John G. Cherng

Vibration reduction of pneumatic percussive rivet tools: Mechanical and ergonomic re-design approaches

This paper presents a systematic design approach, which is the result of years of research effort, to ergonomic re-design of rivet tools, i.e. rivet hammers and bucking bars. The investigation was carried out using both ergonomic approach and mechanical analysis of the rivet tools dynamic behavior. The optimal mechanical design parameters of the re-designed rivet tools were determined by Taguchi method. Two ergonomically re-designed rivet tools with vibration damping/isolation mechanisms were tested against two conventional rivet tools in both laboratory and field tests. Vibration characteristics of both types of tools were measured by laboratory tests using a custom-made test fixture. The subjective field evaluations of the tools were performed by six experienced riveters at an aircraft repair shop. Results indicate that the isolation spring and polymer damper are very effective in reducing the overall level of vibration under both unweighted and weighted acceleration conditions. The mass of the dolly head and the housing played a significant role in the vibration absorption of the bucking bars. Another important result was that the duct iron has better vibration reducing capability compared to steel and aluminum for bucking bars. Mathematical simulation results were also consistent with the experimental results. Overall conclusion obtained from the study was that by applying the design principles of ergonomics and by adding vibration damping/isolation mechanisms to the rivet tools, the vibration level can significantly be reduced and the tools become safer and user friendly. The details of the experience learned, design modifications, test methods, mathematical models and the results are included in the paper.

Application of acoustic metrology for detection of plate thickness change

Dimensional control is one of the most important procedures in the manufacturing process. As the acoustic properties of an object depend closely on the geometry of its structure, the resonant frequencies of a product can be used to monitor its dimensional change. In this paper, the thickness changes of a rectangular plate are studied intensively. Plate thickness is primarily measured by micrometers. This process is tedious and time consuming, especially when the size of the plates is large. Therefore, a technique that can easily monitor thickness change is highly desirable. Through both experimental and theoretical studies, it is found that the technique presented in this paper is sensitive to thickness change, and thickness changes of less than 0.01 mm can be detected. Acoustic metrology appears to be able to provide an alternative for the plate thickness inspection processes.

Effects of area change and friction on acoustic propagation in compressible flow through long ducts

An analytical study of the effects of area change and friction on the sound propagation through the fluid which flows steadily in a long duct is made in this paper. The sound wave originating at the entrance of the duct is carried by the fluid flowing through ducts at velocities which are large enough to influence the sound wave transmission. The problem is analysed by using the governing differential equations in the unsteady one-dimensional gas dynamics and the transmission of the sound wave is treated as a perturbation to the otherwise steady main flow. As a result, an analytic expression of the sound pressure level as a function of the axial distance is obtained in this paper. A family of numerical solutions are presented.

Acoustic metrology for dimensional conformance

Abstract This study presents an innovative concept —acoustic metrology—for on-line dimensional conformance inspection. It investigates the linear and radial dimensions as well as the true position of a center. It conclusively finds that as these dimensions change, the resonant frequencies of tested cylindrical and flat plate parts also shift. The high resonant frequencies appear to shift more than low resonant frequencies with linear and radial dimensional deviations of cylindrical parts. However, the dimensional deviations of a flat plate part only influence certain numbers of resonant frequencies. The amount of the frequency changes of all tested parts is proportional to the dimensional deviations. The test results reveal a feasible gaging method that can be used for inspection of a production line for a “Go” or “No Go” decision.

An objective method for determining soundboard material quality

For a stringed instrument of the guitar or violin family, the dynamic characteristics of the soundboard are extremely important in determining the sound quality of the finished instrument. Since an exceptional instrument can be worth several tens of thousands of dollars, the importance of getting such a basic step correct are obvious. This paper describes our efforts to describe the desirable characteristics of a guitar soundboard blank using what is currently some of the highest quality test equipment available. Our goal is to provide objective standards that can be implemented in an industrial guitar‐making process to help ensure the highest quality possible sound quality in the finished instruments. Formal modal tests on a range of soundboard blanks ranging from inexpensive ones intended for use by those just learning their craft to master grade blanks suitable for the highest quality instruments have been performed. The subjective ratings used to grade these blanks with objective test results are correlated.