🚀 go-pugleaf

In article <3uu8vg$dbt@lyra.csx.cam.ac.uk>, ard12@eng.cam.ac.uk (A.R.
Duell) wrote:

> tsunami@pnc.com.au (Graham Dinning) writes:
> 
> >The motor assembly in the disk drive would probably make a reasonable SUB
> >SUB woofer motor but in the actual disk drive it is probably servo
> >controlled by feedback from the actual platter(s) it is reading. In the
> 
> I still repair these washing-machine drives (well, somebody has to :-)), 
> and in most cases there are several feedback loops - the DEC RK07 had 3 (The
> position loop from the servo track, the velocity feedback from a 
> coil/magnet on the positioner, and a optical position/velocity feedback 
> transducer used for load/unload). The second of these, the velocity feedback
> would work without the rest of the drive being operation, and would probably
> be useful for this application.
> 
> A basic position feedback system is going to be essential as well - 
> otherwise any offset in the electronics is going to move the coil to one 
> end stop and stick there. The optical load/unload transducer (if present) 
> could be used here, or maybe you could design something to do this.
> 
> 
> >case of old CDC drives the coil is driven hard forward and the tracks are
> 
> The CDC drives I've worked on have a velocity feeback coil inserted in 
> the centre of the magnet assembly - it's the 3-4 wires coming out the 
> back of the positioner.
> 
> >counted as it moves. When the heads are in the right posy the motor is
> >given a huge reverse (Braking) pulse to stop about the right spot. Its
> 
> It's a little more complex than that, at least in the drives I've worked 
> on. The positioner current is controller by a DAC that is driven by an 
> encoded difference between the wanted cylinder and the actual cylinder. 
> This is then combinded using analogue circuitry with the velocity signal 
> (to provide damping), and a few other things. In some drives, 
> particularly winchesters, the velocity information is provided by the 
> positioner coil current.
> 
> >Grajam Dinning 
> >TSUNAMI@Halibut.pnc.com.au
> 
> -tony
That's Interesting Tony, Thanks :-)
Graham Dinning