Hello Guest it is January 17, 2022, 02:13:24 AM

Author Topic: Success! Mini Machining Center under Mach3 control - Video link  (Read 331552 times)

0 Members and 2 Guests are viewing this topic.

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #180 on: April 29, 2010, 02:29:26 PM »
Doing it at the servo drive level won't work either, Tried that as well using the servo brake

Anything you see at the drive level is already BEHIND the time curve of the buffered data AND mach has no idea what is happening at the servo level movement wise so it cannot STOP the data flow out of the port.
My goal it so make the function transparent to Mach so what mach knows or doe not know would be irrelevant. What is or is not in a buffer would also not have any practical effect.

By way of example, a hypothetical scenario would go like this:

Premise:
4th axis is in 'indexer' mode connected to the A axis drive. G-code commanded position: G1 A425 The servo drive only sees A axis steps and no other.

1)Upon reaching azimuth 425, the drive reports 'position reached'
2)That signal (+5V) is used to trigger the lock ON   (** and perhaps simultaneously disable the drive)
3)new A axis steps come into the drive.
4) within 1ms (I am told) the 'position reached' line goes low and the HV to the motor come on (**IF the drive is enabled)
5) that signal (0V) released the lock (** and perhaps enables the drive)
6) Axis moves to new azimuth and the process repeats.

Other than the axis attempting to move before the lock can release, I don't see a fatal flaw in the process, but I would definitely want to know if anyone else does.


Can you elaborate more on what it is you tried at the servo level?

Offline Dan13

*
  •  1,208 1,208
    • View Profile
    • DY Engineering
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #181 on: April 29, 2010, 02:37:59 PM »
I thought you had three modes:
1. Full A axis mode
2. Indexing mode
3. Spindle mode

I don't know where this came from, but it was not from me. I don't recall ever saying 'Full A axis mode' and I really don't even know what that would be.

There is no point in getting into a semantics argument.  There are no defined 'modes' so you can call them whatever you like, but there are only two. There is an A axis and a Spindle axis. One has postion and one does not.  

Sorry, a bad interpretation of mine of your previous post ;)

Dan

Offline Dan13

*
  •  1,208 1,208
    • View Profile
    • DY Engineering
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #182 on: April 29, 2010, 02:48:42 PM »
Other than the axis attempting to move before the lock can release, I don't see a fatal flaw in the process, but I would definitely want to know if anyone else does.

Exactly! This is the main problem and especially because of the requirement to make it "transparent"  to Mach. You got to have something in Mach that would trigger just before it starts sending pulses to the 4th axis. Once it's started sending pulses to the drive it's too late to try and do something on the hardware level to unlock the brake. That is unless may be if you have a servo with an incorporated brake and some clever drive that can take care of it all.

Dan
« Last Edit: April 29, 2010, 02:51:15 PM by Dan13 »
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #183 on: April 29, 2010, 03:25:43 PM »
Here's a thought, probably not fruitful...

First, you need to know precisely how long it takes the brake to lock/unlock. 

Second, what's the pulse rate and how far does it make your 4th travel during that lock/unlock time.

Remember, your axis must also accelerate and decelerate, so it will be moving slower than the rapids rate when it starts or stops.

Now the probably useless thought:

Given that information, can you just let the servo drive catch up?  It's a function of the pulses during the lock/unlock not exceeding the follow error and causing a servo fault.  Obviously a drive that allows you to adjust that would be helpful.

Depending on your feedrates, it might be workable.  It surely would be simple if it is workable. 

Cheers,

BW

PS As you have surmised, lock is probably ok, its unlock that is touchy.
Try G-Wizard Machinist's Calculator for free:

http://www.cnccookbook.com/CCGWizard.html

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #184 on: April 29, 2010, 03:35:16 PM »
Other than the axis attempting to move before the lock can release, I don't see a fatal flaw in the process, but I would definitely want to know if anyone else does.

Exactly! This is the main problem and especially because of the requirement to make it "transparent"  to Mach. You got to have something in Mach that would trigger just before it starts sending pulses to the 4th axis. Once it's started sending pulses to the drive it's too late to try and do something on the hardware level to unlock the brake. That is unless may be if you have a servo with an incorporated brake and some clever drive that can take care of it all.
You do not have to do anything in Mach. I already know this can be done with custom firmware from at least two different vendors, so there is no need to discuss whether it is doable at all, only what approache might be best and why. This is just a dialogue and I am interested in what others have tried and what their issue were.

To addresss your comment specifically, if in theory the lock could be released instantaneously with zero latency when the very first new step crossed the drive's input terminal, then you would have to agree that everything would work just peachy, yes?

So then it is actually only a matter of timing. A servo motor driving a 4th axis with a workpiece does not instantaneously accellerate even to a low G1 speed. If for example, the actual accelleration of the axis is '*********' and we assume for the sake of argument a zero latency for the electrons flying around within the drive, then we only need consider the time to move the physical plunger in the pneumatic solenoid valve and the time it takes for few CCs of air to move thru about 5" or 1/8" tube to atmosphere. I have not measured either of these, nor do I have equipment to do so,  . .  BUT . .  it IS working now using macro commands embedded in the G-code. I started with delays in the macros and then also have used G4 delays. I have whittled those now down to nearly zero and the lock seems to be working fine. There remains a sleep of only 10 in the macro, but that is there to wait on MACH to do something, not the lock mechanism

Interestingly, it has occurred tome as I am typing that I have a video of the entire cycle which I could simply count the number of frames needed and get at least a rough idea of the latency. Look here and observe the red indicator light which signals that the lock is engaged.

http://www.youtube.com/watch?v=B8l6lH4ydd4

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #185 on: April 29, 2010, 03:45:37 PM »
Here's a thought, probably not fruitful...
First, you need to know precisely how long it takes the brake to lock/unlock. 
Second, what's the pulse rate and how far does it make your 4th travel during that lock/unlock time.
Remember, your axis must also accelerate and decelerate, so it will be moving slower than the rapids rate when it starts or stops.
The only part of this that is not 100% accurate is where you say it may not be fruitfull. You are exactly on the mark.

Now the probably useless thought:
Given that information, can you just let the servo drive catch up?  It's a function of the pulses during the lock/unlock not exceeding the follow error and causing a servo fault.  Obviously a drive that allows you to adjust that would be helpful.
Depending on your feedrates, it might be workable.  It surely would be simple if it is workable. 
This is my conclusion as well. By both theory and observation. You give me another idea of how to quantify. The Dugong drive has a real time Encoder DRO in its tuning software which can be active while the drive is ruining . .  a very neat feature that I have used many times. I could simply monitor the error during program execution. I don't know why I did not think of that  :-[. . .  so . .  I'll just blame Dan  . . . Dan, this is all your fault . .  ;)
PS As you have surmised, lock is probably ok, its unlock that is touchy.
Batting 1000

Offline BR549

*
  •  6,952 6,952
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #186 on: April 29, 2010, 08:24:18 PM »
"THE "problem we ran into was that the servo BRAKE as fast as it is was way too slow in releasing the brake to prevent the servo from erroring on position error.The next moves were already at the drive BEFORE the brake could react. You have to be able to regulate that data stream of pulses to alow time for the brake to react BEFORE it gets the next move command. That fact that we had high resolution servos that require high step feedrates may have contributed to the problem 45000 steps per inch.

At full speeds that is not a lot of time in between pulses to activate the brake(;-)

Now sometimes it would work fine depending on the code and other times it would error depending on the code. TO me if it cannot operate 100% of the time it is a bust.

OF course IF you used a special buffered input servo drive THEN it may work on simple A axis "non interpolated" moves as the drive MIGHT be able to buffer the data stream enought to allow the brake time to release before it errors on position.

BUT THEN you have created a unique realtime mini drive system that the average user does not have. (;-)

Like I said earlier it  worked  fine in a reatime enviroment as the controller (PCcontroller or motion card) can regulate the closed loop data stream.


BUT hey maybe you have figured out a better mouse trap, GO FOR IT and let us know how it goes.

By the way good job on the 4th axis setup. Have you looked at the system that TORMACH uses with their 4th axis indexer/lathe set?

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #187 on: April 30, 2010, 02:06:45 AM »
OF course IF you used a special buffered input servo drive THEN it may work on simple A axis "non interpolated" moves as the drive MIGHT be able to buffer the data stream enough to allow the brake time to release before it errors on position.
It had not occurred to me that you were trying to do this on a linear axis! That would be a LOT more crucial since you would be cutting metal during the period. It is impressive that you could get that to work at all. My application is strictly 4th axis and within that, only non simultaneous A axis rotations, with no cutting going on during the period. Following error can be very high allowing, as Bob said, the servo to fall behind and catch up after the Lock released. This would have no practical effect on the machining phases because the period in question (possible fall behind) would strictly be at the beginning of positioning moves between cuts. I have no intention to have spindle locking active during simultaneous multi axis cutting. If fact, I specifically designed a double reduction belt drive for that purpose. 

It would be necessary for any servo drive to buffer the input stream to some degree in order to track following error, I would imagine. However, I can see where a fixed small following error that some drives have together with a high res encoder would leave precious little time for releasing a mechanical lock.

BUT THEN you have created a unique realtime mini drive system that the average user does not have. (;-)

I am going to try and avoid this if possible, but I am only looking at drives that have field flashable firmware. If there is no other alternative, I could provide a custom firmware for certain drives, if not the entire drive. I am already be providing the swapaxis hardware, TTL splitter, and solid state relay.

Offline simpson36

*
  •  1,369 1,369
    • View Profile
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #188 on: April 30, 2010, 02:08:23 AM »
By the way good job on the 4th axis setup. Have you looked at the system that TORMACH uses with their 4th axis indexer/lathe set?

Is this the one where they have an entire small lathe that is mounted on the mill table?

Offline Dan13

*
  •  1,208 1,208
    • View Profile
    • DY Engineering
Re: Success! Mini Machining Center under Mach3 control - Video link
« Reply #189 on: April 30, 2010, 03:16:15 AM »
I don't know why I did not think of that  :-[. . .  so . .  I'll just blame Dan  . . . Dan, this is all your fault . .  ;)

Huh... ??!!  ???