Patent Application
20090127279
This invention relates generally to automatic riveting machines used in large-scale riveting operations, and more specifically concerns a rivet injector system for moving an incoming rivet from a feed tube to spring-closed fingers on a rivet ram which thereafter insert the rivet into a previously drilled hole in a workpiece, where it is formed by action of the ram.
Automatic riveting machines are frequently used for large-scale riveting operations such as in the manufacture of aircraft wing panels. In a typical riveting operation, the machine first clamps together the workpiece parts to be joined. A hole is then drilled in the workpiece parts by one tool mounted on a transfer mechanism, such as a tool shuttle. A rivet is transferred/injected to the riveting assembly, which moves the rivet into the hole. A ram portion of the riveting assembly then forms the rivet in the hole. The ram is withdrawn and then another tool on the tool shuttle is typically moved into position to shave the head of the formed rivet flush to the wing panel or other workpiece, although in some cases, the rivets are not shaved. The tool shuttle is then moved to the next rivet location.
One widely-used commercial rivet injection system is manufactured by Gemcor Engineering Corporation, shown in a variety of U.S. patents, among them U.S. Pat. No. 5,065,818. In that patent, rivets are delivered down a tube, coming to rest on a bottom plate. The rivet is then moved between two jaw-like members and from the jaw-like members the rivet moves across a gap to opposing grasping fingers, which clamp against the outside surface of the rivet. In such a system, however, the rivet is not securely held at all times during injection, and hence there is the possibility of a misalignment of the rivet or a dropped rivet during injection. Further, different length rivets change the axial position of the rivet relative to the ram, resulting in a variable gap between the rivet and the ram. This typically requires that the position of the ram be moved, which can be problematic.
Accordingly, disclosed and claimed herein is a system for transporting rivets, for use in all automatic riveting machine, provided from a feed tube, comprising: a set of rivet fingers mounted on a ram portion of the automatic riveting machine for grasping a rivet; and a rivet injector assembly for receiving a rivet by air pressure from a feed tube, holding the rivet first at opposing longitudinal ends of the rivet, moving it into the grasp of the rivet fingers and then releasing the rivet so that the ram portion can move the rivet held by the rivet fingers into a drilled hole in a workpiece.
The description of the rivet injection system herein follows the movement of a rivet from an infeed tube to a final position in the grasp of a pair of spring-loaded rivet fingers oil ram 13, with a series of partially cutaway views of the injection system and a detailed exploded view of the entire assembly in
In
Although the Figures and their description have the system in a particular orientation, it should be understood that the system can work with the chamber and rivet pad in any orientation.
The rivet chamber 30 is defined by a surface 33 on which the rivet pad 32 is positioned and a slidable cover 40 which is mounted for to-and-fro movement at the top of the rivet transport body 22. Within the forward end of cover 40 is an internal cavity which forms the upper boundary or ceiling of and the sides of chamber 30. Surface 33 of chamber 30 is a portion of a top surface of tower assembly 46. Tower assembly 46 is mounted for up/down sliding action on the forward surface of the rivet transport body 22.
As a rivet 11 is moved through feed channel 24 and then into chamber 30 (
At the rear of rivet chamber 30 is mounted a moveable pop-up stopper pin 70 (
The slidable cover 40 is now moved to the rear by slide cover air cylinder 80, opening chamber 30 and exposing rivet 11 positioned on rivet pad 32, held fast by stopper pin 70 and grip bar end 50 and groove 37 of the rivet pad, as shown in
The tower assembly 46 is then slidably moved up the front of the rivet transport body 22 by action of the tower air cylinder 82, until the rivet 11 encounters an opposing pair of horizontally positioned grasping rivet fingers 86 and 88. The rivet fingers 86 and 88 are elongated metal members which are spring-loaded and mounted on opposing sides of a rivet ram 13. The fingers include notched portions at the forward ends thereof which enable the fingers to grasp the curved outer longitudinal surface of the rivet. The spring-loading of the grasping rivet fingers tends to force the forward ends of rivet fingers 86 and 88 in a closed position (against each other). When the tower assembly 46 is raised, rivet 11 is forced between the rivet fingers 86 and 88. The tower assembly is stopped by a mechanical stop when the rivet is positioned between the rivet fingers. The rivet is still held between stopper pin 70 and rivet bar end 50 and supported on groove 37 of the rivet pad 32 at this point, as well as between the notched portions of the forward ends of the rivet fingers. This is shown in
The stopper pin 70 is then retracted by its associated air cylinder 72 and the gripper bar 52 is retracted by air cylinder 68, as shown in
One important aspect of the system is that the rivet is first held at three surfaces, between its respective ends by the stopper pin 70 and the grip bar end 50, and supported on a side surface by rivet pad 32. The holding of the respective ends is referred to as an axial hold or gripping of the rivet. This arrangement helps to maintain proper alignment and secure holding of the rivet during the injection process. This three-surface holding of the rivet (the two ends and the side support) is maintained until the rivet is positioned between the spring-loaded rivet fingers. For a brief time, before assembly 46 is lowered, the rivet is held at both ends, opposing sides by the grasping fingers and supported along another side surface, i.e. it is held at five surfaces, prior to the rivet being held just by the two fingers. The rivet is held positively by the injector system at all times.
The axial gripping arrangement, as the rivet is moved into the chamber 30, always results in the rivet being moved first against the grip bar end 50, and then to the rear in chamber 30, against the stopper pin 70, which is fixed in position relative to the ram. Hence, there is always a fixed distance between the rear end of the rivet and the die 12, regardless of the length of the rivet. The system thus easily accommodates different length rivets, without having to change the position of the ram. The difference in rivet length simply changes the distance between the forward end of the rivet and the workpiece.
The rivet chamber, specifically the slidable cover 40, can have openings therein to permit airflow to pass around the rivet and out of the chamber, while still holding it against the grip bar end. The present arrangement allows only one rivet in the chamber 30 at a time. The operating distance (defined as the distance from the grip bar end 50 to the stopper pin 70 within chamber 30) is longer than the longest rivet to be injected but shorter than twice the shortest rivet. If more than one rivet is fed into the chamber 30, then the stopper pin is not able to fully extend from its retracted position (it will hit the rear-most rivet). This produces an automatic purge sequence in which the rivet chamber is opened and all the rivets are blown out of the chamber 30. A new rivet is then fed into the chamber.
Accordingly, the rivet injector system described and shown herein accomplishes the injection of rivets and the subsequent feeding of rivets into a workpiece fast and reliably, by combining a rivet injection assembly which axially holds a rivet and supports a side surface thereof with a pair of horizontally arranged grasping rivet fingers to which the rivet is transferred by the injection system for subsequent insertion into the workpiece opening and forming of the rivet. The rivet is positively held at all times.
Although a preferred embodiment of the invention has been disclosed here for the purposes of illustration, it should be understood that various changes, modifications and substitutions may be incorporated in the embodiment without departing from the spirit of the invention, which is defined by the claims which follow.
