In the years of maintenance work, many faults concerning the CNC servo feed servo system have been dealt with, and the common faults of the feed servo system have been summarized. Common feed servo faults are as follows:
1. Overtravel When the feed motion exceeds the software limit or the hardware limit switch position set by the software, an overtravel alarm will occur, and the alarm content will be displayed on the display of the CNC system, according to the manual of the CNC system. The electrical schematic can be eliminated and the alarm can be cancelled. Note: If an over-travel alarm occurs when one of the axes of the machine is not moved to the end position, it is usually because the limit switch is broken or the limit switch is stuck when the machine is running.
2, overload usually when the load of the feed motion is too large, frequent positive and negative movements and poor lubrication of the transmission chain or slanting iron, grounding of the motor power line, etc., will cause the servo motor current is large, the motor temperature is too High or motor overload alarm. Sometimes the drive control unit, drive components, and the motor itself may malfunction during the operation of the machine. Alarm information such as servo motor overload, overheating or overcurrent is usually displayed on the display of the CNC system. At the same time, on the feed drive unit in the power cabinet, the indicator light or the digital tube will prompt the drive unit to overload, over current and other information.
The model of the large equipment manufacturing plant is TK42160C CNC boring machine. The numerical control system of SIEMENS840D is used. The X axis has caused overload alarm due to the grounding of the servo motor power line in the drag chain. The machine is normal after replacing the new motor power cable.
3. Crawl occurs when starting the acceleration section or low-speed feed, which is generally caused by factors such as poor lubrication of the feed chain, low gain of the servo system, and excessive load. In particular, the coupling between the servo motor and the ball screw is not synchronized with the rotation of the servo motor due to loose coupling or defects in the coupling itself, such as cracks, so that the feed is made. The movement is slow and slow, causing creep.
The model of the large-scale equipment manufacturing branch is 2A637гФ1 CNC boring machine. The X-axis has a phenomenon of low-speed feed instability (ie crawling phenomenon). After inspection, it was found that the X-axis oblique iron was slightly damaged due to the slippery oil. After treatment, The X-axis low-speed feed is normal.
4. When the vibration is in the feed (especially at low speed), the vibration phenomenon of a certain axis of the machine tool is usually due to the instability of the speed measurement signal, such as the speed measuring device failure, the speed feedback signal interference, etc.; the speed control signal is unstable or interfered; the terminal contact Bad, such as loose screws. When the vibration occurs in the commutation moment of the forward direction and the reverse motion, it is generally caused by the backlash of the feed chain or the servo system gain being too large. When the machine is running at high speed, vibration may occur and an overcurrent alarm will occur. Machine vibration problems are generally speed problems, so you should look for the speed loop; and the entire adjustment process of the machine speed is done by the speed regulator, that is, any speed-related problems, you should look for the speed regulator, so the vibration problem Look for the speed regulator. Mainly from the given signal, feedback signal and speed regulator itself to find faults.
5. The servo motor does not turn the CNC system to the feed drive unit. In addition to the speed control signal, there is also an enable control signal, which is generally DC+24V DC voltage. The servo motor does not rotate. Commonly used diagnostic methods are: check whether the CNC system has a speed control signal output; check whether the enable signal is turned on. Observe the I/O status through the display of the numerical control system, analyze the plc ladder diagram (or flow chart) of the machine tool to determine whether the starting condition of the feed axis, such as lubrication and cooling, is satisfied; for the servo motor with electromagnetic brake, check it. Whether the electromagnetic brake is released; check if the feed drive unit is faulty and the servo motor is faulty.
The large-scale equipment manufacturing plant used the SIEMENS840D numerical control system model XK2425/2 Wuhan CNC gantry milling machine to have a failure of the Z-axis servo motor. The fault phenomenon is that the Z axis does not move regardless of the positive and negative Z axis (Z axis motor does not rotate), but there is no alarm. By observing the "Diagnostics" - "Service Display" - "Drive Adjustment" menu displayed on the display of the CNC system, the pulse enable signal of the axis is found to be absent. The enable signal of the shaft is given by the control board of the drive unit of the shaft, so it is preliminarily determined that the control panel of the shaft is faulty or the control board is disconnected from the enablement signal of the numerical control unit. First, replace the Z-axis drive control board with the Y-axis drive control board, and find that the Z-axis is normal at this time, and the same failure phenomenon as the Z-axis occurs when the Y-axis is opened. The fault can be determined that the Z-axis drive control board is faulty, and the Z-axis is replaced after replacing the new drive control board.
6. Position error When the servo axis moves beyond the position tolerance range, the numerical control system will generate an alarm with excessive position error, including following error, contour error and positioning error. The main reasons are: the allowable range of the system setting is small; the gain of the servo system is improperly set; the position detection device is contaminated or improperly adjusted; the cumulative error of the feed drive chain is too large: the balance device (such as the balance hydraulic cylinder) when the spindle box moves vertically Unstable.
7. Drift drift means that when the given command value is zero, the coordinate axis still moves. It is eliminated by the CNC system error compensation and the zero speed adjustment of the drive unit.
8. Clearance and looseness of mechanical transmission components In the feed drive chain of CNC machine tools, the transmission is often damaged due to the gap between the keyway and the key of the transmission component. Therefore, in addition to careful selection of the key coupling mechanism during design, Processing and assembly must be strictly investigated. The preload of the bearing should be checked when assembling the ball screw to prevent axial movement of the ball screw, as clearance is another cause of significant drive clearance.
Floating Ball Liquid Level Sensor
The floating ball liquid level transmitter is composed of magnetic floating ball, measuring conduit, signal unit, electronic unit, junction box and mounting parts. Generally, the specific gravity of the magnetic floating ball is less than 0.5, which can float above the liquid level and move up and down along the measuring conduit. The conduit is equipped with measuring elements, which can convert the measured liquid level signal into a resistance signal proportional to the change of liquid level under the action of external magnetism, And convert the electronic unit into 4 ~ 20mA or other standard signal output.
The liquid level sensor is a modular circuit, which has the advantages of acid resistance, moisture resistance, shock resistance and corrosion resistance. The circuit contains a constant current feedback circuit and an internal protection circuit, which can make the maximum output current no more than 28ma, so it can reliably protect the power supply and prevent the secondary instrument from being damaged.
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