Difference between a positive and negative dobby

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	Negative dobby
1. The dobby can raise and lower the heald shaft.	1. It can raise the heald shaft and lower is done by other mechanisms.
2. The additional arrangement is not required.	2. Additional arrangement (dead wt. /spring) is required.
3. Normally open shed is produced.	3. Closed/semi-open shed produced.
4. Low speed.	4. High speed.
5. Less stress & strain on the warp.	5. More stress & strain on the warp.
6. Heavy fabric like worsted is produced.	6. Light fabric like cotton is produced.
7. This loom is driven by the crankshaft.	7. Driven by the bottom shaft.