Year: 1897

page_text: I, WILLIAM NELSON PARKES, of 28 Harman Street, Brooklyn, in the County of
Kings and State of New York, in the United States of America, Sewing Machine
Tealer, 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:-
My invention has reference to improvements in ratchet feeds or movements an:1
especially to a device for preventing the wheel from jumping or throwing ahead,
when running at high speeds. It is a well known fact that when running at high
speeds with ordinary ratchet feeds, the momentum of the ratchet wheel will carry
it ahead and thus cause un irregular and inaccurate feed. Assuming, as un
example, that the actuating pawl is set to feed three teeth at each stroke, the
momentum will sometimes carry the ratchet wheel ahead, say two-thirds of a tooth
beyond the stroke of the pawl, so that when the pawl returns for the next actuating
stroke, it travels the distance of two-thirds of a tooth before engaging the teeth.
The contact, therefore, is in the nature of an impact, so that at this stroke of the
pawl, the wheel practically gains more than two-thirds of a tooth, and the error
therefore accumulates. The error, of course, will increase with increased speeds.
The usual method for attempting to overcome this error in the feed has been to
apply only a fixed friction to the ratchet wheel, but this has been found to be
ineffective at high rates of speeds, or under variable speeds. An excess of friction
beyond a certain point strains the pawl-lever and its connections and in this manner
again causes an uneven feed.
of
The object of my present invention is to overcome this defect in ratchet move-
ments, and, to this end, I combine with the ratchet wheel a frictional retarding
device adapted to act on said wheel and subjected to the action
an elastic pull back, such for instance 19 a spiral spring having a
tendency to turn the retarding device in a direction opposite to that of the ratchet
wheel. The retarding device, therefore, tends to hold the corresponding tooth of
the ratchet wheel constantly against the feed pawl and to turn said wheel against
the holding-pawl on the return stroke of the feed pawl.
The nature, of my invention will best be understood when described in connection
with the accompanying drawings, in which :-
-
Fig. 1 represents a face view of a ratchet movement embodying my invention.
Fig. 2 is a top view.
Fig. 3 is a section on the line 3-3, Fig. 1.
Similar letters and numerals of reference designate corresponding parts through-
out the several views of the drawings.
Referring to the drawings, the letter a designates a ratchet wheel, keyed, or
otherwise secured to the shaft b to which an intermittent rotary motion is to bo
imparted. is the pawl lever adapted to be vibrated in any usual manner about an
axis co-incident with that of the ratchet-wheel. Said lever is provided with a
077

page_text: usual actuating or feed pawl 1. 2 is a usual holding pawl subjected to the action
of a spring and adapted to prevent retrograde motion of the ratchet wheel.
All of the aforesaid parts may be of any usual construction, as their construction
and arrangement formi no part of my present invention. The retarding device I
have, in the present example, shown to consist of a lever d having two arms swung
from the hub of the ratchet wheel and formed with friction shoes 3 and 4 made of
leather, rubber, or other suitable material adapted for the purpose; said shoes being
arranged to bear upon the ratchet wheel from opposite sides and placed as near as
possible to the periphery thereof. The pressure with which the shoes bear upon the
ratchet wheel can be regulated by any suitable adjusting device, such as the
spring 5 and the adjusting nut 6. To the outer end of said lever is attached a
spiral pull back spring c, the tension of which can be regulated by a suitable
adjusting screw 7. 8 is a stop against which the retarding device is drawn by the
puil-back spring.
The tension of the pull back spring is so adjusted as to enable the retarding
device to turn the ratchet wheel backward against the existing resistance and
therefore said retarding device will always tend to hold the corresponding tooth of
the ratchet wheel against the feed pawl and to bring the wheel back against the
...ding pawl 2 during the return stroke of the said feed pawl.
On
It will now be readily understood that as the actuating or feed pawl turns the
ratchet wheel forward, the friction between said wheel and the retarding device
carries the latter along against the resistance offered by the pull back spring,
thereby overcoming, to a great extent, the forging ahead from the feed pawl.
the return stroke of the actuating or feed pawl, the retarding device, under the
action of the pull back spring, invariably brings the ratchet wheel against tho
holding pawl 2. If therefore, owing to any cause, the ratchet wheel should be
carried ahead, it is brought back through the corresponding distance on the return
stroke of the actuating or feed pawl, and consequently, an accurate and reliable
feed is obtained.
By properly regulating the tension of the friction shoe spring and that of the
pull back spring, the device can be set for different speeds.
In view of the fact that the motion of the ratchet wheel is an intermittent one,
the tension of the pull back spring increases with an increased speed, and said
spring pulls stronger on the retarding device, thereby compensating for the increase d
tendency of the ratchet wheel to throw ahead. In practice, I so adjust the tension
of the pull back spring that it will stretch a little under a moderate rate of speed.
It is of course, to be understood that the construction and arrangement of the
retarding and tension devices can be varied in many respects, therefore, I do not
wish to restrict myself to the construction shown.
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. The combination with a ratchet wheel, its actuating device and holding pawl,
of a frictional retarding device acting on said ratchet wheel, and a spring acting on
said retarding device in a direction opposite to the direction of the rotation of the 4
wheel, substantially as described.
2. The combination with a ratchet wheel, its actuating device and holding
pawl, of a frictional retarding device acting on said ratchet wheel and provided
with means for adjusting the friction, and an adjustable pull back spring attached
to said retarding device, substantially as described.
. The combination with a ratchet wheel, its actuating device and holding aw
of a lever provided with friction shoes adapted to engage with the ratchet wheel
from opposite sides, means for varying the pressure of said shoes upon the wheel
and a pull back spring acting on said lever, substantially as described.
4. The combination with a ratchet wheel, its actuating device and holding pawl, 5
of a lever having its axis of oscillation coincident with the centre of the ratchet

page_text: wheel and provided with friction shoes, and a spring attached to said lever sub-
stantially as described.
5. In a ratchet movement, a frictional retarding device combined with means for
subjecting the same to a force acting in a direction opposite to the direction of the
rotation of the ratchet wheel, substantially as described.
6. In a ratchet movement, a frictional retarding device engaging with the ratchet
wheel to participate in part in the rotation thereof, combined with a pull back
spring acting on said retarding device, substantially as described.
7. The combination with a ratchet wheel and its actuating device, of a frictional
retarding device bearing on the ratchet wheel, and an elastic retracting device
neting on said retarding device, substantially as described.
Dated this 29th day of June 1897.
HARRIS & MILLS,
23 Southampton Buildings, London, W.C., Agents.