How do i adapt flex motion to control force?

[DuncW]

I am using a force sensor connected to ADC1 of the MID 7654 as feedback, and would like to use this signal to control the force (current)being applied by the linear servo motor??. How do I send the input signal to AXIS 1 to complete the PID loop ????....Do use load position as a psuedo force/current control, or can i send a voltage signal direct to the axis using load DAC. ( the force pattern required, is sinusoidal with a frequency of 1 Hz). Any help would be much apprectiated.

[Jochen]

In MAX you can select the feedback source for your system under -> Axis Configuration -> Primary Feedback. By default the setting is Encoder-1 for Axis 1 but you can change it to ADC Channel-1 for your purpose.
After that you need to tune the system by using Servo Tune under -> Calibration in MAX. Please don't use the auto tune as it's not intended to be used for force feedback control loops. Better use manual tuning and the step response to tune your system.
Please take into account that the resolution of your feedback signal is 12 bit so you can control your force in max. 4096 discrete steps.
To create a sinusoidal force pattern you could either use contouring mode or the circular interpolation mode while using a second axis that's configured as open loop stepper to c
omplete the 2D vector space needed. You would waste one axis but circular interpolation is easier to be used than contouring.

Regards,

Jochen Klier
Applications Engineering Group Leader
National Instruments Germany GmbH