System Integration and Real-Time Control
A mechatronic product fails or succeeds at integration. Good parts are not enough; sensors, actuators, mechanics, power, firmware timing, communications, and safety states must behave as one system.
Learning Objectives
By the end of this lesson, you should be able to plan control-loop timing, separate real-time and non-real-time tasks, build a state-machine structure, handle faults, and verify integrated behavior.
Timing Matters
A control loop must run at a predictable interval. Jitter changes derivative estimates, filter behavior, and stability margins.
$$
f_s=\frac{1}{T_s}
$$
where fs is sample frequency and Ts is sample time. Choose fs high enough for the plant dynamics and low enough for reliable computation.
Real-Time Task Structure
Keep time-critical control separate from slow displays, network communication, file logging, and user-interface work.
State Machines
Use explicit states such as BOOT, IDLE, HOMING, READY, RUNNING, FAULT, and ESTOP. State machines make startup, shutdown, and fault recovery understandable.
Every transition should have a condition and a safe actuator action. For example, entering FAULT should disable motion power or command a controlled stop depending on the hazard analysis.
Integration Interfaces
Define electrical and software contracts:
- voltage levels and connector pinouts;
- sensor update rates and units;
- actuator command range and saturation behavior;
- fault codes and recovery rules;
- calibration data and versioning;
- watchdog and heartbeat behavior.
Verification Strategy
Start with unit tests and bench tests, then integrate one subsystem at a time. Use logs that include timestamps, setpoints, measurements, actuator commands, faults, and supply voltage.
Common Mistakes
- Running control loops from a variable-delay main loop.
- Letting communication delays block actuator updates.
- No explicit fault state.
- Mixing units such as counts, degrees, radians, and millimetres.
- No integration test for startup and emergency stop.
Summary
System integration turns working components into a reliable machine. Fixed timing, explicit states, clear interfaces, safe fault handling, and logged verification are as important as the motor or controller equation.
Further Reading
- NASA, software safety and state-machine guidance.
- FreeRTOS documentation, task timing and priorities.
- IEC 61508 overview for functional safety concepts.