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# How to calculate safety distance of safety light curtain?

Safety light curtain is a safety device to protect personal safety from damages. And personal safety here refers to finger, palm and arm. As when the machine is running, operators will often place their hands in dangerous areas.
According to characteristics of human body, ATO safety light curtain includes 10mm/14mm (finger protection), 20mm/25mm (palm protection) and 30mm/40mm (arm and human body protection) as per distance of optical axis. Once human body or certain part of human body intrudes into the range of safety light curtain and touches the optical axis, machine will stop. Customers can select a concrete type by practical production situations.

In practical application, after human body intrudes into the range of safety light curtain, besides that safety light curtain needs certain response time, the machine also needs certain braking time. Therefore, to guarantee personal safety of operators, installation position of safety light curtain must meet requirements of safety distance. Otherwise, there is still the possibility of an accident.

Then, how to calculate safety distance correctly?
First, we should know that safety distance refers to the minimum distance between light curtain plane and mould cutting edge, and calculating method should be decided according to braking mode of press machine, or take a reference from the chart below:

1. For press machine whose sliding block can stop at any position, safe distance should be calculated according to formula 1.
Formula 1: Ds=1.6(T1+Tz)
In the formula: Ds is safe distance, unit (m) 1.6 is the stretching speed of human hand, unit (m/s).
T1 is the response time of safety light curtain, 0.02 (s).
Tz is the braking time of press machine, the time from machine perception to slicing block stop, unit (s), calculated according to practical braking situation.

2. For press machine whose slicing block cannot stop at any position, safe distance should be calculating according to formula 2.
Formula 2: Ds=1.6Ts
In the formula: Ds is safe distance, unit (m).
1.6 is the stretching speed of human hand, unit (m/s).
Ts is the time from human hand leaving light curtain (sliding block is allowed to start) to sliding block of press machine reaching to the bottom dead centre, unit (s), that is, the time of sliding block down stroke. It can be calculated according to formula 3 or practically measured.
Formula 3: Ts=(1/2+1/N)Tn
In the formula: N is the number of connecting though of clutch.
Tn is the time when crank rotates one week, unit (s).

During usage, if mould is replaced, safe distance must be readjusted. When safe distance surpasses 400mm, other auxiliary safeguard measures such as guard railing should be adopted to prevent body of operators from entering into inside of light curtain plane.