferred to a step  540  where a 27 second time out is decremented and tested for. If the time out is zero, the state is set as indicating that the door has stopped in mid travel. A step  542  is executed to test for either a radio or wall control command flag having been set and, if so, the state is set as stop in mid travel. The routine is then executed in a step  544 . 
     In the event that the state has been set equal to 5, a routine  506  to handle down limits, as shown in FIG. 7, is entered. In a step  550 , a hold door closed flag is tested to determine whether it is set or not. If it is not set, control is transferred to a step  552  to determine whether the 27 seconds timer has timed out following the down limit having been set, indicating that the door has safely closed and did not contact an obstruction or obstacle. In the event that the hold door closed flag has been set, as tested for in step  550 , control is transferred to a step  554  testing whether the down limit indicates the door is open and whether the motor has been given enough current or turned on long enough to provide 10 rpm pulses. In the event that the 27 second clock has not been timed out as indicated by step  552 , control is transferred to a step  556 , switching the motor off, and starting a watchdog timer. Control is then transferred to a step  558  to determine if the work light command flag has been set and, if it has, the work light is toggled. Control is then transferred to a step  560 , testing for whether there is a radio command or wall control command flag. If so, the state is set equal to 1 and the routine is exited in a return step  562 . In the event that the down limit does not indicate that the door is open and the motor has been turned enough to give 10 rpm pulses, control is transferred to a step  564  setting the state equal to 4 and setting the hold door closed flag. The state equal 4 indicates that the door is to be traveling down, thereby causing the barrier to close after the 27 second limit has timed out. 
     In the event the state has been set equal to 4 to command the door to travel down, the routine  508  is entered as shown in FIGS. 8A and 8B. In a step  570 , the work light is turned on, and if the light had previously been off, a delay of 40 milliseconds occurs following which down motor output is turned on and the up motor output is turned off, the watchdog is also started. In a step  572 , a test is made to determine whether the 1 second timer has exceeded 1 second and whether the rpm period is indicative of a force limit having been exceeded. If so, indicating that the door is stalled on an obstacle, control is transferred to a step  574 , setting a state equal to zero and the routine is exited in a step  576 . If the door has not been indicated to be stalled by the step  572 , control is transferred to a step  578  testing the status of the down limit input. If it is low, the debounce is increased. If it is high, the debounce is decreased. In a step  580 , the limit debounce is tested to determine whether it is greater than or equal to 24 milliseconds. If it is, the state is set equal to 5 in a step  582  and the routine is exited in a step  584 . If it is not, the 27 second time out is decremented and tested to determine if it is zero. If it is zero, the state is set equal to zero in a step  586 . In a step  588 , a test is made to determine whether the radio or wall control command flag has been set and, if so, the state is then set equal to 6. In a step  590 , as shown in FIG. 8B, the timer associated with the optical detector is tested to determine whether it is greater than 10 milliseconds and, if it is, indicating that an obstacle is blocking the light path, the state is set equal to zero to cause the auto-reverse routine  512  to be entered following exiting from this routine. It will be entered on the next interrupt which is in less than 2 milliseconds. Control is then transferred to a step  592 , testing whether the motor speed indicated that the door had been forced upward. If it is not the routine is exited in a step  594 . If the rpm sensing indicates that the door has been forced upward, a test is made in the step  596  to determine if the command is still valid, indicating the door is to move upward. If it is not, control is transferred to a step  598  setting the state equal to zero which will cause the door to auto reverse and move down. Control is then transferred to a step  600  exiting the routine. 
     In the event that the state has been set equal to 6, the routine  510  shown in FIG. 9 is entered. A test is made to determine whether the motor motion indicates that the door has been forced upward. If so, a flag is set to turn off the light and the electric motor is switched off and the watchdog is started. If the worklight command flag has been set in a step  604 , the work light is then toggled. In a step  606 , a test is made to determine whether the radio command or wall control command flag has been set and, if it has, the state is then set equal to 4 which will cause entry of the traveling down routine  508 . The routine is then exited in a step  608 . 
     In the event that the state has been set equal to zero indicating that an auto reverse is to be commanded, the routine  512  is entered in a step  620 , the motor is turned off and a watchdog timer is started. In the step  622 , the delay timer is decreased and if 0.5 seconds has expired, the state is set equal to 1 to cause the door to travel upward on the next 2 millisecond interrupt. In a step  624 , a test is made for the radio command or wall control command flag being set. If it has, the stopped in middle routine  510  will be entered on the next interrupt. The routine  512  is then exited in a step  626 . 
     While there has been illustrated and described a particular embodiment 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.

Summary:
A movable barrier or garage door operator has a barrier drive for moving the movable barrier or garage door between open and closed positions. Motion of the barrier is detected by a tachometer connected to the barrier drive or by upper and lower barrier travel limit switches. A test is made to determine if the barrier has been commanded to be in a closed state and to determine if a preselected time interval has elapsed following closure of the barrier. When both of those conditions are present and the door is moved upward without authorization an alarm signal is generated and can signal the barrier drive to apply a closing force. The timer prevents the barrier from being closed on a person or obstacle during normal operation and prevents injury. An obstacle detector also prevents unwanted closure on an obstacle.