how can i use the trigger of the umi 7774 to start the motion?

[giuan]

I ahve an aleatory delay between the assertion of the enable signal and the first step signal; i would like to fix this delay. Is this delay due to the umi? Is it possible to use the trigger input to have a fix delay between the trigger (trigger input or enable signal) and the first step signal that starts the motion?

Thank you in advance for your help

[Jochen]

The delay introduced by the UMI-7774 should be very very small as the inhibit signals just run through a couple of gates so I suppose that the delay you are talking about is caused by the motion control board.
You should be able to get a very tight synchronization to your trigger signal by waiting for the trigger signal in an onboard program. Please refer to this example.
If this method doesn't provide the accuracy you need please tell me more about your application and about the hardware you are using and we can discuss some alternatives.

Best regards,

Jochen Klier
National Instruments Germany

[giuan]

Dear Jochen,

thanks a lot for your help

I am going to test the program that you suggested me; now i would like to explain better the question.

I am not using the inhibit signals; i have a simple program where i can set the position, then i enable the axis and then i start the motion with start motion.flx; on the oscilloscope i noted a delay between the rising edge of the enable signal and the first step coming out from the umi; this delay is aleatory and variable between 2 ms up to  a maximum of 9 ms. The controller board, that i am using, is the NI 7334; i don't understand why this delay is not fixedand if it is a software problem or an hardware problem

I try to use your software and i let you know

Please,could you let me know if you have other suggestions.

Thank you for your support

[Jochen]

The inhibit signal is the signal that is generated on the 7334 to enable your drive. So I'm pretty sure you are using this signal but please correct me if I'm wrong.
As you probably enable the axis and start motion in a program running under Windows a nondeterministic delay is expected (Windows is not a real-time OS). Running both calls in an onboard program should result in a more deterministic behavior.

Best regards

Jochen Klier
National Instruments Germany

[Jochen]

I have done some mistakes in my last posting:

1. I didn't realize that you are using a 7334 and not a 7344. The 7334 doesn't support onboard programming at all.
2. I had a discussion with motion R&D about this issue. I have just learned that onboard programs run with low priority on the CPU of the board so even if you were using a 7344 an onboard program might not result in the deterministic behavior that you are looking for.

I still have some difficulties to understand your needs in terms of real-time behavior. Could you please clarify why you need a deterministic delay between the enable signal and the first step? Could you provide a timing diagram? Could you please explain what you try to accomplish in your application?

Best regards,

Jochen

[giuan]

dear jochen

sorry if i was nor clear

I have to command the motion of a stepper motor; i want a delay less than 1 ms between the signal that i use as trigger and the first step signal coming out from the umi; as trigger, i am using the enable signal and i have a delay greater than 1 ms and, what is worse, that delay is variable.

If i use the trigger input of the board, keeping always asserted the enable, could i solve my problem

I hope that the question is clear, if not, please, ask me more about.

thank you  

Regards

Giuan

[Jochen]

Giuan,

as there is no hardware based correlation between the enable signal and the first step that is generated this approach will probably not work.
Is a delay of approximately 0 ms ok for you? In this case you could program the board to generate a breakpoint (trigger) at a certain position. E. g. if your current position is 0 and you program the board to set the breakpoint signal at position 1 you would get a trigger signal almost exactly when the first step is generated. Would this work for you? If this is the case please refer to the breakpoint examples that ship with NI-Motion.

Best regards,

Jochen

[giuan]

dear Jochen

a dealy about 0 ms is fine for me; the problem is that i want to decide the starting of the motion with an external trigger in input to the board; what you suggested me will give me a signal output sinchronized with the first step; is it right?

Infact i want to use the trigger signal input of the board but i cannot find the functions to configure the event;

Do you think it is possible?

Regards

Giuan

[Jochen]

Giuan,

ok, so you need a tight synchronization of the start of the move to an external trigger signal.
To be honest I don't see a good way to do this but maybe you could start your move before the trigger event occurrs and then read back the axis' position at the time the trigger occurred by using high speed capturing. I don't know if this helps.
I may come up with some other ideas but to do that I really need to know what you try to do in your application. Why do you need this tight synchronization?

Best regards,

Jochen

[giuan]

Dear Jochen

I have an external trigger that i have to use to start the motion of a stepping motor; the requirement for such project is that the delay between the external trigger and the motion of the motor has to be less than 1 ms to have a good synchronization.

I tried to use the trigger input of the board but i have a delay around 8 ms; in attached you can find the simple vi that i used; i connected to the input trigger1 a digital output of the board.

Do you have any suggestion to improve? Is it better if i use the RTSI lines?

Thank you

Regards

Giuan