Shuttle Picking Mechanisms in Weaving
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Objective of picking is to propel the weft carrying element (shuttle, projectile or rapier) or the
weft yarn along the correct trajectory maintaining requisite velocity through the shed in order
to provide lateral sets of yarns in the fabric.
Classification of Shuttle Picking Mechanism
1.
cone over-pick mechanisms
2.
cone under-pick mechanisms.
Cone Over-Pick Mechanism
•
A picking cam attached to bottom shaft displaces the cone (picking cone) which is attached
with the upright picking shaft.
•
This causes rotation of the picking shaft.
•
As a result, the picking stick, which is attached to the uppermost end of picking shaft, swing
in a horizontal plane over the loom and transmits the motion to shuttle through picking
strap and picker guided by a spindle.
•
Here picker is constrained by the spindle to move in a
straight line which otherwise would have followed a
path of arc.
•
Moreover, pairs of picking cam and follower installed at
either end of the loom have seldom ensured picking of
equal strength (force).
•
Frequent adjustment of picking-strap or picking cam
and nose settings is required.
Possible Adjustments for Strength and Timing of Over-
Pick
•
Shortening picking-strap increases the shuttle speed,
but timing of picking advances.
•
The picking tappet can be turned over bottom shaft for
the adjustment of picking timing.
•
Lowering the picking cone in the slot increases the
shuttle speed but timing of picking is delayed.
•
Angular adjustment between picking shaft and picking
stick also changes shuttle speed and timing
(unpredictable).
•
Large change in shuttle speed for wider loom can be
achieved by changing either nose bit or the entire
picking cam.
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a picking cam attached
to bottom shaft
displaces the cone
turning the picking shaft
(side shaft) located
horizontally.
•
The other end of the
picking shaft is
connected with upright
picking stick through
the picking strap (lug
strap).
•
This causes the picking
stick to move in a
vertical plane and
transmits the motion to
shuttle by the picker
attached at the upper
end of it.
•
In this system the picking stick and other appendages are located below the shuttle
trajectory while picking cams and follower, as usual, below the loom and driven from
bottom shaft.
•
The system is naturally suitable for automatic looms.
•
Here picker slides over its spindle and picking timing is regulated by cam adjustment like in
over pick motion.
•
An almost inextensible lug strap allows shuttle speed adjustment by either raising or
lowering it around picking stick.
•
Absence of stretchable parts in under-pick system ensures the retention of correct setting
over long period in contrast with the cone over-pick mechanism.
Possible Adjustments for Strength and Timing of under-Pick
•
Timing of picking is changed by turning the cam on the bottom shaft.
•
Raising and lowering of the lug strap (picking strap) reduces and increases shuttle velocity
respectively.
•
Two independent adjustments for velocity and timing of shuttle make the under-pick
system less complicated.
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In a modified under-pick system, picker guiding
spindle is eliminated and picker itself is kept
attached to the stick.
•
The lower end of the stick is made to oscillate
over a curvilinear shoe which rests upon a plate.
•
The shoe and picker trajectory form the
circumference of a semi-circle.
•
This ensures picker movement in a perfect
straight line and hence that of the shuttle which
is a prime requirement for high speed looms.
•
Picking stick in its extension passes through the
slot of a plate and connected with loom frame
through a spring for proper return.
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Attempt to increase loom speed further creates one
unfavorable situation where contact between shoe and
plate is often disrupted resulting undesirable picker
movement which deflects shuttle from its right path or
undue wear of it and even fly-out.
•
Modification through link pick is done to overcome this
limitation.
•
Here a metal piece (M) attached to the lower end of the
picking stick.
•
M connects itself to a bracket (B) fastened to the sley
sword through two arms (A).
•
Such four bar linkages are, as if, an irregular quadrilateral
whose shape and sizes in relation to the length and
angular movement of the picking stick, if properly
designed can deliver very good result in terms of
accuracy over a distance of 15-20 cm along shuttle path
and truly exercises positive control in the system even at
very high speed.
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Let us assume the following notations:
P
= Loom speed (picks/min.) or number of revolution of crank shaft/min.
R
= Width of the reed (m)
v
= Average shuttle velocity (m/s)
L
= Effective length of shuttle (m)
θ = Degree of crank shaft rotation available for the passage of the shuttle through
the shed.
t
= time required for the shuttle passage through the shed (s)
Now the distance covered by the shuttle in
t
sec = (
R+L
) m
•
It can be noted that from Equation 4 that for a given loom width and shuttle
length, if we desire to increase the loom speed, we must increase either v or θ or
both.
•
an increase in θ can be achieved by increasing the sley eccentricity (
e
) as sley
remains towards the back centre of the loom for a longer duration if sley
eccentricity is more.
•
Thus the shuttle can avail greater duration for its flight through the shed.
•
A high value of sley eccentricity should be avoided to reduce wear and tear of the
loom.
•
In addition, an increase in θ causes problem for fast reed warp protector
motion, because in order to prevent the shuttle trapping, the shuttle should
strike the swell in proper time.
•
It, therefore, restricts the increase of θ.
•
On the other hand, an increase in
v
requires more kinetic energy to be dissipated
during shuttle checking which increase wear of the loom frame. From this above
argument, it is clear that the loom speed is limited in the shuttle loom.
•
The product of
P
and
(R+L)
is known as the Weft Insertion Rate (WIR), which is a measure of
loom productivity. Unit of WIR is m/min.
•
From
Equation 4
, for a given
v
and θ, we have:
•
However, this theoretical relationship largely deviates from the actual practices.
•
A good approximation of the relationship between the loom speed and loom width can be
expressed by using the inverse-square-root rule, i.e.
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The energy used to
accelerate the shuttle is
equal to its kinetic
energy when it leaves
the picker.
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The objective of the shuttle checking is to retard the shuttle nullifying its kinetic energy to
zero.
Mechanism
•
The incoming shuttle gets rubbed on the spring loaded swell and thereby the frictional force
slows down the shuttle velocity. The velocity of the incoming shuttle is reduced around 30%
by the action of swell. The shuttle is finally stopped as it collides with the picker, which is
cushioned by a suitable buffer system.
B
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To push the newly inserted pick up to the cloth
fell
•
To ensure uniform pick spacing in the fabric
Sley Motion
•
Beat-up is done by the reed which is carried by
the sley.
•
Sley derives its rectilinear reciprocating motion
from the rotating crank shaft through the
connections of crank and crank arm which makes
a four-bar linkage mechanism.
•
Radius of the crank = OA= r, lengthy of the crank
arm= AB =l
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As sley motion deviates from SHM,
•
during its backward journey, sley covers more displacement from rotation of crank shaft
than the rotation of crankshaft.
•
Similarly during its forward journey, sley covers less displacement from rotation of
crankshaft than the rotation of crankshaft.
•
This difference in the sley displacement during its backward and forward movement is
termed as sley eccentricity
Shuttle picking mechanisms play a crucial role in propelling the weft carrying element to maintain the required trajectory and velocity in fabric weaving. Two common mechanisms are cone over-pick and cone under-pick, each offering unique adjustments for strength and timing. The cone over-pick involves a picking cam displacing a cone to drive the shuttle, while the cone under-pick positions the components below the shuttle trajectory, ideal for automatic looms. Adjustments in both mechanisms affect shuttle speed and timing for efficient weaving operations.
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Presentation Transcript
Picking Picking Objective of picking is to propel the weft carrying element (shuttle, projectile or rapier) or the weft yarn along the correct trajectory maintaining requisite velocity through the shed in order to provide lateral sets of yarns in the fabric. Classification of Shuttle Picking Mechanism 1. cone over-pick mechanisms 2. cone under-pick mechanisms. Cone Over-Pick Mechanism A picking cam attached to bottom shaft displaces the cone (picking cone) which is attached with the upright picking shaft. This causes rotation of the picking shaft. As a result, the picking stick, which is attached to the uppermost end of picking shaft, swing in a horizontal plane over the loom and transmits the motion to shuttle through picking strap and picker guided by a spindle.
Here picker is constrained by the spindle to move in a straight line which otherwise would have followed a path of arc. Moreover, pairs of picking cam and follower installed at either end of the loom have seldom ensured picking of equal strength (force). Frequent adjustment of picking-strap or picking cam and nose settings is required. Possible Adjustments for Strength and Timing of Over- Pick Shortening picking-strap increases the shuttle speed, but timing of picking advances. The picking tappet can be turned over bottom shaft for the adjustment of picking timing. Lowering the picking cone in the slot increases the shuttle speed but timing of picking is delayed. Angular adjustment between picking shaft and picking stick also changes shuttle speed and timing (unpredictable). Large change in shuttle speed for wider loom can be achieved by changing either nose bit or the entire picking cam.
a picking cam attached to bottom shaft displaces the cone turning the picking shaft (side shaft) located horizontally. The other end of the picking shaft is connected with upright picking stick through the picking strap (lug strap). This causes the picking stick to move in a vertical plane and transmits the motion to shuttle by the picker attached at the upper end of it. Cone Under Cone Under- -Pick Mechanism Pick Mechanism
In this system the picking stick and other appendages are located below the shuttle trajectory while picking cams and follower, as usual, below the loom and driven from bottom shaft. The system is naturally suitable for automatic looms. Here picker slides over its spindle and picking timing is regulated by cam adjustment like in over pick motion. An almost inextensible lug strap allows shuttle speed adjustment by either raising or lowering it around picking stick. Absence of stretchable parts in under-pick system ensures the retention of correct setting over long period in contrast with the cone over-pick mechanism. Possible Adjustments for Strength and Timing of under-Pick Timing of picking is changed by turning the cam on the bottom shaft. Raising and lowering of the lug strap (picking strap) reduces and increases shuttle velocity respectively. Two independent adjustments for velocity and timing of shuttle make the under-pick system less complicated.
Parallel Pick Mechanism: cone Parallel Pick Mechanism: cone underpick underpick In a modified under-pick system, picker guiding spindle is eliminated and picker itself is kept attached to the stick. The lower end of the stick is made to oscillate over a curvilinear shoe which rests upon a plate. The shoe and picker trajectory form the circumference of a semi-circle. This ensures picker movement in a perfect straight line and hence that of the shuttle which is a prime requirement for high speed looms. Picking stick in its extension passes through the slot of a plate and connected with loom frame through a spring for proper return.
Link Pick Mechanism: cone Link Pick Mechanism: cone underpick underpick Attempt to increase loom speed further creates one unfavorable situation where contact between shoe and plate is often disrupted resulting undesirable picker movement which deflects shuttle from its right path or undue wear of it and even fly-out. Modification through link pick is done to overcome this limitation. Here a metal piece (M) attached to the lower end of the picking stick. M connects itself to a bracket (B) fastened to the sley sword through two arms (A). Such four bar linkages are, as if, an irregular quadrilateral whose shape and sizes in relation to the length and angular movement of the picking stick, if properly designed can deliver very good result in terms of accuracy over a distance of 15-20 cm along shuttle path and truly exercises positive control in the system even at very high speed.
Shuttle Velocity and Loom Speed Shuttle Velocity and Loom Speed Let us assume the following notations: P = Loom speed (picks/min.) or number of revolution of crank shaft/min. R = Width of the reed (m) v = Average shuttle velocity (m/s) L = Effective length of shuttle (m) = Degree of crank shaft rotation available for the passage of the shuttle through the shed. t = time required for the shuttle passage through the shed (s) Now the distance covered by the shuttle in t sec = (R+L) m
It can be noted that from Equation 4 that for a given loom width and shuttle length, if we desire to increase the loom speed, we must increase either v or or both. an increase in can be achieved by increasing the sley eccentricity (e) as sley remains towards the back centre of the loom for a longer duration if sley eccentricity is more. Thus the shuttle can avail greater duration for its flight through the shed. A high value of sley eccentricity should be avoided to reduce wear and tear of the loom. In addition, an increase in causes problem for fast reed warp protector motion, because in order to prevent the shuttle trapping, the shuttle should strike the swell in proper time. It, therefore, restricts the increase of . On the other hand, an increase in v requires more kinetic energy to be dissipated during shuttle checking which increase wear of the loom frame. From this above argument, it is clear that the loom speed is limited in the shuttle loom.
The product of P and (R+L) is known as the Weft Insertion Rate (WIR), which is a measure of loom productivity. Unit of WIR is m/min. From Equation 4, for a given v and , we have: However, this theoretical relationship largely deviates from the actual practices. A good approximation of the relationship between the loom speed and loom width can be expressed by using the inverse-square-root rule, i.e.
Power Required Power Required for Picking for Picking The energy used to accelerate the shuttle is equal to its kinetic energy when it leaves the picker.
Picking Picking The objective of the shuttle checking is to retard the shuttle nullifying its kinetic energy to zero. Mechanism The incoming shuttle gets rubbed on the spring loaded swell and thereby the frictional force slows down the shuttle velocity. The velocity of the incoming shuttle is reduced around 30% by the action of swell. The shuttle is finally stopped as it collides with the picker, which is cushioned by a suitable buffer system.
Beat up Beat up To push the newly inserted pick up to the cloth fell To ensure uniform pick spacing in the fabric Sley Motion Beat-up is done by the reed which is carried by the sley. Sley derives its rectilinear reciprocating motion from the rotating crank shaft through the connections of crank and crank arm which makes a four-bar linkage mechanism. Radius of the crank = OA= r, lengthy of the crank arm= AB =l
Sley Sley Eccentricity Eccentricity As sley motion deviates from SHM, during its backward journey, sley covers more displacement from rotation of crank shaft than the rotation of crankshaft. Similarly during its forward journey, sley covers less displacement from rotation of crankshaft than the rotation of crankshaft. This difference in the sley displacement during its backward and forward movement is termed as sley eccentricity
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