Automated machines perform their tasks in a definite order, and they must prevent actions that would be unsafe or damaging. Interlocks and sequencing are the logic that governs this, ensuring that a machine does the right things in the right order and never does the wrong thing at the wrong time. They are fundamental to safe, correct operation.
Sequencing: the right order
Most machine operations must happen in a particular sequence. A clamp must close before machining begins; a part must be in position before a process acts on it; one motion must complete before the next starts. Sequencing logic enforces this order, guiding the machine through its cycle step by step. Each step waits for the conditions that confirm the previous step succeeded before proceeding, so the machine advances only when it is truly ready.
Interlocks: preventing the wrong action
Interlocks are conditions that must be satisfied before an action is allowed, existing to prevent actions that would be unsafe or harmful. A machine might be interlocked so it cannot start unless guards are closed, cannot move an axis unless it is clear, or cannot perform two conflicting actions at once. Interlocks act as guardians, blocking dangerous or damaging combinations regardless of what else the logic commands.
Confirmation, not assumption
Robust sequencing and interlocking rely on confirming conditions rather than assuming them. Rather than simply commanding a clamp to close and moving on, good logic waits for a sensor to confirm the clamp has actually closed. This confirmation catches faults, a jammed clamp, a missing part, a stuck cylinder, before they cause damage, and it makes the machine’s behaviour trustworthy.
Designing for safety and clarity
Well-designed sequencing and interlocking make a machine both safer and easier to understand and troubleshoot. When each step waits for clear conditions, a machine that stops mid-cycle reveals exactly what it is waiting for, guiding a quick diagnosis. Safety interlocks, in particular, must be reliable and, where protecting people, designed to the appropriate safety standards so they cannot be defeated by a single fault.
Interlocks and sequencing are the logic of orderly, safe machine operation, ensuring actions happen in the correct order and unsafe actions are prevented. By insisting on confirmation rather than assumption and by guarding against dangerous combinations, they make automated machines both trustworthy and diagnosable. Understanding them is central to designing, operating, and maintaining automation that behaves correctly and safely.