Hall element is a magneto-sensitive element that performs magnetoelectric conversion according to Hall effect, and its typical working schematic diagram is shown in the figure. The Hall element is an N-type semiconductor wafer. If the control current I is applied to two opposite sides of the wafer and a magnetic field is applied in the vertical direction of the wafer, a voltage will be generated on the other two sides of the semiconductor, and the amplitude of the voltage is proportional to the product of the current and the magnetic field B. This phenomenon is the Hall effect.

The four-station electric tool rest receives the command in the form of pulsed electric waves, and one end of the four-station electric tool rest is provided with a worm tool rest with a turbine, and two stops are arranged on the contact surface of the base. Under normal circumstances, when the two end gears are engaged, the base is equipped with a motor and a coupling worm. When the tool change instruction is received, the motor rotates the worm forward to drive the turbine, and at the same time, the worm of the tool rest rotates, so that when the tool rest rises to a certain extent, the gear at the tool rest end rises and separates. When the tool holder rotates 90 degrees with the tool holder worm, it meets the stop. When the stopping force of the motor reaches a certain level, it starts to reverse. The natural tool rest descends at the end face of the base, and the gear engages and locks with the stopper to complete the tool change.