Patent Description:
A gas turbine engine typically includes a high pressure spool, a combustion system and a low pressure spool disposed within an engine case to form a generally axial, serial flow path about the engine centerline. The high pressure spool includes a high pressure turbine, a high pressure shaft extending axially forward from the high pressure turbine, and a high pressure compressor connected to a forward end of the high pressure shaft. The low pressure spool includes a low pressure turbine, which is disposed downstream of the high pressure turbine, a low pressure shaft, which typically extends coaxially through the high pressure shaft, and a low pressure compressor connected to a forward end of the low pressure shaft, forward of the high pressure compressor. The combustion system is disposed between the high pressure compressor and the high pressure turbine and receives compressed air from the compressors and fuel provided by a fuel injection system. A combustion process is carried out within the combustion system to produce high energy gases to produce thrust and turn the high and low pressure turbines, which drive the compressors to sustain the combustion process.

Gas turbine engines used in certain applications, such as helicopters and industrial power generation, include a third spool that is a power spool. The power spool includes a power turbine, which is disposed downstream of the low pressure turbine, and a power shaft, which typically extends forward coaxially through the high and low pressure shafts. The power shaft provides torque that can turn, for example, a rotor or a generator. The high and low pressure spools as well as the power spool include alternating cascades of stators and rotors in order to work on the primary fluid in the flow path. Gas turbine engines typically include a variety of internal components or airfoil components such as, for example, turbine blades and turbine vanes. The turbine blades and vanes are typically made of a metal or metal alloy and can include internal cooling passages which are exposed to hot temperature environments that can contain oxygen and water vapor. Exposure to these environmental conditions can lead to corrosion of the internal walls of the cooling passages over time. This internal passage corrosion can decrease the thickness of non-corroded wall portions, which can reduce the overall integrity of blades and/or vanes. Accordingly, an inspection of these gas turbine engine components is typically performed at different times during the service life of a gas turbine engine to verify the integrity of these components, and/or to indicate the need for repair or replacement of affected components.

A known means of inspecting the internal passages of a metallic gas turbine engine component for internal corrosion is to use a magnetic probe that detects the magnetic permeability of the component, thereby giving an indication of the amount of internal corrosion. From this, and knowing the original wall thickness of the component, the remaining unaffected wall thickness can be calculated. In a known inspection process, a human operator glides the magnetic probe by hand over the surface of the component while observing and/or recording a signal that is produced by the magnetic probe. Greater accuracy is generally obtained by holding the magnetic probe perpendicular to the surface of the component while moving it at a steady linear speed over the surface. Accordingly, considerable training and experience can be required of an operator to develop a high level of proficiency in holding and moving the magnetic probe. Moreover, a modern gas turbine engine component can have a complex internal geometry that requires the magnetic probe be positioned with care, assuring that the magnetic probe is moved over underlying hollow areas of the component. A template can be positioned over the surface of the component, directing the operator to move the magnetic probe in a particular path over the component to help assure that the underlying hollow area of the component is inspection. A sleeve that slips over the component is an example of a template. The time that an operator must spend performing an inspection on a gas turbine engine component having a complex internal geometry directly contributes to the cost of performing the inspection. Moreover, an operator typically requires training and practice to perform the described inspection proficiently. Accordingly, there is a need for an automated means of using a magnetic probe to perform an inspection of a gas turbine engine component.

A device for inspecting a metallic component comprising a magnetic probe is known from <CIT>.

According to a first aspect of the present invention, there is provided a system for magnetically inspecting a metallic component as set forth in claim <NUM>. According to a further aspect of the present invention, there is provided a method of inspecting a metallic component as set forth in claim <NUM>.

Turbine blades and vanes used in gas turbine engines typically include various metallic materials that can be susceptible to corrosion under some conditions. Nickel (Ni) is an exemplary metal that is used in a metal alloy used to make turbine blades and vanes. The internal corrosion of turbine blades and/or vanes can cause depletion of pure nickel (Ni) from a base metal alloy, which in turn can cause deposition of corrosion byproducts on the internal wall(s) of the corroding component. Nickel oxide (NiO) and cobalt oxide (CoO) are exemplary corrosion byproducts. These corrosion byproducts can have ferromagnetic properties that can be sensed by a magnetic probe that measures the magnetic permeability and/or a change in magnetic permeability. A MAGNETOSCOP™ (also known as "Magnetoscop") is an exemplary magnetic inspection probe that can be used to provide an indication on the magnetic permeability of an adjacent material, thereby giving an indication of corrosion byproducts. This in turn gives an indication of the amount of corrosion in a gas turbine blade or vane in an interior region adjacent to the magnetic inspection probe. For example, magnetic inspection probes (also known as magnetometers, magnetic probes, and magnetoscopes) are capable of generating a magnetic flux density and measuring a relative magnetic permeability (i.e., permeability) of a wide array of metal alloys, including low-permeable (non-magnetic) alloys. Magnetic inspection probes can also detect changes in a material (e.g., sulfidation, degradation of lamination, structural changes) based on comparative magnetic permeability measurements (i.e., magnetic field anomalies). Gas turbine engine components having hollow geometries (e.g., internal cooling passages) can complicate the use of a magnetic inspection probe (e.g., MAGNETOSCOP™), and it can be necessary to know the underlying internal structure of a component when operating a magnetic inspection probe on the exterior (i.e., external) surface.

<FIG> is a partial cross-sectional view of a gas turbine engine. Gas turbine engine <NUM> is an exemplary non-limiting embodiment of the present disclosure. Gas turbine engine <NUM> is a two-spool turbofan that generally incorporates fan section <NUM>, compressor section <NUM>, combustor section <NUM>, and turbine section <NUM>. In other embodiments, gas turbine engine <NUM> can include other systems or features. Fan section <NUM> drives air along a bypass flow path B in a bypass duct, while compressor section <NUM> drives air along a core flow path C for compression and communication into combustor section <NUM> and then expansion through turbine section <NUM>. Although depicted as a two-spool turbofan gas turbine engine in the illustrated embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as these teachings may be applied to other types of turbine engines including three-spool architectures.

Gas turbine engine <NUM> includes low speed spool <NUM> and high speed spool <NUM> mounted for rotation about central longitudinal axis A relative to engine static structure <NUM> via several bearing systems <NUM>. Various bearing systems <NUM> at various locations may alternatively and/or additionally be provided, and the location of bearing systems <NUM> may be varied as appropriate to any particular embodiment.

Low speed spool <NUM> generally includes inner shaft <NUM> that interconnects fan <NUM>, low pressure compressor <NUM>, and low pressure turbine <NUM>. In the illustrated embodiment, inner shaft <NUM> is connected to fan <NUM> through geared architecture <NUM> (i.e., a speed change mechanism) to drive fan <NUM> at a lower speed than low speed spool <NUM>. High speed spool <NUM> includes outer shaft <NUM> that interconnects high pressure compressor <NUM> and high pressure turbine <NUM>. Combustor <NUM> is arranged in exemplary gas turbine <NUM> between high pressure compressor <NUM> and high pressure turbine <NUM>. Engine static structure <NUM> supports bearing systems <NUM> in turbine section <NUM>. Inner shaft <NUM> and outer shaft <NUM> are concentric and rotate via bearing systems <NUM> about central longitudinal axis A which is collinear with their respective longitudinal axes.

The core airflow is compressed by low pressure compressor <NUM> then by high pressure compressor <NUM>, mixed and burned with fuel in combustor <NUM>, then expanded over high pressure turbine <NUM> and low pressure turbine <NUM>. High pressure turbine <NUM> and low pressure turbine <NUM> rotationally drive low speed spool <NUM> and high speed spool <NUM>, respectively, as a result of the aforementioned expansion. In other embodiments, the positions of fan section <NUM>, compressor section <NUM>, combustor section <NUM>, turbine section <NUM>, and fan drive gear system <NUM> may be varied. In some embodiments, gear system <NUM> can be located aft of combustor section <NUM>, or even aft of turbine section <NUM>. In these or other embodiments, fan section <NUM> can be positioned either forward or aft of gear system <NUM>. In any of these embodiments, gas turbine engine <NUM> includes a variety of internal components, including vanes and blades. Turbine blade <NUM> is an exemplary internal component that will be discussed in regard to the present disclosure. In an embodiment, gas turbine engine can include numerous turbine blades <NUM>, each of which is subject to corrosion. Therefore, it is desirable to be able to inspect turbine blades <NUM> for internal corrosion at various times over the service life of gas turbine engine <NUM>.

<FIG> is a perspective view of turbine blade <NUM> shown in <FIG>. <FIG> is a perspective cross-sectional end view of turbine blade <NUM> shown in <FIG> taken at cut line 2B - 2B. Shown in <FIG> are interior section <NUM>, pressure-side wall <NUM>, suction-side wall <NUM>, ribs <NUM>, and cooling passages <NUM>. Although turbine blade <NUM> is shown as an example, the present disclosure can be directed to the inspection of other components such as, for example, a gas turbine engine vane (not shown). Turbine blade <NUM> includes hollow cooling passages <NUM> defined by pressure-side wall <NUM> and suction-side wall <NUM>. Cooling passages <NUM> pass cool air therethrough as pressure-side wall <NUM> and suction-side wall <NUM> are exposed to heated core gas flow. A number of ribs <NUM> extend between pressure-side wall <NUM> and suction-side wall <NUM> to define each individual internal cooling passage <NUM>.

<FIG> is an enlarged cross-sectional end view showing interior section <NUM> of turbine blade <NUM> shown in <FIG>. Shown in <FIG> are turbine blade <NUM>, interior section <NUM>, outer pressure-side wall surface <NUM>, inner pressure-side wall surface <NUM>, outer suction-side wall surface <NUM>, inner suction-side wall surface <NUM>, first corroded element <NUM>, and second corroded element <NUM>. Also labeled in <FIG> are expected first wall thickness DREF1, expected second wall thickness DREF2, first remaining non-corrosion wall thickness DY1, second remaining non-corrosion wall thickness DY2, first corrosion element thickness DX1, and second corrosion element thickness DX2. In a particular embodiment, turbine blade <NUM> can be inspected prior to being made available for field operation, i.e., prior to being employed in gas turbine engine <NUM> for first time use, thereby generating a reference profile for turbine blade <NUM>. In an alternative embodiment, a reference profile of turbine blade <NUM> can be generated from a computer aided design (CAD) model of turbine blade <NUM>. From the reference profile, expected first wall thickness DREF1 and expected second wall thickness DREF2 can be calculated. <FIG> is simplified, and in a practical embodiment, a large number of expected wall thicknesses DREF1, DREF2,. DREFn can be established from reference profile of turbine blade <NUM>. A magnetic inspection probe (e.g., MAGNETOSCOP™) can be used to determine first corrosion element thickness DX1 and second corrosion element thickness DX2, from which first remaining non-corrosion wall thickness DY1 and second remaining non-corrosion wall thickness DY2 can be calculated by subtracting corrosion element thickness DX from expected wall thickness DREF at any particular point. For example: DY1 = DREF1 - DX1.

<FIG> is a side view showing a handheld magnetic probe of the prior art. <FIG> is a side view showing an inspection technique using the handheld magnetic probe on turbine blade <NUM>. Shown in <FIG> are turbine blade <NUM>, handheld magnetic probe <NUM>, probe tip <NUM>, and sleeve <NUM>. Also labeled in <FIG> is the probe axis. Labeled in <FIG> is the scan direction. In the illustrated embodiment, handheld magnetic probe <NUM> is a MAGNETOSCOP™, (i.e., Magnetoscop, Magnetoscop probe) that includes probe tip <NUM>. During an inspection process, probe tip <NUM> is glided over an exterior surface of turbine blade <NUM> in either scan direction with the probe axis being perpendicular to the exterior surface while making light contact with the exterior surface. Handheld magnetic probe <NUM> (e.g., MAGNETOSCOP™) measures the relative magnetic permeability of the material in the vicinity of probe tip <NUM>, being able to detect material changes caused by corrosion and the like. Because of the complex interior geometry of turbine blade <NUM> (e.g., as shown in <FIG> and <FIG>), sleeve <NUM> can be placed over turbine blade <NUM> to help guide the operator in positioning probe tip <NUM> adjacent to a cooling passage (not shown in <FIG>). Sleeve <NUM> is made of a nonmagnetic material such as plastic to not interfere with the operation of handheld magnetic probe <NUM>. Sleeve <NUM> can have one or more edges or channels (not labeled in <FIG>) to assist an operator in guiding probe tip <NUM> along a desired path. An example of a desired path is along the exterior surface, following the centerline of an internal cooling passage. In some embodiments, multiple sleeves <NUM> can be used for a particular turbine blade <NUM> in order to assist an operator in inspecting all cooling passages of turbine <NUM>. Moreover, multiple sleeves <NUM>, each having a different configuration, may be required for a particular gas turbine engine <NUM> in order to provide inspection guidance for all internal components (e.g., blades and vanes). Sleeve <NUM> can also be referred to as an inspection template. In some embodiments of using handheld magnetic probe <NUM> on turbine blade <NUM>, sleeve <NUM> can be omitted, thereby relying on the skill of the operator to glide probe tip <NUM> over the exterior surface adjacent to a cooling passage <NUM>.

While performing a corrosion inspection of turbine blade <NUM> using handheld magnetic probe <NUM>, care should be taken by the operator to hold handheld magnetic probe <NUM> such that the probe axis is perpendicular to the surface of turbine blade <NUM> at the point where probe tip <NUM> contacts turbine blade <NUM>. Turbine blade <NUM> typically has a curved surface, thereby requiring the operator continuously adjust the orientation of handheld magnetic probe <NUM> to maintain the perpendicularity (i.e., normality) of the probe axis to the surface of turbine blade <NUM>. Error can be introduced in the signal that is generated by handheld magnetic probe <NUM> in response to internal corrosion. During the inspection process, care should be taken by the operator to move handheld magnetic probe <NUM> at a steady linear speed in the scan direction, while maintaining light contact between probe tip <NUM> and the surface of turbine blade <NUM>. The steady linear speed can be referred to as a target speed, or as a target scan speed. An exemplary target speed is <NUM>/s (<NUM> inch/s). In some embodiments, the target speed can range from about <NUM> - <NUM>/s (<NUM> - <NUM> inch/s). Maintaining the linear speed of probe tip <NUM> as steady as possible (i.e., as near the target speed as possible) will minimize the error that is introduced in the signal that is generated by handheld magnetic probe <NUM> in response to internal corrosion. A lower target speed can be beneficial in helping an operator maintain the probe axis perpendicular to the surface of turbine blade <NUM> while maintaining light contact between probe tip <NUM> and the surface of turbine blade <NUM>, particularly for a less-experienced operator, but this can result in increased inspection time. The cost of performing a corrosion inspection is related to the time it takes to complete the inspection. It can be difficult for an operator to follow an inspection path marked by sleeve <NUM> at a higher speed while the maintaining probe axis perpendicular to the surface while also maintaining light contact between probe tip <NUM> and the exterior surface of turbine blade <NUM>.

Accordingly, the skill of an operator can establish an upper limit to the target speed and accordingly, the overall time that it can take to complete an inspection. Preferably, light contact should be maintained between probe tip <NUM> and the exterior surface of turbine blade <NUM>. An exemplary contact force is about <NUM> N (<NUM> pounds force (lbf)), and a preferred (i.e., target) contact force can range from about <NUM> - <NUM> N (<NUM> - <NUM> lbf). If the contact force is too low, probe tip <NUM> can momentarily leave the exterior surface of turbine blade <NUM> while under the control of a human operator, thereby introducing error in the signal that is generated by handheld magnetic probe <NUM> in response to internal corrosion. It is estimated that a human operator trying to maintain a contact force less than about <NUM> N (<NUM> lbf) can result in intermittent instances of probe tip <NUM> breaking surface contact, particularly at a higher linear speed. If the contact force is too great, damage to probe tip <NUM>, probe <NUM>, and/or sleeve <NUM> can occur. Moreover, maintaining a high contact force can increase the onset of fatigue in the operator who is performing the corrosion inspection, which can impede the progress of the inspection.

<FIG> is a perspective view showing an automated magnetic inspection system and turbine blade <NUM>. Shown in <FIG> are turbine blade <NUM>, automated magnetic inspection system <NUM>, platform <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, probe cable <NUM>, manipulator <NUM>, actuator <NUM>, holder <NUM>, manipulator cable <NUM>, and controller <NUM>. Automated magnetic inspection system <NUM> includes magnetic inspection probe <NUM> which is fixtured to platform <NUM>. In the illustrated embodiment, magnetic inspection probe <NUM> is a MAGNETOSCOP™ (i.e., Magnetoscop, Magnetoscop probe) that includes probe tip <NUM>. Magnetic inspection probe <NUM> is connected to controller <NUM> by probe cable <NUM>. Automated magnetic inspection system <NUM> also includes manipulator <NUM> which is attached to platform <NUM>. Manipulator <NUM> can be referred to as a specialized industrial robot and includes actuator <NUM> which is attached to holder <NUM>. In the illustrated embodiment, manipulator <NUM> is a six-axis manipulator that can position holder <NUM> in the x, y, and z planes as well as positioning holder using roll, pitch, and yaw movements. Manipulator <NUM> includes actuator <NUM> which helps perform six-axis positioning of holder <NUM>. Holder <NUM> is configured to hold turbine blade <NUM> by securely gripping the blade root (not labeled) of turbine blade <NUM>. Manipulator <NUM> is connected to controller <NUM> by manipulator cable <NUM>, which carries power and control signals to manipulator <NUM> (including actuator <NUM>).

Accordingly, in the illustrated embodiment, magnetic inspection probe <NUM> is held stationary while turbine blade <NUM> is guided over probe tip <NUM> to perform an automated corrosion inspection of turbine blade <NUM>. A few advantages of this configuration (i.e., as opposed to fixing turbine blade <NUM> stationary while moving magnetic inspection probe <NUM>) are that probe cable <NUM> is not continuously flexed during the inspection process which can result in material fatigue, and magnetic inspection probe <NUM> is not near actuator <NUM> which can introduce stray magnetic fields in the vicinity of probe tip <NUM>, thereby contributing to error. Actuator <NUM> includes several electromechanical devices (i.e., motors) that can produce stray magnetic fields in their vicinity. Moreover, the stray magnetic fields can vary over the course of an inspection depending on the positioning of holder <NUM> (i.e., as controlled by actuator <NUM>) throughout the inspection. In a method of the prior art as shown in <FIG>, an operator generally has an easier task of moving handheld magnetic probe <NUM> because of its relatively light weight compared to turbine blade <NUM>. However, manipulator <NUM> of automated magnetic inspection system <NUM> can quite readily handle the weight of turbine blade <NUM> as shown in the exemplary embodiment. In other embodiments, automated magnetic inspection system <NUM> can be configured to hold turbine blade <NUM> stationary while moving magnetic inspection probe <NUM> by manipulator <NUM> (i.e., including by actuator <NUM>). In an exemplary embodiment where turbine blade <NUM> is particularly large and/or massive (e.g., it cannot be removed from a large and/or massive component), it can be beneficial to hold turbine blade <NUM> stationary while moving magnetic inspection probe <NUM>. In either configuration, automated magnetic inspection system <NUM> develops steady relative motion between the surface of turbine blade <NUM> and probe tip <NUM>. Both configurations are included in the present disclosure.

Referring again to <FIG>, controller <NUM> controls the operation of manipulator <NUM> to move turbine blade <NUM> over probe tip <NUM> while receiving the signal from magnetic inspection probe <NUM>. Controller <NUM> includes one or more processors and computer-readable storage or memory encoded with instructions that, when executed by the one or more processors, direct turbine blade <NUM> over probe tip <NUM> such that probe tip <NUM> follows a path over a designated path on the exterior surface of turbine blade <NUM> at a steady linear speed while maintaining the probe axis (not labeled in <FIG>) perpendicular to the exterior surface of turbine <NUM> at the point of contact. In the illustrated embodiment, controller <NUM> stores a CAD model of turbine blade <NUM> which is used for establishing a designated path over the exterior surface of turbine blade <NUM>. In some embodiments, controller <NUM> can store a route map of the designated path over the exterior surface of turbine blade <NUM>. In these embodiments, the route map can be preconfigured (i.e., in a process outside of controller <NUM>) for a particular turbine blade <NUM> based on a CAD model of turbine blade <NUM>. An exemplary designated path can be for probe tip <NUM> to follow the exterior surface aligned with an interior cooling channel. According to the invention, controller <NUM> produces a magnetic anomaly map of turbine blade <NUM> based on the signal received from magnetic inspection probe <NUM>, which is used to calculate corrosion element thickness DXn and remaining non-corrosion wall thickness DYn (the descriptions of which were provided above in regard to <FIG>). In some embodiments, controller <NUM> can calculate and store a corrosion map that is representative of areas of corrosion within turbine blade <NUM>. In other embodiments, controller <NUM> can calculate a material remaining map that indicates the non-corroded (i.e., unaffected) regions withing turbine blade <NUM>. In yet other embodiments, controller <NUM> can store a magnetic anomaly map representing magnetic anomalies along the surface of turbine blade <NUM>. The magnetic anomalies map can be offloaded from controller <NUM> for processing by a system that is separate from automated magnetic inspection system <NUM> to analyze and calculate the corrosion inspection results of turbine blade <NUM>. In the illustrated embodiment, manipulator <NUM> is a six-axis manipulator. In other embodiment, manipulator can have fewer than or greater than six axes of motion. In exemplary embodiments, manipulator <NUM> can have three, four, or five axes of motion. In another exemplary embodiment, manipulator <NUM> can have seven or more axes of motion.

<FIG> is a block diagram of a second embodiment of an automated magnetic inspection system. Shown in <FIG> are automated magnetic inspection system <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, force transducer <NUM>, manipulator <NUM>, controller <NUM>, processor <NUM>, manipulator controller <NUM>, input-output (I/O) module <NUM>, storage <NUM>, processor instructions <NUM>, CAD model <NUM>, magnetic anomaly map <NUM>, and operator interface <NUM>. Magnetic inspection probe <NUM> includes probe tip <NUM>, having a description that is substantially as provided above in regard to <FIG>. A signal representing the magnetic permeability measurements (i.e., magnetic field anomalies) from magnetic inspection probe <NUM> is communicated to controller <NUM> via the probe cable (not labeled in <FIG>). Magnetic inspection probe <NUM> also includes force transducer <NUM> which measures the contact force on probe tip <NUM> (i.e., the contact force between probe tip <NUM> and the exterior surface of turbine blade <NUM>). A signal representing the probe tip contact force is generated by force transducer <NUM> is also communicated to controller <NUM> via the probe cable. The description of manipulator <NUM> is substantially similar to that provided above in regard to <FIG>. Manipulator <NUM> includes an actuator (not shown in <FIG>). During an inspection process, the actuator is connected to a holder (not shown in <FIG>) which supports and manipulates turbine blade <NUM> in a manner as described above in regard to <FIG>.

Controller <NUM> includes processor <NUM>, actuator controller <NUM>, I/O module <NUM>, and storage <NUM>. Processor <NUM> is connected to storage <NUM> and can also include internal and/or connected memory. Processor <NUM> Storage <NUM> includes processor instructions <NUM>, CAD model <NUM>, and magnetic anomaly map <NUM>. Processor <NUM> can include one or more processors (not shown in <FIG>) that are configured to implement functionality and/or process instructions for execution within processor <NUM>. The one or more processors can be capable of processing instructions stored in processor instructions <NUM> (i.e., in storage <NUM>). Examples of processors can include any one or more of: a microprocessor, a microcontroller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other equivalent discrete or integrated logic circuitry. In the illustrated embodiment, a three-dimensional digital model of turbine blade <NUM> is stored in CAD model <NUM> when automated magnetic inspection system <NUM> is inspecting turbine blade <NUM>. As noted above in regard to <FIG>, in some embodiments, a route map of the designated path over the exterior surface of turbine blade <NUM> can be stored in storage <NUM>. As used in this disclosure, CAD model <NUM> refers to a model that is used by controller <NUM> to direct the motion of manipulator <NUM> relative to the surface of turbine blade <NUM> (i.e., regardless of whether CAD model <NUM> is a route map model or a three-dimensional model of turbine blade <NUM> from which controller <NUM> renders a route map). During the operation of automated magnetic inspection system <NUM>, processor <NUM> executes instructions stored in processor instructions <NUM> to provide instructions to manipulator controller <NUM> which in turn communicates with manipulator <NUM> to position the actuator and holder (not shown in <FIG>), thereby positioning and moving turbine blade <NUM> such that the exterior surface of turbine blade <NUM> is moved along probe tip <NUM> to perform an inspection. Processor <NUM> utilizes CAD model <NUM> to calculate the proper positioning and motion of manipulator <NUM> to perform the corrosion inspection. The positioning of turbine blade <NUM> will be discussed in more detail later, in <FIG>.

Referring again to <FIG>, as the corrosion inspection is performed during the operation of automated magnetic inspection system <NUM>, the signal from magnetic inspection probe <NUM> is received by processor <NUM>. In the illustrated embodiment, magnetic anomalies that are representative of the inspection results are stored in magnetic anomaly map <NUM>. In an embodiment, data from magnetic anomaly map <NUM> can be offloaded from controller <NUM> for processing by a system that is separate from automated magnetic inspection system <NUM> to analyze and calculate the corrosion inspection results of turbine blade <NUM> using a map of the exterior and interior of turbine blade <NUM>. From this, a non-corroded (i.e., unaffected material) map of turbine blade <NUM> can be calculated. In another embodiment, processor <NUM> can calculate a corrosion map or a non-corroded map based on a three-dimensional model of turbine blade <NUM> that is stored in CAD model <NUM>. In any of these foregoing embodiments, data from storage <NUM> (e.g., magnetic anomaly map <NUM>) can be transferred to an external system via I/O interface <NUM>. In an exemplary embodiment, data representing the results of the corrosion inspection (i.e., inspection data) can be transferred via I/O interface after the inspection is completed. In other embodiments, inspection data can be transferred continuously or in batches during the inspection. In any of the foregoing embodiments, I/O interface <NUM> can be used to upload data stored in CAD model <NUM> to perform an inspection on a particular turbine blade <NUM>. Examples of uploaded data include an inspection route map model, a three-dimensional exterior model, and a three-dimensional interior and exterior model. An operator supervising the corrosion inspection can control automated magnetic inspection system <NUM> via operator interface <NUM>.

<FIG> is a perspective side view showing automated magnetic inspection system <NUM> shown as a block diagram in <FIG> along with turbine blade <NUM>. Shown in <FIG> are turbine blade <NUM>, automated magnetic inspection system <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, probe cable <NUM>, force transducer <NUM>, probe fixture <NUM>, actuator <NUM>, and holder <NUM>. Turbine blade <NUM>, automated magnetic inspection system <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, probe cable <NUM>, and force transducer <NUM> all have descriptions as provided above in regard to <FIG>. Actuator <NUM> supports holder <NUM>, which in turn holds turbine blade <NUM> in a manner similar to that described above in regard to <FIG>. Magnetic inspection probe <NUM> is held in place by probe fixture <NUM> which is supported by a platform (not shown in <FIG>). Force transducer <NUM> detects the lateral force applied to probe tip <NUM> against probe fixture <NUM>. An exemplary force transducer is a piezoelectric cell which develops a signal representative of the applied force. A person skilled in the sensor art is familiar with various means of sensing an applied force. Controller <NUM> receives the force signal generated by force transducer <NUM> to adjust the position of manipulator <NUM> in order to maintain a desired contact force between probe tip <NUM> and the surface of turbine blade <NUM>. By using a closed-loop feedback control system that includes force transducer <NUM>, positional errors can be compensated for, thereby assisting automated magnetic inspection system <NUM> in maintaining the desired contact force, thereby contributing to the accuracy of the corrosion inspection being performed by automated magnetic inspection system <NUM>. Exemplary sources of positional errors include the ability of manipulator <NUM> to maintain a desired position and deviations between actual surface profile of turbine blade <NUM> and the digital surface profile that is modeled in CAD model <NUM>. Preferably, light contact should be maintained between probe tip <NUM> and the exterior surface of turbine blade <NUM>. An exemplary contact force is about <NUM> lbf (<NUM> Nt), and a preferred (i.e., target) contact force can range from about <NUM> - <NUM> lbf (<NUM> - <NUM> Nt).

Automated magnetic inspection system <NUM> is superior to a human operator in the ability to maintain a constant light contact force because of the solidness of electromechanical devices as opposed to a human hand and arm. Accordingly, automated magnetic inspection system <NUM> can maintain a target contact force with a high accuracy. In an exemplary embodiment, automated magnetic inspection system <NUM> can maintain a target contact force of <NUM> lbf (<NUM> Nt) within a tolerance of ± <NUM>%. In some embodiments, automated magnetic inspection system <NUM> can maintain a target contact force that is zero or near-zero. Accordingly, in some embodiments automated magnetic inspection system <NUM> can be used to inspect components having delicate surfaces that would otherwise be susceptible to damage when using handheld magnetic probe <NUM> of the prior art.

<FIG> is a cross-sectional side view showing a third embodiment of an automated magnetic inspection system and turbine blade <NUM>. Shown in <FIG> are turbine blade <NUM>, automated magnetic inspection system <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, and probe effector <NUM>. Also labeled in <FIG> is the probe axis, the surface tangent line at the point of contact between probe tip <NUM> and the surface of turbine blade <NUM>, probe angle β, and a velocity vector. Turbine blade <NUM>, magnetic inspection probe <NUM>, and probe tip <NUM> all have descriptions as provided above in regard to <FIG>. Probe tip <NUM> is supported by probe effector <NUM> which includes two features. Probe effector <NUM> includes a force transducer (not labeled) that provides an electrical signal representative of the contact force on probe tip <NUM> in a manner similar to that described above in regard to force transducer <NUM> shown in <FIG>. Probe effector <NUM> also includes a mechanical biasing component (i.e., mechanically compressible component) that compresses in response to an increase in applied force, thereby mitigating the increase in applied force. A mechanical spring is an exemplary compressive biasing component. Accordingly, automated magnetic inspection system <NUM> having probe effector <NUM> can help automated magnetic inspection system <NUM> maintain a highly stable contact force by providing mechanical biasing (i.e., mechanically compressible biasing) in addition to the closed-loop feedback control system as described above in regard to <FIG>. In an embodiment, probe effector <NUM> can include only a mechanical biasing device (e.g., spring), while omitting a force transducer. In this embodiment, probe effector <NUM> helps maintain the contact force within a desired range while omitting the closed loop feedback that is provided by the force transducer.

Referring again to <FIG>, the probe axis forms probe angle β with the surface tangent at the point of contact between probe tip <NUM> and the surface of turbine blade <NUM>. Automated magnetic inspection system <NUM> controls the position of turbine blade <NUM> such that probe angle β is <NUM> degrees. <FIG> depicts magnetic inspection probe <NUM> and turbine blade <NUM> in two dimensions for ease of illustration. In a practical embodiment, turbine blade <NUM> can have a three-dimensional surface curvature. Accordingly, the probe axis intersects with a surface tangent plane, and probe angle β can be measured with respect to an unlimited number of surface tangent vectors. Using a conventional Cartesian coordinate system, x- and y-orthogonal axes (not shown) can be defined at the point of contact, with probe angle β being resolved in each of the x- and y-axes (i.e., thereby providing component probe angles βx and βy). Accordingly, in a practical embodiment, automated magnetic inspection system <NUM> controls the position of turbine blade <NUM> such that component probe angles βx and βy are each <NUM> degrees. In the illustrated embodiment, automated magnetic inspection system <NUM> maintains probe angle β (i.e., component probe angles βx and βy) within <NUM> degrees of perpendicular (i.e., <NUM> ± <NUM> degrees). In some embodiments, automated magnetic inspection system <NUM> can maintain probe angle β within <NUM> degrees of perpendicular. In other embodiments, automated magnetic inspection system <NUM> can maintain probe angle β within <NUM> degree of perpendicular. In yet other embodiments, automated magnetic inspection system <NUM> can maintain probe angle β within less than <NUM> degree of perpendicular. Controlling the probe angle β within specified limits can be referred to as the probe axis angle tolerance, or as a predetermined angle delta.

Automated magnetic inspection system <NUM> continuously adjusts and controls the position of turbine blade <NUM> such that the surface of turbine blade <NUM> moves at a steady speed (i.e., velocity) along probe tip <NUM>. The accuracy of automated magnetic inspection system <NUM> (i.e., magnetic inspection probe <NUM>) is improved by maintaining a steady relative speed (i.e., velocity) between probe tip <NUM> and turbine blade <NUM>. The relative speed can be referred to as a scanning speed and can be programmed to be a desired target speed. In the illustrated embodiment, magnetic inspection probe <NUM> is fixed in place and turbine blade <NUM> is manipulated by the manipulator (not shown in <FIG>) of automated magnetic inspection system <NUM>. In other embodiments, turbine blade <NUM> fixed in place and magnetic inspection probe <NUM> can be manipulated by the manipulator.

In an exemplary embodiment, automated magnetic inspection system <NUM> can be programmed to a desired target speed of <NUM>/s (<NUM> inch/s). while maintaining the scan speed within + <NUM>% of the target speed. In some embodiments, the desired target speed of can range from <NUM> - <NUM>/s (<NUM> - <NUM> inch/s). In other embodiments, the desired target speed of can be less than <NUM>/s (<NUM> inch/s) or greater than <NUM>/s (<NUM> inch/s). In any of these foregoing embodiments, automated magnetic inspection system <NUM> can maintain the scan speed within a tolerance other than ± <NUM>% of the target speed. Exemplary tolerance values include ± <NUM>%, ± <NUM>%, ± <NUM>%, and ± <NUM>%.

Whereas a human operator can have difficulty controlling a hand-held probe of the prior art while maintaining a scan speed of greater than about <NUM>/s (<NUM> inch/s), automated magnetic inspection system <NUM> can control the relative motion between probe tip <NUM> and turbine blade <NUM> at practically any scan speed. For example, in an exemplary embodiment, automated magnetic inspection system <NUM> can be programmed to a desired target speed that is greater than <NUM>/sec (<NUM> inches/s), with the upper limit on scan speed being established by the ability of magnetic inspection probe <NUM> (e.g., MAGNETOSCOP™) to resolve magnetic anomalies at a particular speed. Moreover, automated magnetic inspection system <NUM> can be programmed to utilize adaptive scan speed depending on the underlying structure of turbine blade <NUM>. For example, automated magnetic inspection system <NUM> can be programmed to use a lower scan speed (i.e., a first scan speed) when in a region of turbine blade <NUM> where the underlying structure is complicated. Examples of complicated underlying structures are a wall thickness gradient and near the vicinity of internal ribs or other discontinuities. Automated magnetic inspection system <NUM> can be programmed to use a higher scan speed (i.e., a second scan speed) when in a region of turbine blade <NUM> where the underlying structure is uncomplicated. An example of an uncomplicated underlying structure is a uniform wall thickness that is not near an internal discontinuity. Automated magnetic inspection system <NUM> can set a particular scan speed based on the CAD model of turbine blade <NUM> that is stored within the controller. In an embodiment, three or more scan speeds can be established by automated magnetic inspection system <NUM>. In another embodiment, the scan speed can be continuously variable.

<FIG> is a perspective view showing a fourth embodiment of an automated magnetic inspection system and turbine blade <NUM>. Shown in <FIG> are automated magnetic inspection system <NUM>, magnetic inspection probe <NUM>, probe tip <NUM>, manipulator <NUM>, actuator <NUM>, holder <NUM>, and holder extension <NUM>. Also labeled in <FIG> is holder extension length L. The descriptions of magnetic inspection probe <NUM>, probe tip <NUM>, manipulator <NUM>, and actuator <NUM> are substantially similar to those provided above in regard to <FIG>. In some embodiments, magnetic inspection probe <NUM> can include a force transducer and/or a mechanical biasing component as described above in regard to <FIG>. Actuator <NUM> includes several electromechanical devices (i.e., motors) that can produce stray magnetic fields in their vicinity, as described above in regard to <FIG>. These stray magnetic fiends can interfere with the signal being produced by magnetic inspection probe <NUM> (e.g., MAGNETOSCOP™), particularly when probe tip <NUM> is on a region of turbine blade <NUM> that is near actuator <NUM>. Automated magnetic inspection system <NUM> shown in <FIG> physically separates turbine blade <NUM> from actuator <NUM> by using holder extension <NUM>. In the illustrated embodiment, holder extension <NUM> is made of a nonmagnetic polymer material, with Nylon being an exemplary material. In other embodiments, holder extension <NUM> can be made of plastic, resin, and the like. Holder extension <NUM> can be referred to as a nonmagnetic holder extension. In the illustrated embodiment, holder extension length L is about <NUM> (<NUM> inches). In some embodiments, holder extension length L can range from about <NUM> - <NUM> (<NUM> - <NUM> inches). In other embodiments, holder extension length L can be less than about <NUM> (<NUM> inches) or greater than about <NUM> (<NUM> inches). In an embodiment, holder extension length L can be selected to provide a standoff distance (not labeled) from magnetic inspection probe <NUM> that eliminates or reduces magnetic interference caused by actuator <NUM> to a tolerable level. The standoff distance can be referred to as a critical separation distance, referring to the separation between actuator <NUM> and either turbine blade <NUM> or magnetic inspection probe <NUM> that reduces the effect of stray magnetic fields from actuator <NUM> to a tolerable level. While stray magnetic fields produced by actuator <NUM> can affect the operation of magnetic inspection probe <NUM>, these stray magnetic fields can also affect the magnetic flux density within turbine blade <NUM>, which can affect the accuracy of the corrosion inspection.

Claim 1:
A system for magnetically inspecting a metallic component having a surface, the system comprising:
a holder (<NUM>; <NUM>; <NUM>) configured to hold the metallic component;
a probe fixture (<NUM>) configured to hold a magnetic probe (<NUM>; <NUM>; <NUM>; <NUM>), the magnetic probe (<NUM>; <NUM>; <NUM>; <NUM>) having a probe tip (<NUM>; <NUM>; <NUM>; <NUM>) aligned with a probe axis, the magnetic probe (<NUM>; <NUM>; <NUM>; <NUM>) configured to measure a magnetic permeability of the metallic component;
a manipulator (<NUM>; <NUM>; <NUM>) configured to manipulate a relative position between the holder (<NUM>; <NUM>; <NUM>) and probe fixture (<NUM>); and
a controller (<NUM>; <NUM>) configured to:
control the manipulator (<NUM>; <NUM>; <NUM>) to trace an inspection route upon the surface of the metallic component along which the probe tip (<NUM>; <NUM>; <NUM>; <NUM>) contacts the metallic component such that an angular difference between the probe axis and a surface tangent plane of the metallic component is <NUM>±<NUM> degrees;
receive the magnetic permeability of the metallic component measured by the magnetic probe (<NUM>; <NUM>; <NUM>; <NUM>) along the inspection route;
determine a magnetic anomaly map based on the magnetic permeability of the metallic component;
determine a first corrosion element thickness (DX1) based on the magnetic anomaly map;
the system being characterized in that the controller is further configured to determine a first remaining non-corrosion wall thickness (DY1) based on a calculation using the first corrosion element thickness (DX1) and a three-dimensional model of the metallic component; and
transmit the first remaining non-corrosion wall thickness (DY1) via an input-output interface (<NUM>).