Master Thesis - Hochschule Bonn-Rhein-Sieg

6. Evaluating the safety Master Thesis Björn Ostermann page 113 of 126
The safety distance of 1100 mm, according to EN 13857 in chapter 6.2.1, has not to be added,
according to EN 999. The EN 999 already takes into account the crawling below the lowest beam of
the protective device. For the used device setup, it gives the recommendation for the height of the
“lowest beam” of protective equipment to be at 300 mm. Thus the 120 mm, which were applied in
accordance with EN 13857 are just an enhancement of the safety measures.
The result for the determination of the necessary safety distance is:
- 664.05 mm for the evasion path
- 767.65 mm for the speed control
The distance of 767.65 mm, determined in the speed control is farther than the distance covered by the
assumed 14 lines at which the algorithm starts to react. Increasing the lines would reduce the reaction
time further, thus demanding another increase and so on. It has to be kept in mind that this particular
algorithm was designed with respect to its presentability and not its speed in execution. Further
projects have to implement alternative algorithms, that focus more on their execution time.
Since those distances are not yet practical for demonstration, especially when the robot is only moving
slowly, additional or alternative protective equipment was used, as proposed by the methodology of
the standard EN 999. Thus, to be able to demonstrate the algorithms with shorter distances between
robot and human, the hold to run button of the control panel was used in the course of this project as
alternative protective equipment.
6.4 Desired safety
To be able to use the system in praxis, a safety distance of 500 mm, according to EN 349 [68] the
safety distance against crushing of the human body, would be applicable. In this chapter it is shown,
how short the reaction time of a system needs to be, in order to allow such a safety distance, while still
operating the robot at full speed.
Equation 16 is expanded by the distance the robot can move during the reaction time of the system,
resulting in Equation 18.
�K �T
�� C � �V �T
�
SR �
R
Equation 18: Safety distance of the robot, including the robot’s velocity
In Equation 19 the values are inserted, including the maximum speed of the robot, 4 m/s. This speed is
far greater than the safety speed (250 mm/s), used in this project.
500mm
�
452mm
� T �
5600mm
/ s
� T � 81ms
�1600mm / s �T
��48mm � �4000mm / s �T
�
Equation 19: Desired reaction time of the complete system