Motion Control and Motor Drives

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Stepper Pulse Voltage Level in Open Collector

I am using the PXI-7344 Motion Controller to drive three stepper motors and 5 servos. I am running into unexpected problems with PXI-7344 Motion Controllers to drive stepper motors.
Steppers are configured as CW & CCW and open loop.

At first,I started with two PXI-7344 Motion Controller for 8 axes control.
But two axes stepper control with two axes servo on a one PXI-7344 gave a problem that one of stepper axis speed was faster than a given command speed on a certain moment during all four axes were running simultaneously. In spite of new firmware upgrade, that problem could not be fixed.
So now I am using three PXI-7344 Motion Controllers for 8 axes.

The second problem is the output voltage level of stepper pulse.
-7344 Motion Controllers and stepper amplifiers are interfaced with "open collector".
Stepper amplifiers are driven with +24Volts and +24Volts is supplied from stepper amplifiers.
As hooked up to a scope to monitor,stepper amplifiers are working correctly as the output voltage level of stepper pulse over +15V for a rise but incorrect as below +15V causing fast speed and more pule move than the given command.

The problem is that the pulse voltage level is not uniform for axes on PXI-7344 Motion Controllers. For an instance,Axis one always gives +15V pulses but other axes are not. And other PXI-7344 Motion Controller's axes always gives only around +13V level pulses even if it is new one.
So it could not be replaced with other one except that gives +15V level pulses.

Why does such strange thing happen?
And how could that problem be fixed?

Any help would be greatly appreciated!

Thanks in advance.

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Message 1 of 3

The stepper outputs on the PXI-7344 Motion Controllers output TTL pulses ranging from 0 to 5 volts. I'm a bit confused by your explaination that the "PXI-7344 Motion Controller's axes always give only around +13V level pulses." Does this mean that the 7344 is outputting 13 volts, or is this the output of the stepper motor amplifier? Also the voltage level of each pulse should never effect speed, just torque.

I recommend going to and contacting one of our NI-Motion specialists. That may provide a better forum for getting to the heart of your odd behavior.
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Yes,the stepper outputs on the PXI-7344 Motion Controllers output TTL pulses ranging from 0 to 5 volts when it is disconnected with a motor amplifier.
The problem is that when the stepper motor amplifier supplys +24Volts and is connected with UMI7764,the voltage level of each pulse drops to +13V level.That means UMI7764 drops +24V of stepper motor amplifier to +13V though it is connected as "open collect system".

Thanks for your comments.

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