Messages

51

Mach4 General Discussion / Re: Mach4 positioning error

« on: December 12, 2019, 02:47:01 PM »

 

Dont get angry at me, of course i am going to measure the pitches tomorrow as u suggested but i am %90 sure thats not the case, this was what i meant.

It rules out the zero error window because of this logic; as u know thats a preprogrammed  encoder count which feeds back it to the driver, by that way driver knows the commanded position reached, so to do that, there should be a encoder attached to the motor shaft. But in open loop stepper motor(16Nm one which i attached to the X axis instead of the servo) there is no encoder, its open loop and repeated the same error as the servo.

Is my logic wrong?

Regards,

Hakan

52

Mach4 General Discussion / Re: Mach4 positioning error

« on: December 12, 2019, 02:23:14 PM »

Once again hi Craig,

How are u?

I am sure about the pitches, these are metric and i ordered them directly from the manufacturer not from the distributor, so we can rule that out, also i attached an open loop 14Nm stepper motor to the X axis to check if the servo motor/driver is faulty, i thought there may be a tuning problem but it repeated the same exact error. I think this also rules out the zero error window, any other suggestions?

I noticed this odd thing while doing the measurements; i repeated the measurements in every axis multiple times, for example i commanded the axis to move to 1, then 2, then 3 until it reaches 10mm and repeat this set of commands 10 times in every axis. In one of the axis i think it was Zth, axis moved within 1 micron to the commanded positions in first set, but then in 9 sets it repeated this error. I am not noticing any noise issue in general in limit switches etc. but is it possible that this error maybe because of the noise within the control cabinet especially which may effect the ESS and pmdx? i am not sure if noise can lead this kind of consistent errors, u may know it better.

Regards,

Hakan

53

Mach4 General Discussion / Mach4 positioning error

« on: December 12, 2019, 12:40:09 PM »

Hi all,

there is a problem which made me take apart the new built machine, there is a positioning error in every axis, here is the machine details;

Windows 10 32bit, Mach4, ESS, PMDX 126 as controller,

X Axis:

1300mm stroke, 25mm diameter with 25mm pitch Taiwan made single nut ballscrew directly attached to a servo motor with coupling(this motor replaced with 16Nm step motor to rule out the motor/driver combo error, it gave same results with servo system),
Ballscrew aligned with the guideways within 0.01mm from one end to another both vertically and horizontally,
there is a measured 10-15micron backlash.

Y Axis:

1000mm stroke, 25mm diameter, 5mm pitch Taiwan made double nut ballscrew directly attached to a closed loop step motor with coupling,
Ballscrew aligned with the guideways within 0.01mm from one end to another both vertically and horizontally,
there is a measured 4-5micron backlash.

Z Axis:

1000mm stroke, 25mm diameter, 5mm pitch Taiwan made double nut ballscrew directly attached to a servo motor with coupling,
Ballscrew aligned with the guideways within 0.01mm from one end to another both vertically and horizontally,
there is a measured 4-5micron backlash.

All the guideway(30mm schneeberger) beds scraped and aligned/paralleled within 15microns in both vertical and horizontal plane.

This is a very rigid machine which weighs 4tons, it is precisely leveled, motors has no problem while driving, no noise, no heat, there is no other error in the setup other than this positioning error.

At first i thought maybe servos doing it but Y axis has a closed loop step motor and a double nut ballscrew aligned within 10microns, which makes the exact same error with X and Zth axis.

I am confused with it, tomorrow i am going to reinstall Mach4 and ESS plugin from scratch and make the test with the standard screen which comes with Mach4 but other than that nothing comes to my mind.

It also does not cut the circles true, in 30mm diameter it makes +60micron error.

below images are the measurements in one way(to rule out the backlash), first command is 1mm forward, next is 2mm forward etc.. it always comes short, there is no errors in ballscrews or motors and their tuning, thats for sure, i am focusing on Mach4 and ESS right now, anyone has any idea about the possible cause of this positioning error? or anyone faced with a similar problem?

Regards,

Hakan

54

General Mach Discussion / Re: Linear axis error compensation

« on: September 07, 2019, 05:13:13 PM »

There is a new development in Mach4 in the form of a wizard called mcMapSurface. The essential idea is that you probe
the bed or table of your mill (X and Y axes) and record the variance of the height (Z axis). Mach stores those values
and thereafter automatically compensates the Z axis where and whenever the machine is at any particular X,Y location,
no formula required, no tricky Gcode.

Mach3 has no similar feature.

Craig

This is what i am looking for, my illustration includes a graph thats the only difference if i understand the Mach4 image u attached correctly, so i assume that i can do the measuring with a granite straight edge-micrometer and enter the error value so it will compensate automatically on the fly.

Can u add it to Mach4 anytime soon and include it in to manual? Because there is too many boxes in there ;-)

Also, probing the bed or table is useful for making the guideways parallel to table, but this is good only if the table manufactured correctly. I was aiming to get rid of the guideway errors(which is under 20microns in my case) when i connect a long part to table on 3-4 points. So compensating the X and Y axis movement of the machine close to true 0 can only be done by measuring manually a 000 granite straight edge or make the measurement by a laser. What i mean is; it would be better if u can enter the error values manually and see the pattern on a simple graph(like motor graph), because by that way u can also see how much Mach4 can compensate the error. Then u can prove it by making the physical measurements.

Regards.


Thanks

55

General Mach Discussion / Linear axis error compensation

« on: September 07, 2019, 08:41:55 AM »

Hi all,

I am sure i am not the first one who get to this idea about fixing the error of a linear axis but i couldnt find the topic related with it in the forums and couldnt find what u guys call it so i posted it in here, if u have a knowledge related with the matter please direct me to the related post, thanks.

The idea is simple;

If there is a fixed and measured error of a linear axis(lets say, up and down error for the X axis), u should be able to compensate it with the Zth axis(by moving the Zth axis up and down in predefined positions of the X axis).

U can understand what i mean in the attached image better, in this image there is a graph which illustrates the up and down error of the X axis and the movement required to fix that error by the Zth axis. This is an interface illustration for this compensation so that user can enter the measured error in means of distance according to the machine coordinates and the error measured by the straight edge-micrometer or laser interferometer. For example, X axis length is 1300mm and the total error is 60 microns.

We are assuming that the error is fixed and repeating in every X axis movement, body of the machine is rigid and we have ability to move the axises to exact positions, they can be precisely controlled.

This error fixing can be adapted to gcode or by manually to MDI but better then that if u can find a way to adapt it directly to the controller(Mach4) there wont be any user activity needed to fix it in each time, machine will automatically move the Zth axis incrementally according to the reached predefined machine coordinate and the error will be compensated automatically.

The main idea in here is to fix the physical error of the machine bed by means of programming the controller to avoid that error without the need of disassembling the machine and fixing the error physically.

So i am looking for help to adapt this directly to Mach4, is there a way to do this by scripting? or a plugin is necessary?

Thanks in advance.

56

Mach4 General Discussion / Re: Mach4 Spindle At Speed, Spindle Zero Problem

« on: January 11, 2018, 07:07:52 AM »

Hi Craig,

I will go with servo option next time for sure but in this machine i need to solve it somehow, thanks anyway.

Hakan

57

Mach4 General Discussion / Re: Mach4 Spindle At Speed, Spindle Zero Problem

« on: January 10, 2018, 06:01:12 PM »

Hi Craig,

It was not of course 0 but what i meant was it was very close to zero, actually what i meant was this;

https://www.youtube.com/watch?v=fzHWudx2wgU

but the strange thing is, this happens my case in the opposite way. When i adjust the vfd as vector drive there is no torque in low speed, but when i change it to v/f mode there is torque and u can not stop the shaft with hand.

As u suggested before i gave up from the idea of intalling an encoder at the end of the shaft, but now if i want to implement the ATC function i need to align the shaft of the spindle to an angle.
The reason is the drive dogs on the tip of the spindle has to go in to a slot in the bt40 holder(at the atc side). So to do this i need to stop the spindle shaft at a point lets say parallel to x axis.

As u know Delta Vfd s has encoder cards PG01 i think or something like that, i thought matbe i install an encoder on the shaft and connect it to vfd through this encoder card it may be possible to stop it at a count number of the encoder. For example if i is 1024 pulse per turn i can program the vfd to stop at pulse 512 in every stop command. I asked this to the Delta support in here they say it is not possible on VFD-E series but it is possible with VFD-C2000 series. But in VFD-E booklet it says u can make speed and position control with this card so i am confused.

do u know anything about this? i attached the related portions of the booklet.

If this is not possible according to u too, can u think of anyway other than the mechanical option?

Thanks in advance.

Hakan

58

Mach4 General Discussion / Re: Mach4 Spindle At Speed, Spindle Zero Problem

« on: December 26, 2017, 06:31:55 PM »

Thanks for the detailed explenation Craig, i didnt understand the half of it  but u say an induction motor may have 17.5Nm torque on the shaft in 0 speed? if so my induction motor sucks because it has 0Nm at 0 speed 

Regards,

Hakan

59

Mach4 General Discussion / Re: Mach4 Spindle At Speed, Spindle Zero Problem

« on: December 26, 2017, 05:30:15 PM »

Hi Craig,

As much as i read from their web site they say its special designed servo-induction motor and it has high positioning accuracy, it is driven by a servo drive so i dont think its a regular encoder mounted induction motor, i think they put permenant magnets in it somehow, as u know there are special motors nowadays like magnomatics.. so they modified the induction motor and make an hybrid servo-induction motor as they state.

Also i saw some videos on youtube from ctb servo, by the way they also say it has an holding torque of 17.5Nm at 0 speed of 5.5kw 12000rpm motor so it cant be just a regular induction motor.

Hakan

60

Mach4 General Discussion / Re: Mach4 Spindle At Speed, Spindle Zero Problem

« on: December 26, 2017, 04:30:56 PM »

Craig,

I think best way is to get a high torque 3000rpm servo motor and connect it to the spindle with 1/4 ratio pulley so it will have less torque but spindle will turn in 12000rpm and u can have absolute control of it. But in my current setup i can not make it because of the shape of the Zth axis, in next machine i will do that altough pulley and belt setup has its negative sides like u can not get smooth surface because of the belt vibration..

Or better than servo-pulley setup i can buy one of these new type high torque high rpm induction servo motors 

https://ctbservo.en.alibaba.com/product/60413434018-802808822/CTB_7_5kw_CNC_milling_servo_spindle_motor.html?spm=a2700.8304367.prewdfa4cf.2.49792a76dr9rjN

Hakan