In order to achieve rapid measurement of larger travel translation stages’ roll-angle error in industry and to study the roll characteristics, this paper designs a small roll-angle measurement system based on laser heterodyne interferometry technology, test and researched on the roll characteristics of ball screw linear translation stage to fill the blank of the market. The results show that: during the operation of the ball screw linear translation stage, the workbench’s roll angle changes complexly, its value is not only changing with different positions, but also shows different levels of volatility, what’s more, the volatility varies with the workbench’s work speed . Because of the non uniform stiffness of ball screw, at the end of each movement, the elastic potential energy being stored from the working process should release slowly, and the workbench will cost a certain time to roll fluctuate before it achieves a stable tumbling again.
A roll-angle measurement interferometer with good stability and high sensitivity is presented. In the system, two sets of spatial parallel beams with different frequencies are formed with the help of a Koster prism, a corner cube, a quarter-wave plate, a wedge prism, and a wedge mirror. The wedge prism is used for the roll-angle sensing component, the roll of which will cause the changes of the optical path of the two beams with different frequencies. This interferometer complies with the principle of common path which minimizes the dead path; the cross talk of straightness, pitch, and yaw errors are avoided in this specific structure which enhances the stability and precision of the measurement. The experimental result fits well with the theoretical analysis and a measurement resolution of 2 μrad is achieved with an electronic interpolation of 2π/512.
Due to the coherence of laser light source it could produce coherent noise in parallel confocal microscopy based on Digital Micromirror Device (DMD) and thus affect the resolution. LED light source instead of the laser light source can give full play because of its incoherence characterization. In this paper, free-form surface lens is used for LED secondary optics design. According to the LED characteristics and the law of refraction, we have established differential equations of free-form surface. We solved equations with the method of Runge-Kutta by Matlab and the model was built in Tracepro for optical simulation. The results show that the uniformity on the DMD is better than 90% and the lighting efficiency is higher than before. The measured data show us a much more uniform illumination on DMD and LED uniform illumination system successfully avoided the gray error which was caused by the uneven illumination. The LED driver circuit using DC power supply provides us a more stable light source. The axial optical tomography is more accurate and the reconstruction of three-dimensional image is more clearer.
A roll angle interferometer with high sensitivity is designed in this paper. Two sets of centrosymmetric beams are used to travel through the measurement and reference arms of the roll angle interferometer which contains two specific optical devices: wedge prism assembly and wedge mirror assembly. The optical path change in both arms caused by roll is converted into phase shift which can be measured by interferometer. Because of the adoption of the centrosymmetric measurement structure, the straightness errors, yaw error and pitch error can be avoided and the dead path is minimized, so that the stability and the accuracy of the measurement can be greatly enhanced. The resolution for the roll measurement is about 0.006″ with the measurement range of ±1°.
Confocal microscope has been a powerful tool for three-dimensional profile analysis. Single mode confocal microscope
is limited by scanning speed. This paper presents a 3D profilometer prototype of parallel confocal microscope based on
DMD (Digital Micromirror Device). In this system the DMD takes the place of Nipkow Disk which is a classical parallel
scanning scheme to realize parallel lateral scanning technique. Operated with certain pattern, the DMD generates a
virtual pinholes array which separates the light into multi-beams. The key parameters that affect the measurement
(pinhole size and the lateral scanning distance) can be configured conveniently by different patterns sent to DMD chip.
To avoid disturbance between two virtual pinholes working at the same time, a scanning strategy is adopted. Depth
response curve both axial and abaxial were extract. Measurement experiments have been carried out on silicon structured
sample, and axial resolution of 55nm is achieved.
A new design is made for Differential Plane Mirror Interferometer, which has simpler construction, but broader
applications for nano-measurement. Due to its symmetrical optical configurations, the high measurement accuracy of
geometrical parameters can be achieved with sub-nanometer. With this special arrangement and the use of some
additional optical components, several specification measurements have become easily to implement and have higher
exactness, such as for linear displacement, small rotation, straightness, perpendicularity, parallelism and etc. In addition,
because of its simpler optical configuration with few optical components, it is easier for manufacturing and thus
decreases the cost. This will make it possible to create new measurement instruments and broaden the market for laser
interferometer. The stability and resolution of both Michelson interferometer and our new type of Differential Plane
Mirror Interferometer were tested. The experiment results proved its outstanding capabilities.
Recent development of research on the nonlinearity of the heterodyne interferometers provides an approach to eliminate
the nonlinearity of heterodyne interferometer using a simple phase compensation system by rotating a polarizer which is
set up before the detector in the interferometer. This paper shows the experiment results which proved its general
validity for elimination of the nonlinearity errors whether it is a first-order or a higher-order error. It explains which
accuracy can be expected and provides the application opportunities based on theoretical analyses and experiment results.