JP2996485B2 - Light intensity detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for projecting a document image on a photoconductor by optical scanning, and more particularly, to a document reflection light amount detection device for detecting a background density of a document. .

[Conventional technology]

FIG. 3a shows a conventional light amount detection circuit, which includes an amplifier A1,
A2, A3, microcomputer with built-in A / D converter (hereinafter referred to as MCU) 20, multiplying D / A converter (hereinafter referred to as DAC) 5, photodiode D, capacitors C1 and C2, resistor R
1, R2, R3, R4, etc.

The light amount detection circuit converts the light amount data from the MCU 20 into a DAC 5
, And compares it with a preset reference value to set the amplification gain of the light amount detection signal ( _ID ).

However, in the above circuit, the input is V _REF terminal of DAC 5, OUT terminal functions as an output, DAC 5 is a current output. For this reason, it is necessary to convert to a voltage output by the amplifier A2, and in order to use it as an inverting amplifier, in order to provide a positive output to the AN terminal of the MCU 20, two positive and negative power supplies are absolutely necessary. In addition, an extra amplifier is required.

For this reason, there is room for improvement in the above circuit.

Therefore, a light amount detection device having an automatic adjustment function has already been proposed. FIG. 3b is a block diagram showing the configuration of another conventional example.

This circuit is a multiplying D / A converter (hereinafter referred to as DAC)
5 (AD7528 manufactured by Analog Devices, Inc.) as the voltage switching mode, and the light intensity data from
, And sets a coefficient so that a preset reference value is obtained. At this time, the relationship between the input voltage Va of DAC5 and the output voltage (voltage at point c) Vc is as follows: Vc = (D / 256) · Va (1) (D is It is a digital quantity determined according to D0 to D7, and is represented by a value in the range of 0 to 255).

[Problems to be solved by the invention]

However, in the above device, when a high voltage is input to the OUT terminal of DAC5, the linearity of DAC5 deteriorates.

That is, the relationship between the output from the terminal V _{REF of} DAC5 and the input voltage Va is as follows: V _REF = (D / 256) · Va (2), but the input voltage range in which Va is present (1.2 V or more) Beyond the above, the output change with respect to the input is not linear. The output V _REF for D also has poor linearity. Therefore, this circuit can be used only for a certain range of light quantity change.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light amount detecting device that expands an automatic adjustment range for a light amount change with a simple circuit configuration.

[Means for solving the problem]

An illumination unit (2a) for illuminating an original; a photoelectric conversion unit (D1) for receiving light reflected from the original by the illumination unit (2a) and outputting an electric signal at a level corresponding to the amount of received light; OP1); non-inverting amplifier means (OP2) for amplifying the electric signal of the photoelectric conversion means (D1, OP1) with a gain corresponding to the level of the given gain instruction signal; electricity amplified by the non-inverting amplifier means (OP2) A / D conversion means (20) for converting a signal into digital data; a gain indication signal of a level corresponding to the electric signal of the photoelectric conversion means (D1, OP1) and the applied digital data, and amplifying the signal by a non-inverting amplification means ( OP2) is provided with gain instructing means (10); and gain instructing means (10) with gain setting means (20) for providing digital data for gain setting.

The symbols in parentheses indicate the corresponding elements of the embodiment shown in the drawings and described later.

[Action]

The gain instructing means (10) generates a gain instructing signal of a level corresponding to the electric signal of the photoelectric conversion means (D1, OP1) and the digital data provided by the gain setting means (20), and outputs this to the non-inverting amplifying means (OP2 ), The linearity of the gain instructing means (10) is maintained, and the automatic adjustment range for the change in the input light amount is widened.

Other objects and features of the present invention will become apparent from the following description of embodiments with reference to the drawings.

〔Example〕

FIG. 2a schematically shows the mechanism of the optical system of a copying machine incorporating one embodiment of the present invention, and FIG.

Referring to FIG. 2a, a scanner optical system 2 is provided below a contact glass 1 on which an original (not shown) is set, and an image formed by reflected light from the original is scanned by the scanner optical system 2. Is imaged on the drum-shaped photoconductor 3 via the. The scanner optical system 2 includes an illumination light source 2a, a reflector 2b,
A first carriage 51 including a first mirror 2c and the like; a second carriage 52 including a second mirror 2d and a third mirror 2e;
It comprises an imaging lens 2f, a fourth mirror 2g and the like. 2h is dustproof glass. The first carriage 51 and the second carriage 51
Reference numeral 52 denotes a reciprocating scanning drive by the DC motor M7 at a speed ratio of 2: 1 so that the path length of the reflected light from the document does not change during scanning.

This will be described with reference to FIG. 2b. A drive wire 61 connected to the scanner optical system 2 is wound around a pulley 60 fixed to the shaft of the DC motor M7. From one end 61a of the drive wire 61, a stud pulley 62, a drive pulley 63 connected to the second carriage 52, a turn pulley 64, a blanket pulley 66, a blanket 67 connected to the first carriage 51, a drive pulley 63, and a tightener pulley 68. It is connected to the other end 61b through which it has passed to form a closed loop.

HP1 shown in FIG. 2b is a switch (photo sensor) for detecting the home position of the scanner. Similarly, RP1 is a limit switch for detecting one forward scan end position of the scanner, and RP2 is a limit switch for detecting another forward scan end position. Although not shown in this drawing, a photo sensor HP2 for detecting the home position is also provided in the zoom mechanism (ie, lens). This switch is turned on when the lens is at the home position and the enlarged position. The reason why the forward scanning end position is detected by the two limit switches is that one is to perform a zooming operation by performing a zooming operation at the time of a scanner full scan,
In particular, the position of the lens is changed, and the scanner collides with the lens. The RP1 switch is provided at the forward scanning end position, and the RP2 switch is provided at the zoom mechanism.

In such a configuration, the scanner optical system 2 is driven to scan rightward from the HP state as schematically shown in FIG. 2a to expose and scan the original surface.

The scanner optical system 2 that has completed the exposure scanning moves backward toward the home position again. In general, the scanner optical system 2 is driven at a higher speed than the forward movement at the time of backward movement, and deceleration control is performed when approaching the home position HP. Then, when HP1 detects the home position HP, the rotation direction of the motor M7 is switched from reverse rotation (scanner backward movement direction) to normal rotation (scanner forward movement direction) to return from the overrun position to the home position HP. is there.

Next, FIG. 2c shows a longitudinal sectional view centering on the first carriage 51 shown in FIG. 2a, and FIG. 2d shows an external perspective view of the first carriage 51.

In FIG. 2c, 25 is a pressure plate, and 26 is a document. 27 is
An optical fiber whose one end faces the vicinity of the illumination lamp 2a, and 28 is a guide rod for moving the carriage.

As shown in FIG. 2d, three optical fibers 27a, 27b and 27c are provided in the longitudinal direction of the illumination lamp 2a, and the reflected light illuminating the original 26 by the illumination lamp 2a is reflected by the plurality of optical fibers 27a. , 27b, and 27c are guided to a light amount detection circuit described later.

In the optical fibers 27a, 27b, and 27c, the spectral sensitivities of the photodiodes that receive the light amount are different.
The corresponding photodiode has a peak at a wavelength of about 580 nm, and the others have a peak at a wavelength of about 420 nm.

The output from the optical fiber 27a is used as the document density. When the document is exposed and scanned, this output is checked, and the peak value of the output is considered as the background density of the document. Determine the bias voltage and the like.

Outputs from the optical fibers 27b and 27c are used for document size detection.

In FIG. 2c, the platen 25 is colored yellow and has a very low reflectance for light having a wavelength of 420 nm, but has a low reflectance for light having a wavelength of 580 nm, which is highly sensitive to the photosensitive drum 14. high. Prior to the exposure scan of the original 26, a pre-scan for size detection is executed, and when the scanner returns, the pressure plate 25 and the original 2 are set based on the output change by the optical fibers 27b and 27c.
Judge the size of 6.

The optical fiber 27b is for detecting the document length, and the optical fiber 27c is for detecting the document width.

FIG. 1 shows an electric control unit for controlling these constituent elements.

The electric control unit includes a microcomputer (hereinafter, referred to as MCU) 20 for controlling the entire copying machine, a ROM 21 connected to an address bus, a control bus, a data bus, and the like of the MCU 20 and storing fixed data and a control program. It comprises a RAM 22 for reading and writing various flags and the like, a document density detecting circuit 30, document size detecting circuits 40 and 50, and the like. In addition,
The document size detection circuit 50 is the same as 40.

 The document density detection circuit 30 will be described.

This circuit is a multiplying D / A converter (hereinafter referred to as DAC)
10 (AD7524 manufactured by Analog Devices, Inc.), photodiode D1, negative-phase amplifier OP1, positive-phase amplifier OP2, etc.

When light guided by the optical fiber 27a hits the photodiode D1, a photocurrent ID flows. This photocurrent ID is
From the gain resistor R5, Va = ID · R5 (3) This voltage Va is input to the _VREF terminal of the DAC 10. The approximate expression of the voltage Vc output from the DAC 10 is as follows: Vc = ID · R5 × (256 / D) (4) (D is a digital amount determined according to D0 to D7 from the MCU 20 and 0 (Value in the range of ~ 255).

The OUT terminal of the DAC 10 is connected to the inverting input terminal of the positive-phase amplifier OP2. Therefore, the output voltage Vc of the DAC 10 is non-inverted amplified by the positive-phase amplifier OP2 and the resistors R6 and R7, and is input to the A / D converter input terminal AN1 of the MCU 20 via the resistor R8. The voltage Vb input to the AN1 is expressed as follows: Vb = Vc × (1 + R7 / R6) + ID · R7 (5) From equations (4) and (5), the photocurrent ID and
The relationship of the voltage Vb input to the AN1 terminal is an approximate expression of Vb = ID · R5 × (256 / D) × (1 + R7 / R6) + ID · R7 (6). It can be seen that the gain changes. Therefore, the feedback gain can be changed by the digital data D.
UT terminal voltage can also be controlled. For example, in equation (4),
When the light amount is large and the ID is large, Vc (OUT terminal voltage of the DAC 10) can be controlled to be small by increasing the digital data D. Conversely, when the light amount is small and the ID is small, Dc
If Vc is reduced, Vc can be controlled to be large.

That is, since the OUT terminal voltage Vc can be suppressed within a certain input voltage range, the linearity of the DAC 10 with respect to the input light amount is maintained.

D0 to D7 of the DAC 10 are connected to data buses D0 to D7 of the MCU 20, and a control line (not shown) is connected to the MCU 20. As a result, the MCU 20 supplies the digital data D to the DAC 10 in the same manner as writing data to the memory.

At the time of voltage adjustment, the optical system shown in FIG. 2a is started by software, the reflected light of the reference document is detected by the optical fiber 27a shown in FIG. 2d, and the A / D input voltage of the MCU 20 is adjusted to the preset reference document. The digital data D is changed and written into the DAC 10 so as to match the corresponding storage information.

For example, if the A / D input voltage is larger than the stored information corresponding to the reference document, the digital data D is incremented by one to reduce the feedback gain, and this is repeated until the two match, and the A / D input voltage Is smaller than the stored information corresponding to the reference document, the digital data D is decremented by one to increase the feedback gain, and the process is repeated until the two match.

Alternatively, a reference reflecting member may be provided to detect a change in lamp voltage and automatically correct the change.

The document size detection circuits 40 and 50 have the same configuration as the above-described circuit, and the document size detection circuit 40 sets the document length of the reference document to the document size detection circuit 50 by the optical fiber 27b.
Detects the document width of the reference document by the optical fiber 27c, compares the width with the preset information, and sets the digital data D of the DAC 10 in a direction in which both match. In the document size detection circuits 40 and 50, the circuit including the resistor R9 and the capacitor C6 is a smoothing circuit for removing noise.

The peak hold circuit composed of the diode D2 and the capacitor C3 of the document density detection circuit 30 discharges the voltage of the capacitor C3 by the output from the PORT terminal by the MCU 20 before starting the exposure scanning of the document, and During scanning, the peak value of the output is charged in the capacitor C3 through the diode D2. The MCU 20 detects the peak value of this output as the background density of the document.

In the prior art, this peak value detection is detected by software, but the output is changed by the 50 Hz ripple of the lamp and the black and white state of the document, and the software is complicated. In the embodiment shown in FIG. 1, since the peak value is detected by the diode D2 and the capacitor C2, the timing for reading the peak value and the timing for resetting the peak value (turning the transistor Tr on) are determined and read in software. AN1 at the timing
It is simple because it is only necessary to convert the analog signal into a digital signal.

Further, the voltage V _D of the capacitor C3 has a non-inverting because it is connected to the input terminal DAC10 of OUT terminal voltage of the positive-phase amplifier OP2
Same as Vc.

〔The invention's effect〕

As described above, according to the present invention, the gain indicating means (10)
Generates a gain instruction signal of a level corresponding to the electric signal of the photoelectric conversion means (D1, OP1) and the digital data given by the gain setting means (20) and gives this to the non-inverting amplifier (OP2). The linearity of the means (10) is maintained, and the automatic adjustment range for the change in the input light amount is widened.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electric control unit of a copying machine which implements the present invention as an example. FIG. 2a is a side view showing the outline of the mechanism of the optical system of the copying machine, and FIG. 2b is an external perspective view thereof. 2c is a longitudinal sectional view centering on the first carriage 51 shown in FIG. 2a, and FIG. 2d is an external perspective view of the first carriage 51. FIGS. 3a and 3b are block diagrams showing an electric control unit of a conventional copying apparatus. 1: contact glass, 2: scanner optical system 2a: illumination light source (illumination means), 2b: reflector 2c: first mirror, 2d: second mirror 2e: third mirror, 2f: imaging lens 2g: fourth mirror , 2h: dustproof glass 10: DAC (gain indicating means) 20: MCU (A / D conversion means, gain setting means) 21: ROM, 22: RAM 27: optical fiber 30: document density detection circuit, 40, 50: document Size detection circuit 51: first carriage, 52: second carriage D1: photodiode, OP1: amplifier (D1, OP1: photoelectric conversion means) OP2: amplifier (non-inverting amplification means)

Claims (1)

(57) [Claims] An illumination means for illuminating the original; a photoelectric conversion means for receiving reflected light of the original by the illumination means and outputting an electric signal of a level corresponding to the amount of received light; and receiving an electric signal of the photoelectric conversion means. Non-inverting amplifying means for amplifying with a gain corresponding to the level of the gain instruction signal; A / D converting means for converting the electric signal amplified by the non-inverting amplifying means into digital data; A light amount detection device comprising: a gain instruction unit that generates a gain instruction signal having a level corresponding to data and supplies the same to the non-inverting amplification unit; and a gain setting unit that supplies the gain instruction unit with digital data for gain setting. .