With the increasing popularity of automobile automatic driving and the increasing demand for electric power steering system, the steering shaft electric power steering gear is the most cost-effective and widely used type of electric steering gear in electric steering, in which the torsion bar structure is an essential component. When the steering wheel is rotated, the steering shaft drives the output shaft to rotate through the torsion bar connecting the input shaft and output shaft of the steering gear, The difference between the rotation angle of the motor and the rotation angle of the steering wheel can be judged by the rotation angle of the motor.