Abstract:
A recording paper conveying apparatus is disclosed. The recording paper conveying apparatus includes a conveying part for conveying a recording paper, the conveying part including a first encoder, and a driving part for driving the conveying part, the driving part including a second encoder, wherein the first and second encoders have different resolutions.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   This disclosure relates to a recording paper conveying apparatus, an inkjet recording apparatus, and a method for controlling the conveyance of recording paper, and more particularly, to a recording paper conveying apparatus, an inkjet recording apparatus, and a method for controlling the conveyance of recording paper by a recording paper conveying apparatus with high precision. 
   2. Description of the Related Art 
   Recently, in the field of inkjet recording technology, the types of ink used for recording are shifting from dye type inks to pigment type inks for improving light resistance and aging resistance (resistance against deterioration in association with time). In addition, the viscosity of the ink is becoming higher. Although the increase in the viscosity of the ink has reduced creation of bleeding on the recording paper considerably, inaccurate disposition of ink droplets where ink droplets deviate from a target contact area (e.g. white stripes, black stripes, banding) is more visible. Since the disposition of ink droplets largely relies on the precision of the stop position during conveyance of a recording paper in a sub-scanning direction, it is desired to increase the precision in conveying the recording paper. 
   Conventionally, a grinding conveyor roller or a conveyor belt is employed in a sub-scan recording paper conveying mechanism used for inkjet recording. In controlling the amount of conveyance with the conveying mechanism, a code wheel is provided on an axle of a conveying roller for allowing an encoder sensor to read and control the conveyance according to a value obtained from the code wheel. For example, Japanese Laid-Open Patent Application No. 2002-248822 shows a configuration where a conveying roller and a discharge roller are situated at an upstream side and a downstream side of a platen for conveying a recording paper in a sub-scanning direction. This configuration has a code wheel provided on an axle of the conveying roller for allowing an encoder sensor to read and control the conveyance according to a value obtained from the code wheel. 
   However, the conventional recording paper conveying mechanism using the code wheel and the sensor for controlling the conveyance of the recording paper has difficulty in achieving stop position control with satisfactory precision due to overlapping error among its components (e.g. pulley, conveying roller, etc.). 
   SUMMARY 
   In an aspect of this disclosure, there is provided a recording paper conveying apparatus including: a conveying part for conveying a recording paper, the conveying part including a first encoder; and a driving part for driving the conveying part, the driving part including a second encoder; wherein the first and second encoders have different resolutions. 
   In an embodiment of this disclosure, when the recording paper is conveyed for a predetermined amount by the conveying part, a relation of N=a·n 1 +n 2  may be satisfied, wherein “a” is a correlation function representing a ratio between “L 1 ” and “L 2 ”, wherein “L 1 ” is the amount of conveyance of the conveying part corresponding to a single pulse of a signal output from one of the first encoder and second encoder having a lower resolution, wherein “L 2 ” is the amount of conveyance of the conveying part corresponding to a single pulse of a signal output from one of the first encoder and second encoder having a higher resolution, wherein “N” is the number of pulses of the signal of the encoder having the higher resolution being output in correspondence with the predetermined amount of conveyance of the conveying part, wherein “n 1 ” is the number of pulses of the encoder having the lower resolution, wherein “n 2 ” is the number of pulses of the encoder having the higher resolution, wherein “n 2 ” is an integer that satisfies a relation of 0≦n 2 &lt;a. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the driving part may be driven by employing closed-loop control based on the output signals of the first and second encoders. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the driving part may be driven by employing open-loop control. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the recording paper conveying apparatus may further include a correcting part for correcting the correlation function “a”. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the recording paper conveying apparatus may further include a temperature detecting part for detecting a predetermined temperature, wherein the correcting part corrects the correlation function “a” in accordance with the detected temperature. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the conveying part may include a conveyor belt. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the conveyor belt may include an attracting part for holding the recording paper. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the attracting part may include an electrostatic attraction part. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the attracting part may use negative pressure for attracting the recording paper. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the first encoder may include a linear encoder having a linear scale provided on the conveyor belt and a first sensor for reading the linear scale, wherein the second encoder may include a rotary encoder including a code wheel mounted on the driving part and a second sensor for reading the code wheel, wherein the rotary encoder may have a resolution higher than that of the linear encoder. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the linear scale may be disposed at a rear face of the conveyor belt. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the linear scale may be fabricated by aluminum evaporation. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the recording paper conveying apparatus may further include a border detection sensor for detecting a border of the linear scale, wherein data of the linear encoder is complemented with data of the rotary encoder when the border detection sensor detects the border of the linear scale. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the linear encoder and the rotary encoder may output a predetermined signal in accordance with the reading from the linear scale and the code wheel, respectively, wherein the predetermined signal includes a rectangular digital signal. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the linear encoder and the rotary encoder may output a predetermined signal in accordance with the reading from the linear scale and the code wheel, respectively, wherein the predetermined signal includes an analog signal. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the resolution of the linear encoder may be no less than 100 LPI. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the resolution of the rotary encoder may be no less than 300 LPI. 
   In the recording paper conveying apparatus according to an embodiment of this disclosure, the output signal of the rotary encoder may be multiplied by a predetermined value. 
   Further, there is provided an inkjet recording apparatus including the recording paper conveying apparatus according to an embodiment of this disclosure, the recording paper conveying apparatus being mounted onto an inkjet engine portion for conveying the recording paper in a sub-scanning direction. 
   Further, there is provided a method for controlling conveyance of a recording paper conveying apparatus including a conveying part for conveying a recording paper and a driving part for driving the conveying part, the conveying part including a first encoder, the driving part including a second encoder, the first and second encoders having different resolutions, the method including a step of: controlling the amount of conveyance of the conveying part based on signals output from the first and second encoders. 
   Other aspects and further features will be apparent from the following detailed description when read in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-sectional view of an exemplary configuration of an inkjet recording apparatus including a recording paper conveying apparatus according to an embodiment of the present invention; 
       FIG. 2  is a detailed drawing of an exemplary configuration of a recording paper conveying apparatus according to an embodiment of the present invention; 
       FIG. 3  is a schematic drawing of an exemplary configuration of a recording paper conveying apparatus according to an embodiment of the present invention; 
       FIG. 4  is a diagram for schematically illustrating signal processes executed by a rotary encoder and a linear encoder according to a double sensor method; 
       FIG. 5  is a block diagram for explaining functions of a drive control system for sub-scanning with the inkjet recording apparatus shown in  FIG. 1 ; and 
       FIG. 6  is a block diagram showing a control part of the inkjet recording apparatus shown in  FIG. 1 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In the following, embodiments of the present invention are described with reference to the accompanying drawings. 
     FIG. 1  is a cross-sectional view of an exemplary configuration of an inkjet recording apparatus  100  including a recording paper conveying apparatus  1  according to an embodiment of the present invention. In this example, the recording paper conveying apparatus  1  is able to intermittently convey a recording paper(s). Furthermore, in this example, the inkjet recording apparatus  100  serves as a copying apparatus having a scanner portion  30  situated above a printer part  50 . A paper discharge portion  40  is situated between the scanner portion  30  and the printer portion  50 . 
   In the scanner portion  30 , a scanning part  32  is provided below a contact glass  31  in a manner operable to execute scanning. Accordingly, the light irradiated from a light source is reflected from an original and introduced to a CCD  33  via a mirror lens, etc., to thereby allow the CCD  33  to read an image of the original. A platen  34  is provided in an openable-closable manner above the contact glass  31 . 
   A recording paper conveyance path, which starts from a paper feed cassette  27  situated at a lower part of the printer portion  50  and terminates at the paper discharge portion  40 , is formed in a manner indicated with a one-dot chain line in  FIG. 1 . One or more conveying rollers  25  are suitably provided at predetermined parts of the recording paper conveyance path. It is to be noted that reference numeral  24  indicates a paper feed roller and reference numeral  26  indicates a paper discharge roller. Furthermore, a manual feed tray  28  is provided at a side of the inkjet recording apparatus  100 , so that recording paper may also be fed from the manual feed tray  28  via the paper feed roller  24 . 
   An inkjet engine  20  includes the recording paper conveying apparatus  1 . In this example, the recording paper conveying apparatus  1  employs a system which conveys the recording paper in a sub-scanning direction by using an electrostatic attraction belt (conveyor belt)  2 . The conveying system using the electrostatic attraction belt is able to convey paper more steadily compared to using a conventional roller conveying type. A carriage  21 , which is situated above the recording paper conveying apparatus  1 , is mounted with a print head(s)  22 . A printing operation is executed by moving the carriage  21  back and forth in a main scanning direction (vertical direction in  FIG. 1 ) and jetting ink droplets from the print head  22 . The print head  22  is provided with a nozzle alignment with a length of 1.27 inches, being longer than that of a conventional print head. In this example, the print head  22  may be of a four head configuration, in which one head corresponds to each color of cyan (C), magenta (M), yellow (Y), and black (Bk). The number of heads is not limited to four heads. Alternatively, the print head  22  may be of a two head configuration, in which one head corresponds to two colors. 
   In this example, ink cartridges  23  corresponding to each color are mounted on the inkjet recording apparatus  100  separately from the aforementioned print head  22 . The inks contained in the ink cartridges  23  are supplied to the print head  22  via a supply tube (not shown). The configuration provided with separately mounted cartridges and the print heads is suitable for business purposes since the configuration allows a large capacity type cartridge to be used in handling increased ink consumption along with accelerated print speed. 
     FIG. 2  is a detailed drawing of the recording paper conveying apparatus  1  according to an embodiment of the present invention. 
   In  FIG. 2 , the electrostatic attraction belt (conveyor belt)  2 , which is a conveying part for conveying a recording paper in a sub-scanning direction, is formed as an endless belt hung around by a conveying roller  3  and a tension roller  4 . A charge roller  5  for applying charge to the electrostatic attraction belt  2 , a charge removing brush  6  for removing electric charge from the electrostatic attraction belt  2 , and a cleaning blade  7  for cleaning the electrostatic attraction belt  2  are disposed abutting an outer surface of the electrostatic attraction belt  2 . The charge roller  5 , the charge removing brush  6 , and the cleaning blade  7  are supported by a bracket  16 . A collecting part is provided on the bracket  16  for storing residual paper particles, ink stains, etc., removed from the electrostatic attraction belt  2  by the cleaning blade  7 . 
   A pressure roller  13  supported by a pressure plate  14  is disposed in a manner facing the conveying roller  3 . A tip pressure roller  15  is supported at a tip of the pressure plate  14 . The tip pressure roller  15  serves to press the electrostatic attraction belt  2  against a platen  10  situated at an inner side of an upper plane portion of the electrostatic attraction belt  2  (See  FIG. 3 ). 
   A guiding member  35  is disposed at a side of the conveying roller  3  by which the recording paper fed from the paper feed portion is guided to an area between the conveying roller  3  (electrostatic attraction belt  2 ) and the pressure plate  14 . The recording paper, which is electrostatically attracted to and held on an upper surface of the electrostatic attraction belt  2  by electrostatic force, is conveyed in a sub-scanning direction(s) (for example, from right to left in  FIGS. 1 ,  2 ,  3 ) by the electrostatic attraction belt  2  rotating in a predetermined direction(s) (for example, the counterclockwise direction in  FIGS. 1 ,  2 ,  3 ). 
   A pair of paper discharge rollers including a paper discharge roller part  17  and a spur part  18  is disposed at a downstream side of the tension roller  4 . A separating claw  19  for separating the recording paper from the electrostatic attraction belt  2  is provided at a portion at which the tension roller  4  is situated. The recording paper separated from the electrostatic attraction belt  2  is then delivered further downstream by the pair of paper discharge rollers including the paper discharge roller part  17  and the spur part  18 . 
   A code wheel  8  having a high resolution is attached to an axle of the conveying roller  3 . A slit(s) (not shown) is formed in the code wheel  8 . A transparent type encoder sensor  9  is provided for detecting the slit(s). A rotary encoder according to an embodiment of the present invention includes the code wheel  8  and the encoder sensor  9 . It is preferable to use a rotary encoder having an LPI value no less than 300 LPI and a CR (CPR) value no less than 4800 CR (CPR). 
   Furthermore, a linear scale (not shown) may be formed at a predetermined portion of the electrostatic attraction belt  2 , such as a rear face of the electrostatic attraction belt  2 . The linear scale may be fabricated by, for example, depositing aluminum to the rear face of the electrostatic attraction belt  2  (forming stripe patterns by performing aluminum deposition and laser irradiation on the rear face of the electrostatic attraction belt  2 ). The linear scale is disposed at the predetermined portion for preventing the platen  10  situated on the rear face of the electrostatic attraction belt  2  from obstructing the linear scale. A reflection type encoder sensor  11  is disposed within the loop of the electrostatic attraction belt  2  for reading the linear scale. A linear encoder according to an embodiment of the present invention includes the linear scale and the encoder sensor  11 . It is preferable to use a linear encoder having an LPI value (resolution) no less than 100 LPI. The linear encoder used in this example has a resolution of 150 LPI. It is to be noted that a border detection sensor  12  for detecting a joint area (border) of the linear scale is situated adjacent to the encoder sensor  11 . 
   One of the features of the recording paper conveying apparatus  1  according to an embodiment of the present invention is that the electrostatic attraction belt  2 , being the conveying part, is controlled with use of two kinds of encoders where one is the rotary encoder and the other is the linear encoder. 
   Next, the control of the conveyance of the electrostatic attraction belt  2  according to an embodiment of the present invention is described with reference to  FIGS. 3 and 4 . It is to be noted that  FIG. 3  is a schematic drawing of the recording paper conveying apparatus  1  illustrated in detail in  FIG. 2 . Furthermore,  FIG. 4  is a diagram for schematically illustrating signal processes executed by the rotary encoder and the linear encoder according to a double sensor method according to an embodiment of the present invention. 
   As the electrostatic attraction belt  2  is moved by the rotation of the conveying roller  3 , the linear scale disposed at the rear face of the electrostatic attraction belt  2  is also moved so as to allow information (data) to be read therefrom by the reflection type encoder sensor  11 . Then, signals are output in accordance with the read information. The signals may be analog sinusoidal waves or rectangular waves. Here, the signals are described as being rectangular waves. 
   In this example, the reflection type encoder sensor  11  reads position information for a cycle of 150 LPI (See  FIG. 4 ) and outputs a rectangular wave signal(s) (linear encoder signal). In the same manner, the transparent type encoder sensor  8  reads information from the code wheel  8  situated on the axle of the conveying roller  3  and outputs another rectangular wave signal(s) (rotary encoder signal). It is to be noted that, in this example, the resolution of the rotary encoder is set with a resolution greater (higher) than that of the linear encoder. 
   Although the resolution of the linear scale provided on the electrostatic attraction belt  2  is indicated in an amount as it is, the amount (distance) of a single resolution of the code wheel  8  with respect to the electrostatic attraction belt  2 , on the other hand, is to be determined in accordance with the number of pulses in a single rotation, the conveying roller  3  diameter, and the electrostatic attraction belt  2  thickness. That is, the number of pulses for a single rotation becomes greater as the resolution of the code wheel  8  (i.e. density of the pitch of the slits) and/or the outer diameter of the code wheel  8  becomes greater. Furthermore, the amount of conveyance (movement) corresponding to a single pulse of the rotary encoder becomes smaller as the diameter of the conveying roller  3  becomes smaller. In this example, the resolution (output) of the code wheel  8  being 600 LPI is multiplied (in this example, by 4) to a value of 2400 LPI. Furthermore, since the relation between the diameter of the code wheel  8  and the diameter of the conveying roller  3  (including the thickness of the electrostatic attraction belt  2 ) is set at 4:1, the multiplied value is further multiplied by a value of 4 (2400 LPI×4). Accordingly, the resolution of the rotary encoder converted with respect to the electrostatic attraction belt  2  is 9600 LPI. Hence, the amount of conveyance of the electrostatic attraction belt  2  corresponding to a single resolution of the rotary encoder is approximately 2.65 μm. 
   That is, as shown in  FIG. 4 , a linear scale cycle L 1  is equal to 150 LPI and approximately 169.3 μm (i.e. L 1 =150 LPI=approximately 169.3 μm). On the other hand, the converted value L 2  of the rotary encoder with respect to the electrostatic attraction belt  2  is equal to 9600 LPI (600 LPI×4×4) and approximately 2.65 μm (i.e. L 2 =9600 LPI=approximately 2.65 μm. It is to be noted that the value of the resolution can be designated in accordance with desired precision and cost. 
   This example is a case where the electrostatic attraction belt  2  is moved (or conveys the recording paper) for a predetermined amount (distance) in correspondence with N pulse(s) of the rotary encoder signal. Here, in this example, the distance L 1  corresponding to a single pulse of the linear encoder and the distance L 2  corresponding to a single pulse of the rotary encoder satisfy a relation of L 1 =L 2 ×64. The amount of movement corresponding to N pulses is indicated with the below-given formula (1), wherein the number of pulses of the linear encoder is n 1 , and the additional fraction of the rotary encoder is n 2  (0-63).
 
 N= 64× n   1 + n   2   formula (1)
 
   In indicating the amount of movement in the form of distance, the amount of movement (conveyance) satisfies a relation of 2.65 μm×N=169.3 μm×n 1 +2.65 μm×n 2  (however, the values of 169.3 μm and 2.65 μm differ depending on the encoders that are used). In a case where N=1000 pulses (amount of movement 2.65 μm), n 1 =15 and n 2 =40. 
   It is to be noted that, since the value of 64 in formula (1) represents the ratio of L 1  and L 2 , this can be expressed as the below-given formula (2) using “a” as a correlation function.
 
 N=a·n   1 + n   2   formula (2)
 
   Accordingly, in a case of obtaining the number of pulses n 1  of the linear encoder and the number of pulses n 2  of the rotary encoder for moving the electrostatic attraction belt  2  for a predetermined amount (distance), first, the number of pulses N (in this example, 1000 pulses) is divided by the correlation function “a” of L 1  and L 2  (in this example, 9600 LPI/150 LPI=64). The integer part (in this example, 15) of the quotient (in this example, 15.625) is the number of pulses n 1  of the linear encoder. Next, the number of pulses n 2  of the rotary encoder is obtained by using the formula (2), in which
 
 n   2 = N−a·n   1 =1000−64×15=1000−960=40.
 
   In other words, in obtaining the amount of movement, first, the number of pulses of the encoder having a low resolution is determined (to an extent not surpassing the amount of movement), and then the number of pulses of the encoder having a higher resolution, which corresponds to the fraction (remaining distance), is obtained. For example, in a case where the amount of movement is 5.3 mm, N=2000. Therefore, the integer part  31  of the quotient for 2000÷64 is the number of pulses n 1  of the linear encoder. Thus, the number of pulses n 2  of the rotary encoder is 16 (n 2 =2000−64×31=16). 
   In this example, the amount of movement (conveyance) is designated according to the number of pulses N for the rotary encoder. Nevertheless, since only the fractions (0-63) of the signals of the rotary encoder are actually used, the influence of errors among the components can be reduced. A large portion of the amount of movement (amount of conveyance) can be controlled according to the linear encoder signals n 1 . In this example, the rotary encoder covers a small proportion with respect to the actual movement amount of the electrostatic attraction belt  2  since the distance L 2  of a single pulse of the rotary encoder is 1/64 the distance L 1  of a single pulse of the linear encoder. Accordingly, the influence of the errors among the components can be controlled. 
   Although the foregoing examples employ the relation of L 1 =L 2 ×64 for the sake of convenience, there may be a case where the correlation function is not an integer (e.g. 64.2 instead of 64) by comparing the rotary encoder signal corresponding to a single rotation of the conveying roller with the linear encoder signal. Furthermore, the stretch of the electrostatic attraction belt  2  due to temperature may be corrected by changing the correlation function. For example, by providing a temperature sensor for detecting a predetermined temperature (e.g. temperature of the electrostatic attraction belt  2 ) and changing the correlation function “a” based on an output detected by the temperature sensor, correction of the temperature stretch of the belt can be automatically executed. 
     FIG. 5  is a block diagram for explaining functions of a control system for executing the sub-scan drive control as described above. 
   As shown in  FIG. 6 , the signals from the linear encoder (encoder sensor  11 ) and the rotary encoder (encoder sensor  9 ) are converted to speed/position information (data) at a signal processing portion  72  in a sub-scan motor drive control portion  71 . The information is synthesized at an ASIC (Application Specific Integrated Circuit)  73  and is compared at a comparison/calculation portion  74  with respect to the speed/position profile stored in a storage portion  77 . Based on the deviation obtained from the comparison, a PID control calculation portion  75  calculates a PWM signal(s) for controlling the drive of a motor driver  76 . The PWM signal is transmitted to the motor driver  76  for allowing a predetermined amount of current to flow from the motor driver  76  to a motor  39 . This flow of current serves to drive a sub-scan drive portion. 
   Using the sensor information from the linear scale provided to the electrostatic attraction belt  2  and the sensor information from the code wheel  8  in combination enables the speed/position of the electrostatic attraction belt  2  to be controlled by employing closed loop control (feedback control). Thereby, the stop position of the electrostatic attraction belt  2  can be accurately controlled. It is to be noted that, although closed loop control is employed in this embodiment of the present invention, other methods of control such as an open loop control may alternatively be employed. 
   Even if the conventional recording paper conveying apparatus is provided with a high resolution rotary encoder for controlling a rotary member, recording paper cannot be conveyed with high precision due to overlapping of errors among the components resulting from, for example, eccentricity or run-out of the drive member (e.g. gear, pulley) and/or the conveying roller, deviation of belt thickness, and/or error caused by temperature change (changes in diameter). 
   Meanwhile, according to the above-described embodiment of the present invention, a large proportion of conveyance control is handled by the linear encoder having the encoder sensor  11  reading the linear scale provided to the electrostatic attraction belt  2 . Therefore, the conveying roller  3  (rotary encoder), which is susceptible to the problem of overlapping errors, handles only a small proportion of conveyance control. Thus, by providing the rotary encoder with a high resolution, the precision of controlling the electrostatic attraction belt  2  (conveyance of recording paper) can be further improved. 
   In the above-described embodiment of the present invention, the amount (distance) of movement of the electrostatic attraction belt  2  may be considered as corresponding to the amount (distance) of conveyance (movement) of the recording paper since the recording paper is conveyed in a manner attracted (held) on the electrostatic attraction belt  2 . Therefore, precise control of the electrostatic attraction belt  2  results in precise control of the position of the recording paper. With the inkjet engine  20  according to the embodiment of the present invention, the stop position of the recording paper in the sub-scan direction can be precisely controlled, to thereby prevent degradation of image quality caused by ink droplets deviating from a target position. As a result, high image quality can be obtained. 
   Meanwhile, according to an embodiment of the present invention, the border detection sensor  12  is situated upstream of the encoder sensor  11  for detecting the border (joint area) of the linear scale prior to reaching the encoder sensor  11 . In this example, the border detection sensor  12  is a reflection type photosensor. When the border detection sensor  12  detects the border (joint area) of the linear scale, the position of the electrostatic attraction belt  2  is controlled by complementing the data of the linear encoder with data of the rotary encoder before the border (joint area) of the linear scale reaches the encoder sensor  11 . Thereby, position control can be prevented from degrading at the border (joint area) of the linear scale. 
   Furthermore, the outputs of the linear encoder (encoder sensor  11 ) and the rotary encoder (encoder sensor  9 ) are processed as rectangular digital signals. Since the outputs of the linear encoder and the rotary encoder are digital signals, the above-described multiplication operation (in this example, multiplied to 4 in the rotary encoder output) and/or various calculation operation (for example, calculation of speed with use of a counter) can be performed easily. This also prevents degradation of precision due to staining of the linear scale (electrostatic attraction belt  2 ) or the code wheel  8 , to thereby attain satisfactory endurance and high reliability. Since printing is executed by moving (main scanning) the cartridge  21  in over the upper surface of the electrostatic attraction belt  2 , the electrostatic attraction belt  2  is susceptible to staining. Nevertheless, degradation caused by the staining can be reduced by using digital signals as the linear encoder output signals. 
   The output signals of the encoders are, however, not limited to digital signals. Alternatively, analog signals may also be used. High resolution can be achieved with the use of analog signals as the output signals. Furthermore, by using analog signals for controlling the stop position of the electrostatic attraction belt (conveyor belt)  2 , the electrostatic attraction belt  2  can be stopped more accurately with respect to a target position. 
   Next, a control portion  60  of the inkjet recording apparatus  100  shown in  FIG. 1  is described with reference to  FIG. 6 . 
   As shown in  FIG. 6 , the control portion  60  includes, for example, a CPU  61 , a ROM  62 , a RAM  63 , a nonvolatile RAM (NVRAM)  64 , a scanner control portion  65 , an ASIC  66 , an I/O (input/output) portion  67 , a host I/F (interface)  68 , a head drive control portion  69 , a main scan motor drive control portion  70 , and a sub-scan motor drive control portion  71 . 
   The scanner control portion  65  controls the scanner portion (image reading portion)  30 . The I/O portion  67  receives output signals from, for example, the linear encoder (encoder sensor  11 ) and the rotary encoder (encoder sensor  9 ). Furthermore, the I/O portion  67  may also receive output signals from the linear encoder  38  that outputs signals in correspondence to the movement (main scanning) of the carriage  21  (see  FIG. 1 ). The host I/F  68  exchanges data and/or control signals with external devices such as a personal computer. Furthermore, the control portion  60  inputs/outputs signals with respect to a control panel  36 . 
   The head drive control portion  69  controls the carriage  21  and the recording head (print head)  22  via a head driver  90 . The main scan motor drive control portion  70  controls a main scan motor  37  via a main scan motor driver  91  for controlling the movement of the carriage  21  in the main scanning direction. The sub-scan motor drive control portion  71  controls a sub-scan motor  39  via the sub-scan motor driver  76  for controlling the sub-scan drive portion including, for example, the conveying roller  3  and the electrostatic attraction belt  2 . 
   Although not shown in  FIG. 6 , the control portion  60  also controls, for example, the cassette  27  and the paper feed rollers  24  disposed in the inkjet recording apparatus  100  and/or the conveying rollers  25  and the discharge roller  26  disposed in the recording paper conveyance path (paper conveyance portion). 
   Although the present invention is described by referring to the above-described drawings, the present invention is not to be limited to the foregoing description. 
   For example, although the electrostatic attraction belt  2  is described as an example of a conveying part for conveying the recording paper in the sub-scanning direction, a typical conveyor belt may alternatively be employed. In this case, however, it is preferable to provide the conveyor belt with a part having an attracting function (e.g. use of negative pressure), so as to prevent deviation of recording paper and attain more precise conveyance/stop performance. 
   Furthermore, the location at which the linear scale is disposed is not limited to the rear face of the conveying part (conveyor belt), but may be given another location (e.g. front face of the conveyor belt). It is, however, preferable to dispose the linear scale at the rear face of the conveyor belt for avoiding ink stains, etc. The sensor for reading the linear scale may be situated at a position where the linear scale is disposed. 
   The location at which the code wheel included in the rotary encoder is not limited to the conveying roller, but may be another location. For example, the code wheel may alternatively be disposed on the axle of the sub-scan drive motor, the axle of an intermediary gear, or the axle of the tension roller  4  (shown in  FIG. 2 ). Furthermore, a roller member, for example, that abuts and is driven by the conveyor belt may be provided for allowing the code wheel to be disposed on the axle of the roller member. 
   Furthermore, various methods may be employed in fabricating the linear scale. A scale can be obtained as long as contrasts in the strength of reflected light can be formed. For example, the linear scale may be fabricated by applying an aluminum evaporated tape and shaping the surface of the aluminum evaporated tape with a laser. As another method, the linear scale may be fabricated by forming black and white contrasts on a surface of a white color tape by irradiating a laser thereto. Furthermore, various configurations may be applied to the sensors of the linear encoder and the rotary encoder. For example, in a case of using a photosensor, a transparent type sensor or a reflection type sensor may be employed depending on the configuration of the encoder. 
   Furthermore, as described above, the output signals of the encoder sensors are not limited to digital output signals, but may alternatively be analog output signals. Furthermore, the type of control is not limited to closed-loop control (feedback control), but may alternatively be open loop control. 
   The number of colors used for the inkjet recording apparatus of the present invention is not limited to four colors, but may be of a given number of colors. Furthermore, a given number of heads may provided in the inkjet recording apparatus of the present invention. Alternatively, the ink cartridge may be included in the head part, instead of being formed separately from the head. The configuration of the scanner portion or inclusion of an ADF (Automatic Document Feeder) is optional. The image forming apparatus may alternatively be a multi-functional apparatus including a facsimile function and/or a printer function. The image forming apparatus may alternatively be a printer without a scanner portion. 
   Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention. 
   The present application is based on Japanese priority application No.2004-141094 filed on May 11, 2004, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.