GB2135063A

GB2135063A - Vibration testing apparatus

Info

Publication number: GB2135063A
Application number: GB08303689A
Authority: GB
Inventors: Robert William Stimpson
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1983-02-10
Filing date: 1983-02-10
Publication date: 1984-08-22
Also published as: GB2135063B; GB8303689D0

Abstract

In vibration testing apparatus for subjecting a testpiece to controlled vibratory motion, movement of a testpiece carrier (10) in the x axis (100) is provided by a ram (15) actuated with respect to a first yoke (11). First yoke (11) is nested in a second yoke (12) which is further nested in a third yoke (14) permitting movement in the y axis (101) and z axis (102) respectively by means of sliding contact between the yokes and fixed guide rods (16, 17 and 18, 19). Actuation of second yoke (12) and first yoke (11) is by means of double acting ram actuators formed in the yokes and cooperating with fixed pistons on the guide rods. The free-standing testing apparatus is capable of providing complex vibration patterns from orthogonal vibration components. Where actuators based on electrorheological fluids are used, high frequency (typically 2 KHz) vibration testing may be performed. <IMAGE>

Description

SPECIFICATION Vibration testing apparatus This invention relates to vibration testing apparatus for subjecting a testpiece to controlled vibratory motion.

It is increasingly important that equipment which is expected to function in a vibration environment is adequately tested for reliable performance during and after vibration. The complex vibratory motion to which for example an electrical circuit board for installation in a high performance aircraft is subjected in use must be reliably duplicated during testing if there is to be a reasonable level of confidence placed on the test results. Simple single axis, or random vibration testing may not be reliable.

Existing methods for multi-axis simultaneous vibratory motion testing can be exceptionally bulky equipment, over 30 m3 in volume, and often of low frequency capability (at best 1 KHz). Where the existing art has used three electrical actuators in three orthogonal axes linked to the test piece carrier, sophisticated means of linkage and actuator control are necessary to ensure accurately reproducible conditions are seen by the test piece carrier.

According to the present invention vibration testing apparatus for subjecting a test piece to controlled vibratory motion includes a test piece carrier, a first yoke constraining relative movement of the carrier to one axis only, the first yoke nested in a second yoke constraining movement of the carrier to prevent relative movement in at least that axis permitted by the first yoke and permit relative movement in at least one further axis, and first and second actuating means acting between the carrier and first yoke and the first yoke and second yoke respectively to provide independently controllable vibration components in the permitted axes.

Preferably the second yoke permits relative movement in one axis only and is nested in a further yoke permitting movement in a further axis only. In a preferred form of the present invention nested first, second and third yokes, permit relative movemept in three orthogonal axes. The yokes are nested in that movement in a first axis is achieved by relative movement of the carrier with respect to the first yoke, movement in a second axis is achieved by relative movement of the first yoke with respect to the second yoke, and movement in a third axis by relative movement of the second yoke with respect to the third yoke. It will be appreciated that complex vibration patterns may be achieved by control of the vibration components for each yoke.

Preferably relative movement between first yoke and second yoke is by sliding contact between the first yoke and a guide means secured to the second yoke. Movement may be ram actuated. Preferably the actuator comprises a double acting ram formed between a piston on a cylindrical guide rod and a cylinder formed in the first yoke. As the guide rod is fixed with respect to the second yoke, actuation gives rise to cylinder movement, and hence movement in the permitted axis of the first yoke. Actuation between a second and third yoke may be similarly achieved.

It will be appreciated that the present invention permits axial actuation to occur in close proximity to the test piece carrier, and that actuation is guided as to have effect in one axis only. By resting actuators in yokes, three orthogonal axial actuators can control the test piece carrier without mechanical linkage errors. The resulting system is also compact when compared with existing art.

Actuation may be hydraulic or alternatively pneumatic. Where a high frequency vibration is required an electro-rheological fluid actuator may be advantageously employed.

In order that features and advantages of the present invention may be appreciated an embodiment will now be described with reference to the accompanying diagrammatic drawings of which: Figure 1 represents three axis vibration test apparatus, and Figure 2 shows detail of the actuating means.

In vibration testing apparatus (Fig. 1 ) a test piece carrier 10 is supported through the agency of nested yokes 11, 12, 14. The carrier is in the form of a table, intended for use laying horizontally. Carrier 10 is mounted on a cylindrical ram 1 5 relative movement of which is constrained to the vertical axis only by first yoke 11. If cartesian axes (x,y,z) are defined, the relative movement may be thought of as constrained to the x axis 100.

Relative movement of the first yoke is constrained to the horizontal y axis 101 only by second yoke 12, which carries guide rods 16, 1 7 which cooperate with bores in the first yoke 11. Sliding contact between rods 16, 1 7 and the bores permits relative movement in the y axis. Second yoke 1 2 is itself nested in third yoke 14, which carries guide rods 18, 1 9 and similarly cooperates with bores in the second yoke 1 2 to permit relative movement in the z horizontal axis 102 only and prevent relative motion in the x and y axes. Third yoke 14 forms a base for the testing apparatus which may be secured to a seismic block or vibration isolating mounts in accordance with conventional testing practice.

It will be appreciated that actuating means provided to establish vibratory motion between the test piece carried 10 and first yoke 1 1, the first yoke 11 and second yoke 12, and second yoke 12 and third yoke 14 may be controlled to subject a test piece to a vibration pattern having components in the x, y and z axes Suitable actuating means will now be described by way of example.

Guide rod 1 7 (Fig. 2) carries a piston 20 which cooperates with a cylinder 21 formed within first yoke 11 to provide a double acting actuator in the y axis. Guide rod 1 7 is fixed with respect to second yoke 1 2 such that ram actuation results in movement of the first yoke 11 (ie the cylinder). The combined effect of piston 20, cylinder 21 and annular seals 22, 23 prevent relative movement in the x and z axes. Actuation is by introduction or exhaust of fluid at actuation ports 24, 25 and may be by conventional hydraulics or pneumatics or by electro-rheological fluids. A similar actuator is formed between guide rod 1 8 and second yoke 1 2 to provide actuation in the axis.

Actuation in the x axis is provided by vertically acting ram 1 5 acting relative to first yoke 11. Since ram actuators of this type are well known in the art the ram assembly will not be described here.

The present embodiment is intended for testing components subjected to small displacement high frequency vibration. With actuators based on electro-rheological fluids a band width of 2 kHz has been achieved.

Electro-rheological techniques are usefully summarized by Brooks in "Electro-Rheological Devices", Chartered Mechanical Engineer, September 1 982. Actuators of the type based on a bridge arrangement are suitable. Such actuators may be accurately controlled by electrical signals, including signals derived from accelerometers giving x, y and z components of vibration measured at an installation site and played back on a suitable machine from magnetic tape.

Claims

CLAIMS The matter for which the applicant seeks protection is:

1. Vibration testing apparatus for subjecting a test piece to controlled vibratory motion including a test piece carrier, a first yoke constraining relative movement of the carrier to one axis only, the first yoke nested in a second yoke constraining movement of the carrier to prevent relative movement in at least that axis permitted by the first yoke and permit relative relative movement in at least one further axis, and first and second actuating means acting between the carrier and the first yoke and the first yoke and second yoke respectively to provide independently controllable vibration components in the permitted axes.

2. Vibration testing apparatus as claimed in claim 1 and wherein the second yoke permits relative movement in one axis only and is nested in a further yoke permitting relative movement in a further axis.

3. Vibration testing apparatus as claimed in claim 2 and wherein three nested yokes permit movement in one of three orthogonal axes.

4. Vibration testing apparatus as claimed in any preceding claim and wherein relative movement between at least two yokes is by sliding contact between one yoke and guide on the other yoke.

5. Vibration testing apparatus as claimed in claim 4 and wherein the actuating means includes a double acting ram formed between a piston on a cylindrical guide rod and a cylinder formed in the nested yoke.

6. Vibration apparatus substantially as herein described with reference to the accompanying drawings.