On-machine Measurement System Research Articles

Development of ultra-precision machining system for small lens mould

An ultra-precision machining system for smaller lens mould was developed. It is composed of an ultra-precision machine, which uses linear guide and linear servo motor for the X and Z tables, On-Machine Measurement (OMM) system and ultra-precision CAM system. It combines diamond turning, grinding and OMM functions in one system, realising highly efficient and ultra-precision machining of lens mould by the compensation function based on OMM results. Experimental results demonstrated that ultra-precision and high-efficiency machining of small lens mould can be achieved using the developed system.

A Web-based on-machine mould matching and measurement system based on CAD/CAM/CAI integration

The purpose of this study is to develop a Web-based on-machine mould identification and measurement system. The Web-based mould identification system matches obtained vision information with CAD database. Developed Web-based system is to exchange messages between a server and a client by making of ActiveX control, and the result of mould identification is shown on Web-browser at remote site. For effective feature classification and extraction, the signature method is used to make meaningful information from obtained image data. For on-machine measurement of the matched mould, inspection database is constructed from CAD database using developed inspection planning methods. The results are simulated and analyzed using developed system to verify the effectiveness of the proposed methods.

On-machine measurement using a noncontact sensor based on a CAD model

Once a machining process is finished, an inspection process is carried out to check whether the part is within dimensional tolerances. A coordinate measuring machine (CMM) is a general metrological device for assessment of dimensions on the shop floor. It cannot be ignored, however, that CMM measurements require significant resources in operating time and cost, which has led to many studies into on-machine measurement (OMM) systems. This study aims to develop an OMM system with a noncontacting laser displacement sensing apparatus and a computer-aided design (CAD) model for ease of operation, improved operating speed, and free form profiling. The system is composed of two software modules, one for sensor alignment with the machine tool and the other for measurement based on CAD/CAM (computer-aided machining). Consequently, the system was verified on the shop floor at a numerical control (NC) machining center.

406 レーザ式非接触加工機上測定システムの開発(OS-12 ELID加工)

Optical components with micro groove structures like diffraction gratings, light guide plates or holographic optical elements require extremery high form accuracy and ultra-fine smooth surface quality of sub-nanometer or sub-angstrom in Ra. To achieve these requirements, ultaprecision on-machine measurement system in very important, by which the profile measurement and evaluation is conducted on the machine, the form accuracy by the compensating machining when the form accuracy in not enough. So, on-machine profile measuring system with non-contact laser type probe has been developed.

313 高精度低測定力機上測定機の開発(OS-10 加工計測・評価)

This paper describes an instrument called nanoshape for measuring surface forms of aspheric optical elements on the processing machine. The effectiveness of the on-machine measurement system is confirmed by the result of compensation processing based on the measurement data. The instrument employs a contact-type scanning stylus. An original inclined self-weight method is designed to control the contact force. In this method, the contact force is generated by inclining the air slider of the instrument, on which the stylus is attached, from the horizontal plane only a little below the stylus. As a result, an extremely steady low contact force (measuring force) can be easily achieved. This method has a peculiar error that occurs by inclining. This error tends to increase as the angle of inclining grows. The evaluated radius variation can be reduced enough by setting the measuring force to tens of milligrams.

Integrated machining error compensation method using OMM data and modified PNN algorithm

This paper presents an integrated machining error compensation method based on polynomial neural network (PNN) approach and inspection database of on-machine-measurement (OMM) system. To improve the accuracy of the OMM system, geometric errors of the CNC machining center and probing errors are compensated. Machining error distributions of a specimen workpiece are measured to obtain error compensation parameters. To efficiently analyze the machining errors, two machining error parameters, W err and D err , are defined. Subsequently, these parameters can be modeled using the PNN approach, which is used to determine machining errors for the considered cutting conditions. Consequently, by using an iterative algorithm, tool path can be corrected to effectively reduce machining errors in the end-milling process. Required programs are developed using Ch language, and modified termination method are applied to reduce computation times. Experiments are carried out to validate the approaches proposed in this paper. The proposed integrated machining error compensation method can be effectively implemented in a real machining situation, producing much fewer errors.

An Ultraprecision On-Machine Measurement System

Ultraprecision optical components require ultra-fine smooth surface quality of sub-nanometer or sub-angstrom in Ra. To satisfy these requirements, ultraprecision on-machine measurement system is very important, by which the profile measurement and evaluation is conducted on the machine. The form accuracy is improved by compensating machining when the form accuracy is not enough. Ultraprecision on-machine measurement systems were developed for measurement with high-accuracy and high-efficiency. It was confirmed that the on-machine measurement with AFM was possible for surface roughness or complex form for local areas. In addition, a laser probe unit with a maximum resolution of 1nm, a measuring range of 10mm, a repeatability of 5.6nm and a maximum measurable angle of 60 degrees was developed. The possibility of the non-contact on-machine form measurement was confirmed for global form accuracy control.

Ultraprecision Fabrication of Large-Scale SiC Spherical Mirror Using ELID Grinding Process

Lightweight mirrors of SiC (Silicon Carbide) are currently used for numerous space telescopes. The most favorable characteristics of the material are high specific stiffness, high thermal conductivity and low thermal expansion (CTE). For large-scale SiC mirrors, however, the machining cost is very high using traditional polishing process. In this study, a large-scale SiC spherical mirror (φ360mm) was designed as reducing-weight structure with many open-back triangular cells. The ELID mirror grinding technique was conducted to finish the mirror. A unique jig composed of many hydrostatic actuators was developed for reducing the deformation resulted from the grinding force. By using an on-machine measurement system, the form error of the finished surface was measured. The surface roughness of the mirror was also examined with a mobile AFM. As result, a high quality mirror surface, which has form accuracy 0.8µm P-V and roughness of Ra 7.8nm, was achieved. This paper presents the experimental procedure and results.

Reduction of machining errors of a three-axis machine tool by on-machine measurement and error compensation system

This paper suggests a method to reduce the machining errors of a three-axis machine tool by implementing an on-machine measurement with a touch probe. Probing errors of a touch probe and positioning errors of a machine tool, inevitably included in the measurement data, are compensated for to obtain the true machining errors for the repeated machining process. Positioning errors of a tool/probe tip are modelled by approximating error components as polynomial functions and considering the effects of backlash errors. To estimate the unknown model parameters, a cube array artifact composed of eight cubes is proposed and calibrated on a CMM. Simulation results and verification experiments showed that the measured and predicted positioning errors agree well within less than 10μm for all axes. The actual cutting test of a simple block and two-dimensional curves showed that the machining errors are reduced to within 10μm after error compensation.

516 円筒面大面積3次元微細形状の機上ナノ計測に関する研究 : センサの開発と評価実験(機械力学・計測制御)

516 円筒面大面積3次元微細形状の機上ナノ計測に関する研究 : センサの開発と評価実験(機械力学・計測制御)

Integrated error compensation method using OMM system for profile milling operation

This paper presents a methodology of machined surface error compensation based on an inspection database by using an on-machine measurement system in profile milling. First, we make compensation for the geometric errors of the machining center by using a closed-loop configuration for the improvement of machining and inspection accuracy. The probing errors are also taken into account. We manufacture a specimen workpiece and then inspect machined surface error distribution. In order to efficiently analyze the surface errors, two characteristic surface error parameters W err and D err are defined. Subsequently, it is possible to fit these parameters by using polynomial functions. These polynomial functions allow us to determine the surface errors in the domain of modeled cutting conditions. Based on these functional relationships between cutting conditions and surface errors, we try to correct the tool path in order to effectively reduce the errors by using an iterative algorithm. An iterative algorithm allows us to integrate changes of the cutting conditions according to the corrected tool path. To compensate for the surface errors, manufacturing tolerances are also taken into account. Experimentation is carried out in order to validate the approaches proposed in this paper.

Probe Radius Compensation of Workpiece Localization

Workpiece localization has direct relations with many manufacturing automation applications. In order to gain accurate workpiece measurement by on-machine measurement system or coordinate measuring machines (CMM), the touch trigger probe is widely adopted. In spite of the high repeatability of the touch trigger probe, there are still error sources associated with the probe. In this paper, we will focus on probe radius compensation. We first show the sources of probe radius error. Then, several compensation methods in related papers are reviewed. After that, a new radius compensation method is proposed in this paper. Simulation and experimental results of probe radius compensation by different methods are given. It is shown that our proposed method has the best performance both in terms of compensation accuracy and computational time. The method is also implemented in a computer aided setup (CAS) system.

On-machine inspection system: accuracy improvement using an artifact

A correction methodology for measurement data is proposed for accuracy improvement of an on-machine measurement system. A volumetric error model to synthesize transient thermal and geometric errors is developed. Geometric errors are determined by an off-line calibration procedure. Under the assumption that the on-machine measuring procedure is a pure cooling process, the transient thermal errors are modeled as exponential functions with different thermal time constants and gains. The thermal time constants characterize transient thermal responses of machine elements during the on-machine measurement. The gains are determined by measuring a 3-D artifact twice when the on-machine measurement of a machined part is required. Total time taken for measuring the artifact is less than 5 minutes. Experiments are performed to verify the proposed method. The measuring accuracy of the on-machine inspection system has been improved from 60 μm to 10 μm.

2811 脆性材料の高精度切削加工のための機上測定システム

This paper presents on-machine measurement system of ultra-precision lathe. The work piece in this study is a brittle material, such as optical glass. To establish a technique of crack free machining of brittle materials, nano metric tool controlling for material is necessary. The on-machine measurement before cutting is very important to decide precise tool feed. From the measurement data, the profile generation data not to propagate crack can be decided. However, the on-machine measurement system was set to the ultra-precision lathe, It was still difficult to connect correctly between the measurement data origin and the cutting data origin. When we use the center point of rotating main axis as datum point, we can connect measurement data and cutting data. Then in this study, we propose new method to detect center of rotation using the flat skew surface and on-machine measurement sensor. Experimental results showed good detecting for center of rotation and its repeatability was 0.01mm. The cutting data was decided from measurement result and profile generation experiment performed. The minute pattern over optical glass without any crack was obtained, and this showed the efficiency of our proposal method.

On-Machine Measurement of Large Mirror Profile by Mixed Method

This paper presents a new differential method called the mixed method, which was developed to measure the profile accurately under the circumstances of on-machine measurement. In comparison with the 2-point method, this method can more remarkably reduce the datum errors due to scanning, vibration and thermal drift. This method also has the advantage of obtaining the high-frequency component of profiles accurately. An optical sensor was designed and constructed to realize both the 2-point method and the mixed method. With a modulation technique, the sensor has been made to have good thermal drift characteristics. It can measure the displacement and angle of two points on a mirror surface simultaneously with a resolution higher than 0.1μm and 1. Using this sensor ; an on-machine measurement system has been constructed, and measurements of the straightness of cylindrical mirrors have been attempted with the 2-point method and the mixed method. Comparing the results, the favorable characteristics of the mixed method have been confirmed.

A differential laser autocollimation probe for on-machine measurement

An optical probe based on the principle of differential laser autocollimation has been developed for the purpose of on-machine measurement of mirror shapes. The probe is so compact that it can be mounted on diamond lathes. It can be rotated by a stepping motor about an axis perpendicular to the optical axis of measurement, and has been used to measure mirror shapes on an apparatus that imitates the conditions of an on-machine measurement system. The probe can reduce remarkably the measurement errors due to vibrational and thermal noises that could not be avoided previously in on-machine measurement. Estimating from repeatability, accuracy is better than 0.1 μm in measurement of a parabolic curve whose depth is >1 mm and length is ≈ 100 mm.

On-Machine Measurement of Large Mirror Profile by Mixed Method.

This paper presents a new differential method called the mixed method, which was developed to measure the profile accurately under the circumstances of on-machine measurement. In comparison with the 2-point method, this method can more remarkably reduce the datum errors due to scanning, vibration and thermal drift. This method also has the advantage of obtaining the high-frequency component of profiles accurately. An optical sensor was designed and constructed to realize both the 2-point method and the mixed method. With a modulation technique, the sensor has been made to have good thermal drift characteristics. It can measure the displacement and angle of two points on a mirror surface simultaneously with a resolution higher than 0.1μm and 1. Using this sensor ; an on-machine measurement system has been constructed, and measurements of the straightness of cylindrical mirrors have been attempted with the 2-point method and the mixed method. Comparing the results, the favorable characteristics of the mixed method have been confirmed.