1.2DESIGN AND HANDLING PRECAUTIONS

To maintain the initial level of performance of the printer and to prevent future problems from occurring, observe the following precautions.

1.2.1Design Precautions Design precautions

zIf too much energy is applied to the thermal head, it may overheat and become damaged. Always use the printer with the specified amount of energy.

zThe current capacity of the thermal head is 13.6A. Design the circuit so that the average current does not exceed this value. (However, when the current capacity standard of harness is MAX.1A/pin, since the numbers of VP and GND pins are 8 pins and 9 pins, respectively, the current will be 8A and 9A each.

zUse C-MOS IC chips (74HC240 or equivalent) for interfacing the CLK, LATCH, DAT and DST signals of the thermal head.

zWhen turning the power on or off, always DISABLE (put in “high” state) the DST terminals.

zTo prevent the thermal head from being damaged by static electricity:

•Fix the printer to the Frame Ground (FG) by FG connection portions shown in Figure 7-1to Figure 7-3.

•Connect the GND terminal (SG) to FG through an approximately 1 MΩ resistor.

zKeep the Vp power off while not printing in order to prevent the thermal head from being electrically corroded. In addition, design the printer so that the signal GND of the thermal head and the frame GND of the printer mechanism become the same electric potential.

zWire resistance should be 50 mΩ or less and 30 cm or less (however the less the better) between the power supply and the Vp, and the GND terminals on the thermal head controller. Maintain a considerable distance from signal lines to reduce electrical interference.

zA surge voltage between Vp and GND should not exceed 28 V.

zAs a noise countermeasure, connect the capacitor noted below between the Vdd and GND

terminals near the thermal head control connector. Capacitor: 0.1 ∝F/15 V (aluminum electrolytic)

zAlways detect the outputs of the platen position and paper detectors. Incorrect activation of the thermal head may reduce the life of the thermal head and the platen and damage them.

zThe head activation time period may become longer according to the printing condition. If so, hold the phase of the motor and keep the pause time of the head activation for 0.1 msec or more. A continuous printing without a pause time may damage the thermal head.

1-2