Year: 1886

page_text: Date of Application, 20th Mar., 1886.
Complete Left, 7th Dec., 1886.
Complete Accepted, 25th Jan., 1887.
[Communicated from abroad by the firm of SCHÄFER and MONTANUS, of Frankfort-
on-Main, in the Empire of Germany, through their Agents, Wirth and Company,
of the same place.]
I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of this Invention to be as follows:-
This Invention relates to a switch and resistance regulator for electric motors used
for working dental drills and similar tools. Heretofore such devices have been under
the control of the foot of the operator, the freedom of whose movements has con-
sequently been impeded by the necessity for keeping his foot on a certain spot.
The object of this Invention is to obviate this inconvenience by bringing the switch
within easy reach of the hand of the operator in which the dental tool is held.
The Invention consists of a switch constructed as hereafter described in com-
bination with a number of resistance wires constituting a rheostat. The switch which
may be mounted on the tool holder or on the tubular sheath wherein the flexible tool
shaft rotates consists of a metal ring turning loose upon a boss fixed to a short tube
of vulcanite which may be slipped on to the tool holder or sheath and to which
vulcanite tube are fixed a number of springs whose free ends project towards the ring
and are slightly radial and stand in position to be embraced or overlapped by and to
make contact with a segmental flange on the ring when the latter is partially rotated
upon its centre. The motion of the ring is limited by a stop and the flange may
make contact with one or more of the springs. These contact-springs are insulated
from one another and the first one of the series is connected by a cord of copper wire
with the one terminal of the dental electric motor. To each of the other springs is
ID Q77

page_text: connected a covered wire of Britannia Metal the several wires being collectively con-
nected to the other terminal of the motor, the whole of these conductors being
carried to the motor by being wound spirally around the sheath of the flexible
tool shaft.
When the segmental flange of the switch ring is in contact only with the first
spring of the series the circuit is broken but when the ring is turned so as to bring
its flange in contact with the next and succeeding springs the circuit is completed
through one or more of the resistance wires the resistance of the circuit being
inversely as the number of wires through which the current is switched.
By this means the motor can be started or stopped, and its speed can be regulated.

page_text: Electric Motors.
I, ALEXANDER MELVILLE CLARK, of the firm of A. M. and Wm. Clark, of
53, Chancery Lane, in the County of Middlesex, Fellow of the Institute of Patent
Agents, do hereby declare the nature of this Invention (a communication to me from
abroad by the firm of Schäfer and Montanus of Frankfort-on-Main in the Empire of
Germany (through their Agents Wirth and Company of the same place) and in what
manner the same is to be performed, to be particularly described and ascertained in
and by the following statement:-—
This Invention relates to a switch and resistance regulator for electric motors used
for working dental drills and similar tools. Heretofore such devices have been under
the control of the foot of the operator the freedom of whose movements has con-
sequently been impeded by the necessity for keeping his foot on a certain spot.
The object of this Invention is to obviate this inconvenience by bringing the switch
within easy reach of the hand of the operator in which the dental tool is held.
The Invention consists of a switch constructed as hereafter described in com-
bination with a number of resistance wires, the whole being mounted on the tool
holder or on the tubular sheath whereon the flexible tool shaft rotates whereby the
motor can be conveniently started and stopped and its speed can be regulated.
Reference is to be had to the accompanying drawings forming part of this
specification wherein Figure 1 is a perspective view of the device as mounted on
the sheath of the flexible drill shaft, and figure 2 shews the switch and resistance
regulator in an elementary manner. The same letters of reference indicate the same
parts in both figures.
The switch consists of a brass ring A turning loose upon a flanged boss screwed to
the end of short tube of vulcanite B which may be slipped on to the tool holder or
sheath, as shewn in figure 1, and to which vulcanite tube are screwed at slight
intervals apart a number of springs c¹² c³ce whose free ends project towards the
ring A and are slightly radial and stand in position to be embraced or overlapped by
and to make contact with a segmental flange a on the ring when the latter is partially
rotated upon its centre. The motion of the ring is limited by a stop and the flange a
may make contact with one or more of the springs. These contact springs are
insulated from one another, and the first and last ones of the series are connected
by cords of copper wire D, whilst to each of the intermediate springs is connected a
thin covered wire d of German silver, these intermediate wires being collectively
connected to one of the wires D which is connected with the magnet E of the electric
motor, the whole of these conductors being collected in the form of a cable F carried
to the switch by being wound spirally around the sheath of the flexible tool shaft.
When the segmental flange a of the switch ring A is in contact only with the first
spring of the series, the circuit is broken, but when the ring A is turned so as to

page_text: bring its flange in contact with the second and succeeding springs the circuit is
completed through one or more of the resistance wires, the resistance of the circuit
being inversely as the number of wires through which the current is switched. Thus,
as shewn in figure 2, the current entering through the cord or braid D passes to the
spring through the flange a of ring A. (which is omitted in figure 2) to the spring c²
thence through a German silver wire d to the motor and back to the source. The
motor is driven slowly by the current passing through a single wire d. If its velocity
is to be increased, the ring must be turned so that its flange makes contact with the
first, second, and third springs simultaneously, and so on.
The current then passes
through two or more wires d so that the resistance is diminished.
Having now particularly described and ascertained the nature of the said Invention
and in what manner the same is to be performed, I declare that what I claim is :—
The herein described switch and resistance regulator for dental electric motors
mounted on the tool holder or sheath of the tool shaft, and constructed of a rotating
flanged contact ring in combination with a series of contact springs to which are
respectively connected copper and German silver wires, so conìbined and arranged
that, by turning the ring it will make contact with one, two, or more of the springs,
in such manner that the motor can be switched on and off and its velocity regulated
as specified.
A. MELVILLE CLARK.
By A. M. & Wm. Clark,
53, Chancery Lane, London,
Patent Agents.