GB2567174A

GB2567174A - Motion arrangement

Info

Publication number: GB2567174A
Application number: GB1716197.7A
Authority: GB
Inventors: Richard Glover Anthony; Murray Charles Odhams Andrew; Owen Sexton Michael; Braysher Steven
Original assignee: McLaren Applied Technologies Ltd
Current assignee: McLaren Applied Ltd
Priority date: 2017-10-04
Filing date: 2017-10-04
Publication date: 2019-04-10
Anticipated expiration: 2037-10-04
Also published as: WO2019069077A1; GB201716197D0; GB2567174B

Abstract

A motion arrangement for a vehicle simulator for moving a load with six degrees of freedom is disclosed. The motion arrangement comprises struts 4, 5, 6, 7, each being rotatably attached to a respective primary sled 8, 11, 12, 13 and coupled to the load 1. An intermediate link 24, 25 is attached respectively to struts 4, 5 and secondary sleds 9, 10. The intermediate links are attached to the struts at a location between their respective sleds and the load and thus movement of the pair of the intermediate links causes the associated struts to pivot, in turn imparting motion onto the load. An elastic support 70 is coupled to the first support and exerts an upwards force on the load via the first support. The elastic support is mounted so that the rate of compression of the elastic support reduces with increasing downward vertical motion of the load.

Description

MOTION ARRANGEMENT

This invention relates to a motion arrangement for moving a load. The motion arrangement may support a load. The motion arrangement may be especially suitable for use for a motion simulator, particularly a land vehicle motion simulator.

Motion simulators are widely used for simulating the motion of vehicles for training purposes and in games installations. A position for an occupant is mounted on a movable platform, and the platform is moved, usually by pistons that are mounted to it, to simulate the motion of the vehicle. In applications such as games where low fidelity of movement is acceptable a simple pivoting arrangement can be used to mount the platform. In higher fidelity applications such as aircraft training simulators the platform is normally mounted on a Stuart platform or hexapod. The Stuart platform has a platform which is connected to a base by six hydraulic or electromechanical pistons. The pistons are pivotally mounted to the base and to the platform. The occupant position is fixed on the platform. The pistons are operated in order to move the platform in three dimensions. Since there are six pistons the platform can be moved in six degrees of freedom, thereby offering realistic simulation.

The Stuart platform is well suited for simulating aircraft motion because it allows substantial movement of the platform in three dimensions. However, in order for significant horizontal motions to be imparted to the platform it must be located well above the base; otherwise the pistons do not have sufficient freedom of movement in the horizontal plane. Typically the base is mounted at ground level, so in order to simulate substantial horizontal motion the platform, with the occupant on it, must be lifted some distance off the ground. This is inconvenient for the occupant. It also means that a large volume of space around the simulator must be available in order to allow the simulator to move freely over its full spatial operating envelope.

Normally a structure is built on the platform to hold the occupant and to give the appearance of the environment that is being simulated. Another problem with the Stuart platform is that the entire weight of the platform and any occupant structure must be borne by the pistons. Therefore, the pistons must be powerful enough not just to move the platform and the structure but also to carry its weight. Applications in which substantial horizontal forces must be imparted include the simulation of motion of land vehicles such as racing cars.

In an alternative design of simulator the load could be supported on six or more rigid rods. At their upper ends the rods are attached to the load by flexible joints. At their lower ends each rod is attached by a spherical joint to a respective sled which runs on one of three horizontal tracks. The tracks are arranged spaced apart but parallel. By moving the sleds on the tracks the load can be moved with six degrees of freedom.

Another design of motion simulator is disclosed in GB 2 378 687. A simulator platform is supported on rocker mechanisms. Each rocker mechanism comprises a rocker arm slidably linked to the side of the platform. The base of the rocker arm is mounted on a first sled which can move the base of the arm along a linear track. A connecting rod extends between the upper end of the rocker arm and a second sled also movable on the track. The attachment point between the platform and each rocker arm can be moved vertically and in one horizontal direction by means of the sleds. Coordinated operation of all the rocker mechanisms is used to manipulate the simulator platform as required. This arrangement has some advantages over other structures described above, but has some drawbacks. In particular the rocker mechanisms must be large if the system is to impose larger amounts of vertical travel, as is required if the system is to simulate the motion of conventional road cars.

With a simulator that provides motion in six degrees of freedom, it can be desirable to configure the system so that the actuators that drive motion of the system are not required to support the entire weight of the payload. This can reduce the forces required of the actuators, meaning that they can be reduced in size and cost, and can operate at lower power.

There is a need for an improved form of motion system, for example for road vehicle simulators.

According to a first aspect there is provided a motion arrangement for moving a load with six degrees of freedom, the motion arrangement comprising: a first support coupled to the load for at least partially supporting the load, the first support being rotatably mounted on a first moveable drive element; an intermediate link extending between the first support and a second moveable drive element, the intermediate link element being mounted on the second drive element and the second drive element being capable of driving relative to the first drive element so as to cause the intermediate link to alter the attitude of the first support; and an elastic support coupled to the first support for exerting an upwards force on the load via the first support, the elastic support being mounted so that the rate of deflection of the elastic support with vertical motion of the portion of the load to which the first support is coupled reduces with increasing deformation of the elastic support from its neutral position.

Preferably the said deformation is compression. Preferably the said vertical motion is downward vertical motion.

The motion arrangement may be configured so that as the load is lowered a reduction in mechanical advantage of the elastic support over the load counteracts increased force developed by the elastic support.

In the neutral position of the elastic support it is exerting an elastic force which exactly balances the portion of load supported by the first support.

The rate of deflection of the elastic support with vertical motion of the portion of the load to which the first support is coupled may reduce with increasing downwards motion of that portion of the load.

The said rate may be the ratio of the distance by which the elastic support is deflected to the distance moved vertically by the said portion of the load.

The elastic support may be a spring, for example a gas spring. The gas spring may be pre-loaded with a gas pressure such that the load is held substantially at the mid point of its operational travel without force being applied by the first or second drive elements.

The elastic support may be mounted so that, without adjustment of the elastic support, the upwards force applied to the load by the elastic support is substantially constant throughout the vertical operating range of the load.

The elastic support may extend between a first location at which it is coupled to the first support and a second location at which it is coupled to the first drive element.

The first and second locations may be spaced from the location where the first support is mounted to the first drive element.

The second location may be inboard of the location where the first support is mounted to the first drive element.

The elastic support may be rotatably coupled to the first support at the first location.

The elastic support may comprise a first mount coupled at the first location to the first support, a second mount coupled at the second location to the first drive element and a flexible elastic element extending between the first and second mounting regions. The motion arrangement may comprise an alignment mechanism configured to maintain alignment between the first and second mounts by causing the first mount to rotate relative to the first support as the first support rotates relative to first drive element. The alignment mechanism may be a four-bar linkage.

The alignment mechanism may comprise a first link fast with the first support and extending on the opposite side of the first location to the first support, and a second link rotatably mounted to the first link and to the first drive element.

There may be a second support coupled to the load for at least partially supporting the load. The second support may be rotatably mounted on a third moveable drive element. There may be a second intermediate link extending between the second support and a fourth moveable drive element, the second intermediate link element being mounted on the fourth drive element and the fourth drive element being capable of driving relative to the third drive element so as to cause the second intermediate link to alter the attitude of the second support. There may be a second elastic support coupled to the third support for exerting an upwards force on the load via the second support, the second elastic support being mounted so that the rate of deflection of the second elastic support with vertical motion (conveniently downward vertical motion) of the load reduces with increasing deformation (conveniently compression) of the second elastic support from its neutral position.

The motion arrangement may be configured so as the load is lowered a reduction in mechanical advantage of the second elastic support counteracts the increased force in the second elastic support.

Each drive element may be a linearly acting drive element. Each drive element may be a linear motor. The first, second, third and fourth drive elements may operate on a common motion axis.

According to a second aspect there is provided a motion arrangement for moving a load with six degrees of freedom, the motion arrangement comprising: first, second and third primary link elements, each primary link element being (i) rotatably attached to a respective linearly movable driver element and (ii) slidably and rotatably attached to the load; a first intermediate link element attached to the first primary link element and to a fourth linearly movable drive element; a second intermediate link element attached to the second primary link element and to a fifth linearly movable drive element; the first intermediate link element being attached to the first primary link element at a location between the locations where the first primary link element is attached to its respective driver element and to the load, and the second intermediate link element being attached to the second primary link element at a location between the locations where the second primary link element is attached to its respective driver element and to the load; and comprising an elastic support acting between one ofthe first, second and third primary link elements and the drive element to which that one of the link elements is attached, for at least partially supporting the load, the elastic support being mounted so that the rate of deflection of the elastic support with vertical motion (conveniently downward vertical motion) ofthe portion ofthe load to which that one of the link elements is coupled reduces with increasing deformation of the elastic support (conveniently as a result of downward motion of the portion ofthe load) from its neutral position.

The motion arrangement may comprise a third intermediate link element attached to the third primary link element and to a sixth linearly movable drive element, the third intermediate link element being attached to the third primary link element at a location between the locations where the third primary link element is attached to its respective driver element and to the load.

The driver elements may be sleds driveable relative to a base.

The motion arrangement may comprise a fourth primary link element, the fourth primary link element being (i) rotatably attached to a respective linearly movable driver element and (ii) slidably and rotatably attached to the load.

The locations at which the first, second and third primary links are coupled to the load may be non-collinear.

There may be means mounted between the load and the driver elements for moving the load relative to a ground or base in a direction parallel to a basal plane and/or parallel to a basal plane of the load. Such means may be slidable couplings between each primary link element and the load.

The linearly movable driver elements may be configured for exclusively linear motion. The linearly movable drivable elements may each be drivable only along a single linear path. Those paths may be coplanar. Those paths may be parallel. The first and second drivable elements may be drivable along a common path. That/those paths may be parallel with the paths along which the first to third drivable elements are drivable. The first and second drivable elements may be drivable by a common linear motor. The fourth and/or fifth drivable elements may be drivable along/by the same path/motor. The third drivable element may be drivable along a path orthogonal to that along which the first and second drivable elements are drivable.

The first primary link element may be slidably attached to the load such that the load can translate with respect to the first primary link element along a first axis. The second primary link element may be slidably attached to the load such that the load can translate with respect to the second primary link element along a second axis. The first and second axes may be convergent. The first and second axes may be coplanar.

The driver elements of the first, second and third primary link elements may be linearly movable in a common plane.

The driver elements of the first, second and third primary link elements may be linearly movable in mutually parallel directions.

The range of motion of the motion arrangement may be such that for all configurations of the arrangement the locations of attachment of the first intermediate link element to the first primary link element and of the second intermediate link element to the second primary link element are lower than the locations of attachment of the first and second primary link elements to the load. The point of attachment of one or more of the intermediate link elements to the respective primary link elements may be such that it is between (a) a plane perpendicular to a line joining the points of attachment of that primary link element to its respective linearly drivable element and to the load and passing through the point of attachment of that primary link element to its respective linearly drivable element and (b) a plane parallel to that plane and passing through the point of attachment of that primary link element to the load. The range of motion of the motion arrangement may be such that that criterion is satisfied for all configurations of the arrangement.

One or more primary link elements may be attached by a respective revolute joint to their respective driver element.

One or more primary link elements may be attached by a respective spherically mobile joint to the load.

Each intermediate link element may be attached by a revolute joint to its respective primary link element. One or more primary link elements may be attached to the load at an attachment joint, and at least one intermediate link may be attached to its respective primary link element by the attachment joint. The attachment joint may be a respective spherically mobile joint to attach the respective primary link element to the load.

The driver element of each intermediate link element may be moveable along an axis collinear with the axis along which the driver element of the respective primary link element is movable.

The driver element of each intermediate link element is located inboard or outboard, with respect to the load, of the driver element of the respective primary link element.

Each primary link element may be in the form of a wishbone. Each wishbone may be broader at its attachment to its respective driver element than at its attachment to the load.

Each driver element may be a drivable component of a linear motor. Each driver element may be drivable with respect to a ground.

The motion arrangement may comprise an elastic element acting between components of the motion arrangement to at least partially support the weight of the load. The elastic element may be coupled to act between one of the primary link elements and one of the linearly movable driver elements. The elastic element may be coupled to act between (i) the linearly movable driver element to which one of the first, second and third primary link elements is attached and (ii) one of the fourth and fifth (and optionally the sixth) linearly movable driver elements.

The motion arrangement may comprise four primary sleds, each primary sled being coupled to the load by a respective connector strut that is attached to its primary sled by a revolute or spherical joint and to the load by a joint that permits rotation and linear motion, for example a cylindrical joint. Two, three or four of the connector struts may be coupled to respective secondary sleds by further connector struts, each further connector strut being attached to its connector strut by a revolute or spherical joint and to a respective secondary sled by a revolute or spherical joint. One or two of the connector struts may be not provided with such a further connector strut.

The sleds may be arranged so that the primary and secondary sleds serving a particular connector strut are constrained to slide along a common motion axis, for example defined by a single rail.

The load may include a cockpit for an occupant of the simulator.

Figure 1 shows a movable load platform for a simulator.

Figure 2 shows in detail the joint between a wishbone and the load platform of figure

1.

Figure 3 shows the platform of figure 1 arranged to perform as a land vehicle simulator.

Figure 4 illustrates a control system for the simulator of figure 3.

Figure 5 shows an elastic support mechanism.

The load platform 1 of figure 1 is supported by four wishbones 4, 5, 6, 7. The lower end of each wishbone is attached to a respective sled 8, 11, 12, 13. Each sled runs on one of a pair of linear tracks 2, 3. The lower ends of intermediate links 24, 25 are also attached to respective sleds 9, 10. Each of sleds 9, 10 also runs on one of tracks 9, 10. The upper ends of the intermediate links 24, 25 are attached to respective ones of the wishbones at points intermediate between the load platform and their respective sleds. The attachment of the upper ends of the intermediate links 24, 25 may be made to the wishbones themselves or to the attachment between the wishbones and the load platform. In this arrangement, the position of the load platform can be controlled with six degrees of freedom by positioning the six sleds appropriately. Because the intermediate links are attached to the wishbones at points that are between the load and the tracks, the load can readily be given substantial vertical travel, permitting it to be used to simulate the motion of normal road vehicles.

In more detail, figure 1 shows a load platform 1 for a simulator together with an arrangement for supporting and moving the platform. The load platform is generally trapezoidal in this example, but need not be. The load platform may be generally diamond-shaped and/or rhombus-shaped. The side edges 14, 15 of the load platform may be curved along at least part of their length. The side edges 14, 15 of the load platform are convergent. The side edges are co-planar in this example, but need not be. For convenience the end of the platform where the side edges are further apart will be termed the rear of the platform, and the opposite end the front.

The load platform may be generally shaped as two trapezoids joined together at one of their parallel sides. Such a load platform may be a six-sided polygon. In this case, the side edges 14,15 may be convergent with each other at each of their ends. The angle at which the side edges 14,15 are convergent with each other at each of their ends may be different.

Below the load platform are two tracks 2, 3. In this example the tracks are linear, coplanar and parallel. The sleds 8-13 run on the tracks, and are arranged so that they can each independently be driven to a desired position on their track in order to control the position of the load platform. To that end the tracks can conveniently incorporate magnetways of linear motors, which interact with the sleds to move the sleds. The sleds could be driven in other ways. For example the tracks could comprise racks and the sleds could comprise motors and pinions which engage the racks and which are driven by the motors to move the sleds; alternatively the sleds could be moved along the tracks by threaded worms or lead screws; alternatively the sleds could be moved hydraulically. By virtue of running on a respective one of the tracks each sled is constrained to follow the path of that track; in this example to move along the linear path defined by that track. The tracks 2, 3 are disposed generally transversely to the side edges 14, 15 of the load platform 1.

Four rigid wishbones 4, 5, 6, 7 run between the tracks 2, 3 and the load platform 1. Each wishbone is arranged so that at its upper end it has a single attachment point to the load platform; and at its lower end, where it is broader than at the upper end, it has two attachment points to a respective sled. The attachment structure at the upper end of the wishbones will be discussed in detail below with reference to figure 2. At the lower end of each wishbone the attachment points to the respective sled constitute a common revolute joint between the wishbone and the sled. The revolute joints between the wishbones and the sleds are designated 20, 21,22, 23 in figure 1. The axis of each of those revolute joints is perpendicular to the track on which the respective sled runs. Two of the wishbones (4, 5) run on one of the tracks (2), and two of the wishbones (6, 7) run on the other track (3). One wishbone running on each track is attached to each of the sides 14, 15 of the load platform. Thus the upper ends of wishbones 4, 6, which run on different ones of the tracks, are both attached to side 14; and the upper ends of wishbones 5, 7, which also run on different ones of the tracks are both attached to side 15.

In the case of the load platform being generally shaped as two trapezoids joined together, one wishbone of each of the sides 14, 15 are attached to one of the trapezoids and one wishbone of each of the sides 14, 15 are attached to the other trapezoid.

The intermediate links 24, 25 are rigid and extend between respective ones of the wishbones and further sleds 9, 10. Intermediate link 24 extends between wishbone 4 and sled 9. Intermediate link 25 extends between wishbone 5 and sled 10. In this example the sled of each intermediate link runs on the same track as the sled of the wishbone to which it is attached, but it could run on another track, which need not be a track on which the sled of any wishbone runs. In this example the sled of each intermediate link is arranged inboard of the sled of the wishbone to which it is attached, but it could be arranged outboard. In this example the intermediate links are attached to the rear wishbones 4, 5, but they could instead be attached to the front wishbones or to one of the front wishbones and one of the rear wishbones. Each intermediate link is attached flexibly to its sled by a joint 26, 27. This may be a spherical joint or a revolute joint whose axis is perpendicular to the axis of the track on which the sled of that intermediate link runs. Each intermediate link is attached flexibly to its wishbone by a joint 28, 29. This may be a spherical joint or a revolute joint whose axis is perpendicular to the axis of the track on which the sled of that intermediate link runs. Whilst joints 28, 29 are shown being attached to respective wishbone 4, 5, it will be appreciated that one or more of joints 28, 29 may be attached to respective runner 31 associated with its respective wishbone 4, 5.

The linear motors for the front sleds could have common magnetways. The individual linear motors for moving each front sled would then be defined electrically in operation of the motors. The same could be done for the rear sleds.

Figure 2 shows in more detail the mechanism by which wishbone 4 is attached to the side 14 of the load platform 1. The attachments between the other wishbones and the rails are analogous. A linear rail 30 is disposed along the side 14 of the load platform. At the upper end of the wishbone 4 is a runner 31 which can slide along the rail 30. The runner may comprise a bearing race to permit it to move freely along the rail. The runner 31 is attached to the wishbone 4 by spherical joint 16. Joint 16 could be a Cardan joint or of another form. The other wishbones are attached to respective runners by respective spherical joints 17-19. A similar rail extends along the opposite side 15 of the platform 1. Joint 28 and/or join 29 may be attached to the respective runner 31 of wishbone 4, 5.

The rails (e.g. rail 30) along the sides of the platform are non-parallel. They are closer together where they pass over one of the tracks (3) than where they pass over the other of the tracks (2).

Figure 1 shows the runners of the wishbones on each side of the load being connected to a common rail (e.g. 30). There could be additional rails, and the runners of the wishbones on each side could be connected to different rails. The rails to which the wishbones on each side of the load are connected could be parallel or could be angularly offset from one another.

The operation of the system will now be described. The positions of the sleds 8-13 are independently controllable by a controller 50. (See figure 4). When the sleds are in a particular set of positions along their tracks, the position of the platform 1 is fixed both translationally and rotationally. By moving the sleds the platform 1 can be controlled in six degrees of freedom. For example, with the axes defined as shown in figure 1 motions can be obtained as follows:

- Surge (translation along the X axis): When the sleds 8, 9, 12 that are coupled to one side rail 14 are moved towards the sleds 10, 11, 13 that are coupled to the other side rail 15 the platform 1 can be forced to move rearwards by the rails (e.g. 30) which are disposed along its sides 14, 15 sliding with respect to the runners (e.g. 31) on the ends of the wishbones. This motion arises because the sides of the platform are convergent. Conversely, when the sleds 8, 9, 12 that are coupled to one side rail 14 are moved away from the sleds 10, 11, 13 that are coupled to the other side rail 15 the platform 1 can be forced to move forwards.

- Sway (translation along the Y axis): When all the sleds 8-13 are moved together in a common direction along the tracks the platform 1 can be translated in that direction.

- Heave (translation along the Z axis): When the sleds 8, 12 that bear the wishbones 4, 6 on one side of the platform are moved away from the sleds 11,13 that bear the wishbones on the other side of the platform, and also the sleds 9, 10 that bear the intermediate links are moved towards each other, the platform can be lowered.

- Roll (rotation about the X) axis). Roll can be achieved by moving the sleds that bear the wishbones on one side of the platform (e.g. sleds 8, 12) in a common direction whilst moving a sled (e.g. sled 9) that bears one of the intermediate links so as to alter the inclination of the wishbone to which it is attached.

- Pitch (rotation about the Y axis). Pitch can be achieved by moving the sleds 9, 10 that bear the intermediate links so as to alter the inclination of the wishbones to which they are attached.

- Yaw (rotation about the Z axis). Yaw can be achieved by moving the forward sleds 12, 13 in one direction and the rear sleds 8-11 in the opposite direction.

The individual motions described above can be combined to give composite motions of the platform. The intermediate links may be attached to other ones of the wishbones, in which case the behaviours described above can be adapted accordingly.

Figure 3 shows the platform of figure 1 arranged to function as part of a simulator for simulating the motion of a land vehicle, for example a car. A cabin 40 for an occupant is mounted on the platform. The cabin may be a part vehicle chassis. It may include a cockpit to hold the occupant. The cabin includes user input devices such as accelerator and brake pedals 41 and a steering wheel 42. A display screen 43 is arranged around the platform for displaying a view of the environment that is being simulated. Alternatively the display can be borne by the platform, or the occupant could wear a headset incorporating a display. Loudspeakers 44 are located on or near the platform.

Figure 4 shows a control system for the simulator. The control system comprises a controller 50 having a processor 51 and a memory 52. The memory stores in a nontransient way:

(i) code 53 that is executable by the processor to enable the controller to control the motion of the platform in the desired way;

(ii) environment data 54 which defines the environment that is to be simulated: for example the layout of a track, the appearance of the track and its surrounding scenery and the performance characteristics of the track such as its heights, grip levels and cambers;

(iii) performance data 55 which defines the performance characteristics of the vehicle being simulated, for example its acceleration and deceleration rates, its roll and grip characteristics and the noises it makes.

To provide feedback to the control system illustrated in figure 4 each linear motor has a position sensor which generates a signal indicative of the position of the motor. The position sensors could be linear encoders mounted next to the linear motor tracks.

In operation the controller 50 receives inputs 56 from position sensors on the sleds 813 and control inputs 57 from the user input devices 41, 42. By executing the code 53 processor 51 forms a model of how the simulated vehicle defined by data 55 would behave under those control inputs in the environment defined by data 54. The outputs of that model are a desired position of the platform 1 with six degrees of freedom, sound to be played out by loudspeakers 44 and a video feed to appear on display screen 43. The sound and video are passed at 58 and 59 to the loudspeakers and the display. The desired position is passed to a sled controller 60. The sled controller receives the current positions of the sleds as input at 56 and the desired position and acceleration of the platform with six degrees of freedom at 61 and forms control outputs 62 for each of the six sleds so as to drive them to cause the platform to adopt the required position. The sled controller 60 could be implemented in software or hardware. The processor 51 could be implemented by one or more CPUs. The memory 52 could be implemented by one or multiple physical memory units. The controller 50 could be in a single physical unit or divided between multiple such units.

Springs (not shown in the figures), which could be mechanical or gas springs, can be coupled between each intermediate link 24, 25 and its respective wishbone 4, 5 to help support the weight of the platform. In the case of gas springs the pressure in the springs could be actuated by the controller, e.g. in dependence on the static weight of the load. Mechanical or air springs could be provided so as to act between any pair of the wishbones and/or between any wishbone and its sled and/or between any wishbone and the load. End stop buffers (not shown) can be provided at the ends of the rails to prevent over-travel.

In addition to achieving surge through urging the sleds of each side together or apart, as described above, one or more actuators could be added to drive the surge axis more directly. For example, this could be achieved by mounting one or more linear motor magnetways on the platform, parallel to the platform rails. The slider of each motor would be attached to one of the brackets (e.g. 31) on the distal ends of the wishbones.

To reduce the load on the sled motors during prolonged surge excursions a movable counter-weight could be attached to the mechanism (e.g. to the load or to the distal ends of the wishbones). The counter-weight is arranged to be driven in the opposite direction to the principal load in surge. Motion of the counter-weight could be driven by a motor carried by the load and arranged to drive the counter-weight relative to the load in the surge direction, or by the action of the wishbones on a second pair of rails which are attached to the counterweight and which converge in the opposite direction to the rails that are attached to the load. In one convenient arrangement the counterweight could be provided with one or more pair of rails that converge in the opposite direction to the rails on the load. Those rails could be slidably attached to a pair of the primary supports I wishbones which are attached to opposing rails of the load so that when the attachment points of those supports move together or apart the load and the counterweight will move in opposite directions.

In the arrangement shown in the figures the load is supported by four wishbones, two of which are attached to independently controllable intermediate links. In an alternative configuration the load could be supported by only three wishbones, each of which is flexibly attached to an independently controllable intermediate link. In the latter configuration, there are three linearly movable primary sleds, each of which is carries a respective primary support strut (e.g. a wishbone) which is also flexibly attached to the load. There could be a revolute joint between each primary strut and its sled and a spherical joint between each primary strut and the load. The primary struts are rigid, and preferably attached at their opposite ends to the sleds and the load. There are also three secondary sleds. Each secondary sled is linearly movable and is flexibly attached to a respective secondary support strut which is in turn flexibly attached to a respective one of the primary support struts at a point intermediate between its connection to its primary sled and to the load. Each secondary strut may be attached by a revolute joint to its sled and by another revolute joint to its primary strut. The secondary struts are rigid, and preferably attached at their opposite ends to the sleds and the primary struts. The sleds of each pair of an interattached primary and secondary strut may be movable linearly along parallel axes, and optionally collinearly. Two of the primary sleds may be attached to the side rails of the load so as to oppose each other for forcing the load to move in surge. The remaining primary strut may be attached centrally to the load, for example by a single rail running along the centreline of the side-rails by which the other wishbones are attached to the load, or by one of those other side-rails, or by a side-rail at a different angle to those other side-rails.

In the example shown in figure 1 supports 4 and 5 are driven by primary sleds 8, 11 and secondary sleds 9, 10, whereas supports 6 and 7 are driven only by primary sleds 12, 13. In other examples one or both of supports 6, 7 could be driven by a primary and a secondary sled. This could give greater control authority, particularly over jacking motion in Z of the end of the sled at which supports 4 and 5 are attached. A further alternative is for only one ofthe sleds 8, 11 at a first end of the sled to be driven by a secondary sled, and for only one of the sleds 12, 13 at the other end of the sled to be driven by a secondary sled. In each case a secondary sled is coupled to the respective support by a rigid element that can pivot with respect to the sled and the support, as with elements 24, 25 in the example of figure 1.

Instead of a secondary sled and additional connector element connecting that sled to the respective support 4, 5, 6, 7, other mechanisms could be used to constrain the inclination of the support relative to the sled. For example a rotational drive could be implemented at the rotational joint between the support and its primary sled.

The present structure is arranged to provide a compact mechanism for driving the motion platform with principal motions in the X and Y axes. In comparison to the Stuart platform the present structure allows substantial forces in the X and Y directions to be imparted without requiring the platform to be far above the base. This makes it significantly more convenient for the occupant to enter the chassis. The platform rails and especially the base rails can straightforwardly be made relatively long, allowing relatively large displacements to be imparted in the horizontal plane. For many road vehicles the greatest potential forces are in the surge and sway directions, which correspond to cornering and straight-line acceleration and braking. Therefore, it is preferred that the chassis is mounted relative to the platform rails and the base rails so that the sway and surge axes are in a plane parallel to all those rails. The surge axis is preferably parallel to the forward axis of the chassis and the sway axis is preferably perpendicular to the forward axis and the upward axis of the chassis. The forward and upward axes of the chassis will typically be defined by reference to an occupant/operator position in the chassis. Where the occupant position has a seat the forward axis is typically the forward-facing direction of the seat. The highest potential for force may often be in the sway axis since higher forces may often be expected during cornering than in straight-linear acceleration and braking. Therefore, it is most preferred that the sway axis is parallel to the base rails. This implies that the forward orientation of the chassis is perpendicular to the base rails.

Figure 5 shows an elastic mechanism suitable for providing additional support to any of the wishbones 4 to 7. Figure 5 is a view in the X direction of wishbone support 4 and the sled 8 to which that wishbone is pivotably attached. In figure 5 the wishbone has been sectioned to better show the elastic mechanism. As described above, the support 4 pivots with respect to the sled at revolute joint 20. An elastic unit or spring 70 acts between the support and the sled. The spring is arranged to be in compression in the operating mechanical range of the simulator. The spring applies a force on the support in a direction such as to cause it to apply upwards force on the sled. This resists the gravitational load of the sled and can help to reduce the force required to be applied by the sled motors. In the ideal case, the sled motors would only need to provide drive to accommodate the dynamic load requirements of the system, and the static load requirements would be met by one or more elastic mechanisms such as that shown in figure 5, provided on one or more of the supports 4 to 7. Preferably such elastic mechanisms are provided on all four of the supports 4 to 7.

A first end of the spring 70 is attached to the sled 8 which carries the respective support

4. The first end is attached to the sled at a location 71 spaced from the pivot 20. A second end ofthe spring is attached to the support 4 at a location 72 spaced from the pivot 20. In this example, location 71 is inboard of location 72 with respect to the centreline of the simulator load. This is convenient because the support will typically be angled so that it extends inboard of and higher than pivot 20, and hence the spring can conveniently be packaged between it and the sled. Alternatively, the spring could be located outboard of pivot 20, acting in tension, or could act as a torsion spring about pivot 20.

To avoid bending forces on the spring it is preferred that the one or both of the joints at 71 and 72 permit rotation of the spring relative to the sled 8 and the support 4 respectively. Such rotation is preferably about an axis parallel to the axis of pivot 20. In the example of figure 5, joint 71 is non-rotational and joint 72 permits rotation.

To avoid instability of the spring under compression it is preferred that load is applied axially along the spring. To maintain this configuration the mechanism of figure 5 includes a linkage which forces rotation of the upper part 80 of the spring to take place about joint 72, between the support 4 and the upper end of the spring, when rotation of the support 4 about joint 20 takes place. That linkage comprises a link 73 which is pivotally coupled at 74 to the sled 8. The other end of the link 73 is pivotally coupled at 75 to an extension 76 of upper part of the spring 70. The extension extends on the opposite side of pivot 72 from the elastic part of the spring. The extension 76 is fast with the upper part 80 of the spring. Pivot 74 is located on the opposite side of pivot 20 to joint 71. By suitable choice of the lengths of the extension 76, the link 73, of the location of pivot 74 relative to pivot 20 and of the location of pivot 72 on support 4, the motion of the upper end of the spring can be controlled so that the spring is always axially loaded within the working range of the simulator. Each of pivots 72, 74 and 75 may be revolute joints. Pivots 72, 74 and 75 may permit rotation about respective axes that are parallel to each other. Those axes may be parallel to a rotation axis or the rotation axis of pivot 20. Link 73 may be rigid. Extension 76 may be rigid. Extension 76 may be rigidly attached to the upper end of spring 70. The mechanism which maintains the attitude of the upper end of the spring is a four-bar linkage.

Spring 70 may conveniently be a gas spring, for example an air spring. The spring may comprise a deformable bladder 77 located between end cups 79, 80 which constitute lower and upper ends respectively of the spring. The end cups may conveniently be flexible. They may conveniently be continuations of the rubber bladder. An upper section of each cup may be rolled onto the cylindrical metal pedestal. A lower section of each cup may be fixed to the lower end of the spring and may bear against a plate. The end cups 79, 80 are fixed to point 71 and joint 72 respectively. The wall of the bladder may be elastic or inelastic. The bladder may be filled with a gas such as air. The gas may be at greater than atmospheric pressure. Motion of joint 72 towards point 71 may cause the gas to be elastically compressed, thereby providing or contributing to the springing action of the spring. Conveniently the spring may be a rolling lobe air spring. This permits a considerable stroke length in a relatively small package size. A gas pump can be used to increase the pressure in the interior of the spring chamber. A controllable valve communicating with the interior of the spring chamber can be used to permit the pressure to be reduced. In one mode of operation, the pre-load gas pressure in the spring is set before the simulator is used, in dependence on the expected weight of the payload, including the occupant. The mass of gas is then kept constant during operation. By suitable choice of the inflation pressure, the forces expected to be applied by the drive mechanisms for the sleds can be reduced. The pre-load may be set so that with no force applied to the sled drives the payload sits substantially horizontal and in the mid-range of its vertical travel. In a second mode of operation, the gas pressure in the spring is adjusted during operation in dependence on the weight of the payload and also the expected height to which the payload will be held over the forthcoming time period. The control of the gas pressure may be done to a longer timebase (i.e. at a lower frequency/bandwidth) than the control of the sled drives.

The mechanism shown in figure 5 can be set up so that spring 70 exhibits a substantially constant, and preferably zero, spring rate with vertical motion of the region of the load to which it is most closely attached: i.e. for the motion of joint 16. The spring rate of the spring can be expected to increase with increasing compression of the spring. To help make the spring response linear, and preferably zero, as experienced by the load, the spring is configured so that there is a reducing compression rate on the spring 70 as the payload is lowered. This can offset the increasing spring force. With the configuration shown in figure 5, as the end of the wishbone support 4 closest to the payload is lowered by a given amount, the resulting compression of the spring is less when the payload is near the bottom of its travel than when the payload is near the top of its travel. This effect arises from (a) the fact that joint 72 is located between (i) the pivot 20 of the support relative to its sled and (ii) joint between the support and the payload; and (b) that the spring is disposed on the lower side of the joint 72. The reducing compression rate with downward motion of the payload can counteract the increasing spring force and provide a substantially constant, and preferably zero, spring rate with vertical motion of the load. This effect is advantageous because it can reduce the force required to be applied by the sled drivers and can reduce any need to adjust the spring (e.g. by changing its gas mass) during operation. Once the spring has been set at a suitable pre-load it can continue to substantially counteract gravity on the load (or part of it) throughout the operating range of the simulator. This means that the force applied by the sled drivers can be less throughout the operating range. The gas pressures can be altered during operation to counteract any substantial changes in load on each corner as the load moves in surge. Forward surge can be counteracted by adopting, during operation, increased pressures at the front airbags, and reduced pressures at the rear airbags, in comparison to a previous or mean operational state. Rear surge can be counteracted by adopting, during operation, increased pressures at the rear airbags, and reduced pressures at the front airbags, in comparison to a previous or mean operational state.

An elastic buffer 78 is provided to resist excessive travel of the support arm 4.

The spring 70 may be an elastic device other than an air spring. For example, it could be a coil spring a leaf spring or a body of elastomeric material. It could be formed of a combination of such devices. For example, it could comprise multiple air springs or a combination of an air spring and a coil spring.

Figure 5 illustrates a spring applied to wishbone support 4. An analogous spring could be applied in an analogous way to any one or more of supports 4 to 7 in any combination.

In the arrangement of figure 5 the lower end of spring 70 is mounted to the sled 8. The lower end could alternatively be mounted to another sled. That other sled could be controlled to move with sled 8 or independently of it.

The platform 1 need not be trapezoidal: for instance the platform rails (e.g. 30) could be attached in their tapering configuration to the underside of a square plate.

Alternatively, the platform could be omitted and platform rails could be attached directly to the chassis.

In figure 1 the wishbones are shown as being of bifurcated form. Instead, the equivalent link could be provided by a single strut, or the wishbones could be arranged with their bifurcated ends coupled to the load. In these latter cases the respective elements could be coupled by spherical joints to the sleds and by revolute joints to the load. In general, each wishbone can be constituted by a fully or partially rigid element.

Each revolute joint could be a conventional rotating hinge joint, or a flexure joint, or of another form.

One or more of the intermediate links could have spherical joints at its connection to the respective sled and/or its connection to the respective primary link / wishbone.

The primary links I wishbones and the intermediate links could be rigid. Alternatively any of those links could be flexible and/or elastic, for example a spring cantilever.

The simulator could be configured for simulating a vehicle, such as a road vehicle.

Additional means for supporting the load could be provided, for example an elastic element such as a spring or a driven element such as a hydraulic piston. Such means could be provided under the load and extending between the load and a base, or above the load and extending between the load and an upper support structure such as a gantry or ceiling. Such means could be mounted to the load and/or the base or upper support in such a way that it can accommodate lateral motion of the load with respect to the base or support.

The arrangement described above could be used for other applications such as machine tools, vibration test equipment, pick-and-place machines, and tracking systems.

The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A motion arrangement for moving a load with six degrees of freedom, the motion arrangement comprising:

a first support coupled to the load for at least partially supporting the load, the first support being rotatably mounted on a first moveable drive element;

an intermediate link extending between the first support and a second moveable drive element, the intermediate link element being mounted on the second drive element and the second drive element being capable of driving relative to the first drive element so as to cause the intermediate link to alter the attitude of the first support; and an elastic support coupled to the first support for exerting an upwards force on the load via the first support, the elastic support being mounted so that the rate of deflection of the elastic support with vertical motion of the portion of the load to which the first support is coupled reduces with increasing deformation of the elastic support from its neutral position.

2. A motion arrangement as claimed in claim 1, wherein the elastic support is a spring.

3. A motion arrangement as claimed in claim 2, wherein the elastic support is a gas spring.

4. A motion arrangement as claimed in claim 3, wherein the gas spring is pre4oaded with a gas pressure such that the load is held substantially at the mid-point of its operational travel without force being applied by the first or second drive elements.

5. A motion arrangement as claimed in any preceding claim, wherein the elastic support is mounted so that, without adjustment of the elastic support, the upwards force applied to the load by the elastic support is substantially constant throughout the vertical operating range of the load.

6. A motion arrangement as claimed in any preceding claim, wherein the elastic support extends between a first location at which it is coupled to the first support and a second location at which it is coupled to the first drive element.

7. A motion arrangement as claimed in claim 6, wherein the first and second locations are spaced from the location where the first support is mounted to the first drive element.

8. A motion arrangement as claimed in claim 6 or 7, wherein the second location is inboard of the location where the first support is mounted to the first drive element.

9. A motion arrangement as claimed in any of claims 6 to 8, wherein the elastic support is rotatably coupled to the first support at the first location.

10. A motion arrangement as claimed in claim 9, wherein the elastic support comprises a first mount coupled at the first location to the first support, a second mount coupled at the second location to the first drive element and a flexible elastic element extending between the first and second mounting regions, and the motion arrangement comprises an alignment mechanism configured to maintain alignment between the first and second mounts by causing the first mount to rotate relative to the first support as the first support rotates relative to first drive element.

11. A motion arrangement as claimed in claim 10, wherein the alignment mechanism comprises a first link fast with the first support and extending on the opposite side of the first location to the first support, and a second link rotatably mounted to the first link and to the first drive element.

12. A motion arrangement as claimed in any preceding claim, comprising:

a second support coupled to the load for at least partially supporting the load, the second support being rotatably mounted on a third moveable drive element;

a second intermediate link extending between the second support and a fourth moveable drive element, the second intermediate link element being mounted on the fourth drive element and the fourth drive element being capable of driving relative to the third drive element so as to cause the second intermediate link to alter the attitude of the second support; and a second elastic support coupled to the third support for exerting an upwards force on the load via the second support, the second elastic support being mounted so that the rate of deflection of the second elastic support with vertical motion of the load reduces with increasing deformation of the second elastic support from its neutral position.

13. A motion arrangement as claimed in any preceding claim, wherein each drive element is a linearly acting drive element.

14. A motion arrangement as claimed in claim 14, wherein each drive element is a linear motor.

15. A motion arrangement as claimed in claim 13 or 14, wherein the first, second, third and fourth drive elements operate on a common motion axis.

16. A motion arrangement for moving a load with six degrees of freedom, the motion arrangement comprising:

first, second and third primary link elements, each primary link element being (i) rotatably attached to a respective linearly movable driver element and (ii) slidably and rotatably attached to the load;

a first intermediate link element attached to the first primary link element and to a fourth linearly movable drive element;

a second intermediate link element attached to the second primary link element and to a fifth linearly movable drive element;

the first intermediate link element being attached to the first primary link element at a location between the locations where the first primary link element is attached to its respective driver element and to the load, and the second intermediate link element being attached to the second primary link element at a location between the locations where the second primary link element is attached to its respective driver element and to the load;

and comprising an elastic support acting between one of the first, second and third primary link elements and the drive element to which that one of the link elements is attached, for at least partially supporting the load, the elastic support being mounted so that the rate of deflection of the elastic support with vertical motion of the portion of the load to which that one of the link elements is coupled reduces with increasing deformation ofthe elastic support from its neutral position.

17. A motion simulator comprising a motion arrangement as claimed in any preceding claim, the load including a cockpit for an occupant of the simulator.

18. A method fordriving a motion simulator as claimed in claim 17, wherein the elastic support is adjustable to apply a range of pre-load forces to the load, the method comprising:

estimating the weight of the load, optionally including an occupant thereof; determining in dependence on the weight of the load a pre-load for the elastic support;

adjusting the elastic support to a configuration in which it applies the determined pre-load to the load; and operating the motion simulator to provide motion simulation whilst maintaining the elastic support in that configuration.

19. A method fordriving a motion simulator as claimed in claim 17, wherein the elastic support is adjustable to apply a range of pre-load forces to the load, the method comprising, whilst the simulator is operating to provide motion simulation:

driving the or each drive element to move with a first control bandwidth; and adjusting the pre-load of the elastic support with a second control bandwidth lower than the first bandwidth.

20. A motion arrangement for moving a load with six degrees of freedom, the motion arrangement comprising:

an intermediate link extending between the first support and a second moveable drive element, the intermediate link element being mounted on the second drive element and the second drive element being capable of driving relative to the first drive element so as to cause the intermediate link to alter the attitude of the first support; and an elastic support coupled to the first support for exerting an upwards force on the load via the first support, the elastic support being mounted so that as the load is lowered a reduction in mechanical advantage of the elastic support over the load counteracts increased force developed by the elastic support.