DC motor - constant speed

I 'm a light user of Labview and need some assistance.
My objective is to make the dc motor retain constant speed even when a load is applied.
The tools I have to acquire data with are:
NI USB-6211
Labview 8.2
Optical Encoder - 1000 pulses per revolution
My main concern is writing the PWM VI to do this.
My first guess is to set use a DAQ assistance to acquire a signal as a counter input from the encoder.
Not really sure what to do with that because I am kinda lost from there.
How would I use that info to adjust the PWM of the output signal?
All help is appreciated.

Hi jgarcia,
this doesn't work at all. Your application requires closed loop control. This means you need deterministic behavior (= stable timing of the control loop) for single point I/O operations. With your setup this is not possible due to the fact, that both the USB and Windows introduce a lot of jitter (using a PCI DAQ device would make things a bit better, but you still couldn't get reliable control behavior on a Windows operating system). For a control system reliable timing is at least as important as proper tuning of the control parameters.
For motion control tasks it's much better to use a device like the PCI-7342, that runs all control operations in a realtime environment onboard. Other options include using a realtime operating system and PCI or PXI DAQ hardware or a cRIO-System with drive interface modules. For a single-axis system, the PCI-7342 is probably the most cost-efficient solution.
Sorry for the negative answer, but with your current hard- and software setup you will could easily waste a lot of time on a poor solution.
Kind regards,
Jochen Klier
National Instruments

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My motor runs at a constant speed

i have a
PCI 7342 controller.
MID 7654/7652 servo motor drive
motion control software
motion assistant 1.1.
I have setup the hardware connection.
When I try to run the motor using the motion assistant the motor runs at a constant speed irrespective of the velocity that I specify in the motion assistant.My motor velocity is 7 voltage per 1000RPM.The motor keeps running at a constant voltage of 25volts.I donot have a encoder but I have a tachometer.
pls help.

Hello Sumitha,
In order to use servo motors with National Instruments motion controllers, you must have some form of position feedback. This is required due to the PID control loop implemented on the controller. Without some kind of control loop, there is no way to guarantee that the motor will get to the commanded position following the specified trajectory. Servo Tune is a tool used to adjust the PID parameters, which in turn control the stability of your system.
If you do not have any way of adding position feedback (such as a quadrature encoder), you will not be able to make full use of your motion controller. It is possible to simply read a voltage in and output a specified voltage from the motion controller. However, you lose all hardware timed control and all the benefits of a motion controller. If you are interested in that option, a DAQ board might work better for you. Otherwise, I highly recommend looking into adding a quadrature encoder to your system.
Best Regards,
Jesse D.
Applications Engineering
National Instruments

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Thanks in advance
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Attachments:
Pre-preg Machine Program.vi ‏95 KB
Equal-Greater-Less.vi ‏31 KB
EncoderEvents.vi ‏20 KB

Hi ggpoly,
on your "Equal Great Less"-VI:
- It's RubeGoldberg to convert boolean conditions to enums just to select one of two cases…
- By moving index and output outside the inner case structure you don't need local variables…
- Comparing floats for equality is very dangerous as has been explained a lot of times before…
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
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I wanted to setup an automatic paddle so that this game will works as a one-player game. I have 3 files here. Ball.java, Play.java and pong.java.
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import java.awt.Color;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Toolkit;
import java.awt.event.ItemEvent;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseMotionListener;
import java.awt.geom.Rectangle2D;
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import javax.swing.Timer;
import javax.swing.JPanel;
import java.awt.*;
import java.awt.event.*;
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               ball.setDx(dx>0 ? -(++dx) : -(--dx));
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