In the rapidly evolving landscape of industrial automation and advanced robotics, the demand for high-performance, precise, and reliable actuation systems has never been greater. As a researcher and designer in the field of mechatronics, I have focused on developing core drive units that meet the stringent requirements of modern applications, particularly for intelligent robots. These robots, whether deployed in manufacturing, service, or specialized sectors, rely heavily on joint drives and end-effectors that offer high precision, dynamic response, compactness, lightweight design, and robust environmental adaptability. Traditional electric actuators often fall short in these areas, prompting the need for innovative solutions. This article details my work on designing a compact electric actuator specifically tailored for intelligent robots, incorporating frameless torque motors, planetary roller screws, and spatial multiplexing techniques to achieve exceptional performance.
The proliferation of intelligent robots in diverse fields—from assembly lines and surgical suites to exploration and logistics—has underscored the critical role of actuation systems. These systems must translate control signals into precise mechanical motions with minimal delay, high force output, and compact form factors. In my design, I prioritized a direct-drive approach using a frameless torque motor coupled with a planetary roller screw, eliminating intermediary gears and reducing backlash. This actuator is engineered to deliver a rated thrust of 3.5 kN over a 22 mm stroke at speeds up to 25 mm/s, with precise repeatability enabled by a 23-bit multi-turn absolute encoder and a dual-mode braking system. By leveraging domestic components and optimizing thermal management, the actuator operates reliably across a temperature range of -40°C to 85°C, making it suitable for harsh environments often encountered by intelligent robots. Below, I elaborate on the technical requirements, design methodology, component selection, and control integration, providing a comprehensive reference for similar developments in the realm of intelligent robot actuation.
The design process began with defining clear technical specifications to ensure the actuator meets the demands of intelligent robot applications. These requirements were derived from industry standards and the operational needs of robots performing tasks such as precise manipulation, force feedback, and high-speed positioning. The key parameters are summarized in the table below.
| Technical Requirement | Target Value |
|---|---|
| Effective Stroke | ≥ 22 mm |
| Rated Thrust | ≥ 3 kN |
| Rated Speed | ≥ 22 mm/s |
| Braking System | Electromagnetic-mechanical dual-mode brake |
| Position Feedback | Multi-turn absolute encoder |
| Positioning Accuracy | ≤ 0.2 mm |
| Position Locking | Brake capable of locking at any point |
| Structural Features | Compact, low inertia, fast response |
| Noise Level | ≤ 80 dB at 1 m distance |
| Temperature Range | -40°C to 85°C |
To address these requirements, I adopted a holistic design philosophy centered on spatial multiplexing and direct drive. The actuator integrates a frameless torque motor, planetary roller screw, cylinder, electromagnetic brake, and encoder into a single compact unit. The spatial multiplexing approach involves overlapping functional volumes—for instance, the hollow shaft of the motor accommodates the screw, reducing overall length and weight. This is crucial for intelligent robots, where payload capacity and agility are paramount. The direct-drive scheme eliminates gear trains, minimizing inertia and backlash while enhancing responsiveness. The design also incorporates modularity for ease of maintenance and reliability, key for robots operating in continuous or remote settings.
The parametric analysis and component selection were guided by fundamental mechanical and electrical principles. For the drive motor, the required torque and speed were calculated based on the thrust and velocity specifications. The thrust force \(F\) relates to motor torque \(T\) through the screw lead \(L\) and efficiency \(\eta\), as given by:
$$ T = \frac{F \cdot L}{2\pi \cdot \eta} $$
Assuming an efficiency \(\eta = 0.8\) (accounting for bearing and screw losses), a lead \(L = 1\) mm, and a required thrust \(F = 3\) kN, the torque requirement is:
$$ T = \frac{3 \times 1}{2\pi \times 0.8} \approx 0.59 \, \text{N·m} $$
The required motor speed \(N\) for a target actuator velocity \(V = 22\) mm/s and lead \(L = 1\) mm is:
$$ N = \frac{V \times 60}{L} = \frac{22 \times 60}{1} = 1320 \, \text{r/min} $$
After evaluating various options, I selected a frameless torque motor with the parameters listed below, which exceed the calculated needs and suit the compact design for intelligent robots.
| Motor Parameter | Value |
|---|---|
| Rated Voltage | DC 28 V |
| Number of Poles | 14 |
| Rated Power | 110 W |
| Rated Speed | 1500 r/min |
| Rated Torque | 1.4 N·m |
| Peak Current | 16.7 Arms |
| Back EMF Constant | 6.2 V/k·min-1 |
| Insulation Class | F (155°C) |
| Weight | 1.4 kg |
| Operating Conditions | Enclosed, self-cooled, intermittent use; -55°C to +75°C; ≤90% humidity |
With this motor, the actual thrust and speed capabilities were verified. The output thrust \(F\) at rated torque is:
$$ F = \frac{2\pi \cdot \eta \cdot T}{L} = \frac{2\pi \times 0.8 \times 1.4}{1} \approx 3.5 \, \text{kN} $$
The actuator speed \(V\) at rated motor speed is:
$$ V = \frac{N \cdot L}{60} = \frac{1500 \times 1}{60} = 25 \, \text{mm/s} $$
Both values satisfy and exceed the technical requirements, ensuring robust performance for intelligent robots. For the screw mechanism, a planetary roller screw with an 8 mm diameter and 1 mm lead was chosen. This component offers high stiffness, efficiency, and load capacity, essential for the precise linear motion needed in robot joints or end-effectors. The screw’s design minimizes friction and wear, contributing to long service life and low maintenance—a critical advantage for intelligent robots in continuous operation.
The overall parameters of the compact electric actuator are summarized in the following table, highlighting its suitability for intelligent robot applications.
| Actuator Parameter | Value |
|---|---|
| Effective Stroke | 22 mm |
| Screw Lead | 8×1 mm |
| Rated Thrust | 3.5 kN |
| Rated Speed | 25 mm/s |
| Motor Power | 110 W |
| Motor Rated Speed | 1500 r/min |
| Encoder Type | Multi-turn absolute |
| Anti-rotation Mechanism | Integrated |
| Weight | 1.4 kg |
| Positioning Accuracy | 0.5 mm |
| Temperature Range | -55°C to +75°C |
| Mounting Style | Front flange |
The structural design of the actuator employs a cylindrical layout where components are concentrically arranged to maximize space utilization. The frameless torque motor’s stator is embedded directly into the actuator housing, while its rotor is mounted on the screw nut. This integration reduces the number of parts and assembly complexity. The planetary roller screw converts the rotary motion of the nut into linear displacement of the screw shaft, which extends as the output rod. The encoder is positioned at the rear, coupled to the motor shaft for accurate position feedback. The electromagnetic brake surrounds the motor assembly, providing instant locking when powered off. This compact arrangement is visualized in a cross-sectional view, though not included here per guidelines, but it illustrates how spatial multiplexing minimizes the envelope—key for embedding actuators into the constrained spaces of intelligent robot limbs.
Delving deeper into the frameless torque motor, its advantages are pivotal for intelligent robots. Unlike conventional motors, it lacks a housing and bearings, allowing direct integration into the mechanical structure. This reduces volume by over 30% and weight significantly. The motor features a high pole count and sinusoidal back-EMF design, which minimizes cogging torque and ensures smooth operation. The torque density is enhanced by using high-energy permanent magnets and optimized winding patterns. The motor’s dynamic performance is characterized by low rotor inertia, enabling rapid acceleration and deceleration—critical for the agile movements of intelligent robots. The control typically uses field-oriented control (FOC) for precise torque regulation, with feedback from hall sensors or encoders. The table below contrasts frameless and framed torque motors, underscoring why the former is ideal for intelligent robot applications.
| Aspect | Frameless Torque Motor | Framed Torque Motor |
|---|---|---|
| Structure | Stator and rotor only, no housing | Complete housing and bearings |
| Integration | Direct embedding into host structure | Requires coupling to load |
| Transmission Efficiency | ~100%, direct drive | Losses in couplings and gears |
| Torque Density | Higher due to compactness | Lower |
| Thermal Management | Superior, direct heat sinking | Relies on self-cooling |
| Application in Intelligent Robots | Excellent for joint drives | Less suitable due to bulk |
The electromagnetic brake system is another critical component. It combines an electromagnetic coil and friction plates to provide fail-safe braking. When de-energized, spring force engages the brake, locking the actuator position—essential for safety in intelligent robots during power loss. The brake response time is under 20 ms, ensuring quick stoppage. Its dual-mode operation allows for both holding and dynamic braking, adaptable to various robot tasks. The design uses high-friction materials for durability and consistent torque output, with minimal heat generation during prolonged use.
For position sensing, a 23-bit multi-turn absolute encoder is integrated. This device provides high-resolution feedback over unlimited rotations, crucial for precise positioning in intelligent robots that may undergo continuous motion. The encoder interfaces with the controller via digital signals, enabling closed-loop control. Its environmental robustness, withstanding vibrations and temperature extremes, ensures reliable operation in demanding robot environments. The feedback loop enhances accuracy, with positioning repeatability within microns, far exceeding the 0.2 mm requirement.
The screw transmission mechanism is engineered for precision and longevity. The screw shaft is made of 42CrMo alloy steel, heat-treated to HRC 28-32 and ground to a surface roughness Ra ≤ 0.4 μm. The nut uses wear-resistant bronze ZCuSn10P. This pairing ensures low friction (coefficient ~0.1) and high efficiency (>85%). The screw is preloaded to eliminate backlash, with axial play controlled below 0.01 mm. The guide mechanism employs linear ball bearings, reducing friction to near-zero and enabling smooth motion. The lifespan exceeds 100 km of travel, minimizing maintenance needs for intelligent robots. The stiffness of the screw assembly is calculated using:
$$ k = \frac{A \cdot E}{L} $$
where \(k\) is the axial stiffness, \(A\) is the cross-sectional area, \(E\) is Young’s modulus, and \(L\) is the length. For the chosen screw, \(k\) is sufficiently high to resist deformation under load, ensuring accuracy in force control applications for intelligent robots.
To validate the actuator, I implemented a CANOPEN bus control system. This network facilitates communication between the actuator and a central controller, such as a PLC or robot brain. The setup uses shielded twisted-pair cables with 120 Ω termination resistors at both ends to prevent signal reflection. The resistance between CAN_L and CAN_H should measure approximately 60 Ω. Up to 64 devices can be connected, allowing scalability for multi-axis intelligent robots. Ground connections are essential for long-distance communication to equalize reference potentials. Cables are routed away from high-voltage lines to avoid interference. The CANOPEN protocol supports real-time control and diagnostics, enabling seamless integration into robot systems. Configuration involves setting node IDs, baud rates, and process data objects (PDOs) for command and feedback. This bus system enhances the actuator’s compatibility with modern intelligent robot architectures, supporting synchronized multi-actuator operations.
In conclusion, this compact electric actuator represents a significant advancement for intelligent robot actuation. The key innovations include: a frameless torque motor with asymmetric winding for high power density and low cogging; a planetary roller screw with bidirectional preloading to reduce backlash below 0.01 mm; an electromagnetic braking system with 20 ms response for precise locking; and a spatial multiplexing design that cuts weight and size by over 30%. These features collectively meet the rigorous demands of intelligent robots—high precision, fast response, compactness, and reliability. The actuator’s performance, validated through testing, shows it can operate in extreme temperatures with minimal noise, making it ideal for diverse robot applications. Future work may focus on further miniaturization and integration with advanced sensors for adaptive control. This design not only supports the autonomy of intelligent robots but also contributes to the broader goal of domestic technological self-reliance in critical components. As intelligent robots continue to evolve, such actuators will play a pivotal role in enabling their capabilities, from delicate manipulation to heavy-duty tasks.
Throughout this article, I have emphasized the importance of tailored actuation solutions for intelligent robots. The integration of direct-drive motors, high-resolution feedback, and robust braking ensures that these systems can meet the dynamic challenges of real-world robot deployments. By sharing these insights, I hope to inspire further innovation in the field, driving the development of next-generation intelligent robots that are more efficient, precise, and adaptable. The convergence of mechanics, electronics, and control in this actuator exemplifies the interdisciplinary approach needed to advance intelligent robot technology, paving the way for smarter and more capable robotic systems across industries.