I often work on galvanometer scanners used for positioning laser beams. Some of them scan at 4-6 KHz small angle with harmonic components in the drive amplifier in the 10s of KHz. Until the last year, the cost of DSP based control systems was too expensive for most users, so everything is analog. We use a P-I-D-D loop with separate high frequency and low frequency damping. We have two feedback paths, one from the coil current series resistor and one from the capacitive or optical position sensors that get weighed and summed.
Usually we have one to three notch filters in the feedback path as well to handle shaft torsional and bending resonances that are often in the tens of kilohertz.
As our scan velocity is a complex function based on angle and time, the loop equations are very complex. Still we have fast discrete jumps over a sixty degree mechanical angle if we want, with settling times in the 10s to hundreds of microseconds depending on jump size and mirror mass for the fastest of devices.
We love non technical beginners in the laser show and marking industry who are suddenly confronted with 12 ten turn pots for adjusting each axis. The control interactions are complex, but can be conquered by starting with the basics and using a scope and test patterns. Often users get frustrated and go to EE school or get a degree in Physics to try to understand what they are working on, and no I'm not kidding, I've nominated more then a few laser show folks for undergraduate or graduate school.
As you can actually see subtle changes in the PID settings in your projected images or marking, they can be quite fun to work on once you get the hang of the adjustments. Some wags have referred to galvos as the fastest production analog PID loops on the planet, but I'm more then aware of other applications, often automotive or aerospace, that are considerably faster.
A good galvo with a low mass load is between 10 and 100 times faster in terms of angular velocity then the fastest hard drive positioner arm...
Steve