DG Series hollow rotary actuators

A DGII unit has three working parts: the AZ motor with its pinion, a large ring gear machined around the output table, and a cross-roller bearing that supports the table. The motor sits beside the table (vertical, horizontal or on a pedestal), so the centre of the table is left open as a through-hole.

Cross-roller bearings use rollers arranged at alternating right angles between the inner and outer rings. One bearing therefore resists axial load, radial load and tilting moment at the same time, which is why a disc or arm can be bolted straight onto the table with no extra support bearing. The flip side is that the permissible moment and thrust values are real limits — an arm with a heavy tool at its tip loads the bearing far more than the same mass placed near the centre.

Oriental Motor also notes that a small amount of grease can occasionally seep from the actuator. On pharma, food or clean assembly machines, plan a drip tray or include the unit in routine inspection.

• Single-stage gearing keeps error sources to a minimum
• Vertical-motor types are non-backlash: ±15 arcsec repeatability, 2 arcmin lost motion
• Table runout 0.015 mm and parallelism 0.03 mm on the 85 mm frame
• Oriental Motor reports lost motion changes only slightly after 10 million cycles in its durability testing

Sizing a rotary table is mostly about inertia and index time, not about the mass on the table alone. Work out the load inertia of everything that rotates: a solid disc is J = m × D² / 8, and each fixture or part sitting off-centre adds roughly m × r². Then set the move: the index angle, the time allowed for it and how long the table must dwell.

For a simple triangular speed profile, angular acceleration is 4θ / t² and peak speed is 2θ / t. Acceleration torque is J × α. Add friction and any external torque, apply a safety factor, and compare against the actuator's permissible torque and speed. Example: a 300 mm × 10 mm steel disc (about 5.5 kg) with four 0.5 kg nests at 120 mm radius gives roughly 0.09 kg·m². Indexing 90° in 0.5 s needs about 25 rad/s² and 60 r/min, i.e. about 2.3 N·m before a safety factor — a DG□85R class is the starting point, to be confirmed with Oriental Motor's selection calculation.

Finally check the bearing and the installation: the overhung moment from arms or off-centre tooling, the axial load from pressing or screwing operations, the hollow diameter your cables and tubes need, and which mounting type fits the frame. Send us these numbers and we will run the calculation and confirm the model.

• Load inertia (disc, fixtures, parts) and index angle
• Index time and dwell time, which set acceleration and speed
• Permissible torque and speed of the frame size and gear ratio (18:1 or 36:1)
• Moment load and axial load on the table
• Hollow diameter needed for cables, air tubes or optics
• Motor mount type, AC or DC supply and driver/network type

Many home-built index tables use a stepper or servo, a timing belt, two pulleys, a shaft, a bearing housing and a tensioner. Each part must be designed, sourced, assembled and adjusted, and the belt stretches over time. Oriental Motor's own comparison testing showed the DGII settling without the overshoot and vibration seen on a timing-belt mechanism during acceleration and deceleration.

With a hollow rotary actuator the fixture plate bolts directly to the output table. There is no belt tension to re-set, no pulley alignment and no separate bearing to design, and the hollow centre is free for wiring. For maintenance teams this removes one of the most common causes of drifting index positions.

A mechanical cam indexer is excellent for a fixed, high-speed, heavy-duty index that never changes, and it keeps running with a simple AC motor. Its limitation is flexibility: the number of stations and the motion profile are cut into the cam, so a product change can mean a new indexer. A pneumatic rotary actuator is cheap and simple but moves between two end stops; intermediate positions need extra hardware and the motion is harder to control smoothly.

A DGII actuator sits between them: any angle, any number of stations, speed and acceleration set in software, and absolute position after power loss. It is the better fit for multi-product lines, machines that change formats, and stations where smooth motion protects the part. For very heavy, very fast single-format lines, a cam indexer or a direct-drive servo table may still be the right tool — we will tell you honestly which fits.

Choose the mount type from the space you have. The vertical motor type gives the lowest table height but needs a clearance hole in the base plate. The horizontal type (new slimmer design from 2025) needs no clearance hole, and cables can be routed between the legs under the table. The pedestal type also avoids machining the plate, at the cost of extra height. All types can be installed on the floor, a wall or the ceiling.

Cables and air tubes that pass through the hollow bore turn with the table, so allow a service loop and use flexible, robot-rated cable. Keep index moves within the rotation your cabling allows, and use the AZ driver's no-entry area or ±180° round setting so the table never winds up the cables. The cable outlet direction of the AZ motor can also be selected on most types.

• Vertical mount: lowest height, clearance hole required
• Horizontal mount: no clearance hole, cables between the legs
• Pedestal: no plate machining, taller installation
• Use flexible cable and limit total rotation to avoid cable wind-up