Patent Application
20120111843
Not Applicable
Not Applicable
Welding is a common joining technique for many materials and the most common bonding method for metals. Welding is a commonly automated manufacturing technique for many metal-based products. However, there remain a number of systems that exist at a size, scale or location that do not permit traditional methods of automated welding. Methods that have been proposed, developed and or implemented to provide some level of mechanization or automation to these types of systems might be placed in one of three categories:
This approach makes use of industrial welding robots (generally serial architecture type) located in a facility designed to manipulate large scale manufactured components. In many cases, the base of the conventional manipulator may be mounted to a larger manipulator, for example a gantry system. This approach has several difficulties that generally limit its use: 1) it requires significant capital investment to design and install such a system, which affects the entire manufacture process, 2) This facility is at a fixed location and 3) it is difficult to access many portions of a large structure when assembly begins on a large system.
This approach again makes use of commercially-available, mechanically-guided weld mechanization systems that operate on a fixed guide or rail. These mechanically guided systems generally have 3-4 degrees of freedom (dof), with relatively small range of motion (typically less than 300 mm travel along a linear axis) and operate along a pre-installed mechanical guide or track. The systems can be designed to specific jobs and have a wide range of applications. These systems can operate fully in open loop with a welding operator guiding the motion, or may provide some level of sensing and closed-loop control. The primary difficulty with these systems lies in the requirement to pre-install the mechanical guide or track. This job is generally deemed a non-value added process, and may represent a significant portion of the weld process. Further, the pre-installation process may limit the flexibility of the process in manufacturing; it generally is not feasible to leave the track installed for multiple manufacturing operations.
Mobile-platform type weld systems represent the third approach to mechanizing weld processes on systems of large scale and size. These consist of a mobile platform that obtains locomotion and the ability to traverse a surface without the need for a pre-installed track or rail system. They are generally small, man-portable, and may employ mechanical guidance based on a physical feature, manual guidance by an operator, or use some type of closed loop control for guidance based on sensing some feature associated with the weld seam. Several commercial products of mobile welding systems are available, most designed to operate on a horizontal surface performing a down hand weld. Some of these mobile welding carriages are equipped with suspended electro or permanent magnets or magnetic wheels or tracks for use in all position welding. However, these carriages in general have a few key disadvantages, such as loss of holding strength from the magnets on non-flat surfaces, inability to adapt to curved surfaces or protrusions (for example weld seams) on a generally flat surface, and localization of the holding forces on to a small number of the adhering members when multiple magnetic adhering members are used. These disadvantages have limited their widespread use of mobile welding carriages in automating welding operations in out of position welds. The prior art shows carriages or vehicles for use with welding or other similar manufacturing operations of a few primary types: carriages with suspended magnets, magnetic wheels, or magnetic endless tracks or chains. Examples of these are presented as follows.
U.S. Pat. Nos. 3,764,777, 5,853,655, 6,627,004 and Fisher, Tache and Siegwart (2008) show variations of a welding and cutting carriage with magnetic wheels and positioning arm for performing manufacturing tasks on flat or uniformly curved surfaces. The magnetic wheel systems are affixed to a rigid carriage, which will cause some of the wheels, when four or more wheels are used, to detach when operating on non-flat or non-uniform surfaces causing degradation in holding power.
U.S. Pat. No. 7,309,464 shows a steerable magnetic wheel carriage with wheel frames supported on the carriage frame. The magnetic wheel systems are affixed to a frame which will cause some of the wheels, when four or more wheels are used, to detach when operating on non-flat or non-uniform surfaces causing degradation in holding power.
US Patent application publication US 2010/0176106 A1 shows a magnetic wheel carriage with magnetic wheels that rotate about axes that are able to change orientation relative to the carriage frame. The additional mobility in the wheel axes allow a larger number of wheels to make contact with a climbing surface when operating on non-flat or non-uniform climbing surfaces. However, under equilibrium the loads are transferred according to the relative compliance of the carriage frame and wheel axle system and in general will be localized to a small number of the magnetic wheels causing degradation in holding power.
U.S. Pat. No. 5,435,405 shows an example of a type of climbing carriage or vehicle that contains magnets or similar adhering members attached to endless tracks, with multiple magnets attaching to the climbing surface at any given time. However, these systems tend to either place the magnets on a track without a track guide or mechanism between the end wheels (for example U.S. Pat. No. 5,884,642 or Shen and Shen, 2005) and rely on tension in the track to transfer climbing forces to the adhering members, or on a track with a rigid track guide limiting the ability to conform to a non-uniform climbing surfaces (for example U.S. Pat. No. 5,487,440, Kim et al., 2008) or a guide that has some flexibility but for purposes of pushing in a single direction on the track to make contact with the climbing surface (for example U.S. Pat. No. 4,789,037). When climbing the loads required to maintain equilibrium are transferred to the adhering members according to the relative compliance of the carriage frame and endless track system and in general will be localized to a small number of the adhering members causing degradation in holding power.
Xu and Ma (2002) shows an endless-track type climbing vehicle with type of climbing vehicle with magnets called magnetic suckers. A load distribution mechanism is presented as a three link member connected to the vehicle body with a single spring. The article does not show how the endless track would connect with the load scatter mechanism or how forces are transferred from the track to the mechanism. Further, as presented, the load scatter mechanism localizes moment-balance forces to the leading portion of the load scatter mechanism and similarly the leading edge of the endless track.
U.S. Pat. No. 7,498,542 shows control method and system for trackless all-position welding based on an endless-track type climbing vehicle, tracks here called caterpillar belts. This vehicle places the adhering magnets on a track without a track guide or mechanism between the end wheels and thus relies on tension in the track to carry all climbing forces. This localizes the climbing forces on the magnets lying on the outer ends of the track contact region and degrades the payload capacity of the operating system.
Endless track-type vehicles with adhering members attached to the exterior of the endless track also generally share an additional characteristic of varying pitch length between a driving wheel or sprocket and the climbing surface as the endless track revolves around the driving wheels or sprockets. This variable pitch results in a non-uniform velocity ratio between the drive wheel or sprocket rotation and translation of the vehicle over the climbing surface. This is a problem in manufacturing operations such as welding where precise, controlled travel speeds are required to maintain the quality of the weld process.
Collectively, the prior art demonstrates mobile carriages that meet the primary navigation and control requirements to carry out weld operations in all positions. However, these devices contain several limitations that have restricted their widespread use in manufacturing, including the ability to climb over surfaces with variations or regularities, efficient use of the adhering members by distributing the climbing load in an improved fashion, and maintaining uniform, stabilized motion of the weld torch.
This invention presents a mobile welding system that addresses these issues by providing multiple adhering members, attached to an endless track passing through a flexible suspension capable of accommodating irregularities in the climbing surface, with a load distributing mechanism that is able to distribute loads required for equilibrium among the adhering members causing maximizing holding power of the vehicle in all weld positions over non uniform climbing surfaces, and a means for stabilizing torch motions.
The invention described in this document creates a mobile welding platform capable of climbing all positions, flat, inverted and upside down positions while carrying and manipulating welding or other manufacturing tools. This invention allows a welding operator to perform a weld in a remote fashion in a variety of positions including flat surfaces, inverted surfaces horizontal or vertical, butt welds, lap welds and fillet welds. The invention allows the weld operations to occur surfaces that are not uniform, and provides a high payload to weight ratio of the vehicle by effective use of the adhering members through optimized load distribution.
The invention allows a weld operator to supervise and control the weld process through a hand-held controller that provides feedback of the weld process and allows control of all actuated motions on the welding vehicle that include two degree of freedom control of the weld vehicle and up to five degree of freedom control of the weld torch. The invention allows the weld operator to specify weld motion control parameters for five axes, three translations of the weld torch and two rotations of the weld torch (about the axes orthogonal to the welding access). The invention provides closed loop motion control on all five axes to track the settings input by the welding operator while rejecting disturbances. The invention also provides closed-loop tracking control to maintain the position of the robot along the longitudinal weld seam. The invention achieves this through the following:
1) The invention defines a prescribed magnetic field created by the permanent magnet tracks allowing adaptation with all welding type equipment, particularly welding processes that are most sensitive to external magnetic field (for example pulsed-arc GMAW type weld magnetic). This also allows the torch to be placed in many locations around the mobile platform, and it allows compact design, fit into compact areas by allowing the torch to be near magnetic tracks.
2) The welding platform of this invention integrates a multi-link suspension apparatus that distributes climbing loads to maximize the system payload to weight ratio.
3) The welding platform of this invention integrates a multi-link I suspension apparatus that is adaptive to irregularities in the climbing surface.
4) The invention system contains a torch manipulator that is independently suspended from the tractor. Thus it isolates undesirable motions in the tractor from the torch. This lowers the control requirements on the tractor, allowing it to be small and control only the torch component. This keeps high resolution control components small, reduced mass, reduced dynamic control authority needed. This reduces the size and cost of the torch manipulator.
5) The invention integrates the torch manipulator and mobile platform in a reconfigurable and modular arrangement to position the torch anywhere inside, outside or around the platform, within a minimal distance of the permanent magnet tracks, inside or outside, in front or behind, to achieve a large range of weld types.
The drawings constitute a part of this specification and include exemplary embodiments to the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.
Detailed descriptions of the preferred embodiment are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, specific details disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one skilled in the art to employ the present invention in virtually any appropriately detailed system, structure or manner.
The mobile endless track welding vehicle (1) is illustrated in
This application claims the priority of U.S. Provisional Application Ser. No. 61/456,416 entitled “Mobile, climbing robotic system to perform remote welds on ferrous structures” filed on Nov. 8, 2010, the entire contents and substance of which are hereby incorporated in total by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61456416 | Nov 2010 | US |
