Improvements in Dental Chairs.
Year: 1888

page_text: Date of Application, 23rd Aug., 1888
Complete Specification Left, 22nd May, 1889-Accepted, 22nd June, 1889
PROVISIONAL SPECIFICATION.
Improvements in Dental Chairs.
We, DUNCAN DEWAR HEPBURN, of 6 to 10 Lexington Street, London, W., Chairman
of the Dental Manufacturing Co., and EDWARD GARDNER, of Cornbrook, Manchester,
Engineer, do hereby declare the nature of this invention to be as follows:-
This invention has for its object improvements in dental chairs.
The improved chair is of the class in which the chair proper is capable of being
moved up and down and locked in a frame which is carried by trunnions on suitable
standards, so that the frame can be set to any desired inclination and there secured.
According to this invention in order to raise and lower the chair upon the frame,
hydraulic mechanism worked in conjunction with a treadle lever is employed. The
treadle lever is mounted upon a horizontal axis at the lower part of the frame, and
at its inner end the lever is forked and embraces a hydraulic cylinder which it carries
by trunnions.
Within this cylinder a hollow ram works, and the hollow rau in turn in like
manner has a ram working within it. The ram is connected with the chair by a
joint at the back of the seat. The lower cylinder has a store chamber formed upon
it on either side, in which a supply of oil or liquid is contained. These store vessels
are connected by a passage with the interior of the cylinder at its lower end; there
is a light valve in the passage which opens freely to admit the liquid but closes to
prevent its return.
In the same way at the lower end of the hollow ram there is a
valve which opens to admit liquid into the interior and closes to prevent it passing
out On the side of the lower cylinder there is a cone valve which is opened by means
of a screw and lever when it is desired to allow the liquid to pass out from the
cylinder back into the supply vessels. A spring closes this valve except when it is
opened by means of the lever. This mechanism operates in the following manner :-
When it is desired to raise tho chair in the frame the treadle is depressed by
placing the foot upon it, the hydraulic cylinder and rams are thereby raised and
being full of liquid they move as if in one piece; the upper ram thrusts the chair
upwards a distance along the frame. The chair carries with it an axis on which are
pinions, and these pinions engage with racks on the side bars of the frame. In
connection with the axis of the pinions there is locking gear hereinafter described,
which allows the axis to turn freely as the chair ascends on the frame but prevents the
chair descending. Consequently, when the foot is removed from the treadle the chair
is maintained in the position to which it has been raised, but the hydraulic cylinder
and the hollow ram descend by their own weight, and as they do so liquid flows from
the store vessels to supply the space within them, which otherwise would be left void.
Then, if it be desired to raise the chair higher, the treadle is again depressed and
it operates again to lift the chair in the manner already described. To lower the chair
it is only necessary to disengage the locking gear and to open the cone valve a limited
distance which allows the liquid to escape at a determined rate from the hydraulic
cylinder back into the store vessels. The lower cylinder first empties until the
hollow ram nearly reaches its lowest position, and when it does so the stem of the
valve at the lower end of this ram comes against a stop and is thereby lifted from its
seat; At the same time the rau itself at the lower end, bodily enters a shallow
closed socket formed in the bottom of outer cylinder leaving only a very small annular
space for the exit of the fluid, thus retarding it in a degree corresponding with the
lesser diameter of ram about to fall. The liquid then escapes from the interior of
the hollow ram, but through' a diminished area, so that the upper ram descending in
turn, does so, at about an equal speed with its predecessor, until it reaches its
lowest position.

page_text: In the treadle lever a double joint is provided which allows the outer end of the
treadle to be first raised and then turned to one side. When it is so turned a
projection at its inner end passes beneath a stop which sustains the outer end of the
treadle lever in this position. The object of this is, to secure a second and more
convenient position of trendle lever, so that when the chair is tilted backwards the
operator may still have full control of the lifting apparatus, which he otherwise would
not have, from the altered position of chair. This movement is also useful in a
secondary sense, as by it the treadle may be folded up out of the way when the chair
is in its upright position.
The locking gear above referred to and which sustains the chair upon the frame
consists of a disc fixed upon the axis of the pinions and a casing surrounding the
disc but connected with the chair in such manner that it cannot turn with the
axis.
In the casing, a cam of the wedge type is mounted rocking on a pin and a light
spring is provided in the case to keep the can, in casy contact with face of the disc.
A small handle is fixed upon the cam for the purpose of lifting the same out of
contact with the disc, and a stop is also provided to hold it in that position when
necessary. When the disc revolves, as the chair is lifted by the frame, the eccentric
turns slightly so as to relieve the disc from any pressure upon it, but, on the contrary,
when the disc tends to rotate in the other direction, as when the chair descends in
the frame, the cam jams against the surface of the disc sufficiently to prevent further
movement.
In order to adjust the inclination of the frame in which the chair moves up and
down we connect to the lower cross bar of the frame a piece to which a screw is
jointed. This screw enters a tube within which a corresponding screw thread is
formed. The tube is able to turn in a trunnion ring which is carried in a bearing
fixed to the foundation plate. The tube has a ratchet wheel fixed upon it, and a
double pawl piece engages with the teeth of the ratchet. The pawl piece is carried
by a treadle which is free to turn upon the tube. Two coiled springs surround the
boss of the treadle they are fixed to it at one end and the other they come against
a stop on the foundation plate. The arrangement is such that the lever after it has
been depressed by the foot is always raised again by one or other of the springs to an
inclination of about 80 degrees from the horizontal. The lever can be turned over and
worked on either side to screw and unscrew according as it is required to incline the
chair frame in one or other direction. The double pawl piece has a projection upon it
upon which a spring piece carried upon the treadle lever presses. This spring piece
serves to keep the operating end of the double pawl piece engaged with ratchet teeth
during the downward stroke of the treadle, but it yields to allow the pawl piece to
ride over the teeth as the treadle rises. When the treadle is turned over from one
side to the other, the spring piece upon the lever passes from one side to the other of
the projection upon the double pawl piece, and at the same time one of the operating
ends of the pawl piece passes out of action, whilst the other comes to engage with
the teeth.
We provide the chair with a movable foot rest which, when in place, projects from
the lower platform. This foot rest is carried by two side arms; a pin and a stop
project from each of the arms. The side rails of the platform are grooved to receive
the pin the groove is open at the end to allow the pin to enter and be slidden along
to a convenient position. When the foot rest is in place the projection bears upon the
top of the side rail and so the foot rest is supported..
j
Dated this 23rd day of August 1888
CARPMAEL & Co.,
Agents.
COMPLETE SPECIFICATION.
Improvements in Dental Chairs.
We, DUNCAN DEWAR HEPBURN, of 6 to 10 Lexington Street, London, W.,
Cirman of the Dental Manufacturing Co., and EDWARD GARDNER, of Cornbrook,

page_text: Manchester, Engineer, 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 :-
This Invention has for its object improvements in dental chairs.
The improved chair is of the class in which the chair proper is capable of being
moved up and down and locked in a frame which is carried by trunnions on suitable
standards, so that the frame can be set to any desired inclination and there secured.
According to this invention in order to raise and lower the chair upon the frame,
hydraulic mechanism worked in conjunction with a treadle lever is employed. The
trendle lever is mounted upon a horizontal axis at the lower part of the frame, and at
its inner end the lever is forked and embraces a hydraulic cylinder which it carries by
trunnions.
Within this cylinder a holiow ran works, and the hollow ram in turn in like manner
has a ram working within it. The ram is connected with the chair by a joint at the
back of the seat. The lower cylinder has a store chamber formed upon it on either
side, in which a supply of oil or liquid is contained. These store vessels are connected
by a passage with the interior of the cylinder at its lower end; there is a light valve
in the passage which opens freely to admit the liquid but closes to prevent its return.
In the same way at the lower end of the hollow ram there is a valve which opens to
admit liquid into the interior and closes to prevent it passing out. On the side of the
lower cylinder there is a cone valve which is opened by means of a screw and lever
when it is desired to allow the liquid to pass out from the cylinder back into the supply
vessels. A spring closes this valve except when it is opened by means of the lever.
This mechanism operates in the following manner :-
When it is desired to raise the chair in the frame the treadle is depressed by placing
the foot upon it, the hydraulic cylinder and rams are thereby raised and being full of
liquid they move as if in one piece; the upper ram thrusts the chair upwards a
distance along the frame. The chair carries with it an axis on which are pinions, and
these pinions engage with racks on the side bars of the frame. In connection with the
axis of the pinions there is locking gear hereinafter described, which allows the axis
to turn freely as the chair ascends on the frame but prevents the chair descending.
Consequently, when the foot is removed from the treadle the chair is maintained in
the position to which it has been raised, but the hydraulic cylinder and the hollow ram
descend by their own weight, and as they do so liquid flows from the store vessels to
supply the space within them, which otherwise would be left void. Then, if it be
desired to raise the chair higher, the troadle is again depressed and it operates again to
lift the chair in the manner already described. To lower the chair it is only necessary
to disengage the locking gear and to open the cone valve a limited distance which
allows the liquid to escape at a determined rate from the hydraulic cylinder back into
the store vessels. The lower cylinder first empties until the hollow ram nearly reaches
its lowest position, and when it does so the stem of the valve at the lower end of this
ram comes against a stop and is thereby lifted from its seat; at the same time the ram
itself at the lower end, bodily enters a shallow closed socket formed in the bottom of
outer cylinder leaving only a very small annular space for the exit of the fluid, thus
retarding it in a degree corresponding with the esser diameter of ram about to fall.
The liquid then escapes from the interior of the hollow ram, but through a diminished
area, so that the upper ram descending in turn, does so, at about an equal speed with
its predecessor, until it reaches its lowest position.
In the treadle lever a double joint is provided which allows the outer end of the
treadle to be first raised and then turned to one side. When it is so turned a projec-
tion at its inner end passes beneath a stop which sustains the outer end of the treadle
lever in this position. The object of this is, to secure a second and more convenient
position of treadle lever, so that when the chair is tilted backwards the operator may
still have full control of the lifting apparatus, which he otherwise would not have,
from the altered position of chair. This movement is also useful in a secondary
sense, as by it the treadle may be folded up out of the way when the chair is in its
upright position.

page_text: The locking gear above referred to and which sustains the chair upon the frame
consists of a disc fixed upon the axis of the pinions and a casing surrounding the
dise but connected with the chair in such manner that it cannot turn with the axis.
In the casing, a cam of the wedge type is mounted rocking on a pin and a light
spring is provided in the case to keep the cam in easy contact with face of the disc.
A small handle is fixed upon the cam for the purpose of lifting the same out of contact
with the disc, and a stop is also provided to hold it in that position when necessary.
Whethe disc revolves, as the chair is lifted by the frame, the eccentric turns slightly
so as to relieve the disc from any pressure upon it, but, on the contrary, when the disc
tends to rotate in the other direction, as when the chair descends in the frame, the cam
jams against the surface of the disc sufficiently to prevent further movement.
In order to adjust the inclination of the frame in which the chair moves up and
down we connect to the lower cross bar of the frame a piece to which a screw is
jointed. This screw enters a tube within which a corresponding screw thread is
formed. The tube is able to turn in a trunnion ring which is carried in a bearing
fixed to the foundation plate. The tube has a ratchet wheel fixed upon it, and a double
pawl piece engages with the teeth of the ratchet. Tho pawl piece is carried by a treadle
which is free to turn upon the tube Two coiled springs surround the boss of the
treadle they are fixed to it at one end and at the other they come against a stop on the
foundation plate. The arrangement is such that the lever after it has been depressed
by the foot is always raised again by one or other of the springs to an inclination of
about 80 degrees from the horizontal. The lever can be turned over and worked on
either side to screw and unscrew according as it is required to incline the chair frame
in one or other direction. The double pawl piece has a projection upon it upon which a
spring piece carried upon the treadle lever presses. This spring piece serves to keep the
operating end of the double pawl piece engaged with ratchet teeth during the down-
ward stroke of the treadle, but it yields to allow the pawl piece to ride over the teeth
as the treadle rises. When the treadle is turned over from one side to the other, the
spring piece upon the lever passes from one side to the other of the projection upon the
double pawl piece, and at the same time one of the operating ends of the pawl piece
passes out of action, whilst the other comes to engage with the teeth.
We provide the chair with a moveable foot rest which, when in place, projects from
the lower platform. This foot rest is carried by two side arms a pin and a stop
project from each of the arms. The side rails of the platform are grooved to receive
the pin the groove is open at the end to allow the pin to enter and he slidden along
to a convenient position. When the foot rest is in place the projection bears upon the
top of the side rail and so the foot rest is supported.
In order that our said invention may be fully understood and readily carried into
effect, we will proceed to describe the drawings hereunto annexed.
DESCRIPTION OF THE DRAWINGS.
Figure 1 is a vertical section and Figure 2 is a rear elevation, of a dental chair
constructed in accordance with our invention.
Figure 3 is a longitudinal section of the telescopic hydraulic apparatus.
Figure is a transverse section taken on the line 4, 4, in Figure 3.
Figure 5 is a side elevation of the lifting treadle together with the lower part of the
hydraulic lifting apparatus.
Figure 6 is a plan of the treadle lever.
Figure 7 is a plan of the gear for altering, the inclination of the chair.
Figure 8 is an elevation of the treadle lever which actuates the gear ishown by
Figure 7.
a a are standards upon a base frame which support at a' the trunnions of a frame b.
On the frame the parts marked c which constitute the chair proper are carried, they
can be raised up and down and can be locked upon the frame in any position to which
they may have been raised. d is a treadle which is depressed for the purpose of raising
the chair, it turns about the horizontal axis d'. The axis d' is held in brackets fixed to
the bottom rail of the frame b. d d are springs which tend to lift the treadle, but

page_text: yield to the pressure of the foot. The treadle d is jointed in the following manner.
the part of the lever next the axis d' carries between pivots d² d a disc which is fiited
into a horizontal slot in the other part of the lever and an upright pin or axis d³
connects this part of the lever with the disc. The lever is thus universally jointed.
There are lugs on the two parts of the lever at which render the lever stiff in the
position shown in Figure i to transmit downward pressure. The outer end of the
lever however can be lifted and moved sideways which brings the lug upon it beneath
one or other of the lugs d on the inner end of the lever. Thus the operative position
of the treadle can be altered as circumstances may require. The treadle lever d
carries the hydraulic cylinder e and in connection with this cylinder the store vesselƒ”
is provided. e is a valve which will allow liquid to pass from the store vessel into the
cylinder e but will prevent return. g is a hollow rain working through a gland at
the top of the cylinder e. is a valve opening to permit liquid to enter the hollow
ram but closing to prevent return. When however the ram is fully down the stem of
the valve g' rests at the bottom of the cylinder e and the valve g' is then open. and g
are fitted surfaces on the ram and cylinder which allow but a narrow passage for the
liquid when it is escaping from the ram g. is a second ram contained within the
ram g; at h¹ it supports the chair proper by the aid of a ball and socket joint. i is a
screw cone valve which when open allows liquid to pass from the cylinder e into the
store vesself; the valve is closed by a spring and opened by the lever 3.
kk are pinions the axis of which is carried in bearings upon the back of the
chair proper these pinions gear with racks b b on the frame b. is a disc on the
same axis with the pinions k. is a casing attached to the chair proper and surround-
ing the disc k². m is a cam piece or eccentric on an axis carried by the casing 1; a
light spring canses the cam piece to bear against the disc. m² is a handle on the cam
piece by which it can be turned so that it ceases to bear on the disc; the pinions kare
then free to turn and the chair proper to descend when the hydraulic apparatus
permits. n is a screw connected by a joint, with the lower cross bar of the frame b.
o is a hollow screw receiving the screwn within it. o' is a trunnion ring jointed to
the bed plate in which the screw o is held. ' is a ratchet pinion fast upon the screw o.
p is a treadle lever which can turn on the screw o. p pare springs coiled around the
boss of the lever p, they allow it to be turned over from side to side but whether on
one side or the other they tend to raise it to an inclination of about 80 degrees.
These springs however yield to the pressure of the foot. 7 is a double pawl carried on
the lever and is a spring piece upon the lever which causes one or other end of the
double pawl piece to engage with the teeth of the ratchet according to the side on
which the treadle lever is working. s is right and left hand screw locking gear
worked by a foot lever to lock the frame b at any inclination to which it may be set ;
this gear however may be dispensed with.
P
c' is the lower platform of the chair proper, in
to receive a foot rest which consists of the board
stops entering the slots and other stops t³
edges of the platform c¹.
it slots c² c² are provided to receive
fixed to side arms t¹ on which are
³ resting upon surfaces c³ ³ on the
Having now particularly described and ascertained the nature of our said Inven-
tion and in what manner the same is to be performed we declare that what we
claim is:
-
1. In a dental chair the combination substantially as described consisting of the
clair proper; a frame in which the chair proper is held and in which it can be raised
and lowered; a treadle; telescopic hydraulic apparatus connecting the treadle with
the chair proper and retaining apparatus by which the chair proper can be held at
any height to which it may be raised by the treadle operating upon it through the
hydraulic apparatus.
2. In dental chairs substantially as described the combination consisting of the
hydraulic cylinder e; the ram g; the second ram h contained within the first; the
store vessel f, the valve e' which permits liquid to pass into the cylinder from the store
vessel; the valve g¹ in the bottom of the hollow ram g which controls the passage of

page_text: liquid to and from the interior of the ram; and the escape valve which permits
liquid to return from the cylinder e to the store vessel f.
3. In dental chairs substantially as described the combination consisting of the
hydraulic cylinder e; the hollow ram g; the valve gl in the bottom of the hollow ram
and the surfaces e² and g in the cylinder and ram respectively which control the
escape of liquid from the interior of the ram when the same is in its lowest position.
4. In denial chairs substantially as described the combination consisting of the
chair proper the telescopic hydraulic apparatus; the treadle d, joints d2d and
lugs dd permitting of the use of the treadle in different positions.
thereon; the
5. In dental chairs substantially as described the frame band racks
chair c; the axis carried thereby the pinions & on the axis k¹ which engage with
the teeth the disc on the axis the casing connected with the chair cand the
locking cam m therein engaging with the disc k.
6. In dental chairs substantially as described the apparatus for adjusting the
inclination of the frame consisting of the screws n and o the treadle lever p
movable
about one of them and capable of being turned to either side; the springs pl pt which
raise the treadle the ratchet o² on the screw and the double pawl g on the treadle
lever p.
7. In dental chairs the guide slots c² ² and the guide surfaces on the lower
platform c¹ 3 the rest board t the arms t¹ t¹ fixed thereto the stops on the arms
entering the guide slots c² and the stops t³ ³ resting on the guide surface c³ c³.
Dated this Twentieth day of May 1889.
DUNCAN D. HEPBURN.
EDWARD GARDNER.