40 February 2011 www.drives.co.uk
Driverless transportation systems (DTS) are becoming increasingly popular forhandling materials in many industries because of their potential costsavings, resulting from the absence of human operators. However the
planning costs for these systems can be high. Depending on the navigationsystem used, structural changes may be necessary in the surroundingenvironment to accommodate induction loops or magnets in the floor, orreflectors for 2D laser scanners on the walls or equipment.
The flexibility of such systems to allow later changes to the vehicle’s routings ortasks also depends on the technology. Production-related or structural changes –such as changes in racking, or the location of machines – can disrupt thenavigation system, which can be rectified only by costly structural or operationalmodifications.
Siemens’ innovative Autonomous Navigation System (ANS) takes driverlessvehicles to a new dimension. It is based on a laser distance measurementtechnology and uses the ceiling for navigation, cutting installation costs becauseno navigation aids need be installed on the floor, walls or machinery. It alsoprovides flexibility for future route changes when the production environment ismodified.
For many years, area-scanning distance sensors have been available that supply2D depth information with a detection angle of 190°. They can be used to detectthe width, position and orientation of objects. They are also used for 3D contourmeasurements, gripper positioning, access controls or collision detection, as wellas for positioning systems such as travelling cranes.
For its ANS, Siemens is using Leuze electronic’s ROD 4 laser system which has a
The ceiling’s the limit for laser-guided navigation
SEN
SORS An driverless industrial vehicle
fitted with Siemens’ laser-basedAutonomous Navigation System(shown in close-up below right)
fast pulse propagation time technology that allowsthe detection of 3D profiles generated by a swivellingor a linear feed motion of the measured object, or ofthe laser scanner, relative to one another.
The scanner is mounted on a swivel motor on thetop of the vehicle where it captures a spatialrepresentation of the building’s ceiling, which it usesfor navigation.
The system operates by measuring pulsepropagation times. Pulses of light are emitted atshort intervals. The time difference between thetransmission and reception of a pulse reflected fromthe ceiling is used to calculate the distance to theceiling. This is almost independent of the shape,colour or structure of the ceiling. The captured data issent via a high-speed interface to a computer whichcalculates the vehicle’s position.
“The new 3D laser navigation system can beinstalled on a wide range of different types of indoorvehicles, from high-lift trucks to industrial trucks,”explains Walter Beichl, Siemens’ ANS projectmanager.
The accuracy of positioning and travel depend onthe surroundings and on the vehicles. With forklifts,for example, a positioning accuracy of ±30mm canbe achieved; for industrial trucks, the accuracy is±5mm.
Compared to conventional DTS installations, ANS ismuch easier and quicker to install. The route isdefined using the structural contours of the ceiling,so no structural changes are needed. Travel routesare taught using a “teach-in” technique, allowingroute changes to be made in a few minutes at shortnotice.
Almost as a by-product, the swivelling laserscanner ensures high reliability, because it can alsodetect obstacles in the vehicle’s path. While this is nota “secure” obstacle detection system for protectingpersonnel, it can detect static obstacles and apply thevehicle’s brakes when this happens. Furthermore, itcan detect load carriers, such as pallets, and recordthem automatically within a defined range withoutneeding precise positioning. D&C
Driverless transportation systems usually rely on opticalscanners for navigation and need reflectors to bemounted on the building structure or on machinery. Analternative approach, which aims 3D laser scanners at theceiling, cuts costs and is more flexible.
P36-43_d&c_0211 Edited_Short features 30/01/2011 22:37 Page 40
