The principle of 3D scanner

A 3D scanner is a scientific instrument used to detect and analyze the shape (geometric structure) and appearance data (such as color, surface reflectivity, etc.) of objects or environments in the real world. The working principle of 3D scanners does not rely on a single technology, but is based on multiple different technologies, mainly including the following:

1、 Structured light technology

The structured light 3D scanning method is an active optical measurement technique, whose basic principle is to project controllable light spots, light strips, or smooth structures (such as stripes, points, or grids) onto the surface of the object being measured by a structured light projector, and obtain images from an image sensor (such as a CCD camera). The three-dimensional coordinate point cloud of the object surface is calculated using the principle of triangulation.

Point structured light method: A laser projects a light spot onto the surface of the object to be measured, and the spatial coordinates of the measured point can be calculated based on the line of sight spatial position determined by the spatial position of the projected beam and the imaging position of the measured point. Due to the fact that only one point is measured at a time, in order to form a complete three-dimensional surface, it is necessary to scan and measure the object point by point. Its advantage is that signal processing is relatively simple, but the disadvantage is that the time required for image capture and processing increases sharply with the size of the object being measured, making it difficult to complete real-time measurement.

Line structured light method: Using line structured light instead of point light sources, only one-dimensional scanning is needed to obtain depth image data of objects, greatly reducing data processing time. Compared with the point structured light method, its hardware structure is relatively simple and the time required for data processing is shorter.

Surface structured light method: This system consists of a projector and a surface array CCD. The structured light illumination system projects a two-dimensional shape (which can be in various forms) onto the surface of the object to be measured, such as projecting a grid like pattern of light beams onto the surface of the object. The three-dimensional surface shape can also be calculated using the triangulation method. Its characteristic is that it does not require scanning and is suitable for direct measurement.

2、 Principle of laser triangulation

For short distance scanning (usually with a focusing distance of less than 1m), laser triangulation 3D scanner technology can be used. The principle is that light source A emits a laser line or a single laser point to illuminate an object C, sensor B obtains the laser reflection signal, and the system uses the principle of triangle measurement to calculate the distance between the object and the scanner. The distance between the laser source and the sensor, as well as the angle between the laser source and the sensor, are known and very accurate. As the laser scans the object, the system can obtain the distance and angle values from the laser source to the surface of the object.

3、 Phase measurement technology

By projecting sine wave shaped light onto the surface of an object and detecting the phase change of the reflected light, the three-dimensional shape of the object surface is determined. This method is typically used for fast and high-precision measurements.

4、 Principle of Time of Flight Measurement

Laser pulses or light waves are emitted onto the surface of an object and their return time is measured. By measuring the flight time of light, the distance from an object to the scanner can be determined. The infrared laser scanner based on the Time of Flight (ToF) principle uses this technology. Firstly, the device emits pulsed light while receiving reflected light from the target object at the emission point. The photosensitive chip requires a femtosecond shutter (1 femtosecond is only one billionth of a billionth of a second) to measure the flight time of the light.

5、 Stereoscopic vision measurement technology

Similar to the working principle of the human eye, two cameras are used to simultaneously capture objects from slightly different angles. By analyzing the difference (i.e. disparity) between the images captured by two cameras, the three-dimensional coordinates of surface points of an object can be calculated.

6、 Three coordinate measurement technology

A coordinate measuring machine (CMM) establishes a Cartesian coordinate system with three mutually perpendicular axes of motion X, Y, and Z. The probe (usually a probe with a small ball) moves in the coordinate system and comes into contact with the surface of the object. The detection system records the precise position of the center point of the measuring ball in the coordinate system. By moving the measuring head and measuring multiple points, the geometric dimensions, shape, and positional tolerances of the object can be calculated.

Different 3D scanners may use one or more combinations of the above principles to achieve accurate 3D measurements. The choice of principle depends on specific application requirements, measurement accuracy, speed, object characteristics (such as material, color, shape, etc.), and cost factors.