Accurate measurement of filament feed rate.

Hello All

Perhaps this has already been covered, but I was thinking about the control one has over the feed rate of the 3mm filament which directly affects the extrusion rate.

Measuring the rotation of the motor, whether by steps or by a shaft encoder I imagine will not let you know if the filament is slipping or not.

How about hacking a optical mouse and mounting the laser eye to watch the rate at which the filament enters the extruder housing?

Is the 'eye' of an optical mouse accurate enough?
Will the 'eye' be able to watch the filament or will the filament be too smooth? (can scour the filament before)

or are the existing methods more than accurate enough?

If the plastic slips with a threaded pulley drive then the teeth become clogged and you have to strip it down and floss it. Having a sensor would tell you when it had failed but would not give more accurate results as it doesn't slip when it is working properly.

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Maybe you could draw radial lines on the idler wheel and use it as an encoder.