Dobby Drive Mechanism Explained
A double-acting dobby requires a mechanism capable of both lifting and positively lowering the healds to create complex patterns. Understanding the source of this drive motion is key.
Driving Source Identification
The primary motion for operating a double-acting dobby in a loom comes from the main drive system. This system provides the necessary rotational input to power the dobby's intricate shedding mechanism.
Role of the Bottom Shaft
- The bottom shaft (also known as the primary or main shaft) is a fundamental component of the loom's drive train.
- It receives power from the motor and transmits it to various parts of the loom, including the picking motion and often the shedding mechanism.
- For a double-acting dobby, the rotational motion from the bottom shaft is typically converted via gears, cams, or linkages to drive the dobby's internal levers and jacks, which control the precise movement of the healds.
Why Other Shafts Are Less Likely
- Crank shaft: While essential for the loom's operation, it primarily drives the picking mechanism or the main loom speed.
- Tappet shaft: Used in tappet looms for controlling shedding, not typically the primary input for a dobby.
- Rocking shaft: Often part of the dobby's internal mechanism or connected to the healds, but not usually the initial drive source from the loom's main power transmission.
Therefore, the bottom shaft provides the essential input power required to operate the double-acting dobby mechanism.
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.
