AU682943B2

AU682943B2 - A vibrational exciter

Info

Publication number: AU682943B2
Application number: AU20043/95A
Authority: AU
Inventors: Alan John Russell
Original assignee: Russell Mineral Equipment Pty Ltd
Current assignee: FLSmidth AS
Priority date: 1994-05-12
Filing date: 1995-05-12
Publication date: 1997-10-23
Anticipated expiration: 2015-05-12
Also published as: AU2004395A

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIF I CATION FOR A STANDARD PATENT

ORIGINAL

.e *00 Name of Applicant: Actual Inventor: RUSSELL MINERAL EQUIPMENT PTY LTD, A.C.N. 010 708 406 ALAN JOHN RUSSELL Address for Service: SHELSTON WATERS Margaret Street SYDNEY NSW 2000 0* Invention Title: "A VIBRATIONAL EXCITER" Details of Associated Provisional Application No. PM5567 dated 12th May, 1994 The following statement is a full description of this invention, including the best method of performing it known to me/us:- _pl 2 The present invention relates to vibrational exciters.

The invention has been developed primarily to apply a linear vibrational mode to a sorting screen or the like. However, it will be appreciated that the invention is not limited to this particular field of use.

The most common principle utilised in linear exciters involves the use of two eccentric masses which are normally rotated in opposite directions, 1800 out of phase. This produces a net accelerating force in one direction only, varying sinusoidally in magnitude.

One known type of exciter comprises two counter ee rotating parallel shafts respectively supporting the 15 eccentric masses and drivingly connected by a pair of intermeshing gears. One of the shafts is driven S.directly by an electric motor whilst the other shaft is driven indirectly via the interconnecting gears. An advantage of this configuration is that the gears positively maintain the eccentric masses In constant synchronisation. However, a major disadvantage is that S" the gears themselves generate an unacceptable level of noise, which is multiplied in the case of machines such as vibrating screens which are commonly installed in large numbers. Further, the vibration can impose shock loads on the gears, resulting in fatigue failure of the teeth.

In a second type of known exciter the shafts are 3 independently rotated by separate electric motors.

This type of exciter relies on a phenomenon known as "phase-locking" to achieve synchronisation. This phenomenon occurs when two independently driven eccentric masses of similar speed achieve and hold synchronisation, without the need for some form of externally imposed synchronisation, such as gears.

Since gears are not required, these exciters are relatively quiet in operation. However, because the eccentric masses are not positively synchronised, by mechanical or other means, they often lose synchronisation, particularly during start up, shut down or with sudden load changes. This can result in violent and uncontrolled vibration which, in addition 15 to generating considerable noise, can cause rapid wear equimen Sor failure in the equipment itself.

It is an object of the present invention to overcome or at least ameliorate at least one of these s. disadvantages of the prior art.

20 Accordingly, the invention provides a vibrational exciter comprising: a pair of eccentric masses mounted for counter rotation on respective shafts; a pair of corresponding drive means associated respectively with the shafts; and synchronisation means adapted to establish a predetermined velocity and phase relationship between the rotating eccentric masses and to allow effectively I- i 4 independent rotation thereof when the predetermined velocity and phase relationship is achieved.

Preferably, the synchronisation means includes a pair of intermeshing gears respectively connected to the shafts.

In a particularly preferred embodiment, the gears are provided with a predetermined degree of backlash, such that mating teeth of the gears do not make contact when the predetermined velocity and phase relationship is achieved under conditions of phase lock.

In other embodiments, the exciter may alternatively include disengagement means adapted selectively to disengage the synchronisation mechanism o oo when the predetermined velocity and phase relationship 15 is achieved.

In such embodiments, the disengagement mechanism may be adapted to displace at least one of the gears along its rotational axis such that the gears are moved axially out of meshing engagement. Alternatively, the 20 disengagement means may be adapted to displace at least o one of the gears in a direction normal to its axis of .i rotation and away from the other gear such that the gears are moved radially out of meshing engagement.

In another such embodiment, the disengagement mechanism may include a clutch selectively operable to allow at least one of the gears to idle with respect to its corresponding shaft. The clutch may be a centrifugal clutch radially interposed between at least 5 one of the gears and its corresponding shaft.

Alternatively, the clutch may be a friction disc clutch interposed between at least one of the gears and its corresponding shaft.

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic plan view of a first embodiment of a vibrational exciter according to the invention; Figure 2 is a sequential series of diagrammatic front views, showing the movement of the eccentric masses used in the vibrational exciter of Figure 1; Figure 3 is a diagrammatic plan view of a second 15 embodiment of the invention; off@ Figure 4 is a diagrammatic plan view of a third embodiment of the invention;

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Figure 5 is a diagrammatic plan view of a fourth do e embodiment of the invention; and

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Figure 6 is a diagrammatic plan view of a fifth embodiment of the invention.

Sb" Referring firstly to Figure 1, the invention provides a vibrational exciter 10 comprising a pair of eccentric masses 12 and 14 mounted for counter rotation on respective shafts 16 and 18. The exciter also includes a corresponding pair of drive means in the form of electric motors 20 and 22 associated respectively with the shafts 16 and 18. The shafts are 6 supported within a housing 24 in spaced apart parallel relationship by bearings 26 and 28. To assist in dynamic balancing complementary pairs of eccentric masses are preferably mounted on opposite ends of the shafts. Synchronising means, in the form of a pair of intermeshing gears 30 and 32, are adapted to establish a predetermined velocity and phase relationship between the rotating eccentric masses 12 and 14, as described in more detail below.

In a prototype gear box built according to the first embodiment of the invention, the following gear parameters were used: number of teeth: 32 module: 15 pressure angle: pitch circle diameter: 320 tIm addendum: oversize face width: 60 mm material: 4140 steel (not hardened) 20 backlash: 4 mm In the first of these gears the key way centre line and tooth centre line are in line 0.15 mm. Measured at the gear PCD this is equivalent "to 0.0541.

In the mating gear, the key way centre line and the centre line gap between gears are aligned within similar tolerances.

Figure 2 shows a sequence of diagrammatic front 7 elevation views of the eccentric masses 12 and 14 which are mounted on shafts 16 and 18 for rotation in opposite directions (as indicated by the arrows) 1800 out of phase. In the upper view, the eccentric masses are horizontally aligned and so produce only horizontal centripetal forces Fx, which cancel each other out.

When the masses are rotated through 450, as shown in the middle view, centripetal forces F are produced in which the horizontal components F x cancel out whilst 10 the vertical components F add together. When ~y rotated through a further 450, as shown in the bottom view, only vertical centripetal forces F are y produced, and again these add together. Thus, it will be appreciated that as the eccentric masses rotate, the S* 15 horizontal components of force F always cancel one o *ex another out whilst the vertical components F add y *together. Accordingly, as the masses rotate, the S"resultant acceleration occurs in the vertical di-ection only, and varies sinusoidally in magnitude, to produce the desired "linear vibration" Referring back to Figure I, the gears 24 and 26 are provided with a predetermined degree of backlash, such that when the predetermined velocity and phase e relationship is achieved and "phase locking" occurs, the mating teeth of the gears do not make contact with one another, or at least the contact pressure is substantially reduced. Consequently, the noise produced by the gears is substantially reduced.

8 However, any disturbance to the synchronisation of the eccentric masses results in the mating teeth of the gears once again coming into contact and imposing sufficient force to mechanically re-establish synchronisation. This is particularly important if load changes occur or during the start-up or shut-down phases, when any minor deviations from synchronisation are immediately corrected by the mating teeth of the gears coming into contact, without allowing the dynamic balance of the system to be disturbed.

Turning now to Figure 3, where like numerals designate like features, there is shown a second embodiment of a vibrational exciter according to the invention. In this embodiment, the exciter includes 15 disengagement means adapted selectively to disengage the synchronisation gears when the predetermined velocity and phase relationship is achieved. The

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disengagement mechanism takes the form of a sliding bearing 34 adapted to displace gear 32 along its S: 20 rotational axis 36 such that the gears are moved axially out of meshing engagement, as shown in phantom.

As before, the disengagement means is activated when the predetermined velocity and phase relationship is achieved and results in the mating teeth of the gear not coming into contact whilst the eccentric masses are synchronised. The sliding bearing 36 is electronically actuated by a control system monitoring the rotational speeds and angular positions of the eccentric masses.

9 A third embodiment of the invention is shown in Figure 4. In this embodiment, the disengagement means takes the form of a retractable hydraulic cylinder 38 or the like which is adapted to displace the gear 32 in a direction normal to the axis of rotation 36 and away from the gear 30 so that the gears are moved radially out of meshing engagement, as shown in phantom. A control system similar to that described in relation to the second embodiment can be used to actuate the hydraulic cylinder when synchronisation has been achieved.

Figure 5 shows a fourth embodiment of a vibrational exciter according to the invention in which the disengagement means is in the form of a clutch. In S S j S 15 this embodiment, driving clutch plate 40 is attached to shaft 18. Driven clutch plate 42 is a clearance fit over shaft 18 and is attached to gear 32. In this way, when the clutch discs are engaged, gear 32 will rotate *.":with shaft 18 and eccentric mass 14. However, when 20 synchronisation is achieved a similar control system to that previously described is used to disengage the .clutch plates and allow gear 32 to idle with respect to shaft 14. In this embodiment, the mating teeth of the gears may still make contact but the noise produced by the gears is lessened because no force is transmitted between the gears.

Figure 6 shows a similar embodiment to that of Figure 5, where the disengagement means is in the form 10 of a centrifugal clutch 44 interposed between gear 32 and shaft 18. Once again, whilst the clutch is engaged, the gear 26 rotates with shaft 18 and eccentric mass 14. When synchronisation is achieved, a control system is used to disengage the clutch allowing gear 32 to idle with respect to the shaft 18.

The exciter according to the invention provides a number of major advantages over prior art devices of this type.

Firstly, the eccentric masses remain positively synchronised during the start-up and shut-down phases of the machine. However, during normal running, the gears do not generate the noise levels previously associated with known gear driven exciters.

15 A second advantage is the exciter does not produce the uncontrolled vibration seen in known devices relying solely on phase-locking for S"synchronisation, particularly during the start-up or shut-down phases. A further advantage arises from the fact that the invention may be retrofitted to existing machines. Thus, the invention represents a commercially significant improvement over the prior art.

e09* Although the invention has been described with reference to specific examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms.

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Claims

2. A vibrational exciter as claimed in claim 1 wherein said synchronisation means includes a pair of intermeshing gears respectively mounted to said shafts.
3. A vibrational exciter as claimed in claim 2 wherein said gears are provided with a predetermined minimum degree of backlash, such that contact between mating teeth of the gears is eliminated or substantially reduced when said predetermined velocity and phase relationship is achieved.
4. A vibrational exciter as claimed in any one of 0**0 the preceding claims, further including disengagement means adapted selectively to disengage said synchronisation means when said predetermined velocity and phase relationship is achieved. A vibrational exciter as claimed in claim 4 wherein said disengagement means are adapted selectively L i i 12 to displace at least one of said gears along its rotational axis such that the gears are moved axially out of meshing engagement.
6. A vibrational exciter as claimed in claim 4 wherein said disengagement means are adapted selectively to displace at least one of the gears in a direction normal to its axis of rotation and away from the other gear such that the gears are moved radially out of meshing engagement.
7. A vibrational exciter as claimed in claim 4 wherein said disengagement means include a clutch selectively operable to allow at least one of said gears to idle with respect to its corresponding shaft.
8. A vibrational exciter as claimed in claim 7 wherein said clutch is a centrifugal clutch radially ••go **interposed between at least one of said gears and the omel corresponding shaft.
9. A vibrational exciter as claimed in claim 7 wherein said clutch is a friction disc clutch interposed between at least one of said gears and its corresponding shaft. A vibrational exciter as claimed in any one of the preceding claims wherein said shafts are disposed in substantially parallel side by side relationship.
11. A vibrational exciter as claimed in any one of the preceding claims, wherein said predetermined velocity and phase relationship, said shafts rotate at substantially equal speeds, in opposite directions, 1800 t L 13 out of phase, to produce linear vibration.
12. A vibrational exciter as claimed in any one of the preceding claims wherein said gears are equal in size.
13. A vibrational exciter as claimed in any one of the preceding claims wherein said gears are contained within a housing.
14. A vibrational exciter as claimed in claim 13 wherein said shafts are supported for rotation on bearings mounted in said housing. A vibrational exciter as claimed in claim 14 wherein at least one pair of ends of said shafts extend external to said housing and said eccentric masses are mounted respectively on said pair of external ends. 15 16. A vibrational exciter as claimed in claim 14 *wherein both pairs of ends of said shafts extend "%too external to said housing and two pairs of said eccentric "masses are respectively mounted on corresponding pairs of said external ends. 20 17. A vibrational exciter as claimed in any one of the preceding claims wherein said drive means associated .,with each of said shafts is an electric motor.
18. A vibrational exciter as claimed in any one of S the preceding claims wherein said eccentric masses are substantially equal in mass and eccentricity.
19. A vibrational exciter substantially as hereinbefore described with reference to the i i 14 accompanying drawings. DATED this 12th day of May 1995 RUSSELL MINERAL EQUIPMENT PTY LTD Attorney: STUART M. SMITH Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS So. 0 00 0 Y ABSTRACT A vibrational exciter (10) comprising a pair of eccentric masses (12,14) mounted for counter rotation on respective shafts (16,18), a pair of corresponding drive means (20,22) disposed respectively to effect rotation of the eccentric masses (12,14) and synchronisation means adapted to establish a predetermined rotational velocity and phase relationship between the eccentric masses (12,14). The synchronisation means allow effectively independent rotation thereof when the predetermined velocity and phase relationship is achieved. 4 499* *9 6*O* 4f .4 6« r* *c i