Improvements in Dental and other Chairs.
Year: 1891

page_text: Date of Application, 23rd Apr., 1891
Complète Specification Left, 22nd Jan., 1892-Accepted, 27th Feb., 1892
PROVISIONAL SPECIFICATION.
Improvements in Dental and other Chairs.
We, THOMAS HARRY GARDNER, and EDWARD GARDNER, both of Cornbrook,
Manchester, Engineers, do hereby declare the nature of this invention to be as
follows:-
At each side of the chair there is a standard which consists of three parts sliding
in grooves upon each other, so that the standards can be elongated telescopically.
The three parts of each standard lie side by side the inner part of each being
rigidly fixed to the foot or legs of the chair. The inner and outer parts of each
standard carry racks and the middle portions carry bearings for two parallel
transverse shafts, one of these shafts having at its two ends pinions gearing into
the racks of the outer parts of the two standards whilst the other shaft has near
its ends pinions gearing into the racks upon the inner parts. The two shafts are
geared together by equal pinions upon them, so that they always revolve at equal
speeds.
The two middle parts are connected by cross bars to give greater rigidity and
to these cross bars is fixed a central rack with which gears a pawl at the end of
a rod worked up and down by a treadle in such manner that each time the pawl is
moved upwards the central parts of the standards are lifted and when this is done
the racks upon the fixed inner parts cause the shafts to revolve and thus raise the
two outer parts not only relatively to the inner parts but also to the middle parts.
One of the shafts is provided with a silent pawl consisting of a cylindrical casing
surrounding a circular rack turning on the shaft. The casing is fixed at one end
of a tube fitting loosely on the shaft and with its other end fixed to it. Between
the rack and the casing are cylinders or bowls which, when the rack is turned in the
direction required to elongate the standards drop to the bottoms of the inclines of
the rack and so allow the shaft to turn freely. When however the rack turns in
the other direction the cylinders or bowls run up the inclines and so jam the rack
and cylindrical casing together. Fixed to the rack is a worm wheel gearing with
a worm upon an axis mounted in bearings fixed to the frame and provided with a
hand or foot wheel. The pitch of the teeth of the worm and worm wheel is so
arranged that the worm is only just prevented from being driven by the worm
wheel, thus when a very slight impulse is given to the hand or foot wheel the worm
wheel continues to drive the worm for some little time and if the impulse is
sufficient this motion continues during the whole descent of the chair and, by
giving the proper impulse, the chair will descend any desired distance and
then stop.
The seat of the chair is fixed to the outer parts of the standards. The back of
the chair is pivotted to the seat as nearly as possible at the hip joints of the
person occupying the chair, so that, when the cushions and head rest, which are
carried by the back, have been placed in any positions the adjustments need not be
altered when the inclination of the back of the chair is varied. The back of the
chair has pivotted to its rear a rod which passes downwards through a pivotted
clutch consisting of a cone or incline containing a number of cylinders or bowls
surrounding the rod so that when the rod is pushed downwards these cylinders or
bowls are pressed into contact with the rod and with the cone or incline and thus
jam the rod, preventing it from being forced down, but the rod is always free to
move upwards through the bush. Upon the rod inside the cone or incline there is
a tube which can be pushed upwards by a handle so as to raise the balls and thus
free the rod when desired.
The back of the chair or the axis upon which it pivots carries a lever to whose

page_text: end is fixed a spring tending to counterbalance the weight of the back of the chair
and part of the weight of the person sitting in the chair, so that the operator can
raise or lower the patient without difficulty. On the back of the chair there is a
plate free to slido up and down and which can be secured in any position by a
handle. To this plate is pivotted the upper end of a cushion carrying a rack at
its lower end, so that the lower end can be pushed in and out and secured. Sliding
on the plate is a support carrying at its upper end a guide for a slide to which the
head rest is pivotted, so that the head rest can not only be set forward or back but
can also be raised and lowered and turned to any inclination. Lock nuts are
provided so as to secure it in any position.
Dated this 23rd day of April 1891
CARPMAEL & Co.,
A cents
COMPLETE SPECIFICATION.
Improvements in Dental and other Chairs.
We, THOMAS HARRY GARDNER, and EDWARD GARDNER, both of 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 :-.
Figure 1 is a side elevation of a chair constructed according to our invention the
seat being in the lowest position.
Figure 2 is a rear elevation of the back of the chair.
Figure 3 is a section on the linear Figures 1 and 2.
Figure 4 is a rear view of the lower part of the chair looking in the direction of
the arrow y y Figure 1.
Figure 5 is a side elevation of the chair with its seat in the highest position.
Figure 5 is a horizontal section on the line 1, 1, Figure 5 and
Figures 5 and 5° are vertical sections on the lines 2, 2 and 3, 3 Figure 5*
respectively.
Figures 6 to 12 show details to a larger scale, Figure 6 being a longitudinal
section of the axis d' and parts connected to it and Figure 7 a transverse section
on the line z z Figure 6 omitting the hand wheel k. Figure 8 is a rear elevation
of the worm wheel and wormshewing the shaft d' but omitting the cylindrical
casing and wheel k, and Figure 9 is an end elevation of the same partly in section.
Figure 10 is a rear elevation, Figure 11 a longitudinal section and Figure 12 a
plan of the mechanism for clutching the bar m³ to the rod m².
In these figures parts are sometimes omitted to show the others more clearly.
At each side of the chair there is a standard which consists of three parts a¹ a² a³
sliding in grooves upon each other, so that the standards can be elongated tele-
scopically. The three parts of each standard lie side by side the inner part a' of
each being rigidly fixed to the foot or legs 6 of the chair. The inner part a¹ and
outer part a of each standard carry racks c and c¹ respectively and the middle
portions a³ carry bearings for two parallel transverse shafts d and d', one of these
shafts & having at its two ends pinions & gearing into the racks c¹ of the outer
parts of the two standards whilst the other shaft has near its ends pinions d
gearing into the racks c upon the inner parts. The two shafts are geared together
by equal pinious d' d' upon them, so that they always revolve at equal speeds.
The two middle parts are connected by cross bars ee to give greater rigidity and
to these cross bars is fixed a central rack f with which gears a pawl g' at the end
of a rod g worked up and down by a treadle h in such manner that each time the
pawl is moved upwards the central parts a² of the standards are lifted and when
this is done the racks ac upon the fixed inner parts a' a' cause the shafts dd' to
revolve and thus raise the two outer parts a³ a³ not only relatively to the inner
parts but also to the middle parts. The shaft d' as shewn in Figures 6 to 9 is
provided with a silent pawl consisting of a cylindrical casing ; surrounding a

page_text: circular rack turning freely on the shaft. The casing is fixed at one end of a
tubefitting loosely on the shaft d' and with its other end fixed to it or to the
pinion upon it. Between the rack and the casing ; are cylinders or bowls j
which, when the rack is turned in the direction required to elongate the standards to
drop the bottoms of the inclines of the rack and so allow the shaft d' to turn freely.
When however the rack turns in the other direction the cylinders or bowls run up
the inclines and so jam the rack and cylindrical casing together. Fixed to the
rack is a worm wheel gearing with a worm upon an axis mounted in bearings
fixed to the frame and provided with a hand or foot wheel k. The pitch of the
teeth of the worm j and worm wheel is so arranged that the worm is only just
prevented from being driven by the worm wheel. The angles for the threads as
shewn in Figures 8 and 9 are suitable, thus when a very slight impulse is given to
the hand or foot wheel k the worm wheel continues to drive the worm for some
little time and if the impulse is sufficient this motion continues during the whole
descent of the chair and, by giving the proper impulse, the chair will descend any
desired distance and then stop.
The seat of the chair is fixed to the outer parts as of the standards. The back
of the chair m is pivotted at m² to the seat as nearly as possible at the hip joints of
the
person occupying the chair, so that, when the cushion m² and head rest m³
which are carried by the back m have been placed in any positions the adjustments
need not be altered when the inclination of the back of the chair is varied. The
back m of the chair has pivotted to its rear a rod m which passes downwards
through a clutch upon a bar m pivotted to brackets fixed to the outer portions a³
of the standards consisting of a cone or incline n Figures 10 to 12 containing a
number of cylinders or bowls n', surrounding the rod so that when the rod is pushed
downwards these cylinders or bowls are pressed into contact with the rod and with
the cone or incline and thus jam the rod, preventing it from being forced down, but
the rod is always free to move upwards through the bush. Upon the rod inside the
cone or incline there is a tube n³ which can be turned by a handle n³ and a pin n
working in an incline then causes it to rise and so lift the balls and thus free the rod
when desired.
The back m of the chair or the axis m' upon which it pivots carries a lever o to
whose end is fixed a spring o' tending to counterbalance the weight of the back of
the chair and part of the weight of the person sitting in the chair, so that the
operator can raise or lower the patient without difficulty. On the back of the chair
there is a plate p free to slide up and down and which can be secured in any position
by a handle p'. To this plate is pivotted the upper end of a cushion m³ carrying
a rack at its lower end, so that the lower end can be pushed in and out and
secured. Sliding on the plate is a support y carrying at its upper end a guide gl
for a slide to which the head rest m³ is pivotted, so that the head rest can not only
be set forward or back but can also be raised and lowered and turned to any
inclination. Lock nuts are provided so as to secure it in any position.
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 chairs the combination of a foot or base, a seat, telescopic mechanism
connecting the foot or base to the seat, mechanism for elongating the same, and an
axis for operating the mechanism, such axis being prevented from turning in one
direction by a worm and worm wheel of such pitch that when started the weight of
the chair causes the worm wheel to drive the worm for a time dependent upon the
initial speed.
2. In a chair the combination of a foot or base, a standard fixed to it, a seat, a
standard fixed to the seat and a third standard interposed between the other two
and working telescopically upon them, the standards fixed to the foot or base and
to the seat carrying racks and the intermediate standard carrying pinions gearing
with the racks and their axes being geared together.

page_text: 3. In a chair the combination of a foot or base, a standard fixed to it, a seat, a
standard fixed to the seat and a third standard interposed between the other two
and working telescopically upon them, the standards fixed to the foot or base and
to the seat carrying racks and the intermediate standard carrying pinions gearing
with the racks and their axes being geared together, one or other axis being pre-
vented from turning in one direction by a worm and worm wheel of such pitch
that when started the weight of the chair causes the worm wheel to drive the
worm for a time dependent upon the initial speed.
4. In chairs the combination of a seat, a back pivotted to the seat near the hip
joints of the person occupying the chair and retaining mechanism for holding the
back at any angle.
5. In chairs the combination of a seat, a back pivotted to the seat near the hip
joints of the person occupying the chair, an adjustable stop for preventing the back
from moving backwards and a spring tending to move the back forwards.
6. In chairs the combination of a seat, a back pivotted to the seat, a rod pivotted
to the back, a friction clutch operating on the rod and tending to prevent
the back from moving backwards and mechanism for throwing the clutch out
of operation.
7. In chairs the combination of a seat, a back pivotted to the seat, a rod pivotted
to the back, a friction clutch operating on the rod and tending to prevent the back 2
from moving backwards, mechanism for throwing the clutch out of operation and
a spring tending to move the back forwards.
8. Chairs substantially as described and shown in the drawings.