Improvements in Dental and other Chairs, and in Lifting and Lowering Apparatus applicable to the same.
Year: 1892

page_text: Date of Application, 11th Aug., 1892
Complete Specification Left, 9th May, 1893-Accepted. 24th June, 1893
PROVISIONAL SPECIFICATION.
Improvements in Dental and other Chairs, and in Lifting and
Lowering Apparatus applicable to the same.
We, THOMAS HARRY GARDNER and EDWARD GARDNER both of Hadfield
Street, Cornbrook, Manchester, Engineers, do hereby declare the nature of this
invention to be as follows:-
In the dental chair to which the invention is applicable, there is a fixed chair
standard; an intermediate moving part sliding on the fixed standard up and down;
and an upper moving part sliding upon the intermediate part and carrying the chair
seat.
These three parts are so geared by racks and pinions that for every increment of
rise given to the intermediate part, the upper part rises a corresponding increment
in relation to the intermediate part. Consequently in relation to the fixed standard
the upper moving part rises and falls twice as fast as the intermediate moving
part.
The improved lifting apparatus is arranged as follows:-On a spindle mounted
on the intermediate part and carrying pinions gearing into racks on the other parts
is fixed a silent clutch worked by a tread lever so that as the lever is depressed the
spindle is turned and so raises the chair. One end of a controlling arm is fixed
loosely on the spindle, the other end is slotted and rides loosely on a pin fixed on
the upper moving part of the chair. In the periphery of the clutch case which
also is loose upon the spindle is fixed a projection which normally is held by a spiral
spring hard down on a similar projection on the controlling arm. The tread lever
and the controlling arm project on opposite sides of the spindle and when the
extremity of the controlling arm is raised by its connection with the upper moving
part, the extremity of the tread lever is depressed. Thus the tread lever is
arranged to stand ready for use with its foot end always at the same distance from
the ground.
The
The silent clutch consists of a disc rigidly connected with the spindle and is
enclosed in the clutch case. The case at one part of its circumference is slotted
through to the inside and receives a tongue which is pivotted in the case.
tread lever is attached by a joint to the tongue and when the tongue is depressed
by the lever it presses on the disc. One end of a helical spring connects a boss
on the clutch case with the tread lever. When the tread lever is depressed the
tongue presses against the periphery of the disc causing sufficient friction to carry
the disc and spindle round.
When the tread lever is lifted by the spring the tongue ceases to touch the disc
thus leaving the chair free to be lowered.
The lowering is effected by improved lowering apparatus.
A spindle is provided and is geared with the spindle before referred to. This
spindle through a worm drives an axis and the worm is so proportioned that it will
just turn and permit the load to descend unless restrained. Upon the axis there is
a flanged disc and concentric with this is a stationary disc, the flange and the
stationary disc being in the same plane.
Two levers are pivotted to the flanged disc. The levers at the pivot ends are so
shaped as to embrace a portion of the periphery of the disc in such a manner that
one or other end of the arc of embrace on the levers presses on to the disc rim
according as the lever arms are pulled away from or pressed towards the centre a
spring on each lever presses the levers towards the axis and they act after the
manner of a brake sufficiently to prevent the axis from revolving under the load.

page_text: The action is as follows:-When the chair is to be lowered the flanged disc is
started to revolve and if sufficient impetus be given the levers under the action of
centrifugal force fly outwards against the action of the springs and cease to press on
the disc. The speed then accelerates and the levers begin to press on the edge of the
disc at the other end of the arc of embrace. When a certain speed is reached
the pressure due to centrifugal force prevents further acceleration and the descent
continues at a uniform rate. The levers thus govern the rate of descent.
We have devised an improved method of adjusting the swinging back of the
chair. A horizontal bar swivelling on centres in the intermediate moving part of
the chair is provided. It is recessed to receive a taper bar or rod and a wedge
piece. The bar or rod is jointed at its upper end to the swinging back.
The wedge is provided with a pivot which is received in the fork end of a foot
lever which lever is pivotted at the middle of its length in the horizontal bar. A
spring acts on the fork end of the lever so as to continually press the wedge
downwards.
To depress the back the lever is depressed at the foot end which action lifts the
wedge, the back then is pulled down to the point required. When the lever is
released the back is then locked. When it it is desired to raise the back it is
pressed forward to the point required and the wedge automatically locks it in any
position.
Dated this 11th day of August 1892.
CARPMAEL & Co.,
Agents.
COMPLETE SPECIFICATION.
Improvements in Dental and other Chairs, and in Lifting and
Lowering Apparatus applicable to the same.
WC, THOMAS HARRY GARDNER and EDWARD GARDNER both of Hadfield
Street, Cornbrook, Manchester, Engineers, do hereby declare the nature of this
invention and in what manner the same is to be performed to be particularly
described and ascertained in and by the following statement:-
In the dental chair to which the invention is applicable there is a fixed chair
standard, an intermediate moving part sliding on the fixed standard up and down,
and an upper moving part sliding upon the intermediate part and carrying the chair
seat.
The chair seat is raised by the aid of a foot lever which is carried upon the
intermediate moving part but is nevertheless so arranged that the tread to which
the foot is applied remains at approximately the same distance from the ground.
The parts are retained in any position to which the seat may have been raised by
a frictional brake. The brake pieces are mounted upon a hand wheel which is
geared with the parts to be retained by means of a worm wheel and worm of rapid
pitch. The brake pieces press upon a stationary cylindrical surface concentric with
the hand wheel. When the wheel is rotated centrifugal force by overcoming
springs withdraws the brake pieces from the disc and the descent of the weight is
permitted.
When a certain speed is exceeded the centrifugal force operates to' again 'apply
the brake pieces and so the velocity of descent is regulated.
The height of the chair back or head rest is regulated by means of a taper strut
or support which connects the back or head with a horizontal bar pivotted to the
chair frame. The strut lies in a groove formed for it in the bar and a wedge locks
it therein so as to prevent downward movement but permitting it to be raised. By
means of a foot lever the wedge can be withdrawn.
Figure 1 of the annexed drawings is a side elevation of a dental chair constructed
in accordance with our invention. The seat in this figure is represented in its
lower position.

page_text: the back of the chair is not represented in this figure.
Figure 2 is a rear elevation and Figure 2B is a horizontal section of a portion.
Figure 3 is a side elevation of the lifting gear to a larger scale.
Figure 4 is a plan partly in section of the lifting gear and Figure 5 is a sectional
elevation of a portion of the same.
Figures 6 and 7 are sectional views of parts of the lowering gear.
Figure 8 is a rear elevation of apparatus for the adjustment of the back of the
chair.
Figure 9 is a plan partly in section of the parts shewn by Figure 8.
In the dental chair to which the invention is applicable,
A is the fixed chair standard;
B is the intermediate standard or moving part sliding on the fixed standard up
and down; and
C is the upper moving part sliding upon the intermediate part and carrying the
chair seat.
These three parts are so geared by racks and pinions that for every increment of rise
given to B the intermediate part, the upper part C rises a corresponding increment
in relation to the intermediate part. Consequently in relation to the fixed standard
the upper moving part C rises and falls twice as fast as the intermediate moving
part B.
The improved lifting apparatus is arranged as follows:-On a spindle D mounted
on the intermediate part and carrying pinions gearing into racks on the other
parts A and C is fixed a silent clutch worked by a tread lever E. As the lever is
made to incline the spindle is turned and the chair is raised. One end of a
controlling arm F is fixed loosely on the spindle D, the other end is slotted and
rides loosely on a pin G fixed on the upper moving part C of the chair. This pin
controls the angular motion of lever Fround the spindle D. In the periphery of
the clutch case a which also is loose upon the spindle fixed a projection >> which
normally is held by a spiral spring hard down on a similar projection c on the
controlling arm. The tread lever E and the controlling arm F project from opposite
sides of the spindle D and when the extremity of the controlling arm is raised by
its connection with the upper moving part C the extremity of the tread lever is
depressed. Thus the tread lever is arranged to stand ready for use with its foot
end always at the same distance from the ground.
The silent clutch consists of a disc d rigidly connected with the spindle D and is
enclosed in the clutch case a. The case at one part of its circumference is slotted
through to the inside and receives a tongue e which is pivotted in the case at f.
The tread lever E is attached by a joint to the tongue e. When the tread lever is
depressed the tongue e presses against the periphery of the disc d causing sufficient
friction to carry the disc and spindle round. is a coiled spring connecting m on
the case a with n on the tongue e. When the tread lever is lifted by the spring.h
the tongue ceases to touch the disc thus leaving the chair free to be lowered.
When the tread lever E is depressed the spring stretches, the tongue touches the
disc at and so begins to grip the disc.
Thus during the downward movement of the lever E the tongue e locks the case a
and the disc d fast together. In the upward movement, when the lever E is raised
by the springs, the case a turns about the axis D, whilst the axis and the disc d
remain at rest, being held by the lowering apparatus which we will now describe.
The lowering is effected by improved lowering apparatus.
A spindle H is provided. The spindle D through a worm wheel and worm and
ratchet drives the axis H and the worm is so proportioned that it will just turn
and permit the load to descend unless restrained.
Upon the axis there is a flanged disc J and concentric with this is a stationary
disc K the flange and the stationary disc being in the same plane.
Two levers Land L are pivotted to the flanged disc J at M M.
The levers at the pivot ends are so shaped as to embrace a portion of the

page_text: .
periphery of the disc in such a manner that one or other end of the arc of embrace
on the levers presses on to the disc rim according as the lever arms are pulled away
from or pressed towards the centre. A spring N on each lever presses the levers
towards the axis H and they act after the manner of a brake sufficiently to prevent
the axis from revolving under the load.
The action is as follows:-When the chair is to be lowered the flanged disc J i3
started to revolve and if sufficient impetus be given the levers L, L, under the
action of centrifugal force fly outwards against the action of the springs N and
cease to press on the disc. The speed then accelerates and the levers begin to press
on the edge of the disc at the other end of the arc of embrace. When a certain
speed is reached the pressure due to centrifugal force prevents further acceleration
and the descent continues at a uniform rate. The levers thus govern the rate of
descent.
We have devised an improved method of adjusting the swinging back of the
chair. A horizontal bar Z swivelling on centres in the part of the chair is
provided. It is recessed to receive a taper bar or rod Y and a wedge piece X.
The bar or rod Y is jointed at its upper end to the swinging back W.
The wedge is provided with a pivot w which is received in the fork end of a
lever U which lever is pivotted at the middle of its length at in the horizontal
bar Z. A spring (not shewn in the drawing) acts on the fork end of the lever U
so as to continually press the wedge downwards.
To lower the back W the lever U is depressed at the foot end which action lifts
the wedge, the back then is pulled down to the point required. When the lever is
released the back is then locked. When it is desired to raise the back it is
pressed forward to the point required and the wedge automatically locks it in any
position.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed, we declare that what
we claim is :-
1. The combination consisting of the parts A B and C geared together by racks
and pinions; a disc d fast on an axis D which turns with the pinious and which
axis is carried upon the intermediate part B, silent pawl gear and foot lever
turning about the axis, a stop controlled by the upper moving part C and a spring
or its equivalent operating upon the pawl gear and tending to raise the foot lever
as far as the controlled stop admits; the whole so arranged that notwithstanding
the movement of the part B the position of the outer end of the foot lever varies
but little.
2. The retaining and lowering gear consisting of an axis H geared with the part
to be raised or lowered; a wheel J fast upon the axis; weighted brake pieces L
pivotted upon the wheel; springs N operating upon the brake pieces; and a
stationary cylindrical surface K; the whole so arranged that when the wheel J is
at rest the springs hold the brake pieces against the discs and when in motion the
centrifugal force first overcomes the springs and when a certain speed is attained
again brings the brake pieces into contact.
3. Retaining and lowering apparatus consisting of a wheel J suitably geared
with the weight to be controlled; weighted brake pieces mounted on the wheel
springs N pressing the brake pieces inwards towards the centre and a stationary
surface Kupon which the brake pieces may bear; the whole so arranged that the
springs hold the brake pieces against the surface K with sufficient force to retain
the load whilst nevertheless allowing the wheel to be turned by hand and also so
that when the wheel attains a certain speed the centrifugal action upon the brake
pieces first overcomes the springs and afterwards at a higher speed again brings
the brake pieces into contact with the stationary surface.
4. The mechanism for adjusting the chair back consisting of the tapered strut Y:
jointed to the back; the cross bar Z; the wedge X which with the strut Y passes
through an inclined recess in the bar Z and the lever U for lifting the wedge; the

page_text: whole so arranged that the taper of the strut and wedge when the tendency is
downwards locks the parts until the wedge is withdrawn but when the tendency is
upwards allows the strut to be raised.
Dated thin 10th dow of A11002
T. H. GARDNER.
EDWARD GARDNER.