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AC Servo Drives

AC servo drives regulate current, voltage, and frequency output to AC servo motors in closed-loop feedback systems, enabling precise control of position, speed, and torque on machine axes where accuracy and dynamic response are critical. PLC Direct supplies AC servo drives including servo amplifiers and servo inverters from leading automation manufacturers as surplus sealed, refurbished, and used hardware, supporting replacement and lifecycle maintenance of installed AC servo drive systems in manufacturing, packaging, and machine tool environments.

Where Are AC Servo Drives Used in Industrial Environments?

AC servo drives are used wherever a machine axis demands encoder-based closed-loop control with the bandwidth and dynamic response that open-loop drives and standard variable-frequency drives cannot provide. The defining application requirement is not the industry but the performance specification: sub-millimeter positioning repeatability, multi-axis synchronization accuracy, or high-bandwidth torque response that directly governs product quality or machine throughput.

Facilities and operations that depend on AC servo drives include:

CNC machine tool installations where servo amplifiers control feed and spindle axes in close coordination with the CNC controller and motor encoder feedback.

Packaging and filling equipment running high-speed synchronized axes where AC servo drives govern registration, indexing, and cut-to-length functions across multiple coordinated axes.

Automotive assembly and stamping operations using industrial servo amplifiers for press, transfer, and weld axis control on production lines.

Plastics and injection molding facilities where closed-loop servo drives control clamp, injection, and ejector axes on installed molding machines.

Printing and converting lines where precise tension and registration across multiple web axes depend on matched servo inverter and motor configurations.

When an AC servo drive fails on a production axis, sourcing a matched replacement by part number is the fastest way to restore motion control and return the machine to service.

Which Brands of AC Servo Drives Does PLC Direct Stock?

PLC Direct stocks AC servo drives, servo amplifiers, and servo inverters from major industrial automation manufacturers.

Siemens SINAMICS S120: The SINAMICS S120 is a modular multi-axis AC servo drive system with Motor Modules, Control Units, and Line Modules for coordinated closed-loop servo drive applications in CNC, packaging, and machine tool installations.

Schneider Electric Lexium 32: The Lexium 32 is a single-axis servo amplifier family for machine applications from 0.15 kW to 7 kW, compatible with BMH and BSH servo motors, available across multiple current and voltage ratings.

Yaskawa Sigma Series SERVOPACKs: Sigma-7 and earlier generation SERVOPACKs are AC servo drives for precision positioning and speed control, available alongside compatible Sigma Series servo motors and encoder cables.

Lenze Series 9300 Servo Inverters: The Lenze Series 9300 EVS93-xx family are servo inverters for AC servo motor applications, available across multiple power ratings as a legacy AC servo drive for installed Lenze motion systems.

Indramat DDS, TDM, and KDS Series: The Indramat DDS, TDM, and KDS series are legacy AC servo drives for machine tool and production machinery axis applications, available across multiple power and current variants for maintenance teams supporting installed Indramat servo drive systems where replacement with current-generation hardware is not yet feasible.

All AC servo drives at PLC Direct are available as surplus sealed, refurbished, and used, depending on current inventory.

What Should You Know Before Ordering AC Servo Drives?

Hardware condition options: PLC Direct supplies AC servo drives as surplus sealed, refurbished, and used hardware. Surplus sealed units are factory-sealed stock in original packaging; refurbished units have been tested and restored to operational condition. Used hardware has been previously installed and carries the same 1-year PLC Direct warranty as all other condition grades.

Compatibility and part identification: AC servo drives are matched to specific motor families by encoder interface type, power rating, and, in many cases, firmware version; a replacement servo amplifier must match the installed unit's full part number to ensure compatibility with the motor, feedback device, and machine controller. For legacy servo inverters such as the Lenze Series 9300, the original nameplate part number is the most reliable reference, as these systems are no longer in active production and cross-variant substitution is not straightforward.

Warranty: All AC servo drives hardware purchased from PLC Direct carries a standard 1-year warranty covering defects and functionality, applicable to surplus sealed, refurbished, and used products.

PLC Direct supplies AC servo drive hardware for replacement and maintenance, and does not provide system design, programming, or integration services.

Frequently Asked Questions

Incremental and absolute encoders are the two main types used with AC servo drives. Incremental encoders require homing on startup to establish position reference; absolute encoders retain position information through power cycles, which is required in applications where the axis position must be known immediately on power-up without a homing routine.

Yes. Many AC servo drives support both position-controlled axis operation and speed-controlled spindle operation, often selectable by mode parameter. The Siemens SINAMICS S120, for example, is commonly used for both functions within the same CNC machine tool system.

A regenerative resistor, also called a braking resistor, dissipates excess energy generated when an AC servo drive rapidly decelerates a motor. It is fitted externally when the drive's internal dissipation capacity is insufficient for the application's braking duty cycle, and its sizing depends on the motor inertia, deceleration rate, and cycle frequency.

STO stands for Safe Torque Off, a functional safety feature that prevents the drive from generating torque when mains power is removed, enabling controlled, safe stops without a full power cycle. It is required in many machine safety architectures and is encoded in the drive part number for families such as the ABB ACS355 and Schneider Electric Lexium 32.

Overcurrent trips are most commonly caused by mechanical overload on the motor, a winding fault in the motor itself, incorrect current limit parameters, or an encoder feedback fault that causes the drive to lose position reference and command excessive current. Diagnosing whether the fault originates in the drive or the motor typically requires isolating each component.