Improvements in Electric Motor Apparatus.
Year: 1894

page_text: Date of Application, 1st Jan., 1894-Accepted, 24th Feb., 1894
COMPLETE SPECIFICATION.
Improvements in Electric Motor Apparatus.
We, WILLIAM ARMOUR JOHNSTON, of Prince's Bay, in the County of
Richmond, and State of New York, United States of America, Manufacturer,
ARTHUR WILLIAM BROWNE, of Amboy Road, Prince's Bay, aforesaid,
Manufacturer, and JOHN CLARENCE DAVIDSON, of Prince's Bay, aforesaid,
Electrician, 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 :-
Our invention relates to certain improvements applicable to electric motors of
the class employed for imparting motion to dental tools or other devices requiring
but little power to actuate them, and embraces improvements in means for starting,
stopping, reversing and controlling the speed of the motor; in the arrangement
and manner of supporting various parts of the apparatus, and in sundry details, all
as hereinafter specifically claimed.
In the accompanying drawings
Fig. 1 is a view in perspective showing our improvements as employed for
actuating a rotary dental instrument.
Fig. 2 is a side elevation showing a portion of the motor stand with the
adjustable bracket frame which supports a countershaft and its attachments and a
bracket for mounting a dental engine standard; and Fig. 3 a view in elevation of
said adjustable frame and parts carried by it, with a modification.
Fig. 3 shows a plan of part of the belt guard.
Fig. 4 is a view partly in elevation and partly in section on the lines 4 of Figs. 2
and 5, and Fig. 5 à section on the lines 5 of Figs. 3 and 4, representing details of
construction of the electro-magnetic clutch mechanism and adjacent parts.
Fig. 5 is a section on the line 5 of Fig. 4.
Fig. 6 is a view showing parts in plan and parts in elevation on the line 6 of
Fig. 1, showing details of construction.
Fig. 7 is a front view of the rheostat box, detached.
Fig. 8 represents a vertical central section through a portion of the rheostat
box, the front being shown as opened, and the rheostat partly represented in
elevation.
Fig. 9 shows in elevation the inner side of the cable coupler for making
electrical connection between the rheostat and the pedal switch; and Fig. 10 is a
section on the line 10 of Fig. 9.
Fig. 104 shows a portion of a modified cable coupler.
Fig. 11 is a plan view of the pedal switch devices; Fig. 12 a plan view of a
portion of said devices, the top of the switch box being removed;
Fig. 13 a view of the underside of the switch box top with its connections, the
switch-actuating rock shafts being partly represented by dotted lines;
Fig. 14 a section on the line 14 of Figs. 11 and 12;
Figs. 15 and 16 are diagram sections on the same lines as Fig. 14, with the
arms or levers of the switch actuating rock shafts shown by dotted lines, and
different adjustments of the switch being represented; and Fig. 17 is a view in
perspective of one of the switch actuating rock shafts and its attachments.
Fig. 18 is a diagram designed to illustrate the various electrical connections and
the operation of the apparatus.
Fig. 19 is a diagram designed to show the switch set for the highest speed with
all conductors not in use in this adjustment broken away to more clearly illustrate
the operation. Fig. 20 a similar diagram with the switch set for the next lower

page_text: speed. Fig. 21 a similar diagram with the switch set for quickly stopping the
motion of the countershaft.
Fig. 22 is a diagram showing modifications to adapt the invention to the
employment of a shunt wound motor.
Conductors A. A' for the current of electricity, a safety fuse or automatic cut
off a, and a switch a¹ to open and close the circuit are provided as usual. By
means of the two-strand insulated conductor A2 the current is transmitted by way
of one of the binding posts a² a³ (in this instance by way of binding post a²) at the
front of the rheostat box through the field coils B B of the motor to a terminal
shown as constituted by the binding post 1× of the conductor 1 of the cable C
which makes electrical connection with a pedal switch C'. This insulated cable is
in this instance shown as composed of ten conductors 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
connected with their respective terminals or binding posts of the series 1, 2, 3×,
4*, 5, 6, 7, 8, 9 and 10x by the series of terminals shown as constituted by
plates b, one for each binding post. These terminals bare mounted upon the
inner surface of a single supporting plate preferably of insulating material, such
as vulcanized fibre, which I term the cable-coupler B. This cable-coupler
which may be of metal with the terminal plates properly insulated therefrom, is
detachably connected with the front B2 of the rheostat box B³ in the following
manner: The terminal plates are slotted at their ends to constitute catches, as
plainly shown by Figs. 7 and 9 to engage with the heads of the binding
posts 1, 2, 3, 4, 5, 6x, 7, 8, 9, 10%, secured to a non-conducting plate C²
fastened by screws c at its opposite ends to the inner side of the front of the
rheostat box. The binding posts a² a are secured to this plate C². A fixed
pin 2, or equivalent projection, on the front of the rheostat box beneath the
cable-coupler serves to guard against the improper connection of the cable-
coupler with the front of the rheostat box. Obviously the coupler could not
be slid into position to engage with its securing screws from beneath, as this
guard pin would off set the coupler and prevent its engagement with its
retaining screws. Obviously the slotted terminal plates and the binding posts
with which they respectively engage may be so arranged that the attachment
in the proper way only can be made, thus dispensing with the use of the pin
or fixed projection 63. For instance: the binding posts 1 to 10x may be zig-
zagged, and the terminal plates slotted longitudinally, instead of transversely as
will be understood by reference to Fig. 10. The registering of the parts can
only result under proper adjustment. The rheostat box is made to open at
front, the front of the box being in this instance hinged at its bottom to the
box by way of a cross rod d and two radius links D one near each end of the
rod. The outward swing of the box front is limited by a stop at its lower end
as will be understood by reference to Fig. 8. Screws dd serve to secure the
hinged front in its closed position. By hinging the front of the rheostat box,
t will be seen that access to the rheostat and conductors connected therewith
s readily had; and that the renewal of a conductor is easily accomplished
without disturbing the connections of the others. No particular form of hinge
is necessary but the one above described is deemed best as it gives a wide
range of movement. If preferred the opening front might even be without a
hinge and the front of the box opened by removing the screws which hold the
opening front, care being taken to keep the opening front near enough to the
box to prevent breaking or disturbing the connections.
The rheostat E may be of any ordinary suitable construction with terminals to
provide for variable resistance by actuations of the pedal switch. I prefer,
however, to construct it as follows:-Two spiders E' E' are secured to the opposite
ends of a bolt e and are separated by a sleeve (see dotted lines Fig. 6) surrounding
the bolt and constituting a distance piece as will readily be understood. The
radial arms of the spider are slotted and the coils of the rheostat are separated by
insulated strips or layers e¹ (which may be of wood) entering the spider slots at
their opposite ends.

page_text: One of
The rheostat is held in position by pointed screws at the opposite ends of its
central bolt which screws enter countersinks or notches in the bolt ends.
said screws is shown at e², Fig. 1. The conducting wires of the cable are connected
with contacts of a foot-actuated or pedal switch C¹ in the following way:-
Conductor 1 connects with the starting contact spring 1" and with clutch contact
piece 1"; conductor 2 connects with the reversing contact bridges 2 and 2b;
conductor 3 connects with the reversing contact spring 3"; conductor 4 connects
with the two reversing contact pieces 4ª 4" and with the two contact pieces 4° 4d;
conductor 5 with the clutch contact spring 5ª ; conductor 6 with the contact
spring 6ª and contact 6b; conductor 7 with the contact piece 7" and with contact 7b;
conductor 8 with the regulating contact piece 8ª; conductor 9 with the regulating
contact 9, and conductor 10 with the regulating contact piece 10.
The above recited contacts are located partly within and partly on top of a
box F through the front of which the cable of conductors passes, and this box is
provided with a removable non-conducting top F2 which is secured in place by
screws. The bottom of the box is composed of a metal plate or casting F3 having
a flanged edge fso as to provide room for a horizontally swinging lever & fulcrumed
at one end to this bottom plate by a pivot fl. See Figs. 11, 12 and 14. At the
rear end of the bottom plate there is provided a rest for the heel of the operator's
foot. This heel rest is shown as formed by a flexible attachment G₁ secured at
its forward edge to the metallic portion of the bottom plate. The heel-plate is
preferably made of sheet rubber to lower the heel-rest and also to lessen liability
of the operator's heel slipping when he is actuating the switch. There is also
more friction created between such flexible attachment and the floor than where
metal is used in lieu thereof and faced on top with rubber, leather, etc., for the
operator's heel, with or without a bottom facing of rubber, etc., to increase friction
with the floor.
Starting, stopping, reversing and speed controlling switch devices are employed
as follows: A switch actuating rockshaft H is mounted in a bearing at the
rear side of the switch box F₁, and has two arms or levers H' H' projecting
sidewise and upwardly from it. The length and upward curvature or inclination
of these arms are such that normally their outer ends to receive the pressure of the
operator's foot terminate in the same horizontal plane above the level of the top
of the switch box. At its inner end the rock shaft has two oppositely inclined
cams ¹² of non-conducting material, such as vulcanized fibre. The rockshaft is
also provided with a cam arm H³ provided with an anti-friction roller ³ which roller
might, however, be dispensed with. A spring I is secured upon a lug I' of the
switch box (see Figs. 12, 14, 15 and 16) and bears upward at its free end against
the cam roller 3, or directly against the cam end if no roller is used. The free
end of this spring is shaped in peculiar manner for purposes to be explained.
From the above description it will be seen that when the switch actuating rock-
shaft H is in its normal position the cam roller ³ rests in the depression k of the
spring I, (see Fig. 15), and that the upward pressure of the spring yieldingly locks
the rockshaft against movement. With the lever in this position the apparatus is
out of operation, the spring contact 1* being free from the contact piece 7ª. With
the rockshaft brought to the position indicated by Figs. 11 and 14 by depressing
the arm H' by the foot, the circuit is closed and the apparatus is started into
operation. In this position of the lever it will be seen that the spring contact 1*
is elevated and caused to touch contact piece 7" by the action of the cam h. The
rockshaft is yieldingly held in this position by the pressure of the inclined end k¹
of the spring I against the cam roller ³. To quickly throw the apparatus out of
operation, by the action of an electro magnetic clutch to be further on described,
the foot pressure is brought to bear upon the lever arm H2 thus moving the rock-
shaft into the position indicated by Fig. 16, with the cam roller ³ borne upon by
the incline of the spring I. In this position of the rockshaft the cam h² acts
upon the contact spring 5" and makes connection with contact 1°. As soon as the
rockshaft is relieved from the pressure of the foot it is caused to assume its normal

page_text: position (Fig. 15) by the action of the spring I. A second switch-actuating rock-
shaft L having bearing in the switch box at 1, is substantially similar to rock-
shaft H, being provided with the arms L'L, the oppositely inclined non-conducting
cams, and the cam arm L³ and roller. In the position in which the rockshaft
is shown in Figs. 11, 12 and 14 the cam l' actuates contact spring 3 to make
connection with contact piece 4ª. At the same time the contact spring 6" is
relieved from pressure of the cam 12 and makes connection with contact bridge 2"
which is connected by wire with contact bridge 2°. To reverse the direction of
the rotation of the motor the rockshaft arm L is depressed and the cam 12 acts
upon contact spring 6ª raising it to make connection with contact piece 4. At
the same time contact spring 3ª is freed by the cam and makes connection with
contact bridge 2b after breaking connection with contact piece 4ª.
For varying the speed of the motor regardless of the direction of its rotation the
lever G is provided with an upwardly projecting part or arm M at the front of the
pedal switch, having a side projection M' constituting a securing seat for a
non-conducting carrier m of a spring contact bridge m'. Upon the non-conducting
top of the switch box are secured the hereinbefore referred to contact pieces 9, 6,
8, 10, 4, 7 and 4ª. These contact pieces are arranged in two rows in the form of
segments of circles concentric with the pivot f¹ of the lever G, and by their binding
screws are connected with the cable conductors as already explained. The contact
bridge m¹ serves to make connection between opposite segments of the two rows,
this bridge swinging with the lever G. The upwardly projecting part of the lever
is pushed by a sidewise movement of the foot of the operator into any desired
position, and the curved or bent termination of this part enables the operator by his
foot to lift and change the position of the pedal switch on the floor.
Το
The motor stand is mounted upon rollers so that it can be readily moved into any
desired position, and the rheostat box is secured to the stand frame in suitable way.
Upon the back plate N of the rheostat box is supported a bracket frame N¹ of the
stand, upon which is mounted a countershaft actuated from the motor, an electro-
magnetic clutch, and a dental engine standard. The bracket frame N' is shown as
vertically adjustable in order to act as a belt tightener as will further on be under-
stood, and has an attaching plate N2 fitted to slide in a guideway formed between
vertical ribs n n' on the back plate N of the rheostat box. Four screws having
metallic washers n² overlapping the edges of the attaching plate engage with the
back plate at its ribbed portion n n' (two for each rib, one near the top and the other
near the bottom thereof) and leather or equivalent washers are interposed between
the metallic washers and the attaching plate to ensure a snug fitting of the parts
and prevent rattling. The bracket frame is provided at top with a ribbed seat o
for a bracket O' having a socket o' for the standard (2 of a dental engine of any
well known construction. A screw o³ and a groove o³ in the base of the socketed
bracket engaging the ribbed seat o serve to securely connect the parts.
vertically adjust the frame there is provided an adjusting screw P engaging with a
female screw in the attaching plate N, and provided with fixed collars pp, between
which it is fitted to turn in a bearing 1" on the back plate N, endwise movement of
the screw in its bearing being prevented, as will be readily understood. A down-
wardly projecting arm P of the frame is provided at its lower extremity with a
bearing for the outer end of a countershaft, the inner end of which is supported
by a bearing on the attaching plate of the frame. A pulley Q on this counter-
shaft drives the belt of the dental engine to impart rotation to the instrument to
be actuated. Motion is imparted to the countershaft by a belt R passing from a
pulley R on the motor armature shaft to an actuating pulley R2 loosely mounted
on the countershaft. The rotation of the countershaft may be quickly arrested by
the operation of an electro-magnetic clutch constructed as follows:- -An armature
clutch disk S rotating with the countershaft is adapted to be engaged with and
disengaged from the countershaft pulley R². This armature clutch disk is provided
with a sleeve S¹ slotted at s and is acted upon by a spring s which presses upon the
disk with a tendency to hold it in its operative position—that is, engaged with the

page_text: pulley R³. A screws secured to a sleeve S2 fast on the countershaft projects at
its head into the slots of the disk sleeve and whilst allowing of movement of this
sleeve end wise causes it to rotate with the fast sleeve S². Frictional clutch
engagement of the disk with the pulley R² is provided for by means of blocks T of
any desired number secured by screws to the face of the armature clutch disk
adjacent to the pulley. These blocks are made of vulcanized fibre, but may be
composed of any other suitable material producing requisite friction against the
pulley or instead of blocks a single ring may be employed. The outer edge of
each block (or of the ring if employed) is beveled to engage the beveled annular
shoulder upon the inner face of the pulley adjacent to its periphery. An
annular electro magnet U secured to the frame bracket has inserted within its
annular chamber U¹ a coil of insulated wire U which is held in position by a
non-magnetic ring u secured in place by screws u³ passing through its lugs u³, as
will be understood by reference to Figs. 4, 5 and 54. The coil U³ is electrically
connected with the binding screws V, V, as will be understood by reference to
Figs. 2, 3, 4 and 5. When a current is passed through the magnet coil the magnet
is caused to attract the armature clutch disk and disengage it from the pulley R²,
the pressure of the spring being overcome. At the same time the frictional contact
between the armature clutch disk and the non-magnetic ring u quickly arrests the
rotation of the countershaft.
When, instead of a dental engine such as shown, a suspension engine supported
from a wall bracket or the ceiling is used, the socketed bracket O' is detached from
its seat and an adjustable belt guard (see Figs. 3 and 34) is attached to the seat o in
its place. This belt guard is constructed as follows:-An attaching block W
carries a longitudinally slotted supporting bar W₁ through the slot of which passes
a clamp screw w provided with a washer w' for adjustably securing the supporting
bar to the attaching block. At its outer end the supporting bar is provided with a
pivoted head Y, which may be rocked about the supporting bar on the screw y
which serves both as a clamp and pivot. Forks y y projecting in opposite
directions from the pivoted lead embrace the engine driving belt and guard against its
being accidentally thrown from the pulley Q. It will be obvious that this belt guard
may be adjusted to embrace the belt whether it pass from the pulley in a horizontal
line or upward therefrom, at an angle or vertically, and that in the possible event
of the belt being thrown from the pulley it will be held by the pivoted head (on
opposite sides of which it passes) in convenient position to be readily replaced.
From the foregoing description aided by reference to the diagrams the operation
of the apparatus will be understood. In Fig. 18 which shows the apparatus as set
for the slowest speed, the current passes through the various conductors in circuit
in the direction indicated by the arrow heads. In this figure the conductors
represented by dotted lines indicate a modification whereby the dead resistance
of the rheostat is dispensed with and additional coils are wound about the field
magnets to increase their strength. In Fig. 19 which shows the apparatus as set
for the highest speed all dead conductors are broken away and the direction in
which the current passes can be traced by the arrow heads. In Fig. 20 which
shows the apparatus as set for next to the highest speed the dead wires are broken
away and the direction of the current indicated by arrow heads. Fig. 21, in which
all dead wires are broken away, and the direction of the current indicated by
arrow heads, shows the operation when the apparatus is set to actuate the electro-
magnetic clutch. The direction in which the current passes when the apparatus is
set for next to the lowest speed and for medium speed can be understood by
reference to Fig. 18, the only difference being that additional portions of the
rheostat are cut in. Z indicates the point at which the rheostat is cut in for next
to the lowest speed, and z¹ the point at which the rheostat is cut in for medium
speed. It is obvious that when the direction of rotation of the motor is reversed by
the actuation of the rockshaft L the current passes to the armature in directions
the reverse of those indicated by the arrow heads.

page_text: Where a motor of the shunt wound type is substituted for a motor of the series
wound type, as indicated by Fig. 22 the operation of the apparatus would be
substantially as before described.
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. The combination of a series of conductor terminals occupying fixed positions
relatively to each other, the cable of conductors, a series of terminals for the
conductors of said cable corresponding in number and adapted to register with the
terminals of the first named series, and the cable coupler carrying and maintaining
in fixed position relatively to each other the terminals of the cable of conductors
and adapted to be secured in operative position only so as to make proper connection
between each of the terminals carried thereby and the respectively registering
terminals of the other series, substantially as set forth.
2. The combination of the series of conductors, terminal plates with which they
are respectively connected, and the supporting plate to which said terminal plates
are connected, substantially as set forth.
3. The combination of the series of conductors, the slotted terminal plates with
which they are respectively connected, the supporting plate to which said terminal
plates are connected, and the binding posts engaged by the slotted terminal plates,
substantially as set forth.
4. The combination of the series of conductors, the slotted terminal plates with
which they are respectively connected, the supporting plate to which said terminal
plates are connected, the binding posts engaged by the slotted terminal plates, and
the fixed projection which ensures the proper adjustment of the supporting plate,
substantially as set forth.
5. The box containing the rheostat, having an opening front carrying binding
posts, substantially as set forth.
6. The combination of the rheostat, its box, and the box front carrying
binding posts connected with conductors and hinged in place, substantially as set
forth.
7. The combination of the spiders having the slotted arms, the rheostat coils,
the central bolt, and the separating strips entering the spider arm slots, substan-
tially as set forth.
8. The flexible heel rest for the foot-actuated switch mechanism, substantially as
set forth.
9. The box for the foot-actuated switch mechanism provided with the bottom
plate having the heel rest at its rear, substantially as set forth.
10. The combination, in electric motor switch mechanism, of an actuating
rockshaft provided with the cam arm, and the spring acting on the cam arm,
substantially as set forth.
11. The combination, in electric motor switch mechanism, of an actuating
rockshaft, two oppositely inclined cams at its inner end, the cam arm, and the
spring acting on the cam arm, substantially as set forth.
12. The combination, in electric motor switch mechanism, of an actuating
rockshaft, its two levers, the two oppositely inclined cams, the cam arm, and
the spring acting on the cam arm, substantially as set forth.
13. The combination in electric motor switch mechanism, of an actuating rock-
shaft, its two oppositely inclined cams, the cam arm, the spring acting on the cam
arm, and contacts actuated by the oppositely inclined cams, substantially as and
for the purpose set forth.
14. The combination of the foot-actuated switch mechanism, its box having the
flanged bottom plate, and the speed-varying lever fulcrumed at the underside of
the bottom plate, substantially as set forth.
15. The combination in electric motor switch mechanism, of the switch box, and

page_text: the speed-varying lever fulcrumed at its rear end beneath the switch box and
having a part projecting above the switch box, whereby it may be actuated by
sidewise pressure of the foot, substantially as set forth.
16. The combination, in electric motor switch mechanism, of the switch box, the
lever fulcrumed at one end beneath the switch box and having a part projecting
above the switch box, the spring contact bridge supported by the lever above the
switch box, and the two segmental rows of contact pieces, whereby speed of the
motor may be varied, substantially as set forth.
17. The combination of the stand, the electric motor carried thereby, the
rheostat, its box secured to the stand, the bracket frame of the stand, the counter-
shaft carried by the bracket frame, and the pulley thereon actuated from the motor,
substantially as set forth.
18. The combination of the stand, the electric motor carried thereby, the bracket
frame having supporting connection with the stand, the countershaft carried by the
bracket frame, its actuating pulley, the pulley on the motor armature shaft, the
belt passing about this pulley and the actuating pulley of the countershaft, and
means for vertically adjusting the bracket frame to tighten said belt, substantially
as set forth.
19. The combination of the stand, the electric motor carried thereby, the bracket
frame of the stand provided with the seat to secure the socketed bracket or belt
guard, the countershaft carried by the bracket frame, its actuating pulley, the
pulley on the motor armature shaft, and the belt passing about this pulley and the
actuating pulley of the countershaft, substantially as set forth.
20. The belt guard provided with the longitudinally slotted supporting bar, the
head pivoted to the outer end of the supporting bar and provided with forks
projecting in opposite directions therefrom, and the screw which serves as a pivot
for the head and to clamp it in position, substantially as set forth.
21. The belt guard for attachment to the stand of an electric motor, consisting
of the attaching block, the longitudinally slotted supporting bar, the clamp screw
adjustably securing the supporting bar to the attachment block, the head pivoted to
the outer end of the supporting bar and provided with forks projecting in opposite
directions therefrom, and the screw which serves as a pivot for the head and to
clamp it in position, substantially as set forth.
22. The combination of the countershaft, the loosely mounted pulley by which
it is actuated, the armature clutch disk rotating with the countershaft and capable
of sliding movement relatively thereto, the spring by the actuation of which the
clutch is normally held engaged with the loosely mounted pulley to cause rotation
of the countershaft with the pulley, and the electro magnet between which and the
pulley the clutch disk is mounted and which when excited causes disengagement of
said disk and pulley, substantially as set forth.
23. The combination of the countershaft, the loosely mounted pulley by which it
is actuated, the armature clutch disk rotating with the countershaft and capable of
sliding movement relatively thereto, the spring by the action of which the clutch
disk is normally held engaged with the loosely mounted pulley to cause rotation of
the countershaft with the pulley, the annular electro-magnet containing the coil in
its chamber, between which magnet and the pulley the clutch disk is mounted and
which when excited causes disengagement of said disk and pulley, and the non-
magnetic ring, substantially as set forth.
D
L
1000
WILLIAM ARMOUR JOHNSTON.
ARTHUR WILLIAM BROWNE.
JOHN CLARENCE DAVIDSON.