How to Choose a High-Precision Rotary Actuator for Industrial Applications?

1. Start by Screening Rotary Actuator Series Based on Their Structural Features

Hello everyone, I'm Theodore Li, Technical Director at HONPINE.

When selecting a high-precision rotary actuator for industrial applications, the first step is to understand the structural characteristics of different product series and narrow down the options according to your installation requirements.

Today, I'd like to introduce four of HONPINE's best-selling precision rotary actuator series and explain their key differences.

HAS Series – Solid Shaft, Compact Design

The HAS series features a solid-shaft structure with a compact overall design. It is suitable for applications where installation space is limited and there is no requirement for internal cable or pneumatic line routing through the actuator.

HAT Series – Hollow Shaft for Internal Cable Routing

The HAT series features a hollow-shaft structure, allowing cables and pneumatic lines to pass through the center of the actuator. This makes it suitable for automated equipment that requires internal wiring or pneumatic connections.

HAM Series – Larger Hollow Bore

The HAM series provides a larger central through-hole, offering more installation space for cables, air lines, and other internal connections. It is particularly useful for equipment with more demanding internal routing requirements.

HPG Series – High Precision and Rigidity for Machine Tools

The HPG series is designed for machine tool applications where high positioning accuracy and structural rigidity are critical. It is suitable for precision rotary positioning systems that require stable performance under demanding operating conditions.

2. Calculate the Required Torque and Select the Appropriate Gear Ratio

After narrowing down the actuator series, the next step is to calculate the actual torque required by the load and select an appropriate gear ratio.

An actuator must provide sufficient torque not only to support the load during operation but also to overcome the resistance generated during acceleration and deceleration.

Step 1: Calculate the Theoretical Load Torque (Gravity Torque + Acceleration Torque)

During startup and stopping, the actuator needs to overcome two main torque components:

1. Gravity Torque (TG)

Gravity torque occurs when the actuator carries an offset load or performs rotational motion against gravity.

Formula:

TG = M × g × L × cosθ

Where:

M = Load mass (kg)

g = Gravitational acceleration (9.8 m/s²)

L = Distance from the load's center of gravity to the rotational axis (m)

θ = Angle between the gravitational force direction and the lever arm

For purely horizontal rotation with the load's center of gravity located on the rotational axis, the gravity torque component can be ignored.

2. Acceleration Torque (Ta)

Acceleration torque is the torque required to accelerate a load from rest to the target speed within a specified time.

Formula:

Ta = J × α

Where:

J = Load moment of inertia (kg·m²), which can be obtained from 3D CAD software after assigning the appropriate material properties. Make sure the coordinate system origin is positioned at the rotational axis.

α = Angular acceleration (rad/s²), calculated according to the required machine cycle time. For example, if the actuator must accelerate to the target speed within 0.2 seconds, the required angular acceleration should be calculated accordingly.

Step 2: Calculate the Combined Peak Torque Required During Startup and Stopping (ΣT)

Once gravity torque and acceleration torque have been calculated, add them together and apply an appropriate safety factor based on the industrial application.

Formula:

ΣT = (TG + Ta) × Safety Factor

Recommended Safety Factors:

Operating Conditions

Recommended Safety Factor

1.2 – Generally smooth loads, such as standard material handling.

1.5 – Moderate impact loads, such as frequent forward and reverse rotation.

2.0 or higher – Heavy loads or severe impact conditions, such as heavy machining or stamping-related loading and unloading.

ps for selecting a precision rotary actuator, from initial product screening and torque calculations to final configuration and installation considerations.

Step 3: Verify the Calculated Torque Against the Actuator Specifications

The calculated ΣT represents the required peak torque during acceleration and deceleration. At this stage, you need to check the actuator datasheet and verify two critical parameters.

1. Peak Torque Verification (During Startup and Stopping)

Requirement:

ΣT ≤ Actuator's allowable maximum instantaneous torque

Depending on the manufacturer's specifications, this may be listed as maximum instantaneous torque or maximum acceleration torque (T2B).

It is important to distinguish between the maximum instantaneous torque, which may be permitted for only a few seconds, and the maximum acceleration/deceleration torque, which applies to repeated startup and stopping conditions.

When selecting an actuator, the calculated torque must remain below the applicable limits specified by the manufacturer. For frequent acceleration and deceleration cycles, pay particular attention to the lower allowable torque limit.

If the calculated ΣT is below the actuator's specified intermittent peak torque rating (for example, a peak torque permitted for less than 2 seconds), the actuator may be mechanically capable of handling the required short-term load, subject to the manufacturer's duty-cycle and operating restrictions.

2. Rated Torque Verification (Continuous Operation)

Requirement:

Actual continuous operating torque ≤ Actuator's rated torque

Even if the peak torque remains within the allowable limit, the continuous operating torque must also be checked.

If the actuator continuously operates above its rated torque, excessive heating and accelerated fatigue of the harmonic reducer's flexspline may occur, significantly reducing service life.

For industrial equipment, a common preliminary design guideline is to keep continuous operating torque below approximately 80% of the rated torque, leaving sufficient operating margin.

Important: The required load torque must remain below the allowable peak torque during startup and stopping, with sufficient safety margin. At the same time, continuous operating torque must remain within the actuator's rated torque.

The mounting structure is another important consideration when selecting a rotary actuator.

HONPINE offers different structural configurations to accommodate different installation requirements.

HAM – Cylindrical, Flange-Free Design

The HAM series features a cylindrical body without an integrated mounting flange. It is suitable for equipment designs where the customer has a customized mounting structure or prefers a more flexible installation arrangement.

HAMF – Integrated Mounting Flange

The HAMF series features an integrated mounting flange, making mechanical installation and positioning more convenient.

The choice between HAM and HAMF should depend on the equipment's mechanical layout, mounting space, and installation requirements.

4. Do You Need an Electromagnetic Brake?

Whether an electromagnetic brake is required depends on the operating conditions and safety requirements of the equipment.

HONPINE rotary actuators provide brake specifications with corresponding holding torque ratings. When selecting a model, check the specified braking torque to ensure it meets the load-holding requirements.

In the model designation:

B indicates a brake-equipped configuration.

A indicates a configuration without a brake.

For applications where the actuator needs to hold its position when the motor is powered off, an electromagnetic brake may be necessary.

Typical applications include vertical positioning systems, lifting mechanisms, and equipment where the load could move under gravity after power loss.

The brake configuration should be selected according to the actual load, required holding torque, and safety design of the equipment.

[Image: Comparison of rotary actuators with and without electromagnetic brakes]

5. Confirm the Motor Encoder Resolution and Type

Encoder selection directly affects the feedback resolution and position monitoring capability of the rotary actuator.

HONPINE offers two multi-turn absolute encoder options:

23-bit Multi-Turn Absolute Encoder

17-bit Multi-Turn Absolute Encoder

Both options are multi-turn absolute encoders that retain position information even after power is disconnected.

Unlike incremental encoders, which require position referencing after power loss, multi-turn absolute encoders can retain absolute position information across multiple revolutions, helping simplify system startup and position management.

The appropriate encoder resolution should be selected according to the positioning requirements, control architecture, and overall accuracy requirements of the equipment.

It is also important to distinguish encoder resolution from actual positioning accuracy. The final positioning performance depends on the complete transmission system, mechanical rigidity, backlash, control strategy, and other factors.

6. Confirm the Cable Exit Direction

The final consideration is the cable exit direction, which directly affects installation convenience and internal cable management.

HONPINE rotary actuators offer two cable exit configurations:

End-Face Cable Exit: Cables exit from the end face of the actuator. This configuration is suitable for equipment layouts where axial cable routing is more convenient.

Side Cable Exit: Cables exit from the side of the actuator, making it suitable for installations where axial space is limited or side routing is preferred.

Before selecting the cable exit configuration, consider the actuator's installation orientation, surrounding mechanical components, available space, and cable bending radius.

Choosing the appropriate cable exit direction can help simplify assembly and reduce cable interference during equipment operation.

Need Help Selecting a High-Precision Rotary Actuator for Your Industrial Application?

Selecting a high-precision rotary actuator involves more than simply choosing a model based on its rated torque.

You also need to consider the actuator's structural design, load inertia, acceleration requirements, gear ratio, mounting configuration, braking requirements, encoder resolution, and cable routing.

At HONPINE, we offer multiple precision rotary actuator series, including HAS, HAT, HAM, and HPG, to accommodate different industrial motion control and positioning requirements.

If you are selecting a high-precision rotary actuator for your industrial equipment, contact HONPINE to request the latest product datasheets and discuss the most suitable actuator configuration with our technical team.