{"id":3497,"date":"2025-08-27T19:57:38","date_gmt":"2025-08-27T11:57:38","guid":{"rendered":"https:\/\/taichungbro.com\/?p=3497"},"modified":"2025-08-27T19:57:40","modified_gmt":"2025-08-27T11:57:40","slug":"motor","status":"publish","type":"post","link":"https:\/\/www.taichungbro.com\/en\/2025\/08\/27\/motor\/","title":{"rendered":"Linear Motors vs. Servo Motors \u2013 5 Key Selection Guides"},"content":{"rendered":"<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<div class=\"wp-block-rank-math-toc-block\" id=\"rank-math-toc\"><h2>Table of Content<\/h2><nav><ul><li class=\"\"><a href=\"#\u5f9e\u89e3\u6790\u5ea6\u3001\u91cd\u8907\u7cbe\u5ea6\u5230\u7d55\u5c0d\u5b9a\u4f4d\u7cbe\u5ea6\">From resolution and repeatability to absolute positioning accuracy<\/a><\/li><li class=\"\"><a href=\"#\u7cbe\u5ea6\u8207\u6027\u80fd\u6bd4\u8f03\">Accuracy and performance comparison<\/a><\/li><li class=\"\"><a href=\"#\u9078\u578b\u6d41\u7a0b\u8207\u67e5\u8868\u8a08\u7b97\">Selection process and table lookup calculation<\/a><ul><li class=\"\"><a href=\"#step-1-\uff5c\u7cbe\u5ea6\u9700\u6c42\u62c6\u89e3\">Step 1 | Breaking down accuracy requirements<\/a><\/li><li class=\"\"><a href=\"#step-2-\uff5c\u52d5\u614b\u8207\u525b\u6027\u9700\u6c42\">Step 2 | Dynamic and Rigid Demands<\/a><\/li><li class=\"\"><a href=\"#step-3-\uff5c\u89e3\u6790\u5ea6\u8207\u7de8\u78bc\u5668\u63db\u7b97\">Step 3 | Resolution and Encoder Conversion<\/a><\/li><li class=\"\"><a href=\"#step-4-\uff5c\u8aa4\u5dee\u9810\u7b97\">Step 4 | Error Budgeting<\/a><\/li><\/ul><\/li><li class=\"\"><a href=\"#\u5982\u4f55\u8abf\u6821\u8207\u91cf\u6e2c\">How to calibrate and measure<\/a><ul><li class=\"\"><a href=\"#\u63a7\u5236\u8abf\u6821\">Control Adjustment<\/a><\/li><li class=\"\"><a href=\"#\u6a5f\u69cb-\u74b0\u5883\">Organization\/Environment<\/a><\/li><li class=\"\"><a href=\"#\u91cf\u6e2c\u9a57\u8b49\">Measurement and verification<\/a><\/li><\/ul><\/li><li class=\"\"><a href=\"#\u4ec0\u9ebc\u60c5\u6cc1\u9078\u8ab0\uff1f\u5de5\u7a0b\u5e2b\u7684\u6c7a\u7b56\u6e05\u55ae\">When to Choose Whom? An Engineer&#039;s Decision Checklist<\/a><\/li><\/ul><\/nav><\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<p class=\"wp-block-paragraph\">In industrial automation, &quot;positioning accuracy&quot; often determines whether equipment can accept orders: from bonding and dispensing to laser processing and optical inspection, errors range from tens of micrometers to units of micrometers and even nanometers. When designing linear axes, many engineers hesitate between direct-drive linear motors and servo motors paired with ball screws or belts. Which is more accurate? The answer depends on whether you prioritize resolution, repeatability, absolute positioning accuracy, dynamic tracking, or cost and maintenance. From an engineering practice perspective, we will break down the accuracy components and common error sources of both, providing design parameters and a selection calculation example to help you grasp accuracy and budget from the early stages of a project.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u5f9e\u89e3\u6790\u5ea6\u3001\u91cd\u8907\u7cbe\u5ea6\u5230\u7d55\u5c0d\u5b9a\u4f4d\u7cbe\u5ea6\">From resolution and repeatability to absolute positioning accuracy<\/h2>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Resolution: The smallest position increment that the system can distinguish.<\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Rotary encoder to linear conversion:\n<ul class=\"wp-block-list\">\n<li>Linear resolution = Screw lead (\u00b5m\/revolution) \u00f7 Count per revolution (CPR).<\/li>\n\n\n\n<li>Example: Lead 5 mm, encoder 20,000 CPR \u2192 5,000 \u00b5m \u00f7 20,000 = 0.25 \u00b5m\/count.<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li>Linear encoder: Determined by the grid pitch and interpolation factor. With a grid pitch of 1 \u00b5m and an interpolation factor of 1,000, the theoretical resolution can reach 1 nm.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Repeatability: The discrete range of the final position when the same instruction position is reached multiple times.<\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Key factors include friction, backlash, rigidity, and temperature. Direct drive systems have less transmission backlash and generally offer better repeatability.<\/li>\n<\/ul>\n\n\n\n<ol class=\"wp-block-list\">\n<li>Absolute positioning accuracy: the deviation between the commanded position and the measured position.<\/li>\n<\/ol>\n\n\n\n<ul class=\"wp-block-list\">\n<li>It is affected by geometric errors (lead error, straightness), sensor accuracy, structural thermal expansion, and control compensation.<\/li>\n\n\n\n<li>Common error budget notation (RSS can be used for independent approximations):\n<ul class=\"wp-block-list\">\n<li>E<sub>total<\/sub>\u2248\u221a(E<sub>encoder<\/sub><sup>2<\/sup>+E<sub>mechanical<\/sub><sup>2<\/sup>+E<sub>thermal<\/sub><sup>2<\/sup>+E<sub>control<\/sub><sup>2<\/sup>)<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Dynamic accuracy: Error during acceleration\/deceleration and constant-speed following (following error, overshoot). It is determined by servo parameters, rigidity, and driver bandwidth.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u7cbe\u5ea6\u8207\u6027\u80fd\u6bd4\u8f03\">Accuracy and performance comparison<\/h2>\n\n\n\n<figure class=\"wp-block-table aligncenter\"><table class=\"has-fixed-layout\"><thead><tr><th>index<\/th><th>linear motor<br>(Direct drive + optical scale)<\/th><th>Servo motor + ball screw<\/th><th>Servo motor + belt<\/th><\/tr><\/thead><tbody><tr><td>Resolution<\/td><td>1 nm\uff5e50 nm<br>Common 10\u2013100 nm practical<\/td><td>0.1\u20131 \u00b5m<br>Visual guidance and CPR<\/td><td>5\u201320 \u00b5m<br>High-order can be &lt;5 \u00b5m<\/td><\/tr><tr><td>Repeatability<\/td><td>\u00b10.2\uff5e\u00b11 \u00b5m<br>A good platform can achieve &lt;\u00b10.5 \u00b5m<\/td><td>\u00b12\uff5e\u00b110 \u00b5m<br>Preloading and compensation can improve<\/td><td>\u00b120\uff5e\u00b150 \u00b5m<\/td><\/tr><tr><td>Absolute positioning accuracy<\/td><td>5\u201320 \u00b5m\/m<br>Laser compensation can be &lt;5 \u00b5m\/m<\/td><td>20\u201350 \u00b5m\/m<br>(Screw grades vary greatly)<\/td><td>50\u2013150 \u00b5m\/m<\/td><\/tr><tr><td>speed<\/td><td>2\u20135 m\/s is common<\/td><td>0.5\u20131.5 m\/s<br>Limited by critical speed<\/td><td>2\u20133 m\/s<\/td><\/tr><tr><td>acceleration<\/td><td>5\u201320 m\/s\u00b2, load depends on design<\/td><td>1\u20135 m\/s\u00b2<\/td><td>3\u201310 m\/s\u00b2<\/td><\/tr><tr><td>Back gap effect<\/td><td>Almost none, no mechanical transmission backlash<\/td><td>There is back clearance, which is compensated by double nut preload\/compensation.<\/td><td>Influence of belt elasticity and tooth backlash<\/td><\/tr><tr><td>Fever\/Clean<\/td><td>The coil generates heat and requires heat dissipation; it has no particulate abrasion and is cleanroom friendly.<\/td><td>The screw generates heat through friction and may carry dust.<\/td><td>High wear particles in belts<\/td><\/tr><tr><td>cost<\/td><td>Height (scale + drive + platform)<\/td><td>Medium (depending on screw grade)<\/td><td>Low to medium (suitable for long journeys)<\/td><\/tr><tr><td>Typical applications<\/td><td>High-precision bonding, exposure, and precision measurement<\/td><td>CNC, module equipment, general positioning<\/td><td>Long-distance rapid handling and packaging conveying<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">Practical judgment:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Target repeatability \u2264 \u00b11 \u00b5m, high dynamic tracking requirements \u2192 linear motors preferred.<\/li>\n\n\n\n<li>Target repeatability of 2\u201310 \u00b5m, cost-sensitive, high load capacity \u2192 Screw servo is a practical solution.<\/li>\n\n\n\n<li>Long stroke, high speed, medium precision requirements \u2192 Servo + belt is the most cost-effective.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u9078\u578b\u6d41\u7a0b\u8207\u67e5\u8868\u8a08\u7b97\">Selection process and table lookup calculation<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Objective: 300 mm stroke, repeatability \u2264 \u00b11 \u00b5m, absolute positioning accuracy \u2264 \u00b110 \u00b5m, maximum speed 1 m\/s, load 8 kg (fixture + workpiece), level installation.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-1-\uff5c\u7cbe\u5ea6\u9700\u6c42\u62c6\u89e3\">Step 1 | Breaking down accuracy requirements<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Repeatability \u2264 \u00b11 \u00b5m \u2192 Belt conveyors are basically excluded; screw solutions require high-grade screws, preloaded double nuts + linear scale closed loop to be viable.<\/li>\n\n\n\n<li>Absolute positioning \u2264 \u00b110 \u00b5m \u2192 300 mm, equivalent stroke 33 \u00b5m\/m; screw lead error and thermal expansion must be able to compensate for this level. This is relatively easy to achieve with a linear motor and a high-order linear scale.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-2-\uff5c\u52d5\u614b\u8207\u525b\u6027\u9700\u6c42\">Step 2 | Dynamic and Rigid Demands<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>1 m\/s speed, general acceleration requirements (assuming 5 m\/s\u00b2) \u2192 The critical speed of the screw may be approaching the limit, requiring a large-diameter, short-lead screw and a high CPR encoder.<\/li>\n\n\n\n<li>The workpiece weighs 8 kg, the estimated total moving mass of the machine is 15 kg, and the target acceleration is 5 m\/s\u00b2. Therefore, the required thrust is approximately 75 N. Adding friction and margin, we can estimate 150\u2013200 N. Standard linear motor modules typically provide continuous thrust of 100\u2013300 N, with higher peak values, which is sufficient.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-3-\uff5c\u89e3\u6790\u5ea6\u8207\u7de8\u78bc\u5668\u63db\u7b97\">Step 3 | Resolution and Encoder Conversion<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A. Screw servo (lead 5 mm)<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>20,000 CPR \u2192 Linear resolution = 5,000 \u00b5m \u00f7 20,000 = 0.25 \u00b5m<\/li>\n\n\n\n<li>80,000 CPR \u2192 0.0625 \u00b5m<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">*Note: Sufficient resolution does not guarantee good repeatability. Backlash and heat can widen the repeatability range.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">B. Linear motor + optical scale<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>A resolution of 5 nm to 10 nm is feasible with a gate pitch of 1 \u00b5m \u00d7 interpolation of 200 (in practice, after controlling noise, a resolution of 50\u2013100 nm is used to prevent jitter).<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"step-4-\uff5c\u8aa4\u5dee\u9810\u7b97\">Step 4 | Error Budgeting<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Assuming a target of \u00b110 \u00b5m (full range), estimated using RSS:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Optical scale grade: E after laser compensation<sub>encoder<\/sub>=4\u00b5m<\/li>\n\n\n\n<li>Geometry and Assembly: Straightness, Parallelism E<sub>mechanical<\/sub>=6\u00b5m<\/li>\n\n\n\n<li>Thermal expansion: Aluminum base \u03b1\u224823\u00d710^-6\/\u00b0C, \u0394T=2\u00b0C \u2192 \u0394L \u2248 300\u00d723\u00d710^-6\u00d72 \u2248 13.8 \u00b5m; through temperature control and compensation pressure to Ethernet=5\u00b5m.<\/li>\n\n\n\n<li>Control (following error, compensating for residuals) E<sub>control<\/sub>=3\u00b5m \u2192 E<sub>total<\/sub>\u2248\u221a(4<sup>2<\/sup>+6<sup>2<\/sup>+5<sup>2<\/sup>+3<sup>2<\/sup>The accuracy is approximately 9.5\u00b5m, but temperature control\/compensation and proper assembly are required for safety.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Conclusion: With repeatability of \u00b11 \u00b5m and absolute accuracy of \u00b110 \u00b5m, linear motor direct drive is more reliable; screw servo requires high-specification parts and more compensation, and the overall risk and time are usually higher.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u5982\u4f55\u8abf\u6821\u8207\u91cf\u6e2c\">How to calibrate and measure<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u63a7\u5236\u8abf\u6821\">Control Adjustment<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>The position\/velocity loop gain should balance stability and bandwidth; linear motors can have higher bandwidth to reduce dynamic tracking error, but attention should be paid to the plateau resonance point.<\/li>\n\n\n\n<li>Feedforward control (velocity, acceleration FF) can reduce following errors, especially for constant velocity scanning or S-curve motion.<\/li>\n\n\n\n<li>Friction\/backlash compensation: The screw system needs to undergo dead zone and friction model compensation, and the backlash compensation needs to be adjusted.<\/li>\n\n\n\n<li>Filtering: Add a notch filter to the resonant frequency band; measure the bode before proceeding, and do not blindly add filters to reduce bandwidth.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u6a5f\u69cb-\u74b0\u5883\">Organization\/Environment<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Geometric accuracy: The straightness, parallelism, and torsional rigidity of the guide rail are directly written into the accuracy; the machining and assembly fixtures of the guide rail base must be in place.<\/li>\n\n\n\n<li>Thermal management: Motor and drive heat generation, ambient temperature drift; plus the difference in thermal expansion between aluminum and iron materials, compensation should be made accordingly.<\/li>\n\n\n\n<li>Wiring and noise: The signal quality of linear scales can be affected by the scale from hundreds of nanometers to micrometers. Pay attention to grounding, isolation and cable routing.<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\" id=\"\u91cf\u6e2c\u9a57\u8b49\">Measurement and verification<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Laser interferometer: Corrects positioning accuracy and pitch error, and establishes a compensation table.<\/li>\n\n\n\n<li>Golf cue\/positioning ruler: Used for quick health checks.<\/li>\n\n\n\n<li>Repeatability test: Take 3\u03c3 by making N round trips from multiple points; the curve should be uniform along the journey, and the middle section should not be measured only.<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\" id=\"\u4ec0\u9ebc\u60c5\u6cc1\u9078\u8ab0\uff1f\u5de5\u7a0b\u5e2b\u7684\u6c7a\u7b56\u6e05\u55ae\">When to Choose Whom? An Engineer&#039;s Decision Checklist<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Linear motor direct drive: repeatability \u2264 \u00b11\u20132 \u00b5m; high dynamic tracking requirements (high-speed scanning), cleanroom, low particle count, low maintenance frequency; acceptable higher initial cost and calibration.<\/li>\n\n\n\n<li>Servo + ball screw: repeatability in the range of 2\u201310 \u00b5m; cost-effective and with high load capacity; vertical axis has self-locking advantage (does not fall when power is off); can approach higher accuracy through linear scale closed loop + compensation.<\/li>\n\n\n\n<li>Servo + Belt: Long stroke, high-speed handling and sorting; medium accuracy requirements (10\u201350 \u00b5m); lowest cost, easy maintenance.<\/li>\n<\/ul>\n\n\n\n<div style=\"height:var(--wp--preset--spacing--30)\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<h5 class=\"wp-block-heading has-text-align-center\" id=\"\u60f3\u4e86\u89e3\u6709\u95dc\u7ba1\u87ba\u7d0b\u3001\u76f4\u87ba\u7d0b\u3001\u9310\u87ba\u7d0b\u3001\u5c3a\u5bf8\u8868\u793a\u3001\u82f1\u5236\u7ba1\u87ba\u7d0b\u3001\u516c\u5236\u7ba1\u87ba\u7d0b\u7684\u77e5\u8b58\u55ce\uff1f-\u5ef6\u4f38\u95b1\u8b80\uff1a\u300a\u7ba1\u87ba\u7d0b\u767e\u767e\u7a2e-\u4f60\u90fd\u8a8d\u8b58\u55ce-\u300b\">Want to learn about precision transmission components such as ball bearings and roller screws? <br>Further Reading :<a href=\"https:\/\/www.taichungbro.com\/en\/2025\/07\/07\/ball-roller-screw\/\" data-type=\"link\" data-id=\"https:\/\/taichungbro.com\/2023\/10\/28\/screw\/\" target=\"_blank\" rel=\"noopener\">How to Choose Between Ball Screws and Roller Screws? Three Key Indicators: Lifespan, Efficiency, and Preload<\/a><\/h5>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity is-style-wide\"\/>\n\n\n\n<div style=\"height:11px\" aria-hidden=\"true\" class=\"wp-block-spacer\"><\/div>\n\n\n\n<p class=\"wp-block-paragraph\"><\/p>","protected":false},"excerpt":{"rendered":"<p>\u7dda\u6027\u99ac\u9054\u8207\u4f3a\u670d\u99ac\u9054\u8ab0\u66f4\u6e96\uff1f\u672c\u6587\u7528\u5de5\u7a0b\u5be6\u52d9\u89d2\u5ea6\u6bd4\u8f03\u89e3\u6790\u5ea6\u3001\u91cd\u8907\u7cbe\u5ea6\u3001\u7d55\u5c0d\u5b9a\u4f4d\u8207\u52d5\u614b\u8ddf\u96a8\uff0c\u4e26\u9644\u53c3\u6578\u8868\u8207\u9078\u578b\u6d41\u7a0b\u3002\u5f9e\u87ba\u687f\u5c0e\u7a0b\u8207\u7de8\u78bc\u5668\u63db\u7b97\uff0c\u5230\u71b1\u81a8\u8139\u8207\u88dc\u511f\u3001\u63a7\u5236\u8abf\u6821\u8207\u91cf\u6e2c\u9a57\u8b49\uff0c\u4e00\u6b21\u641e\u61c2\u5728\u6210\u672c\u3001\u901f\u5ea6\u3001\u7cbe\u5ea6\u9593\u7684\u6700\u4f73\u53d6\u6368\u3002<\/p>","protected":false},"author":2,"featured_media":3499,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[45],"tags":[372,375,374,327,371],"class_list":["post-3497","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industrial-knowledge","tag-372","tag-375","tag-374","tag-327","tag-371"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts\/3497","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/comments?post=3497"}],"version-history":[{"count":0,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/posts\/3497\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/media\/3499"}],"wp:attachment":[{"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/media?parent=3497"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/categories?post=3497"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.taichungbro.com\/en\/wp-json\/wp\/v2\/tags?post=3497"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}