Dingguo Xiao

Kinematic constraint analysis in a twin-robot system for curved-surface nondestructive testing

Purpose – Nondestructive testing based on cooperative twin-robot technology is a significant issue for curved-surface inspection. To achieve this purpose, this paper aims to present a kinematic constraint relation method relative to two cooperative robots. Design/methodology/approach – The transformation relation of the twin-robot base frame can be determined by driving the two robots for a series of handclasp operations on three points that are noncollinear in space. The transformation relation is used to solve the cooperative motion problem of the twin-robot system. Cooperative motions are divided into coupled and combined synchronous motions on the basis of the testing tasks. The position and orientation constraints for the two motion modes are also explored. Findings – Representative experiments between two industrial robots are conducted to validate the theoretical developments in kinematic constraint analysis. Artificial defects are clearly visible in the C-scan results, thereby verifying the validi...

Magnetic field analysis and optimal design of magnetic bearing

Magnetic field distribution of a radial magnetic bearing with sixteen-pole was analyzed by using finite element method. It was verified by magnetic field measurement. Magnetic bearing structure was optimized based on finite element analysis (FEA) and magnetic circuit method. Optimization was done in object of maximum magnetic force. Two optimizations had similar results. Analysis showed that FEA-based optimization is more accurate and efficient, which had been performed with FEA software-ANSYS 10.0.

Ultrasonic Adaptive Detection for Aerospace Components with Varying Thickness

Automatic inspection of microdefects located in the aerospace components is difficult due to the imprecise scanning trajectory, especially for those specimens with varying thickness. In this paper, a new ultrasonic nondestructive testing (NDT) system using the robotic scanning trajectory is constructed for inspecting turbine blades. Additionally, an approach based on the analysis of ultrasonic signals is proposed to calibrate the trajectory; the ultrasonic image based on the threshold function represents the distribution of inner defects when the following gate is used to track the flaw echo. Therefore, the characteristic parameters of the flaw echo signals are easy to be discriminated if the reflection waves are stable in the time domain. Experimental result verified the effective and feasibility of the proposed approach; the distribution of inner defects can be shown with a higher resolution than other NDT methods when robotic orientation is correct at each point of scanning trajectory. Furthermore, the feature signals can be tracked more accurately during the ultrasonic signal processing if the ultrasonic distance was considered as a calibration coefficient of positional matrix. The proposed ultrasonic adaptive detection is adapted to complex geometric structure with a minimum resolution of equivalent diameter of the inner flaw being 0.15 millimeters.

Measurement methods of ultrasonic transducer sensitivity

Sensitivity is an important parameter to describe the electro-acoustic energy conversion efficiency of ultrasonic transducer. In this paper, the definition of sensitivity and reciprocity of ultrasonic transducer is studied. The frequency response function of a transducer is the spectrum of its sensitivity, which reflects the response sensitivity of the transducer for input signals at different frequencies. Four common methods which are used to measure the disc-vibrator transducer sensitivity are discussed in current investigation. The reciprocity method and the pulse-echo method are based on the reciprocity of the transducer. In the laser vibrometer method measurement, the normal velocity on the transducer radiating surface is directly measured by a laser vibrometer. In the measurement process of the hydrophone method, a calibrated hydrophone is used to measure the transmitted field. The validity of these methods is checked by experimental test. All of the four methods described are sufficiently accurate for transducer sensitivity measurement, while each method has its advantages and limitations. In practical applications, the appropriate method to measure transducer sensitivity should be selected based on actual conditions.

An incident angle optimization method for transverse defects detection of pipes based on Zoeppritz's equation

Zoeppritzs equation is a set of equations that describe the relationship between the displacement amplitude of the reflection and refraction waves and the one of the incident plane wave at the interface of two media, from which the partitioning of wave energy at the interface can be inferred. The echo signal energy is directly affected by the value of the incident angle when oblique incidence of sound beam is applied in the detection of the pipes, therefore it is necessary to adjust the incident angle to the optimal range for an ideal flaw detection sensitivity. A method of echo signal energy estimation based on Zoeppritzs equation is put forward in this paper to seek out the optimal range of the incident wave, with which the echo signal energy-incident angle relation curve can be calculated. As a verification, an experiment of detecting the transverse defects on both the inner and the outer wall of a φ165.1mm pipe is conducted, using a 0.5inch/5MHz water immersion probe. The experimental results are in accordance with the calculated ones, proving that the method of incident angle optimization proposed is valid.

A voltage-current method of measuring ultrasonic transducer impedance

Impedance is one of the most important characteristics of ultrasonic transducer. This paper focuses on the measurement method of ultrasonic transducer impedance, studying many methods mentioned in domestic and international standard. The voltage-current method is proposed in this paper. Whats more, a measurement system based on this method is constructed. Then lots of experiments are performed to prove this method. The result is compared with that measured by using the impedance analyzer, which proves that the voltage-current method can measure the transducer impedance correctly.

Response characteristics of ultrasonic transducer under different excitation pulses

For analyzing response characteristics of ultrasonic transducer under different excitation pulses, response function for ultrasonic transducer must be known. In this paper, the transmission transfer function for an ultrasonic transducer is developed based on a two-port network with KLM model. Transducer response characteristics under different excitation pulses are analyzed and compared by MATLAB simulation. The method to measure the impulse response with a laser interferometer is applied. The experimental results are compared with the theoretical ones. Results showed that the amplitude of ultrasonic transducer impulse response has a relationship with the type of excitation pulses.

A method of optical non-contact measurement to rotary part's profile

The research on the technology of non-contact measurement of rotary parts profile has important academic significance and practicability for improving the rotary parts manufacture precision. In this paper, a method of non-contact measurement to rotary parts profile is studied. This method can be used to measure rotary parts more efficiently and accurately. In order to measure the rotary parts profile continuously, a laser beam-blocking method is presented. One or two laser beam-blocking sensors are used. The part that be measured is placed between the sensors emitter and receiver. The part will block some laser beam. From the sensor, the diameter in a certain section of the part can be got directly. In order to eliminate the influence brought by the parts position error, we should obtain the axes equation and contour line equations through curve fitting. Then we get the real surface size through coordinate transformation. In this paper, genetic algorithm is used to fit the contour line equations and the axes equation in order to improve the speed and precision of data processing. The experiments results show that the scheme presented in the paper is feasible, and the data processing method is correct.

Experimental research on residual stress measurement for tubule surface

Tubules are one of the most significant parts in mechanical field, and they are widely used in every field of manufacturing equipment. With thes development of technology, tubules are extensively used in the field of aerospace engines and hydraulic pipe. Therefore, it becomes more and more crucial to test the residual stress of tubules. In this paper, an ultrasonic method involving the longitudinally critically refracted (LCR) wave was used to measure the tubule surface residual stress. The special sensor was actuated by a piezoelectric wafer and ultrasonic transducer. An examination of the transmission principle of ultrasonic waves in the tubules revealed that measurements of the residual stress of the tubules surface using LCR waves were feasible.

Calibration Principle for Acoustic Emission Sensor Sensitivity

Acoustic emission sensors are the most important part of an acoustic emission detection system, which directly determines the validity and accuracy of the detection result. In order to improve the reliability of acoustic emission test results, the sensor’s sensitivity must be calibrated ahead of time. This chapter investigates the face-to-face secondary calibration method and presents the laser vibrometer primary calibration method for acoustic emission sensor sensitivity. A sensor sensitivity calibration system was built. Calibration experiments have been carried out. Finally, measurement uncertainty was analyzed.