Distance measurement using airborne sound

Abstract

Inspection of manufactured material and components often involves characterization of size or shape. If large quantities of components must be inspected, as is usually the case on a production line, a rapid automated inspection process is desirable. This presentation reviews the use of airborne ultrasound as the basis for such a system. Time‐of‐flight measurements of acoustic pulses through air can be used for distance measurement with range resolution of 0.01 mm (0.0004 in.). Coupling this instrumentation to a data acquisition system permits high‐speed, automated dimensional checks. But a more important feature of an airborne sound system is that contacting the part is not required enabling rapid characterization of components difficult to measure by other means. These include runout on abrasive surfaces such as grinding wheels or discontinuous surfaces, such as tire treads. Finally, since ultrasonic distance measurements can be updated at several hundred hertz noncontact time motion studies are possible. No loading is applied to the structure under investigation so that characterization of “delicate” vibrating components is possible.