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视觉行业的初学者,甚至是做了1-2年的销售也许还会困惑这样的事情,就是在拿到检测要求后,不知道根据图纸上的公差,应该选用多少万像素的相机。同时还不明确为什么要三个类似的专有名词来描述同一个事情。
这一期内容就是为了讲明白这一件事情:分辨率,精度,公差的关系。从而指导相机的选型。
分辨率(Resolution)
比如我要看的产品大小是30mm*10mm,使用200万像素(1600pixel*1200pixel)的相机。因为产品是长条形,为了把产品都放入到视野内,我们计算分辨率的时候要考虑长边对应,此时分辨率为:
精度(Accuracy)
精度的单位是mm。根据产品表面和照明状况的不同,我们可以通过放大图像观察辨别稳定像素的个数,从而得出精度。如果条件不允许实际测试观察,一般的规律是,如果使用正面打光,有效像素为1个,使用背光,有效像素为0.5个。
这个例子我们取1 Pixel,得到精度为0.019mm约等于0.02mm。
公差(Tolerance)
一般情况下,精度和公差的对应关系如下:
对一个项目来讲,我们是先从图纸上读到公差的要求。然后再根据上述关系,反推得出我们需要多少像素的相机。我这里有一个简单的表格,输入视野,可以自动算出不同相机的精度矩阵,方便快速选型。哪位如果想要,可以给我发邮件免费索取。