Patent Grant
7055625
This invention relates to a self-propelled drilling device which can autonomously drill deep holes while moving into the ground, in order to eliminate the need for the conventional type of drill-string drilling rig used in conventional deep drilling operations. The device is particularly desired for use in autonomous deep drilling applications such as for probes on extraterrestrial bodies, as well as for applications on Earth.
In the prior art, there have been many types of drill platforms that are erected at the site of drilling and use a large number of drill strings (tubes) that are strung one after another to drill down deep into the soil or rock. This approach requires a substantial amount of mass and volume as well as power to perform deep drilling with a long string of drill tubes into the ground. In all cases where conventional drill rigs are used, a flushing mechanism is also required for the purpose of removing cuttings from the hole as well as for cooling and lubricating the drill bit far down in the hole.
The disadvantages of the prior art are many. The conventional drill platform requires a great deal of mass and packaging volume to accomplish its task. Typically, there is a degree of assembly or deployment involved as well as manpower to perform the drilling operations that adds to the overall complexity and therefore risk. They also must employ a flushing system, whether it is air or a liquid of some kind, for the removal of cuttings from the hole as well as for drill bit lubrication and cooling. This type of massive, high power, complex machinery and associated flushing system would be totally unacceptable for use as probes that have to be flown and landed on any extraterrestrial bodies. Moreover, the massive amounts of material that would have to be left behind would be a waste of resources and might contaminate the alien surroundings, thus compromising scientific objectives.
There have been recent proposals to use drilling devices that have autonomous mobility underground using the “inch-worm” type of locomotion in which a forward section drills forward into the ground while a rearward section contracts to the position of the forward section, then the rearward section plants itself in place while the forward section extends itself and drills further ahead. However, in the proposed devices cuttings from the unit are passed back up to the ground station through a vacuum-powered tether or umbilical tube. The tether is also used to supply electric power down to the unit. However, tether management for a subsurface probe that travels to depths below a kilometer may be an insurmountable engineering problem, especially in a planetary exploration setting.
It is therefore a principal object of the present invention to provide an autonomous subsurface drilling device that eliminates the problems posed by tethers or umbilical tubes used for passage of cuttings. It is a particular object of the invention that the autonomous deep drilling device requires only modest support hardware, and that it is configured to be small, robust in mobility, and energy self-sufficient.
In accordance with the present invention, an autonomous subsurface drilling device has spaced-apart forward and rearward “feet” sections that operate using an inchworm method of mobility with a drill head mounted on least the forward section of the device. In the inchworm walking method, the two feet sections alternately move forward by extending their feet radially to provide a secure grip on the borehole. An axial thrust mechanism is located between the two feet sections for the purpose of advancement during walking. The rearward feet section locks onto the borehole while the axial thrust mechanism is extended, thereby pushing the forward feet section and the drill bit set further down the mobility path. In turn, the forward feet section locks onto the borehole wall, while the rearward feet section unlocks from the borehole and moves forward with retraction of the axial thrust mechanism to a position ready for the next step of the inchworm mobility sequence. The device has an on-board depository for cuttings or core samples, so that they do not have to be passed to the surface through management of a tether tube while the device is in operation deep below the surface.
In one preferred embodiment, a pair of forward and rearward drill sections carried respectively on said forward and rearward “feet” sections for drilling into material in the borehole in both forward and rearward directions, whereby the device can maneuver in any direction underground. A science instrument section is provided to take samples from the borehole radially from the main axis of the device.
In another preferred embodiment, a front drill section has a drill head for cutting into the borehole and conveying cuttings through a center spine tube along the main axis of the device to an on-board depository for collecting the cuttings, so that cuttings do not have to be passed to the surface while the device is in operation deep below the surface. The feet sections of the device employ a foot scroll drive unit which spins about the longitudinal axis of the device in order to extend and provide radial thrust to the feet for gripping the borehole wall as well as providing coaxial alignment of the mechanism to the borehole. The axial thrust mechanism has a tandem set of thrusters in which the second thruster is used to provide the thrust needed for drilling, but not walking. The drilling thruster allows both feet sections to be locked onto the borehole wall while the drilling thruster is extended. Further, the forward feet section is placed as close to the drill head as possible so that a high level of drilling stiffness is insured.
In the latter preferred embodiment, the center spine tube is a main structural component of the device to which all elements of the drill are either directly fixed or on which they are supported through linear bushings. The drilling thruster, both drill bit motor drive plates and the cutting depository are directly attached to the spine whereas all other components are held to the spine via linear bushings. A dual system of drill bits is provided in which a small-diameter drill bit is fixed to an auger that is almost as long as the overall system and resides along the center axis of the system. A second, larger-diameter drill bit has a hole through the center in which the smaller drill bit is concentrically positioned. The larger drill bit has fluting along its outer diameter and bottom that is shaped in such a way so as to direct the cuttings to the center of the bit, and the smaller drill bit has a long fluted shaft shaped to convey the cuttings along the fluting through the center spine tube to the rear of the device where the cutting depository is located. The cuttings are then stored into the depository's interior volume without requiring external cutting removal. A steering mechanism composed of concentric inner and outer eccentric rings may be provided with the forward feet section to allow small corrections to the drilling direction as drilling commences.
Other objects, features, and advantages of the present invention will be explained in the following detailed description of the invention having reference to the appended drawings.
a shows a rendering of an autonomous subsurface drilling device in accordance with the present invention having an on-board power source and forward and rearward drill tips.
b is a schematic sectional view of the embodiment of the autonomous subsurface drilling device of
c is a schematic sectional view of another variation of the autonomous subsurface drilling device having large “snowshoes” for travel through soft material.
d is a perspective view of another embodiment of the autonomous subsurface drilling device using a power cable connected to an external power source.
a and 3b illustrate a radial sample acquisition sequence of the autonomous subsurface drilling device.
a and 9b illustrate a steering system for steering the autonomous subsurface drilling device in alignment with a desired direction for the borehole.
a and 10b are schematic diagrams showing an opposition configuration compared to a tandem configuration for the eccentric ring components of the steering system.
Referring to
In
c illustrates a variation the autonomous subsurface drilling device having large “snowshoes” 10b for travel through soft material. The science payload section 20′ may also be made larger.
In
The inchworm method of walking is independent of gravity and allows for the device to drill back up to the surface if necessary. Should the borehole wall be composed of very soft or unconsolidated material, the feet of the device can be made large like a “snowshoe” for stability.
a and 3b illustrate a radial sample acquisition sequence of the autonomous subsurface drilling device. The minicorer sample acquisition system 21 is situated in the device between the forward and rearward feet sections and can take a sample from the borehole walls at points along the extension length of the thrust mechanism. The coring tip extends radially from the device and retrieves a sample core into the device housing. An oven that supports a Gas Chromatograph Mass Spectrometer investigation may also be provided. Other science tools may be positioned in the science instrument section, such as an optical window 22 in the device wall and a microscope 22a. The optical microscope may used to allow for direct view of the borehole walls or drill cuttings thereby eliminating the need for complicated sample manipulation.
The concentric drill bits within the device operate as follows. The small diameter, center drill bit 64 is fixed to an auger shaft that is almost as long as the whole system and resides along the center of the system. The main, larger diameter drill bit 70 has a hole through the center that is the same size as the cutting diameter of the smaller drill bit. The larger drill bit has fluting along its outer diameter and bottom that is shaped in such a way so as to direct the cuttings to the center of the bit rather than toward the outer wall as is typical with all conventional drilling devices. The smaller drill bit with its long fluted shaft is shaped in the conventional way so as to lift the cuttings it generates as well as the cuttings generated by the larger drill bit up along the fluting to the rear of the device where they are stored in the depository bin 63.
Other improvements may be provided in the use of two coaxial drill bits. The drill bits are driven independently of each other, and therefore may be rotated in the same or opposite direction. When rotating in opposite directions, the torque induced on the entire device is reduced by the difference between each drill bits' torque reaction, rather than the sum of each bits' torque reaction. Since the difference in cutting diameters of each of the drill bits is significant, this system allows for the smaller drill bit to rotate at a different (higher) rotational velocity than the larger drill bit, thus minimizing vibration and heat generation which will improve the overall cutting efficiency. The internal fluting in the opening of the main, larger-diameter bit is shaped to convey the cuttings toward the center of the drill where they are collected and conveyed by the fluting on the shaft of the inner drill bit to the depository bin.
The device uses the inchworm method of mobility with the set of drill bits mounted on the front of the device. Referring to
The central spine 61 is the main structural component of the device. All elements of the drill are either directly fixed to the spine or are supported by the spine through linear bushings. The drilling thruster, both drill bit motor drive plates and the bucket are directly attached to the spine whereas all other components are held to the spine via linear bushings. Power can be provided to the device in either of two preferred ways. As shown in
At a point where the depository bin is full of cuttings, the device can walk back up the borehole wall all the way to the surface and up the launch tube until the bin fully extends above the top of the launch tube. At this point, the bin opens and ejects the cuttings along the outside of the launch tube and onto a collecting surface. The length of the launch tube is sufficient to allow for a great deal of cuttings to be ejected and deposited onto the collecting surface without the risk of having the cuttings envelope the launch tube and fall back into the borehole. In the case where a tether is used to provide power to the device, the tether can be used to winch the drill up and down the borehole much more quickly than the device can walk, thereby increasing the overall penetration rate of the system dramatically especially as the depth increases. In the event the device becomes stuck either on its way up or down the borehole, the walking capability of the system can be employed to navigate beyond the stuck region and proceed up or down the hole.
An additional feature that can be used with the system is a steering mechanism that will enable the drill to make small adjustments to the drilling direction in order to insure the drill proceeds along a desired path aligned with the planned drill path or with a chosen reference path such as parallel to the local gravity vector. A preferred embodiment of a steering mechanism is shown in
Other enhancements that may be desirable include the ability to change drill bits while the device is within the launch tube. Various science instruments can be added to the system. For example, a coring device can be embedded within the smaller drill bit and auger for the purpose of collecting core samples at any depth for scientific study. Other science instruments can be located within a designated section of the device that could include temperature sensors, vibration detectors or virtually any kind of detector deemed necessary that can fit within a reasonably small envelope.
In summary, the device of the present invention provides notable advantages over the prior art. By using the inchworm mobility method in an autonomous drilling device, the conventional large surface rig and drill strings can be avoided. This saves an enormous amount of mass and volume, especially for extraterrestrial applications. Additionally, once the drill has penetrated into the ground so that at least the forward set of feet are capable of locking onto the borehole wall, no force or torque reaction is imposed on the launch tube or lander. This is a tremendous benefit to the design requirements of the spacecraft. Furthermore, there is no frictional increase as a function of depth with such an approach as the dynamics of drilling do not change with depth. In other words, the drilling characteristics will remain the same at say 100-meter depth as it would at the first meter of depth. This drilling system is also well suited for the addition of on board scientific instrumentation without the need for major changes to the drill design as all needed power and data storage/transmission are already incorporated in the design.
Another improvement feature in the invention is the incorporation of tandem axial thrusters: the first designed for high thrust generation needed for drilling, while the second thruster is designed to provide high speed, low thrust for use in walking. The use of tandem thrusters allows both sets of feet to be locked onto the borehole while the drill head is advanced into the rock. This provides a much more secure grip on the borehole and additional stiffness. Since the forward set of feet can lock onto the borehole while drilling, the steering mechanism allows the drill direction to be corrected while the feet are locked to insure that drilling commences along the desired path. This steering mechanism allows the system to continually monitor the path of the drill and to make small corrections in both direction and magnitude as drilling commences.
Regardless of what depth the device is drilling at, the length for conveying the cuttings into storage is the same, short traverse to the depository bin, thereby reducing the possibility of the transport system clogging or an increase in torque diminution caused by friction between the fluting and cuttings within the confines of the borehole, as would be the conventional case if the cuttings are transported to the surface via fluting in a long tether up the entire depth of the hole. Additionally, the cuttings are transported by fluted contained within the inner diameter of the spine, which is a smooth steel tube rather than a relatively rough rock borehole that will further enhance the ease in which the cuttings are transported.
A variety of scientific instruments can be added to the device with little to no changes required of the drill. As the system already has provisions for power and data, all that would be required for a suite of instrumentation is some additional volume. This can easily be accommodated with a length extension either near the locking feet or in the electronics housing. Because the device has the ability to grip the borehole wall with a great deal of force (hundreds to thousands of pounds), both thermal and seismology sensors would benefit well from the intimate contact that can be made between such foot mounted sensors and the borehole wall. Microscopic imagers can be placed within the body of the device and have a consistent focal distance to the borehole wall because of the way the feet and body are mechanically arranged.
While certain embodiments and improvements have been described above, it is understood that many other modifications and variations thereto may be devised given the above description of the principles of the invention. It is intended that all such modifications and variations be considered as within the spirit and scope of this invention, as defined in the following claims.
This U.S. patent application claims the priority of U.S. Provisional Application No. 60/443,215 filed on Jan. 27, 2003, entitled “Inchworm Deep Drilling System”, with inventors in common herewith.
The subject matter herein was developed in part under a research contract provided by the U.S. Government, National Aeronautics and Space Administration (NASA), Contract No. NAG5-12839. The U.S. Government retains certain rights in the invention.
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| Number | Date | Country | |
|---|---|---|---|
| 60443215 | Jan 2003 | US |
