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Mach Discussion => General Mach Discussion => Topic started by: tstbeyaz on January 08, 2011, 10:52:31 AM

Title: Why is there no effort for the true closed loop control on the mach3 level
Post by: tstbeyaz on January 08, 2011, 10:52:31 AM

I am building machine tools and have access and make use of   Heidenhein itc530 (germany) , Fanuc 18imB (japan), sytnec (taiwan) , LNC (China), GSK (china).  All use the true close loop control such as following error and velocity error in the Gcode level as standard. I am well informed that Mach3 is open loop controlled, But I wish that the MACH3 software come to the level of above with the help of improving technologies such as external motion hardware and availibity of very fast interconnection standards such as USB3.0 (5gbps) and sata III (6gbps).

What are the main concerns?

- Unreliability of USB3.0 and sataIII for real time control and feedback

-Development effort is huge that a 1-2 man team can not handle.

- Is the path too long (the feedback should come first from the servo to the motion control hardware and then transferred to the Mach3. ). How does heidenhein do this with a celeron 400Mhz PC and a motion controller?


Does a concept exist towards thşs implementation for future maybe in 3-4 years.  Or this is totally another type of business or method that does not/ can not belong to the future of Mach3.

Best regards.

tstbeyaz
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: BR549 on January 08, 2011, 12:00:09 PM
ALL those controllers use an independant MOTION controller for closing the loop. Some of them even run 2-4 processors JUST to keep up.

EVEN then NONE of them do axis corrections to correct a falut. They are just using a PID to help the servo keep up with the motion data stream. Let that servo LAG far enough and it just faults ands stops the controller.

You can have that with steppers in MACH. Rogers machine sells the board and provides the plugin to drive it. WORKS VERY WELL

You can have that same feature in mach by running a digital servo drive( the loop is close in the drive ) OR use a motion controller JUST like the big boys and clos it on the MC card.

NONE of them cost $175.00(;-)

IF you want Free closed loop PC control you have EMC2(;-)

Take your pick, (;-) TP
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: DaOne on January 08, 2011, 12:37:25 PM
I think the main reason why we don't have closed loop is it would require a major rewrite. I could be wrong but I think running on windows is the biggest problem. Timing issues are most likely the culprit.

Best bet is a hardware controller such as a galil. That closes the loop in the hardware control and will give you the same results as a real control.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: BR549 on January 08, 2011, 12:54:58 PM
YEP you have many that can do the job.

Galil
Dsmpmc
Mesa
Kflop
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: tstbeyaz on January 08, 2011, 02:15:49 PM
I think I have missed the point that Kflop/Mesa/Dsmpmc/galil are more than smoothsteppers. It is good news so that I may start to investigate and try some setups thncoder inpute ones above. Do these cards have a seperate encoder input,   Do they function basically so that they get the encoder data from the servo drive without requiring to install additional encoders other than the ones readily installed at the back of servomotors. I believe I must investigate how they communicate with the servodrive control. Any comments which one has broad support for common servo drives from Fanuc/alfaseries,  Panasonic and Mitsubishi.

What abaout look ahead buffer, and increasing and decreasing the velocity dependant on the path and the inertia/power rating of the system. cancelling the jerk (ensuring that the derivative of the acceleration is not sharp to avoid vibrations) . How are these tasks coordinated (through mach3 or motion control card or mixed handling)

tstbeyaz.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: BR549 on January 08, 2011, 02:44:37 PM
Mach has a simple bang bang trapazoidal planner you get what you get.

Most MC cards except the servo encoder signal and close the loop at the MC card.

As far as advanced motion control like you want?? I dought it. Most are used to control a Dumb servo amp that excepts analog +/-10v.

Most simple MC's just emulate the input signals they are given.  THE vey high end ones can convert the simple input into a complex output based on parameters like you wanted.

BUT that is why high$ controllers are high$$$$$ controllers.

Just a thought, (;-) TP
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: rcaffin on January 09, 2011, 06:14:23 PM
Quote
- Unreliability of USB3.0 and sataIII for real time control and feedback
I don't think the reliability of USB or SATA is the issue. It's the UNreliability of Windows that is the biggest problem!

Some other points should be made here as well.

The older closed-loop control was created before the n86 chips reached their current level of speed. They relied totally on dedicated hard-wired logic chips to do the motion control for servos: there was no other way to get the control for linear servo motors.

Mach is, to some degree, based on the concept of a stepper motor. You do not (really) need closed loop control with steppers: either they have the power to drive the axes, or they don't. Feedback will not change this.

Working forward from the idea of steppers, some drive units for linear servo motors now emulate a stepper. You feed them 'stepper pulses' and they convert that to DC (or AC) servo drive. If the system is working OK all is well; if the servo drive cannot cope it flags a fault and Mach3 stops. This is conceptually the same as a stepper system.

You are right in your statement that SmoothStepper has nothing to do with this. In this context it is just a logic interface, nothing more.

Now, going on to smooth changes in acceleration (3rd derivative) - that is more difficult. If it was really necessary then customer demand might lead to Mach including it. But normally you get this for free from the power amplifier: it cannot produce instant acceleration in practice, as there are peak power limits. So for most people there is no need for Mach to do this.

Cheers

Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: kf2qd on January 10, 2011, 05:46:05 PM
Plain and simple - COST. Mach is a very nice controller at a very inexpensive price. It has the features that are appropriate for its cost. If you need these other features - Closed Loop Motion - you will have to buy (or invest the time and use EMC2) a controller at a higher price than a 'hobby' controller. Mach requires a minimal investment in hardware and thus you trade off some options - fully closed loop - for lower cost. Some have been able to use it successfully in production environments, but it is still a "hobby" control.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: rcaffin on January 10, 2011, 05:53:50 PM
Some have been able to use it successfully in production environments, but it is still a "hobby" control.

A bit more than 'hobby' today. One can do serious production with it IF you know how.

Cheers
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Promech on January 12, 2011, 07:09:58 PM
I retrofited am Emco lathe using Mach 3 and it works quite well in an industrial environment.  My opinion is that if some aditional money is spent in industrial components such as servos, VFD and a PLC then one can come up with a decent system.  Industrial grade servos allow for closed loop (with their drives) and homing using their index pulse.  A VFD with braking resistors allow for good spindle control and the PLC is necessary for processing information from sensors, generating alarms and controlling periferal devices such as the hydraulic unit, tool changers, part catchers, bar feeders etc. 
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Tweakie.CNC on January 13, 2011, 05:08:50 AM
Some have been able to use it successfully in production environments, but it is still a "hobby" control.

A bit more than 'hobby' today. One can do serious production with it IF you know how.

Cheers



I second this, in fact there are a great number of people using Mach3, in it's present form, for serious production.

Providing a CNC system is designed and built reasonably well there really is no need for closed loop operation - yes it would be nice but accurate, reliable and repeatable work can be achieved without closed loop.

Tweakie.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: DaOne on January 13, 2011, 05:29:19 AM
I don't really understand why it matters to have mach close the loop anyways. I might be wrong but if the loop is closed on the hardware controller card there should be no difference. As long as the card is capable of issuing an alarm when the encoder to command error reaches a set threshold. On most real controls it works this way. It does try to speed up an axes to catch up. That would cause other problems. What they do is command an external e-stop when an out of sink error is detected. About the only thing it cant do is show a dro for the encoder if the servo power is turned off and the machine is in manual mode however you can always display that encoder in mach and use a script to set it to what it reads when you switch the servos back on. Also you cant show exactly where you are if you push your servos beyond there abilities and get an alarm but once again... you can always show the encoder in a dro.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Tweakie.CNC on January 13, 2011, 05:51:54 AM
I agree and anyways if a position error occurs and is subsequently corrected (by closed loop) there is a good chance that the job has already been spoiled (obviously this, to a certain extent, depends on the 'steps per' or resolution of the machine). The secret to success is no error in the first place.

Tweakie.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Promech on January 13, 2011, 06:20:48 AM
With industrial servos the drive can display the position error in real time  (the difference between the encoder feedback position and command value).  In my initial trials these errors show mostly in acceleration and desceleration movements (G0) but when cutting is initiated with G01, G02 and G03 the system has had time to catch up.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Jeff_Birt on January 13, 2011, 09:13:01 AM
Quote
I don't really understand why it matters to have mach close the loop anyways.

Very good question! Much of the 'closed loop back to the PC' is just sales hype. The only real advantage of having some form of real time feedback to the planning stage of the CNC control is to allow all axis to slow to match a slow axis. If you machining a multi-thousand dollar part this might be very, very important to you as it could be the difference between a scrapped part or not. For the most part though you won't have a 'slow' axis unless you have really messed up in your programming.

So that begs the question, what is closed loop? Stepper motors are designed to move in discrete steps so as long as you don't overload them they will always be where you tell them to be. Servo motors on the other hand must have an encoder on them to tell the servo control the angular position of the motor. The control looks at the pulses coming back from the encoder and changes the signal sent to the motor. For example when a servo is standing still it is actually being driven back and forth very quickly. So, the upshot of this is that if you have servos you already have a closed loop system. It is closed to the servo control which is fine in 99% of cases.

More advanced motion controls like Galil, DSPMC, etc can actually make use of the encoder signals to do electronic gearing and all the fancy stuff that the big name CNC controls do. The reason they can do so is that all real time the motion control stuff is done in dedicated hardware designed for that purpose. PCs stink at real time motion control but they are great at reading big CNC files, path planning, and user interfaces. Dedicated motion controllers suck at reading large files, the complex path planning that goes with then and user interfaces but they are great at motion control. Using PC + a motion control card gets you the best of both worlds the big name CNC control guys figured that out more than a decade ago.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: kf2qd on January 13, 2011, 02:28:30 PM
Seems that some folks are just finding a way to say that closed loop is a waste of time.

Closed loop means that the machine is always compensating for position errors. THose errors must remain small, and if they get very big then there is a problem and the control can shut things down as this is a fault situation. Open loop like mach can have huge errors because of hardware failure and never know (or care) that those errors exist. Closed loop takes more computing time than does open loop, and is well within the capabilities of a PC running Win2k or XP. I have used controls running both. The software is more complex and the hardware is more complex. The motion control software on a closed loop can never miss a cycle or the whole machine is out of position. Many have dedicated encoder circuits and require Analog to digital converters for each axis. And they will be more accurate and repeateble and at higher speed. And they cost money.

Mach requires relatively simple hardware and can work with some rather sophisticated hardware. BUT it is open loop and has no way of sensing when the move is not correct. It just send a string of pulses and expects that the drives/machine will keep up. If the drives don't keep up it has no way of knowing how much out of position the hardware is.

Closed loop and open loop are like trying to control the mouse on a computer. If you can see the screen it is easy, yopu instantly compensate for any problems with how you move teh mouse. Open loop is like trying to tell someone over the phone how to do the same operation. You can't see what is happening and can only hope that things are enough identical that they do the same thing you are telling them.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: rcaffin on January 13, 2011, 03:09:34 PM
Closed loop means that the machine is always compensating for position errors. THose errors must remain small, and if they get very big then there is a problem and the control can shut things down as this is a fault situation.
Quote
BUT it is open loop and has no way of sensing when the move is not correct.

While true that correct machining requires that any position errors be corrected very quickly, the implication that a CNC system based on Mach does not have this sort of feedback is WRONG. You have to look at the whole CNC system, not just the Mach part.

In any CNC system there are several parts all working together, as Jeff has just written. In a Mach system the servo drive does the feedback part, with Mach relying on the servo drive to flag the error if one happens. In older more expensive systems the distribution of work may be different. Big deal.

But focusing on the distribution of responsibilities misses the entire point. No matter how the system is designed, if any significant errors start to occur the part is scrap. If you drive any sort of system so hard it goes into a fault situation then YOU at at fault for misusing it. Don't expect the software to compensate for that.

Some of this misunderstanding is probably due marketing spin from the vendors of the older more-expensive systems. They don't want potential customers thinking that the newer designs are as good. Haven't we seen this before?

Cheers
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Tweakie.CNC on January 14, 2011, 02:02:30 AM
kf2qd

Quote
Seems that some folks are just finding a way to say that closed loop is a waste of time.

Just to pick up on this one point - "If you have a good machine, of small size, closed loop is totally unnecessary". If you doubt that go to my website and take a look at some of the stuff I have made. OK I can improve on all of it by using higher resolution, smaller cutting tools etc etc but no improvement would be gained by me using closed loop.

The debate between servo's and steppers will go on forever and it is "horses for courses". Mach has proved to be good for driving both.

Tweakie.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: skunkworks on January 14, 2011, 09:58:41 AM
More advanced motion controls like Galil, DSPMC, etc can actually make use of the encoder signals to do electronic gearing and all the fancy stuff that the big name CNC controls do. The reason they can do so is that all real time the motion control stuff is done in dedicated hardware designed for that purpose. PCs stink at real time motion control but they are great at reading big CNC files, path planning, and user interfaces. Dedicated motion controllers suck at reading large files, the complex path planning that goes with then and user interfaces but they are great at motion control. Using PC + a motion control card gets you the best of both worlds the big name CNC control guys figured that out more than a decade ago.

*Hi - my name is sam and I am an emc person.  hi sam  ;)
Emc2 actually does that.  It uses a realtime extensions to the linux kernal.  The external hardware used by emc is 'dumb' in effect.  All the hardware does is count encoders really fast, output high frequency pwm, switch i/o and or output high step rates.  No motion control is done in it.  So - you don't need expenive hardware to do real closed loop.  Motion control, trajectory planning and such is all done in the pc.  That is why emc doesn't work with the motion cards like galil - emc wants to be the one in control.  Internally the stepper setups are actually closed loop.  It is just that the step generator feeds the info back into the motion control itself.  Some have actually unhooked that virtual connection within emc and hooked in encoders as feedback.  (that is also the reason why stepper machines that are not configured correctly will get following errors with emc2 - throws people off initally) ;)

As far as 'why you would ever want true closed loop'
My following error is .00016" peak right now - what is yours? ;)
I can estop the machine without rehoming.
while the servo drives are disabled I can move the machine around without it loosing its position.
The machine will go into estop if my following error is greater than the amount I have set.
The dro is displaying actual machine position - not what it thinks the position is.
(I am sure there is more but it is early)

BTW - because all the big stuff is done in emc - electronic gearing can be done also - so rigid tapping, gear hobbing and the like are possible.  (gear hobbing is sort of a expert level configuration though... ;))

emc was built on the philosophy 'sense, model, act'

Mach is great software.  I just like to expand the conversation.

sam
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Jeff_Birt on January 14, 2011, 10:08:21 AM
Quote
closed loop

Closed loop is closed loop, there is to 'real' or 'fake' about it. The implementation may differ from system to system but that does not make one implementation more 'real' than another.

Quote
I can estop the machine without rehoming.
while the servo drives are disabled I can move the machine around without it loosing its position.
The machine will go into estop if my following error is greater than the amount I have set.
The dro is displaying actual machine position - not what it thinks the position is.

You can do all of these things in Mach as well. EMC approaches things a bit different than Mach and does a few nifty things itself that Mach does not. But, motion control done on a PC (real time OS or not) will always be inferior to motion control done via a motion controller in dedicated HW. This is not because EMC or Mach is deficient, it is a limitation of the PC hardware.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: skunkworks on January 14, 2011, 02:09:34 PM
I am not that elegant on getting my point across and this is just my thoughts.
when I say 'real closed loop'  I think of real machines like fanuc or whatever.  The machine control commands a motion - reads back its speed/vel calculates  and adjust accordingly - this is how emc does closed loop.

step servos or steppers machines don't do that.  Emc or Mach blindly sends out pulses that relate to how the control wants the motion to go.  Yes - you can setup the step servos so that if they loose position - the machine will estop (rogersmachine interface gets you at least position - if I understand it right)...  but I don't consider that 'true close loop' as the control doesn't know its position at that point and isn't reading back and constantly correcting while moving.

I kinda like the mouse analogy above..

I don't know how mach handles the more expensive solutions..  (Galil, DSPMC, etc)

This was a quote from a motion control expert..

'I suppose PC hardware is inferior above some sample rate (maybe 10-20 KHz) but unless you have very exotic CNC mechanics those sample rates wont buy you anything.'

sam

(we might have to agree to disagree :))
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: ASC on January 14, 2011, 02:11:04 PM
Had to pipe in on this one!

Using Mach I've had no problem getting resolutions of 5 uM or less using open loop steppers.  The real key is to have an extremely rigid machine with tight smooth motion and a good microstepping driver.

That said, on the closed loop end, I've used mach to supply the motion signal to copley servo drives and reached resolutions of 500 nM.  Mach supplies the control interface and trajectory planning and the servo drive and encoder do the rest.  Mach may not be closed loop but the driver its controlling sure is.
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: Jeff_Birt on January 14, 2011, 04:17:28 PM
Sam, I'm not trying to give you a hard time. Nor am I saying that what EMC does is not great. There is just a lot of mysticism related to 'closed loop back to the control'. All I want to do is get the facts out and let everyone decide what type of control they want/need.


Quote
step servos or steppers machines don't do that.  Emc or Mach blindly sends out pulses that relate to how the control wants the motion to go.  Yes - you can setup the step servos so that if they loose position - the machine will estop (rogersmachine interface gets you at least position - if I understand it right)...  but I don't consider that 'true close loop' as the control doesn't know its position at that point and isn't reading back and constantly correcting while moving.


You have the general idea, but you don't quite right. EVERY servo system knows exactly where it is, that is what the encoder tells it. EVERY servo system is never exactly where you tell it to go, there is always a bit of error. If the error is too great you get an error signal. Simple servo drives keep all the encoder information to themselves but will tell the controller if the error is too great. The important part is that they go where they are told or an error is generated, the controller that is telling them where to go knows exactly where they are unless an error occurs. If an error occurs than your part/fixturing is likely scrap so it does not matter either way.

More complex servo controllers can share the encoder position with the control logic and the control logic can 'sync' multiple axis movements together. So, if one axis is lagging behind everything can slow down and you might be able to avoid an error. For 99.99% of cases this ability to 'sync' axis' together dynamically is superfluous. Why? Well if what you are doing is bogging down an axis to the point of tripping an error then you have most likely ruined the part and/or tool anyhow. For some operations like threading it is important to synchronize the axis' movement with the spindle. This really only requires an index pulse from the spindle for single point threading. For more complex operations you need more synchronization, but again that is outside what is really needed for the vast majority of cases.

Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: RICH on January 14, 2011, 05:19:34 PM
I will comment that this is an interesting discussion but you may never get an answer to the original question.

Art gave some thoughts some time ago relative to EMC and Mach and I will post a link if I can find it.  I think, as Jeff has pointed
out, that many users are miss-informed on their understanding of closed loop. Tell that to somebody that spent a lot of money and realy didn't get what they expected once informed. ;)

RICH
Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: rcaffin on January 14, 2011, 06:02:56 PM
Emc or Mach blindly sends out pulses that relate to how the control wants the motion to go.
Actually, that is what the motion planning part of other systems do. They send signal to the lower-level motor control sections. Does it matter where the error sensing is done? Once you get near to an error state you are dead anyhow.

Quote
Yes - you can setup the step servos so that if they loose position - the machine will estop (rogers machine interface gets you at least position - if I understand it right)...
Correct up to a point. If I estop at full speed I will lose position. Instead I 'pause', which is the right way of doing things. But if I estop, something has gone WRONG.

Each servo amplifiers has a magnetic breaker. It that trips then I also lose position. But again, I have done something WRONG, and may have wrecked the job or need to completely restart a new piece.

Quote
but I don't consider that 'true close loop' as the control doesn't know its position at that point and isn't reading back and constantly correcting while moving.
As long as I operate in a conservative regime, Mach DOES know where the control point is. It is where Mach has told the INTELLIGENT servo amplifiers to go. If they can't obey that order they flag a fault.

Mind you, I think Rich has hit the nail on the head:
I think... that many users are miss-informed on their understanding of closed loop. Tell that to somebody that spent a lot of money and really didn't get what they expected once informed.

Nothing quite as upsetting as finding out later that there is a cheaper but equally effective solution! Happens to all of us. Everyone needs to design and build a couple of CNC systems before they get it right...  :-)
(I'm on my 3rd or 4th.)

Cheers


Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: tstbeyaz on January 15, 2011, 01:53:24 PM
Closing the loop in the Gcode layer is for me important, Why?,
let me describe you my dream how it should function. ex: 6000 lines ahead.
The software should anaylze the whole 6000 lines and build up mathematically defined spline
segments. For example gathering 16 gcode lines to a bezier curve, for a simpler explanation
just think abaout the vector drawing in corel draw, when you draw a line corel draw connects the points
through a spline curve which has analog continiuty and can be defined with maybe 3 or 4 constants.

a simpler spline p(x)= ax^3+bX^2+cx+d  , these coefficients a,b,c,d are calculated in real time in dependance of
the given follow error by the user. EX: in pick and place applications the user can increase the trajectory follow error and
decrease the follow error just at the end of the (last point of the polynomial function).For surface fini sing according to roughing or finising passes,
the user can define lower or by demand higher follow error for roughing and very low follow error for finising.

After you have a,b,c,d  you dont deal with the gcode data anymore, your polynom sends the position data to the servo,
But here I also think abaout an important connection, the polynom data is so optimized that the sppeeds and acceleration are regulated in real time,

think abaout a life feedback that servo tells the controller, hey I am %80 loaded you can drive me more severly, or hey my decceleration is %73 in capacity you can do more decceleration.

In this art of regulation you get an error only when there is hardware fault. Why I am telling this. Think abaout a Gcode program that has many small curves.

Everytime I run such a programm I never reach the feedrate that I have given, Maybe %10 of the feedrate is there, because of inefficient acceleration decceleration profiles.

The polynomes can be chosen according to the computing power. maybe p(x)=ax^3+bxsin(wx) or a logaritmic one to smoothen the velocity and accelerations curves and speed up the responsiveness of the whole system.

Naturally an additional computation should be there so that if we have defined 200 polynoms in 6000 lines of gcode , the endpoint of each polynom shuold be the first point of adjecant polynom function.


The computational overhead is with a 8 core i7 not a problem. A 100$ GPU card with from Nvidia (ex:CUDA interface) can also compute simultaneously the polynom coefficients.

A regular GPU we all have has 96 computing cores. and the matrix multiplication is peanuts for the GPU.


What do you think abaout spline interpolation and servo regulation for a higher dynamic.Very important is the inertia feedback from the servo if possible.

The fault signal is not enough between the servo and gcode interpreter,  There should  be a dynamic regulator for the inertia reserve,power demand reserve, braking reserve, regenerative reserve.

Any ideas?

Title: Re: Why is there no effort for the true closed loop control on the mach3 level
Post by: rcaffin on January 15, 2011, 11:50:41 PM
let me describe you my dream how it should function. ex: 6000 lines ahead.  The software should anaylze the whole 6000 lines and build up mathematically defined spline
segments. For example gathering 16 gcode lines to a bezier curve, for a simpler explanation
Two very major problems with this.

* The first is that this is high-level planning, which Mach is perfectly capable of doing if that was what the market wanted. This sort of planning is totally disconnected from the 'feedback' issue.

*The second problem is that I do NOT WANT Mach doing that sort of thing, EVER! If I program the control point to go to a series of locations, that is what I want it to do. I do NOT want some smart-alec programmer who has absolutely NO idea of what I am machining trying to alter what I have programmed ! ! ! ! !

Quote
EX: in pick and place applications the user can increase the trajectory follow error and
decrease the follow error just at the end of the (last point of the polynomial function).
Yeah, sure but pick&place is NOT CNC machining. Yes, I have designed and built successful P&P machines. And Mach is NOT designed for P&P machines. (Read the manual.)

Quote
think abaout a life feedback that servo tells the controller, hey I am %80 loaded you can drive me more severly, or hey my decceleration is %73 in capacity you can do more decceleration.
I do NOT want the machine changing what I have deliberately programmed into it. NEVER. I may be running the machine slowly because the material I am machining will melt at a higher speed. You can think of other reasons for me.

Quote
In this art of regulation you get an error only when there is hardware fault. Why I am telling this. Think abaout a Gcode program that has many small curves. Everytime I run such a programm I never reach the feedrate that I have given, Maybe %10 of the feedrate is there, because of inefficient acceleration decceleration profiles.
In that case you may be using the wrong machine. Don't expect software to compensate for an inadequate machine. That's a bit like trying to put sophisticated fault-tolerant software on top of Windows98 ....

Cheers