Powerflex 527 drive instruction

Hi, I am having an application in which we are having a Roller rotating via Powerflex 527 drive. The operator can change the speed of this roller from the HMI. In the PLC program, I see the programmer has used MAJ instruction for reading this speed from the HMI.


The operator is not able to change the speed on the fly, the speed change only takes place when he stops and starts the roller again, I guess it is due to MAJ instruction. Because as per the definition of the instruction it maintains a const. speed.


Is there any way around this so that the value of new speed entered by the operator in the HMI is updated in drive speed on the fly.

I am thinking of using MCD instruction instead. Will, that work?


Thank you,

You are exactly correct; instruction like the Motion Axis Move (MAM) and Motion Axis Jog (MAJ) use the speed that is given when the instruction is executed.

The Motion Change Dynamics (MCD) is how you send a new speed value to the axis while it's already in motion.

Thanks, Ken for replying!

1. While using MCD what type of motion do I select Jog or Move?

2. In MAJ it has a parameter which allows you to select the Direction of the rotation, which is not present in MCD?

3. I will be deleting the existing MAJ instruction and MCD instruction instead. Do I need to take care of anything else such as MSF instruction, I mean is there anything that works with MAJ and not with MCD that I should look for too?



Thank you,

Hang on there, you're making some incorrect presumptions.

MCD changes the dynamics of an existing Move that is already in progress. It has accel/decl and speed values. It does not change direction (MAJ's) or the position endpoint (MAM).

So if you already have an MAJ and it does what you need it to, then you can trigger an MCD when the operator changes the speed. Tell the MCD that the existing move is a Jog.

Motion Change Dynamics modifies the behavior of a CIP Motion Axis (like the PowerFlex 527). It does not replace the actual motion axis command like the MAM or MAJ.

So do you mean I should keep the existing MAJ instruction as it is. And just add a logic which triggers MCD instruction when the operator changes the speed in the HMI.

And select motion type as "JOG", in the MCD instruction.

Right?

Exactly correct.

If your HMI allows you to set a bit when the operator enters a new value, use that bit to trigger the MCD instruction. Otherwise, just compare the speed setpoint to an "old speed setpoint" and trigger the MCD when they are not equal.

Thanks, Ken
It worked. Attached is the program Image.

One thing to note, the MCD doesn't have a direction like MAJ. So if you are going reverse and fire a MCD you will need to send a negative speed. If not, it will change directions on you.

Phrog30, I have used two separate MAJ instructions for forward and reverse direction, with a common Motion Axis but with the different Motion control name.

And just added an MCD instruction for same motion axis again with different motion control name tag, which has nothing to do with the direction, just facilitates the change of speed of the motion axis. It should be fine in that case.

No need for the Operator to put a negative value if he wants to run the axis in the reverse direction.

The MCD absolutely has to do with direction. One, I've experienced it myself. Two, Rockwell tech note to support. I think it's based on kinetix, but the 527 applies as well.

https://rockwellautomation.custhelp.com/app/answers/detail/a_id/54829/related/1

Phrog30 is right.

As soon as you are able to jog in both directions, you will need aditional code to determine if the speed setpoint if the MCD instruction should be positive or negative.
If you have started a MAJ in the negative direction, and you execute a MCD with a positive setpoint, then your axis with change its direction.

I always use 1 MAJ instruction, where the direction bit is set deppending wheater the operators choose to jog in the positive or negative direction. When ever a new setpoint is applied by the operators, the same MAJ instruction will be triggered again.

This is done by comparing the setpoint entered by the operator, and a tag which holds the "Old" value of the operator setpoint. Whenever the MAJ instruction is triggered, the operator setpoint, is moved to the "Old" tag.

Thanks, Phrog30 & Jobbe9000:beer:

You guys are right. But in my application, I want to change the speed only when it's running in forward direction. and the MCD instruction is activated only when the operator in running in the fwd direction.

And for the reverse direction, I am just using MAJ and not activating MCD at that time. So it works fine!