Linear Module Selection Guide: From Load and Speed to Accuracy

1. Start with the application, not the catalog

Before looking at model numbers, write down five facts about your axis:

What must move? (tooling + workpiece + fixtures)

How far must it move? (stroke and positions)

How fast must it do that? (speed, acceleration, cycle time)

How precisely must it arrive? (accuracy and repeatability)

In what environment will it operate? (clean, dusty, coolant, high temperature, etc.)

These answers drive every later decision in linear module selection.

2. Step 1 – Load and moments

2.1 Calculate moving mass

Moving mass includes:

Tooling and grippers

Workpiece or payload

Any adapter plates or brackets

A portion of cables and hoses if they move with the carriage

Call this total mass m (in kg).

2.2 Include dynamic effects

During motion, the drive must provide force for:

Acceleration and deceleration: $F = m \cdot a$

Overcoming friction

Any process forces (cutting, pressing, pushing)

Choose a safety factor (often between 1.3 and 2) so the axis is not constantly working at its limit.

2.3 Consider moments and overhang

Linear modules have limits not only for straight-line load, but also for:

Mx: rolling moment

My: pitching moment

Mz: yawing moment

These come from offset loads: tall fixtures, cantilevered tools, or side-mounted payloads.

When you choose a linear module, check:

Maximum allowable load in your mounting orientation

Maximum allowable moments around each axis

If your design has a long overhang, you may need:

A larger module size

Two modules in parallel

Two rails with four blocks instead of one rail with two blocks

Ignoring moments is a common cause of premature guide and bearing failure.

3. Step 2 – Stroke and working envelope

3.1 Working stroke vs total stroke

Define:

Working stroke: distance between your furthest positions

Extra travel for homing and cushioning: 10–20 mm at each end is typical

Total module stroke = working stroke + margins.
If you later add extra positions, you will appreciate those extra millimetres.

3.2 Deflection and support

The longer the stroke, the more important the support:

Long, unsupported axes can deflect under load

Deflection reduces accuracy and can cause collisions

For long strokes, consider:

Larger cross-section modules

Additional supports along the base

Timing belt or linear motor instead of long ball screws

Stroke length is a key driver in linear actuator sizing.

4. Step 3 – Speed, acceleration and cycle time

4.1 Define the motion profile

For each move, define:

Distance

Maximum speed

Acceleration and deceleration

Dwell time at each end

From this, calculate:

Required cycle time

Duty cycle (% of time the axis is in motion)

4.2 Match drive type to dynamics

Ball screw: good for medium speeds and precise positioning

Timing belt: best for high speed over long strokes

Linear motor: best for very high acceleration and smooth motion

If your axis must shuttle several times per second over a long stroke, a belt or linear motor is usually a better fit than a long screw.

5. Step 4 – Choose the drive technology

A simple filter you can use in linear module selection:

Short–medium stroke, high accuracy, significant load

Favour a ball screw linear module.

Long stroke (1–3 m+), high speed, moderate accuracy

Favour a timing belt linear module.

Very high dynamics, smooth scanning motion

Consider a linear motor module.

Once you know the drive family, you can choose the exact series and size from your supplier’s range.

6. Step 5 – Accuracy and repeatability

Accuracy requirements are often overstated. Be clear about what you really need.

Repeatability: how close the axis returns to the same command position each time. Important for assembly and pick-and-place.

Positioning accuracy: difference between commanded and actual position across the full stroke. Important for machining, measuring and patterning.

Typical rules:

Transfer and simple loading: ±0.1 mm is often enough

General assembly and vision positioning: ±0.02–0.05 mm

Precision processes: tighter, sometimes in the few-micron range

Match your needs to:

Drive technology (ball screw vs belt vs linear motor)

Screw pitch and preload (for ball screw modules)

Encoder or feedback resolution

Over-specifying accuracy can make the axis unnecessarily heavy and expensive.

7. Step 6 – Mounting, stiffness and orientation

Even the best linear module will perform poorly if mounted on a weak or twisted frame.

7.1 Base structure

Use a flat, machined surface when possible

Avoid mounting across gaps in weldments

If mounting on aluminium profiles, add plates or brackets where needed to increase stiffness

7.2 Orientation

Check how the module’s load ratings change with orientation:

Horizontal (carriage on top)

Vertical (Z-axis)

Side mounting

Vertical axes often need:

Higher safety factors

Brakes on the motor

Attention to counterbalance if loads are large

7.3 Multi-axis combinations

When building XY or XYZ systems:

Check how stacked masses affect lower axes

Design the frame so gantry beams do not sag

Consider two modules in parallel for wide, heavy gantries

Mounting quality is often as important as the module’s own stiffness.

8. Step 7 – Environment and protection

Environment directly influences module choice and lifetime.

Questions to answer:

Is there dust, powder, metal chips, or sawdust?

Is there oil mist or cutting fluid?

Is the temperature stable?

Is it a cleanroom or medical environment?

Possible responses:

Choose fully or semi-enclosed modules for harsh environments

Add bellows, covers or strips to protect screws and guides

Specify stainless-steel components if corrosion is an issue

Use low-particle guides and belts for cleanrooms

The same load and stroke can require very different modules depending on environment.

9. Example: sizing a simple horizontal axis

Imagine you need a horizontal axis to move boxes between two stations.

Payload (box + gripper + tooling): 8 kg

Stroke: 800 mm

Required move time (one-way, including accel/decel): 0.7 s

Position tolerance: ±0.3 mm

Environment: relatively clean

From this:

Moving mass m ≈ 10 kg (including carriage and brackets).

To travel 0.8 m in 0.7 s with a trapezoidal profile, you probably need max speed around 1.5 m/s and acceleration roughly 3–4 m/s².

Force fora cceleration: F = m·a ≈ 10 × 4 = 40 N, plus friction and safety factor → select a drive capable of ~80–100 N.

Accuracy tolerance is moderate (±0.3 mm).

Conclusion:

Longish stroke, high speed, moderate accuracy → a timing belt linear module of medium size is appropriate.

A ball screw axis could do the job, but it would be slower and less cost-effective for this profile.

No special sealing is needed, but standard wipers and covers are still recommended.

This is how linear actuator sizing should connect directly to your application numbers.

10. Final checklist for linear module selection

Before you place an order, verify that the chosen module:

Handles your payload and moments with a reasonable safety factor.

Offers the required stroke, including homing and safety margins.

Meets or exceeds the speed and acceleration needed for your cycle time.

Delivers the accuracy and repeatability your process truly requires.

Fits your mounting space and orientation with adequate stiffness.

Is suitable for the environment (dust, coolant, temperature).

Has clear documentation for motor mounting, lubrication and maintenance.