The Conveyor That Was Twice as Fast as It Needed to Be
A packaging line had a belt conveyor running at 30 m/min. The design said “as fast as possible.” The result: the product arrived at the labeler in a blur, the labeler missed 5% of the parts (it could not keep up), and the product jumbled at the outfeed. We measured the labeler’s required feed rate: it needed parts spaced at 200 mm, arriving at 30 parts per minute. That called for a belt speed of 6 m/min — not 30. We slowed the conveyor to 6 m/min. The labeler caught 100% of the parts. The jumbling stopped. The conveyor was 5× too fast; the excess speed was causing the defects. “Faster” was the problem, not the solution.
Conveyor speed is not a setting you maximize. It is a number you calculate from the downstream process. Here is how to size it.
The Speed Is Set by the Slowest Process
The conveyor’s job is to feed the downstream machine at the rate that machine can process. If the labeler processes 30 parts per minute, the conveyor must deliver 30 parts per minute — no faster. A faster conveyor just piles parts at the labeler (it cannot take them), or feeds them too fast for the sensor to detect. The conveyor speed is the bottleneck’s required rate, not the motor’s maximum.
The formula is simple:
Belt speed (m/min) = Required parts/min × Part spacing (m)
For 30 parts/min at 0.2 m spacing: 30 × 0.2 = 6 m/min. The 30 m/min conveyor was delivering 150 parts/min — five times what the labeler could take.
The conveyor rule: Size the belt speed to the downstream process rate, not the motor’s maximum. Faster is not better — it creates piles, misses, and jumbles. The labeler that missed 5% was fed 5× too fast.
The Accumulation Case: When the Conveyor Should Stop
If the downstream machine stops (a jam, a changeover), the conveyor should stop too — or accumulate. A conveyor that keeps running into a stopped machine piles product. Use a photoeye at the outfeed: when product backs up to the eye, the conveyor stops. This is accumulation control. Without it, the line creates a mountain of product at the jam.
Product Spacing: The Sensor Needs a Gap
A sensor (photoeye, vision) needs a gap between parts to detect each one. If the parts touch end-to-end, the sensor sees one continuous object. The spacing must be at least the sensor’s response time × belt speed. At 6 m/min (0.1 m/s) and a 100 ms sensor, the gap is 10 mm — marginal. At 30 m/min (0.5 m/s), the gap needs 50 mm. This is why fast conveyors miss parts: the sensor cannot resolve them. Slow the belt, and the sensor sees every part.
Belt Sizing: Width and Length
The belt width must clear the widest part plus 50 mm margin (so the part does not catch the frame). The length is set by the layout (distance between stations). The motor is sized by the total load on the belt (product weight + belt weight × friction coefficient). A common mistake is to undersize the motor for a loaded belt — the belt runs fine empty but stalls when loaded. Calculate the required torque, add a 2× safety factor.
A Conveyor Sizing Example
| Parameter | Value |
|---|---|
| Required output | 30 parts/min |
| Part length | 150 mm |
| Required gap (sensor) | 50 mm |
| Part spacing (center-to-center) | 200 mm = 0.2 m |
| Required belt speed | 30 × 0.2 = 6 m/min |
| Belt width | Part width + 50 mm |
| Motor torque | Calculate loaded, 2× safety factor |
A Conveyor Design Checklist
- What is the downstream machine’s required parts/min?
- What is the required part spacing (sensor gap)?
- Calculate belt speed = rate × spacing.
- Size belt width to part width + 50 mm.
- Size motor torque for the loaded belt (2× safety).
- Add accumulation control (stop when backed up).
- Verify the sensor resolves each part at the chosen speed.
- Test with actual product (not empty).
- Check for product jumble at the outfeed (too fast).
- Recheck after any product change (new size, new rate).
The Bottom Line
The conveyor that was 5× too fast was a design that maximized speed instead of matching the process. Belt speed is calculated from the downstream rate and the sensor’s required gap. Slowing the labeler feed to 6 m/min fixed the misses and the jumble. The conveyor that works is the one that delivers parts at the rate the next station can take — not the fastest the motor can spin.
