M E C H A N O T R O N I C D Y N A M O M E T E R FOR T E S T I N G ELASTIC ELEMENTS G. S. B e r l i n
and
A. M. R o s t o v t s e v
UDC
531.787
For raising the precision of measuring efforts of elastic elements, it is necessary to increase the stiffness of the dynamometer devices [1]. However, in raising stiffness, the value of deformations required for converting measurement efforts into electrical or some other signals is reduced, thus leading to a reduction in the precision of measurements [2]. One of the possible ways of solving this contradiction, when the measurement error must not exceed 1.5% consists of using highly-sensitive mechanotronic transducers [3]. The circuit of a dynamometer based on a mechanoelectronic device is shown in Fig. 1. This instrument, the mechanotronic dynomometer, consists of the elastic block 1, to which the mechanotron 2 is rigidly fixed. The measttred effort P acts on the dynomometer step 3 and deforms the block 1, The de.formation is transmitted through the diaphragm 4 to the bushing 5 fixed to the pin of the mechanotron 2. The block 1 is rigidly fixed to the left-hand projection of the shaped base 6. The right-hand projection of this base has between it and the block the spacing S, which is 1.3-1.5 times larger than the maximum working sagging of the block. In the case of accidental overloading of the dynomometer device, the block comes to rest on the base left-hand projection, thus preventing any damage to the mechanotron. The absence of friction units, high sensitivity, capacity to withstand overloading, and the small deformations of the elastic element ensure its operation virtually without mechanical hysteresis or lagging, and this provides an advantage for the above mechanotronic dynamometer as compared with similar instruments [4, 5]. For a comparative evaluation of various dynomometers used for testing elastic elements, it is advisable to apply the relationship of the dynamometers' stiffness to the measured efforts' range for a given dynamometer precision. This relationship is known as the effective stiffness I; (1)
I -~ ]/Pm~x,
where j is the dynamometer stiffness, N/ram; Pmax is the maximum measured effort, N. The reciprocal of effective stiffness consists of the dynamometer's working sag V for the maximum measured effort V=
'g
,5
I Pmax -i 1
(2)
TABLE I J[easure-
2 Name of device
Effective[ Working1 Stiffness stiffness sag V, j, N/mm I, ram-1 mm Pmax, N
]ment range
I
Instrument UP- 03 I ,Gastronom" scales Mechanotronic dynamometer
I 6 i0
3 0,2 600
0,5 0,02 I20
1 50 0,0084
Fig. 1 Translated from Izmeritel'naya Tekhnika, No. 1, pp, 44-45, Ianuary, 1972. Original article submitted Iuly
6, 1971. @1972 Consultants Bureau, a division of Plenum Publishing Corporation, 227 West 17th Street, New York, N. Y. 10011. All rights reserved. This article cannot be reproduced ]'or any purpose whatsoever without permission of the publisher. A copy of this article is available from the publisher for $15.00.
70
The effective stiffness I and the working sag V serve to c o m pare the stiffness of various dynamometric instruments with the same measurement precision. Such comparisons are provided in Table 1 for the instrument U P / 0 3 [5], the "Gastronom" scales, which are widely used at present in testing the efforts of elastic elements, and for the above mechanotronic dynamometer.
R~ ~--~* :,5gV(stab)
ij
IS
r~-
+Urns|]p,
[
- - -
#
~ j' ~v . - - + - - -
' S
I U
- }k.-Z i NA-T, 1--o
| T2 ~Z--~--------~ T F - I
[
.
o [ J 4 'J "i~ 5 I l l T - E r a ,
[ -k, ~ E j V~ (stab)
----
L_~_~.._]_-- IT2
-~ - sta R -~6.~V-( b) ~ -z~
~;
~
"=
r~ D, !D~ R'o l - -
Fig. 2
" [
The application of a mechanotron serves to produce an electronic dynamometer with a base measurement error below 1o/cin readings of an electrical measuring instrument's pointer, and not exceeding 2.5% in using an amplifier with a reIay output according to the circuit of Fig. 2. This circuit represents a de bridge with a stabilized supply source connected to one of the bridge diagonals. The reading instrument MI is connected to the other diagonal. The fixed resistors RI and R2 provide the anode loading of the mechanotron tube T 1 type 6MKhlS [3], and the variable resistor Ra is used for zero correction of the measuring circuit. The instrument's relay output, whose signals correspond to the upper and lower boundaries of the tested effort's tolerance field, consists of a balanced dc amplifier using the double triode T2 and the diode (D l - D4) comparison circuit.
The resistors R4 and Rs of the dc amplifier provide the required grid bias, and the resistors Rs and R7 serve as anode loads for the tube T2. The resistor Rs is used for setting the amplifier zero, and the resistor R9 for shunting the reading instrument MI. The double switch S serves to connect the reading instrument to the amplifier output (lower position of the switch), to the mechanotron anodes (middle position), and to disconnect the measuring instrument when the circuit is operating as a controlling device and the reading instrument is not required. The comparison circuit comprise the voltage divider consisting of the polarized relays Pl and P2, and the resistors R10 and Rn with the diodes D 1 and D z connected between them. The stabilized voltages Us1 and Us2 are fed through the resistors Rio and Rlt, and diodes D 2 and D 4. The stabilized voltages which correspond to the maximum and minimum values of the tested effort are compared with the measured voltage Ums tapped off the anodes of the tube T 2 (more precisely from the part which is obtained across the resistors Rio and Rn). If the compared voltage across the resistors Rio and Rn is larger than the stabilized one (Usl or UsB), the diode becomes conducting (D 1 or Ds) and the polarized relay (Pl o r P2) operates thus connecting the actuating or signalling device. It is advisable to use tubes type 6 N3P and 6N15P for the amplifier T 2, The polarized relays Pl and P2 must be of the high-resistance type (for instance, of the RP-7 or RP-5 types with a resistance not lower than 10 kS). The reading instrument MI consists of a microammeter type M-265M or M-266M with a range of the order of 100-200 ~tA. Experimental utilization of a mechanotronic dynamometer in the course of several years has shown its high reliability, simplified considerably the servicing of devices used in testing elastic elements, raised precision, and improved efficiency of testing. LITERATURE 1. 2. 3. 4. 5.
CITED
G . N . Frolov, Precision in Manufacturing Elastic Elements of Instruments [in Russian], Mashinostroenie, Moscow (1966). P . M . Pflier, Electrical Measurements of Mechanical Quantities [in Russian], Mashgiz, Moscow (1948). G . S . Berlin, Izmeritel '. Tekh., No. 9 (1970). K . I . Strizhevskii, Author's Certificate No. 243913, Byull. Izobr., No. 17 (1969). G . N . Frolov, Author's Certificate No. 124182, Byull. Izobr., No. 22 (1959).
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