Linear Module Selection Guide: 7 Practical Steps from Load and Speed to Precision and Stroke

1. Start with the Motion, Not the Catalog

1.1 Define the job in one sentence

Before looking at models, answer this in one clear sentence:

“Move a ___ kg payload over ___ mm in ___ seconds, with ___ mm accuracy, in a ___ environment.”

Example:

“Move a 3 kg camera over 400 mm in 0.5 s, with ±0.02 mm repeatability, inside a clean lab.”

That single sentence already hints at:

• Required stroke length
• Speed and acceleration
• Load and precision
• Environment (dusty factory vs cleanroom)

Write this sentence down and keep refining it. Every choice you make about the linear guide rail, ball screw drive, or belt will come back to this statement.

1.2 Identify the real “critical axis”

Not all axes are equal. In a multi-axis system:

• One axis is usually the bottleneck for cycle time (often the longest X axis).
• Another axis is precision-critical (e.g., short Z axis for dispensing).

You might end up with:

• High-performance servo motor linear module on the critical axis
• Simpler stepper motor linear module on non-critical ones

This mixed strategy keeps performance where it matters and cost under control.

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2. Choose the Drive Type: Screw, Belt, or Linear Motor?

2.1 Ball screw drive: when you care about precision and stiffness

A ball screw drive converts rotary motion into linear motion via a threaded screw and ball nut.

Best when you need:

• High positioning accuracy and repeatability
• Good stiffness and thrust (pushing / pressing)
• Short to medium stroke (typically up to ~1 m)

Typical use cases:

• Pick-and-place heads
• Precision assembly and inspection
• Z-axes for dispensing, soldering, or probing

If you’re asking “how to choose linear module for a demanding Z axis?”, a screw module is often the default answer.

2.2 Timing belt drive: when you need speed and long travel

A timing belt drive uses a toothed belt and pulley instead of a screw.

Best when you need:

• Long stroke (1–5 m and beyond)
• High speed and moderate accuracy
• Lower moving mass and quieter operation

Use belts for:

• Transfer systems between stations
• Packaging and palletizing
• Large gantry systems over conveyors

If your spec sounds like “2 m stroke, ±0.1 mm is fine, must be fast”, a belt-driven linear module is usually the right call.

2.3 Linear motor: when dynamics are the bottleneck

A linear motor module is a direct-drive system: no screw, no belt, just a moving coil and magnets.

Choose it when:

• You need very fast acceleration and deceleration
• You want smooth motion at all speeds
• You are building high-end machines (semiconductor, metrology, advanced inspection)

Linear motors are powerful, but they demand a stiff structure and a higher budget. Use them when screw or belt systems can’t meet throughput or precision, especially in linear module for semiconductor equipment or advanced inspection machine designs.

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3. Don’t Ignore the Linear Guide Rail: It Carries the Real World

Many selection discussions focus on the drive type, but the linear guide rail quietly does the heavy lifting:

• Carries static and dynamic loads
• Resists moments from overhanging tooling
• Keeps motion straight and smooth

3.1 Check load and moment ratings

Manufacturers usually provide:

• Permissible radial and lateral loads (N)
• Permissible Mx, My, Mz moments (Nm)

Example: a camera mounted 150 mm away from the carriage center introduces a significant Mz moment, even if the mass is small.

If those moments exceed the rating of your linear guide rail, you’ll see:

• Vibration and chatter
• Uneven wear
• Shortened life and unexpected failures

3.2 Use twin-rail or wider profiles when needed

If you have:

• Tall tools
• Offset grippers
• Heavy fixtures

You may need a wider module, twin guide blocks, or even twin rails. Don’t try to “save money” by undersizing the guide system; it’s one of the most common causes of premature axis failure.

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4. Size for Load and Inertia First

4.1 Calculate total moving mass

Include:

• Tooling, grippers, workpiece
• Cable carriers and brackets
• Any part of the linear module that moves (carriage, sometimes motor)

This total mass feeds into motor and screw sizing.

4.2 Combine mass with acceleration

Use the simple relation:

Required force ≈ mass × acceleration

If you want a 5 kg payload to reach 1 m/s in 0.2 s, the average acceleration is 5 m/s², so you need ~25 N just to accelerate—plus friction, safety margin, and process forces (pressing, cutting, etc.).

Screw-driven modules can deliver higher thrust; belt-driven versions can move lighter loads faster. Make sure your ball screw drive or belt, plus motor, can handle both continuous and peak forces.

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5. Stroke, Speed, and Precision: The Classic Trade-offs

5.1 Stroke vs screw critical speed

With longer screws, there is a limit called critical speed. Above this, the screw starts to whip.

Rules of thumb:

• For strokes under ~600–800 mm, a screw module is usually fine at high speed.
• Beyond that, you may need larger screw diameters, screw supports, or a belt instead.

If your spec says “2 m stroke, 1.5 m/s speed”, don’t force a screw solution; consider a timing belt drive linear module.

5.2 Speed and acceleration vs precision

Higher speeds and accelerations:

• Increase vibration and settle time
• Demand a stiffer frame and better tuning
• May push you toward a servo motor linear module rather than a basic stepper

If you need high precision but moderate throughput, it’s often better to slow the axis slightly and enjoy easier tuning and longer life.

5.3 Repeatability vs absolute accuracy

For most automation tasks:

• Repeatability (coming back to the same point) matters more than absolute accuracy.
• Vision systems or calibration routines can correct small offsets.

Ball-screw modules typically offer excellent repeatability (±0.01 mm or better) with proper mounting. Belt systems offer looser numbers, but still fine for many tasks.

When you’re writing your specs or asking a linear actuator supplier for data, be crystal clear whether you care more about repeatability or absolute accuracy.

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6. Don’t Forget the Environment: Open, Semi-Closed, or Fully Enclosed?

6.1 Match protection to reality, not hope

Ask bluntly:

• Is there dust, chips, powder, or spray?
• Will people clean with aggressive chemicals?
• Is it inside a cleanroom or on a dirty shop floor?

For clean labs and light duty, an open or semi-closed linear module is often enough.
For machining, woodworking, battery slurry, or powder, you should look at a fully enclosed linear module or at least an IP rated linear actuator.

6.2 Enclosure extends lifetime

A fully enclosed linear module with cover strips, seals and integrated lubrication:

• Keeps contaminants away from screw and guides
• Extends service intervals
• Maintains performance in harsh environments

The extra hardware cost is usually small compared with lost production and emergency repairs caused by contamination.

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7. Integration: Motors, Controllers, and the Rest of the Machine

7.1 Motor choice: stepper vs servo

• Stepper motor linear module
  • Good for simple motion, moderate speeds, open-loop or basic closed-loop
  • Lower cost, simpler wiring
• Servo motor linear module
  • Better for high speed, varying loads, and precise control
  • Built-in feedback and torque control

For high-value processes, pairing your linear axis with a servo and a capable motion controller will pay back in smoother motion and easier diagnostics.

7.2 End effectors and vertical axes

Your horizontal axes are only part of the story. Often you’ll add:

• An electric cylinder for vertical motion or pressing
• A robot gripper for handling parts or labware
• A rotary axis for orientation

Make sure the linear module you select can carry these loads and that your control system can coordinate all axes together. That’s how you turn a single axis into a complete, reliable motion subsystem.

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8. A Simple 7-Step Linear Module Selection Checklist

To summarize the whole guide, here is a quick checklist you can keep on your desk:

1. Describe the task in one sentence: load, stroke, time, precision, environment.
2. Pick a drive principle
   • Screw for precision and stiffness
   • Belt for long stroke and speed
   • Linear motor for extreme dynamics
3. Evaluate the linear guide rail
   • Check load and moment capacity, not just drive thrust.
4. Calculate mass and forces
   • Include tooling, cables, and process loads.
5. Balance stroke, speed, and precision
   • Watch screw critical speed and settle times.
6. Match enclosure to environment
   • Open, semi-closed, or fully enclosed linear module as needed.
7. Confirm integration details
   • Motor type, encoder, motion controller, safety, and cabling.

If you can confidently answer these seven points, you’re already ahead of most “spec sheet only” selection processes and much closer to choosing the right product—rather than the cheapest line item.