Readout electronics for Sony Magnescale linear scales - Page 1
Forum section: electronics / projects

author: Tugge
author_rank: Newbie
timestamp: April 03, 2020, 09:31:09 pm
content: Hello folks,I have acquired two Sony magnescale linear scales (model number SR108) and I would like to use them as linear scales for my cnc. How ever I did run in to the problem. I thought at first that you could pull out quadrature signals or sin/cos signals from the D9 connector, but oh how wrong was I.Then I started to investigate the technology more but I haven't found out the exact principle of operation (at least from the electronics point of view). But this is how much I already know:The sensor head has 6 wires (three pairs). One (red and white) is some kind of excitation pair. You need to put some ac-signal to this pair to get something out from the other pairs.The second (blue and yellow) and the third (brown and orange) are the sensing pairs. Other gives the sine equivalent and other cosine equivalent ac-signals.These input pair signals are filtered, amplified etc. in the pcb, which is located inside the D9-connector. I have reverce engineer the pcb, but I don't fully understand it. The first stage of both input channels is quite obvious, but then how the second and the third stage merges the two signal paths is unclear for me. Also the last opamps reference input is just connected to D9_4 so I don't have any idea what to connect there. One option is that maybe the excitation signal is some how fed back to here.So the conclusion here is. If someone has better knowledge of these linear scales (about the electronics) I would love to know more.If someone can help me to understand the amplifier circuit, I would be appreciated.Here you can find photos, schematic etc.:https://1drv.ms/u/s!AgPyAY1uBgJNh-sdVxojHfEbLKOsZQ?e=wECd03And here is video of me explaining the stuff:https://1drv.ms/v/s!AgPyAY1uBgJNiMM4kiqgmLOtfsZuoQ?e=aV99dWThank you in advance,// Tomi L

author: duak
author_rank: Super Contributor
timestamp: April 04, 2020, 12:09:02 am
content: I was interested in how these scales worked to see if I could do something similar. I remembered that Sony developed the technology in the 1980s and that the magnetic grating had to be written on the magnetic material.I googled "magnescale theory of operation" and found a clue in an on line book about rolling steel. see attached file.A link to a newer version of the book is:https://books.google.ca/books?id=quc4T0VTeggC&pg=PA183&lpg=PA183&dq=magnescale+theory+of+operation&source=bl&ots=ruWS2egBCs&sig=ACfU3U0zQ_8DY02IE6eaDMMlf_j_PQt6Hg&hl=en&sa=X&ved=2ahUKEwjtu6fNuc3oAhVmIjQIHWY-DrQQ6AEwCnoECAsQNA#v=onepage&q=magnescale%20theory%20of%20operation&f=falseI don't know if the link will work for you.Are you familiar with signal processing? I expect that synchronous demodulators will be needed to extract the position information from the scale. These are not too difficult to design but will take some effort to refine to get best resolution and accuracy.When I look at the schematic though, it doesn't make sense. U3 appears to be an inverting stage to send the sum of the two input signals to the display but capacitor C5 complicates things. It would take some analysis and experimentation to see how the circuit works. Perhaps Out- is the 2nd harmonic that the above document mentions?If you experiment with the scales, be careful not to apply too large a signal to the excitation winding as it might damage the winding or even erase the grating. Test close to the ends of the scale rather than the middle.This is an interesting product and has some advantages over optical scales in that it is much more resistant to coolant and debris.Cheers,

author: Martinn
author_rank: Frequent Contributor
timestamp: April 04, 2020, 05:15:19 pm
content: What about resolver interfaces?https://www.analog.com/en/products/analog-to-digital-converters/integrated-special-purpose-ad-converters/synchroresolver-to-digital-converters.htmlIf you just want working linear scales, why not buy a few chinese optical ones, these are hard to beat in terms of price/performance.

author: amyk
author_rank: Super Contributor
timestamp: April 04, 2020, 09:39:34 pm
content: Yes, that looks like a linear version of a synchroresolver.

author: Tugge
author_rank: Newbie
timestamp: April 05, 2020, 09:09:57 am
content: duak: Thank you for the link. It explains the theory really well. Now that I understand better how it is working, it is easier to create the readout electronics. About the schematics the C5 is the hard part. But you have a really good guess, so I will try to analyze the circuit more. And recheck my reverse engineering.I have played with signal processing a little, but creating the quadrature output with signal processor can be tricky. I think only valid option is to use fpga for this purpose and I don't want to choose that path.Martinn: At quick glance of these devices, they would work really well, if I can get nice sine and cosine waves from the head. At the moment I get something else, which makes things a little harder. But I need to investigate more of these devices. And yes I know that there are some dirty cheap linear scales on the web but normally the resolution is only 5 um, and it is not good enough for my purposes.So now that I know the theory, I can start to develop the electronics. I will probably rebuild the whole amplifier electronics. My idea is to use sample&hold ic synchronized to excitation signal to sample the exact moment of readout signal. That signal should be looking like sine/cosine vawe and those signals are fed to these IC-MG interpolator ic, which transfers them to quadrature A/B signal. Other option is to use these analog devices resolver adc:s. I have used IC-MG before, so I will probably use that first.But keep you posted how the project evolves.

author: duak
author_rank: Super Contributor
timestamp: April 05, 2020, 08:48:35 pm
content: Tugge, sampling synchronous to the excitation is a form of synchronous demodulation! Since you have to generate the excitation, just start with a clock 4X the excitation frequency. Use a Johnson ring counter as in the attached file to generate the quadrature sampling clocks: I & Q or sine & cosine. The I clock is filtered to remove harmonics and is then applied to the scale for excitation.You can use analog switches to sample the scale outputs. You will have to experiment with the value of the hold capacitors and will require some low pass filtering before digitizing the signals. After that you will have to figure out how Sony's circuit affects the signals from the scale. Since Sony developed the Magnescale in the 80's, they may have done some of the hard work in analog to simplify the digital section.The overall method is an incredibly sensitive way to detect low level signals. see:https://www.analog.com/en/analog-dialogue/articles/synchronous-detectors-facilitate-precision.html

author: viewgsm
author_rank: Newbie
timestamp: April 01, 2023, 07:49:09 am
content: I know this has been an old topic but I thought I would add to it just for reference, tested PL20/PL22-AF and I can confirm the following:1- excitation frequency is 10KHz2- excitation amplitude is around 2V Peak-Peak (AC coupled)

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: April 01, 2023, 11:10:56 am
content: Quote from: duak on April 05, 2020, 08:48:35 pmmind to explain how the circuit in the attached file is supposed to work?