New Approach in Non- Contact 3D Free Form Scanning

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1 New Approach in Non- Contact 3D Free Form Scanning Contents Abstract Industry Trends The solution A smart laser scanning system Implementation of the laser scanning probe in parts inspection Conclusion Abstract Mechanical touch probes are the most common sensors used for CMM inspection. Most CMM Applications today are based on a touch trigger probe for point -topoint measurement. The amount of data that can be collected using the touch probe is limited and most of the applications are limited to simple prismatic geometry parts. With the industry trend of moving towards free form 3D geometry shapes, the traditional solution of touch trigger probes is limited since the geometry definition of complex free form surface requires thousands of data points. The recent trend from the touch trigger probe to a mechanical (Analog) scanning probe is a step in the right direction, in terms of data collection rate, however it is still limited by some major fundamental characteristics of the mechanical analog sensor: a. A mechanical probe needs to maintain continuous contact with the surface and thus is limited in its scanning speed b. By nature, the dynamic range of a touch probe is practically zero, which makes the scanning pattern and thus the programming of the path more complicated. c. Programming a mechanical probe for a scanning operation requires operator skill and experience. d. The resolution and size of the features that can be scanned are limited by the diameter of the stylus. The need for an efficient, accurate and fast non-contact laser based metrology system has been a major challenge for the last few years. While various non-contact systems 1

2 exist in the market for vision, calibration and digitizing, none has overcome the technology barriers and provided the required performance to bring efficient, fast and accurate 3D sensor to the CMM world. The traditional design of laserbased probes is built around the fundamental triangulation principle (figure 1). It involves the manipulation of a laser beam projected from the object through dedicated set of optics in a fixed position and angle and an optical detector (a Position Sensing Device - PSD or a CCD). These sensors are very sensitive to the optical parameters of the measured object, including color, material, glare & reflection, surface finish and relative angle between the laser beam and the object. This sensitivity generates large deviations and unreliable output in the measurement results. Non-contact vision systems are starting to penetrate various 3D applications leveraging on their 2D performance capabilities. When used for 3D applications, the vision systems provide fast scanning with very limited accuracy in the 3 rd dimension. A real breakthrough in this area is a 3D laser-based scanning sensor, combining advanced laser and vision technologies. It comprises an adaptable laser source; a sophisticated set of optics, twodimensional CCD sensor and an advanced real time adaptive control. In addition, this sensor utilizes an extensive set of image processing algorithms to analyze the acquired image Industry Trends With the growing demand for complex geometry parts and a continuous search for higher quality control standards, the need for automatic comparison of part dimensions with its CAD design becomes a major quality control requirement. In addition, the industry is continuously seeking: Higher production throughput and yield High accuracy free form parts Uniform quality outputs on the production floor in remote sites Higher measurement speed Real time process control Typical 3D scanning and digitizing applications include: Free form parts Plastic Injection Molding Rapid Prototyping Mold & Dye Turbine Blades Soft Material Parts Cutting Tools 2

3 The solution - Smart Laser Scanning To address the new challenges imposed by the 3D free form shapes, a 3D laser-based scanning sensor, combining advanced laser and vision technologies has been developed. It comprises of an adaptable laser source; a sophisticated set of optics; an advanced real time adaptive control and a two-dimensional CCD sensor. An extensive set of image processing algorithms analyzes and elaborates the high-quality data gathered (fig. 2). This implementation provides single point precision of six microns (1 sigma) and a feature precision of 1 micron (100 points best fit, 1 sigma), meeting the high precision requirements. The small laser spot size enables to scan very fine geometry details down to 30 microns. Based on the proprietary optics, the unique adaptive control feature and the sophisticated image processing software, the probe handles almost all materials and surface finish types, automatically performing self-calibration via real time closed loop adaptive control. The combination of a large dynamic range and high accuracy, makes it very simple to set up the scanning path and collect thousands of points fast and accurate, with no noise and no need to filter or post process the cloud (figures 3,4). The probe advantages Over Mechanical touch probes Speed, Accuracy, Setup, Materials, Complex geometry Over existing laser sensors Accuracy, Adaptive control Real data output Over Vision systems Accuracy High-resolution 3D Capability 3

4 Light Source B 1 A 1 Manufacturers are constantly seeking solutions for improving their scanning capabilities and for integrating these into their systems. They are looking for the successful and proven implementation of the non-contact sensor technology into their products. A Target Surface B The integration of the new laser into a smart digitizing machine is required in order to best utilize the benefits of the probe. The required capabilities are: Figure 1: Standard Triangulation Method Target Surface Light Source Figure 2: Multiple Triangulation Method Implementation of the laserscanning probe in parts inspection Digitizing and rapid scanning of 3D surfaces Automatic contour tracking capability Fine details verification Data display and record in real time Export to CAD/CAM systems Ability to create a CNC program User-friendly digitizing software Easy set up of the scanning path The probe can be easily mounted on a conventional CMM, digitizing system, production Robot or any other on-line measuring system. Probe integration onto the CMM requires two major tasks: 1. Integration with the CMM motion control to enable data acquiring on the fly 4

5 (encoder latching for every point measured along the path without backoff and without stopping 2. Application software Integration, in order to incorporate the key functions of the probe (START, STOP, CALIBRATION, VIEW etc.) solutions that should provide an answer for the fast growing demand for accuracy and speed, along with simple utilization and minimum setup time. The modern technology of 3D software along with a rapid growth in the PC processing capabilities enables to offer new solutions to support the modern industry needs. Figure 3: Pointcloud sample Processed with Metris Base Figure 4: Shaddiing - STL Format Conclusion The industry trend is pushing for new scanning and digitizing 5