"Accuracy" describes the correctness of a physical quantity, reflecting the error between the measured value and the true value. "Resolution," on the other hand, describes the scale divisions, reflecting the smallest change that can be read during numerical reading. A simple analogy: A common ruler with a range of 10 centimeters has 100 divisions, and the smallest effective value it can read is 1 millimeter. We say this ruler has a resolution of 1 millimeter; it can only read values 1, 2, 3, 4...100. Its actual accuracy is unknown, because we don't know the error between a 2 millimeter reading and the true absolute 2 millimeters. However, if we heat it with fire and stretch it, then examine it again, we can easily see that it still has 100 divisions, so its "resolution" remains 1 millimeter—the same as before! However, its accuracy has clearly changed.
For encoders , "resolution" is related to the number of lines and is also affected by electrical signals. It is adjustable and controllable, changing with the subdivision of the signal. The higher the subdivision factor, the lower the resolution, but the higher the subdivision factor, the greater the introduced error. Accuracy, on the other hand, is more mechanically related. Once a product is manufactured, its accuracy is basically fixed (although some high-precision products can improve accuracy through signal compensation). This value is determined through testing and is closely related to the product's workmanship, materials, and other comprehensive performance characteristics. It's difficult to calculate a specific value as a basis for accuracy; it can mostly only be judged during use.
For example, for a 13-bit encoder, the absolute position count on the code disk is 8192. Therefore, the calculated resolution is 158 arcseconds. This means that when reading values, the jump between values must be 158 arcseconds. If the first value to be read is 0, the second value must be greater than 158; if it's less than 158, a smaller resolution is needed. When reading the value 158, due to errors, an absolute 158 seconds cannot be obtained. The error between the 158 seconds read by the encoder and the absolute true 158 seconds depends on the precision. Therefore, precision is discussed based on resolution.
It's not true that the finer the subdivision, the better. Subdivision introduces and amplifies errors, and excessive subdivision will compromise accuracy! The required and achievable subdivision level must be determined within the bounds of maintaining accuracy. High subdivision is irresponsible because accuracy is not visible before use. Higher code disk quality, better engraving, and better signal quality result in smaller errors after subdivision. This is influenced by the overall performance of the encoder, which explains why encoders with the same parameters can be from different brands and at different price points.
For example, if we want to read values 1, 2, 4, 7, and 8, we must choose a resolution of at least one unit. Choosing a resolution of two units is obviously not possible, because if we read the value 1, we cannot read 2. The error between the 1 we read and the true absolute value of 1, based on a resolution of one unit, is the precision. CNC systems on machine tools have resolution settings for linear encoders. If the interval between the values to be read is less than the resolution, the machine tool may vibrate or malfunction.
For absolute encoders with incremental signals, the absolute position value and incremental value transmitted serially are precisely synchronized. The absolute value corresponds exactly to one incremental signal, and the position value is always within the sine cycle of one incremental signal. For example, a 13-bit absolute encoder with 512 incremental lines and an absolute position interval of 158 seconds is not suitable for reading the position between two code disk positions. However, we can subdivide the 1Vpp incremental signal, such as by a factor of 100. This is equivalent to introducing several subdivided positions between the two absolute positions. We can read the position value between the two absolute positions by calculating the number of incremental pulses after subdivision. For example, with 512 lines subdivided by 100, the absolute position 1 value is 0, and the absolute position 2 value is 158. Then, the position between these two positions can be read by adding one pulse to the value of 0 in position 1, which is 25. For two positions, it is 25 x 2 = 50, and so on. However, absolute encoders with incremental signals do not have subdivision capabilities, which requires users to perform subdivision processing on the incremental signal themselves.
