Adjusting the ribbon position drives the leading edge of the panels forward or backward relative to the printhead, the aim being to ensure that each swipe of the head is centered in its color panel (this you can easily check by inspecting image negatives from on the takeup roll). The photos below show the effect of incorrect ribbon positioning.

Ribbon positioning problems: The arrows show the

direction of card movement. In the example at left, the ribbon has advanced too far, with the result that the head swipes a few millimeters of the following panel - see inside the circle. Reduce the ribbon position parameter to correct this. The example at right is the exact opposite - ribbon not advancing far enough, so increase the position parameter to correct.

Ribbon - Torque Adjust (%): Adjusts the current applied to the ribbon take-up motor (more current = more torque), thus controlling the ribbon tension between print head and take-up. Lowering the value, default = 100%, can help reduce ribbon wrinkling (but note that there are other factors, see Ribbon Wrinkling, inset below).

The downside of reducing the ribbon torque is an untidy, loosely wrapped takeup roll. That isn’t important, except aesthetically, but low torque does matter if the ribbon fails to advance when it should, see Ribbon Position, left.

Printhead Position - Adjust: Adjusts the downward motion of the printhead. The higher the number, the greater the amount of overrun following sensor activation. Ribbon Wrinkling

Printhead - Resistance (Ohms): This value should match what is written on the printhead. Enter a new value if the printhead is changed. If you enter a lower number than what is printed on the head itself, the printed image will be lighter than expected, and vice versa.

The printhead drive train comprises a stepper motor, a gear quadrant, and a crank arm directly coupled to the printhead bracket, photos below. In the down position, the printhead spring is slightly compressed, with the crank arm extended (which means that the torque demand on the motor is at its lowest).

Increasing the printhead position parameter does not result in a mesurable increase in head pressure, which is more or less binary - it is either under spring pressure, firmly in contact with the card, or not in contact at all.

Keep in mind the following:

•The amount of ribbon drag exerted by the supply arbor is con- trolled by a friction clutch. This is set for a torque of approxi- mately 5 oz-ins (36 mN.m), and should not be adjusted unless you have a torque gauge.

•Ribbon drag exerted by the takeup arbor is controlled by varying the current applied to the motor.

Ribbon wrinkling can be caused by one or more of the following factors (but always try adjusting ribbon torque first):

•Takeup torque too high

•Supply torque (drag) too high

•Too much preheat - ribbon sticking

•Dense patches with sharp transitions (text, graphic elements) on a dark image

•Card thickness not uniform

•Printhead too hot because resistance value in flash memory higher than actual head resistance

•Printhead angle adjust screwed down too far

•Printhead not pivoting freely

•Printhead rattling in frame

•Printhead not right-angled relative to card motion (yaw adjust)

Wrinkle control is essentially a balancing act of several variables - especially the balance between takeup and supply torques.

Example of ribbon wrinkling

Note the random curved, colored lines. The cure in this case was reduction of takeup torque.

Adjustment procedure : If the printhead doesn’t press firmly on the card during the printing “swipe”, there is nothing to stop uncontrolled advancement of the ribbon due to the takeup drive. To correct this, increase the adjust parameter to the point where the ribbon ceases to advance freely, then add 40 more to the number.

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P640i Card Printer User Guide

980541-001 Rev. A