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INNOVATIVE ARM RELIES ON THK
BNS ballscrew splines from THK are being used by OC Robotics in an unusual robotics application to provide Ringhals AB in Sweden with a method of repairing a pipe inside the containment vessel of its Boiling Water Reactor. The innovative project required precision movement in all directions due to limited accessibility to the Boiling Water Reactor, meaning that the robot and all associated components had to be robust enough to withstand extremely aggressive operating conditions.
Ringhals is the largest nuclear power plant in Sweden, and one of the biggest in Europe, and generates around 16% of the country’s energy requirements. Built in 1976, the Ringhals 1 Boiling Water Reactor was expected to be reaching the end of its anticipated operating life, but a recent comprehensive audit found that it was still in excellent condition. Consequently, the Swedish Government permitted Ringhals 1 to continue functioning, on the condition that the reactor remained in the current state.
Unfortunately, a damaged section was recently identified on an interior pipe that had to be repaired. The damaged pipe forms part of a complex and closely packed series of pipes, with a maximum indirect access path of 90mm by 800mm, in the Common Insulation Room (CIR) directly below the reactor core. One option to repair the pipe work was to cut a human sized path through the pipe system to allow a person to replace the damaged pipe. Cutting these pipes would have been extremely difficult, however, as it could have been impossible to replace them afterwards, resulting in the reactor being permanently shut down.
Conventional means of repair was therefore impractical, so a bespoke solution was required centred around the idea of using a robot that could access the confined area, capable of negotiating the numerous twists and turns to carry out the necessary remedial work. In addition, the solution developed had to be capable of repairing or maintaining any of the other 156 pipes in the reactor, should a similar problem occur in the future.
As a result, OC Robotics, a Bristol based company specialising in the manufacture of snake-arm robots was approached to design a snake-arm specifically to solve the problem of repairing the damaged pipe work. The technology developed by OC Robotics is used by a wide range of customers requiring cutting edge robotics solutions, in applications such as the security forces, aerospace and nuclear industries. These snake-arm robots are specially designed to reach inside difficult areas such as jet engines or nuclear reactors.
In essence, the snake-arm robots are similar in operation to that of the human spine. Comprising a large number of vertebrae, the snake-arm essentially has a tendon driven arm with wires terminating at various points along the length of the arm. Dedicated motors are used to control the length of individual vertebrae, with control software that calculates the necessary length of all the wires to produce the desired shape. Finally, all services are carried within the arm so that the external surface is smooth and continuous.
Crucial to the movement and precision targeting of the snake-arm robots are THK’s BNS integrated ball screw and ball splines, which provide reliable and accurate linear, spiral and rotational motion with zero backlash resulting in high precision positioning.
Rob Buckingham, one of the Founding Directors of OC Robotics, says, “THK BNS ballscrew splines were undoubtedly the best solution for this unusual application. In addition, excellent service and support was required for this project; THK met all of our requirements on time, and provided first class technical support.”
The BNS ballscrew splines combine the latest advanced ball screw and ball spline technology and consist of a single shaft holding two nuts, one of which moves along a ball spline groove, the other along a ball screw groove, enabling travel in rolling, linear or spiral motion as required. To meet the specific requirements of the snake-arm robots, THK modified the BNS ballscrew splines through a special machining process to fit the size constraints of each motor. In addition, the flanges were altered to fit flush against the motors themselves, minimising space inside the control box even further.
Two snake-arm robots were designed by OC Robotics: one to enter the Ringhals reactor from the top, and the other to reach from below. To get to the damaged pipe in the CIR, the Overhead Arm (OA) had to access it from the CIR itself, while the Underneath Arm (UA) gained access via 62mm holes cut in the 150mm thick stainless steel of the CIR floor. Although similar in design, each of these robots met a specific requirement, to allow for precision placement and allowing the pipe to be repaired.
The precision of the robotic snake arms was critical, as it had a multitude of tasks to perform within the confirmed space available: most robots have six degrees of freedom, but the Overhead Arm has 13 and the Underneath Arm 23 in this specific application. Some of the tasks the robot had to complete included placing the fixtures to immobilise the free end of the post cut pipe, securing the pipe section during cutting, removing the cut section, locating tools and using them to reshape the cut surfaces, introducing the new pipe section, tack welding it in place, locating a gas shield for the final internal weld, and finally, to remove all fixtures and exit the reactor control room without touching any pipe work along the way.
Rob summarises, ‘THK worked in close consultation with us throughout the entire project to design bespoke versions of the BNS ballscrew splines that met our needs exactly. As a result, both of the snake-arm robots were built to the highest possible specifications and in the correct time, allowing the project to be completed on schedule.’
The snake-arm robots proved to be the perfect solution to help Ringhals fix the leak within its 42mm diameter steel pipe, and inspect a further 156 similar pipes within the pipe system. In addition, the process has been approved by an independent panel, to be retained by Ringhals AB, for use as a generic method for inspecting and replacing pipes in the future.
Ringhals is the largest nuclear power plant in Sweden, and one of the biggest in Europe, and generates around 16% of the country’s energy requirements. Built in 1976, the Ringhals 1 Boiling Water Reactor was expected to be reaching the end of its anticipated operating life, but a recent comprehensive audit found that it was still in excellent condition. Consequently, the Swedish Government permitted Ringhals 1 to continue functioning, on the condition that the reactor remained in the current state.
Unfortunately, a damaged section was recently identified on an interior pipe that had to be repaired. The damaged pipe forms part of a complex and closely packed series of pipes, with a maximum indirect access path of 90mm by 800mm, in the Common Insulation Room (CIR) directly below the reactor core. One option to repair the pipe work was to cut a human sized path through the pipe system to allow a person to replace the damaged pipe. Cutting these pipes would have been extremely difficult, however, as it could have been impossible to replace them afterwards, resulting in the reactor being permanently shut down.
Conventional means of repair was therefore impractical, so a bespoke solution was required centred around the idea of using a robot that could access the confined area, capable of negotiating the numerous twists and turns to carry out the necessary remedial work. In addition, the solution developed had to be capable of repairing or maintaining any of the other 156 pipes in the reactor, should a similar problem occur in the future.
As a result, OC Robotics, a Bristol based company specialising in the manufacture of snake-arm robots was approached to design a snake-arm specifically to solve the problem of repairing the damaged pipe work. The technology developed by OC Robotics is used by a wide range of customers requiring cutting edge robotics solutions, in applications such as the security forces, aerospace and nuclear industries. These snake-arm robots are specially designed to reach inside difficult areas such as jet engines or nuclear reactors.
In essence, the snake-arm robots are similar in operation to that of the human spine. Comprising a large number of vertebrae, the snake-arm essentially has a tendon driven arm with wires terminating at various points along the length of the arm. Dedicated motors are used to control the length of individual vertebrae, with control software that calculates the necessary length of all the wires to produce the desired shape. Finally, all services are carried within the arm so that the external surface is smooth and continuous.
Crucial to the movement and precision targeting of the snake-arm robots are THK’s BNS integrated ball screw and ball splines, which provide reliable and accurate linear, spiral and rotational motion with zero backlash resulting in high precision positioning.
Rob Buckingham, one of the Founding Directors of OC Robotics, says, “THK BNS ballscrew splines were undoubtedly the best solution for this unusual application. In addition, excellent service and support was required for this project; THK met all of our requirements on time, and provided first class technical support.”
The BNS ballscrew splines combine the latest advanced ball screw and ball spline technology and consist of a single shaft holding two nuts, one of which moves along a ball spline groove, the other along a ball screw groove, enabling travel in rolling, linear or spiral motion as required. To meet the specific requirements of the snake-arm robots, THK modified the BNS ballscrew splines through a special machining process to fit the size constraints of each motor. In addition, the flanges were altered to fit flush against the motors themselves, minimising space inside the control box even further.
Two snake-arm robots were designed by OC Robotics: one to enter the Ringhals reactor from the top, and the other to reach from below. To get to the damaged pipe in the CIR, the Overhead Arm (OA) had to access it from the CIR itself, while the Underneath Arm (UA) gained access via 62mm holes cut in the 150mm thick stainless steel of the CIR floor. Although similar in design, each of these robots met a specific requirement, to allow for precision placement and allowing the pipe to be repaired.
The precision of the robotic snake arms was critical, as it had a multitude of tasks to perform within the confirmed space available: most robots have six degrees of freedom, but the Overhead Arm has 13 and the Underneath Arm 23 in this specific application. Some of the tasks the robot had to complete included placing the fixtures to immobilise the free end of the post cut pipe, securing the pipe section during cutting, removing the cut section, locating tools and using them to reshape the cut surfaces, introducing the new pipe section, tack welding it in place, locating a gas shield for the final internal weld, and finally, to remove all fixtures and exit the reactor control room without touching any pipe work along the way.
Rob summarises, ‘THK worked in close consultation with us throughout the entire project to design bespoke versions of the BNS ballscrew splines that met our needs exactly. As a result, both of the snake-arm robots were built to the highest possible specifications and in the correct time, allowing the project to be completed on schedule.’
The snake-arm robots proved to be the perfect solution to help Ringhals fix the leak within its 42mm diameter steel pipe, and inspect a further 156 similar pipes within the pipe system. In addition, the process has been approved by an independent panel, to be retained by Ringhals AB, for use as a generic method for inspecting and replacing pipes in the future.
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