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Ts
Stop time of the machine tool measured at the final control
element.
Tc
Response time of the control system
T
and T
are usually measured by a stop time measuring device.
s
c
Tr
Response time of the presence sensing device (safety light curtain)
and its interface, if any. This value is generally stated by the device
manufacturer or it can be measured by the user.
Tbm Additional time allowed for the brake monitor to compensate for
variations in normal stopping time.
Dpf Depth penetration factor. It is an added distance to allow for how
far into the protective field an object, such as a finger or hand, can
travel before being detected. D
curtain's object sensitivity. Object sensitivity is the smallest
diameter object which will always be detected anywhere in the
sensing field.
Example:
In opto-electronic safeguarding, such as with a perpendicular safety light
curtain applications with object sensitivity (effective resolution) less than
2.5 inches, the D
can be approximated based on the following formula:
pf
D
(inches) = 3.4 × (Object Sensitivity – 0.276),
pf
but not less than 0.
European Safety Distance Formula
A safety distance must be maintained between the light curtain and the
point of danger. This safety distance ensures that the point of danger can
only be reached after the dangerous state of the machine has been
completely removed.
The safety distance as defined in EN ISO 13855 and EN ISO 13857
depends on:
• Stopping/run-down time of the machine or system. (The
stopping/run-down time is shown in the machine documentation
or must be determined by taking a measurement.)
• Response time of the protective device, e.g. GuardShield Safe 2
(for "Response Time" see page 6).
• Reach or approach speed.
• Resolution of the light curtain and/or beam separation.
Safety distance S (D
s
Protective field height
Distance to avoid standing behind
the safety curtain ≤75mm
Figure 3: Safety distance from the point of danger
R
is related to the safety light
pf
)
Point
of
danger
Original instructions
GuardShield™ Safe 2 Safety Light Curtain User Manual
How to Calculate the Safety Distance S for GuardShield Safe 2 Systems
with a resolution ≤40 mm. According to EN ISO 13855 and EN ISO 13857:
-> First, calculate S using the following formula:
S = 2000 × T + 8 × (d – 14) [mm]
Where ...
T = stopping/run-down time of the machine
+ response time of the protective device [s]
d
= resolution of the light curtain [mm]
S
= safety distance [mm]
The reach/approach speed is already included in the formula.
-> If the result S is ≤ 500 mm (19.6 in.), then use the determined
value as the safety distance.
-> If the result S is > 500 mm (19.6 in.), then recalculate S as follows:
S = 1600 × T + 8 × (d – 14) [mm]
-> If the new value S is > 500 mm (19.6 in.), then use the newly
determined value as the minimum safety distance.
-> If the new value S is ≤ 500 mm (19.6 in.), then use 500 mm
(19.6 in.) as the safety distance.
Example:
Stopping/run-down time of the machine = 290 ms
Response time = 30 ms
Resolution of the light curtain = ___ mm (____ in.)
T = 290 ms + 30 ms = 320 ms = 0.32 s
S = 2000 × 0.32 + 8 × (14 – 14) = 640 mm (25.1 in.)
S > 500 mm, therefore:
S = 1600 × 0.32 + 8 × (14 – 14) = 512 mm (20.1 in.)
How to Calculate the Safety Distance S for
GuardShield Safe 2 PAC Systems
In the case of perimeter systems or light curtains with a resolution d > 40
mm, the safety distance is calculated for vertical mounting light curtains
and horizontal approach, according to the formula:
S = 1.6 mm/ms x T + 850 mm
More detailed information regarding safety distance and safety heights
can be found in standard EN 13855 (2010).
Minimum Distance from Reflecting Surfaces
The infrared light from the sender may be reflected off of shiny surfaces
and be received by the system's receiver. If this condition occurs, it can
result in an object not being detected when it enters the GuardShield
Safe 2 sensing field.
All reflecting surfaces and objects (e.g. material bins) must therefore be
located at a minimum distance a from the protective field of the system.
The minimum distance a depends on the distance D between sender and
receiver.
7
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