JP3716594B2 - Image reading device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image reading apparatus that scans a document by a scanning unit driven by a motor and reads an image on the document surface.
[0002]
[Prior art]
As is well known, in an image reading apparatus such as a copying machine, a document surface is scanned by a scanning unit that moves relative to the document. FIG. 7 shows the configuration of the optical system of this type of image reading apparatus, and FIG. 8 shows the configuration of the control system of the image reading apparatus.
[0003]
First, the configuration of the optical system of the image reading apparatus will be described with reference to FIG. In FIG. 7, a document table 101 is made of transparent glass, and a document 102 is placed on the document table 101. A full rate carriage 103 including a light source 103a and a mirror 103b, a half rate carriage 104 including mirrors 104a and 104b, a lens 105, and a color image reading sensor 106 are provided below the document table 101. . Here, the full rate carriage 103 and the half rate carriage 104 constitute a scanning unit that scans the document 102. That is, the output light of the light source 103 a in the full rate carriage 103 is irradiated on the surface of the original 102, and the reflected light is guided to the color image reading sensor 106 through the mirror 103 b, the mirrors 104 a and 104 b in the half rate carriage 104 and the lens 105. . The full rate carriage 103 is driven in the arrow direction at a speed V, and the half rate carriage 104 is driven in the same direction at a half speed. By driving the full-rate carriage 103 and the half-rate carriage 104, the irradiation position of the original 103 is moved, and electrical signals corresponding to images at the respective irradiation positions on the original 103 are sequentially obtained from the color image reading sensor 106.
[0004]
Next, the control system of the image reading apparatus will be described with reference to FIG. The image reading apparatus includes a main CPU 201, an image processor 202, and an image reading control processor 203 as control processors. Here, the main CPU 201 is a processor that controls the entire image reading apparatus.
[0005]
The image processor 202 generates various control information such as a page synchronization signal PS, a line synchronization signal LS, and scanning information necessary for image reading control under the control of the main CPU 201, and the color image reading sensor 106 and the image. An image signal is generated by the signal processing unit 204 and is delivered to the main CPU 201. Here, the scanning information includes information for determining scanning conditions of the full rate carriage 103 and the half rate carriage 104, such as an image reading magnification and a scanning length. These pieces of information are determined by a magnification designation or the like performed by the user on the image reading apparatus.
[0006]
The image reading control processor 203 is means for performing timing control for an image reading operation. In addition to the image reading operation, the illumination 209 and the cooling fan 208 are also controlled by the image reading control processor 203.
[0007]
As already described, in the image reading operation, the full rate carriage 103 and the half rate carriage 104 in FIG. 7 are driven. The image reading drive motor 209 is a motor that drives the full rate carriage 103 and the half rate carriage 104 during the image reading operation.
[0008]
Here, a stepping motor or a servo motor is generally used as a motor for driving a carriage as a scanning unit of the image reading apparatus. This is because, when these motors are used as the driving means of the scanning unit, the rotation speed can be freely adjusted to reduce and enlarge the read image. However, in recent years, for reasons such as ease of control and cost advantage, stepping motors are often used as carriage driving motors in low and medium speed image reading apparatuses. In particular, in a color image reading apparatus that does not have a page memory and sequentially reads color image information by scanning a document a plurality of times, a stepping motor is generally used as a carriage driving motor.
[0009]
Therefore, also in the image reading apparatus shown in FIG. 8, a stepping motor is used as the image reading drive motor 209 for driving the full rate carriage 103 and the half rate carriage 104. The motor drive driver 206 is means for supplying an excitation current pulse to the image reading drive motor 209 to drive the image reading drive motor 209 stepwise.
[0010]
As described above, the full-rate carriage 103 and the half-rate carriage 104 move at a speed ratio of 2: 1 while interlocking to scan the original 102. In order to read an image at a desired image reading magnification, The scanning speed needs to be a speed corresponding to the image reading magnification. The scanning speed is determined by the rotational speed of the image reading drive motor 209, and this rotational speed depends on the frequency of the excitation current pulse supplied to the motor. Therefore, in the image reading, it is necessary to control to increase the frequency of the excitation current pulse supplied from the motor driving driver 206 to the image reading driving motor 209 from 0 to a frequency corresponding to the final scanning speed.
[0011]
Therefore, in the image reading apparatus shown in FIG. 8, the image reading control processor 203 outputs the excitation current pulse to the drive motor driver 206 in order to increase the frequency of the excitation current pulse as described above to reach the final value. An instruction pulse is supplied.
[0012]
On the other hand, when the image reading drive motor 209 is accelerated by increasing the frequency of the excitation current pulse as described above, the step of the image reading drive motor 209 is synchronized with the step-out, that is, the supply of the excitation current pulse. Do not cause the phenomenon to disappear. In order not to cause this step-out, the current value of the excitation current pulse supplied from the motor drive driver 206 to the image reading drive motor 209 is increased to some extent, and a torque exceeding a certain lower limit value is rotated by the image reading drive motor 209. It is necessary to make it part.
[0013]
In the image reading apparatus shown in FIG. 8, the voltage setting and the current setting of the drive motor driver 206 are performed by the image reading control processor 203 in order to supply such an excitation current.
[0014]
[Problems to be solved by the invention]
By the way, the above-described conventional image reading apparatus supplies a sufficient excitation current to the image reading drive motor 209 so that a sufficient torque that does not cause the step-out is generated. In the case of reading a color image, there has been a problem that color deviation occurs. Hereinafter, this problem will be described in detail.
[0015]
First, general characteristics of a stepping motor used as the image reading drive motor 209 will be described with reference to FIG. The plurality of curves shown in FIG. 9 show the relationship between the frequency of the excitation current pulse and the torque generated by the stepping motor. As illustrated, in order to increase the torque generated by the stepping motor, it is necessary to increase the current value of the excitation current pulse. When the current value of the exciting current pulse is constant, the torque generated by the stepping motor decreases as the frequency of the exciting current pulse (that is, the scanning speed) increases.
[0016]
On the other hand, the moment of inertia of the rotating system including the rotating part and the scanning part of the stepping motor is M, the viscosity coefficient of the rotating system is D, the operating speed is V, the friction load Is FL and the angular acceleration of the rotating system is α, the load torque TL of the stepping motor is TL = M · α + D · V + FL. However, since the viscosity coefficient D is very small, the above equation can be approximated by the following equation.
TL = M ・ α + FL
[0017]
Therefore, in order to drive the scanning unit with the acceleration α, at least Mα + FL It is necessary to supply the exciting current so that the above torque is generated by the motor.
[0018]
A1 and A2 in FIG. 9 indicate load torques obtained for each case where the acceleration is the same and the set speed is different according to this concept.
[0019]
However, in order to drive the scanning unit without causing the stepping motor to step out, it is not sufficient to consider only the acceleration of the scanning unit. That is, the stepping motor has a delay element, and even if an excitation current corresponding to a certain set torque is supplied to the motor, the set torque cannot be obtained immediately from the motor. In determining the excitation current pulse to be supplied to the stepping motor, it is not necessary to consider the above-mentioned minimum required torque, and it is necessary to consider the influence of this delay element. Hereinafter, the delay element of the stepping motor and its influence will be described with reference to FIG.
[0020]
FIG. 10 exemplifies a temporal change in torque generated by the stepping motor when the current setting value of the excitation current pulse supplied to the stepping motor is raised from 0 to a current value corresponding to the setting torque at a certain time. Is. In the upper diagram in FIG. 10, three curves C1, C2 and C3 are drawn. When the rotation speed of the stepping motor is V1, the curve C2 has the same rotation speed V2 (> In the case of V1), the curve C3 shows the torque generated by the motor when the rotational speed is V3 (>V2> V1). As shown in FIG. 10, when the set value of the excitation current is raised stepwise, the torque generated by the stepping motor increases along a time constant curve corresponding to a delay element inherent in the motor, and a predetermined delay The set torque is reached after a lapse of time. Further, the time constant of the delay element of the stepping motor increases depending on the rotational speed of the motor. In the example shown in FIG. 10, when the rotation speed of the stepping motor is increased from V1 → V2 → V3, the delay time until the generated torque of the motor reaches the set torque is T1 → T2 → T3. It has increased.
[0021]
Since the stepping motor includes a delay element as described above, if the current value of the excitation current pulse supplied to the motor is controlled with the necessary minimum torque as described above, Torque is delayed in time to become the magnitude corresponding to the excitation current pulse. Eventually, the generated torque of the motor becomes less than the necessary minimum torque, and in the worst case, step-out occurs. It becomes.
[0022]
A1 and A2 in FIG. 9 indicate the required acceleration torque for each case with the same acceleration and different set speeds. Conventionally, in consideration of the time delay of the rise of the torque described above, the motor is In order to prevent step-out, excitation current pulses corresponding to the acceleration torques A1 ′ and A2 ′ are supplied to the motor.
[0023]
However, when such an excessive excitation current is supplied, after the torque generated by the stepping motor reaches a set torque necessary for driving the scanning unit, the excessive excitation current generates an excessive torque, and the scanning unit This will cause a large vibration. This vibration causes problems such as the above-described distortion of the read image and color misregistration in the case of reading a color image.
[0024]
The present invention has been made in view of the circumstances described above, and does not cause the above-described step-out, and does not cause distortion of a read image or color shift at the time of reading a color image, and can perform stable scanning. An object of the present invention is to provide an image reading apparatus capable of reading an image.
[0025]
[Means for Solving the Problems]
The present invention provides an image reading apparatus that generates an image signal by driving a scanning unit by a motor and scanning an image by the scanning unit. Storage means for storing information relating to the time for passing an excessive excitation current in association with a plurality of types of image reading magnifications; After starting to drive the scanning unit by the motor, A period indicated by information corresponding to the set image reading magnification among the information stored in the storage means Until Then An excitation current corresponding to a torque that is larger than a set torque required for driving the scanning unit is supplied to the motor, and an excitation current corresponding to the set torque is supplied to the motor after the period has elapsed. The gist of the present invention is an image reading apparatus comprising a control means for performing the supply control.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a configuration of a drive control system of a scanning unit in an image reading apparatus according to an embodiment of the present invention. In FIG. 1, a CPU 1 and a storage unit 2 are provided for controlling an image reading operation in the image reading apparatus, and correspond to the image reading control processor 203 in FIG. The stepping motor 3 is a driving unit for a scanning unit (not shown) (corresponding to the full rate carriage 103 and the half rate carriage 104 in FIG. 7), and corresponds to the image reading drive motor 209 in FIG. The motor drive unit 4 is means for supplying an excitation current pulse to the stepping motor 3 under the control of the CPU 1, and corresponds to the drive motor driver 206 in FIG.
[0027]
Here, the configuration and function of the motor drive unit 4 will be described. The motor drive unit 4 includes a pulse divider 41, an excitation current output unit 42, a reference signal generator 43, a current detector 44, a comparator 45, and a chopper 46.
[0028]
First, the pulse divider 41 is a unit that divides a pulse having a constant frequency and supplies it to the exciting current output unit 42. The exciting current output unit 42 supplies the exciting current pulse to the stepping motor 3 when the pulse is supplied from the pulse divider 41. Here, the rotation speed of the stepping motor 3 depends on the frequency of the excitation current pulse supplied from the excitation current output unit 42 to the stepping motor 3. The CPU 1 sets the frequency of the excitation current pulse by setting the frequency division ratio of the pulse divider 41.
[0029]
Further, the current value of the excitation current pulse supplied from the excitation current output unit 42 to the stepping motor 3 is adjusted by chopper control. The reference signal generator 43, the current detector 44, the comparator 45 and the chopper 46 constitute a control means for performing this chopper control.
[0030]
First, a reference voltage corresponding to the current setting value of the excitation current pulse is supplied from the CPU 1 to the reference signal generator 43. The reference signal generator 43 generates a reference signal Vref in which a triangular wave having a predetermined frequency and amplitude is superimposed on the reference voltage. FIG. 2A illustrates the waveform of the reference signal Vref. In addition, the broken line in the same figure represents the reference voltage supplied from CPU1.
[0031]
On the other hand, the current detector 44 detects the excitation current supplied to the stepping motor 3 from the excitation current output unit 42 and outputs a detection voltage Vm proportional to the current value. Here, since the chopper control of the excitation current is performed at a sufficiently high frequency, the current detected by the current detector 24 has a sufficiently low level of ripple, and therefore the detection voltage Vm is also regarded as a substantially DC voltage. Can do.
[0032]
The comparator 45 compares the reference signal Vref output from the reference signal generator 43 with the detection voltage Vm output from the current detector 44, and is high level only during a period when the level of the reference signal Vref is higher than the detection voltage Vm. A gate pulse G is output. 2B illustrates the waveforms of the reference signal Vref and the detection voltage Vm, which are comparison targets of the comparator 45, and FIG. 2C illustrates the gate pulse G obtained from the comparator 45 in this case. A waveform is shown.
[0033]
The chopper 46 performs switching control of the output operation of the excitation current output unit 42 so that the excitation current is output only during the period when the gate pulse G is at the high level. The excitation current output unit 42 outputs a pulse from the pulse divider 41 as an excitation current pulse. The excitation current pulse is output by intermittently outputting the excitation current under switching control by the chopper 46. It is done.
[0034]
3A to 3C show the relationship between the output pulse of the pulse divider 41, the gate pulse G, and the excitation current pulse output from the excitation current output unit 42 under such chopper control. Is.
[0035]
According to the configuration described above, when the excitation current is small, the detection voltage Vm is small, so that the gate pulse G having a wide pulse width is output as is apparent from FIGS. 2B and 2C. However, when the pulse width of the gate pulse G is increased, a large excitation current is output from the excitation current output unit 42, so that the detection voltage Vm is increased and the pulse width of the gate pulse G is reduced. As a result of this negative feedback control, the excitation current corresponding to the reference voltage output from the CPU 1 is eventually output from the excitation current output unit 42.
[0036]
Next, the contents of control performed by the CPU 1 will be described. When an image reading operation is performed in this image reading apparatus, the CPU 1 supplies excitation to the stepping motor 3 from the motor drive unit 4 based on various control information in the storage unit 2 so as to scan a scanning unit (not shown). The frequency of the current pulse and the current value are controlled. The greatest feature of the image reading apparatus according to the present embodiment lies in the specific contents of the excitation current control of the stepping motor 3 performed by the CPU 1.
[0037]
First, the frequency control of the exciting current pulse of the stepping motor 3 in this embodiment will be described. FIG. 4C illustrates the temporal change in the scanning speed during the period from the start of driving of the scanning unit to scanning at the set speed for each case where the image reading magnification is 100%, 200%, and 400%. It is a thing. As shown in this figure, in this embodiment, at the time of image reading, the scanning speed is increased exponentially from 0 to reach the final scanning speed corresponding to the image reading magnification. In the present embodiment, the scanning speed reaches the final scanning speed in a certain time TR regardless of the image reading magnification.
[0038]
In order to perform such control of the scanning speed, the frequency of the excitation current pulse of the stepping motor 3 is always set to the target value of the scanning speed (scanning speed at that time) throughout the entire period from the driving start time of the scanning section to the end of scanning. During the period in which the change is made, it is necessary to adjust the frequency of the exciting current pulse every moment so as to correspond to the instantaneous value of the scanning speed at that time).
[0039]
Therefore, in this embodiment, for each image reading magnification, a mode of temporal change of the scanning speed as illustrated in FIG. 4C is determined in advance, and a pulse divider necessary for obtaining such a scanning speed. The time series data of the frequency division ratio of 41 is obtained in advance and stored in the storage unit 2 in advance. During the image reading operation, the CPU 1 sequentially reads out the data corresponding to the image reading magnification designated by the user from the time-series data of the frequency division ratio stored in the storage unit 2 and sequentially sets them in the pulse divider 41. As a result, the frequency of the excitation current pulse supplied from the motor drive unit 4 to the stepping motor 3 temporally changes within the period from the start of driving of the scanning unit to scanning at the set speed, and the scanning speed is as shown in FIG. This is a time change as exemplified in (c).
[0040]
The above is the details of the frequency control of the exciting current pulse of the stepping motor 3 in the present embodiment.
[0041]
Next, control of the current value of the excitation current pulse of the stepping motor 3 in this embodiment will be described.
[0042]
If the temporal change in the scanning speed during image reading is as shown in FIG. 4C, the angular acceleration of the rotating portion of the stepping motor 3 increases as the final scanning speed increases. . As illustrated in FIG. 5, when the angular acceleration of the rotating part of the stepping motor 3 increases, the torque required for acceleration of the rotating part also increases in proportion to this.
[0043]
Therefore, as illustrated in FIG. 6, as the final scanning speed increases, the set current value of the excitation current pulse required when the stepping motor 3 is accelerated during image reading also increases.
[0044]
Here, the set torque of the stepping motor 3 is preferably the minimum torque necessary for preventing the step-out in order to reduce the vibration of the scanning unit, and the set current value of the excitation current pulse of the motor is also shown in FIG. Ideally, the minimum required size as illustrated in FIG. However, the torque generated by the stepping motor 3 responds with delay to the rise of the excitation current. Accordingly, during the period until the generated torque of the stepping motor 3 reaches the set torque necessary for driving the scanning unit, an excitation current corresponding to a torque larger than the set torque is supplied to the motor in order to compensate for the response delay. There is a need to.
[0045]
On the other hand, after the generated torque of the stepping motor 3 reaches the original set torque, if the same exciting current as before is applied to the motor, the generated torque becomes excessive and a large vibration is generated in the scanning unit. Become.
[0046]
Therefore, in this embodiment, for each image reading magnification, a delay time until the generated torque of the stepping motor 3 reaches the set torque is obtained, and the period from the start of driving of the scanning unit until the delay time elapses is: An excitation current pulse is supplied at a first set current value that generates a large torque obtained by adding an increment for compensating for a response delay with respect to the set torque, and a second period corresponding to the original set torque for the subsequent period. The excitation current pulse is supplied with the set current value. Further details are as follows.
[0047]
First, FIG. 4A shows the torque generated by the stepping motor when the excitation current supplied to the stepping motor 3 is stepped up to a value corresponding to the set torque as shown in FIG. 4B. This is an example of temporal changes. In FIG. 4 (a), three curves D1, D2 and D3 are drawn. These curves D1, D2 and D3 are obtained when the image reading magnification is 100%, 200% and 400%, respectively. The change with time of the torque generated by the stepping motor 3 is shown respectively. In FIG. 4A, the generated torque normalized by the set torque is represented as curves D1 to D3 in order to facilitate the comparison of the delay of the generated torque with respect to the excitation current.
[0048]
In the example shown in FIG. 4A, when the image reading magnification is 100%, 200%, and 400%, the delay times until the generated torque of the motor reaches the set torque are T3, T2, and T1, respectively. Become. In this embodiment, prior to the implementation, the delay times T1 to T3 are obtained in advance.
[0049]
The storage unit 2 uses, for each image reading magnification, a delay time until the generated torque of the stepping motor 3 reaches the set torque and a period from when the scanning unit starts driving until the delay time elapses. The first set current value to be used and the second set current value to be used after the lapse of the period are stored in advance.
[0050]
In the present embodiment, during the image reading operation, the delay time corresponding to the image reading magnification designated by the user among the information stored in the storage unit 2 in this way, the first set current value, and the second set current The value is read by CPU1. Then, the reference voltage corresponding to the first set current value is sent from the CPU 1 to the reference signal generator 43 of the motor driving unit 4 until the read delay time elapses after the scanning unit starts driving. After the elapse of the period, the reference voltage corresponding to the second set current value is sent to the reference signal generator 43. As a result of such control, the set current value of the excitation current pulse of the stepping motor 3 changes as illustrated in FIG. 4D, the stepping motor 3 does not step out, and the scanning unit Scanning is performed without generating large vibrations.
[0051]
In the above embodiment, the setting current value of the excitation current pulse supplied to the stepping motor is changed stepwise, but the mode of change of the setting current with time is not limited to this. In the above embodiment, the frequency of the exciting current pulse and the set current value are temporally changed according to the time-series information stored in the storage unit 2, but the temporal change of the frequency and the set current value is expressed by a function. The frequency of the exciting current pulse and the set current value may be controlled by the CPU using this function. In the above embodiment, the image reading apparatus using the stepping motor as the driving unit of the scanning unit has been described as an example. However, the present invention can also be applied to an image reading apparatus that drives the scanning unit with a servo motor.
[0052]
【The invention's effect】
As described above, according to the present invention, when the scanning unit is driven by the motor at the time of image reading, the period until the motor torque reaches the set torque is a sufficiently large set current in consideration of the response delay of the torque. The motor is driven with the value, and after the period, the motor is driven with the set current value corresponding to the minimum necessary torque that does not cause step-out. There is an effect that image reading can be performed by stable scanning without causing image distortion or color misregistration during color image reading.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a configuration of a drive control system of a scanning unit in an image reading apparatus according to an embodiment of the present invention.
FIG. 2 is a waveform diagram showing waveforms of respective parts of the motor drive unit 4 in the same embodiment.
FIG. 3 is a waveform diagram illustrating chopper control of excitation current pulses performed in the same embodiment.
FIG. 4 is a diagram for explaining excitation current pulse frequency control and current value control in the same embodiment;
FIG. 5 is a diagram showing the relationship between the acceleration of the stepping motor 3 and the torque required for the acceleration in the same embodiment.
FIG. 6 is a view for explaining how to obtain a set current value of an exciting current pulse in the same embodiment;
FIG. 7 is a diagram illustrating a configuration of an optical system of a conventional image reading apparatus.
FIG. 8 is a block diagram illustrating a configuration of a control system of the image reading apparatus.
FIG. 9 is a diagram showing the relationship between the frequency of the excitation current pulse supplied to the stepping motor and the torque of the motor.
FIG. 10 is a waveform diagram showing a delay in the rise of the torque of the stepping motor with respect to the rise of the excitation current.
[Explanation of symbols]
1 ... CPU (control means), 2 ... storage unit, 3 ... stepping motor,
4 ... Motor drive unit.

Claims (3)

In an image reading apparatus that generates an image signal by driving a scanning unit by a motor and scanning an image by the scanning unit,
Storage means for storing information relating to the time for passing an excessive excitation current in association with a plurality of types of image reading magnifications;
After the start of the driving of the scanning unit by the motor, the period indicated by the one corresponding to the image reading magnification is set among the information stored in said storage means elapses until, settings required for driving of the scanning unit supplying an excitation current corresponding to the excessive torque than the torque to the motor, after this period and a control means for controlling the supply of the exciting current to supply the exciting current corresponding to the set torque to the motor An image reading apparatus. The image reading apparatus according to claim 1, wherein the period indicated by the information is a time corresponding to a delay in a change in torque generated by the motor with respect to a change in excitation current.   The image reading apparatus according to claim 1, wherein the motor is a stepping motor.

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