Dobby Shedding Mechanism?

Dobby Shedding Mechanism?

Dobby Shedding:

This is a compact, electronically guided shedding motion and capable of getting up to twenty-eight shafts. additional complicated and versatile shedding motion. A dobby loom, therefore, will have up to twenty-eight shafts, and far larger weave repeat is possible. the design could also be woven with 2 or additional basic weaves and their variation. Such fabrics could also be referred as dobby cloths or dobby weave, towels typically show geometric designs when the pattern is provided by dobby.

The scope of Dobby:

• It can produce the more complex design.
• Theoretically, it can control maximum 48 heald frame but practically 36.
• For cotton yarn, it can control maximum 48 heald frame.
• Production is less than tappet.

Classification of dobby:

1. According to lift:
(a) Single lift
(b) Double lift

2. According to figuring capacity (no. of heald shaft):
48’s, 36’s, 24’s, 20’s, 16’s, 12’s

3. According to the position of heald shaft:
(a) Vertical
(b) Horizontal

4. According to the driving of heald shaft:
(a) Positive
(b) Negative

5. According to shed:
(a) Bottom close shed
(b) Centre close shed
(c) Semi-open shed
(d) Open Shed

6. According to no. of jack lever:
(a) Single jack lever
(b) Double jack lever

7. Broadly dobby shedding can be classified as below:
(a) Ordinary dobby (i.e. single jack lever, single lift dobby)
(b) Special dobby (i.e. double jack lever, 48’s dobby)

The principle of Negative Dobby Shedding:

In this variety of shed, lowering of the heald frame occurred automatically.

Construction:

In the negative shedding, the heald frames are operated by the jack & lever. The levers are connected with the knife and also the knifes are connected with the driving rod by means that of connecting needle. A pattern is used here in line with the weave plan. when the teeth of the chain come to the contact of chain drum then whole the arrangement moves along and lowering of the heald frame is occurred by the spring.

Working Principle:

The lowering of the heald frame is happening here by spring or jack lever. when the pattern cylinder doesn’t find peg on the pattern drum then bauck lever and jack lever bring the heald frame downward direction, so the the lowering of the heald frame is occurred by means that of spring tension.

Advantages of Negative Dobby:

• Highly complex and critical fabrics can be weaved.
• At a time it can control many heald frame
• More faster than the positive dobby as well as over conventional loom
• Can produce close bottom shed

Disadvantages of Negative Dobby:

• In this shed only lowering of the shed is possible
• Due to more stress, yarn breakages additional
• It is not good for heavier fabric
• It does not provide more high speed to the loom

Positive Dobby Shedding:

Principles of positive dobby, In this variety of shed lifting & lowering of the heald frame, each is possible. lifting is occurred by means that of jack & lever, and lowering is occurred by means that of spring under tension.

Construction and Working Principle:

Positive dobby shedding is that the combination of 3 Cylinders, jack lever, spring and a shaft. Between the 3 cylinders, a shaft is a pin in one side the upper cylinder moves because the opposing clockwise and lower cylinder moves because of the clockwise direction. the main cylinder when getting motion from the shaft when it found peg or pattern plan then the cylinder connected to the higher half-toothed disc. so the heald frame is up,& when the pattern cylinder doesn’t found peg then the main cylinder connected to the lower half-toothed disc and also the spring retains the heald frame to the downward direction.