Temperature Correction; Line Count Correction - Sony UP-895 Service Manual

(4) When IC501 inputs STB pulse "1" to the head, the 1st stair data is transferred to the latch section and
the next 2nd stair data is input to the shift register section. At the same time, the DR pulse goes low,
and the "H" data input as the 1st stair data turns on the corresponding output-stage transistors to heat
up the resistors. The "L" data turns off the corresponding output-stage transistors so that the resistors
do not heat up.
This operation is carried out 1 through 64 times. If "H" data is sent 1 through 64 times, the resistors
generate heat at all times and the printing is the darkest possible. If "H" data is sent 1 through 32
times, the printing is an intermediate stair (gray). In such a way, the stair data with the number of
sending times corresponding to the size of the original 8-bit data is sent to the head, and the
intermediate stair is represented by the number of heat generation times in a heat generator.
(5) Thus, by controlling the time until the next data is transferred to the latch, the darkness of
intermediate stairs can be controlled. In other words, the darkness of each intermediate stair can be
changed by changing the STB intervals (T
In this unit, IC502 controls intervals T
called a γ characteristic control.
(6) If the DR pulse is also controlled as described in "4-5-2. Basic Operation", finer stairs can be
expressed.
Portion 1 in the figure is generated when the T interval of a STB pulse is shorter than the
transmission time to the shift register.
Therefore, this unit provides the smooth expression of intermediate stairs by controlling the STB pulse's
T interval and DR pulse.

4-5-4. Temperature Correction

As explained in "4-5-3. Stair Generation", intermediate stairs are expressed by controlling the STB
pulse's T interval and DR pulse. However, the print energy required for thermosensitive paper varies
with the room temperature and with the heat generated by and stored in the printing head during
continuous printing. Correction is thus required.
In this unit, a system control (IC304) measures the temperature change of the head from the thermistor
incorporated into the thermal head and converts it into 8-bit head temperature data. Moreover, IC304
reflects it on the γ characteristic control of IC501 and corrects the density change for the temperature.
As in stair generation, IC501 performs the temperature correction by controlling the STB pulse's T
interval and DR pulse. In other words, when the temperature rises, the STB pulse's T interval and DR
pulse decrease. When the temperature falls, the STB pulse's T interval and DR pulse increase.

4-5-5. Line Count Correction

The total current flowing through the head when all resistors of the head are turned on differs from the
case where they are turned on partially. Therefore, an error occurs in the energy applied to each resistor.
If printing operation is performed without correcting this error, as a result, there is a line on the print
where the number of resistors in which the head is turned on changes rapidly. This unit has IC501 that
incorporates this correction circuit.
4-16
... T
, T , T , T , T ) shown in the figure.
1 2 3 4 5 64
according to the γ characteristics of paper. This is
to T
1 64
UP-895/(E)