Calibration of Endoscopic Systems Coupled to a Camera and a Structured Light Source

We propose a calibration method for measuring accurate 3D coordinates inside hollow parts using an endoscopic system consisting of a fiberscope, a camera coupled to the eyepiece of the fiberscope, and a power LED adjusted to the front end of the fiberscope’s bundle. The power LED was adapted to generate a structured light plane (SLP). The calibration method reduces the uncertainty of intrinsic camera parameters by using a traceable printed pattern fixed to a glass flat. The extrinsic camera parameters or SLP position and orientation (POSE) on the camera system are assessed with the projection of the SLP on printed flats. Part of the SLP POSE is the SLP to camera distance, which is measured and adjusted using calibrated ring gauges as follows: we projected the SLP on the inner surface of a calibrated ring gauge, then we obtained the parameters of the circumference (i.e. its diameter) and compared it to the calibrated parameters. Next, we adjusted the distance of interest until measured and calibrated ring parameters were close enough. Using this calibration method, we measured the diameter of several ring gauges and a break master cylinder, finding an average error between ±0.03 mm with a diameter uncertainty around 0.055 mm.