Planetary gear reducer:
The main transmission structure consists of planetary gears, a sun gear, and an external gear ring.
Due to their structure, planetary gear reducers have a minimum single-stage reduction of 3 and a maximum of generally no more than 10. Common reduction ratios are 3, 4, 5, 6, 8, and 10. The number of gear reducer stages generally does not exceed 3, but some custom-made gear reducers with large reduction ratios have 4 stages.
Compared to other speed reducers , planetary speed reducers have the characteristics of high rigidity, high precision (single-stage can achieve within 1 minute), high transmission efficiency (single-stage is 97%-98%), high torque/volume ratio, and lifetime maintenance-free operation.
Because of these characteristics, planetary gear reducers are mostly installed on stepper motors and servo motors to reduce speed, increase torque, and match inertia.
The rated input speed of the reducer can reach up to 18,000 rpm (related to the size of the reducer itself; the larger the reducer, the lower the rated input speed). The output torque of industrial-grade planetary reducers generally does not exceed 2,000 Nm, while specially made ultra-high torque planetary reducers can reach over 10,000 Nm. The operating temperature is generally around -25℃ to 100℃, and its operating temperature can be changed by changing the lubricating grease.
Several concepts about planetary gear reducers:
Number of stages: The number of sets of planetary gears. Since one set of planetary gears may not be sufficient for a large transmission ratio, sometimes two or three sets are needed to meet the requirements of a larger transmission ratio. Due to the increased number of planetary gears, the length of a 2-stage or 3-stage reducer will increase, and its efficiency will decrease.
Backlash: With the output end fixed, the input end is rotated clockwise and counterclockwise to produce a torque of ±2% of the rated torque. The resulting small angular displacement at the input end of the reducer is called the backlash. The unit is 'minute', which is one-sixtieth of a degree. It is also sometimes referred to as backlash.
Planetary cycloidal pinwheel reducer: The entire transmission device can be divided into three parts: input section, reduction section, and output section. A double eccentric sleeve with a 180° offset is mounted on the input shaft. Two roller bearings, called swing arms, are mounted on the eccentric sleeve, forming an H-mechanism. The central holes of the two cycloidal wheels serve as the raceways for the swing arm bearings on the eccentric sleeve. The cycloidal wheels mesh with a set of annularly arranged pin teeth on the pin gear, forming an internal meshing reduction mechanism with a tooth difference of one tooth. (To reduce friction, in reducers with small speed ratios, the pin teeth are fitted with pin tooth sleeves). When the input shaft rotates one revolution with the eccentric sleeve, due to the characteristics of the tooth profile curve of the cycloidal wheels and the restriction by the pin teeth on the pin gear, the motion of the cycloidal wheels becomes a planar motion involving both revolution and rotation. When the input shaft rotates one revolution, the eccentric sleeve also rotates one revolution, and the cycloidal wheels rotate one tooth in the opposite direction, thus achieving reduction. Then, with the help of the W-output mechanism, the low-speed rotational motion of the cycloidal wheels is transmitted to the output shaft through a pin, thereby obtaining a lower output speed.
Features of cycloidal pinwheel reducer
A high-speed ratio and high-efficiency single-stage transmission can achieve a reduction ratio of 1:87 with an efficiency of over 90%. If a multi-stage transmission is used, the reduction ratio can be even greater.
The compact structure and small size are achieved by using the planetary transmission principle, with the input and output shafts on the same axis, making the model as small as possible.
The smooth operation and low noise of the cycloidal pin teeth, along with their large number of meshing teeth, high overlap coefficient, and mechanism for balancing components, minimize vibration and noise.
Reliable and long-lasting, its main components are made of high-carbon chromium steel and hardened (HRC58～62) to achieve high strength. Furthermore, some transmission connections utilize rolling friction, resulting in durability and a long service life. The design is reasonable, easy to maintain, and readily disassembled for easy assembly, requiring minimal parts and simple lubrication.
