Encoder and analog feedback together

I am using a PCI 7344 board that will operate up to 4 axis with both encoder and transducer feedback.
The user will have the ability to switch between the two types of feedback whilst on the fly with the system momentarily executing a stop command before re-configuring itself in the other mode be it encoder or transducer. This works fine.
My problem is - when I am in encoder feedback mode, I do not get a feedback reading from my transducer as my primary feedback device is the encoder and as such the output given is for the primary device. I need to be able to see the analog feedback device whilst operating with the encoder and primary feedback.
I may have a solution to this, by using one of the feedbacks as the secondary feedb
ack although could not find any information regarding secondary feedback on NI's web site.

Hello,
First of all, analog feedback can not be used as secondary feedback. When you are running on analog signal as your primary feedback, you should be able read encoder data calling the Read Encoder Position.flx. When you are running on encoder as your primary feedback, you should be able read analog data calling the Read ADC.flx. If you do the enabling/disabling properly when you are switching from one feedback mode to other, you should be able to read all the signals.
Hope this helps!
Regards,
Yusuf C.
Applications Engineering
National Instruments

Similar Messages

Problem when combinning PWM signal and Analog signal TOGETHER!

Hello everybody,
first of all i have DAQmx 6212, and i need to run a small water pump (9V-16V) which needs to be driven by a PWM signal; also i have a motor (5V-13V) for a water valve that needs to be driven by a analog signal and it has a built in a force feedback potentiometer, i connected on the extremeties of this potentiometer +5V from the DAQmx and used the output voltage from the third extremety as a diagnose value for knowing the position of the motor.
my VI shows:
1. is a normal Counter output to create my PWMout signal.
2. is an analog input i use it as a PWMin to the LabVIEW to diagnose what is happenning in my water pump through the duty cycle and the frequency.
3. is an analog input from the third extremety of the potentiometer.
4. is an analog output which i have used as a power supply for the motor valve and i have used an AC/DC amplifier to aplify the signal from the DAQmx and drive the motor, between (3. and 4.) i have made a feedback with some calculations i had a P-controller to know the actual position of the motor valve.
My Problem:
when putting 1. and 2. in the same VI alone, i am getting a clean PWM in/out with no problems mentioned;
also when putting 3. and 4. in the same VI alone i can control the motor valve without any problems;
but when i put all these 4 together as found in the attached VI, i have a problem that the motor valve is running continously without stopping even if i change the valve position between 0 and 100 %, i should mention that i am seeing a normal PWM out/in signal on my oscilloscope, one other thing that if i delete one of (1. or 2.) and run the VI the motor valve is working fine without any problems.
so this my problem, if you can think of any solution please let me know.
thanks in advance for your help.
Regards,
Alosh
Solved!
Go to Solution.
Attachments:
pwm.out.in.analog.out.in.vi ‏45 KB

Dear nathand thanks for your reply,
i have ran the vi again and i am have error no 50103 from the (AI, number 3. ) but it is not displaying the error message, the VI keeps running without any error notification.
adding to that, i have tested the VI again today by placing (1. and 2.for the PWM inout) together in one VI and (3. and 4.for the motor valve) in another VI and ran them one after the other, i had another problem. if i turn the motor valve vi, the motor will run smoothly but in the pwm vi i will have a problem in which the AI did not read any value. also doing this vice versa by running the pwm vi first it will work perfect but the motor vi will have problem in reading the measured voltage in AI during this the motor will keep on running without stopping.
so i think now the problem is in AI (2. and 3.) readings they are interfering on each other but i am not discovering where is my problem...
Q: does the AI's seems well build or i can do it in an another way so to get over the interfering?
Regards,
Alosh

Switching from analog feedback to encoder feedback

Greetings,
I am having problems with switching feedback sources in my Labview App. I am using a 7344 board. I initialize the board in encoder feedback as primary. Then I am able to switch to analog feedback, but then the problem is when I switch back to encoder feedback it acts like it is still using analog feeback as a Primary. I can only get it back to encoder feedback only if I reinitialize the controller. I am disabling the axis before I am making config changes and then re enabling axis to run axis on both accounts. However it doesn't seem to be getting back to encoder feedback. Any Ideas?
Wade

Hey wade,
As mentioned in this Forum Thread, you should be able to switch back and forth between feedback sources on the 733X motion controller by disabling/enabling the axis. However, this is what you say you are doing. Perhaps changing the order in which you make the feedback switch. What happens if you make the feedback change and then simple disable/enable the axis? Are you seeing this same behavior on all of your axis? What version of the NI Motion driver are you using?
Hope this helps.
-Ben
WaterlooLabs

Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?

My system
PXI 1052 chassis
PXI 8196 RT controller
Flexmotion 7356 motion controller
Flexmotion 7354 motion controller
6259 M series DAQ
1520 SCXI
1520 SCXI
1314 SCXI frount mounting terminal block
DSM strain gage load cells
Exlar SR Brushless PM motors
Kollmorgen servo star CD series 5 drives
My objective:
I want to measure the force on the load cells with the 1520 SCXI (i.e. excite the load cell then amplify and condition its output) then I want to use this analog (force) signal as the primary feedback for my motion control system (7356 and 7354 motion controller connected to my drives and motors).
The problem:
The motion controller boards (7356 and 7354) can be configured for force feedback control via analog feedback from a load cell. However the boards implicitly expect the load cell signal to be amplified and conditioned with and external signal conditioner rather then using an NI SCXI module. Currently I’m am reading the SCXI signals via the 6259 M seriers DAQ and consequentially have no way to route the signal into the 735X boards for force feedback control. I can use softmotion to control the motors but then I loose the fast PID update rates possible with the 735X boards.
The question:
Is it possible to condition a load cell signal with a 1520 SCXI and then use it as the primary analog feedback for a 735X motion control board?
Thanks
Patrick Aubin
Ph.D Candidate
University of Washington &
VA MedicalCenter of Excellence for
Limb Loss Prevention and Prosthetic Engineering

Hi GG,
Thank you for your feedback.
>create your own external circuitry to amplify the signal.>
True a few op-amps could amplify and filter the signal externally but the performance of such an amateur built system will never match the accuracy and functionality of the 1520 SCXI. That’s why we spent the $2500 for the professional version.
>One thing that you could do is to use a UMI with your motion controller and then wire your signal from your SCXI to the UMI.>
As I understand it the UMI is basically a break out connectivity interface for third party drives. After conditioning and amplifying the analog force signal with the SCXI module the analog signal isn’t available to wire into a UMI. To my knowledge the conditioned signal of the SCXI resides only in the PXI backplane (i.e. there is no physical access to the conditioned analog signal). Can you explain how the UMI could be help here.
Again thanks for your input GG.
Patrick

Torque control is not working for my system using analog feedback

In the test bed, we are testing a brushless DC motor and a load motor generates torque to the test motor. The test motor is running with torque control scheme. They were connected together and I measured the torque signal to feedback the signal and control it. However, I just realized it only control when the torque was static. If I commanded a certain torque value (in this case, counts command), it kept generating that value. However, it did not generate the same torque in different position. I heard NI motion controller could develop torque values by mapping the torque signal with encoder signal. If it's true, the torque generation based on analog feedback, also, needs constraint by rotor position, right? W
hen I turned on the load machine with constant speed (50 RPM), the torque from the test motor did not provide the constant torque that I commanded. It generated the fluctuated torque values. This means the max torque was generated at one point and decreasing by rotating the shaft and increasing the torque. Keep going in this way. Could you please tell me if this is the correct response when we are using analog torque feedback?
Thank you.

Try the following:
1.-Set your test motor to encoder feedback instead of analog feedback.
2.-Load a velocity move on the axis for the test motor.
3.-Set the following error limit on you axis to 0 (disable following error).
4.-Use the load torque limit function to limit the amount of torque the 73xx PID loop will generate,this value is in volts, so you will need to do a correlation between the voltage output from the controller and the torque reported by your torque cell.
5.- Start the load motor.
6.-Engage the cluch.
7.-Start the velocity move on the test motor, you will see the torque ramp up to the torque limit.
8.-Call the load torque limit function on the fly to vary the torque setpoint to where you want it.

Problem using analog feedback on pix7340

Hi,
I am trying to use analog force feedback on one of my axis on pxi 7340. The problem is that MAX always uses encoder as feedback even if i configure it to be analog. In MAX i disabled encoder and enabled the appropriate ADC for the axis and set the position to few hundred counts so the controler stops the axis when force is above a small value (around 1V). If i start motion it moves the same as if the feedback was encoder (for few hundred counts). I dont know what is happening. I red the motion manual and if i understood it correctly the axis should move at the configured speed until the force is larger as value i set in position field.
Thanks
Solved!
Go to Solution.

Hi toni939,
please have a look at this document to get a full understanding how analog feedback works with NI motion control boards. I have also gathered all discussions with my involvement about analog feedback under the AnalogFeedback tag.
Kind regards,
Jochen Klier
National Instruments
Message Edited by Jochen on 02-03-2010 04:20 PM

Trigger based on Position when using analog feedback

I am developing an application that uses two hydraulic cylinders to move a model in a pitching and plunging motion.
My hardware consists of a P4 computer running windows XP SP2. The motion controller is a PCI-7350, 2 axis board.
The two hydraulic cylinders are equipped with analog position sensors which provide the primary feedback signal for the motion control.
The drive signal from the motion controller is used to open or close a hydraulic valve, closing the loop. The motion portion works great.
I am using buffered contouring to generate a precise motion on the two axis using a vector space. The update rate is 10mSec and the motion appears to be correct. Is the contour update rate a precise 10mSec if the PID is running at 62.5 uSec?
My problem is I need to generate a trigger when the controller is on specific positions of the contour. I can't use breakpoints as I am using analog feedback instead of an encoder. I wrote an onboard program that monitors the contour buffer and toggles the breakpoint line when the controller is on or beyond the specific point. It runs ok and is close but, I am getting an occasional timing discrepency of roughly 16 mSecs. ie the trigger will occasionally be late by more than 1 contour period.
I tried increasing the size of the buffer to hold all the points as I thought the delays might be occuring when the buffer was being updated. No change in performance. I tried assigning more time to the trigger program as it is the only on board program, but again it seemed to make no difference. I reduced host communications to a minimum, no change.
I have attached my entire application and a test sample waveform in a zip file. You can run the application without any hydraulic cylinders if you set max following error to 32768. You should have a trigger pulse on the breakpoint line every 500 mSec.
Any pointers would be greatly appreciated.
Attachments:
M22PitchPlunge.zip ‏524 KB

Brian,
Yes, you can reach exactly 10 mS update interval with a PID rate
of 62,5 µSec. You can calculate the actual interval with the forumla
provided here.
Of course the accuracy is limited by the accuracy of the onboard
oscillators of the board but this shouldn't be really relevant.
Generating triggers based on 2D position data is not a trivial
task. I have tried to examine your program but it's a bit hard to read.
I had a look at your onboard program. I don't understand exactly how
you determine if the axes have reached a trigger position or not. It
looks like you are only reading values from buffers. For an exact match
with the physical positions you should read the real position values
from the axes and compare them with your trigger position buffer. In
your comparison algorithm you will need to add some tolerance to allow
some deviation from the ideal trigger position (see image).
There are several possible solutions for your application. You could
either try to implement the more advanced comparison in your onboard
program but I'm not sure if this will result in the performance you
need. The 7350 provides only a limited amount of CPU power for onboard
programs. At last it all comes down to the question how good your
deterministic real-time behavior needs to be. If some ms delay and
jitter are ok for you then you probably could stick with this approach.
If you need a better real-time behavior you should consider using
either an additional real-time board like the PCI-7041/6040E that could run the 2D trigger algorithm or a PCI-7830R board that could run the algorithm on an FPGA.
There are even more options including the NI SoftMotion Development Module to design your own motion controller using LabVIEW RT but again, this depends on your application needs.
Best regards,
Jochen Klier
National Instruments Germany
Message Edited by Jochen on 09-09-2005 10:47 AM
Attachments:
Image1.jpg ‏19 KB

New to PRE and need feedback on my system build

I played around with the trial version on my old computer and decided to go ahead and purchase PRE 9 and PSE 9 together. I have built a few PC's in my day and recently completed my current build running my purchased software. I was hoping that I could get some feedback on what I have and what I might change to get better performance. PRE is very jittery when scrolling through content and playing back the timeline. Sometimes I don't even see a transition. I am new to video editing in general and capture in HD with my Canon HF S100, so I am planning on editing in HD as well. Sorry for the NoBo question, but my machine smokes until I fire up PRE. I may be using the application incorrectly, but I am assuming that my low end video card, is an area of concern/bottleneck. I don't want to blow $800 on a Quadro 4000 if it won't make a huge difference, but I assume it will. Thanks in advance for any and all help.
High level build
MoBo - ASUS P6X58D Premium LGA 1366 Intel X58 SATA 6Gb/s USB 3.0 ATX Intel Motherboard
PSW - CORSAIR HX Series CMPSU-620HX 620W ATX12V v2.2 and EPS12V 2.91 SLI Certified
Proc - Intel Core i7-950 Bloomfield 3.06GHz LGA 1366 130W Quad-Core Processor
Mem - 12GB Mushkin Enhanced Redline 240-Pin DDR3 SDRAM
Drives
     OS - Crucial RealSSD C300
     Media - Western Digital VelociRaptor WD6000HLHX 600GB 10000 RPM SATA 6.0Gb
OS - Windows 7 x64 SP1
Video - NVIDIA GeForce 9500 GT
Detailed DxDiag output below.
System Information
Time of this report: 2/27/2011, 19:30:14
Operating System: Windows 7 Ultimate 64-bit (6.1, Build 7601) Service Pack 1 (7601.win7sp1_rtm.101119-1850)
Language: English (Regional Setting: English)
System Manufacturer: System manufacturer
System Model: System Product Name
BIOS: BIOS Date: 05/25/10 14:57:23 Ver: 08.00.15
Processor: Intel(R) Core(TM) i7 CPU         950 @ 3.07GHz (8 CPUs), ~3.1GHz
Memory: 12288MB RAM
Available OS Memory: 12280MB RAM
Page File: 8908MB used, 15647MB available
Windows Dir: C:\Windows
DirectX Version: DirectX 11
DX Setup Parameters: Not found
User DPI Setting: Using System DPI
System DPI Setting: 96 DPI (100 percent)
DWM DPI Scaling: Disabled
DxDiag Version: 6.01.7601.17514 32bit Unicode
Display Devices
Card name: NVIDIA GeForce 9500 GT
Manufacturer: NVIDIA
Chip type: GeForce 9500 GT
DAC type: Integrated RAMDAC
Display Memory: 4069 MB
Dedicated Memory: 997 MB
Shared Memory: 3071 MB
Current Mode: 1920 x 1080 (32 bit) (60Hz)
Monitor Name: Generic PnP Monitor
Monitor Model: ASUS VH242
Monitor Id: ACI24FA
Native Mode: 1920 x 1080(p) (60.000Hz)
Output Type: DVI
Driver Name: nvd3dumx.dll,nvwgf2umx.dll,nvwgf2umx.dll,nvd3dum,nvwgf2um,nvwgf2um
Driver File Version: 8.17.0012.5896 (English)
Driver Version: 8.17.12.5896
DDI Version: 10
Driver Model: WDDM 1.1
Driver Attributes: Final Retail
Driver Date/Size: 7/10/2010 04:38:00, 12471400 bytes
WHQL Logo'd: n/a
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Driver Strong Name: oem3.inf:NVIDIA_SetA_Devices.NTamd64.6.1:Section003:8.17.12.5896:pci\ven_10de&dev_0640
Rank Of Driver: 00E62001
Video Accel: ModeMPEG2_A ModeMPEG2_C ModeVC1_C ModeWMV9_C
D3D9 Overlay: Supported
DXVA-HD: Supported
DDraw Status: Enabled
D3D Status: Enabled
AGP Status: Enabled

This ARTICLE will give you some tips on your I/O sub-system setup for video-editing.
As for the Scratch Disks, think of those as the "working files," that PrE produces and needs to edit video. Part of those will be the Media Cache, where you will have the CFA (Conformed Audio) files, the PEK files for Waveform Display, etc. For a bit of background on Conforming, see this ARTICLE.
Now, for ultimate performance, one would want to spread the I/O load over as many discs, as is possible. The OS and programs accessing the HDD is a given, but you have already segregated them onto C:\. Then, one has the Scratch Disks, which also require quite a bit of access. The media is accessed often for many operations, and then there is the need to Export/Share. In a perfect world, one would allocate a separate HDD for each of those operations, with one caveat: when one has finished a Project, there will then be the cleanup of the files. If one has spread the Project over multiple physical HDD's, they must go to each, and do the cleanup. OTOH, and at the sacrifice of ultimate spead with I/O access, if one has placed their Project into a root folder, say [Project Name], and then accepted the default location for the Scratch Disks, for Same As Project, all they have to do is Delete that Project Name root folder, and everything else comes with it. As I migrate Projects between computers, I locate everything in a Project Name root folder on an external, and then everything is below that folder structure. For media, I leave my Assets on an NAS, and just Copy over what I need to the various media sub-folders, like Video, Stills, Music, Audio, etc. I give up performance, but have everything that I need to move the Project about, and cleanup is easy. In my case, each external has a permanent drive letter assignment in the OS of each computer, so that drive Z:\ is always Z:\ on each computer, and regardless of what else might be plugged-in to that computer. Makes life simple for me.
Hope that this helps.
Good luck,
Hunt

Exporting to Media Encoder and file locating issue

Ok, Now I've read a LOT of threads trying to find a solution to this but none of them have answered my problem exactly, so here's what I have:
Running a New computer with a clean install of Windows 7 64 bit and Adobe CS4 Master Suite
Hardware:
Dell Precision M6400
Intel(R) Core(TM)2 Duo CPU T9900 @ 3.06 Ghz, 3.07 Ghz
12.0 GB Ram
Premiere ran fine for a while, but soon I've run into a problem where I try to export to the Media Encoder and I keep getting the error:
"Could not read from the source. Please check if it has moved or been deleted" over and over
I have deleted recently imported media one at a time to try and locate what's causing it since it wasn't doing this before, but no luck. So I restarted the program but now the Premiere project won't open. The task bar loads until about 2/3 in and stops there indefinitely, I've left and came back to it 2 hours later and it hadn't moved. I back tracked and found a previous save that will open, but it still will not export, it still says "Could not read from the source. Please check if it has moved or been deleted". And as soon as I update anything and save a new file that one will not open either.
I've tried recompressing each video file into a format I know works well with Premiere but still no difference.
This problem has plagued my workflow for a while now and I can't take it anymore. I've had to restart clean project files to try to work around it but I lose so much progress, and the work around by rendering the premiere file through After effects hasn't worked either. The error I get there says "Dynamic link server is busy".
Here's what the problem is not: It is not because I uninstalled CS3 or any other previous version, I've never had it on this computer. It's not a plugin problem, I don't have any plugins on this install except for the default ones that Came with Adobe Master Suite for Premiere Pro.
Someone please help me, this is ridiculous that I have had to trouble shoot the program this much. Both CS4 and Windows 7 have been around for over a year now and neither are in Beta Editions

Wow, sorry, forgive me if I've seen most forums work with a lot less, and your dismissiveness led me to assume you hadn't read my post.
All of this is new and up do date as far as Adobe and Windows updates go, that's Version 4.2.1.
My projects for this are all in NTSC Widescreen DV 24P, the particular sequence that I render from is in that format as well, although regardless of which one I use the problem keeps occurring.
My renders for my recent purposes have been compressed in .h264, IPOD video Large. The codec I'm rendering in also doesn't seem to matter, because I've tried this in .avi., .mov, .h264, .wav, etc. and all with various settings that I thought might help, but the encoder quits encoding 4 seconds in and gives me the error that it can't find the media.
And I didn't mention the media type and what not because it seems irrelevent of what I use this problem keeps happening. I'm pretty sure it's a problem with the project file or perhaps the media encoder or both.
And I don't know what you mean by "disks"
Do I have a Raid set up on my hard disk? No, I have two 0.5 TB hard drives, Programs on one (C:\) Projects on the other (D:\).
What address am I saving the scratch disks to? I use the default of "same as Project". Have I tried Clearing it? Yes.
I don't think I'm getting at what you're asking.
And I don't think I've ever used an .xlsm (which is excel?) file and I've definitely never used a Power point project (PPS?) file in my projects. And they open in their respective programs, although I'm not sure why you asked about that. Again I'm not sure I know what you mean.
The Premiere Project (.prproj) file is what I'm trying to open when the progress bar stops at 2/3 the way through and forces me to terminate the process with the task manager to close it.
It would help to mention that all my projects are animated and I use premiere to cobble them together, so no problems that relate to transferring media from a camera to the computer would apply here. Most of the files I get out of Maya are in Default .avi or .mov files, and I also use a handful of .wav files for the dialogue and .jpgs for cards and placeholders.
I believe that this problem began when I updated a few of the files in my project, but I've been doing that for weeks without incident. I've been updating them by saving over the old media file with the updated one of the same name, length, and type.
I don't work exclusively with Premiere, in fact it's not what I usually use, that would be Final Cut Pro.

Problem when analog feedback is set as primary feedback

I have a simple labview program for pressure control. Primary feedback is set to ADC 1 in MAX. ADC 1 is connected to a voltage signal which represents a pressure. When the motor run from program, the motor stopped after certain time because move complete turn to True, but the position reading didn't reach the desired position at this time. If the motor run from MAX, the motor didn't stop untill the position reading reached the desired value.
The configuration file exported from MAX and lv program are attached. I would appreciate you very much if anybody could find problems in my program or configuration.
I am using PCI 7342.
Thanks.
Attachments:
ADC_primary_feedback.xml ‏581 KB
pressure_control_2.vi ‏74 KB

Hello Ya-hoo.
I first just want to clarify what I think your issue is. It sounds like you essentially have a servo motor system with analog feedback. This system is moving to the desired position (pressure) when it is run through 1-D interactive in MAX, but it does not correctly move in your LabVIEW program.
This situation is uncommon but it can happen. Generally speaking, the things to make sure of:
Be sure the settings are saved in MAX and that the board is initialized with those settings before running the LabVIEW program
Make sure you are not calling the stop VI too early. In the while loop you are polling the move complete criteria. What happens if you take that out and simply wait until the user pushes the stop button? If this fixes
the problem, try adjusting some of the Move Complete criteria (Trajectory Settings in MAX) and see if that changes the behavior.
As far as the tuning is concerned, I will refer you to the following tutorial on Understanding Servo Tune. This should go over some tuning concepts.
Hope this helps.
Regards,
Colin C.
Applications Engineering
Colin Christofferson
Community Web Marketing
Blog

Scaling Settings Analog Feedback for 7354

Hello,
I would like to use a Torque sensor as an analog feedback in 7354. The sensor range is +/- 100 Nm, The output is 10 VDC for 100 Nm and 0 VDC for -100 Nm so Zero Nm is 5 VDC.
How should I scale torque values as counts ? When I program with Labview, What should i do ?
Thanks
TallTale

Hello TallTale,
Thank you for using National Instruments discussion forums. Some more information might help in understanding what type of motion control system you have such as: Is your Torque related linearly to the position of the motor or are you changing the velocity due to the torque value? You can set the ADC range in Measurement and Automation Explorer for each axis analog inputs under "ADC Settings". The difficulty comes
in understanding the "paradigm shift" in the standard NI-Motion API
terms; specifically target position, velocity, acceleration, and
deceleration. I have attached a really good document that discusses how to setup your motion control system for analog feedback. I hope this information helps. Thanks and have a great day.
Regards,
Mark T
Applications Engineer
National Instruments
Attachments:
How to setup a system for analog feedback control.doc ‏1188 KB

Analog feedback 7344 0-5V non liniar

Hi.
Having a 7344 left over from an aborted project, I wondered if this controler would accept a non liniar 0-5V position feedback in PID closed loop.
I know the analog input is "only" 12bit, but this gives by far the required position on the travel I need for this application which is to be an automatic throttle control on my enginedyno. It is not possible (nor practical) to mount encoders on the many different throttlesystems, so the 0-5V from the throttlepositionsensor is all I have.
If ok, then what kind of motor should I look into, stepper og servo since the application is more still standing in any position than actual turning (running is expected to be very few turns when geared to move throttle 0-80 grd. I have both a SX and CX Nudrive.
Thanks in advance
Peter Rene

It should be possible to use the 0-5V signal as an analog feedback. You can configure the ADC settings for a 0 to 5 V range that maps the full 12 bit resolution to your feedback range. For position control it doesn't matter that your feedback signal is non-linear as long as you know how the voltage of your feedback signal corresponds to the position of the motor. Still you will see the same amount of non-linearity in the velocity profile of your axis as long as you don't run your axis always in contouring mode to compensate it.
Even though most time your axes are static which I agree would suggest to use a stepper I recommend to use a servo instead. The reason is the fact that closed loop steppers are not controlled in the same way as servos. In theory, analog feedback for stepper motors should work correctly; however, there are several problems that will arise when you attempt to control a stepper motor from an analog feedback. In this type of system, the analog feedback is converted into a position and compared against the desired position, and then the stepper motor is "pulled in" to that position. One of the problems with analog feedback for stepper motors is noise, another one are non-linearities of the feedback signal. Closed loop stepper mode relies on a fixed ratio between the generated steps and the feedback. This is not the case if the feedback signal is non-linear. Thus you will have to use a servo motor.
As an alternative you should consider using a stepper motor in open loop mode (without feedback). If you can make sure that you don't loose steps this would be the best and easiest option.
I hope this helps,
Jochen Klier
National Instruments Germany

Analog feedback

Is there any way to manipulate the analog feedback signal used by a 7354 motion controller within Labview?
I.e. implementing things such as lookup tables, averaging, filtering, etc in the control loop?
For instance, for a noisy signal is a hardware filter right at the input to labview the only option?

Cronin,
the 7354 doesn't offer a way to manipulate the feedback signals before
they are used in the control loop. The DSP of the board talks directly
to the analog inputs so any manipulation would have to be done in the
firmware which can't be changed by the end user. If necessary filtering
should be done in external signal conditioning hardware.
On the other hand NI offers products to build your own motion
controller based on LabVIEW Realtime and (optionally) LabVIEW FPGA
hardware. The NI
SoftMotion Development Module for LabVIEW gives you the the flexibility
to choose from a variety of hardware platforms the best fit for your
application. As the trajectory generation and the control loop are
running in LabVIEW you can manipulate literally every single piece of
the motion controller including the feedback signals and the control
algorithm.
Please have a look at this link for more details.
Best regards,
Jochen Klier
National Instruments Germany

When using the analog inputs and analog outputs of the PCI-7344, what is the conversion between the voltage entering the card to counts? Similarly, what is the conversion between counts to voltage at the output of the card?

I am using the PCI-7344 to control my system. The analog inputs are connected to the output of my system while the analog outputs serve as feedback to the system. The system is a servo. I want to know what is the conversion between the voltage read at the input, to card counts, and finally to the voltage output to the system.

Carole,
If you are trying to do analog feedback with a servo motor, Chapter 14 of the manual talks about how to set up the torque feedback. Also linked below is a LabVIEW example of analog feedback.
Chapter 14
NI-Motion User Manual
Automatic Analog Feedback with FlexMotion example
A. Talley
National Instruments

Isolated Ground and Analog Ground in Multisim

What is the availability of isolated or analog grounds in Multisim? Multisim allows for 2 primary types of grounds, standard ground (can also be called earth ground, represented always as net '0') and digital ground, however sometimes in a design you will need multiple ground references for the various areas of the design including an earth or chassis ground point, digital ground and analog ground and sometimes an isolated ground.
How can this be accomodated in Multisim from both a modeling and layout standpoint?
Regards,
Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group
50 Market St 1-A
South Portland, ME 04106
Phone: 207 892-9130
Email: [email protected]
Solved!
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For isolated ground - from a modeling standpoint - one method involves creating a netname (such as isognd) and creating a physically isolated connection from standard ground (net 0) with a large resistor value (or other appropriate high impedance network).   From a layout standpoint however, managing a single netname can be cumbersome and error prone.
Attached is an alternative approach using specially created symbols (IGND, V_ISO, AGND and CGND) providing for an isolated ground, isolated DC voltage source (referenced to IGND) and an Analog Ground, respectively.   These similar to a previous post created, allowing for multiple VCC or VDD connections in a design.
NOTE: When IGND and AGND are initally placed, they will be set at '5V', you will need to manully change the value to 0V to make them properly function. Here are the components and notes on each.
IGND   : Isolated ground with a built-in 10M Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgrr)
V_ISO : Isolated DC source referenced to IGND. IGND must be present in the isolated circuit for functioning properly
AGND : Analog ground with a small built-in 0.001 Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgr)
CGND : Chassis ground with a small built-in 0.001 Ohm resistor to standard ground (this can be changed in the SPICE model if needed from the DB Mgr)
Typically AGND, DGND, CGND and standard GND (net 0) would be tied together in layout with a star ground connection. This can be done in Ultiboard by using a net bridge connection.
Regards,
Patrick Noonan
Business Development Manager
National Instruments - Electronics Workbench Group
50 Market St 1-A
South Portland, ME 04106
Phone: 207 892-9130
Email: [email protected]
Message Edited by _user32 on 09-08-2009 04:22 PM

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