Messages

451

General Mach Discussion / Re: Probing accuracy measurements

« on: March 22, 2021, 06:23:12 PM »

Thanks TP, the learning curve to use the tooltable was fairly simple as I had been through it before.  I don't really want to devote much more time to learning Mach 3 as I'm likely to be moving to Mach 4 or something else fairly soon.  This does the job.

452

General Mach Discussion / Re: Probing accuracy measurements

« on: March 20, 2021, 03:17:23 PM »

Thanks for the suggestions and help.  In the end I did this by writing a simple macro, derived from a tool setting macro, that would take up to 225 probe readings and write them to a tool table, which I then exported as a text file and opened in Excel for analysis.  Slightly clunky but does the job.  Measuring the performance of a Sharp photointerrupter, 87% of 100 measurements were at exactly the same point, the rest being within +/- step at 1600 steps/mm, so better than a micron.  I will repeat the exercise with: different supply voltages to the opto; on positive edge triggering rather than negative (i.e. with the obstruction moving out of the gap); with and without ambient light; and with my "conductive" probe.

453

General Mach Discussion / Re: Mach 3: Programmatic change to config

« on: March 20, 2021, 05:36:23 AM »

Thanks!

I'll give that a whirl.

John.

454

General Mach Discussion / Re: Mach 3: Programmatic change to config

« on: March 20, 2021, 02:15:16 AM »

Thanks for pointing these out.  The wording is a bit ambiguous on the second, does it mean if you set bool to 1 it's active low, or bool=0 it's active high?  I guess I might need to try it!

455

General Mach Discussion / Mach 3: Programmatic change to config

« on: March 19, 2021, 12:17:47 PM »

This is maybe a strange question, but I'm wanting to write a macro to add to a screen that will allow me to make repeated measurements on the probed position on executing a G31 - basically I am interested in the variance of the sensed position, or how accurate the probe is.  This is partly to evaluate probes, but more because what I'm actually wanting to do is evaluate the precision of photointerrupters sensing a vane.  At the moment my Mach 3 is set up to trigger on a negative going (i.e. grounded) signal when the probe touches which is fine for the photointerrupter when looking at one edge, but they also display hysteresis so I'd also like to look at the other sense, when the vane moves out of the gap and the signal goes positive.  What I'd really like to do is change the sensing polarity of the digitise signal from within the macro.  Can anyone advise if this is possible please?

John.

456

General Mach Discussion / Re: Probing accuracy measurements

« on: March 16, 2021, 05:39:44 AM »

Right!  Thanks for the explanation.  So there could be a small error because of the time taken to decelerate to a stop but this should be constant for a given probing speed?  And if the speed is low and deceleration profile not too flabby it should be small as well.

And once the probe move is complete, Mach 3 should have the probed position in the appropriate DRO?

457

General Mach Discussion / Re: Probing accuracy measurements

« on: March 15, 2021, 12:33:07 PM »

Thanks TP - your description is how I thought it worked.  For this experiment I will use a slow probing speed and make sure the approach is from a reasonable distance.

458

General Mach Discussion / Re: Probing accuracy measurements

« on: March 14, 2021, 01:40:19 AM »

Thanks Craig, that's useful.  My motivation is only partly to characterise a probe, I also want to investigate the sensing accuracy of an opto interrupter for use on pendulum clocks.  I'm thinking that using my CNC mill to do slow traverse of the opto past a thin vane or rod in the chuck, and using the opto to drive the probe input, should provide an accurate and automatic way to do this.  I will be using a very slow G31 feed - in fact I tend to play it very safe using F5 usually for probing, manually positioning the probe close to the surface first.  Could you possibly share the Mach 3 macro please?

John.

459

General Mach Discussion / Probing accuracy measurements

« on: March 13, 2021, 04:28:37 AM »

Investigating various touch-trigger probe types, I've noticed that their developers often gather statistical information on performance.  For example, if the probe touches off on the same surface 100 times, what is the mean and standard deviation of the resulting measurement?  This should be a fairly easy thing to automate with a Mach 3 macro, but before I do so I was wondering if anyone has been here before me and could share the code please?

John.

460

General Mach Discussion / Re: Encoder setup (feedback in mach3)

« on: April 19, 2020, 07:12:11 AM »

I think you'll find that as far as Mach 3 is concerned the servo motor works just like a stepper.  There is no concept of feedback in Mach 3.