Glossary for Linear Motion
A Linear Motion glossary is a reference document that defines the core terminology used across linear motion components. In fact, a Glossary for Linear Motion helps users and engineers clearly understand these terms. These are the mechanical and electromechanical systems that move a load in a straight line. They do this rather than following a rotary path, which is why a Glossary for Linear Motion is essential for clarity. In summary, the Glossary for Linear Motion is a valuable tool for anyone working in this area. It typically covers drive types (ball screws, linear motors, rack and pinion, electric cylinders). Additionally, it includes guidance systems (linear guide rails, cross roller guides) and performance specs (repeatability, backlash, load rating, preload).
Category Term Definition
Linear Motion Fundamentals
Linear Motion The movement of an object along a straight-line path, as opposed to rotary motion, achieved in industrial automation through screws, rails, belts, or direct electromagnetic drive. Linear Axis A single-degree-of-freedom motion system that constrains and drives an object along one straight path, typically combining a guide, a drive method, and a carriage. Carriage The moving platform of a linear motion system that travels along the guide rail or screw and serves as the mounting surface for the payload. Stroke Length The total usable travel distance of a linear motion component between its fully retracted and fully extended positions. Positioning Accuracy The maximum deviation between a commanded target position and the actual position the carriage reaches, usually specified in microns or millimeters. Repeatability The ability of a linear motion system to return to the same position across repeated cycles, regardless of approach direction. Backlash The small amount of free play or lost motion in a drive mechanism, such as a screw or rack, that occurs when direction of travel reverses. Load Rating The maximum force a linear motion component can sustain, typically split into dynamic load rating (under motion) and static load rating (at rest). Preload An internal force applied during assembly of a screw, guide, or bearing to eliminate backlash and increase stiffness, at the cost of slightly higher friction.
Linear Module
Linear Module A pre-engineered, self-contained linear motion unit that integrates a guide rail, drive mechanism, carriage, and housing into a single ready-to-mount assembly. Belt-Driven Linear Module A linear module that uses a toothed belt and pulley system to move the carriage, favored for long strokes and high speed over high precision. Screw-Driven Linear Module A linear module that uses a ball screw or lead screw as the drive mechanism, favored for higher positioning accuracy than belt-driven designs. Module Housing The extruded aluminum profile that encloses and protects the guide and drive components of a linear module while providing the mounting structure. Multi-Axis Gantry A motion system built from two or more linear modules stacked or combined at right angles, commonly arranged as XY or XYZ configurations for pick-and-place or dispensing tasks. Cleanroom Linear Module A linear module designed with low-particle-generating materials and sealed construction to meet cleanroom contamination standards for semiconductor or medical use.
Rack & Pinion
Rack and Pinion A drive mechanism that converts rotary motor motion into linear motion using a circular gear, the pinion, that meshes with a straight, toothed bar, the rack. Rack The straight, linearly toothed bar in a rack-and-pinion system that the pinion gear travels along, available in standard lengths and joinable for long strokes. Pinion The small rotating gear in a rack-and-pinion system, mounted to a motor or gearbox shaft, that engages the rack teeth to produce linear travel. Helical Rack and Pinion A rack-and-pinion variant with angled gear teeth instead of straight teeth, providing smoother engagement, reduced noise, and higher load capacity than a straight-tooth design. Dual-Pinion Anti-Backlash Drive A rack-and-pinion configuration using two pinions preloaded against each other from opposite sides of the rack to cancel backlash and improve positioning accuracy. Module (Gear) The standardized size index of rack and pinion teeth, determining tooth pitch and how much torque and load the gear set can transmit.
Linear Motor
Linear Motor An electric motor that produces direct linear thrust without a rotary-to-linear conversion mechanism, by unrolling a conventional motor's stator and rotor into flat, opposing tracks. Forcer (Coil Unit) The moving component of a linear motor that contains the electromagnetic windings and travels along the magnet track, equivalent to the rotor in a rotary motor. Magnet Track The stationary component of a linear motor containing a row of permanent magnets that the forcer travels along to generate continuous thrust. Ironless Linear Motor A linear motor design that omits iron core material from the forcer, eliminating cogging force and reducing moving mass for very smooth, high-acceleration motion. Ironcore Linear Motor A linear motor design that uses an iron core in the forcer to concentrate magnetic flux, producing higher force density than an ironless design at the cost of some cogging. Cogging Force A force ripple in iron-core linear motors caused by magnetic attraction between the iron core and the magnet track, which can introduce small velocity variations if uncompensated. Linear Encoder A position feedback device that reads a scale mounted along the travel path, giving a linear motor or stage direct, high-resolution position data without mechanical backlash.
Electric Cylinder
Electric Cylinder A linear actuator that converts servo motor rotation into linear force and motion through an internal screw, replacing the function of a pneumatic or hydraulic cylinder with electric drive. Rod-Style Electric Cylinder An electric cylinder design where a non-rotating rod extends and retracts through the front of the housing, directly mimicking the form factor of a pneumatic cylinder. Rodless Electric Cylinder An electric cylinder design where the carriage rides externally along the cylinder body rather than extending on a rod, saving overall installed length for a given stroke. Thrust Tube The non-rotating outer tube of a rod-style electric cylinder that the internal screw drives forward and backward while resisting rotation. Anti-Rotation Mechanism A feature inside a rod-style electric cylinder that prevents the rod from spinning as the internal screw rotates, keeping the end-of-rod attachment fixed in orientation. Dynamic Load Capacity The maximum thrust force an electric cylinder can sustain while in motion without exceeding the rated life of its screw and bearing components. Side Load Force applied perpendicular to an electric cylinder's axis of travel, which accelerates wear on the rod seal, screw, and nut if it exceeds the rated limit.
Linear Guide Rail
Linear Guide Rail A precision-ground steel rail combined with a recirculating ball or roller block that constrains motion to a straight line while supporting radial and moment loads. Guide Block (Carriage) The bearing block that rides along a linear guide rail, containing recirculating balls or rollers that carry the load while allowing low-friction travel. Recirculating Ball Bearing The internal ball bearing path inside a linear guide block that continuously cycles balls between the load-bearing zone and a return channel, enabling unlimited travel length. Rail Accuracy Class A manufacturer-defined grade, such as normal, high, precision, or super precision, that specifies the dimensional and running-parallelism tolerance of a linear guide rail. Moment Load A rotational load applied to a guide block around the pitch, yaw, or roll axis, which a linear guide rail must resist in addition to straight-line forces. Wiper Seal A flexible scraper fitted to the ends of a guide block that removes dust and debris from the rail surface before it can enter the bearing raceway.
Linear Ball Screw
Ball Screw A mechanical linear actuator that converts rotary motion into linear motion using recirculating ball bearings riding in helical grooves on a screw shaft and a matching nut. Screw Lead The linear distance a ball screw nut travels per one full revolution of the screw shaft, which sets the relationship between motor speed and linear speed. Ball Nut The component that surrounds the ball screw shaft and contains recirculating ball bearings, converting the screw's rotation into the nut's linear travel. Ball Return System The internal channel or external tube in a ball screw nut that guides balls from the end of the load path back to the beginning, enabling continuous recirculation. Critical Speed The rotational speed at which a ball screw shaft begins to resonate and whip due to its own mass and unsupported length, setting an upper limit on safe operating speed. Column Strength The maximum compressive force a ball screw shaft can withstand along its axis before buckling, dependent on shaft diameter, unsupported length, and end-mounting method. Rolled Ball Screw A ball screw manufactured by rolling the helical groove into the shaft rather than grinding it, offering lower cost and accuracy suited to general industrial use. Ground Ball Screw A ball screw manufactured by precision grinding the helical groove into the shaft, offering higher accuracy and smoother operation than a rolled screw, at higher cost.
Cross Roller Guide Rail
Cross Roller Guide A precision linear guide that uses cylindrical rollers arranged in alternating perpendicular orientations between two hardened rails, providing very high rigidity and load capacity in a compact profile. Crossed Roller Bearing The internal bearing arrangement of a cross roller guide, where rollers alternate at 90 degrees to each other so the assembly carries loads from multiple directions equally well. V-Groove Rail The V-shaped track machined into a cross roller guide's rail surfaces, against which the cylindrical rollers ride to maintain alignment under load. High Rigidity Guide A descriptive term for guide systems, such as cross roller guides, engineered to minimize elastic deflection under load, critical for precision machining and metrology equipment. Retainer (Roller Cage) A component within a cross roller guide that maintains even spacing between individual rollers, preventing roller-to-roller contact and uneven wear.
Drive & Transmission
Servo Motor An electric motor paired with a position or speed feedback device, used to precisely control motion in linear modules, electric cylinders, and rack-and-pinion systems. Stepper Motor An electric motor that moves in discrete angular increments per electrical pulse, often used in lower-cost or lower-speed linear motion applications without closed-loop feedback. Coupling A mechanical component that connects a motor shaft to a screw, rack pinion, or other drive element while accommodating slight misalignment between the two. Gearbox (Reducer) A mechanical assembly that reduces motor speed and increases torque before it reaches a drive mechanism such as a ball screw or rack-and-pinion pinion. Timing Belt A toothed, reinforced belt used in belt-driven linear modules to transmit motor rotation to the carriage without slipping.
Performance & Specification Terms
Travel Speed The maximum linear velocity a motion component can sustain along its stroke, dependent on the drive method, motor power, and critical speed limits. Acceleration Rating The maximum rate of speed change a linear motion system can achieve, limited by motor torque, moving mass, and mechanical stiffness. Service Life (L10) The calculated travel distance or cycle count at which 90 percent of a population of identical linear components, such as ball screws or guide rails, are expected to remain free of fatigue failure. IP Rating An international standard, such as IP54 or IP65, describing how well a linear motion component resists dust ingress and water exposure. Straightness and Parallelism Geometric tolerances describing how closely a guide rail's travel path holds to an ideal straight line and how closely two parallel rails align with each other. You are welcome to visit our other social media or video gallery as follows. For more information, our Glossary for Linear Motion is available on our website. In addition, the Glossary for Linear Motion can answer many questions about terminology. Youtube: https://www.youtube.com/@tallmanrobotics Tiktok: https://www.tiktok.com/@tallmanrobotics Facebook: https://www.facebook.com/tallmanroboticslimited Linkedin: https://www.linkedin.com/in/tallman-roboticsAs a final point, a comprehensive Glossary for Linear Motion supports both beginners and experienced engineers in the field.