JPH10215348A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized middle speed machine having read speed equal to a high speed machine, by correcting a maximum valid scanning length to a short prescribed scanning length when a scanning speed exceeds a predetermined speed. SOLUTION: In a temporary scanning length register, a value for which a form length is divided by a scanning magnification is set. In the case that an obtained temporary scanning length is longer than 432mm for instance, the temporary scanning length is uniformly changed to 432mm. On the other hand, in the case of being shorter than 432mm, the obtained temporary scanning length is held as it is. Then, in the case that the scanning magnification set to this device is less than 0.6 times for instance and the temporary scanning length exceeds 420mm, the temporary scanning length is uniformly reset to 420mm. In the other case, the set temperature scanning length is held as it is. Then, the temporary scanning length set to the temporary scanning length register in respective steps by then is transferred to a scanning length register. The scanning length set in such a manner is referred to when a scanning optical system 3 performs scanning next and the scanning optical system 3 is controlled so as to perform scanning for a length matched with the scanning length from an original start end and to be braked thereafter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus, and more particularly to an improvement of a document scanning means.

[0002]

2. Description of the Related Art In an image forming apparatus, it is required to realize contradictory demands for high-definition recording and high copy speed. In order to make the above two requirements compatible with each other, a scanner as a document scanning means scans at a low speed at the time of enlargement copying to perform high-definition image reading, but scans at a high speed at the time of reduction copying.

[0003]

The scanning speed of the scanner is proportional to the braking distance of the scanner, and the magnitude of the braking distance affects the size of the apparatus. Therefore, in an image forming apparatus called a high-speed machine, the size of the apparatus is determined depending on what scanning speed is set at the time of reduction copying, particularly at the time of minimum reduction copying.

[0004] However, since the minimum reduction copy is a copy mode that is rarely used, there is a problem that it is unreasonable to determine the size of the apparatus based on the copy mode. On the other hand, it is possible to shorten the braking distance to a medium-speed machine or a low-speed machine by strengthening the scanner drive mode and the brake mechanism, but this will inevitably increase the cost.

In view of the above points, the present invention provides an image forming apparatus capable of performing the same high-speed scanning as a high-speed machine at the time of the minimum reduction copy without strengthening the motor and the brake mechanism or increasing the size of the apparatus. It is intended to be.

[0006]

In order to achieve the above object, the present invention provides a document scanning means, a means for calculating a scanning length, a means for calculating a scanning speed from a copy magnification, and a method for determining the position of the document scanning means. Means for detecting, and means for correcting the calculation result so that the scanning length of the document scanning means is a predetermined amount shorter than the maximum effective scanning length when the scanning speed exceeds a predetermined speed. Means for driving the document scanning means with the calculated scan length, and with the corrected scan length if there is a correction.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention shown in the drawings will be described. FIG. 1 schematically shows an image forming section of a copying machine. A scanning optical system 3 is provided between the platen glass 1 and the photosensitive drum 2 thereunder. The scanning optical system 3 includes an illumination lamp 5 held on a first movable table 4 forming a scanner and a first
It comprises a mirror 6, second and third mirrors 9 and 10 held on a second movable table 8, a projection lens 11 and a fourth mirror 12. A pair of drive wires 21 are stretched on both sides of a portion where the first moving table 4 and the second moving table 8 move. Each drive wire 21 is laid between the left and right pulleys 22, 23 from above, and a portion 21 a on the pulley 22 side is wrapped around the lower side of the pulley 22, and is attached to the end plate outer surface of the second movable base 8. After being hung below the provided pulley 22, it is hung around a pulley 24 provided on the outer surface of the end plate of the second movable base 8 and folded back, and its end 21 c is fixed to the fixing member 25. I have. The portion 21d on the pulley 23 side is wound around the lower side of the pulley 23, and
And the end 21e is fixed to the fixing portion 26.
Is fixed thereto via a tension spring 27.

A portion of the wire 21 on the pulley 22 side between the pulley 22 and the pulley 24 is fixed to the first movable table 4 at a part thereof. Reference numeral 28 denotes the fastening portion. A DC motor 30 is connected to a rotation shaft 29 of the pulley 23 via a transmission gear 31 and a timing belt 32. Further, an encoder 33 is attached to the rotating shaft 30a of the motor 30.
Are connected to generate a pulse in synchronization with the rotation of the motor 30.

When the motor 30 is operated in the direction of arrow a, the wire 21 is driven in the direction of arrow b. At this time, the first movable table 4 directly fixed to the wire 21 is moved in the direction of arrow c at the same speed as the wire 21 at 1 / n (n: copy magnification). Is scanned in the range according to the copy size and the magnification, and the first to fourth mirrors 6,
The images of the original are sequentially slit-exposed on the photosensitive drum 2 by the projection lenses 9, 10, 12 and the projection lens 11. At this time
When the wire 21 is driven in the direction of the arrow b, the movable table 8 moves through the pulley 24 through the pulley 24 by a movement in which the portion 21d on the pulley 23 side becomes longer as the portion 21a on the pulley 22 becomes shorter. Is moved at a speed of 1 / 2n in the direction, and the light exposure length of the scanning optical system 3 is kept constant during scanning.

The photosensitive drum 2 is provided with an eraser lamp, a charging charger, a developing device, a transfer charger, and a cleaning device (not shown) around the photosensitive drum 2. The surface of the photosensitive drum 2, which is uniformly charged by the charging, receives the exposure. An electrostatic latent image is formed. The electrostatic latent image is developed by a developing device to be visualized as a toner image, and is transferred by a transfer charger onto a transfer material sent in synchronization with the toner image.

After the surface of the photosensitive drum 2 after the transfer is cleaned of residual toner by a cleaning device, residual charge is removed by an eraser lamp. The copy magnification is changed by, for example, moving the projection lens 11 or the like in the optical axis direction to adjust the conjugate length. At the end of the scan, the motor 30 is reversed. As a result, the wire 21 has an arrow b
And the first and second movable tables 4 and 8 are moved in the direction opposite to the arrow c and returned to the home position.

To control the operation of the scanning optical system 3,
The motor 30 is driven by the drive circuit shown in FIG. 2 and is controlled by the control circuit shown in FIG. Further, for this control, a switch 34 for detecting whether or not the scanning optical system 3 is at the home position is provided on the moving path of the first moving table 4, and is pushed when the first moving table 4 is at the home position. .

As shown in the drive circuit of FIG. 2, a direct current E is connected to the motor 30 via four bridge-connected switching transistors Tr1 to Tr4.
The transistors Tr1 and Tr3 are turned on when the base voltage is "L", and the transistors Tr2 and Tr4 are turned on when the base voltage is "H". The motor 30 is properly adjusted by a combination of the ON and OFF states. Invert, reverse, or stop.

Diodes D1 to D4 are connected in parallel to the transistors Tr1 to Tr4, respectively, to form a bypass when a back electromotive voltage is generated. The input terminal 35a receives an "H" signal as a forward rotation signal or an "L" signal as a reverse rotation signal. The input terminal 35a is connected to the input side of the AND gate AND1 and the base of the transistor Tr1. Connected to the input side of AND gate AND2 and the base of transistor TR3.

Another input terminal 35b is an "H" signal as an energizing ON signal by a motor energizing pulse d,
An "L" signal is inputted as an energization OFF signal, and is connected to the input sides of AND gates AND1 and AND2. The output of the AND gate AND1 is at the base of the transistor Tr2, and the output of the AND gate AND2 is the transistor T2.
Each is connected to the base of r4.

ON / OFF of each of the transistors Tr1 to Tr4 by a combination of input signals to each of the input terminals 35a and 35b.
Table 1 below shows the F state and the ON / OFF state of the motor 30 and the forward / reverse rotation at the ON state.

[0017]

[Table 1] FIG. 3 shows a control circuit of the scanner. This circuit is a one-chip microcomputer (hereinafter referred to as a microcomputer)
Reference numeral 41 is dedicated to the control of the scanning optical system 3, and is controlled by a microcomputer (hereinafter, referred to as a master) (not shown) for controlling various other operations of the copying machine.

The microcomputer 41 has a CPU 42, a ROM 43,
RAM 44, input port 45, output port 46, PWM output port 47, register 48, timer unit 49, oscillator circuit 50 for generating internal system clock fclk.
Of each. In addition to a counter XF that counts the encoder pulse e as it is as the position information of the first mobile unit 4, the timer unit 49 generates an interrupt by dividing the input of the encoder pulse e during return of the first mobile unit 4 by four. There is a frequency dividing circuit FDC for counting the count of the counter XF by four each time the interrupt occurs. Even if the power is supplied at a low power during the return and the motor rotates at a high speed, the edge of the encoder pulse e is detected four times. The counter XF does not need to count, and the processing time of the software will be in time. The encoder pulse e is obtained by shaping the output FG from the encoder 33 into a rectangular wave by the waveform shaping circuit 150.
1 is input.

A scanning mode signal MOD from the master, a scanning start request signal SCAN, and a signal HOME indicating whether the scanning optical system 3 is at the home position are input to the input port 45.
Is given. The signal MOD is a general term for the signals of the scanning magnification, the length of the copy sheet, and the length of the original. Based on this signal MOD, the microcomputer 41 calculates the scanning speed by calculation.

The signal SCAN is normally "L" and is set to "H" when a scan start request is made. The signal HOME is set to "H" only when the scanning optical system 3 is at the home position, and is set to "L" otherwise. A forward / reverse rotation signal f of the motor 30 is output from the output port 46.
Is input to the input terminal 35a of the drive circuit 51 of FIG. PWM
From the output port 47, a PWM pulse for low-speed scanning control at a frequency obtained by _{dividing the} system lock f _CLK oscillated by the oscillation circuit 50 by 256, or when the scanning system 3 rises up to low-speed scanning or starts return after low-speed control. Deceleration control,
For deceleration return control following full power return,
The duty of the pulse is set to 100%, and a PWM motor energizing pulse d such as a pulse in which the OFF time is controlled by an interrupt performed by a timer setting based on each ON / OFF edge of the encoder pulse e is output. The signal is input to the input terminal 35b of the circuit 51. The motor 30 is controlled by these inputs.

[0021] As this control is shown in FIG. 4, the acceleration operation A to the scanning optical system 3 reaches from zero velocity to the target velocity V _i
To control the state of the constant scanning B in which a predetermined range is scanned at a constant speed when the target speed V _i is reached, and to move the scanning optical system 3 backward when the constant speed scanning is completed. The control of the state of the deceleration scan C in which the motor 30 is once decelerated to the speed 0, the control of the state of the full power return D in which the motor 30 is reversely rotated at full power to move the scanning optical system 3 backward, and the state of the full power return D In order to stop the scanning optical system 3 in the state at the home position, a brake is operated to control the state of the deceleration return E in which the motor 30 is decelerated to the speed 0 and stopped.

The control in the acceleration scan A is performed by the input terminal 35a.
Is input to the input terminal 35b, and each O of the encoder pulse generated according to the rotation of the motor 30 is input to the input terminal 35b.
Set a constant OFF time t _OFF from the N edge as a timer,
ON time t _ON until the ON edge of the next encoder pulse
Is input. Accelerated scanning (A)
In the initial stage, the rotation of the motor 30 is slow and the interval between the encoder pulses e is long, so that the ON time t _ON of the motor 30 is sufficiently longer than the OFF time t _OFF , and the motor 30 is strongly accelerated by the strong energizing torque. As the speed approaches the target speed V for the constant speed scanning B, the ON time t _{ON and} the OFF time t _{OFF as the} encoder pulse e interval decreases.
And the acceleration for driving the motor 30 gradually decreases.

In the case where the scanning optical system 3 is accelerated from a position at the home position, the home sensor 34 even if the scanning optical system 3 is slightly away from the home position.
Is still in the ON state. Home sensor 34 is O
The transition to FF occurs when the scanning optical system 3 reaches the position indicated by K in FIG. The position X of the scanning optical system 3 at which the home sensor 34 turns OFF is set as a reference position, and the counter XF counts the pulses generated by the encoder 30 thereafter. Although the scanning optical system 3 has no sensor for detecting the start and end of the original, the scanning optical system 3 has a predetermined length (e.g., 420 mm) from the count of the counter XF when the original has passed the original start, at the instant when the original has passed the end, and from the original start. However, it is possible to detect the moment of passing.

The scanning optical system 3 can be sufficiently accelerated in the acceleration zone A, reaches the Figure 4F point as a target speed V _i, determined by the microcomputer 41 to have reached from the interval of the encoder pulses e at that time to the target V _i Is done. Based on this, the motor 3
The control of 0 is switched to the control of low-speed scanning B. Incidentally, the target speed V _i is determined by whether the scanning magnification is set to much. In this embodiment, the reciprocal of the scanning magnification in the target speed V _i. Because the target speed V _i is changed by such scanning magnification, when the acceleration curve of the scanning optical system 3 are identical, the position of the scanning optical system 3 shifts to constant-speed running varies depending on the value of the target speed V _i . FIG. 5 shows this state. P ₁ P ₂ ... _Pn is the target speed V ₁ V _2.
-The position where V _n is reached. The reading start position of the document as understood from FIG. 5, even in the case of transition to constant speed running is reached at the earliest target speed V _n, as in the downstream side of the constant-speed running transition position P _n Is set.

[0025] While a constant speed control of the motor 30 to the PWM pulse control in the constant speed running B as a motor driving pulse d, the acceleration alpha _ON when energized upon reaching the target speed V _i, the acceleration at the time of non-energization α _OFF is calculated, and thereafter the duty of the PWM motor energizing pulse d is rewritten for each encoder pulse using these two as parameters. During constant speed running, the CPU monitors the count value of the counter XF, and when the count value corresponding to the document start end is reached, reading of the document is started, and the count value corresponding to the document end or the position corresponding to a position close to the end of the predetermined length from the document start end. When the count value reaches the required count value, the reading is completed, and deceleration traveling (C) is performed.

When the speed of the constant speed running (B) is low, the reading end coincides with the document end position unless the document length exceeds the allowable maximum scanning length. When the height is higher (V _n−2 or more in FIG. 5), the document is set at a position of a predetermined length from the document start even if the document length is less than the maximum scanning length. This achieves the initial object of realizing a small-size device while enabling high-speed reading. Specific examples of how to set the maximum scan length and the predetermined length and the reference speed will be described later.

In the deceleration scanning (C), the scanning optical system 3
The input terminal 35a is switched to "L" to apply a braking force to the motor, and the OFF time is controlled by the motor energizing pulse d as in the case of the acceleration scanning (A). Input terminal 35
FIG. 2 shows a state in which a is "L" and the input terminal 35b is "L".
In only the transistor Tr ₁ is ON. At this time, since the scanning optical system 3 is moving in the scanning direction, the shaft 30a of the motor 30 is rotated by this movement, and the motor 3
0, a back electromotive voltage in the direction opposite to the arrow a is generated in the closed loop of the diode D ₃ and the transistor Tr ₁ , and the braking is applied to the rotation of the motor 30 rotating in the scanning direction a. This is what is called regenerative braking.

On the other hand, in the state of the input terminal 35b is "H" at the input terminal 35a is "L" transistor Tr ₁ and Tr ₄
Is turned on, the current of the DC power supply E flows in the direction opposite to the arrow a, and applies a brake in order to rotate the motor 30 in the return direction. The case where the braking is performed by rotating the motor 30 in the direction opposite to the moving direction of the scanning optical system 3 is the so-called forced braking.

In the initial stage of the deceleration scanning (C) in FIG. 4, the interval between the pulses e of the encoder is shorter than the set OFF time, so that only the regenerative brake operates. The braking force by this regenerative brake is relatively weak, and the scanning optical system 3 is gradually decelerated. When the deceleration progresses and the interval between the encoder pulses e becomes longer than the OFF time, the forced brake works together with the regenerative brake, and the deceleration with strong braking is performed.

Next, when the interval between the encoder pulses e becomes longer than a predetermined time, the process enters the return process of FIG. This is because the input terminal 35b is kept ON to shorten the return time, that is, the motor energizing pulse d is turned ON.
By keeping it as it is, it is fixed to “H” and always energized. A so-called full power return (D) is performed. Here, it is desired that the scanning optical system 3 is accurately stopped at the home position after the full power return. To satisfy this, the mode is switched from the full power return (D) to the deceleration return (E) at a position slightly before the home position.

The start timing of the deceleration return (E) is as follows: the encoder pulse e is output from the counter X
During the return from the time of FIG. 4 (I) when the scanning is completed and the count value Xof up to that time is subtracted, the position of the first movable table 4 during the return is obtained, and the home switch 34. Is determined when the count value X1f corresponding to the distance from the brake start position to the predetermined brake start position (FIG. 4J) is reached.

As described above, when the ON and OFF edges of the encoder pulse e are detected four times as described above, the subtraction is performed by four each time the above-described external interrupt is generated, thereby corresponding to the software processing. When the count value reaches X1f, the same OFF time control as in the case of the deceleration scanning (C) is performed, and the apparatus is stopped at the home position.

FIGS. 6 to 8 are diagrams for explaining the determination of the specific values of the maximum scanning length, the length from the start of the original document to the end of reading, and the reference speed when determining whether the scanning speed is higher or lower than the reference speed. is there. FIG. 6 shows the correlation between the scanning speed and the time required for braking from the end of scanning to the stop. still,
In this specification, the “scanning speed” refers to the speed in the constant speed scanning (B) section. Similarly, "after the end of scanning" means after the end of the constant-speed scanning (B).

In FIG. 6, the horizontal axis represents time, and the vertical axis represents scanning speed. Here, the numbers given along the vertical axis are scanning magnifications. The scanning magnification is shown in two columns for a high-speed machine and a medium-speed machine. Also, the characteristic curve indicated by a broken line in the figure is for a high-speed machine, and the solid line is for a medium-speed machine. For example, in a high-speed machine, when the magnification is 1.0, the braking time takes 3T, and when the magnification is 0.5, the braking time takes 6T. In addition, it is understood that the braking time is 2T when the magnification is 1.0 and 4T when the magnification is 0.5 in the medium speed machine. Therefore, it can be said from FIG. 6 that the scanning speed V and the braking time t have a relationship of V = αt (1).

FIG. 7 shows the relationship between the scanning speed and the braking distance after the end of scanning. The horizontal axis is the braking distance. The vertical axis is FIG.
Similarly to the above, the scanning magnification of the high-speed machine and the medium-speed machine is graduated. 11 on the horizontal axis indicates a physical limit (such as a housing wall surface) at which the scanning optical system 3 can move, and in this embodiment, is 475 mm from the scanning start reference position. The scanning start reference position is shown in FIG.
Note that it is not the origin of the The origin in FIG. 7 is the braking start position (= scan end position). Thus l
Braking must be completed in the area to the left of 1.
In the case of the medium-speed machine, as shown in FIG. 7, even at the re-scaling magnification of 0.5, the braking is completed in the area on the left side of l1, so there is no problem. .5 times, the braking distance becomes l as shown by the chain line in FIG.
2 (485 mm from the scan start reference position), and reaches the area on the right side of l1. According to actual measurement, in the case of a high-speed machine, the magnification is 0.6 and the braking distance is 11. Therefore, in order to increase the scanning speed while keeping the size of the apparatus at the medium speed, it is necessary to shorten the scanning length when the scanning magnification is less than 0.6 times. Then, since l2 to l1 is 10 mm, it can be seen that the length should be shortened by 12 mm in view of a margin.

FIG. 8 is a diagram showing the relationship between the scanning speed and the maximum scanning length. The horizontal axis is the scanning length, which is graduated by the distance from the starting end of the document. When the magnification is less than 0.6 times, the maximum scanning length is 420 mm, and when it is 0.6 times or more, it is 432 mm as before. The value of 420 mm is shown in FIG.
It is shorter than 432 mm by 12 mm obtained in the above.

FIG. 9 is a schematic flowchart showing the main routine of the original reading control by the microcomputer 41. When the microcomputer is reset and the program starts,
Initialization of the microcomputer such as clearing of the RAM, setting of various registers, and initial setting for setting the apparatus to the initial mode are performed (S1).

Next, an internal timer built in the microcomputer and whose value is set in advance by default is started (S2). Subsequently, the subroutines (S3 to S6) shown in the flow chart are sequentially called, and when all the subroutine processes are completed, one routine is terminated after the end of the internal timer set first (S7).

Using the length of time of this one routine, the end of each timer value appearing in the subroutine is determined by how many times this main routine is counted. In the figure, the scanning panel input routine, other processing routines, and communication with other CPUs are well known, and thus description thereof will be omitted.

FIG. 10 shows a subroutine of S4. First, a value obtained by dividing the paper length by the scanning magnification is set in the temporary scanning length register (S41). The paper length is the length of the recording paper. The recording paper is standardized as A4, A3, B4, and when the operator selects a paper of any size, the corresponding paper length is read from the area storing the paper size in the RAM. Then, the temporary scanning length is obtained by dividing by the scanning magnification input by the operator.

The provisional scanning length obtained in S41 is 4 in S42.
It is determined whether it is longer than 32 mm, and if it is longer, the provisional scanning length is uniformly changed to 432 mm (S43).
If it is shorter than mm, the provisional scanning length obtained in S41 is kept as it is. Then, in S44, it is determined whether the scanning magnification set in the apparatus is 0.6 times or more. If the scanning magnification is less than 0.6 times and the temporary scanning length exceeds 420 mm (S45), the temporary scanning length is reset to 420 mm uniformly (S46).

In other cases, the temporary scanning length set in S41 or S42 is left as it is. Then, in S47, the temporary scanning length set in the temporary scanning length register in each step up to that point is transferred to the scanning length register. Thus, the scanning length set in the scanning length register is referred to when the scanning optical system 3 performs the next scanning, and the scanning optical system 3 is controlled to scan from the starting end of the original by a length corresponding to the scanning length, and thereafter to control the braking. I do.

According to the above processing, when the scanning magnification is 0.6 times or more, the scanning optical system scans the scanning length obtained from the paper length and the magnification in the range of the maximum scanning length of 432 mm to read the original. On the other hand, when the scanning magnification is 0.6
If it is less than twice, the maximum scanning length is reduced to 420 mm and the original is read within the range of the scanning length. In this case, if the scanning magnification is less than 0.6 times, the actual reading will be 420 mm from the original end even if the scanning length calculated by the paper length and the scanning magnification exceeds 420 mm. Most of the target documents are text documents, and in the case of a text document, there is much blank space without characters at the end of the document (the lower end or the left end of the document).

Further, when the scanning speed is set to a scanning magnification of 0.6
Even in the case of less than 2 times, the speed can be increased in accordance with the scanning magnification, enabling high-speed copying, and also preventing the scanning optical system from colliding with the inner wall of the apparatus housing when reading a document, thereby reducing the size of the apparatus. There is a benefit to contribute.
In the embodiment, the maximum scanning length is 432 m.
Although values such as m and 420 mm are used, and a value of 0.6 times is adopted as a scanning magnification for switching the maximum scanning length, this is merely an example, and it is to be understood that the present invention is not limited to these values. Not even.

Further, in the above-described embodiment, an example has been described in which the rear end of the original is image-deleted and the speed of the scanning system is switched from constant speed to deceleration before the rear end of the original. The image may be missing at the reading start position). Specifically, before the scanning system moves to the reading start position, acceleration is terminated at a magnification larger than 0.6, and at a magnification smaller than 0.6, the scanning system is moved to the reading start position and then accelerated. May be terminated and the speed may be shifted to the constant speed. In this manner, as described above, the leading end portion of the document having a small image and a large margin (near the reading start position) has an image defect, which can further contribute to downsizing of the apparatus.

[0046]

As described above, according to the present invention, in an image forming apparatus for changing the original scanning speed in accordance with the copy magnification, when the scanning speed exceeds a predetermined speed, the maximum effective scanning length is reduced. Since the scanning length is corrected to a predetermined amount, the document can be read at a higher speed in a smaller space than the conventional apparatus, and there is an effect that a small-sized medium-speed machine having a reading speed comparable to a high-speed machine can be provided.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating a document scanning unit of an image forming apparatus according to the present invention.

FIG. 2 is a diagram illustrating a driving circuit of a motor that drives a document scanning unit.

FIG. 3 is a control circuit for controlling the document scanning unit.

FIG. 4 is a velocity diagram of a document scanning section and a corresponding change diagram of encoder pulse counts.

FIG. 5 is a diagram illustrating a relationship between a scanning speed of a document scanning unit and a brake required time.

FIG. 6 is a diagram illustrating a relationship between a scanning magnification of a document scanning unit and a brake required time.

FIG. 7 is a diagram illustrating a relationship between a scanning magnification of a document reading unit and a required braking distance.

FIG. 8 is a diagram illustrating a relationship between a scanning magnification of a document scanning unit and a maximum effective scanning length.

FIG. 9 is a flowchart illustrating a main routine of control software of the image forming apparatus.

FIG. 10 is a flowchart illustrating a scanning length setting routine.

Claims (1)

[Claims] A scanning means for calculating a scanning speed from a copy magnification; a means for detecting a position of the scanning means; and a scanning speed of the scanning means. Means for correcting the calculation result so that the scanning length becomes a predetermined amount shorter than the maximum effective scanning length when the scanning speed is exceeded, and the calculated scanning length if the scanning length is not corrected, and the corrected scanning length if corrected. Means for driving a document scanning means with a scanning length.