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  • New interferometer setup

    Putting together a newer interferometer setup than the nearly 40 year old one I have. This one is pretty neat, USB based control box that is actually a ISA to USB backplane that hold the two HP/Agilent cards that receive the signal as well as atmospheric and material conditions. Right now I am using an older (2008) Agilent 5517D stabilized laser and an old (late 70's) HP receiver. I am transferring the receiver to the head so it can do straightness measurements with he right optics. Ill post pics of that as I get further along, I am waiting for some delrin to show up.

    This also has a feature where you can hook an encoder up to the box and you can do stuff like ball screw comp and measure table droop and sag on machines as well as do flatness testing of surface plates. ultimate resolution with this model is .5nm

    The laser is the gold box on the left, the receiver is the little thing with the cable coming out the back, then the interferometer and finally the bounce mirror on the micrometer slide on the left. The rest of the stuff on the table is a spectrometer which is unrelated, I just needed a long flat surface for testing.

    Untitled by Jerry Biehler, on Flickr

    Untitled by Jerry Biehler, on Flickr

    Untitled by Jerry Biehler, on Flickr

  • #2
    that level of useful resolution is gonna make some guys jealous

    Comment


    • #3
      Macona- I always find this stuff interesting. Talk about inspiring things, or people- take a bow.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

      Comment


      • #4
        Originally posted by macona View Post
        Putting together a newer interferometer setup than the nearly 40 year old one I have. This one is pretty neat, USB based control box that is actually a ISA to USB backplane that hold the two HP/Agilent cards that receive the signal as well as atmospheric and material conditions. Right now I am using an older (2008) Agilent 5517D stabilized laser and an old (late 70's) HP receiver. I am transferring the receiver to the head so it can do straightness measurements with he right optics. Ill post pics of that as I get further along, I am waiting for some delrin to show up.

        This also has a feature where you can hook an encoder up to the box and you can do stuff like ball screw comp and measure table droop and sag on machines as well as do flatness testing of surface plates. ultimate resolution with this model is .5nm

        Is it an interferometer or a time-of-flight laser rangefinder?

        I guess time-of-flight would not be giving you that level of accuracy so it must be interferometer.

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        • #5
          how do you measure flatness with the interferometer?

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          • #6
            looks like microns were harmed
            --
            Tom C
            ... nice weather eh?

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            • #7
              No, interferometers measure distance be measuring the different aspects of the light. Two kinds off lasers are used, homodyne and heterodyne setups. Little explanation of the two types here: https://spie.org/publications/tt61_5...erometer?SSO=1

              The old one I have is a homodyne, the newer one is a heterodyne. They use dual axis setups like this as a replacement for encoders on semiconductor equipment like the memory repair machines we used to make at work.

              To measure flatness and straightness you need a different set of optics than what I have up there. To measure flatness you are using a carrier that slides along a straightedge that is carrying optics that measure angular deflection.

              I have a scanned copy of there manual that shows setups for all sorts of situations like measuring distance, straightness, angular displacement, and so on. Flatness starts on section 9

              https://drive.google.com/drive/folde...L5?usp=sharing

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              • #8
                interesting. so the software uses the end point method to create the reference line for flatness?

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                • #9
                  Im not sure what the end point method is.

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                  • #10
                    based on the available points you have to establish a base line of reference for the deviations. "endpoint method" would be one way and i had the impression thats what is being done. but never mind.

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                    • #11
                      LASERs? Ahhhhhhhhhhhhhhhhh, you bastard! Now I'm blind. xzqq..//?-))))oiwjuoiu iooi

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                      • #12
                        Hah, this laser puts out 225 microwatts, you could stare into that beam for days and it wouldn't do anything.

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                        • #13
                          Got the receiver made for the HP head that I mentioned in the first post. Tool and old HP 10780a receiver and gutted it and took the photodiode and circuit board and mounted it in an enclosure that attaches to the front cover of the laser. I machined a little slot in a spare cover and installed a small .1" header that matches up with the pins I installed on the board. Im waiting for a DigiKey order with the last couple parts I need to get it wired in.

                          Untitled by Jerry Biehler, on Flickr

                          Untitled by Jerry Biehler, on Flickr

                          Front cover with the header installed in the corner

                          Untitled by Jerry Biehler, on Flickr

                          Untitled by Jerry Biehler, on Flickr

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                          • #14
                            Oh! And I got a rensishaw interferometer from HGR. Took a bit more work, it powered up but was locking in at about 1/3 the max power you would see while warming up. I managed to figure out the analog board and was able to get it readjusted to lock in the middle, around 330uw. This laser has a receiver built in and talks to a computer though RS-485 or something though a proprietary "datelink" protocol and the adapters are unobtainium. The board does have differential quadrature output like an encoder so I did some modifications to bring those signals out instead and also added a little circuit that would keep the quadrature signal output off until the laser has warmed up and stabilized. Dead-bugged a 74HCT373 in there just for one buffer in it. While warming up it has a red light that blinks which eventually turns yellow and then green when it is locked. I could have just tied the green signal to the enable of the line driver but the green output pulses during a period of the tube cycle. So I used a '373 which has an inverting enable and passes through the green signal only when the red signal is off. Had to add some pull downs to the differential output because there was some 60hz noise being induced from the transformer below the board.

                            Waiting for a line receiver to show up and then Ill put together a USB interface with a Teensy to connect it to the PC software.

                            Untitled by Jerry Biehler, on Flickr

                            Mods, added the '373, pull downs on the 26ls31, and brought out the enables.

                            Untitled by Jerry Biehler, on Flickr

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                            • #15
                              Originally posted by dian View Post
                              based on the available points you have to establish a base line of reference for the deviations. "endpoint method" would be one way and i had the impression thats what is being done. but never mind.
                              I think I get what you are saying. Like what is done usually with 1"-2" sets of lens that are ground.

                              Still need the light box. Nothing fancy, just straight light. Not laser straight.

                              Collimated at least, its a wooden BOX LOL.

                              Oh! Its partner is also in a wooden box.

                              The largest Optical Flat I have seen (12"x2"). Very heavy and very flat. I dont know how to use them? The Lamp and the Flat?

                              I dont touch it. I dont have a Lab..

                              JR
                              My old yahoo group. Bridgeport Mill Group

                              https://groups.yahoo.com/neo/groups/...port_mill/info

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