INITIAL ASSUMPTIONS FOR ELECTRONIC MODELING OF VIBRATION ISOLATION AND DAMPING IN PNEUMATIC HAMMERS

V. I. BABUROV, V. F. GORBUNOV, V. M. RAZIN, I. G. SMYSHLYAEVA
A. V. TRIKHANOV

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

Studies of the isolation and damping of vibration in hand-held impact machines of various purposes, which exert a harmful effect on the worker’s organism, are at present exceptionally important [1]. These studies are carried out experimentally and theoretically. Each of these approaches is characterized by certain assumptions.

In experimental studies, which are conducted on special test stands, the force of pressing on the hammer handle is produced by a pneumatic feed device, the main part of which is a rod with a piston of a definite mass [2], by a spring device [3], and also by a mass together with a spring [4]. Naturally, each feeding device is characterized by specific dynamic properties which, with varying degrees of fidelity and objectivity, imitate the action of a person on the hammer handle. In this regard, contradictory opinions exist in the literature.

In the USSR, pneumatic feed devices with a piston-and-rod weight from 1 kg to 3 kg [2] have become most widespread. It is considered that part of the mass of the worker’s arms participates in the dynamics of the oscillations of the hammer body and therefore affects the results of the experiment. Precise data for taking this influence into account are not known to us.

In the works of the German scholars Scheffler, Diekmann, Schlobach, and others [3, 5], it is proposed to create such mechanical models of a human being as would be characterized by an impedance magnitude from 10 to 30 kg·sec/m; that is, it is asserted that the action of a human being on a hammer is equivalent to the influence of viscous friction.

Sometimes, in experimental studies, the pressing force is applied by hand.

In theoretical studies an even larger number of assumptions is adopted because of the complexity of formulating and solving the nonlinear differential equations that describe the operation of a hammer under real conditions [6]. Owing to substantial assumptions, the results of theoretical and experimental studies in most cases differ sharply from one another. Especially crude are the assumptions concerning the character of variation of the disturbing forces, the physical properties of the medium being processed, the interaction between a human being and the hammer handle, and the motion of all the component parts of the hammer.

Usually, in all theoretical studies it is assumed that the disturbing force varies according to a harmonic law with a fixed axis; the physical properties of the medium being worked are essentially not taken into account at all, since the motion of the striker and the tool is not considered, and the shank of the tool is replaced by a fixed stop; the mass of the operator is assumed to be infinite, which makes it possible to reduce his influence on the hammer to a constant force. In a number of cases friction is not taken into account, and the impact is considered nonelastic.

On the basis of theoretical studies under such assumptions it has been established that, when designing a hammer, the frequencies of the disturbing force cannot be chosen arbitrarily, since one may fall into one of the resonance zones of the subharmonics. The working frequency range must be selected between the resonance peaks. This introduces substantial limitations and complicates the calculation of the vibration parameters of an impact-action machine.

The dependences obtained in these studies are unsuitable for a quantitative evaluation of vibration parameters; they are used chiefly to determine the conditions under which resonance is possible.

The emergence of computer technology has made it possible to conduct theoretical studies connected with the vibration of hand-held impact-action machines at a higher scientific level [7, 8].

It should be noted that at present electronic modeling installations are beginning to be used ever more widely for the study of dynamic systems. Their application is connected with the use of the method of mathematical modeling, which, by general recognition, is a continuation of experiment, but by other means—namely, with the aid of computer technology.

The method of electronic modeling has already found application in the study of the processes of percussive rope drilling, in the study of vibration strikers, in the study of the vibration characteristics of the springs of transport machines, and in the study of internal processes in pneumatic hammers.

We were the first to apply the method of electronic modeling to the study of the isolation and damping of vibration in hand-held impact-action machines; later, similar studies began to be carried out at the Novosibirsk Electrotechnical Institute for electromagnetic hammers, and at the Institute of Mining of the Siberian Branch of the Academy of Sciences of the USSR.

In our previous studies, there was first considered [7] the system “elastic stop—elastic element—handle,” with allowance for viscous friction and with a sinusoidal form of the disturbing force, for a coefficient of restitution of the body velocity equal to unity; then [8] the same system was considered with less stringent assumptions. In particular, the coefficient of restitution of the body velocity during its impacts against a fixed stop was varied within the limits from 0 to 1; the sinusoidal form of the disturbing force had a corresponding displacement of its axis because of the inequality of the forces acting on the hammer body during the working and idle strokes of the striker.

The results of these works revealed only one resonance phenomenon for the body, and it has practically no effect on the smooth motions of the handle.

This is, unquestionably, a new positive fact, making it possible not to fear a reduction in the effect of vibration isolation under unfavorable oscillations of the hammer body. It permits a new approach to the question of calculating the elastic link.

The method of electronic modeling makes it possible to go further along the path of a more complete reflection of all factors affecting the vibration of the housing of a hand-held impact machine, and along the path of investigating other methods of vibration isolation and damping.

Recently, for the purposes of vibration isolation and damping, the following improvements have found practical application in some models of pneumatic hammers, in the course of theoretical investigations:

a) the creation of machine models with vibration-damping devices (elastic handles separated from the hammer housing by springs, pneumatic chambers, etc.);

b) the reduction of vibration from reverse blows of the tool by using various elastic elements installed between the hammer housing and the shank of the tool;

c) the use of tool handles made of elastic materials;

d) the creation of machine models operating with the use of a modified cycle—the “Sudnishnikov cycle.”

Recently many have come to hold the view that the struggle against vibration must be carried out comprehensively, by using various methods.

In this connection, at present the following requirements must be imposed on the electronic model of a hand-held impact machine:

1) the model must take into account the motion of all component parts of the hammer, with all their possible interactions;

2) the model must make it possible to take into account the influence of various causes (interaction of parts, parameters and conditions of use of the hammer) on vibration;

3) the model must be convenient for investigating the effectiveness of various methods of combating vibration, applied both individually and in combination;

4) the model must rapidly, and with sufficient accuracy, record and process the results of investigations.

LITERATURE

1. N. N. Malinskaya. Hygienic assessment of mechanized tools. Mashinostroitel, No. 8, 1963.

2. O. P. Alimov, I. G. Basov, V. F. Gorbunov, D. N. Malikov. Drilling Machines. Gosgortekhizdat, 1960.

3. E. Schlobach. Bestimmung der Leistung von Drucklufthämmern mit dem Einheitsprüfgerät. Glückauf, Nr. 2, 1, 37, S. 29—40.

4. O. Voigt. Kennzeichnung des Rückstoßes von Druckluftherkengen. Glückauf, Nr. 38, 1932, S. 848—850.

5. H. Scheffler. Die Mechanik des Rückstoßes von Druckluft—Schlagwerkzeugen. Glückauf, Nr. 15/16, S. 404—410, 1954.

6. V. I. Kopylov. Some questions of the theory of recoil in impact machines. Candidate’s dissertation, TPI, Tomsk, 1959.

7. V. F. Gorbunov, A. V. Trikhanov. Investigation of the oscillations of a breaker hammer with an elastic handle on an electronic model. Mechanisms and Machines of Impact, Rotary, and Rotary-Impact Action. Interuniversity collection of papers, issue I, Novosibirsk, 1963.

8. V. F. Gorbunov, V. M. Razin, A. V. Trikhanov. Some results of modeling the oscillations of pneumatic hammers with vibration-isolating devices. Proceedings of the conference “Mathematical Methods in Mining,” part I, Publishing House of the Siberian Branch of the Academy of Sciences of the USSR, 1963.