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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image reading apparatus for
photoelectrically reading an image of an original.
2. Related Background Art
Various image reading apparatuses have been proposed as an apparatus for
inputting an image into a facsimile machine, digital copying machine, or a
computer, wherein the image of an original is exposed by a light source
and an image signal is formed by photoelectric conversion of the light
reflected by the original.
In such image reading apparatus, one of the points requiring caution for
accurate reading of the image with proper density and contrast is the
adjustment of the light quantity of the light source used for exposure of
the original at a proper level. The assignee of the present invention
proposed systems for adjusting the light quantity of the light source at
the proper level in U.S. Pat. No. 4,677,287 and U.S. Pat. No. 4,691,365.
However, for example, when a fluorescent lamp is used for the light source,
there is a drawback in that a longer waiting time is required at low
temperature (FIG. 1B) in comparison with such waiting time at normal
temperature (FIG. 1A) until the light quantity reaches the proper level.
Thus the throughput in unit length of time of reading decreases.
In order to shorten such waiting time, it may be useful to provide a heater
for heating the light source, but the cost of the apparatus should
increase too much.
SUMMARY OF THE INVENTION
In one aspect, the present invention has been made in view of the above
facts and provides an image reading apparatus which improves the
throughput of reading of an original.
In another aspect, the present invention provides an image reading
apparatus capable of reading an original at low cost, without an extended
waiting time even when environmental temperature is low.
In still another aspect, the present invention provides an image reading
apparatus which suppresses variation of the level of image data of an
original owing to variation of the light quantity, and thus enabling
proper reading of the original.
The aforesaid objective, effect and other objectives and effects shall be
evident from the following explanation.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A and 1B are views indicating the rise characteristics of light
quantity of a fluorescent lamp.
FIG. 2 is a perspective view of the appearance of an image reading
apparatus according to a first illustrative embodiment of the present
invention.
FIG. 3 is a view illustrating an internal construction of the apparatus
shown in FIG. 2.
FIG. 4 is a block diagram indicating an important circuit of FIG. 3.
FIG. 5 is a circuit diagram of a photoelectric conversion apparatus.
FIG. 6 is a performance timing chart of image sensor 22.
FIG. 7 is a flow chart indicating a performance of an illustrative
embodiment of the present invention.
FIG. 8 is a layout view of white reference member 28.
FIG. 9 is a timing chart indicating an output timing of SG302.
FIG. 10 is a block diagram showing a construction of an image reading
apparatus according to a second illustrative embodiment of the present
invention.
FIG. 11 is a flow chart showing an example of a scanning speed control
procedure at the time of "Book Mode" of ROM508A.
FIG. 12 is a view showing the layout of original white indicator member 28.
FIG. 13 is a view showing an example of slope of the rise of peak detecting
signal Vpk, and an example of the corresponding process of carrying an
original or moving an optical system.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention will be explained hereinafter in reference to the
illustrative embodiments.
FIG. 2 is a perspective view of the appearance of an example of an original
image reading apparatus according to the present invention, and FIG. 3
illustrates an internal construction thereof.
Referring now to FIGS. 2 and 3, 1 is the entire original image reading
apparatus (hereinafter abbreviated as a reader). 2 is a reader main body
which is so arranged that an original on a platen glass 29 (image facing
downward) is illuminated by original illuminating unit 24, and via
reflective mirrors 25, an original image is formed by lens 26 on the image
sensor 22, as disclosed in U.S. Pat. Application Ser. No. 325,023, filed
MAR. 20, 1989, which comprises a plural number of light receiving elements
arranged in a main scanning direction.
Original illumination unit 24 and mirrors 25 can move in a subscanning
direction, which is perpendicular to the main scanning direction, by means
of a driving system (not shown) employing stepping motor 27.
3 is an automatic document feeder (hereinafter abbreviated as ADF) wherein
a sheet shaped original (image facing upward) on a original placing table
31 is delivered in a direction of arrow B (shown by broken line in FIG. 3)
by a delivery system not (shown) employing stepping motor 33, and then
discharged on original discharge table 32.
In this illustrative embodiment, it is so arranged, for example, that ADF3
is able to turn around the axis 40 as against reader main body 2, and ADF3
is set at a position indicated in the drawing.
21 is a control unit and 23 is an image sensor unit, an example of circuit
construction of the two being shown in FIG. 4.
The performance of reader 1 will be explained in reference to FIGS. 3 and
4. The reader 1 of this illustrative embodiment has two modes, one being a
"sheet (through) mode" wherein a sheet original having no binded part is
read while being carried by ADF3 in the subscanning direction, and another
being a "book mode" wherein an original having binded part such as a book
is read while being placed on platen glass 29 by keeping ADF3 in a
released state and moving original illumination unit 24 and mirror 25 in
the subscanning direction.
First, the "sheet (through) mode" will be explained.
(1) "Sheet mode"
Reader 1 of this illustrative embodiment is always connected to an external
apparatus (for example, digital printer, personal computer etc.), and
communication with the these external apparatuses and feeding of image
data to these external apparatuses are executed via an interface circuit
207.
Various mode instructions are entered by the external apparatus while the
original is placed on the H) original placing table 31 of ADF3 (image
facing upward). Such instructions are ones, for example, as to which one
should be selected among pixel densities 300 dpi, 150 dpi and 75 dpi, or
whether the pixel signal should be a binary signal or a multi-level
signal, etc. When such instruction is received by CPU208, CPU208 (208A is
the ROM housing the control program while 208B is the RAM for work)
delivers a control signal to timing signal generating circuit 209 or
packing circuit 205, and previously sets said pixel density, pixel signal
form, etc.
An original read reference position sensor (not indicated in the drawing)
in "sheet mode" checks as to whether the original illumination unit 24 of
an optical system is at an original reading position (the position
indicated by P2 in FIG. 3) for use in a sheet mode using ADF3.
The system is so constructed that if the original illumination unit 24 is
not at the ADF original read position, it shall be moved prior to start of
a reading operation by an instruction for start of reading of the next
original.
When the original read start instruction is given by an external apparatus
in such a condition, CPU208 outputs a lamp control signal to turn on a
lamp of illumination unit 24, and outputs an instruction for start of
original feeding to ADF3. Thus, the original placed on the original
placing table 31 of ADF3 is carried in a direction of arrow B along the
route indicated by the broken line of FIG. 3.
The reader 1 of this illustrative embodiment employs a stepping motor for
carrying originals from ADF3 and for driving of an optical scanning
system. In such a motor, the speed of the carrying or the scanning can be
freely changed by changing the frequency of the pulse signal (SG301) for
motor driving. In ADF3, in order to detect whether the leading edge of the
original being now carried has reached the original illumination position
of reader 1, an original leading edge detecting sensor (not indicated in
the drawing) provided on ADF3 can be used.
The image formed on the image sensor 22 is converted into digital values by
analog-digital converter 202, to be described later, and stored
temporarily in buffer memory 204. However since the digital values
obtained before the original reaches the original reading position P2 by
ADF3 are not those of the image of the original to be read, a control
signal "DO NOT STORE" is given by CPU208 to the buffer memory control
circuit 212 so that the memory does not store the image data delivered in
the meantime.
When the original reaches the original reading position P2, CPU208 gives
the control signal "READY TO STORE" to the buffer memory control circuit
212, and a line of image data having been read are stored in the buffer
memory 204.
In this illustrative embodiment, buffer memory 204 has a 4 line buffer
construction, so that the image data shall once be stored in buffer memory
204 and then read out.
The image data read out from buffer memory 204 are binary encoded by binary
encoding circuit 206 and entered to packing circuit 205 or directly
supplied to the packing circuit 205 as multi-level (8 bits in the case of
this illustrative embodiment) data and then applied to interface circuit
207 to be transferred to the external control devices one after another.
At the time when the original leading edge detecting sensor detects the
trailing edge of the original, CPU208 outputs the control signal "DO NOT
STORE" to the buffer memory control circuit 212 and after the lapse of a
predetermined time, outputs the original reading end signal to the
external apparatus. If no instruction for original reading is received
from an external apparatus within a predetermined time thereafter, CPU208
turns off the lamp of original illumination unit 24 and disengages the
stepping motor 33 to complete a series of operations.
(2) "Book mode"
In the case of "Book mode", the original is placed on the platen glass of
FIG. 3 in such way that the right end of the original becomes its leading
edge (the image facing downward).
The image illumination unit 24 of the optical system is so constructed that
its initial position is at the right end in FIG. 3 (P1 position) and
similar to the case of said "sheet mode", the reference position (P1
position) is checked by the read reference position sensor for "Book mode"
(not indicated in the drawing). Here, the procedures of setting pixel
density and the image signal prior to start of original reading are the
same as in the case of the aforesaid "Sheet mode".
When an original read start instruction is entered by an external
apparatus, CPU208 first outputs a lamp control signal to turn on the lamp
of the original illumination unit 24 and then it causes the original
illumination unit 24 to scan in the direction of arrow A of FIG. 3.
The distance from the initial position of the original illumination unit 24
to the front end of the original on the platen glass 29 is about 2-3 mm
and during the course of this distance there is provided such a control
that scanning of the optical system by the stepping motor 27 is
stabilized.
In the meantime, CPU208 outputs a control signal "DO NOT STORE" to buffer
memory control circuit 212 as in the case of "Sheet mode" and when
original illumination unit 24 reaches said original leading edge position,
CPU208 outputs the control signal "READY TO STORE" to buffer memory
control circuit 212 and as in the case of "Sheet mode", the image data are
transferred to external apparatus one after another via interface circuit
207.
Since the scanning length of the optical system is determined primarily by
the number of pulses from CPU208 to drive stepping motor 27, when the
necessary number of pulses are supplied to motor drive signal generating
circuit 211, CPU208 judges that reading of the original is over and turns
off the lamp and provides a reversing control of stepping motor 27, and
after the lapse of a predetermined time, outputs the original read end
signal to the external apparatus.
By the reversing control of stepping motor 27 by CPU208, original
illumination unit 24 proceeds in the direction of arrow C of FIG. 3 and
stops when the read reference position sensor for "Book mode" detects that
the unit 24 has reached an initial position. Unless the succeeding
instruction for start of original reading is given by the external
apparatus during such a resetting period of the optical system, the unit
24 sits at the initial position and a series of operations ends.
(3) Circuit performance
Next, the performance of the circuit of the circuit block diagram shown in
FIG. 4 will be explained.
In FIG. 3, image sensor 22 on image sensor unit 23 is driven by a timing
signal generated by timing signal generation circuit 209 (210 of FIG. 4
indicates an oscillator) on the control unit 21, via image sensor driving
circuit 203 (details are given later). The analog image signals (VIDEO A)
given by image sensor 22 are amplified by amplifier 201 and entered into
the analog/digital (A/D) converter 202. The image signal is converted from
an analog signal into 8 bit digital signal (VIDEO D) by the timing signal
ADCLK generated in timing signal generation circuit 209 and given to
control unit 21.
Control unit 21 operates in the following manner upon receipt of said 8 bit
digital signal (VIDEO D: hereinafter called image data).
Image data entered into control unit 21 are supplied to arithmetic
operation circuit 213 which performs, for example, shading compensation
operation, .gamma.-compensation operation etc., where the data are
processed and temporarily stored in buffer memory 204.
In this illustrative embodiment, buffer memory 204 has a 4 line buffer
construction and it is controlled by buffer memory control circuit 212
which functions according to the timing signal generated by timing signal
generating circuit 209. When conversion of pixel density is necessary,
conversion to low density is effected for example by thinning the pulse
entered into buffer memory 204.
Image data stored in buffer memory 204 are read out after a predetermined
time and entered into binary encoding circuit 206 and packing circuit 205.
Binary encoding circuit 206 is a circuit which turns the data into binary
data comparing them with a predetermined threshold level, while packing
circuit 206 is a circuit where binary data of 8 picture elements are
byte-packed in the case of said binary data and 8 bit data of one pixel
are byte-packed in the case of multi-level data.
Image data packed in packing circuit 205 are transmitted to the external
apparatus via the interface circuit 207.
FIG. 5 illustrates an example of the circuit of image sensor 22 used in
this illustrative embodiment, and FIG. 6 shows an example of input signal
fed to terminals 102-105 and transistors T2-Tn of image sensor 22 and the
peak detecting signal from amplifier 112. FIG. 5 shows the circuit
described in U.S. Pat. Application Ser. No. 325,023, filed MAR. 20, 1989,
its details being described in the specification of said application. In
FIG. 5, the arrangement of light shading bit S1 comprising the
photoelectric conversion cell and aperture bits S2-Sn are shown.
Capacitor electrode 401 of each bit is commonly connected to terminal 103
and a constant positive voltage is impressed on collector electrode 402.
Electrode 403 of the reset MOS transistor is grounded and gate electrodes
404 are commonly connected to terminal 105.
Emitter electrodes 405 of the bits S2-Sn are respectively connected to
perpendicular lines L2-Ln. Perpendicular lines L2-Ln are connected to
condensers C2-Cn for accumulation of electric charge via transistors
Ta2-Tan and connected to output signal line 101 via transistors T2-Tn.
Output signal line 101 is grounded via the reset transistor Ts1 and
connected to amplifier 109. Gate electrodes of transistors T2-Tn are
respectively connected to the parallel output terminals of the scanning
circuit and Transistors T2-Tn become ON one after another along the
scanning circuit 113.
Perpendicular lines L2-Ln are grounded via transistors Tbs-Tbn and gate
electrodes of transistors Tb2-Tbn are commonly connected to terminal 104.
Emitter electrode 407 of shading bit S1 is connected to the condenser C1
for accumulation of electric charge and line 107 via perpendicular line L1
and transistor Ta1.
Other emitter electrodes 408 are commonly connected to line 108 as in the
case of the emitter electrodes of aperture bits S2-Sn.
Line 107 is grounded via transistor Ts2 and connected to amplifier 110.
Output terminals of amplifiers 110 and 111 are respectively connected to
the input terminals of differential amplifier 112.
Hereunder is explained the performance of this illustrative embodiment.
Refresh operation
First the signal .phi. res is impressed on terminal 105 and the reset MOS
transistor of each bit is turned on to make the potential of P base region
of the all bits constant. Thereupon signal .phi. vrs is impressed on
terminal 104 and transistors Tb1-Tbn, Ts2 and Ts3 are turned on and
emitter electrodes 405-408 of all bits are grounded. A refresh pulse is
impressed on the terminal 103, thus removing the accumulated carrier in
the P base region as stated above.
Accumulating operation
Reset MOS transistor of each bit is set at OFF and a carrier corresponding
to the luminous intensity of the light incident is accumulated in the P
base region of the aperture bit.
Reading operation
Transistors Tb1-Tbn, Ts2 and Ts3 are turned off and emitter electrodes
405-408 of the bits are held in a floating state.
Subsequently, signal .phi..sub.t is impressed on terminals 106 and
transistors Ta1-Tan are turned on and a read pulse is impressed on
terminal 103. Thereby a dark signal is read out of the shading bit into
perpendicular line L1 and accumulated in condenser C1 and signals from
each aperture bit are entered into the perpendicular lines L2-Ln and
accumulated respectively in condensers C2-Cn.
Then transistors Ta1-Tan are turned off, transistors T2-Tn are turned on
one after another by scanning circuit 113 and signals are read into the
output signal line 101 one after another and output via amplifier 109. At
such time, upon the output of each signal, transistor Ts1 is turned on by
signal .phi. hrs. and a residual electric charge of the output signal line
101 is refreshed.
Peak detecting operation
In parallel to the aforesaid reading action, peak detecting action is
performed. By the read pulse being impressed on terminal 103 at the
reading action, a dark signal from the shading bit S1 is accumulated in
the condenser C1 and read onto line 107 while the signals from shading bit
S1 and open bits S1-Sn are read into the line 108. However, since line 108
is connected to the common line, peak values of signals from shading bit
S1 and aperture bits S2-Sn appear in the line 108. As the result, dark
signal Vd is output from amplifier 110 and peak signal Vp is output from
amplifier 111 and by calculating the difference of these signals
.vertline.Vp-Vd.vertline. by differential amplifier 112, peak detecting
signal Vpk removed of a noise component produced by the dark signal is
obtained.
Quantity of light emitted by the lamp of illumination unit 24 is detected
by the peak detecting signal Vpk and the aforesaid accumulation time and
the speed of moving of the original or the illumination unit by stepping a
motor are regulated line by line in accordance with the results of such
detection.
In FIG. 6, .phi..sub.T2, .phi..sub.T3. . . .phi..sub.Tn are the read
signals given from scanning circuit 113 to transistors T2, T3 . . . Tn of
FIG. 5 while Vpk shown in FIG. 6 is the peak detecting signal of FIG. 5.
Next, the action of the real time detection of the proper level of electric
signal data of the image having been read and the action to read original
image will be explained with reference to FIGS. 4, 5, 6, 7, 8 and 9.
FIG. 7 is an example of the flow chart of this illustrative embodiment. At
step S1 of FIG. 7, the system is waiting for the output of an original
read instruction by the external apparatus.
When said original read instruction is given, the lamp of original
illumination unit 24 is turned on at step S2 and the timer (not indicated
in the drawing) in the CPU208 is started up at step S3 and the system
waits for the engagement of SG302 at step S4. Here SG302 is the signal
given by the proper level detecting circuit 214 of FIG. 4 and as shown in
FIG. 9, it is the signal which becomes ON when the peak detecting signal
Vpk of image sensor 22 agrees with the value Vt preset by CPU208 in the
proper level detecting circuit 14. If the light quantity is sufficient,
peak detecting signal Vpk agrees with the predetermined value Vt set
earlier, while if light quantity is deficient, long time is required
before peak detecting signal Vpk reaches the predetermined level Vt.
When SG302 is engaged, image sensor driving circuit 203 is caused to output
.phi.t and .phi.r signals one after another. At step S5, CPU208 reads the
value of said timer and at step 6, the timer is reset and restarted.
Thereafter at step S7, the driving rate of the stepping motor is
calculated based on the time having passed till peak detecting signal Vpk
reaches the predetermined level Vt.
When the time having elapsed until the predetermined level Vt is reached is
short, the movement of subscanning of one line is made quicker and if such
time is long, the movement of subscanning is made slower. At step S8, the
stepping motor is driven at the said driving rate calculated in step S7.
At step S9, whether or not the original or the original illumination unit
has passed the original reading position is judged and if it has not, the
mode returns to step S4.
If it has already passed said original reading position, the mode proceeds
to step S10 and a judgment is made whether reading of the original is over
or not.
If reading of the original is not over, the image is read out at step S11
and the mode returns to step S4. When reading of the original ends at step
S10, the lamp is turned off at step S12 and at step S13, the stepping
motor is driven for a predetermined length of time until the original is
discharged on original discharge table 32 in the case of "Sheet mode" and
the motor is driven in reverse in the case of "Book mode".
Thereafter, the mode returns to step S1 and waits for the issuance of the
next read instruction.
FIG. 8 is an example of arrangement of white reference member 28 used for
detection of the proper level of electric signal data of the image to be
read. In FIG. 8, white reference member 28 is arranged in the direction of
subscanning. Image sensor 22 performs reading of the original including
the said white reference member 28. Therefore, as illustrated in FIG. 9,
the electric signal obtained by photoelectric conversion of the reflected
light coming from the said white reference member 28 at the reading of
each line is output from image sensor 22 as peak detection signal Vpk, and
SG302 is engaged when the said signal Vpk agrees with the predetermined
level Vt. When image sensor 22 is observing the image data of the nth
line, if the time until the succeeding SG302 is engaged is assumed to be
t1, the stepping motor is driven at the rate calculated from t1 when
reading the (n+1)th line which follows the nth line.
The illustrative embodiment described above uses a stepping motor for the
driving means but the driving means may be a DC motor with an encoder.
In the explanation of performance given above, the system is so constructed
that the time until Vpk reaches predetermined level Vt is measured by the
timer inside the CPU, but if exclusive hardware for such an observation is
provided, overhead in CPU processing is eliminated and the system may be
controlled with higher precision.
Further, it has been explained that the stepping motor is driven while
waiting for the engagement of SG302 before the original reading position
is reached, but it may be so designed that the stepping motor is driven by
the internal timer of CPU208 until the said original reading position is
reached.
It goes without saying that the present invention may be applied also to a
facsimile machine, a handy scanner, etc.
As explained above, even when, for example, a preheating heater is not
provided to the fluorescent lamp, the original can be read without
excessive waiting time and thus the throughput of the reading of original
is increased. Besides, even when the light quantity fluctuates, the
original can be read at proper density.
It is also possible to detect the degeneration of the fluorescent lamp and
report the findings.
FIGS. 10-13 illustrate the second illustrative embodiment of the present
invention.
In this second illustrative embodiment, the appearance and internal
construction of the original image reading apparatus are the same as those
of the apparatus shown in FIGS. 2 and 3 described above, except that the
illumination unit 24 in the second illustrative embodiment is moved by a
DC motor.
FIG. 10 is a drawing to illustrate an example of circuit construction used
in the second illustrative embodiment.
22 is the image sensor with the construction indicated in FIGS. 5, and 23
is the lens. 503 is an image sensor driving circuit which drives image
sensor 22 by the timing signal generated by timing signal generation
circuit 509 which will be described later. 501 is an amplifier (AMP) to
amplify the image analog signal sent from the image sensor. 502 is an A/D
converter (A/D) which converts the amplified image analog signal (VIDEO A)
into 8 bit digital signal (VIDEO D) by the timing signal ADCLK generated
by timing signal generation circuit 509.
515 is a comparator circuit which compares the level of the peak detecting
signal Vpk with the standard level Vt and, upon their agreement, outputs
agreement signal SG30L. 514 is a differential circuit which detects the
slope of the peak detecting signal Vpk given by image sensor 22, i.e., the
rate of increase of light quantity. 513 is an operation circuit which
performs shading compensation, .gamma.-compensation, etc. of digital
signal (VIDEO D). 504 is a buffer memory having a 4-line buffer
construction which temporarily stores the digital signal processed by
operating circuit 513. 512 is a buffer memory control circuit which
controls the buffer memory 504. 506 is a binary circuit which converts the
image data stored in the buffer memory 504 into binary data comparing them
with the predetermined threshold level. 505 is the packing circuit which
byte-packs the binary data of 8 picture elements in the case of binary
data or byte-packs 8 bit data of one picture element in the case of
multivalue data. 507 is an interface circuit for external apparatus such
as a digital printer, a personal computer, etc. Communication with an
external apparatus and output of image data signal to the external
apparatus are executed via interface circuit 507.
516 is a position detecting circuit which detects the read position based
on the encoding data to be described later or ADF position data. 511 is a
motor driving control circuit which starts up the driving of the DC motor
when the level of peak detecting signal Vpk agrees with the standard level
Vt and at the same time controls the speed of motion of original
illumination unit 24 or ADF3 according to the read position data and the
differential (slope) data of peak detecting signal Vpk to be given by the
differential circuit 514 i.e., the slope angles .alpha., .beta. and
.theta. indicated in FIG. 13. The voltages impressed on the DC motor shall
be A.alpha., B.beta., and C.theta. as illustrated in FIG. 13.
508 is a CPU and the speed control means is composed of image sensor 22,
differential circuit 514, and motor driving control circuit 511. 508A is
ROM which houses the control program. 508B is the RAM for work.
509 is a timing signal generation circuit which generates the timing
signals for image sensor driving circuit 503, A/D converter 502, operation
circuit 513, binary encoding circuit 506, packing circuit 505, interface
circuit 507, and motor driving control circuit 511 out of the standard
signal of oscillator (OSC) 510.
FIG. 12 is a drawing to illustrate an example of layout of the original
white indicating member 28 provided near platen glass 29.
Original white indicator member 28 is composed of the reference white part
W which gives a reference of original white and the position indicating
part L comprising the black and white stripe pattern. Image sensor 22 is
so constructed that it reads the area wider than platen glass 29 and in
"Book mode", it reads the position indicating part L of original white
indicating member 28 and outputs the encoding data D. However, in "Sheet
mode", it reads the black and white stripe pattern provided on the
original carrying roller (not indicated in the drawing) by the width S
shown in FIG. 12 and outputs the encoding data D.
Therefore, in "Book mode", the scanning length of the optical system is
known by reading the position indicator section L by image sensor 22.
FIG. 11 is the flow chart of an example of scanning speed control procedure
in "Book mode", stored in the ROM508A.
After turning on the lamp 24l of original illumination unit 24, whether the
level of peak detecting signal Vpk has reached a predetermined white
signal level Vt or not is judged at step S21.
If it has, the rising slope .alpha. of the level of peak detecting signal
Vpk is determined at step S22 and by position detecting circuit 516,
position data are determined.
Then at step S23, voltage A.alpha. is impressed on the DC motor based on
the slope angle .alpha. and position data, and original illumination unit
24 and mirror 25 are caused to shift and the step returns to step S21.
Thereafter, the steps S21-S23 are repeated for each line, and original
illumination unit 24 and mirror 25 are moved based on the slope angle
.theta. and position data and slope angle .theta. and position data.
If it is so devised that the original carrying speed is controlled in
"Sheet mode", the intended objective is attained.
At stated above, when peak detecting signal Vpk reaches the predetermined
level Vt earlier, the quantity of light irradiating the original is
sufficient and therefore the moving speed of the original or illumination
unit may be raised and if, on the contrary, the time until the
predetermined level Vt is reached is long, the quantity of light exposing
the original is deficient and therefore the moving speed for subscanning
is reduced.
Since subscanning is thus executed at the speed corresponding to the
quantity of light irradiating the original, a stable image reading is
always possible and even when light quantity is small, proper reading of
the original image can be executed.
In this illustrative embodiment, an explanation has been given of the
example where position data are obtained by reading the position indicator
section L shown in FIG. 12 in "Book mode" and the black and white stripe
pattern provided on the original carrying roller in "Sheet mode" but it
may be so constructed that position data are obtained through an encoder
slit provided on the shaft of a DC motor.
Carrying of the original and the moving of the optical system may also be
made by a stepping motor and the driving pulse rate of the stepping motor
may be controlled based on the differential data of white reference data.
The present invention may be applied also to a facsimile apparatus.
The present invention has been explained with reference to the preferred
embodiments, but the present invention is by no means restricted to the
constructions of these embodiments, and it goes without saying that
modification and alteration thereof are possible within the scope of the
claims.
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