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Factors affecting the ultra-precision motion platform positioning precision analysis

Time:2016-08-03 10:04    Search keywords:Precision motion platform    writer:admin

A detection system positioning accuracy on moving platform

CNC equipment detection system usually consists of grating, encoders, sensors and other commonly used synchronous position detecting elements. The main element is to detect motion detection platform position movement mechanism and the detected value is fed back to the controller or associated servo motor.

Effect of the motion detection device platform targeting accuracy mainly in the following three aspects:

1, when the mounting position detection element coupled to appear loose when in use, this time a position signal detection elements will be abnormal, thus affecting the position control accuracy.

2, when the detection element by dust, oil pollution, will lead to the loss of the position signal detection, thus affecting the position control accuracy.

3, when a bad job stability sensing element itself, which detects data will be unstable, thus affecting the positioning accuracy.

Second, the impact of the servo system positioning precision motion platform

Control precision servo motion control system platform a huge impact in the servo control system platform precision motion control accuracy under the premise of the servo control system to influence the positioning accuracy of the motion platform mainly in terms of the parameter setting of the servo system [2] . Which mainly include the setting position loop gain, speed and ramp exchange gain and other parameters.

Position loop gain of the servo system mainly affect the following error of the drive motor, position loop gain can not be set too high, but also can not be set too low. If the position loop gain is set too high, make the machine vibration phenomenon occurs, if the position loop gain is set too low, the system will greatly reduce the ability to follow, thus affecting the positioning accuracy, and the position loop and velocity loop influence each other .

Speed loop gain of the servo system controls the operation of the main motor speed, reasonable speed loop gain may play a role in the elimination of the steady-state error. However, if the velocity loop gain is set too high, the machine will shock phenomenon; if the speed loop gain is set too low will make the motor creeping phenomenon. Thus affecting the accuracy of the positioning of the platform.

Deceleration curve setting servo motor is directly related to the motion control platform positioning accuracy, acceleration and deceleration curve setting reasonable assurance can improve the positioning accuracy of the moving platform moving platform under the premise of stable operation. If the deceleration is set too large, the machine positioning accuracy improved, but there will be the phenomenon of jitter motion platform start and stop. If the deceleration is set too low, relatively stable platform motion when transport stops, but positioning accuracy will decline.

Third, the transmission on the motion platform positioning accuracy.

Transmission system transmission accuracy directly affects the accuracy of the motion platform targeting system. When the drive mechanism using a ball screw mechanism, ball screw manufacturing precision, sensitivity and stability will affect the accuracy of the drive transmission mechanism [3]. Its effect on the motion platform positioning accuracy of the main problems:

1, when manufacturing precision ball screw is mainly the transmission system transmission accuracy will not meet the system requirements, thus affecting the positioning accuracy of the motion platform.

2, when the pressure of overburden pressure ball screw support shaft together bad, ball screw support shaft breakage, the drive motor and ball screw loose couplings, poor lubrication of ball screw, ball screw nut when the ball will be damaged directly affect the precision ball screw drive, thereby affecting the positioning accuracy of the motion platform.

When the linear motor drive mechanism, straightness guide will directly affect the accuracy of the transmission gear mechanism. Since the motion platform long run, will lead to system components CNC equipment to produce stress and deformation, which will change the motion platform rail geometric accuracy [4]. When the horizontal and parallelism rail deformed, will increase the motion platform rail and slider between the contact force and friction, which will inevitably lead to each mating surface on the moving platform and the rail between the sliding body appears not uniform clearance, resulting in movement of the platform straightness reduced, thereby reducing the positioning accuracy of the motion platform.


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