Accuracy is the closeness between the observed value and the true value.Eachphysical quantityTo usenumerical valueWhen representing, you must first formulate a standard and select a unit.The formulation of such standards is usually based on people's knowledge and understanding of the physical quantities to be measured, and it is necessary to consider whether the standards are easy to replicate, or whether the measurement process is easy to operate and other practical issues.
The quantity reflecting the closeness of the measurement result to the true value is called precision, which corresponds to the size of the error. Therefore, the size of the error can be used to indicate the accuracy. A small error means high precision, and a large error means low precision.
Accuracy can be divided into: 1) Accuracy indicates the consistency between the measurement result and the true value, which reflects the synthesis of systematic error and random error in the measurement result.Its quantitative characteristics can be expressed by the measurement uncertainty (or limit error);2) Precision refers to the degree to which the measured results are consistent with each other when multiple measurements are made under certain conditions. It reflects the degree of influence of random errors in the measured results;3) Accuracy indicates the degree of systematic error in the measurement result, reflecting the synthesis of all systematic errors in the measurement result under specified conditions.[1]
Accuracy class
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accuracy
Under normal use conditions, the accuracy of the instrument measurement results is called the accuracy of the instrument.The smaller the reference error is, the higher the accuracy of the instrument is. The reference error is related to the range of the instrument. Therefore, when using instruments with the same accuracy, the range is often compressed to reduce the measurement error.In industrial measurement, in order to indicate the quality of the instrument, the accuracy level is usually used to indicate the accuracy of the instrument.The accuracy level is the maximum quotation error minus the positive, negative and percent signs.Accuracy grade is one of the important indicators to measure the quality of instruments.
Accuracy level is usually called accuracy level.[2]
Representation method and characteristics
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Accuracy is often characterized in three ways.
1) The percentage of the maximum error in the true value, such as the measurement error of 3%;
3) ErrorNormal distributionFor example, errors of 0%~10% account for 65%, errors of 10%~20% account for 20%, errors of 20%~30% account for 10%, and errors of more than 30% account for 5%.
Comparing the above three representations, we can see that:
1. The maximum error percentage method is simple and intuitive.Because based onTrue value, not specific.Without knowing the true value, it is impossible to interpret the specific size of the error.
2. The maximum error mode is simple and intuitive, reflecting the specific value of the error, but it is one-sided.
3. The normal distribution of error is scientific, comprehensive and systematic, but the expression is more complex, so it is not as widely used as the first two.[1]
Reasonable configuration accuracy
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Figure 1
The overall accuracy of a mechanical system consists of the accuracy of each link in the system, but the accuracy of different links has different effects on the overall accuracy of the system.In structural design, different precision should be set for different links, and higher precision should be set for sensitive links, so that higher overall working precision can be obtained through more economical methods.[3]
stayMachine tool spindleIn structural design, improving the rotation accuracy of the front end of the spindle is an important design goal.The precision of the front fulcrum bearing and the rear fulcrum bearing of the main shaft will affect the rotation precision of the front end of the main shaft, but the degree of influence is different.It can be seen from Figure 1 that the error of the front fulcrum has a greater impact on the precision of the front end of the spindle.Therefore, in the structural design of the main shaft, bearings with high accuracy are usually set for the front fulcrum.[3]
Practical significance
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In the process of mold design and mold change, sometimes the mold volume block construction fails (especially when the design part shape is more complex or the parting surface is more complex).This is often due to the low quality of the designed part or parting surface, which leads to the system being unable to calculate the correct volume block.In this case, in addition to trying to use other parting methods for mold design, the accuracy of the mold model can also be properly adjusted so that the system can successfully build the mold volume block.This is one of the most common methods to solve parting failure.[4]
There are two forms of model precision, one is relative precision, the other is absolute precision. By default, only the relative precision of the model can be adjusted.Generally speaking, the precision of the model is related to the size of the model, and the default relative precision is usually used.However, adjusting the absolute precision (so that the absolute precision of each model is the same) can improve the matching of models of different sizes and improve the probability of success of some operations.The absolute accuracy shall be adjusted when performing the following operations:
(1) Copy geometry from one model to another, such as merging and cutting among components.
(2) Design and manufacture parts and mold design.
(3) Enter the matching accuracy of the geometry into its target part.[4]
