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Preliminary Study on System Reform of Import Processing Center
The MC340/TWIN is a double-spindle machining center manufactured by STAMA GmbH in Germany. Due to severe damage, the original system could not be restored, prompting a comprehensive technical renovation. The project involved replacing the original Japanese FANUC-15M control system with the German SIEMENS-840D system, which required extensive hardware and software modifications. This article outlines the key transformation methods and technologies applied during the upgrade.
Originally imported in 1994, the machine was nearly scrapped due to accidents. Beyond repairing mechanical components, the control system was also modernized. The original system controlled eight axes—two spindles (C-axis), X, Y, Z, A, C2 (rotary table), Q (magazine axis), and V (linear robot axis)—with the PLC managing some functions via STAMA’s proprietary interface. The PLC used 288/192 I/O points, while the C2 axis allowed for two work areas, enabling simultaneous processing of up to eight parts per cycle.
The tool change process was complex, involving three axes (Q, V, Z) and robotic actions. When a tool change command was issued, the Q axis moved to the correct position, the V axis retrieved the tool from the magazine, and the Z axis assisted in the exchange. After a 180° rotation, the new tool was inserted into the spindle, and the old one returned to its original location. This process required precise coordination of multiple axes, solenoids, and position sensors.
During the renovation, the FANUC-15M system was replaced with the Siemens 840D, a four-axis linkage CNC system that fully met the original specifications. The PLC was optimized, reducing I/O points from 288/192 to 192/160. The Q-axis, once controlled through analog signals, now used an external incremental encoder for accurate positioning, improving reliability and precision. The V-axis, previously reliant on an absolute encoder, now used a built-in Siemens motor encoder for higher accuracy and stability.
The C2 axis, originally controlled by limit switches, was upgraded to a digital servo motor with real-time feedback. To prevent unintended full rotations, it was designated as a linear axis, limiting movement between 0° and 180°. The PLC program was modified to simulate a reference return operation without additional hardware, ensuring smooth startup.
The Q and V axes had large gaps and elastic deformation, requiring adjustments in gain, speed, and detection time to stabilize the system. Coordination between the Q and V axes during tool changes posed challenges, but this was resolved through segmented motion programming in the PLC.
After the renovation, all original functions were restored, and performance exceeded factory specifications. The X, Y, Z axes reached rapid speeds of 22m/min, feed speeds up to 10,000mm/min, and a spindle speed of 6000r/min. Positioning accuracy was within 6.546μm (X), 8.254μm (Y), and 9.621μm (Z), with repeatability under 3.15μm (X), 3.533μm (Y), and 3.25μm (Z). The system proved stable, reliable, and user-friendly, ensuring safe and efficient operation.