Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: adprinter on March 03, 2017, 02:28:19 AM

Title: What would be the best sensor method to detect spindle speed?
Post by: adprinter on March 03, 2017, 02:28:19 AM

Is there a way, to wire a speed sensor (light source, and photo-cell perhaps), and set up Mach3 to trigger an error (And thereby STOP program execution at the current line number)? The reason I ask, is because motor brushes wear out! And when they wear down enough, they no longer contact the armature, so the router motor stops running. Invariably resulting in a broken bit, as Mach3 continues to run (unaware that the router motor has actually stopped!). Has anyone else done this? What sort of circuit, and speed sensor device could be used for this purpose?
Thanks, in advance for any help!
-Michael

Title: Re: What would be the best sensor method to detect spindle speed?
Post by: Tweakie.CNC on March 03, 2017, 03:10:49 AM

My approach would be to sense the current drawn by the spindle motor.

The detection circuit would be different for a.c. or d.c. motors but the result would be that if the signal on the M3/M4 Output#  is present and the current draw on the motor is nil (or below a preset value) trigger the EStop.

Tweakie.

Title: Re: What would be the best sensor method to detect spindle speed?
Post by: Tweakie.CNC on March 04, 2017, 01:32:40 AM

Another method may be to fit a single slot disk to the spindle motor and using an opto-switch set up Mach3 to display spindle RPM. Then use a Brain to read spindle speed and if below a predetermined value when the spindle Output# is active trigger the EStop.

Tweakie.

Title: Re: What would be the best sensor method to detect spindle speed?
Post by: adprinter on March 07, 2017, 08:52:42 PM

Tweakie,
I appreciate your suggestions. Since my router motor is AC powered, I was thinking of wiring a relay into the ground side of the circuit. Which would drop out, anytime the (return) current drops to zero (brushes no longer in contact with armature). This relay could be easily wired, (using a DC power supply) to trigger one of the five available inputs of the Gecko G540 I am using to drive the machine. Thanks for the advice! It was needed, to get MY mind thinking in the physical logic it will take to accomplish this task!
Sincerely,
-Michael

Title: Re: What would be the best sensor method to detect spindle speed?
Post by: Tweakie.CNC on March 08, 2017, 04:31:34 AM

Hi Michael,

Series relay sounds good but you may also need to use a shunt (unless the relay coil can handle the spindle motor current). Another approach may be to use a current transformer to drive the relay.

Tweakie.