為了減少系統(tǒng)的早期失效，機(jī)床制造廠可以對(duì)控制元件進(jìn)行篩選，即使每臺(tái)元件在實(shí)際使用條件下連續(xù)工作一定次數(shù)，把失效產(chǎn)品排除，以減少裝到系統(tǒng)中的元件早期失效。元件進(jìn)入耗損失效期以后，失效率將明顯上升。為了防止這種情況影響系統(tǒng)的可靠性，可以在有效壽命（或偶然故障期）將結(jié)束時(shí)，不管元件是否損壞，也進(jìn)行更換。采用篩選和預(yù)防性更換，可以保證系統(tǒng)中的元件工作在偶然失效期內(nèi)，在這個(gè)前提下才可以用元件的偶然失效率來(lái)計(jì)算系統(tǒng)的失效率。

在選擇方案時(shí)，應(yīng)考慮盡量減少控制元件數(shù)、接點(diǎn)數(shù)和焊點(diǎn)數(shù)，以降低系統(tǒng)的失效率。采用可編程控制器（PC）來(lái)代替由繼電器等組成的控制柜可以提高系統(tǒng)的可靠性。在比較可編程序控制器和繼電器控制柜兩種方案時(shí)，除了購(gòu)置價(jià)格以外，還應(yīng)充分估計(jì)前者在提高可靠性、縮短開(kāi)發(fā)周期和減小工作量以及節(jié)省維修時(shí)間等有利因素。

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