GB928948A - Improvements in or relating to inspection apparatus - Google Patents

Abstract

928,948. Testing assemblies by acoustic analysis. GLASS DEVELOPMENT Ltd., and D. O. SPROULE. Jan. 11, 1962 [Jan. 12, 1961], No. 1356/61. Class 40 (7). In apparatus for inspecting assemblies to ensure that parts within the assemblies which are required to be movable are free to move and that other parts which should be rigidly secured are in fact so, each assembly is subjected to an acceleration and by means of an electro-acoustic transducer, signals derived from sounds produced within the assembly and resulting from such acceleration are compared with a predetermined programme to determine whether or not the assemblies have been correctly manufactured. The embodiment described is concerned with inspecting an assembly comprising a one-way valve which, as shown in Fig. 1, consists of a body part 10, two threaded inserts 15, and 16, which should be immovably assembled with respect to the body 10 and a ball 20 which should be free to move in the insert 15. Fig. 2 shows the inspection apparatus which comprises a motor-driven cam 31 arranged to deflect downwards and then suddenly release a support member 25 secured to a rigid block 26 by means of a flexible member 27 and on which the assembly 29 to be inspected is clamped by means 28. When member 25 is released by the camstep the elasticity of member 27 causes the assembly 29 to move rapidly in an upward direction until it is suddenly brought to rest by means of a stop 33 and any sounds produced within the assembly by this (negative) acceleration are converted into electrical signals by a barium titanate transducer 30 fitted to member 25. Fig. 3 shows the waveform of such signals as displayed on an oscilloscope 34 (Fig. 2). As shown, no signals are produced during the interval 0 to t 1 , this being the period between the instant of release of member 25 and its arrest by means of stop 33. During this interval any relatively movable parts of the assembly undergo movement from their positions of rest. Since free movement (if present, due to incorrect assembly) of either of the inserts 15, 16 must be less than that of the ball 20, looseness of either or both inserts is indicated by a damped sinusoidal wave commencing at t 1 and freedom of the ball by a similar waveform commencing at t 2 and repeating with diminishing amplitude at periods t 3 , t 4 &c. due to rebounds within the counterbore 18. For the assembly to be acceptable there must be no signals produced in the interval t 1- t 2 (i.e. the inserts 15, 16 must not be loose) and signals must be produced during the intervals t 2 -t 3 , t 3 -t 4 &c. (i.e. the ball 20 must be free to move). Fig. 4 shows an arrangement for automatically controlling acceptance or rejection in accordance with the latter requirements of assemblies tested by the apparatus of Fig. 2. In this arrangement three gates G1, G2, G3 are rendered conducting in turn for the respective intervals t 1 -t 2 , t 2 -t 3 and t 3 -t 4 by the output of respective series-connected monostable multivibrators MV1, MV2, MV3. The triggering of the first multivibrator MV1 is effected by a pulse on line I 2 derived from a break contact associated with member 25 and as the gates open in turn the signals from transducer 30 on line I 1 are fed successively to relays KL1, RL2, RL3. If RL1 responds (indicating looseness of either or both of the inserts 15, 16) a " reject " mechanism is operated which overrides operation of the other relays. If RL1 does not respond and RL2 does respond (ball free) an " accept " mechanism is conditioned and the subsequent response of relay RL3 (ball rebound) is utilized to conform such acceptance. Non response of RL2 and/or RL3 likewise operates the " reject " mechanism. In an alternative arrangement for automatic control of the "accept " and " reject " mechanism (Fig. 5, not shown) the signals from transducer 30 are fed to three frequency filters which pass signals characteristic of the respective conditions " inserts loose," " ball free " and " ball rebound " via individual rectifiers to respective relays corresponding to relays RL1, RL2, RL3 of Fig. 4.