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 This application is a continuation of copending U.S. patent application Ser. No. 10/032,114, filed on Dec. 21, 2001 and entitled “Method and Apparatus for Determining Position in Pipe”, which claims the benefit of U.S. patent application Ser. No. 09/286,650, filed Apr. 6, 1999 and entitled “Method and Apparatus for Determining Position in Pipe”, now U.S. Pat. No. 6,333,699 B1, which in turn claims the benefit of U.S. Provisional Patent Application Ser. No. 60/098,284, filed on Aug. 28, 1998.
 This application is related to the following copending patent applications: U.S. patent application Ser. No. 09/586,648, filed on Jun. 1, 2000 and entitled “Method and System for Performing Operations and for Improving Production in Wells”; U.S. patent application Ser. No. 09/656,720, filed on Sep. 7, 2000, entitled “Method and System for Performing a Casing Conveyed Perforating Process and Other Operations in Wells”, and issued on Mar. 25, 2003 as U.S. Pat. No. 6,536,524 B1; U.S. patent application Ser. No. 09/843,998, filed on Apr. 27, 2001 and entitled “Process and Assembly for Identifying and Tracking Assets”; U.S. patent application Ser. No. 10/323,536, filed on Dec. 18, 2002 and entitled “Method and System for Performing Operations and for Improving Production in Wells”; and U.S. patent application Ser. No. 10/726,027, filed on Dec. 1, 2003 and entitled “Method and System for Transmitting Signals Through a Metal Tubular”.
 1. Field of the Invention
 The present invention relates generally to devices for detecting intermediate points within wells, gas and oil pipelines, and the like, and more specifically to a system using radio frequency resonant devices installed at various points in the well or pipe. A detector is inserted into the pipe, and detects the resonant devices where installed to transmit location or depth and other information back to a station at the surface or along the pipe. The present invention may provide for the storage of the information gathered for downloading upon retrieval of the device from the well or pipe.
 2. Description of the Related Art
 The need for accurate measurement of the depth of a drilled well is critical, as oftentimes the stratum of interest in the well, resides within a relatively narrow band. Wells are typically cased after drilling, with cement being poured between the casing and the wall of the drilled hole in order to seal and stabilize the hole. The casing and cement are perforated at the desired depth in order to access the stratum of interest (oil bearing deposits, gas, water, etc.), with the casing and cement serving to prevent the flow and mixing of undesired fluids with the fluid of interest from the well (e.g., water with oil, etc.).
 In view of the above, it is critical that the well be perforated at precisely the proper depth in order to avoid drawing an undesirable fluid into the well, and/or missing the desired stratum of interest in the well. As wells typically extend from a few to several thousand feet below the surface in the case of oil and gas wells, the precise measurement of the depth of the well to within a few feet, poses a difficult problem. U.S. Pat. No. 5,279,366 provides an excellent and detailed discussion of the problem in the Background of the Invention, columns 1 through 4, for further background.
 Accordingly, numerous devices and systems have been developed in the past for logging or measuring the precise depth of the well, for perforating the well or for other purposes as required. Such principles as MRI (magnetic resonance imaging), gamma ray detection, and others, have been utilized in order to enable a detector lowered into the well casing to determine its position or depth within the hole. However, none of the systems or principles utilized in the past, provide the needed accuracy to enable an operator to determine precisely the depth of the tool within the hole. It is very easy for the well to be logged incorrectly, or for the tool to detect the wrong joint or point in the casing, and thus throw off all calculations and measurements accordingly. As the conventional well casing pipe has a length of some thirty feet, it will be seen that an error in the detection of one joint location, could cause a perforating gun or other tool to miss the stratum of interest completely.
 Those skilled in the art are aware that the limitations of the prior art extend to other types of pipelines and the like, and are not limited only to generally vertical well bores. For example, the standard procedure for examining a cross-country oil, gas, or other pipeline, is to “pig” the line, i.e., send a mechanical device (called a “pig”) through the line, generally by pneumatic means. The “pig” may sense various information relating to the condition of the line, or other factors, which information may be stored within the device until it is recovered at some point in the line. However, any flaws or other problems in the line must be identified as to location, and the mechanical “pigs” used for such operations have no means of determining their position in the line. Rather, their location must be detected externally, by a worker stationed along the pipe or line as the “pig” travels through the line, and who logs the passage of the “pig” at various points along the line, relative to time. By knowing the time that any information was gathered in the pipe, and the time of passage of the “pig” at various points, the location of any anomalies may be indirectly determined.
 However, it will be seen that it can be difficult to determine the precise location of various anomalies or other points of interest in such a pipeline, as the detection of the passage of the “pig” through the line, is determined at only a relatively few widely separated points along the line. Thus, when the record of the recovered “pig” is examined, it may not be possible to narrow the location of some point of interest in the line, to an area smaller than perhaps a few hundred feet of pipeline, or perhaps more.
 Accordingly, a need will be seen for a system which positively identifies the location or depth of a well tool at various points within the well. The system comprises a plurality of passive or active radio frequency resonant devices, which are installed at several, or all, of the joints in the well casing. Each of the devices is preferably constructed or tuned to provide a unique individual signal. A well tool is provided which transmits a low power and/or directional signal on an appropriate frequency for reception by the devices, which then resonate to provide a responding signal to the well tool. The responding signal passes up the wire line to the well operator at the surface, who is able to determine precisely the location or depth of the well tool in the well. Alternatively, the information may be stored within the downhole tool, for downloading into a computer or other suitable reading device at the surface, after recovery of the tool.
 A further need will be seen for a system which is capable of positively identifying the location of a tool which is passed through a pipeline or the like, and recording the location corresponding to the tool at various points in time as the tool passes through the pipeline. The system may utilize active or passive radio frequency resonant devices, with information being stored within the pipeline tool for later recovery when the tool is recovered from the line.
 A discussion of the related art of which the present inventor is aware, and its differences and distinctions from the present invention, is provided below. U.S. Pat. No. 4,572,293 issued on Feb. 25, 1986 to James G.
 Wilson et al., titled “Method Of Placing Magnetic Markers On Collarless Cased Wellbores,” describes the magnetic polarizing of well casing by positioning one or more electromagnets within the casing, and activating the electromagnets to impart a permanent magnetic field at the location of the electromagnet(s) within the casing or pipe. The magnetically polarized area may be detected using a conventional magnetic reading casing collar locator. The Wilson et al. method does not provide any means of differentiating between magnetically marked spots, nor of precisely positioning the magnetically polarized areas at predetermined points in the casing. Moreover, Wilson et al. do not disclose any means of logging or determining the position of a device in a cross country or other fluid pipeline, as provided by the present method and apparatus.
 U.S. Pat. No. 4,630,044 issued on Dec. 16, 1986 to Rudolf Polzer, titled “Programmable Inductively Coupled Transponder,” describes a passive radio identification device (PRID) including a memory for modulating the response signal when triggered by an appropriate transmitter. Polzer describes the placement of the resonating transponder on a moving object, e.g., a railroad car, with the triggering transmitter having a stationary mounting. This configuration is precisely the opposite of the present invention, with its stationary responding devices and triggering transmitter being mounted within a moving well hole or pipeline “pigging” tool. Moreover, Polzer makes no suggestion of using his invention for determining depth or other characteristics in a well casing or other fluid pipeline, as provided by the present invention.
 U.S. Pat. No. 4,808,925 issued on Feb. 28, 1989 to Gary K. Baird, titled “Three Magnet Casing Collar Locator,” describes a magnetic device for detecting pipe or casing joints in a well. The device provides a specially shaped toroidal magnetic field, which magnetically affects the ferrometallic casing and casing joints. A detector associated with the device detects variations in the magnetic field as the field changes as it passes each casing joint. Baird makes no provision for detecting any differences in the joints. Rather, each joint appears essentially the same when detected, and the operator cannot determine precisely where in the casing the device is located. Each joint must be counted in order for the location to be determined, and no other information is provided by the Baird device. Baird does not disclose any means of logging or determining the precise location of a pigging tool in a cross country or other than vertical fluid pipeline, as provided by the present invention.
 U.S. Pat. No. 5,279,366 issued on Jan. 18, 1994 to Patrick L. Scholes, titled “Method For Wireline Operation Depth Control In Cased Wells,” describes the use of both magnetic and radioactive location markers in a well casing. The detector device is capable of detecting both high energy radiation (gamma rays) and magnetic anomalies, thus making it easier to confirm that well depth logs using either system separately, are properly “tied in.” The Scholes '366 U.S. patent provides an excellent explanation of the problem of well depth control and logging, as well as the importance of a solution for the problem, in the Background of the Invention portion of the disclosure, as noted further above. However, Scholes does not provide any means of differentiating between different joints or other locations along the length of the casing, nor any radio frequency resonant means for doing so. Moreover, Scholes is silent regarding any form of logging or determining the position of a tool in other than a vertical line, whereas the present system may be applied to any fluid line in a generally vertical or other than vertical orientation.
 U.S. Pat. No. 5,361,838 issued on Nov. 8, 1994 to Marion D. Kilgore, titled “Slick Line Casing And Tubing Joint Locator Apparatus And Associated Methods,” describes a device which is usable with a slick line, i.e., a monofilament metal or other line which does not carry an electrical signal. The device relies upon an integral magnetic anomaly detector for detecting pipe or casing joints. When a joint is detected, the device drives a drag producing structure against the inner surface of the casing, with the drag registering as a momentary increase in tension on the line at the surface as the device passes the joint. Thus, the Kilgore device can only be used when being drawn upwardly through the pipe, and does not utilize any radio frequency resonance means. The Kilgore device is also unworkable in other than a generally vertical line, whereas the present system is operable in any fluid line, regardless of its orientation.
 U.S. Pat. No. 5,457,447 issued on Oct. 10, 1995 to Sanjar Ghaem et al., titled “Portable Power Source And RF Tag Utilizing Same,” describes a radio frequency (RF) device providing an interrogation signal and receiving a response from the interrogation signal. The device may be powered by any one or more of several electrical sources, including conventional battery power, solar or infrared cells, etc. However, Ghaem et al. are silent regarding a responding unit for their RF tag device. While the present invention makes use of an RF transmitter and receiver disposed within a well downhole tool, pipeline pigging tool, or the like, the present invention also makes use of inert or active resonant responding devices which are triggered by the RF transponder device of the well or pipeline tool, which resonant responding devices are not a part of the Ghaem et al. disclosure.
 U.S. Pat. No. 5,497,140 issued on Mar. 5, 1996 to John R. Tuttle, titled “Electrically Powered Postage Stamp Or Mailing Or Shipping Label Operative With Radio Frequency (RF) Communication,” describes a small and very thin radio receiver and transmitter, including a memory chip for modulating the transmitted signal to provide certain specific information, e.g., routing, etc. The Tuttle disclosure provides for a thin, flat battery for power of the device, and accordingly includes “sleep” and “wake” circuitry which is triggered by a transmission from another device. The present invention does not require any integral electrical power in the specific form of an electric battery, but resonates when power is received from a nearby transmitter. The present device may include active circuitry requiring electrical power, but the electrical power is generated by electrochemical means using the fluid within the well or pipe, as an electrolyte. The Tuttle device is not a resonant device.
 U.S. Pat. No. 5,626,192 issued on May 6, 1997 to Michael L. Connell et al., titled “Coiled Tubing Joint Locator And Methods,” describes a tube which is lowered into the well pipe string for locating pipe joints. The device includes a fluid passage formed generally axially therethrough, and an electromagnetic joint detector which senses the increased mass of each joint, according to the disclosure. When a joint is detected, a lateral valve is opened, which decreases the fluid flow resistance through the device and produces a pressure drop which is transmitted to the surface. The Connell et al. device can only sense each joint, and cannot detect any difference between different joints, whereas the present device may provide means for differentiating between different joints in the well casing or fluid pipeline.
 U.S. Pat. No. 5,720,345 issued on Feb. 24, 1998 to Timothy M. Price et al., titled “Casing Joint Detector,” describes a magnetic anomaly detector which detects the variations in magnetic flux across pipe or casing joints, as in other devices of the prior art discussed further above. The detector may also measure the distance traveled down the borehole, and correlate this distance with the number of joints passed. However, Price et al. make no provision for distinguishing between different casing or pipe joints, for determining precisely which joint is being passed at any given point. Also, as with other magnetic anomaly detectors, the device must be moving at some minimum velocity through the casing in order to generate the spike in electromagnetic energy for generating a detection signal. The present active or passive RF system is operable at any practicable velocity in vertical, horizontal, or otherwise oriented fluid pipelines of virtually any type, i.e., ferromagnetic or other material.
 European Patent Publication No. 013,494 published on Jul. 23, 1980 to British Gas Corporation, titled “Measurement Of Velocity And/Or Distance,” describes a device which produces a magnetic anomaly in the wall of a ferrometallic pipe, and then detects the anomaly as the device passes. The device may thus measure its velocity through the pipe, by measuring the time between the production of the magnetic anomaly and its detection by another part of the device, with the distance between the two components being known. As in other devices using magnetic principles or means discussed further above, the British Gas device cannot distinguish between different magnetic anomalies produced thereby, but can only count the total number of magnetic anomalies along the length of the pipe and provide a distance measurement based upon the distance between the magnetic anomaly producer and detector. No RF means, nor use in other than a generally vertical downhole, is disclosed in the British Gas Corporation patent publication.
 European Patent Publication No. 412,535 published on May 11, 1994 to Michael L. Smith, titled “Tubing Collar Position Sensing Apparatus, And Associated Methods, For Use With A Snubbing Unit,” describes a device for electromagnetically detecting tubing or joint collars for progressively opening and closing the blowout pressure seals of a blowout valve. Accordingly, there is no need, and no teaching, of any means for distinguishing between different joints along the length of the tube or pipe. Smith notes that the measurement of the pipes cannot be accomplished by odometer means alone, due to slight variations in pipe length and in the length of engaged threads at each coupling, to which problem the present invention responds. Moreover, the present system is adaptable to both generally vertical well holes, as well as generally horizontal or other orientation gas and other fluid lines.
 European Patent Publication No. 651,132 published on May 3, 1995 to the Halliburton Company, titled “Method For Locating Tubular Joints In A Well,” describes a device which applies lateral pressure to the walls of the pipe whenever a joint is detected. The increased drag of the device increases the tension on the line as the device is raised up the pipe, thus enabling the joints to be detected without requirement for an electrical connection between the device in the pipe and the surface. The device described in the '132 European Patent Publication is the same as that described in the '838 U.S. patent, and discussed further above. The same differences and distinctions noted in the above discussion, are also seen to apply here.
 Finally, European Patent Publication No. 730,083 published on Sep. 4, 1996 to the Halliburton Company, titled “Method And Apparatus For Use In Setting Barrier Member In Well,” describes a device using conventional magnetic anomaly detection means for detecting pipe or casing joints, for positioning a barrier within the pipe or casing so that the barrier is not positioned on the joint. There is no need, and no teaching, for the device to distinguish between different joints, as all that is necessary for the Halliburton device is to determine that the barrier or seal will not be positioned directly on a joint.
 None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.
 The present invention comprises a method and apparatus for determining position in a pipe or the like, for detecting pipe or casing joints in an oil, gas, or other drilled well or pipe, and for distinguishing between joints. The system includes a passive radio identification device (PRID), or alternatively an active device, installed at each pipe or casing joint, with a well or pipeline tool including a radio frequency transmitter and receiver. The transmitter of the tool provides a constant transmission signal, which is attenuated or directionally modified so as to be received only by an identification device at an immediately adjacent pipe or casing joint. When the device receives the transmission from the tool, the identification device circuit resonates to transmit a response, which is received by the tool receiver. The signal received by the receiver is then transmitted up the wireline between the tool and the surface, where it is processed. Alternatively, the tool may include means for recording the information received, with the information being downloaded from the tool upon retrieval of the tool at the surface or access point in a pipeline.
 Information relating to each of the radio identification devices may be stored at the surface, with the operator being able to determine the location of the downhole tool at any time, and other characteristics which have been logged into the computer or information system, such as pipe or casing size, geological characteristics or stratum at any particular point as previously logged and entered into the system, depth of the well at that point, etc. Again, the present system is adaptable for use in generally horizontal fluid (oil, gas, water, etc.) pipelines as well as generally vertical downholes, and may be used in pipes of virtually any non-horizontal or non-vertical orientation as well. The present invention may also utilize identification devices which provide a distinct signal from one another, in order that the downhole tool is able to distinguish between each device, and therefore the joint with which any particular device is associated and the physical characteristics previously logged at that location.
 While passive radio identification devices (PRIDs) which resonate when a specific frequency or frequencies are detected, may be used in the present invention, the present method and apparatus may also make use of active devices, i.e., devices requiring electrical power for operation. The present invention provides such electrical power in the form of an electrical battery, with two dissimilar metals being provided in the resonant device, or the resonant device and tool, with the fluid within the well or pipe serving as an electrolyte for the device.
 Accordingly, it is a principal object of the invention to provide an improved method and apparatus for determining position in a pipe or the like, utilizing a radio frequency transmitter and receiver in a downhole or pipeline tool, with passive radio identification devices (PRIDs) or active devices located at each joint in the pipe or casing.
 It is another object of the invention to provide an improved pipeline position determining method and apparatus which may include an information storage and retrieval system, such as a computer, at the surface or outside the pipeline, with the downhole or pipeline tool transmitting a signal to the system whenever a radio frequency identification device is detected.
 Yet another object of the invention is to provide an improved pipeline position determining method and apparatus which may use a tool having recording means therein, for recording information detected during tool passage through the pipe, and for downloading the information from the tool recording means upon recovery of the tool.
 It is a further object of the invention to provide an improved pipeline position determining method and apparatus which computer or other information system is programmed with various facts relating to each of the identification devices in the well or pipe, such as the stratum or geological characteristics at each identification device installed in the well, the pipe or casing diameter, distance between each of the identification devices in the pipe or casing string, etc.
 An additional object of the invention is to provide an improved pipeline position determining method and apparatus which identification devices may be distinguished from one another, in order that the tool distinguishes the specific identification device with which it is communicating at any given location in the well or pipe.
 Still another object of the invention is to provide an improved pipeline position determining method and apparatus which may utilize resilient seals disposed between each pipe or casing joint, for holding each of the identification devices in place.
 Another object of the invention is to provide an improved pipeline position determining method and apparatus which may utilize active RF identification devices which draw electrical power from an electrochemical source provided by dissimilar metals in the RF device and/or tool, with the fluid within the well or pipe serving as an electrolyte.
 It is an object of the invention to provide improved elements and arrangements thereof in an apparatus for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
 These and other objects of the present invention will become apparent upon review of the following specification and drawings.
 Similar reference characters denote corresponding features consistently throughout the attached drawings.
 The present invention comprises a method and apparatus for determining position in a pipe or the like, for oil, gas, and other drilled wells having a jointed casing therein, and for cross country pipelines and other non-vertical gas, oil, water, and other fluid wells and pipelines. The present system provides for the determination of the precise location of a well or pipe tool within the casing or pipe, and associated characteristics of the well or pipe at the location of the tool.
 The well tool
 Alternatively, the responding device
 The transceiver
 Alternatively, the antenna of the transceiver
 In many instances, the line
 Normally, a drilled well is “logged” before casing is installed, in order to determine the exact depths of specific geological structures (e.g., impervious rock, oil and/or gas bearing strata, etc.). The information logged, as well as other information, such as the diameter or size of the casing, well name and/or number, depth of the well, etc., is entered into an information storage and retrieval system database, conventionally a computer
 Thus, as the well downhole tool
 It will be seen that each of the PRIDs or active devices
 In this manner, each PRID or active device
 It will further be seen that it is not absolutely essential to provide a separate and distinct response signal for each of the PRIDs or active devices
 While the discussion to this point has been directed to the well of
 As an example of such use in a cross country pipeline, such lines are conventionally used for the transport of oil, gas, etc. between various points. It is necessary to inspect the interior of such lines from time to time, and this is conventionally accomplished by means of an automated tool, called a “pig,” which is passed through the pipeline (generally “blown” through the line by increasing the pressure on one side of the pipeline relative to the tool). Such tools may include means of detecting various flaws within the pipeline, but may not include any means of determining their position in the line. Accordingly, a worker stationed along the pipeline logs the time when the “pig” passes, and travels to another point along the line where the process is repeated. When the “pig” is recovered from the pipeline, the data recorded by the conventional data recording means therein, is downloaded to some form of data recovery means (e.g., computer and database). The times at which any anomalies in the line were recorded by the data recording means in the “pig” are noted and compared to the times logged by the worker who noted the passage of the “pig” at various points along the line.
 As can be seen, this provides only a very approximate idea of the position of the “pig” at any point where a pipeline anomaly was recorded, by interpolation of the times of passage at various points. Thus, the narrowing of the location where a more detailed inspection and/or repair is required, can be time consuming and costly. Moreover, such a system may result in the unnecessary replacement of a larger length of pipeline than is absolutely required, merely because the precise location of a flaw could not be accurately determined.
 The present system provides a solution to the above problem, by means of installing a series of PRIDs or active radio frequency devices at various predetermined locations within the pipeline. Such PRIDs or active devices may be installed at joints in the pipeline, somewhat in the manner described above for the well casing or pipe, or in other areas of the pipeline as desired. The “pig” may include a transmitter and receiver similar to the conventional units which may be used in well downhole tools as described above, with the transmitter unit sending a continuous signal which is received by each of the radio frequency devices in turn as the “pig” travels through the pipeline. The devices sequentially provide responses as they are triggered by the transmitter in the “pig,” with the receiver in the “pig” receiving the responding signals and the conventional recording means within the “pig” storing the location signals from the PRIDs or active devices, in a manner similar to that described above for well downhole tools having self contained recording means therein.
 The data stored within the recording means, including the responding signals from the PRIDs or other active responding devices, is downloaded after the “pig” is recovered and is examined to determine if any flaws or other anomalies are present in the pipeline. If an anomaly is noted in the pipeline data, its location is easily determined relatively precisely by noting the PRID or active device signal at that location, or to either side of the location of the anomaly. Workers may then repair the problem as required, without need to spend substantial amounts of time and effort searching a relatively long length of pipeline for the problem, and/or replacing a large amount of the line in order to be sure that the problem was taken care of.
 It may be desirable to provide a separate, relatively short section of pipe which incorporates a responding device therein, and which may be added to an existing pipeline or string as desired. Such a unit
 As noted further above, the signal strength of the responding devices (PRIDs or active devices) need not be particularly high, as the receiver in the pipeline tool will always be located quite close to the passive or active responding device. However, additional signal strength may be desirable in certain circumstances, particularly in the case of PRIDs which do not have any supplemental electrical power but rely upon the electromagnetic energy provided by the transmitted signal. Accordingly, it may be desirable to provide some means of enhancing the signal received for such PRIDs. One such means is disclosed in
 The loop antenna
 In some instances, it may not be possible or convenient to install a PRID or other radio frequency responding device
 As noted herein, the responding devices
 However, the present invention may also include another means of generating electrical power for such active responding devices, as illustrated in
 The fluid
 As an example, a first electrical connector may be connected between one terminal of the active responding device and the first dissimilar metal component
 In summary, the present method and apparatus for determining position in a pipeline provides a much needed system for easily and precisely determining the position of a well tool within a drilled oil, gas, or other well having a jointed well casing, or the position of a pipeline tool or “pig” within a pipeline. The present system is relatively simple and yet robust, with the PRID or active devices being used having great durability and reliability. The imbedding or sealing of each of the PRIDs or active devices within the resilient O-ring (rubber, Teflon; tm, etc.) located at each casing or pipe joint, provides further protection for the devices while simultaneously locating them precisely at each joint. The prior logging of the well hole characteristics, such as geological characteristics, depth of various strata of interest, well name and/or number, diameter of the casing to be used, etc., into a database, provides an operator at the surface with all information necessary to determine the appropriate action to take and the appropriate positioning of the tool for perforating the casing or other operations in the pipe.
 It will be appreciated to those skilled in the art that the invention can be used in any type of pipe or casing, either vertically or horizontally oriented, and as found in refineries, chemical plants, oil and gas pipelines, underground water systems, or in any system where it is necessary to know the exact location of a tool or instrument being run through a pipe in any particular pipe system. The use of conventional self contained recording means within the well or pipeline tool, enables the present invention to be used with “slickline” type tools as well, as no electrical or other communication is required through the line. Accordingly, the present system will provide well drillers and operators, pipeline operators, and others working with similar systems, with a much needed means of quickly, easily, and relatively inexpensively, determining the precise location of a well tool in a well and correlating that location with previously logged information for accurate operations.
 It is to be understood that the present invention is not limited to the sole embodiment described above, but encompasses any and all embodiments within the scope of the following claims.