JPH03293818A - A/d converter - Google Patents

Abstract

PURPOSE:To prevent the occurrence of a control defect by providing a gain adjusting means which converts the output signal of an amplifying means to digital data and adjusts the gain of the amplifying means so that the level of digital data is lower than a set level in the case of digital data equal to or higher than the set level. CONSTITUTION:Amplifying means A2 and POT which have the adjustable gain and amplify an analog signal and a gain adjusting means MCU are provided, and this means MCU converts an output means V2 of amplifying means to digital data AN; and when digital data AN is equal to or lower than the set level, the means MCU adjusts the gain of amplifying means A2 and POT so that digital data is lower than the set level. When the output signal V2 of amplifying means A2 and POT is larger than a set value, the gain of amplifying means A2 and POT is so adjusted that it is smaller than the set value. Consequently, digital conversion data is not deviated from a prescribed range. Thus, a control defect is prevented.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a device for converting an analog signal into digital data, and in particular, although not limited thereto, it is a device for detecting the background density of a document when copying the document. The present invention relates to a document density detection device that converts an analog density signal from a density sensor into digital data.

[Conventional technology]

An image processing device that reads original images by optical scanning.

For example, in copying machines, facsimile machines, image editing machines, and the like, the density of the background portion of a document is an important factor in processing. In other words, if there are colors or patterns on the background of the original, the copies or images will become dirty and difficult to see unless they are removed during the processing process.

Otherwise, the data will be noisy.

Therefore, an image processing apparatus has been developed that detects the background density of a document as one parameter in one image process and sets copy density and various processing data accordingly.

FIG. 4 shows an example of a copying apparatus that sets the copy density according to the original density. This copying apparatus is of a fixed original type, and an original 2 placed on a contact glass 1 is optically scanned in synchronization with the rotation of a photoreceptor 4 by an optical system 3 including an exposure lamp 3a and a large number of mirrors.

At this time, the light that scanned the original (light reflected from the original) is irradiated onto the photosensitive surface of the photoreceptor 4, but the photosensitive surface of the photoreceptor 4 is uniformly charged by the charger 5 before being irradiated with this light. The charge outside the latent image area is removed by the eraser 6. therefore.

When this latent image area is irradiated with light reflected from the original, photoconduction occurs depending on the intensity of the light, and an electrostatic latent image is formed.

This electrostatic latent image is developed by adhering toner by a developing device 7, and is transferred onto recording paper by a transfer charger 8.

Thereafter, residual toner is removed from the photosensitive surface of the photosensitive member 4 by a cleaner 9, and the recording paper is fixed by a fixing device 10.

Each of these constituent elements is controlled by a microcomputer MCU shown in FIG.

By the way, in this type of copying machine, the exposure lamp 3
The amount of light a, the charging potential of the photosensitive surface of the photosensitive member 4, the developing bias of the developing device 7, etc. are factors that affect the image (copy) on the recording paper. In other words, by adjusting these elements, it is possible to reduce the influence of background dirt, background color, and pattern of the original 2 on copies.

Therefore, a light receiver 12 is provided on the carriage that moves the exposure lamp 3a of the copying apparatus shown in FIG. This light receiver 12 guides the reflected light of the document beyond the optical scanning part by the optical system 3 to the photodiode PD. A photocurrent Is corresponding to the intensity of the irradiated light flows through the photodiode PD. This photocurrent Is is converted into a voltage and amplified in the amplifier A1, inverted and amplified in the amplifier A2, and further inverted and amplified in the amplifier A2. is input.

The microcomputer MCU determines whether the background of the original 2 is dirty or not when copying, depending on the magnitude of the signal v2.

In order to minimize the influence of background color and pattern, the light intensity of the exposure lamp 3a, the charging potential of the photosensitive surface of the photosensitive member 4, and/or the developing bias of the developing device 7, etc. are adjusted.

[Problem to be solved by the invention]

Conventionally, no matter what the input value, the amplifiers A1 to A3 remain fixed at the gain set during the initial adjustment of one machine, so if the input value increases for some reason, the A/D Damage to the converter (MCtJ) or A
/D conversion failure occurs.

When the input signal level is outside the predetermined range.

There is no guarantee for A/D conversion in the A/D converter, and the digital conversion data will be random with no continuity with the data within the predetermined range, and input signals outside the predetermined range may Control based on correspondingly obtained digital data becomes haphazard.

For example, as shown in FIG. 1, the concentration detection signal of the photodiode PD is amplified by amplifiers A1 to A3,
When the output voltage of amplifier A1 is digitally converted by the microcomputer MCU, when the output voltage v1 of amplifier A1 is 8V, the output voltage of amplifier A3 is set to 4V, and the output voltage of amplifier A3 is
Assuming that 2 is digitally converted to 255 stages, increase @ @
The combined gain of A2 and A3 is 255 x 4/8 =
128. vl is the reference voltage V for A/D conversion
Since it needs to be below raf (=5v), the input voltage v2 is determined so that even when vl is the highest, it is below V ref. When the gain is set to 128 as described above, the highest voltage gt of vl, 5 x 2
55/12g (approximately 10v), but due to some reason, such as noise, a defect in the photosensor PD, or a defect in the circuit connected to the PD, vl becomes 1.
When the number of cram schools exceeds 0, the control failure described above occurs.

The diode D1yD2 connected to the A/D conversion input terminal AN of the microcomputer MCU is for preventing MCU from being destroyed by excessive voltage being applied to AN. Excessive positive voltage is detected by diode D1 as Vcc(+
5v) Noveino(s) is placed on the line.

Further, the negative voltage is bypassed to the equipment ground line by diode D2. This prevents damage to the MCU, etc. However, if an excessive positive voltage is applied, for example, the A/D
Since the voltage at the conversion input terminal AN is at a level equal to Vcc (+5V) plus the voltage drop (forward voltage drop) of the diode D1, it exceeds V ref (5V), resulting in poor control. This relationship is shown in FIG.

The purpose of the present invention is to improve the discontinuity of digitally converted data with data within a specified range due to input analog signal levels exceeding a specified range, and to prevent the occurrence of control failures as described above. shall be.

[Means to solve the problem]

The AD conversion device of the present invention includes an amplification means (A2.POT) that amplifies an analog signal and whose gain is adjustable: A that converts the output signal (v2) of the amplification means (A2.POT) into digital data (AN). /D conversion means (MCU); and when the digital data (AN) indicates the set level (Vth) or more, - Set the gain of the amplification means (A2.POT) to a gain that is less than the set level (Vth). A gain adjustment means (MCu) for adjustment is provided.

[Effect]

When the output signal (v2) of the amplification means (A2.POT) is greater than or equal to the set value (Vth), the gain of the amplification means (A2.POT) is adjusted so that it becomes less than or equal to the set value (vth). The digital conversion data does not fall outside the specified range, that is, the set value (V
By determining the amplification means (A2.PO
The output signal (v2) of T) is automatically suppressed to a range that can be properly converted into digital data.

Due to the gain adjustment described above, the relationship between the digital data and the source analog signal changes, and the accuracy of the digital data decreases slightly, but the continuity with the digital conversion data within a certain range is relatively high (the error value is small). ), this prevents the data from becoming random and disconnected from the digital conversion data within the specified range.

There is no possibility of poor control. That is, the stability of control based on digital data is ensured.

Other objects and features of the invention will become apparent from the following description of an embodiment with reference to one drawing.

〔Example〕

FIG. 1 shows an embodiment of the present invention. This embodiment is incorporated in the same copying apparatus as the copying apparatus already described with reference to FIG. Guided by PD.

As described above, since a photocurrent Is corresponding to the intensity of the irradiated light flows through the photodiode PD, the amplifier A1 converts this photocurrent Is into a voltage and amplifies it.

Amplification AI! AI output is input resistance Ri, 1all
fltA3. A2 and an electronic volume POT are input to a variable gain amplifier. Assuming that the input voltage of the variable gain amplifier is V1y, the output voltage is V2+, and the feedback resistor is Rf, these relationships are expressed by the following equation.

V2 =VIX (Rf/Rr)...(
1) Feedback resistance Rf is electronic volume POT
The resistance value is changed by

FIG. 2 shows the circuit configuration of the electronic volume POT.

This electronic volume POT has a 7-bit counter 21,
Non-volatile memory 22 for storing count data of a 7-bit counter. Programming control/power-on detection circuit 23*r1~ that detects power input and starts control
Circuit 25 consisting of a 9941 resistor array of rag and a 100 switch array of SWO to 5W99. and S
It is composed of a decoder 24 that selects on/off of the switches Wo to SW99. In addition, non-volatile memory 2
2 stores the set number of pulses N in the memory when an H signal is input to the terminal C8, and once the stored number of pulses N is turned off, it does not disappear even if the power is turned off.This memory is stored in the TV. It consists of an EEPROM that stores channels and is used in place of DIP switches.

While a normal variable resistor changes the resistance value mechanically, this electronic volume POT changes the resistance value electronically. In other words, 99 resistors r1 to r99 are connected between the terminals vH and VL of the electronic volume POT, and if the value of these resistors is r, then the terminal V
The resistance value between VH and VW when L and VW are connected, that is, the feedback resistance Rf, is the switch SWO to SW
99 can be changed from 0 to 99r by sequentially turning on 6. For example, if the switch 5W99 is on, the feedback resistance Rf = O, if the switch SW98 is on, the resistance Rf = r, and if the switch 5W97 is on, the feedback resistance Rf = r. For example, resistance Rf=2r, . . ., if switch SWO is on, resistance Rf=99r.

Also, which switch to turn on is determined by the terminal INC.
It is determined by the number of pulses N input into the resistor Rf, and whether the resistor Rf is increased or decreased is determined by whether the terminal U/D- is set to an H signal or an L signal.

Therefore, when the terminal U/D is an H signal, the relationship between the number N of pulses input to the terminal INC and the resistance value Rf between VHVw is expressed by a linear equation.

Rf = Rf o + NX r ... (2) R
fO is the resistance value (1) corresponding to the number of pulses stored in the memory, and from equation (2), V2 = V1 x (Rf o + NX r) /R1''
'(3) becomes.

In equation (3), Rfo, r, and Ri are constant, so by appropriately selecting N, even if 1 changes, v
l can be kept constant.

Further, when the terminal U/D is an L signal, the relationship between the number N of pulses input to the terminal INC and the resistance value Rf between VH and VW is expressed by a linear equation.

Rf=RfO−NXr...” (4) (1)
, from formula (4), V2 = VIX(Rfo NXr)/Ri... (
5).

In equation (5), as in equation (3), Rfo.

Since r and Ri are constant, by appropriately selecting N, vl can be kept constant even if vl changes.

The output of the variable gain amplifier is input to the analog input port AN of the microcomputer MCU as a voltage signal v2 indicating the background density of the original.

The microcomputer MCU receives the signal v as described above.
2, in order to minimize the influence of background dirt, background color, and pattern on the original 2 on the copy.
The amount of light from the exposure lamp 3a, the charging potential of the photosensitive surface of the photosensitive member 4, and/or the developing bias of the developing device 7, etc. are adjusted.

The amplification factor of the digital data (AN) corresponding to the voltage signal v2 input to the analog input port AN of the microcomputer MCU is determined by the digital data (AN) of the reflected light of the standard document being set in the microcomputer MCU in advance. Each time the switch Sm is turned on, it is automatically controlled to match predetermined digital density data (Vs) corresponding to the standard original density.

The switch Sm is a switch provided inside the copying machine for use by a service person. When the service person needs to adjust (calibrate) the voltage signal 2, the service person turns on the switch Sm and places the standard document on the contact glass 1. and turn on the print key provided on the operation board.

The operation of the microcomputer MCU at this time will be explained with reference to the flowchart shown in FIG. 3a.

In the microcomputer MCU, switch Sm is on,
That is, when an H signal is input to the input port (P5) (step 1: hereinafter, the word step is omitted and only the number is written in parentheses), the density of the standard document stored in advance in the microcomputer MCU is changed. The corresponding digital density data (Dx) is read out and set to Vs) (2). Then, output a mustard signal from the output port (P4) to turn on the lamp driver and start scanning with the optical system 3. 3) Output an L signal from the output port (P3) to enable the main terminal 2 of the electronic volume POT. do(
4).

Next, the voltage signal v2 input to the input port AN is digitally converted and read (ADC-A), and the digital signal (ADC-A) is read.
Check whether N) and digital concentration data (Vs) are equal5). If they are equal, the output port (P3)
Outputs an H signal from the output port (P4) to disable terminal O8 of the electronic volume and store the count data of the counter 21 in the memory 22 (12), and outputs an H signal from the output port (P4) to turn off the lamp driver and turn off the optical system 3. The scan is ended (13). If the two are different, the two are compared (6).

In step 6, a digital signal (AN
) is larger than the digital concentration data (Vs), an L signal is output from the output port (P2) to the terminal U/D of the electronic volume to instruct a down count in order to reduce the feedback resistance Rf. If the digital signal (AN) is smaller than the digital concentration data (v8), an H signal instructing up-counting to increase the feedback resistance Rf is output from the output port (P2) to the terminal U/D of the electronic volume (7).

Next, in steps 9 to 11, the count 21 is counted down or up by outputting one pulse to the counter 21 to change the feedback resistance by one step, and in step 5, the digital signal (AN) corresponding to the voltage signal v2 is and the digital density data (Vs) are compared again. Then step 5 → 6 → 7 until both are equal.
(or 8) → 9 → 10 → 11 → 5... repeats the loop, during which the digital signal (AN
) becomes equal to the digital density data (Vs), an H signal is output from the output port (P3), the terminals P of the electronic volume are disabled, and the counter 2 is stored in the memory 22.
The count data of 1 is updated in the memory 12), the H signal is output from the output port (P4), the lamp driver is turned off, the scan of the optical system 3 is completed (13), and the calibration control is completed.

While changing the gain, the value indicated by the conversion data (8N) remains at the set level v slightly lower than Vref (Sv).
th (see Fig. 5) or more (14), and if it is more than that, an error is displayed on the operation board (15).

Clears the error display when vth is not dripped (16),
Therefore, when the amplified output v2 exceeds the set level vth while the sensor detection level is being calibrated as described above, an error can be displayed.

When the sensor detection level calibration is completed without any error display, an appropriate gain has been set.

Incidentally, when the power is turned on to each part of the electric circuit shown in FIG. 1, the programming control/power-on detection circuit 23 of the electronic volume POT is activated.

Since this memory data is not updated while Sm is open, the calibration (Sm
Until the closing) is performed, the document density detection signal is amplified with an amplification factor corresponding to the data written in the memory 22 and is applied to the port AN of the MCU.

In the manner described above, the voltage signal v2 input to the analog input port AN correctly corresponds to the document density.

The microcomputer MCU digitally converts and reads (2) at a predetermined timing while controlling the sequence of the copy cycle, and correspondingly sets the copy density parameter in order to set the copy image contrast within a predetermined range. Adjust or change. The contents of the digital conversion reading at this time are shown in FIG. 3b.

Referring to FIG. 3b, first, vl is digitally converted and read (21). Then, compare the level indicated by the data (AN) obtained by reading with the set level vth (22), and if the former is higher than the latter, lower the gain by one step (23).
~26), and also digitally convert and read vl (
21) In the same way, check whether the read level is above vth.22) If it is above Vth, it will return 1 again.
Decrease step gain. In this way, vl becomes vt
h Lower the gain one by one until it becomes dark. With this gain adjustment, for example, as shown in FIG.
When the level of V1 rises temporarily, the gain of amplifier A2 is automatically lowered so that vl becomes less than vth. As vl falls, v2 naturally falls, but the gain remains low. This may cause the copy image density adjustment to deviate slightly from the normal value, but the error signal (fifth
Since haphazard density adjustment due to the peaks of vl shown in the figure) is prevented, the stability of density adjustment is high.

When the power of the copying machine is turned off and then turned on again, the non-volatile memory 22 is stored in the counter 21 of the electronic volume POT.
The gain specification data (previous sensor calibration: value set in Figure 3a) is set as the initial value, so the above
The gain adjustment according to the flow shown in FIG. 3b is canceled by turning off the power once, and the gain set in the sensor calibration (FIG. 3a) is reset by turning the power back on. In this way, the reduction in gain corresponding to the abnormal rise in the analog signal (vl) is automatically canceled when the copier power is turned off and then turned on again.

Moreover, if the sensor calibration (FIG. 3a) is executed with the switch S⊙ set to idle, then the calibration will be automatically canceled.

FIG. 6a shows a signal Vin from an external document density detection sensor (AE sensor), showing a second embodiment of the present invention.
It consists of a multiplication type DA converter AD7528 and an operational amplifier. A zero-multiplying DA converter AD75 is connected to the built-in A/D converter input AN of the one-chip microcomputer NEC μPD7811 via a programmable gain amplifier.
AD bus & control signal lines (address/data bus) are connected to AD7528 from microcomputer μPD7811 through these.
Gain data up to 55 is transmitted.

In this example, the gain of the operational amplifier section is 1, and the total gain of the programmable gain amplifier is:

The gain data is divided by 255. Therefore.

V a n =V i n·gain data/255.

In order to correct the sensitivity of the AE sensor in copying machines, Van
The gain data is obtained so that the following is achieved, and the density of the document during normal copying operations is detected using this reference gain data. For example, if the AE sensor output of a standard original is 8■, V a
Suppose we set the value of n to 4v.

Gain data (reference gain data) = 255
4/8=128.

During normal copying operation, 128 is set as gain data, and the AD converter that detects the original density is Van,
: & Vre
It is set to be less than f (5V in this example). In other words, at most Vin=5X255/128 (=about 10V
) is as follows.

However, Vtn may exceed IOV due to some reason, noise, or defective AE sensor. Then, V a n ) V r e f and the control failure described above occurs. The two diodes DI and D2 connected to the AN input section are for input protection (to prevent damage).
(Conversion data is not guaranteed), but even if this diode is used, Van will exceed Vref. by the voltage drop Vd of the diode.

FIG. 6b is a program flowchart of input protection processing in the second embodiment. (ANDATA) is the digital value of the AN input of the AD converter.

(Setting gain) is gain data to be loaded into the AD7528 after performing protection processing. Vth is a value that satisfies the threshold value 5V>Vth.

The reference gain is the gain determined at the time of initial adjustment.

Flowchart 6b is incorporated into the loop routine of the copying machine program. In this flowchart, the AN input is first converted to AD (ANDATA) (31), and then this value is compared with vth (32). ),
(Setting gain) is loaded to the AD7528 (34) and the process ends. If NO in step 33, add 1 to (set gain).

Perform steps 35.34 and exit. If NO in step 32, (set gain) is -1 (36), (
Load the set gain) to the AD7528 (37) and return to step 31 again.

In this second embodiment as well, Vin increases for some reason and V a n becomes 4.5V (in this example, Vth is 4.5V).
When V in decreases from its peak, the set gain is increased until it reaches the reference gain. Once reached, the gain correction ends.

Since the AD converter input value V a n is constantly monitored and the programmable gain is reduced when it reaches a certain threshold value Vth, V a n will never obtain vth, and if Vin becomes abnormal for some reason. Even if the value increases, destruction of the AD converter or control failure due to unguaranteed AD readings can be prevented.

〔Effect of the invention〕

As explained above, according to the present invention, the A/D conversion data (AN) does not become random and disconnected from the digital conversion data within the specified range, so the control using the digital conversion data is greatly disturbed. Things will go away. That is, the stability of control based on digital data is ensured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of the present invention. FIG. 2 is a block diagram showing an outline of the configuration of the electronic volume POT shown in FIG. 1. 3a and 3b are flowcharts showing part of the operation of the microcomputer MCU shown in FIG. 1.6 FIG. 4 is a block diagram showing the configuration of a copying machine in which the embodiment device is incorporated. . FIG. 5 is a time chart showing time-series changes in electrical signals of various parts in the first embodiment shown in FIG. FIG. 6a is a block diagram showing a second embodiment of the present invention. FIG. 6b is a flowchart showing the operation of the second embodiment. FIG. 7 is a time chart showing time-series changes in the analog signal v2 given to the A/D converter in a conventional AD converter. ]: Contact glass 2: Original 3: Optical system 3a = Exposure lamp 4: Photo sensor 5: Charger 6: Eraser 7: Developing device 8: Transfer charger 9: Cleaner 10: Fixing device 12: Photo receiver PD: Photo Diode 1. A2: Amplification 11 POT
:Electronic volume (A2. [:Amplification hand m
21 Near bit counter 22: Non-volatile memory 23 = Programming control/power-on detection circuit 24: Decoder 11-79g: Resistor array S0-5W99: Switch array MCU: Microcomputer (A/D conversion means, gain Adjustment aid R1: Resistor
-: Switch vR: Variable resistor

Claims (1)

[Claims] Amplifying means for amplifying an analog signal, the gain of which is adjustable; A converting the output signal of the amplifying means into digital data;
/D conversion means; and gain adjustment means for adjusting the gain of the amplification means to a gain that is less than the set level when the digital data indicates a set level or higher.