The value of the linear scale

Grating ruler, also known as raster ruler displacement sensor (grating ruler sensor).

Grating ruler is often used in closed-loop servo system of nc machine tools, can be used for detection of linear displacement or angular displacement. The measurement of the output signal of digital pulse, with wide detection range, high precision, fast response characteristics. In the numerical control machine tool, for example, often used for cutting tool and workpiece coordinate, to observe and track feeding error, to play the role of a motion error compensation of cutting tool.

Grating ruler is made up of rod grating and the grating reading of the first two parts.

General scale grating fixed on the machine fixed parts, grating reading head installed on the machine moving parts, indicating grating in a grating reading head.

Raster detection device is a key part of the grating reading head, it consists of light source, convergent lens, grating, optoelectronic components and the adjusting mechanism, etc. Grating structure of reading head form a lot, according to the reading head structure characteristic and using occasion are divided into direct receive type reading head (or silicon photocell reading head, image reading, reading head, metal grating spectroscope type reflection type reading head).

The working principle of

When indicating grating lines and scale of the lines on the grating lines formed between a small Angle theta, and two relative of parallel grating ruler facets, in under the irradiation of light source, is located in a nearly vertical grid lines, the formation of light and dark stripes.

Has the following characteristics

(1) the change of moire fringe patterns

Two pieces of grating relative move through a lattice spacing, moire fringe moving over a stripe distance. By light diffraction and the interference effect, the changing rule of the moire fringe approximation (more than) string function, change cycles and the relative displacement of the grating lattice spacing for synchronization

(2) the amplification effect

In the case of two raster grid line Angle smaller, moire fringe width W and raster grid, the grid line omega has the following relationship between Angle of theta. Type, theta unit for rad, W unit is mm. Because the Angle is small, the sine theta is small, then W = / omega if theta omega = 0.01 mm, theta = 0.01 rad, is the type available W = 1, the grating magnified 100 times.

(3) the homogenizing error function

Moire fringe is formed by several grating stripe share, 100 lines per mm grating, for example, 10 mm width of moire fringe has 1000 lines, and such lattice spacing between adjacent error is averageness, eliminated due to uneven blade spacing error caused by, fracture, etc