Frequency controlled door locks

APPLICATIONS

This application is a continuation-in-part of copending application Ser. No. 568,178, filed July 27, 1966, and now abandoned. A further copending CIP application is Ser. No. 588,667, filed Sept. 30, 1966, and now abandoned.

BACKGROUND OF INVENTION

Parent application Ser. No. 568,178, filed July 27, 1966, describes various arrangements which are effective in causing predetermined operations to take place. These operations include identifying people, opening locks, turning on lights, starting automobile ignitions, and many other like operations. The arrangement of the parent application includes a transmitting device which may be worn or carried by the user and which transmits, for example a pair of preselected frequencies. When this device is disposed near a receiver specifically designed to detect these frequencies, the receiver permits the operation to take place such as withdrawing a lock so that a door knob can be turned by the user to open a door.

Although the arrangements described in the parent application and in copending application Ser. No. 588,667, filed Sept. 30, 1966, are effective in carrying out their intended purposes, there is always a desire to provide practical safeguards to prevent unauthorized actuation of the device. Additionally, there is a desire to increase the possible combinations of frequencies which may be used for operating the device.

SUMMARY OF INVENTION

An object of this invention to to provide an arrangement of the above type which assures only authorized use thereof.

A further object of this invention is to provide such an arrangement which has an increased number of possible combinations of actuating frequencies.

In accordance with one aspect of this invention, the arrangement includes both triggering means for operating the actuating device and lockout means for preventing the operation of the triggering means, in the absence of one or more precisely predetermined frequencies. This is accomplished in such a manner that it would be very difficult for an unauthorized person to determine the critical key frequencies by testing with a signal generator or by any other means. In use, all circuits of the lock, including the triggering circuits, are energized when the door knob is turned. If, however, the proper signals are not detected within milliseconds of the time of circuit actuation, the g lockout feature of the devce dominates the circuit to prevent any actuation. Thus, the proper signals must be present at the instant the circuits are energized and cannot be later applied.

In accordance with another aspect of this invention the IQ lock circuits incorporate at least one pair of independent radio frequency amplifiers, both deriving their inputs from a common signal source. One of these channels functions so as to promote the operation of lockout means to prevent the actuation of the lock, and the other functions 15 so as to inhibit operation of these lockout means, thereby allowing the lock to be actuated. In one of these two channels may be incorporated a quartz crystal or other very sharply tuned filter device.

If the filter is included in the lockout channel, it is so 20 designed as to peak sharply at the desired key frequency, key frequency, for which it exhibits a null. At this one frequency, therefore, the other channel dominates, inhibiting the lockout and permitting the lock to be actuated.

If the filter is included in the actuate channel, it is so 25 designed as to peak sharply at the desired key frequency. At this one frequency the actuate channel dominates, inhibiting the lockout and permitting the lock to be actuated.

More than one pair of channels may be incorporated 30 in the lock to correspond to more than one frequency emitted by the key, as will be more fully described below.

THE DRAWINGS

FIG. 1 is a perspective view of an arrangement of this 35 invention for unlocking a door;

FIG. 2 is a schematic view of a circuit in accordance with this invention;

FIG. 3 is a schematic view of a circuit in accordance With this invention utilizing a quartz crystal resonator in 40 the lockout channel;

FGIS. 4-7 are schematic views of various circuits in accordance with this invention; and

FIGS. 8-9 are graphical illustrations of the effects of the circuits shown in FIGS. 6 and 7, respectively.

⁴⁵ DETAILED DESCRIPTION

The descriptions in parent application Ser. No. 568,178, filed July 27, 1966, and copending application Ser. No. 588,667, filed Sept. 30, 1966, are incorporated herein by reference thereto where desirable to facilitate an understanding of this invention.

The arrangements described in the aforesaid applications generally include a low powered transmitter which is worn or carried by the user. The transmitter emits signals which, when picked up by a receiver, cause the predetermined operation to take place.

FIG. 1 shows this general arrangement used for opening a lock. As illustrated therein lock 10 is responsive to signals received from, for example microwatt radio transmitter 12 which serves as the key. The advantage of this system over a conventional mechanical lock lies in the fact that no conscious effort on the part of the key carrier is required as in finding the proper key, inserting it in the lock, etc. The close proximity of the key transmitter 12 is all that is necessary for releasing the lock when the door handle 14 is turned. This close proximity actuates, for example a receiver 20 which acting through a solenoid permits the lock to be opened in the manner described in parent application Ser. No. 568,178, filed July 27,1966.

The key transmitter is advantageously so small and so low powered that it can be worn on the person by, for

3,564,501 ³ example wrist band 16. Alternatively, the transmitter 12 may be in the form of any conventional pocket device or in any other desirable form.

FIG. 2 schematically illustrates a circuitry for the trigger portion of receiver 20 which makes it very difficult for an unauthorized person to determine the critical key frequencies by testing with a signal generator. The circuit is actuated when the door knob 14 (FIG. 1). is turned to close or actuate interrogation switch 22 which activates all of the circuits of the lock receiver 20. This circuitry may be considered as including an actuate trigger composed of a silicon controlled rectifier 24 which is the main trigger for operating a 12 ohm solenoid 26 to open the door. The other trigger is the lockout trigger composed of elements 28, 30 in combination. The lockout trigger 28, 30 is so connected that when it conducts it connects point 32 to ground thereby biasing the input of rectifier 24 so that it cannot operate. Both of the trigger circuits are binary in that they are either opened or closed, and once closed cannot be reopened without completely de-energizing the system.

When switch 22 is closed, condensers 34, 36 begin charging. As the condensers charge, points 32 and 33 start rising from their initial negative voltage supplied by a —2.7 volt battery, toward the positive 12 volt supply. Condenser 34 is smaller than condenser 36 so that point 33 rises faster than point 32. As soon as point 33 is more than about 0.5 volt positive with respect to ground, the lockout trigger fires bringing point 32 nearly to ground potential and stopping the charging of condenser 36. Rectifier 24 can never fire once this has happened.

If the receiver is the superheterodyne type as described in my copending applications, its intermediate frequency output signal appears at point 38 only if a “key” is present. This signal is rectified or detected by diodes 40, 42. Diode 42 is connected to produce a positive signal at point 33 and is connected to this point by a very small condenser 43. If high frequency “noise” pulses are present, they are conducted to point 33 by this condenser to trigger the lockout channel.

If no high frequency noise is present and the proper key signal is detected, diode 40—connected to produce a negative signal—conducts and drives point 33 in the negative direction. This counteracts the positive swing of point 33 due to the charging of condenser 34 and delays the firing of the lockout trigger. If enough signal is present, the lockout trigger firing is postponed until after rectifier 24 has fired and opened the door. With a receiver as described in my copending applications, one milli-volt at the door knob is enough to open the door.

The arrangement schematically illustrated in FIG. 2, thus includes retarding means to delay the operation of the lockout means so that if a predetermined key frequency is present, the triggering means may open a door. When the key frequency is not immediately present, however, the lockout means dominates to prevent the triggering means from actuating the device. This arrangement also includes means for detecting the presence of high frequency noise to actuate the lockout means and thus assure that the device will not be operated by signals containing high audio frequency modulation, such as “static.”

It will be noted that point 33 on FIG. 2 represents a summing junction, where the effects of a positive-going time-dependent bias and the effects of various inputs from a receiver are added together. If the net effect of all these inputs is such that point 33 goes positive before rectifier 24 fires, lockout means 28, 30 are actuated. If the net effect is such that point 33 remains negative until after that time, rectifier 24 is allowed to fire causing the predetermined operation to take place.

In accordance with another aspect of this invention, one or more pairs of separate radio frequency amplifiers and detectors may be connected to point 33, both deriving their inputs from a common point near the low level input circuits. One of these amplifier-detector channels converts radio frequency input signals to a positive DC voltage at point 33, thereby accelerating the operation of lockout means 28, 30. The other produces a negative DC voltage at point 33, thereby retarding or preventing the operation of lockout means 28, 30. The positiveoutput (lockout) channel may be made more sensitive than the negative-output (actuate) channel at all frequencies in the pass band of the input circuits, with the single exception of one critical frequency wherein there is a very sharp null in the sensitivity of the lockout channel. At this exact frequency, therefore, the sensitivity of the actuate means is greater than that of the lockout means and the lock can open. All other frequencies in the pass band of the system, however, are guarded by the sensitivity of the lockout means.

Alternatively, the crystal filter having a peaking characteristic may be incorporated in the negative amplifier causing its sensitivity to have an abrupt peak at the desired frequency. Thus, at this peak, the sensitivity of the activating means is greater than that of the lockout means.

With this concept which uses either the null or the peaking characteristic of a quartz crystal resonator, a number of things are possible. For example, when applied to a two carrier system as in the parent and copending applications, one of the two channels can be guarded. Any intense noise or any other strong signal which is not exactly at the correct frequency in the guarded channel will lockout the system. Additionally, the critical nature of this guard provides greater selectivity in addition to the already critical selectivity in the detection of the difference between the two carriers. Thus, in effect instead of merely determining the difference between the two key signals critically as in my parent application, there is also a precise determination of one of the signals. The net effect is to increase the number of discrete keys possible from about 10,000 to about 10,000,000.

Moreover, if both key signals are guarded as later described, it is possible to omit the determination of the difference between the two signals which was essential in my parent application. This can be done because the inventive arrangement in this application demands that both signals be present, both signals be strong, and both signals be critically and absolutely correct, thus, leading to important economical advantages in the circuitry.

Essentially, the further aspect of this invention may be considered as providing two receiver channels which examine the same limited part of the spectrum. One channel is connected so as to promote operation of the lockout, and the other so as to inhibit or postpone this operation. The channel which promotes operation of the input means is more sensitive, dominating or overriding the operate or trigger channel everywhere except at the exact frequency corresponding to a desired key signal. The attainment of this result of detecting the exact frequency may be achieved by the resonance of a quartz crystal, or by other very sharply defined resonance means.

FIG. 3 schematically illustrates a receiver MA in accordance with this further aspect of the invention. As indicated therein, receiver 20A includes a pair of input amplifiers 46, 48 and an actuate channel including mixer 50 and difference frequency amplifier 52, whose negative output inhibits the lockout or trigger 54. Receiver 20A also includes the lockout or inhibit channel 56 incorporating a null characteristic quartz crystal resonator 58, whose positive output promotes operation of the lockout in trigger 54. With this system not much selectivity would be required in the signal channels. The front end selectivity would be provided by a sharp null at frequency f₂ in the lockout channel. At frequencies near /₂ the lockout am3,564, . . S pl'ifier 56 would be more sensitive and override the triggering device but at this precise frequency f₂ because of the null, the triggering mechanism could operate. For correct operation the quartz crystal 58 is an exact duplicate of the crystal which controls one of the key oscilla- tors so as to emit a signal at frequency f₂.

The effect of the arrangement shown in FIG. 3 is to provide very sharp selectivity at the input as well as at the difference frequency 52. Thus, any signal not exactly at the lockout crystal resonance would actuate the lockout channel to prevent opening of the lock.

If good selectivity is provided in the difference amplifier 52, for example, by making it a superheterodyne receiver, both input frequencies are uniquely determined and the net effect is to multiply the number of available 15 discrete channels by a large factor.

The stability of the system illustrated in FIG. 3 depends not only on its ability to keep two quartz crystal resonators in exact match but also in the ability to provide a stable local oscillator in the receiver 52. FIG. 4, 20 however, illustrates a further embodiment of this invention which would eliminate the necessity of a superheterodyne receiver such as 52 and replace it by a more economical but poorly selective amplifier 53. In this arrangement a further inhibit amplifier 60 is provided to 25 guard signal fa by the inclusion of a quartz resonator 62 having its null at the frequency fa. Thus, both input amplifiers are guarded with high gain inhibit channels, each having a quartz crystal resonator.

Using conventional crystal filter circuits, the quartz 30 crystal can be designed to exhibit a peak at its resonant frequency instead of a null, and can then be used in accordance with a further modification of this invention, which is illustrated in FIG. 5. As indicated therein quartz crystal resonators 64, 66 are provided in one or both of 35 the input channels 46, 48. The inhibit amplifier 68 has greater sensitivity at all frequencies except the peak frequencies fa, f₂ of the quartz crystal resonators 64, 66. Thus at all other frequencies the lock would be inoperative by the domination of inhibit amplifier 68. 40

FIGS. 6-7 illustrate a quite simplified electronic lock or other actuating arrangement in accordance with this invention. Essentially, each of these figures utilizes only one frequency in the key. The lock would consist of a tuned radio frequency amplifier 70 (FIG. 6) with poor _ selectivity whose output is detected at 80 and applied as a negative voltage to the trigger 54. A separate amplifier and detector 82 is connected to this output of RF amplifier 70, and applies a positive DC output to the lockout input of the trigger 54. This lockout amplifier 82 contains a quartz crystal filter 84 which has its null at the predetermined frequency. Thus, any signal at the input passed by amplifier 70, except the sharply defined null frequency, would override detector 80 and inhibit operation of the device. The key emits at this null frequency. _gg

FIG. 7 shows a similar but alternative arrangement ⁰to that shown in FIG. 6. As indicated therein, amplifier 80 is provided with a peak type quartz crystal resonator 86 and lockout amplifier 82 does not have a quartz crystal resonator. In the arrangement shown in FIG. 8 the circuits are peaked near the predetermined frequency by tuned coupling networks. The lockout amplifier 82 has a higher gain than amplifier 80 at all frequencies except at the peak frequency.

FIGS. 8 and 9 schematically illustrate how the char- _6gacteristics of a quartz resonator are utilized in this invention. FIG. 8 relates to a situation where the quartz crystal resonator is provided in the lockout amplifier and the quartz crystal has a gain characteristic 88 such that it has a sharp null at the frequency fa. The triggering cir- γθ cuit has a gain 90. As is apparent from FIG. 8, the lockout means thus dominates or overrides the operate channel at all frequencies except the null frequency fa.

FIG. 9 illustrates the use of this invention wherein the quartz crystal resonator is provided in the operate chan- 75

501 nel and has a gain characteristic 92 with a peak at frequency fa. The lockout amplifier has a relative gain characteristic 94. Thus, again at all frequencies except the peak frequency fa, the lockout channel overrides the operate channel to prevent actuation of the trigger.