BACKGROUND ART There are various known types of vibratory conveyors. In one type, a conveyor tray or table is yieldably mounted. on a base by flexible beam springs, and a vibrating mechanism mounted on the base imparts vibratory forces directly to the tray.

In another type, the conveyor tray is yieldably mounted on a frame by flexible beam springs. The frame, in turn, is mounted to a base, usually through vibration-absorbing mounts. A vibrating mechanism is mounted on the frame and imparts vibratory forces to the frame. The vibration is transferred from the frame to the conveyor tray through the springs. An example of this second type of conveyor, sometimes referred to as an "excited frame''vibratory conveyor, can be found in US patent 4313535.

The vibratory conveyor of US patent 4313535 comprises a tray yieldably mounted on a frame. The frame is vibrated by a vibratory drive means which comprises a balanced counter rotating vibrator which produces a vibratory motion in the longitudinal direction of the conveyor tray. The vibrator includes counter rotating elements for rotation about respective offset eccentric axes arranged transversely to the longitudinal direction of the conveyor.

It has been found that such excited frame conveyors have several inherent disadvantages. First, due to the relatively high inertia of the counter rotating elements of the vibrator, the conveyor is unable to stop and start quickly.

Secondly, as the conveyor slows down, it passes through a stage during which its frequency of vibration is equal to the natural resonant frequency of the conveyor assembly, leading to unstable or undesirable vibration of the whole assembly.

Thirdly, the counter-rotating mechanism needs to be manufactured precisely and ruggedly for correct balance and reliability of the drive.

As a consequence of the above, known excited frame conveyors generally require a high degree of maintenance. Moreover, they are relatively expensive to construct, and operate.

Finally, the vibration characteristics of the conveyor tray are not easily

changed in known excited frame conveyors. To modify the throw or travel imparted to a vibratory tray, it is normally necessary to change the eccentric weights mounted on the vibrating shafts. This requires disassembly of the drive components and substitution of different eccentrics. This, in turn, requires substantial"down time", which may result in significant loss of production.

US patent 6279731 discloses a vibratory mechanism which facilitates modification of the amplitude of vibration of the conveyor table. In the vibratory conveyor table of US 6279731, a vibratory mechanism mounted on a base imparts vibratory motion to a conveyor tray through flexible connector plates. Adjustable stiffening plates are fixed to the connector plates, and serve to reinforce a segment of the connector plates against flexure. The stiffening plates can be changed to vary the vibratory characteristics of the conveyor tray, such as its throw or travel. However, the teaching of US patent 6279731 is limited to use of the vibratory mechanism for direct drive of a conveyor table. Furthermore, a conveyor constructed according to the teaching of US patent 6279731 is unbalanced and must be fixed rigidly to a stiff massive structure to restrict vibration of the whole conveyor assembly.

It is an object of this invention to provide an improved excited frame vibratory machine which overcomes or ameliorates at least some of the above described disadvantages, or which at least provides a useful choice.

SUMMARY OF THE INVENTION In one broad form, the invention provides a vibratory conveyor having a frame, a conveyor member movably supported on the frame by first flexible connector means and being capable of vibratory movement relative to the frame in a substantially longitudinal direction of the conveyor member, a vibratory drive means mounted to the frame, and at least one vibratile mass connected to the frame by second flexible connector means.

In one embodiment, the vibrating mechanism is connected to the vibratile mass by third flexible connector means. In use, the mass is vibrated by the vibrating mechanism.

In another embodiment, the vibrating mechanism is connected to the conveyor member by third flexible connector means, and provides direct excitation of

the conveyor member.

One or more vibratile masses may be connected to the frame. Each vibratile mass is typically a counterweight. The conveyor member, which may be a tray, table or screen, vibrates with equal and opposite amplitude to the counterweight, to provide balanced motion. This allows the amplitude of vibration of the frame to be minimized while still achieving the desired amplitude of vibration of the conveyor member.

Typically, the vibratory conveyor includes a base, and the frame is flexibly mounted on the base. However, the frame may be suspended, or wall- mounted.

The connector means may comprise stiff, but resiliently flexible, strap- like connectors having sufficient flexure to permit operative vibratory motion.

The vibratory drive means typically includes a motor, and an eccentric rotated by the motor. The eccentric preferably comprises a shaft joumalled at its ends for rotation about an axis of rotation orientated transversely to the longitudinal direction of the conveyor member. The shaft has an eccentric portion along its length which is journalled in one or more bearing housings fixed to the third connector means. Typically, that eccentric portion has a circular periphery which has a geometric centre radially offset from the axis of rotation. Rotation of the shaft imparts vibration to the third connector means, which is transferred to the counterweight. The shaft has low inertia, thereby enabling fast starting and stopping of the vibratory conveyor, without conveyor instability.

A weight may be mounted eccentrically on the shaft to balance the shaft about its axis of rotation.

In order that the invention may be more fully understood and be put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of the underside of a vibratory conveyor according to one embodiment of the invention.

Fig. 2 is an underside perspective view of a cutaway portion of the

conveyor of Fig. 1.

Fig. 3 is a perspective view from above and one side of the conveyor of Fig. 1.

Fig. 4 is a perspective view from above and the other side of the conveyor of Fig. 1.

Fig. 5 is a schematic sectional side elevation of the conveyor of Fig. 1.

Fig. 6 is an end elevation of the conveyor of Fig. 1.

Fig. 7 is a perspective view of part of the vibrating mechanism of the conveyor of Fig. 1.

Fig. 8 is an end view of the shaft of Fig. 7.

Fig. 9 is schematic block diagram representing the vibrational characteristics of the embodiment of Fig. 1.

Fig. 10 illustrates vibration amplitude versus vibration frequency for the frame, conveyor and counterweight of the embodiment of Fig. 1.

Fig. 11 is a schematic sectional side elevation of a portion of a conveyor according to a second embodiment of the invention.

Fig. 12 is an underside perspective view of the portion of the conveyor of Fig. 11.

Fig. 13 is a schematic sectional side elevation of a portion of a conveyor according to a third embodiment of the invention.

Fig. 14 is an underside perspective view of the portion of the conveyor of Fig. 13.

DESCRIPTION OF PREFERRED EMBODIMENTS As shown in the drawings, a vibratory conveyor 1 comprises a frame 10 formed from two side walls 11,12 joined by transverse tubular struts 13. The frame is typically made from a suitable metal, such as mild steel or stainless steel.

A conveyor member in the form of a table or tray 20 is moveably supported on the frame 10 by a plurality of connectors 21 on each side of the tray. The tray 20 is typically made from stainless steel, and may be mounted at a slight inclination to the horizontal, with at least the discharge end of the tray being open.

However, the conveyor member may take other forms, such as a screen or sieve.

Each connector 21 is a single or multiple beam spring comprising one or more stiff, but resiliently flexible, straps, each having one end fixed to the frame 10 and the other end fixed to the conveyor tray 20. The strap-like connectors 21 are typically made of cross laminated, fiberglass reinforced material which, although stiff enough to support the weight of the conveyor tray 20 and any articles thereon, has sufficient flexure to permit the required vibratory motion of the conveyor tray in use.

The vibratory conveyor 10 also includes a base 30 which comprises four spaced legs 31 joined by transverse and longitudinal bracing members 32,33.

Each leg 31 may be suitably provided with an adjustable foot 34. The frame 10 is flexibly mounted on the base 30 by spring mounts 35,36. Other types of flexible mounts, such as rubber mounts, may be used where appropriate. The mounts 35,36 substantially absorb any vertical or horizontal vibratory forces which would otherwise be imparted to the base 30 by the frame 10. This enables the base 30 to stand motionless on a floor, despite the vibratory motion of the conveyor tray.

Although the illustrated vibratory conveyor has a floor-standing base, the frame 10 can alternatively be suspended from an overhead structure, or mounted to a wall structure.

The vibratory conveyor 1 is also provided with vibratory drive means 40 which can be seen in more detail in Figs. 2,4, 5 and 7. The vibratory drive means 40 comprises a shaft 42 having its opposite ends journalled in respective bearings mounted on the side walls 11,12, and orientated transversely to the longitudinal direction of the conveyor tray 20. The shaft 42 is rotated by an electric motor 41 via a timing belt and pulley arrangement 43 which is normally shielded under cover 14.

As shown in Fig. 7, the shaft 42 has an eccentric portion 44 along its length. This eccentric portion is formed by an enlarged circular section 44 having a geometric centre which is offset from the axis of rotation of the shaft. The eccentric portion 44 is journalled in two axially-spaced bearings 45, each held within a respective saddle housing 46 which, in turn, is bolted to one end of a respective one of a pair of elongate connectors 47. The other end of each connector 47 is fixed to a vibratile mass, which is typically in the form of a counterweight 48.

Each connector 47 is typically a strap-like laminated fiberglass plate.

The connectors 47 are stiff but resiliently flexible, with sufficient flexure to permit the

required degree of relative vibratory motion between the shaft 42 and the counterweight 48.

The counterweight 48 may suitably comprise one or more steel plates of predetermined mass. The counterweight 48 is suspended from the frame 10 by a plurality of connectors in the form of single or multiple beam springs 49. The beam springs 49 may be of similar construction as the beams springs 21. The beam springs 49 are located at opposite sides of the counterweight 48, with each beam spring having one end fixed to the counterweight, and the other end fixed to a respective side wall 11,12 of the frame 10.

Since the eccentric portion 44 of the shaft 42 has a geometric centre which is offset from the axis of rotation of the shaft 42, it imparts vibratory motion to the connectors 47 as the shaft 42 rotates about its axis of rotation, and such vibratory motion is imparted to the counterweight 48. This vibratory motion is in a direction perpendicular to the plane of the flexible connectors 21, and has a substantial component in the longitudinal direction of the tray 20. The vibratory motion of the counterweight 48 will, in turn, impart vibratory forces on the frame 10 to which it is resiliently connected, and these vibratory forces will be transferred to the tray 20 which is flexibly connected to the frame 10.

By suitable selection of rotational speed, dimensions and weights of the vibratory drive means, the counterweight 48 can be made to vibrate with a greater amplitude then the bearing housings 46 on the shaft 42. Furthermore, since the natural or resonant frequency of the frame 10 is quite removed from the forcing frequency, these forces will be transferred to the conveyor tray 42 which has a natural resonance close to, or equal to, the forcing frequency and will therefore vibrate with a much greater amplitude than the frame 10. Thus, the required amplitude of vibration of the conveyor tray 20 can be obtained with only minimal vibration of the frame 10.

Due to the shape of the shaft 42 and, in particular, the eccentric portion 44 of the shaft, the centre of mass of the shaft will be offset from the axis of rotation.

Specifically shaped and dimensioned balance weights 50 can be mounted on the shaft, for the purpose of aligning the centre of mass of the shaft 42 with its own axis of rotation. Thus, the shaft 42 provides a balanced, low inertia, vibratory drive.

It can be shown that, in mathematical terms with several simplifying assumptions, the complete vibratory conveyor system can be represented by the simple schematic shown in Fig. 9. All coil springs 36 are shown as a single schematic spring. Similarly, all flexible connectors 21 between the frame 10 and the conveyor member 20 are shown as a single schematic spring. The frame 10, conveyor member 20 and counterweight 48 are shown as discrete masses. The drive springs 47 and flexible connectors 49 have been combined and shown as a single schematic spring.

The drive force due to the eccentric shaft 42 and drive springs 47 is also shown.

The motion of the three discrete masses 10,20 and 48 can be described by a second order matrix differential equation with respect to time. Upon solving this equation, the motion of the three discrete masses 10,20 and 48 can be examined and analysed, to enable selection and tuning of parameters to produce the desired behaviour. The equation, solution process and selection of parameters will not be detailed here. However, an example of the system response predicted by the solution to this equation is shown in Fig. 10, for a typical set of system parameters.

Fig. 10 shows the amplitude of harmonic motion of each of the three discrete masses 10,20 and 48 for a given rotational frequency of the eccentric shaft 42. The range of rotational frequencies shown corresponds to a typical region of operation of the system. At the point at which the movement of the frame 10 is equal to zero, the amplitudes of the conveyor member 20 and the counterweight 48 are exactly equal in magnitude. This is the point at which the conveyor is designed to operate, although small deviations from this point still exhibit acceptable amplitudes of the frame 10, as Fig. 10 shows.

The above described conveyor has several advantages, including: 'the conveyor can be started and stopped quickly, as the vibrating mechanism has low inertia; vibrational characteristics can be changed by changing the sizes or numbers and distribution of the flexible connectors 21 and 49, or by using adjustable clamp plated on the flexible connectors 47, or by substituting a drive shaft 42 of different eccentricity.

'the shaft 42 can be balanced by balance weights 50 to provide a balanced vibratory drive;

'the conveyor requires little maintenance and is relatively inexpensive to manufacture, particularly as the counterweight is of simple construction 'the vibratory drive mechanism can be designed so that the counterweight 48 has a higher amplitude of vibration than the offset eccentricity of the shaft 42, typically twice the amplitude.

Figs 11 and 12 illustrate a second embodiment of the invention. For the sake of clarity, only the relevant portion of the vibratory conveyor is illustrated in Figs 11 and 12. As shown in those drawings, a vibratory conveyor 60 has a conveyor member in the form of a table, tray or pan 61 which is movably supported on a frame 62 by a plurality of single beam springs 63.

The conveyor 60 has a vibratory drive similar to that shown in Fig 1, and for the sake of clarity, not all components of the vibratory drive are shown in Figs 11 and 12. The vibratory drive comprises an eccentric shaft 64 which is driven by a motor (not shown). The shaft 64 is jounzalled in at least 1 bearing mounted to one end of a respective strap connector 65 (analogous to the strap connector 47 of Fig 1).

However, the other end of strap connector 65 is connected to the conveyor pan 61 to impart vibratory motion direct to the pan 61.

A vibratile mass in the form of a counterweight 66 is flexibly connected to the frame 62 by single beam springs 67. The beam springs 67 are connected between the frame 62 and a bracket 68 connected to the counterweight 66.

In the vibratory conveyor 60, the counterweight 66 vibrates at approximately the same amplitude as, but in an opposite sense to, the pan 61 so that the frame 62 has minimal vibration. The illustrated system, having a driven pan and a single counterweight, is effectively equivalent in mathematical terms to the first embodiment, as modeled in Fig 9.

By extension, this theory also applies to a vibratory conveyor having multiple counterweights, as illustrated in the embodiment of Figs 13 and 14.

Figs 13 and 14 illustrate part of a vibratory conveyor 70 having multiple counterweights. Again, for the sake of clarity, only a portion of the conveyor is illustrated, as the remaining components are similar to those of the embodiment of Fig 1. The vibratory conveyor 70 comprises a pan 71 flexibly mounted on a frame 72

by a plurality of single beam springs 73. A vibratory drive mechanism, similar to that of the embodiment of Fig 1, is mounted on the frame 72 and includes an eccentric shaft 74 which is journalled in one or more bearings connected to an end of a respective connecting strap 75. The other end of the connecting strap 75 is fixed to the pan 71. As with the embodiment of Fig 11, the vibratory mechanism provides direct vibratory drive to the pan 71.

Multiple counterweights 76 are flexibly connected to the frame 72, each by a respective pair of single beam springs 77. Each beam spring 77 has one end connected to the frame 72, and its other end connected to a bracket 78 fixed to the associated counterweight 76.

The embodiments of Figs 11 to 14 are designed to operate in a similar manner to the embodiment of Fig 1, i. e. at or near the point at which the movement of the frame is equal to zero, with the amplitudes of the conveyor pan and the counterweight (s) being of equal magnitude. In this manner, there will be minimal or negligible vibration of the frame.

The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art can be made thereto without departing from the scope of the invention as defined in the following claims.

For example, the conveyor tray may include, or be replaced by a screen so that the apparatus 10 can operate as a vibratory screen or other vibratory machine.