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Acoustic control fine-tunes grinding.

Acoustic control fine-tunes grinding

The sound produced when a grinding wheel meets the workpiece has a distinct characteristic, and can be isolated at frequencies above the ambient sounds of neighboring gears, bearings, and pumps up to 200 kHz. With the latest piezoelectric transducers and analytical instruments, this sound spectrum can be broken into several characteristic frequency bands keyed to specific grinding phenomena.

Gap Control is a new acoustic gaging system for grinding that uses a series of four microphones, each tuned to a different phenomena, to improve grinder performance. It was developed in Switzerland by Meseltron SA, and is offered here by Movomatic, USA, Greenville, RI.

The four gaging functions are:

1. Eliminate air gaps. In external grinding of rough parts, the wheel infeed must slow down and creep up on the part OD because of its wide variation in diameter. With gap control, this air-cutting time is eliminated. A rapid in-feed is used, right up to the point of contact. The wheel "crashes" into the part, and the system senses this sound and switches in milliseconds to rough-grind in-feed.

2. Avoid part collisions. When a part is positioned wrong (typically, backwards), the sound of the wheel crashing into the part is picked up quickly enough to prevent serious damage--an in-feed stop command can be generated in 10 msec.

3. Monitor wheel condition. During the wheel-dressing cycle, the gaging system analyzes the sound produced to deduce wheel condition, based on its characteristic and time. This will detect rounded wheel corners or breakage, and tell the machine to dress again or decide that the wheel needs changing and initiate that cycle in automatic wheel-changing machines.

4. Optimize the grind. Once the gage is tuned to the correct sound coming off the wheel, grinding rate can be optimized. The system says, in effect, to the machine "Ease up, you're too heavy, or boost in-feed, you're not grinding heavy enough."

The gap-control system has been applied so far only to OD grinding. It has distinct advantages, says Movomatic, over prior systems that sense wheel-head motor load. With those systems and large wheels, the wheel can do considerable damage before any change in wheel-load current is sensed. With acoustic gap control, you can sense the initial touch of wheel to part, and if wheel in-feed is capable of responding in milliseconds, use that intelligence to eliminate gouging the part.

For more information from Movomatic, circle 260.

PHOTO : When a part is loaded in the grinder backwards, the gage senses wheel contact with the part at the wrong point in the grinding cycle and stops in-feed.
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Publication:Tooling & Production
Date:Jan 1, 1992
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