JPH0341825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a document density reading device for a copying machine.

A method of scanning a document in a copying machine prior to starting image formation, detecting the density or lightness of the document, and controlling parameters of the copying process, such as exposure amount, development bias, etc., based on the results,
JP-A-53-93836 and JP-A-Sho 54-1 aim to obtain the best copy without bothering the user of a copying machine even if the density of each original differs.
It is known from Publication No. 62833. Here, there is a method for detecting the density of the original document that detects the maximum density and minimum density of the original document, and another method that detects the background density of the original document.

However, this method has the disadvantage that it is not possible to obtain accurate timing for reading the density of the original, and the density of the original cannot be read correctly. Japanese Patent Application Publication No. 2005-120000 has proposed that the timing for reading the density of the original can be set to the time when a portion corresponding to the size of the transfer paper set in the copying machine is being scanned, or even to the time when a narrow area is being scanned. It is disclosed in Publication No. 54-62833. However, with copying machines that have a manual paper feed function, it is often difficult for the machine to know the size of the transfer paper at the stage of detecting the density of the original, and the timing for reading the density of the original is determined according to the size of the transfer paper. I can't configure the settings. Furthermore, in general, the size of the original document and the size of the transfer paper do not always match. A problem arises when the original is smaller than the transfer paper. In this case, if the pressure plate is closed, the density of the pressure plate will be read in a place where there is no document, and there is a possibility that the density of the pressure plate will be read as the background density or minimum density of the document. If the pressure plate is open, the density of the open area of the pressure plate where there is no original will be read as the maximum density of the original. Furthermore, even if the area for reading the density of the original is narrowly limited, if there is a gap between the leading edge of the original and the original abutment plate against which this leading edge abuts, or if the area for reading the density of the original is larger than the original, The same drawback occurs when the timing of reading the density of the original is related to the size of the transfer paper. Furthermore, since the area for reading the density of the original is limited, there is a high possibility that the maximum density, minimum density, and background density of the original cannot be read correctly.

The present invention eliminates the above-mentioned drawbacks, automatically determines the range for reading the density of a document, and
It is an object of the present invention to provide a document density reading device which can prevent the density from being read out of the range of the document and can correctly read the density of the document.

The invention set forth in item 1 provides a document density reading device that scans a document, detects the density of the document by a density detection means, and extracts a minimum density from the detected density signal of the document, comprising: the density detection device; a delay unit for delaying a density signal of the original detected by the density detection unit for a predetermined time; a waveform shaping unit for shaping a change in the density signal of the original detected by the density detection unit; a rising edge detecting means for detecting a rising edge from a low concentration to a large concentration and outputting a rising signal; counting means for outputting a detection permission signal when the detection permission signal is set; time-limiting means for outputting a set signal for a time equal to the delay time of the delay means when set by the rising signal; and both the detection permission signal and the set signal , and extraction means for extracting a minimum density from the density signal of the document delayed by the delay means.

Further, the invention as set forth in item 2 provides a document density reading device that scans a document, detects the density of the document by a density detection means, and extracts a maximum density from a signal of the detected density of the document, comprising the steps of: a delay means for delaying a density signal of the original detected by the detection means for a predetermined time; a waveform shaping means for shaping a change in the density signal of the original detected by the density detection means; falling detection means for detecting a fall in which the concentration of the signal changes from a high concentration to a small concentration, and outputting a falling signal; counting the number of falling signals; counting means for outputting a detection permission signal when the detection permission signal and the detection permission signal are equal to or less than a set value of the detection permission signal; A document density reading device characterized in that it is provided with an extracting means for extracting the maximum density from the density signal of the document delayed by the delay device using both signals of the set signal.The present invention will be described below with reference to the drawings. This will be explained by giving examples.

1A and 2B and FIGS. 2A and 2B show schematic density patterns read from a document as it is scanned by a copying machine. In this figure, the vertical axis represents concentration, with higher concentrations at the top, and the horizontal axis represents time. These density patterns correspond to the output of a logarithmic amplifier or the output of a buffer, which will be described later.
The times A to D on the horizontal axis correspond to the time for scanning the copyable range on the document table to read the density of the document. This time is set as the maximum reading time, and the maximum density or minimum density of the document is not read outside this time. As a more practical example, the maximum reading time can be set as short as within times A to D in order to avoid erroneous reading due to reflected light from a document abutting plate at the end of the document table, a scale, etc. Times B and C on the horizontal axis are times for scanning the leading edge and trailing edge of the document. The scanning direction of the original when reading the density of the original may be the same or the opposite of the scanning direction of the original during image creation, but in these cases, the direction of the time axis is reversed and the scanning direction is A to B, C to
D is the same except that there is a gap between the original and the original support plate or the scale, so the case of the time axis in the figure will be explained. FIG. 1A shows a case where the original density is read when the original is smaller than the reading range, the minimum value of the original density is greater than the density of the pressure plate, and the pressure plate is closed. In this case, since the density of the pressure plate is lower than the minimum density of the original, the density of the pressure plate is read as the minimum density of the original, making it impossible to control the parameters of the copying process according to the density of the original. However, even in this case, the maximum density of the document can be read correctly. This is because it is not an ordinary copying machine where the density of the pressure plate is higher than the maximum density of the original. FIG. 2A shows a case where the pressure plate is open and the maximum density of the original cannot be obtained correctly. If the density (equivalent density) in the open area of the pressure plate is higher than the maximum density of the original, the density of the open area of the pressure plate will be read as the maximum density of the original, so it is necessary to control the parameters correctly in the copying process according to the density of the original. I can't do it. If the density of the open part of the pressure plate is lower than the maximum density of the original, there is no problem because the maximum density of the original can be read correctly. Furthermore, since the density of the open pressure plate part is high, as is known from the fact that it appears black on copies, it does not affect the reading of the minimum density of the original.

Next, as shown in FIGS. 1A and 2A, an embodiment of the present invention is shown in which the correct original density can be read even when the conventional apparatus cannot correctly read the maximum and minimum values of the original density. This will be explained using Figure 3.

Prior to an image forming operation in which the original image is exposed to a photoconductor, the original is scanned by an optical system or by moving the original platen (or the original is transported by an original transport device), and the density of the original is detected by a density detection means, In the copying machine known from the above-mentioned publication, which automatically controls the parameters of the copying process based on the results, the photoamplifier 1 constitutes the density detection means. When the original is illuminated by a light source, reflected light corresponding to the density pattern of the original enters the photoamplifier 1 as the original is scanned, which is converted into an electrical signal and amplified. The output signal of the photoamplifier 1 is input to the logarithmic amplifier 2 and converted into a voltage proportional to the concentration, and the schematic waveforms of this voltage are shown in FIG.
This corresponds to that shown in FIG. 2A. Logarithmic amplifier 2
The output signal is input to a delay circuit 4 via a buffer 3. This delay circuit 4 is a BBD (Backet)
Brigade Device) and CCD (Charge Coupled Device)
Device), etc. Figures 1B and 2B show the waveforms of Figures 1A and 2B delayed by a delay time T _D.
This corresponds to the output of the delay circuit 4. Delay circuit 4
The output is sent to a positive peak hold circuit 6 via a switch 5 which is closed only during the period when the maximum document density is read.
, the maximum value is detected and retained. Therefore, an extraction means for extracting the maximum value of the original density from the output signal of the delay circuit 4 is constituted by the switch 5 and the positive peak hold circuit 6. In addition, the output of the delay circuit 4 is shifted to a voltage by the shift circuit 7.
The signal is subtracted by V _S and level-shifted, and is input to the negative peak hold circuit 9 via the switch 8, which is closed only during the period for reading the minimum value of the document density, where the minimum value is detected and held. Therefore, an extraction means for extracting the minimum value of the document density from the output signal of the delay circuit 4 is constituted by the switch 8 and the negative peak hold circuit 9. The output signal D _MaX of the positive peak hold circuit 6, the output signal (D _MIN −V _s ) of the negative peak hold circuit 9, and the shift voltage V _s are added and inverted by the inverting adder circuit 10, and −[D _MaX +(D _MIN −V _s )+V _s ]=−(D _MaX +D _MIN ) and is inverted by the inverting circuit 11. The output of the inversion circuit 11 is an output proportional to the sum of the maximum and minimum document density, that is, an output proportional to the average density of the document, and a circuit (not shown) controls the light amount of the exposure light source according to this output. The image forming apparatus automatically provides the best copy by giving the optimum exposure amount to each original or by controlling the developing bias and the like. The positive peak hold circuit 6 and the negative peak hold circuit 9 are reset by a reset signal prior to the start of scanning the original for reading the density of the original, and then control the imaging parameters in the copying cycle for at least the original whose density has been read. The set state is maintained so that the maximum value and minimum value are held until the end of the process. Further, the output signal of the buffer 3 is waveform-shaped by a waveform shaping circuit 12 and then inputted to a counter 13, a timer 14 composed of a negative edge trigger type mono multivibrator, and a timer 15 composed of a positive edge trigger type mono multivibrator. Ru. The counter 13 is reset to an initial state by a reset signal prior to the start of reading the document density. This counter 13 counts changes in the density pattern by counting input signals. In this case, the counter 13 counts changes in the density pattern, and includes a rising edge detection means for detecting a rising edge when the density of the original changes from low density to high density based on the output signal of the waveform shaping circuit 12 and outputting a rising signal; The apparatus includes a falling edge detection means for detecting the falling edge of the density of the document from high density to small density and outputting a falling signal, and counts the rising and falling signals. The output of the counter 13 is input to a count determination circuit 16. The count determination circuit 16 is supplied with a set number N corresponding to the time to start reading the maximum density and minimum density of the document, and a set number M corresponding to the time to finish reading the original from the preset circuit 17. An output signal is generated during the period from N to M counts. Therefore, the counter 13 and the count number determination circuit 16 count the rising signal and falling signal, and the count value becomes the first set value N.
A counting means is configured to output an output signal as a detection permission signal when the value is above and below the second set value M. If a number greater than or equal to 1 is given as the set number N, it is possible to avoid problems when reading the original density due to the whiteness or openness of the pressure plate as shown in FIGS. 1A and 2A. Generally, this setting is made to avoid areas of high density occurring due to the shadow of the boundary between the edge of the original and the pressure plate, or the presence of a border around the original that is separate from the pattern you want to copy, resulting in the maximum density. It is desirable that the number N be 2 or more. Number of settings M
is an integer larger than the set number N. The number of changes in the density pattern that occur during scanning of an average document ranges from tens to hundreds, so if you set the number M to be smaller than these, the white of the pressure plate will pass through the trailing edge of the document. It is possible to avoid reading the area as the minimum density or reading the open part of the pressure plate as the maximum density. In this example, the reading range of the original density is limited by utilizing the properties of the density pattern of the original, so that more accurate density information can be obtained than in the case where the reading range is limited in advance to a specific narrow part. When reading the original density, it is possible to read the density information on one line of the original, or to read the density information on multiple lines of the original, but it is necessary to scan and read the entire surface of the original. Since this is difficult in terms of cost and reading time, it is useful to determine whether reading is complete by counting changes in concentration. The timer 14 is constituted by a negative edge trigger type mono multivibrator that is triggered by the fall of the output signal of the waveform shaping circuit 12 and outputs an output signal for the same time as the delay time of the delay circuit 4. It includes a falling edge detection means for detecting the falling edge of the density of the document from high density to small density based on the output signal and outputting a falling signal. It serves as a time limit means for outputting a set signal for the same period of time. Similarly,
The timer 15 is constituted by a positive edge trigger type mono multivibrator that is triggered by the rise of the output signal of the waveform shaping circuit 12 and outputs an output signal for the same time as the delay time of the delay circuit 4.
It includes a rising edge detecting means for detecting the rising edge of the density of the document from low density to high density based on the output signal of the waveform shaping circuit 12 and outputting a rising signal, and the delay time of the delay circuit 4 is set by the rising signal. This is a time limit means that outputs a set signal for the same period of time. The output signals of the timers 14 and 15 are processed by AND circuits 18 and 19 to the count number determination circuit 1.
6 is logically ANDed with the output signal of 6, and their output closes switches 5 and 8. That is, when the density pattern changes between N and M, the maximum density and minimum density of the original are detected and held within the time limits of the timers 14 and 15. The operation for reading the minimum density (generally corresponding to the background density) of a document will be explained in detail with reference to FIGS. 1A to 1C. Figure 1A is the original density pattern obtained by scanning the original, Figure 1B is the density pattern delayed by T _D , and Figure 1C is the document density pattern obtained by scanning the original.
indicates when to close. This timing is determined by the timer 1 at the third or later rising edge of the waveform shown in Figure 1A.
5 is the minimum value reading time of the time limit _T2 created by setting the time limit device 14, 15, and the time limit devices 14 and 15 may be retriggerable devices in which the time limit is set with priority given to the trigger signal. The output of the timer 15 is generated many times according to the density pattern of the original as shown in FIG. Detection and retention occur. Among the rising edges of the original data shown in FIG. 1A, at point B and the next rising edge, the count number of the counter 13 is smaller than the preset number N and no output is output from the count number discrimination circuit 16, so the timer 15 is enabled. Switch 8
is closed and the low density data due to the whiteness of the pressure plate between A and B is not read. The low density data between C and D on the trailing edge side of the document scan is also processed by the timer 15.
Since there is no output and Sweetui 8 does not close, it cannot be read. The delay time T ₂ of the timer 15 is set to be the same as the data delay time _TD . If this relationship does not exist and T ₂ is larger than T _D , when the density rises due to the shadow at the rear edge of the document, the low density of the portion corresponding to C to D will be read as the minimum density. When detecting and holding the maximum concentration, the switch 5 is closed by the output of the timer 14 at the falling edge of the original data, and the maximum concentration is detected and held only within the time limit T1 of the timer ₁₄ . At this time, it is also not preferable that the time limit _T1 is too long, and it is preferable that the time limit T1 be the same as the delay time _TD . However, since it is rare that there is a change in the density pattern near the edge of the document, there is often no practical problem even if the time limit _T1 of the timer 14 is long. Timing device 14,1
5 determines the time limit T ₁ and T ₂ using the clock of the analog delay circuit 4 including BBD and CCD.
T ₁ and T ₂ can be made to accurately match the delay time T _D of the delay circuit 4, and it is possible to avoid reading the shadow that occurs at the boundary between the trailing edge of the document and the pressure plate.
When the count number of the counter 13 reaches M, the switches 5 and 8 remain open and reading of the original density is terminated. Even if the count number of the counter 13 does not reach M, the density is read up to the rear end of the document, so that problems such as failure to read or reading the density of the open part of the pressure plate or the density of the pressure plate do not occur. For general originals, the number of density changes in the density pattern is relatively large, and unless the original is a special original, reading the density can be completed by scanning a fraction of the length of the original. By increasing the scanning speed of the document after completion of reading and bringing the document to the image forming start position earlier, more efficient copying can be achieved. In particular, in a copying machine that scans the original for density reading from the same direction as the forward direction of original scanning during image formation, and then returns to the start position after reading the original density to start the copying cycle, reading the original density is not possible. By aborting the forward scanning of the original and returning it to the start position upon completion, the time required to read the density of the original can be shortened and more efficient copying can be performed. Further, as an additional effect, since the document scanning is reversed midway through, the user of the copying machine can also know that the document density reading has been carried out normally.

Above, we have described an example in which the polarity of the concentration signal is such that the voltage is high when the concentration is high.
Even when the polarity of the concentration signal is reversed, the present invention can be easily applied by selecting the trigger polarities of the timers 14 and 15 so as to avoid erroneous reading due to the pressure plate and the open part of the pressure plate. Also timer 1
The trigger polarities 4 and 15 may be set based on the relationship between the density and the reflected light according to the density pattern from the original. The above embodiment is an example in which both the maximum density and the minimum density of the original are read, but in the case where the copying process is controlled by detecting the background density of the original, the minimum density of the original in the above embodiment may be read. Only the reading portion can be a device that reads the background density of the document.

As described above, according to the present invention, it is possible to automatically determine the range in which the density of the original is read, and also based on the delay time of the delay means for delaying the density signal of the original detected by the density detection means and the rising signal. The set time of the timer for outputting the set signal for extracting the minimum density is the same as the set time of the timer for outputting the set signal for extracting the minimum density. Since the set time of the timer that is set by the downstream signal and outputs the set signal for extracting the maximum density is the same, even if the number of changes in the density of the original does not reach the predetermined number, the density of the original changes. Therefore, the density of the original can be read correctly regardless of whether the original is smaller than the transfer limit or whether the pressure plate is opened or closed.

[Brief explanation of the drawing]

1 and 2 are diagrams for explaining the present invention, and FIG. 3 is a block diagram showing one embodiment of the present invention. 1... Photo amplifier, 4... Delay circuit, 5, 8
...Switch, 12...Waveform shaping circuit, 13...
Counter, 14, 15... Time limit device, 16... Count number discrimination circuit, 18, 19... AND circuit.

Claims (1)

[Scope of Claims] 1. In a document density reading device that scans a document, detects the density of the document by a density detection means, and extracts a minimum density from a signal of the detected density of the document, the density detection device comprises: a delay unit for delaying a density signal of the original detected by the density detection unit for a predetermined time; a waveform shaping unit for shaping a change in the density signal of the original detected by the density detection unit; a rising edge detecting means for detecting a rising edge from a low concentration to a large concentration and outputting a rising signal; counting means for outputting a detection permission signal when the detection permission signal is set; time-limiting means for outputting a set signal for a time equal to the delay time of the delay means when set by the rising signal; and both the detection permission signal and the set signal , extraction means for extracting a minimum density from the density signal of the document delayed by the delay means. 2. In a document density reading device that scans a document, detects the density of the document by a density detection means, and extracts the maximum density from the detected density signal of the document, the density of the document detected by the density detection means is a delay means for delaying a signal for a predetermined time; a waveform shaping means for shaping a change in the density signal of the original detected by the density detection means; and a waveform shaping means for changing the density of the original from high density to low density by the output of the waveform shaping means. falling detection means for detecting a falling edge of the falling signal and outputting a falling signal; and counting the number of falling signals, and detecting when the count value is greater than or equal to a first set value and less than or equal to a second set value. a count means for outputting a permission signal; a time limit means set by the falling signal and outputting a set signal for a time equal to the delay time of the delay means; 1. A document density reading device comprising: extraction means for extracting a maximum density from the density signal of the document delayed by a delay means.