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