data acquisition used for system identification

[ggenc]

Hi everybody,

I'm wondering if it is possible to acquire necessary motor data using NI Motion in order to develop a reliable plant model?

I'm using PCI-7358 motion controller and MID-7654 to drive some brushed servo drivers and I want to deploy a model of the plant. We are planning of purchasing System Identification Toolkit for this purpose but I don't understand how I will acquire the estimation and validation data sets of the plant.

I would appreciate your opinions and information.

Gencer Genc

[Jochen]

Gencer,

for system identification you typically need to send a test signal to the system to identify and measure the response. The PCI-7358 is optimized for control tasks by running the control algorithm and the I/O access onboard on a DSP. That means that from a host PC you don't have direct access to the I/Os, but you will always have to channel your I/O access through several communication layers on the board, which is not very fast and doesn't provide stable timing (jitter). These are the reasons why it's hard or even impossible to use a 73xx board in an open-loop mode that is required for system identification.

With this said, you should think of using a DAQ device for the system identification process instead of a 73xx board.

Kind regards,

Jochen Klier
National Instruments

[ggenc]

Jochen I thank you again for your answer.

This is the same things I thought but I need to make sure of it. I started looking through NI DAQ cards which may be suitable for my system, but I want to ask you if there is any specific card you can offer me. My major concern is the interface between the DAQ card and the driver because I will need the MID-7654 in any case to amplify the test signal before applying to the motorized system which is to be modelled.

I thank you again for your efforts...

Gencer Genc

[Jochen]

Gencer,

you are right about the concerns about the interface to the MID. The MID-7654's connector is designed for direct cabling to a 73xx board. If you want to connect it to a DAQ board, you will have to connect both, the DAQ board and the MID to connector boxes and wire the appropriate signals between the connector boxes. As an alternative you could think of building a custom cable, but because of the high density connectors this would become very tough.

Here is a list of material that could be used:

2 x SCB-68 (shielded connector block)
or 2 x CB-68LP (unshielded connector block; may be used in a lab environment with very low electromagnetic noise)
1 x NI SHC68-68-EPM (cable to DAQ device)
1 x SH68-C68-S (cable to MID)

It's up to you if you want to use shielded or unshielded connector blocks, but you should consider this choice carefully, as noise could could cause significant interferences with your command signals and measurements.

Jochen

[xf]

Hi,

I want to model my printer belt drive system using system identification. Using PCI 7831R.

Sorry, I don't understand. Have read this, http://zone.ni.com/reference/en-XX/help/371002B-01/gswlvsi/steptwo-loadingfiles/  . If I wish to determine an accurate model of my system, then can I still use the dc_motor_data.lvm as stimulus signal and the supposed-to-be response signal? If i use dc_motor_data.lvm , am I modelling my system?

Thanks, would appreciate your help and replies....