New Mine Theodolites TGO and TGS

A. I. Volkov

(Presented by the scientific seminar of the Departments of Mine Surveying and Geodesy)

For surveying mine workings with an inclination angle greater than 50–55°, ordinary theodolites cannot be used, since in this case the limb obscures the sighting object and surveying becomes impossible.

In order to overcome this difficulty and to introduce the theodolite more widely into the practice of mine-surveying work, as early as 1847 it was proposed to supplement the design of an ordinary theodolite with an eccentric telescope [1].

The presence of an eccentric telescope in the set of a mine theodolite fully solves the problem of surveying steeply inclined workings; however, this version of the mine theodolite also has a number of shortcomings, the most significant of which is the impossibility of directly measuring the angles we need, which leads to additional computational operations and requires obligatory repeated measurements for control purposes. All this leads to a sharp increase in the volume of field and office work and quite justifiably causes a negative attitude among practicing mine surveyors toward the theodolite with an eccentric telescope, who insistently demand the creation of another design of mine theodolite, free from the shortcomings indicated above.

As a result of work carried out to meet this practical demand, a special prism attachment was proposed—both in this country and abroad—which is fastened to the objective of the central telescope. Such an optical device makes it possible, with an ordinary central telescope, to sight at an inclination angle from \(+45^\circ\) to \(+90^\circ\) and from \(-45^\circ\) to \(-80^\circ\) [2]. However, this, at first glance, simple solution of the problem of sighting with the central telescope at large inclination angles has in practice still not been implemented; even a satisfactory experimental model of a theodolite with a prism attachment has not yet been created. Experimental and theoretical investigations of this question show that the use of a prism attachment always leads to a reduction in the accuracy of measuring vertical and horizontal angles. The degree of distortion of horizontal angles may vary within wide limits and depends on the accuracy and rigidity with which the prism is fastened to the objective. This circumstance requires that, after each fastening of the prism attachment to the objective, a special verification be performed, which under mine conditions is highly undesirable [3].

The accuracy of measuring a vertical angle with a theodolite fitted with a prism attachment is reduced not only because of the incorrect fastening of the latter to the objective of the telescope, but also because of the measurement procedure.

When a prism attachment is used, the angle of inclination is computed by the formula [2]:

\[ \delta=\frac{1}{2}\,(KP-KЛ\pm180^\circ)\pm\Theta, \tag{1} \]

where \(\Theta\) is the dihedral angle of the prism and is determined as the difference of the vertical angles \(\delta_1\) and \(\delta_2\), measured respectively when sighting a distant point without the prism and with the prism. Thus, from formula (1) it is seen that the error of the angle of inclination measured with the aid of a prism attachment is \(\sqrt{3}\) times greater than the error of an angle measured directly.

The presence of an additional device in the theodolite set—the objective prism—the decrease in the accuracy of measuring vertical and horizontal angles, the need to perform special checks under mine conditions, and sighting by a broken ray are, undoubtedly, negative aspects of this variant of solving the problem indicated above.

The author of [2] recommends using the prism attachment only for surveying secondary steeply dipping workings and at the same time considers it necessary to carry out further investigations in order to clarify the possibility of using an objective prism in precise surveys.

Recently, for surveying secondary steeply dipping workings, it has been proposed to use a theodolite with a reflecting attachment [4]. Tests of this method of surveying steeply dipping workings were carried out with an MT theodolite, and satisfactory results were obtained.

The reflecting attachment is fastened to the vertical supports of the theodolite telescope and is brought outside its limb. The main part of the reflecting attachment is a plane mirror rotating about a horizontal axis, with a micrometric device for determining the angle of inclination of the mirror.

When measuring horizontal and vertical angles, sighting is performed, with one position of the vertical circle, at the image of the traverse points in the mirror. The angle of inclination of the straight line connecting the sighting point with its image in the mirror is computed by the formula:

\[ \gamma=2\beta+\alpha+MO, \tag{2} \]

where
\(\beta\) — angle of inclination of the mirror;
\(\alpha\) — angle of inclination of the theodolite telescope;
\(MO\) — index error.

If it is assumed that all quantities entering expression (2) are measured with the same accuracy, then the angle \(\gamma\) will be determined by this method twice as poorly as in its direct measurement.

This method is original, but it is applicable only to the surveying of secondary workings. Among the shortcomings of the method, its author in [4] includes a certain deterioration of visibility when sighting at the image of a point in the mirror. It should be thought that the application of this method in wet workings will encounter additional difficulties.

In 1952, the staff of the Department of Mine Surveying—A. I. Volkov, B. A. Ponko, and I. G. Savinykh—developed the basic designs of two variants of a new mining theodolite, taking into account the above-mentioned shortcomings of the theodolite with an eccentric telescope.

The main idea of these two variants is the same and consists in making it possible to sight with the theodolite’s central telescope directly through the limb.

The design features of the first variant of the proposed theodolite are as follows:

1. In the casing of the limb, on the objective and eyepiece sides of the telescope, “windows” are cut, closed by doors hinged to the casing of the limb (Fig. 1).

Fig. 1.

1. In the limb, as in its casing, one or two windows are cut, leaving the numbered part of the limb in the form of a narrow strip (Fig. 2). The windows in the limb are cut in the region of the limb divisions close to 90–270°.

2. The width of the windows in the casing of the limb and in the limb itself is determined by the diameter of the objective of the theodolite telescope; in length (in the direction of the radius of the limb), their dimensions should be as large as possible.

3. The theodolite’s alidade should have a design that makes it possible to make full use of the window dimensions when sighting downward. Such an alidade is, for example, the alidade of the TG-1 theodolite.

4. The levels of the horizontal circle should be arranged as they are in the TT-2 theodolite.

5. The dimensions of the telescope should make it possible to transit it through the zenith with both the eyepiece end and the objective end.

6. The telescope should be equipped with a bent eyepiece, allowing convenient sighting upward.

Measurement of horizontal angles in steeply dipping workings with a theodolite of this version is proposed to be carried out by the geodetic method, rather than by the mine-surveying repetition method, beginning measurements at the first and second positions of the telescope with approximately one and the same reading.

The second version of the proposed mining theodolite differs from the first only in the design of the limb. In this version it is proposed to use a limb with spokes (Fig. 3). The dimensions (width and thickness) of the “spokes” and of the graduated ring of the limb must be coordinated with the optical characteristics of the theodolite telescope and must ensure adequate strength of the limb (width 3–4 mm, thickness 4–5 mm).

Fig. 2.

Fig. 3.

1. Limb spokes.
2. Graduated part of the limb.
3. Limb windows.

The use of a limb with verniers makes it possible to measure horizontal angles by any method, regardless of the angle of inclination of the mine workings, including the method widely used in mine-surveying practice. This is an indisputable advantage of this variant of the theodolite.

In 1952–53, in the workshop of the Department of Mine Surveying of the Tomsk Polytechnic Institute, an experimental prototype of the new mining theodolite was made in accordance with the description of the first variant (Fig. 4).

Fig. 4.

The experimental prototype was made on the basis of the TG-1 theodolite, with the telescope of the latter replaced by a telescope of shorter length. In the casing of the limb of the experimental prototype, two windows were cut, each of them 3.6 cm wide and 4.6 cm long, and in the limb itself one window was made,

whose width and length are respectively equal to 3.6 cm. The width of the graduated part of the limb in the region of the window is 0.3 cm.

A prototype of the theodolite with a window in the limb was tested under mine conditions. Its tests showed good results; in particular, it was established that the adopted window dimensions make it possible to sight with this theodolite at an inclination angle of up to 80°.

In 1953, the Ministry of the Coal Industry, to which we had submitted the relevant materials on the first and second variants of the new mining theodolite, instructed the Kharkov Plant of Mine-Surveying Instruments to manufacture prototypes of the new mining theodolite according to our application. In 1956 these instruments were manufactured by the plant and, by order of the Ministry, were transferred for industrial testing to the “Severnaya” mine of the “Kemerovougol” trust.

In all, two theodolites were made, one of them in accordance with the first variant, and the second with the second. Both instruments were made on the basis of the TG-1 theodolite, using the telescope from a small mining theodolite. The theodolite corresponding to the first variant was given by the plant the abbreviated designation TGO—mining theodolite with a window in the limb; the theodolite corresponding to the second variant was given the designation TGS—a mining theodolite having a limb with spokes.

In making the prototypes at the plant, the cutouts in the limb and in the casing, toward the center, were made of smaller dimensions than in the department’s model, as a result of which downward sighting with these theodolites is limited to an inclination angle of 74°. We believe that the plant had no grounds for such a reduction in the downward sighting range, even taking into account certain difficulties connected with converting the TG-1 theodolite into the TGO and TGS theodolites.

Testing of the TGO and TGS prototypes showed that these theodolites are very convenient in operation and have a number of advantages over the theodolite with an eccentric telescope. During the tests it was also established that, of these two theodolites, preference should be given to the TGS theodolite, which in all cases permits the measurement of horizontal angles by the generally accepted method of surveying repetitions, since with this theodolite one can sight downward with the central telescope at any point of the limb.

The TGS theodolite was recommended by the commission that conducted the tests for introduction into production.

Since October 1956 and up to the present time, the prototype of the TGS theodolite has been at the “Severnaya” mine and is being used successfully for surveying steeply dipping workings. Its prolonged use under difficult conditions shows that the spokes reliably ensure the stability of the limb and make the theodolite universal, suitable for surveying horizontal and steeply dipping workings with the accuracy characteristic of theodolites of this class.

The direct measurement of horizontal and vertical angles and the absence of additional attachments are indisputable advantages of this theodolite in comparison with the theodolites considered above.

In 1958 A. F. Dudin [5], who had become acquainted while still a student with the department’s model of the theodolite with a window in the limb, proposed, in order to increase the range of downward sighting with the central telescope through the limb, changing the direction of taper of the axes of the limb and alidade and interchanging these parts. Such design changes in the theodolite make it possible, in the author’s opinion, to increase the inclination angle for sighting with the central telescope to 85–86°.

We believe that such a general redesign of the theodolite is unnecessary, since a sighting limit of \(85^\circ\) is easily attainable while retaining the existing theodolite design.

In conclusion, we would like to think that the TGS theodolite we propose, which solves the problem of sighting at large inclination angles with exceptional simplicity and reliability, will find broad application in practice. Such a theodolite may be either conventional or optical. Angle-measuring instruments for surveying secondary workings should also be manufactured according to this principle.

References

1. Outstanding Figures of Russian Mining Science. P. A. Olyshev. Ugletekhizdat, 1952.
2. S. N. Tyukin. Mine-Surveying Instruments. Ugletekhizdat, 1957.
3. Collected Articles on Mine Surveying, collection XXXV. Gosgortekhizdat, 1960.
4. N. K. Faizulin. Surveying rising workings with a theodolite equipped with a reflecting attachment. Mining Journal, No. 8, 1960.
5. A. F. Dudin. A New Mining Theodolite. Mining Journal, No. 5, 1958.