JP5609201B2 - Serial printer - Google Patents

Description

  The present invention relates to a serial printer, and more particularly to feedback control for accurately conveying a sheet such as paper or film.

  Conventionally, in a serial printer, a sheet such as paper or film is conveyed by driving a roller or an endless belt. The conveyance distance of the sheet can be approximately detected by the rotation angle of the roller. However, if the sheet slips with respect to the roller, or the roller is eccentric or worn, an error occurs in the conveyance distance derived from the rotation angle of the roller.

  As described in Japanese Patent Application Laid-Open No. H10-228561, a technique for detecting a sheet conveyance distance by analyzing moving image data obtained by photographing a sheet being conveyed with a digital camera is known. By using this technique, in addition to feedback control of the rotation angle of the motor, it is possible to feedback control the conveyance distance of the sheet. Specifically, in a serial printer that alternately repeats printing of a belt-like image and conveyance of a sheet, a subsequent conveyance section so as to cancel a conveyance error detected in the conveyance section from the start of conveyance of the sheet to the stop. Correction of the transport control amount is performed. In addition, a tendency of transport error that occurs in a plurality of transport sections is acquired, and the transport control amount is corrected so as to cancel the transport error that has already occurred.

  Further, as described in Patent Document 2, a technique for correcting the control amount of the rotation angle of the roller according to the amount of eccentricity of the roller that conveys the sheet, or as described in Patent Document 3, the paper feeding side A technique is known in which a conveyance error caused by a difference in peripheral speed between a roller and a paper discharge side roller is set as a correction function that is a function of the position in the sub-scanning direction, and the rotation angle of the roller is controlled using the correction function.

Patent No. 4014535 JP 2004-276425 A JP 2004-182420 A

However, each of the above-described conventional techniques corrects the transport control amount applied when transport is resumed based on the transport error that occurs until it stops once. It is not intended to reduce the transport error until stopping based on this. Therefore, according to the above-described conventional technique, when a different transport error occurs in each transport section from the start to the stop of the transport, the transport error cannot be canceled out, so that the transport error accumulated over one page becomes considerably large. There is.
In addition, as described in Patent Documents 2 and 3, when the correction amount is fixed during printing, there is a problem that it cannot cope with disturbance during printing at all.
If the conveyance distance is detected each time the sheet is conveyed and stopped for one conveyance section and the sheet is conveyed again by a distance corresponding to the error each time, the conveyance error is eliminated, but the sheet conveyance time is included. There is a problem that the printing time for the entire page becomes very long.

  The present invention has been created in view of these problems, and an object of the present invention is to improve the accuracy of the distance for conveying a sheet while suppressing the printing time.

(1) A serial printer for achieving the above object outputs a conveying unit that repeatedly conveys and stops a sheet, a printing unit that prints an image on the stopped sheet, and moving image data that captures the conveyed sheet A digital camera that performs analysis of the moving distance of the sheet by analyzing the moving image data, and a conveyance control until the sheet is stopped based on the conveyance distance of the sheet detected before the sheet is stopped. Transport control means for feeding back the quantity.
According to the present invention, it is possible to specify the elapsed value of the conveyance error during sheet conveyance by detecting the sheet conveyance distance during sheet conveyance. A conveyance error that occurs during the conveyance of the sheet can be canceled by the conveyance control amount until the sheet stops. Therefore, according to the present invention, it is possible to improve the accuracy of the distance to convey the sheet while suppressing the printing time. The “conveyance error” is the difference between the distance that the sheet is actually conveyed and the distance that the sheet is to be conveyed.

(2) In the serial printer for achieving the above object, the conveyance control means detects the sheet detected before the sheet stops for each conveyance section from the conveyance of the sheet to the stop thereof. May be fed back to the conveyance control amount until the sheet is stopped.
According to this configuration, since the sheet conveyance distance can be accurately controlled for each conveyance section, it is possible to improve the print image quality.

(3) In the serial printer for achieving the above object, the conveyance control unit, according to the conveyance control amount from the start to the stop of the conveyance of the sheet and the detected conveyance distance of the sheet, A conveyance error that occurs until the sheet is stopped may be predicted, and a conveyance control amount until the sheet is stopped may be updated according to the predicted conveyance error.
Based on the conveyance control amount from the start of conveyance of the sheet until it is stopped and the detected conveyance distance, the distance at which the sheet is to be conveyed until it is stopped, that is, the remaining distance is specified. The conveyance error that occurs in the remaining distance is determined according to the length of the remaining distance. That is, the longer the remaining distance is, the larger the transport error that occurs in the remaining distance. Therefore, a transport error that occurs until the sheet is stopped can be predicted according to the transport control amount from the start to the stop of the transport of the sheet and the detected transport distance of the sheet. By updating the conveyance control amount until the sheet is stopped according to the conveyance error predicted in this way, the accuracy of the sheet conveyance distance can be further increased.

(4) In the serial printer for achieving the above object, the conveyance control unit predicts a conveyance error that occurs from when the conveyance distance of the sheet is detected to when the sheet is stopped according to a conveyance mode, The conveyance control amount until the sheet is stopped may be updated according to the predicted conveyance error.
The conveyance mode is a control mode in which a specific conveyance speed and acceleration / deceleration characteristics are set. A conveyance error that occurs after the sheet conveyance distance is detected until the sheet is stopped has a strong correlation with the sheet conveyance speed and acceleration / deceleration characteristics. Therefore, it is possible to predict the conveyance error that occurs until the sheet is stopped according to the conveyance mode. By setting the conveyance control amount until the sheet is stopped according to the conveyance error predicted in this way, the accuracy of the distance for conveying the sheet can be further increased.

(5) In the serial printer for achieving the above object, the conveyance control unit predicts a conveyance error that occurs from the detection of the conveyance distance of the sheet to the stop of the sheet according to the type of the sheet. The conveyance control amount until the sheet is stopped may be updated according to the predicted conveyance error.
If the sheet type is different, the friction coefficient and mass of the sheet are different. A conveyance error that occurs after the sheet conveyance distance is detected until the sheet is stopped has a strong correlation with the friction coefficient and mass of the sheet. Accordingly, it is possible to predict a conveyance error that occurs until the sheet is stopped according to the type of the sheet. By setting the conveyance control amount until the sheet is stopped according to the conveyance error predicted in this way, the accuracy of the distance for conveying the sheet can be further increased.

(6) In the serial printer for achieving the above object, the conveyance control unit determines the type of the sheet based on image data output from the digital camera each time the sheet is inserted into the conveyance unit. You may judge.
By adopting this configuration, it is possible to predict a conveyance error that occurs between the detection of the sheet conveyance distance and the stoppage of the sheet according to the sheet type without having the user set the sheet type.

(7) In the serial printer for achieving the above object, the conveyance control unit learns, after stopping the sheet, a conveyance error that occurs after the sheet conveyance distance is detected until the sheet is stopped. The conveyance error that occurs between the detection of the conveyance distance of the sheet and the stop of the sheet may be predicted according to the learning result.
When this configuration is adopted, the accuracy of the distance for conveying the sheet can be further increased.

It is a block diagram concerning the embodiment of the present invention. It is a graph concerning embodiment of this invention. It is a flowchart concerning embodiment of this invention. It is a graph concerning embodiment of this invention. It is a schematic diagram concerning embodiment of this invention. It is a schematic diagram concerning embodiment of this invention. It is a graph concerning embodiment of this invention. The length of one frame period corresponds to the interval between thin lines. It is a graph concerning embodiment of this invention. It is a graph concerning embodiment of this invention. The size of the rectangle represented by the thin line indicates the frame size of the corresponding frame image. Further, the position in the horizontal axis direction of the rectangle represented by the thin line indicates the timing at which the corresponding frame image is captured.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the corresponding component in each figure, and the overlapping description is abbreviate | omitted.
1. Overview A printer 1 shown in FIG. 1 is an ink jet printer including a sheet feed sensor as an embodiment of the present invention. The motor 15 intermittently conveys the sheet P such as printing paper. That is, as shown in FIG. 2, the sheet P conveyed by the motor 15 repeats acceleration, deceleration, and stop for each conveyance section. The conveyance section is a section from the start of conveyance of the sheet P to the stop. The conveyance distance of the sheet P detected using the digital camera 20 in each conveyance section is fed back to the control amount of the motor 15 by the CPU 33 in the conveyance section. Such feedback control by the CPU 33 is performed only once for each conveyance section. The timing at which the conveyance distance of the sheet P can be fed back to the control amount of the motor 15 by the CPU 33 corresponds to the timing at which the analysis of the frame image output from the digital camera 20 ends. The shorter the period when the analysis of the frame image output from the digital camera 20 is completed, the longer the timing at which the conveyance distance of the sheet P is fed back to the control amount of the motor 15 by the CPU 33 can be extended until just before the stop. Therefore, the digital camera 20 is controlled to increase the frame rate in the deceleration section within each transport section. For this reason, the period when the timing at which the conveyance distance of the sheet P can be fed back to the control amount of the motor 15 is short in the deceleration section. Therefore, it is possible to extend the timing of feedback control of the motor 15 to the point just before it is stopped. As a result, the distance over which past conveyance errors cannot be canceled by feedback control is shortened, so that the accuracy of the sheet conveyance distance can be improved.

2. Configuration The printer 1 includes, as a conveyance unit for intermittently conveying the sheet P, a motor 15, a conveyance roller 11a driven by the motor 15, a driven roller 11b that rotates following the conveyance roller 11a, and a motor. And a motor driver 16 which is a drive circuit having a rotary encoder 161 for detecting 15 rotation angles and rotation speeds. The printer 1 also includes a carriage 12 having a print head as a printing unit for printing a strip-shaped image each time the sheet P stops, and a guide rod that is installed in the main scanning direction and guides the movement direction of the carriage 12. 14, an endless belt (not shown) for pulling the carriage 12, and a motor (not shown) for driving the endless belt are provided. A print head (not shown) ejects ink supplied from an ink cartridge 13 mounted on the carriage 12 from a nozzle (not shown) by a piezoelectric element.

The printer 1 includes a digital camera 20 that outputs moving image data obtained by imaging the sheet P. The moving image data is composed of a series of frame images that are still image data that is continuously output at a cycle that is the inverse of the frame rate. The digital camera 20 includes a light source 22 such as an LED (Light Emitted Diode) that illuminates the back surface of the ink receiving surface of the sheet P on which ink ejected from the nozzles lands, a lens for imaging the surface of the sheet P, and the like. An optical system 21, an image sensor 24 for imaging the surface of the sheet P imaged by the optical system 21, and an FPGA (for controlling the light source 22 and the image sensor 24 and processing the output of the image sensor 24. And a control unit 23 including a field programmable gate array. In the present embodiment, the image sensor 24 is a CMOS image sensor having 640 pixels × 480 pixels. The image sensor 24 is arranged so that the long side corresponds to the sub-scanning direction (sheet feed direction) of the printer 1.
The printer 1 includes a camera control unit that controls a frame rate and a frame size of the digital camera 20, an analysis unit that detects the conveyance distance of the sheet P by analyzing moving image data output from the digital camera 20, and a detection A computer that functions as a transport control unit that controls the motor 15 while feeding back the transported distance to the control amount of the motor 15 is provided. The computer includes a CPU 33, a RAM 31, a ROM 32, and an interface 30. The CPU 33 controls the transport unit, the printing unit, and the digital camera 20 by executing a print control program loaded from the ROM 32 to the RAM 31.

3. Sheet Feeding Method FIG. 3 is a flowchart illustrating a sheet feeding method in the printer 1. The process shown in FIG. 3 is controlled by the CPU 33 that executes the print control program, and after the belt-like image having a width corresponding to the width of the print head (sub-scanning direction length) is printed on the sheet P, the next belt-like image is printed. This is executed to move the sheet P to the position for printing. That is, the process shown in FIG. 3 is executed for each conveyance section.

  First, the CPU 33 sets the stop position and conveyance mode of the motor 15 to the motor driver 16 and instructs activation thereof, and starts detection of the sheet conveyance distance (S100). The stop position as the conveyance control amount of the sheet P is specified by the rotation angle of the motor 15, for example. The transport mode corresponds to the print image quality setting. The acceleration / deceleration characteristics of the motor 15 are determined by setting the transport mode. The higher the print image quality, the smaller the absolute value of the angular acceleration of the motor 15 in the acceleration section and the deceleration section. When the stop position and the conveyance mode are set, the motor driver 16 can stop at the set stop position as shown in FIG. 4 while detecting the rotation angle and rotation speed of the motor 15 by the rotary encoder 161. The rotation angle of the motor 15 is feedback-controlled.

Here, a method for detecting the conveyance distance of the sheet P will be specifically described with reference to FIG. The conveyance distance of the sheet P is detected by pattern matching of local regions of two consecutive frame images. First, the frame image 25 is output from the digital camera 20 to the RAM 31 in accordance with the frame size and frame rate set in the digital camera 20 by the CPU 33. The frame size (image size) F ₀ of the frame image 25 when the motor 15 is activated is 640 pixels × 480 pixels corresponding to the number of effective pixels of the image sensor 24. Setting a frame rate S ₀ at the time of activation of the motor 15 is, for example, 30 frames / sec. Each time the frame image 25 is stored in the RAM 31, the CPU 33 searches for an area where the local pattern appearing at the end of the previous frame image 25a appears in the current frame image 25b. The search for the local pattern is similar to the pattern cut from the end region of the previous frame image 25a by the window 251 having a size smaller than the frame image 25 and the pattern cut by the window 251 from any region of the current frame image 25b. This is performed based on the result of detecting the degree. Specifically, in the current frame image 25b, the window 251 is moved pixel by pixel from the end region (left end region in FIG. 5), and the pattern cut by the window 251 and the end region of the previous frame image 25a are used. The degree of similarity with the cut pattern is detected and stored in association with the position of the window 251, and the length V in the sub-scanning direction corresponding to the position where the degree of similarity between these two patterns is the highest in the current frame image 25b. Is detected as the inter-frame movement distance indicating the distance that the sheet P has moved in one frame period (the time interval at which two consecutive frame images are captured, ie, the reciprocal of the frame rate). The CPU 33 accumulates the inter-frame movement distance V of the sheet P detected in this way from the start of conveyance, and detects the integrated value as the conveyance distance of the sheet P.

  Next, the CPU 33 detects the timing at which the motor 15 starts to decelerate (S101). Specifically, for example, the timing at which the motor 15 starts to decelerate is detected based on the status signal of the motor driver 16 indicating the rotation speed or rotation angle of the motor 15.

When the motor 15 starts decelerating, the CPU 33 detects the timing at which the inter-frame movement distance of the sheet P becomes V ₁ or less (S102). That is, it is repeatedly determined whether or not the conveyance speed of the sheet P is equal to or lower than the first predetermined speed. Specifically, whether the moving distance between the detected frame in the last frame image 25 becomes V ₁ or less is determined.

When the frame interval moving distance of the sheet P becomes _{V 1} or less, CPU 33 is a digital frame size of the camera 20 with reduced from _{F 0} to _{F 1,} the frame rate of the digital camera 20 to change up from _{S 0} to _{S 1} ( S103). Frame rate _{S 1} in the present embodiment, a 60 frames / sec. When the frame size is reduced, the pixels of the image sensor 24 corresponding to the center of gravity of the image data before and after the reduction are matched. Note that when the frame size is reduced, the sides of the image data before and after the reduction may be matched with the sides of the effective pixel area of the image sensor 24.

Here, the relationship between the frame size of the digital camera 20 and the angle of view will be described. Circle A _L in FIG. 6 shows the imaging range of the digital camera 20 which is determined by the focal length of the optical system 21. The field angle corresponding to the frame size F ₁ smaller than the frame size F ₀ corresponding to the number of effective pixels of the image sensor 24 is narrower than the field angle corresponding to the frame size F ₀ . That is, when reducing the frame size from F ₀ to F _1, the angle of view of the digital camera 20 becomes narrow. For this reason, the frame size F ₁ is longer than the moving distance between frames, which is the moving distance of the sheet P in one frame period, that is, 1 / S ₁ second when the digital camera 20 is driven at the frame rate S ₁ . The side (side corresponding to the sub-scanning direction) must be set to be long. Since the frame rate changes during deceleration, the inter-frame movement distance after the change-up does not become longer than the inter-frame movement distance at the change-up timing. Therefore, the frame size F ₁ may be set according to the inter-frame movement distance immediately before or immediately after the reduction from F ₀ to F ₁ .

Specifically, for example, a frame size F _{0 obtained} by multiplying a frame size F ₀ at the start of the motor 15 by a predetermined reduction coefficient D ₁ , a mode coefficient m determined according to the conveyance mode, and a sheet coefficient μ determined by the sheet type is F. _Set to ₁ .
That is,
If F ₀ = h ₀ pixel × v ₀ pixel F ₁ = h ₁ pixel × v ₁ pixel,
F ₁ = F ₀ × D ₁ × m × μ
It becomes. In the present embodiment, the frame size is reduced while maintaining the aspect ratio, but the frame size may be reduced by changing the aspect ratio.

Reduction factor _{D 1} in the present embodiment is set to 0.7. The mode coefficient m is a coefficient to be multiplied because the conveyance speed and acceleration differ depending on the conveyance mode. The sheet coefficient μ is a coefficient to be multiplied because the friction coefficient and the mass vary depending on the type of the sheet P, and as a result, the conveyance error varies depending on the type of the sheet P. A plurality of types of appropriate sheet coefficients μ may be stored in advance, and corresponding sheet coefficients may be set according to the sheet type setting operation by the user. Since the surface state that determines the friction coefficient of the sheet P can be determined by analyzing the frame image output from the digital camera 20, the sheet coefficient can be set based on the result of image analysis, or the type of sheet Can be classified based on the result of image analysis, and an appropriate sheet coefficient corresponding to the type can be learned. When the sheet coefficient is set based on the image analysis result, the sheet type is classified based on the image analysis result, and an appropriate sheet coefficient according to the type is learned, an unknown type of sheet is inserted into the conveyance unit. Even if it is done, accurate feedback control can be realized.

Then CPU33 determines repeatedly whether interframe moving distance of the sheet P becomes _{V 2} below (S104). That is, it is repeatedly determined whether or not the conveyance speed of the sheet P has become equal to or lower than the second predetermined speed.

When the frame interval moving distance of the sheet P becomes _{V 2} below, CPU 33 along with further reduce the frame size of the digital camera 20 to the _{F 2} from _{F 1,} further change up the frame rate of the digital camera 20 to _{S 2} from _{S 1} (S105). Frame size F ₂ also may be set according to the same manner reduced before or interframe moving distance immediately from F ₁ to F ₂ and F _1. For example, if F ₂ = h ₂ pixels × v ₂ pixels and the reduction coefficient is D ₂ ,
F ₂ = F ₀ × D ₂ × m × μ
And Reduction factor _{D 2} in this embodiment is 0.5.

  Next, the CPU 33 detects timing for feeding back the conveyance distance of the sheet P to the stop position which is the conveyance control amount (S200). In the present embodiment, the feedback timing corresponds to the timing at which a frame image obtained by capturing the sheet P immediately before the stop during the deceleration period is output from the digital camera 20. Specifically, when the frame image is output from the digital camera 20 immediately before the stop, it is determined that the timing for feeding back the transport distance of the sheet P to the stop position that is the transport control amount has arrived. The frame image for determining the feedback timing is specified for each transport mode. Specifically, a counter corresponding to the number of frame images continuously output after starting the motor 15 and starting detection of the sheet conveyance distance is prepared, and each time a frame image is output, the counter The threshold value determined according to the transport mode may be compared with the counter value while incrementing.

When it is time to feed back the conveyance distance of the sheet P to the stop position, the CPU 33 is more accurate than the set value at the time of starting the motor 15 according to the conveyance distance, conveyance error, conveyance mode, and sheet type of the sheet P. A stop position as a control amount is estimated (S201). The conveyance distance of the sheet P, which is the integrated value of the inter-frame movement distance detected during the period from when the motor 15 is started to when the digital camera 20 outputs the frame image immediately before the stop, is set to L _c , and the motor 15 is started. conveying distance of the sheet P which is determined by the rotation angle of the motor 15 detected by the rotary encoder 161 in the period of the immediately preceding frame image stopped until the digital camera 20 outputs the (transport control amount) When L _p from the conveying distance Is determined by the following equation (1).
E = L _p −L _c (1)

If the remaining distance to the stop position held by the motor driver 16 at the timing when the digital camera 20 outputs the frame image immediately before the stop is L _g , the true remaining distance to the stop position at that timing is L _p + L the _g -L _c. If α is a predicted value (predictive error) of the remaining transport error that occurs until the stop position, the remaining transport distance L _t to be set as the control amount of the motor driver 16 is expressed by the following equation (2).
L _t = L _p + L _g −L _c + α = E + L _g + α (2)

Here, the prediction error α is a function of the true remaining distance (L _p + L _g −L _c ) until the stop position at the timing when the digital camera 20 outputs the frame image obtained by capturing the sheet P immediately before the stop. This function is called an error function. The deceleration characteristics of the motor 15 vary depending on the conveyance mode, and the slip characteristics between the conveyance roller 11a and the driven roller 11b and the sheet P during deceleration vary depending on the characteristics (friction coefficient, mass, etc.) of the sheet P. Therefore, the coefficient of the error function for obtaining α is determined for each combination of the conveyance mode and the sheet type. This coefficient can be corrected by learning for each combination of the conveyance mode and the sheet type. The coefficient corrected by learning can be applied to the next conveyance section. As described above, the type of the sheet P can be specified by image analysis. Therefore, when the sheet P is inserted into the conveyance unit, image data obtained by capturing the sheet P by the digital camera 20 is acquired, and the type of the sheet P is determined by analyzing the acquired image data, and the characteristics of the sheet P are determined. The coefficient of the error function corresponding to may be initialized.

Next, the CPU 33 updates the setting of the motor driver 16 to the stop position (remaining transport distance L _t ) as the accurate control amount derived in this way (S202).
Next, the CPU 33 repeatedly determines whether or not the sheet P has stopped (S203). Specifically, when the rotational speed held by the motor driver 16 as the status or the inter-frame movement distance derived by analysis of the frame image becomes zero, it is determined that the sheet P has stopped.
When the sheet P is stopped, the CPU 33 learns the coefficient of the error function according to the conveyance distance and the conveyance control amount detected by analyzing the frame image after the sheet P is stopped, and the next conveyance is performed based on the learning result. The coefficient of the error function applied to the section is set (S204).

  According to the sheet feeding method described above, the elapsed value of the conveyance error can be specified during sheet conveyance by detecting the sheet conveyance distance during sheet conveyance. Since the conveyance distance is feedback-controlled so as to cancel the conveyance error that occurs in the middle of the conveyance section within the conveyance section, an error in the sheet conveyance distance for each conveyance section can be reduced. For this reason, the positional accuracy in the sub-scanning direction on the sheet on which the belt-like image is printed in the sub-scanning direction is increased, and as a result, the print image quality is improved.

  In addition, since the conveyance distance of the sheet is feedback-controlled so as to cancel the conveyance error in the conveyance section for each conveyance section, it can cope with local fluctuations and is resistant to disturbance. In addition, since the sheet conveyance distance, which is a variable independent of the peripheral speed of the roller, is fed back to the conveyance control amount, it is possible to relax the manufacturing crossing criteria for the parts constituting the conveyance mechanism such as the roller. For this reason, manufacturing cost can be reduced. In addition, a correction table for reducing a conveyance error due to wear or the like of components constituting a conveyance mechanism such as a roller becomes unnecessary.

Further, as shown in FIG. 7, the frame rate of the digital camera 20 is increased in the deceleration section, and one frame period is sequentially switched to t ₁ , t ₂ , and t _{3 in} order, so that the digital camera 20 is used as compared with the case where switching is not performed. The timing for feeding back the transport distance of the sheet P detected in this way can be extended. Therefore, the conveyance distance as a control amount to be applied by predicting the conveyance error is shortened, and as a result, the accuracy of the sheet conveyance distance for each conveyance section can be further increased. This effect will be described in detail with reference to FIG. Assume that the frame rate is changed from 1 / t ₁ to 1 / t ₃ (t ₁ = 3t ₃ ) in the deceleration zone. When the frame rate is changed to 1 / t ₃ , the timing at which the conveyance distance is fed back to the conveyance control amount is compared with the case where the frame rate is maintained at 1 / t ₁ with reference to the moment when the sheet P stops. It stretched from the time _{T 1} to time _{T 3} immediately before the stop. That is, the period for controlling the motor 15 by applying the prediction error is shortened to _{１ ／} from t ₁ to t ₃ , and the control amount of the motor 15 to which the prediction error is applied is also reduced from L ₁ to L ₃ . The As a result, when the frame rate is changed to 1 / t ₃ , the transport error through the transport section is reduced from Δd ₁ to Δd ₃ compared to the case where the frame rate is maintained at 1 / t _1. It is.

Further, as shown in FIG. 9, the frame size of the digital camera 20 is increased as the conveyance speed is lowered, and at the same time the frame size is reduced from F ₀ to F ₁ and F ₂ . An increase in the amount of image data can be suppressed. Therefore, the accuracy of the sheet conveyance distance for each conveyance section can be further increased by increasing the frame rate while suppressing the processing capability required for the computer used for image analysis.

3. Other Embodiments Although the present invention has been specifically described with the embodiment, it is needless to say that the technical scope of the present invention is defined by the scope of the claims and is not limited to the above-described embodiment.
For example, the conveyance distance detected by the sheet feed sensor may be detected for each frame period or may not be detected for each conveyance section. Further, the switching between the frame rate and the frame size may be two steps instead of three steps, or the frame rate and the frame size may be changed for each frame period in the deceleration zone. The timing for switching the frame rate and the frame size may be determined without detecting the sheet conveyance speed. For example, the frame rate and the frame size may be switched at a timing when a time determined according to a predetermined conveyance speed control curve elapses from the start of conveyance. In this case, it is desirable to determine the switching timing by taking a margin in consideration of seat slip.

  Furthermore, the timing for feeding back the conveyance distance may be provided twice or more for each conveyance section. For example, if the period between the timing at which the conveyance distance is feedback-controlled and the timing at which the sheet stops is excessively short, a conveyance error that has already occurred in the remaining section may not be canceled. Conversely, if the period between the timing at which the conveyance distance is feedback-controlled and the timing at which the sheet stops becomes longer, the period during which the motor 15 is driven by applying the prediction error becomes longer, and the error in the conveyance distance becomes larger. . Therefore, for example, the feedback control may be executed twice as follows. In other words, the first feedback control may be executed at a timing at which the already generated conveyance error can be reliably canceled in the remaining section, and the timing at which the second feedback control is executed may be extended as much as possible until just before the sheet stops. .

  Also, the frame rate and the frame size may be changed in the acceleration section where the seat accelerates. Even in the acceleration section where the sheet conveyance speed is not constant, there is a difference in the degree of subject blurring that occurs in two consecutive frame images, as in the deceleration section. When the difference in the degree of subject blur increases, the accuracy of pattern matching decreases, and the detection accuracy of the interframe movement distance decreases. Therefore, if the frame rate and the frame size are changed in accordance with the sheet conveyance speed even in the acceleration section where the sheet is accelerated, the detection accuracy of the inter-frame movement distance is increased. Can be increased.

  In addition to applying the learning result of the prediction error of the transport distance in the latest transport section to the next transport section, the prediction error of the transport distance is learned in the acceleration section, and the learning result is applied to the deceleration section of the same transport section. It may be applied. Specifically, first, immediately before the end point of the acceleration section, that is, immediately before the start point of the constant speed section, the conveyance distance is feedback controlled and the coefficient of the error function is learned in the same manner as in the above-described embodiment. Then, based on the error function coefficient learned in the acceleration section, an error function coefficient applied to the deceleration section of the same transport section may be set. Furthermore, an error function coefficient to be applied to the acceleration section of the immediately following transport section may be set based on the error function coefficient learned in the deceleration section of the immediately preceding transport section. In addition, you may fix for every conveyance mode, without learning the coefficient of an error function.

  Further, in the present specification, the feedback control of the sheet conveyance distance is performed so as to cancel the conveyance error across two or more conveyance sections without performing feedback control so as to cancel the conveyance error for each conveyance section. The described sheet feed sensor is effective. Further, for example, the frame rate and the frame size may be changed for each transport mode in which the transport speed in the low speed section is different without changing the frame rate and the frame size in the transport section.

In addition, the sheet feed sensor described in this specification is applicable not only to an ink jet printer but also to other serial printers such as a thermal sublimation printer and a page printer. Further, the sheet feed sensor described in this specification may be applied to an ADF (Auto Document Feeder) of an image scanner. Of course, it goes without saying that the type of image sensor, the number of effective pixels, the frame rate, the frame size, and the reduction factor are merely examples. For example, the image sensor may be a CCD image sensor, the number of effective pixels of the image sensor may be QVGA or SVGA, the reduction coefficient D ₁ may be 0.8, 0.6, 0.5, or the reduction coefficient D _2. May be 0.4, 0.3, or 0.2.

DESCRIPTION OF SYMBOLS 1 ... Printer, 11a ... Conveyance roller, 11b ... Driven roller, 12 ... Carriage, 13 ... Ink cartridge, 14 ... Guide rod, 15 ... Motor, 16 ... Motor driver, 20 ... Digital camera, 21 ... Lens, 22 ... Light source, 23 ... controller, 24 ... image sensor, 25 ... frame image 25a ... frame image 25b ... frame image, 30 ... interface, 161 ... rotary encoder, 251 ... window, E ... transport error, F 0 _... frame size, F ₁ ... Frame size, F ₂ ... Frame size, P ... Sheet

Claims (7)

A conveyance unit that repeats conveyance and stopping of the sheet;
A printing unit for printing an image on the stopped sheet;
A digital camera that outputs moving image data obtained by imaging the conveyed sheet;
Analyzing means for detecting the transport distance of the sheet by analyzing the moving image data;
A conveyance control unit that feeds back a conveyance distance of the sheet detected before the sheet stops to a conveyance control amount until the sheet is stopped;
Equipped with a,
A serial printer that changes a frame rate of the digital camera between the start and the stop of conveyance of the sheet . The conveyance control means controls the conveyance distance until the sheet is stopped for the conveyance distance of the sheet detected before the sheet is stopped for each conveyance section from the start to the conveyance of the sheet. Feedback on quantity,
The serial printer according to claim 1. The conveyance control unit predicts a conveyance error that occurs until the sheet is stopped according to a conveyance control amount from the start to the stop of conveyance of the sheet and a detected conveyance distance of the sheet, Update the conveyance control amount until the sheet is stopped according to the predicted conveyance error.
The serial printer according to claim 1 or 2. The conveyance control unit predicts a conveyance error that occurs from when the conveyance distance of the sheet is detected until the sheet is stopped according to a conveyance mode, and until the sheet is stopped according to the predicted conveyance error. Update the transport control amount,
The serial printer according to any one of claims 1 to 3. The conveyance control unit predicts a conveyance error that occurs between the detection of the conveyance distance of the sheet and the stop of the sheet according to the type of the sheet, and stops the sheet according to the predicted conveyance error. Update the transport control amount until
The serial printer as described in any one of Claim 1 to 4. The conveyance control unit determines the type of the sheet based on image data output from the digital camera each time the sheet is inserted into the conveyance unit.
The serial printer according to claim 5. The conveyance control unit learns a conveyance error that occurs between the detection of the conveyance distance of the sheet and the stop of the sheet after the sheet is stopped, and detects the conveyance distance of the sheet after detecting the conveyance distance of the sheet. Predict the transport error that occurs before stopping according to the learning result,
The serial printer as described in any one of Claim 1 to 6.

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