Towing AGVs

Definitional Boundaries & Taxonomy

Towing Automated Guided Vehicles (AGVs), often referred to as autonomous tuggers or logistics trains, represent a specific class of mobile robots designed not to carry payloads directly on their chassis, but to pull one or multiple passive or semi-active trailers. The fundamental architectural distinction between a Towing AGV and a unit-load AGV lies in the decoupling of the traction unit from the load-bearing unit. This decoupling introduces significant dynamic complexity, transforming a singular rigid body problem into an $N$-body articulated system.

The taxonomy of Towing AGVs is generally structured around three axes:

1. Drawbar Pull Capacity: Ranging from light-duty (<1,000 N, typical in ecommerce and electronics assembly) to ultra-heavy-duty (>50,000 N, utilized in aerospace and automotive chassis transport).
2. Kinematic Configuration of the Tractor: Differential drive, tricycle drive (steer-drive wheel), or quad-steer, which dictates the turning radius and maneuverability of the lead vehicle.
3. Hitching Mechanism: Manual pin-and-clevis, automated hook, or advanced active ball-hitches equipped with absolute rotary encoders to measure the articulation angle $\theta$ in real-time.

Historical Evolution

The lineage of Towing AGVs traces back to 1953 when Arthur "Mac" Barrett developed the "Macar", a modified towing tractor that followed an overhead wire. By the 1970s, this evolved into inductive wire-guided systems buried in the concrete floors of factories. While robust, these systems were inherently inflexible, turning factory layouts into rigid, monolithic structures. The 1980s and 1990s saw the advent of magnetic tape and RFID grids, which lowered installation costs but still required physical infrastructure modifications.