What does functional safety mean?

 "The primary objective of functional safety is to reduce the risk of personal injury."      

Source: www.netzwerk-baumaschinen.de 

An electronic module, controller or sensor is considered to be functionally safe if a fault in this module does not cause unacceptable damage to persons.

How is functional safety linked to the construction machinery sector?

Here is an example of a possible safety-critical situation that can occur during the operation of a construction machine:

A length sensor measures the wrong distance, causing a hydraulic cylinder to extend too far and the machine to reach a dangerous tilted position.

Many people think directly of an aerial work platform (EN 280), but also a road milling machine (EN 500) could get into a dangerous tilted position by uncontrolled extension of one crawler track.

Another example of functional safety in the construction machinery market would be an uncontrolled lateral movement of a grader blade, which could endanger people or other vehicles. For this reason, a distinction is made between road travel and construction site travel in the case of earth-moving machinery (EN 474). In road travel, e. g. during transfer journeys, the hydraulics are usually inactive and there is no safety risk for other vehicles and their occupants.

How do you begin when a module or a system is to be developed according to functional safety requirements?

At the beginning of the system and module design, a risk analysis is always necessary to determine which dangers are present on and around the machine and what effects a misbehaviour of the machine would have on the probability of personal injury and the severity of a possible injury.

To do this, it is first necessary to define the individual safety functions.

Using the example of an aerial work platform, one of the safety functions would be to safely switch off all movements before reaching the tipping point of the machine.

The risk analysis of the stability of an aerial work platform would come to the following conclusion:

• The operator in the basket is particularly at risk due to the height of the machine, which could result in serious injury if the machine is overturned. S2
• As an operator in the basket, he is permanently exposed to danger. F2
• However, there is a possibility of preventing the machine from tipping over by using safe sensors and evaluation units. P1

If we now look at the risk graph, we come to a required Performance Level D.

How do you achieve the required Performance Level D? 

One of several possibilities is the completely redundant execution of sensors, logic and actuators.

This means that the measurement signal is acquired twice, read in twice, processed twice and compared with each other in the logic units. Only if both logic units come to the same result, it is allowed to control the corresponding output.

Back to the aerial work platform:

In order to realize the stability analysis of an aerial work platform, various signals are recorded redundantly.

• Extension length of the support legs
• Ground contacts of the support legs
• Extension length of the telescopic arm
• Inclination angle of the telescopic arm
• Weight in the working basket
• …and many more

From these sensor values, which are read in doubly and thus reliably, a diagram for load moment limitation can be calculated and the machine may only work within this space. When the load limit is reached, the movement is automatically stopped and only load-reducing movements are permitted in order to bring the persons safely back to the ground.

Which role does MOBA project management play in the design of a module or system according to functional safety criteria?

• Functional safety is already considered at MOBA during the hole product development process:
• In addition to the function of the product to be developed, a risk analysis and an FMEA are prepared from the very beginning.
• Special development methods and secure development environments are used.
• Special safety libraries are available and are constantly being expanded.
• During the development of the first code lines, parallel test scenarios are programmed in order to verify and validate the software with unit tests and in connection with the hardware in so-called integration tests.
• Communication networks are built up securely and CAN protocols are extended by properties to meet functional safety requirements. 

All these points are an integral part of a project plan at MOBA.

This makes MOBA to the right partner when it comes to the development and design of modules and systems for functional safety.

Think safe, think MOBA.