Using the GPS Global Positioning System the vehicle receives timing signals from several GPS satellites. The vehicle calculates its distance to the individual satellites and then calculates its position using the distance information from several satellites. In the vehicle a GOETTING guidance controller combines the GPS information and odometric data from wheel encoders etc. to give direct commands to the vehicle’s steering system.
The basic GPS system has only a precision of approximately ± 16 feet, which is insufficient for vehicle guidance. Goetting KG uses several measures to increase the performance of a GPS based guidance system to a precision of ± 0.4″ (1 cm).
- DGPS Differential GPS: a fixed-location GPS receiver positioned on site evaluates the precision of the GPS signals and calculates correction signals, which are radioed to the vehicle system.
- PDGPS Precision DGPS: The vehicle receiver in-creases its precision using carrier phase evaluation algorithms.
- Sensor Fusion: GOETTING uses odometric information from the vehicle’s wheel decoders to in-crease quality and to bridge brief interruptions and errors of the GPS signal.
ADVANTAGES AND CHALLENGES
- No field installations (a DGPS reference station is needed, if no sufficient public reference signal is available). Changes of site or vehicle path are handled by self-learning” or changes to a virtual computer map.
- Performance of this guidance system is not affected by adverse light conditions including operation at night, under fog, airborne dust, lint, fluid spraying, bright daylight and welding or by objects on the path like debris, spills, snow, ice, standing water, fluids and ground irregularities etc. In most situations temporary interference of GPS data reception by sun activity is resolved by Goetting’s sensor fusion technology.
- The precision of the guidance system (± 0.4″) is sufficient to stack and pick-up ISO shipping containers automatically, if the vehicle/crane offers precision controls. Customers reached an overall vehicle precision of up to ± 0.75″.
- All GPS antennas need to be mounted with an unobstructed line of sight to the sky, opening angle 170°(5° elevation). Indoor operation is not possible, high buildings, container stacks and overhead cranes can pose challenges. CTS and Goetting offer site surveys to determine mounting positions of GPS antennas.
- The satellites as a part of the system are operated by the US government, which could decide to temporarily decline this service e.g. for reasons of national security.