I thought I would let anyone interested know about a project I am workin on for my CNC wood router. The problem I am trying to solve is two fold, first an attempt to maintain a constant cutting bit speed under varying load conditions, and second to generate a fault to the CNC if the spindle motor stalls. When cutting wood the bit can not be too fast or the chips produced are too small and do not carry away the heat generated and the wood burns. If the bit is turning too slow the router stalls. It is a bit of a balancing act to get the feed rate and the spindle speed just right. The problem I have is that when I get it just right, it doesn't stay just right.
So, I am designing a circuit that interfaces to my CNC machine and provides a constant speed control. The inputs to the system from my CNC are:
1.) Spindle On
2.) Spindle Desired speed
There is an output from my system that indicates a motor stall.
I use a magnet mounted on my router shaft and a hall sensor to provide actual speed feedback to my circuit. I have a small microcontroller that takes all this info and controls a triac that controls the power to the spindle motor.
Just for grins I also added a circuit that provides an LCD readout of the spindle speed.
Right now the circuit is a bunch of breadboards spread over my work bench. I use TurboCNC to drive my machine and am working out how do define the desired spindle speed.
I'll get some pictures taken of the breadboards. I just wanted to see if anyone is interestted in this project or has had similiar problems.
Greg