Research Of Grating Pitch Measuring System Based On Laser Interference Comparator

Grating scale has been widely used in precision measuring instruments. With the increasing demand for accuracy, the grating scale is required to have higher quality. The grating ruling error can directly affect the quality of grating scale’s Moiré fringe signals. As interval error is an important index in evaluating the quality of grating, measuring the grating pitch accurately will be of great importance in improving the quality of grating products.Laser interference comparator is a device which can measure standard line scale of line spacing in 0.1mm and 1mm with highest accuracy. But for the special line scale, such as grating which line spacing is less than 0.02 mm, it cannot measure out the line spacing directly. In order to meet the needs of industry for grating verification, this dissertation designs a high-magnification photoelectric microscope, which can be used in laser interference comparator for measuring the interval of grating scale.The main contents of this dissertation are as follows:(1) Double optical paths signal acquisition system is designed to measure the grating pitch. The line image is converted to electric signal by using photomultiplier tubes.(2) A circuit board is developed to process the signals from the photomultiplier tubes and generate a pulse to indicate the position of the line center.(3) Double-frequency laser interference system is built to measure the grating pitch. A compensating system is built to measure the air refractive index, which is used in improving the precision of interferometer.(4) Experimental platform is built to verify the ability of measuring system.