Balance mechanism mounting equipment

Abstract

A mounting apparatus (100) comprising a housing adapted to be removably attachable to a support means, the mounting apparatus further comprising a platform (102) attached to a housing pivotally attached to the housing and rotatable relative thereto about an axis (O), where the housing has an annular cam (106) arranged therein, the annular cam (106) being adapted to engage with the platform (102), and the platform (102) being adapted to engage with the platform (102). The invention relates to a device (100) for operating a motor vehicle, comprising a cam (110, 116) arranged concentrically with said axis and having an inner cam surface (118), and comprising a cam follower (110, 116) comprising a cam engagement surface adapted to engage with and follow said inner cam surface upon rotation of said cam about said axis, said cam follower having a yoke engagement surface adapted to engage with and follow said inner cam surface upon rotation of said cam about said axis. The yoke engagement surface is adapted to engage with a yoke (136) and to transfer a force between the cam follower and the yoke. Rotation of the housing relative to the housing provides transmission of force between the platform and a spring arrangement.

Description

Technical Field

[0001] The inventive concept relates to a balancing mechanism having a wide range of applications, particularly in the audio-visual field, and providing a tiltable mounting for a payload, such as a camera. Background Art

[0002] Panoramic heads are commonly used to support cameras in the film, streaming and broadcast industries. The camera and lens are mounted on a rotatable and tiltable support member so that the camera operator can move them. A restoring torque device is provided to counteract the unbalanced moment caused by the weight of the camera when the platform is tilted, and on some heads this device is arranged so that the unbalanced moment caused by the tilt of the camera is accurately balanced by the restoring torque device within the operating range of the head. Such heads are considered to be "perfectly balanced" because the camera and lens can be moved by the operator to any tilt angle and will then remain at that angle without the operator applying a balancing torque.

[0003] Prior patents have disclosed means of providing a restoring torque device through the application of various mechanical systems that produce the correct restoring moment at any tilt angle by compressing a spring and reacting the spring force through a non-linear mechanical linkage or coupling. Such a mechanical device can not only be arranged to provide the correct restoring torque, but can also be adjusted to operate correctly with different payloads, where the mass and the height of the center of mass above the tilting platform may be different. This may occur, for example, if different cameras and lenses are mounted on the platform.

[0004] There are several previously disclosed mechanical systems that use springs to provide the correct restoring torque to achieve a perfectly balanced gimbal.

[0005] WO-A-03 / 081121 of Vitec Group of Companies discloses a tiltable mount for a payload having a platform for receiving the payload. It discloses a spring drive device for controlling the tilting of the platform about the axis of rotation of the mount on either side of a neutral position, in which a cam rotates with the mount and a cam follower moves a rod to convert the rotation of the rod into linear motion to affect a spring.

[0006] EP-A-1640653 to Cartoni discloses a tiltable mount for a payload having a connecting rod eccentric to the axis of rotation of the mount and a wing element pivoted on one side and coupled to the connecting rod to follow its movement. A spring is coupled to the wing element so that it can slide relative to the wing element for adjustment.

[0007] GB-A-2469199 of the Vitec Group of Companies discloses an arrangement in which a spring provides a balancing force for the rotation of a platform, the spring being mounted eccentrically with respect to the axis of rotation of the platform, the spring tension being adjustable by a leadscrew coaxial with the spring.

[0008] Important attributes of a balancing mechanism for a tilting camera platform include how adaptable the system is to balancing different weights or different center of mass heights of payloads to accommodate different cameras and lenses; the operating tilt angle of the platform when balancing, which is preferably plus or minus 90 degrees; the minimum and maximum payloads that can be balanced; the size of the mechanism, which is preferably compact enough to fit underneath the tiltable platform; the weight of the mechanism, which is preferably as light as possible to make it easier to carry the pan / tilt platform; and the manufacturing cost of the unit.

[0009] The cited prior systems suffer from deficiencies in one or more of these attributes that the present invention seeks to improve.

[0010] An object of the inventive concept is to provide a counterbalancing mechanism mounting apparatus for a tiltable mount to provide a counterbalancing force when a payload is tilted, which apparatus is adapted to operate with a variety of payload weights and sizes, and which is precisely adjustable, compact and relatively easy to manufacture. Summary of the invention

[0011] The present invention provides a mounting device, comprising a housing adapted to be detachably attached to a support device, the mounting device further comprising a platform for supporting a payload, the platform being attached to the housing, the housing being pivotally attached to the housing and being rotatable relative to the housing about an axis, wherein the housing has an annular cam arranged therein, the cam being arranged concentrically with the axis and having an inner cam surface, the device further comprising a cam follower having a cam follower arm, the cam follower arm comprising a cam engagement surface adapted to engage with the inner cam surface when the cam rotates about the axis and following said inner cam surface, said cam follower being pivotally attached to the housing at a pivot point eccentric to said axis, and the cam follower further having a yoke engaging surface between the pivot point and the cam follower, the yoke engaging surface being adapted to engage a yoke and transfer force between the cam follower and the yoke, said yoke engaging the yoke engaging surface at a yoke engaging point, said yoke being adapted to engage a spring arrangement and transfer force between the yoke engaging surface and the spring arrangement, such that rotation of the housing relative to the outer shell provides transfer of force between the platform and the spring arrangement, wherein the spring arrangement is arranged such that an axis of the spring arrangement is substantially orthogonal to an axis of rotation of the cam.

[0012] In use, tilting of the platform causes the housing to rotate about the axis and relative to the housing, which remains stationary. Rotation of the housing causes the annular cam to move the cam follower and in turn transmit force between the cam follower and the yoke, which in turn engages the spring arrangement. Therefore, when the platform is tilted, the spring arrangement is able to resist rotation of the housing relative to the housing. This in turn resists the tilting movement of the platform.

[0013] As described above, the cam follower forms a single-sided lever in which the cam engaging surface and the yoke engaging surface are located on the same side of a pivot point; the pivot point of the cam follower forms the fulcrum.

[0014] Said support is outside the scope of protection of the inventive concept and may be of a known type such as a tripod.

[0015] The cam follower, yoke and spring arrangement may typically be attached to the housing, rather than directly to the housing, so that they do not rotate with the housing when the housing rotates when tilted.

[0016] The arrangement of the annular cam and cam follower provides a more precise and accurate arrangement than previously known arrangements. Such an arrangement can also be lighter.

[0017] The spring arrangement may be arranged substantially orthogonally relative to the cam axis of rotation. This arrangement provides a direct coupling of the payload force to the spring arrangement, thereby providing a simpler, lighter mechanism than previously known arrangements, particularly those where the force must actually be rotated 90 degrees. The arrangement also provides a compact arrangement within the housing.

[0018] The spring arrangement may be arranged substantially perpendicular to the platform when the platform is in a neutral position, ie when the platform is substantially horizontal in use, the spring arrangement may be arranged substantially vertically. Thus, the spring arrangement axis will be perpendicular to the cam rotation axis in two planes.

[0019] Alternatively, the spring arrangement may be arranged such that the spring arrangement axis is angled with a perpendicular to the platform while still being orthogonal to the cam axis of rotation. In other words, the spring arrangement may have a neutral position within the housing wherein the spring arrangement axis is orthogonal to the cam axis of rotation, but the spring arrangement axis is not vertical in the neutral position.

[0020] An angle of 23 degrees from the spring arrangement axis to the vertical (vertical when the platform is in a neutral position (i.e. substantially horizontal)) has been found to be advantageous. Other angles between 0 and 90 degrees from the vertical are possible. The angle of the spring arrangement axis relative to the vertical of the platform is not usually adjustable by the user - the angle is usually fixed in each exemplary unit of the device.

[0021] The spring arrangement is usually chosen to provide a spring force to balance the force when the payload is tilted so that the payload does not fall quickly under the force of gravity when the payload is tilted. The user is therefore able to carefully control the amount of tilt of the payload - this is useful when using a camera, for example.

[0022] The spring arrangement may comprise two springs. Optionally, the spring arrangement may comprise more than two springs. Preferably, the spring arrangement comprises two or more springs arranged parallel to each other. Parallel springs provide a good trade-off between spring force and the risk of spring coils binding. Optionally, the spring arrangement may comprise two or more springs arranged coaxially to each other.

[0023] The yoke engaging surface of the cam follower may have a substantially planar portion.

[0024] The yoke may include a spring roller having a cylindrical portion in the area where the yoke engages the yoke engagement surface of the cam follower, wherein the spring roller is rotatable. Thus, as the cam follower moves, the spring roller may roll along the yoke engagement surface of the cam follower. This rolling action facilitates smooth engagement between the cam follower and the yoke.

[0025] The spring arrangement and yoke may be mounted on a slider adapted to be movable relative to the housing. Thus, the spring arrangement, and in particular the yoke, is movable relative to the yoke engagement surface of the cam follower. Preferably, the slider is adapted to be movable in the plane of the pivoting action of the cam follower. For a particular position of the slider, the yoke and the yoke engagement surface of the cam follower engage at a particular distance from the pivot point of the cam follower. As the slider moves to different positions, the yoke engages with the yoke engagement surface of the cam follower at different distances from the pivot point of the cam follower. The distance between the pivot point to the cam engagement surface of the cam follower is substantially fixed. Thus, the mechanical advantage of the lever between the force on the cam and the force on the spring can be varied. This provides the advantage that the resistance to rotation of the cam when the platform is tilted can be varied. This is useful because the balancing mechanism contemplated by the present invention can be used over a range of payload masses and center of mass heights.

[0026] By carefully adjusting the position of the sliders, the mounting apparatus is able to provide a substantially balanced arrangement so that a user can tilt the payload precisely and in a stable manner so that when the user stops applying force to the payload, the platform stops moving.

[0027] The slider can be moved by a balance adjuster, for example, which includes a threaded rod. Its rotation causes the slider to move relative to the housing. The balance adjuster may further include a balance adjustment wheel. The wheel can provide a mechanical advantage to easily rotate the rod. The balance adjuster can be mounted relative to the housing so that it does not move when the platform is tilted.

[0028] The contour and / or periphery of the inner cam surface can be arranged to move the cam follower in a particular relationship to the angle of inclination of the platform.

[0029] The cam follower can be shaped and / or sized so that the cam engagement surface moves in a particular relationship to the angle of inclination of the platform.

[0030] Those skilled in the art will appreciate that the inventive concept may be arranged such that, when the platform is tilted, the cam remains stationary and the cam follower and spring arrangement rotate with the platform. Such an arrangement may be advantageous, for example, if the counterbalance adjuster is mounted relative to the housing or platform, rather than relative to the casing. Those skilled in the art will appreciate that such suggested alternative arrangements are intended to be equivalents within the scope of the inventive concept.

[0031] The cam as described above may be described as a first cam in an arrangement in which a second cam is also provided within the mounting device.

[0032] The mounting device may comprise two annular cams substantially as described above, arranged coaxially within a housing. In other words, a second cam may be provided within the housing coaxially with the first cam, the second cam being substantially identical to the first cam. In such an arrangement, each of the two cams may have a cam follower with a cam engagement surface, the cam follower in turn being connected to a single common rod and yoke engagement surface adapted to engage with a single common yoke. Alternatively, a mounting device having two annular cams may comprise separate cam followers associated with respective annular cams as described above.

[0033] In the example described, the cam follower forms a single-sided lever in which the two load points (cam engagement surface and yoke engagement point) are located on the same side of the pivot point. The skilled practitioner will note that in another embodiment, a double-sided lever arrangement may be chosen in which the two load points are located on opposite sides of the pivot point.

[0034] Some important advantages of the described embodiments are:

[0035] Perfect or near-perfect balance - By selecting the appropriate cam profile, the mechanism will accurately balance payloads of varying masses and heights throughout the entire operating range.

[0036] Large tilt angles - The mechanism can be arranged to provide plus or minus 90 degree tilt. Previous mechanisms may be mechanically constrained to lower tilt angles, which is a disadvantage. The possibility to tilt the platform vertically upwards and / or downwards is an advantage.

[0037] Ability to balance a wide range of payload weights - Prototypes of the mechanism are able to balance down to zero weight and up to payloads greater than 25kg. This is unusual in a single balancing mechanism and means that a single mount is able to replace several previous designs, each with a narrower payload range. This is due to the simple and wide range adjustment mechanism (thus being able to go down to zero without mechanism binding) and the short and direct load path, which reduces the forces that need to be contained by the mechanism and thereby reduces its bulk.

[0038] Compact packaging - uses two cams with a rod and spring between to hold the internal load down and eliminates any torsional moments that need to be contained by the mechanism. It also maximizes the use of space under the platform. The mechanism also provides a simple and direct adjustment mechanism (by moving the spring arrangement) and simple integration of a damper mechanism that can be retrofitted on the outside of the platform hinge bearing.

[0039] · Easy to manufacture - The number of components is limited and all components are easy to manufacture, which reduces the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 The basic principle of this mounting device is shown.

[0041] Figure 2 One embodiment of the invention is shown, constructed within a typical panoramic head.

[0042] Figure 3 Here is another view of the same embodiment showing how the lever ratio and counterweight are adjusted. Other arrangements of the adjustment mechanism are possible (rack and pinion, screw and nut, cam).

[0043] Figure 4 is a view of an embodiment of the invention in which two cams are used, one on either side of the cam follower and spring mechanism. This balances the forces on the cam followers, reducing the forces on the cams, thereby reducing manufacturing cost and weight.

[0044] Figure 5 An alternative embodiment of the mounting device of the present invention is shown. DETAILED DESCRIPTION

[0045] The principle of the present invention is described by referring to Figure 1 To best describe it, Figure 1 Only certain key elements are shown in schematic form in an embodiment of the installation. Figure 1 In the specification, the key element is shown in two discrete positions, which are intended to indicate the first position and the second position. Figure 1When considered together, these should be clear to those skilled in the art. Figure 1 Not to scale, but only to aid understanding of the operation of the balancing mechanism.

[0046] The mounting apparatus 100 has a tiltable platform 102 having a pivot point 104 - an axis marked O. When the platform 102 is in a first position, directly above the pivot point 104, the payload (not directly shown) has a center of mass A. When the platform 102 is tilted through an angle θ in use, the payload center of mass shifts to B. The distance OA is equal to the distance OB and is shown as r, and the new height of the payload above O is shown by OC, which in trigonometry is equal to rcos(θ).

[0047] Also attached to the tiltable platform 102 and rotating about the same pivot point is a cam 106 (only a portion of the cam is shown here for clarity). Due to the inner profile of the cam 106, a roller 108 (a portion of a cam follower 110) can be displaced by the cam 106 when the cam moves. The cam follower 110 pivots at R, and as the roller 108 rolls on the inside of the cam 106, the cam follower 110 is displaced due to the displacement of the roller 108. When θ equals zero, the roller 108 is at S_1, and when at an angle θ, the roller is at S_θ. The end of the cam follower 110 is thus displaced a distance d, from S_1 to S_θ. The length of the cam follower RS_1 = RS_θ = b.

[0048] A return spring 112 is supported on the lever 110 at a junction 114 along the length of the cam follower 110. The spring 112 has a spring axis X that is substantially orthogonal to the axis of rotation O. The distance from the lever pivot point R to the junction 114 is a and is adjustable. When the platform 102 is tilted, the roller end of the cam follower 110 is displaced by the cam a distance d, and by geometry, the junction 114 is displaced a distance x=da / b.

[0049] The absolute height of the payload's center of mass above the ground will change as the platform 102 is tilted. In this case, the tilt angle is θ, and the payload moves downward, which reduces its potential energy by mgr(1-cos(θ)), where m is the mass of the payload, r is the distance of the center of mass from the platform's tilt hinge, and g is the gravitational constant.

[0050] In order for the platform and payload to remain in equilibrium, the potential energy lost by the payload must be equal to the elastic energy gained by the restoring spring. This elastic energy gained is equal to 1 / 2kx 2 , where x is the deflection of the spring.

[0051] x depends on the lever ratio and the cam function. There are several ways to define a cam profile. In this example, we define the cam profile in terms of the end deflection d of the cam follower at a given angle θ: d = C(θ).

[0052] If the cam function is C(θ), then x = a / b C(θ), where b is the total length of the cam follower and a is the distance from the pivot point to the spring fulcrum. Therefore, for balance, And if the cam profile is arranged so that Where c is a constant, so by adjusting a, Able to achieve balance.

[0053] In this equation, b, c, k are all constants set by the geometry of the mechanism, and g is a universal constant. The cam profile C(θ) depends only on θ and therefore does not change with different configurations or adjustments of the payload. m and r are the mass and height of the payload, so if a is adjusted so that they are balanced in any position, then the payload will be balanced at any tilt angle θ.

[0054] The equation also shows how the mechanism balances very small payloads, down to payloads of zero mass. If m is zero, the equation shows that balance can be achieved by setting a to zero. In practice, this would mean moving the yoke engagement point on the cam follower to coincide with the pivot point.

[0055] The maximum payload that can be fully balanced will be when a reaches its maximum value. It is practical to extend the yoke engagement point beyond the cam engagement surface so that a>b, and the payload moment mgr that can be balanced is then 2 ck / 2b 2 .

[0056] Figure 2 An example of a counterbalance mechanism 100 is shown in actual implementation within a panoramic head, showing a vertical section through the head.

[0057] The tiltable platform 102 rotates about the axis O. The cam 106 has an annular inner cam surface 118; the cam 106 is arranged coaxially with the axis O and is fixed to the platform 102. One end of the cam follower (110 and 116) is attached to the roller 108; when the cam 106 rotates, the roller 108 rolls around the cam surface 118. The other end of the cam follower pivots at R, and the cam follower 116 also has a yoke engagement surface (at Figure 2 The yoke (also not shown) has a flat portion. Figure 2The yoke 100 is shown clearly in the figure and has a spring roller 124 attached thereto, which in turn is attached to a double spring block 126. The yoke bears against the flat portion of the cam follower 116 for adjusting the balance. The balance mechanism 100 can be attached to a tripod via a bowl mount 128 and a translation bearing (not shown).

[0058] Figure 3 Shown through Figure 2 Different cross-sections of the same embodiment shown. In use, the platform 102 drives the cam 106 (not shown) via the roller 108 (not shown) and the pivot R, thereby driving the cam follower 110. The cam follower 110 is displaced at its other end 110' by the movement of the cam 106; the cam follower 110 has a flat portion 130 along which the spring roller 124 can move. The spring roller 124 drives two springs 132, 134 via a yoke 136, and these springs bear against a slide 138, which slides on a base block 140. The two springs 132, 134 form a spring arrangement with a spring arrangement axis X. The spring arrangement axis X is substantially orthogonal to the cam rotation axis O (as shown in Figure 1). Figure 2 130). Adjustment is made by sliding the slider 138 and therefore the point on the flat portion 130 of the cam follower 110 where the spring roller 124 bears against the cam follower 110. The position of the slider 138 is adjusted by a threaded rod (not shown) located in the threaded portion 142 of the slider 138 and having two bearings 144 and 146 in the base block 140. An adjustment knob is located at the end of the threaded rod so that turning the knob displaces the slider 138 and thereby the point at which the spring roller 124 contacts the cam follower 110. The balancing mechanism 100 can be attached to a tripod via the bowl mount 128 and the translation bearing (not shown).

[0059] Figure 4An embodiment using two cams 106 and 106a is shown, which are equally arranged around a single central cam follower 110 and spring block 126. In use, the platform 102 drives the cams 106 and 106a, and thus the cam follower 110, via the roller 108 and the pivot R (not shown). The cam follower 110 is displaced at its other end (not shown) by the movement of the cams 106 and 106a; the cam follower 110 has a flat portion 130 along which a single spring roller 124 can move. The spring roller 124 drives two springs 132, 134 via a yoke 136, and these springs bear against a slide 138, which in turn slides on a base block 140. The cam follower is arranged with a second roller (not shown) in relation to the cam 106a. Adjustment of the balance is performed by sliding the slider 138 and the point on the flat portion 130 of the cam follower 110 where the spring roller 124 bears against the cam follower 110. The position of the slider 138 is adjusted by a threaded rod (not shown) located on a threaded portion 142 (not shown) of the slider 138 and having two bearings 144 and 146 (not shown) in the base block 140. An adjustment knob is located at the end of the threaded rod so that turning the knob displaces the slider 138 and thereby displaces the point where the spring roller 124 contacts the cam follower 110. Figure 4 It is also shown how a drag mechanism 148 (which is not the subject of the present application) can be conveniently placed on the outside of the balancing mechanism 100. The balancing mechanism 100 can be attached to a tripod via the bowl-shaped mount 128 and a translation bearing (not shown).

[0060] Note that in the example shown and described, the spring and cam follower mechanism is stationary and the cam rotates with the tilted platform. This allows the adjustment knob to be in a fixed position on the counterbalance mechanism. The spring is shown vertical, but it can be positioned at any angle in a plane orthogonal to the tilt axis to aid packaging or adjustment knob positioning.

[0061] Figure 5 Shows Figure 2 and Figure 3 An alternative arrangement is shown in which the spring arrangement is arranged such that the spring arrangement axis X is angled with a perpendicular P to the platform 102 whilst still being orthogonal to the cam rotation axis. Figure 5 Some other features described herein and shown in other drawings are not included for the sake of clarity.

[0062] Figure 5A mounting device 100 is shown in which a platform 102 drives a cam and thus a cam follower 110 via a roller 108 (not shown) and a pivot R. The cam follower 110 is displaced at its other end by the movement of the cam; the cam follower 110 has a flat portion along which a spring roller 124 can move. The spring roller 124 drives two springs 132, 134 via a yoke 136, and these springs bear against a slide which slides on a base block as described herein. The two springs 132, 134 form a spring arrangement with a spring arrangement axis X. The spring arrangement axis X is substantially aligned with the cam rotation axis O (not shown). Figure 5 But if Figure 2 The spring arrangement axis X is at an angle to the vertical line P of the platform 102, as shown in FIG. Figure 5 , as shown by the corresponding dotted lines in . In this example, the angle of the spring arrangement axis X relative to the vertical line P is about 23 degrees. Adjustment of the mounting device 100 is performed by sliding the slider and therefore a point on the flat part of the cam follower 110, wherein the spring roller 124 bears against the cam follower 110, as described herein. The position of the slider is adjusted by a threaded rod located on the threaded part of the slider and has two bearings in the base block. The adjustment knob is located at the end of the threaded rod so that rotating the knob displaces the sliding block and thereby the point where the spring roller 124 contacts the cam follower 110. The balancing mechanism 100 can be attached to a tripod by means of a bowl-shaped mount and a translation bearing.

[0063] from Figure 5 It can be seen in FIG. 1 that when the platform 102 is in a neutral position (ie substantially horizontal), the spring arrangement has a neutral position within the housing, wherein the spring arrangement axis X is orthogonal to the cam rotation axis, and the spring arrangement axis X is not vertical. Figure 5 In the embodiment, the spring is arranged at approximately 23 degrees relative to the vertical line P in the neutral position, which has been found to be advantageous.

Claims

1. A mounting device comprising a housing adapted to be removably attached to a support device, the mounting device further comprising a platform for supporting a payload, the platform being attached to the housing, the housing being pivotally attached to the housing and being rotatable relative to the housing about an axis, wherein the housing has an annular cam disposed therein, the cam being disposed concentrically with the axis and having an inner cam surface, the device further comprising a cam follower, the cam follower having a cam engagement surface adapted to engage with and follow the inner cam surface as the cam rotates about the axis, The cam follower is pivotally attached to the housing at a pivot point eccentric to the axis, the cam follower also having a yoke engagement surface, the yoke engagement surface being adapted to engage with a yoke and to transfer force between the cam follower and the yoke, the yoke engaging the engagement surface at a yoke engagement point, the yoke being adapted to engage with a spring arrangement and to transfer force between the yoke engagement surface and the spring arrangement, such that rotation of the housing relative to the housing provides for transfer of force between the platform and the spring arrangement, wherein the spring arrangement is arranged such that an axis of the spring arrangement is substantially orthogonal to an axis of rotation of the cam.

2. The mounting device according to claim 1, wherein: The cam follower, yoke and spring arrangement are typically attached to the housing rather than directly to the casing so that they do not rotate with the casing as the casing tilts and rotates.

3. A mounting device according to any preceding claim, wherein: The spring arrangement is arranged to be arranged substantially perpendicular to the platform when the platform is in a neutral position.

4. A mounting device according to any preceding claim, wherein: The spring arrangement comprises two springs.

5. The mounting device according to claim 4, wherein: The spring arrangement comprises two or more springs arranged parallel to each other.

6. A mounting arrangement according to any preceding claim, wherein: The yoke engaging surface of the cam follower has a substantially planar portion.

7. A mounting arrangement according to any preceding claim, wherein: The yoke includes a spring roller having a cylindrical portion in an area where the yoke engages the yoke engagement surface of the cam follower, wherein the spring roller is rotatable.

8. A mounting arrangement according to any preceding claim, wherein: The spring arrangement and the yoke are mounted on a slide which is adapted to be movable relative to the housing.

9. The mounting device according to claim 8, wherein: The slide block is adapted to be movable within the plane of the pivoting action of the cam follower.

10. A mounting device according to claim 8 or claim 9, wherein: The slide block is movable by means of a balance adjuster.

11. The mounting device according to claim 10, wherein: The balance regulator further includes a balance adjustment wheel.

12. A mounting arrangement according to any preceding claim, wherein: The spring arrangement is arranged such that a spring arrangement axis is angled with a perpendicular to the platform.

13. The mounting device according to claim 12, wherein: The spring arrangement is arranged such that the spring arrangement axis is at an angle of approximately 23 degrees to a perpendicular to the platform.

14. A mounting arrangement according to any preceding claim, wherein: The mounting device comprises a second cam coaxially arranged within the housing, the second cam being substantially identical to the cam.

15. The mounting device according to claim 14, wherein Each of the two said cams has a cam follower having a cam engagement surface which in turn is connected to a single common lever and yoke engagement surface adapted to engage with a single common yoke.

16. The mounting device of claim 14, wherein: Each annular cam includes a discrete cam follower associated with the respective annular cam.

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