axis intermittently takes off by itself and does not respond to commands. here are the particulars:

- ack bit toggles to command but axis does not respond
- when axis takes off by itself the target and actual positions are always equal as it moves
- if new command is sent with at least one of the parameters different the axis will respond (i.e. if same command is resent axis does not respond)

 

On May 13, 2004, Anonymous wrote:
> axis intermittently takes off by itself and does not respond to commands. here are the particulars:
>
> - ack bit toggles to command but axis does not respond <

What command? Not all commands execute in one scan. The 'P' command may not as the memory that makes up the M files must be accessed and that is a slower than the very efficient I and O files.

> - when axis takes off by itself the target and actual positions are always equal as it moves <

When axis is a open loop mode the target position is always set to the actual position. If you get an error the axis will either stop in closed loop or openloop mode depending on the autostop bits and the error. When in open loop the cylinder can still drift even if the control output is zero because the valve is not nulled.

> - if new command is sent with at least one of the parameters different the axis will respond (i.e. if same command is resent axis does not respond) <

Yes, that way the same command does not get issued over and over again. Some commands should not be issued continuously for instance the relative move command. To keep a command from being issued over and over again each scan there is a table inside the QS that compares the last output data ( old command ) with the new output data ( new command ). Only if they are different will the new data will be considered a command. The cure is to clear the command register at the top of the scan. There shouldn't be a need to issue a command each scan. If you do need to issue commands each scan the are the 'G' and 'g' commands that are considered to be different.

Finally, follow the example program. Use the command log (^L from QSCFG ). It logs all the command from the SLC. Use the plots. The plots can also be configured to store the command data as well as the positons, status bit and output.