Patent Publication Number: US-9839998-B2

Title: Control system and apparatus for power wrench

Description:
BACKGROUND OF THE INVENTION 
     The present disclosure relates generally to control systems and apparatuses which include or interact with a power wrench. More specifically, the present disclosure relates to systems and apparatuses with a controller for controlling the torqueing processes of a power wrench based on various conditions. 
     Two or more individual components of a machine assembly, such as those found in power generation systems, may be mechanically coupled to each other by the use of fastening elements, such as bolts wound onto threaded fasteners. These fastening elements, in a conventional process, can be installed manually by the use of tools such as wrenches, bolting devices, etc. During installation and service operations, acceptable margins of error for particular variables may be very small. One sensitive variable, known as “bolt stretch,” can be defined as a bolt&#39;s amount of elongation from the surface of a reference component. Bolt stretch is one example of a variable which affects the operation and stability of the machine assembly. 
     To reduce the likelihood of human errors, some process steps for installing a fastening element can be automated. In one example, ultrasonic measuring instruments can partially automate some parts of an installation process, such as one of the processes discussed above. However, this approach may not be applicable or preferable for some types of machines. Providing greater accuracy and speed during construction, installation, and servicing of a machine assembly continues to be a technical challenge for particular applications. 
     BRIEF DESCRIPTION OF THE INVENTION 
     A control system and an apparatus for a power wrench are discussed herein. Although embodiments of the present disclosure are discussed by example by reference to power generation systems, it is understood that embodiments of the present disclosure may be applied to broadly to controlling a torqueing process for joining two or more components together. 
     A first aspect of the invention provides a system including: a power wrench; and a controller operatively connected to the power wrench, wherein the controller is configured to perform actions including: directing an operative head of the power wrench to turn in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, defining an origin at an angular position of the operative head where the pressure-angle derivative of the operative head exceeds the predetermined threshold, directing the operative head to turn by an angular step in response to: (a) the pressure-angle derivative of the operative head exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the amount differential represents an total amount of rotation of the operative head from the origin; and directing the operative head to cease turning in response to the angular differential of the operative head being approximately equal to or greater than the target value. 
     A second aspect of the invention provides an apparatus including: a power wrench including an operative head for turning a rotatable workpiece; a pressure sensor operatively connected to the power wrench, the pressure sensor measuring a pressure against the operative head; an angular encoder operatively connected to the power wrench and configured to determine an angular position of one of the operative head and the rotatable workpiece relative to an origin; a controller operatively connected to the power wrench, the pressure sensor, and the angular encoder, wherein the controller is configured to: direct the operative head to turn in response to turn in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, define an origin at an angular position of the operative head where the pressure-angle derivative of the operative head exceeds the predetermined threshold, direct the power wrench to turn by an angular step in response to: (a) the pressure-angle derivative of the operative head exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the angular differential represents an total amount of rotation of the operative head from the origin, and direct the operative head to cease turning in response to the angular differential of the operative head being approximately equal to or greater than the target value. 
     A third aspect of the invention provides a system including: a hydraulic wrench, wherein the hydraulic wrench further includes a hydraulic fluid pressure sensor, an angular encoder, an operative head for turning a rotatable workpiece; and a controller operatively connected to the hydraulic wrench and configured to perform actions including: turning the rotatable workpiece with the operative head in response to a pressure-angle derivative of the operative head being below a predetermined threshold, wherein the pressure-angle derivative is defined as a change in pressure against the operative head arising from a change to an angular position of the operative head of the power wrench, defining an origin at a position where the pressure-angle derivative of the operative head exceeds the predetermined threshold, turning the rotatable workpiece with the operative head by an angular step in response to: (a) the pressure-angle derivative of the power wrench exceeding the predetermined threshold, and (b) an angular differential of the operative head being less than a target value, wherein the angular differential represents an total amount of rotation of the operative head from the origin, and decoupling the operative head from the rotatable workpiece in response to the pressure-angle derivative of the operative head exceeding the predetermined threshold and the angular differential of the operative head from the origin being approximately equal to or greater than a target value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features of this invention will be more readily understood from the following detailed description of the various aspects of the invention taken in conjunction with the accompanying drawings that depict various embodiments of the invention, in which: 
         FIG. 1  provides a perspective view of a power wrench according to embodiments of the present disclosure. 
         FIG. 2  depicts a system and apparatus according to embodiments of the present disclosure. 
         FIG. 3  depicts an illustrative environment which includes a controller interacting with a power wrench and rotatable workpiece according to embodiments of the present disclosure. 
         FIG. 4  depicts a plot of pressure “P” against an operative head of a power wrench versus angular position “a” of the operative head according to an example embodiment of the present disclosure. 
         FIG. 5  provides a representative flow diagram of process steps performed with a controller according to embodiments of the present disclosure. 
         FIG. 6  provides a representative flow diagram of another group of process steps performed with a controller according to embodiments of the present disclosure. 
     
    
    
     It is noted that the drawings of the invention are not necessarily to scale. The drawings are intended to depict only typical aspects of the invention, and therefore should not be considered as limiting the scope of the invention. In the drawings, like numbering represents like elements between the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As discussed herein, aspects of the present disclosure relate generally to control systems and apparatuses which include or interact with a power wrench. More specifically, aspects of the present disclosure relates to systems and apparatuses with a controller for controlling the torqueing processes of a power wrench based on various conditions. 
     Embodiments of the present disclosure generally include systems and apparatuses with a controller for directing a power wrench to perform particular actions, including steps for automatically rotating a rotatable workpiece such as a bolt. The term “power wrench” can be defined as a wrench powered at least in part by sources other than a human operator, and can include particular components for generating power such as electric, mechanical, hydraulic, and/or pneumatic power sources. In an example embodiment, a power wrench can be in the form of a hydraulic wrench with a hydraulically-actuated piston for powering an operative head of the power wrench, such as a torqueing ratchet. 
     Aspects of the present disclosure can include components for directing and/or otherwise manipulating a power wrench with an operative head for acting on a rotatable workpiece. A rotatable workpiece can include, e.g., a nut for interfacing with a threaded bolt, a screw or screw head, and/or another type of rotatable coupling component. Embodiments of the present disclosure can determine, e.g., by reference to a sensor such as a pressure sensor and/or angular encoder, an angular position where a change in pressure against the operative head of the power wrench relative to a corresponding change in the angular position of the rotatable workpiece reaches or exceeds a predetermined threshold. A predetermined threshold can represent, e.g., a pressure below which the torqueing operation can proceed through an initial torqueing phase where angular position is not significantly related to the pressure imparted against operative head of the power wrench. The predetermined threshold can optionally be calculated or determined by way of calibration for multiple workpiece configurations. Bolt stretch can be defined as an amount of elongation from the surface of a reference component. Embodiments of the present disclosure can define a reference point at an angular position where the predetermined threshold is exceeded. This reference point can be referred to as an origin. Embodiments of the present disclosure can then direct the operative head of the power wrench to turn the rotatable component by a particular amount of motion, known as an “angular step.” The controller can continue to direct the operative head to turn by a particular number of angular steps until a target value of pressure against the operative head is met or exceeded. A full, three-hundred and sixty degree rotation of a rotatable workpiece can move the rotatable workpiece by a particular axial distance along a retaining fixture. For example, one full rotation of a nut can move the nut by approximately 3.0 millimeters axially along a threaded fastener. Although example amounts of movement, stretch, etc., are provided by example herein, it is understood that embodiments of the present disclosure can be calibrated for operation for varying dimensions. For instance, it is understood that the amount of axial movement by a rotatable workpiece corresponding to one full rotation may be on the order of magnitude of one one-thousandth of a millimeter (i.e., approximately 0.001 millimeters). By way of a known or predicted relationship between the position of a rotatable workpiece and the pressure against the rotatable workpiece, embodiments of the present disclosure can define a target pressure against the operative head. The target pressure can correspond to a desired amount of stretch and an amount by which the operative head has turned the rotatable workpiece. In addition, the amount of stretch resulting from a particular amount by which rotatable workpiece turns can be derived from a known pitch diameter of the threaded fastener. To further increase the accuracy of torqueing, embodiments of the present disclosure can also perform various processes for correcting the angular position of the rotatable workpiece by further movement of the operative head. 
     Referring to  FIG. 1 , a power wrench  30  can be provided in the form of, e.g., a torqueing device, powered at least in part by a component other than a human operator. As non-limiting examples, power wrench  30  can be powered wholly or partially by mechanical, electrical, hydraulic, and/or pneumatic power sources. In  FIG. 1 , power wrench  30  is shown by example as being a hydraulic wrench including a hydraulic cylinder  32 . Hydraulic cylinder  32  can be mechanically coupled to a transmission (not shown) to provide mechanical torqueing based on action of hydraulic cylinder  32 . Hydraulic lines  34  of power wrench  30  can provide a pressured hydraulic fluid to hydraulic cylinder  32  from a compressor. A body  36  of power wrench  30  can be coupled to hydraulic cylinder  32  by way of fasteners  38 . Fasteners  38  can be in the form of, e.g., mechanical fixtures such as bolts, screws, and/or other types of connectors. Body  36  can include an operative head  40  for operating on a rotatable workpiece, e.g., by engaging and rotating the workpiece. In an example embodiment, the rotatable workpiece can be in the form of a crimped nut positioned upon and/or circumferentially engaging a threaded bolt. Operative head  40  is shown by example in  FIG. 1  as including a substantially hexagonal cross-section, but it is understood that operative head  40  can be provided in the form of a component with a substantially circular, triangular, rectangular, octagonal, and/or other type of cross-section. In operation, hydraulic fluid provided to power wrench  30  through hydraulic lines  34  can actuate hydraulic cylinder  32  to turn operative head  40 . A transmission (not shown) between hydraulic cylinder  34  and operative head  40  can convert the extension or retraction of hydraulic cylinder  32  into a torqueing action of operative head  40  by any currently known or later developed energy conversion or transmission techniques. 
     Turning to  FIG. 2 , a system  50  according to embodiments of the present disclosure is shown. System  50  can include power wrench  30  connected to other components, etc., as discussed herein. Power wrench  30  can be operatively connected to a controller  60  by any currently known or later developed form of operative connection between a wrench and a controller or similar device. For instance, power wrench  30  can be electrically or wirelessly connected (e.g., by paired receivers and transmitters) to controller  60  by way of a network or other operative connection by which instructions, information, etc., can be shared or transmitted between both components. Power wrench  30  and controller  60  can also be connected by ordinary wires, data couplings, etc. Several operative connections are discussed by example elsewhere herein. Controller  60  can generally include any type of computing device capable of performing operations by way of a processing component (e.g., a microprocessor) and as examples can include one or more computers, computer processors, electric and/or digital circuits, and/or similar components used for computing and processing electrical inputs. Various sub-components and operational characteristics of controller  60  are discussed in further detail elsewhere herein. 
     In embodiments where power wrench  30  is in the form of a hydraulic wrench, power wrench  30  can be coupled to and/or in fluid communication with a pump-reservoir assembly  70 . Pump-reservoir assembly  70  can transmit hydraulic fluids into or out of power wrench  30  to control the action of components thereof, e.g., operative head  40 . Pump-reservoir assembly  70  can include a reservoir  72  for storing a supply of hydraulic fluid for operating power wrench  30 . A pump  74  of pump-reservoir assembly  70  can govern the transmission of hydraulic fluid between power wrench  30  and pump-reservoir assembly  70 . Pump  74  can be powered by, e.g., a motor such as an electric motor, a combustion engine, etc., mechanically coupled to pump  74  through a rotatable shaft, or can be powered by any other currently known or later developed device, technique, etc. for generating or transmitting energy. Controller  60  can directly or indirectly manipulate power wrench  30 . For example, controller  60  can relay instructions to activate, deactivate, or otherwise adjust valves within power wrench  30  to control the position of hydraulic cylinder  32  and/or the amount of power, fuel, operating fluid (e.g., hydraulic fluid), etc., flowing into or out of power wrench  30  through hydraulic lines  34  connected to pump reservoir assembly  70 . 
     Power wrench  30  of system  50  can operate upon a rotatable workpiece  80 . Rotatable workpiece  80  can be mounted, for example, upon a bolt  82  extending through a first component  84  and a second component  86 . In an embodiment, bolt  82  can be a threaded bolt and first and second components  84 ,  86 , can be structural components or sub-components of a larger assembly configured to be fastened to each other. Rotatable workpiece  80  can be embodied as a nut rotated about bolt  82 , and more specifically may be a crimped nut which includes projecting fixtures for preventing movement of rotatable workpiece  80  away from first and second components  84 ,  86 . Operative head  40  of power wrench  30  can be positioned upon rotatable workpiece  80  to impart torque. Operative head  40  can turn rotatable workpiece  80  about bolt  82 . Initially, the change in pressure against operative head  40  as rotatable workpiece  80  rotates can be approximately zero. Rotatable workpiece  80  may contact first component  84  after a particular amount of turning occurs. Physical contact between rotatable workpiece  80  and first component  84  may impart greater pressure against operative head  40  as rotatable workpiece  80  continues to rotate about bolt  82 . More specifically, contact between rotatable workpiece  80  and first component  84  can create an opposing tensile force, thereby requiring operative head  40  to impart greater torque against rotatable component  80  to continue turning rotatable component  80 . These types of forces can be known as and referred to as “anti-rotation,” and in summary can be any force which acts against the turning of rotatable workpiece  80  by operative head  30 . As discussed herein, controller  60  can determine the amount of torqueing to apply to rotatable workpiece  80  through power wrench  30  based on the pressure imparted against power wrench  30  and the position of rotatable workpiece  80  relative to a defined origin. 
     The various components and devices discussed herein can together form an apparatus  100  according to embodiments of the present disclosure. Apparatus  100  can include power wrench  30  with operative head  40  for turning rotatable workpiece  80 . Power wrench  30  can also be operatively connected to controller  60 , an angular encoder  90 , and a pressure sensor  92 . Where power wrench  30  is in the form of a hydraulic wrench, apparatus  100  can also include pump-reservoir assembly  70  connected to power wrench  30 . 
     As discussed in further detail herein, controller  60  can control the operation of power wrench  30  based on, e.g., the pressure imparted by rotatable workpiece  80  against operative head  40  and the angular position of operative head  40 . In a first or initial phase, controller  60  can direct power wrench  30  to turn (e.g., by rotating operative head  40 ) in response to a pressure-angle derivative of power wrench  30  being below a predetermined threshold. As used herein, the term “pressure-angle derivative” can be defined mathematically as the change in pressure imparted against operative head  40  divided by a corresponding change in the angular position of operative head  40 . In an example, the pressure-angle derivative may be close to or approximately zero where operative head  40  turns rotatable workpiece  80  without being opposed by significant reactionary mechanical forces. For example, before rotatable workpiece  80  contacts first component  84 , turning rotatable workpiece  80  by approximately ten degrees with operative head  40  can cause the pressure against operative head  40  to remain constant. In a contrasting example, the pressure-angle derivative may increase at the point where rotatable workpiece  80  on bolt  82  contacts first component  84  when being turned by operative head  40 . The pressure-angle derivative meeting or exceeding a particular positive value (i.e., a predetermined threshold) can correspond to bolt  82  contacting first component  84 . In an illustrative example, the predetermined of the pressure-angle derivative can be approximately 30 pascals (Pa) per degree of rotation. 
     Where the pressure-angle derivative exceeds the value of the predetermined threshold, controller  60  can define an origin of operative head  40  and/or rotatable workpiece  80 . The origin can correspond to a position at which the pressure-angle derivative of operative head  40  exceeds a predetermined threshold. For instance, a user may wish to define the origin where rotatable workpiece  80  contacts first component  84 . At this point, opposing mechanical forces, e.g., tensile forces imparted against operative head  40  from first component  84 , can cause rotation of rotatable workpiece  80  along bolt  82  to become more difficult. When these forces cause the pressure-angle derivative to exceed the predetermined threshold (e.g., 30 Pa per degree of rotation), controller  60  define the origin at this position before torqueing continues. At the origin, controller  60  can direct operative head  40  to turn incrementally by a predetermined “angular step.” The angular step can be a discrete amount of rotation for imparting a particular increase in pressure, e.g., turning rotatable workpiece  80  by approximately one-hundred and twenty degrees to cause a corresponding increase in pressure of approximately four kilopascals (kPa). Controller  60  can direct operative head  40  to turn rotatable workpiece  80  by the angular step successively until the angular position of rotatable workpiece  80  with respect to the origin reaches a target value. The target value can correspond to a particular amount of rotation from the origin. In addition or alternatively, the target value can correspond to a desired amount of stretch of bolt  82  from first component  84 , determined by reference to the amount of rotation from the origin. For example, the target position may be an approximately six-hundred degree rotation of rotatable workpiece  80  from the origin, which in turn can cause bolt  82  to stretch approximately 3.0 millimeters from rotatable workpiece  80 . When operative head  40  and/or rotatable workpiece  80  reaches the target value, controller  60  can direct power wrench  30  to cease turning and/or decouple from workpiece  80 . 
     Embodiments of the present disclosure can also include, e.g., an angular encoder  90  and a pressure sensor  92 . Angular encoder  90  can be in the form of a disc-type angular encoder and/or any other currently known or later developed type of encoder which measures or derives the angular position or movement of a rotating element with respect to an origin. More specifically, angular encoder can convert the angular position of a rotatable disc into an electrical signal provided to controller  60 . Angular encoder  90  can be operatively connected to power wrench  30 . More specifically, the rotation of operative head  40  can be mechanically linked to the rotation of disc-type components in angular encoder  90 . The operation of angular encoder  90  can measure, e.g., the angular position of operative head  40  with respect to the origin. To determine the amount of rotation with respect to the defined origin, controller  60  can define a position of angular encoder  90  as being zero at the origin, the pressure-angle derivative of operative head  40  first exceeds the predetermined threshold. Angular encoder  90  can be embedded within power wrench  30  as a component thereof, or can be provided as a separate component external to power wrench  30  and controller  60 . 
     Pressure sensor  92  can be embodied as a general purpose pressure sensor or an internal pressure sensor of power wrench  30 . As non-limiting examples, pressure sensor  92  can be in the form of a mechanical pressure gauge, an electrical pressure transducer, a piezoelectric pressure sensor, an optical pressure sensor, a resonant pressure gauge, etc. Where power wrench  30  is in the form of a hydraulic wrench, pressure sensor  92  can be in the form of a wrench driving fluid pressure sensor. More specifically, pressure sensor  92  can directly measure pressures imparted by a hydraulic fluid of power wrench  30  (i.e., water, oil, synthetic fluids, etc.). In any event, pressure sensor  92  can determine an amount of pressure imparted against power wrench  30  from rotatable workpiece  80 . Similar to angular encoder  90 , pressure sensor  92  can be positioned within power wrench  30  or can be provided as an external component. In any event, controller  60  can be operatively connected to angular encoder  90  and pressure sensor  92 . Controller  60  can read and/or otherwise receive determined values of pressure operative head  40 . 
       FIG. 3  provides a schematic illustration of apparatus  100  including controller  60  operatively connected to power wrench  30  and rotatable workpiece  80  according to embodiments. To this extent, apparatus  100  includes controller  60  for performing processes to direct the operation of power wrench  30 , and/or associated systems and components. Although power wrench  30  is discussed by example herein as being a hydraulic wrench, it is understood that power wrench  30  can be embodied as any currently known or later developed type of power wrench. Further, it is understood that apparatus  100  with controller  60  can be used with one or more rotatable workpieces  80 . Controller  60  is shown as including a wrench control system  102 , which makes controller  60  operable to direct power wrench  30  and/or associated systems and tools described herein for implementing any/all of the embodiments described herein. In operation, wrench control system  102  can issue electrical commands, which in turn may be converted into mechanical actions (e.g., turning operative head  40  of power wrench  30 ) in response to particular conditions. The conditions for turning operative head  40  can include, e.g., a pressure-angle derivative of power wrench  30  relative to rotatable workpiece  80  being above or below a predetermined threshold, rotatable workpiece  80  reaching a target position, a pressure against operative head  40  being outside of a tolerance band of pressures, etc. 
     Controller  60  is shown including a processing component  104  (e.g., one or more processors), a memory  106  (e.g., a storage hierarchy), an input/output (I/O) component  108  (e.g., one or more I/O interfaces and/or devices), and a communications pathway  110 . In an embodiment, processing component  104  may execute program code, such as wrench control system  102 , which is at least partially fixed in memory  106 . While executing program code, processing component  104  can process data, which can result in reading and/or writing transformed data from/to memory  106  and/or I/O component  108  for further processing. Pathway  110  provides a communications link between each of the components in controller  60 . I/O component  108  can comprise one or more human I/O devices, which enable a human or system user  112  to interact with controller  60  and/or one or more communications devices to enable user(s)  112  to communicate with controller  60  using any type of communications link. To this extent, wrench control system  102  can manage a set of interfaces (e.g., graphical user interface(s)) that enable user(s)  112  to interact with wrench control system  102 . Further, wrench control system  102  can manage (e.g., store, retrieve, create, manipulate, organize, present, etc.) data, such as system data  114  (including recorded pressures, angular positions, etc.) using any solution. 
     In any event, controller  60  can comprise one or more general-purpose or specific-purpose computing articles of manufacture (e.g., computing devices) capable of executing program code, such as wrench control system  102 , installed thereon. As used herein, it is understood that “program code” means any collection of instructions, in any language, code or notation, that cause a computing device having an information processing capability to perform a particular function either directly or after any combination of the following: (a) conversion to another language, code or notation; (b) reproduction in a different material form; and/or (c) decompression. To this extent, wrench control system  102  can be embodied as any combination of system software and/or application software. 
     Further, wrench control system  102  can be implemented using a set of modules  116 . In this case, each module can enable controller  60  to perform a set of tasks used by wrench control system  102 , and can be separately developed and/or implemented apart from other portions of wrench control system  102 . A comparator module can compare two or more mathematical quantities, such as measured and/or pre-calculated values. A calculator module can perform mathematical operations, such as adding, subtracting, multiplying, dividing, etc., on data. A determinator module can make determinations based on results yielded by other operations performed with controller  60  and/or rules defined in an algorithm. When fixed in memory  106  of controller  60  that includes processing component  104 , a module is a substantial portion of a component that implements the functionality. Regardless, it is understood that two or more components, modules and/or systems may share some/all of their respective hardware and/or software. Further, it is understood that some of the functionality discussed herein may not be implemented or additional functionality may be included as part of controller  60 . 
     Regardless, controller  60  can include multiple computing devices, and the computing devices can communicate over any type of communications link. Further, while performing a process described herein, controller  60  can communicate with one or more other computer systems using any type of communications link. In either case, the communications link can comprise any combination of various types of wired and/or wireless links; comprise any combination of one or more types of networks; and/or use any combination of various types of transmission techniques and protocols. In other embodiments, using system  50  and/or apparatus  100  can provide for manual operation of controller  60  (e.g., via user(s)  112  such as one or more technicians) or automatic operation of controller  60  by the intervention of one or more computer systems operatively connected thereto. It is understood that controller  60  may serve technical purposes in other settings beyond providing a control system or apparatus for a power wrench, including without limitation: inspection, maintenance, repair, replacement, testing, etc. 
     When controller  60  comprises multiple computing devices, each computing device may have only a portion of wrench control system  102  fixed thereon (e.g., one or more modules). However, it is understood that controller  60  and wrench control system  102  are only representative of various possible equivalent computer systems that may perform a process described herein. To this extent, in other embodiments, the functionality provided by controller  60  and wrench control system  102  can be at least partially implemented by one or more computing devices that include any combination of general and/or specific purpose hardware with or without program code. In each embodiment, the hardware and program code, if included, can be created using standard engineering and programming techniques, respectively. 
     Wrench control system  102  can be in the form of a computer program fixed in at least one computer-readable medium, which when executed, enables controller  60  to direct the operation of power wrench  30 . To this extent, the computer-readable medium includes program code which implements some or all of the processes and/or embodiments described herein. It is understood that the term “computer-readable medium” comprises one or more of any type of tangible medium of expression, now known or later developed, from which a copy of the program code can be perceived, reproduced or otherwise communicated by a computing device. For example, the computer-readable medium can comprise: one or more portable storage articles of manufacture; one or more memory/storage components of a computing device; paper; etc. 
     Referring to  FIG. 4 , an example chart of pressure “P” imparted against operative head  40  ( FIGS. 1-3 ) of power wrench  30  ( FIG. 1-3 ) versus angular position “a” of operative head  40  is shown as a further illustration. In the example of  FIG. 4 , rotatable workpiece  80  is in the form of a nut being wound onto a stud, where the stud joins two components (e.g., first and second components  84 , 86  ( FIG. 2 )) of a structure. Initially, a pressure against operative head  40  during the turning of rotatable workpiece  80  can have a value P CTQ  which does not increase as rotatable workpiece  80  continues to rotate. This process stage, in which pressure against operative head  40  does not significantly increase before reaching angle a 1 , can be known and referred to as “initial torqueing.” During initial torqueing, the pressure-angle derivative (represented as dP/da) can be zero because rotatable workpiece  80  contacts only operative head  40  and bolt  82 . As operative head  40  continues to move rotatable workpiece  80  along bolt  82 , forces against operative head  40  from other sources (e.g., friction between bolt  82  and rotatable workpiece  80 ) can be negligible. 
     Where rotatable workpiece  80  becomes “loaded” (i.e., rotatable workpiece  80  in the form of a rotating nut contacts first component  84  in this example), the pressure-angle derivative becomes greater than zero and meets the predetermined threshold. In an example, rotatable workpiece  80  can contact first component  84  to impart a bolting force as rotatable workpiece  80  continues to move along bolt  82 . This stage of torqueing can be known and referred to as the “angle of turn operation.” Wrench control system  102  ( FIGS. 2-3 ) of controller  60  can define an origin for further torqueing of rotatable workpiece  80  in response to the pressure-angle derivative being exceeded at angle a 1 . As operative head  40  turns rotatable workpiece  80  and moves consecutively from angle a 1  to angle a 2  to angle a 3 , and eventually to a F , the pressure imparted against operative head  40  can increase as operative head  40  turns rotatable workpiece. The increase in pressure imparted against operative head  40  can derive from opposing forces imparted by first component  84  against operative head  40  through rotatable workpiece  80 . The opposing forces can result from first and second components  84 ,  86  contacting each other and being pressed against each other by rotatable workpiece  80 , thereby causing the pressure-angle derivative to become greater than zero. Each labeled change in angle of operative head  40  can correspond to a single “angular step.” Angle a f  can represent a target position where rotatable workpiece  80  reaches an angular differential (a F -a 1 ) with respect to the origin (a 1 ). At angle a f , rotatable workpiece  80  can be in a target position. In the example shown in  FIG. 4 , the pressure against operative head  40  can be within a tolerance band of pressures. In other embodiments discussed herein, controller  60  can instruct operative head  40  to correct the position of rotatable workpiece  80  when the pressure against operative head  40  is outside the tolerance band. As is illustrated in  FIG. 4 , controller  60  in embodiments of the present disclosure can direct operative head  40  of power wrench  30  to turn rotatable workpiece  80  according to the process steps described herein, to provide automatic torqueing of rotatable workpiece  80 . 
     Referring to  FIGS. 3 and 5  together, an illustrative method flow diagram is shown according to embodiments of the present disclosure. A different process flow is also shown in  FIG. 6 . The process flows shown in  FIGS. 5 and 6 , may apply, e.g., to torqueing operations where rotatable workpiece  80  is in the form of a crimped nut of a power generation system. However, it is understood that the example process flow discussed herein can be modified to suit alternative applications. Processes according to the present disclosure are described herein by reference to an example of torqueing operations for two components of a turbine system, and a plot of torqueing operations in this example is shown in  FIG. 4 . More specifically, the process flow can provide for torqueing of rotatable workpiece  80  along bolt  82  to join first and second components  84 ,  86  of a turbine system. However, it is understood that the example discussed herein is non-limiting, and that embodiments of the present disclosure can be applied to other settings with or without modifications. 
     At process P 1 , wrench control system  102  can calculate the value of a pressure-angle derivative (dP/da) of power wrench  30  for a particular instance. As is discussed elsewhere herein, the pressure-angle derivative generally refers to a change in pressure against power wrench  30  relative to a corresponding change to an angular position of operative head  40  of power wrench  30 . The pressure-angle derivative is represented graphically in  FIG. 4  as the slope of the plot of pressure versus angular position. In an embodiment, modules  116  can calculate the pressure-angle derivative in process P 1  from values of pressure from pressure sensor  92  relative to corresponding changes in angular position measured with angular encoder  90 . According to an example, modules  116  can calculate the pressure-angle derivative by dividing a change in pressure against operative head  40 , measured with pressure sensor  92 , by a corresponding change in angular position of operative head  40 , measured with angular encoder  90 . 
     At process P 2 , modules  116  can compare the pressure-angle derivative calculated in process P 1  with the predetermined threshold. Where the comparison indicates the pressure-angle derivative as below the predetermined threshold (i.e., “no” at process P 2 ), the flow can proceed to a process P 3  where controller  60  directs operative head  40  to turn rotatable workpiece  80 . To turn rotatable workpiece  80  in process P 3 , controller  60  can instruct operative head  40  to turn a constant speed for a particular amount of time, turn for a particular angular distance, and/or provide other instructions for turning operative head  40  by a particular amount of rotation. Where controller  60  directs operative head  40  to turn rotatable workpiece  80  in process P 3 , the flow can return to process P 1  where wrench control system  102  can again calculate the pressure-angle derivative. Although process P 3  can be executed sequentially following each comparison in process P 1  and determination in process P 2 , it is understood that process P 3  can occur simultaneously or substantially simultaneously with processes P 1  and P 2 . In an example embodiment, rotatable workpiece  80  may not yet be in contact with first component  84 . In this case, modules  116  can calculate a pressure-angle derivative of approximately zero in response to rotatable workpiece  80  being rotated by approximately ten degrees, and thereby causing a negligible increase in pressure against operative head  40  (e.g., a pressure increase of less than one Pa). Where the predetermined threshold is approximately zero, a negligible (i.e., less than the predetermined threshold of 30 Pa per degree of rotation) pressure-angle derivative would not exceed the predetermined threshold. 
     Where the pressure-angle derivative exceeds the predetermined threshold (i.e., “yes” at process P 2 ), the flow can proceed to a process P 4  for defining an origin as a reference position of angular displacement for operative head  40 . The pressure-angle derivative exceeding the predetermined threshold can indicate where rotatable workpiece  80  contacts another component (e.g., first component  84 ). This contact can cause tensile forces exerted from first component  84  to oppose further turning of rotatable workpiece  80 . In addition, other forces such as friction between the contacting surfaces of rotatable workpiece  80  and first component  84  can impede further torqueing. According to an example, modules  116  can calculate a pressure-angle derivative of 33 Pa per degree based on the pressure against operative head  40  increasing by approximately 330 Pa after rotatable workpiece  80  rotates by approximately ten degrees. Where the predetermined threshold is approximately 30 Pa per degree, a pressure-angle derivative of 33 Pa per degree exceeds the predetermined threshold of 30 Pa per degree. 
     At process P 4 , modules  116  of wrench control system  102  can define an origin, e.g., by recording a position of angular encoder  90  where the pressure-angle derivative exceeds the predetermined threshold. The origin defined with controller  60  can designate a value of zero angular displacement of operative head  40 , at the beginning of the angle of turn operation. As a result of the pressure-angle derivative being exceeded, wrench control system can switch to the angle of turn operation, where among other things controller  60  can instruct power wrench  30  to rotate rotatable workpiece  80  by a particular amount, i.e., by a predetermined angular step. According to the example discussed herein, wrench control system  102  can instruct operative head  40  to turn rotatable workpiece  80  by an angular step of approximately one hundred and twenty degrees. 
     At process P 5 , controller  60  can direct operative head  40  of power wrench  30  to turn rotatable workpiece  80  by the amount of a predetermined angular step. The angular step can refer to an instance of angular movement measured by an amount (e.g., in degrees, radians, centimeters, etc.) which imparts an incremental increase in pressure against operative head  40 . This incremental increase in pressure against operative head  40  can be known as and referred to as a pressure differential. The angular step may be defined by user  112  and/or stored within memory  106  of controller  60  (e.g., as system data  114 ). In an illustrative example, the angular step can be a rotation of approximately one hundred and twenty degrees, with a corresponding pressure differential of approximately 4.0 kilopascals (kPa). 
     At process P 6 , modules  116  can calculate an angular differential between the current position of operative head  40  and the origin defined in process P 4 . For example, modules  116  can subtract an angular measurement for the origin from an angular measurement representing the current position of operative head  40 . In an example embodiment, a data exchange module  122  can read and/or otherwise receive angular position data from angular encoder  90 , e.g., as system data  114 . According to the example discussed herein, modules  116  can calculate an angular differential of approximately three-hundred and sixty degrees (i.e., one full turn) after operative head  40  turns rotatable workpiece  80  by the angular step (i.e., by one hundred and twenty degrees) for the third time. 
     At process P 7 , modules  116  can compare whether the angular differential calculated in process P 6  is approximately equal to or otherwise greater than the angular differential for a target position. The target position refers to a desired position where operative head  40  has rotated from the defined origin by a particular amount, and where operative head  40  may be subject to a desired amount of pressure. The target location can be a location where rotatable workpiece  80  provides a corresponding elongation of bolt  82  from first component  84 . In an embodiment, the target position may be a position where the position of rotatable workpiece  80  creates a desired amount of stretch, e.g., a predetermined bolt stretch of bolt  82  ( FIG. 2 ). The desired amount of stretch may be calculated based on a correlation between the turning of rotatable workpiece  80  and a change in the amount of stretch. For example, a particular rotatable workpiece  80  moving along bolt  82  may cause stretch to increase by, e.g., approximately 0.50 millimeters for each one-hundred degrees that rotatable workpiece  80  turns. Where the angular differential has not reached the angular differential for the target position (i.e., “no” at process P 7 ), the flow can return to process P 5  of again turning rotatable workpiece  80  with operative head  40  by the value of the angular step. In the example scenario, a target position for rotatable workpiece  80 , stored in memory  106  of controller  60 , can be approximately six-hundred degrees from the origin, which in turn can correspond to approximately 3.0 millimeters of bolt stretch. Where the angular differential is less than six hundred degrees, controller  60  can instruct operative head  40  to turn by another angular step. 
     Where the angular differential is approximately equal to or greater than the target position (i.e., “yes” at process P 7 ), the flow can proceed to a process P 8  where wrench control system  102  calculates the amount of pressure exerted against operative head  40 . In an embodiment, modules  116  can calculate the pressure imparted against operative head  40  by reference to measurements obtained with pressure sensor  92 . More particularly, pressure sensor  92  can measure the amount of pressure imparted against operative head  40  and transmit these values to wrench control system  102 . In the example, rotatable workpiece  80  being in the target position (i.e., with an angular differential of approximately six-hundred degrees from the origin) may cause operative head  40  to experience a pressure of, e.g., approximately 25 kPa from rotatable workpiece  80 . In this case, the pressure of 25 kPa may be greater than the predicted or desired amount of pressure against operative head  40  in the target position. 
     In process P 9 , modules  116  can compare the pressure against operative head  40 , calculated in process P 8 , with a range of highest and lowest acceptable pressures, otherwise known as a “tolerance band.” The pressure value(s) being compared with the tolerance band can be measured with and/or received from pressure sensor  92 , or can be transmitted to controller  60  by any currently known or later developed process. The tolerance band can represent an acceptable margin of error for the torqueing of rotatable workpiece  80 , and can be determined by constraints of a particular application or user preference. For example, the tolerance band can represent a maximum difference in actual pressure and a target pressure in terms of percentage points, e.g., up to ten percent above or below a target pressure. Returning to the example, modules  116  may calculate a desired pressure against operative head  40  at the target the position as being approximately 20 kPa, with the tolerance band being 2.0 kPa above or below this pressure (i.e., between approximately 18 kPa and approximately 22 kPa). 
     Where the pressure against operative head  40  is outside the tolerance band (i.e., “no” at process P 9 ), controller  60  can direct power wrench  30  to apply an angular correction in process P 10 . The angular correction can generally include further adjustment of rotatable workpiece  80 , e.g., by turning operative head  40  by a particular number of degrees in a positive or negative direction relative to the origin defined in process P 4 . Process P 10  can thus correct for discrepancies between a desired pressure and an actual pressure when operative head  40  of power wrench  30  reaches the target position. According to the example, a pressure of approximately 25 kPa would be above the tolerance band by approximately 3.0 kPa. Controller  60  in process P 10  can instruct operative head  40  to turn rotatable workpiece  80  in the opposite (i.e., negative) direction by a desired amount, e.g., by increments of thirty degrees, until the pressure against operative head  40  is within the tolerance band (i.e., between approximately 18 kPa and approximately 22 kPa). 
     Where the pressure against operative head  40  is within the tolerance band (i.e., “yes” at process P 9 ), the flow can proceed to a process P 11  where controller  60  directs power wrench  30  to cease turning. Following process P 11 , the flow can optionally proceed to a process P 12  where controller  60  directs power wrench  30  to decouple operative head  40  from rotatable workpiece  80 . In the example, controller  60  can direct power wrench  30  to decouple from rotatable workpiece  80  after the pressure against operative head  40  is between approximately 18 kPa and approximately 22 kPa. Alternatively, the method can complete (i.e., “done”) without the decoupling in process P 12  as shown by the corresponding phantom process flow. Where operative head  40  is decoupled from rotatable workpiece  80  in process P 12 , the process flow can end (i.e., “done”) after the decoupling. 
     Turning briefly to  FIG. 6 , an alternative process flow methodology is shown. Here, the correcting operations in processes P 8  through P 10  can be skipped entirely. More specifically, where the angular differential is approximately equal to or greater than the target position, controller  60  can immediately instruct operative head  40  of power wrench  30  to cease turning. The process flow shown in  FIG. 6  may be applicable to applications where correcting processes are not desired, or where the pressure against operative head  40  is within the tolerance band immediately after rotatable workpiece  80  reaches the target position. For instance, the process flow of  FIG. 6  may apply where the pressure against operative head  40  is between approximately 18 kPa and approximately 22 kPa when operative head  40  reaches the target position (i.e., reaches an angular differential from the origin of approximately six-hundred degrees). 
     The apparatus and method of the present disclosure is not limited to installation or servicing operations performed on power generation systems, and may be applicable to other machines. In the case of a power generation system, embodiments of the disclosure are not limited to the torqueing of components within any one system, e.g., any particular gas turbine, steam turbine, power generation system or other system, and may be used with other power generation systems and/or systems (e.g., combined cycle, simple cycle, nuclear reactor, etc.). Additionally, the apparatus of the present invention may be used with other systems not described herein that may benefit from the increases to operational range, efficiency, durability, and reliability provided by embodiments of the present disclosure. 
     Technical effects of the present disclosure can include full automation of a power wrench during bolting, fastening, and/or other torqueing processes and/or other fastening process. As opposed to a multi-step process with only partial automation, embodiments of the present disclosure can provide a unified procedure by which a rotatable workpiece is first wound onto a fixture before angle of turn operations begin. The angle of turn operations can be performed by reference to an automatically determined point of origin. In addition, embodiments of the present disclosure introduce the ability to measure bolt stretch and/or identify a point of origin for a rotatable workpiece by reference to rates of change (e.g., a pressure-angle derivative). Embodiments of the present disclosure can also reduce the time required for torqueing processes, and can provide greater consistency of torqueing by repeated application of a particular algorithm or group of algorithms. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. 
     This written description uses examples to disclose the invention, including the best mode, and to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.