WO2023026224A1

WO2023026224A1 - Linear motion exciter

Info

Publication number: WO2023026224A1
Application number: PCT/IB2022/057955
Authority: WO
Inventors: Martin Nare MASITISE
Original assignee: Mohlalefi (Pty) Ltd
Priority date: 2021-08-25
Filing date: 2022-08-25
Publication date: 2023-03-02

Abstract

A linear motion exciter, comprising axially aligned, out of balance weights, and which is typically used to generate vibrations in vibration machines. The linear motion exciter comprises a drive shaft operatively driven in a first rotational direction about an axis of rotation. A first weight is fixed relative to the drive shaft and configured to rotate about the axis of rotation in the first rotational direction. A second weight is fixed relative to or carried by the drive shaft and configured operatively to rotate about the axis of rotation in a second, opposite rotational direction

Description

LINEAR MOTION EXCITER

BACKGROUND TO THE INVENTION

This invention relates to a linear motion exciter. More particularly, the present invention relates to a linear motion exciter with axially aligned out of balance weights.

Linear motion exciters are used to generate vibrations in vibration machines, commonly used in industrial processes.

Typically, these exciters have two pairs of weights, the weights of each pair fitted to opposing ends of a drive shaft (the exciter therefore typically comprises two parallel drive shafts). The weights are mounted eccentrically, such that a “radius of gyration” is defined between the rotational axis of the drive shaft and a centre of mass of each particular weight.

The weights of both sets are identical. Typically, the two shafts are driven to rotate in opposite angular directions. The weights are mounted in synchronisation with each other, such that a suitable nett vibration (related to a force and a frequency) is generated.

The excitation force generated is defined by the following equations: - mass x velocity² r Centrifugal = ~ or

where:

- m = mass in (kg);

- w = angular velocity in rps (revolutions per second); and

- r = radius of gyration.

From the above it follows that the excitation force can be increased by increasing the mass of the weights, increasing the angular velocity of the shafts, or by increasing the radius of gyration. However, the above factors are typically limited by practical considerations.

For example, the permissible mass of the weights cannot readily be increased, as this has a direct impact on the power required to drive the exciter. This also has an impact on the overall size of the exciter, the sizes of the shafts, the sizes of the bearings and the like.

Also, increasing the angular velocity of the shafts is not possible since the frequency of the vibrations is typically predetermined (typically 50 to 60 Hz, or depending on the specific application).

The most cost-effective means of increasing the excitation force is therefore to increase the radius of gyration, which can be achieved by adding high density inserts (manufactured from lead, for example) to the extremities of the weights, or by optimising the shape or size of the weights.

That said, increasing the radius of gyration is also often physically limited by the spacing between the parallel drive shafts, the sizes of the drive gears, etc., the changing of which will ultimately have a bearing on the overall design of the exciter.

It is accordingly an object of the invention to provide a linear motion exciter that will, at least partially, address the above disadvantages.

It is also an object of the invention to provide a linear motion exciter which will be a useful alternative to existing linear motion exciters.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a linear motion exciter, comprising: a drive shaft defining an axis of rotation, the drive shaft, in use, driven in a first rotational direction about the axis of rotation; a first weight, fixed relative to the drive shaft, configured operatively to rotate about the axis of rotation in the first rotational direction; and a second weight, fixed relative to the drive shaft, configured operatively to rotate about the axis of rotation in a second rotational direction which is opposite to the first rotational direction.

The linear motion exciter may further comprise a transmission arrangement associated with the second weight. The transmission arrangement may include a side shaft, which may be arranged parallel to the drive shaft, and may be spaced from the drive shaft by a spacing distance. The side shaft may be supported by a carrier body by means of a bearing, which may allow operative rotation of the side shaft relative to the carrier body.

The carrier body may be supported by the drive shaft by means of a bearing. The bearing may allow operative rotation of the drive shaft relative to the carrier body.

The second weight may be fixed relative to, and operatively driven by, the carrier body.

The side shaft may operatively be driven by the drive shaft by means of a first transfer arrangement, which may comprise a first transfer member fixed to the drive shaft and a second transfer member fixed to the side shaft.

The transmission arrangement may include a second transfer arrangement, comprising a third transfer member fixed to the side shaft and a fourth transfer member arranged about the drive shaft. The drive shaft may operatively be rotatable relative to the fourth transfer member.

The first and second transfer members may comprise first and second sprockets or pulleys, connected via a chain or belt, while the third and fourth transfer members comprise third and fourth sprockets or pulleys, connected via of a second chain or belt. Alternatively, the first and second transfer members may comprise first and second gears arranged in mesh, while the third and fourth transfer members may comprise third and fourth gears arranged in mesh.

The fourth transfer member may be fixed to or relative to a main body (such as a frame, base, or bearing housing which is fixed to the frame or base) of the linear motion exciter. This means that the fourth transfer member may be substantially stationary relative to the main body, in use, and therefore does not rotate relative to the main body. The drive shaft and first and second weights may rotate relative to the fourth transfer member. The fourth transfer member may be carried by a bearing on the drive shaft.

The first transfer arrangement may have a ratio of 1 :2. The second transfer arrangement may have a ratio of 1 :1.

The transmission arrangement may be configured to cause operative rotation of the drive shaft and the second weight in opposite rotational directions.

The transmission arrangement may include a transmission housing. The second weight may be shaped to receive the transmission housing (at least partially).

Each of the first and second weights may have a mass, an operative axis of rotation and a radius of gyration. The radii of gyration of the first and second weights may be substantially equal. The first and second weights may furthermore operatively be driven at the same angular speed but in opposite rotational directions.

The linear motion exciter may furthermore include a third weight, which may be fixed relative to the drive shaft, and which may be configured operatively to rotate about the axis of rotation of the drive shaft.

The first and third weights may be substantially identical. Each of the first and third weights may have a mass which may be substantially half of that of the second weight. The first and third weights may be synchronised operatively to rotate together. The first and third weights may be fixed directly to the drive shaft towards opposite sides of the second weight.

Alternatively, the second and third weights may be substantially identical. In such a case, each of the second and third weights has a mass which may be substantially half of that of the first weight, while the second and third weights may be synchronised operatively to rotate together. In this alternative embodiment, the third weight may be associated with a transmission arrangement of its own, and the second and third weights may be fixed relative to the drive shaft towards opposite sides of the first weight.

The drive shaft may be supported by a first and second bearing, which are fixed to a main body of the exciter by means of bearing housings.

The exciter may include a driving mechanism, in the form of a motor, such as an electric motor, a hydraulic motor, a pneumatic motor, an internal combustion motor, or the like, which may be provided to drive the drive shaft.

In accordance with a second aspect of the invention, there is provided a vibration machine, comprising a main structure, and a linear motion exciter according to the first aspect of the invention, which is fixed to the main structure of the vibration machine.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which:

Figure 1 shows a front perspective view of a linear motion exciter in accordance with the invention;

Figure 2 shows a front perspective view, in use, of the linear motion exciter of Figure 1 , where first and third weights have been displaced relative to a second weight of the linear motion exciter;

Figure 3 shows a front view of the linear motion exciter of Figure 1 ;

Figure 4 shows a top view of the linear motion exciter of Figure 1 ;

Figure 5 shows a side view of the linear motion exciter of Figure 1 ;

Figure 6 shows a side view in use of the linear motion exciter of Figure 1 ; Figure 7 shows a front perspective view of a first weight forming part of the linear motion exciter of Figure 1 ;

Figure 8 shows a front perspective view of a second weight forming part of the linear motion exciter of Figure 1 ;

Figure 9 shows a sectioned front view of the linear motion exciter of Figure 1 , comprising a first example embodiment of a transmission arrangement;

Figure 10 shows a partial side view of the linear motion exciter of Figure 9, in which certain components have been omitted to show details of a second transfer arrangement forming part of the first example embodiment of the transmission arrangement;

Figure 11 shows a partial side view of the linear motion exciter of Figure 9, in which certain components have been omitted to show details of a first transfer arrangement of the first example embodiment of the transmission arrangement;

Figure 12 shows an exploded perspective view of the first example embodiment of the transmission arrangement forming part of the linear motion exciter of Figure 9;

Figure 13 shows a sectioned front view of the linear motion exciter of Figure 1 , comprising a second example embodiment of the transmission arrangement;

Figure 14 shows a partial side view of the linear motion exciter of Figure 13, in which certain components have been omitted to show details of a first transfer arrangement forming part of the second example embodiment of the transmission arrangement;

Figure 15 shows a partial side view of the linear motion exciter of Figure 13, in which certain components have been omitted to show details of a second transfer arrangement forming part of the second example embodiment of the transmission arrangement; and

Figure 16 shows an exploded perspective view of the second example embodiment of the transmission arrangement forming part of the linear motion exciter of Figure 13. DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of "including," "comprising," or "having" and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms "mounted", "connected", "engaged" and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings and are thus intended to include direct connections between two members without any other members interposed therebetween and indirect connections between members in which one or more other members are interposed therebetween. Further, "connected" and "engaged" are not restricted to physical or mechanical connections or couplings. Additionally, the words "lower", "upper", "upward", "down" and "downward" designate directions in the drawings to which reference is made. The terminology includes the words specifically mentioned above, derivatives thereof, and words or similar import. It is noted that, as used in this specification and the appended claims, the singular forms "a," "an," and "the," and any singular use of any word, include plural referents unless expressly and unequivocally limited to one referent. As used herein, the term “include” and its grammatical variants are intended to be non-limiting, such that recitation of items in a list is not to the exclusion of other like items that can be substituted or added to the listed items.

Referring to the drawings, in which like numerals indicate like features, a non-limiting example of a linear motion exciter (or just “exciter”) in accordance with the invention is generally indicated by reference numeral 10.

It will readily be appreciated, that the linear motion exciter is used as part of a vibration machine (which is not shown), such as a vibration table for example, to generate or excite vibrations or oscillations. The exciter 10 comprises a frame or main body 12, which is firmly fixed to a main body of the vibration machine. Also, the exciter is typically driven by a motor, such as an electric, pneumatic, hydraulic or internal combustion motor. This is also not shown. The exciter 10 comprises a drive shaft 14 which is coupled to the motor via a coupling 16, in known fashion. As discussed in more detail below, the exciter 10 is therefore driven through the drive shaft 14.

The drive shaft 14 extends along an axis of rotation 18 (shown in figures 9 and 13). The configuration is such that, in use, the drive shaft 14 is driven about the axis of rotation 18, in a first direction of rotation (as shown by the arrow marked 20 in figure 6). It will be appreciated that the first direction of rotation may be either a clockwise or anti-clockwise direction, while a second direction of rotation, as discussed below, will always be an opposite direction of rotation.

The exciter 10 furthermore comprises a first weight 22, a second weight 24 and a third weight 26.

As shown, the first and third weights (22, 26), in this example embodiment, are substantially identical.

As best shown in figures 7 and 8, each of the first, second and third weights (22, 24, 26) have a centre of mass 28 (shown at an arbitrary location in the figures) and an (operative) axis of rotation 30. The configuration of the exciter 10 is such that, in use, and as will be discussed more fully below, the weights are rotated about their respective axes of rotation 30.

Each weight (22, 24, 26) furthermore defines a radius of gyration 32. It follows that the centres of mass 28 of the weights are spaced from the respective axes of rotation 30 by the radii of gyration 32. Therefore, in use, the centres of mass 28 revolve around the axes of rotation 30, which causes centrifugal forces to be exerted in known fashion. Importantly, and as will be discussed in more detail below, the radii of gyration 32 of the first and third weights (22, 26) are equal to that of the second weight 24.

Each of the weights (22, 24, 26) has a predetermined mass. The masses of the first and third weights (22, 26) are substantially equal. Furthermore, the combined mass of the first and third weights (22, 26) are substantially equal to that of the second weight 24 (or put differently, the mass of each of the first and third weights (22, 26) is half of that of the second weight 24).

The first weight 22 is fixed relative to the drive shaft 14 such that it rotates with the drive shaft 14 in use. The axis of rotation 30 of the first weight 22 therefore aligns with the axis of rotation 18 of the drive shaft 14. Furthermore, the first weight 22 is fixed to the drive shaft 14 such that it rotates in the same rotational direction (the first rotational direction 20) and at the same angular velocity as the drive shaft 14. The first weight 22 is therefore coupled directly to the drive shaft 14.

The second weight 24 is fixed relative to the drive shaft, and such that the second weight 24 also rotates about the axis of rotation 18 of the drive shaft. Again, the configuration is such that the axis of rotation 30 of the second weight 24 is aligned with the axis of rotation 18 of the drive shaft. However, the second weight is not directly coupled to the drive shaft 14. Rather, the second weight 24 can rotate relative to the drive shaft 14 (within the mechanical constraints provided by other components, as will be discussed below).

As discussed below in more detail, the second weight 24, when driven in use, rotates in a second rotational direction 34 about the axis of rotation 18 of the drive shaft 14, which is opposite to the first direction of rotation 20.

The third weight 26 is fixed relative to the drive shaft 14 such that it rotates with the drive shaft 14 in use. The axis of rotation 30 of the third weight 26 therefore again aligns with the axis of rotation 18 of the drive shaft 14. Furthermore, the third weight 26 is fixed to the drive shaft 14 such that it rotates in the same rotational direction (the first rotational direction 20) and at the same angular velocity as the drive shaft 14. The third weight 26 is therefore coupled directly to the drive shaft 14. Furthermore, the first and third weights (22, 26) are aligned in synchronisation with each other (in other words, they are angularly substantially aligned relative to the drive shaft 14). In practice, this means that the first and third weights (22, 26) rotate together.

Since the first and third weights (22, 26) are synchronised and fixed to the drive shaft such that they rotate together, and provided the first and third weights (22, 26) rotate at an angular velocity having a magnitude similar to that of the second weight 24, the combined magnitude of the centrifugal force associated with the first and third weights (22, 26) is substantially equal to the magnitude of the centrifugal force associated with the second weight 24.

It will be readily appreciated that the axes of rotation 30 of all three weights (22, 24 and 26) are all aligned with each other and the axis of rotation 18 of the drive shaft 14.

The first and third weights (22, 26) are fixed towards opposite ends of the drive shaft 14, while the second weight 24 may be located between the first and third weights (22, 26). Each of the first and third weights (22, 26) may be associated with a key received in a keyway of the respective weight and the drive shaft 14. The drive shaft 14 is supported by a bearing within a housing 36 on either side of the second weight 24, which housing is fixed to the frame or main body 12.

The weights (22, 24, 26) are typically manufactured from a metal such as steel and may all include inserts 38 of a denser material, such as lead, to increase the mass, and adjust the position of the centre of mass of the particular weight. The use of other types of materials in the manufacture of the weights (22, 24, 26) or the inserts 38 is possible.

The exciter 10 comprises a transmission arrangement or system, which is generally referred to by reference to numeral 40. A first example embodiment of the transmission arrangement is shown in figures 9 to 12 and indicated by reference numeral 40.1 , while a second example embodiment of the transmission arrangement is shown in figures 13 to 16 and indicated by reference numeral 40.2.

Features which are common between the first and second example embodiments (40.1 are 40.2) are denoted by like numerals and will be described generally in relation to the transmission arrangement 40. Such features will therefore be taken to be common to both example embodiments and will be taken to have similar characteristics and functions irrespective of whether they are used with the first or the second embodiment of the transmission arrangement 40.

The transmission arrangement 40 includes a side shaft 42 which is spaced from the drive shaft 14 by a spacing distance 44. The side shaft 42 is associated with a side shaft axis of rotation 46 which runs parallel to the axis of rotation 18 of the drive shaft 14.

The side shaft 42 is supported in position by a first and second carrier body 48. The carrier bodies are carried on the drive shaft 14 by bearings 69. The side shaft 42 is received within or by bearings 50 which allow the side shaft to rotate relative to the carrier bodies 48. The transmission arrangement 40 furthermore comprises a transmission housing 52, which encloses certain internal components of the transmission arrangement 40. The carrier bodies 48 serve as endcaps of the housing 52.

In the case of the first example embodiment 40.1 of the transmission arrangement shown in figures 9 to 12, the side shaft 42 is driven by the drive shaft 14, by means of a first transfer arrangement 54, in the form of a first transfer member 56 which is fixed to, and rotate with, the drive shaft 14, and a second transfer member 58, which is fixed to, and rotate with, the side shaft 42. The first and second transfer members (56, 58) are fixed to the respective shafts (14, 42) such that torque may be transferred between a respective transfer member and its associated shaft. Furthermore, the transfer members interact to transfer torque from one to the other. In the example shown in figures 9 to 12, the first and second transfer members (56, 58) take the form of first and second sprockets or toothed pulleys, interacting through or connected via a suitable belt 59 (such as a toothed belt) or a chain.

The transmission arrangement 40.1 comprises a second transfer arrangement 60, in the form of a third transfer member 62 which is fixed to, and rotates with, the side shaft 42, and a fourth transfer member 64, which rotates about (but is not fixed to and does not rotate with) the drive shaft 14.

The third transfer member 62 is fixed to the side shaft 42 such that torque may be transferred between the side shaft 42 and the third transfer member 62. Furthermore, the third and fourth transfer members (62, 64) interact to transfer torque from one to the other. In the example shown in figures 9 to 12, the third and fourth transfer members (62, 64) take the form of third and fourth sprockets or pulleys interacting through or connected by a chain or belt 66. The belt may be a toothed belt and the third and fourth transfer members (62, 64) may be suitable sprockets or toothed pulleys.

The fourth transfer member 64 is supported on the drive shaft 14 by a bearing 68, to allow relative displacement between the fourth transfer member 64 and the drive shaft 14.

That said, the fourth transfer member 64 is fixed (directly or indirectly) to the frame or main body 12 of the exciter 10. As shown in the figures, the fourth transfer member 64 has or is associated with an extension or shoulder, which is fixed directly or indirectly to the frame or main body 12, and in this case, directly to the housing 36 of the bearing. Therefore, in use, the fourth transfer member 64 does not rotate relative to the frame or main body 12 of the exciter 10.

The first transfer arrangement 54 has a gear ratio of 1 :2. Therefore, the first transfer member 56 has a diameter which is half the size of that of the second transfer member 58. When driven, the drive shaft 14 and side shaft 42 rotate in the same rotational direction. Furthermore, because of the arrangement of the second transfer arrangement 60, the housing 52 rotates at a rotational speed of the same magnitude as the drive shaft, but again, in an opposite rotational direction. In the case of the second example embodiment 40.2 of the transmission arrangement shown in figures 13 to 16, the side shaft 42 is again driven by the drive shaft 14, through a first transfer arrangement, which is now denoted by reference numeral 154, which again comprises a first transfer member 156 which is fixed to, and rotates with, the drive shaft 14, and a second transfer member 158, which is fixed to, and rotates with, the side shaft 42. The first and second transfer members (156, 158) are fixed to the respective shafts (14, 42) such that torque may be transferred between a respective transfer member and its associated shaft. Furthermore, the transfer members interact to transfer torque from one to the other. In the example shown in figures 13 to 16, the first and second transfer members (156, 158) take the form of first and second gears arranged in mesh.

The first and second transfer members (gears, in this case) (156, 158) have a ratio of 1 :2. Therefore, the first gear 156 is half the size of the second gear 158. This results in the drive shaft 14 and side shaft 42 rotating at equal rotational speeds (again, it should be borne in mind that the transmission arrangement revolves about the drive shaft).

The transmission arrangement 40.2 comprises a second transfer arrangement 160, comprising a third transfer member 162 which is fixed to, and rotates with, the side shaft 42, and a fourth transfer member 164, which rotates about (but is not fixed to and does not rotate with) the drive shaft 14.

The third transfer member 162 is fixed to the side shaft 42 such that torque may be transferred between the side shaft 42 and the third transfer member 162. Furthermore, the third and fourth transfer members (162, 164) interact to transfer torque from one to the other. In the example shown in figures 13 to 16, the third and fourth transfer members (162, 164) take the form of third and fourth gears provided in mesh.

The fourth transfer member 164 is supported on the drive shaft 14 by a bearing, to allow relative displacement between the two.

That said, the fourth transfer member 164 is fixed (directly or indirectly) to the frame or main body 12 of the exciter 10. As shown in the figures, the fourth transfer member 164 has or is associated with an extension or shoulder 165, which may be fixed directly or indirectly to the frame or main body 12, and in this case, directly to a housing 36 of the bearing. Therefore, the fourth transfer member 164 does not rotate relative to the frame or main body 12 of the exciter 10. The second transfer arrangement (60, 160) (in both example embodiments) has a gear ratio of 1 :1.

The configurations of the first and second transfer arrangements, are such that, when driven, the drive shaft 14 and side shaft 42 rotate at rotational speeds of the same magnitude (in opposite rotational directions) relative to each other. Furthermore, because of the arrangement of the second transfer arrangement 160, the housing 52 rotates at a rotational speed of the same magnitude as the drive shaft, but again, in an opposite rotational direction.

Since the second weight 24 is fixed to and rotates with the housing 52, the second weight, when driven, therefore rotates in the second rotational direction 34 when the drive shaft 14 (and therefore also the first and third weights) is driven in the first rotational direction 20.

The second weight 24 defines an internal cavity within which the transmission arrangement 40 is at least partially received. The second weight 24 also includes a removable cap, to enable installation and removal of the second weight to or from the transmission arrangement 40.

It will be appreciated that the inclusion of the integral transmission arrangement 40 enables the first, second and third weights to be axially aligned. In this way, the requirement for a second drive shaft is removed, and the radius of gyration can be increased without an associated increase in the overall size of the exciter (associated with the spacing between drive shafts, which is furthermore associated with larger transfer arrangements, heavier components, and the like).

It will be appreciated that the above description only provides example embodiments of the invention and that there may be many variations without departing from the spirit and/or the scope of the invention.

For example, a configuration is possible (though not necessarily optimal) where the second and third weights rotate in the second direction while the drive shaft and first weight rotate in the first direction, but in which the second and third weights are arranged on opposite sides of the first weight (in this configuration, the first weight rotating with the drive shaft is therefore a centre weight). Concomitant changes will have to be made to the transmission arrangement, such as, providing each of the second and third weights with a separate transmission arrangement, adapted for the specific use. It will be appreciated that the mass of the second weight 24 includes the mass of the transmission arrangement and associated components, when same is received within or on the second weight 24.

Also, it is possible to provide an exciter comprising only a first and second weight, in which case, the first and second weights will be substantially identical.

It will be appreciated that transfer members shown in the figures are merely illustrative and that sizes of the transfer members shown in the figures are not necessarily to scale. Therefore, the dimensions of the transfer members in the figures are not to be used to determine gear ratios or the like.

Furthermore, references to “the main body” will be taken to include components or structures fixed without relative displacement, to the main body. For example, a base, frame members, bearing housings 36 and the like all form part of the “main body”. The main body, in use, is stationary relative to the drive shaft 14, the weights (22, 24, 26) and the transmission arrangement.

It is easily understood from the present application that the particular features of the present invention, as generally described and illustrated in the figures, can be arranged and designed according to a wide variety of different configurations. In this way, the description of the present invention and the related figures are not provided to limit the scope of the invention but simply represent selected embodiments.

The skilled person will understand that the technical characteristics of a given embodiment can in fact be combined with characteristics of another embodiment, unless otherwise expressed or it is evident that these characteristics are incompatible. Also, the technical characteristics described in a given embodiment can be isolated from the other characteristics of this embodiment unless otherwise expressed.

Claims

1 . A linear motion exciter, comprising: a drive shaft defining an axis of rotation, the drive shaft, in use, driven in a first rotational direction about the axis of rotation; a first weight, fixed relative to the drive shaft, configured operatively to rotate about the axis of rotation in the first rotational direction; and a second weight, fixed relative to the drive shaft, configured operatively to rotate about the axis of rotation in a second rotational direction which is opposite to the first rotational direction.

2. The linear motion exciter according to claim 1 , further comprising a transmission arrangement associated with the second weight.

3. The linear motion exciter according to claim 2, wherein the transmission arrangement includes a side shaft, which is arranged parallel to the drive shaft, and spaced from the drive shaft by a spacing distance.

4. The linear motion exciter according to claim 3, wherein the side shaft is supported by a carrier body by means of a bearing, allowing operative rotation of the side shaft relative to the carrier body.

5. The linear motion exciter according to claim 4, wherein the carrier body is supported by the drive shaft by means of a bearing, allowing operative rotation of the drive shaft relative to the carrier body.

6. The linear motion exciter according to claim 4 or claim 5, wherein the second weight is fixed relative to, and operatively driven by, the carrier body.

7. The linear motion exciter according to any one of claims 4 to 6, wherein the side shaft is operatively driven by the drive shaft by means of a first transfer arrangement comprising a first transfer member fixed to the drive shaft and a second transfer member fixed to the side shaft.

8. The linear motion exciter according to claim 7, wherein the transmission arrangement comprises a second transfer arrangement, comprising a third transfer member fixed to the side shaft and a fourth transfer member arranged about the drive shaft, such that the drive shaft is operatively rotatable relative to the fourth transfer member. . The linear motion exciter according to claim 8, wherein the first and second transfer members comprise first and second sprockets or pulleys, connected via a chain or belt. 0. The linear motion exciter according to claim 9, wherein the third and fourth transfer members comprise third and fourth sprockets or pulleys, connected via of a chain or belt. 1 . The linear motion exciter according to claim 8, wherein the first and second transfer members comprise first and second gears in mesh. 2. The linear motion exciter according to claim 11 , wherein the third and fourth transfer members comprise third and fourth gears in mesh. 3. The linear motion exciter according to any one of claims 9 to 12, wherein the fourth transfer member is fixed to a main body of the linear motion exciter. 4. The linear motion exciter according to claim 13, wherein the fourth transfer member is carried by a bearing on the drive shaft. 5. The linear motion exciter according to any one of claims 9 to 14, wherein the first transfer arrangement has a ratio of 1 :2, and wherein the second transfer arrangement has a ratio of 1 :1. 6. The linear motion exciter according to any one of claims 2 to 15, wherein the transmission arrangement is configured to cause operative rotation of the drive shaft and the second weight in opposite rotational directions. 7. The linear motion exciter according to any one of claims 2 to 16, wherein the transmission arrangement includes a transmission housing, and wherein the second weight is shaped to receive the transmission housing at least partially. 8. The linear motion exciter according to any one of the preceding claims, wherein each of the first and second weights has a mass, an operative axis of rotation and a radius of gyration and wherein the radii of gyration of the first and second weights are substantially equal. 17 The linear motion exciter according to any one of the preceding claims, wherein the first and second weights are operatively driven at the same angular speed but in opposite rotational directions. The linear motion exciter according to any one of the preceding claims, further including a third weight, fixed relative to the drive shaft and configured operatively to rotate about the axis of rotation of the drive shaft. The linear motion exciter according to claim 20, wherein the first and third weights are substantially identical, wherein each of the first and third weights has a mass which is substantially half of that of the second weight, wherein the first and third weights are synchronised operatively to rotate together, and wherein the first and third weights are fixed directly to the drive shaft towards opposite sides of the second weight. The linear motion exciter according to claim 20, wherein the second and third weights are substantially identical, wherein each of the second and third weights has a mass which is substantially half of that of the first weight, wherein the second and third weights are synchronised operatively to rotate together, wherein the third weight is associated with a transmission arrangement and wherein the second and third weights are fixed relative to the drive shaft towards opposite sides of the first weight. The linear motion exciter according to any one of the preceding claims, wherein the drive shaft is supported by a first and second bearing, fixed to a main body of the exciter. The linear motion exciter according to any one of the preceding claims, wherein the exciter includes a driving mechanism, in the form of a motor, to drive the drive shaft. A vibration machine, comprising a main structure, and a linear motion exciter according to any one of claims 1 to 24, fixed to the main structure.