Three-phase asynchronous motor stroke control circuit

Stroke control is a control method that issues instructions according to the distance moved by moving parts. It is widely used in production. For example, moving
parts (such as machine tool worktables) move left, right, up, and down, including stroke control, Automatic reversal, reciprocating cycle, terminal limit protection, etc. Stroke
control is achieved with a stroke switch .
    (1>! The stroke switch (also called the limit switch) is a device that operates according to the stroke signal of the production machinery. Its structure
and working principle are similar to those of the button. It also has moving and closing contacts and moving and breaking contacts. .The travel switch, like the button, must be connected in the control circuit.
  The travel switch is installed on a fixed base. When it collides with the impact block installed on the moving parts of the production machinery controlled by it, the impact block presses the
travel switch. The roller will send out a contact on or off signal. When the impact block leaves, some travel switches automatically reset (such as single-wheel rotary type), while some
travel switches cannot automatically reset (such as two-wheel rotary type). The latter It must rely on a secondary collision in the other direction to reset.
    (2) Principle of stroke control circuit The stroke control circuit is shown in Figure 4-7a. It is basically a motor forward and reverse rotation control circuit.
The motor rotates forward and reverse. Drive the moving parts forward and backward. The installation positions of the impact blocks 1 and 2 on the moving parts and the travel switches ST1~ST4
are shown in Figure 4-7b. ST1 and STZ are compound travel switches with a moving contact and a The moving contact, sn, is used to cut off the forward control circuit and
close the reverse control circuit f. Correspondingly, ST2 is used to cut off the reverse control circuit and close the forward control circuit. In this way, the limit switch is in the impact of the impact blocks 1 and
2. down, the motor can be controlled to rotate forward and reverse, driving the moving parts forward and backward. The travel switches ST3 and ST4 have a movable contact
t. When the impact block hits the travel switch ST1 or STZ, and ST1 or ST2 does not move due to a fault , the moving parts continue to move in the original direction
, causing the impact block to hit ST3 or ST4. The control circuit is cut off and the motor is stopped, thus playing the role of terminal limit protection.