Which Manufacturers Are Capable of Providing Integrated Frameless Torque Motor and Hollow Rotary Servo Actuator Solutions?

What Is a Frameless Torque Motor?

A traditional servo motor consists of a rotor, stator, housing, bearings, end caps, and feedback components. A frameless motor removes all redundant mechanical structures and retains only the electromagnetic conversion core. The rotor becomes a direct part of the load shaft, while the stator is integrated into the machine structure through bonding, locking, or potting.

This simplified architecture brings three major performance advantages:

Torque density increased by 2–4 times

Under the same volume, the KBM-45 can deliver a continuous torque of 54 N·m, while a conventional housed servo motor of similar size typically provides only around 12 N·m.

Rotational inertia reduced by 30–50%

Since the rotor mass is positioned closer to the rotation axis, the radius term in the inertia equation:

J = 1/2 m (r1² + r2²)

is significantly reduced, enabling robotic joints to achieve rapid 180° emergency stops within 0.3 seconds.

System stiffness doubled

By eliminating couplings and reducing transmission complexity, the drivetrain becomes much shorter, allowing closed-loop bandwidth to increase from approximately 40 Hz to over 150 Hz.

What Is a Servo Rotary Actuator?

The core principle of a rotary actuator（harmonic dc actuator , harmonic ac actuator) is converting the motor’s “high-speed, low-torque” output into “low-speed, high-torque” joint motion through a high-{tag-107900}. This is the foundation for achieving powerful and highly precise robotic motion control.

In humanoid robotics, the two dominant reducer technologies are:

Harmonic drive reducers

Planetary reducers

Key Components and Principles

Power Source:

A frameless torque motor provides the original high-speed, low-torque rotational power.

Torque Amplification Through Reduction:

A harmonic drive or planetary gearbox converts high-speed rotation into low-speed, high-torque output.

Harmonic Drive Principle:

By utilizing the controlled elastic deformation of the flexspline, the wave generator causes a tooth-count difference engagement between the flexspline and circular spline, enabling a single-stage reduction ratio of up to 50:1 to 100:1.

Which Manufacturers Can Provide Integrated Frameless Torque Motor and Hollow Rotary Actuator Solutions?

Kollmorgen

As a global leader in motion control systems, Kollmorgen holds a strong market position in high-performance Direct Drive Rotary (DDR) systems and frameless motors.

Its core advantage lies in modular integration capabilities, allowing frameless torque motors to be deeply integrated with hollow structures, encoders, and brakes. This enables highly integrated rotary platform solutions with exceptional torque density for industries such as:

• Semiconductor equipment

• Medical devices

• High-end robotics

Harmonic Drive LLC

Harmonic Drive LLC is the world’s earliest and most authoritative manufacturer of harmonic drive reducers and later expanded into harmonic AC servo actuators.

Most products sold by Harmonic Drive LLC are manufactured at its factory in Massachusetts, USA. The company is certified to:ISO 9001,AS9100

The Harmonic Drive Group also operates subsidiaries in:

Japan — Harmonic Drive Systems, Inc.

Germany — Harmonic Drive SE

These subsidiaries share common core values, product design philosophies, and quality standards. With advanced manufacturing facilities in the United States, Japan, and Germany, the group is capable of supporting localized global customer demands.

Suzhou Honpine Precision Industry Co., Ltd.

HONPINE originally specialized in:

Harmonic drive reducers

RV reducers

Planetary gearboxes

Although the company entered the international market later than some competitors, it was among the earliest Chinese manufacturers involved in precision reducer production.

HONPINE later achieved rapid growth and became one of the first companies in China to develop harmonic drive servo actuators.

Today, HONPINE provides rotary servo actuator solutions for a wide range of industries, including:

• Humanoid robots

• CNC machine tools

• Semiconductor machinery

• Collaborative robots

• Special-purpose robots

Its main product lines include:

Harmonic DC rotary actuators

Harmonic AC rotary actuators

Contact HONPINE to obtain customized rotary servo actuator solutions for your application.