It’s possible there’s no bigger topic than safety. Every endeavor, every environment and every manufacturer must address safety—and every component within a larger system must achieve its own safety metrics for the overall system to be safe.
When it comes to the design and manufacture of computer-controlled systems, the International Electrotechnical Commission (IEC) publishes an international standard, IEC 61508, that defines the concept of “functional safety.” Functional safety is the baseline safety achieved when a system or equipment operates correctly in response to its inputs. To ensure functional safety, malfunctioning behaviors of the electrical/electronic/programmable electronic (E/E/PE) systems cannot create an unreasonable risk.
Failures are what compromise E/E/PE safety, and they can be divided into two categories:
- Systematic failures are related to design and manufacturing processes and can only be alleviated by making a relevant change to those processes.
- Random hardware failures can occur unpredictably during the lifetime of a hardware element.
Safety standards are in place to mitigate both types of failure, so users can have confidence their electronic systems will not pose an undue hazard. Standards intended to protect against systemic failures generally address environmental protection, failure modes, effects, and diagnostic analysis (FMEDAs), separation and segregation of signal paths, diversity of design, and adequate training of personnel. The chance of random hardware failure can be minimized by measures such as adding redundant failure paths and subjecting the parts to less severe environmental stress.
Designers and manufacturers of E/E/PE systems have numerous individual standards to choose from. For example, while IEC 61508 is a general standard, the IEC and the International Organization for Standardization (ISO) also publish many specific standards, each applicable to a different industry, such as automotive, agriculture, machinery, earth moving and more. Furthermore, manufacturers may choose between harmonized standards. In the industrial machinery sector, for example, the ISO standard EN ISO 13849 may be chosen over IEC 62061, or a combination of both may be applied. IEC provides more design analysis flexibility for more complicated electronic subsystems, while ISO 13849 is applicable to mechanical, electromechanical. and simpler electronic systems. ISO/TR 23849 provides guidance on how to apply these two standards.
Manufacturers follow flow charts and other methods to determine which design, manufacturing, operating procedures and safety checkpoints to employ. This carefully considered approach ensures the lowest risk for installed systems. For E/E/PE system engineers, safety is a science in and of itself, and customers can rest assured they are getting equipment that is functionally safe.
The Science of Safety in Use
One example of when these safety standards are important is when E/E/PE systems such as Steer-by-Wire (SbW) Tactile Feedback Devices (TFDs) are integrated into the control systems of marine, industrial and off-highway equipment.
The TFD steering unit is a key component of fully-electric and electro-hydraulic SbW systems. These devices provide an integrated solution that combines bearing support, steering position sensing, communication and continuously variable resistive steering torque, all to deliver high-fidelity tactile feedback and maximum control to the operator. The steering response can be programmed for partial or multiple rotations, to be speed sensitive, and to generate end-stop control, position detents and more. Integration with other devices and technologies, such as electric motors, GPS and vision systems, can provide sophisticated hybrid steering control.
Interested in learning more about safety protocols for E/E/PE systems? Here are a few resources to check out:
- ISO/TR 23849:2010 - Guidance on the application of ISO 13849-1 and IEC 62061 in the design of safety-related control systems for machinery.
- Safety Critical Systems Handbook, David J. Smith and Kenneth G. L. Simpson, ISBN 978-0-08-096781-3.
Contact Parker LORD to get further information on our SbW TFD solutions and other controllable electromechanical systems for industrial use.