refining the spring stiffness of a motor alternate directions

[ryanalma]

Hi

I have a control system in which i am using a DC motor and have designed a controller to compare the output of torque and position in order to make the motor shaft mimic the action of a spring however i want different amount of spring stiffness in the clockwise anticlockwise direction any ideas i'm baffled myself??

Thanks in advance any help very much appreciated

 

[israelkk]

Did you take the time delay of the motor into account? A mechanical spring act instantaniously with no delay. However, a motor needs time to build the reaction torque due to the coil inductance and resistance added to the motor inertia. Add to this the controller time delay.

 

[UKpete]

Could you modify the measured torque signal? As the torque signal reverses polarity when changing between clockwise and anticlockwise, and using a potential divider could be used to modify the signal: a diode added in parallel with one of the resistors in the potential divider would give differing gains (and therefore spring stiffness) for CW and CCW directions.

A simple diode would introduce some non-linearity but I believe it can be done linear-fashion using op-amp circuits.