Unable to move backward, it moves only forward (one direction)

[Buechsenschuetz]

Measuring means "comparing", and it's almost useless to measure anything on the inputs of your motor driver unit without being able to compare the results to the specs of the motor driver unit.

Sink vs. sourcing configuration: The outputs of the NI controllers have circuitry which allows to output a voltage and a certain amount of current. The output current is limited by the on-board pull-up resistor (3K3). So the maximum current the board is able to supply (when the output is in logic high level) is defined by the permitted voltage drop across the pull-up resistor (the source voltage is 5V, the permitted voltage drop is defined by the input specs of your driver) divided by the resistor value. The max current, of course, should be equal or greater than the input current of the inputs of your motor driver.

Of course you can increase output current by using a smaller resistor, or, since you cannot change the on-board resistor, by connecting a resistor in parallel with the one on board (i.e. between +5VDC and the output). Unfortunately, the current which should flow into the input of your driver will flow through the resistor(s) and output transistor of the NI driver and will dissipate heat.

Since the output acts as a current source in this case, this configuration is called "source mode".

As NI uses a single transistor on the outputs, the outputs can also be used as "current sink". If you connect one terminal of the load (the input device of your motor driver is regarded as such) to +5VDC and the other one to the output, current will flow through the load into the output transistor which acts as a sink - hence the designator of this mode. You will have to add a suitable resistor in the current path to limit current through the load (and the resistor), otherwise the load and/or output transistor might be overloaded. Again, to determine the resistor value we need the input specs of your motor driver unit.

In many cases motor driver units use opto-isolators as input devices which will need about 1.5V and a current of 5mA (in case of low-current devices) or 10 to 20mA (in case of standard opto isolators).

[NAXE]

Update:

Finally I checked the voltages on the UMI, there is no +5V on direction pins.
Sorry for late checking but the UMI box is hard to access.

Further investigations revealed that there are problems on the UMI connectors.
Some pins are damaged, and also the blu patch seems damaged.

I'll thank you both for the support and excuse me because I'll never imagine a problem like this becuase all the cabling is in a safe positions and no people could access it.

On the PC side there was no problem, luckly, because there are no pins and the connectors seems better.

Thanks.

[xing]

I'm using UMI7764&PCI7340.

I found same problem."Unable to move backward, it moves only forward (one direction)"

But I already check the "Direction" signal.

When move forward, the CW output Pulse and CCW output 5V.

When move backward,the CW output pulse and CCW output 0V.

But the motor just can move forward, unable to move backward.

I need your help.

[Buechsenschuetz]

With the SINK configuration, the load of the output (the input LED of the optocoupler of the peripheral device in this case) is connected between the power supply and the output. Check whether your peripheral device has current limiting resistors for the input of the optocouplers. In most cases, these are designed for 5VDC operation. Connect the cathode of the input LED to +5VDC (but NOT directly, you ALWAYS need a current limiting resistor!!!) and the anode to the output of the NI device. The +5VDC power supply must have common GND connection with the GND terminal of the NI device. Some NI devices have a terminal with +5VDC but this pin should NOT be used as a supply pin as the available current is limited (to 100mA on the 7344 boards).

Anyhow, it seems to turn out that there is rather something wrong with one of your driver units. If they worked correctly with the connections you made there is no reason to change them.

[xing]

Thanks for your reply.

Now I change some connection:

1.The Motor CW+/CCW+ connect to the power supply(5V), not connect to the power suyyly 5V of  UMI-7764.

2. The +5VDC power supply  have common GND connection with the GND terminal of the NI device.

3.I change another motor

Next step I will try to change another motor driver.

If the motor driver is ok,I don't know what 's problem?

[hanyang19861017@163.com]

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