An Improved Safety Device for Starting-switches of Electric Motors,
Year: 1899

page_text: Date or Application, 13th Nov., 1899-Accepted, 23rd Dec., 1899
COMPLETE SPECIFICATION.
An Improved Safety Device for Starting-switches of Electric Motors,
I, ANDERS JOHAN ATTERBERG, of 8, Hamngatan, Gothenburg, in the Kingdom
of Sweden, Engineer, do hereby declare the. nature of this invention and in
what manner the same is to be performed, to be particularly described and ascer-
tained in and by the following statement:-
This invention relates to a safety device for starting-switches of electric
motors, and has for its object to automatically stop or render stationary the
starting crank or switch lever as soon as a given maximum of electric current
has been switched on.
The safety device consists of an electro magnet which arrests the starting
crank or switch lever at a given moment, but allows the same to be moved
backward unimpededly. When the starting crank or switch lever is moved
backward, or the strength of current diminishes, the magnet again automatically
releases it.
In the accompanying drawings,
Figure 1 is a vertical section; and
Figure 2, a sectional plan view of a starting switch provided with such an
arrangement.
0
Contacts a are coupled in the ordinary manner with the resistance coils.
A coil & connected with the main conductor of the motor forms with a casing
an electro magnet, and is mounted on a plate d. A hollow cylinder acting
as an armature, is adjustably mounted in the casing e of the magnet, which hollow
cylinder is provided with a central adjustable bolt f, the upper end of which
extends into the starting crank or switch lever g and there acts on an elbow
lever h. The free end of this lever is formed as a bevelled pawl and engages
in a ratchet wheel mounted on the plate and provided with inclined teeth.
When the electro magnet has brought the pawl A into the position shown, the
starting lever can no longer be moved forwards in consequence of the teeth
of the ratchet wheel but may be moved backwards. The bolt or pin f is
provided with a spiral spring k which may be adjusted by means of a nut in such
a way that the armature of the electro magnet cannot be attracted before the
current in the wire coil has reached the desired strength. The armature and
the locking device are then retained in their position until the current strength
is so far diminished that the drawing power of the electro magnet has become
smaller than the pressure of the spiral spring k. When the spiral spring has
moved the pawl back, the starting crank or switch lever can be again moved
forwards.
Figures 3 and 4 show a vertical section and plan view of a similar device,
but this form of construction differs from the first named in that the under side
of the starting crank or switch lever is formed as the ratchet wheel in which
the pin of the electro magnet engages and prevents the further movement
of the starting crank or switch lever on an increase of current.
[Price 8d1

page_text: 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. A safety device for starting-switches of electric motors characterised by
the main conductor being formed as or connected with an electro magnet (6),
the armature (e) of which is connected with a locking device for the starting
crank or switch lever, in such a way that the said crank may be locked and
cannot be moved forwards upon the current strength reaching a given maximum,
substantially as hereinbefore described.
2. The general construction and combination of parts taken as a whole forming
the improved safety device for starting-switches of electric motors, substan-
tially as herein before described and illustrated with reference to Figures 1
and 2, or Figures 3 and 4 of the accompanying drawings.
L
Dated this 11th day of November
W. P. THOMPSON & Co.,
Of 6, Lord Street, Liverpool, Agents for the Applicant.