REPOSITION mode in a SmartStep application 智能向导应用复位模式

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概观
REPOSITION模式用于驱动过程到约束内，从而使得阶跃测试可能恢复。在TEST, TEST NO-PULSE或SUSPEND模式下，当CV在测试限（STCVMIN/ STCVMAX）外STCVDELTA以上时其将自动触发。（详情请参阅CORRECTING模式帮助中有关配置CV违反约束时REPOSITION或CORRECTING模式是否会自动触发的内容。）当触发REPOSITION模式后，当前的MV阶跃测试将被放弃，DMCplus引擎将恢复对该组的控制。为将每个CVs都移动到测试限内，测试组中所有的MVs都将变得活跃。

REPOSITION模式遵循以下规则：
•当一个CV超出测试限（STCVMIN和STCVMAX）STCVDELTA以外时将触发REPOSITION模式。
•REPOSITION模式触发的最少时间由STREPOMAX* SSMINS指定。经过STREPOMIN* SSMINS后如果所有的CVs都在测试限内至少1/2STCVDELTA，测试组将继续测试。
•经过STREPOMAX* SSMINS后如果所有的CVs都在测试限内，那么测试组将继续测试。
REPOSITION模式可以通过手动设置STGREQ至REPOSITION触发。这对测试初期或发生显著测试限变化时为流程做好准备是非常有用的。

避免CORRECTING和REPOSITION模式
尽管一些CORRECTING, REPOSTION和CONTROL模式的数据也可用于模型识别，测试过程中一个主要目标是限制应用处于CORRECTING或REPOSITION模式的时间。在不违反最大MV阶跃大小和CV测试限的前提下，智能向导引擎所使用的阶跃大小算法将尽可能尝试最大的阶跃输出。鉴于各种不确定性，若CV违反约束，测试人员依然可以进入CORRECTING或REPOSITION模式。测试人员是不断将过程推向测试限的，但由于可能使用较差的模型，它会经常对限制响应过量或不足。

整定以避免CORRECTING或REPOSITION模式包括以下内容：
•设置适当的测试限(STCVMIN和STCVMAX)。限制应设置成假设它们很可能被侵犯。
•CV安全裕度(STCVDELTA)是一个指示触发REPOSITION模式前超出限制容忍量的整定参数。
•在测试模式中，STSTEPFRAC是一个影响所有MV阶跃大小的全局参数。它反映了你对模型的信心，以及可以用来避免过多的违反约束。
在测试中一个好的策略是将界限和安全裕度设置在合理的值，然后使用STSTEPFRAC参数尽快动作。随着新的，改进的模型被投用，测试中可以通过增加STSTEPFRAC来最大化阶跃尺度。

也可以看看
智能向导应用的校正模式
智能向导应用中的校正动作
智能向导应用的参数整定

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附原文：
Overview
REPOSITION mode is used to drive the process within constraints so that step testing may resume. It may be triggered automatically from TEST, TEST NO-PULSE or SUSPEND modes when a CV is more than STCVDELTA outside of the test limits (STCVMIN/STCVMAX). (See CORRECTING mode for help on configuring whether REPOSITION or CORRECTING mode will be triggered automatically by CV violations.) When REPOSITION mode is triggered the current MV step test is abandoned and the DMCplus engine resumes control of the group. This means that all of the MVs in the group may become active with the goal of moving each of the CVs within their test limits.

REPOSITION mode is governed by the following rules:
•REPOSITION mode is triggered by a CV that is more than STCVDELTA outside of its test limits (STCVMIN and STCVMAX).
•REPOSITION mode is triggered for a minimum of time specified by STREPOMAX×SSMINS. After STREPOMIN×SSMINS if all of the CVs are at least ½ STCVDELTA inside the test limits then the group will resume testing.
•After STREPOMAX×SSMINS if all the CVs are inside the test limits then the group will resume testing.
REPOSITION mode can be triggered manually by setting the STGREQ to REPOSITION. This can be useful for getting the process ready for testing initially or when significant test limit changes have been made.

Avoiding CORRECTING and REPOSITION mode
Although some CORRECTING, REPOSTION and CONTROL mode data can be used for identification, a major goal during testing is to limit the amount of time the application spends in CORRECTING or REPOSITION mode. The step size algorithms used by the SmartStep engine will try to make the largest step that does not violate either the maximum MV step size or any CV test limits. Because of various uncertainties, the tester may still enter CORRECTING or REPOSITION mode due to CV limit violations. The tester is constantly pushing the process toward test limits, but since it is using potentially poor models, it will frequently overshoot or undershoot the limits.

Tuning to avoid CORRECTING or REPOSITION mode includes the following:
•Setting the test limits appropriately (STCVMIN and STCVMAX). The limits should be set with the assumption that they will likely be violated.
•The CV Safety Margin (STCVDELTA) is the tuning parameter that indicates how much overshooting of the limits will be tolerated before triggering REPOSITION mode.
•STSTEPFRAC is the overall parameter that affects all MV step sizes in test mode. It reflects a confidence in your models, and it can be used to avoid excessive constraint violation.
A good strategy is to set the limits and the safety margins to reasonable values, and then use the STSTEPFRAC parameters to temper moves early in the test. As new, improved models are brought online, STSTEPFRAC can be increased to maximize the step size used during the test.

See Also
CORRECTING mode in a SmartStep application
Correcting moves in a SmartStep application
Tuning parameters in a SmartStep application

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2015/10/28