JPH04104242A - Gain adjustment circuit for automatic exposure - Google Patents

Abstract

PURPOSE:To automatically execute gain control by providing a means for setting the gain of an amplifier for amplifying a signal from a sensor, which expresses the intensity of reflected light from an original, in accordance with the level of the signal. CONSTITUTION:The output of the operational amplifier 23 is connected to the input port of a CPU 21 which control an entire copying machine through a resistance, and the noninverted input of the amplifier 23 is connected to the output of an AE sensor through a resistance R6. After setting a simulation mode, the blank original, for example, is set and a copying lamp is turned on, then the signal expressing the intensity of the reflected light from the original is transmitted from the sensor to the amplifier 23, where it is amplified. The level of the signal outputted from the amplifier 23 is read and the amplification factor thereof is switched to a value corresponding to the level. In the succeeding ordinary copying modes, automatic exposure is controlled by using the signal from the sensor, which is amplified at a newly set amplification factor. Thus, the dispersion of the output of the AE sensor is automatically corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an image forming apparatus such as a copying machine or a laser printer having an AE (automatic exposure) function.

[Prior Art] An image forming apparatus having an AE function, such as a copying machine or a laser printer, is equipped with an AE sensor for detecting the intensity of reflected light from an original (original density). The exposure amount is controlled to be appropriate using signals from
Since there are variations in lens transmittance, etc., there are also variations in the output of the AE sensor.

As a countermeasure to this, the output of the AE sensor as shown in Figure 6
By adjusting the gain (amplification factor) of the amplifier 12 for amplifying the ES with the volume 13, the C from the amplifier is adjusted.
The exposure level control signal AESO output to the PU (central processing unit) 11 is adjusted to compensate for the above-mentioned variations.

[Problems to be Solved by the Invention] However, in the conventional device described above, in order to adjust the gain, it is necessary to remove the cabinet of the device and adjust the volume while checking the level from the sensor. The problem is that it takes time.

In particular, if the operating section of the device and the control board to which the volume is attached are far apart, gain adjustment may not be possible by one person.

The present invention has been made in view of the above-mentioned problems with conventional devices, and it is an object of the present invention to provide a means for automatically correcting variations in the output of an AE sensor in an image forming device having an AE function, such as a copying machine or a laser printer. With the goal.

[Means for Solving the Problems] The object of the present invention is to provide an automatic exposure gain adjustment circuit for an image forming apparatus having an automatic exposure function, which outputs a signal representing the intensity of reflected light from an original to the apparatus. means for receiving a signal from a sensor disposed within the sensor; amplifying means for amplifying the received signal; means for setting an amplification factor of the amplifying means to a value corresponding to the level of the signal; and means for supplying a signal to a control circuit of the image forming apparatus so that the document is exposed with an intensity corresponding to the level of the signal.

[Operation] After setting the simulation mode, for example, set a blank original and turn on the copy lamp. A signal representing the intensity of reflected light from the original is sent from the sensor to an amplifying means and amplified. The level of the signal output from the amplifying means is read, and the amplification factor of the amplifying means is switched to a value corresponding to this level.

In the subsequent normal copy mode, automatic exposure control is executed using the signal from the sensor amplified by this newly set amplification factor.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram of an automatic exposure gain adjustment circuit according to the present invention.

In the figure, 23 is an operational amplifier, and the output of this amplifier is passed through a resistor to the CPU 2 which controls the entire copying machine.
+ is connected to the input port.

The inverting input of the amplifier 23 is connected to the inverter 2 via the resistor R1.
2 output, and is further connected in series with a resistor R.
2, R3, and R4.

Furthermore, the non-inverting input of the amplifier 23 is connected to the AE through a resistor R6.
Connected to the output of the sensor. The output of the amplifier 23 is fed back to the non-inverting input via a resistor R5.

From the output port of CPU21, the signals are EGO and AEGI.
AEG2 is output in parallel, and the signal EG2 is supplied to the input of the inverter 22. Also, the signal AEGI
is applied to the connection point between resistors R2 and R3, and the signal n is applied to the connection point between resistors R3 and R4.

The gain of the amplifier 23 can be changed by changing the logic level of the signal AEG2 and AEG2. For example, if ■Healing and AEGI are set to H level and AEG2 is set to L level, the amplification factor ^ESO/AES is [R1+R2
+R3+R4+R5) / (R1+R2+R3+R4
), and when the resistance value of each resistor is set as shown in FIG. 1, the amplification factor is 1.46.

The port for outputting the signals ① and ② of the CPU2+ has an open drain structure, where H level means an open state, and L level means GND level (approximately Ov). In addition, the boat that outputs AEG2 has a CMO3 structure, and when the H level is set, approximately 5V is output and the intended circuit operation is not executed, so the inverter 22
is provided, and an open state is obtained by turning off the inverter 22 when EG2 is at L level.

FIG. 4 shows the relationship between each logic level of the signals Go, AEGI and AEG2 and the amplification factor. As shown in the figure, the amplification factor is increased to 1.4 by changing the logic level of each signal.
It can be changed in four steps from 60 (gain rank 0) to 2.154 (gain rank 3).

Figure 2 shows the circuit diagram of the AE sensor. When the reflected light from the original enters the photodiode 2o, a voltage corresponding to the level of the reflected light is generated, and this voltage is amplified by amplifiers 24 and 25 and output as a signal AES.

Next, the operation of the automatic exposure gain adjustment circuit will be explained with reference to the flowchart shown in FIG.

First, in step S1, a simulation mode is set using a switch (not shown) in order to adjust the exposure gain.

In step S2, the signals n and D are set to H level, and the signal AEG2 is set to L level, thereby setting the gain flag to 0''.

Next, in step S3, the copy lamp is turned on, and a signal ES representing the intensity of reflected light from the original is output from the AE sensor. Since the gain flag is set to “0”, A
ES is amplified by 1.46 times and C as signal AESfl.
It is input to PU21.

Next, in step S4, it is checked whether 8ESO is smaller than 2.774v, that is, whether AES is smaller than 1.9■. If AESO is smaller than 2.774V, the signal EG2 is set to H level in step S5, thereby setting the gain flag 3''.

When AESO is 2.774V or more, the process proceeds to step S6, and it is checked whether AESD is smaller than 3.212V, that is, whether AES is smaller than 2.2V. AES
If O is smaller than 3.2+2V, select ■ in step S7]
is set to L level, thereby setting the gain flag to “2”.
is set.

If AESD is 3.2+2V or more, the process further advances to step S8 to determine whether AESQ is smaller than 3.65V or not.
That is, it is checked whether AES is smaller than 2.5v.

If AESQ is smaller than 3.65V, the surface is set to L level in step S9, thereby setting the gain flag to “
The gain flag is set to "1". If AESO is 3.65V or higher, the gain flag is left at "0".

As a result of the above operations, as shown in FIG. 5, the AES is 1.
62V to 2.8V (7)
ESO automatically outputs 3.5v to 4.5v without adjusting the volume etc. like conventional copying machines. It is set in the IV range. Note that the present invention is not limited to the above embodiments. For example, in the embodiment, the gain of the amplifier is divided into four stages, but if it is necessary to set the exposure level finely, it is possible to divide it into more stages.

Further, in the embodiment, the simulation mode is set and the gain adjustment is executed, but the gain adjustment may be executed during the copy cycle or during warm-up.

Further, the signal AEGOAEG is sent from the parallel port of the CPU.
1. Instead of outputting AEG2 as a parallel signal, these signals may be output as serial signals from a serial port and converted into parallel signals by a serial-parallel converter.

[Effects of the Invention] The automatic exposure gain adjustment circuit of the present invention has means for setting the gain of an amplifier that amplifies a signal from a sensor representing the intensity of reflected light from a document according to the level of the signal. As a result, gain adjustment for correcting sensor variations is automatically performed, so it is possible to eliminate the need for a gain adjustment volume or the like.

Further, gain adjustment can be easily performed by simply placing a blank original on the platen, without adjusting the volume or the like while looking at the copy results as in conventional devices.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the automatic gain adjustment circuit of the present invention, Fig. 2 is a circuit diagram of an AE sensor, Fig. 3 is a flowchart for explaining the operation of the circuit of Fig. 1, and Fig. 4 is a diagram of the circuit shown in Fig. 1. 5 is a graph showing the gain adjustment characteristics of the circuit in FIG. 1, and FIG. FIG. 3 is a circuit diagram of a gain adjustment circuit having the following. 11.21...CPU, 12.23.24
．． 25...Operation amplifier, 22...Inverter, 2o...Photodiode, R1-R
6...Resistance. Hebujinbu FF! l! Atsushi Uesakai Figure 2 Figure 3

Claims (1)

[Claims] An automatic exposure gain adjustment circuit for an image forming apparatus having an automatic exposure function, the apparatus comprising: means for receiving a signal representing the intensity of reflected light from a document from a sensor disposed within the apparatus;
amplification means for amplifying the received signal; means for setting the amplification factor of the amplification means to a value corresponding to the level of the signal; An automatic exposure gain adjustment circuit comprising means for supplying the signal to a control circuit of the image forming apparatus so as to be exposed.