The crane problem: measuring the same gap twice a second, for years
Two overhead cranes on the same runway, or a gantry approaching a fixed buffer, need a distance that never lies. Not a measurement that is right when the technician commissions it — a number that stays right through summer heat, winter condensation, a reflector that has collected a year of dust, and the vibration of a 40-tonne trolley braking.
The usual first attempt is a mechanical limit switch or an encoder on the travel drive. Both measure the machine’s own motion, not the actual gap to the thing it is about to hit. A laser distance sensor measures the gap itself, which is why it is used as the independent channel.
Modules used in crane and gantry anti-collision
| Model | Published range | Price | Why it suits a crane |
|---|---|---|---|
| LRF200H | 0.05–200 m at 90% reflectivity; 0.05–70 m at 10% | $250 | 9–36 V DC supply matches a 24 V crane circuit; centimetre output |
| LRF300H | 0.05–300 m at 90%; 0.05–100 m at 10% | $280 | Longer runways and larger bays |
| LRF600H | 0.05–600 m at 90%; 0.05–200 m at 10% | $350 | Port RTG / RMG spans and rail-mounted transfers |
| LRF1500H | 0.05–1,500 m at 90%; 0.05–300 m at 10% | $400 | Very long travel distances, ship-to-shore geometry |
| LR2000E2 | 4–2,000 m | $120 | Lowest-cost long range, but a 4 m minimum range and a UART-TTL host rail |
| LRF3000A1 | Long range on a building target in clear weather, visibility ≥ 4 km | $200 | Outdoor standoff on a large fixed target |
Four things that decide whether it works outdoors
- Ambient sunlight. A 905 nm receiver is fighting the sun. That is precisely why each H-series model publishes a second figure at 10% reflectivity — a dull steel surface in bright light is closer to that column than to the 90% one. Specifying against the 90% figure and commissioning in winter is how these projects fail in July.
- The target you actually hit. A flat plate mounted square to the beam is a gift. A painted steel leg at an angle returns far less light. If you can mount a cooperative target at a known position, do it — it converts an unknown into a constant.
- Alignment drift. The beam is narrow. A bracket that moves 5 mm at 100 m can walk the spot off the target. The mounting needs to be rigid to the structure, not to a panel that flexes.
- Contamination. Dust on the window is a mechanical problem that presents as an electrical fault. The acceptance test for the window, and its cleaning interval, belong in the maintenance plan. See protective window acceptance.
Using one measurement in a control system
The sensor gives you a distance; the crane controller needs a decision. The useful engineering is in the middle: a warning zone, a slow-down zone and a stop zone, each with hysteresis so the output does not chatter when the gap sits exactly on a threshold. Threshold hysteresis describes the technique on a smaller module, and it applies unchanged here.
Two more behaviours are worth designing in from the start. First, a staleness timeout: if no valid frame arrives for N milliseconds, the controller must treat the gap as unknown, not as clear. Second, a plausibility check: a reading that jumps by more than the maximum travel speed allows is a bad return, not an emergency stop.
The honest boundary
A laser module sold as a component is not a certified anti-collision system. If the installation must meet a machinery safety category or a port authority requirement, the certified device is the system that carries that rating, and this module is a sensor input to it. What the module can do is give the system a fast, independent, physical gap measurement instead of a derived one.
Next step
Send the travel distance, the supply voltage on the crane, the target surface and the sunlight exposure to tommy@erdimail.com. We will name a model and the measurement condition behind its range figure, within one business day (Chengdu, UTC+8).
Where two source documents for a model conflict, the model page states the conflict rather than choosing one value, and the current datasheet governs the order.