Probe Camera Alignment

Probe Camera Alignment

The Camera alignment system permits the user to align in X/Y with accuracies of the order of tens of micrometer using a web camera mounted on the Z-axis next to the spindle.

Configuration

• The camera alignment system requires the presence of python-opencv module
• Select the camera from "Tools -> Config -> Camera".
• Select the appropriate rotation. Note: for the moment v0.9.2 the configuration is disabled, you have to manually edit the .bCNC file

Hardware

Any USB camera that can be recognized by opencv will work with bCNC. In my machine

• I've bought a cheap web camera, with a clip that mounts on top of the laptop screen. The resolution is a bit crapy 352x288, despite that it gives very nice results.
• I removed the plastic cover and milled a plexiglass base.
• I've inserted the camera using a double sided adhesive tape.
• On the side I've added 2 high power leds connected to the USB 5V via a 100Ohm resistor. The resistors are used to reduce a bit the light from the high power leds otherwise the camera is blinded.
• I've adjust the lens of the camera to focus to the appropriate distance.
• Note: Focusing at small distances the camera distorts a lot the image like a fish eye lens

• The plastic base is mounted on an aluminium angle with 3 screws and a spring in between to align the camera perpendicular to the X-Y plate.

• I've mounted the camera with an aluminium bar that I've drilled a few holes to adjust the height. I can go from 1cm up to 4cm height with respect to the spindle. At 1cm I have a spatial resolution of about 20um and at 4cm around 80um. Most of the time I keep it at 4cm to have bigger clearance with respect to the spindle.

Calibration

• Turn on the camera visualization from the tool bar on top of the Canvas.
• First jog the spindle to some location on top of a scrap material.
• Turn on the spindle and jog inside the scrap to drill a small hole 1-2mm is enough.
• Move upwards the spindle to a safe height.
• Note: All calibration and motion of the camera will be performed with this height.

• Go to 'Probe->Camera' and click on 'Register' 1.Spindle

• Jog the camera to center the hole.
• At this point you can set the Diameter of the tool used in the Camera dialog
• Experiment with the Scale so that the cross hair circle fits exactly the hole. Note: this step is not important but gives nicer visual results.

• With the hole fitting exactly on the cross hair, click on 'Register' 2.Camera
• The offset of the camera with respect to the spindle should be disabled in the input fields.
• Calibration is complete.

Orientation of gcode

• This is an example on how to orientate the g-code to fit the object present in the machine.
• For testing I've placed at a random position and orientation a PCB that I've made some time ago.

• Switch to the camera system, by clicking the "Switch" button on the ribbon. The button is creating a virtual offset with G92 on the present workspace so as the center is moved to the camera location.
• By switching back to the spindle, the offset is canceled with a G92.1 command

• Change to the "Probe -> Probe" tab
• In the PCB the holes are 0.6mm, so I set the Diameter to 0.6mm
• Jog the camera to a known location. In this example I've used a couple of drilled holes.
• Click on the Orient -> Add button
• Click with the mouse to the line on the center of the hole. Note: there is a snapping mechanism in bCNC, that will snap to the closest gcode control point

• Jog to the 2nd marker

• Zoom and align the camera on the second marker
• In this quick example I had to make steps of 20um to align the holes

• Click on Orient->Add
• Click on the second marker gcode point on the canvas

• Repeat with a 3rd marker

• Add the 3rd marker
• Note: 2 markers are sufficient, but the more you provide the more accurate the system is going to be determined. bCNC is solving an overdetermined system to find the best match.
• Note: observe always the error for each marker. If too high you can move the marker with the mouse or delete and add again.

• At this point clicking on the Orient -> Orient button the gcode will be transformed to match the markers.

• I've changed the location of the Camera display from Bottom Right to Gantry so that the camera image follows the gantry location when displayed in X-Y

• Inspect some points and see the camera image with the gcode overlay.
• Note: The image distortion from the macro focusing is visible. The gcode is matching close to the center but at larger distances is distorted.