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The Benefits of Multi-Sensor Alignment

  • By Liam Brennan

With 6 degrees 6 of freedom (6DOF)


Many of today’s inline quality control applications require vision systems to inspect targets that are larger than a single sensor’s field of view. Examples include log scanning, electronic parts (PCB, tablets, laptops) inspection, large automotive component and assembly inspection (doors, engine blocks, cylinder heads), and inspection of factory panels.

Multi-sensor networking using 3D smart sensors is the ideal solution to this challenge. The ability to synchronize scanning and perform alignment and stitching across multiple scan devices offers several key benefits.

Multi-Sensor networks are

  1. Flexible – Users can set up a network in any layout they want, including ring, opposing, angled, and staggered.
  2. Scalable – Users can network any number of sensors to meet the needs of their particular application.
  3. Simple – In a smart sensor, the required software for networking is already onboard. A single cable connects the sensor to a dedicated master network controller that handles power distribution and micro-second data synchronization.

 

“6 degrees of freedom in sensor alignment allows the user to choose the axes on which offsets and rotations are calculated.”

 

6 DoF in Flexible Sensor Alignment

Industrial inspection applications present a number of variables that need to be compensated for in the setup of a sensor network. This includes inaccurate mounting, or the need for a specific rotation to optimize scan results (e.g., angling the sensor to improve the signal on reflective targets).

For non-reflective targets a straight sensor setup is ideal (left). For specular targets, the sensor is rotated on the X-axis to minimize reflected light and generate cleaner scan data (right). 6 DoF alignment supports this type of angled sensor setup

3D smart sensors such as Gocator® solve these challenges by providing advanced alignment options with 6 degrees of freedom (6 DoF). In essence, this means sensors can be staggered, rotated, angled, or offset in every coordinate direction (X,Y,Z) to fit specific applications. Gocator produces fully stitched 3D models in a single, world coordinate system which can then be used for accurate absolute measurement.

How is the data handled?

Many vision engineers are specialized in identifying and measuring defects from a completed 3D height map. However, they don’t want to deal with the complexity of triggering and combining data accurately from multiple sensors into one 3D point cloud/height map.

A 3D smart sensor takes care of this by extracting the data from multiple sensors and automatically aligning, merging, and resampling it into an aggregate 3D height map. The scan results are combined within a single world coordinate system, which allows the engineer to extract high-precision measurements on the combined 3D profile data.

As a result, engineers no longer have to carry out Software Development Kit (SDK) programming to combine the raw data. Everything is done natively onboard the sensor using built-in multi-sensor networking capabilities

Application Examples

A. Z-rotation angle correction is critical for data correlation of small electronic parts

  • Electronics, machining tools, and medical supplies inspection requires correlating results to CMM measurements
  • Correlation is done by comparing height data at specific XY locations
  • Slight Z-rotation misalignment results in skewed data, which affects correlation results
  • 6 DoF alignment allows engineers to correct for this skew

B. High accuracy scanning of large automotive components

  • Six Gocator® line profilers are networked to cover the full part
  • The sensors automatically combine profile data and generate a single 3D height map for measurement and inspection
  • Six Gocator® line profilers are networked to cover the full part

Conclusion

6 degrees of freedom in sensor alignment allows the user to choose the axes on which offsets and rotations are calculated. This functionality provides important options to improve scan results and measurement accuracy in specific application scenarios.

Here is a quick recap of the benefits for today’s busy vision engineer:

  • Choose the axes on which offsets and rotations are calculated
  • Align multi-sensor systems with built-in 6 DoF software
  • Stagger multi-sensor systems using Y offset (e.g., for small FOV sensors)
  • Automatically correct for inaccurate mounting or purposeful rotation using X rotation (e.g., in specular mounting) and Z rotation (e.g., angling the sensor to reduce edge noise).

 

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