Clearing the 7344 commands buffer ?

[absgtr]

Problem Statement:
If an e-stop or other condition occurs while one of my axes is in motion, the hardware-hardwiring will disable the servo drive(s).
After recovering from an e-stop or another fault condition, if I re-enable the servo drive the servo axis will "jump" or "lurch".

Question:
How do I programmatically flush the 7344's command buffers when recovering from an E-stop condition before enabling the servo drives in LAbVIEW with the Flex motion VI's ?



I am using LabVIEW 6.02, NI Flex Motion 5.1.1 and a PCI-7344 card to control 2 servo axes (linear stages).

[JR_A.]

There is a Knowledge Base that describes how to impliment and e-stop. KB 264AFAOA The solution is to enable the controller card to be 'killed' on the hardware signal. Then in order to use it again you must reinitialize it just as you would at beginning of the program. Otherwise, the drive is killed but the controller is still trying to keep the trajectory. When the drive is reenabled then the controller tries to catch up because it didn't know that anything happened. Setting up the controller to shutdown is a much better way to implement an e-stop.

Cheers,

JR A.
Application Engineering
National Instruments

[absgtr]

Having worked with other brands of motion controllers over the years I would have expected the 7344 to get a following error (position feedback overflow error) because the 7344 is issuing commands but because the encoder is not moving it is not decrementing a command buffer.
With a following error/position error other brands of motion controllers error out and actually disable the axis dac out as well as a digital signal to the servo drive.
Then when the e-stop and drive are re-enabled in hardware the motion controller has long since errored out and will not attempt to "pick up where it left off".

Thanks for your response.

[JR_A.]

True, and the 7344 is capable of that as well. The reason you are probably not seeing that behavior now is that the default value for a following error is 32767 counts and depending on your system could be a long distance. You can set the following error in Measurement and Automation Explorer on the "Trajectory Settings" tab. However, if it doesn't move far enough to give you a following error the system will still jump which is why I recommended setting the 7344 to be 'killed' on the hardware signal.

Cheers,

JR A.