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Direct Drive Motors

A direct drive motor is a servo motor that rotates a load by mounting it directly on the rotor, without a reducer or belt. Its multi-pole structure delivers high torque at low speed, so there is no gear backlash, giving high positioning accuracy and responsiveness. It is mainly used for rotary tables and indexing devices. Units generally incorporate a high-resolution absolute position detector and a large cross roller bearing, and have a hollow bore through which cables and piping can be routed. Outer rotor type (outer part rotates) and inner rotor type (inner part rotates) are available, along with low-profile types, types with holding brakes, and dust-proof and waterproof types. They are used in semiconductor and electronic component inspection equipment, assembly equipment, turntables, and similar applications.

How to choose Direct Drive Motors

  1. 1. Select a rated torque suited to continuous load

    Confirm that the effective torque over the operating cycle (root mean square of friction and acceleration/deceleration torque from the load) is at or below the rated torque. Rated torque of the listed products is 2 to 45 N·m. A small margin causes the motor to overheat and may lead to a stop by overload protection.

  2. 2. Check the maximum torque required for acceleration and deceleration

    For applications requiring positioning in a short time, confirm that the acceleration torque, calculated from the load inertia and angular acceleration, falls within the maximum torque. Listed products range from 6 to 135 N·m, with maximum torque set at about three times the rated torque. Also confirm that the load is within the permissible load inertia moment range.

  3. 3. Check that outer diameter and height fit the equipment

    Outer diameter is 100 to 286 mm and height from the mounting surface is 35 to 170 mm. Where space under the table is limited, a low-profile type or a low center-of-gravity inner rotor type is suitable. Models with higher torque tend to have larger outer diameter and mass (2.4 to 48 kg), so also check the strength of the base structure.

  4. 4. Match the hollow bore to the cables and piping

    When passing sensor cables or air piping on the rotary table through the hollow bore, ensure the bore diameter accommodates the outer dimensions of the cable bundles and fittings. The hollow bore of listed products is 32 to 56 mm. If cables will twist with rotation, also consider the permissible rotation angle and the use of a rotary joint.

  5. 5. Verify permissible loads applied directly to the rotor

    Because the workpiece or jig is mounted directly on the rotor, confirm that axial load (1000 to 9500 N), radial load, and moment load (20 to 200 N·m) are within permissible values. Moment load tends to be the limiting factor for eccentric or overhanging loads.

  6. 6. Compare accuracy, speed, and environmental specifications

    Listed products have a repeatability of ±2 arc-sec, an absolute positioning accuracy of 60 to 70 arc-sec, and a maximum rotational speed of 2 to 10 s⁻¹. For applications that must hold position during power loss, such as vertical axes, select a type with a brake; for environments with water, oil, or dust, select an environment-resistant type equivalent to IP66M.

This guide was written by AI based on the listed products' documents and specification items. Check each manufacturer's documents before adopting.