Proximity-based safety improves robot movement and efficiency

Moving to proximity-based safety can release space and improve production efficiency by allowing robots and workers more freedom of movement on the shop floor.

By Oliver Giertz December 28, 2019

Physical cages with safety interlocks and frames with light curtains take-up valuable floor space and obstruct the movement of personnel and equipment around them. While a robot will increase productivity by performing repetitive tasks quickly without stopping, the space around them is holding back potential logistical efficiencies. Releasing the value in existing manufacturing floor space clearly requires investment. Hence, there is a balance to be struck between the added capacity and logistical efficiency to be gained, and the cost of updating the robot cell.

A complete stop of the robot is required for service and maintenance work. It is also required when personnel are working in close proximity to the robot’s reach of movement. This is often the case for loading and unloading tasks or checking individual processes and inspecting work done after a changeover. A full cage is helpful to the operator, because the robot is effectively shut down as the barrier is broken. However, the start-up time after the person has left the area can be significant, so time is lost and another opportunity to improve efficiency presents itself.

By using dedicated proximity sensors, it is possible to slow the robot down to a safe speed while personnel work close by, and then bring the robot to a controlled stop quickly if the person enters the same physical workspace as the robot. In this way tasks such as inspection and loading can be carried-out next to the robot, while the robot moves slowly and can stop if necessary. Service and maintenance full stops can be achieved easily from the robot controller, for this reason a cage is not required.

The major advantage – apart from removing the cage and freeing up floorspace – is that using this methodology, the robot can return to full-speed quickly after a period of safer low-speed operation. The transition takes seconds; rather than the minutes required to restart an entire production process if a robot cell has to be stopped by entering a safety interlocked cage or hitting an e-stop button.

Making it possible

With no physical barrier, the safety sensor has to work with additional safety measures to ensure contact is avoided, and if it happens while the movement is slowed down, then the robot stops immediately. Safe limited speed (SLS), safely limited position (SLP), and safe torque off (STO) form the basis of achieving the progressive shutdown process.

The proximity sensor allows for an adjustable zone system to be created around the robot, this provides feedback that can be used to limit the position, torque and speed of the robot as the human approaches. Safety light curtains and lasers can also be used as secondary feedback options, improving the failsafe modes.

The aim is to make a robot cell as small and compact as possible with optimum safety provision. More activity can happen around a robot and the space allows for far more efficient production area logistics. The robot goes from high-speed to slow-speed and back again quickly, allowing both the robot and the human to work quickly and efficiently without stops.

Better robot safety and interaction solutions allow for a continuous work process, maximizing the robot’s potential for speed, accuracy and repeatability, while maintaining safe human access and interaction to achieve optimum overall productivity.

This article originally appeared on the Control Engineering Europe website. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media,

Author Bio: Oliver Giertz is product manager for servo/motion and robotics, Factory Automation EMEA, Mitsubishi Electric Europe B.V.