(Translation of German Websites)
Do you plan a cobot project? Then you should know what to do not ending in a deadlock. Unfortunately, sometimes companies are driving projects which will be no longer used after a short time. How can this happen? And: How can backlashes be avoided or can be used for a new restart.
Living with limitations. With this attitude you should start your selection of an appropriate cobot application. Because it is not true that cobots can replace traditional robots always 100 percent. For the so-called fenceless operation in most cases limits have to be accepted, e.g. for speed, force, pressure, mass and moving space
Speed
If a cobot robot provides for instance a maximum speed of 2000 mm/s at the Tool-Center-Point (TCP) you cannot be sure taking advantage of it under real operation conditions. According to the biomechanical limits of ISO TS 15055 in the region of free bump to the body only 500 mm/s in most cases are possible. In case of clamping, e.g. at the tool area only 250 mm/s or even less.
Force and pressure
If the cobot machine provides free access to the working area or can an accidental contact of robot and human not be excluded then the biomechanical limits according to ISO TS 15055 shall be fulfilled. Already at the point of robot selection, this aspect becomes very important. The planned application can already fail at this point when for instance parts shall be grasped or placed by a certain pressure or force which are higher than the biomechanical limits. Therefore, applications avoiding any transmission of high force or pressure from robot to environment are potentially more suitable for cobot applications. Examples are placement of glue lines or visual camera inspections.
Mass and weight
Is the moving of heavy objects part of your application than in many cases the designer is searching for a cobot with high payload. But, is then anything o.k.? Unfortunately, heavy moving mass includes high inertia. In case of contact between cobot machine and human these inertias have to be stopped until standstill. According to the physics we know E=(m/2)v² . Therefore, in such cases the speed has to be reduced such that in the end the cobot travels only at a creep speed. A frustrating scenario for all participated people. From experience, we know that work pieces having a mass of more than 10 kg frequently providing problems.
Space
As we know from traditional robots normally the robot program is not safety related. I.e. it does not provide any safety category, PL or SIL. Therefore, unfortunately unexpected movements cannot be excluded. Only an overlay of independent safety functions can encapsulate movements to a restricted space. This is necessary e.g. for sensible body parts like head and neck.
Collaboration and Co-existence
In case of critical applications sometimes it is highlighted that any person is not required to be near to the cobot. The situation is called co-existence instead of collaboration. And the question is: Am I allowed to be not so fussy about standard requirements of ISO TS 15066? However, in most cases a clamped or wrong located work piece motivates the operator for intervention i.e. access to the working area. According experience there is no chance for ignoring such reflex actions. Therefore, these possible clamping or bumping points shall be implemented into risk assessment as possible contact points.
Henry Ford: Failure is simply the opportunity to begin again, this time more intelligently.
Planed applications focusing from the beginning on success or even a specific return of invest (ROI) bear high risk. On one hand economically. On other hand also for the safety of employees. If any cobot machine does not comply to the safety rules it must be perhaps shut down or expensively retrofitted.
However, if a cobot machine has been installed in order to test and learn the new technology at the own company the expectations about production efficiency are not such high. Solving any problem provides new knowledge which can be applied successful in a possible second project
