IMPROVEMENTS IN SAFETY APPARATUS FOR LIFTS OR
Year: 1882

page_text: LETTERS PATENT to Alexander Melville Clark of the firm of A M and
W Clark of 53, Chancery Lane, in the County of Middlesex, Patent Agents,
for an Invention of IMPROVEMENTS IN SAFETY APPARATUS FOR LIFTS OR
Communicated to him from abroad by Volney William Mason,
of Providence, State of Rhode Island, United States of America and at present
ELEVATORS
of Wiechaden in the Empire of Germany
PROVISIONAL SPECIFICATION left by the said. Alexander Melville Clark
at the Office of the Commissioners of Patents on the 12th July 1882.
ALEXANDER MELVILLE CLARK of the firm of A. M. & W. Clark of 53 Chancery
Lane in the County of Middlesex, Patent Agents, IMPROVEMENTS IN SAFETY
APPARATUS FOR LIFTS OR ELEVATORS [Communicated to him from abroad by
Volney William Mason, of Providence, State of Rhode Island, United States of
America and at present of Wiesbaden in the Empire of Germany]
This Invention of an improved safety apparatus for the cages of lifts or
elevators, is designed to prevent the falling of the cage in the event of the hoisting
rope or other part of the apparatus giving way and it is characterised by its
simplicity and unfailing action which is immediate and dependent upon the speed
at which the cage is moving.
The apparatus consists of vertical racks along the guides of the cage and pawls
pivoted to the cage either above or below the same, in combination with guides of
undulating or serpentine form alongside the racks, and arms or extensions forming
with the pawla elbow levers, which arms bear against said guides in such manner
that the pawls are prevented from engaging with the teeth of the racks when the
cage is moving at its normal speed but are caused to engage therewith and arrest
the cage immediately the cage begins to fall at a high speed. The undulations of
the guides correspond in pitch and position with the teeth of the rack and the
pawls are caused to oscillate by their arms working against the undulations of the
guides in such manner that the pawls swing in and out of the teeth of the racks

page_text: without however engaging therewith when the cage is moving slowly. Under
these circumstances the pawls just clear the points of the teeth, but when the cage
begins to descend at too high a speed, the motion of the pawl and arm, caused by
the latter ascending an undulation of the guide, persists after the arm attains the
summit of the said undulation and the pawl is consequently thrown farther into
the rack and fails to clear the point of the next succeeding tooth, thus arresting
the cage.
To ensure simultaneous action of the safety apparatus at the opposite sides of
the cage, the two pawls are connected to the opposite ends of a swinging lever by
connecting rods having springs upon them.
It is preferred that the undulating guides should be cast in one with the rack
and at each side thereof and that the arm or extension of the pawl should be
double or forked and carry a friction roller to work against the undulating guides.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Alexander Melville Clark in the Great Seal Patent Office on
the 12th January 1883.
ALEXANDER MELVILLE CLARK of the Firm of A, M, and W, Clark of 53 Chancery
Lane in the County of Middlesex Patent Agents "IMPROVEMENTS IN SAFETY
APPARATUS FOR LIFTS OR ELEVATORS," A communication to me from abroad by
Volney William Mason of Providence, State of Rhode Island, United States of
America, and at present of Wiesbaden in the Empire of Germany.
This Invention of an improved safety apparatus for the cages of lifts or
elevators, is designed to prevent the falling of the cage in the event of the rope or
other part of the hoisting apparatus giving way and it is characterised by its
simplicity and unfailing action which is immediate and dependent upon the speed
of the cage itself.
The apparatus consists of vertical racks along the guides of the cage and pawls
pivoted to the cage either above or below the same, in. combination with guides
of undulating or serpentine form alongside the racks and arms or extensions forming
with the pawls elbow levers, which arms bear against said guides in such manner
that the pawls are prevented from engaging with the teeth of the racks when the
cage is descending at its normal speed, but are caused to engage therewith and
arrest the cage immediately it begins to fall at an excessive speed. The undula-
tions of the guides correspond in pitch and position with the teeth of the rack and
the pawls are caused to oscillate by their arms working against the said
undulations in such manner that the pawls swing in and out of the teeth of the
racks without however engaging therewith when the cage is moving slowly.
Under these circumstances the pawls just clear the points of the teeth, but when
the cage begins to descend at too high a speed, the motion of the pawl and arm
caused by the latter riding over an undulation of the guide, persists by the inertia
of the parts, after the arm attains the summit of the said undulation, and the pawl
is consequently thrown farther into the rack and fails to clear the point of the
next succeeding tooth, thus arresting the cage. The two pawls are connected to
the opposite ends of a swinging lever in order to ensure simultaneous action of the
safety apparatus at the two opposite sides of the cage.
It is preferred that the undulating guides should be cast in one with the rack
and at each side thereof, and that the arm or extension of the pawl should be
double or forked and carry a friction roller to work against the undulating guides.

page_text: strength to support the strain due to the sudden arrest of the cage. Each pawl
is provided with a forked or double arm or tail C¹ which makes an angle with the
pawl C and carries a friction roller c¹, the ends of the pawl and its arm or
extension approaching the guide of the cage. D is a rack of ratchet teeth of the
form and direction shown, between two shrouds E whose edges form undulating
guides corresponding in pitch to the ratchet teeth and so proportioned, having
regard to the relative lengths of the pawl C and its arm C¹, that the pawl will, by
the friction roller c' running upon the undulating guides E, be caused to oscillate
in and out of the teeth of the rack without engaging therewith when the cage is
descending slowly, the pawl being so weighted that the roller c¹ shall keep in
contact with the guides E at the normal speed of the cage. The guides E are
preferably cast in one with the rack teeth between them, and the lateral faces and
base flange of the shrouds may form the guides against which the shoes F of the
cage slide, the combined rack and guide being bolted to any suitable support, or
the rack and guide DE may be placed alongside the usual guide or in any other
convenient position, either at two opposite sides of the cage as here shown, or at
the four corners of the cage if desired. In any case. the pawls at two opposite.
sides of the cage are coupled by connecting rods g to the opposite ends of an equal
armed lever G oscillating about; a centre so as to ensure their simultaneity of
action.
Having described the nature of the said Invention and the manner of performing
the same, I would observe that I do not limit myself to the pitch of the racks or
to the precise forms and proportions of the pawls and other parts here shown as
such may be varied without departing from the Invention, and that I do not claim
the application of safety pawls and racks to the cages and guides of lifts, as catches
held back by the hoisting rope and thrown into gear by a spring upon breakage of
the rope, are known, but what I claim as the Invention to be protected by the
hereinbefore in part recited Letters Patent is :—
The improved safety mechanism for lifts or elevators consisting of the rack, the
undulating guides, and the pivoted pawl with an arm or tail piece working against
the undulating guides and oscillating the pawl, the whole combined for operation
and applied to a lift or elevator substantially as herein specified.
In Witness whereof I the said Alexander Melville Clark have hereunto set my
hand and seal this twelfth day of January, A.D. 1883.