Position Detection

[ASU]

Forum,

I have a motor system I'm thinking about building. To prevent the motors from traveling too far I'm going to insert a SPDT switch to indicate it has reach a certain position. What I'm looking for is a NI device that will tell me that the switch is either open or closed therefore shutting down the motor. Can someone maybe offer some suggestions on what I should consider?

thanks

Newbie D

[JB]

Use a motion control board. See here for a general information about limit switches with this type of boards and post back if you need further help.

[ASU]

Well, I was trying to stay away from using a motion board unless it can do some of the functions of a Multifunctional DAQ

[Jochen]

The main advantage of a motion control board is the fact that all time critical tasks like PID control and limit switch monitoring is done onboard in real-time. Of course you could use a multifunction DAQ board or a digital I/O board to detect the state of a digital signal but unless you are using a real-time operating system (Windows is not a real-time OS), there is a certain amount of uncertainty if and how fast your software can react on a signal change.

There are multiple hardware options available for your application (e. g. motion control boards, cRIO, multifunction DAQ with LV RealTime,...).
Depending on your application these options could be a perfect fit or an overkill. Please provide some more information about the type of application and the level of motion control (e. g. start/stop motor, velocity control, position control, velocity profiling,...) that you require, so I can give you a better advice.

Thanks and kind regards,

Jochen Klier
National Instruments

[ASU]

Thanks Jochen,

I wouldn’t have a problem using a motion control board if it did more than just motion control functions. I also need 12 I/Os and a 5V AO signal. That’s the reason I was asking about a multifunctional DAQ. Below I will summarize my application.

I have total of seven motors that I want computer control over. Of the seven 5 drivers have a serial interface to a pc for remote control.  The remaining two drivers can be controlled by a series of logic highs and lows. Three of the motors will have a limit switch to detect a certain position which is fed back to a control device telling it to stop.

Currently I was planning on using an 8 port rs232 to USB to interface/communicate with the 5 drivers and a DAQ card for the other 2 drivers requiring TTL signals.

This is the jest of the system so let me know what you think

Darryl

[Jochen]

Darryl,

in general your approach should be feasible, but I'm still not sure, if you it is a good idea to control the two remaining motors with a DAQ device. So here are some more questions.

"Three of the motors will have a limit switch to detect a certain position which is fed back to a control device telling it to stop."
Is the control device you are referring to already defined?

My other questions refer to the two motors that are controlled by TTL signals. Could you please provide some more specifics? How does the signal look like? Is it a step and direction signal as it is typically used for stepper motors? Do you need to vary the frequency of the signal (e. g. for acceleration ramps)? What frequencies do you need? Do you need to control the position of the motors or just the velocity?

Thanks,

Jochen

[ASU]

Hi Jochen,

The device telling the motors to stop has not been defined, also the two independent motors is a step and direction as pointed out (40105 driver http://www.hsi-inc.com/).. The frequency will be fixed no higher than 1200 Hz and is not that important compared to the precision of the position.

Thanks,

Darryl

[Jochen]

Darryl,

if you really don't need a higher level of control than generating a finite pulse train with a fixed frequency, you could do this with the digital I/Os or the counters of an M-Series DAQ board. Things become much more complicated, if you nee dto generate acceleration and deceleration ramps. You also may run into some difficulties if you need to control both motors completely independently.
In cases like thes the additional cost for your development time will quickly exceed the cost of a motion control device like the PCI-7332.

Jochen