JP4568624B2 - Recording paper transport device and inkjet recording device - Google Patents

Description

  The present invention relates to a recording paper transport apparatus capable of transporting recording paper with high accuracy and an ink jet recording apparatus including the recording paper transport apparatus.

JP 2002-248822 A JP 2004-17505 A

  In recent years, in the field of ink jet recording systems, ink has been changed from a dye system to a pigment system in order to improve the light resistance and deterioration with time of the ink, and the ink viscosity has been increased. Although the blurring on the recording paper has been drastically reduced due to the increase in viscosity, conversely, the poor positioning accuracy of the ink droplet landing position of the ink droplets can be clearly seen (white stripes, black stripes, banding). In particular, since the contribution ratio of stop position accuracy during conveyance of recording paper in the sub-scanning direction is large, it has become an indispensable technical problem.

  In the conventional sub-scanning recording paper transport mechanism of the ink jet recording system, a transport method using a grindstone transport roller or a transport belt has been generally used. For the feed amount control, a code wheel is installed on the transport roller shaft, and this value is measured by an encoder sensor. In general, the reading control is performed by the above method. For example, Patent Document 1 discloses a configuration in which a conveyance roller and a discharge roller are arranged on the upstream side and the downstream side of a platen and a recording paper is conveyed in the sub-scanning direction. A printer that controls the conveyance of recording paper by reading with a sensor is disclosed. However, this method has a problem that it is difficult to perform stop position control with high accuracy by accumulating component accuracy such as pulleys and transport rollers.

  Therefore, for example, Patent Document 2 describes that a scale (linear scale) is provided on a conveyance belt that is a member that actually conveys recording paper, and the linear scale is detected by an encoder sensor to control the conveyance belt. .

  However, the method described in Patent Document 2 has a problem that the accuracy of the recording paper feed amount deteriorates when the conveyance belt (linear scale) expands and contracts due to the environment or time.

  The present invention provides a recording paper transport apparatus that solves the above-described problems in the conventional recording paper transport apparatus, detects the expansion and contraction of the transport belt, corrects the control amount, and transports the recording paper with high accuracy. This is the issue.

  It is also an object of the present invention to provide an ink jet recording apparatus that can obtain excellent image quality and stability by conveying recording paper with high accuracy.

According to the present invention, in the recording paper transport apparatus capable of intermittently transporting the recording paper according to the present invention, a linear encoder is provided in the transporting means for transporting the recording paper, and a rotary encoder is provided in the rotating member involved in driving the transporting means. And controlling the feeding amount of the conveying means based on the outputs of the two encoders, and the linear encoder is arranged at a predetermined distance from the linear scale attached to the conveying means in the sub-scanning direction. Two linear sensors that detect the difference between the linear scale and the two linear sensors, and a calculating unit that calculates expansion / contraction of the conveying unit based on a detection phase difference between the two linear sensors. This is solved by providing a glass scale for defining the distance between the sensors .

  Further, it is preferable that the calculation unit calculates the expansion rate or expansion amount of the transport unit based on a detection phase difference between the two linear sensors in an ideal state and a detection phase difference between the two linear sensors at the time of detection. .

  Further, it is preferable that the reference value of the linear scale used for the feed amount control of the transport unit is corrected by the expansion rate or expansion amount of the transport unit calculated by the calculation unit.

  The detection phase difference between the two linear sensors is preferably counted by the number of output pulses of the rotary encoder.

The glass scale is preferably configured as an optical slit.
Moreover, it is preferable that the pitch of the optical slits of the glass scale is equal to the pitch of the linear scale.

Further, it is preferable that the two linear sensors are provided integrally.
Further, it is preferable that a temperature detection unit is provided in the vicinity of the transport unit, and an output of the temperature detection unit is used for determination of expansion or contraction when the expansion / contraction of the transport unit is calculated by the calculation unit.

Further, it is preferable that the two linear sensors and the temperature detecting means are provided integrally.
It is preferable to have timer means and use the output of the timer means for the determination of expansion or contraction when the calculation means calculates the expansion / contraction of the transport means.

Further, it is preferable that the transport unit is a transport belt, and the transport belt includes a suction unit that sucks the recording paper.
Moreover, it is preferable that the linear scale is formed on the back surface of the conveyor belt.

According to the present invention, the above-described problem is characterized in that the recording paper transport device according to any one of claims 1 to 12 is mounted as a recording paper transport means in the sub-scanning direction in the ink jet engine section. This is solved by the ink jet recording apparatus.

According to the recording paper conveyance device of the present invention, the recording paper conveyance device includes the calculation unit that calculates the expansion and contraction of the conveyance unit based on the detection phase difference between the two linear sensors that are arranged at a predetermined distance in the sub-scanning direction and detect the linear scale. By calculating the expansion / contraction of the recording medium, it is possible to carry out the conveyance means, that is, the recording paper, with high accuracy conveyance control / stop position control.
In addition, since the glass scale for defining the distance between the two linear sensors is disposed between the linear scale and the two linear sensors, the expansion and contraction of the conveying means can be detected with high accuracy.

  According to the configuration of claim 2, since the expansion rate or expansion amount of the transport unit is calculated based on the detection phase difference between the two linear sensors in the ideal state and the detection phase difference between the two linear sensors at the time of detection, the transport unit It is possible to appropriately calculate the expansion / contraction rate or the expansion / contraction amount.

  According to the configuration of the third aspect, the reference value of the linear scale used for the feed amount control of the transport unit is corrected. Therefore, when the transport unit is expanded or contracted, the correction is performed and the recording paper can be fed with high accuracy. .

  According to the configuration of the fourth aspect, since the detected phase difference between the two linear sensors is counted by the number of output pulses of the rotary encoder, the phase difference can be detected with high accuracy using a high-resolution rotary encoder.

With the configuration of the fifth aspect , since the glass scale is configured as an optical slit, the distance between the two linear sensors can be easily defined with high accuracy.
According to the configuration of the sixth aspect , since the pitch of the optical slits of the glass scale is set equal to the pitch of the linear scale, the phase difference detection accuracy of the two linear sensors can be increased.

With the configuration of the seventh aspect , by providing the two linear sensors in an integrated manner, it is possible to reduce the cost by integrating the circuit board. In addition, the distance between the sensors can be easily maintained.

According to the configuration of the eighth aspect , the temperature detecting unit is provided in the vicinity of the conveying unit, and the output of the temperature detecting unit is used for determination of expansion or contraction when the expansion / contraction of the conveying unit is calculated by the calculating unit. It is possible to prevent erroneous determination of the expansion or contraction of the means.

According to the configuration of the ninth aspect , by providing the two linear sensors and the temperature detecting means in an integrated manner, it is possible to reduce the cost by integrating the logic circuit and increasing the efficiency of the assembling work. In addition, the distance between the sensors can be easily maintained.

According to the structure of claim 10 , since the timer means is used, and the output of the timer means is used for the determination of the expansion or contraction when calculating the expansion / contraction of the conveying means by the calculating means, the extension or contraction of the conveying means is erroneously determined. Can be prevented.

According to the configuration of the eleventh aspect, since the conveyance means is a conveyance belt, and the conveyance belt includes an adsorption means for adsorbing the recording paper, the recording paper is prevented from being displaced during conveyance, and the recording paper is stably stabilized by the conveyance belt. Can send.
According to the structure of the twelfth aspect , since the linear scale is formed on the back surface of the transport belt, it is possible to obtain high durability and high reliability by eliminating the influence of ink stains.

According to the ink jet recording apparatus of the thirteenth aspect , the expansion and contraction of the conveying means can be calculated and the conveying means, that is, the recording paper can be controlled with high accuracy, and the stop position can be controlled. Can achieve high image quality.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram showing an example of an ink jet recording apparatus provided with a recording paper conveying apparatus according to the present invention. The ink jet recording apparatus 100 shown in this figure is configured as a copying apparatus with a scanner unit 30 disposed above a printer unit 50. A paper discharge unit 40 is formed between the scanner unit 30 and the printer unit 50.

  The scanner unit 30 is provided with a scanning unit 32 below the contact glass 31 so that the scanning unit 32 can travel. The scanner unit 30 guides reflected light from a document illuminated by a light source to a CCD 33 via a mirror lens or the like, and reads a document image. Is done. A pressure plate 34 is provided above the contact glass 31 so as to be openable and closable.

  In the printer unit 50, a recording paper conveyance path from the paper feeding cassette 27 disposed below to the paper discharge unit 40 is formed as indicated by a one-dot chain line in the drawing, and a conveyance roller is provided at a predetermined position in the recording paper conveyance path. 25 is installed as appropriate. Reference numeral 24 denotes a paper feed roller, and reference numeral 26 denotes a paper discharge roller. A manual feed tray 28 is provided on the side of the apparatus, and recording paper is also fed from the manual feed tray 28 via a paper feed roller 29.

  The ink jet engine 20 includes a recording paper conveyance device 1. In this embodiment, a system for conveying the recording paper in the sub-scanning direction using an electrostatic adsorption belt is employed. The conveyance system using the electrostatic adsorption belt can feed the paper more stably than the conventional roller conveyance system. A carriage 21 positioned on the recording paper transport apparatus 1 is mounted with a print head 22 and reciprocates in the main scanning direction (direction perpendicular to the drawing), and prints by ejecting ink droplets from the head 22. The print head 22 has a nozzle row length of 1.27 inches, which is wider than before, and in this example, one head is provided for each color of cyan (C), magenta (M), yellow (Y), and black (Bk). 4 head configuration. However, the number of heads is not limited to this, and a two-head configuration of two heads with two colors may be used.

  In the ink jet recording apparatus 100 of this example, each color ink cartridge 23 is mounted separately from the print head, and ink in the cartridge 23 is supplied to the print head 22 via a supply tube (not shown). A method of mounting each color ink cartridge separately from the head is a method suitable for business use because a large-capacity type cartridge corresponding to an increase in ink consumption accompanying an increase in printing speed can be used.

FIG. 2 is a schematic diagram schematically showing the configuration of the recording paper transport apparatus 1.
In this figure, an electrostatic attraction belt 2 as a conveying means for conveying recording paper in the sub-scanning direction is formed in an endless loop shape and is stretched between a conveying roller 3 and a tension roller 4. A charging roller 5 for applying an electric charge to the electrostatic attraction belt 2, a neutralizing brush 6 for neutralizing the electrostatic attraction belt 2, and a cleaning blade 7 for cleaning the electrostatic attraction belt 2, respectively. It is in pressure contact with the outer peripheral surface.

  A pressure roller 13 supported by a pressure plate (not shown) is disposed to face the conveying roller 3, and a tip pressure roller 14 is supported at the tip of the pressure plate. The tip pressurizing roller 14 functions to press the electrostatic attraction belt 2 against the platen 10 disposed inside the upper side portion of the electrostatic attraction belt 2. The recording paper fed from the paper feed cassette 27 is electrostatically attracted to the upper surface of the electrostatic adsorption belt 2, and the electrostatic adsorption belt 2 that rotates counterclockwise in the figure moves from right to left in the figure. That is, it is conveyed in the sub-scanning direction.

  On the downstream side of the tension roller 4, a paper discharge roller pair including a paper discharge roller 17 and a spur 18 is provided. The tension roller 4 is provided with a separation claw (not shown), and the recording paper separated from the electrostatic attraction belt 2 by the separation claw is disposed downstream by a paper discharge roller pair including a paper discharge roller 17 and a spur 18. Sent.

  A high resolution code wheel 8 is mounted on the shaft of the transport roller 3. The code wheel 8 is formed with a slit (not shown), and a transmission type encoder sensor 9 for detecting the slit is provided. The code wheel 8 and the sensor 9 constitute a rotary encoder. As the rotary encoder, it is preferable to use 300 LPI or more and 4800 CR or more.

  As shown in detail in FIG. 3, a linear scale 15 is formed on the back surface of the electrostatic attraction belt 2. The linear scale can be formed by, for example, aluminum vapor deposition on the back surface of the belt (aluminum vapor deposition and flying with a laser to form a stripe pattern). Reflective encoder sensors 11 and 12 for reading the linear scale 15 are arranged in the loop of the belt 2. The linear scale 15 and sensors (linear sensors) 11 and 12 formed on the back surface of the belt constitute a linear encoder. As a linear encoder, it is preferable to use 100 LPI or more. In this example, a linear encoder having a resolution of 150 LPI is used. A thermistor 19 serving as temperature detecting means is disposed between the encoder sensors 11 and 12.

  Now, the double encoder system enables high-precision control of the conveyor belt (high-precision sub-scanning stop position control). However, if the linear scale expands or contracts due to the environment or time, it becomes the reference for belt feed control. The linear scale reference value (scale pitch) changes, and the accuracy of the recording paper feed amount decreases. Therefore, the present invention is characterized in that the linear scale reference value is corrected based on the outputs of the two linear sensors 11 and 12.

  Here, before describing the features of the present invention, feed control of the transport belt (electrostatic chucking belt 2) by the double encoder method will be described. 2 to 4 are mainly referred to in this description, and FIG. 4 is a schematic diagram conceptually showing the signal processing of the double sensor system by the rotary encoder and the linear encoder.

  When the electrostatic attraction belt 2 is conveyed by the rotation of the conveying roller 3, the linear scale 15 processed on the back of the belt also moves together and is read by the reflective linear sensor 11 and output as a signal (by the sensor 12). It may be read, but here it is referred to as sensor 11). This signal may be an analog sine wave or a rectangular wave. Here, description will be made assuming that the wave is a rectangular wave.

  When the electrostatic attraction belt 2 moves, the reflective encoder sensor 11 reads the position information of the 150 LPI cycle in FIG. 4 and outputs it as a rectangular wave (linear encoder signal). Similarly, a rectangular wave signal is output from the code wheel 8 and the transmission encoder sensor 9 arranged on the axis of the transport roller 3 (rotary encoder signal).

  As shown in FIG. 4, the linear scale period L1 = 150 LPI = about 169.3 μm. On the other hand, the conveyance belt conversion value L2 = 9600 LPI = about 2.65 μm in the rotary encoder. This number (resolution) itself can be selected with the required accuracy and cost.

Here, let us consider moving the belt 2 by N pulses by a signal from the rotary encoder. It is assumed that the relationship between the linear encoder 1 pulse distance L1 and the rotary encoder 1 pulse distance L2 is L1 = L2 × 64. The amount of movement of N pulses in terms of rotary encoder is expressed by the following equation 1 where n1 is the number of pulses of the linear encoder and n2 (0 to 63) is the fraction of the rotary encoder.
N = 64 × n1 + n2 [Equation 1]

When this is expressed as a movement amount, it becomes 2.65 μm × N = 169.3 μm × n1 + 2.65 μm × n2 (however, the numerical values of 169.3 μm and 2.65 μm differ depending on the encoder to be used).
For example, when N = 1000 pulses (movement amount 2.65 mm), n1 = 15 and n2 = 40.

Since 64 in Equation 1 is the ratio between L1 and L2, this can be expressed as Equation 2 when this is expressed as a correlation coefficient.
N = a · n1 + n2... [Formula 2]

  As described above, the idea for obtaining the pulse numbers n1 and n2 of the linear encoder and the rotary encoder for moving the belt 2 by a certain movement amount is as follows. First, the pulse number N (1000 pulses) is set to L1 and L2. The correlation coefficient is divided by a (here 9600 LPI / 150 LPI = 64), and the integer part (15) of the quotient (here 15.625) is set to the number of pulses n1 of the linear encoder. Next, n2 = N−a · n1 = 1000−64 × 15 = 1000−960 = 40 is obtained from Equation 2 above. In other words, when calculating the amount of movement, the number of encoder pulses with low resolution should be determined first (to a value that does not exceed the amount of movement), and the number of encoder pulses with high resolution corresponding to the fraction (remaining distance) should be obtained. . For example, when the amount of movement is 5.3 mm, N = 2000 pulses, so the integer part 31 of the quotient of 2000 ÷ 64 is the number of pulses n1 of the linear encoder, and n2 = 2000−64 × 31 = 16 (n1 = 31, n2 = 16).

  In this example, the movement amount is designated by the number of pulses N by the rotary encoder. However, since the signal of the rotary encoder is actually used only in the fraction (0 to 63), the influence of the accuracy of the parts can be suppressed. Most of the feed amount is controlled based on the linear encoder signal n1. In this example, since the distance L2 of the rotary encoder 1 pulse is 1/64 of the distance L1 of the linear encoder 1 pulse, the ratio of the rotary encoder to the actual belt movement amount is small, and the influence of the component accuracy can be suppressed.

  For ease of explanation, L1 = L2 × 64, but 64 is a phase relationship other than an integer such as 64.2 by comparing the rotary encoder signal per rotation of the conveyance roller and the signal of the conveyance belt linear encoder. May be a number.

  In this way, by processing the sensor information from the linear scale 15 provided on the electrostatic attraction belt 2 and the sensor information from the code wheel 8 in combination, high-accuracy stop position control of the belt 2 can be realized. . In addition, although it demonstrated as what performs closed loop control here, it is not necessarily limited to closed loop control, and open loop control is also possible.

  Since the linear scale 15 is provided on the electrostatic adsorption belt 2 that actually conveys the recording paper and the linear sensor that reads the linear scale 15 with the encoder sensor 11 or 12 is used to control most of the feed amount, the component accuracy and the assembly accuracy are increased. It is possible to reduce the proportion of the transport roller 3 (rotary encoder) that is affected by. And the control precision of the electrostatic attraction belt 2 (recording paper) is improved by controlling it together with a high-resolution rotary encoder.

  Since the recording paper is adsorbed to the belt 2 and conveyed, the movement amount of the belt can be regarded as the actual movement amount of the recording paper, and the belt 2 can be controlled with high accuracy, so that the position of the recording paper can be controlled with high accuracy. It will be possible. Therefore, in the inkjet engine 20, the stop position of the recording paper in the sub-scanning direction is controlled with high accuracy, and it is possible to obtain high image quality by preventing deterioration in image quality due to positional deviation of ink droplets.

  Next, correction control using the two linear sensors 11 and 12, which is a feature of the present invention, will be described. In the following description, the linear sensor 11 is referred to as sensor A, and the linear sensor 12 is referred to as sensor B.

  As shown in FIG. 3, in this example, two sensors A and B are arranged at a position separated by a predetermined distance: Lc. By detecting the linear scale 15 with these two sensors A and B, respective encoder signals are output (outputs A and B). The phase difference between the two outputs A and B is always equal if there is no expansion / contraction of the electrostatic attraction belt 2 or creep of the linear scale 15 (here, the distance Lc between the sensors is assumed to be constant). The phase difference between sensors A and B is counted by the output pulse of the rotary encoder.

  Here, as shown in FIG. 5, the deviation (phase difference) of the detection phases by the sensors A and B in the ideal state (state 1) in which the belt 2 does not expand and contract and the scale 15 does not creep is assumed to be δ1. In an ideal state, the distance F1 (169.3 μm) of one pitch of the linear scale 15 is 64 pulses at the output of the rotary encoder. Assume that the phase difference δ1 in the ideal state by the sensors A and B is 5 pulses (the number of output pulses p1 of the rotary encoder).

Next, as shown in FIG. 6, when the electrostatic attraction belt 2 changes (elongates) from the state 1 to the state 2, the phase shift from the rise of the output of the sensor A to the rise of the output of the sensor B ( (Phase difference) changes from δ1 to δ2. Assume that the phase difference δ2 in state 2 is 25 pulses (the number of output pulses p2 of the rotary encoder). Accordingly, the elongation amount δx is δx = δ2−δ1 = 2.65 μm × (p2−p1).
Here, δx = 25−5 = 20 pulses = 2.65 μm × 20 = 53 μm
It is.

If the distance between the sensors A and B is Lc, the expansion / contraction rate η is
η = (Lc + δx) / Lc
It becomes.

If the distance between the sensors A and B is Lc = 10 mm = 10000 μm, the expansion / contraction rate η is
η = (10000 + 53) /10000=1.0053≈1.005
And an increase of about 0.5%.

Therefore, one pitch of the linear scale 15 is F2 = 169.3 μm × 1.005≈170.15 μm in the state 2
It becomes.
Therefore, by correcting the reference value (scale pitch) of the linear scale 15 in the above-described transport control of the electrostatic attraction belt 2 from F1 (169.3 μm) to F2 (170.15 μm), the belt height is corrected. Accurate sub-scanning position control can be realized.

Further, as shown in FIG. 7, the phase difference between the sensors A and B when the electrostatic attraction belt 2 changes (shrinks) from the state 1 to the state 3 is denoted by δ3. Assume that the phase difference δ3 in state 3 is 3 pulses (the number of output pulses p3 of the rotary encoder). Therefore, the shrinkage amount δx is δx = δ1−δ3 = 2.65 μm × (p1−p3).
Here, δx = 5-3 = 2 pulses = 2.65 μm × 2 = 5.3 μm
It is.

If the distance between the sensors A and B is Lc, the expansion / contraction rate η is
η = (Lc−δx) / Lc
It becomes.

If the distance between the sensors A and B is Lc = 10 mm = 10000 μm, the expansion / contraction rate η is
η = (10000−5.3) /10000=0.999947≈0.9995
And shrinkage of about 0.05%.

Therefore, one pitch of the linear scale 15 is F3 = 169.3 μm × 0.9995≈169.2 μm in the state 3
It becomes. Therefore, by correcting the reference value of the linear scale 15 in the above-described conveyance control of the electrostatic attraction belt 2 from F1 (169.3 μm) to F3 (169.2 μm), high-precision sub-scan in which the belt shrinkage is corrected. Position control can be realized.

  As shown in FIG. 8, when the electrostatic attraction belt 2 has changed from the state 1 to the state 4 by more than half in the linear scale phase, it is expanded or contracted only by counting the phase difference between the sensors A and B. I can not judge. Therefore, in this example, if the temperature detected by the thermistor 19 (FIG. 3) which is a temperature sensor provided in the loop of the belt 2 is higher than the previous correction, it is determined that the temperature is increased, and if the temperature is decreased, the temperature is reduced. to decide.

When it is determined that the line is elongated, the linear scale reference value is corrected in the same manner as in the state 2 described with reference to FIG.
If it is determined to be contraction, it is assumed that the phase difference δ4 in state 4 is 4 pulses (the number of output pulses p4 of the rotary encoder). The shrinkage amount δx is obtained by adding δ1 in state 1 and δ4 in state 4.
δx = δ1 + δ4 = 2.65 μm × (p1 + p4).
Here, δx = 5 + 4 = 9 pulses = 2.65 μm × 9 = 23.85 μm
It is.

If the distance between the sensors A and B is Lc, the expansion / contraction rate η is
η = (Lc−δx) / Lc
It becomes.

If the distance between the sensors A and B is Lc = 10 mm = 10000 μm, the expansion / contraction rate η is
η = (10000−23.85) /10000=0.997615≈0.9976, and the shrinkage is about 0.24%.

Therefore, one pitch of the linear scale 15 is F4 = 169.3 μm × 0.9976≈168.9 μm in the state 4
It becomes. Therefore, by correcting the reference value of the linear scale 15 in the above-described conveyance control of the electrostatic attraction belt 2 from F1 (169.3 μm) to F4 (168.9 μm), high-precision sub-scan in which the belt shrinkage is corrected. Position control can be realized.

As a specific correction method, first, a correlation coefficient a = L1 / L2 which is a ratio of the distance of one pulse between the linear encoder and the rotary encoder is obtained, and then based on the phase difference between the sensors A and B. A value obtained by dividing one pitch of the calculated linear scale 15 (here, F2 = 170.15 μm) by the correlation coefficient a: β is obtained. Then, the value of β is used in the following Equation 3 when obtaining the number of pulses N described above.
N = X / β [Equation 3]
X: Target value for belt movement

  For example, if there is belt elongation and the correlation coefficient a when F2 = 170.15 μm is detected as 64.2, β = F2 / a = 170.15 ÷ 64.2 = 2.65 Become. If X, which is the target value for belt movement, is 5.3 mm (5300 μm), N = 5300 ÷ 2.65 = 2000 pulses from the above equation 3. According to the N = 2000 pulses, the number of pulses n1 and n2 of the linear encoder and the rotary encoder used for actual control is obtained as described above.

  In this example, a = L1 / L2 is calculated from the number of output pulses of the linear encoder and the number of output pulses of the rotary encoder when the conveying roller 3 is rotated by an integral multiple. Thereby, the influence of the eccentricity of the transport roller or the rotary wheel can be eliminated. When obtaining a = L1 / L2, only one of the two linear sensors A and B may be used.

  Further, the distance Lc = 10 mm between the sensors A and B used in the description here is an example, and the present invention is not limited to this. For example, Lc can be set to an appropriate value such as an integral multiple (for example, 100 times) of one pitch of the linear scale in an ideal state.

FIG. 9 is a flowchart illustrating correction control processing using the two linear sensors 11 and 12 in the inkjet recording apparatus 100 of the present embodiment.
First, correlation coefficient a = L1 / L2 is detected in advance at an appropriate timing (S1). In this embodiment, correction is performed in real time during printing. For example, the correlation coefficient a is detected when recovering from the energy saving mode, and the same correlation coefficient a is used if the temperature does not change by 5 ° C. or more thereafter. can do. Next, a target value for the feed amount of the belt 2 is set based on the print instruction (S2) (S3). Then, the belt is driven (S4), and the phase difference between the two linear sensors A and B is detected (S5).

  Next, it is determined whether the temperature (T1) detected by the thermistor 19 is lower than the value (T0) at the previous detection (S6). If T1 is smaller than T0, that is, if the temperature falls, it is determined as “shrinkage” and the process proceeds to S7. Otherwise, it is determined as “extension” and the process proceeds to S9. If it is determined as “shrinkage”, the amount of contraction is calculated (S8), and if it is determined as “elongation”, the amount of expansion is calculated (S10).

  Then, the expansion / contraction rate “η” is calculated based on the calculated amount of contraction or expansion (S11), and the linear scale reference value is corrected as described above (S12). Then, as described above, the actual control amount (feed amount) of the electrostatic adsorption belt 2 is calculated as the number of pulses of the linear encoder: n1 and the number of pulses of the rotary encoder: n2 (S13). To control.

  The accuracy of correction using the two linear sensors 11 and 12 is verified by applying specific numerical values. In state 2 (when the belt is stretched), the correlation coefficient a when the stretch rate is 0.5% is detected (calculated) as L1 / L2 = 64.2. This is supported by dividing F2 = 170.15 μm by 2.65 μm, which is the distance of one pulse of the rotary encoder, to 64.2.

In state 2, β = 170.15 ÷ 64.2≈2.65. Here, for example, when trying to move the electrostatic attraction belt 2 by 5.3 mm (5300 μm), N = 5300 ÷ β = 5300 ÷ 2.65 = 2000 pulses, so 2000 ÷ 64.2 = 31.15. n1 = 31 pulses,
From 2000−64.2 × 31 = 2000−1990.2 = 9.8, n2 = 9 pulses.

  That is, 31 pulses can be moved by the linear encoder and 9 pulses can be moved by the rotary encoder. When the belt movement amount at this time is calculated, 170.15 × 31 + 2.65 × 9 = 5274.65 + 23.85 = 5298.5 μm = 5.2985 mm, and the difference from the target value of 5.3 mm is 0.0015 mm (1. 5 μm).

  If correction by sensors A and B is not performed, calculation is performed with correlation coefficient a = 64, so 2000 ÷ 64 = 31.25, n1 = 31 pulses, 2000−64 × 31 = 2000−1984 = 16. N2 = 16 pulses. When the belt movement amount at this time is calculated, 170.15 × 31 + 2.65 × 16 = 5274.65 + 42.4 = 5317.0 μm = 5.317 mm, and the difference from the target value of 5.3 mm is 0.017 mm (17 μm). If the correction is not performed, the difference is increased by one digit. Therefore, it can be seen that the correction based on the phase difference between the linear sensors A and B according to the present invention allows the recording paper to be positioned with high accuracy even when the belt expands or contracts over time. In the states 3 and 4 (shrinkage), high-accuracy correction is similarly performed.

  By the way, in the correction using the two linear sensors 11 and 12 according to the present invention, it is important that the distance between the sensors for detecting the phase difference (the above Lc) does not vary. When the distance between the sensors changes, a phase shift occurs even if the belt does not expand and contract (the phase difference fluctuates). Therefore, in this embodiment, as shown in FIG. 10, a glass scale 16 is disposed between the sensors A and B (11, 12) and the linear scale 15 (electrostatic adsorption belt 2), and the sensor is detected by the glass scale 16. The value of Lc as an inter-distance is defined.

  The glass scale 16 of this example is configured as an optical slit in which the light transmitting portions 16a and the light shielding portions 16b are alternately arranged, and has almost no expansion and contraction as a characteristic of the glass. In this example, the width (length in the sub-scanning direction) of the light transmitting portion 16a and the light shielding portion 16b is equal, and the width of the reflecting portion 15a and the non-reflecting portion 15b of the linear scale 15 in the ideal state (sub-scanning direction). Length). Of course, in FIG. 10, the glass scale 16 and the linear scale 15 are enlarged and shown in an easy-to-understand manner, and the width of the light transmitting portion 16a and the light shielding portion 16b is a distance of 1/2 pitch of the linear scale 15 in an ideal state. From this, it is 84.65 μm in this example.

  The sensors A and B are composed of a light emitting element (LED in this example) and a light receiving element (photodiode: PD in this example), and light emitted from the light emitting element is reflected by the reflecting portion 15a of the linear scale 15 and received. Light is received by the element. At this time, since the reflected light from the linear scale 15 is cut at the outer end (both ends) of the light shielding portion 16b between the sensors A and B (the position indicated by the alternate long and short dash line in the figure), these two one-dot chain lines. The distance between the sensors is defined as an inter-sensor distance Lc. Since the glass scale 16 does not expand and contract as described above, even if the sensor itself is slightly displaced in the left-right direction in the figure, the value of Lc set as the inter-sensor distance does not change. Therefore, the distance Lc between the two sensors A and B serving as a reference for detecting the phase difference is always constant. Therefore, when the belt expands or contracts, a phase shift (phase difference fluctuation) is accurately detected.

  In this example, as described above, the width (length in the sub-scanning direction) of the light transmitting portion 16a and the light shielding portion 16b of the glass scale 16 is set to the width of the reflecting portion 15a and the non-reflecting portion 15b of the linear scale 15 (sub-scanning direction). Length). Thereby, the phase detection of the linear scale 15 is accurately performed. As schematically shown in FIG. 11, the linear sensor actually used in this example receives reflected light from the linear scale 15 that is simultaneously transmitted through eight slits (the transparent portion 16a of the glass scale). Yes. Here, when the linear scale 15 moves on the glass scale 16, the reflecting portion 15a and the non-reflecting portion 15b of the linear scale 15 pass one after another on the slit of the sensor detecting portion. At this time, the amount of light received by the sensor is maximized when the positions of the reflecting portion 15a of the linear scale and the light transmitting portion 16a of the glass scale coincide, and the amount of received light of the sensor is minimized when the non-reflecting portion 15b and the light transmitting portion 16a coincide. Become. In the middle, the amount of received light changes continuously. Therefore, when the temporal change in the amount of received light is graphed, it becomes a sine curve, and the high level and low level of the sensor output are accurately inverted by an appropriate threshold (threshold), and the linear scale phase can be detected with high accuracy.

  Also, as shown in FIG. 12, it is preferable that two linear sensors A and B (11, 12) are integrated and provided as a single sensor unit 35 on a substrate 36. Thus, by integrating the two linear sensors A and B (11, 12), the cost can be reduced by integrating the circuit boards, and the distance between the sensors can be easily maintained. There is also an effect that the deterioration of accuracy can be prevented.

  In addition, as shown in FIG. 13, the two linear sensors A and B (11, 12) and the temperature sensor 16 may be integrated and provided as a single sensor unit 37 on the substrate 36. Thus, by integrating the temperature sensor 16 in addition to the two linear sensors A and B (11, 12), it is possible to reduce the cost by integrating the logic circuit and increasing the efficiency of the assembly work. Further, since the distance between the sensors can be easily maintained, there is an effect that a reduction in correction accuracy can be prevented.

  Further, although not shown, a phase difference detected by the two linear sensors A and B when the ink jet recording apparatus 100 is not used for a long period of time (more than a predetermined period) is mounted on the apparatus main body. The reverse rotation (the phase difference in the ideal state: the phase difference detected from the rotary count: when the rotary count is decreased, for example, state 4 in FIG. 8) is preferably configured to determine that the belt is not stretched but stretched. This can prevent erroneous detection (erroneous determination of belt expansion / contraction) when the apparatus has not been used for a long time due to storage or the like.

As mentioned above, although this invention was demonstrated by the example of illustration, this invention is not limited to this.
For example, the resolution of a linear encoder and a rotary encoder can be set as appropriate. The pitch of the linear scale and the rotary scale is also arbitrary, and the ratio L1 / L2 between them is not limited to 64. The distance (Lc) between the two linear sensors is also arbitrary.

  Furthermore, an appropriate glass scale configuration can be used. The slits of the glass scale 16 do not have to be located between the sensors A and B, but it is necessary to exceed eight slits at a position separated by the distance Lc.

  Further, the conveyance belt, which is a conveyance means for moving the recording paper in the sub-scanning direction, is not limited to the electrostatic adsorption belt, and may be a normal conveyance belt. However, having some kind of suction means (for example, one using a negative pressure) is suitable for highly accurate conveyance / stop because there is no deviation of the recording paper.

  Further, the linear scale provided in the conveying means for moving the recording paper in the sub-scanning direction is not limited to the back surface of the belt, but can be provided at an arbitrary place, for example, the belt surface. However, it is more advantageous for ink stains to be provided on the back side of the belt as in this example. The installation place of the sensor for reading the linear scale may be provided at a position corresponding to the formation place of the linear scale. It is also possible to make the linear scale transmissive.

  Further, the code wheel constituting the rotary encoder is not limited to the conveyance roller of this example, and can be arranged at an appropriate place. For example, it can be provided on the axis of the sub-scanning drive motor or on the axis of the gear in the middle. Alternatively, it may be provided on the axis of the tension roller 4 in FIG. Furthermore, it is also possible to provide a roller member or the like that is pressed and driven by the conveyance belt, and to provide a code wheel on the shaft.

  As a method for forming the linear scale, an appropriate method can be adopted. For example, if the contrast of the intensity of reflected light is obtained, such as a method of forming a scale by using an aluminum evaporated tape to fly the aluminum evaporated surface with a laser, or a method of forming a black and white contrast by laser processing on a white tape. It holds as a scale. In addition, the linear encoder and the rotary encoder can have arbitrary configurations, and when a photo sensor is used, a transmission type or reflection type sensor can be employed depending on the configuration of the encoder.

  As described above, the output of the encoder sensor is not limited to digital, and an analog output may be used. Further, not only closed loop (feedback) control but also open loop control is possible.

  In the ink jet recording apparatus, the number of ink colors is not limited to four, and can be configured with an arbitrary number of colors. The number of heads is also arbitrary. A configuration in which the ink cartridge is not separated from the head and the head portion includes the ink cartridge may be employed. The configuration of the scanner unit and the presence / absence of ADF are also arbitrary. The image forming apparatus may be a multifunction machine having a facsimile or printer function. Alternatively, it can be configured as a printer that does not have a scanner unit.

1 is a cross-sectional configuration diagram illustrating an example of an ink jet recording apparatus including a recording paper conveyance device according to the present invention. It is a schematic diagram which shows a recording paper conveying apparatus schematically. It is a schematic diagram which expands and shows a linear scale and a linear sensor part. It is a schematic diagram which shows notionally the signal processing of the double sensor system by a rotary encoder and a linear encoder. It is a wave form diagram for demonstrating the phase difference of two linear sensor outputs. It is a wave form diagram which shows the phase difference of two sensor outputs in the state which the belt extended. It is a wave form diagram which shows the phase difference of two sensor outputs in the state which the belt contracted. It is a wave form diagram when a phase difference becomes more than 1/2 pitch of a linear scale. It is a flowchart which shows the process of the correction control using two linear sensors. It is a schematic diagram which shows the glass scale which prescribes | regulates the distance between two sensors. It is a figure which shows a linear sensor detection part typically. It is a side view which shows the sensor unit which integrated two linear sensors. It is a side view which shows the unit which integrated two linear sensors and temperature sensors.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Recording paper conveyance apparatus 2 Electrostatic adsorption belt (conveyance means)
3 Conveying roller 4 Tension roller 8 Code wheel 9 Encoder sensor 10 Platen 11 Linear sensor (Sensor A)
12 Linear sensor (Sensor B)
DESCRIPTION OF SYMBOLS 15 Linear scale 15a Reflective part 16b Non-reflective part 16 Glass scale 16a Translucent part 16b Light-shielding part 19 Thermistor (temperature sensor)
20 Inkjet engine 21 Carriage 23 Ink cartridge 100 Inkjet recording apparatus

Claims (13)

In a recording paper transport device capable of intermittently transporting recording paper,
A linear encoder is provided in the conveying means for conveying the recording paper, a rotary encoder is provided in the rotating member related to the driving of the conveying means, and the feed amount of the conveying means is controlled based on the outputs of the two encoders.
The linear encoder has a linear scale attached to the conveying means and two linear sensors that are arranged at a predetermined distance in the sub-scanning direction and detect the linear scale,
A calculating means for calculating expansion and contraction of the conveying means based on a detection phase difference between the two linear sensors ;
A recording paper conveying apparatus, wherein a glass scale for defining a distance between two linear sensors is disposed between the linear scale and the two linear sensors . The calculating means calculates an expansion rate or an expansion amount of the conveying means based on a detection phase difference between the two linear sensors in an ideal state and a detection phase difference between the two linear sensors at the time of detection. The recording paper transport device according to claim 1. The recording paper transport according to claim 2, wherein a reference value of the linear scale used for feed amount control of the transport unit is corrected based on an expansion rate or expansion amount of the transport unit calculated by the calculation unit. apparatus. The recording paper transport device according to claim 1, wherein the detected phase difference between the two linear sensors is counted by the number of output pulses of the rotary encoder. The recording paper transport apparatus according to claim 1 , wherein the glass scale is configured as an optical slit. 6. The recording paper conveying apparatus according to claim 5 , wherein the pitch of the optical slits of the glass scale is set equal to the pitch of the linear scale. The recording paper conveying apparatus according to claim 1, wherein the two linear sensors are integrated. The temperature detecting means is provided in the vicinity of the conveying means, and the output of the temperature detecting means is used for determination of expansion or contraction when the calculating means calculates the expansion / contraction of the conveying means. 2. A recording paper conveyance device according to 1. 9. The recording paper conveying apparatus according to claim 8 , wherein the two linear sensors and the temperature detecting means are provided integrally. 2. The recording paper transport apparatus according to claim 1, further comprising a timer unit, wherein the output of the timer unit is used for determination of expansion or contraction when the calculation unit calculates expansion / contraction of the transport unit. . The recording paper transport apparatus according to claim 1, wherein the transport unit is a transport belt, and the transport belt includes a suction unit that sucks the recording paper. The recording paper transport apparatus according to claim 11 , wherein the linear scale is formed on a back surface of the transport belt. An ink jet recording apparatus characterized by mounting a recording sheet conveying means in the sub-scanning direction of the ink jet engine part recording sheet conveying apparatus according to any one of claims 1 to 12.

Images