Logix - Determine when motion axis is at speed

[ASF]

I'm using a 1769-L18ERM to control two Kinetix 5500 servo drives. I am setting up a virtual axis, which I will use the MAJ instruction to run, and then both physical axes will use the MAG instruction to follow the virtual axis. These servos are running a position loop but are simply conveyors that will run at a constant speed in the forward direction.

My question is: how can I easily determine when the virtual axis and the physical conveyors are "at speed", to give the upstream enable to the equipment behind them? With a powerflex drive there is an AtReference bit that serves this purpose, but I can't find anything to match that on the virtual/physical axis data structure. I could use a running status and then check that the accel and decel status are both false, but I'm not sure how sensitive those bits are - e.g. does it constantly turn those on and off as it adjusts the outputs to maintain the set speed? I don't want my At Speed bit turning off just because the servo had to tweak it's output by 0.01%.

 

[DarrylR]

I'll take a stab at it... Maybe try using the MDAC instruction? (Master Driven Axis Control) The functionality is similar to gearing in that you select a master, slave, and motion type for slave control. Also, it offers a "Tracking Master" status bit which is set when the slave axis completes acceleration and is locked with the master. I'm pretty sure the Compactlogix controllers support this.

 

[Ben Pugh]

I would check out the GearingLockStatus bit in the axis data structure. Below is what Studio 5000 help says about it.

Set whenever the slave axis is locked to the master axis in a gearing relationship according to the specified gear ratio. The clutch function of the gearing planner is used to ramp an axis up, or down, to speed in a gearing process (MAG with Clutch selected). This bit is cleared during the intervals where the axis is clutching.

 

[Smeltz]

Reference the Axis within your Motion Group. You should find a tag labeled "ActualVelocity". Compare that to the tag labeled "CommandVelocity" .

 

[ASF]

I would check out the GearingLockStatus bit in the axis data structure. Below is what Studio 5000 help says about it.

Thanks, that looks to be just what I want with the MAG. It would be good to have a similar status for the MAJ but it doesn't look like there is one.

 

[ASF]

Reference the Axis within your Motion Group. You should find a tag labeled "ActualVelocity". Compare that to the tag labeled "CommandVelocity" .

The only problem with that is determining the tolerance window. I'm trying to construct this as a generic AOI, and the tolerance would depend entirely on the scaling and application. For one application +/- 0.01m/s might be a good window, but for another application with different transmission ratios, I might need +/- 1m/s. It just adds additional complexity to the AOI that I'd like to avoid.

 

[ASF]

I'll take a stab at it... Maybe try using the MDAC instruction? (Master Driven Axis Control) The functionality is similar to gearing in that you select a master, slave, and motion type for slave control. Also, it offers a "Tracking Master" status bit which is set when the slave axis completes acceleration and is locked with the master. I'm pretty sure the Compactlogix controllers support this.

I'll check that out with a view to potentially using it next time - I've got most of the code already done using MAJ and MAG now, but it sounds like it could be a good fit. Thanks!