JP2009012895A - Carrying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To immediately and certainly detect a skew of printing paper generated in the middle of printing, and to promptly and accurately remove the generated skew. <P>SOLUTION: The carrying device comprises a skew detecting means for detecting the skew of the printing paper 20 generated during carrying, and a skew correcting means correcting the skew of the printing paper 20 according to a detection result of the skew by the skew detecting means. The skew detecting means is a pair of sensor rollers 41 (41R, 41L) driven to rotate while contacting with both side ends of the printing paper 20 and detecting the carrying speed of both side ends of the printing paper 20. In the skew correcting means, when the sensor rollers 41 (41R, 41L) detect that the carrying speeds of both end portions of the printing paper 20 are different, both end portions rotate a left end portion 21 or a right end portion 21R of a capstan roller 21 which can be individually rotated, thereby guiding the recording medium in a direction resolving the difference of the carrying speed of both side ends of the printing paper 20. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a conveying apparatus and an image forming apparatus that convey a recording medium by rotating a capstan roller that is sandwiched between a capstan roller and a pinch roller and pressed against the recording medium. More specifically, the present invention relates to a technique that can quickly correct skew of a recording medium accompanying conveyance.

  Conventionally, as an image forming apparatus, for example, a thermal printer including a thermal head facing a platen roller is known. In this thermal printer, by selectively energizing the line-shaped heating resistors (heating elements) arranged in the thermal head according to the gradation level, and using the thermal energy generated at that time, Printing is performed on photographic paper (recording medium).

  Here, the photographic paper is one in which an ink receiving layer is formed on the surface of the base material portion. When printing is performed, photographic paper is fed onto the platen roller with the receiving layer facing up. Next, the thermal head that has been lifted away from the platen roller is lowered, and the thermal head is pressed against the platen roller via the ink ribbon and the photographic paper. In this state, the heating resistors arranged in the thermal head are heated based on a signal output from the drive circuit of the thermal head, and the photographic paper is conveyed. Then, the ink applied to the ink ribbon is transferred to the receiving layer of the photographic paper, and printing is performed.

  When color printing is performed, the thermal head is raised after the first color printing is finished, and the pressure on the platen roller is released. Thereafter, the photographic paper is conveyed in the reverse direction, and reversely fed to the printing start point, and then the printing is performed by superimposing the second color on the first color in the same manner as the first color printing.

  As described above, when printing, it is necessary to transport the photographic paper, but the photographic paper is transported by rotating the capstan roller. In other words, the capstan roller is arranged on the base part side of the photographic paper, the pinch roller is arranged on the receiving layer side of the photographic paper, and the photographic paper is sandwiched between the capstan roller and the pinch roller. Is rotated (in the case of color printing, reverse rotation is also performed), and the printing paper is conveyed. For this reason, the capstan roller is required to transport the photographic paper at a constant speed without positional deviation. In addition, in the case of a color printer, particularly high conveyance accuracy is required to prevent color misregistration when the second and subsequent colors are superimposed.

  However, skew may occur in the printing paper during printing. Then, even if printing is performed without color misregistration, the printed image is inclined with respect to the printing paper. For this reason, when skew occurs in the photographic paper, it is necessary to immediately detect and correct the skew.

Therefore, optical sensors are installed on both ends of the roll paper (printing paper), and when the roll paper is skewed, the light from the optical sensor is blocked by the skewed roll paper. There is known a technique that can detect the occurrence of the above. When skew occurs, the rotational resistance when the roll paper is rotated and pulled out can be changed to correct the skew (see, for example, Patent Document 1).
JP-A-1-17745

In addition, a technology that can correct the skew of photographic paper by providing a pair of side fences that regulate both ends of the photographic paper and making the photographic paper regulating surface of this side fence oblique to the printing direction Is known (see, for example, Patent Document 2).
JP 2000-16640 A

  However, although the technique described in Patent Document 1 can detect the skew of the photographic paper, the detection is an alternative of whether or not the skew is performed. It is not clear how much correction can correct the skew. Also, if paper dust or dust adheres to the optical sensors installed on the top and bottom of the photographic paper, there is a risk that the detection sensitivity will drop or false detection will occur.

  Furthermore, when installing the optical sensor, it is necessary to make a space in the intermediate area (transition area) between the region without skew and the region with skew, so that the optical sensor is turned ON (or OFF) after the skew starts. A time lag occurs until skew is detected. Therefore, it is difficult to set the installation position of the optical sensor. In addition, there is a problem in that there is a lack of immediacy from the occurrence of skew to the time when correction is performed, and the correction is delayed, and skew correction can only be applied to roll paper.

  On the other hand, since the technique described in Patent Document 2 does not include the skew detection means like the optical sensor of Patent Document 1, the above-described problem does not occur. The line cannot be detected. That is, there is a problem in the reliability of correcting the skew because the side fence can only correct the skew of the photographic paper.

  Also, if the side fence does not function, or if skewing occurs beyond the side fence regulations, the printing paper is pinched between the capstan roller and the pinch roller during printing. It cannot be corrected and must wait until after printing. In addition, it is necessary to cancel the state in which the photographic paper is sandwiched in order to correct skew. For this reason, the technique described in Patent Document 2 also has a problem that rapid correction cannot be performed.

  Therefore, the problem to be solved by the present invention is to make it possible to immediately and reliably detect the skew of the photographic paper that occurs in the middle of printing, and to correct the generated skew quickly and accurately. It is.

The present invention solves the above-described problems by the following means.
According to a first aspect of the present invention, a capstan roller for transporting a recording medium and a pinch roller facing the capstan roller are provided, and the recording medium is sandwiched between the capstan roller and the pinch roller. A conveying device that conveys the recording medium by rotation of the capstan roller in pressure contact with the recording medium, the skew detecting means detecting the skew of the recording medium accompanying the conveyance, and the skew detecting means by the skew detecting means. Skew correction means for correcting the skew of the recording medium based on the detection result of the line, the skew detection means detects the conveyance speed at both ends of the recording medium, and the skew correction means When the skew detection means detects that the conveyance speeds at both ends of the recording medium are different, the recording medium is guided in a direction to eliminate the difference in the conveyance speeds.

(Function)
According to the first aspect of the present invention, the skew detection means detects the skew of the recording medium accompanying the conveyance as a difference in the conveyance speed at both ends of the recording medium. That is, at the beginning of the skew of the recording medium, the conveyance speed is different at both ends (the skew is generated because the conveyance speed is different at both ends of the recording medium). It can be detected. Then, the skew correction means guides the recording medium in a direction to eliminate the difference in the conveyance speeds at both ends of the recording medium based on the skew detection result by the skew detection means, and corrects the skew.

  The invention according to claim 4 includes a thermal head in which a plurality of heating elements are arranged, a capstan roller for conveying a recording medium, and a pinch roller facing the capstan roller, and the capstan roller An image forming apparatus that performs printing by causing each heating element of the thermal head to generate heat while conveying the recording medium by rotation of the capstan roller that is sandwiched between the pinch roller and pressed against the recording medium. A skew detection means for detecting skew of the recording medium accompanying the conveyance, and a skew correction means for correcting the skew of the recording medium based on the skew detection result by the skew detection means, Printing control means for controlling printing on the recording medium on the basis of the skew detection result by the skew detection means, and the skew detection means is configured to carry both sides of the recording medium. Each of the skew correction means detects the speed, and when the skew detection means detects that the transport speeds at both ends of the recording medium are different, the skew correction means moves the recording medium in a direction to eliminate the difference in the transport speed. The printing control means interrupts printing by the thermal head until the skew correction is corrected by the skew correction means.

(Function)
In the invention according to claim 4, when the skew detection means detects that the conveyance speeds at both ends of the recording medium are different, the skew correction means records in a direction to eliminate the difference in the conveyance speeds. Guide the media and correct skew. The printing control means interrupts printing by the thermal head until the skew is corrected.

  According to the present invention, since the skew detection means detects the difference in the conveyance speed between the both ends of the recording medium, it is ensured that the skew according to the difference in the conveyance speed from the beginning of the skew (deformation of the skew). Degree). If the skew detection means detects that the conveyance speed is different, the skew correction means guides the recording medium in a direction to eliminate the difference in the conveyance speed and corrects the skew. You can correct lines quickly and accurately. Furthermore, since the printing is interrupted until the skew is corrected by the printing control means, it is possible to prevent the printing from being performed while the recording medium is skewed.

Embodiments of the present invention will be described below with reference to the drawings.
In the following embodiments, a thermal printer 10 that performs color printing on a printing paper 20 (recording medium) with a sublimation thermal head 11 will be described as an example of the image forming apparatus of the present invention. That is, the thermal printer 10 of the present embodiment uses an ink ribbon 30 that is coated with three color inks of yellow (Y), magenta (M), and cyan (C) and a transparent laminate ink (L). Then, each ink is transferred using heat energy generated when current is supplied to a plurality of heat generating resistors 11a (corresponding to the heat generating elements in the present invention) arranged in the thermal head 11, so that the color is applied to the photographic paper 20. This is for printing.

  In the following embodiments, the conveying device of the present invention is installed in the thermal printer 10, and the photographic paper 20 is sandwiched between the capstan roller 21 and the pinch roller 22 so as to be pressed against the photographic paper 20. The photographic paper 20 is conveyed by the rotation of the capstan roller 21.

FIG. 1 is a side view showing an outline of a thermal printer 10 of the present embodiment capable of color printing.
As shown in FIG. 1, the thermal printer 10 of this embodiment includes a thermal head 11 and a platen roller 12. Here, the thermal head 11 is provided so as to face the platen roller 12, and can be displaced in the contact / separation direction with respect to the platen roller 12. When printing is performed, the thermal head 11 moves downward as indicated by an arrow and is displaced so as to press the platen roller 12.

  In such a thermal printer 10, the ink ribbons 30 that are color-coded for each color are stored in a ribbon cassette (not shown), and the arrows shown in FIG. 1 correspond to the gradation data that has undergone color conversion processing. As shown in FIG. 1, after being pulled out from the supply reel 31 and guided to a guide roller (not shown), it passes between the thermal head 11 and the platen roller 12 and toward the take-up reel 32 in the left direction in FIG. Be transported.

  On the other hand, the photographic paper 20 has a base portion and an ink receiving layer, and is set at a predetermined location in the thermal printer 10. And it is pulled out from there as needed and is transported. That is, the drawn photographic paper 20 is guided by a paper conveyance path (not shown), and is fed so that the thermal head 11 and the ink ribbon 30 side is a receiving layer, and the platen roller 12 side is a base material portion. Then, it passes between the thermal head 11 and the platen roller 12, and is set so that the printing start point faces the heating resistor 11 a of the thermal head 11.

  Here, when a print command is input to the thermal printer 10, the thermal head 11 (the state shown in FIG. 1) that has been raised is lowered as indicated by an arrow, and the platen roller 12 is pressed by the heating resistor 11a. . Then, the ink ribbon 30 and the photographic paper 20 are sandwiched between the thermal head 11 and the platen roller 12. That is, when the thermal head 11 is displaced toward the platen roller 12 as indicated by an arrow, a pressing force acts between the thermal head 11 and the platen roller 12 via the ink ribbon 30 and the photographic paper 20. As a result, the ink ribbon 30 and the receiving layer of the photographic paper 20 are pressed. Further, the photographic paper 20 is sandwiched between the capstan roller 21 and the pinch roller 22.

  When gradation data is input in this state, the photographic paper 20 is conveyed in the printing direction (left direction in FIG. 1) by the capstan roller 21 driven to rotate counterclockwise and the driven pinch roller 22. . At the same time, the ink ribbon 30 is pulled out from the supply reel 31 as indicated by the arrow and conveyed toward the take-up reel 32. Each heating resistor 11 a of the thermal head 11 is selectively energized and heat generated from the heating resistor 11 a is transmitted to the ink ribbon 30. Then, the yellow (Y) color ink on the ink ribbon 30 is sublimated and transferred onto the receiving layer of the photographic paper 20 for printing.

  Since color printing is performed for each color, the thermal head 11 is raised and the capstan roller 21 is rotated in reverse each time the ink ribbon 30 is conveyed and the color to be transferred is changed (this time, the clock The printing paper 20 is conveyed in the reverse direction (rightward in FIG. 1) and returned to the printing start point. Then, in the same manner as in the case of yellow (Y), the magenta (M) and cyan (C) color inks are transferred in a superimposed manner to form a color image.

  Furthermore, the transparent laminating ink (L) is transferred to the entire printed area (on the color image) of the photographic paper 20, and the printing is completed. Then, after such a printing operation is completed, a paper discharge operation is performed, and the photographic paper 20 is conveyed in the printing direction as it is, cut to a predetermined length by the cutter 23, and then discharged from a paper discharge port (not shown). The paper is ejected.

  As described above, the thermal printer 10 according to the present embodiment shown in FIG. 1 has the printing paper 20 sandwiched between the capstan roller 21 and the pinch roller 22 and is rotated by the rotation of the capstan roller 21 pressed against the printing paper 20. Each heating resistor 11a of the thermal head 11 is heated while conveying the photographic paper 20, and the three color inks of yellow (Y), magenta (M) and cyan (C) on the ink ribbon 30 and a transparent laminate are used. Ink (L) is transferred to the photographic paper 20 to perform printing, and the printed photographic paper 20 is discharged.

  Further, the thermal printer 10 of the present embodiment has a capstan in which a plurality of protrusions 21a are formed on the pressure contact surface with respect to the photographic paper 20, as shown in FIG. 1, in order to prevent color misregistration when the second and subsequent colors are superimposed. A roller 21 is used. That is, the capstan roller 21 on which the protrusion 21 a is formed is pressed against the photographic paper 20, so that the protrusion 21 a bites into the base material portion (lower side) of the photographic paper 20 by the pressure contact force of the capstan roller 21 during conveyance. By doing so, a sufficient conveying force is secured and color misregistration does not occur.

  However, when skew occurs on the photographic paper 20 during printing, the image formed on the discharged photographic paper 20 is not printed on the photographic paper 20 even if printing is performed without color misregistration. It will be inclined and the print quality will deteriorate. For this reason, when skew occurs as the photographic paper 20 is conveyed, it is required to detect the skew immediately and correct the skew appropriately.

  Therefore, the thermal printer 10 according to the present embodiment is a skew detection means for detecting the skew of the photographic paper 20 accompanying the conveyance. The thermal printer 10 contacts both side edges of the photographic paper 20, and the protrusion 41a is formed when the photographic paper 20 is conveyed. A sensor roller 41 is provided that bites into the substrate portion of the photographic paper 20 and rotates in a driven manner. That is, the photographic paper 20 is sandwiched between the opposing sub-rollers 42, and the conveyance speed at both ends of the photographic paper 20 is converted into the rotation speed of the sensor roller 41. Can be detected and used as a skew detection means.

FIG. 2 is a plan view showing the configuration of the skew detection means in the thermal printer 10 of this embodiment.
As shown in FIG. 2, the photographic paper 20 is sandwiched between a capstan roller 21 and a pinch roller 22. Then, printing is performed while the printing paper 20 is conveyed in the printing direction (left direction in FIG. 2). In other words, the capstan roller 21 on which the protrusions 21a are formed is pressed against the substrate portion side (lower side) of the photographic paper 20, and if the capstan roller 21 is rotated counterclockwise, the photographic paper 20 is printed. Is conveyed in the printing direction.

  A pair of left and right sensor rollers 41 (corresponding to the skew detection means in the present invention) and a pair of left and right sub rollers 42 facing the sensor roller 41 are disposed upstream of the photographic paper 20 in the printing direction. ing. The sensor roller 41L (and the opposing sub-roller 42) on the left side (the lower side in FIG. 2A) in the printing direction is in contact with the left end of the photographic paper 20. Similarly, the right side (upper side in FIG. 2A) sensor roller 41 </ b> R (and the opposing sub roller 42) is in contact with the right end of the photographic paper 20.

  As described above, in the thermal printer 10 according to the present embodiment, the sensor roller 41 is in pressure contact with the base material side of the photographic paper 20, and the photographic paper 20 is sandwiched between the sub roller 42. Therefore, when the photographic paper 20 is conveyed by the rotation of the capstan roller 21, the sensor roller 41 and the sub roller 42 are driven to rotate according to the conveyance speed of the photographic paper 20 due to the pressure contact force with the photographic paper 20. Accordingly, the sensor rollers 41 can detect the conveyance speeds at both ends of the photographic paper 20. A protrusion 41a is formed on the surface of the sensor roller 41 so that the sensor roller 41 can be easily rotated.

  Here, when the photographic paper 20 is fed for the first time, the sub-roller 42, the pinch roller 22, and the thermal head 11 are raised, and the lower side thereof is open. Therefore, the photographic paper 20 is in a state of being freely movable from the sub roller 42 toward the pinch roller 22. When the photographic paper 20 passes through the capstan roller 21, the sub-roller 42 and the pinch roller 22 that have been raised so far are lowered, and the photographic paper 20 is sandwiched between the sensor roller 41 and the sub-roller 42. The photographic paper 20 is sandwiched between the capstan roller 21 and the pinch roller 22.

  At this time, the sensor roller 41 and the sub roller 42 are set so as to be in an appropriate pressure contact state. In other words, this pressure contact state is for driven rotation of the sensor roller 41 as the photographic paper 20 is conveyed. If the pressure contact force is too weak, the sensor roller 41 will idle even if the photographic paper 20 is conveyed. The conveyance speed of the photographic paper 20 and the rotation speed of the sensor roller 41 do not match. As a result, the conveyance speed of the photographic paper 20 by the sensor roller 41 cannot be detected. On the other hand, if the pressure contact force is too strong, spike marks caused by the protrusions 41a of the sensor roller 41 become conspicuous on the photographic paper 20 and the print quality is lowered. Therefore, the sub-roller 42 is lightly pressed to the extent that the sensor roller 41 does not idle, and the sensor roller 41 is pressed in a range where the spike marks are not noticeable. The pressing force of the pinch roller 22 is set so that a sufficient conveying force for the photographic paper 20 can be obtained.

  As will be described later, when skew occurs in the photographic paper 20, the conveyance speed of the photographic paper 20 becomes different at both ends of the photographic paper 20. Therefore, the sensor roller 41 is brought into pressure contact with a position as close as possible to both ends of the photographic paper 20 (a position where the difference in the conveyance speed due to the occurrence of skew is large) so that the difference in the conveyance speed can be detected with high sensitivity. However, the position where the pressure contact width becomes too narrow and the sensor roller 41 does not idle is set.

  The thermal printer 10 of this embodiment starts printing in this state. However, when the photographic paper 20 is conveyed straight without being skewed, the conveyance speeds at the left and right ends of the photographic paper 20 are the same. Therefore, the rotational speeds of the sensor roller 41L on the left side (lower side in FIG. 2A) and the sensor roller 41R on the right side (upper side in FIG. 2A) are the same. If the heat generated from the heating resistor 11a of the thermal head 11 is transmitted to the ink ribbon 30 in this state and the ink is transferred to the photographic paper 20, normal printing is performed.

  On the other hand, when the photographic paper 20 is conveyed obliquely, the transferred image is inclined with respect to the photographic paper 20 and the print quality is deteriorated. Therefore, the skew is detected by the sensor roller 41. That is, when the photographic paper 20 starts skewing, the conveyance speed becomes different at both ends of the photographic paper 20 (because the conveyance speed is different at both ends of the photographic paper 20, skew is generated). The rotational speeds of the sensor roller 41L and the sensor roller 41R are also different. Therefore, the skew can be detected by detecting the rotation speed of the sensor roller 41.

  For example, at the beginning of the skew, the photographic paper 20 starts to rotate counterclockwise (downward in FIG. 2A), and as a result, tilts to the left (lower side in FIG. 2A). Suppose that a state skew occurs. In this case, since the counterclockwise rotation speed is added to the conveyance speed of the photographic paper 20 when skewed, the right side (the upper side in FIG. 2A) that is outside the left side that is the inside of the rotation is conveyed. Increases speed. Therefore, the rotation speed of the sensor roller 41R is faster than the rotation speed of the sensor roller 41L. On the other hand, if skewing in a state tilted to the right side occurs, the rotation speed of the sensor roller 41L becomes faster than the rotation speed of the sensor roller 41R.

  Accordingly, the left skew of the photographic paper 20 is “L side skew”, the right skew is “R side skew”, the rotation speed of the left sensor roller 41L is “L side rotation speed”, and the right side. When the rotational speed of the sensor roller 41R is “R side rotational speed”, it means “R side rotational speed> L side rotational speed = L side skew”, and “L side rotational speed> R side rotational speed = R”. It means “side skew”. Further, the stability at “L-side rotational speed = R-side rotational speed> 0” means that skew does not occur in the photographic paper 20, and “L-side rotational speed = R-side rotational speed = 0” This means that the conveyance of the photographic paper 20 has stopped (sticking due to idling or slipping of the capstan roller 21). Furthermore, a state where the L-side rotational speed and the R-side rotational speed are not stable (such as fluctuation in a short time) means the occurrence of uneven feeding of the photographic paper 20 in the printing direction.

  As described above, the thermal printer 10 according to the present embodiment prints the skew of the photographic paper 20 accompanying the conveyance by the pair of sensor rollers 41 (41L, 41R) that are driven to rotate by contacting the left and right ends of the photographic paper 20. This can be detected as a difference in transport speed between the left and right ends of the paper 20. Various behaviors of the photographic paper 20 (for example, feeding unevenness, sticking, etc.) can also be detected as changes in the rotational speed of the sensor roller 41 (41L, 41R).

  Here, as shown in FIG. 2, an encoder drive gear 43 (43L, 43R) is connected to the sensor roller 41 (41L, 41R), and the encoder drive gear 43 (43L, 43R) is a frequency generator. 44 (44L, 44R). Therefore, when the sensor roller 41 (41L, 41R) rotates, the frequency generator 44 (44L, 44R) rotates via the encoder drive gear 43 (43L, 43R). The rotational speed of the frequency generator 44 (44L, 44R) is detected by the photocoupler 45 (45L, 45R).

  Accordingly, the conveyance speed at both ends of the photographic paper 20 is converted into the rotational speed of the sensor roller 41 when the photographic paper 20 is sandwiched between the sensor roller 41 and the sub-roller 42, and then the encoder drive gear 43 and It is detected by the photocoupler 45 via the frequency generator 44. Therefore, the sensor roller 41, the sub roller 42, the encoder drive gear 43, the frequency generator 44, and the photocoupler 45 constitute a skew detection means. The thermal printer 10 of this embodiment includes a skew correction unit that corrects the skew of the photographic paper 20 based on the skew detection result of the skew detection unit.

FIG. 3 is a conceptual diagram showing the configuration of the skew correction means in the thermal printer 10 of the present embodiment.
As described above, the conveyance speed at both ends of the photographic paper 20 is converted into the rotation speed of the sensor roller 41 (see FIG. 2), and is finally detected by the photocoupler 45.

  Here, the photocoupler 45 detects the number of rotations of the frequency generator 44 as shown in FIG. That is, the frequency generator 44 is formed with a plurality of detection units 44 a, and when the detection unit 44 a passes through the photocoupler 45, the rotational speed of the frequency generator 44 is detected. The conveyance speed of the left end of the photographic paper 20 is detected by the frequency generator 44L and the photocoupler 45L, and the conveyance speed of the right end of the photographic paper 20 is detected by the frequency generator 44R and the photocoupler 45R. In order to improve the resolution of the conveyance speed of the photographic paper 20, the gear ratio of the encoder drive gear 43 (see FIG. 2) may be increased.

  When the conveyance speeds at the left and right ends of the photographic paper 20 are detected in this way, the detection result is transmitted to a printer control unit (not shown) functioning as a skew correction unit in the present invention, and the printer control unit Controls the rotation of the capstan roller 21 based on the detection result. In other words, the capstan roller 21 has a left end portion 21L, a central portion 21C, and a right end portion 21R that can be rotated separately, and the left end portion 21L is a skew correction motor 51L (in accordance with the present invention) according to a command from the printer control unit. The right end portion 21R is rotated by driving a skew correction motor 51R (corresponding to the skew correction means in the present invention) according to a command from the printer control unit. .

  Therefore, the capstan roller 21 in the thermal printer 10 of the present embodiment rotates not only the normal photographic paper 20 but also the left end portion 21L or the right end portion 21R by the skew correction motor 51 (51L, 51R). The skew of the photographic paper 20 can be corrected. Therefore, the left end portion 21L and the right end portion 21R serve as skew correction means in the present invention.

  For example, if the photocoupler 45R detects that the rotation of the frequency generator 44R has become faster, the printer control unit (not shown) determines that skewing tilted to the left has occurred on the photographic paper 20 (“ R side rotation speed> L side rotation speed = L side skew ”). Then, the skew correction motor 51L is controlled by the printer controller, and the rotation of the left end portion 21L of the capstan roller 21 becomes faster than the right end portion 21R. Therefore, due to this rotation of the left end portion 21L, a force in a direction tilting in the direction opposite to the skew direction (a direction in which the difference in transport speed between the both ends of the photographic paper 20 is eliminated) acts on the photographic paper 20, and printing is performed in that direction. Since the paper 20 is guided, the skew is immediately corrected.

  At this time, if the printing by the thermal head 11 is continued after the occurrence of the skew of the photographic paper 20 is detected until the skew is corrected, the print quality is deteriorated. For this reason, in the thermal printer 10 of the present embodiment, a printer control unit (not shown) also functions as a print control unit in the present invention. Until the skew is corrected, a command from the printer control unit is provided. Thus, printing by the thermal head 11 is interrupted. That is, the thermal head 11 is lifted by a command from the printer control unit, and printing is not performed during skew correction. Note that after the skew is corrected, the thermal head 11 is quickly lowered and printing is resumed.

  If the photocoupler 45L and the photocoupler 45R detect that both the frequency generator 44L and the frequency generator 44R have stopped rotating, the printer control unit (not shown) performs a sticking or the like such that the photographic paper 20 has stopped. Judge that it is in a state. In this case, the printer control unit as the printing control means raises the thermal head 11 to prevent printing at the same place.

  Furthermore, if the photocoupler 45L or the photocoupler 45R detects that the rotation of the frequency generator 44L or the frequency generator 44R fluctuates, the printer control unit (not shown) may cause feed unevenness on the photographic paper 20. Judge that Then, the printer control unit controls driving of the skew correction motor 51L or the skew correction motor 51R to adjust the rotation of the left end portion 21L or the right end portion 21R of the capstan roller 21. For this reason, even if the feeding unevenness occurs in the photographic paper 20, the normal printing is immediately restored.

  As described above, in the thermal printer 10 of the present embodiment, the left end portion 21L or the right end portion 21R of the capstan roller 21 can be rotated separately, and by rotating the left end portion 21L or the right end portion 21R individually, Not only the normal conveyance of the photographic paper 20, but also the skew of the photographic paper 20 can be corrected, and sticking and feeding unevenness can be dealt with.

FIG. 4 is a partial cross-sectional view showing the capstan roller 21 in the thermal printer 10 of the present embodiment.
As shown in FIG. 4, the capstan roller 21 is composed of three parts, a left end part 21L, a central part 21C, and a right end part 21R. And the protrusion 21a is formed in the three surfaces, respectively. Therefore, sufficient conveyance force is ensured for each part. The outer diameters of these three parts are the same.

  A left drive shaft 52L is connected to the left end portion 21L, and a right drive shaft 52R is connected to the right end portion 21R. The left drive shaft 52L is connected to the skew correction motor 51L (see FIG. 3), and the right drive shaft 52R is connected to the skew correction motor 51R (see FIG. 3). Therefore, the left end portion 21L and the right end portion 21R can be rotated separately.

  Here, a one-way clutch 53 is disposed in each of the left end 21L and the right end 21R. That is, the left drive shaft 52L is connected to the left end portion 21L via the one-way clutch 53L, and the right drive shaft 52R is connected to the right end portion 21R via the one-way clutch 53R. Therefore, when the left drive shaft 52L is driven, the left end portion 21L rotates in the forward direction but idles in the reverse direction. Similarly, when the right drive shaft 52R is driven, the right end portion 21R rotates in the forward direction but idles in the reverse direction.

  Further, the middle drive shaft 52C is connected to the central portion 21C. The middle drive shaft 52C is also connected to the left end 21L and the right end 21R via the one-way clutch 53. Therefore, when the middle drive shaft 52C is rotationally driven in the positive direction, the left end portion 21L, the central portion 21C, and the right end portion 21R all rotate in the positive direction. On the other hand, when the middle drive shaft 52C is rotationally driven in the reverse direction, only the central portion 21C rotates in the reverse direction, and the left end portion 21L and the right end portion 21R rotate idle.

FIG. 5 is a plan view showing a method of conveying the photographic paper 20 by the capstan roller 21 of the thermal printer 10 of the present embodiment.
When the photographic paper 20 is conveyed, the capstan roller 21 is pressed against the photographic paper 20 by the pressing force of the pinch roller 22 (see FIG. 1).

  In this state, when the middle drive shaft 52C (see FIG. 4) is rotationally driven in the forward direction, all of the left end portion 21L, the central portion 21C, and the right end portion 21R are integrally rotated in the forward direction. Therefore, the photographic paper 20 is conveyed straight as shown in FIG. At the time of printing, the thermal head 11 (see FIG. 1) is lowered, and normal printing is performed by straight conveyance. When returning the paper for printing the second and subsequent colors, the thermal head 11 (see FIG. 1) and the sub-roller 42 (see FIG. 1) are raised, and the middle drive shaft 52C (see FIG. 4) is rotated in the reverse direction. To do. Then, the central portion 21C rotates in the reverse direction, and the photographic paper 20 is conveyed in the reverse direction and returned to the printing start point.

  Here, the state at the time of conveyance of the photographic paper 20 is confirmed by the sensor roller 41 (41L, 41R). In other words, the conveyance speed at both ends of the photographic paper 20 is converted into the rotation speed of the sensor roller 41 (41L, 41R), and then passes through the encoder drive gear 43 (43L, 43R) and the frequency generator 44 (44L, 44R). Then, it is detected by the photocoupler 45 (45L, 45R). Therefore, if the detection result of the photocoupler 45L and the detection result of the photocoupler 45R are the same, the photographic paper 20 is traveling straight without being skewed.

FIG. 6 is a plan view showing a skew correction method of the photographic paper 20 by the capstan roller 21 of the thermal printer 10 of the present embodiment.
When the photographic paper 20 is skewed leftward, as shown in FIG. 6, at the beginning of the skew, the photographic paper 20 rotates counterclockwise in the printing direction, and is located outside the right side (right side). The end) is faster. Then, the rotational speed of the sensor roller 41R becomes higher than the rotational speed of the sensor roller 41L. The rotational speed of the sensor roller 41 (41L, 41R) is determined by the encoder drive gear 43 (43L, 43R) and the frequency generator 44 (44L, 44R) and is detected by the photocoupler 45 (45L, 45R).

  Here, since the degree of skew of the photographic paper 20 can be grasped by the difference in rotational speed between the sensor roller 41L and the sensor roller 41R and the duration of this speed difference, the degree of skew of the photographic paper 20 (photocoupler). 45 (the detection result of 45L, 45R)), the rotation speed of the left end portion 21L of the capstan roller 21 is corrected. That is, the left end portion 21L is rotated faster than the right end portion 21R, and the photographic paper 20 is tilted to the right opposite to the skew feeding direction (the difference in the conveyance speeds at both ends of the photographic paper 20 is eliminated). Then, the photographic printing paper 20 is guided straight by the high-speed rotation of the left end portion 21L, and the skew is corrected.

  At this time, the difference in rotational speed between the left end portion 21L and the right end portion 21R and the duration of this speed difference are matched when the skew occurs. That is, the same speed difference as the rotation speed difference between the sensor roller 41L and the sensor roller 41R detected by the photocoupler 45 (45L, 45R) is set between the left end portion 21L and the right end portion 21R. Further, the left end portion 21L is rotated at high speed for the same time as the duration of the speed difference between the sensor roller 41L and the sensor roller 41R. While the skew correction is being performed, detection by the photocoupler 45 (45L, 45R) is invalidated.

  Such high-speed rotation of the left end portion 21L is restored when the skew of the photographic paper 20 is corrected and straightened, and is the same as the right end portion 21R and the central portion 21C. Further, the detection by the photocoupler 45 (45L, 45R) is enabled again. Then, the left end portion 21L, the central portion 21C, and the right end portion 21R all rotate together to return to the state where the photographic paper 20 is conveyed straight, and if there is a skew after that, Is detected. Note that when the photographic paper 20 is skewed to the right, it is corrected in the same manner as when skewed to the left.

  As described above, according to the thermal printer 10 of the present embodiment, the skew of the photographic paper 20 accompanying the conveyance is different between the conveyance speeds at both ends of the photographic paper 20 (differences in the rotation speed between the sensor roller 41L and the sensor roller 41R). ) Can be detected. When it is detected that the conveyance speeds at the both ends of the photographic paper 20 are different, the left end 21L or the right end 21R of the capstan roller 21 is individually rotated to convey the both ends of the photographic paper 20. The photographic paper 20 is guided in a direction to eliminate the difference in speed, and the skew is corrected.

  Accordingly, the difference in conveyance speed (change in behavior) at both ends of the photographic paper 20 can be grasped sequentially, and when skew occurs in the photographic paper 20 during printing, the skew can be detected immediately and reliably. . In addition, the degree of skew that has occurred can be grasped, and skew can be corrected quickly and accurately even during printing. Furthermore, not only skewing (skew) of the photographic paper 20, but also sticking (stop of the photographic paper 20 due to slipping), uneven feeding of the photographic paper 20 in the printing direction, and the like can be detected and corrected. Therefore, a high-quality printing result can always be obtained.

The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and various modifications such as the following are possible.
(1) In this embodiment, the photographic paper 20 (paper medium) is used as a recording medium. However, the present invention is not limited to this, and a plastic medium may be used. Further, the skew detection means is not limited to the sensor roller 41 (41L, 41R), but may be any one that can detect the conveyance speeds at both ends of the photographic paper 20 respectively. Furthermore, the skew correction means is not limited to the capstan roller 21 (the left end portion 21L and the right end portion 21R), but may be any device that can guide the photographic paper 20 in a direction that eliminates the difference in the conveyance speed of the photographic paper 20. .

  (2) In this embodiment, the protrusion 41a is formed on the surface of the sensor roller 41, and the protrusion 41a bites into the photographic paper 20 so as to be driven and rotated. However, the surface of the sensor roller 41 is not limited to the protrusion 41a. There may be a flat surface as long as it does not idle with respect to the photographic paper 20. Further, in the present embodiment, the capstan roller 21 is configured with three portions, that is, the left end portion 21L, the central portion 21C, and the right end portion 21R. However, if at least both end portions can be rotated separately, the capstan roller 21 includes two portions. It may be composed of four or more.

It is a side view which shows the outline | summary of the thermal printer of this embodiment. It is a top view which shows the structure of the skew detection means in the thermal printer of this embodiment. It is a conceptual diagram which shows the structure of the skew correction means in the thermal printer of this embodiment. It is a partial cross section figure which shows the capstan roller in the thermal printer of this embodiment. It is a top view which shows the conveyance method of the printing paper by the capstan roller of the thermal printer of this embodiment. It is a top view which shows the skew correction method of the printing paper by the capstan roller of the thermal printer of this embodiment.

Explanation of symbols

10 Thermal printer (image forming device)
11 Thermal head 11a Heating resistor (heating element)
20 photographic paper (recording medium)
21 Capstan roller 21L Left end (skew correction means)
21C center part 21R right end part (skew correction means)
22 Pinch roller 41, 41L, 41R Sensor roller (skew detection means)
42 Sub-rollers 51, 51L, 52R Skew straightening motor (skew straightening means)

Claims (4)

A capstan roller for conveying a recording medium;
A pinch roller facing the capstan roller,
A conveying device that sandwiches a recording medium between the capstan roller and the pinch roller and conveys the recording medium by rotation of the capstan roller pressed against the recording medium;
Skew detection means for detecting skew of the recording medium accompanying conveyance;
A skew correction means for correcting skew of the recording medium based on the skew detection result by the skew detection means,
The skew detection means detects the conveyance speed at both ends of the recording medium,
The skew correction means guides the recording medium in a direction to eliminate the difference in the conveyance speed when the skew detection means detects that the conveyance speeds at both ends of the recording medium are different. Conveying device to do. In the conveyance apparatus of Claim 1,
The skew detection means is a pair of sensor rollers that respectively detect the conveyance speed at both ends of the recording medium by contacting and rotating the both ends of the recording medium. In the conveyance apparatus of Claim 1,
The capstan roller can rotate separately at least at both ends,
The skew correction means guides the recording medium in a direction to eliminate the difference in the conveyance speeds at both ends of the recording medium by individually rotating the left end portion or the right end portion of the capstan roller. Conveying device. A thermal head in which a plurality of heating elements are arranged;
A capstan roller for conveying a recording medium;
A pinch roller facing the capstan roller,
A recording medium is sandwiched between the capstan roller and the pinch roller, and each heating element of the thermal head is heated while the recording medium is conveyed by the rotation of the capstan roller pressed against the recording medium, thereby performing printing. An image forming apparatus for performing

Skew detection means for detecting skew of the recording medium accompanying conveyance;
Based on the skew detection result by the skew detection means, skew correction means for correcting skew of the recording medium;
Printing control means for controlling printing on the recording medium based on the skew detection result by the skew detection means,
The skew detection means detects the conveyance speed at both ends of the recording medium,
The skew correction means guides the recording medium in a direction to eliminate the difference in the conveyance speed when the skew detection means detects that the conveyance speed at both ends of the recording medium is different,
The image forming apparatus, wherein the printing control unit interrupts printing by the thermal head until the skew feeding is corrected by the skew feeding correcting unit.

Images