Describes about the picking mechanism in weaving machine and types of picking in shuttle and projectile loom

1. PICKING MECHANISM
A.MURALIKRISHNAN
LECTURER,
P.A.C.RAMASAMY RAJA POLYTECHNIC COLLEGE
RAJAPALAYAM, TN

2. Introduction:
Picking is the 2nd primary motion in weaving.
The action of inserting weft yarn through the warp yarns is
called picking.
The objectives of picking mechanism are:
* To propel the weft carrying element (shuttle, projectile or
rapier) along the correct trajectory .
* To throw the weft carrying element at a predetermined
speed.

3. Types of weft insertion in weaving
Weft Insertion
Conventional
Shuttle
Over pick
Under
pick
Un
conventional
Projectile Rapier Air jet Water jet

4. Mechanism of picking
1st method:
• Mechanisms will generate the energy for picking when it is
required
• Done by means of cam to displace the picker.
– Example : shuttle loom
2nd method:
• Mechanisms will generate the energy required for picking
and stored in springs or torsions and release it suddenly
when it required
– Example : Projectile loom

5. Ideal picking
• Should have minimum consumption of power
• Should have minimum momentum of a shuttle on entering into
shuttle box (i.e. at checking)
• Kinetic energy in the picking mechanism should remain
constant irrespective of fluctuation in the speed and variation in
shuttle weight
• Shuttle should have slow speed at start, high at middle and
again slow at other end
• Shuttle should be under complete control
• Picking and checking mechanism should be integrated so that
kinetic energy of shuttle as it enters a box can be utilized for
subsequent picking instead of dissipating as a heat and noise.
This will reduce the power required for picking

6. Complexities of shuttle propulsion
• A shuttle weighting about half Kg is used to insert a weft yarn
weighting only a few grams
• During shuttle movement, it follows a complex path in all the
three axis with the motion of sley
• If there is a variation in loom speed resulting in a variation in
picking force
• If there is a variation in the checking and leads to variation in
shuttle speed
• Shuttle is accelerated from rest to a speed of 10 – 15 m/s in a
distance of only 15 – 20 cm.

7. Mechanism in shuttle loom
• The energy generated by the cam is used to displace
the picker against the inertial resistance offered by
the shuttle
• The shuttle speed varies with the loom speed
• The force acting on the shuttle tends to increase to
a maximum about the half way through the period
of acceleration.
• Then to decrease to zero at the instant at which the
shuttle loses contact with the picker.

8. Timing diagram
Picking occupies
1/3 of loom timing in a cycle
Picking and Checking
• 80°-110° : Picking mechanism operates
• 105°-110° : Shuttle enters in the shed
• 240°-250° : Shuttle leaves the shed
• 270° : Shuttle strikes the swell in the shuttle box
• 300° : Shuttle comes to rest

9. Cone over Pick
•

10. • A picking cam attached to bottom shaft displaces the picking
cone (picking cone) which is attached with the picking shaft.
• This causes rotation of the picking shaft. As a result, the
picking stick attached to the picking shaft swing in a horizontal
plane over the loom .
• This motion is further transferred to the picker by the picking
strap.
• The picker is constrained by the spindle to move in a straight
line which otherwise would have followed a path of arc.
• Finally, picker hits the shuttle and passed through
the warp shed.
• It is robust and easy to adjust and maintain.
Mechanism of Over Picking

11. How to Increase PPM:
- By increasing motor speed.
- By setting the cone stud nearer to the picking tappet.
- By decreasing the picking strap.
- By altering the position of picking arm towards the centre
of the loom.
- By decreasing the length of the stroke of picking tappet.

12. Under picking mechanism

13. Phases in shuttle movement
• There are 3 phases in weft
carrier motion
– Acceleration
– Free flight
– Checking ( Retardation)

14. Initial speed of shuttle
• It is a speed at the instant, shuttle leaves the picker and starts
its free flight.
• Initial speed of shuttle should be almost equal to the average
shuttle speed.
• Unless the shuttle is seriously impeded by the top shed.

15. Relation between 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)
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

17. Power Required for Picking
• The energy used to accelerate the shuttle is equal to its
kinetic energy when it leaves the picker

18. Cost of power required for picking
• From the previous equation 7, for a given width of loom,
the power required for picking is proportional to the cube of loom speed
(picks/min).
• if the loom speed is increased by 20%,
– the power requirement for picking will increase by 73%
• (1.23 times = 1.728 times).
– the productivity of fabric (m/min) will also increase by 20% due to
increase loom speed.
– So, power cost per unit length (m) of fabric will increase by 44%
(1.728/1.2 times).
Power of picking is also influenced as follows.
• Increases linearly with the mass of the shuttle.
• Increases proportionately with the square of loom width
• Decreases proportionately with the square of degree of crank shaft
rotation available for the passage of the shuttle through the shed

19. Nominal Vs Actual Displacement of Shuttle
during Picking
• If the loom is turned over slowly by hand, the profile of cam
gives the nominal movement to shuttle when all the flexible
parts become rigid. This movement is called nominal
displacement.
• But, in actual running, the displacement differs from nominal
because all the parts become flexible. Under actual running
condition of loom is known as actual displacement of shuttle.
• This study is more useful for the machine designer to get better
understanding of movement of shuttle.

21. Projectile picking

22. Mechanism used in projectile loom
• The generated energy is stored in a spring or torsion rod and
release it suddenly when required.
• Because the energy is released suddenly, the weft carrier
speed is independent of the loom speed.
• The force exerted by the torsion rod is greatest at the instant
of release and decreases steadily to zero.
• In this mechanism, we can obtain more uniform acceleration
is achieved.

23. Features of projectile picking
• Picking unit and projectile receiving unit is separated from
moving sley.
• The weft is drawn directly from a large, stationary cross
wound package. No pirn winding
• Projectile is picked across the warp at very high speed.
• Small amount of shed opening is sufficient to pass the small
projectile
• Projectile runs in a steel guides, so that warp threads are not
touched neither by projectile nor by weft thread

27. Torsion mechanism – Before picking

28. Torsion bar mechanism – After picking

29. Velocity and acceleration of projectile
• The velocity is continuously
varying through out the
projectile movement.
• Acceleration of projectile
occupies only 0.007 sec.
• Retardation of projectile
takes longer time and
projectile comes to rest in
gentle manner.