Key Engineering Materials Vols. 295-296

Abstract: This paper describes a scanning multi-probe measurement system for local alignment of linac components. The system consists of two probe-units, each having three displacement probes. The two probe-units, which are placed on the two sides of the cylindrical linac components, are moved by a scanning stage with a scanning range of 5 m to simultaneously scan the two opposed straightness profiles of the linac cylinders. A differential output calculated from the probe outputs in each probe-unit cancels the influence of error motions of the scanning stage, and a double ntegration of the differential output gives the straightness profile. The difference between the unknown zero-values of the probes in each probe-unit of zero-difference, which introduces a parabolic error term in the profile evaluation result, is calculated and compensated for by a zero-adjustment method so that accurate straightness profiles of the linac cylinders can be obtained. The effectiveness of the measuring system is confirmed by experimental results.

Abstract: This paper describes a multi-probe method for measuring the straightness error of a leadscrew-driven stage. Two displacement probes are employed to scan a flat artifact mounted on the stage. The surface profile error of the flat artifact is separated from the straightness error of the stage in a differential output of the probes. The straightness error can thus be obtained accurately from an integration operation of the differential output without the influence of the surface profile error. An improved technique of data processing is adopted for measurement of straightness error components with periodicity shorter than the probe spacing. The influence of the angular error of the stage is compensated for by using the result measured by an autocollimator. Experiments of straightness measurement of a leadscrew-driven stage with a lead of 1 mm were carried out by using two flat artifacts with different degrees of precision. The successful detection of the short-periodicity component of the straightness error with a periodicity equal to the lead indicated the feasibility of the multi-probe method.

Abstract: In industry, disk type products with a highly accurate surface such as silicon wafer and hard disk, are important elements. To measure these surfaces, an interferometer is used. However, this method generally needs a highly accurate reference surface. Another method to obtain the disk surface profile is by a scanning displacement sensor. However, the output of this sensor is influenced by the parasitic motions of the scanning along the reference guide. This article presents novel measurement procedures, a reversal method, an improved reversal method and a multi-prove method, to measure the circular profile on a disk without any references but with high accuracy.

Abstract: In ultra high precision roundness measurement, a high accuracy and high integrated measuring circuit system equipped with inductive sensor are a developing trend. In order to meet the demand, a novel method to improve the accuracy of measuring circuit of amplitude modulation sensor using digital synthesizing, digital phase sensitivity detection (PSD), and digital set average techniques, is presented. The measuring circuit system based on the method is easy to realize and to operate. It can be plugged directly into an ISA Bus slot for use. Experimental results show that the stability of the sensor measuring system that consists of the measuring circuit system and a Taylor inductive sensor reaches nanometer accuracy. The digital measuring circuit of amplitude modulation can not only be applied widely in amplitude modulation measuring circuit for use of inductive sensors to improve the accuracy of the sensor measuring circuit system but also used in the one for use of capacitance sensors and magnetic grating sensors.

Abstract: Hough Transform (HT) is an image edge detection technique which is widely used in pattern recognition and computer vision. In this paper the fundamental principle of HT is analyzed and the defect of HT and Randomized Hough Transform (RHT) is indicated. An algorithm based on RHT and the information of grayscale and gradient in image is proposed. It uses the property of the pattern and is mainly used for detection of circle and arc contour measurement. This algorithm can decrease memory usage in computer by a multi to one mapping, accelerate the calculation speed by parallel algorithm, improve the edge detection accuracy by subpixel division, obtain the parameters of object by applying least square fitting algorithm. Based on the principle, a measurement system with high accuracy and efficiency in image capturing and processing is developed. Experiments are carried out in the system. The result of experiment has certified the feasibility and validity of the algorithm.

Abstract: Combining the non-diffracting beam datum-line method with the roundness measuring technology, a high precision coaxiality measurement method for a hole whose diameter is more than 40mm is proposed. The principle of the measuring system is introduced and error analysis and test to verify it are presented. The measuring uncertainty of this coaxiality system is less than 1µm when the measuring range is within 1.5m. The measuring uncertainty of error of roundness is less than 0.4µm when the error measuring range is -200~+200µm. This system has many advantages and it can be applied widely for coaxiality measurement.

Abstract: DBB was originally manufactured and proposed for checking the accuracy of NC machine tools. The device can also be used to study the relations between motion error of trace and the machine motion error for the purpose of error compensation. The nominal angle obtained through rotation feed rate and sampling time was adopted instead of actual angle which cannot be measured by the device. This project examined in details the effect of the angle deviation problem caused by non-perpendicularity between the movements in axis X and axis Y. The analysis and calculation verified that a squareness deviation would lead to more than 3 times error at some special points, decreasing the accuracy of NC machines for error compensation. For this reason, a device called as Two-Dimensional Ball Bar is proposed based on the DBB.

Abstract: For flexible 3D positioning of a complex 3D mechanism, it is needed to measure 3D displacement of the end-effecter of the mechanism in high precision and by non-contact method. It was common to use plural sensors or scales together to measure the 3D displacement. However, it is difficult to calibrate the sensitivities of the plural sensors or scales. A novel 3D displacement measurement is proposed using an optical system in which lens focuses are collected at the center of the sphere, which has been used for the radius measurement of the sphere. Instead of facing in the XY direction that has high sensitivity, new ideas are necessary for the measurement in the Z direction of the optics where focuses are collected at the center of the sphere. The displacement in the XY direction and the one in the Z direction can be measured at the same time by using a ring-shaped laser beam instead of a simple ray.

Abstract: Ultrasonic distance measurement in air is broadly used for industrial and commercial low cost applications with medium or small resolution. Configurations for the applications are usually restricted to passive reflection and A-B measurement. This paper gives a survey of the ultrasonic distance measurement method with high resolution based on pulse compression. Improvements resulting from this method include good noise suppression, possibility to operate several systems in parallel without disturbing influence of cross talk, and high measurement rate. Modified configurations and the available high resolution lead to new applications which are summarized.

Abstract: A multi-fiber reflection displacement micrometer is developed. The device consists of a light source and a receiving fiber-array of identical fibers and photo detectors that detect the light reflected from the surface being measured. The differential output of each neighboring fiber pair is proportional to the surface displacement in a section of the total range. The light intensity variation of the source and the reflectance change of the surface are compensated when the differential output is divided by the summation output. A scale voltage is given to each output of neighboring fibers in order to shift each output to correspond to the actual displacement within the total range, which can be varied by selecting the number of fibers in the receiving fiber array. The micrometer offers the advantages of wide range, non-contact, no electrical interference, simplicity, and low cost. It can be used in medical experiments and laboratory instruments.