JP6418492B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus having a line head composed of a plurality of head units.

  2. Description of the Related Art Conventionally, as an image forming apparatus, for example, a line-type ink jet printer or the like, on a recording medium, ink droplets are ejected from a plurality of head units arranged from the upstream side toward the downstream side in the recording medium conveyance direction. It is known to perform printing.

  A technique is described in which edge position information of a recording medium is detected by edge sensors provided in the vicinity of a plurality of head units, respectively, and the position of each head unit is corrected based on these pieces of information. Specifically, in the recording medium conveyance direction, an edge sensor (upstream edge sensor) arranged corresponding to the upstream head unit and an edge sensor (downstream side) arranged corresponding to the downstream head unit. The edge position information of the recording medium detected by the edge sensor), and the edge position of the recording medium at a position where the upstream head unit is located and the edge position of the recording medium where the downstream head unit is located The relative positional relationship of is calculated. Then, an actuator for moving the head unit on the downstream side in the conveyance direction of the recording medium is controlled according to the relative positional relationship to correct the position of the downstream head unit. As a result, even if the position of the recording medium fluctuates when transporting the recording medium, each head unit can eject ink droplets to the intended location of the recording medium, and the location where the ink droplets are ejected is shifted. It is said that printing defects can be suppressed.

  Due to assembly errors during device assembly and individual differences in the edge sensor itself, the edge position of the recording medium detected by the edge sensor does not coincide with the actual edge position, and is somewhat different from the actual edge position. The error is included. However, in the technique of Patent Document 1, the downstream head unit is assumed on the assumption that the end positions of the recording medium detected by the upstream edge sensor and the downstream edge sensor respectively coincide with the actual end position of the recording medium. The position is corrected.

  When the relative positional relationship between the end position of the recording medium at a position where the upstream head unit is located and the end position of the recording medium at a position where the downstream head unit is located as in Patent Document 1, the relative position is calculated. The positional relationship is inaccurate by the error. In the technique of Patent Document 1, the position of the head unit is corrected based on the relative positional relationship that is inaccurate by the amount of the error. Therefore, the position where the ink droplets are ejected is shifted even after the head unit position is corrected. There was a risk of printing failure.

In order to solve the above-described problems, the present invention is directed to conveying a recording medium, and a discharge unit that discharges ink droplets on the recording medium that are arranged in parallel at a predetermined interval with respect to the conveyance direction of the recording medium. A plurality of head units having a plurality of discharge ports, and at the end position of the recording medium in a direction perpendicular to the conveyance direction of the recording medium that is arranged corresponding to each of at least two of the plurality of head units. A plurality of edge sensors for detecting a position of an end of a certain recording medium, and an actuator for moving at least one of the head units in which the corresponding edge sensor is arranged in a direction orthogonal to the conveyance direction of the recording medium; in the image forming apparatus and a control unit for controlling the actuator, a memory for storing standard values Wherein said control unit is the transfer of the recording medium generates said reference value based on the recording medium end position of the information read via the respective plurality of edge sensor in a state where stable and the product storing the reference value in the memory, and to correct the position of the head unit with the actuator to control the actuator by using the said reference value and the recording medium end position read via the edge sensor It is characterized by this.

  According to the present invention, it is possible to suppress the occurrence of color misregistration in printing on a recording medium in a configuration having a plurality of head units arranged on the recording medium from the upstream side to the downstream side in the conveyance direction of the recording medium. become.

FIG. 3 is a diagram illustrating an example of the overall configuration of a production printer. FIG. 2 is a side sectional view schematically showing an example of a schematic configuration of an image forming unit in the production printer. FIG. 2 is a plan view schematically showing an example of a schematic configuration of an image forming unit of the production printer. FIG. 3 is a block diagram illustrating a configuration of a control system that corrects the position of the ink head unit in the image forming unit. FIG. 3 is an explanatory diagram illustrating an outline of correction of the position of the ink head unit. FIG. 3 is a block diagram showing a configuration of a control system that performs a reference value adjusting operation in correcting the position of the ink head unit. Explanatory drawing about the method of determining the stability of conveyance of the continuous paper W in the KY control part of the control system which performs the same reference value adjustment operation. 7 is a flowchart showing an example of reference value adjustment control in a control system that performs the reference value adjustment operation. 7 is a flowchart showing an example of processing for determining the conveyance stability of the continuous paper W in the KC control unit of the control system performing the reference value adjusting operation. Explanatory drawing about the detail of judgment whether the conveyance of the continuous paper W in step S37 of FIG. 9 was stabilized.

FIG. 1 is a diagram illustrating an example of the overall configuration of a production printer 110 as an image forming apparatus according to the present embodiment.
The production printer 110 is a high-speed printer used for mass printing of, for example, 100 pages or more per minute, and is configured so that ink can be applied to a continuous recording medium such as continuous paper W. The continuous paper W is conveyed in the direction of arrow X in the figure by one or a plurality of delivery rollers 130 and is sent out of the production printer 110. At that time, the delivery roller 130 performs positioning and tension adjustment of the continuous paper W.

The image forming unit of the production printer 110 is an ink jet type that performs printing on a recording medium by ejecting ink droplets from ink heads respectively provided in a plurality of ink head units corresponding to image data.
FIG. 2 is a side sectional view schematically showing an example of a schematic configuration of the image forming unit in the production printer 110.
As shown in FIG. 2, the image forming unit of the production printer 110 includes a transport unit 201 that holds and transports the continuous paper W to be printed, and the continuous paper W that is held and transported by the transport unit 201. And a printing unit 202 that executes printing.

  The conveyance unit 201 includes a first drive roller 232, a second drive roller 233, a guide roller 234, and the like. At least one of the first drive roller 232 and the second drive roller 233 is rotationally driven by a drive source such as a motor (not shown). The tension of the continuous paper W is adjusted between the first drive roller 232 and the second drive roller 233.

  The printing unit 202 includes a first head unit 310a, a second head unit 310b, a third head unit 310c, and a fourth head unit 310d that eject ink droplets.

FIG. 3 is a plan view schematically showing an example of a schematic configuration of the image forming unit of the production printer 110.
As shown in FIG. 3, the first head unit 310a, the second head unit 310b, the third head unit 310c, and the fourth head unit 310d are sequentially arranged from the upstream side in the direction of conveyance of the continuous paper W (arrow X in the figure). However, they are lined up at regular intervals. There are no particular restrictions on the type of ink droplets used in each ink head unit. For example, in each ink head unit, ink droplets of black (K), cyan (C), magenta (M), and yellow (Y) may be used. There is no particular limitation as to which ink head unit uses which color ink droplet. For example, black (K) is used for the first head unit 310a, cyan (C) is used for the ink head unit 310b, and magenta ( M), yellow (Y) ink droplets may be used in the ink head unit 310d.

  The first head unit 310a, the second head unit 310b, the third head unit 310c, and the fourth head unit 310d have ink discharge nozzles 313a, 313b, 313c, and 313d as discharge ports for discharging ink droplets, respectively. doing. The ink head units 310b, 310c, and 310d include actuators 311b, 311c, and 310b for moving the ink head units 310b, 310c, and 310d in a direction perpendicular to the conveyance direction of the continuous paper W (arrow Y in the figure). 311d is also included. In this embodiment, the ink head unit 310a at the most upstream in the transport direction of the continuous paper W is used as an ink head unit, and the position in the direction perpendicular to the transport direction of the continuous paper W of the ink head unit 310a is fixed. It was. For this reason, no actuator is provided in the ink head unit 310a. However, similarly to the other ink head units, an actuator may be provided in the ink head unit 310a, and the position of the ink head unit 310a may be moved in a direction perpendicular to the conveyance direction of the continuous paper W.

  In the vicinity of the ink head units 310a, 310b, 310c, and 310d on the upstream side in the direction of conveyance of the continuous paper W (arrow X in the figure), the continuous paper W in the direction perpendicular to the conveyance direction of the continuous paper W is shown. Edge sensors 312a, 312b, 312c, and 312d for detecting the end position of each are arranged. The positions of the ink head units 310b, 310c, and 310d are corrected using the edge position information of the continuous paper W detected by the edge sensors 312a, 312b, 312c, and 312d, respectively. The correction of the position of the ink head unit will be described in detail later.

FIG. 4 is a block diagram showing the configuration of a control system that corrects the position of the ink head unit.
In the reading control unit 410, output values of the edge sensors 312a, 312b, 312c, and 312d are detected for each sampling period, and converted into data (hereinafter referred to as “sensor reading values”) from which unnecessary frequency components are removed by filtering. To do. These sensor readings are stored in memory 416. The sensor reading value in the edge sensor 312a is held in the memory 416 until the end position of the continuous paper W read by the edge sensor 312a passes through the edge sensor 312d. The reading values of the edge sensors other than the edge sensor 312a are overwritten as needed. The recording position correction control unit 417 performs necessary arithmetic processing on the data stored in the memory 416, and controls the actuators 311b, 311c, and 311d based on the arithmetic processing result.

FIG. 5 is a diagram illustrating an outline of correction of the position of the ink head unit. In the following description, FIG. 4 will be referred to as appropriate.
For example, as shown in FIG. 5A, the color misalignment does not occur in printing on the continuous paper W. The line connecting the ink discharge nozzles 313a, 313b, 313c, and 313d and the end of the continuous paper W are used. This is when the line formed by is parallel. In this way, a line formed by the end of the continuous paper W in an ideal state where no color misregistration occurs in printing is set as a reference line L. In such a state, the sensor read values at the end positions of the continuous paper W detected through the edge sensors 312a, 312b, 312c, and 312d are set as reference values r1, r2, r3, and r4. The reference values r1, r2, r3, and r4 are different for each device and for each edge sensor position due to an assembly error of the device and individual differences of the sensors. For this reason, when the apparatus is installed or when the edge sensor is replaced, it is necessary to perform a reference value adjustment for determining a reference value described later.

  As shown in FIG. 5B, when the line formed by the end of the continuous paper W is shifted from the reference line L, the lines connecting the ink ejection nozzles 313a, 313b, 313c, and 313d are not parallel to the reference line L. Therefore, color misregistration occurs in printing on the continuous paper W. In order to suppress the occurrence of color misregistration, it is necessary to correct the position of the ink head unit.

With reference to FIGS. 5C and 5D, a specific method of correcting the position of the ink head unit will be described by taking the ink head unit 310b as an example.
As shown in FIG. 5C, the sensor reading value at the edge sensor 312a when a certain range of the continuous paper W (shaded area S in the figure) passes through the edge sensor 312a is defined as p1. The recording position correction control unit 417 calculates a difference (deviation amount d1) between the sensor reading value p1 and the reference value r1 of the edge sensor 312a.
As shown in FIG. 5D, the sensor reading value at the edge sensor 312b when a certain range of the above-described continuous paper W (shaded area S in the figure) passes through the edge sensor 312b is defined as p2. The recording position correction control unit 417 calculates a difference (deviation amount d2) between the sensor reading value p2 and the reference value r2 of the edge sensor 312a.

  The edge position of the recording medium detected by the edge sensor includes an error with respect to the actual edge position. Since both the sensor read value p1 and the reference value r1 of the edge sensor 312a are values read through the edge sensor 312a, errors of the same magnitude are included. Therefore, the error is canceled out in the difference (deviation amount d1) between the sensor read value p1 and the reference value r1 of the edge sensor 312a. Similarly, the error is canceled out in the difference (deviation amount d1) between the sensor read value p1 and the reference value r1 of the edge sensor 312a.

  The relative deviation value D1 is obtained by calculating the difference between the positional deviation amount d1 and the positional deviation amount d2 in the reading control unit 410. The relative deviation value D1 is a relative positional relationship between the end position of the continuous paper W at a position where the ink head unit 310b is located and the end position of the continuous paper W where the ink head unit 310a is located. Represents. As described above, since the error is canceled in the positional deviation amount d1 and the positional deviation amount d2, the relative deviation value D1 calculated by the difference between the positional deviation amount d1 and the positional deviation amount d2 includes an error. Absent. The recording position correction control unit 417 corrects the position of the ink head unit 310b by controlling the actuator 311b according to the relative deviation value D1.

  The recording position correction of the ink head units 310c and 310d is also corrected by the same method as the recording position correction of the ink head unit 310b described above. That is, the relative deviation values D2 and D3 of the end position of the continuous paper W at the position where the ink head units 310c and 310d are located with respect to the end position of the continuous paper W at the position where the ink head unit 310a is respectively set. calculate. Then, the positions of the ink head units 310c and 310d are corrected by controlling the actuators 311c and 311d according to the relative deviation values D2 and D3.

  When the position of the ink head unit 310a can be moved in the direction perpendicular to the conveyance direction of the continuous paper W, the amount of movement of the ink head unit 310a is set to relative deviation values D1, D2, and D3. Can be added to each other.

Here, an outline of the reference value adjustment will be described.
When the conveyance of the continuous paper W is stable, the line connecting the ink ejection nozzles 313a, 313b, 313c, and 313d and the line formed by the end of the continuous paper W are parallel to each other, and the continuous paper is It was confirmed by experiments that no color misregistration occurred in printing on W. It was confirmed by experiments that no color misregistration occurred in printing on the continuous paper W. In other words, whether or not the line connecting the ink discharge nozzles 313a, 313b, 313c, and 313d is parallel to the line formed by the end of the continuous paper W is determined based on the stable conveyance of the continuous paper W. Can be done by the process of determining whether or not.

  In a state in which the conveyance of the continuous paper W is determined to be stable, the sensor reading values of the end positions of the continuous paper W detected through the edge sensors 312a, 312b, 312c, and 312d are used as reference values. r1, r2, r3, r4 may be used. The process for determining whether the conveyance of the continuous paper W is stable can be automatically determined as described below. Therefore, according to the present embodiment, the reference value adjustment can be automatically performed.

FIG. 6 is a block diagram illustrating a configuration of a control system that performs reference value adjustment.
The reference value adjustment control unit 411 includes an individual control unit of the K-C control unit 412, the KM control unit 413, and the KY control unit 414, and an overall control unit 415 that supervises these individual control units. ing. The K-C control unit 412 reads the reading value p1 of the edge sensor 312a and the reading value p2 of the edge sensor 312b in the memory 416, and calculates the difference between them to determine whether the transport of the continuous paper W is stable. Judge whether or not. The K-C control unit 412 determines that the conveyance of the continuous paper W is stable when the calculated difference is within a specified range for a certain time. The overall control unit 415 detects the end position sensor of the continuous paper W detected through the edge sensors 312a, 312b, 312c, and 312d in a state where the conveyance of the continuous paper W is determined to be stable. Reference values r1, r2, r3, r4 are calculated from the read values. These reference values r1, r2, r3, r4 are stored in the memory 416, respectively.

  The KM control unit 413 and the KY control unit 414 also determine the stability of the continuous paper W conveyance in the same manner as the KC control unit 412. In the KM control unit 413, the continuous book is determined by the difference between the reading value p1 of the edge sensor 312a and the reading value p3 of the edge sensor 312c, and in the KY control unit 414 by the difference between the reading value p1 and the reading value p4 of the edge sensor 312d. Judge the stability of transport of the paper W.

FIG. 7 is a diagram illustrating a method for determining the stability of the continuous paper W conveyance in the KY control unit 414.
In FIG. 7, the horizontal axis represents time, and the vertical axis represents the read value. Curves K and Y in the figure are plots of the reading values of the edge sensors 312a and 312d, respectively. The curve K_Shift is obtained by shifting the curve K by the time obtained by dividing the distance between the edge sensor 312a and the edge sensor 312d by the conveyance speed of the continuous paper W. In this way, it is possible to compare the read values p1 and p4 obtained by reading the end positions via the edge sensors 312a and 312d in the same area on the continuous paper W, respectively. By comparing the read values obtained by reading the end positions in the same area on the continuous paper W, it is possible to determine the stability of the conveyance of the continuous paper W more accurately.

  Curve Y-K_Shift is the difference between curve Y and curve K_Shift. A curve Y-K_Shift makes it possible to know the degree of fluctuation of the end of the continuous paper W between the edge sensor 312a and the edge sensor 312d in the direction in which the continuous paper W is conveyed and in the vertical direction. In other words, if the variation of the curve YK_Shift is large, it can be said that the continuous paper W is unstablely conveyed between the edge sensor 312a and the edge sensor 312d. Further, if the variation of the curve YK_Shift is small, it can be said that the continuous paper W is stably conveyed between the edge sensor 312a and the edge sensor 312d.

  In the period shown between PQ in FIG. 7, the fluctuation range of the curve YK_Shift is within a predetermined fixed range ± α over a predetermined constant time T. Therefore, the KY control unit 414 determines that the conveyance of the continuous paper W is stable during the period indicated by PQ. Hereinafter, a curve indicated by a curve YK_Shift in FIG. 7 is referred to as a “variation curve”. Further, a period in which the individual control unit determines that the conveyance of the continuous paper W is stable, such as a period T indicated between PQ in FIG. 7, is referred to as an “individual stable period”.

  Regarding the method for determining the stability of the conveyance of the continuous paper W in the K-C control unit 412 and the KM control unit 413, the method for determining the stability of the conveyance of the continuous paper W in the KY control unit 414 described above. It is the same. That is, also in the K-C control unit 412 and the K-M control unit 413, when the fluctuation range of each fluctuation curve is within a certain range ± α for a certain time T, the continuous paper W It is determined that the transport of the is stable.

  When the overall control unit 415 shown in FIG. 6 determines that the conveyance of the continuous paper W is stable in all of the K-C control unit 412, the K-M control unit 413, and the KY control unit 414, It is determined that the conveyance of the book paper W is stable. That is, in the overall control unit 415, when the individual stable periods in the KC control unit 412, the KM control unit 413, and the KY control unit 414 all overlap, the conveyance of the continuous paper W is stable. It is judged that. Hereinafter, the time when all of the individual stable periods are overlapped is referred to as the “total stable period”. The overall control unit 415 calculates a reference value for each edge sensor based on the sensor reading value read via each edge sensor during this overall stable period.

  The determination of the stability of the conveyance of the continuous paper W in each individual control unit is related to the time required for the continuous paper W to be conveyed between the reference edge sensor 312a and an edge sensor other than the edge sensor 312a. doing. For this reason, in each individual control part, the timing which the judgment result about the conveyance stability of the continuous paper W comes out is not simultaneous. In the present embodiment, the timing at which the determination result of the KY control unit 414 that determines the stability of the conveyance of the continuous paper W between the edge sensor 312a and the edge sensor 312d serving as a reference is the latest. Therefore, the overall control unit 415 determines whether the continuous paper W is stably conveyed at the timing when the determination result in the KY control unit 414 is output.

  If the overall control unit 415 determines that the conveyance of the continuous paper W is not stable, the individual control unit continuously monitors the stability of the conveyance of the continuous paper W. To do. The K-C control unit 412 and the K-M control unit 413 perform the previous operation even while the monitoring by the KY control unit 414 continues in preparation for a case where the overall control unit 415 determines that the result is not stable. As soon as this cycle is completed, monitoring of the next cycle is started. If it is determined that the continuous paper W is not stable even after a predetermined time has passed, an error display may be displayed.

The reference value may be calculated as follows, for example.
The reference value r1 in the edge sensor 312a is calculated by averaging the sensor reading values read through the edge sensor 312a during the entire stable period. The edge sensors 312b, 312c, and 312d are calculated by adding the reference value r1 of the edge sensor 312a to the average of the plot values of the difference curve during the entire stable period.

FIG. 8 is a flowchart illustrating an example of reference value adjustment control in a control system that performs reference value adjustment.
In step S1, conveyance of the continuous paper W is started. In step S2, reading of the end part value of the continuous paper W is started via each edge sensor. In step S <b> 3, each individual control unit monitors the stability of the conveyance of the continuous paper W based on the reading value of each edge sensor stored in the memory 416. Details of step S3 will be described later.

  In step S4, the overall control unit 415 determines whether or not the conveyance of the continuous paper W is stable based on the result of monitoring the stability of the continuous paper W conveyance performed by each individual control unit. If the conveyance of the continuous paper W is not stable, the process returns to step S3. If the conveyance of the continuous paper W is stable, the process proceeds to step S5. In step S5, a reference value for each edge sensor is calculated. In the subsequent step S6, the reference value calculated in step S5 is stored in the memory 416.

The process in step S3 in FIG. 8 will be described by taking the process in the KC control unit 412 as an example. The processes in the KM control unit 413 and the KY control unit 414 are basically the same as the processes in the KC control unit 412.
FIG. 9 is a flowchart illustrating an example of a process for determining whether the continuous paper W is stably conveyed in the KC control unit 412.
In step S30, it is determined whether or not there is an end instruction from the overall control unit 415. If there is an end instruction, the process ends. If there is no end instruction, the process proceeds to step S31. In step S31, the latest sensor reading value of the edge sensor 312b and the sensor reading value of the previous edge sensor 312a by the time obtained by dividing the distance between the edge sensor 312a and the edge sensor 312b by the conveyance speed are acquired from the memory 416. To do. In step S32, the difference between the two sensor reading values acquired in step S31 is calculated. In step S33, the difference value calculated in step S32 is added to the addition variable sum (initial value 0), and the difference data number count k (initial value 0) is incremented by one.

  In step S34, it is determined whether or not the difference data number count k has reached a specified number. If the difference data number count k has not reached the specified number, the process returns to step S30. When the difference data number count k has reached the specified number, the process proceeds to step S35. In step S35, the addition variable sum is divided by the difference data number count k, and the average value is calculated for the difference between the two sensor reading values acquired in step S31. The value data count n (initial value 0) is increased by 1.

  In step S36, it is determined whether or not the average value data number count n has reached a specified number. If the average value data count n has not reached the specified number, the process returns to step S30. When the average value data number count n has reached the specified number, the process proceeds to step S37. In step S37, it is determined whether or not the conveyance of the continuous paper W is stable using the average value data obtained in step S35. Details of this determination will be described later. If it is determined in step S37 that the paper is not stable, the process proceeds to step S38, and if it is determined that the continuous paper W is transported stably, the process proceeds to step S39. In step S38, the oldest data among the average values calculated in step S35 is discarded, and the average value data number count n is decreased by 1, and the process returns to step S30. In step S39, the average value data number count n is set to 0, and the process proceeds to step S4 in FIG.

FIG. 10 is a diagram for explaining details of the determination as to whether or not the conveyance of the continuous paper W in step S37 of FIG. 9 is stable.
In FIG. 10, the vertical axis represents the average value obtained in step S35, and the horizontal axis represents the cycle number of the average value (corresponding to the average value data number count n). The cycle number is incremented by 1 in order from the oldest one, with the oldest average value being 1. In the present embodiment, the number of average values used for determining the stability of conveyance of the continuous paper W is 5 and the threshold is ± 5 [μm]. The threshold value was determined from an allowable deviation amount with respect to the average value when the deviation from the average value between colors was included in a range of ± 3σ or less. If the average value of cycle number 1 is used as the reference value, and the difference between the average value and the reference value is within ± 5 [μm] in the subsequent average values of cycle numbers 2, 3, and 4, continuous paper It is determined that the conveyance of W is stable.

  The reference value adjustment method described above is merely an example, and is not limited to the method of determining the stability of the conveyance of the continuous paper W with reference to the read value p1 via the edge sensor 312a. You may make it determine the stability of conveyance of the continuous paper W on the basis of the reading value via an edge sensor other than the edge sensor 312a. In this embodiment, since there are four ink head units, the number of individual control units is three. However, if the number of ink head units is increased or decreased, the number of individual control units may be increased or decreased accordingly. Good. Even in this case, the method of adjusting the reference value is basically the same as the method described above. In the reference value adjustment, it is desirable to make conditions (such as the type of continuous paper W and the conveyance speed) so that the running of the continuous paper W is stable.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
An ink head unit 310a having discharge ports such as ink discharge nozzles 313a, 313b, 313c, and 313d, which are arranged in parallel with a certain interval in the conveyance direction of the recording medium and discharge ink droplets onto the recording medium; A plurality of head units such as 310b, 310c, and 310d, and an end portion of the recording medium in a direction perpendicular to the conveyance direction of the recording medium that is arranged corresponding to at least two of the plurality of head units. A plurality of edge sensors such as edge sensors 312a, 312b, 312c, and 312d that detect positions and at least one head unit among the head units on which the corresponding edge sensors are arranged are orthogonal to the conveyance direction of the recording medium. Actuators 311b, 311c, 3 for moving in the direction In an image forming apparatus including an actuator such as 1d and a control unit such as a recording position correction control unit 417 that controls the actuator, end position information of the recording medium read through the plurality of edge sensors is obtained. A memory such as a memory 416 to be stored, and a reference value of each edge sensor obtained by reading the edge position of the recording medium as a reference through the plurality of edge sensors is previously stored in the memory; The control unit calculates a difference between the edge position of the recording medium read through the edge sensor and a reference value of the edge sensor for each of the plurality of edge sensors, and uses the difference to calculate the actuator And the position of the head unit having the actuator is corrected.
The end position of the recording medium read through each edge sensor includes an error caused by assembly of the apparatus and individual differences of the edge sensors. Since the end position of the recording medium read through a certain edge sensor and the reference value of the edge sensor are both values read through the same edge sensor, errors of the same magnitude are included. For this reason, if the difference between the end position of the recording medium read through a certain edge sensor and the reference value of the edge sensor is taken, the error is canceled out. By taking the difference between the difference in the edge sensor arranged corresponding to a certain head unit having an actuator and the difference in the edge sensor arranged corresponding to a different head unit, the former head unit is It is possible to accurately obtain the relative positional relationship between the end position of the recording medium at the disposed position and the end position of the recording medium at the position at which the latter head unit is disposed. By correcting the position of the former head unit based on the relative positional relationship, it is possible to improve the correction accuracy and suppress the occurrence of color misregistration in printing on a recording medium.

(Aspect B)
In aspect A, if there is a head unit that does not have the actuator among the head units in which the corresponding edge sensor is arranged, one of them is used as a reference head unit, and the head unit in which the corresponding edge sensor is arranged If none of the actuators has the actuator, one of the head units having the actuator is used as a reference head unit, and the control unit determines whether the recording medium is stably transported by the control unit. An end position of the recording medium read through the edge sensor arranged corresponding to a head unit that is not the reference head unit, and an edge sensor arranged corresponding to the reference head unit. Calculate the difference with the end position of the read recording medium, And determining the end position of the recording medium in a state where the conveyance of the recording medium is stable, by determining whether or not the fluctuation range of the recording difference is within a predetermined threshold range for a predetermined time. The end position of the recording medium is set as a reference.
The determination of the state in which the conveyance of the recording medium is stable can be automatically performed by the control unit determining whether the fluctuation range of the difference is within a predetermined threshold range for a predetermined time. it can. Experiments have shown that color misregistration does not occur when printing on a recording medium in a state where the conveyance of the recording medium is stable. By setting the end position of the recording medium with the end position of the recording medium in a state where the conveyance of the recording medium is stable as the reference, the end position of the recording medium as a reference can be automatically determined. It becomes like this. This makes it possible to automatically set the reference value for each head unit, and it takes time and effort to set the reference value when the reference value for the replaced head unit must be set again by replacing the edge sensor. Can be reduced.

(Aspect C)
In any one of aspects A and B, the edge sensor is disposed upstream of the corresponding head unit in the conveyance direction of the recording medium.

(Aspect D)
In any one of the aspects A to C, the recording medium may be used even when a predetermined determination period is exceeded in determining whether or not the fluctuation range of the difference is within a predetermined threshold range for a predetermined time. An error message is displayed when it is not possible to obtain a judgment result that the transport is stable.
According to this, when there is an abnormality in the conveyance system of the recording medium, it can be prevented that the determination as to whether or not the state is parallel is continued for an unnecessarily long time.

(Aspect E)
In any one of the aspects A to D, the threshold is determined by an allowable deviation amount with respect to the average value when the deviation from the average value between colors is included in a range of ± 3σ or less.

201 Conveying units 310a, 310b, 310c, 310d Ink head units 312a, 312b, 312c, 312d Edge sensors 311b, 311c, 311d Actuators

JP 2011-136526 A

Claims (4)

Conveying means for conveying a recording medium, a plurality of head units that are arranged in parallel with a certain interval in the conveying direction of the recording medium and have ejection openings for ejecting ink droplets on the recording medium; A plurality of edge sensors which are arranged corresponding to at least two of the head units of the recording medium and which detect a recording medium end position which is an end position of the recording medium in a direction perpendicular to the conveyance direction of the recording medium And an actuator that moves at least one of the head units in which the corresponding edge sensor is disposed in a direction orthogonal to the conveyance direction of the recording medium, and a control unit that controls the actuator. In the forming device,
A memory for storing standard values,
The control unit generates the reference value based on information of the recording medium end position read through the plurality of edge sensors in a state where the conveyance of the recording medium is stable, and the generated storing the reference value in the memory, and to correct the position of the head unit with the actuator to control the actuator by using the said reference value and the recording medium end position read via the edge sensor An image forming apparatus. The image forming apparatus according to claim 1.
If there is a head unit that does not have the actuator among the head units in which the corresponding edge sensor is arranged, one of them is set as a reference head unit, and the actuator in the head unit in which the corresponding edge sensor is arranged. If there is nothing not, one of the head units having the actuator is used as a reference head unit, and the determination of the state in which the conveyance of the recording medium is stable is performed by the control unit of the head unit having the actuator. Of these, the recording medium end position read through the edge sensor arranged corresponding to the non-reference head unit and the recording medium read through the edge sensor arranged corresponding to the reference head unit Calculate the difference from the end position, and the fluctuation range of the difference The reference value is generated based on the information on the end position of the recording medium in a state where the recording medium is stably transported by determining whether it is within a predetermined threshold range over a period of time An image forming apparatus. The image forming apparatus according to claim 1, wherein
2. The image forming apparatus according to claim 1, wherein the edge sensor is disposed upstream of the corresponding head unit in the conveyance direction of the recording medium. The image forming apparatus according to claim 2.
In determining whether the difference fluctuation range is within a predetermined threshold range for a predetermined time, it is determined that the conveyance of the recording medium is stable even if a predetermined determination period is exceeded. An image forming apparatus, wherein an error is displayed when a result cannot be obtained .

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