1. The frequency bandwidth is wide.2. Resonant frequency and flat bandfrequency transducers can be used in awide bandwidth, such as 0.1 to1.0 MHz.3. The frequency characteristics of theacoustic emission signal aredominated by the frequencycharacteristics of the acoustic emissiontransducers.The transducer placement in acousticemission testing is also a major concern ingrinding applications. Except for surfacegrinding and many other machiningprocesses, both the cutting tool (grindingwheel) and workpiece are in rotation inthe grinding process. The rotation of thespindles makes it difficult to attach thetransducer to a grinding area. If atransducer is placed in a stationarylocation, such as a bearing supporter, thebearings or gears generate a lot of noise.The actual acoustic emission signalgenerated during grinding is usuallysmaller than the background bearingnoise and is hard to distinguish fromnoise. Moreover, a stationary place wherea transducer can be attached is probablytoo far from the grinding zone and signalattenuation is significant.Alternatively, other noncontacttransducers, such as noncontact signaltransmitting transducers and coolantcoupled transducers, have been used. Thecoolant coupled transducer seems to bemost viable for acoustic emissiondetection during grinding and dressing.During acoustic emission testing, acoolant fitting transducer is not directlyin contact with either the grinding wheelor the workpiece. Instead, it serves as apart of the coolant system of the grindingmachine. The coolant jet from the Tfitting directs to either the workpiece orthe grinding wheel. It not only plays arole for cooling the grinding zone but alsothe coolant jet serves as a waveguide,creating a path that allows the acousticemission signal to reach the acousticemission test transducer inside theTfitting. There are several advantages ofsuch a configuration:1. It is convenient to place thetransducer close to the grinding anddressing zone. No machine retrofittingwork is needed for transducerinstallation.2. Noises induced by dynamic movementcomponents, such as bearings, gears,belts and lead screws, can be greatlyreduced.3. The distance from the grinding zoneto the transducer location is fixed sothat the wave traveling distance staysconstant, unaffected by changes in therelative position of wheel andworkpiece.4. More importantly, this configurationcan be used in many kinds of grindingand dressing processes where a contacttransducer cannot get a high enoughratio of signal to noise because of theinfluence of rotary parts (wheel,dresser and workpiece) in cylindricalgrinding (internal, external andcontour), centerless grinding androtary tool dressing.Figure 32 shows some examples of howcoolant coupled transducers are applied todifferent grinding and dressing processes(internal grinding on Figs. 32a and 32b,centerless grinding on Fig. 32c, externalgrinding on Fig. 32d, single-diamond tooldressing on Fig. 32e, contour tool dressingon Fig. 32f, rotary diamond truing onFig. 32g and rotary diamond dressing on
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