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
Crank, cam and dobby mechanisms control the harnesses which lift the shafts. Jacquard machines control the individual warp yarns. Each system is outlined below:
Crank shedding mechanisms are simple and relatively cheap to use. However it 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. This system is only used in air-jet and water-jet machines where high speed is achieved.
Cam shedding is also simple and inexpensive. 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.