ACC (Adaptive Cruise Control) -systems are able to influence the vehicle speed, based on radar or laser measurements of the traffic ahead. Its proper function requires the angular alignment of the radar or laser sensors within small tolerances. During calibration, the sensor of each vehicle is aligned in azimuth und elevation along the driving direction of the vehicle.
The driving direction is either ascertained by fixating the vehicle on a VisiCon centraliser, or measured with a VisiCon dPP 3D-Sensor at each wheel position.
"Viewing"-Direction of ACC-Sensors
The method of aligning the optical axis ("viewing"-direction) of an ACC-sensor to the driving direction depends on the ACC-sensor type. Some types are aligned actively by the ACC control unit. For calibration, a mirror is placed in front of the ACC sensor. The orientation of the mirror needs to be known accurately. Some sensor types require the mirror to be tilted horizontally and vertically in defined steps during the calibration.
The "viewing"-direction of the ACC-sensor may be defined by means of a retro-reflector. In order to allow an accurate calibration, this reflecting unit needs to be positioned as far away from the vehicle as possible (> 6 m).
VisiCon has developed a solution, that employs a movable pillar that is placed in front of the sensor during calibration. The effective distance to the vehicle is more than doubled by means of a 90 degree-mirror, so that the overall space requirement does not exceed the size of a regular headlamp aiming machine.
Some ACC types feature a reference surface (mirror) beside the radar sensor, that defines the "viewing"-direction of the sensor.
With an integrated light source, that is precisely aligned within a light collecting box, the reference surface is illuminated. The angle of the reflected light beam is measured with the light collecting box (for example of a headlamp aiming machine), and is transferred to the control unit of the ACC sensor during the calibration process.
VisiCon offers calibration units for infrared-based ACC systems. With our light collecting boxes, the optical axis of ACC sensors, that operate with IR-laser light, is measured and reported to the ECU of the ACC sensor.