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Precision engineering and practice

1. INRODUCTION
There are three terms often used in precision methods, and they are often used incorrectly or in a vague manner. The term has a precision, repeatability and resolution. Because the present discussion on processing and production methods, the definition is in terms of machine tools. However, these terms have applicability to metrology, instrumentation and experimental treatments as well.
1.1 Accuracy
It is the ability of the car to go to A position he hasn't commanded the posetilbefore before. This means the machine has calculated the new position from the point of view of the parameters of the STI system feedback, or lack thereof, and then move on to the post. This does not mean machine "Showing" or "taught" ithe position feedback stored parameters, as in robotic applications frequently. Precision brings the whole machine, equipment and controls, to carry on his task and is therefore demanding specifications posted on the machine.
In the field of measurements, the number of never known accuracy Measured is therefore essential. Here točnost′the the ability to specify a value for the unknown parameter of quantifiable. This is in addition to the measures of accuracy in the machine where nahodâtsâthe "unknown" is the true state of the cutting tool, for example, which was calculated and gdethe phenomena (machine output) should be known and understood with a certain level of confidence. In instrumentation, permission to exit (number of digits after the decimal point is shown), is often thought of incorrectly as the accuracy of the device. Accuracy is best in quantity compared to the fundamental standards and careful calibration.
1.2 Repeatability
It is the ability of machines to visit places and other consequences of the direction of the otthe movement has produced. If the point is approached from the same direction, the term repeatability is used. If the point is approached from two directions, such as the regular table milling machine, the term is bidirectional repeatability. Good bi-directional repeatability is more difficult to achieve because it hysteresis repeatability mechanical movements, other factors, such as the dead band feedback.
When measuring devices, the frequency of occurrence of over might be tougher than the tools.TheIzmerâemoj values with the year it always depends on the tool, and it can modify an unrecognized option, especially over time, which can have a significant impact on the frequency of occurrence. This does not mean that do not affect the metrological tools and machines in a similar way. Above the figure, distribution of time points is related to the frequency of occurrence of errors and events associated with the tool.
1.3 the Permission
This movement is the smallest increment of machine is capable of doing. Because the machines use discrete digital controllers and motors with feedback, for example, gauge, or slit Interferometer fringes, resolution is the number of all the movements that has made. Permission, if p, then all multiples of p movements there. This does not mean that permission is the least of any component of the system, and is the largest Nothe.AMašina, which can calculate movement controller 0.1 micrometres cannot reliably move machines year increase 0.1 micrometers, if encoder feedback with reliably has only one micrometer.TheSistema control will never "see" política a small movement. So you have to be very careful in interpreting the meaning of performance cars.
Above I mentioned, allowing the least number of output year instrument. As digital devices mainly, it is very easy to show with many insignificant digits, and you must be very careful when interpreting date política. If the temperature recorder, for example, displays a one-hundredth degree, there's no guarantee that it reports the right temperature! One April Reportedly know the temperature with high resolution, but it could be soveršennothe wrong temperature! Producers and users of equipment often use the term "accuracy" to describe the resolution could lead to a false conclusion about precision instruments
1.4. the accuracy and precision
Accuracy in science, engineering, industry and statistics, is the extent to which the measured/estimated number of current (true) STI. The precision (repeatability or reproducibility is also called) is the degree to which further measurements or calculations show the same or similar results.
The results of calculations or measurement precision CAN BE-but not precise, precise but not accurate, neither, or both; If the result is both accurate and reliable, it is valid.