IMPROVEMENTS IN DENTAL ENGINES OPERATED BY ELECTRICITY
Year: 1886

page_text: Date of Application, 27th Mar., 1886.
Complete Left, 27th Jan.; 1887.
Complete Accepted, 8th Mar., 1887.
I, AMOS KIRBY of 34 Harpur Street Bedford Dental Surgeon do hereby declare
the nature of my invention for IMPROVEMENTS IN DENTAL ENGINES OPERATED BY
ELECTRICITY to be as follows:-
I employ an electro motor of any suitable kind for giving rotary motion to the
usual cutting burrs or other instruments used in dental operations but I prefer to use
a motor in which the field magnets and those of the armature are made in what is
known as the horseshoe form. The first part of my invention consists in constructing
these magnets with enlarged poles or pole pieces forming flanges so that each pole
resembles the end of a bobbin but instead of the end forming a flat dise I make it
slightly conical or bevilled so that each pole approaches the opposite one gradually
until the central and most prominent parts are opposite to each other. The second
part of my Invention consists in the application of governors to control the speed of
the revolutions of the engine or motor by intercepting the electric current when it is
running too fast. This may be accomplished by an arrangement similar to any of
those used for controlling the speed of steam engines or in any other convenient
inanner.
The third part of my invention consists in suspending or fixing the apparatus in
such a way that the action of moving it forward into the place where it is required to
operate shall actuate a switch and cause contact in the electric wires which set the
machine in motion. The reverse action causing interruption in the current and
stoppage of the machine.
The fourth part of my invention consists in attaching a switch to some suitable
part of the wires which carry electricity to the motor so that the current may be
intercepted or diverted from or reversed in the magnets which form the field of the
motor whilst it is allowed to pass to those which form the armature or vice versa the
effect of this action being to produce the instant stoppage of the machine.
My invention consists in the application of each of these improvements separately
or of their use in combination in the construction of Dental Engines and not in their
application for other purposes.
AMOS KIRBY.

page_text: COMPLETE SPECIFICATION.
Improvements in Dental Engines Operated by Electricity.
I, AMOS KIRBY, of 34 Harpur Street, Bedford, do hereby declare the nature of
my said invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The object of my invention is to effect improvements in the construction of electro
motors for driving cutting burrs and other instruments used in stopping teeth, or in
preparing them for stopping, and for other purposes in connection therewith.
My invention consists in the application of specially shaped pole-pieces to the
magnets which form the field and the armature, when these are constructed in
the horse-shoe form: In the application of governors for controlling the speed of
revolution: and, in improved methods of mounting the apparatus, in order to effect
the starting and stopping of the machine.
And in order that my said invention may be particularly described and ascertained,
reference is hereby made to the accompanying drawings, in which similar letters of
reference indicate corresponding parts.
My improvements in the motive parts of the machine relate to that kind of machine
in which magnets of the form known as the "horse-shoe" are employed; or to those
with a combination of horse-shoe and bar magnets, similar to the form known as
Jacobi's motor; and consists in constructing the magnets which form the field, and
those which form the armature (one or both) with enlarged poles, or pole-pieces, the
outer surfaces of which are chamfered or bevelled.
Figs. 1, 2 and 3 are sections, shewing methods of constructing my improved poles
or pole-pieces. a a are the enlarged poles fitted to the stationary magnets, having
enlarged pole-pieces (as shewn). bb are corresponding poles and pole pieces fitted to
the revolving magnets, moving in the direction of the arrows.
The effect of enlarging the poles is to increase the field of force, and the effect of
bevelling the ends is to produce an oblique approach between the poles of the field
and those of the armature, which I find are practically very advantageous in such
magnets used for this purpose.
In fitting governers to electro-magnetic engines, used for the above named purposes,
I make use of any forms of governors, acting by centrifugal force or fluid pressure
arising from rotation, in any of the well known forms, or modifications thereof, and
utilise the effect arising from such force or pressure, in cutting off, breaking, or
diverting the currents; whereby the speed of rotation is kept under perfect control,
and the desired speed is ensured.
Two examples of means of carrying out this part of my invention are shown in
Figs. 4 and 5.
In Fig. 4c is the rotating spindle. d d are two weighted levers pivotted to the
arms e e which are fixed to the spindle c. ff are two pins fixed to the levers d d, and
passing through holes in the arms of the conical block g. h is the commutator and
i is one of the brushes. is a spring, which presses against the short arms of the
weighted levers d d.

page_text: When the levers d d expand their orbit, by centrifugal force, the pins ff move the
sliding cone g against the screw m of the brush i, and thereby lift the brush out of
contact with the commutator. xx are wires connecting the different parts of the
commutator with the wrapping wires of the magnets.
In Fig. 5 c is the rotating spindle, e e are arms fitted thereto and rotating therewith.
dd are two weights, free to slide on the arms e e. n is a pulley linked to the
weights d d, as shewn, k is a spiral spring impinging against the pulley n and
arms e e: the pulley n being free to slide on the spindle. The lever o may be used to
convey the electric current to the conductor p, or it may be used to make and break
the current in any desired manner, and in any part of the circuit. When the
centrifugal force of the weights d d is in excess of that required, the pulley n is
drawn towards e, and the lever o leaves contact with the conductor p, and the current
is thereby interrupted until the speed is again reduced.
Fig. 6 shows a method of mounting the motor so that connection and disconnection
may take place, according to the position of the motor on its spindle. 9 is the motor,
or the case containing the motor, is a bracket fixed to the motor, whereby it is
pivotted to the spindle s. The lower part of the bracket ¹ may be bevelled, so that it
may act as a rising hinge upon the screw s¹. The spindle s is of metal. t is a tube
of insulating material surrounding 8. u is a short piece of metallic tube, having a
tongue u¹ resting against the insulating tube t. is a portion of the bracket rin
which an insulating plug vis fitted, and through which plug the binding screw w is
placed, binding the wire y, leading to one of the fixed magnets in the motor, and
connecting it with the brush or switch .
When the motor is moved round upon the support s, the switch z comes in contact
with the tongue u¹, and the electric current passes through the wire y, screw w,
switch 2, and tongue u¹ to the wire 1; the return current being conveyed by the
wire 2, spindles and bracket r which is connected to the other end of the wrapping
wire of the magnets.
Fig. 7 is intended to impart a general idea of one of the methods of mounting the
motor in which contact is effected by the spring 4 touching the insulated pin connected
with the wire 1. Fig. 8 is another of such methods in which the motor is placed
below the operative arm, and the power conveyed thereto by pulleys and cord. When
the operative end 3 is drawn towards the operator, the switch . (Fig. 6) or its
equivalent, connects the parts which convey the electric current, as before mentioned,
and vice versa.
It is obvious that my improved apparatus may be mounted so as to move and act
horizontally, vertically or obliquely.
Having now particularly described and ascertained the nature of my said invention,
and in what manner the same is to be performed, I declare that what I claim is :-
1. In the construction of electric motors of the horse-shoe type for the purposes
aforesaid, the method of forming pole-pieces to fixed and revolving magnets, sub-
stantially as herein before described and shewn in Figs. 1, 2 and 3 of the drawings.
2. In the construction of electrical motors for the purposes aforesaid, the application
and use of governors, substantially as herein before described and partially illustrated
on the drawings.
3. In the construction of electrical dental engines as aforesaid, the method of and
means and appliances for making and breaking contact, substantially as herein before
described and illustrated on the drawings.
4. The general construction of the several and respective parts, and the combination
of any two or more of them, constituting my improvements in dental engines operated
by electricity, substantially as herein before described.