1. Er . Bhushan Kumar www.er-bhushan.in Shedding Mechanism …..
Er . Bhushan Kumar
Weaving Executive
Raymond Textiles Ltd
Vapi, Gujarat, India

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Shedding Mechanisms:
Shedding is a process of raising and lowering of warp yarns by harnesses to make an opening for the filling (weft) yarn to pass through. 
All weaving machines control the warp yarns to create a shed. This can be accomplished with the following systems:
Crank shedding
Cam shedding or tappet shedding
Dobby shedding
Jacquard shedding
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Crank Shedding:
Crank shedding mechanisms can only be used for plain weave fabric constructions.
In this system the harnesses are controlled by the crank shaft of the weaving machine. For each crank shaft revolution a wheel is rotated half a turn, which changes the harness position.
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Cam Shedding:
A cam is a disk which has grooved or conjugated edges which corresponds to the lifting plan. The lifting plan controls which harnesses are lifted. The disadvantage of cam shedding is that when the woven design has to be changed the cams have to be rearranged to suit the new design. Pattern design is also limited due to the amount of harnesses the cams can control.
cams convert the rotary motion of the main shaft of the weaving machine into the reciprocating motion of the Heald frame .
It has two types
Positive cam shedding
Heald shaft raised or lowered by the cam or eccentric system
Negative cam shedding
Heald shaft raised by the mechanism but returned by the external devices such as spring.
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Jacquard Shedding:
In jacquard weaving a device called a ‘jacquard’ selects and lifts the warp yarns individually. 
It has types.
Mechanical Jacquard
Electronics Jacquard
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Dobby Shedding
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10. Path followed by the warp threads in an open shed is longer
Shed Geometry and shed characteristics require a great consideration and precision because it is the zone in which the yarns are converted into fabric . The basic function of weaving are performed in this area
Path followed by the warp threads in an open shed is longer
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The path followed by the warp threads in an open shed is longer.
The additional length required for warp ends should be taken either by the warp extension or
by the regulation of the yarn delivery
(in this case the warp yarns are withstood the higher tension forces when the shed is opened)
(In this case tension acting on the warp yarn is constant but position of the cloth fell is moveable).
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Longer back shed is preferable to get a less degree of warp tension in open shed
Shorter back shed length assists in separation of the upper and lower warp sheet and formation of clear shed , preferable for weaving fabrics from hairy coarse yarns
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14. The means of weft insertion
Size of shed
Shed opening is determined by
The means of weft insertion
Beat up motion
It is desirable to have a small shed opening in order to reduce the lift of Heald frames and therefore to reduce the stress non the warp
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Raising Back Rest
If the back rest is above normal position alternate warp threads will be relatively slack and therefore free to move laterally to achieve a more uniform spacing
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Types of Shed
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Timing of shedding
Shedding timing is synchronized with picking and beat-up timing
There are three shedding timing
Normal shedding
Early shedding n
Late shedding
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Normal shedding
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Heald staggering is done ton reduce the abrasion between the warp yarns when healds are crossing each other.
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During the weaving of heavy fabric like denim , canvas, satin duck, etc. the force required to push the weft is high.
so there may be bumping of fabric To avoid this weaving resistance, asymmetric shedding is used. In this shedding the time and duration of movement of the tap and bottom shed line is so adjusted that they cross below the mid lift position. At this point of crossing the yarns at the bottom shed line are under high tension and those at the top shed line.
as the reed beats up the weft , the slack top shed line yields and permits the weft to be pushed to the fell of the cloth with relative ease. So it is easy to weave even heavy fabric.
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