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Determination of the safety distance

Calcolo distanza sicurezza
 

NotE

When calculating the safety distance, also consider installation tolerances, accuracy of the measured response time and possible decay of the brake system performance of the machine.

 

It is advisable to increase the calculated value by at least 10% in order to take into account installation tolerances, accuracy in response time and possible degradation of brake system performance.

 

As can be seen from the formulas, the total stopping time plays an important role in calculating the safety distance; When a deterioration in braking time is expected, a Stopping Time monitoring device (SPM) is required.  Checking of the stopping time is not necessary when:

  • The system is very reliable and not subject to deterioration
  • The machine is only rarely stopped
  • Effective preventive control of the braking systems of the machine is implemented.

The effectiveness of the protection depends mostly on the correct positioning of the light curtain with respect to the danger.

 

The light curtain must be located at a distance greater or equal to the minimum safety distance, S, so that reaching the dangerous point will be possible only when the dangerous action of the machine has been stopped.

 

The light curtain must be positioned so that:

  • It avoids from reaching the dangerous point without going through the zone controlled by the light curtain.
  • A person cannot be present in the dangerous zone without his/her presence being detected. It might be necessary to resort to additional safety devices (i.e..: photoelectric light curtains arranged horizontally). 

European Standard EN SO 13855 provides the elements for the determination of the safety distance.

 

If the machine is governed by a specific C type Standard, the latter shall be taken into due account.

 

If the calculated distances proves excessive, it is necessary to:
a) reduce the total stopping time of the machine,
b) improve the detection capability (resolution) of the light curtain.

fig22One-side protection
 
fig23Three-side protection using deflection mirrors


GENERAL FORMULA FOR THE DETERMINATION OF THE MINIMUM SAFETY DISTANCE 

S = K x T + C

      S minimum safety distance between the protection and hazardous point, expressed in mm.
      K

speed of approach of the body or parts of the body, expressed in mm / sec.
K = 2000 mm/sec. for safety distance up to 500 mm (for arm movement speed)
K = 1600 mm/sec. for safety distance higher than 500 mm (body movement speed)

      T total stopping time of the machine, consisting of:
t1 reaction time of the protective device in seconds
t2 reaction time of the machine in seconds, until it stops the hazardous action.
      C additional distance in mm.


DIRECTION OF APPROACH PERPENDICULAR TO THE PROTECTED PLANE WITH Α=90° (± 5°)
 Logo ditoLogo mano Light curtains with resolution for the detection of hands and fingers.
Light curtains resolution (d): 14 - 20 - 30 - 40 mm

 perpendicolare

1. Hazardous point
2. Sensitive area
3. Reference plane
S. Safety distance
a. Height of the hazardous point

Determination of the minimum safety distance:

S = K x T + C

 

S=2000xT+8x(d-14)

  • The distance S must not be lower than 100 mm
  • If the distance S is greater than 500 mm it is possible to re-calculate the distance using K=1600 but In these
    circumstances, the distance must in no case be lower than 500 mm

S=1600xT+8x(d-14)

K = 2000 or 1600 (see following
calculations)


T = t1 + t2 “General formula for the
determination of the safety distance”


C = 8x(d-14)

Logo accesso Light curtains with a resolution for detection of arms and legs. Light curtains resolution (d): 50 - 90 mm

perpendicolare

1. Hazardous point
2. Sensitive area
3. Reference plane
S. Safety distance
a. Height of the hazardous point

Determination of the minimum safety distance:

S = K x T + C

 

S= 1600xT + 850

K = 1600


T = t1 + t2 “General formula for the
determination of the safety distance”


C = 850

Logo ditoLogo manoLogo accesso Possibility to reach the hazardous point by leaning over the edge of the sensitive area

caso2

1. Hazardous point
2. Sensitive area
3. Reference plane
a. Height of the hazardous point
b. Height of the highest beam
S. Safety distance

Determination of the minimum safety distance:

S = K x T + C

 

S= KxT + CR0

 

Note:

  • Interpolation is not allowed.
  • If distances a, b or CRO fall between values listed in the table, use the higher.
  • CRO (reaching over) calculated using Table 1 of of ISO 13855:2010 must be compared to C as conventionally calculated (see paragraph 1). Always select the higher value.

In this case C, called “CRO” is obtained from the following Table 1 of ISO 13855:2010.

 

K = 2000 or 1600 (see following calculations)

 

T = t1 + t2 “General formula for the
determination of the safety distance“

 

Height of
hazard
zone “a”

Height “b” of upper edge of area protected by photoelectric light curtain
900 1000 1100 1200 1300 1400 1600 1800 2000 2200 2400 2600
Alternative distance CR0
2600 0 0 0 0 0 0 0 0 0 0 0 0
2500 400 400 350 300 300 300 300 300 250 150 100 0
2400 550 550 550 500 450 450 400 400 300 250 100 0
2200 800 750 750 700 650 650 600 550 400 250 0 0
2000 950 950 850 850 800 750 700 550 400 0 0 0
1800 1100 1100 950 950 850 800 750 550 0 0 0 0
1600 1150 1150 1100 1000 900 800 750 450 0 0 0 0
1400 1200 1200 1100 1000 900 850 650 0 0 0 0 0
1200 1200 1200 1100 1000 850 800 0 0 0 0 0 0
1000 1200 1150 1050 950 750 700 0 0 0 0 0 0
800 1150 1050 950 800 500 450 0 0 0 0 0 0
600 1050 950 750 550 0 0 0 0 0 0 0 0
400 900 700 0 0 0 0 0 0 0 0 0 0
200 600 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0

 

 Logo ditoLogo manoLogo accesso For combined mechanical and electrosensitive protections (as shown), where it would be possible to lean against the mechanical protection and bypass the light curtain

caso2a

1. Hazardous point
2. Sensitive area
3. Reference plane
a. Height of the hazardous point
b. Height of the upper edge
S. Safety distance

For the calculation of the parameter C should use

  • Table 1 (for low risk applications) or
  • Table 2 (for high-risk applications)

of ISO 13857:2007 (formerly EN 294) in place of the table on the previous page.


In this catalog the two tables of ISO 13857:2007 (formerly EN 294) - Safety distances to prevent danger zones being reached by upper and lower limbs - are not mentioned.

Logo corpo Light curtains for the detection of the presence
of the body in a dangerous area.
Light curtains with 2 - 3- 4 beams

4 raggi

1. Hazardous point
3. Reference plane
S. Safety distance
Hra. Height of the highest beam
Hrb. Height of the lower beam

Determination of the minimum safety distance:

S = K x T + C

 

S= 1600xT + 850

Note for 2 beams light curtains:

  • H lower beam = 400 mm (can be used if allowed by risks analysis).
  • H higher beam = 900 mm

Note for 3 beams light curtains:

  • H lower beam = 300 mm
  • H middle beam = 700 mm
  • H higher beam = 1100 mm

Note for 4 beams light curtains:

  • H lower beam = 300 mm
  • H middle beam 1 = 600 mm
  • H middle beam 2 = 900 mm
  • H higher beam = 1200 mm

Height of the beams from the reference plane (eg. floor).

K = 1600


T = t1 + t2 “General formula for the
determination of the safety distance”


C = 850

DIRECTION OF APPROACH PARALLEL TO THE PROTECTED PLANE WITH Α=0° (± 5°)
Logo corpo Horizontal light curtains for presence control in a dangerous area
orizzontale1. Hazardous point
2. Sensitive area
3. Reference plane
a. Height of the hazardous point
x. Distance between end of the detection zone and
    machine edge
S. Safety distance
H. Height of the sensitive area

Determination of the minimum safety distance:

S = K x T + C

 

S= 1600xT + (1200-0,4xH)

 

Note:

  • C = 1200 - (0,4 x H) must be equal to or greater than 850 mm
  • The maximum height allowed is: Hmax = 1000 mm
  • The height H depends on the resolution d of the light curtains and is determined through the following formula:
    H = 15 x (d - 50)
  • This formula can also be used to determine the maximum resolution that can be used at the different heights
    d = H / 15 + 50
  • For example, the maximum resolution limits will be:
    for H = 1000 mm    d = 116 mm
    for H = 0 mm    d = 50 mm
  • If H is greater than 300 mm, at the stage of risk assessment it becomes necessary to take into consideration the possibility of access from beneath the beams

When using the light curtain as a combination of trip and presence sensing device, the distance x must be less than or equal to the detection capability

K = 1600

 

T = t1 + t2 “General formula for the
determination of the safety distance”

 

C = 1200 - (0,4 x H)

DIRECTION OF APPROACH ANGLED TO THE PROTECTED PLANE WITH 5°< Α <85°
Logo mano  Logo corpo Slanted light curtains to detect hands and arms and for presence control in the dangerous area

 

inclinato

1. Hazardous point
2. Sensitive area
3. Reference plane
a. Height of the hazardous point
S. Safety distance
x. Distance between end of the detection zone and
    machine edge
Hra. Height of the highest beam
Hrb. Height of the lower beam

With angle α >30° refer to the case of “APPROACH PERPENDICULAR TO THE PROTECTED PLANE”.

Note:

  • The distance S refers to the beam farthest away from the hazardous point
  • The height of the beam farthest away from the hazardous point must not be greater than 1000 mm

With angle α <30° refer to the case of “APPROACH PARALLEL TO THE PROTECTED PLANE”.


Note:

  • For the determination of height H or
    resolution d apply the following formulas to the lowermost beam:
    H = 15 x (d - 50)
    d =   H / 15 + 50
  • When using the light curtain as a combination of trip and presence sensing device, the distance x must be less than or equal to the detection capability.

 

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