Patent Publication Number: US-2022215771-A1

Title: Motion generator

Description:
FIELD OF INVENTION 
     This invention relates to the field of motion systems especially for simulating motion such as driving or flying. In particular, though not exclusively, the invention relates to motion generators, and to motion systems including such motion generators, and to methods of using motion generators, and motion systems for example for use as driving simulators, and to methods for their production. 
     BACKGROUND 
     A motion generator is a device capable of applying movements, forces and accelerations to a payload in one or more directions or degrees of freedom. The payload can be, for example, a human undergoing a simulated experience in a motion simulator incorporating a motion generator. Alternatively, the payload may also be a further motion generator which is said to be in series with the first motion generator. Motion generators are used in motion systems. Motion systems include a control system for controlling the motion generator. 
     Motion systems are used in motion simulators. Motion systems are used in a variety of applications, including motion simulation (for example, flight simulators, vehicle and driving simulators), robotics, 3D printing, vibration and seismic simulation. The most common type of motion system currently used in motion simulation is the Stewart platform (or “hexapod”) motion generator. This is a type of parallel manipulator that has six actuators, normally attached in pairs to three positions on the base of a platform and crossing over to three mounting points on a platform, or top plate (or “end effector”). Devices or payloads such as a human user placed on the platform, usually in some form of cockpit, driver area or model vehicle, can be moved in the six degrees of freedom in which it is possible for a freely-suspended body to move, i.e. the three linear movements x, y, z (lateral, longitudinal and vertical), and the three rotations (pitch, roll and yaw). Generally speaking, in a parallel manipulator, several computer-controlled actuators are arranged to operate in parallel to support the payload. In this context “parallel” means that only one actuator exists in each separate load path between the payload and the base, whereas in a series manipulator, one or more of the possible load paths between the payload and the base includes at least two actuators. 
     A motion simulator is a simulation system incorporating at least one motion generator that can create, for an occupant, the effects or feelings of being in a moving vehicle. Motion simulators are used, professionally, for training drivers and pilots in the form of driving simulators and flight simulators respectively. They also are used, industrially, in the creation, design, and testing of the vehicles themselves, as well as in the design of vehicle components. Professional motion simulators used for driving and flying simulation typically synchronise a visual display—provided for example by a projection system and associated screens and audio signals with the movement of a carriage (or chassis) occupied by the driver or pilot in order to provide a better sensation of the effect of moving. The advent of virtual reality (VR) head-mounted displays (HMDs) makes the aspect of an immersive simulation less costly with current motion systems and has the ability to deliver virtual reality applications to leisure uses such as in passive amusement park or arcade driving, riding-first-person, or flying rides and in active gaming, where one or more players has some control over the driving, riding, flying or first-person game experience. The payload of a motion generator used in motion simulation—for example a chassis or cockpit—is relatively heavy often being of the order of 100&#39;s of kg. Motion simulation applications for motion generators require the precise control of such relatively heavy payloads over significant movements, often being of the order of 1 metre or more. 
     The type of hexapods typically used for motion simulation for human participants typically have a relatively low bandwidth of up to about 20 Hz. This means that they can create oscillatory movements and vibrations of a consistent amplitude, with a frequency of up to 20 times per second, beyond which the amplitude of the movements reduces as the frequency increases. This is sufficient for replicating most car suspension movements, but it does not transmit the frequency content associated with vibrations from the car engine, tyre vibrations, road noise, and the sharp-edged kerbs on racetracks. A low bandwidth also means the signals are delayed, meaning that the driver cannot respond as quickly. 
     Current motion systems, especially those intended for high-end use such as in military and commercial flight instruction and training applications, are typically very large, heavy, complex, and very expensive. Their complexity necessitates extensive programming and maintenance, further increasing the cost to users. 
     Dedicated driving simulator motion systems have been developed by the likes of McLaren/MTS Williams/ABD and Ansible, but these tend to be extremely mechanically complex, and therefore expensive, featuring precision machined custom components and often expensive linear motors. These dedicated driving simulator motion systems are more responsive than hexapods when moving in some directions but are still limited in others. The use of ball screws in such systems is disadvantageous in that, whilst good at establishing position, they inhibit force transfer and can only achieve a lower bandwidth. This results in a less natural motion simulation experience for a human user. 
     The motion simulator disclosed in EP2486558, comprises a mechanism that uses a three degree of freedom parallel manipulator comprising three upright arms driven by bell cranks to control movement in pitch, heave and roll, and therefore is responsive and has high bandwidth in those degrees of freedom. A rotary table driven in rotation by a linear actuator is required to provide yaw. The motion simulator is intended to be relatively compact. However, its horizontal degrees of freedom are provided by series manipulators which introduce compliance, inertia, and friction which limits the responsiveness and bandwidth of the system in the horizontal degrees of freedom. 
     U.S. Pat. No. 5,919,045 discloses an interactive racing car simulator, including a primary motion generator comprising a simple arrangement of overlaying rectangular frames arranged to move in the X and Y directions respectively on linear guides, under pneumatic control, and termed the “X and Y frames”. Whilst the simple arrangement of frames of the type disclosed in this document provides good excursions in the X and Y directions, as the frames are stacked above each other in the motion generator is not especially compact in the vertical dimension. Furthermore, the movements in the X and Y directions are not especially precise, and also the simulator would have a relatively low bandwidth. 
     An example of a primary motion generator for use in a driving simulator is given in EP2810268A which discloses a three degree of freedom motion generator in series with a six degrees of freedom motion generator which can sustain large movements in the horizontal plane using the primary motion generator, while simultaneously achieving the maximum vertical travel of the secondary motion generator. Therefore, the two motion generators in series can achieve combinations of movements in different degrees of freedom which are impossible with a similarly sized hexapod. However, the hexapod described in this document uses linear actuators and specifically recirculating ball screw-driven linear actuators. As noted above, recirculating ball screw actuators have considerable friction, and so lead to poor responsiveness and bandwidth. The use of other linear actuators in a hexapod architecture leads to further problems. In the case that the linear actuator is mobile as part of the moving strut then it has high moving mass which leads to mechanical resonance at low frequencies, limiting system responsiveness and bandwidth. In the case that the linear actuator is fixed relative to a base, and one end of the hexapod strut translates along the linear actuator, then the weight and inertial loads of the system are reacted by a linear bearing which again involves considerable friction. 
     US2017/0053548A discloses a motion system including a cable/actuator-controlled platform which is slidable on a large low friction fixed base, and which allows for significant horizontal movement of the platform. The cables and actuators are disposed around the periphery of the large base, allowing the significant horizontal movement of the platform. A hexapod-based secondary motion generator is in turn mounted on the platform and supports a model cockpit in order to provide further movement of the cockpit. 
     An object of the present invention is to provide an improved motion generator, especially one which is useful for driving and vehicle motion-type simulation applications, and improved motion systems incorporating such motion generators, which are again especially suitable for those applications. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the invention there is provided a motion generator comprising an effector for applying forces, moments and movements to a payload relative to a surface, the effector being connected to one or more elongate rigid struts, each strut being connected at one end thereof by a first joint to the effector and being connected at its other end by a second joint to an associated rocker (i.e. the rocker to which a particular strut is connected), the rocker having a pivot axis such that movement of a rocker about the pivot axis leads to movement of the effector, and forces applied to a rocker lead to forces being applied to the effector, in which the movement of a rocker and forces applied by the rocker are controlled by an actuator, the actuator being in the form of an elongate belt, cable, rope drive, or linear motor arranged to apply a force to a point on the rocker away from the pivot axis of the rocker. 
     According to a second aspect of the invention there is provided a motion generator comprising an effector for applying forces, moments and movements to a payload relative to a surface, the effector being connected to four or more elongate rigid struts, each strut being connected at one end thereof by a first joint to the effector and being connected at its other end by a second joint to an associated rocker (i.e. the rocker to which a particular strut is connected), the rocker having a pivot axis, such that movement of the rocker leads to movement of the effector, and forces applied to the rocker lead to forces being applied to the effector, in which the movement of a rocker and forces applied by the rocker are controlled by an actuator, the actuator being arranged to apply a force to a point on the rocker away from the pivot axis of the rocker. 
     The surface may be generally planar. For example, in many applications the surface may be the floor of a building in which the motion generator according to either aspect of the invention is installed, but it could be a baseplate for the motion generator. In other situations, such as the combinations described below and where the secondary motion generator is a motion generator in accordance with the invention, the surface may be a reference plane above the physical surface on which the combination is installed, typically provided by or defined by the primary motion generator and that surface may move with the primary motion generator. 
     In this context, a rocker conventionally means a solid body being attached to one end of an elongate revolute joint or pivot, the body being able to rotate about a pivot axis provided by this joint or pivot, thereby rotating relative to another solid body attached to the other end of the joint. The rocker will typically also have other joints and pickup points on its body, attached to other moving elements. Rockers are typically used in mechanical systems to control relative motions of moving elements, controlling mechanical advantages, and to change directions of motion. Mechanical elements such as bell cranks and levers are forms of rockers. For example, rockers are often used in car suspension e.g. in pushrod or pull-rod suspension arrangements. The term “rocker” also embraces for the purposes of this disclosure a solid body attached to or integral with a flexure, such that the body is able to describe an arc about an imaginary axis generally extending upwards at a midpoint on the flexure, that imaginary axis being equivalent to a pivot axis as referred to above for other rockers. 
     Thus, the invention provides a motion generator in the form of a parallel manipulator with one, two, three, four, five or preferably six degrees of freedom comprising one, two, three, four or more, typically six, actuators each capable of producing responsive and high bandwidth movements. The motion generators of this invention are therefore able to provide responsive and high bandwidth motion in all six degrees of freedom. 
     A motion generator in accordance with either aspect of the invention may be advantageous in some or all of several respects compared with known motion generators. It may have low levels of friction within its moving parts. The motion generator design of the invention minimises friction, and therefore is responsive and has high bandwidth because the weight and loads imparted upon the payload are reacted by a rocker (typically along with its rotary bearings) which have less friction than linear bearings or linear guides used in conventional designs. It may have low inertia due to the lower mass of moving elements compared with known designs. It may have high bandwidth typically better than 50 Hz, in more than one degree of freedom. In some embodiments it may have significantly higher bandwidth than 50 Hz in multiple degrees of freedom, for example 80 Hz, 90 Hz, or 100 Hz or more which is a significant advance over comparably priced motion generator designs. Another advantage of a motion generator in accordance with the invention is that it may be relatively compact in the vertical direction compared to certain current motion generator designs. Furthermore, it does not require, for example, the precision-machined metal base required by the motion generator of EP2810268A as it may be installed on a conventional building floor. 
     The first and second joints in a motion generator of the invention may together have a total number of degrees of freedom which is at least five. One of the first or second joints may include a universal, cardan, spherical joint, or flexure, while the other may be a spherical joint. 
     A motion generator in accordance with either aspect of the invention typically comprises a plurality of rockers. In most arrangements, the motion generator may comprise six rockers. The pivot axis of at least one, preferably each, rocker may be fixed relative to the surface where the surface is a physical surface on which the motion generator is installed. Alternatively, (typically in the context of a combination including a motion generator in accordance with the invention mounted as a secondary motion generator on a primary motion generator), the pivot axis of the rocker may not be fixed relative to that surface, but is fixed relative to a plane above the physical surface, that plane moving with the primary motion generator. The rocker pivot could be a revolute joint, an axle with bearings, or a flexure. Each rocker may move parallel with the surface. Alternatively, at least one, preferably each, rocker may be inclined at an angle of greater than zero degrees to the surface. For example, at least one, preferably each rocker may rotate about a pivot axis inclined from 0 to 90°, preferably about 45 degrees (for example 40 to 50 degrees) to the surface. Some or all of the rockers may form an obtuse angle with their connected strut. This may reduce resonance in the motion generator. Additionally, or alternatively, this may make the motion generator more compact. 
     A motion generator according to either aspect of the invention may typically comprise 4, 5, 6 or more elongate struts. For example, the motion generator may comprise X elongate struts, where X is less than six, and at least one mechanical constraint means which constrains Y degrees of freedom of the effector where Y=6−X. Alternatively there could be more than 6 elongate struts. Pairs of elongate struts may be arranged on opposing sides of the effector. In one typical embodiment, a motion generator comprises three pairs of elongate struts. 
     At least one actuator may be arranged so that it can react the load back to the surface. The actuator may be, for example, an elongate actuator such as a belt, cable or rope drive, or linear motor. Each form of actuator may have its own advantages. For example, belt, cable or rope drive actuators may be relatively less expensive. Where the actuator is a linear motor it may be connected via a linkage to an associated rocker. 
     Where the motion generator is powered by an actuator such as an elongate belt, cable or rope drive, the elongate belt, cable or rope drive may be actuated by a pulley or capstan. Such a pulley or capstan may be driven by an electric motor or gearmotor. 
     Where the actuator includes a belt, cable or rope drive, both the ends of the belt, cable or rope drive may be attached to an associated rocker, forming a closed loop in the belt, cable or rope between two attachment points on the rocker. A passive tensioning device including a pulley may be applied to one end of, or portion of, the closed belt, cable or rope drive to maintain tension in the belt, cable or rope drive and to accommodate its fixed length within the changing geometry of the system. The passive tensioning device including a pulley may accommodate a change in geometry of the rocker. The other end of, or another portion of, the belt, cable or rope drive may be attached to a passive force application device which maintains tension in the belt, cable or rope. The passive force application device in this case may be, for example, a spring, gas strut, or bungee. 
     In a motion generator according to either aspect of the invention, a passive force application device may be connected to a rocker so as to provide assistance to the actuator such as static preload or damping, or to support the weight of the payload. This assistance could be provided by a passive force application device such as a spring, gas strut or bungee. 
     One or more passive force application device such as a spring, gas strut, bungee may be connected to the effector or the payload to provide further or alternative assistance such as static preload or damping to the actuator. 
     At least one rocker and/or actuator may be mounted on or to the surface. Alternatively, or additionally, at least one rocker and/or actuator may be mounted on a frame or other support fixed to the surface. 
     The payload supported by the effector may be more than 10 kg, preferably more than 80 kg, preferably more than 250 kg, or preferably more than 500 kg. Typically, in motion simulation applications, the payload may be a vehicle chassis or cockpit or a model thereof. 
     A motion generator according to either aspect of the invention may be arranged to operate as a secondary motion generator in series with a primary motion generator. Such a combination arrangement comprising a primary and secondary motion generator, may provide a user with a greater range of motion for a payload. For example, the combination may the achieve excursions of the order of 1 metre required in motion, especially vehicle, simulation applications. Furthermore, such a combination arrangement may permit the use of a relatively simple, and therefore cost-effective, primary motion generator providing motion for example in the X and Y directions only with the secondary motion generator providing more complex motions. Alternatively, the primary motion generator could have X, Y and yaw degrees of freedom. One example of a known motion generator suitable for use as a primary motion generator, with a motion generator in accordance with the invention as a secondary motion generator is that disclosed in US2017/0053548. In such a combination, a motion generator according to the invention is arranged as a secondary motion generator in which at least one rocker and or actuator of that generator is mounted on a frame, the end effector of, or as the payload of, the primary motion generator. For example, the primary motion generator may include a frame, or platform, as end effector and at least one rocker of the secondary motion generator may be pivotally mounted to the frame of the primary motion generator. 
     According to another aspect of the invention there is provided a motion system, the motion system comprising at least one motion generator according to either aspect of the invention, and a control system. The control system may control the operation of at least one motion generator actuator, preferably that of all actuators. The control system may compute the positions, accelerations and/or forces required to be produced at each actuator in order to generate a demanded motion profile. 
     According to another aspect of the invention there is provided a driving or vehicle simulator including a motion generator according to either aspect of the invention or a motion system according to the invention, and at least one environment simulation means selected from visual projection, or display means, and audio means. The driving or vehicle simulator may comprise a cockpit or chassis and/or vehicle simulation element. The driving or vehicle simulator may include means for simulating an environment comprising at least one of display apparatus, virtual reality apparatus, projection apparatus, and software means for modelling a virtual environment, and a vehicle model. 
     Another aspect of the invention provides a method of producing a motion system comprising producing or providing a motion generator according to either aspect of the invention and connecting the control system to the motion generator. 
     Other features of the motion generators, motion systems, and driving simulators will be apparent from the description and further claims. Where reference is made to apparatus such as motion generators, motion systems, motion simulators and certain aspects or embodiments of the invention, the skilled addressee will appreciate that other aspects and embodiments of the invention may equally apply to such apparatus. References to such apparatus being in accordance with the invention may refer to any aspect of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Motion generators, motion systems, and driving simulators and their operation and production in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings,  FIGS. 1 to 28 , in which: 
         FIG. 1  is a schematic perspective view of a motion system in accordance with the invention, from above and one side; 
         FIG. 2  is a schematic perspective view of the motion system of  FIG. 1  with the frame removed for clarity; 
         FIG. 3  is a plan view of the motion system as shown in  FIG. 2 ; 
         FIG. 4  is a schematic detailed plan view of a rocker of the motion system of  FIG. 1 ; 
         FIG. 5  is a schematic perspective view of the rocker shown in  FIG. 4 ; 
         FIG. 6  is a detailed plan view of a different rocker for use in a motion generator in accordance with the invention; 
         FIG. 7  is a detailed view of passive tension devices of a motion generator in accordance with the invention; 
         FIG. 8  is a perspective view of the motion system as shown in  FIG. 2  in a surge forward condition; 
         FIG. 9  is a plan view from below of the motion system in the surge forward condition of  FIG. 8 ; 
         FIG. 10  is a perspective view of the motion system as shown in  FIG. 2  in a sway left condition; 
         FIG. 11  is a plan view from below of the motion system in the sway left condition of  FIG. 10 ; 
         FIG. 12  is a perspective view of the motion system as shown in  FIG. 2  in a heave up condition; 
         FIG. 13  is a plan view from below of the motion system in the heave up condition of  FIG. 12 ; 
         FIG. 14  is a perspective view of the motion system as shown in  FIG. 2  in a roll right side down condition; 
         FIG. 15  is a plan view from below of the motion system as shown in  FIG. 14  in the roll right side down condition; 
         FIG. 16  is a perspective view of the motion system as shown in  FIG. 2  in a pitch nose down condition; 
         FIG. 17  is a plan view from below of the motion system in the pitch nose down condition of  FIG. 16 ; 
         FIG. 18  is a perspective view of the motion system as shown in  FIG. 1  in a yaw nose left condition; 
         FIG. 19  is a plan view from below of the motion system in the yaw nose left condition shown in  FIG. 18 ; 
         FIG. 20  is a perspective view of a driving simulator in accordance with the invention; 
         FIG. 21  is a schematic perspective view of another motion system in accordance with the invention; 
         FIG. 22  is a perspective detail view of another motion generator in accordance with the invention; 
         FIG. 23  is a further detail view of the motion generator of  FIG. 22 ; 
         FIG. 24  is a partial view of another motion generator showing an alternative rocker arrangement; 
         FIG. 25  is a further partial rear view of the motion generator of  FIG. 24  showing the inclination of a rocker arrangement; 
         FIG. 26  is a schematic view of a control system for use with motion generators of the invention; 
         FIG. 27A  is a schematic view of a combination including a motion generator in accordance with the invention, and another motion generator; and 
         FIG. 27B  is a schematic view of another combination including a motion generator in accordance with the invention, and another motion generator; and 
         FIG. 28  is a schematic view of an alternative rocker arrangement. 
     
    
    
     References in this specification to particular orientations and positions, such as upper or lower refer to those orientations or positions as shown in the accompanying drawing. 
     DESCRIPTION 
     Motion System Including a Motion Generator 
     A motion system  1  including a motion generator  2  in accordance with a first aspect of the invention is shown in  FIGS. 1 to 19 . The motion system  1  comprises a motion generator  2  mounted on a surface  4 , and supports a vehicle chassis  3 , which, in this embodiment, constitutes the payload of the motion generator  2 , and control means (for example as described in relation to  FIG. 26 ) above a frame  5 . The frame  5  has a generally triangular shape and is constructed of a lightweight rigid material such as aluminium. Other shapes and types of frames, such as space frames, and other materials are contemplated for use in such frames. In the embodiment shown, the chassis  3  is a replica of a racing car cockpit. The chassis  3  is supported by pairs of elongate rigid rods or struts,  11 ,  12 ;  13 ,  14 ; and  15 ,  16  which at their upper ends are connected by upper joints  11  UJ,  12  UJ,  13  UJ,  14  UJ,  15  UJ, and  16  UJ respectively to the chassis  3 . The elongate rigid rods  11 - 16  may be made, for example, of carbon fibre to reduce resonance. The upper joints  11 UJ- 16 UJ may be spherical, cardan, or universal joints, and/or may comprise flexures. The lower end of each elongate rod  11 - 16  is connected by a lower joint  11 LJ,  12 LJ,  13 LJ,  14 LJ,  15 LJ, and  16 LJ respectively to an associated rocker  11 R,  12 R,  13 R,  14 R,  15 R, and  16 R, respectively which are arranged for pivotal movement on the inside of the triangular frame  5  of the motion generator  2 . The lower joints  11  LJ- 16  LJ may also be spherical, cardan or universal joints, and/or may comprise flexures. Linear actuators  11 LA- 16  LA which may be, for example, belt drives, linear motors (a suitable example of which would be an I-Force Ironless Linear Motor by Parker) or ball screw-driven actuators (a suitable example of which would be a PC Series Actuator by Thomson driven by an AKM2G Servo Motor by Kollmorgan). Belt drives are preferred. The connection between the rockers  11  R- 16 R and the linear actuators  11  LA- 16  LA is shown in more detail in  FIGS. 4-7 . 
     It is contemplated that a motion generator in accordance with the invention may not include a frame  5 . In such an arrangement, at least some of, or all, the rockers and/or actuators could be mounted directly on the surface  4  rather than to a frame. Such a motion generator may be advantageous in that the surface may be more rigid than the frame. The frame has the advantage that it can be used to carry the entire the motion generator, particularly when it is used as a secondary motion generator in series with a primary motion generator. 
       FIGS. 4 and 5  show rocker  16 R and connected elements in more detail. The continuous toothed belt B connects with the rocker  16 R via rounded elements E which reduce wear on the connected belt B. An example of a suitable toothed belt is a Conti® Synchrochain Carbon belt made by Continental. In  FIGS. 4 and 5 , the elements E are circular. In  FIG. 6 , the corresponding elements E are curved. It should be noted that the belt B shown in  FIG. 6  is spaced away from the curved elements simply for clarity, in practice the belt will closely fit to the curved elements. The toothed belts B pass around drivable correspondingly toothed electrically powered capstans (indicated as “C”). A suitable example of an electrically-powered capstan would be a synchronous belt sprocket by Martin, driven by an AKM2G Servo Motor by Kollmorgan. The capstans C operate under the control of a control system (for example as described in relation to  FIG. 26 ). 
     It will also be noted that the passive tension elements P in the embodiment of  FIGS. 4 and 5  are bungees or springs. In the embodiment shown in  FIGS. 6 and 7 , the passive tension elements are compression springs. The belt B passes round freely rotating pulleys marked as P which are tensioned by the passive tensioning devices PT which provide a preload tension on a connected rocker  11 R- 16 R against the belt B connected to that rocker. By movement of one or more of the rockers  11 R- 16 R driven by the associated belts B and capstans C under the control of the control system, the rods or struts  11 - 16  move the chassis  4 , at high bandwidth in any of six degrees of freedom into a wide variety of conditions, some of which are described below. 
     The motion generator  2 , is particularly compact in a vertical direction. This compactness is advantageous when the motion generator is included in a motion system used in driving simulators. 
     In the following description, the position of the rockers  11  R- 16 R in use is described in more detail. For simplicity, only the position of the rockers  11  R- 16  R is described, and those rockers identified in the drawings with other elements unnumbered in some drawings. It will be appreciated by the skilled addressee that the other elements, such as the elongate struts  11 - 16 , belt drives, and connected passive tension devices will also be affected by movement of the rockets but this is not described in detail in the description below in relation to  FIGS. 1 to 3 and 7-17 . 
     The motion generator  2  is shown with the chassis  3  in a neutral condition in  FIGS. 1 to 3 . In this condition, the state of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position from below 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 Neutral 
               
               
                   
                 12R 
                 Neutral 
               
               
                   
                 13R 
                 Neutral 
               
               
                   
                 14R 
                 Neutral 
               
               
                   
                 15R 
                 Neutral 
               
               
                   
                 16R 
                 Neutral 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a surge forward condition in  FIGS. 8 and 9 . In this condition, the states of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position from below 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 Anti-clockwise 
               
               
                   
                 12R 
                 Anti-clockwise 
               
               
                   
                 13R 
                 NEUTRAL 
               
               
                   
                 14R 
                 Neutral 
               
               
                   
                 15R 
                 CLOCKWISE 
               
               
                   
                 16R 
                 CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a sway left condition in  FIG. 10  and  FIG. 11 . In this condition, the position of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rockers 
                 Position from below 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 CLOCKWISE 
               
               
                   
                 12R 
                 CLOCKWISE 
               
               
                   
                 13R 
                 ANTI-CLOCKWISE 
               
               
                   
                 14R 
                 ANTI-CLOCKWISE 
               
               
                   
                 15R 
                 CLOCKWISE 
               
               
                   
                 16R 
                 CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a heave up condition in  FIG. 12  and  FIG. 13 . In this condition, the position of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position (from below) 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 CLOCKWISE 
               
               
                   
                 12R 
                 ANTI-CLOCKWISE 
               
               
                   
                 13R 
                 CLOCKWISE 
               
               
                   
                 14R 
                 ANTI-CLOCKWISE 
               
               
                   
                 15R 
                 CLOCKWISE 
               
               
                   
                 16R 
                 ANTI-CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a roll right side down condition in  FIG. 14  and  FIG. 15 . In this condition, the position of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position (from below) 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 CLOCKWISE 
               
               
                   
                 12R 
                 ANTI-CLOCKWISE 
               
               
                   
                 13R 
                 Neutral 
               
               
                   
                 14R 
                 Neutral 
               
               
                   
                 15R 
                 ANTI-CLOCKWISE 
               
               
                   
                 16R 
                 CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a pitch nose down condition in  FIG. 16  and  FIG. 17 . In this condition, the position of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position (from below) 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 ANTI-CLOCKWISE 
               
               
                   
                 12R 
                 CLOCKWISE 
               
               
                   
                 13R 
                 CLOCKWISE 
               
               
                   
                 14R 
                 ANTI-CLOCKWISE 
               
               
                   
                 15R 
                 ANTI-CLOCKWISE 
               
               
                   
                 16R 
                 CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     The motion generator is shown with the chassis  3  in a yaw nose left condition in  FIG. 18  and  FIG. 19 . In this condition, the position of the rockers is as follows: 
     
       
         
           
               
               
               
             
               
                   
                   
               
               
                   
                 Rocker 
                 Position (from below) 
               
               
                   
                   
               
             
            
               
                   
                 11R 
                 CLOCKWISE 
               
               
                   
                 12R 
                 CLOCKWISE 
               
               
                   
                 13R 
                 CLOCKWISE 
               
               
                   
                 14R 
                 CLOCKWISE 
               
               
                   
                 15R 
                 CLOCKWISE 
               
               
                   
                 16R 
                 CLOCKWISE 
               
               
                   
                   
               
            
           
         
       
     
     It will be noted that only a limited number of conditions is described above in relation to the motion generator  2 . It will be appreciated by the skilled addressee that the motion generator  2  may be operated into many more conditions including, and not exclusively surge rearward, sway right, heave down, roll left side down, pitch nose up and yaw nose right. Furthermore, it will also be appreciated by the skilled addressee that the motion generator  2  may be operated into multiple combinations of such conditions. For example, the motion generator may be operated into a combined heave up and yaw nose left condition. The motion generator has the advantages of the invention including high bandwidth, low friction and low inertia which increase the accuracy of the movements of the payload, chassis  3 . 
     Control System 
       FIG. 26  shows a control system  501  for use in controlling operation of a motion generator in accordance with the invention. In relation to  FIG. 26 , the motion generator is referred to as  502 , but the control system  501  is applicable to the other motion generators, motion systems, and motion simulators described herein. The control system  501  comprises a motion controller  504  which executes a computer program, preferably in a deterministic or real time manner, and which takes motion demand inputs  505  from a demand generator such as a simulation environment  503  or a set point generator  506 . The motion controller computes the positions, accelerations and/or forces  507  required to be produced at each actuator  509  to in order to generate the demanded motion profile  505 . The control system  501  also comprises servo drives  508  which provide precisely controlled electrical currents  510  to drive the actuators  509 . 
     In operation, the motion controller sends to each servo drive  508  a demanded position or force  507 . The actuator  509  has a motion measurement device  511 , such as an encoder, which provides motion feedback  512  to the motion controller, optionally via the servo drive. The motion controller compares the demanded motion profile  505  to the one measured  512  and updates the actuator demand  507  accordingly. 
       FIG. 26  also shows the control system with a simulation environment  503 , such as a driving simulation in which the physics of a simulated vehicle and its environment, such as a racetrack or city roads, are computed. In this embodiment the control system  501  receives motion demands from the simulation environment  503 , which represent the motion of a virtual vehicle. The computer program determines the motion of the vehicle in a virtual world  514 , then applies a motion cueing algorithm  513  (MCA, also known as washout filters) to transform the simulated vehicle motions into those that can be represented by the motion generator. These calculated motions are then provided to the control system as motion demands  505 . The MCA  513  could be part of the simulation environment  503  or the control system  501  or separate to both. The simulation environment  503  may receive inputs signals  515  from control devices  516  such as steering, throttle or brake inputs, which an operator, I.e. a human user such as a driver, passenger or pilot uses to control the virtual vehicle in the simulation environment. The operator would likely be a passenger on the motion generator  502 . These inputs  515  may be passed back to the simulation environment via the control system or directly. The simulation environment is also likely to produce an output on a visual display  517  for the driver, passenger, or other user or operator. The simulation environment may also require additional data  518  from the control system, such as relating to the position of the motion generator, or control device inputs signals. 
     Combination of Motion Generators 
     A motion generator in accordance with either aspect of the invention may be used in series with a further motion generator. For example, a motion generator in accordance with the invention may be used as a secondary motion generator, that is to say the motion generator itself becomes the payload of a primary motion generator.  FIG. 27A  shows a combination  600 , which is in accordance with the invention, and comprising a first (or “primary”) motion generator  602 , and a second (or “secondary”) motion generator  604  (which is a motion generator in accordance with the invention). The combination is installed on a planar surface  601  (not shown) typically a building floor. The primary motion generator  602  is a simple X and Y frame arrangement, comprising a lower frame  606 , including lower frame members  607 ,  608 , and an upper frame  610 . The lower frame member  608  supports a motor  612  which can be operated, under commands from a control system  605  (for example as shown in  FIG. 26 ) to move the frame  610  in the X direction. A similar motor  614  is correspondingly arranged on the frame  610  to move that frame in the Y direction under commands from the control system  605 . The secondary motion generator  604 , which is a motion generator in accordance with the first aspect of the invention mounted on the primary motion generator  602 , comprises a rocker  616  (directly mounted on upper frame  610  of the primary motion generator i.e. it is mounted in a plane above the surface  601 ) which is drivably connected to an actuator (comprising a motor  617 , and elongate belt  618  which is attached to the movable end of the rocker, which passes around capstans  618 CA), and to an elongate rigid strut  620 . The elongate strut  620  is connected by a joint at one end to the free end of the associated rocker  616  and at its other end by a joint to an end effector supporting payload  619 . When the motor  617  is operated under commands from the control system, it drives a driven capstans  618 CA and in turn the belt  618  to move the associated rocker  616 . The rocker  616  pivots about a vertical pivot axis (passing though rocker pivot  616 P), with the rocker arm describing a horizontal arc (shown as A). The movement of rocker  616  moves the associated strut  620  to move the end effector/payload  618 / 619  in the X and Y directions, as well permitting yaw, heave and pitch motions. The combination  600  is advantageous in that the primary motion generator  602  is relatively inexpensive but provides good excursion ranges in the X and Y directions and the secondary motion generator  604  provides a higher bandwidth and lower levels of inertia and friction which increase the accuracy of the movements imparted to the payload. 
     Combination of Motion Generators 
       FIG. 27B  shows another combination  300  in accordance with the invention, comprising a first (or “primary”) motion generator  302 , and a second (or “secondary”) motion generator  304  (which is a motion generator in accordance with the invention). The combination  300  is installed on a planar surface  301  such as a floor in a driving simulator building. The primary motion generator  302  is a simple X and Y frame arrangement, generally as described above in relation to primary motion generator  602 , comprising a lower frame  306 , including lower frame members  307 ,  308 , and an upper frame  310 . The lower frame member  308  supports a motor  312  which can be operated, under commands from a control system  305  (for example as shown in  FIG. 26 ) to move the frame  310  in the X direction. A similar motor  314  is correspondingly arranged on the frame  310  to move that frame in the Y direction under commands from the control system. The secondary motion generator  304  which is a motion generator in accordance with the second aspect of the invention, comprises six rockers  316 A-F, each rocker being drivably connected to an actuator (comprising motors  317 A-F and associated elongate toothed belts  318 A-F which pass around a correspondingly splined capstan of the associated motor  317 A-F and a free-moving capstan e.g.  318 CA or  318 CB), generally as described in relation to the  FIG. 1  motion generator, and to an elongate rigid strut (struts  320 A-F). Each of the elongate rigid struts  320 A-F is connected by a joint at one end to the free end of the associated rocker  316 A-F and at its other end by a joint to an end effector (platform  321  supporting payload  3322 . It will be noted that the rockers  316 A-F are mounted on the upper frame  310  of the primary motion generator  302  in a plane defined by the upper surface of that frame  310  which is spaced above the surface  301 . When a motor  317 A-F is operated under commands from the control system, it drives an associated belt  318 A-F so that the associated rocker  316 A-F pivots about a horizontal pivot axis with the rocker arm describing an arc (for example as shown as A for rocker  316 A). The movement of a rocker  316 A-F therefore moves the associated strut  320 A-F to move the end effector/payload  318 / 319  in the X and Y directions, as well permitting yaw, heave and pitch motions. The combination  300  is advantageous in that the primary motion generator  302  is relatively inexpensive but provides good excursion ranges in the X and Y directions and the secondary motion generator  304  provides a higher bandwidth and lower levels of inertia and friction which increase the accuracy of the movements of the payload. 
     Driving Simulator 
     A driving simulator  200  in accordance with the invention is shown in  FIG. 20 . The driving simulator  200  comprises a motion system  202  including a motion generator  204  in accordance with the invention, for example as described above in relation to  FIGS. 1 to 19  or below in relation to  FIGS. 21-23 , or a combination as described in relation to  FIG. 27B . The motion system  202  mounted on a surface  206  in front of a projection system  206  on which can be displayed images of a driving environment, the projection system constituting an example of an environment simulation means. An audio system (not shown) provides sound to the user replicating the sounds of a driving environment, constituting another example of an environment simulation means. The motion generator  204  of the driving simulator  200  is operated under the command of a control system  207  (for example, as described in relation to  FIG. 26 ). 
     A motion generator in accordance with the invention, as described in several embodiments above, which is suitable for use as used in a driving simulator as described in this embodiment may be advantageous in some or all of several respects compared with known motion generators for such applications. First, it may have low levels of friction within its moving parts owing to a) the use of revolute joints or rotary bearings rather than linear bearings for reacting weight and inertial loads b) dispensing with recirculating ball screw linear actuators. Second, it may have low inertia particularly where rotary motors rather than linear motors are used, particularly linear actuators that move in their entirety with a strut in a mechanism. Where a linear motor is used as an actuator in a motion generator according to this invention, only its forcer need move while its stator or magnetway can remain stationary. Third, it may have high bandwidth typically better than 50 Hz, in more than one degree of freedom. In some embodiments it may have significantly higher bandwidth than 50 Hz, for example 80, 90, 100 or more Hz. It will also be appreciated that the motion generator  204  used in the driving simulator  200  may be especially compact in the vertical direction. This better replicates the height of a vehicle being simulated, in comparison with other motion systems requiring ramps/bridges for a user to enter/exit the driving simulator. 
     Motion System Including a Motion Generator 
     Another motion system  700  in accordance with the invention is shown in  FIG. 21 . The motion system  700  includes a motion generator  702  in accordance with the invention which supports a payload  704  above a surface  706 . The motion generator  702  comprises four rocker systems  710 ,  712 ,  714  and  716  (rocker systems  714  and  716  being obscured in  FIG. 21 ) which are generally as described above. Linear constraints  720  and  722  are arranged at right angles between rocker arrangements  710 ,  716  and  716 ,  714  respectively. The motion system  700  also includes a control system (for example as described in relation to  FIG. 26 ). 
     In use, the rockers  710 - 714  are moved by belt drives B, generally as described above so that elongate struts interposed between the rockers and the payload  704  (again generally as described above) move the payload in four degrees of freedom with high bandwidth. The constraints  720 ,  722  prevent excessive movement of the payload  704  in the fore and aft and side to side directions respectively. 
     It will be appreciated by the skilled addressee that the motion system  700  may be relatively simple yet offer good performance in terms of bandwidth. The system could have a bandwidth in excess of 50 Hz or even 100 Hz in all degrees of freedom, despite having a lower bandwidth primary motion generator, because the secondary motion generator is highly performing in this regard. 
     Further Motion Generator 
     A further motion generator  400  in accordance with the invention is shown in  FIGS. 22 and 23 . The motion generator  400 , which is constructed and arranged generally as described above in relation to the motion generator  2  shown in  FIGS. 1 to 19 , except that the six belt-drive linear actuators  11 LA- 16  LA are replaced by six linear motors and six linkages which drive corresponding rockers and struts to move a platform  402 , which constitutes an effector. The six linear motors are operable to move a platform  402  in six degrees of freedom.  FIGS. 22 and 23  show one of the six linear motors  411  in more detail. More specifically,  FIG. 22  shows the coil  412  and magnetway  414  of linear motor  411 . The linear motor  411  is pivotally connected by pivot  416  to an elongate lower strut  418 . A further pivot  419  connects the strut  418  to a rocker  420 . The rocker  420  is mounted for horizontal pivotal movement on pivot  421  above and parallel with a surface on which the motion generator  400  is mounted. An upper strut  422  is connected by its lower end to the rocker  420  by a clevis joint  424 . The upper strut  422  is, in turn, pivotally connected at its upper end by a further clevis joint  425  (shown in  FIG. 23 ) to the platform  402  (omitted for clarity in  FIG. 23 ). In use, linear movement of the coil (e.g.  412 ) under operation of the linear motor (e.g.  411 ) as controlled by a control system (for example, as described in relation to  FIG. 26 ) moves the associated rocker (e.g.  420 ) and connected struts (e.g.  418 ,  422 ) to move the platform ( 402 ) in six degrees of freedom. 
     Alternative Rocker Arrangement 
     An alternative rocker arrangement is shown schematically in  FIGS. 24 to 25 . In this embodiment, a motion generator  100  is mounted on a planar surface generally indicated as  102 , and supports a chassis  103 , which constitutes the payload of the motion generator  102 , and control means (not shown) above a triangular frame  105  (omitted for clarity). The chassis  103 , which is constructed of a lightweight rigid material such as aluminium, or carbon fibre, is a replica of a racing car cockpit. The chassis  103  is supported by pairs of elongate rigid rods or struts,  111 ,  112 ;  113 ,  114 ; and  115 ,  116  which are connected at their upper ends by upper joints  111  UJ,  112  UJ,  113  UJ,  114  UJ,  115  UJ, and  116  UJ respectively to the chassis  103 . The elongate rigid rods  111 - 116  may be made, for example, of carbon fibre to reduce resonance. The upper joints  111 UJ- 16 UJ may be spherical, cardan, or universal joints, and/or may comprise flexures. The lower end of each elongate rod  111 - 116  is connected by a lower joint  111 LJ,  112 LJ,  113 LJ,  114 LJ,  115 LJ, and  116 LJ (which may also be spherical, cardan or universal joints and/or may comprise flexures) respectively to rockers  111 R,  112 R,  113 R,  114 R,  115 R, and  116 R, respectively which are arranged for pivotal movement on the inside of the triangular frame  105  of the motion generator  100 , being driven by linkages  111 L,  112 L;  113 L,  114 L; and  115 L,  116 L connected to linear actuators  111 LA,  112  LA;  113  LA,  114  LA; and  115 LA,  116  LA. 
     In contrast with previous embodiments, where the rockers move parallel with the surface on which the motion generator is mounted, as the pivot axis for each rocker is perpendicular to the surface, the rockers  111 R,  112 R,  113 R,  114 R,  115 R, and  116 R are arranged for angled pivoting movement which is non-parallel with the surface (in this case  102 ) on which the motion generator is mounted. In this description, the opposite end of the rocker to the pivot axis is termed the free end. In this embodiment, the rockers are inclined at 45° from the surface (The angle indicated as Θ, between the surface  102  and the axis A around which the rocker  113 R pivots is shown in  FIG. 25 ). In other embodiments, the pivot rockers may be inclined at 0 to 45° from the surface. Where the surface on which the motion generator is mounted is not planar, the angle of inclination of the rockers is taken from a datum line. Where the motion generator is arranged in a combination as a secondary motion generator, the angle of inclination of the rockers may be taken from a plane defined above the surface, such as by a planar surface of an upper frame of the primary motion generator on which the rockers are mounted. Such a plane may be considered as a “surface”. In some situations, such an inclined rocker arrangement is preferable as it may reduce unwanted resonances. An inclined rocker arrangement may also be more compact. It may also reduce loads reacted by bearings thereby further reducing friction. 
     Further Alternative Rocker Arrangement 
     A further alternative rocker arrangement suitable for use in a motion generator in accordance with the invention is illustrated in  FIGS. 28  A and B.  FIG. 28  A shows a rocker  400  which includes a rocker base  402 , connected by a flexure  404 , to rocker arm  406 . The flexure is formed from a predictable elastic material such as spring steel, tool steel, or a composite such as E-glass or S-glass. The flexure  404  allows an arcing movement ((indicated as arc C) of the rocker arm  406  in a plane perpendicular to the flexure  404  which approximates rotation around an imagined axis in the middle of the flexure  404 . The rocker arm  406  is shown in one position on arc C in  FIG. 28  B. The imagined axis may be considered as an equivalent to the pivot axis of the other rockers described above. Such a rocker arrangement incorporating a flexure may be advantageous in that it avoids the use of bearings, it may eliminate backlash, and/or provides increased stiffness. 
     Methods of Producing Motion Systems 
     A motion system in accordance with the invention including a motion generator, such as those described above, and control means may be assembled from custom and standard components by conventional means. In particular, a motion system may be produced by connecting a motion generator in accordance with the invention with a control system.