Here: as safety device of CNC machining centers. With the help of a light barrier, the operator shall be prevented from entering certain areas while the machine is working and thus risking to get injuries from the collision with moving machinery parts.

Mode of Operation:

• For a light barrier, a source of light (usually infrared light, or laser) on one side and a recipient made of a light-sensitive electric element (photo transistor) on the other side is necessary. Once the light beam between these two elements is interrupted, the photo transistor activates a switch (usually an emergency stop for safety devices on machines).
• To monitor an area in front of the machine, a configuration of several light barriers in a row is necessary, since a single light barrier is always only one line.
• Light barriers can also be used in alternating field processing. Here, two pairs of light barriers (one on the left and one on the right) are used. In the central region, the respective counterpart (light source or photo transistor) need to be located. Thus, this area is permanently not to be entered.

Advantages:

• Simple and cost-effective security system.

Disadvantages:

• More space is required, since the light source and the receiver have to be installed on both sides of the machine; under certain circumstances, there might be an obstruction for feeding and unloading the machine - especially for machines with alternating field processing.