deadband stepper motor and linear encoder

[tweekzilla]

Hi All,

 

I'm driving a stepper motor using a linear encoder as the feedback for the position. I would like to setup a deadband of say 0.3 mu from the Position error. This works fine using Kbreak and BreakPosErr so long as I don't have the integral term enabled. However to get the following error I need I do need to have a small integral term.

 

I looked into using OutDbon and OutDboff but they are only valid when the DesVelZero is True and with the integral term on that value switches from false to true.

 

Is there a way to use the integral term when moving and then setup the deadband such that Ki is disabled inside of 0.3mu?

 

Cheers,

 

Ross

[curtwilson]

The "input deadband" set up by the BreakPosErr and Kbreak terms modifies the following error that the servo terms use. If you have Kbreak = 0, then when the magnitude of the following error is less than BreakPosErr, the proportional term Kp and the integral term Ki will operate on an effective input of 0.

 

This means that the output of the integrator will not change as long as you are within the deadband. The integrator output does not have to be zero in this case, and probably will not be, but its value will be constant.

 

Note that the velocity feedback (derivative) gain is still active within the input deadband, counteracting non-zero actual velocity.

 

When using the output deadband, it is important to realize that the DesVelZero bit refers to trajectory velocities into the servo loop position command node. It does not refer to any states internal to the servo loop. So when the trajectory generator is commanding a stop, DesVelZero will be true and the output deadband function will be active even if the integral term is acting to try to reduce the following error.