CNC Controller Research Articles

Influences of Closed Loop Control Componentson the Performance of Ultra-Precision Machines

At Fraunhofer IPT a test bench has been setup to analyze closed loop control components and their interfaces with focus on their application in ultra-precision machining applications. This paper will present the results of the analysis of feedback and servo drive systems and will give a close inside on the influences of linear scales and analog and digital servo drives for applications in ultra-precision machining. The performed measurements include the analysis of the position accuracy and repeatability (step response test) as well as the determination of the dynamic frequency characteristics (stiffness / compliance) of an air bearing axis. With respect to the aforementioned measurements the tests have been performed under the variation of linear scales (vendor, pitch, signal, sampling frequency, etc.) and servo drives (vendor, switching or linear amplifiers, PWM frequency, control architecture, DC bus voltage, etc.). The paper will give a summary on the results of the analyzed topics, carefully chosen regarding their relevance to ultra-precision machining. Finally, a short outlook to future research work concerning the analysis of CNC controls will be given.

Study of an efficient real-time monitoring and control system for BUE and cutter breakage for CNC machine tools

If machining abnormalities, such as build-up-edge and cutter breakage, occur during machining, serious damage on the workpiece surface and deterioration of production efficiency will happen, and cause additional energy consumption for rework and increase the manufacturing cost. To minimize the effects, an on-line diagnosis method with use of Fast Fourier Transform and algorithm of shorttime signal variation analysis was developed to analyze the vibration signals to quickly detect the two abnormalities in this study. In addition, the real-time machining information from CNC controller was extracted through a bi-lateral communication module to prevent misdiagnosis. The control commands were automatically generated by the proposed system and directly sent to the CNC controller to stop the machine for cutter replacement. Without complex computation, the system can detect the occurrence of BUE or cutter breakage within 1 second and complete machine control within 3 seconds. The system can instantly transmit and save the real machining information and diagnosis/control results to the remote central monitoring platform for further process improvement. With use of TCP/IP communication protocol the central monitoring platform can remote log into the on-site monitoring computer to directly operate the diagnosis/control system. Experimental results showed the feasibility and effectiveness of the proposed system.

Detection and Compensation of Positioning Accuracy Based on the Laser Interferometer

The positioning accuracy of CNC machine tool is the best moving position accuracy which the machine tool can reach under the control of CNC control system. The principles of frequency laser interferometer measurement are described in this paper, and pitch error is compensated by taking DAHE V1500 CNC machine with FANUC system as example. The result shows that the precision of CNC machine tool is effectively improved.

Research on a Long Travel Nanopositioning Air Bearing Stage with the Linear Motors

The objective of this research is to develop a PC-based closed-loop nanopositioning system using the dual-frame two-axis drive single mobile independent framework. The stage body was supported by an air bearing on a granite base to reduce the frictional force. The developed stage was driven by the PC-Based interface of ANCA 5DX CNC controller, for the precision motion control of the linear motors. The laser scales were used as the feedback sensors so that the closed loop control of the developed system was possible. Based on the test results, the designed closed loop nanopositioning system was capable of precision positioning within the travel of 100 mm along X-axis and Y-axis. The Z-direction stage stability of the developed system was 20 nm, the maximum yaw error of the stage moving along X-axis was about 3.77 arc-seconds, and the maximum pitch error of the stage moving along Y-axis was about 1.04 arc-seconds, based on the test results. By utilizing the PC-Based interface of ANCA 5DX CNC controller based closed-loop PID control system, the positioning capability of X-axis and Y-axis was about 20 nm. Performing the circular test with radius of 20 mm, the deviation of circular positioning test was about 223 nm. Based on the tracing speed test results, the standard deviation along X-axis and Y-axis was 5 nm under tracing speed of 0.05 mm/min.

Ballbar dynamic tests for rotary axes of five-axis CNC machine tools

This paper proposes a new ball bar test method for the inspection of dynamic errors of rotary axes in five-axis CNC machine tools. The test circle is defined in a workpiece coordinate system and the ball bar test is performed by simultaneously driving of linear–rotary axis couple. The effects of the center position and the radius on the setting values, rotational range and measurement sensitivity of the rotary axis were investigated. The proposed ball bar test is performed in two steps: the circular positioning and the circular tracking with a continuous feed. Axial dynamic errors are obtained by subtracting the measured tracking errors from the positioning errors. A ball bar test system (BBTS) was developed to plan the tool path and the tool orientation, to communicate with the five-axis CNC controller and to process the measured data. Error patterns were simulated regarding the gain mismatch, backlash and tracking direction to help a fast diagnosis of the error sources. Simulations and experimental results prove the effectiveness of the new test method.

Wireless CNC Motion Controller Designed with PSoC

Numerical control (NC) technology is a kind of technology combined with electronics, machinery manufacturing, and other interdisciplinary combination of technologies. It is an important part of modern manufacturing. Currently, NC technology is developing towards the open CNC system with extensibility and interchangeability, while the modern electronic technology is developing towards the programmable technology and SoC (System-on-Chip) technology. However, current CNC controller designed with SoC is still in the research stage and not practical yet. In this paper, a practical CNC motion controller is built with modern PSoC (Programmable System-on-Chip) with wireless Ethernet interface. This controller has a high-performance microprocessor, numbers of free configurable analog and digital devices and IO (input/output) interfaces, and many kinds of communication interfaces. Therefore, it has good real-time control functions and communication functions. Experiments for controlling a three joint-axis engraving machine show that the controller can achieve high performance of parallel control of the three joint-axis linear interpolation and two joint-axis circular interpolation, and high performance of the trapezoidal and S-shape speed control. In addition, in order to reduce the impact to the motor and increase the system efficiency, a kind of look-ahead algorithm for velocity control with low time cost is used.

Performance Evaluation of Machine Tool Probe for In-process Inspection of 2D and 3D Geometries

Abstract Dimensional measurement of work piece in between the manufacturing process is an essential method to achieve the precision components. The machine tool probing system can measure machined features of work piece placed on the machine table after partial or final machining operation. The in-process machine tool probing system is helpful in minimising the lead time of component by eliminating the unloading time on the machine and loading and inspection time on the measuring instrument. It also improve the part quality through process control. In this research, the component inspection is performed by optical machine tool probe when position into the spindle of CNC milling machine. The relative movement between the probe and job are programmed by developing a CNC part program. The probe touches the machined surface as per the program codes and the optical machine interface (Transceiver) receives signal data through infrared optical waves and these signals transformed into the CNC controller through wired network. The CNC controller displays the data points on the screen. These data points were transferred into CAD system for generating lines, curves and thereafter surfaces and these generated surfaces were analysed against CAD model of the designed component for dimensional evaluation. The results obtained by this machine tool probe for 2D features are validated through digital height gauge and 3D features are by coordinate measuring machine (CMM). It was found that the optical probing system can be employed during in-process inspection and can be replaced measurement by costly CMMs for inspection of 3D features of low precision components.

Advanced programming of machine tools: interests of an open CNC controller within a STEP-NC environment

NC programming still bases upon a heterogeneous and divided CAD/CAM/CNC data chain. Its performances are consequently limited. Tool paths online optimisation is hardly possible. In parallel, emerging new processes like incremental sheet forming or laser additive manufacturing widens the application area of CNC machines. Integrating these processes within intelligent design and manufacturing environments is a great scientific challenge. Meeting these requirements necessitates the use of STEP-NC programming approach (ISO 14649), which benefits from a large support from international industrials and academics. A major interest of STEP-NC is to transfer a large part of the decisions concerning the process implementation to the CNC controller. This paper introduces the advanced CNC programming platform developed at the IRCCyN laboratory, STEP-NC Platform for Advanced and Intelligent Manufacturing (SPAIM). An extension of SPAIM for machines equipped with open CNC controller is proposed as well. These research works are carried out within the FP7 European Project Fofdation.

A STEP-NC approach for multi-process manufacturing, simulation and optimisation

With STEP-NC object oriented programming standard, the next generation of CNC machine tools promises to be more open, intelligent and interoperable. As this ISO standard totally integrates CNC controllers into the CAD/CAM/CNC numerical chain, it provides an opportunity to stand as a common data model for various manufacturing processes. This paper first proposes a multi-process manufacturing approach by using STEP-NC as the optimal data model for process planning, process specificities and inter-processes simulations. Then, experimental validations are ensured by the advanced CNC platform for multi-process manufacturing developed in the laboratory. Finally, the realisation of a part on the platform by using the multi-process manufacturing concept shows the efficiency of the proposed approach.

Real-time Thermal Error Compensation Module for Intelligent Ultra Precision Turning Machine (iUPTM)

Accuracy & precision are 1he main requirements for ultra precision machine tools. Many factors affect 1he performance of 1he system 1hat in turns affect 1he product quality. Among all sources of errors, the thermo mechanical deformation errors are the main contributor for 1he overall geometrical errors. This paper mainly aims at establislunent of methodology to compensate thermal deformation errors in real-time for ultra precision machine tools. The real-time thermal error compensation module has been developed and integrated to intelligent Ultra Precision Turning machine. The module includes temperatures as inputs, neural network algorithm for computing the thermal deformations errors, ‘C’ programming for real-time calculations and integration with open architecture CNC controller. The module runs in silent mode which avoids human intervention for correction of thermal deformation errors.

Development of a Virtual Milling Machining Center Simulation System with Switchable Modular Components

The application of traditional three-axis milling machine center is very popular and the related application technology is also much matured resulting in mechanical components to be machined with good quality. Machine tool has therefore become an inevitable facility in precision manufacturing. Furthermore, the pursuit of higher precision machining has thus demanding five-axis machine tool to be adopted owing to its flexibility and capability in machining more precise mechanical components in shorter time. However, one of the key factors for the popularity in smooth introduction of five-axis machine tool would be based on a very user friendly learning and teaching environment. This is partly because two more rotational axes in a five-axis machine tool could generate very complex toolpath movement that is out of the imagination of a general operator. Furthermore, the price of an industrial five-axis machine tool is not normally affordable by an educational institute; to the worse, the maintenance cost is also very high. There is very high risk for a novice to collide during the learning process and this will generally cause big worry of a teacher. This paper aims for the development of a virtual machining center simulation system with switchable modular components to ease the learning process in getting acquainted with a five-axis machine tool. A five-axis machine tool consists generally of two modules: (1) CNC controller and Operation panel, and (2) machine tool hardware. The developed system will provide the novice with four CNC controller with operation human machine interface (HMI), and three typical types of five-axis machine tool, Head-Head (HH), Head-Table (HT), and Table-Table (TT), are also supported. The developed modularized and switchable machining center simulation system has been successfully developed and is very helpful to both learner and teacher

An Adaptive Parameter Tuning Method with On-Machine Weight Identification Function for CNC Machine Tools

Different inertia effect causes different control errors. To have an optimal control performance, the control parameters of a CNC machine tool should be adaptively tuned based on the variation of the weight of the workpiece in machining process. In this study, simulation based on a theoretical model was made to investigate the influence of inertial effect and friction force on the servo accuracy of a CNC machine tool’s. By using empirical method, an adaptive tuning system that can auto-tune the CNC control parameters based on the detected weight of workpiece was developed. An on-machine weight identification system that can on-machine identify the weight of the workpiece was developed. After integrating the two systems, a control parameter tuning system which can be implanted into CNC controller was developed with the macro executor. Experimental results have shown that the system can effectively improve the accuracy of a machine tool through adaptively tuning control parameters based on the current weight of the machined.

Tracking error reduction in CNC machining by reshaping the kinematic trajectory

In this paper, a method of reducing the tracking error in CNC machining is proposed. The structured neural network is used to approximate the discontinuous friction in CNC machining, which has jump points and uncertainties. With the estimated nonlinear friction function, the reshaped trajectory can be computed from the desired one by solving a second order ODE such that when the reshaped trajectory is fed into the CNC controller, the output is the desired trajectory and the tracking error is eliminated in certain sense. The proposed reshape method is also shown to be robust with respect to certain parameters of the dynamic system.

Study on Open CNC System Platform Architecture and its Application

On the market today, the hardware and most software of CNC system are not exclusive and incompatible, and the system institutions vary, which makes the control systems of different manufacture relatively independent, closed to each other. In order to break this situation, this paper conducted a project design on the hardware and software of CNC system which is based on PC platform. On the hardware, ultimately determine the NC embedded PC architecture, design and motion control card based on PCI bus; in the aspect of software design, use Windows2000/XP operating system to achieve multitasking real-time CNC control, and design the software in the Visual C++ environment .Using the platform to achieve the application of the laser welding system, the design is proved to be feasible, it also reflects the basic idea of the open architecture.

Time-optimal interpolation for CNC machining along curved tool pathes with confined chord error

In this paper, two new interpolation algorithms for CNC machining along curved tool pathes are proposed: a time-optimal interpolation algorithm under chord error, feedrate, and tangential acceleration bounds, and a greedy interpolation algorithm under the chord error and tangential jerk bounds. The key idea is to reduce the chord error bound to a centripetal acceleration bound which leads to a velocity limit curve, called the chord error velocity limit curve. Then, the velocity planning is to find the proper velocity curve governed by the acceleration or jerk bounds “under” the chord error velocity limit curve. For two types of simple tool pathes, explicit formulas for the velocity curve are given and the methods are implemented in commercial CNC controllers.

High Accuracy Articulated Robots with CNC Control Systems

A robotic arm manipulator is often an appealing method to position drills, bolt inserters, automated fiber placement heads, or other end effectors. In a standard robot the flexibility of the cantilevered arm as well as backlash in the drive system lead to large positioning errors. Previous work has greatly reduced this error through the use of secondary scales and a mathematical model of the robot deflection running on a CNC controller. Further research improved upon this model by accounting for linear deformation of each robot link regardless of position. The parameters describing these deformations are determined through a calibration routine and then used in real time to guide the end effector accurately to any reachable pose. In practice this method has been used to achieve total on-part positioning accuracy of better than +/- 0.25mm.

Simulation Study on Feed Rate Optimization Technique Based on Generalized Predictive Control

Optimization is an important way to improve the machining quality, efficiency, security and safety. In traditional way, feed rate is specified off-line in CAM system by process planner, which leads to the low machining efficiency. In the paper feed rate optimization technique based on generalized predictive control is researched. The open architecture is adopted to develop an adaptive controller, where the feed rate can be real-time adjusted in CNC system according to the measured cutting force. An open CNC controller with the function of feed rate optimization is implemented, which consists of a series of software modules. Simulation experiment has been finished to prove the proposed method.

초정밀 데스크탑 마이크로 NC 선반 개발 및 성능평가

This study introduces a recently designed desktop-sized NC turning system and its components. This machine is designed for the ultra-precise turning of parts with a diameter of 0.5-20 mm with minimum space usage for the machine. This study aims to achieve submicron-level accuracy of movements and good rigidity of the machine for precision machining using the desktop-sized machine. The components such as the main machine structure, air bearing servo spindle, and XZ stage with needle roller guides are designed, and the designed machine is built with a PC-based CNC controller. Its static and dynamic stiffness performances and positioning resolutions are tested. Through machining tests with single-crystal diamond tools, a form error less than <TEX>$0.8{\mu}m$</TEX> and surface roughness (Ra) of <TEX>$0.03{\mu}m$</TEX> for workpieces are obtained.

Pattern recognition based surface roughness prediction in turning hybrid metal matrix composite using random forest algorithm

PurposeThe purpose of this paper is surface roughness prediction using pattern recognition for the aluminium hybrid metal matrix composite (HMMC).Design/methodology/approachHybrid composites were manufactured using liquid metallurgy technique. The cast HMMC was machined using an industrial CNC turning centre and the machining vibration signals were acquired using an accelerometer. The acquired signals were processed and used to build a machine learning model for predicting surface finish based on the tool signature.FindingsThe authors established a technique for predicting and monitoring the surface quality during machining using a low cost accelerometer. It is capable of being integrated with the machine controller for online warning of deviations in surface roughness. The system is reconfigurable for any machining condition with a very short training period. The use of this model facilitates online surface roughness monitoring, avoiding the need for costly measuring equipment.Originality/valueThe model developed is innovative and not reported widely to the best of the authors' knowledge. The use of accelerometer‐based surface roughness prediction and control is an innovative approach for automation of machining process monitoring. These can be integrated into any existing machining centre as a standalone system or can be integrated into the CNC controller like Fanuc or Siemens.

Toward a Real Time Control of Toolpath in Milling Processes

Real-time control of manufacturing processes is a challenging issue for nowadays industry. The need for ever more efficient production requires new strategies in order to make correct decisions in an acceptable time. In a large number of cases, operators working on a CNC machine tool have a reduced number of possibilities for interacting in real-time with the machine. Numerical simulation based control is in that sense an appealing alternative to the conventional approach since it provides the operator with an additional source of information, confirming his choices or in reverse suggesting a more adapted strategy. The main goal of this work is to propose a method to move from a bilateral approach (operator and CNC controller) to a trilateral one where the simulation is an active component of the manufacturing process. This paper focuses on a simple issue sometimes encountered in milling processes: how to remove a constant thickness of material at the surface of a part whose exact geometry is unknown The difficulty lies in the choice of an appropriate trajectory for the tool. So far the method which is employed consists in acquiring the geometry of the part thanks to a palpation step made prior to milling. However, this step has to be repeated for each part and can become rather fastidious as the size of the part increases. The approach presented here gets rid of the palpation step and makes use of online measurements for identifying the real geometry and correcting the trajectory of the tool in accordance. By monitoring the forces applying on the tool (directly on the NC), we have access to the milling depth and therefore to the geometry of the part at several locations along the trajectory of the tool. This information is used as an input data for our numerical model running on an external device, which finally derives an approximation for the geometry. An optimized trajectory is then obtained and is updated on the machine. This procedure is repeated as the tool moves forward and it allows for a fast and robust on-line correction of the toolpath.