METHOD AND SYSTEM FOR MANUFACTURE OF A WIRE CAGE

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. Ser. No. 60/913,166, filed April 20, 2007, the disclosure of which is incorporated herein by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

Wire cages are commonly used as the reinforcing structure for concrete pipes and other cast concrete products. Typically, the wire cages consist of a series of longitudinal steel rods interconnected by a circumferential spiral wire that is welded to the longitudinal rods. Wire cages are made using a machine composed of a pair of wheels; one of which is stationary and the other of which is movable. The wheels carry clamps that hold the rods as the spiral wire is welded to the rods. The wheels are mechanically coupled to one another by a drive shaft that is rotated by an electric motor to synchronize rotation of the wheels to incrementally present the steel rods and spiral wire to a welding unit. More particularly, the electric motor spins the drive shaft, which then through gears and a chain mounted on the outer edge of both wheels, causes the wheels to rotate. These mechanical connections can deteriorate over time, thereby causing inconsistencies in the rotational velocity of the wheels and ultimately defects in the finished wire cage.

Thus, in one aspect, the present invention is directed to a wire cage forming machine in which the two wheels are not mechanically coupled to one another by a drive shaft. Each wheel is rotated by a separate drive motor, and feedback from the drive motors is used to control the rotational speed of the wheels. For instance, the motors may be controlled by a programmable logic controller (PLC) and arranged in a master-slave arrangement. The rotational speed of the movable wheel may thus be controlled to match the rotational speed of the stationary wheel.

With a conventional wire cage making machine, the wheels are rotated at substantially same speed by the drive shaft. As such, the longitudinal rods are uniformly aligned along the length of the wire cage. That is, the rods are not only parallel with one another along the length of the wire cage, but the angular position of the rods relative to the center axis of the wire cage is constant along the entire length of the rods. This can be problematic for wire cages used in the concrete pipe industry, as the concrete pipe manufacturing machinery can twist the wire cage while the concrete is being formed around the wire cage. This twisting may cause torsional stress in the wire cage, and once the concrete pipe is released from its mold the wire cage has a tendency to straighten from the twisted

state back to its original configuration. This can cause cracks to form in the concrete pipe. Thus, it may be desirable to intentionally twist the rods of the wire cage during the cage making process, so as to counteract the rotational forces applied to the wire cage by the pipe-making equipment during production of the concrete pipe. Twisting the rods using a conventional cage making machine is generally not possible given the mechanical coupling of the wheels. The present invention, howeve,r discloses decoupled wheels that are separately driven by respective electric motors. The electric motors can thus be controlled to rotate the wheels at different speeds or in opposite directions to twist the rods during production of the wire cage. In accordance with another aspect, the invention discloses a friction wheel drive for rotating the wheels. The friction wheel drive reduces vibrations in the cage making machine and therefore provides for smoother operation at higher rotational speeds, hi addition, it is believed that the friction drive is more reliable and less prone to premature mechanical failure.

The wheels of a conventional wire cage making machine include central hubs and spokes extending from the hubs to outer annular rims. Each spoke carriers a rod clamp capable of holding a longitudinal rod at two different radial positions. Thus, the wire cage making machine can make a wire cage having one of two diameters. A single wire cage having certain lengths at one diameter and other lengths at a different diameter may be made by manually changing the position in the clamp where the rods are held, but this is a labor intensive process and, as such, can be costly. hi accordance with another aspect, the present invention discloses an apparatus capable of adjusting the radial spacing of the longitudinal rods without requiring manual repositioning of the rods in their spoke-mounted clamps. Moreover, the apparatus allows the radial spacing to be changed in real-time. In general, the apparatus includes a chain mount slidable along a guide tube. An actuator pushes or pulls the chain mount toward or away from the hub of the stationary wheel. As the chain mount is translated along the guide tube, the radial position of the rod clamps, which are connected to the chain mount by chains, is varied. The radial position of the clamps can be changed independent of the rotation of the stationary wheel. Accordingly, the apparatus of the present invention may be used to produce a wire cage having any desired diameter, hi addition, the diameter of the wire cage can be varied as the cage is being produced, the provide a cage having any desired profile.

Various other features, objects and advantages of the invention will be made apparent from the following description taken together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings illustrate the best mode presently contemplated of carrying out the invention.

In the drawings:

FIG. 1 is an isometric view of a wire cage making machine having a stationary wheel and a movable wheel which are separately and independently driven by respective drive motors, which allows the wheels to be rotated at different speeds and/or different directions, according to one aspect of the invention;

FIG. 2 is a top plan view of the wire cage making machine of FIG. 1; FIG. 3 is a front end elevation view of the stationary wheel incorporated in the wire cage making machine of FIG. 1;

FIG. 4 is a front end view of the movable wheel incorporated in the wire cage making machine of FIG. 1;

FIG. 5 is a front isometric view of the stationary wheel end of the wire cage making machine of Fig. 1, showing a welding head mounted to a pivot arm proximate the stationary wheel, according to one aspect of the invention;

FIG. 6 is a schematic of a welding unit incorporated in the wire cage making machine of FIG. 1, according to one aspect of the invention;

FIG. 7 A is a simplified section view of a cage diameter control system incorporated in the wire cage making machine of FIG. 1, coupled to the stationary wheel and having a chain mount positioned at a first linear position along a guide tube to position rod clamps mounted to spokes of the stationary wheel at a first radial position; FIG. 7B is a simplified section view of the cage diameter control system similar to FIG. 7B, with the chain mount at a second linear position along the guide tub to position the rod clamps at a second radial position along the spokes of the stationary wheel;

FIG. 8 is a schematic diagram of a wire cage produced using the wire cage making machine of FIG. l,with uniformly aligned longitudinal rods; FIG. 9 is a schematic diagram of a another wire cage produced using the wire cage making machine of FIG. 1, with twisted longitudinal rods; and

FIG. 10 is a schematic diagram of a wire cage produced using the wire cage making machine of FIG. 1, with twisted longitudinal rods and variations in cage diameter along the length of the wire cage.

DETAILED DESCRIPTION OF THE INVENTION

This invention relates to a system and method for making wire cages that may be particularly useful for reinforcing concrete pipe or other tubular concrete structures. A wire cage generally consists of a series of longitudinal rods interconnected by a circumferential or spiral rod or wire that is welded to the longitudinal rods at each point at which the circumferential rod or wire intersects the longitudinal rods . A wire cage making machine 10 is shown in FIG. 1 and is composed of four general components or systems: a rod support frame or carriage 12, a cage diameter control system 14, a welding unit 16, and a control station 18. Each of these systems will be described in greater detail below, but generally these systems provide increased flexibility in defining the contour of a wire cage. It is noted that a wire cage making machine may have additional components or systems not specifically described herein.

Rod Support Carriage

Referring to FIGS. 1, 2 and 4, the rod support carriage 12 includes a stationary wheel 20 and a movable wheel 22 supported by a frame 24. The frame 24 includes a pair of rails 26, 28 that support the movable wheel 22 and house a pair of racks 30, 32, respectively, along which the movable wheel 22 may be translated to pull longitudinal rods through the stationary wheel 20, as will be explained further below. The frame further includes a base 34 that supports the stationary wheel 20. The movable wheel 22 is translated along the racks 30, 32 by a drive motor 36 that drives a pair of pinions 38, 40 through a drive shaft 41, along the pair of racks 30, 32. In operation, longitudinal rods are fed through the stationary wheel 20 and fastened to the movable wheel 22.

During the cage making process, the movable wheel 22 is moved away from the stationary wheel 20 by operation of the drive motor 36 rotating the pinions 38, 40 to move along the racks 30, 32, until a desired cage length is reached. It should be noted that the carriage 12 may support more than the one movable wheel shown in the figures. The movable wheel 22 is comprised of an annular rim 42, a hub 44, and a series of radially spaced spokes 46 connected between the rim 42 and the hub 44. A cover 48 generally encloses a

bottom half of the annular rim 42 to prevent unintended contact with the movable wheel 22. Each spoke 46 carries a rod clamp 50, each of which holds the end of a respective longitudinal rod during the cage making process. The rod clamps 50 also hold their respective rods as the wheel is rotated about a central axis 52 extending through the hub 44. The movable wheel 22 is supported on a carriage 53, to which drive motor 36 is mounted.

The movable wheel 22 is supported for rotation on carriage 53 by a central axle oriented along axis 52, which is rotatably mounted within a suitable bearing 55 that is secured to carriage 53.

The movable wheel 22 may be rotated in either a clockwise or counterclockwise direction by a drive motor 54, which drives a roller 56. The drive roller 56 frictionally engages and drives the annular rim 42 in a controlled manner, so as to impart rotation to wheel 22 in response to operation of drive motor 54. It is understood that any other satisfactory type of driving engagement between drive motor 54 and rim 42 may be employed, such as a gear or chain drive.

With additional reference to FIG. 3, the stationary wheel 20 is similar in construction to the movable wheel 22. The stationary wheel 20 includes an annular rim 58, a center hub 60 aligned with axis 52, and a series of spokes 62 that extend between, and are connected to, the hub 60 and the rim 58. Each spoke 62 also carries a rod clamp 64 that retains a respective longitudinal rod but does so in a manner that allows the rods to be pulled through the wheel 20 as the movable wheel 22 is moved.

The stationary wheel 20 is also rotatable about the central axis 52 by a drive motor 65, which rotates a drive roller 66. An annular ring 59 is mounted to the annular rim 58, and the drive roller is engaged with ring 59 to frictionally drive or rotate the annular rim 58. Alternatively, it is understood that any other satisfactory type of driving engagement between drive motor 65 and ring 59 or rim 58 may be employed, such as a gear or chain drive. The stationary wheel 20 is partially encased by a generally arch-shaped bulkhead 68. Rollers 70, 72, and 74 are mounted to an inside surface of the bulkhead 68 and ride along ring 59. Rollers 70, 72, and 74 function to stabilize and guide movement of the wheel 20 as it is rotated.

In one representative embodiment, the stationary wheel 20 and the movable wheel 22 are each frictionally driven by their respective drive motors and rollers. This is in contrast to gear and chain drive systems that are typically employed to rotationally drive the wheels. Frictionally driving the wheels 20, 22 reduces vibrations thereby providing smoother operation at higher rotational speeds. The drive motors are controlled by a programmable logic controller (PLC), with drive motor

54 used as a slave motor and drive motor 65 used as a master motor. In this configuration, the stationary wheel 20 will act as the master and the rotational velocity of wheel 20 will be calculated by the PLC. The velocity of the movable wheel 22 is then calculated and through a feedback system the rotational velocity of movable wheel 22 is correlated to the rotational velocity of the stationary wheel 20. In an application in which a cage having straight longitudinal rods, the rotational velocity of movable wheel 22 is made to match that of stationary wheel 20. This feedback system also allows the slave motor 54 to rotate the wheel 22 at an advanced or retarded pace relative to the stationary wheel 20, to provide the longitudinal rods with a spiral or zig-zag configuration, when desired. This provides considerable benefits and flexibility in the manufacture of wire cages for various applications. hi the illustrated embodiment, a drive shaft does not extend between the wheels (in contrast to known prior art). However, it is understood that the wheels could be connected to a common drive shaft that is rotated by a single drive motor, e.g., drive motor 65 when it is desired that the wheels be rotated in unison. For such an embodiment, a clutch or similar device could be used to disconnect the wheels from the drive shaft when it is desired to separately rotate the wheels.

Welding Unit

As shown in FIGS. 1, 3, and 5, the welding unit 16 is positioned proximate the stationary wheel 20 and generally includes a power unit 76 and a welding head 78. The welding head 78 is mounted to an arm 80 that is pivotably attached to the frame or carriage 12, such as rail 28. More particularly, the arm 80 is pivotably supported by a pivot pin that is engaged with a bracket 82 attached to the rail 28. The bracket 82 allows the arm 80 to pivot about the pivot pin to accommodate for variations in the diameter of the cage, as will be explained further below.

The power unit 76 is supported by a stanchion 84 to which a pair of cylinders 86, 88 are mounted. The cylinders 86, 88 include rams 90, 92, respectively, that are coupled to the arm 80. When the rams 90, 92 are extended, the arm 80, and thus the welding head 78, is pivoted about bracket 82 to move welding head 78 inwardly. Likewise, when the rams 90, 92 are retracted, the arm 80, and thus the welding head 78, is pivoted about bracket 82 to move welding head 78 outwardly. In one embodiment, the cylinders are hydraulic cylinders, but other types of cylinders or actuators may be used, such as pneumatic cylinders, or similar mechanized devices, such as screw drives or other linear actuators.

The welding head 78 is designed to spot weld wire circumferentially around the longitudinal rods extending between the wheels 20, 22 that form the body of the wire cage. The welded circumferential wire effectively joins the longitudinal rods together to form the cage. In this regard, the circumferential wire is fed from a wire supply 94, FIG. 1, to the welding head 78. The circumferential wire is guided by an arcuate guide channel 96 supported by table 98, which may be integrally formed with the frame or carriage 12. The circumferential wire is fed through a eye 99, and is held against the guide wall by rollers 100 that are supported by the table 98. The wire is then threaded through rollers 102 and a pinch 104. From the pinch 104, the wire is passed under rollers 106, 108 that are mounted to arm 80, and is then fed to the welding head 78 for welding to the longitudinal rods .

During the cage making process, the circumferential wire is presented to the welding head 78, which spot welds the circumferential wire to the longitudinal rods extending through the stationary wheel 20 and held by the movable wheel 22 as the longitudinal rods are rotated by the wheels 20, 22 and moved axially away from the stationary wheel 22 by movement of movable wheel 20. The spot welding operation is carried out as the stationary and movable wheels 20, 22 are rotated so that the longitudinal rods are successively presented to the welding head 78 along with the circumferential rod. The constant rotation of the stationary wheel 20 ensures that the circumferential wire is maintained taut against the longitudinal rods, so that a good weld can be made. The welding head 78 may then weld the wire to the next longitudinal rod. The movement of movable wheel 22 along the rails 26, 28 as the welding operation is taking place provides the circumferential wire with a spiral configuration a around the longitudinal rods,.

In one embodiment, the welding unit 16 welds wire to the steel rods at 1000 Hz with a 400A current. In this regard, the welding unit 16 offers a number of advantages over the welding machines conventionally used in cage manufacturing. Specifically, the welding unit creates less slag and spark while welding, along with creating a stronger weld that is less tempered than the weld produced by conventional welding units. Additionally, weld time is less with welding unit 16 compared to conventional welding units, which yields reduced cage production time that can be realized in increased productivity for the manufacturer. The welding unit 16 also provides less tempering of the steel rods. This allows steel to be used which contains more carbon than can be used with traditional welding units. Moreover, high carbon steel wire is generally less expensive than low carbon steel wire thereby providing a decrease in manufacturing costs.

As shown in the table above, the weld time of welding unit 16 may be half the time of a conventional welding unit. This provides extra time for the welding unit 16 to create a ramp effect using pulse width modulation in order to allow the steel to cool relatively slowly over an additional 10 ms period of time. During this cooling process the carbon contained in the steel is kept misaligned, which permits the steel to retain its malleable properties. This is in contrast to conventional manufacturing techniques which utilize multiple heating and cooling cycles for a single weld, which may result in steel that is tempered, where the carbon molecules in the steel align with one another and create very hard and brittle portions near the weld area thereby reducing the strength of the overall wire cage.

In one embodiment, the welding operation carried out by the welding head 78 uses a pair of rollers and brushes to transfer electrical current to the wire and longitudinal rods, such as illustrated in FIGS. 3 and 5. However, in another embodiment, which is schematically illustrated in FIG. 6, the welding head 78 has a copper welding contact 110 that forms the welding arc with the steel rods 112 during welding of wire 114 to the longitudinal steel rods 112 without the aforementioned rollers and brushes, which tend to create relatively large resistance that must be overcome. The welding head 78 utilizes two hydraulic cylinders 116, 118 to maintain proper position of the copper contact 110. Copper contact 110, in one embodiment, is much smaller than that used in conventional welding heads, which greatly reduces the weight and cost of the head. In addition, the welding unit 78 uses a linear welding head which increases the flow of current to the copper contact and steel rods resulting in a stronger weld.

The hydraulic cylinders 116, 118 may be controlled to minimize the wear of the copper contact as it contacts the wire and steel rods. The use of a hydraulic system instead of a pneumatic system allows for less expensive "soft copper" to be used as the contact for the welding head rather than "hard copper". "Soft copper" is less expensive than the "hard" copper alloy which is typically used to make the contacts.

As noted above, a linear welding head may be used rather than rotating copper wheels and brushes. This may provide greater efficiency in the welding circuit as a result in the decrease in the resistance between the connection of the copper contact 110 and the transmission wires 120, which are used to transmit the current from the welding transformer 122 to the contact 110. When transmitting 15 kilo-amperes of current, for example, a change of resistance of even one ohm can make a very large difference in efficiency. With a linear welding head the connection between the welding transformer 122 and the copper contact 110 is a constant contact and has a very low resistance compared to copper brushes contacting the spinning copper wheels.

Rod Radial Spacing Control

Referring again to FIGS. 1 and 2, and with further reference to FIGS. 7 A and 7B, the rod radial spacing control system 14 includes a guide tube 124 connected at one end to the hub 60 of the stationary wheel 20 and connected at an opposite end to a post 126. The guide tube 124 is designed to rotate with rotation of the stationary wheel 20. In this regard, the guide tube 124 is fixed to the hub 60 of the stationary wheel 20 and is coupled to the post 126 through a bearing 128.

A chain mount 130 is mounted to the guide tube 124 and rotates with the guide tube 124. A series of chain guides 136 are mounted to a forward face of the chain mount 130. The number of chain guides 136 is equal to the number of rod clamps 64 carried by the spokes 62 of the wheel 20. Chain guides 138, 140, which are in the form of sprockets, are secured to a rear surface of a hub mount 143 that is coupled to the hub 60 of the wheel 20. Chain guides 138 are spaced inwardly of chain guides 140. An additional set of chain guides 142, which are also in the form of sprockets, are mounted to the spokes 62 of the wheel. More particularly, a flange 144 is mounted to each of the spokes 62 and the chain guides 142 are coupled to the flanges 144.

Two respective chains 146, 148 are associated with each spoke 62 of the stationary wheel 20. Chain 146 has a first end 150 coupled to a bracket 152 to which clamp 64 is connected and a second end 154 connected to a carrier bracket 156. A cylinder 132 is housed within the guide tube 124 and includes a ram 134 that is coupled to the carrier bracket 156 through a slide block 157. The ram 134 is preferably fixed to the slide block 157 so as to rotate with the slide block 157. However, the cylinder 132 is arranged within the interior of guide tube 124 so as not to rotate along with guide tube 124. To this end, suitable bearings may be positioned between the cylinder 132 and the inner wall of guide tube 124, so that cylinder 132 does not rotate.

When the ram 134 is retracted, the carrier bracket 156 is moved along the guide tube 124 and away from the wheel 20. Similarly, when the ram 134 is extended the carrier bracket 156 moves toward the wheel 20.

Chain 148 has a first end 158 that is coupled to the clamp bracket 152 and a second end 160 that is coupled to the carrier bracket 156. When the ram 134 is extended, the carrier bracket 156 is pushed toward wheel 20 which results in the chains 146, 148 moving in a clockwise direction (in the illustrated figure). As the clamp 64 is coupled to chains 146, 148, the clamp 64 will move in response to movement of the carrier bracket 156. Thus, when the ram 134 is extended, the clamps 64 are pushed away from the hub 60 by their respective chains 146, 148. Each clamp 64 carries a rod guide tube 162 through which the longitudinal rods extend. As such, the rods are pushed away from the hub 60 as the ram 134 is extended.

Conversely, when the ram 134 is retracted the ram 134 forces the carrier bracket 156 away from the hub 60. As a result, chains 146, 148 are pulled in a counterclockwise direction. Each clamp 64 is thus moved toward the hub 60 to decrease the distance of each rod from the hub 60 decreasing the diameter of the wire cage. This is particularly evident by comparing FIGS. 7 A and 7B. FIG. 7 A shows the clamps 64 at a decreased radial distance resulting from retraction of the ram 134, and FIG. 7B shows the clamps at an increased radial distance resulting from extension of the ram 134.

A linear position sensor is used to detect the linear position of the ram 134 and provide a corresponding signal to the control station 18, which may include a computer or similar processor for determining the radial position of the clamps 64 from the position of the ram and move the welding head described above accordingly. Representatively, the linear position sensor may be a magnetoresistive transducer-type position sensor such as is available from Gefran under its model number IKlA, although it is understood that any other satisfactory type of position sensor may be employed.

Control Station

The control station 18 can be of conventional design and, as such, includes various operator input controls and system monitoring devices including dials, meters, and other displays. The control station 18 includes a computer (not shown) or other processor to effectuate operator control of the cage making process including, but not limited to automated control of the various

components of the cage making machine 10 such as those described herein. In one embodiment, the control station 18 includes controls that allow an operator to interface with the rod spacing control components to change the diameter of a wire cage, or portions thereof, in real-time. The welding unit 16 can also be controlled, either manually or in an automated fashion, to respond to changes in the spacing of the longitudinal rods so that welding head is suitably pivoted toward or away from the longitudinal rods. Additionally, the control station allows an operator to interactively control the rotational speed of each wheel 20, 22 or execute a stored program that independently controls the rotational speed of each wheel 20, 22 which may include driving the wheels 20, 22 to rotate at different speeds or in different directions.

Exemplary Wire Cage Contours

As illustrated in FIGS. 8-10, the present invention allows flexibility in the contour of a wire cage. FIG. 8 shows a schematic for a wire cage 164 made with wheel 20 and 22 being rotated at the same velocity. The wire cage 164 is generally cylindrical in shape and is defined by a number of longitudinal steel rods 166 joined together by a circumferential wire 168. The circumferential wire 168 has a generally spiral or helical shape which occurs by moving the movable wheel 22 away from wheel 20 as the wheels 20, 22 are rotated. FIG. 9 shows a wire cage 164(a) in which the longitudinal steel rods 166(a) are angled from end-to-end. The diameter of the wire cage 164(a) is uniform along the length of the wire cage 164(a). The angling of the rods 166(a) is created by rotating the wheels 20, 22 at different speeds. The wire cage 164(a) is advantageous in countering the torsional stresses placed on the wire cage during concrete pipe formation. More particularly, the twist in the longitudinal rods may be made to oppose the twist generated by the concrete pipe manufacturing process.

FIG. 10 shows a wire cage 164(b) in which the longitudinal rods 166(b) are angled and the radial spacing of the rods is not uniform along the length of the cage 164(b). As noted above, the rods can be twisted by rotating the wheels 20, 22 at different speeds and/or directions. A radial distance of the rods 166(b) from the center axis of the cage 164(b) can be achieved by extending and retracting the ram 134 so that the position of the rods along their respective spokes varies during the cage making process. It is appreciated that contours and shapes other than those shown in FIGS. 8- 10 may be achieved through control of wheel rotational speed, wheel translation speed, and translation of the rod clamps.

Various alternatives and embodiments are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter regarded as the invention.