Key Engineering Materials Vols. 295-296

Abstract: As aspheric surfaces are more often used in optical systems, suitable error evaluation methods and suitable accuracy calibration methods for related test instruments are urgently required. The two unsolved but important issues are addressed. For evaluation of aspheric surfaces, a scheme is proposed to separate the surface errors into radius error and local error. The effects of the two errors on image quality are discussed. For test instrument calibration, a practical method using a defocused spherical surface is described and verified with an absolute testing instrument based on laser deflectometry, which was developed at Beijing Institute of Technology. The feasibility of the schemes is shown and experimental results are presented.

Abstract: A new method for order tracking filtering of rotating machinery based on instantaneous frequency estimation and zero-phase distortion digital filtering is proposed. Compared with the traditional methods for order tracking filtering, the new method has a number of attractive features such as tacholess, no hardware-based tracking filter and no frequency shift to the original sampling data. The theorems and algorithms of the method are discussed. Filtering of overlapped data blocks, used to restrain the edge effect, which is caused by digital filtering, is introduced. An actual test example of run-up and coast down vibration of a motor is presented to demonstrate the validity of the method.

Abstract: Machining precision deficiency and installing error are very common problems for many sensors, which may result in unstable amplitude i the signal detected by the probe and further cause measurement errors of the sensors. The concept of using electronic technology to offset machinery precision deficiency is utilized. A new method of electronic rectifying is proposed. The automatic gain control (AGC) technology used in the field of wireless communication is applied for sensor signal processing. An AGC circuit consisting of a multiplier and divider AD534 is designed. A new smart time grating displacement sensor currently under development by us is used to provide experimental results for comparison with and without the AGC technology.