Galvo details for beginners? - Photonlexicon Laser Forum

Hi,

I wonder if there are some resource available somewhere that describe how a galvo works in detail.

The theory is clear for me: there are two lines for power where a +- voltage is feed into, depending on the polarity and voltage the galvo moves into one or the other direction.

And there are some feedback-channels that show at what position the galvo really is. And that's the interesting part - how is the current position sent back? Via encoder pulses? Via an analogue signal? Something else?

Happy if someone could shed some light on this or point me to some useful information sources.

Thanks you :-)

Feedback is typically from a differential pair of photodiodes. There is an (IR) LED in the rear housing of the galvo that shines on a pair of photodiodes, and in between is a flag attached to the galvo shaft. As the shaft rotates, the flag moves to obscure one photodiode, the other, or some combination of the two. The photodiode produces a current proportional to the amount of light incident on it, so as the flag moves from covering more of photodiode A to covering more of photodiode B, the photocurrent from A increases and the photocurrent from B decreases. The difference between those two photocurrents is converted to a voltage that represents the position of the galvo. Typically there is an AGC circuit that monitors the combined photocurrent from both photodiodes and regulates the LED drive current to a level that produces a useful signal range from the photodiodes.

The attached picture of a cheap galvo shows the flag attached to the shaft in the center, the LED at the bottom, and the two photodiodes top left and top right. In the position shown, the flag is obscuring more of the left photodiode than than the right photodiode. Other galvos use photodiodes mounted flat on the PCB, with a flag mounted normal to the shaft axis, and an LED above. The exact arrangement chosen is a balance of manufacturability, mechanical performance, feedback accuracy, patents, etc.

Attached Thumbnails  

For closed loop (position detection) galvos, there is feedback from the galvos to the amp. The feedback is analog. Some of the early galvos used capacitance feedback. Most, if not all, modern galvos use optical feedback. An infrared emmiter and a photodiode detector(s) . The rotor of each galvo axis will have a flag or some interrupter to attenuate the infrared from the emitter to the detector. Some even use mirrors or other reflection means.

Effectively, galvos are an optical servo. With the position detection in the galvo, the amps will try to match the feedback signal from the galvos to the signal coming from the source. As far as amp design, it's basically a tunable comparator circuit and the complexities can go from basic to exotic!

Looks like I was beat out while typing!

See attached

More later when I'm home...

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J1 is the cable going to the Galvo.
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Photodiode bridge of either a pair or quad of detectors go on J1(5) and J1(9) with common to J1(4) Resulting in currents IA and IB flowing from the sensor to the Galvo Driver board.
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R19 gets very carefully calculated as in most cases the LEDs are pushed very hard.
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U4(A) an U4(c) are the transimpedance amplifiers that convert the PD currents (IA,IB) to voltages.
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Points "A" and "B" connect the detector to the LED current source and the linearization feedback.

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The term "AGC" is a holdover from the classic General Scanning G120 which used a capacitive position sensor that needed feedback from the amplifier to ensure accuracy.

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You know you have repaired too many galvo amps for people when you keep the older basic schematic on your ..

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Steve

Please note that modern galvos do not self center except for a few Scannermax products that have a magnetic field designed for centering. . This means that if you apply power to the drive coil (1.2 to 7 Ohms, Model Dependent) without a working feedback loop, the Galvo slams to one side and stays there. In many cases it can then heat up and blow the fragile coil.
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Older open loop and some closed loop General Scanning products have a torsion rod that acts as a centering force. New generation designs, ie post , do not.
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Steve

Choosing suitable galvo mirrors depends on several factors, including your application requirements, technical specifications and budget. Here's a guide to help you choose suitable galvo mirrors.

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1. Galvo mirror Application Requirements

Scanning Speed: Determine the speed at which you need to scan or deflect the laser beam or light source.

Accuracy: Consider the level of precision required for your application.

Resolution: Determine the smallest incremental movement you need from the galvo mirrors.

Operating Environment: Consider factors like temperature, humidity, and vibration levels where the galvo mirrors will operate.

2. Galvo mirror Technical Specifications

Mirror Size: Choose the appropriate mirror size based on the beam diameter and scanning area requirements.

Reflectivity: Select mirrors with high reflectivity to minimize energy loss and maximize efficiency.

Coating: Ensure that the mirrors have coatings suitable for your wavelength range (e.g., UV, visible, IR).

Frequency Response: Consider the frequency response of the galvo mirrors, which determines how fast they can move.

3. Galvo Mirror Budget Considerations

Galvanometer mirrors come in a wide range of prices based on their specifications and quality. Determine your budget and look for mirrors that offer the best value within your budget constraints.

4. galvo mirror Supplier and Support

Choose a supplier known for providing high-quality galvo mirrors and reliable customer support. Sino-Galvo provide 2D / 3D laser marking, laser cleaning, laser welding, laser medical beauty galvo scanner, and provide 18 months warranty for most model. Below are some important parameters of our galvo mirrors.

(1) Coating wavelength: 355nm, 405nm, 532nm, 840nm, 915nm, nm, nm, nm, nm, nm, nm

(2) Spot size: 3mm, 5mm, 7mm, 10mm, 12mm, 14mm, 16mm, 20mm, 30mm

(3) Base material: K9, Silicon, Quartz

(4) Incident angle: X:45°±15°/ Y:37.5°±15°

(5) Surface accuracy: affects lens reflectivity and field lens focal length

(6) Reflectivity: The higher the reflectivity, the stronger the laser energy and the lower the lens temperature.

(7) Power: Generally nanosecond laser; power is determined by lens material, coating, and laser

Commonly used Galvo mirror Parameters comparison table Wavelength Spot Size Material Incident Angle Surface Quality Surface Accuracy Reflectivity Power nm mirrors 7 Glass X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 50W nm mirrors 7 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 50W nm mirrors 7 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 100W nm mirrors 10 Glass X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 50W nm mirrors 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 150W nm mirrors 10 quartz X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 350W

Continuous W

nm mirrors 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 200W 355nm mirrors (UV) 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99%@355nm,

R＞80%@650nm

Pulse 30W 405nm mirrors (blue light) 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99%@405nm,

Contact us to discuss your requirements of laser galvo scanner. Our experienced sales team can help you identify the options that best suit your needs.

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R＞80%@650nm

Pulse 100W 532nm mirrors (green light) 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm

R＞99%@532nm,

R＞80%@650nm

Pulse 100W 450~nm silver-coated mirrors 10 silicon X:45°±15°/ Y:37.5°±15° 20-10 λ/4@633nm R＞96%@450~nm

Pulse 20W

Continuous 100W

nm mirrors 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 500W

Continuous W

nm mirrors 20 quartz X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse W

Continuous W

nm mirrors 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse 500W 355nm mirrors (UV) 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99%@355nm,

R＞80%@650nm

Pulse 40W 405nm mirrors (blue light) 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99%@405nm,

R＞80%@650nm

Pulse 150W 532nm mirrors (green light) 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99%@532nm,

R＞80%@650nm

Pulse 150W 450~nm mirrors 20 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm R＞96%@450~nm

Pulse 50W

Continuous 200W

nm mirrors 30 quartz X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse W

Continuous W

nm mirrors 30 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse W

Continuous W

nm mirrors 30 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm

R＞99.5%@nm,

R＞80%@650nm

Pulse W 450~nm silver-coated mirrors 30 silicon X:45°±15°/ Y:37.5°±15° 40-20 λ/2@633nm R＞96%@450~nm

Pulse 100W

Continuous 500W

Related Article

Article: How to replace the galvanometer mirror

By considering these factors and consulting with suppliers or experts in the field, you can select galvo mirrors that best suit your specific application needs.

If you want to learn more, please visit our website laser marking software.