When Several Cranes Share One Sky: How Group Anti-Collision Keeps Them Apart

▌  APPLICATION NOTE  ·  OCTOBER 2026  ·  GROUP ANTI-COLLISION ON MULTI-CRANE SITES

When Several Cranes Share One Sky: How Group Anti-Collision Keeps Them Apart

Put two or more tower cranes on one site and the sky above the deck becomes a shared workspace. Each crane has its own slewing circle, its own jib length and its own operator, yet the jibs sweep through the same airspace and the loads cross the same ground. A lift plan that is perfect for any single crane can still leave the site exposed, because the risk that matters sits between the cranes rather than inside one of them. Group anti-collision exists to turn that shared airspace into something both operators can see and act on.

This application note looks at the group anti-collision function of the ZNAO-TG2 tower crane safety monitoring system. On sites with more than one tower crane, the system auto-networks the machines, calculates their positions relative to one another, and issues a pre-warning when two cranes are approaching a zone of conflict. It sits alongside the other duties of the black box, such as overload protection and zone limiting, and it supports the coordination that standards such as ISO 12480-1, EN 14439 and BS 7121 already expect of a multi-crane site.

01  WHY A MULTI-CRANE SITE NEEDS A SHARED PICTURE

A single tower crane is a well-understood machine. The operator watches the load, the trolley and the slewing circle, and the site keeps the ground under the jib clear. Add a second crane and the geometry changes. Two slew circles overlap, two jibs can point at the same place, and two loads can be travelling through the same volume at the same time. None of the individual cranes is doing anything wrong, and yet the two machines are now negotiating an airspace without a common reference.

Traditional control of that problem is procedural. The lift plan assigns zones, the crane coordinator sequences the lifts, and the operators talk on the radio. This works, but it depends on human timing. A radio call describes where a crane was a moment ago, and a jib that is slewing is somewhere new by the time the message is understood. Group anti-collision does not replace the coordinator or the radio. It gives both operators a continuously updated picture of where the neighbouring cranes actually are.

▌  SHARED AIRSPACE  Two or more cranes over one site share a volume of air, so a safe single-crane lift can still create conflict between machines.

▌  PROCEDURE HAS LIMITS  Zoning and radio calls depend on human timing, and a jib that is slewing has already moved by the time a message lands.

▌  ONE PICTURE, TWO CABS  The goal is a common view of who is where, so each operator can judge the neighbour as well as the load.

02  HOW THE CRANES AUTO-NETWORK

The ZNAO-TG2 does not need a wired backbone between the cranes to build the group. The crane units auto-network, so the machines on a site find one another and exchange the data that group anti-collision needs. Each black box already knows its own machine through the sensors it reads: load weight, moment, trolley radius, hook height, slew angle, wind speed and tilt. That own-crane picture is what the group shares.

The radio layer is 4G plus 433M wireless. The 433M link gives a direct short-range channel between the cranes for the low-latency exchanges that anti-collision depends on, while 4G extends the view where the site or a platform needs it. Because the sensors are IP67 and the host is built for a wide range of conditions, from minus 20 to 60 degrees Celsius and 5 to 95 percent relative humidity non-condensing, the same networking behaviour holds across a hot steel yard or a cold morning start.

▌  AUTO-NETWORKING  The crane units on a site form the group themselves, without a separate wired backbone between the machines.

▌  4G PLUS 433M  A 433M channel carries fast crane-to-crane data, while 4G extends the picture where the site needs it.

▌  OWN-CRANE DATA  Each black box contributes its own load, radius, height, slew, wind and tilt readings to the shared group view.

03  RELATIVE-COORDINATE CALCULATION, PLAINLY EXPLAINED

Group anti-collision works on relative coordinates. Rather than treating each crane as an isolated machine at an unknown spot, the system places the cranes in relation to one another, so the group can reason about the distance and direction between jibs as they move. Relative-coordinate calculation is what turns a set of independent readings into a statement about two cranes and how close they are becoming.

The underlying measurements are precise. Radius is tracked to 0.1 m, height to 0.1 m, slewing angle to 0.1 degrees, load to 0.01 percent and wind speed to 0.1 m per second. Those figures matter because relative positions are built from them: a small, reliable change in slew angle or radius is what tells the group that a jib has begun to enter the space of a neighbour. The output is not an abstract number but a judgement about whether the cranes are drifting toward conflict.

▌  RELATIVE, NOT ABSOLUTE  The system reasons about cranes in relation to each other, so it can judge the space between jibs rather than each machine alone.

▌  PRECISE INPUTS  Radius and height to 0.1 m, slew to 0.1 degrees, load to 0.01 percent and wind to 0.1 m per second feed the calculation.

▌  A MOVING JUDGEMENT  As the cranes slew, the relative picture updates, so the group tracks an approach rather than one frozen snapshot.

04  PRE-WARNING: WHAT THE OPERATOR ACTUALLY FEELS

When two cranes approach a conflict, the system issues a pre-warning. The word pre matters. The point is to give the operator time to act before the situation becomes critical, not to announce it after the fact. In the cab, the operator works from an 11.6-inch 1920 by 1080 sunlight-readable industrial display, so the warning appears on the same screen that carries the crane readings. The pre-warning is meant to arrive while there is still room to slow a slew or hold a lift.

That early notice changes the operator routine. Instead of watching only the load and the signal, the operator also holds an awareness of the neighbour and adjusts before the gap closes. On a busy site the pre-warning is a prompt rather than a punishment: it tells the operator that the other crane is close and that the next movement should be deliberate. The coordinator still runs the sequence and the radio still carries the commands, but both now sit on top of a warning that fires on its own.

▌  PRE, NOT POST  The warning is designed to arrive early enough for the operator to slow a slew or hold a lift.

▌  ON THE CAB DISPLAY  It appears on the 11.6-inch sunlight-readable industrial display alongside the crane readings.

▌  A PROMPT, NOT A PENALTY  The pre-warning tells the operator that the neighbour is close, so the next movement can be deliberate.

05  SETTING UP THE GROUP ON A LIVE SITE

Setting up group anti-collision belongs to the commissioning stage. The cranes on the site are brought into the group so they can auto-network, and the relationships between them are established before the first shared shift. Because the host is a Linux platform with a 220 V AC input and RS485, USB and LAN outputs, the unit integrates with the infrastructure the crane already has, and the display feeds the cab directly. The outputs are there for integrators who want to route the data onward.

The practical work is a checklist. Confirm every crane that shares airspace is on the group and networking. Confirm the position picture is live on the cab display. Confirm the pre-warning behaves as expected during a controlled approach before the site relies on it. Then keep the routine, because the system logs alarms for audit, inspection and accident back-trace, so the record of a warning is as useful as the warning itself. A group that is set up once and left unverified is a group nobody can trust.

▌  COMMISSION TOGETHER  Bring every crane that shares airspace into the group and confirm the networking before the first shared shift.

▌  USE THE OUTPUTS  RS485, USB and LAN outputs and the cab display connect the unit to the infrastructure the crane already has.

▌  KEEP THE LOG  The system logs alarms for audit, inspection and back-trace, so warnings leave a record as well as a prompt.

PROCUREMENT IMPACT

●  If more than one tower crane works over a shared deck, group anti-collision is the function that links the machines, not a feature of any single crane.

●  Ask how many cranes a site can bring into one group, and confirm the auto-networking behaviour on the machines that will actually run together.

●  Check that the pre-warning is visible in the cab, since a warning that arrives only at a platform is too late to change a slew.

●  Confirm the group is part of commissioning, with a controlled approach test before the site relies on the shared picture.

●  Treat the log as an asset: alarms recorded for audit and back-trace support both inspection and the accident review nobody wants to need.

WHAT TO WATCH

●  Watch whether the group covers every crane in the shared airspace, because a group that misses one machine has a blind spot exactly where conflict is most likely.

●  Watch the pre-warning timing, since a warning that arrives too late is a notification rather than a pre-warning.

●  Watch the radio environment, because a site and its surroundings change over time and the group depends on a healthy link.

●  Watch the routine after commissioning, because a picture nobody checks can drift out of step with the machines it describes.

●  Watch the plan. Group anti-collision supports the coordinator, and it does not take over the sequencing of a busy site.

ABOUT  ZN Industrial (Shandong Zhinuo) designs and manufactures crane safety monitoring systems, positioning systems and mechanical auxiliary handling equipment for overseas construction, industrial and steel markets.

Standards and regulations vary by market — local rules still govern your site.

▌  CONTACT  shandongzhinuo@outlook.com  +86 176 6371 0314 · en.znaqkj.com

SOURCES · ISO 12480-1 · EN 14439 · BS 7121 · ASME B30.3