US3539894A - Garage door control circuit - Google Patents

Description

Nov. 10, 1970 H. FELDMAN 3,539,894 GARAGE DOOR CONTROL CIRCUITI Filed May 27, 1968 3 Sheets-Sheet 1 I 13 I 23w i I MoA/asmaLE 2 7 5W] TC FAD/0 I 33.1

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I GARAGE DOOR CONTROL CIRCUIT Filed May 27, 1968 3 Sheets-Sheet 5 United States Patent Office 3,539,894 Patented Nov. 10, 1970 U.S. Cl. 318-463 8 Claims ABSTRACT OF THE DISCLOSURE A garage door control circuit responsive to the speed of rotation of the output shaft of a slip clutch coupled between a drive motor output shaft and the garage door, the control circuit including a monostable circuit responsive to the speed of the slip clutch output shaft and having a normal stable state which deenergizes said motor and an unstable state which operates said motor, and means for holding the monostable circuit in its unstable state while the slip clutch output shaft is running at a normal speed and permitting the monostable circuit to return to its stable state when the slip clutch output shaft operates at a lower speed indicating substantial slippage between the slip clutch output shaft and the motor output shaft.

This invention relates primarily to garage door control circuits for starting and stopping the motors which operate the garage doors, particularly motors as used in radio controlled garage door operators. However, the invention has other possible applications where, for example, a motor controls the movement of a member between extreme limits and it is desirable to shut the motor off when a physical obstruction to such movement occurs.

Modern residential garage door operators are nearly always equipped with a radio receiver for starting and stopping the door in response to transmitted pulsations generated by a transmitter in the owners automobile. The radio control, for reasons of economy, convenience of use and reliability of operation, is a single channel communication system analogous to a single pair of wires in a wire communications system. The output of the receiver generally provides a momentary, circuit closing, ground signal across the output terminals of the receiver when the garage door opening or closing operation is desired. Consequently, it is universal practice to provide the starting and stopping functions by sequential action of the motor controller in the door operator mechanism. This sequential control thus requires only a pair of wires running from the receiver output terminals and one or more manually operable wall mounted pushbutton switches inside the garage or home which provide a momentary circuit closing ground signal when a garage door opening, closing or stopping operation is desired.

A large variety of sequential or stepping type relays are available for controlling the garage door operator motor. The earliest versions of these relays use a ratchet and pawl mechanism. Each impulse indexes a shaft to provide a fixed amount of rotation. Cams attached to the shaft operate contacts that open and close with alternate impulses. Other versions employ arocker'arm arrangement that operates in toggle fashion to provide the alternate action. One of the most popular types uses a mechanism that latches on the first impulses and unlatches with the second impulses. These relays are commonly known as sequence, ratchet, mechanically held, or single coil impulse relays.

The use of mechanical sequence relays like those described above are used in many door operators being manufactured today. These relays are generally more expensive than the general purpose types, often costing two or three times as much. Furthermore, they are far less reliable than general purpose relays and as a result have always accounted for a large part of the failures and service costs in residential garage door operators.

The present invention provides a more economical and reliable system for controlling the garage door operator motor by replacing mechanical sequence relay circuits with a solid state sequencing or toggle control circuit which controls a general purpose relay and which is designed to be operated also by safety and limit switches for stopping the motor automatically when the garage door reaches the end of its path of travel or is prevented from reaching the normal end of its path of travel by an obstruction or the like. Furthermore, it is usually desirable that the safety and limit switches be given priority over the pushbutton and radio control, so that the limits will not be overrun nor the safety defeated by a failure in the radio control, a short circuit in the pushbutton wiring or someone deliberately holding a button down. The circuit to be described provides for these features with no added cost.

Motor drive arrangements for garage door operators commonly employ a mechanical slip clutch to limit the load on the drive motor where the garage door movement is obstructed between its extreme limits of travel. Adjustment of this slip clutch is usually made in the field so that the linear output effort exerted by the garage door operator is not greatly in excess of that required to reliably move the door. Thus, the force exerted upon an object or person which obstructs the door can be minimized for reasons of safety.

It is also highly desirable, in the event that the door is obstructed, to remove power from the motor to reduce the hazard potential and to protect the garage door mechanism from damage. Many styles of mechanically actuated centrifugal type safety switches have been employed for this purpose. These mechanical type safety switches all suffer from several disadvantages which are eliminated by the present invention. Mechanically actuated centrifugal safety switches are difficult to produce in a small size for the very low rotational rates of the output shaft of garage door motor output shafts (commonly about two revolutions per second). Since it is often most convenient and desirable to have the slip clutch operative between the motor output shaft and the driven element, a centrifugally operated switch required to sense an obstruction of the door which causes the clutch to slip must be capable of responding at the low rotational rates of the slip clutch output shaft.

Furthermore, it is desirable to have some delay in the response so that the slip clutch output shaft is permitted to rotate at low rotational rates (compared to the normal running rate) for short periods of time such as may be required to overcome the inertia of the door in starting, or overcoming a binding area at some point in the doors travel. This delay permits the safety shut-off system to operate with lower settings of the clutch adjustment without inadvertent or unwanted shut-off. The result of this permissible lower clutch setting is smoother acceleration of the door and greater safety because the maximum output effort of the garage door operator is set at a lower level that would be required with a fast acting centrifugal switch, such as the mechanical type which cannot be easily adjusted for very low rotational rates.

The present invention replaces the centrifugal switch preferably by a simple switch which opens and closes at a rate which is a function of the speed of the slip clutch output shaft. The switch is connected to a monostable circuit in a manner to be described.

A monostable circuit is a circuit which has a stable state and an unstable state. The circuit is triggered to its unstable state by a pulse at an input terminal and returns automatically to its stable state after a given predetermined delay period unless externally prevented from doing so. In the preferred form of the present invention, the aforesaid switch is connected to the monostable circuit so the circuit is held in its unstable state as long as the slip clutch output shaft turns at a normal speed. If an obstruction slows down the slip clutch output shaft to a given low speed for a minimum period which is greater than that required to accelerate the garage door from rest to normal speed, the monostable circuit returns to its stable state to de-energize the motor. The monostable circuit most advantageously a flip-flop type of monostable circuit so it can also be operated to its stable state while the slip clutch output shaft is operating at full speed by signals generated by momentary closure of the limit switches or the manually initiated pushbutton or radio signal operated switches connected to inputs of the monostable circuit.

The above and other advantages and features of the present invention will become apparent upon making reference to the specification to follow, the claims and the drawings wherein:

FIG. 1 shows the inside of a garage provided with the various components which make up a radio controlled garage door operating system;

FIG. 2 is a block diagram of an exemplary garage door control circuit of the invention;

FIG. 3 shows a preferred control circuit of the invention;

FIG. 4 shows the charge path for the control capacitor of the circuit of FIG. 3 when the monostable circuit is triggered into its unstable condition 'by the grounding of the input terminal by the pressing of a pushbutton switch;

FIG. 5 shows the discharge of the control capacitor due to the bouncing of the pushbutton switch contacts which reopens the input circuit;

FIG. 6 shows the condition of the circuit of FIG. 5 when the bouncing pushbutton contacts reclose; and

FIG. 7 shows the condition of a circuit like FIG. 5 when the bouncing pushbutton contacts reclose but with part of the circuit removed.

FIG. 1 shows, in part, a garage door operator system installed in a garage having a garage door 1 which rides on side tracks 3, only one of which is shown. The means for closing and opening the garage comprises a door operating unit having a carriage arm 4 which connects to the garage door at one end and to the housing 7 of the operator unit 5 at the other end. The housing 7 is movably supported on a guide rod 8. The housing 7 includes a garage door drive motor (not shown) which, when energized, will cause a drive wheel to frictionally ride along the guide rod 8 and thus cause the entire housing 7 to move along the guide rod 8. As the housing 7 moves on the guide rod 8, the carriage arm 4 attached thereto will move the garage door 1 along with it. When the housing 7 reaches one extreme position, a limit switch operating arm 9 will engage a stationary flange 10 and stop the motor, the housing 7 and garage door 1 coupled thereto. In the other extreme position of the housing 7, a limit switch operating arm (not shown) like the arm 9 will engage a flange 10' similar to flange 10 to operate a limit switch causing de-energization of the motor.

The housing 7 includes, in addition to the motor various other equipment such as an operator circuit (not shown in FIG. 1) which controls the operation of the garage door drive motor.

The garage door drive motor may be of a type where the motor reverses in direction each time it is re-energized. In such case, the motor reverses automatically by a centrifugal switch which sets up a starting winding thereof in opposite polarity with respect to a running winding thereof each time the motor comes to rest.

The garage door operator unit is actuated from the vicinity of the garage by manual pushbutton switch 11 shown mounted on the wall of the garage. A pair of conductors 12 extend in a conduit from the switch 11 to the door operator circuit within the housing 7.

When the user desires to open the garage door, he presses the manual pushbutton switch 11, whereupon the drive motor in the housing 7 becomes energized and effects movement of the housing 7 to the right which raises the garage door. When the door reaches the end of its path of travel, a limit switch shuts off the motor. When the manual switch 11 is depressed again, the garage door drive motor becomes energized again and moves the housing 7 to the left which lowers the garage door. A limit switch automaitcally terminates the operation of the motor when the garage door is completely closed. Depression of the pushbutton switch 11 during movement of the garage door be tween its extreme position will stop the garage door drive motor. Also, a safety switch (not shown) is provided which will stop the garage door drive motor if a force is applied against the door tending to stop its movement.

It is common to incorporate remote radio control from the users car, in addition to the manual control as described, over the operation of the garage door. To this end,

a transmitter (not shown in FIG. 1) is installed in the users automobile. The transmitter usually includes a pushbutton control which when depressed will cause the transmitter to generate an amplitude modulated signal. The modulation frequency of the radio signal is varied within a given location encompassing the range of the transmitter involved, so that the signal from a given transmitter will only operate the desired garage door.

The radio signal is received by a radio receiver which is sometimes incorporated within the housing 7. In such case, when trouble develops in the receiver, the inaccessibility thereof usually requires a service man to disconnect the radio receiver and bring the same to a radio servicing shop. The preferred control circuit of the present invention allows the radio receiver to be energized solely from the voltage appearing across the terminals of the pushbutton switch 11. A special unique receiver circuit is required for this purpose. Such a receiver is disclosed in copending application Ser. No. 495,563, filed Oct. 13, 1965. In such case, it is very advantageous to mount the radio receiver identified by reference numeral 13 in FIG. 1, on a mounting frame 16 including the manual pushbutton switch 11. The connections between the radio receiver and the mounting frame may be a simple removable type plug-in or similar connections. Thus, when the radio receiver 13 is mounted in place on the frame 16, the radio receiver is automatically connected to the terminals of the switch 11. If the radio receiver needs servicing, the user merely pulls the exposed receiver from the frame 16 and takes the same to a service shop. thereby saving much time and expense for all concerned.

The control circuit of FIG. 2, identified generaly by reference numeral 20, has the important advantage that it is a very reliable and economical circuit needing only a single conventional direct current relay 22. Also, the main control terminals 24-24 of the circuit 20 provide a direct current voltage which is capable of providing standby power for the radio receiver 13.

The armature of the relay 22 controls one or more sets of contacts. In the circuit shown in FIG. 2, the relay has a pair of normally-open motor control contacts 22-1. When the relay is energized, the armature of the relay is pulled into a position where the contacts 22-1 will close to energize the motor 25.

The source of voltage for energizing the relay 22 is a source of direct current voltage 26 having terminals 26a and 26b across which the direct current output voltage thereof appears. One of these terminals 26b, which will be designated as a negative voltage terminal for convenience, is connected to a common reference point or ground 29, and the other terminal 26a, which is the positive terminal, is coupled through a conductor 27 to a monostable circuit 28 which controls the relay 22.

The aforementioned main control terminals 24-24 are connected by wires 12-12 across the terminals of the pushbutton wall switch 11 which is assumed to be normally-open, so that the control terminals 24-24 are normally-open circuited. The control terminals 24-24 are connected to the output terminals 13a-13b of the radio receiver 13, so that the terminals 24-24 are momentarily short circuited by either depression of the switch 11 or the reception by the radio receiver 13 of a radio signal. The radio receiver 13 is unique in that the terminals 13a-13b serve as output terminals and power-receiving terminals for the receiver. As above indicated, such a radio receiver is disclosed in said application Ser. No. 495,563.

One of the control terminals 24' is preferably connected to ground and the other terminal 24 is connected through a resistor 32 to the conductor 27 leading to the positive terminal 26a. The resistance of resistor 32 is preferably made small (e.g. one tenth) relative to the standby impedance across the power receiving terminals 13a-13b of the radio receiver 13, so that practically all of the voltage of the source of direct current voltage 26 will normally appear across the control terminals 24- 24' when the same are connected to the power receiving terminals of the radio receiver and practically all of the power normally delivered by the source of voltage will be supplied to the radio receiver rather than being absorbed by the resistor 32. (It should be understood that in accordance with the invention, the power for operating the receiver need not be supplied from across the control terminals 24-24).

When the control terminals 24-24 are momentarily short circuited for the first time, an input 28a of the monostable circuit 28 receives a pulse (negative pulse) which triggers it to its unstable state. The relay 22 is connected to the monostable circuit 28 so it becomes energized during the unstable state of the monostable circuit. The energization of relay '22 closes motor control contacts 22-1 coupled between a source of voltage, shown as an alternating current voltage source 34, and the garage door drive motor 25. It is assumed that the motor is of a type which includes within the same a well known centrifugal switch mechanism 36 which automatically changes the connections to the field windings thereof to reverse the direction of the drive motor each time the motor stops. The drive motor 25 has a drive shaft 38 connected to a slip clutch 40 having an output shaft 42 which drives the garage door operating mechanism 46 which imparts movement to the housing 7 in the embodiment shown in FIG. 1. The shaft 42 is coupled to a safety switch 48 which is preferably a switch which is open and closed at a rate depending on the speed of rotation of the shaft 42. The safety switch is connected to an input 28b of the monostable circuit so that it holds the monostable circuit in its unstable state as long as the switch opens and closes at a rate indicating that the slip clutch output shaft is rotating at normal speed. The effect of the safety switch can be overcome so as to return the monostable circuit to its stable state by closure of the switch 11 or the reception of a radio signal of proper frequency by the receiver 13 or by the closure of limit switch contacts 49-1 or 49-1, connected to input 28c of the monostable circuit 28. The de-energization of the relay 22 opens contacts 22-1 to de-energize the drive motor 25.

If the speed of operation of the safety switch 48 is decreased to a given lower speed because the garage door is arrected for any reason, the monostable circuit automatically returns to its stable state to de-energize the motor 25.

Refer now to FIG. 3 which illustrates a preferred transistor monostable circuit 28 which is similar to the circuit shown in FIG. 3 of copending application Ser. No. 732,115 filed on the same date as this application. This circuit 28 includes a PNP transistor 53 having an emitter 53a, base 53b and collector 53c and a NPN transistor 55 having an emitter 55a, base 55b and collector 550. The PNP transistor 53 forms part of a first branch circuit connected across the positive and negative terminals 26a and 26b of the source of DC. voltage 26 and the NPN transistor 55 forms part of a second branch circuit in parallel with the first mentioned branch circuit across the voltage source terminals 26a and 26b. The emitter 53a of the transistor 53 is connected to the positive voltage source terminal 26a, and the collector 53c is connected to a resistor 59, in turn, connnected to a resistor 61 which completes the first mentioned branch circuit. (The resistors 59 and 61 are sometimes referred to as load impedance means.) The second mentioned branch circuit includes a second load impedance means which, in the embodiment of the invention now being described, is the relay 22. One end of the relay 22 is connected to the voltage source terminal 26a and the other end is connected to the collector 55c of the transistor 55. The emitter 55a of the transistor 5 is connected to the negative voltage source terminal 26b which is shown grounded.

The base 55b of the transistor 55 is connected to the load impedance means of the transistor 53, so that conduction of the transistors 53 will effect conduction of the transistor 55. In the circuit illustrated, the base 55b is connected to the juncture of resistors 59 and 61. Once the transistor 55 becomes conductive, the conduction of the connection from the collector 55c of the transistor 55 to transistor 53 is at least temporarily maintained by the the base to emitter circuit of the transistor 53. To this end, a conductor 65 extends between the collector 55c and one plate of a capacitor 66 whose other plate is connected to the end of a current-limiting resistor 67. The other end of the resistor 67 is connected to the base 53b of the transistor 53. To improve the reliability of the circuit and the thermal stability of the transitsor 53, a resistor 69 is preferably connected between the base 53b and the emitter 53a of the transistor 53.

In the stable state of the monostable circuit, the transistors 53 and 55 are both non-conductive so the circuit takes little or no current from the battery 26. When, as above explained, the circuit is triggered into a conductive state, the transistor 53 will first become conducting and then the transistor 55 will become conducting. The drive power for the transistors 53 and 55 must be maintained if the transistors 53 and 55 are to continue in a conductive state. When the transistor 53 is initially triggered into a conductive state, the capacitor 66 instananeously acts as a short circuit so that the transistor 53 receives drive power through a circuit extending through the resistor 67 and the emitter and collector of the transistor 55. However, the capacitor 66 then begins to charge up to a given limiting voltage, and, when the capacitor becomes fully charged, the capacitor acts as an open circuit interrupting the drive power to the transistors 53 and 55 which then become non-conductive.

As previously indicated, one of the aspects of the pres ent invention is the manner in which the monostable circuit is held in its unstable condition as long as the slip clutch output shaft continues to move at a normal speed. To this end, means for inhibiting the full charge of the capacitor 66 is provided comprising a transistor 71, preferably a NPN transistor, having an emitter electrode 71a connected to the bottom plate of the capacitor 66, a collector electrode 71c connected through a resistor 73 to the upper plate of the capacitor 66, and a base 71b connected to the emitter 71a through a resistor 75. In a manner to be described, the transistor 71 is rendered alternately conductive and non-conductive at a rate depending upon the speed of rotation of the slip clutch output shaft 42. When the transistor 71 becomes conductive, the capacitor 66 will discharge partially through the transistor 71 which thereby inhibits the full charging of the capacitor 66. When the transistor 71 is non-conductive,

the capacitor 66 continues to charge to a limiting value. When the transistor 71 is alternately rendered conductive and non-conductive at a relatively high rate, the capacitor 66 is never able to fully charge so that the monostable circuit cannot return to its stable non-conductive state. However, when the transistor 71 is rendered non-conductive at a relatively low rate, during the relatively long period that the transistor 71 is non-conductive, the capacitor 66 has a chance to fully charge, thus enabling the circuit to be returned to its stable non-conductive state.

The means for alternatively rendering the transistor 71 conductive and non-conductive is the safety switch 48 which is coupled to the slip clutch output shaft 42. As shown in FIG. 3, the safety switch 48 ma comprise a commutator like a rotor 48a having circumferentially spaced peripheral ribs 48b which are engaged by a wiper blade 480. The rotor 48a is connected to ground so the wiper blade 480 is periodically grounded at a rate depending on the speed of rotation of the rotor 48a. The wiper blade 480 is connected through a capacitor 77 and a resistor 78 to the base 71b of the transistor 71 and is connected through a resistor 80 and a rectifier 82 to the collector 530 of the transistor 53. It can thus be seen that in each interval during which the wiper blade 48c does not contact any of the rotor segments 48b, the capacitor 77 will charge through a circuit including the emitter and collector of the transistor 53, conductor 65, rectifier 82, resistor 80, resistor 78, resistor 75 and the collector and emitter of the transistor 55. The positive voltage pulse developed across the reistor 75 during each charging of the capacitor 77 will develop a positive voltage on the base 71b of the transistor 71 which will render the same conductive. Transistor 71 will be nonconductive in the absence of such a pulse. When the wiper blade 480 contacts a grounded rib 48b on the rotor 48a, the resultant grounding of the capacitor 77 will cause the discharge of the capacitor 77. The rectifier 82 serves the function of preventing a leakage current path to the base 55b of the transistor 55 when the circuit is supposedly in a non-conductive state. In the absence of the rectifier 82, a leakage path can be traced through the relay 22, the conductor 65, resistor 75, resistor 78, resistor 80, resistor 59, and the conductor connected to the base 55b of the transistor 55.

Although a variety of means may be utilized to trigger the monostable circuit to its unstable state, it is most advantageous from the standpoint of economy, simplicity and reliability that such means include a capacitor 84 having one plate 84a preferably connected directly to the input 28a of the circuit and another plate 84b coupled to the positive voltage source terminal 26a through a resistor 86 of relatively large value, a resistor 88 of a relatively small value, and a circuit branch including the capacitor 66 in parallel with resistor 73 and transistor 71, resistor 67, and resistor 69 in parallel with the emitter to base electrode of the transistor 53. Although, in some cases, the resistor 88 may be eliminated completely, it is preferably present for a number of reasons including the isolation of the capacitor 84 from the collector 55c of the transitsor 55.

The resistor 86 is shunted by a rectifier 90 having its cathode 90a connected to the capacitor connected side of the resistor 86. As will appear, the rectifier 90 by-passes the resistor 86 during the charging of the capacitor 84 when the input 28a is grounded, but forces the capacitor 84 to discharge through the relatively large resistor 86 when the input 28a is groupded at an instant when the capacitor 84 is reverse charged, that is when the left plate 84a is positive with respect to the right plate 84b. The capacitor 84 discharges through a circuit including the resister 86, rectifier 92 and resistor 89 connected to the load resistor 61 of the transistor 53. The rectifier 92, among other things, isolates the base 55b of transistor 55 from the positive voltage terminal 26a when power is initially turned on.

8 The grounding of the input 28a is accomplished by the interconnection of the control terminals 2424 in the manner described. Thus, when the input 28a is grounded by the circuit described, a charge path is established for the capacitor 84 extending through resistors 69, 67, 88, capacitor 66 and rectifier 90, as best illustrated in FIG. 4, where the plate 84b of the capacitor 84 will be positive with respect to the other plate 84a. The flow of this charging current through resistor 69 develops a drive voltage for transistor 53 (FIG. 3) which triggers it into conduction. The resulting current fiow will generate a positive voltage across resistor 61 coupled to the base 55b of transistor 55 to trigger it into conduction to energize relay 22 and start the movement of the garage door. The inertia of the garage door will require a certain time to reach full speed. It is important, therefore, that the time it takes capacitor 66 to fully charge from zero be longer than the period during which transistor 71 is non-conductive in the interval between successive positive pulses generated across resistor 75 as the slip clutch output shaft speeds up from rest. Resistor 67 in series with capacitor 66 is made sufiiciently large to prevent capacitor 66 from fully charging during the longest of these intervals. A capacitor 96 placed across resistor 69 provides the circuit with immunity from short duration electrical disturbances of the type generated from near-by motors, sparking switches, etc. which could undesirably trigger the monostable into the conductive state. Similarly, capacitor 105 placed across resistor 61 operates in conjunction with resistor 61 to provide a similar immunity against such false triggering of the circuit.

When ground is removed from the input 28a, as by cessation of the radio signal or release of the pushbutton switch 11, a discharge and reverse charge path for the capacitor 84 is established as shown in FIG. 5 through a circuit including the resistor 32 connected between the input 28a and the positive voltage source terminal 26a, resistor 86, resistor 88, and the collector 55c, and emitter 55a of the then conducting transistor 55. The capacitor recharges to a voltage where the plate 84a connected to the input 28a will be positive with respect to the plate 84b. The resistor 86 makes the discharge circuit time constant so long that a momentary opening of the pushbutton switch 11 used to ground input 28a due to bouncing of the pushbutton conducts when it is depressed will not allow the capacitor to reverse charge until the pressure on the pushbutton switch is released. If the capacitor is allowed to reverse charge during such contact bouncing, the second reclosure of the bouncing contacts would cause discharge of the capacitor through the disharge circuit including the resistor 86, rectifier 92, resistor 88 and resistor 61 where a negative voltage would be developed across resistor 61 which would render the transistor 55 and the whole monostable circuit non-conductive to de-energize the motor 25. FIG. 7 illustrates how the second reclosure of the bouncing pushbutton contacts would cause an undesired resetting of the circuit if resistor 86 and rectifier 90 were removed permitting the reverse charging of the capacitor 84 under these conditions. FIG. 6 illustrates how the reclosure of the bouncing pushbutton switch 11 before capacitor 84 reverse charges cannot establish fiow of current through resistor 61 to reset the circuit. The desired reverse charging of the capacitor 84 obtained by the cessation of the radio signal or release of the pushbutton switch, may be used to manually stop the motor by a subsequent reclosure of the pushbutton switch 11 which causes the discharge of the capacitor through resistor 61 in a manner like that shown in FIG. 7.

When the transistor 55 is rendered non-conductive for any reason, the sudden cessation of current flow through the transistor 55 will result in the generation of a relatively high voltage across the inductance of the relay 22. This voltage causes current to flow through the resistors 67 and 69 in the base circuit of transistor 53 which renders the transistor 53 non-conductive. It should be noted that the capacitor 84 then has a possible charge path through resistors 67 and 69 which, if such path were allowed to be established, would prevent the turning off of the transistor 53. Thus, the voltage build-up across the relay 22 prevents the, establishment of this circuit when transistor is triggered into its non-con ductive state. The time constant of the circuit in which relay 22 acts must be such as to prolong the effect of this voltage until capacitor 84 becomes substantially fully charged through a DC. path including the relay 22.

To prevent the generation of an excessive voltage across the relay 22 when transistor 55 becomes non-conductive, a resistor 97 connected in series with a rectifier 99 is placed across the relay. When the transistor 55 becomes non-conductive, the rectifier 99 and the resistor 97 forms an alternate path for flow of current in the relay. However, the resistor 97 provides only a partial path for the current flow through the relay. The remainder of the current flows through the base circuit of the transistor 53 to keep the transistor 53 in a non-conductive state as just explained.

As above indicated, although the monostable circuit 28 may be turned off by the manual operation of the pushbutton switch 11, or the slowing down of the slip clutch output shaft 42 by an obstruction to the movement of the garage door, the circuit is normally rendered non-conductive or reset by the closure of limit switches 49-1 or 49-1 as the garage door reaches one of its limits of travel. The monostable circuit is hereby reset by the generation of a negative voltage across the resistor 61 coupled to the base 55b of the transistor 55 through a circuit including a resistor 100 and a capacitor 102 connected in series between one of the terminals of the limit switches 49-1 and 49-1 and the resistor 61. The other terminals of the limit switches 49-1 and 49-1' are grounded. A resistor 104 is connected between the ungrounded terminals of the limit switches 49-1 and 49-1' and the juncture of the rectifier 82 and resistor 80. It should thus be seen that, when the transistor 53 is in a conductive state, the capacitor 102 will charge to a voltage where the upper plate 102a is positive with respect to the lower plate 10211 through a circuit including resistor 104, resistor 100 and resistor 61. When the limit switch 49-1 or 49-1' is closed, the capacitor 102 discharges through a number of resistors including resistor 61, thereby creating a negative voltage across the resistor 61 which will render the transistor 65 non-conductive. The limit switches 49-1 and 49-1 can be relatively inexpensive switches where bouncing or other momentary opening of the contacts 49-1 or 49-1' is possible because the action of switches 49-1 and 49-1' is such that any momentary closure can only produce a turn-off command to the monostable circuit. Successive closures of the limit switch can only attempt to turn transistor 55 off, which is redundant after the first closure.

Exemplary Values for many of the circuit parameters in FIG. 1 are as follows:

Resistor 32-100 ohms Capacitor 84O.22 microfarad's Resistor 862.2 megohms Resistor 8610,000 ohms Resistor 675,000 ohms Resistor 69-5,000 ohms Capacitor 6625 microfarads Resistor 97330 ohms Resistor 104-10 megohms Capacitor 102-0.1 microfarads Resistor -22,000 ohms Resistor 78-33,000 ohms Capacitor 770.1 microfarads Resistor 8010,000 ohms Capacitor 96-.05 microfarads Resistor 5910,000 ohms 10 Resistor 6110,000 ohms Resistor 89-3,300- ohms Capacitor -105-0.l microfarads Relay 22-resistance typically 300 ohms, inductance 2.4

(minimum) millihenries Resistor 73-270 ohms Resistor 100-3,300 ohms It should be understood that numerous modifications may be made in the most preferred form of the invention described above, without deviating from the broader aspects thereof.

I claim:

1. In a system for controlling the movement of a member from a first to a second position, said system including an electric motor having a shaft coupled to a slip clutch having an output shaft which is coupled to said member and slows down relative to said motor shaft when free movement of said member is hindered, and control means which has a motor operating condition which effects energization of said motor and a nonoperating condition which elfects de-energization of said motor, and control signal generating means for generating a signal to operate said control means to said operating condition, the improvement comprising a monostable circuit which controls said control means, said monostable circuit having a first stable state which operates said control means to said nonoperating condition and an unstable state which operates said control means to said operating condition, said monostable circuit including a capacitor which, when it is charged to a given level, effects the return of said monostable circuit to said stable condition, and charge inhibiting means responsive to the speed of rotation of said slip clutch output shaft for inhibiting the charge of said capacitor in accordance with the speed of said slip clutch output shaft, the degree of inhibition thereof being sufiicient to keep said capacitor from reaching said given charge level when the slip clutch output shaft is rotating at normal speed and being insuflicient to keep said capacitor from reaching said given charge level when the slip clutch output shaft is rotating at a much lower than normal speed.

2. The system of claim 1 wherein there is provided delay means for inhibiting the effect of said capacitor on said monostable circuit when charged to said given level for a given period suificient to permit the movable mem ber to be accelerated by said motor from rest to its normal speed.

3. The system of claim 1 wherein said charge inhibiting means comprises switch means in parallel with said capacitor, means for alternately rendering said switch means conductive and non-conductive at a rate depending upon the speed of said slip clutch output shaft, the switch means being non-conductive for a suflicient period to permit said capacitor to charge to said given level only when said clutch output shaft is at said lower speed.

4. The system of claim 3 wherein said monostable circuit includes first and second complimentary transistors each having a base terminal and collector and emitter load terminals; a source of DC voltage having first and second voltage output terminals across which a DC voltage appears; first load impedance means; second load impedance means; means for connecting the load terminals of said first transistor and said first load impedance means in series in the order named between said first and second voltage output terminals of said source of DC. voltage; means for connecting said second load impedance means and the load terminals of said second transistor in series in the order named between said first and second voltage terminals of said source of DC. voltage; means for connecting said first load impedance means to the base terminal of said second transistor for effecting conduction of said second transistor when current flows through the terminals of said first transistor and the first load impedance means; means coupling the base terminal of said first transistor through said capacitor to the load terminal of the second transistor remote from said Second voltage output terminal for rendering said first and second transistors non-conductive when said capacitor becomes substantially fully charged; and means for coupling said signal generating means to the base of said first transistor to trigger the same into conduction upon moe mentary operation thereof.

5. In a system for controlling the movement of a member between extreme limits, said system including an electric motor having a shaft coupled to a slip clutch having an output shaft which is coupled to said member and slows down relative to said motor shaft when free movement of said member is hindered, the improvement comprising: a flip-flop type monostable circuit for controlling the energization and de-energization of said motor, said monostable circuit having a stable state which effects the de-energization of said motor and an unstable state which effects energization of said motor, means responsive to the speed of operation of said slip clutch output shaft for holding said monostable circuit in said unstable state while said slip clutch output shaft is operating at a normal speed and for allowing said monostable circuit to return to said stable state when the speed of operation of said slip clutch output shaft drops to a speed below said normal speed, and control means for instantaneously terminating the unstable state of said flip-flop monostable circuit independently of the speed of said input shaft to de-energize the motor.

6. The system of claim 5 wherein there is provided delay means which inhibits the return of the monostable circuit from its unstable to its stable state despite the operation of said slip clutch output shaft at a speed below the normal speed for a period sufficient to permit the movable member to be accelerated from rest to its normal speed.

7. In a trigger circuit including a source of DC. voltage having first and second voltage output terminals across which a DC. voltage appears; first normally open contacts operable momentarily from an open to a closed condition; a capacitor having a pair of plates, said switch means coupling one of the platesof said capacitor to one of said voltage output terminals; first control impedance means; first capacitor charge circuit-forming means connecting the other plate of said capacitor to said control impedance means and the other voltage output terminal for charging said capacitor in one direction when said switch contacts are first momentarily closed; means coupling the voltage across said control impedance means during said charging of said capacitor therethrough to trigger the circuit from an initial state into a given state; first capacitor discharge and reverse charge circuit-forming means including means coupled between said other plate of the capacitor and said one voltage output termi nal and betw'eenthe one plate of said capacitor and said other voltage output terminal for effecting the discharge and then the reverse charging of said capacitor when said momentarily operated contacts return to their open condition; second control impedance means; second capacitor discharge circuit-forming means coupling said second control impedance means between said other plate of said capacitor and said one voltage output terminal for discharging said capacitor through said second control impedance means upon the second operation of said switch means to said closed condition; and means coupling the voltage across said second control impedance means during said discharging of said capacitor for resetting said trigger circuit to said initial state; the improvement comprising means for preventing the bouncing of said contacts from resetting said trigger circuit comprising a rectifier coupled in series with said capacitor during said charging thereof for permitting charge current to flow thereto during saidfirst mentioned closure of said contacts but blocking the discharge thereof when said contacts momentarily open and suddenly reclose a second time before the capacitor has a chance to reverse charge, and a relatively large impedance in parallel with said rectifier and connected in the discharge and reverse charging circuit of said capacitor for slowing down the discharge of said capacitor during the first opening of said contacts for preventing the reverse charging of said capacitor during said momentary opening of said contacts to prevent the resetting of the trigger circuit during the bouncing of said contacts.

8. The system of claim 5 wherein said member is a garage door movable between extreme garage opening and closing positions, and said control means includes first means responsive to a manual operation for triggering said monostable circuit to said unstable state and second means responsive to the movement of the garage door to either of said extreme positions for triggering said monostable circuit to said stable state.

References Cited UNITED STATES PATENTS 2,472,526 6/1949 Frazee 318461 XR 3,199,857 8/1965 Klamp 318266 3,365,615 1/1968 Bart 318461XR 3,389,321 6/1968 Miller 318-461 XR 3,427,521 2/1969 Goldstcin 3 l8266 ORIS L. RADER, Primary Examiner A. G. COLLINS, Assistant Examiner US. Cl. X.R. 318266, 469

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