PCI-7344 motor interfacing help

[blstz]

Hi,

I've been provided with a PCI-7344 together with a UMI-7764 by my university for my course final year project. My project consist of controlling 1 stepper motor, 3 dc motors and 1 servo motor. Also included is 4 digital proximity sensors. As im still new with motion control cards, I would appreciate it anyone can help guide me.

I'll be using thrid party motor drivers for the stepper motor and dc motors (H-bridge). I know that i'll be connecting the stepper motor output to my stepper motor driver but im confused about where would i get a output for my dc motors. Can i use the digital output for motion i/o (inhibit) to generate a pwm signal for my dc motors or it's possible to connect my dc motor driver to the stepper output? Finally, is it possible to use the digital inputs for the motion i/o (encoder, home switch) with my proximty sensors?

The problem is that i only can use the I/O from the motion i/o port because the SCB-68 that is required for the digital I/O port may not be accessible to me.

Any help and suggestions would be greatly appreciated. Thank you

-Terence

[Jochen]

Terence,

the PCI-7344 can control up to four axes. Any combination of 0 to 4 open loop or closed loop stepper motors and 0 to 4 servo motors (always closed loop) is allowed.

I don't see a good way to control 5 motors with this board. If you need PWM signals to control (not to drive!) additional DC motors in open loop mode, you could use two static PWM outputs on the Digital I/O connector (yes, you will need an SCB-68 to access those). These outputs are static. That means, that you can adjust the frequency and the duty cycle in software only so you can't generate trajectory profiles on these outputs.
In general you can't use stepper outputs to control DC motors, as you can't control the duty cycle of a stepper output. All other digital I/O signals are static and can't be used to generate control signals. If you really need to provide PWM signals for you DC motors' drives, you could use an additional counter board like the PCI-6601. Still you won't be able to generate trajectories with this board. If you need to create trajectories for open loop DC motors, it might be a better option to generate analog waveforms on the analog outputs of a mutlifunction DAQ board and use a DC motor drive, that converts an analog input signal to a PWM power signal.
Please note that the 7344 can't drive motors directly, so you will have to use power drives for all axes.

You can use proximity sensors as limit switches with a 7344 but you need to be careful with that. The lilmit switch inputs of the 7344 are pulled up to +5V with 3.3 kOhm. Many proximity sensors switch between +5V and 0V but they typically have a high output impedance, resulting in a voltage divider with the 3.3 kOhm resistor. You may get around this issue by connecting a resistor from the limit switch input to ground to reduce the voltage level when the proximity sensor has switched to low level. This is not a very clean approach and you should use a potentiometer instead of a fixed resistor to find the right value for the resistance.

A much better approach is using a UMI-7774 instead of the UMI-7764, which provides direct connectivity for proximity sensors.

I hope this helps,

Jochen Klier
National Instruments

[blstz]

Thanks for the reply!

Actually i do not need a high precision trajectory for my servo and dc motors. It's only to start and stop the motors (for a conveyor and rack/pinion mechanism). Only the stepper motor requires slight precision as it will be moving a gantry type crane mechanism. No arc or contoured moves. How about if i use the digital or analog output for switching relays connected to the dc motors? Can this be an alternative?

Also, when connecting the servo motor, do i connect it to the analog output ports or the stepper output ports? Do i need a thrid party driver for the servo? Since i'm only able to choose either servo or stepper at the axis configuration in MAX, does that mean that i can only control one motor per axis?

Im still not familiar with the card so thanks for the patience

[Jochen]

Yes, you could use the digital I/Os to switch relays. The digital I/Os can sink up to 64 mA (open collector).
You definitely need a 3rd party drive to provide the power for you motors. If you use a stepper drive and a stepper motor, you will use the axis' step and direction outputs. If you use a servo drive and a servo motor, you will have to connect the axis' analog output signal.

As already stated, the board can drive four axes. Each axis can be configured either as stepper axis or as servo axis.

Jochen

[blstz]

Hi,

Since you said that the output from my pci-7344 are only to drive, are they any thrid party servo drivers available if i can get my hands on a power motor driver by National Instruments? So i should need a servo driver that takes a signal input of +- 10V and then convert the signal to PWM output for my RC servo? 

Can anyone suggest a multifunction daq card that's just enough for my application? Need the card to be able to generate PWM signals.

Finally, is there a reason why i specifically need to use the UMI-7764 for the pci 7344 instead of just a normal unshielded terminal block? Is it because for the built-in driver inhibit control?

Thank you!

[Jochen]

• Here is a link to a document in our KnowledgeBase, that explains the difference between a UMI and a passive terminal block.
• As already recommended before, you could use a PCI-6601 to generate up to four independent PWM signals (still a simple power amplifier is required)

I hope this helps,

Jochen

[blstz]

Thanks Jochen for your reply. It does give me a whole lot more ideas about how to use the card.

Anyway, if i would like to use the Digital I/O ports on my PCI-7344 card, i would need an additional cable and SCB-68, correct? I was wondering that instead of using that SCB-68, can i use the CB-68LPR unshielded screw terminal block? Would it work or damage the motion control card?

Thank you!

[blstz]

Sorry i forgot to add that my university has a spare CB-68LPR unshielded terminal block and SH68-C68-S cable. Can i use it to access the Digital I/O ports on my PCI-7344?

[Jochen]

Yes, you can use the terminal block and the cable.

[blstz]

Great! It certainly gives me more options now.

I understand that it's necessary to supply a +5v to the umi-7764, what's the minimum and maximum current limits?

Thanks!