GB2256974A - A vibratory testing machine with an adjustable air gap - Google Patents

Abstract

The machine comprises a vibratory device having a first part in the form of an electromagnet 20 and a second part in the form of an armature 30. The electromagnet 20 is mounted on structure 62 and 65 - 68 which does not transmit vibration to a workpiece S during testing. A spring 23 is provided through which a mean load can be applied to the workpiece S. The electromagnet 20 and armature 30 are spaced apart by a desired distance D to define a gap 34 between them which accommodates vibratory movement of the armature. The gap can be adjusted by means of a rotary adjustment member 62 which moves the supporting structure for the electromagnet. <IMAGE>

Description

A VIBRATORY TESTING MACHINE The invention relates to a vibratory testing machine for testing materials such as metal bars or structural components for ascertaining, for example, fatigue life, modulus of elasticity and the like.

A known type of vibratory testing machine comprises a vibratory device having a first part in the form of vibration inducing means on a supporting structure and a second part through which vibration is transmitted to an object to be tested, and resilient means for applying a mean load to an object to be tested, the first and second parts of the vibratory device being spaced apart by a desired distance to define a gap which accommodates vibratory movement of the second part. Such a vibratory testing machine is hereinafter referred to as a vibratory testing machine of the kind described.

In vibratory testing machines of the kind described, testing is performed at resonance frequencies and the gap between the first and second parts of the vibratory device (normally an electromagnet and an armature respectively) is quite critical to the correct operation of the machine. The second part is normally adjustably mounted to enable the gap to be varied. However, in any given set of tests, it may be necessary to vary the mean load applied by the resilient means and such variation will always cause the aforesaid gap to change Therefore in any one test, the gap may need to be adjusted several times to ensure that it is accurately set for correct operation of the machine.It is not possible to make such adjustments with the machine running and so each time the mean load is varied substantially, it is necessary to stop the machine, make adjustments to correct the gap and then start the machine again.

An object of the present invention is to provide an improved vibratory testing machine of the kind described in which the aforesaid problem involved in adjusting the gap between the first and second parts of the vibratory device are substantially reduced.

According to the invention there is provided a vibratory testing machine of the kind described in which adjustment means is provided to enable the position of the first part of the vibratory device to be adjusted relative to the second part.

As the first part is mounted on the structure and does not transmit vibratory movement, it is possible to make the necessary adjustments without having to stop the machine.

In vibratory testing machines of the kind described, adjustment of the gap normally involves an operator having to climb steps and use special spanners. In the present invention, this can be avoided by providing actuating means for actuating the adjustment means in response to an applied signal.

The actuating means may comprise an electric motor or fluid operable actuator.

In a first embodiment, the adjustment means comprises a rotary adjuster such as a ballscrew arrangement.

In such a case a suitable motor can be provided for rotating, say, a screw of the arrangement in response to said applied signal or other signal.

In a second embodiment, the first part of the vibratory device is supported by bearing means which permits rotation of adjustment means, the latter including a rotary adjustment member. The first part of the vibratory device may include a mounting such as a plate and the bearing means is preferably disposed between the mounting and the rotary adjustment member. Conveniently, the bearing means can comprise a thrust bearing, e.g., of a ball or roller type.

The rotary adjustment member may be mounted on a screw thread which can conveniently be provided on the exterior of a sleeve-like element carried by, for example, the screw threaded shaft which is used in connection with variation of said mean load. The bearing means is preferably concentric with the screw thread. A suitable motor may be provided for operating the adjustment member. In the second embodiment, the bearing means and adjustment means are arranged substantially above a member through which the said screw threaded shaft or other suitable device transmits load to enable the mean load to be varied.

A third embodiment in accordance with the invention is similar to the second embodiment except that the bearing means and adjustment means are arranged substantially beneath a member through which said screw threaded shaft or other suitable device transmits load to enable the mean load to be varied.

Instead of the above options for adjustment, the adjustment means may comprise a fluid operable ram.

A plurality of adjustment means may be provided which are preferably operable simultaneously.

In the second or third embodiment, damping means may be provided to minimise separation of parts of said bearing means during vibratory testing. The damping means may be connected between the aforesaid mounting of the first part of the vibratory device and a further part of the machine, e.g, the part through which said mean load is applied. Preferably the damping is effected by means of a restrictor which controls flow of fluid between compartments on each side of a piston in a cylinder of the damping means.

The aforesaid signal may be derived from a load sensing element on the machine which senses loading applied to the object being tested. Typically, the load sensing element will be a load cell or the like which can conveniently be mounted on a bed of the machine, for example beneath a carrier on which the second part of the vibratory device may be mounted, the object to be tested being positioned between the carrier and the load sensing element.

Variation of the mean load applied by the resilient means will create a deflection of the resilient means and a variation in the gap between the said first and second parts. Preferably a load/deflection relationship of the resilient means is linear and, therefore, a variation in load will relate directly to a variation in the gap.

For a given mean load, the correct gap is initially set. Where, say, there is an increase in the given mean load, the increase in applied mean load will tend to change the gap by an amount corresponding to deflection of the resilient means. However the load sensing element, which senses the increase in load, is preferably arranged to generate a signal related to the increase in load which is used by the adjustment means to maintain the gap at its correct value. Where the given mean load is reduced, the signal, again, can be used to restore the gap to its correct value.

Therefore, even when a change in mean load is applied during running of the machine, the adjustment means can be operated to adjust the gap automatically in response to such a change Preferably a displacement sensing means is provided which senses the amount of movement applied to the adjustment means and provides a signal which is used to terminate adjustment of the gap when it has reached the required value.

Limit means such as one or more switches can be provided to prevent the gap being reduced or increased too far.

Vibratory testing machines in accordance with the invention will now be described by way of example only with reference to the accompanying drawings in which: Fig.1 is a diagrammatic view of a vibratory testing machine of the kind described, Fig.2 is a diagrammatic elevation of a first embodiment of a vibratory testing machine in accordance with the present invention and Figs.3 and 4 are diagrammatic elevations shown partly in cross section of respective second and third embodiments of vibratory testing machines in accordance with the invention.

With reference to Fig.1, the vibratory testing machine of a kind known as a "Vibrophore" comprises a bed 10 on which there is mounted two vertical pillars 12 having their upper ends connected by means of an upper cross beam 13. The upper cross beam supports a screw threaded bar 14 the vertical position of which can be adjusted by means of nuts 15, 16. If desired, a drive motor can be provided for adjustment of the bar 14. The lower end of the bar is connected to a plate 17 mounted on a lower cross beam 18 by means of mounting rods 19. The plate 17 supports an electromagnet 20 having a flat lower face 22.

The lower cross beam 18 carries a spring 23 having flat upper and lower sections 24, 25 respectively.

The flat upper section 24 is rigidly connected to the lower cross beam 18 by the lower ends of connecting bars 19. The cross beam 18 is formed with apertures 18a through which the pillars 12 pass slidably. The flat lower section 25 of the spring 23 is rigidly connected to a screw threaded carrier 26 having a plate 27 fast with its lower end. The carrier 26 carries a mounting plate 28 between adjusting nuts 32. The mounting plate 28 supports mounting legs 29 for an armature 30. The mounting legs 29 pass with clearance through apertures in the lower cross beam 18 and the flat upper and lower sections 24, 25 of spring 23 and are rigidly connected to the mounting plate 28.

The armature 30 has an upper surface 31. The surfaces 22, 31 are spaced by a distance D to define a gap 34 which can be adjusted by means of the adjustment nuts 32.

The electromagnet 20 and armature 30 together constitute the aforesaid vibratory device and form the respective first and second parts thereof.

The plate 27 is arranged above a load cell 33 (or a strain gauged load sensor) on the bed 10 of the machine. A specimen to be tested e.g. a metal bar or structural component generally indicated at S, is connected between the plate 27 and the load cell 33.

In use, the specimen S is placed in position and a mean load is applied to the specimen through the spring 23 by urging the bar 14 upwards or downwards depending upon whether or not a compressive or tensile mean load is to be applied to the specimen.

For correct operation of the machine, the gap 34 needs to be set to a specific value. As the application of the mean load will cause the upper and lower sections 24, 25 of the spring either to move towards each other or away from each other and bearing in mind that the armature 30 is effectively mounted on the lower section 25 of the spring, the distance D between the surfaces 22, 33 defining the gap 34 will vary depending upon the mean load applied. However, as mentioned hereinbefore, the machine will operate correctly only when the gap 34 is set to a specific value and, therefore, once the mean load has been applied, it is necessary to use the adjustment nuts 32 to vary the position of the armature 30 relative to the electromagnet 20 and thereby set the gap.Alternating or pulsating current is then applied to the electromagnet 20 so as to excite the system into resonance via armature 30 and thus test the workpiece S.

During certain tests, it may be necessary to alter the mean load significantly. Whilst it is possible to alter the preload during operation of the machine, it is not possible to alter the gap 34 during operation of the machine as the armature 30 along with the adjustment nuts 32 will be vibrating.

Therefore, to correct the gap 34 after adjustment of the mean load, it is necessary to stop the machine and then adjust the nuts 32. Typically, the nuts 32 are positioned well above head height and an operator has to climb on steps to reach them when setting the gap.

A first embodiment of a machine in accordance with the invention is shown in Fig.2 and parts corresponding to parts shown in Fig.1 carry the same reference numerals and will not be described in detail.

In Fig.2, a supplementary plate 40 is fixed immediately beneath plate 17 and extends outwardly of the plate 17 towards the pillars 12 at right angles or at any other suitable angle to the pillars 12. In the embodiment shown, the supplementary plate 40 has two ballscrew spindles 42 rotatably mounted thereon and drivable by means of respective stepper motors 44. The spindles 42 extend into ballscrew nuts 43 carried by an electromagnet mounting plate 45. The plate 45 slidably receives the connecting bars 19.

A displacement transducer 46 is mounted on the supplementary plate 40 and has a slidable member 46a attached to the mounting plate 45. Two limit switches 47, 47a are provided on the auxiliary plate 40. The limit switches co-operate with the mounting plate 45.

The load cell 33 provides an output signal a control circuit 48 which provide a drive signal for the stepper motors 44 simultaneously and which receives signals from the displacement transducer 46 and the limit switches 47, 47a when operated. The circuit 48 is calibrated at installation so that a nominal distance D can be set initially. The circuit 48 is preferably arranged to send a signal to a visual display 48a which indicates the distance D e.g. in millimetres, or other information.

The load/displacement characteristic of spring 23 will be linear, i.e., the displacement of the flat lower section 25 of the spring 23 will always be proportional to the applied mean load. Therefore, e.g., with the gap 34 set at a nominal distance for zero mean load, a 10t change in the mean load will tend to produce a 10t decrease in distance D. The percentage change in load will be sensed accurately by the load cell 33 and so, once the gap 34 has been set the application of a mean load will be sensed by the load cell 33 which will provide a signal to the circuit 48. As the rate of the spring 23 is known and the circuit 48 calibrated accordingly, the circuit 48 will sense the distance by which the plates 40, 45 should be separated to restore the gap 34.The circuit 48 then sends the simultaneous signals to stepper motors 43 so as to turn the ballscrew spindles 42 in the appropriate direction by the amount required to restore gap 34 to its pre-set nominal value. The displacement transducer provides a feedback signal to the circuit 48 so that when the correct gap is restored the circuit will cease operating the stepper motors.

Once the machine is running and the mean load is changed at a certain point during a test, the change in mean load will be sensed by the load cell which will transmit its signal to the circuit 48 so that appropriate adjustments can be made to restore the gap 34 during the test itself.

If a specimen under say a tensile mean load begins to yield, rapid reduction of gap 34 can occur. The change in mean load at the load cell due to yield will cause the circuit 48 to operate the stepper motors 43 to restore the gap and the speed of the motors is sufficient to prevent interengagement of the faces 22, 31 of the electromagnet and armature respectively.

Instead of using stepper motors, other types of motors could be used.

Limit switches 47, 47a will operate so as to switch off the machine at extremes of travel of the mounting plate 45 to ensure that the gap 34 cannot be increased or decreased excessively.

In Fig.3 a second embodiment in accordance with the invention is illustrated and parts corresponding to parts shown in Figs.1 and 2 carry the same reference numerals and will not be described in detail.

The screw threaded bar 14 has an internally screw threaded sleeve 60 at its lower end where it is connected to the plate 17. The sleeve 60 is suitably locked against rotation on the bar 14. The sleeve 60 is externally screw threaded and has a screw-threaded adjustment member 62 rotatably mounted thereon. The adjustment member 62 is drivably connected to a gear wheel 63 which meshes with a pinion 54 drivable by a stepper motor 55 or other suitable drive device. The adjustment member 62 has an annular flange 64 on which an annular lower race 65 of a thrust bearing 66 is mounted. An upper race 67 carries an annular thrust plate 68 mounted rigidly on rods 69 which pass slidably through the plate 17 and are connected at their lower ends to the electromagnet 20.In that way the plate 68, races 65, 67, bearing 66 and adjustment member 62 form a supporting structure for the electromagnet 20.

To vary the gap 34, the motor 55 rotates the gear wheel 63 so as to turn the adjustment member 62.

Rotation of the adjustment member causes it to move up or down the screw-threaded sleeve 60 dependent on the direction of rotation of gear wheel 63. The thrust bearing 66 carries the weight of the electromagnet 20 via plate 68 so that downward movement of the adjustment member 62 will reduce the gap 34 and upward movement of the adjustment member 62 will increase the gap. The motor 55 is controlled from the circuit 48 as in Fig.2 and a displacement transducer 46 and limit switches 47, 47a will be provided in association with the adjustment member 62 or other suitable part or parts of the machine.

Fig.4 shows a third embodiment in accordance with the invention and is very similar to the embodiment in Fig.3 except that the plate 17 lies above the adjustment components instead of beneath as in Fig.3.

In Fig.4, parts corresponding to parts in Fig.3 carry the same reference numerals and are not described in detail. The flange 64 of adjustment member 62 has teeth 62a formed on its periphery and the gear wheel 63 is not required. The adjustment member 62 is mounted on a screw-threaded stud 70 carried on a mounting plate 71. The mounting plate 71 is fast with the underside of plate 17. The teeth 62a mesh with the pinion 54 driven by motor 55. The gap 34 is varied in the same way as in Fig.3 and the circuit 48, displacement transducer 46 and limit switches 47, 47a will be provided in association with the adjustment member 62 or other suitable part or parts of the machine.

In both Fig.3 and Fig.4 one or more damper cylinders 73 can be provided as shown in broken lines. In Fig.3 the damper cylinder 73 is rigidly connected to the plate 17 and a rod 72 of a damper piston 74 in the cylinder 73 is rigidly connected to the thrust plate 68. The piston 74 divides the cylinder into upper and lower chambers 73a, 73b. The upper and lower chambers 73a, 73b are interconnected through a flow path 75 including a variable flow restrictor 76.

Where two or more damper cylinders 73 are provided, the upper chambers 73a may be interconnected by a first fluid line, the lower chambers 73b may be interconnected by a second fluid line and the first and second fluid lines then interconnected by a single flow path 75 having the variable flow restrictor 76. The flow restrictor 76 is set to give a high impedance during relative movement between the plates 17, 68 at high frequencies, e.g., 60-150Hz, and a low impedance during low speed relative movement, e.g. Smm/minute. In that way, the damper arrangement will help to inhibit separation of the races 65, 66 from the bearings 66 during vibration testing but will offer little resistance to adjustment movement of member 62.

In Fig.4 the damper cylinder 7-3 is connected to the thrust plate 68 and the piston rod 72 is connected to the plate 17. The operation of the damper arrangement in Fig.4 is the same as in Fig.3.

Where two or more damper cylinders, which can be hydraulic or pneumatic, are provided they are preferably spaced apart circumferentially by equal angles, i.e. two damper cylinders will be spaced by 1800.

Claims (23)

1. A vibratory testing machine comprising a vibratory device housing a first part in the form of vibration inducing means on a supporting structure and a second part through which vibration is transmitted to an object to be tested, resilient means for applying a mean load to an object to be tested, the first and second parts of the vibratory device being spaced apart by a desired disance to define a gap which accommodates vibratory movement of the second part, and adjustment means for enabling the position of the first part of the vibratory device to be adjusted relative to the second part.

2. A vibratory testing machine according to Claim 1 in which actuating means is provided for actuating the adjustment means in response to an applied signal.

3. A vibratory testing machine according to Claim 2 in which the actuating means is a motor.

4. A vibratory testing machine according to Claim 1 or 2 in which the adjustment means comprises a rotary adjuster.

5. A vibratory testing machine according to Claim 4 in which the rotary adjuster is a ballscrew arrangement.

6. A vibratory testing machine according to any of Claims 1 to 4 in which the first part of the vibratory device is supported by bearing means which permits rotation of adjustment means, the latter including a rotary adjustment member.

7. A vibratory testing machine according to Claim 6 in which the first part of the vibratory device includes a mounting and the bearing means is disposed between the mounting and the rotary adjustment member.

8. A vibratory testing machine according to Claim 6 or 7 in which the bearing means is a thrust bearing.

9. A vibratory testing machine according to Claim 6, 7 or 8 in which the rotary adjustment member is mounted on a screw thread.

10. A vibratory testing machine according to Claim 9 in which the screw thread is provided on the exterior of a sleeve-like element carried by the screw threaded shaft which is used in connection with variation of said mean load.

11. A vibratory testing machine according to Claim 10 in which the bearing means is concentric with the screw-threaded shaft.

12. A vibratory testing machine according to any of Claims 6 to 11 in which a motor is provided for operating the adjustment member.

13. A vibratory testing machine according to any of Claims 6 to 12 in which the bearing means and adjustment means are arranged substantially above a member through which the said screw threaded shaft or other suitable device transmits load to enable the mean load to be varied.

14. A vibratory testing machine according to any of Claims 6 to 12 in which the bearing means and adjustment means are arranged substantially beneath a member through which said screw threaded shaft or other suitable device transmits load to enable the mean load to be varied.

15. A vibratory testing machine according to Claim 6 or any of Claims 7 to 14 when appendant to Claim 6 in which damping means is provided to minimise separation of parts of said bearing means during vibratory testing.

16. A vibratory testing machine according to Claim 15 when appendant to Claim 7 in which the damping means is connected between the mounting and a further part of the machine.

17. A vibratory testing machine according to Claim 16 in which the said further part is a part through which said mean load is applied.

18. A vibratory testing machine according to Claim 15, 16 or 17, in which the damping is effected by means of a restrictor which controls flow of fluid between compartments of a cylinder on each side of a piston in the cylinder.

19. A vibratory testing machine according to any preceding Claim in which actuating means is provided for actuating the adjustment means in response to an applied signal derived from a sensor on the machine.

20. A vibratory testing machine according to Claim 19 in which the signal is derived from a loading sensing element on the machine which senses loading applied to the object being tested.

21. A vibratory testing machine according to any preceding Claim in which a displacement sensing means is provided which senses the amount of movement applied to the adjustment means and provides a signal which is used to terminate adjustment of the gap when it has reached the required value.

22. A vibratory testing machine according to any preceding Claim in which limit means is provided to prevent the gap being reduced or increased too far.

23. A vibratory testing machine constructed and arranged substantially as described herein with reference to Fig.2, 3 or 4 of the accompanying drawings.