Printer

A printer printing an image on a print medium based on print data including print dot data for each of print lines. The printer includes a print head including heating elements arranged along a direction of the print lines, and a controller finding the number of print dots on each print line and determining a first or second control mode as a control mode of the heating elements for printing each print line based on the found number of print dots. In the first control mode, the heating elements are divided into first groups including two or more adjacent heating elements and are heated at a different timing. In the second control mode, the heating elements are divided into second groups including two or more heating elements with at least two thereof spaced apart and are heated at a different timing.

FIELD

The present invention relates to a printer that prints an image on a print medium based on print data.

BACKGROUND

A printer to print an image on a print medium having a thermosensitive layer includes a print head having a plurality of heating elements. The heating elements are arranged along a direction of a print line. Such a printer causes each heating element to generate heat independently by applying voltage separately to each heating element. When the print medium is heated by the heat-generating heating element, the thermosensitive layer of the print medium is colored for each print line. Thus, an image is printed on the print medium.

For printing a pictorial figure (e.g., a filled rectangle or ruled line) having many print dots on a single print line, it is required to cause many heating elements to generate heat at the same timing. Accordingly, power consumption of the printer becomes large. Recently, such power consumption is required to be suppressed. In particular, usable power is restricted with respect to remaining battery charge for a portable printer operating with a battery. Accordingly, power consumption is strongly required to be suppressed.

Conventionally, as a technology to suppress power consumption for printing a pictorial figure having many print dots on a single print line, there has been known a technology that a plurality of heating elements is divided into a plurality of groups and the heating elements generate heat at different timings for each groups (e.g., Japanese Patent Application Laid-open No. 2009-148948).

BRIEF SUMMARY

Technical Problem

According to the technology in Japanese Patent Application Laid-open No. 2009-148948, when some heating elements among the plurality of heating elements are caused to generate heat at a certain timing, temperature of heating elements without generating heat decreases with time. Consequently, temperature variation occurs among the heating elements. Owing to such temperature variation, variation also occurs in density of an image to be printed on a print medium. Accordingly, print quality of the image to be printed on the print medium deteriorates.

In short, according to the technology in Japanese Patent Application Laid-open No. 2009-148948, although power consumption of a printer can be suppressed, print quality of an image to be printed on a print medium decreases.

An object of the present invention is to suppress power consumption of a printer and prevent deterioration of print quality of an image to be printed on a print medium.

Solution to Problem

According to a first aspect of the present invention, it is provided a printer configured to print an image on a print medium based on print data that includes print dot data for each of a plurality of print lines, comprising:

a print head including a plurality of heating elements arranged along a direction of the print lines; and

a controller configured to find the number of print dots on each print line and determine a first control mode or a second control mode as a control mode of the heating elements for printing each print line based on the found number of print dots, wherein

in the first control mode dividing the heating elements into a plurality of first groups the controller controls the plurality of heating elements to generate heat at a different timing for each first group including two or more adjacent heating elements, and

in the second control mode dividing the heating elements into a plurality of second groups the controller controls the plurality of heating elements to generate heat at a different timing for each second group including two or more heating elements, at least two of which are spaced apart.

The may determine based on the print data whether each print line is an edge line being a print line including an edge portion of the image or a non-edge line being a print line including a non-edge portion of the image, and determine the first control mode as a control mode for the edge line, and determine the second control mode as a control mode for the non-edge line.

The controller may calculate, among the print lines, a variation between the number of print dots of a target line being a print line for which the control mode is to be determined and the number of print dots of a reference line being a print line adjacent to the target line, and determine the target line as the edge line when the variation is equal to or larger than a predetermined first threshold value, and determine the target line as the non-edge line when the variation is smaller than the first threshold value.

A second aspect of the present invention, it is provided a printer configured to print an image on a print medium based on print data that includes print dot data for each of a plurality of print lines, comprising:

a print head including a plurality of heating elements arranged along a direction of the print lines; and

a controller configured to find the number of print dots on each print line and determines any of first to third control modes as a control mode of the heating elements for printing each print line based on the found number of print dots, wherein

in the first control mode dividing the heating elements into a plurality of first groups the controller controls the plurality of heating elements to generate heat at a different timing for each first group including two or more adjacent heating elements, and

in the second control mode dividing the heating elements into a plurality of second groups the controller controls the plurality of heating elements to generate heat at a different timing for each second group including two or more heating elements, at least two of which are spaced apart, and

in the third control mode, the controller controls the plurality of heating elements to generate heat at the same timing.

The controller may calculate, among the print lines, a variation between the number of print dots of a target line being a print line for which the control mode is to be determined and the number of print dots of a reference line being a print line adjacent to the target line, and determine the first control mode as a control mode for the target line when the variation is equal to or larger than a predetermined first threshold value and the number of print dots on the target line is equal to or larger than a predetermined second threshold value, determine the second control mode as a control mode for the target line when the variation is smaller than the first threshold value and the number of print dots on the target line is equal to or larger than the second threshold value, and determine the third control mode as a control mode for the target line when the number of print dots on the target line is smaller than the second threshold value.

The printer may further comprise a feed portion configured to feed the print medium,

wherein the controller determines a first pattern as a control pattern of the feed portion for printing a print line for which the first control mode is determined as the control mode, and determines a second pattern having a print period that is longer than the first pattern as the control pattern of the feed portion for printing a print line directly following the print line for which the first control mode is determined as the control mode.

The controller may determine a first voltage as a voltage to be applied to the heating elements for printing a print line for which the first control mode is determined as the control mode, and determine a second voltage being higher than the first voltage as a voltage to be applied to the heating elements for printing a print line directly following the print line for which the first control mode is determined as the control mode.

Advantageous Effects

According to the present invention, it is possible to suppress power consumption of a printer and to prevent deterioration of print quality of an image to be printed on a print medium.

DETAILED DESCRIPTION

1. First Embodiment

A first embodiment will be described.

1-1. Structure of Printer (FIGS. 1 and 2)

Description will be provided on a structure of a printer of the first embodiment.FIG. 1is a schematic side view illustrating the structure of the printer of the first embodiment.FIG. 2is a schematic view illustrating a plurality of heating elements of a print head12inFIG. 1.

As illustrated inFIG. 1, a printer10of the present embodiment includes a platen roller11, the print head12, and a holder13.

The holder13is configured to hold a roll-shaped print medium PM. The print medium PM is a label continuum having a thermosensitive layer and an adhesion layer. The thermosensitive layer is colored in response to heat.

The platen roller11is configured to feed the print medium PM in a predetermined feeding direction Y (+Y or −Y). The platen roller11is connected to a stepping motor (not illustrated) via a timing belt (not illustrated). When the stepping motor is driven, the platen roller11is rotated.

When the platen roller11is rotated in a forward direction, the roll-shaped print medium PM held by the holder13is extracted in a belt-like manner on feeding path from a side of the holder13(hereinafter, called an upstream side) toward a side of an ejection port17(hereinafter, called a downstream side) (i.e., toward direction +Y). The belt-shaped print medium PM extracted from the holder13is fed toward the ejection port17as being nipped by the platen roller11and the print head12.

When the platen roller11is rotated in a reverse direction being opposite to the forward direction, the print medium PM is fed from the downstream side to the upstream side (i.e., toward direction −Y).

The print head12is configured to print an image on the print medium PM. The print head12has a print face12a. The print face12ais opposed to the platen roller11out of faces of the print head12.

For easy understanding, in the present embodiment, description will be provided on an example that 12 pieces of heating elements E1to E12are arranged on the print face12aof the print head12as illustrated inFIG. 2. The heating elements E1to E12are arranged along direction X of a print line perpendicular to direction Y (hereinafter, called a feeding direction) in which the print medium PM is fed.

When the thermosensitive layer of the print medium PM nipped by the platen roller11and the print head12is heated by the heating elements E1to E12of the print head12, the heated thermosensitive layer is colored. Thus, an image is printed on the print medium PM.

Examples of the image include texts, figures, bar codes, and combinations thereof.

As illustrated inFIG. 1, an optical sensor16is disposed on the feeding path of the print medium PM from the holder13to the print head12. The optical sensor16includes a light-receiving element16aand a light-emitting element16b. In the printer10, print timing is controlled in accordance with detection results of the optical sensor16.

1-2. Control Unit of Printer (FIG. 3)

Description will be provided on a control unit of the printer of the first embodiment.FIG. 3is a functional block diagram of a control unit100of the printer10inFIG. 1.

As illustrated inFIG. 3, the control unit100includes a central processing unit (CPU)101, a storage device102, an input device103, a display device104, a communication interface105, a feed control circuit106, and a print control circuit107.

The storage device102includes, for example, a ROM, a RAM, and an electrically erasable programmable read-only memory (EEPROM). The storage device102stores a program (hereinafter, called firmware) of an application for controlling a process (e.g., print process) of the printer10, data to be referred by the CPU101, and data generated by the CPU101.

The CPU101executes the firmware stored in the storage device102to actualize a function of the printer10.

The input device103is, for example, an input button, a touch panel, or a combination thereof.

The display device104is a liquid crystal display, for example.

The communication interface105is configured to control communication between the printer10and an external apparatus. The communication interface105is a wired interface, a wireless interface, a near field communication wireless communication interface (e.g., an NFC) or a combination thereof. The external apparatus is, for example, a computer, a cellular phone, a flash memory (e.g., a universal serial bus (USB) memory), or a combination thereof.

The feed control circuit106is configured to control rotation of the platen roller11. When a control signal (e.g., a pulse signal) for controlling driving of a stepping motor is received from the CPU101, the feed control circuit106drives the stepping motor in accordance with the control signal.

The print control circuit107is configured to control heating of the heating elements E1to E12. When a control signal for controlling heating of the heating elements E1to E12is received from the CPU101, the print control circuit107applies voltage selectively to the heating elements E1to E12in accordance with the control signal. The heating elements E1to E12to which the voltage is applied generates heat.

1-3. Control Mode of Heating Element

Description will be provided on a heating element control mode of a first embodiment. The heating element control mode of the first embodiment includes a first control mode and a second control mode.

The first control mode will be described.

FIG. 4is an explanatory view of the first control mode of the first embodiment.

With the first control mode, the heating elements E1to E12are divided into a plurality of first groups as illustrated inFIG. 4. Specifically, the heating elements E1to E12are divided into a first group consisting of the heating elements E1to E4, another first group consisting of the heating elements E5to E8, and another first group consisting of the heating elements E9to E12.

At timing T1, only the first group consisting of the heating elements E1to E4is heated. Here, heating elements corresponding to print dots among the heating elements E1to E4of the first group are heated.

At timing T2subsequent to timing T1, only the first group consisting of the heating elements E5to E8is heated. Here, heating elements corresponding to print dots among the heating elements E5to E8of the first group are heated.

At timing T3subsequent to timing T2, only the first group consisting of the heating elements E9to12is heated. Here, heat is generated by heating elements corresponding to print dots among the heating elements E9to E12of the first group are heated.

In short, with the first control mode, the heating elements E1to E12are divided into the plurality of first groups.

Each of the first groups includes two or more adjacent heating elements (e.g., E1to E4). Then, the print head12is controlled so that print dots on a single print line are printed on the print medium PM at different timings T1to T3for the respective first groups. In other words, in the first control mode, the heating elements heated at a single timing are located adjacently (i.e., such heating elements are arranged continuously).

The second control mode will be described.

FIG. 5is an explanatory view of the second control mode of the first embodiment.

In a first example of the second control mode, the heating elements E1to E12are divided into a plurality of second groups as illustrated inFIG. 5. Specifically, the heating elements E1to E12are divided into a second group consisting of the heating elements E1, E4, E7, and E10, another second group consisting of the heating elements E2, E5, E8, and E11, and another second group consisting of the heating elements E3, E6, E9, and E12.

In other words, with the first example of the second control mode, all the heating elements heated at a single timing are spaced apart (i.e., such heating elements are arranged discontinuously) from one another.

At timing T1, only the second group consisting of the heating elements E1, E4, E7, and E10is heated.

At timing T2subsequent to timing T1, only the second group consisting of the heating elements E2, E5, E8, and E11is heated.

At timing T3subsequent to timing T2, only the second group consisting of the heating elements E3, E6, E9, and E12is heated.

In a second example of the second control mode, the heating elements E1to E12are divided into a plurality of second groups. Specifically, the heating elements E1to E12are divided into a second group consisting of the heating elements E1, E2, E7, and E8, another second group consisting of the heating elements E3, E4, E9, and E10, and another second group consisting of the heating elements E5, E6, E11, and E12. In other words, in the second example of the second control mode, the heating elements heated at a single timing include a plurality of combinations each having two adjacent heating elements and such combinations are spaced apart (i.e., such heating elements are arranged discontinuously) from one another.

At timing T1, only the second group consisting of a combination of the heating elements E1and E2and a combination of the heating elements E7and E8is heated.

At timing T2subsequent to timing T1, only the second group consisting of a combination of the heating elements E3and E4and a combination of the heating elements E9and E10is heated.

At timing T3subsequent to timing T2, only the second group consisting of a combination of the heating elements E5and E6and a combination of the heating elements E11and E12is heated.

In short, in the second control mode, the plurality of heating elements E1to E12are divided into the plurality of second groups. Each of the second groups includes two or more mutually-separated heating elements (e.g., E1, E4, E7, and E10). Then, the print head12is controlled so that print dots on a single print line are printed on the print medium PM at different timings T1to T3for the respective second groups. In other words, in the second control mode, at least a part of the heating elements is heated at a single timing is spaced apart (i.e., such heating elements are arranged discontinuously).

1-4. Flow of Print Process (FIGS. 6 to 9)

Description will be provided on flow of a print process of the first embodiment.FIG. 6is a flowchart illustrating the flow of the print process of the first embodiment.FIG. 7is a flowchart illustrating detailed flow of a control mode determination process (S12inFIG. 6) of the first embodiment.FIG. 8is an explanatory view of control modes corresponding to the flowchart inFIG. 7.FIG. 9is a table showing an example of control data to be created in a control data creation process (S13inFIG. 6) of the first embodiment.

Each step inFIGS. 6 and 7is a part of a process when the CPU101executes the firmware.

In description withFIGS. 7 to 9, variable n (n is integer being 1 or larger) represents an identification number of a print line, constant M represents the maximum value of n (i.e., the number of print lines included in print data), K(n) represents the number of print dots on a print line L(n), D(n) represents a variation of print dots on the print line L(n), and TH1represents a first threshold value.

The variation D(n) of print dots on the print line L(n) is obtained as an absolute value of a difference between the number K(n) of print dots on the print line L(n) and the number K(n−1) of print dots on a print line L(n−1) directly preceding the print line L(n), or a difference between the number K(n) and the number K(n+1) of print dots on a print line L(n+1) directly following the print line L(n).

As illustrated inFIG. 6, first, the CPU101creates print data (S10). Specifically, the CPU101receives data of an image to be printed (hereinafter, called image data) from a computer via the communication interface105.

Next, the CPU101converts the received image data into print data. The print data includes print dot data corresponding to the heating elements E1to E12for each print line.

Next, the CPU101stores the print data in the storage device102.

Next, the CPU101specifies the number of print dots on each print line (S11).

Specifically, the CPU101specifies the number of print dots on each print line included in print date stored in the storage device102at the step S10.

InFIG. 8, since the number M of print lines included in the print data is 100, the variable n is an integer between 1 and 100 inclusive.

The numbers K(1) to K(19) of print dots on print lines L(1) to L(19) are 0 and the number K(20) of print dots on a print line L(20) is 100. Between print lines L(21) and L(79), the number K(n) of print dots gradually increases from the number K(21) to the number K(79), that is, from 100 toward 200. The number K(80) of print dots on a print line L(80) is 200 and the numbers K(81) to K(100) of print dots on print lines L(81) to L(100) are 0.

Next, the CPU101determines a control mode (S12).

Detailed flow of S12will be described with reference toFIG. 7.

As illustrated inFIG. 7, the CPU101sets1as an initial value to the variable n (S120). Accordingly, a print line L(1) at the top is set as a print line for which a control mode is to be determined (hereinafter, called a target line).

Next, the CPU101determines whether or not the number K(n) of print dots on the target line L(n) is 0, that is, whether or not the target line L(n) includes print dots (S121).

When the number K(n) of print dots on the target line L(n) is 0 (YES at S121), the CPU101performs the step S126without performing the steps S122to S125. In this case, since the control mode is not determined, the target line L(n) is recognized as a print line without including a print dot, that is, recognized as non-print target.

Next, the CPU101calculates a variation D(n) of print dots between the target line and a reference line (S122).

The reference line represents a print line adjacent to the target line L(n), that is, a print line L(n−1) directly preceding the target line L(n) or a print line L(n+1) directly following the target line L(n).

Specifically, the CPU101calculates, as the variation D(n), a first absolute value of a difference between the number K(n) of print dots on the target line L(n) and the number K(n−1) of print dots on the reference line L(n−1) directly preceding the target line L(n).

Here, when the variable n is equal to 1 (i.e., the minimum value), the variation D(n) is set to be equal to the number K(n) of print dots.

After the target line L(n) providing the first absolute value being equal to or larger than the first threshold value TH1is found, the CPU101calculates, as the variation D(n), a second absolute value of a difference between the number K(n) of print dots on the target line L(n) and the number K(n+1) of print dots on the reference line L(n+1) directly following the target line L(n). Here, when the variable n is equal to 100 (i.e., the maximum value), the variation D(100) is set to be equal to the number K(100) of print dots.

After the target line (n) providing the second absolute value being equal to or larger than the first threshold value TH1is found, the CPU101calculates again, as the variation D(n), the first absolute value and the second absolute value alternately.

In the case ofFIG. 8, variations D(1) to D(19) of print dots on the target lines L(1) to L(19) are 0, a variation D(20) of print dots on the target line L(20) is 100, variations D(21) to D(79) of print dots on the target lines L(21) to L(79) are equal to a constant value below 100, a variation D(80) of print dots on the target line L(80) is 200, and variations D(81) to D(100) of print dots on the target lines L(81) to L(100) are 0.

Next, CPU101compares the variation D(n) with the first threshold value TH1(S123).

When the variation D(n) is equal to or larger than the first threshold value TH1(YES at S123), the CPU101determines the target line L(n) as a print line including an edge portion of an image IMG (hereinafter, called an edge line) and determines the first control mode as a control mode for the edge line (S124).

When the variation D(n) is smaller than the first threshold value TH1(NO at S123), the CPU101determines the target line L(n) as a print line without including an edge portion of the image IMG (hereinafter, called a non-edge line) and determines the second control mode as a control mode for the non-edge line (S125).

In the case ofFIG. 8, the first threshold value TH1is 50.

Regarding the target lines L(1) to L(19), since the numbers K(1) to K(19) of print dots are 0 (YES at S121), the CPU101does not determine a control mode for the target lines L(1) to L(19), that is, recognizes the target lines L(1) to L(19) as non-print targets.

Regarding the target line L(20), since the number K(20) of print dots is equal to 1 or larger (NO at S121) and the variation D(20) is equal to or larger than the first threshold value TH1(YES at S123), the CPU101determines the first control mode as the control mode for the target line L(20) (S124).

Regarding the target lines L(21) to L(79), since the numbers K(21) to K(79) are equal to 1 or larger (NO at S121) and the variations D(21) to D(79) are smaller than the first threshold value TH1(NO at S123), the CPU101determines the second control mode as the control mode for the target lines L(21) to L(79) (S125).

Regarding the target line L(80), since the number K(80) of print dots is equal to 1 or larger (NO at S121) and the variation D(80) is equal to or larger than the first threshold value TH1(YES at S123), the CPU101determines the first control mode as the control mode for the target line L(80) (S124).

Regarding the target lines L(81) to L(100), since the numbers K(81) to K(100) of print dots are 0 (YES at S121), the CPU101does not determine the control mode for the target lines L(81) to L(100), that is, recognizes the target lines L(81) to L(100) as non-print targets.

In short, regarding the print line L(n) that provides the number K(n) of print dots being equal to or larger than 1 (i.e., the print line L(n) to be a print target), the CPU101determines the first control mode as the control mode for an edge line that provides the variation D(n) being equal to or larger than the first threshold value TH1, and determines the second control mode as the control mode for a non-edge line that provides the variation D(n) smaller than the first threshold value TH1.

In other words, the CPU101determines the target line L(n) that provides the variation D(n) being equal to or larger than the first threshold value TH1as the edge line and determines the target line L(n) that provides the variation D(n) smaller than the threshold value TH1as the non-edge line. Then, the CPU101determines the first control mode as the control mode for the target line L(n) that is determined as the edge line and determines the second control mode as the control mode for the target line L(n) that is determined as the non-edge line.

Next, the CPU determines whether or not the variable n reaches the maximum value M (being 100 in the case ofFIG. 8) (S126).

When the variable n is smaller than the maximum value M (NO at S126), the CPU101increments the variable n by 1 (i.e., the target line L(n) is shifted by one print line) (S127). Subsequently, the CPU101performs the steps S121to S126on the new target line L(n).

When the variable n is equal to the maximum value M (YES at S126), the CPU101ends the processes inFIG. 7and performs the step S13inFIG. 6.

As illustrated inFIG. 6, when the processes inFIG. 7(i.e., the step S12) are completed, the CPU101creates the control data (S13).

As illustrated inFIG. 9, the control data includes a “print line” field and a “control mode” field.

Information for identifying print lines (hereinafter, called line ID) is stored in the “print line” field.

Flags indicating the control modes determined by the CPU101at the step S12are stored in the “control mode” field. Here, flag0indicates that the control mode is not determined, that is, that the corresponding print line does not include a print dot, flag1indicates the first control mode, and flag2indicates the second control mode. After the control data is created, the CPU101stores the created control data in the storage device102.

Specifically, the CPU101sends a control signal to the print control circuit107in accordance with the information in the “control mode” field of the control data stored in the storage device102at the step S13. The print control circuit107applies voltage individually to the heating elements E1to E12in accordance with the control signal sent from the CPU101. Consequently, the heating elements E1to E12generate heat in accordance with the control mode (the first control mode or the second control mode) set for each print line.

Here, for the print line with the flag “0” stored in the “control mode” field thereof, the print control circuit107does not apply voltage to any of the heating elements E1to E12. Consequently, no image is printed on such print line.

After the printing (S14) is completed, the print medium PM on which the image IMG inFIG. 8has been printed is ejected through the ejection port17.

The first embodiment is summarized as follows.

According to the printer10of the first embodiment, an image IMG is printed on a print medium PM based on the print data including print dot data for each of the plurality of print lines.

The printer10includes the print head12including the plurality of heating elements arranged along direction X of the print lines, and the CPU101(an example of a controller) that specifies the number of print dots on each print line and determines the first control mode or the second control mode as the control mode of the heating elements for printing on each print line in accordance with the found number of print dots.

In the first control mode dividing the heating elements into the plurality of first groups, the CPU101controls the heating elements to generate heat at a different timing for each first group. Each first group includes two or more adjacent heating elements.

In the second control mode dividing the heating elements into the plurality of second groups, the CPU101controls the heating elements to generate heat at a different timing for each second group. Each second group includes two or more heating elements at least two of which are spaced apart.

Two or more heating elements of each first group are adjacent to each other. In other words, in the first control mode, the heating elements heated at a single timing are located adjacently (i.e., such heating elements are arranged continuously). Two or more heating elements of a single first group are heated at the same timing. Heating elements of different first groups are heated respectively at different timing. Accordingly, on the print line printed in the first control mode, steps appear only at boundaries between the respective first groups (at a position between the heating elements E4and E5and a position between the heating elements E8and E9inFIG. 4). Accordingly, steps do not stand out on the image IMG.

On the other hand, in the first control mode, heating elements are heated at each timing are congregated. Thus, temperature of heating elements which are not heated is likely decreased. Accordingly, variations in density are likely appeared on the image IMG on the print line printed in the first control mode.

At least two heating elements among the heating elements of the second group are spaced apart. In other words, in the second control mode, at least a part of the heating elements is heated at a single timing is spaced apart (i.e., such heating elements are arranged discontinuously). Two or more heating elements of a second group are heated at the same timing. Heating elements of different second groups are heated respectively at different timings. Accordingly, on the print line printed in the second control mode, steps appear at positions corresponding to boundaries between the respective second groups (at positions of all the heating elements E1to E12in the first example of the second control mode inFIG. 5, and at positions of the heating elements E2, E4, E6, E8, and E10in the second example of the second control mode). Thus, more steps appear in the case of printing in the second control mode than those in steps appearing in the case of printing in the first control mode.

On the other hand, in the second control mode, heating elements heated at each timing are dispersed. Accordingly, variations in density are unlikely appeared on the image IMG on the print line printed in the second control mode.

As described above, the first control mode has an advantage of less appearing of steps, while having a disadvantage of more variations in density. In contrast, the second control mode has an advantage of less variation in density, while having a disadvantage of more appearing of steps.

In the present embodiment, a control mode being appropriate in accordance with the number of print dots is applied to each print line selected from the two kinds of control modes (i.e., first and second control modes) in which a plurality of heating elements are divided into a plurality groups for each print line and the respective groups are heated at different timings. Accordingly, this embodiment has advantages of the first and second control modes without disadvantages thereof. Consequently, it is possible to suppress power consumption of the printer10and prevent deterioration of print quality of an image IMG printed on a print medium PM.

The CPU101of the first embodiment determines based on print data whether each print line is an edge line including an edge portion of an image or a non-edge line including a non-edge portion of the image. Then the CPU101determines the first control mode as a control mode for the edge line and the second control mode as a control mode for the non-edge line.

In this case, since the first control mode is applied to the edge line, two or more adjacent heating elements generate heat. Accordingly, steps stand out less at the edge portion. Thus, it is possible to prevent deterioration of print quality at the edge portion of the image IMG.

Further, since the second control mode is applied to the non-edge line, at least two separately-located heating elements among two or more heating elements generate heat. A heating element (without generating heat) located between heat-generating heating elements is heated with heat generated by the heat-generating heating elements. Accordingly, temperature variations of the heating elements can be suppressed. Thus, it is possible to prevent deterioration of print quality at the non-edge portion of the image IMG.

The CPU101of the first embodiment calculates, among the print lines, a variation between the number of print dots of a target line for which a control mode is to be determined and the number of print dots of a reference line adjacent to the target line. Then, the CPU101determines the target line as the edge line when the variation is equal to or larger than a predetermined first threshold value and determines the target line as the non-edge line when the variation is smaller than the first threshold value.

In this case, since the first control mode is applied to the edge line, two or more adjacent heating elements generate heat. Accordingly, steps stand out less at the edge portion of the image IMG. Thus, it is possible to prevent deterioration of print quality at the edge portion of the image IMG.

Further, since the second control mode is applied to the non-edge line, at least two separately-located heating elements among two or more heating elements generate heat.

A heating element (without generating heat) located between heat-generating heating elements is heated with heat generated by the heat-generating heating elements.

Accordingly, temperature variations of the heating elements can be suppressed. Thus, it is possible to prevent deterioration of print quality at the non-edge portion of the image IMG.

2. Second Embodiment

A second embodiment will be described. In the first embodiment, description is provided on the example to determine of two control modes (i.e., first and second control modes) as a control mode for each print line. In the second embodiment, description will be provided on an example to determine any of three control modes (i.e., first to third control modes) as a control mode for each print line.

Here, description being the same as in the first embodiment will not be repeated.

2-1. Control Mode of Heating Elements (FIG. 10)

A control mode of the heating elements of the second embodiment will be described.

The control mode of the heating elements of the second embodiment includes first to third control modes.

Here, the first and second control modes are the same as those in the first embodiment.

The third control mode of the second embodiment will be described.FIG. 10is an explanatory view of the third control mode of the second embodiment.

In the third control mode, all the heating elements E1to E12are heated at a single timing T1as illustrated inFIG. 10.

That is, the third control mode is different from the first and second control modes in that the heating elements E1to E12are heated at the same timing without being divided into groups.

2-2. Flow of Print Process (FIGS. 11 to 13)

Description will be provided on flow of a print process of the second embodiment.

FIG. 11is a flowchart illustrating detailed flow of a control mode determination process (S12inFIG. 6) of the second embodiment.FIG. 12is an explanatory view of control modes corresponding to the flowchart inFIG. 11.FIG. 13is a table showing an example of control data to be created in a control data creation process (S13inFIG. 6) of the second embodiment.

Each step inFIG. 11is a part of a process when the CPU101executes the firmware.

In description withFIGS. 11 to 13, variable n, constant M, K(n), D(n), and TH1represent the same as in the first embodiment, while TH2represents a second threshold value.

As illustrated inFIG. 11, after performing the steps S120and S121as in the first embodiment, the CPU101compares the number K(n) of print dots on the target line L(n) with the second threshold value (S220).

When the number K(n) of print dots on the target line L(n) is smaller than the second threshold value TH2(NO at S220), the CPU101determines the third control mode as a control mode for the target line L(n) (S221).

When the number K(n) of print dots on the target line L(n) is equal to or larger than the second threshold value TH2(YES at S220), the CPU101performs the steps S122to S125as in the first embodiment.

In the case ofFIG. 12, the first threshold value TH1is 50 and the second threshold value TH2is 150.

Regarding the target lines L(1) to L(19), since the numbers K(1) to K(19) of print dots are 0 (YES at S121), the CPU101does not determine the control mode for the target lines L(1) to L(19), that is, recognizes the target lines L(1) to L(19) as non-print targets. Regarding the target line L(20), since the number K(20) of print dots is equal to or larger than the second threshold value TH2(NO at S121and YES at S220) and the variation D(20) is equal to or larger than the first threshold value TH1(YES at S123), the CPU101determines the first control mode as the control mode for the target line L(20) (S124).

Regarding the target lines L(21) to L(50), since the numbers K(21) to K(50) are equal to or larger than the second threshold value TH2(NO at S121and YES at S220) and the variations D(21) to D(50) are smaller than the first threshold value TH1(NO at S123), the CPU101determines the second control mode as the control mode for the target lines L(21) to L(50) (S125).

Regarding the target lines L(51) to L(80), since the numbers K(51) to K(80) of print dots are equal to or larger than 1 (NO at S121) and smaller than the second threshold value TH2(NO at S220), the CPU101determines the third control mode as the control mode for the target lines L(51) to L(80) (S221).

Regarding the target lines L(81) to L(100), since the numbers K(81) to K(100) of print dots are 0 (YES at S121), the CPU101does not determine the control mode for the target lines L(81) to L(100), that is, recognizes the target lines L(81) to L(100) as non-print targets.

Subsequently, the CPU101creates the control data (S13inFIG. 6).

As illustrated inFIG. 13, the control data in the second embodiment is different from the control data (FIG. 9) of the first embodiment in that flag3indicating the third control mode is stored in the “control mode” field in addition to flag0indicating that the control mode is not determined, flag1indicating the first control mode, and flag2indicating the second control mode.

The second embodiment is summarized as follows.

According to the printer10of the second embodiment, an image IMG is printed on a print medium PM based on the print data including print dot data for each of the plurality of print lines.

The printer10includes the print head12including the plurality of heating elements arranged along direction X of the print lines, and the CPU101(an example of the controller) that specifies the number of print dots on each print line and determines any of the first to third control modes as the control mode of the heating elements for printing on each print line in accordance with the found number of print dots.

In the first control mode dividing the heating elements into the plurality of first groups the CPU101controls the heating elements to generate heat at different timings for each first groups. Each first group includes two or more adjacent heating elements.

In the second control mode dividing the heating elements into the plurality of second groups, the CPU101controls the heating elements of respective second groups to generate heat at different timings for each second group. Each second group includes two or more heating elements at least two of which are spaced apart.

In the third control mode, the CPU101controls the plurality of heating elements to generate heat at the same timing.

Similarly to the first embodiment, the first control mode has an advantage of less appearing of steps, while having a disadvantage of more variations in density. Similarly to the first embodiment, the second control mode has an advantage of less variation in density, while having a disadvantage of more appearing of steps.

In the third control mode, the heating elements corresponding to all print dots on a print line (i.e., all the heating elements are heated) generate heat at the same timing. Thus, the third control mode has an advantage less appearing of steps and variations in density on the print line. However, owing to restriction of power consumption of a battery or the like, the third control mode has a disadvantage that it is impossible to be adopted for a print line on which the number K(n) of print dots is equal to or larger than the second threshold value TH2.

In the present embodiment, a control mode being appropriate in accordance with the number of print dots is applied to each print line selected from the two kinds of control modes (i.e., first and second control modes) in which a plurality of heating elements are divided into a plurality of groups for each print line and the respective groups generate heated at different timings and the control mode (i.e., third control mode) in which the plurality of heating elements generate heat at the same timing. Accordingly, it is possible to obtain advantages of the first to third control modes while preventing disadvantages thereof. Consequently, it is possible to suppress power consumption of the printer10and prevent deterioration of print quality of an image IMG printed on a print medium PM.

The CPU101of the second embodiment calculates, among the print lines, a variation between the number of print dots of a target line for which a control mode is to be determined and the number of print dots of a reference line adjacent to the target line. Then, the CPU101determines the first control mode as the control mode for the target line when the variation is equal to or larger than a predetermined first threshold value and the number of print dots on the target line is equal to or larger than a predetermined second threshold value, determines the second control mode as the control mode for the target line when the variation is smaller than the first threshold value and the number of print dots on the target line is equal to or larger than the second threshold value, and determines the third control mode as the control mode for the target line when the number of print dots on the target line is smaller than the second threshold value.

In this case, since the first control mode is applied to a print line having a large number of print dots and a large variation of the print dots, two or more adjacent heating elements generate heat. Accordingly, steps stand out less at the portion of the image IMG where the variation is large. Thus, it is possible to prevent deterioration of print quality at such portion.

Further, since the second control mode is applied to a print line having a small variation of print dots, at least two separately-located heating among two or more heating elements generate heat. A heating element (without generating heat) located between heat-generating heating elements is heated with heat generated by the heat-generating heating elements. Accordingly, temperature variations of the heating elements can be suppressed. Thus, it is possible to prevent deterioration of print quality at the portion in the image IMG where the variation of print dots is small.

A third embodiment will be described. In the above embodiments, description is provided on the examples to determine a control mode of the print head12. In the third embodiment, description will be provided on an example to determine, for each print line, a period of time (hereinafter, called a strobe period) during which voltage is applied to the heating elements generating heat for printing each print line in addition to the control mode of the print head12.

Here, description being the same as in the above embodiments will not be repeated.

3-1. Control Pattern of Platen Roller (FIG. 14)

Description will be provided on control patterns of a platen roller of the third embodiment.

FIG. 14is a time chart illustrating waveforms of a pulse signal to be sent by the CPU101to the feed control circuit106and voltage to be applied to heating elements, according to the third embodiment. The pulse signal is a control signal for controlling driving of the stepping motor.

In the third embodiment, the CPU101determines the control pattern of the platen roller11in addition to the control mode of the print head12in the step S12inFIG. 6.

InFIG. 14, the vertical axis OUT represents output of the pulse signal, the vertical axis V represents voltage to be applied to the heating elements to generate heat, and the horizontal axis TIME represents time. A first pattern is represented by P1. A second pattern is represented by P2. A strobe period is represented by each of Q1and Q2. A period of time (hereinafter, called a stop period) during which rotation of the platen roller11is stopped is represented by each of R1and R2.

As illustrated inFIG. 14, the CPU101determines the first pattern P1or the second pattern P2, for each print line L(n), as a pattern of a pulse signal to be sent to the feed control circuit106and voltage to be applied to the heating elements.

In the first pattern P1, after the platen roller11is rotated to feed a print medium PM by one print line, rotation of the platen roller11is kept stopped for the period R1and voltage is applied to the heating elements for the period Q1(Q1<R1) in the period R1during which rotation of the platen roller11is kept stopped.

In the second pattern P2, after the platen roller11is rotated to feed the print medium PM by one print line, rotation of the platen roller11is kept stopped for the period R2being longer than the period R1and voltage is applied to the heating elements for the period Q2(Q2<R2) being longer than the period Q1in the period R2during which the rotation of the platen roller11is kept stopped. Among the print lines to be printed on, the first pattern P1is applied to print lines other than a print line directly following a print line to which the first control mode is applied, and the second pattern P2is applied to the print line directly following the print line to which the first control mode is applied.

For example, for printing the image IMG inFIG. 12, the CPU101determines the first pattern P1as the pattern for printing on the print line L(20) to which the first control mode is applied. In this pattern, the CPU101continues to apply voltage to the heating elements to generate heat during the period Q1. Accordingly, the heating elements continue to generate heat during the period Q1.

The CPU101determines the second pattern P2as the pattern for printing on the print line L(21) directly following the print line L(20) to which the first control mode is applied. In this pattern, the CPU101continues to apply voltage to the heating elements to generate heat during the period Q2. Accordingly, the heating elements continue to generate heat during the period Q2.

Each of the strobe periods Q1and Q2corresponds to a period during which printing is performed (hereinafter, called a print period). That is, the print period in the second pattern P2is longer than that in the first pattern P1.

The CPU101determines the first pattern P1as the pattern for printing on the print line L(22) directly following the print line L(21) to which the second control pattern is applied. In this pattern, the CPU101continues to apply voltage during the period Q1. Accordingly, the heating elements continue to generate heat during the period Q1.

As illustrated inFIG. 14, the print line L(20) is printed in the first control mode. In the first control mode, temperature at the heating elements E1to E4having generated heat at timing T1decreases at timings T2to T3.

The print line L(21) is printed in the second control mode. Here, voltage is applied only during the period Q2to the temperature-decreased heating elements E1to E4among the heating elements of the second group in the second control mode.

In general, print density of an image IMG printed on a print medium PM is proportional to the product of a strobe period and voltage applied to a heating element. Accordingly, at the print line L(21) with the strobe period Q2being longer than the strobe period Q1, it is possible to prevent print density decrease due to temperature decrease of the heating elements E1to E4.

In other words, average feeding speed of the print medium PM in the second pattern P2(feeding distance of the print medium PM/required time of the second pattern P2) is lower than that in the first pattern P1(feeding distance of the print medium PM/required time of the first pattern P1). That is, for printing on the print line directly following the print line to which the first control mode is applied, the CPU101reduces the feeding speed of the print medium PM compared to printing on other print lines. Accordingly, the print period for the print line L(21) to which the second pattern P2is applied is longer than the print period for the print lines L(20) and L(22) to which the first pattern P1is applied.

The third embodiment is summarized as follows.

The printer10of the third embodiment further includes the platen roller11(an example of a feed portion) that feeds the print medium PM.

The CPU101determines the first pattern P1as a control pattern of the platen roller11for printing a print line for which the first control mode is determined as the control mode and determines the second pattern P2with which the print period is longer than the first pattern P1as a control pattern of the platen roller11for printing on a print line directly following the print line for which the first control mode is determined as the control mode.

As described above, in the first control mode, temperature of heating elements which do not generate heat is likely decreased. Accordingly, temperature of heating elements for printing a print line directly following a print line to which the first control mode is applied is lower than temperature for printing other print lines. Consequently, print density of the print line directly following the print line to which the first control mode is applied is likely decreased in comparison to print density of the other print lines.

In the third embodiment, the print period for the print line directly following the print line to which the first control mode is applied is longer than that for the print line to which the first control mode is applied. Accordingly, the strobe period for printing on the print line directly following the print line to which the first control mode is applied is longer than that for printing on the print line to which the first control mode is applied. The longer the strobe period is, the higher the print density of the image printed on the print medium PM is. Accordingly, the print density becomes high on the print line directly following the print line to which the first control mode is applied, so that print quality deterioration can be prevented.

3-3. Modified Example

A modified example of the third embodiment will be described.

In the modified example, so-called multi-strobe is performed for printing on a print line directly following a print line to which the first control mode is applied.

For example, the CPU101sends, to the print control circuit107, a control signal for multi-strobe during the period R2of the second pattern P2inFIG. 14. Here, multi-strobe represents that voltage is applied multiple times to the same heating element (i.e., the same heating element generates heat multiple times) during rotation of the platen roller11is kept stopped. The print control circuit107controls the heating elements that correspond to print dots among the heating elements of the second group to generate heat multiple times in accordance with the control signal. Consequently, the strobe period when multi-strobe is performed becomes longer than that when multi-strobe is not performed.

Multi strobe may be performed at every timing (e.g., at timings T1to T3inFIG. 5) or only at the first timing (e.g., at timing T1inFIG. 5).

According to the present modified example, since multi-strobe is performed for printing a print line directly following a print line to which the first control mode is applied, the strobe period becomes longer compared to the print line to which the first control mode is applied. Accordingly, at the print line directly following the print line to which the first control mode is applied, print density reduction due to temperature decrease of the heating elements can be prevented and power consumption can be suppressed.

A fourth embodiment will be described. In the third embodiment, description is provided on the example that a strobe period is determined for each print line. In the fourth embodiment, description will be provided on an example that voltage to be applied to heating elements is determined for each print line.

Here, description being the same as in the above embodiments will not be repeated.

4-1. Voltage Applied to Heating Element (FIG. 15)

Description will be provided on voltage to be applied to heating elements in the fourth embodiment.

FIG. 15is a time chart illustrating waveforms of a pulse signal to be sent by the CPU101to the feed control circuit106and voltage to be applied to heating elements according to the fourth embodiment.

In the fourth embodiment, the CPU101determines, in the step S12inFIG. 6, voltage to be applied to the heating elements E1to E12in addition to the control mode of the print head12.

InFIG. 15, the vertical axis OUT represents output of the pulse signal, the vertical axis V represents voltage to be applied to the heating elements to generate heat, and the horizontal axis TIME represents time. The patterns P1, P2and the periods Q1and R1represent the same as in the third embodiment.

The patterns P1and P2of the third embodiment have the common stop period R1and the common strobe period Q1, and are different from the voltage V1and V2to be applied to the heating elements in the third embodiment.

Specifically, as illustrated inFIG. 15, the CPU101determines a first voltage V1or a second voltage V2being higher than the first voltage V1as a voltage to be applied to the heating elements E1to E12for each print line L(n). The CPU101sends, to the print control circuit107, a control signal for continuing to apply the determined voltage (the first voltage V1or the second voltage V2) to the heating elements E1to E12for the period Q1.

Among the print lines to be printed on, the first voltage V1is applied to print lines other than a print line directly following a print line to which the first control mode is applied, and the second voltage V2is applied to the print line directly following the print line to which the first control mode is applied.

For example, for printing the image IMG inFIG. 12, the CPU101determines the first voltage V1as a voltage to be applied to the heating elements E1to E12for printing on the print line L(20) to which the first control mode is applied.

The CPU101determines the second voltage V2as a voltage to be applied to the heating elements E1to E12for printing on the print line L(21) directly following the print line L(20) to which the first control mode is applied.

The CPU101determines the first voltage V1as a voltage to be applied to the heating elements E1to E12for printing on the print line L(22) following the print line L(21) to which the second voltage V2is applied.

As illustrated inFIG. 15, the first voltage V1is applied to the heating elements E1to E12for printing on the print line L(20). In the first control mode, temperature of the heating elements E1to E12decreases after the first voltage V1is applied.

For printing on the print line L(21), the second voltage V2being higher than the first voltage V1is applied to the heating elements E1to E12.

In general, print density of an image IMG printed on a print medium PM is proportional to the product of a strobe period and voltage applied to a heating element. Accordingly, at the print line L(21) with the second voltage V2being higher than the first voltage V1being applied to the heating elements, it is possible to prevent print density decrease due to temperature decrease of the heating elements E1to E12.

In other words, for printing on a print line directly following a print line to which the first control mode is applied, the CPU101increases voltage to be applied to the heating elements E1to E12compared to printing on other print lines. Accordingly, even if the heating elements E1to E12are cooled down after printing on the print line to which the first control mode is applied, it is possible to prevent print density reduction of the print line directly following the print line to which the first control mode is applied.

The fourth embodiment is summarized as follows.

The CPU101of the fourth embodiment determines the first voltage V1as a voltage to be applied to the heating elements for printing a print line for which the first control mode is determined as the control mode and determines the second voltage V2being higher than the first voltage V1as a voltage to be applied to the heating elements for printing a print line directly following the print line for which the first control mode is determined as the control mode.

As described above, in the first control mode, temperature of heating elements which do not generate heat is likely decreased. Accordingly, temperature of heating elements for printing on a print line directly following a print line to which the first control mode is applied is lower than temperature for printing on other print lines. Consequently, print density of the print line directly following the print line to which the first control mode is applied is likely decreased in comparison to that of the other print lines.

In the fourth embodiment, the voltage to be applied to the heating elements for printing on the print line directly following the print line to which the first control mode is applied is higher than that for printing on other print lines. The higher the voltage to be applied is, the higher the print density of the image printed on the print medium PM is. Accordingly, the print density becomes high on the print line directly following the print line to which the first control mode is applied, so that print quality deterioration can be prevented.

Further, in the fourth embodiment, since the strobe period Q1for printing on the print line directly following the print line to which the first control mode is applied is the same as the strobe period Q1for printing on the print line to which the first control mode is applied, the total print period can be shortened in comparison to the third embodiment.

5. Other Modified Examples

Although description of the above embodiments is provided on examples that the print medium PM is in a form of a continuous label, the form thereof is not limited thereto.

The print medium PM may be in a form of that a plurality of labels are temporarily stuck onto a continuous liner, in a form that radio frequency identification (RFID) is mounted therein, or in a form without having a stick layer (e.g., a tag, a wrist band, and the like).

Numerical examples (e.g., the number of heating elements included in the print head12, the number of print lines, the number of adjacent heating elements in the second group, and values of the first threshold value TH1and the second threshold value TH2) in the above embodiments are simply examples and the embodiments are not limited thereto.

Further, the first threshold value TH1and the second threshold value TH2may be changed based on a user's instruction. For example, when a user provides an instruction to change the threshold value TH1and the threshold value TH2using the input device103, the CPU101stores the values based on the instruction in the storage device102. Then, the CPU101refers the values stored in the storage device102at S123inFIGS. 7 and 11and S220inFIG. 11. Thus, a print process is performed using the first threshold value TH1and the second threshold value TH2which are changed based on the user's instruction.

Although description of the above embodiments is provided on the example that the printer10creates print data from image data received via the communication interface105, the embodiments are not limited thereto. The printer10may create print data based on a user's instruction, for example, received via the input device103.

Description of the above embodiments is provided on the example that the printer10causes a thermosensitive layer to be colored for print. However, the above embodiments may be applied, for example, to a printer in which an image is transferred onto a print medium PM using an ink ribbon.

In the above, although description is provided in detail on the embodiments of the present invention, the scope of the present invention is not limited to the above embodiments. Further, the embodiments may be modified or varied variously without departing from the scope of the present invention. Further, the embodiments and modified examples described above may be combined.

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