How do I use the analog input (ADC) to drive a motion profile in MAX

[Staffan Erickson]

We are trying to use an anolog input signal from a DAQ card to control the motion contol axis.  For now, we want the motor speed to follow a sinusoidal voltage waveform, and later on, we will be using a more complex velocity profile. 

In order to accomplish this task, we have searched the user forum, and found information suggesting to operate the servo motor in 'slave' mode under the 'gearing' option.  Therefore, we have set the Gear Master to 'ADC Channel-1', Mode set to 'absolute', Gear ratio 1:1, and provided the sinusoidal voltage (+/- 5V, 3 Hz) to the AIN1 connector on the MID-7654 controller.  When using the 1-D Interacitve 'single axis' control panel, the motor runs at constant speed in one direction only.  It does not react to the sinusoidal speed profile request as we expected. 

How do we 'turn on' the 'slave' mode in MAX?  Please talk us through the necessary steps and settings?  Thanks.

[Maclean]

Hi Staffan,

Thank you for posting to the NI Forums! Do you have a DAQ card, or a Motion card?  If you have a DAQ card, you can just create a sinusoidal signal on the analog output using the Waveform Buffer Generation (multi).vi for example.  If you have a Motion card, you can find instructions here. If you believe the output to the motor is incorrect, I suggest probing the output with an oscilloscope or connecting it to an analog input on a DAQ card.

Hope this helps!

[Staffan Erickson]

Dear Mclean,

Thank you for your quick reply.  Your suggestion to use the Motion Card as a secoond option makes sense now.  However, I was hoping to be able to operate the MAX via an external voltage command using the existing DAQ card (or any other voltage command for that matter)!  How is this done? 

As indicated in my original question, I believe that the 'slave' mode is the correct way to control a motor with an external command.  However, if there is another way to route the external control signal into the MID-7654 Controller for velocity control purposes, please let me know and talk me through the necessary steps.  All of my attempts to use 'slave' mode so far have been without success.

In addition, which method is prefered to provide the highest system bandwidth response?

[Jochen]

Staffan,

you can configure and enablethe Gearing mode in MAX and it should be activated after saving the settings and initializing the board. In 1D-Interactive you can't use Gearing. For better flexibility I recommend not using MAX for configuring and enbling Gearing. You better should do this in your application.

In fact there is a perfect LabVIEW-example that ships with the NI-Motion driver (Master Analog Input - Slave Axis Gearing.vi)



I hope this helps,

Jochen Klier
National Instruments

Message Edited by Jochen on 10-02-2007 08:37 AM

[Staffan Erickson]

Jochen and Maclean,

Your feedback was most helpful.  I now understand the 2 setup options, and the Slave Axis Gearing VI is working well.  My next step will be to tie all the features I want into a single VI for flexibility and ease of use.  Glad you clarified MAX config and enabling Gearing constraint too.  Thank you very much!