The helical rack drives the "mobile station" to move up and down. When it is necessary to stop, as long as the clutch is disconnected (operating), the mobile station stops moving and the motor keeps running.

The helical rack mechanism cannot be self-locking. In order to prevent the mobile station from falling under the load (gravity) after the clutch is disconnected, an accident is caused, so the brake is added.

The start switch LS1 and the stop switch LS2 form a start-stop self-locking loop, and the control relay coil has an output clutch; the relay normally closed contact is connected to the brake, and the normally closed contact is connected in parallel with the start-stop self-locking loop.

There are several ways to eliminate the helical rack clearance:

When the feed force is not large, a double-sliced ​​gear structure similar to that in the spur gear transmission can be used to eliminate the gap by the method of wrong teeth;

When the feed force is large, the transmission structure of the double thick gear is usually adopted. The feed motion is input by the shaft 2, and the motion is transmitted to the shaft 1 and the shaft 3 through the two pairs of helical gears, and then the two spur gears 4 and 5 are used to drive the rack to drive the table to move. The spiral of the two helical gears on the shaft 2 is opposite in direction. If an axial force F is applied to the shaft 2 by the spring, a slight axial movement of the helical gear is produced, at which time the shaft 1 and the shaft 3 are rotated by a slight angle in opposite directions, so that the gears 4 and 5 are respectively toothed The two tooth faces of the strip are in close contact, eliminating the gap.