Weave Analysis: Heald Shaft Movement in 2/2 Twill Sheds
The question asks about the heald shaft movement in a 2/2 twill weave over one complete repeat, specifically identifying which shed type results in the least movement.
Understanding Shed Types and Movement
In weaving, the shed is the temporary gap formed between raised and lowered warp yarns through which the weft yarn is passed. Heald shafts control the raising and lowering of warp yarns.
- Open Shed: This mechanism involves one set of heald shafts moving upwards while the other moves downwards, creating a clear opening. This typically requires significant vertical movement.
- Bottom Closed Shed: In this type, one set of heald shafts remains stationary (at the bottom) while the other set moves upwards.
- Centre Closed Shed: A variation where the shed opening is formed towards the centre.
Heald Shaft Movement in 2/2 Twill
A 2/2 twill weave has a specific interlacing pattern. The lifting plan dictates the sequence in which heald shafts move up and down over a complete weave cycle (repeat). This pattern involves sequential raising and lowering actions.
Reasoning for Least Movement
While seemingly counter-intuitive, the open shed configuration can be associated with the least complex or most direct heald shaft movement pattern required to execute the specific sequence for a 2/2 twill weave over its complete repeat. The standard open shed mechanism directly facilitates the necessary up and down motions inherent in the twill's lifting plan, potentially involving less complex intermediate positioning compared to variations required for closed shed mechanisms executing the same 2/2 twill pattern.
Therefore, for the specific requirements of the 2/2 twill weave cycle, the open shed results in the least overall complexity or necessity for non-standard movements.
Important Questions from FABR Loom Mechanisms Shedding
- Group I lists the components of the weaving machine and Group II lists their functions. Match the component with its function.
Group I Group II P Conjugate/matched cams 1 Driving the cloth roller with slip
driveQ Worm and worm wheel 2 Continuous positive take up
motionR Friction clutch device 3 Motion of sley in rapier loom S Lease rod 4 Separation of the warp sheet
forming the shed Amongst the following, the correct condition(s) that will reduce bumping during weaving is/are
- Group I lists weaving machine related parameters and Group II contains the shortcomings of these parameters. Match the machine related parameter with its shortcoming.
Group I Group II P. Variable heald staggering 1. Not favourable for heavy fabric Q. High eccentricity ratio 2. Reduction in shed height R. Fixed heald staggering 3. Reduction of sley dwell S. Late shedding 4. Higher vibration in weaving machine Group I gives a list of loom motions and Group II contains loom systems. Match the motion from Group I with the corresponding system from Group II.
Group I Group II P. Shedding 1. Matched cam Q. Picking 2. Seven wheel R. Beat-up 3. Rapier S. Take-up 4.Jacquard Determine the correctness or otherwise of the following Assertion [a] and Reason [r]
Assertion: In shuttle loom, late shedding is preferred for filament weaving.
Reason: In late shedding, the timing of shed dwell matches with the timing of shuttle travel through the shed, and therefore, it minimises the rubbing of warp yarns.
