PCI-7344 motor interfacing help

Question

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

Answer 1

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