Selecting the Correct Camera

Major items to be checked before introducing machine vision

机器视觉应用程序可以大致划分into four categories—quantity/count inspections, foreign matter/defect inspections, dimension inspections, and position inspections—with each type used in a variety of industries. This section introduces various tips for selecting a camera that appropriately suits the purpose.

Selecting the devices required for inspection

选择符合检查要求的正确设备。

Camera / Controller / Lighting / Lens / Monitor
Sensing and judgment

Perform testing on the actual target with the machine vision system.

Reference parts for OK and NG products
Inspection cycle time
Variety of inspection items
Selecting the installation location and procedure

Review the specific installation locations.

摩托/固定的目标
Environmental conditions, including ambient light and vibration
Controls for automation

查看机器视觉系统的I / O控件。

图像捕获时序/判断输出/ PLC控制/数据输出
On-site testing

Test the machine vision system on the actual production line.

Fine setup adjustment
Statistics
I/O control check
Understanding basic operations

Basic setup procedures to maintain stable inspection.

Setting tolerances / Sensitivity adjustment
更改检验设置/项目注册

The types of cameras used in machine vision can be broadly grouped into the categories below.
根据这些类别，选择为预期应用和目的提供最佳图像的相机类型。

（1）高分辨率类型（2）高速型（3）标准型（4）紧凑型每种类型都有颜色和单色版本可用。

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选择检查所需的仪器[相机选择]

步骤1：基于分辨率（高或标准分辨率）选择。

在视觉相机中使用的图像传感器（CCD或CMOS）是布置在网格中的小像素的聚集体。标准型图像传感器通常具有310000像素（640×480），而高分辨率类型可容纳2至2100万像素。应用要求将决定适合的相机类型。

作为一般规则，基于视野和像素分辨率的大小选择相机。视野的大小是在检查目标上捕获的区域，可以通过所使用的镜头来改变。像素分辨率意味着每个像素等于多少毫米，并且关系由以下等式表示。

像素分辨率= y方向（mm）中视野的大小（mm）÷传感器像素计数在y方向上

For an example of pixel resolution, 30 mm 1.18" field of view in the Y direction will be used. The image sensor types that will be used in this example are the 310000-pixel standard model (Y = 480 pixels) and the general-purpose 2-megapixel high-resolution model (Y = 1200 pixels).

[Pixel resolution of a 310000-pixel camera] = 30 mm 1.18" / 480 pixels = 0.063 mm 0.002"/pixel
[Pixel resolution of a 2-megapixel camera] = 30 mm 1.18" / 1200 pixels = 0.025 mm 0.001"/pixel

如果已知应用所需的像素分辨率，则可以使用相同的等式来计算相机将提供的视图近似场景。外观检验和尺寸检测是机器视觉的典型应用。当执行通过/失败判断时，考虑检测能力进行外观检查，并且考虑尺寸检查的尺寸容差。

The following general principles can be applied as reference for calculation:
Detection capability = 4 pixel area
Dimensional tolerance = ±5 pixels

Using the pixel resolution calculated above, the detection capability for appearance inspection can be obtained.
[Detection capability of a 310000-pixel camera] = 0.063 mm 0.002"/pixel × 4 pixel area = 0.25 mm 0.01" area
[Detection capability of a 2-megapixel camera] = 0.025 mm 0.001"/pixel × 4 pixel area = 0.1 mm 0.004" area

基于这些计算，如果检查需要检测到具有30mm 1.18的视场的外来颗粒，则需要分辨率为2mp或更高的视野。

Reference: Enlarged view of 0.5 mm 0.02" foreign particle in a 30 mm 1.18" field of view

310000 pixels / 2 megapixels [2 megapixel cameras can capture images that show fine changes in higher contrast.]

Point 1:

You can select a camera with the optimal number of pixels by considering pixel resolution as the criteria for pass/fail judgment.

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步骤2：基于颜色或单色型图像传感器选择

One common question when selecting a camera type is whether to use a color or monochrome type. Generally speaking, if the differences at the sensing points are detected based on hue, the color cameras may have an advantage. The following shows an example of using color processing to detect a yellow stain on a white base, which is not easily detectable by a monochrome camera.

(1)Image captured by a color camera (2)Color-processed image (3)Stain inspection contrast image / Image captured by a monochrome camera > In cases like this, when there is little difference in brightness, the contrast difference with the background is so slight that a monochrome camera is less likely to provide correct detection. Picture (2) shows that internally, the contrast between yellow and white is clearly detected with the color camera. Picture (3) shows a contrast image obtained by using the stain inspection tool. This shows that stable detection is available for actual inspections using color processing.

然而，单色相机确实具有优于颜色的一些优点。对于使用背光的尺寸测量，如下所示，单色相机是理想的，因为存在大的对比度变化。此外，由于彩色摄像机使用拜耳滤波器（其中每个像素取决于相邻像素以获得全色信息），它们通常比使用边缘的尺寸型测量的单色相机更低。

Dimension inspection of metal workpieces using backlight

第2点：

在选择图像传感器时，确定感测点是否具有色调变化或亮度变化！

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Step 3: Selecting based on image transfer speed (high-speed or standard models)

Cameras used in machine vision can have different image transfer speeds even when the pixel counts are the same. Using a 310000-pixel type as an example, standard models offer a transmission time of 16.0 ms while high-speed models can achieve a transmission time of 1.7 ms. Even higher speeds can be achieved via a partial capture function. High-speed cameras are not only effective for fast production lines, but they are advantageous for normal speed applications as there is more processing time available for image filtering and tools that can stabilize the inspection.

[ Appearance inspection of chips (7× speed + 310000 pixel monochrome camera) ] Inspections: Stain inspection of the molded parts / Dimension inspection / Position correction XYθ) | Trigger interval： 3 ms / Inspection capability： 19,980 items per minute [ Appearance inspection of caps (7× speed + 310000 pixel full color camera) ] Inspections: Print quality inspection / Position correction (XY) / Angle correction (360 degrees) | Trigger interval: 12 ms / Inspection capability：4,999 items per minute — Applications using high-speed cameras

Point 3:

Benefits of selecting a high-speed camera include stable processing in addition to faster inspection cycle time!

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Step 4: Selecting based on camera size (compact or standard models)

Compact cameras are reduced in size, but are equipped with the same specifications as larger-sized cameras. Standard and high-resolution (2MP) compact types are available in color or monochrome. Compact types are primarily selected to efficiently use limited installation space. Particularly in cases where machine vision is to be installed in the available space of an existing facility, it is beneficial to use compact cameras to fit in a limited area without changing the machinery.

Calculation of required installation space

As shown below, the installation space needed for a camera is the sum of A (WD: working distance, which is the distance between the tip of the lens and the workpiece), B (lens size), C (camera size), and D (cable space, including bends).

示例：使用带镜头的标准相机，焦距为6 mm 0.24“，和30mm 1.18的视野

Point 4:

Selecting compact cameras based on the known required installation space can prevent unnecessary changes to the production machine.

选择检查所需的设备：相机（摘要）

相机类型是要选择的键元以用于图像处理，以确保稳定检查。以下快速参考图表提供了可用的不同摄像机类型的摘要。

[步骤1]通过外观选择：像素如何满足所需的准确性？
[Step 2] Select by transmission speed: select high-speed type when you need high-speed or more stable processing.
[步骤3]按相机尺寸选择：安装空间有限时选择紧凑型。
[Step 4] Select by CCD type (color/monochrome): select a color camera when you want to recognize changes in hue.

【1】		21 million pixels	5 million pixels			2 million pixels
【1】		5104×4092	2432×2040.		2432×2050.	1600×1200.
【2】		109.9ms	27.6ms^{* 1} 50.3ms^{* 2}	29.0ms.^{* 1} 52.4ms^{* 2}	61.2ms	11.6ms^{* 1} 20.1ms^{* 2}	11.6ms^{* 1} 20.2ms^{* 2}	29.2ms	58.5ms
【3】		Standard	Standard		Standard	Standard		Standard	Standard	Standard/Compact *
【4】	Monochrome	CA-H2100M.	CA-HX500M.	-	CV-H500M	CA-HX200M	-	CV-H200M	CV-200M	CV-S200M
【4】	Color	CA-H2100C.	-	CA-HX500C.	CV-H500C	-	CA-HX200C	CV-H200C.	CV-200C	CV-S200C

【1】		310000 pixels～470000 pixels
		784×596	512×480	784×596	512×480	640×480
【2】		2.9ms^{* 1} 5.2ms.^{* 2}	1.7ms^{* 1} 2.8ms.^{* 2}	2.9ms^{* 1} 5.3ms.^{* 2}	1.7ms^{* 1} 2.9ms^{* 2}	4.7ms	16.0ms
【3】		Standard		Standard		Standard	Standard	Standard/Compact *
【4】	Monochrome	CA-HX048M.		-		CV-H035M	CV-035M	CV-S035M
	Color	-		CA-HX048C.		CV-H035C	CV-035C	CV-S035C

* 1 during use CV - X 400 series and CV - X 200 series + CA - EC 80 HX / EC 80 L * 2 When using CV - X 100 series or CV - X 200 series + CA - EC 80