Abstract:
A feeding device for feeding an optical fiber from a coil and for recoiling unused fiber for use in an apparatus for measuring the temperature of a melt is provided. The feeding device includes a support for a coil, a feeding mechanism for decoiling the optical fiber from the coil and recoiling the optical fiber, at least one motor for driving the feeding mechanism, and a load for the optical fiber which avoids a spring back effect of the optical fiber from the coil. Blockage is avoided when decoiling and recoiling the optical fiber from the coil.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a feeding device for feeding an optical fiber from a coil and for recoiling unused fiber for use in an apparatus for measuring the temperature of a melt. The device according to the present invention comprises a support for a coil, a feeding mechanism for decoiling the optical fiber from the coil and recoiling the optical fiber, and at least one motor for driving the feeding mechanism. The present invention also relates to an apparatus for measuring the temperature of a melt, particularly of a molten metal, for example molten steel, with an optical fiber. 
         [0002]    As known from EP 2 799 824 A1, an Electric Arc Furnace (EAF) process for the production of molten steel is a batch process made up of the following operations: furnace charging of metallic components, melting, refining, de-slagging, tapping and furnace turnaround. Each batch of steel, called a heat, is removed from the melting furnace in a process called tapping and hence, a reference to the cyclic batch rate of steel production is commonly a unit of time termed the tap-to-tap time. A modern EAF operation aims for a tap-to-tap cycle of less than 60 minutes and is more on the order of 35-40 minutes. 
         [0003]    EP 2 799 824 A1 relates to a robotic immersion device for measuring the temperature in a metallurgical vessel using a molten metal immersed consumable optical fiber and immersion equipment capable of inserting a temperature device through the side wall of an EAF to a predictable molten steel immersion depth with a temperature-to-temperature measuring frequency of less than 20 seconds. The ability to sample on-demand, singularly or in rapid succession, allows a measuring strategy that can update a mathematical predictive model for EAF operations at key times during the process with the ability to measure in rapid succession providing near continuous temperature data at a low cost. 
         [0004]    EP 2 799 824 A1 discloses providing a spot measurement rather than a continuous measurement. EP 2 799 824 A1 discloses a low cost solution for temperature measurements suitable to be utilized at a sufficiently high sampling frequency to meet the updating demands of the mathematical models of the EAF melting process, while solving the problems associated with immersed optical fiber in harsh environments. The solution provides a near continuous temperature measuring output comprised of immersing an optical fiber into the molten metal through the slag covering without first contacting the slag, maintaining a predetermined immersion depth during the measuring period by controlled feeding, protecting the non-immersed portion against devitfication in the high ambient heat of the EAF interior, removing and recoiling unused fiber after the measurement, measuring the bath level upon recoiling and an immersion equipment for repeating the measuring processes always duplicating the initial starting conditions. 
         [0005]    Feeding the optical fiber, particularly a metal coated optical fiber, from the coil and recoiling unused fiber after the measurement may have the effect that the optical fiber becomes entangled for example due to an elastic spring back effect. For this reason, the feeding machine known from EP 2 799 824 A1 is adapted with additional means to avoid an elastic spring back effect from the coil or spool. The feeding machine comprises two servo motors or feeding motors to control the fiber movement. One feeding motor takes care of the de-coiling and recoiling of the fiber and pre-feeds fiber in such a way that the feeding motor can accelerate very fast. 
         [0006]    An apparatus for automatically uncoiling a spool of wire is known from U.S. Pat. No. 4,742,973. An arrangement for facilitating the withdrawal of flexible material is known from U.S. Pat. No. 2,716,008. Temperature measurement systems for high temperature object employing an optical fiber are known from JP 9101206 A, JP 701 26 50 A and JP 9280958 A. 
         [0007]    It is an objective of the present invention to avoid blockage when decoiling and recoiling a fiber from a coil of a feeding device for feeding an optical fiber. 
       BRIEF SUMMARY OF THE INVENTION 
       [0008]    An embodiment of the present invention relates to device for feeding an optical fiber from a coil and for recoiling unused fiber. The device comprises a support for a coil, a feeding mechanism for decoiling an optical fiber from the coil and recoiling the optical fiber, and at least one motor for driving the feeding mechanism. The device comprises a load for the optical fiber which avoids a spring back effect of the optical fiber from the coil. As a result, a blockage is avoided when decoiling and recoiling the fiber. 
         [0009]    A weight attached to the optical fiber may act as the load. In addition, or as an alternative, a spring may act as the load. 
         [0010]    As a rule, the optical fiber is metal coated and the diameter of the metal coated fiber is, as a rule, more than 1 mm, for example 1-15 mm, preferably 1-3 mm. 
         [0011]    Preferably, the weight acting as the load is a guide for the optical fiber in the form of a flexible tube, in order to provide a simple technical solution which works in a reliable manner. 
         [0012]    In a preferred embodiment, the flexible tube is formed from metal. As a rule, the weight of the flexible tube is sufficient for providing a load which avoids the spring back effect. 
         [0013]    In a preferred embodiment, a degree of stiffness of the flexible tube supplies resistance to its bending. That is, the flexible tube has a spring type behavior which provides a load to avoid the spring back effect. 
         [0014]    In a preferred embodiment, the flexible tube comprises a non-fixed end for providing an appropriate load which avoids the spring back effect, and thus avoids a blockage. 
         [0015]    Preferably, the non-fixed end of the flexible tube ends below the axis of the coil when the coil has been inserted into the support, in order to provide an appropriate load in a technical simple manner. 
         [0016]    In a preferred embodiment, the inner diameter of the flexible tube is more than 10 mm, preferably more than 30 mm and/or the length of the flexible tube is more than 100 mm, preferably more than 200 mm. On one hand, the weight of the flexible tube is, as a rule, sufficient due to these dimensions in order to provide a load which avoids the spring-back effect. On the other hand, an inner diameter of more than 10 mm, preferably of more than 30 mm (which is, as a rule, much larger than the outer diameter of a metal coated optical fiber) avoids a pinch effect, and thus a blockage in the course of de-coiling and recoiling the fiber. 
         [0017]    For this reason, the inner diameter of the flexible tube is, in a preferred embodiment, at least five times larger than the outer diameter of the metal coated optical fiber, preferably at least ten times larger. 
         [0018]    In a preferred embodiment, the device comprises a housing which covers the support for the coil and the load for the optical fiber. As a result, the coil and the load for the optical fiber are protected against an outer influence, particularly a disruption which may stop the process of de-coiling and recoiling the fiber. Thus, this embodiment contributes to the solution of the above-stated objective of the present invention. 
         [0019]    In a preferred embodiment, the housing is a cabinet especially comprising a first accessible compartment for the coil and a second compartment for an electrical equipment of the device. In this way, the coil, and thus the optical fiber, is separated from other parts in order to solve the above-stated objective of the present invention in a more reliable manner. The first compartment is accessible for an end-user and thus is not closed, for example, by a lock. As a result, an end user can insert or replace a coil if necessary. 
         [0020]    Preferably, the second compartment comprising an electrical equipment of the feeding device is closed, for example, by a door lock. As a result, the electrical equipment is well protected, which avoids a disturbance for example due to misuse. 
         [0021]    In a preferred embodiment, the cabinet, preferably at least and/or only the first compartment of the cabinet, is air-conditioned. In this way, the first compartment is protected against overheating. Overheating may disturb the process of de-coiling and recoiling the fiber. Thus, this embodiment also contributes to the solution of the above-stated objective of the present invention. Further, the air conditioning prevents condensation. As a result, erroneous measurements are avoided. 
         [0022]    The present invention also refers to a robotic immersion device comprising the feeding device. In a preferred embodiment, the robotic immersion device comprises a disposable guiding tube, having an immersion end and a second end, opposite to the immersion end, whereby the optical fiber can be partially arranged in the disposable optical guiding tube. The inner diameter of the disposable guiding tube is bigger than the outer diameter of the optical fiber. At least one elastic plug is arranged at the second end of or within the disposable guiding tube. The optical fiber is fed through the elastic plug reduces a gap between the optical fiber and the disposable guiding tube. There is a need for this robotic immersion device to decoil and recoil the optical fiber in a very fast manner. For this reason, the robotic immersion device preferably comprises a feeding device according to the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0023]    The foregoing summary, as well as the following detailed description of the invention, will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the invention, there are shown in the drawings embodiments which are presently preferred. It should be understood, however, that the invention is not limited to the precise arrangements and instrumentalities shown. 
           [0024]    In the drawings: 
           [0025]      FIG. 1  shows a consumable optical fiber; 
           [0026]      FIG. 2  shows the leading section of a metal coated optical fiber; 
           [0027]      FIG. 3 a    shows an immersion device before immersing of the optical fiber; 
           [0028]      FIG. 3 b    shows the immersion device of  FIG. 3 a    after immersing of the optical fiber; 
           [0029]      FIG. 3 c    shows the immersion device according to  FIG. 3 b    with a different melt container, such as a molten metal ladle or tundish; 
           [0030]      FIG. 4  shows a view of both the position of the immersion end of the outer tube and the immersion end of the optical fiber during immersion; 
           [0031]      FIG. 5  shows a side view of the feeding device; and 
           [0032]      FIG. 6  shows a front view of the feeding device of  FIG. 5 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0033]      FIG. 1  shows a consumable metal coated optical fiber  10 , typically employed in the measurement of liquid metals. The metal coated optical fiber  10  comprises an optical fiber  11 , a jacket  12  covering the optical fiber  11  and a protective metal tube  14  covering the surface of the plastic jacket  12 . The optical fiber  10 , typically a graded index multi-mode fiber, is made of quartz glass with an inner core  11  (diameter of 62.5 μm) and an outer cladding  12  (diameter of 125 μm) and is covered with a polyimide or similar material  13 . The protective metal tube  14  is typically stainless steel and has a 1.32 mm outer diameter (OD) and a 0.127 mm wall thickness. Although a metal covered optical fiber is preferred, additional embodiments where components  14  and/or  13  are replaced by a singular plastic material do not depart from the intended invention. 
         [0034]      FIG. 2  shows the leading section  10  of a metal coated optical fiber  10 , as fed from a spool  20  through a gas retaining elastic plug  30 , affixed to the opposite immersion end  50  of an outer disposable guiding tube  40 . The metal coated optical fiber  10  and the outer disposable guiding tube  40  are not in a fixed arrangement and, as such, can move independent of each other and thus can be independently inserted through the slag layer  51  and into the molten bath  52  at different velocities, while maintaining a gas seal  31  at the opposite end. The disposable guiding tube  40  is preferably low carbon steel having a wall thickness of 0.8 to 1 mm, but may be selected from a variety of metal materials, as well as ceramics and glasses, cardboard and plastics or a combination of materials. In the case that the disposable guiding tube  40  is selected from a material that reacts with the molten bath, it is advisable that the immersion portion  50  is prepared in a way that it does not splash molten metal on the inside of the disposable guiding tube  40  by the application of coating or coverings of a materials known in the art for the purpose of splash reduction. 
         [0035]    Immersing the open ended outer disposable guiding tube  40  in the steel through the slag layer  51  without the plug  30  will result in ingress of slag and steel in this tube. Molten slag resulting from the refining process is high in oxides, such as iron oxide which is easily absorbed into the optical fiber structure. The fiber  10  fed through the outer disposable guiding tube  40  containing slag and steel will be damaged before reaching the open end of the outer disposable guiding tube  40 . 
         [0036]    In a preferred embodiment, the outer disposable guiding tube  40  is 2 m long with an immersion depth of 30 cm and open at both ends, and the upwelling of molten material inside the outer disposable guiding tube  40  will be 30 cm. In case of a closed end outer disposable guiding tube  40 , the upwelling will be approximately 16 cm. This is calculated ignoring the gas expansion of the enclosed air which will undergo expansion due to an increase in its temperature. Tests show that the steel ingress can be minimized by reducing the air gap between the inner diameter (ID) of the outer disposable guiding tube  40  and the outer diameter (OD) of the optical fiber  10  metal covering. It is particularly preferred to reduce this gap to the minimum. However, practically, for tubes with an ID of 10 mm, this gap should be less than 2 mm 2 , preferably less than 1 mm 2 . Tubes with a smaller ID would allow for a bigger gap due to the faster heating rate of the enclosed air. 
         [0037]    One of the preferred features of the immersion device is to avoid molten ingress utilizing the expansion of the gas contained in the disposable guiding tube  40 . The use of an elastic plug  30  to effectively seal the end opposite the immersion end of a certain sealing quality will ensure that gas will bubble out of the immersed end during immersion, thus keeping the disposable guiding tube  40  clear. 
         [0038]    Notwithstanding, any means of creating an overpressure in the disposable guiding tube  40  while immersing also avoids steel ingress, such as an internal coating of a material vaporous at minimal temperatures. A prominent concept towards creating a positive pressure in the outer disposable guiding tube  40  is to avoid the upwelling and intrusion of metal, slag or other contaminants inside of the disposable guiding  40  tube that could impede the free feeding of the metal coated fiber  10 . 
         [0039]    The plug  30  should be suitably elastic in order to compensate for an un-ideal optical fiber end resulting from the prior immersion. In the preferred embodiment, plug  30  is replaced with each outer disposable guiding tube  40 . Each replacement assures a proper seal. However, the plug  30  could be constructed in such a way as to be reused with multiple outer disposable guiding tubes and replaced as a matter of maintenance. The preferred location of the plug  30  at the terminal end of the outer disposable guiding tube  40  is selected for ease of application. However, placing the plug  30  closer to the immersion end is equally acceptable and will accomplish a superior overpressure during immersion, aiding the error free immersion of the optical fiber  10 . The design of the plug  30  facilitates its placement at the extremity of disposable guiding tube  40 , showing a lip that rests upon the tube end. Other configurations are possible. The exact embodiment of the plug  30  should reflect the ease of positioning and location of its position, without departing for the main purpose of the plug to restrict the escape of air in the outer tube, thus ensuring a build-up of inner pressure. 
         [0040]    The steel ingress in the steel tube while immersing in the steel tube increases with: 
         [0041]    an increase of the immersion depth; 
         [0042]    an increase of the tube length; 
         [0043]    an increase of the air gap (at the other end); 
         [0044]    a lower bath temperature; 
         [0045]    a thicker wall thickness; and/or 
         [0046]    a higher oxygen content of the steel bath. 
         [0047]    The immersion device is described in  FIG. 3 . Machine  100  is suitably constructed and instrumented in such a manner that assembly plug  30  is aligned to outer disposable guiding tube  40  so the metal coated optical fiber  10  can be inserted through plug  30  into the interior of the outer disposable guiding tube  40 . Both the outer disposable guiding tube  40  and the metal coated optical fiber  10  are fed at approximately 2000 mm/s through the side wall of an EAF through suitable access panels  80 . These panels  80  are not part of the machine  100 . The machine  100  has independent 100% reversible drive or feeding motors  25  and  45 . Motor  25  drives the optical fiber  10  and motor  45  drives the disposable guiding tube  40 , so that the velocity of the outer disposable guiding tube  40  in either direction is independent of the velocity of the optical fiber  10  in either direction. 
         [0048]    The machine  100  is capable of independent feeding of the optical fiber  10  into the bath with a speed less than, equal to or higher than the speed of the outer disposable guiding tube  40 . Preferably, the metal coated optical fiber  10  is fed faster so that both the immersion end  50  of the outer disposable guiding tube  40  and leading section  10  of the metal coated optical fiber  10  arrive at the predetermined surface of the metal at approximately the same time. Once the bath level position is reached, the outer disposable guiding tube  40  is decelerated to a nearly stationary position in the molten metal  52 . The leading section  10  of the metal coated optical fiber  10  continues to move slowly deeper in the steel at about 200 mm/s for approximately 0.7 seconds. Both the outer disposable guiding tube  40  and the metal coated optical fiber  10  are constantly moving at unequal speeds to avoid welding the two metal surfaces together, thereby solving a problem stated in the prior art. 
         [0049]    The problem of the acceleration and deceleration of the metal coated optical fiber  10  is more complicated than moving the outer disposable guiding tube  40 . The metal coated optical fiber  10  is constantly decoiled and recoiled from a coil or spool  20  with its coil weight that is constantly changing due to fiber consumption. The feeding machine, particularly the feeding device, is adapted with additional mechanics to avoid the elastic spring back effect from the coil or spool  20  itself as well as the weight of the pyrometer connected to the coil. For this reason, there are two servo motors or feeding motors  25 ,  45  to control the fiber movement. One feeding motor  25  takes care of the decoiling and recoiling of the metal coated optical fiber  10  and pre-feeds the metal coated optical fiber  10  in such a way that the feeding motor  25  can accelerate very fast. 
         [0050]    The consumable metal coated optical fiber  10  receives the radiation light emitted from the molten metal, conveys such to a photo-electric conversion element mounted on the opposite end of the coiled consumable metal coated optical fiber  10  and, combined with associated instrumentation, measures the intensity of the radiation, using this to determine the temperature of the metal. The metal coated optical fiber coil or spool  20  and instrumentation are located at a distance away, and separated from the EAF, but are suitably robust to withstand the harsh conditions of the steel making environment. The location of the immersion end of the metal coated optical fiber  10  is constantly known and monitored by machine instrumentation throughout the immersion, measuring and removal portions of the immersion cycle. The machine is equipped with position encoders that determine the passage of metal coated optical fiber length and inductive switches that register the metal coated optical fiber end. 
         [0051]    After the measurement is complete, both the consumable metal coated optical fiber  10  and the outer disposable guiding metal tube  40  are withdrawn from the steel with different speeds in such a way that the metal coated optical fiber  10  stays relatively deeper in the bath. During this movement, it is possible to determine the bath-level due to a change in the light intensity when correlated with the length of metal coated optical fiber  10  extracted between predetermined positions. The post measurement bath level determination is subsequently used for the next immersion. It is also contemplated that the bath level could be determined during immersion using various techniques well described in the literature without departing from the method of the present invention. 
         [0052]    Once the metal coated optical fiber  10  is clear of the EAF interior, the direction of the outer disposable guiding tube  40  is reversed towards the furnace interior. The outer disposable guiding metal tube  40  is then ejected, disposed and consumed in the furnace interior. A new outer disposable guiding tube  40  and gas plug  30  are positioned to receive the metal coated optical fiber  10  for the next measurement. The remaining metal coated optical fiber  10  is recoiled during removal and returned to a starting position. 
         [0053]    Some key abilities of the present invention are:
       accurate payout and recoil of fiber;   detection of fiber end;   loading of outer disposable guiding tube;   guide fiber at starting position into gas plug;   fully reversible drives for both fiber and outer disposable guiding tube;   independent speed profits for fiber and outer disposable guiding tuber;   registration of fiber output for level detection; and   attachable to furnace shell for tilt compensation of bath level.       
 
         [0062]    The method is described by way of example of a total cycle description. This concept should bring us to an operator free control of EAF&#39;s. It is envisioned that the best operation is to take multiple temperature immersions in quick succession (about five). Each immersion is approximately 2 second. The total cycle time should be less than 20 seconds during a single heat. 
         [0063]    The schematic of  FIG. 4  gives a view of both the position of the immersion end  50  of the outer disposable guiding tube  40  and the immersion end or leading section  10  of the metal coated optical fiber  10  during two immersions of a measurement cycle. For fiber movement, the end position of the fiber is tracked. 
         [0064]    With tube movement, the position of the immersed end of the disposable guiding tube  40  is indicated. The opposite of the immersion end  50  of the outer disposable guiding tube  40  is the gas plug  30 . For the purpose of this schematic, the outer disposable guiding tube  40  is already in ready to immerse position. Gas plug  30  is already attached to the back end and the metal coated optical fiber  10  is just inside the gas plug  30 . The relative dimensions shown are for descriptive purposes, understanding that the absolute distances are predicated upon the actual furnace size which is a variable from steel shop to steel shop. 
         [0065]    The starting position  1  at time  0  of the fiber within the outer metal tube is set at 350 cm above the molten metal/bath level. The starting position is outside of the furnace. The starting position  1  at time  0  of the immersion end of the outer metal tube is located at 150 cm above the bath level. The metal coated optical fiber  10  is fed from position  1  to position  2  while the outer disposable guiding tube  40  remains nearly stationary. Between time 0.8 seconds and 1.2 seconds covering positions  2  through  4 , both the metal coated optical fiber  10  and the outer disposable guiding tube  40  advance to a location just above the molten slag  51 . At 1.2 seconds and position  4 , the fiber is advanced slightly faster than the outer disposable guiding metal tube  40  passing through the slag  51  and into the molten metal  52 . The outer disposable guiding metal tube  40  slows while the metal coated optical fiber  10  advances at approximately 200 mm/s reaching the maximum immersion at position  6  and 1.5 seconds into the immersion. Both metal coated optical fiber  10  and outer disposable guiding tube  40  are extracted within 0.1 seconds. The metal coated optical fiber  10  continues to be withdrawn and recoiled returning to its load position  8  while the remains of the outer disposable guiding metal tube direction is reversed at position  7  and discarded. The metal coated optical fiber  10  is still protected by the remaining portion of the discarded outer disposable guiding tube  40 . 
         [0066]      FIG. 5  is a side view of the feeding device for feeding the optical fiber  10  from the coil  20  and for recoiling unused fiber  10 . The coil  20  is inserted into the support  21 . The support  21  comprises an axis  22  for the coil so that the coil  20  can rotate around its axis  22 . A flexible tube  23  acts as the load for avoiding a spring back effect of the optical fiber  10 . The flexible tube  23  is a guide for the optical fiber as shown in  FIG. 5 . In other words, the fiber  10  is fed through the flexible tube  23 . 
         [0067]    The flexible tube  23  is formed from metal. The flexible tube may comprise a plurality of metal rings or metal sleeves which are connected to each other in a flexible manner. The upper end  25  of the flexible tube  23  is attached to the housing  24  of the feeding device. The opposite non-fixed end  26  is free to move and ends below the axis  22 . As a result, at least a lower part flexible tube acts as load for the fiber  10  which avoids a spring back effect. 
         [0068]    The inner diameter of the flexible tube  23  is at least five times larger than the outer diameter of the coated optical fiber  10 . The housing  24  is a cabinet which covers and protects the support  21  for the coil  20  and the flexible tube  23 . 
         [0069]    The feeding device comprises an electrical motor drive (not shown) which can rotate the coil in a desired direction, especially for recoiling the fiber  10 . 
         [0070]      FIG. 6  is front view of the feeding device. The cabinet  24  comprises a first accessible compartment  27  for the coil support and the flexible tube  23  and a second compartment  28  for an electrical equipment of the feeding device. The compartment  27  is separated from the compartment  28  by an inner wall  29 . There is a door (not shown) for the compartment  27  which comprises the support and the flexible tube  23 . The door is unlocked so that the compartment  27  is accessible for an end user. The compartment  28  for the electrical equipment of the feeding device comprises a door having a locking mechanism. Due to the locking mechanism, the compartment  28  for the electrical equipment is only accessible for authorized persons. 
         [0071]    At least the first compartment for the support and the flexible tube  23  of the cabinet is air-conditioned. The feeding device comprises means for converting the light transmitted by the optical fiber into a temperature. 
         [0072]    It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this invention is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the present invention as defined by the appended claims.