Controlling noise mainly starts from two aspects: first, finding ways to eliminate or weaken the intensity of the sound source, which is the fundamental method of controlling noise and the focus of this article; The second is to take measures such as sound absorption and insulation from the transmission path of noise to weaken or shield the propagation of noise. There are two main sources of noise in synchronous belt transmission: one is due to the excitation of unbalanced centrifugal force when the two belts rotate, and the other is due to the disturbance of gas caused by the meshing of the belt and pulley, resulting in aerodynamic noise. The main factors causing noise in two aspects are listed below.

1. Main factors causing rotational imbalance

(1) The shape tolerance and position tolerance of the pulley itself, including the tooth profile tolerance, tooth thickness tolerance, and axial and radial runout of the pulley. The higher the manufacturing accuracy of the belt and pulley, the smaller the impact during meshing, and the higher the precision of synchronous belt transmission, the lower the noise is bound to be. Due to the fact that both the synchronous belt and pulley are produced by professional manufacturers, the manufacturing accuracy can be effectively controlled, and will not be further elaborated here.

Parallelism of two wheel axles: Generally, as the parallelism error increases, the sound pressure level gradually increases. Therefore, when installing the spindle axis and the motor axis, the parallelism of the installation should be ensured, and the parallelism of the two axes should be limited to (0.003-0.005) c (c is the center distance between the two belt wheel axles).

(2) Rotation accuracy of two belt wheel axles

Due to the high-speed rotation required by both pulleys, with a rotation speed of over 6000r/min, if dynamic balancing is not carried out, the unbalanced centrifugal force during high-speed rotation will cause vibration between the main shaft and the motor shaft, thereby exciting strong noise. For most manufacturers, only dynamic balancing is performed during the manufacturing and assembly of the main shaft (including the pulley), and the motor shaft must also undergo dynamic balancing. The pulley is installed on the motor shaft, and the entire rotating shaft is tested using a linear dynamic balancing instrument and material removal method is used for dynamic balancing (drilling holes on the pulley). The final dynamic balancing accuracy level is required to reach G2.5. After this treatment, the vibration and noise of the transmission can be reduced to varying degrees, which is also very beneficial for improving the service life of synchronous belts and spindles.

(3) Pre tensioning force of synchronous belt

Unlike flat belts and V-belts, synchronous belts rely on toothed meshing to transmit power, so they do not require a large amount of pre tension. Excessive tension will seriously affect the service life of the belt and produce serious noise. Under the action of starting and impact torque, too little tension may cause the synchronous belt to jump teeth, resulting in tooth root fracture. The most accurate method for selecting the appropriate tension is to use an ultrasonic tension tester. If there is no tester, a simple fixture can be self-made and measured as follows: as shown in Figure 1, apply a test force on one side of the rear belt near the center of the two pulleys, and the belt will bend inward to produce a deformation d. If d=S/64 (s is the single measured length of the belt, unit: mm), it can be considered that the tension of the belt is appropriate. Otherwise, adjust the tension of the belt until it is appropriate, as shown in the schematic diagram of pulley tension calculation in Figure 1. The value of d varies with the type and bandwidth of the belt, and specific information can be found. For example, for a 40mm wide 8YU (8M) synchronous belt, d is set to 39N. Experimental results have shown that appropriate tension can significantly reduce high-frequency noise, commonly known as "whistling".