DC motor control

[softmotion_trajectory]

dear all,

I should control 2 DC servo motors with labviw.

currently i have Labview 7.1 and PCI-6221 M-Series DAQ card.

what i need is to implement a  control algorithm to control the motors at each millisecond.

i actually have a profile of motion and i should differentiate it with respect to time for velocity and acceleration information and i dont know how to do that 😞

plz help me to solve my problem. 

best regards,

masood

[s_a_s]

Masood,

It will be difficult to develop a robust program for motion control using the PCI-6221.  The PCI-6221 DAQ card will only source 5 mA, which will most likely not be enough power to effectively drive both servo motors.  So the first thing you will need is a drive or amplifier for your motor.  Also, it will be very difficult, and probably impossible to get windows to run code deterministicly at 1ms intervals. 

I would recommend using one of our motion controllers (7330, 7340 series controllers).  This would be the fastest and easiest method.  Another option would be our SoftMotion control module.  The SoftMotion control module will be the the least expensive of the two.  If there is no budget for additional hardware/software, you will need to develop your own control algorithm. Here is some information to get you started:

Introduction to Mechatronics
http://sine.ni.com/apps/we/niepd_web_display.display_epd4?p_guid=BD3CD96DA0C3692EE034080020E74861&p_node=DZ52000_US&p_source=External 

Fundamentals of Motion Control
http://zone.ni.com/devzone/conceptd.nsf/webmain/722ECF56222AAD5086256F7B007072C4 

Basics of Feedback
http://zone.ni.com/devzone/conceptd.nsf/webmain/147F72A0CD247A6586256841006AEC57?opendocument 

[softmotion_trajectory]

dear Arves,

first of all, thanks for your fast response.

currently i use PWM servo amplifiers and also 2 incremental encoders for detecting the position of motor shaft.

is it possible to use softmoton control module without using motion control cards?(since i can't bye any other hardware)

labview RT software is available.

here is a labview program for one of the motors, but it has some problems

1. i reset the angle position after each 360 deg, other wise the motor can't follow so i can control the position between -360 to 360

2.the setlling time is about 1.5 sec  

3. at the begining there is a great error 

4.i cant use any other motion profile rather than trapazoidal

would you plz take a look at it and guide me?

[lrallen]

Masood,

Yes, NI SoftMotion is designed to write your own control algorithms to run on non-motion hardware in RT.  As Arves said, this will be your best option given your hardware budget.  Please take a look at the link below to learn more about NI SoftMotion.  Regarding your vi, when you say you get a great error, could you please provide some more details about the error number and description.

http://zone.ni.com/devzone/conceptd.nsf/webmain/B1817AB5751B602E86256F0000535887 

Regards,

LA

[softmotion_trajectory]

Dear LA,

thanks for your information.

Actually my program runs and the error i mentioned was the tracking error of the motor (for example i want the motor shaft to go to 90 deg, but the motor first goes to -15 deg and then goes to 90 )

Regards,

masood

[rachadeepak]

Mr arve  ,

presently i am working on my final thesis , speed control of two pmdc motors with pxi 1010 system using labview in that with ni pxi 6221 daq card and i am using a3949 as the driver for this application , i have implement this in labview with pwm technique , i have achieved a stable turn on/off , forward and reverse and braking operations , but i am unable to control the speed of the motors , by varying the pulse width. i.e the duty ratio the average voltage applied to the motors is changing but flickering to a large extent . can u send  me the  vi which can generate a pwm signal of variable duty ratio for the 6221 daq card  to a3949 driver circuit. i have used a pulse wave of variable duty cycle and converted into digtal signal , and also sinusoidal pwm technique.but failed in achieving the target .

how to decide on what frequency should we generate the pulse width digital signal  for this application ?, please suggest me on this

regards

deepak

[Ryan_V[DE]]

Deepak,

The best way to generate a PWM signal with your M Series device is through the use of one of the board's counters. Here is a great tutorial on programming PWM in DAQmx. As for the PWM frequency, I'm sure that depends on your motor and your driver. I would start with something around 10kHz.

Regards,