Angle measurement of practical skills of video measuring instrument

How to improve the accuracy of angle measurement has always been a difficult difficulty for two-dimensional measurement instruments to overcome
.

There are basically two methods for angle measurement on the popular two-dimensional measuring instruments on the market, one is the tangent method, and the other is the point calculation method
.

The tangent method refers to the method of manually rotating the engraved lines on the screen or in the lens, aligning the two edges of the workpiece respectively, and measuring the angle by counting the encoder or the circular grating
.

This method is further divided into two types: projection tangent method, such as projector, tool microscope, etc.
, and image tangent method, such as imager, tool microscope with video function, relying on the meter line rotation measurement that comes with the software
.

The tangent method is convenient and simple to operate, but the measurement precision is low, and it is suitable for rapid batch inspection.
If the angle precision reading of the measured piece is high, another method, the point calculation method, is more suitable
.

All geometric elements are composed of points, including the basic elements straight lines, curves and arcs
.

A two-dimensional plane angle consists of two straight lines, the basic geometric element, and a straight line consists of an infinite number of points
.

Therefore, whether the angle measurement is accurate or not, the point is the most critical
.

 　　Angle measurement technique 1: The straight line acquisition is as long as possible
.

 　　Image measuring instrument, due to limited screen display and large magnification (generally 0.
7 to 4.
5, 28X to 180X), the size of the workpiece displayed on the screen is actually only a few millimeters, and many surveyors are used to testing only on the screen Point and line elements are collected on the display part
.

If the collected points are deviated, the shorter the line segment is, the greater the deviation of the measured angle value will be, and the longer the line segment, the smaller the deviation of the measured angle value will be
.

As shown in Figure 1, the theoretical angle is 30 degrees, and the point deviation is 0.
25mm, we can clearly see the influence of the length of the line segment on the measured value
.

 　　Therefore, when we measure the angle, try to collect the lines on both sides of the angle as long as possible.
If the display range of the screen is too small, you can move the worktable and pick a point near the starting point of the line where the angle is located, and then pick a point at the end point.
The angle measurement error will be greatly reduced
.

 　　Angle measurement technique 2: The deviation of the regression line is small
.

 　　Many inspectors have responded that the repeatability is very poor when measuring the angle.
The same person uses the same method, and the repeatability of the two measurements reaches as much as 0.
5 degrees
.

 　　In many image measurement software, including three-coordinate measurement software, the default line acquisition is two points
.

For some relatively regular parts with good linearity, it will not cause too much error, but for parts with poor linearity and more burrs, the method of two-point collection of straight lines will bring a lot of errors.
And the repeatability is very poor, and the repeatability of multiple measurements will definitely not be good for the angle formed by such a straight line
.

 　　If we use the method of finding the regression line from multiple points to determine the two sides of the angle, the straight line will be closer to the actual edge of the workpiece to be measured, and the straight line deviation will be reduced.

.

 　　Angle measurement technique 3: The magnification is as large as possible
.

 　　For many mechanical parts, the edge of the measured angle is very short, only 2mm to 3mm, for example, the chamfering of shaft parts
.

If we also use the minimum lens gear of 0.
7 or 1 to take point measurement, the image of the workpiece is only 48mm to 120mm, and the point deviation will have a great impact on the measurement value
.

If we switch to a magnification of 3 or 4, the workpiece imaging can reach 240mm to 480mm, the real situation of the image edge is easier to observe, and the deviation of the sampling point will be reduced
.

However, this method also brings a lot of inconvenience, the graphics are too large, and the display window can only display a small part, but for skilled inspection personnel and quality control who pursue high precision, these should not be a problem
.

 　　The image measuring instrument is the instrument with the most functions and applicable scope among the two-dimensional measuring instruments, and its basic functions are limited: the collection of points, lines, circles, and arcs
.

However, the functions of its combined calculation are quite extensive.
As long as you use your brain and use it well, many measurement problems can be solved well
.