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Case study and equipment offset solution collection

2019-09-21 16:22:17

Quick positioning deviation

One of the common problems faced by equipment debugging personnel is "deviation", which has different causes and countermeasures. Today we're going to summarize it by combining different applications. It is used to help the debugging staff of the equipment manufacturer to quickly locate the problem, take various appropriate measures to improve the anti-interference of the equipment, and ensure the normal operation.

01

Regular offset

Case 1: the equipment does reciprocating motion, and the further forward it is, the more (less) it is.


01. Wrong pulse equivalent


The motion control card (PLC) does not set the exact pulse equivalent


Reason analysis: whether the equipment transmission is synchronous wheel structure or rack and pinion structure, there are machining accuracy errors, but the motion control card (PLC) is not set accurate pulse equivalent.


For example, if the last batch of synchronous wheel motor rotates for one turn and the equipment moves forward by 10mm, the larger batch of synchronous wheel motor moves forward by 10.1mm for one turn, the machine will travel 1% more distance than the previous equipment each time.


Solution: draw a square as large as possible with the machine before the machine, then measure the actual size with ruler, compare the ratio between the actual size and the control card, and then add it to the control card operation, repeated three times will get a more accurate value.


02. Sequence conflict of instruction transformation


The trigger of the pulse instruction is in conflict with the level transformation sequence of the direction instruction


Reason analysis: the driver requires the sequence requirement of the instruction level transformation along and along the direction of the pulse instruction issued by the upper computer.


Some PLC or motion control card programming did not meet this requirement (or its own rules do not meet the requirements of the driver), resulting in pulse and direction timing can not meet the requirements and offset.


Solution: control card (PLC) software engineer will direction signal in advance. Or the driver application technician changes the pulse along the count mode.


Case 2: in the process of motion, the motor vibrates at the fixed point. After passing this point, the motor can run normally, but it can walk a short distance


01. Mechanical assembly problem


The mechanical structure has a high resistance at some point


Reason analysis: due to the parallelism, perpendicularity or unreasonable design of the mechanical installation, the resistance of the equipment is relatively large at a certain point. The torque variation rule of the 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 when the speed drops, it can pass.


Solution: check the mechanical structure of the cause of death, is the friction resistance is large or the slide is not parallel, and so on.


02. Insufficient torque of stepper motor


Torque is not enough, resulting in high-speed section block rotation


Reason analysis: the torque of stepper motor is not enough. Due to the requirements of the end customer to speed up or increase the load, the motor that could meet the requirements is not enough in the high-speed torque, resulting in the phenomenon of blocking rotation in the high-speed section.


Solution: the solution is to set a higher output current through the driver or increase the supply voltage within the allowable voltage range of the driver, or replace the motor with a higher torque.


Case 3: the motor does not move in place and the deviation is fixed


01. Belt gap


The reverse clearance results in an empty pass


Reason analysis: there is a reverse gap between the belt and the synchronous wheel, so there will be a certain amount of empty path.


Solution: if the motion control card has the function of belt reverse clearance compensation, it can be used. Or tighten the belt.


Case 4: the cutting track does not coincide


01. Too much inertia


Large inertia, poor motor response


Cause analysis: painted plate cutting machine ink jet process is controlled by a grating, scanning movement, cutting the interpolation motion, the trajectory is not coincidence, because similar devices X car smaller moment of inertia and the grating orientation, print position accurately, and the Y axis gantry structure inertia is larger, poor motor response and interpolation part Y follow sex is bad cause moving track offset.


Solution: increase Y-axis deceleration ratio and use notch function to improve servo actuator rigidity to solve the problem.


02. The coincidence degree is not adjusted properly


The contact degree between knife and nozzle is not well adjusted


Reason analysis: because the cutting and drawing machine knife and nozzle are mounted on the X-axis car, but there is a coordinate difference between them. The software of the cutting and drawing machine can adjust this coordinate difference to make the track of the knife and nozzle coincide. If not properly adjusted, the cutting and drawing track will be separated as a whole.


Solution: modify the position compensation parameters of knife and nozzle.


Case 5: draw an ellipse


01.XY axis platform two axes are not perpendicular


Large inertia, poor motor response


Reason analysis: when the X axis and Y axis of the gantry structure are not perpendicular, the figure deviation will be caused, such as drawing a circle into an ellipse, square deviation into a parallelogram.


Solution: the problem can be solved by adjusting the perpendicularity of X axis and Y axis of gantry.






Let's look at another situation


02


Irregular deviation


Case 1: deviation occurs irregularly during operation, which is accidental and uncertain


01. Deviation of motor caused by interference


Pulse signal interference source pulse


Cause analysis: aperiodic offset is mainly caused by interference, and a small part is caused by narrow pulse emitted by the motion control card or loose mechanical structure.


Solution:


1. If the interference occurs frequently, the oscilloscope can be used to monitor the pulse frequency to determine the time when the interference occurs and then determine the interference source, and remove or keep the pulse signal away from the interference source to solve part of the interference.


2. If the interference occurs accidentally, or it is difficult to determine the position of the interference source or the electrical cabinet is fixed and difficult to move, the following measures can be considered to solve the problem:


(1) driver grounding,


(2) pulse line replacement double stranded shielding wire,


(3) parallel 103 ceramic capacitor filter (pulse frequency less than 54kHz),


(4) pulse signal set magnetic ring,


(5) driver and controller power front increase filter.


Note: common interference sources include transformers, coil relays, frequency converters, solenoid valves, high-voltage wires, etc. When planning electrical cabinets, signal lines should not be near these interference sources. Signal lines and high-voltage power supply lines should be arranged in different slots.


02. Narrow pulse appears in pulse train


Narrow pulse, driver unrecognized


Problem analysis: the pulse train sent by the customer motion control card has a relatively small or too large duty cycle, resulting in a narrow pulse, which cannot be recognized by the driver, resulting in deviation.


Solution: find the reason of this problem in the controller, whether it is the pulse interface problem or the software algorithm problem.


03. Loose position of mechanical structure


Loose connecting parts cause clearance


Problem analysis: connecting parts such as shaft coupling, synchronous wheel and reducer fixed with the top wire or clamped with screws may become loose during a period of operation in a rapid impact situation, resulting in deviation. With the keys and keyways with fixed synchronous wheel, pay attention to whether there is a gap between the keys and keyways, the rack and pinion structure pay attention to the gap between the two.


Solution: the key part, the stress of the structure of the screw must use elastic pad, and the screw or the top wire should be coated with screw glue. Motor shaft and coupling as far as possible with a keyway connection.




04. Filter capacitance is too large




The valid signal cannot be detected by the driver correctly


Problem analysis: filter capacitance is too large, common RC filter cutoff frequency is 1/2 PI RC, capacitance, the smaller the cut-off frequency, the greater the general drive pulse resistance of 270 ohms, RC filter circuit, composed of 103 ceramic capacitor cutoff frequency is 54 KHZ, frequency higher than this will lead to some effective for large amplitude attenuation signal cannot be detected correctly drive, eventually led to the deviation.


Solution: when the filter capacitor needs to calculate the pulse frequency, must ensure the maximum pulse frequency to meet the requirements.


05.PLC or motion control card problem


The maximum pulse frequency is not high enough


Reason analysis: generally PLC allows the output of the maximum pulse frequency of 100kHz, the motion control card according to its pulse chip is not the same difference, especially the common SCM development of the motion control card may cause deviation because the pulse frequency is not high enough.


Solution: if the upper computer maximum pulse frequency is limited, in order to ensure the speed, can appropriately reduce the drive subdivision, in order to ensure the motor speed.


In THE END


There are many cases when the equipment may not work properly. I hope our summary can help you.




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