Dobby Shedding
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Transcript of Dobby Shedding
Dobby Shedding
Dobby Mechanisms have higher initial and
maintenance costs, are normally built to control
12, 16, 20, 24, 28 up to to 30 heald frames
Picks per repeat are virtually unlimited in dobby shedding
Due to their complexity, dobby mechanisms tend to produce more faults than cam systems
Dobby Mechanisms
Negative
PositiveRotary
Negative dobby shedding, the Harnesses are lifted by the dobby and lowered by a spring reversing motion.
Positive dobby shedding, the dobby raises and lowers the shafts.
Rotary dobby shedding, is a positive machine operating according to the rotary principle.
Dobby Mechanisms
Single-lift dobbies (oldest) All system elements perform their
function once every weaving cycle to open a shed. And then they return to their original position before a new cycle
The shed is closed after every weft insertion and the pick is beaten up at the closed shed
Advantageous in wool weaving in the past The speed of single-lift dobbies is limited
to 160 to 180 rpm
Double-lift dobbies All new type dobbies are double-lift in
action. System elements operate once every
two weaving cycles, but the shed opening is achieved every pick.
Most of the motion in dobby occurs at half time loom speed.
Open shed is produced: unnecessary, wasted movements are eliminated.
Suitable for high speed operations.
Dobby MechanismsDobby consists of three mechanisms1. Drive mechanism: An auxiliary shaft
is permanently driven from the weaving machine.
2. Selection mechanism: It is operated by dobby card
3. Lifting mechanism: operates the heald shaft motion
Card cylinder
Card cutting machine
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