Metal working – Method of mechanical manufacture – With testing or indicating
Reexamination Certificate
2002-04-04
2004-07-20
Bryant, David P. (Department: 3726)
Metal working
Method of mechanical manufacture
With testing or indicating
C029S430000, C029S464000, C029S525110, C029S714000, C029S721000, C029S787000, C029S798000
Reexamination Certificate
active
06763564
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an automated manufacturing process, and more specifically to an automated method and apparatus for driving fasteners into an electric fan assembly.
BACKGROUND OF THE INVENTION
Many types of electric fans comprise a fan motor and fan blade assembly that are housed within a housing that includes a peripheral shroud of a generally flat material, such as sheet metal, to create an outer peripheral surface of the housing. The shroud is typically formed into a generally square-shaped periphery, leaving a front portion and a rear portion of the housing open. To enclose the housing, a generally planar front and rear grill are attached to the shroud. The grills are typically made of a plastic material and include a peripheral lip portion generally transverse to the grill plane that provides a planar surface through which the fasteners may be driven. Likewise, the shroud also includes a peripheral lip portion, or flange, to provide material to accommodate the fasteners.
Typical fan assembly processes require a worker to lay each grill onto the housing and align the grill to the housing by sight. To fasten each grill to the housing, a worker, typically using a hand held automatic screw driver, drives screws into the grill and housing around the periphery of the housing. In square-shaped fan housings, this typically involves driving a total of six screws per side of the square periphery.
When the worker initially begins driving each screw, some initial pressure needs to be applied to facilitate penetration of the screw into the lip portion of the grill. Thereafter, each screw moves relatively easily though the grill material, especially when the material is a plastic material. However, when each screw reaches the metal material of the housing, the worker typically needs to add additional pressure, or continue applying sufficient pressure, to allow the screw to pierce the metal. Threads of each of the screws then engage the metal, and the worker continues to apply pressure until the screw has sufficiently engaged both the grill and the metal shroud. The worker then repeats this same process to complete the assembly for each grill.
This manual process is time consuming and increases labor costs significantly, especially when the large quantities of fans are being assembled. Other disadvantages come to mind in utilizing human labor for such a significant amount of driving, including human error and possible injuries. While the manual process does allow for a certain level of torque control, especially when penetrating multiple layers of differing material having different properties, the torque control still remains subjective and vulnerable to error. The lack of consistent control over the torque and penetration of the fasteners, exacerbated by the application of multiple material types, creates a significant challenge to both manual and automated processes.
Some automated processes are well-known in the art. For example, U.S. Pat. No. 4,672,866, to Riera et al. and entitled “Automatic Fastener System With Fastener Detection Means,” discloses an automatic fastener driving system suitable for robotic applications utilizing a modified fastener driver having a detection mechanism in the head of the driver working in combination with a pneumatically operated advance and retract mechanism, and control circuitry, to detect when a fastener is present in the driver, to advance and drive the fastener into the workpiece, and to then automatically retract therefrom. The driving system uses a fastener detecting means which is capable of providing a signal when a screw, or other fastener, is present. In addition, a slide system is provided to advance and retract the driver head. Both of these features are operated by a suitable control means to accomplish this functionality. However, this arrangement does not allow the torque load to be preset and does not sufficiently control the torque of the drivers during various stages of screw penetration.
U.S. Pat. No. 5,229,931 to Takeshima, entitled “Nut Runner Control System and Method of Monitoring Nut Runners,” discloses a means to prevent the torques of each fastener from varying with respect to each other. This function is accomplished by driving the fasteners to a preliminary torque level which is slightly less than the desired torque level. When the preliminary torque level has been reached, the drivers are temporarily stopped and then restarted after a certain period of time. While some level of torque control is provided, this arrangement does not prevent over tightening and stripping because it does not sufficiently control the torque of the drivers near the final stage of screw penetration. Because of the multi-material construction presented by fan assemblies, such control is extremely important to prevent overtorquing, stripping and defective or incomplete screw penetration.
The present invention offers a solution to these and other problems by providing a means for reducing the pneumatic pressure supplied to the driver at a gradual rate so that the velocity of the fastener reduces over time, thereby mechanically simulating manual tightening.
The present invention also provides an assembly apparatus particularly suitable for fast, efficient and accurate assembly of grills to shrouds of a fan housing.
Other features and advantages will be apparent to those skilled in the art after review of the description herein.
SUMMARY OF THE INVENTION
An apparatus and method for assembling a fan grill to a shroud of a fan housing. The apparatus includes a support structure having a moveable carriage disposed in a horizontal plane. The moveable carriage is adapted to align and carry the fan grill and shroud combination. A clamping structure is moveably attached to the support structure and has clamps adapted to clamp the fan grill and shroud combination in a fixed position. A plurality of automatic drivers attached to the clamping structure are moveable in a direction transverse to the horizontal plane of the carriage. The automatic drivers drive a plurality of fasteners into the fan grill and shroud combination.
According to a particular aspect of the invention, the moveable carriage is adapted to carry more than one fan grill and shroud combination to allow an operator to load a second fan grill and shroud combination onto the carriage while a first fan grill and shroud combination is engaged by the drivers.
According to another particular aspect of the invention, the fan grill and shroud combination includes a second fan grill and the apparatus further includes a second plurality of automatic drivers and clamps attached to the clamping structure. The second plurality of drivers are moveable in a direction transverse to the horizontal plane of the carriage to drive a plurality of fasteners into the second fan grill and shroud.
According to another particular aspect of the invention, each of the automatic drivers are independently controllable in relation to each other via a control system.
According to another particular aspect of the invention, the apparatus includes a control system that is capable of controlling torque of a pneumatic driver. A canister having a fixed volume is in selective communication with an air source in communication with the driver. An adjustable air regulator is connected to the canister and a sensor is connected to the pneumatic driver. The sensor is in communication with the control system and communicates with the control system to terminate communication of air flow to the cannister upon penetration of the fasteners into the fan shroud. The air regulator regulates a flow rate of air from the canister to the pneumatic driver upon termination of air flow to the cannister, thereby regulating torque generated by the pneumatic driver in relation to the regulation of the flow rate of air from the canister.
According to yet another aspect of the invention, a sensor is in communication with at least one of the automatic drivers, wherein the sensor capable of sensing a drive fault associated
Bryant David P.
Lakewood Engineering and Manufacturing Co.
Wallenstein Wagner & Rockey Ltd.
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