Báo cáo thí nghiệm về screw thread

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 meas

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

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

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

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

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

C 7.177 0.078 0.086 7.162

D 7.185 0.096 0.094 7.170

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

.

P m

m

=

=

2 1.247

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

α = −α α = °

0 2 29 3 ”

α =α α− = ° α1 = 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)