Abstract:
A garage door opening and closing apparatus having improved operational safety includes a control circuit which responds to a number of input stimuli to generate commands to open and close a garage door as well as to stop garage door movement. Three relays respond to the commands via drive circuitry to actually connect door operating voltages to the windings of a door controlling motor. By redundancies in the operation of the three relays, faults in the operation of those relays result in safe door operating conditions. Additionally, the control circuitry upon issuing a door stop command, performs a test to determine whether or not the door is still moving. If the door is still moving, door up commands are generated by the control circuitry to place the door in a safe position.

Description:
This is a continuation of prior application Ser. No. 09/156,064, filed Sep. 17, 1998, now U.S. Pat. No. 5,998,980 which is a Continuation of application Ser. No. 08/823,727, filed Mar. 25, 1997, now U.S. Pat. No. 5,841,253, which is a continuation of application Ser. No. application Ser. No. 08/588,227, filed Jan. 18, 1996, now U.S. Pat. No. 5,684,372, which is a continuation of application Ser. No. 08/465,606, filed Jun. 5, 1995, now abandoned, which is a Continuation of application Ser. No. 08/367,920 filed Jan. 3, 1995, now abandoned, which is a Continuation of application Ser. No. 08/200,292, filed Feb. 22, 1994, now abandoned, which is a Continuation of application Ser. No. 07/964,566, filed Oct. 21, 1992, now abandoned, which is a Continuation of application Ser. No. 07/682,671, filed Apr. 9, 1991, now abandoned, which are hereby incorporated herein by reference in their entirety. The entire disclosure of the prior application, from which a copy of the oath or declaration is supplied under paragraph 3 below, is considered as being part of the disclosure of the accompanying application, and is hereby incorporated by reference therein. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to door opening and closing apparatus and particularly to methods and apparatus for improving the operational safety of door opening and closing apparatus. 
     A garage door operator for opening and closing doors typically includes an electrical motor having an up winding and a down winding. When the up winding is energized by an operating voltage, the motor shaft rotates in one direction to raise the door and when the down winding is energized by the operating voltage, the motor shaft rotates in the opposite direction to lower the door. A control unit responds to external stimuli such as door open and close request signals by energizing the proper winding to serve the request. The actual connection of the operating voltage to the up and down windings is provided by a pair of relays, one associated with each winding, the relays respond to signals from the control unit by connecting the source of operating voltage to their associated windings. The control unit frequently comprises integrated circuit logic which individually operates the relays via relay drivers. 
     Integrated circuit logic is subject to faults as are relay drivers and relays themselves. Thus, improper relay control signals can be generated by the integrated circuit logic or proper control signals can be inappropriately responded to by the drivers and relays. Although such faulty operation is infrequent, the effects of such are to be avoided, since they can, in extreme situations, cause injury to people in the vicinity of the apparatus. 
     The problem of faulty operation has been recognized and systems devised to protect individuals from faulty operation. U.S. Pat. No. 4,338,553 to Scott, discloses an apparatus which, when a door limit controlling oscillator fails, generates relay control signals to move a door to the up position. The Scott arrangements checks only the proper oscillator operation, and does not determine proper door operation in response to generated control signals. U. K. Patent Application No. 2 072 884 to Matsuoka, et al., discloses an apparatus which uses timers to check for proper door operation. When a door operation such as opening the door, is not completed within a period of time, e.g., 23 seconds, representing the maximum time for the completion of the operation, the timer signals a fault and remedial action is taken. The remedial action is to remove the driving voltage from both up and down motor windings by means of a first relay and to energize the up winding by means of a second relay. Importantly, no fault will be sensed by the disclosed arrangement until a door movement should b completed, e.g., 23 seconds, by which time injury may have occurred. Also importantly, the additional relays and circuitry required for the response to faulty door operation are not normally exercised so that faults within them will remain untested and the additional relays and circuitry add to the expense and complexity of the apparatus. 
     Known fault protection systems for garage door operators do not detect inappropriate door movement rapidly enough, are not tested by normal operation, and add unncessarily to the expense and complexity of the overall apparatus. 
     SUMMARY OF THE INVENTION 
     The present invention solves the problems of prior systems by rapidly sensing inappropriate door movement and terminating such inappropriate movement using a minimum amount of additional circuitry, which is routinely exercised to protect against latent faults. The apparatus of the present invention includes circuitry for sensing the rotation of the door driving motor shaft and checking such rotation after issuing door operating commands. When the measured rotation is not appropriate for the last door operating command, fault control signals are generated. The door controlling circuitry of the apparatus includes three (3) door controlling switch arrangements for selectively energizing the up and down motor windings of the door driving motor. A control unit operates in cooperation with the motor shaft rotation sensor to detect improper door movement and to control the switching circuits to stop and move the door up. Upward movement of the door is assured when faced with any single fault in the door control circuitry. 
     An apparatus for opening and closing a garage door in accordance with the present invention comprises a motor with a rotatable member for rotating in a first direction to open the garage door and in a second direction to close the garage door, and motor control circuitry responsive to control commands for selectively connecting electrical power to the motor to cause rotation of the rotatable member. A control arrangement, shown in the embodiment as a logic unit, responds to external stimuli by selectively sending control commands specifying rotation of the rotatable member in the first direction, rotation of the rotatable member in the second direction or no rotation by the rotatable member. After predetermined control commands, the actual rotation of the rotatable member is sensed and when actual sensed rotation is not in accordance with the last control command, fault control signals are sent to the motor control circuitry. The fault control signals can be used to cause the motor to raise the door to its safe upper limit. 
     Advantageously, the motor control circuitry comprises a plurality of relays which cooperate to provide safe operation of the door when faults occur within the motor control circuitry. In the preferred embodiment, the motor includes up and down windings for controlling the two directions of rotatable member rotation. The motor control circuitry includes a first relay which responds to control commands by connecting electrical power to either the up motor winding or to an intermediate conductor. A second relay responds to control commands by selectively connecting the intermediate conductor from the first relay to the down winding, and a third relay responds to control commands by connecting electrical power to the up winding. By this interconnection of relays, door movement can always be stopped and in most situations, it will be stopped in the upmost door position. 
     The logic unit of the embodiment responds to the external stimuli by generating upward movement control commands, downward movement control commands and door stop commands. When the door movement after a command is not in accordance with the command, the logic unit generates fault control signals which cause upward movement of the door. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the garage door operator of the invention installed to operate a garage door; 
     FIG. 2 is a block diagram of a control circuit of the garage door operator; 
     FIG. 3 illustrates the control of limit switches by a rotatable member of a garage door operator; 
     FIG. 4 illustrates a garage door operator motor and rotation determining apparatus; and 
     FIG. 5 is a state diagram of the operation of the garage door operator control circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 illustrates the garage door operator  10  of the invention installed to move a garage door  14  positioned proximate with a door opening  14   a , which is mounted on tracks in a conventional manner. A head unit  11  of the garage door operator  10  includes a motor ( 211  FIG.  4 ), which is mounted in the head unit and has an output which drives an endless chain  15 . A trolley  13  is engageable with the chain  15  and moves on a rail  12 . Trolley  13  includes an arm  16  which is connected by a bracket  17  to the door  14  to move the door up and down. A control unit  19  is connected by an electrical cable  22  to control circuitry mounted in head unit  11 . Control unit  19  has a plurality of buttons which can be actuated for the control of the garage door operator  10 . A transmitter  24  can be used to actuate the garage door operator  10  remotely by transmitting a radio signal which is received by a receiver mounted in the head unit  11 . 
     FIG. 2 is a block diagram of the control circuit contained in head unit  11 . The control circuit includes a multi-function integrated circuit logic unit  101 , which responds to a plurality of inputs in the manner discussed below, by selectively sending one of a plurality of motor control commands to motor control circuitry  147  to control the opening and closing of the garage door. Power is supplied to the circuitry of FIG. 2 from a transformer and diode combination (not shown) which supply approximately 28 volts DC to a positive terminal  102   a  of a capacitor  102 . The 28 volt DC is also coupled to a 5 volt regulator  103  which produces approximately 5 volts for use by the integrated circuit logic  101  and certain of the circuits connected thereto. 
     One input to logic  101  is a command signal CMD-R on a conductor  105  from a receiver/decoder  106 . The receiver/decoder  106  receives an encoded electromagnetic radiation signal from the remote transmitter  24  at an antenna  107 , detects the received encoded signal and verifies accuracy of the detected signal by comparing it to one or more stored permitted code words. When signal detected by receiver/detector  106  matches a permitted code word stored within the receiver/detector, a transitory logic  1  signal is sent to logic unit  101  via conductor  105 , as the signal CMD-R. The details of code reception from remote transmitters and the verification of received codes are described in detail in U.S. Pat. No. 4,750,118 to Heitschel, et al., and application Ser. No. 626,909 to Heitschel, et al. 
     Another command signal, CMD-P, is a transitory logic  0  which is applied to logic  101  via a conductor  108 , when a push-button  39  is pressed at control unit  19 . The signals CMD-R and CMD-P are the primary operator controlled input signals to logic unit  101 . The signal CMD-R indicates that a verified code was detected by receiver/detector  106  and the signal CMD-P indicates that push button  39  was pressed. As discussed in greater detail later herein, logic unit  101  interprets the receipt of these signals based on the state of the logic unit when they are received to control the operation of door  14 . Other input signals such as signals from an up limit switch  110  and a down limit switch  111  are provided by the operation of the door opening and closing apparatus itself. 
     Up and down limit switches  110  and  111  are contained in head unit  11  and are controlled by an assembly  200  shown in FIG.  3 . The limit switch assembly  200  of FIG. 3 includes a threaded drive shaft  201 , which is attached to (not shown) and rotated by a motor  211  through a gear  203 . Gear  203  is connected to the shaft  201  of driving motor  211  so that the rotation of the motor shaft  213  causes the rotation of threaded drive shaft  201 . A switch actuating member  205  having an threaded aperture therethrough is threaded onto drive shaft  201  and kept from rotating by a securing member  207 . When the motor  211  is energized to rotate in a direction to raise the door  14 , shaft  201  rotates in a first direction and the actuation member  205  rises by the rotation of the shaft  201  acting through the threads. Similarly, as the motor shaft  213  and the shaft  201  rotate in the reverse direction, actuating member  205  travels downwardly. Actuating member  205  includes a protruberance  209  which engages and closes up limit switch  110  at the top of door travel and at the bottom of door travel, engages and closes down limit switch  111 . When the door opening apparatus  10  of FIG. 1 is first fitted to the door  14 , the positions of limit switches  110  and  111  are adjusted so that down limit switch  111  closes when the door  14  is in its maximum closed position and up limit switch  110  closes when the door  14  is in its maximum open or raised position. After initial adjustment, maximum open position is determined when the up limit switch  110  connects an electrical ground  112  to an up limit conductor  113  and the maximum down position is detected when switch  111  connects electrical ground  112  to a down limit conductor  115 . Up limit conductor  113  and down limit conductor  115  are connected as inputs UL and DL, respectively, to logic unit  101 . 
     The apparatus of FIG. 2 also includes an infrared obstruction detector  117 . Obstruction detector  117  transmits an infrared light beam from one side of the door opening  14   a  to the other at a suitable height, such as one foot, in order to detect people or objects which might be contacted by a closing door. Normally, the infrared beam will pass fresly from one side of the door opening  14   a  to the other and, the obstruction detector  117  will send a low logic level signal to the base of an NPN transistor  119 . The low logic level signal will not turn transistor  119  n and an approximately 5 volt signal is applied to an input AOBS of logic unit  101 , via conductor  120  and the operation of resistors  121  through  123 , energized by a positive 28 volt potential. Alternatively, when the infrared bean strikes an object in the doorway and does not pass from side to side, a logic high signal is applied to the base of transistor  119 , resulting in a signal near electrical ground being applied to the input AOBS of logic unit  101 . 
     Logic unit  101  also receives at an input RPM a signal indicative of the rotation of the shaft  213  of motor  211 . FIG. 4 shows motor  211  and an apparatus  214  for sensing the rotation of its shaft  213 . A disk  215  is attached to shaft  213  normal to the shafts its access of rotation. Five light obstructing pins  217  are attached to the disk  215  in equally spaced relationship a common distance from the center of shaft  213 . A light transmitting element, such as a light emitting diode  127 , is fixedly attached to the same substrate as the motor  211  and in a position between the pins  217  and the center of shaft  213 . A light receiver, such as a phototransistor  128 , is attached outside the circle traced by pins  217  to receive light from the light emitting diode  127 . As the motor shaft  13  rotates, light is transmitted from light emitting diode  127  to a base  128   a  of a phototransistor  128  when no pin is therebetween and no light is passed when a pin  217  is present between light emitting diode  127  and phototransistor  128 . The electrical connections from light emitting diode  127  and phototransistor  128  are shown in FIG.  2 . When motor shaft  213  is rotating, light will alternately be blocked and passed between light emitting diode  127  and the base of phototransistor  128 , causing phototransistor  128  to alternately be turned on and off. By connection to a 5 volt supply through a resistor  129 , a square wave is applied by phototransistor  128  to conductor  125 , when motor shaft  213  is rotated. Conductor  125  is connected to the input RPM of logic unit  101 . The duty cycle of the square wave applied to the input RPM is determined by the spacing between pins  217  relative to the diameter of pins  217 , and is not critical in the present invention. 
     The signal from phototransistor  128  is also applied via conductor  125  to a pulse counter  251  and a monostable multi-vibrator  252 . Pulse counter  251  is used to generate and transmit a signal MOV to logic unit  101  on conductor  256  when the motor shaft  213  is rotating at or above a predetermined rate. The pulse counter  251  includes a resettable binary pulse counter which counts each low to high transition on conductor  125  and records the count in binary format in an 8-bit shift register (not shown). When the shift register counts 25 or more transitions without being reset, a logic  1  signal is sent by the pulse counter  251  via the conductor  256  to the MOV pin of the logic unit  101 . Logic unit  101  comprises an internal oscillator and circuitry for generating a number of timing signals. The period of the oscillator is determined by the value of a resistor  254  and a capacitor  255  connected between ground and terminals OSC  1  and OSC  2  of the logic unit  101 . One timing signal is generated by the logic unit  101  every 0.5 seconds and is applied as a reset signal to pulse counter  251  via a conductor  257 . The register of pulse counter  251  is cleared to zero in response to each reset signal. Thus, the value counted by counter  251  will exceed 25 only if 25 or more low to high transitions occur on conductor  125  during a 0.5 second interval. That is, when shaft  213  is not rotating or rotating at a rate which causes fewer than 25 transitions during each 0.5 second interval, no signal NOV will be received at the NOV terminal by logic unit  101 , because pulse counter  251  will be reset prior to its counting to 25. Alternatively, a signal MOV will be received by logic unit  101  when shaft  213  is rotating at a rate which produces greater than 25 pulses each 0.5 second. 
     Monostable multi-vibrator  252  is used to determine the movement resistance forces applied to the door during its movement. When the movement resistance forces exceed a predetermined amount, a force obstruction signal OBS is applied by monostable  252  to logic unit  101  via a conductor  258 . The basic principle of operation is that the rate of rotation of the door motor shaft  213  decreases as the resistance forces on the door increase. Monostable  252  is set by potentiometer  253  to generate a pulse OBS on conductor  258  at a predetermined interval unless the monostable is reset by a low to high transition of the signal on conductor  125  during an interval. When monostable  252  is reset, timing for a new pulse begins again. In the present embodiment, monostable  252  is adjusted by potentiometer  253  to produce a pulse on conductor  258  25 milliseconds after being reset by the signal on conductor  125 . When the rotation of motor shaft  213  causes the phototransistor  128  to produce pulses on conductor  125  at intervals less than 25 milliseconds, monostable  252  will continue to be reset thereby without generating a signal OBS on conductor  258 . Alternatively, should the motor shaft rotation rate slow sufficiently that the pulses are generated on conductor  125  at intervals greater than 25 milliseconds, monostable  252  will time out and generate a signal OBS on conductor  258 . 
     Pulse counter  251 , monostable  252  and their associated circuitry are shown separated from logic unit  101 . The functions of these devices could be incorporated into the single integrated circuit of logic unit  101  such that the signals MOV and OBS would be generated entirely internal to the logic unit  101 . 
     Logic unit  101  responds to the previously described input signals by sending a selected one of a plurality of motor control commands to motor control circuitry  147  including three relays  130 ,  131  and  132 , thereby opening and closing door  14  on command. Door motor  211  includes an up winding  225  connected between an incoming motor conductor  220  and common  221  by a thermal reset switch  229  and a down winding  227  which is connected between an incoming motor conductor  222  and common  221  via the thermal reset switch  229 . Door  14  is controlled to move up by selectively connecting 120 volts AC to up winding  225  via the conductor  220  and is controlled to move down by the connection of 120 volts AC to down winding  227  via conductor  222 . The selective connection of the 120V operating voltage to the up and down windings  225  and  227  is performed by motor control circuitry relays  130 ,  131  and  132  which operate in response to control commands from logic unit  101 . 
     Relay  130  includes a normally open contact set  136  which is connected in series between the 120 volt operating voltage applied to a conductor  134  and both the up winding  225  and a normally open contact  138  of relay  131 . The state of relay  130  is controlled by signals from logic unit  101  on a conductor  140 . When the UPMTR2 signal on conductor  140  from logic unit  101  is a low level, a transistor  141  which has its emitter-collector path connected in series with the coil of relay  130  is in a high impedance state and relay  130  is not energized. Alternatively, when the signal UPMTR2 from logic unit  101  is a high level, transistor  141  is driven to a low impedance state energizing the relay  130  and closing contact set  136  so that the 120V AC potential is supplied to up winding  225 . 
     The relay  131  includes an armatur  137  which is connected to the 120 volt conductor  134 , a normally open stationary contact  138  and a normally closed stationary contact  139 . The particular on of stationary contacts  138  and  139  which is connected by armatur  137  to the 120 volt supply, is determined by signal UPMTR1 from line unit  101  on conductor  142 . In a manner similar to the operation of relay  130 , relay  131  is energized and de-energized by the operation of transistor  143  in response to the signal UPMTR1. The normally closed contact  139  connects the 120 volt conductor  134  to armature of relay  132  while the normally open contact  138  of relay  131  is connected to up winding  225  via conductor  220 . 
     Relay  132 , which is controlled by a signal DWNMTR on a conductor  144  operating through a transistor  145 , includes a normally open stationary contact set  146  connected in series with down winding  227 . Whenever relay  132  is non-energized, no voltage is applied to the down winding  227 . Alternatively, when relay  132  is energized either the 120 volt conductor  134  or an open circuit is applied to down winding  227 , depending on the state of relay  131 . 
     The connection and operation of relays  130  through  132  provides certain redundancies in operation so that no single fault from the logic unit  101  through the relays  130  through  132  will prevent the door  14  from moving to the up position, which is considered safe. Logic unit  101  generates motor control commands consisting of the signals shown in Table 1 to control the movement of door  14  up and down and to stop the door. The door  14  is moved up by sending high level (logical  1 ) signals on both UPMTR1 and UPMTR2 and a low level (logical  0 ) signal on DWNMTR. Both relays  130  and  131  are energized by the up signals which redundantly apply 120 volts to up winding  225  via contact  136  of relay  130  and contact  138  of relay  131 . Also, energizing relay  131  removes the connection of 120 volts to the down direction controlling relay  132 . 
     The door  14  is moved down by energizing relay  132  while de-energizing relays  130  and  131 . De-energizing relay  131  connects the 120 volts from conductor  134  to the armature of relay  132  which is connected to down winding  227  by closure of relay  132 . In the stop condition, none of the relays  130  through  131  is energized and neither of the motor windings  225  or  227  receives the 120 volts from conductor  134 . 
     
       
         
               
               
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 MOTOR CONTROL 
                   
                   
                   
               
               
                   
                 COMMAND 
                 UPMTR1 
                 UPMTR2 
                 DWNMTR 
               
               
                   
                   
               
             
             
               
                   
                 Up 
                 1 
                 1 
                 0 
               
               
                   
                 Down 
                 0 
                 0 
                 1 
               
               
                   
                 Stop 
                 0 
                 0 
                 0 
               
               
                   
                   
               
             
          
         
       
     
     FIG. 5 is a state diagram showing the various states of the logic unit  101  and the inputs thereto which cause state changes. In the following description, it is assumed that the up and down limit switches  110  and  111  are properly set, that the movement force adjustment is set by potentiometer  253  and that the garage door operator  10  has just been powered up. Also, in the terminology of FIG. 5, any signal with a bar above it refers to the absence of that signal and the term CMD refers to either a command signal CMD-P from control unit  19  or a command signal CMD-R from the receiver/decoder  106 . 
     Upon power up, an idle state  150  (FIG. 5) is entered. The idle state  150  is the normal waiting state when the door  14  is at its up or down limit. In the idl state, the stop signals of Table 1 are sent to control relays  130  through  132  via respective driver transistors  141 ,  143  and  145 . When the circuitry and relays are operating without fault, the stop signals de-energize the windings  225  and  227  of motor  211  and motor shaft  213  is stationary. For reasons of safety, the rotation of motor shaft  213  is checked whenever the motor  211  is commanded to stop. When the rotation indicating signal MOV is detected by logic unit  101  one second after generating the stop command, control is transferred to the move up state  154  where the door  14  is raised to its safe upper limit position, if possible. When the motor  211  does stop rotating in response to the stop command, control remains in a loop  152  of the idle state  150  as long as no command is received (CMD) or as long as both the up and down limit signals (DL:UL) are received. Simultaneous up and down limit signals indicate a fault and no door movement is initiated during such conditions. 
     Assuming that the simultaneous UL and DL signals do not exist, control leaves the idle state  150  when either command signal CMD-R or CMD-P is received. When the command is a CMD-P signal, logic unit  101  checks whether the door  14  is at its up limit UL or its down limit DL as indicated by the states of up and down limit switches  110  and  111 . If the door  14  is at the down limit DL, control proceeds from the idle state  150  to a move up state  154  via a path  156 . In the move up state  154 , the up signals of Table 1 are sent to control relays  130  through  132  and a loop  158  is entered. When the up limit UL is reached without encountering a force obstruction (OBS) control returns via a path  160  to the idle state  150 . Control will also return to the idle state  150  when 27 seconds have passed in the move up state  154  without receiving an up limit signal UL. This last mentioned condition is a fault condition, since door travel time should never be as long as 27 seconds. 
     When control is in the idle state  150  and a command signal CMD-P is received while the door  14  is up (UL), control passes via a path  162  to the move down state  164 . In move down state  164 , the down signals of Table 1 are sent to relays  130  through  132  and a loop  166  is entered which will be exited if any of the signals AOBS, CMD or OBS are received or if 27 seconds pass in the move down state  164 . When the signal DL is received without a force obstruction (OBS) having occurred, control moves from move down state  164  to the idle state  150  via a path  168 . Should 27 seconds expire or one of the signals AOBS, OBS or CMD be received by the logic unit  101  while in the move down state  164 , control proceeds to a stop and wait state  170  via a path  172 . Control pauses in the stop and wait state  170  for one-half second then proceeds to the move up state  154 , which is discussed above, via a path  174 . 
     In the preceding description, control exits the idle state  150  in response to a command signal CMD-P from control unit  19 . When a command signal CMD-R is received from receiver/decoder  106  while in the idle state  150 , control moves to a move up state  176  via a path  178  when the down limit is present and moves to a move down state  180  via a path  182  when the up limit signal UL is present. In move up state  176 , the up signals of Table 1 are sent to control relays  130  through  132  and a pause of 1.2 seconds occurs in a loop  184 . During the 1.2 second pause, other command signals CMD-R are ignored so that multiple transmissions from remote transmitter  24  (FIG. 1) will not each be responded to as a separate signal. Should the up limit signal UL occur while in the move up state  176 , control will return to the idle state  150  via a path  186 . However, the more likely state change via a path  188  occurs when the 1.2 second period expires, giving control to move up state  154 , which has been previously discussed. 
     The move down state  180  is entered from idle state  150  when the door  14  is at its up limit (UL) and a CMD-R command is received. In move down stat  180 , the down signals of Table 1 are generated and a 1.2 second pause, similar to the 1.2 second pause of move up state  176 , is inserted before transferring control to the previously discussed move down state  164  via a path  190 . Should the down limit signal DL be received while in the move down state  180 , control returns to the idle state  150  via a path  192 . Also, if either a force obstruction (OBS) or infrared obstruction (AOBS) occurs while in the move down state  180 , control moves to the stop and wait state  170  via a path  194 . 
     The state diagram of FIG. 5 also includes a stop state  195  which is entered via a path  196  if an up limit signal (UL) is received in the stop and wait state  170 , via a path  197  if a force obstruction signal (OBS) occurs in the move up state  176  and via a path  198  if either a force obstruction (OBS) or a command CMD is received while in the move up state  154 . In the stop state  195 , the stop signals of Table 1 are sent to control relays  130  through  132 . As previously described, whenever the control relays  130  through  132  are commanded to stop door movement, the motor shaft rotation is checked to make certain that the motor  211  has actually stopped. When a signal MOV indicating motor shaft rotation is sensed by logic unit  101  in the stop state  195 , logic unit  101  detects a fault and control moves via a path  199  to the move up state  154  to raise the door  14  if possible. The up command sent to the control relays  130  through  132  in this situation, is considered a fault control signal intended to recover the garage door operator  10  from the detected motor rotation fault. When no motor rotation is detected in stop state  195 , control will remain in stop state  195  until a command CMD signal is received which moves control to the previously discussed move down stat  164  via path  193 . 
     Any of the relays  130  through  132  can fail in the energized or in the non-energized position due to faults in the relay e.g.,  130 , its drive circuitry e.g., transistor  141  or the control signal source, e.g., logic unit  101 . Should relay  130  fail in the non-energized position, the door  14  will respond normally to signals UPMTR2 and DWNMTR from logic unit  101  to raise and lover door  14 . Alternatively, should relay  130  fail in the energized position, the door  14  will only travel up. Both of the failure states of relay  130  are safe since the door  14  either operates correctly or is being moved up. When the command down (Table 1) is generated with relay  130  failing in the energized position, both up and down windings  225  and  227  are energized, stopping motor rotation. Thermal switch  229  protects from any overheating in this dual winding energized mode by interrupting current to the windings  225  and  227 . 
     Should relay  131  fail in the non-energized position, up and down movement of the door  14  is still correctly controlled by signals UPMTR1 and DWNMTR. Alternatively, should relay  131  fail in the energized position, the door  14  will travel up to the up limit and stop. No down movement of the door  14  is then possible, which is a safe failure mode. 
     Should relay  132  fail in the non-energized position, the door  14  is limited to upward movement. Alternatively, should relay  132  fail in the energized position, the door  14  will travel down during a stop command (Table 1). However, the continued movement during a stop command will be sensed by the signal NOV and the door  14  will be raised to its up limit. 
     While a preferred embodiment of the invention has been illustrated, it will be obvious to those skilled in the art that various modifications and changes may be made thereto without departing from the scope of the invention as defined in the appended Claims.