JP2005088338A - Inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus which can correctly correct a striking position deviation of ink droplets for each of a plurality of recording heads even when there is a variation of a distance to an optical axis of a detection light for each of the plurality of recording heads. <P>SOLUTION: In the inkjet recording apparatus which has a plurality of recording heads, ink droplets are discharged from nozzles of the recording heads to intersect the optical axis of a light emitting element and a light receiving element. A discharge velocity of the ink droplets is detected by detecting a time interval from the discharge start to shade detection because of passing of the ink droplets, and a driving condition is changed on the basis of the detected result. The inkjet recording apparatus has a distance difference detecting means for detecting a difference of the distance between a nozzle face of each recording head and the optical axis, and an operating means for correcting the distance difference detected by the distance difference detecting means to the detected time interval for each recording head detected by a velocity detecting means. A driving control means controls to change the discharge velocity of the ink droplets on the basis of the operation result of the operating means for each recording head. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inkjet recording apparatus that records an image on a recording medium by ejecting ink droplets from nozzles of a recording head, and more particularly, to accurately detect the speed of ink droplets ejected from nozzles of a recording head. The present invention relates to an ink jet recording apparatus that can be used.

  Small ink droplets are ejected from a large number of nozzles formed on the recording head, landed on a recording medium arranged to face the nozzle surface of the recording head, and desired while the recording head performs bi-directional main scanning. In the ink jet recording apparatus that records the image of the above, if the ejection state of the ink droplets is not kept constant, the landing position of the recording head during bidirectional main scanning will be displaced, which causes the recording image to be disturbed. Image quality is significantly reduced. Further, since the change in the ink droplet ejection speed appears as a change in the ink droplet amount, there is a problem in that the density of the recorded image changes and the image has a different color balance.

  This change in ink droplet ejection speed is related to the difference in ink viscosity, and since the ink viscosity is affected by the environmental temperature, the ink droplet ejection speed always occurs due to a change in the environmental temperature.

For this reason, conventionally, the speed of the ink droplet is detected based on the time from the start of the ejection of the ink droplet from the recording head until the ink droplet passes through the optical axis of the detection light, and the driving condition of the recording head is determined from the detection result. Japanese Patent Application Laid-Open No. H10-228561 describes a technique for changing and controlling the above. Similarly, in order to detect the ejection speed of the ink droplet, the ink droplet speed is detected based on the time from the start of ejection of the ink droplet from the recording head until the ink droplet passes through the optical axis of the detection light. This is described in Patent Document 2.
JP-A-11-300944 JP 2003-35719 A

  Inkjet recording apparatuses that record full-color images generally include a plurality of recording heads corresponding to each color of YMCK. Since the plurality of recording heads are normally mounted on the carriage independently so that they can be individually replaced, the distance between the nozzle surface of each recording head and the optical axis of the detection light for speed detection is Due to mechanical tolerances and the like, not all recording heads are the same, and there is variation for each recording head.

  Therefore, as described in Patent Documents 1 and 2, only by measuring the time from the start of ink droplet ejection to the passage of the optical axis, there is variation in the distance from the nozzle surface of each recording head to the optical axis of the detection light. There is a problem that appears as a speed error. For example, assuming that the distance between the nozzle surface of a certain recording head and the optical axis of the detection light is 5 mm, the distance between the nozzle surface of the other recording head and the optical axis with respect to that recording head. If the variation is ± 0.1 mm, a speed error of ± 2% appears even if there is no error in the detection time from the start of ink droplet ejection to the passage of the optical axis.

  For this reason, it was impossible to grasp the accurate ink droplet ejection speed simply by measuring the time from the start of ink droplet ejection to the passage of the optical axis.

  In addition, the recording head performs image recording by reciprocating along the width direction (main scanning direction) of the recording medium, but the nozzle surface of each recording head can be used to correct the deviation of the bi-directional landing position accurately. And the variation in the distance to the optical axis of the detection light has caused a problem that the landing position is not accurately matched.

  Accordingly, the present invention provides an ink jet capable of accurately correcting the landing position deviation of the ink droplets for each of the plurality of recording heads even if there is a variation in the distance to the optical axis of the detection light for each of the plurality of recording heads. It is an object to provide a recording device.

  Another object of the present invention is to provide an ink jet recording apparatus capable of easily matching the two-way landing positions regardless of variations in the distance to the optical axis of the detection light for each of a plurality of recording heads.

  Other problems of the present invention will become apparent from the following description.

  Each of the above problems is solved by the following inventions.

  A plurality of recording heads having a plurality of nozzles arranged on a nozzle surface, drive control means for controlling ejection of ink droplets from the nozzles toward a recording medium, a light emitting element and a light receiving element, And a speed detecting means for detecting an ink droplet ejection speed by ejecting an ink droplet from the nozzle so as to cross the optical axis and detecting a time from the start of ejection until the detection of a shadow due to the passage of the ink droplet. In the ink jet recording apparatus in which the drive condition in the drive control unit is changed based on the detection result of the speed detection unit, a difference in distance between the nozzle surface of each recording head and the optical axis is detected. A distance difference detection means; and a calculation means for correcting the distance difference detected by the distance difference detection means with respect to the detection time for each recording head detected by the speed detection means; A, the drive control means, for each recording head, an ink jet recording apparatus and controls to change the ejection speed of the ink droplets on the basis of the calculation result of the calculating means.

  According to a second aspect of the present invention, there are provided a plurality of recording heads having a plurality of nozzles arranged on a nozzle surface, drive control means for controlling ink droplets to be ejected from the nozzles toward a recording medium, a light emitting element, and a light receiving element. The speed at which the ink droplet ejection speed is detected by ejecting the ink droplet from the nozzle so as to cross the optical axis and detecting the time from the start of ejection until the detection of the shadow due to the passage of the ink droplet An ink jet recording apparatus comprising: a detecting unit that changes a driving condition in the driving control unit based on a detection result of the speed detecting unit, wherein the height of the optical axis is the height of the recording surface of the recording medium. The ink jet recording apparatus is characterized by being matched to the above.

  According to the first aspect of the present invention, based on the distance difference detection means for detecting the difference in distance between the nozzle surface of each recording head and the optical axis, the speed difference is detected based on the distance difference detected by the distance difference detection means. Calculating means for correcting the detection time for each recording head detected by the detecting means, and the speed detecting means detects the ejection speed of the ink droplets from each recording head based on the detection time corrected by the calculating means. By doing so, even if there is variation in the distance to the optical axis of the detection light for each recording head, ink jet recording that can accurately correct the landing position deviation of the ink droplets for each of the plurality of recording heads. An apparatus can be provided.

  According to the second aspect of the present invention, since the height of the optical axis is matched with the height of the surface of the recording medium, it is related to the variation in the distance to the optical axis of the detection light for each of the plurality of recording heads. In addition, it is possible to provide an ink jet recording apparatus capable of easily matching the two-way landing positions.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the main part of an ink jet recording apparatus according to the present invention, and FIG. 2 is a block diagram showing the main part.

  In FIG. 1, the recording head is composed of four independent recording heads 1A to 1D here, but in the present invention, a plurality of recording heads may be used, and a specific number is not limited. The lower surface of each of the recording heads 1A to 1D is a nozzle surface in which a large number of nozzles (not shown) are arranged in a line along a direction orthogonal to the main scanning direction. The controller (CPU) 5 shown in FIG. 1 controls the driving circuit 6 under predetermined driving conditions (driving voltage, driving frequency), so that microdrop-shaped ink droplets a from the nozzles on the nozzle surface are respectively transferred at the lower timing in FIG. By ejecting in the direction, a desired image is recorded on a recording medium (not shown).

  Each of the recording heads 1A to 1D is mounted on a common carriage (not shown), and the carriage is reciprocated along the main scanning direction by a moving unit (not shown), so that both are integrated along the main scanning direction. It is possible to reciprocate in the direction.

  Reference numeral 2 denotes a droplet detector for detecting the passage of ink droplets a ejected from the nozzles of the recording heads 1A to 1D of the recording head 1, and a light-emitting element 21 including a light-emitting diode that emits detection light, and the like. 2 includes a light receiving element 22 made of a photodiode or the like for receiving the detection light emitted from the light emitting element 21, and a detection unit 23 shown in FIG.

  The light emitting element 21 and the light receiving element 22 in the droplet detector 2 are disposed at a position such as the home position where the recording head 1 does not record on the recording medium, and the recording head 1 can be disposed therebetween. Are provided opposite to each other at a certain distance.

  The optical axis 20 of the detection light is orthogonal to the main scanning direction of the recording head 1 and parallel to the arrangement direction of the nozzles of the recording heads 1A to 1D, and the height positions along the ejection direction of the ink droplets a are each different. The recording heads 1 </ b> A to 1 </ b> D are disposed at positions lower than the positions of the nozzle surfaces. Accordingly, when the nozzle row of any of the recording heads 1A to 1D is positioned on the optical axis 20 of the detection light between the light emitting element 21 and the light receiving element 22, the ink droplet a ejected from each nozzle The traveling path intersects with the optical axis 20.

  The light emitting element 21 and the light receiving element 22 are both mounted in the casings 21a and 22a that optically shield the light. The light receiving element 22 receives the detection light from the light emitting element 21 in the casing 21a on the light emitting element 21 side. A light emitting opening 21b for emitting light toward the side is formed. The housing 22 a on the light receiving element 22 side has a light receiving opening 22 b for receiving detection light from the light emitting element 21 so that the light receiving element 22 can detect it.

  The light receiving opening 22b has an elliptical shape in which the diameter (long diameter) d2 along the direction perpendicular to the diameter (short diameter) d1 along the direction perpendicular to the nozzle surface of the recording head 1 is long (see FIG. 3). Generally, the light receiving opening 22b is narrower in the direction perpendicular to the nozzle surface of the recording head 1, that is, in the ejection direction of the ink droplet a, so that the detection accuracy when detecting the velocity of the ink droplet a is improved. This is advantageous in that it can. However, if the width in the direction orthogonal to this is narrowed, the output of the signal detected by the light receiving element 22 is reduced, and on the contrary, since the margin for the optical axis shift of the recording head 1 in the main scanning direction is reduced, the output is stable. Therefore, the opening shape is elliptical, and the short diameter d1 is provided in the housing 22a on the light receiving element 22 side so as to be along the direction perpendicular to the nozzle surface of the recording head 1. Therefore, it is possible to achieve both improvement in detection accuracy of the ink droplet a and reduction in detection error. An example of the shape of the light receiving opening 22b is d1 = 1.5 mm and d2 = 3 mm.

  The detection signal detected by the light receiving element 22 is sent to the detection unit 23 shown in FIG. The detection unit 23 includes a current amplification unit 231 that amplifies the detection signal of the light receiving element 22, an AC amplification unit 232 that amplifies only the variation of the detection signal amplified by the current amplification unit 231, and the AC amplification unit 232. The comparator 234 compares the output signal with a reference signal generated through the low-pass filter 233 and outputs a signal exceeding the reference signal level to the controller 5 as a defect-out signal. .

  The light emitting element 21 of the droplet detector 2 is controlled to be turned on / off by the controller 5.

  Reference numeral 3 denotes an ink tray, which is disposed so as to face the nozzle surface of the recording head disposed on the optical axis of the detection light among the recording heads 1A to 1D, and the ink droplet a ejected from the recording head. To accept.

  Reference numeral 4 denotes a distance detector that detects the distances between the recording heads 1A to 1D. Here, it is composed of a reflection type distance sensor having a light emitting element 41 composed of a light emitting diode or the like for emitting detection light and a light receiving element 42 composed of a photodiode or the like for receiving detection light emitted from the light emitting element 41. The configuration is not particularly limited as long as the distance between the nozzle surfaces of the recording heads 1A to 1D can be detected.

  The distance detector 4 has a height position along the ejection direction of the ink droplet a on the side of the pair of the light emitting element 21 and the light receiving element 22 in the droplet detector 2 and the nozzle surface of each of the recording heads 1A to 1D. When the recording heads 1A to 1D are moved in the main scanning direction and the recording heads 1A to 1D are respectively arranged above (shown by broken lines in FIG. 1). ), When the detection light emitted from the light emitting element 41 is reflected by the nozzle surfaces of the recording heads 1A to 1D by the light receiving element 42, the surface of the distance detector 4 (with the light emitting element 41 and The distance between the surface exposed to the light receiving element 42) and the nozzle surfaces of the recording heads 1A to 1D is detected.

  The distance between the recording heads 1A to 1D and the nozzle surfaces of the recording heads 1A to 1D by the distance detector 4 can be detected, for example, at the time of factory shipment or when any recording head is replaced. The detection result is output to the controller (CPU) 5 shown in FIG.

  As shown in FIG. 4, the controller 5 includes a control unit 51, a distance difference detection unit 52, a time detection unit 53, and a calculation unit 54.

  The control unit 51 outputs a discharge start signal (FIRE-M signal) to the drive circuit 6 according to a predetermined drive condition, thereby constituting a drive control means for driving the recording head 1 and simultaneously detecting the distance difference. The operations of the unit 52, the time detection unit 53, and the calculation unit 54 are controlled.

  The distance difference detection unit 52 receives the detection values of the distances between the nozzle surfaces of the recording heads 1A to 1D detected by the distance detector 4 and the distance detector 4 to thereby input the recording heads 1A to 1D. The distance difference detecting means for detecting the distance difference between the nozzle surface and the distance detector 4 is configured. The distance difference data detected here is stored in a predetermined area in the distance difference detection unit 52.

  The distance difference is detected by using any one of the recording heads 1A to 1D (for example, the recording head 1a) as a reference head, and the distance between the nozzle surface of the reference head 1a and the distance detector 4. And the difference between the distances between the nozzle surfaces of the other recording heads 1 </ b> B to 1 </ b> D and the distance detector 4.

  The time detector 53 starts the ejection when the control unit 51 outputs the FIRE-M signal to the drive circuit 6, and the ejected ink droplet a passes through the light receiving element 22 of the droplet detector 2, and the shadow is generated. The detection time is obtained based on the time until the defect-out signal is input from the detection unit 26 to the controller 5. Specifically, as shown in FIG. 5, from the time when the ejection start signal (FIRE-M) is output to the recording head to be detected until the fall (Tf) of the defect-out signal, the rise (Tb) ) Until the median (Tn) is detected.

  The computing unit 54 constitutes computing means for correcting the distance difference detected by the distance difference detecting unit 52 with respect to the detection time for each of the recording heads 1A to 1D detected by the time detecting unit 53.

  That is, if there is variation in the height position of the nozzle surface for each of the recording heads 1A to 1D, even if the ejection speed of the ink droplets a in each of the recording heads 1A to 1D is the same, the droplet detector 2 There is a difference in detection time until it passes through the optical axis 20, and an error occurs with respect to the actual discharge speed unless the variation in the height position of the nozzle surface is taken into consideration. For this reason, the calculation unit 54 corrects the distance difference detected by the distance difference detection unit 52 with respect to the detection time for each of the recording heads 1A to 1D detected by the time detection unit 53, thereby recording. Determine the desired detection time of the head.

  For example, the ratio (h1 / h2) of the distance difference between the height position (h1) of the nozzle surface of a certain recording head and the height position (h2) of the nozzle surface of the reference head is L (mm), and the actuality of the recording head When the detection time is T (ms), the originally desired detection time of the recording head is L · T.

  The calculation result of the calculation unit 54 is sent to the control unit 51, and the control unit 51 corrects the drive condition (drive voltage) output to the drive circuit 6 from the calculation result, and changes and controls the ejection speed of the ink droplet a. .

  Next, a specific processing operation will be described with reference to the flowchart shown in FIG.

  Since the ejection speed of the ink droplet a is detected from the head on the moving side along the main scanning direction (hereinafter referred to as No. 1 head), the controller 5 turns on the light emitting element 21 (S1). The recording head to be detected first is designated as the No. 1 head among the plurality of recording heads (S2), the carriage is moved in the main scanning direction, and the nozzle row of the No. 1 head is set as a droplet. Align with the optical axis 20 of the detection light of the detector 2 (S3).

  Next, the controller 5 outputs a discharge start signal (FIRE-M) to the drive circuit 6 and discharges a plurality of ink droplets a continuously from all the nozzles of the No. 1 head as a measure for discharging normal ink droplets a. (Preliminary discharge) is performed (S4).

  After preliminary ejection, a plurality of ink droplets a are ejected from the first nozzle (hereinafter referred to as No. 1 nozzle) of all nozzles of the No. 1 head (S5). If a plurality of ejections are performed in this way, the plurality of ink droplets a can be regarded as a lump of a single ink droplet group. The output level of the detection signal detected by the detector 2 can be increased, and detection can be performed with high accuracy.

  When the ejected ink droplet a passes through the optical axis 20 of the droplet detector 2, a part of the detection light is blocked by the light receiving element 22, and the received light amount signal is temporarily reduced, so that the defect is detected from the detection unit 26. -out signal is output. The controller 5 determines whether or not the defect-out signal is input from the detection unit 26 (S6).

  After discharging the ink droplet a, the control unit 51 determines a predetermined time-out time, that is, a time sufficiently estimated that the ink droplet a will cross the optical axis 20 of the detection light after the ink droplet a is discharged. If the progress is detected and the defect-out signal is not output from the detection unit 26 even after the time-out period elapses, the nozzle shifts to error processing as a missing nozzle in which the ink droplet a is not ejected.

  On the other hand, when the controller 5 receives a defect-out signal from the detection unit 26, the time from the ejection start signal (FIRE-M) of the ink droplet a to the detection of the defect-out signal from the detection unit 26 (in FIG. 5). (Tn time) is detected and stored as the No. 1 nozzle detection time (S7).

  Thereafter, the controller 5 detects the detection time of the ink droplet a from all the nozzles of the No. 1 head, and then repeats the same processing as described above for the No. 2 head, No. 3 head,... (S8, S9).

  When the detection of all the recording heads is completed, the controller 5 turns off the light emitting element 21 (S10). Subsequently, the detection times of all the recording heads 1A to 1D and the respective recording heads 1A calculated in advance are obtained. Based on the detection result of the 1D distance difference, the calculation unit 54 calculates the average ejection speed of the ink droplets a for each of the recording heads 1A to 1D (S11).

  The average ejection speed of the ink droplets a for each of the recording heads 1A to 1D is stored in the controller 5, and the controller 5 thereafter drives the drive circuit 6 for each of the recording heads 1A to 1D based on the stored calculation results. By changing the driving condition (driving voltage), the ejection speed of the ink droplets a is changed and controlled for each of the recording heads 1A to 1D, and the landing position deviation is accurately corrected for each of the recording heads 1A to 1D. Is possible.

  FIG. 7 is a schematic perspective view showing another embodiment of the ink jet recording apparatus according to the present invention. Parts having the same configuration as in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the height position of the optical axis 20 of the detection light of the droplet detector 2 is recorded on a recording medium (not shown) on which an image is recorded by ink droplets a ejected from the recording heads 1A to 1D. ) Surface (image recording surface). That is, the distance L1 between the nozzle surfaces of the recording heads 1A to 1D shown in FIG. 7 and the optical axis 20 of the detection light of the droplet detector 2 (here, the nozzle surface of the recording head 1D and the droplet detector 2). Is the distance between the nozzle surface of each of the recording heads 1A to 1D and the surface of the recording medium during image recording.

  Thus, by matching the height position of the optical axis 20 of the detection light of the droplet detector 2 with the height position of the surface of the recording medium, the ink drop a is moved from the optical axis 20 from the start of ejection of the ink droplet a. 5 (Tn time in FIG. 5) for each of the recording heads 1A to 1D, the ink droplet a is landed on the recording medium even if there is a mechanical tolerance of each of the recording heads 1A to 1D. Therefore, the landing positions of the ink droplets a in both directions along the main scanning direction can be easily matched.

  In order to adjust the time from the start of ejection of the ink droplet a until the ink droplet a passes through the optical axis 20 for each of the recording heads 1A to 1D, as described above, the recording detected by the time detection unit 53 of the controller 5 is performed. After obtaining the detection time for each of the heads 1A to 1D, the drive condition (driving) to the drive circuit 6 is changed so that the ejection speed for each of the recording heads 1A to 1D is changed based on the time difference between the detection times of the recording heads 1A to 1D. The voltage can be corrected.

  By adopting the above configuration, a speed difference of the ink droplet a corresponding to the height error of each of the recording heads 1A to 1D occurs. However, it is desired to reduce image quality deterioration due to bidirectional landing error rather than density difference due to this. In the case of using a recording head having a configuration in which a plurality of heads are integrated and the nozzle surface height is the same, the distance detector 4 as shown in FIG. Improved landing position can be achieved.

The figure which shows schematic structure of the principal part in the inkjet recording device which concerns on this invention. Configuration block diagram of main parts in inkjet recording apparatus Front view showing shape of light receiving opening Controller block diagram Timing chart of discharge start signal and detection signal Diagram showing control flow of detection operation Schematic perspective view showing another embodiment of the ink jet recording apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1A-1D: Recording head 2: Droplet detector 20: Optical axis 21: Light emitting element 22: Light receiving element 23: Detection part 3: Receptacle 4: Distance detector 41: Light emitting element 42: Light receiving element 5: Controller 51: Control Unit 52: Distance difference detection unit 53: Time detection unit 54: Calculation unit 6: Drive circuit a: Ink droplet

Claims (2)

A plurality of recording heads having a plurality of nozzles arranged on a nozzle surface; drive control means for controlling ejection of ink droplets from the nozzles toward a recording medium; a light emitting element and a light receiving element; A speed detecting means for detecting an ink droplet ejection speed by ejecting an ink droplet from the nozzle so as to intersect and detecting a time from the start of ejection until detection of a shadow due to the passage of the ink droplet; In the inkjet recording apparatus configured to change the drive condition in the drive control unit based on the detection result of the detection unit,
Distance difference detection means for detecting a difference in distance between the nozzle surface of each recording head and the optical axis;
Calculating means for correcting the distance difference detected by the distance difference detecting means with respect to the detection time for each recording head detected by the speed detecting means;
The ink jet recording apparatus, wherein the drive control unit controls each recording head to change an ink droplet ejection speed based on a calculation result of the calculation unit. A plurality of recording heads having a plurality of nozzles arranged on a nozzle surface; drive control means for controlling ejection of ink droplets from the nozzles toward a recording medium; a light emitting element and a light receiving element; A speed detecting means for detecting an ink droplet ejection speed by ejecting an ink droplet from the nozzle so as to intersect and detecting a time from the start of ejection until detection of a shadow due to the passage of the ink droplet; In the inkjet recording apparatus configured to change the drive condition in the drive control unit based on the detection result of the detection unit,
An ink jet recording apparatus, wherein the height of the optical axis coincides with the height of the recording surface of the recording medium.

Images