I have been tasked with designing a piezoelectric actuator driver at its resonant frequency. This is to replace an arrangement where the sine wave source is a function generator chip (the obsolete XR-2206) that must be individually tweaked on a unit, by unit basis, to match the crystal’s resonant frequency. The crystal is used as an actuator to vibrate a mirror used in a laser system. We have had systems come back from the field because the function generator’s sinewave frequency became too different for the system to work. My idea is to use the crystal itself as part of an oscillator circuit so that frequency is always exactly the crystal’s resonant frequency. I have prepared an abbreviated concept schematic that can be viewed here: https://i.imgur.com/4eBFQuD.png This is an op amp version of a Colpitts Oscillator. RV2 adds energy to the crystal to sustain its oscillations. I do not know right now its optimum value. U1 controls the oscillation amplitude by controlling the voltage on the op amp’s power supply lines. The circuit is designed to have a single supply so two regulators need not be ganged together. I am aware there should be more capacitors in the U! adjustable regulator circuit, and ops amp circuits. U1 also needs protection diodes to prevent it being back driven in by capacitors during power down. All this has been removed for clarity. U1 might have to be replaced with an adjustable DC DC Converter. I do not know right now how much current the crystal will require. The cable to the crystal might be as long as five feet. My questions are whether this should work in principle, and whether there are any bettor ways to do it.
Crystal Controlled Oscillator
Started by ●January 3, 2022
Reply by ●January 3, 20222022-01-03
On a sunny day (Sun, 2 Jan 2022 23:03:26 -0800) it happened Artist <sepflanze@sj.gmail.com> wrote in <squ740$eh0$1@dont-email.me>:>I have been tasked with designing a piezoelectric actuator driver at its >resonant frequency. This is to replace an arrangement where the sine >wave source is a function generator chip (the obsolete XR-2206) that >must be individually tweaked on a unit, by unit basis, to match the >crystal’s resonant frequency. > >The crystal is used as an actuator to vibrate a mirror used in a laser >system. We have had systems come back from the field because the >function generator’s sinewave frequency became too different for the >system to work. > >My idea is to use the crystal itself as part of an oscillator circuit so >that frequency is always exactly the crystal’s resonant frequency. I >have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > >This is an op amp version of a Colpitts Oscillator. > >RV2 adds energy to the crystal to sustain its oscillations. I do not >know right now its optimum value. > >U1 controls the oscillation amplitude by controlling the voltage on the >op amp’s power supply lines. The circuit is designed to have a single >supply so two regulators need not be ganged together. > >I am aware there should be more capacitors in the U! adjustable >regulator circuit, and ops amp circuits. U1 also needs protection diodes >to prevent it being back driven in by capacitors during power down. All >this has been removed for clarity. > >U1 might have to be replaced with an adjustable DC DC Converter. I do >not know right now how much current the crystal will require. > >The cable to the crystal might be as long as five feet. > >My questions are whether this should work in principle, and whether >there are any bettor ways to do it.If you can find a crystal that matches the pieze frequency... Or have one made. I would personally go for a PIC with for example a 10 MHz crystal as clock use the PWM outputs for the much lower frquency piezo drive, it will always be locked to that crystal.. http://panteltje.com/pub/ultrasonic-anti_fouling_circuit_diagram_IMG_5132.JPG Or use the PIC's internal oscillator if accurate enough (as I do). Add a nice OLED didplay http://panteltje.com/pub/ultrasonic_anti_fouling_status_on_display_IMG_5124.JPG Have it do whatevver you want automatically (avi file) http://panteltje.com/pub/ultrasonic_anti_fouling_OLED_running_5120.avi and the part count is even less... BUT.. you need to know how to program a micro (PIC 18F14K22 here), and [1] wind transformers http://panteltje.com/pub/ultrasonic_antifouling_bigger_transformer_IMG_5179.JPG Wonder if I should publish it in my new book 'The Fart Of Electronics' Maybe I should keep it *secret* now that Russia and China know all about Dr Hobbs lidar they may soon invade and take over, oh wait, already happening? [1[] calcujaluate or something
Reply by ●January 3, 20222022-01-03
On Monday, January 3, 2022 at 6:03:34 PM UTC+11, Artist wrote:> I have been tasked with designing a piezoelectric actuator driver at its > resonant frequency. This is to replace an arrangement where the sine > wave source is a function generator chip (the obsolete XR-2206) that > must be individually tweaked on a unit, by unit basis, to match the > crystal’s resonant frequency. > > The crystal is used as an actuator to vibrate a mirror used in a laser > system. We have had systems come back from the field because the > function generator’s sinewave frequency became too different for the > system to work. > > My idea is to use the crystal itself as part of an oscillator circuit so > that frequency is always exactly the crystal’s resonant frequency. I > have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > > This is an op amp version of a Colpitts Oscillator.<snip> I suspect that what you want is a phase-locked loop. I did it once, but forced the sustaining current to be exactly in-phase with the voltage across the device, which didn't give the maximum excursion. If I'd been able adjust the phase match to hit the actual resonant frequency of the actual device (and my circuit did offer a straight=forward way of doing it, but I was on holiday in Australia when the hardware came together) it probably would have gone in to production, but production device ended up having a remarkably consistent resonant frequency, so we didn't need it. -- Bill Sloman, Sydney
Reply by ●January 3, 20222022-01-03
On Sunday, January 2, 2022 at 11:03:34 PM UTC-8, Artist wrote:> I have been tasked with designing a piezoelectric actuator driver at its > resonant frequency > My idea is to use the crystal itself as part of an oscillator circuit so > that frequency is always exactly the crystal’s resonant frequency. I > have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > > This is an op amp version of a Colpitts Oscillator.That's not clearly an oscillator; the offset voltage of the U3 op amp allows lockup, for instance. A negative resistance oscillator is possible, but the piezo might have more than one resonance (i.e. it wouldn't be a stable sinewave drive), and there's startup issues to consider. A triangle wave oscillator (like the XR206 core) can easilly be made adjustable, and a microprocessor can be made to scan a range of frequencies and look at the response, so could self-calibrate and park at or near a resonant frequency. Or, you could twiddle knobs and find the resonance, then glue a frequency-determining component (resistor?) to the piezo device, and run a four-wire cable to the control center. Two wires to the resistor to determine the frequency, and two to drive the piezo. That way, all the piezo targets and control modules are interchangeable.
Reply by ●January 3, 20222022-01-03
Artist wrote: ========== ** Who are you ? What is you job title? Why is the " BS" in front of your fake handle missing ??> I have been tasked with designing a piezoelectric actuator driver at its > resonant frequency.** Piezo actuators are not " crystals " so have no special frequency.>This is to replace an arrangement where the sine > wave source is a function generator chip (the obsolete XR-2206) that > must be individually tweaked on a unit, by unit basis, to match the > crystal’s resonant frequency.** Piezo actuators are not " crystals " so have no special frequency.> The crystal is used as an actuator to vibrate a mirror used in a laser > system.** So much like a piezo disk driving a high frequency horn speaker ? AKA a piezo tweeter.> We have had systems come back from the field because the > function generator’s sinewave frequency became too different for the > system to work.** So tweak it.> My idea is to use the crystal itself as part of an oscillator circuit so > that frequency is always exactly the crystal’s resonant frequency.** Errr - what frequency is that exactly ? The mechanical resonance of the whole mirror and wot not kaboodle ? Surely you can reveal that here.> U1 might have to be replaced with an adjustable DC DC Converter. I do > not know right now how much current the crystal will require.** You seem to know SFA - pal .> The cable to the crystal might be as long as five feet.** Shit eh ? > My questions are whether this should work in principle, and whether> there are any bettor ways to do it.** Bettor find an engineer - cos YOU are not one ..... Phil
Reply by ●January 3, 20222022-01-03
On Sun, 2 Jan 2022 23:03:26 -0800, Artist <sepflanze@sj.gmail.com> wrote:>I have been tasked with designing a piezoelectric actuator driver at its >resonant frequency. This is to replace an arrangement where the sine >wave source is a function generator chip (the obsolete XR-2206) that >must be individually tweaked on a unit, by unit basis, to match the >crystal�s resonant frequency. > >The crystal is used as an actuator to vibrate a mirror used in a laser >system. We have had systems come back from the field because the >function generator�s sinewave frequency became too different for the >system to work. > >My idea is to use the crystal itself as part of an oscillator circuit so >that frequency is always exactly the crystal�s resonant frequency. I >have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > >This is an op amp version of a Colpitts Oscillator. > >RV2 adds energy to the crystal to sustain its oscillations. I do not >know right now its optimum value. > >U1 controls the oscillation amplitude by controlling the voltage on the >op amp�s power supply lines. The circuit is designed to have a single >supply so two regulators need not be ganged together. > >I am aware there should be more capacitors in the U! adjustable >regulator circuit, and ops amp circuits. U1 also needs protection diodes >to prevent it being back driven in by capacitors during power down. All >this has been removed for clarity. > >U1 might have to be replaced with an adjustable DC DC Converter. I do >not know right now how much current the crystal will require. > >The cable to the crystal might be as long as five feet. > >My questions are whether this should work in principle, and whether >there are any better ways to do it.This kind of self-excited resonator circuit is very common. Look into crystal oscillator circuits (low power, but frequency stable), and/or ultrasonic transducer drivers (high power, frequency stability not expected). It may be simpler to use discrete bipolar transistors or FETs in this circuit. The actual frequency will likely vary with local temperature and DC power voltage. Is a clean sinewave necessary, or can it be distorted or truly ragged? What power level is needed? Also think of how the resulting mirror-wobbled laser beam will be used. Is synchronous detection in the picture? If so, you will need to pick off and forward a copy of the actual drive signal to the detectors function. And so on. Joe Gwinn
Reply by ●January 3, 20222022-01-03
On Sun, 2 Jan 2022 23:03:26 -0800, Artist <sepflanze@sj.gmail.com> wrote:>I have been tasked with designing a piezoelectric actuator driver at its >resonant frequency. This is to replace an arrangement where the sine >wave source is a function generator chip (the obsolete XR-2206) that >must be individually tweaked on a unit, by unit basis, to match the >crystal�s resonant frequency. > >The crystal is used as an actuator to vibrate a mirror used in a laser >system. We have had systems come back from the field because the >function generator�s sinewave frequency became too different for the >system to work. > >My idea is to use the crystal itself as part of an oscillator circuit so >that frequency is always exactly the crystal�s resonant frequency. I >have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > >This is an op amp version of a Colpitts Oscillator. > >RV2 adds energy to the crystal to sustain its oscillations. I do not >know right now its optimum value. > >U1 controls the oscillation amplitude by controlling the voltage on the >op amp�s power supply lines. The circuit is designed to have a single >supply so two regulators need not be ganged together. > >I am aware there should be more capacitors in the U! adjustable >regulator circuit, and ops amp circuits. U1 also needs protection diodes >to prevent it being back driven in by capacitors during power down. All >this has been removed for clarity. > >U1 might have to be replaced with an adjustable DC DC Converter. I do >not know right now how much current the crystal will require. > >The cable to the crystal might be as long as five feet. > >My questions are whether this should work in principle, and whether >there are any bettor ways to do it.That circuit has problems, but I suggest that you understand the crystal first. Get a sinewave sig gen, a dual-channel scope, and a resistor. Drive the piezo through the resistor and measure the relative phase and amplitudes of the scope traces vs frequency. Then hack a Spice model that behaves the same. You can also connect the gen directly to the piezo and figure out how much voltage it needs to do your optical thing. Now you can Spice an actual oscillator. We can do that here. Artists sometimes need help. -- I yam what I yam - Popeye
Reply by ●January 3, 20222022-01-03
Artist wrote:> I have been tasked with designing a piezoelectric actuator driver at > its resonant frequency. This is to replace an arrangement where the > sine wave source is a function generator chip (the obsolete XR-2206) > that must be individually tweaked on a unit, by unit basis, to match > the crystal’s resonant frequency. > > The crystal is used as an actuator to vibrate a mirror used in a > laser system. We have had systems come back from the field because > the function generator’s sinewave frequency became too different for > the system to work. > > My idea is to use the crystal itself as part of an oscillator circuit > so that frequency is always exactly the crystal’s resonant frequency. >That's a good approach in general.> I have prepared an abbreviated concept schematic that can be viewed > here: https://i.imgur.com/4eBFQuD.png > > This is an op amp version of a Colpitts Oscillator. > > RV2 adds energy to the crystal to sustain its oscillations. I do not > know right now its optimum value.You're going to want a better oscillator circuit than that, for sure. I doubt it would actually oscillate, for one thing--unless the resonator has a lot of delay (e.g. a SAW device) it'll just look like an inductor or a capacitor depending on frequency. There may be a higher-order resonance that has enough delay.> U1 controls the oscillation amplitude by controlling the voltage on > the op amp’s power supply lines. The circuit is designed to have a > single supply so two regulators need not be ganged together.Most of the piezo actuators I've used have resonated in the 30 kHz region, with Qs around 30. That's low enough that the nonsinusoidal waveform of a self-limited oscillator can cause all sorts of uglies in the motion--when the Q is low, the mechanical overtones often aren't far enough from the electrical harmonics to get good rejection. The other issue is that the electrical resonance won't be the same as the mechanical resonance in general, so the vibration amplitude will be tuning-sensitive. The mechanical resonance is what it is, and generally coincides closely with the electrical series resonance. A Colpitts has to run at a frequency where the piezo looks inductive. Getting it to run exactly at its series resonance requires a series inductor of just the right size. <snip>> The cable to the crystal might be as long as five feet.Not a giant problem for a kilohertzy oscillator.> > My questions are whether this should work in principle, and whether > there are any bettor ways to do it.If you want to avoid tuning issues, I'd suggest using an external sinusoidal VCO and driving the piezo via a resistor. Servo the VCO frequency to where the phase shift across the resistor is zero. That should nearly coincide with the amplitude minimum. You might need an amplitude adjustment to take out unit-to-unit variations in the piezoelectric sensitivity, but at least it'll be running at its mechanical resonance. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●January 3, 20222022-01-03
On Tuesday, January 4, 2022 at 8:41:36 AM UTC+11, Phil Hobbs wrote:> Artist wrote: > > I have been tasked with designing a piezoelectric actuator driver at > > its resonant frequency. This is to replace an arrangement where the > > sine wave source is a function generator chip (the obsolete XR-2206) > > that must be individually tweaked on a unit, by unit basis, to match > > the crystal’s resonant frequency. > > > > The crystal is used as an actuator to vibrate a mirror used in a > > laser system. We have had systems come back from the field because > > the function generator’s sinewave frequency became too different for > > the system to work. > > > > My idea is to use the crystal itself as part of an oscillator circuit > > so that frequency is always exactly the crystal’s resonant frequency. > > > That's a good approach in general. > > I have prepared an abbreviated concept schematic that can be viewed > > here: https://i.imgur.com/4eBFQuD.png > > > > This is an op amp version of a Colpitts Oscillator. > > > > RV2 adds energy to the crystal to sustain its oscillations. I do not > > know right now its optimum value. > You're going to want a better oscillator circuit than that, for sure. > > I doubt it would actually oscillate, for one thing--unless the resonator > has a lot of delay (e.g. a SAW device) it'll just look like an inductor > or a capacitor depending on frequency. There may be a higher-order > resonance that has enough delay. > > U1 controls the oscillation amplitude by controlling the voltage on > > the op amp’s power supply lines. The circuit is designed to have a > > single supply so two regulators need not be ganged together. > Most of the piezo actuators I've used have resonated in the 30 kHz > region, with Qs around 30. That's low enough that the nonsinusoidal > waveform of a self-limited oscillator can cause all sorts of uglies in > the motion--when the Q is low, the mechanical overtones often aren't far > enough from the electrical harmonics to get good rejection. > > The other issue is that the electrical resonance won't be the same as > the mechanical resonance in general, so the vibration amplitude will be > tuning-sensitive. The mechanical resonance is what it is, and generally > coincides closely with the electrical series resonance. > > A Colpitts has to run at a frequency where the piezo looks inductive. > Getting it to run exactly at its series resonance requires a series > inductor of just the right size. > > <snip> > > The cable to the crystal might be as long as five feet. > Not a giant problem for a kilohertzy oscillator. > > > > My questions are whether this should work in principle, and whether > > there are any bettor ways to do it. > If you want to avoid tuning issues, I'd suggest using an external > sinusoidal VCO and driving the piezo via a resistor. Servo the VCO > frequency to where the phase shift across the resistor is zero. That > should nearly coincide with the amplitude minimum. > > You might need an amplitude adjustment to take out unit-to-unit > variations in the piezoelectric sensitivity, but at least it'll be > running at its mechanical resonance.As usual Phil has got it pretty right. My problem was with a micro-stirrer which didn't need to produce a well-controlled excursion, but we did want to run it at the mechanical resonance , which was pretty sharp. My problem was that maximum amplitude didn't happen when the phase shift across the resistor was zero. The argument is that the phase shift goes from leading below resonance to lagging about resonance, but the reality is that it isn't exactly zero at resonance. If you want to define resonance as maximum excursion, you can't use amplitude monitoring to get it exactly, because the amplitude doesn't change with frequency at the peak. Happily, phase does change quite rapidly at that frequency. An approach that can work is to measure the phase when the amplitude is 50% down from the peak below resonance , and 50% down above resonance - both give well defined frequencies and thus phases, and set the system to lock the phase half-way between. There's no guarantee that this will give the absolute maximum amplitude, but it will get you close, and close enough to let you work out almost the exact phase shift that will give you the maximum amplitude at the time. The over-kill approach would be to use a direct digital synthesis (DDS) chip to generate the sine wave drive, and waveforms to drive in-phase and quadrature phase detectors. You'd have to digitise the outputs of both phase detectors and turn them into amplitude and phase signal and let a microprocessor do the tweaking. There are simpler, cruder approaches. You can make a crude approximation to a sine wave as a "modified sine wave" - which is a switched drive which is off from 0 degrees to 30 degrees, high from 30 degrees to 150 degrees, off again from 150 degrees to 210 degrees, low from 210 degrees to 330 degrees and off again from 330 degrees to 360 degress. That can be done with voltage controlled oscillator (VCO) in 4046 running at twelve times the desired frequency, and a bunch of digital dividers to spit out the drive waveforms and the outputs to drive the in-phase and quadrature phase detectors. If you run the VCO faster you can push out waveforms at the operating frequency that can drive the "in-phase" detector to pick up the output amplitude at the phase you get when the system is operating at resonance and the "phase detector" so that its output goes through zero as the system goes through resonance, but you do have to know roughly where these points are. That was what I was trying to do back in 1992, but I hadn't spelled it out to my colleagues in enough detail. -- Bill Sloman, Sydney
Reply by ●January 4, 20222022-01-04
Artist wrote:> I have been tasked with designing a piezoelectric actuator driver at its > resonant frequency. This is to replace an arrangement where the sine > wave source is a function generator chip (the obsolete XR-2206) that > must be individually tweaked on a unit, by unit basis, to match the > crystal’s resonant frequency. > > The crystal is used as an actuator to vibrate a mirror used in a laser > system. We have had systems come back from the field because the > function generator’s sinewave frequency became too different for the > system to work. > > My idea is to use the crystal itself as part of an oscillator circuit so > that frequency is always exactly the crystal’s resonant frequency.Then *use* the crystal that way, instead of fiddling around with any of the other driving schemes proposed? BTW, your circuit as-is puts an adjustable (RV2) filtered (C1) DC voltage on the crystal.> I > have prepared an abbreviated concept schematic that can be viewed here: > https://i.imgur.com/4eBFQuD.png > > This is an op amp version of a Colpitts Oscillator. > > RV2 adds energy to the crystal to sustain its oscillations. I do not > know right now its optimum value. > > U1 controls the oscillation amplitude by controlling the voltage on the > op amp’s power supply lines. The circuit is designed to have a single > supply so two regulators need not be ganged together. > > I am aware there should be more capacitors in the U! adjustable > regulator circuit, and ops amp circuits. U1 also needs protection diodes > to prevent it being back driven in by capacitors during power down. All > this has been removed for clarity. > > U1 might have to be replaced with an adjustable DC DC Converter. I do > not know right now how much current the crystal will require. > > The cable to the crystal might be as long as five feet. > > My questions are whether this should work in principle, and whether > there are any bettor ways to do it.-- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus
