As a typical comprehensive error measurement method, the double-ball-bar (DBB) has been invented and used widely for evaluating and diagnosing the accuracy of NC machine tools. However, due to the expansion length of DBB’s bar is very limited, the working efficiency of the DBB is greatly reduced and different length bars are mostly used to realize different measurement ranges. In this paper, a novel DBB with two spatial linkages and one spherical joint was presented to implement a wide detection range and simplify the operation. The structure of the proposed device was firstly introduced. The working principle of the device was then described, and the mathematical model for detecting machine’s accuracy was also built. According to the angle of spatial linkages and lengths of two bars, circular motions trajectory which is caused by interpolation movement of two shafts can be calculated and compared with theoretical value to evaluate machine tool’s accuracy. Finally, the simulation was done to validate the feasibility of the proposed device. The results show that the proposed DBB has reasonable structures. Moreover, the measuring range can cover a large region of space and it is continuous.
The articulated arm coordinate measuring machine (AACMM) is a new type of non-orthogonal coordinate measuring machine (CMM). Unlike the traditional orthogonal CMM which has three linear guides the AACMM is composed of a series of linkages connected by rotating joints. Firstly, the coordinate systems of the AACMM are established according to D-H method, the homogeneous transformation matrixes from the probe to the base of the AACMM are derived. And the graphic simulation system of the AACMM is built in Matlab, which verify the magnitude and direction of the joint angles qualitatively. Then, the data acquisition software of the AACMM is compiled by Visual C++, and there is a statistical analysis on the calculated measuring coordinates and actual coordinates, which indicates that the kinematic model of the AACMM is correct. The kinematic model provides a basis for measurement, calibration and error compensation of the AACMM.
A novel cylindrical capacitive sensor (CCS) with differential, symmetrical and integrated structure was proposed to measure multi-degree-of-freedom rotation errors of high precision spindle simultaneously and to reduce impacts of multiple sensors installation errors on the measurement accuracy. The nonlinear relationship between the output capacitance of CCS and the radial gap was derived using the capacitance formula and was quantitatively analyzed. It was found through analysis that the thickness of curved electrode plates led to the existence of fringe effect. The influence of the fringe effect on the output capacitance was investigated through FEM simulation. It was found through analysis and simulation that the CCS could be optimized to improve the measurement accuracy.
This paper describes a novel cylindrical capacitive sensor (CCS) to measure the spindle five degree-of-freedom (DOF) motion errors. The operating principle and mathematical models of the CCS are presented. Using Ansoft Maxwell software to calculate the different capacitances in different configurations, structural parameters of end face electrode are then investigated. Radial, axial and tilt motions are also simulated by making comparisons with the given displacements and the simulation values respectively. It could be found that the proposed CCS has a high accuracy for measuring radial motion error when the average eccentricity is about 15 μm. Besides, the maximum relative error of axial displacement is 1.3% when the axial motion is within [0.7, 1.3] mm, and the maximum relative error of the tilt displacement is 1.6% as rotor tilts around a single axis within [-0.6, 0.6]<sup>°</sup>. Finally, the feasibility of the CCS for measuring five DOF motion errors is verified through simulation and analysis.
Proc. SPIE. 9446, Ninth International Symposium on Precision Engineering Measurement and Instrumentation
KEYWORDS: Clocks, Sensors, Computing systems, Field programmable gate arrays, Data acquisition, Telecommunications, Signal processing, Virtual colonoscopy, Voltage controlled current source, Diffraction gratings
A novel cylindrical capacitive sensor (CCS) with differential, symmetrical and integrated structure was proposed to measure multi-degree-of-freedom rotation errors of high precision spindle simultaneously and to reduce impacts of multiple-sensors installation errors on the measurement accuracy. The nonlinear relationship between the output capacitance of CCS and the radial gap was derived using the capacitance formula and was quantitatively analyzed. It was found through analysis that the thickness of curved electrode plates led to the existence of fringe effect. The influence of the fringe effect on the output capacitance was investigated through FEM simulation. It was found through analysis and simulation that the CCS could be optimized to improve the measurement accuracy.
Now the basic structures of capacitive sensors always use cylindrical fixed electrodes and the measurement for different diameter hole requires different specifications of sensor probe. For the shortfall of the measurement method for hole profile with capacitive sensor, this paper introduces the principle of capacitive sensor for micro/mini hole measurement and the capacitance-based device used in different diameter micro/mini holes’ profile measurement through the structural improvements of the capacitive sensor probe, then simulation and error analysis are conducted. The simulation results indicate the error is less than 5%, and it verifies the feasibility of the profile measurement principle for different diameter hole with capacitance sensor.
Laser scanning is widely applied to reverse engineering. Nonetheless, the involvement of scanning equipment and laser probe, as well as the measurement environment itself renders the process more vulnerable to noise which will cause failures in boundary detection, data segmentation and reconstruction of smooth curves and surfaces, thus putting forward the demand for noise reduction. Among the methods used in noise reduction of laser scanning data, the angular method is particularly suitable for scan line data. However, this method as well entails threshold that largely relies on the experience of engineers, which may introduce unwanted uncertainty. In this paper, an algorithm based on self-estimated angular threshold for reducing noise of laser scanning data is proposed. Firstly, the factors affecting angular threshold are analyzed and a mathematical model for SAT is established. Then the concrete algorithm that consists of judgment of impulse noise, modification of the coordinates and average filtering is described. Finally, a simulation test and an experimental case are employed to evaluate the performance of the algorithm on noise reduction of laser scanning data.
This paper presents a novel piezodriven X-Y stage utilizing flexure hinges. Levers of high amplifying rate were adopted
to magnify the output displacement of the piezoelectric actuator and a complex parallel four-bar mechanism was used to
guide the mobile platform. In order to describe the static and dynamic behaviour of the stage, an analytical model was
built and a series of formulae were deduced. Based on mathematical analysis, the configuration of the stage was
optimized. Then Finite Element Analysis was applied to analyze travel ranges, natural frequencies and stress distribution.
The simulation computation results demonstrate that the stage could reach a motion range of 200mby 200m and has a
first order natural frequency of 265 Hertz, which is of good concordance with the theoretical estimate. Now a prototype
is being fabricated.
Utilizing DCT based enhancement approach, an improved small defect detection algorithm for real-time leather surface inspection was developed. A two-stage decomposition procedure was proposed to extract an odd-odd frequency matrix after a digital image has been transformed to DCT domain. Then, the reverse cumulative sum algorithm was proposed to detect the transition points of the gentle curves plotted from the odd-odd frequency matrix. The best radius of the cutting sector was computed in terms of the transition points and the high-pass filtering operation was implemented. The filtered image was then inversed and transformed back to the spatial domain. Finally, the restored image was segmented by an entropy method and some defect features are calculated. Experimental results show the proposed small defect detection method can reach the small defect detection rate by 94%.