CNC machine semaphore application, using expressions (Expr.txt) – Part 2
What is a State Machine and how it is used?
If you google State machine, this would be the average result more or less:
“A state machine is a behaviour model. It consists of a finite number of states and is therefore also called finite-state machine (FSM). Based on the current state and a given input the machine performs state transitions and produces outputs.”
Sounds exactly what we need for our application doesn’t it? 5 states, which can transition one from another based on the pre-defined conditions.
Each semaphore state has its outputs and inputs. State outputs are semaphore light configurations where specific relay output will be activated. State inputs are conditions that will cause the state transitions.
Both will be described in detail in Part 3 of this tutorial.
What is an Expr.txt file and how it is used?
- Expr.txt is a file which contains functions that are evaluated by PlanetCNC TNG expression evaluator.
- it can be very practical for PLC type applications where periodical evaluation is necessary or for program events
- Expr.txt file can contain and use vast array of expression functions, parameters and other commands supported by PlanetCNC TNG
- Expr.txt file is located in the profile folder of TNG software
- Profile folder can contain multiple Expr.txt files. Specific Expr file naming convention is available for better distinction. e.g.: Expr_Semaphore
- If multiple expr files use same function, then function will be called first in first file and only then the with the next file
- Local variables(e.g. name convention of local variables: red_light, global variables: _red_light ) have scope only within the parent Expr file.
- Each Expr file contains functions that are marked with symbol #.
- Each function begins with symbol # and ends with the next # symbol.
- Each expr file can use built-in functions that are related with program events
Built-in Expr functions:
- #OnInit -> When TNG software is started/initialized, code under this function will be executed.
- #OnShutdown -> On PlanetCNC TNG software shutdown request, code under this function will be executed, then TNG will shutdown.
- #OnStart -> On NC program Start event, code under this function will be executed.
- #OnEnd -> On NC program End event, code under this function will be executed.
- #OnStop -> On NC program Stop event, code under this function will be executed.
- #OnEStop -> On Estop event, code under this function will be executed.
- #OnJog -> On Jogging event, code under this function will be executed.
- #OnWheel -> On handwheel event, code under this function will be executed.
- #OnCmd -> On MDI command event, code under this function will be executed.
- #Loop -> this loop is executed every 83ms, or the value of refresh rate set in settings, under: File/Settings/User Interface/Refresh Rate
- #Loop5 ->this loop is executed every 5s
- #Loop15 ->this loop is executed every 15s
- #Loop60 ->this loop is executed every 60s
- #Loop300 ->this loop is executed every 300s