Note: Descriptions are shown in the official language in which they were submitted.
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7361-65
OPENSHED DWELL TYPE DOBBY
The invention relates to openshed dwell type dobbies for
weaving looms, and more particularly to dobbies having their drive
mechanism operated at the loom frequency. The object of the inven-
tion is to provide such dobbies with a reciprocating drive which
gets its motion delivered selectively and in full to the swing
levers that shed the loom harnesses.
In the design weaving process, openshed dwell type
dobbies offer the most desirable mode of shedding performance.
Openshed permits the warp threads to be selectively shed from two
base positions, and dwell allows the shed to remain narrow and
stationary during the weft insertion. Openshed thus eliminates
the wasted thread motion that was once needed when the selection
was made from a single base, and dwell avoids the extra warp
tension and breakage that occurs if the shed opening is large and
non-stationary. Dobbies which operate at the loom frequency
usually depend on a gear system of drive, and are represented by
the well-known Leeming and Knowles dobbies. Essentially they
include a drive gear which is operated uninterruptedly at the loom
frequency, and a crank gear which is driven selectively, a half
turn at a time. Each half turn of the crank is then transmitted
to the swing lever through a crank rod, while the two end posi-
tions of the crank define the two base positions of the openshed.
In;the L~eeming dobby, it is the drive gear which is operated to
achieve the selectlon, and in the Knowles dobby it is the driven
gear which is operated for this purpose. The drive gear, in each
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case, carries teeth only on a half of the circumference, so that
the blank half represents an idle motion and yields the dwell.
Gear system dobbies are highly suitable for positive shedding, but
cannot cope with high loom speeds. ~his speed limitation is due
to the following known factors: Resistance of the gear components
to quick selection, inertia of the crank mechanism to motion
transmission, infinite acceleration of the driven gear at the
start of each motion, and the non-adjustable nature of the dwell.
Nevertheless, the gear system dobbies offer the inherent advantage
10 of shed stability, due to the fact that the drive and the driven
components remain disconnected with each other during the openshed
and dwell operations.
Reciprocating drives are very common in dobbies which
operate at half the loom frequency, e.g. the well known Keighley ?
dobby and its derivatives. However, it is not common to use a
reciprocating drive in dobbies which operate at the full loom
frequency. One exception is the present inventor's early work
(Swiss Pat. No. 370,025 and U.K. Pat. No. 988,690), which was like
a Leeming dobby in that the selection process was applied on the
20 drive mechanism. The present invention is more like a Knowles
dobby in that the selection process is applied on the dri~en
mechanism. Moreover, in conformity with the standard technology
of dobby looms, the present invention makes use of swing levers
for shedding the loom harnesses. It will be noted that the main
advantages of the present invention are That it links the full
motion of the drive with the swing levers, that it achieves the
selection through hooks that are easy to operate and select, that
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it ensures a perEect shed stability by keeping the driven
components disconnected from the drive during the openshed and
dwell, that it allows each driven motion to commence with a mild
acceleration, that it has the provision ror a variable dwell, and
that i-t economises the size of the dobby mechanism.
Essentially, the present invention, an openshed dwell
type dobby comprises a drive mechanism having two drive knives
which reciprocate radially out of phase at the loom frequency;
means of selection which operate on each loom cycle; and a
plurality of swing levers which carry each a hook and are shed
from two separate base positions by linking the hooks selectively
with the drive. It will be seen that a simple combination of
these dobby components can very logically provide the above noted
important advantages.
Therefore this invention seeks to provide an openshed
dwell type dobby for shedding warp harnesses of a weaving loom,
comprising: i) a pair of drive knives which reciprocate out of
phase at a full frequency of a related loom between two fixed base
positions; ii) a plurality of swing levers which are rested at
said two base positions and are selectively shed from each
different of these positions to the other simultaneously by a
particular knife of the said pair such that both knives, on
completing respective shedding strokes, return concurrently
through idle strokes to respective original positions; iii) swing
~levers (ii) connected individually to harnesses of said related
;loom and deliver,~on said shedding strokes, the full motion of
each knife to the harnesses be;ng shed; iv) hook means pivoted
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directly onto each of said swing levers to engage said swing
levers with said particular knives from said different positions;
v) means of selection for selectively actuating said hook means
from said two base positions according to a given pattern.
The invention is now described with the help oE a
concrete example given in the following drawings, in which:
Fig. 1 is a front view in section and shows the swing
lever at the upper base position mechanism Eor the operation of
the knives is omitted Eor the sake of clarity.
Fig. 2 corresponds to Fig. 1, but shows the swing lever
at the lower base position and includes the mechanism omitted in
Fig. 1.
Fig. 3 shows one possible arrangement mounting the dobby
on a loom.
Referring to Fig. 1 of the drawings, drlve knives 1 and
2 reciprocate at the loom frequency radially out of phase and, as
shown by full arrows, each knife commences its shedding stroke
from
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a different base or position. After the shedding stroke, the
knives return to their original positions, but these return
strokes are idle, occur concurrently, and yield the dwell. A
number of swing levers 3, each carrying a ~ixed notch 4 and a
two-way hook 5 pivoted at 25 to lever 3, are placed in such a
manner that the hooks are disposed in between the two knives and
can be selectively linked with either knife from its particular
base. Swing levers 3 are pivoted on fixed shaft 12. Fig. 1 shows
a representative swing lever resting in the upper base position,
which corresponds to the base of knife 2. In this position, the
notch 4 is engaged by an elevator 6, held on a fixed pivot in the
cross bar 7. The means of selection consists of a series of
composite levers 24, one for each swing lever and composed of a
rigid portion 8 and a spring portion 9, and a pattern cylinder 10,
which is rotated intermittently, one step on each return stroke of
the knives. The mechanism for intermittent motion is not shown,
since such mechanisms are very common. In each step, the cylinder
10 presents a fresh stud or blank 10' to each composite lever 24,
a stud 10' being presented i~ the swing lever 3 is required to
occupy the upper position. This upper position, and also the
corresponding positions of the related hook 5 and elevator 6, is
shown in Fig. 1. It can be seen that the swing lever 3 and its
hook will remain completely disconnected from the knives in this
partlcular position, as long as a stud 10' is followed by a stud
on the pattern cylinder 10.
~ When the swing lever 3 is required to shed from the
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upper position, thé composite lever 24 is made to drop and rest on
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131 16~4
a common rod 19, by presenting a blank on cylinder 10. This makes
the hook 5 drop to a position in which it is engageable by knife 2
and, simultaneously, the spring 9 is withdrawn from the elevator
6. As the knife 2 now approaches the end of its idle stroke, it
engages the hook 5, releases the elevator 6 and sheds the swing
lever 3, in that order~ The lower base position is reached when
the swing lever comes to rest against a fixed cross bar 17 and, in
that position, the hook 5 again occupies a neutral position
between drive knives 1, 2, as shown in Fig. 2. It will be seen
later that the swing lever 3 is biased downwards by string 21,
which bias allows the lower base position of Fig. 2 to be defined
by the cross bar 17, on which all the swing levers rest when
selected by blanks.
Fig. 2 shows the drive arrangement for knives 1, 2, and
the swing lever 3 resting in the lower base position. The drive
knives 1, 2 are mounted respectively on shafts 11 and 12, through
gears 13, 14 and side arms 15, 16. Gear 13 and arm 15 operate
integrally and are fixed on shaft 11; gear 14 and arm 16
also operate integrally, but are free on shaft 12. Gear 13 and 14
are mutually coupled. However, shaft 11 is free in the dobby
frame, but shaft 12 is fixed, and thus the drive knives 1, 2 can
both be made to reciprocate in opposite directions by oscillating
the shat 11. Figs. 1 and 2 both represent the same inner side of
the dobby frame 20. The opposite side of the frame (not shown)
supports the other ends of shafts 11, 12, on which are mounted the
counterparts of gears 13, 1~ and side arms 15, 16. Thus the
knives 1 and 2 are actually operated by respective arm pairs 15
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and 16, located one inside the other. The two sides of the dobby
frame 20 are held together by cross bars 17, 18. Only one repres-
entative swing lever 3, with its related elevator 6 and composite
lever 24, is shown in the drawings; but usually their number
varies from 12 to 24, and all are placed on the same centre to
operate selectively in the same manner.
The shedding of the swing lever 3 by knife 1, from the
base position in Fig. 2, is done by presenting a stud 10' on the
pattern cylinder 10. The stud raises the composite lever 24, and
hence the related elevator 6 and hook. The hook is thus engaged
by knife 1 on the start of its shedding stroke, and the full
motion of the knife is subsequently communicated to the swing
lever. When the upper position of the swing lever 3 is reached
and knife 1 has just reversed its motion, elevator 6 engages the
notch 4, the hook 5 drops on the composite lever 8, and the cycle
is repeated from the position of Fig. 1. A close study will
reveal that the elevator 6 needs resilient pressure to disengage
the hook 5 from knife 2 and also to engage the hook 5 with knife
1. This pressure is supplied by the spring portion 9 of the
composite lever.
Fig. 3 shows diagrammatically a ront view of a loom
equipped with the present dobby. A string 21 connects each swing
lever 3 with a loom harness 22 of loom 23. The mounting arrange-
ment lS according to the conventional practice used in negative
dobby shedding. The loom harness 22 is biased downwards by spring
action, supplied by a bottom motion, and the bias is carried to
the swing lever 3 through string 21. The shaft 11 is oscillated
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at the loom frequency by coupling it with the crank shaEt of the
loom through a crank mechanism, (not shown). The crank arm of
shaft 11 is shown in dotted lines as it is hidden from the view.
When the shaft 11 is thus oscillated by a simple crank, the two
strokes of the drive are equal and the dwell equals a half of the
loom cycle. However, if a shorter dwell is required, say for
small width looms, the shaft 11 can be made to oscillate by a
quick return motion. Such motions are well known and not shown in
the present drawings. It is important to note that the drive
knives 1 and 2 must operate at different swing angles to deliver
the same motion to the swing lever 3. This provision is made
while designing the gear ratio between the gears 13 and 14.
It will be noted that the hooks introduced for the
selective transmission of motion are comparatively lighter in
weight and easier to select than the corresponding components used
in dobbies which operate at the loom frequency. Moreover, each
motion of the drive commences with a zero acceleration, and the
driven components follow the same motion. Another point to note
is that the swing levers receive not only the full motion of the
drive, bat also oscillate in a wide angle of swing. This is
rendered possible by allowing the swing levers and the drive
knives to be operated on axes which are either identical or close
to each other. In consequence, swing levers of very small length
can be used to transmit the full motion required for the shedding
purpose, and this same economy is reflected in the rest of the
dobby mechanism.
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