JP2009248559A - Inkjet printing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable to accurately regulate the interval of a head unit and a material to be printed by quickly following the drive of an inkjet head having a large weight in a vertical direction even when the interval of the inkjet head and the surface to be printed of the material to be printed conveyed at a high speed according to the warp, etc. of the material to be printed to be conveyed at a high speed. <P>SOLUTION: The interval of the inkjet head 1 and the printing surface of the material to be printed can be accurately regulated by quickly following the drive of the head unit 2 having a large weight in the vertical direction even when the interval between the inkjet head 1 and the printing surface of the material to be printed A to be conveyed at the high speed by providing an air suspension 10 as a head unit energizing means for upwardly energizing to reduce the downward weight of the head unit 2 loaded to an actuator 4. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an inkjet printing apparatus that performs printing with a plurality of inkjet heads arranged in the width direction on a printing surface of a sheet-like printed material that is conveyed and supplied at high speed.

  An ink jet printing apparatus that prints on a printing surface of a sheet-like substrate to be transported and supplied with an ink jet head has a discharge angle of ink droplets due to a change in the distance between the ink jet head and the printing surface due to warping or waviness of the substrate. An actuator that drives the inkjet head in the vertical direction is provided to prevent deviations in the landing position due to dispersion of ink droplets, a decrease in flying speed of ink droplets, and an increase in deviation in landing position due to airflow during conveyance of the printing medium. In some cases, the interval between the inkjet head and the printing surface is adjusted to be constant (see, for example, Patent Documents 1 and 2).

  The ink jet printing apparatuses described in Patent Documents 1 and 2 both scan the ink jet head in the width direction of the print medium, and those described in Patent Document 1 are caused by warping of the print medium of the recording paper. On the other hand, the device described in Patent Document 2 adjusts the interval between the ink jet head and the printing surface with respect to the warpage or undulation of the substrate such as a substrate or a panel.

  In addition, a head unit in which a plurality of inkjet heads are arranged in the width direction of a plate-like body such as a steel plate as a substrate to be transported and supplied is arranged, and the head unit is an actuator according to the plate thickness of the plate-like body. There is also an inkjet printing apparatus that is driven in the vertical direction to adjust the interval between the inkjet head and the printing surface (see, for example, Patent Document 3).

  An ink jet printing apparatus provided with a head unit in which a plurality of ink jet heads are arranged in the width direction of a printing medium as described in Patent Document 3 does not need to scan the ink jet head in the width direction of the printing medium. Therefore, it is used for printing a wide printed material such as a steel plate or a corrugated cardboard sheet, or for printing a printed material conveyed and supplied at high speed. Incidentally, in the case of scanning the inkjet head in the width direction, although depending on the printing width of the printing medium, the conveyance speed of the printing medium is usually 10 m / min or less, while a plurality of inkjet heads are arranged in the width direction. In the arrangement, the conveyance speed of the printing medium can be 100 m / min or more.

JP 11-291475 A JP 2005-305811 A JP-A-8-90766

  When printing on a substrate that is wide and warped, such as corrugated cardboard sheets, with an inkjet printer equipped with a head unit with multiple inkjet heads arranged in the width direction As described in Patent Documents 1 and 2, when the head unit is driven up and down by an actuator to adjust the distance between the inkjet head and the printing surface, the size of the head unit including the support frame is large. Since the weight is applied to the actuator, the head unit's vertical drive cannot follow the rapid change in the interval due to the warp of the substrate to be conveyed and fed at high speed, and the interval between the inkjet head and the printing surface There is a problem that cannot be adjusted accurately. For example, when the maximum width of the printing medium is 2 m and 20 inkjet heads are arranged, the weight of the head unit including the support frame is as large as about 40 kg.

  Like what was described in Patent Document 3, the thickness of the plate-like body changes abruptly when the interval between the inkjet head and the printing surface is adjusted in accordance with the plate thickness of the plate-like body as the printing target. There is no need to drive the head unit quickly, so there is no problem even if the weight of the head unit is large. In addition, Patent Document 3 has a description that it can cope with displacement in the thickness direction of the printing surface caused by bending or warping of the plate-like body. The head unit cannot be driven in the vertical direction in response to a sudden change in the distance from the inkjet head due to bending or warping of the body.

  Therefore, the problem of the present invention is to make the heavy-duty inkjet head drive in the vertical direction agile even if the distance between the inkjet head and the printing surface changes suddenly due to warpage of the printing medium conveyed at high speed. Thus, the distance between the head unit and the printing medium can be adjusted accurately.

  In order to solve the above-described problems, the present invention supplies a sheet-like printed material that is conveyed and fed at a high speed along the conveyance surface, or is supplied from an ink tank with an interval between the upper and lower sides of one sheet. A head unit in which a plurality of inkjet heads having nozzles for ejecting ink to be printed on a printing surface are arranged in a width direction orthogonal to the conveyance direction of the printing medium, and a distance between the inkjet head and the printing surface is set to a predetermined value In an inkjet printing apparatus provided with an actuator that drives the head unit in the vertical direction so as to adjust the interval, with a head unit that biases upward so as to reduce the downward weight of the head unit loaded on the actuator And a displacement sensor for detecting the vertical displacement of the printing surface of the substrate on the upstream side of the position where the head unit is disposed. And an ink jet head when the printing surface reaches the position where the head unit is disposed based on the displacement sensor and the detection output of the speed sensor. The configuration is such that the head unit is driven in the vertical direction so as to adjust the interval between the inkjet head and the printing surface to a predetermined interval based on the calculation result.

  That is, the head unit urging means for urging upward to reduce the downward weight of the head unit loaded on the actuator is provided, and the vertical displacement of the printing surface of the printing medium is set upstream of the position where the head unit is disposed. And a speed sensor for detecting the conveyance speed of the printing medium, and based on the detection output of the displacement sensor and the speed sensor, when the printing surface reaches the position where the head unit is disposed. The distance between the inkjet head and the printing surface is calculated, and based on the calculation result, the head unit is driven in the vertical direction so that the distance between the inkjet head and the printing surface is adjusted to a predetermined interval. Even if the distance between the inkjet head and the printing surface changes suddenly due to the warping of the printed substrate, the head unit is heavier in the vertical direction. And agile to follow the driving, and to be able to accurately adjust the distance between the printing surface. As the actuator for driving the head unit in the vertical direction, a system that converts the rotation of the motor into a linear drive using a screw screw or an eccentric cam, or a system that directly drives a linear drive using an air cylinder or the like can be adopted. . Moreover, examples of the conveying means for the printing medium include a belt conveyor and a roller conveyor. Among these, a suction belt conveyor having a suction function for suppressing the lifting of the printing medium is preferable.

  The ink jet printing apparatus is suitable for the apparatus in which the conveyance speed of the substrate to be conveyed and fed is a high speed of 100 m / min or more.

  The distance L (m) from the position where the head unit is arranged to the upstream displacement sensor is 0.02 V ≦ L ≦ 0. Where the transport speed of the printing medium is V (m / sec). A range of 5 should be set. When the distance L (m) is less than 0.02 V, the time required for the portion of the printing medium detected by the displacement sensor to reach the position where the head unit is disposed is less than 0.02 seconds, and responds to driving of the head unit by the actuator. This is because a delay may occur. Further, if the distance L (m) exceeds 0.5, the warping or waviness of the printing medium may change during conveyance.

  The head unit biasing means may be a spring or an air suspension that biases the head unit upward.

  An ink reservoir is provided in an ink supply path from the ink tank to the inkjet head, a pump for circulating ink between the ink tank and the ink reservoir is provided, and a circulation path is provided, and the ink reservoir is used as the head unit. By moving the head unit up and down, fluctuations in the water head difference between the ink jet head and the ink reservoir due to the vertical movement of the head unit can be eliminated, and ink can be ejected from the ink jet head without unevenness.

  The predetermined interval between the inkjet head and the printing surface is 0.5 to 10 mm, preferably 1 to 5 mm. If the interval is less than 0.5 mm, the conveyed printing medium may collide with the ink jet head. If it exceeds 10 mm, the landing position is uneven due to variations in the ejection angle of the ink droplets, and the flying speed of the ink droplets is reduced. This is because the deviation of the landing position due to the airflow during conveyance of the printing medium becomes large, and clear printing becomes difficult.

  An ink jet head when a plurality of the displacement sensors are arranged in the width direction of the substrate to be printed, and the printing surface reaches the arrangement position of the head unit from the detection outputs of the plurality of displacement sensors and the speed sensor. And the printing surface are calculated at a plurality of positions in the width direction, and the plurality of inkjet heads are adjusted so that the distance between the calculated inkjet head and the printing surface at the plurality of positions in the width direction is adjusted to a predetermined interval. By providing individual actuators that individually drive the parts up and down, the spacing between each inkjet head and the printing surface can be adjusted even with respect to the warp in the width direction of the printing medium. As this individual actuator, a piezoelectric system using a piezoelectric element, an electromagnetic system using a solenoid, an air cylinder system, or the like can be used.

  At least one of the plurality of displacement sensors is disposed at an end in the width direction of the printing body, and the displacement sensor disposed at the end in the width direction is arranged in the width direction according to the width dimension of the printing body. By moving to the end position, even if the width dimension of the printing medium changes, it is possible to adjust the change in the interval between the inkjet head and the printing surface due to the warp in the width direction that occurs at the end in the width direction. This sensor is desirably disposed at at least three positions in the width direction at both ends and the center of the substrate, and is preferably a non-contact type sensor such as an ultrasonic sensor, a photoelectric sensor, or a laser sensor.

  End guide means for guiding both ends in the width direction of the printing body along the transport surface is provided, and the end guide means is moved to a predetermined width direction position according to the width dimension of the printing body. By doing so, it is possible to suppress the change in the interval between the inkjet head and the printing surface due to the warp in the width direction that occurs at the end in the width direction. Moreover, the change of the space | interval by longitudinal direction curvature can also be indirectly suppressed by restraining the width direction edge part of the to-be-printed body by an edge part guide means.

  Each of the ink jet printing apparatuses is suitable for a substrate in which the substrate to be printed is a corrugated cardboard sheet in which a liner paper is bonded to a corrugated medium.

  If the corrugated top of the corrugated sheet extends in a direction perpendicular to the conveying direction, and the printing surface has a height difference in the conveying direction between the corrugated top corresponding to the corrugated top and the level between them, the displacement The sensor sampling cycle is set to 500 μsec or less, and the fluctuation of the detection output caused by the height difference between the top of the displacement sensor is smoothed to cope with the slight height difference between the top and the step. Unnecessary vertical driving of the actuator can be eliminated. As a smoothing method of the detection output of the displacement sensor, for example, a method of smoothly connecting the peak value of the detection output generated at a position corresponding to the vicinity of the top of the stage can be employed.

  When the sampling period of the displacement sensor is set to 2000 μsec or less, and a vertical displacement greater than or equal to a predetermined interval between the inkjet head and the printing surface is detected, the head unit is released, so that a large protrusion is formed on the printing surface. In some cases, the protrusion can be prevented from colliding with the head unit.

  The ink jet printing apparatus of the present invention is provided with head unit urging means for urging upward so as to reduce the downward weight of the head unit loaded on the actuator, and the vertical displacement of the printing surface of the printing medium is adjusted. A displacement sensor for detecting the upstream side of the arrangement position and a speed sensor for detecting the conveyance speed of the printing medium are provided. Based on the detection output of the displacement sensor and the speed sensor, the print surface is arranged for the head unit. The distance between the ink jet head and the printing surface when reaching the position is calculated, and the head unit is driven in the vertical direction so that the distance between the ink jet head and the printing surface is adjusted to a predetermined distance based on the calculation result. Therefore, even if the distance between the inkjet head and the printing surface changes suddenly due to warpage of the substrate to be conveyed and fed at high speed, the weight is large. There are agile to follow the vertical driving of the head unit, it is possible to adjust accurately the distance between the printing surface.

  An ink reservoir is provided in the ink supply path from the ink tank to the inkjet head, a pump for circulating ink between the ink tank and the ink reservoir and a circulation path are provided, and the ink reservoir is moved up and down together with the head unit. By moving the head unit, it is possible to eliminate the fluctuation of the water head difference between the ink jet head and the ink reservoir due to the vertical movement of the head unit, and to eject the ink from the ink jet head evenly.

  A plurality of the displacement sensors are arranged in the width direction of the printing medium, and the inkjet head and the printing surface when the printing surface reaches the arrangement position of the head unit from the detection outputs of the plurality of displacement sensors and speed sensors. Are calculated at a plurality of positions in the width direction, and a part of the plurality of ink jet heads is individually adjusted so that the distance between the ink jet head and the printing surface at the calculated positions in the width direction is adjusted to a predetermined distance. By providing individual actuators that are driven up and down, the distance between each inkjet head and the printing surface can be adjusted even with respect to warpage in the width direction of the printing medium.

  At least one of the plurality of sensors is disposed at an end portion in the width direction of the printing body, and the sensor disposed at the end portion in the width direction is positioned at the end position in the width direction according to the width dimension of the printing body. By moving, even if the width dimension of the substrate to be printed changes, it is possible to adjust the change in the interval between the inkjet head and the printing surface due to the warp in the width direction that occurs at the end in the width direction.

  End guide means for guiding both ends in the width direction of the printing body along the transport surface is provided, and the end guide means is moved to a predetermined width direction position according to the width dimension of the printing body. Thereby, the change of the space | interval of the inkjet head and a printing surface by the width direction curvature generate | occur | produced in the width direction edge part can be suppressed. Moreover, the change of the space | interval by longitudinal direction curvature can also be indirectly suppressed by restraining the width direction edge part of the to-be-printed body by an edge part guide means.

  The substrate to be printed is a corrugated cardboard sheet, and a corrugated top portion of the shin core extends in a direction perpendicular to the conveying direction, and a printing surface has a height difference in the conveying direction between the corrugated top portion and the step between them. In some cases, the sampling period of the displacement sensor is set to 500 μs or less, and the fluctuation of the detection output caused by the difference in height between the top of the displacement sensor is smoothed, so that the slight height between this top and the bottom is reduced. It is possible to eliminate useless vertical driving of the actuator corresponding to the difference.

  The sampling period of the displacement sensor is 2000 μsec or less, and when a vertical displacement greater than or equal to a predetermined interval between the inkjet head and the printing surface is detected, the head unit is released, so that there is a large protrusion on the printing surface. In addition, the protrusion can be prevented from colliding with the head unit.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 6 show a first embodiment. This inkjet printing apparatus performs printing on the upper surface of a wide corrugated cardboard sheet A that is conveyed and supplied at a high speed of 100 m / min or more, and is centered by a side guide 21 as shown in FIGS. A head unit 2 in which a plurality of ink-jet heads 1 are arranged in the width direction of the transport line is disposed close to the upper side of the corrugated cardboard sheet A that is transported while being attracted to the transport surface of the suction belt conveyor 22 by negative pressure. The unit 2 is driven in the vertical direction by an actuator 4 which is attached to the upper frame 3 and drives a screw screw 4b by a servo motor 4a. Up and down of the printing surface on the upper surface of the cardboard sheet A on the upstream side. The displacement sensors 5a and 5b for detecting the displacement and the lower surface of the suction belt conveyor 22 are brought into rolling contact with each other. Speed sensor 6 of the encoder type for detecting the conveying speed of Rushito A is provided. Further, at both ends in the width direction, hook-shaped pressing guides 7 are provided as end guide means for pressing and guiding both ends of the cardboard sheet A against the suction belt conveyor 22.

  Three displacement sensors 5a and 5b are arranged at the center and both ends in the width direction. The center displacement sensor 5a has a fixed position in the width direction, and the displacement sensor 5b and the pressing guide 7 at both ends in the width direction are provided. Depending on the width of the cardboard sheet A, the cardboard sheet A moves in the width direction in conjunction with the side guide 21 and is set at the end position in the width direction of the supplied cardboard sheet A. The distance from the displacement sensors 5a and 5b to the position where the head unit 2 is disposed is set to 0.2 m. Therefore, the time for the portion of the corrugated cardboard sheet A detected by the displacement sensors 5a and 5b to reach the position where the head unit 2 is disposed is 300 m / min (5 m / sec) where the conveying speed V of the corrugated cardboard sheet A is high. However, it is 0.04 seconds, and there is no possibility that a response delay occurs in driving the head unit 2 by the servo motor 4a of the actuator 4.

  The detection outputs of the displacement sensors 5a and 5b and the speed sensor 6 are input to the controller 8, and the printing surface where the vertical displacement is detected reaches the position where the head unit 2 is disposed based on these detection outputs. The intervals at the three positions of the inkjet head 1 and the center of the printing surface in the width direction and both ends are calculated. The controller 8 drives the actuator 4 based on the calculated center distance in the width direction, and drives a piezo element 9 as an individual actuator described later based on the distance between both ends in the width direction.

  Support frames 2a are provided at both ends of the head unit 2, and a head loaded on the actuator 4 by an air suspension 10 as a head unit urging means for urging the receiving plate 2b at the lower end of the support frame 2a upward. The downward weight of the unit 2 is reduced. Therefore, even if the gap between the inkjet head 1 and the printing surface changes suddenly due to the warp of the corrugated cardboard sheet A, the head unit 2 can be driven up and down quickly by the actuator 4 so as to adjust these gaps constant. it can. In addition, the space | interval of the inkjet head 1 and a printing surface is set so that it may become 1-5 mm.

  As shown in FIG. 4 (a) in an enlarged manner, the corrugated cardboard sheet A is obtained by laminating upper and lower liner papers on a corrugated medium shin A1, and the corrugated top of the medium shin A1 has a conveying direction indicated by an arrow. It extends in a perpendicular direction. For this reason, a slight height difference δ is generated between the top corresponding to the wave top and the level between them in the conveyance direction of the printing surface. The sampling period of each of the displacement sensors 5a and 5b is set to 500 μsec or less, and several displacements are sampled in the span between the tops of the steps. Therefore, as shown in FIG. In the detection output of 5b, fluctuation due to the height difference δ occurs. The controller 8 connects the peak value of the detection output generated at a position corresponding to the vicinity of the top of the step with a straight line as shown in FIG. 2 is calculated at each position in the width direction between the inkjet head 1 and the printing surface when the position 2 is reached. Therefore, useless driving of the actuator 4 and the piezo element 9 due to the slight height difference δ between the top and the step can be eliminated.

  When the displacement sensors 5a and 5b detect a displacement greater than the set interval between the inkjet head 1 and the printing surface, the controller 8 drives the actuator 4 so as to release the head unit 2 upward. ing.

  As shown in FIG. 5, a supply path 11 a from the ink tank 11 that supplies ink to the inkjet head 1 is provided with a small-capacity ink reservoir 12, and the ink reservoir 12 is connected to the head unit 2. 13, and moves up and down together with the head unit 2. The ink tank 11 and the ink reservoir 12 are flexibly connected by a circulation path 11b provided with a pump 14, and the liquid level of the ink reservoir 12 is held constant. A flow control valve 15 and a filter 16 are also provided in the circulation path 11b. Therefore, even when the head unit 2 moves up and down, the liquid head difference between the ink reservoir 12 and the ink jet head 1 is kept constant, and the ink is ejected from the ink jet head 1 without any unevenness.

  As shown in FIGS. 6A and 6B, the inkjet head 1 has a rectangular parallelepiped shape, the lower head surface 1a is rectangular, and a large number of nozzles 1b are arranged in two rows in the longitudinal direction of the head surface 1a. Has been. Flange 1c is provided on both end faces on the long side of ink jet head 1, and these flanges 1c are attached to both sides of window 2c extending in the width direction provided on the bottom surface of the case of head unit 2, and are attached to the head. The surface 1a protrudes from the window 2c to the bottom surface of the case. FIG. 6C shows a modification of the inkjet head 1. In this modified example, in place of the flange 1c, concave grooves 1d are provided on both end surfaces on the long side, and the concave grooves 1d are engaged with both sides of the window 2c on the bottom surface of the case so as to be attached to the head unit 2. It has become.

  FIG. 7 shows an arrangement form of the inkjet head 1. Each inkjet head 1 is arranged in one row in the width direction of the transport line with the end face on the short side facing the adjacent inkjet head 1. In this embodiment, the length of the long side of each inkjet head 1 is 100 mm, and as shown in FIG. 3, 20 inkjet heads 1 are arranged in the width direction, and the corrugated cardboard sheet A has a maximum width of 2 m. Can be printed.

  As shown in FIGS. 8A and 8B, among the 20 inkjet heads 1, each of the five inkjet heads 1 arranged at both ends in the width direction has a piezoelectric element whose flange 1c is an individual actuator. 9 is attached to the case of the head unit 2 via 9 and is individually driven up and down. Each piezo element 9 is driven based on the detection output of the sensor 5b at both ends, and the vertical position of the inkjet head 1 when the piezo element 9 is not driven matches the vertical position of the central inkjet head 1. ing. The reason why the five inkjet heads 1 at both ends in the width direction can be individually driven up and down is that the inkjet head 1 located at the width end changes depending on the width of the cardboard sheet A. One or two inkjet heads 1 positioned at the width end of the cardboard sheet A detected by the sensors 5b at both ends are driven up and down by the piezo element 9.

  FIGS. 9A, 9B, and 9C show a modification of the inkjet head 1 and its arrangement. This modification is different in that the flanges 1c of the inkjet head 1 are provided on both end surfaces on the short side and are arranged in two rows in a staggered manner in the width direction of the transport line. Each inkjet head 1 is arranged by wrapping both ends including adjacent inkjet heads 1 and flanges 1c in other rows so that the two lines can cover the conveyance line in the width direction without gaps. The flanges 1c on both sides are attached to the windows 2c so as to project from the windows 2c provided in a staggered pattern on the bottom surface of the case of the head unit 2. The other portions are the same as those in the embodiment, and on the rectangular head surface 1a of the inkjet head 1, a large number of nozzles 1b are staggered in two rows in the longitudinal direction.

  Using the above-described inkjet printing apparatus, printing was performed on a large number of cardboard sheets A including those having a warp in the longitudinal direction and a warp in the width direction, but good even when the conveyance speed of the suction belt conveyor 22 was increased to 200 m / min. We were able to confirm that it was possible to print smoothly.

  10 and 11 show a second embodiment. This ink jet printing apparatus performs printing on the upper and lower surfaces of a corrugated cardboard sheet A that is conveyed and fed at a high speed. The corrugated cardboard is centered by a side guide 21 and conveyed along the conveying surface of a suction roll 23 as a conveying roll. A head unit 2 in which a plurality of ink jet heads 1 are arranged in the width direction is disposed close to the upper and lower sides of the sheet A, and the upper and lower head units 2 are attached to the upper and lower fixed frames 3 respectively. Displacement sensors 5a and 5b, which are driven in the vertical direction by the actuator 4 and detect the vertical displacement of the upper and lower printing surfaces of the corrugated cardboard sheet A at the center and both ends in the width direction above and below the conveying surface on the upstream side thereof, Is provided with an encoder type speed sensor 6 that detects the conveying speed of the cardboard sheet A. To have. As in the first embodiment, the detection outputs of the displacement sensors 5a and 5b and the speed sensor 6 are input to the controller 8, and the printing surface where the vertical displacement is detected reaches the arrangement position of the head unit 2. The interval between the inkjet head 1 and the printing surface when doing so is calculated. The head unit 2, the actuator 4, and the sensors 5a and 5b are the same as those of the first embodiment, except that the lower ones are vertically opposite. The head unit 2 and the sensors 5a and 5b are arranged so that the upper and lower ones are slightly shifted in the transport direction.

  In this embodiment, the end guide means of the cardboard sheet A is a pair of bowl-shaped pinching guides 17 that pinch and guide the cardboard sheet A from the upper and lower sides between the suction rolls 23. Also, the upper and lower head unit urging means suspends the support frame 2a of the head unit 2 by a coil spring 18 as a spring and urges it upward. The head unit biasing means may be a spring such as a leaf spring that biases the support frame 2a of the head unit 2 so as to push it up. The other portions are the same as those in the first embodiment, and among the 20 inkjet heads 1, five inkjet heads 1 arranged at both ends in the width direction are individually moved up and down by the piezo elements 9. It is designed to be driven.

  In each of the above-described embodiments, the actuator that drives the head unit up and down is driven by a screw screw with a servo motor. However, the actuator that drives a ball screw or an eccentric cam with a servo motor, or a linear drive directly with an air cylinder or the like. It can also be done. Also, the individual actuators that individually drive the inkjet heads arranged at both ends in the width direction are not limited to the piezoelectric type using the piezoelectric element of the embodiment, but the electromagnetic type using a solenoid Or air cylinder type.

  Further, in each of the above-described embodiments, an encoder-type sensor in which a speed sensor is incorporated in a rolling roller is used. However, the encoder is incorporated in a conveyance roll, or indirectly by a wattmeter of a motor that drives the conveyance belt or the conveyance roll. It can also be detected automatically.

  Furthermore, in each of the embodiments described above, the substrate to be printed is a corrugated cardboard sheet. However, the inkjet printing apparatus according to the present invention may use a sheet of resin, metal, or the like as well as a paper sheet other than cardboard. it can.

Front sectional view showing the ink jet printing apparatus of the first embodiment Side sectional view of FIG. 1 is a plan view excluding the fixed frame of FIG. a is an enlarged cross-sectional view of the corrugated cardboard sheet of FIG. 2, and b is a graph for explaining a method of smoothing the detection output of a displacement sensor that detects the height difference of the printed surface of a. FIG. 2 is a side view showing an ink supply form to the inkjet head of FIG. 1. a is a bottom view of the inkjet head of FIG. 1, b is a front view of a, and c is a side view showing a modification of b. The top view which shows the arrangement | sequence form of the inkjet head of FIG. a is an enlarged front sectional view showing a part of the head unit of FIG. 1, and b is a sectional view taken along line VIIIb-VIIIb of a. a and b are a bottom view and a side view showing a modified example of the ink jet head of FIG. 6, respectively, and c is a plan view showing a modified example of the arrangement form of the ink jet head of FIG. Front sectional view showing an ink jet printing apparatus of a second embodiment Side sectional view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inkjet head 1a Head surface 1b Nozzle 1c Flange 1d Concave groove 2 Head unit 2a Support frame 2b Support plate 2c Window 3 Fixed frame 4 Actuator 4a Servo motor 4b Screw screw 5a, 5b Displacement sensor 6 Speed sensor 7 Pressing guide 8 Controller 9 Piezo Element 10 Air suspension 11 Ink tank 11a Supply path 11b Circulation path 12 Ink reservoir 13 Connecting member 14 Pump 15 Flow control valve 16 Filter 17 Clamp guide 18 Coil spring 21 Side guide 22 Suction belt conveyor 23 Suction roll

Claims (12)

  A plurality of nozzles for ejecting ink supplied from the ink tank to the printing surface at a distance from the upper and lower sides of the sheet-like printed material that is conveyed and fed at a high speed along the conveying surface. A head unit in which the inkjet head is arranged in a width direction perpendicular to the conveyance direction of the substrate to be printed is disposed, and the head unit is vertically moved so as to adjust the interval between the inkjet head and the printing surface to a predetermined interval. In the ink jet printing apparatus provided with the actuator to be driven, a head unit urging means for urging upward to reduce the downward weight of the head unit loaded on the actuator is provided, and the printing surface of the printing medium is provided. A displacement sensor that detects the vertical displacement upstream of the position where the head unit is disposed, and a conveyance speed of the substrate to be printed are detected. A degree sensor is provided, and based on detection outputs of the displacement sensor and the speed sensor, the interval between the inkjet head and the printing surface when the printing surface reaches the position where the head unit is disposed is calculated. The ink jet printing apparatus according to claim 1, wherein the head unit is driven in the vertical direction so as to adjust the distance between the ink jet head and the printing surface to a predetermined distance.   The inkjet printing apparatus according to claim 1, wherein a conveyance speed of the substrate to be conveyed is a high speed of 100 m / min or more.   The distance L (m) from the position where the head unit is arranged to the upstream displacement sensor is 0.02 V ≦ L ≦ 0. Where the transport speed of the printing medium is V (m / sec). The inkjet printing apparatus according to claim 1, wherein the inkjet printing apparatus is set to a range of 5.   4. The ink jet printing apparatus according to claim 1, wherein the head unit biasing means is a spring or an air suspension that biases the head unit upward.   An ink reservoir is provided in an ink supply path from the ink tank to the inkjet head, a pump for circulating ink between the ink tank and the ink reservoir is provided, and a circulation path is provided, and the ink reservoir is used as the head unit. The ink jet printing apparatus according to claim 1, wherein the ink jet printing apparatus is moved up and down together.   The inkjet printing apparatus according to any one of claims 1 to 5, wherein a predetermined interval between the inkjet head and a printing surface is 0.5 to 10 mm.   An ink jet head when a plurality of the displacement sensors are arranged in the width direction of the substrate to be printed, and the printing surface reaches the arrangement position of the head unit from the detection outputs of the plurality of displacement sensors and the speed sensor. And the printing surface are calculated at a plurality of positions in the width direction, and the plurality of inkjet heads are adjusted so that the distance between the calculated inkjet head and the printing surface at the plurality of positions in the width direction is adjusted to a predetermined interval. The ink jet printing apparatus according to claim 1, further comprising an individual actuator that individually drives the part up and down.   At least one of the plurality of displacement sensors is disposed at an end in the width direction of the printing body, and the displacement sensor disposed at the end in the width direction is arranged in the width direction according to the width dimension of the printing body. The ink jet printing apparatus according to claim 7, wherein the ink jet printing apparatus is moved to an end position.   End guide means for guiding both ends in the width direction of the printing body along the transport surface is provided, and the end guide means is moved to a predetermined width direction position according to the width dimension of the printing body. The ink jet printing apparatus according to claim 1, wherein the ink jet printing apparatus is made to perform.   The inkjet printing apparatus according to any one of claims 1 to 9, wherein the substrate to be printed is a corrugated cardboard sheet in which liner paper is bonded to a corrugated medium.   The corrugated top of the corrugated sheet sheet extends in a direction perpendicular to the conveying direction, and the printing surface has a height difference in the conveying direction between the corrugated top corresponding to the corrugated top and the steps between them, The inkjet printing apparatus according to claim 10, wherein a sampling period of the displacement sensor is set to 500 μsec or less, and fluctuations in detection output caused by a difference in height between the top and the top of the displacement sensor are smoothed.   The sampling unit of the displacement sensor is set to 2000 μsec or less, and the head unit is allowed to escape when a vertical displacement greater than or equal to a predetermined interval between the inkjet head and a printing surface is detected. The inkjet printing apparatus as described.

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