In recent years, three-dimensional scanning, as a rapid three-dimensional digital technology, has been applied increasingly in various fields, including reverse engineering, industrial testing, computer vision, CG production, etc., especially in the fields of 3D printing and intelligent manufacturing, which are currently developing rapidly. Three-dimensional scanning, as a front-end three-dimensional digital and three-dimensional visual sensing technology, has become an important segment of the industrial chain; meanwhile, various types of applications have demanded higher requirements in numerous aspects of the three-dimensional scanning device, such as cost, practicality, accuracy and reliability, etc.
Optical three-dimensional scanning is the most common modern technical means in the field of three-dimensional digitization, and it is the prominent feature of the technology for having both relatively high measurement efficiency and high precision. White light three-dimensional scanning is a conventional optical scanning technology, where a coding mark is made on the surface of an object by grating projection and then a triangulation is made by photographing of a camera. Being widely applied in the field of three-dimensional measurement, white light three-dimensional scanning is characterized by high precision, high spatial resolution and relatively fine data quality. With the continuous expansion of the application field, various complex utilization environments have brought forward new requirements on three-dimensional scanning technology. For example, it is expected that the device have a better scanning convenience and better optical anti-interference performance, and that the scanning process can be more rapid and simple, and unnecessary steps could be omitted as much as possible, and the measurement can be completed in the majority of light environments. Due to the grating projector structure and the limitation of relying on sequential coding, white light scanning device is large in volume and weight, and needs stable support structures such as tripod to assist measurement, thereby limiting the convenience of measuring; additionally, since the luminance of white light sources is limited, the measurement is considerably influenced by ambient lights and optical properties such as the color and material of the object, it is difficult to measure effectively in a brighter environment or on darker objects.
In order to make up for the shortcomings of white light three-dimensional scanning technology, a scanning technology with line laser as light source emerges. Although still based on the triangulation principle of multi-vision, this technology is different in that the line laser is employed as pattern projector, the patterns are simple and do not change over time, the laser is small and simple in structure; accordingly, the scanning device becomes light and does not need additional support and stabilization device to assist measuring, therefore hand-held measurement as its typical characteristic is capable; meanwhile, the luminance in the center of the laser line is extremely high, thus adaptable to scanning in the majority of light environments or on dark objects. However, before the existing laser three-dimensional scanning technology pervades the entire field of three-dimensional scanning, there are still several significant problems to be solved:
The scan efficiency and cost advantages cannot be achieved both. Single-line laser scanning technology is relatively simple in realization, and low in cost, while its scanning performance is greatly limited, and its scanning speed is slow, leading to limited practicality; whereas multi-line laser scanning technology is largely improved in scanning speed, but due to the reliance on special customized laser generator, its process is complex and its cost is high, thereby also hindering the popularization of applying the technology.
The service life is short. Continuous full-power scanning expedites the light attenuation for optic devices, particularly for various types of optical elements (laser LD and LED lights, etc.), which directly leads to a degraded scanning performance (including data quality and scanning speed); additionally, a lot of heat generated by the continuously working LEDs also brings in cooling problems for the device, since good heat dissipation performance contradicts with small and light overall structure, and poor heat dissipation performance not only causes early failure of the optical elements, but also results in a small deformation in the entire scanning structure, leading to a loss of scanning accuracy.
The scanning mismatching rate is high, and lacks of reliability. There is a high mismatching rate in the conventional marker-based matching technology, which is presented that multi-scanned data appear ambiguity when uniformly registered to the same coordinate system, leading to a piece of scanning data being separated from the whole data, thus generating a wrong model. This problem can be solved in the white light three-dimensional scanning process by manually deleting etc. after each single-side scanning, but cannot be solved by employing similar methods in the laser three-dimensional scanning process under a continuous scanning mode. Thus, there is usually a re-scanning after a mismatching occurs, which remarkably affects the working efficiency.
The scanning accuracy is low. The quality of laser scanning data is related to a variety of factors, wherein working distance control is a major factor. Under the circumstance that the depth of field is determined, an image blurring may be caused when the change of working distance goes beyond the depth of field, which results in large data noise and significant accuracy reduction. In the conventional laser scanning technology, working distance mainly relies on an operator's subjective evaluation. Therefore, it is difficult to precisely control the working distance in continuous scanning process, leading to a relatively low scanning accuracy.