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