WO1991009195A1 - Autodialer-resistant combination lock - Google Patents

Abstract

A conventional combination lock (10) is improved by the addition of elements (38, 26) which cooperate to detect excessive manipulation of the lock and to disable the lock's unlocking mechanism (32) if such manipulation is detected.

Description

AUTODIALER-RESISTANT COMBINATION LOCK

Field of the Invention The present invention relates to combination locks, and more particularly to combination locks adapted to resist opening by autodialers.

Background and Summary of the Invention Combination locks have long been trusted to secure valuables in safes, file cabinets and the like. Recently, however, such locks have become susceptible to unauthorized opening by electromechanical autodialers. These microprocessor-controlled, stepper motor-driven devices attach to the dials of combination locks and sequentially try every possible combination in rapid succession until the correct combination is found. While such devices may take, on average, fifteen hours to happen across the correct combination, they nonetheless pose an unacceptable risk to security in many applications.

It is an object of the present invention to reduce the risk to combination lock security posed by such autodialers.

In accordance with one embodiment of the present invention, a combination lock is provided with one or more sensors to detect manipulation of the lock. Associated electronic circuitry monitors signals from the sensors and disables the unlocking mechanism if the number of manipulations is excessive.

The foregoing and additional objects, features and advantages of the present invention will be more readily apparent from the following detailed description thereof, which proceeds with reference to the accompanying drawings.

Brief Description of the Drawings Fig. 1 is a simplified plan view of a conventional combination lock modified in accordance with the present invention and illustrated in an operative mode.

Fig. 2 is a section view taken on line 2 - 2 of Fig. l Fig. 3 is a plan view of the lock of Fig. 1 illustrated in a disabled mode.

Fig. 4 is a section view taken on line 4 - 4 of Fig. 3 Fig. 5 is a simplified schematic diagram of a control circuit used with the present invention.

Detailed Description To provide a comprehensive disclosure without unduly lengthening this specification, applicant incorporates by reference the disclosures of U.S. Patents 3,073,145, 3,106,083, 3,120,117, 3,170,316, 3,237,435, 3,254,519, 3,339,382, 3,339,383, 3,373,583, 3,383,887, 3,418,951, 3,436,941, 3,518,856, 3,600,789, 3,702,551, 3,719,064, 3,968,667, 4,163,376, 4,238,942, 4,275,576 and 4,831,851 which illustrate combination locks to which the principles of the present invention can be applied.

Referring now to Figs. 1 - 4, there is shown a combination lock 10 modified according to one embodiment of the present invention. The basic lock is conventional and familiar to those of ordinary skill in the art. A dial (not shown) is mounted on a spindle 12, which passes into a lock housing 14. Disposed within the lock housing and rotatably mounted about the spindle are three tumblers 16, 18, 20, each of which has a gate 22 at its periphery. Fixedly mounted to the end of the spindle 12 is a driving wheel 24, with a drive notch 26 defined therein.

The lock further includes a bolt 28 coupled by a pivotal linkage 30 to a fence lever 32. The fence lever includes a fence bar 34 extending perpendicularly therefrom, which normally rides on the upper peripheries of the tumblers. The fence lever further includes a nose portion 36.

In operation, the dial is alternately rotated clockwise, counter-clockwise, and clockwise to effect entry of the lock combination. If the proper combination is entered, the gates of the tumblers will be left in a condition of alignment, permitting the fence bar 34 to drop into the aligned gates. This lowering of the fence bar also lowers the associated fence lever 32, thereby bringing the nose portion 36 of the fence lever into engagement with the drive notch 26 of the driving wheel 24. With the fence nose portion 36 and drive notch 26 so engaged, clockwise rotation of the spindle 12 pulls the bolt 28 to a retracted position, permitting opening of a container secured by the bolt.

In the preferred embodiment of the present invention, this basic construction is supplemented by a few additional elements which cooperate to detect excessive manipulation of the lock and to disable the lock's unlocking mechanism if such manipulation is detected. These elements in the illustrated embodiment include first and second microswitches 38, 39, a lock disabling solenoid 40, a power source 42, and associated circuitry 44 (Fig. 5) .

The first microswitch 38 is of the normally- closed variety and is mounted inside the lock housing 14 with its actuator 46 pressed against the periphery of the drive wheel 24, thereby maintaining an open circuit through the switch. Each time the spindle is rotated one revolution, the actuator springs momentarily into the drive notch 26, thereby closing briefly.

As shown in Fig. 5, this first microswitch 38 is electrically connected to the input 48 of a circuit 50.

Each time the actuator 46 expands into the drive notch 26, the switch 38 is closed, bringing the input 48 of the circuit 50 momentarily to ground. (This input is normally held high by a pull-up resistor 52a.) Repeated rotation of the drive spindle 12, regardless of direction, thus produces a train of pulses to the input 48 of circuit 50.

Circuit 50 is a divide-by-N counter, such as a Texas Instruments SN74LS161A, and operates to produce one output pulse on its output 54 for every N input pulses applied to its input 48. The 74LS161A, like most counters, is presettable, permitting the number N to be programmably varied (as illustrated by the "N" input in Fig. 5) . In an exemplary embodiment, N is set to 16 (which is the default value for the 74LS161A) . That is, for every 16 input pulses (i.e. 16 rotations of the lock's dial spindle 12) , circuit 50 produces one output pulse. The output pulse from circuit 50 in response to 16 rotations of the lock spindle is passed through a capacitor 56 and is applied to the trigger input 58 of a timer 60. The timer 60 can be a simple monostable multivibrator, such as a Signetics MC555, and produces an output pulse of a predetermined duration (such as five minutes) on its output 62 in response to a transitory input trigger pulse. The output pulse is used to turn on a power transistor 64, which energizes the lock-disabling solenoid 40 for the predetermined interval.

The plunger 66 of solenoid 40 is normally spring- biased to its retracted position shown in Figs. 1,2. In this retracted position, the solenoid has no effect on lock operation. When the solenoid is energized (Figs. 3,4), however, the solenoid plunger 66 drives a fence lever-holding member 68 into a hole 70 in the fence lever 32. The positioning of the member 68 in the fence lever hole 70 immobilizes the fence lever and prevents the fence bar 34 from dropping into the tumbler gates 22, even if the gates are aligned by entry of the proper combination. The lock opening mechanism remains disabled as long as the solenoid 40 remains energized.

At the conclusion of the predetermined interval, the output pulse from the timer circuit 60 terminates, causing the power transistor 64 to shut off and returning the solenoid 40 to its deenergized, retracted state. The lock is then permitted to operate normally until the circuit 50 again detects 16 rotations of the lock spindle, at which time the solenoid will be reenergized and the lock will be again disabled for the predetermined interval. In the illustrated embodiment, the member 68 on the solenoid plunger 66 is bevelled to lift the fence lever slightly as it engages the hole 70. This lifting prevents the fence bar from riding on the periphery of the tumbler wheels during subsequent manipulations. This lifting is advantageous in resisting attacks by sophisticated autodialers, which may listen to the fence bar riding on the tumblers to help decipher the proper combination.

It will be recognized that the disabling mechanism described above will temporarily disable the lock after any 16 rotations of the spindle 12, even if the rotations lead to successful opening of the lock. To prevent the disabling mechanism from interfering with the lock's normal operation, the second microswitch 39 is connected to a reset input 72 of the divide-by-N counter 50 and serves to zero the counter each time the bolt 28 is successfully retracted. Thus, if a user rotates the spindle five times while entering the proper combination and then opens the lock, these five rotations will not accumulate with subsequent rotations in the count towards 16.

From the foregoing it will be recognized that the present invention greatly enhances the security of combination locks against unauthorized opening by autodialers. The invention is readily adapted to existing locks, thereby permitting large inventories of autodialer- susceptible locks to be retrofit rather than replaced. Having described and illustrated the principles of my invention with reference to a preferred embodiment, it should be apparent that the invention can be modified in arrangement and detail without departing from such principles. For example, while the illustrated embodiment detects excessive manipulation by a switch that senses spindle rotations, in other embodiments other detection schemes can be used. In some alternative embodiments, manipulation is still sensed by spindle rotation, but the spindle rotation is detected differently. In one such embodiment, a magnet is mounted on the periphery of the drive wheel 24 and closes a reed switch. In another embodiment, such a magnet can be used instead to induce a current to flow through an adjacent coil, and the current can then be sensed. In yet another embodiment, a light source and photodetector are positioned on opposite sides of the drive wheel 24 and serve to sense the passing of one or more holes in the wheel therebetween. (This technology, sometimes termed photochopping, is widely used in other applications to convert linear rotation of a dial into a series of electrical pulses to drive digital circuitry) . A variety of other manipulation sensors based on rotation of the spindle can similarly be devised. It should be recognized that while a single sensor is illustrated (i.e. microswitch 38) , in other embodiments a plurality of sensors can be used. Plural- sensor systems are advantageous because the spindle need not be turned one full revolution in order to produce an output signal.

Manipulation sensors that don't rely on rotation of the spindle can also be used. One such alternative sensor uses a microphone inside the lock housing to "listen" for prolonged periods of lock manipulation. Another sensor senses prolonged periods of large capacitive coupling between the dial and the lock housing, as may be caused by prolonged attachment of an autodialer to the lock dial. (This particular embodiment requires that the lock dial be electrically isolated from the lock housing, which can readily be achieved by use of Teflon bushings and tumbler wheels.) Thus, it will be seen that many normal artifacts of lock operation can be used as indicia of excessive lock manipulation by sensing their continued presence over long intervals. Still other sensors rely on changes in the lock's physical characteristics during autodialer manipulation. One such characteristic is the lock temperature, which rises markedly during autodialer manipulation. A thermistor can produce a temperature-dependent signal which is fed to the lock disabling circuitry. A high pass filter can be used to prevent false triggering based on slow changes in the ambient temperature. In the illustrated embodiment, the duration of the disable interval is set by a simple MC555 timer circuit 60. The associated time interval is dependent on the values of resistors and capacitors used with the MC555. In other embodiments, other timer circuits can readily be used, some of which offer programmable time intervals. In a sophisticated embodiment, the timer 60 and the divide-by-N circuit 50 are implemented by a simple microprocessor that is programmed to perform these circuit's functions and many more. The programmability of such a system makes it well suited for use in a variety of applications.

In the illustrated embodiment, normal operation of the lock is differentiated from autodialer manipulation by the large number of lock manipulations that occur without retracting of the bolt. In other embodiments, this differentiation can be based not on bolt movement, but rather on other characteristics of normal lock usage, such as occasional periods of inactivity. For example, the counter 50 can be reset by a circuit that monitors spindle rotation and produces a reset signal if the spindle is stationary for a predetermined interval, such as five minutes.

In the illustrated embodiment, the disabling is effected by holding the fence lever 32 in an inoperative, out-of-the-way position. In other embodiments, myriad other disabling mechanisms can be used, most (but not necessarily all) of which rely on an electromechanical operator, such as a solenoid. In one such alternative embodiment, the spindle is physically seized and prevented from turning upon detection of excessive lock manipulation. This seizing can be effected by a solenoid- driven locking pin that is extended transversely through the spindle. A similar pin-stop arrangement can be applied to the lock bolt 28 itself. In still other embodiments, a solenoid-driven catch can be spring-biased at an angle against the periphery of the drive wheel 24, causing it to engage and stop the drive wheel from clockwise rotation.

While the preferred embodiment relies on electric signals to effect the sensing of excessive lock manipulation and electromechanical actuators to respond thereto, corresponding systems can be implemented with mechanical signals and purely mechanical movements. For example, a pair of oppositely arranged, one-way gearing arrangements can be used to wind a spring from rotation of the lock spindle, regardless of the spindle's direction of rotation. When the force stored in the spring exceeds a threshold, an associated mechanism can trigger and release this energy, driving a lock disabling member to a disabling position. Part of the released energy can also be used to cock a mechanical timer which, when it times- out, returns the lock disabling member to a normal, out- of-the-way position.

In view of the variety of embodiments to which the principles of my invention may be applied, it should be recognized that the detailed apparatus and method are illustrative only and should not be taken as limiting the scope of my invention. Rather, I claim as my invention all such apparatuses and methods as may come within the scope and spirit of the following claims and equivalents thereto.

Claims

1. A method of rendering a combination lock resistant to unauthorized opening comprising the steps: producing an electrical signal in response to manipulation of a mechanical element associated with the lock; monitoring the electrical signal to discern whether it is characteristic of an unauthorized lock manipulation; and electrically energizing a lock-disabling mechanism if monitoring of the electrical signal indicates that the signal is characteristic of an unauthorized lock manipulation.

2. The method of claim 1 in which: the producing step includes closing a switch each time a lock spindle is rotated past a certain point and producing an electrical signal in response thereto.

3. The method of claim 1 in which the monitoring steps includes counting electrical signals.

4. The method of claim 1 in which: the energizing step includes energizing a solenoid.

5. The method of claim 1 which further includes: deenergizing the lock-disabling mechanism after the passage of a predetermined period of time.

6. In a combination lock, an improvement comprising: first means for sensing manipulations of the lock and for producing an output signal corresponding thereto; second means coupled to the output signal of the first means for determining whether the sensed manipulations are excessive; and third means for disabling the lock from opening if the second means determines that the sensed manipulations are excessive.