During the last 50 years or so, industrial robots have been increasingly used in manufacturing industries around the world. The technology has been evolving and adapting to the needs of its users. Over the years people have been doing their best to analyze the safety aspects related to a robotic cell. Of course, accidents happened and risk assessments became more crucial. At the same time, safety standards and safety components have also been evolving to better address safety issues related to robotics. Let’s look at where we stand today.
From the moment when the first robots were introduced into factories, the industry has been studying how certain robots and their surrounding equipment could potentially harm the human workers who must interact with them. We have been looking at automation as a whole. Asking ourselves questions like:
These types of questions allow users to perform risk assessments; to identify safety features that could be added to the robotic cell to keep human employees safe while the robot is running. The common solution to keeping humans safe usually involves locking the robot inside safety fences that prevented any contact between the robot and the human workers. Thus this solution became common to people involved in the risk assessment process. These ideas are very prevalent and almost automatic. This way of thinking is still what we use today when it comes to doing a risk assessment for a robotic cell. It looks like our mindset is programmed this way and this may seem like the best way to do it.
However, robots have evolved and we should take advantage and adapt to these changes. Believe it or not, with collaborative robots becoming ever more frequent in the market today we have to change our mindset. We have been creative in the past in finding new applications for robots, now it's the time to be creative about how we do risk assessments. I recently attended a conference on collaborative robots given by our partner, Advanced Motion and Controls, in Montreal in February and this conference completely changed my thinking on the risk assessment process. As Universal Robots users discussed applications and risk assessments that they had done at different factories, two important quotes stuck in my mind.
Let me describe these two ideas and explain how they changed my thoughts about risk assessment.
Saying that the risk assessment of a collaborative application is sequentially based rather than volume based means that you have to approach your risk assessment differently. Instead of looking at the big picture for the robotic cell and working the risk analysis on the entire process with all its components, you should split up the various aspects and analyze them one by one.
For the purpose of this article we will consider the following example. You have a robot that is used to load parts onto a workstation for assembly by a human. Once the assembly is done, the robot picks up the assembled part and places it on a conveyor. In this example, the robot and human worker can work in two distinct assembly regions. Therefore, while the human is assembling one part, the robot is already loading parts and preparing for the next assembly (See the schematic below). Also note that the human cannot physically reach the conveyor.
So the old way of thinking when we looked at traditional industrial robots would be something like this:
Now with collaborative robots designed to work alongside humans and doing the analysis on a sequential level rather than the entire robotic cell, we will do something like this:
Another example of a sequentially based safety analysis is where a robot has to carry a sharp object from one point to another as part of its task. The old way of thinking would probably be to say that since the object is sharp, the robot can severely injure a human worker, but let’s look at this more closely. The robot will pick up a sharp object from point A and move it to point B. Assume that in all other steps of the process the robot is not carrying this object. The question should then be how can I make that move from A to B safe while carrying the sharp object? The answers can be as simple as carrying the object in a certain path or orientation, such that the sharp edge is facing backward during the motion therefore eliminating the risk of someone getting stabbed or cut by the object as the robot is moving. Also, reducing the speed for this move is another potential solution. So instead of finding ways to prevent stabbing in all aspects of the cell, you could consider only the potentially dangerous sections and do the analysis on these. Of course, it would be a good idea to make sure that you lock these programs with a password to prevent modification without a revised risk assessment. So every time the robot’s program is altered you should review your risk assessment and verify that the modification does not affect the cell’s safety. This is why it is an evolving risk assessment process.
So you can easily see how collaborative robots might have initially been perceived as a nightmare by people responsible for workplace safety, especially if they thought that risk analysis was complex for robots. But breaking the risk analysis down into sequential steps and knowing that the process is not set in stone makes the whole process more manageable. This will also make it easier to convince management or workers about the safety of these robotic cells. Changing your way of thinking about safety analyses and remembering that the evaluation process can be changed as circumstances dictate will definitively convince more people to try collaborative robots.
Also don’t forget that when performing a risk assessment with a force limited collaborative robot, like Universal Robots, the severity level of possible injury can be lowered when the cobot is properly adjusted for force and speed. Using a cobot like this should help you reach the proper performance level rating (PLR) for your automation task.