FTA (изд-во). Flexography: Principles And Practices. Vol.1-6

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The press is typically equipped with one or

two spindles capable of rewinding rolls to a

diameter of 30" to 40" (762 mm to 1016 mm).

These spindles are independently driven.

Depending on the control mechanism, the

product will be wound under a constant

torque, a constant tension or a controlled

taper tension. Turret rewinds are also avail-

able for continuous operation.

Another means of delivery is in a sheeted

form, known as sheeting. Narrow-web press-

es have a die slot located immediately after

the exit nip and pacing rollers. Ty p i c a l l y, a

rotary crosscut tool is placed in this position

to cut the product to the desired length.

Through-cutting tools are also used in this

position to cut the product into special

shapes. The individual pieces are collected

in either a stacker or a conveyor for easy

bundling and removal. A stacker will gather

the items in a vertical stack. A conveyor will

shingle the pieces horizontally. The stacker

or conveyor must be located immediately

adjacent to the cutting tool. After the web is

cut, only its momentum carries the piece to

the delivery unit. After the product is in the

stacker or conveyor, an acceleration section

transports the individual pieces and creates

a slight gap between them.

The delivery of cut-to-shape folding car-

tons often requires a specialized system. The

unique shape of the cartons, and the need to

minimize waste, create situations where

multiple shapes are interleaved or “nested.”

x To create individual stacks in these cases, it

is necessary to laterally separate the cartons,

or to “de-nest” them. The stackers and con-

veyors used for this process are highly spe-

cialized. Unique delivery systems are also

incorporated into the flat bed die-cutters

used to shape cut folding cartons. These

delivery systems must have the capability to

remove both the waste and the cartons from

the die cutter, as well as to de-nest them.

Narrow-web presses can also be equipped

to deliver the product as a fan-folded stack.

With this delivery system, a perforated web

is fed into a fan-folding and conveying sys-

tem, which is timed to the press speed either

mechanically or electronically. Fan-folding

is commonly used for EDP labels and for

pharmaceutical labels.

PRESSES AND PRESS EQUIPMENT 33

34 FLEXOGRAPHY: PRINCIPLES & PRACTICES

hile this discussion on

web tension applies

mostly to flexographic

presses, it is also rele-

vant for coaters, lami-

nators, slitters, winders,

sheeters and other machines familiar to the

flexographer.

Web-tension control is a very important

function of any web-process machine

because it determines, in large part, the

machine’s production efficiency and the

product’s quality. Inadequate tension control

can severely limit the performance of new

machines. And modern tension controls,

retrofitted to older machines in good condi-

tion, can raise performance to equal or some-

times beyond that of the newest machines.

Web breaks and wrap-ups around driven

rolls (caused by slack web) are only the

most obvious consequences of inadequate

tension control. Here are some others:

• loss of color-to-color registration while

running at speed, splicing or changing

speed;

• deformation of web due to stretching or

wrinkling;

• print-length variations; interleaving of slit

webs; web shifts side-to-side;

• curling or wrinkling of laminating webs;

• variation of coating thickness;

• unwind or rewind core crushing;

• reduction of machine speed to accom-

modate web-handling problems or sheet

length;

• excessive waste of web material; inabili-

ty to run a wide range of web thickness-

es, widths or materials;

• the need for excessive labor to operate

the machine; and

• in general, poor productivity and high

waste.

Many of these problems are simply accept-

ed as normal and are not usually attributed

to web tension, as they should be. However,

anyone who experiences these problems

and recognizes the relationship can improve

efficiency, and profits, by using better ten-

sion-control methods.

TENSION ZONES

A typical flexographic press has more than

one tension zone. This separation exists

because the process in any individual zone

may require a different tension level or pat-

tern than the processes in other zones.

A tension zone is that length of web that

extends from one tension-affecting device

(TAD) to the next. Typical tension-affecting

devices are: unwind or rewind core shaft

with attached motor, clutch or brake; driven

rolls; braked rolls; nip rolls where at least

one roll is driven or braked; drag bars; and

any other device that may add or subtract a

significant amount of tension to or from the

web. Printing, coating or slitting stations are

not normally considered to be tension-

affecting devices, even though driven rolls

are involved because the web is not gripped

firmly. An exception is the gravure printing

station, which uses a high-pressure nip and

driven rolls. The following describes the dif-

ferent tension zones.

Unwind Tension Zone

Constant tension from full roll to core is

desirable here. Any significant deviation

Tension Systems

from constant tension may be reflected in

the next tension zone, causing problems

there. The unwind tension level should be

equal to or less than the tension used while

winding the roll. Greater tension can cause

the roll to tighten on itself and telescope.

This problem is more serious with smooth,

low friction materials than with rough or

sticky webs.

Extensible webs, such as polyethylene and

unsupported vinyl, are run with much lower

tension than nonextensible webs, such as

paper or foil, to prevent wrinkling, stretch-

ing and reduction of width.

Intermediate Tension Zone

Constant tension is also desirable here,

but the level may be higher or lower than the

unwind tension. The process, the web mate-

rial, and its thickness and width usually

determine the correct tension. Extensible

films must be run with low tension to pre-

vent stretching, which causes short print

lengths and curling upon release of tension.

Rewind Tension Zone

Either constant or tapered tension is used

in this zone. The choice is determined by the

web material, the buildup ratio (full roll

diameter divided by core diameter) and the

tension capability of the rewind drive.

Usually, buildup ratios (full roll:core size) of

more than 5:1 require tapered tension, which

refers to a tension profile having less tension

at the full roll than at the core. A profile hav-

ing a decrease of 40%, for example, is said to

have 40% taper; full roll tension is 60% of

core tension.

The rewind-tension profile is almost

always dictated by the necessity to produce a

good quality rewound roll rather than by prior

processes in the machine. But this priority is

only possible if the rewind tension zone is

effectively isolated from the tension in the

preceding zone by an efficient nip-roll system.

If the nip is not a good isolator, rewind ten-

sion will affect tension in the preceding zone

and the rewind-tension profile may have to be

adjusted to accommodate its requirements,

consequently roll quality may suffer.

Low-friction web materials, such as plas-

tics and high gloss paper, are normally

wound with high taper, 50% or more, while

extensible webs are wound with low taper or

constant tension. Webs requiring high ten-

sion and large buildup ratios need high taper

to keep from exceeding the capability of the

rewind drive. For example, a roll wound with

50% taper requires half the horsepower of the

same roll wound with constant tension.

Table 1 lists some common converting

materials and some typical tensions for

them. The values shown come from practice

rather than theory, so they may be different

from those listed in charts from other

sources. However, they closely represent

tensions actually used by converters.

Tension is often used to correct web-han-

dling problems. For example, the web may

have a loose edge, so the machine operator

increases tension to stretch the web and elim-

inate the looseness. Or the web may not track

properly through the machine so, once again,

tension is increased to correct the problem.

Unfortunately, this adjustment may create

other problems such as web breakage,

stretching, wrinkling and print-length varia-

tion. It would be more beneficial to correct the

cause of the web-handling problems than to

create more problems by increasing tension.

TENSION DRIVES

Tension dirves fall into two catergories:

motors or brakes and clutches.

Motors

Both alternating current (AC) and direct

current (DC) motors can be used as tension

drives. Direct current motors may be used in

all tension zones, but they are most common

in the intermediate tension zone and least

PRESSES AND PRESS EQUIPMENT 35

36 FLEXOGRAPHY: PRINCIPLES & PRACTICES

often used in the unwind zone, where the

additional expense and complication of a

regenerative controller as compared with a

brake controller can not usually be justified.

In the rewind zone, when the roll approach-

es maximum diameter and the DC motor

operates at high torque and low speeds, aux-

iliary blowers are needed to cool the motors.

The commutators and brushes may suffer

overheating and burning if the motor is left

stationary under high torque output, condi-

tions which exist when the machine is

stopped for a while and full tension is main-

tained. However, in spite of these shortcom-

ings, DC motors are commonly used because

they have the following advantages: they are

usually smaller than eddy current clutch/AC

motor units of the same horsepower; their

dynamic response is faster than any clutch;

their minimum torque output is quite small,

which permits operation at low tensions; and

they are more energy-efficient than a clutch.

Alternating-current motors are gaining

popularity for use in intermediate tension

zones. Their advantages are low cost and low

maintenance (no commutators, slip rings or

brushes). But the controllers that operate the

motors are quite complicated and are not

available for large horsepower units, and fur-

thermore torque output tends to be jerky at

low speeds. DC motors are the choice for

intermediate tension zones and eddy current

clutches, or for rewinds. The trend is toward

dual-disk pneumatic brakes for unwind ten-

sion development because of their wide

torque range and high heat capacity.

Brakes and Clutches

Brakes are usually used to create tension

in the unwind zone. There are several differ-

ent kinds, including manually actuated fric-

tion devices, pneumatic brakes with either

single or dual disks, electric friction brakes

and electric magnetic-particle brakes.

It is hard to imagine any case where a man-

ually actuated friction brake would be the

best choice, except possibly on laboratory

test machines, small pilot lines or inexpen-

sive, low-production machinery. Pneumatic

brakes, whether air cooled or water cooled,

can dissipate much more heat than electric

types. They also have a wider torque range,

especially those that have been designed

specifically for tension control (constant

slip) applications. So they are most desirable

when high speeds, high torque and wide ten-

Table 1

MATERIAL TENSION

(per mil per inch of width)

Acetate .50 lb.

Foil (aluminum) .50 lb.

Foil (copper) .50 lb.

Cellophane .75 lb.

Nylon .25 lb.

Polyethylene .12 lb.

Polyester .75 lb.

Polypropylene .25 lb.

Polystyrene 1.00 lb.

Saran .15 lb.

Vinyl .05 lb.

Paper* (per inch of width)

15 lb. .40 lb.

20 lb. .50 lb.

30 lb. .75 lb.

40 lb. 1.25 lb.

60 lb. 2.00 lb.

80 lb. 3.00 lb.

100 lb. 4.00 lb.

*based on 3,000 sq. ft. ream

Paperboard (per inch of width)

8 pt. 3.0 lb.

12 pt. 4.0 lb.

15 pt. 4.5 lb.

20 pt. 5.5 lb.

25 pt. 6.5 lb.

30 pt. 8.0 lb.

TYPICAL TENSION FOR

WEB MATERIALS

sion ranges are involved. In addition, most

pneumatic tension brakes are available with

linings having several different coefficients

of friction. They can be installed in combina-

tions on the same brake and also have multi-

ple cylinders that can be turned on or off as

needed to produce the desired torque. These

brakes also produce the lowest minimum

torque of any brake, which makes them

most desirable for low-tension applications.

Electric friction brakes are usually cheap-

er than pneumatic brakes and are simpler to

apply because no compressed air is needed.

But they have limited torque range and can

dissipate only a fraction of the heat. They

may also squeak because of the metal-to-

metal rubbing contact necessary to com-

plete the magnetic circuit. Minimum torque

tends to be high because of residual magnet-

ism and drag.

Electric magnetic-particle brakes are dif-

ferent because they have no surface-to-sur-

face rubbing contact. Instead, they produce

torque by forming linkages of particles, sim-

ilar to iron filings, in the gap between the

rotating and stationary members. The parti-

cles arrange themselves in the gap along the

magnetic flux lines produced by the electric

current in the coil of the brake. Strength of

the linkages (and therefore torque) varies

with strength of the field, which is deter-

mined by the current.

Magnetic-particle brakes are well suited

for very-slow-to-moderate-speed applica-

tions. Torque output at slow speed is very

smooth because the stick/slip condition

caused by rubbing contact in other types of

brakes is missing. They are also completely

sealed, preventing wear products from being

released to the environment. Compared with

pneumatic brakes, their minimum torque is

high and heat dissipation ability low.

The clutch versions of the brakes listed

above are sometimes used to create tension

in the rewind zone. The comments made for

the brakes also apply to the clutches.

Eddy-current clutches are another type of

non-contact, variable-torque electric clutch.

They are available in sizes ranging from less

than 1 horsepower to over 100 horsepower,

with an attached AC motor. They are typical-

ly used on rewinds because of their high

heat-dissipation capability and smooth

torque output. Also, they can be easily con-

trolled by a simple, variable-voltage power

supply and can remain “parked” at full torque

output for long periods without damage.

PRESSES AND PRESS EQUIPMENT 37

38 FLEXOGRAPHY: PRINCIPLES & PRACTICES

rakes, clutches and motors can

only create tension and therefore

a method is needed to adjust the

torque of these devices in order to

produce the correct web tension.

There are only two tension con-

trol systems: the machine operator or some

kind of automatic controller.

MANUAL SYSTEMS

Manual tension-control systems require

the machine operator to judge the tension in

the web and make appropriate adjustments

to the brake, clutch, or motor torque or

speed by hand. Such systems are called

“open loop” because the torque or speed out-

put does not depend on what is happening in

the machine, only on the person making the

adjustments. Skill, experience and constant

adjusting are required to achieve a satisfac-

tory result. The machine operator is the ten-

sion controller and the quality of control

depends on that person’s judgment, skill and

attentiveness. The machine operator must

compensate for changes in machine, speed,

roll diameter, brake and web characteristics,

and quality, with nothing more to help him

than his best guess and experience.

Consequently, manual tension-control sys-

tems provide tension profiles that are very

erratic, and change from roll to roll over time

and from operator to operator. Manual con-

trol is best used in slow machines having

small diameter unwind and rewind rolls

where product quality and material waste are

not important.

Roll Diameter Followers

Roll followers are an improvement on

manual control systems. There are three

basic types: follower arms, sonic range find-

ers and diameter computers. All measure the

diameter of the unwind or rewind roll and

adjust the brake or clutch torque as it

changes. Torque adjustment is the basic func-

tion of any unwind and is proportional to

diameter change according to the formula:

TORQUE  TENSION  DIAMETER

This torque adjustment process is some-

times mistakenly called “taper tension,” but

the correct term is “taper torque.” Taper ten-

sion refers to the rewinding tension control

Roll followers are not true tension con-

trollers. The machine operator manually sets

tension, and the roll follower only compen-

sates for roll diameter variation. There is no

compensation for speed changes, brake fade

or other factors affecting web tension.

Follower arms have a roller or wheel on the

end of a lever arm attached to a rotary posi-

tion sensor. The wheel rides on the roll sur-

face and the arm rotates as the roll diameter

changes. The sensor detects the arm move-

ment and signals the controller to adjust

brake or clutch torque accordingly.

The follower arm is the simplest and least

expensive type of roll follower. But it has two

disadvantages. First, it requires touching the

stock roll surface, which is not always desir-

able, and it gets in the way of loading and

unloading rolls. Second, setting torque is

more difficult than with the other types.

Roll followers eliminate the constant read-

justment required by manual systems and

Tension Control Systems

free the machine operator for other tasks.

However, they share some of the disadvan-

tages of manual systems.

There is no compensation possible for

speed changes, brake fade, temperature and

humidity variation, web characteristic varia-

tion, and other factors affecting tension.

With a roll follower system, setting correct

tension remains difficult, as this is done

manually by guessing.

Non-Contact

Roll Diameter Followers

Sonic range-finders operate by bouncing

sound waves off the roll surface and measur-

ing the time it takes to make the trip. Most

systems use the same sonic transmitter/

receiver unit found in Polaroid cameras. As

the roll diameter changes, the range-finder

control unit adjusts brake or clutch torque

accordingly to maintain roughly constant

tension.

Diameter computers use tachometer gen-

erators or pulse generators to measure roll

rpm and web speed. The two speeds are then

electronically divided to produce an output

voltage that varies directly with the roll diam-

eter. As with other types of roll followers, the

diameter signal is fed to a control unit that

adjusts brake or clutch torque to maintain

more or less constant tension.

Range finders and diameter computers are

mechanically and electronically more com-

plicated and expensive but do not require

touching the roll and don’t get in the way of

loading and unloading the rolls.

INTERMEDIATE TENSION

OR DRAW SYSTEMS

“Draw” controls are used only in interme-

diate zones. The nip rolls at the upstream end

of the zone are slaved to the main drive either

mechanically or electrically. The nip is over-

sped a small amount, stretching the web and

creating tension (or draw) in the zone.

The most common mechanical draw sys-

tem has a continuously variable speed trans-

mission driving the nip with a shaft from the

main drive gear train. The transmission’s out-

put speed is adjusted manually with a hand

wheel. The speed range is quite small, usual-

ly ±0.5% of the input speed.

Electrical draw systems eliminate the

need for a driveshaft. Instead, a speed-regu-

lated DC motor drives the nip following a

speed-reference signal from the main drive.

The draw is accomplished by an operator

adjustment that over-speeds the nip motor.

Using digital techniques, very precise speed

control is possible, with a draw accuracy of

.05% or better.

The correct draw is arrived at by trial and

error and, for best results, must be reset each

time a change is made in web thickness,

width, speed or material. Moisture content of

paper webs must also be considered and the

draw adjusted accordingly. Excessive draw

will cause web breaks, stretching and wrin-

kling. Inadequate draw results in folding and

wander or sideways drift.

AUTOMATIC CONTROLS

Automatic control systems relieve the

operator of the need for constant manual

adjustments of the tension level. While they

do not require a great deal of skill and expe-

rience, their greatest benefit is vastly im-

proved tension control.

There are several kinds of automatic ten-

sion-control systems, each with its own

advantages and disadvantages. However,

keep in mind that no automatic system will

eliminate tension problems caused by

mechanical deficiencies or poor-quality web

material. The effects of bad bearings, bent

shafts, worn gears and bad machine design

can not be negated simply by installing an

automatic tension-control system, no matter

how sophisticated. To get the most from an

automatic system, the machines must be

PRESSES AND PRESS EQUIPMENT 39

40 FLEXOGRAPHY: PRINCIPLES & PRACTICES

properly designed and in good condition,

particularly when low tensions and extensi-

ble or low-friction webs are involved.

Dancer Roll Systems

A dancer is an idler roll that is free to

move in a straight line or arc under the influ-

ence of web tension (Figure

). A counter-

force created by a weight or air cylinder

opposes the tension force, and a sensor is

connected to the dancer to detect its posi-

tion. The position signal is fed to a regulator,

where it’s compared to a desired-position

signal, usually representing the mid-point of

the dancer travel, set by the machine opera-

tor. In theory, the counter-force is equal to

about twice the desired web tension, and

the dancer will maintain position in the mid-

dle of its travel as long as this condition

exists. If tension increases, the dancer will

rise, moving the sensor and signaling the

controller to reduce torque, allowing the

dancer to return to its original position. If

tension decreases, the opposite sequence

occurs. Tension is determined by adding or

removing weights to the roll, or by varying

air pressure to a loading cylinder according

to a chart set up to show the relationship

between pressure and tension.

Dancers are mechanically complicated and

require at least two other properly positioned

idler rolls (one before and one after the

dancer) to operate. These rolls require extra

space in the machine. A properly designed

dancer is lightweight so it can react quickly,

but strong so it won’t deflect and steer the

web to either side. Its mechanism must also

be designed with very low friction in its mov-

ing parts so it can react to small changes in

tension. Motion dampers, such as shock

absorbers, should never be used to stabilize

its movement because they degrade the

dancer’s sensitivity and response time, caus-

ing excessive tension fluctuations.

Dancers usually begin to have difficulty

maintaining control at web speeds over 500

feet per minute because of the inherent fric-

tion and inertia of the dancer itself and the

relatively low gain (sensitivity) of its con-

troller. Low tensions and wide tension

ranges are a problem for dancers, again

because of friction, inertia and low gain. The

dancer roll will oscillate or “hunt” along its

travel path, causing tension variations, web

length variation and shifting to the side. If

the hunting is severe, the dancer may reach

the ends of its travel and causes web breaks

or slack in the web, resulting in wrap-

arounds. This disrupts the printing, coating

or other process taking place in the machine

and causes waste and loss of quality. The

typical cures for hunting are to mechanical-

ly dampen the dancer’s movement or bypass

the dancer and operate manually. The result

is degradation of tension control, which

results in waste, reduced productivity and

poor product quality. Dancer systems are

most suitable for moderate web speeds and

narrow tension ranges.

Disadvantages of Dancer-roll Systems. Dan-

cers are actually position controllers, not

tension controllers. Tension plays an inci-

dental part in the operation of the system.

Dancer systems do not measure or display

tension. Dancers must move to operate,

therefore they always disturb and change

the length of web in their tension zone. This

A dancer roll is an idler

roll that is free to move

in a straight line or arc

under the influence of

web tension. A counter-

force is created to

oppose the tension

force, and a sensor is

connected to the dancer

to detect its position.

Pivoting

Dancer

Pivot

Linear

Dancer

movement may actually cause some of the

problems associated with inadequate ten-

sion control.

Tension Transducer Systems

Tension transducer systems are specially

designed force transducers that measure

actual web tension. They are normally used in

pairs, installed on each end of an ordinary

idler roll. Most transducers use either strain

gauges or variable inductors to develop a volt-

age proportional to tension and are accurate

to within 1%. Sometimes a single transducer

is used, but accuracy is very poor because

transducer output becomes dependent on

web width, the placement of the web relative

to the transducer, and the location of the

tightest part of the web, which can change

continuously throughout a roll of material.

Dual transducer systems are not subject to

these factors because the transducers are

electrically connected so that their outputs

are averaged (Figure

Transducer output is displayed on an ana-

log or digital meter. The most useful arrange-

ment has a meter that is calibrated to display

actual total web tension expressed in

pounds, ounces, grams, newtons or any

other suitable unit. Sometimes the meter is

calibrated to read 0% to 100% of some arbi-

trarily assigned maximum tension value.

This arrangement is clumsy because the

maximum tension must be remembered and

then multiplied by the meter reading to

determine the actual tension. The only

advantage is for the manufacturer, who has

to make only one type of meter scale.

Meter calibration is very simple and quick

(Figure

). Required equipment comprises

a small screwdriver, a rope and a known

weight of at least 20% of the meter full scale.

To calibrate: Turn the power on, turn the

“zero” adjustment on the circuit card so the

meter reads zero. Run the rope over the

transducer roll in exactly the same path the

web follows, and tie one end in the machine.

Attach the known weight to the other end

and let it hang free. Turn the “calibrate”

adjustment on the circuit card so the meter

reads the same as the weight.

Transducers are made in many different

sizes, load ratings and mounting styles.

Transducers are selected in a two-step pro-

cedure. First, decide which mounting style is

best for the particular use. Second, deter-

mine the load rating. The appropriate load

rating depends on the weight of the idler roll

mounted in the transducers, web tension

and wrap angle. These factors are consid-

ered in simple mathematical formulae to

arrive at the correct load rating. Unlike

dancers, transducers take up no extra space

and don’t need specially located rolls.

The analogue indicator is the simplest kind

PRESSES AND PRESS EQUIPMENT 41

In a dual transducer

system, the transducers

are electronically

connected so their

outputs are averaged.

To calibrate a transducer

output meter, a rope is

run over the roll in the

same path the web

follows. A weight is

attached to one end of

the rope, and the meter

is adjusted until it

matches the value of

the weight.

–

Left

Transducer

Tension Signal

(Output)

Force Due to

Tension in

Web, F+

Right

Transducer

5 Volt DC Excitation

(Input)

Machine

Frame

Machine

Frame

Rope

Transducer

Roll

42 FLEXOGRAPHY: PRINCIPLES & PRACTICES

of transducer system. It consists of a pair of

transducers; an enclosure with a display

meter on the front, containing a circuit card

to excite the transducers and amplify their

output; and a pair of interconnecting cables.

The circuit card usually has voltage and cur-

rent outputs that are proportional to tension

and can be fed directly to variable-speed dri-

ves, recorders or computers.

The transducer system does not directly

control tension by itself. Controllers also indi-

cate tension but, in addition to being dis-

played on the meter, the tension signal is fed

to a regulator circuit where it is compared

against a desired tension signal set by the

machine operator. The regulator outputs a

voltage or current to a servo valve, motor,

brake or clutch to automatically control ten-

sion in a “closed loop” control scheme.

Closed loop tension systems are very accu-

rate because actual web tension is measured

continuously and compared against the

desired tension set by the operator. The regu-

lator circuit automatically adjusts its output

to eliminate any difference between actual

and desired tensions. The term “closed loop”

comes from the fact that the output of the sys-

tem (tension in this case) is fed back to the

input. The output forms a continuous path

through the regulator and back to the input,

circulating endlessly in an unbroken loop.

There are two kinds of transducer systems:

full control and tension trim. Full-control sys-

tems have torque outputs completely deter-

mined by the transducer signal (Figure

If tension is very high, output will go to zero.

This type of control system is used on

unwinds and rewinds but not in the interme-

diate zone.

Tension trim systems operate in interme-

diate zones and use the transducer signal to

vary the motor, clutch or brake torque with-

in a narrow range, typically ±10% of operat-

ing level, which is determined by another

signal, usually speed (Figure

). The trans-

ducer signal allows the system to control

tension and will automatically compensate

for variations in speed, drive accuracy and

web thickness to maintain proper tension.

Full control transducer

systems have torque

oututs completely

determined by the

transducer signal.

In this tension control

system, the transducer

signal allows the system

to control tension and

will automatically

compensate for

variations in speed,

drive accuracy and web

thickness to maintain

proper tension.

Unwind Brake

Control

Main Tension

Setting

Line Speed

Tachometer

Intermediate

Drive Control

Main

Drive

Unwind

Main Print or Intermediate

Printing

Process

Rewind

Rewind Brake

Control