尺寸检查的基础知识
尺寸/边缘检测
使用边缘检测的尺寸测量是最近的图像传感器应用的趋势。在使用图像传感器的尺寸检查中，可以通过在两个维度中捕获物体并检测边缘来测量位置，宽度，角度。这里，根据处理过程解释边缘检测原理。
理解原理使得可以将检测设置为最佳状态。此外，我们使用边缘引入代表性检查示例，并解释如何选择用于检测稳定的预处理滤波器。
Principle of Edge Detection
An edge is a border that separates a bright area from a dark area within an image. To detect an edge this border of different shades must be processed. Edges can be obtained through the following four process steps.
（1）执行投影处理
Projection processing scans the image vertically to obtain the average intensity of each projection line. The average intensity waveform of each line is called the projected waveform.
投影处理是什么？
投影处理用于获得在测量区域内噪声引起的平均强度并减少假检测。
（2）执行差分处理
当色调差异更明显时，获得较大的偏差值。
什么是差分处理？
差分处理消除了测量区域内绝对强度值的变化造成的影响。
（示例）如果阴影没有变化，则绝对强度值为“0”。如果从白色（255）变为黑色（0），则变化为-255。
（3）最大偏差值始终需要100％
为了在实际生产方案中稳定边缘，执行内部补偿，以便最大偏差值始终保持在100％。然后，从差分波形的峰值点确定边缘位置，在那里它超过预设边缘灵敏度（％）。这种边缘归一化方法可确保始终检测到边缘的峰值点，稳定易于频繁变化照明的图像检查。
（4）执行子像素处理
Focus on the adjacent three pixels of the maximum differential waveform and perform interpolation calculations. Measure the edge position in units down to 1/100 of a pixel (sub-pixel processing).
Examples of inspection using edge detection
边缘检测包括下面所示的许多工具。本节介绍了常用工具的一些示例。
示例1.使用边缘位置检查
By setting an edge position window at several places, the X and Y coordinates of the target object are measured.
示例2.使用边缘宽度工具检查
By using the “outer diameter” feature of the edge width tool, the width of the metal plate and the diameter of the hole in the X and Y directions can be measured.
Example 3. Inspections using the circumference area of the profile position
By setting the measurement area as “circumference,” the angle (phase) of the notch is measured.
Example 4. Inspections using the profile width
Use the "trend edge width" tool to scan the internal diameter and evaluate the degree of flatness.
个人资料位置工具
The profile position tool combines a group of narrow edge windows to detect the edge position of each point. Since all of the data is collected within one inspection tool, it becomes easy to detect minute fluctuations by calculating minimum, maximum, and average values over the entire part.
Detection principle
By moving the narrow area segments in small pitches, the edge width and edge position of each point is detected.
- 如果需要高精度的位置检测，
- 减少分段大小。
- 如果需要高精度的位置检测，
- Reduce the shift width of the segment.
- 如果需要高精度的位置检测，
- The direction towards which the segment is moved.
预处理过滤器进一步稳定边缘检测
在边缘检测中，抑制边缘的变化非常重要。“中位数”和“平均”过滤器在稳定边缘检测时有效。本节介绍了这些预处理过滤器的特性和有效选择方法。
Original image
Averaging
Averaging filter with 3 × 3 pixels. This filter is effective in reducing the influence of noise components.
Median
中位过滤器，带3×3像素。该滤波器降低了噪声分量的影响而不会模糊图像边缘。
如何优化预处理过滤器
Though “median” and “averaging” generally lead to the stabilization of edges, it is difficult to know which is effective for the target object. This section introduces a method of statistically evaluating the variations of measurements when these filters are used.
CV-X系列(CV2000或更高版本)是装备a statistical analysis function. This function records the measured data internally and performs statistical analysis simultaneously.
By repetitively measuring the static target with “no filter,” “median,” “averaging,” “median + averaging,” and “averaging + medial” the optimum filter can be selected.
概括
注意以下四个点以有效利用具有图像传感器的边缘工具：
- 通过了解边缘检测原理，可以轻松地进行适当的调整。
- 通过了解不同边缘工具的能力，精确检查的可能性显着提高。
- By referencing typical detection examples, accurate detection can be implemented quickly.
- By selecting an optimum pre-processing filter, detection can be stabilized.
The next topic is the principle and applications of position measurement (search mode). Let's look at the principle and applications of search mode, which is not only used for the positioning of parts in assembly processes, but also used as a position correction function.
