The working principle of linear scale！

Moire fringes
In the case of a transmission grating, a small angle θ is formed between the lines on the grating and the lines on the ruler grating, and when the two grating facets are placed in parallel, the light source is located in an almost vertical Grating, the formation of light and dark stripes. This stripe is called "moiré fringe" (pictured right). Strictly speaking, the direction of the moire fringes is perpendicular to the bisector of the angle between the two grating lines. Moore fringes in the two lines or two obscure lines between the distance known as the width of the moire fringes, expressed in W.
 Moire fringe W = ω / 2 * sin (θ / 2) = ω / θ. [1] Moire fringes have the following characteristics:
(1) Moore fringe changes in the law
The two gratings are relatively moved over a pitch, and the moire fringes over a striped distance encoder. Due to the diffraction and interference of light, the variation of moire fringes is similar to the positive (residual) string function, and the number of change periods is synchronized with the number of gratings relative to the grating.
(2) magnification
In the case where the angle between the two grating lines is small, the moire fringe width W and the grating pitch ω and the gate angle θ have the following relationship. In the formula, the unit of θ is rad and the unit of W is mm. As the inclination is small, sinθ is small
W = ω / θ
If ω = 0.01mm, θ = 0.01rad, then the above formula can be W = 1, that is, the grating amplification of 100 times.

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