Use of Safety Light Curtain

Figure 1: Safety light curtain.
(Go to Okmarts and pick the Safety light curtain you need)

The safety light curtain is essentially an electric sensitive protection device.

1.Electric Sensitive Protection Equipment

The electric sensitive protection equipment can play the role of protection tripping or induction, and its composition at least includes:

--A sensing device;

--Control / monitoring devices;

--Output signal switching device.

In general, the function of our light curtain and grating is to control the equipment to stop running through our PLC program to ensure safety when an object intrusion is detected.

Figure 2: Structure of the safety light curtain.

2.Usage Scenario of Safety Light Curtain

Generally, the safety light curtain is applicable to the situation that people / limbs need to enter the dangerous area frequently during the operation time.

We can consider whether to install fixed protective devices or protective devices with safety interlock if we enter infrequently.

Figure 3: Protective devices with safety interlock.

3.Resolution of Safety Light Curtain

There is an effective optical resolution for sensing equipment to obtain detection capability:

• finger protection, 14 mm

• hand protection, ≤ 30 mm

• arm protection, ≤ 40 mm

• body protection: ≤ 200mm

We can find this information on the light curtain as follows.

Figure 4: Resolution of the light curtain.

4.Safety Distance Between Light Curtain and Dangerous Area

The meaning of safe distance. We all know that there is a response time for the installation of all protective devices. The purpose of setting a safety distance is to avoid the situation that the human body has reached the dangerous area, but the equipment still fails to stop due to the insufficient response speed of the equipment.

First of all, the distance between the light curtain and the dangerous area should not be less than 100mm, which is the minimum standard. The rest we need to calculate.

The calculation formula is: S = (K * T) + C

S is the distance from the light curtain to the nearest dangerous point, in millimeters. The parameter K is the speed of the body in mm / s.

Approaching speed of finger= 2m /s

Approaching speed of limbs = 1.6m/s

T is the response time of the whole system, in seconds (this time depends on the response time of each component, including light curtain, PLC, action mechanism, etc.). T = T1 + T2 + T3. The response time can be found in the product manual or directly obtained from the manufacturer.

C is the intrusion distance, in millimeters, depending on the resolution of the light curtain grating. In case of finger or hand detection:

C = 8 x (d-14mm)

d (d≤ 40mm) is the resolution of light curtain grating.

Figure 5: Safety distance of the devices.

If the calculated minimum protection distance is less than 100mm, the design distance shall be 100mm;

If the calculated minimum protection distance is greater than 100mm, the design distance shall be at least in accordance with the minimum protection distance.

If the minimum protection distance cannot be met, a two handed start button needs to be added.

In addition, when installing the equipment, we should fully consider and avoid personnel bypassing the light curtain to enter the dangerous area.

Related Info