Advanced safety features for robotic systems

14 January 2013

For industrial robots to work together with people, the speed at the tool center point must be safely monitored. B&R offers TÜV-certified function blocks for creating the necessary integrated safety applications via openSAFETY, to provide advanced safety features for robotic systems, regardless of the control technology used.

Traditional methods for ensuring safety in situations where robots and humans need to interact, for example during system set up, employ an E-stop that is triggered when a safety gate is opened. This is no longer sufficient.

It is important to implement safety concepts specific to robotics, in which safe monitoring of the movement speed accounts not only for the individual axes, but also for the entire robotic system, including the tool center point (TCP). Derived from the requirements specified in the standards EN ISO 10218-1 and EN ISO 10218-2 for safety in industrial robotics and robotic systems operating in collaboration with human operators, B&R can offer advanced robotic safety with the safely limited speed (SLS) function implemented at the TCP.

This new function is an extension of the advanced safety functions for Safe Motion Control integrated directly in the ACOPOSmulti servo drives. These advanced functions, known as SafeMC, are said to lower error detection and response times from 80 to 7 ms and the stopping distance by a factor of 100. SafeMC also offers a number of alternatives to the abrupt halt of a simple E-stop, including ‘Smart Safe Reactions’

Monitored kinematic chain
To limit the speed at the tool center point to the 250 mm/sec –required by the regulations for collaborative operation – without using additional sensors, the first step is to determine the actual speed. This is done by combining data describing the status, position and speed of the individual axes in a kinematic transformation.

This data is obtained from the SafeMC modules in the ACOPOSmulti servo drives on the individual axes and transferred to the SafeLOGIC controller via the fieldbus-independent safety protocol, openSAFETY. This is where the transformation is performed and the resulting speed is compared against the specified safe value. The SafeLOGIC controller provides safe transfer to ensure that requests to execute safety functions reach their destination where they are executed directly on the drive.

TÜV-certified function blocks
A library of TÜV-certified parameter and function blocks is available for developing the necessary safety-related control programs.

A safe function block compares the speeds of all joints and enabled tools against the specified limit speeds. The operator can select up to four different limits and switch safely between them. A variety of tool dimensions can also be defined, and multiple tool points can be traced simultaneously. This might be used to implement safe monitoring of workpieces with a large surface being handled by the robot. The response to safety violations output by this module is defined in the safety application, so the processing that is performed depends on what type of robot is used.

The geometric dimensions of the robotic system, the unit system used and the relationships between the joint axes and the base joint are all described in a parameter block compatible with any reasonable kinematics system. Another parameter block is used to define the tool dimensions in relation to the coordinate system of the end effector. These dimensions are required to determine the speed on the enabled tool center points.

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