6A-5-1
Focal Plane Image Assembly of Subpixel
Si-Dong Zhong Tian chan Mei
Department of Optical Instrument, Wuhan Technical University of Surveying and Mapping,
Luoyu Road 39, 430070 Wuhan, Hubei, P.R.China
E-mail: hvztó dns.WTUSM.edu.cn
Deren Li
LIESMARS, Wuhan Technical University of Surveying and Mapping, China
KEY WORDS : CCD, Focal plane, Scanning assembly, Moiré fringe, Judging accuracy.
ABSTRACT
The assembly technique of CCD is put forward to meet the requirement of optical device with large field of view and
high resolution. At present, the assembly technique of CCD is to be improved in such aspects as assembly precision
and total pixel numbers. Based on the principle of human vision, a new assembly technique of CCD, focal plane
scanning assembly, is presented in this paper. This paper describes the scanning assembly principle and construction
of scanning assembly sample. The factors that affect assembly accuracy are analyzed. There are two steps in CCD
focal plane scanning assembly. The first is rough assembly, there is a special pattern target in the field of view, and
the target is made up of many white cross strips. When the assembly is completed, it can be distinguished assembly
error less than 1/2 pixel. The second is accurate assembly, the special pattern target be exchanged Ronchi grating,
after assembly is completed by using Moiré fringes, it can be distinguished assembly error less than 1/20 pixel. In this
paper, the moiré fringe is introduced in judging assembly accuracy directly and accurately. The equation for optical
transmission characteristics of CCD Moiré fringes is presented. The measurement of Moiré fringes can be completed
when some conditions are satisfied. 2D-assembly error can be obtained by using digital correlation filtering technique.
Finally, the result of focal plane scanning assembly is presented. The result is in good accordance with theory. These
papers open a path for CCD assembly and judge assembly accuracy and lay a foundation for further research work.
1 INTRODUCTION
The measure system with CCD receiver has high
demand on view field, resolution and in real time. The
present CCD camera can’t meet all above needs
simultaneously. While the single chip CCD meets the
needs of speed, its total number of pixels is less than 10 7 ,
and hard to reach high accuracy. On the other side when
it has enough number of pixels to meet the needs of
accuracy, it runs into the problem of time lag. The
assembly technique of CCD is an effect way to solve the
problem. In the early 80’s, the air force of United States
has completed focal plane assembly of line array of
CCD. Then assembly of CCD develop from line array to
area array [Lawrence, 1998]. The Chinese researcher
has performed relevant study, finishing CCD assembly
from 2 chips to 4,10 chips [Shen, 1991], [Ma, 1994],
[Chen, 1992]. The assembly error is less than 1.5pm. All
the research work has overcome the difficulty to meet
the practical needs of large view field, high resolution
and real-time on some extent. However, at present, the
assembly error is limited to about 1/5 pixel. How to
improve the assembly accuracy to a high level is what
this paper concerned.
2 HARDWARE SYSTEM
The hardware system (Fig. 1) is composed of optical lens,
CCD image sensor, x, y direction guide track, step
motor and position measure system on both direction (x
& y). When the system starts to run, the lens keeps still
while the work stage can move in x, y direction. The
slip board of guide track was driven by step motor with
screw transmission. Then CCD is driven to the
instructed position. The position accuracy is guaranteed
by displacement sensor. The whole system is open loop
control system. The major function parameter and
logical control chart is as followed as Table 1 and Figure
2.
Fig.l Experiment system
