JP2001150654A - Printer and printing method using ink drop having different quantity of ink - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a printer forming dots of different quantity of ink in which positional shift of each dot is suppressed. SOLUTION: Each pixel can be formed arbitrarily of a small ink drop IPS and/or an intermediate ink drop IPM by outputting two kinds of driving waveform WM, WS continuously during main scan. The driving waveforms are set to satisfy conditions that each ink drop is ejected at a speed ensuring stabilized flight, and conditions that an interval INT for preventing ejection of one ink drop from causing variation in the quantity of other ink drop is ensured. In case of a micro ink drop IPS, the flight time is limited by increasing the ejection speed sufficiently because the trajectory may be curved. Driving waveform satisfying these conditions stably can be set by ejecting a small drop following to an intermediate drop.

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 forming dots by ejecting ink droplets having different amounts of ink.
More specifically, the present invention relates to a printing apparatus capable of stably forming dots by very fine ink droplets on each pixel.

[0002]

2. Description of the Related Art In an ink jet printer, dots are formed on a print medium by discharging ink from a head, and an image is recorded. In conventional inkjet printers, the amount of ink ejected from the head was constant, but in recent years,
In order to realize smooth gradation expression, an ink jet printer in which the amount of ejected ink is variable has been proposed. FIG. 22 is an explanatory diagram illustrating an example of a printer that forms dots having different amounts of ink. In this printer, while the carriage CA is moving as the main scan, for each pixel,
A drive signal W1 for ejecting small ink droplets IPs with a small amount of ink and a drive signal W2 for ejecting medium ink droplets IPm with a slightly large amount of ink are continuously output. The flight speed of the small ink droplet IPs is lower than the flight speed of the medium ink droplet IPm. In the conventional printer, the discharge speed of the small ink IPs <the discharge speed of the medium ink IPm is set in consideration of the moving speed of the carriage CA, and the interval Δ from the discharge of the small ink IPs to the discharge of the large ink IPm is set.
By adjusting W, each ink droplet is landed at almost the same position. After setting the ejection timing in this way, a small dot can be formed by outputting a signal for masking the drive signal W2 to the head, and a medium dot can be formed by masking the drive signal W1. If neither drive signal is masked, large dots can be formed by combining small ink droplets and medium ink droplets.

[0003] Other types of printers that form dots with different amounts of ink at each pixel include a drive signal for forming small ink drops and a drive signal for forming medium ink drops for each pixel. There is also one that selectively outputs the data. Instead of changing the amount of ink by masking one of the two types of drive signals as shown in FIG. 22, the type of the drive signal itself output to each pixel is changed according to the amount of ink to be ejected. . In such a printer,
Since it is not necessary to consider the interval ΔW in FIG. 22, even if the ink amounts are different, the landing speed can be matched by setting the flight speed of each dot to the same value and outputting a drive signal at the same timing.

[0004]

In recent years, in ink-jet printers, dots have been miniaturized in order to realize higher resolution and higher image quality printing. Further, in order to increase the printing speed, the moving speed of the carriage during the main scanning is increased. Since the flying direction of the miniaturized dot is shifted by a slight disturbance, it is difficult to land the dot stably. Further, when the moving speed of the carriage increases, the air resistance acting on the ink droplet increases, so that the flight trajectory of the ink droplet is more likely to shift. Therefore, as ink droplets become finer and the carriage speeds up, it becomes very difficult to align the landing positions of the dots. In the related art, the conditions of the ejection speed and the ejection interval that can stably match the landing positions of the large and small ink droplets can be set relatively easily. It has become very difficult to find.

[0005] The difficulty in finding such conditions is two fold.
There are two main factors. The first difficulty is that each of the ink droplets does not fly stably due to the finer dots and the higher speed of the carriage. Secondly, the higher the speed of the carriage, the smaller the degree of freedom of the ejection interval for continuously ejecting ink droplets having different amounts of ink to each pixel. Among them, the second difficulty is a problem unique to a printer of a type that continuously outputs a plurality of drive signals to each pixel. On the other hand, the first difficulty is a problem common to printers of a type that selectively outputs any one of drive signals corresponding to ink droplets having different ink amounts. Therefore, even in a printer of a type that selectively outputs a drive signal, it is difficult to make the landing positions of the ink droplets coincide with each other at a constant ejection speed and ejection timing.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problems, and suppresses the displacement of the landing positions of dots having different amounts of ink even when extremely fine dots are used, thereby achieving high-quality printing. It is an object of the present invention to provide a printing apparatus that realizes the above.

[0007]

Means for Solving the Problems and Their Functions / Effects To solve at least a part of the above-mentioned problems, the present invention provides:
The following configuration was adopted. The present invention provides a printing apparatus that prints an image by forming dots on each pixel on a print medium using a head capable of discharging a plurality of types of ink droplets having different ink amounts, wherein at least one of the head and the print medium is used. Main scanning means for performing main scanning by driving, and head driving for driving the head at a timing set for each of the plurality of types of ink droplets to form any one of the plurality of types of dots in each pixel Means, wherein the timing is a timing set so that a flight time of an ink droplet having a minimum ink amount among the plurality of types of dots is the shortest.

[0008] The landing position deviation of the ink droplet is caused by the ejected ink droplet flying on a trajectory different from the original trajectory. The deviation of the flight trajectory is reduced by shortening the flight time. Here, comparing ink droplets having different ink weights, since the ink droplet having the minimum ink amount has the smallest mass, the flight trajectory shift (hereinafter referred to as flight bend) occurs due to various factors such as non-uniform ejection pressure and air resistance. That)
Tends to occur. Therefore, as disclosed in the present invention, by controlling the ejection timing of each ink droplet so as to minimize the flight time of the ink droplet having the smallest amount of ink that is most susceptible to the influence, it is possible to suppress the displacement of the landing position of the dot And high quality printing can be realized.

[0009] The flight time can be reduced by improving the discharge speed. That is, in the printing apparatus of the present invention, the ejection speed of the ink droplet with the minimum ink amount is set to the highest. Further, by setting the ejection speed in this way, the ejection timing for forming dots in each pixel is necessarily the latest timing for the ink droplet with the minimum ink amount. The latest timing means that when a plurality of drive signals are continuously output to each pixel as shown in FIG. 22, the drive signal corresponding to the minimum ink amount is output last. Also, when any one of the drive signals corresponding to each ink amount is selectively output, it means that the relative positional relationship with the pixel on which the dot is to be formed is closest. That is, in the printing apparatus of the present invention, when the distance between the head and the pixel at the time when each drive signal is output to the head is compared, the distance corresponding to the drive signal with the minimum ink amount is the minimum.

Conventionally, fine dots were not used so that flight deflection due to the above-mentioned factors was remarkable. Therefore, when setting the ejection timing, there was almost no problem in flight stability. Even in the case of using a very fine dot in a printing apparatus of a type that continuously outputs a drive signal, initially, as shown in FIG. 22, “ejection speed of small ink IPs <ejection speed of large ink IPm”. It was discharging. However, it has been found that when dots are formed under such conditions, the image quality is not significantly improved even if the dots are miniaturized. The inventor of the present application has found, through detailed experiments and analysis, that the essential cause of this phenomenon is flight bending.

The present application has found that when using such finely-divided dots, it is necessary to sufficiently set the ejection timing in consideration of flight stability, which need not be considered conventionally. Has the first technical significance. Also, while keeping the ejection speed of each ink droplet within a realistic range,
The second technical significance is that it has been found that it is efficient to minimize the flight time of the minimum ink amount in order to suppress the flight deflection of the ink droplet having the minimum ink amount. In other words, the inventors overturned the usual setting method in which the smaller the ink amount, the smaller the ejection pressure had to be, and found the necessity to set the ejection speed to the maximum for the ink droplet with the smallest ink amount, and found the technical effect. .

In the present invention, the ejection timing of ink droplets other than the minimum ink droplet can be variously set, but the timing is set so that the larger the ink amount is, the earlier the ink droplet is ejected for each pixel. It is desirable that the timing be set. In other words, it is desirable to set the timing so that the flight time becomes longer in the order from the smaller ink amount. As described above, an ink droplet having a smaller amount of ink is more likely to bend. Therefore, by doing so, not only the ink droplet having the minimum amount of ink but also other ink droplets can be minimized.

The present invention can be applied to a printing apparatus that selectively outputs one type of drive signal to one pixel. It is desirable to configure a printing apparatus in which the ejection timing of each ink droplet is set and a dot of an arbitrary amount of ink can be formed in each pixel in each main scan. In order to continuously eject a plurality of ink droplets, it is necessary to satisfy strict conditions for the ejection speed and ejection interval of each ink droplet, but these conditions are satisfied by applying the timing disclosed in the present invention. It will be easier.

The printing apparatus of the present invention can be applied to both a head that discharges ink using distortion of an electrostrictive element and a head that discharges ink using bubbles generated by heating the ink. Of course, it is not limited to these.

The present invention can be configured as a printing method in addition to the aspect as a printing apparatus. Further, a print control device or a print control method for controlling the head mounted on the printing device at the above-described timing may be employed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples in the following order. A. Overall configuration of device: Generation of drive waveform: Discharge timing setting: Analytical setting method of discharge timing: Modification Example Regarding Analytical Setting Method of Discharge Timing: Printing apparatus of the second embodiment:

A. FIG. 1 is an explanatory diagram showing a schematic configuration of a printing system as an embodiment. The printing system of the present embodiment includes a printer PRT connected to a computer P
Connected to C. The computer PC transfers the printer data to the printer PRT by transmitting print data including raster data for specifying which type of dot is to be formed in each pixel during main scanning, and print data for specifying the feed amount for sub-scan. It serves to control the operation of the PRT. These processes are performed based on a program called a printer driver. Printer PRT is
The control circuit 40 performs printing by performing main scanning and sub-scanning based on the print data.

The printer PRT has a mechanism for transporting the paper P by a paper feed motor 23, a mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 by the carriage motor 24, and print heads 61 to 64 mounted on the carriage 31. And a control circuit 40 that controls the exchange of signals with the paper feed motor 23, the carriage motor 24, the print head 28, and the operation panel 32.

A mechanism for reciprocating the carriage 31 in the axial direction of the platen 26 includes a sliding shaft 34 laid parallel to the axis of the platen 26 and holding the carriage 31 slidably.
A pulley 38 for extending an endless drive belt 36 between the carriage motor 24 and a position detection sensor 39 for detecting the origin position of the carriage 31 are provided.

The carriage 31 has a cartridge 71 for black ink (Bk) and a cartridge 72 for color ink containing three color inks of cyan (C), magenta (M) and yellow (Y). It is possible. Below the carriage 31, a total of four ink ejection heads 61 to 64 corresponding to these inks are formed. A cartridge 71 for black (Bk) ink is mounted on the carriage 31.
When the color ink cartridge 72 is mounted from above, the ejection heads 61 to 6
4 is supplied.

FIG. 2 shows ink ejection heads 61 to 64.
FIG. 2 is an explanatory diagram showing a schematic configuration of the device. For convenience of illustration, the illustration of the yellow head is omitted. The heads 61 to 64 are provided with 48 nozzles Nz at regular intervals for each color. Further, a piezo element PE is arranged for each nozzle at a position in contact with the ink passage 68 for guiding the ink to the nozzle Nz. When a voltage having a predetermined time width is applied between the electrodes provided at both ends of the piezo element PE, the piezo element PE expands by the voltage application time and deforms one side wall of the ink passage 68 in the direction indicated by the arrow in the drawing. . As a result, the ink corresponding to the contraction amount becomes the particles Ip and is ejected at a high speed from the tip of the nozzle Nz. Printing is performed by the ink particles Ip soaking into the paper P mounted on the platen 26.

The printer PRT of this embodiment can form dots with different ink amounts by applying voltages with different waveforms to the piezo element PE. This principle will be described. FIG. 3 shows the driving waveform and the ink Ip ejected.
FIG. 4 is an explanatory diagram showing a relationship with the above. The drive waveform indicated by a broken line in FIG. 3 is a waveform when a normal dot is ejected. Once a voltage lower than the reference voltage is applied to the piezo element PE in the section d2, the piezo element PE is deformed in a direction to increase the cross-sectional area of the ink passage 68. Since there is a limit to the ink supply speed to the nozzles, the ink passage 6
8, the supply amount of ink is insufficient. As a result, as shown in the state A of FIG. 3, the ink interface Me is depressed inside the nozzle Nz. When the drive waveform shown by the solid line in FIG. 3 is used and the voltage is rapidly lowered as shown in the section d2, the supply amount of the ink becomes further insufficient. Therefore, as shown in the state a, the ink interface is inwardly depressed largely in comparison with the state A.

Next, when a high voltage is applied to the piezo element PE (section d3), ink is ejected based on the principle described above. At this time, the state B and the state C are changed from the state (state A) where the ink interface is not depressed much inside.
Large ink droplets are ejected as shown in (a), and small ink droplets are ejected as shown in states (b) and (c) from the state where the ink interface is largely dented inward (state a). As described above, the dot size can be changed according to the change rate when the drive voltage is lowered (section d1, d2). Further, by adjusting the slope and the peak value of the drive waveform in the section d3, the flying speed of the ejected ink droplet can be adjusted.

The printer PRT continuously outputs two types of drive waveforms so that dots with different amounts of ink can be arbitrarily selected and formed in each pixel. FIG. 4 is an explanatory diagram showing a driving waveform and a state of ejection of ink droplets to each pixel. The carriage 31 ejects ink droplets on the paper P while moving from left to right in the figure. Two types of drive waveforms WM and WS are output to the head at the same timing as this movement. The drive waveform WM is a waveform for discharging the medium ink droplet IPM forming a medium dot, and the drive waveform WS is a waveform for discharging the small ink droplet IPS forming a small dot.
By discharging both of them to one pixel, a large dot can be formed.

This embodiment is characterized in that the small ink droplet IPS is ejected after the medium ink droplet IPM. Since the ink droplets are ejected in such an order and land both on substantially the same pixel, the ejection speed from the head is adjusted so that the medium ink droplet IPM is ejected at a low flight speed and the small ink droplet IPS is ejected at a high flight speed. Has been adjusted. Also, in general, the meniscus vibrates for a certain period after the ink droplet is ejected, so that a stable ink droplet cannot be ejected. In order to stably eject the small ink droplet IPS, the driving waveform WM and the driving waveform WM are used. A predetermined interval INT is provided between WS. The setting of the ejection speed of each ink droplet and the interval INT will be described later in detail.

B. Generation of drive waveform: Next, printer PRT
Of the control circuit 40 will be described, and a method of generating a drive waveform will be described. FIG. 5 is an explanatory diagram showing the internal configuration of the control circuit 40. As shown, the control circuit 40 includes a CPU 41, a PROM 42, a RAM 43, and a PC for exchanging data with a computer 90.
A peripheral input / output unit (PIO) 45 for exchanging signals with the interface 44, the paper feed motor 23, the carriage motor 24, the operation panel 32, and the like, and a timer 4 for timing.
6. A driving buffer 47 for outputting a dot on / off signal is provided in each of the heads 61 to 64, and these elements and circuits are interconnected by a bus 48. Further, the control circuit 40 includes a transmitter 50 for outputting a driving waveform for driving the piezo element PE of each nozzle at a predetermined frequency, a driving signal generating unit 55, and a distribution output for distributing the driving waveform to the heads 61 to 64. A vessel 49 is also provided.

The control circuit 40 receives the print data processed by the computer 90 and temporarily stores the print data in the RAM 4.
3 and output to the driving buffer 47 at a predetermined timing. From the driving buffer 47, data indicating on / off of dots for each nozzle is output to the distribution output unit 49. As a result, a drive waveform for driving the piezo element PE is output to the nozzles on which dots are to be formed, and dots are formed.

FIG. 6 is an explanatory diagram showing the internal configuration of the drive signal generator 55. As shown, the drive signal generator 55
Is a memory 51 for storing parameters for specifying the shape of the drive waveform, a first latch 52 for reading and temporarily storing the contents of the memory 51, and an output of the first latch 52 and a second latch 54 to be described later. An adder 53 that adds the output of the second latch 54 to a D / A converter 56 that converts the output of the second latch 54 into analog data; and a voltage amplifier 5 that amplifies the converted analog signal to a voltage amplitude for driving the piezo element PE.
And a current amplifying unit 58 for supplying a current corresponding to the amplified voltage signal. Here, the memory 51 stores predetermined parameters for determining the drive waveform. As shown, the drive signal generation unit 55
Are supplied with clock signals 1, 2, 3, a data signal, an address signal, and a PTS signal.

The clock signals 1, 2, 3 are three types of timing signals output from the transmitter 50. The clock signal 1 is a signal that controls synchronization when a data signal is input to the memory 51. The clock signal 2 is a signal that controls the timing of switching data used for generating a drive waveform among a plurality of slew rates stored in the memory 51.
The clock signal 3 is a signal that controls the voltage change of the drive waveform. The PTS signal is a signal output corresponding to each pixel, and is a signal for instructing the start of the output of the driving waveform. P
The TS signal also plays a role in specifying the timing for inputting and outputting data corresponding to each pixel from the driving buffer 47.

FIG. 7 is an explanatory diagram showing how a drive waveform is generated. Prior to generating the drive waveform, some data indicating the slew rate of the drive signal is sent to the memory 51. The slew rate is the amount of change in voltage per unit time. When the slew rate is positive, the voltage increases at a constant rate of change, and when the slew rate is negative, the voltage decreases at a constant rate of change.
The memory 51 stores a maximum of 32 types of slew rates at each address. Here, the slew rate Δ0, Δ
The case where the data of 1, Δ2, Δ3... Is stored is shown.

When the PTS signal is input and the generation of the drive waveform is started, when the first address is specified, the slew rate Δ corresponding to the first address is stored in the memory 51.
0 is held in the first latch 52 in synchronization with the clock signal 2. On the other hand, the second latch 54 holds a value obtained by sequentially adding the slew rate Δ0 in synchronization with the clock signal 3. As a result, the voltage output from the second latch 54 is
It changes stepwise as shown in FIG. The output drive signal is smoothly shaped by a D / A converter 56, amplified by a voltage amplifier 57 and a current amplifier 58, and output to each head.

When the clock signal 2 is input, the slew rate Δ1 corresponding to the second address is output from the first latch 52 to the adder 53, and the rate of change of the voltage becomes a value corresponding to the slew rate Δ1. . In this embodiment, Δ1 has a value of 0. Therefore, as shown in the figure, the voltage is kept flat in the section where the second address is specified. The slew rate Δ2 corresponding to the third address is set to a negative value. Therefore, as shown in the figure, the voltage decreases at a constant rate in the section where the third address is set.

The memory 51 stores a slew rate and a maintenance time during which the slew rate is maintained.
Referring to FIG. 7, the maintenance time is n0 for the slew rate Δ0, and the maintenance time is n1 for the slew rate Δ1. The maintenance time is stored as the number of pulses of the clock 3 output during that time. Clock 2
Are output at intervals according to the maintenance time.

As described above, by appropriately transmitting the clock signal 2 to the drive signal generator 55, the voltage can be changed at a predetermined change rate, and a drive waveform can be generated. Further, by changing the value stored in the memory 51, the shape of the driving waveform can be variously changed.
In this embodiment, the drive waveforms WM and WS satisfying the predetermined ink amount, the ejection speed, and the ejection interval are generated in this manner.

C. Setting of ejection timing: Next, the method of setting the ejection timing of each ink droplet, that is, the ejection speed and interval of each ink droplet will be described. First, an outline of the setting method will be described, and then a specific setting example will be described. FIG.
FIG. 4 is a process diagram showing a method of setting a discharge timing. When setting the ejection timing, first, a speed range in which the ink can fly stably for each ink droplet is specified (step S1).
0). To be able to fly stably means that the landing position deviation of dots falls within a predetermined error range set based on the effect on image quality. Which error range is set depends on the requirement for image quality. In general, the lower the flight speed, the longer the flight time. Therefore, various disturbances act and the landing position deviation of dots tends to increase. In particular,
The smaller the ink droplet, the higher the lower limit value of the speed range in which flight can be performed more stably. The speed range in which the airplane can fly stably can be obtained by experiment or analysis according to the volume of the ink droplet. On the other hand, since the head has an upper limit at which the ink droplets can be ejected mechanically stably, it is necessary to set the speed range in step S10 in consideration of the upper limit.

Next, the moving speed of the main scanning is set (step S20). In order to improve the printing speed, it is desirable that the moving speed of the main scanning be higher. On the other hand, the moving speed of main scanning has an upper limit on the mechanism and the computer P
There is an upper limit due to the speed of transferring data from C. Also, if the moving speed is too high, the interval between the output of the two types of drive waveforms becomes short, and the subsequent ink droplets cannot be stably ejected due to the vibration of the meniscus remaining after the ink is ejected with the first drive waveform. There are cases. In step S20, considering these conditions,
The main scanning movement speed is set within an appropriate range.

The values set in steps S10 and S20 serve as constraints when setting the ejection timing. Here, for convenience of illustration, the case of executing the setting of the flight speed (step S10) and the setting of the moving speed of the main scanning (step S20) has been exemplified, but the setting of both may be performed in the reverse order. Good or may be performed in parallel.

Next, based on the constraint conditions thus set, an interval at which each ink droplet can be stably ejected is set (step S30). In order to eject ink droplets with a stable amount of ink, the interval needs to be set within a range in which the residual vibration when previously ejecting ink droplets is sufficiently attenuated.

Next, the ejection speed is set so that the formation position of each dot formed in each pixel falls within a predetermined range (step S40). Needless to say, it is desirable to set the positions at which the dots are formed so as to be substantially the same. If there is no solution, that is, if the setting cannot be realized, the ejection timing that satisfies the request is set while changing the moving speed of the main scanning set in step S30 (step S50). Step S3
0 and S40 can be performed in the reverse order or in parallel.

As described above, in general, the lower limit of the speed range in which stable flight is possible tends to be higher for smaller ink droplets. Therefore, by setting the ejection timing so that the smaller ink droplets are ejected later. It is relatively easy to find settings that satisfy the requirements. The ejection timing may be set in accordance with the above-described process while experimentally obtaining a speed range in which a stable flight is possible.In the present embodiment, the ejection timing is calculated by analyzing the flight of the ink droplet. Was. Hereinafter, the method will be described.

D. Analytical Setting Method of Discharge Timing: FIG. 9 is an explanatory diagram showing parameters used when setting an analytical discharge timing. Here, the case where two types of drive waveforms WM and WS are continuously output is illustrated. In order to specifically show, based on the analysis result, that it is preferable to perform ejection in the order of “medium ink droplet → small ink droplet”, the ejection order is not fixed here yet. The interval Δt (μsec) when both are continuously output is the ejection time difference of each ink droplet. The volume of the medium ink droplet ejected by the drive waveform WM is VOLm (pl), the ejection speed is vm (m / sec), the volume of the small ink droplet ejected by the drive waveform WS is VOLs (pl), and the ejection speed is VOLs (pl). vs (m / sec). The platen gap, that is, the distance between the carriage 31 and the sheet P is L (mm), and the moving speed of the carriage 31 is vc (m / sec). Each ink droplet flies at a combined speed of the ejection speeds vm and vs and the carriage movement speed vc.

In the analytical setting method, first, conditions for stably flying an ink droplet are represented using the above-mentioned variables. Then, the flight speed is set for each of the small ink and the medium ink ejected in the embodiment so as to satisfy this condition. Further, a discharge time difference is set based on the flight speed calculated in this manner.

FIG. 10 is an explanatory diagram showing the concept of obtaining conditions for the ink droplet to fly stably. FIG.
As shown in FIG. 0 (a), the ink droplets are ejected at a speed v in a vertical direction from a nozzle Nz provided in the head, that is, in a direction from the head to the paper. One of the causes of the deflection of the ink droplet flight is non-uniformity of the nozzle surface due to manufacturing variations. That is, the ink droplets are ejected in a direction slightly deviated from the vertical direction due to the influence of the shape of the nozzle Nz deviating from a perfect perfect circle, the non-uniformity of the plating applied to the inside of the nozzle surface, and the like. The horizontal velocity component caused by the ejection from the vertical direction is denoted by w. This speed component w does not always coincide with the moving direction of the carriage. The ink droplet flies in a direction in which the horizontal velocity component w and the vertical velocity component v are combined. If the momentum in the horizontal direction is sufficiently smaller than the momentum in the vertical direction of the ink droplet, the ink droplet flies stably and lands at a position almost as designed.

Here, the momentum of the ink droplet in the vertical direction and the horizontal direction is obtained. FIG. 10B is an explanatory diagram schematically showing the state of the ink droplet at the moment when it is ejected from the nozzle. Here, the momentum of the ink droplet is approximated to a cylinder having a radius R and a height V × T (hereinafter referred to as an ink column for convenience). T means the ejection time from the start to the end of ink ejection, and is substantially constant regardless of the amount of ink.

In the case where the ink droplet is approximated by a cylinder, if the density of the ink droplet is ρ, the mass m of the ink droplet is represented by density × volume, and therefore the momentum mv is represented by the following equation (1). mv = ρ × π × R ² v ² T (1);

On the other hand, the momentum in the horizontal direction is mainly due to the resultant force F of the surface tension σ acting on the nozzle surface, and its magnitude is proportional to the circumferential length of the ink column. FIG. 10C is an explanatory diagram showing a difference in surface tension acting on the ink columns Ips and Ipm having different ink amounts. The small ink column Ips is shown by hatching. In the case of the medium ink column Ipm, a resultant force Fm due to the surface tension σ acts on a region having a circumference of 2π (Rm). In the case of the small ink column Ips, the circumference 2π (Rs)
The resultant force Fs due to the surface tension σ acts on the region. The resultant force F acting in the horizontal direction is proportional to the circumference × σ. This proportional coefficient is set to k1. Since the time during which the resultant force F acts is equal to the discharge time T, the impulse F × T acts in the horizontal direction. The momentum mw generated in the horizontal direction is
Since it is equal to this impulse, using the above-mentioned proportional coefficient k1,
It is expressed by the following equation (2). mw = F × T = k1 × 2πR × σ × T (2);

The above equations (1) and (2) and the volume V of the ink column
Considering OL = πR ² VT, the horizontal momentum mw
And the ratio between the vertical momentum mv and the momentum mv in the vertical direction are expressed by the following equation (3). mw / mv = k1 × 2πR × σ × T / (ρ × π × R ² V ²
T) = 2k1 × σ / (ρRV ² ) = {K / (V ³ × VOL)} (3); where K is a proportional coefficient. If the value of the above expression (3) is sufficiently small, it can be said that the ink droplet flies stably. As described above, since K is a constant, the function f = v ³ × with the flying speed v of the ink droplet and the volume VOL of the ink droplet as variables.
When the VOL exceeds a predetermined value, it can be said that the flight is stable.

Based on the conventional results, a value to be held by the function f is calculated to stably fly the ink droplet. Conventionally, a printer equipped with a head having the same mechanism as that of this embodiment has a track record of achieving sufficiently stable flight when a 6 pl ink droplet is ejected at 6 m / sec.
By substituting this value, the value f of the above function is as follows. f = v ³ × VOL = 6 ³ × 6 = 1296 (pl ³ · m
/ Sec) Of course, this is the printer PRT of this embodiment.
Is not a general-purpose value. This is a value to be obtained for each printer based on the past performance.

From the above, the conditions under which the ink droplet flies stably were obtained. The lower limit v of the flight speed may be set according to the volume VOL of the ink droplet so as to satisfy the condition “f = v ³ × VOL = 1296”. FIG. 11 is a graph showing the relationship between the volume of the ink droplet and the ejection speed at which the ink can fly stably. The calculation results are shown based on the above conditions. It can be seen that as the ink volume increases, the lower limit of the ejection speed for flying stably decreases. For example, if the small ink droplet is 2 pl, it can be seen that the ejection speed needs to be 8.7 m / sec or more in order to fly stably. If the medium ink droplet is 10 pl, the ejection speed is 5 m in order to fly stably.
/ Sec or more.

Next, the ejection timing for setting two types of ink droplets to land on one pixel is set. FIG. 12 is an explanatory diagram showing the concept when setting the ejection timing.
FIG. 12A shows a timing setting method in the case of discharging in the order of “small dot → medium dot”. Point P in the figure
It is assumed that small ink is ejected at s, medium ink is ejected at point Pm, and lands at point Pp on the paper. The distance from the ejection points Ps, Pm to the sheet corresponds to the platen gap L described above with reference to FIG.

When the carriage ejects small ink while moving to the right in the drawing, if no air resistance acts, the ink droplet flies along a locus indicated by a broken line in the drawing. The flight distance of the small ink at this time is defined as La. However, since air resistance acts on the actual ink droplet in the direction opposite to the moving direction of the carriage, the flight distance becomes shorter than La, and the ink droplet lands on the point Pp. The flight distance reduced by the air resistance is Lb. On the other hand, the medium ink is ejected after a predetermined ejection interval Δt has elapsed after the ejection of the small ink. The distance that the carriage moves during this time is Lc
And The medium ink ejected at the point Pm flies at a combined speed of the ejection speed and the moving speed of the carriage, and lands at the point Pp along a locus indicated by a solid line in the drawing. The distance over which the medium ink flies during this time is Lm. Although air resistance acts on the middle ink, its influence is small and is ignored here.

As is clear from FIG. 12A, the following equation (4) is established between the above-mentioned distances. Lm = La−Lb−Lc (4); Lc can be calculated based on the moving speed vc of the carriage and the ejection time difference Δt. La can be calculated based on the small ink ejection speed vs. the carriage moving speed vc. Lb can be approximately determined as described later. Therefore, the right side of the above equation (4) is a known amount, and Lm can also be obtained. As a result, the horizontal flight distance L
Using the ratio of m to the platen gap L and the moving speed vc of the carriage, the ejection speed vm of the medium ink can be obtained by the following equation (5). vm = vc × L / Lm (5);

Here, a method of calculating the displacement Lb by the air resistance will be described. During a flight, it is assumed that the ink drop during the period when the air resistance acts is substantially spherical. As is well known in the field of hydrodynamics, the resistance Fd of a fluid acting on a sphere is generally expressed as “Fd =
6πR (vc) ”.
Here, μ is the static viscosity coefficient of the fluid, and is 1.8 × 10 ⁻⁵ (pas) in the case of air. R is the radius of the sphere and v is the flight speed.

Strictly speaking, since the flight speed gradually decreases, the air resistance also gradually decreases. However, since the time from discharge to landing is very short, the above-described air resistance acts almost uniformly. It is considered that a uniform acceleration a occurs in the direction opposite to the moving direction of the carriage. Therefore, the displacement Lb due to the air resistance can be obtained by the displacement in the so-called constant acceleration motion, and assuming that the flight time from ejection to landing is t, the following is obtained. Lb = here ^{0.5 × a × t 2 = 0.5} × (Fd / m) × t 2, ( density of ρ ink droplet) Fd = 6πμRv, and ^{m = ρ4πR 3/3, t} = L / By substituting (vs), Lb is given by the following equation (6). Lb = 9 μL ² (vc) / (4ρR ² (vs) ² ) (6);

The results of calculating the ejection speed of the medium ink using the above equations (4) to (6) will be specifically shown. FIG. 13 is a graph showing the relationship between the ejection speed of medium ink, the volume of small dots, and the ejection time difference. The dot-dash line in the figure indicates that the ink is ejected in the order of “small dot → medium dot”, ie, FIG.
It is a calculation result in the state shown in (a). Here, among the above constants, the ink density ρ = 1070 kg / m ³ ,
The radius R was calculated as a value corresponding to the medium ink volume of 10 pl, the carriage moving speed vc was 1 m / sec, and the platen gap L = 1 mm. The flying speed of the small ink was a value shown in the graph of FIG. Further, the ejection time difference Δt from small dot ejection to medium dot ejection is 10, 20, 3
The calculation was performed by changing to five stages of 0, 40, and 50 μsec.

The range in which the head of this embodiment can stably discharge ink is a discharge speed of about 6 to 9 m / sec. Considering such a limitation, as shown in FIG. 13, for example, when a small ink of 2 pl is used, the ejection speed vm of the medium ink is set to about 9 m / sec, and the ejection time difference Δ
It can be seen that t needs to be a very small value of 10 μsec. If the ejection time difference Δt becomes short, the residual vibration of the meniscus after the ejection of the small ink affects the ejection of the medium ink, and the possibility that the ink amount of the medium ink fluctuates increases. Also, the point at which the ejection speed is high also causes the ejection of the medium ink to be unstable. If the small ink droplet is to be made finer, the ejection speed of the medium ink droplet needs to be increased to an unrealistic value. Therefore, when ejecting with “small ink → medium ink”, it is very difficult to land each ink droplet at almost the same position.

Next, the ejection order is changed to “medium ink → small ink”.
The following is a description of the case. FIG. 12B shows a timing setting method when ink is ejected in such an ejection order. The symbols in the figure are the same as those in FIG. Due to the difference in the ejection order, in the case of “medium ink → small ink”, Lm. La. Lb. The following equation (4) ′ is established between the distances Lc. Lm = La−Lb + Lc (4) ′; In the case of “medium ink → small ink”, the above equation (4) ′
By using (5) and (6), the ejection speed of the medium ink can be obtained.

The calculation result in the case of “medium ink → small ink” is shown by a solid line in FIG. The conditions applied to the calculation are:
This is the same as the case of “small ink → medium ink”. As is clear from FIG. 13, when the small ink of 2 pl is used, even if the ejection time difference Δt is 50 μsec, about 7.5 m / sec.
It can be understood that it is enough to discharge the ink in the nozzle. In other words, it is possible to secure a sufficient ejection time difference to attenuate the residual vibration of the meniscus after ejecting the small ink, and to set the ejection speed of the medium ink within a range where the ejection can be performed with sufficient stability. You can do it. In the present embodiment, based on the analysis result, the setting is made such that the ejection speed and the ejection time difference are ejected in the order of “medium ink → small ink”.

As described above, when very fine small ink is used, it is possible to stably land on the same pixel by discharging in the order of “medium ink → small ink”. Conversely, when the small ink becomes slightly larger, it is preferable to discharge in the order of “small ink → medium ink”. As shown in FIG. 13, when the volume of the small ink is large, when the ink is ejected in the order of “small ink → medium ink”, the ejection speed of the medium ink becomes too low, and the ejection may be unstable. Because. In the case of the present embodiment, if a small ink finer than the small ink is used at the boundary of the small ink of 4 to 5 pl, “medium ink → small ink”
When the amount of the small ink is larger than the boundary area, the order of “small ink → middle ink” has a preferable result. Of course, this is only an analysis result under the calculation conditions shown in FIG. 13, and if the calculation conditions are changed, such as further increasing the ejection time difference or further increasing the carriage moving speed, 4 to 5 pl or more is obtained. In some areas, the ejection order of “medium ink → small ink” may be more preferable.

The principle of forming dots with different amounts of ink by the printer PRT of this embodiment and the method of setting the ejection timing for landing dots with different amounts of ink on one pixel have been described. According to the printer PRT of the present embodiment described above, the discharge timing is set so as to discharge in the order of “medium ink → small ink” while using very fine small ink of 2 pl and medium ink of 10 pl. By doing so, it is possible to land both ink droplets at substantially the same position while ensuring an ejection speed at which each ink droplet can fly stably. Therefore, according to the printer PRT of this embodiment, application of very fine dots and
By both suppressing the displacement of the formation position, the image quality can be greatly improved.

In the above example, the case where two kinds of inks, small ink and medium ink, are successively ejected has been described. However, if the ink ejection timing is set based on the steps described in this embodiment, three inks can be set. Even when more than two types of inks are used, it is possible to set the ejection timing at which the landing position can be suppressed. As shown in FIG. 11 and FIG. 13, considering that the speed at which the ink droplet can fly stably increases as the ink droplet becomes smaller, when the ink droplet of a different ink amount is ejected, the ink amount becomes smaller. The timing may be set so that the smaller one is ejected last.

E. Modification Example of Analytical Setting Method of Discharge Timing: In the present embodiment, the discharge timing is set on the assumption that the main cause of the flight deflection of the ink droplet is non-uniformity of the nozzle. Therefore, only the case where the air resistance acts on the small ink is considered. The mechanism by which the ink droplets bend is not fully understood,
As for the method of analytically setting the ejection timing, various modifications can be considered as long as sufficient validity can be ensured. In the following, as one of such modified examples, a calculation method will be described on the assumption that the flight bend is mainly caused by air resistance.

In the modified example, since it is assumed that the main cause of the flight bending is the air resistance, it is necessary to calculate the influence of the air resistance during flight as precisely as possible. The air resistance is
The resistance created by the relative speed of the ink droplets with the air when flying. Therefore, when strictly studying the air resistance, it is necessary to consider the flow field in the space where the ink droplet flies. FIG. 14 is an explanatory diagram showing a flow field between the carriage and the printing paper P. The carriage 31 moves at a speed vc in the x direction, that is, rightward in the figure. Carriage 31
Is sufficiently large in comparison with the platen gap, so that it can be treated as an infinite flat plate in hydrodynamics. Therefore, the flow field generated when the carriage 31 moves is equivalent to the flow field generated between the infinite flat plates that move relatively in parallel, and becomes a Couette flow well known in the field of viscous fluid. FIG. 14 shows the velocity distribution of the flow field. The air has a velocity of 0 and a carriage 3 on the printing paper P due to the influence of viscosity.
On 1, the moving speed becomes equal to the moving speed vc, and the flow speed during that time changes linearly.

The ink droplet IP flies in such a flow field. At this time, the discharge speed in the x direction is vx, and the discharge speed in the y direction is vy. The flying speeds vx and vy of the ink change every moment due to the influence of air resistance. Here, the relative velocity between the ink droplet and the air is considered. Since the flow field generated by the movement of the carriage has no velocity component in the y direction, the relative velocity in the y direction is equal to the flying velocity vy of the ink droplet. On the other hand, since the above-mentioned flow field exists in the x direction,
Assuming that the velocity of the flow field is va, the relative velocity is “vx−v
a ". In the vicinity of the carriage, the velocity va of the flow field is substantially equal to the flying velocity vx of the ink droplet, so that no air resistance acts in the x direction. From the above, the relative speed of the ink droplet to the air is obtained. That is, in the ink droplet, vd = {(vx-va) ² + vy ² } in the air.
The same resistance works when flying at Assuming that the ink droplet is spherical, the air resistance Fd is, as described above, Fd = 6.
πμR (vd). If the air resistance can be calculated in this way, the acceleration generated in the ink droplet can be obtained, and the flight trajectory can be obtained by integrating the acceleration.

FIG. 15 shows “ink drop volume = 6 pl, carriage moving speed = 0.5 m / sec, ejection speed 6 m / s
It is an explanatory view showing a flight locus under conditions of “ec”. This is a simulation result obtained by calculating the air resistance by the above-described calculation formula and integrating by numerical calculation. Various quantities such as ink density and air viscosity are the values used in the previous embodiment (FIG. 11, 1).
3). The solid line in the figure is a trajectory when air resistance is considered. If the difference between the landing position and the trajectory (dashed line in the figure) where the air resistance is not taken into consideration is defined as the landing error, a landing error of about 2.9 μm occurs under this condition.

FIG. 16 shows "Ink droplet volume = 6 pl, carriage moving speed = 1 m / sec, ejection speed 6 m / sec.
It is an explanatory view showing a flight locus under the condition of “c”. In this case, since the velocity component in the x direction at the time of discharge is large, the flight distance is increased and the influence of air resistance is also increased.
A landing error of 8 μm occurs.

FIG. 17 shows "Ink droplet volume = 2 pl, carriage moving speed = 1 m / sec, ejection speed 6 m / sec.
It is an explanatory view showing a flight locus under the condition of “c”. In this case, the influence of air resistance appears more as the ink droplets become smaller, and the landing error increases to about 12.9 μm.

FIG. 18 shows "ink drop volume = 2 pl, carriage moving speed = 1 m / sec, ejection speed 8.7 m / s.
It is an explanatory view showing a flight locus under conditions of “ec”. In this case, the flight time is shortened by increasing the ejection speed, and the landing error is reduced to about 6.2 μm.

As described above, the landing position error under each flight condition can be obtained by the simulation considering the air resistance. Therefore, if the simulation is executed while changing the ejection conditions variously, it is possible to set the ejection conditions that can suppress the landing position error to a predetermined value or less for each ink droplet volume. The predetermined value can be set arbitrarily based on the influence on the image quality and the like. It may be set by the absolute value of the error, or may be set by the ratio with the radius of the ink droplet.

After setting the range of the ejection speed at which the flight can be performed stably in this way, the ejection timing is set according to the ejection order using the same relational expression as in the embodiment. For example, when ejecting with “small ink → medium ink”, the relationship “Lm = La−Lb−Lc” shown in equation (4) of the embodiment is used.
Holds. Here, in the case of the modified example, since the flight distance La of the small ink can be obtained in consideration of the air resistance, it is not necessary to consider the influence Lb due to the air resistance in the relational expression. Further, the flight distance Lm of the medium ink can also be obtained in consideration of the air resistance. Therefore, in a modified example, the above equation is modified to “Lc = La−Lm”, and the moving distance Lc of the carriage moving during the ejection time difference is obtained.
By calculating “Δt = Lc / (vc)”, the ejection time difference Δt can be set. Similarly, in the case of “medium ink → small ink”, equation (4) ′ in the embodiment is changed to “Lc
= Lm−La ”, and the moving distance Lc of the carriage that moves during the ejection time difference is obtained, and“ Δt = Lc / (v
c)), the ejection time difference Δt can be set.

The setting of the ejection timing can be set by various analytical methods as described above. Needless to say, it is desirable to confirm the validity of each analytical method by experiment or the like in a specific case. In the example,
The case where attention is focused mainly on the non-uniformity of the nozzle is shown, and the case where the effect is mainly focused on the air resistance is shown in the modified example. However, it is needless to say that the analysis can be performed by strictly considering both. .

F. The printing apparatus according to the second embodiment. In the above-described embodiment, when two types of driving waveforms can be continuously output to one pixel by a head using a responsive piezo element, the ejection timing The setting method was explained. Next, as a second embodiment, a method of setting ejection timing will be described by taking as an example a printer that selectively outputs two types of driving waveforms for each pixel.

The printer of the second embodiment differs from the printer of the first embodiment in the mechanism for ejecting ink from the head. FIG. 19 is an explanatory diagram showing the principle of ejecting ink in the printer of the second embodiment. As shown, the nozzle Nz is provided with a heater HT in the ink passage. When the heater HT is energized, bubbles BU are generated in the ink, and the pressure causes the ink droplet IQ to be ejected. In the second embodiment, two types of dots, large dots and small dots, are formed by providing two heaters for each nozzle and changing the energization state of each heater. If only one of the two heaters is energized, a small dot is formed. When both heaters are energized, large dots are formed.

As the head mechanism is different, the configuration of the drive signal generator 55 in the printer PRT is also different from that of the first embodiment. FIG. 20 is an explanatory diagram showing the configuration of the drive signal generator in the second embodiment. As shown in the figure, an original drive signal is output from the transmitter to the heaters HT1 and HT2 provided for each nozzle via the delay circuit DL at a timing corresponding to each pixel. Mask circuits MSK1 and MSK2 are interposed in the heaters HT1 and HT2, respectively, and mask the drive waveform in accordance with the print data. In the case of print data indicating that no dot is formed, power is not supplied to either of the heaters HT1 and HT2,
Both mask circuits MSK1 and MSK2 mask the drive waveform. In the case of print data indicating the formation of small dots, only the mask circuit MSK2 masks the drive waveform so that only heater HT1 is energized. In the case of print data indicating formation of a large dot, the heaters HT1, HT1,
Neither mask circuit masks the drive waveform so that current is supplied to both HT2.

In the printer of the second embodiment, only one of the small ink droplet and the medium ink droplet can be ejected to each pixel. Therefore, when both are set to the same ejection speed, which ink droplet is ejected is determined. Irrespective of this, it suffices to discharge ink droplets to each pixel at a fixed timing. However, as described in the first embodiment, when the size of the small ink droplet is reduced, it is necessary to increase the ejection speed in order to fly stably. Therefore, in order to align the landing positions, the ejection timing for each pixel must be adjusted. I need to change.

FIG. 21 is an explanatory diagram showing the setting of the ejection timing in the second embodiment. Small ink drop IP
S, the ejection speed for causing the large ink droplet IPL to fly stably can be calculated by the same method as in the first embodiment. In addition, the flight distance L of the small ink droplet IPS
S, the flight distance LL of the large ink droplet IPL can also be calculated by the same method as in the first embodiment. Therefore, in order for both to land at the same position PP, the small ink droplet IP
S may be ejected at a distance LS to the pixel PP, and the large ink droplet IPL may be ejected at a distance LL to the pixel PP. In the second embodiment, since either the large ink droplet or the small ink droplet is selectively ejected, there is no limitation on the ejection time difference Δt between the two. When the ejection position is specified in this way, the timing for outputting each drive signal is set. Normally, a reference signal PTS for ink ejection is output to the head for each pixel, so that each ejection timing can be set by a delay time from the signal PTS. As shown in FIG. 21, a short delay time DTL is used for a large ink drop.
Is set, and a long delay time D is set for a small ink drop.
TS is set. By setting the timing so that the small ink droplets are ejected at a late timing in this way, large and small ink droplets can be ejected at a stable flying speed, and the dot formation position shift is suppressed to achieve high image quality. Printing can be realized.

According to the printer of the present embodiment described above, a plurality of ink droplets can be continuously discharged to each pixel by discharging in the order of “medium ink or large ink → small ink”. In such a case, the landing position can be stabilized in any case of selectively discharging. Here, the case where two types of ink droplets are used is exemplified,
It is also possible to apply when three or more types are used.
When three or more types of ink droplets are used, the ejection timing can be set in various modes under the condition that at least the minimum amount of ink droplets is ejected last.
For example, when three types of large ink, medium ink, and small ink are used, it is desirable to discharge in the order of the ink amount, that is, in the order of “large ink → middle ink → small ink”,
The order may be “medium ink → large ink → small ink”. As described in the embodiment, it is necessary to increase the ejection speed sufficiently to secure the flight stability when the dots are very fine, and it is generally considered that only small inks are applicable. As long as is ejected last, it is possible to set the ejection timing at which the flight can be performed sufficiently stably without necessarily ejecting the ink droplets of the other ink amounts in the order of the ink amount.

Although various embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that various configurations can be adopted without departing from the spirit of the present invention.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a schematic configuration of a printing system as an embodiment.

FIG. 2 is an explanatory diagram showing a schematic configuration of ink discharge heads 61 to 64.

FIG. 3 is an explanatory diagram showing a relationship between a driving waveform and ejected ink Ip.

FIG. 4 is an explanatory diagram showing a driving waveform and a state of ejection of ink droplets to each pixel.

FIG. 5 is an explanatory diagram showing an internal configuration of a control circuit 40.

FIG. 6 is an explanatory diagram showing an internal configuration of a drive signal generation unit 55.

FIG. 7 is an explanatory diagram showing how a drive waveform is generated.

FIG. 8 is a process chart showing a method of setting an ejection timing.

FIG. 9 is an explanatory diagram showing parameters used when setting analytical ejection timing.

FIG. 10 is an explanatory diagram showing a concept of obtaining a condition for an ink droplet to fly stably.

FIG. 11 is a graph showing the relationship between the volume of an ink droplet and the ejection speed at which the ink droplet can fly stably.

FIG. 12 is an explanatory diagram showing a concept when setting ejection timing.

FIG. 13 is a graph showing the relationship between the ejection speed of medium ink, the volume of small dots, and the ejection time difference.

FIG. 14 is an explanatory diagram showing a flow field between a carriage and a print sheet P.

FIG. 15 is an explanatory diagram showing a flight trajectory under the condition “ink droplet volume = 6 pl, carriage moving speed = 0.5 m / sec, ejection speed 6 m / sec”.

FIG. 16 is an explanatory diagram showing a flight trajectory under the conditions “ink droplet volume = 6 pl, carriage moving speed = 1 m / sec, ejection speed 6 m / sec”.

FIG. 17 is an explanatory diagram showing a flight trajectory under the conditions “ink droplet volume = 2 pl, carriage moving speed = 1 m / sec, ejection speed 6 m / sec”.

FIG. 18 is an explanatory diagram showing a flight trajectory under the conditions of “ink droplet volume = 2 pl, carriage moving speed = 1 m / sec, ejection speed 8.7 m / sec”.

FIG. 19 is an explanatory diagram illustrating the principle of discharging ink in the printer of the second embodiment.

FIG. 20 is an explanatory diagram illustrating a configuration of a drive signal generation unit according to a second embodiment.

FIG. 21 is an explanatory diagram showing setting of ejection timing in a second embodiment.

FIG. 22 is an explanatory diagram illustrating an example of a printer that forms dots having different amounts of ink.

[Explanation of symbols]

 23 ... Paper feed motor 24 ... Carriage motor 26 ... Platen 31 ... Carriage 32 ... Operation panel 34 ... Sliding shaft 36 ... Driving belt 38 ... Pulley 39 ... Position detection sensor 40 ... Control circuit 46 ... Timer 47 ... Driving buffer 48 ... Bus 49 ... Distribution output device 50 ... Transmitter 51 ... Memory 52 ... First latch 53 ... Adder 54 ... Second latch 55 ... Drive signal generation unit 57 ... Voltage amplification unit 58 ... Current amplification unit 61-64 ... Head 68 ... Ink passage 71: Cartridge 72: Cartridge for color ink 90: Computer

Claims (6)

[Claims] 1. A printing apparatus which prints an image by forming dots on each pixel on a print medium using a head capable of discharging a plurality of types of ink droplets having different amounts of ink, comprising: Main scanning means for performing main scanning by driving at least one of the plurality of types of ink droplets; and driving the head at a timing set for each of the plurality of types of ink droplets to form any one of the plurality of types of dots in each pixel. A printing apparatus, comprising: a head driving unit configured to set the timing so that a flight time of an ink droplet having a minimum ink amount among the plurality of types of dots is set to be shortest. 2. The printing apparatus according to claim 1, wherein the timing is set such that an ink droplet having a larger ink amount is ejected earlier for each pixel. 3. The printing apparatus according to claim 1, wherein the ejection timing of each ink droplet is set at an interval at which a plurality of ink droplets can be continuously ejected to one pixel. 4. The printing apparatus according to claim 1, wherein the head is a head that discharges ink using distortion of an electrostrictive element. 5. The printing apparatus according to claim 1, wherein the head discharges the ink by using bubbles generated by heating the ink. 6. A printing method for printing an image by forming dots on each pixel on a print medium using a head capable of ejecting a plurality of types of ink droplets having different amounts of ink, comprising the steps of: Performing main scanning by driving at least one of the plurality of types of ink droplets, and driving the head at a timing set for each of the plurality of types of ink droplets such that the flight time of the ink droplet having the minimum amount of ink is the shortest. Forming dots in each of the pixels.