Technical notes and assessments. Every claim comes with its primary source.
How relative grating displacement becomes quadrature signals and a fine output step: connected transmission optics, grating overlap, sine/cosine phase and interpolation. Distinguish signal period, grating period, resolution and accuracy.
How a voice coil creates axial force, why a carriage still needs guidance, how coil/field overlap sets useful travel, and why sustained force causes heating.
A linear motor applies force directly to the carriage with no screw in between, eliminating lead error and backlash; positioning precision is then set by the optical linear encoder and rails, so it can reach sub-micron. A coreless mover avoids detent force and is smoothest; an iron-core mover gives more force but has cogging. The cost is higher price, mover mass affecting acceleration, and a magnetic field that needs shielding.
Motion platforms classify along two dimensions — drive principle (screw, linear motor, piezo, voice coil) and axis configuration (single-axis, multi-axis, hexapod). Selection is driven by four requirements: accuracy, travel, speed, and load. Separate the five spec quantities first, then match to a type.
A piezo stack directly moves a short-travel flexure stage; a walking motor accumulates longer travel. The figures distinguish low static power from mechanical self-locking, and show hysteresis, creep and actual-position feedback.
Connected serial XY stages and six-leg parallel geometry, with clear translation/rotation labels and geometric squareness/Abbe-error examples.
A screw-driven stage converts motor rotation to linear travel via a screw. Trapezoidal screws are friction-driven, have backlash, and are cheap; ball screws use ball recirculation, near-zero backlash, and higher precision. Steppers run open-loop from step angle; DC servos use encoder closed-loop, faster and tighter. Motor-axis angle, platform positioning, and workpiece tolerance are three different quantities.
From Oriental Motor steppers with ball screws to Newport DC servo and linear-motor stages: separate step angle, feedback position, minimum increment, and positioning accuracy. Converting ±0.05° to ±1.4 μm is only the motor-error component at a 10 mm lead; a 1 nm minimum increment is not a stage or workpiece tolerance.
Write the 1 μm acceptance definition clearly, then hold the error with carriage-position feedback, error compensation, thermal management, and work-point geometry. The XMS ±0.75 μm is the compensated axial guarantee, corresponding to a 1.5 μm total band; a material elongation or a scale reading is not directly the work-point positioning error.