Kinetix 6500 Servo Speed Adjustment

jakejhill

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Jan 2019
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I question about a kinetix 6500, hooked up to a Allen Bradley Control Logix 5572 controller. The current program uses MAM instruction to bring the servo forward until a target reading is achieved from an analog input. The rung that enables the servo MAM move goes false when the target is reached from the analog input (Keyence touch probe). Is there a way to adjust the servo speed constantly as the target is reached. The idea here is start the motion at a fast speed and come to a stop as the target reading from the probe is achieved. What would be the best motion instruction to use for this??? (Target- Probe reading)/ coefficient = Servo Speed..... Any thoughts??
 
... (Target- Probe reading)/ coefficient = Servo Speed..... Any thoughts??

This doesn't answer your question, but you did ask for any thoughts.

Unless I forgot something in the past four+ decades, the differential equation for motion speed you suggested will never get there; I think you want to either model this as a a constant rate with a ramp at the end, or add a small constant speed to your equation, from which speed an immediate stop is acceptable. But there are people way better at motion control than me who will eventually give you an answer.

That said, it reminds me of the old joke: a mathematician was put in a room at the opposite corner from his wife and told to kiss her, but that he could only take a step at most half of the remaining distance to her for any single step. The mathematician sat down and started crying.

The same direction was given to an engineer, who immediately started across the room while obeying the rule about step size, knowing he could get close enough for all practical purposes.
 
Last edited:
Thanks drbitboy, I figure I will have to add a small constant speed to that equation. My main question is what is the best way to go about adjusting the speed value into a MAM instruction while its enabled.
 
At that point you no longer want to use an MAM since the motion profiler is no longer really controlling the motion (your speed equation is). In your case you would use an MAJ and change the speed setpoint every scan by retriggering the MAJ or using a MCD instruction.

There is likely another way to approach this but I don't know enough about exactly what you are doing to recommend anything else. What you are talking about is very similar to a move with a registration offset.

Keith
 
One basic thing to understand is that a MAM instruction starts to control an axis move when its rung goes false -> true. You don't need to keep the rung True in order to keep the motion move going.

Once a move is in process, you can change its velocity or acceleration values with the MCD (Motion Change Dynamics) instruction.

Please describe in more detail the mechanism and desired action.

Another thing you might consider is running an MAJ with an MAM on top of it.

The MAJ starts the axis moving in a velocity mode, and then depending on how you configure the merge options, the MAM will take over the speed and position control and bring the axis to a stop at the target position.

The merge options are described well in Knowledgebase article 721593 (Access Level: Everyone).
 

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