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BACKGROUND OF THE INVENTION
The present invention relates to electronic locking systems, and more
particularly to electronic locking systems of a type including a
reprogrammable key which electronically and mechanically interacts with a
reprogrammable lock cylinder.
Electronic security systems have been well known for a number of years, and
recent years have seen the marriage of electronic technology with
traditional door locking devices such as mortise locks. Some of the early
commercial systems have required a hard-wired connection between a central
processor and the electronics of the locking systems of given doors. A
disadvantage of such systems is the requirement of cable connections
between the central controller and individual lock assemblies. This
requires expensive remodelling, and such installations are vulnerable to
tampering.
Other systems integrate hardware elements for control of functions of
locking systems within the lock assembly itself, typically by housing
circuit boards, power supplies, etc. within the door or in a module
attached to the door. This approach also requires considerable remodeling
of the installations to adapt to the specifications of the given locking
systems. There is a need for improved locking systems which permit
retrofitting of locking assemblies of a type compatible with traditional
installations, thereby facilitating the conversion from traditional
mechanical locking systems to electronic locks.
The use of innovative techniques for coding locks, such as for example
optical, magnetic, electronic, and other techniques, offers the
possibility of a number of significant advantages as compared with
mechanical bitting. Electronic coding and the like holds the promise of
increased information content with attendant improvements to system
capabilities; the flexibility of recoding the cylinder or key (or both);
networking with other electronic systems of an installation; effective new
countermeasures against "lock-picking" attempts; and developments of
versatile management systems for hotels and other institutions. Prior art
electronic locking systems have just begun to realize some of these
advantages, and are hindered by limitations on the loads of information
exchanged between key and lock.
U.K. Patent Application GB No. 2112055A and Australian Patent Application
AU-A No. 21588/83 disclose combination (cylinder plug) and "stator"
(cylinder shell). The stator houses a solenoid-actuated locking bolt which
is oriented parallel to the keyway and which has a retaining member at one
end. The retaining member mates with a grooved blocking member fixed to
the rotor, the cam groove being profiled to include a "blocking notch" (in
2112055A) or "retaining ring" (in 21588/03) which prevent rotation of the
rotor in certain states of the solenoid.
U.K. Patent Application GB No. 2155988 A discloses a mechanical/electronic
key in which an electronic assembly (such as a dual-in-line standard
package integrated circuit is mounted in a casing which serves as the key
grip. The casing is fixed to the key shank and includes a connecting part
for electrical contacts. This application does not show the use of
electronically eraseable programmable read-only-memory (EEPROM) for
storing keying code, nor the mounting of an IC directly to the key shank.
It is a primary object of the invention to provide an electronic door
locking system type including a self-contained lock cylinder. A related
object is to design a system of this type which is compatible with
pre-existing mechanical lock installations, facilitating conversion from
mechanical to electronic locks.
Another object of the invention is to design a reliable locking system.
Such system should avoid failures due to a variety of physical conditions,
such as mechanical stresses, poor electronic connections, and
electrostatic discharges
Desirably such system should be a purely electronic one, i.e. not dependent
on mechanical bitting or the key to open the lock cylinder.
Still another object is to provide the ability to electronically transfer
information from the key to the cylinder, and from the cylinder to the
key. A related object is to permit recoding of the cylinder by the key,
and vice versa. Such a system should be versatile in operation, allowing
multilevel master keying and a variety of other significant keying
functions.
SUMMARY OF THE INVENTION
The above and additional objects are successfully realized in the locking
system of the invention, which is characterized by the encoding of keying
codes in nonvolatile, electrically alterable memory elements housed in a
key and in a lock cylinder. Recognition by the lock cylinder's logic
circuitry of a suitable code from the key memory actuates a release
mechanism, which withdraws a locking pin from the cylinder plug and
permits rotation of the cylinder plug by the key. In the preferred
embodiment, turning the cylinder plug by the key then opens the lock
through conventional mechanical action. The lock cylinder and key both
carry reprogrammable integrated circuit (IC) memory elements, such as
EEPROM IC's, which store keying system codes subject to bidirectional
read/write communication. The key and cylinder designs permit the
miniaturization of components to provide a self-contained electronic
cylinder and key--i.e. requiring no external power source, control system
hookup, or other hardwired connections.
A principal aspect of the invention is the electromechanical relationship
between the key and the lock cylinder. The system relies on a purely
electronic "bitting" of the key to determine whether or not to permit
turning of the cylinder plug; i.e. no mechanical bitting of the key other
than possibly a bit used for plug centering and key retention. In the
preferred embodiment, information is exchanged between key and cylinder
via ohmic contacts in both structures. A variety of integrated circuit
packaging and mounting arrangements are disclosed which are compatible
with the design of a key closely resembling that used with a conventional
mechanical lock cylinder. Such constructions preferably house the IC
package within a cavity in the key blade.
Yet another aspect of the invention is the protection of sensitive
electronic components within the lock cylinder from damage or disruption
due to electrostatic discharges (ESD). The cylinder and key designs reduce
the susceptibility to ESD, in such aspects as connector placement,
protective circuitry within the key and cylinder electronics, packaging
and mounting of key electronics, and capacitive coupling of integrated
circuits to the cylinder.
Still another feature of the invention is the nature of the release
mechanism--i.e. the device which controls the ability of the key to rotate
the cylinder plug. As its basic elements, this mechanism includes an
electronically driven actuator which controls the position of a locking
member (preferably, a locking pin) which selectively engages the cylinder
plug. This device translates relatively small amounts of electrical energy
into the physical force required to extend and retract one or more
radially oriented locking pins from the cylinder plug. This device may
include a primary locking pin directly acted upon by the actuator; this
primary locking pin when extended resists the force of attempted forced
entry, and when withdrawn permits rotation of the plug. Alternatively, the
release mechanism may combine an electromechanically actuated latching
member with a separate locking pin. An additional pin may be included for
key centering and retention.
The electronic locking system of the present invention provides powerful,
flexible "keying system" capabilities--i.e. access control functions. Key
and cylinder access codes may be associated with a broad range of keying
system features. The ability to read and write in both directions provides
additional capabilities which may be achieved through suitable software
control and keying system management.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and additional aspects of the invention are illustrated in the
following detailed description of the preferred embodiment, which should
be taken in conjunction with the drawings in which:
FIG. 1 is a schematic drawing of the electronic locking system of the
invention;
FIG. 2 is a sectional view of a lock cylinder in accordance with the
preferred embodiment, taken along the plane of a fully inserted key
(section 2--2 of FIG. 3);
FIG. 3 is a plan view of the lock cylinder of FIG. 2;
FIG. 4 is a sectional view of the lock cylinder of FIG. 2, taken along the
section 4--4;
FIG. 5 is a sectional view of a preferred electromagnetic actuator, acting
as a primary release mechanism for the locking system of FIG. 1;
FIG. 6A is a sectional view of a secondary release mechanism employing the
actuator of FIG. 5, taken along the plane of a fully inserted key;
FIG. 6B is a sectional view of the secondary release mechanism of FIG. 6A,
in a section taken along the lines 6B--6B;
FIG. 7 is a sectional view of an alternative electromagnetic release
mechanism;
FIG. 8 is a perspective view of a preferred design of an IC-bearing key for
the locking system of FIG. 1, showing an IC package insert in phantom;
FIG. 9 is an exploded view of the IC package insert of FIG. 8;
FIG. 10 is a fragmentary view of the key blade of an alternative key design
in accordance with the invention;
FIG. 11 is a diagrammatic view of the integrated circuit mounting area of
the key blade of FIG. 10;
FIG. 12 is a block schematic diagram of electronic logic circuitry for the
lock cylinder of FIG. 1;
FIG. 13 is a flow chart schematic diagram of a basic operating program for
the electronic logic of FIG. 12;
FIG. 14 is a flow chart schematic diagram of a Basic Zone/One Use
Subroutine for the cylinder logic of FIG. 20;
FIG. 15 is a perspective view of an advantageous design of key/cylinder
recombination console;
FIG. 16 is a schematic view of a preferred management system configuration
for the electronic locking system of FIG. 1, embodying the console of FIG.
15;
FIG. 17 is a sectional view of a release assembly in accordance with a
further embodiment of the invention, in its locked configuration; and
FIG. 18 is a sectional view of the release mechanism of FIG. 17, with key
inserted and solenoid enabled.
DETAILED DESCRIPTION
One should now refer to FIGS. 1-4 for a general overview of an electric
locking system 10 according to a preferred embodiment of the invention.
FIG. 1 shows highly schematically the principal elements of locking system
10, in which a key 30 is inserted into mortise lock cylinder 50 to open
the lock. Electronic logic circuitry 100 within cylinder 50 recognizes the
full insertion of key 30, and extracts electronically encoded information
from the key memory 40 via key connectors 45 and lock connectors 59.
Control electronics 100 stores and processes keying codes received from
key memory 40 as well as resident cylinder codes. The logic circuitry 100
can alter the codes in key memory 40 based on data transmitted from
cylinder 50, and can alter codes stored within the cylinder based on data
from key memory 40.
The processing of access codes from the key and cylinder by cylinder
electronics 100 results in a decision to grant or deny access. If an
"authorized access" decision is made, release assembly 70 receives a drive
signal from control electronics 100, causing it to withdraw a radially
oriented locking pin 72 from cylinder plug 55. A user may then turn key 30
to rotate cylinder plug 55 as in a mechanical mortise lock, and rotate a
cam (not shown) to release a door locking mechanism. Although locking
system 10 is described in the context of a mortise lock, any compatible
mechanical system may be employed. Optionally, cylinder 50 also houses a
key centering and retention device 90, which interacts with a single bit
37 or notch in the key to ensure the proper location of key 30 within
keyway 57.
CYLINDER OVERVIEW
FIGS. 2-4 show in various views a preferred design for lock cylinder 50,
with a fully inserted key 30. The sectional view of FIG. 2 shows key blade
33 of key 30 inserted in the keyway 57 of plug 55. Centering/retention pin
92, biased by spring 94, fits within a notch 37 along the upper edge of
the key 30 the interface 95 between pin segments 92a and 92b. Pin 92 is
comprised of discrete upper and lower segments 92a, 92b. Pin 92 prevents
the withdrawal of key 30 except when in its illustrated, "home" position,
at which point the rear camming surface of notch 37 exerts an upward force
during key withdrawal. When pin 92 is in its extended position, the
interface 95 between pin segments 92a and 92b is aligned with the
cylinder-plug shear line 56, to permit plug rotation. With key 30 in its
home position, ohmic contacts 45a-45d (FIG. 3) abut against cylinder
contacts 59a-59d, which are in this embodiment placed along the lower edge
of key 30 for reasons of spatial economy. (Cf. FIG. 4).
Having reference to both FIGS. 3 and 4, the illustrated, self-contained
configuration of lock cylinder 50 includes an upper cavity 52 to house the
release assembly 70, power supply 68, and cylinder electronics 100. Key
centering/retention assembly 90 is shown housed in a separate chamber 96.
This packaging of components is compatible with the form factor of a
standard U.S. 11/8" mortise cylinder, thus permitting the retrofitting of
electronic cylinders 50 in conventional lock installations.
As seen in FIG. 4, release assembly 70 must fit within a limited volume.
Its pin 72 must have requisite size and mass, and firmly engage cylinder
plug 55, to resist the torque of an attempted forced entry. That portion
of cylinder shell 51 housing the locking pin 72 should include adequate
bearing material for the operation of mechanism 70. When release motor 75
is actuated to allow access, it retracts pin 72 which moves clear of the
shear line 56 (FIG. 2) to allow plug 55 to rotate.
Power supply 68 provides sufficient peak current and power to power the
release mechanism driver circuitry 110 (FIG. 12). Although a variety of
self-generating power sources and battery technologies may be employed,
excellent results have been obtained using lithium thionyl chloride
batteries. In an alternative embodiment, not illustrated in the drawings,
the cylinder electronics and power supply are packaged externally to the
cylinder in a separate module. This approach allows more flexibility in
packaging the remaining cylinder components, and facilitates the
adaptation of the invention to a standard 11/8" mortise cylinder.
RELEASE MECHANISM
FIG. 5-7 show various designs for the release assembly 70, the device which
prevents rotation of plug 55 until the control logic 100 commands it to
allow access (permit plug rotation). Release assembly 70 is designed to
translate limited amounts of electrical energy into the physical force
required to move radially oriented locking pin 72. FIG. 5 illustrates an
advantageous design 210 for the release mechanism motor 75 of FIGS. 2-4.
Release actuator 210 includes a permanent magnet 213 with pole pieces 211,
212, whose field acts on a bobbinless voice coil 214. Coil 214 is attached
to a two layer disc spring, comprised of a bistable snapover spring 215,
and outer, deflection spring 217. Snap spring 215 is affixed to the
central pole piece 212 at its center and to voice coil 214 at its
perimeter, and locates voice coil 214 in the center of the gap between
pole pieces 211, 212. Deflection spring 217 is joined to snap spring 215
at its periphery, and is firmly affixed at its center to locking pin 218.
In operation, when locking pin 218 is in its outward, locking position, it
is necessary in order to retract the pin to provide current through coil
214 to generate a field of opposite polarity to that of permanent magnet
211, of sufficient strength to overcome the snap action of bistable spring
215. If pin 218 is free to move, deflection spring 217 will pull the pin
toward magnet 211. If pin 218 is jammed, spring 217 will deflect in order
to permit spring 215 to toggle; when the pin is freed, deflection spring
217 will then pull pin 218 toward magnet 211.
When current of opposite polarity is applied, coil 214 will move away from
magnet 211, and toggle spring 215 will snap to its outward position.
Again, if pin 218 is constrained, the deflection spring 217 will allow the
motion of coil 214 and apply an outward force on the pin until it is free
to move.
In the preferred application of magnetic actuator 210, this device is used
as a "primary release mechanism"--i.e. pin 218 serves as the locking pin
72 (FIGS. 2-4). When key 30 is inserted in keyway 57 and a valid code is
recognized by the lock electronics 100, assembly 210 will apply a
retraction force to pin 72. If the key is applying a torque to the plug
55, pin 72 will not move until the torque is removed by jiggling the key.
The pin will then move toward magnet 211 allowing plug 55 to rotate. When
the key rotations have been completed, key 30 is returned to its home
position to be withdrawn from cylinder 50. A sensor (not shown) detects
the withdrawal motion of the key, and sends a signal to motor 75 to push
the locking pin back into plug hole 54. Assembly 90 ensures that key 30
can be removed only when pin 72 is aligned over the plug hole 54.
In an alternative embodiment of the invention, illustrated in FIGS. 6A and
6B, the magnetic actuator device of FIG. 5 is combined with a separate
locking pin to achieve a release mechanism that also provides the key
withdrawal alignment function--a "secondary" release assembly. FIG. 6A
shows release assembly 230 in its unlocked configuration, seen along the
plane of fully inserted key blade 33', The separate locking pin assembly
231 includes a blocking pin 234, locking pin 233 and compression spring
232; pins 233 and 234 meet at an indented interface 238, while locking pin
233 includes a circumferential groove 239. As seen in the transverse
sectional view of FIG. 6B, the release mechanism incorporates a magnetic
motor 237 such as that of FIG. 5, which reciprocates a sear tongue 236.
Before a key 30' is inserted locking pin assembly 231 is held in an upward
position by the insertion of sear tongue 236 into groove 239, as shown in
FIG. 6B. Upon an "allow access" decision by the key electronics after the
full insertion of an authorized key (FIG. 6A), motor 237 is activated
pulling sear tongue 236 free of the locking pin 233. Drive spring 232
pushes the pins 233, 234 downwardly until the locking pin 233 seats in
cylinder plug 55 against the notch 37' in key blade 33'. At this position,
the interface 238 between pins 233 and 234 lines up with shear line 56
allowing the plug 55 to rotate. While pin assembly 231 is extended, the
mating between locking pin 233 and key notch 37' prevents key 30' from
being withdrawn. If plug 55 is properly aligned with key 30' in its home
position, the key can be removed urging pin 233 upwardly due to the key's
ramp profile. During key withdrawal, motor 237 is actuated in the opposite
polarity to push sear tongue 236 against pin assembly 231. When key blade
33' pushes pins 233, 234 to the proper height, sear tongue 236 enters
groove 239 preventing further movement.
The blocking pin 234 abuts against the cylinder shell to prevent the
forcing of pin assembly 231 upwardly beyond the shear line. Pin 235
resists tampering with pin assembly 231 using a drill or like device.
FIG. 7 illustrates a further electromagnetic release mechanism 250. This
assembly is designed to protect against manipulation using an external
magnetic field, as well as against forced entry by vibration, using a
sharp impact against the lock cylinder housing, etc. Furthermore, assembly
250 requires very little energy in operation, thereby prolonging the
intervals between battery replacements.
As seen in FIG. 7, release assembly 250 consists of two locking pins 251
and 262, solenoids 252 and 255, permanent magnets 253 and 257, flat spring
(clock spring) 258, spring loaded pin 261 (comprised of parts 261a, 261b),
a winding 256 on the lower locking pin 262, and a spring 254. When spring
loaded pin 261b has fully engaged cylinder plug 55, it is mechanically
constrained in its locked position by spring 259, which is coupled to pin
261b. Clock spring 258 constrains locking pin 251 in its locked position.
Upon insertion of a properly bitted key, spring loaded pin 261b is ramped
up, thereby aligning the gap 263 between pins 261a, 261b with the shear
line 56. This urges clock spring 258 upwardly and removes the mechanical
restraint on locking pin 251, which is now free to move up to its unlocked
position. If the cylinder logic recognizes a valid, key, solenoid 252 is
energized, pulling locking pin 251 against permanent magnet 253. Plug 55
is thereby unlocked and free to rotate. Upon removal of key 30 from the
keyway, spring loaded pin 261 returns to its fully depressed position,
blocking the shear line 56 and unloading flat spring 258. Spring 258 in
turn pushes locking pin 251 into a locked position.
A second, coaxial solenoid-actuated locking pin 262 is incorporated into
release assembly 250 to protect against unauthorized opening of the lock
while using a key blank to ramp up the spring loaded pin 261. If an
external force is applied to the locking cylinder envelope to attempt to
move locking pin 251 up against permanent magnet 253, lower locking pin
262 will simultaneously move upward under the action of spring 254. Pin
262 will thereby move against permanent magnet 257 into its locked
position and prevent rotation of plug 55. Upon subsequent insertion of a
valid key, a slight momentary current through solenoid winding 255 induces
a voltage differential in the output terminals in winding 256. The
resulting voltage differential will be processed by the cylinder
electronics 100 to energize solenoid 255, pulling locking pin 262 back and
allowing plug 55 to rotate freely. Solenoid 255 is thus energized only in
the event that locking pin 262 has been moved upwardly into its locked
position, thereby changing the relative position of windings 255 and 256.
An alternative version of the solenoid release assembly of FIG. 7 omits the
lower locking assembly and replaces the conventional solenoid 252 and
permanent magnet 253 with a bistable solenoid assembly. Such bistable
solenoid assembly will exhibit a toggle characteristic when energized; in
either of its two positions, it will be much less susceptible to external
magnetic fields, sharp impacts to the lock envelope, etc.
In the release assembly of FIG. 7 the flat spring 258 and spring loaded pin
261 serve as a bistate mechanical assembly which acts in cooperation with
the solenoid-locking pin components. Such assembly mechanically restrains
the locking pin in its locked position when the release mechanism is in
its locked configuration; is moved to a second state by the key during
insertion of the latter, thereby providing a clearance region for the
locking pin so that the latter may be moved to its unlocked position by
the solenoid; and upon removal of the key reverts to its first
configuration due to a mechanical bias, thereby forcing locking pin 251
into its locked position.
FIGS. 17 and 18 illustrate a further release assembly 470 incorporating a
bistable mechanical assembly having the functional characteristics
discussed above. Release assembly 470 includes a solenoid 480 which is
radially aligned relative to the keyway, the solenoid plunger being
coupled to locking pin 485 which when extended prevents rotation of the
cylinder plug 50. When release assembly 470 is in its locked
configuration, locking pin 485 is restrained in its extended position by
cam member 475, and a further pins 471a and 471b are also held down by cam
member 475. Absent a countervailing force the cam member 475 is biased in
this position by compression spring 474. Upon insertion of a key 430, the
pins 471a, 471b are ramped up until they rest against the key ledge 435,
at which point the gap 472 is aligned with the shear line 56; pin 471a
displaces cam member 475 via ramp surface 476, providing a clearance
region 478 for the end 477 of locking pin 485. At this point, if solenoid
480 is actuated the locking pin 485 can retract from cylinder plug 50;
magnet 479 latches the pin 485 in this retracted position so that the
solenoid need not be constantly powered or pulsed to maintain this
configuration. Upon removal of the key, compression spring 474 drives cam
member 475 to its original position, thereby camming down locking pin 485
and pins 471a, 471b.
In the embodiment of FIGS. 17 and 18, centering/retention assembly 90 has
like structures and functions to that of FIGS. 2-4.
KEY WITH IC
FIGS. 8-11 illustrate various constructions of the key 30. A suitable
design for key 30, shown in FIG. 8, is quite similar to that of a
conventional mechanical key. The lower edge 34 of the key has no bitting,
and has a rectangular slot or cavity 35, which houses integrated circuit
package 42 (shown in phantom) and,key contacts 45. Contacts 44 are located
flush with the lower key edge 34.
The embodiment of FIGS. 8 and 9 utilizes a surface mounting technique,
wherein the integrated circuit 41 is mounting in a compact surface mount
package 42 having adequate size and pin outs for the electrically
alterable ICs 41 within each package. Surface mount package 42 is retained
within a rectangular insert 141, shown in phantom in FIG. 8, which is
closely fitted within a complementary cavity in the bottom edge 34 of key
30. The IC package 42 electrically communicates with a set of four
contacts 45a-45d which are mounted flush with the outer wall of insert 141
as well as within key edge 34. FIG. 9 shows in an exploded view the
various elements of the IC package insert 141 (only two contacts 45 are
shown). The surface mount package 42 comprises a standard S08 dual in-line
package, including 8 pin-outs 46. Appropriately shaped contacts 45 are
embedded in insert 141 and include flange portions 45a-f, 45b-f, etc.
which fit within apertures 145 in rectangular insert 141, to provide flush
contacts. In an operative embodiment of surface-mounted IC package 42,
mounting insert 141 was a filled nylon substrate in accordance with FIG.
9, with four imbedded noble metal alloy contacts 45a-45d. Insert 141 was
press fitted into a rectangular slot cut in the bottom edge 34 of key 30.
The alternative IC mounting embodiment of FIG. 10 and 11 uses a "chip and
wire" mounting technique. The integrated circuit die 41 is inserted into a
cavity 161 which was milled or coined into one face of key 160 Cavity 161
has previously had a layer of insulating ceramic fired on to create a
dielectric layer over the metal body of the key. The integrated circuit's
pads 41p were electrically coupled by conductors 163 to key contacts 165
using well known porcelain-over-metal thick film hybrid techniques.
Contacts 165a-d comprised noble metal alloy clips which were clipped or
bonded to conductors 163, and anchored at an indented region of the
opposite face of key 160. Contacts 165 were electrically isolated from the
metallic body of key 160 by plate or potting 164, and all required
components were encapsulated with a conventional potting material to
hermetically seal the integrated circuit 41.
OHMIC CONTACTS
In all of the embodiments of FIGS. 8-11 ICs 41 are electrically connected
to a set of ohmic key contacts 45. Advantageously, contacts 45 are
composed of a hard noble metal alloy which allow adequate contact pressure
to force contact through dirt or film by a wiping action, and which
withstands corrosion under typical environmental conditions. Excellent
results have been observed with Paliney noble metal alloys (Paliney is a
registered trademark of J. M. NEY Company). In a particular embodiment of
the invention, key contacts 45 were formulated of Paliney 8 alloy
(comprising palladium, silver, and copper) and cylinder contacts 59 of
Paliney 7 alloy (comprising the above elements plus gold and platinum).
With further reference to FIGS. 2-4, cylinder contacts 59a-59d provide
firm, reliable ohmic contact with the respective contacts 45a-45d of a
fully inserted key 30. As best seen in FIG. 4, contacts 59 are
cantilevered members mounted to a contact holder 61 at one side of
cylinder plug 55, with dished tips pressed firmly against the contacts 45
in key 30.
Advantageously, locking system 10 relies on a suitable protocol for data
communication between key memory 40 and cylinder logic 100, to ensure
accurate data transmission over noisy paths (ohmic contacts 45, 59). Such
protocol includes redundant, error-detection data bits in all
transmissions. The data receiver, whether key or cylinder, compares the
transmitted access code bits and the error-detecting bits to see that
these match A number of well known encoding methods allow the detection of
errors as well as the correction of simpler errors. Such technique enables
error-free data transmission in the face of intermittent contact problems
due to dirt, films, premature key withdrawal, and the like. Defective
transmissions can be recognized and often reattempted. Significantly, such
encoding techniques allow the key or cylinder to avoid writing erroneous
data, or writing data to the incorrect location. Preferably, this protocol
is implemented both in the cylinder control logic 100 and in I/O circuitry
within the electronically alterable memory 40 in key 30.
ELECTRONICALLY ALTERABLE KEY MEMORY
Electronically alterable key memory 40 has the ability to store a
substantial number of access codes, each of which will have a much larger
range of possible values then found in traditional mechanical locks. This
non-volatile integrated circuit technology involves memory which may be
read like traditional read-only-memory (ROM), and may be written to after
being electronically erased. Such memory devices are commonly known as
EEPROM integrated circuits. EEPROM is a medium density memory, which
retains adequate key memory within devices on the order of 2-3 mm micron
geometry. To store data in such devices, the word must be erased and then
written. Typical erase/write cycles (E/W) are on the order of 20
milliseconds, and require less than 15 milliamperes.
Although a variety of EEPROM process technologies are available, it is
desirable to utilize a type which achieves high reliability over an
extended service life. Various SNOS (Silicon Nitride Oxide Silicon) and
CMOS (Complementary Metal Oxide Semiconductors) process technologies have
been developed for the design and production of EEPROM devices of suitable
characteristics for key memory 40 and cylinder memory 180 (FIG. 12).
EEPROM cells have a normal life expectancy of 10,000 E/W cycles, ater
which there will be an increased risk of catastrophic failure. For SNOS
process technologies, these failure parameters are related in that data
written to a given memory cell on the 10,000th erase/write cycle will be
retained for at least ten years, and subsequent erase/write cycles to the
same cell will be retained for a somewhat shorter period.
It is important to include in key memory 40 on-board | | |
