Odometry

Odometry or Hodometrie (from Greek Hodos, way ' and métron, dimension ' - ie " position measurement " ) is a method of estimating position and orientation ( pose estimation ) of a mobile system based on the data of its propulsion system. Driven by wheels systems use for the number of wheel revolutions during current systems use their number of steps (eg, robots). A device that uses the odometry to the location estimate is an odometer. The odometry is in interaction with the dead reckoning navigation is a fundamental method for ground-based vehicles of all types (cars, robots), but it is used because of its error characteristics rarely as the sole method.

Method

The number of wheel revolutions between two time points is counted ( for example, with incremental encoders ) and together with the known circumference of the wheel, where the wheel diameter imagines, converted to a path difference:

Of the steering angle of the individual wheels, the direction of vehicle movement can be detected, the calculation rule for the steering angle of the type of the chassis ( front-axle, Hinterachslenker ) depends.

Odometry measurement methods allow relative positioning, since they only work with path differences. For an absolute position specification a position must be known, to which the position differences can be obtained. In the one-dimensional case ( rail vehicle ) results in the equation

Error analysis

The following variables may affect the accuracy of the position measurement.

• Wheel geometry ( runout, wear, incorrect measurement of the diameter )
• Soil texture ( roughness, slip)
• Chassis geometry ( game, incorrect measurement of the wheel distances and steering equipment)
• Vehicle weight ( unequal distribution: greater stress and deformation of individual wheels )
• Wind

All errors are incorporated into the position difference, which is added to the last known position. Thus, adding the error at each measured step, and with prolonged measurement arises an increasing deviation. This deviation (following error) in the odometric position calculation is virtually impossible to avoid, even if all error sources are minimized.

Application

Vehicle Technology

Odometry refers here to a function that determines at certain times, the position, orientation, and the running state of a vehicle. The input variables are usually measured variables from the chassis ( wheel rotation direction), the yaw rate sensor (ESP / ABS ) and the steering ( steering angle, steering wheel angle). In the car navigation it is used in addition to GPS positioning, in order to bridge areas without reception as tunnels and refine the GPS results.

Robotics

In autonomous robotics is the odometry one of the easiest and thus one of the most common tools for localization. In general, the odometry measurements are more sensors - typically echolocation or GPS - supplements to get better results.

• Automotive Technology
• Robotics
• Dimensional Metrology
• Navigation