DEEP DIVE · 2026-05-27 · ~11-min read

Multi-Zone Protective Field Configuration on Industrial Safety Scanners — Warning Fields, Protective Fields, and Speed-Dependent Switching

A single protective field is enough for a static machine. For anything that moves, changes speed or shares space with people, it is not even close. Multi-zone field configuration is where a safety scanner stops being a sensor and starts being a system.

Multi-zone regional protection — nested warning and protective fields switched dynamically with operating state.

In short: A modern safety laser scanner can store anywhere from a handful to about seventy independent field sets, each one a paired protective and warning shape. The scanner switches between them in real time using a speed signal from an encoder, a discrete signal from a safety PLC, or a position trigger from a localiser. ISO 3691-4 treats the switch itself as a safety function at PLd; the field depth comes from ISO 13855’s safety distance formula. Get the switching trigger, the field shapes and the fallback right and a vehicle can run fast on a long straight and creep through a narrow aisle without ever hard-stopping unnecessarily.

The zone configuration basics article covers the ground a newcomer needs — what a warning field is, what a protective field is, how teach-in works at the simplest level. This piece picks up where that one stops. The question now is not “what is a protective field” but “how do I configure twelve of them, switch between them safely, prove the switch happens at the right moment, and keep the whole arrangement auditable”.

Why a single field is not enough

A static machine has one operating mode and one stopping distance, so a single protective field works fine. Almost nothing real is like that. An AGV travelling at 1.2 m/s on the main aisle needs a protective field roughly 1.4 m deep ahead of it — that is the stopping distance plus the constants demanded by ISO 13855. The same vehicle creeping into a pick station at 0.2 m/s only needs about 0.3 m. If you use the 1.4 m field everywhere, the AGV cannot enter the pick station at all without triggering a stop. If you use the 0.3 m field everywhere, it will run a person down on the main aisle.

The whole point of multi-zone configuration is to let one scanner present the right field for the right moment — faster speed, deeper field; turning, asymmetric field; narrow aisle, slimmer field with the warning band pulled in tight. Done well, this is how a mobile robot achieves both safety and throughput. Done badly, it is how field switching becomes a way of hiding nuisance stops — an audit failure waiting to happen.

Field sets — what a scanner actually stores

Internally, a safety scanner stores a list of field sets, sometimes called monitoring cases. A field set is a complete configuration unit: one protective field shape, one or more warning field shapes, the response time assignment for that case, and the conditions under which this set becomes active. The scanner remembers the entire library in non-volatile memory and can hot-swap between sets within its response time.

The number of available field sets is one of the more honest markers of scanner class:

Compact obstacle-avoidance scanners typically offer four to eight switchable sets. That is enough for an AGV with three speed bands plus a turning case.
Mid-range industrial safety scanners commonly support sixteen to thirty-two switchable cases — suitable for AMRs that handle multiple zones, dock approaches and shared-space corridors.
Flagship platforms can hold roughly seventy independent configurations, intended for vehicles operating across very different environments or for stationary cells that cycle through many distinct hazard states.

More is not automatically better. Seventy field sets is seventy things you must validate, document and re-validate every time the firmware moves. Most real installations end up using six to twelve and that is plenty.

What triggers the switch

Three trigger families cover almost every real installation. They can be combined — an AGV often uses two of them at once.

1) Vehicle speed via an encoder

The dominant pattern for AGVs and AMRs. An incremental encoder is mounted on a non-driven wheel, and its A and B channels (offset by ninety degrees) are wired into two dual-channel encoder inputs on the scanner. Two channels give the scanner both speed and direction; internal cross-checking of the channels delivers the diagnostic coverage needed for a PLd safety function under ISO 13849-1. You then declare speed thresholds in the configuration tool — below 0.3 m/s pick set A, between 0.3 and 0.8 m/s pick set B, above 0.8 m/s pick set C — and the scanner does the switching itself.

A few scanners accept an absolute encoder or even a safety analog speed signal instead, useful where the geometry of the vehicle makes a wheel encoder awkward. Whichever interface you use, the source must be PLd-rated end to end — ISO 3691-4 is explicit that the speed signal feeding field selection on a driverless truck is itself part of a safety function.

2) Machine state from a safety PLC

Common on stationary cells. The safety controller knows what mode the machine is in — setup, automatic, robot at home, robot extended, conveyor running forward, conveyor running reverse — and signals the scanner over a small number of dual-channel discrete inputs or, increasingly, over a safety fieldbus. The scanner maps each input combination to a field set. Two safe inputs already give you four states; four inputs give you sixteen.

This is the cleanest model when the application has clear, discrete modes. It is harder to argue against in an audit because the trigger is deterministic and the safety chain is short.

3) Position from a localiser

A vehicle that knows where it is on a map can pre-select a field set just before it enters a known geography — the narrow aisle, the pick station, the docking bay. Position triggers are almost always layered on top of speed switching rather than replacing it, because the localiser itself is rarely safety rated. A common pattern: position selects a candidate field set; speed decides which protective depth inside that set is active; the scanner enforces the final geometry.

DAIDISIKE DLD-series obstacle-avoidance laser scanner used on AGV and AMR — The DAIDISIKE DLD-series obstacle-avoidance scanners support multiple switchable field sets driven by vehicle speed or by controller inputs.

Trigger types compared

Trigger	Effective response	Wiring complexity	Typical use
Incremental encoder (dual channel)	Continuous — sub-100 ms band changes	Moderate (two encoder channels, wheel mount)	AGV, AMR speed-based fields
Absolute encoder / safety analog	Continuous	Moderate	Drives where wheel encoders are impractical
Discrete safe I/O from PLC	Step change at PLC scan rate	Low (a few dual-channel inputs)	Stationary cells, mode-based switching
Safety fieldbus from controller	Step change at bus cycle	Low cabling, higher integration effort	Modern integrated machinery
Localiser position (non-safety)	Pre-select only, gated by safe signal	Software	AMR geographic pre-selection

Sizing each field with ISO 13855

The protective field for each speed band is not a guess. It comes from the safety distance formula in ISO 13855: the minimum distance between protective field edge and hazard equals the approach speed multiplied by the total safety function response time, plus a constant distance derived from the detection capability of the device. For a person walking into the field horizontally the approach speed constant is 1.6 m/s; for a vehicle approaching a person the constant is the vehicle’s maximum speed in that band.

The total response time you plug in is the worst-case sum of scanner response time, controller reaction time, brake actuation time and any latency in the safety chain. Run the formula for each speed band you plan to allocate a field set to, add a margin for tyre wear, payload variation and gradient, and you have the minimum protective field depth for that band. Anything smaller than that is by definition unsafe; anything much larger throws throughput away. The 2024 edition of ISO 13855 keeps the same fundamental approach with refinements to the constants and a tightened treatment of detection-capability margin.

Teach-in — what it does and what it does not do

The teach-in tool inside a scanner configuration package lets you capture the static contour of the protected area as a starting shape for a field. Park the AGV in position, take a teach scan, and the scanner now knows where the racks and walls and floor features actually are. From that contour you sketch the protective and warning fields, either by tracing the contour with a software offset, by drawing polygons or by specifying rectangles.

What teach-in does not do is verify that your field is large enough. The depth you set still has to satisfy the ISO 13855 calculation for the speed and response time of the case it belongs to. After every teach-in cycle you should:

Measure the field on paper against the calculated minimum depth for that speed band.
Walk a calibrated test piece into every edge of the protective field and confirm the safety outputs switch.
Record the test result with date, witness, scanner serial number and field set identifier in the safety file.

Safety interlock and field configuration expanding the protected area on an industrial cell — Nesting multiple field sets — tight protective fields for slow approach, wide warning bands for higher-speed transit.

Common configuration patterns

Three-band AGV pattern

The workhorse. One field set per speed band — slow / medium / fast. The protective field grows with speed, the warning field stays roughly proportional, and a separate “turning” field set handles the asymmetric geometry when the vehicle is rotating. Four sets total, sometimes six if forward and reverse travel each get their own pair.

Mode-based stationary cell

Two to four field sets driven by safe inputs from the cell PLC. Typical cases: automatic mode (full protective area), teach mode (reduced area around the operator pendant), maintenance access (entire field disabled with the cell power-isolated).

Pedestrian-shared corridor

A warning field deep enough to give the AGV time to slow to walking pace before pedestrians reach the protective field. The protective field itself stays sized for walking-pace transit. This is the configuration that earns its keep in mixed pedestrian/vehicle aisles — it stops the AGV bouncing off its own emergency stop every time someone walks past.

Fork-truck shared zone

One of the hardest. The protective field has to ignore the AGV’s own forks at certain extension positions while still detecting a pedestrian. This is usually solved with a separate field set per fork height, switched from a discrete safe signal, and a contour reference that includes the forks at that height.

Common mistakes

Muting abuse. Using field switching to effectively mute the protective field whenever the machine misbehaves. The field that runs when something is wrong is usually the field a person gets hurt in.
Field overlap conflicts. Two sets that can both legitimately be active at the same moment because their switching conditions are not mutually exclusive. The scanner will pick one — usually the wrong one.
Switching delay too long. A safety function response time that includes scanner response, controller scan time and switching delay can quietly exceed the stopping distance the field was sized for. Re-run the ISO 13855 sum any time you add a step to the switching chain.
Default-to-smallest fallback. On signal loss or encoder fault the scanner must default to the largest, safest field, not the smallest. Check this is the way the scanner is configured.
Treating teach-in as design. Teach-in captures the room. It does not size the field.

Edge cases worth thinking about

Turning AGVs. A vehicle rotating in place has a stopping distance defined by angular momentum, not linear speed. Use a dedicated turning field set with a circular or sector shape, triggered by the speed of the inner wheel falling below a threshold while the outer wheel is moving.

Narrow aisles. A protective field sized for the aisle width may overlap the rack profile and trip continuously. The right answer is a teach-in that includes the rack contour plus a contour-following protective field; the wrong answer is to shrink the field until it stops tripping.

Outdoor sections. If the AGV transitions from indoor to outdoor lanes, switch to a field set with more tolerant object-loss handling and longer minimum reflectivity targets, and confirm the scanner is rated for the environment in the first place.

Loaded vs unloaded. A laden vehicle takes longer to stop. Either size every field for the worst case (laden) or add a load-state input to the safe signal set so the scanner can pick the right field depth.

Validation — the part nobody enjoys

Validation is per-configuration. A scanner that passes its factory acceptance test on one field set is not validated for any of the others. For each field set you have to:

Force the switching condition that selects this set and confirm it becomes active (the scanner’s diagnostic output normally indicates the active case).
Walk a calibrated test piece into the protective field at multiple points around its perimeter and confirm the safety outputs switch within the response time.
Measure the machine stopping distance from each safety output switch and confirm it falls inside the field boundary.
Repeat the test piece check at the very edge of the warning field to confirm the non-safety reaction works.
Induce relevant faults — disconnect an encoder channel, mismatch two PLC inputs — and confirm the scanner falls back to the largest field, not the smallest.

Then record the result of every test with date, witness, scanner serial number and the exact field set identifier. The fact that the safety file contains those records is what allows the next person who looks at the machine — auditor, integrator, incident investigator — to trust the configuration.

Where the DAIDISIKE DLD-series fits

The DAIDISIKE DLD-series obstacle-avoidance scanners are built around exactly this multi-zone pattern. The DLD05A3 (5 m class) and DLD20A5 (20 m class) cover compact and full-size AGV/AMR obstacle avoidance and support multiple switchable field sets driven by vehicle-speed or controller inputs — the three-to-four-set workhorse pattern covers the great majority of deployments. The SDLD-05A 14 m time-of-flight scanner sits in between for mid-range hazard-area monitoring. For perimeter and long-range area guarding, the DLD30T-5N 40 m platform stays in a mode-based configuration driven by the cell or perimeter controller. Specifying any of them, the conversation we always come back to is the same: how many real operating modes do you have, what is your stopping distance in each, and what is the safety-rated signal that tells the scanner which mode it is in. Get those three answers right and the rest is wiring.

References

IEC 61496-3 — Safety of machinery: electro-sensitive protective equipment, Part 3 (active opto-electronic protective devices responsive to diffuse reflection).
ISO 13855:2024 — Positioning of safeguards with respect to the approach speeds of parts of the human body.
ISO 13849-1 — Safety-related parts of control systems: general principles for design, Performance Levels.
ISO 3691-4 — Industrial trucks: safety requirements and verification for driverless industrial trucks and their systems.
ANSI/A3 R15.08 — Industrial mobile robots: safety requirements.

Frequently asked questions

How many field sets does a typical safety laser scanner support?

It varies widely by device class. A compact obstacle-avoidance scanner aimed at small AGVs may switch between four to eight pre-stored field sets, which is enough for most single-vehicle duty cycles. Mid-range industrial safety scanners commonly offer sixteen to thirty-two switchable cases. The flagship platforms used on complex AMR fleets and large hazard cells can store and switch between roughly seventy independent configurations, each one a full pair of protective and warning field shapes. The right number is the smallest one that covers every real operating mode without forcing you to compromise a field shape. Sixteen field sets handled well is far better than seventy half-configured ones.

How is speed-dependent field switching wired on an AGV?

The most common pattern uses an incremental encoder mounted on a non-driven wheel, wired into a pair of dual-channel encoder inputs on the safety scanner. Two channels offset by ninety degrees give the scanner both speed and direction, and the scanner internally cross-checks the two channels to satisfy the diagnostic-coverage requirements expected of a PLd safety function under ISO 13849-1. The scanner is then configured with speed thresholds — for example below 0.3 m/s use field set A, between 0.3 and 0.8 m/s use field set B, above 0.8 m/s use field set C. When the wheels stop, an encoder fault, channel-mismatch fault or loss of signal forces the scanner to the largest, safest field, not the smallest.

What does ISO 3691-4 say about protective field switching on driverless trucks?

ISO 3691-4 treats the switch from one protective field to another as itself a safety function — because if the wrong field is active for the actual speed, the vehicle cannot stop in time. The standard expects field selection to be performed with a safety function achieving Performance Level d under ISO 13849-1, with the selected field always matching real vehicle speed. In practice that means the speed signal must come from a safety-rated source, the selection logic must be in a safety controller or in the scanner itself, and the chosen field has to envelope the worst-case stopping distance at the speed it is allocated to. Default to the largest field on any fault.

Is the teach-in feature on a safety scanner a replacement for proper field design?

No. Teach-in is convenient for capturing a background reference — the walls, racks and floor features the scanner should treat as the contour of the protected area — and for sketching an initial field shape that follows that contour. It does not, on its own, design a safe field. The minimum field depth still has to be computed from the formula in ISO 13855, factoring in the safety function response time, the machine stopping time and the approach-speed constant. Teach-in tells the scanner what the room looks like; the engineer is still responsible for proving the field is big enough. After any teach-in, the field must be measured against the stopping-distance calculation, witnessed and recorded.

Can I use machine state (a PLC signal) instead of an encoder to switch fields?

Yes, and it is common on stationary machinery — switching field sets based on cell mode, robot pose, conveyor direction or door state, with the trigger coming from a safety PLC over dual-channel I/O or a safety bus. The same rules apply: the source signal must have the PL or SIL needed by the risk assessment, the switching logic must be inside a safety device, and the default on any fault is the most restrictive field. On mobile vehicles, encoder-based speed switching is usually the right answer because the field must follow a continuously varying quantity. On a fixed machine, discrete mode-based switching from the safety controller is cleaner and easier to validate.

How do I validate that the field actually protects across every configuration?

Validation is per-configuration, not per-scanner. For each field set you have to walk a calibrated test piece — typically a 70 mm diameter test rod for ankle-height scanners — into every edge of the protective field and confirm the safety outputs switch and the machine stops within the calculated time. You then force each switching condition: drive the AGV through each speed band, toggle every PLC input, and verify the correct field becomes active each time. Finally, induce faults — disconnect an encoder channel, force a mismatch — and confirm the scanner falls back to the safest field. Record the result of every test in the safety file, with date, scanner serial number and field set ID.

About DAIDISIKE: Foshan-based long-established industrial safety sensor manufacturer. The DLD-series safety LiDAR scanners — DLD05A3 (5 m), DLD20A5 (20 m), DLD30T-5N (40 m perimeter) and the SDLD-05A 14 m TOF scanner — support multi-zone field-set switching for AGV/AMR and stationary applications, alongside the DAIDISIKE safety light curtain range. Working through a multi-zone configuration for an AGV fleet or a mixed-mode cell? Talk to our engineering team or browse the DAIDISIKE LiDAR scanner range.

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