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First of all, the machine tool was thoroughly tested. It was found that the servo system and hydraulic system of the machine tool can still be used. The mechanical components still maintain high accuracy, but the computer control system and some interface units have been damaged. Under the premise of considering the price and restoring various control functions of the original machine tool, it was decided to select the Siemens 810M system to achieve four-axis control of three-axis linkage, retaining the original mechanical, hydraulic systems and servo drive devices, using incremental encoders Instead of the original linear induction synchronizer as a position feedback element, Siemens incorporates PLC to control the I/O points of the machine tool to improve the reliability of the interface.
The original machine tool uses an inductive synchronizer as a position feedback element to perform closed-loop feedback, while the basic configuration of the Siemens 810M system can only process the feedback signal of the encoder. An additional conversion module is required to process the output signal of the inductive synchronizer. Taking into account the high price of the conversion module, but the accuracy of the original machine is not too high (positioning accuracy of 0.02mm), the number of the CNC system compensation unit is as many as 1000, so determine, increase the pulse encoder and servo motor shaft directly connected , achieving a semi-closed-loop feedback control of the position. This will also make the entire system easier to adjust and more stable in operation. The two-axis encoder is used here to connect with the motor shaft and the tachogenerator, which respectively constitute the speed and position feedback. In addition, using the numerous compensation units provided by the numerical control system, the pitch compensation and clearance compensation of the positive and negative lead screw are performed to achieve the original machine tool accuracy.
The Siemens built-in PLC is used to control the machine limit switches, hydraulic system, cooling system, spindle tool change, magazine management, spindle and feedrate override, and operation panel.
The original system's PLC operating voltage is AC 110V, and the Siemens PLC operating voltage is DC 24V. Therefore, it is necessary to configure the DC relay module to realize the connection between Siemens PLC and the original machine input and output points in the case of AC-DC isolation.
Spindle part: The spindle drive of the machine tool is only a speed unit, open-loop control; the exact stop of the spindle is controlled by the mechanical device and PLC. The control process is: Cancel spindle enable, hang neutral, spindle decelerate to below 20r/min, insert positioning pin to make spindle position, send out completion signal.
The process of the spindle gear catching is: receiving the gear signal, canceling the enable, confirming that the spindle is stopped by time delay, gear swinging, and sending a completion signal.
Tool magazine management: It mainly completes the tool magazine 40, manual, automatic operation, automatic memory of the tool holder number, and determines the direction of the tool movement and the number of rotation steps according to the shortest path.
Automatic tool change: When the system issues a tool change command, the Z axis will retreat to the tool change position. At the same time, the spindle will start the positioning program. The tool magazine will start the tool selection program. Through the robot's automatic tool change, the Z axis will return to the machining position and start the spindle.
DNC interface program: The memory of the numerical control system is relatively small, and the NC machining program for complex surfaces can only adopt the method of edge processing and edge transmission. This communication method uses a circular buffer register and is implemented by PLC programming.
Establishment of machine tool alarm text: detection of voltage, current, pressure of hydraulic circuit, hydraulic oil level, lubrication status and other sensors of the machine tool, establishment of alarm texts for abnormal conditions, and display on the monitor to provide maintenance basis for the operator.
After the modified machine tool is compensated and tested by the laser interferometer, the positioning accuracy and repeat positioning accuracy of the machine tool can reach the accuracy of the original machine tool; the test specimen of the test-cutting standard is measured by a coordinate measuring machine, and the straightness, roundness, and hole positioning accuracy are measured. All reached the original machine tool specimen machining accuracy. It shows that the reconstruction plan is economically feasible and the equipment worth 2 million yuan is put back into use. The machine currently plays an important role in undergraduate teaching and laboratory production.
CINCINNATI l 0HC is a horizontal machining center imported from the laboratory of the School of Mechanical Engineering of our school in the late 1980s. It was originally equipped with ACRAMATIC 900MC CNC system and DC servo drive. Its processing range is 1000mm in X axis, 1000mm in Y axis and 800mm in Z axis. With a ¢800mm indexing table, the capacity of the rotary magazine is 3 knives, which are large and medium-sized machining centers. Due to the earlier import time and the low integration of the electrical control unit, the system often malfunctions in recent years. In the end, due to the lack of spare parts, the machine tool cannot be used.