Apparatus For Establishing A Line In The Same Plane As A Reference Line

Abstract

This disclosure relates to surveying apparatus and, in particular, to the use of a laser beam for producing a subsurface line in the same vertical plane as a reference line so as to establish direction of tunneling.

Parent Case Text

This invention relates to methods and apparatus for establishing a line in the same plane as a reference line and, more particularly, to improvements in the art of surveying. This application is a continuation-in-part of my application Ser. No. 203,358 filed Nov. 30, 1971 now abandoned.

Description

A problem common in several fields of precise surveying is the transfer of a reference direction from one plane to another. This problem is encountered, for example, when interrelated parts of a large machine must be installed on several different levels of a building; when fabrication jigs must be set up for the building of ships and aircraft; in tunneling and mining operations. This problem is probably most acute in mining and tunneling because of the conditions under which the work must be done and the extent of the operations. Tunnels must follow known surface directions and frequently radiate from vertical shafts of comparatively small diameter. Further difficulties arise because techniques used today involve the duplication of the reference line rather than the mere transfer of it, thus introducing errors that vary with the time and equipment available or that simply cannot be entirely overcome.

The surveyor has several techniques available to him for transferring a known horizontal direction down a narrow shaft. One common technique is to stretch a pair of strings across the top of the shaft at right angles to each other, one string in line with the intended direction of the tunnel. A theodolite (a precise angle-measuring instrument) is set up at the foot of the shaft. The operator sights vertically through the theodolite and moves the instrument until the cross-hairs of the theodolite are coincident with the two strings. He then rotates the telescope of the theodolite parallel with the string that runs in the same direction as the tunnel until the telescope is horizontal. The theodolite is then pointing along the axis of the proposed tunnel.

A second solution involves the use of an optical plummet, a device that enables the operator to look vertically upward or downward. This instrument is set up on the floor of the shaft and shifted until it is directly beneath one end of the string that lies along the intended direction of the tunnel. A mark is placed on the floor of the shaft beneath the plummet. This operation is repeated on the opposite side of the shaft. A line connecting these two points, as determined by a transit, for example, lies along the axis of the tunnel.

A third solution involves substituting wires and plumb bobs for the optical lines produced by the plummet. Marks are placed on the shaft floor directly beneath the plumb bobs or a transit is manipulated until it is on line with the two wires. This technique also allows tunnels to be run from shafts at levels other than the floor.

The difficulty with these solutions is that they all result in approximations of the true direction: The width of the string, the oscillations of the wires, the time consumed in making observations that eliminate misadjustments in the instruments, the dependence upon the diameter of the shaft, are all matters that limit effectiveness.

Experiments with laser plummets are appearing in the literature, and azimuths are being measured underground with gyrotheodolites, instruments that seek north with a gyroscope and permit angles to be turned from this direction as a means of establishing azimuth directly. These are very expensive instruments, and the technique of using them is quite slow, for it is simply time-consuming for the instrument to settle on the meridian, regardless of its design.

My device substitutes a laser beam for the stringline across the top of the shaft, for the two vertical lines represented by the plumb lines or the plummet, and the line across the bottom of the shaft reproduced by the transit or theodolite.

Other objects and advantages of my invention will be apparent upon consideration of several embodiments thereof in conjunction with the annexed drawings wherein:

FIG. 1 is a schematic perspective view of a laser beam and one form of apparatus which I have developed for dividing and changing the direction thereof to accomplish some of the objectives of my invention; and

FIG. 2 is also a schematic perspective view of a laser beam and my preferred apparatus for dividing and changing the direction thereof to accomplish the objectives of my invention in the best fashion known to me at this time.

Referring now to FIG. 1 in further detail, a laser beam is projected from a suitable source 10 across the top of a tunnel shaft and on line with the intended direction of the tunnel. An optical assembly 11, consisting, for example, of two 45.degree. beamsplitters 12 and 13, is introduced into this beam. This device 11 is leveled by conventional means and then oriented until its longitudinal axis is coincident with that of the original laser beam. When this occurs, part of the beam is deflected vertically downward 17 and part passes undeflected through the device. At the foot of the shaft the arriving beam is received and redirected upward in an adjacent path 18 to the first device by a second optical device 14, also consisting essentially of two 45.degree. beamsplitters 15 and 16. The lower device 14 is oriented (leveled, revolved about axis 17, and shifted by conventional means) until the remnant of the original beam being sent upward 18 from beamsplitter 16 is collected at the surface by the first device 13 and is in coincidence with the original laser beam. ("Coincidence" may be determined visually, by using lenses to transmit an image through the system, or electronically, by measuring beam intensity, for example.) When coincidence occurs, the longitudinal axis of the lower device is parallel with the original laser beam. That is, the system is auto-collimating.

If provision is made in the lower device to allow the laser beam to escape horizontally, this beam 19 will be parallel with the original beam and will display the direction the tunnel should take.

The principal contribution this device makes to solving the problem of transferring reference lines is that the method is relatively independent of the entrance aperture; that is, the device will operate in shafts of significantly smaller diameter than current methods will permit. A second benefit of this device is that the solution of transferring the original line includes the line itself. Finally, the device transfers azimuth and position simultaneously, since if the position of the upper assembly is known, axis 17, for example, the position of the lower assembly will be known also.

The foregoing embodiment has two limitations, however, which are that:

1. The ascending front beam 18 is not deflected by the upper assembly 11 in a manner corresponding precisely to the rotational movement of the lower assembly. That is, a rotation of the lower assembly about the axis, 17 results in a direct horizontal sweeping motion of the lower horizontal beam, causes, in the upper assembly, a shift in the horizontal beam 20 parallel to the original beam rather than angular to it; and

2. The dependence upon the upper assembly for collimation creates an interdependence between the two assemblies that may cause difficulties in use.

In the preferred embodiment, see FIG. 2, these limitations are obviated by the disclosed construction. In FIG. 2, again there is a laser beam projected from a source 20, but here the upper assembly 21 is comprised of two 45.degree. prisms or front surface mirrors 22 and 23 sloping faces being parallel rather than convergent, as is the case in FIG. 1. The back prism or mirror 22 is so coated that 50 percent of the light striking the coated face is deflectd vertically downward along a path 27 and the remainder of the light is allowed to continue on its original path. The front prism or mirror 23 is fully coated and thus reflects all of this remaining light vertically downward along a path 28.

The lower assembly 24 also consists of two 45-degree prisms or mirrors with the sloping faces slanting in the same direction. The back prism surface 25 is fully coated and so reflects forward all of the light striking it. The front mirror 26 reflects forward the descending beam 28 and transmits the light striking it from the rear reflecting surface 25.

In operation, the reference laser beam will be interrupted by putting the upper assembly 21 into the beam, after suitable leveling and calibration (to assure the parallelism of the reflecting surfaces). Two beams of nearly equal intensity will be reflected vertically downwardly at 27 and 28.

At the foot of the shaft, or at some other suitable point, the second assembly 24 will be introduced such that the back beam 27 strikes the approximate center of the back surface 25. This lower assembly, also leveled and calibrated, is rotated on a normally vertical axis 31 of the back surface 25 until the front descending beam 28 is intercepted by the front surface 26.

Two beams will now be reflected forward, one resulting from the reflection of the descending forward beam 28 off the front surface of mirror 26 and one resulting from the reflection of the back beam 27 off the back surface 25. When the lower assembly 24 is rotated about the vertical axis 31 of the back prism, these two horizontal beams are brought into coincidence and produce the subsurface reference line. When this occurs, the horizontal axes of both the upper and lower prism assemblies will be parallel. The system is auto-collimating as before, with the difference that the process of achieving auto-collimation is accomplished at one point, rather than at two.

The lower assembly 24 may be leveled, in which case the forward beam will be horizontal, or the lower assembly may be tilted about the axis 32 normal to the rotational axis, so that a predetermined grade may be projected. As long as the two lower beams remain in coincidence, they are in the same vertical plane as the reference beam.

Coincidence of the two lower beams may be determined visually, or a suitable sensor may be used to indicate the point at which the coinciding beams reach their maximum intensity.

Claims

What is claimed is:

1. Apparatus for surveying comprising means to establish a horizontal reference laser beam in a desired direction, upper and lower beam reflecting means each comprising two mutually spaced reflecting elements, a first element of said upper means intercepting said beam and directing a portion of it vertically downwardly, one of said elements of said lower means intercepting said vertical beam, and means relatively to adjust the position of the elements of said lower means to cause coincidence of the beam reflected from said one element of said lower means with said reference beam in one of said other elements with said beam between said elements of said lower means in the same plane as said reference beam.

2. Apparatus as claimed in claim 1 in which said other element of said lower means is bodily rotatable about said one element thereof.

3. Apparatus for surveying comprising means to establish a horizontal laser beam reference line in a desired direction, a means for intercepting and dividing this reference line into two beams and for deflecting these resulting beams vertically downward, and an assembly including two reflective elements, one for intercepting each of the two descending beams and means for rotating one of said elements relative to the other to reconstitute the two vertical beams into a single beam in the same vertical plane as the reference line, one of the reflective elements of said assembly projecting a beam substantially coaxial with that between said elements.

4. Apparatus as claimed in claim 3, further comprising means to tilt said assembly to direct the reconstituted single beam at a desired vertical angle to the reference beam but within the same vertical plane.

5. Apparatus for surveying in tunnels comprising means to establish a laser beam reference line in the desired direction of tunneling, a prism assembly for intercepting said reference line beam at the edge of said tunnel shaft and for reflecting a portion of said reference line beam vertically downward while the remainder thereof continues in its original direction, a first prism at the foot of said tunnel shaft for redirecting said reflected portion approximately in the desired direction of tunneling, a dividing prism for returning a portion of said redirected reflected portion toward the surface while the remainder continues in its said approximate desired direction, a deflecting prism assembly at the surface of the shaft for redirecting the arriving vertical beam along the original laser path, means to orient said first and said dividing prisms to cause said remainder of said redirected reflected beam in the tunnel to assume the same parallel direction as the reference line.