On a packaging or printing line, the material carries features that never sit in exactly the same place twice: a printed mark, a seam, a perforation, a die-cut. To cut, seal, or print in the right spot, the machine must lock onto that feature and correct itself to it, and it must do so while the material is flying past. Registration is how motion controllers do this. A sensor spots the feature, the controller instantly latches the axis position at that moment, and it nudges the axis so the operation lands on the feature. This guide explains hardware position latching, mark sensing, and on-the-fly correction, and why registration is essential in packaging and web converting.
Registration in one line: Registration is a motion-control function in which a mark or feature sensor triggers a hardware latch that captures an axis's exact position at the instant the feature is detected, so the controller can correct the axis to align an operation with that printed or physical feature. Because the capture is done in hardware the instant the sensor fires, it is immune to software timing delays, which lets the controller correct on the fly to features that shift position from cycle to cycle on a moving web or product stream.
The heart of registration is capturing exactly where an axis was at the precise moment a sensor detected a feature. This has to be done in hardware because of speed. If the controller waited to notice the sensor in its normal scan and then read the axis position, the material would have moved a variable distance in the meantime, and that timing jitter would ruin the accuracy. Instead, the sensor's signal is wired to a fast hardware input that instantly freezes the axis's position count into a register the moment it fires, with no software in the loop, so the captured position corresponds to the sensor event to a fraction of the encoder's resolution.
This hardware-latched capture is known by several names, including position latch, position capture, and, on many controllers, a touch probe input, borrowing the term from machine tools where a probe touching a part latches position the same way. Whatever it is called, the principle is identical: a physical trigger event causes an immediate, deterministic snapshot of position that the controller can then read at its leisure. The determinism is the whole point, because the value of registration rests on knowing the position at the trigger extremely precisely and consistently.
Once the controller has that latched position, it knows exactly where the axis, and therefore the material, was when the feature passed the sensor. Comparing that captured position against where the feature was expected tells the controller how far the material has drifted from its nominal position this cycle. That drift is the registration error, and everything the controller does next is about cancelling it so the subsequent operation lands on the feature rather than on nominal, blind coordinates.
The feature the sensor watches for is often a deliberately printed registration mark, a small block of contrasting colour placed on the material precisely so the machine has something reliable to lock onto. A registration mark sensor, tuned to the mark's colour and contrast, produces a crisp edge signal as the mark passes, and that edge is what triggers the position latch. The mark exists purely to give the machine a repeatable, high-contrast target, which is why so many printed webs carry a line of small marks along one edge that never appear in the finished product.
Registration is not limited to printed marks. The trigger can come from any feature a sensor can detect: a seam, a notch, a hole, an edge of a label, or a change in material. Vision systems and other sensors extend the idea to features that a simple photoeye could not distinguish. What matters is that some sensor reliably fires at a repeatable point on the feature so the position latch captures a meaningful reference. The rest of the registration logic is the same regardless of what kind of feature is being sensed.
Having measured the registration error, the controller corrects for it while the line keeps running, which is the on-the-fly part. It adjusts the axis, often by shifting the phase of a following or camming axis, so that the operation, the cut, the seal, the print, or the placement, occurs at the feature rather than at the nominal position. Cycle after cycle it re-measures the error from each new mark and applies a fresh correction, continuously chasing the wandering feature so every operation lands correctly even as the material stretches, slips, and shifts. The correction is usually applied gently over the cycle so the material is not jerked, blending accuracy with smooth motion.
Registration is indispensable wherever a repeating operation must align with a repeating feature on a moving material. In flexible packaging, it ensures the sealing jaws close and the knife cuts on the printed mark so each bag or pouch shows the artwork centred and is cut to the right length, rather than drifting further off with every cycle as the film stretches. In printing and web converting, it keeps successive print stations and die-cutters aligned to the same reference so colours overlay correctly and cuts fall in the right place across a fast-moving web.
Without registration these processes would slowly wander out of alignment, because the material never feeds perfectly and small errors accumulate. By locking onto a physical feature every cycle and correcting to it, registration turns an open-loop guess into a closed-loop correction against the material itself, which is what makes cut-to-length, print placement, and pouch making accurate at production speed. It is one of the reasons high-speed packaging can maintain tight tolerances on stretchy, slippery films that would otherwise defeat purely position-based control.
The fast latch and correction all happen inside the machine's motion controller, but the quality of registration is exactly the kind of production metric a plant follows through cloud SCADA. The registration error the controller measures each cycle, how much correction it is applying, and whether it is losing marks are all data that a platform such as Merobix can trend and alarm on across many lines. A registration error that is creeping up, or a rising rate of missed marks, points to a fading sensor, a dirty lens, a print-quality problem, or slipping material, often before it produces visible scrap. Bringing that registration health into a central view lets a team catch a drifting line early and compare performance across sites, so a converting or packaging operation spread across several plants can be watched and diagnosed without standing at every machine.
Because the material is moving fast, any delay between the sensor firing and the controller reading the axis position translates into a variable position error that would ruin registration accuracy. A hardware latch freezes the axis position the instant the sensor triggers, with no software scan in between, so the captured position corresponds to the feature to a fraction of the encoder's resolution. That determinism is what makes registration accurate and repeatable at production speed.
They are essentially the same hardware mechanism under different names. Both use a fast input that latches the axis position the instant a trigger fires, so the controller can read exactly where the axis was at that event. The term touch probe comes from machine tools where a probe touching a part triggers the latch, while registration is the packaging and converting term for latching on a mark or feature sensor. The underlying position-capture function is identical.
It compares the latched position at the mark against where the mark was expected, giving the registration error for that cycle, then shifts the axis, often by adjusting the phase of a following or camming axis, so the next operation lands on the feature rather than on nominal coordinates. It re-measures from each new mark and applies a fresh correction every cycle, usually blended gently over the cycle, so it continuously tracks the wandering feature without jerking the material.
Merobix reads your field devices into a cloud SCADA - the real thing behind these terms, live in days from any browser.