Application of the Body Acoustic Sensor
During any dressing process, the dressing wheel and grinding wheel both produce a noise (Acoustic Emission = AE) whose spectral frequency distribution is, for the main proportion, in the ultrasonic range. Additional noises, produced by components such as gearbox, bearings, hydraulic components, etc., are mainly composed of lower frequencies. Consequently the frequency gap between grinding noise and machine noise is sufficient. When the dressing wheel touches the grinding wheel the ultrasonic level increases dramatically and a reliable evaluation criterion is reached.
Reducing the Air-Grinding Time
During conventional dressing, the infeed speed must – for safety reasons – be reduced to Process Grinding Speed some time before the dressing wheel touches the grinding wheel. With a SENSITRON 2 fitted to the machine the noise emission of the machine is picked up by an AE Sensor and fed via cable to the electronic unit.
At the beginning of a dressing cycle the dressing wheel is fed with rapid infeed speed to a certain safety position to the grinding wheel. The machine control gives a command to change the infeed to the (slower) Air Grinding Speed. The AE Sensor picks up the basic machine noise which is made visible at the 30-element bar graph array of the SENSITRON 2.
As soon as the dressing wheel touches the grinding wheel the Acoustic Emission (ultrasonic noise) increases instantaneously and exceeds a preset threshold value. Within 10 milliseconds the SENSITRON 2 gives a LOW signal to the machine control. This causes the machine control to reduce the machine’s infeed from Air Dressing Speed to Process Dressing Speed.
This application is suitable for surface and external cylindrical grinding.
Particularly when dressing CBN grinding wheels the recognition of the first touch is very important in order to remove as little material as necessary. This will enable the control of the sharpness and profile of the wheel by means of defined infeed increments (Touch dressing). Additionally it saves money.
By the use of non-contact transmission, AE signals travelling along the rotating spindle from the ‘first contact’ between the roll dresser and the grinding wheel, are able to be detected by the sensor and transmitted to the receiver at an economical cost. This technology considerably increases the grinding noise against the machine noise ratio, and consequently improves the safety of the system.
The sensor, mounted centrally on the rotating dresser or grinding wheel shaft or can be ring shaped, picks up the AE Signal at its source and transmits it to the fixed receiver unit. Through a shielded cable the signal is then fed to the SENSITRON 2 and evaluated. Connected to the machine control, sharpness and profile of the grinding wheel may be controlled by defined infeed.
Monitoring the Dressing Process
The SENSITRON 2 in conjunction with the machine control is able to recognise whether the dressing unit is in touch over the whole width of the grinding wheel. If the dresser loses contact, the noise emission decreases and a HIGH-signal is fed via pin 4 of connector #11 to the machine control.
The HIGH- or LOW signal lasts at least 10 milliseconds to give the machine control the possibility to recognise ‘contact loss’ or ‘contact’. If there is any irregularity the machine control signals another infeed of the dressing wheel or diamond till the contact, and therefore the Acoustic Signal, is available over the whole width of the grinding wheel.