Introduction
Belt driven linear module or ball screw module — the question shows up whenever one axis has to be both long and fast. Screws get expensive and start to whip; belts feel loose and imprecise.
Both feelings are real, but neither is a rule. The right answer comes from a fixed decision order: cycle time first, then speed and acceleration, then the mechanical limits of each drive.
Suzhou Zhongbai Robot Technology Co., Ltd. is a non-standard linear module integration solution provider based in Suzhou, China. Large module makers will not run non-standard, small-batch builds; small non-standard shops take too long. Zhongbai sits between them, integrating belt, screw and rack drives into one axis.
What is the difference between a belt driven linear module and a ball screw module?
A belt driven linear module converts motor rotation into linear motion through a toothed belt and pulley. The moving block rides on a linear guide.
A ball screw module uses a threaded screw and a ball nut instead. Rotation becomes linear motion through rolling contact.
The mechanical consequence is what matters. A belt adds mass and stretch as it gets longer. A screw adds a critical-speed limit that falls with length.
Why does stroke hurt a ball screw faster than a belt?
The critical speed of a screw is roughly proportional to 1/L², where L is the unsupported length between supports. Double the length and the safe rotary speed falls to about a quarter.
Sag is the second problem. A longer, thinner screw sags under its own weight, so you either add a support or increase the diameter.
A larger diameter raises inertia and cost. Inertia then fights the acceleration you wanted in the first place. Long stroke plus high speed pushes a screw axis into a cost spiral.
At what stroke should you switch from belt to ball screw?
There is no universal number, but the order of calculation is fixed. Get the required cycle time, derive the velocity and acceleration profile, then check the screw against its critical speed and DN value.
If the required speed at full stroke stays below the screw's critical speed with margin, the screw is still viable — and its accuracy is usually worth having.
If the profile needs speeds the screw cannot reach without a support or a much larger diameter, the belt is the correct answer. Published crossover strokes vary by diameter, support and duty cycle; treat any rule-of-thumb figure as [待确认] until you run the numbers.
How much accuracy do you give up with a belt driven linear module?
Belt accuracy is limited by belt stretch, tooth engagement and thermal growth. Screw accuracy is tied to screw grade, preload and mounting accuracy.
For long-stroke transfer, pick-and-place and scanning axes, belt repeatability is normally sufficient. For metrology, machining or force-controlled pressing, it usually is not.
Typical repeatability figures for both drives: [待确认]. Never accept a general figure without stroke, load and duty cycle attached to it.
Can a belt driven linear module handle high speed and high load together?
Speed and load pull against each other on a belt axis. Higher belt tension raises stiffness but loads the belt, the bearings and the moving block.
The honest constraints are belt width, pulley tooth engagement, and how much of the stroke is spent accelerating rather than at constant velocity.
If an axis needs both high thrust and long stroke, a gear rack module is often a better third option than either belt or screw. One example from our range is the KCT22 series.
How do you size a drive for a long-stroke, high-speed axis?
Six steps, in this order:
- Define stroke, cycle time, payload and duty cycle.
- Derive the velocity and acceleration profile, including the accelerating fraction of the stroke.
- For a screw: check critical speed, DN value, buckling on vertical axes, and sag.
- For a belt: check tension, tooth shear, pulley diameter and belt natural frequency.
- Size the linear guide and moving block for the moment loads at maximum acceleration.
- Define cover, lubrication and cable management over the full stroke.
When is a ball screw module still the right answer?
Short strokes, high thrust, vertical axes, and any axis with a tight error budget.
A screw also holds position better under static load and is easier to preload against backlash.
The rule of thumb: if the stroke is short enough that critical speed never becomes the limit, the screw normally wins on accuracy and on total cost.
How does cost and lead time compare at long stroke?
Belt cost scales roughly with stroke length. Screw cost scales faster, because diameter, grade and support hardware climb together.
Price and lead time for a specific build: [待确认]. Quote against your travel, speed, payload and duty cycle — not against a catalogue page.
What does Zhongbai build for these axes?
We build and integrate both families: synchronous belt silent modules (ZW/A series), rail-embedded belt modules (ZTA series), rail-embedded screw modules (ZTH series), semi-enclosed screw modules (ZTS series), semi-enclosed belt modules (ZTP series), and gear rack modules (ZTM and KCT22 series). Model numbers are examples only, not fixed specifications.
For a long-stroke, high-speed axis, our starting point is a belt module; the screw option is evaluated rather than assumed.
One-sentence conclusion
For a long-stroke, high-speed axis, choose the belt driven linear module unless your error budget forces a screw — and prove the choice by checking critical speed before anything else.