EEVblog 1400 - Hard Drive Micro Actuators are AMAZING! 

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.

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).

Hook up an oscilloscope to the piezo and see if tapping the tip generates power...

Not only mechanically but also the software and algorithm to maintain data consistency and keep data uncorrupted is remarkable.

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.

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.

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'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.

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.

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.

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

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.

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.

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.

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 ;)

It's like image stabilization, but for your data! That is pretty neat.

These videos made be realize how cool hard drives are

All this talking about harddrives made get the "Get perpendicular" song stuck in my head. Thanks Dave! ;)

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.

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...

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 🤯

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 :)

The silver glob of glue is conductive and grounds the back side of the transducer.

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!

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 :)

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.

Regularly used Piezo nano-positioners for laser mirror, and lens alignment.

7:25 - "A thing of beauty is a joy for ever" - John Keats, Endymion

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.

Truly amassing & taking for granted 10/10

HECK yeah a Whole Dedicated Video about these! Absolutely Wonderful!

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.

I would say that it is actually addictive to follow you in trying to understand the beast.

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.

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.

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.

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.

Good heavens, How do they even manage to get those exact and most precise movements. Just, really unbelievable😱😱😱😱

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.

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?

Thank you Dave for this technology introspection, of so called "mundane" things but for not entrained eye's.

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 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.

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!

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.

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 .

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.

Both OxTools and AvE have done good discussions on flexures, like what you're seeing in this actuator arm.

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! 👍👍

That blows my mind actually. I love hard drives

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.

I think this is a job for the Slo-Mo guys ;)

Thanks so much for sharing. 😎👌🏼

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.

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.

Works of Art..

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.

Wow Finally you catch micro actuator!👏👏👏👏

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.

Actually, another interesting question would be what is the resonance frequency of those actuators? (It could be found with a spectrum analyzer.)

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.

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.

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.

The multi-stage actuator seems to serve two purposes when I saw the animation: more precise head positioning, PLUS keep the azimuth perpendicular to the radius even though the head travels in an arc.

The little flexures allow for 'front-back- motion, to be converted at the head into 'left/right' motion

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.

I have always thought they were amazing and never heard anyone else talk about the actuators.

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.

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.

I think the voltage applied is DC. piezos will expand or contract depending on the polarity of the DC. Also when a piezo is manufactured they are polarized in what ever plane is useful for the application. BobC and Egwene22 got it right.

This would be a cool topic for Applied Science. He's got an electron microscope.

HDDs are impressive mechanical beasts. Though, sometimes I wonder why manufactures don't just go to a larger form factor. It would increase material costs a bit, but increasing the disk diameter by just 10% makes a fairly huge impact to disk area and hence capacity. And most of the cost of the drives isn't material cost, but rather assembly costs, and that should remain largely the same for a drive that is physically 10% larger. Micro actuators like this would also help combat a lot of the issues with going to a physically larger disk. I for one wouldn't mind seeing a 5.25" HDD if it has a good price per TB. Though, the big issue with hard drives at current is that they are starting to suffer from their low read write speeds compared to their capacity. In short, moving data away from it takes a considerable amount of time, and if one is repairing a raid array, then this time is time that another drive can die within and one's data ends up lost. So there is some concern in regards to write speed per TB as well. Then there is SMR drives, something that could be handled a lot better by RAID systems. Though, a fair few drives are hiding the SMR operation away from the OS and drive controllers and such... Then there is the other extreme called Host Managed SMR, but that at least has advantages when rebuilding the array, since one can much more intentionally work with the shingled blocks and therefor not end up rewriting the same block x many times just because the RAID system didn't know it were the same block.

First, they store data on top and bottom of the platters. Second, the position control has two loops: coarse control using electromagnetics and fine control using piezoelectrics. The micro actuators eliminate residual overshoot, ringing, vibration, etc. once the heads are close to decrease seek time. Third, the two piezoelectric elements are operated differentially so that one pushes while the other pulls and the head bracket rotates about an intermediate pivot. Check to see whether the opposite sides are connected to power for one and ground for the other. Also, piezoelectrics generally operate on tens or hundreds of Volts. Finally, the motion might not be visible without X500 or so magnification or an optical lever.

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.

Wow!!! Thanks.

Fascinating!!!

Apply 40kHz to the piezos for ultrasonic platter cleaning!

If you have two coplanar piezo elements, or a single element with two coplanar electrodes on the side opposite a common electrode, the area in between the two elements/two electrodes will twist if one side expands and one side contracts. This configuration can also be used to control up and down motion simultaneously. It could be that this is how the side to side motion is performed, but who knows given that you can't really tell how a piezo element moves just by looking at it. There's a homemade scanning tunneling microscope design that does this using a piezo speaker element with the silver electrode cut into four quadrants. Each "diagonal" pair of electrodes forms the X or Y axis. The movement on the Z axis is controlled by a voltage uniformly applied to all four electrodes (making each one expand or contract identically) and the movement on the X and Y axes are controlled by the difference in voltage between each complementary pair (creating a "twist" in between them.) Commercial STMs use three linear elements, one for each axis, but this design works well enough that one hobbyist managed to image individual carbon atoms on the surface of graphene with it, and at a cheaper price for his whole setup than one single purpose-made STM actuator costs.

Getting footage of the movement may be a project for the Applied Science Channel. Someone get a hold of Ben.

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.

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

that microscope camera is beautiful

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.

So it is basically the same prinicple behind the way optical disk drive's read/write heads are mounted in a springy way, extremely precisely movable by electro magnets! Because for optical disks drives, it is the same thing. The head assembly is moved by a spindle but the disk's tracks are too small and not as perfectly centered on the disk, so the head by itself needs to follow the tracks on a very fine scale.

hard disk is always amazing to me, they have unbelievabe precision, yet still dirt cheap( you can get 1TB hdd for less than $50)

Amazing stuff.

I don't know about being the most precise mechanism we own. Those phone Gyro and accelerometers are pretty precise and mechanical

Now that's a real artwork.

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.

Last time I played with one of these. I powered the acuator on accident with the diode range poking around. If memory serves. The actuator energized will contract the head on the same side. It pivets in the metal between the two elements. Also if memory serves under those conditions the movement was indeed visible even with the naked eye.

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?

Thanks

You should be able to read the signal generated by the piezo when you force it with your hands. Maybe you can use that to confirm you’re in the right track.

Afaik it's very likely that these go up and down to control azimuth due to pressure changes (for different altitudes) + IIRC they would try to retract if they detect a drop so that there's a lower risk for the heads to touch the platters.

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.

Could be the perfect topic for another Applied Science video!

the piezo actuators expand and contract on the application of voltage giving side movement.

That design is super shmick! Although the physical deflection is likely in the micron range, I wonder if you’d need differential signals feeding both transducers to effect an appropriate lateral deflection?