Why I can't initialize the PCI-7344 after E-Stop

[terp]

I have a E-Stop button on my machine. When the button is pressed, PCI-7344's shutdown input (pin 62) will be grounded.

I'm trying to write the program in LabView to respond after the E-stop button is release. In my program, the 1st step is to run "Clear Power Up Status.flx"; the 2nd step is to run "Initialize Controller.flx" with the setting in MAX.

Here comes the problem. When I release the E-stop button and then run my labview code. An error message pops up, which is "70072(NIMC_board In Power Up Reset State Error)_The FlexMotion controller is in power up reset state. Please execute the Clear Power Up Status function or VI before sending any commands to the controller." This error occurs the step in which the 7344 is b
eing initialized, after "Clear Power Up Status.flx" is run.

I tried a couples of times and one way to work is to press "Reset Device" button in MAX, under the 7344 board setting. After this button is pressed, then board initialization can be done.

Can someone tell me what's wrong in my program or in the hardware setting? Thanks!

[Jochen]

The shutdown input really kills the board and the only way to reactivate it is using the Reset button in MAX or power cycling the computer. That's expected and documented behavior. To anticipate your next question: No, there is no way to reset the board in your program.

To implement a E-Stop functionality with your 7344 you better should use the Inhibit all terminal (INH ALL) on your UMI-77xx connector block (are you using a UMI at all?). This input is ored with all inhibit outputs on the UMI and will kill motion on all axes. If you only want to be able to kill a specific axis use the Inhibit Inputs (INHINx) that are available for all axes on the UMI.

I hope this helps,

Jochen Klier
National Instruments Germany

[terp]

Jochen, thanks for your reply.

First question, what's "power cycling the computer" mean? Reboot the computer?

The INH ALL terminal can't serve as E-Stop very well. Once it's grounded, yes the motor will stop, but the 7344 still working and generate pulses (it's stepper in my case). If the E-Stop button is released before the pulses generation is done, the motor will immediately be driven by the left-over pulses, which is not good. Any way to work around this?

[terp]

Is there any good example for implementing software response to E-Stop button? thanks.

[Jochen]

Power cycling means more than rebooting. In some cases you will also need to turn off the power of the computer and reboot it in order to reactivate the board but in most cases rebooting will be enough.

If you want the board to stop after the E-Stop became active, wire a digital input or a trigger input of the board to the E-Stop terminal. Then you could use a simple onboard program that either polls the digital input or waits for the trigger to occurr. Based on this event you can stop motion on the desired axes then.

I haven't found an example that does exactly that but there are plenty of examples for onboard programming available that should guide you. Please refer to the shipping examples and to the additional examples that can be found <
a href="http://www.ni.com/devzone/dev_exchange/ex_search.htm"> here.
Search for "+motion +onboard" (without the quotes).

[terp]

Jochen,

1. How many on-board programs can be simultaneously run on PCI7344?

2. If I put the EPO monitor program on-board, can other host labview programs for the same PCI7344 be run at the same time?

[Buechsenschuetz]

Didn't you recommend NOT to use a digital i/o of the 7344 for implementing safety features recently? Software polling of an e-stop is not a very safe way, and maybe it's even not legal in some countries (AFAIK in Germany an e-stop button has to interrupt the power supply directly).

However, implementing a safe e-stop when working with drives is not easy. Wiring the e-stop terminal to the INH_ALL input of the UMI box or the INH_x inputs of the 7344 will stop the drives, but all stepper motor drives I have seen yet stop delivering current to the stepper motor as soon as their INH input is activated. In case of non self-latching drives (even many worm gears or spindle drives are not self latching) there is risk that the drive will mov
e due to the load (gravity) applied. In these cases you will have to add mechanical brakes (which brake when not powered) for fail safe operation.

[Jochen]

If we are talking about a real E-Stop feature (red button on yellow ground) then I agree with you that it's not allowed to run this functionality in software because of legal reasons (at least in Germany). But in the case that the E-Stop button breaks the power to the drive AND it stops the trajectory generation on the board, it's still a good idea to use the digital inputs for this purpose.

However using an onboard program to stop motion when a digital input becomes active will be as reliable as using the real limit switches on board. In fact the limit switches are polled by the 68331 in their own time slot.

[Jochen]

1. The 68331 can run up to 10 onboard programs in individual time slots.
2. The 68331 will always provide a time slot for host communication so yes, it's possible to run an onboard program in parallel to a host program.

[terp]

Jochen,

I wrote the attached small onboard program to test the approach you suggested. Once this program is downloaded to the PCI7344, I enable it to run through MAX.

The way I simulated the EPO press is to ground the Trigger#1. The 1st ground after the onboard program is enabled always worked, the axes halted. But after that even I keep the Trigger#1 open (un-grounded), the axes somehow are still halted. In order to make them move again, I have to stop the onboard program first.

Got any idea why this happened?