Hiroyuki KAWANO^1*, Tatsuki OKAMOTO¹, Taku MATSUZAWA², Hajime NAKAJIMA¹, Junko MAKITA¹, Yoshitaka TOYODA¹, Tetsuo FUNAKURA¹, Takahito NAKANISHI², Tatsuya KUNIEDA², and Tadashi MINOBE²

¹Advanced Technology R&D Center, Mitsubishi Electric Corporation, Amagasaki, Hyogo 661-8661, Japan
²Communication Systems Center, Mitsubishi Electric Corporation, Amagasaki, Hyogo 661-8661, Japan

(Received August 9, 2012; Revised October 19, 2012; Accepted November 6, 2012)

We designed a compact and large depth of field image scanner targeted for auto document feeders (ADF) by using a compound eye system design with plural optical units in which the ray paths are folded by a reflective optics. Though we have previously proposed the principle concept, we advance the design using a free-form surface mirror to reduce the F-number for less illumination energy and to shrink its optical track width to 40 mm. We achieved large depth of field (DOF) of 1.2 mm, defined as a range exceeding 30% modulation transfer function (MTF) at 300 dpi, which is about twice as large as a conventional gradient index (GRIN) lens array contact image sensor (CIS). The aperture stop has a rectangular-shaped aperture, where one side length is as large as 4.0 mm for collecting much light, and another side length is as small as 1.88 mm for avoiding interference of folded ray paths.

Key words: copier, compound eye, scanner, free-form surface mirror, concave mirror, auto document feeder, folded reflective optics

^*E-mail address: Kawano.Hiroyuki@ap.MitsubishiElectric.co.jp