Real-time Interpolation Research Articles

Automation of main pipe-rotating welding scheme for intersecting pipes

Main pipe-rotating welding scheme for intersecting pipes can enhance welding quality by translating all of the welding position to horizontal vertical position. For purpose of the automation of this welding scheme, this article presents an automatic welding algorithm with a general description of the kinematic character, which is applicable to different welding equipment. Geometrical models containing pipes’ parameters and welding torch’s posture and dynamic model adequately expressing the welding process are established successively. Two different piecewise linear fitting methods used for real-time interpolation and off-line programming are introduced and analyzed subsequently. A three-dimensional simulation and a welding experiment with a 6-axis machine tool verify the feasibility of the algorithm.

The moving minimum audible angle is smaller during self motion than during source motion.

We are rarely perfectly still: our heads rotate in three axes and move in three dimensions, constantly varying the spectral and binaural cues at the ear drums. In spite of this motion, static sound sources in the world are typically perceived as stable objects. This argues that the auditory system—in a manner not unlike the vestibulo-ocular reflex—works to compensate for self motion and stabilize our sensory representation of the world. We tested a prediction arising from this postulate: that self motion should be processed more accurately than source motion. We used an infrared motion tracking system to measure head angle, and real-time interpolation of head related impulse responses to create “head-stabilized” signals that appeared to remain fixed in space as the head turned. After being presented with pairs of simultaneous signals consisting of a man and a woman speaking a snippet of speech, normal and hearing impaired listeners were asked to report whether the female voice was to the left or the right of the male voice. In this way we measured the moving minimum audible angle (MMAA). This measurement was made while listeners were asked to turn their heads back and forth between ± 15° and the signals were stabilized in space. After this “self-motion” condition we measured MMAA in a second “source-motion” condition when listeners remained still and the virtual locations of the signals were moved using the trajectories from the first condition. For both normal and hearing impaired listeners, we found that the MMAA for signals moving relative to the head was ~1–2° smaller when the movement was the result of self motion than when it was the result of source motion, even though the motion with respect to the head was identical. These results as well as the results of past experiments suggest that spatial processing involves an ongoing and highly accurate comparison of spatial acoustic cues with self-motion cues.

NURBS Curve Real-Time Interpolation Feed Speed Planning for CNC Machining

In order to solve the problem of large amount of calculation and real time is not high in the process of NURBS real-time interpolation feed speed planning, offline feed speed planning method is proposed, the method plan speed in non real-time cycle, and generate the feed speed curve. In order to meet the machine tool dynamics constraint, the maximum acceleration and the jerk constraints were considered fully in the planning process. The simulation analysis show that the proposed method can greatly reduce the amount of computing tasks in real-time interpolation cycle, improve the real-time performance of interpolation; At the same time, the speed curve of the planning satisfies the requirement of machine tool dynamics, has the good effect of feeding speed smooth, is helpful to improve the interpolation precision.

Hardware Development of CNC System Based on OMAPL138 and FPGA

In order to realize high speed, high precision, high reliability, miniaturization performance of the CNC (Computer numerical control) system, this paper proposed a hardware platform of embedded CNC system based on OMAPL138 and FPGA. OMAPL138 is a SOC using C6748 DSP kernel and ARM9 kernel dual-core structure, the kernel frequency can achieve up to 375/456 MHz. ARM kernel of the CNC system which runs the Linux operation system is responsible for task management, DSP kernel is in charge of real-time interpolation and look-ahead algorithm, and FPGA module generates pulses to control the movement of the servo motor. Firstly, the overall hardware architecture of the embedded CNC system was designed. Meanwhile the hardware circuit design of CPU core module based on OMAPL138, human-computer interaction module, EMIFA bus interface of the FPGA core module were emphasized in detail, and also the serial port, Ethernet, USB communication interface module were introduced. A serial test experiments have been conducted and the results have shown that this embedded CNC system is powerful and stable.

A CNC Manufacturing Method for Parts with Trochoidal Profile

AbstractThis paper presents a manufacturing method for parts with trochoidal profile on CNC milling machines. The method is based on a new real-time interpolation algorithm capable to drive the cutter along the offset of trochoid curves with precision equal to the resolution of the machine. The structure of the presented algorithm may be adapted accordingly so as to be used either for parts with an epitrochoidal or a hypotrochoidal profile. Both types of curves, known as trochoid curves, have important industrial applications such as gears with trochoidal tooth-profile, cams, trochoidal-shaped housings for rotary internal combustion engines and rotary piston pumps etc. The effectiveness and accuracy of the proposed method is verified by simulation tests of the generated tool path for the machining of two representative mechanical parts, an inner rotor of a hypogerotor pump and an epitrochoidal-shaped housing.

FIR Sine Interpolation Algorithm Based on Pipeline and Parallel Technology

According to the problem that the existing data interpolation algorithm has low efficiency when handling high-speed data, this paper proposes a FPGA-based FIR sine interpolation algorithm based on pipeline and parallel technology. The algorithm not only reduces the critical path so that improve the system working clock effectively, but also increases the speed of data processing to improve the speed of interpolation process significantly. Finally, according to the experiment based on FPGA, the result shows that the proposed algorithm improves the speed of data interpolation process, and reduces the system power consumption effectively. It can realize the real-time interpolation process of high-speed or hyper-speed data stream.

Real-Time Continuous-Scale Image Interpolation with Directional Smoothing

A real-time, continuous-scale image interpolation method is proposed based on a bilinear interpolation with directionally adaptive low-pass filtering. The proposed algorithm was optimized for hardware implementation. The ordinary bi-linear interpolation method has blocking artifacts. The proposed algorithm solves this problem using directionally adaptive low-pass filtering. The algorithm can also solve the severe blurring problem by selectively choosing lowpass filter coefficients. Therefore, the proposed interpolation algorithm can realize a high-quality image scaler for a range of imaging systems, such as digital cameras, CCTV and digital flat panel displays.

A real-time look-ahead interpolation algorithm based on Akima curve fitting

To process the complex geometric-shapes consisting of discrete data points, this paper presents a real-time look-ahead interpolation algorithm based on Akima curve fitting. The algorithm consists of two modules: pretreatment module and real-time interpolation module. The pretreatment module firstly adopts the bi-chord and tangent-chord criteria to identify those continuous Akima blocks and calculates the linking velocity between two adjacent blocks according to the required machining accuracy. Then the five-point Akima method is used to fit the continuous blocks into a Akima spline curve. In the real-time interpolation module, the look-ahead interpolation is executed to ensure that the processing error is limited in a satisfying range, and the Newton iteration method is employed to calculate the parameters when interpolating Akima spline blocks. Simulations and experimental results demonstrate that the Akima spline is more suitable when processing discrete data points. And the proposed look-ahead interpolation algorithm could reduce the feedrate fluctuation to satisfactory level and implement high-quality CNC processing.

Design and Implementation of High-Performance Real-Time Free-Form NURBS Interpolator in Micro CNC Machine Tool

This paper provides a suitable methodology to implement a high-performance and precise NURBS interpolator considering machine dynamics. The NURBS tool path curve is realized in real time by mapping the feedrate with a cubic curve with respect to time satisfying the machine dynamics and chord error. This is done by analyzing the feedrate profile offline and scheduling it with respect to time using a time optimal jerk limited algorithm. The proposed and the conventional NURBS interpolators are implemented in a three axis micro machine tool and the machining performance with respect to surface finish at different feedrates is compared. It is found that the feedrate profile obtained using the proposed interpolator scheme results in improved surface finish. Experimental evidences regarding the improvement in surface finish using a NURBS interpolator are shown for the first time according the authors knowledge. The proposed interpolator is designed with flexibility so that it can be implemented in all types of conventional CNC 3 axis machines also.

Experimental performance analysis of an inverse dynamics CNC compensation scheme for high-speed execution of curved toolpaths

Experimental results from the implementation of an inverse dynamics compensation scheme on a three-axis CNC mill with an open-architecture software controller are presented. The scheme amounts to imposing a continuously variable displacement on the commanded toolpath, which compensates for the physical limitations (inertia and damping) of each machine axis, producing accurate execution of the prescribed toolpath. Numerical values for the dimensionless parameters that characterize the second-order inverse dynamics model are determined by feeding input and output data from machine runs into a system identification software tool. For a basic P-type controller, exact a priori solutions for the modified path geometry are possible, allowing implementation by simple alterations to the real-time interpolator. The experimental results based on a P-type controller indicate that the inverse dynamics scheme is highly effective in suppressing both feed (lag/lead) error and contour error (deviation from the desired path), even at high feedrates along strongly curved toolpaths. The scheme thus provides a practical means of achieving smooth and accurate execution of free-form paths, without appealing to more complicated “active” control strategies.

Space Trajectory On-Line Interpolation Technique of Six-DOF Robot

This paper presents a real-time interpolation algorithm of the space trajectory which based on the theory of coordinate transform. The algorithm can solve the path planning problem of six-DOF robot. According to the actual movement state of robot, the algorithm can obtain some key points for the robot motion path by teaching. Then it can realize the dimensional random trajectory interpolation by coordinate transformation after building a suitable dimensional coordinate. Finally it can obtain the corresponding joint angle though the inverse kinematics solution. The experimental results show that this algorithm has a good rapidity and practicality, it suit for the six-DOF robot real-time trajectory interpolation, so it is worth promoting.

Construction of [formula omitted] rounded corners with Pythagorean-hodograph curves

The problem of designing smoothly rounded right-angle corners with Pythagorean-hodograph (PH) curves is addressed. A G1 corner can be uniquely specified as a single PH cubic segment, closely approximating a circular arc. Similarly, a G2 corner can be uniquely constructed with a single PH quintic segment having a unimodal curvature distribution. To obtain G2 corners incorporating shape freedoms that permit a fine tuning of the curvature profile, PH curves of degree 7 are required. It is shown that degree 7 PH curves define a one-parameter family of G2 corners, facilitating precise control over the extremum of the unimodal curvature distribution, within a certain range of the parameter. As an alternative, a G2 corner construction based upon splicing together two PH quintic segments is proposed, that provides two free parameters for shape adjustment. The smooth corner shapes constructed through these schemes can exploit the computational advantages of PH curves, including exact computation of arc length, rational offset curves, and real-time interpolator algorithms for motion control in manufacturing, robotics, inspection, and similar applications.

Universal real-time NURBS interpolator on a PC-based controller

It is complex and divergent for the conventional motion controllers to process various G codes using different interpolation algorithms. This impairs programming efficiency and robustness of the controller. In this paper, we propose the universal non-uniform rational B-splines (NURBS)-based interpolator which can simplify the architecture of interpolation in spite of interpreting different kinds of inputs. Direct conversion of long G01 and G02/G03 numerical control (NC) segments to NURBS segment is first implemented. The fitting of multiple short segments into a continuous and smooth NURBS segment is then carried out. More importantly, the universal NURBS-based interpolator utilizes the Cox–de Boor algorithm which is highly efficient and can take advantage of the parallel computing scheme to accelerate the processing speed. Furthermore, due to the construction of real-time environment, the proposed algorithm enables interpretation, look-ahead functions, and motion control to work simultaneously. A 2D NC program possessing hundreds of short G01 segments and long segments (i.e., G02, G03, and long G01) is tested on an in-house developed XY-table with a PC-based motion controller. The results have shown the effectiveness and feasibility of the proposed real-time NURBS-based interpolator.

Development of Real-Time Look-Ahead Methodology Based on Quintic PH Curve with G<sup>2</sup> Continuity for High-Speed Machining

Curving tool paths composed of straight lines, which are often represented as G01 blocks, are still the most widespread format form in the machining process chain of CAD/CAM/CNC. At the junctions between consecutive segments, the tangency and curvature discontinuities may lead to feedrate fluctuation and acceleration oscillation, which would deteriorate the machining efficiency and quality. In this paper, a real-time look-ahead interpolation methodology is proposed, which adopts a curvature-continuous PH curve as a transition to blend corner at the junction of adjacent lines in the tool path. The blending algorithm can guarantee the approximation error exactly, and the control points of the curve can be calculated analytically. On the other hand, the arc length and the curvature of the transition curve, which are important items in speed planning, also have analytical expressions. All the advantages are the guarantee of calculation efficiency during the interpolation. Except for a curvature-continuous tool path, our look-ahead algorithm adopts a speed planning window strategy to achieve a balance between the calculation capabilities and the real-time interpolation requirements. In this window, the corner transition algorithm and speed planning are implemented simultaneously and dynamically during the interpolation. By defining the width of this window, which is actually the number of linear segments contained in this window, can adjust the time consuming of speed planning. Simulation and experiments on our own developed CNC platform are conducted. The results demonstrate the feasibility and efficiency of the proposed algorithms.

Design and Implementation of an Interpolation Processor for CNC Machining

As the demand for high speed and high precision machining increases, the fast and accurate real-time interpolation is necessary in modern computerized numerical control (CNC) systems. However, the complexity of the interpolation algorithm is an obstacle for the embedded processor to achieve high performance control. In this paper, a novel interpolation processor is designed to accelerate the real-time interpolation algorithm. The processor features an advanced parallel architecture, including a 3-stage instruction pipeline, very long instruction word (VLIW) support, and asynchronous instruction execution mechanism. The architecture is aimed for accelerating the computing-intensive tasks in CNC systems. A prototype platform was built using a low-cost field programmable gate array (FPGA) chip to implementation the processor. Experimental result has verified the design and showed the good computing performance of the proposed architecture.

Development of FPGA based NURBS interpolator and motion controller with multiprocessor technique

The high-speed computational performance is gained at the cost of huge hardware resource, which restricts the application of high-accuracy algorithms because of the limited hardware cost in practical use. To solve the problem, a novel method for designing the field programmable gate array(FPGA)-based non-uniform rational B-spline(NURBS) interpolator and motion controller, which adopts the embedded multiprocessor technique, is proposed in this study. The hardware and software design for the multiprocessor, one of which is for NURBS interpolation and the other for position servo control, is presented. Performance analysis and experiments on an X-Y table are carried out, hardware cost as well as consuming time for interpolation and motion control is compared with the existing methods. The experimental and comparing results indicate that, compared with the existing methods, the proposed method can reduce the hardware cost by 97.5% using higher-accuracy interpolation algorithm within the period of 0.5 ms. A method which ensures the real-time performance and interpolation accuracy, and reduces the hardware cost significantly is proposed, and it’s practical in the use of industrial application.

Simulation and Implementation of an Improved Inscribed Chord Interpolation Algorithm

In order to improve the shortcomings of the realization of the traditional quadratic curve interpolation inscribed chord method, this paper proposes an improved internal chord interpolation algorithm. The program flow chart of the algorithm achievement and the interpolation method of circular arc interpolation and linear interpolation of a detailed operation process is given in this paper. Finally through a calculation example the simulation is conducted, and the point by point comparison method were compared. The simulation results show the improvement on the quadratic curve interpolation in the inner string interpolation speed, good flexibility, and it worth popularizing in the interpolation algorithm for real time interpolation.

New CNC Programming Functions Based on Elliptical Motion

AbstractThis paper proposes a set of four elliptical features that can enhance the programming capabilities of a modern CNC system. Namely, a real-time interpolation algorithm for motion generation along an ellipse and its offset, machining of an elliptical pocket, and drilling a series of equidistant holes along an elliptical path. The paper analytically describes the implementation of the new functions while the G-codes, along with their complementary requisite data needed to be introduced in the CNC part program, are exemplified with simulation and actual machining tests for each feature.

Research & Design of the Multifunctional Landscape Hedge Trimmer

This paper presents a multifunctional landscape hedge trimmer. It has 6 degrees of freedom, and it can trim the shape of flat, cylinder, cone, sphere, etc. The controller takes the embedded LINUX ARM9 processor as the core. It has a high-speed real-time online interpolation function, and an error compensation function. With the help of the developed control software it can control the trimming process automatically, making the trimming speed faster and the precision higher, and with its single-person operation feature, it greatly reduces the labor intensity and improves the labor efficiency.

Study on the Algorithm for Real-time Interpolation of NURBS Curve and Simulation

In the paper, In order to meet the needs of high-speed and high- accuracy computerized numerical control machining and guarantee the smooth running in the interpolation processing, A NURBS curve calculation based on adaptive acceleration and deceleration control of look-ahead s-shaped for the real-time interpolation is presented in this paper. The algorithm has merits such as higher position accuracy, short processing time, no variation and so on. Through dynamic path simulation and interpolation results analyses with MATLAB, the interpolation algorithm is proved to be correct and rational. Through actual machining by OPEN platform with VC++, the algorithm is proved to be real-time and practicable. DOI: http://dx.doi.org/10.11591/telkomnika.v11i5.2482