What is A Safety Light Curtain?

Figure 1: Safety light curtain.
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1. Overview

Safety light curtain is a safety certified light curtain product, which is composed of two parts-light sender and light receiver. The sender emits modulated infrared light, which is received by the light receiver to form a protection network. When an object enters the protection network and light is blocked by the object, the light receiver circuit responds immediately through the internal control line, that is, a signal is output for the emergency braking of machine tools such as punch press and press.

Figure 2: Light sender and light receiver.

The light curtain has a very wide range of applications. For example, on the stamping equipment that needs continuous feeding and reclaiming, if the contact safety protection door is installed, the operator needs to open and close the protection door frequently, which not only increases the workload of the operator, but also reduces the production efficiency. In this case, using safety light curtain is the best choice. When the operator is feeding and reclaiming materials, as long as any part of the body blocks the light, the machine will enter a safe state without injury to the operator.

2. Principle

A plurality of infrared transmitting tubes are installed on one side of the safety light curtain, and the same number of infrared receiving tubes are arranged on the other side. Each infrared transmitting tube has a corresponding infrared receiving tube, and they are installed on the same straight line. When there is no obstacle between the infrared transmitting tube and the infrared receiving tube on the same straight line, the modulation signal (optical signal) sent by the infrared transmitting tube can reach the infrared receiving tube smoothly. After the infrared receiving tube receives the modulation signal, the corresponding internal circuit outputs a low level. In the case of obstacles, the modulation signal (optical signal) sent by the infrared transmitting tube cannot reach the infrared receiving tube smoothly. At this time, the infrared receiving tube cannot receive the modulation signal, and the corresponding internal circuit output is high level. When no object passes through the light curtain, the modulation signal (optical signal) sent by all infrared transmitting tubes can smoothly reach the corresponding infrared receiving tube on the other side, so that all internal circuits output low level. In this way, the information of whether the object exists or not can be detected by analyzing the internal circuit state.

Figure 3: Infrared transmitting tube and infrared receiving tube.

The safety light curtain is divided into linear scanning mode and cross scanning mode. In the linear scanning mode, the MCU sends the same signal to the sender and receiver every time. That is, the first route sends and the first route receives, the second route sends and the second route receives,... The fifteenth route sends and the fifteenth route receives, the sixteenth route sends and the sixteenth route receives. In the cross scan mode, the MCU sends different signals to the sender and receiver each time. That is, the first route sends the second route receives, the second route sends the first route receives,... The 15th route sends the 16th route receives, the 16th route sends the 15th route receives. In contrast, the cross scan mode is more accurate in measuring the height of objects. However, considering the actual needs, the safety light curtain of linear scanning mode is widely used now.

3. Operation Steps

1. Check whether the safety light curtain is firmly fixed on the equipment to be equipped, whether the sender and receiver are in the same plane. And the protection area bounded by the sender and receiver should be a rectangle in the plane

2. Check whether the sender and receiver are accurately assembled with their respective cables. Check whether the terminal of the cable is accurately and firmly connected with the power supply and control unit.

3. Power on the safety light curtain sensor. At this time, the light curtain sensor starts self inspection, synchronization and self calibration. After about 1 second, the yellow indicator of the sender will be stable and all the indicators of the receiver are off indicating that the light curtain sensor is in normal working state.

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