6A-5-2
Table 1
CCD image sensor :
Control System:
Image Device
1/2 interline transfer CCD
Maximum responsive frequency
750 KHZ
Image Area
2.94mm x 6.45 mm
Step Equivalent
0.2 y m
Picture Elements
795(E1) x 596(V)z
Displacement
Resolution
600 TV Line horizontal
Linear range
+ 20mm
Electronic Shutter
1/125—1/10000 sec
Linearity
0.05
Grama Correction
r=0.25 0.45 1
Resolution
0.5 u m
Grain Control
AGC on/off
Lens:
Vertical frequency
50 HZ
Focal
50mm
S/N Ratio
Better than 48 dB
D/f
1/2
Initializatio
Input order
Select direction
Run x motor
Run y motor
Give direction
Input steps
Output positions
End
Fig.2 Control procession
making one pixel assembly error.
3 PRINCIPLE OF ASSEMBLY AND ACCURACY
JUDGING 3.1 Rough Assembly and Judging
Before the system complete the assembly process, we
first perform assembly error correction. Two steps
complete this calibration. The first step is rough
assembly. That is to control the assembly error on x, y
direction less than 1/2 pixel. Although the displacement
sensor of x, y direction can have this resolution, the
sensor can’t detect the assembly error resulted from
guide track linear error and vertical error between x, y
direction. The second step is accurate assembly process.
That is to precise measuring the residual error after
rough assembly. This is done through the moiré pattern
generated from CCD moiré effect [Zhong 1997]. Since
the residual error is detected, we can adjust the number
of steps of step motor to correct the residual error and
record the data of displacement sensor at each assembly
position: So far, the process of assembly is finished. The
reason we limit the rough assembly error smaller than
1/2 pixel is to prevent the assembly process from
The whole target is separated into four areas(Fig.3),
named 1,2,3,4 related to the four imaging areas in the
CCD assembly process. We set area 1 as reference and
adjust the position of CCD according to the large
receiver until the assembly error is small enough. We
take area 1,2 as example to explain how to adjust the
error. When the error is not corrected the result is shown
as Fig.4. It indicates that CCD assembly has errors on x,
y direction. At first we adjust the assembly error on y
direction to make strips on the whole image align on y
direction (Fig.5). At this time, CCD assembly error on y
direction is small enough to meet the need of rough
assembly. There still remains assembly error on x
direction, we adjust the position of CCD until the image
after assembly is as Fig.6. In the same way, we set area
2,3 as reference respectively to perform the CCD
assembly of area2-3 and area 3-4.
Fig.3
Fig.4
Fig.5
Fig.6
