Mendel in the Cambrian

So, after weeks of building non-functional extruders, I decided to turn my attention to other things that I have left on the backburner for far too long. Herewith, is a short description of a computer-vision application, specifically written to monitor mendel movements. I have included a video, of my findings…. but firstly, the video does require some explanation.

This video is the output of a C++ application, that tracks mendel motion, as that motion relates to instructions, received from reprap host software, and consequently executed by the mendel hardware. The application generates a clear, visual comparison between true- and target positions.

The application takes two inputs:

1. It reads a text file/stream of GCODE

2. It reads a video stream/camera/file

 

The application interprets input data as follows:

1. The GCODE file is interpreted, and a target position is calculated, for the extruder and y-axis, respectively. The target position, appears as a green rectangle.

2. In addition, the GCODE time-stamp is read, and compared to the incoming time-stamp of the video stream. If the former is greater, then the video stream information enjoys priority, and all data from the latter gets updated.

3. From the data of the video stream, the actual position is calculated, for the extruder and y-axis, respectively. The actual position appears as a red rectangle.

4. The extruder rectangles appears at the approximate centre-left of the screen, while the y-axis rectangles, appear at the bottom-left of the screen.

 

Currently, the application generates a stand-alone video file (see attachment).

Future plans and testing include the following:

1. Run the application in real-time. Currently, all video- and gcode data is fed to application via offline files.

2. Integrate application with RepRap Host software, so that real-time corrective gcode can be sent to mendel (camera-in-the-loop). A socket connection can be used for inter-process communication purposes. To send gcode information from host software to application, a pipe can be used. 

3. Incorporate and interpret STL build information, so that build progress can be monitored, and problems can be identified (and avoided, as far as possible) during build.

4. Test “visibility” of extruded plastic, and test whether this can be monitored as well.

5. Test “visibility” of geared/pinch-wheel extruders.

6. Automate object recognition viz. all objects to be tracked, must be “recognised” auto-magically, on program start-up.

 

 

The basic camera setup, as well as measured distances, can be seen in the following diagram:

Cambrian Mendel

 The cam configuration above, together with video graphics resolution, gives a movement resolution of approximately 0.5mm per pixel. No camera calibration model has been included in the code.

 

A little bit of printing….but not too much

So, I have a mendel that prints little bits at a time. And the main culprit, barring me from full functionality at this time, is definitely the extruder. I have mastered such esoterica as; axis belt tensioning, homing, axis squaring, printbed preparation, extruder preparation etc.

At the present, my printbed is not heated. To compensate for this, I have temporarly put double sided tape on the print surface. I will experiment with Kapton tape at a later date, once I have optimised my extruder settings, and built the electrnics for the heated bed.

I am experimenting with different extrusion temperatures, and tentatively settled on 230C. This is the temperature as reported by the RepRap Host software, and I have no idea how close this reported value is to the “actual”/true temperature value. The extrusion rate is glacial.  Even when applying a considerable amount of manual force, i.e. bypassing the motor all-together. And I am left wondering which of the following might be the reason for my slow extrusion:

1. There is some adhesion chemistry going on inside the hot-end
2. My extruder motor needs to be more “burly” i.e. requires more torque
3. There is something peculiar about the chemical make-up of my particular batch of ABS 

 

There is another peculiarity of my current mendel setup: my heater stops working at random times. I am not sure whether this is due to some software configuration issues like firmware/RepRap host software compatibility, or maybe something completely different. Loose electrical connections could also cause erratic temperature readings, but I have located and fixed all loose connections….I hope.

Below are some sample pictures of the Mendel geared extruder.

Mendel extruderMendel extruder

 And another view….

Mendel extruder

 The blue tape, is a little bit of insulation wrapped around the melting zone, which includes the kapton tape  insulated nichrome wire, and thermocouple sensor. The PTFE thermal barrier was inserted into lasercut portion with epoxy.

The printbed has been covered with double-sided tape, as a temporary measure, until I get the extruder configured correctly.