Is there a way to reverse encoder convention without rewiring?

[Dr_Laine]

I am running a brushless linear motor quadrature encoder through UMI-7774 to a PXI-7350 motion control board. All encoder channels are configured as active high.

I want to reverse the slide direction convention. Is there a way to do this through MAX without rewiring? Just change to active low? Otherwise, I think I must physically swap A with /A, etc.

This is from the UMI manual:
"You can accommodate encoders with various phase relationships by swapping the signals and/or connecting them to the inverting inputs as required by the application. A + 5V output, generated by the UMI-7774/7772 internal power supply, is also available on the connector for powering encoders. Figure 3-12 shows the default encoder phasing for National Instruments motion controllers You can configure this phasing using Measurement and Automation Explorer (MAX) or NI-Motion driver software."

but I cannot see how to configure the phasing using MAX, nor do I see how to access the NI-Motion driver software. Please show me my error.

Laine

[ChadE]

Hello Laine,

To change the polarity in MAX, do the following: 1. Expand devices and interfaces. 2. Expand the PXI-7350. 3. Expand "Default 7350 Settings" and select "Encoder Settings". Change the polarity of A or B, but not both.

The NI-Motion driver software, refers to the Motion VI's in LabVIEW or the dll function calls available in C or VB. You can find more information on these functions if you go to "Start>>All Programs>>National Instruments>>NI-Motion>>Documentation." To change the polarity in LabVIEW use the VI "Configure Encoder Polarity". In C or VB use the function "flex_configure_encoder_polarity".

If you are doing index reference moves, they may not work properly after you change the encoder polarity. You may need to adjust the Index Reference Criteria so that it will work again. The "Index Reference Criteria" specifies what the state of lines A and B must be in order to detect an index pulse. To set the Index Reference Criteria in MAX, do the following: 1. Expand devices and interfaces. 2. Expand the PXI-7350. 3. Expand "Default 7350 Settings". 4. Expand "Find Reference Settings" and select the axis that you are configuring. You can use an oscilloscope or just trial and error to find out what you need to set these settings to.

Also, you will want to save the settings to flash. We recently found a bug in the initialize sequence that allows the system to energize before the encoder polarity is set. Note: this bug will be fixed in NI-Motion 7.0 (coming soon). As a workaround you can save the settings to flash. This allows the correct encoder polarity to be set when the controller powers up. To save the settings to flash, do the following: right-click on the Motion Controller in MAX and select "Save Initialization Settings to Flash".

I hope that you find this information useful.

Regards,

[Dr_Laine]

Thanks Chad, the reversal worked like a charm.

One other question - is there also a way to change the limit switch conventions through software (swap Forward and Reverse limits)? Here I'm pretty sure a physical rewire will be necessary.

Thank you for the help!

L

[ChadE]

Hello Laine,

You will need to rewire the limit switches. We don't have any way to change this in software.

Have a great day,