Senior Capstone Project: Inresa S-300 Inductive Casting Machine - Page 1
Forum section: electronics / projects

author: ratdude747
author_rank: Regular Contributor
timestamp: October 15, 2014, 11:37:09 pm
content: I'd like to share my current senior project, which I think is worth discussing/showing off.What happened was an aquiantance and former FIRST mentor of mine owns a design/prototyping business (he used to be a 24 patent IBM engineer) and to help with his hobby of building model engines, he bought a non-functional Inresa S-300 Casting machine, originally made for casting precious metals for jewelry. Unfortuantly, the machine was missing all of it's control circuitry (3 cards/boards) and despite initial offerings, replacements could not be sourced. He was able to obtain the original schematics and low-resoltion pictures of the missing cards.This is where I come in. He contacted my college (as he was buddies with one of my professors) and I found out about and accepted the project, which is to redo the missing control circuity (PCBs 305 308, and 380), in a (where reasonable) more modern way that is also modding-friendly. It will also be open sourced upon completion, which will be no later than the end of April, 2015.As determined this summer during reverse engineering, the system uses a SCR based phase controlled primary to control and rectify the 240VAC line supply, and a TRIAC (used as SCR) based 4-pulse Secondary which is used to produce near-pure sinusoidal 18.6KHz power to the LC Heater. It is controlled by a 15-0V control knob input, and a 20-0mA PID controller input, and a ±170-0V primary rail check input (50/50 voltage divider between rails), along with on/off switches, and air pressure switch (also used to determine casting plug state), and a cooling water flow switch. The machine runs off of 240VAC (50/60Hz) 25A, compressed air, vacuum (used to draw the metal), cooling water I/O, and argon (for the inert casting atmosphere)Overall, the design I chose was to use an atmel ATmega328P (arduino uno chip) to be the "brain", which is used to directly control the secondary. The TCA785 based primary circuit was retained from the old design, which is controlled by an MCP4811 SPI DAC and a non-inverting amplifier. Various basic analog circuitry is used to interface the analog inputs, with the digital inputs externally pulled up and debounced. The current boost stages were, for the most part, retained from the old design. Also retained/tweaked was the EMI filtering and local power supplies (24V, 15V, and 5V). To make it modding-friendly, The unused UART was routed to a header, along with the SPI bus (allowing for up to 3 SPI expansion devices OR a single UART expansion). Also provided is an atmel ISP header and a power supply header. The microcontroller is socketed as it is to be used with an arduino uno for intial and future programming (along with the ISP).The code is written in C for AVR, which is written using CodeVisionAVR's upload to arduino function. The secondary pulses are synthesized using an interrupt using timer2 (the highest priority timer). The ADC is also run off of an interrupt, with everything else (state logic and SPI) done free-running.Presently, 99% of the design work is done, minus testing one last circuit (Verifying that 5V logic will work with the TCA785 phase controller); once some red tape is sorted out with the college, I'll be ordering parts and getting the PCBs made.Now, for some pictures and other files:This Post:-The original schematics, in german (I have translated ones too but they have a few errors, not my work)-The new board's schematic, source code, and pinout tablesOffsite but available:-the above new part files, plus KICAD files (which is what I used for the design work)Comments?