In the working process of mechanical presses, reciprocating piston compressors, and internal combustion engines, the driving force and process resistance often change periodically. For a certain working cycle of a machine, because the driving force does work and the resistance does work equally, the machine can maintain a stable operation, but the equivalent driving torque and the equivalent resistance torque on the main shaft are not always equal during a stable operation. When the equivalent drive torque is greater than or less than the equivalent drag torque, "surplus work" or "loss work" occurs, and the increase or decrease in kinetic energy will cause the machine to accelerate or decelerate, thus causing periodic fluctuations in speed. The fluctuation of speed in the process of mechanically stable operation will affect the quality of the mechanical process. For example, the rotational speed fluctuation of the main shaft of the alternator driven by the diesel engine may cause the AC voltage waveform to be distorted; the speed fluctuation of the shearing machine driven by the AC motor may cause the working condition of the motor to deteriorate. The maximum, minimum, and average angular velocity of the spindle are represented by ωmax, ωmin, and ωm, respectively. The non-uniform velocity coefficient δ=(ωmax-ωmin)/ωm can be used as an index to measure the uniformity of the rotation speed. The non-uniform coefficient of allowable speed for certain machines is shown in the attached table.