Structure Synthesis and Mechanical Parameters Choice for a Manipulating Mechanism for Acoustical Measurements in Anechoic Chamber

Abstract

The article presents the structural and geometric synthesis and mechanical parameter choice for a manipulation mechanism for measurement microphone positioning during acoustical tests in anechoic chamber. Usually the aims of acoustical measurements in anechoic chamber are: noise source Sound Power Level estimation, electroacoustical transducer directional characteristics measurement, sound diffusing characteristic of a structure measurement, measurement of Sound Pressure Level on a given measurement grid The specific of that kind of measurements brings up the need of measurement microphone positioning in many points of the measurement space accordingly to relevant standards. In most cases during the tests it is necessary to position the microphone in certain points on the hemisphere. In such cases utilizing of typical microphone stands impedes the measurement and extends the time needed for the tests. Those circumstances led to idea of measurement manipulator construction that would allow changing the microphone position during the measurement accordingly to a specified algorithm. The following assumptions for construction were taken: measurement microphone moves on the hemisphere with a maximal radius of 2 m, the weight of transported object (microphone or other) does not exceed 1 kg, positioning accuracy is 1 mm. Structural and geometric synthesis was made taking into account mounting conditions in anechoic chamber in Department of Mechanics and Vibroacoustics AGH-UST. There were several variants labored that fulfilled the assumptions. The choice of particular solution was made based on: • manipulator drives possible installation analysis with regard to their acoustical noise emission • structure stiffness analysis with regard to assumed positioning accuracy of the microphone Finally a modular construction of manipulator was chosen, which is composed of industrial turntable (built in the level of the wire netting) and two linear motion modules (long axis, short axis). That solution means that the device under test fixed on the turntable rotates in the range of 2π, and the measurement microphone moves on the track of one quarter of a circle. Specific angular position of the linear modules was chosen which allows minimal dimensions of linear modules. Simultaneously the control structure and the software part are developed. The usefulness of the manipulator will be definitely confirmed by a research that should evaluate the influence of the construction elements on the acoustical free field in an anechoic chamber.