Electro-sensitive protective equipment testing is crucial for collaborative robots

Electro-sensitive protective equipment (ESPE), such as light guards and laser scanners, are crucial for collaborative robots, but inspection and testing is often neglected.

By Lee Ray June 18, 2020

Because collaborative robots are designed to work alongside human co-workers, they cannot be caged by a physical guarding mechanism. This means electro-sensitive protective equipment (ESPE), such as light guards and laser scanners, is more prevalent than ever before. However, ESPE inspection and testing is often neglected as many machinery owners are unsure how often it should be assessed.

The International Electrotechnical Commission’s EN 61496 series specifies requirements for the design, construction and testing of ESPE designed specifically to detect persons as part of a safety-related system, employing active opto-electronic protective devices (AOPDs) for the sensing function. This is then used in conjunction with EN ISO 13855 to determine the correct installation location for the light guard, which should be verified after installation.

The complete system for detection, actuation and stopping is not solely reliant on the electrical signals. There are normally wear components that are installed as part of that system to enable a shorter stopping time. Through the lifecycle of use, there is potential for these parts to wear and this could introduce a situation where access can be gained through a light guard, to a hazardous part of the machine, while it is still in run down.

The Amended Use of Work Equipment Directive (AUWED) places requirements on machinery users to inspect and maintain the equipment and safety critical functions of the equipment. The testing frequency of the light guard cannot be determined by the component manufacturer for the stop time, as they are not responsible for installing the system as a whole. It is the light guard integrators responsibility to select and configure the system correctly, and the user must conduct testing and maintenance to ensure this function does not deteriorate.

Inspection and tests must first be done when the complete ESPE and machine package is installed, and thereafter when modification or repairs have been made or the installation is relocated. In addition, EN IEC 62046 states in clause 7.3 that periodic inspection and testing should not be greater than 12 months unless local regulations state otherwise. This is to ensure that deterioration has not occurred in the stopping performance for the lifecycle of the machine.

Following guidance from local enforcing authorities is strongly recommended. For example, in the UK the HSE has created HSG180 which defines the recommended maximum period between each periodic inspection and test as being six months for type 4 ESPE and 12 months for type 2 ESPE. However, this is still quite subjective as the guidance then says that the frequency of inspections ultimately depends upon on the equipment that the ESPE is fitted to and the risk as a whole.

The good news for machinery end-users is that HSG180 requires the machine and the ESPE supplier to supply information relating to routine maintenance and inspection requirements. This should help the end-user to develop a robust inspection and set an initial test regime frequency. The guide also requires that the initial inspection and test is carried out by competent persons, such as an in-house inspector, the installer or supplier, or an independent assessor.

The results of any inspections must also be recorded. The HSG180 guide also helps the inspector to ensure that the inspection and test process achieves a good general standard of performance. For example, it should not be possible for the dangerous parts of the machine to be set in operation while any part of a person is in such a position as to actuate the AOPD.

We have seen multiple instances where the need for light guard testing has not been realized. While functional safety checks are recognized as good practice, they are no substitute for the required periodic testing. The stop time test, performed as part of the periodic test, would detect any deteriorating system parts which no longer offer the required protection. This is something that usually cannot be seen, like in fixed guarding, and therefore can only be proven by testing.

This article originally appeared on Control Engineering Europe’s website. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, cvavra@cfemedia.com.

Author Bio: Lee Ray is operations manager for Industrial Products (UK) at TÜV SÜD.