Robots designed with collaborative, traditional traits for improved efficiency, safety

Cooperative robots interact with operators, but do not necessarily work alongside them and are designed to offer the performance advantages of traditional industrial robots without the need for the traditional safety guarding arrangements.

09/28/2017


Cooperative robots interact with operators, but do not necessarily work alongside them and are designed to offer the performance advantages of traditional industrial robots without the need for the traditional safety guarding arrangements. Courtesy: Mitsubishi ElectricCollaborative 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 are, in effect 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 implemented this level of safety functionality through their 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 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 of a collaborative robot.

Oliver Giertz is product manager for robotics, servo, and motion at Mitsubishi Electric Europe B.V., Factory Automation – European Business Group. This article originally appeared on Control Engineering Europe's 
website
. Edited by Chris Vavra, production editor, Control Engineering, CFE Media, cvavra@cfemedia.com.

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