JPH0688421B2 - Drive pulse width controller for thermal print head - Google Patents

Description

Description: (a) Technical Field The present invention relates to a drive pulse width control device for a thermal print head that controls the drive pulse width of a heating resistor according to the temperature rise of the head body.

(B) Conventional technology and its drawbacks When a driving pulse is simultaneously supplied to a large number of heating resistors of a thermal print head, a large current flows at a time,
It is necessary to increase the power supply capacity and also increase the area of the common electrode of the wiring pattern. Therefore, in general, a large number of heating resistors are divided into a plurality of blocks in order to reduce the power supply section and the area of the wiring pattern, and a synchronization signal (hereinafter referred to as strobe) for driving the heating resistors is provided for each block. Signal is used to AND the driving pulse of each heating resistor and the synchronizing signal in the AND gate. Further, if the number of times each heating resistor drive pulse is turned on per unit time increases, the temperature of the heating resistor itself when turned off rises, so the heating resistor is kept at a constant temperature when the driving pulse is turned on next time. The above power will be consumed. Therefore, in order to prevent such waste, a temperature sensor such as a thermistor is placed in the head body to detect the temperature rise of the entire head body and to drive each heating resistor according to the temperature of the pulse of the drive pulse. I try to control the width. However, since the conventional drive pulse width control device is designed to directly control the pulse width of the strobe signal, when there are n strobe pulses, independent pulse width control is required for each strobe pulse. Another device has been proposed that controls on / off of a common signal, but since the common signal is at a high level, a special circuit such as a step-down circuit is required, which complicates the circuit configuration and reduces the cost. Had the drawback of rising.

(C) Object of the Invention It is an object of the present invention to provide a drive pulse width control device for a thermal print head capable of controlling the pulse width of a drive pulse with a simple circuit configuration.

(D) Configuration and Effect of the Invention A plurality of heat generating resistors, a temperature sensor, and a thermal print head containing a plurality of AND gate elements that directly drive the plurality of heat generating resistors, respectively, and a plurality of the logics. Data input means for inputting individual data to each of the product gate elements, and a sync signal input for dividing the plurality of AND gate elements into a plurality of blocks and sequentially inputting a sync signal to each block And a pulse width control signal input for collectively inputting a drive pulse width control signal formed on the basis of the output of the temperature sensor to all of the plurality of AND gate elements in synchronization with the synchronization signal. Means and are provided.

FIG. 1 shows a signal terminal diagram of a thermal print head according to an embodiment of the present invention, and FIG. 2 shows a circuit diagram around a heating resistor of the thermal print head. As signal terminals, strobe signal (synchronous signal) input terminals STR1 to STRN for driving the heating resistor for each block, data input terminal D, clock input terminal CP, latch pulse input terminal LA, drive pulse width control signal input terminal PCONT and thermistor TH
There are temperature detection terminals TH1 and TH2 that output the detection signal of. Here, the total number of blocks is N. Temperature detection terminal
TH1 and TH2 are connected to the voltage / frequency converter V / F, where the drive pulse width control signal PCON having a pulse width according to the temperature
T is formed in synchronization with the strobe signal. The drive pulse width control signal PCONT shortens the pulse width of the signal in proportion to the temperature detected by the thermistor TH.

As shown in FIG. 2, each of the _m heating resistors R _{1 to} R _m has one terminal connected to the common terminal COM and the other terminal connected to each of the NAND gates G _{1 to} G _m . Each NAND
The gate has three input terminals, and each gate also serves as a driver of a heating resistor. Drive pulse width control signal PCONT and strobe signal STR are respectively applied to the three input terminals.
i, latch data is input. Of these, the signal PCONT is each NAN
Commonly connected to the D gate. The strobe signals are commonly connected for each block. With the above configuration, the pulse width of the drive pulse for driving the heating resistor R is controlled by the pulse width of the drive pulse width control signal PCONT. That is, when the temperature of the entire print head main body rises, the pulse width τ _{w of the} drive pulse width control signal PCONT becomes smaller in proportion to the temperature rise amount, and accordingly the pulse width t _ON for actually driving the heating resistor is The pulse width also becomes smaller. Further, as the entire print head main body cools and the pulse width τ _{w of the} drive pulse width control signal PCONT increases, the pulse width of the pulse t _ON that actually drives the heating resistor also increases. In this manner, the pulse width of the drive pulse can be controlled according to the temperature of the print head main body simply by inputting the drive pulse width control signal PCONT to the NAND gates G _{1 to} G _m .

(E) Effects of the Invention As described above, according to the present invention, the AND gate element for ANDing the individual data, the synchronizing signal and the pulse width control signal is built in the thermal print head, and the heating resistor is directly connected by this element. By driving, there is an advantage that the circuit configuration is simplified.

(F) Embodiment FIG. 4 is a schematic external view of a thermal print head according to an embodiment of the present invention. In the figure, reference numeral 1 is a heat dissipation plate made of aluminum or the like, a ceramic substrate 2 is arranged on the heat dissipation plate 1, and a heating resistor layer 3 is formed by printing in front of it. Substrate 2 is substantially entirely covered by cover 4 except the front portion including heating resistor layer 3, and signal terminal 5 including a power supply terminal is formed on the rear portion thereof. Further, a thermistor TH is embedded in a substantially central portion of the heat dissipation plate 1, and both terminals are connected to the terminal 5.

FIG. 5 is a schematic circuit diagram of the thermal print head. The terminals include a common terminal COM, a drive pulse width control signal input terminal PCONT, strobe signal input terminals STR1 to STRN, a latch pulse input terminal LA, a clock input terminal CP, a data input terminal D, and temperature detection terminals TH1 and TH2. Output terminals of three input terminal NAND gates are connected to each of the _m heating resistors R _{1 to} R _m , and a total of m NAND gates G ₁
˜G _m is divided into _N blocks D ₁ ˜D _N. One of the three input terminals is commonly connected to all NAND gates and is supplied with the drive pulse width control signal PCONT.
The remaining two input terminals receive the strobe pulse and the latch data, respectively. Input data is input from the data input terminal D to the shift register SR and set to a predetermined state by a clock pulse. The data set in the shift register SR is latched by the latch circuit L by a latch pulse, and is output as latched data to one input terminal of the NAND gate.

The thermistor TH is connected to the terminals TH1 and TH2.
As shown in FIG. 1, the signal of the thermistor TH output from the terminals TH1 and TH2 is formed into a drive pulse width control signal synchronized with the strobe pulse by the voltage / frequency converter.

In the above structure, the input data set in the shift resistor SR is latched by the latch circuit L, and then the heating resistor corresponding to the latched data is driven in synchronization with the strobe pulse. The strobe pulse is continuously output in order from STR1 and is sequentially driven from the heating resistor of the first block. At this time, the temperature of the print head body is detected by the thermistor TH, and a signal corresponding to the detected temperature is output to the terminals TH1 and TH2. A voltage / frequency converter (not shown) V / F (see Fig. 1) forms a pulse width signal corresponding to this detected temperature, that is, a drive pulse width control signal PCONT in synchronization with the strobe pulse, and outputs it to each NAND gate. To do. Since the number of blocks is N in this embodiment, N driving pulse width control signals PCONT are also output during one cycle. As a result, the width of the pulse that actually drives the heating resistor becomes the optimum pulse width according to the temperature of the printhead body, and wasteful power consumption can be prevented.

[Brief description of drawings]

FIG. 1 is a signal terminal diagram of a thermal print head using a drive pulse width control device according to the present invention, FIG. 2 is a circuit diagram of a heating resistor peripheral portion of the thermal print head, and FIG. 3 is a signal waveform diagram. Show. Further, FIG. 4 is a schematic external view of a thermal print head according to an embodiment of the present invention, and FIG. 5 is a circuit diagram of the thermal print head. G _{1 to} G _m …… NAND gate, TH …… Thermistor, R _{1 to} R _m …… Heating resistor.

Claims (1)

[Claims] 1. A plurality of heating resistors, a temperature sensor, and
A thermal print head having a plurality of AND gate elements for directly driving the plurality of heating resistors individually; and a data input means for inputting individual data to each of the plurality of AND gate elements. , The plurality of AND gate elements are divided into a plurality of blocks, a synchronization signal input means for sequentially inputting a synchronization signal to each block, and the temperature sensor for all of the plurality of AND gate elements Pulse width control signal input means for collectively inputting a drive pulse width control signal formed on the basis of the output of the above in synchronization with the synchronization signal, and a drive pulse width control for a thermal print head. apparatus.