Patent Application
20240379021
This invention relates to the field of motion systems especially motion systems 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 or motion systems especially for use as driving simulators, and to methods for their production.
A motion generator is a device capable of applying movements, forces, and accelerations to an effector or an effector payload in one or more directions or degrees of freedom. The effector is part of the motion generator. The effector payload can be, for example, a human undergoing a simulated motion experience in a motion simulator incorporating a motion generator. Alternatively, the payload may be a further motion generator which is said to be in series with the first motion generator and provides additional or alternative motion for the effector, or effector payload to that provided by the first motion generator. Motion generators are used in motion systems. Motion systems, in the context of this invention, comprise a motion generator and include a control system for controlling the motion generator. The most common type of motion generator 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 the manipulator and crossing over to three mounting points on a platform, or top plate (i.e., the “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 directions of movement X, Y, Z (lateral, longitudinal and vertical), and the three rotations (pitch, roll and yaw). Generally speaking, in a parallel manipulator-based motion system, 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.
Motion simulators including motion systems are used in a variety of applications, including motion simulation (for example, flight simulators for fixed and rotary wing aircraft, vehicle and driving simulators), vibration, and seismic simulation.
A motion simulator is a simulation system incorporating at least one motion generator/motion system that can create, for an occupant, the effects or feelings of being in a moving vehicle or aircraft. 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 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's of kg, although smaller payloads are possible in certain applications such as gaming (e.g., motorsport gaming simulation applications). Motion simulation applications for motion generators require the precise control of such relatively heavy payloads over significant movements (or “excursions”), often being of the order of 1 metre or more.
The type of hexapods typically used for motion simulation for human participants conventionally 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. In simulating automotive vehicle motion, this may be sufficient for replicating most car suspension movements, but it does not transmit the higher frequency content such as that 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 vehicle, 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 custom linear motors. These dedicated driving simulator motion systems are more responsive than hexapods when moving in some directions but are still limited in other directions. The common usage of ball screws in such systems is disadvantageous in that, whilst good at establishing position, the ball screws inhibit force transfer and can only achieve a lower bandwidth. These issues result in a significantly less natural motion simulation experience for a human user. For example, they lead to poor latency which requires additional correction measures to minimise motion sickness (see e.g., Lucas, G et al.—Study of latency gap corrections in a dynamic driving simulator—In: Driving Simulation Conference & Exhibition, France, 2019-09-04—DSC 2019 EUROPE VR—2019).
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 movements in 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 series 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 X and Y 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, the series 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 in a combination with another motion generator for use in a driving simulator is given in EP2810268A which discloses a three degree of freedom primary motion generator arranged in series with a six degrees of freedom secondary 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 working in series can achieve combinations of movements in different degrees of freedom which are impossible with a similarly sized one hexapod arrangement. However, the hexapod described in this document uses linear actuators, 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. Alternatively, 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 in this design. A hexapod-based secondary motion generator is in turn mounted on the platform and supports a model vehicle cockpit in order to provide further movement of the cockpit. The motion system is not compact for the excursion levels provided by the large low friction fixed base design. US2012/0180593 discloses a hexapod-based system for use in flight simulators or driving simulators (but principally for flight simulation) in which each leg moves along a linear guide, and in some embodiments the legs are powered by a linear motor. These linear guides are heavy and involve significant friction which is especially disadvantageous in driving simulation applications where responsiveness is especially important. US2014/157916 discloses a motion simulation system including a series of actuators each having a planetary gearbox driven by an associated servomotor which engages with a crank. This direct drive system is a high friction and high latency arrangement intended for use in applications such as amusement parks (see
Applicant's patent publication WO2020/228992 (EP20020225) discloses a rocker-based motion generator in which the rockers are driven by an actuator in the form of an elongate belt, cable, rope drive, or linear motor. The motion generator provides high bandwidth motion with low latency. US2005/0277092 and applicant's EP3751543 and EP3731213 are of relevance to the technological background of the invention disclosing other motion generators and motion simulation systems.
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.
According to a first aspect of the invention there is provided a motion generator comprising an effector, the motion generator mechanism being arranged to apply forces, moments and movements to the effector of the motion generator and/or effector payload relative to a surface, in which the effector is operably connected to free ends of rocker arms provided by a plurality of rockers, each rocker pivoting about a pivot axis, such that the movement of the rockers about the respective pivot axes leads to movement of the effector, in which at least one rocker is driven by a curved linear motor concentric with an arc swept by the free end of the associated rocker, and in which at least one rocker carries, comprises, or includes a coil or magnet way of an associated curved linear motor. The free end of the rocker may sweep an arc having a radius of the length from the free end of the rocker to the rocker pivot axis. The associated curved linear motor may be concentric with that arc.
The term “curved” which is used in this context in relation to a linear motor and components thereof embraces a linear motor which is generally curved, curvilinear, arc-shaped, or polygonal or facetted (as many “curved” linear motors are in terms of the arrangements of short straight electromagnets along their length) but does not extend to form a complete circle. Typically, the curved linear motor extends about 90 degrees of arc or less.
In motion generators according to the invention, the combination of a rocker and curved linear motor form an axial flux electric machine whereby the coil (or “forcer”, or “windings”) for an ironless curved linear motor form only part, or an arc, of a complete circle thereby facilitating a direct drive mechanism. This combination significantly improves responsiveness, reduces friction and inertia, compared to known motion generators, by placing the coil at a large radius on the rocker, and typically close to the actuation path to the end effector. This minimises any bending moments in the rocker which could introduce compliance and hamper responsiveness, while allowing a large rocker radius to maximise excursion which is highly desirable in motion simulation applications, especially driving simulation applications.
It has been found that such a motion generator in accordance with the invention provides excellent levels of bandwidth and positional control, with low latency.
Preferably, the rocker comprises or includes the coil, rather than the magnet way of the associated curved linear motor as this reduces the rocker's inertia. Alternatively, if the rocker comprises or includes the magnet way, then this arrangement may involve simpler cable management. The coil may be integrated into the rocker construction.
The curved linear motor may be an ironless or iron core linear motor. In practice, a plurality of curved linear motors may be associated with each rocker, such a combination of linear motors still being referred to herein as a linear motor. Preferably the curved linear motor is an ironless motor, which does not exhibit cogging, an undesirable position-dependent torque disturbance caused by the iron-core in the presence of the magnets. An example of a curved linear motor is an Akribis ironless ACR series motor such as an ACR820-5S or ACR335-58. Other curvilinear motors from manufacturers such as Aerotech or PBA Systems may be suitable.
In this context, a rocker conventionally means a solid body (which may also be referred to as a rocker arm) being attached to one end of an elongate revolute joint, or pivot, such as a shaft moving in a bearing, the free end of the body being able to pivot or sweep 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, or pivot. The rocker will typically also have other joints and pickup points on its body, typically at the free end, 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. Rockers are often used, for example, 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 free end of the body is able to describe an arc about an imaginary axis at a midpoint on the flexure, that imaginary axis being equivalent to a pivot axis as referred to above for other rockers. In a preferred embodiment a rocker pivots on a shaft rotating in a bearing, the bearing being arranged above the associated motor components. As noted below, a rocker is preferably symmetrical about its mid-plane.
The rocker, especially the rocker body or rocker arm may be made of composite material or metal, preferably aluminium, construction. A lightweight rocker construction is preferred as it increases responsiveness of the motion generator. For example, the rocker may be a perforated “tea bag” shape (comprising two pairs of opposed substantially triangular faces, in which adjacent triangular faces are inverted with respect to each other) and in which the rocker pivot shaft is housed along a lower linear edge of the “tea bag” whilst the upper outer edge and adjacent surface is formed in an arc shape in a plane perpendicular to the pivot axis and provides a mounting seat for the circular linear motor coil. In preferred embodiments, the motor components are below the pivot axis of an associated rocker. In this case the rocker may have a “swing boat” form.
Thus, the invention provides a motion generator which is in the form of a parallel manipulator with one, two, three, four, five or preferably six degrees of freedom comprising two, or more, typically six, curved linear motors each capable of producing responsive and high bandwidth movements. In a motion generator according to the invention, the effector (e.g., platform or chassis) may typically be connected to four or more elongate rigid struts, more typically six such struts.
Advantageously, the rockers are symmetrical so that they are not handed. For example, a rocker may be symmetrical about its mid-plane. Accordingly, one rocker is immediately replaceable with a further such rocker saving on spare part costs.
A motion generator in accordance with the invention may be advantageous in some or all of several respects compared with known motion generators. The motion generators of this invention are therefore able to provide responsive and high bandwidth motion in all six degrees of freedom. In particular, the motion generator is able to achieve very accurate positioning and low latency.
The first and second joints in a motion generator of the invention, i.e., the upper and lower joints may together have a total number of degrees of freedom which is at least five. Preferably, one of the first or second joints may include a universal, Cardan, spherical joint, or flexure, while the other may be, for example, a spherical joint. Offsetting the two axes of rotation of a Cardan joint is particularly preferred as this arrangement permits the joint to be stiffer in axial motion even when compared to conventional Cardan joints where the axis of rotation intersect.
A motion generator in accordance with the invention typically comprises a plurality of rocker units. In most arrangements, the motion generator may comprise six rockers. At least one rocker unit may be mounted on or to the surface. Alternatively, or additionally, at least one rocker may be mounted on a frame, base, or other support fixed to the surface. A rocker arranged to pivot above an associated motor is preferred.
The pivot axis of at least one, preferably each, rocker is fixed generally parallel relative to the surface where the surface is a physical surface on which the motion generator is installed i.e., the pivot axis is in a horizontal plane. 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 generally parallel relative to a plane above the physical surface, that plane moving with the primary motion generator. The rocker pivot is preferably a revolute joint, an axle shaft with bearings, or a flexure. Low friction rotary bearings are especially preferred. In another embodiment each rocker may rotate in a plane which is perpendicular to the surface.
A motion generator according to the invention may typically comprise 4, 5, 6 or more elongate struts, but motion generators comprising 1-3 struts are also contemplated. 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 end effector. In one typical embodiment, a motion generator comprises three such pairs of elongate struts.
The motion generator may include brakes to retard the motion of the rockers. Various forms of brakes are contemplated for this application, such as disc brakes, regenerative brakes, and linear brakes. Regenerative braking, also called Safe Dynamic Braking, can be achieved by using the existing curved-linear motors to convert kinetic energy into heat energy in the motor coil. Typically, regenerative braking torque is proportional to the speed of the motor. A combination of regenerative and disc brakes may be preferred in a motion generator.
The payload supported by the effector may be more than 10 kg, preferably more than 80 kg, preferably more than 250 kg, or even more than 500 kg for vehicle motion simulation applications. Typically, in motion simulation applications, the payload may be a vehicle chassis or cockpit or a model thereof.
A motion generator according to the invention may, in another aspect of the invention, 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 an effector/effector payload. For example, by use of a suitable primary motion generator, a combination of motion generators may achieve excursions of the order of 1 metre or more as required in motion simulation, especially vehicle motion 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 a secondary motion generator in accordance with the invention providing more complex motions. Alternatively, the primary motion generator could provide movements in the X and Y directions 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 being 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 unit of that secondary motion 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 the end effector and at least one rocker motor arrangement of the secondary motion generator (a motion generator in accordance with the invention) 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 the invention, and a control system. The control system may control the operation of at least one motion generator actuator (i.e., one of the curved linear motors), preferably that of all such actuators. The control system may compute the positions, accelerations and/or forces required to be produced at each curved linear motor in order to generate a demanded motion profile. The rocker of a motion generator or motion system may include a linear encoder, especially a curved linear encoder, which gives particularly high-resolution control, for example about 1 million counts per radian, in use, over the position of the rocker.
According to another aspect of the invention there is provided a driving or vehicle simulator including a motion generator according to 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 as the payload of the motion generator. The driving or vehicle simulator may include means for simulating an environment comprising at least one of a 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 the invention and connecting a control system to the motion generator to produce a motion system.
Other features of the motion generators, motion systems, and driving simulators will be apparent from the description and further claims set out below. 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.
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,
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 drawings.
A motion generator 10 in accordance with the invention is shown in
One of the rocker motor arrangements, RM5, is shown in more detail in
The motion generator 10 is suitable for use in motion systems, in driving simulators, or in combinations of motion generators all in accordance with the invention.
Another motion generator is shown in
Components of one of the modular rocker motor units, 2RM1 are shown in more detail in
The motion generator 20 is also suitable for use in motion systems, in driving simulators, or in combinations of motion generators in accordance with the invention.
In operation a motion generator in accordance with the invention such as motion generator 10 or 20 is operated by means of an associated control system (not shown but, for example, as generally described in WO2020/228992) which forms a motion system together with the motion generator. The control system operates with a simulation environment, 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. For example, the driving simulation may be in the context of a driving simulator in accordance with the invention as described below. In such an embodiment the control system receives motion demands from the simulation environment, which represent the motion of a virtual vehicle. The computer program determines the motion of the vehicle in a virtual world, then applies a motion cueing algorithm (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. The MCA could be part of the simulation environment or the control system or separate to both. The simulation environment may receive inputs signals from control devices 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 (driver) in a chassis as payload on the motion generator (e.g., motion generator 10 or 20 in the example embodiments). These inputs 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 for the driver, passenger, or other user or operator. The simulation environment may also require additional data from the control system, such as relating to the position of the motion generator, or control device inputs signals.
The motion generator can be operated to move the end effector such as chassis 14 or 22 from the nominal condition described above through various motions or conditions, such as roll, pitch, yaw, sway right or left, heave up, heave down, surge forward and 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. Examples of such motions or conditions, and the corresponding effector, rocker, and strut positions are shown in
A motion generator of the invention operated in these ways has the advantages including high bandwidth, low friction, and low inertia which increase the accuracy/positioning of the movements of the payload/end effector and low latency.
As mentioned above, a motion generator in accordance with 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 in a combination, that is to say the motion generator itself becomes the payload of a primary motion generator. The combination is advantageous in that the primary motion generator may be relatively inexpensive but provides good excursion ranges in the X and Y directions and the secondary motion generator provides a higher bandwidth, and positional accuracy and lower levels of inertia and friction which further increase the accuracy of the movements imparted to the payload. Such a combination, or “two-stage” motion generator, is shown in
A driving simulator 30 in accordance with the invention is shown in
A motion generator in accordance with the invention, as described in the above embodiments may be advantageous when used in a driving simulator in some or all of several respects compared with known motion generators for such applications. A driving simulator incorporating a motion generator in accordance with the invention has low latency, avoiding or minimising the need for latency correction needed in other driving simulators especially significantly more expensive driving simulators.
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 for example as described above 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 as described above. It will be noted that the rocker units are preferably modular in that one rocker unit may be replaced by another such unit in any position in the motion generator.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2114324.3 | Oct 2021 | GB | national |
| 22020231.1 | May 2022 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2022/025458 | 10/5/2022 | WO |
