Sinusoidal Velocity

[chris.b]

What PCI card are you using?  If you use contouring and the One-Axis Contour Move with Position Monitor.vi, you are only limited by your PID loop on your card, which usually runs at 250 microseconds (but can be pushed even faster).

[2photonGuy]

Actually u r a bit wrong.

It is limited by the time setting of the buffer config vi, min is 10ms i guess...which is huge... 😞

[task]

That is correct...with the Contour Move the fastest you can output is 10ms.

[chris.b]

Hi Sneh@l!

Below is the LabVIEW help article for "Configure Buffer".  I've added some comments for clarification.

Requested Interval (10 ms) is additional data for the Position buffer type. The Position buffer type requires a Requested Interval parameter, and indicates the time between contouring data points in milliseconds. For all other buffer types, the Requested Interval parameter is ignored.
 
The controller uses the closest value it can that is greater than or equal to the interval value you requested. Your time interval must be an even multiple of the PID rate [default 250 microseconds, which can be as fast a 62.5 microseconds with one axis]. Refer to the description for the Actual Interval parameter for more information.

Example:
PID control loop update period: 250 µs (as set in Measurement and Automation Explorer)
Run One-Axis Contour Move with Position Monitor.vi
Position Mode: Absolute Contouring
Request Interval: 10ms
Result:
The control will monitor and update the motor's position every 250 µs, or 40 times between each contouring point, resulting in an update frequency of  4000 Hz.

[Jochen]

Hi,

just a little comment on this:
The 73xx boards use a spline algorithm to interpolate between the contouring points provided by the contouring buffer. Thus the PID gets a new setpoint at each iteration of the control loop. This results in a very smooth contouring move even with a timing intervall of 10 ms or above.

Regards,

Jochen Klier
National Instruments

[2photonGuy]

Hi Jochen

I would like to execute a velocity profile onboard at high frequency 10-15Hz. I would just generalte positions for a single sinewave and it would be executed again and again at high frequency.

[2photonGuy]

Hi Jochen

I would like to execute a velocity profile onboard at high frequency 10-15Hz. I would just generalte positions for a single sinewave and it would be executed again and again at high frequency.

[2photonGuy]

Yeah Bolin,

But still the minimum possible time for loading the next position is 10ms which is a bit large. As I want 10 Hz with 300 samples = 1/(10*300) = .33 ms

[Jochen]

Well Sneh@l, this brings me back to my favorite topic: The NI SoftMotion Development Module for LabVIEW.
There is obviously no good way to meet your requirements with a 73xx board and it would be probably hard to find a 3rd party product that provides these timing capabilities, too. A possible solution is using a LabVIEW FPGA target like a PCI-7831R. This device can run PID loops with up to 200 kHz and you could feed contouring data with the same frequency to the control algorithm. 200 kHz control loop rate might be a bit too fast for a motion control application, but as you can define the timing by your own, this board provides enough headroom for your application.

The R-Series boards are general purpose multifunction I/O boards with an FPGA onboard. The before mentioned SoftMotion module makes it quite easy to convert this board into a user defined motion control device.

Regards,

Jochen

[2photonGuy]

Hi Jochen thanks for the reply

I am now providing analog signal to the board. But when i read out the signal is not that smooth. So I am now installing a new encoder. But will I be able to read out the data so fast using read position VI 73xx.

Also, do tell if there is any way to execute the countouring motion OnBoard. I read in a PDF it speeds up the program a bit..

Thanks