Z-axis balancing device of gantry machining center in Jinan No. 2 Machine Tool Works
Z-axis balancing device of gantry machining center
The total design weight of the Z axis of the XH2430-80 gantry machining center of Jinan Second Machine Tool Works is about 6t, so when the Z axis moves up and down, the Z axis motor is seriously biased. In order to solve this problem, the company adopts a single pull rod balance cylinder installed on both sides of the Z-axis. The problem of additional load of Z-axis motor is solved by balancing oil circuit of hydraulic system. Figure 1 is the schematic diagram of the Z-axis balancing device of the machine tool. The hydraulic system is always supplied with oil. The pressure oil body is adjusted to 14 MPa by one-way valve 1 and pressure reducing valve 2. When the given command of the machine tool is in the upward motion of the Z-axis ram, the solenoid valve 8 does not act, and the main oil circuit enters the upper chamber of the balance cylinders 5 and 6 through the hydraulic control check valve 3. At this time, the system pressure oil has played a balancing role in the rise of the Z-axis. At the same time, the pressure oil enters the lower chamber of accumulator 7, and the compression airbag maintains the system pressure and the pressure during shutdown. Pressure gauge 4 shows the system pressure. When the given command of the machine tool is at Z-axis lowering, under the action of the Z-axis ball screw drive pair, the oil discharged from the upper chamber of the oil cylinder cannot return under the action of the check valve 3. At the same time, the solenoid valve 8 in the system acts, and the pressure oil opens the hydraulic control check valve through the control oil circuit, so that the pressure oil of the system can be adjusted by the pressure reducing valve 2, so as to achieve the relative balance between the weight of the hydraulic system and the Z-axis. The design of the oil system is relatively simple Single, but there is a certain defect. When the Z axis moves up and down, the entire oil pressure system is always in the state of adjustment. If the oil pressure regulated by pressure reducing valve 2 is too high, the torque and current of Z-axis motor will increase, causing Z-axis to crawl during operation. On the contrary, the low oil pressure regulated by pressure reducing valve 2 will cause the Z-axis to overshoot when the operation stops. To prevent creeping and overshoot during Z-axis movement, the oil pressure regulated by pressure reducing valve 2 should be adjusted according to the current of Z-axis motor.
The test data shows that when the moving speed of Z-axis is F100%, the rising current is 6.5% and the falling current is 7.2%. It indicates that the decrease of Z-axis current is greater than the increase, and there is back pressure in Z-axis transmission pair.
In fact, it is difficult to solve the problem of whether a three-axis CNC machining center is better or a four-axis machining center is better. There is only a problem that is not suitable for machining some kinds of parts. Basically, all three-axis machining centers can process the parts that can be processed by a four axis machining center, while the parts that can be processed by a four axis machining center may not be processed by a three-axis machining center.
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