The robot joint module is the core execution unit of industrial robots, responsible for key functions such as power transmission, attitude adjustment, and precision control. Its composition directly determines the robot's load capacity, motion accuracy, response speed, and reliability. Industrial grade joint modules are usually designed in an integrated manner (different from civilian or research grade split structures), and their core components can be divided into four modules: mechanical structure, drive system, sensing feedback system, lubrication and protection system. Each module works together to achieve a complete closed-loop of "power input motion conversion precision control". The following is a detailed disassembly:
1, Mechanical structure module (core load-bearing and motion transmission)
The mechanical structure is the physical foundation of the joint module, which needs to meet the three requirements of "high rigidity, lightweight, and high-precision transmission" simultaneously. The core components include:
1. Harmonic reducer/RV reducer (core transmission component)
Function: Convert the high-speed low torque output of the motor into low-speed high torque, while ensuring transmission accuracy and rigidity. It is the "power amplification core" of the joint module.
Types and application scenarios:
Harmonic reducer: composed of a wave generator, flexible wheels, and rigid wheels, with a transmission ratio range of 50-320 and a return clearance of ≤ 1 arc minute. It is lightweight, compact in structure, and suitable for joints such as the forearm and wrist of small and medium-sized load robots (with a load of 10-50kg);
RV reducer: composed of cycloidal pinwheel, planetary carrier, and needle gear housing, with a transmission ratio range of 30-120 and a return clearance of ≤ 0.5 arc minutes. It has strong rigidity and outstanding impact resistance, and is suitable for key joints such as the base, boom, and shoulders of heavy-duty robots (with a load of over 50kg).
2. Motor output shaft and coupling
Motor output shaft: made of high-strength alloy steel, surface treated with carburizing and quenching to ensure wear resistance and torsional strength, rigidly connected to the input end of the reducer;
Coupling: Used to compensate for the coaxiality error between the motor shaft and the input shaft of the reducer, it is divided into rigid couplings (such as key connections, expansion sleeves) and elastic couplings (such as rubber pads, corrugated tube types). Rigid couplings are commonly used in industrial robots to avoid transmission lag.
3. Shell and installation flange
Shell: Made of aluminum alloy, aluminum alloy is suitable for lightweight requirements, and cast iron is suitable for high rigidity scenarios; The internal design of the shell includes a reducer installation chamber, a motor installation seat, a sensor installation groove, and external reserved heat dissipation ribs and sealing grooves;
Installation flange: Using standard interfaces for connecting joint modules and robot arm segments, the flange surface is precision machined (flatness ≤ 0.01mm) to ensure installation accuracy.
4. Output shaft and bearing components
Output shaft: connected to the output end of the reducer, used to transmit torque to the robot arm section, the surface needs to be precision machined, and the end is designed with keyway, threaded hole or expansion sleeve interface;
Bearing components: Cross roller bearings or harmonic bearings are usually used. Cross roller bearings have strong load-bearing capacity (radial+axial composite load) and high rigidity. Harmonic bearings are suitable for matching harmonic reducers, and the accuracy level of the bearings needs to reach P4 or above to ensure joint rotation accuracy.
2, Drive system module (power output and control core)
The drive system provides power to the joint module, achieving precise adjustment of speed and torque. The core components include:
1. Servo motor (power source)
Type: The joint modules of industrial robots all use permanent magnet synchronous servo motors, which have the characteristics of high power density, high response speed, low inertia, etc. According to the installation method, they are divided into internal type (the motor and reducer are integrated into the housing) and external type (the motor is connected to the housing through a flange);
Key parameters: rated power (100W-15kW), rated speed (3000-6000rpm), rotor inertia (0.01-0.5kg · m ²), torque constant (0.1-5N · m/A), to be matched with the gearbox transmission ratio (motor output torque x transmission ratio=joint output torque).
2. Servo drive (control unit)
Function: Receive control instructions (position, speed, torque signals) from the upper computer (robot controller), output PWM signals through PID regulation to drive the servo motor to operate, and achieve protection functions such as overcurrent, overvoltage, overload, and overheating;
Core technology: Supports position mode (controlling joint rotation angle), speed mode (controlling joint speed), and torque mode (controlling output torque). Some high-end drivers integrate electronic gearboxes, vibration suppression, and adaptive control algorithms to improve motion smoothness and accuracy.
3. Power cables and interfaces
Power cable: It transmits the three-phase power supply (U/V/W) and brake signals of the servo motor, using flexible cables (with a bending resistance of ≥ 10 million times), and the outer skin material is PVC or PUR, with oil resistance, wear resistance, and anti-interference characteristics;
Interface: Adopting industrial standard interface, the power interface and signal interface are designed separately to avoid electromagnetic interference.
3, Sensor feedback system module (precision control and status monitoring)
The sensor feedback system collects real-time data on joint position, velocity, torque, etc., providing a basis for closed-loop control and is the key to ensuring robot motion accuracy. The core components include:
1. Position sensor (core feedback component)
Type: The mainstream adopts absolute value encoders, which are divided into photoelectric, magneto electric, and capacitive types. In industrial robots, photoelectric absolute value encoders are mainly used (resolution ≥ 17 bits, some high-end products up to 25 bits);
Installation method: directly installed at the tail of the servo motor (to detect the motor speed), or coupled through the output shaft of the reducer (to directly detect the actual position of the joint and eliminate transmission errors);
Function: Real time output of absolute position information (angle value) of joints. The upper computer calculates the position error based on this data and adjusts the operation status of the servo motor to ensure joint positioning accuracy (repeated positioning accuracy ≤ ± 0.02mm).
2. Speed sensor
Usually integrated with position sensors (such as the speed measurement function of encoders), the joint speed is calculated by detecting the frequency of the encoder pulse signal. Some high-end joint modules will additionally install Hall sensors or speed generators to improve the speed detection accuracy during low-speed operation.
3. Torque sensor (optional component)
Function: Detect the output torque of joints for load monitoring, collision detection, and force control operations (such as assembly and polishing);
Types: Strain gauge, magneto elastic, and optical. Strain gauge torque sensors have low cost and high accuracy (± 0.5% FS), and are the mainstream choice for industrial robots. They are installed between the output shaft and arm section or inside the reducer.
4. Temperature sensors and vibration sensors
Temperature sensor: installed on the motor winding and reducer housing to detect component temperature. When the temperature exceeds the threshold (usually 80-100 ℃), the servo drive triggers overheating protection;
Vibration sensor: using an acceleration sensor to detect the vibration amplitude and frequency during joint operation, used for fault warning (such as reducer wear, bearing damage), only configured in high-end industrial robot joint modules.
4, Lubrication and protection system module (reliability assurance)
The lubrication and protection system is used to extend the service life of joint modules and adapt to harsh environments in industrial sites. The core components include:
1. Lubrication components
Lubricant: special grease with high viscosity index, anti-wear and anti-aging characteristics is used for reducer, and lubricating oil or grease is used for motor bearing;
Lubrication structure: The reducer is designed with oil injection holes and oil discharge holes inside, and some high-end products are equipped with automatic lubrication systems (timed and quantitative oil injection). A lubricating grease observation window is reserved outside the housing for easy maintenance.
2. Sealing components
Static sealing: using O-ring and flat gasket for the connection between the shell and flange, motor and shell, to prevent lubricating oil leakage and dust from entering;
Dynamic sealing: using skeleton oil seals and V-shaped sealing rings, used for the rotating parts of the output shaft and housing. Skeleton oil seals are suitable for medium and low-speed scenarios.
3. Protective coating and heat dissipation structure
Protective coating: The surface of the shell is treated with anodizing (aluminum alloy) and painting (cast iron), which has anti-corrosion and wear-resistant characteristics. Some products use a three proof coating (anti salt spray, anti humidity, anti mold), suitable for outdoor or harsh workshop environments;
Heat dissipation structure: The motor housing is designed with heat dissipation ribs, and some high-power joint modules are equipped with heat dissipation fans or water-cooled channels to ensure stable temperature of the motor and driver during long-term operation.