JP5716314B2 - Liquid discharge defect detection device, adjustment method thereof, and ink jet recording apparatus - Google Patents

Description

  The present invention relates to a liquid ejection failure detection device that detects ejection failure of ink droplets, an adjustment method thereof, and an inkjet recording apparatus including the device.

  The ink jet recording apparatus includes an ink jet head of each color for ejecting minute ink droplets from minute nozzles, and ejects ink droplets while moving the ink jet head with respect to a recording medium such as paper. Perform image formation. In order to form a high-resolution image, it is necessary to reduce the size of the ink droplets by reducing the size of the nozzles. In this case, since the nozzles are fine, nozzle clogging occurs due to drying of the ink when printing is stopped, ink droplet ejection failure occurs, dot dropout occurs in the image, and the image quality is degraded.

  Conventionally, an ink jet recording apparatus has been provided with a liquid discharge failure detection device that detects a liquid discharge failure in order to prevent image quality deterioration due to nozzle clogging. Such a liquid ejection failure detection device, for example, irradiates droplets such as ink droplets ejected from a nozzle with laser light emitted from a light emitting element such as a laser diode to generate scattered light, and the scattered light is photogenerated. Light reception by a light receiving element such as a diode is performed, and an output voltage based on the output of the light receiving element is compared with a reference voltage value to determine whether or not an ink droplet has been normally discharged, thereby detecting a liquid discharge failure.

  For example, in Patent Document 1, in order to perform reliable non-ejection detection without receiving light diffraction even when the recording head is long, two light receiving elements that detect two beams are opposite to each other in the sub-scanning direction. The nozzles located near the light receiving elements are used, and the ink droplets are sequentially ejected from these nozzles toward the beam in a time-series manner, and the ink droplet ejection timing and the light receiving element detection timing are set. A method for identifying a discharge failure based on this has been proposed.

  However, in Patent Document 1, since it is necessary to provide two sets of light emitting elements and light receiving elements, the cost becomes high and the control becomes complicated.

  Further, in Patent Document 2, in order to increase the accuracy of detection of an inactive nozzle, the direction of the light beam point along the optical axis is set so that the light beam point is positioned on the locus of the ink droplet according to the nozzle position to be inspected. A configuration for moving to is disclosed. The movement of the luminous flux point is adjusted by a driving unit that changes the distance between the light emitting element and the lens.

  However, in Patent Document 1, since high positional accuracy is required for the drive unit that changes the distance between the light emitting element and the lens, the cost becomes high and the control becomes complicated.

Japanese Patent No. 3501599 Japanese Patent No. 4273627

  The present invention has been made in view of the above, and it is possible to easily adjust the output of the liquid discharge failure detection device with a low-cost configuration, a method for adjusting the same, and ink jet recording. An object is to provide an apparatus.

In order to solve the above-described problems and achieve the object, the present invention provides a light receiving element that receives light after a liquid droplet ejected from each nozzle provided in a head collides with a light beam emitted from the light emitting element. And a determination unit that detects an ejection failure of a droplet based on a light reception result by the light receiving element, the light beam is condensed so as to have a predetermined focal position, and the light receiving element is the light beam The light intensity distribution in the optical axis direction of the light beam and the light received by the light receiving element when the focal position of the light beam is set to infinity. The intensity is set to a height at which the distribution obtained by inverting the distribution according to the position of the nozzle that ejects the droplet colliding with the light beam is substantially the same.

In order to solve the above-described problems and achieve the object, the present invention receives light after a liquid droplet ejected from each nozzle provided in the head collides with a light beam irradiated by a light emitting element. An adjustment method for a liquid ejection failure detection apparatus comprising: a light receiving element; and a determination unit that detects a droplet ejection failure based on a light reception result of the light receiving element, wherein the light beam has a predetermined focal position. A light intensity distribution in the optical axis direction of the light beam, and a focal position of the light beam generated by condensing the light receiving element so that the light beam has the focal position. Adjust the height of the light received by the light receiving element at infinity to a height that is substantially the same as the distribution obtained by inverting the distribution according to the position of the nozzle that ejects the droplet colliding with the light beam. Including the step of And features.

  According to the liquid discharge failure detection device according to the present invention, a liquid discharge failure detection device capable of easily adjusting the output of the liquid discharge failure detection device with a low-cost configuration, an adjustment method thereof, and an ink jet recording apparatus are provided. There is an effect that it becomes possible to provide.

FIG. 1 is a front view illustrating a structure of an example of an ink jet printer (ink jet recording apparatus) including a liquid ejection defect detecting device according to an embodiment. FIG. 2 is a view of a part of the ink jet printer observed obliquely from above. FIG. 3 is a block diagram showing an example of a main configuration of the ink jet printer according to the present embodiment. FIG. 4A is a diagram of a configuration example of the moving unit. FIG. 4B is a diagram of another configuration example of the moving unit. FIG. 5 is an explanatory diagram for explaining the operation principle of the liquid ejection defect detection device. FIG. 6 is a diagram illustrating an example of an intensity distribution of a light beam. FIG. 7 is a diagram illustrating the positional relationship between the light beam and the ink droplets ejected from the nozzles. FIG. 8 is a diagram illustrating voltage values obtained when the light receiving element receives scattered light generated when the ink droplet intersects with the light beam. FIG. 9 shows a state in which ink droplets are ejected from the nozzles n1 to n5 in a state where the light beams are parallel (focal point is infinity), and scattered light S corresponding to each ink droplet is received at a light receiving element at an arbitrary position. It is a figure which shows the case where it measures by PD. FIG. 10 is a diagram showing the measurement result of the scattered light output value in the case of FIG. FIG. 11 is a diagram showing the intensity distribution 1-1 of the scattered light S at each angle θ from the optical axis L. FIG. 12 is a diagram showing the incident angle θ of the scattered light S generated at each ink droplet ejection position on the light receiving surface of the light receiving element. FIG. 13 is a diagram showing the intensity distribution 1-1 of the scattered light output value. Figure 14 is definitive when alienated height H _PD from the optical axis L of the light receiving element is a diagram showing the incident angle to the light receiving surface of the light receiving elements of the scattered light S from the ejection position. Figure 15 is a diagram showing the relationship between the height H _PD and intensity distribution of the optical axis L of the light receiving element PD. FIG. 16 is a diagram illustrating the relationship between the ink droplet ejection position, the X-direction distances _{XPDn1 to XPDn5} to the light receiving element, and the light beam intensity when the light beam LB is focused behind the light receiving element. It is. FIG. 17 is a diagram in which the intensity distribution 1 and the intensity distribution 2 are combined. FIG. 18 is a diagram showing an example of a flow for explaining a processing procedure of an adjustment method for making the scattered light output constant at each ink ejection position of the head. FIG. 19 is a diagram illustrating an example of a flow for explaining a light emitting element height adjustment process and a light emitting element output adjustment process of the liquid ejection failure determination apparatus shown in FIG. FIG. 20 is a diagram illustrating a modification.

  Hereinafter, embodiments of a liquid discharge failure detection apparatus, an adjustment method thereof, and an ink jet recording apparatus according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. In addition, constituent elements in the following embodiments include those that can be easily assumed by those skilled in the art or those that are substantially the same.

  Exemplary embodiments of a liquid ejection defect detecting device, an adjusting method thereof, and an ink jet recording apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

[Configuration of liquid discharge failure detection device]
FIG. 1 is a front view showing a structure of an example of an ink jet printer (ink jet recording apparatus) 1 provided with a liquid ejection defect detecting device according to an embodiment. Moreover, FIG. 2 shows the figure which observed a part of the inkjet printer 1 from diagonally upward.

  As shown in FIG. 1, a guide shaft 13 and a guide plate 14 are provided in parallel on the left and right side plates 11 and 12 of the housing 10 of the inkjet printer 1. The guide shaft 13 and the guide plate 14 are slidably penetrated through the carriage 15. An endless belt (not shown) is attached to the carriage 15. The endless belt is wound around a driving pulley and a driven pulley (not shown) provided on the left and right sides of the housing 10. Then, the driven pulley is driven to rotate along with the rotation of the driving pulley, and travels on the endless belt. As a result, the carriage 15 is moved to the left and right as indicated by the arrows in FIG.

  In the carriage 15, inkjet heads 16 y, 16 c, 16 m, 16 b of four colors of yellow, cyan, magenta, and black (hereinafter referred to as representative of the head 16) are arranged in parallel in the moving direction of the carriage 15. . Each head 16 has a nozzle row in which a plurality of nozzles are linearly arranged on a downward nozzle surface. Although not shown, the linear nozzle row is provided in a direction orthogonal to the moving direction of the carriage 15.

  When the carriage 15 is in the rightmost home position as shown in FIG. 1, each head 16 faces the single recovery device 18 installed on the bottom plate 17 in the housing 10. The single recovery device 18 is a device that sucks out ink from the nozzle that has detected the ink droplet discharge failure by the liquid discharge failure detection device 20 and recovers the liquid discharge failure by the inkjet printer 1 itself.

  The liquid ejection failure detection device 20 is disposed on the bottom plate 17 in the housing 10 adjacent to the single recovery device 18. Details of the liquid discharge failure detection device 20 will be described later.

  A plate-like platen 22 is installed at a position adjacent to the liquid discharge failure detection device 20. On the back side of the platen 22, a paper feed base 24 that supplies the paper 23, which is a recording medium, onto the platen 22 is provided to be inclined. Although not shown, a paper feed roller for feeding the paper 23 on the paper feed table 24 onto the platen 22 is provided. Further, a transport roller 25 is provided for transporting the paper 23 on the platen 22 in the direction of the arrow and discharging it to the front side.

  On the bottom plate 17 in the housing 10, a driving device 26 is further installed at the left end. The driving device 26 drives a feed roller (not shown), a conveying roller 25, and the like, and drives the above-described driving pulley to travel the endless belt and move the carriage 15.

  At the time of recording, the paper 23 is moved onto the platen 22 by being driven by the driving device 26 and positioned at a predetermined position. Further, the carriage 15 is moved and scanned on the paper 23, and ink droplets are sequentially ejected from the respective nozzles using the four-color heads 16y, 16c, 16m, and 16b while moving to the left. An image is recorded. After image recording, the carriage 15 is returned to the right and the paper 23 is conveyed by a predetermined amount in the direction of the arrow in FIG.

  Next, while the carriage 15 is moved leftward again, ink droplets are sequentially ejected from the respective nozzles using the four-color heads 16 y, 16 c, 16 m, and 16 b on the forward path, and an image is recorded on the paper 23. Similarly, after image recording, the carriage 15 is returned to the right and the sheet 23 is conveyed by a predetermined amount in the direction of the arrow in FIG. Thereafter, the same operation is repeated, and an image is recorded on one sheet of paper 23.

  Next, the configuration of the inkjet printer 1 according to the present embodiment will be described. FIG. 3 is a block diagram showing an example of a main configuration of the inkjet printer 1 according to the present embodiment. Note that FIG. 3 mainly shows a configuration related to the liquid ejection defect detection device, and a configuration related to image recording is omitted. The ink jet printer 1 according to the present embodiment includes a head 16, a light emitting element 30, a discharge control unit 101, a light emission control unit 120, a light receiving unit 103, a good / bad determination unit 104, and a movement control unit 105. The moving unit 106 is mainly provided.

  The ink jet printer 1 according to the present embodiment performs a liquid ejection failure detection process for detecting whether or not ink droplets are normally ejected from nozzles nx (1 ≦ x ≦ M, where M is the number of nozzles). In the liquid ejection failure detection process, a light beam is emitted from the light emitting element 30 to the flight path of the ink droplet, and the ink droplet is ejected from the nozzle nx to the emitted light beam to generate scattered light from the ink droplet. The light receiving element PD receives the scattered light, and the good / bad determination unit 104 detects whether or not the ink droplet has been normally ejected based on the output voltage obtained by receiving the scattered light.

  Further, the liquid ejection failure detection device 20 includes at least the light emitting element 30, the light emission control unit 120, the light receiving unit 103, the good / bad determination unit 104, the movement control unit 105, and the movement unit 106 in FIG. It has.

  The ejection control unit 101 controls ejection processing for ejecting ink droplets from each nozzle of the head 16. In the liquid discharge failure detection process, the discharge control unit 101 has a size that is determined according to the distance between the light emitting element 30 and the nozzle nx or the distance between the light receiving element PD and the nozzle nx from the nozzle nx of the head 16. Control to eject ink droplets.

  The light emission control unit 120 functions as a second adjustment unit. The light emission control unit 120 controls light emission processing for causing the light emitting element 30 to emit light. In the liquid discharge failure detection process, the light emission control unit 120 sends a light emission control signal having a constant voltage value to continuously light up the light emitting element 30. In addition, the light emission control unit 120 includes a table that defines the relationship between the scattered light output value and the drive current. TP2 (scattered light output value) that is fed back with reference to the table in the light emitting element output adjustment process described later. ) To change the drive current to adjust the light quantity of the light beam LB.

  The light emitting element 30 is a light emitting element such as a semiconductor laser, for example, and is turned on according to a light emission control signal sent from the light emission control unit 120 to generate a light beam LB. When the head 16 is short, the cost can be reduced by using a laser diode as the light emitting element 30.

  The light receiving unit 103 mainly includes a light receiving element PD, an I / V conversion unit 111, a first stage amplification unit 112, a high-pass filter 113, and a second stage amplification unit 114.

  The light receiving element PD is an element that receives light such as a photodiode, for example, and generates a current in proportion to the intensity of the received light. As shown in FIG. 5, the light receiving element PD is disposed at a position shifted from the optical axis L of the light beam LB generated by the light emitting element 30 by an angle θ and further away from the light emitting element 30 than immediately below the nozzle. In the liquid ejection failure detection process, the light receiving element PD detects the forward scattered light S1 scattered in the optical axis direction of the light beam LB when the ink droplet 36 is irradiated to the light beam LB and the scattered light S1 to S7 is generated. S3 is received, and a current corresponding to the intensity of the received light is generated. As another aspect, the light receiving element PD may include a current-voltage conversion unit that converts the generated current into a voltage, and may be configured to output the voltage.

  The I / V conversion unit 111 converts the current generated in the light receiving element PD into a voltage corresponding to the magnitude of the current value.

  The first stage amplifying unit 112 amplifies the voltage that has been subjected to current-voltage conversion by the I / V conversion unit 111, and outputs an output signal TP1. The offset voltage can be measured by this output signal TP1.

  The high pass filter 113 removes and reduces the DC component (noise component) of the output signal TP1.

  The second stage amplifying unit 114 amplifies the voltage obtained by the high pass filter 113. In the liquid ejection failure detection process, the output signal TP2 representing the output voltage (scattered light output value) corresponding to the scattered light is output by the second stage amplification unit 114.

  The configuration of the light receiving unit 103 as shown in FIG. 3 is an example, and any configuration can be applied as long as it outputs output voltages (output signals TP1, TP2) corresponding to the received light beam LB.

The good / bad determination unit 104 detects an ink droplet ejection defect from the output signal TP <b> 2 output from the light receiving unit 103. For example, good / bad determination unit 104, an output signal TP2, compares the threshold value V _SH predetermined as a reference voltage for determining ejection failure, when the output signal TP2 is smaller than the threshold value V _SH, ink Detect that the droplet has bent. Detection unit 104, if the threshold V _SH is smaller than a predetermined output signal TP2 than the threshold value is small, may be configured to detect that the state of non-ejection. Further, the good / bad determination unit 104 may be configured to eliminate fluctuations in output due to noise components by applying hysteresis when comparing the pulse waveform of the scattered light with the reference voltage (threshold value V _SH ). Good.

The moving unit 106 can move the light receiving element PD in the height direction (vertical direction) with respect to the optical axis L under the control of the movement control unit 105, and the optical axis-light receiving element distance H _PD.
(Also referred to as “light receiving element height H _PD with respect to the optical axis L of the light beam LB”) is adjustable, so that the light receiving element PD can be moved closer to or away from the optical axis L. It has become.

  The movement control unit 105 determines the movement direction and movement amount of the light receiving element PD based on the output signal TP2 output from the light receiving unit 103 in the light receiving element height adjustment process described later, and determines the determined movement direction and movement. The moving unit 106 is moved by the amount. The movement control unit 105 and the movement unit 106 function as a first adjustment unit.

  FIG. 4A is a diagram illustrating a configuration example of the moving unit 106. As shown in FIG. 4A, the light receiving element moving unit 42 includes a holder 43 that holds the light receiving element 35 having the light receiving surface 37, and an upper end side fixed to the holder 43 and slides along the holder 43 in the length direction thereof. The slider rod 44 is freely supported, and a drive motor 47 having a motor gear 46 that meshes with a rack 45 on the lower end side of the slider rod 44. Then, by driving the drive motor 47, the motor gear 46 is rotated, the slider rod 44 is slid in the length direction, the holder 43 is moved, and the light receiving element height HPD with respect to the optical axis L of the light beam LB is variable. In addition, the light receiving element PD can be moved closer to or away from the optical axis L.

  FIG. 4B is a diagram illustrating another configuration example of the moving unit 106. As illustrated in FIG. 4B, the moving unit 106 includes a holder 43 that holds the light receiving element 35 having the light receiving surface PDm, a screw shaft 49 on which a screw portion 48 on the upper end side is screwed to the holder 43, A drive motor 47 having a motor gear 46 that meshes with an outer peripheral screw 50 provided on the lower end side of the screw shaft 49. Then, by driving the drive motor 47, the motor gear 46 is rotated to rotate the screw shaft 49, the holder 43 is moved, and the offset height OH of the light beam LB with respect to the optical axis L is varied. On the other hand, the light receiving element PD can be moved closer or far away.

[Operation Principle and Adjustment Principle of Liquid Discharge Defective Detection Device]
Next, the operation principle and adjustment principle of the liquid ejection failure detection device 20 will be described with reference to FIGS. FIG. 5 is an explanatory diagram for explaining the operation principle of the liquid ejection failure detection device 20. .., NN of the nozzles n1, n2,..., NN in FIG. In the head 16, the surface 37 of each nozzle n1, n2, ..., nx, ..., nN on the ink droplet discharge port side is referred to as a nozzle head surface 37. In the inkjet printer 1 provided with the liquid ejection failure detection device 20 of Embodiment 1, ink droplets 36 are ejected from one nozzle nx at a time in this nozzle row.

  The diffused light emitted from the light emitting element 30 is converted into a light beam LB that connects the focal point ST at an arbitrary position by the collimator lens 32. In the example shown in the figure, the focal point ST is behind the light receiving element PD. The light emitting element 30 is arranged in a direction in which the optical axis L of the light beam LB is orthogonal to the ejection direction of the ink droplets 36.

  The light receiving element PD is made of, for example, a photodiode (PD), and generates a current proportional to the amount of light received by the light receiving surface PDm. The current generated in the light receiving element PD is converted into a voltage value in the light receiving unit 103. The light receiving element PD is disposed in the housing 10 of the ink jet printer 1 so as to be able to receive scattered light generated when the light beam LB irradiated from the light emitting element 30 collides with the ink droplet 36.

  Here, the light receiving element PD is disposed at a position outside the beam diameter of the light beam LB. Specifically, the light receiving element PD is disposed as offset as close to the center of the optical axis L as possible at a position where the light receiving surface does not overlap the beam diameter of the light beam LB. Thereby, efficient detection becomes possible. FIG. 5 shows an example in which the light receiving element PD is arranged at a position below the light beam LB and further from the light emitting element 30 than immediately below the nozzle.

In the configuration illustrated in FIG. 5, when the ink droplet 36 is ejected from the nozzle nx of the head 16 and intersects with the light beam LB, scattered light S <b> 1 to S <b> 7 is generated. Light-receiving element PD, of the scattered light S1 to S7, in particular the light intensity received strong forward scattered light S1 to S3, and outputs a voltage value V _PD representing the light intensity of the received scattered light as the optical output value. When the light beam LB has a high light intensity, the light intensity of the scattered light S1 to S7 also increases.

  FIG. 6 shows an example of the intensity distribution of the light beam LB. When a semiconductor laser is used as the light emitting element 30, light is emitted at angles in the vertical and horizontal directions. The vertical and horizontal angles of a general semiconductor laser are 14 ° and 30 °, respectively. In the following description, it is assumed that a semiconductor laser is used as the light emitting element 30. When such light is collimated by the collimator lens 32, the cross section in the direction perpendicular to the traveling direction has an elliptical shape with different aspect ratios as illustrated as the beam cross section 40 in FIG.

  Here, in FIG. 6, the X direction, that is, the horizontal direction indicates a direction perpendicular to the ink droplet ejection direction. In addition, the Y direction, that is, the vertical direction indicates the ink droplet ejection direction. Thereby, it can be seen that the light intensity is strongest at the center (optical axis L) of the light beam LB, and the light intensity decreases toward the edge, resulting in a Gaussian distribution.

  FIG. 7 is a diagram showing the positional relationship between the light beam LB and the ink droplets ejected from the nozzle nx, and is a diagram in which the ink droplet 36 ejected from the nozzle nx is observed from the ejection direction, that is, the vertical downward direction. FIG. 7 shows an example of the ink droplet 36a at the time of normal ejection and the ink droplet 36b at the time of ejection failure ejected from the nozzle nx arranged at the back of the drawing in the light beam LB.

  When the nozzle row of the head 16 exists on the optical axis L of the light beam LB, the normally ejected ink droplets 36a fly in the vertical direction as they are. Therefore, the ink droplet 36a passes through the center of the light beam LB. On the other hand, the bent ink droplet 36b passes through a position deviated from the center of the light beam LB. In addition, when the ink is not ejected, the ink droplet 36 is not ejected, and therefore does not pass the light beam LB.

FIG. 8 is a diagram showing a voltage value V _PDTP2 obtained when the light receiving element PD receives scattered light generated when the ink droplet 36 intersects with the light beam LB. The normally ejected ink droplet 36a passes through the center of the light beam LB having the highest light intensity, so that the scattered light intensity also increases. In FIG. 8, the maximum value V ′ of the voltage value represented by the solid line corresponds to the scattered light output value (output signal TP2) output in this case.

  On the other hand, since the ink droplet 36b in which the bending has occurred is deviated from the center of the light beam LB, the scattered light intensity is lowered. In FIG. 8, the maximum voltage value V ″ (<V ′) represented by a broken line represents the scattered light output value output in this case.

  Further, when the ink droplet 36 is not ejected, the ink droplet 36 does not pass through the light beam LB, so that scattered light is not generated and the scattered light intensity is not measured. In FIG. 8, the voltage value represented by the alternate long and short dash line represents the scattered light output value (V0 = 0) output in this case.

Here, if the threshold for determining whether or not the ejection is defective is V _SH , the output signal TP2 = V ′ for the ink droplet 36a is larger than the threshold V _{SH, and} thus the ink droplet 36a is normally ejected. I can judge. On the other hand, the ink droplets 36b for the output signal TP2 = V '' is smaller than the threshold value _{V SH,} for example an ink droplet 36b can be determined that bending occurs. As described above, by using the threshold lower than the threshold value V _SH, it is possible to detect the state of non-ejection.

In the following description, a case where there are five nozzles of the head 16 will be described for the sake of simplicity. FIG. 9 shows that the ink droplets 36 are ejected from the nozzles n1 to n5 in a state where the light beams LB are parallel (the focal point is infinity), and the scattered light S corresponding to each ink droplet 36 is placed at an arbitrary position. The case where it measured with the light receiving element PD of is shown. In the _{figure, X PDN1} an ink droplet ejection position and the distance of the light receiving element PD of the nozzle _{n1, X PDn5} an ink droplet ejection position and the distance of the light receiving element PD of the nozzle _{n5, H PD} is the light beam LB optical axis L The height of the light receiving element PD from is shown.

FIG. 10 is a diagram showing the measurement result of the scattered light output value in the case of FIG. In FIG. 10, the horizontal axis indicates the distance X _PD between the light receiving element PD and the ink droplet 36, and the vertical axis indicates the scattered light output value V _PDTP2 . As shown in FIG. 10, the scattered light output value is different at each nozzle position ( _{XPDn1 to XPDn5} ) of the head 2 (intensity distribution 1). This is because (1) the scattered light intensity is angularly dependent, and (2) the ejection position of the ink droplet 36 and the X-direction distances _{XPDn1 to XPDn5} (light beam irradiation direction) to the light receiving element PD. Yes.

  First, the angle dependency of the scattered light intensity (1) will be described. When the light beam LB is parallel, the light intensity of the light beam LB is constant regardless of the location, but the scattered light intensity of the scattered light S varies depending on the angle θ from the optical axis L. FIG. 11 is a diagram showing the intensity distribution 1-1 of the scattered light S at each angle θ from the optical axis L. In the figure, the horizontal axis indicates the angle θ of the scattered light S from the optical axis, and the vertical axis indicates the scattered light intensity. As shown in the figure, the intensity distribution 1-1 is such that the scattered light intensity is high near the optical axis L (θ = 0) and the scattered light intensity decreases as the distance from the optical axis L increases. Recognize.

  Next, (2) the ink droplet ejection position and the light receiving element X direction distance will be described. FIG. 12 is a diagram illustrating an incident angle θ of the scattered light S generated at each ink droplet ejection position on the light receiving surface PDm of the light receiving element PD. In the drawing, for the sake of simplicity of explanation, only the ink droplet ejection positions of the nozzle n5 closest to the light receiving element PD and the nozzle n1 farthest are shown. As shown in the figure, the angle θ incident on the light receiving surface PDm of the light receiving element PD differs depending on each ink droplet ejection position. The angle from the ink droplet ejection position of nozzle n1 to the upper side of the light receiving surface is θ1U, the angle from the ink droplet ejection position of nozzle n1 to the lower side of the light receiving surface is θ1D, and the angle from the ink droplet ejection position of nozzle n5 to the upper side of the light receiving surface. The entering angle is θ5U, and the angle entering the lower side of the light receiving surface from the ink droplet ejection position of the nozzle n5 is θ5D. At the ink discharge position (n5) close to the light receiving element PD, the incident angle (θ5 = θ5D−θ5U) is wide. Conversely, at the ink discharge position (n1) far from the light receiving element PD, the incident angle (θ1 = θ1D−θ1U). Is narrow.

As a result of the above conditions (1) and (2) overlapping, an intensity distribution 1-1 of the scattered light output value as shown in FIG. 13 is generated. For example, when the nozzle position is _XPDn5 , the scattered light S can be taken in as much as the incident angle is wide (θ = θ5). The scattered light output value measured by the PD does not increase (area S = S5). On the other hand, when the nozzle position is _XPDn1 , even if the incident angle is narrow (θ = θ1), the scattered light output value is high (area S = S1) because the light intensity of the scattered light S taken in is high. .

In addition to the above (1) and (2), the intensity distribution is changed by the height _{H PD} from the optical axis L of (3) a light receiving element PD. Figure 14 shows the angle of incidence on the light receiving surface PDm of the light-receiving element PD of the scattered light S from the definitive, the ejection position when alienated height H _PD from the optical axis L of the light receiving element PD. Figure 15 is a diagram showing the relationship between the height H _PD and intensity distribution of the optical axis L of the light receiving element PD.

As shown in FIG. 14, when the light receiving element PD is moved away from the optical axis L (light receiving element height H _PD → H _PD ′), the incident angle becomes narrower (θ1> θ1 ′, θ5> θ5 ′) and the scattered light S As the light receiving element PD is moved away from the optical axis L, the scattered light output value becomes smaller as shown in FIG. In FIG. 15, the distance from the optical axis L increases in the order of H _PD1 <H _PD2 (intensity distribution (slope α)) <H _PD3 <H _PD4 .

With reference to FIG. 5 and FIGS. 16 to 18 described above, a method of adjusting the scattered light output to be constant at each ink discharge position of the head 16 will be described. First, as shown in FIG. 5, the light emitted from the light emitting element 30 is focused on the rear side ST of the light receiving element PD by the collimator lens 32. FIG. 16 shows the relationship between the ejection position of the ink droplet 36 and the X-direction distances _{XPDn1 to XPDn5} to the light receiving element PD and the light beam intensity when the focus of the light beam LB is focused behind the light receiving element PD. FIG. As shown in FIG. 16, when the focal point ST is formed behind the light receiving element PD, a light intensity distribution 2 (inclination β) having an inclination in the direction of the optical axis L is obtained. This is because the light intensity increases because the density of the light beam LB increases near the position of the focal point ST. On the other hand, since the density is low on the collimating lens 32 side, the light intensity is low.

As described above, the distance X _PD from the angle dependence of the ink discharge position of the scattered light S to the light receiving element PD, there is intensity distribution 1 (see FIG. 10) in the scattered light output values received by the light receiving element PD. The intensity distribution 1 has an inclination reversed from that of the intensity distribution 2 obtained by condensing the light beam LB. FIG. 17 is a diagram in which the intensity distribution 1 and the intensity distribution 2 are combined, and the intensity distribution 1 shows the case of the light receiving element height _HPD2 in FIG. 17, as the height H _PD from the optical axis L of the light receiving element PD, to be inclined beta (dotted line) and opposite slope of the intensity distribution 2 due to the light beam LB focused (-beta = alpha) Adjust to. This makes it possible to acquire a substantially uniform scattered light output value regardless of each ink droplet ejection position, as indicated by a solid line. In the example shown in FIG. 5, the focal point ST is formed behind the light receiving element PD. As long as the intensity distribution 2 is obtained by focusing, the focal position ST may be in front of, behind the light receiving element PD, or in the vicinity of the light receiving element PD.

  FIG. 18 is a flowchart for explaining the processing procedure of the adjustment method for making the scattered light output constant at each ink ejection position of the head 16. When the ejection failure detection device 20 is incorporated into an actual machine or an inspection machine, the arrangement position of the head 16 (ink droplet ejection position) and the optical system is roughly determined due to mechanical limitations. Therefore, first, the ink ejection position-light receiving element distance XPD is determined (step S1). Thereby, the inclination α of the intensity distribution 1 of the scattered light incident on the light receiving surface PDm of the light receiving element PD as shown in FIG. 13 can be grasped.

  Next, the position of the focal point ST is determined so as to be close to the intensity distribution 2 having an inclination (−α = β) opposite to the intensity distribution 1, and the distance between the light emitting element 30 and the collimating lens 32 is fixed (step S2). ). Thereby, the position shift | offset | difference by continuous use and vibration of an apparatus can be prevented. The reason why the distance between the light emitting element 30 and the collimating lens 32 is fixed is that the position of the focal point ST is greatly displaced due to a deviation of several μm of the collimating lens 32, and as a result, the intensity distribution collapses from the initial one. . Although it depends on the performance of the collimating lens 32, a positional deviation of about 10 μm causes a deviation of the focal length of about 10 mm. In addition to fixing the distance between the light emitting element 30 and the collimating lens 32, a mechanism capable of adjusting the distance may be provided. However, it is desirable that the position accuracy is good and that it is resistant to changes with time.

As a method of fixing the collimating lens 32, a method of mechanically screwing or a method of using an adhesive can be used. When the collimating lens 32 is fixed, a deviation occurs. Therefore, finally, the light receiving element PD is moved away from the optical axis L (light receiving element height _HPD adjustment), and the scattered light output value at each ink droplet ejection position is adjusted (step S3). As an adjustment method, for example, ink droplets 36 are alternately ejected from the nozzles (n1 and n5 in FIG. 9) at both ends of the head 16, and the light receiving element PD is moved so that the respective outputs are the same.

Up to this point, the scattered light output value at each ink droplet ejection position can be substantially uniform, but there is a possibility that a predetermined output cannot be obtained. In the defect / bent determination, as shown in FIG. 8, the defect / bent is detected by comparing the obtained scattered light output value with an arbitrary threshold value V _SH .

Therefore, the light output of the light emitting element 30 is adjusted so that an appropriate scattered light output value is obtained with respect to the threshold value V _SH (step S4). As a method of adjusting the light output of the light beam LB, there is a method of increasing / decreasing the value of the drive current to the light emitting element 30 so that the scattered light output value becomes a target value. Further, a method of feeding back the scattered light output value obtained by the light receiving element PD and automatically adjusting the drive current may be used.

  In this way, by adjusting the light output of the light emitting element 30, the intensity distribution of the light beam LB at the ink droplet ejection position can be changed without changing the slope of the intensity distribution. As a result, the light intensity of the scattered light S can be adjusted, and as a result, the scattered light output value obtained by the light receiving element PD can be set to an optimum value, and it is possible to easily determine a defect or a bend. Become.

  Once the optical system is set, a substantially constant scattered light output value can be obtained without adjusting the optical system for each ejection of the nozzles n1 to n5. By setting the output value of the scattered light to be almost constant, it is possible to unify the threshold values used in the good / bad determination unit 104, and to simplify the program of the good / bad determination unit 104. Further, in the method of uniforming the scattered light output value by data processing, there is a possibility that necessary information may be deleted. Therefore, as in this embodiment, the scattered light output value is set with an optical and mechanical configuration. The method of making it almost uniform is superior.

  FIG. 19 is a diagram illustrating an example of a flow for explaining the light emitting element height adjustment process and the light emitting element output adjustment process of the liquid ejection failure determination apparatus shown in FIG. It is assumed that the optical axis L and the head nozzle row are arranged in parallel.

In the figure, first, the light emission control unit 120 drives the light emitting element 30 to start the irradiation of the light beam from the light emitting element 30 (step S11). The head controller 16 causes ink droplets to be ejected from the nozzle n1 (step S12). The light receiving unit 103 measures the scattered light output value _VPDn1 , and the movement control unit 105 records it in the memory as the scattered light output value _VPDn1 of the nozzle n1 (step S13).

Next, the light emission control unit 120 ejects ink droplets from the nozzle n5 (step S14). The light receiving unit 103 measures the scattered light output value _VPDn5 , and the movement control unit 105 records it as the scattered light output value _VPDn5 of the nozzle n1 (step S15). The movement control unit 105 determines whether or not the scattered light output value Vn1 of the nozzle n1 = the scattered light output value _VPDn5 of the nozzle n5 (step S16).

When the scattered light output value V _{PDn1 of the} nozzle n1 is not equal to the scattered light output value V _PDn5 of the nozzle n5 (“No” in step S16), when V _PDn1 > V _PDn5 , the movement control unit 105 moves the moving unit 106. Is controlled to move the light receiving element PD closer to the optical axis L by a predetermined amount. When V _PDm1 <V _PDm5 , the movement control unit 105 controls the moving unit 106 to move the light receiving element PD by a predetermined amount. Move away from the axis L (step S17). Thereafter, the flow returns to step S12, until the scattered light output value _{V PDn5} of the scattered light output value _{V PDN1} = nozzle n5 nozzles n1 (in step S16 "Yes"), repeatedly executes the processing of step S12 to S17.

On the other hand, in the case of the scattered light output value _{V PDN1} = scattered light output value _{V PDn5} the nozzle 1 ( "Yes" in step S16), and the light emission control unit 120, the scattering of the scattered light output value _{V PDN1} or nozzle n5 nozzles n1 It is determined whether or not the optical output value V _PDn5 is the target value V _TARGET (step S18). If the scattered light output value _{V PDn5} of the scattered light output value _{V PDN1} or nozzle n5 nozzles n1 is not the target value _{V TARGET} is ( "No" in step S18), and the light emission control unit 120, the scattered light output value of the nozzle n1 When VPDn1 or the scattered light output value V _{PDn5 of the} nozzle n5> target value V _TARGET , the output of the light emitting element 30 is lowered and the scattered light output value VPDn1 of the nozzle n1 or the scattered light output value V _{PDn5 of the} nozzle n5 <target value V _In the case of _TARGET , the output of the light emitting element 30 is increased (step S19). Thereafter, the flow returns to step S12, until the scattered light output value _{V PDn5} = target value _{V TARGET} of the scattered light output value _{V PDN1} or nozzle n5 nozzles n1 (in step S18 "Yes"), the process of step S12~S19 Repeatedly.

When it becomes a scattered light output value _{V PDn5} = target value _{V TARGET} of the scattered light output value _{V PDN1} or nozzle n5 nozzles n1 to stop irradiation of ( "Yes" in step S18), and the light beam from the light emitting element 30 .

As described above, according to this embodiment, the first adjustment means (movement control unit 105, the moving portion 106) to adjust the height H _PD to the light receiving element PD from the optical axis L of the light beam LB and And a second adjustment means (light emission control unit 120) for adjusting the light quantity of the light beam LB emitted from the light emitting element 30, so that the output adjustment of the liquid ejection defect detection device can be performed at a low cost (adjustment). (A configuration with a minimum number of sections) and can be easily performed. In addition, output adjustment can be performed without adjusting the optical system for each ejection of the nozzles n1 to n5. An almost constant scattered light output value can be obtained.

Further, from the optical axis L to the light receiving element PD height H _PD after adjusting, since the order of adjusting the light quantity of the light beam LB, is possible but shorten the adjustment time.

The adjustment of the height H _PD from the optical axis L to the light receiving element PD, since the position of the light receiving sensitivity intensity distribution of the irradiation direction of the light beam LB by the position of the pre-determined focal ST and the opposite slope, It is possible to obtain a substantially constant scattered light output value without adjusting the optical system for each ejection of the nozzles n1 to n5.

  In addition, since the liquid discharge defect detection device of the present embodiment is mounted on the ink jet recording apparatus, it is possible to determine discharge defect detection and to realize a low cost ink jet recording apparatus with stable printing performance. It becomes.

[Modification]
Up to this point, a method has been shown in which once the optical system is determined, an almost constant output can be obtained without adjusting the optical system for each ejection of the nozzles n1 to n5, but the structure is complicated. Depending on the ejection position of the ink droplet B, a method of automatically adjusting the height HPD from the optical axis L to the light receiving surface PDm of the light receiving element _PD and the output of the light beam LB may be used. Further, although the positional accuracy becomes severe, a method of automatically adjusting the distance between the light emitting element 30 and the collimating lens 32 and the output of the light beam LB may be used.

FIG. 20 is a diagram illustrating a modification. Although the structure is large, as shown in FIG. 20, the light beam LB is made substantially parallel light, and the ink is separated from the light receiving element PD (where the change in the incident angle distribution of the scattered light S on the light receiving surface PDm is small). It is good also as a structure which arrange | positions a discharge location (head 16). This makes it possible to obtain a uniform scattered light output value irrespective of the ink droplet ejection position X _{PD1 '~X PD5'} in the head 16. In this case, if the distance XPDn5 ′ from the light receiving element PD to the ink droplet S is long, the incident angle θ of the scattered light S to the light receiving surface PDm becomes small as described above with reference to FIG. Although the scattered light output value is also reduced, by bringing the light receiving surface PDm close to the optical axis L, a portion where the scattered light S is strong can be incident on the light receiving surface PDm, and thus the scattered light output value is increased. be able to.

DESCRIPTION OF SYMBOLS 1 Inkjet printer 16 Head 30 Light emitting element 31 Light beam 101 Discharge control part 103 Light receiving unit 104 Good / defective judgment part 105 Movement control part 106 Moving part 111 I / V conversion part 112 First stage amplification part 113 High pass filter 114 Second stage Amplifier 120 Light emission controller PD Light receiving element PDm Light receiving surface LB Light beam L Optical axis

Claims (3)

A light receiving element that receives light after a liquid droplet ejected from each nozzle provided in the head collides with a light beam emitted by the light emitting element;
A determination unit that detects an ejection failure of a droplet based on a light reception result by the light receiving element,
The light beam is focused to have a predetermined focal position;
The light receiving element is
The light receiving element receives the light intensity distribution in the optical axis direction of the light beam, which is generated by condensing the light beam so as to have the focal position, and when the focal position of the light beam is set to infinity. The liquid discharge defect detection is characterized in that the distribution of the intensity of the light is approximately the same as the distribution obtained by inverting the distribution according to the position of the nozzle that discharges the droplet colliding with the light beam. apparatus.   An ink jet recording apparatus comprising the liquid discharge defect detecting device according to claim 1. A light receiving element that receives light after a liquid droplet ejected from each nozzle provided in the head collides with the light beam emitted from the light emitting element, and detects a liquid droplet ejection failure based on the light reception result of the light receiving element. An adjustment method for a liquid ejection defect detection device comprising:
Condensing the light beam to have a predetermined focal position;
When the light receiving element is focused so that the light beam has the focal position, the light intensity distribution in the optical axis direction of the light beam and the focal position of the light beam are set to infinity. Adjusting the height of the light received by the light receiving element to a height that is substantially the same as the distribution obtained by inverting the distribution according to the position of the nozzle that ejects the droplet colliding with the light beam ;
The adjustment method of the liquid discharge defect detection apparatus characterized by including this.

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