This website uses cookies primarily for visitor analytics. Certain pages will ask you to fill in contact details to receive additional information. On these pages you have the option of having the site log your details for future visits. Indicating you want the site to remember your details will place a cookie on your device. To view our full cookie policy, please click here. You can also view it at any time by going to our Contact Us page.

Robotics: Getting the best of both worlds

23 August 2017

Collaborative robots deliver on the promise of reduced investment costs, simple programming and inherent safety. The compromise, of course, is that they cannot offer the performance of traditional industrial robotics. But, suppose it was possible to have the best of both worlds? Oliver Giertz defines ‘cooperative robotics’.

Collaborative robots (cobots) have been created to address an area of the automation market that traditional industrial robots were not designed to satisfy – working alongside humans. Working alongside humans, this new breed of robots can provide support roles, helping to optimise workflow and improve productivity.

Typical applications might include loading and unloading a machine or aiding with assembly operations, with the important distinction between them and standard industrial robots being that cobots are mainly slower, but don’t need any safety guarding around them. They are designed to be inherently safe.

This safety is built around three key performance aspects. The first is that cobots are speed limited and tend to have soft-touch surfaces. Because they can’t move quickly, they can’t do any real harm or damage. The second is their limited torque, which again ensures there is minimal risk involved in their deployment. The third is torque monitoring, which ensures the robot is promptly stopped if a collision is detected.

This is not to say that guarding is never required. For example, if the robot’s task is to wield a sharp cutting tool, then even the low speed and low torque wouldn’t prevent a worker being cut if they strayed within the path of the robot arm. Every robot application, therefore, requires a thorough and complete risk assessment of the application including process, gripper, clamp and robot.

Traditional industrial robots are more associated with the need for high levels of support due to the difficulty of programming, adjusting and maintaining them. With some cobots, however, even a robot novice is able to program the robot, often just using teach functions. 

Cooperative robots
This makes a compelling case for cobots in certain applications, but the caveat will always be the characteristically limited performance. What if we could have all of the benefits of cobots, but in a ‘cooperative’ role rather than a collaborative role, and with the performance of traditional robotics?

Cooperative robots interact with operators, but do not necessarily work alongside them. They offer the performance advantages of traditional industrial robots without the need for the traditional safety guarding arrangements. Inherent safety technologies allow them to monitor where the operator is in relation to the robot arm, and adjust the performance of the robot accordingly.
Cooperative robotics is the name that Mitsubishi Electric has given to its class of robots with MELFA SafePlus option that offers these benefits. In effect, they are standard industrial robots but with in-built safety technologies that allow them to be deployed more flexibly in production cells to work in cooperation with operators rather than standing alone, and which also offer ease of programming.

In a traditional industrial robot installation, the robot would typically be isolated in a cell, with physical guarding around it. With secure access, either through a physical door with safety interlocks or through a light curtain. 

This arrangement does not lend itself to true cooperation between the robot and the operator. But suppose we could define zones around the robot where it would simply adjust its speed downwards as the operator approached, perhaps also limiting its torque and/or its reach. This scenario starts to emulate the inherent safety of collaborative robots, but without compromising performance when the operator is outside of the safety zone.

Safety technology
Mitsubishi Electric implements this level of safety functionality through the MELFA SafePlus safety system, along with additional technology such as a safety scanner in the robot base. 

A pre-defined, reduced operating speed or a movement stop is then assigned to the robot in real time, enabling operators to work in close proximity to the moving industrial robot without the need for a safety cage. As a result, operators and robots are able to work side by side in an environment where the risk of danger is significantly reduced. 

Five key safety functions are embedded within the MELFA SafePlus system – reduced speed control, limited range control, torque monitoring, safety input, and safe torque off/safe stop 1.

With reduced speed control, two zones around the robot can be defined. The robot doesn’t automatically stop when an operator enters the first zone, but just reduces its speed. With limited range control, the robot cannot move beyond a given range when an operator enters the defined zone. The control system monitors four particular points of the robot arm, and if any one of these exceeds any set plane, the robot will stop immediately. 

In torque limit mode, the operator can be interactive with the robot while it is running in automatic mode, thanks to its low speed, reduced torque and collision detection. Finally, if the operator gets too close to the robot or if an error is detected, the safe torque off and safe stop 1 inputs will shut off the motors to stop the robot.

With all of these safety functions, because the robot does not need to stop automatically if an operator moves within the defined zones, downtime is reduced and productivity improved. But at the same time, safeguarding costs are reduced and less space is needed for the robot installation.

This reduction in the need for physical guarding also makes it easier to redeploy a robot from one task to another. Indeed, any small industrial robot can now be redeployed with exactly the same flexibility as you might enjoy with a collaborative robot.

Oliver Giertz is product manager for Robotics, Servo and Motion at Mitsubishi Electric Europe B.V., Factory Automation – European Business Group.


Contact Details and Archive...

Related Articles...

Most Viewed Articles...

Print this page | E-mail this page