Selecting an assembly robot and where to start

A recent blog “Lessons for post-pandemic manufacturing automation”, suggested using robots for labour-intensive applications. Mitsubishi Electric’s Barry Weller looks at selecting an assembly robot that best suits your application and how to integrate it.

If speeding up operations is the goal for deploying a robotic solution, conventional industrial robots are the simplest to adopt. An example of these is a SCARA robot like the Mitsubishi Electric RH Series robot arm. SCARA robots are compliant in the X-Y axis and rigid in the Z-axis. They meet the demand for high-speed low-cost pick and place and auto-insertion applications. For more general assembly work, an articulated arm robot like the Mitsubishi Electric MELFA RV Series offers more flexibility.

But both ranges can move at high speed. This makes them unsuitable for applications sharing the workspace with human operators without using extra safety provisions. Integrating them needs physical safety perimeter guards or systems with automated speed control for when humans approach the working area.

On the other hand, if the main goal is assisting employees in their activities, for example by passing or holding parts, the application is collaborative. This means any conventional physical separation between humans and robots would obstruct the application.

A case for collaborative robots (cobots)

In this case, the ISO/TS 15066:2016 standard supports the development of suitable safety measures, as defined by a risk assessment. The standard uses the term collaborative for systems or applications where autonomous robots share the same workspace with humans.

As with any other robot type, selecting an assembly robot for collaborative applications still needs a risk assessment. An example of a robot designed explicitly for collaborative applications is Mitsubishi Electric’s MELFA RV series Assista articulated arm robot.

The guidelines define different types of collaborative applications that include safety-rated monitored stop, speed and separation monitoring, hand guiding as well as power and force limiting.

This is where the grey area between industrial and collaborative robots starts to appear. With the increase in safety options now available, industrial robots can also achieve many of the requirements needed in a collaborative application. Choosing a robot depends on the setting in which the machine operates, how operators need to interact with the robot and its main functions. Designed to work alongside human operatives, collaborative robots or ‘cobots’, also provide a safe solution.

Selecting an assembly robot

There are different industrial operations whose risk assessment would support the use of cobots. For example, if the robot works alongside the human as part of the assembly process to pass objects to operators. Here the chance of a collision between the two is high and so this application would fall into the robot category of power and force limiting. Essential features such as a safe torque range detect the impact and stop prevent injury to the operator.

There are situations when selecting an assembly robot needing extra safety measures. For example, if harmful chemicals, sharp edges or hot items need handling, the robot would need enclosing behind physical safety perimeter guards to protect human operators. For these applications, the use of a conventional robot is likely to be the right choice.

On occasions, where humans may need to enter a robot’s workspace to interact with the application. These systems will run as fast as possible under normal operation and only slow down when there is a risk of collision. A conventional high-speed robot would be suitable for this application. The most effective way to make such applications fast, safe and reliable would be to use standard industrial robots operating cooperatively, coupled with extra safety features such as physical guards or safety light curtains and scanners.

Mitsubishi’s SafePlus safety system also supports using high-speed, high payload articulated arm robots. On detection by safety sensors, SafePlus limits the speed, range of movement or torque of the robot. This allows humans and robots to work together in safety and harmony.

Making the right choice

As robotic and safety technologies evolve, the boundary between industrial and collaborative robotic applications also changes. When selecting an assembly robot system, it must meet the needs of the application and deliver against the user requirements. It must also deliver the expected throughput in a safe environment for operators in line with the risk assessment.

The inclusion of collaborative robots has expanded the choice and the type of applications that are suitable for robotics. It is not a question of which is best, industrial or collaborative robotics but which is best for the application. The experience of the robotics team at Mitsubishi Electric and its Robot Partners help businesses find the right solution at an affordable price.


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