This invention relates to a beam scanning copying apparatus for reading out document information by a scanning laser beam and recording this information onto a recording medium. More particularly, the invention relates to a copying apparatus having a transmitting and receiving function, in addition to a simple reproduction function, for use in a facsimile system apparatus.
Generally, a copying apparatus has a function to reproduce documents locally while a facsimile apparatus has a function to reproduce document information sent by electrical signals from a remote apparatus. The prior art contains systems which combine both a copying apparatus function with a facsimile function; see for example, Japanese patent disclosure No. 54-31217 dated Mar. 18, 1979. A prior art copying method is described in Japanese patent disclosure No. 53-58245. In this disclosure a rotating light deflector having six light reflecting faces is irradiated by two laser beams. One beam irradiates one face of the deflector and is thereby reflected onto the document to be read. The other beam irradiates the other face and is reflected onto a recording medium. Consequently, scanning of the document and scanning of the recording medium occur simultaneously by the rotation of the light deflector. Light from the document is concentrated and converted into electrical signals for modulating the other laser beam scanning the recording medium. As a result, a reproduction image is obtained on the recording medium simultaneously with the scanning of the document.
A prior art high speed facsimile apparatus is described in Japanese patent disclosure No. 53-89311 for transmitting and receiving document images. In this disclosure, two laser beams, formed by splitting a single beam, irradiate two faces of a rotating mirror. The beam reflected from one face is directed onto a document, light reflected from the document is converted into signals for facsimile transmission to a remote apparatus. The beam reflected from the other face is modulated by a signal received from the remote apparatus; this modulated beam is then directed onto a recording medium to obtain the received document image.
If scanning is effected using a light deflector as described in the above-identified Japanese patent disclosures, the obtained picture signals have a higher resolution then used by other methods; for example, the signals obtained by solid scanning devices (i.e., diode arrays). However, the signals produced by a constantly rotating light deflector have inherent timing distortion. That is, since documents are generally placed in a planar position, the distance between the light deflector and the face of the document varies depending upon the scanned positions. Consequently, the scanning speed of the reflected light along the document will change. The electrical signals produced by the light reflected from the document will, likewise, be subject to this variation. If these signals are then transmitted to a remote copier as part of the facsimile system which does not also employ a rotating light deflector, the image produced at the remote copier will also be distorted. If, however, the remote receiving unit also employs a rotating deflector, the inherent distortion in such a receiving unit will cancel the signal distortion which modulates the light beam in the receiving unit. Because of the difficulty of matching rotating type deflector systems at both the receiving and transmitting end, it is desirable to eliminate timing distortion whenever possible.