You can find the diffences between mechanical and electronical dobby mechanisms in principle in this presentation. Also , you can reach the details of dobby mechanisms type like as of single , double and negative dobby systems.

1. DOBBY MECHANISMS
-KEIGHLEY DOBBY (NEGATIVE- DOUBLE LIFT)
Fall Term Project
Submitted by:Aybala ÖZCAN
Submitted to: Prof.Dr.Mehmet TOPALBEKİROĞLU
10.01.2013

2. DOBBY MECHANISMS
 are more complicated than cam systems,
 have higher initial and maintenance costs,
 can produce more sophisticated weaves,
 are normally built to control 12, 16, 20, 24, 28 up to 30heald
frames.
 Picks per repeat are virtually unlimitedin dobby shedding.
 Due to their complexity, dobby mechanisms are moreliable to
produce fabric faults than cam systems.

3. DOBBY MECHANISMS
 Dobby mechanisms are classified as negative,positive
and rotary dobbies, they can be mechanical or electronic.
 In negative dobby shedding the heald frames are liftedby
the dobby and lowered by a spring reversing motion.
 In positive dobby shedding, the dobby both raises
and lowers the heald shafts.
 Today, the trend is away from negative dobby to
electronically controlled positive dobby mechanisms,
whichcan operate at very high speeds.
 Rotary dobbies have been largely replaced the Hattersley
dobbies in the last decade.

4. Mechanical Dobby Electronic Dobby
The mechanical dobby chain and
pegs are used
Computer controlled shaft selection
The construction of shaft sequences
is done by building a mechanical
dobby chain.
Construction is done on computer
screen with weave software’s.
A little bit tougher way to design
fabric.
More intuitive way to design fabric.
Unable to visualize the repeated
designs in fabric in mind.
Can visualize the repeated weave
design on the screen.
Loading and swtching of weave drafts
takes longer time.
Loading and switching of weave
patterns can be done in seconds
without getting up from the loom.
Tedious work in designing and
producinh fabric.
Emove tedious work in designinh and
producing the fabric.

5. DOBBY MECHANISMS
Depending on their performance they are divided into single-lift
and double-lift dobbies.
 Single-lift dobbies are the oldest:
• All system elements perform their function once every
weaving cycle to open a shed, and then they return to their
original positions before a new cycle.
• The shed is closed after every weft insertion and the pick is
beatenup at the closed shed (center-closed shed)
• Advantageous in the wool weaving in the past.
• The speed of single-lift dobbies is limited to 160 to 180 rpm.

6. DOBBY MECHANISMS
 Double-lift dobbies:
• All new type dobbies are double-lift in their action.
• Its cycle occupies two picks.
• System elements operate once every two weaving
cycles, butthe shed opening is achieved every pick.
• Most of the motions in dobby occur at half time loom
speed.
• Open shed is produced; unnecessary, wasted
movements are eliminated.
• Suitable for high speed operations.

7. DOBBY MECHANISMS
 The dobby consists of three principal mechanisms:
The drive mechanism:An auxiliary shaft is permanently
drivenfrom the weaving machine.
-It operates two steel bars (knives), having a regular
reciprocating motionor
-It operates coupling rings on a rotary dobby.
The selection mechanism:It is operated by a dobby card (or
by some form of pattern chain or by a magnetic disc.)
-It reads or checks the design information punched on a
dobby card, and transmits the necessary movement from
the drive mechanism to thelifting mechanism.
The lifting mechanism operates the heald shaft motion.

8. DOBBY MECHANISMS
 Dobby mechanisms are classified as negative,positive and
rotary dobbies, they can be mechanical or electronic.
 In negative dobby shedding, the heald frames are liftedby the
dobby and lowered by a spring reversing motion.
 In positive dobby shedding, the dobby both raises and lowers
the heald shafts.
 Today, the trend is away from negative dobby to electronically
controlled positive dobby mechanisms, which can operate at
very high speeds.
 Rotary dobbies have been largely replaced the Hattersley
dobbies in the last decade.

9. Selection electro
magnetic unit
ratchet
jack
drive
Lifting:controllable crank disk
(cam unit) and jack

10. STÄUBLI ROTARY DOBBY OF THE SERIES
2600
Jack
Cam Unit
Connecting Rod
Driver
Ratchet
Control Lever
Selector
Magnet Bar

11. Selection:
1-magnetbar;
2-selector;
3-control lever
Harness frame
motion:
4-ratchet ;
5-driver;
6-cam unit;
7-connecting rod;
8-jack
Drive: modulator
STÄUBLI ROTARY DOBBY OF THE SERIES 2600

14.  In the diagram, the heald shaft has been raised by moving thetop
end of the baulk B away from its stop bar S
 This has happened because the top knife K has previously engaged
thehook H, and has drawn the top end of the baulk B away from its
stop bar S, this action causing the baulk to pivot about the point of
contactbetween its lower end and the stop bar S.
 The knife K was able to engage the hook H, because a peg in the
lag forming part of the pattern chain had raised the right-hand end
of thefeeler F, which thus allowed the rod R to lower the hook H,
onto theknife K . In the diagram, there is no peg to support the
right-hand end of the feeler F, which has therefore fallen, this fall
allowing its upturned left-hand end to raise the hook Hclear of the
knife K

15. KEIGHLEY DOBBY (NEGATIVE- DOUBLE LIFT)
 As the action continuous, the top end of the baulk will be
returned toits stop bar, and at the same time the bottom knife
will move to theright without disturbing the bottom end of
the baulk.
 The shaft will therefore be lowered and will remain down for
the nextpick.In the absence of a peg, the shaft is lowered or
remains down.
 A peg will lift the shaft, and a succession of pegs will keep the
shaftraised.
 Some form of spring undermotion, acting through the shaft and
itsconnections to the baulk, keeps one end of the baulk in
contact withits stop bar while the other end is being displaced.
Alternatively, itkeeps both ends of the baulk in contact with the
stop bars when theshaft is not being raised.

16. THE FULL CYCLE OF OPERATIONS BY THE
SIMPLIFIED LINE DIAGRAMS
In each diagram,the knives are shown at one extreme of their movement.Selection
for the next pick
Necessarily takes place while the hook is in contact with its stop bar because only
then can the hook engage or disengage its knife

17. THE MECHANISM OF PEGGING THE LAGS FOR
A KEIGHLEY DOBBY

18. THE MECHANISM OF PEGGING THE LAGS FOR A
KEIGHLEY DOBBY
 The method of pegging the lags for
a Keighley dobby
 Each lag serves for two picks.
 The holes in the lags are staggered
to correspond with the positions
of the feelers.
 The pattern barrel is turned
intermittently by a Geneva wheel
orsimilar motion so as to present a
new lag every second pick.
 In the diagram of the lags, a filled
circle represents a peg.
 In practice, it would be necessary to
peg two or more repeats of
the weave in order to have a pattern
chain sufficiently long to encircle
therotating barrel that presents the
lags to the feelers.

19. HEALD SHAFT CONNECTIONS FOR NEGATIVE
DOBBIES
 There are many different
methods of connecting the
centers of the baulksto their
heald shafts.
 Negative dobbies are always desi
gned to raise the shafts, and thec
onnections are therefore made
between the baulks and the tops
of theshafts.
 In diagram A, the main jack, J,
has a fixed fulcrum at F. It is
connectedby a link L to a
secondary jack, J, which is
fulcrummed at F.The healdshaft
is suspended from cords attached
to the outer ends of the two
jacks. Alternative points of conn
ection allow the lift of individual
shafts to bead justed.

20. HEALD SHAFT CONNECTIONS FOR NEGATIVE
DOBBIES
 In diagram B, an elbow lever,
L,which is fulcrummed at F,
carries atoothed quadrant , Q,
which engages a similar
toothed quadrant, Q. This
iscarried on an extension of
lever L, which is fulcrummed
at F. The upperend of the
lever L, is connected by a
strap S to the top of the jack J.
Thispoint of attachment
provides adjustment for the
lift of the shaft.
 A disadvantage of the systems
of connection shown in C and
D is that thetwo ends of the
heald shaft do not necessarily
receive the same lift.

21. HEALD SHAFT CONNECTIONS FOR NEGATIVE
DOBBIES:FOURPOSSIBLE ARRANGEMENTS
In each diagram, the arrow represents the link from the center of
the baulk tothe heald frame .

22. HEALD SHAFT CONNECTIONS FOR NEGATIVE
DOBBIES
 Type of connections which necessitate thepositioning of
bearings, and of numerous metal partsin rubbing contact with
each other,above the warpmay causesome problems.
 It is essential to fix a tray underneath the moving
partsto catch oil drips, which are always heavily contaminated
with dark-colored metallic impurities.
 Stains on the warp produced by dirty oil are very difficult to
remove, and, if not completely removed,may cause tendering of
the yarn during bleaching.

23. SPRING UNDERMOTIONS FOR NEGATIVE
DOBBIES
 Similar to the cam shedding, spring reversing motion is an
inefficientarrangement because the tension in the springs is
the least when theshafts are down, which is when the springs
should be performing boththeir functions.
 Nevertheless, this simple system has been widely used for
weaving lightweight fabrics, which can be woven with a
relatively low warptension.
 As the warp tension increases, stronger springs have to be
used toovercome the vertical component of the warp tension.
This tends tobend the heald-shaft frames when the shafts are
lifted and the springsare fully extended.
 A widely used device, which is designed to avoid an increase
in spring tension when the shafts are raised, is the Kenyon
undermotion.

24. DISADVANTAGES OF NEGATIVE DOBBIES
 Negative dobbies consume much energy to overcome
the warp tension, the heald shaft weight and the reversing motion
pull during heald shaft lifting.
 This results in increased irregularity in the operation of
the weaving machine.
 Another disadvantage is the somewhat uncertain bottomposition
of the heald shaft and an irregular shed is formed.
 To avoid this,positive dobbies have been developed which
operate with a constrained heald shaft motion in bothdirections,
i.e. with positive heald shaft lifting and lowering.

25. REFERENCES
1-http://tr.scribd.com/doc/54758469/8-Weaving-C4c-
Dobby-09
2-http://tr.scribd.com/doc/104507645/Shedding-
Dobbies
3-http://tr.scribd.com/doc/62223628/E-DOBBY