KR20080006215A - Image forming apparatus and control method thereof - Google Patents

Abstract

An image forming apparatus and a control method thereof are provided to compensate printing concentration which changes depending on the temperature of printer head elements by predicting temperatures of a plurality of printer head elements respectively, thereby maintaining consistent level of printing concentration. An image forming apparatus comprises a printer head part(140), a thermistor(144), an image processing part(120), and a head temperature predicting part(110). The printer head comprises a plurality of printer head elements(142). The thermistor, as a temperature measurement element, measures ambient temperature around the printer head part. The image processing part prints out a print image data by controlling a gamma variable with respect to the printing concentration of the image based on the predicted temperature of each print head element. The head temperature predicting part calculates predicted temperature of each printer head element based on the measured temperature and temperature difference of each printer head element calculated by the print image data, and provides the predicted temperature to the image processing data.

Description

Image forming apparatus and control method therefor {IMAGE FORMING APPARATUS AND CONTROL METHOD THEREOF}

1 is a diagram showing the configuration of an image forming apparatus according to the present invention;

2 is a flowchart for obtaining values of each storage unit of the image processing unit according to the present invention;

3A to 3E are graphs illustrating a modeling process according to the flowchart shown in FIG. 2.

4A and 4B are diagrams showing changes in print density according to the progress of each printing line when the present invention is not applied and when it is applied.

Explanation of symbols on the main parts of the drawings

110: head temperature prediction unit 112: temperature accumulation amount storage unit

114: temperature variation calculation unit 116: head element temperature calculation unit

120: image processing unit 122: initial gamma variable storage unit

124: sensitivity coefficient storage unit 126: gamma variable control unit

130: print head drive unit 140: print head unit

142: print head element

The present invention relates to an image forming apparatus and a control method of the apparatus, and more particularly, to an image forming apparatus and a control method of the apparatus capable of compensating for the printing density that changes depending on the temperature of the print head element.

BACKGROUND OF THE INVENTION A thermal transfer type image forming apparatus can obtain a density within one pixel by modulating the applied energy of a heating element which is a print head element, and is widely used in color image forming apparatuses such as a photo printer. However, in this thermal transfer method, the print density is easily affected by the ambient temperature or the heat accumulated in the heating element which is the print head element, and thus it is difficult to obtain a stable print density.

In order to improve the above-mentioned problem, US Patent No. 5,539, 433 calculates pulse width correction data from the detected temperature detected by the heat dissipating portion of the print head and the integrated value of the pulse width data of one print row assigned to the print head. An image forming apparatus for compensating a print density according to a temperature change is disclosed.

However, since the image forming apparatus averages and uses the pulse width data of all the pixels in one print row, the print density compensation is not accurately performed for each print head element.

An object of the present invention is to provide an image forming apparatus and a control method of the apparatus capable of compensating an image density printed on a print medium by predicting a temperature of each print head element.

In order to achieve the above object, the present invention provides an image forming apparatus, comprising: a printhead portion having a plurality of printhead elements, a temperature measuring element measuring ambient temperature of the printhead portion, and prediction of the printhead elements; An image processing unit for outputting print image data by adjusting a gamma parameter related to print density based on a temperature value, and a temperature change amount of each of the print head elements calculated according to the print image data, A head temperature predicting unit is provided for calculating a predicted temperature value of each of the print head elements based on the measured measurement temperature and providing the predicted temperature value to the image processing unit.

The image processing unit preferably adjusts the gamma variable by using an initial gamma variable determined using the print image data variation curves for the print density and a sensitivity coefficient according to the temperature change.

Preferably, the head temperature predicting unit calculates a temperature change amount of each print head element by using the accumulated temperature up to the previous print row and the print image data of the previous print row.

Meanwhile, the present invention provides a method of controlling an image forming apparatus, the method comprising: outputting a test input image for each predetermined temperature, calculating variation curves of the print image data for each predetermined temperature by the test input image, and calculating the curves Determining an initial gamma variable from the first step, obtaining a sensitivity coefficient at which the first gamma variable changes as the predetermined temperature changes, and calculating a gamma variable for each temperature using the first gamma variable and the sensitivity coefficient. The above object can also be achieved.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

The configuration of the image forming apparatus according to the present invention is shown in FIG. The image forming apparatus according to the present invention includes a head temperature predicting unit 110, an image processing unit 120, a print head driving unit 130, and a printer head unit 140.

The head temperature prediction unit 110 includes a temperature accumulation amount storage unit 112, a temperature change amount calculation unit 114, and a head element temperature calculation unit 116, and print image data of each pixel output from the image processing unit 120. The temperature change amount is calculated for each print head element of the current print line by using the accumulated temperature of each print head element up to the previous print line and the print image data of each print head element of the previous print line. The temperature value of each print head element is predicted based on the temperature change amount calculated for each print head element in the row and the temperature measured by the thermistor 144 of the print head unit 140.

The image processing unit 120 includes an initial gamma variable storage unit 122, a sensitivity coefficient storage unit 124, and a gamma variable adjusting unit 126, using the initial gamma variable and the sensitivity coefficient according to the temperature change. By adjusting, the input image is corrected according to the predicted temperature value of each print head element 142 to output the print image data.

The print head driver 130 controls the print image data output from the image processor 120 to be printed on the print medium using the print head elements 142.

The print head unit 140 includes a plurality of print head elements 142 for printing a print medium and a thermistor 144 that is a temperature measuring element for measuring the temperature of the print head unit 140.

Before describing the operation of the present invention by the configuration of FIG. 1 in detail, modeling for obtaining values stored in each storage unit shown in FIG. 1 will be described with reference to the flowchart of FIG. 2 and FIG. 3.

Printed image data means energy to be printed, and in the case of an actual image forming apparatus, it is mainly expressed by the number of pulses or the pulse width. Therefore, in order to facilitate the description of FIG. 3 of the modeling process, the description of the print image data is limited to the number of pulses.

The modeling of the image processor 120 outputs a test input image of the type shown in FIG. 3A for each of a plurality of temperatures within the operating temperature, that is, a predetermined temperature (S200). The predetermined temperature means 35.8 ° C, 40.9 ° C, 45,9 ° C, and 50.1 ° C shown in FIGS. 3B and 3C. The test input image is a mixture of a horizontal lamp image and a vertical lamp image as shown in FIG. 3A. Use burn.

Scanning is sequentially performed from the first printed line outputted according to the test input image to obtain the print density for the number of pulses as shown in FIG. 3B (S202). That is, the print density can be expressed as a function of the number of pulses and the temperature.

3B, the number of pulse changes for obtaining a constant print density is calculated as shown in FIG. 3C. The initial gamma variable G (To) is calculated from the number-of-pulse variation curve of FIG. 3C (S204), and the first gamma variable may be determined by selecting a curve of a specific temperature, and the first gamma variable may be determined using the average of these curves. It may be. The first gamma variable G (To) determined here is stored in the first gamma variable storage 122 of FIG. 1.

The sensitivity coefficient indicates the degree to which the initial gamma variable changes as the predetermined temperature changes. The sensitivity coefficient is expressed by two types, SH and SL, where SH means the number of pulses corresponding to the maximum print density of the print head element, and SL means the number of pulses corresponding to the minimum print concentration of the print head element (S206). ). Sensitivity coefficients SH and SL are functions of temperature and become smaller as the temperature increases, as shown in FIG. 3D. The sensitivity coefficients SH and SL calculated here are stored in the sensitivity coefficient storage unit 124 of FIG.

The gamma variable for each temperature is calculated using the first gamma variable and the sensitivity coefficient (S208), which is represented by Equation (1).

………(1)

… … … (One)

3E shows the result of Equation (1), and it can be seen that the lower the temperature, the more pulse counts are required to maintain the same print density.

On the other hand, modeling of the head temperature prediction unit 110 indicates how much the number of pulses for displaying image print data in the previous print row changes the temperature of the print head element in the current print row.

The equation for obtaining the temperature change amount of the print head element in the current printing line is expressed in equation (2).

P (m, n) = α * P (m-1, n) + β * E (m-1, n)... … … (2)

Where P (m, n) is the temperature change at position (m, n), α is the temperature loss parameter, β is the temperature conversion parameter for the number of pulses, and E (m, n) is (m, n) The number of pulses at the position.

As can be seen from Equation (2), the temperature accumulation amount of each printhead element up to the previous print line and the number of pulses corresponding to each pixel of the previous print line are used for each printhead element 142 of the current print line. Calculate the temperature change.

The equation for obtaining the predicted temperature value of each print head element 142 supplied to the image processing unit 120 is expressed in equation (3).

Th (m, n) = P (m, n) + k * (Tt (m) -Ts) + Ts... … … (3)

Where Th (m, n) is the predicted temperature value of the printhead element, Tt (m) is the thermistor temperature value at the mth print line, and Ts is the thermistor temperature value at the start of printing, which is the same as Tt (1) , k is the thermistor temperature spreading parameter.

The configuration and operation of FIG. 1 using the values stored in each storage unit by the above-described modeling will be described in more detail.

The head temperature predicting unit 110 includes a temperature accumulation amount storage unit 112, a temperature change amount calculating unit 114, and a head element temperature calculating unit 116 in order to predict a temperature value of each print head element.

The cumulative amount storage unit 112 stores the cumulative temperature P (m-1, n) up to the previous printing line. In the temperature change amount calculating unit 112, the temperature accumulation amount P (m-1, n) up to the previous printing line stored in the cumulative amount storing unit 112 and the previous printing output from the image processing unit 120 in Equation (2). The amount of temperature change P (m, n) at the position (m, n) of the printhead element is calculated using the pulse number E (m-1, n) representing the print image data of the row. The head element temperature calculating unit 116 is expressed by equation (3), that is, the measured temperature Tt (m) measured by the thermistor 144 and the temperature change amount P (m, n) of the print head element calculated by the temperature change amount calculating unit 114. The estimated temperature value of each printhead element 142 is calculated and provided to the image processor.

The image processing unit 120 corrects the input image according to the predicted temperature value of each print head element 142 to output the print image data. The initial gamma variable storage unit 122, the sensitivity coefficient storage unit 124, and the gamma Variable adjustment unit 126 is included.

The initial gamma variable storage unit 122 stores an initial gamma variable G (To) determined by selecting a curve of a specific temperature of the number-of-number variation curves for the print density of FIG. 3C or using an average value of the curves. The sensitivity coefficient storage unit 124 stores the above-described sensitivity coefficients SH and SL indicating the extent to which the initial gamma variable changes as the predetermined temperature changes. The gamma variable adjusting unit 126 uses the first gamma variable G (To) stored in the first gamma variable storage unit 122 and the sensitivity coefficients SH and SL stored in the sensitivity coefficient storage unit 124 to adjust the temperature. Calculate the star gamma variable.

The process of calculating the predicted temperature value of the printhead element of the current print line and the process of outputting the print image data using the gamma variable will be described.

When the input image of the first print line input from the PC or the like is input to the image processing unit 120, the value stored in the temperature accumulation amount storage unit 112 is 0, and a pulse for displaying the print image data output from the image processing unit 120. Since the number is also zero for all the pixels, the values in the temperature change calculation unit 114 are all zero. Therefore, since the ambient temperature of the print head unit 140 by the thermistor 144 is input to the head element temperature calculating unit 116, the temperature value of each print head element 142 becomes the ambient temperature value of the print head unit. The predicted temperature values of the printhead elements input to the gamma variable adjusting unit 126 are equal to each other, and the gamma variable adjusting unit calculates a gamma variable using Equation (1). Accordingly, each pixel of the input image of the first print line is corrected using the calculated gamma variable, converted into the number of pulses, and output to the print head driver 130. This number of pulses is also supplied to the temperature change calculation unit 114.

When the input image of the second print line is input to the image processing unit 120, all of the values stored in the temperature accumulation amount storage unit 112 are 0 or the number of pulses of the first printing line output from the image processing unit 120 changes in temperature. Since it is supplied to the calculation unit 114, the temperature change amount in the temperature change amount calculation unit 114 is calculated by the number of pulses in the first printing line, and this temperature change amount is stored in the temperature accumulation amount storage unit 112.

When the input image of the third printing line is input to the image processing unit 120, the temperature change amount calculating unit 114 stores the accumulated temperature stored in the temperature accumulation amount storage unit 112 and the second printing line output from the image processing unit 120. Using the number of pulses, the temperature change amount of the printer printing element of the current printing line is calculated.

Figure 4a shows the change in magenta print density according to the progress of each print line when the present invention is not applied, Figure 4b shows the change in magenta print density according to the progress of each print line when the present invention is applied It is displayed. Comparing FIG. 4A with FIG. 4B, it can be seen that a more consistent print density can be obtained when the present invention is applied.

As described above, according to the present invention, it is possible to maintain a constant image density by estimating the temperature of each print head element to compensate for the image density printed on the print medium.

Claims (4)

In the image forming apparatus, A print head unit having a plurality of print head elements; A temperature measuring element measuring an ambient temperature of the print head; An image processing unit for outputting print image data by adjusting a gamma parameter related to a print density based on an estimated temperature value of each print head element; A head temperature prediction is provided to the image processing unit by calculating an estimated temperature value of each of the print head elements based on the temperature change amount of each of the print head elements calculated according to the print image data and the measured temperature measured by the temperature measuring element. An image forming apparatus comprising a portion. The method of claim 1, And an image processor to adjust the gamma variable by using an initial gamma variable determined by using print image data variation curves for the print density and a sensitivity coefficient according to temperature change. The method of claim 1, And the head temperature predicting unit calculates a temperature change amount of each print head element by using the accumulated temperature up to the previous print row and the print image data of the previous print row. In the control method of the image forming apparatus, Outputting a test input image for each predetermined temperature; Obtaining variation curves of the print image data with respect to the print density for each predetermined temperature by the test input image, and determining an initial gamma variable from the curves; Obtaining a sensitivity coefficient at which the initial gamma variable changes as the predetermined temperature changes; Calculating a gamma variable for each temperature using the first gamma variable and the sensitivity coefficient.

Images