3.3 Frameless motor: Domestic enterprises are expected to accelerate breakthroughs with cost-effective advantages

Frameless motor can directly assemble the rotor components in the machine, which facilitates the high integration of the end product and reduces the size. A frameless motor is the part of a conventional motor used to generate torque and speed, but without shafts, bearings, housings or end caps. Frameless motors have only two parts: the rotor and the stator. The rotor is usually an internal component, consisting of a rotating steel ring assembly with permanent magnets, mounted directly on the machine shaft. The stator is the external component, and the gear is surrounded externally by steel sheets and copper windings to generate an electromagnetic force tightly attached to the machine housing.

Frameless motors are usually installed in advanced machines and have advantages such as compact structure and easy maintenance, which can improve machine performance.

Frameless motors can be used in a variety of robotics and automation fields, including robotics, medicine, machine tools, packaging, printing, processing and general automation. In the field of humanoid robots, frameless motors are also expected to play their advantages of compact structure and high performance, and are applied in fields such as robot limbs. Robots need frameless motors with strong overload capacity, high responsiveness and reliability. Robots such as walking, running, jumping and other actions are driven by the robot joint motor. As the core hardware of robot, robot joint motor directly determines the important performance of robot. The overall requirements of the robot motor are light weight, small volume and large torque. For example, when the robot is running fast and bouncing, the motor needs to have instantaneous explosive power output capability, so the joint motor needs to have high overload capability and high dynamic response capability.

IC693MDL655E

On the other hand, high reliability of the joint motor is required under complex working conditions. Referring to Wang Sheng’s “Frameless torque motor Design and Optimization of leg-foot robot”, the frameless motor series of the United States Kollmorgen TBM(S), the ILM series of frameless motors developed by TQ Company of Germany, and the high-performance frameless torque motor developed by Aerotech Company are widely used in robot joint motors.

The torque density and torque fluctuation requirements are high, and the integrated magnetic steel is conducive to improving the efficiency of frameless motors and saving space. Referring to Wang Zhihui’s “Design and Analysis of High Torque Density Permanent magnet Torque Motor Based on radial Ring Magnetization”, the core component of robot joint is the joint permanent magnet torque motor, and the high torque density and low torque fluctuation of the torque motor are the basis for achieving lightweight and high-precision operation of robot joint. The traditional splice tile permanent magnet has large magnetic leakage, which reduces the motor efficiency and the gap magnetic density, and thus reduces the torque density of the joint motor. According to Wang Zhihui’s “Design and Analysis of High Torque Density Permanent magnet torque Motor Based on Radial ring Magnetization”, most of the magnetic rings of permanent magnet motors use spliced-tile magnets or magnetic ring bonding structures :1) Because of the appearance of non-magnetic phases such as adhesives, the magnetic function of magnetic ring bonding is quite low; 2) Tile sintered magnet processing process is long, material consumption is large, magnetic pole splicing gap leakage is quite large; 3) Based on the full density radiation orientation Nd-Fe-B overall permanent magnet ring, its magnetization orientation is radiating, thus forming N and S poles at both ends of the magnetic ring. It can replace many traditional square or tile magnets, streamline the motor installation process, improve the installation accuracy, and increase the smooth operation of the motor. Reasonable reduction of component volume and improvement of its performance, which realizes the intention of improving efficiency and saving energy. Take Kollmorgen integrated magnetic steel products as an example: 1) Improve the power density, the new generation of TBM2G frameless motor compared with the previous generation of TBM products, power increased by more than 70%, power density increased by more than 80%, so that the torque increase can be as high as 45%; 2) The increase in the inner diameter increases the diameter of the torque arm and further improves the valuable space inside the motor.