主题：如何理解增益的概念？

原文由 bluefleet 发表:
在AFM中主要有integral gain and proportional gain 这两个增益的概念应该如何去理解？

这两个参数在调节AFM图像质量是非常重要，这是控制反馈回路的两个参数，具体的物理含义比较复杂，应该是修正误差的两个系数，在各个厂家的说明书里，都能够看到这样的文字，尽可能的调大这两个参数，直到没有oscillation为止。可以这样理解，这是两个控制反馈速度的参数，如果这两个参数不够大，反馈速度就不能跟上扫描速度，高度图像就会出现拖尾的现象，而此时defelection（也称为误差像)像会非常清晰，因为反馈速度和扫描速度相差越大，误差就越大。这是个人理解，可能不对，欢迎讨论！可以直接询问厂家技术人员！谢谢！

integral gain and proportional gain 这两个值再调节时，是前者大于后者还是相反，我怎么看的资料中两种观点都存在呀，到底哪个正确呀

原文由 bluefleet 发表:
integral gain and proportional gain 这两个值再调节时，是前者大于后者还是相反，我怎么看的资料中两种观点都存在呀，到底哪个正确呀

当然不会是相反，实际经验最重要。不同厂家的仪器定义稍有不一样，但调节方法都是一样的，尽可能大（不是最大哦）。前者大还是后者大都没有关系，关键是看图像来来调节参数。

一个是积分增益，一个是比例增益。

原文由 hansyangts 发表:
一个是积分增益，一个是比例增益。

原文由 bluefleet 发表:
在AFM中主要有integral gain and proportional gain 这两个增益的概念应该如何去理解？

从我的个人经验来看，在一定程度上增加积分增益是可以改善图像质量的，而比例增益似乎没有什么效果。不管怎样，根据图像来调节是没有错的。

Thiis is right "从我的个人经验来看，在一定程度上增加积分增益是可以改善图像质量的，而比例增益似乎没有什么效果。不管怎样，根据图像来调节是没有错的。"

The gain value is for tip pixel Z height reference. If Gain value is high, the scanner will lift tip higher for next pixel and then down the tip for signal feedback (Deflection setting for contact mode, differentation for Tapping mode). So you can image

If Gain is too big, the scanner will lift too high for next pixel, when system hope to make feedback reasonably within pixel staying time (calaculted by scan rate and pixel numbers of a scan line-trace and retrace), this will make scanner unstable and generate oscillation.

If Gain is too slow, it is dangerous for tip to scratch surface becasue tip is lifted not high enough.

So gain must be setted reasonably. Basically integral gain dominate the feedback. If I Gain is in reasonable range, P Gain will not affect feedback too much. So P gain can be setted as I gain value.

You can use scope mode to check the feedback gain is reasonable, otherwise sometimes the wrong initial gain will wear tip. D3100 software also has a special engage auto gain adjutment. But no so many people can use it.The right manual operation way is

(1) Use reasonable inintial gain before engaging. The smoot surface use small gain. The rough surface use higher gain.This depend on on your surface feature.

(2) Ususally, use 1 um scan size for engaging. After engage, turn off slow scan axis and open scope mode.

(3) To reduce amplitude set point to make trace and retrace stable. It mean keep reduing set point will not change trace/retrace curve on scope mode image. This mean it is right amplitude set point for this scan line. If your surface is uniform surface, set point willbe use for whole image. If your surface has some special feature, such as bump or trench, you need to find a scan line cover these feature for set point adjustment. Otherwise the the set point and later gain value can not be used for whole image. Basically, SPM system is not so smart to change gain value automatically. If someone say yes, it is just for well know feature.

(4) After amplitude set point is ok. Adjust I gain from initial value. If trace and retrace scope is with oscillation, it mean the gain is too high. Please reduce I gain value. If there is no oscillation, you can increase I Gain value to see oscillation and then reduce I gain a little without oscillation. Then you will see trace and retrace will overlap perfectly. At least you can see trace and retrace is with sampe shape becasue sometimes retrace and retrace is not on perfect timing difference which can be adjust from scanner calibration value tunning.

(5) To let P gain value as I Gain.

Hope this can help you a little.

Thanks

应该是前者大于后者的，P gain是不能大于I gain的二分之一的。

比例增益是为了及时地反映控制系统的偏差信号，一但系统出现了偏
差，比例调节作用立即产生调节作用，使系统偏差快速向减小的趋势变化。当比例增益大的时候，PI控制器可以加快调节，但是过大的比例增益会使调节过程出现较大的超调量，从而降低系统的稳定性，在某些严重的情况下，甚至可能造成系统不稳定。
    积分作用的引入是为了使系统消除稳态误差，提高系统的无差度，以保证实现对设定值的无静差跟踪。
    具体这两个参数的大小关系，应该和不同型号的仪器是有关的，因为不同厂家不同型号的产品在控制器的实现方法上是有区别的。一般而言，先调节积分增益，直到产生震荡，然后减小积分增益，使振荡消除，这时候的值就是最合适的。比例增益一般要比积分增益大些（与工作模式也有关系）。就DI的SPM而言，比例增益为积分增益的1.2倍左右。
    一些拙见，望达人指点.
 

Please do not care PID gain value difference too much becasue they are affected by scan rate, set point...Just make feedback stable with reasonable range. The web site http://www.tbcl.com.tw/Product/SPM/SPM.htm provide a AFM simulator. You can download program and check the relationship among setpoint, scan rate and Gain value.