Inductive guidance
General Information
The above picture is showing the principle with a receiving antenna with two coils, which detects the electro-magnetic field around the wire in the floor.
Inductive guidance (also known as wire guidance) in an AGV is based on the fact that an electrical conductor through which an AC current is flowing will create an electromagnetic field around itself. This field is stronger close to the conductor, and is reduced with increased distance from the conductor.
An electromagnetic field, which passes through a coil, will induce an electric voltage across the coil ends. This voltage can be detected across the termination of the coil. The voltage is proportional to the strength of the field.
A guiding antenna contains two coils positioned on each side of the wire, which is embedded in the floor. The difference in electric voltage between the two coils will create the steering signal to the steering motor of the AGV.
When the antenna is centered over the guide wire, the voltage in the coils will be the same and the steering signal is equal to zero. If the antenna is positioned to either side of the guide wire, the voltage will be increased in one coil and reduced in the opposite coil. This voltage difference will generate a steering signal, which will control the rotation direction of the steering motor.
The floor loops will have different frequencies that the control board in the AGV can detect separately.
The AGV will have minimum one antenna for guiding and one cross antenna for detecting guide wires that are perpendicular to the guide wire. The cross wires are used to update the exact position of the AGV. Many AGVs will also have further guide antennas for reverse travel and guiding by support leg of a forklift AGV.
Floor installation
The floor installation is made very easy today as there are several companies specializing in this technique. Special floor cutting machines are developed which cut the floor without excessive noise, concrete dust or water spillage and leaves a clean slot ready for installation of the wires. These companies will do the complete floor installation including floor marking, floor cutting, wire installation in floor and enclosures, sealing the slots and grinding if necessary.
The conducting wire is normally a 1,5mm2 wire of flexible type (H05V-K). The wire is installed in a thin slot in the floor. The slot is cut by a concrete cutting machine with a hard metal blade.
The depth of the slot is normally 20 mm, and the width is determined by the number of wires in the slot. Normal width is 4 mm in a normal guide slot and 8 mm if more than three wires are combined in the same slot.
The wire is positioned in the bottom of the slot and a foam strip is squeezed down over the wire for best protection. On top of the foam strip is special polyurethane or epoxy filling added. The filling has a neutral color and is very wear-resistant.
The wire in a guide path may not be positioned close to solid iron constructions for a longer distance, as it will distort the magnetic field.
The guide wires are laid out in the floor in a loop and connected to a frequency generator . There can normally be four different frequencies which each have their own wire loops.
Advantages/disadvantages
Wire guidance is proven technology and is well known by suppliers and users. The AGVE wire guidance system has high accuracy by use of high quality components. The components onboard the AGV are standard components from AGV Electronics. The system is easy to install and program. End users may install and extend existing systems as the technology and programming an AGV is easy to understand.
The AGV Electronics inductive wire guidance is a modern navigation method where floor cutting is minimized. Curves do not normally need to be cut in the floor. Curves may be programmed by using the teach-in function using limited free ranging by dead reckoning.
As a safety feature in an inductive guided system can the guide wire, or a separate control wire, be disconnected to instantly stop all vehicles in a system.
In some cases can environmental and system demands make it hard and expensive to install wires in the floor, under these circumstances other types of navigation methods are used.
Guide antenna
The guide antenna is a standard component from AGV Electronics. The guide antenna is a low cost component. The guide antenna gives two signals to the control board which are used for guiding the AGV.
AGV types
Inductive wire guidance can be used for all types of vehicles, such as tricycles as well as vehicles with dual steer/drive units. AGV Electronics has experience from AGVs with up to six steered and driven wheels.
The inductive wire guidance system may also be combined with Magnet-Gyro guidance. This can be useful to avoid running wires in the floor over long distances where gyro guidance and magnet updates may be used.