Traditional permanent magnet synchronous motors have a synchronous speed inversely proportional to the number of pole pairs. Therefore, high-speed operation is unsuitable for many applications, making speed reducers indispensable. Adding a speed reducer not only lowers the output shaft's rotational speed but also proportionally amplifies the motor's output torque to the reducer's output shaft. The negative effects of speed reducers include reduced efficiency, increased noise, structural complexity, lubricant leakage, transmission clearance, wear, and frequent maintenance. Different applications require different reduction mechanisms. Engineers strive to design low-speed, high-torque motors that can directly drive the load, simplifying and refining the system. I. Performance Characteristics of High-Performance Direct-Drive AC Torque Servo Systems Speed ​​range is a crucial parameter for servo systems. It refers to the speed adjustment range of the motor within 100% of its rated load, from the rated speed downwards to the speed at which it stops crawling. For good servo systems, the speed ratio under closed-loop speed conditions is typically over 5000 times. Because torque motors operate directly at low speeds, the system encounters problems recognizing low speeds when the speed is reduced by a factor of 5000. This is because commonly used encoders are limited by the number of pulses per cycle, leading to feedback lag errors and even oscillations due to excessively long pulse intervals at very low speeds. Taking a torque servo motor with a rated speed of 200 r/min as an example, to achieve a speed ratio of 5000, it must operate stably at 0.04 r/min. If the feedback encoder on the motor uses a typical 2500-line encoder, the pulse frequency is only 1.67 Hz. With a feedback pulse only once every 0.6 seconds, achieving good control characteristics is clearly impossible. To address this, Xingchen Servo, a domestic company specializing in high-power servo systems, with the support of the National Science and Technology Enterprise Innovation Fund, successfully developed a hybrid magnetic speed encoder. This enables Xingchen Servo's high-performance direct-drive AC torque servo system to achieve a speed ratio reduction of 10000 times from 200 r/min. The ability of a low-speed torque servo system to respond to extremely low-speed given signals and detect extremely low speeds is undoubtedly a prerequisite for achieving high-precision speed and position control in a direct-drive system. Because of the direct-drive approach, any torque pulsation output from the motor shaft will be directly reflected in the controlled object. Many factors can generate torque pulsations in such motors, such as reluctance, cogging, and high-order harmonic pulsations. This requires the torque servo system to effectively suppress these pulsating torques. Xingchen Servo employs the following methods: a three-phase current smoothing control device for AC motors (patent pending), a nonlinear dynamic correction method for permanent magnet synchronous motors (patent pending), and a compensation control method for torque disturbances in AC servo motors (patent pending) . II. Typical Applications of High-Performance Direct-Drive AC Torque Servo Systems In the positioning control of the guide belt of a flatbed printing machine, since there is generally a 20-30 times reduction gear between the transmission roller and the servo motor, gear transmission backlash is unavoidable. The rapid start and stop of the servo motor will cause wear on the reduction gear, further increasing the transmission backlash. III. Screw Drives for Injection Molding Machines and Precision Extruders In the injection molding machine industry, existing pre-plasticizing and extrusion power configurations typically consist of hydraulic motors and hydraulic injection propulsion systems. With the increasing trend towards electrification of injection molding machines, AC torque servo systems have been widely adopted in Japan and South Korea, enabling the next generation of electric injection molding machines to be high-speed, environmentally friendly, and energy-efficient. In the screw extruder industry, existing extrusion power configurations typically include: 1. Z4 series DC motor + DC speed controller + gear reducer; 2. Three-phase asynchronous motor + frequency converter + gear reducer; 3. High-performance direct-drive AC torque servo system. A comparison of the economic and technical indicators of these three systems is shown in the attached table . IV. Typical Applications of High-Performance Direct-Drive AC Torque Servo Systems 1. Gearless Elevators: High-performance direct-drive AC torque servo systems are applied in the elevator industry, forming gearless elevators and ushering in the "third wave" in the elevator industry. Gearless elevators offer advantages such as high efficiency and energy saving, small overall size, light weight, simple structure, high torque at low speeds, and low noise. Furthermore, the gearless transmission makes it possible for elevators to unconditionally escape obstacles and directly level with floors. 2. Other applications include direct-drive electric vehicle hubs, rotary flying shear systems, and aviation and aerospace testing platforms. High-performance direct-drive AC torque servo systems have the following characteristics when applied to automated equipment: 3. High efficiency and significant energy savings. The transmission efficiency of typical reduction mechanisms is approximately: cylindrical gear reducers 70%–90%, worm gear reducers 20%–70%. Using a high-performance direct-drive AC torque servo system, along with the driver and motor, the total efficiency at the rated point can exceed 85%. Even far from the rated operating point, the overall efficiency remains around 80% over a wide power range. Compared to a conventional AC permanent magnet synchronous servo system + reducer solution, empirically evaluated energy savings can reach approximately 30%. 4. Noise Reduction: In this torque servo mechanism, the mechanical noise from gear meshing in the reduction mechanism is eliminated. Furthermore, since there are no high-speed rotating parts, vibration and noise caused by the imbalance of rotating components are greatly reduced. Faults such as wear, loosening of parts, deformation, and fatigue failure caused by high-speed rotation and vibration are also significantly reduced. 5. Simple Structure and Low Maintenance Requirements: Lubricating grease leakage in the reduction mechanism has always been a problem in the machinery industry. By eliminating the reduction mechanism, the mechanism is greatly simplified. The problem of lubricating oil leakage is eliminated, and the requirements for installation, debugging, and maintenance are greatly reduced. 6. Backlash-Free Transmission and Improved Control Precision: Backlash in the reduction mechanism not only increases transmission control errors but also lowers the structural resonant frequency of the entire system. During rapid and precise speed and position control, the backlash severely limits the response bandwidth of the control system, lowering the frequency of the unstable section and making motion control prone to oscillations or even control failure. With torque servo, the entire shaft system is connected as a single unit using a sleeve shaft method, further improving system gain and effectively controlling both the dynamic and static errors of the controlled object.