System and method for straightening and elongating a glass core rod

A lathe-based system may include chucks to retain a glass core rod, an arm, a slip joint, an actuator system, and a control system. The slip joint may couple the arm and a first chuck in fixed relation against relative axial motion with respect to an axis of rotation. The slip joint may also couple the arm and the first chuck in two-dimensionally movable relation with respect to a plane normal to the axis of rotation. The actuator system may be configured to two-dimensionally adjust a position of the first chuck in the plane. The control system may measure straightness of the glass core rod and control the actuator system in response to optical measurements of the straightness. In this manner, the system may straighten the glass core rod. The system may simultaneously elongate the glass core rod as it straightens the glass core rod.

BACKGROUND

In optical fiber manufacturing processes, fiber is drawn from a large-diameter glass structure known as a preform. Processes for making a preform include modified chemical vapor deposition (MCVD), outside vapor deposition (OVD) and vapor axial deposition (VAD). In MCVD, a hollow glass tube is collapsed inwardly to form a solid glass core rod to which cladding layers are then added. In OVD and VAD, particles are deposited on a glass core rod (also known as a seed rod or bait rod). In some types of processes for making a preform, it is important that the core rod be straight before the core rod is drawn or further elongated.

One method for straightening a glass core rod of the tubular type used in MCVD uses a rotating machine having a heating torch to soften the rod and a machine-vision feedback system to control the speed of rotation. The machine-vision feedback system measures the amount of bow in a rotating core rod and adjusts the speed of rotation to allow gravity to pull any upward bow in the core rod downwardly. While this method may be suitable for straightening the thin-walled tubes used in MCVD, it may be less suitable for straightening the solid (and thus more massive) core rods used in OVD and VAD.

Another method for straightening a glass core rod involves placing the core rod in a rotating machine, commonly referred to as a straightening lathe, and manually straightening the core rod. As a heating torch, which may be mounted on a carriage, is moved to different positions along the length of the core rod, an operator visually judges the straightness of the rotating core rod and presses a tool against portions of the rotating core rod judged to be bowed, until the operator judges the rod to be straight. After the core rod has been straightened, it may be transferred to a similar rotating machine, commonly referred to as an elongation lathe. The elongation lathe stretches or elongates the core rod while a heating torch, which may be mounted on a carriage, traverses the length of the core rod.

Some lathes of the types described above that are used to straighten or elongate core rods may include an optical measuring system comprising a laser and an optical sensor. The laser may direct a beam toward the core rod, and the optical sensor may receive the beam partially blocked by the core rod. Based on the optical sensor, the measuring system may display for the operator a measurement of the diameter or displacement of the core rod. The optical measuring system may be mounted on the same carriage as the torch.

SUMMARY

Embodiments of the invention relate to systems, devices, and methods for straightening a glass core rod. In some embodiments, the systems, devices, and methods may also elongate the glass core rod.

In one aspect, embodiments of a system may include a first chuck, an arm, a slip joint, an actuator system, and a control system. The first chuck may have a first chuck axis of rotation and is configured to retain a first end of a glass core rod in an orientation wherein a longitudinal axis of the glass core rod is substantially aligned with the first chuck axis of rotation. The arm may have an arm axis substantially aligned with the first chuck axis of rotation. The slip joint may couple the arm and the first chuck in fixed relation against relative axial motion with respect to the first chuck axis of rotation. The slip joint may also couple the arm and the first chuck in two-dimensionally movable relation with respect to a plane normal to the first chuck axis of rotation. The actuator system may be coupled to the arm and may be configured to two-dimensionally adjust a position of the first chuck in the plane. The control system may include an optical sensing system configured to measure straightness of the glass core rod. The control system may be configured to control the actuator system in response to optical measurements of the straightness of the glass core rod.

In another aspect, embodiments of a system may include a lathe, an arm, a slip joint, an elongation drive system, an actuator system, and a control system. The lathe may have a first chuck and a second chuck, each rotatably mounted with respect to a lathe axis of rotation, and configured to retain first and second ends of a glass core rod, respectively. The lathe may include a rotational drive system configured to rotate the first and second chucks. The arm may have an arm axis substantially aligned with the lathe axis of rotation. The slip joint may connect the arm and the first chuck in fixed relation against relative axial motion with respect to the lathe axis of rotation. The slip joint may also connect the arm and the first chuck in two-dimensionally movable relation with respect to a plane normal to the lathe axis of rotation. The elongation drive system may be coupled to the arm and configured to translate the first chuck along the lathe axis of rotation via the slip joint. The actuator system may be coupled to the arm and configured to two-dimensionally adjust a position of the first chuck in the plane via the slip joint. The control system may include an optical sensing system configured to measure straightness of the glass core rod. The control system may be configured to control the actuator system in response to optical measurements of the straightness of the glass core rod.

Embodiments of a method may include mounting a glass core rod in a lathe by retaining first and second ends of the glass core rod in first and second chucks, respectively. The method may further include rotating the glass core rod in the lathe. The method may also include measuring straightness of the glass core rod in the lathe using an optical sensing system. The method may further include heating a portion of the glass core rod in the lathe. The method may still further include two-dimensionally adjusting a position of the first chuck in a plane normal to the lathe axis of rotation using an actuator system and a control system responsive to measurements received from the optical sensing system.

Other devices, systems, methods, features, and advantages will be or become apparent to one of skill in the art upon examination of the following figures and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the specification, and be protected by the accompanying claims.

DETAILED DESCRIPTION

As illustrated inFIG. 1, in an illustrative or exemplary embodiment of the invention, a system10is configured to rotate and otherwise work upon a glass core rod12(workpiece). System10thus may have characteristics of a lathe. The term “lathe” as used herein broadly means a machine in which a workpiece is rotated about an axis, without limitation as to the manner in which the workpiece may be worked upon. Accordingly, in system10, a first chuck14is configured to retain a first end of glass core rod12, and a second chuck16is configured to retain a second end of glass core rod12. First and second chucks14and16may be of a conventional type known to be usable in glassworking lathes or similar lathes. For example, first and second chucks14and16may have sets of jaws15and17, respectively, which an operator can adjust to clamp the ends of glass core rod12. Second chuck16is coupled to a headstock18, and first chuck14is coupled to a tailstock20in a manner that allows first and second chucks14and16to rotate about a lathe axis (of rotation)22. The terms “headstock” and “tailstock” are used for convenience and do not indicate any spatial relationship to each other or other elements of system10.

Headstock18and tailstock20are connected to a base24. In the illustrated embodiment, the connection between headstock18and base24may be configured to fix headstock18in place. The connection between tailstock20and base24may be configured to allow tailstock20to traverse or move along base24parallel to lathe axis22. Although tailstock20may move in a direction away from headstock18during a process (described in further detail below) of elongating glass core rod12, tailstock20may be moveable in either direction, as indicated by the double-headed arrow26. Although in the exemplary embodiment, headstock18may be mounted in a fixed position on base24, in other embodiments both the headstock and tailstock may be moveable with respect to the base. Although not shown inFIG. 1, base24may contain a rotational drive system configured to rotate first and second chucks14and16through drive mechanisms in tailstock20and headstock18, respectively. Similarly, although not shown inFIG. 1, base24may contain a translational or elongation drive system configured to move tailstock20in the directions indicated by arrow26. Although not shown for purposes of clarity, base24may have a track or rail that tailstock20engages to guide or otherwise control the movement of tailstock20.

System10includes a device30that couples first chuck14to tailstock20and functions in a manner described below to aid straightening glass core rod12. System10also includes a torch32and an optical sensing system34. Torch32may function in a manner described below to heat a portion of glass core rod12, so that it softens and becomes workable (e.g., bendable). Optical sensing system34may be configured to measure the displacement of a portion of glass core rod12. Measurements of such a distance may be used to estimate the straightness of glass core rod12. The straightness of glass core rod12may be characterized in any way, such as deviations of points on glass core rod12from a line parallel to lathe axis22that would indicate glass core rod12is bowed, bent, etc. Torch32and optical sensing system34may be mounted on a carriage36configured to move in the directions indicated by the double-headed arrow37. Carriage36may engage the above-referenced track or rail in base24to guide or otherwise control the movement of carriage36. Although in the illustrated embodiment torch32and optical sensing system34are mounted on the same carriage36, in other embodiments (not shown) such a torch and optical sensing system may be mounted on separate carriages that are independently movable. Also, although in the illustrated embodiment there is only a single torch32and a single optical sensing system34, in other embodiments there may be more than one torch or more than one optical sensing system.

As illustrated inFIGS. 2 and 4, device30may include a body38coupled to an arm40. Body38may be generally cylindrical in shape. Arm40likewise may be generally cylindrical or rod shaped. Arm40is configured to rotate about the above-described lathe axis22. First chuck14is connected in fixed relation to body38. As the internal structure of first chuck14may be conventional and well known to one of ordinary skill in the art, first chuck14is not shown in cross section inFIG. 4.

A slip joint is defined by the coupling between arm40and body38(and thus between arm40and first chuck14). The slip joint is defined by the manner in which a pin42, which is connected to an end of arm40, is retained in a retaining cavity44in body38. More specifically, in the illustrated embodiment, pin42and retaining cavity44are each cylindrical in shape, and pin42is slip fit within retaining cavity44. That is, retaining cavity44has a width (dimension in the direction of lathe axis22) that is just slightly greater than the width of pin42, such that pin42can slide within retaining cavity44in two dimensions in a plane normal to lathe axis22. The slip joint may be lubricated to reduce friction between pin42and the adjacent walls of retaining cavity44.

As illustrated inFIG. 3, the above-referenced plane normal to lathe axis22may be described by a two-dimensional (X-Y) coordinate system. InFIG. 3, arrows indicate a positive X axis, a negative X axis, a positive Y axis, and a negative Y axis in an X-Y coordinate system that has lathe axis22at its origin. Note that pin44is free to move or slide with respect to retaining cavity44in any direction in a plane normal to lathe axis22(i.e., two dimensionally), and that such a direction may be defined using the X-Y coordinate system. Freedom of movement of pin42is limited or constrained by the spacing between the periphery of pin44and the walls of retaining cavity44. As the shapes of pin42and retaining cavity44are cylindrical in the illustrated embodiment, freedom of movement of pin42in plane normal to lathe axis22is limited or constrained by the difference between the diameters of pin42and retaining cavity44.

Referring again toFIG. 4, arm40extends from pin42through an opening46in body38to connect with tailstock20. Opening46may have a diameter less than the diameter of pin42to capture or retain pin42within retaining cavity44. Note that while pin42is free to move or slide with respect to body38in a plane normal to lathe axis22, pin42is coupled essentially in fixed relation to body38with respect to lathe axis22. Stated another way, the slip joint couples arm40and first chuck14in movable relation to each other with respect to a plane normal to lathe axis22, yet couples arm40and first chuck14in fixed relation against axial motion relative to each other with respect to lathe axis22(and thus the first chuck axis of rotation). Accordingly, in operation, as described in further detail below, motion of arm40in an axial direction (i.e., along lathe axis22) is transferred to body38and thus also transferred to first chuck14.

Arm40also extends through a frame48, which is connected in fixed relation to arm40and thus is configured to rotate with arm40about lathe axis22. Frame48may be generally cylindrical and have a cup shape defined by an interior space50. A portion of body38extends into interior space50.

An actuator system comprising actuator motors52,54,56, and58may be arranged at equidistant intervals about the periphery of frame48and thus, correspondingly, about the periphery of the portion of body38that extends into interior space50. The actuator system is thus coupled to arm40via frame48. Although in the illustrated embodiment there are four actuator motors52-58, in other embodiments (not shown) there could be three actuator motors. Each of actuator motors52-58has a pushrod60. A portion of each pushrod60is threaded. The threaded portion extends through a threaded nut or collar62in a wall of frame48. Each of actuator motors52-58is individually controllable to rotate its pushrod60either clockwise or counterclockwise. The threaded collar62converts this rotary motion into linear motion. Accordingly, each of actuator motors52-58is individually controllable to extend its pushrod60toward body38or retract its pushrod60away from body38. The distal end of a pushrod60may contact body38. Extending a pushrod60thus can displace body38(and first chuck14, which is connected in fixed relation to body38) a controllable distance with respect to lathe axis22. Each of actuator motors52-58may include a motor controller64. Motor controller64is configured to receive control signals using a wireless (e.g., radio frequency, optical, etc.) communication link.

By extending its pushrod60, actuator motor54can displace first chuck14in the positive X-axis direction. Similarly, by extending its pushrod60, actuator motor52can displace first chuck14in the negative X-axis direction. Likewise, by extending its pushrod60, actuator motor58can displace first chuck14in the positive Y-axis direction. And by extending its pushrod60, actuator motor56can displace first chuck14in the negative Y-axis direction. When one or more of actuator motors52-58extend their pushrods60, one or more others of actuator motors52-58may retract their pushrods by corresponding distances, so that the distal ends of all pushrods60remain in contact with body38.

In a neutral position (e.g.,FIG. 4), first chuck14is centered on lathe axis22, and each of pushrods60is extended the same amount. In the neutral position, the distal end of each pushrod60is in contact with body38. From the neutral position, each of pushrods60may be configured to be extendable and retractable a certain distance. That distance may be less than or equal to one-half the difference between the diameters of pin42and retaining cavity44.

As illustrated inFIG. 5, a control system66may include a light source68, a photosensor70, a wireless transmitter72, a processor74, a memory76, a rotational drive system78, a translational or elongation drive system80, and a carriage drive system82. Light source68, photosensor70, and a portion of other elements of control system66may be included in optical sensing system34(FIG. 1). Light source68may comprise a laser, and photosensor70may comprise a photodiode or other sensor configured to detect an optical signal. As described above with regard toFIG. 1, optical sensing system34may be configured to measure a displacement of a portion of glass core rod12from a reference point. For example, light source68and photosensor70may be positioned on opposite sides of lathe axis22. Thus, the extent to which glass core rod12obstructs or attenuates the optical signal received by photosensor70represents the extent of displacement of glass core rod12from lathe axis22. Although not shown inFIG. 1for purposes of clarity, portions of control system66may be contained within base24, carriage36, headstock18, or tailstock20.

Processor74may be configured by software or firmware84stored in memory76to control the methods described below and otherwise control the operation of system10(FIG. 1). In other embodiments (not shown), the methods may be controlled by a programmable logic controller (PLC) or similar industrial control device instead of the combination of a more general-purpose processor and memory. Processor74may control wireless transmitter72to transmit control signals86to motor controllers64associated with actuator motors52-58. The communication link or links over which control signals86are transmitted may be based on radio frequency (RF) communication, optical communication, or other technology. For example, the communication links may be Bluetooth. Processor74may, for example, compute a direction and magnitude (i.e., distance) in the X-Y coordinate system of motion to be applied to body38. The direction and magnitude may be encoded in control signals86. In response to such control information, actuator motors52-58two-dimensionally adjust the position of body38(and thus first chuck14) in the manner described above.

Electrical power to actuator motors52-58may be provided through an endcap88(FIG. 1). Although not shown for purposes of clarity, brushes or a similar rotary electrical contact system in endcap88may be included to transfer the electrical power from power supply wires90to distribution wires91(FIG. 4) or similar conductors in device30. Motor controllers64receive the electrical power from distribution wires91and receive control signals86via the wireless communication link with wireless transmitter72. Based on the control information in control signals86, motor controller64may apply electrical power in a controlled manner to actuator motors52-58.

Processor74may also control rotational drive system78to rotate first and second chucks14and16at a controlled or selected speed. Processor74may further control elongation drive system80to move tailstock20in the manner described above at a controlled or selected speed. Processor74may further control carriage drive system82to move carriage36in the manner described above at a controlled or selected speed. Although not shown for purposes of clarity, rotational drive system78may include one or more motors and drive trains (e.g., gears, pulleys, etc.) that, in conjunction with features of device30described above, transfer rotational motion to first and second chucks14and16. Similarly, elongation drive system80and carriage drive system82may include motors, etc.

As illustrated inFIG. 6, an alternative system92may be similar in some respects to above-described system10. For example, system92may include a first lathe chuck96, a second lathe chuck98, a headstock100, a tailstock102, a base104, a carriage106, a torch108, an optical sensing system110, an endcap112, wires114, etc., which may be identical in structure and function to corresponding elements described above with regard toFIGS. 1-4. System92may include the above-described control system66(FIG. 5). System92is configured to operate in the same manner as above-described system10except for the manner in which a first device chuck116of a device118is coupled to tailstock102. In addition to first device chuck116, device118includes a body120, a frame122, an arm124, and actuator motors126,128,130, etc., which may be identical in structure and function to corresponding elements described above with regard toFIGS. 1-4. However, the end of arm124is not directly connected to tailstock20but rather is coupled to tailstock20by being retained in first lathe chuck96. In system92, first device chuck116is configured to retain a first end of a glass core rod132, and second lathe chuck98is configured to retain a second end of glass core rod132. Conveniently, system92may be provided by retrofitting with device118a conventional lathe of a type used for elongating glass core rods, the above-described control system66, and related features.

As illustrated inFIG. 7, an exemplary method for straightening and elongating a glass core rod may use above-described system10, system92, or a similar system. The method may be controlled by processor74being programmed or otherwise configured with software or firmware84(FIG. 5). Although certain acts or steps in the method naturally precede others for the exemplary embodiments to operate as described, the invention is not limited to the order of those acts or steps if such order or sequence does not alter the functionality of the invention. That is, it is recognized that some acts or steps may be performed before, after, or in parallel (i.e., substantially simultaneously) with other acts or steps without departing from the scope and spirit of the invention. In some instances, certain acts or steps may be omitted or not performed, without departing from the scope and spirit of the invention. Further, words such as “thereafter,” “then,” “next,” etc., are not intended to limit the order of the acts or steps. Rather, such words are used to aid in guiding the reader through the description of an exemplary method.

As indicated by block134, an operator may mount a glass core rod in the system. For example, first and second ends of the rod may be mounted in the first and second chucks, respectively. The first chuck may be the above-described first chuck14(FIG. 1) or first device chuck116(FIG. 6), which are movable in the manner described above.

As indicated by block136, the system may rotate the glass core rod. As described above, the system can control the speed of rotation of the glass core rod. As indicated by block138, the torch or similar heat generator may heat a portion of the glass core rod. As described above, the system may control when the heat is applied (or not applied), the amount of heat applied and, by controlling movement of the torch, to what portion of the glass core rod the heat is applied. Mounted on a carriage, the torch may continuously move along the glass core rod. The speed of the torch may be controlled. Such control parameters may be determined by the processor using an algorithm embodied in the software.

As indicated by block140, the system may measure straightness of the glass core rod using the optical sensing system. The system may move the optical sensing system along a path that traverses the length of the glass core rod, obtaining displacement measurements at various points along the path. The collected displacement measurements may be expected to vary from each other within a tolerance amount if the glass core rod is straight. The collected displacement measurements may be expected to vary from each other by greater amounts if the glass core rod is not straight. The collected displacement measurements may describe a profile of the glass core rod, such as a bowed shape. The extent and shape of the curvature of the glass core rod is bowed can be used to determine at what points on the glass core rod to apply displacement forces. The displacement forces may also be applied continuously based on bow calculated over each rotation of the glass core rod.

The measurements may be obtained while the glass core rod is rotated and while the torch heats the glass core rod and advances along the glass core rod, in a continuous process. As the optical sensing system may be mounted on the carriage along with the torch, the optical sensing system may obtain a measurement a fixed distance in advance of the torch. The displacement measurements may comprise an input to the algorithm. The processor, in accordance with the algorithm, may determine a magnitude and direction of a bow in the glass core rod.

As indicated by block142, the processor, in accordance with the algorithm, and based on the magnitude and direction of a bow in the glass core rod, may determine a position (with respect to a plane normal to the lathe axis of rotation) to which the first end of the glass core rod is to be two-dimensionally moved or displaced. The processor provides corresponding control signals to the actuator system (motors) to two-dimensionally move the first chuck. The heated portion of the glass core rod bends or otherwise deforms in compliance with the displacement of the first end of the glass core rod in the first chuck. The system may continue to adjust the position of the first chuck in this manner while the glass core rod is rotated and while the torch heats the glass core rod and advances along the glass core rod, in a continuous process.

As indicated by block144, the system may elongate the glass core rod by activating the elongation drive system while the torch heats a portion of the glass core rod. As described above, the elongation drive system advances the tailstock, to which the first chuck is coupled via the arm and the slip joint. That is, translational motion of the tailstock is transferred to the first chuck via the arm and the slip joint. Note that although the first chuck is movable with respect to the arm in a plane normal to the lathe axis of rotation, the first chuck is essentially not movable with respect to the arm in directions along the lathe axis of rotation. The system may continue to elongate the glass core rod while the torch heats the glass core rod, while the glass core rod is rotated, while displacement measurements are obtained, and while adjusting the position of the first chuck, in a continuous process.

One or more illustrative or exemplary embodiments of the invention have been described above. However, it is to be understood that the invention is defined by the appended claims and is not limited to the specific embodiments described.