Terminology glossary
Error Motion:
In an ideal scenario, the moving part of the positioner( the carrier) would have only one degree of freedom along the intended positioning direction. However, in reality, the motion of the carriages is not ideal. As a carriage moves, manufacturing imperfections within the stages, improper mounting, and surface quality issues can cause unwanted angular, translational and radial errors. Consequently, variations can occur in all six degrees of freedom during positioner movement. Key error terms include angular motions such as Pitch, Roll, and Yaw, as well as translational motions like Straightness. According to ASME B. 5.64, these error motions are categorized as follows:
• The first letter, E, indicates an error.
• The first subscript denotes the direction or orientation of the error.
• The second subscript represents the intended axis motion. In this context, rotational axes( A, B, C) are assigned based on the corresponding linear axes( X, Y, Z)( see Figure 4a and 4b).
Roll( E AX
)
Angular error motion of the YZ-axes of the moving coordinate system( csM) around the X-axis of the fixed coordinate system( csF) as the target position changes, causing side-to-side tilting. The rotational axis A corresponds to rotation around the X-axis( see Figure 5a).
Pitch( E BX
)
Angular error motion of the ZX-axes of csM around the Y-axis of csF as the target position changes, causing up and / or down tilting. The rotational axis B corresponds to rotation around the Y-axis( see Figure 5a).
Yaw( E CX
)
Angular error motion of the XY-axes of csM around the Z-axis of csF as the target position changes, causing rotational deviation left or right from the intended path. The rotational axis C corresponds to rotation around the Z-axis( see Figure 5a). lateral Z-straightness( E ZX
)
Translational error motion: deviation from a reference straight line of oM in the Z-axis direction of csF as the target position is varied, indicating out-of-vertical-plane motion( see Figure 5a). lateral Y-straightness( E YX
)
Translational error motion: deviation from a reference straight line of oM in the Y-axis direction of csF as the target position is varied, indicating out-of-horizontal-plane motion( see Figure 5a).
Note: In specific contexts within the motion industry, lateral straightness is categorized into two distinct parameters: " straightness " and " flatness ". According to ASME B. 5.64, straightness error motion is divided into two components: Y and Z. Here, " lateral Y-straightness " corresponds to straightness, while " lateral Z-straightness " refers to flatness. We adhere to these terminologies.
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