Documentation HG G-73650ZD | English, Revision 05 | Date: 09.03.2017 | www.goetting-agv.com
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Chapter 2: Basic Principles of Track Guidance
Note
Since odometric calculations tend to be load-dependent the installation of a Gyro is recom-
mended.
If an external sensor fusion (determination of position and angle) shall be applied it can be
connected via the CAN Bus. The relevant protocol is described in chapter 6 on page 103.
This may be e.g. laserscanner HG 43600. As long as they are compliant with the CAN Bus
protocol requirements it is possible to use other position- determination systems as well.
By the use of a short-term stable odometry in combination with an absolute position sensor
the advantages of both systems are united. The absolute position sensor initializes the odo-
metric data and thus provides both the position as well as the vehicle heading at every
point. During operation the cumulative inaccuracies in the odometry will be reset at those
points where an absolute position is available.
In addition to the position and the steering angle the sensor fusion provides the speed as
well as an accuracy estimation. This estimation is based on the accuracy table (see Table 47
on page 121). The table is structured in such a way that the error is small right after e.g. a
transponder has been passed over. With the distance traveled the error tends to grow more
rapidly, as the angle is also steadily worsening. So with every meter travelled the value of
the accuracy assessment is decreased by one position, i.e. it moves one line upwards in the
corresponding Table 47.
When using GPS technology the GPS system determines the position's estimated accuracy
in meters. If GPS and transponder antennas are used simultaneously the accuracy estima-
tion is defined by the system in use. Switching between systems can be automated via ac-
curacy thresholds or set manually via segment specific attributes.
2.3.1 The Odometry
The odometric system uses wheel rotations, the steering angle and/or a Gyro to determine
the change in vehicle position and vehicle heading.
The odometry has the advantage to be highly accurate over short distances and to supply
the vehicle position at any time. The odometry has to be initilized at start-up. However while
traveling longer distances the system immanent errors accumulate. This can cause consid-
erable deviations.
2.3.2 Sensors for Navigation
2.3.2.1 Transponder Antenna
The transponder system outputs the position and the code of the transponder currently lo-
cated underneath the antenna. The position lateral to the direction of travel has an accuracy
between ± 5mm and ±20mm, depending on the antenna type (mostly its size). Also depend-
ing on the antenna type the detection range is between ±125 and up to ± 500mm, the read-
ing distance varies between 50 - 200 mm. Possible antennas are e.g. the Götting types HG
98810, HG 98820 and HG 98850.
