Fault Analysis of Software and Hardware of cnc pipe bending machine Servo Motor

Servo system is the link between numerical control device and cnc pipe bending machine host. It is used to receive the feeding pulse or the feeding displacement information sent by the interpolator of the numerical control device. After a certain signal conversion and voltage power amplification, the servo motor drivers the transmission mechanism. Finally, it is converted into linear displacement or rotary displacement of the machine tool workbench relative to the mold.

cnc pipe bending machine

What are the common faults of the cnc pipe bending machine servo motor? How to eliminate these faults?

In order to improve the performance of the cnc steel pipe bending machine, high requirements are put forward for the servo system of the pipe bender. Due to the different processing tasks completed by various numerical control machine tools, the requirements for the feed servo system are also different. The following is some common faults of the servo system:

servo system

1、 The overrun

When the soft limit set by the software or the hard limit set by the limit switch is exceeded by the feed motion will trigger the overrun alarm. The alarm will be displayed on the CRT. The worker can remove the fault according to the instructions of the numerical control system. And the alarm can be released.

2、 The overload

When the load of feed motion is too large, the machine moves forward and backward frequently or the drive chain has poor lubrication; the overload alarm will be triggered. Generally, the CRT can display the alarm information of servo motor overload, overheating or overcurrent. And on the feed drive unit in the strong current cabinet, the indicator light or the digital tube can also point out that the drive unit is overload, overcurrent and other information.

axis cnc pipe bending machine


Movement during feeding:

  • The speed measurement signal is unstable. For example, speed measuring device fault, speed measuring feedback signal interference etc.
  • The speed control signal is unstable or disturbed
  • The wire terminal is poor contact such as loose screws etc.

When the movement occurs at the reversing moment of positive and reverse motion, it is generally caused by the reverse clearance of the feed drive chain or the lager gain of the servo system.

4、 crawling

The machine crawling occurs when the acceleration section is started or the feed speed is low, generally due to the lubrication condition of feed drive chain is poor, the gain of the servo system is low, the applied load is too large or other factors. And we should pay special attention to the coupling used for the connection of servo motor and ball screw. The loose connection may cause defects or defects in the coupling itself, such as cracks in the coupling. All this can cause the rotation of the ball screw and the rotation of the servo motor to be out of synchronization. And this can make the feed action to be fast and slow, resulting in crawling.

5、The machine tool vibrates

The vibration may occur when cnc hydraulic pipe bending machine is running at high speed, and the overcurrent alarm will also appear. Generally speaking, the vibration of machine tools is a speed problem, so we should look for the speed link. But the whole adjustment process of the machine speed is completed by the speed regulator. This means that you should look for the speed regulator for any problems related with speed. According to this argument, when you are faced with vibration problems, you should check the speed regulator. When looking for faults, you should mainly look for the given signal, feedback signal and speed regulator itself.

cnc hydraulic pipe bending machine

6、The servo motor does not rotate

In addition to the speed control signal, the CNC system to the feed drive unit also has the enabling control signal, which is generally the DC 24V relay coil voltage. If the servo motor does not rotate, you can use these methods to diagnose:

  • Check whether the NC system has speed control signal output;
  • Check whether the enabling signal is on. Observe the I/O status through CRT and analyze the PLC ladder diagram (or flow chart) of the machine tool to determine the starting conditions of the feed shaft. For example, check whether the lubrication and cooling degree meet the starting conditions.
  • If the servo motor is equipped with electromagnetic brake, check whether the electromagnetic brake is released.
  • Feed drive unit fault;
  • Servo motor fault

7、The position error

When the servo axis movement exceeds the allowable error range of position, the CNC system will generate an alarm. This position error includes following error, contour error and positioning error and so on. There are some reasons:

  • The error range set by the system is too small
  • The servo system gain is set improperly.
  • The position detection device is contaminated
  • The accumulated error of feed drive chain is too large
  • The balancing device (such as balance hydraulic cylinder) is unstable when the headstock moves vertically.


The position error may occur when the command value is zero, the coordinate axis still moves. It can be eliminated by error compensation and zero-speed adjustment of the drive unit.

9、The clearance and looseness of the mechanical transmission parts

In the feed transmission chain of the cnc steel pipe bending machine, the transmission is often damaged by the clearance between keyway and key of drive element. So, in addition to careful selection of key structure in design, the processing and assembly should also be strictly checked. When installing the ball screw, check the preload of the bearing. Because of the clearance is also another reason for obvious transmission clearance. So, you do this can avoid the axial movement of the ball screw.

We have twenty years experience in production of NC and CNC pipe bending machine, and we have rich working experience of metal forming in many industries before(such as automobile, motorcycle, ship, aircraft, building, furniture, etc.). If you want to know more about pipe bending machine cnc, you can look for our blog or contact with cnc pipe bending machine manufacturer.

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