Messages

41

General Mach Discussion / Grex + printer port for MPG

« on: May 27, 2008, 06:12:50 AM »

Firstly,
thanks all for the previous help. I'm just getting back to the machine for the trials.

My question is I am using a Grex and have myself a remote MPG pendant from CNC4PC.

On the config side. I wish to plug the MPG pendant into the printer port and use Mach via ethernet. I'm just trying to get my head around the ports/pins settings to use both via different ports.  Any advice

Thanks
Jason

42

General Mach Discussion / Re: Hot stepper Motor

« on: May 11, 2008, 07:42:14 PM »

Thanks for the information.

Regarding the feeds and speeds, I do wish to run them at 5000m/min and higher if possible

To give you a better understanding of where I'm at and a big thank you to all the moderators that have gotten me this far with my build.

I'm using the cutting table to cut  a velour material similar to the auto trimmers hood lining and seat inserts using standard preprogrammed nested patterns. I use Rhino to create iges files and Mastercam for the tool path.
The shapes donot have to be super acccurate and I have my linerisation set to 0.5mm. Its not about the accuracy it's all about the speed. However the A axis has to be accurate or the knife gets dragged around the table dragging the material with it.

With the tangential control in Mach3 the A axis position is configred within Mach3 and the combination of this is that A axis runs in exact stop mode. Not really a problem until you turn up the feed rate and then it becomes very jerky.
On previous advice from the great moderators I have got myself a optical switch to home the A axis. (I have yet to install this) this will help with accurate referenceing at the click of a button. In the past I have been do a visual alignment of the A axis

So the plan is to find a balance of speed verses jerky verses lost steps. I have a GREX as my BOB, but after do a lot of reading I may seem that the clock speed my not be able to handle the feeds I wish to run at and that a Smooth Stepper may be a better bet.

Regarding the A axis stepper. I thought that voltage would be it's friend. It does not have a lot of load. I have a pneumatic actuator that drives the z axis and this is set to 20Kpa and I have a spring to help the z retract. The bead is made from HDPE to assist the cutting blade from bluntning.

So I will give my 24V PS a try on the A stepper and I can also wire this unipolar for a test also.

Any other advice appreciated

Regards
Jason

43

General Mach Discussion / Re: Hot stepper Motor

« on: May 04, 2008, 06:49:32 PM »

Thanks guys for the tips.

Yes I have wired it bipolar and set the gecko to limit the current to 2A. The stepper I replaced with the Vextra had no markings and was of similar size. I limited the current to 0.5A and it still got hot and lost steps. That's why I replaced it.

I understand the voltage/torque relationship at speed. Yes as a tangential knife it rarely does one full turn. I am in a postion to hook up and 24V PS and give it a go. Hopefully  this will cure the heating problem. It's the lost steps that is my main concern. I am thinking that I may have to add a home axis type of code and insert i into the .NC file mid script so that the knife does not tear the cutting table and material apart the moment it get's out of alignment

I  could also do with a program that can convert the X-Y code and write an A axis tangential code. This way I can turn tangential control off in Mach3 getting away from the exact stop bug.

What other ays are there of testing the a axis to find out where the steps are lost.

Thanks
Jason

44

General Mach Discussion / Hot stepper Motor

« on: May 03, 2008, 01:03:44 AM »

I have a Vextra PV264-02BA on a A axis to rotate a tangential knife using the tangential control feature in Mach3 and 2.5D to control the Z axis. I have fitted a thrust bearing between the cutter and the stepper so that when the z axis is lowered into the cutting postion it does not put any axial load on the stepper.

My problem is that the stepper is hot to touch even when idle. An when I run a large file the A axis looses steps and ends up dragging the knife around. When in tangential mode the system runs in exact stop meaning that the A axis has to complete the move prior to the X-Y axis moving. This is the limitation of Mach3 tangential control

I have lowered my motor tuning to 5000m/min with accel of 800m/s/s with units set at 5.555555555 and it stil looses steps on the A. I have even run the gcode with out the knife attached ie cutting air and it still looses steps. We are talking 2-8 deg at the end of the program cycle. Some times I have to stop the program re-reference the A axis to stop the problem of the knie getting dragged around the table

THe stepper is wired bipolar to a gecko and I have limited the current to 2A with a voltage of 56VDC. I did have a cheapy stepper doing the same thing that I replaced with the Vextra

Any thoughts on the hot stepper problems.


Thanks
Jason

45

General Mach Discussion / Re: 360 deg A Axis homing using an encoder

« on: March 07, 2008, 12:45:27 AM »

Thanks for your help.

I will definetly go down this path for setting up this A axis

Thanks again

46

General Mach Discussion / Re: 360 deg A Axis homing using an encoder

« on: March 06, 2008, 07:26:19 PM »

Thanks Overload,

Regarding this optical switch. With homing and limits being operated by this type of switch, what would be the results if during normal operation the swicth was activated.
Some times due to the code the axis will pass through zero and number of times and in either direction

47

General Mach Discussion / Re: 360 deg A Axis homing using an encoder

« on: March 06, 2008, 03:44:39 PM »

Thank you for the responses.

A pizza wheel is a rotary knife similar to the one you use to cut pizza's with. This sits on the end of the A axis.

When I refernce all axises home all is ok for the X,Y and Z however because I'm using the tangential feature in mach my A axis never ends up in a 0 deg position. So I have to visually align the A axis and zero. As the machine is up againt a wall it is hard to acurately check if the a is exactly in the correct zero position. If it is a few deg off the knife is dragged around the table. this dragging/ not inline with direction of travel increased the load to a point where the stepper looses steps.

Regarding the encoder. Haven't encoders been used for linear DRO's before. ie just to measure distances??

Iam using a GREX so may be I could get a pulse to voltage converter and use a analog input for measurment of the A axis angle??


Jason

48

General Mach Discussion / 360 deg A Axis homing using an encoder

« on: March 05, 2008, 08:59:57 PM »

I have a tangential cutting machine with the A axis stepper motor rotating a pizza wheel.

I wish to install a Encoder on the A axis so I can reference this axis to a home 0deg position using the encoder as position feedback

I imagine setting up a DRO for the Axis is the way to go??? or are there other solutions??

I did read some where that Gecko may be building a closed loop stepper drive

Has any one elso installed encoders on a rotating A axis with stepper for monitoring postion??

Cheers
Jason

49

General Mach Discussion / Re: Tangential Cutting Table and Feedrate

« on: December 29, 2007, 06:57:52 AM »

OK,

I have read every Yahoo post back to 2004 with regards to Tangental Control.

I have figured out Mach 3 needs G1 codes to calculate the Tangent angle

I have also realised the square wave limitations of Mach3 with regards to CV and acceleration values.

It looks like that a test of Quantum is of the order.

I need a little reasurance that I'm heading in the right direction

50

General Mach Discussion / Re: Tangential Cutting Table and Feedrate

« on: December 29, 2007, 06:05:28 AM »

OK,

I have been reading some old Yahoo post and this came up

Hi Stuart:

It may simple be the fact the table must stop at the line temrination
points to do the correction of the tangental axis. There is no way to smooth
it out except to use G2/G3 arcs to follow gently on a given path..

Thanks,
Art
www.artofcnc.ca


OK now I have to find out how to draw patterns so that when post processed Gcodes ends up with G2/G3 interpolation