VFDs for Direct Drive High Torque Servo Motors

The key to maximizing the performance of a high torque direct drive motor is selecting the right variable frequency drives (VFDs). KEB’s expertise spans over 25 years, controlling various torque motors with drives that use standardized hardware and software.

This approach eliminates the need for proprietary motor-drive pairings, allowing machine builders to choose the optimal motor for their application without being locked into a single solution.

Why Use High Torque Direct Drives

High torque servo motors, commonly used in industrial machinery, offer direct drive capabilities that eliminate the need for gear reduction systems. These motors, when paired with VFDs, provide precision control and reduced maintenance.

They also increase efficiency across various demanding applications, such as robotics, printing, and heavy-duty industrial machines like metalworking machinery.

What is a High Torque Motor?

A torque motor is essentially an AC motor designed with a higher pole count, which increases torque while reducing operational speed. Traditional AC servo motors typically operate at higher speeds (2,000-6,000 rpm), often requiring gear systems for speed reduction to achieve the desired torque.

However, high torque motors – thanks to their increased pole count – operate at lower speeds (100-300 rpm), making them ideal for direct drive applications like rotary tables or industrial shredders. This lower operational speed also results in reduced wear and tear on components, contributing to the motor’s long-term reliability.

The number of motor poles can be calculated with some basic information that should be on the motor nameplate:

Why Direct Drive?

Direct drive motors, also called torque motors, deliver high precision by eliminating gear backlash, making them perfect for applications requiring high accuracy, such as machine tools, printing presses, and precision measurement devices. In contrast to traditional motors requiring intermediate gearing or belts, direct drive motors offer a more robust and streamlined solution.

Furthermore, direct drive systems reduce maintenance and operational costs by eliminating the need for mechanical components. Industries such as semiconductor manufacturing and medical devices rely heavily on the reliability and low maintenance benefits of direct drive systems.

These industries place a premium on systems that minimize downtime and ensure continuous, uninterrupted performance.

Critical VFD Features for Direct Drive Applications

VFDs play a crucial role in providing precise speed and torque control in direct drive motors. Unlike traditional systems, where speed adjustment might require complex mechanical modifications, VFDs offer real-time, dynamic control over motor performance.

This level of control is especially important in applications like extrusion processes, where motor speed can directly influence the quality of the product being manufactured.

Versatile Motor Control

KEB drives, such as the S6 platform, support a wide range of motor types, including high-pole torque motors. The ability to adjust drive parameters based on the motor being used provides significant flexibility in motor selection.

Machine builders can leverage this versatility to standardize their VFD platforms across multiple applications, reducing complexity and inventory costs.

Furthermore, VFDs capable of controlling different motor types provide the flexibility to easily switch between various processes, such as moving between linear motors and induction motors, without needing separate drive solutions.

Motor Learn & Encoder Learn Procedures

KEB drives use advanced motor and encoder learning functions through our proprietary Combivis 6 software that directs the drive to optimize motor control. These learning procedures allow the drive to adapt to the specific motor characteristics, such as inductance and resistance, even in highly dynamic load conditions.

In high-precision applications, this level of customization enables the motor to achieve smooth, accurate control at very low speeds. This is a critical requirement for applications like CNC machining or coordinate measurement systems.

Furthermore, KEB’s Combivis 6 software allows the drive to perform these learn procedures quickly and accurately, even when the motor is coupled with a load or under braking. This minimizes system calibration time and ensures optimal motor performance even in environments with high-load inertia.

Scalable Power

From small systems to large-scale applications exceeding 1,000 HP, KEB’s VFDs scale efficiently with high-power requirements. This scalability allows manufacturers to develop larger machines (industrial presses or large machining centers), confident that the drive system can handle the increased demands without compromising performance or efficiency.

Additionally, KEB’s modular drive systems are designed to be easily upgradable, offering future-proofing as machinery requirements evolve or expand.

Standard Hardware, Standard Software

Being pushed into a “matched pair” solution, where the motor and drive must be used together, may limit your options and restrict long-term scalability. This setup could be less economical and potentially hinder performance if the companies do not excel in both motor and drive technologies.

KEB’s drives that run AC torque motors use standard hardware and firmware, offering a truly off-the-shelf product.

The S6 drive platform, for example, runs various motors, including torque, linear, and induction motors. This versatility eliminates the need for specialized hardware, resulting in easier integration and maintenance.

For machine builders, using one drive series for multiple motor types means reduced training, simpler support, and a more streamlined supply chain. This capability is particularly valuable in complex manufacturing settings, where different stages of production may use different motor types but still benefit from a unified control platform.

Support for Absolute Encoders

Since torque motors are often used in precision applications without gear reduction, they usually require very high-resolution absolute feedback. Absolute encoders provide critical positioning information for accurate motor control, even when the motor operates near 0 rpm. This is especially important in applications like elevators or dynamometers, where precise movement control at low speeds is vital.

KEB drives support all major absolute encoder formats, such as BiSS, EnDat, and Hiperface. This wide range of compatibility allows machine builders to select the most appropriate encoder for their application without being constrained by drive limitations. The newer KEB drive platforms feature a multi-encoder interface, allowing seamless integration with any encoder type and further enhancing the system’s flexibility and adaptability.

High Power

Machine tools, extruders, and similar applications often deal with high power requirements – sometimes 300 kW or more. The scalability of KEB drives, from small power systems up to 1,000 HP, ensures that even the most power-hungry applications can be adequately supported.

Knowing that the drive solution will scale with their needs is essential for manufacturers building large systems. This scalability is especially important in industries such as automotive manufacturing or aerospace, where system demands can vary greatly depending on the specific process.

Final Thoughts on Direct Drive Motors

When selecting a drive for high torque servo motors, prioritize flexibility, scalability, and support for advanced feedback systems. The combination of these features ensures that your direct drive application will meet the demands of modern industrial machinery, achieving both high precision and long-term reliability.

With KEB’s proven track record, your direct drive system is in capable hands. If you have questions, contact one of our engineers for assistance.