Download - Cam Dobby and Heald Reversible motion
Presentation Topic:-Cam Dobby & Heald Reversing Motion
Submitted to:- Er. Urvashi Malhotra
Submitted by:- Suraj ( BT4090032)
T.E.-4th sem.
SHEDDING MECHANISM
INTRODUCTION
Shedding is the raising of the warp yarns to form a shed
through which the weft yarn, carried by the shuttle, can be
inserted. The shed is the vertical space between the raised and
upraised warp yarns.
The shedding mechanism separates the warp threads into two
layers to form a tunnel known as shed. A shed may be formed
by means of tappets, dobby, and jacquard.
CLASSIFICATION
Shedding mechanism
TappetShedding Dobby Shedding Jacquard Shedding
Negative Positive Negative Positive
*Dobbies are further subdivided into;(a) single lift, single jack;
(b) double lift, double jack.
The production of the patterns on tappet shedding is
limited to 8 or 16 heald frames.
Dobby shedding is one such improved mechanism for
patterns requiring upto 24 heald frames.
In this case the healds are all operated by jacks and
leavers and occupy less spaces as compared to tappet
shedding mechanism.
DOBBY SHEDDING
In case of modern dobbies the knives are actuated by
means of cams mounted on a shaft.
The T-lever and the connecting rod to the bottom shaft
sweep is totally discarded.
The cams are driven by a chain from the crank shaft.
With the design of cam shape, a dwell can be provided as
obtained in the case of tappet shedding.
CAM DOBBY
CAM DOBBY
•The actuating of the knives by
cams.
•The bowls on the knife levers are
kept always in contact with the
cams, by special springs.
• the knives are only pushed by the
cams and returning is carried out by
springs.
•Therefore these cams can be
considered as negative in action.
A= Cams; B= I-lever; C= Knife; D= Hook; E= Baulk
lever; F= Jack; G= Connecting rod; H=Sector; I= Chain;
M= Feelers; N= Needles.
Clearer loom alley space.
Reduced warp breakages.
Very smooth movement of healds which protects heald frames
and heald wire from damage.
Amount of lift can be raised or reduced that is suitable for
particular type of warp.
Cams can be designed to give the required dwell period,for
60º,90º and 120º of crank shaft revolution according to loom
width, speed of operation and type of fabric.→ other
advantages like
clearer passage for shuttle flight.
Economy in power due to reduction in picking force.
ADVANTAGE OF CAM DOBBY
HEALD REVERSING MOTION
Main disadvantage of this motion:-
• When the heald frame is raised →
spring stretches thus adding strain
on the lifting mechanism.
• Heald frame will vibrate in case
the spring position is not correct or
very light springs are used or
elasticity of springs is reduced due
to constant oscillating movement.
A= Single jack , B= Heald Frame,
C= Spring.
HEALD REVERSING MOTION
• It consists two stands M which
are mounted on a rail beneath
the heald frame.
• At the top of the stand there is a
tumbler lever N fulcrumed at O
and held against a check pin P by
springs.
• Lower end of tumbler lever is
connected to heald frame by
means of a spring.
M= Stand, N= Tumbler lever, O= Fulcrum,
P=Check pin, S= Spring.
HEALD REVERSING MOTION
• When heald frame is raised→
point of connection for spring
passes the centre and so the
stress is transferred to fulcrum
point O, & there is less tension
on heald frame.
• Max. tension is exerted on heald
frame when point of connection
is below the check pin P, i.e., the
heald is down.
M= Stand, N= Tumbler lever, O= Fulcrum,
P=Check pin, S= Spring.
Thank you