Master Thesis - Hochschule Bonn-Rhein-Sieg

6. Evaluating the safety Master Thesis Björn Ostermann page 104 of 126
Among other values, the EN 13857 [73] gives a maximum height of 120 mm above ground that can be
left free when installing a fence. Thus this value was chosen as the desired value for the programmed
“flexible fence”.
If those 120 mm are applied, the safety distance to the hazard zone has to be 850 mm for the safety of
upper appendages, respectively 1100 mm for the safety of lower appendages.
6.2.2 Safety of machinery – The positioning of protective equipment in respect of
approach speeds of parts of the human body
EN 999:1998
The goal of the project is to safely avoid the collision between robot and humans. When using
protective equipment in this task, in the case of this project the 3D camera combined with the data
evaluating algorithms, safety distances have to be kept to compensate the systems stopping
performance.
The standard EN 999 gives formulas, regarding the positioning of protective equipment in respect of
approach speeds of parts of the human body. Applying those formulas to the present system results in
the necessary safety distance that has to be kept between robot and human at all times.
Critical for the positioning of the protective devices is the overall system stopping performance T
(see Equation 14).
T � t � t
1
Equation 14: Overall system stopping performance, according to [69]
t 1 is the maximum time between the actuation of the sensing function and the output signal switching
devices being in the full state, [69]
t 2 is the maximum response time of the machine, i.e. the time required to stop the machine or remove
the risk after receiving the output signal from the protective equipment. [69]
Since the used 3D camera in this project has a maximum detection capability of below 40 mm in
diameter (20 mm resolution at 4 m distance and 25 mm resolution at 5 m distance, according to [55])
the formula given in chapter 6.1.1 of the standard EN 999 has to be applied to the reaction time
(Equation 15):
2
�K �T
� C
S � �
Equation 15: Minimum distance S from the danger zone to the detection zone [69]
S is the desired distance between the danger zone and the detection zone,
K is a fixed factor:
- 2000 mm/s if S is below or equal to 500 mm