PCB News - Examples of maintenance methods for CNC equipment in the PCB industry

Examples of maintenance methods for CNC equipment in the PCB industry

For maintenance personnel, as long as they have a good professional theory as a foundation, and then have a certain understanding of the structure and principle of the equipment, it is very easy to solve the general problems of the equipment. Finding the problem is the first step to solve the problem, and it is the most important step. Especially for the external faults of CNC machine tools, sometimes the diagnosis process is more complicated. Once the problem is found, it is easier to solve. For the diagnosis of external faults, I have summarized two points of experience. First, I should be proficient in the working principle and sequence of actions of the machine tool. Then you must be proficient in using the electrical schematic diagram provided by the manufacturer, using some of the NC system's status display function or the system's own test software to determine the point of failure.

The following is a detailed explanation of the maintenance of CNC equipment in the PCB industry in the form of examples:

Example 1: A Hitachi drilling rig has a spindle abnormality when the system is reset to zero. When the reset starts, the third spindle directly rushes to the table, and then the third axis servo alarms, and the computer displays that the third axis is out of control. This kind of phenomenon generally makes people confused. The fault phenomenon is too abstract and seems to be impossible to start, but as long as you carefully think about its principle, you can slowly figure out the way of thinking. Observe carefully that the Z-axis of the device adopts a semi-closed loop control method, and the position of the Z-axis is controlled by an encoder. According to the principle of this structure, the Z-axis should find the zero point and then rise to find the relative position when the Z-axis is initialized to zero. However, there are two reasons why the device has not even completed the first action.

1. The Z axis cannot find the zero point when it is initialized.

2. There is no signal output when the encoder fails.

For the first reason, it is only possible that the zero-point sensor switch is faulty, and you can know the quality of the position detection sensor switch, and for the second possibility, the encoder must be replaced. Based on the above inference, it was decided to check the zero-point sensor switch of the third axis first. After inspection, it was found that it was indeed the zero-point sensor switch due to too much grease and the signal line was not in good contact.

Example 2: Dongyuan SOZ4L CNC milling machine appears to be out of circle after a period of use. When the machine fails, the x- and y-axis dynamic performance of the machine is tested and it is found that the y-axis dynamic parameters deviate greatly from the normal values. It is normal to start milling circle after stopping for a period of time, and the dynamic parameters are normal. Analysis believes that there may be three reasons.

1. In terms of machinery, the non-uniform load changes may be caused by thermal deformation, degumming of the plastic guide rail, partial damage of the ball screw, screw bearing or improper adjustment, etc., which leads to the instability of the feed system.

2. There may be a problem inside the servo motor.

3. Electrically, it may be due to changes in the parameters of a component in the servo amplifier that cause the dynamic characteristics of the system to change, leading to system instability, etc.

Taking into account the mechanical complexity of the equipment, only the electrical possibility can be ruled out. First, the servo amplifiers of the x and y axes are exchanged and then tested, and it is found that the fault still appears on the y axis. Then we can only proceed to the next step to check the mechanical part. The screw part was disassembled to check the plastic guide rails and the plastic fixed part. It was found that the inner end cover of the screw bearing was loose. The analysis indicated that there would be a certain degree of dynamic performance. Impact, but not too much. In order to confirm this conclusion, the equipment was tested, and the fault remained. Finally, the fault is locked in the servo motor. After the x-axis and y-axis motors are exchanged, the fault is transferred. It is determined that the y-axis motor is faulty. After the motor is replaced, the equipment is normal.

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