Overhead Crane & AGV Collision Avoidance & Path Arbitration
The overhead crane and AGV/RGV collaborative system enables fully automatic material flow on smart factory production lines through a three-tier architecture: the scheduling and management layer (OPC UA + MES), the equipment control layer (crane PLC + AGV controller), and the execution and sensing layer (sensors + safety devices). Three core technologies drive the system — path arbitration and task allocation, a four-level interlock protocol with status sharing, and collision avoidance algorithms (DWA + VO + artificial potential field). The solution has been deployed in 30+ installations across automotive final assembly, steel cold rolling, and lithium battery production lines.
In a smart factory, the coordinated operation of overhead cranes (bridge/gantry type), AGVs (Automated Guided Vehicles), and RGVs (Rail Guided Vehicles) is the backbone of fully automatic material flow. The crane handles inter-bay and cross-station lifting, AGVs provide flexible floor-level transport, and RGVs deliver high-speed transfer along fixed rails. Each of these systems has its own independent control architecture, and safe, efficient collaboration requires a unified scheduling platform and interlock protocol. This article breaks down the engineering implementation of crane–AGV/RGV collaboration, covering system architecture, three core technology pillars, and typical configuration options.
Three-Tier System Architecture and Data Flow Design
The crane + AGV/RGV collaborative system is organized into three functional tiers. The scheduling and management layer serves as the decision-making core — it receives material handling tasks from MES or WMS, decomposes each task into a crane lifting segment and an AGV/RGV ground transport segment, and assigns the work to the most suitable equipment based on path arbitration algorithms. This layer runs on a scheduling server (industrial PC with an i7 processor and 16 GB RAM) or a high-performance PLC (Siemens S7-1500). Communication uses OPC UA for MES/WMS integration and MQTT for data exchange with individual equipment controllers, with a scheduling cycle of ≤100 ms.
The equipment control layer consists of the independent controllers for each piece of equipment. The crane uses a Siemens S7-1200/1500 PLC (Profinet-controlled VFD with closed-loop encoder feedback), the AGV runs on an industrial PC with an STM32 low-level driver (laser SLAM navigation + differential drive control), and the RGV uses a Mitsubishi FX5U or Siemens S7-1200 (VFD-driven rail travel plus hydraulic power unit for platform lifting). Each controller executes local motion commands received from the scheduling layer and reports its position, speed, status, and fault information back every 100 ms. The execution and sensing layer is the physical endpoint for actuation and detection. The crane's three mechanisms (hoisting, bridge travel, trolley travel), the AGV's drive and steering, and the RGV's rail travel and platform lifting are each equipped with encoders, limit switches, and safety sensors (laser anti-collision, safety edges, and audible and visual alarms).
Core Technology Comparison for Crane–AGV/RGV Integration
The core technologies behind crane–AGV/RGV collaboration fall into three areas: path arbitration and task allocation (addressing the efficiency question of "who does what"), a four-level interlock protocol with status sharing (addressing the safety question of "how to coexist safely"), and collision avoidance algorithms (addressing the real-time question of "what to do about dynamic obstacles"). Each technology area has distinct objectives, algorithms, and data cycles, and they are combined in practice based on equipment count and site complexity. The comparison below covers five dimensions — core objective, primary algorithm, data cycle, resource consumption, and implementation complexity:
| Comparison Parameter | Path Arbitration and Task Allocation | Four-Layer Architecture Interlock Protocol | Collision Avoidance Algorithm |
|---|---|---|---|
| Core Objective | Multi-Task Optimal Assignment, Overall Efficiency Maximization | Safe Coexistence of Multiple Equipment, Zero Collision Incidents | Real-Time Dynamic Obstacle Avoidance, Path Optimality |
| Primary Algorithm | Priority Queue+Time Window+Shortest Path | zone interlock/distance interlock/priority interlock | DWA/VO/Artificial Potential Field |
| Data Cycle | Scheduling Cycle≤100ms | Status Broadcast≤100ms/Times | DWAComputation Cycle≤200ms |
| PLCComputing Resources | High(Priority Sorting+Path Search) | Medium(Distance Calculation+Interlock Logic) | High(Start Button Sampling+Evaluation Function) |
| Applicable Equipment Count | ≥5Units(Includingoverhead crane+AGV+RGV) | 3~12Units | 3~8Units |
| Implementation Complexity | High(Requires MESInterface+Scheduling Algorithm Development) | Medium(PLCProgram+Communication Configuration) | High(Requires Edge Computing Box) |
| Kruud Recommended Scenarios | Automotive Final Assembly/Lithium Battery/Steel Cold Rolling | All Collinear Multi-Equipment Scenarios | Yards with High Dynamic Obstacle Density/Workshop |
Typical System Configurations by Scale
The coordinated system configuration for overhead cranes and AGVs/RGVs is categorized into three tiers based on equipment count and site complexity. Each tier has clearly defined boundaries in dispatching logic, hardware setup, and communication architecture.
Small System (3–5 Units) — Designed for a single workshop with a few cranes and AGVs working together, such as a small-to-medium machining workshop. Dispatching: One Siemens S7-1200 (CPU 1215C) handles all dispatching tasks, running a basic priority queue with zone interlock logic. The crane PLC and dispatching PLC are combined (dispatching functions are integrated into the crane's main PLC). AGVs connect directly to the dispatching PLC via Modbus TCP (200 ms cycle). No SCADA/HMI server is used; operators view dispatching status on the crane's HMI (Siemens KTP700). Key features: Low hardware cost (dispatching solution only requires a PLC expansion of approx. $440), fast deployment (1–2 weeks), but does not support complex path search or dynamic replanning. Kelude's small-scale solution has been deployed in multiple single-crane + 2–3 AGV collaboration scenarios.
Medium System (6–12 Units) — Suited for medium-sized production lines, e.g., a lithium battery electrode workshop (2 cranes + 4 AGVs + 2 RGVs). Dispatching: A dedicated dispatching PLC (S7-1500 CPU 1516-3 PN/DP) runs full path arbitration, time-window conflict detection, and dynamic replanning. Each equipment controller connects to the dispatching PLC network via Profinet IRT (cycle ≤ 100 ms). The dispatching PLC interfaces with MES via OPC UA. Includes an industrial network switch (Siemens SCALANCE XB208) and an industrial touch screen (IPC227E + WinCC) for dispatching monitoring. Communication cycles: crane 50 ms, AGV 100 ms, RGV 50 ms. Key features: Low dispatching latency (path arbitration + conflict detection ≤ 8 ms/cycle), supports priority task insertion and automatic reassignment after faults, deployment period 4–6 weeks.
Large System (12–64 Units) — Designed for large plants, e.g., an automotive final assembly workshop (12 cranes + 24 AGVs + 8 RGVs). Dispatching: Multiple dispatching PLCs handle zone-based control, with a host computer for global optimization. Each S7-1500 manages up to 12 units (divided by zone); zones exchange boundary tasks via PN/PN Couplers. The host computer (industrial PC i7 16GB + dispatching software) runs global optimization algorithms (genetic algorithm/particle swarm optimization for task allocation, optimized every 30 seconds). Dispatching PLCs handle fast response (100 ms cycle), while the host computer handles mid-to-long-term optimization (30-second to 5-minute cycles). If the host computer fails, each zone's dispatching PLC degrades to independent operation (basic interlocks remain active). Key features: Supports very large scale, efficiency improvement is 15–25% higher than medium systems, deployment period 8–12 weeks.
Technology Selection Guide: Interlock, Collision Avoidance, Path Arbitration
Path arbitration, interlock protocols, and collision avoidance algorithms are not mutually exclusive — they are selected in layers based on site complexity. Here are clear recommendations:
Interlock-Only Scenario (Minimum Configuration) — For up to 4 units with no complex path planning needs, where the sole requirement is preventing crane-AGV collisions. Solution: Deploy only the four-layer interlock protocol (zone interlock + distance interlock + priority interlock + emergency stop interlock), adding interlock logic to each unit's PLC. No dispatching PLC is required; unit PLCs exchange status directly via Profinet. Cost: Approx. $440–$740 per unit for communication module + programming, 1–2 week timeline. Suitable for: Small-to-medium workshops, retrofitting existing equipment.
Interlock + Collision Avoidance (Standard Configuration) — For 5–10 units in workshops with many obstacles and dynamic changes (e.g., yards with personnel or forklifts crossing). Solution: Interlock protocols serve as the safety baseline, while collision avoidance algorithms provide dynamic evasion. On top of interlocks, each crane is fitted with an edge computing box (Jetson Orin NX, 100 TOPS) running DWA/VO algorithms. Collision avoidance results are written to the crane PLC's speed setpoint via Ethernet (overriding the VFD speed command with the highest safety priority). Cost: Interlock solution approx. $4,400–$7,400 + edge computing box approx. $1,180 per crane + AI algorithm license approx. $1,480 per unit. Suitable for: Storage yards, steel mills, workshops with mixed personnel traffic.
Complete Solution (Interlock + Collision Avoidance + Path Arbitration) — For 10+ units with MES/WMS automatically dispatching tasks, where overall efficiency optimization is required. Solution: All three technology layers are deployed. The dispatching PLC (S7-1500) handles path arbitration, conflict detection, and task allocation (100 ms cycle). Each crane is equipped with an edge computing box for local collision avoidance (DWA algorithm). Interlock protocols serve as the final safety net. The dispatching PLC interfaces with MES via OPC UA, and a host computer provides global efficiency optimization and KPI dashboards. Cost: Medium systems approx. $22,000–$44,000; large systems approx. $74,000–$296,000 (depending on equipment count and plant area). Suitable for: Automotive final assembly, lithium battery production lines, steel cold rolling, new smart factories.
Kelude Heavy Industry provides full-service support from site survey to system commissioning. All three configurations support future upgrades — an interlock-only system can be upgraded to the complete solution without replacing hardware. For more detailed selection guidance, refer to the related articles on path arbitration dispatching and AGV interlock solutions.
Frequently Asked Questions
Q: How are the crane and AGV coordinate systems unified? Can positioning accuracy be aligned?
A: The crane uses a one-dimensional rail coordinate (X-axis along the rail direction), while the AGV uses a two-dimensional plant coordinate (X/Y + heading angle). The unification approach is to maintain a "device position mapping table" in the dispatching PLC — the crane's X coordinate is mapped to the Y direction of the plant coordinate, while the AGV's X/Y coordinates are used directly. Crane positioning accuracy is ±2–5 mm (laser + encoder fusion), and AGV positioning accuracy is ±10–30 mm (laser SLAM + reflectors). At transfer stations (crane unloading to AGV), the AGV first moves to the docking point and stops within ±10 mm, then the crane lowers the load onto the AGV platform. Kelude has achieved a crane-AGV docking accuracy of ±5 mm with a 99.7% success rate at an automotive plant's final assembly workshop.
Q: How do we implement interlocks between legacy cranes and newly added AGVs? Do we need to replace the PLC?
A: No PLC replacement is needed, but the crane PLC requires an Ethernet communication module (Siemens CP1542-1, approx. $440) and an AGV interlock program (approx. 20 lines of FBD logic). The crane PLC receives broadcast device status (position/speed/direction/operation mode) from the AGV dispatching system via Profinet or Modbus TCP, and interlock logic is added to the PLC program: when the projected distance between the crane and AGV along the X direction falls below the safety threshold, the crane automatically decelerates or stops. For older cranes with pure relay control, an upgrade to PLC is required first (S7-1200 approx. $440 + programming approx. $740). Kelude offers retrofit solutions for adding AGV interlocks to legacy cranes, with on-site installation taking approximately 3–5 days per unit.
Q: When multiple cranes and AGVs operate simultaneously, where is the processing bottleneck in the dispatching system?
A: The bottleneck comes down to three areas: ① Path search computation — each additional crane increases the complexity of path conflict detection by O(n²). With 6 cranes, 15 conflict pairs must be checked per cycle; with 12 cranes, that number rises to 66; with 18, it reaches 153. The solution is to divide the factory floor into sub-zones and only run conflict detection between cranes within the same zone — cranes in different zones operate independently. ② Communication bandwidth — each crane broadcasts a status message (about 200 bytes) every 100 ms. With 12 cranes, that generates 12 × 10 × 200 = 24 KB of data per second, which Profinet/OPC UA handles with ease. ③ PLC scan cycle — the scheduling PLC executes path arbitration, conflict detection, and task assignment in each cycle. Code execution takes about 2–5 ms with 6 cranes, and roughly 8–15 ms with 12 cranes, so the 1 ms scan cycle of the S7-1500 remains more than sufficient.
Q: What site survey data is required for an overhead crane + AGV collaborative system?
A: The pre-installation survey requires four categories of data: ① Production line layout — crane rail position/length/lifting height, AGV/RGV travel aisle width and turning radius limits, and precise coordinates of equipment docking stations; ② Equipment parameters — crane lifting capacity/span/lifting speed/travel speed, AGV load capacity/speed/navigation method (magnetic tape, laser, or QR code), and RGV rail length/travel speed/lifting stroke; ③ Production takt time — number of material handling moves per hour, material demand timing at each workstation, and peak concurrent equipment usage; ④ Network conditions — 4G/5G signal strength inside the factory building, WiFi coverage, or Profinet wired network availability. Kelude offers a free site survey and delivers the survey report along with a preliminary proposal within 2 days.
