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With a CNC the main goal is to get a platform to a location. This location can be specified by different coordinate systems. Currently I'm limiting the aim to a 2D plane. Most hobby CNCs use the two drive axis as the basis for the CNC's coordinate system. From a user perspective we want to print what we see on screen to a physical environment. On screen the basis are orthogonal, so we also expect the CNC's basis to also be orthogonal. This usually mean careful construction and calibration to ensure the two drive axis are orthogonal. On screen the units also constant, forming a uniform grid, this also means the CNCs have to ensure uniform 'steps', usually achieved by stepper motors.
With limited resources I was unable to construct a CNC which meets these requirements. Below is a visualization of the desired grid (black) and the grid from the uncalibrated hardware (red):
It might be slightly exaggerated but it makes a point. If the CNC was used as is to plot an item without calibration, the output will be badly distorted.
To solve this I add a feedback element which will then allow me to use the basis of the feedback device instead of the basis of the CNC. The feedback element I chose was the humble webcam. It was a iSight striped out of a long expired iMac. My experience with these cameras used OpenCV tells me that the spatial accuracy are quite impeccable. There are very little distortion, but even if there where distortion, OpenCV has a plethora of information to remove the distortion. So now the projected grid of the camera will become our reference to my CNC. A visualization with the ideal (black), camera (purple):
The two grids are close enough for now. So let the software start to implement this. The aim to to move the platform to a location observed by the webcam. Now all this might be a bit confusing right now but I'm sure a bit of code and a video will clear it all up.
[フレーム]
After a little thinking, there is finally a direction for this project. The ideal outcome is to create a generic control board that will allow the use of any sensorless mechanical drive system in a closed loop system. The board will include basic H-bridge and servo PWM drivers so that users can just plug in simple DC motors and have a working CNC. It would be nice to have a full self calibration routine which allows the board to auto identify the axis to make it even easier to use.
The board will most likely have a camera, fpga and a micro. With a bit of luck the BOM should be less than 25ドル. And with cheaper hardware, it should bring cheaper CNCs.
The dev. has slowed due to an inconsistent Z axis on the machine. The milling motor was too slow and has lead to damage to the cutting head and then the whole Z axis. And the X and Y is too slow. There are plans to upgrade the axis to a belt driven system from multiple inkjet printers. More to come when the hardware is replaced.
The end goal of this CNC was to be able to mill PCB, make stencils and any other tedious tasks of fine cutting. So adding a V mill bit is getting the machine one step closer. The software has just been moved to a g-code input as oppose to a image input.
The bit is mounted in a head cut off from mini hand-drill, which has been soldered to the motor. The bit itself was a bit of rod with the tip ground to a V. There is very little lateral movement and can put a good scratch on a piece of aluminum.
The new software has issues with commanding the CNC. There are overshoots and Z-axis issues. New controls for cutting diagonal lines should also be considered. The current lines are in little steps.
It's not all bolted down, nor is it all off-breadboard, but the CNC is stable with ove 10hr operation time under its belt. The control board need to be isolated from the drive side due to power spiking issues, whcih may (or may not) need to be fixed. May also need add a few limit switches in case the CNC runs out of bounds while I'm out of the room. It's done it once resulting in the need to regear the motors...
TIME FOR SOFTWARE DEV!
Quite excited about it as the current software is horrible. Once the software is semi-presentable it will be uploaded.
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I am working on a new project and this CV project will be a helpful guide for me you can see my furniture removals website project for further details.