#lostmotion

For your reference, here is a quick glossary dedicated to rotary motion concepts. To clarify, this section acts as your reference Glossary regarding Rotary Motion. In fact, when searching for rotary motion information, this is the glossary you need. To help you even more, keep reading this glossary to discover essential motion terms. You will also find the rotary concepts covered in our Glossary for Rotary Motion. For added clarity, this resource acts as a comprehensive glossary for rotary motion topics. To summarize, this page provides a complete glossary for all topics and concepts related to rotary motion. Glossary for Rotary Motion defines the core terminology behind components that rotate a load around a fixed axis, rather than moving it in a straight line. It covers indexing and positioning devices (hollow rotary tables, cam indexers). Further, it explains speed-and-torque components (planetary gear reducers, RV reducers) and connecting hardware (couplings). It also details performance specs like backlash, repeatability, and torsional stiffness.

Category Term Definition

Rotary Motion Fundamentals

Rotary Motion The movement of an object around a fixed axis, as opposed to linear motion, used in automation to index, position, or continuously rotate a load. Rotary Axis A single-degree-of-freedom motion system that rotates a load around one fixed centerline, typically built from a bearing, drive mechanism, and output platform. Indexing The motion of stepping a rotary table or platform through a series of fixed angular positions, pausing at each station for a process step. Positioning Accuracy The maximum angular deviation between a commanded target position and the actual position a rotary system reaches, usually specified in arc-seconds or arc-minutes. Repeatability The ability of a rotary system to return to the same angular position across repeated cycles, regardless of approach direction. Backlash The small amount of angular free play in a rotary drive train, such as a gear mesh or reducer, that appears when rotation direction reverses. Torque The rotational force a rotary motion component transmits or withstands, the rotary equivalent of linear force, usually specified in Newton-meters. Moment Load A tilting or overturning load applied off-axis to a rotary platform, which the supporting bearing must resist in addition to pure torque. Lost Motion The combined angular deviation from backlash and torsional deflection in a rotary drive system, often used interchangeably with backlash in reducer specifications.

Hollow Rotary Table

Hollow Rotary Table A rotary positioning platform built around a central through-bore, allowing cables, pneumatic lines, optical paths, or shafts to pass through the axis of rotation. Through-Bore The open central channel running through a hollow rotary table or hollow shaft actuator, sized to route wiring, fiber optics, or fluid lines without external routing. Direct-Drive Rotary Table A hollow rotary table configuration where a torque motor drives the output platform directly, without a gear reducer, eliminating backlash and maximizing dynamic response. Cross Roller Bearing (Rotary) The internal bearing type commonly used in hollow rotary tables, providing high moment load capacity and rotational accuracy within a thin, compact ring profile. Rotary Encoder A position feedback device mounted on a hollow rotary table that reports angular position to the controller, enabling closed-loop positioning accuracy. Slip Ring An electromechanical component sometimes routed through a hollow rotary table's bore, allowing continuous electrical signal or power transfer across an unlimited rotation range.

Cam Indexer

Cam Indexer A mechanical indexing device that converts continuous input rotation into intermittent output motion, advancing a turret or table through fixed angular steps using a precision-ground cam. Globoid Cam The barrel-shaped, precision-machined cam at the core of a cam indexer, whose contoured groove drives the output turret through a smooth accelerate-dwell-decelerate motion profile. Dwell Time The portion of a cam indexer's cycle during which the output turret remains stationary, allowing a process step such as assembly or inspection to occur at each station. Index Time The portion of a cam indexer's cycle during which the output turret is actively rotating between stations, distinct from the dwell period. Turret The rotating output platform of a cam indexer or rotary table, fitted with tooling or fixtures at each station to carry parts through a sequence of operations. Station Count The number of equally spaced stopping positions a cam indexer's output turret completes per full revolution, such as 4-station, 6-station, or 8-station configurations. DT-Type Indexer A cam indexer product family characterized by a heavy-duty turret and globoid cam design, suited to medium-to-heavy payloads in general assembly automation. DA Ultra-Thin Indexer A cam indexer product family built with a reduced-height housing profile, suited to applications where vertical installation space is limited.

Planetary Gear Reducer

Planetary Gear Reducer A speed-reduction and torque-multiplication device using a central sun gear, surrounding planet gears, and an outer ring gear, valued for compact size and high torque density. Sun Gear The central gear of a planetary gear set, typically connected to the input shaft, around which the planet gears orbit. Planet Gear One of several gears in a planetary reducer that meshes simultaneously with the sun gear and the ring gear, orbiting the sun gear while also spinning on its own axis. Ring Gear The outer, internally toothed gear of a planetary gear set that meshes with the planet gears, typically held stationary in single-output reducer configurations. Planet Carrier The structural component that holds the planet gears in position and transmits their combined orbital motion to the output shaft. Reduction Ratio The ratio between input shaft speed and output shaft speed in a gear reducer, determining how much input torque is multiplied at the output. Gear Stage A single set of sun, planet, and ring gears within a planetary reducer; multiple stages are combined in series to achieve higher reduction ratios. Angular Transmission Accuracy A planetary reducer specification describing the maximum angular error between commanded and actual output rotation, critical for precision servo positioning applications.

RV Reducer

RV Reducer A two-stage speed reducer combining a planetary gear input stage with a cycloidal disc output stage, delivering high reduction ratios, high torsional stiffness, and very low backlash. Cycloidal Disc The curved, lobed disc at the core of an RV reducer's second stage, which rolls against fixed pins to convert eccentric input motion into precise, low-backlash output rotation. Eccentric Shaft The input shaft of an RV reducer's cycloidal stage, offset from the centerline so its rotation drives the cycloidal disc in an orbiting motion. Cycloid Pin One of the fixed pins surrounding an RV reducer's cycloidal disc, against which the disc's lobed profile rolls to generate output rotation. Torsional Stiffness A reducer's resistance to angular deflection under load, a key performance metric for RV reducers used in robot joints where positioning rigidity affects overall arm accuracy. SC Washdown RV Reducer An RV reducer variant built with sealed housings and corrosion-resistant materials, rated for sanitary washdown environments such as food and pharmaceutical processing. Robot Joint Reducer A common application category for RV reducers, where the component's high stiffness and near-zero backlash support precise multi-axis articulated robot motion.

Couplings

Coupling A mechanical component that connects two rotating shafts, such as a motor shaft and a reducer input, transmitting torque while accommodating some degree of misalignment. Rigid Coupling A coupling design that joins two shafts with no flexibility, requiring precise shaft alignment but offering maximum torsional stiffness and zero backlash. Flexible Coupling A coupling design that accommodates small amounts of angular, parallel, or axial shaft misalignment through a flexible element, reducing stress on connected bearings. Bellows Coupling A flexible coupling type using a thin-walled, corrugated metal tube to transmit torque while tolerating misalignment, known for high torsional stiffness and zero backlash. Diaphragm Coupling A flexible coupling type using one or more thin metal discs to transmit torque, offering high torque capacity and misalignment tolerance in a compact design. Jaw Coupling A flexible coupling type using interlocking hubs with an elastomer spider insert between them, providing vibration damping and moderate misalignment tolerance at low cost. Set Screw Coupling A simple shaft coupling that secures to each shaft using threaded set screws, suited to light-duty applications without the need for keyways. Clamping Coupling A coupling that secures to shafts by clamping force around a split hub, allowing easier installation and removal than a set screw design while maintaining strong torque transfer.

Drive & Motor Integration

Servo Motor An electric motor paired with a position or speed feedback device, commonly mounted to reducers, indexers, and rotary tables to provide precise rotary motion control. Torque Motor A direct-drive motor design optimized for high torque output at low speed, commonly used in direct-drive hollow rotary tables without a gear reducer. Output Flange The mounting interface on a reducer, indexer, or rotary table where the driven load attaches, typically machined with a bolt circle and pilot bore. Input Shaft Adapter A component that mates a specific servo motor's shaft and mounting flange to the input side of a reducer or indexer, since motor and reducer brands often use different standards. Cross Roller Output Bearing An integrated bearing at the output stage of a reducer or rotary table, using crossed rollers to support both radial load and moment load in a single compact element.

Performance &

Specification Terms