When the equipment manufacturer is debugging or using the equipment, the problem of deviation often occurs in the process of stepping or servo motion control. The deviation may be caused by improper mechanical assembly, mismatching of control system and driver signal, electromagnetic interference in equipment, mutual interference of equipment in workshop or improper ground wire treatment during equipment installation.
一、 When irregular deviation occurs:
1. Phenomenon description: the deviation occurs irregularly during operation, and the deviation is not clear
Possible cause 1: interference causes motor offset
Analysis reasons: most of the aperiodic deflection is caused by interference, and a small part is caused by the narrow pulse from the motion control card or the mechanical structure loosening.
Solution: if the interference occurs frequently, the oscilloscope can be used to monitor the pulse frequency to determine the time of the interference, and then determine the interference source. Removing or keeping the pulse signal away from the interference source can solve part of the interference. If the interference occurs occasionally, or it is difficult to determine the location of the interference source or the electrical cabinet is fixed and difficult to move, the following measures can be taken to solve the problem:
A ：Ground the driver
B ：Replace pulse line with twisted pair shielded wire
C ：pulse positive and negative ends parallel 103 ceramic capacitor filter (pulse frequency less than 54khz)
D ：pulse signal increases magnetic ring
Add a filter to the front end of e driver and controller power supply
Common interference sources include frequency converter, solenoid valve, high voltage wire, transformer, coil relay, etc.
When planning the electrical cabinet, the signal line should be avoided to be close to these interference sources, and the signal line and high-voltage power supply line should be wired in different trunks.
Possible cause 2: the pulse train appears narrow pulse
Cause analysis: the duty cycle of the pulse train sent by the customer motion control card is small or too large, resulting in a narrow pulse, which can not be recognized by the driver, resulting in offset.
Possible cause 3: loose mechanical structure
Cause analysis: coupling, synchronous wheel, reducer and other connectors fixed with jacking screw or clamped by screws may be loose during running for a period of time under the condition of rapid impact, resulting in deviation. If the synchronous wheel is fixed by the key and keyway, the clearance between the key and keyway should be paid attention to, and the fit clearance between the key and keyway should be paid attention to in the rack and pinion structure.
Solution: the key parts and structural screws with large force must be spring pads, and screws or jackscrews should be coated with screw glue. The motor shaft and coupling shall be connected with keyway as far as possible.
Possible cause 4: filter capacitance is too large
Analysis reasons: the filter capacitance is too large. The cut-off frequency of common RC filter is 1 / 2 π RC. The larger the capacitance, the smaller the cut-off frequency. The resistance at the pulse end of the general driver is 270 ohm, and the cut-off frequency of the RC filter circuit composed of 103 ceramic capacitors is 54 kHz. If the frequency is higher than this, some effective signals can not be detected by the driver due to excessive amplitude attenuation, and finally lead to offset.
Solution: when adding filter capacitor, it is necessary to calculate pulse frequency and ensure that the maximum passing pulse frequency meets the requirements.
Possible reason 5: the maximum pulse frequency of PLC or motion control card is not high enough
Cause analysis: the maximum allowable pulse frequency of PLC is 100kHz, and the motion control card varies greatly according to its pulse chip, especially the motion control card developed by ordinary single chip microcomputer may cause offset due to insufficient pulse frequency.
Solution: if the maximum pulse frequency of the upper computer is limited, in order to ensure the speed, the driver subdivision can be appropriately reduced to ensure the motor rotation.
二、 When regular deviation occurs:
1. Description of the phenomenon: the more forward you move, the more (or less) you deviate
Possible reason 1: the pulse equivalent is wrong
Analysis reason: no matter the synchronous wheel structure or the gear rack structure, there are machining accuracy errors. The motion control card (PLC) does not set the accurate pulse equivalent. For example, if the motor of the last batch of synchronous wheels rotates one circle and the equipment moves forward by 10.1 mm when the motor of the last batch of synchronous wheels rotates a circle, the motor of this batch of synchronous wheels will travel 1% more distance than the previous equipment each time.
Solution: before leaving the machine, draw a square as large as possible with the machine, then measure the actual size with a ruler, compare the proportion between the actual size and the size set by the control card, and then add it to the control card operation. After repeated three times, a more accurate value will be obtained.
Possible cause 2: the trigger of pulse instruction conflicts with the level conversion sequence of direction command
Cause analysis: the driver requires the upper computer to send out pulse instructions along and in the direction of command level conversion has certain timing requirements. When some PLC or motion control cards do not meet the requirements (or their own rules do not meet the requirements of the driver), the pulse and direction sequence can not meet the requirements and deviate from the position.
Solution: the software engineer of control card (PLC) will advance the direction signal. Or the driver Application Technician changes the way the pulses are countede
2. Phenomenon description: during the movement, the motor vibrates at a fixed point. After passing this point, it can run normally, but it can travel a short distance
Possible cause: mechanical assembly problem
Analysis reason: the resistance of mechanical structure at a certain point is large. Due to the parallelism, perpendicularity or unreasonable design of mechanical installation, the resistance of the equipment at a certain point is large. The torque variation law of stepper motor is that the faster the speed is, the smaller the torque is. It is easy to get stuck in the high-speed section, but it can walk through when the speed drops down.
Solutions:
1. Check whether the mechanical structure is jammed, whether the friction resistance is large or the slide rails are not parallel.
2. The torque of stepper motor is not enough. Due to the requirement of increasing the speed or increasing the load of the terminal customers, the torque of the motor which can meet the requirements is not enough at high speed, which leads to the phenomenon of locked rotor in high speed section. The solution is to set a larger output current through the driver, or increase the supply voltage within the allowable voltage range of the driver, or replace the motor with greater torque.
3. Phenomenon description: motor reciprocating motion did not go to the position and offset fixed
Possible cause: belt clearance
Cause analysis: there is a reverse clearance between the belt and the synchronous wheel, and there will be a certain amount of idle travel when going back.
Solution: if the motion control card has belt reverse clearance compensation function, it can be used; or tighten the belt.
4. Phenomenon description: the cutting and drawing tracks do not coincide
Possible reason 1: too much inertia
Analysis reasons: the inkjet process of the flat cutting plotter is controlled by grating, scanning motion, and interpolation motion is taken during cutting. The reason is that the inertia of x-axis trolley of similar equipment is small and located by grating, and the position of inkjet is accurate. However, the inertia of y-axis gantry structure is large, and the motor response is poor. The track partial deviation is caused by poor Y-axis tracking during interpolation movement.
Solution: increase the y-axis deceleration ratio, use Notch function to improve the rigidity of servo driver to solve the problem.
Possible reason 2: the coincidence degree of knife and nozzle is not adjusted well
Analysis reason: because the cutter and nozzle are installed on the x-axis trolley, but there is a coordinate difference between them. The upper computer software of the cutting and drawing machine can adjust the coordinate difference to make the path of the knife and the nozzle coincide. If not, the cutting and drawing track will be separated as a whole.
Solution: modify the position compensation parameters of knife and nozzle.
5. Description of the phenomenon: drawing a circle causes ellipse
Possible cause: the two axes of XY axis platform are not vertical
Analysis reasons: XY axis structure, graphics offset, such as drawing a circle into an ellipse, square offset into a parallelogram. This problem can be caused when the x-axis and Y-axis of the gantry structure are not vertical.
Solution: the problem can be solved by adjusting the perpendicularity of x-axis and Y-axis of gantry.
Post time: Aug-17-2020