Compact fast-steering tip/tilt laser scanner for high power material processing applications
Compact fast-steering tip/tilt laser scanner for high power material processing applications
复制标题
DOI：
10.5075/epfl-thesis-2247
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
M. Hafez
中科院分区：
文献类型：
--
作者：
M. Hafez
用于在两个维度上偏转激光束的常见配置是基于彼此垂直放置的两个单轴振镜扫描仪。近年来，这些快速扫描仪已被证明是非常可靠和非常准确的。它们在市场上广泛可用，并具有广泛的技术规格。然而，这样的配置相当庞大，并且不能满足寻求紧凑解决方案以将这些扫描头容易地集成到其生产线中的工业的需求。此外，当这些扫描头与扫描透镜结合使用时，两个单独的反射镜会导致光学像差，扫描透镜是专门为单个入射光瞳设计的。因此，具有单个反射镜的紧凑型快速转向倾翻/倾斜激光扫描仪将作为各种应用的关键部件，例如在材料加工、天文学、卫星间激光通信、成像系统、生物医学和眼科应用中。在这项工作中提出的紧凑型双轴倾斜激光扫描仪可以执行各种功能，如图像跟踪，光束稳定和对准，视线指向，和场景扫描。设计这样一个扫描仪需要一个多学科的方法，涉及光学，机械，电磁学，传感器和控制理论。扫描仪由一个具有大有效面积的单镜组成，并且具有用于两个倾斜轴的单旋转点。此外，重心与旋转中心重合，以达到最佳的动态性能。扫描仪的紧凑尺寸允许在各种光学系统中轻松集成。此外，反射镜易于互换，这在选择激光源时提供了更大的灵活性。所提出的设计的另一个主要优点是其能够按比例缩小到小型化版本。缩放主要取决于镜子的有效表面，这通常由应用指定。反射镜越大，其惯性越高，并且为了保证高性能，致动器也越大。采用两对推拉式直线电磁驱动器驱动扫描器的反射镜。反射镜悬架基于由锥球接触组成的滑动轴承，具有优化的摩擦和磨损性能。磁预加载力用于保持反射镜并提供足够的旋转刚度。此外，基于光电探测器和微型激光笔的位置传感器集成在模块中，用于闭环反馈定位。该反射镜可以绕两个轴倾斜± 61 mrad（± 3.5°），精度优于50μrad。此外，差分分辨率为2.5μrad，最大倾斜和倾斜偏转的建立时间分别为10 ms和14 ms。扫描仪的总体积为30 x 40 x 50 mm 3，总重量不超过90 g。在这项工作中进行了设计，模拟和实验研究，以优化不同组件的倾斜/倾斜扫描仪。这些组件是：电机，轴承系统，位置传感器和反馈控制回路。提出了一种基于矩形线圈和磁体的电磁致动器的几何参数优化的分析模型。该模型具有很高的可靠性，可推广到各种电磁驱动系统的设计中。此外，一个广泛的分析时，一个单一的反射镜是围绕两个轴旋转产生的光束路径失真。此外，提出了用于补偿由这种配置引起的系统误差的校正方程。倾斜扫描器适用于工业材料激光加工中的各种应用。这些应用不仅限于焊接、切割、钻孔和打标等传统工艺，还包括激光微操作等新技术。在这种新方法中，由于激光照射导致材料弯曲和收缩，从而允许以亚微米精度快速调整和定位微机械和光机械部件。此外，形状记忆合金的局部退火，导致整体部件，如微夹持器的刚度变化，代表了智能材料中的一个非常创新的应用。另一方面，扫描仪也是生物医学和眼科应用中的关键部件。第一次测量进行了扫描仪的光学断层扫描的视网膜似乎非常有前途。此外，光镊设置已实现使用扫描仪，允许容易和灵活的操纵激光束捕获的细胞和分子。
The common configuration for deflecting laser beams in two dimensions is based on two single-axis galvanometric scanners placed perpendicular to each other. Over recent years, these fast scanners have proved to be both very reliable and very accurate. They are widely available in the marketplace and have wide-ranging technical specifications. However, such a configuration is rather bulky and can not satisfy the needs of industry which seeks compact solutions for an easy integration of these scanning heads into their production lines. In addition, two separate mirrors leads to optical aberrations when these scanning heads are used in conjunction with scanning lenses, which are specially designed for a single entrance pupil. Therefore, a compact fast-steering tip/tilt laser scanner with a single mirror would act as a key component in diverse applications, e.g. in material processing, astronomy, intersatellite laser communications, imaging systems, bio-medical and ophthalmologic applications. The compact two-axis tilt laser scanner presented in this work can perform a variety of functions such as image tracking, beam stabilization and alignment, line-of-sight pointing, and scene scanning. Designing such a scanner required a multi-disciplinary approach involving optics, mechanics, electromagnetics, sensors and control theories. The scanner is composed of one single mirror with a large active area and has a single point of rotation for the two axes of tilt. Moreover, the center of gravity coincides with the center of rotation to reach optimum dynamic behavior. The scanner's compact dimensions allow an easy integration in the various optical systems. Furthermore, the mirror is easily interchangeable which gives greater flexibility in the choice of the laser source. Another major advantage of the proposed design is its ability to be scaled down to miniaturized versions. The scaling depends mainly on the active surface of the mirror, which is generally specified by the application. The larger the mirror, the higher its inertia and the larger are the actuators in order to guarantee high performance. Two pairs of push-pull linear electromagnetic actuators are used to drive the mirror of the scanner. The mirror suspension is based on a sliding bearing composed of a cone-ball contact with optimized friction and wear behavior. A magnetic pre-load force is used to hold the mirror and to give sufficient rotational stiffness. Furthermore, a position transducer based on a photodetector and a miniature laser pen is integrated in the module and is used for closed loop feedback positioning. The mirror can be tilted around both axes by ± 61mrad (± 3.5°) with an accuracy better than 50μrad. Moreover, a differential resolution in the order of 2.5μrad, and settling times for maximum tip and tilt deflections of 10ms and 14ms respectively are achieved. The overall volume of the scanner is 30 x 40 x 50 mm3, and its total weight does not exceed 90g. Design, simulations and experimental investigations were carried out in this work in order to optimize the different components of the tip/tilt scanner. These components are: the motors, the bearing system, the position transducer and the feedback control loop. An analytical model that allows an optimization of the geometrical parameters for an electromagnetic actuator based on rectangular coils and magnets is proposed. This model proved to be very reliable and can be extended to the design of a variety of electromagnetic driving systems. In addition, an extensive analysis of the beam path distortions generated when a single mirror is pivoted around two axes is covered. Furthermore, correcting equations used to compensate for the systematic errors resulting from this configuration are proposed. The tip/tilt scanner is suited to a variety of applications in industrial material laser processing. These applications are not just restricted to conventional processes like welding, cutting, drilling, and marking, but also to new technologies such as micro-manipulation of parts by laser. In this new approach, bending and shrinkage of the material result due to laser irradiation, allowing fast adjustment and positioning of micro-mechanical and opto-mechanical components with sub-micron accuracy. Furthermore, local annealing of shape memory alloys, leading to stiffness variation in monolithic parts such as micro-grippers, represents a very innovative application in smart materials. On the other hand, the scanner is also a key component in bio-medical and ophthalmologic applications. The first measurements carried out with the scanner for optical tomography of the retina appeared very promising. Furthermore, an optical tweezers set-up has been realized using the scanner, allowing easy and flexible manipulation of laser beam trapped cells and molecules.