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Cause S-curve velocity ramp

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I am commanding the AKD drive in velocity mode.  I would like to obtain an S-curve velocity profile.  The way the drive is controlled now is to command 0rpm and then 80 rpm to go that speed.  The standard motion creates some problems in control including overshoot.

I know how to compute the path by setting a Jerk value and laying out the acceleration and velocity profile.  My question is what could be a way to entice the drive to perform this.   It is being controlled via the Modbus commands over ethernet. I have two ideas:

1. periodically enter a new velocity target, at specific intervals of time (setting the accleration limit above the highest that would exist in this profile)


2. Enter an acceleration limit of 0, then a step velocity command for the end target and then periodically enter a new acceleration limit.

or is there another way that this can be achieved?



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You didn't indicate what hardware model of AKD you have but the only S-Curve functionality built into the drive is using the Motion Profile Table in  tandem with a motion task in the Motion Task table which requires an AKD-P drive in Service Position mode.

Velocity Mode requires the velocity command is given by the external controller or master.

Changing the velocity setpoint on the fly makes sense to me but keep in mind with Modbus TCP the X11 Service Port on the AKD is limited to a poll rate

down to 20msec. Anything faster will overrun the communications buffer. Therefore latency may affect your profile. A fieldbus option like EtherCAT or CANopen can achieve faster update rates.

Analog Velocity overcomes the communications latency but can add noise into the mix.



thank you for the prompt reply. The drive does have motion tasking. It would be a curious workaround but I do see a way this could be done. our test has a fixed duration so I could set up a somewhat fake task to move to a relative position far away and I assume it will be possible to limit the peak speed. This might cause the drive to move in the velocity profile that I wish for.
I had not considered the analog command, but I don't think I will do that as it introduces so many other things.

I think I will try a series of velocity commands.

mark_uwp94 - Mon, 06/08/2020 - 13:25
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