Lock (fastening device)
| INTRODUCTION |
Key and Lock Mechanism
This diagram shows the way a key opens its corresponding
lock. When the key is inserted into the lock, its grooves raise spring-loaded
pins of corresponding sizes. This permits the key to turn the cylindrical plug
and open the lock. Only a key with grooves that exactly correspond to the size
of the pins will permit the plug to rotate in the lock barrel.
Lock (fastening
device), mechanical device used for fastening doors, chests, and lids,
consisting essentially of a bolt guarded by a mechanism released by a
key or a combination.
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Mechanical Bolt Lock
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The simplest form of lock is a ward lock, which
is essentially a bolt containing a notch known as a talon. The bolt is moved
backward or forward by engaging a key in the talon. A back spring attached to
the bolt holds it in place once it is released by the key. The tumbler or lever
lock, similar to the ward lock, contains one or more pieces of metal of
different heights, known as tumblers, levers, or latches, which intercept the
bolt and prevent it from being moved until the tumblers are raised or released
by the action of an appropriate key. The so-called pin-tumbler cylinder lock, or
Yale lock, introduced about 1860 by the American inventor Linus Yale, was the
first device to employ a small, flat key in place of a large, cumbersome one.
The Yale lock consists essentially of a cylindrical plug placed in an outer
barrel. The plug is rotated by a key and in turn moves the bolt of the lock by
means of a cam. In order to rotate the plug the inserted key must raise five
pins of different sizes into corresponding holes in the plug. Five similar pins
are contained in the upper part of each of the holes. If the pins are not raised
to the circumference of the plug, the plug cannot be turned. The most common
form of cylinder lock used in the home is the so-called night latch, operated by
a key from the outside and a knob from the inside. Another type of lock that is
increasing in use is the magnetic lock, which is essentially the same as a
cylinder lock, except the pins need a suitably magnetized key to bring them into
alignment to allow the plug to be turned.
Of the various types of locks that are not
operated by keys, the dial, or combination, lock is the most common. A set of
tumblers, or wheels, is actuated by a spindle that can be rotated by a graduated
dial on the outer end of the lock. Spinning the dial according to the proper
combination arranges the tumblers so that the bolting mechanism is released.
Combination locks of intricate design, incorporating various electronic
safeguards, are produced for safes and bank vaults, and can have more than 100
million changes of combination. The combination locks are sometimes safeguarded
by a time lock, which only allows the vault to be opened at certain specific
times.
| II. | HISTORY |
The earliest lock in existence is an Egyptian
lock made of wood, found with its key in the ruins of Nineveh, in ancient
Assyria. In construction it is the prototype of the modern cylinder lock. Locks
and keys are also mentioned in the Old Testament, and the Greeks and Romans used
locks of simple design. Medieval artisans designed locks of exquisite detail,
the perforations and carvings often having no relation to the working of the
lock. With the exception of the development of ward locks, however, little was
done to improve the efficiency and convenience of locks until the late 18th
century. In the 19th century ward locks were improved, and tumbler or lever
locks, pin-tumbler or cylinder locks, and keyless locks were invented and
improved. Subsequent development has focused on mass production, improvement of
materials, and increasing complexity of the working mechanisms, including the
increasing use of automatic electronic alarm and safety
devices.
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