The Application of Reducer in Industrial Robots
The reducer is the "joint core" of industrial robots, which converts the high-speed and low torque output of servo motors into the low-speed and high torque required by the robot joints, and ensures the motion accuracy and rigidity of the robot through high-precision transmission. In industrial robots, the performance of the gearbox directly determines the robot's load capacity, motion accuracy, response speed, and service life.

1、 The core role of reducers in industrial robots
The joints of industrial robots (such as waist, upper arm, lower arm, wrist, etc.) need to be rotated or swung through power transmission, and the characteristics of servo motors are "high speed, low torque", which cannot directly drive joint motion. The core functions of a gearbox include:

Deceleration and torque increase: By meshing gears or mechanical structures, the motor speed is reduced (the reduction ratio is usually 10:1-100:1), while the torque is amplified by the same factor to meet the requirements of joint driven loads;

Ensuring accuracy: By using high-precision transmission structures (such as backlash free meshing) to reduce the "return clearance", the positioning accuracy of the robot's motion is ensured (usually within ± 0.01mm);

Enhancing rigidity: By using rigid structures such as high-strength gears and bearings to resist joint deformation under stress, the stability of the robot is ensured during loading or high-speed motion;

Buffer impact: Absorb the instantaneous impact between the motor and the load (such as when starting/stopping heavy objects), and protect the motor and mechanical structure.

2、 Application scenarios of different types of reducers in industrial robots
The commonly used reducers for industrial robots include RV reducers, harmonic reducers, and planetary reducers, which have significant differences in application scenarios due to their different structural characteristics.

1. RV reducer: the "main force" of heavy-duty joints
The RV reducer is composed of planetary gear transmission and cycloidal pinwheel transmission, and has the characteristics of high rigidity, high load capacity, low return clearance (≤ 1 arc minute), and long service life (usually>10000 hours). It is suitable for "heavy-duty joints" of industrial robots.

Application location:

Robot waist (base rotating joint): It bears the weight and load of the entire robot, and needs to withstand axial, radial, and overturning moments. The high rigidity and impact resistance of the RV reducer can ensure stable rotation of the waist;

Arm joint (a rotating joint connecting the waist and the upper arm): The load includes the upper arm, lower arm, wrist, and end load, and the RV reducer can provide sufficient torque to drive the swing of the upper arm;

Arm joint (a rotating joint connecting the upper arm and lower arm): It needs to drive the movement of the lower arm, wrist, and load, and the high torque output of the RV reducer can meet its power requirements.

Typical scenarios: Almost all of the 1, 2, and 3 axes (base, boom, and forearm) of six axis industrial robots use RV reducers, such as handling robots (with a load of over 50kg), welding robots (with the boom driving the welding gun to move at high speed), palletizing robots (with a load capacity of up to tons), and other heavy-duty scenarios.

2. Harmonic reducer: the "core" of lightweight high-precision joints
Harmonic reducer is composed of wave generator, flexible wheel, and rigid wheel. Its characteristics are compact structure (small volume, light weight), large transmission ratio (50:1~320:1), extremely small return clearance (≤ 0.5 arc minutes), smooth motion, but lower load capacity than RV reducer, suitable for "light load, high-precision joints".

Application location:

Wrist joint (a rotating joint connecting the forearm and wrist): It needs to drive end effectors (such as grippers and welding guns) to perform fine movements, requiring high positioning accuracy (such as wrist positioning accuracy for assembly robots requiring ± 0.005mm), and the low return clearance of the harmonic reducer can meet the requirements;

End axes (such as the 4th, 5th, and 6th axes of a six axis robot): These joint loads are relatively small (usually<50kg), but require fast response and flexible movement (such as wrist flipping of sorting robots). The compact structure of harmonic reducers can reduce joint volume and improve flexibility.

Typical scenarios: assembly robots (requiring high-precision alignment), spraying robots (flexible wrist swing), collaborative robots (lightweight design), etc. For example, in the 3C industry's mobile phone assembly robots, the harmonic reducer of the wrist joint can ensure micro meter level accuracy in screw tightening and part fitting.

3. Planetary gearbox: a supplement to auxiliary joints
The planetary reducer is driven by the meshing of the sun gear, planetary gear, and internal gear ring, and has the characteristics of high transmission efficiency (90%~98%), simple structure, and low cost. However, the return clearance is large (usually>3 arc minutes), and the rigidity is moderate, making it suitable for "auxiliary joints" or low precision demand scenarios of industrial robots.

Application location:

Linear joints of robots (such as the translation axis of slide rail robots): no rotational motion is required, only linear drive is needed, and planetary reducers can be used in conjunction with screws or racks to achieve low load, medium precision translation;

The end effector drive of lightweight robots (such as small grippers): with a load of less than 10kg and low precision requirements (within ± 0.1mm), the low-cost advantage of planetary reducers is obvious.

3、 The Influence of Reducer on the Performance of Industrial Robots
Load capacity: The load capacity of RV reducers is 3-5 times that of harmonics (for example, the rated torque of RV-80 reducers can reach 800N · m, while harmonic reducers of the same size are usually less than 200N · m), which directly determines the maximum weight that the robot can carry;

Positioning accuracy: The return clearance of the harmonic reducer (≤ 0.5 arc minutes) is much smaller than RV (≤ 1 arc minute), so the positioning accuracy of the wrist joint is higher (such as the welding gun positioning error of the welding robot needs to be less than 0.05mm, relying on the harmonic reducer);

Response speed: The harmonic reducer has a small moment of inertia, and when combined with a servo motor, it can achieve faster start stop (such as the wrist of a sorting robot flipping 3 times per second);

Life and maintenance: The gears of RV reducers have low wear and can last up to 15000 hours (about 2 years), while the flexible wheels of harmonic reducers are prone to fatigue (about 8000 hours) and need to be replaced regularly, which affects the maintenance cost of the robot.

4、 Typical application cases
Handling robot: RV reducers are used for the waist and upper arm joints (with a load of 50~500kg), and harmonic reducers are used for the wrist (to adjust the gripping angle) to ensure stable handling under heavy loads;

Assembly robot: The forearm and wrist joints are mainly equipped with harmonic reducers (accuracy ± 0.01mm) to meet the high-precision assembly of electronic components such as chips and connectors;

Collaborative robots: Due to the need for lightweight design, harmonic reducers are commonly used for all body joints (small RVs are used for some heavy-duty joints) to achieve flexible response and safe buffering when collaborating with humans.

summarize
The reducer is the "power conversion center" of industrial robots, in which the RV reducer dominates the heavy-duty joints, the harmonic reducer dominates the lightweight high-precision joints, and the planetary reducer serves as an auxiliary supplement. Its performance directly determines the "strength", "accuracy", and "durability" of the robot, and is one of the core limiting factors for the development of industrial robots towards "higher load, higher accuracy, and more compact".