JPH05238038A - Control system of resistance measurement of thermal head - Google Patents

Abstract

PURPOSE:To discover the defective of a thermal head during operation early by self-diagnosis in a printer using the thermal head. CONSTITUTION:An output from a printing gate AND1 reaches '0' by bringing the GATE signal of a microprocessor 1 to '0', and a printing driving transistor TQ1 is turned 'OFF' to block current flow through the TQ1. An output from a resistance measuring gate ANM1 reaches '1' and a driving transistor MQ1 for measuring resistance is turned 'ON' by bringing a driving data D1 to '1', and a current I1 flows through a path of a thermal head resistor THR1, the MQL, a standard resistor Rs and a GND from a power supply VHD. Voltage across the standard resistor Rs is taken into the microprocessor 1 through an A/D converter 5 at that time. Since Rs and VHD are known, the thermal head resistance is computed from the following formula. I1=V1/Rs, THR1=(VHD- V1)/I1o.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal head control system, and more particularly to a thermal head control system based on resistance measurement.

[0002]

2. Description of the Related Art In a conventional thermal head control system, the resistance of a heating element of a thermal head is measured by a special measuring instrument when the thermal head is manufactured. H / individually
It was set as W information.

[0003]

In the conventional thermal head control method, since a difference in applied thermal energy occurs depending on the resistance value of the heating element, each heating element is measured by a special measuring instrument when manufacturing the thermal head alone. When the thermal head is installed in the device, it is set as H / W information individually based on the resistance value measured above, so the productivity is poor, and in terms of operation after installing the device, use Even if the thermal head resistance becomes defective due to burning or the like, it is difficult to visually judge the printing result, and there is a problem that the discovery is delayed.

It is an object of the present invention to provide a thermal head resistance measurement control system which self-diagnoses a defect of the thermal head during operation and finds it early.

[0005]

In order to achieve the above-mentioned object, the thermal head resistance measurement control system according to the present invention comprises:
A print drive transistor and a resistance measurement drive transistor for separating normal printing and resistance measurement by a thermal head, a print gate and a resistance measurement gate for separating drive of the print drive transistor and the resistance measurement drive transistor, and a head It has a standard resistance for measuring resistance and an A / D converter for measuring voltage.

[0006]

It has a resistance measuring gate, a resistance measuring transistor, and a standard resistance for measuring the head resistance, and measures the resistance value of each heating element of the thermal head at any time.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic circuit diagram showing an embodiment of the present invention.

In FIG. 1, the microprocessor 1 is
It controls the overall printing. The ROM 4 stores a program for controlling printing. RAM3
Is for the work used by the program.

The thermal head controller 2 is for converting the print data and controlling the applied heat energy at the time of printing, and is well known, so the description thereof will be omitted.

The thermal head resistances THR _{1 to} THR _n are heating elements, and are portions that come into contact with thermal paper to develop color.

The A / D converter 5 measures the voltage across the standard resistor R _S and supplies it to the microprocessor 1.

Next, a specific operation example will be described.

[0013] In initial diagnosis at power-on by outputting the GATE signal of the microprocessor 1 as a logic "0", all the output of the print gate AND ₁ ~AND _n is a logic "0", the printing driving transistor TQ ₁ ~ T
All Q _n are turned off, and the print drive transistor T
Q ₁ current through ～TQ _n does not flow.

Further, by setting the drive data D _{2 to} D _n to logic “0”, the outputs of the resistance measuring gates ANM _{2 to} ANM _n become logic “0” and the resistance measuring drive transistors MQ _{2 to} MQ _n. is "OFF", and the even longer current flow through the resistor for measuring the driving transistor MQ ₂ ~MQ _n.

Next, by making the short-time drive data D ₁ which is equal to or lower than the color development temperature of the thermal paper to be logic "1", the output of the resistance measuring gate ANM ₁ becomes "1" and the resistance measuring transistor MQ. ₁ is turned on, and the current I ₁ flows from the power source V _{HD through the} thermal head resistance THR ₁ , resistance measurement drive transistor MQ ₁ , standard resistance R _S , and GND.

At this time, the voltage V ₁ across the standard resistor R _S is taken into the microprocessor 1 through the A / D converter 5.

The thermal head resistance THR ₁ is a standard resistance R _S
And the power supply V _HD are known, they are calculated by the following equation.

I ₁ = V ₁ / R _S (1) THR ₁ = (V _HD −V ₁ ) / I ₁ (2)

The resistance value obtained from the equation (2) is used as the RAM 3
Store it in. Next, the drive data D _{1 is set} to “0”, the drive data D _{2 is set} to “1”, and the above operation is repeated to repeat the resistance measurement of the thermal head from THR ₁ to THR _n. The presence / absence of a heating element whose head resistance value is out of the standard is determined and the average resistance value is calculated.

Next, the drive data D _{1 to} D _n are all set to "0" and the GATE output of the microprocessor 1 is set to "1" to end the initial diagnosis and shift to the normal state.

During printing in the normal state, the above-mentioned average resistance value is used as a parameter for controlling the amount of applied heat energy to be applied.

The resistance measurement described above can be performed not only when the power is turned on, but also when printing is not being performed.

[0023]

As described above, according to the present invention, the resistance measuring gate, the resistance measuring driving transistor, and the standard resistance are provided, so that the resistance value of each heating element of the thermal head can be measured at any time. It is possible to detect defects in the thermal head quickly even after the device is installed.

Further, when the thermal head is incorporated in the apparatus, it becomes unnecessary to set H / W information depending on the magnitude of the resistance value of the thermal head, so that the productivity is improved.

[Brief description of drawings]

FIG. 1 is a schematic circuit diagram showing an embodiment of the present invention.

[Explanation of symbols]

1 Microprocessor 2 Thermal head control unit 3 RAM 4 ROM 5 A / D converter D _{1 to} D _n drive data AND _{1 to} AND _n print gate ANM _{1 to} ANM _n resistance measurement gate V _HD power supply TQ _{1 to} TQ _n print drive Transistor MQ _{1 to} MQ _n Resistance measurement drive transistor THR _{1 to} THR _n Thermal head resistance _RS Standard resistance INV Inverter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location B41J 29/46 A 8804-2C G01R 27/02 R 9213-2G 8804-2C B41J 29/00 U

Claims (1)

[Claims] 1. A print drive transistor and a resistance measurement drive transistor for separating normal printing and resistance measurement by a thermal head, and a print gate and resistance measurement for separating the drive of the print drive transistor and the resistance measurement drive transistor. A thermal head resistance measurement control method comprising: a gate for measurement; a standard resistance for measuring head resistance; and an A / D converter for measuring voltage.