What Is a Direct Drive Motor?
Normally, AC servo motors use an intermediate mechanism (speed reducer, belt, chain, etc.) to extract a large amount of torque effectively.
In contrast, a direct drive motor is a motor that directly couples a motor and a load (driven object) to transmit power and motion.
The main advantages of a direct drive motor are as follows:
- Space Saving
A direct drive motor does not require a reduction gearbox. Therefore, the entire drive system can be made smaller and more space-efficient. - Maintenance-free
The combination of AC servo motor and reduction gear requires disassembly, cleaning, assembly, and adjustment to remove metal powder, deteriorated grease, and other debris due to wear on the gear sliding parts of the reduction gear. In contrast, the direct drive motor has a simple configuration with no gear sliding parts themselves and basically requires no maintenance. In addition, since there is no deceleration mechanism, there is no risk of malfunction or damage, even if rapid acceleration or deceleration is performed. - High Response
The low-inertia rotating parts and increased rigidity of the drive system directly reflect the control characteristics of the servo, thus improving the machine’s performance. - Realization of high-precision speed control
Since the direct drive motor does not require a reduction gear, there is no backlash and the large number of motor poles minimizes output torque variation, resulting in high-speed stability.
Principle of Direct Drive Motors
The structure of direct drive motors consists of four major components: the stator, rotor, bearing, and rotary position sensor (encoder).
Crossed roller bearings are often used for the bearings, which can support radial, axial, and moment loads with a single bearing, enabling thinner and significantly more rigid bearings compared to double-row angular contact ball bearings. Furthermore, the adjustable bearing clearance structure allows preload to be applied, resulting in highly accurate rotation.
In combination with a high-resolution encoder, precision control is possible. While a typical AC servo motor has 8 to 12 poles, direct drive motors have more than 20 poles, and a large direct drive motor has more than 100 poles, resulting in low torque ripple and high torque.
Uses of Direct Drive Motors
Direct drive motors can be used as a drive source for various equipment that require higher performance and environmental friendliness.
They are mainly used in precision drives for various semiconductor manufacturing processes, high-speed transport drives for processing and inspecting minute electronic components, and endurance test drives for automobile transmissions, engines, etc.
They are also used for processing and transport drive of large flat panels, solar panels, ultra-low speed stable drive of astronomical observation equipment, fine grinding drive of optical lenses, and precision feed drive for high-performance film molding.
Major Industries and Equipment Where Direct Drive Motors Are Used
- Semiconductor and electronic component industries
Wafer dicing equipment, mounters, test handlers, wafer transfer equipment, wafer chamfering equipment, grinder equipment, inspection equipment, etc. - Automotive industry
Torque testers, endurance testers, steering testers, parts processing machines, transfer equipment, etc. - FPD industry
Lamination equipment, scriber, inspection equipment, laser processing equipment, etc. - Converting and printing machine industry
Film forming equipment, stretching equipment, roll coaters, unwinding and winding mechanisms, laminating equipment, PE printing machines, screen printing machines, rotary printing machines, etc. - Food equipment industry
Cappers, food conveying equipment, filling machines, etc.