In the robot joint precision reducer Selection, accuracy and backlash are the core indicators that determine the robot"s motion quality, positioning accuracy and dynamic response. To scientifically select these two parameters, it is recommended to consider the following dimensions:
1. Clarify core concepts and application requirements
Backlash (backlash) refers to the tiny angular displacement produced by the output end when a small rated torque in the forward and reverse directions is applied to the output end when the input end is fixed. The unit is arcmin (arcmin, 1 degree = 60 arc minutes). The lower the backlash value, the more accurate the transmission, but the corresponding cost is also higher.
The first step in selection is to back-calculate the required accuracy level based on the robot’s application scenario:
Extremely high-precision scenarios (such as medical surgical robots, semiconductor equipment, precision assembly): Micron-level positioning is required, and a reducer with close to zero backlash must be selected. Harmonic reducers and RV reducers are the first choice, and their backlash is usually ≤1 arc minute, and can even reach the arc second level.
High-precision scenarios (such as six-axis robotic arms, collaborative robot wrists/elbows): require smooth and accurate trajectory tracking, and the backlash is generally required to be between 1 and 3 arc minutes. This type of light-load or medium-load precision joints are usually adapted to harmonic reducers.
Heavy-load and highly dynamic scenarios (such as humanoid robot hip/knee joints, palletizing robots): need to bear the weight of the entire machine, frequent starts and stops, and impact loads. The requirements for absolute accuracy can be appropriately relaxed to 3~5 arc minutes or even higher. At this time, priority should be given to planetary reducers or RV reducers with strong impact resistance and long life.
2. Evaluate the technical characteristics of different reducers
Different types of reducers have essential differences in accuracy and backlash performance, and their physical characteristics need to be matched when Selection:
Harmonic reducer: Relying on the elastic deformation of the flexspline to achieve simultaneous meshing of multiple teeth, it is born with "zero backlash" characteristics, high repeatability positioning accuracy, and small size. However, its limitation is that its impact resistance is weak, and the flexspline is prone to fatigue wear under long-term heavy load, resulting in increased backlash.
RV reducer: It adopts a double cycloid pin tooth structure, which is extremely rigid and impact resistant, with ultra-high precision and long life. It is suitable for the dual requirements of heavy load + high precision such as base joints, but the cost and weight are relatively high.
Planetary reducer: Relying on multi-stage gear pairs in series, each meshing point will accumulate a small gap, so the backlash is usually 3-5 arc minutes and above. Although the ultimate accuracy is not as good as the first two, it has excellent performance in terms of large torque output, heat dissipation and high duty cycle, and has outstanding cost performance.
3. Pay attention to the impact of dynamic working conditions and actual installation
The ideal parameters on the sample are often compromised in actual applications, and the following engineering variables must be considered when selecting:
1. Dynamic response and torsional stiffness: In high-speed reciprocating motion, a reducer with a large inertia moment will cause dynamic response lag. In addition to static backlash, you also need to pay attention to torsional stiffness. Excessive flexibility will weaken the system rigidity, cause vibration and reduce servo performance.
2. Thermal expansion effect: The temperature rise caused by continuous operation will cause thermal expansion of internal parts, thus changing the size of the backlash. For example, a harmonic reducer generates heat due to internal friction, and the accuracy decrease after temperature rise may be greater than that of a planetary reducer. Under high temperature or long-term continuous operation conditions, it is necessary to reserve an accuracy margin or increase active heat dissipation design.
3. Installation error amplification: The accuracy of the reducer is measured under ideal coaxiality. In actual assembly, the eccentricity or uneven mounting surface of the input shaft of the motor and reducer will significantly increase the backlash (excessive deviation can increase the backlash by more than 30%), and this error will be multiplied by the reduction ratio.
