JP2011051747A - Printer and end part detecting method of printing medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printer and an end part detecting method of a printing medium capable of reducing damage to the printing medium, and capable of also detecting an end part of the printing medium by following a carrying speed of the printing medium. <P>SOLUTION: This printer 1 has an optical sensor 8 being a center paper feeding system and arranging a distance from the center of a carrying passage 34 for carrying printing paper P in a position nearer than 1/2 of a width of the printing paper narrow in a first width among the printing paper of the size loadable in the printer 1, a control part 9 being an end part detecting means for detecting the end part in the carrying direction of the printing paper P carried in the carrying passage 34 by comparing a detection signal provided by this optical sensor 8 with a predetermined threshold value, and a control part 9 being a changing means for changing the threshold value or detecting sensitivity of the optical sensor 8 or light projection intensity of the optical sensor 8 in response to a printing surface state of the printing paper. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a printing apparatus and a printing medium edge detection method.

  A printing apparatus that performs printing on a printing medium such as printing paper is configured to perform printing while transporting the printing medium in a direction (sub-scanning direction) orthogonal to the printing direction (main scanning direction) by the print head. There is something. In addition, there are roughly two types of printing medium conveyance methods of such a printing apparatus. One is a method in which the print medium is transported in a state of being moved to one side of the transport path, and the other is a center in the direction perpendicular to the transport direction of the print medium in the center of the transport path in the main scanning direction. This is a so-called center paper feeding method in which transport is performed in a positioned state. In this center paper feeding type printing apparatus, the print medium is transported along the center of the printable range in the left-right direction by the print head.

  In a printing apparatus that transports a print medium in a state where the print medium is brought close to one side of the transport path, the print medium is moved toward the roller that transports the print medium because of the necessity to cope with print media of a plurality of sizes. It is necessary to be biased to one side. Therefore, there is a possibility that the recording medium is conveyed while being skewed. On the other hand, the center paper feeding method has an advantage that a skew is hardly generated when a recording medium is conveyed because the rollers for conveying the printing medium can be arranged symmetrically with respect to the center of the conveying path.

  In a center paper feeding type printing apparatus, for example, as disclosed in Patent Document 1, by using a retract lever that can optically detect displacement by an optical sensor, Detection can be performed.

JP 2007-119153 A

  However, when the end of the print medium is detected using the retract lever, there is a problem that the print medium is damaged because the retract lever contacts the print medium. Further, when the printing medium conveyance speed is high, there is a problem that the displacement speed of the retract lever may not be able to follow the conveyance speed.

  Accordingly, the present invention provides a printing apparatus and a printing medium edge detection method capable of reducing damage to the printing medium and further detecting the edge of the printing medium following the conveyance speed of the printing medium. The purpose is to provide.

  In order to solve the above-described problem, in a center-feed-type printing apparatus, the distance from the center of the conveyance path through which the recording medium is conveyed is the narrowest print medium of a size that can be loaded into the printing apparatus. An end in the transport direction of the print medium transported on the transport path by comparing the optical sensor disposed at a position closer than half the width of the medium and a detection signal obtained by the optical sensor with a predetermined threshold value. And edge changing means for changing the threshold or the detection sensitivity of the optical sensor or the light projection intensity of the optical sensor in accordance with the state of the printing surface of the printing medium.

  In addition to the above invention, the changing unit of the printing apparatus changes the threshold value, the detection sensitivity, or the light projection intensity according to the state of printing already performed on the printing medium when the printing apparatus is in the duplex printing mode. I decided to.

  In addition to the above invention, the printing apparatus includes a counting unit that counts the number of occurrences of the threshold.

  In addition to the above invention, the optical sensor of the printing apparatus is a reflection type optical sensor, and when there is no print medium within the projection range of the light emitted from the light projecting unit, the portion that receives the light from the light projecting unit is Suppose that the light from the light projecting part is not reflected in the direction of the light receiving part of the reflective photosensor.

  In order to solve the above-described problem, in a print medium end detection method for detecting an end in a transport direction of a print medium loaded and transported in a center paper feeding type printing apparatus, a transport path through which a recording medium is transported The optical sensor is arranged at a position where the distance from the center is closer than half the width of the narrowest print medium of the size that can be loaded into the printing apparatus, and a detection signal obtained by the optical sensor Is compared with a predetermined threshold value to detect an end portion in the conveyance direction of the print medium conveyed on the conveyance path, and the threshold value or the detection sensitivity of the optical sensor or the optical sensor according to the state of the printing surface of the print medium. The light projection intensity is changed.

It is a figure which shows schematic structure inside when the printing apparatus which concerns on embodiment of this invention is seen from a side surface direction. FIG. 2 is a block diagram illustrating an overall configuration of the printing apparatus illustrated in FIG. 1. FIG. 3 is a diagram illustrating a schematic configuration of the photosensor illustrated in FIGS. 1 and 2. It is a graph which shows the change of the output voltage from a photosensor. It is an enlarged view which expands and shows the arrangement | positioning part of an optical sensor and a lower guide. It is a figure which shows arrangement | positioning of the optical sensor when a printing apparatus is seen from upper direction. It is a graph which shows the change of the output voltage of an optical sensor when the printing paper by which the black solid printing was detected. It is a graph which shows the change of the output voltage of an optical sensor when the printing paper by which the black solid printing with the border was detected is detected.

(Embodiment)
Hereinafter, a printing apparatus 1 according to an embodiment of the present invention will be described with reference to the drawings. Note that the edge detection method of the print medium will be described in conjunction with the operation of the printing apparatus 1.

(Overall configuration of inkjet printing apparatus 1)
FIG. 1 is a diagram showing a schematic internal configuration of a printing apparatus 1 according to an embodiment of the present invention as viewed from the side. FIG. 2 is a block diagram illustrating an overall configuration of the printing apparatus 1. The printing apparatus 1 is a so-called center supply that transports the printing paper P in a state in which the center of the printing paper P that is a printing medium is aligned with the center of the printable range in the left-right direction (main scanning direction) by the printing mechanism 2. It has a paper-type configuration. In the following description, the direction indicated by the arrow X1 in FIG. 1 is the front (front side), the opposite direction X2 is the rear (rear side), and when looking from the front to the rear, the left hand side (see FIG. 6 in the Y1 direction) is left. (Left side) and right hand side (Y2 direction see FIG. 6) will be described as the right side (right side). Further, the description will be made assuming that the direction indicated by the arrow Z1 in FIG. 1 is the upper side (upper side) and the opposite direction Z2 is the lower side (lower side).

(Configuration of printing apparatus 1)
The printing apparatus 1 includes a printing mechanism 2, a rear paper feeding mechanism 3, a front paper feeding mechanism 4, a transport mechanism 5, a paper discharge mechanism 6, a reversing mechanism 7, an optical sensor 8, a control unit 9 (see FIG. 2), and the like. .

  The printing mechanism 2 includes a carriage 10 and a print head 11, and is a mechanism for forming an image on the print paper P by ejecting ink from the print head 11 while moving the carriage 10 left and right. The carriage 10 is guided by the guide shaft 12 and can move in the left-right direction.

  The rear paper feeding mechanism 3 is a mechanism for feeding the printing paper P stored in the paper stocker 13 provided on the back surface of the printing apparatus 1 to the transport mechanism 5. The rear paper feed mechanism 3 includes a paper stocker 13, a hopper 14, a paper feed roller 15, a retard roller 16, and the like. The hopper 14 is driven by a hopper drive motor (not shown). The paper feed roller 15 is driven by a paper feed roller drive motor (not shown).

  The front paper feeding mechanism 4 is a mechanism for feeding the printing paper P stored in the paper tray 17 that can be loaded from the front surface of the printing apparatus 1 to the transport mechanism 5. The front paper feed mechanism 4 has a pickup roller 18, a paper feed roller 19, a separation roller 20 and the like in addition to the paper tray 17. The pickup roller 18 is driven by a pickup roller drive motor (not shown). The paper feed roller 19 is driven by a paper feed roller drive motor (not shown).

  The transport mechanism 5 is a mechanism for transporting the print paper P fed from the rear paper feed mechanism 3 or the front paper feed mechanism 4 to a predetermined position with respect to the print head 11. The transport mechanism 5 includes a transport roller 21 and a transport-side driven roller 22. The transport roller 21 is driven by a transport roller drive motor (not shown).

  The paper discharge mechanism 6 is a mechanism for discharging the printed printing paper P to the outside of the printing apparatus 1. The paper discharge mechanism 6 includes a paper discharge roller 23, a paper discharge side driven roller 24, and the like. The paper discharge roller 23 is driven by a paper discharge roller drive motor (not shown).

  The reversing mechanism 7 is a mechanism for reversing the front and back surfaces of the printing paper P when the operation mode of the printing apparatus 1 is set to a double-sided printing mode in which printing is performed on both sides of the printing paper P. In the double-sided printing mode, the printing paper P printed on one side is sent to the paper discharge mechanism 6 side and then conveyed backward from the paper discharge mechanism 6 side. Then, the reversing mechanism 7 is reversed so that one surface on which printing is performed is directed downward and the other surface is directed upward facing the print head 11. The reversing mechanism 7 has a movable guide 25, a reversing roller 26, and the like.

  The transport mechanism 5 has a function of transporting the print paper P fed from the rear paper feed mechanism 3 or the front paper feed mechanism 4 to a predetermined position with respect to the print head 11, and in the duplex printing mode. It also has a function of transporting the printing paper P from the paper discharge mechanism 6 side to the reversing mechanism 7.

  The optical sensor 8 has a function for detecting the leading edge and the trailing edge of the printing paper P conveyed in the printing apparatus 1.

  The control unit 9 includes an arithmetic processing unit such as a CPU (Central Processing Unit) or a microcomputer, a PROM (Programmable Read-Only Memory) in which processing programs relating to various operations of the printing apparatus 1 are stored, a personal computer PC (FIG. 2), a RAM (Random Access Memory) that functions as a working memory, and an EEPROM (Electrically Erasable Programmable Read-Only Memory) that stores various information about the printing apparatus 1. ) And the like, and controls the entire printing apparatus 1. The controller 9 can print on the printing paper P by controlling each mechanism based on print data received from an external device such as a personal computer PC (see FIG. 2).

(Operation of the printing apparatus 1)
Next, the operation of the printing apparatus 1 will be described. The operation and driving timing of each mechanism of the printing apparatus 1 is controlled by the control unit 9.

(Rear feeding operation)
First, a rear paper feeding operation in which the printing paper P accommodated in the paper stocker 13 provided on the back surface (rear side) of the printing apparatus 1 is fed to the transport mechanism 5 will be described.

  At the start of paper feed, the control unit 9 issues a paper feed start command to the rear paper feed mechanism 3. By this command, a hopper drive motor (not shown) is driven, and the hopper 14 is rotated clockwise around the shaft portion 14A as a rotation shaft. As a result, the uppermost printing paper P among the printing papers P placed on the hopper 14 comes into contact with the paper feed roller 15. The printing paper P in contact with the paper feed roller 15 is fed forward by the rotation of the paper feed roller 15 and is sandwiched between the paper feed roller 15 and the retard roller 16. The printing paper P is transported from the paper stocker 13 onto the lower guide 27 and fed to the transport mechanism 5 by the rotation of the paper feed roller 15 and the retard roller 16. The printing paper P conveyed on the lower guide 27 passes below the optical sensor 8 and reaches the conveyance mechanism 5.

(Front feed operation)
Next, a front paper feeding operation in which the printing paper P stored in the paper tray 17 provided on the front side of the printing apparatus 1 is fed to the transport mechanism 5 will be described. Note that one of the above-described rear paper feeding operation and front paper feeding operation is selectively performed, and the rear paper feeding operation and the front paper feeding operation are not performed at the same time. For example, the control unit 9 performs either a rear paper feeding operation or a front paper feeding operation based on a user's instruction for rear paper feeding or front paper feeding to the printing apparatus 1.

  At the start of paper feed, the control unit 9 issues a paper feed start command to the front paper feed mechanism 4. By this command, a pickup roller drive motor (not shown) is driven, and the pickup roller 18 is rotated. In the paper tray 17, the pickup roller 18 is in contact with the uppermost printing paper P among the printing papers P placed on the paper tray 17. Therefore, when the pickup roller 18 rotates, the printing paper P is sent to the paper feed roller 19.

  The printing paper P sent out from the paper tray 17 to the paper feed roller 19 side is sandwiched between the paper feed roller 19 and the separation roller 20. The printing paper P is transported from the paper tray 17 onto the lower guide 27 by the rotation of the paper feed roller 19 and the separation roller 20 and is fed to the transport mechanism 5. The printing paper P sent out from the paper tray 17 onto the lower guide 27 is guided from the paper tray 17 onto the lower guide 27 by the lower guide surface 25A formed on the lower side of the movable guide 25, and the lower guide surface 25A. Then, the sheet is conveyed onto the lower guide 27 through the paper path 28 between the lower guide 27 and the lower guide 27. The printing paper P conveyed on the lower guide 27 passes below the optical sensor 8 and reaches the conveyance mechanism 5.

(Transport / discharge operation)
The print paper P fed from the rear paper feed mechanism 3 or the front paper feed mechanism 4 is sandwiched between the transport roller 21 and the transport-side driven roller 22. Then, the printing paper P is transported forward by the rotation of the transport roller 21. The controller 9 controls the amount of rotation of the transport roller 21 and transports the print paper P while controlling the position of the print paper P with respect to the print head 11. The printing paper P conveyed by the conveyance roller 21 is supported from below by the platen 29. In the following description, the forward conveyance of the printing paper P is referred to as a forward conveyance, and the conveyance when conveying the printing paper P toward the rear is described as reverse conveyance, as will be described later. Further, the leading edge and the trailing edge of the printing paper P are described with reference to the traveling direction of the printing paper P. Therefore, the front end and the rear end at the time of forward conveyance and reverse conveyance are reversed.

  When the printing paper P is sequentially conveyed to a position facing the printing head 11, the printing operation of the printing mechanism 2 is performed by the control unit 9. That is, ink is ejected from the print head 11 as the carriage 10 moves, and an image is formed on the printing paper P. The printing paper P is sequentially conveyed while being printed by the printing mechanism 2, and the leading end reaches the paper discharge roller 23 and the paper discharge side driven roller 24 of the paper discharge mechanism 6. After the leading end of the printing paper P reaches the paper discharge mechanism 6, the printing paper P is sequentially transported by the transport roller 21 and the paper discharge roller 23. The transport roller 21 and the paper discharge roller 23 are controlled by the control unit 9 so as to rotate in synchronization. If the forward conveyance is continued in this state, the rear end portion of the printing paper P passes through the optical sensor 8 and also passes through the conveyance mechanism 5.

  After the trailing edge of the printing paper P passes through the transport mechanism 5, the rotation amount of the paper discharge roller 23 is controlled by the control unit 9, so that the printing paper P is positioned with respect to the printing head 11. It is transported in order while being controlled. When the printing of the image on the printing paper P is completed, the control unit 9 further rotates the paper discharge roller 23 to discharge the printing paper P to the outside of the printing apparatus 1.

(Reverse transfer operation)
By reversely rotating the transport roller 21 and the paper discharge roller 23, it is possible to perform reverse transport in which the printing paper P is transported backward. In the double-sided printing mode, the control unit 9 reverses the paper discharge roller 23 and the conveyance roller 21 after the printing in the forward conveyance is completed. As a result, the printing paper P is conveyed backward toward the reversing mechanism 7. The printing paper P that has been reversely conveyed to the reversing mechanism 7 is turned upside down by the reversing mechanism 7 between the printed surface and the back surface that has not yet been printed. In the reverse conveyance of the printing paper P after the printing in the forward conveyance is performed, the leading end portion of the printing paper P (the rear end portion in the case of the sequential conveyance) passes through the conveyance roller 21 and then passes through the optical sensor 8. Will do. When the reverse conveyance is further continued, the trailing edge of the printing paper P (the leading edge during forward conveyance) passes through the paper discharge roller 23, passes through the conveyance roller 21, and then passes through the optical sensor 8. Become.

(Reversing mechanism)
When the printing paper P is transported in the reverse direction, the movable guide 25 is rotated counterclockwise about the shaft portion 25B as the rotation axis, and the paper path 28 is closed. The printing paper P transported in the reverse direction from the printing mechanism 2 side is closed on the upper guide surface 25 </ b> C formed on the upper side of the movable guide 25 without entering the paper path 28 because the paper path 28 is closed. It is conveyed toward 26. The printing paper P conveyed on the upper guide surface 25C is guided toward the rear upper side in the drawing by a flip-up mechanism (not shown) and reaches the reverse roller 26. The printing paper P is transported along the periphery of the reversing roller 26, whereby the transport direction is changed to the front (forward transport). The printing paper P whose transport direction is changed to the front is sequentially transported on the lower guide 27 along the upper guide surface 25C of the movable guide 25, passes below the optical sensor 8, and reaches the transport mechanism 5.

  After printing in the forward conveyance, an image is printed on one surface (front surface) of the printing paper P that is reversely conveyed from the paper discharge mechanism 6 to the reversing mechanism 7. When the printing paper P is supplied to the reversing mechanism 7 and then forwarded to the transporting mechanism 5 again, one printed surface (front surface) is on the lower side, and the back surface of the printing paper P is It is on the upper side. The printing paper P reversed by the reversing mechanism 7 is printed on the back surface by the printing mechanism 2 while being sequentially conveyed by the conveying mechanism 5. That is, double-sided printing is performed on the printing paper P. In the present embodiment, the upper surface of the printing paper P before being reversed by the reversing mechanism 7 is described as “front surface”, and the upper surface of the printing paper P after being reversed is described as “back surface”. Yes.

  However, as described above, the printing apparatus 1 has a configuration of the center paper feeding method. Therefore, members such as the paper feed roller 15 and the retard roller 16 that convey the printing paper P are arranged symmetrically with respect to the center of the printing paper P in the left-right direction. Therefore, the occurrence of skew of the printing paper P during backward feeding, forward feeding, forward conveyance, and reverse conveyance can be suppressed, jamming can be suppressed, and the printing paper P can be placed at a predetermined position. Can print.

(Light sensor 8)
Next, the configuration of the optical sensor 8 will be described with reference to FIGS. 3 to 5. FIG. 3 is a diagram showing a schematic configuration of the optical sensor 8. FIG. 4 is a graph showing changes in the output voltage Vs from the photosensor 8. FIG. 5 is an enlarged view showing an arrangement portion of the optical sensor 8 and the lower guide 27 in an enlarged manner.

  As shown in FIG. 3, the optical sensor 8 is a so-called reflective optical sensor in which the light projecting unit 30 and the light receiving unit 31 are arranged in the same direction. The light projecting unit 30 is configured by, for example, a light emitting diode, and emits infrared rays, for example. The light receiving unit 31 is configured by, for example, a phototransistor. A light shielding plate 32 is provided between the light projecting unit 30 and the light receiving unit 31 so that the light emitted from the light projecting unit 30 does not directly enter the light receiving unit 31. In the light receiving unit 31, it is possible to obtain an output voltage Vs corresponding to the amount of light emitted from the light projecting unit 30, reflected by the subject and incident on the light receiving unit 31. That is, when the subject exists in the projection range of the light emitted from the light projecting unit 30 and the light emitted from the light projecting unit 30 is reflected by the subject and enters the light receiving unit 31, the output voltage Vs is low. It becomes. On the other hand, when the subject does not exist in the light projection range of the light projecting unit 30 and the light emitted from the light projecting unit 30 is not reflected by the subject and does not enter the light receiving unit 31, the output voltage Vs is high. It becomes. Therefore, based on the output voltage Vs, it can be detected whether or not the subject exists in the light emission range of the light projecting unit 30.

(Detection of printing paper P by optical sensor 8)
Next, a mechanism for detecting the end portion (front end portion, rear end portion) of the printing paper P using the above-described optical sensor 8 will be described. The optical sensor 8 is disposed above the lower guide 27. Accordingly, the printing paper P passes between the lower guide 27 and the optical sensor 8. The light projecting unit 30 and the light receiving unit 31 are arranged in the left-right direction. Further, the emission direction of the light projecting unit 30 and the incident direction of the light receiving unit 31 are directed downward, that is, toward the lower guide 27.

  As shown in FIG. 5, a hole 33 is formed in the lower guide 27 in a range where the emitted light emitted from the optical sensor 8 is irradiated. Further, the light emitted from the light projecting unit 30 enters the hole 33, and the light that passes through the lower guide 27 does not enter the light receiving unit 31. Therefore, when there is no printing paper P below the optical sensor 8, the light emitted from the light projecting unit 30 enters the hole 33 and does not enter the light receiving unit 31. That is, as shown in the upper part (A) and the lower part (B) of FIG. 4, the output voltage Vs is higher than the threshold values P1 and Q1, that is, H level. On the other hand, when the printing paper P exists below the optical sensor 8, the light emitted from the light projecting unit 30 is reflected by the printing paper P and enters the light receiving unit 31. That is, as shown in FIGS. 4A and 4B, the output voltage Vs is lower than the threshold values P1 and Q1, that is, at the L level. Therefore, the control unit 9 that also functions as an edge detection unit can detect whether or not the printing paper P is present at the position of the optical sensor 8 based on the output voltage Vs of the optical sensor 8.

  When the edge of the printing paper P passes through the position of the optical sensor 8, the output voltage Vs of the optical sensor 8 changes from H level to L level or from L level to H level. The change in the output voltage Vs in FIG. 4A indicates a change from a state in which the printing paper P is not present at the position of the optical sensor 8 to a state in which the printing paper P is present. When the front end portion of the printing paper P (the front side in the transport direction) passes through the projection range of the light emitted from the light projecting portion 30, the output voltage Vs decreases from the H level to the L level. Part HL is presented. Further, the change in the output voltage Vs in FIG. 4B indicates a change from the state in which the printing paper P is present to the state in which the photosensor 8 is not present. When the rear end of the printing paper P (the rear side in the transport direction) passes through the projection range of the light emitted from the light projecting unit 30, the output voltage Vs changes from the L level to the H level. The ascending portion LH is exhibited.

  Therefore, it is possible to detect that the end portions (leading end portion and rear end portion) of the printing paper P have passed the predetermined positions with reference to the predetermined threshold values P1 and Q1. That is, in FIG. 4A, the control unit 9 can determine that the leading end portion of the printing paper P has passed a predetermined position with respect to the optical sensor 8 when the output voltage Vs reaches the threshold value P1. 4B, when the output voltage Vs reaches the threshold value Q1, the control unit 9 determines that the rear end portion in the transport direction of the printing paper P has passed a predetermined position with respect to the optical sensor 8. it can.

The control unit 9 detects the position of the end of the printing paper P as described above, and thus the operation and driving of each mechanism of the printing apparatus 1 such as the conveyance distance and speed of the printing paper P, the timing of paper feeding, and the like. Timing and the like can be controlled.
Note that the threshold value P1 and the threshold value Q1 may be the same value or different values depending on a predetermined position that is a detection position of the end portion.

  Further, as shown in FIG. 6, the optical sensor 8 is disposed so as to be positioned at the center M in the left-right direction of the conveyance path 34 which is an area where the printing paper P in the printing apparatus 1 is conveyed. The printing apparatus 1 is a center paper feeding method. That is, the printing paper P is in a state in which the center of the printing paper P coincides with the center M of the conveyance path 34 in the left-right direction, that is, the center M of the printable range in the left-right direction by the print head 11 (see FIG. 1). Be transported. Therefore, by arranging the optical sensor 8 at the center M in the left-right direction of the transport path 34, the print paper P can be detected regardless of the size of the transported print paper P.

  The optical sensor 8 is located at a position where the distance from the center of the transport path 34 is closer to half the width of the narrowest printing paper P among the printing papers P of a size that can be loaded into the printing apparatus 1. By arranging the print paper P, the print paper P can be detected regardless of the size of the print paper P.

(Detection operation of printing paper P by optical sensor 8)
Next, the detection operation of the printing paper P will be described along the conveyance operation of the printing paper P.

(Detection operation during forward conveyance)
First, an operation for detecting the end portions (the front end portion and the rear end portion) of the print paper P by the optical sensor 8 when the print paper P is sequentially conveyed will be described. The light emitted from the light projecting unit 30 is sent to the lower guide 27 until the leading end of the printing paper P sent from the paper stocker 13 or the paper tray 17 to the lower guide 27 reaches the position of the optical sensor 8. It passes through the formed hole 33. Therefore, the reflected light of the light emitted from the light projecting unit 30 does not enter the light receiving unit 31. That is, as shown in FIG. 4A, the output voltage Vs is at the H level (eg, 3.3 V).

  When the leading end of the printing paper P reaches the position of the optical sensor 8 and the leading end passes through the projection range of the light projected from the light projecting unit 30, the output is output according to the position of the leading end in the projection range. The voltage Vs changes. That is, as the amount of the printing paper P entering the projection range increases, the light projected from the light projecting unit 30 is reflected by the printing paper P and the amount of light incident on the light receiving unit 31 increases. As the amount of light incident on the light receiving portion 31 increases, the output voltage Vs decreases as shown by the descending portion HL in FIG. Then, in a state where the tip portion completely passes through the light projection range of the light projecting unit 30, all the light projected from the light projecting unit 30 is incident on the printing paper P. For this reason, the amount of light reflected by the printing paper P and incident on the light receiving unit 31 is increased, and the output voltage Vs is in the L level (for example, 0.5 V).

  Therefore, the value of the output voltage Vs when the tip portion is located at a predetermined position in the projection range of the light emitted from the light projecting unit 30 is determined in advance, and this value is set as the threshold value P1, whereby the control unit 9, when the output voltage Vs reaches the threshold value P <b> 1, it can be determined that the leading edge of the printing paper P is at a predetermined position.

  The forward conveyance is continued, the rear end of the printing paper P reaches the position of the optical sensor 8, and the rear end passes through the projection range of the light emitted from the light projecting unit 30. The output voltage Vs changes according to the position of the rear end. That is, from the state in which the light projected from the light projecting unit 30 is reflected by the printing paper P toward the light receiving unit 31, the printing paper P disappears from the light projection range of the light projecting unit 30 and enters the hole 33. Change to state. The amount of light projected from the light projecting unit 30 reflected by the printing paper P decreases as the printing paper P deviates from the projection range, and the output voltage Vs increases as shown by the rising portion LH in FIG. To do.

  Therefore, the value of the output voltage Vs when the rear end portion is located at a predetermined position in the projection range of the light emitted from the light projecting unit 30 is determined in advance, and this value is set as the threshold value Q1. The unit 9 can determine that the trailing edge of the printing paper P is at a predetermined position when the output voltage Vs reaches the threshold value Q1.

(Detection operation during reverse conveyance)
By the way, in the double-sided printing mode, the printing paper P that has been printed on the surface of the printing paper P is reversely conveyed from the conveyance mechanism 5 toward the reversing mechanism 7. At that time, in order to perform reverse conveyance control such as detection of a jam of the printing paper P, it is necessary to detect a front end portion located in the front direction of the printing paper P and a rear end portion located rearward in the conveyance direction. . The leading edge of the reversely transported printing paper P is the trailing edge during forward transportation, and the trailing edge of the reversely transporting printing paper P is the leading edge during forward transportation.

  By the way, printing is performed on the surface of the printing paper P that is reversely conveyed during the forward conveyance. Therefore, the reflection amount of the light emitted from the light projecting unit 30 and incident on the printing surface may be reduced as compared with the case where printing is not performed. For example, even when the printing paper P is in the projection range of the light emitted from the light projecting unit 30, as shown in the upper (A) and lower (B) of FIG. 7, the L level of the output voltage Vs May rise, and based on the thresholds P1 and Q1 during forward conveyance, it may not be possible to detect that the leading end and the trailing end are at predetermined positions.

  Therefore, in the double-sided printing mode, the detection of the leading end portion and the trailing end portion is determined using threshold values P2 and Q2 that are higher than the threshold values P1 and Q1 for forward conveyance. That is, when the output voltage Vs reaches the threshold values P2 and Q2, it is determined that the front end portion and the rear end portion are respectively at predetermined positions. Note that the change in the output voltage Vs in FIG. 7A is a change in the state in which the printing paper P is not present at the position of the optical sensor 8 when the printing paper P printed on the surface is reversely conveyed. Is shown. Further, the change in the output voltage Vs in FIG. 7B shows a change from the state where the printing paper P is present at the position of the optical sensor 8 to the state where the printing paper P is not present.

  In general, when printing a color with low brightness (low reflectance) such as black solid on the surface, the L level of the output voltage Vs greatly increases as shown in FIGS. 7A and 7B. . On the other hand, when the printing on the surface is character printing or color printing other than solid black, the L level of the output voltage Vs increases as the relationship between the threshold values P1 and Q1 and the leading edge and trailing edge shifts greatly. It will not rise. Therefore, the control unit 9 that also functions as a changing unit prints data when printing is performed on the surface or the color of the ejected ink before the reverse conveyance is performed after the printing in the forward conveyance is finished. The amount of reflection on the printed surface is determined based on the amount and the amount.

  That is, when the control unit 9 determines that the printing state of the front surface is a state in which the front end portion and the rear end portion cannot be detected based on the threshold values P1 and Q1, the threshold value P2 is set. , Q2 is used to determine the detection of the leading edge and trailing edge of the printing paper P. As described above, by using the threshold values P2 and Q2 that are higher than the threshold values P1 and Q1, the printing paper P that is printed with a low-brightness lightness, that is, a color with low reflectance, is also applied to the leading edge. It is possible to suppress a decrease in accuracy of detection of the front and rear end portions.

  By the way, when the printing state already performed on the surface of the printing paper P is black solid printing and border printing, the optical sensor 8 when the printing paper P is reversely conveyed is used. The output voltage Vs is, for example, as shown in FIG. Of the ranges K1 and K2 which are L levels of the output voltage Vs shown in FIG. 8, the range K1 corresponds to the edge portion on the leading edge side of the printing paper P, and the range K2 is the edge portion on the trailing edge side of the printing paper P. Corresponding to Between the ranges K1 and K2, it is a portion with little reflected light, and corresponds to a printed portion.

  As shown in FIG. 8, when the printing paper P on which the border printing FR around the black solid print portion BB is formed is conveyed in the reverse direction, the output voltage Vs is four times the threshold value. It becomes the value of P1, and becomes the value of the threshold value Q1 four times. The case where the output voltage Vs first reaches the threshold value P1 corresponds to the time when the tip portion passes a predetermined detection position of the optical sensor 8. Further, when the output voltage Vs becomes the threshold value Q1 for the fourth time, this corresponds to the case where the rear end portion passes a predetermined detection position of the optical sensor 8.

  Therefore, prior to double-sided printing, the control unit 9 determines that the surface-side printing state is bordered printing based on the printing data when printing is performed on the surface or the color and amount of the ejected ink, and Then, it is determined whether the printing is solid black. In this determination, when it is determined that the printing is bordered and the printing is solid black, the control unit 9 having a function as a counting unit determines that the output voltage Vs becomes the threshold value P1 and the threshold value Q1. Count. Then, when the output voltage Vs first reaches the threshold value P1, it can be determined that the tip has passed a predetermined detection position of the optical sensor 8. Further, when the output voltage Vs becomes the threshold value Q1 for the fourth time, it can be determined that the rear end portion has passed a predetermined detection position of the optical sensor 8. When the threshold value P1 and the threshold value Q1 are the same value, it can be determined that the tip has passed a predetermined detection position of the optical sensor 8 when the output voltage Vs first becomes the threshold value P1. . Then, when the output voltage Vs becomes the threshold value P1 for the fourth time, it can be determined that the rear end portion has passed the predetermined detection position of the optical sensor 8.

(Modification)
Instead of changing the threshold value as described above, the light receiving sensitivity of the optical sensor 8 may be increased. By increasing the light receiving sensitivity of the optical sensor 8, the L level of the output voltage Vs when receiving the light reflected by the portion where the printing paper P is printed with low lightness can be lowered. Even when the light receiving sensitivity of the optical sensor 8 is increased, when there is no printing paper P at the position of the optical sensor 8, the projection light is projected into the hole 33, and therefore the H level of the output voltage Vs does not change. Therefore, the difference between the L level and the H level of the output voltage Vs can be increased. Therefore, the output voltage Vs when the front end and the rear end are located at predetermined positions can be close to the threshold values P1 and Q1. That is, even when the threshold values P1 and Q1 are used, it is possible to suppress a decrease in accuracy of position detection of the front end portion and the rear end portion.

  Further, the light emission amount of the light projecting unit 30 of the optical sensor 8 may be increased. By increasing the light emission amount of the light projecting unit 30, the amount of light reflected from the printing paper P can be increased even when the printing paper P is printed with low brightness, and the optical sensor 8 can print the printing paper. The L level of the output voltage Vs when P is detected can be lowered. Even when the light emission amount of the light projecting unit 30 is increased, when there is no printing paper P at the position of the optical sensor 8, the projection light is projected into the hole 33, so the H level of the output voltage Vs does not change. Therefore, the difference between the L level and the H level of the output voltage Vs can be increased. Therefore, the output voltage Vs when the front end and the rear end are located at predetermined positions can be close to the threshold values P1 and Q1. Even when the threshold values P1 and Q1 are used, it is possible to suppress a decrease in accuracy of position detection of the front end portion and the rear end portion.

  As described above, the printing apparatus 1 of the present embodiment is a center paper feeding method, and the distance from the center of the conveyance path 34 on which the printing paper P as a recording medium is conveyed is a size that can be loaded into the printing apparatus 1. By comparing the detection signal obtained by this optical sensor 8 with a predetermined threshold value, the optical sensor 8 arranged at a position closer than half the width of the narrowest printing paper among the printing papers of Depending on the state of the printing surface of the printing paper and the control unit 9 that detects the edge of the printing paper P conveyed in the conveyance path 34 in the conveyance direction, detection of the threshold or the optical sensor 8 And a control unit 9 which is a changing means for changing the sensitivity or the light projection intensity of the optical sensor 8.

  By configuring the printing apparatus 1 in this way, the end detection state can be set appropriately, and the end position can be accurately detected. In the above-described embodiment, the control unit 9 determines the printing state, and changes the threshold value, the detection sensitivity of the light sensor 8 or the light projection intensity of the light sensor 8 based on the determination. On the other hand, the user may determine the printing state and change the threshold, the detection sensitivity of the optical sensor 8 or the light projection intensity of the optical sensor 8 based on the determination. Further, when the detection accuracy of the end portion is lowered due to deterioration of the optical sensor 8 or the like, the threshold value, the detection sensitivity of the optical sensor 8 or the light projection intensity of the optical sensor 8 may be changed.

  Further, the control unit 9 of the printing apparatus 1 determines whether the threshold value or the detection sensitivity of the optical sensor 8 or the light projecting unit 30 depends on the state of printing already performed on the printing paper P in the duplex printing mode. The projection intensity of the emitted light is changed.

  By configuring the printing apparatus 1 in this way, it is possible to detect the edge of the printing paper P with high accuracy regardless of the printing state of the printing paper P that is reversely conveyed.

  The control unit 9 of the printing apparatus 1 is configured to be able to count the number of appearances of the threshold.

  By configuring the printing apparatus 1 in this way, the edge of the printing paper P can be detected with high accuracy even when the printing paper P transported in the reverse direction is printed with a border. .

  The optical sensor 8 of the printing apparatus 1 is a reflection type, and receives light from the light projecting unit 30 of the lower guide 27 when there is no printing paper P within the projection range of the light emitted from the light projecting unit 30. In the portion, a hole 33 is formed so as not to reflect the light from the light projecting unit 30 in the direction of the light receiving unit 31 of the optical sensor 8.

  By configuring the printing apparatus 1 in this manner, it is possible to prevent erroneous detection of the optical sensor 8 due to the light reflected by the lower guide 27 entering the light receiving unit 31. In the present embodiment, the hole 33 is formed, but instead of forming the hole 33, a slope 35 may be formed as shown by a dotted line in FIG.

  As described above, in the present embodiment, an end detection method in the transport direction of the print paper P loaded and transported in the center paper feed type printing apparatus 1 is used as the transport path 34 for transporting the print paper P. The optical sensor 8 is arranged at a position where the distance from the center is closer to one half of the width of the narrowest printing paper P of the size of the printing paper P that can be loaded into the printing apparatus 1. By comparing the obtained detection signal with a predetermined threshold value, an end portion in the conveyance direction of the printing paper P conveyed on the conveyance path 34 is detected, and the threshold value is determined according to the state of the printing surface of the printing paper P. Alternatively, the detection sensitivity of the optical sensor 8 or the light projection intensity of the optical sensor 8 is changed.

  By configuring the printing apparatus 1 in this way, the end detection state can be set appropriately, and the end position can be accurately detected.

  DESCRIPTION OF SYMBOLS 1 ... Printing apparatus 8 ... Optical sensor 9 ... Control part (edge detection means, change means, counting means) 34 ... Conveyance path P ... Printing paper (recording medium)

Claims (5)

In a center-feed printing device,
The distance from the center of the conveyance path through which the recording medium is conveyed is disposed at a position closer to one half of the width of the narrowest print medium among the print media having a size that can be loaded into the printing apparatus. A light sensor,
End detection means for detecting an end in the transport direction of the print medium transported through the transport path by comparing a detection signal obtained by the optical sensor with a predetermined threshold;
Change means for changing the threshold, or the detection sensitivity of the photosensor or the light projection intensity of the photosensor, according to the state of the print surface of the print medium,
A printing apparatus comprising: The printing apparatus according to claim 1,
The changing unit is configured to change the threshold value, the detection sensitivity, or the light projection intensity according to a state of printing already performed on the print medium when the printing apparatus is in a double-sided printing mode. Characteristic printing device. The printing apparatus according to claim 1,
Having counting means for counting the number of appearances of the threshold;
A printing apparatus characterized by the above. The printing apparatus according to any one of claims 1 to 3,
The light sensor is a reflection type light sensor, and when there is no print medium within the projection range of light emitted from the light projecting unit, the portion that receives light from the light projecting unit is from the light projecting unit. The printing apparatus is a portion that does not reflect the light in the direction of the light receiving portion of the reflective photosensor. In the edge detection method of a print medium for detecting an edge in a conveyance direction of a print medium loaded and conveyed in a center paper feeding type printing apparatus,
The optical sensor is placed at a position where the distance from the center of the conveyance path through which the recording medium is conveyed is closer to one half of the width of the narrowest print medium of the size that can be loaded into the printing apparatus. By arranging and comparing the detection signal obtained by the optical sensor with a predetermined threshold, the end in the transport direction of the print medium transported through the transport path is detected,
According to the state of the printing surface of the printing medium, changing the threshold, or the detection sensitivity of the photosensor or the light projection intensity of the photosensor,
A method for detecting an edge portion of a print medium.

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