Should we set the robots free?
03 October 2016
Science fiction novels portray robots in a huge variety of ways, often in collaborative roles with humans. Barry Weller considers how this could work in reality.
In a famous story ‘I,Robot,’ Isaac Asimov poses a solution to the dangers of robot development with his Three Laws of Robotics which try to prevent anything ever going wrong.
1. A robot may not injure a human being or, through inaction, allow a human being to come to harm
2. A robot must obey the orders given it by human beings except where such orders would conflict with the First Law
3. A robot must protect its own existence as long as such protection does not conflict with the First or Second Laws.
In real life, in the manufacturing environment robots are very different and are designed mainly for function and reliability and do not have abstract decision making capacity. We keep them in locked cages away from humans to protect the operators from the robots and also the process from the operator.
However, this trend is now being challenged with new generations of robots designed to operate with no or minimal guarding. These so called ‘collaborative robots’ have the potential to open up a lot of new opportunities for robotic automation. However, they also have the potential to introduce new risks, so they need to be developed with safety principles in mind.
Users need to carry out rigorous risk assessments to show that all eventualities when it comes to robot and humans interaction have been considered. This is both time consuming and expensive. Failure to do this adequately could result in personal injury or even death and the inevitable HSE investigation.
The problem becomes clearer when you take a look at why robots are used in manufacturing. Often they are installed to increase productivity. Modern robots are capable of carrying out over 150 pick and place cycles a minute and have the strength to manipulate heavy objects very quickly. Putting people alongside robots operating at these speeds is inherently unsafe.
To prevent injury, collaborative or assistive robots have so far been limited in speed, typically to around 250mm/min. Some are also covered in soft-touch materials and have touch sensitive control surfaces. They are already used on automotive production lines helping operators to lift and position heavy components and assemblies. The issue here is these collaborative robots can help lift heavy items, but cannot meet the cycle time of a skilled worker, let alone a caged robot, thus nullifying one of the key advantages of robots - high operating speeds. They are also expensive.
Surely, the best solution then is to have a standard industrial robot that works at high speed while no one is within the danger area and then when the operator enters the danger area it switches into a safe speed operation mode or pauses until the operator leaves the danger area.
This is the route Mitsubishi Electric has taken to offer what it sees as an ideal solution. The MELFA SafePlus enables a standard robot arm to be integrated into a system with which an operator can safely interact without stopping the process. MELFA SafePlus uses a safety sensor to detect when a person is within the operation range of the robot, and switches it into one of three safety modes, Safe Limited Speed (SLS), Safe Limited Position (SLP) or Safe Torque Range (STR).
Because the process has not been stopped, as soon as the operator is out of harm’s way the robot can resume full speed operation. This gives the work cell the best compromise between protecting the employee and the need to achieve maximum production flexibility and productivity.
One application where Mitsubishi Electric has successfully used MELFA SafePlus is in an automotive plant where multiple components had to be screwed together to form an assembly. Originally, an operator sat at a workstation for many hours doing repetitive tasks. Robots were brought in to screw the components together, leaving the operator with the task of loading and unloading the machine. This resulted in increased quality and productivity because one operator could tend multiple robotic workstations.
Using the MELFA SafePlus mode ‘Safe Limited Speed’ the operator could approach the workstation without having to isolate the robot, open mechanical guarding and reset the system. This saved valuable machine cycle time for every operation, which over the course of a year added up to several production shifts and dramatically improved plant efficiency.
But, what if there is a collision? There are two types of collision that need to be considered, the first is a glancing blow where the robot makes contact with a body part and the person is able to recoil and is not trapped against anything. These impacts are usually of short duration and if at low speed will not cause serious harm.
The second is a constrained contact where the body part is trapped, the duration is extended and injury is likely. Robots can be designed to detect these impacts and stop the movement of the arm. For instance MELFA SafePlus has a function called Safe Torque Range which detects when the robot arm impacts with an object. However, with a trapped limb the damage could already have been done.
Another solution is to try and prevent the robot from working in the same area as the operator. MELFA SafePlus implements a function called Safe Limited Position. This prevents the robot from working in an area occupied by the operator and allows the robot to remain working at a higher speed while allowing the operator to interact with the process as required.
The robot is only really half the story, consideration also needs to be made regarding the type of part the robot is handling and the tooling being employed at the end of the arm. A gripper that pinches the product with a force large enough to lift several kilograms of weight could also crush a finger. A hot glue bead or gasket material could cause a burn and a moving knife could puncture skin even at slow speed. If the robot moves a part at high speed and then releases it unexpectedly, for instance due to compressed air failure, as the gripper releases the part it could become a projectile.
Taking all this into account, is it safe to use robots alongside operators? One thing is certain; manufacturing operation will always have its hazards and we need to use training, signage and technology to minimise the risk. If we are truly to set the robots free from their cage, an amount of risk needs to be accepted and who is going to decide this?
If we balance the risk to bring it in-line with a level of common sense that is already required by everyone to avoid personal injury in life generally, then there is at least a safety starting point. Many production environments have autonomous vehicles of various sizes and configurations safely moving around delivering parts and moving assemblies to different work stations for example. This aspect then has already become common place.
In conclusion, some assistive robots will remain slow and demand a price premium, relative to standard industrial robot solutions. If the priority is to maximise manufacturing output, then for now at least, the best solution is to keep some robots in their cage. The new generation of industrial robots from Mitsubishi Electric however, can work collaboratively using sophisticated presence detectors to slow-down in the presence of human workers, so offer the best of both worlds. They are already being adopted by industry for certain applications.
Barry Weller is product manager for Robots at Mitsubishi Electric.
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