A servo system common faults form.
1.1 overtravel.
When the feed movement over the soft limit set by software or hardware determined by limit switch limit occurs when the overtravel alarm,cast bronze general alarm in the CRT display the contents of the instructions under the numerical control system, you can troubleshoot lift overtravel.
1.2 crawling.
Generally due to feed poor drive chain lubrication, bronze bushing servo system gain is too low and load is too large and other factors. In particular, note that the connection of the servo and ball screw coupling, due to loose connections or defects in the coupling itself, such as crack, causing the rotation of ball screw or servo rotation is not synchronized, so that the feed suddenly Fast suddenly slow,dry bushing resulting in creeping phenomenon.
1.3 traverse.
Ran in the feed when the phenomenon,plain bearing its possible causes are: 1, blocks access to undesirable, such as fastening screws loose; 2, the position control signal interference; 3,sleeve bushing speed signal instability, such as speed measurement equipment failure, speed feedback signal interference. If the traverse in the forward and backward movement of the moment,DU bushing is generally due to the feed or the drive chain backlash caused by the servo system gain is too large.
1.4 overload.
When the feed movement of the load is too large, parameter setting errors, frequent forward and backward movement and feed drive chain lubrication is poor, bushing the overload will lead to failure. The failures are generally machine can be self-diagnosed and displayed on the CRT display overload, overheating or over-current alarm. Meanwhile, in the feed servo module with LED or digital display driver overload,brass bushing over current and other alarm information.
1.5 Servo motor does not turn.
When the speed and position control signal is not output or enable signal (ie the servo enable signal, typically DC +24 V relay coil voltage) is not connected and feed drive unit failure will cause this failure. NC device should be measured at this time the command signal output terminal is normal, observed by CRT I / O status,Mould guide plate analysis of machine PLC ladder diagram (or flow chart) to determine the axis of the launch conditions, observation, such as lubrication, cooling, such as whether met. Case of fault, the feed drive unit with the exchange, can determine the corresponding unit is defective.
2 common faults of servo system for a typical case analysis.
(1) a processing center supporting FANUC7M system, feed processing and found that Y-axis vibration.
In order to determine the cause of the malfunction, machine operation will be placed manually, with the Y-axis manual pulse generator controlling feeding and found that there are Y-axis vibration. In this way, after moving through the longer period of time, Y axis speed unit OVC warning lights. Y axis servo drive proved occurred over current alarm, plasic bushing according to the above phenomenon, possible reasons are as follows:
① Motor overload; ② poor mechanical transmission system; ③ position loop gain is too high; ④ bad servo motor, and so on.
Maintenance through the exchange of law recognized a cause of the malfunction in the DC servo motor. Remove the Y-axis motor, checked that the two brushes in one of the springs had blown, causing the armature current imbalance, the motor output torque imbalance. In addition, the discovery also damage the motor bearings, and therefore cause - axis Vibration and over-current. Replace motor bearings and brushes, the machine back to normal.
(2) a processing center supporting FANUC6ME system. Shaft speed of instability in the movement. By the movement to stop the process, there was a substantial position in the stop of oscillation, sometimes can not complete the orientation, must be shut down before they can work again.
Analysis and treatment process: careful observation of the vibration machine and found that, X-axis oscillation frequency is low, and no abnormal sound. From the oscillation point of view, the Failure and closed-loop system parameter settings on, such as: system gain set too high, set the integral time constant is too large and so on.
Check the system parameters set in the drive gain, integration time potentiometer adjustment Dengjun in the right range, and the adjustment with exactly the same pre-fault, it can initially determine the axis of oscillation and parameters related with the regulation. In order to further verification, maintenance, adjustment in the value of the original records under the premise of the above parameters were re-regulation and testing, found fault still exists to prove the correctness of the judge.
In the above, based on the parameters and adjust the value back to the original settings, the servo motor and measuring system was checked. First clean up the tachometer generator and the servo motor commutator surface and check the tachometer generator with digital meter winding situation. Examination revealed that the servo motor and the motor rotor shaft speed connection between the existence of loose, bonded parts have been torn off; after re-connected, the boot test, fault disappears, the machine to resume normal work.
(3) a CNC milling machine, a body with FUNAC6M series of three-axis servo drive, boot, X-axis is working, but manually move the Z axis was found to a lesser extent, Z-axis to exercise, but continued to move the Z axis, system in the servo alarm. Analysis and processing: According to the symptoms, the actual work of checking machine and found that you can boot a small amount of movement Z axis, the temperature rose rapidly near the surface hot.
Analysis of the causes of these causes may be electrical machine control system failure or mechanical transmission bad. To determine the fault position, taking into account the semi-closed-loop structure of the machine, maintenance, and screw the servo when the first release the connection, and re-start experiments, found the same symptoms, it is confirmed that the alarm was caused by bad due to electrical control system.
With the machine Z axis servo brakes, power brakes measuring the input voltage normal, in the system, the drive is powered down, adding a separate power supply for the brake test, manual Z-axis rotation, found that the brake release, the manual shaft smooth, easy prove brakes to work well.
In order to further reduce the fault position, confirm the work of Z-axis servo, maintenance, use of different specifications of the X-axis in the machine side of the exchange experiment, the same fever that put on the phenomenon, and the work of the same symptoms, thereby excluding causes the servo itself.
In order to confirm the work of the drive, repair the drive side of the Z-axis drive swap experiments, about X-axis and Z axis servo drive link, Z-axis with the X-axis drive connection. The experiment found that fail to X axis, Z axis working back to normal.
According to the above experiment, pleased to confirm the following points:
① normal machine mechanical transmission, brakes work well;
② NC system working properly, because when the Z-axis drive, drive X-axis, the machine without warning;
③ Z axis servo works, because it in the machine side and the X-axis after the exchange, working properly;
④ Z-axis drive is working properly, because the drive through the X-axis exchange in the electric cabinet side, control, Z axis, the same failure.
The above judgments, can confirm that failure is due to Z-axis servo caused the cable connection.
Check the servo cable carefully and found that the machine at the factory armature wire connection error, that is, the drive L / M / N terminal is not connected to plug A / B / C connector correspondence, phase sequence errors, reconnect , the fault disappears, Z-axis to work properly.
(4) a processing center supporting FUNAC6ME systems, X-axis in the stationary machine working properly, no alarm; but in the X-axis movement, the emergence of vibration, accompanied by noise.
Analysis and treatment process: the machine in the X-axis when the machine is working still, without warning, the preliminary determination and drive CNC system trouble-free. When taking into account the X axis positioning is correct, therefore, to further determine the X position loop system working properly. Check the X-axis vibration, the observation that the vibration frequency and movement velocity, movement speed and high frequency vibration, the vibration frequency of slow motion is low, the preliminary view that the relevant failure and the speed loop. Caused by the above analysis of the possible reasons for failure are:
① tachogenerator bad; ② poor connection speed generator; ③ DC servo motor bad.
Maintenance, first check the X-axis servo motor tachometer generator connections and found no bad. Check the X-axis servo motor with built-in tachometer generator and found to have more toner commutator surface, using compressed air to clean up, the fault is not eliminated. Further use of digital multimeter, tachometer generator for measuring the resistance between the chip, the comparison found a pair of pole piece between the resistance of the pole piece than the other resistance between the much larger, indicating speed power Machine winding circuit that exist within the phenomenon. Replacement of the tachometer generator, the machine back to normal.