A modified algorithm for tracking laser Doppler vibrometer (TLDV) is introduced to measure the vibration of rotating objects. The proposed algorithm unlike the old algorithm for TLDV can be used when the speed of the object to be tracked varies continuously or alternating in a small range. The proposed algorithm is to use encoder only as a position sensor. The position from the encoder is used to calculate the driving signals to the galvanometers. To verify the proposed method, experimental modal analysis of the circular plate in stationary and rotating cases are made.
The topology image of an atomic force microscope is obtained by picking up a controlled output of a force-feedback loop that is proportional to the height of a sample under the assumption that no dynamics in a z-axis actuator exist. However, the dynamic effects such as hysteresis and creep in a PZT driving z-axis actuator cannot be ignored. To solve this problem, a strain-gage sensor is used as an additional sensor, which enables measurement of the absolute displacement of a z-axis PZT nano scanner. The advantage of using an additional sensor is experimentally provided and validated in topology images.
In time-of-flight based laser scanners, measurable distance and accuracy are the most important parameters to determine performances. The optical system of the laser scanner should be optimally designed since a high intensity of measured signal increases the measurable distance and accuracy. Therefore, it is important to understand how the optical component layout affects the laser scanner performances. Optical component design for co-axial and bi-axial mechanisms are considered in the paper.
The performance of Atomic Force Microscope depends on the control gains. However, the optimal gains have uncertainties which are impacted by cantilever properties, sample properties and measurement environment. In commercial AFM, it is not easy to get good AFM imaging results since the controller is manually tuned by user. In this paper, auto gain tuning algorithm is suggested for the high performance and automation of AFM. Auto gain tuning algorithm is evaluated by step responses, frequency responses and AFM imaging results.
In the phase-shift based lidar system, a distance between the lidar and an object can be determined via the phase difference between the reference signal and measured signal. The maximum unambiguous range for the phase-shift based lidar is inversely proportional to the modulation frequency of the signal. When the modulation frequency is increased for high distance resolution, the unambiguous range is decreased. In this paper, we described a method to extend the unambiguous range of the lidar, which is a considerable disadvantage of the phase-shift measurement method. In addition, we propose a method for implementing dual frequencies modulation technique with two laser diodes.
To have higher resolution of distance in the laser range finder using the phase demodulation method, signal should be
modulated with a high frequency. In the signal processing of modulation and demodulation, it is inevitable to amplify the
signals. However, it is not easy to amplify the high frequency since the amplifying gain is restricted by the frequency
bandwidth. It is advantageous to demodulate using an intermediate frequency in which high gain amplification as well as
less contaminated signal are obtained. Analytical and experimental results are presented to show how the intermediate
frequency demodulation method works and how good performance are obtained in the time and frequency domains.
Making a map by using global sensor information is a mainstream tool in a mobile robot's navigation. It requires specific vision system such as a CCD camera, range finding system, and many other things. A laser range finder has highly collimated beams that can be obtained easily, thus achieving high lateral resolution, and the short wavelengths involved cause the light to be backscattered, rather than reflected by the target. For signal processing, the phase difference method using frequency modulation/demodulation is addressed in this paper. We used a diffused reflected beam to detect the phase shift in this system. But this beam has a minute signal and can be easily buried in nose. A modulation/demodulation method is used to measure the signals which are buried in noise.
The optical sensor is a measurement sensor that is widely used to measure the 3-D shape profile of object surface as a non-contact type. However, because the operating range of the sensor should be wide to measure the shape of objects that have lots of variation of a slope or bend, the accuracy of height measurement gets weak. If the surface of objects has a lot of variation of slope or bends, the gain of the optical sensor is varied according to the slope. Because height information obtained with the constant gain is incorrect information, it should be compensated without a large error. In order to improve performance measurement for this reason, if the method of scanning the object surface along the x and y directions using a gap control between the optical laser displacement sensor and object surface is applied, the nonlinearity could decrease. Moreover, compared with the method of maintaining the constant height of the sensor, the method of the gap control could reduce the measurement range of the sensor, so that the accuracy of height measurement for the sensor increases. In addition, the accurate information of shape
measurement can be obtained, because the error caused by the slope or bend on the object surface can be reduced. Therefore, 3-D shape profile measurement using the method of constant gap control between the optical laser sensor and object surface shows better performance rather than the method of maintaining the fixed height of the sensor from the bottom.
A high-speed FM demodulation method for measuring mechanical vibration using a homodyne laser interferometer is presented. The Doppler frequency, which represents the surface velocity of a vibrating object, is obtained by using the homodyne laser interferometer, and converted to a voltage signal by using the proposed analogue FM demodulation circuit. The dc offsets of the interference signals obtained from the homodyne laser interferometer are eliminated by using simple subtraction. The new method for compensation of the asymmetry of each interference signal is presented. The laser power variation of the interferometer is normalized by using an auto-gain controller (AGC). The performance of the proposed FM demodulation algorithm is proved by using theoretical methods, and validated by using experimental results. In the experiments, the proposed FM demodulation algorithm is compared with a conventional demodulation method.