Non-Linear Transfer Characteristic (5-Point)
A non-linear transfer characteristic is suitable in situations where a sensor output is non-linear due to e.g.
sensor mounting geometry.
Scenario
Applying a linear transfer characteristic (3-point) to a non-linear steered wheel angle sensor in a closed-
loop application (auto-guidance or GPS) may result in incorrect steered wheel positions for set-points not
equal to neutral or the end-positions. Furthermore, the steered wheel angle may not be symmetrical
around neutral. The effect of non-linearity may become apparent in auto-steering applications where a
vehicle shall drive in precise circles.
In general, it is recommended to have “an as linear as possible” relation between the steered wheel angle
and the steered wheel angle sensor. This can be achieved by clever mechanical sensor mounting.
However, it may not always be possible to achieve linearity mechanically. To electronically compensate
for a non-linear sensor characteristic, two extra points are included in the calibration.
The two extra points represents the steered wheel angle, where the steered wheel is precisely in between
neutral and right or left end-stop respectively.
0
Sampled AD value
Scaled value
Margin
Short-circuit
AD1(2)_1000_Right
AD1(2)_Neutral
AD1(2)_1000_Right
AD1(2)_500_Right
AD1(2)_1000_Left
AD1(2)_500_Left
AD1(2)_500_Right
AD1(2)_500_Left
AD1(2)_1000_Left
-1000
1000
Symbol
Index
Default
Value range
AD1_1000_Left
65080
100
[30;957]
AD1_500_Left
65055
300
AD1_Neutral
65086
500
AD1_500_Right
65062
700
AD1_1000_Right
65083
900
AD1_Linear
65087
0
0 (Non-linear), 255 (Linear)
AD2_1000_Left
65089
100
[30;957]
AD2_500_Left
65069
300
AD2_Neutral
65095
500
AD2_500_Right
65076
700
AD2_1000_Right
65092
900
AD2_Linear
65096
0
0 (Non-linear), 255 (Linear)
•
When building a transfer characteristic, the characteristic shall be monotonically increasing or
decreasing. An attempt to build illegal characteristics is not possible.
•
AD values for Neutral shall be between the AD values for left and right.
Steering Actuator Position Signal
The steering actuator position signal can be mapped to either AD1 or AD2. Scaling parameters Max left
and Max right are set respectively equal to the digital converted voltage at the left and right end-lock
Operation Manual
PVED-CL Controller for Electro-Hydraulic Steering, Version 1.38
Installation
34 |
©
Danfoss | May 2016
11025583 | AQ00000216en-US0302
