3.4 Step 4: Calculating safety distance
Optoelectronic protective devices can only perform their protective function if they are installed with a sufficient safety distance from the nearest danger point of operation. The safety distance from the protective device to the point of operation must big enough that the dangerous movement will have stopped before a part of the person’s body can reach the point of operation (see also, ANS IB11.19-2003). After calculating the safety distance it should be checked and ensured that this minimum distance allows an ergonomic operation of the machine for the operator. If this is not the case either an entire stop time of the machine or an AOPD with higher resolution must be selected.
The following overview refers to the calculation formulas of ISO 13855/EN 999 Safety of machinery – Positioning of protective equipment with respect to the approach speeds of parts of the human body and the recommendations of IEC TS 62046. If the machine is the subject of a certain specification, such as machine-specific European C-standards and OSHA / ANSI standards, then reference must be made to this. This overview does not, of course, detract from the observation of the installation notes of the operating instructions.
Safety distance calculation in accordance with ISO 13855/EN 999 and IEC TS 62046
The minimum distance of a stop-activating protective device from the nearest danger point of operation on the machine must be calculated with the following formula:
S = (K x T) + C
| S |
The minimum safety distance in millimeters from the next point of operation to the detection point (protective field) of the protective device. An S of 100 mm must be observed regardless of the calculated value.
|
| K |
Approach speed in millimeters per second, derived from data of the approach speeds of the body and body parts.
Speed (lower limbs): K = 1600 mm/s
Speed (upper limbs): K = 2000 mm/s
|
| T |
Stopping time of the entire system (protective device response time + interface response time + machine stopping time) in seconds (IEC TS 62046 requires at least an additional
10 % on top of the determined stopping time to allow for possible deteriorations).
|
| C |
An additional distance in millimeters. This additionally added distance is based on the fact that, depending on the resolution of the protective device, a body part can get a certain distance closer to points of operation before it is detected by the protective device. |
Handling a possible circumvention of electro-sensitive protective equipment by reaching over the protective field acc. to ISO 13855:
Legend:
| 1 |
electro-sensitive protective equipment |
| 2 |
Hazard zone |
| 3 |
reference plane |
| a |
Height of hazard zone |
| b |
Height of the upper edge of the protective field of the electro-sensitive protective equipment |
| CRO |
Additional distance in which a body part can move in the direction of the hazard area before the protective device is triggered (see values in Table 1) |
| S |
Minimum distance for reaching over |
Figure 8 - reaching over the vertical protective field of
electro-sensitive protective equipment
| Height of hazard area a |
Height of the upper edge of the protective field of electro-sensitive protective equipment
b |
| 900 |
1 000 |
1 100 |
1 200 |
1 300 |
1 400 |
1 600 |
1 800 |
2 000 |
2 200 |
2 400 |
2 600 |
Additional distance to hazard area
CRO |
| 2 600 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2 500 |
400 |
400 |
350 |
300 |
300 |
300 |
300 |
300 |
250 |
150 |
100 |
0 |
| 2 400 |
550 |
550 |
550 |
500 |
450 |
450 |
400 |
400 |
300 |
250 |
100 |
0 |
| 2 200 |
800 |
750 |
750 |
700 |
650 |
650 |
600 |
550 |
400 |
250 |
0 |
0 |
| 2 000 |
950 |
950 |
850 |
850 |
800 |
750 |
700 |
550 |
400 |
0 |
0 |
0 |
| 1 800 |
1 100 |
1 100 |
950 |
950 |
850 |
800 |
750 |
550 |
0 |
0 |
0 |
0 |
| 1 600 |
1 150 |
1 150 |
1 100 |
1 000 |
900 |
850 |
750 |
450 |
0 |
0 |
0 |
0 |
| 1 400 |
1 200 |
1 200 |
1 100 |
1 000 |
900 |
850 |
650 |
0 |
0 |
0 |
0 |
0 |
| 1 200 |
1 200 |
1 200 |
1 100 |
1 000 |
850 |
800 |
0 |
0 |
0 |
0 |
0 |
0 |
| 1 000 |
1 200 |
1 150 |
1 050 |
950 |
750 |
700 |
0 |
0 |
0 |
0 |
0 |
0 |
| 800 |
1 150 |
1 050 |
950 |
800 |
500 |
450 |
0 |
0 |
0 |
0 |
0 |
0 |
| 600 |
1 050 |
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 |
| If the value 0 is specified, the calculation of minimum distance S should take place in accordance with 6.2 to 6.4 |
When determining the values according to table 1, interpolation is not allowed. If known values a, b or CRO are between two values in Table 1, the larger value of the minimum distance must be used.
To prevent a cirumvention by reaching over the ESPE, minimum distance S in millimeters between the protective field and the hazard area cannot be smaller than the value calculated using the equation.
The values determined in the table apply for CRO. The value specified for CRO in the table corresponds to the additional distance in millimeters which is based on the distance a body part (normally a hand) can move in the direction of the hazard area before the electro-sensitive protective equipment is triggered. Table 1 refers exclusively to reaching over the protective field of the ESPE.
If the height of the ESPE is already determined, the table can be used to derive minimum distance S. If the minimum distance of the ESPE is already determined, the table can also be used to ascertain the necessary height of the ESPE.
S = (K x T) + CRO
Whereas
K = 2 000 mm/s.
Consequently,
( ) S = 2 000 x T + CRO
This equation applies for all minimum distances S up to and including 500 mm. Minimum value S cannot be
smaller than 100 mm. First, S is to be calculated using equation (11). If the values of S
exceed 500 mm, equation (12) can be used. Value S cannot be smaller than 500 mm.
( ) S = K x T + CRO
Whereas
K = 1 600 mm/s.
Consequently,
S = (1 600 x T) + CRO
|
