Harmonic Rotary Actuator for Medical Equipment: ≤10 Arcsec Repeatability and High Overturning Stiffness

Medical equipment requires motion transmission systems that deliver exceptional positioning accuracy, structural stability, and operational safety. From surgical robots and medical imaging systems to rehabilitation devices, even minor positioning deviations or mechanical deflections can affect equipment performance.

How can medical equipment manufacturers achieve precise, stable, and reliable rotational motion?

HONPINE HAS, HAT, and HAM harmonic rotary actuators feature high repeatability of up to ≤10 arcsec, zero-backlash transmission, high overturning stiffness, and hollow-shaft configurations to address the demanding motion control requirements of modern medical equipment.

1. Safety Is the First Priority in Medical Equipment

During surgical robot operations or CT and MRI scanning procedures, an unexpected power failure can create serious safety risks. For example, an uncontrolled robotic arm may drop under gravity, while a scanning table may slide out of position, potentially endangering patients.

Medical equipment manufacturers therefore need motion transmission solutions with reliable braking, accurate position retention, and predictable behavior during power interruptions.

A. Permanent Magnet Brakes for Fail-Safe Holding

HONPINE harmonic rotary actuators with external drivers can be optionally equipped with permanent magnet brakes.

Unlike conventional spring-applied electromagnetic brakes, permanent magnet brakes use magnetic force to engage the braking mechanism when power is removed, helping lock the output shaft and maintain its mechanical position during unexpected power interruptions.

Reduced Heat Generation and Energy Consumption

Depending on the brake design, the permanent magnet brake does not require continuous electrical power to maintain its released state. This helps reduce brake-related heat generation and power consumption, supporting the thermal management requirements of medical equipment designed for extended operating periods.

Considerations for Electromagnetic Compatibility

For medical equipment operating in environments with strong magnetic fields, such as MRI systems, brake selection requires careful evaluation. Magnetic materials, residual magnetic fields, electromagnetic compatibility, and MRI safety requirements must all be assessed to ensure that the complete actuator assembly is suitable for the intended installation environment.

B. Absolute Encoders and Zero-Backlash Transmission for Position Retention

HONPINE harmonic rotary actuators with external drivers can be configured with absolute encoders and zero-backlash transmission.

An absolute encoder retains position information within its specified operating conditions, allowing the control system to identify the actuator's position after a power interruption without necessarily performing a conventional homing operation.

Combined with the zero-backlash characteristics of harmonic transmission, the actuator helps minimize motion errors caused by mechanical backlash.

This is particularly important for medical equipment requiring precise and repeatable movements, such as minimally invasive surgical robots, biopsy positioning systems, and medical imaging mechanisms.

C. Hollow-Shaft Design Prevents Cable Interference

Medical equipment often contains complex internal wiring and fluid or pneumatic lines.

For example, endoscopic surgical robots require space for camera cables and pneumatic lines, while large medical imaging systems may need to accommodate cooling pipes and electrical wiring. During repeated rotational movements, externally routed cables can become twisted, tangled, or damaged.

For medical equipment requiring internal cable routing, the HONPINE HAT Series features a hollow-shaft design with a central through-hole, allowing cables and other components to pass through the actuator's center and reducing external cable interference.

For applications requiring greater load-bearing capability, the HONPINE HAM Series features a large hollow-shaft structure and high overturning stiffness. This helps maintain rotational stability under heavy loads and reduces angular deflection in long cantilevered structures.

2. High Repeatability Determines Medical Positioning Accuracy

Positioning accuracy is a critical performance factor in surgical robots, biopsy systems, ophthalmic surgical equipment, and high-precision medical imaging devices.

For these applications, the actuator must not only reach a target position but also return to the same position consistently over repeated operating cycles.

A. Repeatability and Uni-directional Positioning Accuracy

HONPINE harmonic rotary actuators offer the following positioning performance, depending on the model and configuration:

Uni-directional positioning accuracy: ≤30–90 arcsec

Repeatability: ≤10–20 arcsec

How Does High Repeatability Benefit Medical Equipment?

Typical applications include:

• Robotic arms for minimally invasive surgery

• Ophthalmic surgical equipment

• Dental implant positioning and navigation systems

• Medical biopsy positioning mechanisms

Repeatability of ≤10 arcsec means that the actuator can return to nearly the same position when repeatedly executing the same movement under specified test conditions.

This is particularly valuable for medical robotic systems that need to perform precise movements within confined anatomical spaces, where positioning deviations may affect the accuracy of surgical instruments.

For engineers developing medical robotic equipment, high repeatability helps improve motion consistency and provides a more reliable mechanical foundation for precise positioning control.

3. High Overturning Stiffness Improves Structural Stability Under Heavy Loads

Medical equipment, especially large imaging systems and surgical support mechanisms, often features long cantilevered structures carrying relatively heavy loads.

When a cantilevered arm extends outward, gravity and external forces generate an overturning moment at the actuator. Insufficient structural stiffness can cause angular deflection, affecting the positioning stability of the equipment.

HONPINE harmonic rotary actuators are designed to address these mechanical challenges through high structural rigidity and bearing support.

A. High Overturning Stiffness for Long Cantilevered Structures

Typical medical applications include:

• Cantilevered DR and X-ray imaging systems

• Surgical microscope support arms

• Large rehabilitation and exoskeleton equipment

Why Is Overturning Stiffness Important?

The longer the cantilevered structure, the greater the potential angular deflection under an external load.

High overturning stiffness, supported by the actuator's structural design and cross-roller bearing arrangement, helps resist external overturning moments and minimize unwanted angular displacement.

For medical imaging equipment, this contributes to more stable positioning of the imaging assembly and helps reduce motion-related image deviations.

For surgical microscope support arms and rehabilitation equipment, improved structural rigidity also helps maintain stable positioning during operation.

The actual load capacity and allowable overturning moment should be evaluated according to the selected actuator model, mounting configuration, and operating conditions.

4. Why Choose HONPINE Harmonic Rotary Actuators for Medical Equipment?

HONPINE HAS, HAT, and HAM harmonic rotary actuators combine precision harmonic transmission, integrated mechanical structures, and flexible configuration options to address the motion control requirements of medical equipment manufacturers.

Key advantages include:

High repeatability: Repeatability of ≤10–20 arcsec, depending on the model.

Zero-backlash transmission: Helps minimize mechanical positioning errors caused by backlash.

High overturning stiffness: Supports long cantilevered structures and external loading.

Hollow-shaft options: Simplifies internal cable routing and reduces cable interference.

Optional braking solutions: Supports position holding during power interruptions.

Absolute encoder options: Helps retain position information and simplify system recovery after power interruptions.

If you are developing surgical robots, medical imaging systems, rehabilitation equipment, or other precision medical devices, contact HONPINE to request the latest harmonic rotary actuator catalog and discuss a suitable transmission solution for your application.

5. Frequently Asked Questions About Harmonic Rotary Actuators for Medical Equipment

Q1. How Do You Select a Harmonic Rotary Actuator for Medical Equipment?

Selecting a harmonic rotary actuator requires evaluating several factors, including required output torque, radial and axial loads, overturning moment, positioning accuracy, repeatability, rotational speed, and installation space. Engineers should also consider cable routing requirements, braking configurations, encoder types, and the operating environment. The actuator should be selected based on the actual mechanical and motion control requirements of the complete medical device.

Q2. What Is the Difference Between Repeatability and Positioning Accuracy in a Rotary Actuator?

Repeatability describes how consistently an actuator returns to the same position when performing repeated movements. Positioning accuracy describes how closely the actual position matches the commanded target position. Both parameters are important in medical equipment, but they evaluate different aspects of motion performance. Engineers should consider both when selecting actuators for surgical robots and precision medical positioning systems.

Q3. How Does a Hollow-Shaft Harmonic Rotary Actuator Simplify Medical Equipment Design?

A hollow-shaft harmonic rotary actuator provides a central passage for electrical cables, signal lines, pneumatic tubes, or other components. This design can simplify mechanical integration in rotating medical mechanisms, reduce external cable interference, and provide greater flexibility for equipment layout.

Q4. What Should Engineers Consider When Using Rotary Actuators in MRI Equipment?

Actuator selection for MRI equipment requires special attention to magnetic compatibility. Engineers should evaluate the magnetic properties of the motor, brake, encoder, bearings, and other components, as well as electromagnetic interference and MRI safety requirements. Standard permanent magnet brakes and conventional actuator configurations should not be assumed to be MRI-compatible without appropriate assessment and validation.

Q5. Why Should the Allowable Overturning Moment Be Considered When Selecting a Medical Rotary Actuator?

In medical equipment with long cantilevered arms, external loads generate overturning moments at the actuator mounting interface. If the allowable moment is insufficient, the structure may experience excessive angular deflection, affecting positioning stability. Engineers should evaluate the actuator's allowable overturning moment, bearing stiffness, load distribution, and mounting conditions rather than considering output torque alone.