创建组件识别数据的方法.pdf - 第175页

175/178 IM-SMT-VSNDI C-0002 -000 For exam ple, if the brightnes s is distributed as shown in Figure 146 along the line b eing scanned, the leads c an be detected c orrectly with the difference in detection leve ls (thres…

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The top figure in the middle in

Figure 144

shows the result after compressing the image on the

left by 1 pixel. As shown in this example, if the gray area is compressed by 1 pixel, a section

consists of two or less pixels in the component is deleted. As multiple pixels can be

specified for compression, the section containing the multiple pixels (noise) is deleted.

Performing expansion processing following the compression processing produces an image

without the noise (See the top figure on the right in

Figure 144

Appendix 2. Detection level differences used to detect leads (threshold value)

This parameter is used when leads are being detected. For lead detection, scanning is

performed within the search range in order to separate the leads from the background.

During the scanning process, if there are any pixels that are brighter than the value specified

as the difference in detection level from the background density, those pixels are recognized

as leads. Consequently, setting a lower value for this parameter makes it possible to detected

dark leads. If the value is too low, however, the results are more easily affected by the noise.

Moreover, setting a larger value is more effective in terms of noise, but there is a greater

possibility of error in detecting the leads themselves.

The recognition conditions should be set in such a way that the illumination produces a

strong contrast between the background and the leads. In the figure below, the illumination

has been set to maximize the difference in levels between the lead section and the

background section. If the lighting is too dark, the brightness of the lead itself decreases,

and there will be no contrast. Conversely, if the lighting is too bright, the brightness of the

background increases, eliminating contrast between the background and the lead.

Figure 145

Brightness

With dark lighting

With appropriate

lighting

With bright lighting

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For example, if the brightness is distributed as shown in

Figure 146

along the line being

scanned, the leads can be detected correctly with the difference in detection levels (threshold

A), but with detection level difference B, reaction to the noise can be seen. With detection

level difference C, the leads cannot be detected at all.

Figure 146

Consequently, the largest possible value should be set as the detection level difference

in order not to detect the noise within a range in which there is no error in lead detection.

Normally, a value that is approximately half of the difference between the maximum

luminance and the background luminance is thought to be appropriate.

In a search for the appropriate value, the center value of the range where recognition is

performed successfully is obtained as the set value, while changing the combination of the

illumination level and the detection level difference.

However, as searches for the appropriate value are conducted only on one component,

disparities between components are not taken into consideration.

Appendix 3. Creating simple data in the special recognition modes

Some recognition modes provide modes called “special recognition modes”. These are used

to recognize components that cannot be recognized with the standard settings. In this case, a

special mode is also used for the component data settings.

All of the setting items can be entered in this mode, in other words, it is necessary to set all of

the required setting items manually. In order to minimize the manual work, the data can be

created using the standard procedure described below and then the recognition mode

changed in order to eliminate delays in creating the data.

For example, when the SOP data is created in a normal manner by using the Special 1

algorithm for SOP recognition, the following changes are made:

Alignment Group : Special component ( IC component)

Alignment Type : Special shape ( SOP)

Then the following are set in order to eliminate delays in creating the data:

Algorithm : Special 1

Base Alignment Type : SOP

The data for the lead length, Lead Width, Lead Pitch and reference lead position (Find Pos)

can be created automatically by entering the data as usual.

After that, the data set automatically is retained just as it is, and the correction is required to

be made only for the necessary items.

Detection level difference C

Detection level difference A

Detection level difference B

Background intensity

Brightness distribution on the scan line

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Appendix 4. Lead position check

Using the position where the lead tips should exist (the black dots at the lead tips in Figure

147) as the center, it checks whether the center of the actually detected lead tip is in the

allowable range or not.

In other words, this checks the offset between the actual lead tip position and the ideal

position that was determined from the component data, the component center that was

determined, and the tilt.

If the check range is 1.0 mm, this checks to see if the detected lead is within a range of +-1.0

mm.

Figure 147

Allowable range

Allowable range where the

lead

tip should be as its center