Electricity: measuring and testing – Of geophysical surface or subsurface in situ – For small object detection or location
Patent
1990-02-27
1991-05-07
Snow, Walter E.
Electricity: measuring and testing
Of geophysical surface or subsurface in situ
For small object detection or location
175 45, G01V 308, G01V 310, E21B 2516, E21B 4702
Patent
active
050140086
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the detection of inaccessible objects, and is particularly concerned with the location of underground bodies such as pipes.
It is common practice to extend the use of conventional metallic pipe and cable locators, which detect low frequency electro-magnetic fields, to the location of non-metallic pipes by inserting a transmitting coil into such pipes. The coil may be energised by wires running back to the insertion point or the coil, drive circuitry and battery may be housed in a self contained unit.
GB-2175096A describes arrangements for producing a rotating field that could be used with underground pipe locators or remotely controllable mobile elements, such as soil piercing tools or "moles". The field is that induced in an elongated ferromagnetic element at an acute angle to the axis of rotation of the shaft on which it is mounted, and the exciting coil; energised with A.C. is usually co-axial with the shaft and preferably stationary.
This has a number of disadvantages. For example, the mole or locator body does not necessarily rotate, and indeed must be prevented from doing so for certain remote control systems to operate properly. Therefore a rotary shaft has to be fitted, with the means to drive it. Also, although the ferromagnetic element may be in static balance, once rotating there will in effect be two masses diametrically opposed but at axially spaced positions, thus creating a dynamic imbalance leading to substantial vibration. While this is cured by an elaborate counterbalancing system, the whole apparatus is then complex and expensive, as well as being quite bulky.
GB-2197078A describes a positional information system applicable to moles, where the mole is equipped with a receiver having three coils with mutually perpendicular axes to pick up signals from a corresponding transmitter coil assembly. The transmitter coils are energised in pairs to produce a response at the receiver, which is fed back along an umbilical cable trailing behind the mole. From this, the roll, pitch and yaw of the mole can be determined and, if it is a steerable mole, control signals can be fed back along the cable.
That system also has certain drawbacks. The transmitter is positioned below ground in an access pit, in line with the projected hole to be bored. It has to be accurately set up so that all the coil axes are correctly oriented. This is tricky and time consuming, and it is very vulnerable to being knocked skew, particularly if the pit is used by workmen while boring is in progress. Also, on a long bore, the transmitted signals may be weak and distorted, by anomalies in the ground or buried ferromagnetic objects for example, by the time they reach the reciver, giving an incorrect response. It is not a good system for tracing a travelling probe in existing pipelines, since placement and securing of the transmitter is not always possible in the confined space available, and since pipelines often bend or snake to a degree that, as with long bores with a mole, the signal transmission is unreliable. Moreover, providing signal lines in the trailing cable adds to its bulk and weight, which accentuates the drag as the bore advances.
It is therefore highly desirable to provide a simple, more robust system, avoiding if possible the radiation over long distances of a complex mix of accurately oriented signals towards an inaccessible object such as a pipe locator or mole. At the same time it is important to provide the facility for determining the orientation of the body with reference to a caretesian frame, that is to measure the roll, yaw and pitch of the object. That has particular application to underground boring and tunnelling devices and may constitute part of the location and guidance system for such devices.
According to one aspect of the present invention there is provided a system for detecting the location and orientation of a temporarily inaccessible object, such as a boring mole or a locator unit in an underground pipeline, comprising providing that object with first means for gene
REFERENCES:
patent: 3529682 (1970-09-01), Coyne et al.
Radiodetection Limited
Snow Walter E.
LandOfFree
System for detecting the location and orientation of a temporari does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System for detecting the location and orientation of a temporari, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System for detecting the location and orientation of a temporari will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-941850