Dynamic balancer

[alsinaj]

I'm mulling over an idea for a dynamic balancer for HSM-sized things that need to be nicely balanced. Consists of an arbor running in bearings supported by two pillars, a fan on one end of the arbor that would be propelled by a compressed air jet (to avoid pulleys and belts), a degree wheel on the other end of the arbor, and a sensor mounted in the foot of each pillar - perhaps a disc-shaped piezo element like those found in alarm buzzers.

Signals from the sensors go through a low-pass filter, then a zero-crossing detector (from positive to negative only), then trigger a high-powered white LED used as a strobe to read the degree wheel. The angular position at the zero crossing is 90 degrees after the position of the excess weight. An additional peak detector would indicate the magnitude of the imbalance. Those who know more than I will know how to detect and correct out-of-center-plane imbalances by comparing the readings from the two sensors. The balancer's first job, of course, is to balance its own rotating parts. The second job is to calibrate the peak detector output using a known imbalance.

The thing I can't grasp is what type of sensor to use (pressure, strain, ??) and how to mount them. Ideas?

[Don Young]

I think balancers generally use accelerometers for sensors. As I recall, the old on the vehicle wheel balancers with a strobe used a permanent magnet sliding inside a coil for a pickup. A suitable pickup could give you amplitude and phase data from the same pickup. You need your work supports to be somewhat flexible in only one plane. You might want to check on automotive driveshaft balancers for some idea.