Motion Dirrect Commands

Studio5000 software.

I have a few questions regarding Motion Dirrect commands.

I often use commands like MAJ, and MAM to move a
Servo motor when necessary. There seems to be limits to how fast I can actually move a drive regardless of my entered velocity settings.
There's been times I'd like to go as fast as when the program speed.

Is there a setting I'm overlooking?

Also, I have never tried to move a Motion Group for fear of crashing something.

What's generally involved in moving a Master and Slave axis.

Can you explain how you MAG or MSP to move a group?

No one?

In others words, is there a maximum jog or move speed when using MD commands?

You should be able to jog just as fast as you do when doing an absolute or incremental move. So, it sounds like you have a setting wrong. I don't have software in front of me and it's been a while since I've done motion, so I won't be of much help in determining what that setting is.

Not sure if this is best practice, but I've seen people use an absolute move for jog. If they want to stop before the move it complete, they issue a stop command. To the operator it looks no different than a jog.

There are maximum speed, accel, decel, jerk, etc in the motion axis properties.



Accessed by drilling down in the Logix 5000 Project organizer pane (on the left side, where the programs, IO tree, etc.. are).



I believe they are on a tab called "Dynamics".



These will never be exceeded regardless of a command speed. They will be greyed out unless you shut down the motion group, if memory serves. They can be changed with SSVs while the motion group and axis are running.

Sorry didnt read your whole post before replying. An MAG gears a slave axis to a master axis. The command is executed on the axis you wish to follow the master. There is also i think a gear ratio and maybe direction (same as master or opposite). The slave axis will still respect it's limits that are configured (the speed and accel/decel mentioned above, as well as any travel limits), so crashing usually wouldn't be an issue, but without knowing the mechanical arrangement of your axes hard to say.

Phrog30 said:

You should be able to jog just as fast as you do when doing an absolute or incremental move.

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Nope, I can vary the speed for a MAJ or MAM up to a point, but it's well below the normal speed when the machine is running in Auto.

ruairicussen said:

There are maximum speed, accel, decel, jerk, etc in the motion axis properties. ...

I believe they are on a tab called "Dynamics".

These will never be exceeded regardless of a command speed. They will be greyed out unless you shut down the motion group, if memory serves. They can be changed with SSVs while the motion group and axis are running.

Click to expand...

Thanks, I'll check that out. I wouldn't expect these maximum speeds to be set below the normal operation of the machine? Unless the program is doing something fancy like a SSV to change speed?

My understanding of motion is weak.
I don't really understand the difference between Speed and Velocity.
I understand acc and dec as the time to speed up or slow before stopping, but I have no idea what "jerk" is or how it impacts motion. Is this relating to torque?

I will investigate further when I get back.

ruairicussen said:

Sorry didnt read your whole post before replying. An MAG gears a slave axis to a master axis. The command is executed on the axis you wish to follow the master. There is also i think a gear ratio and maybe direction (same as master or opposite). The slave axis will still respect it's limits that are configured (the speed and accel/decel mentioned above, as well as any travel limits), so crashing usually wouldn't be an issue, but without knowing the mechanical arrangement of your axes hard to say.

Click to expand...

Ok, I think I get it.
For example if motor A is master and motor B slave move together 1:1.

I select MAG for motor B and select it to master motor "A" from drop down menu.
Then I can MAJ or MAM motor A and both will move together. The slave will follow speed, acc, dec of the master. If I want to stop I can execute a MAS.
Is that right?

I appreciate you sharing your knowledge.

PiperJohn said:

I don't really understand the difference between Speed and Velocity.

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Speed is a scalar i.e. a magnitude only, Velocity is a vector that has both a magnitude (speed) and a direction (probably limited to forward or backward along the axis in this context, but it could be three-dimensional).

Position, acceleration, and jerk are also vectors.

PiperJohn said:

I understand acc and dec as the time to speed up or slow before stopping,

Click to expand...

That is actually the reciprocal of acceleration. Acceleration is the time rate of change of velocity. If my car's velocity vector is initially 45m/s(speed; magnitude) to the east (direction), and I press the accelerator a bit and my final velocity is 55m/s to the east 5s later, then the average acceleration vector over that 5s period is 2m/s/s (metre per seccond, per second; (55-45)m/s ÷ 5s) toward the east. If I then press the brake pedal and over 20s change my velocity to 45m/s to the east, then the average acceleration vector is -0.5m/s/s ((45-55)m/s ÷ 20s) toward the east; it could also be +0.5m/s/s toward the west. Deceleration is simply negative acceleration.

PiperJohn said:

but I have no idea what "jerk" is or how it impacts motion. Is this relating to torque?

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• Jerk is the rate of change of acceleration.
• Acceleration is the rate of change of velocity.
• Velocity is the rate of change of position.

I realize answers this concise might not help without the background of the first few weeks of Physics 101 and some calculus, but in the end you will end up back here. Here is a very brief video that might help visually: https://www.youtube.com/watch?v=STcgrV2L4tw.

Thanks Dr very helpful!

Why doesn't this forum have "Like" or "thumbs-up" button?

When I try to insert one It inserts a �� symbol.

Ok, I get excited when I learn something.

Yes, in the MAG case you would just stop your Master axis and slave will stop. I haven't used gearing a lot but i believe if the axes are controlling position the slave will stop at the position dictated by the master. If velocity is what is being controlled they should stop at the same time.



One other possibility for differing max speeds (i very much doubt the maximums are being dynamically changed with SSVs), there is a "Speed Units" option for the MAM and MAJ. This can be "Units Per Second" of "% of Maximum". Is it possible the Speed Units selection is different on the Motion direct commands you are executing and the logic commands?


It is also possible depending on speed, accel, decel, settings that the generated motion profile never reaches the command speed (it is spending all it's time in Accel and Decel). Would it be possible to post screenshots of a command in logic that is reaching the higher speed, and a motion direct command you are trying that is not reaching that speed? Would be helpful to see all the command parameters in both cases.

ruairicussen said:

..there is a "Speed Units" option for the MAM and MAJ. This can be "Units Per Second" of "% of Maximum". Is it possible the Speed Units selection is different on the Motion direct commands you are executing and the logic commands?

It is also possible depending on speed, accel, decel, settings that the generated motion profile never reaches the command speed (it is spending all it's time in Accel and Decel). Would it be possible to post screenshots of a command in logic that is reaching the higher speed, and a motion direct command you are trying that is not reaching that speed? Would be helpful to see all the command parameters in both cases.

Click to expand...

Ok.
Next time I'll try changing the units to "% of max" to see if it's still limited.
But honestly, I don't see how it would matter wither it was set to 100% of max, or 500,000,000 units per sec. It should go the max provided it doesn't exceed the max.

Yes, when i get back I'll dig in to logic and see what the parameters are.

Thanks

PiperJohn said:

Why doesn't this forum have "Like" or "thumbs-up" button?

When I try to insert one It inserts a �� symbol.

Ok, I get excited when I learn something.

Click to expand...

Because even though this is free, our private data are not the product, and we are all already so impressed with ourselves that () that we don't have any use for likes from social media. We usually simply reply with "+1" or an emoji: :site:

+1

What?

drbitboy said:

Speed is a scalar i.e. a magnitude only, Velocity is a vector that has both a magnitude (speed) and a direction (probably limited to forward or backward along the axis in this context, but it could be three-dimensional).

Click to expand...

Yes,

Position, acceleration, and jerk are also vectors.

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Are you dealing in two or three dimensional space? The motion controllers usually just take scalar numbers for each axis. Position can be negative depending on the coordinate system. Velocity, acceleration and jerk are entered into the controller as positive numbers. The motion controller can figure out the sign depending on the difference in position.

That is actually the reciprocal of acceleration.

Click to expand...

What is "that"?



Most position control motion is simply back and forth. Don't make it hard. The user defines the coordinate system so motion is in either the positive direction or negative direction. The motion controller figures out the sign of the velocity, acceleration and jerk it should use to get to the new command position.


An exception is open loop jogging and velocity mode commands where the sign of the velocity determines the direction


Rockwell and Delta use pretty much the same terminology but I have forgotten whether a MAJ command is open loop or closed loop. It has been 20+ years now since I played with the Rockwell motion commands.