Transformation of CINCINNATI l 0HC CNC System for Imported Horizontal Machining Center

CINCINNATI l 0HC is the horizontal machining center imported from the laboratory of the School of Mechanical Engineering of our school in the late 1980s. It is equipped with the ACRAMATIC 900MC numerical control system and DC servo drive. Its processing range is 1000mm for X axis, 1000mm for Y axis and 800mm for Z axis. There is a mm800mm indexing table, and the rotary turret has a capacity of 3 knives, which is a large and medium-sized machining center. Due to the earlier import time, the integration of the electrical control unit is low. In recent years, the system often fails, and finally the machine tool cannot be used due to the lack of spare parts.

Firstly, the machine tool was thoroughly tested. It was found that the servo system and hydraulic system of the machine tool were still available, and the mechanical components still maintained high precision, but the computer control system and some interface units were damaged. Under the premise of considering the price and restoring the various control functions of the original machine tool, it is decided to choose the Siemens 810M system to realize the four-axis control three-axis linkage, retain the original mechanical, hydraulic system and servo drive, and adopt the incremental encoder. Instead of the original linear induction synchronizer as the position feedback component, Siemens built-in PLC controls the I/O point of the machine tool to improve the reliability of the interface.

The original machine tool uses the inductive synchronizer as the position feedback component for closed-loop feedback, while the basic configuration of the Siemens 810M system can only process the feedback signal of the encoder. It is necessary to add a conversion module to process the output signal of the inductive synchronizer. Considering that the price of the conversion module is high, and the accuracy of the original machine tool is not too high (positioning accuracy is 0.02mm), there are more than 1000 compensation units of the numerical control system, so it is determined that the pulse encoder is directly connected to the shaft end of the servo motor. , semi-closed loop feedback control of position. This also makes the entire system easy to adjust and runs more stable. Here, the two-axis end encoder is used to connect with the motor shaft and the tachogenerator, which respectively constitute the speed and position feedback. Moreover, using the numerous compensation units provided by the numerical control system, the positive and negative lead screw pitch compensation and the clearance compensation are performed to achieve the original machine tool precision.

Siemens internal PLC is used to complete control operations such as machine limit switches, hydraulic system, cooling system, spindle tool change, tool magazine management, spindle and feedrate override, and operation panel.

The PLC working voltage of the original system is AC 110V, and the Siemens PLC working voltage is DC 24V. Therefore, the DC relay module needs to be configured. In the case of AC/DC isolation, the connection between the Siemens PLC and the original input and output points of the machine tool is realized.

Spindle part: The machine tool spindle drive is only a speed unit, open loop control; the quasi-stop of the spindle is controlled by the mechanical device and PLC. The control process is: cancel the spindle enable, suspend the neutral gear, the spindle decelerates to less than 20r/min, insert the positioning pin to position the spindle, and send the completion signal.

The spindle hanging process is: receiving the gear signal, canceling the enable, delaying the spindle stop, gear swinging gear, and issuing the completion signal.

Tool magazine management: Mainly complete the tool magazine four zero, manual, automatic operation, automatic memory of the tool holder number, and the number of steps to determine the movement direction of the tool and the rotation according to the shortest path.

Automatic tool change: When the system issues a tool change command, the Z axis retreats to the tool change position, and the spindle starts the positioning program. The tool magazine starts the tool selection program and automatically changes the tool by the robot. The Z axis returns to the machining position and starts the spindle.

DNC interface program: The memory of the numerical control system is small, and the numerical control machining program for complex curved surfaces can only adopt the method of processing while transmitting. This communication method utilizes a circular buffer register, which is implemented by PLC programming.

The establishment of the machine alarm text: the detection of the voltage, current, hydraulic circuit pressure, hydraulic oil level, lubrication status and other sensors of the machine tool, the alarm text of the abnormal situation is established, and displayed on the monitor to provide the operator with the basis for maintenance.

After the modified machine tool is compensated by the laser interferometer, the positioning accuracy and repeat positioning accuracy of the machine tool reach the accuracy of the original machine tool; the test specimen is measured by the coordinate measuring machine, and the straightness, roundness and hole positioning accuracy are measured. Both achieve the machining accuracy of the original machine tool test piece. It shows that the transformation plan is economically feasible, and the equipment worth 2 million yuan has been put into use again. The machine currently plays an important role in undergraduate teaching and laboratory production.