JPH02297460A - Video printer - Google Patents

Abstract

PURPOSE:To minimize variation of irregularity of the recording density resulting from errors of a resistance and a saturation voltage by recording correcting data at the initial setting after measuring a resistance of a heat generating body and a saturation voltage of a driver element of a thermal head, thereby allowing individual heat generating bodies to further generate heat in accordance with said correcting data when an image is recorded. CONSTITUTION:A system controlling part 10 measures a resistance of a resistant heat generating body and a saturation voltage of a driver element via a resistance and saturation voltage measuring part 30 in the set-up mode, and obtains correcting data of each resistant heat generating body from the values of the resistance and saturation voltage. The correcting data is stored in a correcting data memory 22. Then, the system controlling part 10 drives a thermal head 4 in accordance with image data temporarily stored in an image memory 6. At this time, the system controlling part 10 controls the driving state of the head 4 in accordance with the correcting data stored in the correcting data memory 22 and set for correcting the variation of the thermal head 4. Accordingly, the irregularity of the recording density resulting from the variation of the values of the resistance and saturation voltage is minimized.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a video printer, and more specifically to a video printer, such as a thermal transfer printer, which receives a video signal and records an image on an image receiving medium.

For example, a thermal transfer printer, as is well known, records visible information by heating a heat-sublimating dye with a thermal head and transferring it to a transfer medium such as paper. The heat-sublimable dye is applied to a sheet, for example, and the dye-coated side of the sheet is brought into contact with a transfer or image-receiving medium, and the opposite side is heated by a thermal head. The thermal head has a heating element array in which a large number of heating element elements are arranged in a straight line, and each of them generates heat according to the information to be recorded. As a result, the dye in the heated portion of the sheet is diffused and transferred to the transfer medium. Such thermal transfer printers are effectively applied to video printers, for example.

To print color still images using a video printer,
High quality is required. As described in m1, the thermal head has an array of a large number of heating elements and a driver element for driving them. In actual products, there are variations in the resistance values of the resistance heating elements in one thermal head. As is well known, resistors depend on the specific resistance and mechanical dimensions of their materials. Although resistivity is material-specific, there are tolerances in the mechanical dimensions of individual heating element elements that cause resistance values to vary.

This variation in resistance value causes a difference in heat generation temperature between individual elements of the heating element. Therefore, variations occur in the transfer state of the heat-diffusible dye, which sometimes causes variations in print density. Therefore, in order to solve this problem, for example, in Japanese Patent Application Laid-Open No. 63-317359, the resistance value of the resistance heating element of the thermal head is measured and stored.
A technique has been proposed for correcting the width of the driving pulse for the heating element in accordance with this measured value during recording. Furthermore, in the patent application pending by the present applicant, Japanese Patent Application No. 63-214889,
A proposed method is to measure and store variations in the resistance values of the individual heating elements of the thermal head during the initial setup of the device, and to have each heating element generate additional heat according to those values during recording. . Furthermore, patent application No. 63-183646
proposed a method of temperature compensation by using a thermistor material with positive temperature characteristics for the heating element of the thermal head. However, even with these methods, correction of print density variations was incomplete.

The heat generation temperature of a heating element is determined not only by the resistance value of the heating element itself, but also by
It also depends on the characteristics of the drive element. More specifically, variations in the characteristics of the transistors used in the drive elements also cause errors in the drive current of the heating element, which may cause print density to vary from element to element. It was found that sufficient print quality could not be obtained unless such variations in characteristics of the driving elements were compensated for.

OBJECTS It is an object of the present invention to provide a video printer that eliminates the drawbacks of the prior art and minimizes deterioration in print quality.

DISCLOSURE OF THE INVENTION According to the present invention, an image represented by a video signal is received by selectively driving a plurality of resistive heating elements to generate heat according to the video signal using an input means for receiving a video signal and a plurality of resistive heating elements corresponding to the driver element. A video printer having a recording means for recording on a medium, a control means for driving a plurality of resistance heating elements according to a video signal received by the input means, thereby recording an image represented by the video signal on the image receiving medium; Measures the resistance values of multiple resistance heating elements and the saturation voltages of the corresponding driver elements, and corrects the drive of the resistance heating elements to compensate for variations in the image receiving medium caused by the measured resistance values and saturation voltages. The control means includes a measuring means for deriving correction data and a storage means for accumulating the correction data, and the control means measures the resistance values of the plurality of resistance heating elements and the saturation voltage of the corresponding driver element by the measuring means, and calculates the saturation voltage. and derives correction data according to the resistance value, stores the correction data in the storage means in correspondence with the resistance heating element, and when the input means receives the video signal, drives the plurality of resistance heating elements according to the video signal. Description of an embodiment in which correction data corresponding to the driven resistance heating element is read out from the recording means and the driving of the resistance heating element is corrected in accordance with the read correction data when recording an image. Next, an embodiment of a color video printer to which a thermal head according to the present invention is applied will be described in detail with reference to the accompanying drawings. See Figure 1! ! In the case a, the color video printer of the embodiment has an input terminal 2, and a color image represented by a color video signal input thereto is recorded onto an image receiving medium (not shown) by a thermal head 4. The thermal head 4 is a thermal transfer print head, and when its performance deteriorates due to aging, for example, it can be replaced with a new one. The thermal head 4 heats a dye sheet coated with a thermally diffusible dye using a resistance heating element (both not shown), and diffuses the dye in the heated portion onto a transfer medium such as paper, that is, an image receiving medium. Visible information is recorded by transcription. The recording density is controlled by adjusting the number and width of pulses applied to the normal head 4, and controlling the temperature and heating time.

The color video signal is input from the input terminal 2 to the image memory 6 in the form of digital data of color component signals such as three primary color signals and complementary color signals. This video signal is obtained from a video signal source such as a video camera, VTR, or personal computer.

The image memory 6 is, for example, a RAM having a storage capacity to store color video signal data for l horizontal scanning lines,
The storage control is performed from the system control unit IO through the control line 8. Image memory 6 has data readout output 1
2, which is connected to one input of the head control section 14.

The head control section 14 mainly has a head control function of driving the thermal head 4 based on a color video signal inputted from the image memory 6. Control data necessary for controlling measurements by the resistance and saturation voltage measuring section 30, which will be described later, is prepared in advance in the control memory 20, supplied to the head control section 14 through the control input 18, and set therein.

The head control unit 14 is a functional unit that drives the thermal head 4 according to set control data, and includes drive elements such as transistors that drive the head 4. The head control section 14 and the thermal head 4 integrally constitute a print head assembly, and this assembly can be replaced as a unit.

The head control unit 14 has three input lines 12 in this embodiment.
．． 16 and 18, which are connected to image memory 6, correction data memory 22 and control memory 20, respectively.

The thermal head 4 has, for example, 512 resistance heating elements (not shown), which are arranged in a straight line to form a print head array that prints one line.

One terminal of the heating element is commonly connected to each element, and terminal 5
3 to the switch 54. The switch 54 has two selective connection positions a and b, and one of the two connection positions can be selectively connected to the terminal 53 of the head 4 by the system control unit IO, as conceptually indicated by a dotted line 55. This is a selection circuit. The terminal a is connected to the connection line 32 of the resistance and saturation voltage measuring section 30, and the same is connected to the thermal head 4.
The latter is connected to a driving power source 56, and the voltage E is supplied to the latter.

The other terminal of the heating element is individually connected to the output of a driver element (not shown). Each resistance heating element corresponds to each bit position of the information to be recorded and is driven independently in correspondence with the bits, that is, in correspondence with the dots. That is, when a certain driver output is "0", a resistance heating element connected to that driver generates heat. For temperature control of the resistance heating element, pulse width modulation or pulse number modulation is advantageously applied.

For example, in the case of a thermal transfer method, dots desired to obtain high density are heated to a relatively high temperature for a relatively long time. To achieve this, the width or number of drive pulses that bring the output of the driver element to a low level is increased. Conversely,
If you want to obtain a low concentration, shorten the driving pulse width or reduce the number of pulses.

In this embodiment, the density is controlled by increasing or decreasing the number of pulses. A strobe signal output from the system control unit 1O is supplied to the head control unit 14 through a signal line 28. The strobe signal includes a single pulse with a relatively wide pulse width for starting up the resistive heating element, and a predetermined number of pulses with a relatively narrow pulse width for adjusting the concentration. These pulses are
For example, it is often composed of 32 to 256 pieces. In this way, by increasing or decreasing the number of strobe signals, the recording density is adjusted.

The system control unit 10 is a processing system that controls the entire apparatus, and is advantageously realized by a microprocessor, for example. More specifically, the system control section IO controls each section of the apparatus to drive the thermal head 4 according to the image data temporarily stored in the image memory 6, and at this time, the system control section IO controls each section of the apparatus to drive the thermal head 4 according to the image data temporarily stored in the image memory 6. Control is performed to correct the driving state of the head 4 in accordance with correction data for correcting variations in the thermal head 4.

The system control unit 10 also has a setup mode, in which the resistive heating element and driver element of the thermal head 4 are energized to measure the resistance value of the resistive heating element and the saturation voltage of the driver element. . For this reason, this embodiment is equipped with a circuit for measuring errors in resistance values and errors in saturation voltage, that is, a resistance and saturation voltage measuring section 30.

FIG. 2 shows a schematic block diagram of the resistance and saturation voltage measuring section 30. Power supplies 26 with different positive voltages (voltage E
1) and 40 (voltage E2) are prepared, and these output voltages are switched by a switch 38 and selectively connected to the power line 32 to the thermal head 4. The switch 38 is connected to the system controller 10 as conceptually indicated by a dotted line 52.
controlled by A resistor 24 is inserted into the power supply line 32 to the thermal head 4, and both ends of the resistor 24 are connected to the voltage measuring section 3.
I am drawn to 4. The resistor 24 has a known resistance value, and the voltage measuring section 34 is a measuring circuit that measures the voltage drop occurring across the resistor 24.

A value indicating the voltage drop across the resistor 24 measured by the voltage measuring section 34 is inputted from its output 42 to an analog-to-digital converter TADC) 44. analog·
Digital converter 44 is a signal conversion circuit that converts the value of input 42 into corresponding digital data and outputs it to its output 46. The output 46 is connected to a correction coefficient calculation section 48.

The correction coefficient calculation unit 48 calculates the resistance value Rn of each resistance heating element of the head 4 and the saturation voltage Vce of its driver element.
Measure n and use this to calculate the correction amount △ of the driving power of the resistance heating element.
There is a function to approximately calculate Pn.

For example, only the n-th heating element among the many resistance heating elements of the thermal head 4 is driven by the method described later, and the voltage measuring section 34 measures the voltage across the resistor 24 at that time. The measuring circuit at this time becomes as shown in FIG. 5 in an equally economical manner.

As will be seen, the voltage V between the terminals of the head 4 is the voltage across the heating element resistance value Rn and the saturation voltage V of the driver element.
Contains cen. Therefore, the switch 38 is switched for the n-th heating element, and the voltages across the resistor 24 are measured for each of the power supply voltages E1 and E2. For both measurements, assuming that the saturation voltage Vcen of the driver element hardly changes, the resistance value Rn of the nth heating element is
Rn=(Vl-V21R/(El-E2-Vl+V2)
fl) Also, the saturation voltage Vcen is Vcen-fV2El-VIE2) / (El-E2
−V1+V21 Obtained from (2). However, vl and v2 are the input voltages of the head 4 at the power supply voltages El and E2, respectively, which are equal to the sum of the measured voltage across the resistor 24 and the power supply voltage E1 or E2. Further, R is the resistance value of the resistor 24 and is known.

When this measurement is performed for all the resistance heating elements of the head 4, the correction amount ΔPn of the driving power of each heating element, for example, the correction amount ΔPn for the n-th resistance heating element, is calculated by the following formula, ΔPn=2E (Vcen-Vceave ) /Rav
e+ (E/Rave) ・(Rn-Rave)
[3] Can be found more approximately.

However, Rave is the average value of the resistance value of the heating element Vceav
e is the average value of the saturation voltage of the driver element E is the voltage of the drive power source 56 of the head 4 during printing.

In this embodiment, a strobe pulse that drives the heating element of the thermal head 4 is followed by a correction pulse. Compensation is achieved by combining correction pulses and additionally energizing the heating element.For example, if a constant voltage of the power supplies 26 and 40 is guaranteed, the resistance heating element may have a high resistance value or the driver element. Among them, the higher the saturation voltage, the lower the amount of heat generated.

Therefore, in order to obtain a uniform recording density, it is sufficient to additionally energize such a heating element with a correction pulse. The correction data calculated by the correction coefficient calculation unit 48 is used to control this additional energization.

The correction coefficient calculation unit 48 derives correction data corresponding to the amount of current applied to the heating element, and outputs this to the correction data memory 22. The correction data memory 22 is a RAM that stores such correction data corresponding to each heating element. Its output is connected to the head control section 14.

Next, the operation will be explained. In initializing the system when turning on the power to this apparatus or replacing the thermal head 4, the system control section 10 executes a setup sequence (FIG. 3). When this sequence is started, the system control unit 10 first connects the switch 54 to the a side and connects the thermal head 4 to the resistance and saturation voltage measurement unit 3.
Connect 0 (100). Next, the system control section 10 controls the head control section 14 via the control line 28, reads out the measurement control data from the control memory 20, and loads it into the head control section 14. As a result, the thermal head 4
For example, data for driving the first heating element is set (101). The system control unit 10 has a control line 52
The switch 38 is first connected to the a side (102).

Therefore, the system control unit 10 outputs a strobe pulse to the control line 28 (103), thereby energizing the resistance heating element along the path from the power supply 26 through the resistor 24 to the output of the driver element. The system control unit 10 controls the voltage measurement unit 34 via the control line 50 to measure the voltage drop that occurs across the resistor 24 at this time. The system control unit IO then connects the switch 38 to the d side via the control line 52 f105.106+ and performs similar measurements 103 and 104. Using this measured voltage value, the resistance value R1 of the first heating element and the saturation voltage Vce1 of the driver element are derived from equations fl) and (2), respectively. f1
04). Such resistance values and saturation voltage measurements are performed for all elements of the thermal head 4 (107
).

The value measured by the voltage measurement unit 34 is converted into corresponding digital data by an analog-to-digital converter 44, and is taken into a correction coefficient calculation unit 48. The correction coefficient calculation unit 48 calculates correction data ΔPn for each resistance heating element from the measured resistance value and saturation voltage using equation (3) (108
1.09) The system control unit 10 takes in the calculated correction data from the measurement unit 30 through the data line 51, and stores it in the storage location of the address corresponding to each heating element in the correction data memory 22.

Exit setup mode.

The recording operation proceeds as follows. In the recording operation mode, the system control unit IO first connects the switch 54 to the b side and connects the power source 56 to the thermal head 4 (1201
At this time, the recording mechanism is controlled to feed, for example, the cyan portion of the dye sheet to the image receiving medium. Next, the video signal data of the cyan component of the color video signal representing the image to be recorded, in this example, is sequentially taken into the input terminal 2 line by line by rask scanning. This line data is stored in the image memory 6 under the control of the system control unit IO, as shown in step 121 in FIG.

The system control unit IO outputs a control signal to the control line 28 to read the line data of the image memory 6 to the head control unit 14 and sets it therein (1221°) Then, the system control unit IO sends a strobe pulse to the control line 28. Output to f123). As a result, the driver element to which significant dot data is input is driven, and the corresponding resistance heating element is supplied with power from the power supply terminal 56 and generates heat.

For example, if the nth dot is to be recorded at a certain density, the n1 driver elements output a single output pulse and a number of pulses corresponding to the dot data in response to the strobe pulse. do. As a result, the n-th resistance heating element generates heat, and an amount of dye corresponding to the number of pulses is transferred from the dye sheet to the image receiving medium. That is, for dots recorded at relatively high density, a large number of output pulses are output. Furthermore, for dots recorded at a relatively low density, a relatively small number of pulses are output.

If the resistance heating element driven in this way shows the lower limit of the rated resistance value, or if the saturation voltage of the driver element shows the lower limit, the correction data memory 22 stores the correction level as data related to the correction pulse. "0" is stored. Therefore, the system control unit 10 does not apply a correction pulse to such a heating element. For resistive heating elements whose rated resistance values vary within the allowable range from the lower limit to the upper limit, or driver elements whose saturation voltage varies within the allowable range from the lower limit to the upper limit of the rated saturation voltage, the system control unit 10 uses the above-mentioned correction data. A correction pulse is generated accordingly to drive the head 4.

In this way, among the heating elements of the head 4, those with a high resistance value,
And for driver elements with high saturation voltage,
Correction is performed by increasing the total amount of current applied. This compensates for variations in recording density due to variations in resistance value and saturation voltage. From the experimental results, it was found that the strobe pulse group and correction pulse group Rather than outputting them completely separately, for example, if you output a strobe pulse four times and then output a correction pulse once, you can naturally correct from low-concentration areas to high-concentration areas. ing.

In this way, one line is recorded, and by repeating this for one frame of scanning lines, one screen of cyan image is recorded on the image receiving medium. This recording is also performed for images of other color components, thereby completing one frame of color image on the image receiving medium.

As described above, in this embodiment, in the initial settings of the apparatus, the resistance values of the individual resistance heating elements of the thermal head 4 and the saturation voltage of the driver element are measured, and correction data for compensating for the variations thereof is stored, and image recording is performed. Sometimes, by causing each heating element to generate additional heat in accordance with the correction data, unevenness in recording density caused by variations in the resistance value or saturation voltage of the head 4 is minimized. Therefore, even if the thermal head 4 is replaced with another one due to failure or end of life, density compensation can be performed appropriately by executing the setup sequence.

Thus, according to the present invention, in the initial setting, the resistance value of the heating element of the thermal head and the saturation voltage of the driver element are measured and correction data is stored, and when recording an image, the correction data is stored. By causing each heating element to generate additional heat depending on the data, variations in recording density caused by resistance errors and saturation voltage errors are minimized. Therefore, deterioration in print quality is minimized. Further, when the head is replaced, if both errors are measured and the storage sequence processing is performed, appropriate density compensation can be performed thereafter.

[Brief explanation of drawings]

FIG. 1 is a functional block diagram showing an embodiment in which the present invention is applied to a color video printer, FIG. 2 is a block diagram showing an example of the configuration of a resistance and saturation voltage measuring section used in the embodiment, and FIG. FIG. 4 is a flowchart showing an example of the operation flow of the system control unit in the setup mode in the same embodiment; FIG. 4 is a flowchart showing an example of the operation flow of the system control unit in the recording mode in the same embodiment; FIG. FIG. 2 is a circuit diagram showing an isochoric circuit for measuring the resistance value and saturation voltage of the head in the same embodiment. Explanation of main part 1 29. , input terminal 410. Thermal head 6010 Image memory 10, System control section 14, Head control section 20. , , control memory 229. Correction data memory 30, resistance and saturation voltage measuring section Patent applicant: Fuji Photo Film Co., Ltd. Agent Number: Takao Kazan Takao RI

Claims (1)

[Scope of Claims] An input means for receiving a video signal; and a plurality of resistive heating elements are selectively driven to generate heat according to the video signal using corresponding driver elements, thereby transmitting an image represented by the video signal to an image receiving medium. In the video printer, the printer drives the plurality of resistive heating elements according to the video signal received by the input means, thereby transferring an image represented by the video signal onto the image receiving medium. a control means for recording; and a control means for measuring the resistance values of the plurality of resistive heating elements and the saturation voltage of the corresponding driver elements, and for compensating for variations in the image receiving medium caused by the measured resistance values and saturation voltages. and a measuring means for deriving correction data for correcting the driving of the resistance heating elements, and a storage means for accumulating the correction data, and the control means includes: a resistance value of the plurality of resistance heating elements,
and measuring the saturation voltage of the corresponding driver element,
The correction data corresponding to the saturation voltage and resistance value is derived, the correction data is stored in the storage means in correspondence with the resistance heating element, and when the input means receives the video signal, the video signal is When recording the image by driving the plurality of resistance heating elements in accordance with the above, the correction data corresponding to the driven resistance heating elements is read from the storage means, and according to the read correction data. A video printer characterized in that the drive of the resistive heating element is corrected by using the resistive heating element.