Open source control units for control of machine tools and robots
In the way that the open source influenced revolutionary growth of PC industry, open source control units for machine tools should contribute faster machine tools industry growth as well as development of SMEs in mechanical engineering field through modernization of existing tools with minimal investments. Modernization of main industrial capacities of the Republic of Serbia requires retrofitting of machines with obsolete technology which form greater part of domestic manufacturing industry. Mainly, this means modernization of control systems. They will increase productivity by opening possibilities for usage of modern CAD/CAM systems with effective increase in cutting speeds.
Nowadays, commercial program suites and systems are present in this sector. However, high application demands, closed architecture and high price make them inaccessible for domestic market. Open source control unit makes possible configuring not only trivial kinematics machine but also nontrivial kinematics and industrial robots. Universal applicability of the new control that is one of its main features along with very low price makes main difference relative to commercially available systems.
Concept of Open-Architecture CNC
EMC2 (Enhanced Machine Controller) is real-time software for controlling machine tools with source code that can be freely used, modified and distributed (GNU General Public License ). It was designed to work under Linux/UNIX operating system with real-time extension. Base of this software that is used and modified today was developed by NIST - National Institute of Standards and Technology.
A transparent system integrating the functions of forward and inverse kinematics, as well as a simple change of control configuration, makes EMC2 ideal for machine tools control, of standard and specific configuration, and reconfigurable machining centers.
The realization of control unit for multi-axis machine control requires the provision of stable hardware platform, real-time operating system and control software with open architecture, having the corresponding performances. The choice for hardware platform, in our case, is industrial PC computer platform compatible with corresponding operating system for real-time operations. It is the price that is of particular importance being by several times lower than that of commercially available CNC hardware platforms. As a very reliable and widely used, the Ubuntu real-time Linux has found its place in our development project. This operating system meets fully the choice criteria for time critical processes of the CNC software. The period of executing the servo loop of 1 ms and generation of a new interpolation segment of the trajectory every 5 ms, as well as timely execution of equally important lower priority level processes, and user's comfortable work with other lesser demanding applications, are all major criteria taken into account in CNC hardware platform building and choice of the operating system. To make the concept of control unit complete, the corresponding CNC interface cards should be plugged in the PC platform. PCI interface into the computer mother board was one of the principle criteria for the choice of MOTENC Lite card. Two of such cards, added to the primary computer platform, have the total of eight analog outputs for the connection to the frequency regulators and eight quadrature digital inputs with optical measurement systems. There are a multitude of digital inputs and outputs for the connection with sensors and micro-switches from machine tools.
Structure of open-architecture CNC developed on PC platform