{"id":2422,"date":"2026-07-14T05:08:40","date_gmt":"2026-07-14T05:08:40","guid":{"rendered":"https:\/\/speed-reducer-gearbox.com\/linear-actuator-planetary-gearbox-force-and-precision-selection\/"},"modified":"2026-07-14T05:08:40","modified_gmt":"2026-07-14T05:08:40","slug":"linear-actuator-planetary-gearbox-force-and-precision-selection","status":"publish","type":"post","link":"https:\/\/speed-reducer-gearbox.com\/da\/linear-actuator-planetary-gearbox-force-and-precision-selection\/","title":{"rendered":"Linear Actuator Planetary Gearbox: Force and Precision Selection"},"content":{"rendered":"
\n

A planetary gearbox in a linear actuator converts the rotary output of a servo or stepper motor into linear force and displacement through a ball screw, lead screw, or rack-and-pinion stage. The gearbox sits at the centre of the actuator’s performance characteristics: it determines the force the actuator can exert (by multiplying motor torque), the speed the actuator achieves (by setting the ratio between motor speed and screw speed), and the positioning resolution (by controlling how much linear movement results from each motor encoder count). Specifying the planetary gearbox correctly is the single most important mechanical design decision in a high-performance linear actuator.<\/p>\n

\"Precision<\/p>\n

Force, Speed, and Ratio: The Fundamental Trade-off<\/h2>\n

The relationship between gearbox ratio and actuator performance is governed by two equations: actuator force = motor torque \u00d7 ratio \u00d7 2\u03c0 \u00f7 screw lead \u00d7 efficiency, and actuator speed = motor speed \u00d7 screw lead \u00f7 ratio. These equations immediately show the trade-off: increasing the ratio by 2\u00d7 doubles the maximum force but halves the maximum speed. For a given motor and screw, there is a ratio that maximises power output (force \u00d7 speed) \u2014 this occurs when the reflected load inertia equals the motor inertia, which for a screw system is when ratio = \u221a(screw_mass \/ motor_rotor_inertia \u00d7 screw_lead \/ (2\u03c0)).<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Application<\/th>\nRequired Force<\/th>\nRequired Speed<\/th>\nScrew Lead<\/th>\nMotor Torque<\/th>\nRequired Ratio<\/th>\n<\/tr>\n<\/thead>\n
Small automation gate<\/td>\n500 N<\/td>\n200 mm\/s<\/td>\n5 mm<\/td>\n0.5 N\u00b7m<\/td>\n1:3.2\u2192 1:3<\/td>\n<\/tr>\n
CNC Z-axis quill<\/td>\n5 000 N<\/td>\n50 mm\/s<\/td>\n5 mm<\/td>\n2.0 N\u00b7m<\/td>\n1:16\u2192 1:15<\/td>\n<\/tr>\n
Injection mould clamp<\/td>\n50 000 N<\/td>\n20 mm\/s<\/td>\n10 mm<\/td>\n5.0 N\u00b7m<\/td>\n1:64\u2192 1:60<\/td>\n<\/tr>\n
Aircraft landing gear<\/td>\n100 000 N<\/td>\n5 mm\/s<\/td>\n5 mm<\/td>\n10 N\u00b7m<\/td>\n1:100\u2192 1:100<\/td>\n<\/tr>\n
Stage lift (slow)<\/td>\n20 000 N<\/td>\n2 mm\/s<\/td>\n5 mm<\/td>\n8.0 N\u00b7m<\/td>\n1:38\u2192 1:40<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Required ratio = force \u00d7 lead \u00f7 (motor torque \u00d7 2\u03c0 \u00d7 efficiency). Efficiency assumed 0.90.<\/p>\n<\/div>\n

\"Planetary<\/p>\n

Ball Screw vs Lead Screw: Efficiency Implications<\/h2>\n

Ball screws achieve 90\u201395% linear conversion efficiency (rotary torque to linear force), while lead screws (ACME or trapezoidal thread) achieve only 30\u201350%. This difference matters for the planetary gearbox in two ways: first, the gearbox must be sized for the higher required input torque if a lead screw is used; second, the self-locking property of a lead screw (at low lead angles) means the actuator may not need a separate brake to hold position when power is removed \u2014 the lead screw itself holds. Ball screws are not self-locking, so a brake must be provided by the motor or gearbox if the actuator must hold under load without continuous motor current.<\/p>\n

Backlash and Repeatability in Precision Linear Actuators<\/h2>\n

The backlash budget for a linear actuator is shared between the gearbox (arc-minute backlash converted to linear by the screw pitch) and the ball screw or lead screw nut (linear backlash from nut wear). The AD047 right-angle planetary series<\/a> provides right-angle output in a compact format suited to actuators where the motor must be perpendicular to the screw axis \u2014 common in machine tool and automation designs where envelope width is constrained. The AF075 flange output series<\/a> provides inline high-ratio planetary reduction for actuators requiring high force in a direct coaxial configuration.<\/p>\n

Self-Locking in Planetary-Driven Actuators<\/h2>\n

A planetary gearbox does not self-lock \u2014 if the motor is de-energised, the load can back-drive the screw, through the gearbox, and spin the motor. This means a separate brake is required on any actuator that must hold position under load without continuous motor current. The brake may be mounted on the motor shaft (most compact) or on the gearbox input shaft (allows independent brake sizing). The brake spring force must be sufficient to hold the worst-case backdrive torque, which equals the maximum actuator force \u00d7 screw lead \u00f7 (2\u03c0 \u00d7 screw efficiency). For a 50 000 N clamp force with a 10 mm lead ball screw at 92% efficiency: motor brake torque = 50 000 \u00d7 0.01 \u00f7 (6.28 \u00d7 0.92) = 86.5 N\u00b7m \u2014 much higher than most motor brakes. A gearbox-mounted brake or a dedicated shaft-mounted brake between gearbox and screw is the practical solution.<\/p>\n

\"Linear<\/p>\n

Environmental Protection for Industrial Actuator Applications<\/h2>\n

Industrial linear actuators operate in environments ranging from cleanroom semiconductor fabs to outdoor construction equipment. The planetary gearbox sealing must match the operating environment. For indoor automation, IP54 is generally adequate. For outdoor, wash-down, or high-humidity applications, IP65\u2013IP67 is required. For food processing or pharmaceutical actuators where lubricant contamination is a food-safety concern, specify NSF H1 grease and Viton seals. The PGV planetary gearbox<\/a> series provides a reference for compact precision planetary drives used in automation actuators across a range of industrial environments.<\/p>\n

Frequently Asked Questions<\/h2>\n
\n
\n1. How do I calculate the required gearbox ratio for a linear actuator?+<\/span><\/summary>\n
Use: ratio = required_force \u00d7 screw_lead \u00f7 (motor_rated_torque \u00d7 2\u03c0 \u00d7 efficiency). This gives the minimum ratio for force. Then check that motor_speed \u00f7 ratio \u00d7 screw_lead gives adequate actuator speed. If not, increase motor speed or reduce ratio and accept lower force, or choose a higher-torque motor. Finally check inertia matching: reflected_inertia = load_mass \u00d7 (screw_lead \u00f7 (2\u03c0 \u00d7 ratio))\u00b2. This should be within 5:1 of motor rotor inertia for good dynamic performance.<\/div>\n<\/details>\n
\n2. Can I use a planetary gearbox with a lead screw on a vertical actuator without a brake?+<\/span><\/summary>\n
Depends on the lead screw efficiency. A trapezoidal thread lead screw at 5 mm lead and typical surface finish is usually self-locking \u2014 the screw efficiency is below 50% and the thread helix angle is below the friction angle. In this case, the actuator holds its position when power is removed without a separate brake. Verify the specific lead screw’s self-locking condition with the supplier \u2014 efficiency varies with thread geometry, lubrication, and load direction.<\/div>\n<\/details>\n
\n3. What is the maximum duty cycle for a planetary gearbox in a linear actuator?+<\/span><\/summary>\n
The duty cycle limit is set by thermal capacity \u2014 the gearbox generates heat proportional to power loss (input power \u00d7 (1 \u2212 efficiency)). Planetary gearboxes at 97% efficiency generate only 3% of input power as heat. For most compact servo planetary gearboxes in actuator applications (input power below 500 W), the housing area is sufficient for 100% duty cycle. At higher power levels, check the housing temperature after 30 minutes of continuous operation \u2014 if it exceeds 70\u00b0C, either reduce duty cycle or upsize the gearbox.<\/div>\n<\/details>\n
\n4. How does the gearbox ratio affect actuator positioning resolution?+<\/span><\/summary>\n
Resolution = screw_lead \u00f7 (encoder_ppr \u00d7 ratio \u00d7 interpolation_factor). Higher ratio improves resolution (finer positioning) but reduces speed. For a 2 500 ppr encoder with \u00d74 quadrature interpolation (10 000 counts\/revolution), a 5 mm pitch screw, and 1:10 ratio: resolution = 5 \u00f7 (10 000 \u00d7 10) = 0.00005 mm = 50 nm \u2014 sub-micrometre resolution from readily available components.<\/div>\n<\/details>\n
\n5. Can I use a hollow shaft planetary gearbox to pass the ball screw through the gearbox?+<\/span><\/summary>\n
Yes \u2014 the EPL double-shaft series and some AF\/AD variants with hollow bore allow the screw to pass through the gearbox centre, enabling a very compact inline actuator where the motor, gearbox, and screw are all coaxial. The gearbox output bore must be large enough for the screw diameter; verify this against the specific frame size bore range. This configuration is used extensively in compact servo actuators for machine tools and automation equipment.<\/div>\n<\/details>\n<\/div>\n
\n

Speak with a Planetary Drive Specialist<\/h3>\n

Share your torque requirement, ratio, and application environment \u2014 our team at Condell Park NSW returns a sized recommendation and stock check within one business day. No obligation.<\/p>\n

\n
\n
ADDRESS<\/div>\n

27 Harley Crescent
Condell Park NSW 2200<\/div>\n

\n
PHONE<\/div>\n

+61 2 9708 3322<\/p><\/div>\n

\n
EMAIL<\/div>\n

sales@speed-reducer-gearbox.com<\/p><\/div>\n<\/div>\n

Send Enquiry →<\/a><\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

A planetary gearbox in a linear actuator converts the rotary output of a servo or stepper motor into linear force and displacement through a ball screw, lead screw, or rack-and-pinion stage. The gearbox sits at the centre of the actuator’s performance characteristics: it determines the force the actuator can exert (by multiplying motor torque), the […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[2918],"tags":[],"class_list":["post-2422","post","type-post","status-publish","format-standard","hentry","category-industrial-robots-servo"],"_links":{"self":[{"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/posts\/2422","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/comments?post=2422"}],"version-history":[{"count":0,"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/posts\/2422\/revisions"}],"wp:attachment":[{"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/media?parent=2422"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/categories?post=2422"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/da\/wp-json\/wp\/v2\/tags?post=2422"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}