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# PIV Parameter Definitions

 Kpp Position Loop Proportional Gain. This is the proportional gain on the loop that surrounds the velocity loop. Kip Position Loop Integral Gain. This is the integral gain on the loop that surrounds the velocity loop. Kpv Velocity Loop Proportional Gain. This is the proportional gain on the velocity loop. Kpff Position Feed Forward Gain. Compensates for position-based effects in a system. Acts much like a spring attached to the stage. (DAC counts / position counts) Kvff Velocity Feed Forward Gain. Scaling factor to match commanded velocity and actual velocity scaling. If a single encoder is used for the axis feedback (common practice), then Kvff should be set to 1.0. Kvff can be raised to compensate for viscous friction effects. Even under severe viscous friction effects, Kvff rarely exceeds 1.3. (unitless) Kaff Acceleration Feed Forward Gain. Compensates for mass in a system. (DAC counts / (commanded position counts / sample period2 )) Kfff Friction Feed Forward Gain. Compensates for Friction in a stage. (DAC counts) IMaxMoving Position Integral (Kip) Limit During Motion. The position integral is clipped to this value while the motion is taking place. The motion is determined in motion that is based on commanded velocity. If this is set to zero, the position integral is effectively turned off during motion. A common way to enhance stability is to set ImaxMoving to half of Output Limit if it is used. Setting ImaxMoving to zero can help settling time in non-ideal systems. (DAC counts) IMaxRest Position Integral (Kip) Limit During Rest. The position integral is clipped to this value while the motion is idle. The motion is determined in motion that is based on commanded velocity. If this is set to zero, the position integral is effectively turned off when there is no motion. A common way to enhance stability is to set ImaxRest to half of the Output Limit (if it is used). (DAC counts) Kdv Currently not used. Output Limit Control Loop Output Limit. The absolute value of the control output will never exceed this value. Commonly used to limit current going to a motor. The smaller (more negative) value contained between Output Limit and Output Limit High will take precedence. The smaller (more positive) value contained between Output Limit and Output Limit Low will take precedence. (DAC counts) Output Limit High Control Loop Output Positive Limit. The control output will never exceed this value in the positive sense. The smaller (more negative) value contained between the Output Limit and Output Limit High will take precedence. (DAC counts) Output Limit Low Control Loop Output Negative Limit. The control output will never exceed this value in the negative sense. The smaller (more positive) value contained between Output Limit and Output Limit Low will take precedence. (DAC counts) Output Offset Control Loop Offset. Creates an offset to the control output. Useful for counter acting gravity on vertical stages. The Output Offset is not removed from the DAC in an Abort condition. (DAC counts) Kiv Velocity Loop Integral. The velocity loop is make of a PI (proportional and integral) loop. Kiv is similar to proportional gain in a PID loop. Do not use Kiv and Kip together, because changing Kiv will affect Kip's effect on the control loop. If you are using Kiv > 0, Kpp acts as the position loop integral. If you are using Kiv = 0, Kip acts as the position loop integral. If you are using Kiv > 0 and Kpp > 0, then Kpp acts as a second derivative on the position loop. This is usually not desired. VintMax Velocity Integral (Kiv) Limit. The velocity integral is clipped to this value. This value takes effect regardless of whether or not there is motion on the axis. Make sure VIntMax is > 0 if Kiv > 0. Kiv has no effect if VIntMax = 0. Ka0 Used only for noise injection during testing. Ka1 Smoothing factor for the velocity estimate from the encoder. Ka1 controls a single order low pass filter. Valid values are 0 <= Ka1 < 1. What is Ka1?
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