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七郎 / Seven Liu

科学与艺术,恰如人生中的红颜知己。 本博内容保留所有权利.

 
 
 

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4.12.4 Reference servo requirements 参考伺服之要求  

2012-06-29 15:49:29|  分类: 读点英文 |  标签: |举报 |字号 订阅

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In order to analyze the performance of the servo a relation that is important to study is the maximum allowed track deviation before the servo starts having problems following the track. This relation is given by the transfer function from track to ephys, see Equation 4-3 below (and Figure 4.15):

为了分析伺服的性能,研究伺服与轨道偏差之间的关系,即在轨道跟踪过程中开始出现伺服问题之前可允许的最大轨道偏差是多少,具有重要意义。这个关系可用track与ephys两者的转换函数描述。请参考等式4-3(和图4-15):

Equation 4-3

等式4-3

The interesting part of the sensitivity function is the amplitude of 1+H(s), which is what the servo requirements of the BD Physical Specifications are based on, se Figure 4.18 below.

灵敏度函数中最值得关注的部分是1+H(s) 振幅,这是BD物理规格书中对伺服之要求的基础。请看下图。

The higher the gain, the better the controller will follow the track at the frequency in question. The red line represents the disc requirements. There is a limit on how much eccentricity or how much unroundness a disc is allowed to have. At low frequencies, a disc may deviate more from a perfect spiral than at high frequencies. The requirements of the servo, (and are represented by the grey area) have naturally to be higher than the disc requirements. The lower bound of the grey area ensures a minimum performance of the servo whereas the upper bound is for correlation purposes. As previously explained it is desired to be able to compare the results of different optical disc testers. If there is no upper limit, some drives may have significantly higher performance than others, yielding a poor correlation between the servo error signals of different drives. Obviously consumer drives are not subjected to these requirements giving the possibility to, for example, better attenuate low frequency disturbances such as eccentric and skewed discs.

讨论频率的时候,一般认为增益越高,控制器的轨道跟踪效果越好。红线是对盘片的要求。盘片的偏心和不圆度是有规格限制的,低频时,盘片轨道与理想螺旋线相比的偏差会比在高频状态下高。对驱动器伺服的要求,(如图中灰色区域所示)自然应该比对盘片的要求更高。灰色区域的下边界用以确保伺服的最低性能,而上边界亦有相关之目的。前面已经提过,不同的测试仪测试结果应具有可比性,如果没有上边界,会因有些驱动器的性能会太过出众,而使不同驱动器之间伺服误差信号的相关性很差。当然,消费用驱动器不受这个限制,也就是说,低频状态下降低干扰的能力越强越好。

Below 0[dB] (blue line), the servo is not longer attenuating but amplifying the track deviations. This is of course an unwanted behavior, which can be dealt with by reducing the gain of the servo at high frequencies.

在0dB以下(蓝色线),伺服机构不再消除干扰,而是放大轨道偏差。通过降低高频状态下的伺服增益当然也是不必要的。

 

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Key Words:

·bound 边界、范围;限制、束缚

·be subjected to 受到….

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