Positioning accuracy
Definition: refers to the degree of conformity between the actual arrival position and the theoretical target position when a moving part such as a machine tool worktable moves from one position to another target position. In simple terms, it is the accuracy of the machine tool coordinate axis moving to the specified position.
Repeatability positioning accuracy
Definition: refers to the degree of closeness between the actual positioning positions of moving parts such as machine tool worktables when they are repeatedly positioned to the same theoretical position. That is, the consistency of the positioning position when the machine tool repeatedly executes the same motion instruction under the same conditions.
Mechanical structure
Transmission system
Ball screw |
Its accuracy level, pitch error, installation accuracy, etc. directly affect the positioning accuracy and repeat positioning accuracy. High-precision ball screws have small pitch errors and can more accurately convert rotational motion into linear motion. If there are coaxiality errors, screw distortions, etc. during installation, the workbench will have position deviations during movement. |
Gear rack |
The processing accuracy, tooth shape error, meshing clearance, etc. of gears and racks have an impact on accuracy. If the clearance is too large, the workbench will have empty travel when moving forward and backward, affecting the positioning accuracy; the tooth shape error will make the movement unstable and reduce the repeat positioning accuracy. |
Guide rail system
Guide rail accuracy |
Precision indicators such as straightness and flatness determine the linearity and stability of the worktable movement. High-precision guide rails can enable the worktable to move accurately in the predetermined direction, reducing deviation and shaking. |
Guide rail lubrication |
Good lubrication can reduce the friction coefficient, reduce guide rail wear, and ensure the smoothness of the worktable movement. Poor lubrication will cause increased and uneven friction, causing jamming in the worktable movement, affecting positioning and repeat positioning accuracy. |
Worktable and support structure
Worktable rigidity |
If the worktable is not rigid enough, it will deform when bearing the workpiece and tool cutting force, causing changes in the processing position and affecting accuracy. |
Support structure stability |
The stability of support structures such as gantry and columns is crucial. Unstable support structures may vibrate and deform during machine tool operation, which in turn affects the relative position accuracy of the worktable and tool. |
Measurement system
Grating ruler
It is a commonly used position measurement element. Its accuracy, resolution and installation quality determine the accuracy of the measurement. High-precision grating rulers can accurately measure the actual position of the worktable and provide accurate feedback for the control system. If the grating ruler is not parallel to the direction of movement of the worktable or there is a gap during installation, measurement errors will occur.
Encoder
used to measure the rotation angle of the motor and then calculate the moving distance of the worktable. The accuracy and resolution of the encoder affect the accuracy of position feedback. If the encoder fails or the accuracy decreases, the control system will deviate from the judgment of the worktable position.
Control system
Servo system
Including servo motors and drivers, whose performance determines the motion control accuracy of the worktable. The response speed, speed range, torque output capacity, etc. of the servo system affect the positioning accuracy and repeatability of the worktable. A servo system with fast response speed, wide speed range and stable torque output can more accurately control the movement of the worktable.
Control system algorithm
Advanced control algorithms can accurately compensate and optimize machine tool motion. For example, through the error compensation algorithm, the error feedback from the measurement system can be compensated in real time; the interpolation algorithm can accurately calculate the tool path and improve the contour processing accuracy.
External environment
Temperature
Temperature changes will cause the various components of the machine tool to expand and contract, causing the geometric accuracy of the machine tool to change. Especially in high-precision machining, thermal deformation caused by temperature changes may significantly affect positioning accuracy and repeatability.
Vibration
Vibration from the machine tool itself, such as spindle rotation, table movement, etc., and vibration from the external environment, such as the operation of other nearby equipment and vehicle driving, will affect the relative position of the tool and the workpiece, and thus affect the accuracy.
