EEVblog 1400 - Hard Drive Micro Actuators are AMAZING!
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- เผยแพร่เมื่อ 16 มิ.ย. 2021
- Dave takes a closer look the micro actuator used in the 6TB Western Digital RED hard drive.
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It still amazes me that HDDs are able to operate this precisely and reliably usually for a very long time, and the fact you can buy such thing new for just 10s of dollars.
Some of my old stock hard drives can't work anymore somehow, data can't be got.
I designed ICs for hard drives back in the mid 80's. At that time hard drive design was considered the most difficult and technically challenging of all mechanical engineering tasks. I'm sure it is still so.
@@tsites1 Thankyou for your service Tim :)
@@ray-charc3131 Maybe the electrons have fallen out.
@@EndlessDelusion perhaps the resistors are in rebellion as well?
Hook up an oscilloscope to the piezo and see if tapping the tip generates power...
that's an amazing idea
You can use a 4-10khz signal for the actuator to hear the actuator. Also you should touch the head with something like a pingpong ball to adapt the mechanical vibration to air.
You may need 50V-100V to operate the piezo actuator
For a given mounting orientation, you can fabricate piezo actuators to move in any axis (x, y, z, roll, pitch, yaw). For these disk arms, my guess would be they lengthen and shorten (rather then bend or curl). And they would likely need to be operated as an opposing pair to manage bending stress on the arm: Firing only a single actuator would cause MUCH less than half the head motion as the non-operating actuator acts as a solid opposing block (the single actuator forces against two fixed points).
Yep, I speculated an asymmetrical drive in the video. Would be silly if it's just one side driven. But if movement is visible then you should be able to see something driving just one I suspect. But the distances are just to small, so it's all moot it seems. But might do some more experiments which would entail taking out one arm completely for access.
Not sure you can manufacture thin flat transducers like that that contract in lenth?
Yeah. That's what I was thinking too. An opposing pair to move from side to side. And the little "springs" on either side provide some stabilizing force.
documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/western-digital/collateral/white-paper/white-paper-dual-stage-actuator.pdf like that?
@@EEVblog from the white paper that evergreen linked, the geometry shown in your video, and what I remember from Smart Structures in grad school, they're only extending and contracting the length of the PZT elements by ~100nm. The voltage applied to the tops and bottoms of the transducers makes them thicker and thinner. Since they're trying to maintain constant volume, the length contracts or extends to compensate for the thickness change.
This is actually great for this application because it essentially gives a sort of mechanical advantage to the actuation, requiring much less voltage on the PZT element to pull very hard on the read head. The stiffness of the polymer mounting the PZT elements to the read head would be very precisely accounted for in calculating how much motion transfers to the read head and the material could even theoretically be tuned to adjust down the amount the read head moves with PZT contraction.
Bloody brilliant stuff.
I would think is is a length change in the ceramic. As stated above a piezo ceramic can be engineered to change length. I once used length changing piezo ceramic in a micro fluid pump.
Not only mechanically but also the software and algorithm to maintain data consistency and keep data uncorrupted is remarkable.
partial response maximum likelihood is witchcraft!
When you said "you dont need much current to move these micro actuators" I for some reason imagined the guy over at Photonicinduction pushing 1000 amps through it just for lulz.
Awwww… He *POPPED* it 🤦
😝
it is not a knife ;)
..no more harddrive..it´s popped! LOL . All what left is a molten blob of metall on his burned carpet...where is my beer?
That would be fun to see. I'd love to see how the heads would react to that much current. If they'd just pop or if they'd move some before popping
@@thomasvlaskampiii6850 The assembly would most likely just vaporize.
I fondly remember the satisfying clunk-thump-clunk of my first 5MB hard drive as my programs read & wrote data. Hats off to the engineers of modern disk drive designs.
And the satisfying clunk as you sent it the head park command. On some drives this made the entire table shudder.
Then there were the old Shugart drives. The disks were huge, at least 8 inch possibly larger, and the head assembly did indeed weigh more than a pound. The actuator was a huge coil acting on a big magnet that moved several inches for a full stroke. Yes the magnet was a part of the head assembly and the coil was stationary. Given the huge mass involved the access times was pretty amazing. Running a butterfly seek test the actuator moved so fast it looked like a spooky half transparent image of it, but you didn't want to get your fingers anywhere close to that as it made a full stroke about 25 times per second. It had to accelerate the assembly and then stop it after it had moved about three inches 25 times per second. With the heavy head assembly that takes some serious power and it made the whole building shudder. It sounded amazing when you ran calibration tests. The first time I heard it I thought someone was using a jackhammer on the floor.
People was coming from several floors to see what was making such a racket. I think that drive was some where between 5 and 20 MB...
I remember hearing "high-tech sci-fi computery squeaky sounds" from tech scenery, playing through first location of Unreal.
They seem to be, in fact, made up from an ancient MFM drive sounds, seeking repeatedly. The one that had a stepper motor for an actuator :)
I reckon. My very first HDD was an ACTUAL Seagate ST-504. It weighed nearly 10kg for a 10MB drive.
Fascinating to see this stuff up close and realize that they make these in extreme quantities - fully automated. 24/7.
The in-process QC challenge is mind boggling.
I can’t believe humans being build these things. Period.
@@andyapple9 yes, it almost feels like this stuff comes from another planet... it was all made by aliens.
@@xissburg no, it doesn't feel like that when you have the precise history of development and the thing getting better each stage since the time those things used to weight half a ton
@@xissburg if the limit of your understanding is “hurr hurr, light switch goes click” it probably does, yes. But then some people are dumb enough to think the pyramids were built by aliens… who used only local materials and tooling to cut the blocks and deliberately made the simplest possible shape for a stable tall structure.
I've seen hard drives since the beginning. Those old things where the heads looked like magnetic tape heads and the platters were 18" in diameter. I worked with ones were you needed to do a low level format before you actually formatted the disk. And now these where the low level format is done by a precision device at the factory. You can really see all the years of science that has gone into these things.
One place where I worked in the late 1970s, they had a WANG computer. It had a 5MB fixed hard drive and a 5MB removable hard drive pack, about 18" in diameter. It was VERY noisy. When we started it, it sounded like a jet engine starting. Funny thing, when they upgraded from 5MB to 10 MB, they backed up, removed a resistor, reformatted, and restored. That was a very expensive resistor.
Yeah, I've got a DEC RK05 disk pack drive that weighs 110-lbs (~50-kg) with heads/arms nearly 6-inches (~15-cm) long, if I remember correctly. I think the storage capacity is 1.6 (12-bit) megawords, or 14.5K (12-bit) words/pound (32K words/kg). ;) Damn, HDD technology improvement over the years has been amazing!
I know a guy who worked with *really* early ones. The platters were huge, made of Cadmium, and held a whopping 1 Megabyte.
@@dylantowers9367 I saw a collection of old platters that a Professor had. The largest I remember was between 3 & 4 feet (0.9-1.2-m) in diameter and about 1/4-inch (~6-mm) thick, but I don't recall whether he told what its capacity had been.
@@dylantowers9367 I worked att a radar surveillance mountain once and even if everything was state of the art they had put up some "thread memories" on a wall from way back in the time. It was just a long very thin coiled up thread of metal that when "hit" on one end whit piezo material it held that information for certain time before it reflected back. 1 bit fast memory back in the early -50.
Interesting stuff! In my experience piezo actuators operate with higher voltages.. Given that there's no specs I would start with a 30Vpp (some piezo actuators can even go up to 600-3000Vpp but I don't think this is the case) also, for an actuator application the frequency needs to be under 200~300Hz.. I'm curious to see their driver schematics given that the voltage has to be boosted, driven differentially, drive multiple actuators
That's a big advance from about 100TPI on 14" platters on drives I worked on in the seventies to >400,000TPI in today's drives.
Its incredible the level of engineering that's in Hard Drives, you buy one for $40 and just dont realise the crazy development that's been involved. Amazing engineering for the masses.
I think most of you got it wrong. The piezzo mechanisms is to dampen the vibrations of
1) final position of arm. Without the this mechanism, the system control mechanism can never stop the shaking of the arm by itself since the arm is long. It is considered a secondary system of fine tuning, much the same as multiple stages in power supply design. In PS design, if you want to have a very low ripple noise, you must use multiple stages and filters.
2) step motor (spindle) which constantly shakes the hard disk. The piezo electric mechanism can vibrate in the higher frequency whereas the arms step motor cannot.
3) other small higher frequency noises like fans in the motherboard and chassis.
This has not been a new idea. It has been around since 2005.
Besides, the heads have multiple read and write sensors much like a video camera or scanners. They can read multiple tracks at once. If track 8 needs to be read and the arm goes near there, one of the heads detects the right track and the arm may not need to move to get track 8.
Hard disks are one of the most sophisticated electromechanical systems ever invented in such a small space. I'm surprised how cheap they are regardless of number of them being made.
Videotape recorders had piezo actuators for track following starting in the 70's. Ampex won an Emmy Award for its Automatic Scan Tracking. If the AST servo was misaligned, you could hear the head tips sing.
First seen in a mass produced VCR in the Philips V2000 format machines and then later on became pretty well standard in most high end VHS machines
Similar idea to what optical discs players have had since ever (IIRC), an stepper takes the head next to the read position, and then the lens is moved with two coils to get to the exact track, and keep the lens focused too.
I was thinking that there is probably a lot of cross-over technology from optical drives to hard drives. The Law of Accelerated Returns.
Visible light is usually defined as having wavelengths in the range of 400-700 nm. You can not expect to see movements in range of 50 nm. Sometimes I did not manage to get sharp images of 50 nm structures with the SEM.
Well, with interferece you could
@@kramnecknerf I know Daves office light is not monochromatic and I guess he hasn't a Michelson interferometer at his bench.
Anyone who remembers the Philips VCC series videorecorders: they had piezo actuators connected to the tiny heads on the rotating drum and those video heads could follow the videotrack much more accurate than the VHS and Betamax recorders could. It could for example display perfect stills and stripeless fast forward/reverse searching. So not so new technology just on a much smaller and more accurate scale in harddrives now.
I have repaired some, so I do remember they were a pain in the b... to calibrate. But quite neat that you could use both sides of the tape, like a compact cassette.
All this talking about harddrives made get the "Get perpendicular" song stuck in my head. Thanks Dave! ;)
Hahahhaa good vibes! Old school :-)
The silver glob of glue is conductive and grounds the back side of the transducer.
It's like image stabilization, but for your data! That is pretty neat.
Oh jeez, just imagining the sort of block allocation algorithms you'd need to be able to take advantage of being able to independently micro-actuate each head while having them still not totally independent at the main arm.
From what I read the displacement of the micro actuators is in the order of 1µm and below. So not a huge surprise we couldn't see any movement when you applied a few volts ;)
That’s what I was going to say. Probably too small to actually see the movement.
How come your comment is 2 days old when Video came out today Sir.
@@abhijithanilkumar4959 probably patreon
@@garretr4488 Obviously magic.
@@abhijithanilkumar4959 Oh, in Australia is it tomorrow already or something like that, so the comment could have been made somewhere near the international date line, going around in the wrong direction and arriving two days before it was made, instead of a day after, if it makes any sense. :)
7:25 - "A thing of beauty is a joy for ever" - John Keats, Endymion
The control loop strategy is also very interesting, using a macro-micro topology with complementary paths. The low pass response is actuated by the arm and the high-pass part by the micro actuators. Neat complex system equations 🤯
High end disks use 3 actuators now. Whole arm and two smaller joints
@@cannesahs I had a huge 20MB hard disk and it was highly educative to see the anatomy --- you do not need a microscope (and I was younger then)
Hey! you got a nice channel there! I subscribed. Keep making those videos...more power to you!
@@seeker4430 Thank you!! 😄😄
These videos made be realize how cool hard drives are
Regularly used Piezo nano-positioners for laser mirror, and lens alignment.
11:49 I remember about 30 years ago, Tim Hunkin said something similar about a VCR head chip on "The secret life of machines" episode :)
Look up Tim Hunkin's YT channel. He's posting remastered Secret Life of Machines videos with added commentaries. Enjoy! :-)
@@WilliamDye-willdye Exactly what I did - what a nice surprise!
Shame about the 3rd season, existing recordings were mildly corrupted at the ends as far as I can remember.
Great video! I have had success observing motion of piezo devices using a poor man's strobe, e.g. a blinking LED. If you can excite the actuator at mechanical resonance, it should deviate more (perhaps greater than the design calls for). You can find the resonance frequency electrically with a 1-port network analyzer or sig gen and scope. If the strobe frequency is slightly different from the excitation frequency by a few Hz, you might see a slow oscillation of the arm. You can do some back of the envelope math to determine how much deviation you can measure with a given magnification. Just a thought...
@EEVblog Assuming the HDD drive spins at 7200rpm I would expect it to wiggle at and above 120Hz to keep the head on an elliptic / excentric track, so you might try it with a higher frequency. This would allow it to be heard in operation. Reminds me on the movement of a Laser pickup lens in a CD drive and its movement on an excentric CD.
HECK yeah a Whole Dedicated Video about these! Absolutely Wonderful!
Dude you have more energy right now than I had in that part of my teens after I discovered Red Bull, and before they made them age restricted.
Awesome. I love the video!, there's some awesome technology in these things and it's easy to take them for granted!
Amazing as always, Dave!
Truly amassing & taking for granted 10/10
If you think about it, your finger on your hand on the end of your arm is a multi stage actuator too -- so you're wiggling the HD's micro actuator with your own micro actuator :)
Gae.
@@sjm2029 Homophobes are ‘gae’
no u
@@SproutyPottedPlant I am not a homophobe , why would you think that?
Wow Finally you catch micro actuator!👏👏👏👏
Thanks so much for sharing. 😎👌🏼
I would say that it is actually addictive to follow you in trying to understand the beast.
The amount of precision involved makes it amazing that I've seen LAPTOPS that are 10 years old with their original hard disks still going strong! When I took the one out of my Macbook, it was still in working order I was just wanting to upgrade the speed by putting in a solid state disk. By the way, it was a Toshiba hard disk, for what it's worth. :)
Perhaps try setting it up with a record player stylus against the head and try to see if you can get some audio to go through that.
My sharpshooter friend actually adds mass to his gun. This helps him keep it steady.
The mass of the arm would help hold the heads steady while the fine tuning is accomplished by the micro actuator.
Good one! And a shout out to the sheet metal stamping, forming and punching die designers for those parts as well; I'd love to do a field trip to see those presses in operation making the parts for the read/write actuator.
Thank you Dave for this technology introspection, of so called "mundane" things but for not entrained eye's.
That blows my mind actually. I love hard drives
I did'nt know any of that. Cheers, Dave.
Amazing stuff.
I think this is a job for the Slo-Mo guys ;)
Works of Art..
One of my co-workers used to be a QA dude at Hutchinson Tech (Hutchinson, MN) who specialized in making these little tiny hard disk parts. Sadly he doesn't have "engineer brain" so he didn't notice a lot of the technical stuff I know I would have, which limited his ability to tell fun stories about the amazing tolerances they had... but it still sounded like they had a pretty extensive test regime, to make sure nothing that didn't pass all specifications was shipped.
9:15 The "spring arm" on the back is one electrode, and the bridge across the red insulator on this side grounds this side to the frame of the arm. Piezoelectric crystals shorten along the current path, lengthening along the plane perpendicular to that path. When current is applied, the piezo-actuator wedges both red insulators apart, causing the "I" shaped flexure ( en.wikipedia.org/wiki/Flexure ) to deform at the weakest point which would be where there is a hole punched through seemingly for no reason between the actuators.
I perceived this as shifting the magnetic field up and down to vertically access the surfaces of magnetic plates laminated to a single plate. Am I wrong.
Now that's a real artwork.
Wow!!! Thanks.
Perfect, Dave!
Just *perfectly roight* , Mr. Jones.
Thanks
Fascinating!!!
Your loss (the RED drive failing) was our gain, your teardown. Thanks. The familiar pattern of your better reviews always includes a teardown before a power on. Would be interesting to see a follow-on where the replacement RED gets an almost inevitable teardown, tearup (reassemble)and power up - without a teardrop (without issues) e.g. “how hard can it be” to put back the helium in an 8TB RED, for a Pro?
The little flexures allow for 'front-back- motion, to be converted at the head into 'left/right' motion
I'd like to see if you could aim a laser at the head and observe the reflected beam - perhaps a couple of metres away. The principle is the same as a mirror galvanometer - presuming you could find a suitable point on the head.
I do have a laser displacement device, can't remember the resolution though. Most likely not good enoguh.
I worked at a factory that built those suspension heads was very different machine in the process to bond and install those actuators. Plus the white damper installed on the suspension arm it’s self.
Not only does the mass of the arm contribute, but at speed, the elastic nature of the whole arm starts to become dominant in position error. You get lots of ringing and in order to reduce settling time, which is inversely related to read speed, the piezo actuators help keep the head inside the desired track. Its counteracting the large read arm vibrating like a rubber band. The voice coil motor has a lower bandwidth typically too. The piezo can be driven at a much higher control rate, which will help when chasing higher transfer speeds.
Hello those micro-actuators are for adjustment of head vertical distance from the disks, it usually is like this : 1 for GND ,2 for differential read element,2 for write element
and 1 for vertical z micro-actuator and other two are horizontal x-y micro actuators. total of 8 connection .
I'd love to see Ben at Applied Science take a crack at getting measurable motion out of these - He's done some experiments in the past with very small movements, like those magnetostrictive strips used for product tracking in some stores.
Dave - the read and write heads dont hover tens of nm over the plater :) - they hover 3-6 nm since quite a very long time - there is even a speciaj heater in the write head that bumps the head and brings it closer to the surface ;) - Very nice you took that topic here in eevblog, thank you!
Apply 40kHz to the piezos for ultrasonic platter cleaning!
I first came across mindbogglingly small, fast & accurate piezo positoning back in the 80's on an Ampex VPR2 broadcast video recorder. The playback head could bend up & down to keep in the middle of the magnetic track laid on the tape. As the years passed, this technology appeared on more and more and cheaper and cheaper devices. Basically the same application as this by the look of it. Cool.
Hard Drives have come a long way.
I remember in 1984 changing out 75 lbs 10MB Honeywell Hawk Hard Drives. One removable and one fixed platter Repairing a crash on the fixed platter called for buffer the RW head with 200 grit sandpaper (yes, that's right) and then washing it out in a cup of alcohol and then put it back in with a new platter -- and most of the time that worked.
That was the procedure when some company President or Accountant is tapping his heels anxious to get the drive going because they have to print payroll or something.
As broadcast videotape technology progressed the track widths on tape reduced. At some point 'dynamic tracking' (my phrase) was introduced where the head was mounted directly (or nearly) on a piezo transducer to enable precise tracking. Head and drum servos took care of the basic positioning but the dynamic tracking did the rest.
Could be the perfect topic for another Applied Science video!
This is really cool I never knew HDD heads had this kind of micro-actuators at the tip. It is so ironic with all this technology in spinning HDD and it’s all virtually obsolete technology except for the largest multi TB drives used in data center servers and large workstation PCs. Everything else has already transitioned to flash.
Next stage after flash already exists.. But flash needs to hit it's limits before next switch.. mram...
Yeah, it has recently occurred to me that we are probably now in the golden age of magnetic media. Pretty soon, economies of scale are going to be working against magnetic storage and the incredibly low cost-per-TB we see now is going to go away. Hopefully that only happens when the alternative media are all at least as dense. (But the sentimentalist in me will miss spinning disks when they vanish for good.)
@@nickwallette6201 No, magnetic is the future, but in solid state.. MRAM and things like STT-MRAM.. But yes, these mechanical beasts we have today will eventually vanish... Many thought they would be gone by now, but I think they will survive flash...
One has to be thinking what kind of storage medium is best for long storage archiving. Mechanical spinner HDD may be the best for archiving, as long as it’s powered down for the archived period of time. Or it may be the worst form of storage I don’t know
@@ericcindycrowder7482 DNA is honestly pretty damn good if it's temperature controlled. You get 2 bits of data per about 30 atoms if I've imagined it correctly (it won't be far off if it is, certainly not an order of magnitude)
Read speed is kinda rubbish currently but stability is great
The faster rotation of the disc, the smaller friction force on the head, it will ease the work of the coil/transducer, and maybe on the coil/transducer voltage is AC with high frequency controlled by PWM system.
The Philips V2000 VCR system also had piezo elements on the heads. This was called DTF (Dynamic Track Following) and because of that system they could use smaller tracks. Technically this V2000 system was much better than VHS.
Good heavens, How do they even manage to get those exact and most precise movements. Just, really unbelievable😱😱😱😱
I can only imagine. Maybe the heads are tuned individually before the drive is marked as a PASS. This means each head will require a unique amount of residual voltage governed by hdd board. This could be regarded as part of the low low formatting of the drive ???
Absolutely incredible! Controlling something physical, at the nanometer scale, and it’s something most of us use everyday and have no idea.
der8auer recently did a few videos at a lab that has a SEM with probes small enough to test INDIVIDUAL TRANSISTORS on like 7nm process CPUs 🤯
It also uses piezoelectric elements to get such fine positioning.
I didn’t know about using piezoelectric elements for positioning until that video, now this shows me it’s a lot more common than I knew! Very cool.
Depending on the type of head those may actually have been the 2nd stage and controlled the tilt and up and down movement. Modern hdd have a 3rd stage attached to that ladder looking thing underneath (right where he cut the demo clip) and it moves the head side to side quite a bit but is also voice coil powered. Other heads only have 2 stages and use piezo side to side actuators with flexure springs.
Hats Off science folks and engineers and the motivated wealthy industrials who believe and finance/invest in the researches to where it has become now! Joy Forever indeed! 👍👍
Actually, another interesting question would be what is the resonance frequency of those actuators? (It could be found with a spectrum analyzer.)
Mwahahaha great question
Normal person: Sad by the loss of a hd and replacement cost. Tosses crashed disk in the bin.
Nerd: Curious about disk crash. Provides hours upon hours of exiting exploration time of the remains.
Don't pass up the magnets that are in there, you will be hard pressed to find anything stronger than you can get out of a hard drive.
@@JWH3 I collect those magnets, and they're so damn handy. You can hold a photo on the wall, mount a utility lamp to the wall (metal steel stud or frame) or a shelf, hang a space rack on the fridge, the possibilities are endless.
nice one
I suspect that those could be shear mode piezos. And then if you hook them up in opposite polarity and excite them, they will twist in the opposite directions moving the head.
If you have an impedance/network analyzer -- hook it up -- the resonant frequency would indicate the mode in which they move.
This would be a cool topic for Applied Science. He's got an electron microscope.
The micro actuators are not simply for locating a track with high precision, they are actually there to overcome oscillations in the main part of the arm. When the arm moves from one track to another, it can't simply stop when it reaches the desired track. The arm will flex and if the drive coil simply stops when the head is over the track, the head will continue past the track and vibrate back and forth. Feedback to the drive coil is used to dampen this vibration, but given the extremely small distances between the tracks, the latency necessary to dampen this vibration and settle on the track using only the primary drive coil is significant. By using the micro actuators, the head can remain over the track even as the main arm continues to oscillate slightly. So the primary purpose of the micro actuators is to reduce latency.
But how is the feedback to the drive coil picked up ? I thought to see piëzo sensors in them.
@@erikdenhouter I'm quite sure the feedback is readfrom the actual track, some kind of data encoding that will ensure not all zeros or ones written for any significant length of track, so the intensity of the signal can be used to calculate the offset (in radial direction) Ols harddisks used 'dithering'to be able to know the sign of the erroro (am I moving in or out of the track), Not sure how it is done here,maybe two slightle offset heads?
Great job Dave. Funny at 10:52, half a bee's WHAT? LOMAO.
NICE SCOPE! Got a link? Is there a delay when viewing and finger movement?
It's actually pretty fascinating that we can store information this way. Just think about all the manhours put into the hardware, firmware and driver software.
Cool, never noticed that when I've ripped apart hard drives.
A lot of inkjet printers work via rows of piezo ink bubble pushers. Pretty cool too.
Reminds me of the Drivetec floppy drive of the late 70s/early80s. Has two positioners--"coarse" and a "fine" ones. Used embedded servo recording to get around 3 MB on a 5.25" floppy. Disks had to be factory-formatted, which was a deal-breaker. Kodak eventually bought out the bankrupt company and marketed improved versions of the drive for a short time.
Piezos are very prone to cracking if they are ever stretched so they almost always work in compression. By preloading the piezos and only letting them work in expansion they are always experiencing a compressive force.
That’s awesome
The helical scan head in a video cassette recorder used to be the most precisely engineered thing in the home back in the day.
Info from the Sony patent: The track width of the magnetoresistive head is 0.5 to 0.8 μm, the distance between shields is 0.13 to 0.145 μm.
Yes, and Video 2000 used piezo crystal to move the heads for trick playback. It worked quite well.
The little thing that holds the laser on a cd drive is pretty neat as well.
I believe that the "Flying " heads can be flown like a wing. The "flexing" of a micro movement is much like the moving the control surfaces to cause a bigger movement of the wing.
You should talk to The Slow Mo Guys, and get them to videotape one of these hard drives with the cover off. I think you will find that the two peizo actuators are fired in near ultrasonic speeds, and at those frequencies, even solid metal starts to bend and wobble in some amazing ways. All they need to do is to work with the harmonics of the head and it will wobble back and forth in a very predictable manner, and they could use that to steer them right to the tracks they want to access while the data is under the heads.
I have always thought they were amazing and never heard anyone else talk about the actuators.
Both OxTools and AvE have done good discussions on flexures, like what you're seeing in this actuator arm.
The best practical approach to flexures that I've seen is from prototyping course for scientists by Dan Gelbart. It's on TH-cam, look it up, great stuff
@@shimmerite_ua Genius this guy!
The Philips Video 2000 system from the 1980s used piezo elements to move the video heads for "dynamic track following". I seem to remember the voltage they used was pretty high, like 70V or something. Of course those piezo elements were much bigger than those in that hard disk.
If I understand correctly, putting a voltage over a piezo element makes it bend along the longest side, so I imagine the elements go ever so slightly U-shaped and pull their ends towards each other by just a bit. The springs on the side will keep the head assembly from bending with the piezos; they're not needed to make everything go back in place when the voltage goes off.
it would be an idea to reflect a laser from the tip and see if the point on the wall moves if you apply a signal to the actuator.
You might not see movement in the laser beam itself but you'd probably see some kind of shifting in the interference pattern at least.
I think the shiny metal you see top and bottom surrounding the actuators is just a guide that is not connected to the head at all, it looks like the lighter colour metal that makes up the head is coupled either side to the actuators and it slides side to side within the shinier metal, if that makes sense.
that microscope camera is beautiful
And it has separate micro-steppers for each head pair, further reducing the mass it has to move, just one pair of heads. So it's moving a fraction of the mass of the whole assembly.
Thank you for the video, I think this is the most concise and accurate description.
But completely on a different topic, can we measure switching transients which measure upto 4KV with a time duration of 50ns using 10X CAT II probes , or should we be using Differential probes.
For your kind information I am measuring these transients that are effecting near GPIO pins of the micro controller.
Any help or advice is most appreciated.
I've got ideas for how to test it precisely...cast a shadow that make it bigger and easier to see small movements... Put a lever on it so it makes a small movement into a big one.... Lean a micrometrer onto the head so you can measure how much itt moves
The engineering itself is amazing enough, but the design for manufacture is what really blows me away. Meaning, it's one thing to make a device that does what that drive does, but it's another thing entirely to be able to make it cheaply, reliably, without too many exotic materials or processes involved, with a minimal amount of customized tooling, etc. In other words, despite the insane sophistication we know is involved, it's the way that design screams "i have been refined to an extreme degree" that gets me. Those read arms are in a sense so simple they almost look like a high school robotic hobby project, yet you know they are basically space alien technology.
That is fucking incredible!