Is anybody interested in phasing axes?

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Last month there was a thread
http://www.plctalk.net/qanda/showthread.php?t=38904
A solution was found but I think it was very complicated.

Is anybody interested in seeing an example of phasing? I have a simple example that shows simple gearing and phasing complete with program and graphs. The documentation is almost complete however if I complete it that would ruin some of the fun. When phasing you usually want to do it a quickly as possible but it can't be done too quickly because the slave may exceed a velocity and acceleration limit. Sometime there is a option to phase positive or negative. How does one know which way to go so the phasing is done in the minimum distance? There is more to 'simple' phasing than what you might think.
 
Hi, Using a Delta Tau PMAC i would FRAX the axes together. Are you talking in general terms ?

Cheers
 
What does FRAX do?

In simple terms phasing could mean getting two wheels or motors that rotate from 0 - 360 degrees so they are same angle. In a recent thread the phasing was necessary to make up for slippage.

Tell us more about the FRAX instruction. What does FRAX stand for? What parameters does the FRAX instruction require. Our phasing command is called phase. It requires a master offset and and the distance over which the master position is offset. We copied the IEC specification only I believe we simplified it a bit. Phasing can be done with a superimposed move. We have a more mathematical approach that provides the same results.

Can you get graphs of what the FRAX instruction does?
 
Hi I misunderstood the question. FRAX is used to link 2 axes toether and match speeds/ angles etc (follower type applications).

I will look up the phase matching stuff later when i have a chance

Cheers
 
When phasing you usually want to do it a quickly as possible but it can't be done too quickly because the slave may exceed a velocity and acceleration limit. Sometime there is a option to phase positive or negative. How does one know which way to go so the phasing is done in the minimum distance?
In my simple mind it would be just like transitions in curves.
Transition Types

This command provides the following transition options:
  • Seek (0)
    The axis will move toward the requested profile using the Max Speed and Accel Rate. When the position and velocity of the axis come close to the position and velocity of the profile, the axis will "lock" onto the profile. Use this option to get to the requested profile quickly and smoothly.

    Reach (1)
    The axis will move toward the requested profile using the Max Speed and Accel Rate. When the position reaches the position of the profile, the axis will "lock" onto the profile. Notice that this option does not require that the velocities be close when it locks on, and therefore may cause the axis to jerk. Use this option to get to the requested profile as quickly as possible.
  • Superimposed (2)
    A trapezoidal or S-curve move using the Max Speed and Accel Rate will be superimposed onto the requested profile such that the axis will reach the profile. Notice that since the move is superimposed onto the profile, the axis will not necessarily move at the specified speed and acceleration, but rather at the sum of the speeds and accelerations from the requested profile and the superimposed portions of the move.
This method will always guarantee that the axis will lock on to the requested profile, even if the Max Speed and Accel Rate are slower than that of the profile. The time it takes to lock on will be based on how far the axis position is from the requested profile and on the Max Speed. For example, if the axis is at 3, the profile is at 9, and the Max Speed is 6, it will take roughly one second to lock on. The "lock-on" of the Superimposed method will be as smooth or smoother than Seek.

I think thats what we want to do but how do we get there?
 
Last edited:
cjd1965 said:
Hi I misunderstood the question. FRAX is used to link 2 axes toether and match speeds/ angles etc (follower type applications).

I will look up the phase matching stuff later when i have a chance

Cheers
cjd1965, I think we are talking about the same thing.

CharlesM, the transition commands are much more sophisticated than the much simpler phase command I am referring to. You can connect to our controller on the internet and see what I am talking about.
 
Hi I misunderstood the question. FRAX is used to link 2 axes toether and match speeds/ angles etc (follower type applications).
If I remember correctly FRAX is for feedrate axis. It controlles which axis in a coordinate system controls the feedrate of the coordinate system. So if you have X,Y,Z axis and you give it a FRAX,X then The axis would move together with X going its feedrate and the others would adjust thier feedrate to end at the same time. This would be a Sync Move in the RMC world.

CharlesM, the transition commands are much more sophisticated than the much simpler phase command I am referring to. You can connect to our controller on the internet and see what I am talking about.
I will take a look.

edit.
I can see it running but a nice plot would be great. I would setup a plot to show the phase take place. I would also add the program step into the plot config.

Would anyone else like to watch it run? It's real easy.
 
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Off topic

CharlesM said:
If I remember correctly FRAX is for feedrate axis. It controlles which axis in a coordinate system controls the feedrate of the coordinate system. So if you have X,Y,Z axis and you give it a FRAX,X then The axis would move together with X going its feedrate and the others would adjust thier feedrate to end at the same time. This would be a Sync Move in the RMC world.
We were told about this command by a Delta Tau customer so we implemented the same thing with some added capabilities.
We calculate which axis is the most limiting automatically. You don't need to specify it. During operation the most limiting axis may change depending the the distances to travel relative to the axes' speed and acceleration. Then all the other axes are synchronized to the most limiting axis.

I plan to develope and syncrhonize move like command but this one would make sure the motion in 3 dimensions would be limited to the desired speed and acceleration. There would be one velocity and acceleration for all the syncrhonized axes. This would mean that:

TargetVelocityxyz(t)= sqrt( velx(t)2 + vely(t)2+velz(t)2).

This assumes the axes are in cartesian coordinates. One needs to know the geometric relationships between the axes to do this in a general case.

Phasing is much simpler than syncrhonized moves.
 
Pmac

It is correct that FRAX is for 'Feed Rate Axis'. We do a lot of follower applications here and provided you specify the motors I variables correctly it is very simple to do with FRAX.

As far as making motor A match motor B physical phasing i have attached a sample from the PMAC manual, so it looks like there is no command to actually do this directly. It maybe be useful for tips to the intial question (I have never had the need to try and do this)

Cheers
 
Peter you have some good examples here. You have not added any in a few days are you done or just looking for more ideas?

new_examples.JPG
 
I am taking a breather

Export the programs you want and save them. I put the programs in the RMCTools directory and the projects are in sub directories. Notice the TunePIDDDFF. It will quickly and accuyrately calculate the gains for your current simulator settings with the auto tune procedure.

I did a lot of that on a weekend while sitting on my patio. I have recently run into problems where other people want to play with the on-line rmc70 and they have priority. I have another controller that I can play with. I just haven't updated the on-line controller with my latest user version of the project.

Note, the Flying shear doesn't work with the way the axes are set up. I need to find ways to have each program do more configuration of the axes rather than just use one configuration for all examples. I am finding out that one axis configuration will not work well for all programs.

I also need to make a LineSpeed/Radius winder example. Since we can support huge cam tables we can pretty much change the gear ratio as a function of how much material has been wound or peeled off a block. This allows tightly coupled control. None of the dancer stuff is required. I have a customer getting this to go now. We may add a command that does this application. A command would not require the cam tables.

I still have the postion force examples to make too. On rmc150.deltamotion.com I will implement a 4 corner press and more sophisticated axes coordination examples.

No one wanted to know about phasing. There is more to it than what is immediately obvious. I didn't want to ruin the fun in case someone actually wanted to cover the topic. No one seems to care so I will finish it off too. It would make a good Friday night math quiz.

I have been busy doing other far out geek stuff.
Did you see the latest Hydraulics and Pneumatics?

A 6 degrees of freedom motion platform controller example would be good too.
 
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Originally posted by Peter Nachtwey:

I also need to make a LineSpeed/Radius winder example. Since we can support huge cam tables we can pretty much change the gear ratio as a function of how much material has been wound or peeled off a block. This allows tightly coupled control. None of the dancer stuff is required.

You assume much, young Jedi.


Originally posted by Peter Nachtwey:

No one wanted to know about phasing.

There is an interesting duality on this website. Quite often when a question like this comes up the answer is 'why worry about that; just get a motion controller to do it'. But then we can find post like this one that would, at least outwardly, seem to show how to accomplish this outside of a motion controller. Is the intent to show that it is unreasonable to attempt in a plc without a motion cntroller by providing an example?

Keith
 
kamenges said:
You assume much, young Jedi.
Yes, the feed forwards and gains must be tuned very well.

There is an interesting duality on this website. Quite often when a question like this comes up the answer is 'why worry about that; just get a motion controller to do it'.
The question is still the same whether you are using a motion controller or not. When should you phase forward and when should you phase backward.

But then we can find post like this one that would, at least outwardly, seem to show how to accomplish this outside of a motion controller. Is the intent to show that it is unreasonable to attempt in a plc without a motion cntroller by providing an example?
Keith
There are two issues here. Phasing forward or phasing backward, or whether one can synchronize axes at all. There was a previous thread where phasing was much more complicated than it should be. Linear phasing should be easy and it usually is.
 
Peter Nachtwey said:
No one wanted to know about phasing. There is more to it than what is immediately obvious. I didn't want to ruin the fun in case someone actually wanted to cover the topic. No one seems to care so I will finish it off too. It would make a good Friday night math quiz.
Peter, I'm interested...for the purpose of understanding how I could have setup my system in the previous thread without disconnecting the servo's encoder from the M02AE and closing the loop on the auxillary encoder.

I'm just sitting back and listening because I really don't know where I would have began
 
Did you see the latest Hydraulics and Pneumatics?
I got it in the mail yesterday and looked at it this morning. I always keep an eye out for your work.

I like the examples because they make me think. I can't always use what I see but I like seeing other ways to do things. I think most people here don't worry about it until it hurts. Then they want all the help they can get.
 

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