> For the complete documentation index, see [llms.txt](https://infosys.selmotech.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://infosys.selmotech.com/selmo-solution/selmo-solution-en/selmo-documentation/3-the-selmo-method-ptf/ptf-process-technology-function.md). # PTF – Process · Technology · Function PTF is the **methodical foundation of Selmo**.\ It describes **how one must think about a machine before it is modeled**. PTF is: * no modeling * no technical description * not a tool * not a diagram But: > **A structured thinking and analysis process,**\ > **which necessarily precedes modeling.** *** ### Why PTF is necessary Without upstream analysis, the following often happens: * modeling is started too early * thinking in technical instead of functional terms * complexity is shifted into the model * safety is compensated afterwards This leads to: * overloaded sequences * implicit assumptions * states that are hard to explain * unnecessary special cases **PTF exists to systematically avoid these errors.** *** ### Overview: The three levels of PTF PTF deliberately separates three levels of consideration: * **P – Process**\ What should happen professionally? * **T – Technology**\ Which physical and technical principles are used? * **F – Function**\ What verifiable requirements result from that? These levels are: * logically separated from each other * not interchangeable * necessarily to be considered in this order *** ### P – Process #### What does “Process” mean? The process describes the **professional sequence**: * from the perspective of product, material, or task * independent of automation * independent of the technology used Examples: * Insert workpiece * Fix part * Perform processing * Check result * Release part The process answers **not**: * how something is implemented technically * which sensors are used * which actuators are moved > **The process describes *****what***** happens –**\ > **not *****how***** it happens.** *** #### Typical errors without a clear process view * Technology determines the sequence * PLC structures define the process * Process logic is no longer explainable * Special cases arise uncontrolled *** ### T – Technology #### What does “Technology” mean? Technology describes: * physical principles of operation * machine technology used * relevant forms of energy * mechanical, electrical, pneumatic or hydraulic relationships Examples: * Clamping via pneumatics * Positioning via servo axes * Gripping via vacuum * Measuring via sensors Technology answers: * what is physically possible * what must be monitored necessarily * where risks and limits lie *** #### Why technology must be understood before function Without understanding the technology: * wrong functions are formulated * unnecessary safety assumptions arise * monitoring is placed incorrectly > **Functions can only be derived from technology –**\ > **not the other way around.** *** ### F – Function #### What does “Function” mean? Functions are **formalized requirements for the behavior of the machine**. They are derived from: * the professional process * the technological boundary conditions Examples: * "Workpiece must be clamped before processing" * "An axis may only move if the protective condition is met" * "Processing may only start when position is reached" Functions are: * not implementations * not PLC function blocks * no states > **Functions are verifiable statements about expected behavior.** *** #### Result of well-formulated functions From clear functions arise: * necessary states * meaningful sequences * relevant zones * required monitorings This makes modeling: * not a creative activity * but a **consistent derivation** *** ### PTF and the Selmo model The roles are clearly separated: | Level | Task | | ----------- | ------------------- | | PTF | Thinking & Analysis | | Selmo model | Formal description | | PLC / HMI | implementation | PTF decides: * **what** is modeled * **why** it is modeled Selmo decides: * **how** this behavior is described formally > **PTF limits the model.**\ > **Selmo structures it.** *** ### Typical errors without PTF * Modeling starts too early * Sequences take over process decisions * Zones are defined technically instead of functionally * Safety logic compensates for missing analysis * Models become unnecessarily complex Rule of thumb: > **When a model becomes confusing,**\ > **PTF is almost always missing.** *** ### Summary PTF is: * the methodical entry into every Selmo project * Prerequisite for explainable models * Protection against implicit logic * Reduction of complexity PTF is **not a substitute for Selmo**\ and **no alternative to the model**. > **Think first.**\ > **Then model.**\ > **Then automate.** --- # Agent Instructions This documentation is published with GitBook. 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