The invention relates to apparatus and methods for performing automated assembly operations such as riveting, tacking, or the like, on large panel-shaped workpieces, using positioners that manipulate tool-supporting yokes or frames on which assembly tools are supported.
Large panel-shaped structures used in the construction of airframes commonly have reinforcing members, usually called stringers, attached to outer skins so as to form strong yet lightweight panels. The stringers are usually affixed to the skins by riveting. In a commonly used assembly technique, opposed riveting tools are positioned by two spaced legs of a yoke or C-frame such that the tools are on opposite sides of a workpiece. The C-frame is carried by a multi-axis positioner, which moves the C-frame along the workpiece for riveting at various locations of the workpiece. Typically, the C-frame can be positioned adjacent only one edge of the workpiece, and the legs of the C-frame are used to reach widthwise across the workpiece. In this type of assembly apparatus, if riveting is to be done near the opposite edge of the workpiece, the throat of the C-frame must have a depth about equal to the maximum width of the widest workpiece that is to be processed in the apparatus. Consequently, the C-frame becomes large and heavy. Because the C-frame has a high mass and inertia, the foundation and traversing mechanism that support and move the positioner on which the C-frame is carried must be made very substantial. Accordingly, the overall cost of the assembly apparatus is relatively high. The high inertia of the C-frame and positioner also means that the maximum acceleration of the positioner is relatively low, and thus the apparatus is slow.
As an alternative to sizing the C-frame large enough to reach across the full width of the workpiece, the C-frame positioner can be movable so that it can be positioned at either edge of the workpiece, or the workpiece can be turned 180xc2x0 so that each edge of the workpiece can be positioned adjacent the C-frame. The former possibility necessitates a significantly more complicated positioning system, and the latter possibility is cumbersome and inefficient, particularly where very large workpieces, such as wing panels or the like, are being processed.
A further drawback associated with C-frame type assembly machines, and other types of assembly machines using positioners for manipulating tool-supporting frames (whether C-shaped or of other shapes) that support assembly tooling, is that when the tool-supporting frame and/or its associated assembly tooling require maintenance or tool changes, the frame and its positioner must generally be positioned in a location near the workpiece, and this prevents other positioners from accessing the area of the workpiece near the inactive frame to continue the assembly operations. This same problem also affects gantry-type machines and other types of frame-based machines. Thus, while maintenance or tool changes are being performed, the utilization rate for the assembly cell drops significantly.
The above needs are met and other advantages are achieved by the present invention, which provides assembly apparatus and methods that, in a first aspect of the invention, enable the entire area of a panel-shaped workpiece to be accessed by assembly tooling while avoiding the necessity of using large and heavy C-frames.
To this end, an assembly apparatus in accordance with a preferred embodiment of the invention includes a bed defining a support surface extending along orthogonal X- and Y-axes, and workpiece supports adapted to support a workpiece in a position spaced from the support surface with opposite first and second longitudinal edges of the workpiece extending generally parallel to the X-axis and a width of the workpiece extending generally parallel to the Y-axis. The apparatus also includes at least first and second positioners each supporting and positioning a C-frame having a pair of spaced legs adapted to support tooling for operating upon the workpiece when the workpiece is positioned between the legs. Each positioner comprises a platform operable to travel along the support surface of the bed in a direction parallel to the X-axis and a carriage on which the respective C-frame is mounted and which is supported on the platform so as to be movable relative thereto. The first positioner is arranged to carry its respective C-frame adjacent the first longitudinal edge of the workpiece such that free ends of the legs extend toward the opposite second longitudinal edge of the workpiece. The second positioner is arranged to carry its respective C-frame adjacent the second longitudinal edge of the workpiece such that free ends of the legs extend toward the first longitudinal edge of the workpiece. The legs of each C-frame have sufficient length to carry the tooling across at least about half of a maximum width of the workpiece, and the carriages are movable generally away from each other on the respective platforms to enable the positioners to pass by each other as they travel along the bed parallel to the X-axis. Thus, each positioner can access the entire length of the workpiece with interference from the opposite positioner. Because each C-frame need be no longer than necessary to reach halfway across the workpiece, each positioner and C-frame can be made relatively lightweight and, therefore, can be moved relatively quickly from one position to another.
In another aspect of the invention, apparatus and methods are provided enabling improved utilization rate of an assembly cell by allowing maintenance and/or tooling changes to be made to a tool-supporting frame in a location remote from the associated positioner, so that the positioner can be used with a replacement tool-supporting frame while the original tool-supporting frame is being serviced. To these ends, an apparatus in accordance with a preferred embodiment of the invention comprises a bed defining a support surface extending along orthogonal X- and Y-axes, and workpiece supports adapted to support a workpiece in a position spaced from the support surface with opposite first and second longitudinal edges of the workpiece extending generally parallel to the X-axis and a width of the workpiece extending generally parallel to the Y-axis. The apparatus also includes a first positioner supporting and positioning a tool-supporting frame that supports tooling for operating upon the workpiece. The first positioner comprises a platform operable to travel along the support surface of the bed in a direction parallel to the X-axis and a carriage on which the tool-supporting frame is mounted and which is supported on the platform so as to be movable relative thereto. The tool-supporting frame is releasably mounted on the carriage such that the tool-supporting frame can be removed and replaced. The apparatus further includes at least one additional replacement tool-supporting frame, a service station proximate the bed for storing tool-supporting frames and for performing work operations thereon, and a frame changer operable to remove the tool-supporting frame from the carriage, transport the replacement tool-supporting frame from the service station to the carriage and install the replacement tool-supporting frame into the carriage, and transport the removed tool-supporting frame to the service station such that work can be performed thereon.
The frame changer advantageously comprises a ground vehicle operable to travel to the service station and pick up the replacement tool-supporting frame, travel to a position proximate the positioner having the tool-supporting frame to be replaced, remove the tool-supporting frame from the carriage of the positioner, install the replacement tool-supporting frame into the carriage, travel back to the service station, and unload the replaced tool-supporting frame at the service station. The vehicle can be guided in its movements by any suitable position sensors and a controller.
Preferably, the assembly apparatus includes at least a second positioner supporting a carriage and a tool-supporting frame releasably retained in the carriage, whereby the second positioner can continue to perform work operations on the workpiece while the frame changer is removing and replacing the tool-supporting frame on the first positioner, and vice versa. The first and second positioners are arranged to carry the respective tool-supporting frames along opposite sides of the workpiece, and are preferably configured so they can pass each other as they travel in the lengthwise direction of the workpiece. Depending on the size of the workpiece, it may be advantageous to employ more than one positioner on a given side of the workpiece. Regardless of the number of positioners used, the invention enables improved efficiency and utilization rate by allowing service to be performed on the tool-supporting frames in an xe2x80x9coff-linexe2x80x9d fashion so that positioners are not tied up while the servicing is being performed.
The invention also provides a method for performing assembly operations on panel-shaped workpieces. A preferred method of the invention comprises engaging the workpiece with tooling members supported on a first tool-supporting frame so as to perform assembly operations on the workpiece; moving the first tool-supporting frame relative to the workpiece by a positioner, the positioner releasably supporting the first tool-supporting frame and being operable to travel along the bed to move the first tool-supporting frame lengthwise along the workpiece such that assembly operations are performed at a plurality of locations on the workpiece; taking the first tool-supporting frame out of action so that service can be performed thereon, by moving a frame changer into a position adjacent the positioner, activating a transfer mechanism to cause the first tool-supporting frame to be released from the positioner and to be transferred onto the frame changer and to cause a second tool-supporting frame to be transferred from the frame changer and to be installed into the positioner; moving the frame changer from the position adjacent the positioner to a service station remote therefrom, and transferring the first tool-supporting frame from the frame changer to the service station; and performing service operations on the first tool-supporting frame at the service station. Accordingly, service operations on the first tool-supporting frame and assembly operations on the workpiece with the second tool-supporting frame can be simultaneously performed.