JPH0356461B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is a copying machine control device that reads the density of a document and controls the copying process.

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.

Therefore, there is a method that counts the changes in the density of the original detected by the original density detection means and calculates the maximum density and minimum density of the original during the period until the counted number reaches the first set number and the second set number. Proposed. According to this method, the time for reading the density of the original is determined by the density pattern of the original, and the density of the original can be read correctly regardless of whether the original is smaller than the transfer paper or whether the pressure plate is opened or closed. However, if the density change of the original document does not reach the set number, the density of the original document cannot be read, and the copying process is controlled based on abnormal original density information.

In view of these circumstances, it is an object of the present invention to provide a control device for a copying machine that can take appropriate measures when the density of a document cannot be read.

The present invention will be described below by way of examples with reference to the drawings.

FIGS. 1 and 2 show schematic density patterns read from a document as it is scanned by a copying machine. In this figure, the vertical axis is the concentration, with higher concentrations at the top, and the horizontal axis is time. This density pattern corresponds to the output of a logarithmic amplifier or the output of a buffer, which will be described later. Time A to D on the horizontal axis
corresponds to the time required to scan the copyable range of the document table to read the density of the document. This time is the maximum reading time. As a more practical example, the maximum reading time may be set to a shorter value in order to avoid erroneous reading due to light reflected from the original abutment plate, scale, etc. at the end of the original table. Time B on the horizontal axis,
C is the time for reading the density at 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 as or opposite to the scanning direction of the original, but in these cases, only the directions of the time axes in Figures 1 and 2 are reversed. Therefore, the case of the time axis in the figure will be explained. FIG. 1 shows a case where when reading the density of a document, the document is smaller than the reading range and the minimum density of the document is larger than the density of the pressure plate and the pressure plate is closed, resulting in incorrect reading of the minimum density. In this case, the density of the pressure plate is lower than the minimum density of the original, so the density of the pressure plate is read as the minimum density of the original.
It becomes 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. Second
The figure shows a case where the pressure plate is open and the maximum density of the original cannot be obtained correctly. If the density at the open area of the pressure plate (equivalent density) is higher than the maximum density of the original, the density at the open area of the pressure plate will be read as the maximum density of the original, making it impossible to control the parameters of the copying process according to the density of the original. It will disappear.
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 obtained correctly. Since the concentration in the open part of the pressure plate is generally high,
It does not affect the reading of the minimum density of the original.

Next, an embodiment of the present invention will be explained using an implementation circuit shown in FIG. 3, which makes it possible to read the correct original density even when the maximum density and minimum density of the original shown in FIGS. 1 and 2 cannot be read correctly. do.

Prior to an image forming operation in which the original image is exposed to a photoreceptor, 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 publication, etc., 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 waveform of this voltage is the first
This corresponds to that shown in FIG. The output signal of the logarithmic amplifier 2 passes through a buffer 3 and is input to a positive peak hold circuit 5 via a switch 4 that is closed only when reading the density of the original, where the maximum positive value corresponding to the maximum density of the original is detected and held. Ru.
In addition, the output signal of the buffer 3 is transferred to the level shift circuit 6.
The signal is subtracted by a predetermined shift voltage V _S and level-shifted, and is input to the negative peak hold circuit 8 via the switch 7, which has the same function as the switch 4, so that the maximum negative value corresponding to the minimum density of the original is determined. detected and retained. The output signal D _Max of the positive peak hold circuit 5, the output signal D _MIN −V _S of the negative peak hold circuit 8, and the shift voltage V _S are calculated by the inverting and adding circuit 9 to −[D _Max +(D _MIN −V _S )+V _S ]=-
(D _Max +D _MIN ), and is inverted by the inverting circuit 10. The output signal of the inversion circuit 10 is a signal proportional to the sum of the maximum and minimum document density values, that is, a signal proportional to the average value, and a circuit (not shown) controls the light amount of the exposure light source according to this signal. to automatically obtain the best copy by controlling the exposure amount to the optimum value for the original, controlling the developing bias, etc. peak hold circuit 5,
8 is reset by being given a reset signal prior to the start of reading the original density, and thereafter the set state is maintained so that the maximum value and minimum value are held at least until the copying cycle of the original whose density has been read is completed. be done. The output signal of the buffer 3 is waveform-shaped by a waveform shaping circuit 11 and then input to a counter 12 . This counter 12 is reset to an initial state by a reset signal prior to the start of reading the original density, and counts changes in the original density pattern by counting the output signal of the waveform shaping circuit 11. In this case, the counter 12 may count one polarity of changes in the output signal of the waveform shaping circuit 11, that is, one of the rising edge and the falling edge. The output of the counter 12 is input to a count determination circuit 13. The count determination circuit 13 determines a set number N corresponding to the time when the switches 4 and 7 are closed to start reading the maximum and minimum density of the document, and a set number N corresponding to the time when the switches 4 and 7 are opened to finish reading the original. A preset number M is given from the preset circuit 14, and the switch ties 4 and 7 are controlled according to the contents of the counter 12. Therefore, when the contents of the counter 12 reach the set number N, the switches 4 and 7 are closed and reading of the maximum and minimum density of the original is started, and when the contents of the counter 12 reach the set number M, the switches 4 and 7 are opened and the original is read. The reading of the maximum density and minimum density is completed. If a number greater than or equal to 1 is given as the set number N, it is possible to avoid problems at the start of document density reading due to the whiteness of the pressure plate or the opening of the pressure plate as shown in FIGS. 1 and 2. In a copying machine in which the leading edge of the original is brought into contact with the original abutment plate and density reading is started from the leading edge of the original, the set number N may be set to zero. 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. The setting number M is an integer larger than the setting 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. Furthermore, by displaying that the content of the counter 12 has reached N or M, the user can determine whether the density information of the original to be copied has been read into the machine. 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 using multiple density detection means, but it is possible to read the density information on multiple lines of the original using multiple density detection means. Since it is difficult to scan and read the entire area in terms of cost and reading time, it is useful to determine whether reading is completed by counting changes in density. On the other hand, the RS flip-flop 15 is provided to determine whether reading of the original density has been completed. This flip-flop 15
is set by a signal that starts scanning the original for reading the density of the original, and is set by the output signal of the count number discrimination circuit 13 when the contents of the counter 12 reach the set number N. Therefore, if there are fewer than M changes in the density of the original, the flip-flop 15 is not reset, and it is determined that the density information of the original cannot be read. flip flop 15
An AND circuit 16 performs an AND operation between the output signal of the copying machine and a signal generated after the scanning of the original for reading the density of the original. The display device that is being used lights up to display that the document density could not be read, alerting the user that copying under optimal process conditions is not possible. In this state, the start of the copy cycle may be stopped, the original is placed in a different position, and the density of the original is read again. However, in this example, the output signal of the AND circuit 16 opens the analog switch 17, and the analog switch 18 Close.
Therefore, a preset voltage from the preset circuit 19 is output instead of the output signal of the inverting circuit 10, and this voltage controls the parameters of the copying process. Therefore, when the original density cannot be read, the parameters of the copying process are controlled by an abnormal signal from the inverting circuit 10, and instead, the output of the preset circuit 19 is used to set the conditions under which an averagely good image can be obtained for a general original. controls the parameters of the replication process.

As described above, according to the present invention, if the density of the original cannot be read, it is determined and displayed, so that the user can be alerted and take appropriate measures such as changing the way the original is placed. can be set. Furthermore, if the density of the original cannot be read, abnormal control of the copying process can be prevented by controlling the copying process using predetermined information instead of original density information.

[Brief explanation of drawings]

1 and 2 are diagrams for explaining the present invention, and FIG. 3 is a block diagram showing one embodiment of the present invention. 15...Flip-flop, 16...AND circuit.

Claims (1)

[Claims] 1. Prior to exposing the original image to the photoreceptor, the original is scanned, the density of the original is detected by a density detection means, and the copying process is performed based on the maximum or minimum density of the original. A control device for a copying machine that automatically controls a copying machine, comprising: a waveform shaping means for shaping a density signal of a document detected by the density detection means; and a counting means for counting the number of rises or falls of the density signal. , when the number counted by the counting means reaches a predetermined first setting number and a second setting number larger than the first setting number at the end of scanning the original, the first setting is The copying process is controlled based on the maximum density or minimum density of the document detected during the period from when the number is reached to when the second set number is reached, and the number counted by the counting means is set to a predetermined value. 1. A control device for a copying machine, comprising: control means for displaying that the document density cannot be read when the second set number has not been reached. 2. When the number counted by the counting means does not reach a predetermined first set number and a second set number, the control means displays that the density of the document could not be read, and also displays a preset number. 2. The copying machine control device according to claim 1, wherein the copying machine control device controls the copying process based on set values set by the copying machine.