JP2006279717A - Apparatus and method for image formation - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation apparatus and an image formation method for improving the picture quality of the read image of an original, and for reducing a noise. <P>SOLUTION: This image formation apparatus is provided with a linear image sensor; an optical system where an optical path is formed from an original to the light receiving face of the linear image sensor; a stepping motor for relatively moving the scanning line of the linear image sensor to the original by moving at least one of the original, the optical system, and the linear image sensor; a driver for driving the stepping motor; and a control unit for accelerating the stepping motor by the driving part until the rotating speed of the stepping motor reaches a predetermined reading speed, and for micro-step driving the stepping motor at the reading speed by the driving part. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an image forming method.

  Patent Document 1 discloses a stepping motor control method in which a stepping motor is accelerated by microstep driving, switched to full step driving at a predetermined rotation speed, and the stepping motor is rotated at a constant speed by full step driving. According to such a stepping motor control method, the vibration of the rotor of the stepping motor (hereinafter referred to as the vibration of the stepping motor) can be suppressed during acceleration of the stepping motor, so that noise caused by the vibration can be reduced. .

However, in an image forming apparatus such as an image scanner, the scanning line of the linear image sensor is moved relative to the original by a stepping motor and the optical image on the scanning line of the linear image sensor is periodically read to read the original. ing. In such an image forming apparatus, since the original is read on the assumption that the scanning line of the linear image sensor is moving at a constant speed, if the rotation speed of the stepping motor is uneven, the scanning position by the linear image sensor is shifted and the original is scanned. The image quality of the scanned image is degraded. In the image forming apparatus as described above, the period during which the document is read by rotating the stepping motor at a constant speed (hereinafter referred to as document reading) is longer than the period during which the stepping motor is accelerated.
Therefore, even if the stepping motor control method disclosed in Patent Document 1 is applied to the image forming apparatus as described above, since the full-step driving is performed when the document is read, the image quality of the read image of the document is improved. The noise of the forming device cannot be reduced sufficiently.
US Pat. No. 6,750,627

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus and an image forming method capable of improving the image quality of a read image of a document and reducing noise.

(1) An image forming apparatus for achieving the above object includes a linear image sensor, an optical system that forms an optical path from a document to a light receiving surface of the linear image sensor, the document, the optical system, and the linear image. A stepping motor that moves the scanning line of the linear image sensor relative to the original by moving at least one of the sensors, a drive unit that drives the stepping motor, and a rotation speed of the stepping motor is predetermined. And a control unit that causes the driving unit to accelerate the stepping motor until the reading speed is reached, and then causes the driving unit to microstep drive the stepping motor at the reading speed.
The control unit causes the stepping motor to micro-step drive at a predetermined reading speed. Here, generally, when the stepping motor is micro-step driven, vibration of the stepping motor can be suppressed. Therefore, according to the image forming apparatus of the present invention, it is possible to suppress the vibration of the stepping motor at the time of reading the document, and thus it is possible to reduce the noise caused by the vibration. Similarly, since the vibration of the stepping motor at the time of reading a document can be suppressed, the shift of the scanning position by the linear image sensor can be suppressed, and the image quality of the read image of the document can be improved.

(2) The control unit may accelerate the stepping motor by micro-step driving by the driving unit until the rotation speed of the stepping motor reaches the reading speed.
(3) The control unit may accelerate the stepping motor by half-step driving by the driving unit until the rotation speed of the stepping motor reaches the reading speed.
(4) The control unit may accelerate the stepping motor by full-step driving by the driving unit until the rotation speed of the stepping motor reaches the reading speed.

(5) An image forming method for achieving the above object includes: moving an at least one of an original, a linear image sensor, and an optical system that forms an optical path from the original to a light receiving surface of the linear image sensor. The stepping motor is accelerated by the driving unit until the rotation speed of the stepping motor that moves the scanning line of the linear image sensor relative to the original reaches a predetermined reading speed, and then the stepping motor is driven by the driving unit. Including a step of micro-step driving at a reading speed.

  Note that the functions of each unit provided in the present invention are realized by hardware resources whose functions are specified by the configuration itself, hardware resources whose functions are specified by a program, or a combination thereof. In addition, the function of each unit is not limited to that realized by hardware resources that are physically independent of each other.

Hereinafter, an embodiment of the present invention will be described based on an example.
FIG. 2 is a schematic diagram showing an image scanner (hereinafter referred to as a scanner) 1 as an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a block diagram of the scanner 1. Note that the image forming apparatus may be a multifunction machine, a copying machine, a facsimile machine having a copying function, or the like.
As shown in FIG. 2, the housing 8 is formed in a box shape having an opening at the top, and supports the document table 10 on the opening side. The document table 10 is formed of a transparent plate such as a generally rectangular glass plate. A document 11 is placed on the surface 10 a of the document table 10.

The carriage 22 is slidably held by the guide rod 20. On the carriage 22, a linear image sensor (hereinafter referred to as an image sensor) 12, a reflection original light source 18, a mirror 16, a lens 14, and the like are mounted. Although the carriage moving type scanner 1 is illustrated, the scanner 1 fixes the positions of the image sensor and the lens with respect to the document table 10 and moves the plurality of mirrors in conjunction with each other to move the main scanning line in the sub scanning direction. It may be a mirror moving type scanner that is moved to.
The image sensor 12 includes a CCD linear image sensor, a CMOS linear image sensor, or the like that includes a group of photoelectric conversion elements arranged in a straight line. Although a lens reduction type image sensor has been exemplified, the image sensor 12 may be a contact type image sensor.

The reflection original light source 18 is constituted by a tube illumination device using a xenon lamp or the like, and the longitudinal axis is arranged in a posture parallel to the main scanning line of the image sensor 12. The reflective document light source 18 illuminates the document 11 placed on the document table 10 from below the document table 10. The light source 18 for the reflection original may be a lighting device including a light emitting diode and a light guide that uniformly spreads light emitted from the light emitting diode in a direction parallel to the main scanning line.
The mirror 16 and the lens 14 as an optical system form an optical image of the document 11 that is radiated from the reflection document light source 18 and reflected by the document 11 on the light receiving surface of the image sensor 12.

  As shown in FIG. 3, the motor driver 52 as a drive unit drives the stepping motor 53 under the control of the control unit 60. Specifically, the control unit 60 outputs a pulse signal for controlling the rotation speed of the stepping motor 53, an excitation mode signal for controlling the excitation method of the stepping motor 53, and the like to the motor driver 52 (see FIG. 1). The motor driver 52 drives the stepping motor 53 with a current having a waveform corresponding to these signals (see A-phase drive current and B-phase drive current shown in FIG. 1). Details will be described later. The stepping motor 53 is a two-phase bipolar stepping motor. The carriage 22 is pulled by the drive belt 46 driven by the stepping motor 53 and reciprocates along the guide rod 20. When the image sensor 12 moves in the sub-scanning direction together with the carriage 22, a two-dimensional image can be scanned (see FIG. 2).

The sensor driving unit 50 is a circuit that outputs a pulse signal for driving the image sensor 12. The AFE (analog front end) unit 54 includes an analog signal processing unit, an A / D converter, and the like. The digital image processing unit 56 performs image processing on the digital signal output from the AFE unit 54 to generate an image. The interface unit 58 is configured in accordance with a communication standard such as USB (Universal Serial Bus). The scanner 1 is communicably connected to a personal computer (PC) (not shown) via the interface unit 58.
The control unit 60 includes a CPU 62, a ROM 64, and a RAM 66. The CPU 62 executes computer programs stored in the ROM 64 to control each unit of the scanner 1. The ROM 64 is a memory that stores various programs and data, and the RAM 66 is a memory that temporarily stores various programs and data.

FIG. 4 is a schematic diagram for explaining the control of the stepping motor 53 during document reading. FIG. 1 is a schematic diagram showing the control of the stepping motor 53 near the start of scanning (see ts) by the image sensor 12.
First, the control unit 60 receives a setting of reading conditions such as the reading resolution of the document 11 and a request to read the document 11. The control unit 60 causes the motor driver 52 to drive the stepping motor 53 as described below according to the reading conditions received at this time, the elapsed time since the reading request was received, and the like. Specifically, the control unit 60 stores a relational expression defining the pulse generation timing of the pulse signal and the switching timing of the excitation mode signal in the ROM 64 or the like using the above-described reading conditions and elapsed time as variables, and the relational expression is stored in the relational expression. Based on this, a pulse signal and an excitation mode signal are generated. The control unit 60 may store a table corresponding to the above-described relational expression in the ROM 64 or the like, and generate a pulse signal and an excitation mode signal based on the table.

  When the control unit 60 receives a reading request for the document 11, the control unit 60 accelerates the carriage 22 until the moving speed reaches a predetermined speed. Specifically, as shown in FIG. 1, the control unit 60 starts the stepping motor 53 at a pulse rate lower than the self-starting pulse rate, and gradually increases the pulse rate. At this time, the control unit 60 outputs an excitation mode signal M1 for setting half-step driving as an excitation method of the stepping motor 53. Accordingly, the control unit 60 causes the motor driver 52 to accelerate the rotation of the stepping motor 53 to the reading speed by half-step driving. Here, the reading speed is the rotation speed of the stepping motor 53 when the control unit 60 causes the image sensor 12 to read the document 11, and is the rotation speed of the stepping motor 53 set according to the reading resolution of the document 11. . For example, the reading speed is set so as to decrease as the reading resolution of the document 11 increases.

  The control unit 60 switches the excitation method of the stepping motor 53 from half-step driving to micro-step driving at the timing (see ts) when the moving speed of the carriage 22 reaches the above-described predetermined speed, and the motor driver 52 causes the stepping motor 53 to be changed at that time. Are driven at a rotational speed of (ie, reading speed). As a result, the carriage 22 moves at a constant speed at the predetermined speed described above. Then, the control unit 60 causes the image sensor 12 to read the document 11. Specifically, the control unit 60 sets the microstep drive from the excitation signal M1 that sets the half step drive as the excitation method of the stepping motor 53 at the timing (see ts) when the rotation speed of the stepping motor 53 reaches the reading speed. The signal level is changed to the excitation signal M2. The motor driver 52 switches the excitation method of the stepping motor 53 from the half-step drive to the micro-step drive in accordance with the change of the excitation mode signal (see A-phase drive current and B-phase drive current shown in FIG. 1). Then, the control unit 60 causes the image sensor 12 to periodically read the optical image on the scanning line of the image sensor 12 of the document 11.

  5 to 7 are schematic diagrams showing measurement results of noise generated by the stepping motor 53 driven by microsteps and noise generated by the stepping motor 53 driven by half steps. This measurement result is a noise level obtained by standardizing the noise of the stepping motor 53 with the ambient noise, and the larger this level, the greater the noise. Here, to normalize the noise of the stepping motor 53 with the ambient noise means that the noise level when the stepping motor 53 of the scanner 1 is not driven is subtracted from the noise level when the stepping motor 53 of the scanner 1 is driven. The ratio to the noise level when the stepping motor 53 is not driven is calculated. In this measurement, as shown in FIG. 5, the peak value and effective value of the noise level at a predetermined pulse rate (250 pps, 500 pps,..., 3000 pps) of the pulse signal are measured during microstep driving and half step driving, respectively. is doing. In FIG. 6, a graph 100 and a graph 102 show the relationship between the pulse rate of the pulse signal and the peak value of the noise level during microstep driving and half step driving, respectively. In FIG. 7, graph 104 and graph 106 show the relationship between the pulse rate of the pulse signal and the effective value of the noise level during microstep driving and half step driving, respectively.

From the measurement results shown in FIG. 5 to FIG. 7, it can be seen that the noise of the stepping motor 53 can be reduced by microstep driving the stepping motor 53 compared to the case where the stepping motor 53 is half step driven.
As described above, in the scanner 1, since the stepping motor 53 is micro-step driven at the reading speed and the carriage 22 is moved at a constant speed when reading the document, the noise when the stepping motor 53 reads the document can be reduced. it can. Further, since the stepping motor 53 is smoothly rotated by micro-step driving at the time of reading the document, it is possible to suppress the shift of the scanning position by the image sensor 12 and to improve the image quality of the read image of the document 11.

  In the scanner 1 described above, it has been described that the control unit 60 causes the motor driver 52 to drive the stepping motor 53 in half steps when the stepping motor 53 is accelerated. However, any method may be used as the excitation method when the stepping motor 53 is accelerated. For example, the control unit 60 may cause the motor driver 52 to drive the stepping motor 53 at full step when the stepping motor 53 is accelerated as shown in FIG. At that time, at the timing when the rotation speed of the stepping motor 53 reaches the reading speed, the control unit 60 changes the excitation signal M0 that sets the full step drive as the excitation method of the stepping motor 53 to the excitation signal M2 that sets the microstep drive. Change the level. Further, as shown in FIG. 9, the control unit 60 may cause the motor driver 52 to micro-step drive the stepping motor 53 during the acceleration of the stepping motor 53 (see FIG. 9).

Further, it has been described that the control unit 60 switches the excitation mode of the stepping motor 53 by the excitation mode signal. However, any method for switching the excitation mode of the stepping motor 53 may be used. For example, the excitation mode of the stepping motor 53 may be switched by a multi-bit signal indicating the current value of the drive current.
The stepping motor 53 has been described as a two-phase bipolar stepping motor. However, the stepping motor 53 may be a unipolar stepping motor or a stepping motor having two or more phases.

The schematic diagram for demonstrating control of the stepping motor which concerns on one Example. 1 is a schematic diagram of an image scanner according to an embodiment. FIG. 1 is a block diagram of an image scanner according to an embodiment. The schematic diagram for demonstrating control of the stepping motor which concerns on one Example. The schematic diagram which shows the measurement result of the noise which a stepping motor generates. The schematic diagram which shows the measurement result of the noise which a stepping motor generates. The schematic diagram which shows the measurement result of the noise which a stepping motor generates. The schematic diagram for demonstrating control of the stepping motor which concerns on one Example. The schematic diagram for demonstrating control of the stepping motor which concerns on one Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image scanner (image forming apparatus), 11 Document, 12 Linear image sensor, 14 Lens (optical system), 16 Mirror (optical system), 52 Motor driver (drive part), 53 Stepping motor, 60 Control part

Claims (5)

A linear image sensor,
An optical system that forms an optical path from a document to the light receiving surface of the linear image sensor;
A stepping motor for moving a scanning line of the linear image sensor relative to the original by moving at least one of the original, the optical system, and the linear image sensor;
A drive unit for driving the stepping motor;
A control unit for accelerating the stepping motor by the driving unit until the rotational speed of the stepping motor reaches a predetermined reading speed, and then driving the stepping motor by the driving unit at the reading speed;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the control unit accelerates the stepping motor by microstep driving by the driving unit until a rotation speed of the stepping motor reaches the reading speed.   The image forming apparatus according to claim 1, wherein the control unit accelerates the stepping motor by half-step driving by the driving unit until a rotation speed of the stepping motor reaches the reading speed.   The image forming apparatus according to claim 1, wherein the control unit accelerates the stepping motor by full-step driving by the driving unit until a rotation speed of the stepping motor reaches the reading speed.   The scanning line of the linear image sensor is moved relative to the original by moving at least one of the original, the linear image sensor, and an optical system that forms an optical path from the original to the light receiving surface of the linear image sensor. A step of accelerating the stepping motor by the driving unit until the rotational speed of the stepping motor to be moved reaches a predetermined reading speed, and then driving the stepping motor by the driving unit at the reading speed; An image forming method.

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