JUL-AUG 2017

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22 INTECH JULY/AUGUST 2017 WWW.ISA.ORG FACTORY AUTOMATION of what each collaborative method re- quires. For instance, a safety-rated moni- tored stop requires that the robot does not move at all if a person enters the shared space. The benefit is a quicker restart after the human leaves, compared to a noncol- laborative system. But in this case, it is not a situation in which human and robot are working together at the same time and in the same space, which is what most peo- ple think of when they think of "collabora- tive robots." Similarly, hand guiding is very similar to a common method of "teaching" the robot its tasks. When used to describe a type of collaborative operation, howev- er, hand guiding indicates a condition where the robot and person occupy a shared space and the robot is only moving when it is under direct con - trol of the person. In speed and separation mon- itoring, both the robot and the p e r s o n c a n b e present in the space, but if the distance between the robot and the person becomes too close, the ro- bot first slows, and then stops. This is effectively the first scenario of a safety-rated monitored stop. In power and force limiting, there can be contact be- tween the person and the robot, but the robot is power and force limited and sufficiently padded. If there is any impact, there is no pain and no injury. It is also possible to have any mix of some or all of these four methods of collaborative operation in one robot system. The new TS 15066 specification in- cludes formulas for calculating the pro- tective separation distance for speed and separation monitoring. But perhaps the most interesting part of the techni - cal specification is Annex A. It contains guidance on pain threshold limits for various parts of the body, for use when designing power- and force-limiting ap - plications. These pain thresholds were established by a study from the Univer - sity of Mainz, Germany, using male and female volunteer human test subjects of a variety of ages, sizes, and occupations. The data can be used to set limits on lev - els of power and force used by the col- laborative robot system or application. Risk assessment – Application, not robot The most important aspect for any col- laborative robot integration is a risk assessment. But it is important to re- member that when assessing risk, the application, not the robot, is the main concern. In fact, the standard document rarely uses the term "robot." Instead, it discusses collaborative work cells or col- laborative applications: all the elements involving cables, jigs, clamps, the robot, and the gripper that are inside the cell. If the application requires somewhat higher force or power than what is stat- ed in the document, it does not mean the application is not safe. The techni- cal specification relates to pain, while what is required from 10218 is that no injury should occur. There is a difference between pain and injury. Tests could show that even if the impact is above the amount stated in 15066, the application may still be safe if it can be proven that the robot cannot hurt or injure the people in those circumstances. Another common misconception is that if the robot is "inherently safe," then the operation is safe. The term "inher- ently safe" is similar to the term "collab- orative robot." It describes built-in safety The FANUC CR-35iA collaborative robot has six-axis articulation and a 35-kg payload. In this palletizing stacking operation, its soft cover and force sensors protect workers who are in direct contact with the robot for training or operation. The ISO standard TS 15066 and TR 606, which explains safety requirements specific to collaborative robots and robot systems, establish pain thresholds to guide appropriate use of safety guards or protective devices. Minor injury Reversible injury Irreversible injury Touch sensation P&F collaborative OK maybe Power and force limited collaborative operation NO Why is TS 15066/TR 606 important? Decrease exposure + Use guards and protective devices Reduce risks Pain sensation (pain onset) Threshold for... Applied force or energy

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