JP4567354B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium by an inkjet method.

  In general, in an inkjet image forming apparatus, a plurality of recording heads are arranged at equal intervals, and an image is formed by ejecting ink onto a recording medium such as recording paper. For example, at least four color inks [Black, Cyan, Magenta, Yellow] are used to form a color image.

  FIG. 8 is a diagram illustrating a conceptual configuration example of four recording heads and a medium transport mechanism for forming a color image in a conventional image forming apparatus. FIG. 8 is a diagram showing image formation timing of image data in each recording head.

  In this image forming apparatus, the fixed recording heads that discharge the four color inks above the recording medium transport path in the medium transport mechanism are the recording head K (black), the recording head C (cyan), the recording head from the upstream side, respectively. The head M (magenta) and the recording head Y (yellow) are arranged at equal intervals, that is, offset, and are driven and controlled by one data controller. Further, a transmission type inlet TOF sensor (medium sensor) 61 for detecting a recording medium is provided on the upstream side of the recording head K, and similarly, a transmission type outlet TOF sensor 62 is provided on the downstream side of the recording head Y. Is provided. These sensors 61 and 62 detect the front and rear ends of the recording medium 63 (63a, 63b) being conveyed on the conveyance path of the medium conveyance mechanism.

  In such a configuration, when an image is formed on the recording medium 63, the recording medium 63 a, for example, a recording sheet is taken out one by one from a recording medium cassette (not shown), and the medium conveyance mechanism at a constant speed in the conveyance direction X. Transport to the recording position. At this time, as will be described later, one color image data is assigned to each recording head K, C, M, Y from the data controller and input for each color.

  When the leading edge of the recording medium 63a is detected by the entrance TOF sensor 61 shown in FIG. 7, inks of different colors are sequentially ejected by the recording heads K, C, M, and Y at predetermined timing to form an image. The The recording medium 63a on which image formation has been completed is conveyed as it is, and after the trailing end of the recording medium is detected by the outlet TOF sensor 62, the recording medium 63a is discharged out of the apparatus and stored in a storage cassette (not shown).

  As for color image data in this configuration, image data for one page is input for each color from a host device (not shown) to each recording head at the time of image formation. As shown in FIG. 8, this image data is obtained by adding white data representing a margin portion before and after each color image data in accordance with the offset amount L of each recording head.

Such color image data of each recording head is transferred to each recording head, and image formation is performed by each recording head at the timing shown in FIG.

  FIG. 8 shows how the color image data transferred to each recording head is recorded, and the relationship with the image formation time in the image data portion of each recording head.

  A time t11 in FIG. 8 is a time obtained by dividing the offset amount L1 between the first recording head K and the last recording head Y in the transport direction by the moving speed of the recording medium, and the time t12 is transported in advance. It shows the time obtained by dividing the distance L2 between the trailing edge of the recording medium and the leading edge of the recording medium conveyed following the recording medium by the moving speed of the recording medium. It is assumed that the moving speed of the recording medium is constant. Accordingly, the lengths of the time t11 and the time t12 are relatively suggestive of the distance.

  Such color image data is transferred to the recording heads K, C, M, and Y. Even if the recording heads are offset along the medium conveyance direction, the image data of each color is included in the color image data. Since the offset is made according to the recording head position, a color image without color misregistration can be formed on the recording medium 63.

  When image formation by the most downstream recording head Y is completed and the next recording medium is conveyed, the color image data of the next page is transferred to the recording head of each color, and the recording heads K, C, Image formation is performed by M and Y.

  By the way, as the recording heads K, C, M, and Y described above, one recording head extending along the lateral width direction X of the medium is used. On the other hand, there is a recording head in which a plurality of head units K1, K2,... Are connected as shown in FIG. These recording head units K1 and K2 are arranged so that there is no gap during image formation in two rows (K1 row and K2 row) in the transport direction Y of the recording medium 63, and each of the nozzle rows 71 of each head unit is arranged. They are arranged alternately so that the ends overlap slightly.

In such a recording head, a color image without color misregistration is similarly formed by considering the offset amount L3 between the head units (nozzle rows) and the offset amount between recording media (inter-recording medium distance) L4. be able to.
Japanese Patent Laid-Open No. 2003-1879

  In the conventional image forming apparatus as shown in FIGS. 8 and 9, the detection signal of the outlet TOF sensor 62, that is, the image formation by the last recording head Y is completed by the drive control of one data controller, and then again. Color image data including white data starts to be transferred to all the recording heads K, C, M, and Y, and image formation is performed from the K image data. That is, unless the image formation by the last recording head Y is completed, the image formation by the first recording head K on the next recording medium cannot be started, and all the recording heads K, C, M, The number of recording media that can be conveyed while facing the recording head through Y is limited to one.

This is a factor that makes it difficult to achieve high-speed image formation (throughput improvement). That is, when there is a recording head offset amount (distance between nozzle rows of recording head K and recording head Y) L1, the interval between the recording medium conveyed first and the recording medium conveyed next (medium conveyance interval). ) L2 must be larger than the offset amount L1, that is, L2> L1 (t12> t11), as shown. In other words, the time interval between the medium transported before and the medium transported later requires at least time t11 + time for image formation by the recording head Y, even if the time required for image formation is short.
Accordingly, since one color image is formed by each of the recording heads K, C, M, and Y, the color image of the next page is not printed for each recording head unless the ink ejection by the recording head Y is completed. Data cannot be transferred and image formation cannot be performed.

  In addition to the offset amount in the recording head, as shown in FIG. 10, when a recording head in which, for example, two rows of head units K1 and K2 are arranged alternately in the transport direction is mounted, the image formation time is increased. In order to shorten the distance, the offset amount (interval between nozzle rows) L3 between the head units K1 and K2 must be taken into consideration. When this offset amount L3 is present, the interval (medium conveyance interval) L4 between the recording medium 63a that is transported first and the recording medium 63b that is transported next is as shown in FIG. Must be large, that is, L4> L3. In other words, since one image is formed by the head units K1 and K2, each printhead unit cannot accept the image data of the next page unless ink ejection by the K2 row is completed. Also, the image cannot be formed. Accordingly, if L4> L3, the first image is formed on the previous recording medium, and then the second image is formed on the subsequent recording medium.

As described above, the medium conveyance interval of the recording medium is affected by the interval between the recording heads and the interval between the nozzle rows in the medium conveying direction, and the interval between the recording media cannot be easily reduced. The number of image forming processes, that is, the throughput could not be increased.
On the other hand, when the throughput is increased by configuring each recording head to be able to be driven independently, for example, as shown in FIG. 11, each recording head forms an image on a different recording medium.

  In general, a recording head has a head temperature that changes with the elapsed driving time, and even if it is driven with the same driving voltage, the amount of ink that is ejected differs. Darkness) will be different. In general, when the temperature of the recording head increases, the amount of ink discharged increases and the density of the image increases. Conversely, when the temperature decreases, the density of the image tends to decrease. For this reason, it is necessary to adjust the drive characteristics, that is, the drive voltage in accordance with the temperature of the recording head.

Regarding the adjustment of the drive voltage, if the apparatus forms an image on the next second recording medium after the formation of one recording medium as shown in FIG. 9 is completed, the recording head is driven for each image. The voltage can be adjusted.
However, in the configuration in which each recording head can be driven independently as described above, the following problems occur when trying to adjust the image density by controlling the drive voltage.

  In FIG. 11, for example, the first image formation is completed when a yellow image is formed by the recording head Y arranged on the most downstream side. When the color adjustment for the next second image, that is, the drive voltage of the print head is changed, the print head K arranged on the most upstream side has already finished forming the second image on the second print medium. In this state, several recording media are greeted, and the recording heads C and M are also in image formation (C4 and M3) for the fourth and third recording media, respectively. If the drive voltages of all the recording heads are corrected and changed at the same time at this time, the color density of the images (C4 and M3) formed by the recording heads C and M changes from the middle, resulting in image quality. Will deteriorate.

  Also, since the frequency of use differs for each recording head, that is, there are recording heads whose temperature is sufficiently high and those that are not, and recording heads with a large amount of ink discharge depending on the image. There are recording heads with a small ink discharge amount. In this case, it is not appropriate to change the driving voltage uniformly for all the recording heads simultaneously.

  Therefore, the present invention confirms the position and presence of the recording medium, and sets the interval of the recording medium to be transported to be short regardless of the interval between the recording heads or the nozzle rows in the medium conveying direction. An object of the present invention is to provide an image forming apparatus capable of realizing high throughput and high image quality by improving and driving each recording head independently.

In order to achieve the above object, the present invention provides a transport mechanism for transporting a plurality of recording media so as to form a predetermined gap, and a recording element array extending in a direction perpendicular to the transport direction of the recording medium. A plurality of recording heads arranged at intervals along the conveying direction;
Data controller for generating input image data for each of the recording element arrays of the plurality of recording heads, a drive circuit for driving the recording heads at a predetermined timing, and presence / absence of the recording medium transported by the transport mechanism And a drive characteristic control unit that controls the drive characteristic of the recording head, and the drive characteristic control unit follows the recording medium conveyed in advance from the detection result of the position sensor. The medium gap between the recording medium and the recording medium conveyed is calculated, and the recording head in which the recording area of the recording element array opposes the medium gap is selected from the plurality of recording heads. An image forming apparatus is provided that changes the drive characteristics of the recording head while the recording area of the recording element array faces the medium gap.

  The image forming apparatus having the above-described configuration is provided with a data controller for each print head drive circuit, and is independently driven and controlled to change the print head drive characteristics such as parameter rewriting and drive voltage at a suitable timing. Based on the print head temperature detection signal detected by the temperature detection unit provided in each print head, the print head drive voltage output by the print head drive circuit is independently changed to control the ink discharge amount. , To reduce the change in the density of the formed image.

  The present invention improves the image forming efficiency by checking the position and presence of the recording medium and setting the interval of the conveyed recording medium to be short regardless of the interval between the recording heads or nozzle rows in the medium conveying direction. In addition, it is possible to provide an image forming apparatus capable of realizing high throughput and high image quality by driving each recording head independently.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a configuration example of an image forming apparatus according to the first embodiment of the present invention.
This image forming apparatus is an ink jet type and includes at least four sets of recording heads 1 (1a to 1d), and inks of four different colors [for example, black (K: Black), cyan (C: Cyan)]. , Magenta (M: Magenta), yellow (Y: Yellow)] to form a color image. In this embodiment, the recording head 1a is black K, the recording head 1b is cyan C, the recording head 1c is magenta M, and the recording head 1d is yellow Y from the upstream side to the downstream side of the recording medium conveyance mechanism. It is arranged to eject ink.

  In the configuration example shown in FIG. 1 in the present embodiment, the recording heads 1a to 1d are recording element arrays, specifically, a nozzle array in which a plurality of nozzles are arranged in a line with a length exceeding the lateral width of the recording medium (see FIG. Not shown).

  Each of these recording heads 1 (1a to 1d) is driven by a recording head drive circuit 2 (2a to 2d), and forms an image by discharging ink onto a recording medium (not shown) being conveyed. The recording head 1 and the recording head drive circuit 2 are driven and controlled by a data controller 3 (3a to 3d). The recording head driving circuit 2 generates a driving voltage instructed by the voltage controller 17 having a function of controlling the driving characteristics of the recording head based on the detected temperature of the recording head, and drives the recording head 1. ing. Accordingly, the drive characteristics of the recording head 1 are controlled by controlling the voltage control unit 17. Here, the drive characteristics indicate, for example, the amount of ink ejected from the nozzle arrays (storage element arrays) provided in the recording heads 1a to 1d, and the driving voltage applied to each recording head varies. By doing so, it is possible to control the density and hue of the image.

  Further, a temperature detection unit 13 (13a to 13d) that detects the temperature of the ink discharge unit provided with the nozzle row is provided. These temperature detection units 13 measure the temperature of the ink ejection unit of the recording head 2 and output the detected temperature detection signal to the voltage control unit 17. Based on the temperature detection signal, the voltage control unit 17 outputs a voltage control signal for adjusting the ink discharge amount to the recording head drive circuit 2 so that the image density is uniform or appropriate. The recording head driving circuit 2 applies a driving voltage (voltage value) according to the voltage control signal to change the driving characteristics of the recording head 1. In addition to changing the voltage value of the drive voltage, the application time of the drive voltage may be changed.

  In the present embodiment, at least one data controller 3 is provided for each recording head 1. That is, if the configuration includes four sets of recording heads 1a to 1d, at least four data controllers 3a to 3d are provided, and each recording head 1 transfers image data, sets image formation timing, and parameters. The configuration can be set.

  As shown in FIG. 2, each of these data controllers 3a to 3d stores a plane memory 4 capable of storing image data of a plurality of images and parameters for properly driving the recording heads 1a to 1d. An image based on a parameter memory 5, a head drive synchronization signal generation circuit 6 that generates and sends drive synchronization signals to the recording head drive circuits 2a to 2d, and an area (or an address indicating a range) designated from the plane memory 4 The data processing circuit 7 reads data and transfers it to the recording heads 1a to 1d.

  The above parameters are information relating to image formation that is unique to each print head. Specifically, the start and end information of the image data, the address indicating the image data area to be formed, or the nozzles of the print heads 1a to 1d to be driven. Address (nozzle number), timing correction information for driving each nozzle, and the like. Further, the parameters of the image formation information may include correction parameters for correcting manufacturing variations in the recording heads 1a to 1d.

  Furthermore, each of the data controllers 3a to 3d includes a USB controller 8 that functions as an interface for inputting image data (color image data) formed from the host 12 to the plane memory 4, a CPU 9 for setting parameters, and a recording A medium is provided on the upstream side of the recording head 1a on the conveyance path, and a medium position sensor 10 that detects the front and rear ends of the recording medium, and an encoder that is attached to the conveyance mechanism and generates a reference signal for the amount of movement of the recording medium. 11 is provided.

Moreover, the temperature detection part 13 is comprised by temperature sensors, such as a thermistor, for example. In addition to the thermistor, the temperature sensor may be a non-contact type temperature sensor that performs temperature detection using infrared light. Further, a sensor for detecting the discharge of the recording medium on which the image is formed may be provided.
Next, image formation in the first embodiment will be described with reference to the image formation timing chart shown in FIG.

  FIG. 3 shows the timing of image formation and the image formation time for each image data transferred to four sets of recording heads for four recording media that are continuously conveyed (horizontal). Axis is time).

  Here, it is assumed that the image data of black K is 21K, 22K, 23K, 24K, and the time required for image formation of these data is 21K1, 22K2, 23K3, 24K4. In addition, cyan C image data is 21C, 22C, 23C, 24C, and the time required to form these images is 21C1, 22C2, 23C3, 24C4. The image data of magenta M is 21M, 22M, 23M, and 24M, and the time required to form these images is 21M1, 22M2, 23M3, and 24M4. Furthermore, yellow Y image data is represented as 21Y, 22Y, 23Y, and 24Y, and the time required to form these images is represented as 21Y1, 22Y2, 23Y3, and 24Y4.

  Also, the time t1 in FIG. 3 is a time obtained by dividing the offset amount between the recording heads (distance between the recording heads) by the conveyance speed of the recording medium, and the time t2 is an interval between the recording media being conveyed (or The interval between image areas in page units) is shown as the time divided by the conveyance speed of the recording medium. It is assumed that the recording medium conveyance speed is constant. Therefore, the lengths of time t1 and time t2 are relatively suggestive of distance.

  In this example, the offset amount (or time t1) between the recording heads is larger (longer) than the recording medium interval (or time t2). Here, the offset amount is defined by the physical size of the members constituting the recording head and the peripheral members, and the recording medium interval is defined by the processing time such as data transfer. Accordingly, regardless of the size relationship, if both are small (short) and the conveyance speed of the recording medium is constant, the shorter the time t1, the shorter the image forming time per recording medium. Throughput can be improved as t2 is shorter, that is, the recording medium interval is narrower.

  First, as an initial setting, a plurality of color image data for forming images on a plurality of recording media from the host computer 12 is stored in the plane memory 4 via the USB controller 8. At the same time, parameters necessary for image formation from the CPU 9 to the first recording medium 21 by the recording heads 1 a to 1 d are stored in the respective parameter memories 5. The parameter setting in the parameter memory 5 may be stored after receiving the recording medium detection signal from the medium position sensor 10 (see FIG. 2).

  Also, different parameters can be set for each recording medium so that the image data of different recording media can be simultaneously formed in each of the recording heads 1a to 1d. That is, normally, when image data is considered in units of recording media (page units), the image forming information (parameters) for the recording head is the same, but the image forming information (parameters) is different for each recording medium. There is, and can cope with this.

  Next, when the medium position sensor 10 detects the first recording medium transported by the transport mechanism, image data to be formed on the recording medium is selected from among a plurality of image data stored in the plane memory 4. It is read out and transferred to the data processing circuit 7. In this case, the image data in the area (address) designated by the parameter is read from the plane memory 4 in synchronization with the head drive synchronization signal of the most upstream recording head (here, the recording head 1a) in the medium transport direction. At this time, the read image data may be the entire image data for one recording medium or a part thereof.

  Next, when receiving the recording medium presence signal from the medium position sensor 10, the head drive synchronization signal generation circuit 6 corresponds to the offset amount between the recording heads 1a to 1d in the recording medium presence signal according to the designated parameter. A delay (here, time t1) is generated to generate a head drive synchronization signal corresponding to each of the recording heads 1a to 1d. These delay amounts are determined by counting encoder signals synchronized with the medium conveyance speed generated by the encoder 11. The recording head driving circuits 2a to 2d refer to the head driving synchronization signal and drive the driving heads 1a to 1d in synchronization with the encoder signal synchronized with the conveyance of the recording medium.

  Accordingly, the head drive synchronization signal generated by the head drive synchronization signal generation circuit 6 is asserted after the offset amount between the recording heads 1a to 1d, that is, the time t1 is delayed from the medium presence signal, and negated upon completion of image formation. .

Further, the head drive synchronization signal generation circuit 6 calculates a medium gap between the recording medium conveyed in advance and the recording medium conveyed following the detection result of the medium position sensor 10, and the recording head 1a. A recording signal of the recording element array, that is, a recording head in which the nozzle array is opposed to the medium gap is selected from 1d, and an instruction signal (timing) for changing the drive voltage of the recording head Is output to the voltage controller 17.

  Specifically, the first K image data 21K is transferred to the recording head 1a, and based on this image data 21K, an image is formed on the recording medium at a time indicated by 21K1 as shown in FIG. Thereafter, the recording medium is moved downstream, and the next image data 22K begins to be transferred to the recording head 1a during the interval with the next recording medium, that is, during time t2. At this time, if the parameter is changed, the change is performed. Thereafter, image formation 22K1 is performed on the recording medium conveyed later.

  Further, the image data 21C starts to be transferred to the recording head 1b arranged on the downstream side in the medium conveyance direction within a time t1 corresponding to the offset amount, and an image is formed on the image 21K1 already formed on the previous recording medium. Image formation based on the data 21C is performed at a time indicated by 21C1. Thereafter, in the recording heads 1c and 1d, image data M and Y are transferred and images are formed after time t1 corresponding to the offset amount.

  In the configuration of this embodiment, by providing a data controller for each recording head, parameter setting to the image data processing circuit and transfer of image data to the recording heads 1a to 1d can be performed independently for each recording head. . For this reason, as described above, even if the recording head 1b downstream of the recording head 1a is in the middle of image formation by the image data C (for example, 21C), the next page with respect to the upstream recording head 1a. The image data K (for example, 22K) can be transferred, parameters can be changed, and the drive voltage can be changed. As a result, there is no restriction on the timing of voltage adjustment associated with the temperature change of the recording head during image formation due to the conventional batch transfer of data to the recording head and parameter setting.

  As described above, in an ink jet recording head, even if it is driven with the same driving characteristics, that is, with a driving voltage, the temperature of the recording head changes and the amount of ink discharged changes because the driving time increases. The concentration changes. Therefore, in the present embodiment, as shown in FIG. 1, the temperature of the recording head 1 is constantly detected, that is, monitored, while the apparatus is operating by the temperature detection unit 13 provided in each recording head 1.

  The voltage control unit 17 is provided with a comparison circuit, for example, and compares the temperature detection signal detected by the temperature detection unit 13 with a preset reference value. This reference value is a value by which the ink ejection amount is adjusted so that an image having an appropriate density is formed by the recording head. That is, when the temperature detection signal exceeds the reference value, it is assumed that the temperature of the recording head has risen, and a voltage control signal based on the degree of exceeding the reference value is generated and output to the recording head drive circuit 2. . The recording head driving circuit 2 reduces the amount of ink ejected from the ink ejecting section by applying the driving voltage to the recording head 1 lower than before according to the voltage control signal.

As described above, each print head can adjust the drive characteristics, that is, the ink discharge amount by controlling the drive voltage, at a suitable timing based on the detected head temperature. This timing corresponds to the time from the completion of image formation on the first recording medium in each recording head 1 until the next recording medium reaches the recording head, or from the formation of image data for one page. It is within the time between the image data formation of the next page, and specifically within the time t2 shown in FIG.

  Therefore, each recording head 1 is monitored during driving, and when the head temperature rises, the recording head 1 is formed by reducing the amount of ink ejected by lowering the driving voltage at a suitable timing according to the image forming state of each recording head. However, when the head temperature is lowered, the drive voltage is increased to increase the amount of ejected ink and reduce the density change of the formed image.

  Accordingly, when changing the ink discharge amount accompanying the temperature change of the recording head 1, even if an image is being formed on another recording head, there is no influence on the recording head during the image formation. According to this embodiment, even if a large number of identical images are formed, it is possible to form a high-quality image with no difference in color density between recording media.

FIG 4 will be described showing a first modification definitive the temperature detecting unit 1 3. In the first modification, instead of the temperature sensor 14 for detecting the temperature of the ink discharge section of the print head 2 as described above and the comparison circuit, the temperature detection section 13 previously detects the temperature of the print head 1 and the discharge speed. The drive voltage parameter generation unit 15 is associated with the drive voltage with respect to the amount of ink.

The drive voltage parameter generation unit 15 refers to the temperature detection signal detected by the temperature sensor 14 in the table, extracts the drive voltage parameter, and outputs it to the printhead drive circuit 2. The drive voltage parameter generation unit 15 can store a plurality of data so that the drive voltage can be referred to based on the ejection amount level, ink characteristics, recording medium characteristics, and the like due to production variations of the printheads. It is possible to change the table.

The recording head driving circuit 2 generates a correction driving voltage obtained by multiplying the driving voltage applied to the nozzles of the recording head 1 by a driving voltage parameter, and drives the nozzle with the correction driving voltage. The timing for adjusting the recording head 1 by generating the correction driving voltage is the same as in the first embodiment until the next recording medium reaches the recording head after the image formation on the preceding recording medium is completed. 3 or the time from the image formation by the preceding image data to the time before the image formation by the next image data, specifically, the time t2 shown in FIG. At the time t2, a predetermined gap between the recording media, that is, a so-called medium gap and a nozzle row (printing element row) of the recording head 1 are opposed to each other. According to this modification, compared with the first embodiment, the recording head drive circuit does not require an internal comparison circuit, and the configuration is simplified.

In FIG. 5, the 2nd modification of the temperature detection part 13 is shown and demonstrated.
In the second modification, the temperature detection unit 13 includes a temperature sensor 14, a drive voltage parameter generation unit 15 in which a relationship table of the drive voltage with respect to the temperature of the print head and the amount of ejected ink is provided in advance, and a print head drive circuit. having an ink ejection frequency calculation unit 16 that counts the ink ejecting number in each nozzle from 2.

  The ink discharge number calculation unit 16 indicates the use frequency or use state of the print head based on the number of ink discharges per unit time, and is used as a guide for the temperature rise of the print head 1. This use frequency can predict a change in the temperature of the recording head 1 and can be used as a detection signal with good response if it is associated with the drive voltage for the amount of ejected ink together with the temperature detection signal.

Next, a second embodiment according to the present invention will be described.
FIG. 6 shows a configuration example of an image forming apparatus according to the second embodiment.
In the first embodiment described above, the nozzle rows of the recording head are arranged in a single row. However, in this embodiment, the nozzle row intervals L3 are alternately arranged in the medium conveyance direction as shown in FIG. An example is a recording head composed of a plurality of head units arranged in two rows at intervals. These recording heads are, for example, an ink jet system and include at least four sets of recording heads, and inks of four different colors [for example, black (K: Black), cyan (C: Cyan), magenta (M: Magenta), yellow (Y: Yellow)] to form a color image. Here, a configuration example of the recording head 1a shown in FIG. 1 will be described, and the other recording heads 1b to 1d are the same, and the description thereof will be omitted.

  The recording head 1a is also composed of n K1 to Kn head units, and one image is created from the divided images formed by the respective head units. Here, the K1 head unit and the K2 head unit having the nozzle row interval L3 will be described as representatives. 6 that are the same as those shown in FIG. 2 are assigned the same reference numerals.

  These K1 and K2 head units 31a and 31b are driven by K1 and K2 head unit drive circuits 32a and 32b, respectively, to discharge black (K) color ink onto a recording medium (not shown) being conveyed. A divided image is formed. These K1, K2 head units 31a, 31b and K1, K2 head unit drive circuits 32a, 32b are driven and controlled by a K data controller 33. In the present embodiment, at least one K data controller 33 is provided for each head unit. That is, if the recording head includes four sets of head units, at least four data controllers are provided. With this configuration, it is possible to set recording timing and parameters for each head unit of each recording head, as will be described later.

  The K data controller 33 includes a plane memory 34 that stores image data of a plurality of images, K1, K2 parameter memories 35a, 35b that store parameters for properly driving the K1, K2 head units 31a, 31b, K1 and K2 head drive synchronization signal generation circuits 36a and 36b that generate and send head drive synchronization signals to the K1 and K2 head unit drive circuits 32a and 32b, and an area (or an address indicating the range) designated from the plane memory 34 Is constituted by K1, K2 data processing circuits 37a, 37b for reading image data based on the above and transferring them to the K1, K2 head units 31a, 31b.

  Each head unit 31a, 31b is provided with a temperature detection unit 38 (38a, 38b) for detecting the temperature of the ink ejection unit provided with the nozzle row for ejecting ink. These temperature detection units 38 output a temperature detection signal, which detects the temperature of the ink discharge units of the head units 31a and 31b, to the voltage control unit 39. Based on this temperature detection signal, the voltage control unit 39 outputs a voltage control signal for adjusting the ink discharge amount to the head unit drive circuits 32a and 32b so that the image density is uniform or appropriate. The head unit drive circuits 32a and 32b apply drive voltages according to the voltage control signal to change the drive characteristics of the head units 31a and 31b, respectively.

The temperature detecting unit 38, as in the first embodiment described before mentioned, consists of a temperature sensor or an infrared temperature sensor such as a thermistor. Further, similarly to the first and second modifications, the temperature detection unit 38 may include the drive voltage parameter generation unit 15 and the ink discharge number calculation unit 16. Further, the K data controller 33 is provided with the USB controller 8, the CPU 9, the medium position sensor 10, and the encoder 11 described above.

  The above parameters are information relating to image formation. Specifically, the start and end information of the image data, the address indicating the image data area to be formed, or the address (nozzle number) of the nozzle of the head unit to be driven, each nozzle It consists of timing correction information to be driven. Further, a correction parameter for correcting variations in manufacturing of the recording head may be included in the parameter of the image formation information.

  Image formation in the second embodiment will be described with reference to the image formation timing charts shown in FIGS. 6, 10, and 7.

  FIG. 7 shows the image formation timing and image formation time of black K image data for four recording media that are continuously conveyed. Here, the image data transferred to the K1 head unit 31a is 41Ka, 42Ka, 43Ka, 44Ka, and the image data transferred to the K2 head unit 31b is 41Kb, 42Kb, 43Kb, 44Kb, the K1 head. The time required for image formation by the unit 31a is indicated as 41K1, 42K1, 43K1, and 44K1, and the time required for image formation by the K2 head unit 31b is indicated as 41K2, 42K2, 43K2, and 44K2.

  Further, a time t3 in FIG. 7 is a time obtained by dividing an offset amount L3 (interval between nozzle rows) between nozzle rows as shown in FIG. 10 by a conveyance speed of the recording medium, and a time t4 is carried. An interval between two recording media (interval between the trailing edge of the recording medium conveyed first and the leading edge of the recording medium conveyed later) L4 divided by the conveying speed of the recording medium. Yes. Here, the conveyance speed of the recording medium is assumed to be constant. Therefore, the lengths of time t3 and time t4 are relatively suggestive of distance. In this example, the recording medium interval (or time t4) is smaller (shorter) than the nozzle row interval (or time t3), and image formation starts from the leading edge of the recording medium. Yes.

  First, K image data that is a part of a plurality of color image data for forming images on a plurality of recording media from the host computer 12 is stored in the plane memory 34 via the USB controller 8. At the same time, parameters necessary for image formation from the CPU 9 on the first recording medium 41 by the K1, K2 head units 31a, 31b are stored in the respective parameter memories 35a, 35b. The parameter settings in the K1 and K2 parameter memories 35a and 35b may be stored after receiving the recording medium detection signal from the medium position sensor 10.

  Further, in each of the K1 and K2 head units 31a and 31b, different parameters can be set for each recording medium so that image data of different recording media can be simultaneously formed. As a result, when the image formation information (parameter) is different for each recording medium, it can be changed.

  Next, when the medium position sensor 10 detects the first recording medium transported by the transport mechanism, the image data 41K is read out from a plurality of image data stored in the plane memory 34, and K1 The data is transferred to the data processing circuit 37a. In this case, the image data of the area (address) designated by the parameter is read from the plane memory 34 in synchronization with the head drive synchronization signal for the K1 head unit 31a.

  Next, when receiving the recording medium presence signal from the medium position sensor 10, the K1 head driving synchronization signal generation circuit 36a generates a K1 head driving synchronization signal in accordance with the timing of the recording medium presence signal according to the designated parameter. generate. Since the K1 head unit 31a is disposed on the most upstream side, there is no need to perform a delay due to the offset L3.

  Further, when the K2 head drive synchronization signal generation circuit 36b receives the recording medium presence signal from the medium position sensor 10, the offset amount L3, that is, between the head units, is determined at the timing of the recording medium presence signal according to the designated parameter. A K2 head drive synchronization signal is generated with a delay corresponding to the interval (here, time t3). The head drive synchronization signal is generated after the medium presence signal is received, and is invalidated when the image forming process on the recording medium is completed.

  This will be described with reference to a specific example. For example, as shown in FIG. 10, when image data 41K is formed with two rows and six head units, the image data 41K is recorded in the width direction of the recording medium (nozzle of the recording head). The image data is divided into six (array direction). The image formation timing is delayed from the head unit in the rear row as compared with the head unit in the front row. Here, the partial image data transferred to the K1 row as the front row is 41 Ka and the K2 row as the rear row. The partial image data to be transferred is collectively referred to as 41 Kb. In the following, for convenience of explanation, the recording head unit will be described as a two-row, two-row head unit configuration of the front row and the rear row.

  As shown in FIG. 7, the partial image data 41Ka starts to be transferred to the K1 head unit 31a, and the partial image formation (41K1) based on the image data 41Ka is performed on the recording medium conveyed earlier by the K1 head unit 31a. Done. After the image formation, the recording medium is conveyed to the downstream side, and after time t4, the next recording medium reaches the K1 head unit 31a. During this time t4, the partial image data 42Ka of the area (address) designated by the parameter is read from the plane memory 34 and transferred to the K1 data processing circuit 37a. Thereafter, partial image formation (42K1) on the next recording medium is started by the K1 head unit 31a.

On the other hand, the previous recording medium reaches the next K2 head unit 31b after the delay time t3 corresponding to the offset amount L3 described above. During this time t3, partial image data 41Kb in the area (address) designated by the parameter from the plane memory 34 starts to be transferred to the K2 data processing circuit 37a. Then, after elapse of t3, the partial image formation by the K2 head unit 31b is performed adjacent to the image on the previous recording medium (image formed during the image formation time indicated by 41K1) (41K2).

  In the configuration of this embodiment, by providing a data controller for each head unit, parameter setting to the image data processing circuit and transfer of image data to the K1, K2 head units 31a, 31b can be performed independently. It is not necessary to add blank white data to the image data as in the prior art. Therefore, when the recording head 1a forms a black K image, even if the K2 head unit 31b on the downstream side of the K1 head unit 31a is performing image formation with the partial image data 41Kb, the upstream K1 head. For the unit 31a, the next partial image data 42Ka can be transferred, parameters can be changed, and an image can be formed. As a result, it is possible to transfer the image data to which the white data of the same page is added to a plurality of head units at once, or to set parameters, so that the interval between the recording media to be conveyed is reduced. There is no restriction that must be greater than the spacing of the nozzle rows.

  Further, there is no restriction on the adjustment timing for the temperature change of the recording head during image formation due to the conventional batch transfer of data to the head unit and parameter setting.

  As described above, according to the second embodiment, the apparatus is operated by the temperature detection unit 38 provided in each of the K1, K2 head units 31a, 31b as in the first embodiment described above. During this time, the temperatures of the head units 31a and 31b are constantly detected, that is, monitored.

  Further, the voltage control unit 39 also compares the temperature detection signal detected by the temperature detection unit 38 with a preset reference value, generates a voltage control signal for forming an image with an appropriate density, Output to the unit drive circuits 32a and 32b.

  The head unit drive circuits 32a and 32b generate a drive voltage reflecting the voltage control signal and apply it to the head units 31a and 31b at a suitable timing. In each of the head units 31a and 31b, the ink discharge amount is adjusted by the applied drive voltage. This preferable timing is formed within the time until the next recording medium reaches the head units 31a and 31b after the image formation on one recording medium is completed in each head unit 31a and 31b, or first. It is within the time from the image formation of the image data to before the image formation of the next image data to be formed, specifically within the time t2 shown in FIG.

  Therefore, when the ink discharge amount is changed due to the temperature change of the upstream head unit 31a, the head unit 31b is not affected even if an image is being formed in the downstream head unit 31b. According to this embodiment, even if a large number of identical images are formed, it is possible to form a high-quality image with no difference in color density between recording media.

  In each of the above-described embodiments, a four-color color image is used by using four recording heads. However, the present invention is not limited to this, and the arrangement order and number can be changed according to specifications as appropriate. In each embodiment, a printer using an ink head is used as an example for forming an image on a recording medium. However, the present invention is not limited to this, and can be easily applied to an image forming apparatus such as a copier. it can. The recording medium may be a flat member that can form an image on the surface, such as a recording medium such as recording paper or a resin. Furthermore, the constituent parts of each of the described embodiments and modifications may be combined, or some constituent parts may be deleted from those constituent parts as desired.

1 is a diagram illustrating a configuration example of an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the structural example of the data controller in 1st Embodiment. 3 is a timing chart of image formation for explaining image formation in the first embodiment. It is a figure which shows the 1st modification of the temperature detection part in 1st Embodiment. It is a figure which shows the 2nd modification of the temperature detection part in 1st Embodiment. It is a figure which shows the structural example of the image forming apparatus which concerns on 2nd Embodiment. 6 is a timing chart of image formation for explaining image formation in the second embodiment. FIG. 10 is a diagram illustrating a relationship between image forming positions of a conceptual recording head and a recording medium in a conventional image forming apparatus. It is a figure which shows the relationship of the image formation position of the recording head and recording medium in the conventional image forming apparatus. FIG. 4 is a diagram illustrating a configuration example of a recording head having a configuration in which a plurality of head units are alternately arranged in a recording medium conveyance direction. FIG. 6 is a diagram for describing timing for changing a driving voltage of a recording head in an image forming apparatus configured to be driven independently of the recording head.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,1a-1d ... Recording head, 2, 2a-2d ... Recording head drive circuit, 3, 3a-3d ... Data controller, 4 ... Plane memory, 5 ... Parameter memory, 6 ... Head drive synchronous signal generation circuit, 7 ... Data processing circuit, 8 ... USB controller, 9 ... CPU, 10 ... medium position sensor, 11 ... encoder, 12 ... host computer, 13 ... temperature detection unit, 17 ... voltage control unit.

Claims (11)

A transport mechanism for transporting a plurality of recording media so as to open a predetermined gap;
A plurality of recording heads provided with a recording element array so as to extend in a direction orthogonal to the conveyance direction of the recording medium, and arranged at intervals along the conveyance direction;
A data controller that generates input image data for each of the recording element arrays of the plurality of recording heads, and a drive circuit that drives the recording heads at a predetermined timing;
A position sensor for detecting the presence or absence of the recording medium conveyed by the conveyance mechanism;
A drive characteristic control unit for controlling the drive characteristic of the recording head;
Comprising
The data controller calculates a medium gap between a recording medium transported in advance and a recording medium transported following the detection result of the position sensor, and from among the plurality of recording heads, While the recording area of the recording element array is opposed to the medium gap, a recording head is selected, and while the recording area of the recording element array of the recording head is opposed to the medium gap, the control of the drive characteristic control unit An image forming apparatus characterized by changing the drive characteristics of the recording head. In the image forming apparatus,
Comprising a temperature detector having a temperature sensor for detecting the temperature of the recording head;
The image forming apparatus according to claim 1, wherein the drive characteristic control unit changes the drive characteristic of the recording head based on a detection result of the temperature sensor . In the image forming apparatus,
The image forming apparatus according to claim 2, wherein the drive characteristic control unit includes a voltage control unit that changes a drive voltage of the recording head. In the image forming apparatus,
The image forming apparatus according to claim 3 , wherein the voltage control unit changes a driving characteristic of the recording head by changing a driving time during which a predetermined driving voltage is applied to the recording head. In the image forming apparatus,
The image forming apparatus according to claim 1, wherein the position sensor calculates the medium gap by detecting a leading end of the recording medium that is conveyed following the position sensor. In the image forming apparatus,
The position sensor detects a leading end and a trailing end of a recording medium to be conveyed, The data controller is
The medium gap is calculated from a rear end in the transport direction of the recording medium transported in advance and a front end in the transport direction of the recording medium transported following the position detected by the position sensor. The image forming apparatus according to claim 1, wherein: The data controller is
Plain memory that can store image data for multiple pages,
A parameter memory that is provided for each recording head and stores various parameters for reading out image data in units of pages when each recording head forms an image in units of pages.
A head drive synchronization signal generation circuit that is provided for each recording head and generates a head drive synchronization signal based on a sheet detection result from the position sensor;
A data processing circuit that is provided for each of the recording heads, captures predetermined image data according to a predetermined parameter at a timing according to the head drive synchronization signal, and performs image processing;
The image forming apparatus according to claim 1, further comprising: The drive characteristic control unit changes the drive characteristic of the recording head when the gap between the preceding recording medium and the recording medium that follows later reaches the recording area of the recording head, and 2. The image forming apparatus according to claim 1, wherein when the recording medium following the recording medium reaches the recording area of the recording head, an image is recorded with the changed drive characteristics. A transport mechanism that transports a plurality of recording media along the transport direction with a predetermined gap therebetween;
A position detector that is provided on a transport path of the transport mechanism and detects the presence and end of the recording medium;
A plurality of recording heads arranged at intervals so as to extend a recording element array for forming an image in a direction orthogonal to the conveyance direction of the recording medium;
A data controller that is provided for each of the plurality of recording heads and that generates image data to be input for each of the recording element arrays and parameters for image formation;
A drive circuit configured to drive the recording head to form an image based on image data reflecting the parameter generated in the data controller;
A temperature detector for measuring the temperature of the recording element array of the recording head and detecting a temperature detection signal;
A voltage control signal based on the temperature detection signal is generated and output to the driving circuit, and a controlled driving voltage is applied from the driving circuit to the recording head so as to obtain a desired image density. A voltage control unit for controlling
Consists of
The data controller calculates a timing at which the predetermined interval opposes the recording element array from a result of the recording medium position detected by the position detection unit, and the voltage control unit is formed based on the timing. An image forming apparatus, wherein the drive voltage output from the drive circuit is changed so that an image density of an image becomes appropriate. A transport mechanism that transports a plurality of recording media along the transport direction with a predetermined gap therebetween;
A position detector that is provided on a transport path of the transport mechanism and detects the presence and end of the recording medium;
The recording element array so as to extend in the orthogonal direction and having a plurality of head units arranged with respect to the conveying direction of the recording medium, for a divided area obtained by dividing the image formation area of recording medium to be conveyed, respectively A plurality of head units that are provided with an offset in the medium conveyance direction to create one image by forming a divided image by the head unit of
A data controller that is provided for each of the plurality of head units, and that generates image data to be input for each recording element array and parameters for image formation;
A head unit driving unit that is provided in each of the head units and drives the head unit to form a divided image on the recording medium;
A drive circuit that forms an image by driving the head unit based on image data reflecting the parameter generated in the data controller;
A temperature detector for measuring the temperature of the recording element array of the head unit and detecting a temperature detection signal;
A voltage control signal based on the temperature detection signal is generated and output to the drive circuit, and a controlled drive voltage is applied from the drive circuit to the head unit to achieve a desired image density. A voltage control unit for controlling
Consists of
The data controller calculates a timing at which the predetermined interval opposes the recording element array from a result of the recording medium position detected by the position detection unit, and the voltage control unit is formed based on the timing. An image forming apparatus, wherein the drive voltage output from the drive circuit is changed so that an image density of an image becomes appropriate. The temperature detection unit further includes an ink discharge number calculation unit that calculates the number of ink discharges,
The image forming apparatus according to claim 3, wherein the drive characteristic control unit changes the drive characteristic of the recording head based on a detection result of the temperature sensor and a calculation result of the ink ejection number calculation unit.

Images