PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Volume 141　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1966

A DEVICE FOR AUTOMATIC COMPUTATION OF VIBRATION AMPLITUDE IN THE STUDY OF THE VIBRATION CHARACTERISTICS OF HAND-HELD IMPACT MACHINES ON ELECTRONIC SIMULATING INSTALLATIONS

A. V. TRIKHANOV, I. G. SMYSHLYAEVA, N. I. SABLIN, V. M. RAZIN

(Presented by the seminar of the Faculty of Automation and Computer Engineering)

Vibration isolation of the operator from a pneumatic hammer is at present problem No. 1 among all the problems connected with the design and operation of these hammers. Therefore, in many scientific-research organizations, higher educational institutions, specialized plants, and production organizations, intensive work is being carried out on 1) developing hammers with reduced vibration, and 2) monitoring the vibration characteristics of hammers during their operation.

This work is being significantly restrained by the lack of proper vibration-measuring instruments. The existing methods for recording and processing measurements of the vibration amplitude of pneumatic (and electromagnetic) hammers are, at best, associated with the use of various kinds of electrical sensors, multiloop oscillographs, and photographic equipment. These methods are not distinguished by high accuracy and require the expenditure of a considerable amount of time and service personnel.

At present, a number of organizations are carrying out work on the creation of special vibration-measuring devices distinguished by the necessary accuracy and high speed of operation.

At the Tomsk Polytechnic Institute, as a result of many years of research on pneumatic hammers of the Tomsk Electromechanical Plant and on electromagnetic hammers developed at the institute, both on experimental stands equipped with various kinds of measuring apparatus and on electronic simulating installations, the idea arose of automating the determination and subsequent processing of measurement results for one of the main vibration indices—the vibration amplitude.

According to the established procedure, the amplitude \(A\) of vibration of the hammer body is determined as the arithmetic mean of the deviations of the body \(x_i'''\) and \(x_i''\) for \(n\) oscillations (Fig. 1).

\[ A=\frac{1}{n}\sum_{i=1}^{n}\frac{x_i'''+x_i''}{2}, \tag{1} \]

where

\[ x_i'''=x_i-x'_{i-1}, \qquad x_i''=x_i-x_i'. \]

With existing instruments it is possible to carry out only measurements of the ordinates \(x_i\) and \(x_i'\), or to record a vibration diagram. In both cases it is then necessary to perform a great many calculations, adding and multiplying the ordinates. The subsequent processing of the diagrams and computation of the results takes a very long time in investigations. Therefore the question of automating the computations naturally arises.

Fig. 1. Vibration diagram of the hammer body.

On the basis of expression (1), an algorithm has been developed for obtaining the average double amplitude of vibration over \(n\) oscillations.

It has the form

\[ A=\frac{1}{n}\left\{\sum_{i=1}^{n}(x_i-x_i')-\frac{x_0'-x_n'}{2}\right\}. \tag{2} \]

The quantities entering into this expression are explained in Fig. 1. The quantity

\[ \frac{x_0'-x_n'}{2} \]

may be neglected, since in the steady-state regime the ordinates \(x_0'\) and \(x_n'\) are either equal or differ by an insignificant amount. Then expression (2) is rewritten in the following form:

\[ A=\frac{1}{n}\sum_{i=1}^{n}(x_i-x_i'). \tag{3} \]

In accordance with (3), it is necessary to measure the ordinates \(x_i\) and \(x_i'\), sum them over \(n\) oscillations with a simultaneous change of sign at \(x_i'\), multiply the sum by \(\frac{1}{n}\), and record the results.

Since the vibration frequency on the electronic analog computer is fractions of a hertz, all the listed functions can be performed with the aid of direct-current devices used in computing technology. However, such a version of the instrument turns out to be too bulky and complex. The most convenient approach proved to be the use of elements of discrete technology, especially since in this case an electronic digital printing voltmeter of the EShTsPV-1 type [1], with some modernization, can be taken as the basis.

The block diagram of the device for computing the vibration amplitude on an electronic analog computer is presented in Fig. 2.

Multiplication of the quantity \(U_x\), corresponding to \(x\) in the hammer, by \(\frac{1}{n}\) is performed by means of a constant-coefficient block in the model. Blocks 1, 3, 4, 2, 5 are included in the EShTsPV. The first three of these blocks are used

are used without change; blocks 2 and 5 are modified, and blocks 6 and 7 are additional.

In accordance with the diagram presented in Fig. 3, the operation of the circuit can be described as follows. The ordinates \(U_x\) and \(U'_x\), which must be measured, correspond to the points at which the derivative crosses zero,

Fig. 2. Block diagram of the automatic vibration-amplitude meter.

\[ \frac{dU_x}{dt}. \]

This quantity is available at the output of one of the blocks of the machine, since it participates in the modeling. From the output of the zero-fixer, which is an asymmetrical trigger, pulses corresponding to the points at which the derivative \(\frac{dU_x}{dt}\) crosses zero (Fig. 3, c) are fed to the starting circuit 4; the signal from this circuit starts time-interval gating block 1 for a time proportional to the value of \(U_x\) at the given point (Fig. 3, d). During the time in which the gating block is open, pulses from frequency generator 3 are fed to reversible decimal counter 2. Thus the number of pulses that have passed to the counter is proportional to the voltage at the point being measured.

The reversible counter, built according to one of the known circuits [2], is used as an arithmetic device that, in the forward direction, sums the pulses arriving at the input and, in the reverse direction, subtracts them (Fig. 3, e). The result obtained after the passage of \(n\) oscillations is read out on the printing attachment 5 of the electronic digital voltmeter. Permission to print is supplied from recalculating circuit 7 at every \(n\)-th pulse from zero-fixer 6.

Fig. 3. Time diagram of the operation of the automatic vibration-amplitude meter:
a) measured voltage curve;
b) derivative of the voltage curve with respect to time;
c) triggering of the trigger at the crossings of the curve through zero;
d) conversion of voltage into the number of pulses;
e) operation of the reversible counter;
f) operation of the printing device.

The device for measurement is switched on by pressing the “start” button, which closes the input circuit of the zero-fixator.

Use of the device for measuring vibration amplitude on electronic analog computers will reduce the time required for processing vibrograms. The principle of this device can be used for testing hammers on test stands and for periodic checking of their vibration characteristics during operation under production conditions.

REFERENCES

1. Electronic digital printing voltmeter—ÉTsPV-1. Technical description and operating instructions.
2. P. I. Pavlenko. Pulse-counting chronometer. Fizmatgiz, 1963.