Maximum Position Error Research Articles

SCALAR: Simultaneous Calibration of 2-D Laser and Robot Kinematic Parameters Using Planarity and Distance Constraints

In this paper, we propose SCALAR, a calibration method to simultaneously calibrate the kinematic parameters of a 6-DoF robot and the extrinsic parameters of a 2D Laser Range Finder (LRF) attached to the robot's flange. The calibration setup requires only a flat plate with two small holes carved on it at a known distance from each other, and a sharp tool-tip attached to the robot's flange. The calibration is formulated as a nonlinear optimization problem where the laser and the tool-tip are used to provide planar and distance constraints, and the optimization problem is solved using Levenberg-Marquardt algorithm. We demonstrate through experiments that SCALAR can reduce the mean and the maximum tool position error from 0.44 mm to 0.19 mm and from 1.41 mm to 0.50 mm, respectively.

A positional error compensation method for industrial robots combining error similarity and radial basis function neural network

To solve the problem of low absolute position accuracy for industrial robots in application, a positional error compensation method combing error similarity and RBF neural networks is proposed. The positional errors experience error similarity when describing the degree of error similarity developed with the error model based on a robot kinematic model. The experimental semivariogram is fitted by using a set of robot joint angles and corresponding positional errors. The bandwidth of the RBF neural network is modified by using the parameter of semivariogram. Then, an RBF neural network is constructed to estimate the positional errors of the target positions. The estimated positional errors are used to modify the target position. The modified position is given to the robot controller. To verify the proposed method, a simulation study and experiments are respectively carried out with a simulated robot and a KUKA KR210 industrial robot. The experimental results show that, after compensation, the average residual positional error is reduced by 91.99% from 1.361 mm to 0.109 mm and the maximum residual positional error is reduced by 85.41% from 1.741 mm to 0.254 mm. In addition, the proposed method can enhance the absolute position accuracy of industrial robots.

Vision guided geometric regulation of PTC frame structures

PurposeGeometric structure error of parabolic trough concentrator (PTC) frame affects the installation accuracy of mirrors and absorber tubes and thus decreases the solar energy concentrating efficiency. Until now, there is no effective method to instruct the assembly and regulation of PTC frames. This paper aims to propose a vision guided method for fast and accurate regulation of mirror and absorber supports to improve the geometric quality of PTC frames.Design/methodology/approachThe PTC frame support regulating system consists of a general-purpose online photogrammetry system, frame support measurement adaptors and data analyzing software. First, the positions and angles of all the supports are measured in real time by the online photogrammetric system. Then, the measured positions and angles are aligned to the design reference frame through the transformation calculated by an absorber position constrained nonlinear optimization so as to get the geometric errors and regulating amounts. Finally, a graduated pseudo-color-based visualization method is proposed to assist the manual or automated regulation of PTC frame supports in site.FindingsThe proposed method does not need to construct a reference system nor specify the rotation attitude of the PTC frame, and it is capable of conducting efficient and accurate regulation on PTC frame assembly line. The method is applied to manual regulation of a light type PTC frame structure. After regulation, the maximum position and angle errors of supports are reduced to less than 0.15 mm and 0.15° respectively and the intercept factor is increased to 97%, which meets the requirement for a qualified PTC concentrator.Originality/valueTo the authors’ knowledge, this paper is the first to propose a vision guided assembly or regulation method for PTC frame structures. The research uses online photogrammetry system to provide real-time geometric quality information feedback, elaborates the data analysis algorithm and provides the visualization method for accurate and efficient in site regulation. Furthermore, this paper also provides theories, methods and experiences for other applications that use vision guidance for attitude regulation and digital flexible assembly of large equipment.

A 3D-printed patient-specific applicator guide for use in high-dose-rate interstitial brachytherapy for tongue cancer: a phantom study

A patient-specific applicator guide system (PSAG) for tongue-cancer high-dose-rate (HDR) interstitial brachytherapy (ISBT) was developed by utilizing a 3D printing technique. An effectiveness of the 3D-printed PSAG (3D-PSAG) was evaluated for HDR ISBT. Six patients with tongue cancer were retrospectively selected for this study. For each patient, a total of three virtual clinical target volumes (CTV) requiring the insertion of four catheters (CTV4), six catheters (CTV6), and eight catheters (CTV8) were defined. For each CTV, treatment plans were generated to deliver 45 Gy in nine fractions. The 3D-PSAG was fabricated using a 3D-printer and the patient’s CT-images. The resulting 3D-PSAG took the form of a shell conforming to the patient’s contours with tubes for catheter insertion. For each CTV, catheters were inserted into the phantom with and without the 3D-PSAG. After that, CT-images of the phantom with the inserted catheters were acquired. Differences between the planned positions and those of the actually inserted catheters were evaluated from the CT-images. Given the actual catheter insertion positions, the dose distributions were reconstructed and analyzed. The maximum positional errors with and without the 3D-PSAG were 0.2 mm and 4.5 mm, respectively. For CTV6, the D90% values of the original plan, the reconstructed plan with the 3D-PSAG, and the reconstructed plan without the 3D-PSAG, were 48.8 ± 1.7 Gy, 49.0 ± 2.9 Gy, and 45.6 ± 3.3 Gy, respectively. The D1cc values for the mandible were 51.3 ± 9.2 Gy, 61.6 ± 8.3 Gy, and 81.1 ± 16.7 Gy, respectively. The dose homogeneities in the CTVs into which the catheters had been inserted with the 3D-PSAG were always superior to those into which the catheters had been inserted without the 3D-PSAG. The present phantom study demonstrated the feasibility of more accurate interstitial tongue brachytherapy while simplifying the treatment process by utilizing the 3D-PSAG.

Tolerance Analysis of Planar Mechanisms Based on a Residual Approach: A Complementary Method to DLM

The kinematic performance of mechanisms is affected by different uncertainty sources involved in the manufacturing and assembling cycle; among these are the geometric variations. It is known that the effects of these variations produce position errors which are not usually included in the design process. With this objective, a complementary method for the tolerance analysis of planar mechanisms that incorporate geometric variations is presented in this paper. The approach is based on Direct Linearization Method (DLM) that does not consider all the kinematically admissible solutions. DLM naturally minimizes a residual functional H; however it is possible to maximize the residual by means of a proposed complementary method called H-Based Residual Method (RMH). From the proposed methodology, local and global error domains can be defined to predict the maximum and minimum position errors caused by the input variations. DLM and RMH were applied in a four-bar mechanism with dimensional and angular variations to estimate positioning errors. The results show intervals where output positions were invariant with respect to angular variations of the crank. These computations were performed through a distance ratio established with the output deviations determined with nominal angular variations. Furthermore, domain errors were predicted for a set of positions generated by a multivariate normal random algorithm with 1000 combinations of input variations (links lengths). These domains delimited all solutions created in each position stage. It means that by applying the proposed methodology it is possible to estimate the geometric errors of any combination of variations.

다중 자기센서를 이용한 실내 자기 지도 기반 보행자 위치 검출 정확도 향상 알고리즘

This research proposes a indoor magnetic map matching algorithm that improves the position accuracy by employing multiple magnetic sensors and probabilistic candidate weighting function. Since the magnetic field is easily distorted by the surrounding environment, the distorted magnetic field can be used for position mapping, and multiple sensor configuration is useful to improve mapping accuracy. Nevertheless, the position error is likely to increase because the external magnetic disturbances have repeated pattern in indoor environment and several points have similar magnetic field distortion characteristics. Those errors cause large position error, which reduces the accuracy of the position detection. In order to solve this problem, we propose a method to reduce the error using multiple sensors and likelihood boundaries that uses human walking characteristics. Also, to reduce the maximum position error, we propose an algorithm that weights according to their importance. We performed indoor walking tests to evaluate the performance of the algorithm and analyzed the position detection error rate and maximum distance error. From the results we can confirm that the accuracy of position detection is greatly improved.

A targeting method for robot-assisted percutaneous needle placement under fluoroscopy guidance.

Minimally invasive procedures are rapidly growing in popularity thanks to advancements in medical robots, visual navigation and space registration techniques. This paper presents a precise and efficient targeting method for robot-assisted percutaneous needle placement under C-arm fluoroscopy. A special end-effector was constructed to perform fluoroscopy calibration and robot to image-space registration simultaneously and automatically. In addition, formulations were given to compute the movement of robot targeting and evaluate targeting accuracy using only one X-ray image. A pre-clinical experiment showed that the maximum angle error was 0.94° and the maximum position error of a target located 80 mm below the end-effector was 1.31 mm. And evaluation of the system in a robot-assisted pedicle screws placement surgery has justified the accuracy and reliability of proposed method in clinical applications. The positioning accuracy was increased by using present method. Moreover, radiation exposure and operation time were reduced significantly compared to other commonly used methods.

A targeting method for robot-assisted percutaneous needle placement under fluoroscopy guidance

Minimally invasive procedures are rapidly growing in popularity thanks to advancements in medical robots, visual navigation and space registration techniques. This paper presents a precise and efficient targeting method for robot-assisted percutaneous needle placement under C-arm fluoroscopy. In this method, a special end-effector was constructed to perform fluoroscopy calibration and robot to image-space registration simultaneously. In addition, formulations were given to compute the movement of robot targeting and evaluate targeting accuracy using only one X-ray image. With these techniques, radiation exposure and operation time were reduced significantly compared to other commonly used methods. A pre-clinical experiment showed that the maximum angle error was 0.94° and the maximum position error of a target located 80mm below the end-effector was 1.31mm. And evaluation of the system in a robot-assisted pedicle screws placement surgery has justified the accuracy and reliability of proposed method in clinical applications.

A New Array Pseudolites Technology for High Precision Indoor Positioning

Global Satellite Navigation System (GNSS) can't provide normal location service in the indoor environment because the signal can be blocked by buildings. The pseudolites system can supplement GNSS, especially in the indoor environments. A new indoor array pseudolites system is introduced, its multi-channel transmitter has an identical clock source. The high-precision Doppler positioning method based on Z-fixed Known Point Initialization (Z-KPI) is developed without ambiguity resolution. Some static and dynamic tests are conducted to evaluate the positioning accuracy of this new method. In the static testing, the average Doppler measurement error is 1x10-5 m/s, which lays the foundation of the high precision velocity measurement, and the average positioning error is 0.02 m in X axis, 0.004 m in Y axis, and the average velocity error is 3.28x10 -5 m/s in X axis, 1.94x10 -5 m/s in Y axis. In the dynamic test, the maximum positioning error is 0.39 m in X axis, 0.34 m in Y axis. Finally, the reason for adopting the Z-fixed KPI algorithm is explained by the horizontal dilution of precision (HDOP), meanwhile, the influence of the known initialization point error on indoor positioning accuracy is analyzed, when a deviation from -1.5 m to 0.9 m is added to the Z-axis of the KPI, the maximum positioning error is 0.311 m in X axis, 0.08 m in Y axis; when the horizontal deviation tolerance of the KPI is set from - 0.5 m to 0.5 m, the maximum horizontal positioning error is less than 0.5 m.

Digital Twin-Based Optimization for Ultraprecision Motion Systems With Backlash and Friction

A digital twin-based optimization procedure is presented for an ultraprecision motion system with a flexible shaft connecting the motor to the (elastic) load, which is subject to both backlash and friction. The main contributions of the study are the design of the digital twin and its implementation, assuming a two-mass drive system. The procedure includes the virtual representation of mechanical and electrical components, non-linearities (backlash and friction), and the corresponding control system. A procedure for digital twin-based optimization is also presented, in which the maximum absolute position error is minimized while maintaining accuracy with no significant increase in the control effort. The optimal settings for the controller parameters and for the backlash peak amplitude, the backlash peak time, and the hysteresis amplitude are then determined, in order to guarantee an appropriate dynamic response in the presence of backlash and friction. The surface quality of certain manufactured components, such as hip and knee implants, depends on the smoothness and the accuracy of the real trajectory produced in the cutting process that is strongly influenced by the maximum position error. The simulations and experimental studies are presented using a real platform and two references for trajectory control, and a comparison of four digital twin-based optimization methods. The simulation study and the real-time experiments demonstrate the suitability of the digital twin-based optimization procedure and lay the foundations for the implementation of the proposed method at an industrial level.

A Stable SINS/UWB Integrated Positioning Method of Shearer Based on the Multi-Model Intelligent Switching Algorithm

The accurate stable measurement of position for a shearer is a key technology in realizing an automated fully mechanized coal mining face. Using as a base of SINS/UWB integrated positioning system, the signal interference and node damage of UWB often cause an invalid integrated positioning system, because of the bad working environment of the shearer in the coal mine. Consequently, the positioning accuracy of the SINS/UWB integrated system decreases quickly, due to the drift error of SINS. Aiming at two invalid styles include partial anchor node failure and all anchor nodes failure of UWB, this paper proposes a stable SINS/UWB integrated positioning system of a shearer using the multi-model intelligent switching method based on a tightly coupled integrated model and a decision tree fault-tolerant model. First of all, the tightly coupled integrated model and the decision tree fault-tolerant model are built using measured distance and the final position of UWB, respectively. Second, the multi-model intelligent switching algorithm can be established based on the shearer Markoff movement state and residual threshold judgment of a Kalman Filter. Finally, the experimental results show that the multi-model intelligent switching fault-tolerant positioning algorithm can effectively overcome increased positioning error of the tightly coupled model and the decision tree model based on these two invalid styles. The maximum position error with the positioning model proposed in this paper is 0.93 m in 327 s, and the positioning accuracy with a multi-model intelligent switching model is much greater than that with tightly coupled integration and the decision tree fault tolerant models.

Validation of Geostationary Earth Orbit Satellite Ephemeris Generated from Satellite Laser Ranging

This study presents the generation and accuracy assessment of predicted orbital ephemeris based on satellite laser ranging (SLR) for geostationary Earth orbit (GEO) satellites. Two GEO satellites are considered: GEO-Korea Multi-Purpose Satellite (KOMPSAT)-2B (GK-2B) for simulational validation and Compass-G1 for real-world quality assessment. SLR-based orbit determination (OD) is proactively performed to generate orbital ephemeris. The length and the gap of the predicted orbital ephemeris were set by considering the consolidated prediction format (CPF). The resultant predicted ephemeris of GK-2B is directly compared with a pre-specified true orbit to show 17.461 m and 23.978 m, in 3D root-mean-square (RMS) position error and maximum position error for one day, respectively. The predicted ephemeris of Compass-G1 is overlapped with the Global Navigation Satellite System (GNSS) final orbit from the GeoForschungsZentrum (GFZ) analysis center (AC) to yield 36.760 m in 3D RMS position differences. It is also compared with the CPF orbit from the International Laser Ranging Service (ILRS) to present 109.888 m in 3D RMS position differences. These results imply that SLR-based orbital ephemeris can be an alternative candidate for improving the accuracy of commonly used radar-based orbital ephemeris for GEO satellites.

Modeling Tube Clearance and Bounding the Effect of Friction in Concentric Tube Robot Kinematics.

The shape of a concentric tube robot depends not only on the relative rotations and translations of its constituent tubes, but also on the history of relative tube displacements. Existing mechanics-based models neglect all history-dependent phenomena with the result that when calibrated on experimental data collected over a robot's workspace, the maximum tip position error can exceed 8 mm for a 200-mm-long robot. In this paper, we develop a model that computes the bounding kinematic solutions in which Coulomb friction is acting either to maximize or minimize the relative twisting between each pair of contacting tubes. The path histories associated with these limiting cases correspond to first performing all tube translations and then performing relative tube rotations of sufficient angle so that the maximum Coulomb friction force is obtained along the interface of each contacting tube pair. The robot tip configurations produced by these path histories are shown experimentally to bound position error with respect to the estimated frictionless model compared to path histories comprised of translation or mixed translation and rotation. Intertube friction forces and torques are computed as proportional to the intertube contact forces. To compute these contact forces, the standard zero-clearance assumption that constrains the concentrically combined tubes to possess the same centerline is relaxed. The effects of clearance and friction are explored through numerical and physical experiments and it is shown that friction can explain much of the prediction error observed in existing models. This model is not intended for real-time control, but rather for path planning-to provide error bounds and to inform how the ordering of tube rotations and translations can be used to reduce the effect of friction.

Self-Calibration of an Industrial Robot Using a Novel Affordable 3D Measuring Device.

This work shows the feasibility of calibrating an industrial robot arm through an automated procedure using a new, low-cost, wireless measuring device mounted on the robot’s flange. The device consists of three digital indicators that are fixed orthogonally to each other on an aluminum support. Each indicator has a measuring accuracy of 3 µm. The measuring instrument uses a kinematic coupling platform which allows for the definition of an accurate and repeatable tool center point (TCP). The idea behind the calibration method is for the robot to bring automatically this TCP to three precisely-known positions (the centers of three precision balls fixed with respect to the robot’s base) and with different orientations of the robot’s end-effector. The self-calibration method was tested on a small six-axis industrial robot, the ABB IRB 120 (Vasteras, Sweden). The robot was modeled by including all its geometrical parameters and the compliance of its joints. The parameters of the model were identified using linear regression with the least-square method. Finally, the performance of the calibration was validated with a laser tracker. This validation showed that the mean and the maximum absolute position errors were reduced from 2.628 mm and 6.282 mm to 0.208 mm and 0.482 mm, respectively.

Calibration of a three-dimensional laser Doppler velocimeter in a land integrated navigation system.

In the land navigation field, a laser Doppler velocimeter (LDV), which is able to measure the speed of a carrier, can be combined with a strapdown inertial navigation system (SINS) to form an integrated navigation system. To realize the integrated navigation positioning of a free motion carrier on the ground accurately, this paper introduces a split-reuse three-dimensional (3D) LDV. For the error parameters during application, a Kalman filtering calibration method with the assistance of a differential global positioning system (DGPS) is put forward in this paper. Two groups of integrated navigation experiments are designed to validate the effectiveness of this method and the universality of the obtained parameters. The experimental results show that the calibration method proposed in this paper is effective and the 3D LDV after compensation can greatly improve the positioning accuracy of the integrated navigation. The maximum horizontal position errors of the two experiments calculated by the dead reckoning of the 3D LDV and the gyroscopes are 4.2m and 2.9m, and the maximum altitude errors are 0.8m and 0.9m, respectively.

Experimental Verification of a Magnetic Levitation Transport System for the OLED Display Evaporation Process Under Vacuum

The manufacturing process of OLED displays requires a high accuracy and a highly clean transport system because during the evaporation process, organic materials are inherently sensitive to contamination and uniform deposition of an organic layer is important. Roller-based transfer systems are not suitable for OLED evaporation processes because the roller-based system has a poor driving performance due to nonlinear factors such as friction and generates a large amount of dust. On the other hand, the magnetic levitation transport system has the advantage of not generating any dust, and it is possible to achieve high-precision control. In this letter, a magnetic levitation transport system for the OLED evaporation process is introduced. In particular, experimental verification of the developed system under vacuum is addressed. In terms of levitation control performance, the maximum fluctuation of the levitation airgap at a standstill is 15.3 $\mu$ m $_{pp}$ , and in low-speed and high-speed operation modes, it is 95.0 and 282.3 $\mu$ m $_{pp}$ , respectively. In terms of propulsion control performance, the maximum position error based on ISO-230-22006 standard is 1.5 $\mu$ m, and the maximum speed error at constant speed of 30 mm/s is 0.43 $\%$ . To achieve such a highly precise control, especially under vacuum, novel control algorithms such as intelligent section control are applied to minimize abrupt changes in the activation of electromagnets as the carrier moves, and command shaping algorithms are applied to prevent excitation of the resonance mode of the system while at a higher control bandwidth. Moreover, to verify long-term reliability, a 12-hour continuous operation test is conducted.

TESTING DJI PHANTOM 4 PRO FOR URBAN GEOREFERENCING

Abstract. The urban environment is dynamic and is constantly changing. In Brazil, it has been recently published a decree for urban land regulation for the cadastre – Decree No 9.310 of 2018 15 of March which fixes 8,0 centimeters as the maximum spherical positional error for vertex of an urban property stock being georeferenced by Global Navigation Satellite System – GNSS equipment or aerial orthophotograph. Nowadays it has been noticed a growing use of Unmanned Aircraft Vehicle System – UAVS for remote sensing. This work aims to test if the accuracy of orthophoto-mosaic from a small UAVS mapping data of an urban area for a parcel scale georeferencing is answering the new decree of urban land regulation for the cadastre. It is intended to check the number of Ground Control Points (GCPs) to reach the best quality in terms of geometric resolution according to the necessity of positional quality for the urban parcel georeferenced for the cadastre. As a final consideration, the results implied that mapping a small surveying area with small UAVS is worth, being a potential tool for georeferencing city blocks, and using 20 pairs of GCPs is enough to reach the quality of positional geometry adequate to the Brazilian legislation.

Auto Takeoff and Precision Terminal-Phase Landing Using an Experimental Optical Flow Model for Global Positioning System/Inertial Navigation System Enhancement

The high estimated position error in current commercial-off-the-shelf (GPS/INS) impedes achieving precise autonomous takeoff and landing (TOL) flight operations. To overcome this problem, in this paper, we propose an integrated global positioning system (GPS)/inertial navigation system (INS)/optical flow (OF) solution in which the OF provides an accurate augmentation to the GPS/INS. To ensure accurate and robust OF augmentation, we have used a robust modeling method to estimate OF based on a set of real-time experiments conducted under various simulated helicopter-landing scenarios. Knowing that the accuracy of the OF measurements is dependent on the accuracy of the height measurements, we have developed a real-time testing environment to model and validate the obtained dynamic OF model at various heights. The performance of the obtained OF model matches the real OF sensor with 87.70% fitting accuracy. An accuracy of 0.006 m/s mean error between the real OF sensor velocity and the velocity of the OF model is also achieved. The velocity measurements of the obtained OF model and the position of the GPS/INS are used in performing a dynamic model-based sensor fusion algorithm. In the proposed solution, the OF sensor is engaged when the vehicle approaches a landing spot that is equipped with a predefined landing pattern. The proposed solution has succeeded in performing a helicopter auto TOL with a maximum position error of 27 cm.

A Compensation Method for Enhancing Aviation Drilling Robot Accuracy Based on Co-Kriging

The positional error of aviation drilling robot has a great influence on the strength and lives of aircrafts in the aircraft assembly. In order to improve the position accuracy of aviation drilling robot, an error compensation method based on co-kriging is proposed in this paper. The error similarity based on the kinematic of drilling robot is proposed firstly. Then, the positional errors of a set of points in the workspace are measured by using precision laser tracker. The measurement data are used to fit the cross-variogram of positional error. After the cross-variogram is obtained, the predicted positional errors of verification points can be estimated based on co-kriging. The positions after compensation are given to the drilling robot. The proposed method is carried out on an aviation drilling robot for practical compensation to verify the correctness and effectiveness of the error compensation method. The experimental results show that the average absolute positional error is reduced to 0.1150 mm from 0.7168 mm, and that the maximum absolute positional error is reduced to 0.2664 mm from 1.3073 mm. The experimental results also demonstrate that the proposed method can improve the absolute position accuracy of aviation robot and could meet the requirement of aircraft assembly.

New Vehicle Positioning Method Based on RMINS/KC and Robust Adaptive KF

Aiming at the characteristics of vehicle positioning, a new vehicle positioning method based on the rotation modulation (RM) technology, kinematic constraint (KC), and the robust adaptive Kalman filter (RAKF) is proposed. On the one hand, on the basis of RM inertial navigation system and KC, this method achieves the whitening of colored measurement noise by improving the measurement equation; on the other hand, the RAKF algorithm is used to suppress the influence of the dynamic model error and observation anomaly on the estimation of the state parameters. Finally, the proposed new method is applied to the practical vehicle positioning system. Compared with the results of KF or MEMS-RMINS, the maximum position error of the proposed method by using RAKF is less than that of the KF algorithm or MEMS-RMINS, and the positioning accuracy is improved by 26.7% than that of the KF algorithm and only 21.87% of the MEMS-RMINS. At the same time, when the system has the observation anomaly, this method can also ensure the positioning accuracy of the system. The experimental results show that the new method can effectively suppress the influence of the system model error and observation anomaly to improve the vehicle positioning accuracy.