JP2019166691A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can suppress printing unevenness by dealing with the instantaneous speed variation in a conveyance path of a recording medium without increase in the size of the apparatus.SOLUTION: An image formation apparatus forming an image by using a print head to a conveyed recording medium includes: conveyance means which conveys the recording medium in the prescribed direction; recording means including a print head; and control means which has a storage unit and controls the conveyance means and recording means. In the image formation apparatus, the storage unit has control data related to the printing control based on the variation in the conveyance speed of the recording medium conveyed by the conveyance means, and the control means controls at least one of the conveyance means and recording means based on the control data stored in the storage unit.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image on a transported recording medium using a print head.

  In an image forming apparatus that forms an image on a paper that is a recording medium, a technique is disclosed that solves uneven printing due to fluctuations in the conveyance speed of the paper. For example, in the ink jet recording apparatus disclosed in Patent Document 1, the web conveyance speed when an image is drawn by the ink jet head is detected, and the image is drawn at a constant density even if the speed fluctuates. The dot arrangement data is corrected according to the detected speed.

  Japanese Patent Application Laid-Open No. 2004-228688 corresponds to a conveyance roller that conveys a recording medium, an encoder unit that outputs a signal according to the rotation of the conveyance roller, a detection unit that detects a reference position of the encoder unit, and a conveyance speed. A memory for storing correction data relating to drive control of the printhead, and a control means for performing drive control of the printhead using the correction data stored in the memory based on a signal from the encoder and a signal from the detection means. A recording apparatus is disclosed. In this recording apparatus, even if there is a variation in the roller diameter, the positional deviation of the dots is appropriately suppressed.

  Further, in Patent Document 3, in a recording apparatus that performs recording using an encoder unit attached to a conveyance roller, speed information of the conveyance belt acquired by a laser Doppler type detection unit, and a conveyance roller acquired by an encoder unit A recording apparatus that controls recording using the speed information is disclosed. In this recording apparatus, the positional deviation of the recording due to the eccentricity of the conveying roller is suppressed.

  In addition, the apparatus disclosed in Patent Document 4 discloses a compensation apparatus that compensates for fluctuations in the rotational speed of a motor in a recording apparatus that uses a motor as a recording medium conveyance power source.

JP 2012-45836 A JP 2012-839 A JP 2009-6655 A Japanese Patent Laid-Open No. 01-281259

  In an image forming apparatus that forms an image on a transported recording medium, the use of an encoder, a paper speed detecting means, etc. in order to eliminate uneven printing due to fluctuations in the transport speed of the recording medium causes an increase in the size of the apparatus. It will be. In addition, since there is a time lag from the detection of the recording medium being transported to the start of image formation (until the detection of the recording medium is reflected in the control of image formation), printing unevenness is detected against instantaneous speed fluctuations in the transport path. It is difficult to sufficiently suppress the occurrence of.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of suppressing uneven printing in response to instantaneous speed fluctuations in a recording medium conveyance path without increasing the size of the apparatus.

  In order to solve the above problems, an aspect of the present invention is an image forming apparatus that forms an image on a recording medium to be transported using a print head, and a transport unit that transports the recording medium in a predetermined direction; A recording unit including a print head, and a control unit that includes a storage unit and controls the conveying unit and the recording unit. In this image forming apparatus, the storage unit has control data related to print control based on a change in the conveyance speed of the recording medium conveyed by the conveyance unit, and the control unit is based on the control data stored in the storage unit. It is characterized by controlling at least one of the conveying means and the recording means.

  According to such a configuration, since the storage unit stores the control data related to the printing control based on the change in the conveyance speed of the recording medium, based on the control data, at least one of the conveyance unit and the recording unit is stored. By controlling this, it is possible to suppress uneven printing due to fluctuations in the conveyance speed of the recording medium. Further, since control is performed using control data stored in advance in the storage unit, a complicated configuration for detecting the conveyance speed is not required.

  In the image forming apparatus, the control data may include at least data based on fluctuations in the conveyance speed associated with a load that the recording medium conveyed by the conveyance unit receives during conveyance. As a result, it is possible to suppress printing unevenness due to speed fluctuations during the conveyance of the recording medium.

  In the image forming apparatus, the control data may include at least data based on fluctuations in the conveyance speed accompanying a load received when the recording medium conveyed by the conveyance unit reaches the position of the print head. As a result, it is possible to suppress uneven printing due to a speed change when the recording medium reaches the position of the print head.

  The image forming apparatus may further include a sensor that is provided upstream of the position of the recording unit in the conveyance path by the conveyance unit and detects the recording medium. In this image forming apparatus, the control unit may be provided to control at least one of the conveying unit and the recording unit in accordance with the timing at which the recording medium reaches the print head based on the detection result of the sensor. Accordingly, it is possible to accurately grasp the timing at which the recording medium reaches the print head based on the detection result of the sensor, and it is possible to suppress print unevenness due to the speed fluctuation of the recording medium.

  In the above image forming apparatus, the recording unit has a gap portion narrower than the thickness of the recording medium in the middle of the conveyance path by the conveying unit, and the recording medium rushes into this portion to apply the pressure necessary for recording to the recording medium. The control data may include at least rush speed fluctuation data relating to a change in the transport speed when the recording medium rushes into this portion. As a result, it is possible to suppress uneven printing due to speed fluctuations that occur when the recording medium enters the recording means.

  In the image forming apparatus, the control unit may be provided to control the conveyance speed of the recording medium by the conveyance unit based on the control data. Thereby, since the conveyance speed of the recording medium is controlled based on the control data, it is possible to suppress uneven printing due to fluctuations in the conveyance speed of the recording medium.

  In the image forming apparatus, the control unit may be provided to control energization energy of one dot by the recording unit based on the control data. As a result, the energization energy of one dot by the recording means is controlled based on the control data, so that it is possible to suppress uneven printing due to fluctuations in the conveyance speed of the recording medium.

  In the image forming apparatus, the control unit includes the conveyance unit and the recording unit so that the energy per unit area given from the print head to the recording medium being conveyed becomes a preset amount based on the control data stored in the storage unit. It may be provided to control at least one of the means. Thereby, even if the conveyance speed of the recording medium varies, the energy per unit area of the recording medium can be set to a preset amount to suppress uneven printing.

  According to the present invention, it is possible to provide an image forming apparatus capable of suppressing uneven printing in response to instantaneous speed fluctuations in a recording medium conveyance path without increasing the size of the apparatus. .

1 is a perspective view illustrating an image forming apparatus according to an embodiment. (A) And (b) is sectional drawing which illustrates the image forming apparatus which concerns on this embodiment. 1 is a block diagram illustrating an image forming apparatus according to an embodiment. (A)-(d) is a schematic diagram which illustrates a printing process. 6 is a flowchart illustrating print processing. (A) And (b) is a figure explaining the example of conveyance speed control of a recording medium. (A) And (b) is a figure which shows the example of a measurement of the conveyance speed of a recording medium. (A) And (b) is a figure explaining the example of other control.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same members are denoted by the same reference numerals, and the description of the members once described is omitted as appropriate.

(Configuration of image forming apparatus)
FIG. 1 is a perspective view illustrating an image forming apparatus according to this embodiment.
2A and 2B are cross-sectional views illustrating the image forming apparatus according to this embodiment.
2A shows a cross-sectional view taken along the line AA of FIG. 1, and FIG. 2B shows a partially enlarged view of the recording means.
FIG. 3 is a block diagram illustrating an image forming apparatus according to this embodiment.

  The image forming apparatus 1 according to the present embodiment is an apparatus that forms an image on a transported recording medium P using a print head 21. For example, a thermal head is used for the print head 21, and thermal paper is used for the recording medium P. Thermal paper is used for single-color printing or full-color printing that produces different colors depending on the temperature applied from the thermal head. In the image forming apparatus 1, printing on the recording medium P is performed when the recording medium P passes through the position of the print head 21. The recording medium P after printing is discharged from the front panel 105.

  The image forming apparatus 1 includes a conveyance unit 10 that conveys the recording medium P in a predetermined direction, a recording unit 20 including a print head 21, and a control unit 30 that includes a storage unit 32 and controls the recording unit 20. .

  The transport unit 10 transmits a transport roller 15 for feeding the recording medium P one by one in a predetermined transport direction, a motor 17 that is a driving source for rotating the transport roller 15, and a driving force of the motor 17 to the transport roller 15. And a transmission unit 13 such as a gear. The conveyance roller 15 is provided between the pair of side frames 103, and sends the recording medium P in the direction of the recording unit 20 by the frictional force between the rotating conveyance roller 15 and the recording medium P. A plurality of recording media P shown in the figure are set so as to overlap each other, and only one sheet contacting the conveying roller 15 is sent out.

  The motor 17 and the transmission unit 13 are attached to the side frame 103, for example. The rotational force of the motor 17 is transmitted to the transport roller 15 via, for example, a gear of the transmission unit 13. A stepping motor is used for the motor 17, and rotation control is performed by pulse power sent from the control means 30.

  The recording unit 20 includes a print head 21 and a platen roller 25. The print head 21 is provided in a line shape in a direction orthogonal to the conveyance direction of the recording medium P. When a thermal head is used as the print head 21, a plurality of heating elements are arranged in the direction in which the print head 21 extends.

  In the present embodiment, the top plate 101 is passed between the pair of side frames 103, and the print head 21 is attached to the top plate 101. The platen roller 25 is disposed so as to face the print head 21.

  The shaft of the platen roller 25 is supported by the swing frame 24, and the clearance G between the platen roller 25 and the print head 21 can be changed by swinging the swing frame 24. The swing frame 24 is biased by a spring 26 and biased in a direction in which the platen roller 25 and the print head 21 approach each other. The swing frame 24 keeps the gap G between the platen roller 25 and the print head 21 at a preset value, for example, by abutting against a position restricting portion (not shown).

  In the present embodiment, the gap G between the platen roller 25 and the print head 21 is slightly narrower than the thickness of one recording medium P. As a result, when the recording medium P is fed between the platen roller 25 and the print head 21, it is fed in the transport direction while overcoming the biasing force of the spring 26 and widening the gap G. When the recording medium P passes between the platen roller 25 and the print head 21, the recording medium P advances while being pressed against the print head 21 by the urging force of the spring 26. In other words, the recording medium P is required for recording because the recording medium P enters a gap (gap G between the platen roller 25 and the print head 21) narrower than the thickness of the recording medium P located in the middle of the conveyance path by the conveyance means 10. Pressure is applied to the recording medium P.

  In this embodiment, the platen roller 25 is swingably provided by the swing frame 24. However, the print head 21 may be swingably provided, or both the platen roller 25 and the print head 21 may be provided. May be provided so as to be swingable.

  The platen roller 25 rotates using the motor 17 as a drive source. The transmission unit 13 transmits the rotational force of the motor 17 to the conveyance roller 15 and also to the platen roller 25. In the present embodiment, the rotation speed of the platen roller 25 is set to be slightly higher than the rotation speed of the transport roller 15. Thus, the recording medium P is transported by the rotational force of the transport roller 15 in a state where it is in contact with the transport roller 15, and is transported by the rotational force of the platen roller 25 when it is in contact with the platen roller 25. The conveyance roller 15 is provided with an intermittent mechanism. When the recording medium P is in contact with both the platen roller 25 and the conveyance roller 15, the driving force of the conveyance roller 15 becomes free and depends on the rotation difference. An increase in the transport load can be suppressed.

  A sensor 23 is provided between the conveyance roller 15 and the platen roller 25 in the conveyance path of the recording medium P (upstream side of the position of the recording unit 20). The sensor 23 detects the recording medium P being conveyed. The sensor 23 is, for example, a reflection type or transmission type detection unit, and can detect the leading end position of the recording medium P being conveyed. Various controls by the control means 30 are performed based on the detection timing of the sensor 23. As the sensor 23, a sensor for detecting the conveyed recording medium P can be used for a general image forming apparatus, and no new detection means is required, and the apparatus can be reduced in size and simplified. it can.

  The control unit 30 includes a central processing unit 31 and a storage unit 32. The control unit 30 is connected to the transport unit 10 and the recording unit 20 via, for example, a flexible cable 35. The central processing unit 31 controls the conveying unit 10 and the recording unit 20 by predetermined software. For example, the central processing unit 31 performs rotation control of the motor 17 and energization control of the print head 21 based on the detection result of the sensor 23.

In the present embodiment, control data related to printing control based on the variation of the conveyance speed with respect to the position of the recording medium P conveyed by the conveyance unit 10 is stored in the storage unit 32. The control data is data fetched in advance by the image forming apparatus 1. The control data is, for example, speed variation data with respect to the position of the recording medium P being conveyed. The speed variation data may be data for each model of the image forming apparatus 1 (such as an average value of the model) or may be unique data for each image forming apparatus 1. Further, the data may be different depending on the type (paper quality, thickness, etc.) of the recording medium P. Further, the speed fluctuation data may be data calculated by simulation from the type of the recording medium P and the transport conditions (roller rotation speed, friction coefficient, etc.) of the transport unit 10.
Further, the speed variation data may be data obtained by actually measuring the speed of the recording medium P at the time of printing by a speed measuring device such as a laser or Doppler, or data calculated by simulation or the like. Furthermore, data corresponding to an actual measurement value of the gap G between the print head 21 and the platen roller 25 may be used. In addition, a detection unit such as a printing temperature or humidity may be provided in the image forming apparatus 1 and the data may be different depending on the environment.
Here, the speed fluctuation based on the conveyance path of the recording medium P and the driving system of the conveyance depends on the configuration of the conveyance path and the driving system, and therefore has high reproducibility. Therefore, in the present embodiment, it is possible to stably suppress uneven printing due to fluctuations in the conveyance speed of the recording medium P.

  Control data such as speed variation data can be updated as firmware, and may be downloaded via a network and stored in the storage unit 32. For example, the control data may be stored in the storage unit 32 when the image forming apparatus 1 is shipped, and the control data corresponding to the new recording medium P may be updated as firmware after the shipment.

  In addition, a plurality of control data such as a plurality of speed fluctuation data is stored in the storage unit 32 for each type of the recording medium P and for each printing condition, and automatically by the central processing unit 31 depending on the user's arbitrary or printing conditions. You may be able to switch.

  In the present embodiment, the control unit 30 (central processing unit 31) controls at least one of the transport unit 10 and the recording unit 20 based on the control data stored in the storage unit 32. As a result, it is possible to suppress uneven printing due to fluctuations in the conveyance speed of the recording medium P.

  For example, the control data is data indicating the relationship between the position on the transport path of the recording medium P and the transport speed. That is, the recording medium P is sent to the conveyance path by the conveyance roller 15 and reaches the recording means 20 to be printed. The conveyance speed of the recording medium P varies depending on the position of the conveyance path from the start of conveyance of the recording medium P to the end of printing. In particular, fluctuations in the conveyance speed while the printing process is being performed while the recording medium P is in contact with the print head 21 is a main cause of uneven printing.

  Therefore, the control data of the recording medium P is stored in the storage unit 32 in advance, and the printing control by the control means 30 is performed based on the relationship between the transport position and the speed of the recording medium P, so that the transport speed of the recording medium P is reached. Even if a change occurs, the influence on the print quality can be suppressed.

In the present embodiment, the control unit 30 performs control using control data stored in the storage unit 32 in advance. For this reason, the complicated structure which detects and controls a conveyance speed in real time becomes unnecessary, and the enlargement of an apparatus can be suppressed.
The stored data may be from the start of conveyance of the recording medium P to the end of printing, or a part thereof. For example, the control based on the speed fluctuation data may be started from the print position corresponding to the speed fluctuation data with the passage position of the sensor 23 that detects the recording medium P as a reference.

(Print processing)
Next, the printing process in the image forming apparatus 1 according to the present embodiment will be described.
4A to 4D are schematic views illustrating the printing process.
FIG. 5 is a flowchart illustrating print processing.
As shown in FIG. 4A, the driving of the motor 17 is operated with the recording medium P set, and the transport roller 15 is rotated (step S101 in FIG. 5). The recording medium P in contact with the transport roller 15 is sent out in the transport direction by the rotation of the transport roller 15.

  As shown in FIG. 4B, when the leading edge of the recording medium P sent out by the conveying roller 15 reaches the position of the sensor 23, the recording medium P is detected by the sensor 23 (step S102 in FIG. 5). . The central processing unit 31 of the control means 30 receives the detection result by the sensor 23 and counts a predetermined time based on the transport speed by the transport roller 15 (step S103 in FIG. 5). Here, the predetermined time is a time from when the recording medium P is detected by the sensor 23 until it reaches the position of the print head 21 of the recording means 20. The count of the predetermined time may be a time count or a count of the number of steps of the pulse signal sent to the motor 17.

  When the predetermined time is counted, the leading edge of the recording medium P reaches between the platen roller 25 and the print head 21 as shown in FIG. 4C (step S104 in FIG. 5). Thereafter, as shown in FIG. 4D, the recording medium P is fed by the rotation of the platen roller 25, and printing is performed by the print head 21.

  The central processing unit 31 of the control unit 30 controls at least one of the transport unit 10 and the recording unit 20 until the leading end of the recording medium P reaches between the platen roller 25 and the print head 21 and passes through. I do. In the example shown in FIG. 5, the conveyance speed of the recording medium P by the conveyance means 10 is controlled (steps S105 to S106).

(Conveyance speed control)
Here, an example of the conveyance speed control shown in steps S105 to S106 in FIG. 5 will be described.
FIGS. 6A and 6B are diagrams for explaining an example of conveyance speed control of a recording medium.
FIG. 6A shows a graph illustrating a change in the conveyance speed of the recording medium P. The horizontal axis of the graph shown in FIG. 6A is time, and the vertical axis is the conveyance speed of the recording medium P. FIG. 6B shows a graph illustrating a change in the rotation speed of the platen roller 25. The horizontal axis of the graph shown in FIG. 6B is time, and the vertical axis is the rotational speed of the platen roller 25. FIG. 6B shows an example of a pulse for driving the motor 17.

  The conveyance speed V1 in the graph shown in FIG. 6A indicates a change in the conveyance speed of the recording medium P when the conveyance speed control according to the present embodiment is not performed, and the conveyance speed V2 is related to the present embodiment. The change of the conveyance speed of the recording medium P at the time of controlling conveyance speed is shown.

  First, the conveyance speed V1 of the recording medium P when the conveyance speed according to the present embodiment is not controlled will be described. That is, at time t1, the recording medium P is transported according to the rotation speed of the transport roller 15. When the leading edge of the recording medium P reaches between the platen roller 25 and the print head 21, the conveyance speed of the recording medium P decreases (time t2). This is because, since the gap G between the platen roller 25 and the print head 21 is slightly narrower than the thickness of the recording medium P, the conveyance speed of the recording medium P is increased until the urging force of the spring 26 is overcome and the gap G is expanded. It is because it falls.

  As a result, the conveyance speed of the recording medium P decreases at time t2, and then the conveyance speed of the recording medium P increases due to the rotation of the platen roller 25 when the recording medium P starts to advance due to the gap G widening (time t3). . This is because the rotation speed of the platen roller 25 is set to be slightly higher than the rotation speed of the transport roller 15.

  Then, at time t4, an overshoot occurs due to an increase in the conveyance speed, and thereafter, at time t5, the conveyance speed conforms to the rotation speed of the platen roller 25. Printing on the recording medium P is started immediately after the leading edge of the recording medium P reaches the print head 21, that is, between time t1 and time t2. For this reason, uneven printing occurs due to a decrease in the conveyance speed at time t2 and an overshoot at time t4.

  Next, the conveyance speed V2 of the recording medium P when the conveyance speed according to the present embodiment is controlled will be described. That is, at time t1, the recording medium P is transported according to the rotation speed of the transport roller 15. When the leading edge of the recording medium P reaches between the platen roller 25 and the print head 21, the rotational speed of the motor 17 is increased under the control of the control means 30 (central processing unit 31) to compensate for the decrease in the speed of the recording medium P. Control to do so. As shown in FIG. 6B, the pitch P2 of the pulse signal to the motor 17 at time t2 is made narrower than the pitch P1 of the pulse signal at time t1. As a result, the rotation speed of the motor 17 is increased, and a decrease in the conveyance speed of the recording medium P is suppressed.

  Next, at time t3, the motor 17 is returned to the normal rotation speed. That is, the pitch P3 of the pulse signal to the motor 17 at time t3 is made the same as the pitch P1 of the pulse signal to the motor 17 at time t1. At this stage, the conveyance speed of the recording medium P is increased by the rotation of the platen roller 25.

  Next, at time t4, control is performed to reduce the rotational speed of the motor 17 to compensate for the overshoot of the conveyance speed of the recording medium P. As shown in FIG. 6B, the pitch P4 of the pulse signal to the motor 17 at time t4 is made wider than the pitch P1 of the pulse signal at time t1 and time t3. As a result, the rotational speed of the motor 17 is reduced, and overshooting of the conveyance speed of the recording medium P is suppressed.

  Thereafter, at time t5, the motor 17 is returned to the normal rotation speed. That is, the pitch P5 of the pulse signal to the motor 17 at time t5 is made the same as the pitch P1 and pitch P3 of the pulse signal to the motor 17 at time t1 and time t3. As a result, the recording medium P has a conveyance speed according to the rotation speed of the platen roller 25.

  When the conveyance speed according to the present embodiment is controlled as described above, when the recording medium P reaches between the platen roller 25 and the print head 21 as in the conveyance speed V2 illustrated in FIG. And the overshoot after the leading edge of the recording medium P passes between the platen roller 25 and the print head 21 can be suppressed.

  In the present embodiment, data (speed variation data) indicating a change in the transport speed V1 when the transport speed control according to the present embodiment is not performed is acquired and stored in the storage unit 32 in advance. The control means 30 controls the pitch of the pulse signal applied to the motor 17 based on the speed fluctuation data stored in the storage unit 32 as shown in FIG. Thereby, the conveyance speed V1 of the recording medium P becomes the conveyance speed V2, and the speed reduction and overshoot can be suppressed.

  By suppressing such a decrease in speed and overshoot of the recording medium P, it is possible to suppress uneven printing due to a change in the conveyance speed.

7A and 7B are diagrams illustrating measurement examples of the conveyance speed of the recording medium.
FIG. 7A shows an example of measurement of the conveyance speed when the conveyance speed control according to this embodiment is not performed, and FIG. 7B shows the conveyance speed control according to this embodiment. An example of measuring the conveyance speed is shown. In either example, the result of measurement performed by a plurality of image forming apparatuses is shown.

  As shown in FIG. 7A, when the conveyance speed according to the present embodiment is not controlled, the conveyance speed of the recording medium P is reduced or overshoot occurs. On the other hand, as shown in FIG. 7B, it can be seen that by controlling the conveyance speed according to the present embodiment, a decrease in the conveyance speed of the recording medium P and an overshoot are suppressed.

  In recent years, it has become possible to measure the speed fluctuation of the recording medium P with high accuracy by improving the accuracy of a measuring machine using a laser or the like. Therefore, the fluctuation of the conveyance speed of the recording medium P is measured for each image forming apparatus 1, and an average or the like is taken for each model to obtain data (speed fluctuation data) on the relationship between the position of the recording medium P and the conveyance speed, for example. The data is stored in the storage unit 32 as data.

  The control data may include data regarding fluctuations in the conveyance speed associated with the load that the recording medium P conveyed by the conveyance unit 10 receives during conveyance. Further, the recording medium P transported by the transport unit 10 may include data related to fluctuations in transport speed due to a load received when the recording medium P reaches the position of the print head 21. Further, it may include rush speed fluctuation data relating to fluctuations in the transport speed when the recording medium P rushes between the platen roller 25 and the print head 21.

  Based on this control data, the rotation speed of the motor 17 is controlled by the control means 30, so that it is possible to suppress printing unevenness due to the conveyance speed fluctuation of the recording medium P.

(Other control examples)
Next, another example of control will be described.
FIGS. 8A and 8B are diagrams illustrating another example of control.
FIG. 8A shows an example of control for changing the width of the pulse signal applied to the motor 17. That is, the rotational speed of the motor 17 is controlled by changing the duty ratio of the pulse signal. The central processing unit 31 of the control unit 30 controls the duty ratio of the pulse signal applied to the motor 17 based on the control data based on the change in the conveyance speed of the recording medium P stored in the storage unit 32.

  For example, the duty ratio of the pulse signal at time t1 is M1, and the duty ratio of the pulse signal at time t2 is M2, which is higher than M1. Thereby, the rotational speed of the motor 17 increases. The duty ratio M3 of the pulse signal at time t3 is the same as M1, and the rotational speed of the motor 17 is lower than that at time t2. The duty ratio M4 of the pulse signal at time t4 is lower than M3, and the rotational speed of the motor 17 is lower than time t3. The duty ratio M5 of the pulse signal at time t5 is the same as that of M1 and M3, and the rotational speed of the motor 17 increases from time t4.

  By such control, it is possible to suppress a decrease in the conveyance speed and overshoot of the recording medium P indicated by the conveyance speed V1 in FIG. 6A, and to suppress uneven printing due to fluctuations in the conveyance speed. .

FIG. 8B shows an example of control based on the amount of energy applied to the recording medium P.
For example, when printing is performed using a thermal head as the print head 21 and thermal paper as the recording medium P, the density varies depending on the amount of thermal energy applied from the print head 21 to the recording medium P. If the conveyance speed of the recording medium P varies, the amount of thermal energy given to the recording medium P deviates from the amount necessary for printing, resulting in printing unevenness. For example, if there is such a change in the conveyance speed of the recording medium P, horizontal line-shaped printing unevenness occurs in the printing at the front end of the recording medium P.

  In the control example shown in FIG. 8B, the amount of energy given from the print head 21 to the recording medium P is controlled by the central processing unit 31 of the control means 30 to suppress uneven printing. The amount of energy is controlled based on control data based on fluctuations in the conveyance speed of the recording medium P stored in the storage unit 32.

  For example, when the heat generation amount of the thermal head is constant, the energy amount per unit area of the recording medium P increases as the conveyance speed of the recording medium P decreases, and the recording medium P increases as the conveyance speed of the recording medium P increases. The amount of energy per unit area decreases. Therefore, the central processing unit 31 of the control unit 30 reduces the amount of energy per unit area of the recording medium P at the timing when the conveyance speed decreases based on the control data of the recording medium P stored in the storage unit 32. The amount of energy per unit area of the recording medium P is increased at the timing when the conveyance speed increases.

  As an example, when the leading edge of the recording medium P reaches between the platen roller 25 and the print head 21 (time t2), the conveyance speed of the recording medium P decreases. The central processing unit 31 of the control unit 30 reduces the energization energy per dot of print of the print head 21 (thermal head) at this timing. On the other hand, at time t4 when the conveyance speed of the recording medium P overshoots, the energization energy per dot of the print of the print head 21 (thermal head) is increased. Accordingly, it is possible to suppress unevenness in printing by suppressing fluctuations in the amount of energy given from the print head 21 to the recording medium P due to fluctuations in the conveyance speed.

  In the above example, the central processing unit 31 of the control unit 30 controls the conveyance speed of the recording medium P based on the control data of the recording medium P stored in the storage unit 32, or prints per one print dot. Although the example in which the energization energy to the head 21 (thermal head) is controlled is shown, the central processing unit 31 is based on the control data of the recording medium P stored in the storage unit 32 and the recording medium P being conveyed from the print head 21. It is only necessary to control at least one of the conveying means 10 and the recording means 20 so that the energy per unit area given to is a preset amount. Thereby, even if the conveyance speed of the recording medium P varies, the energy per unit area of the recording medium P can be set to a preset amount to suppress uneven printing. The energization energy is controlled by controlling the energization pulse width and amplitude of the print head 21 or the energization pitch, for example.

  As described above, according to the present embodiment, an image forming apparatus that can suppress uneven printing in response to instantaneous speed fluctuations in the conveyance path of the recording medium P without increasing the size of the apparatus. 1 can be provided.

  In addition, although this embodiment and its specific example were demonstrated above, this invention is not limited to these examples. For example, although an example of a thermal head is shown as the print head 21, an image printing mechanism other than the thermal head may be used. In addition to the configuration connected by the flexible cable 35, the control unit 30 may be separated from the transport unit 10 and the recording unit 20, and may be configured to perform data communication via a network, for example.

  Further, those in which those skilled in the art appropriately added, deleted, and changed the design of the above-described embodiments or specific examples thereof, and combinations of the features of each embodiment as appropriate are also included in the present invention. As long as the gist is provided, it is included in the scope of the present invention.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 10 ... Conveyance means 13 ... Transmission part 15 ... Conveyance roller 17 ... Motor 20 ... Recording means 21 ... Print head 23 ... Sensor 24 ... Swing frame 25 ... Platen roller 26 ... Spring 30 ... Control means 31 ... Center Calculation unit 32 ... storage unit 35 ... flexible cable 101 ... top plate 103 ... side frame 105 ... front panel G ... gap P ... recording media V1, V2 ... transport speed

Claims (8)

An image forming apparatus for forming an image on a transported recording medium using a print head,
Conveying means for conveying the recording medium in a predetermined direction;
Recording means including the print head;
A control unit having a storage unit and controlling the transport unit and the recording unit;
With
The storage unit has control data related to print control based on a change in a conveyance speed of the recording medium conveyed by the conveyance unit;
The image forming apparatus, wherein the control unit controls at least one of the transport unit and the recording unit based on the control data stored in the storage unit.   The image forming apparatus according to claim 1, wherein the control data includes at least data based on a change in a conveyance speed associated with a load that the recording medium conveyed by the conveyance unit receives during the conveyance.   3. The image according to claim 1, wherein the control data includes at least data based on a variation in a conveyance speed caused by a load received when the recording medium conveyed by the conveyance unit reaches the position of the print head. Forming equipment. Provided further upstream of the position of the recording means in the transport path by the transport means, further comprising a sensor for detecting the recording medium;
The control unit according to any one of claims 1 to 3, wherein the control unit controls at least one of the transport unit and the recording unit in accordance with a timing at which the recording medium reaches the print head based on a detection result of the sensor. The image forming apparatus described in 1. The recording means has a gap portion narrower than the thickness of the recording medium in the middle of the conveying path by the conveying means, and the recording medium enters the recording medium to apply pressure necessary for recording to the recording medium. Having a configuration to give,
5. The image forming apparatus according to claim 1, wherein the control data includes at least rush-time speed fluctuation data related to a change in transport speed when the recording medium enters the portion.   The image forming apparatus according to claim 1, wherein the control unit controls a conveyance speed of the recording medium by the conveyance unit based on the control data.   The image forming apparatus according to claim 1, wherein the control unit controls energization energy of one dot by the recording unit based on the control data.   The control unit is configured so that energy per unit area given to the recording medium being conveyed from the print head based on the control data stored in the storage unit becomes a preset amount. The image forming apparatus according to claim 1, wherein at least one of the recording units is controlled.