Real-time calibration of car manufacturing robots using tungsten ball markers and laser tracker for thermal drift compensation and early Body-in-White defect detection
The customer developed a line laser system to measure Body-in-White (BiW) feature positions—particularly hole locations—for early defect detection. The line laser itself provided excellent local accuracy in controlled conditions. However, when mounted on a robot end-effector in the factory environment, accuracy degraded rapidly due to thermal effects on the robot's link parameters.
As factory temperature fluctuates throughout shifts, robot link lengths and joint offsets change, causing the end-effector position to drift. This meant the line laser, despite its intrinsic accuracy, was measuring from incorrect positions. Detecting BiW defects early saves massive costs—imagine discovering a missing nut only after the entire car is assembled—but the system couldn't deliver its value without accurate robot positioning.
CalibWorks developed a real-time robot calibration solution that continuously estimates changing link parameters during production. Using tungsten ball markers on carbon fiber fixtures and laser tracker measurements during 10-second cycle time breaks, the system recalibrates every 3 cars, compensating for thermal drift and restoring the line laser's measurement accuracy.
Real-time calibration in uncontrolled manufacturing environments
Customer's line laser had excellent local accuracy, but when robot-mounted, thermal changes in link lengths caused the laser to measure from wrong positions, negating its precision.
Uncontrolled factory temperature causes robot link parameters to drift continuously, degrading end-effector positioning accuracy throughout production shifts.
Only 10-second cycle time breaks available for measurements. Required optimized pose planning to maximize observability within minimal time windows.
Calibration fixtures themselves must not drift with temperature. Traditional materials expand/contract, introducing errors into the reference measurement.
With limited measurement time, robot poses must be carefully selected to provide maximum information about link parameter errors.
BiW defects discovered at final assembly are catastrophically expensive—imagine finding a missing nut after the entire car is built. Early detection is critical.
Real-time calibration metrics
Tungsten ball markers with thermal stability
The key innovation is the combination of tungsten ball markers mounted on carbon fiber fixtures. Tungsten's high density enables precise laser tracker center estimation, while carbon fiber's near-zero thermal expansion coefficient ensures the reference positions remain invariant across factory temperature fluctuations.
During each 10-second cycle time break, the robot moves to pre-planned poses that maximize observability of link parameter errors. The laser tracker measures tungsten ball centers at multiple heights on the carbon fiber fixture. Over 3 production cycles, a complete calibration dataset is collected and robot link parameters are re-estimated in real-time.
Before and after calibration optimization
Measurable improvements in ADAS performance
CalibWorks delivered a game-changing solution for our radar-camera fusion challenges. Their innovative corner reflector design and calibration algorithms exceeded our performance targets by 200%. The system now operates reliably in conditions where our previous solution completely failed. This has accelerated our ADAS product roadmap by at least 12 months.
Unlock the full potential of radar-camera fusion with our advanced calibration solutions.