cams knitting technology

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Documentation On Knitting Cams By: Amalesh,Kalpana, Preet(A.P-4) NIFT-Bangalore

Topic: Knitting Cams

Submitted To: Mr. Abdul Salam Sait

(Dept. Of Fashion Technology)

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ACKNOWLEDGEMENT

This is to express our heartfelt gratitude to Mr. Abdul salam Sait, faculty

in-charge(knitting technology) for his constant guidance and support

throughout the course of the study. We would also like to thank our

friends for all their help and assistance.

AMALESH DEKA

KALPANA

PREETKAMAL

(APPARELPRODUCTION-4)

NIFT-Bangalore

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CONTENTS

1. INTRODUCTION........................................................4

2. KNITTING CAMS...................................................7

3. USAGE OF CAMS IN VARIOUS KNITTING

MACHINES.....................................................14

4. ANNEXURES.............................................18

5. BIBLIOGRAPHY.........................................19

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INTRODUCTION

A cam may be defined as a machine element having a curved outline or a curved

groove, which, by its oscillation or rotation motion, gives a predetermined specified

motion to another element called the follower. The cam has a very important function

in the operation of many classes of machines, especially those of the automatic type,

such as printing presses, shoe machinery, textile machinery, gear-cutting machines,

and screw machines. In any class of machinery in which automatic control and

accurate timing are paramount, the cam is an indispensable part of mechanism. The

possible applications of cams are unlimited, and their shapes occur in great variety.

The transformation of one of the simple motions, such as rotation, into any other motions is often conveniently accomplished by means of a cam mechanism. It is a rotating or sliding piece in a mechanical linkage used especially in transforming rotary motion into linear motion or vice versa. A cam mechanism usually consists of two moving elements, the cam and the follower, mounted on a fixed frame. Cam devices are versatile, and almost any arbitrarily-specified motion can be obtained. In some instances, they offer the simplest and most compact way to transform motions. A common example is the camshaft of an automobile, which takes the rotary motion of the engine and translates it into the reciprocating motion necessary to operate the intake and exhaust valves of the cylinders.

A CAM has two parts,

The FOLLOWER and

The CAM PROFILE.

Fig 1.1CAM WITH NOMENCLATURE

http://en.wikipedia.org/wiki/Camshaft

http://en.wikipedia.org/wiki/Automobile

http://en.wikipedia.org/wiki/Poppet_valve

http://en.wikipedia.org/wiki/Cylinder_(engine)

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TYPES OF FOLLOWERS

There are different types of follower but they all slide or roll on the edge of the cam.

Follower Configuration

1. Knife-edge follower (Figure 1-2a) 2. Roller follower (Figure 1-2b,e,f) 3. Flat-faced follower (Figure 1-2c) 4. Oblique flat-faced follower 5. Spherical-faced follower (Figure 1-2d)

Fig 1.2 TYPES OF FOLLOWERS

http://www.cs.cmu.edu/~rapidproto/mechanisms/chpt6.html#HDR87




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CLASSIFICATION OF CAM MECHANISMS :

We can classify cam mechanisms by the modes of input/output motion, the

configuration and arrangement of the follower, and the shape of the cam. We can

also classify cams by the different types of motion events of the follower and by

means of a great variety of the motion characteristics of the cam profile.

Cam classification on the basis of cam shape

1. Plate cam or disk cam: The follower moves in a plane perpendicular to the axis of rotation of the camshaft. A translating or a swing arm follower must be constrained to maintain contact with the cam profile.

2. Grooved cam or closed cam : This is a plate cam with the follower riding in a groove in the face of the cam.

Fig. 1.3 Grooved cam

3. Cylindrical cam or barrel cam (Figure 1.4a): The roller follower operates in a groove cut on the periphery of a cylinder. The follower may translate or oscillate. If the cylindrical surface is replaced by a conical one, a conical cam results. 4. End cam (Figure 1.4b): This cam has a rotating portion of a cylinder. The follower translates or oscillates, whereas the cam usually rotates. The end cam is rarely used because of the cost and the difficulty in cutting its contour.



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Fig 1.4 Cylindrical cam and end cam

Cam classification on the basis of follower arrangement

1. In-line follower: The center line of the follower passes through the center line of the camshaft.

2. Offset follower: The centre line of the follower does not pass through the center line of the cam shaft. The amount of offset is the distance between these two center lines. The offset causes a reduction of the side thrust present in the roller follower.

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KNITTING CAMS

All needles have a reciprocating action .In knitting technology cams are the devices which convert the rotary motion drive into a suitable reciprocating action for the needles and other elements.

The needle displacements necessary for knitting together with the closing element displacements in the case of compound needles and the sinker movements are all derived from cam systems that traverse the machine and are located within the carriage.

In essence the butts of the needle are caused to impact with the inclined plane of the cam system and the reaction forces cause the needle to move in the required direction for the required displacement.

The angular knitting cams act directly onto the butts of needles or other elements to produce individual or serial movements in the tricks of a latch needle weft knitting machine. The knitting cams are hardened steels and they are the assembly of different cam plates so that a track for butt can be arranged. Each needle movement is obtained by means of cams acting on the needle butts.

In the diagram the cam moves from the right and strikes the projecting butt of the needle. The normal reaction force r between the butt and the cam generates a vertical component of force upwards of (Fr cos a ) together with a vertical component downwards of (Fr sin a). The cam angle “a” is designed in such a way that Fr cos a > Fr sin a and the needle moves upwards.

However the balance of forces within the knitting zone is complex and the choice of cam angle has a profound effect on the quality of the fabric.

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Two cam arrangements exist in Knitting Machine:

1. REVOLVING CYLINDER MACHINE:

The needle butts pass through the stationary cam system and the fabric hanging from the needles revolves with them.

REVOLVING CYLINDER CAM SYSTEM CONSISTS OF:

Clearing cam

Stitch and

guard

cams

Upthrow

cam

Guard cam

Cams

provide the

track for

the idling

needles.

2. RECIPROCATING CAM-CARRIAGE FLAT MACHINES OR ROTATING CAM-BOX CIRCULAR MACHINE:

The cams with the yarn feeds pass across the stationary needle beds.

In weft knitting, the yarn feed position is fixed in relation to the cam system.The yarn feed moves with or remains stationary with the cam system ,as do the yarn packages and tackle.( except in the case of flat machines where the cam-carriage only reciprocates away from and towards the stationary yarn packages and does not revolve).

In the past, most garment length knitwear and underwear machines have had revolving cam boxes because changes to the cam settings during the garment sequence can be initiated from a single control position as the cam boxes pass by; also the garment lengths are stationary and may be inspected or removed whilst the machine is knitting.

Fig. 2.1SIMPLEST CAM DESIGN

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Now, most new electronically- controlled garment-length machines are of the revolving cylinder type as electronics have removed the need for the complex arrangement of the rods and level found, for example, on mechanically-controlled half-hose machines.

Knitting cams are attached, either individually or in unit form, to a cam-plate and, depending upon machine design, are fixed, exchangeable or adjustable. In the last case, on garment-length machines this might occur whilst the machine is in operation. Elements such as holding-down sinkers and pelerine(loop transfer) points are controlled by their own arrangement of the cams attached to a separate cam-plate.

At each yarn feed position there is a set of cams consisting of atleast a raising cam, a stitch cam and an upthrow cam whose combined effect is to cause a needle to carry out a knitting cycle if required. On circular machines there is a removable cam section or door so that knitting elements can be replaced.

ROTATING CAM-BOX CIRCULAR MACHINE OR DIAL CAM SYSTEM

CONSISTS OF:

Raising cam

Dial knock-over cams

Guard cam

Knock-over cam

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THE NEEDLE CAM RACE CONSISTS OF

1. CLEARING CAM

Clearing cam is a cam which displaces needles to clearing height.

TUCK cam – a modified clearing cam that raises needles part-way to clearing height such that the old loop remains on the opened latch when a new loop is taken – technically known as tucking in the hook;

miss-knit cam – a modified clearing cam that causes no displacement of the needles at the point where clearing would take place so that the needles neither clear their old loop nor take a new loop into the hook.

2. STITCH CAM

Stitch cam is that cam which displaces cleared needles to the knock over position. The stitch cam controls the downward movement of the needles by adjusting its vertical movement. If the stitch cam is raised then a shorter loop is drawn below the sinker level and a tighter fabric will result. With lowering of the stitch cam, a stitch length will increase and a flimsy fabric will result. It controls the depth to which the needle descends, thus controlling the amount of yarn drawn into the needle loop; it also functions simultaneously as a knock-over cam.

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3. UP-THROW CAM (which are vertically adjustable together for alteration of stitch length.)

The upthrow or counter cam takes the needles back to the rest position and allows the newly formed loops to relax. The stitch cam is normally adjustable for different loop lengths and it may be attached to a slide together with the up throw cam, so that the two are adjustable in unison.

4. GUARD CAM

The guard cams are often placed on the opposite side of the cam-race to limit the movement of the butts and to prevent needles from falling out of track A guard cam when used in conjunction with a stitch cam at a feed in latch needle-knitting machines, which, with the stitch cam, provides there between a confined path of travel for the needless in their stitch-drawing movement and which, by itself, prevents undesirable needle overthrow and provides proper paths of travel for needles moving at the tuck and welt levels. The guard cam is adjustable in a direction at right angles to the direction of adjustment of the stitch cam whereby a fixed distance may be maintained there between.

5. RETURN CAM

Sinkers are supposed to move backward and forward in relation to needles. A

separate set of separate cams is contained in the sinker ring. Its time is

synchronised to needle timing and is called a return cam.

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6. Raise CAM

The raising cam causes the needles to be lifted to either tuck, clearing, loop transfer or needle transfer height, depending upon the machine design.

Sometimes, swing cams or auxiliary cams are placed between the rising cams and the stitch cams to change the path of the needle butts to form a raceway and the needle butts travel in this restricted path according to the different stitch requirements.

7. SINKER WITHDRAWING CAM 8. SINKER-RETURN CAM (which is adjustable in accordance with the stitch

length.)

The swing cam is fulcrummed so that the butts will be unaffected when it is out of the track and it may also be swung into the track to raise the butts.

The bolt cam can be caused to descend into the cam track to control the element butts or be withdrawn out of action so that the butts pass undisturbed across its face; it is mostly used on garment-length machines to produce changes of rib set-outs.

Separate cam-boxes are required for each needle bed or associated element bed and they must be linked together or co-ordinated. If the cam-box itself is moving from right-to-left, the needle butts will pass through in a left-to-right direction.

On circular fabric machines, the cams are designed to act symmetrically arranged to act in both directions of cam-box traverse, with only the leading edges of certain cams in action.

All cams systems are a compromise between speed, variety, and needle control and selection systems.

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Carriage movement and its influence on knitting:

The needle tracks through the cam system as shown by the blue line in the following

diagram.

USAGE OF CAMS IN VARIOUS KNITTING MACHINES

PURL KNITTING MACHINE (LINKS-LINKS)

In purl knitting machines, there is a cam carriage which moves from right to left and

left to right alternatively, above the needle beds. The carriage has cams which

activate the needles in knitting action.

DOUBLE CYLINDER MACHINES

The double cylinder machine, has divided cams with internal holding down sinkers

and stationary cam boxes. The dividing cam is an internally profiled cut through

recess in a flat plate attached horizontally and externally to the cylinders at the

position, half way between them. There is a recess cam position for the top cylinder

and another for the bottom cylinder in a different position in the same plate. The

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principle of the dividing cam operation is that it forms a wedge shape of increasing

thickness between the upper surface of the needle hook and the under surface of the

extended nose of the delivering slider, pivoting it away from the cylinder so that it

disengages from the needle hook .

1) The delivering slider advances with its nose so that the nose of the slider

enters the profiled recess of the dividing cam so that the outer hook of the

needle contacts the hook underneath the head of the receiving slider pivoting

it, out of the cylinder but it immediately returns.

2) It engages with the needle hook due to

the pressure of the coiled spring band,

which surrounds each cylinder, so that

the slider heads are depressed into

contact with the needle hook.

3) As slider revolves with the cylinder, it

passes along with the wall of the dividing

cam which when increases in thickness

causes the slider pivot outwards and

disengages from the needle hook as

shown in this sketch. Slider then returns

to its cylinder while the slider retires into

its cylinder taking the needle with it, ready

for the next knitting head.

FORMATION OF FLOAT AND TUCK LOOPS

To intermesh a newly formed loop, the needle hook in which the new looped yarn is

trapped should rise high enough to clear the old loop resting in the closed latch or

„needle hook‟ by raising or clearing cam acting on the butt of the needle. The

clearing cam is the most important cam in the system because by simple

modification or adjustment of this clearing cam, a float (or miss) stitch and tuck stitch

can be formed in addition to a „knit stitch‟.

FLOAT (OR MISS) LOOP:

If the needle is not raised by the clearing cam it does not receive the new yarn and

the yarn goes behind the needle. The yarn remains behind the needle and appears

in the fabric as a float .The knit loop not cleared is called the „held loop‟. When the

needle is raised on the subsequent course the new knit loop is pulled through the

held loop only.

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TUCK LOOP:

If the needle is not raised to its clearing position or not raised at all but is partially

raised by the clearing cam so that the old loop is not cleared from the latch of the

needle but the feeder has fed a new yarn into the hook then a tuck stitch is formed

when the needle moves down. In this case the new yarn and the held loop is in the

hook of the needle. This forms a „tuck stitch‟ when the needle moves down. The held

loop and the new yarn-both are in the hook.

THE SWING CAM:

In order to produce tuck/or float loop, the clearing cam must be modified. One

common way to this is to replace the solid „clearing or raising cam‟ with an adjustable

swing cam. Tuck stitches may occur singly or on the same needle at successive

knitting cycles or across adjacent needles.

For knitting double jersey structure either a four cam tracks in cylinder and/or

dial or many needle selection and controlling devices are required to be

provided on a weft knitting machine. These machines are complex in their

mechanism, just as dobbies or jacquards are, for woven structures.

For non jacquard machines cam tracks upto four tracks in cylinder and two

tracks with swing cams for dial are used. The needles used are not only long

and short needles but needles to work in different cam tracks to form knit, tuck

and float stitches in the same course. With float or welt loops generally

narrower and elastic fabrics than fabrics comprised entirely of normal knit

loops are produced. Tuck loop fabrics are generally wider, thicker and shorter,

than plain-knit ones.

CAMS IN SINGLE KNIT MACHINES

Plain knit or single jersey fabrics are

made on machines having a single cam

track. Cam track is the guided that the

needle butt takes through the group of

cams. The adjustable cams in the

system are the stitch cam and the

raising (clearing cam). This swing cam

may be actuated to cause all the

needles to knit, tuck or miss. Pre-set

positions are indicated on the exterior of

the cylinder.

The swing cams act only on long butts.

And the stitch cam acts on both long

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butt needles operating in the track A and also on the short butts belonging to needles

running in the other tracks. With these multi-track machines many non-jacquard

designs are produced. Jack raising cam is also used in multi-step pattern drum.

THE CAM SYSTEM OF THE V-BED MACHINE

The single knitting cam-box is symmetrically designed for knitting a course of loops

on both the front bed and back bed needles during a right-to-left traverse and a

second course during the return left-to-right cam box traverse.

The cam system on a v-bed machine reciprocates and therefore the cam system

must allow the needle to travel through in either direction. For this reason v-bed cam

systems are essentially symmetrical.

The needle butts will enter the traversing cam system from the right during a left-to-

right cam box traverse and from the left during the right-to-left traverse. For each

needle bed there are two raising cams, two cardigans cams and stitch cams.

In the direction of traverse, the leading raising cam is responsible for knitting and the

trailing raising cam acts as a guard cam. The leading stitch cam is raised out of

action and the trailing stitch cam is in operation. In the reverse direction of traverse,

the roles of the two raising cams and of the two stitch cams are reversed. A raising

cam lifts the needle to tuck the height, but if the cardigan cam above it is in action

the needle is lifted to full clearing height. Thus the cardigan cam is taken out of

action if a tuck stitch is required. To produce a miss stitch, both the raising cam and

the cardigan cam are out of action . To produce a course of tubular plain knitting, a

pair of raising cams that are diagonally opposite each other in each bed are out of

action.

V-bed Cam geometry

Sl :LHS Stitch Cam

Sr :RHS Stitch Cam

Al :LHS Raising Cam

Ar :RHS Raising Cam

B :Clearing Cam

C:Guide Cam

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ANNEXURES

KEY TERMS RELATED TO CAMS

ONE CYCLE one rotation/revolution of the cam

DWELL when the cam rotates but the follower does not rise or fall

THE RISE that part of the cam that causes the follower to rise.

RETURN is the motion of the follower toward the cam centre

CAM NOMENCLATURE

Trace point: A theoretical point on the follower, corresponding to the point of a fictitious knife-edge follower. It is used to generate the pitch curve. In the case of a roller follower, the trace point is at the centre of the roller.

Pitch curve: The path generated by the trace point at the follower is rotated about a stationary cam.

Working curve: The working surface of a cam in contact with the follower. For the knife-edge follower of the plate cam, the pitch curve and the working curves coincide. In a close or grooved cam there is an inner profile and an outer working curve.

Pitch circle: A circle from the cam centre through the pitch point. The pitch circle radius is used to calculate a cam of minimum size for a given pressure angle.

Prime circle (reference circle): The smallest circle from the cam centre through the pitch curve.

Base circle: The smallest circle from the cam centre through the cam profile curve.

Stroke or throw: The greatest distance or angle through which the follower moves or rotates.

Follower displacement: The position of the follower from a specific zero or rest position (usually it‟s the position when the follower contacts with the base circle of the cam) in relation to time or the rotary angle of the cam.

Pressure angle: The angle at any point between the normal to the pitch curve and the instantaneous direction of the follower motion. This angle is important in cam design because it represents the steepness of the cam profile.

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BIBLIOGRAPHY

KNITTING TECHNOLOGY BY DAVID J.SPENCER Knitting Views www.wikipedia.com www.knitepedia.co.uk/.../Cam_technology.htm

http://www.wikipedia.com/

http://www.knitepedia.co.uk/browse/knit_tech/knit_tech/V_bed_machine/Cam_technology.htm

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cams knitting technology