1. The human element
Because of the errors caused by human elements, including misreading, miscalculation and parallax. Misreading often occurs in measuring tools such as vernier rulers and centimeter cards. The vernier scale is likely to misread a small reading, such as 10.02 mm or 9.98 mm at 10.00 mm. The centimeter card scale is easy to misread the size of a pitch, such as 10.70 mm or 9.70 mm at 10.20 mm. Miscalculations often occur when calculating faults or entering faulty data. Parallax often occurs when the direction of reading the measurement value is different or the scale plane is not in the same plane, and the difference between the two scale planes is about 0.3-0.4 mm, and if the reading scale is not perpendicular to the scale plane, the error amount will occur. In order to eliminate this error, the manufacturer of the measuring tool designs the carving of the vernier to be the same height or close to the same height as the engraving of the ruler, (the vernier is engraved with an arc-shaped composition and the ruler is almost the same height, the vernier is concave V-shaped and the ruler is convex V-shaped, thus constituting two carved equals.)
2. Gage elements
Because the errors caused by the elements of the measuring tool include scale errors, wear errors and unproofed before use. Whether the scale division is accurate or not must be calibrated and traced by more sophisticated instruments. After a period of use, the measuring tool will be worn to a considerable extent, so it must be calibrated or repaired before it can be used again.
3. Strength Factor
Because of the contact force used in the measurement or the deflection error caused by the contact. According to Hooke's law, when measuring the scale, if the measuring shaft is in contact with the machine with a certain measuring force, the shaft and the machine will be partially or fully elastically deformed, in order to prevent this elastic deformation, the shaft and the machine should be made of the same data. Secondly, according to Hertz's law, if both the axle and the machine are made of steel, the amount of error caused by its elastic deformation
When the workpiece is measured with a gauge, the gauge is fixed on the support, and the bracket will be elastically deformed due to the measured force, in order to prevent this error, the pillar can be enlarged and the length of the measuring axis can be shortened as much as possible. In addition, larger gages such as centimeter cards, vernier rulers, straight gauges and long gauge blocks have twists and turns due to their own weight and load. In general, when the fulcrum bearing of the two end faces parallel to the vertical line is 0.577 full length, the two end faces can remain parallel, and this fulcrum is called the Airey Points. The fulcrum of the line scale gauger is 0.5594 in the direction of its full length, and its full-length zigzag error is *small, which is called Bessel Points here
4. Measure the elements
During the measurement, errors caused by poor instrument design or placement, including cosine error, Abbe error, etc. The cosine error occurs when the measurement axis and the surface to be measured are oblique to the viewpoint, which is the actual measurement length. In general, cosine errors occur in both measurement directions and must be treated with special care. For example, when measuring the inner hole, the radial measurement scale needs to be *large scale, and the axial measurement needs to take *small scale. In the same way, when measuring the outside, it is also necessary to pay attention to its correct orientation. The anvil and the appearance of the workpiece to be measured must be carefully selected, such as the surface of the workpiece to be measured is flat, the spherical anvil should be selected, and the workpiece is cylindrical or spherical. Abbe' Law states that the axis of the measuring instrument and the axis of the workpiece to be measured should be on the same line. Otherwise, an error occurs, and this error is called Abbe's error. In general, if the axis of the measuring instrument and the axis of the workpiece to be measured cannot be together, the interval should be shortened as much as possible to reduce the error value. If the vernier ruler measures the workpiece as an example, the error is, so if you want to reduce the measurement error of the vernier ruler, you need to reduce the angle formed by the gap between the ruler and the vernier ruler and measure as close to the scale mark as possible. If the workpiece is measured by the gauge as an example, the probe of the gauge is spherical, the workpiece is cylindrical, and the two axes have an offset amount, and the amount of contact error is . If the probe and workpiece of the gauge are both flat, if the two planes are inclined to the viewpoint, the error is called a sinusoidal error. In order to reduce wear, the end of the follower is often designed as a ball or cylinder with a radius of , and the pressure angle between the two is , which causes an error of .
5. Environmental elements
When measuring, depending on the environment or place, the errors that may be constituted include thermal deformation error and random error are the most significant. Thermal deformation errors generally occur due to room temperature, human contact and the temperature of the workpiece after processing, so it must be controlled by temperature and humidity, and the workpiece and measuring tools cannot be touched by hand, and the workpiece is measured after cooling. However, in order to shorten the processing time, it is necessary to measure in real time during processing, so it is necessary to consider the thermal expansion coefficient of various data as compensation, so as to cope with the error caused by the different thermal expansion coefficients of temperature data. In general, the following formula must be applied: CMR: The length of the workpiece at 20°C.
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