The Customer:

The robotic system, the Weigh and Leak Check System (WALS), is scheduled to replace a manual process at the Department of Energy (DOE) facility at Pantex by which nuclear material is inspected for weight and leakage.

The Work:

This research effort investigated the use of a Failure Modes and Effects Analysis for the safety assessment of a robotic system being developed at Sandia National Laboratories.
 

Failure Modes and Effects Analyses were completed for the robotics process to ensure that safety goals for the system have been met. These analyses have shown that the risks to people and the environment are acceptable.

For the WALS safety analysis, FMEAs were developed for each robotic process step and included the important qualitative hazard levels. The analysis focused attention on several issues important to the development of the system. Two of the most significant are:

1. The available failure rate data is derived primarily from service call information supplied by the robot manufacturer and not on an organized test program to evaluate the system (including safety measures) in response to off-normal situations which include potential robot movements that are not part of designed operations.

2. The WALS system places a strong dependence on software systems to prevent accidents and/or mitigate their consequences.

Key Benefits:

The most important contribution of the approach taken was that the problem broken down into parts became much easier to tackle. In fact, the nature of the robot allowed the analysis of much of the hardware to be performed only once and then replicated for other processes. The FMEAs of processes with roughly similar configurations could then easily share failure modes with each other. The analysis could then be focused around the many other differences in the WALS process steps: robot location, robot configuration, tooling, and payload.
     Upon completion of a FMEA for a process step, an estimate of the potential risks is made. The system designers could then judge whether the level of risk was acceptable or if the system needed to be modified to reduce the risk.

 Results:

The safety analysis iterated around the process steps until an acceptable level of safety is achieved for the overall system and its operation. This procedure ensured that safety was explicitly integrated into the system design process.

 Contacts: 

Chris Atcitty, Dave Robinson, Sandia National Laboratories

References:

1.  Atcitty, C., D. Robinson, (1996), Safety Assessment of a Robotic SystemHandling Nuclear Material, 2nd Conference on Robotics for Challenging Environments, Albuquerque, NM, June 1-6.