A calibrated sensor is one that is able to deliver engineering units as output (as verified by a traceable calibration artifact). Without this ability, a sensor is essentially useless to customers who are trying to perform dimensional analysis (metrology).

Many scanners or sensors today are not pre-calibrated, leaving system integrators with the onerous task of converting 3D point clouds into something useful. Integrators might handle this issue once, but what about applications that need absolute uniformity across many sensors where consistency and accuracy are paramount? For these reasons pre-calibration is a necessary feature in a 3D sensor.

Requirements for Sensor Calibration

Calibrating a sensor requires (1) removing the non-linearities in component alignment and lens distortion (through a process called linearization), and (2) ensuring linearity throughout the measurement volume with traceability based on the use of calibration artifacts.

When an optical system is calibrated, there is a mapping established between the field of view to the pixels on a camera in engineering units. This mapping is often encoded into a calibration table that is stored on a sensor then loaded at startup for use at runtime. A pre-calibrated sensor, therefore, delivers engineering units on power up and is ready for use in inline quality control applications where re-calibration is not practical.

2D vs. 3D Calibration

3D sensor calibration presents a number of challenges that make it difficult for the end user to complete themselves. Unlike 2D camera calibration that relies on a checkerboard artifact to map pixels to engineering units, 3D requires a much more elaborate approach to deliver high accuracy. In 3D calibration, a precision motion-controlled artifact is moved through the measurement range (Z) where a precise mapping of artifact features to pixels is observed. This process requires specialized equipment and 3D mathematical methods to transform pixels to 3D coordinates in engineering units

For this reason, it is far easier for a customer to purchase a factory pre-calibrated sensor––a major feature offered in leading 3D sensors.

Many Types of Optical Models

With factory pre-calibrated sensors, many models are needed to cover the various combinations of field of view and resolution.

Gocator users have the choice of different sensor families, each calibrated to a specific combination of field of view and resolution. Sensor families are based on two proven technologies – laser triangulation and structured light fringe projection. For laser triangulation where the applications involve high speed motion of an object, either single point or line profiler sensors are offered. For structured light where objects are stationary, snapshot sensors are used.

Benefit to the User

The beauty of a pre-calibrated 3D smart sensor is that the user can simply power up the sensor upon delivery and start scanning immediately with optimal results––straight out-of-the-box––with no extra time, cost, effort or concern. Smart sensors can be deployed into complex machinery with no need for recalibration later offering operational lifetimes up to 10 years.