Brown & Sharpe MicroVal Axis Error Fixed
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  1. #1
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    Default Brown & Sharpe MicroVal Axis Error Fixed

    Folks,

    This is for people who get a 'axis error' message on a Brown
    and Sharpe MicroVal machine. I'm posting this for the next
    person who has to deal with this - my problem is solved but
    reply if you want to ask questions or discuss it. Also, if
    anyone knows how to set the dip switches on the controller
    board for one of these cmm's, I'm interested.

    Mark
    ----

    Adjusting Brown & Sharpe MicroVal CMM Axis Quadrature Signal

    11/25/09 - m. mcdade

    Each 9-pin axis plug contains a small circuit board with
    four pots for adjusting the quadrature signal waveforms.
    I did not trace out and understand the exact function of
    the circuitry supporting the sensors but at the time of
    this work, both the x and y axes functioned well while
    the z axis produced a 'axis error' message. Cleaning and
    resetting the sensors on the scales helped (several years
    ago, cleaning completely eliminated an error on the y axis)
    but, eventually, the z axis could not be used any more and
    required adjustment.

    What I found was that the 4 pots on each little board in an
    axis plug are associated with two test points on the counter
    board in the cmm control (into which the plugs are inserted).
    There are two test points for each axis. To adjust a given
    axis, connect a scope probe for the 'upper' waveform (i.e.,
    the one associated with the upper two pots when looking at
    the plug board) to the upper test point and a scope probe
    for the 'lower' waveform to the lower test point for the
    axis. Set both channels to 2v/division on the scope and,
    in auto mode, set the upper trace to the middle line of the
    screen and the lower trace to the bottom line of the screen.
    With power on and while moving the axis in question, you
    should see sine waves from each channel. The top two pots
    are used to adjust the upper signal (on the upper test pin
    for the axis of interest). The upper pot of each pair sets
    the offset of the waveform and the lower pot of each pair
    sets the amplitude of the waveform. The following numbers
    were derived by looking at the two good axes and served to
    set the third so it now works perfectly. My z-axis voltages
    were way off before my resetting and the fact that it
    (mostly) worked for a long time indicates to me that these
    are not terribly tight tolerance numbers.

    top of upper waveform - 7.1 volts
    bot of upper waveform - 2.7 volts
    top of lower waveform - 3.5 volts
    bot of lower waveform - 1.0 volt

    ---

    Each scale unit has four pairs of emitters and sensors that
    see out through a pattern of bars which one of the older
    user manuals indicates are spaced a quarter space smaller than
    the bars on the scale. It is easy to trace the wiring back to
    the plugs and see that the pots on the plug are used to adjust
    the voltage level to the emitters, apparently one per pot.
    What isn't clear is how that translates to the two (unequal)
    sine waves at the test points. These seem to form a
    quadrature pair (the phase difference is clearly visible on
    the scope) but how the circuitry gets from the four physical
    signals to two logical ones is not clear to me.

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  3. #2
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    Dear Sir!
    Have you the same plugs and counter board like in photo? (attach in the post)
    Attached Thumbnails Attached Thumbnails b-s-counter-board.jpg   b-s-head-connectors.jpg  

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    Default

    Aike - did you notice that the thread is 5 years old?

    Mike

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    Default Display monitoron Microval CMM

    Can you tell me what type monitor you are using on the Microval CMM and does it use a DB-9 connection to control box, Also do you have to have en and mouse connected to control box for it to display. Thanks [email protected]


    Quote Originally Posted by mmcdade View Post
    Folks,

    This is for people who get a 'axis error' message on a Brown
    and Sharpe MicroVal machine. I'm posting this for the next
    person who has to deal with this - my problem is solved but
    reply if you want to ask questions or discuss it. Also, if
    anyone knows how to set the dip switches on the controller
    board for one of these cmm's, I'm interested.

    Mark
    ----

    Adjusting Brown & Sharpe MicroVal CMM Axis Quadrature Signal

    11/25/09 - m. mcdade

    Each 9-pin axis plug contains a small circuit board with
    four pots for adjusting the quadrature signal waveforms.
    I did not trace out and understand the exact function of
    the circuitry supporting the sensors but at the time of
    this work, both the x and y axes functioned well while
    the z axis produced a 'axis error' message. Cleaning and
    resetting the sensors on the scales helped (several years
    ago, cleaning completely eliminated an error on the y axis)
    but, eventually, the z axis could not be used any more and
    required adjustment.

    What I found was that the 4 pots on each little board in an
    axis plug are associated with two test points on the counter
    board in the cmm control (into which the plugs are inserted).
    There are two test points for each axis. To adjust a given
    axis, connect a scope probe for the 'upper' waveform (i.e.,
    the one associated with the upper two pots when looking at
    the plug board) to the upper test point and a scope probe
    for the 'lower' waveform to the lower test point for the
    axis. Set both channels to 2v/division on the scope and,
    in auto mode, set the upper trace to the middle line of the
    screen and the lower trace to the bottom line of the screen.
    With power on and while moving the axis in question, you
    should see sine waves from each channel. The top two pots
    are used to adjust the upper signal (on the upper test pin
    for the axis of interest). The upper pot of each pair sets
    the offset of the waveform and the lower pot of each pair
    sets the amplitude of the waveform. The following numbers
    were derived by looking at the two good axes and served to
    set the third so it now works perfectly. My z-axis voltages
    were way off before my resetting and the fact that it
    (mostly) worked for a long time indicates to me that these
    are not terribly tight tolerance numbers.

    top of upper waveform - 7.1 volts
    bot of upper waveform - 2.7 volts
    top of lower waveform - 3.5 volts
    bot of lower waveform - 1.0 volt

    ---

    Each scale unit has four pairs of emitters and sensors that
    see out through a pattern of bars which one of the older
    user manuals indicates are spaced a quarter space smaller than
    the bars on the scale. It is easy to trace the wiring back to
    the plugs and see that the pots on the plug are used to adjust
    the voltage level to the emitters, apparently one per pot.
    What isn't clear is how that translates to the two (unequal)
    sine waves at the test points. These seem to form a
    quadrature pair (the phase difference is clearly visible on
    the scope) but how the circuitry gets from the four physical
    signals to two logical ones is not clear to me.

  7. #5
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    Default

    Did you every figure out the bank of switches in control box. thanks lynn

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    Default

    All,
    We are putting a B&S Microval back on the road after being on blocks for a long time. Mechanically it is "fine" and I believe the scales were OK.

    I am using the Deva037 USB Interface, along with a Deva018 Interpolator and Deva023 Pre-amp on each axis. The Pre-amp takes the place of the original pre-amp and features the 4 adjustment Pots just like in the above original posts.
    Deva Electronics - Products

    The Deva Documentation does not seem to offer any guidance on tuning the pots, or what we should be looking for on the scope waveforms.
    The X and Z read OK on the interface side, the Y jitters when moved but isn't reading correctly. I hope this can be solved by tuning the pre-amp.

    The above post is the most helpful, and only info I have been able to dig up as to what we are looking for when tuning. Its a starting place but I was hoping for a more definitive resource.

    Any help would be appreciated. I have reached out to Deva but not heard back yet.

    Thanks

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    Wery intresting thread..

    Detailed Pictures of the internals (both side of the pcb’s) of the Deva023 and Deva 018 units would be much apreciated…

    Considering geting these for my Tesa Micro-MS

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    Default Pot adjustments

    From my understanding of it, (while trying to figuring out my missing electronics) The potentiometers adjust the current through the individual LED’s in the read head. Thereby changing the amplitude of the sine waves at the four outputs of the readhead when it moves across the scales.
    The four potentiometers controlls the intensity of the four individual light beams in the scales, each representing the 0, 90, 180, 270 degree outputs of scale. In the end the 0 and 180 outputs are used as a differential pair, and the 90 and 270 is another pair. These signals represent the sin/cos output.

    The pots shall be adjusted so that the pairs are balanced, ie identical amplitude of the positive and negative signal output of each pairs. The pairs shall also be balanced relative to eachother.
    Note that the read head has to move to generate the sinus cosinus signals.

    Each of the signals in one pair shall have aproximately 0,5v peak to peak amplitude, and about +2,5v offset. (To comply with the normal 1v sin/cos interface) When these signals are received by a balanced receiver the offsets will be canceled out, the sinus shaped signals will add upp. So you will get a 1Vp-p signal with no offset. And due to the balancing, induced cable noice will also be canceled out.
    Then it is up to the interpolator to find subdivisions of the signals by using trigonometry, using the sin/cos signals to get a position between the scale lines… one increment of the scale (movement of one line) equals one period of the sin/cos signal).

    By trimming the potentiometers, and establish identical amplitude and offsets, we get the best linearity and precission wich minimizes the errors in the trigonometry functions of the interpolator.

    The offset error is the primary aspect to correct, as it will have the biggest influence in the trigonometry math functions.


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