A whole slew of updates to the RMOD software
Posted: Fri Oct 30, 2015 9:21 pm
Hello, i've done a whole bunch of updates to the RMOD software at my local fork: https://github.com/Knaster/LitePlacer-ver2 - i'm hoping people can help me test it and make sure it works before submitting a pull request to Juha. I realize i should not have done as many edits at once, however i started this a while ago and i didn't have git at the time and i have never used it before. I also didn't want to try and go back and add features piece-by-piece to the original code as they're inter-dependent and the possibility of errors would be much greater that way.
The majority of the changes i've made concerns calibrations and placement accuracy, basically my thought on the lite placer is that it's able to be a much cheaper alternative to "professional" machines because it can be made DIY-style by people not needing to be excellent mechanical engineers, using much cheaper / imperfect materials than what's found in commercial alternatives. This being said i've had a number of issues in regards to the fact that i myself am a fairly bad mechanical engineer and seemingly i cannot get my machine mechanically perfect despite my best efforts. Luckily todays software technology is cheap and good enough that most, if not all, mechanical issues can be compensated for in software - which in terms of open source, is free.
I've made a bunch of calibration routines using a specially designed calibration paper that should be printable on any semi-accurate printer, to be used with the down looking camera. The file is called "calibrationsheet.png" and can be found in the root directory.
Calibrate XY/mm rev: This calibration is used to make sure that the X & Y mm / revolution settings are set correctly, the optimal value of 40mm / rev isn't necessarily spot-on depending on belt tightness and probably other factors too. This calibration requires that the user moves the X and Y axis according to instructions.
Calibrate skew: This calibration uses the calibration paper to automatically calculate the squareness correction necessary.
Calibrate Z / XY compensation: This calibration came out of the fact that in my machine, the Z axis does not go down in a perfectly straight angle. This results in the fact that the camera-to-needle offset will be dependent on height and thus compensation is needed for the X and Y axis at all levels of Z height. This routine requires that the camera is mounted on the Z axis and moves with the needle, it does *not* seem to work perfectly right now but you can use the "Height offset" instead.
Height Offset: This is a manual version of the "Calibrate Z / XY compensation" which does not require the camera to be mounted on the Z axis. This routine requires that the original Camera Offset is set correctly:
Verify placements: This routine will show the calculated placements of all fiducials and 10 random components and is used to let the user verify and recalibrate if necessary.
I have modified the Calibrate Needle function to average rotation around a virtual zero, essentially the old routine assumed that the needle would be in the dead center of the up looking camera which isn't always true - and doesn't need to be. Furthermore if your up looking camera is slightly tilted in any directions you may not *want* to have the needle in the dead center as you will get a perspective view of the needle in that case.
I have also modified the Camera Offset routine to subtract the current needle wobble from the offset and made sure to use the TrueX position (no squareness correction) making for more accurate offset for all possible rotations of the A-axis. For this to work with the X/Y compensation of Z, the Camera Offset should *not* be measured at PCB level but at Z 0.
Despite all calibrations being very accurate now, i still didn't get perfect results so i reimplemented the Kabsch algorithm in a way that i could understand it. The new implementation takes in X and Y scaling if the measured fiducial distances differs from the nominal. My tests so far has yielded *much* more accurate placements, but it probably needs to be tested more.
I've modified the manual "Pickup this" and "Place here" buttons routines to take in the X/Y compensation for Z.
I added simple feeder support to the Tape Positions - tab. Use it by focusing the camera on the middle of the given component and input the number of components on your reel in the dialog. This function i believe is not perfect yet, i am going to change it to use TrueX and see if i get better results.
I also added a "Set first hole" / "Set last hole" procedure for tapes, this will automatically calculate angle and bypasses the down looking camera routines, making for more exact and much faster pickup.
I was also getting timeouts due to the fact that the machine was trying to move axises to the current position they were at, this seems to make the TinyG not issue "SR"-responses so i added a check for this.
The image attached is of the difference in placement before and after the reimplementation of the Kabsch-algorithm.
Any feedback very welcome!
-Karl
The majority of the changes i've made concerns calibrations and placement accuracy, basically my thought on the lite placer is that it's able to be a much cheaper alternative to "professional" machines because it can be made DIY-style by people not needing to be excellent mechanical engineers, using much cheaper / imperfect materials than what's found in commercial alternatives. This being said i've had a number of issues in regards to the fact that i myself am a fairly bad mechanical engineer and seemingly i cannot get my machine mechanically perfect despite my best efforts. Luckily todays software technology is cheap and good enough that most, if not all, mechanical issues can be compensated for in software - which in terms of open source, is free.
I've made a bunch of calibration routines using a specially designed calibration paper that should be printable on any semi-accurate printer, to be used with the down looking camera. The file is called "calibrationsheet.png" and can be found in the root directory.
Calibrate XY/mm rev: This calibration is used to make sure that the X & Y mm / revolution settings are set correctly, the optimal value of 40mm / rev isn't necessarily spot-on depending on belt tightness and probably other factors too. This calibration requires that the user moves the X and Y axis according to instructions.
Calibrate skew: This calibration uses the calibration paper to automatically calculate the squareness correction necessary.
Calibrate Z / XY compensation: This calibration came out of the fact that in my machine, the Z axis does not go down in a perfectly straight angle. This results in the fact that the camera-to-needle offset will be dependent on height and thus compensation is needed for the X and Y axis at all levels of Z height. This routine requires that the camera is mounted on the Z axis and moves with the needle, it does *not* seem to work perfectly right now but you can use the "Height offset" instead.
Height Offset: This is a manual version of the "Calibrate Z / XY compensation" which does not require the camera to be mounted on the Z axis. This routine requires that the original Camera Offset is set correctly:
Verify placements: This routine will show the calculated placements of all fiducials and 10 random components and is used to let the user verify and recalibrate if necessary.
I have modified the Calibrate Needle function to average rotation around a virtual zero, essentially the old routine assumed that the needle would be in the dead center of the up looking camera which isn't always true - and doesn't need to be. Furthermore if your up looking camera is slightly tilted in any directions you may not *want* to have the needle in the dead center as you will get a perspective view of the needle in that case.
I have also modified the Camera Offset routine to subtract the current needle wobble from the offset and made sure to use the TrueX position (no squareness correction) making for more accurate offset for all possible rotations of the A-axis. For this to work with the X/Y compensation of Z, the Camera Offset should *not* be measured at PCB level but at Z 0.
Despite all calibrations being very accurate now, i still didn't get perfect results so i reimplemented the Kabsch algorithm in a way that i could understand it. The new implementation takes in X and Y scaling if the measured fiducial distances differs from the nominal. My tests so far has yielded *much* more accurate placements, but it probably needs to be tested more.
I've modified the manual "Pickup this" and "Place here" buttons routines to take in the X/Y compensation for Z.
I added simple feeder support to the Tape Positions - tab. Use it by focusing the camera on the middle of the given component and input the number of components on your reel in the dialog. This function i believe is not perfect yet, i am going to change it to use TrueX and see if i get better results.
I also added a "Set first hole" / "Set last hole" procedure for tapes, this will automatically calculate angle and bypasses the down looking camera routines, making for more exact and much faster pickup.
I was also getting timeouts due to the fact that the machine was trying to move axises to the current position they were at, this seems to make the TinyG not issue "SR"-responses so i added a check for this.
The image attached is of the difference in placement before and after the reimplementation of the Kabsch-algorithm.
Any feedback very welcome!
-Karl
anyway on my board (0603) they were pretty spot on using mounting holes as fiducials.
Camera's are cheap , vision is pretty good and computer power is plentiful.