Measuring Screw Thread Parameter with Universal Microscopy Nguyễn Khánh Hiệp-group 3-20100290 Hanoi University of Science and Technology Abstract In the industrial production, as an important transmission part, the screw thread is applied extensively in many automation equipments. In this paper, as a new kind of real-time and non-contact measurement method, a screw thread parameter measurement system based on image processing method is developed to accurately measure the outside diameter, inside diameter, pitch diameter, pitch, thread height and other parameters of screw thread. The experimental results show that the measurement uncertainty of screw thread average diameter can reach 1 μm. I. Introduction Thread pieces as a connecting are commonly used in manufacturing and aerospace industries, particularly in the case of some aircraft systems, many components are connected to a thread. With the development of modern technology, requires high reliability and interchangeability to thread, and the accurate detection of thread parameters for improving interchangeability and thread reliability is of great significance. Universal Microscopy is one of the most important measurement instruments for dimensional parameters measurement. It is very universal instrument with wide equipment for two axis contact-less measurement in horizontal plane. This instrument is suitable for measurement of distances, diameters, angles, threads, radii and evaluation of its geometrical parameters. Big advantage of this kind of optomechanical instruments is its long lifetime in the case of right handling. II. Main approach 1. Terminology: Screw thread is a helical ridge produced by forming a continuous helical groove of the uniform section on the external or internal surface of a cylinder or cone. A screw thread formed on a cylinder is known as straight or parallel. Screw thread, while the one formed on a cone or frustum of a cone is known as tapered screw thread. In the present experiment, parameters of a straight 1 screw thread of small magnitude are measured. Parameters of small screws such as screws used in watches, electrical plugs, and toys cannot be measured by instruments like vernier calipers or micrometers. Unless they are magnified it is not possible to measure all the parameters.Some parameters of a straight screw thread are defined as follows: Crest of a thread is defined as the prominent part of thread. Root of a thread is defined as the bottom of the groove between two flanks of thread. Flanks of thread are straight edges which connect the crest with the root. Angle of the thread also known as included angle is the angle between the flanks of the thread measured in axial plane. The pitch of a thread is the distance measured parallel to the axis of the thread, between corresponding points on adjacent thread forms in the same axial plane and on the same side of axis. Major diameter is the diameter of an imaginary cylinder Co-axial with the screw which just touches the crests of an external thread or roots of an internal thread. Minor Diameter is the diameter of an imaginary cylinder co-axial with the screw which just touches the roots of an external thread or the crest of an internal thread. 2. Learning objectives: - To understand the working of optical profile projector. - To measure the parameters of gear threaded component. 3. Experiment program: Fig 1.Universal Microscopy in C8-209 Hanoi University of Science & Technology a. Determination of the major diameter To measure pitch of the thread, align the intersection of two diagonal lines at the point on the flank which is between of crest and root. At this 2 position take the x value of micrometer . Next move the intersection of two diagonal lines along the x axis that the next point is set in the line which have the same direction with old flank. Again note- down the reading of the x value. Difference of the two readings gives the pitch of the thread. In order to get more exactly value of pitch, we repeat all step with another point, and take the average value of two times. b. Determination of Pitch To measure pitch of the thread, align the intersection of two diagonal lines at the point on the flank which is between of crest and root. At this position take the y value of micrometer . Next move the intersection of two diagonal lines across 3 (or 5) crests along the y axis that the next point is set in the line which have the same direction with old flank. Again note-down the reading of the y value. Difference of the two readings gives the pitch of the thread. In order to get more exactly value of pitch, we repeat all step with another point, and take the average value of two times. 3 c. Determination of the angle To measure the included angle of the thread coincide one of the lines of the cross lines with the flank of the thread as below figure. Note-down the reading of the protractor. Now rotate the protractor in turn the cross lines in such a way that same line coincides with the opposite flank as shown in below. Note-down the reading of the protractor. Difference of the two reading gives the included angle of the thread. III.Experiment results Experimental data and calculated result of the survey 1. Measure the average diameter Times 1 2 3 4 A 7.175 0.099 0.098 7.178 B 7.186 0.099 0.096 7.190 C 7.177 0.078 0.086 7.162 D 7.185 0.096 0.094 7.170 Times 1 2 3 4 ( ) ( ) 2 2 A B D C x x x x d − + − = 7.07 8 7.095 7.088 7.083 Average diameter: 2 1 2 7.078 7.095 7.088 7.083 7.086 4 n i i d d n = + + + = = = ∑ 2. The average measured step Times Y E Y F Y I Y K 1 0.672 3.169 0.040 2.543 2 0.091 2.581 0.019 2.518 3 5.630 8.131 6.281 8.752 4 1.908 4.382 2.545 5.032 Times ( ) ( ) ( ) 2 2 . F E K I y y P m y y m − + − = = 1 1.250 4 2 1.247 3 1.243 4 1.240 Average Step: 1 1.250 1.247 1.243 1.240 1.245 4 n i i P P n = + + + = = = ∑ 3. Half-page thread angle 60 2 2 2 19”tr ph α α α = = °∆ − 1 0 30 4 ” 2 1tr α α α °= − = 0 2 29 3 ” 2 8ph α α α °= − = α 1 = 329°19” α 0 =0°(360°) α 2 = 29°38” Conclusion As a new kind of real-time and non- contact measuring system, the screw thread parameter measurement system based on image method is developed for accurately measuring inside diameter, outside diameter, pitch diameter, pitch, and thread height of screw thread. The system has some advantages, such as easy and quick operation, high measuring accuracy and fast speed of error analysis. The two-dimensional coordinate data obtained by scanning the axis section of thread teeth shaped contours can reflect the geometrical shape error of screw thread completely. Experiment result shows that measuring resolution is 0.5 μm, with error’s percentage is about 0.4%. Reference [1]. Wu Jingchun, Li chunmei, Feng Hutian. Non-contact measurement system design of ball screw thread surface parameters. Modular machine tool and automation processing technology, (11), 52-54(2011). [2]. Yuan Pengbin, Yuan Zongming, OuYang Zhiying. Non-contact easurement of thread parameters based on machine vision systems. Pipeline technology and equipment, (4), 21-22(2008). 5 . pitch, thread height and other parameters of screw thread. The experimental results show that the measurement uncertainty of screw thread average diameter can reach 1 μm. I. Introduction Thread. as straight or parallel. Screw thread, while the one formed on a cone or frustum of a cone is known as tapered screw thread. In the present experiment, parameters of a straight 1 screw thread of small. straight screw thread are defined as follows: Crest of a thread is defined as the prominent part of thread. Root of a thread is defined as the bottom of the groove between two flanks of thread. Flanks