L) µm. Here, L is the effective range (in mm) and 0a±εErrora2εError07-55Error = reference value indicated by the laser length measuring machine – Corresponding value indicated by the linear scaleAs shown in Figure 1, the accuracy of a linear scale is determined by comparing the positional value indicated by the linear scale with the reference value from a laser length measuring machine at regular intervals using the accuracy inspection system. The inspection environment temperature is 20 °C, so the accuracy is at this temperature. The inspections are performed with other inspection conditions and standard values that comply with Mitutoyo's internal standards.The accuracy (error) at each measured point is determined according to the following formula.Here, the words "accuracy" and "error" have the same meaning.We refer to the plot on a graph of the error at each measured point in the effective range as an accuracy chart.Based on this accuracy chart, the accuracy of the linear scale is noted as the range between the maximum error and minimum error. There are the following two notation methods.(1) Note the size of the range between the maximum error and minimum error as 'a'. The value 'a' shown in Figure 2-1 indicates the accuracy. This standard value is indicated using the conversion formula (each model. For example, for a linear scale with an accuracy standard value of (3 + 3L/1000) µm and an effective range L of 1000 mm, 'a' is 6 µm.(2) Note the size of the range between the maximum error and minimum error as '±a/2'. The center value between the maximum error and minimum error is 0, the maximum value is noted as '+a/2', the minimum value is noted as '-a/2', and the size of the error range is noted as '±a/2'. This notation is mainly applied to ST scales.In notations (1) and (2), 'a' in (1) and '±a/2' in (2) are the same accuracy standard value. Linear scales use a straight-line scale that has fixed-pitch graduations as the reference to detect the amount of movement and the amount of change in position. By detecting graduations, a linear scale obtains 2-phase sinusoidal signals that have the same pitch as the graduations. The linear scale is designed so that it can perform readings with greater detail than the straight-line scale by interpolating this sine wave signal with an electronic circuit. Interpolation means that these 2-phase sinusoidal signals are interpolated, and the result is divided into pulse signals corresponding to the resolution. For example, if the graduation pitch is 20 µm, readings can be performed with a resolution of 1 µm. Here, error within the graduation pitch range will occur according to the accuracy of this interpolation processing. This is called interpolation accuracy. The accuracy standard value of a linear scale includes the aforementioned errors inspected at fixed intervals and interpolation accuracy. + and are coefficients that are set on Laser length measuring machine counterInterferometerLaser sourceOptical axis of laser beamAccuracy chart (error plot)Effective rangeEffective rangePCCube cornerFixtureX: Measurement positionX: Measurement positionDigital counterScale unitMovable tableAccuracy: a (µm)Accuracy: ±a/2 (µm)[Figure 1] Linear scale accuracy inspection device, overview[Figure 2-1] Accuracy notation method (1)[Figure 2-1] Accuracy notation method (2)Explanation of termsTechnical InformationLinear scale accuracy1) Linear scale indication accuracy
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