Dynamometer for Statistical Methods of Load Investigation
Abstract Generated abstract
This paper describes an electrical inductive dynamometer developed for long-duration statistical investigation of slowly varying or low-frequency loads in machine elements under operating conditions. The device, designated ID-50, was designed to measure the reaction force on the stationary sun gear lever of a planetary differential reducer in coal settling centrifuges, using a U-shaped elastic transducer with differential reactive coils powered at 50 Hz and direct recording by a standard self-recording millivolt microammeter. The authors outline the sensor construction, measurement circuit, balancing and range adjustment arrangements, and recording method. Laboratory tests and practical use are reported to indicate good sensitivity, reliability, and operational simplicity, suggesting applicability to broader load investigations of machines and mechanisms.
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DYNAMOMETER FOR STATISTICAL METHODS OF LOAD INVESTIGATION
S. I. SHUBOVICH, E. M. MEDVEDEVSKII
(Presented by the scientific seminar of the Department of Applied Mechanics)
In statistical methods for investigating nonstationary variable loads acting on machine elements or metal structures, it becomes necessary to record forces or moments over a long period of time under operating conditions, sometimes amounting to months and even years. The use of standard strain-gauge devices with recording of the measured quantity by a loop oscillograph during such prolonged tests becomes disadvantageous for reasons of cost and the labor intensity of the tests.
In a number of cases, when loads vary slowly or when it is necessary to investigate the change in the low-frequency component of a variable load, electrical dynamometers with signal recording by a self-recording instrument—for example, a millivolt microammeter that records the current or voltage value in ink on a paper tape continuously for several hours—may be used in long-duration tests. Below is a description of an electrical dynamometer with such recording, developed by the laboratory of the Department of Applied Mechanics of TPI for long-term tests of coal settling centrifuges [1], for the purpose of investigating nonstationary variable loads of a planetary differential reducer, which is one of the most highly stressed units of these machines.
The sun gear of the planetary reducer of a coal centrifuge is usually made stationary and is held by a reaction lever connected to the machine frame; therefore, in order to measure the load (moment) on this gear, it is sufficient to measure the magnitude of the force at the end of the reaction lever. To measure and record this force, an electric inductive dynamometer was developed, given the conventional designation ID-50, with the transducer powered by industrial-frequency current (50 Hz) and with signal recording without intermediate amplification by a standard multipurpose millivolt microammeter of type N-373-2.
The general view of the dynamometer is shown in Fig. 1, and its electrical circuit in Fig. 2.
The dynamometer transducer (Fig. 3) consists of a U-shaped elastic member 1 with eyelets for hinged attachment between the end of the lever of the sun-gear shaft and the centrifuge frame; on one arm of this member two reactive coils with iron cores are rigidly fastened, ...
cores 2, and on the second—the armature 3, closing the magnetic flux of the cores. When the elastic element is deformed under the action of the load being measured, the armature moves between the end faces of the cores, the gaps in the magnetic circuit change and, consequently, the inductive resistances of the coils change. To obtain a linear characteristic—
Fig. 1. General view of the ID-50 dynamometer: 1 — transducer, 2 — power-supply unit, 3 — H-373-2 self-recording millivolt-microammeter.
Fig. 2. Electrical circuit of the dynamometer.
of the output signal of the transducer, the stiffness of the elastic element is selected so that, within the range of the loads being measured, the change in the gaps does not exceed $\pm 20$ microns with an initial gap of $0.15$ mm.
The reactive coils are connected (Fig. 2) in a so-called differential circuit, which is more sensitive in terms of current than a bridge circuit [2, 3]. Each of the coils constitutes part of an independent closed circuit with a power source and a rectifier assembled according to a full-wave circuit. A T-shaped filter for removing the carrier frequency and a current meter are connected in the branch common to both circuits. In visual observation of the magnitude of the measured force, a micro-...
an M494 ammeter mounted in the panel of the power-supply unit (Fig. 1), and, for recording, an N-373-2 self-recording instrument. In order to use the entire scale of the meter at small and large loads, the circuit includes a group of additional resistances and a switch for changing the range of the measured forces. Balancing of both circuits of the reactive coils before beginning work with the instrument is achieved by means of two wire potentiometers connected into the circuits of one of the loops.
Fig. 3. Dynamometer sensor: 1 — elastic link, 2 — reactive coils, 3 — armature.
Laboratory tests of the ID-50 dynamometer and experience with its practical use have shown its good sensitivity, high reliability, and also simplicity and convenience in operation. These positive properties give grounds to believe that such measuring devices should find wide application in statistical investigations of the loads of machines and mechanisms.
REFERENCES
- Coal centrifugal machine UTsMIVT, maintenance and operating manual, GOSINTI, 1963.
- F. E. Temnikov, R. R. Kharchenko. Electrical Measurements of Nonelectrical Quantities. Gosenergoizdat, 1948.
- D. V. Kozhevnikov. Dynamometers with inductive sensors for measuring cutting forces in turning and drilling. Scientific Reports of Higher Education. Machine Building and Instrument Making, No. 3, 1958.