HK40050037A - Mechanical shock resistant mems accelerometer arrangement, associated method, apparatus and system - Google Patents

Description

Mechanical shock resistant MEMS accelerometer arrangements, related methods, devices and systems

This application is a divisional application of a patent application entitled "mechanical shock resistant MEMS accelerometer arrangement, related method, apparatus and system" filed on 2/7/2015 with application number 201580020102.2.

RELATED APPLICATIONS

This written document claims priority to U.S. provisional patent application serial No. 62/019,887 filed on day 7-month-2 2014, U.S. provisional patent application serial No. 62/021,618 filed on day 7-month-7 2014, and U.S. non-provisional patent application serial No. 14/789,071 filed on day 7-month-1 2015, each of which is incorporated herein by reference in its entirety.

Technical Field

This written document relates generally to MEMS accelerometers, and more particularly, to MEMS accelerometer kits having enhanced resistance to mechanical shock and related methods, devices, and systems.

Background

In modern electronics, accelerometers have become ubiquitous. In this regard, measuring acceleration along three orthogonal axes may provide a substantially complete characterization of the orientation of the device. Accelerometers configured to measure acceleration along three orthogonal axes in a single, convenient package are commonly referred to as tri-axial accelerometers.

Many modern electronic systems employ accelerometers for a variety of different purposes. As a general example, the operational state or physical orientation of the associated device may be characterized. As another more device-specific example, an accelerometer may be used to detect that a hard disk drive is in a free-fall condition, so that the driven read/write head may be registered in anticipation of mechanical shock caused by an impending crash. As another device-specific example, modern cellular smartphones typically include accelerometers to determine the orientation of the phone for display orientation management, and may be used by many applications that may be installed on the smartphone. It is noted that the demand for accelerometers suitable for consumer-grade electronics, such as cellular smartphones, has driven the development of MEMS triaxial accelerometers, which are typically low cost.

As another installation-specific example, an accelerometer may be used as part of a transmitter carried by an inground tool ("inground tool") in a horizontal directional drilling system for monitoring the orientation and movement of the inground tool. Such monitoring may facilitate manipulation and monitoring of the position of the inground tool. As will be described in detail below, it has been recognized that the use of consumer grade, low cost accelerometers in devices that subject the accelerometers to mechanical shock and vibration environments can cause failure of these devices. Although the overall failure rate has not been high in the past, any premature failure of the transmitter would result in significant problems, including idling personnel and equipment when obtaining a new transmitter, missing deadlines, and the expense involved in purchasing a new transmitter. To date, the industry has continued to use these accelerometers due to a lack of approved, practical alternatives.

This written document provides a new way to provide for the use of low cost consumer grade accelerometers in high mechanical shock and vibration environments in a manner that enhances reliability.

Disclosure of Invention

The embodiments and aspects thereof are described and illustrated below in conjunction with systems, tools, and methods which are meant to be exemplary and illustrative, not limiting in scope. In various embodiments, one or more of the above-described problems have been reduced or eliminated, while other embodiments are directed to other areas of interest.

In general, an accelerometer arrangement and method are described for determining acceleration of an inground tool along three orthogonal axes during an inground operation that exposes the accelerometer arrangement to mechanical shock and vibration. In one aspect of the disclosure, an accelerometer arrangement includes a first MEMS triaxial accelerometer and a second MEMS triaxial accelerometer, each including a set of three orthogonally arranged accelerometers that sense an axis including a pair of an in-plane ("in-plane") sensing axis and a perpendicular ("normal") sensing axis, such that the perpendicular sensing axis experiences a higher failure rate when responding to mechanical shock and oscillation than the in-plane sensing axis. The support structure supports the first and second tri-axial accelerometers such that a vertical sensing axis of the first tri-axial accelerometer is at least generally orthogonal to a vertical sensing axis of the second tri-axial accelerometer. The processor determines accelerations along three orthogonal axes based on a combination of sensed axis outputs from one or both of the first and second triaxial accelerometers.

In another aspect, an accelerometer arrangement includes a first MEMS triaxial accelerometer and a second MEMS triaxial accelerometer, each including a weaker sensing axis that is more susceptible to mechanical shock and oscillation than the other two sensing axes. The support structure supports the first and second triaxial accelerometers such that the weaker sensing axis of the first triaxial accelerometer is at least approximately perpendicular to the weaker sensing axis of the second triaxial accelerometer. The processor determines accelerations along the three orthogonal axes based on a combination of the sensed axis outputs from the first and second tri-axial accelerometers without using the weaker sensed axis of each of the first and second tri-axial accelerometers.

In another aspect, an accelerometer arrangement includes a first accelerometer assembly and a second accelerometer assembly, each accelerometer assembly including one or more sensing axes, such that the first accelerometer assembly and the second accelerometer assembly collectively provide a total of at least four sensing axes for sensing along three orthogonal axes. The support structure supports the first accelerometer and the second accelerometer such that at least one sensing axis of the first accelerometer assembly is redundant with respect to at least one sensing axis of the second accelerometer assembly. The processor is configured to select a combination of three sensing axes from the total counted sensing axes to determine acceleration along three orthogonal axes.

In another embodiment, the accelerometer arrangement comprises a first MEMS triaxial accelerometer and a second MEMS triaxial accelerometer. The support structure supports the first and second triaxial accelerometers such that the first triaxial accelerometer is supported in a first plane that forms an angle of at least approximately 45 degrees with respect to a second plane that supports the second triaxial accelerometer. The processor determines accelerations along three orthogonal axes based on a combination of the sensed axis outputs from the first and second tri-axial accelerometers.

Drawings

Exemplary embodiments are shown in the referenced figures. The embodiments and figures disclosed herein are intended to be illustrative rather than restrictive.

Fig. 1 is a diagrammatic front view of a transmitter of the present disclosure in accordance with the use of a dual triaxial MEMS accelerometer.

Fig. 2 is a diagrammatic perspective view of an embodiment of an accelerometer arrangement of the transmitter of fig. 1.

Fig. 3 is a schematic diagram illustrating an embodiment of the transmitter of fig. 1.

Fig. 4 is a flow chart illustrating an embodiment of the operation of the transmitter of fig. 1.

Fig. 5 and 6 are diagrammatic views of an embodiment of the accelerometer arrangement of fig. 1.

FIG. 7 is a flow chart illustrating an embodiment of a method for operating a transmitter according to the present application based on a priority table of sensing axis combinations derived from two or more accelerometers.

FIG. 8 is a perspective view of a diagrammatic illustration of another embodiment for supporting dual accelerometers according to the present disclosure, with the accelerometers supported in planes that are not perpendicular to each other.

Detailed Description

The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the described embodiments will be readily apparent to those skilled in the art, and the generic principles taught herein may be applied to other embodiments. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and features described herein, including modifications and equivalents, as defined by the following claims. It is noted that the drawings are not to scale and are diagrammatic in nature in a manner that is believed to best illustrate features of interest. Descriptive terminology may be used in relation to these descriptions, however, the terminology is employed with the intent of promoting an understanding of the reader and is not intended to be limiting. Further, for clarity of illustration, the drawings are not to scale.

Turning now to the drawings, wherein like components are designated by like reference numerals throughout the various views, attention is immediately directed to FIG. 1, which is a front view that diagrammatically shows an embodiment of a transmitter, designated generally by reference numeral 10, for use in a horizontal directional drilling system. The transmitter 10 is supported by an inground tool 14 such as, for example, a drill tool for performing drilling operations or a tension monitoring arrangement for use with a back-boring tool ("back-drilling") for performing pull-back operations. As will become apparent, the present disclosure is relevant to any application that subjects certain components to mechanical shock and vibration environments.

The transmitter 10 includes a processor 20 in communication with a transmitter portion 22 coupled to an antenna 24 for transmitting a signal 28, such as a positioning signal, which may be a dipole signal, for example. When mounted therein, the transmitter may include an elongate axis 30 that is at least generally aligned with the elongate axis of the inground tool 14. Note that inter-component wiring is not shown in fig. 1 for clarity of illustration, but should be understood to exist. In another embodiment, the transmitter section 10 may include a transceiver for also receiving incident electromagnetic signals. In yet another embodiment, above-ground communication may be achieved through the use of a drill string (not shown) attached as an electrical conductor to the inground tool 14 as described, for example, in U.S. patent application No. 2013/0176139, the entire contents of which are incorporated herein by reference. It should be understood that the teachings herein remain applicable regardless of the particular communication path or paths implemented. Any suitable combination of sensors may be provided as part of the transmitter, such as, for example, the pressure sensor 32, the temperature sensor 36, and the accelerometer arrangement 40. The data collected by the processor 20 from these various sensors may be transmitted, for example, by a modulated signal 28.

Referring to fig. 2 in conjunction with fig. 1, in one embodiment, an accelerometer arrangement 40 is included in the transmitter 1A MEMS accelerometer arrangement supported within 0. The MEMS accelerometer arrangement includes a first MEMS triaxial accelerometer 44a and a second triaxial accelerometer 44 b. Note that these accelerometers may be collectively referred to by reference numeral 44. FIG. 2 is an enlarged diagrammatic perspective view of the MEMS accelerometer package 40. The first three-axis MEMS accelerometer 44a includes an orthogonal sensing axis x₁、y₁And z₁And a second three-axis MEMS accelerometer 44b includes an orthogonal sensing axis x₂,y₂And z₂. Note the axis x₂And z₁May be at least approximately aligned with or parallel to the elongate axis 30, although this is not required. The three-axis accelerometer may be supported and electrically connected in any suitable manner. In the present example, the first printed circuit board 50 supports and electrically connects the three-axis MEMS accelerometer 44a and the second printed circuit board 52 supports and electrically connects the second three-axis MEMS accelerometer 44 b. Typically, the same part number may be used for both triaxial MEMS accelerometers, although this is not required. The triaxial MEMS accelerometer can be an inexpensive, consumer grade MEMS accelerometer, such as found in a cellular telephone, for example. One non-limiting example of such a consumer grade tri-axial accelerometer is MMA8451Q manufactured by ciscarl semiconductor. In the present embodiment, accelerometer 44 is configured with an I2C interface such that processor 20 accesses readings along each axis by making readings from specific memory within each tri-axis accelerometer, although any suitable form of interface, including analog, may be used.

Triaxial MEMS accelerometers have become widely available and in many cases are the least expensive accelerometers available in the market. These accelerometers have become ubiquitous in applications ranging from cell phones to toys. However, subsurface drilling may subject the accelerometer to higher and/or more prolonged levels of mechanical shock that may, in some circumstances, exceed the threshold for which these components are typically designed. In particular, applicants have recognized that the z-axis of a three-axis MEMS accelerometer (which may be referred to as the vertical axis or the weaker axis) tends to fail more than the other axes when exposed to extreme oscillatory conditions, thereby limiting the overall performance of the assembly. Despite this limitation, manufacturers of positioning systems still use these components without a more suitable alternative. The teachings disclosed herein compensate for this limitation, providing a significantly higher level of reliability potential when these accelerometers are used in subterranean drilling applications or under other conditions of extreme mechanical shock.

As best seen in the perspective view of FIG. 2, MEMS accelerometer 44a is mounted orthogonal to MEMS accelerometer 44b such that z of accelerometer 44a₁The axis is at least approximately orthogonal to the z2 axis of accelerometer 44b, and x₁,y₁The face being at least approximately orthogonal to x₂,y₂And (5) kneading. Note that the x and y sensing axes of a given accelerometer may be referred to as in-plane axes, as these axes define a plane that is at least generally parallel to the plane supporting the three-axis accelerometer package, while the z axis may be referred to as the vertical axis. In one embodiment, this may be based on an axis x along accelerometer 44a₁And axis x of accelerometer 44b₂And y₂To obtain accelerometer readings for three orthogonally arranged axes such that x is used₁Accelerometer readings instead of z from accelerometer 44b₂And (6) reading. In another embodiment, this may be based on an axis x along accelerometer 44a₁And y₁And along axis x of accelerometer 44b₂So that x is used to obtain accelerometer readings₂Accelerometer readings instead of z from accelerometer 44a₁And (6) reading. In one of these embodiments, no sensor readings from the z-axis of the dual accelerometer are needed. Stated another way, two three-axis MEMS accelerometer packages can be mounted perpendicular or orthogonal to each other, thereby allowing the perpendicular accelerometers in one package to be replaced by in-plane accelerometers in the other package. This solution provides a simple redundancy beyond using multiple accelerometers in a standard manner (i.e. using all three axes) as this would still expose the device to a potential failure in the z-axis. By comparison, applicants' configuration was specifically designed to eliminate the weakest link, the z-axis, recognized in these components.

Referring to fig. 3, a schematic diagram of one embodiment of the transmitter 10 is shown. For purposes of clarity, the description of similar components will not be repeated. In the present embodiment, the I2C interface 100 connects the three-axis MEMS accelerometers 44a and 44b to the CPU 20. If one of the pressure sensor 32 and the temperature sensor 36 is an analog sensor, it may be interfaced to the processor 20 using an analog-to-digital converter 104.

Fig. 4 is a flow chart illustrating one embodiment of a method, indicated generally by the reference numeral 200, for operating the transmitter 10 in accordance with the present disclosure. The method begins at start 204 and proceeds to 208, where axis x of accelerometer 44a is read₁. At 210, axis x of accelerometer 44b is read₂Next, at 212, axis y of accelerometer 44b is read₂. Based on the parameter or parameters being determined, the various accelerometer axes may be read separately, in any suitable order or combination. By way of non-limiting example, such parameters include the pitch angle ("pitch") and roll angle ("roll") of the inground tool 14. At 216, accelerometer readings are used to perform determinations such as pitch angle and/or roll angle orientation parameters, for example.

Fig. 5 and 6 are diagrammatic perspective views of one embodiment of an accelerometer arrangement 40 shown for further illustrative purposes.

It will be appreciated that in addition to using a low cost tri-axial MEMS accelerometer to provide a robust accelerometer arrangement, further advantages are provided by the embodiments described above. For example, redundancy may be provided with respect to accelerometer readings. With reference to FIG. 2, in the use of axis x₁,x₂And y₂In embodiments where the axis y of the accelerometer 44a is not used₁And for example if y is experienced₂Using the axis y of the accelerometer 44a₁Instead of the axis y of the accelerometer 44b₂。

The teachings disclosed may be readily applied to other embodiments deemed to be within the scope of the present application, so long as the given embodiment practices avoids the use of a weaker axis. For example, in one embodiment, a dual accelerometer arrangement may include a pair of dual-axis accelerometers such that a perpendicular z or weaker axis is not present in either embodiment, and the dual accelerometers are supported at least approximately perpendicular or orthogonal to each other such that the in-plane axis of one of the dual-axis accelerometers serves as the z or vertical axis. In another embodiment, a three-axis accelerometer may be paired with a two-axis accelerometer such that the in-plane axis of the two-axis accelerometer is supported for replacement of the weaker z-axis or vertical axis of the three-axis accelerometer. In yet another embodiment, a three-axis accelerometer may be paired with a single-axis accelerometer such that the single-axis accelerometer is supported in place of the weaker z-axis or vertical axis of the three-axis accelerometer. In yet another embodiment, a dual-axis accelerometer having a pair of in-plane accelerometers may be paired with a single-axis accelerometer such that the single-axis accelerometer is disposed at least approximately perpendicular or orthogonal to the in-plane accelerometers of the dual-axis accelerometer.

While the above teachings generally provide a tougher accelerometer package, additional robustness can be obtained from two tri-axial packages, as will be described below.

It should be understood that two tri-axial assemblies may provide eight combinations of accelerometers that may be used as a single tri-axial accelerometer, where two accelerometers may be used for each Cartesian direction. Table 1 lists combinations of accelerometer axes according to that shown in fig. 2. Note that a set of primary coordinate axes X, Y, Z is shown in fig. 2, such that the last column of table 1 indicates, for each sense axis of a given combination, the sign associated with the respective primary coordinate axis.

TABLE 1

Usable combination of dual triaxial accelerometers

Enhanced reliability

As indicated by the asterisks in table 1, there are two combinations 1 and 4 that provide the toughest arrangement by eliminating all use of vertical accelerometers in two accelerometer packages.

For the combination 1,2. 4 and 8, are indicated asThe pitch angle of (c) is given as follows:

for combinations 1 and 5, the roll angle indicated as β is given by way of example as follows:

for combinations 2 and 6, the roll angle is given by way of example as follows:

applicants recognized that the proper functionality of each combination in table 1 could be verified by summing the squares of the three accelerations for each combination. And should correspond to the square of the gravitational acceleration g. The variables a, b, and c are typically used to represent three accelerometer readings for each combination:

g²＝a²+b²+c²equation (4)

In practical applications, a range limit may be imposed on the sum of the squares of equation 4 to account for accelerometer accuracy and other measurement errors, so that the accelerometer associated with a particular sum of equation 4 may be considered to operate correctly, as long as the sum falls withinAndin the meantime. By way of non-limiting example, forAndare suitably at least approximately 0.958g, respectively²And 1.05g²Or +/-5% change from 1 g.

In one embodiment, an ordered list of accelerometer combinations, which has as preference the most reliable combination at the top of the list, may be used to determine which accelerometer combination to use. Table 2 represents one embodiment of such a sorted list, in which the combination numbers from table 1 are described.

TABLE 2

Priority table for dual triaxial accelerometer

Priority order	Combination numbering	Combined shaft
			1	1*	x2,y2,x1
2	4*	x2,y1,x1
			3	2	x2,y1,z2
4	3	z1,y2,z2
			5	5	z1,y2,x1
6	6	z1,y1,z2
			7	7	z1,y1,x1
8	8	x2,y2,z2

Enhanced reliability

It should be understood that the use of a priority table such as table 2 does not require the use of one or more accelerometers having a weaker axis. The priority assignment may be made according to any type of consideration concerning reliability. Such considerations may be derived from physical mounting, supported electrical connections, environmental exposure, and historical reliability, as non-limiting examples. In some embodiments, a priority table may be used to provide an overall priority level not seen before, even when the accelerometer axle combinations are all considered to exhibit at least generally the same reliability.

Referring to fig. 7, an embodiment of a method of operating the transmitter 10 based on a priority table such as table 2 is shown and is indicated generally by the reference numeral 200. Method 200 begins at start 204, for example, when the transmitter and accelerometer are first turned on andproceed to 208. This latter step sets each priority counter and loop counter to a value of 1. The purpose of the loop counter will be disclosed at a suitable point below. At 210, a sum of squares of the accelerometers in Table 2 for the first or highest order combination of accelerometers is generated. At 214, for gmin²And gmax²The sum of the squared values is tested and if the value is within the range, operation is routed to 218 so that the current combination of accelerometers is used for normal operation. During normal operation, the selected accelerometer combination may be periodically monitored and/or tested for faults at 220, e.g., based on equation 4 and/or any suitable factor. If no fault is detected, normal operation resumes at 224. If an accelerometer fault is detected at 220, operation returns to 208, causing the process to resume.

Returning to the discussion of 214, if the sum of the squares is out of range, operation proceeds to 230 where the priority order counter value is incremented by 1. At 234, the value of the priority order counter is tested against the total number of available accelerometer combinations in Table 2. If the current value of the priority order counter does not exceed the total number of available combinations, operation returns to and proceeds from 210. Otherwise, operation proceeds to 238 where the current value of the loop counter is tested against the loop count limit. The purpose of the cycle counter relates to the potential of the MEMS accelerometer becoming temporarily stuck due to static charge forces. Accordingly, the accelerometer selection process need not be stopped based on reaching the bottom of the priority table list. Conversely, the priority table list may be cycled through several times repeatedly before declaring that the accelerometer kit is unavailable, or the selection process may continue indefinitely until the accelerometer becomes operational. As part of the loop architecture, it should be understood that each available combination of sense axes may be tested or retested, including the combination that invoked the test procedure in the first instance, for example, based on the detection by step 220. In this way, a combination of previous failures that subsequently become operational may be placed into service. Note that the test step 238 and loop architecture are not required. In embodiments that do not use a cycle count, step 214 may notify the operator that an accelerometer test is being performed each time this step is entered. If the loop count is not exceeded at 238, operation proceeds to 240, which increments the loop count and sets the priority order counter to 1. Operation then returns to and proceeds from 210. On the other hand, if 238 determines that the cycle count exceeds the cycle count limit (which is established, for example, by the manufacturer), an alert may be issued to the operator at 244.

The above-described methods and related apparatus may be used with additional accelerometer packages having any number of sensing axes and/or a single sensing axis for even more redundancy. Further, the processes of FIGS. 4 and 7 are not limited to a three-axis accelerometer package and do not require an accelerometer package to be mounted perpendicular to each other, so long as three Cartesian acceleration directions can be solved from the selected accelerometer, as will be described in detail below.

Attention is now directed to FIG. 8, which is a diagrammatic perspective view of another embodiment of a support dual accelerometer according to the present disclosure. Note that the accelerometer axes are shown separately from the physical package and are indicated using reference names from fig. 1 and 2. For simplicity of illustration, the first circuit board 50 and the second circuit board 52 are shown as planar surfaces, while the accelerometers 44a and 44b are considered to be located at the origin of their respective coordinate axes. In the present embodiment, the second circuit board 52 is supported at an acute angle β with respect to the first circuit board 52. The angle β may have any suitable value. In one embodiment, β may be at least approximately 45 °. As can be seen in fig. 1, x₂The axis may be at least approximately aligned with or parallel to the elongate axis of the transmitter, although this is not required. In-plane axis x of accelerometer 44a in FIG. 1₁And y₁Remains at least approximately parallel to the first circuit board 50, but has been rotated through a certain angle. z is a radical of₁The axis is at least approximately orthogonal to the plane of the circuit board 50. In the present embodiment, the angle α is at least approximately equal to 45 °. In other embodiments, any suitable angle for α may be used. For example, α may be in the range from 20 ° to 160 °, which would allow for the axis of interestIs sufficient.

Still referring to fig. 8, it should be understood that the angles a and β may be determined at the time of manufacture and/or based on a calibration procedure performed, for example when the transmitter and accelerometer arrangement are supported at known physical locations. The calibration process may position the transmitter in six cardinal orientations based on three orthogonal axes that may be referenced to the housing of the transmitter. These base orientations may correspond to roll angle positions of 0 °, 90 °, 180 ° and 270 °, with one pitch angle being 0 ° and multiple pitch angles being +/-90 °. In this way, the angles α and β and the axis x can be determined₂Any angle change relative to the elongate axis of the transmitter. The orientation of each axis may be characterized in a known manner, for example based on euler angles using the transmitter elongation axis and the 0 roll angle orientation as references. Based on the values described for angles α and β, each axis of accelerometer 44a is tilted or exhibits an angular offset with respect to each axis of accelerometer 44 b. As will be seen, the accelerometer arrangement depicted in fig. 8 and its variations provide a combination of a significant number of axes and flexibility for measuring roll and pitch azimuths.

Table 3 sets forth combinations of axes that may be used for roll and pitch azimuth according to the embodiment of fig. 8. Note that for each combination, two axes are used to detect roll angle azimuth and a different axis is used to detect pitch angle azimuth. For a particular combination, the axis used to detect roll angle azimuth is labeled with R and the axis used to detect pitch angle azimuth is labeled "P". As listed in the last column of the table, when the axis for the pitch angle measurement is relative to the axis x₂During tilt, the pitch angle measurement may be sensitive to angle β or angles α and β, where for purposes of this example axis x is assumed₂Parallel to the elongate axis of the transmitter. Since the axis x is assumed₂Parallel to the axis of elongation, relative to the use x₂Does not exhibit that sensitivity (indicated as "N/a" in the table).

TABLE 3

Accelerometer shaft combination for pitch angle and roll angle

Rolling angle combination

x1

y1

z1

x2

y2

z2

Pitch angle sensitivity is proportional to:

1a

P

R

R

N/A

1b

P

R

R

sinβ

1c

P

R

R

cosβ,sinα

1d

P

R

R

cosβ,cosα

2a

R

P

R

N/A

2b

R

P

R

cosβ,cosα

2c

R

P

R

sinβ

3a

R

P

R

N/A

3b

R

P

R

sinβ

4a

R

P

R

N/A

4b

R

P

R

cosβ,cosα

4c

R

P

R

sinβ

5a

R

P

R

N/A

5b

R

P

R

sinβ

5c

P

R

R

cosβ,sinα

accordingly, fifteen different combinations are available. It should be understood that these combinations may be prioritized. For example, combinations that rely on z1 or z2 may be assigned a relatively lower priority than combinations that do not rely on these axesAnd (4) first-level. Dependent on z₁And z₂The combination of (c) may still be assigned a lower priority. Applicants believe that a wide range of axle combinations in table 1 may provide significant immunity to failure of one or more accelerometer axles with respect to pitch and roll angle measurements. Note that 14 of the 15 combinations given in table 3 use the output from two three-axis accelerometers.

Still referring to FIG. 8, additional combinations utilizing all three axes of each accelerometer may be used. In these embodiments, the orthogonal x, y, and z accelerometer measurements made by either accelerometer 44a or 44b are resolved on a reference axis of the transmitter, e.g., an elongation axis to the transmitter and an axis corresponding to a zero roll angle orientation. In the example of fig. 8, the transmitter elongation axis is additionally labeled Gx and is assumed to be x₂At least approximately parallel to the axis of elongation, corresponds to the axis x₂. The roll angle orientation reference axis Gy corresponds to the axis y₂Assume that the transmitter is positioned at a roll angle reference position of zero degrees and that the reference axis Gz is orthogonal to Gx and Gy. Where these values are obtained, and in one embodiment, the roll angle orientation may be determined based on the following equation:

roll-atan 2(Gy, Gz) equation (5)

It should be understood that the function atan2 is an arctangent function that has two arguments and returns to the appropriate quadrant for a determined roll angle.

In another embodiment, the roll angle orientation may be determined based on the following equation

Accordingly, even more flexibility in terms of the ability to determine the roll angle orientation may be provided based on equations 5 and 6.

The foregoing description of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form or forms disclosed, and other modifications and variations may be possible in light of the above teachings. Accordingly, those skilled in the art will recognize certain modifications, permutations, additions and sub-combinations of the above disclosed embodiments.

Preferably comprising all the elements, components and steps described herein. It will be understood that any of these elements, components and steps may be replaced by other elements, components and steps, or deleted altogether as will be apparent to those skilled in the art.

In general, this written document discloses at least the following:

an accelerometer arrangement and method for determining acceleration of an inground tool is described. The first and second triaxial accelerometers are supported such that the vertical sensing axis of the first triaxial accelerometer is at least generally orthogonal to the orthogonal sensing axis of the second triaxial accelerometer for determining accelerations along the three orthogonal axes based on a combination of sensing axis outputs from one or both of the first and second triaxial accelerometers. The weaker sensing axis of one triaxial accelerometer may be supported at least approximately perpendicular to the weaker sensing axis of the other triaxial accelerometer such that the weaker axis is not used. The three-axis accelerometers may be supported such that one axis of one accelerometer is redundant with respect to another axis of another accelerometer. One triaxial accelerometer may be mounted on an inclined plane relative to the other triaxial accelerometer.

This written document also sets forth at least the following concepts.

Concept 1. an accelerometer arrangement for determining acceleration of an inground tool along three orthogonal axes during an inground operation that exposes the accelerometer to a mechanical shock and vibration environment, said accelerometer arrangement comprising:

a first MEMS tri-axial accelerometer and a second MEMS tri-axial accelerometer, each tri-axial accelerometer comprising a set of three orthogonally arranged accelerometer sense axes comprising a pair of in-plane sense axes and a vertical sense axis, such that the vertical sense axis experiences a higher failure rate than the in-plane sense axes when responsive to the mechanical shock and vibration environment;

a support structure for supporting the first and second tri-axial accelerometers such that the vertical sensing axis of the first tri-axial accelerometer is at least generally orthogonal to the vertical sensing axis of the second tri-axial accelerometer; and

a processor for determining the accelerations along the three orthogonal axes based on a combination of sensed axis outputs from one or both of the first and second triaxial accelerometers.

Concept 2 the accelerometer arrangement according to concept 1, wherein the processor does not need to use the perpendicular sensing axis of each of the first and second triaxial accelerometers in determining the acceleration along the three orthogonal axes.

Concept 3 the accelerometer arrangement according to concept 1 or 2 supported within a transmitter carried by the inground tool.

Concept 4. the accelerometer arrangement of concept 3, wherein the transmitter comprises an elongation axis, and wherein one sensing axis of the first triaxial accelerometer and another sensing axis of the second triaxial accelerometer are at least generally parallel to the elongation axis.

Concept 5. the accelerometer arrangement of concept 3 or 4, wherein at least one in-plane sensing axis of the first and second triaxial accelerometers is arranged to sense a pitch orientation of the transmitter.

Concept 6 the accelerometer arrangement of concept 3-5 wherein a pair of in-plane sensing axes of one of the first and second triaxial accelerometers is supported for detecting a roll angle orientation of the transmitter.

Concept 7 the accelerometer arrangement of concepts 1-6 wherein the support structure includes a first printed circuit board supporting the first triaxial accelerometer and a second printed circuit board supporting the second triaxial accelerometer.

Concept 8 the accelerometer arrangement of concept 7 wherein the second printed circuit board is supported by the first printed circuit board at least generally orthogonal thereto.

Concept 9 the accelerometer arrangement of concepts 1-8, wherein the processor is configured to select a combination of the sensing axis outputs based on a priority table.

Concept 10 the accelerometer arrangement of concept 9, wherein the first and second triaxial accelerometers provide a set of sensing axis combinations, and the priority table is set according to reliability of at least some of the set of sensing axis combinations.

Concept 11 the accelerometer arrangement of concept 10, wherein a first combination and a second combination are assigned to a first priority and a second priority in the priority table, and each of the first combination and the second combination excludes the vertical sensing axis of the first triaxial accelerometer and the second triaxial accelerometer.

Concept 12 the accelerometer arrangement according to concepts 9-11, wherein the processor is configured to detect a failure of one or more sensing axes in the combination and, in response thereto, cycle through the priority table to find an available sensing axis combination from the set of sensing axis combinations.

Concept 13 the accelerometer arrangement of concept 12, wherein the processor is configured to cycle through the priority table a plurality of times.

Concept 14 the accelerometer arrangement of concept 13, wherein the processor is configured to issue an alert in response to cycling through the priority table the plurality of times without identifying an available combination.

Concept 15 the accelerometer arrangement of concepts 12-14 wherein the above combination of sensing axis outputs is identified as a failed combination and the failed combination is retested as part of cycling through the priority table to find the available combination.

Concept 16 the accelerometer arrangement of concept 15, wherein the processor is configured to place the failed combination into service in response to detecting that the failed combination has become operational.

Concept 17 the accelerometer arrangement of concepts 12-16 wherein the processor detects the fault based on a sum of squares of a set of three outputs for a combination of sense axes.

Concept 18. a method for determining acceleration of an inground tool along three orthogonal axes during an inground operation that exposes the accelerometer to mechanical shock and vibration conditions, said method comprising:

supporting first and second MEMS tri-axial accelerometers to arrange a vertical sensing axis of the first tri-axial accelerometer at least generally orthogonal to a vertical sensing axis of the second tri-axial accelerometer, each tri-axial accelerometer comprising a set of three orthogonally arranged accelerometer sensing axes including a pair of in-plane sensing axes and a vertical sensing axis such that the vertical sensing axis experiences a higher failure rate than the in-plane sensing axes in response to the mechanical shock and vibration environment; and

for determining the accelerations along the three orthogonal axes based on a combination of sensed axis outputs from one or both of the first and second triaxial accelerometers.

Concept 19. an accelerometer arrangement for determining acceleration of an inground tool along three orthogonal axes during an inground operation that exposes the accelerometer arrangement to a mechanical shock and vibration environment, said accelerometer arrangement comprising:

a first MEMS triaxial accelerometer and a second MEMS triaxial accelerometer, each comprising a weaker sensing axis that is more susceptible to the mechanical shock and vibration environment than the two other sensing axes;

a support structure for supporting the first and second triaxial accelerometers such that the weaker sensing axis of the first triaxial accelerometer is at least generally perpendicular to the weaker sensing axis of the second triaxial accelerometer; and

a processor for determining the accelerations along the three orthogonal axes based on a combination of sensed axis outputs from one or both of the first and second triaxial accelerometers without using a weaker sensed axis of each of the first and second triaxial accelerometers.

Concept 20. an accelerometer arrangement for determining acceleration of an inground tool along three orthogonal axes during an inground operation, said accelerometer arrangement comprising:

a first accelerometer assembly and a second accelerometer assembly, each accelerometer assembly including one or more sensing axes, such that the first accelerometer assembly and the second accelerometer assembly collectively provide for sensing a total of at least four sensing axes along the three orthogonal axes;

a support structure for supporting the first and second accelerometers such that at least one sensing axis of the first accelerometer assembly is redundant with respect to at least one sensing axis of the second accelerometer assembly; and

a processor configured to select a combination of three sensing axes from a total number of sensing axes for determining the acceleration along the three orthogonal axes.

Concept 21 the accelerometer arrangement of concept 20, wherein at least one of the first accelerometer assembly and the second accelerometer assembly comprises a sensing axis that is weaker than another sensing axis of the accelerometer assembly in that it is more susceptible to mechanical shock and vibration, and the processor selects the combination without using the weaker sensing axis to determine the acceleration.

Concept 22 the accelerometer arrangement of concept 20 or 21, wherein the processor is configured to select the combination of sensing axis outputs based on a priority table.

Concept 23 the accelerometer arrangement of concept 22, wherein the first accelerometer and the second accelerometer provide a set of sensing axis combinations based on a total number of sensing axes, and the priority table is set according to a reliability of at least some combinations of the set of sensing axis combinations.

Concept 24 the accelerometer arrangement of concepts 20-23, wherein the processor is configured to detect a failure of one or more sensing axes of the combinations and, in response thereto, select a different combination of the sensing axes.

Concept 25 the accelerometer arrangement of concept 24 wherein the processor detects the fault based on a sum of squares of a set of three outputs for a combination of sense axes.

Concept 26. an accelerometer arrangement for determining acceleration of an inground tool along three orthogonal axes during an inground operation that exposes the accelerometer to a mechanical shock and vibration environment, said accelerometer arrangement comprising:

a first MEMS triaxial accelerometer and a second MEMS triaxial accelerometer;

a support structure for supporting the first and second triaxial accelerometers such that the first triaxial accelerometer is supported in a first plane forming an angle of at least approximately 45 degrees with respect to a second plane supporting the second triaxial accelerometer; and

a processor for determining accelerations along three orthogonal axes based on a combination of sensed axis outputs from the first and second triaxial accelerometers.

Claims (25)

1. An accelerometer arrangement configured to determine accelerations along three orthogonal axes during operation of exposing the accelerometer arrangement to mechanical shock and vibration environments, the accelerometer arrangement comprising:

a first MEMS tri-axial accelerometer and a second MEMS tri-axial accelerometer, each tri-axial accelerometer comprising a set of three orthogonally arranged accelerometer sense axes comprising a pair of in-plane sense axes and a vertical sense axis, wherein the vertical sense axis has a higher failure rate than the in-plane sense axes in response to the mechanical shock and vibration;

a support structure configured to support the first and second tri-axial accelerometers such that the vertical sensing axis of the first tri-axial accelerometer is at least generally orthogonal to the vertical sensing axis of the second tri-axial accelerometer; and

a processor configured to determine the accelerations along the three orthogonal axes based on a combination of sense axis outputs from the first and second triaxial accelerometers without using the perpendicular sense axis output of each of the first and second triaxial accelerometers.

2. The accelerometer arrangement of claim 1 supported within a transmitter.

3. The accelerometer arrangement of claim 2 wherein the transmitter comprises an elongation axis, and wherein one sensing axis of the first triaxial accelerometer and another sensing axis of the second triaxial accelerometer are at least generally parallel to the elongation axis.

4. The accelerometer arrangement of claim 2 wherein at least one in-plane sensing axis of the first and second triaxial accelerometers is arranged to sense a pitch orientation of the transmitter.

5. The accelerometer arrangement of claim 2 wherein a pair of in-plane sensing axes of one of the first and second triaxial accelerometers is supported for detecting a roll angle orientation of the transmitter.

6. The accelerometer arrangement of claim 1 wherein the support structure comprises a first printed circuit board supporting the first triaxial accelerometer and a second printed circuit board supporting the second triaxial accelerometer.

7. The accelerometer arrangement of claim 6 wherein the second printed circuit board is supported by the first printed circuit board at least generally orthogonal thereto.

8. The accelerometer arrangement of claim 1 wherein the processor is configured to detect a failure of one or more detection axes in the combination and, in response thereto, cycle through a priority table to find an available combination of sensing axes from a set of sensing axis combinations of the first and second three-axis accelerometers.

9. The accelerometer arrangement of claim 8 wherein the first and second triaxial accelerometers provide a set of sensing axis combinations and the priority table is set according to the reliability of at least some of the set of sensing axis combinations.

10. The accelerometer arrangement of claim 8 wherein the processor is configured to cycle through a priority table a plurality of times.

11. The accelerometer arrangement of claim 10 wherein the processor is configured to issue an alert in response to cycling through the priority table the plurality of times without identifying an available combination.

12. The accelerometer arrangement of claim 8 wherein the above combinations of sensing axis outputs are identified as failed combinations and the failed combinations are retested as part of cycling through the priority table to find the available combinations.

13. The accelerometer arrangement of claim 12 wherein the processor is configured to place the failed combination into service in response to detecting that the failed combination has become operational.

14. The accelerometer arrangement of claim 1 wherein the acceleration is an acceleration of an inground tool and wherein the operation is an inground operation.

15. A method for determining accelerations along three orthogonal axes during exposure of an accelerometer arrangement to mechanical shock and vibration environments, the method comprising:

supporting first and second MEMS tri-axial accelerometers to arrange a vertical sensing axis of the first tri-axial accelerometer at least generally orthogonal to a vertical sensing axis of the second tri-axial accelerometer, each tri-axial accelerometer comprising a set of three orthogonally arranged accelerometer sensing axes including a pair of in-plane sensing axes and a vertical sensing axis, wherein the vertical sensing axis has a higher failure rate than the in-plane sensing axes in response to the mechanical shock and vibration environment; and

determining the accelerations along the three orthogonal axes based on a combination of sense axis outputs from the first and second triaxial accelerometers without using the perpendicular sense axis output of each of the first and second triaxial accelerometers.

16. The method of claim 15, wherein the acceleration is an acceleration of an inground tool, and wherein the operation is an inground operation.

17. An accelerometer arrangement configured to determine accelerations along three orthogonal axes during operation of exposing the accelerometer arrangement to mechanical shock and vibration environments, the accelerometer arrangement comprising:

a first MEMS tri-axial accelerometer and a second MEMS tri-axial accelerometer, each tri-axial accelerometer comprising a set of three orthogonally arranged accelerometer sensing axes including a pair of in-plane sensing axes and a vertical sensing axis such that each vertical sensing axis experiences a higher failure rate in response to mechanical shock and vibration than the in-plane sensing axes, and the first MEMS tri-axial accelerometer and the second MEMS tri-axial accelerometer supported by a vertical sensing axis of the first MEMS tri-axial accelerometer, the vertical sensing axis of the first MEMS tri-axial accelerometer being at least generally orthogonal to the vertical sensing axis of the second MEMS tri-axial accelerometer; and

a processor configured to determine the accelerations along the three orthogonal axes of the inground tool based on a combination of the sense axis outputs from the first and second tri-axial accelerometers without using the vertical sense axis output of each of the first and second tri-axial accelerometers.

18. The accelerometer arrangement of claim 17 wherein the acceleration is an acceleration of an inground tool and wherein the operation is an inground operation.

19. The accelerometer arrangement of claim 18 supported within a transmitter carried by the inground tool.

20. The accelerometer arrangement of claim 19 wherein the transmitter defines an elongation axis, and wherein one sensing axis of the first triaxial accelerometer and another sensing axis of the second triaxial accelerometer are at least generally parallel to the elongation axis.

21. The accelerometer arrangement of claim 20 wherein the vertical sensing axis of one of the first and second MEMS triaxial accelerometers is at least generally parallel to the elongation axis.

22. The accelerometer arrangement of claim 18 wherein at least one in-plane sensing axis of the first and second MEMS triaxial accelerometers is arranged to sense a pitch orientation of the transmitter.

23. The accelerometer arrangement of claim 18 wherein a pair of in-plane sensing axes of one of the first and second triaxial accelerometers is supported for detecting a roll angle orientation of the transmitter.

24. The accelerometer arrangement of claim 18 wherein the transmitter comprises a first printed circuit board supporting the first triaxial accelerometer and a second printed circuit board supporting the second triaxial accelerometer.

25. The accelerometer arrangement of claim 24 wherein the second printed circuit board is supported by the first printed circuit board at least generally orthogonal thereto.