— BACKGROUND OF THE INVENTION —

This invention relates to vibration apparatus. This invention has particular but not exclusive application to vibratory conveyors, and for illustrative purposes reference will be made to such application.

However, it is to be understood that this invention could be used in other applications, such as feeders, sorters, mixers and the like.

Vibratory conveyors are used in many industries for conveying materials which may be damaged by conventional belt conveyors, and furthermore hygiene can be a problem with flexible belts. Such conveyors may be vibrated'by connecting them to a base through an oscillatory actuator, and most such conveyors are suspended on springs which turn the conveyor into an oscillatory system. The actuator is then operated at or near the resonant frequency of the system to minimise power demand.

While such a conveyor can function satisfactorily, there is no conservation of momentum in such a system, and thus the base is subjected to a vibrating load regime which is equal and opposite to the forces vibrating the conveyor. This can lead to vibration and noise problems in buildings, and unacceptable increases in the cost of supports for such conveyors.

-- DISCUSSION OF THE PRIOR ART —

A partial solution to this problem involves connecting the oscillatory actuator between the conveyor and an equivalent mass, the two being driven in opposite phase by

the actuator. Unfortunately, this results in a virtual doubling of the mass of the conveyor assembly.

A further consideration with conventional vibrating conveyors is their inability to keep the sum of the kinetic energy of the reciprocating masses constant throughout the vibration cycle, and thus it becomes necessary to add energy storage means such as flywheels or springs , with a consequent increase in the mass of the conveyor assembly. The need to operate a spring system at or near its resonant frequency in order to minimise power demand limits the usefulness of spring-supported conveyors to a narrow range of speeds, and makes throughput control difficult.

— SUMMARY OF THE PRESENT INVENTION —

The present invention aims to alleviate the above disadvantages and to provide vibration apparatus which will be reliable and efficient in use. Other objects and advantages of this invention will hereinafter become apparen .

With the foregoing and other objects in view, this invention in one aspect resides broadly in vibration apparatus including:- support means adapted for supporting an article to be subjected to oscillatory motion, said support means being supported for oscillatory movement in a selected direction; counterbalance means supported for oscillatory movement in said selected direction; and actuation means adapted for urging said support means and said counterbalance means in oscillatory motion, the phase and amplitude of said motion of said counterbalance means being selected relative to said motion of said support

means whereby the vector sum of the momenta of the oscillating components may be minimised.

The support means may include any desired support apparatus, such as a mixing vessel or cleaning apparatus. It is preferred, however, that the support apparatus include conveying apparatus whereby articles to be conveyed may be advanced therealong by vibratory motion thereof, or separation apparatus including sizing screens whereby articles may be separated by size differential, or whereby fluid may be separated from solids.

The support means may be supported by any desired support apparatus, such as springs or gas-filled isolators attached to a base, and may include linkages, slides or the like for restraining movement of the support means and the counterbalance means in directions other than the desired direction. Preferably, however, the support apparatus includes support links attached between a base and the support means, and counterbalance links attached between the base and the counterbalance means such that the support means and the counterbalance means may move substantially freely in the desired direction of movement. Suitably, the links are in the form of flat members having minimal thickness in the direction of the vibratory motion such that the support and counterbalance means may move by their deflection in transverse bending, while restraint is offered to motion in undesirable directions. It is preferred that the links be formed from a plastics material of high flexibility, such as NYLON or POLYETHYLENE.

Preferably, the counterbalance means includes a mass or masses which are small relative to the mass of the support means such that the mass of the vibration apparatus may be minimised, and the vector sum is minimised by vibrating the counterbalance means at a greater amplitude than the support means. Of course, if desired, the counterbalance means may

have any desired mass, and the vector sum may be minimised by controlling the amplitude of the counterbalance means relative to the amplitude of the. support means.

The counterbalance means may include a single counterbalance which may be oscillated substantially in opposite phase to the oscillations of the support means. Preferably, however, the counterbalance means includes a first counterbalance mass and a second counterbalance mass arranged for oscillation at respective differing phase angles relative to the support means such that kinetic energy from the oscillation of the support means may be transferred through the actuation means to the counterbalances whereby the requirement for external energy storage may be minimised and preferably the sum of the kinetic energies stored in the respective reciprocating components may remain constant throughout the vibration cycle.

Suitably, the phase angle from the first counterbalance to the support means is equal and opposite to the phase angle from the second counterbalance to the support means. In a preferred embodiment, the first and second counterbalances are substantially equal in mass, and are arranged to oscillate at substantially equal amplitudes. Where the amplitude of each counterbalance is equal to that of the support means, it is preferred that the phase angle be approximately one hundred and twenty degrees. Suitably, where the amplitude of the counterbalance is between one and ten times the amplitude of the support means, it is preferred that the phase angle be between one hundred and twenty degrees and one hundred and thirty-five degrees. In a preferred embodiment, the amplitude of the counterbalances is twice the amplitude of the support means, and the phase angle is approximately one hundred and twenty-six degrees. The mathematical analysis below allows the optimum mass ratio to be calculated for a given amplitude ratio, and the optimum

phase angle to be calculated from the mass ratio and the amplitude ratio.

NOMENCLATURE

M = Mass of support means m- _L = Mass of first counterbalance m ₂ = Mass of second counterbalance w = angular velocity θ = angular displacement ø = phase lead of first counterbalance - ø = phase lead of second counterbalance

S = linear displacement

V = linear velocity of support means v _x = linear velocity of first counterbalance v ₂ = linear velocity of second counterbalance a = linear acceleration

T = torque

F = force

R = support means half amplitude of oscillation r** _. = First counterbalance half amplitude r ₂ = Second counterbalance half amplitude

The mass ratio is defined as m ¹ = M/(m ₁ + m ₂ )

The velocity ratio v ¹ is defined as:

Maximum Velocity of Counterbalance Maximum Velocity of Support Means MOMENTUM EQUATION

Momentum of Support Means = MV

= MRw Sin θ

Total momentum of counterbalances = viR Sin(θ + ø) + Mv*R Sin(θ - ø)

2m ¹ 2m ¹

Mv-t-R 2 Sin θ Cos ø

2m ¹

Total momentum of reciprocating components

M _τ = MRw Sin θ + Mv^-R 2 Sin ΘCos ø 2m ¹

For M _τ = 0,

1 + v ¹ Cos ø = 0 ¹

Cos ø = - m ¹ v-*

ENERGY EQUATION

Kinetic Energy of Support Means = MV ² /2

MR ² w ² Cos ² θ/2

MR ² w ² (Cos 20 + l)/4 Total kinetic energy of counterbalances

= m ₁ v ₁ ² /2 + m ₂ v ₂ ² /2

Mv ¹² R ² w ² (Cos ² (θ + ø) + Cos ² (θ - φ) ) /*___ _{! Mv} i2 _R 2 _W 2 ( _Cos (2Θ + 20) + 1 + Cos (2Θ - 20) + l)/2

4m _x = Mv ¹² R w ² (Cos 2Θ Cos 20 + 1)

Total kinetic energy of reciprocating masses

= MR ² W ² ( COS 2Θ + 1 ) + R2 _W 2 yl 2 ( _os 2Θ Cos 20 + 1 )

4 4m ¹ For total kinetic energy to be independent of θ,

MR ² w ² = - MR ² w ² v ¹² Cos 20 4 4m ¹

- m ¹ = Cos 20

TORQUE CONSIDERATIONS

Torque required to accelerate support means

MR ² w ² Sin 2Θ 2

Torque required to accelerate counterbalances

_Mv i2 _R 2 _W 2 _S i _n 2(θ + ø) + Mvi ² R ² w ² Sin 2(θ - ø)

2m ⁱ ₂ 2m ⁱ

For the total energy of the reciprocating components to be constant throughout the vibration cycle, the sum of the torques applied to accelerate the support means and the counterbalances must equal zero:

- MR w ² Sin 2Θ = Mv R w Sin 2(9 + ø)+ My ⁱ R w ² Sin 2(9 - ø

V

From the momentum equation above, we have

- m ¹ = Cos ø (1) v Manipulation of the torque equation gives

Combining (1) and (2)

This equation is satisfied only if v ¹ = (2mi ² + _m i)o.5 _{or f as} otherwise expressed, mi = ((1 + 8v ² )°- s - i)/4

The actuator means may include any desired actuators, such as hydraulic or pneumatic or electromagnetic, and the actuators may be interconnected in an arrangement which may produce the desired relative motion. It is preferred, however, that the actuator means includes a mechanical linkage including an actuator shaft attached to the base and having a plurality of eccentrics or cranks formed thereon, one said eccentric being connected to each of the support means and the counterbalances by connecting rods or the like. The positioning and throw of each of the eccentrics relative to one another may be arranged to provide the desired amplitude and phase for the vibration of each component.

The connecting rods may be pivoted to the support means and the counterbalance means, but it is preferred that each of the connecting rods include a flexure element permitting the actuator-shaft end of the connecting rod to move transverse to the direction of the stroke thereof such that the end of the connecting rod remote from the actuator-shaft end may be connected substantially rigidly to the support or counterbalance means. Suitably, the flexure element is formed from a plurality of layers of a high-flexure material such as NYLON or POLYETHYLENE. In a preferred embodiment, the centres of gravity of the two counterbalance masses are arranged to lie substantially adjacent to a straight motion line which passes through the centre of gravity of the support means and coincides with its direction of motion such that the resultant out-of-plane forces and torques on the counterbalances produced as a by-product of the desired oscillation may be minimised. It is preferred that the axis of the actuator shaft be arranged to intersect with the motion line such that the internal stresses induced in the support links may be minimised.

In another aspect of this invention, vibration apparatus is disclosed, including:-

support means adapted for supporting an article to be subjected to oscillatory motion, said support means being mounted for oscillatory movement in a selected direction; a first counterbalance supported for oscillatory motion in said selected direction and arranged for oscillatory motion at a selected phase angle relative to the motion of said support means; a second counterbalance supported for oscillatory motion in said selected direction and arranged for oscillatory motion at a phase angle substantially equal in magnitude and opposite in phase to said selected phase angle; and actuation means adapted for urging said support means and said counterbalance means in oscillatory motion, the phase and amplitude of said motion of said counterbalance means being selected relative to said motion of said support means whereby the vector sum of the momenta of the support means and the counterbalances may be minimised and the total kinetic energy of the support means and the counterbalances may be held substantially constant during the vibration cycle. In a preferred embodiment, the selected phase angle has a magnitude between one hundred and twenty degrees and one hundred and thirty-five degrees, and is preferably approximately one hundred and twenty-six degrees, and the amplitudes through which respective said counterbalances are vibrated are greater than the amplitude through which said support means vibrates, and preferably twice the amplitude of the support means.

In a further aspect, this invention resides in a method of forming a vibration apparatus, including:- providing support means adapted for supporting an article to be subjected to oscillatory motion, said support means being supported for oscillatory movement in a selected direction;

providing counterbalance means supported for oscillatory movement in said selected direction; ^' providing actuation means adapted for urging said support means and said counterbalance means in oscillatory motion, the phase and amplitude of the motion of the counterbalance means being selected relative to the motion of the support means whereby the vector sum of the momenta of the oscillating components may be minimised; and assembling said support means, said counterbalance means and said actuation means to form said vibration apparatus.

The counterbalance means may include a first counterbalance mass and a second counterbalance mass oscillating at differing phase angles relative to said support means such that kinetic energy from the Oscillation of the support means may be transferred through the actuation means to the counterbalances whereby the requirement for external energy storage may be minimised and preferably the sum of the kinetic energies stored in the respective reciprocating components may remain constant. If desired, further counterbalance masses, such as a third counterbalance mass, may also be provided, and the counterbalance masses may be arranged with amplitudes and phase angles such that the vector sum of the momenta of the oscillating components is minimised and the sum of the kinetic energies of the oscillating components remains substantially constant.

— BRIEF DESCRIPTION OF THE DRAWINGS —

In order that this invention may be more easily understood and put into practical effect, reference will now be made to the accompanying drawings which illustrate a preferred embodiment of the invention, wherein:-

FIG. 1 is an upper pictorial view of a vibrating conveyor according to the invention; FIG. 2 is a lower pictorial view of the vibrating conveyor shown in FIG. 1; FIG. 3 shows a cross-sectional view of the actuator assembly of the vibrating conveyor of FIGS. 1 and 2; FIG. 4 is a part-section of portion of the actuator assembly of FIG. 3;

FIG. 5 shows an upper pictorial view of a vibrating separator according to the invention, and

FIG. 6 is a lower pictorial view of the vibrating separator of FIG. 4.

— DESCRIPTION OF THE PREFERRED EMBODIMENTS —

The vibrating conveyor 10 shown in FIGS. 1, 2, 3 and 4 includes a conveyor assembly 11 which is supported from a base frame 12 by flat transverse conveyor support straps 13 clamped to strap attachment pads 14 formed on the outer sides of the base frame 12 and the conveyor assembly 11. The base frame 12 also supports drain trays 15 located beneath the conveyor assembly 11, permitting the conveyor 10 to utilised for dewatering a product placed thereon. An upper counterbalance 16 and a lower counterbalance 17 are supported beneath the conveyor assembly 11 on flat counterbalance support straps 20. The masses of the counterbalances 16 and 17 are equal in this application, and the selected mass is calculated from the formulae given in the specification to be approximately forty-two per-cent of the mass of the conveyor assembly 11.

An actuator assembly 21 is mounted to the base frame 12, and comprises a drive motor 22 which drives an actuator shaft 23 carrying a conveyor eccentric 24, an upper counterbalance eccentric 25 and a lower counterbalance eccentric 26. The

eccentricities of the counterbalance eccentrics 25 and 26 are equal, and the magnitude of the eccentricity is chosen as the product of the eccentricity of the conveyor eccentric 24 and the selected velocity ratio, which in this application is chosen as two. The upper and lower counterbalance eccentrics 25 and 26 are offset circumferentially relative to the conveyor eccentric 24 by phase angles which have a magnitude equal to the calculated value for the selected mass and velocity ratios (in this case one hundred and twenty-six and thirty-seven hundredths degrees), and are of opposite phase. The eccentrics 24, 25 and 26 are maintained in their correct phase relationship by alignment pins 27. Rotary counterweights 28 and 29 are attached to the actuator shaft 23 to balance the rotating components attached thereto. The eccentrics 24, 25 and 26 are coupled tσ the conveyor assembly 11 and the upper and lower counterbalances 16 and 17 by respective connecting rods 30, 31 and 32. Each of the connecting rods 30, 31 and 32 comprise a lower portion 33 carrying a self-aligning bearing 34 connected about an eccentric 24, 25 or 26, a flexible middle portion 35, and an upper portion 36 rigidly attached to the conveyor assembly 11 and the counterbalances 16 and 17 respectively. The flexible middle portion 35 comprises a stack of flat drive elements 37 formed from a flexible material such as NYLON and having relatively thin inclined drive bars 38 formed therein. The drive elements 37 are stacked with the inclined drive elements 38 in adjacent elements 37 inclined in opposite attitudes to produce an assembly having a relatively low bending stiffness within the plane of reciprocation of the rods 30, 31 and 32, a relatively high column strength in tension and compression, and a relatively high bending stiffness transverse to the plane of reciprocation. This permits the lower portions 33 to reciprocate upon their respective eccentrics 24, 25 and 26 while allowing the upper

portions 36 to be rigidly attached to the conveyor assembly 11 and the counterbalances 16 and 17 ^' respectively. Rod apertures 40 are formed in the counterbalances 16 and 17 to clear the rods 30 and 31 passing therethrough. The plane within which the upper portions 36 reciprocate is aligned perpendicular to the transverse planes containing the support straps 13 and 20 such the resistance of the latter to the vibratory motion induced in the conveyor assembly 11 and the counterbalances 16 and 17 is minimised. In use, the motor 22 is started and turns the shaft 23 and the eccentrics 24, 25 and 26. The desired component of the motion of the conveyor eccentric 24 is transferred through the connecting rod 30 into the conveyor assembly 11, which is thus able to convey a material placed thereon. The eccentrics 25 and 26, through the rods 31 and 32, impart to the counterbalances 16 and 17 motion which causes the vector sum of the momenta of the reciprocating components (the conveyor assembly 11 and the counterbalances 16 and 17) to be minimised and the total kinetic energy of the reciprocating components to remain substantially constant over the full cycle of oscillation.

The vibrating separator 50 illustrated in FIGS. 5 and 6 is similar in construction to the vibrating conveyor 10. A separator assembly 51 comprising a stack of sorting screens 52 is supported from a base frame 53 by flat separator support straps 54 clamped to strap attachment pads 55 formed on the outer sides of the base frame 53 and the separator assembly 51. An eccentric shaft assembly 56 is driven by a belt 60 from a drive motor 61, and connecting rods 62 extend from the shaft assembly 56 to the separator assembly 51, the upper counterbalance 63 and the lower counterbalance 64, the counterbalances 63 and 64 being supported from the base on flat transverse counterbalance supports 65 formed of NYLON.

It will of course be realised that while the above has been given by way of illustrative example of this invention, all such and other modifications .and variation ^' s thereto as would be apparent to persons skilled in the art are deemed to fall within the broad scope and ambit of this invention as is defined in the appended claims.