Positive
dobby: The dobby which can raise and lower the heald frame without the use
of an additional reversing motion is called a positive dobby. positive dobby is used For weaving heavy fabrics such as fancy woolen and worsted
Negative
dobby: only raises the shafts is done by the Negative dobby. Lowering is carried out
by spring under motion. For light to low medium weight fabrics, Negative dobbies are used
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Positive dobby
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Negative dobby
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1. The dobby can raise and lower the heald shaft.
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1. It can raise the heald shaft and lower is done by other mechanisms.
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2. The additional arrangement is not required.
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2. Additional arrangement (dead
wt. /spring) is required.
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3. Normally open shed is produced.
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3. Closed/semi-open shed produced.
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4. Low speed.
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4. High speed.
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5. Less stress & strain on the warp.
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5. More stress & strain on the warp.
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6. Heavy fabric like worsted is produced.
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6. Light fabric like cotton is produced.
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7. This loom is driven by the crankshaft.
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7. Driven by the bottom shaft.
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