Patrick Mongenot

A portable, multiprocess, track-based robot for in situ work on hydropower equipment

In the hydropower industry, in situ maintenance work of turbine runners to address issues such as cavitation damage and cracking is mainly performed manually. Alternatively, the entire turbine requires disassembly and is repaired off site at greater cost. This paper presents the development and fundamentals of robotic technology designed to perform work in situ on hydroelectric equipment. A second paper surveys field implementations carried out with the technology over the past 15 years. A new portable manipulator was designed with unique track-based kinematics well suited to accessing turbine blades in a confined space. The robot is driven by position-controlled stepper motors but relies on a hybrid force/position controller to perform processes in contact with the work piece, such as grinding. A major obstacle for robotic repair is excessive programming time. As most work is done on curved surfaces, the robot relies on a model of curvilinear space for trajectory generation. The robot is coupled to an accurate measurement system to scan surface topography in three dimensions. It has been equipped to perform several processes, such as welding and grinding, to facilitate the manufacture and maintenance of hydropower equipment. Despite the robots inaccuracy and flexibility, surface profiles may be reconstructed with great accuracy through the use of a controlled metal removal rate strategy that relies on an innovative dynamic model of the grinding process.

Field repair and construction of large hydropower equipment with a portable robot

Field repair work on large hydropower equipment is rarely automated due to the high complexity of the task. Generally, the work is done manually or the equipment is dismantled and repaired off site at greatly added cost and time. This paper surveys work carried out with the SCOMPI robot in the field on large hydropower equipment. SCOMPI is a small, portable, multiprocess, track-based robot. This paper is the continuation of another paper in which the fundamentals of the robot technology are described in greater detail. Over the past 15 years, SCOMPIs have been extensively employed for a variety of field applications on equipment such as turbines, head gates, spillway gates, and penstocks. Initially designed to repair cavitation damage to turbines, the robots are now applied to reinforce turbines or to improve their performance in terms of efficiency. More recently, they have been used for the refurbishment of gates and for the construction of penstocks.

Robotic approach to improve turbine surface finish

This paper describes the approach taken by Alstom and Hydro-Quebec (HQ) in the development of robotic polishing to improve turbine efficiency by reducing surface roughness. Modern, large hydraulic turbines are profiled by a 5-axis milling machine and are polished manually. By robotizing the polishing, it becomes possible to obtain a better surface finish at a reasonable cost, and to reduce hydrodynamic friction loss. HQs portable robot Scompi was used to perform the polishing. Recent developments made by the supplier of the abrasives have resulted in their increased durability and improved productivity. A technique was developed to select the polishing process parameters best suited to a given surface waviness and roughness. A polishing test was carried out on a full-scale Francis turbine blade. The surface finish was lowered from Ra=15µm to Ra=0.1µm and the waviness (scallop 0.2mm tall and 30mm wide) was grinded away at a rate of 5 hour/m2.

In-situ robotic interventions in hydraulic turbines

This paper presents the development and implementation of a robotic technology designed to perform in-situ interventions in hydroelectric turbines. A new manipulator was designed with a unique, track-based kinematics well suited to access turbine blades in a confined space. As most work is done on curved surfaces, the robot relies on a curvilinear space model for trajectory generation. Several processes such as gouging, welding, grinding and hammer-peening have been integrated into the robot to facilitate the maintenance of turbines. The robots have been extensively employed by Hydro-Québec (HQ) for cavitation and crack repairs in its turbines. Recently, the robots were used to perform interventions in turbines based on fluid flow numerical analysis. For these new applications, a technology capable of reshaping the surfaces profile with high precision was developed. More than 30 successful field interventions involving up to three robots working simultaneously have been performed in HQ turbines over the last 15 years.

Robotic refurbishment of gate wheel tracks

This paper presents an innovative technique to repair head gate and spillway gate wheel tracks at a fraction of the cost and time usually required, without compromising quality. A small portable robot is used to rectify the wheel track to within very tight tolerances. This is accomplished by coupling the small and flexible robot to an accurate measurement system to scan the wheel track surface topography. Robotic grinding is then performed, using a controlled metal removal rate strategy to iterate toward the desired target profile. If required, a stainless steel plate can be welded over the existing track with an innovative method involving post-heat treatment and hammer peening. This particular welding procedure was developed due to the high carbon content of the steel of the existing track. The technique was successfully tested on a few occasions on gates owned by Rio Tinto Alcan and Hydro Quebec.

Robotic polishing of turbine runners

This paper presents the results of a partnership between Alstom and Hydro-Québec for the development of a new factory robotic polishing process. The goal is to improve turbine efficiency by reducing surface roughness to a level that is unattainable with conventional methods. Three entire axial-flow turbines for Hydro-Québecs Sarcelle power station were polished with this new technique at the Alstom manufacturing plant in Sorel-Tracy as a pilot project between July 2010 and March 2011. The surface finish was lowered from Ra = 15 μm to Ra = 0.1 μm, and the waviness left by numerical control machining was grinded away at an overall rate of 5 h/m2. The reduction of surface roughness from the standard IEC recommendation of Ra=3 μm to Ra=0.1 μm resulted in a 0.5% increase in turbine efficiency. This safe, new method proves its great potential for enhanced surface finish quality, productivity and worker safety.

Robotic refurbishment of a spherical valve

This paper presents a robotic application for in situ repair of the seal surfaces of a large hydropower spherical valve. The repair involves laser scanning, machining, welding and polishing using the portable track-based Scompi robot. To perform the machining, the robot uses a tool guide mechanism that locates accurately the machining tool and holds it against the work surface despite large disturbance forces. The stiffness with which the tool is held is improved significantly. The method was successfully tested in the field at Rio Tinto Alcans Chute-des-Passes generating station in May 2012.