GB2378687A

GB2378687A - Motion arrangement for a vehicle simulator

Info

Publication number: GB2378687A
Application number: GB0120143A
Authority: GB
Inventors: Anthony Richard Glover
Original assignee: Trysome Ltd
Current assignee: Trysome Ltd
Priority date: 2001-08-17
Filing date: 2001-08-17
Publication date: 2003-02-19
Anticipated expiration: 2021-08-17
Also published as: GB0120143D0; GB2378687B

Abstract

To move a platform 2, with six degrees of freedom, a least three motion units (four, 11,12, 13, 14, are shown) connect the platform 2 to a base. The motion units are each mounted on rails 5, 6, 7, 8 to slide in parallel. Each motion unit comprise a pair of sleds and has a rocker mechanism connecting it to a rail 9, 10 on the platform 2 through a flexible joint. Differential movement of the pair of sleds of a motion unit causes the associated rocker to pivot. The sleds are all independently movable through linear motors. A simulated vehicle cabin is supported on the platform 2.

Description

MOTION ARRANGEMENT This invention relates to a motion arrangement for moving a load. The motion arrangement may be especially suitable for use for a motion simulator, especially 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, as shown in figure 1. The Stuart platform has a platform 1 which is connected to a base 2 by six hydraulic or electromechanical pistons 3. The pistons 3 are pivotally mounted to the base 2 and to the platform 1. The occupant position is fixed on the platform 1. 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 substantial horizontal forces 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 of the platform, with the occupant on it, must be lifted some distance off the ground. This is highly 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.

There is therefore a need for a form of simulator that at least partially addresses some of these problems.

According to the present invention there is provided a motion arrangement for moving a load with six degrees of freedom relative to a base, the base extending in a plane in which are first and second directions, the motion arrangement comprising: at least three motion units, each motion unit comprising a sled slideable relative to the base along a first axis parallel to the first direction, an arm pivotally attached to the sled such that the arm can be rotated relative to the base about a second axis parallel to the second direction, and a flexible joint spaced along the arm from the respective second axis whereby the motion unit is attached to the load, the locations at which the joints are attached to the load being non-collinear ; and means mounted between the load and the sleds for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction.

Preferably the first and second directions are perpendicular, although this is not essential.

Preferably the motion arrangement comprises at least four such motion units.

Suitably the first axes of two of the motion units are collinear and the first axes of the other two motion units are collinear and offset from the first axes of the first two motion units. Each such pair of motion units may run on one or more common rails. Suitably the joints of two of the motion units are opposed to the joints of the other

two motion units. Each such pair of motion units may run on different but preferably parallel rails. There are preferably only two such rails.

The sled of each motion unit is preferably driveable to slide relative to the base by a respective linear motor. Most preferably the magnet-way of the linear motor is fixed to the base, but the opposite is possible.

Each sled is preferably constrained so that it is only capable of sliding, and most preferably only linear, motion relative to the base. Each sled may be mounted on a rail in order to achieve this.

Preferably each motion unit comprises a second sled slideable relative to the base in a third axis parallel to the first direction, and a connecting rod pivotally attached to the second sled and to the arm of the respective motion unit at a location spaced along the arm from the respective second axis, whereby the arm may be rotated relative to the base by relative sliding of the first sled and the second sled of the motion unit.

Preferably the first and third axes of each motion unit are collinear. The first and second sleds of each motion unit may run on one or more common rails.

Preferably the second sled of each motion unit is driveable to slide relative to the base by a respective linear motor.

The motion arrangement preferably comprises a motion sensor coupled to each first and second sled for sensing the position of the respective sled relative to the base and generating a position signal indicative of the position of the respective sled relative to the base. The position signals may be analogue position signals.

The motion arrangement may comprise a control system having: a position transformer for receiving the position signals and based on the position signals determining the position of the load with reference to an orthogonal coordinate

system; a controller for receiving a desired position of the load with reference to the coordinate system and based on that and the determined position of the load determining a force to be applied to the load in the coordinate system to cause the load to move from the determined position to the desired position; and a force transformer for determining for each sled, based on the determined force in the coordinate system, a force to be applied to the respective sled to cause the load to move to the desired position and applying a signal to the corresponding linear motor to apply the force to the sled. There is preferably a motion controller for providing the desired position of the load. The desired position of the load is suitably determined by processing the settings of controls and a predetermined behaviour model for the load. The controls may be part of the load.

The means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction is preferably arranged between the joints and the load. The means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction suitably comprises a pair of non-parallel rails attached to the load. Those rails are preferably coplanar. Each joint is suitably slideably attached to one of the rails, at least one of the joints being attached to each of the rails. The means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction may comprise a pair of rails attached to the load and wherein each joint is slideably attached to one of the rails, at least one of the joints being attached to each of the rails, and a motor arranged to drive the joints to slide along the rails relative to the load. That motor may be borne by the rails. The motor may be a linear motor.

The load is preferably a simulated vehicle cabin, most preferably a simulated land vehicle cabin. The cabin suitably has an occupant position having its forward direction perpendicular to the first direction. The forward direction of the cabin could be defined by reference to a seat for the occupant in the cabin. The motion of the cabin is preferably controllable by controls located in the cabin, most preferably in combination with a motion simulation processor which is preferably not movable with the cabin. The motion simulation processor may process inputs from the

controls together with data representing predetermined behaviour in order to determine the motion of the cabin.

The load preferably includes a video display unit, and the arrangement preferably comprises a video controller arranged to control the video display unit to display a moving image the movement of which is synchronised with the motion of the load.

The motion arrangement may take the form of a motion simulator, for example for training or games purposes.

The motion arrangement in combination with the load constitutes an aspect of the present invention.

The present invention will now be described by way of example with reference to the accompanying drawings, in which: figure 1 shows a Stuart platform ; figure 2 shows a side view of a simulator carrying a part vehicle chassis; figure 3 shows a front view of the simulator carrying a part vehicle chassis; figure 4 shows the simulator with the chassis removed; figure 5 shows the simulator with the chassis and a platform removed; figure 6 shows a rocker mechanism of the simulator; and figure 7 illustrates the control circuit of the simulator.

The simulator illustrated by figures 2 to 6 comprises a base 1 which is mounted on the ground. A trapezoidal motion platform 2 is attached to the base by a set of controllable rocker mechanisms. A part vehicle chassis 3 is mounted on the platform. The chassis is shaped to replicate the cabin of a vehicle to be simulated and includes a cockpit 4 to hold an occupant.

The rocker mechanisms are mounted on four parallel base rails 5,6, 7,8 which run along the base. The rocker mechanisms are arranged so that by moving on the base rails they can manoeuvre the platform relative to the base in six degrees of

freedom. With reference to the orthogonal axes indicated in figure 1, and with the front of the simulated vehicle facing along the x axis, the six degrees of freedom are defined as three axial displacements : surge (along the x axis), sway (along the y axis) and heave (along the z axis); and three rotational displacements : yaw (about the z axis), pitch (about the y axis) and roll (about the x axis).

The interrelation of the rocker mechanisms and the platform is illustrated in detail in figure 4. On each side of the platform 2 is a platform mounting rail 9,10. The platform mounting rails are linear and run generally transverse to the base rails 5-8. When the platform rails are connected to the sides of the platform the platform fixes the platform rails in a tapered arrangement in which the platform rails are not parallel but are closer together where they pass over one of the outermost base rails 5 than where they pass over the other outermost base rail 8. Each of the platform rails is slidably attached to a pair of the rocker mechanisms 11,12, 13,14. One rocker mechanism of the pair runs on base rails 5 and 6 and the other runs on base rails 7 and 8. The base rails 5-8 run parallel to the y axis.

As shown in figure 6, each rocker mechanism comprises a front sled 20 and a rear sled 21. The sleds are mounted to and can slide on the pair of the base rails 5-8 on which the rocker mechanism is mounted. Each sled is attached to the slider 22,23 of a respective electric linear motor. The magnet-ways 24,25 of the linear motors (generally indicated by 40 in figure 4) are fixed to the base and run parallel to the base rails. The linear motors are independently controllable and can drive the sleds to slide along the rails. Suitable linear motors are available from the Kollmorgen division of Danaher Corporation of Radford, Virginia, USA. A mounting 26,27 projects upward from each sled, and each mounting carries a bearing 28,29 whose axis is parallel to the plane of the base 1 and perpendicular to the base rails 5-8 and to the axis of the magnet-ways of the linear motors. A rocker block 30 is pivotally mounted to the front sled by the bearing 28. A connecting rod 31 is pivotally mounted to the rear sled by the bearing 29. The rocker block and the connecting rod are pivotally joined to each other by a bearing 32 whose axis is parallel with the bearings 28 and 29. The rocker block 30 is slidably attached to the

platform rail 10 by a universal joint 33 on the side of the rocker block opposite the rear sled 21. The universal joint 33 is connected to the rocker block 30 through a rotatable coupling 50, forming a composite articulated joint capable of permitting rotation about three axes. The universal joint 33 terminates in a bracket 35 which can slide freely along the platform rail. The bracket 35 has lips which fit in grooves 34 running along the top and bottom of the platform rail 10, whereby the bracket is held relative to the platform rail in directions perpendicular to the rail.

In the neutral position of the rocker mechanism the rocker block 30 is generally upright and the sleds 20 and 21 are in the middle of their travels on the linear motors. Coordinated action of the linear motors to slide the each sled along the rails by the same amount in the same direction will urge the universal joint to move parallel to the rails. Movement of the sleds towards or away from each other will urge the rocker block 30 to tilt and thus urge the universal joint to move up or down.

Each linear motor of the four rocker mechanisms connected to the platform can be controlled independently. This allows the platform to be moved relative to the base with six degrees of freedom. To move the platform in yaw the front pair of rocker mechanisms 11,13 are moved in the y direction relative to the rear pair of rocker mechanisms 12,14. To move the platform in pitch the universal joints of the front pair of rocker mechanisms are moved in the z axis relative to the universal joints of the rear pair of rocker mechanisms. To move the platform in roll the universal joints of one side pair of rocker mechanisms 11,12 are moved in the z axis relative to the universal joints of the other side pair of rocker mechanisms 13,14. To move the platform in surge the rocker mechanisms 11,12 on one side of the platform are moved towards or away from the rocker mechanisms 13,14 on the other side of the platform ; due to the tapered configuration of the platform rails, as imposed by their fixing to the platform, this forces the platform rails to slide through the brackets 35.

To move the platform in sway all the rocker mechanisms are moved in the same direction along the base rails. To move the platform in heave the universal joints of all the rocker mechanisms are moved in the same direction in the z axis. It will be appreciated that due to the geometry of the structure, some additional

compensatory movements of the rocker mechanisms may be required to permit the platform to move freely. The individual motions described above can be combined to give composite motions of the platform.

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

A spring 34 (not shown in figures 4 and 6) is connected between the front and rear sleds to help support the weight of the platform, the chassis and the occupant when the rocker mechanism is in the neutral position.

The limits of travel in the horizontal axes are defined by the lengths of the base rails and the platform rails. End stop buffers (not shown) are provided at the ends of each of the rails to prevent over-travel. The limits of travel in the vertical axis are defined by the dimensions of the rocker blocks 30 and the universal joint 33 (which fix the radial offset between the platform rails and the axis of the bearing 28) and the configuration of the sleds (which fix the amount of rocker block rotation that can be achieved). End stop buffers (not shown) are provided to prevent over-travel of each rocker.

The articulated joint comprising the universal joint 33 and the rotatable coupling 50 as shown in the drawings is a three piece mechanism designed to provide zero backlash, high stiffness and low friction. Other forms of flexible joint could be used, for example a spherical or ball joint.

In addition to the eight linear motors as shown in the figures, one or more linear motors could be added to drive the surge axis more directly. For example, this could be achieved by mounting one or more linear motor magnet-ways on the platform, parallel to the platform rails. The slider of each motor would be attached to

a bracket 35 of a respective one of the rocker mechanisms. In this embodiment the platform rails could be parallel.

The arrangement shown in the drawings uses four rocker mechanisms. This provides good support to the payload in all orientations of the platform. A platform with three rocker mechanisms and six linear motor drive units is also possible.

Correctly arranged, this would still offer six degrees of freedom.

To provide feedback to the control system illustrated in figure 6 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 magnet tracks.

The platform can be moved with six degrees of freedom. Since eight linear motor actuators are available to control the motion of the platform, incoherent control of each actuator would lead to an over-constrained system, which would be undesirable. Therefore, the control system illustrated in figure 6 can be used. The control system comprises four processing blocks : a position transformer 60, a controller 61, a force transformer 62 and a simulation unit 63.

The position transformer receives eight inputs 64, each of which represents the position of a respective one of the linear motors. The inputs 64 are derived from the position sensors of the linear motors. The position transformer is programmed to determine from the eight inputs 64 the current position of the platform in the six degrees of freedom. The position transformer generates six output signals 65.

Each output signal indicates the position of the platform in a respective one of the degrees of freedom.

The simulation unit 63 coordinates the motion simulation performed by the simulator. Typically the simulation unit will store a program representing the characteristics of the environment to be simulated and using that program and inputs received from controls 66 operated by the occupant of the simulation unit will

drive a video display 67 as well as driving the motion of the simulator platform. To drive the simulator platform the simulation unit generates six position demand signals 68, each representing the required position of the platform in a respective one of the degrees of freedom.

Video display 67 could be mounted on the cabin or could take the form of a fixed screen, e. g. a projection screen display, located outside the cabin.

The controller 61 receives the six position signals 65 and the six position demand signals 68. The controller 61 is programmed to process these twelve signals to generate six force demand signals 69. Each force demand signal represents the force required to be exerted in a respective one of the degrees of freedom in order to move the platform from its present position to the required position.

The force demand signals 69 are passed to the force transformer 62. The force transformer is programmed to process the force demands in the six degrees of freedom to determine corresponding drive signals for each of the linear motors. The force transformer outputs eight drive output signals 70, each corresponding to a respective one of the linear motors, for controlling the motors to move as required. Each control output signal is fed through a power supply unit to the control input of the respective linear motor.

It would be possible to determine the current position of the platform using only six position sensors. The control system could be adapted accordingly.

The video display 67 is mounted to the chassis so as to be visible to an occupant.

Under the control of the simulation unit 63 a display of scenery on the visual display unit 67 is synchronised to the motion of the chassis.

In comparison to the Stuart platform or hexapod the structure shown in the drawings offers a number of advantages. It allows relatively large displacements and forces to be imparted in the horizontal axes without requiring such a large space in which

to operate. This makes it particularly suited to simulating the motion of land vehicles, in which the major components are typically horizontal. The following table indicates potential requirements for simulator motion to simulate extreme land vehicle conditions such as might be experienced in a racing car:

Motion Displacement Velocity Acceleration Max. Frequency Yaw15 20 /s300 /s15 Hz Pitch0. 4 6 /s200 /s10 Hz Roll ~2 ~15 /s ~600 /s 10 Hz Surge0. 3 m0. 25 m/s 7. 5 m/s2 15 Hz Sway 0. 7 m 1. 5 m/s : t15 m/s2 15 Hz Heave0. 014 m0. 1 m/s5 m/s10 Hz It is apparent that the horizontal displacements : those involving movement on the x and y axes, are significantly greater than those that involve movement on the z axis. The present structure is arranged to provide a compact mechanism for driving the motion platform principally 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 parallel to the forward axis of the chassis and the sway axis is 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 direction of the seat. The highest potential force may often be greatest in the sway axis since higher forces may often be expected during cornering than in straight-line 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.

Linear motor drive units offer high fidelity motion and high frequency of operation.

The rocker mechanisms which couple between the linear motor drive units and the payload can be made of low mass and high stiffness to reinforce this characteristic.

Relatively high velocities of motion can be achieved by the use of suitable linear motors. Instead of linear motors, other drive units could be used. One example is to drive each sled by a respective worm running parallel to the base rails and coupled to a rotational motor.

The platform need not be trapezoidal: for instance the platform rails could be attached in the 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.

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 draws attention to the fact that the present invention may include any feature or combination of features disclosed herein either implicitly or explicitly or any generalisation thereof, without limitation to the scope of any definitions set out above. 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

CLAIMS 1. A motion arrangement for moving a load with six degrees of freedom relative to a base, the base extending in a plane in which are first and second directions, the motion arrangement comprising: at least three motion units, each motion unit comprising a sled slideable relative to the base along a first axis parallel to the first direction, an arm pivotally attached to the sled such that the arm can be rotated relative to the base about a second axis parallel to the second direction, and a flexible joint spaced along the arm from the respective second axis whereby the motion unit is attached to the load, the locations at which the joints are attached to the load being non-collinear ; and means mounted between the load and the sleds for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction.
2. A motion arrangement as claimed in claim 1, wherein the first and second directions are perpendicular.
3. A motion arrangement as claimed in claim 1 or 2, comprising at least four motion units.
4. A motion arrangement as claimed in claim 3, wherein the first axes of two of the motion units are collinear and the first axes of the other two motion units are collinear and offset from the first axes of the first two motion units.
5. A motion arrangement as claimed in claim 3 or 4, wherein the joints of two of the motion units are opposed to the joints of the other two motion units.
6. A motion arrangement as claimed in any preceding claim, wherein the sled of each motion unit is driveable to slide relative to the base by a respective linear motor.

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7. A motion arrangement as claimed in any preceding claim, wherein each motion unit comprises a second sled slideable relative to the base in a third axis parallel to the first direction, and a connecting rod pivotally attached to the second sled and to the arm of the respective motion unit at a location spaced along the arm from the respective second axis, whereby the arm may be rotated relative to the base by relative sliding of the first sled and the second sled of the motion unit.
8. A motion arrangement as claimed in claim 7, wherein the first and third axes of each motion unit are collinear.
9. A motion arrangement as claimed in claim 7 or 8, wherein the second sled of each motion unit is driveable to slide relative to the base by a respective linear motor.
10. A motion arrangement as claimed in any of claims 7 to 9, comprising a motion sensor coupled to each first and second sled for sensing the position of the respective sled relative to the base and generating a position signal indicative of the position of the respective sled relative to the base.
11. A motion arrangement as claimed in claim 10 as dependant on claim 6, comprising a control system having: a position transformer for receiving the position signals and based on the position signals determining the position of the load with reference to an orthogonal coordinate system; a controller for receiving a desired position of the load with reference to the coordinate system and based on that and the determined position of the load determining a force to be applied to the load in the coordinate system to cause the load to move from the determined position to the desired position; and a force transformer for determining for each sled, based on the determined force in the coordinate system, a force to be applied to the respective sled to cause the load to move to the desired position and applying a signal to the corresponding linear motor to apply the force to the sled.

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12. A motion arrangement as claimed in any preceding claim, wherein the means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction is arranged between the joints and the load.
13. A motion arrangement as claimed in any preceding claim, wherein the means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction comprises a pair of non-parallel rails attached to the load and wherein each joint is slideably attached to one of the rails, at least one of the joints being attached to each of the rails.
14. A motion arrangement as claimed in any preceding claim, wherein the means for moving the load relative to the base in a direction parallel to the plane and perpendicular to the first direction comprises a pair of rails attached to the load and wherein each joint is slideably attached to one of the rails, at least one of the joints being attached to each of the rails, and a motor arranged to drive the joints to slide along the rails relative to the load.
15. A motion arrangement as claimed in claim 14, wherein the motor arranged to drive the joints to slide along the rails relative to the load is borne by the rails.
16. A motion arrangement as claimed in claim 14 or 15, wherein the motor arranged to drive the joints to slide along the rails relative to the load is a linear motor.
17. A motion arrangement as claimed in any preceding claim, wherein the load is a simulated vehicle cabin.
18. A motion arrangement as claimed in claim 17, wherein the load is a simulated land vehicle cabin.

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19. A motion arrangement as claimed in claim 17 or 18, wherein the cabin has an occupant position having its forward direction perpendicular to the first direction.
20. A motion arrangement as claimed in any of claims 17 to 19, wherein the motion of the cabin is controllable by controls located in the cabin.
21. A motion arrangement as claimed in any of claims 17 to 20, wherein the load includes a video display unit, and the arrangement comprises a video controller arranged to control the video display unit to display a moving image the movement of which is synchronised with the motion of the load.
22. A motion arrangement substantially as herein described with reference to figures 2 to 7 of the accompanying drawings.
23. A motion simulator comprising a motion arrangement as claimed in any preceding claim.
24. A motion simulator substantially as herein described with reference to figures 2 to 7 of the accompanying drawings.