How to choose the encoder accuracy and resolution！

How to choose the encoder accuracy and resolution

Abstract: "Accuracy" is used to describe the accuracy of the physical quantity, which reflects the error between the measured value and the true value, while the "resolution" is used to describe the scale division, the reaction is the numerical reading process The smallest change that can be read. Simple metaphor: a common range of 10 cm scale, the top 100 scales, the smallest energy ...
     "Accuracy" is used to describe the accuracy of the physical quantity, which reflects the error between the measured value and the real value, and "resolution" is used to describe the division of the scale, the reaction is the numerical reading process can The minimum change value read. Simple metaphor: a common range of 10 cm scale, above the 100 scale, the smallest can read 1 mm RMS. Then we say that this ruler resolution is 1 mm, he can only 1, 2, 3, 4 ... ... 100 such readings; and its actual accuracy is unknown, because the ruler read out 2 mm, we do not know the absolute value of the error between him and the real 2 mm. And when we bake it with fire, and stretch it for a while, and then look at it. We can easily find that it has 100 scale, so its "resolution" or 1 mm, the same as the original! However, its accuracy has clearly changed.
      For the encoder, the "resolution" in addition to the number of lines and the number of grooves, but also because of the impact of electrical signals change, it is adjustable, controllable, it can be with the signal of the sub-change , The higher the subdivision, the smaller the resolution, but the higher the subdivision, the greater the introduction of increased error. The accuracy, more biased in favor of mechanical, a product produced, his accuracy has been fixed (some high-precision products can compensate for signal to improve accuracy, etc.), this value is detected, it and the Products, workmanship, materials and other comprehensive performance is closely related to our difficult to come to a specific numerical calculation as the basis for precision, most of them can only be used in the process of judging the accuracy of good or bad.
      For example, for 13bit, the number of absolute positions on its code disc is 8192, then: The calculated resolution is 158 arcseconds. That is, when reading a value, the jitter between values ​​is 158 arcseconds , If the first value to be read is 0, then the second read value is greater than 158, to less than 158, we need to select a smaller resolution. When the value of 158 to read this time, due to the existence of errors, and can not get an absolute 158 seconds, the encoder read out 158 ​​seconds and absolutely true 158 seconds between the error, it depends on the accuracy of the. Therefore, the accuracy is based on the resolution to talk about.
      Rather than the smaller the resolution is better, because the subdivision will introduce errors and expand the error, excessive subdivision will not guarantee accuracy! How many times the need for sub-segments, can do many times the breakdown of the premise must be based on the accuracy of the guarantee, because the accuracy of the invisible before the use of high-power subdivision is irresponsible. The higher the code quality, the better the score line, the better the signal quality signal, the smaller the error after subdivision, which is affected by the performance of an encoder, which is why under the same parameters, There are different brands, different price coder one reason.
      For example, we want to read the value of 1, 2, 4, 7, 8, I at least select a unit of resolution, select 2 units of resolution is clearly not work, because we read the 1 value , Then 2 is not read out, in the choice of a unit of resolution on the basis of our read out of a real absolute error of 1 is the precision. CNC machine tools for the straight grating is a resolution of the set, you need to read the value of the interval is less than the resolution, the machine may be jitter or error and so on.
      For an absolute incremental encoder, it is possible to keep the absolute position value of the serial transmission synchronized with the incremental value. The absolute value corresponds exactly to an incremental signal, and the position value must lie within the sinusoidal period of an incremental signal . Such as absolute 13-bit, with a 512-line incremental signal, the absolute position interval of 158 seconds, to read the location of the two discs in the middle of a position is not appropriate, but we can bring their 1Vpp The number of sub-sub-100 times, then the equivalent of two absolute position between the introduction of a number of subdivision after the position, we can absolute position value, based on the calculation by subdivision after the increase Read the position between two absolute positions, such as: 512-line subdivision of 100 times, the absolute position 1 value is 0, the absolute position 2 value is 158, then read the position between the two positions You can position 1: the value of 0 on the basis of a pulse is 25, the two are 25x2 = 50 ... ... However, the absolute encoder with incremental signal itself is not subdivided, which requires users The incremental signal can be subdivided on its own.

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