Real-time Interpolation Research Articles

Five-axis STEP-NC controller for machining of surfaces

Five-axis machining is more widely used in manufacturing of freeform surfaces. However, in five-axis machining of freeform surfaces, incomplete information exchange between computer numerical control (CNC) and computer-aided design/computer-aided manufacturing (CAM) results in many limitations need to be rectified. In the paper, a new structure of CNC based on STEP-NC standard is proposed, where tool path planning, tool offset, and inverse kinematics are transferred from CAM to CNC. In order to guarantee good openness, open platform and standard interface are applied in the development. Technology of module collaboration and design of data flow are studied. A five-axis real-time interpolator for non-uniform rational B-spline surfaces machining is realized. Based on these technologies, a five-axis CNC is developed in the manner of software realization, which consists of interpreter, task coordinator, axis group, softPLC, etc. The software CNC system has been applied on a tilt-rotary type five-axis machine tool, where the milling experiment has been performed successfully.

Hardware Engine for Real-Time Pen Tracking on Electrophoretic Displays

Although the electrophoretic display (EPD) has become the main solution to the display of an electronic reader (E-Reader), the latency of displaying a new image on the EPD is much lower than that on liquid crystal displays. This problem leads to poor user experience when a user wants to annotate some important points by supplying with more comments on the EPD. The technical issues that should be dealt with include the pixel interpolation between the plotted pixels and the fast driving waveform design for those interpolated pixels. In this paper, we propose a new hardware engine that performs real-time pixel interpolation to compensate the resolution mismatch between the touch panel and the EPD. In addition, a new fast driving scheme for plotting the interpolated pixels to the black state on the EPD is also proposed. The experimental results show that the engine can complete the pixel interpolation in 2 ms and the pixels will not be overdriven. The overall latency of the pen tracking function is much shorter than that of the previous approaches.

Spatial Interpolation for Real-Time Rainfall Field Estimation in Areas with Complex Topography

AbstractFor many hydrological applications interpolation of point rainfall measurements is needed. One such application is flood early warning, particularly where spatially distributed hydrological models are used. Operation in real time poses challenges to the interpolation procedure, as this should then both be automatic and efficiently provide robust interpolation of gauged data. The differences in performance of ordinary kriging, universal kriging, and kriging with external drift with individual and pooled variograms were assessed for 139 daily datasets with significant precipitation in a study area in Bogotá, Colombia. Interpolators were compared using the percentage of variability explained and the root-mean-square error found in cross validation, aiming at identifying a procedure for real-time interpolation. The results showed that interpolators using pooled variograms provide a performance comparable to when the interpolators were applied to the storms individually, showing that they can be used successfully for interpolation in real-time operation in the study area. The analysis identified limitations in the use of kriging with external drift. Only when the adjusted R2 between the secondary variables and precipitation is higher than the percentage of variability explained found in ordinary kriging, then kriging with external drift provided a consistent improvement. This interpolator was found to give a lower performance in all other cases. The distribution of precipitation over basins of interest for each of the storms, derived through sampling rainfall fields generated through conditional Gaussian simulation, shows that, while differences between the interpolators may appear to be significant, the variability of the precipitation volume is less significant.

Study on NURBS Curve Interpolation Based on before Acceleration/Deceleration with Linear Jerk

In high speed machining, excessive vibration and shock growing out of acceleration and jerk should be suppressed. Therefore, based on before acceleration/deceleration with linear jerk, a new NURBS curve interpolation was proposed. Interpolation feed and acceleration were planned employing before acceleration/deceleration with linear jerk evolution. During real-time interpolation, the interpolation feed and acceleration were calculated with polynomial fitting method, and with the second-order Taylor expansion, the interpolation parameter was computed. A NURBS curve was interpolated with the proposed method and the one with S curve acceleration/deceleration as comparison. The results indicated the proposed method not only maintain high feed but also reduce the interpolation output acceleration and jerk significantly, and its output jerk evolves along with time linearly. The proposed method can be used to reduce the vibration and shock from the high speed moving parts and improve their smoothness.

The Research of Real-Time Trajectory Interpolation Based on Open Numerical Control System

This paper researches on Open Numerical Control System based on the PC platform, in which the motion controller works as the control core, can realize the multiaxis motion control in real time and the sequential logic control. This paper sets out from the hardware structure, use the Real-time trajectory interpolation algorithm, and choose the proper motion-control function. it can realize fast, stable and continuous movement with multistage path, and ensure that the system is open, real-time and reconfigurable.

Low-complexity, full-resolution, mirror- switching digital predistortion scheme for polar-modulated power amplifiers

Proposed is a mirror-switching digital predistortion (DPD) scheme with low complexity and full resolution, tailored for power-efficient polar-modulated power amplifiers with nonlinear AM-AM and AM-PM characteristics. The involved digital circuitry is composed of just one CORDIC operator and two 1D look-up tables, avoiding any real-time interpolation or analogue operation. The DPD scheme is verified on a FPGA and the estimated power using a 65 nm CMOS technology is 5.2 mW. The training time is ∼82 µs at a clock rate of 100 MHz. System-level simulations in MATLAB show significant improvements of error vector magnitude from 104.8 to 2%, and adjacent channel leakage ratio from 21.36 to 49.27 dB, under a 20 MHz-bandwidth 64-QAM OFDM test signal.

Research and implementation of NURBS interpolator with continuous feedrate for high-speed machining

Using non-uniform rational B-splines (NURBS) rather than piecewise lines and arc segments as a toolpath makes it much easier to achieve high-speed control in die and mould machining. When NURBS is used as a toolpath, two issues must be solved. The first is how to convert the discrete cutter location (CL) data offset from a CAD model into a NURBS curve. The second is how to maintain low velocity fluctuation while interpolating the NURBS curve with limited calculation time. This study proposes a NURBS toolpath generation method from line segments and a real-time NURBS interpolator for CNC machines to achieve the goal of high-speed machining. A CL data simplification method with shape holding is presented based on identifying and correcting the defect point from the original CL data, and removing redundant CL data within shape-maintaining requirements. Then the conversion of all simplified CL data to NURBS curves is done by applying NURBS fitting or interpolation with optional directional constraints. A precise method based on nonlinear mapping between the NURBS's parameter and arc length is proposed and implemented to obtain a continuous feedrate and machining quality. The simulation performed on CL points for a wave surface demonstrates that the proposed approach reduces the NC blocks to 6% while staying within the tolerance of deviation. The machining experiment shows that the proposed approach can increase machining quality while reducing machining time by about 22%.

AN IMPROVED EDGE-DIRECTED IMAGE INTERPOLATION ALGORITHM

The paper sets forth an improved edge-directed image interpolation algorithm with low time complexity. The algorithm partitions images into homogeneous and edge areas by setting the preset threshold value based on the local structure characteristics. Specified algorithms are assigned to interpolate each classified areas respectively. The proposed method implements strategy in three steps to interpolate after setting the preset threshold value. In this way, it can achieve the goals of real-time interpolation and good subjective quality. Furthermore, the interpolated images have much more explicit edge regions and better visual effects using our proposed method than that of using other algorithms. Experimental results demonstrate that the method proposed by the authors is high-performed in image interpolation.

Design of a real-time NURBS interpolator with constant segment length for milling EDM

The utilization of the non-uniform rational B-spline (NURBS) toolpaths becomes more important than ever before. However, in traditional milling electrical discharge machining (EDM) of parametric curves, there commonly exist problems such as speed loss and an overincreased sampling period, which directly cause a decrease in machining efficiency. Moreover, traditional approaches normally suffer from a complex toolpath planning. In this paper, a real-time interpolator with a constant segment length is proposed to improve the milling EDM of NURBS curves. The proposed interpolator can directly process NURBS curves with their definition information. The toolpath planning can thus become simpler. A new two-stage interpolation method is adopted such that both a high speed accuracy and a relatively short sampling period can be achieved, and the magnitude of chord errors can also be reduced. While the first-stage interpolation samples a NURBS curve with a constant-length segment, the second-stage interpolation, or the re-interpolation, executes multiple interpolations in a sampling period to generate the required feed rate. A loop buffer is designed for the implementation of the real-time interpolator. Experimental results show that the proposed interpolator demonstrates a superior machining performance to that by traditional interpolators, especially in terms of chord errors and erosion rate.

Curvature-Based Real-Time NURBS Surface Interpolator with Look-Ahead ACC/DEC Control

Real-time parametric surface interpolation is very useful in high-performance machining. A curvature-based NURBS surface interpolator with look-ahead acceleration/deceleration (ACC/DEC) control has been developed. The cutter contact (CC) paths are planned through iso-parametric line method. The CC feedrate profile is optimized using global flexible control strategy and local adaptive ACC/DEC optimization strategy according to the look-ahead algorithm. The real-time surface interpolation algorithm was programmed on Windows XP platform. The stability and efficiency of the proposed interpolation method were verified by a NURBS curve and a NURBS surface. It is shown that the proposed parametric interpolation algorithm can satisfy the high speed and high precision requirements of high-speed CNC systems.

Realization of a 5-axis NURBS Interpolation with Controlled Angular Velocity

5-axis machine tool plays an important role in high-speed and high-precision computer numerical control (CNC) machining of workpieces with complex shapes. A non-uniform rational B-spline (NURBS) interpolation format for 5-axis machining is proposed to adapt to the high speed machining (HSM). With this interpolation format, angles between orientation vectors are chosen as parameters of orientation B-spline constructed by an open controller to achieve reasonable orientation vectors in real-time interpolation process. Coordinated motion between linear axes and rotary axes is achieved by building a polynomial spline which relates interpolation arc lengths of position spline to angles of orientation spline. Algorithm routine of this interpolation format and its realization methods in the supported controller are discussed in detail. Finally, performance of the proposed NURBS interpolation format is demonstrated by a practical example.

2P1-T05 マスタ・スレーブシステムにおける躍度最小軌道生成(手術支援ロボティクス・メカトロニクス(2))

This paper describes a trajectory generation method for a master-slave surgical robotic system. Because the data from the master system is intermittent due to the limit in master-slave communication rate, interpolation is required to achieve the smooth motion of the slave robot. In particular, real-time interpolation is crucial for surgical systems. To cope with this problem, we propose a new smooth trajectory generation method by minimizing jerk using a quintic B-spline. To ensure the third-order continuity in position, velocity and acceleration, the trajectory of next time segment is generated using several fictive control points. In addition, we impose a minimum jerk constraint to obtain a smooth trajectory. The proposed method was tested and compared with a conventional trajectory generation method. The experimental results show that the proposed method generated a smoother trajectory with fewer jerks, which is sufficient for use in real-time control of the surgical robotic system.

The Research of the NURBS Curve Interpolation Algorithm

In this article, the definition, the nature and the parameter of the NURBS (Non-Uniform Rational B-spline) curves are defined, the more thorough analysis and research of the real-time NURBS curve interpolation algorithm and the feed rate adaptive control are carried out.

Design of Pythagorean Hodograph Curve Interpolator Based on NiosII Embedded Processor and FPGA

In this paper, a novel architecture of Pythagorean Hodograph (PH) curve interpolator based on Nios Ⅱ embedded processor and FPGA is proposed. The whole interpolator including NiosⅡ processor is built in a single FPGA chip. The interpolator uses a two-stage interpolation scheme to reduce the computational burden of PH curve interpolator. The Nios Ⅱ embedded processor implements 1st-stage interpolation, the FPGA receives the command from the Nios Ⅱ processor and implements 2nd-stage interpolation simultaneously. Therefore, the interpolator can implement the real-time PH curve interpolation algorithm steadily to meet the needs of high-speed and high-precision machining.

Design and Implementation of Real-Time CNC Interpolation ASIC for Pythagorean Hodograph Curve Based on FPGA

In this paper, a novel architecture of a real-time CNC interpolation ASIC for Pythagorean Hodograph curve based on FPGA is proposed. The ASIC built on a single FPGA chip contains a NikosⅡprocessor core. It uses a two-stage interpolation scheme to reduce the computational burden of PH curve interpolation. Firstly, the 1st-stage interpolation program is operated on the NikosⅡprocessor. The FPGA hardware logic performs the 2nd-stage interpolation and outputs two groups of pulses for the motion control of actuators (two stepper motors)

A NURBS Interpolator Using Multiprocessor on Chip for High Performance Motion Control

Modern CNC system adopts the NURBS interpolation for the purpose of achieving high-speed and high accuracy performance. However, in conventional control architectures, the computation of the basis functions of a NURBS curve is very time consuming due to serial computing constraints. In this paper, a novel multiprocessor-based motion controller on chip utilizing its high-speed parallel computing power is proposed to realize the NURBS interpolation. The motion control algorithm and I/O control are also embedded in the chip to implement real-time control and NURBS interpolation simultaneously. The experimental tests using an X-Y table verify the outstanding computation performance of the multiprocessor-based motion controller on chip. The result indicates that shorter sampling time (0.1 ms) can be achieved for NURBS interpolation and high-accuracy motion control.

A practical real-time non-uniform rational B-spline curve interpolator for computer numerical control machining

Non-uniform rational B-spline (NURBS) interpolator, a key technique in computer numerical control (CNC) machining, has many advantages over linear and circular interpolator. A practical real-time NURBS interpolator based on an off-line algorithm, which is developed to handle the limitation of velocity and acceleration, is presented in this article. Two processing modules are employed to realize the real-time interpolator. In one module, a NURBS curve is split into shorter NURBS curves or approximated as continuous line segments according to the minimum splitting length first, and then the velocity planning of a short curve is applied. Inthe other module, the interpolation according to the velocity planning results is implemented. The proposed algorithm realizes the real-time velocity planning and interpolation of a NURBS curve regardless of the curve length or the continuity. It is also applicable to three-dimensional surface designed by computer-aided design system, which is composed of multiple NURBS curves or both NURBS curves and continuous line segments. Both the simulation and experiment results have proved the effectiveness of the proposed practical real-time NURBS interpolator.

Research on Real-Time NURBS Interpolator with Quintic Curve Acceleration/Deceleration Algorithm

We put up a new fast and steady parameter interpolator on the basis of the present various interpolation algorithms. This proposed algorithm has little rate of speed errors than other algorithms and can save much computing time because of its avoiding derivation operations. Quintic curve acceleration/deceleration algorithm (QCAD) is deduced which can improve the flexibility of the CNC machine. By means of the QCAD planning, the demand velocity is maintained high at large of the time and can be smoothly accelerated/decelerated when needed. Therefore, the parameter interpolator with QCAD can meet the CNC dynamic properties to improve the machine quality. In the end, this NURBS interpolator is validated by matlab, which proves this proposed algorithm not only has the advantages of good flexibility and simple implementation procedure, but also has lower time complexity.

Study on the Algorithm for Real-Time Interpolation of NURBS Curve

In order to meet the needs of high speed and high precision computerized numerical control machining, a calculation based on the control of contour error and feeding acceleration for the real-time interpolation of Non-uniform rational B-spline (NURBS) curves was presented in this paper. On the premise of meeting the error requirement, machine can process parts with the highest feeding speed to achieve interpolation precision and interpolation speed optimization, and improve processing quality and efficiency.

A new CNC turning canned cycle for revolved parts with free-form profile

This paper presents an algorithm for improving the interpolation accuracy in turning operations. The parts considered are formed by revolving a free-form profile which is implemented in terms of Bezier formulation around a center linear axis. The demand for the manufacturing of such geometric shapes is frequently met in parts produced by casting and forging methods. The method employs a computer numerical control (CNC) turning machine and is based on the locus tracing concept. The algorithm described utilizes a real-time CNC interpolator providing the highest possible accuracy of which the turning machine is capable. The whole machining task can be programmed as a canned cycle, essentially extending the feature generating capabilities of the existing G70/G73 CNC turning fixed cycles.