Link Drive Circular Conveyor

A link drive circular conveyor (also known as a connecting rod drive circular conveyor, or Connecting rod drive ) moves workpiece carriers around a closed-loop guideway using a linkage mechanism rather than a belt or chain pull. A crank-and-link drive converts continuous motor rotation into precise intermittent motion, advancing every carrier on the loop by exactly one pitch per cycle and holding it firmly at rest between strokes. Because positioning is defined mechanically, repeatability stays consistent across the whole loop without servo tuning at each station.

A link drive replaces the belt or chain of a conventional circular conveyor with a linkage. Each carrier is coupled to its neighbour by a rod, and the whole train is driven through a cam profile rather than pulled by a flexible element wrapped around a wheel. Earlier material calls the same drive a connecting rod drive; the designation on our model codes is L20.

It is the third of the three drive types offered on our circular conveyor range, alongside timing belt and chain, and it exists because the other two share a limitation at the curves.

Why a linkage instead of a belt or a chain

On a wheel-driven line — belt or chain — the carrier is pulled by an element that wraps the drive wheel at the end of each arc. Entering and leaving that arc, the carrier changes direction while the drive element changes radius, and the carrier experiences a centrifugal reaction that a straight section never produces. At speed and with a heavy fixture, that reaction is what limits how tightly the loop can be turned and how smoothly the carrier crosses from arc to straight.

A link drive removes that mechanism entirely. The linkage constrains each carrier’s path directly, and the motion profile is set by a cam rather than by the geometry of a wrap. In practice that produces four differences worth specifying around:

Smooth transition through the curve. Carriers negotiate the bend without the centrifugal reaction a wheel drive imposes, so the change from straight to arc is gentler for the fixture and its contents.

Cam-curve motion, no impact. The motion profile comes from the cam, which gives a controlled acceleration and deceleration at every index rather than the abrupt take-up a flexible drive element can produce. For fragile workpieces, open containers, or anything positioned only by gravity in its nest, this is the deciding property.

Sectional disassembly. The linkage can be broken and rebuilt section by section, so maintenance on one part of the loop does not mean stripping the whole drive. A belt or chain loop has to be released as a single continuous member.

Small pitch and vertical mounting. Because the drive does not need the wrap radius a belt or chain requires, carriers can be spaced more closely, and the linkage holds position in a vertically mounted loop where a flexible element would sag under its own weight.

Where Link Drive Circular Conveyor fits against the other two drive types

For the repeat positioning figures that go with belt and chain drive, see our Circular Conveyor Systems range page and the engineering data on C Motion.

Configuration in our Link Drive Circular Conveyor

The link drive is available across the standard circular conveyor platform, so track shape, rail width, arc diameter and positioning arrangement are selected in the same way as for the other drive types.

Model designation follows the standard circular conveyor code — for example TMB01-T23-S1000-8LD8-L20 describes a board-frame, horizontally mounted line on 23 mm T-type guideway, 1000 mm arc diameter, eight slides with straight-top positioning, link drive.

Repeat positioning accuracy. The standing accuracy figures — ±0.03 mm chain, ±0.05 mm timing belt, ±0.5 mm without a positioning mechanism.  Guidance module positioning accuracy of link circular conveyor  is ± 0.05 mm.   Corner module positioning accuracy is  ± 0.05 mm too.

Pitch and path are committed earlier. A linkage is built to the loop it runs on. Carrier pitch, station positions and the path are therefore decided at design rather than adjusted later, and a change after the line is built reaches further into the machine than it would on a belt or chain loop.

Where the product tolerates a hard index, carries weight, or sits on a line whose station layout is still moving, timing belt or chain is the more comfortable answer.

Typical applications of Link Drive Circular Conveyor

Link drive is specified where one of its four properties is decisive rather than merely convenient:

• Impact-sensitive products — open containers, unsecured workpieces, components positioned by gravity in a nest, anything where a hard index would disturb the part
• Close station pitch — where the number of process stations in a given footprint is the binding constraint
• Vertically mounted loops — where a flexible drive element would need additional support
• High-duty lines with maintenance access constraints — where being able to break the drive at one section rather than releasing the whole loop shortens planned downtime

Where none of these apply, timing belt or chain drive will usually be the more economical choice, and chain drive carries the higher published positioning accuracy.

What sectional disassembly means in practice

On a belt or chain loop the drive element is one continuous member. Reaching a roller, a carrier or a joint part-way round the loop means releasing tension on the whole element and setting it again afterwards, and the line is down for the length of that operation whether the work itself was large or small.

A link drive is broken at a section. The rods either side of the work area are disconnected, the work is done, and the section is rebuilt — the rest of the train stays where it was. That matters most on lines running long hours, where planned maintenance has to fit into a defined window, and on vertically mounted loops, where releasing a full-length flexible element is awkward in a way that a bolted linkage is not.

It also changes what a spares holding looks like: rods and connecting hardware are discrete items held per section, rather than a full-length element that has to be ordered and fitted as one.

Specifying a link drive line

The enquiry information is the same as for any other line — fixture envelope and weight, cycle time, station count, mounting orientation. Three additions make a difference on this drive type.

Say what the product does when it is disturbed. A part that tips, a liquid that surges, a tray of loose components — describing the failure is more useful than asking for gentle motion, because it tells our engineering team what the index has to avoid rather than how smooth it should feel.

Send the pitch you want, not only the station count. Close pitch is one of the reasons to choose link drive, so the target spacing is a requirement in its own right.

Confirm the orientation early. Vertical mounting is where link drive is strongest, and it is also where the load case is furthest from the horizontal figures, so it has to be settled before the line is sized.

Engineering data

Selection arithmetic — slide load factor, service life, cycle time against station pitch, arc diameter selection against fixture size and weight — is published on our technical site:

• Conveyor Slide Load Calculation
• Conveyor Cycle Time Calculation
• Circular Conveyor Positioning Accuracy

Enquiries about Link Circular Conveyor

Send us the fixture envelope and weight, required cycle time, station count and mounting orientation, and we will return a configured layout. Non-standard track shapes, arc diameters and straight-section lengths are all available.

Frequently asked questions

Why is no repeat positioning accuracy figure published for link drive?

Because the figures we publish are tied to the drive that produces them, and the chain and timing belt values were established on those drives. Carrying either across to a linkage would be an over-claim, and we would rather say so than print a number the line has not been shown to hold. Positioning accuracy on a link drive line is confirmed against the application at quotation. If your specification names ±0.03 mm, that is a chain-drive specification and the enquiry should be quoted on chain.

What can each carrier hold?

Up to 15 kg per individual slide, quoted against the fixture geometry rather than mass alone — a tall or cantilevered fixture consumes capacity through the moment it generates at index. Older material carrying a 10 kg figure for this drive type has been superseded. Where the fixture is heavier than 15 kg, the line moves to chain drive, which reaches 20 kg per carrier on our modular V30 range and 50 kg on V50.

Can an existing belt or chain line be converted to link drive?

Treat it as a new line rather than a conversion. The linkage is built to the loop it runs on, and it changes the carrier attachments, the drive unit and usually the frame with it, so little more than the rails survive the change. Where an existing line is damaging product at index, it is worth checking the cheaper fixes first — positive location in the nest, a longer index time, a larger arc diameter — because those solve a good proportion of impact problems without changing the drive.

Does link drive restrict the track shape?

No. It is available on oval, rectangular, round and custom closed-loop paths, at the standard arc diameters and at non-standard ones, horizontally or vertically. What it does restrict is how late the path can change: the linkage is manufactured to the loop, so the geometry is committed at design confirmation rather than adjustable afterwards. Lines expected to be re-pitched during their life are better served by belt or chain.

Which positioning mechanism is used with link drive?

Swing-arm or straight-top, with the quantity set by the number of positioning stations rather than by the carrier count. They are specified in the same way as the mechanisms on the other drive types — one per station that needs to be held to a datum, none at positions that only need the carrier to arrive. Which of the two suits your line depends on the tooling around the station and on how the fixture is approached, and it is settled with the layout rather than ordered separately.

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