1.1 Research Background
With the rapid advancement of science and technology, intelligent capabilities continue to improve, making smart manufacturing a prevailing trend in industrial development. For instance, data released by China’s Ministry of Information Industry shows that domestic smart manufacturing achieved remarkable growth of 11.6% in 2023—a testament to the nation’s sustained efforts and technological innovation in this field. Furthermore, the number of innovations among smart manufacturing enterprises has surged significantly, spanning sectors such as high-end equipment manufacturing, advanced materials, and environmental technologies, reflecting the industry’s vitality and profound transformation. This trend has not only revolutionized traditional manufacturing production methods but also accelerated industrial upgrading, enhancing both efficiency and quality. Increasingly, automated production lines and industrial robots are replacing human labor.
With the advancement of the intelligent manufacturing era, the highly automated and intelligent technological features of industrial robots align perfectly with the manufacturing industry’s growing demands for high precision, operational ease, and flexibility in production processes. This has elevated their significance in manufacturing, making them a pivotal force driving industrial transformation and upgrading. Collaborative robots—industrial devices capable of achieving both machine-to-machine and human-robot collaboration—have emerged as a key focus in robotics research due to their autonomous behavior and collaborative capabilities, positioning them to play a dominant role in future industrial robotics. In collaborative robot technology, servo motor performance metrics—including torque response speed, torque accuracy, positioning precision, power consumption, and temperature stability—directly determine a robot’s motion efficiency, stability, and accuracy. As the power core of robots, servo systems’ performance critically impacts motion precision and reliability. Notably, joint servo motors play a pivotal role in achieving positioning accuracy. An excellent joint servo motor ensures precise positioning and stable motion during complex tasks, thereby enhancing operational efficiency and minimizing errors.
The “14th Five-Year Plan for Robot Industry Development” emphasizes advancing research on intelligent integrated robotic joints, with such joints being particularly suitable for collaborative robots. Their highly integrated design concept incorporates underlying actuators, sensors, and drivers directly into the joint itself, turning each joint into a standalone control unit. By optimizing internal structure and layout, the distributed control architecture significantly reduces the number of cables between different system levels, thereby lowering maintenance costs and enhancing overall reliability. The modular design also facilitates easier joint replacement and maintenance, substantially boosting the market competitiveness of collaborative robots.
The concept of collaborative robots was first introduced in 1996, with its design philosophy revolutionizing traditional robotics by enabling coordinated operations between robots and humans on production lines. This collaborative approach not only leverages the efficiency and precision of robots but also integrates human intelligence and flexibility, enhancing operational efficiency and fluidity. Compared to conventional industrial robots, collaborative robots exhibit distinct characteristics, establishing themselves as a significant subcategory within the robotics field. Both their physical structures and control systems have undergone substantial modifications. Traditional industrial robots—such as the robotic arm configurations depicted in Figure 1—are primarily used in palletizing, material handling, welding, and laser cutting applications. While these robots feature high rigidity, structural stability, and strong load-bearing capacity, they also present limitations: relatively large size and mass, significant motion inertia, bulky designs with poor flexibility, and inability to perform highly agile assembly tasks. Additionally, their substantial inertial momentum and high-speed movements pose considerable safety risks to personnel within their operational radius, necessitating operation within enclosed enclosed areas.
Figure 1 Traditional industrial robotic arms and collaborative robots
Collaborative robots enable simultaneous operation with humans in shared spaces and facilitate close-range interaction within collaborative zones. Compared to traditional robotic arms, collaborative robots typically bear a maximum load of 20 kg at their end effector, with an operational range comparable to that of a human arm’s reach. Their structure is simpler than that of conventional industrial robotic arms featuring complex transmission mechanisms, while offering sensitive force feedback, lightweight flexibility, and robust perception capabilities. These features allow them to dynamically adjust force during human interactions, effectively preventing violent damage. Consequently, collaborative robots can safely collaborate with humans to complete tasks without requiring traditional safety barriers.
Collaborative robots engage in direct human-contact operations; therefore, safety is an indispensable requirement in human-robot collaboration. It is essential to strictly control operational power and rotational torque while employing technical measures such as current control, torque control, contact sensors, and collision detection to prevent injuries to personnel. The intelligent drive control systems of robots also require further optimization for safety management, enabling adaptive smooth control through dynamic calculations and observer-based modeling.
In a recent study, the International Federation of Robotics (IFR) highlighted that future robot development will primarily exhibit trends toward simplicity, ease of use, flexibility, and safe collaboration. Industrial robots will progressively achieve higher levels of automation and intelligence; their user-friendly design will lower operational barriers, enabling more enterprises to effortlessly leverage robotics technology to enhance production efficiency. Meanwhile, designs featuring flexibility and safe collaboration capabilities will enable robots to better adapt to diverse and complex production environments, facilitating human-robot collaboration and further advancing the intelligent and efficient development of industrial production.
Figure 2: Working area of the collaborative robot
1.2 Research Significance
In the current collaborative robotics market, seven-degree-of-freedom robots are favored for their extensive operational range and flexibility. These robots provide redundant degrees of freedom, offering greater potential for industrial automation and smart manufacturing. Each degree of freedom is achieved through a robotic joint, which serves as a critical factor in determining robotic performance. The four major manufacturers—FANUC, ABB, Yaskawa, and KUKA—each employ distinct transmission systems in their traditional industrial robotic arms; however, they essentially utilize servo motors paired with bevel gears, spur gears, or synchronous belts to transmit power to the joints for rotation. These transmission methods limit the size of robotic joints. While achieving high precision is possible, miniaturization remains challenging. As shown in Figure 3, traditional industrial robots require external control cabinets housing motor servo drives, with numerous wires connecting each motor to the cabinet, thereby restricting the flexible deployment of control systems.
Figure 3 Traditional industrial robot and control cabinet
Given that the traditional joint configurations of industrial robotic arms can no longer meet the requirements of collaborative robots, these joints have abandoned conventional transmission mechanisms in favor of a novel design philosophy. This approach focuses on achieving lightweight, low-voltage, and highly integrated systems by integrating the controller, servo driver, and motor within the joint itself, with underlying electrical connections also implemented internally. Only a minimal number of control interfaces are exposed externally, simplifying external wiring and reducing engineering complexity. Such a design is referred to as an integrated joint.
Given the current development needs and trends in collaborative robot joints, designing a lightweight, low-voltage, highly integrated, and high-performance integrated collaborative robot joint is particularly crucial. Such an integrated joint incorporates all essential components required for joint movement—including actuators, controllers, drivers, and sensors—and can function independently as a standalone module. When connected to the main controller or other modules via simple power and control buses, this highly cohesive yet low-coupling design significantly enhances the scalability of collaborative robots. By utilizing this integrated modular joint and pairing it with appropriately sized robotic arms and end-effectors, collaborative robots tailored to various requirements can be easily assembled.
Figure 4 Schematic diagram of the modular joint
Research on integrated joints for collaborative robots and their servo control systems holds significant importance for the advancement of collaborative robotics. The core technologies of these integrated joints consist of two key components: harmonic reducers and joint motor drive-control systems along with their corresponding control algorithms. Zhixin Drive Technology (Shijiazhuang) Co., Ltd. focuses its research on joint motor drive-control systems for collaborative robots, conducting in-depth studies on joint motor drive and control mechanisms. The company is developing a series of highly intelligent integrated robot joint motor products that enable more flexible and reliable control capabilities for collaborative robot joints, while incorporating critical features such as self-perception, intelligent decision-making, dexterous execution, and precise control—thereby meeting the demands of smart equipment development.
2 Current Research Status Domestically and Internationally
In 1956, American physicist Joe Engelberger and inventor George Devol founded a robotics company named Unimation, which successfully developed the world’s first industrial robot—the Unimate—in 1959.
General Motors first deployed robots in industrial production at its New Jersey facility in 1961. In 1969, Japan introduced robots from Unimation, later licensing its technology to Kawasaki Heavy Industries and the UK-based KUKAI Corporation for robot manufacturing operations in Japan and the UK, respectively. With the advancement of Japan’s automotive industry, an increasing number of robots have replaced human labor in production, fully demonstrating their practical value. Consequently, Japan has placed growing emphasis on industrial robotics development. Starting with Kawasaki Heavy Industries as the pioneer in robot technology adoption, followed by the emergence of world-renowned robotics companies such as FANUC and Yaskawa, Japan has become one of the nations mastering cutting-edge robotic technologies globally.
In 1973, the German company KUKA modified the Unimate robot to create the first six-degree-of-freedom robot, the Famulus, powered by an electric motor. In 1974, ASEA (the predecessor of ABB), a Swedish general electrical company, developed the world’s first fully electric robot, the IRB 6, controlled by a microprocessor, significantly enhancing robotic intelligence. In 1978, the U.S.-based Unimation Company widely deployed its PUMA industrial robot on General Motors’ assembly lines, further demonstrating the practicality and value of industrial robots and marking the full maturity of industrial robotics technology, thereby laying a solid foundation for subsequent technological advancements.
Over the more than four decades of industrial robotics development, technological advancements have been continuous. However, due to safety considerations, robots are typically fixed at specific workstations and isolated by guardrails, preventing them from working side-by-side with humans in the same space. This traditional configuration limits human-robot collaboration, making it difficult to achieve truly efficient cooperative operations. Despite numerous attempts and explorations, achieving safe human-robot collaboration remains a major challenge in the field of industrial robotics.
It was not until 2005 that a major EU-funded project introduced the concept of collaborative robots. The initiative brought together leading industrial robotics companies such as ABB, KUKA, Reis, Comau, and Gudel to jointly develop an affordable, compact, and flexible robot specifically designed for small and medium-sized enterprises, aiming to reduce reliance on labor outsourcing. This project explicitly highlighted the potential of human-robot collaboration, laying a solid foundation for the concept of collaborative robots.
Early collaborative robots were primarily modifications and applications of traditional industrial robots, without fundamentally altering their design philosophy or operational modes. Since its establishment in 2005, Universal Robots has been dedicated to developing collaborative robots capable of working safely alongside human workers. In 2009, the company launched the UR5—the world’s first collaborative robot—marking the dawn of this era. Subsequently, Rethink introduced the dual-arm Baxter and the new single-arm Sawyer robot, gradually establishing collaborative robotics as a recognized and accepted discipline within industrial robotics. This advancement has provided new insights and directions for future industrial automation and intelligent development.
Figure 5: UR5 robot and Sawyer Baxter robot
Siasun Robot Company, affiliated with the Shenyang Institute of Automation of the Chinese Academy of Sciences, first showcased a seven-axis flexible collaborative robot representing China’s advanced technological level at the Industrial Expo in November 2015. Since then, numerous domestic collaborative robot models such as Luoshi and Aobo have gradually gained recognition.
Regarding robotic joints, the primary distinction between collaborative robot joints and those of traditional heavy-duty industrial robots lies in their “flexibility.” This flexibility is manifested through lower mechanical stiffness, reduced inertia, and the ability to sense torque. Currently, the joint flexibility employed in collaborative robotic arms primarily stems from precise position control and torque control.
Figure 6 Typical structure of the integrated joint in collaborative robots
An overview of current research reveals that China’s robotics development started later than that of countries like the United States and Japan. Research on collaborative robots still lags significantly behind existing international products, with key bottlenecks lying in harmonic reducers and joint motor drive control systems. Domestic collaborative robots currently have substantial room for improvement in joint control capabilities, particularly in terms of control precision and intelligent control. Furthermore, global robotics research trends indicate that safety, flexibility, and intelligence are dominant characteristics of technological advancement. Robot joints are evolving toward highly integrated drive-control systems and greater intelligence. Although collaborative robot joints have transitioned from traditional centralized control to distributed drive-control architectures, they currently only execute motor-driven actions, lacking capabilities in autonomous perception, intelligent decision-making, and dexterous execution—resulting in relatively low levels of intelligence. There remains significant potential for expanding demand for intelligent robotics systems.
Post time: May-22-2026
