pm dc motor control using pxi 1010 system

[rachadeepak]

sir ,

I have two PM  dc motors for a closed loop speed control application . one rated 24 v and 12 v , with tacho generators attached to them  giving an output of 6 v /1000 rpm  and running at 1600 and 1200 rpm respectively on no load , i am using the pxi 1010 system in which the ni pxi 6221 multi function daq card to read the tachogenerator outputs using the DAQ mx  . The problem with the VI attached to the mail is that . i am able to read only one of the tacho output reading . i.e either channel 0 or channel 1 at a instant instead of both the readings , though both the machines are running . the two loops are not running simultanoeusly . i made use of a motor driver circuit for this application using A 3949 IC , where the digital signals in the VI are the signals to this driver circuit . please suggest or make the changes in the ac15.vi . also please help in tuning this system seperately , can i use the pid auto tuning vi  as a controller for this application . how to decide on the values of parameters of the pid for this application .

[Jochen]

Hello,

there are a lot of major problems in your code:

1. You can't start multiple tasks for hardware timed data acquisition independently. There is only one DMA channel for all analog input channels so you will have to acquire all analog input channels with a single task. You should do everything within a single loop. This is also very important to guarantee real-time behavior.
   
   
2. The digital output operations are configured and started within the loops. This takes a lot of time and is non-deterministic. You should place the task configuration and start vis outside the loop as you have done for your AI tasks.
   
   
3. The loops contain no timing. This will result in a completely undeterministic behavior with a high amount of jitter.

You haven't written if you are using LabVIEW Real-Time. If you are running Windows on your PXI system you will never reach a stable system behavior so LabVIEW Real-Time is highly recommended.

Best regards,

Jochen Klier
National Instruments Germany

[rachadeepak]

sir ,

thank you for that quick reply , i am using labview 7.1 on windows based systems , and i am not using the labview real time target for this application . any way will start off with that from today on wards as you have suggested to do .  i will make the changes in the vi , sir you did not reply on the pid  controller for the two motors. i.e tuning of the controllers . will get back to you with any queries further .

thanking you

deepak

[Jochen]

Here is a document that describes the tuning process of a DC motor with NI motion control boards. As you don't have a motion control the document is not a perfect fit for you but it describes very well the basics of PID tuning in general.
From my experience I can tell that most autotuning algorithms work only fine for a very specific control environment so I prefer manual tuning as this results typically in a better system behavior.

Jochen Klier
National Instruments Germany

[rachadeepak]

sir ,

As  suggested i have installed the lab view real time module in my system, please guide me how to proceed further on this  for a perfect synchronization between the two motor  . i.e to control the two motors independently from the same VI. what should be further  done with the real time module and pxi 1010 system .any additional cards have to be installed in them . i have pxi 6221 multi function daq card , 7831 r series RIO card and 6528 isolated dio cards in the system . or will the 6221 card suffice for my application .

[Jochen]

The best option for you would be to use the NI SoftMotion Development Module as it provides all the features that you need. Please refer to this link for further information. General information about LabVIEW Real-Time can be found here. Please follow also the related links on this site.

It depends on your motor type and general application needs if you can use the 6221. The SoftMotion Module provides code examples for both, DAQ boards and RIO devices. Just some weeks ago I have used M-Series boards to control two synchronized DC motors with a loop rate of 4 kHz so your 6221 might be sufficient.

Jochen Klier
National Instruments Germany

[rachadeepak]

Mr.Jochen ,

sir ,you said that  some weeks ago you have used M-Series boards to control two synchronized DC motors with a loop rate of 4 kHz , please mail me the vi of that application . was it in real time labview , i am able to operate the PMDC motors in labview itself  i.e to switch on and off , run in forward and reverse mode , brake it  , but to control the speed of the motor with pulse width modulation , the average voltage applied to the motor is flickering and is not stable. i am using A3949 full bridge motor driver circuit for my application i.e closed loop speed control of two pmdc motors with pxi 1010 system and labview. please suggest me on this , i have tried the same with the real time labview also , but there was hardly any change from the latter one .

please suggest me on this and i request you to send me the vi for the appication which u have developed for a reference .

thanking you

deepak

[Jochen]

Deepak,

my motion control application is quite complex and it involves a host PC and two PXIs (synchronized with time triggered shared variables), one controlling a master axis, the other one a geared slave axis. It shouldn't be necessary to run the slave PXI. Please refer to the attached code. Please note that it uses the NI SoftMotion development module.

I have developed this application as a tradeshow demo.

Best regards,

Jochen