Kinematic Test Research Articles

Severity of parkinsonism associated with environmental manganese exposure

BackgroundExposure to occupational manganese (Mn) is associated with neurotoxic brain injury, manifesting primarily as parkinsonism. The association between environmental Mn exposure and parkinsonism is unclear. To characterize the association between environmental Mn exposure and parkinsonism, we performed population-based sampling of residents older than 40 in Meyerton, South Africa (N = 621) in residential settlements adjacent to a large Mn smelter and in a comparable non-exposed settlement in Ethembalethu, South Africa (N = 95) in 2016–2020.MethodsA movement disorders specialist examined all participants using the Unified Parkinson Disease Rating Scale motor subsection part 3 (UPDRS3). Participants also completed an accelerometry-based kinematic test and a grooved pegboard test. We compared performance on the UPDRS3, grooved pegboard, and the accelerometry-based kinematic test between the settlements using linear regression, adjusting for covariates. We also measured airborne PM2.5-Mn in the study settlements.ResultsMean PM2.5-Mn concentration at a long-term fixed site in Meyerton was 203 ng/m3 in 2016–2017 – approximately double that measured at two other neighborhoods in Meyerton. The mean Mn concentration in Ethembalethu was ~ 20 times lower than that of the long-term Meyerton site. UPDRS3 scores were 6.6 (CI 5.2, 7.9) points higher in Meyerton than Ethembalethu residents. Mean angular velocity for finger-tapping on the accelerometry-based kinematic test was slower in Meyerton than Ethembalethu residents [dominant hand 74.9 (CI 48.7, 101.2) and non-dominant hand 82.6 (CI 55.2, 110.1) degrees/second slower]. Similarly, Meyerton residents took longer to complete the grooved pegboard, especially for the non-dominant hand (6.9, CI -2.6, 16.3 s longer).ConclusionsEnvironmental airborne Mn exposures at levels substantially lower than current occupational exposure thresholds in the United States may be associated with clinical parkinsonism.

Effect of biases in integrity monitoring for RTK positioning

Abstract In road transport, continuous high-accuracy positioning is required in real time. To ensure the proper functioning and safety of vehicular applications, integrity monitoring (IM) is needed to protect from the positioning errors under a certain alert limit (AL) with a pre-defined probability of misleading information (MI). In this study, a detailed threat model is developed for real-time kinematic (RTK) positioning application of short baselines. The model distinguishes between ambiguity-float and -fixed scenarios, and considers the influences of phase and code multipath as well as between-receiver atmospheric residuals. With the float ambiguities temporally constrained, the bias contribution that propagates with time-updated ambiguities was studied analytically for the horizontal protection level (HPL) in IM. Based on real data from both static and kinematic experiments, HPL was computed along the direction of the semi-major axis of the horizontal error ellipse. In ambiguity-float and -fixed cases, the HPL was mostly several meters and decimetres, respectively. It was found that time-propagated biases play a dominant role in the ambiguity-float HPL, and among them, phase and code multipath had in general the largest contributions. For ambiguity-fixed case, the phase multipath was found to play a dominant role in the HPL. This shows the importance of considering the biases in the RTK IM for both the ambiguity-float and -fixed scenarios. Given a horizontal alert limit (HAL) of 5 m, the availabilities of ambiguity-float solutions were low, i.e., below 50% for the static roof tests and below 5% for the kinematic road tests. For the ambiguity-fixed scenario, with HAL at 0.5 m, integrity availability was nearly 100% for the static roof tests and above 85% for the kinematic road tests.

Real-time GNSS precise point positioning for low-cost smart devices

Global Navigation Satellite System raw measurements from Android smart devices make accurate positioning possible with advanced techniques, e.g., precise point positioning (PPP). To achieve the sub-meter-level positioning accuracy with low-cost smart devices, the PPP algorithm developed for geodetic receivers is adapted and an approach named Smart-PPP is proposed in this contribution. In Smart-PPP, the uncombined PPP model is applied for the unified processing of single- and dual-frequency measurements from tracked satellites. The receiver clock terms are parameterized independently for the code and carrier phase measurements of each tracking signal for handling the inconsistency between the code and carrier phases measured by smart devices. The ionospheric pseudo-observations are adopted to provide absolute constraints on the estimation of slant ionospheric delays and to strengthen the uncombined PPP model. A modified stochastic model is employed to weight code and carrier phase measurements by considering the high correlation between the measurement errors and the signal strengths for smart devices. Additionally, an application software based on the Android platform is developed for realizing Smart-PPP in smart devices. The positioning performance of Smart-PPP is validated in both static and kinematic cases. Results show that the positioning errors of Smart-PPP solutions can converge to below 1.0 m within a few minutes in static mode and the converged solutions can achieve an accuracy of about 0.2 m of root mean square (RMS) both for the east, north and up components. For the kinematic test, the RMS values of Smart-PPP positioning errors are 0.65, 0.54 and 1.09 m in the east, north and up components, respectively. Static and kinematic tests both show that the Smart-PPP solutions outperform the internal results provided by the experimental smart devices.

Comparative analysis of four different single-frequency PPP models on positioning performance and atmosphere delay retrieval

Single-frequency precise point positioning (SF-PPP) has attracted increasing attention due to its high precision and cost effectiveness. With various strategies to handle the dominant error, i.e., ionosphere delay, the ionosphere-float (IF), ionosphere-free-half (IFH), ionosphere-corrected (IC), and ionosphere-weighted (IW) SF-PPP models are certain to possess different characteristics and performance levels. This study is dedicated to assessing and comparing the four models from model characteristics, positioning performance, and atmosphere delay retrieval. The model comparison shows that IC and IW models are full-rank while IF and IFH models have a rank deficiency of size one that will result in biased estimations, which means the better solvability of IC and IW models. The experiments are carried out based on the 7-day Global Positioning System (GPS) observations collected at 57 global Multi-GNSS Experiment (MGEX) stations and Global Ionosphere Map (GIM) products. The results indicate that the IW model can accelerate SF-PPP convergence and achieve higher positioning accuracy compared to the other three SF-PPP models, especially in kinematic mode. With convergence criteria of 0.25 m in horizontal and 0.5 m in vertical, the east/north/up convergence times of IW model are 0.5/15.0/25.0 min and 0.5/16.0/36.5 min for static and kinematic modes, respectively. The IW model is able to achieve an instantaneous positioning accuracy of 0.28/0.35/0.75 m. In addition, a real kinematic test also demonstrates the best positioning solutions of IW model. Regarding troposphere delay retrieval, the IF, IFH, and IW models obtain a comparable daily accuracy of 3.0 cm on average, while the IC model achieves the worst accuracy of 8.0 cm. For precise ionosphere delay estimation, IW model only needs an average initialization time of 34.3 min, but a longer initialization time of 51.6 min is required for IF model. The daily precision of ionosphere delay estimation for IW model can reach up to 10.8 cm. At the present accuracy of GIM products, it is suggested that the IW model should be adopted for SF-PPP first due to its superior performance in positioning and atmosphere delay retrieval.

GNSS best integer equivariant estimation using multivariant t-distribution: a case study for precise point positioning

A key prerequisite for fast and reliable solution convergence time in precise point positioning with ambiguity resolution is the successful determination of the initial integer ambiguity parameters. In this contribution, a reliable approach of partial ambiguity resolution based on the BIE using the t-distribution (BIE-td) is proposed and compared against existing algorithms, such as the partial ambiguity resolution-based LAMBDA method (PAR-Ps) and the iFlex method proposed by the Trimble Navigation company. A 31-day set of GNSS measurements, collected in 2018 from 17 globally distributed GNSS continuously operating reference stations (CORS), were processed to determine the best-fit distribution for the GNSS measurements. It is found that the t-distribution with three degrees of freedoms provides a better fit compared to the Gaussian distribution. The authors then propose a method for selecting the integer ambiguity candidates when using the BIE-td approach. This method is based on the differences of unknown parameters of interest (i.e. receiver’s coordinates) determined at two consecutive processing steps. Finally, another 30-day set of GNSS measurements, collected in 2019 from the same CORS, confirm that the iFlex method outperforms the PAR-Ps method in the sense of minimizing the position errors of a simulated kinematic test. In particular, compared to the PAR-Ps method for 99th percentile of errors, the iFlex method has an improved convergence time of about 10 min. In addition, the positioning performance using the BIE-td and iFlex methods is comparable, with a similar positioning accuracy for both horizontal and vertical coordinate components.

ПРОЕКТИРОВАНИЕ АВТОМАТИЗИРОВАННОЙ СИСТЕМЫ ПРОСТРАНСТВЕННЫХ СМЕЩЕНИЙ ФАЗОВОГО ЦЕНТРА СПУТНИКОВОЙ ГЕОДЕЗИЧЕСКОЙ АППАРАТУРЫ

Introduction: Usually special experimental installations are using for assessing the accuracy of determining the coordinates which obtained by various positioning methods and data processing technologies. Them also referred as systems of spatial displacements of the antenna phase center. In this paper decried the designing process of an automated system of spatial displacement of the satellite geodetic equipment phase center. Purpose of work: development of an auto mated system of spatial displacements of the phase center of satellite geodetic equipment. Methods: in this course of work, studies were carried out for aiming at potential requirements for an automated system of spatial displacements of the phase center. There're additional analysis of the design and purpose of existing systems as well as the development of a system. The results of this work was list of established requirements. Results: was presented the analysis of domestic and foreign experience in the development and use of such systems, their classification and the most successful technical solutions in that branch. The requirements have been developed for system technical characteristics based on the analysis of the tasks which potentially could be solved. The element base and the design of the system was selected and developed in accordance with the specified technical characteristics. The rotation of the antenna of the Global Navigation Satellite Systems could be made in a circle with a radius of 0 to 500 mm. In this case, the radius can be dynamically changed with an accuracy of 0.2 mm. In addition, the system allows you to change the position of the antenna of the Global Navigation Satellite Systems in height within the range from 0 to 230 mm with an accuracy of 0.05 mm. The developed system does not require permanent fixing and can be moved to the required area of work. The results of the work should be used to assemble a prototype of an automated system of spatial displacements of the phase center of satellite geodetic equipment. Practical significance: The developed system can be used to conduct kinematic tests of satellite geodetic equipment and conduct a wide range of studies within the framework of modeling the movements of a reference satellite geodetic station under conditions of anthropogenic and natural influences. Discussion: Further development of the system may include the determination of its metrological characteristics using methods of near photogrammetry.

Patient-specific cruciate-retaining total knee replacement with individualized implants and instruments (iTotal™ CR G2).

Treatment of tricompartimental osteoarthritis (OA) using customized instruments and implants for cruciate-retaining total knee arthroplasty. Use of patient-specific instruments and implants (ConforMIS iTotalTM CR G2) together with a 3D-planning protocol (iView®). Retropatellar resurfacing is optional. Symptomatic tricompartmental OA of the knee (Kellgren-Lawrence stageIV) with preserved posterior cruciate ligament (PCL) after unsuccessful conservative or joint-preserving surgical treatment. Knee ligament instabilities of the posterior cruciate or collateral ligaments. Infection. Relative contraindication: knee deformities >15° (varus, valgus, flexion); prior partial knee replacement. Midline or parapatellar medial skin incision, medial arthrotomy; distal femoral resection with patient-specific cutting block; tibial resection using either acutting jig for the anatomic slope or afixed 5° slope. Balancing the knee in extension and flexion gap using patient-specific spacer.The final tibial preparation achieved with gap-balanced placement of the femoral cutting jigs. Kinematic testing using anatomic trial components. Final implant components are cemented in extension. Wound layers are sutured. Drainage is optional. Sterile wound dressing; compressive bandage. No limitation of the active and passive range of motion. Optional partial weight bearing during the first 2weeks, then transition to full weight bearing. Follow-up directly after surgery, at 12 and 52weeks, then every 1-2years. Overall 60patients with tricompartmental knee OA and preserved PCL were treated. Mean age was 66 (range 45-76) years. Minimum follow-up was 12months. There was 1septic revision after alow-grade infection, 1reoperation to replace the patellar due to patellar osteoarthritis and 3manipulations under anesthesia (MUAs) to increase range of motion. Radiographic analyses demonstrated an ideal implant fit with less than 2 mm subsidence or overhang. The WOMAC score improved from 154.8points preoperatively to 83.5points at 1 year and 59.3points at 2years postoperatively. The EuroQol-5D Score also improved from 11.1points preoperatively to 7.7points at 1year postoperatively.

Relationship Between Isometric Hip Torque With Three Kinematic Tests in Soccer Players

Introduction: Hip muscle strength has a good component to improve the execution of movement preventing excessive knee movements, such as dynamic valgus, which is a factor related to ACL injuries, however, the relationship between isometric torque and dynamic valgus is not yet well established. Functional tests that resemble sports have been used for movement analysis and possible injury minimizing factor. Objectives: To compare the knee medialization peak in three kinematic tests with different demands, and its correlation with the isometric torque of the abductors and hip extensors. Methods: The isometric torque was collected by the Lafayette hand dynamometer. Two-dimensional kinematics were used to evaluate three functional tests of different requirements, Single Limb Squat, Lateral Step Down Test and Single Leg Drop Landing Tests. For comparison between values we used the Student T test and for correlation the Spearman test, with p Results: No significant differences were found between the three right kinematic tests, different from the left. And no relationship was established between the isometric hip torque and none of the three kinematic tests. Conclusion: There is no correlation between the dynamic knee valgus peak during different tests. It is concluded that the isometric torque test does not seem to be as sensitive when related to functional tests, but it has good applicability for comparing strength between limbs.

Prediction of RTK positioning integrity for journey planning

Abstract Positioning integrity is crucial for Intelligent Transport Systems (ITS) applications. In this article, a method is presented for prediction of GNSS positioning integrity for ITS journey planning. This information, in addition to other route information, such as distance and time, can be utilized to choose the safest and economical route. We propose to combine the Advanced Receiver Autonomous Integrity Monitoring (ARAIM) technique, tailored for ITS, with 3D city models. Positioning is performed by GNSS Real-Time Kinematic (RTK) method, which can provide the accuracy required for ITS. A new threat model employed for computation of the protection levels (PLs) for RTK positioning is discussed. Demonstration of the proposed approach is performed through a kinematic test in an urban area in Tokyo. The comparison between the prediction method and the actual observations show that the two estimate close satellite geometry and PLs. The method produced PLs that bounds the actual position errors all the time and they were less than the preset alert limit.

Investigation of potential use of waste lime sludge in bituminous binder

The amount of waste generation has increased massively owing to the large production in manufacturing industries which has led to the problem of disposal for this waste. The wisest way to reduce the burden on landfills for disposal of waste is to utilize it in construction industry. Therefore, a study has been undertaken to use waste lime sludge containing CaCO 3 from toothpaste industry to amend the properties of asphalt. In this paper, the conventional test of the modified binder prepared by adding waste sludge was compared to unmodified binder. Moisture susceptibility of modified binder was evaluated to check the moisture resistance and to evaluate the grade of bitumen the kinematic viscosity test was conducted. It was found that by adding waste lime sludge, soft grade bitumen was converted to hard grade and it showed better resistance to moisture damage.

Performance analysis of real-time and post-mission kinematic precise point positioning in marine environments

This article focuses on the performance analysis of both real-time and post-mission kinematic precise point positioning (PPP) in challenging marine environments. For this purpose, a real dynamic experiment lasting 6 h was carried out on a lake dam in Çorum City of Turkey. While the kinematic test was continuing, the real-time PPP coordinates were obtained for each measurement epoch with a commercial real-time PPP (RT-PPP) service, namely the Trimble CenterPoint RTX. Then the post-mission PPP (PM-PPP) coordinates were calculated by using Multi-GNSS data and the Multi-GNSS Experiment (MGEX) precise products. The kinematic RT-PPP and PM-PPP results showed that the PPP coordinates were consistent with the relative solution at centimetre and decimetre level in horizontal and height components, respectively. This study implies that PPP technique is a powerful tool for highly accurate positioning in both real-time and post-mission modes, even for dynamic applications in harsh environments.

An attempt to relate dynamic tracking error to occurring situation based on additional rectilinear motion for five-axis machine tools

During five-axis CNC machining, the dynamic tracking error of the five-axis machine tool caused by imperfect servo dynamic performance is the major factor affecting the accuracy during high-speed and high-precision manufacturing. Rotation tool center point (RTCP) test has become a typical kinematic test for the dynamic tracking error of five-axis machine tools. According to the mechanism and characteristics of dynamic tracking error, during the RTCP test, relating the measured dynamic tracking error to corresponding occurring situation is helpful for the research of calibration or reduction of dynamic tracking error. In this paper, a new method to relate dynamic tracking error to occurring situation based on additional rectilinear motion is attempted. During this method, rectilinear motions are added into the RTCP test process, and the dynamic tracking error and corresponding occurring position can be calculated from the scale of rectilinear motion. By six tests with rectilinear motions in and against X, Y and Z directions, the additional error and uncertainty of the test process can be offset by calculation. This method can be implemented without any addition or modification to the instrument or NC system.

Biomechanical Analysis of an Interspinous Process Fixation Device with In Situ Shortening Capabilities: Does Spinous Process Compression Improve Segmental Stability?

The objective of this study was to characterize the biomechanical implications of spinous process compression, via in situ shortening of a next-generation interspinous process fixation (ISPF) device, in the context of segmental fusion. Seven lumbar cadaveric spines (L1-L4) were tested. Specimens were first tested in an intact state, followed by iterative instrumentation at L2-3 and subsequent testing. The order followed was 1) stand-alone ISPF (neutral height); 2) stand-alone ISPF (shortened in situ from neutral height; shortened); 3) lateral lumbar interbody fusion (LLIF)+ ISPF (neutral); 4) LLIF+ ISPF (shortened); 5) LLIF+ unilateral pedicle screw fixation; 6) LLIF+ bilateral pedicle screw fixation. A 7.5-Nm moment was applied in flexion/extension, lateral bending, and axial rotation via a kinematic test frame. Segmental range of motion (ROM) and lordosis were measured for all constructs. Comparative analysis was performed. Statistically significant flexion/extension ROM reductions: all constructs versus intact condition (P < 0.01); LLIF+ ISPF (neutral and shortened) versus stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ USPF versus ISPF (neutral) (P= 0.049); bilateral pedicle screw fixation (BPSF) versus stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ BPSF versus LLIF+ unilateral pedicle screw fixation (UPSF) (P < 0.01). Significant lateral bending ROM reductions: LLIF+ ISPF (neutral and shortened) versus intact condition and stand-alone ISPF (neutral) (P < 0.01); LLIF+ UPSF versus intact condition and stand-alone ISPF (neutral and shortened) (P < 0.01); LLIF+ BPSF versus intact condition and all constructs (P < 0.01). Significant axial rotation ROM reductions: LLIF+ ISPF (shortened) and LLIF+ UPSF versus intact condition and stand-alone ISPF (neutral) (P ≤ 0.01); LLIF+ BPSF versus intact condition and all constructs (P ≤ 0.04). In situ shortening of an adjustable ISPF device may support increased segmental stabilization compared with static ISPF.

A Multi-GNSS Differential Phase Kinematic Post-Processing Method

We propose a multiple global navigation satellite system (multi-GNSS) differential phase kinematic post-processing method, expand the current Track ability, and finely tune processing parameters to achieve the best results for research purposes. The double-difference (DD) phase formulas of GLONASS are especially formulated, and the method of arc ambiguity resolution (AR) in post-processing is developed. To verify the feasibility of this AR method, a group of static baselines with ranges from 8 m to 100 km and two kinematic tests were used. The results imply that 100% of ambiguities in short baselines and over 90% in long baselines can be fixed with the proposed ambiguity resolution method. Better than a 10-mm positioning precision was achieved for all the horizonal components of those selected baselines and the vertical components of the short baselines, and the vertical precision for long baselines is around 20 to 40 mm. In the posterior residual analysis, the means of the residual root-mean-squares (RMSs) of different systems are better than 10 mm for short baselines and at the range of 10–20 mm for baselines longer than 80 km. Mostly, the residuals satisfy the standard normal distribution. It proves that the new method could be applied in bridge displacement and vibration monitoring and for UAV photogrammetry.

Treadmill-Based Gait Kinematics in the Yucatan Mini Pig.

Yucatan miniature pigs (YMPs) are similar to humans in spinal cord size as well as physiological and neuroanatomical features, making them a useful model for human spinal cord injury. However, little is known regarding pig gait kinematics, especially on a treadmill. In this study, 12 healthy YMPs were assessed during bipedal and/or quadrupedal stepping on a treadmill at six speeds (1.0, 1.5, 2.0, 2.5, 3.0, and 3.5 km/h). Kinematic parameters, including limb coordination and proximal and distal limb angles, were measured. Findings indicate that YMPs use a lateral sequence footfall pattern across all speeds. Stride and stance durations decreased with increasing speed whereas swing duration showed no significant change. Across all speeds assessed, no significant differences were noted between hindlimb stepping parameters for bipedal or quadrupedal gait with the exception of distal limb angular kinematics. Specifically, significant differences were observed between locomotor tasks during maximum flexion (quadrupedal > bipedal), total excursion (bipedal > quadrupedal), and the phase relationship between the timing of maximum extension between the right and left hindlimbs (bipedal > quadrupedal). Speed also impacted maximum flexion and right-left phase relationships given that significant differences were found between the fastest speed (3.5 km/h) relative to each of the other speeds. This study establishes a methodology for bipedal and quadrupedal treadmill-based kinematic testing in healthy YMPs. The treadmill approach used was effective in recruiting primarily the spinal circuitry responsible for the basic stepping patterns as has been shown in cats. We recommend 2.5 km/h (0.7 m/sec) as a target walking gait for pre-clinical studies using YMPs, which is similar to that used in cats.

Precise Single-Frequency Positioning Using Low-Cost Receiver with the Aid of Lane-Level Map Matching for Land Vehicle Navigation

Precise positioning with low-cost single-frequency global navigation satellite system (GNSS) receivers has great potential in a wide range of applications because of its low price and improved accuracy. However, challenges remain in achieving reliable and accurate solutions using low-cost receivers. For instance, the successful ambiguity fixing rate could be low for real-time kinematic (RTK) while large errors may occur in precise point positioning (PPP) in some scenarios (e.g., trees along the road). To solve the problems, this paper proposes a method with the aid of additional lane-level digital map information to improve the accuracy and reliability of RTK and PPP solutions. In the method, a digital camera will be applied for lane recognition and the positioning solution from a low-cost receiver will be projected to the digital map lane link. With the projected point position as a constraint, the RTK ambiguity fixing rate and PPP performance can be enhanced. A field kinematic test was conducted to verify the improvement of the RTK and PPP solutions with the aid of map matching. The results show that the RTK ambiguity fixing rate can be increased and the PPP positioning error can be reduced by map matching.

An Improved Relative GNSS Tracking Method Utilizing Single Frequency Receivers.

The Global Navigation Satellite Systems (GNSS) becomes the primary choice for device localization in outdoor situations. At the same time, many applications do not require precise absolute Earth coordinates, but instead, inferring the geometric configuration information of the constituent nodes in the system by relative positioning. The Real-Time Kinematic (RTK) technique shows its efficiency and accuracy in calculating the relative position. However, when the cycle slips occur, the RTK method may take a long time to obtain a fixed ambiguity value, and the positioning result will be a “float” solution with a low meter accuracy. The novel method presented in this paper is based on the Relative GNSS Tracking Algorithm (Regtrack). It calculates the changes in the relative baseline between two receivers without an ambiguity estimation. The dead reckoning method is used to give out the relative baseline solution while a parallel running Extended Kalman Filter (EKF) method reinitiates the relative baseline when too many validation failures happen. We conducted both static and kinematic tests to assess the performance of the new methodology. The experimental results show that the proposed strategy can give accurate millimeter-scale solutions of relative motion vectors in adjacent two epochs. The relative baseline solution can be sub-decimeter level with or without the base station is holding static. In the meantime, when the initial tracking point and base station coordinates are precisely obtained, the tracking result error can be only 40 cm away from the ground truth after a 25 min drive test in an urban environment. The efficiency test shows that the proposed method can be a real-time method, the time that calculates one epoch of measurement data is no more than 80 ms and is less than 10 ms for best results. The novel method can be used as a more robust and accurate ambiguity free tracking approach for outdoor applications.

Analysis of typical working conditions and experimental research of friction stir welding robot for aerospace applications

In an attempt to address the limitations of single function and the poor process flexibility of existing friction stir welding equipment, a new friction stir welding robot has been developed to address practical problems in three-dimensional surface welding. Based on an analysis of the components of the robotic system, a kinematics model was established, and the forward and backward kinematics solutions were derived for the robot. An iterative nearest point algorithm, iterative closest point based on point cloud matching, was used to plan the welding trajectory for the most complex petal welding conditions, and an experimental study was conducted. The results show that the kinematic and dynamic test results were consistent with the acquired simulation curves for specific sizes of the rocket cap flaps under appropriate welding conditions. The normal error of the weld was less than 85 µm, the average tensile strength was 359 MPa, and the elongation was 7.20%, 78.0%, and 72.0% of 2A14-T6 aluminum alloy. The friction stir welding robot exhibited robust performance, and the proposed trajectory planning method is practical and effective. The appearance, geometric dimension, and mechanical properties of the weld achieved the expected criteria, and high-precision welding of large complex thin-walled surfaces is possible.

Design method of a novel variable speed ratio line gear mechanism

Based on the space curve meshing theory, a novel noncircular line gear mechanism was advanced, namely, this paper presented a design method of the variable speed ratio noncircular line gear with coplanar axes. Firstly, the universal contact curve equations of the constant speed ratio and variable speed ratio line teeth were established. After the constraint equations of the rotating angle of the driving and driven variable speed ratio noncircular line gears were analyzed and established, the relationship between the rotating angle of the driven variable speed ratio noncircular line gear and the parameter t in the VSR area was assumed to be a piecewise fourth-order curve. Then, the contact curve equations of the variable speed ratio noncircular line gears were derived, and the entity models of variable speed ratio noncircular line gears were built. The prototypes of the parallel axis and intersecting axis variable speed ratio noncircular line gears were manufactured by Stereo Lithography Apparatus, and the speed ratios were measured on the kinematic test rig. The kinematic and finite element analysis results demonstrate that the relationship between the rotating angle of the driven variable speed ratio noncircular line gear and the parameter t conforms to the designed function and the noncircular line teeth smoothly achieve the preset VSR transmission. The proposed design method is helpful to design the variable speed ratio noncircular line gears with lower theoretical sliding rate and wider variation range of the speed ratio; consequently, the designed variable speed ratio noncircular line gears have better applicability in specific variable speed ratio applications.

Time-Relative RTK-GNSS: GNSS Loop Closure in Pose Graph Optimization

A pose-graph-based optimization technique is widely used to estimate robot poses using various sensor measurements from devices such as laser scanners and cameras. The global navigation satellite system (GNSS) has recently been used to estimate the absolute 3D position of outdoor mobile robots. However, since the accuracy of GNSS single-point positioning is only a few meters, the GNSS is not used for the loop closure of a pose graph. The main purpose of this study is to generate a loop closure of a pose graph using a time-relative real-time kinematic GNSS (TR-RTK-GNSS) technique. The proposed TR-RTK-GNSS technique uses time differential carrier phase positioning, which is based on carrier-phase-based differential GNSS with a single GNSS receiver. Unlike a conventional RTK-GNSS, we can directly compute the robot's relative position using only a stand-alone GNSS receiver. The initial pose graph is generated from the accumulated velocity computed from GNSS Doppler measurements. To reduce the accumulated error of velocity, we use the TR-RTK-GNSS technique for the loop closure in the graph-based optimization framework. The kinematic positioning tests were performed using an unmanned aerial vehicle to confirm the effectiveness of the proposed technique. From the tests, we can estimate the vehicle's trajectory with approximately 3 cm accuracy using only a stand-alone GNSS receiver.