Wire Navigation
AGV wire guidance is based on passing a current through an electrical conductor, which creates an electromagnetic field around the conductor itself. This field is strong when close to the conductor and diminishes with distance from the conductor.
An electromagnetic field passed through a coil will induce a voltage across the coil ends. This voltage can be detected across the coil terminal ends and the voltage is proportional to the strength of the field.
A typical AGV has a drive and steering assembly, which operates from signals produced by the vehicle, guide, and cross antennas. The antennas are attached to the vehicle in such a way that the guiding antenna will be centered over the guide wire and the cross antenna will intersect the cross wire. A guiding antenna consists of two coils positioned on each side of the guide wire, which is embedded in the floor. Amplifying the difference in voltage between the 2-coils creates the steering signal. When the antenna is centered over the guide wire, the voltages in the coils are equal and the resulting steering signal is zero. If the AGV moves to one side of the guide wire the voltage in the coil now closer to the guide wire is increased and the voltage in the coil furthest from the guide wire is decreased. This voltage difference creates a steering signal, which controls the rotational direction of the steering motor. Floor loops have different frequencies, which the AGV control board detects separately. The AGV has a minimum of one antenna for guiding and one cross antenna for detecting wires that are perpendicular to the main guide wire. Cross wires are used to update the exact position of the AGV. Many AGV’s have further guide antennas for reverse travel and many forklift type AGV’s can guide by antennas mounted in the support legs.
Guide wires are laid out in the floor in a loop and connected to a frequency generator. Typically there are 4-different frequencies each having their own wire guide loop. The conductor is normally a 14-gauge flexible type (h05V-K) wire installed in the floor cut or slot. A slot is cut to a depth of approximately 1-inch and the number of wires in the slot determines the width. Typical width for a 4-wire slot is 1/4-inch, the wire is positioned in the bottom of the slot, and a protective foam strip is squeezed down over the wire. A wear resistant neutral colored polyurethane filling is added on top of the foam strip to complete the assembly. Guide wires positioned close to solid metal construction over long distances can distort the magnetic field.
There are several companies today who specialize in floor cutting techniques and can produce clean, wire ready floor slots. Specialty machines with little noise, concrete dust, or water spillage have been developed. These companies can handle complete floor installation including floor marking, floor cutting, wire installation and enclosures, plus sealing and grinding of the slots if necessary.
Wire guidance is a proven technology and is well known by suppliers and end users alike. An Amerden wire guidance system is extremely accurate down to ±1/8” or less thanks to workmanship, quality of components, and design. The standard onboard components are easy to install and program. The Amerden wire guidance system is a modern navigation method where floor cutting is minimized. Curves may be programmed by using a teach-in function using limited free ranging and by dead reckoning. Therefore, there is no need to cut curves in the floor.