Patent Document

CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is the U.S. national phase of International Application No. PCT/EP2013/051678 filed Jan. 29, 2013, which claims priority of European Application No. 12196769.9 filed Dec. 12, 2012, the entirety of which is incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention is concerned with a simulator. More specifically, the present invention is concerned with a three-degree of freedom vibration simulator for simulating the effects of translational or combined translational and rotational vibration on an apparatus or subject. 
     BACKGROUND OF THE INVENTION 
     Vibration simulators are well known, and generally used to simulate the effects of real world phenomena in a controlled environment (such as a laboratory or workshop). Vibration simulators may be used to test mechanical and electrical equipment to ensure it can withstand the environment in which it will eventually be used. For example, vibration simulators may be used in flight simulators to shake a helicopter cockpit (and thereby the cockpit equipment, seat and pilot) to simulate the high frequency vibration experienced in flight. The effects of such vibration on the pilot and surrounding equipment can be monitored and used to improve pilot skills and training and the design of the cockpit equipment. 
     Vibration simulators can be used in devices such as vibration platforms, anti-vibration platforms, flight simulators, driving simulators, earthquake simulators, g-seats, seat shakers and vehicle dynamics simulators amongst others. Vibration platforms are required the so-called “Level D” flight simulator standard of civil aviation regulatory authorities. 
     Various movement simulators exist in the art. One such example is U.S. Pat. No. 6,077,078. The subject device is capable of providing motion in various degrees of freedom and is mounted on a two degree of freedom Cartesian slideway in order to provide movement in perpendicular horizontal directions. A problem with this device is that in order to provide translational movement in all three degrees of freedom, the slideway in combination with the motion platform requires a high number of actuators and it is relatively complex and expensive. It also has a large space requirement. 
     US 2005/0277092 discloses a seat motion simulator which uses three vertically oriented actuators. Each of the actuators is positioned on a horizontal slideway. As is clear from this document, in order to move the seat in a translational degree of freedom, each actuator has to be moved vertically and horizontally. This particular mechanism is complex and large and is not well suited to in-cockpit simulation of vibration. 
     SUMMARY OF THE INVENTION 
     It is an aim of the present invention to provide an improved vibration simulator which is compact and able to provide vibration in at least the three translational degrees of freedom. 
     According to a first aspect of the present invention there is provided a movement simulator comprising: 
     a base; 
     a movable support positioned above the base in use; 
     at least three movable support actuation assemblies connecting the base to the movable support, each movable support actuation assembly comprising: 
     an actuator; 
     a first link having a first end connected to the base such that the first end of the first link is drivable by the actuator to describe an at least part circular locus about a first axis; 
     a second link having a first end connected to the base such that the first end of the second link is drivable by the actuator to describe an at least part circular locus about the first axis; 
     in which the first and second links are connected to the movable support at respective second ends; 
     in which the first and second links comprise universal joints at each of their first and second respective ends; 
     in which the respective first ends of the first and second links are spaced apart; and, 
     in which respective second ends of the first and second links are spaced apart. 
     Advantageously, this type of mechanism allows movement in three translational degrees of freedom and only requires the three actuators (one per actuation assembly). Each assembly forms a four bar-linkage with the base and movable support which can be actuated to move the movable support relative to the base, but also allows relative movement thereof when one of the other actuation assemblies moves. 
     By “universal joint” we mean any joint which is movable in at least two degrees of freedom—for example a cardan joint or spherical joint. 
     The movable support may be a platform or a loading frame with a plurality of attachment points for the equipment on which simulation or testing is to be performed. 
     Preferably at least one movable support actuation assembly comprises a first crank mounted to the base for rotation about the first axis, which first crank, is connected to the universal joint at the first end of the first link. Preferably the first crank extends radially from an axle. Preferably a second crank is provided extending radially from the axle, which second crank is connected to the universal joint at the first end of the second link. 
     The crank can be driven in rotation to drive the movable support through rotational motion. This is advantageous because rotary actuators are preferable to linear actuators, particularly in high frequency applications such as vibration simulation. Linear actuators also need a brake to stop them in emergency situations (to prevent the platform from falling—e.g. when using a hexapod) whereas rotary actuators in the configuration according to the invention do not. 
     The axle may be driven directly, or preferably the assembly comprises a driving crank extending radially from the axle, which driving crank is driven by the actuator. This allows further gearing of the actuator. The driving crank may be driven by a push rod, which in turn is driven by an actuator crank driven in rotation by the actuator. 
     Preferably the actuator crank is arranged to be driven through 360 degrees. This means the motor does not have to continually change direction; an advantage for vibration simulation in particular. 
     The actuators may be positioned internally—that is within the area bounded by the first ends of the links- or where the support actuation assemblies are mounted to the base. This makes the arrangement more compact. 
     Alternatively, the actuators may be positioned externally—that is outside the area bounded by the first ends of the links- or where the support actuation assemblies are mounted to the base. This makes replacement and service of the actuators easier, and allows larger actuators to be used. 
     Preferably: 
     the first link has a first length; 
     the second link has a second length; and, 
     in which the distance between the first respective ends of the links, and the second respective ends of the links is greater than either the first length or the second length. 
     This aspect ratio of the four bar link is preferable for vibration simulation because although the range of motion of the platform is reduced, the stiffness of the assembly is increased. Small movements at high frequency are ideal for vibration simulation, in particular for helicopter cockpit simulation, and as such this aspect ratio of the four-bar link is advantageous. 
     Preferably the distance between the first respective ends of the links, and the second respective ends of the links is at least three times either the first length or the second length, preferably at least five times either the first length or the second length. (That is, at least three or five times their individual lengths). 
     Alternatively, if a large amplitude of vibration is required, the aspect ratio of the four bar link can be altered such that the individual lengths of the first and second links is equal to, or greater than the distance between their ends. This arrangement, although less stiff than the previous embodiment, provides a higher degree of travel for higher-amplitude vibration. Under these circumstances, further stiffening may be required as discussed below, and with respect to the second aspect. 
     Preferably there is provided at least one stiffening assembly forming a load path between the base and the movable support independent of the movable support actuation assemblies. Preferably the stiffening assembly comprises a resilient member which is less stiff in translation than rotation. 
     The four bar link arising from the geometry of the actuation assembly may have various shapes. The first link and the second link may have the same length, in which case the four bar link would be a parallelogram (if both ends of the links are equally spaced from one another) or a trapezium (if not). 
     According to a second aspect of the invention there is provided a movement simulator comprising: 
     a base; 
     a movable support positioned above the base in use; 
     a stiffener extending between the base and the movable support, which stiffener comprises: 
     a first generally U-shaped region attached to the base at its respective ends; and, 
     a second generally U-shaped region attached to the movable support at its respective ends; 
     in which the first U-shaped region is joined to the second U-shaped region between their respective ends, and in which the U-shaped regions are at an angle to each other about a yaw axis extending between the base and movable support in use. 
     Advantageously, this arrangement provides support but suppresses rotation about the yaw axis, which is important in vibration simulation, particularly with an arrangement according to the first aspect which is susceptible to undesirable yaw rotation. 
     Preferably the stiffener comprises: 
     a first and second leg, each attached to the base and connected to define the first U-shaped region; 
     a first and second arm, each attached to the movable support and connected to define the second U-shaped region; 
     in which the legs and arms are constructed from a resilient sheet material. 
     The legs and arms may join at a region normal to the yaw axis. This plate like central region provides yaw stiffness. 
     Preferably the legs and arms are L-shaped, with a portion of each leg and arm being co-planar and normal to the yaw axis. This allows the legs and arms to act as leaf springs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING VIEWS 
       An example vibration simulator in accordance with the present invention will now be described with reference to the accompanying figures in which:— 
         FIG. 1  is a perspective view of a first vibration simulator in accordance with the present invention; 
         FIG. 2  is a view of the simulator of  FIG. 1  with the motion platform omitted for clarity; 
         FIG. 3  is a detail view of a part of the simulator  FIG. 1  with the motion platform omitted for clarity; 
         FIG. 4  is a detail view of a further part of the simulator of  FIG. 1  with the motion platform omitted for clarity; 
         FIGS. 5 a  and 5 b    are side schematic views of an actuator of the simulator of  FIG. 1 ; 
         FIG. 6  is a perspective view of a part of a second vibration simulator in accordance with the present invention; 
         FIGS. 7 a -7 e    are schematic views of five different geometric configurations of part of an actuator for a simulator in accordance with the present invention; and, 
         FIG. 8  is a perspective view of a third vibration simulator in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Turning to  FIGS. 1 to 4 , a vibration simulator  100  in accordance with the present invention is shown. The vibration simulator  100  comprises a base  102 , a movable support in the form of a platform  104  positioned above the base in use, and three individual platform actuation assemblies  106 ,  108 ,  110  driving the platform  104  relative to the base  102 , as will be described below. The platform  104  is also supported on three support assemblies  192 ,  194 ,  196 . 
     The base  102  is a flat, plate-like member shaped as an irregular pentagon in profile. The base  102  is in the shape of a triangle having three long sides  112 ,  114 ,  116  with each corner of the triangle truncated to provide three short sides  118 ,  120 ,  122 . The base  102  is mounted on a surface (usually a floor) in use. Alternatively the base can be the floor with the relevant components attached directly thereto. 
     Turning to the platform  104 , it is similar to the base  102  in as much that it is an irregular pentagon shape formed from a triangle having long sides  126 ,  128 ,  130  with truncated corners forming short sides  132 ,  134 ,  136 . In this embodiment the platform  104  is identically shaped to the base  102  and in a neutral position of the actuator assembles  106 ,  108 ,  110 , is vertically offset relative thereto. 
     In  FIG. 2  the platform  104  is omitted such that the first, second and third actuation assemblies  106 ,  108 ,  110  are visible. The three actuation assemblies  106 ,  108 ,  110  are substantially identical (apart from their orientation relative to the base  102 ) and as such only the first actuation assembly  106  will be described in detail. 
     The first actuation assembly  106  comprises an electric motor  138  having an output shaft  140  which is driven in rotation about a motor axis M by the motor  138 . A motor crank  142  is provided having a first shaft attachment  144  at a first end and a second shaft attachment  146  at a second opposite end. 
     An adjustable link arm  148  is provided, having a first shaft attachment  150  defined at a first end, and a second shaft attachment  152  at a second opposite end. The shaft attachment formations  150 ,  152  are formed as spherical rotational joints with multiple rotational degrees of freedom. The adjustable link  148  can be adjusted in length in a known manner, and as required when setting up the simulator  100 . 
     The first actuation assembly  106  comprises a first axle mount  154  and a second axle mount  156 . Each axle mount  154 ,  156  is attached to the base  106  such that it is rigidly attached thereto. Each axle mount  154 ,  156  comprises a bearing suitable for receiving an axle. Each bearing is a cylindrical joint able to provide movement in a single rotational degree of freedom. The axle mounts  154 ,  156  are spaced apart and proximate opposite ends of the long side  112  of the base  102 . The joint axes of the axle mounts  154 ,  156  are aligned and parallel with a single joint axis X. The joint axis X is slightly offset from the first long side  112  towards the centre of the base  102 . 
     An axle  158  is provided which generally comprises an elongate tube  160  having stub axles  162 ,  164  respectively positioned at either end. 
     A driving crank  166  is positioned and fixed at the axial centre of the axle  158 . The driving crank  166  comprises a first plate  168  and a second plate  170 , which are offset parallel, mirror images of each other. At the free end of the driving crank  166  (opposite the axle  158 ) there is provided a shaft receiving formation  172 ,  174  on each of the plates  168 ,  170  respectively. The shaft receiving formation  172 ,  174  is connected to the spherical joint attachment formation  152  which allows rotation in all rotational degrees of freedom. 
     At each end of the axle  158 , there is provided a first axle crank  176  and a second axle crank  178  respectively, each projecting radially therefrom. Each of the axle cranks  176 ,  178  is fixed to the axle  158  and each crank defines a respective spherical joint  180 ,  182  at the end opposite the axle  158 . 
     A first adjustable axle tie rod  184  and a second adjustable axle tie rod  186  are provided and are adjustable in length as known in the art. 
     A first tie rod mount  188  and a second tie rod mount  190  are provided and attached to the underside of the platform  104  at respective ends of the first long side  126 . Each tie rod mount comprises a spherical joint  189 ,  191  respectively. 
     The first actuator assembly  106  is assembled as follows. 
     Referring to  FIG. 3 , the output shaft  140  is connected to the first shaft attachment point  144  on the crank arm  142  such that the crank arm  142  rotates about the motor axis M as the shaft  140  is driven by the motor  138 . The second shaft attachment  146  of the crank arm  142  is attached to the first shaft attachment  150  of the adjustable link  148  via a stub shaft such that the link  148  is free to rotate relative to the crank arm  142  about a first link axis L 1 , as well as perform minor rotations about axes perpendicular to L 1  (because the attachment  150  is a spherical joint). It will be noted that the crank arm  142  is configured so as the output shaft  140  does not interfere with a 360 degree rotation of the crank arm  142 , and does not foul on the adjustable link  148  as it rotates through 360 degrees. Therefore, the actuator  138  can be continuously driven. 
     The second shaft attachment  152  of the adjustable link  148  is positioned between the shaft receiving formations  172 ,  174  of the plates  168 ,  170  of the driving crank  166 . The components are attached together such that the adjustable link  148  can rotate about a second link axis L 2  relative to the driving crank  166  (N.B. the link  148  can also perform minor rotation about other axes because the attachment formation  152  is a spherical joint). The motor axis M, first link axis L 1  and second link axis L 2  are parallel. 
     The axle  158  is mounted for rotation about the joint axis X which is also parallel to the motor axis M, first link axis L 1  and second link axis L 2 . 
     Each of the axle tie rods  184 ,  186  is attached to the spherical joints  180 ,  182  of the axle cranks  176 ,  178  such that the axle tie rods  184 ,  186  can rotate relative to the axle cranks  176 ,  178  in all three rotational degrees of freedom. The axle tie rods  184 ,  186  are positioned next to the respective axle mounts for stiffness. 
     Each tie rod  188 ,  190  is attached to the underside of the platform  104 . The tie rod mounts  188 ,  190  are generally mounted parallel to and offset from the axle  158  such that a line drawn between the tie rod mounts  188 ,  190  is parallel to, and offset from, the first long side  126  of the platform  104  and towards the centre of the platform  104 . 
     The tie rods  184 ,  186  are parallel and of equal length and thus form a four bar link in the form of a parallelogram at all positions of the platform  104  relative to the base  102 . The platform  104  is thereby always parallel to the base  102  and does not rotate. This range of motion is shown schematically in  FIG. 7   a.    
     The four bar link formed by the tie rods  184 ,  186 , the base  102  and the platform  104  is characterised in that the rods  184 ,  186  are shorter in length than the distance between their respective ends. In other words at both ends, the tie rods  184 ,  186  are spaced apart by a distance further than their respective lengths. This provides stability to the mechanism, and stiffness to the simulator  100 , which undergoes very high reaction forces in use. It will also be noted that the tie rods  184 ,  186  are not vertical, and are not perpendicular to the respective planes of the base  102  and platform  104 . This also confers stiffness on the simulator  100 . 
     Referring to  FIGS. 5 a  and 5 b   , operation of the first actuator assembly  106  is shown schematically.  FIGS. 5 a  and 5 b    are schematic views from direction V in  FIG. 2 . 
     Comparing  FIGS. 5 a  and 5 b   ,  FIG. 5 a    shows the actuator  106  in its starting, neutral position. The position of the platform  104  once it has moved by a small clockwise rotation of the output shaft  140  of the motor  138  is shown in  FIG. 5 b    (with the starting position in hidden line). As can be seen in  FIG. 5 b   , rotation of the crank arm  142  pushes the adjustable link  148 , which in turn rotates the driving crank  166  and thereby the axle  158  about its primary axis. The axle cranks  176 ,  178  are also rotated in a clockwise fashion thus pulling the axle tie rods  184 ,  186  and lowering the platform  104 . 
     As shown in  FIG. 2 , each of the three actuator assemblies  106 ,  108 ,  110  is positioned 120 degrees apart. In other words they are equally spaced about the base  102  and platform  104 . 
     Movement provided by the actuator assembly  106  urges the platform  104  in a first direction D 1 . This is clearly at a 120 degree angle to the movement provided by either actuator assembly  108 ,  110  (D 2  and D 3  respectively). Such motion is permitted by the parallelogram linkage made up by the axle  158 , axle tie rods  184 ,  186  and the platform  104 . The fact that each actuator assembly  106 ,  108 ,  110  has a parallelogram linkage means that translational movement in all three degrees of freedom of the platform (i.e. surge in a fore-aft direction, sway in a side-to-side direction and heave in a vertical direction) is possible. 
     It will be noted that each of the three actuator assemblies  106 ,  108 ,  110  can be simultaneously or alternately activated in order to provide motion in one or more of the three translational degrees of freedom. 
     As can be seen in  FIG. 2 , the platform  104  is mounted on support assemblies  192 ,  194 ,  196 . Each of the support assemblies  192 ,  194 ,  196  is substantially identical and as such only the support assembly  192  will be described in detail here. 
     Referring to  FIG. 3 , the support assembly  192  comprises a base plate  198  which is attached to the base  102 . A shock absorbing cushion  200  extends vertically from, and perpendicular to, the base plate  198  and is connected to a platform mount  202 . The mount  202  is u-shaped, having a base  204  connected to the cushion  200  and two upwardly extending side panels  206 ,  208  which terminate in two outwardly extending flanges  210 ,  212  which are configured to be mounted to the platform  104 . In order to make the assembly as compact as possible, and to provide adequate support for the platform  104 , each of the platform mounts  202  encloses part of the actuator assembly  106 , specifically the adjustable link  148  which sits between the side panels  206 ,  208  within the u-section. The cushions  200  also support the static weight of the payload on the platform  102 . 
     An alternative or additional method of inhibiting yaw rotation (i.e., rotation about a vertical axis) can be seen in  FIG. 6 .  FIG. 6  shows a yaw inhibiting platform support  214  having a first foot  216  and a second foot  218  configured to be connected to the base  102 . 
     Each foot  216 ,  218  is connected to a vertical plate-like member  220 ,  222  respectively, and each plate member  220 ,  222  to a horizontal member  224 ,  226  respectively. As such, two legs  228 ,  230  are formed which are generally shaped as inverted ‘L’ shapes in cross-section. 
     Between the legs  228 ,  230  there is provided a relatively stiff centre plate  232  which connects the horizontal members  224 ,  226 . The centre plate  232  is square and the horizontal members  224 ,  226  connect to it along two opposing sides. Extending from the remaining sides of the centre plate  232 , there are provided two further horizontal members  234 ,  236  which are similar to the horizontal members  224 ,  226 , but extend at 90 degrees thereto in a horizontal plane. The horizontal members  234 ,  236  are joined to two further vertical members  238 ,  240 . The horizontal members and vertical members thereby form two “L” shaped arms  242 ,  244  respectively. Each of the arms  242 ,  244  terminates in a platform mount  246 ,  248  which connect to the platform  104 . 
     Each of the legs  228 ,  230  and arms  242 ,  244  are constructed from a material selected to be flexible and resilient in bending, but stiff in shear (such as sheet metal). As such, each of these members act as a leaf spring. The “L” shape of the arms and legs and the fact that they are disposed at 90 degrees to each other, means that the support  214  permits some movement in all three translational directions and also permits rotation of the platform relative to the base about both horizontal axes. The one degree of freedom that is severely constrained by the support  214  is the yaw degree of freedom; that is rotation about a vertical axis. This is mainly due to the way that the centre plate  232  and horizontal members  224 ,  226 ,  234 ,  236  are horizontally oriented. 
     Variations fall within the scope of the present invention. 
     For example, the tie rod mounts  188 ,  190  may be moved to adjust the orientation of the tie rods  184 ,  186 .  FIG. 7 a   , shows the parallel, equal length tie rods which ensure a non-rotating platform  104  (as described above). 
     As shown in  FIG. 7 b   , non parallel, equal length rods which diverge toward the platform results in translational and rotational motion about a point below the platform. This may be useful for e.g. earthquake simulation. 
     As shown in  FIG. 7 c   , non parallel, equal length tie rods provide rotation about a point above the platform. This may be useful for assessing the vibration of e.g. suspended structures. 
     The embodiments of  FIG. 7 d    (non equal lengths, but parallel) and  FIG. 7 e    (non equal lengths and not parallel) also provide different types of motion. 
     Turning to  FIG. 8 , a vibration simulator  300  is shown which is similar to the simulator  100 . Like the simulator  100 , the simulator  300  comprises a base  302 , a movable support it the form of a platform (not shown) positioned above the base in use, and three individual platform actuation assemblies  306 ,  308 ,  310  driving the platform relative to the base  302 , as will be described below. The platform is also supported on three support assemblies  392 ,  394 ,  396 . 
     The differences between the simulators  100  and  300  are discussed below. 
     Instead of two axle mounts  154 ,  156 , the first actuation assembly  306  comprises a first axle mount  354 , a second axle mount  355 , a third axle mount  356  and a fourth axle mount  357 . Each axle mount  354 ,  355 ,  356 ,  357  is attached to the base  306  such that it is rigidly attached thereto. Each axle mount  354 ,  355 ,  356 ,  357  comprises a bearing suitable for receiving an axle. Each bearing is a cylindrical joint able to provide movement in a single rotational degree of freedom. The joint axes of the axle mounts  354 ,  355 ,  356 ,  357  are aligned and parallel with a single joint axis X. 
     A axle  358  is provided. The axle  358  is mounted for rotation about the axis X, and is supported between the first and fourth axle mounts  354 ,  357 . The axle is also supported mid-way along by the third and fourth axle mounts  356 ,  357 . The second and third axle mounts  355 ,  356  are adjacent. 
     Like the simulator  100 , a driving crank  366  is positioned and fixed at the mid-point of the axle  358 , either side of the third and fourth mounts  355 ,  356 . The driving crank  366  comprises a first plate  368  and a second plate  370 , which are offset parallel, mirror images of each other. At the free end of the driving crank  366  (opposite the axles  358 ,  359 ) there is provided a shaft receiving formation  372 ,  374  on each of the plates  368 ,  370  respectively. The shaft receiving formations  372 ,  374  are connected to a push rod in much the same way as the simulator  100 . 
     Provision of two extra supports in the centre of the axle allows for greater stiffness and stability. 
       FIG. 8  also shows six optional, temporary supports,  400 ,  402 ,  404 ,  406 ,  408 ,  410 . These supports hold the platform in place if any of the actuation assemblies or permanent supports need to be serviced or replaced.

Technology Category: g