Laser Tracking System Research Articles

Analysis of laser spot centroiding errors for laser acquisition system in gravitational wave detection missions.

In space-based gravitational wave detection, establishing ultra-long-distance and ultra-high-precision laser links between satellites is achieved through the laser acquisition and tracking system. The laser spot centroid positioning method, which offers low computational complexity and strong adaptability to beam shape, is currently the core measurement method during the laser acquisition phase. However, due to various interference factors encountered in practical tests, this algorithm often falls short of meeting the extremely high requirements. To address this challenge, this paper first defines the specific performance criteria for the centroid positioning method based on the needs of laser acquisition in gravitational wave detection. It then comprehensively analyzes how detector noise, window truncation effects, and beam wavefront aberrations impact the accuracy of angular measurements. Using derived analytical expressions, an improved centroiding algorithm is proposed to mitigate the effects of detector noise and wavefront aberrations simultaneously. Numerical simulations are conducted to design the specific parameters for the algorithm and the system, resulting in the ability to achieve an angular measurement accuracy of 60 nrad at the telescope front end.

A Combined Sensor Design Applied to Large-Scale Measurement Systems.

The photoelectric sensing unit in a large-space measurement system primarily determines the measurement accuracy of the system. Aiming to resolve the problem whereby existing sensing units have difficulty accurately measuring the hidden points and free-form surfaces in large components, in this study, we designed a multi-node fusion of a combined sensor. Firstly, a multi-node fusion hidden-point measurement model and a solution model are established, and the measurement results converge after the number of nodes is simulated to be nine. Secondly, an adaptive front-end photoelectric conditioning circuit, including signal amplification, filtering, and adjustable level is designed, and the accuracy of the circuit function is verified. Then, a nonlinear least-squares calibration method is proposed by combining the constraints of the multi-position vector cones, and the internal parameters of the probe, in relation to the various detection nodes, are calibrated. Finally, a distributed system and laser tracking system are introduced to establish a fusion experimental validation platform, and the results show that the standard deviation and accuracy of the three-axis measurement of the test point of the combined sensor in the measurement area of 7000 mm × 7000 mm × 3000 mm are better than 0.026 mm and 0.24 mm, respectively, and the accuracy of the length measurement is within 0.28 mm. Further, the measurement accuracy of the hidden point of the aircraft hood and the free-form surface is better than 0.26 mm, which can meet most of the industrial measurement needs and expand the application field of large-space measurement systems.

Effects of Whole-Body Vibration Therapy in Weight-Bearing and Non-Weight Bearing Positions for Upper and Lower Extremities on Balance and Cervical Joint Position Sense in Children With Cerebral Palsy.

Cerebral palsy (CP) is a complex pathological entitythat affects muscular control, coordination, proprioception, fine andgross motor abilities, position, stability, and, in some cases, cognition. This study aimed to compare the effects of whole-body vibration therapy (WBVT) in weight bearing and non-weight bearing positions for the upper and lower extremities on balance and cervical joint position sense in children with spastic CP. A randomized controlled trial was carried out on 60 hemiplegic children with spastic CP aged 5-15 years. Following randomization, all participants were allocated into six equal-sized groups based on the application ofWBVT for upper extremities, lower extremities, or both simultaneously in either weight-bearing or non-weight-bearingpositions. Pediatric balance scale (PBS) and laser tracker system were used to assess functional balance and cervical joint position sense. One-way analysis of variancefor Inter-group analysis showed a statistically significant difference among all groups in PBS and cervical joint position sense (p<0.05). WBVT was found to be beneficial in improving balance and cervical joint position sense in both weight-bearing and non-weight-bearing positions for the upper and lower extremities in children with cerebral palsy. However, the simultaneous application of WBVT in weight-bearing positions for both upper and lower extremities showed the most significant improvements in improving both balance and cervical joint position sense, indicating the most efficacious position of this treatment approach in children with cerebral palsy.

Photochemically Induced Propulsion of a 4D Printed Liquid Crystal Elastomer Biomimetic Swimmer.

Underwater organisms exhibit sophisticated propulsion mechanisms, enabling them to navigate fluid environments with exceptional dexterity. Recently, substantial efforts have focused on integrating these movements into soft robots using smart shape-changing materials, particularly by using light for their propulsion and control. Nonetheless, challenges persist, including slow response times and the need of powerful light beams to actuate the robot. This last can result in unintended sample heating and potentially necessitate tracking specific actuation spots on the swimmer. To tackle these challenges, new azobenzene-containing photopolymerizable inks are introduced, which can be processed by extrusion printing into liquid crystalline elastomer (LCE) elements of precise shape and morphology. These LCEs exhibit rapid and significant photomechanical response underwater, driven by moderate-intensity ultraviolet (UV) and green light, being the actuation mechanism predominantly photochemical. Inspired by nature, a biomimetic four-lapped ephyra-like LCE swimmer is printed. The periodically illumination of the entire swimmer with moderate-intensity UV and green light, induces synchronous lappet bending toward the light source and swimmer propulsion away from the light. The platform eliminates the need of localized laser beams and tracking systems to monitor the swimmer's motion through the fluid, making it a versatile tool for creating light-fueled robotic LCE free-swimmers.

Laser tracking system for real-time monitoring the combustion of energetic nanomaterials

This paper discusses a technique for monitoring the combustion of high-energy materials in real time using a laser monitor modified to track the combustion front at the relatively long distance between the object of study and optical system. Options for moving the platform with the sample at a fixed beam of a laser monitor and a system with a motorized rotary mirror are considered. The system provides moving the observation area over the surface of the sample at an adjustable speed up to 22 cm/s. The advantages of the proposed technique are the possibility of high-speed control the combustion front propagation through the sample, full suppression of background lighting and the distance increasing when monitoring high-temperature objects. The paper presents the results of imaging the combustion in air of nanothermite compositions in a real time with movable field of view. The video images allow observing the changes in morphology of the nanopowder surface during combustion. In contrast to previously used laser monitors, the system allows studying the uniformity and linearity of combustion front propagation including the local burning rate at different moments of time.

The implementation of an image-guided system at a proton therapy center facility.

Pencil Beam Scanning (PBS) proton therapy has similar requirements on patient alignment to within 1mm and 1-degree accuracy as photon radiosurgery. This study describes general workflow, acceptance, and commissioning test procedures and their respective results for an independent robotic arm used for Image Guided Radiotherapy (IGRT) for a Proton Therapy System. The system is equipped with kV-imaging techniques capable of orthogonal and Cone-Beam Computed Tomography (CBCT) imaging modalities mounted on an independent robotic arm gantry attached to the ceiling. The imaging system is capable of 360-degree rotation around patients to produce CBCT and kilovoltage orthogonal images. The imaging hardware is controlled by Ehmet Health XIS software, and MIM Software handles the image fusion and registration to an acceptable accuracy of ≤1-mm shifts for patients' alignment. The system was tested according to the requirements outlined in the American Association of Physicists in Medicine (AAPM) Task Group (TG) 142 and TG 179. The system tests included (1) safety, functionality, and connectivity, (2) mechanical testing, (3) image quality, (4) image registration, and (5) imaging dose. Additional tests included imaging gantry isocentricity with a laser tracker and collision-avoiding system checks. The orthogonal and volumetric imaging are comparable in quality to other commercially available On-Board Imagers (OBI) systems. The resulting spatial resolution values were 1.8-, 0.8-, and 0.5-Line Pairs per Millimeter (lp/mm) for orthogonal, full-fan CBCT, and half-fan CBCT, respectively. The image registration is accurate to within 1mm and 1 degree. The data shows consistent imaging-guided system performance with standard deviations in x, y, and z of 0.7, 0.8, and 0.7mm, respectively. The system provides excellent image quality and performance, which can be used for IGRT. The proven accuracy of the x-ray imaging and positioning system at McLaren Proton Therapy Center (MPTC) is 1mm, making it suitable for proton therapy.

Real-time laser spot detection and tracking system based on parallel multi-target detection and determination algorithm.

Laser spot detection and tracking play a critical role in laser techniques. However, traditional detection and tracking systems tend to be bulky and lack portability. Therefore, there is a growing emphasis on developing high-performance and miniaturized systems based on the field programmable gate array (FPGA). In this paper, a novel parallel multi-target detection and determination algorithm is proposed to address the issue of current FPGA-based systems' ineffective detection of laser spots in complex environments. Our simulation results demonstrate that the algorithm can effectively detect laser spots in complex environments. It can process a frame with an 800 × 480 resolution in only 7.88ms at a 50MHz image processing frequency, which means it can process more than 100 f/s and meet the real-time detection requirements. Such excellent detection performance is challenging to achieve with central processing units and advanced RISC machine microprocessors. Then, the algorithm is further deployed on an FPGA to build a prototype laser spot detection and tracking system. Practical tests show that the system can achieve a spot detection accuracy of around 90% under different luminous intensities, indicating excellent robustness of the designed algorithm. Besides, with the use of a piezoelectric actuator, speedy and precise tracking of the laser spot is implemented. The characteristics of speedy response, self-latching in power off, and no electromagnetic interference of the piezoelectric actuator give the system tremendous advantages in developing high-precision wireless communication control technology, which further broadens the application of the proposed system.

Precision Denavit–Hartenberg Parameter Calibration for Industrial Robots Using a Laser Tracker System and Intelligent Optimization Approaches

Precision object handling and manipulation require the accurate positioning of industrial robots. A common practice for performing end effector positioning is to read joint angles and use industrial robot forward kinematics (FKs). However, industrial robot FKs rely on the robot Denavit–Hartenberg (DH) parameter values, which include uncertainties. Sources of uncertainty associated with industrial robot FKs include mechanical wear, manufacturing and assembly tolerances, and robot calibration errors. It is therefore necessary to increase the accuracy of DH parameter values to reduce the impact of uncertainties on industrial robot FKs. In this paper, we use differential evolution, particle swarm optimization, an artificial bee colony, and a gravitational search algorithm to calibrate industrial robot DH parameters. A laser tracker system, Leica AT960-MR, is utilized to register accurate positional measurements. The nominal accuracy of this non-contact metrology equipment is less than 3 μm/m. Metaheuristic optimization approaches such as differential evolution, particle swarm optimization, an artificial bee colony and a gravitational search algorithm are used as optimization methods to perform the calibration using laser tracker position data. It is observed that, using the proposed approach with an artificial bee colony optimization algorithm, the accuracy of industrial robot FKs in terms of mean absolute errors of static and near-static motion over all three dimensions for the test data decreases from its measured value of 75.4 μm to 60.1 μm (a 20.3% improvement).

Near-zero beam drift laser tracking and measurement system with two-stage compression structures.

This paper introduces a scheme of near-zero beam drift tracking technology with two-stage compression structures for the coordinate accuracy measurement of a laser tracker. The Galileo telescope system, with a magnification of 21.43, is designed to compress the beam drift in a dual-frequency interferometer. The azimuth and pitch of the beam drift are compressed to 2.41in. and 2.92in., and the compression rates are 95.0% and 91.9%, respectively. The improved four degrees of freedom position-sensitive detector system is used to further compress the beam drift. The peak-to-peak value of the beam drift is 0.9in. in the azimuth direction and 2.1in. in the pitch direction. The standard deviation of azimuth is within 0.15in, and the pitch is within 0.43in. The coordinate accuracy of the laser tracker can be improved 6.85 parts per million by simulation. The developed two-stage compression near-zero beam drift system can be used in the laser tracker to realize large-scale precision instrument geometric measurement.

Improved Target Laser Capture Technology for Hexagonal Honeycomb Scanning

In laser tracking systems, capturing moving targets is a prerequisite to guaranteeing a tracking system’s performance. Previous studies have confirmed that the capture probability of hexagonal spiral scanning is higher than that for other scanning methods, but there is still room for improvement. This article proposes an improved hexagonal honeycomb scanning capture method based on hexagonal spiral scanning for a prior moving target model with a Gaussian distribution positioned within the scanning range of the visual threshold. Through experimental verification, it was found that, within the same scanning field of view, the capture probability can be increased by 3% compared to that in traditional hexagonal spiral scanning, making the capture probability greater than 98%. The improved hexagonal honeycomb structure scanning method proposed in this article provides a new solution for target acquisition problems in fields such as laser communication, laser docking, and airborne radar.

Laser Beam Jitter Control Based on a LabVIEW FPGA Control System

The thermal blooming effect, platform jitter, and other effects of laser beam propagation cause serious deviation, which will have a negative impact on laser tracking systems. It is important to ensure that the laser beam does not deviate. Based on a fast steering mirror, a CMOS camera, and a Flex RIO system, a laser beam jitter control system is designed and implemented. The error is detected by camera and compensated for by the fast steering mirror (FSM), which is controlled by the Flex RIO device. By using LabVIEW and MATLAB, a closed loop model is realized. The results show that the system response is highly stabilized and has a short rise time, providing a reference for engineering applications.

Multi-Source Data Fusion Method for the Truss Structure Stability Measurement of Space Telescope

It is necessary for large aperture space telescopes to achieve high measurement accuracy for mechanical reference mounting surfaces, complex deformation conditions, and difficulty in describing spatial geometric properties. In this manuscript, we propose a measurement method for evaluating the deformation of the trusses structure by fusing multiple sources of data. The multi-source data are obtained from the theodolite, laser tracker, and photogrammetry systems. The datum alignment of the laser tracker and photogrammetry coordinate systems is achieved by establishing the transition coordinate system method of the datum platform, and the alignment accuracy (3σ) is about 8.8″, 5.1″ and 4.2″. Using the laser tracker to establish the relationship between the cubic mirror coordinate system and the geometric coordinate system of the mounting part, the fast and high-precision measurement of the mounting angle of the cubic prism is realized, and the measurement accuracy reaches 2″. The data from multiple sources are fused through datum transfer and alignment to establish a cosine matrix transfer chain between the mechanical characteristic coordinate system of each component and the transition coordinate system of the datum platform, and the Eulerian rotation angle is obtained to describe the angular relationship between the components after solving. Based on the Monte Carlo mathematical error modeling analysis, the datum transfer and alignment simulations were carried out, and related experiments were conducted. The experiments show that the transfer error (3σ) of the XYZ rotation angle is less than 20.6″ after the datum transfer, the maximum error is within 3″ compared to the simulation results, and the deviation of the comparison photographic measurement data is less than 7.6″. The datum transfer method combined with photogrammetry can describe the deformation trend of large-size trusses under different load conditions more objectively and reasonably.

Smart License Plate in Combination with Fluorescent Concentrator for Vehicular Visible Light Communication System.

Vehicle-to-vehicle communication based on visible light communication has gained much attention. This work proposes a smart license plate receiver incorporated with a fluorescent concentrator, enabling a fast vehicle-to-vehicle communication with a large field of view and high optical gain. Communication performance is experimentally analyzed using off-the-shelf light-emitting diode-based headlamps for low-latency direct line of sight channel. Additionally, a blue laser diode-based beam-steering and tracking system, through image processing of taillights with a steerable mirror, is investigated. Data rates of 54 Mbps from the headlamps and 532 Mbps from the beam-steering channel with ±25° are demonstrated. In addition, real-time video streaming through the beam-steering channel is presented.

Novel laser tracking measurement system based on the position sensitive detector.

The rapid development of modern industrial technology has led to the increase of machinery precision. Laser tracking measurement systems represent a novel type of coordinate measurement method, which was developed on the basis of metrology. In this paper, we aim to define a single-station 3D coordinate rotating laser tracking measurement system based on the principle of the space coordinate method. In view of the current architecture and optical path of the system, we establish the ideal mathematical model of the system and derive the coordinate expression for arbitrary measured points in the measurement space. The output response of the photoelectric position detector to the rotating laser and the linearity of the position signal in the detection circuit have been detected via a concrete experiment. A laser tracking system was used to track the target mirror mounted on the coordinate measuring machine measuring spindle. It is shown that stable tracking is possible during the 3D movement of a cat's eye retroreflector if its velocity is 0.2 m/s and the distance to the moving object is 1-2 m. The corresponding velocity of the object must be 0.4 m/s. Our system provides a feasible implementation method for the tracking of the moving target space position.

The optical collection system designed for EAST edge TV Thomson scattering diagnostic

An optical collection system composed of a collection lens, fibers, and a mounting rack with high luminous flux, high transmission efficiency, and low optical losses has been designed and installed to collect sufficient scattered lights for the edge TV Thomson scattering diagnostic on the EAST tokamak. A collection lens with an on-axis optical structure, aspheric lens, and regular shaped image plane is designed to meet the system requirements in terms of field of view, spectral range, aberration, and assembly. A mounting rack is designed to fix the collection system. Fiber back-illumination and a location system are used to install the system to the designed position, and the measurement positions of each fiber are measured by using a portable laser tracker system. This optimized design of the optical collection system can facilitate the establishment of the edge TV Thomson scattering system on EAST, which verifies the feasibility of TV Thomson scattering used in large-scale fusion devices.

Method for Accuracy Assessment of the Length Measurement Unit of Laser Tracking Systems

Laser tracking systems are widely used in large-scale metrology of geometric quantities. Their importance is confirmed by the fact that one of the parts of the ISO 10360 series of standards has been devoted to the issue of assessing their accuracy (ISO 10360-10). A laser tracker is a device whose final measurement result is calculated using indications from various subsystems included in it, such as devices for measuring length and angle. The analysis of these individual impacts can be useful in creating simulation models of accuracy which, in regard to the Industry 4.0 concept, seem to be the most justified in terms of speed of operation and ease of use. For this reason, it may be particularly important to undertake research on the accuracy of this component in isolation from other factors affecting the measurement of the coordinates of the point. The article describes a method that allows separation of the length measurement error from the other components. The method uses a high-accuracy interferometer which is treated as a reference system that allows for the comparison of indications obtained using the tested distance measurement system. Thanks to the proposed method, it is possible to minimize errors from the optical system and other measuring systems. The use of a precise linear guide allows the reduction of errors related to the implementation of linear motion. The article presents the test method and the results obtained from performed experiments, as well as formulates conclusions and the directions of further development.

APPARILLO: a fully operational and autonomous staring system for LEO debris detection

For safe operation of active space crafts, the space debris population needs to be continuously scanned, to avoid collisions of active satellites with space debris. Especially the low Earth orbit (LEO) shows higher risks of collisions due to the highest density of orbital debris. Laser ranging stations can deliver highly accurate distance measurements of debris objects allowing precise orbit determination and more effective collision avoidance. However, a laser ranging station needs accurate a priori orbit information to track an orbital object. To detect and track unknown orbital objects in LEO, here, a passive optical staring system is developed for autonomous 24/7 operation. The system is weather-sealed and does not require any service to perform observations. To detect objects, a wide-angle imaging system with 10° field of view equipped with an astronomical CCD camera was designed and set up to continuously observe the sky for LEO objects. The system can monitor and process several passing objects simultaneously without limitations. It automatically starts an observation, processes the images and saves the 2D angular measurements of each object as equatorial coordinates in the TDM standard. This allows subsequent initial orbit determination and handover to a laser tracking system. During campaigns at twilight the system detected up to 36 objects per hour, with high detection efficiencies of LEO objects larger than 1 m3. It is shown that objects as small as 0.1 m3 can be detected and that the estimated precision of the measurements is about 0.05° or 7 × the pixel scale.

Combination of geometric and parametric approaches for kinematic identification of an industrial robot

Combination of geometric and parametric approaches of kinematic identification is proposed in this article. The experimental strategy is similar to that used in geometric approach wherein each axis of the robot is actuated one after the other. This adds clarity to experimental strategy, which becomes ambiguous while solely using a conventional parametric approach. Therefore it is easier to conduct experiments even if there are restrictions in workspace. The estimation was done using a parametric technique, but in a stage wise manner using a divide and conquer strategy. This allowed measurement of the robot accuracy after removing the errors arising due to the definition of base and end-effector frames. Additionally it is possible to visualize the reduction in errors during the estimation process. In addition to this, the Jacobian matrix that relates the pose errors to the correction in parameters is adapted during estimation using a damped least squares method depending upon the convergence of the parameters. Results were obtained after extensive experiments on industrial robots using three different measurement instruments namely laser tracker, monocular camera and multi-camera system. The proposed method performs better than the conventional approach which uses only geometric approach. Finally thanks to the new approach, it was possible to conduct experiments after dividing the workspace region into those with high and low levels of observability ; which is not easy while using conventional approaches. It was also possible to perform identification in regions closer and farther away from the robot where there is deterioration of observability. The results show that the proposed method could reduce the errors in pose in a consistent manner, even when different measurement instruments were used, or when there was a deterioration in observability due to the choice of poses during identification. • Combination of geometric and parametric approaches of identification makes it easy and less ambiguous to conduct the experiments even in the presence of restrictions in workspace. • Divide and conquer strategy combined with a damped least squares estimation process with checks on convergence of individual parameters to annul the effect of ill-conditioning of the identification Jacobian. • Possibility of measuring errors in pose at different stages, thus permitting assessment of the positioning accuracy of the robot, and its improvement during the estimation process. Estimation of nominal values defining pose of the base and end-effector coordinate system was used to measure the robot accuracy before identification and after refinement at first stage, such that the accuracy solely due to the robot kinematics could also be measured. • Experimental validation on Fanuc robot was through multiple experiments involving different measurement instruments like monocular camera, multi-camera and laser tracker and results show improvement over geometric approach proposed earlier, irrespective of the measurement region or instrument. Monocular camera could reduce the positioning errors though by a smaller scale compared to other expensive instruments suitable for off-line use. • Possibility of partitioning the robot workspace into different regions on the basis of observability. Experiments in these regions validate that improvement of the positioning accuracy of industrial robot is possible in a consistent manner in all the regions; and while using different measurement instruments.

레이저 추적 시스템의 각도 정확도를 고려한 탐지거리 성능 분석 방법

레이저 추적 시스템은 레이저 지시부와 레이저 수신부로 구성되며, 시스템 성능 분석을 위해 최대 탐지 거리와 각도 정확도를 고려해야 한다. 본 논문은 탐지 거리와 추적 각도 정확도의 관계를 확인하고 최대 탐지 거리와 유효 탐지 거리를 구분하여 분석하는 방법을 제시한다. 탐지 거리 성능은 레이저 신호 세기, 검출기 수신 신호, 레이저 추적 시스템의 출력 신호를 고려하여 계산하였으며, 가우시안 잡음을 적용하여 SNR 변화에 따른 추적 각도 오차를 계산하였다. 전산모사와 실험을 통해 SNR과 추적 각도 표준편차의 관계를 확인하고 비교적 간단하게 추적 각도 정확도를 계산하는 수식을 제시하였다. 탐지거리 분석 결과와 실험 결과의 오차는 4.5 %이다.

Research on Electrical Control and Programmable Controller Based on Laser Tracking Measurement

Different production technology and process have different requirements for control circuit. However, no matter what kind of control circuit, it is composed of some basic control links. Programmable controller is a common electronic data control program, which not only plays a lot of advantages in industrial control system, but also is more and more widely used in people's daily life. It is an essential basic equipment in industrial automation system at present. As a kind of high-precision three-coordinate measuring equipment, laser dynamic tracker can be used to measure the spatial position of various single parts and complete sets of equipment. This paper mainly introduces the application of laser tracking system in electrical control and programmable controller, and looks forward to the development prospect of laser tracking detection technology.