AutofocusInitialRampTime Parameter

Use the AutofocusInitialRampTime parameter to control the behavior of the axis when autofocus is enabled. If you specify zero as the value for this parameter, the controller performs no ramping. With this setting, sudden changes in position command might occur when autofocus is enabled. This can occur if the value of the analog input specified by the AutofocusInput Parameter is significantly different than the AutofocusTarget Parameter. Because of the difference between the analog input and the AutofocusTarget parameter, a large error is immediately introduced into the autofocus loop, and the output of the autofocus loop can change suddenly based on the magnitude of the error and the autofocus gain parameters. Also, if you have a non-zero value set for the AutofocusGainTff Parameter, sudden position command changes can occur when enabling autofocus with a non-zero target.

You can decrease or prevent sudden changes in the position command that are caused by enabling autofocus control if you set the AutofocusInitialRampTime parameter to a non-zero value. To avoid introducing a large error into the autofocus loop, the axis will ramp its internal autofocus target value from the current value of the analog input to the value specified by the AutofocusTarget parameter. If you have a non-zero value set for the AutofocusGainTff Parameter, the initial target ramping only helps to decrease or prevent sudden changes in the position command if the current value of the analog input is near zero when you enable autofocus. This lets the target feedforward position command to ramp up from a starting position near zero.

This target ramping occurs over the time specified in this parameter and only when autofocus is enabled. When the specified AutofocusTarget is achieved, the ramping concludes, and the value of this parameter will not be used again until autofocus is disabled and enabled again.