Ink supply amount adjustment method and apparatus for printing press

The present invention relates to an ink supply amount adjustment method and apparatus for a printing press, which adjust the ink supply amount to a printing plate on the basis of the density value or color value of a printing product.

FIG. 16 shows the main part of the inking device (inker) in each color printing unit of a web offset printing press. Referring to FIG. 16 , reference numeral 1 denotes an ink fountain; 2 , ink stored in the ink fountain 1 ; 3 , an ink fountain roller which forms part of the ink fountain 1 ; 4 , a plurality of ink keys juxtaposed in the axial direction of the ink fountain roller 3 ; 5 , an ink ductor roller which supplies the ink from the ink fountain roller 3 to ink rollers 6 by swinging between these rollers 3 and 6 ; and 8 , a plate cylinder on which a printing plate 7 is mounted on its outer surface, and to which the ink is supplied from the ink rollers 6 . An image is printed on the printing plate 7 .

In this inking device, the ink 2 in the ink fountain 1 is supplied to the ink fountain roller 3 through the gap between the plurality of ink keys 4 - 1 to 4 -n and the ink fountain roller 3 . The ink supplied to the ink fountain roller 3 is supplied to the printing plate 7 through the ink rollers 6 by the duct operation of the ink ductor roller 5 . The ink supplied to the printing plate 7 is transferred onto a printing paper sheet through a blanket cylinder (not shown).

FIG. 17 shows a printing product printed by this printing press. A band-shaped color bar 9 - 2 is printed on the margin portion of a printing product 9 except an image region 9 - 1 in the widthwise direction of the paper sheet. In general four-color printing, the color bar 9 - 2 includes a region S 1 and regions S 2 to Sn including density measurement patches (solid patches at a percent dot area of 100%) 9 a 1 , 9 a 2 , 9 a 3 , and 9 a 4 of black, cyan, magenta, and yellow. The regions S 1 to Sn correspond to the respective key zones of plurality of ink keys 4 - 1 to 4 -n in each color printing unit of the printing press.

[Color Matching]

A reference density value is set in advance for each color (black, cyan, magenta, or yellow) printing unit. In printing the printing product 9 , a color matching operation is done to make the density value of each color coincide with the set reference density value. This color matching operation is executed by the ink supply amount adjustment apparatus during final printing or before final printing on the basis of the density of a density measurement patch 9 a ( 9 a 1 , 9 a 2 , 9 a 3 , or 9 a 4 ) of each color in the color bar 9 - 2 printed on the printing product 9 . “During final printing” means a period of printing printed matters as products. “Before final printing” means a period of preparation for printing when ink supply amount is adjusted while printing, prior to printing printed matters as products.

An ink supply amount adjustment operation will now be described by using the region S 1 in the printing product 9 as a representative. The density value of the density measurement patch 9 a ( 9 a 1 , 9 a 2 , 9 a 3 , or 9 a 4 ) of each color on the printing product 9 , which is extracted before or during final printing, is measured. The difference between the measured density value of each color and the preset reference density value of each color is obtained. The adjustment amount of the opening ratio of the ink key 4 - 1 (the adjustment amount of ink supply amount to the region S 1 ) in each color printing unit is then obtained from the obtained density difference of each color. The resultant adjustment amounts (reference correction amounts) are multiplied by a unique coefficient (control ratio) to obtain a correction amount. The resultant correction amount is fed back to adjust the opening ratio of the ink key 4 - 1 in each color printing unit.

In a similar way, for regions S 2 to Sn as well, the adjustment amounts of the opening ratios of the ink keys 4 - 2 to 4 -n (the adjustment amounts of ink supply amounts to the regions S 2 to Sn) in each color printing unit are obtained. The resultant adjustment amounts (reference correction amounts) are multiplied by a control ratio to obtain a correction amount. The resultant correction amount is fed back to adjust the opening ratios of the ink keys 4 - 2 to 4 -n in each color printing unit.

Note that, in adjusting the opening ratios of the ink keys 4 - 1 to 4 -n in each color printing unit, the only allowable density difference of each color is defined for the density difference (measured density difference) between the measured density value of each color and the preset reference density value of each color. The ink supply amount is adjusted for the corresponding ink key when the obtained measured density differences are larger than the allowable density difference (Japanese Patent Laid-Open No. 2003-118077).

In the above-described conventional ink supply amount adjustment method, an operator arbitrarily sets an allowable density difference for a measured density difference, for each color. When using ink, e.g., process ink of black, cyan, magenta, or yellow, which is generally used in printing, the operator can experimentally set the allowable density difference as an almost adequate value. However, when using ink (special ink) of a special color, which has never (rarely) been used, the operator does not obtain the adequate allowable density difference of each color.

Hence, when a wrong allowable density difference is set, in some cases, the ink supply amount is not corrected although it must be corrected. Alternatively, in some cases, the ink supply amount is corrected although it need not be corrected. This causes the hunting phenomenon (the color tone becomes unstable because of the variation in color density on the printing product) of the ink film thickness on the paper sheet, thus posing a problem. In addition, assume that the allowable density difference is small, and the ink supply amount adjustment interval (printing product sampling interval) is short. While the preceding adjustment of the ink supply amount is not sufficiently reflected on the printing product, the next ink supply amount adjustment is done. In this case, a hunting phenomenon of the ink thickness on the paper sheet also occurs.

In addition, the density value of a specific part of the printing product may temporarily largely vary due to an unexpected accident (paper fold error, paper breakage, or smear) on the printing product. In this case, when the ink supply amount is adjusted from the measured density difference as usual, the ink supply amount is adjusted to a value largely shifted from what the ink supply amount should be. As a result, the amount of wasted paper increases, thus posing a problem.

It is an object of the present invention to provide an ink supply amount adjustment method and apparatus for a printing press, which can automatically set the adequate value of the allowable density difference or allowable color difference, regardless of the color of the ink.

It is another object of the present invention to provide an ink supply amount adjustment method and apparatus for a printing press, which can prevent the occurrence of the hunting phenomenon of an ink thickness on a paper sheet, when the allowable density difference or allowable color difference is small.

It is still another object of the present invention to provide an ink supply amount adjustment method and apparatus for a printing press, which can suppress the amount of wasted paper even when an unexpected accident has occurred on a printing product.

In order to achieve the above objects according to the present invention, there is provided an ink supply amount adjustment method for a printing press, comprising the steps of measuring one of a density value and a color value of a printing product, obtaining a difference between the measurement value and a preset reference value, as a measurement difference, setting a first error ratio allowed with respect to the preset reference value, as a first allowable ratio, obtaining a first allowable difference from the preset reference value and the set first allowable ratio, and adjusting an ink supply amount on the basis of the obtained measurement difference and the obtained first allowable difference.

FIG. 1 is a block diagram showing an ink supply amount adjustment apparatus according to the first embodiment of the present invention;

FIG. 2 is a view showing the structure of a memory unit shown in FIG. 1 ;

FIG. 3 is a side view of a colorimeter shown in FIG. 1 ;

FIG. 4 is a graph showing a relationship between a reference density value and an allowable density difference set in accordance with the reference density value in the ink supply amount adjustment apparatus shown in FIG. 1 ;

FIGS. 5A to 5E are flowcharts showing the processing operation of the ink supply amount adjustment apparatus shown in FIG. 1 ;

FIG. 6 is a flowchart showing the processing operation of an ink key driving motor control device;

FIG. 7 is a block diagram of an ink supply amount adjustment apparatus according to the second embodiment of the present invention;

FIG. 8 is a view showing the structure of a memory unit shown in FIG. 7 ;

FIGS. 9A to 9F are flowcharts showing the processing operation of the ink supply amount adjustment apparatus shown in FIG. 7 ;

FIG. 10 is a block diagram of an ink supply amount adjustment apparatus according to a modification to the first embodiment when “color-value (ratio)” and “color difference” are used in place of “density value (ratio)” and “density difference”;

FIG. 11 is a view showing the structure of a memory unit shown in FIG. 10 ;

FIGS. 12A to 12E are flowcharts showing the processing operation of the modification shown in FIG. 10 ;

FIG. 13 is a schematic view of a memory unit in an ink supply amount adjustment apparatus according to a modification to the second embodiment when “color value (ratio)” and “color difference” are used in place of “density value (ratio)” and “density difference”;

FIGS. 14A to 14F are flowcharts showing the processing operation of the modification shown in FIG. 13 ;

FIGS. 15A and 15B are functional block diagrams of a CPU shown in FIGS. 1 and 7 ;

FIG. 16 is a side view of the ink supply apparatus in each color printing unit of a web offset printing press; and

FIG. 17 is a plan view of a printing product printed by a printing press.

The present invention will be described below in detail with reference to accompanying drawings.

First Embodiment

A density measurement and ink supply amount adjustment apparatus (to be simply referred to as an ink supply amount adjustment apparatus hereinafter) according to the first embodiment of the present invention will be described below with reference to FIGS. 1 and 2 . As shown in FIG. 1 , an ink supply amount adjustment apparatus 10 comprises a CPU (Central Processing Unit) 10 A, RAM (Random Access Memory) 10 B, ROM (Read Only Memory) 10 B, ROM (Read Only Memory) 10 C, input device 10 D, display device 10 E, output device 10 F, input/output interfaces (I/Os) 10 G to 10 K, calorimeter 10 L, calorimeter moving motor 10 M, rotary encoder 10 N, motor driver 10 P, counter 10 Q, A/D converter 10 R, D/A converter 10 S, reference density value measurement colorimeter 10 T, A/D converter 10 U, and memory unit M.

The CPU 10 A operates in accordance with a program stored in the ROM 10 C while obtaining various kinds of input information given through the interfaces 10 G to 10 K and accessing the RAM 10 B or memory unit M. The input device 10 D has a printing state input switch SW 1 , density measurement start switch SW 2 , control end switch SW 3 , allowable value condition input switch SW 4 , reference density value measurement switch SW 5 , and the like. The rotary encoder 10 N generates a rotation pulse for each predetermined number of revolutions (angle) of the motor 10 M and outputs the pulse to the counter 10 Q.

A plurality of ink key driving motor control devices 11 - 1 to 11 -n are arranged in correspondence with the ink keys 4 - 1 to 4 -n of the respective colors shown in FIG. 14 . The ink key driving motor control devices 11 - 1 to 11 -n individually adjust the opening ratios of the ink keys 4 - 1 to 4 -n for an ink fountain roller 3 . Each of the motor control devices 11 - 1 to 11 -n comprises an ink key driving motor driver 11 A, ink key driving motor 11 B, rotary encoder 11 C, and counter 11 D. The motor control devices 11 - 1 to 11 -n are connected to the CPU 10 A of the ink supply amount adjustment apparatus 10 through the interface 10 G. The rotary encoder 11 C generates a rotation pulse for each predetermined number of revolutions (angle) of the motor 11 B and outputs the pulse to the counter 11 D.

The memory unit M comprises memories M 1 to M 19 as shown in FIG. 2 . The ON/OFF state of the printing state input switch SW 1 in the input device 10 D is stored in the printing state memory M 1 . The ON/OFF state of the allowable value condition input switch SW 4 in the input device 10 D is stored in the allowable value condition memory M 2 . The reference density value (the reference density value of each color) with respect to the density measurement patch 9 a of each color in the color bar 9 - 2 ( FIG. 15 ) printed on a printing product is stored in the reference density value memory M 3 .

The first allowable density difference (the first allowable density difference of each color) with respect to the density measurement patch 9 a of each color is stored in the first allowable density difference memory M 4 . The second allowable density difference (the second allowable density difference of each color) with respect to the patch 9 a for each color is stored in the second allowable density difference memory M 5 . In this embodiment, the second allowable density difference of each color is set larger than the first allowable density difference.

A first allowable density ratio (first error ratio allowed with respect to the reference density value) β 1 is stored in the first allowable density ratio memory M 6 . A second allowable density ratio (second error ratio allowed with respect to the reference density value) β 2 is stored in the second allowable density ratio memory M 7 . In this embodiment, the second allowable density ratio β 2 is set larger than the first allowable density ratio β 1 (β 2 >β 1 ).

The minimum value of a measured density difference for adjusting the ink supply amount is set as an allowable density difference minimum value in the allowable density difference minimum value memory M 8 . The measurement position of the patch 9 a of each color is stored in the patch position memory M 9 . The color data of the patch 9 a of each color, which is sampled by the calorimeter 10 L, is stored in the patch color data memory M 10 . A density value (measured density value) obtained from the color data of the patch 9 a of each color, which is sampled by the calorimeter 10 L, is stored in the measured density value memory M 11 .

A conversion curve is stored in the conversion curve memory M 12 . The conversion curve represents the relationship between the difference between the measured density value and the reference density value of each color and the adjustment amount of the opening ratio of the ink key. The adjustment amount (reference correction amount) of the opening ratio of each ink key is stored in the ink key opening ratio reference correction amount memory M 13 . The adjustment amount is obtained from the conversion curve in the memory M 12 . A first coefficient (first control ratio) α 1 is stored in the first coefficient memory M 14 . The first coefficient α 1 is used to correct the reference correction amount of the opening ratio of each ink key. A second coefficient (second control ratio) α 2 is stored in the second coefficient memory M 15 . The second coefficient α 2 is used to correct the reference correction amount of the opening ratio of each ink key. In this embodiment, the first coefficient αl and second coefficient α 2 are different from each other and are set to α 1 >α 2 .

The correction amount of the opening ratio of each ink key is stored in the ink key opening ratio correction amount memory M 16 . The correction amount is corrected by using the coefficient α 1 or α 2 . The difference (measured density difference) between the measured density value of the patch 9 a of each color and the reference density value of each color is stored in the measured density difference memory M 17 . Reference density value measured color information input by the operator is stored in the color information memory M 18 . The color data sampled by the reference density value measurement calorimeter 10 T is stored in the color data memory M 19 .

As shown in FIG. 3 , the colorimeter 10 L is attached to a ball screw (feed screw) 12 - 3 arranged between a pair of columns 12 - 1 and 12 - 2 . The ball screw 12 - 3 is rotated in the forward or reverse direction by the calorimeter moving motor 10 M. As the ball screw 12 - 3 rotates in the forward or reverse direction, the calorimeter 10 L moves between the columns 12 - 1 and 12 - 2 while being guided by the ball screw 12 - 3 . A head portion 10 L 1 of the calorimeter 10 L is directed to a surface 12 - 4 a of a measurement table 12 - 4 on which an object to be measured is placed.

The operation of the first embodiment will be described below with reference to FIGS. 5A to 5E , and FIG. 6 .

[Color Matching Before Start of Final Printing (Color Matching at Time of Preparation for Printing)]

In color matching before the start of final printing, the operator sets, on the measurement table 12 - 4 ( FIG. 3 ), the printing product 9 printed by the printing press as an object to be measured. In this state, the color bar 9 - 2 printed on the printing product 9 is located under the head portion 10 L 1 of the calorimeter 10 L.

Next, the operator instructs the start of the color matching operation through the input device 10 D. Accordingly, the CPU 10 A stores “0” in the memory M 1 (step S 101 shown in FIG. 5A ). The CPU 10 A also stores “0” in the memory M 2 (step S 102 ). When the operator inputs first and second allowable density ratios β 1 and β 2 , the CPU 10 A stores the first allowable density ratio β 1 in the memory M 6 , and the also stores the second allowable density ratio β 2 in the memory M 7 (step S 103 ). When the operator inputs the allowable density difference minimum value, the CPU 10 A stores the input allowable density difference minimum value in the memory M 8 (step S 104 ). When the operator inputs the reference density value of each color in the color bar 9 - 2 from the input device 10 D, the CPU 10 A stores the reference density value of each color in the memory M 3 (step S 105 ). Note that the second allowable density ratio β 2 is input as a value larger than the first allowable density ratio β 1 .

The operator inputs the position of each patch of each color in the color bar 9 - 2 from the input device 10 D (step S 106 ). On the basis of the position of the input patch of each color, the CPU 10 A calculates the position of the patch of each color to be measured by the colorimeter 10 L, i.e., the position (measurement position) of the density measurement patch 9 a of each color. The calculated measurement position is stored in the memory M 9 (step S 107 ).

The operator inputs the first coefficient α 1 and second coefficient α 2 to correct the reference correction amount of the opening ratio of each ink key. The CPU 10 A stores the input first coefficient α 1 in the memory M 14 . The CPU 10 A stores the second coefficient α 2 in the memory M 15 (step S 108 ).

The operator turns on the start switch SW 2 in the input device 10 D. On the basis of the step (“YES” in step S 122 ), the CPU 10 A reads out the reference density value of each color from the memory M 3 (step S 130 ), and then reads out the first allowable density ratio β 1 from the memory M 6 (step S 131 ). Accordingly, the CPU 10 A calculates the first allowable density difference of each color from the readout reference density value and first allowable density ratio β 1 of each color. The resultant difference is stored in the memory M 4 (step S 132 ). In this calculation, the CPU 10 A obtains the first allowable density difference of each color by multiplying the reference density value of each color by the first allowable density ratio β 1 commonly used for each color.

The CPU 10 A reads out the second allowable density ratio β 2 from the memory M 7 (step S 133 ). The CPU 10 A also calculates the second allowable density difference of each color from the reference density value of each color readout in step S 130 and the second allowable density ratio β 2 read out in step S 133 . The resultant value is stored in the memory M 5 (step S 134 ). In this calculation, the CPU 10 A obtains the second allowable density difference of each color by multiplying the reference density value of each color by the second allowable density ratio β 2 commonly used for each color.

The CPU 10 A then reads out the allowable density difference minimum value from the memory M 8 (step S 135 ), and compares the readout allowable density difference minimum value with the first allowable density difference of each color obtained in step S 132 (step S 136 ). If the first allowable density difference is smaller than the allowable density difference minimum value (“YES” in step S 136 ), the first allowable density difference of the corresponding color is changed to the allowable density difference minimum value (step S 137 ). In a similar way, the CPU 10 A compares the allowable density difference minimum value with the second allowable density difference of each color obtained in step S 134 (step S 138 ). If the second allowable density difference is smaller than the allowable density difference minimum value, the second allowable density difference of the corresponding color is changed to the allowable density difference minimum value (step S 139 ).

Accordingly, as shown in FIG. 4 , the proportionality constant of the allowable density difference (first and second allowable density differences) of each color is the allowable density ratio β (β 1 and β 2 ) commonly used for each color. The allowance density difference of each color is defined as the value corresponding to the reference density value of each color. The lower limit of the allowable density difference of each color is controlled to be set equal to or larger than the allowable density difference minimum value. With this control, the allowable density difference is prevented from being set excessively small.

As the allowable density ratio β (β 1 and β 2 ) commonly used for each color is set, the allowable density difference (first and second allowable density differences) of each color can be automatically set as the adequate value corresponding to the reference density value of each color. Hence, not only when using the ink which is generally used, but also when using the special ink which has never (rarely) been used, the adequate value of the allowable density difference can be obtained. That is, the adequate value of the allowable density difference corresponding to the reference density value of the ink can be automatically set only by applying the reference density value of the special ink. Therefore, the present invention can solve the problems that the ink supply amount is not corrected although it must be corrected, and that the ink supply amount is corrected although it need not be corrected, thereby causing the hunting phenomenon of the ink thickness on the paper sheet.

Note that in this embodiment, when the reference density value of the ink is unknown, the reference density value measurement calorimeter 10 T is set to the printing product (the printing product printed by the reference density value) printed by the ink. The switch SW 5 instructing to measure the reference density value is turned on before turning on the start switch SW 2 in step S 122 ( FIG. 5A ).

As the switch SW 5 is turned on (“YES” in step S 121 ), the CPU 10 A urges the operator to input the reference density value measured color information. Accordingly, when the operator inputs the color of the ink on this printing product as the reference density value measured color information in response to the CPU 10 A (“YES” in step S 124 shown in FIG. 5E ), the CPU 10 A stores the input reference density value measured color information in the memory M 18 (step S 125 ) to supply a measurement start signal to the calorimeter 10 T (step S 126 ). Next, the color data is read out from the colorimeter 10 T, and the readout color data is stored in the memory M 19 (step S 127 ).

The CPU 10 A then calculates the density value of the ink printed on the printing product from the input reference density value measured color information and the color data from the calorimeter 10 T (step S 128 ). The calculation result is stored in the memory M 3 as the reference density value of the color of the ink (step S 129 ).

After steps S 130 to S 139 , the CPU 10 A rotates the motor 10 M in the forward direction (step S 140 shown in FIG. 5C ). As the motor 10 M rotates in the forward direction, the ball screw 12 - 3 rotates in the forward direction. The calorimeter 10 L is guided by the ball screw 12 - 3 and moves from the home position in contact with the column 12 - 1 toward the column 12 - 2 .

After step S 108 , the CPU 10 A repeats the loop of step S 109 →S 114 →S 121 →S 122 →S 123 . Accordingly, the states of the switches SW 1 to SW 5 are monitored. In this case, since the density measurement start switch SW 2 is turned on in step S 122 , the flow advances to step S 140 through steps S 130 to S 139 to move the calorimeter 10 L.

The CPU 10 A monitors every moving position of the colorimeter 10 L through the rotary encoder 10 N (step S 141 ). When the colorimeter 10 L has reached the first measurement position stored in the memory M 9 , the color data of the patch 9 a located at that measurement position is sampled by the calorimeter 10 L (step S 142 ). The CPU 10 A stores the color data (calorimetric data) from the calorimeter 10 L in the memory M 10 (step S 143 ).

In a similar way, every time reaching the measurement position stored in the memory M 9 , the CPU 10 A causes the colorimeter 10 L to sample the color data of the patch 9 a located at that measurement position and stores the sampled color data in the memory M 10 . As described above, the CPU 10 A executes automatic scanning control of the calorimeter 10 L to sequentially sample the color data of the density measurement patch 9 a of each patch in the color bar 9 - 2 printed on the printing product 9 .

When the CPU 10 A determines that the color data sampling of all patches 9 a of the color bar 9 - 2 is ended (“YES” in step S 144 ), the forward rotation of the motor 10 M is stopped (step S 145 ). Next, the CPU 10 A rotates the motor 10 M in the reverse direction (step S 146 ). When the CPU 10 A checks that the calorimeter 10 L returns to the home position (step S 147 ), the reverse rotation of the motor 10 L is stopped (step S 148 ).

The CPU 10 A calculates the density value of the patch 9 a of each color from the calorimetric data of the patch 9 a of each color stored in the memory M 10 and stores the density value in the memory M 11 (step S 149 ). In this embodiment, as the calorimeter 10 L, a spectrometer is used. The output value of each wavelength from the spectrometer is multiplied by the transmittance of each wavelength of the filter to be used to measure the solid patch of each color by a densitometer. The calculated values are totalized to obtain the density value of each color.

The CPU 10 A reads out the reference density value of each color from the memory M 3 (step S 150 ). The density difference (measured density difference) and the measured density value of the patch 9 a of each color stored in the memory M 11 is calculated (step S 151 ). The CPU 10 A obtains the adjustment amount of the opening ratio of an ink key corresponding to the measured density difference of the patch 9 a of each color by using a conversion table (representing the relationship between the measured density difference of each color and the adjustment amount of the ink key opening ratio) stored in the memory M 12 . The resultant adjustment amount (reference correction amount) is stored in the memory M 13 (step S 152 ).

Next, the CPU 10 A reads out the contents of the memory M 2 (step S 153 shown in FIG. 5D ). When “0” is stored in the memory M 2 (“YES” in step S 154 ), the CPU 10 A determines that the first allowable density difference should be used as the allowable density difference for color matching. The flow advances to step S 155 . When “0” is not stored in the memory M 2 (“NO” in step S 154 ), the CPU 10 A determines that the first allowable density difference should not be used as the allowable density difference for color matching. The flow advances to step S 158 . In this embodiment, “0” has been stored in the memory M 2 in step S 102 . Hence, the flow advances to step S 155 .

In step S 155 , the CPU 10 A reads out the first allowable density difference of each color from the memory M 4 . The CPU 10 A compares the measured density difference of the patch 9 a of each color, which is calculated in step S 151 , with the readout first allowable density difference of each color, (step S 156 ). For a patch whose measured density difference is determined to be equal to or smaller than the first allowable density difference (“YES” in step S 156 ), the reference correction amount of the opening ratio of the ink key corresponding to this patch is set to zero (step S 157 ). Accordingly, the reference correction amount of the opening ratio of the corresponding ink key is set to a value other than zero only when the measured density difference is larger than the first allowable density difference. Only for this ink key, the opening ratio is adjusted (the ink supply amount is adjusted), as will be described later.

The CPU 10 A reads out the contents stored in the memory M 1 (step S 166 ). If “0” is stored in the memory M 1 (“NO” in step S 167 ), the CPU 10 A determines that it is color matching before the start of final printing. If “1” is stored in the memory M 1 (“YES” in step S 167 ), the CPU 10 A determines that it is color matching during final printing. In this embodiment, “0” has been stored in the memory M 1 in step S 101 . Hence, the CPU 10 A determines that it is color matching before the start of final printing. The flow advances to step S 168 .

In step S 168 , the CPU 10 A reads out the first coefficient α 1 from the memory M 14 . The reference correction amount of the opening ratio of each ink key is multiplied by the readout first coefficient α 1 to obtain the correction amount of the opening ratio of each ink key. The resultant correction amount is stored in the memory M 16 (step S 169 ). The resultant correction amounts of the opening ratios of the ink keys are output to the motor drivers 11 A in the motor control devices 11 - 1 to 11 -n (step S 172 ).

In each of the motor control devices 11 - 1 to 11 -n, upon receiving the correction amount of the opening ratio of a corresponding ink key (“YES” in step S 201 shown in FIG. 6 ), the received correction amount is read (step S 202 ). In addition, the current ink key opening ratio is read through the counter 11 D (step S 203 ). A corrected ink key opening ratio is calculated on the basis of the correction amount of the ink key opening ratio from the CPU 10 A and the current ink key opening ratio (step S 204 ).

If the corrected ink key opening ratio equals the current ink key opening ratio (“YES” in step S 205 ), the ink key opening ratio correction end signal is output to the ink supply amount adjustment apparatus 10 (step S 210 ). If the corrected ink key opening ratio does not equal the current ink key opening ratio (“NO” in step S 205 ), the motor 11 B is driven until the corrected ink key opening ratio equals the current ink key opening ratio (steps S 206 to S 209 ). After that, the ink key opening ratio correction end signal is output to the ink supply amount adjustment apparatus 10 (step S 210 ).

Upon receiving the ink key opening ratio correction end signals from all the motor control devices 11 (“YES” in step S 173 shown in FIG. 6A ), the CPU 10 A of the ink supply amount adjustment apparatus 10 returns to step S 109 ( FIG. 5A ) to repeat the loop of step S 109 →S 114 →S 121 →S 122 →S 123 . In this loop, if the switch SW 3 is turned on (“YES” in step S 123 ), the above-described processing of color matching before the start of final printing is ended. Alternatively, if the switch SW 2 is determined to be turned on (“YES” in step S 122 ), the above-described processing of color matching before the start of final printing is repeated again.

[Change of Allowable Density Difference: When Hunting Phenomenon May Occur]

The operator repeats the above-described color matching before the start of final printing until the density difference between the measured density value of each color and the reference density value of each color becomes equal to or smaller than the first allowable density difference in all the regions S 1 to Sn on the printing product 9 . More specifically, printing is continued for a while until the effect of adjustment of the ink supply amount appears. A new printing product 9 is sampled, and color matching is executed again. This operation is repeated.

The operator checks the result of the preceding color matching. If he/she suspects that the hunting phenomenon of the ink thickness on the paper sheet should occur, the allowable density difference is changed from the first allowable density difference to the second allowable density difference. From the next color matching, the ink supply amount is adjusted only when the measured density difference is larger than the second allowable density difference (>first allowable density difference). That is, the threshold value for adjustment of the ink supply amount is made large. Accordingly, the hunting phenomenon of the ink thickness on the paper sheet can be suppressed.

The allowable density difference is changed by operating the switch SW 4 . In this embodiment, the switch SW 4 is turned on only when it is pressed and immediately returns to the OFF state. When the switch SW 4 is turned on (step S 114 shown in FIG. 5A ), the CPU 10 A reads out the contents of the memory M 2 (step S 115 ).

If “0” is stored in the memory M 2 (“YES” in step S 116 ), the CPU 10 A changes the contents of the memory M 2 to “1” (step S 118 ). If “0” is not stored in the memory M 2 (“NO” in step S 116 ), the flow advances to step S 117 . In this embodiment, “0” has been stored in the memory M 2 in step S 102 . Hence, the flow advances to step S 118 to change the contents of the memory M 2 to “1”.

In this way, the switch SW 4 is turned on once to change the contents of the memory M 2 to “1”. Then, the operator turns on the switch SW 2 . When the switch SW 2 is turned on (“YES” in step S 122 ), the CPU 10 A executes the processing in steps S 130 to S 152 ( FIGS. 5B and 5C ).

After step S 152 , the CPU 10 A reads out the contents of the memory M 2 (step S 153 shown in FIG. 5D ). Since “1” is stored in the memory M 2 , the flow advances to step S 159 through “NO” in step S 154 , and “YES” in step S 158 . The CPU 10 A reads out the second allowable density difference of each color from the memory M 5 . The CPU 10 A compares the measured density difference of the patch 9 a of each color, which is calculated in step S 151 , with the second allowable density difference of each color (step S 160 ). For a patch whose measured density difference is equal to or smaller than the second allowable density difference (“YES” in step S 160 ), the adjustment amount (reference correction amount) of the opening ratio of the corresponding ink key corresponding to this patch is set to zero (step S 161 ). Accordingly, the reference correction amount of the opening ratio of the corresponding ink key is set to a value other than zero only when the measured density difference is larger than the second allowable density difference. Only for this ink key, the opening ratio is adjusted (the ink supply amount is adjusted).

[Change of Allowable Density Difference: When Unexpected Accident has Occurred]

When an unexpected accident such as paper fold error, paper breakage, or smear on the printing product has occurred, and the density value of a specific part of the printing product 9 has temporarily largely varied, the operator changes the allowable density difference range from a range equal to or smaller than the first allowable density difference to a range from the second allowable density difference to the first allowable density difference (both inclusive). Accordingly, from the next color matching, the ink supply amount is adjusted only when the measured density difference is larger than the first allowable density difference and smaller than the second allowable density difference. In this case, even when the measured density difference exceeds the second allowable density value, the ink supply amount is not adjusted. The amount of wasted paper generated by the temporary variation in density value can be decreased.

The allowable density difference is changed by operating the switch SW 4 . When the switch SW 4 is turned on (first time), the CPU 10 A stores “1” in the memory M 2 (step S 114 →S 115 →S 116 →S 118 ). When the switch SW 4 is turned on again (second time), the CPU 10 A stores “2” in the memory M 2 (step S 114 →S 115 →S 116 →S 117 →S 119 ).

In this way, the switch SW 4 is turned on twice to store “2” in the memory M 2 . Then, the operator turns on the switch SW 2 . When the switch SW 2 is turned on (“YES” in step S 122 ), the CPU 10 A executes the processing in steps S 130 to S 152 ( FIGS. 5B and 5C ).

After step S 152 , the CPU 10 A reads out the contents of the memory M 2 (step S 153 shown in FIG. 5D ). Since “2” is stored in the memory M 2 , the CPU 10 A reads out the first and second allowable density differences of respective colors from the memories M 4 and M 5 through “NO” in steps S 154 and S 158 (steps S 162 and S 163 ). The CPU 10 A compares the measured density difference of the patch 9 a of each color, which is calculated in step S 151 , with the first and second allowable density differences of respective colors (step S 164 ). For a patch whose measured density difference is equal to or smaller than the first allowable density difference or equal to or larger than the second allowable density difference (“NO” in step S 164 ), the reference correction amount of the opening ratio of the ink key corresponding to this patch is set to zero (step S 165 ). Accordingly, the reference correction amount of the opening ratio of the corresponding ink key is set to a value other than zero only when the measured density difference is larger than the first allowable density difference and smaller than the second allowable density difference. Only for this ink key, the opening ratio is adjusted (the ink supply amount is adjusted).

[Color Matching During Final Printing]

To execute color matching during final printing, the operator turns on the switch SW 1 . In this embodiment, the switch SW 1 is turned on only when it is pressed and immediately returns to the OFF state. When the switch SW 1 is turned on (step S 109 shown in FIG. 5A ), the CPU 10 A reads out the contents of the memory M 1 (step S 110 ).

If “0” is stored in the memory M 1 (“YES” in step S 111 ), the CPU 10 A changes the contents of the memory M 1 to “1” (step S 112 ). Alternatively, if “1” is stored in the memory M 1 (“NO” in step S 111 ), the CPU 10 A changes the contents of the memory M 1 to “0” (step S 113 ). In this case, “0” has been stored in the memory M 1 in step S 101 . Hence, the contents of the memory M 1 is changed to “1” (step S 112 ).

Next, the operator turns on the start switch SW 2 . When the switch SW 2 is turned on (“YES” in step S 122 ), the CPU 10 A executes the processing in steps S 130 to S 152 ( FIGS. 5B and 5C ).

After step S 152 , the CPU 10 A reads out the contents of the memory M 2 (step S 153 shown in FIG. 5C ). When “0” is stored in the memory M 2 , the CPU 10 A executes the processing in steps S 155 to S 157 . When “1” is stored in the memory M 2 , the CPU 10 A executes the processing in steps S 159 to S 161 . When “2” is stored in the memory M 2 , the CPU 10 A executes the processing in steps S 162 to S 165 .

The CPU 10 A reads out the contents of the memory M 1 (step S 166 ). If “0” is stored in the memory M 1 (“NO” in step S 167 ), the CPU 10 A determines that it is color matching before the start of final printing. If “1” is stored in the memory M 1 (“YES” in step S 167 ), the CPU 10 A determines that it is color matching during final printing. In this case, “1” has been stored in the memory M 1 in step S 112 . Hence, the CPU 10 A determines that it is color matching during final printing, and the flow advances to step S 170 .

In step S 170 , the CPU 10 A reads out the second coefficient α 2 from the memory M 15 . The reference correction amount of the opening ratio of each ink key is multiplied by the readout second coefficient α 2 to obtain the correction amount of the opening ratio of each ink key. The resultant correction amount is stored in the memory M 16 (step S 171 ). The resultant correction amounts of the opening ratios of the ink keys are output to the motor drivers 11 A in the motor control devices 11 - 1 to 11 -n (step S 172 ).

Upon receiving the ink key opening ratio correction end signals from all the motor control devices 11 - 1 to 11 -n (“YES” in step S 173 ), the loop of step S 109 →S 114 →S 121 →S 122 →S 123 is repeated. In this loop, if the switch SW 3 is turned on (“YES” in step S 123 ), the above-described processing of color matching during final printing is ended. Alternatively, if the switch SW 2 is turned on (“YES” in step S 122 ), the above-described processing of color matching during final printing is repeated again.

Second Embodiment

In the first embodiment, the first and second allowable density ratios β 1 and β 2 used in color matching before the start of final printing are the same as those used for color matching during final printing. In color matching before the start of final printing, the ink amount in the inker is often largely different from the ink amount necessary for a printing product to be printed. Hence, the measured density difference is large. To the contrary, in color matching during final printing, the ink amount in the inker is not so different from the ink amount necessary for a printing product to be printed. Hence, the measured density difference is small. In the second embodiment, the first and second allowable density ratios β 1 F and β 2 F for color matching before the start of final printing and the first and second allowable density ratios β 1 M and β 2 M for color matching during final printing are set. The first and second allowable density ratios (during final printing) β 1 M and β 2 M are set smaller than the first and second allowable density ratios (before the start of final printing) β 1 F and β 2 F.

An ink supply amount adjustment apparatus according to the second embodiment of the present invention will be described with reference to FIG. 7 . The same reference numerals as in FIG. 11 denote the same or similar constituent elements in FIG. 1 , and a description thereof will be omitted. In this embodiment, an input device 10 D further comprises an allowable value condition input switch SW 41 for color matching before the start of final printing and an allowable value condition input switch SW 42 for color matching during final printing.

As shown in FIG. 12 , the memory unit M also comprises an allowable value condition memory M 21 for color matching before the start of final printing and an allowable value condition memory M 22 for color matching during final printing as allowable value condition memories. The apparatus also comprises memories M 41 and M 42 as first allowable density difference memories for each color. The memory M 41 stores the first allowable density difference of each color for color matching before the start of final printing. The memory M 42 stores the first allowable density difference of each color for color matching during final printing. The apparatus also comprises memories M 51 and M 52 as second allowable density difference memories for each color. The memory M 51 stores the second allowable density difference of each color for color matching before the start of final printing. The memory M 52 stores the second allowable density difference of each color for color matching during final printing.

In FIGS. 9A to 9F , the processing operation executed by a CPU 10 A of an ink supply amount adjustment apparatus 10 . The same step numbers as in FIGS. 5A , 5 B, and 5 D denote the same processing contents in FIGS. 9A to 9F , and a description thereof will be omitted. Note that, in the second embodiment, FIGS. 5C (steps S 140 to S 152 ) and 5 E (steps S 124 to 129 ) in the first embodiment are applied. Therefore, after step S 139 b shown in FIG. 9D , the flow advances to step S 140 shown in FIG. 5C . After step S 152 shown in FIG. 5C , the flow advances to step S 153 shown in FIG. 5C . If “YES” in step S 121 shown in FIG. 9B , the flow advances to step S 124 shown in FIG. 5E . After step S 129 shown in FIG. 5E , the flow advances to step S 122 shown in FIG. 9B .

In the second embodiment, in step S 103 ′ shown in FIG. 9A , the operator inputs the first and second allowable density ratios (before the start of final printing) β 1 F and β 2 F, and the first and second allowable density ratios (during final printing) β 1 M and β 2 M. In this case, the first and second allowable density ratios (during final printing) β 1 M and β 2 M are input as values smaller than those (before the start of final printing) β 1 F and β 2 F. The input first and second allowable density ratios (before the start of final printing) β 1 F and β 2 F are stored in the memories M 61 and M 71 , respectively. The input first and second allowable density ratios (during final printing) β 1 M and β 2 M are stored in the memories M 62 and M 72 , respectively.

[Change of Allowable Density Difference for Color Matching Before Start of Final Printing]

First, “0” is stored in the allowable value condition memory (before the start of final printing) M 21 . In step S 114 a ( FIG. 9B ), when the switch SW 41 is turned on once, “1” is stored in the allowable value condition memory (before the start of final printing) M 21 (step S 114 a →S 115 a →S 116 a →S 118 a ). When the switch SW 41 is turned on twice, “2” is stored in the allowable value condition (before the start of final printing) memory M 21 (step S 114 a →S 115 a →S 116 a →S 117 a →S 119 a ).

When a switch SW 2 is turned on (“YES” in step S 122 ), CPU 10 A reads out the reference density value of each color from the memory M 3 (step S 130 shown in FIG. 9C ), and the first allowable density ratio (before the start of final printing) β 1 F from the memory M 61 (step S 131 a ). The CPU 10 A calculates the first allowable density difference (before the start of final printing) of each color from the readout reference density value of each color and the first allowable density ratio (before the start of final printing) β 1 F. The calculation result is stored in the memory M 41 (step S 132 a ).

Next, the CPU 10 A reads out the second allowable density ratio (before the start of final printing) β 2 F from the memory M 71 (step S 133 a ). The CPU 10 A calculates the second allowable density difference (before the start of final printing) from the readout reference density value of each color and the second allowable density ratio (before the start of final printing) β 2 F. The calculation result is stored in the memory M 51 (step S 134 a ).

In a similar way, the CPU 10 A reads out the first allowable density ratio (during final printing) β 1 M from the memory M 62 (step S 131 b ), and the second allowable density ratio (during final printing) β 2 M from the memory M 72 (step S 133 b ). The CPU 10 A then calculates the first and second allowable density differences (during final printing) of each color (steps S 132 b and S 134 b ). The calculation results are respectively stored in the memories M 42 and M 52 .

The CPU 10 A then reads out the allowable density difference minimum value from the memory M 8 (step S 135 shown in FIG. 9D ), and compares the readout allowable density difference minimum value with the first allowable density difference (before the start of final printing) calculated in step S 132 a (step S 136 a ). If the first allowable density difference (before the start of final printing) is smaller than the allowable density difference minimum value (“YES” in step S 136 a ), the CPU 10 A changes the first allowable density difference (before the start of final printing) of the corresponding color to the allowable density difference minimum value (step S 137 a ). Next, the CPU 10 A compares the second allowable density difference (before the start of final printing) calculated in step S 134 a with the allowable density difference minimum value. If the second allowable density difference (before the start of final printing) is smaller than the allowable density difference minimum value (“YES” in step S 138 a ), the CPU 10 A changes the second allowable density difference (before the start of final printing) of corresponding color to the allowable density difference minimum value (step S 139 a ).

Similarly, the CPU 10 A compares the first allowable density difference (during final printing) of each color calculated in step S 132 b with the allowable density difference minimum value (step S 136 b ). If the first allowable density difference (during finial printing) is smaller than the allowable density difference minimum value (“YES” in step S 136 b ), the CPU 10 A changes the first allowable density difference (during final printing) of corresponding color to the allowable density difference minimum value (step S 137 b ). Then, the CPU 10 A compares the second allowable density difference (during final printing) of each color calculated in step S 134 b with the allowable density difference minimum value (step S 138 b ). If the second allowable density difference (during final printing) is smaller than the allowable density difference minimum value (“YES” in step S 138 b ), the CPU 10 A changes the second allowable density difference (during final printing) of corresponding color to the allowable density difference minimum value (step S 139 b ).

The CPU 10 A executes the processing in steps S 140 to S 152 ( FIG. 5C ) as in the first embodiment. After step S 152 , the CPU 10 A reads out the contents of a memory M 1 (step S 166 shown in FIG. 9E ). If “0” is stored in the memory M 1 (“NO” in step S 167 ), the CPU 10 A determines that it is color matching before the start of final printing. If “1” is stored in the memory M 1 (“YES” in step S 167 ), the CPU 10 A determines that it is color matching during final printing. Since “0” has been stored in the memory M 1 in step S 101 , the CPU 10 A determines that it is color matching before the start of final printing, and the flow advances to step S 153 a ( FIG. 9F ).

In step S 153 a , the CPU 10 A reads out the contents of the memory M 21 . If “0” is stored in the memory M 21 , the CPU 10 A executes processing in steps S 155 a to S 157 a . Alternatively, if “1” is stored in the memory M 21 , the CPU 10 A executes processing in steps S 159 a to S 161 a . If “2” is stored in the memory M 21 , the CPU 10 A executes processing in steps S 162 a to S 165 a.

Next, the CPU 10 A reads out a first coefficient α 1 from a memory M 14 (step S 168 ). The reference correction amount of each ink key opening ratio is multiplied by the readout first coefficient α 1 to obtain the correction amount of each ink key opening ratio. The resultant correction amount is stored in a memory M 16 (step S 169 ). The resultant correction amounts of the ink key opening ratios are output to motor drivers 11 A in motor control devices 11 - 1 to 11 -n (step S 172 a ). Upon receiving the ink key opening ratio correction end signals from all the motor control devices 11 - 1 to 11 -n (“YES” in step S 173 a ), the flow returns to step S 109 .

[Change of Allowable Density Difference for Color Matching During Final Printing]

First, “0” is stored in the memory M 22 . In step S 114 b ( FIG. 9B ), when the switch SW 42 is turned on once, “1” is stored in the memory M 22 (step S 114 b →S 115 b →S 116 b →S 118 b ). When the switch SW 42 is turned on twice, “2” is stored in the memory M 22 (step S 114 b →S 115 b →S 116 b →S 117 b →S 119 b ).

When the switch SW 2 is turned on (“YES” in step S 122 ), the CPU 10 A executes the processing in steps S 130 to S 152 . After step S 152 , the CPU 10 A reads out the contents of the memory M 1 (step S 166 shown in FIG. 9E ). If “0” is stored in the memory M 1 (“NO” in step S 167 ), the CPU 10 A determines that it is color matching before the start of final printing, and the flow advances to step S 153 . If “1” is stored in the memory M 1 (“YES” in step S 167 ), the CPU 10 A determines that it is color matching during final printing, and the flow advances to step S 153 b ( FIG. 9F ).

To execute final printing, the operator turns on a switch SW 1 (“YES” in step S 109 ). Accordingly, “1” is stored in the memory M 1 (step S 110 →S 111 →S 112 ). After that, the CPU 10 A determines that it is color matching during final printing (step S 167 ), and the flow advances to step S 153 b.

In step S 153 b , the CPU 10 A reads out the contents of the memory M 22 (step S 153 b ). If “0” is stored in the memory M 22 , the CPU 10 A executes processing in steps S 155 b to S 157 b . If “1” is stored in the memory M 22 , the CPU 10 A executes processing in steps S 159 b to S 161 b . If “2” is stored in the memory M 22 , the CPU 10 A executes processing in steps S 162 b to S 165 b.

Next, the CPU 10 A reads out a second coefficient α 2 from a memory M 15 (step S 170 ). The reference correction amount of each ink key opening ratio is multiplied by the readout second coefficient α 2 to obtain the correction amount of each ink key opening ratio. The resultant correction amount is stored in the memory M 16 (step S 171 ). The resultant correction amounts of the ink key opening ratios are output to the motor drivers 11 A in the motor control devices 11 - 1 to 11 -n (step S 172 b ). Upon receiving the ink key opening ratio correction end signals from all the motor control devices 11 - 1 to 11 -n (“YES” in step S 173 b ), the flow returns to step S 109 .

The functional block of the CPU 10 A shown in FIGS. 1 and 7 will be described below with reference to FIGS. 15A and 15B . As shown in FIG. 15A , the CPU 10 A in FIG. 1 includes functional blocks such as a measurement difference calculation unit 101 , first allowable difference calculation unit 102 , second allowable difference calculation unit 103 , comparison unit 104 , and ink supply amount adjustment unit 105 . The measurement difference calculation unit 101 executes the processing in step S 152 ( FIG. 5C ). The first allowable difference calculation unit 102 executes the processing in step S 132 ( FIG. 5B ). The second allowable difference calculation unit 103 executes the processing in step S 134 ( FIG. 5B ). The comparison unit 104 executes the processing in steps S 136 to S 139 ( FIG. 5B ). The ink supply amount adjustment unit 105 executes the processing in steps S 156 , S 157 , S 160 , S 161 , and S 164 to S 173 ( FIG. 5D ), and steps S 201 to S 211 ( FIG. 6 ).

As shown in FIG. 15B , the CPU 10 A in FIG. 7 includes functional blocks such as a measurement difference calculation unit 201 , first allowable difference calculation unit 202 , second allowable difference calculation unit 203 , comparison unit 204 , ink supply amount adjustment unit 205 , and determination unit 206 . The measurement difference calculation unit 201 executes the processing in step S 152 ( FIG. 5C ). The first allowable difference calculation unit 202 executes the processing in steps S 132 a and S 132 b ( FIG. 9C ). The second allowable difference calculation unit 203 executes the processing in steps S 134 a and 134 b ( FIG. 9C ). The comparison unit 204 executes the processing in steps S 136 a to S 139 b ( FIG. 9D ). The ink supply amount adjustment unit 205 executes the processing in steps S 156 a , S 157 a , S 160 a , S 161 a , S 164 a , S 165 a , S 168 , S 169 , S 172 a , and S 173 a ( FIG. 9E ), steps S 156 b , S 157 b , S 160 b , S 161 b , S 164 b , S 165 b , S 170 , S 171 , S 172 b , and S 173 b ( FIG. 9F ), and steps S 201 to S 211 ( FIG. 6 ). The determination unit 206 executes the processing in step S 167 ( FIG. 9E ).

In the above-described embodiments, the density value is obtained on the basis of colorimetric data from the colorimeter. The density value may directly be obtained by using a densitometer in place of the colorimeter. The ink key opening ratio correction value is obtained by multiplying the reference correction amount of the ink key opening ratio by a coefficient (control ratio). Instead, the ink key opening ratio correction amount may be obtained by using a conversion table (storing a conversion curve representing the relationship between the reference correction amount and the correction amount). Before the start of final printing, the correction amount of the ink key opening ratio is obtained by using a first conversion table (storing a conversion curve before the start of final printing). During final printing, the correction amount of the ink key opening ratio is obtained by using a second conversion table (storing a conversion curve during final printing) different from the first conversion table.

Instead of obtaining the ink key correction amount by multiplying the reference correction amount of the ink key opening ratio by a coefficient (control ratio), first and second conversion tables may be arranged. The first conversion table stores the relationship between the density difference and the correction amount before the start of final printing. The second conversion table stores the relationship between the density difference and the correction amount during final printing. In this case, before the start of final printing, the correction amount of the ink key opening ratio is obtained directly from the density difference by using the first conversion table. During final printing, the correction amount of the ink key opening ratio is obtained directly from the density difference by using the second conversion table.

In the first embodiment, the first and second allowable density ratios β 1 and β 2 are commonly used for the respective colors. However, these first and second allowable density ratios may be set for each color. Similarly, in the second embodiment, the first and second allowable density ratios (before the start of final printing) β 1 F and β 2 F and the first and second allowable density ratios (during final printing) β 1 M and β 2 M may be set for each color.

In the above embodiments, the color matching operation is executed by using the density value. However, the same color matching operation can be executed in the modification by using the color value in place of the density value.

In the modification of the first embodiment, as shown in FIG. 10 , the reference density value colorimeter 10 T in FIG. 1 is changed to the reference color value calorimeter 10 T′. As shown in FIG. 11 , the reference density value memory M 3 , first allowable density difference memory M 4 , second allowable density difference memory M 5 , first allowable density ratio memory M 6 , second allowable density ratio memory M 7 , allowable density difference minimum value memory M 8 , measured density value memory M 11 , conversion curve (conversion curve representing relationship between the difference between the density value and the reference density value of each patch of each color and the adjustment amount of the opening ratio of the ink key) memory M 12 , measured density difference memory M 17 , color information (reference density value measured color information) memory M 18 , and color data (color data from the calorimeter 10 T) memory M 19 shown in FIG. 2 are respectively changed to a reference color value memory M 3 ′, first allowable color difference memory M 4 ′, second allowable color difference memory M 5 ′, first allowable color ratio memory M 6 ′, second allowable color ratio memory M 7 ′, allowable color difference minimum value memory M 8 ′, patch color value memory M 11 ′, conversion curve (conversion curve representing relationship between the difference between the color value and the reference color value of each patch of each color and the adjustment amount of the opening ratio of the ink key) memory M 12 ′, measured color difference memory M 17 ′, color information (reference color value measured color information) memory M 18 ′, and color data (color data from the colorimeter 10 T′) memory M 19 ′.

Also, “density value” and “density difference” in steps S 103 to S 105 , S 121 , S 124 to S 139 , S 149 to S 152 , S 155 , S 156 , S 159 , S 160 , and S 162 to S 164 shown in FIGS. 5A to 5E are respectively changed to “color value” and “color difference” in steps S 1103 to S 1105 , S 1121 , S 1124 to S 1139 , S 1149 to S 1152 , S 1155 , S 1156 , S 1159 , S 1160 , and S 1162 to S 1164 shown in FIGS. 12A to 12E . Note that, steps in the range of 100 to 199 in FIGS. 5A to 5E correspond to steps in the range of 1000 to 1999 in FIGS. 12A to 12E .

Similarly, in the modification to the second embodiment, the reference density value colorimeter 10 T shown in FIG. 7 is changed to the reference color value calorimeter (as the reference color value calorimeter 10 T′ shown in FIG. 10 ). As shown in FIG. 13 , the reference density value memory M 3 , first allowable density difference (before the start of final printing) memory M 41 , first allowable density difference (during final printing) memory M 42 , second allowable density difference (before the start of final printing) memory M 51 , second allowable density difference (during final printing) memory M 52 , first allowable density ratio (before the start of final printing) memory M 61 , first allowable density ratio (during final printing) memory M 62 , second allowable density ratio (before the start of final printing) memory M 71 , second allowable density ratio (during final printing) memory 72 , allowable density difference minimum value memory M 8 , measured density value memory M 11 , conversion curve (conversion curve representing relationship between the difference between the density value and the reference density value of each patch of each color and the adjustment amount of the opening ratio of the ink key) memory M 12 , measured density difference memory M 17 , color information (reference density value measured color information) memory M 18 , and color data (color data from the colorimeter 10 T) memory M 19 shown in FIG. 8 are respectively changed to a reference color value memory M 3 ′, first allowable color difference (before the start of final printing) memory M 41 ′, first allowable color difference (during final printing) memory M 42 ′, second allowable color difference (before the start of final printing) memory M 51 ′, second allowable color difference (during final printing) memory M 52 ′, first allowable color ratio (before the start of final printing) memory M 61 ′, first allowable color ratio (during final printing) memory M 62 ′, second allowable color ratio (before the start of final printing) memory M 71 ′, second allowable color ratio (during final printing) memory M 72 ′, allowable color difference minimum value memory M 8 ′, patch color value memory M 11 ′, conversion curve (conversion curve representing relationship between the difference between the color value and the reference color value of each patch of each color and the adjustment amount of the opening ratio of the ink key) memory M 12 ′, measured color difference memory M 17 ′, color information (reference color value measured color information) memory M 18 ′, and color data (color data from the reference color value colorimeter) memory M 19 ′.

Also, “density value (ratio)” and “density difference” in steps S 103 ′, S 104 , S 105 , S 121 , S 130 to S 139 b , S 155 a , S 155 b , S 156 a , S 156 b , S 159 a , S 159 b , S 160 a , S 160 b , S 162 a to S 164 a , and S 162 b to S 164 b shown in FIGS. 9A to 9F are respectively changed to “color value (ratio)” and “color difference” in steps S 1103 ′, S 1104 , S 1105 , S 1121 , S 1130 to S 1139 b , S 1155 a , S 1155 b , S 1156 a , S 1156 b , S 1159 a , S 159 b , S 1160 a , S 1160 b , S 1162 a to S 1164 a , and S 1162 b to S 1164 b shown in FIGS. 14A to 14F . As the modification to the first embodiment, “density value (ratio)” and “density difference” in steps S 149 to S 152 shown in FIG. 5C are respectively changed to “color value (ratio)” and “color difference” in steps S 1149 to S 1152 shown in FIG. 12C . Note that, steps in the range of 100 to 199 in FIGS. 9A to 9F correspond to steps in the range of 1000 to 1999 in FIGS. 14A to 14E .

In two modifications described above, the CPU 10 A obtains not the density value but a color value from the color data sampled by the calorimeter 10 L. A color value indicates an “L* value, a* value, and b* value” represented by the L*a*b* calorimetric system or an “L* value, u* value, and v* value” represented by the L*u*v calorimetric system as a color display method defined by JIS Z8729 in the Japanese Industrial Standard (JIS) and recommended by the Commission Internationale de l'Eclairage (CIE).

Note that, in the above embodiments and modifications, in the relationship between the allowable density difference (color difference) and the allowable density difference (color difference) minimum value, and the relationship between the difference between the measured density difference (color difference) and reference density difference (color difference) and the allowable density difference (color difference), “larger than” and “smaller than” may be changed to “equal to or larger than” and “equal to or smaller than” to obtain the same effect. Alternatively, “equal to or larger than” and “equal to or smaller than” may be changed to “larger than” and “smaller than”.

In this embodiment, since the allowable density ratio (or allowable color ratio) is set, the adequate value of the allowable density difference (or allowable color difference) can be automatically set in accordance with the reference density value (or reference color value) of the ink, even when using special ink which has never (rarely) been used.

According to the present invention, before color matching is performed by the operator or the manager of the site of printing, an adequate ink supply amount adjusting step is selected from the three modes. Hence, the hunting phenomenon of the ink thickness on the paper sheet can be suppressed. In addition, the amount of wasted paper can be decreased even when an unexpected accident has occurred on a printing product.

Assume that the ink supply amount is first adjusted upon selecting the first ink supply amount adjustment mode. Whenever the measured density difference is larger than the first allowable density difference, the ink supply amount is adjusted. On the basis of the color matching result obtained upon selecting the first ink supply amount adjustment mode, when it is determined that the hunting phenomenon of the ink thickness may occur on the paper sheet, the processing operation is changed to adjustment of the ink supply amount by selecting the second ink supply amount adjustment mode. In the second ink supply amount adjustment mode, only when the measured density difference is larger than the second allowable density difference (>first allowable density difference), the ink supply amount is adjusted. That is, the threshold value for adjustment of the ink supply amount is made large. Accordingly, the hunting phenomenon of the ink thickness on the paper sheet can be suppressed.

In addition, when the density value of a specific part of the printing product temporarily largely varies due to an unexpected accident (paper fold error, paper breakage, or smear) on the printing product, the third ink supply amount adjustment mode is selected. In the third ink supply amount adjustment mode, only when the measured density difference falls between the first allowable density difference and the second allowable density difference, the ink supply amount is adjusted. Hence, even when the measured density difference exceeds the second allowable density value, the ink supply amount is not adjusted. Accordingly, the amount of wasted paper generated by the temporary variation in density value can be decreased.

The color matching operation can be selectively done before the start of final printing, or during final printing. In color matching before the start of final printing, the ink amount in the inker is often largely different from the ink amount necessary for a printing product to be printed. Hence, the measured density difference is large. To the contrary, in color matching during final printing, the ink amount in the inker is not so different from the ink amount necessary for a printing product to be printed. Hence, the measured density difference is small.