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Definition of a planetary gearbox:

A planetary gearbox (also known as an epicyclic gearbox) is a compact, high-torque transmission system characterized by a central "sun" gear, multiple rotating "planet" gears meshed with it, and an outer "ring" gear encircling the planets. The planets are held together and orbit the sun gear by a "planet carrier."

1. Standard / Commercial Grade

• Purpose: High torque and durability where positional accuracy is secondary.

• Key Metrics: High backlash (often 30–60 arc-minutes); transmission error is not a controlled specification.

• Manufacturing: Mass-produced components with wider tolerances; manual or semi-automated assembly.

• Applications: Conveyors, winches, agricultural machinery.

2. Precision / Industrial Grade

• Purpose: Controlled, repeatable motion for industrial automation.

• Key Metrics: Tightly controlled backlash (typically 5–15 arc-minutes); transmission error becomes a key measured metric.

• Manufacturing: Ground or hobbled gears; higher-grade bearings; controlled assembly processes.

• Applications: Industrial robots, CNC rotary tables, precision automation.

3. High-Precision / Instrument Grade

• Purpose: Ultimate performance for systems where motion fidelity is critical.

• Key Metrics: Extremely low or "zero" backlash (≤ 1–3 arc-minutes); transmission error measured in arc-seconds; very high specified torsional stiffness.

• Manufacturing: Precision-ground gears; highest-grade bearings; meticulous clean-room assembly; individual unit testing and certification.

• Applications: Surgical robots, aerospace pointing mechanisms, high-end metrology.

In essence, the precision grade of a planetary gearbox sets the performance ceiling for the mechanical system it drives, making it a fundamental determinant of accuracy, smoothness, and dynamic response.