JP2003165251A - Printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer equipped with a print sheet carrying means which can control the carrying speed of a print sheet by detecting unevenness thereof accurately. <P>SOLUTION: The printer comprises means for printing a first pattern under a state of not carrying a sheet and printing a second pattern on the first pattern while carrying the sheet to form a print pattern having interference fringes of the first and second patterns, means for detecting the print density of the print pattern, means for specifying a peak point where the density is maximized or minimized based on the print density detected by the print density detecting means, means for calculating the carrying speed of the print sheet at the peak point, and means for controlling the print sheet carrying means based on the carrying speed calculated by the carrying speed calculating means. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a printing apparatus for carrying out printing while a print roller is carrying print paper, and more particularly to a technique for controlling a print paper transport speed to be constant.

[0002]

2. Description of the Related Art In a general printing apparatus, printing is performed on the basis of print data transmitted from a computer connected to the printing apparatus while the print head is horizontally scanned so as to be orthogonal to the direction in which the printing paper is conveyed. There is a method to do. In recent years, a color printing apparatus which has a plurality of print heads and enables color printing has been generally provided. In particular, this color printing device is required to realize high-resolution and clear printing and to increase the printing processing speed.

However, in order to meet such demands, it is necessary to precisely perform various controls relating to the printing process, and one of them is the conveyance control of the printing paper.
For example, if there is unevenness in the conveyance speed of the printing paper, the printing point based on the printing data will be different from the point actually printed, and the printing quality will be significantly degraded.

By the way, it is known that the unevenness of the carrying speed is caused by a power transmission path such as a gear from the printing paper carrying motor to the carrying roller. Therefore, conventionally, a graduated disc (sometimes called a disc scale) is attached to the end of the transport roller so as to be concentric with the transport roller, and the graduated scale of the disc is read using an optical sensor. The rotation speed of the transport roller is calculated by the above, and the transport speed is controlled by controlling the rotation speed of the transport roller motor so that the rotation speed becomes constant.

[0005]

By the way, in order to accurately detect the rotation speed of the carrying roller by the above-mentioned method using the disk scale, it is necessary to install the carrying roller and the disk scale so as to be concentric with each other. is there. However, in practice, since it is extremely difficult to install the disc scale so that the transport roller and the disc scale are strictly concentric with each other, there arises a problem that the rotation speed of the transport roller detected by the method described above is not always accurate. It was
Therefore, it is difficult to obtain a constant rotation speed even if the rotation speed of the transport roller is controlled based on the detected rotation speed.

Even if the transport roller itself is eccentric, the transport speed becomes uneven, but since the eccentricity of the transport roller cannot be detected by the disc scale, the rotation speed of the transport roller is kept constant by the method described above. However, there is a problem that the conveyance amount of the printing paper is not constant even if the control is performed.

Furthermore, not only the number of manufacturing steps for mounting the disk scale increases, but also the disk scale itself requires high precision, which increases the cost of parts, resulting in an increase in the price of the printing apparatus. There was a problem. Furthermore, because a disc scale requires a certain diameter or more in order to detect the unevenness in the conveyance speed of the printing paper, the storage space becomes large, and the size of the printer main body becomes large, which causes a cost increase. I was getting tired.

From the above, the method of controlling the conveying speed of the printing paper by the disk scale has a problem that the strict conveying speed cannot be controlled and the manufacturing cost becomes high.

It is an object of the present invention to provide a printing apparatus provided with a printing paper carrying means capable of controlling the carrying speed of the printing paper to be constant by accurately detecting the unevenness of the carrying speed of the printing paper.

[0010]

In order to achieve the above-mentioned object, the present invention comprises a printing means for printing while scanning a print head in a direction orthogonal to a printing paper transport direction, and a drive means for rotating a transport roller. By means of a printing paper carrying means for carrying the printing paper at a predetermined speed, and by the printing means printing a first pattern along the printing direction in a state in which the printing paper is not carried, and further by carrying the carrying roller. While rotating the printing paper at a predetermined speed to convey the printing paper, a second pattern is printed on the first pattern by the printing means, and an interference fringe formed by the first pattern and the second pattern is formed. A print pattern creating means for creating a print pattern having the print pattern, and the print density of the print pattern is detected while scanning the print pattern in parallel with the scanning direction of the print head. Print density detecting means, a peak point specifying means for specifying a peak point where the density is maximum or minimum based on the print density detected by the print density detecting means, and a conveyance speed of the printing paper at the peak point. Based on the transport speed calculation means for calculating, and the transport speed calculated by the transport speed calculation means,
Transport speed control means for controlling the print sheet transport means,
Is a printing device provided with.

According to this printing apparatus, it is possible to detect a subtle conveyance speed unevenness from a print pattern having interference fringes (moire fringes). Therefore, the desired conveyance speed can be easily maintained by controlling the conveyance speed based on this. In addition, it is possible to eliminate the unevenness in the transport speed caused by the eccentricity of the transport rollers.

Further, a measuring means for measuring the number of revolutions of the carrying roller when the second pattern is formed is provided,
The peak point specifying means associates the rotation angle of the carry roller with the scanning distance of the print head based on the rotation speed of the carry roller measured by the measuring means, and determines the peak point by the rotation of the carry roller. Expressed in an angle, the carrying speed control means controls the carrying speed at the rotation angle of the carrying roller corresponding to the peak point. In addition, the number of rotations of the transport roller is measured, for example, by marking a mark that can be detected by an optical sensor at one place on the outer periphery of the transport roller, and performing one rotation each time the mark is detected by the optical sensor. It should be measured.

With this configuration, the transport speed can be controlled for each rotation angle of the transport roller, so that the transport speed can be controlled easily.

Specifically, the carrying speed calculating means calculates the carrying speed at the peak point based on the printing paper carrying amount between the peak points and the rotation angle of the carrying roller between the peak points, and carries the carrying speed. The speed control means calculates the average transport speed based on the print paper transport amount when the transport roller makes one rotation, and controls the print paper transport means so that the transport speed at the peak point becomes the average transport speed. I chose

Further, the print density detecting means is constructed so as to be movable on the print paper in accordance with the movement of the print head, and scans the print head to print the second pattern and simultaneously print the print density of the print pattern. It is desirable to be installed so that it can be detected. For example, an optical sensor may be attached to the side surface of the carriage on which the print head is placed, and this may be used as the print density detecting means.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing a hardware structure of an ink jet printer 100 which is an embodiment of a printing apparatus of the present invention, and FIG. 2 is an ink jet printer 100.
4 is a perspective view showing a schematic configuration of a printing unit of FIG. 3, and FIG. 3 is an enlarged view showing a schematic configuration of a sheet conveying roller unit.

Inkjet printer 10 of this embodiment
0 is a CPU 1 that controls the printer 100 as a whole
A memory 2 in which a control program executed by the CPU 1 and control data are stored; an operation panel 16 provided with an input key operable by a user and a display unit for displaying operation contents; and a network. An I / O port 3 for transmitting and receiving data to and from a host computer 200 connected via the image memory 4, an image memory 4 for temporarily storing the received print data, and a print head based on the print data. A head data generation unit 5 for controlling, an ejection control unit 6 for performing ejection control when ejecting ink,
An inkjet print head 7, a density sensor 9 for detecting print density from a print pattern having interference fringes according to the present invention, an A / D converter 8 for converting an analog signal from the density sensor 9 into a digital signal, Carriage transport motor 11 for operating the carriage on which the print head of FIG. 1 is operated, carriage transport motor control unit 10 for controlling the operation of the carriage transport motor, photosensor 13 for detecting the origin attached to the paper transport roller, and photosensor A to convert analog signal from 13 to digital signal
A / D converter 12, a paper feed motor 15 for rotating the paper feed roller, and a paper feed motor control unit 14 for controlling the paper feed motor 15 are provided.

The CPU 1 receives print data and various control data transmitted from the host computer 200 via the I / O port 3, and stores the print data in the image memory 4
The control processing is performed according to various commands and control data stored in the control panel 16 or input from the operation panel 16. Further, the relationship between the rotation angle of the paper carrying roller 21 and the paper carrying amount is calculated based on the detection signal from the density sensor 9, and a control signal for controlling the paper carrying motor 15 is generated based on the calculation result. , To the paper transport motor control unit 14.

The memory 2 has an area for recording the relationship between the rotation angle of the paper carrying roller 21 and the paper carrying amount. For example, the rotation angle of the paper transport roller 21 and the paper transport amount at the rotation angle may be stored in a table format in a one-to-one correspondence.

The image memory 4 stores the print data transmitted from the host computer 200. In this embodiment, the blocks are separate from the memory 2, but the respective areas may be provided in the same memory.

The head data generator 5 rearranges the data according to the nozzle arrangement of the head 7 in order to eject the contents of the image memory 4 to the head 7.

The print head 7 has a mechanism for ejecting ink from each nozzle of the print head in accordance with print data, and has four print heads 7c, 7m, 7y corresponding to four colors of cyan, magenta, yellow and black. It is composed of 7k. The inkjet printer is configured such that a piezoelectric element provided corresponding to each nozzle is energized to apply pressure to the ink in the nozzle to eject the ink from the nozzle, and the printing paper 30 sent to the platen 20.
Print on.

The carriage carrying motor control section 10 carries a carriage carrying motor 11 for reciprocating a sliding section 17 called a carriage on which the print head 7 is placed.
The carriage 1 is a control unit of the carriage 1 according to the ejection of ink.
7 is scanned in a direction orthogonal to the conveyance direction of the printing paper 30. For example, the carriage transport motor 10 is controlled according to the control signal from the CPU 1.

Specifically, the carriage carrying motor 11 moves the belt 18 to move the carriage 17 movably along the belt 18 to the left and right to scan the print paper.

The density sensor 9 is provided, for example, on the side surface of the carriage 17 as shown in FIG. 2, and is configured to be capable of scanning on the print paper 30 together with the carriage 17 by the carriage transport motor 11 so as to print on the print paper 30. The ink density of the print pattern is detected while scanning the pattern.

Further, the A / D converter 8 converts the analog signal from the density sensor 9 into a digital signal and converts it into a CPU.
1, and the CPU 1 generates an instruction signal to be output to the paper transport motor control unit 14 based on this detection signal.

The paper transport motor control unit 14 is a control unit of the paper transport motor 15 for transporting the print paper 30 separately from the carriage 17, and transports the print paper 30 by the amount instructed by the control signal from the CPU 1. As described above, the paper transport motor 15 is operated. Further, the paper transport motor 15 rotates the paper transport roller 21 at a predetermined speed, so that the print paper 3 is moved in synchronization with the scanning of the print head 7.
It is configured so that 0 can be conveyed by a fixed amount.

Further, as shown in FIG. 3, the paper carrying roller 21 has an origin mark M which can be detected by the optical sensor 22 formed on the outer peripheral portion by paint or the like. By detecting the origin mark M with the optical sensor 22, it is detected that the paper transport roller 21 has rotated once, and the number of rotations and the rotation angle φ of the transport roller are counted.

Next, a method of controlling the print sheet conveying speed according to the present invention will be described. In the inkjet printer 100 of the present embodiment, the paper transport speed with respect to the rotation angle φ is calculated based on the rotation angle φ of the paper transport roller 21 and the paper transport amount at that time, and the paper transport motor is calculated based on this calculation result. Control.

A method of calculating the sheet conveying speed with respect to the rotation angle φ of the sheet conveying roller 21 will be described below with reference to the flowchart of FIG. Further, for simplification, when the paper transport speed is constant (FIG. 5), and when the paper transport speed is reduced to 1/2 at a portion where the rotation angle of the paper transport roller 21 is 180 ° or more (FIG. 6). Will be described with reference to.

First, printing is performed while moving the carriage 17 while the paper transport roller 21 is stationary, that is, the printing paper 30 is stationary, and a horizontal line pattern is formed on the printing paper 30 along the scanning direction of the print head. Is printed (step S1). In this embodiment, for example, 21 nozzles out of the nozzles forming the print head 7 are used to eject ink. Therefore, as shown in FIGS. 5A and 6A, step S1 is performed. In, a print pattern consisting of 21 horizontal lines is formed.

Next, printing is performed by superimposing it on the horizontal line printing pattern printed in step S1 and rotating the paper feeding roller 21 this time to feed the printing paper 30 (step S1).
2). Then, a print pattern having the interference fringes (moire fringes) shown in FIGS. 5A and 6A is obtained.

Since FIG. 5A shows an example of a pattern printed when the sheet conveying roller 21 is rotated once while keeping the sheet conveying speed constant, interference fringes appear at equal intervals. On the other hand, FIG. 6A shows the rotation angle φ of the paper transport roller 21.
Since the sheet conveying speed is reduced to 1/2 at a portion of 180 ° or more, the interval of interference fringes appearing in the print pattern at that portion is wide.

Further, paying attention to the one line printed in step S2, in FIG. 5A, the sheet conveying roller 21 traverses three horizontal lines and reaches the fourth horizontal line while making one rotation. Therefore, assuming that the distance between the horizontal lines is l, the paper transport amount when the paper transport roller 21 is rotated once is 4 l.
It turns out that. On the other hand, in the case of FIG. 6A, when the distance between the horizontal lines is l, the paper transport amount when the paper transport roller 21 is rotated once is 3 l.

Next, the pattern obtained in step S2 is divided into 360 corresponding to the rotation angle φ of the sheet conveying roller 21, and the density N _Pn at each point (P _{1 to} P ₃₆₀ ) is calculated.
The density sensor 9 measures (step S3). Specifically, the measurement is performed while scanning the density sensor 9 provided on the side surface of the carriage on the print pattern shown in FIG. 5A or 6A. The concentration Np measured at each point is stored in the memory 2 and is used when obtaining the peak point.

Then, the concentration N _{Pn at} each point P _n
5 is plotted by plotting
The curve shown in (b) is obtained. Since FIG. 5B is a density curve obtained for the printed pattern when the printing paper 30 is rotated once at a constant speed, the curve has a substantially sine waveform.

Next, the densities before and after are compared,
A point at which the concentration N _pn satisfies N _{P (n-1)} <N _Pn > N _{P (n + 1)} is set as a peak point (step S4). Figure 5 (b)
In, the points of P ₄₅ , P ₁₃₅ , P ₂₂₅ , and P ₃₁₅ correspond to peak points.

On the other hand, in FIG. 6B, P ₄₅ , P
The points of ₁₃₅ and P ₂₇₀ correspond to peak points. Further, the point where the concentration N _pn satisfies N _{P (n-1)} > N _Pn <N _{P (n + 1)} (P ₉₀ , P ₁₈₀ , P ₂₇₀ , P _{0 in} FIG. 5B or FIG. 6B It is also possible to use P ₉₀ , P ₁₈₀ , and P ₀ ) of) as peak points.

Next, from the difference between the peaked points P _a and P _b (P _b -P _a ), that is, the rotation angle and the paper conveyance amount M sent during that time, the paper conveyance speed V (= M). / (P _b
-P _a)) and this correction value is a sheet conveying speed the velocity V obtained at point P _a V _a (= the rotational speed of the rotation angle a of the conveying roller 21).

For example, in FIG. 5B, point P
₄₅Paper transport speed V₄₅Is V ₄₅= 1 / (135-
45) = 1/90. Similarly, V₁₃₅, V₂₂₅The value of
It becomes 1/90. Fig. 5 shows the case where the paper transport speed is constant
Therefore, the paper transport speed at each point becomes the same value.
It is natural.

On the other hand, in FIG. 6B, point P ₄₅
The paper conveyance speed V ₄₅ at V ₄₅ = 0.5 / (90-
45) = 1/90. Similarly, the values of V ₉₀ and V ₁₃₅ are also 1/90. Since the number of peak points is small in FIG. 6, the point at which the density N _p is the minimum is also used as the peak point for calculating the paper transport speed. Further, the sheet conveyance speed V _{180 at the} peak point P ₁₈₀ in the portion where the sheet conveyance speed is halved is V ₁₈₀ =
0.5 / (270-180) = 1/180, and it can be confirmed that the paper transport speed is 1/2. In this way, the sheet transport speed at each peak point can be calculated.

Next, the sheet conveyance speed Vφ corresponding to the rotation angle φ of the sheet conveyance roller 21 obtained in step S5 is plotted, and a displacement graph of the sheet conveyance speed when the sheet conveyance roller 21 is rotated once (see FIG. 5 (c) and FIG. 6 (c)) are created (step S6).

In the case of FIG. 5C, the sheet conveying speed at the peak points P ₄₅ , P ₁₃₅ and P ₂₂₅ is 1 at all.
It is / 90. Further, it can be seen that connecting the points of the sheet conveyance speed at each peak point results in a horizontal straight line and the sheet conveyance speed is constant.

Further, in the case of FIG. 6C, the sheet conveying speed at the peak points P ₄₅ , P ₉₀ and P ₁₃₅ is 1/90.
Therefore, it can be seen that connecting the points of the sheet conveyance speed at each peak point results in a horizontal straight line and the sheet conveyance speed is constant at 1/90. Further, since the paper conveyance speed at the peak points P ₁₈₀ and P ₂₇₀ is 1/180, connecting the points of the paper conveyance speed at both peak points results in a horizontal straight line and the print paper conveyance speed is constant at 1/180. I understand.

However, FIG. 5 (c) and FIG.
In (c), since the condition of the paper transportation speed set for the experiment is known, the peak points are connected by a straight line, but only the printing paper transportation speed at the peak point can be calculated in this embodiment. Needless to say. Therefore, in practice, it is preferable to estimate the sheet conveyance speed with respect to the rotation angle φ other than the peak point from the sheet conveyance speed at the peak point and connect the points with a smooth curve.

As described above, by calculating the paper transport speed corresponding to the peak point and estimating the paper transport speed at each point, it becomes possible to detect a subtle change in the paper transport speed. By controlling the paper transportation speed at each point, the paper transportation speed can be kept constant.

By the way, when the paper transport speed is constant, the print pattern obtained by the printing in step S2 of FIG. 4 is a straight line as shown in FIG. However, the printed pattern is not a straight line but a curved line.

FIG. 7 shows an example of one print pattern obtained by the printing in step S2 of FIG. In FIG. 7, reference numeral A is a linear pattern obtained when the above-described sheet conveyance speed is constant, and reference numeral B is a curve obtained when the sheet conveyance speed is not constant (for example, when the conveyance roller 21 is eccentric). It is an example of a pattern. As shown by the curve B, in reality, since there is some variation in the amount of sheet conveyance with respect to the rotation angle φ of the sheet conveyance roller 21, the sheet conveyance speed at that point also varies (uniformity).

In such a case as well, since the paper carrying speed at the peak point can be calculated by the above-described procedure to detect a subtle change in the paper carrying speed, the carrying speed can be controlled based on this. As the number of peak points increases, the transport speed can be controlled more accurately.

In other words, in this embodiment, for simplicity, 21
The case where the ink is ejected from the individual nozzles has been described. However, if the ink is ejected from a larger number of nozzles, the pattern printed in step S2 can be changed step by step while the paper transport roller 21 makes one rotation. S1
Since the number of times of crossing the horizontal line pattern printed by is increased, many interference fringes also appear. Therefore, since more peak points are generated and the paper transport speed at the peak points can be calculated, the change in the paper transport speed can be grasped in detail, and the transport speed can be controlled more accurately. .

Although the invention made by the present inventor has been specifically described based on the embodiments, the present invention is not limited to the above embodiments.

For example, in the above embodiment, the density detecting sensor 9 is provided on the side surface of the carriage, but the location of the density detecting sensor is not limited as long as the density can be measured by scanning the print pattern.

Further, in the above embodiment, the change in the sheet conveying speed is grasped by a graph for the purpose of explanation, but it is not always necessary to make a graph and it is optimum by calculation from the calculated numerical value of the sheet conveying speed. Various controls can be performed.

Further, the conveying speed at the peak point may be calculated from the print pattern when the sheet conveying roller 21 is rotated a plurality of times, and the average thereof may be used as the conveying speed at the peak point. For example, when the rotation angle of 45 ° is the peak point in the print pattern when the paper conveyance roller 21 is rotated three times, the rotation angles of 405 ° and 765 ° after one rotation and two rotations are naturally the peak points. By calculating the transport speed at each peak point and taking the average thereof, the transport speed at the rotation angle of 45 ° can be calculated more accurately.

[0056]

According to the present invention, in a printing apparatus having a printing means and a printing paper carrying means, the printing means forms a first pattern along the printing direction on the printing paper in a state where the printing paper is not carried. Printing is performed, and further, while the conveying roller is rotated at a predetermined speed to convey the printing paper, the printing unit prints the second pattern on the first pattern, and the first pattern and the first pattern are printed. Print pattern creating means for creating a print pattern having interference fringes exhibited by the second pattern, and print density detecting means for detecting the print density of the print pattern while scanning the print pattern in parallel with the scanning direction of the print head. And a peak point specifying hand for specifying the peak point at which the density is maximum or minimum based on the print density detected by the print density detecting means. A transport speed calculating means for calculating the transport speed of the print paper at the peak point, and a transport speed control means for controlling the print paper transport means based on the transport speed calculated by the transport speed calculating means. Since it is provided, it is possible to easily maintain a desired transport speed by detecting subtle transport speed unevenness from a print pattern having interference fringes (moire fringes) and controlling the transport speed based on this. In addition, there is an effect that it is possible to eliminate the unevenness of the conveyance speed caused by the eccentricity of the conveyance roller.

[Brief description of drawings]

FIG. 1 is a block diagram showing a hardware configuration of an inkjet printer 100 that is an embodiment of a printing apparatus of the present invention.

2 is a perspective view showing a schematic configuration of a printing unit of the inkjet printer 100. FIG.

FIG. 3 is an enlarged view showing a schematic configuration of a paper transport roller unit.

FIG. 4 is a flowchart showing a procedure for calculating a sheet conveyance speed with respect to a rotation angle φ of the sheet conveyance roller 21.

FIG. 5 is a print pattern (a), a density curve (b) and a conveyance speed graph obtained when the paper conveyance speed is constant.

FIG. 6 is a print pattern (a), a density curve (b), and a conveyance speed graph obtained when the paper conveyance speed is reduced to 1/2 at a portion where the rotation angle φ of the paper conveyance roller 21 is 180 ° or more. .

FIG. 7 is an example of one print pattern obtained by printing in step S2 of FIG.

[Explanation of symbols]

1 CPU 2 memory 3 I / O ports 4 image memory 5 Head data generator 6 Discharge controller 7 print head 8 A / D converter 9 Optical sensor (density sensor) 10 Carriage transport motor controller 11 Carriage transport motor 12 A / D converter 13 Optical sensor (photo sensor) 14 Paper transport motor controller 15 Paper transport motor 16 Operation panel 17 carriage 18 belts 19 housing 20 Platen 21 Paper transport roller 22 Optical sensor 30 printing paper 100 inkjet printer 200 host computer

Claims (4)

[Claims] 1. A printing unit that prints while scanning a print head in a direction orthogonal to a direction in which a print sheet is conveyed, and a print sheet conveying unit that conveys the print sheet at a predetermined speed by rotating a conveyance roller by a driving unit. And printing a first pattern along the printing direction on the printing paper by the printing means in a state where the printing paper is not conveyed,
Further, while the conveyance roller is rotated at a predetermined speed to convey the printing paper, the printing unit prints the second pattern on the first pattern, and the first pattern and the second pattern. A print pattern creating means for creating a print pattern having interference fringes, and a print density detecting means for detecting the print density of the print pattern while scanning the print pattern in parallel with the scanning direction of the print head; A peak point specifying means for specifying a peak point where the density is maximum or minimum based on the print density detected by the print density detecting means, and a carrying speed calculating means for calculating a carrying speed of the printing paper at the peak point, Transport speed control means for controlling the print sheet transport means based on the transport speed calculated by the transport speed calculation means And a printer. 2. A measuring means for measuring the number of revolutions of the carrying roller, wherein the peak point specifying means is adapted to measure the number of revolutions of the carrying roller measured by the measuring means when the second pattern is created. Based on the relationship between the rotation angle of the transport roller and the scanning distance of the print head, the peak point is represented by the rotation angle of the transport roller, and the transport speed control means is provided for the transport roller corresponding to the peak point. The printing device according to claim 1, wherein the conveyance speed at the rotation angle is controlled. 3. The carrying speed calculation means calculates the carrying speed at the peak point based on the print paper carrying amount between the peak points and the rotation angle of the carrying roller between the peak points, and the carrying speed control means. Is characterized by calculating an average transport speed based on the print sheet transport amount when the transport roller makes one rotation, and controlling the print sheet transport means so that the transport speed at the peak point becomes the average transport speed. The printing device according to claim 2. 4. The print density detecting means is configured to be movable on a print sheet as the print head moves, and scans the print head to print the second pattern, and at the same time, to print the print density of the print pattern. The printer according to any one of claims 1 to 3, wherein the printer detects.