Device and method for detecting flatness of sheet material

A method for detecting a flatness of a sheet material using a device, wherein:

• the device comprise:
• a conveyor;
• a gantry;
• a beam;
• a camera unit a speed measurement unit;
• a vibration measurement unit;
• a multi-line laser for emitting laser beams;
• a cable carrier;
• a controller;
• and a control cabinet wherein, the conveyor is disposed beneath the gantry and comprises a plurality of pinch roll assemblies for feeding a sheet material;
• the beam is disposed on the gantry and comprises a first side and a second side;
• the camera unit is disposed on the first side of the beam and comprises at least two cameras;
• the speed measurement unit is disposed between the at least two cameras;
• the vibration measurement unit is disposed on the second side of the beam and comprises at least two distance measurement devices;
• the multi-line laser is disposed between the at least two distance measurement devices;
• the controller is connected via the cable carrier to the camera unit, the speed measurement unit, and the vibration measurement unit;
• and the controller is connected through a communication cable to the controller;
• and
• the method comprises:
• 1. calibrating the cameras to estimate intrinsic parameters, extrinsic parameters, and lens distortion parameters;
• 2. calibrating a structured-light measurement system formed by each camera and the multi-line laser, and determining an equation of a laser plane in a coordinate system defined by each of the cameras;
• 3. starting the speed measurement unit to detect and measure a position and speed of a sheet material;
• 4. when the sheet material starts moving, starting the speed measurement unit, the distance measurement devices, and the multi-line laser;
• 5. determining a sampling frequency of each camera according to the speed of the sheet material;
• and collecting images taken with each camera;
• 6. analyzing laser beams in each image;
• 7. determining a fast variable value acquired by the vibration measurement unit, calculating a vibrational amplitude of each point on a centerline of each laser beam;
• and compensating for a first point cloud data with the vibrational amplitude, wherein the first point cloud data is a collection of points scanned by the centerline of the laser beams;
• 8. measuring the same position of the sheet material with all of the laser beams;
• obtaining a maximum distance from each camera to each point on the sheet material;
• regenerating a second point cloud data and storing the second point cloud data in a table;
• 9. constructing a sheet material model from the second point cloud data for each camera, thereby reconstructing a partial 3D flatness of the sheet material;
• 10. numbering the cameras from 1 to n from a leftmost camera to a rightmost camera;
• numbering the sheet material model created by each camera with a serial number corresponding to the camera;
• selecting a first sheet material model as a reference, performing a data fusion for an overlapped area between the first sheet material model and a second sheet material model;
• continuing the data fusion in the same manner until no sheet material model is left, thereby reconstructing a complete 3D flatness of the sheet material;
• and
• 11. calculating a deflection and a radius of curvature according to the complete 3D flatness data;
• transferring the deflection and the radius of curvature to the controller to provide a basis for correction of the flatness of the sheet material.