Design and Research on Touch
sensitive Image Measuring Instrument
with High Precision
Zhejiang Industry Polytechnic College, Shaoxing,
Huzhou Vocational and Technology College,
Zhejiang Industry Poly
sensitive monitor, system calibration, image detecting
A digital image detecting system that employs a touch
center is stated here.
use measuring software, its efficiency has been
greatly improved compared to the
manual image instrument.
ts basic structure and
measuring principle are presented first,
s interface and the calibration method,
and finally the fundamental principle of the two key algorithms for image detecting: sampling and
the rapid progress of computer, optical technology and image
the optical image
measuring system has been widely used to measure parts and to detect the size of products and
finished products in industries of machine, mold, and electron.
t has a precise result and an
intelligent procedure as well. Instruments
, and Yixin Suzhou are typical ones
into two types in general: the automatic and the manual.
he former is powerful
in which the detecting personnel can not only drive the motor to work but also program it to detect
t has a higher
cost and price because motor and motion control card are
employed, which are used in measurement laboratory. While the latter has a lower efficiency and
price because the working platform is needed to be moved b
y manpower and the measuring functions
are needed to be chosen by operating the mouse in the computer
which is suitable for
quantities of workpieces.
ased on the digital image processing
sensitive monitor as the interactive center.
he operator measures the workpiece by
choosing buttons on the screen after moving the working platform, and thus reducing the operation of
eanwhile, it has a higher effic
pen is used to do marking measurement
directly along the image border on the screen after choosing corresponding measurement button.
esides, it has a lower manufacturing cost because motor and motion control card are omitted.
suring accuracy is up to 5
m because of the automatic tracing
edge technologies of detecting
pixel, segmenting region, and of compensating precision.
urthermore, the features of being easy
to operate and having short operator
time make it fit for size detecting in production line.
Structure and Basic Principle
Figure 1 is
structural diagram of the touch
sensitive image measuring instrument. Figure 2 is
sensitive monitor 2. Movin
g slider in Direction Z 3 CCD 4. Microscope
s lens 5 Upper lamp source 6.
Column in Direction Z 7. Industrial computer 8. X
Y worktable 9. Lower lamp source 10. Granite platform
Figure 1. Structural Diagram of the Touch
sensitive Image Measuring Instr
As shown in Fig. 1, put the workpiece to be
on the platform and turn on the upper or the
lower lamp, the workpiece is imaged on the target surface of the CCD through the microscope
he optical signal is then converted into electrical
signal by CCD, and finally is
image acquisition card in computer, the digital signal then displays on the touch
he acquisition system has two lighting modes: upper light and backlight.
is composed of
bright LEDs that are assembled annularly at the lamp
s shell according to certain angle and
distribution density that are decided by the lens working distance and the illumination needed to
gather image by CCD; the latter is made up of one high
power LED that locates in the
he beam emerges in parallel from the lens, shining onto the workpiece through the
glass plate. The measurement error caused by
stem uses a zoom lens of 0.7X
4.5X from Guilin
an amplified factor of up to
an working distance of 90mm, an analog CCD camera from MINTRON with a target surface
size of 1/2 inch, an image acquisition card (from Tianmin) of Model SDK3000 t
hat has a frame rate of
40 frames/s and a
analytical pixel of 768
576, and works in PAL mode.
hen the system has an amplified factor of 4.5X, it has a minimum visual field of 2mm
is computed by:
(Where, dimX is the size in Direction X, n is the analytical pixel in Direction X, P is the resolution)
Figure 2. Real graph of the Touch
he measuring accuracy in single image is usually decided by the resolution image, but
by the grating ruler when measuring big size workpieces because the microscope has a narrow
ere, a grating ruler
e resolution of 1
m from Guiyang Xintian is employed to
improve its accuracy through a linear compensation by a glass line scale at the maximum optical
s reading is
the compensation standard.
hen the c
omputer obtains a steady and clear image, the user will measure it by operating the
s buttons on the touch
he measuring software will have
points group by technologies of tracing edge automatically, segmenting reg
and so on.
eometry sizes and parameters of circle, line segment, rectangle and gear are thus obtained
by substituting the corresponding fitting function according to the measurement needs.
Design the Software Interface
is a communication and interactive medium between user and computer.
ased on its response characteristic, buttons and interfaces are designed to be humanized and easy to
he basic interface is shown in Fig.3.
sers observe the wor
kpiece image from the image window
located in the left region of the
o enable the operator to recognize the workpiece
s characteristics, the window is designed
with a maximum
pixel of 768
576. A relevant
to play the
role better and to improve the measurement efficiency. When choosing the geometric
figure to be
in the interface, the operator draws a figure on the border of the image
hen it is convenient for t
he software to obtain the measurement result.
is, what you
see is what you draw.
he prompt message and measurement result is shown in the lower region of the
window, where users can operate according to the prompts and can see the results when finish
right corner is an X
that exhibits the
values got from
the grating ruler.
sers can do a contrastive measurement by moving
worktable without the
accurate result. The lower region of the coordinate
buttons such as circle, line
segment, distance, angle, rectangle, gear
buttons are designed for an easy operating on
hand screen or by touch pen.
Figure 3. Operation Interface of the Software in the Touch
sensitive Image In
of the Detecting System
is an important job for machine vision in size detecting.
he detecting error will be caused
by CCD camera itself, or/and by coordinate conversion between image and space, or/and by external
n optical lens of 1X
4.5X (from Guilin
) that has small distortion is
to meet the requirements of liner
As shown in Fig.4, the image is
by a standard circle from the precise glass standard
emplate that has been checked by a high
accurate measuring instrument.
contour edge is obtained
, and then an accurate coordinate of boundary points and a circle center
are obtained by making
gradient analysis search for
eight neighborhood sub
instrument is calibrated accurately from the corresponding calibration coefficient by comparing
true value with
the pixel equivalence because the true diameter is known.
Figure 4 Image
s Calibration and
Glass Standard Detecting Template
Usually, whether the calibration circle is suitable or not has some influence on the precise of the
image measuring system. In the template, there are circles of diameters of 0.25mm, 0.5mm, 0.75mm,
, and 5mm. Ju
st choose the
of the image window.
Basic Principle of the Image Detecting
Two methods are used to measure geometric figure: sampling and marking.
he detecting procedure
is shown is
. Fig.6 is the
Figure 5 Flowchart of the Detecting
he sampling method is widely used, in which with the interval of 40ms, the computer draws cross
center lines in the center of the touch screen
ove the worktable, ali
gn the cross center
line to the points to be measured, and press the confirmed button in the software
computer draws a detection line of rectangle array based on the center of the starting point that will be
made an accurate eight nei
ghborhood search. Seek the gradient of the gray value for the adjacent
points in all directions, and finally compute its extreme value.
osition of the
value is just the
of the optimal boundary is obta
ined, the world
coordinate is obtained through coordinate transformation. Move the other points, press the
conformed button to repeat the procedure above to record the coordinate.
ubstitute the coordinate
points into the image
computing function and get
the geometry size.
he drawing method is mainly used to measure a complete geometry image in sight.
function button on the touch screen, and draw a corresponding shape along the border of the image by
he computer will draw a rectangle d
etection array for each point based on the drawn
border and search for an optical boundary point.
fter the world coordinate is transformed and all the
points is detected, substitute the points into the computing function for fitting (such as least square
To transform world
for the boundary point
o search from the center of the
o draw a detection line
the center of the starting point
o obtain an optimal border through detection
method, linear regression method [6
), by which, the relevant geometry size and parameter of line
segment, rectangle, distance, and centroid are thus obtained.
Figure 5 Instrumentation Plans of Sampling and Drawing
ive image measuring instrument based on digital image processing integrates touch
screen technology, optical image technology, digital image technology, mechanical manufacturing
the measuring accuracy of up to 1um a
t the maximum
optical rate, it is an innovation base on the traditional image measurement instrument and
hen the instrument is exhibited in the Beijing International Machine Exhibition, dealers and users at
home and abroad show their ken intere
st. Judging from sales and users
tests, the instrument is of high
, and high efficiency.
urthermore, the self
developed software can
SPC statistical program for users, which results in a lower
cost and a
days to come, the main development approach lies to a better
service and a
and fast operation.
This work was finacially supported by Science and Technology Planning Projects, Zhejiang
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