Study Of The Indexing Positioning Control System Of The Varied Line Space Measuring Gratings

Gratings is a kind of optical component which is composed of cable,joints and shafts according to certain laws in the distributions on the surface and have a wide range of applications in the national economy,national defense and science and technology research.With the development and progress of optics and optoelectronic and computor application technology,the varied-line-space(VLS) gratings which has structure of variable cycle or space and grating width has been successfully paid more and more attentions.They have many advantages such as the focal property and the aberration correcting ability and measurement of absolute displacement.At the same time, fabrication technology of the traditional grating including the grating ruling engines has also been a challenge.Based on the analysis of VLS gratings structure principle and the long carved grating ruling engines used to fabricating traditional measurement gratings and the principle of indexing and positioning,achieving for fabricating an absolute displacement measurement of gratings,a closed-loop optoelectonic positioning control system is proposed and designed to achieve varied displacement in the long carved grating ruling engines.The control system has core of STC89C51 microcontroller and drive system composed of stepper motor and worm to drive the screw and drag the table to index to produce pitch shift.Grating displacement sensor is used to measure and feedback the displacement of the range of 1000mm length motion on the table,and then correct displacement error through the servor motor.Meanwhile,the microcontroller real-time controls the carved structure of long carved grating engines to achieve a well-coordinated action between indexing and grooving in the machine.In the design,we use electronic sub-processing for the output pulse signal of the grating displacement sensor and make its resolution up to 0.25um. This paper has done a comprehensive analysis for the error of the control system,and then fabricates a series of VLS groove whose minimum scale lattice-value is 0.25um through the experiment on the glass of 300mm length scale to verify the feasibility of the control system.