Controlling a Robotic Manipulator for Nuclear Decommissioning With CompactRIO and the LabVIEW Robotics Module

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"The NI platform provided a safe, fast, reliable, and cost-effective development environment and allowed us to produce a valuable tool that is able to solve many nuclear decommissioning challenges across the planet."

- Dr. Carwyn Jones, James Fisher Nuclear Ltd

The Challenge:
Developing a cost-effective modular robotic manipulator for use with a range of remote handling tasks in nuclear decommissioning applications, which represent some of the most hazardous environments on the planet.

The Solution:
Using NI CompactRIO hardware, NI LabVIEW system design software, and the NI LabVIEW Robotics Module to develop a cost-effective, safe, and reliable system that provides accurate remote control of a heavy-duty manipulator in an environment that is otherwise inaccessible to humans.

Author(s):
Dr. Carwyn Jones - James Fisher Nuclear Ltd
Dr. David Keeling - Key Engineering Solutions Limited
Justin Gallagher - Key Engineering Solutions Limited

Tough Challenges for the Nuclear Industry

Decommissioning redundant nuclear facilities, coupled with the subsequent decontamination and processing of nuclear waste, is a crucial challenge for the nuclear industry. Many of these processes require the adoption of remote handling techniques to minimise the risk to human operators. Often, these tasks need to be performed in high-radiation environments, frequently complicated by a combination of heat, humidity, caustic or acidic fumes, and limited visibility.

With more than 30 years experience in the nuclear sector, James Fisher Nuclear Ltd (JFN) specialises in robust, remote handling and inspection solutions for the decommissioning of nuclear facilities and processing of nuclear waste. JFN’s remote solutions range from dexterous manipulators that handle heavy loads in harsh environments to high-tech remote inspection or navigation systems. Remote inspection solutions draw on technologies such as ultrasonics, laser scanning, chemical sensing, camera systems, heat monitoring, and defect detection sensing using electromagnetic sources. In several applications, this data is used to navigate or maintain difficult-to-access areas remotely.

ModuMan 100 Concept

Current commercial robotic manipulators are largely inadequate for nuclear decommissioning tasks due to limitations in radiation tolerance, dexterity, working range, and payload. A fundamental difficulty for many arms is that they cannot be inserted into a standard diameter penetration port (smaller than 300 mm) adopted by the nuclear industry. The available manipulators are expensive. JFN wanted to develop a modular manipulator to use for a range of remote handling and decommissioning tasks to suit customer needs while remaining cost effective.

We developed the ModuMan 100 manipulator as a powerful workhorse for the nuclear decommissioning industry. It offers six degrees of freedom (6DoF)  and provides a functional 2.3 metre reach and a payload capacity of 100 kg at full stretch. The arm can be deployed through a standard-size penetration port for radiological cells or by using a carrier system and is compatible with a range of tooling. We selected the construction materials for the harsh operating environment and designed the link lengths to give optimum dexterity to navigate restricted environments.

ModuMan 100 Design

Our design goals included making the manipulator modular, cost effective, and maintainable, whilst making best use of off-the-shelf solutions. We designed the system with in-cell (inaccessible area within harsh environment) and out-cell components. In-cell multiple hydraulic actuators power the joint motion and out-cell powers a dual servo motor arrangement that drives the shoulder to rotate. All the hydraulic sensors and drives are located out-cell to provide ease of maintenance and to minimise downtime. At the end of the arm, a jaw picks out debris or grasps tools such as a shears, drills, and wash-down equipment to aid in decommissioning.

To navigate the environment, the operator uses two 3-axis joysticks, which provides proportional control for each individual joint. An NI USB-6212 module acquires analogue joystick data and controls LED indicators, which confirm the current mode of operation, if the jaws are locked, and if that joystick is active to the operator. A comprehensive user interface uses the NI TPC-2512 touch panel to help the user select which mode to control the arm with, including joint, world, and tool. The touch panel also presents data such as current joint angles and their software limits, the end effector position and orientation, fault analysis, and a teach and repeat interface.

We use NI LabVIEW system design software and NI CompactRIO hardware to control the manipulator within the harsh area. More specifically, we use an NI cRIO-9024 controller, NI cRIO-9118 chassis, NI 9239 analogue input module, NI 9425 sinking digital input module, NI 9485 8-channel relay module, NI 9263 analogue output module, and NI 9401 high-speed bidirectional digital I/O module. The rugged and reliable CompactRIO platform is easy to maintain and scalable for future modifications to the system.

During the system’s development process, CompactRIO was ideal for modular testing and prototyping. Where hardware wasn’t available, we could simulate inputs, which ensured the software was functionally correct before we incorporated it into hardware. When individual hardware components became available during the manufacturing process, we could carry out loaded and unloaded single joint testing using CompactRIO.

ModuMan 100 Implementation

We linked the touch panel human machine interface (HMI) to the CompactRIO system through a combination of TCP communication and network-published shared variables. On the CompactRIO system, the real-time controller runs the kinematics algorithms for the ModuMan 100 as well as the teach and repeat function. The PROFIBUS communications link to the Moog proportional integral derivative (PID) controllers using the COMSOFT PROFIBUS module. The Moog precision control servo valve drives and motor drivers are used throughout the arm.

Aside from the real-time processor, CompactRIO incorporates a Xilinx FPGA. Any code that we deploy to the FPGA effectively becomes a hardware solution, representing the highest performance and reliability. Thus, we reserve the FPGA for all of our safety-critical processing. Following this safety methodology ensures we comply with Machinery Directive 2006/42/EC for the control system. This is essential for us to receive the CE marking, which is a mandatory conformity designation for products sold in the European Economic Area.

Safety is a critical design aspect. The arm can lock out the hydraulic system and electric motors to instantaneously stop motion. All communication paths feature watchdogs checking the status of each part of the system. Any issues or loss of communication stop the system in a safe state and alert the user.

A comprehensive fault analysis system runs on the real-time controller. This system classifies, reports, and acts upon all hardware- and software-defined faults that could occur. Safety-critical faults immediately trigger the FPGA to put the arm into a safe state and inform the user on the HMI. Noncritical faults are logged to the internal nonvolatile memory of the CompactRIO system as well as the HMI’s hard drive. The thoroughness of the fault analysis system eases post-failure investigation.

The NI LabVIEW Robotics Module runs deterministically on the real-time controller to effectively implement the kinematics for the ModuMan 100. This helps users drive the manipulator’s end effector with multijoint resolved motion control. The ability to drive the arm based on the end effector position provides the user essential fine control during operation, which improves movement accuracy and minimises the risk of collisions. The LabVIEW Robotics Module helps define the manipulator using Denavit-Hatenburg parameters, which means we can quickly and easily modify the kinematics control if future design iterations include additional joints or different link lengths.

We implement a teach and repeat facility on the real-time controller to assist with operation of the robotic manipulator for repetitive tasks. This provides 6DoF real world paths that can be defined and replayed easily. These paths can be initiated from the HMI and replayed at any time within 5 mm accuracy at the end-effector during any path.


 

Advantages of the NI Solution

CompactRIO provided a rugged and reliable stand-alone platform at the heart of the ModuMan 100 system. We used the LabVIEW Robotics Module to quickly generate kinematics, which gave us effective deterministic control of the system. The CompactRIO ideally supported the fast-paced development process, which has significantly lowered our development time over competitor’s equipment and has ensured ModuMan 100 is a cost-effective product.

Another major advantage of using the NI platform was access to the NI Alliance Partners, who specialise in many areas of engineering. Key Engineering Solutions, CompactRIO hardware and robotics experts, played a pivotal role in architecting and commissioning our ModuMan 100 software.

Conclusion

We successfully designed and developed the ModuMan 100 to satisfy key customers’ needs including safety, reliability, and versatility. The system has undergone in-house and offsite testing and is being used for longevity trials simulating its designed harsh environment. This process provided us with significant confidence in the equipment and real operator feedback. This feedback highlighted how quick and easy it is for operators to train and master the system, which is a result of our intuitive and easy-to-use user interface.

The NI platform provided a safe, fast, reliable, and cost-effective development environment and helped us produce a valuable tool that is able to solve many nuclear decommissioning challenges across the planet.

Author Information:
Dr. Carwyn Jones
James Fisher Nuclear Ltd
York Road Business Park, Malton
North Yorkshire YO17 6YB
United Kingdom
Tel: 01653 602844
carwyn.jones@jfnl.co.uk

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