Abstract:
A method for detecting a position of a cylinder rod includes depositing a plurality of welds substantially along the length of a steel rod and depositing a corrosion resistant material onto the steel rod by laser cladding. The cylinder rod is then placed proximate to a sensor assembly. One of the cylinder rod and the sensor assembly are moved relative to the other. The sensor assembly detects a change in properties between the steel rod and the welds and generates a corresponding signal. A change in position of the cylinder rod or damage to the cylinder rod can be detected by analyzing the number and strength of the signals.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 61/080,390, filed Jul. 14, 2008, and to U.S. Provisional Patent Application No. 61/133,489, filed Jun. 30, 2008, and which are hereby incorporated by reference in their entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to a cylinder rod, and more particularly, to a system and method for determining a cylinder rod position and method of manufacture 
       BACKGROUND OF THE INVENTION 
       [0003]    One arrangement for providing position sensing for systems utilizing large cylinder rods is to form a gear teeth-like profile on the surface of the cylinder rod, which has ferromagnetic base material. A sensor element, typically a Hall Effect sensor, is mounted to a magnet. As the gear tooth profile, formed on the cylinder rod, passes the Hall Effect sensor a pulse is generated as a result of the Hall Effect sensor detecting the presence of the ferromagnetic material. Each pulse is associated with a distance of travel from one gear tooth on the cylinder rod to the next. 
         [0004]    To form the gear teeth, grooves between each of the gear teeth must be individually machined about the circumference of the cylinder rod. Increasing the number and the proximity of the grooves increases the resolution of the pulse signal obtained for measuring the position of the cylinder rod. However, machining the grooves is a time consuming and expensive task. 
         [0005]    Additionally, the cylinder rod is typically formed of ferromagnetic material, such as steel. Common applications of cylinder rods requiring position sensing include marine and brackish water applications, such as offshore drilling, locks, dams and draw bridges. In order to protect the cylinder rod from corrosion and other damage as a result of these environments, a corrosion resistant, thermal sprayed coating is applied. Typically, a thin bonding layer is applied to the cylinder rod, and the corrosion resistant coating is applied over that forming a mechanical bond with the bonding layer and the cylinder rod. The coating must be applied after all of the gear teeth have been formed, due to the complexity of grinding the grooves to form the gear teeth. Additionally, the two layers of non-magnetic coating reduce the sensors ability to detect the gear teeth. This limits the available thickness of the corrosion resistant coating. However, limited thickness of the corrosion resistant coating reduces the life of the cylinder rods. 
       SUMMARY OF THE INVENTION 
       [0006]    A method for detecting a position of a cylinder rod and damage to the cylinder rod is provided. The method includes depositing a plurality of welds along substantially the length of a cylinder rod and depositing a corrosion resistant material onto the cylinder rod by laser cladding. The cylinder rod is placed proximate to at least one sensor assembly. One of the cylinder rod and the sensor assembly is moved relative to the other of the cylinder rod and the sensor assembly. The sensor assembly measures a change in magnetic properties of the cylinder rod to detect at least one of a change in position of the cylinder rod and damage to the cylinder rod. 
         [0007]    A method for detecting a position of a cylinder rod is also provided. The method includes depositing a plurality of welds substantially along the length of a cylinder rod and depositing a corrosion resistant material onto the cylinder rod by laser cladding. The plurality of circumferential welds are made of a non-ferromagnetic material. The cylinder rod is polished to remove any excess corrosion resistant material. The cylinder rod is placed proximate to at least one eddy current probe. One of the cylinder rod and the eddy current probe are moved relative to the other. The eddy current or magnetic field probe measures a change in one of magnetic properties, electric properties and physical geometry of the cylinder rod to detect a change in position of the cylinder rod. 
         [0008]    The above features and advantages and other features and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a schematic side-view illustration of a cylinder rod for a position sensing system; 
           [0010]      FIG. 1A  is a schematic cross-sectional end view of the cylinder rod of  FIG. 1  taken along the lines  1 A in  FIG. 1 ; 
           [0011]      FIG. 2  is a schematic side view illustration of a first embodiment of the steel rod of  FIGS. 1 and 1A  having a laser cladding; 
           [0012]      FIG. 2A  is a schematic cross-sectional end view of the first embodiment of the steel rod of  FIGS. 1 ,  1 A and  2  having the laser cladding taken along the lines  2 A in  FIG. 2 ; 
           [0013]      FIG. 3  is a schematic cross-sectional illustration of the first embodiment of the cylinder rod for the steel rod of  FIGS. 1-2A ; 
           [0014]      FIG. 3A  is a schematic cross-sectional end view of the first embodiment of the cylinder rod for the steel rod of  FIGS. 1-3  taken along the lines  3 A in  FIG. 3 ; 
           [0015]      FIG. 4  is a schematic side view illustration of a second embodiment of the steel rod of  FIG. 3  for the steel rod of  FIGS. 1 and 1A ; 
           [0016]      FIG. 4A  is a schematic cross-sectional end view of the second embodiment of the steel rod of  FIGS. 1 ,  1 A and  4  having the plurality of welds taken along the lines  4 A in  FIG. 4 ; 
           [0017]      FIG. 5  is a schematic side view illustration of the second embodiment of the cylinder rod for the steel rod of  FIGS. 1 ,  1 A,  4  and  4 A; 
           [0018]      FIG. 5A  is a schematic cross-sectional end view of the second embodiment of the cylinder rod of  FIG. 5  for the steel rod of  FIGS. 1-1A  and  4 - 4 A taken along the lines  5 A in  FIG. 5 ; 
           [0019]      FIG. 6  is a schematic illustration of a graph of signal strength versus distance for the cylinder rods of  FIG. 3  and  FIG. 5 ; and 
           [0020]      FIG. 7  is a schematic illustration of a graph of signal strength versus distance for the cylinder rod of  FIG. 5  illustrating damage to the cylinder rod. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    Referring to the drawings, wherein like reference numbers refer to like components,  FIGS. 2 and 2A  illustrate a steel rod  10  from which the cylinder rod  12 , shown in  FIGS. 3 and 3A , may be manufactured. The cylinder rod  12  and at least one sensor assembly  14  form a position sensing system  16 ,  116  (shown in  FIGS. 3 and 5 ). The steel rod  10  has a generally circular cross-section. The steel rod  10  may be a solid component, as shown, or may be hollow defining an axial opening extending from one end of the steel rod  10  to the other, for reducing the weight of the steel rod  10 . 
         [0022]    Referring to  FIGS. 2-3A , a first embodiment of the position sensing system  16  is illustrated. A cladding  18  is formed about the exterior surface of the steel rod  10 . The cladding  18  is formed by depositing a metallic, non-ferromagnetic material on the steel rod  10 . Appropriate materials may include, Nickel-based or Cobalt based metals, such as INCONEL 625™ and ULTIMET™, STELLITE 21™ and CARPENTER CCW™. The material is deposited onto the steel rod  10  in a spiral manner by fusion welding to create a fusion weld bond and form the cladding  18 . The cladding  18  is applied by a laser weld to the steel rod  10  and may, thus, be referred to a laser cladding. The cladding  18  forms a solid layer over the exterior surface of the steel rod  10 . As shown, the cladding  18  may cover a substantial length of the steel rod  10 , but may not cover the entire length of the steel rod  10 . Due to the application of the filler material to the steel rod  10  by fusion welding, the steel rod  10  mixes with the weld material as it is applied to create a new material for the cladding  18 . 
         [0023]    Referring to  FIGS. 3 and 3A , a plurality of welds  20  are arranged circumferentially about the cylinder rod  12 . The plurality of welds  20  are applied after the cladding  18 . The plurality of welds  20  are preferably applied by laser welding. The plurality of welds  20  may be applied in an autogenous manner where no filler metal is used. Alternatively, the plurality of welds  20  may be applied using a filler material that is a dissimilar metal to the cladding  18 . Preferably, the material forming the cladding  18  and the plurality of welds  20  are both formed from corrosion resistant materials. For example, Nickel-based or Cobalt based metals, such as as INCONEL 625™ and ULTIMET™, would be suitable for forming the plurality of welds  20 . 
         [0024]    The plurality of welds  20  are equally spaced from one another along the length of the cladding  18 . Similar to the cladding  18 , the plurality of welds  20  cover substantially the length of the steel rod  10  (shown in  FIG. 1 ) but may leave the ends exposed. The plurality of welds are uniformly applied and equidistant from one another. The smaller the weld width and the pitch (weld center-to-center spacing) between the welds, the better the resolution the position sensing system  16  will have. 
         [0025]    The plurality of welds  20  are preferably applied by fusion welding using laser beam welding. Other types of fusion welds may also be used such as, Gas Tungsten Arc Welding (GTAW), Gas Meal Arc Welding, and Plasma Arc Welding (PAW). Alternately, a solid-state non-fusion welding method such as friction stir welding may be used to apply the plurality of welds  20 . 
         [0026]    As mentioned above, the closer the plurality of welds  20  are to one another, the more refined the distance measurement for the position sensing system  16  will be. The type of welding and whether or not filler material is used affects the pitch (center-to-center spacing) between the welds, the width of the welds, and the measurable difference between the plurality of welds  20  and the steel rod  10 . One skilled in the art would be able to determine the proper type of material, welding and spacing for a particular cylinder rod sensing system  16 . 
         [0027]    After the plurality of welds  20  are applied to the steel rod  10  the steel rod  10  and the plurality of welds  18  may be ground to remove any weld cap beads formed during the welding process, illustrated in phantom at  28 . The outer surface of the cylinder rod  14  may then be polished, illustrated in phantom at  30 , to facilitate use of the cylinder rod  14  within the cylinder. 
         [0028]      FIGS. 3 and 3A  illustrate the cylinder rod  12  for one embodiment of the position sensing system  16 . The cylinder rod  12  is for use with a cylinder to form a piston (not shown). At least one sensor assembly  14  is positioned proximate to the cylinder rod  12 . A typical placement of the sensor assembly  14  may be on a cylinder head for the cylinder (not shown). Other locations may also be used for mounting or arranging the sensor assembly  14  proximate to the cylinder rod  12 . One skilled in the art would know the proper placement for the sensor assembly  14  relative to the cylinder rod  12 . 
         [0029]    The sensor assembly  14  is preferably an eddy current probe or magnetic field probe. The eddy current probe consists of a driving coil and a signal coil, of a driving coil and two signal coils, or of a driving coil and Hall device(s). The sensor assembly  14  determines the position of the cylinder rod  12  as the cylinder rod  12  moves relative to the sensor assembly  14 , illustrated by arrow S. Alternatively, the sensor assembly  14  may determine the position of the cylinder rod  12  as the sensor assembly  14  moves relative to the cylinder rod  12 . 
         [0030]    One sensor assembly  14  is illustrated in  FIG. 3 . Additional sensor assemblies  14  may also be used, as illustrated in phantom at  14 A. The sensor assemblies  14 ,  14 A would act in the same manner but provide information that is 90 degrees out of phase from one another. This would increase the resolution of the position sensing system  16 . 
         [0031]    As the sensor assembly  14  moves relative to the cylinder rod  12 , the difference in magnetic properties, electric properties and physical geometry between the steel rod  10  and the plurality of welds  20  is registered by the sensor assembly  14 . Specifically, in this instance, the welds  20  each produce a signal resulting from the magnetic properties, electric properties and physical geometry, which is registered as a pulse by the sensor assembly  14 . The welds  20  are all equidistant, at a known distance from one another. Therefore, each pulse recorded by the sensor assembly  14  can be converted into a known distance of travel as the sensor assembly  14  moves relative to the cylinder rod  12 . 
         [0032]    Referring to  FIGS. 4 through 5A , a second embodiment of the position sensing system  116  is illustrated. A plurality of welds  120  are arranged circumferentially about a cylinder rod  112 . The plurality of welds  120  are applied prior to a cladding  118 . The plurality of welds  120  are preferably applied by fusion welding using laser beam welding. Other types of fusion welds may also be used such as, Gas Tungsten Arc Welding (GTAW) and Plasma Arc Welding (PAW). The plurality of welds  120  are applied using a non-ferromagnetic material or a slightly ferromagnetic material that is a dissimilar to the ferromagnetic material of the steel rod  110 . Preferably, the material forming the steel rod  110  is steel and the material forming the plurality of welds  120  is a corrosion resistant material. For example, 310 Austenitic Stainless Steel would be a suitable filler material for the plurality of welds  120 . Nickel-based or Cobalt based metals would also be suitable, such as INCONEL 625™ and ULTIMET™. The filler material can be in the form of rod, wire or powder. One skilled in the art would know the proper material required to provide a difference in magnetic properties between the steel rod  110  and the plurality of welds  120 . 
         [0033]    The plurality of welds  120  are equally spaced from one another along the length of the steel rod  110 . The plurality of welds  120  cover substantially the length of the steel rod  110  (shown in  FIG. 1 ) but may leave the ends exposed. The welds  120  are uniformly applied and equidistant from one another. The smaller the weld width, and the pitch between the welds, the better the resolution the position sensing system  116  will have. 
         [0034]    After the plurality of welds  120  are applied to the steel rod  110 , the steel rod  110  and the plurality of welds  120  may be ground or polished to remove any weld beads formed during the welding process and to prepare the surface for application of a cladding  118 , illustrated in phantom at  128 . Removing the weld beads may increase the strength of the signal recorded by the sensor assembly  14 . However, removing the weld beads is not required for the sensor assembly  14  to be able to sense the difference in magnetic properties, electric properties and physical geometry between the steel rod  110  and the plurality of welds  120 . 
         [0035]    The cladding  118  is formed about the exterior surface of the steel rod  110  and the plurality of welds  120 . The cladding  118  is formed by depositing a metallic, non-ferromagnetic material on the steel rod  110  and the plurality of welds  120 . Appropriate materials may include, Nickel-based or Cobalt based metals, such as INCONEL 625™ and ULTIMET™, STELLITE 21™ and CARPENTER CCW™. The material is deposited onto the steel rod  110  and the plurality of welds  120  in a spiral manner by fusion welding to form the cladding  118 . The cladding  118  is applied by a laser weld and may, thus, be referred to a laser cladding. The cladding  18  forms a solid layer over the exterior surface of the steel rod  110  and the plurality of welds  120 . As shown, the cladding  118  may cover a substantial length of the steel rod  110 , but need not cover the entire length of the steel rod  110 . 
         [0036]    The cladding  118  is applied over the steel rod  10  and the plurality of welds  120 . However, in order to speed the process of applying the plurality of welds  120  and the cladding  118 , the cladding  118  application can begin immediately after the plurality of welds  120  have been applied. The distance between the application of the plurality of welds  120  and the application of the cladding  118  is dictated by the speed of the welding processes and the size of the welding apparatus that are used. 
         [0037]    After the cladding  118  is applied over the steel rod  10  and the plurality of welds  120 , the cladding  118  may be ground or polished to remove any excess material from the cladding process, illustrated in phantom at  130 . Grinding or polishing the cladding  118  prepares the outer surface of the cylinder rod  14  to facilitate use of the cylinder rod  14  within the cylinder (not shown). 
         [0038]      FIGS. 5 and 5A  illustrate the cylinder rod  12  for another embodiment of the position sensing system  116 . The cylinder rod  112  is for use with a cylinder to form a piston (not shown). At least one sensor assembly  14  is positioned proximate to the cylinder rod  112 . A typical placement of the sensor assembly  14  may be on a cylinder head for the cylinder (not shown). Other locations may also be used for mounting or arranging the sensor assembly  14  proximate to the cylinder rod  112 . One skilled in the art would know the proper placement for the sensor assembly  14  relative to the cylinder rod  112 . 
         [0039]    The sensor assembly  14  is preferably an eddy current probe. The eddy current probe consists of a driving coil and a signal coil or of a driving coil and two signal coils. The sensor assembly  14  determines the position of the cylinder rod  112  as the cylinder rod  112  moves relative to the sensor assembly  14 , illustrated by arrow S. Alternatively, the sensor assembly  14  may determine the position of the cylinder rod  112  as the sensor assembly  14  moves relative to the cylinder rod  112 . 
         [0040]    One sensor assembly  14  is illustrated in  FIG. 5 , additional sensor assemblies  14  may also be used as illustrated in phantom at  14 A. The sensor assemblies  14 ,  14 A would act in the same manner but provide information that is 90 degrees out of phase from one another. This would increase the resolution of the position sensing system  116 . 
         [0041]    As the sensor assembly  14  moves relative to the cylinder rod  112  the difference in magnetic properties, electric properties and physical geometry between the steel rod  110  and the plurality of welds  120  is registered by the sensor assembly  14 . Specifically, in this instance, the plurality of welds  120  each disrupt a signal which is produced by the magnetic properties, electric properties and physical geometry of the steel rod  110 . The presence of ferromagnetic material beneath the probe is registered as a pulse by the sensor assembly  14 . The plurality of welds  120  are all equidistant and at a known distance from one another. Therefore, each pulse recorded by the sensor assembly  14  can be converted into a known distance of travel as the sensor assembly  14  moves relative to the cylinder rod  112 . 
         [0042]    Referring to  FIG. 5 , an example of damage  122  to the cylinder rod  112  is illustrated, displayed as unexpected variance in pulses  126  measured in current (amps). The damage  122  may be corrosion of the steel rod  110 , spalling of the cladding  118  or other damage known to occur to cylinder rods  112 . If the damage  122  is corrosion, the steel rod  110  will start to corrode and the magnetic properties, electric properties and physical geometry between the plurality of welds  120  and the steel rod will become less distinct. The sensor assembly  14  may no longer detect as strong a signal in this area. If the damage to the area is spalling, then a portion of the cladding  118  will be missing. The missing portion of the cladding  118  will result in increased signal strength. Being able to determine that damage  122  has occurred, and determine where on the cylinder rod  112  the damage occurred, will allow the operator to repair the damage prior to it spreading. 
         [0043]      FIG. 6  illustrates an output  124  from the sensor assembly  14  as the cylinder rod  12 ,  112  moves relative to the sensor assembly  14 . Each pulse  126  represents a known distance of travel of the cylinder rod  12 ,  112  relative to the sensor assembly  14 . The closer the plurality of welds  20 ,  120  are to one another the more refined the distance measurement will be. For example, in the embodiment shown, the plurality of welds each have a pitch of 2 mm spacing from one another. Therefore, each pulse represents 2 mm of travel of the cylinder rod  12 ,  112 . 
         [0044]      FIG. 7  illustrates an output  128  from the sensor assembly  14  as the cylinder rod  112  moves relative to the sensor assembly  14 . The output  128  is illustrated as the sensor assembly  14  moves over the damaged portion  122  (illustrated in  FIG. 5 ). Each pulse  126  represents a known distance of travel of the cylinder rod  112  relative to the sensor assembly  14 . However, due to the damaged portion  122  on the cylinder rod  112 , the difference in magnetic and electrical properties between the plurality of welds  118  and the steel rod  110  is degraded (representing corrosion). The difference in signal strength indicates that damage has occurred at that area of the cylinder rod  112 . The difference in the amplitude between the signal strength of the cylinder rod  112  at a healthy portion and at the damaged portion  122  may also indicate the extent of damage that has occurred. 
         [0045]    Other forms of damage may result in different signal strengths sensed by the sensor assembly  14 . For example, if the damaged portion  122  is due to spalling then a portion of the cladding  118  will be missing and the signal strength in this area will increase, until corrosions sets in, in which case it will decrease again. Therefore, changes in the signal strength sensed by the sensor assembly  14  will represent damage to the cylinder rod  112 . Another form of damage may be a metal particle that becomes embedded in the cylinder rod  112 . The metal particle would result in an increase in signal strength recorded by the sensor assembly  14 , similar to the spalling. However, the area of increased signal strength would likely be much smaller. Knowing where damage has occurred on the cylinder rod  112 , if any, allows for the damage to be quickly repaired prior to getting worse. 
         [0046]    While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims.