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XF
eXtendo®
Thermal Printer Family
4.6.2 Designing Your Own Paper Roll Holder
It is sometimes desirable for customers to design their own paper roll holder in order to fit
in the available space, or to tailor performance to their specific needs. Based on our
extensive experience in designing printers, we would urge you to consider the following
topics and implement your design with care.
Large Diameter Rolls: When using paper rolls over 150 mm in diameter, a "dancer bar"
may be considered. This usually takes the form of a spring-loaded arm under which the
paper is placed before feeding it into the printer. As the printer starts to print, slack is taken
up from the paper roll. This starts to lift the arm against the spring, which puts force on the
paper roll and starts it moving slowly. As more printing takes place the roll gradually
accelerates until it's up to printing speed. Without the dancer bar, slack paper would be
taken up until it was suddenly no longer slack. Now the printer must accelerate a large,
heavy paper roll from zero speed to full print speed in essentially no time. This usually
causes the paper advance motor to stall or the paper to slip against the platen, causing
shortened characters until the paper roll is up to speed.
Spindle Friction: Another important consideration is spindle friction. As a paper roll
rotates, it slides against the spindle that holds it, assuming a fixed spindle. This friction will
tend to impede the paper roll's free motion, and is dependent upon the weight of the roll,
the smoothness and material of spindle and paper core. When possible, especially with
paper rolls over 100 mm in diameter, design the spindle so that it can rotate, greatly
decreasing friction and drag.
Catch Points: More paper jams and transport problems are caused by catch points than
any other issue. Make sure that the paper path is free of anything that can interfere with
free paper flow, especially any sharp edges or "pinch points" into which the paper may
stray and become caught.
Alignment: Any paper roll holder design must hold the paper square to the printer in all
planes. If the paper is angled in any way, it will enter the printer at an angle and will be
more likely to cause paper jams.
Rigidity: It is important that the paper roll holder support the paper firmly and not move.
This is especially true in high-speed printing applications and in large diameter paper roll
applications. Many paper roll holders are made from metal too thin to support the heavy
paper rolls they are expected to handle. This results in twisting and warpage while printing,
which binds the paper and causes paper jams. Vibration during printing may also cause
undesired movement of the paper roll.
Shipment: Do not ship your product with a paper roll mounted in the paper roll holder.
The heavy weight of the paper roll can easily bend or otherwise damage the paper roll
holder or printer, as witnessed numerous times.
4.7 Power Supply Specifications
Selection of a power supply for thermal printers depends upon the printer's application, what
percentage of the printout is black, frequency with which printouts are generated, and more. In
particular, thermal printers draw high currents for very short time periods. The most important
issue is not peak current, but the length of time that the power supply is able to deliver
instantaneous current over its rated maximum, and for how long the print job prints high black
percentages, thereby drawing high current. It is important that the power supply's over-current
system does not shut down the power supply when these brief, high current surges occur.
Part No. D-684-399
Mod. No. 4 120322 Eli
page 23 of 35
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