Method and apparatus for fabricating helically shaped ribbons of material

Apparatus and methods are utilized to form turbulators. The apparatus includes a first mechanism for accepting a ribbon of material along an axis, a second mechanism for rotating an end of the ribbon of material, and a third mechanism for moving the second mechanism substantially parallel to the axis. The third mechanism is configured to operate independently from the operation of the second mechanism.

BACKGROUND OF THE INVENTION

This invention relates generally to methods and apparatus for forming ribbons of material into helixes, and more particularly to methods and apparatus for fabricating multifaceted ribbons of material having a helical configuration.

Heat exchangers sometimes include turbulators to improve heat transfer efficiency. Typically, these turbulators are formed from sheets, or ribbons, of material. The material is cut to a specific length and rotated to form a helical shape. In addition, the twisted ribbon may include facets or bumps to provide better performance. The inclusion of facets onto the turbulators is difficult to automate due to metal working characteristics of the ribbons. In addition, the formation of consistent, symmetrical facets on the ribbons is even more difficult in an automated production due to operation characteristics of the machinery.

BRIEF DESCRIPTION OF THE INVENTION

In one aspect of the invention, an apparatus is provided for manipulating a ribbon of material. The apparatus comprising a first mechanism for accepting the ribbon of material along an axis, a second mechanism for rotating an end of the ribbon of material, and a third mechanism for moving the second mechanism substantially parallel to the axis. The third mechanism is configured to operate independently from the operation of the second mechanism.

In another aspect, a method of fabricating a turbulator utilizing an apparatus is provided. The method comprising engaging a first end of a ribbon of material with a spindle head and moving the first end of the material along an axis, wherein the movement is performed in a first movement pattern. The method also includes rotating the first end of the material about the axis, wherein the rotation is performed in a second movement pattern. The first movement pattern is different from the second movement pattern.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments of apparatus and methods of fabricating helically shaped ribbons of material are described below. In one embodiment, the helically shaped ribbon of material is a turbulator and the apparatus fabricates the turbulator from a ribbon of material and imparts a plurality of consistent, symmetrical facets to the material. The apparatus includes a first portion that pulls the material at a varied speed in a direction substantially parallel to the ribbon and a second portion that rotates one end of the material as the material is being pulled. The rotation speed is independent of the speed of the pulling movement.

Although exemplary embodiments are described herein, the apparatus and methods are not limited to those specific embodiments. For example, although apparatus and methods are described for a two ribbon machine, machines that employ more or less than two ribbons of material can also be used. Further, although the initial material is described as a ribbon, other starting materials, such as sheets of material or wire may also be used.

The apparatus and methods are illustrated with reference to the figures wherein similar numbers indicate the same elements in all figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate explanation of an exemplary embodiment of the apparatus and methods of the invention.

FIG. 1illustrates a top view of an apparatus10utilized to fabricate turbulators (not shown inFIG. 1) and a feeding mechanism12. Apparatus10is configured to manipulate two ribbons of material simultaneously. It should be understood that devices are also contemplated that are able to manipulate only one ribbon of material as well as devices that are able to manipulate more than two ribbons of material. Feeding mechanism12includes a pair of feeding spools14, each holding a ribbon16of material. In one embodiment, the material is metal, e.g., steel, aluminum, copper, and other metals. Alternatively, the material is plastic. Apparatus10also includes a tensioning device18downstream of feeding mechanism12, and an introducer device20downstream of tensioning device18. A die22is located downstream of introducer device20and an engagement device24is downstream of die22.

In operation, each ribbon16proceeds substantially parallel to an axis26of apparatus10. Ribbon16is fed to tensioning mechanism18which includes two tensioning devices28,30. Each tensioning device28,30is configured to receive a respective ribbon16. Each ribbon16then enters introducer mechanism20that includes two introducer devices32,34. Each introducer device32,34feeds a respective strand of ribbon16to die22. Die22cuts both strands of ribbon16to form a first end on each strand of ribbon16. Each first end of ribbon16is fed to an engagement mechanism24including a first spindle head36and a second spindle head38. Each spindle head36,38engages the first end of a respective ribbon16with a respective pair of jaws40,42. Each pair of jaws is connected to a respective air cylinder44,46that opens and closes jaws40,42. After engagement of ribbon16by spindle heads36,38, engagement mechanism24moves substantially parallel to axis26in a first direction away from die22for a first distance. Die22then cuts ribbons16so the finished product has the correct length. After ribbons16have been cut, engagement mechanism24again moves in the first direction for a second distance. Engagement mechanism24then disengages the cut and formed ribbons and the formed ribbons are released from spindle heads36,38. Engagement mechanism24then moves in a second direction, opposite the first direction for a distance equal to the sum of the first distance and the second distance to reposition at the engagement position.

Spindle heads36,38are moved parallel to axis26by a mechanism including a first servo motor48. First end of first ribbon16is rotated by a mechanism including a second servo motor50and first end of second ribbon16is rotated by a mechanism including a third servo motor52. Each servo motor is electrically connected to a controller54. Controller54separately controls the operation of servo motors48,50,52such that each motor48,50,52is able to operate at a speed different from the operation speed of either of the other two motors. In one embodiment, controller46is an Allen-Bradley controller utilizing a touch screen interface such as a ControlLogix/1756 controller available from Rockwell Automation Corporation, Milwaukee Wis., 53202. Due to the independent operation of servo motors48,50,52, the speed, acceleration, and deceleration at which each ribbon16is rotated by spindle heads36and38can be varied with respect to each ribbon as well as to the speed of movement of engagement mechanism24along axis26.26.

In one embodiment, controller54is programmable to allow the operator to select the slide travel length, slide velocity, slide acceleration/deceleration, and jog slide left/right. Such options enable the operator to custom design turbulators for specific purposes. The customization includes the length of the turbulator, the pitch of the turns of the turbulator, the number, size and consistency of the facets included on the turbulator, and the centering of ribbon16in spindle heads36,38.

FIG. 2is a schematic illustration of a side view of apparatus10mounted to a frame60. Die22is manipulated utilizing a pneumatic cylinder62that moves die22substantially perpendicular to axis26. Pneumatic cylinder62imparts sufficient pressure to die22such that die22is able to cut ribbons16.

Each pair of jaws40,42(only pair of jaws40is shown inFIG. 2) engage the first end (not shown) of ribbon16. Servo motor50is connected to a coupling66that is connected to spindle head36and jaws40. Spindle head36includes appropriate gearing and connections to enable jaws40to rotate at the appropriate speeds during movement of spindle heads36,38along transport beam68. Spindle heads36,38traverse transport beam68and are connected to servo motor48with a drive unit70. In one embodiment, drive unit70is a belt. In another embodiment, drive unit70is a chain. Alternatively, drive unit70is a geared mechanism.

Once ribbons16are formed into turbulators and cut to the appropriate length, the turbulators, once disengaged by jaws64, are released and fall into reception cavity72. In use, a basket, or similar device, is positioned within reception cavity72and is utilized to capture and retain the formed, cut turbulators. Part sensors (not shown) are located within apparatus10to detect part drop. These sensors activate a counter which counts the number of formed parts.

FIG. 3is a perspective view andFIG. 4is a side view of engagement mechanism24. Each of jaws40,42extends through a respective rotating disk80and includes a first member82and a second member84. Rotating disk80is fixedly connected to coupling66. Engagement mechanism24further includes a sliding mechanism86having a sliding collar88that maintains contact with, and travels along a slide rail90. Slide rail90is substantially parallel to axis26.

FIG. 5is a cut away side view of a portion of engagement mechanism24. Jaws40include a biasing member102and a pivot pin104. Biasing member102biases first member82away from second member84such that jaws40are biased to be in an open position. In one embodiment, biasing member102is a compression spring. Spindle head36includes a jaw locking portion106, a piston108, a piston shaft110, a housing112and at least one biasing member114. Biasing member114biases jaw locking portion106to be in the position shown inFIG. 5, i.e., the closed position. Relative movement between jaws40and jaw locking portion106causes jaws40to open and close by allowing first member82to move away from second member84. In an exemplary embodiment, jaw locking portion106, piston108and piston shaft110are unitary and are configured to move away from jaws40. Movement of jaw locking portion106away from jaws40causes jaws40to move away from each other and obtain an open position.

FIG. 6is a schematic illustration of a turbulator150fabricated utilizing apparatus10(shown inFIG. 1). Turbulator150includes ribbon16having a first end152, a second end154and a helical shape therebetween. In addition, turbulator150includes a plurality of facets156. Facets156are triangular in shape and have a consistent size and shape from a facets starting location158to a facets ending location160. The consistency of facets156is attributed, at least in part, to the varied speed at which engagement mechanism24manipulates ribbon16.

In a particular embodiment, turbulators150are formed by initially moving ribbon16at a first speed in a first direction that is parallel to axis26to a first position while imparting a pre-twist to the ribbon. At the first position, jaws40are rotated at a first rate so that a twist is imparted to ribbon16as the ribbon first end traverses along axis26at a second speed to a second position. In one embodiment, the second speed is greater than the first speed. At the second position, jaws40are rotated at a second rate as ribbon16traverses along axis26at a third speed to a third position. At the third position, jaws40are rotated at a third rate as ribbon16traverses along axis26at a fourth speed to a fourth position. At the fourth position, a post-twist is imparted to ribbon16. The post twist is in a direction opposite the direction of the pre-twist and is conducted to relieve the tension from the ribbon such that the ribbon does not create a curl in the last flat. After the post-twist, die22cuts ribbon16and ribbon16is moved along axis26to a fifth position at a fifth speed without rotation of jaws64. The fifth speed is less than the fourth speed. In one embodiment, the second speed, third speed, and fourth speed are the same. In an alternative embodiment, the third speed is less than the second speed and the fourth speed. In a further alternative embodiment, the third speed is greater than the second speed and the fourth speed. In addition, the rotation rate is adjustable independently for each strand of ribbon16being manipulated.

The combination of the twist rate and the speed of ribbon along axis26is responsible for imparting facets156to turbulator150. The consistency of facets156can be varied by altering either or both of the twist rate and the axial speed.

The above described apparatus and methods provide an automated fabrication process for forming turbulators. The process imparts symmetrical and consistent facets during formation of the turbulators. While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.