JPS6117190B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a document reading device such as a facsimile device. In a facsimile machine, the image signal obtained by photoelectrically converting the written image on the document surface is transmitted via a telephone line, etc. In this case, in order to shorten the transmission time, the image signal is band-compressed before being transmitted. things are done. Therefore, the transmission time varies depending on the information amount of characters and images on the document surface, and even within one document, the transmission time varies depending on the portion thereof.
Therefore, the document reading section is required to perform irregular and intermittent reading in response to such irregularly changing transmission times. FIG. 1 is a diagram showing a document-conveying type document reading unit in which documents are conveyed in rolls, where 1 is the document, 2 is the document-conveying roller, 3 is a fluorescent lamp for illuminating the document, 4 is a lens, and 5 is a one-dimensional document. It is a solid-state image sensor. The calligraphy on the paper of manuscript 1 is captured by lens 4.
An image is formed on the light-receiving surface of the one-dimensional solid-state image sensor 5, and photoelectrically converted for each scanning line. At this time, the original 1 is intermittently conveyed for each scanning line in the direction of arrow X in the figure. In the case of a high-speed facsimile, the maximum value of the conveyance speed of the document 1 is selected to be 5 to 20 ms per scanning line, and a small pulse motor is usually used for the conveyance. In the case of the document reading section as shown in FIG. 1, the moment of inertia of the conveying roller 2, which is the load of the pulse motor (not shown), and the document 1 conveyed by it is very small, so the moment of inertia is 5 to 20 ms/min.
A linear document transport speed is possible, and an intermittent transport method as shown in FIG. 2 is used. In FIG. 2, A shows the moving state of the document, and B shows the timing of reading and scanning of the solid-state image sensor. The document reading section shown in FIG. 1 is configured to convey a single thin document 1 with a conveyance roller 2, and therefore cannot read a thick bookcase.
There is a reading section that can read thick bookcases and the like having a configuration as shown in FIG. In the case of FIG. 3, the original 1 is placed on a transparent original platen 6, and the optical block 9 consisting of a fluorescent lamp 3, a lens 4, a one-dimensional solid-state image sensor 5, and reflection mirrors 7 and 8 is pointed at the arrow X. By transporting in the direction of
Read and follow manuscript 1. However, the moment of inertia of the optical block 9 is large, for example, 2 to 3 kg.
cm ² , intermittent conveyance as shown in FIG. 2 is extremely difficult. Therefore, the optical block 9 is conveyed at a constant speed, the original 1 is read at a constant speed, the image signal is stored in a buffer memory with a capacity for one original, and then the transmission speed of the image signal is increased. A method is often adopted in which image signals are read out from the buffer memory accordingly. However, the capacity of the buffer memory in this case is several megabits if the image signal is to be stored as is, and approximately 1 megabit even if the image signal is band-compressed to reduce redundancy and then stored in the memory, which has the disadvantage of being expensive. be. This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and includes a small-capacity buffer memory that temporarily stores the image signal output from the document reading section, and documents are processed according to the free capacity of this buffer memory. An object of the present invention is to provide a document reading device that can significantly reduce the memory capacity of a buffer memory by controlling the document reading speed of a reading section. An embodiment of the present invention will be described below with reference to FIG. When reading the original 1 with the original reading device configured as shown in FIG. 3, a buffer memory 11 is arranged between the original reading section 10 and the band compression section 12 as shown in FIG. Now, it is assumed that the entire capacity of the buffer memory 11 is equal to N lines expressed in terms of the number of scanning lines. The document reading section 10 (corresponding to the optical block 9 in FIG. 3) reads the document 1 at a speed of vline/sec, and also reads the document 1 at the same speed buffer memory 1.
The band compression unit 12 writes buffer memory 1 sequentially to the vacant portion of buffer memory 1 at a speed of Vline/sec.
The image signals written in 1 are read out in the order in which they were written. Maximum speed of document reading v _n ,
Letting V _n be the maximum speed at which the band compression unit 12 reads the contents of the buffer memory, it is sufficient if v _n ≧V _n , but for the sake of simplicity, if v _n =V _n , the following equation holds true. V _n ≧v≧0 [1] V _n ≧V≧0 [2] Here, this document reading speed v corresponds to the transport speed of the optical block 9 of the document reading section in FIG. As mentioned above, the moment of inertia of is 2 to 3 kg cm ² . Therefore optical block 9
A sudden change in speed will cause the drive torque to become very large, the actual speed of the optical block 9 to deviate greatly from the speed of the drive motor due to the delay constant of the mechanical system, and the noise to become very large. Considering the above, it is difficult to realize this. Therefore, it is necessary to suppress the acceleration for reading the original to a value below a certain value, and now, when α _n is the absolute value of the maximum allowable acceleration for reading the original, the following equation holds true. |dv/dt|≦α _n [3] Also, the number of lines in the unwritten portion of the buffer memory 11 in FIG. 4 (the number of empty lines) is n.
Then, the rate of increase dn/dt in the number of empty lines in the buffer memory 11 can be expressed as the difference between the buffer memory reading speed V and the original reading speed v of the band compression section 12, and the following equation holds true. dn/dt=V-v [4] Under the conditions of these formulas [1] to [4], the document reading speed v is expressed as a function of the number n of empty lines in the buffer memory 11, and the function v=f( n)
Let us consider what kind of function N is required for the buffer memory 11 so that the number of lines N required by the buffer memory 11 can be reduced.
Assuming that this function v=f(n) is continuous with N≧n≧0 and satisfies v=0 when n=0 and v=V _n when n=N, [3] and [ 4] The following equation is obtained from the equation. |(V-v)dv/dn|≦α _n [5] (However, dn/dv≠0) Also, when v=V, equation [5] always holds true, so if v≠V, the following equation becomes can get. |dv/dn|≦α _n /|V−v| [6] In order to minimize the number N of line memories in the buffer memory 11, from FIG. 5, dv/dn>0, and dv/dn The higher the value, the better. On the other hand, dv/
The maximum value of dn is limited by equation [6], and the value on the right side of equation [6] changes depending on the buffer memory read speed of band compression section 12. Considering these conditions, it is considered that the number N of line memories in the buffer memory 11 can be minimized when the value of dv/dn is equal to the minimum value on the right side of equation [6], and the following equation is obtained. dv/dn=[α _n /|V−v| _nio [7] When this equation [7] is solved under the conditions of equations [1] and [2], the graph shown in FIG. 5 is obtained. That is, the function v=f(n) satisfies v = V _n −√ _n ² −2 _n when V _n /2≧v≧0, and V _n ≧v>
When V _n /2

The curve satisfies [Formula]. Further, when the document reading speed is equal to the buffer memory reading speed of the band compression section 12, that is, when v=V _n, the number of empty lines in the buffer memory takes a maximum value, and n=3V _n ² /4α _n .
Therefore, the required number of line memories N for the buffer memory is:
3V _n ² /4α _n . Next, based on this result, an example of how large the number N of line memories in the buffer memory 11 is calculated is calculated. The buffer memory read speed V _n of the band compression unit 12 is set to 100 line/sec, and the maximum value α _n of the transport acceleration of the optical block 9 is set to 200 line/sec.
^c2 , the value of the number N of line memories in the buffer memory 11 is 38 lines. Number of bits per line
Converting this to the number of bits as 2K bits,
With 76K bits, the capacity is less than 1/10 compared to the conventional case of preparing buffer memory for one document. In this way, by expressing the document reading speed v as a function of the empty line capacity n of the buffer memory as shown in FIG. 5, the capacity of the buffer memory 11 can be reduced. Approximation using a straight line as shown in FIG. 6 may make it easier to control the document feeding speed. Number of lines of buffer memory capacity in this case N
is calculated as V _n ² /α _n , which requires a buffer memory capacity 4/3 times that of the case shown in FIG. FIG. 7 shows the relationship between the moving state of a document and its reading timing according to an embodiment of the present invention. In the above embodiment, a case has been described in which an optical block 9 having a large moment of inertia is conveyed, as in the document reading device shown in FIG. The present invention can also be applied to a reading device that reads an original because the moment of inertia of the transparent original table 6 is usually large. Furthermore, even if the reading device has a relatively small moment of inertia of the document transport unit as shown in Fig. 1, if the maximum values of the image signal transmission speed and the document reading speed are extremely high, the document It is difficult to carry out intermittent conveyance using the method shown in FIG. 2 due to torque, noise, etc., and the present invention can also be applied to this case. Furthermore, in the embodiment shown in FIG.
1 is provided, but a configuration as shown in FIG. 8 is also possible. In the case of Figure 8, buffer memory 1
1 is not placed between the document reading unit 10 and the band compression unit 12, but is placed between the band compression unit 12 and the modulator 13 for modulating the band compressed image signal and sending it out to the transmission path, and is a buffer memory. The reading speed of the document reading section 10 is controlled according to the state of the free space of the document reading section 11. In this case, assuming that the processing speed of the band compression section 12 is configured to follow the maximum reading speed of the document reading section 10, the document reading speed in the case of FIG. 8 is different from that in the case of FIG. It may be determined using the function shown in FIG. 5 or 6 in exactly the same manner as in FIG. Also, buffer memory 1 in the case of Fig. 8
Since the image signal stored in 1 has its redundancy reduced by the band compression section 12, the capacity of the buffer memory 11 may be smaller than that in the case of FIG. 3, and usually 1/5 to 1/10. As described above, according to the present invention, a buffer memory is provided for temporarily storing image signals output from the document reading section, and the document reading speed of the document reading section is controlled according to the free capacity of this buffer memory. When a document and its document reading unit (optical system) are moved relative to each other, even if the movement is accompanied by a relatively large moment of inertia, there is an effect that the memory capacity of the buffer memory can be significantly reduced.

[Brief explanation of the drawing]

1 and 3 are block diagrams showing the configuration of a general document reading section, FIG. 2 is a timing chart showing the timing of document reading in a conventional document reading device, and FIG. 4 is a diagram showing the timing of document reading in a conventional document reading device. A block diagram of a document reading device according to an embodiment, FIGS. 5 and 6 are operation characteristic diagrams for explaining the operation shown in FIG. 4, and FIG. A timing chart showing the relationship, and FIG. 8 is a block diagram of a document reading device based on another embodiment of the present invention. In the figure, 1...Original, 2...Roller, 3...Fluorescent lamp, 4...Lens, 5...One-dimensional solid-state image sensor, 6...Transparent document table, 7 and 8...Reflection mirror, 9 . . . optical block, 10 . . . document reading section, 11 . . . buffer memory, 12 . . . band compression section, 13 . . . modulation section. In addition, in the figures, the same reference numerals indicate corresponding parts.

Claims (1)

[Scope of Claims] 1. In a document reading device that sequentially reads the document drawings by relatively moving a document and an optical system of a document reading section that photoelectrically converts the document document, an image output from the document reading section is provided. A buffer memory for temporarily storing signals, and a processing circuit for reading and processing image signals stored in this buffer memory at a required speed are provided, and the document reading speed v of the document reading unit is set to Vm/2≧ in accordance with the free memory capacity of the buffer memory. When v≧0, v=Vm−√ ² −2 When Vm≧v≧Vm/2, [Formula] (where, Vm: Maximum value of image signal readout speed of the processing circuit n: Free space of buffer memory αm: A document reading device characterized in that the document reading speed is controlled by the maximum permissible acceleration of the document reading speed. 2. The document reading device according to claim 1, wherein the document reading speed v is a linear function v=Vm ² /αm·n of the free capacity n of the buffer memory.