Adjustment of the speed of feeding logs to sawn into the machine

Develop a reliable scheme and assemble a prototype of an automatic control system for feeding logs to sawing, depending on the detection of metal nails sized from 20 mm to 100 mm in a log diameter from 10 cm to 26 cm coming one in the stream to the sawing machine, and when the detected nail inside the logs to the saw, reduce the speed of feeding logs to the saw by means of a frequency-controlled drive for the time of sawing the nail with a saw, and after sawing the nail (10 mm-50 mm) return to the speed of feeding the logs again in the log.
I mean. To assemble an automatic metal detection system (determining the coordinates of the nail in the log) and control the frequency converter.
(The task is simple and daring.) The nail is sawed at high speed, but the saw fails when sawing 10-20 nails, and with a small speed of sawing the nail, the saw does not change.