Safety in Collaborative Robotics

There is no “Collaborative Robot”. That is one of the first statements you hear from people working in Collaborative Robotics. The reason is because the robot can be designed for a collaborative task, but it is the Application that makes the “Robot Collaborative”.

The reference standard for Collaborative Application is 
ISO/TS 15066:2016 – ROBOTS AND ROBOTIC DEVICES — COLLABORATIVE ROBOTS

Not only for the unfortunate title, the standard will be included in the new edition of 2 important standards on Robots:
ISO 10218-1: Robotics — Safety requirements for robot systems in an industrial environment — Robots
ISO 10218-2: Robotics — Safety requirements for robot systems in an industrial environment — Robot systems and integration

In December 2021 both standards were at DIS Stage. They now fully include requirements for Collaborative Applications. For example in ISO 10218-1:

[ISO 10218-1] 3.1.1.6  Collaborative Application. Applications that implements one or more collaborative task(s)

[ISO 10218-1] 3.1.1.7 Collaborative Task. Portion of the robot sequence where both the robot application and operator(s) are within the same safeguarded space.

There are four important functions a Robot needs to have in order to be suitable for Collaborative Applications:

1- Monitored-standstill

2- Hand-guided controls (HGC)

3- Speed and separation monitoring (SSM)

4- Power and force limiting (PFL)

It requires a software or device to pause the function of robot when the worker is coming closer to the robot in order to prevent dangerous motion. The function, in the new edition of ISO 10218-1 will be called “monitored-standstill” .

[ISO 10218-1] 3.1.8.4  monitored-standstill. Safety function that monitors the position after a stop while drive power is active  

NOTE 1 to entry: In ISO 10218-2:2011, "monitored-standstill" was called “safety-rated monitored stop”. 
NOTE 2 to entry: This safety function can also apply to the robot system, robot application, robot cell and other machinery.  

The method consists in allowing the operator to move the robot by hand-operated device to transmit motion commands.
The robot system needs to have the following: 
⎯ monitored-speed safety function 
⎯ stop category 2 (IEC 60204-1) protective stop 
⎯ monitored-standstill safety function 

A risk assessment needs to be done to determine the monitored-speed limit value

The third method is speed and separation monitoring which is increasing safety by specifying the minimum protective distance between a robot and an operator. 

Collaborative applications using SSM can use a SPE that detects entrance into a safeguarded space or that monitors the presence of any person. 
When a presence-sensing device like a laser scanner or a safety radar, is used to define the detection zones, the size and location of the detection zones shall be set so that the separation distance is maintained, even during detection zone transitions. Please bear in mind that the time for the robot application to decelerate has to be considered.

The SSM can be provided by the robot controller or by an external protective device, or by a mixture of both.  
 

The fourth method allows the contact between on operator and a robot, but the requirement is the control of robot momentum to avoid any injury and pain.
Accomplishing PFL functions can be by inherently safety design which can be fixed, not adjustable or configurable, or by safety functions that can be adjusted or configured.
For robots with adjustable or configurable PFL safety functions, exceeding any parameter limit shall cause a "protective stop".