Printhead Operation Precautions

When printing continuously, the supply energy may need to be reduced to ensure the substrate temperature, monitored by the onboard thermistor, remains below the maximum temperature shown in the detailed specification.   The power “ON” and “OFF” sequence must in the following order to avoid damage to the heating elements:- Turning on: Apply logic voltage Vdd and then apply printhead supply voltage VH. Turning off: Switch off supply voltage VH and then switch off logic voltage Vdd.   Interface each signal input (CLK, LAT, STB, DI) with CMOS level (ex 74HC240). Keep STB signal to “disable” during ON/OFF and no printing conditions.   Heat elements and IC’s should be protected from static influence to avoid electrostatic destruction.   Do not touch the connector pins.   The printhead substrate surface is coated with glass. Mechanical stress or shock (including dust scratch damage) must be avoided.   When printing is complete, the printhead supply voltage VH (including any stored capacitor charge) should be reduced to ground until the next printing operation commences.   The platen roller should be composed of non-conductive materials.   Condensation on the printhead must be avoided. If condensation occurs, ensure the printhead has fully dried before applying the supply voltage VH. If using the printhead in outdoor equipment in colder, damp climates, the use of a space heater within the printer inclosure is recommended to reduce the risk of condensation.   Avoid undue stress when plugging cables into the connector(s).   Print quality will degrade if paper, ink or dust residues stick to the heating elements. Clean the heating elements regularly with ethyl alcohol applied with a clean, lint free cloth or use a proprietary thermal printhead cleaning pen. The frequency of cleaning should be established case by case. Do not use acid or alkali to clean the dot line and tracks nor any kind of abrasive tool or cleaner.   If a “sticking” sound is heard during printing, a set-up adjustment will be needed. Review and adjust where necessary the paper feed mechanism, voltages and timings settings.   Ensure any printhead carrier is perfectly flat and will not cause the printhead to warp when tightening the mounting screws. The mounting design should allow the printhead to “float” to find its own level.   Only use the thermal paper detailed in the printhead specification sheet or a recognised equivalent. The use of an inferior paper may result in poor print quality, increased head abrasion and may jeopardise any warranty issues.   When using pre-printed thermal paper, for example, labels, ensure the printing inks used are suitable for use with thermal printers. Certain inks contain abrasive pigments that will cause the printhead to suffer early failure through abrasion of the protective coating over the printhead elements.   In order to reduce surges, VH and GND cable lengths should be less than 300mm. A 47mfd aluminium electrolytic capacitor is required between VH and GND on the controller board side and a 0.1mfd ceramic capacitor should be placed between Vdd and GND.   Design the mechanics in such a way that the printing media (while printing) and the paper guide do not contact the protective coating over the IC’s or the through hole connector pins on the pcb.   A thermal printhead generates heat and under severe abnormal conditions, smoke or even combustion may occur. It is therefore recommended to use the onboard thermistor to monitor the temperature of the substrate and to design the software to reduce or disconnect the power in the event of a serious over temperature condition. Design the power supply for the head voltage (VH,Vdd) to be shut down when the temperature of the thermal head exceeds the stated maximum while STB is “ON” or the printing media has stopped moving. If the paper jams while the head is still “ON”, the paper will stick to the printhead and may catch fire.   Store printing media in a clean, cool environment. Using paper or label rolls which have been stored in a dirty area, will allow grit to be drawn across the printhead causing mechanical damage to the protective material covering the printing elements.