JP4290487B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus.
[0002]
[Prior art]
[Patent Document 1]
JP 2000-94782 A
[Patent Document 2]
JP-A-8-82964
[0003]
As an image forming apparatus such as a printer, a facsimile machine, and a copying apparatus, for example, an ink jet recording apparatus is known. The ink jet recording apparatus refers to a recording medium (hereinafter also referred to as “paper” from the ink recording head, but is not limited to paper, and includes OHP and the like to which droplets can adhere. It is also called paper etc.) by ejecting ink droplets onto the recording (image formation), high-definition images can be recorded at high speed, running costs are low, noise is low, There is an advantage that it is easy to record a color image using multicolor inks.
[0004]
In an apparatus that forms an image by conveying a recording medium such as an ink jet recording apparatus, position information and size information of the recording medium are important. By accurately acquiring the position information of the recording medium, it is possible to start recording (start image formation) from an accurate position and improve the quality.
[0005]
In particular, in an apparatus that transports a recording medium using a transport belt, when ink droplets are ejected from a recording head at a position off the recording medium, the ink droplets land on the transport belt and the back surface of the recording medium is removed. Defects such as getting dirty.
[0006]
Here, conventionally, as described in, for example, [Patent Document 1], a sensor that measures a sheet length is provided, and the sheet length (length in the sheet conveyance direction) is detected by this sensor. is there. Conventionally, the recording medium reaches the image forming unit (recording unit) (leading edge detection) using a feed amount of the recording medium, a sensor fixed to the paper conveyance path, or the like.
[0007]
In addition, the trailing edge detection position varies depending on the paper transport speed.
For this reason, as disclosed in Japanese Patent Application Laid-Open No. 2004-228561, there is also known a method in which a correction value of the paper length (rear end position) detected according to the conveyance speed is used.
[0008]
[Problems to be solved by the invention]
In the image forming apparatus, when an attempt is made to detect that the paper has reached a specific position by the output of a sensor (detection means) arranged on the conveyance path, there is a deviation between the detection output timing of the detection means and the paper position. There is a problem that it occurs.
[0009]
This will be specifically described. FIG. 6 shows an example of the configuration of a sheet detection means (medium detection means) that detects a sheet using a feeler and a transmissive sensor. In this apparatus, the paper 500 is pressed against the transport roller 501 by the pressure roller 502, and an image is formed on the paper 500 by the recording head 503 while the paper 500 is transported by the rotation of the transport roller 501.
[0010]
A filler 506 that is swung by the sheet 500 and a transmission sensor 507 that is turned on / off by the swing of the filler 506 are disposed in the sheet conveyance path.
[0011]
In this configuration, as shown in FIG. 6A, the paper 500 is transported and passes through the filler 506 from the timing when the trailing edge of the paper 500 corresponds to the filler 506 (sensor output ON state). As shown in (b), a certain time ta is required until the filler 506 swings down in the direction of the arrow and reaches the position where the laser beam of the transmission sensor 507 is shielded (sensor output OFF state).
[0012]
On the other hand, since the paper 500 is fed by the transport roller 501, the paper is fed by a distance X1 (mm) during this time ta. As a result, if the timing at which the sensor 507 is turned off based on the output of the transmission sensor 507 is the paper rear end position, the paper length is detected to be longer by X1 (mm) than is actually detected. become.
[0013]
FIG. 7 shows an example of the configuration of a paper detection means (medium detection means) that detects a paper using an optical sensor (reflection type sensor). Here, an optical sensor 509 that is turned on / off depending on the presence or absence of the paper 500 is disposed in the paper conveyance path.
[0014]
Also in this configuration, the sheet 500 is conveyed from the timing when the rear end of the sheet 500 is at a position corresponding to the optical sensor 509 (sensor output ON state) as shown in FIG. ), A certain time tb is required until the paper 500 leaves the optical sensor 509 (sensor output OFF state). At this time, since the trailing edge of the sheet is detected by comparing the output of the optical sensor 509 with a certain reference value, a time tb until the sensor output reaches the reference value is required.
[0015]
On the other hand, since the paper 500 is fed by the transport roller 501, it is fed by a distance X2 (mm) during this time tb. As a result, if the timing at which the optical sensor 509 is turned off is the trailing edge position of the sheet, the sheet length is detected to be longer than the actual length by X2 (mm).
[0016]
As described above, when the sheet position at the time when the sensor output changes from ON to OFF is detected as the trailing edge of the sheet, the distances X1 and X2 described above are constant if the sheet conveyance speed is constant. Although the amount may be corrected, the conveyance speed actually varies. Further, in an apparatus that forms an image while repeatedly moving and stopping a sheet, such as an ink jet recording apparatus, it is difficult to specify the conveyance speed when the sensor is OFF and ON.
[0017]
Furthermore, the configuration of FIG. 6 also has a problem that the sheet position when the sensor output changes from ON to OFF differs depending on the rigidity of the sheet and the conveyance path.
[0018]
The present invention has been made in view of the above problems, and provides an image forming apparatus that can detect the length, leading edge, and trailing edge of a recording medium with a simple configuration and high accuracy, thereby improving image quality. The purpose is to do.
[0019]
[Means for Solving the Problems]
  In order to solve the above problems, an image forming apparatus according to the present invention provides:
  A medium detection unit configured to detect a recording medium conveyed along the conveyance path, and based on a detection result of the medium detection unit and a feed amount of the recording medium, a length, a rear end position, and a front end of the recording medium; In the image forming apparatus capable of specifying at least one of the positions,
  The medium detecting means includes a member that is provided on the opposite side of the conveyance surface of the recording medium that is held in a conveyance path and that swings and displaces depending on the presence or absence of the recording medium, and the member that swings and displaces Detecting means for detecting
  When specifying at least one of the length, the rear end position, and the front end position of the recording medium based on the detection result of the medium detection means and the feed amount of the recording medium, the correction according to the type of the recording medium is performed. Has the means to do
The configuration.
[0020]
  Here, a storage means for sampling and storing the feed amount of the recording medium at a predetermined period for a predetermined period is provided, and the detection is performed from the time when the swinging displacement member of the medium detection means is swung. A predetermined time corresponding to the time until the detection output of the means changes is traced back from the time when the detection output of the detection means of the medium detection means changes, and the feed amount of the recording medium in the meantime stored in the storage means The length or position of the recording medium can be specified based on the above.
  in this case,The correction can be performed by using different values depending on the type of recording medium during the predetermined time.
  Further, a different value may be used as the predetermined time depending on a conveyance path through which the recording medium passes.
[0021]
  Also,AboveOf media detection meansOutput of detection meansSampling timing andAboveThe timing for sampling the feed amount is performed within the same interrupt process.Can be configured.
  further,AboveOf media detection meansOutput of the detection meansMeans for sampling and storingMore than onceContinuousOutput of the detection means of the medium detection meansBased on the same sampling resultsAboveDetermined as the detection result of the medium detection meansCan be configured.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an explanatory side view for explaining the overall configuration of an ink jet recording apparatus showing an example of an image forming apparatus according to the present invention, and FIG. 2 is an explanatory plan view of a main part of the recording apparatus.
[0023]
In this ink jet recording apparatus, a carriage 3 is slidably held in a main scanning direction by a guide rod 1 and a guide rail 2, which are guide members horizontally mounted on left and right side plates (not shown), and a timing belt 5 is held by a main scanning motor 4. 2 is moved and scanned in the direction indicated by the arrow (main scanning direction) in FIG.
[0024]
The carriage 3 has a recording head 7 composed of four ink jet heads for ejecting ink droplets of yellow (Y), cyan (C), magenta (M), and black (Bk), with a plurality of ink ejection openings. They are arranged in a direction crossing the main scanning direction, and are mounted with the ink droplet ejection direction facing downward.
[0025]
As an ink jet head constituting the recording head 7, a piezoelectric actuator such as a piezoelectric element, a thermal actuator that utilizes a phase change caused by film boiling of a liquid using an electrothermal transducer such as a heating resistor, and a metal phase change caused by a temperature change. A shape memory alloy actuator to be used, an electrostatic actuator using an electrostatic force, or the like as an energy generating means for discharging ink can be used.
[0026]
The carriage 3 is also equipped with sub-tanks 8 for each color for supplying ink of each color to the recording head 7. Ink is supplied to the sub tank 8 from a main tank (ink cartridge) via an ink supply tube (not shown).
[0027]
On the other hand, as a paper feeding unit for feeding paper 12 stacked on a paper stacking unit (pressure plate) 11 such as a paper feed tray 10, a half-moon roller (for separating and feeding the paper 12 one by one from the paper stacking unit 11) A separation pad 14 made of a material having a large friction coefficient is provided facing the sheet feeding roller 13 and the sheet feeding roller 13, and the separation pad 14 is urged toward the sheet feeding roller 13 side.
[0028]
As a transport unit for transporting the paper 12 fed from the paper feed unit on the lower side of the recording head 7, a transport belt 21 for transporting the paper 12 by electrostatic adsorption and a paper feed unit A counter roller 22 for transporting the paper 12 fed through the guide 15 while sandwiching it between the transport belt 21 and the paper 12 fed substantially vertically upward are changed by about 90 ° and copied onto the transport belt 21. A conveying guide 23 for adjusting the pressure and a tip pressing roller 25 urged toward the conveying belt 21 by a pressing member 24. In addition, a charging roller 26 as a charging unit for charging the surface of the transport belt 21 is provided.
[0029]
Here, the conveyance belt 21 is an endless belt, is stretched between the conveyance roller 27 and the tension roller 28, and the conveyance roller 27 rotates from the sub-scanning motor 31 via the timing belt 32 and the timing roller 33. By doing so, it is configured to circulate in the direction indicated by the arrow in FIG. 2 (belt (paper) conveyance direction: sub-scanning direction).
[0030]
This transport belt 21 is a surface layer that is a sheet adsorbing surface formed of a resin material having a pure thickness of about 40 μm that is not subjected to resistance control, for example, ETFE pure material, and resistance control by carbon is performed using the same material as the surface layer. It has a back layer (medium resistance layer, ground layer).
[0031]
Further, the conveyance roller 27 and the counter roller 22 form a conveyance roller nip portion 18, and a sheet constituting medium detection means for detecting the presence or absence of the sheet 12 at a predetermined position upstream of the conveyance roller nip portion 18 in the sheet conveyance direction. A detection sensor 16 and a swingable filler 17 are arranged.
[0032]
The charging roller 26 is disposed so as to contact the surface layer of the conveyor belt 21 and rotate following the rotation of the conveyor belt 21, and applies 2.5N to both ends of the shaft as a pressing force. Further, the transport roller 27 also serves as an earth roller, and is placed in contact with the middle resistance layer (back layer) of the transport belt 21 and is grounded.
[0033]
Further, a guide member 36 is disposed on the back side of the conveyance belt 21 so as to correspond to a printing area by the recording head 4. The upper surface of the guide member 36 protrudes toward the recording head 7 from the tangent line of the two rollers (the conveyance roller 27 and the tension roller 28) that support the conveyance belt 21. As a result, the conveying belt 21 is pushed up and guided on the upper surface of the guide member 36 in the printing region.
[0034]
In order to detect the leading edge of the paper 12 conveyed by the conveyance belt 21, the carriage 3 is provided with a paper sensor 41 made up of a reflection type photosensor as detection means. The sheet sensor 41 is provided on the side positioned on the recording area (image forming area) side (conveying belt 21 side) when the carriage 3 is at the home position (image non-forming area).
[0035]
In addition, an encoder scale 42 having slits is provided on the front side of the carriage 3, and an encoder sensor 43 including a transmission type photosensor that detects the slits of the encoder scale 42 is provided on the front side of the carriage 3. An encoder 44 is configured to detect the position of the carriage 3 in the main scanning direction (position relative to the home position).
[0036]
Further, as a paper discharge unit for discharging the paper 12 recorded by the recording head 7, a separation unit for separating the paper 12 from the conveyance belt 21, a paper discharge roller 52 and a paper discharge roller 53, and paper discharge And a paper discharge tray 54 for stocking the paper 12 to be stored.
[0037]
A double-sided paper feeding unit 61 is detachably mounted on the back. The double-sided paper feeding unit 61 takes in the paper 12 returned by the reverse rotation of the transport belt 21, reverses it, and feeds it again between the counter roller 22 and the transport belt 21.
[0038]
In the ink jet recording apparatus configured as described above, the paper 12 is separated and fed one by one from the paper feed unit, and the paper 12 fed substantially vertically upward is guided by the guide 15, and includes the transport belt 21 and the counter roller 22. The leading end is guided by the conveying guide 23 and pressed against the conveying belt 21 by the leading end pressing roller 25, and the conveying direction is changed by approximately 90 °.
[0039]
At this time, a positive output and a negative output are alternately repeated from the high voltage power source to the charging roller 26 by a control circuit (not shown), that is, an alternating voltage is applied, and a charging voltage pattern in which the conveying belt 21 is alternating, that is, In the sub-scanning direction, which is the circumferential direction, plus and minus are alternately charged in a band shape with a predetermined width. When the paper 12 is fed onto the positively and negatively charged conveying belt 21, the paper 12 is attracted to the conveying belt 21, and the paper 12 is conveyed in the sub-scanning direction by the circular movement of the conveying belt 21.
[0040]
Therefore, by driving the recording head 7 according to the image signal while moving the carriage 3, ink droplets are ejected onto the stopped paper 12 to record one line, and after the paper 12 is conveyed by a predetermined amount, Record the next line. Upon receiving a recording end signal or a signal that the trailing edge of the paper 12 has reached the recording area, the recording operation is finished and the paper 12 is discharged onto the paper discharge tray 44.
[0041]
In the case of double-sided printing, when recording on the front surface (surface to be printed first) is completed, the recording belt 12 is fed into the double-sided paper feeding unit 61 by rotating the conveyor belt 21 in the reverse direction. The paper 12 is reversed (with the back surface being the printing surface), fed again between the counter roller 22 and the transport belt 21, controlled in timing, and transported onto the transport bell 21 as described above. Then, after recording on the back surface, the paper is discharged onto the paper discharge tray 44.
[0042]
Next, details of the sheet detection means will be described with reference to FIGS. FIG. 3 and FIG. 4 are main part enlarged explanatory views for explaining different states.
As described above, the medium detecting means for detecting that the paper 12 as the recording medium has reached a specific position in the transport path includes the filler 17 that swings and displaces depending on the presence of the paper 12, and the swing of the filler 17. The paper detection sensor 16 includes a transmission sensor that blocks / transmits light emitted by displacement.
[0043]
When the filler 17 is not in contact with the paper 12 as shown in FIG. 3, the output (sensor output) of the paper detection sensor 16 is turned off because the emitted light is blocked, and as shown in FIG. Is in contact with the paper 12, the output of the paper detection sensor 16 (sensor output) is turned on because the emitted light is not blocked.
[0044]
The presence or absence of the paper 12 can be detected by comparing the sensor output of the paper detection sensor 16 with a reference value. That is, when the sensor output changes from OFF to ON, it can be detected that the leading edge of the paper 12 has reached the sensor position, and when the sensor output changes from ON to OFF, it can be detected that the trailing edge of the paper 12 has reached the sensor position. If the OFF time and the conveyance speed are known, the paper length can be detected.
[0045]
Next, an outline of the control unit of the ink jet recording apparatus will be described with reference to FIG. This figure is an overall block diagram of the control unit.
The control unit includes a printer controller 70, a motor driver 81 for driving the main scanning motor 4 and the sub scanning motor 31, and a paper feeding clutch 83 for transmitting the rotation of the sub scanning motor 31 to the paper feeding roller 13. A driver 82 for driving, a head driver (configured by a head driving circuit and a driver IC) 84 for driving the recording head 7 (inkjet head), and the like are provided.
[0046]
The printer controller 70 is an interface (hereinafter referred to as “I”) that receives print data and the like from a host side such as an information processing device such as a personal computer, an image reading device such as an image scanner, and an imaging device such as a digital camera. 72), a main control unit 73 including a CPU, a RAM 74 that stores various data, a ROM 75 that stores routines for various data processing, a conveyance amount counter 76, and a timer 77 A drive signal generation circuit 78 for generating a drive waveform for the recording head 7, and an I / F 79 for transmitting print data and drive waveform developed in dot pattern data (bitmap data) to the head driver 84. Send motor drive data to motor driver 81 and send clutch on signal And an I / F80, etc. for transmission to driver 82.
[0047]
The RAM 74 is used as various buffers and work memory. The ROM 75 stores various control routines executed by the main control unit 73, font data, graphic functions, various procedures, and the like.
[0048]
As shown in FIG. 2, the main control unit 73 also receives an output signal of an encoder 34 composed of a slit plate 32 fixed to the shaft 27 a of the conveying roller 27 that is rotationally driven by the sub-scanning motor 31 and a photo sensor 33. .
[0049]
The main control unit 73 performs paper feed control based on a detection signal from the paper detection sensor 16, and performs control according to the present invention using a transport amount counter 76 and a timer 77 to control the paper length and rear end position. Perform detection and so on. The main control unit 73 detects the position of the carriage 3 in the main scanning direction based on the output signal of the encoder 44 and controls the stop position of the carriage 3, and the leading end position of the paper 12 based on the detection signal of the paper sensor 41. Detection and detection of the presence or absence of the paper 12 on the conveyor belt 21 are performed.
[0050]
The main control unit 73 reads and analyzes the print data in the reception buffer included in the I / F 72, stores the analysis result (intermediate code data) in a predetermined area of the RAM 74, and stores the analysis result in the ROM 75. Using the stored font data, dot pattern data for outputting an image is generated and stored again in a different predetermined area of the RAM 74. Note that when image data is expanded into bitmap data and transferred to the recording apparatus by the printer driver on the host side, the received bitmap image data is simply stored in the RAM 74.
[0051]
When the dot pattern data corresponding to one line of the recording head 7 is obtained, the main control unit 73 synchronizes the dot pattern data for one line with the clock signal CLK via the I / F 79. Serial data is sent to the head driver 82, and a latch signal is sent to the head driver 82 at a predetermined timing.
[0052]
The drive signal generation circuit 78 includes a ROM (can be configured by the ROM 75) storing pattern data of a drive waveform (drive signal), and a D / A for D / A converting the drive waveform data read from the ROM. It consists of a waveform generation circuit including a converter, an amplifier, and the like.
[0053]
The head driver 82 is a shift register that receives a clock signal from the main control unit 73 and serial data that is a print signal, a latch circuit that latches a register value of the shift register using a latch signal from the main control unit 73, and a latch circuit A level conversion circuit (level shifter) that changes the output value of the signal and an analog switch array (switch means) whose on / off is controlled by this level shifter, and driving waveform by controlling on / off of the analog switch array Are selectively applied to the head 7.
[0054]
Next, an outline of printing control (recording control) by the main control unit 73 will be described with reference to FIG.
Prior to paper feeding, the main control unit 73 rotationally drives the main scanning motor 4 to move the carriage 3 at the non-recording position, so that the main control unit 73 is moved to the substantially central portion of the transport belt 21 (or the paper of the paper size to be fed). After that, the paper feed clutch 83 is turned on to apply the rotation of the sub-scanning motor 31 to the paper feed roller 13. As a result, the paper feed roller 13 rotates once in the clockwise direction, and the paper 12 is separated from the paper feed tray 10 into one sheet by the friction pad 14 and sent out.
[0055]
Then, the detection signal of the paper sensor 41 is checked to determine whether or not the leading edge of the paper 12 has been detected, and the paper 12 is conveyed (fed) to a predetermined printing start position after the leading edge of the paper 12 is detected. Stop.
[0056]
Thereafter, the carriage 3 is temporarily returned to the home position, and the movement of the carriage 3 to the recording area side is started based on the output of the encoder 44 with reference to the home position. At this time, the detection signal of the paper sensor 41 is checked to check the paper. When the paper 12 is present, the required printing (recording operation) is performed. When the paper 12 is not detected, the recording operation is not performed. Thereby, since printing (ink droplet ejection) is not performed at a place where the paper 12 is not present, ink droplets are not ejected onto the transport belt 21, and contamination of the transport belt 21 and the paper 12 can be prevented.
[0057]
Next, sampling processing of the output of the paper detection sensor 16 will be described with reference to FIGS.
The main control unit 73 starts the processing shown in FIGS. 7 and 8 by interruption processing with a predetermined sampling period, and samples the sensor output of the paper detection sensor 16. And it is discriminate | determined whether the sensor output of the paper detection sensor 16 is the same as the time of the last sampling.
[0058]
At this time, if the sensor output of the paper detection sensor 16 is the same as the previous sampling, the number of continuous sensor output detection is recorded (stored).
[0059]
On the other hand, if the sensor output of the paper detection sensor 16 is not the same as the previous sampling, it is determined whether or not the sensor output has been detected ON after clearing the sensor output continuous detection count record.
[0060]
Then, when the sensor output is detected to be ON, the sheet type and the conveyance path are referred to the feed amount before the predetermined time with reference to the correction value table shown in FIG. The correction value consisting of is added and recorded as the detection position. If the sensor output does not detect ON, a correction value is added to the current feed amount with reference to a correction value table shown in FIG.
[0061]
Here, the feed amount of the paper 12 is obtained by counting the number of detected pulses output from the encoder 34.
[0062]
Then, after recording the detection result, it is determined whether or not the sensor output has been turned ON a predetermined number of times. At this time, when the sensor output is turned ON a predetermined number of times, the sensor ON is notified. When the sensor output has not been turned on a predetermined number of times, it is determined whether or not the sensor output has been turned off a predetermined number of times. When the sensor output has been turned off a predetermined number of times, the sensor OFF is notified.
[0063]
Thus, when the sensor ON / OFF value is continuously detected a predetermined number of times, it is possible to avoid the influence of the nozzle by determining that the sensor output value has changed for the first time.
[0064]
Thereafter, the feed amount is sampled and the count value of the feed amount storage counter is incremented (+1). Then, it is determined whether or not the feed amount storage counter exceeds the maximum value. When the feed amount storage counter exceeds the maximum value, the feed amount storage counter is set to “0”, and the feed amount storage counter does not exceed the maximum value. Sometimes, as it is, the feed amount is saved at the position indicated by the count value of the feed amount saving counter, and the interruption process is terminated.
[0065]
Here, the sampling value of the feed amount is stored in the memory (RAM) 74 as an image as shown in FIG. That is, the RAM 74 also serves as storage means. The current recording position is held in a memory area called a feed amount storage counter, and the feed amount storage counter is incremented by 1 each time sampling is performed, and when the predetermined maximum value is exceeded, it returns to zero.
[0066]
Further, the predetermined retroactive time (predetermined time) determined by the paper type and the conveyance path is stored as fixed data (predetermined time table) on the memory (ROM 75) in the image as shown in FIG. 10, and the predetermined correction value is shown in FIG. 11 is stored as fixed data (correction value table) on the memory (ROM 75). Thereby, the required retroactive time and the correction value can be extracted from the paper type and the conveyance path. The paper type or the like may be given from the host side or set on the apparatus main body side.
[0067]
In this way, the paper position (rear edge position, front edge position) and paper length can be obtained with high accuracy by using different predetermined times and correction values depending on the paper type and transport path.
[0068]
By performing the processing as described above, the sampled feed from the time when the sensor output becomes a specific signal on the memory (when it is detected that the paper has reached the paper detection sensor) to a point that is a predetermined time back The value (detection position) corrected for the amount is stored, and on the side referring to this value, the detection position is obtained by referring to the memory when the sensor output OFF notification or the sensor output ON notification is received. And specify the paper length and the trailing edge of the paper.
[0069]
That is, a storage means for sampling and storing the feed amount of the recording medium at a predetermined period for a predetermined period is provided, and a specific signal when the recording medium reaches a specific position on the conveyance path as a medium detection means. The length of the recording medium and the rear end position (based on the feed amount and the predetermined correction value sampled from the detection of the output of the specific signal from the sensor to the time point that is traced back a predetermined time) Or it can be the tip position). Thereby, the length and rear end position of the recording medium can be specified with high accuracy.
[0070]
Note that the detection position (detection position of the leading edge of the paper) when the sensor is turned on from the sensor OFF is not the target here, so only the detection position recording is described in FIGS. 7 and 8 (in this case) The current feed amount sampling value may be added with a correction value when a predetermined sensor is ON.)
[0071]
In this way, in the above processing, the sensor detection processing (referring to the sensor output value) is also performed in the interrupt processing at the sampling period of the feed amount, so only one timer is required, and the error due to the sampling cycle The calculation can also be simply calculated as the feed rate sampling period.
[0072]
In other words, when the timing for sampling the sheet feed amount and the timing for referring to the sensor output value are defined, the occupancy of the memory, the usage amount of the timer, and the error calculation method are affected depending on the defined method.
[0073]
For example, if the feed amount sampling is 0.50 msec and the sensor output value sampling is 1.00 msec, it is necessary to refer to the feed amount value that goes back 1.50 msec from the sensor ON. The feed amount error to be referred to is 1.0 msec. On the other hand, if the sensor output value is sampled at 3.00 msec, two timers are required, and the error in the feed amount to be referred to also differs.
[0074]
When implemented in software, the amount of resources used such as memory and timers and the amount of calculation of errors are preferably as small as possible from the viewpoint of performance and cost. As mentioned above, interrupts at the sampling period of the feed amount It is preferable to refer to the sensor output value in the processing.
[0075]
In this case, the feed rate sampling period and the sensor sampling period cannot be set arbitrarily. Further, if the sensor detection process is performed once every several interrupt processes, the detection accuracy is sacrificed to some extent, but the load per interrupt process can be reduced.
[0076]
In the above embodiment, the present invention has been described with reference to an example in which the present invention is applied to a shuttle type ink jet recording apparatus using a carriage. However, the present invention can also be applied to a line type ink jet recording apparatus using a line type head. The present invention is not limited to this, and can also be applied to an image forming apparatus such as a copying machine, a facsimile machine, and a copier / printer / facsimile machine.
[0077]
【The invention's effect】
  As described above, according to the image forming apparatus of the present invention, the medium detecting unit is provided according to the presence or absence of the recording medium provided on the side opposite to the conveyance surface of the recording medium held in the conveyance path. The length of the recording medium and the rear end position based on the detection result of the medium detection means and the feed amount of the recording medium. When specifying at least one of the leading edge position and the recording medium, it is possible to detect the position and length of the recording medium with high accuracy.
[Brief description of the drawings]
FIG. 1 is an explanatory side view showing an example of an image forming apparatus according to the present invention.
FIG. 2 is an explanatory plan view of the main part of the apparatus.
FIG. 3 is a main part enlarged explanatory view for explaining the operation of the paper detection means of the apparatus.
FIG. 4 is an enlarged explanatory view of a main part for explaining the operation of the paper detection unit.
FIG. 5 is a block diagram illustrating the control unit of the apparatus
FIG. 6 is a flowchart for explaining the overall processing by the control unit;
FIG. 7 is a flowchart for explaining an example of feed amount and sensor output sampling processing by the control unit;
FIG. 8 is a flowchart for explaining processing subsequent to FIG.
FIG. 9 is an explanatory diagram for explaining a storage table of feed amount sampling values;
FIG. 10 is an explanatory diagram for explaining a predetermined time table;
FIG. 11 is an explanatory diagram for explaining a correction value table;
FIG. 12 is an explanatory diagram for explaining an example of a medium detection configuration using a filler and a transmission sensor;
FIG. 13 is an explanatory diagram illustrating an example of a medium detection configuration using a transmissive sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 3 ... Carriage, 7 ... Recording head, 10 ... Paper feed tray, 12 ... Paper, 13 ... Paper feed roller, 15 ... Guide, 16 ... Paper detection sensor, 21 ... Conveyance belt, 22 ... Counter roller, 26 ... Charging roller, 27: conveying roller, 28: tension roller, 41: paper sensor, 34: encoder.

Claims (6)

A medium detection unit configured to detect a recording medium conveyed along the conveyance path, and based on a detection result of the medium detection unit and a feed amount of the recording medium, a length, a rear end position, and a front end of the recording medium; In the image forming apparatus capable of specifying at least one of the positions,
The medium detecting means includes a member provided on the opposite side to the conveyance surface of the recording medium held in the conveyance path, and a member that swings and displaces according to the presence or absence of the recording medium. Detecting means for detecting
When specifying at least one of the length, the rear end position, and the front end position of the recording medium based on the detection result of the medium detection means and the feed amount of the recording medium, correction according to the type of the recording medium is performed. An image forming apparatus comprising: means for performing the operation. The image forming apparatus according to claim 1.
A storage unit that samples and stores the feeding amount of the recording medium at a predetermined period for a predetermined period;
The detection output of the detection means of the medium detection means has changed for a predetermined time corresponding to the time from when the swinging displacement member of the medium detection means swings until the detection output of the detection means changes. An image forming apparatus characterized in that the length or position of the recording medium is specified based on a feed amount of the recording medium stored in the storage means, going back from time.   The image forming apparatus according to claim 2, wherein the correction is performed by using a different value depending on a type of a recording medium in the predetermined time. 4. The image forming apparatus according to claim 2 , wherein a different value is used as the predetermined time depending on a conveyance path through which the recording medium passes.   5. The image forming apparatus according to claim 2, wherein the timing for sampling the output of the detection unit of the medium detection unit and the timing for sampling the feed amount are performed in the same interrupt process. Image forming apparatus.   6. The image forming apparatus according to claim 2, further comprising a means for sampling and storing the output of the detection means of the medium detection means, wherein the detection means of the medium detection means is performed a plurality of times. An image forming apparatus comprising: determining the detection result of the medium detection unit based on the same output sampling result.

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