Patent Grant
9638030
The application relates generally to a telemetry system for data communications between a downhole drilling assembly and a surface of a well. In particular, the application relates to a receiver for an acoustic telemetry system.
During drilling operations for extraction of hydrocarbons, a variety of communication and transmission techniques have been attempted to provide real time data from the vicinity of the bit to the surface during drilling. The use of measurements while drilling (MWD) with real time data transmission provides substantial benefits during a drilling operation. For example, monitoring of downhole conditions allows for an immediate response to potential well control problems and improves mud programs.
Measurement of parameters such as weight on bit, torque, wear and bearing condition in real time provides for more efficient drilling operations. In fact, faster penetration rates, better trip planning, reduced equipment failures, fewer delays for directional surveys, and the elimination of a need to interrupt drilling for abnormal pressure detection is achievable using MWD techniques.
Currently, there are four major categories of telemetry systems that have been used in an attempt to provide real time data from the vicinity of the drill bit to the surface; namely, acoustic waves, mud pressure pulses, insulated conductors and electromagnetic waves.
With regard to acoustic waves, typically, an acoustic signal is generated near the bit and is transmitted through the drill pipe, mud column or the earth. It has been found, however, that the very low intensity of the signal which can be generated downhole, along with the acoustic noise generated by the drilling system, makes signal detection difficult. Reflective and refractive interference resulting from changing diameters and thread makeup at the tool joints compounds the signal attenuation problem for drill pipe transmission. Such reflective and refractive interference causes interbit interference among the bits of data being transmitted.
In a mud pressure pulse system, the resistance of mud flow through a drill string is modulated by means of a valve and control mechanism mounted in a special drill collar near the bit. This type of system typically transmits at one bit per second as the pressure pulse travels up the mud column at or near the velocity of sound in the mud. It is well known that mud pulse systems are intrinsically limited to a few bits per second due to attenuation and spreading of pulses.
Insulated conductors or hard wire connection from the drill bit to the surface is an alternative method for establishing downhole communications. This type of system is capable of a high data rate and two-way communication is possible. It has been found, however, that this type of system requires a special drill pipe and special tool joint connectors that substantially increase the cost of a drilling operation. Also, these systems are prone to failure as a result of the abrasive conditions of the mud system and the wear caused by the rotation of the drill string.
The fourth technique used to telemeter downhole data to the surface uses the transmission of electromagnetic waves through the earth. A current carrying downhole data signal is input to a toroid or collar positioned adjacent to the drill bit or input directly to the drill string. When a toroid is utilized, a primary winding, carrying the data for transmission, is wrapped around the toroid and a secondary is formed by the drill pipe. A receiver is connected to the ground at the surface where the electromagnetic data is picked up and recorded. It has been found, however, that in deep or noisy well applications, conventional electromagnetic systems are unable to generate a signal with sufficient intensity to be recovered at the surface.
In general, the quality of an electromagnetic signal reaching the surface is measured in terms of signal to noise ratio. As the ratio drops, it becomes more difficult to recover or reconstruct the signal. While increasing the power of the transmitted signal is an obvious way of increasing the signal to noise ratio, this approach is limited by batteries suitable for the purpose and the desire to extend the time between battery replacements. These approaches have allowed development of commercial borehole electromagnetic telemetry systems that work at data rates of up to four bits per second and at depths of up to 4000 feet without repeaters in MWD applications. It would be desirable to transmit signals from deeper wells and with much higher data rates which will be required for logging while drilling, LWD, systems.
Embodiments of the invention may be best understood by referring to the following description and accompanying drawings which illustrate such embodiments. The numbering scheme for the Figures included herein are such that the leading number for a given reference number in a Figure is associated with the number of the Figure. For example, a system 100 can be located in
Methods, apparatus and systems for an acoustic telemetry receiver are described. In the following description, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures and techniques have not been shown in detail in order not to obscure the understanding of this description.
While described with reference to transmitting downhole data to the surface during measurements while drilling (MWD), embodiments of the invention are not so limited. For example, some embodiments are applicable to transmission of data from the surface to equipment that is downhole. Additionally, some embodiments of the invention are applicable not only during drilling, but throughout the life of a wellbore including, but not limited to, during logging, drill stem testing, completing and production. Further, some embodiments of the invention can be in other noisy conditions, such as hydraulic fracturing and cementing.
As further described below, embodiments of the invention attempt to minimize cross correlation between/among the different symbols to allow for the identification of the symbols. Embodiments of the invention allow for a more robust data recovery of acoustic telemetry through tubulars under various noisy conditions. Additionally, embodiments of the invention allowed for an increased data rate of acoustic telemetry through tubulars while maintaining reliable data recovery. Embodiments of the invention may remove intersymbol interference. This removal of intersymbol interference allows for correlation of a symbol with a database of acquired symbols to determine a value of a symbol.
During drilling operations, the drill string 108 (including the Kelly 116, the drill pipe 118 and the bottom hole assembly 120) may be rotated by the rotary table 110. In addition or alternative to such rotation, the bottom hole assembly 120 may also be rotated by a motor (not shown) that is downhole. The drill collar 122 may be used to add weight to the drill bit 126. The drill collar 122 also may stiffen the bottom hole assembly 120 to allow the bottom hole assembly 120 to transfer the weight to the drill bit 126. Accordingly, this weight provided by the drill collar 122 also assists the drill bit 126 in the penetration of the surface 104 and the subsurface formations 114.
During drilling operations, a mud pump 132 may pump drilling fluid (known as “drilling mud”) from a mud pit 134 through a hose 136 into the drill pipe 118 down to the drill bit 126. The drilling fluid can flow out from the drill bit 126 and return back to the surface through an annular area 140 between the drill pipe 118 and the sides of the borehole 112. The drilling fluid may then be returned to the mud pit 134, where such fluid is filtered. Accordingly, the drilling fluid can cool the drill bit 126 as well as provide for lubrication of the drill bit 126 during the drilling operation. Additionally, the drilling fluid removes the cuttings of the subsurface formations 114 created by the drill bit 126.
The drill string 108 may include one to a number of different sensors 151, which monitor different downhole parameters. Such parameters may include the downhole temperature and pressure, the various characteristics of the subsurface formations (such as resistivity, density, porosity, etc.), the characteristics of the borehole (e.g., size, shape, etc.), etc. The drill string 108 may also include an acoustic telemetry transmitter 123 that transmits telemetry signals in the form of acoustic vibrations in the tubing wall of the drill sting 108. An acoustic telemetry receiver 115 is coupled to the kelly 116 to receive transmitted telemetry signals. One or more repeaters 119 may be provided along the drill string 108 to receive and retransmit the telemetry signals. The repeaters 119 may include both an acoustic telemetry receiver and an acoustic telemetry transmitter configured similarly to the acoustic telemetry receiver 115 and the acoustic telemetry transmitter 123.
The following discussion centers on acoustic signaling from acoustic telemetry transmitter 123 near the drill bit 126 to a sensor located some distance away along the drill string. Various acoustic transmitters are known in the art, as evidenced by U.S. Pat. Nos. 2,810,546, 3,588,804, 3,790,930, 3,813,656, 4,282,588, 4,283,779, 4,302,826, 4,314,365, and 6,137,747, which are hereby incorporated by reference. The transmitter 204 shown in
Various acoustic sensors are known in the art including pressure, velocity, and acceleration sensors. The sensor 212 preferably comprises a two-axis accelerometer that senses accelerations along the axial and circumferential directions. One skilled in the art will readily recognize that other sensor configurations are also possible. For example, the sensor 212 may comprise a three-axis accelerometer that also detects acceleration in the radial direction. A second sensor 214 may be provided 90 or 180 degrees away from the first sensor 212. This second sensor 214 also preferably comprises a two or three axis accelerometer. Additional sensors may also be employed as needed.
In some embodiments, the acoustic telemetry receiver receives an acoustic signal across a number of different symbolic intervals. In some embodiments, the acoustic telemetry receiver subtracts the tail of the acoustic signal of a previous symbolic interval from the acoustic signal of a current symbolic interval. To help illustrate,
Different embodiments of an acoustic telemetry receiver are now described. Such embodiments may be different embodiments of the acoustic telemetry receiver 115. In particular,
One embodiment of the operations of the receiver 400 is now described in more detail in conjunction with a flow diagram 500 of
In block 502, a telemetry signal that is transmitted along a transmission channel (having a transmission channel characteristic) is received. With reference to the embodiment of
In block 504, the telemetry signal is correlated to a first stored telemetry signal that includes the transmission channel characteristic to output a first degree of correlation. With reference to the embodiment of
For example, the acoustic telemetry transmitter may generate a sequence of different symbols that are received by the receiver 400 during a period when no drilling operations are performed. The received symbols include the different characteristics of the drill string. In particular, the received symbols include the distortions made thereto as a result of the characteristics of the drill string. Control continues at block 506.
In block 506, the telemetry signal is correlated to a second stored telemetry signal that includes the transmission channel characteristic to output a second degree of correlation. With reference to the embodiment of
In block 508, the telemetry signal is marked as a particular symbolic value based on the first degree of correlation and the second degree of correlation. With reference to the embodiment of
While the flow diagram 500 illustrates the correlation with two stored telemetry signals, embodiments of the invention may correlate with a lesser or greater number of such signals. For example, the received telemetry signal may be correlated with any of a number of the signals stored in a library of signals.
The bandpass filter 608 receives an on-off key (OOK) signal 602. The switch 610 receives a tail signal 604. The tail signal 604 is a tail from a previous timing interval for a tone pulse. The training logic 615 receives a training OOK signal 601. The training logic 615 is coupled to the memory 619. The memory 619 is coupled to a first input of the correlation logic 618 and a first input of the timing recovery logic 614. An output from the bandpass filter 608 is coupled to a first input of the tail subtract logic 612 and a second input of the timing recovery logic 614.
The timing recovery logic 614 may determine the time of the symbolic interval. In some embodiments, the output of the timing recovery logic 614 peaks after the received input most closely matches the shape of the training pulse 617. While the timing recovery logic 614 may be any of a number of different timing circuits, in some embodiments, the timing recovery logic 614 is an early-late-gate correlation timing circuit.
An output of the switch is coupled to a second input of the tail subtract logic 612. An output of the tail recovery logic is coupled to a third input of the tail subtract logic 612, a second input of the correlation logic 618 and a detection logic 620. An output of the tail subtract logic 612 is coupled to a third input of the correlation logic 618.
An output of the correlation logic 618 is coupled to a second input of the detection logic 620. The output of the detection logic 620 is an output signal 622 of the OOK receiver 600. The output signal 622 is coupled an input of the switch 610.
One embodiment of the operations of the OOK receiver 600 is now described in more detail in conjunction with a flow diagram 700 of
In block 702, a training tone pulse for an OOK signal during a training period is determined. With reference to the embodiment of
In block 704, an OOK signal is received during a current symbolic interval during normal operations. With reference to the embodiment of
In block 706, a bandpass filter operation is performed on the OOK signal in the current symbolic interval. With reference to the embodiment of
In block 708, a determination is made of whether the previous symbol is a tone pulse. With reference to the embodiment of
In block 710, the tail of symbol in a previous symbolic interval is subtracted from the symbol in the current symbolic interval to generate a corrected symbol for the current symbolic interval. With reference to the embodiment of
In block 712, the corrected symbol is correlated with the training tone pulse. With reference to the embodiment of
In block 714, a determination is made of whether the correlation is above a threshold. With reference to the embodiment of
In block 716, upon determining that the correlation is above a threshold, the corrected symbol is marked as a tone pulse. With reference to the embodiment of
In block 718, upon determining that the correlation is not above a threshold, the corrected symbol is marked as a non-tone pulse. With reference to the embodiment of
In block 720, the value of the corrected symbol is stored. With reference to the embodiment of
The training logic 815 receives a training OOK signal 801. The training logic 815 is coupled to the memory 819. The memory 819 is coupled to a first input of the f1 timing recovery logic 810, a first input of the f2 timing recovery logic 812, a first input of the f1 correlation logic 818 and a first input of the f2 correlation logic 820.
The bandpass filter 808 receives a FSK signal 802. The switch 814 receives a T(f1) signal 804 and a T(f2) signal 806. The T(f1) signal 804 and the T(f2) signal 806 are tails from a previous timing interval for a first data representation and a second data representation, respectively. An output of the bandpass filter 808 is coupled to a first input of the tail subtract logic 816, a second input of the f1 timing recovery logic 810 and a second input of the f2 timing recovery logic 812. An output of the switch 814 is coupled to a second input of the tail subtract logic 816. An output of the f1 timing recovery logic 810 is coupled to a second input of the f1 correlation logic 818. An output of the f2 timing recovery logic 812 is coupled to a second input of the f2 correlation logic 820. The output of the tail subtract logic 816 is coupled to a second input of the f1 correlation logic 818 and to a second input of the f2 correlation logic 820. An output of the f1 correlation logic 818 and an output of the f2 correlation logic 820 are coupled as inputs into the detection logic 824. The output of the detection logic 824 is an output signal 826 of the FSK receiver 800. The output signal 826 is coupled to a third input of the switch 814.
One embodiment of the operations of the FSK receiver 800 is now described in more detail in conjunction with a flow diagram 900 of
In block 902, a training tone pulse at a first frequency and a training tone pulse at a second frequency for a FSK signal during a training period are determined. With reference to the embodiment of
In block 904, a FSK signal is received during a current symbolic interval during normal operations. With reference to the embodiment of
In block 906, bandpass filter operations are performed on the FSK signal in the current symbolic interval with regard to the first frequency and the second frequency. With reference to the embodiment of
In block 908, a determination is made of whether the previous symbol is at the first frequency. With reference to the embodiment of
In block 910, upon determining that the previous symbol is at the first frequency, the tail of a symbol at the first frequency is subtracted from the symbol in the current symbolic interval to generate a corrected symbol for the current symbolic interval. With reference to the embodiment of
In block 912, upon determining that the previous symbol is not at the first frequency (rather the second frequency), the tail of a symbol at the second frequency is subtracted from the symbol in the current symbolic interval to generate a corrected symbol for the current symbolic interval. With reference to the embodiment of
In block 914, the corrected symbol is correlated with the training tone pulse at the first frequency to generate a first correlated output. With reference to the embodiment of
In block 916, the corrected symbol is correlated with the training tone pulse at the second frequency to generate a second correlated output. With reference to the embodiment of
In block 918, the second correlated output is subtracted from the first correlated output to generate a subtracted output. With reference to the embodiment of
In block 920, a determination is made of whether the polarity of the subtracted output is positive. With reference to the embodiment of
In block 922, upon determining that the polarity of the subtracted output is positive, the corrected symbol is marked as a “data one.” With reference to the embodiment of
In block 924, upon determining that the polarity of the subtracted output is not positive, the corrected symbol is marked as a “data zero.” With reference to the embodiment of
In block 926, the value of the corrected symbol is stored. With reference to the embodiment of
The training logic 1015 receives a training PSK signal 1001. The training logic 1015 is coupled to the memory 1019. The memory 1019 is coupled to a first input of the timing recovery logic 1014, a first input of the (phi-1) correlation logic 1028 and a first input of the (phi-2) correlation logic 1030.
The bandpass filter 1008 receives a PSK signal 1002. The switch 1010 receives a T(phi-1) signal 1004 and a T(phi-2) signal 1006. The T(phi-1) signal 1004 and the T(phi-2) signal 1006 are tails from a first data representation and a second data representation, respectively.
An output of the bandpass filter 1008 is coupled to a first input of the tail subtract logic 1012 and an input of the timing recovery logic 1014. An output of the switch 1010 is coupled as a second input of the tail subtract logic 1012.
A first output of the timing recovery logic 1014 is a timing signal for the first phase, which is a second input of the (phi-1) correlation logic 1028. A second output of the timing recovery logic 1014 is a timing signal for the second phase, which is a second input of the (phi-2) correlation logic 1030.
An output of the tail subtract logic 1012 is coupled to a third input of the (phi-1) correlation logic 1028 and to a third input of the (phi-2) correlation logic 1030. An output of the (phi-1) correlation logic 1028 is coupled to a first input of the detection logic 1034. An output of the (phi-2) correlation logic 1030 is coupled to a second input of the detection logic 1034. The output of the detection logic 1034 is an output signal 1036 of the PSK receiver 1000. The output signal 1036 is coupled to an input of the switch 1010.
One embodiment of the operations of the PSK receiver 1000 is now described in more detail in conjunction with a flow diagram 1100 of
In block 1102, a training tone pulse at a first phase and a training tone pulse at a second phase for a PSK signal during a training period are determined. With reference to the embodiment of
The training PSK signal 1001 may be a sequence of approximately identical widely spaced tone pulses at a first phase and a sequence of approximately identical widely spaced tone pulses at a second phase sent by the acoustic telemetry transmitter 123. In particular, the sequence of tone pulses at the first and second phases is widely spaced such that there is no interference between the pulses. The training logic 1015 may receive the training the PSK signal 1001 during an approximately noise free operating environment. The training logic 1015 may store these trained tone pulses into the memory 1019. As further described below, the (phi-1) correlation logic 1028 and the (phi-2) correlation logic 1030 may correlate these trained tone pulses with the acoustic signals received during normal drilling operations. Additionally, the timing recovery logic 1014 may determine the current symbolic interval for the first phase and the second phase during this training period (as described above). Control continues at block 1104.
In block 1104, a PSK signal is received during a current symbolic interval during normal operations. With reference to the embodiment of
In block 1106, bandpass filter operations are performed on the PSK signal in the current symbolic interval with regard to the first phase and the second phase. With reference to the embodiment of
In block 1108, a determination is made of whether the previous symbol is at the first phase. With reference to the embodiment of
In block 1110, upon determining that the previous symbol is at the first phase, the tail of a symbol at the first phase is subtracted from the symbol in the current symbolic interval to generate a corrected symbol for the current symbolic interval. With reference to the embodiment of
In block 1112, upon determining that the previous symbol is not at the first phase (rather the second phase), the tail of a symbol at the second phase is subtracted from the symbol in the current symbolic interval to generate a corrected symbol for the current symbolic interval. With reference to the embodiment of
In block 1114, the corrected symbol is correlated with the training tone pulse at the first phase to generate a first correlated output. With reference to the embodiment of
In block 1116, the corrected symbol is correlated with the training tone pulse at the second phase to generate a second correlated output. With reference to the embodiment of
In block 1117, a determination is made of whether the correlation for the first phase (the first correlated output) is above a maximum first phase threshold. With reference to the embodiment of
In block 1118, upon determining that the correlation for the first phase is above the maximum first phase threshold, a determination is made of whether the correlation for the second phase (the second correlated output) is below a minimum second phase threshold. With reference to the embodiment of
In block 1120, upon determining that the correlation for the second phase is not below the minimum second phase threshold, the corrected symbol is marked as a symbol representing the first phase. With reference to the embodiment of
In block 1121, upon determining that the correlation for the first phase is not above the maximum first phase threshold or that the correlation for the second phase is not below a minimum second phase threshold, a determination is made of whether the correlation for the second phase (the second correlated output) is above a maximum second phase threshold. With reference to the embodiment of
In block 1122, upon determining that the correlation for the second phase is above a maximum second phase threshold, a determination is made of whether the correlation for the first phase (the first correlated output) is below a minimum first phase threshold. With reference to the embodiment of
In block 1124, upon determining that the correlation for the second phase is above the maximum second phase threshold and that the correlation for the first phase is below a minimum first phase threshold, the corrected symbol is marked as a symbol representing the second phase. With reference to the embodiment of
In block 1126, upon determining that the correlation for the second phase is not above the maximum second phase threshold or that the correlation for the first phase is not below a minimum first phase threshold, the corrected symbol is marked as undefined. With reference to the embodiment of
In block 1128, the value of the corrected symbol is stored. With reference to the embodiment of
While the flow diagrams 700, 900 and 1100 illustrate the generation of the training pulses during an initial training period, such training may be subsequently re-executed. For example, the tails generated during training may be affected by different physical characteristics of the drill string (e.g., the length). In particular, after a given time of drilling operations, the drill string may be physically altered because of the stresses applied thereto during such operations. Additionally, the physical characteristics may be altered by the removal or addition of a section of drill pipe on the drill string. Accordingly, if a section of the drill string is removed or added, the training may be re-executed. The training may also be re-executed after a given time of drilling operations (e.g., 100 hours of operation).
Moreover, while described with reference to an OOK signal, a FSK signal and a PSK signal, embodiments of the invention are not so limited. Any of a number of different types of signaling can be used that allows for different symbols. For example, symbols may be different shaped envelopes, different levels and/or different chirp pulses that represent different values.
In the description, numerous specific details such as logic implementations, opcodes, means to specify operands, resource partitioning/sharing/duplication implementations, types and interrelationships of system components, and logic partitioning/integration choices are set forth in order to provide a more thorough understanding of the present invention. It will be appreciated, however, by one skilled in the art that embodiments of the invention may be practiced without such specific details. In other instances, control structures, gate level circuits and full software instruction sequences have not been shown in detail in order not to obscure the embodiments of the invention. Those of ordinary skill in the art, with the included descriptions will be able to implement appropriate functionality without undue experimentation.
References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.
Embodiments of the invention include features, methods or processes that may be embodied within machine-executable instructions provided by a machine-readable medium. A machine-readable medium includes any mechanism which provides (i.e., stores and/or transmits) information in a form accessible by a machine (e.g., a computer, a network device, a personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.). In an exemplary embodiment, a machine-readable medium includes volatile and/or non-volatile media (e.g., read only memory (ROM), random access memory (RAM), magnetic disk storage media, optical storage media, flash memory devices, etc.), as well as electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.).
Such instructions are utilized to cause a general or special purpose processor, programmed with the instructions, to perform methods or processes of the embodiments of the invention. Alternatively, the features or operations of embodiments of the invention are performed by specific hardware components which contain hard-wired logic for performing the operations, or by any combination of programmed data processing components and specific hardware components. Embodiments of the invention include software, data processing hardware, data processing system-implemented methods, and various processing operations, further described herein.
A number of figures show block diagrams of systems and apparatus for an acoustic telemetry receiver, in accordance with some embodiments of the invention. A number of figures show flow diagrams illustrating operations for an acoustic telemetry receiver, in accordance with some embodiments of the invention. The operations of the flow diagrams are described with references to the systems/apparatus shown in the block diagrams. However, it should be understood that the operations of the flow diagrams could be performed by embodiments of systems and apparatus other than those discussed with reference to the block diagrams, and embodiments discussed with reference to the systems/apparatus could perform operations different than those discussed with reference to the flow diagrams.
In view of the wide variety of permutations to the embodiments described herein, this detailed description is intended to be illustrative only, and should not be taken as limiting the scope of the invention. For example, embodiments of the invention are described in reference to correlations between two different values based on different attributes (phase, frequency, etc.). However, embodiments of the invention are not so limited. Embodiments of the invention may correlate among N number of different values based on a number of different attributes. For example, the pulses may be on multiple frequencies, multiple phases and/or multiple channels. Accordingly, these different pulses may have each have a training pulse for correlations during the acoustic telemetry operations. What is claimed as the invention, therefore, is all such modifications as may come within the scope and spirit of the following claims and equivalents thereto. Therefore, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
The application is a continuation application of U.S. patent application Ser. No. 10/925,267, filed Aug. 24, 2004 now U.S. Pat. No. 7,301,473, which application is incorporated herein by reference.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4210967 | Ingram | Jul 1980 | A |
| 4642800 | Umeda | Feb 1987 | A |
| 5113379 | Scherbatskoy | May 1992 | A |
| 6434084 | Schultz | Aug 2002 | B1 |
| 20030026169 | Schultz | Feb 2003 | A1 |
| Entry |
|---|
| “U.S. Appl. No. 10/925,267, Response filed Apr. 24, 2007 to Restriction Requirement mailed Mar. 28, 2007”, 20 pgs. |
| “U.S. Appl. No. 10/925,267, Restriction Requirement mailed Mar. 28, 2007”, 7 pgs. |
| Number | Date | Country | |
|---|---|---|---|
| 20080137481 A1 | Jun 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10925267 | Aug 2004 | US |
| Child | 11945055 | US |
