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Messages - joeaverage

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781
General Mach Discussion / Re: Start Building a new CNC
« on: March 01, 2022, 10:53:21 PM »
Hi,
the UC100 is made by CNCDrive and their software is called UCCNC. If you are familiar with Mach3 you would also be happy with UCCNC.
The UC100 requires at least one CNC software, so either Mach3 (or Mach4) or UCCNC. If you stick with Mach3 then you will install a plugin
supplied by CNCDrive and that will allow you to make pin assignments and other stuff you are already familiar with.

Quote
So regardless if I choose to use the UC100 or SmoothStepper I will still need drivers for the steppers + a BOB with capabilities to connect my spindle.

Yes, re-reading your initial post I realise you don't have a G540....when I assumed that you  have one already. As you know the G540 has four stepper drivers built-in and doubles
as a breakout board. If you want bigger or better stepper drivers then a breakout board and individual drivers are required.

Craig

782
General Mach Discussion / Re: Start Building a new CNC
« on: March 01, 2022, 08:24:46 PM »
Hi,

Quote
Can someone tell me what parts are required with the USB connection and the SmoothStepper?

Really not much....

First a small explanation that may help. Machs trajectory planner produces numeric data which describe the controlled point in 1 millisecond time slices. The familiar Mach parallel port
takes that numeric data and generates pulse stream to the motors to enact the commands. Machs parallel port did a pretty good job, but it was and still is, FAR from what a PC is good at.

An external motion controller like a UC100 or a SmoothStepper takes the numeric data and converts it into pulse streams. The hardware of the controller is vastly better, faster and more
accurate than a PC is at the same job.

A UC100 is USB connected to the PC and that's how it gets the numeric data from Mach and produces the pulse streams on a DB25 socket. You could plug your G540 straight into it,
nothing extra required.

A SmoothStepper  is Ethernet connected and that's how it gets its data from Mach and it produces pulse streams onto an IDC26 pin socket that replicates a parallel port. With a IDC-to-DB25 adaptor cable
you can plug you G540 straight in, nothing extra required. The ESS actually has three parallel output ports so you could have the G540 plugged into port 1 and if you still want more inputs or outputs
you could plug simple and cheap parallel breakout boards plugged into ports 2&3 to have an extra 34IO's....if you want them.

When I changed from a parallel port to an ESS seven years ago all those extra inputs and output are a pure luxury after having to combine things cleverly with a much more limited parallel port.
For instance I have one input for each of my six limit switches and another three inputs for my home switches, for a total of nine inputs......because I've got them. Mach NEVER gets confused between
a Home event and a Limit event because they are all on individual circuits.....pure luxury, and that doesn't count the five inputs I use for a wired pendant, nor the dedicated Probe input.

Craig

783
General Mach Discussion / Re: Start Building a new CNC
« on: March 01, 2022, 06:19:17 PM »
Hi,
USB connected external motion controllers like a UC100 have been around for many tears. If you go to buy one DON'T buy a knock-off Chinese
copy off Ebay or Amazon, get the real deal or don't bother.

Most manufacturers have gone away from USB connections for motion devices. Too much latency and poor electrical noise immunity, most, including
CNCDrive, have gone to Ethernet and is much preferred.

I use an Ethernet SmoothStepper from Warp9TD, and have done for seven years. I also use Mach4 which is light years ahead of Mach3 IMHO, although
you have much experience with Mach3 and it still works OK.

Craig

784
Hi,
what is it you are trying to do? To activate or de-activate the Keyboard plugin requires a restart of Mach, so I would not of thought that was helpful.

If you are just trying to disable Keyboard jogging when Mach is minimised then I would run a script that disables the buttons individually rather than de-activating
the whole plugin.

785
Hi,

Quote
So we can say 2.2kw servo can drive the 600kg of mass with 1.79ms speed right?

No, not speed but acceleration. An 11Nm torque will cause the 600kg axis to accelerate at 1.79m/s2.

The ultimate speed will depend on the servo. What is the rated speed of the servo?. These medium inertia servos are often 2000 rpm or 1500 rpm rated.
lets say 2000rpm, then the max ultimate speed is:

Vmax= Nmax.p /60 m/s
  =2000 x 0.005 /60
  =0.1666m/s  or 10m/min.

With an acceleration of 1.79m/s2 the time taken to reach Vmax:
taccel=Vmax/acceleration
  =0.1666 / 1.79
  =0.0927 s or 93ms.

93ms from standstill to Vmax is pretty good, and my guess is that your machine will lurch around and you'll probably want to slow it down.
My machine is capable of 25m/min and acceleration of 2.7m/s2, but I slow it down to 15m/s and 1.5m/s2 and even then its still scary fast.

Craig

786
Hi,
whoops, typo in previous post; should be 14.59 x 10-4 kg.m2.

I was only a factor of 10,000 out!

Craig

787
Hi,
just seen a 2kW Delta servo, 130mm flange , and it has a moment of inertia of 14.59 kg.m2.

I took my 750W Delta and multiplied by four to come up with a guess for your servo, may be its not enough. It's still not going to change
the fact that the ballscrew vastly dominates the inertia equation.

Craig

788
Hi,


The mass of the ballscrew:

mass= 0.022. 2. PI.8000    (radius of ballscrew =0.02m, length=2m, density of steel =8000kg/m3)
   =20.1kg
First moment of inertia of a cylinder:

Iballscrew=1/2 . m. r2
   =0.5 x 20.1 x 0.022 
  =40.2 x 10-4 kg.m2

The first moment of inertia of my 750W Delta servo  is 1.13 x 10-4 kg.m2 so your 2.2kW servo will be more, much more lets guess 6 x 10-4 kg.m2

Iservo=6 x 10-4 kg.m2

The equivalent first moment of inertia of the linear axis:
Ilinear= mass. (p/2.PI)2       (p is the pitch=0.005m and mass is the linear axis mass=600kg)
   =600 x (.005/2 x PI)2
   =3.8 x 10-4  kg.m2

So the total first moment is:

Itotal=(40.2 + 6 +3.8 ) x 10-4 kg.m2
   =49.8 x 10-4 kg.m2

Very obviously, and as I predicted, the rotational inertia of the ballscrew dominates  81%, with the armature of the servo in second spot with 12% and the 600kg axis at only 7%.

This result may surprise you but because the ballscrew and the armature have to rotate SO fast while the axis moves but only slowly, the inertia is totally dominated (93%) by the rotating
components and the 600kg axis mass adds only 7%!!!!.

Angular acceleration=torque/ first moment of inertia
  =11 Nm/ 48.9 x 10-4
   =2249 rad.s-2

Converting to linear acceleration:

accellinear=accelangular.(p/ 2.PI)
   =1.79 m.s-2

or  0.18g   which is not too shabby for a 600kg axis.
The inertia ratio is:
Inertia ratio= (Iballscrew+Ilinear)/Iservo
  =7.3

So most good servo software should handle this inertia ratio well, and manual tuning will probablt not get you much extra.

Craig

789
Hi,

Quote
I asked about the oscilloscope because i think to buy one from taobao next month if i can tune the servo with it, it would be very nice because this servo driver has no auto tuning. Its a servo motor at the end there is no meaning to leave it there idle.

Its not going to help. For instance you need to monitor the error between the commanded position and the actual position.
Both are numeric quantities that cannot be displayed by a regular oscilloscope. The oscilloscope provided in the set-up and tuning software
takes those numeric values and displays them, but those value are specific to each servo manufacturer. You might say that its a software scope,
a regular hardware scope will not help.

Craig

790
Hi,
OK, so using manufacturers recommendation is good practice, but that does mean large and expensive ballscrews which will in turn require large and expensive servos,
but that's the nature of CNC.

Yes I used Auto-tune and its pretty straight forward. I did tweak the parameters manually, but its dubious that I made any improvements over Auto-tune, having said that
I did not use the scope, so it probably it not surprising that I could not secure any noticeable improvement.

The inertia ratio in my machine is about 5:1, and is very much within the 'sweet spot' for Auto-tune. At inertia ratios of 10:1 manual retuning after Auto-tune
would be common. At 20:1 I think you can forget Auto-tune, manual tuning is probably your only choice.

Quote
Also, do u think an oscilloscope will be helpful for manually tuning the servos?

I didn't bother, my machine PC is to gutless to do a good job with the software scope. If I were to revisit it I would use a more powerful development PC to run the tuning and set-up software
that would allow me to use the software oscilloscope.

Quote
i still wanna use 11nm 130mm flange servo, its worst performance is still better than open loop stepper i guess. Can i tune it by seeing the signals on oscilloscope? i never used an oscilloscope before but is it useful for this purpose?
 

I am a relative newcomer to AC servos but my experience is they far FAR FAR outperform steppers. They, in practice, seem to be rather more powerful than the specs suggest. I believe
that it because of the overload properties of servos. When a stepper overloads it stalls, no ifs or buts, it just stalls. A servo on the other hand just 'digs' in and does the job.

I you give me some numbers I will do the inertia calculation for you. I can tell you at a glance that the inertia is DOMINATED by the huge ballscrews, the 250kg axis is nothing, likely less than
5% of overall inertia.

What I need is the diameter, length and pitch of the ballscrew, any gear/belt reduction if used, and the weight of the axis and associated linearly moving components. The inertia of the servo
would be helpful, but we can make a pretty good ballpark guess on that.

Once we have the inertia equation then equation then the questions about use of the scope can be answered. If the inertia ratio is moderate then you don't really need to manual
tune....although it is instructive to do so, particularly with a scope to observe the results rather than inferring from movement data.

Craig

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