ADLINK PCI-8258 - Manual (Page 91)

Motion Control Theory 77
PCI-8254 / PCI-8258
Here represents a position command,
represents position feedback, represents speed
command and represents acceleration command. The
PID control plus velocity / acceleration command feedforward control
are added here to reduce tracking error of position command and
improve control performance. The Plant in control shall receive voltage
signal after processed by controller. Its physical meanings may be
velocity command or torque command determined by settings of
actuator.
On the other hand, after servo update speed of PID controller is
changed, user must regulate controller gain at the same. You may
change servo update speed in the Setup Wizard page in range of
50us~2000us. The DSP reboots after setup. The default update
speed is 250us. As the controller's gaining value is limited, the
working range of gaining value can be adjusted with the gain shift
function as shown in the gain-shift figure below. The gain shift
function double enlarges or reduces the gaining value. Take
example. You can set KP gain to 100, KP shift to 2, and PID shift
to 3 to get a equivalent KP of 100Ч22Ч23=3200. In general, the
gain shift value should be changed only when its range is short of
required control power. The auto servo parameter fine-tuning
program described in next chapter may can help you in selecting
proper initial gain shift value.
In addition to changes in all gain values of controller, the Integral
situation, output voltage limit, output voltage offset, and output
voltage inverse can be set up by users. To suppress mechanical
vibration effectively, two Biquad filters are connected in series to the
rear of the controller for Low pass filter and Notch filter. Users may
design their own biquad filters for their own signal processing
purposes. This will be discussed in detail in following chapters.
) (k CmdPos ) (k FbkPos
) (k CmdVel
) (k CmdAcc