RecycleBot v2.3 Controls
by jpearce, published
A RecycleBot is a waste plastic extruder that creates 3-D printer filament from waste plastic and natural polymers.
This is a fully automated version of Recyclebot v2.2 with many improved features. For more info see C. Baechler, M. DeVuono, and J. M. Pearce, Distributed Recycling of Waste Polymer into RepRap Feedstock, Rapid Prototyping Journal, 19(2), pp. 118-125 (2013). open access
For similar see the Open-Source Lab How to Build Your Own Hardware and Reduce Research Costs
The mechanical design is equivalent to RecycleBot v.2.2 http://www.thingiverse.com/thing:12948 - I strongly recommend reading that first. This design is, of course, far from optimized particularly with respect to cost and DYI, it is primarily being used by the Michigan Tech in Open Sustainability Technology Research Group to make new fucntionalized 3-D printing materials (e.g. electrically conductive) to support a full range of products open-source disributed manufacturing...lots more to come.
Some of the improved features over RecycleBot v2.2 are:
- Type of plastic can be selected from the keypad interface and the controller automatically updates the extrusion temperature for the plastic.
- Extrusion temperature can also be feed by the keypad interface for any type of plastic which can be melted and extruded.
- LCD interface for better process monitoring.
- No extrusion until the extrusion temperature is achieved - automatically controlled by microcontroller, with (manual option).
- Low cost power control options using a Triac and MOSFET.
The energy performance of v2.2 can also be significantly improved with insulation.
As the heater is the most important section it must be designed and fabricated precisely for better results as changes in temperature of few degrees can result in different mechanical properties of the extruded plastic. Another important criteria for the heating section is to create uniform heating environment so that the temperature remains nearly constant throughout the barrel such that the extruded plastic is uniform. To achieve this, high temperature ceramic beads were used to insulate the bare nichrome wire so as to achieve electrical isolation from the iron barrel, and an advantage of using this scheme is high-quality thermal insulation from the ambient environment and heat transfers efficiently to the iron barrel as the bottom side of the ceramic beads rest on the metal tightly and the top surface is insulated to the air, which is then insulated as well.
Steps to make the heater section
1. Clean the barrel and then make the top surface rough with a file. 2. Again clean the surface and remove any residing metal debris and dust. 3. Cut the required length of nichrome wire and straighten that up and hook the ends to a clamp. 4. Carefully insert the ceramic beads onto the nichrome wire one by one till the whole wire is completely covered up with ceramic beads. 5. Take the furnace cement and cover-up the iron barrel throughout the surface, it need to be made sure that whole surface is completely covered up with furnace cement as any exposed bare metal can posses the risk of short circuit with the bare nichrome and hence elevating the chances of electric shock (and destroying your power supply). 6. Gently take the nichrome wire and place it over the barrel and slowly cover up the barrel as if making a coil out of nichrome wire. 7. Fix the two free ends of the nichrome tightly to a clamp and apply furnace cement to cover up the whole surface of ceramic beads and it should look like the picture given in gallery. Again it is stressed that the furnace cement must be applied all over to cover the whole surface of ceramic beads so as to adhere strongly to the underlying metal and it should also make an electrical insulation layer such that bare nichrome shouldn't touch the metal anywhere.
- Allow it to dry for at least 24 hours.
- Connect the two free ends with alligator clips to power up the heater.
Safety note use gloves while using furnace cement as its alkaline in nature and can injure you and damage the skin if exposed for a prolonged time, if by chance skin comes in contact with furnace cement, then wash it under running water immediately. It is recommended that you do this in a hood if you have access to one.
Temperature Monitoring and Process Control
Controlling the temperature and other related processes of plastic recycling and extrusion in an efficient manner and simultaneously decreasing the cost is the key challenge for RecycleBot development especially for home applications. In order to promote the RecycleBot for open sustainability, the whole control system is designed to work on Arduino, which is a very popular open source microcontroller based application development platform. Being easy to use and program with excellent user community support, Arduino is a low cost rapid prototyping platform ideal to implement control system for RecycleBot. Arduino Mega was used to design and implement the system, having enough input/ output pins for interfacing LCD, keypad, and other components.
The whole process is divided into two parts: Input mode and Control mode
The process starts with user input of either plastic selection or extrusion temperature. With the option of 10 different types of plastic, user can select the desired type of plastic to recycle and the program automatically loads the optimum temperature range for operation/ extrusion for that particular type of plastic. Alternatively, user can also feed the temperature of extrusion for any type of plastic which can be operated below 350C. After the extrusion temperature is set, program ask the user to confirm the temperature and once the temperature is set, the program steps into the control mode.
In the control mode, the microcontroller is taking the temperature as input and adjusting the output power of heater accordingly such that temperature remains within the set bound range which is 15C above and below the set extrusion temperature. The system is designed in such a way that if by any means the system temperature exceeds the set extrusion temperature, the power of the heater is cut off completely until the system temperature gets within the set bound range. Also, when the temperature is within the set range, the extrusion process starts, i.e. the motor starts feeding the shredded plastic from the hopper to the heater, also the spooler stepper motor starts which wind up the filament and coil over a spool. If the temperature drops 15C below the extrusion temperature, the program stops the feeder motor as well as the spooler motor to ensure that the quality of filament remains the same, and as soon as the system temperature reach the set range of operation, both the feeder and spooler motor resumes working.
The code for RecycleBot was written by Michigan Tech graduate student Ankit Vora at in C on Arduino IDE, using the keypad, LCD and stepper motor libraries. In order to replicate the RecycleBot code on an Arduino Mega, first, all the libraries must be copied into the correct destination of Arduino folder such that Arduino compiler can compiler them along with the program code. On Arduino development platform LCD library is already included, however keypad and stepper motor library need to be registered before compiling the code.
Steps to replicate, compile and upload the program code on Arduino Mega
Download the libraries,unzip and copy every folder exactly into the folder: arduino-1.0\libraries\
(if you are using a new version of Arduino, then copy all the libraries to that folder, in any case the folder of Arduino development platform will be having folder 'libraries' and each and every library used must be copied to this folder.
Run the Arduino development platform, go to the 'sketch' tab, then go to the section 'import library...' one should find the Keypad and AFMotor in the list. If they appear, it means we are all set and ready to use the code. Download the code for RecycleBot and spooler. Copy the RecycleBot code into Arduino IDE or just open the file with Arduino, and then select Arduino Mega from the list of board and upload. The RecycleBot code is now ready to be executed. For spooler, copy the code from the file or open the file for spooler code with Arduino, select the Arduino Uno as board and upload, the spooler is all set to work.
If you have trouble with the files send me an thingiverse mail or email Ankit at avora#mtu.edu (replace # with @, anti-spam)
Download the circuit diagram and fabricate on two separate PCBs in order to get better reliability. One can use a breadboard, but using breadboards sometimes creates reliability issues due to hanging wires, and especially when we are using high power control elements with low power DC control and monitoring components, its better and recommended to make the circuit on general purpose PCB for rapid prototyping. It is recommended to make the temperature sensor and measurement circuit on one PCB and DC motor and heater controller on another PCB. The circuit for temperature sensor is small and works on low voltage of +5 V and needs a good isolation for the AC components and must be fabricated on a separate PCB as shown in the picture gallery. And the circuit for DC motor control and heater controller uses both +5V, +12V and 110V AC, so it must be well isolated from the low voltage DC components like Arduino etc., so that the transients, spikes won't affect the working of temperature and process control, hence it must be also fabricated on a separate PCB. Use good quality copper wire for heater power controller such that it can withstand both high power and temperature.
For a more indepth description including how the circuit works, and how to assemble everything, and costs see this
Lyman also has a spool winder -- which you will likely need depending on what type of plastic you are using: