CRANK (TREADLE) SHEDDING of Modern Shedding
This is the simplest and least expensive shedding system. In this system, the harness motion is provided by the crankshaft of the weaving machine. A wheel is rotated a half turn for each crankshaft revolution. The harness is linked to the wheel through a lever arm and a drive pin. In each weaving cycle, the harness changes its position, therefore, this system is used only for plain weave and its derivatives. These systems are used in air-jet and water-jet machines where speed is generally high.
Cam Shedding
- The heald shaft motion is operated by cams or eccentrics
- These motive cams convert the rotary motion of the main shaft of the weaving machine into the reciprocating motion of the heald frames.
- Cam operated shedding mechanism may be positive or negative in action
- Positive shedding: heald shafts are both raised and lowered by the cams or eccentric system of the shedding mechanism.
- Negative shedding: heald shafts are either raised or lowered by the mechanism, but are returned by the action of some external device, such as springs, hence, they must be provided with reversing motion.
Cam Design -Negative Cam Shedding
Cam design-Positive Cam Shedding
Two types of system are available for positive cam shedding which ensures controlled lifting and lowering of healds. No heald reversing motion is required in case of positive cam shedding.
- Grooved cam
- Matched cam
Positive Cam Shedding- Grooved Cam System
The grooved cam track is formed on a circular disc. The bowl or follower is attached at one end of the quadrant (tappet lever). When the cam rotates, the bowl moves upwards and downwards and this movement is translated into sidewise movement of lower end of tappet lever. The heald is also raised and lowered by using levers and link systems.
Positive Cam Shedding- Matched Cam System
In matched cam system, two cams and two followers are required for controlling a single heald. In the Figure , two followers (shaded and un-shaded) are attached on the two sides of the lever L which is fulcrumed at point F. The shaded follower is controlled by the shaded cam and the un-shaded follower is controlled by the un-shaded cam. The Figure shows that when the shaded follower is touching the minimum radius of the corresponding cam, the un-shaded follower is touching the maximum radius of the corresponding cam. The situation will be reversed when the cam shaft will rotate by 90°. That implies, when the shaded follower will be pushed towards the right side, the un-shaded follower will be accommodated by the corresponding cam. Thus the lever (L) will rotate clockwise about fulcrum point F. This will cause the lifting of the heald through the connections.
