1. Discussion of the Related Art
To achieve high copying speed and high copy quality, an electrophotographic copying machine is frequently used in combination with an automatic document feeder, a sorter for receiving different sets of copies, and the like. Such a systematized copying machine saves much labor.
Where a set of originals are copied to produce a plurality of copies of each original, a sorter is used with the copying machine to sort the copies for each set of originals. In such a case, the copying machine produces a necessary number of copies in the order of the originals supplied, and feeds them to receptacles of the sorter. Accordingly, a user cannot know whether or not the copies are correct until the copying machine completes making a plurality of copies of each original. In the case of a large number of originals and a great number of copies of each original, if an incorrect original is mistakenly contained in the set of originals or the set of originals are stacked in an erroneous order, all of the copies of the set of originals must be verified and correctly arranged. The verification and the arrangement consume much time.
In a copying machine with a finisher in addition to the sorter, to staple the sorted copied documents, if the stapled documents contain an error, significant labor is needed to properly rearrange and staple them again.
To copy a great number of originals, an automatic document feeder (ADF) is typically used. In a copying machine using an ADF, a user can place a large number of originals into the ADF. The ADF automatically feeds documents onto the platen of the copying machine in successive order without aid from the user. The copying machine automatically copies the originals thus fed.
The ADF is not available for every type of original document because the ADF drive mechanism is constructed with roller-belt combinations. The ADF is available for sheet like original documents, except those that are too thin or too thick, and is unavailable for bound and stapled original documents.
To make copies of documents that are a combination of ADF-available documents and ADF-unavailable documents, troublesome and time-consuming manual work is required. For example, after the ADF-available original documents have been copied, all of the documents, both ADF-available and ADF-unavailable, must be manually combined. More specifically, to make copies of a combination of ADF-available and ADF-unavailable original documents, the copying machine with the ADF proceeds with the copying operation of those combined original documents, and encounters the ADF-unavailable originals. At this time, the copying operation of the copying machine in the ADF mode is interrupted. The ADF-unavailable original documents are then manually set on the platen glass sheet by sheet. After completion of copying the ADF unavailable original documents, the copying machine is operated again in the ADF mode.
As described above, in the case where a sorter is used with a copying machine, it is impossible to check the order of copies or copied documents as stacked or gathered until the copying of all of the original documents is completed. However, in the case where an ADF is used, and a sorter is not used, and a set of original documents are automatically fed onto the platen glass, a user can recognize an erroneous order of copies at the time of completing the first copy of the set of original documents. Disadvantageously, when a set of original documents is fed many times onto the platen using an ADF, the original documents may incur damage. In this respect, the use of the ADF is unsuitable for copying important original documents.
In the conventional electrophotographic copying machine, light as reflected on the surface of an original document is guided and imaged on a photoreceptor by means of a lens. Accordingly, the input of an image and the exposure of the photoreceptor to the light progresses concurrently. As a result, such conventional copying machines in which an image cannot be stored cannot include any features that enable the above described problems to be solved.
In order to overcome the above described problems, another type of copying machine has recently been developed, in which image data gathered by an image input section is electronically processed and stored. Such a copying machine of the data storage type reads once an image of an original document that is fed by the ADF, and stores the gathered image data into the data storage unit. When a specific number of copies of the original document is required later, the copying machine reads the image data out of the storage unit and produces that required number of copies. Thus, this type of data storage type copying machine can exercise a function equivalent to the repetitive feeding of an original document into the platen, by using the data storage unit, without actually repetitively feeding the original document.
FIG. 2 is a block diagram showing an electrophotographic digital copying machine capable of electronically processing image data. In the illustrated digital copying machine, an image input terminal (IIT) 20 reads an image of an original document by using a CCD line sensor, and converts into a digital image signal an analog video signal generated by the CCD sensor. An image processing system (IPS) 21 executes signal correction functions and the like. A compressor compresses a data. The data thus compressed is stored in a data storage unit 22 such as a hard disk (HD).
An image output terminal (IOT) 23 reads a data after decompressing the data stored in the storage unit 22 and controls the turning on and off of a light source, such as a laser, according to the data, to thereby form pixels on a photoreceptor. In this manner, the image of the original document is reproduced.
In the digital electrophotographic copying machine with a data storage unit, such as the storage unit 22, the image data is read out of the storage unit, and various types of editing operations may be applied to the image data. Such copying machines may also include a system for compressing the image data for storage There are many systems for compressing the image data. For example, a data compressing system, such as MH, MR, MMR and so on, based on a data compressing algorithm as regulated by the international organization, CCITT (Consultative Committee of International Telegraph and Telephone), is widely employed for facsimile systems.
In the CCITT data compressing algorithm, the image data is encoded according to a predetermined pattern of run-lengths of pixels. The algorithm is an effective means for encoding binary data of black and white such as occurs in a facsimile system. In the case of encoding image data, the data compressing speed and hence the data compressing rate varies with the nature of the image data.
For image data such as is processed by a facsimile system where the image reading speed is not fast, and the resolution of the reading of an image is low, e.g., 200 dpi at most, the variation of the data compressing speed, or the compressing rate, has little influence on the performance of data transmission and data processing.
In an electrophotographic digital copying machine, however, the image resolution is very high, e.g., approximately 400-600 dpi and the image is read at a much higher speed than in the facsimile system and at a much higher density than in the facsimile system. Further, a large amount of image data is processed by the copying machine. Since the data compressing speed varies, the inputting of the image data derived from the image input terminal is asynchronous with the operation of the image output terminal which operates at a fixed speed, such as a xerographic unit. Further, in the case where a compressor is integrally formed with a decompressor, it is impossible to operate the compression and the decompression at the same time. To accommodate this asynchronous operation, the electrophotographic copying machine containing a compressor and a decompressor stores all of the compressed image data in a data storage unit, and the decompressor decompresses previously stored data to enable output of reproduced images. For this reason, the image input terminal and the image output terminal are operable at high speed. However, the operation speed of an overall system of the copying machine is at a slow speed because of the asynchronous nature of the compression, image storage, image retrieval and decompression processes.