Today we talk about the belt drive, which is a mechanical transmission that utilizes a flexible belt tensioned on the pulley for movement or power transmission. According to different transmission principles, there is a friction type belt transmission driven by a friction force between the belt and the pulley, and a timing belt transmission in which the belt is in meshing engagement with the teeth on the pulley.
The stress on the belt drive is:
1, the stress caused by tight edges and loose edges
2, the stress generated by the centrifugal force
3, with bending stress on the pulley bending
According to different uses, belt drives can be divided into general industrial belts, automotive belts, belts for agricultural machinery, and belts for household appliances. Friction-type transmission belts are divided into flat belts, V-belts (also known as delta belts) and special belts (multi-ribbed belts, synchronous belts) according to their cross-sectional shapes.
When the transmission is working, the belt is put on the smooth wheel surface, and the belt and the wheel surface are used for the transmission. The transmission type has open drive, cross drive and semi-cross drive (see the figure above), and it can adapt to the different relative positions of the drive shaft and the driven shaft and different rotation directions. Flat belt drive structure is simple, but easy to slip, usually used for transmission ratio of about 3 drives.
The flexibility is good and the back of the belt can also be used to transmit power. If the angle of containment around each driven pulley is large enough, it is possible to drive several accessories of the vehicle (alternators, fans, pumps, air conditioning compressors, power steering pumps, etc.) simultaneously with one such belt. It has five types of cross-sections such as PH, PJ, PK, PL, and PM types, among which the PK type has been widely used in automobiles in recent years. This type of belt allows the use of narrower belt pulleys (diameter dmin≈45mm) than narrow belts. In order to be able to deliver the same amount of power, the belt pretensioning force is preferably increased by about 20% compared to the narrow belt.
This is a special belt drive. The working surface of the belt is formed into a tooth shape, and the rim surface of the pulley is also made into a corresponding tooth shape, and the belt is mainly driven by meshing engagement with the pulley. Synchronous toothed belts typically use a thin steel wire rope as a strong layer and are covered with a polyester or neoprene rubber. The midline of the strong layer is defined as the pitch line of the belt, and the circumference of the belt line is the nominal length. The basic parameters of the band are the week p and the modulus m. The period p is equal to the size measured along the pitch line between the corresponding points of the adjacent two teeth, and the modulus m=p/π. The synchronous toothed belt in China adopts a modular system, and its specification is represented by modulus×bandwidth×number of teeth. Note: The tooth profile is exactly perpendicular to the V-ribbed belt.
The characteristics of the synchronous toothed belt drive are:
1. The deformation of the strong layer made of steel wire is minimal after being loaded, the circumferential section of the toothed belt is basically unchanged, there is no relative sliding between the belt and the pulley, and the transmission ratio is constant and accurate;
2. The toothed belt is thin and light, which can be used in high speed applications. The transmission speed can reach 40m/s, the transmission ratio can reach 10, and the transmission efficiency can reach 98%.
3 compact structure, good wear resistance;
4. Because of the small pretension, the bearing capacity is also small; the manufacturing and installation precision requirements are very high, and a strict center distance is required, so the cost is high. Synchronous toothed belt drives are mainly used in applications where accurate transmission ratios are required, such as external equipment in computers, movie projectors, video recorders, and textile machinery.
V band (triangular belt)
The V-belt is also the belt drive that most of our robots usually use. When the V-belt drive is working, the belt is placed in the corresponding groove on the pulley, and the belt is driven by the friction between the two walls of the groove. The V-belt is usually a number of pieces and the corresponding number of grooves on the pulley. With the V-belt drive, the belt is in good contact with the wheel, the skid is small, the transmission ratio is relatively stable, and the operation is stable. The V-belt drive is suitable for applications where the center-to-center distance is short and the transmission ratio is large (7 or so). It can also work well in both vertical and inclined drives. In addition, due to the combined use of several V-belts, one of the damages will not cause an accident.