APPLICATION OF ELECTRICAL METHODS TO THE STUDY OF THE WORKING PROCESS OF ELECTROPNEUMATIC IMPACT MACHINES

P. M. ALABUZHEV

Introduction

The theoretical and experimental investigation of the working process of an electropneumatic hammer is covered in works [1—5]. For the purpose of verifying certain previously obtained conclusions and the values of a number of coefficients needed for calculations when selecting the parameters of an electropneumatic drilling hammer, an agreement was concluded, in the form of creative cooperation, between the Tomsk Electromechanical Plant (TEMZ) and the Polytechnic Institute (TPI), according to which the plant manufactured a special experimental installation—a stand for testing electropneumatic rock drills (SIP). On this stand, a TPI team consisting of Associate Professor P. M. Alabuzhev, engineer O. D. Alimov, mechanic K. G. Gyngazov, and senior laboratory assistant I. D. Zolotarev carried out, at TPI, a study of a number of regimes. In the report submitted to the plant, the optimal parameters of the hammer for designing an experimental industrial prototype were indicated. The present article gives a description of the installation for the study of electropneumatic rock drills and sets forth certain questions of further investigations with the use of electrical methods and the corresponding apparatus, which was also made at TPI. The results of the work and a number of separate questions will be set forth in subsequent articles.

Electrical methods for measuring nonelectrical quantities are sufficiently fully covered in the literature [10; 15; 16; 17; 22].

The advantages of electrical methods, in comparison with other methods of measurement, are:

1) simplicity, convenience of observation and readout;
2) ease of selecting the optimal scale of the quantities being observed and recorded;
3) slight influence of the measuring device on the process under study and the possibility of creating inertia-free apparatus, which is especially important in the study of rapidly occurring processes;
4) the possibility of transmitting and observing the processes under study at some distance from the object of study;
5) the possibility of simultaneously observing and recording not only the functional relationships of the phenomena of interest, but also their derivatives and integrals.

The application of electrical methods of measurement in internal-combustion engines is shown in works [6; 8; 9; 18]. At present, radio-engineering methods have varied applications in experimental physics [7]. Of especially great importance for observing and recording the studied—

of the processes being studied is possessed by the cathode oscilloscope, as an instrument having a whole series of indisputable advantages (in comparison with other measuring instruments and devices), the chief of which is the convenience of observation in investigating diverse phenomena and processes.

In constructing the oscilloscope we used the literature [14, 19, 20, 21].

Observation and recording of non-electrical processes on the screen of a cathode oscilloscope can be carried out only when there are sensitive instruments—transducers—serving to convert the values of the physical quantities of interest to us into electrical quantities.

The theory of electrical transducers and electroacoustic apparatus is set forth in the literature we used [12; 17; 22; 23].

Of especially great importance is the question of the influence of the selected method of measurement on the results of measurement, i.e., taking into account the influence of various kinds of interference on the accuracy and reliability of the investigation. In this matter we were guided by the directions given in works [10; 11; 13; 14; 17; 20].

Transducers

The literature on the theory of recording instruments and various kinds of converters (including a number of electrical transducers) represents a statement of the further development and deepening of the works of Academician A. N. Krylov [13] and Corresponding Member of the Academy of Sciences of the Ukrainian SSR A. A. Kharkevich [23]. S. I. Kirpatovskii writes: “The initial equations derived by Prof. A. A. Kharkevich are so general that on their basis there can be developed not only the theory of converters, but also a general theory of electrical transducers [12, p. 235]. In the same work it is indicated that, “with the aim of creating a general theory of electrical transducers, as a basis for their classification, comparison, and selection for one or another practical purpose, it is necessary to develop a theory of specific types of transducers on a unified methodological basis” [12, p. 252]. In the cited article the question of comparing and selecting transducers for definite purposes is not touched upon, and it is noted that “this is a fairly extensive question and constitutes an independent topic” [12, p. 252].

A sufficiently complete and convenient classification of transducers is given in the work of N. P. Raevskii [17, p. 10].

Having acquainted ourselves with the electrical methods of measurement and the circuits of existing transducers [8; 16; 17; 22], we chose the capacitive method of measurement for transducers of pressure, torque, and a single impact. Bearing in mind that the advantages of capacitive transducers are their high sensitivity, comparatively small error (on the order of 0.5–1.0%), absence of inertia, and, finally, ease of calibration, which is carried out by a static method.

In the operation of a transducer it is very important, in practical terms (for purposes of comparison and processing of experimental material), to have a linear conversion function of the output quantity \(M\) with respect to the input quantity \(N\) (i.e., to have a linear dependence: \(M = f(N)\).

In the development of circuits for capacitive transducers, three approaches are known: electrostatic circuits, circuits with amplitude modulation of the carrier frequency, and circuits with frequency modulation of the carrier frequency. We used the method of frequency modulation. Along the same lines, somewhat earlier than us, P. V. Aksiutin [6] proceeded, applying the capacitive method for a torque transducer on an engine shaft. The results obtained by us by this method differ somewhat from those indicated in [6] in the circuit and design of the instrument, and also in the fact that P. V. Aksiutin used a loop oscillograph for recording, whereas we followed the path of constructing a cathode oscilloscope with the possibility of simultaneous observation and recording of several processes.

a) Capacitive pressure transducer

Figure 1 shows the schematic circuit of a capacitive transducer, which consists of a high-frequency generator assembled on tube \(L_1\) and circuit \(L_1, C_1\), according to the inductive three-point circuit, and a frequency detector.

The generated frequency (on the order of \(\simeq 5\) MHz) is determined by the parameters of the generator circuit \(L_1, C_1\), is close to the natural frequency of the circuit, and is found from the well-known formula

\[ f=\frac{1}{2\pi\sqrt{L_1C_1}}. \]

The sensitive element—the capacitor \(C_1\)—is formed by the capacitance of the membrane relative to the base of the transducer housing. The distance between the capacitor plates is on the order of \(\simeq 0.05\) mm. A mica spacer is used as the dielectric. When air pressure acts on the membrane (Fig. 3), the distance between the base of the transducer housing and the membrane changes; thereby the capacitance \(C_1\) changes and, as a consequence, so does the generated frequency.

Fig. 1

Inductively coupled to the generator circuit is the frequency-detector circuit \(L_2 C_2\), which, relative to the frequency generated by tube \(L_1\), is detuned in such a way that the point on the abscissa axis corresponding to the generator frequency \(f_0\) (see Fig. 2) lies in the nearly “linear” part of one half of the circuit resonance curve.

Let us assume that the operating point is selected in the middle of the linear part of one half of the resonance curve, which corresponds to the generated frequency \(f_0\); then the permissible change in frequency, while preserving the linear scale, lies within the limits from \(f_m\) to \(f_M\). If the generator frequency varies sinusoidally with amplitude

\[ \Delta f=\frac{f_M-f_m}{2}, \]

then the voltage on the detector circuit will also vary sinusoidally with amplitude

\[ \Delta u=\frac{u_2-u_1}{2} \]

[14, p. 519].

The operating point of the detector circuit is selected by means of the tuning capacitor \(C'_2\), which is the only adjustment element of the transducer during calibration. Since the air pressure in the electropneumatic hammer varies within the range from 0.5 to 12 atm, in order to make full use of the linear part of one half of the resonance curve, the operating point was set at position \(A^1\) (which corresponds to the normal pressure \(P_0 \simeq 1\) atm).

Thus, as follows from the above, the envelope of the high-frequency voltage on the detector circuit corresponds to the change in

the magnitude of the pressure applied to the membrane. The voltage from the circuit \(L_2 C_2\) is detected by the tube \(Л_2\). From the detector output, a voltage proportional to the change in air pressure is fed to the input of the oscillograph. The capacitor \(C_5\) filters out the high-frequency component of the detector current; the direct-current component of the detector current passes through the resistance \(R_3\), which may be placed outside the transducer, into the oscillograph.

Figure labels visible in the diagram: \(U_{k2}\)—high-frequency voltage across the second circuit; \(U_{\max}\), \(U_2\), \(U_1\); a.m.—amplitude modulation of the high-frequency voltage in the second circuit; frequency \(f\), MHz; frequency modulation of the high-frequency oscillations of the first circuit under the action of the change in the measured quantity.

Fig. 2

Figure labels visible in the construction drawing: power supply plug; \(C'_2\); \(L_2\); \(Л_2\); \(Л_1\); \(L_1\); membrane; mica.

Fig. 3

Figure 3 shows the construction of a pressure transducer mounted in a steel cylinder.

The parameters of the electrical circuit are as follows:

\[ R_1 = R_2 = 22\ \text{k}\Omega,\ \sim 0.25\ \text{W};\quad C_2 = C_3 = C_4 = C_5 = 50\ \text{pF}; \]

\[ Л_1 — 995\ (6Ж1С);\quad R_3 = 0.5\ \text{M}\Omega;\quad C_1 = 50\text{–}90\ \text{pF}\ (\text{sensitive element}); \]

\[ Л_2 — Д\text{–}1\text{–}Д\ (\text{miniature diode});\quad C'_2 = 2\text{–}30\ \text{pF}\ (\text{trimmer capacitor}). \]

The sensitivity of the transducer depends 1) on the magnitude of the relative deviation of the generated frequency, determined by the ratio \(-\dfrac{\Delta c_1}{c_1}\), where

\[ c_1 = \frac{\varepsilon \cdot s}{4\pi \cdot x} \]

is the capacitance of a parallel-plate capacitor (\(s\) is the working area of the plates, \(\varepsilon\) is the dielectric constant, \(x\) is the distance between the plates of the capacitor); 2) on the choice of the membrane parameters.

When the force pressing on the membrane is increased, the pin connected to it and the movable plate of the capacitor (Fig. 3) are raised, i.e., increas-

the distance \(x\) increases; in this case the capacitance decreases and, consequently, the frequency increases; conversely, a decrease in the force acting on the membrane is followed by a decrease in frequency and a corresponding change in the voltage in the second circuit.

The magnitude of the membrane deflection—\(y\) (equal to \(\Delta x\))—as a function of the pressure \(p\), radius \(r\), and its thickness \(h\) is determined from the relation:

\[ \frac{y}{h}+0.488\cdot\left(\frac{y}{h}\right)^3 = \frac{3}{16}\cdot\frac{p}{E}\cdot\left(\frac{r}{h}\right)^4\cdot(1-\sigma^2) \qquad (27,\ \text{p. }275). \]

Here \(E\) is the modulus of elasticity of the membrane, and \(\sigma\) is Poisson’s ratio. As is clear from the formula, for one and the same deflection one can select a number of values of

\[ \frac{r}{h}. \]

In our case the problem is more difficult, since an additional load is located at the center of the membrane, and the selection of the optimal values of the membrane material and dimensions was carried out experimentally.

The total error in determining air pressure by the electrical method consists of the errors introduced by:

1) the oscillograph and amplifiers (of the order of \(\simeq 5\%\));
2) errors of the calibration device (\(\simeq 1\%\));
3) errors in processing the curves (with the error in matching curves recorded on different films being of the order of \(1.0\)—\(1.5\%\), and in planimetry \(0.5\%\));
4) the transducer (sensing element) when measuring pressure.

The errors introduced by the transducer are composed mainly of the following:

a) errors introduced into the process under study by the membrane when its parameters are chosen incorrectly; to reduce distortions, it is necessary that the natural frequency of oscillation of the membrane be at least 10 times greater than the frequency of the disturbing force \([13,\ \text{p. }271]\).

According to the theory of elasticity, for a round plate fixed along its contour, the natural frequency is determined by the formula

\[ f_0=\frac{10.2}{r^2}\sqrt{\frac{g\cdot D}{\gamma h}}, \qquad [26,\ \text{p. }171], \]

where \(\gamma\) is the specific weight of the plate (membrane) material;
\(g\) is the acceleration due to gravity;

\[ D=\frac{Eh^3}{12\cdot(1-\sigma^2)} \]

is the flexural rigidity of the plate.

In the transducers manufactured by us, the natural frequency was of the order of

\[ f_0=1400\text{—}1800\ \text{hertz}; \]

with the number of blows per minute \(z=n=1400\), the frequency of the disturbing force was

\[ f_{\mathrm{v}}=\frac{n}{60}=23.4\ \text{hertz}, \]

and therefore the frequency ratio was

\[ \frac{f_0}{f_{\mathrm{v}}}=60\text{—}77. \]

Consequently, the error due to frequency distortions introduced by the membrane may, to a first approximation, be neglected;

b) errors due to parasitic pickups were practically eliminated by using shielded wires. The filaments of the tubes were supplied from storage batteries;

c) indication error arises from vibration and shaking during operation of the impact machine, which, in addition to comparatively

quickly cause the tubes to fail. Therefore we were forced to connect the pressure indicator to the hammer cylinder by means of a rubber hose of length \(l\) and diameter \(d\). In this case the error in determining the pressure is expressed by the formula

\[ \Delta p = \frac{n}{1250000}\cdot \frac{l}{d}\,p_{\max} \qquad [18;\ \text{p. }156] \]

for \(n = 1400\) rpm, \(d = 4\) mm; \(l = 80\) mm and \(p_{\max}=10\ \text{kg/cm}^2\);

\[ \Delta p = 0.22\ \text{kg/cm}^2, \quad \text{i.e., the error } \frac{\Delta p\cdot 100}{p_{\max}} = 2.2\%. \]

Owing to the presence of an additional volume of air in the rubber hose, further pressure oscillations arise, which are superimposed on the principal curve and also introduce distortions (in the form of small teeth on the pressure curve). This error is due to the specific nature of the operation of a percussion machine. It would undoubtedly be desirable to eliminate this error as well, by placing the sensitive element of the transducer in the machine body flush with the cylinder surface, and to mount the electrical part separately.

a) Piston oil pressure gauge b) Mercury manovacuum gauge

Fig. 4. Diagram of the calibration device for pressure transducers.

The arrangement of the calibration device for the pressure transducers is shown in Fig. 4. Gauge pressure above atmospheric was determined by a piston oil pressure gauge, and vacuum by a mercury manovacuum gauge. In Fig. 4a, the ground steel piston 1 enters the channel of the press column 2, filled with oil 4, which is poured into the press through the top 3 and discharged through valve 5. The weight 6 creates the required pressure in the transducer 7, to which power is supplied (\(+6\) and \(+200\) V) from instrument 8. The deflection of the beam at a given load is observed on the screen of oscilloscope 9. Vacuum was obtained (Fig. 4b) in cylinder 10, from which air was pumped out by a pump through valve 12. The pressure both in the cylinder and in the transducer was measured by mercury manometer 13. The correctness of the calibration was checked before and after the experiment. A linear relationship between pressure and beam deflection was obtained up to 7–8 atm (Fig. 5). The error in calibrating the pressure by dead-weight manometers is of the order of 1% and consists mainly of the error in determining the area of rod 1.

To ensure the “linearity” of the calibration curve, it is necessary that the following relations be satisfied:

\[ \frac{dp}{p} = \frac{dx}{x} = -\frac{dc}{c} = \frac{2df}{f}; \]

i.e., so that changes in the distance between the capacitor plates are linearly related to the change in pressure \((p = kx)\); the remaining relations are easily derived from the formulas already written. Indeed, from the formula

\[ c = \frac{\varepsilon S}{4\pi x} \]

it follows that

\[ dc = -\frac{\varepsilon \cdot S \cdot dx}{4\pi \cdot x^{2}}, \]

whence we obtain:

\[ \frac{dc}{c} = -\frac{dx}{x}; \]

from the formula

\[ f = \frac{1}{2\pi\sqrt{Lc}} \]

it follows that

\[ \frac{df}{dc} = -\frac{1}{4\pi \cdot \sqrt{L} \cdot c^{3/2}} = -\frac{f}{2c}, \]

whence we obtain that

\[ \frac{dc}{c} = -\frac{2df}{f}. \]

Fig. 5

In addition, as N. P. Raevskii quite correctly notes [22, p. 23], “the linearity of the sensor readings is facilitated by the use of materials with a high dielectric constant (for example, mica),” and it is also indicated there that experimentally one can select such a ratio between the size of the air gap and the thickness of the mica spacer between the plates that the characteristic of the sensor, within known limits, will be nearly linear. (In our case the mica spacer was of the order of 0.04–0.05 mm.)

The use of capacitive-type sensors for measuring torque and for investigating the phenomenon of impact can be carried out by means of a constructive modification of the capacitive sensing element and a somewhat different arrangement and installation of the entire circuit.

b) Sensor for measuring angular velocity

The angular velocity of a rotating shaft can be measured by various methods. As a result of familiarization with the literature [10; 15; 16; 22; 24] and of our own experiments, we settled on a direct-current generator.

As the angular-velocity sensor we used a rotary transformer of type RU—11. In this case the e.m.f. in the windings was induced by the residual magnetic flux of the machine.

The curve of the dependence \(u = f(n)\) is shown in Fig. 6.

The influence of the commutator and brushes was manifested in the presence of “teeth” on the angular-velocity curve.

Fig. 6

c) Sensor for synchronizing pulses

It consists of a rod on a clamp, which is mounted on the crankshaft (Fig. 7). In telephone coils placed on the poles of a magnet, when the rod passes by them, emf pulses are induced. The synchronizing pulse is fed to the sweep generator of the oscillograph and thereby sets the beginning of the sweep. By turning the clamp, we can fix the beginning of the sweep at any point in terms of the angle of rotation of the crankshaft.

Circuit of the device for synchronizing pulses.
View of the pulses on the oscillograph screen.

Fig. 7

If it is necessary to have marks according to the angle of rotation of the crankshaft at a specified angular interval, this device can be implemented in the form of a gear with teeth arranged at the specified angle.

d) Measurement of angular accelerations

Since the acceleration \(\varepsilon = \dfrac{d\omega}{dt}\), by applying electrical differentiation to the voltage corresponding to the angular velocity \(\omega\), it is possible simultaneously to obtain the acceleration curve of the crankshaft. Electrical methods of integration and differentiation are examined in considerable detail (as applied to the loop oscillograph) by L. G. Shnirman [25], and, as applied to various circuits, are covered in works [7; 8; 14; 16; 17].

We adopted a differentiating circuit consisting of a capacitance and a resistance.

The plots of the dependences $\omega = f(t)$ and $\varepsilon = f_1(t)$ obtained on the oscilloscope screen are shown in Fig. 8. Simultaneous observation of the curves was carried out on the screen of an EO-5 oscilloscope using the electronic commutator, assembled by us on DC amplifiers, described below.

Fig. 8

Oscilloscope

The work being carried out on the study of the operating dynamics of electropneumatic percussion machines led to the need for an instrument that would make it possible to observe simultaneously a whole series of quantities characterizing the operation of the machine. On the basis of the experience already available, it was decided to develop and practically implement our own cathode-ray oscilloscope for the simultaneous observation of four processes.

It was necessary that an oscilloscope intended for the study of comparatively slowly varying processes should satisfy a number of specific features and requirements; the principal ones are the following: 1) the oscilloscope must have DC amplifiers; 2) the duration of the sweep period must be sufficiently large; 3) the possibility of simultaneous recording of several processes under study by photographing both in steady and in unsteady operating regimes of the machine.

At our disposal there was a two-beam tube ($D = 100$ mm), with a sensitivity of 1 mm/V along $x$ and $y$, with green luminescence.

Fig. 9. Block diagram of the oscilloscope

To make possible the simultaneous study of 4 processes, we decided to use electronic commutators that we had tested in previous work with a differentiating circuit. As a result of satisfying the requirements imposed by practice in designing the oscilloscope, we settled on the block diagram shown in Fig. 9. This circuit includes ampli-

...amplifiers along the \(x\)-axis and along the \(y\)-axis, commutators, a sweep unit, a tube unit, and a power-supply unit.

The oscillograph is assembled on a welded frame made of angle iron. For ease of operation and adjustment, the design is based on a block system: the amplifiers with the commutator, operating for each beam, are assembled in a common unit.

To ensure uninterrupted operation of the oscillograph, and also to make it possible to observe two additional processes (if an additional single-beam oscillograph is available), a spare amplifier unit with a commutator is provided. In this case six processes can be studied simultaneously.

Fig. 10

The general view of the EO-5 oscillograph (left), the oscillograph built at TPI (in the middle), and the power-supply unit (right) during calibration of the pressure transducer on an oil press is shown in Fig. 10.

Features of the Circuit

1) In the oscillograph, identical balanced amplifiers are used both for deflection along the \(y\)-axis and for deflection along the \(x\)-axis. For electronic commutation, the connection to the second tube here is made not through a common cathode resistance, as in a number of similar balanced-amplifier circuits, but by means of the voltage drop across the resistance \(R_{g2}\) in the screen-grid circuit (Fig. 11). Such a circuit provides a linear amplitude characteristic over a wide range.

2) The amplifiers are connected to the deflecting plates (see Fig. 12) through a divider consisting of resistances \(R_9\), \(R_{15}\), \(R_7\), and \(R_{16}\). This connection sets the average potential of the deflecting plates equal to ground potential, which ensures the elimination of beam astigmatism at the edges of the tube screen and makes it possible to connect directly to the deflecting plates circuits whose average potential is equal to ground potential, as is usually the case.

The capacitances \(C_7\) and \(C_8\) improve the frequency characteristic of the oscillograph and help reduce pickup from other circuits, since they reduce the resistance of the deflecting-plate circuits relative to ground. The rolloff...

at the lowest frequencies with such a connection scheme does not exceed 5% of the maximum value of the amplification factor.

3) To provide a high input resistance at the amplifier input, a cathode follower is used. The circuit for transition from the cathode follower to the amplifying stage ensures displacement of the beam over wide—

Fig. 11

—limits with small bias voltages. In this case, regardless of the displacement of the curve under investigation, the deflection of the beam (within the limits of the screen) is proportional to the voltage applied to the input.

4) As the switching element of the circuit, a symmetrical multivibrator assembled with tubes \(L_6\) and \(L_7\) is used. Switching is achie—

Fig. 12

is accomplished by alternately locking the amplifier tubes by means of the current of the corresponding multivibrator tubes, flowing through the common cathode resistances of the corresponding amplifier tubes. Such a commutator circuit with cathode coupling practically ensures independent operation of the amplifiers being commutated. One of the main features of this commutation circuit is the use of a common balancing tube \(L_3\) for both amplifiers. Such a commutation circuit is especially expedient when DC amplifiers are used, since, with direct application of voltage to the deflecting plates of the oscillograph, it makes it possible to use a balancing circuit in both channels. The commutator makes it possible to vary the commutation frequencies and thereby to select their optimum value. The available commutation frequencies are as follows: 500 periods/sec; 2000 periods/sec; 5500 periods/sec. The commutators are switched off by removing the filament voltage from the multivibrator tubes, and also from the corresponding amplifier tube. The gain coefficient of this circuit is of the order of 25. The pass band of the oscillograph is up to 100 kc. The upper frequency of the pass band is limited not so much by the amplifiers as by the construction of the two-beam tube, which is not designed for operation at comparatively high frequencies. Capacitors \(C_1\) and \(C_2\) (provided for convenience in working with the oscillograph) protect the input potentiometers from failure in the event that large DC potentials should possibly be applied to them during preparation of the experiment.

Fig. 13-a              Fig. 13-b

For the purposes of the experiment itself, when very slow processes are being investigated, switching is performed directly at the amplifier input; in addition, capacitors \(C_1\) and \(C_2\) make it possible, if necessary, to separate out the AC component of the input voltage supplied to the oscillograph. The dependence of the gain coefficient on the input voltage is shown in Fig. 13a; the frequency characteristic of the amplifier is shown in Fig. 13b.

5) The sweep circuit in the oscillograph is of the usual type. A sawtooth voltage, formed by the discharge of a capacitor through a pentode, is used as the forward-sweep voltage.

The distinctive features of the sweep include the long duration of the swept voltage (the maximum duration is of the order of 6 sec). The comparatively long voltage-sweep durations are due to the very nature of mechanical measurements. The sweep-frequency range is 0.15–500 cps. The oscillograph provides for a single sweep, switched on by toggle switch \(K_7\) (see the general circuit, Fig. 14), which makes it possible to photograph transient processes. If necessary, the circuit can, without special difficulty, be converted to triggered-sweep operation. By using amplifiers along the \(x\)-axis, provision is made for examining a definite portion of the curve on an enlarged time scale (approximately by a factor of 3).

Fig. 14

6) For photographic recording in the oscillograph, provision is made for applying an increased voltage to the accelerating electrodes of the tube by means of a toggle switch. For synchronous photography of the curves from the oscillograph and the displacement curves of the piston and striker (where the optical method is used), a mechanical sweep on a special drum is used as an attachment to the oscillograph; this drum is connected by a synchronous linkage, by means of selsyns (self-synchronous machines), with another drum on which the displacement curves of the striker and piston are photographed.

To turn on the beam at a definite instant of time corresponding to the beginning of photographing the paths of the piston and striker, switch per. 7 is used; it is mechanically connected with the shutter of the instrument photographing the paths of the piston and striker.

The power-supply unit is made with increased power \((N = 0.7\ \text{kW})\) in order to provide supply for any additional attachments, DC amplifiers in the event that sensors with low output voltage are used, and so forth. To supply the existing capacitive sensors, an electronic voltage stabilizer is provided, giving \(+200\ \text{V}\).

With careful selection of parameters and rational choice of the optimum operating conditions of the individual units, the oscillograph operates stably and reliably. The oscillograph that was constructed proved to be a very flexible instrument with broad capabilities.

The oscillograph circuit was developed in April 1951 by senior laboratory assistant I. D. Zolotarev. On individual questions of the circuit we received consultation from Prof. A. B. Sapozhnikov of SFTI, Assoc. Prof. E. I. Fialko of TPI, and engineer P. P. Boltrukevich. On matters of photography from the oscillograph we used consultations by Assoc. Prof. A. I. Zaitsev and Assoc. Prof. A. F. Gorodetsky. We now proceed to a description of the test stand.

Experimental stand for investigating the working process of an electropneumatic rock drill (SIP)

The experimental installation, designed by us jointly with the engineering and technical personnel of the design bureau of TEMZ, was manufactured by TEMZ.

The layout of the installation is shown in Fig. 15a, b. The electric motor, the impact and rotary units of the machine, and also the necessary measuring apparatus are arranged on a steel plate 1, fastened to a manual screw feed 2, which was mounted on a vertical thrust column 3. Movement of the stand forward (feed toward the face) was effected by a load 4 suspended over a pulley 5 on a cable, while withdrawal of the stand from the face was carried out manually by means of screw 7 and nut 8. The rock being broken 9 was placed on foundation 10 and secured by clamping device 11. Pieces of granite, diabase, and marble, weighing from 400 to 1000 kg, were subjected to drilling.

A number of comparative investigations of different operating regimes of the machine with variable parameters were first carried out by impact against a metal rod replacing drill 15 and fastened on another column by a clamp (the frictional forces developed between the rod and the clamp were of the order of 2700 kg).

The layout of the impact unit is analogous to layouts used in forging air-vacuum hammers and in electric jackhammers of the ZERT type and of double action. The stand also permits investigation of other layouts of impact units. The impact unit consists of cylinder 12, in which piston 13 and striker 14 move. The piston is driven by AC electric motor 16, through V-belt transmission 17, crankshaft 18, connecting rod 19, slide 20, and rod 21. When the piston moves from left to right, a vacuum is created in the space between the pist—

...and the striker. As a result of the excess pressure of atmospheric air, the striker begins to move with acceleration after the piston; then, as the piston moves from right to left, the air between the striker and the piston is compressed, as a result of which the striker changes its direction of motion and, at the end of the working stroke, strikes the shank of drill 15, transmitting a large part

Fig. 15-a

Fig. 15-b

of its energy, and, owing to elastic deformation, rebounds with a certain velocity, after which the described normal cycle is repeated again.

The design of the experimental stand made it possible to vary:

1) the length of the piston stroke by changing the radius of the crank;

2) the length of the air cushion by changing the length of rod 21 and the different length of the shank of drill 15, as well as the length of the striker;

3) the weight of the striker (the feed force);

4) the angular velocity of the crank by changing the gear ratio (the variable diameter of the pulley and gears), and the rotational speed of the electric motor; in addition, it was possible to use a direct-current motor;

5) compensation for air leakage from the space between the striker and the piston by changing the size and location of opening 24 in the wall of the cylinder;

6) the number of revolutions of the drill by means of a specially installed direct-current electric motor 25 and a system of gear wheels.

To record the curves characterizing the course of motion of the striker and the piston, through holes 36 were drilled in the walls of the cylinder of hammer 12, into which plugs made of transparent Plexiglas were screwed on threads. On one side of the cylinder of hammer 12 a reflector was attached, with electric lamps installed along the cylinder; on the other side an apparatus for photography was installed. A description of the method of recording the curves by the optical method and of determining the impact energy is given in [4]; 31—the electric revolution counter of electric motor 25 ($E_2$).

The angular velocity was measured by means of a direct-current tachodynamo 32, connected to the crankshaft by coupling 33. For check measurements a class-2 centrifugal tachometer was used. The synchronizing pulse of the angle of rotation was produced by marker 34 rotating in the field of magnet 35, rigidly connected to the crankshaft by coupling 34.

Electrical circuit of the experimental setup

Fig. 16

The air pressure in the hammer cylinder was measured by capacitive-type transducers constructed by us; observations were made on the screen of the cathode oscillograph described above.

Measurement of the active power of the three-phase current consumed by electric motor $E_1$ (16) was carried out with two class-1 wattmeters (a set of small-sized KMP-10 instruments was used).

The electrical circuit of the experimental setup is shown in Fig. 16.

Here $C_1$ and $C_2$ are selsyns (self-synchronous units), making it possible remotely to synchronize the processes observed and recorded on the cathode oscillograph with the photographic recording of the curves of the path of motion of the striker and the piston.

Selsyn $C_1$ is rigidly connected to the shaft of the photographic apparatus, driven by a special direct-current electric motor—$E_3$. Lenses: 0—1 and 0—2, “Jupiter-3.”

As an illustration of the curves photographed from the oscilloscope screen, we present the photographs below: Fig. 17 shows the pressure curves on the two sides of the striker. The upper curve (almost a straight line) covers the back pressure of the air, which, with a sufficient number of openings, is equal to atmospheric pressure; Fig. 18 shows three curves of beam motion: the middle line (2) is the zero reference line, the upper curve (1) shows the change in angular velocity during one revolution under a steady operating regime, and the lower curve (3) corresponds to the air pressure in the hammer cylinder (between the striker and the piston). Two frames correspond to different values of air compensation with the same other machine parameters; Fig. 19 presents six curves recorded simultaneously, using a mechanical sweep with synchronous coupling, for the transient operating regime of the hammer: the first curve (from the top) shows the marks of the synchronizing-pulse sensor;

Fig. 17

Fig. 18

Fig. 19

the second shows the change in angular velocity; the third is the zero reference line on the oscilloscope; the fourth shows the change in air pressure in the hammer cylinder; the fifth curve depicts the piston displacement as a function of time; the lower curve represents the displacement of the striker.

After 5–6 revolutions, under the same experimental conditions, a definite operating regime of the machine is established.

Conclusion

1. Electrical methods, owing to their inherent flexibility and universality, as powerful methods of investigation, are penetrating all fields of science and technology and can be successfully used in studying the working process of various impact-action machines.

2. The apparatus and methodology developed by us can also be used in investigations in related (borderline) areas of technology, such as internal-combustion engines, compressors, pneumatic impact-action machines, etc.

3. The distinguishing features of the apparatus are its lack of inertia and its reliability under laboratory conditions.

The cathode oscillograph that has been built provides for:

a) switching in direct-current amplifiers; b) the possibility of viewing part of the curve on an enlarged scale; c) the possibility of producing an increased voltage during operation when photographing; d) the presence in it of sweeps: ordinary (sawtooth), single-shot, and mechanical, which makes it possible to investigate not only steady-state processes but also transient processes.

1. We do not consider the possibilities of either the oscillograph or the transducers exhausted. On the principle that has been developed, it is proposed to create other types of transducers for direct recording from the oscillograph screen of the striker travel and the piston travel (measurements of impact and torque during drilling, etc.); moreover, it is proposed additionally to make a number of attachments to the oscillograph, such as: differentiating and integrating circuits (with the possibility of double integration and differentiation of slowly varying processes) and an attachment with the possibility of using a tape recorder to record the pressure curve, etc.

In conclusion, we express our deep gratitude to all comrades who, in one form or another, helped in carrying out the work; especially great and appreciable was the work done by engineers O. D. Alimov, M. G. Serbulenko, and I. D. Zolotarev in the design and installation of the stand, in equipping it with measuring apparatus, and also in developing the investigation methodology.

Literature

1. Alabuzhev P. M. Investigation of the working process of an electro-impact hammer with elastic air coupling. Izv. TPI, vol. 61, no. 1, 1947.

2. Alabuzhev P. M. and Yudin I. P. Experimental investigation of an electropneumatic hammer. Trudy ZSFAN, issue 8, 1950.

3. Alabuzhev P. M. Application of the theory of similarity and dimensions to the investigation (modeling) of impact-action machines. Izv. TPI, vol. 73, 1952.

4. Alabuzhev P. M. and Alimov O. D. Determination of striker energy in impact-action machines. Izv. TPI, vol. 76, 1954.

5. Alabuzhev P. M., Medlina E. K., Nevstruyev E. N. On the methodology for investigating electropneumatic hammers. Izv. TPI, vol. 76, 1954.

6. Aksyutin P. V. Investigation of the starting of high-speed diesels by an electrical method. Scientific Notes of the Lvov Polytechnic Institute, issue X, electrotechnical series, no. 6, 1949.

7. Bonch-Bruevich A. M. Application of electron tubes in experimental physics. GITTL, Moscow–Leningrad, 1950.

8. Volchek L. Ya. Electrical methods of measurements in internal-combustion engines. TsNIDI, book 8, Mashgiz, Moscow–Leningrad, 1948.

9. Volchek L. Ya. Investigation of the working process of an internal-combustion pile-driving hammer. TsNIDI, no. 20, Mashgiz, Moscow–Leningrad, 1952.

10. Kobrinisky N. E. Methods and instruments for measuring angular velocities. Academy of Sciences of the USSR, Moscow–Leningrad, 1941.

11. Karandeev K. B. Methods of electrical measurements. Gosenergoizdat, Moscow–Leningrad, 1952.

1. Kirpatovskii S. I. On the theory of electrical transducers. Lviv Polytechnic Institute, Scientific Notes, issue X, Electrical Engineering series, No. 6, 1949.

2. Krylov A. N. On certain differential equations of mathematical physics that have applications in technical questions, 5th ed., GITTL, Moscow–Leningrad, 1950.

3. Krylov A. N. Theoretical foundations of radio engineering. “Morskoi Transport” Publishing House, Moscow–Leningrad, 1951.

4. Pavlov M. P. Technique for measuring speeds and time. Mashgiz, Moscow, 1950.

5. Pfliier P. M. Electrical measurement of mechanical quantities. Mashgiz, Moscow, 1948.

6. Raevskii N. P. Methods for the experimental investigation of mechanical parameters of machines. Academy of Sciences of the USSR, Moscow, 1952.

7. Soroko-Novitskii V. I. Testing of autotractor engines. Mashgiz, Moscow, 1950.

8. Stekolnikov I. S. The electronic oscilloscope. Gosenergoizdat, Moscow, 1949.

9. Handbook of Radio Engineering, under the general editorship of B. A. Smirenin. Gosenergoizdat, Moscow–Leningrad, 1950.

10. The Modern Cathode-Ray Oscilloscope. Collection of articles, parts I and II, Foreign Literature Publishing House, Moscow, 1951.

11. Temnikov F. E. and Kharchenko R. R. Electrical measurements of nonelectrical quantities. Gosenergoizdat, Moscow–Leningrad, 1948.

12. Kharkevich A. A. Theory of electroacoustic apparatus. Svyazizdat, Moscow, 1940.

13. Chistyakov N. I. Electrical aviation instruments. Oborongiz, Moscow, 1950.

14. Shnirman G. L. Electrical methods of integration and differentiation. Proceedings of the Seismological Institute of the Academy of Sciences of the USSR, No. 105, Moscow, 1940.

15. Experimental Methods for Investigating Combustion Processes in Engines. Collection of articles—Chemical Foundations of Engine Operation. Foreign Literature Publishing House, Moscow, 1948.

16. Encyclopedic Reference Book. Mechanical Engineering, vol. 1, book 2, Mashgiz, 1947.