Error Compensation Algorithm Research Articles

Online absolute pose compensation and steering control of industrial robot based on six degrees of freedom laser measurement

In-situ intelligent manufacturing for large-volume equipment requires industrial robots with absolute high-accuracy positioning and orientation steering control. Conventional robots mainly employ an offline calibration technology to identify and compensate key robotic parameters. However, the dynamic and static parameters of a robot change nonlinearly. It is not possible to acquire a robot’s actual parameters and control the absolute pose of the robot with a high accuracy within a large workspace by offline calibration in real-time. This study proposes a real-time online absolute pose steering control method for an industrial robot based on six degrees of freedom laser tracking measurement, which adopts comprehensive compensation and correction of differential movement variables. First, the pose steering control system and robot kinematics error model are constructed, and then the pose error compensation mechanism and algorithm are introduced in detail. By accurately achieving the position and orientation of the robot end-tool, mapping the computed Jacobian matrix of the joint variable and correcting the joint variable, the real-time online absolute pose compensation for an industrial robot is accurately implemented in simulations and experimental tests. The average positioning error is 0.048 mm and orientation accuracy is better than 0.01 deg. The results demonstrate that the proposed method is feasible, and the online absolute accuracy of a robot is sufficiently enhanced.

Periodic Error Compensation in Fiber-coupled Heterodyne Interferometry

This paper extends the application of a novel wavelet-based periodic error compensation algorithm in fiber-coupled heterodyne interferometry. In this case, the amplitudes of periodic error may be fluctuating and traditional digital algorithms are not well-suited. The wavelet-based method, however, has the ability to compensate non-stationary periodic error. In this work, the algorithm is used to compensate periodic error in simulated and experimental constant and experimental non-constant velocity motions and to reduce the error by approximately 80.1%, 81.2% and 68.3%.

Improved DC Offset Error Compensation Algorithm in Phase Locked Loop System

This paper proposes a dc error compensation algorithm using dq-synchronous coordinate transform digital phase-locked-loop in single-phase grid-connected converters. The dc errors are caused by analog to digital conversion and grid voltage during measurement. If the dc offset error is included in the phase-locked-loop system, it can cause distortion in the grid angle estimation with phase-locked-loop. Accordingly, recent study has dealt with the integral technique using the synchronous reference frame phase-locked-loop method. However, dynamic response is slow because it requires to monitor one period of grid voltage. In this paper, the dc offset error compensation algorithm of the improved response characteristic is proposed by using the synchronous reference frame phase-locked-loop. The simulation and the experimental results are presented to demonstrate the effectiveness of the proposed dc offset error compensation algorithm.

Reconstructing flicker-free surfaces in hybrid particle-grid water simulation

We present a new method for adaptively extracting flicker-free surfaces from time-varying nonuniform point-set data such as a hybrid particle–grid water simulation. When particles are irregularly distributed in hybrid simulations, degenerate triangles and holes may occur when constructing surfaces adaptively. These abnormal surfaces appear unexpectedly between frames, and we call them “flicker” artifacts (see Fig. 1). In this paper, we address this problem by developing: (1) a kernel-based octree technique to avoid degenerate triangles being created because of size discontinuities between adjacent leaf cells; (2) a level-set error compensation algorithm to avoid apertured water surfaces caused by some particles being lost in the triangulation process; and (3) the extraction of sufficient surface particles for efficient reconstruction of surfaces with extreme amounts of spatial adaptivity. Comparisons with previous methods convincingly demonstrate that our technique successfully reduced flicker artifacts.

A 6-DOF acceleration sensor with cylindrical configuration

The paper introduces a novel 6-DOF acceleration sensor based on 8 dual-axes linear accelerometers, which possesses small volume, high reliability, elevated error resistance, and easy-to-integrate properties. To reduce impacts resulting from installation errors of linear accelerometers, and improve redundancy of the sensor, a new spatial geometric configuration of the sensor is proposed. The Geometric Dilution of Procession (GDOP) is introduced to evaluate the configuration of the sensor. Compared with the typical sensor configuration constituted by six linear accelerometers, the value of GDOP is decreased by 35.45%. Furthermore, error models of the sensor are deduced with respect to installation errors of linear accelerometers, and an absolute error compensation algorithm of the sensor is presented. Relative measurement errors of gravity acceleration decrease from 5.18% to 1.68%. Experimental results demonstrate that the proposed sensor is effectiveness in practice.

An online real-time path compensation system for industrial robots based on laser tracker

Industrial robots have been widely used in many areas for the properties such as low cost, high flexibility and relatively large working space. The low absolute accuracy and low stiffness, however, limit the application in high precision areas. This article presents an approach for industrial robots that overcomes the inaccuracy of robotic path in offline programming. Robot Sensor Interface of KUKA robot controller makes the error compensation available. First, the compensation performance of the KUKA KR5 arc robot is investigated and the straight-line and circular arc path compensation strategies are proposed. Besides, an error compensation algorithm is proposed to generate the compensation values as well as to deal with the oscillation of real-time compensation. Finally, experimental results using a KUKA KR5 arc robot verify the correctness and accuracy of the approach.

Off-line error compensation in corner milling process

Tool deflection induced by cutting force could result in dimensional inaccuracies or profile error in corner milling process. Error compensation has been proved to be an effective method to get accuracy component in milling process. This article presents a methodology to compensate profile errors by modifying tool path. The compensation effect strongly depends on accuracy of the cutting force model used. The mathematical expression of chip thickness is proposed based on the true track of cutting edge for corner milling process, which considers the effect of tool deflection. The deflection of tool is calculated by finite element method. Then, an off-line compensation algorithm for corner profile error is developed. Following the theoretical analysis, the effect of the error compensation algorithm is verified by experimental study. The outcome provides useful comprehension about selection of process conditions for corner milling process.

Development and testing of an error compensation algorithm for photogrammetry assisted robotic machining

Robotic machining of relatively small features on large components potentially offers an opportunity to reduce capital expenditure in various industries. A barrier to this is the inability of robotic machine tools to machine to the tolerances of conventional equipment. This paper proposes and tests a photogrammetry-based metrology assistance algorithm to compensate for robotic machining inaccuracy, as measured in the part, and investigates the associated measurement challenges. The algorithm is executed in a two stage process, whereby the closest point to nominal cutting coordinates on an aligned inspection surface is used for compensation, created a penultimate measured cut. Finally, the finishing program coordinates are compensated to correct under-cuts during the measured cut stage. Conceptual tests using simulated measurement data give confidence that the proposed approach works well. In experiments, a key area for further R&D effort is found to be uneven inspect point coverage, which results in alignment issues and a poor surface finish. Ultimately, direction is given to improve measurement system performance to enable the metrology assistance approach proposed to be implemented and therefore the benefits of “process-to-part” robotic machining to be realised.

Canceling the momentum in a phase-shifting algorithm to eliminate spatially uniform errors

In phase-shifting interferometry, phase modulation nonlinearity causes both spatially uniform and nonuniform errors in the measured phase. Conventional linear-detuning error-compensating algorithms only eliminate the spatially variable error component. The uniform error is proportional to the inertial momentum of the data-sampling weight of a phase-shifting algorithm. This paper proposes a design approach to cancel the momentum by using characteristic polynomials in the Z-transform space and shows that an arbitrary M-frame algorithm can be modified to a new (M+2)-frame algorithm that acquires new symmetry to eliminate the uniform error.

Loosely coupled fusion of camera and inertial sensors for distributed error compensation in strapdown inertial navigation system

The problem of error estimation and compensation in strapdown inertial navigation system (SINS) is investigated in this paper. The error dynamic model is derived and employed for this purpose. Information gathered from a micro-electro-mechanical inertial measurement unit (MEMS IMU) is fused with camera information in a loosely coupled integration scenario. Although this integration is computationally efficient, it suffers from fault propagation in the navigation algorithm. To overcome this problem, it is proposed in this paper to estimate and compensate for the propagated faults in a timely manner to provide a short start-up and computation time. This goal is achieved through the design of decentralized error estimation and compensation algorithms running in parallel with the inertial navigation system. To this end, firstly, the sparse error system is decomposed to cascaded subsystems using a combination of structural and behavioural decomposition methods. Then, cascaded Kalman filters (KFs) and decentralized state feedback regulators are designed for error estimation and compensation, respectively. The experimental results based on data from the 3D MEMS IMU and camera system are provided to demonstrate the efficiency of the proposed method.

Compensation of body shake errors in terahertz beam scanning single frequency holography for standoff personnel screening**Project supported by the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. YYYJ-1123).

In the terahertz (THz) band, the inherent shake of the human body may strongly impair the image quality of a beam scanning single frequency holography system for personnel screening. To realize accurate shake compensation in imaging processing, it is quite necessary to develop a high-precision measure system. However, in many cases, different parts of a human body may shake to different extents, resulting in greatly increasing the difficulty in conducting a reasonable measurement of body shake errors for image reconstruction. In this paper, a body shake error compensation algorithm based on the raw data is proposed. To analyze the effect of the body shake on the raw data, a model of echoed signal is rebuilt with considering both the beam scanning mode and the body shake. According to the rebuilt signal model, we derive the body shake error estimated method to compensate for the phase error. Simulation on the reconstruction of point targets with shake errors and proof-of-principle experiments on the human body in the 0.2-THz band are both performed to confirm the effectiveness of the body shake compensation algorithm proposed.

Polygonal model based cutter location data generation with offset error compensation

Purpose As manufacturing technology has developed, digital models from advanced measuring devices have been widely used in manufacturing sectors. To speed up the production cycle and reduce extra errors introduced in surface reconstruction processes, directly machining digital models in the polygonal stereolithographyformat has been considered as an effective approach in rapid digital manufacturing. In machining processes, Cutter Location (CL) data for numerical control (NC) machining is generated usually from an offset model. This model is created by offsetting each vertex of the original model along its vertex vector. However, this method has the drawback of overcut to the offset model. The purpose of this paper is to solve the overcut problem through an error compensation algorithm to the vertex offset model. Design/methodology/approach Based on the analysis of the vertex offset method and the offset model generated, the authors developed and implemented an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. This error compensation method is verified through three polygonal models and the tool paths generated were used for a real part machining. Findings Based on the analysis of the vertex offset method and the offset model generated, the authors developed an error compensation method to correct the offset models and generated the accurate CL data for the subsequent machining process. The developed error compensation algorithm can effectively solve the overcut drawback of the vertex offset method. Research limitations/implications The error compensation method to the vertex offset model is used for generating the CL data with the using of a ball-end cutter. Practical implications On the study of CL data generation for a STL model, most of the current studies are focused on the determination of the offset vectors of the vertexes. The offset distance is usually fixed to the radius of the cutter used. Thus, the overcut problem to the offset model is inevitable and has not been much studied. The authors propose an effective approach to compensate the insufficient distance of the offset vertex and solve the overcut problem. Social implications The directly tool paths generation from a STL model can reduce the error of surface reconstruction and speed up the machining progress. Originality/value The authors investigate the overcut problem occurred in vertex offset for CL data generation and present a new error compensation algorithm for generating the CL data that can effectively solve the overcut problem.

A flywheel error compensation algorithm for engine misfire detection

The crankshaft angular velocity measured at the flywheel is a commonly used signal for engine misfire detection. However, flywheel manufacturing errors result in vehicle-to-vehicle variations in the measurements and have a negative impact on the misfire detection performance. A misfire detection algorithm must be able to compensate for this type of vehicle-to-vehicle variations if it is to be used in production cars to assure that legislations are fulfilled. It is shown that flywheel angular variations between vehicles in the magnitude of 0.05° have a significant impact on the measured angular velocity and must be compensated for to make the misfire detection algorithm robust. A misfire detection algorithm is proposed with flywheel error adaptation in order to increase robustness and reduce the number of mis-classifications. Evaluations using measurements from a number of vehicles on the road are used to quantify the negative impact of the flywheel errors and show that the number of mis-classifications is significantly reduced when performing on-line flywheel error adaptation.

Low-complexity optical phase noise suppression in CO-OFDM system using recursive principal components elimination.

A low-complexity optical phase noise suppression approach based on recursive principal components elimination, R-PCE, is proposed and theoretically derived for CO-OFDM systems. Through frequency domain principal components estimation and elimination, signal distortion caused by optical phase noise is mitigated by R-PCE. Since matrix inversion and domain transformation are completely avoided, compared with the case of the orthogonal basis expansion algorithm (L = 3) that offers a similar laser linewidth tolerance, the computational complexities of multiple principal components estimation are drastically reduced in the R-PCE by factors of about 7 and 5 for q = 3 and 4, respectively. The feasibility of optical phase noise suppression with the R-PCE and its decision-aided version (DA-R-PCE) in the QPSK/16QAM CO-OFDM system are demonstrated by Monte-Carlo simulations, which verify that R-PCE with only a few number of principal components q ( = 3) provides a significantly larger laser linewidth tolerance than conventional algorithms, including the common phase error compensation algorithm and linear interpolation algorithm. Numerical results show that the optimal performance of R-PCE and DA-R-PCE can be achieved with a moderate q, which is beneficial for low-complexity hardware implementation.

A research for error compensation algorithm of Dual Range Pressure Sensor

Large range-high precision measurement has always been a challenge in the field of mechanical measurements. This paper built the input-output differential equation of Dual Range Pressure Sensor (DRPS) and gave an error compensation algorithm of DRPS after analyzing the mathematical model of DRPS. For a given situation, dynamic measurement errors of sensor parameters can be compensated by this method. Finally the accuracy and feasibility of the method were verified using Adams Software.

A precision CNC turn-mill machining center with gear hobbing capability

With ever increasing demand for small parts with complex shapes and high dimensional accuracy, many traditional machine tools have become ineffective for machining these miniature components. Typical examples include dental implants, parts used in mechanical watch movements, and parts used in medical endoscopes. This paper introduces our PC-controlled CNC turn-mill machining center. It has 5 axes, an automatic bar feeder, an automatic part collection tray, and a tool changer. It features a special control algorithm for the synchronization of its axes that produces not only higher accuracy but also makes the machine easier to use. In addition, a volumetric error compensation algorithm is implemented to improve accuracy. Based on experiments, the machining error is ±3μm for turning, ±7μm for milling and the maximum profile error is less than ±7.5μm for gear hobbing.

Infrared micro-scanning error compensation algorithm based on edge location

For area-array thermal imaging devices, an essential factor affecting the system imaging quality is the sub-sampling caused by oversized discrete sampling pitch. In order to obtain higher spatial resolution, staring infrared focal plane array (IRFPA) gets multi-frame sub-sampling images by micro-scanning movement to achieve an adequate spatial sampling frequency. However, influenced by external environment and the accuracy of the scanning system itself, the relative displacement between the detector and the scene cannot be absolutely precisely controlled, but exist some error, which will affect the final performance of the reconstructed high-resolution image. We analyzed the distribution of the error and then proposed an infrared micro-scanning error compensation algorithm based on edge location, which is inspired by human retina fixational eye movement pattern. It first locates the edge point in the reconstruction unit and finds the corresponding characteristic values. Later on, matches the characteristic value with the fixed templates and reorders the pixel responses in reconstruction unit utilizing the gray correlation. Finally, it compensates the error real-timely through repeated update and iteration. We apply the algorithm in video sequences acquired by 4-step infrared micro-scanning system. The experiment results show that when aligning to a static scene or stationary region in dynamic scene, the algorithm possesses good resolution enhancement effect, particularly, can improve the clarity and the accuracy of static image edge details.

Subdivision Error Analysis and Compensation for Photoelectric Angle Encoder in a Telescope Control System

As the position sensor, photoelectric angle encoder affects the accuracy and stability of telescope control system (TCS). A TCS-based subdivision error compensation method for encoder is proposed. Six types of subdivision error sources are extracted through mathematical expressions of subdivision signals first. Then the period length relationships between subdivision signals and subdivision errors are deduced. And the error compensation algorithm only utilizing the shaft position of TCS is put forward, along with two control models; Model I is that the algorithm applies only to the speed loop of TCS and Model II is applied to both speed loop and position loop. Combined with actual project, elevation jittering phenomenon of the telescope is discussed to decide the necessity of DC-type subdivision error compensation. Low-speed elevation performance before and after error compensation is compared to help decide that Model II is preferred. In contrast to original performance, the maximum position error of the elevation with DC subdivision error compensation is reduced by approximately 47.9% from 1.42″to 0.74″. The elevation gets a huge decrease in jitters. This method can compensate the encoder subdivision errors effectively and improve the stability of TCS.

Development of Fast Error Compensation Algorithm for Integrated Inertial-Satellite Navigation System of Small-size Unmanned Aerial Vehicles in Complex Environment

Development of Fast Error Compensation Algorithm for Integrated Inertial-Satellite Navigation System of Small-size Unmanned Aerial Vehicles in Complex Environment

Identification and compensation of geometric errors of rotary axes on five-axis machine by on-machine measurement

The geometric errors of rotary axes are the fundamental errors of a five-axis machine tool. They directly affect the machining accuracy, and require periodical measurement, identification and compensation. In this paper, a precise calibration and compensation method for the geometric errors of rotary axes on a five-axis machine tool is proposed. The automated measurement is realized by using an on-the-machine touch-trigger technology and an artifact. A calibration algorithm is proposed to calibrate geometric errors of rotary axes based on the relative displacement of the measured reference point. The geometric errors are individually separated and the coupling effect of the geometric errors of two rotary axes can be avoided. The geometry error of the artifact as well as its setup error has little influence on geometric error calibration results. Then a geometric error compensation algorithm is developed by modifying the numeric control (NC) source file. All the geometric errors of the rotary errors are compensated to improve the machining accuracy. The algorithm can be conveniently integrated into the post process. At last, an experiment on a five-axis machine tool with table A-axis and head B-axis structure validates the feasibility of the proposed method.