NZ719370B2 - A motion platform - Google Patents

Abstract

apparatus (1) for maintaining a support platform (5) and a payload mountable thereon in near neutral equilibrium relative to a base structure (3), the support platform (5) being spaced from the base structure (3) by a plurality of actuators which provide the support platform (5) with six degrees of freedom relative to the base structure about longitudinal, lateral and vertical axes, the apparatus (1) including: a substantially upright strut mountable between the base structure (3) and support platform (5) for supporting the weight of the support platform (5) and payload, a first balance assembly for counteracting forces imparted on the strut when the payload is moved longitudinally and/or laterally with respect to the base structure, a second balance assembly for counteracting forces imparted on the support platform when the payload is pivoted about the longitudinal and/or lateral axes with respect to the base structure, wherein the forces counteracted by the first balance assembly and the second balance assembly reduce the load imparted on the actuators by the payload. Having the two balance assemblies for counteracting the forces on the struts and support platform allows the apparatus to provide balancing and returning forces in all directions. of freedom relative to the base structure about longitudinal, lateral and vertical axes, the apparatus (1) including: a substantially upright strut mountable between the base structure (3) and support platform (5) for supporting the weight of the support platform (5) and payload, a first balance assembly for counteracting forces imparted on the strut when the payload is moved longitudinally and/or laterally with respect to the base structure, a second balance assembly for counteracting forces imparted on the support platform when the payload is pivoted about the longitudinal and/or lateral axes with respect to the base structure, wherein the forces counteracted by the first balance assembly and the second balance assembly reduce the load imparted on the actuators by the payload. Having the two balance assemblies for counteracting the forces on the struts and support platform allows the apparatus to provide balancing and returning forces in all directions.

Description

/050252 A MOTlON PLATFORM FlELD OF THE INVENTION The present invention relates to a motion platform. More specifically, the present invention relates to an apparatus for reducing the force required to implement movement in six degrees of freedom in a motion platform.

BACKGROUND TO THE iNVENTlON [0002} Motion platforms, ise known as motion simulators, are used to simulate the sensation of being in a moving vehicle, for example an aircraft or motor car. Motion simulators typicallyr comprise some form of enclosure, capsule or cockpit having one or more seats for occupants and a sound and visual y which is synchronised to the movement of the enclosure. The enclosure can be moved within a given working volume through an arbitrary trajectory in a 3 ional space. To facilitate such movement the enclosure is usually mounted on some form of supporting surface or platform having series of underlying actuators to impart , for example a Ste-wart platform. [0003} Stewart platforms are well-known and permit movement with 6 degrees of freedom, i.e. independent and simultaneous ation and rotation about and along each of the three primary Cartesian axes X, Y and Z. A Stewart platform includes six legs each of which is extendible to translate and rotate a supporting platform about all three Cartesian axes. A typical Stewart platform, as shown in Figure 1 of the accompanying gs, es a base structure 3 which is spaced from a support platform 5 by a plurality of extendible legs in the form at hydraulic, pneumatic, or ic actuators 7. [0004} in existing motion simulators the entire weight of the enclosure, including the occupants, is ted solely by the actuators 7. The actuators 7 must therefore be adequately sized to support weight of the enclosure and impart the required motion.

SUMMARY OF THE INVENTIQN [00053 in accordance with the first aspect of the invention there is provided an apparatus for maintaining a support ptatiorm and a payload mountable thereon in near neutrai equilibrium relative to a base ure. The support platform is spaced from the base structure by a piuraiity of actuators which provide the t platform with six degrees of freedom relative to the base structure about longitudinal, lateral and vertical axes. The apparatus des a substantially upright strut mountable between the base structure and support platform for supporting the weight of the support platform and payload. The apparatus further includes a first balance assembty for counteracting forces imparted on the strut when the payload is moved Iongitudinaily andror iateraity with respect to the base structure. The apparatus further includes a second balance assembly for racting forces imparted on the support rrn when the d is pivoted about the udinal and/or lateral axes with respect to the base structure. The forces counteracted by the first balance assembly and the second baiahce assembly reduce the load imparted on the actuators by the payload.

The first balance assembiy preferably inctudes three or more resilient s connected between the strut and the base structure. in this respect, the resilient members may extend outwardly from the strut and be angulariy Spaced apart a substantially" equal ce on the base structure. [000?] The base structure may include three or more outwardiy and ly extending mounting arms which are rty‘ spaced apart a substantialty actual distance. Each resilient member may have" one and secured to a corresponding mounting arm.

Each resilient member preferably inoiudes one or more elastic elements, for example elastic cords! which may extend hack and forth between the strut and the mounting arm.

The strut preferably includes a main housing pivotally mounted to the base ure, and a cylinder verticaliy disptaoeabie with respect to the main housing. The strut may further include a frame structure oned around the main housing and the cylinder. [0010} In one embodiment, the elastic cords of the resilient members are secured to the main housing. in other embodiments, the one or more of the elastic cords can be. secured to the frame structure or the cylinder, the er and the main housing, or any combination of the frame structure, cylinder and main hensing. [001. 1} The second balance assembly preferabiy includes three or more tether lines having a first end connected to the support ptattorm or the payload, and a second and connected to the strut. The tether lines are ably angularly‘ spaced apart a ntiaily equal distance on the support rm or payload. [0012} The frame structure of the etrut may include an upper and secured to the cylinder and a lower end which extends around the main housing. The lower end preferabiy includes a pluratity of rollers, slider or the like which can travel on an outer surface of the main housing when the cylinder is vertically displaced with respect to the main housing, The second end of each tether line is preferably secured to the lower end of the frame structure.

The second balance assembly may r e a plurality of upper s or sprockets mounted on the outer surface of the main housing, and a pluratity of lower pulleys or ets mounted on the base structure. Each tether line can thereby pass from the support platform or payload, under a lower pulley 2014/050252 or Sprocket and then over an upper pulley- or sprocket before passing to the tower and of the frame structure. [001.43 Each tether line preterabty includes a resilient section which is arranged end to end with a non—resilient section. in this respect, the non-resilient section of the tether line is preferably a cable, and the resilient section of the tether line preferably includes one or more elastic cords. to this respect, the one or more elastic cords may extend back and forth between opposing first and second ng blocks of the resilient section.

The support platform preferably includes an upper section and a lower section. in this t, the lower n is preferably able to swivel with respect to the upper section. The first mounting block of each tether line of the second baiance ly is preferabty d to the lower section of the support platform. [0016} in accordance with another aspect of the ion there is provided a motion platform including: a base structure; a support platform for mounting a payload thereon; a plurality of actuators oonneoted between the base structure and the support platform, the actuators providing the support platform with six degrees of freedom retative to the base structure about longitudinal, lateral and vertical axes; a substantially upright strut mounted beMeen the base ure and Support platform for supporting the weight of the support platform and payload; a first balance assembly for ocunteracting forces imparted on the strut when the payload is moved longitudinally andfor laterally with respect to the base structure, and a second balance assembly for counteracting forces ed on the support platform when the payload is pivoted about the longitudinal aridfor lateral axes with respect to the base structure, wherein the forces counteracted by the first balance assembly and the second e assembly reduce the toad imparted on the actuators by the payload. [001.73 The present invention advantageously enables a payload. for example, the enoiosure. capsule or cockpit of a motion simulator to he moved with minimal effort on the part of the actuators due to all or a substantial portion of the weight of the payload being removed from the actuators. in this respect the upright strut supports the weight. of the support pisttorm and payload, the first e assembly provides a force to the strut that is the opposite vector to the movement of the strut, and the second balance assembly provides a tome to the t platform that partially or y cancets out the overturning force acting upon the support platform by the payload. [001.83 Further, the present invention advantegewsly enables the support rm and. d to be maintained in a state ot neutral or near neutral betance or brium over the payioed‘s full range of movement. in this respect, the forces counteracted by the tirst and second balance assemblies provide stability and balance to the payload such that the actuators used to impart motion to the payload can be. r, thereby ng actuators of lower cost to be utilised. The payload can therefore be maintained in a titted or offset position with minimal load on the actuators.

BRIEF DESCRiPTl-ON OF THE DRAWlNGS [0019} Further benefits and advantages of the present invention wilt become apparent from the following description of the preferred embodiments of the invention. The preferred embodiments should not be considered as limiting any of the statements in the us section. In the drawings: Figure l is a perspective View of a motion platform wise known as a Stewart platform) in accordance with the prior art; Figure 2 is a perspective view of the apparatus in accordance with an embodiment of the invention, incorporated into the motion platform illustrated in Figure 1 ; Figure 3 is a perspective View of the apparatus illustrated in Figure 2 with the ors of the motion platform omitted; [0023} Figure 4 is a top ctive View of the apparatus shown in Figure 3, with the second balance assembly also omitted; [0024} Figure 5 is a side View illustrating the strut and various features of a portion of the second balance assembly; and Figure 6 is a perspective View of the tus in accordance with a further embodiment of the invention, incorporated into a motion platform having a twospart support platform.

DESCRlPTiON OF THE PREFERRED MENTS With reference to s 2 to 6 of the accompanying drawings there is shown a motion platform incorporating a baiance mechanism or apparatus 1 for maintaining a support platform 5, and a. payload mountabie thereon, in Substantially neutral balance or equilibrium ve to a base structure 8, The support platform 5 is spaced from the base ure 3 by a ity of actuators 7 which provide the support piatio-rm 5. with six degrees of freedom relative to the base structure 3 about longitudinal, lateral and vertical axes, X, Y and Z respectively. [002?] The apparatus 1 includes one or more substantially upright. struts 9 mountable between the base structure 3 and the support platform 5. The strut 9 supports the ntial weight of the platform 5 and associated payload thereon.

The payload typically includes one or more. occupants in some form of enclosure, capsule or cockpit having one or more seats, a visual dispiay and controls which represent the ride being simulated. [0028} The apparatus 1 further includes atirst balance assembly 11 for counteracting forces impeded on the strut 9 when the payload is moved longitudinally and/or lly with respect to the base structure 3 by the actuators 7‘. The apparatus 1 further includes a second balance assembly 13 for counteracting forces imparted on the support platform 5 when the payload is pivoted about the longitudinal and/or lateral axes with respect to the base structure 3 by the actuators 7. [0029} With reference to Figure 2, the support rm 5 and associated payload can be moved by actuators 7 to rotate the payioad in roii {rotation about the X axis), pitch {rotation about the-Y axis) and yaw (rotation about the Z axis}.

The actuators ? also permit translation in the three perpendicuiar axes X, Y and Z for movement forwards, rds, iett and right, and up and down.

The strut 9 functions to t the substantiai weight of the support platform 5 and payload. The strut 9 may be a “zero rate" , for exempts a low rate metal or an elastomerio spring tuned to exert a force approximateiy equal to the weight of the support platform 5' and payload. A tow spring rate is advantageous in reducing the change in force provided in respect of change in vertioai cement. Preferabiy, the strut 9 is tic and is used with a programmabte logic controiler or simiiar that can measure the weight of the Support platform 5 and paytoad and adjust the pressure dynamically. This is ularly advantageous in deaiing with variations in payload mass. The strut 9' may include a main housing 15 pivotaliy mounted to the base structure 3, and a cylinder 1? verticaliy displaoeabte with respect to the main housing 15. in se to vertical displacement of the support ptatiorm 5 by the actuators 7 andlor changes in ight of the support piattorm 5 and payioad thereon, the amount of fluid within the main housing 15 is adjusted accordingly in order that the strut 9 es constant or near constant support for the payload at all times, The support ptatiorm 5 may be pivotaiiy mounted to a top region of the cylinder i7. ably, the strut 9 further ee a frame structure 25 having an upper platesiike end 27 secured to the cylinder 17' and a lower pirate-like end 29 which extends around the main housing 15.. The frame structure 25 further includes a plurality of te 'bare positioned between the upper and lower plate-like ends 27. 29. [063-13 The vertical strut 9 is pivotally mounted to the base structure 3, The first e assembly 11 stabilises the strut 9 by providing iaterai—IOngitudinal balance. In this t, the first baiance assembly 11 provides a counteracting force to the strut 9 when the support platform 5 and payioacl is moved longitudinally andfor lly with respect to the base strueture 3. [0032} The first balance assembly 11 preferably includes three or more resilient members 18 oonnmted between the strut 9 and the base structure 3. As best-seen in Figure 3, the resilient members 18 extend outwardly and downwardly from the strut 9 and .are angutariy spaced apart a substantiatiy equal distance on the base structure 3.. in this respect, the base structure 3 includes three or more outwardly and ly extending mounting arms 19 which are angularly spaced apart a substantially equal distance. A first end of each resitient member 18 is attached to the strut 9 with an opposite second and secured to a distal end of the mounting arm 19. By mounting the ent members 18 on the mounting arms 19, the resilient members 18 are more horizontaiiy orientated. As the verticai strut 9 is tilted from the al upright position, the resilient members 18 collectively provide a r balancing forced By the selection of appropriate spring rates for the resilient members 18, the rning force can be largely or totaliy cancelled out. Equai resiiient s t8 arranged with edual angular separation to give a zero force vector when the strut 9 is Vertioai is desirable, but other offsets and biases can be chosen for specific applications. Although it is desirable to have resilient members 18 angularty spaced apart a generally equal distance, the resilient members 18 can be more randomly spaced provided that the resilient members 18 stitl collectively provide a zero force vector when the strut 9 is in the desired position. [0033} In a particularly preferred embodiment of the motion platform each resilient member 18 es one or more elastic elements, for example elastic- oords 21 which extend between the strut 9 and the ng arm 19. By Changing the rate or spring constant or adjusting the height of the mounting of the resilient members 1.8. on the mounting arms 19 of the base structure 3. allowances can be made for changes in peyioed mass which can be considerable depending upon the number" and size of occupants in the payload. in Figures 2. 3 and 4. each resilient member 18 is illustrated as a singular element. However each resilient member 18 shown may include one or a multiple number of c elements extending between the strut 9 and the mounting arm 19. A first end" of each resilient member 18 is mounted to a corresponding elongate bar of the frame structure 25. As a result. the first, end of each ent member 18 moves with the frame structure 25 and cylinder 17 during vertical displacement of the cylinder 17 with respect to the main housing of the strut 9. However, in other embodiments the first end of each resilient member 18 can be mounted to. the main housing 15 of the strut 9 such that the first end of each resilient member 18 remains stationary during vertical cement of the cylinder 17. [00.34] The second balance assembly '1' 3 orovide‘s roll—pitch e by providing a racting force to the support platform 5 when the payload rolls or pitches. in this respect, the second balance assembly 13 preferably includes three or more, tether lines 23 having a first end ted to the support platform , or alternatively the payload, and a second end connected to the strut 9. As shown in Figure 3, the tether tines 23 are preterebly singularly spaced apart an equal distance on the support platform 5. in the embodiment shown in Figure 6, the lower plate—like end 29 includes a plurality of rollers 31 which travel ato’hg an outer surface of the main housing 15 when the cylinder 17 and frame structure 25 is vertically displaced with respect to the main housing 15 1.. 0, As shown in the embodiments depleted in Figures 5 and 6, the second balance assembly 13 may further include three or more upper pulleys 32 evenly spaced around the outer surface of the main g 15, and three or more lower pulleys 33 evenly spaced on the base structure 3. Each lower pulley 33 is aligned with a corresponding upper pulley 32. The tether lines 23 pass from the support platform 5, under a lower pulley 33 then over a corresponding upper pulley 32 before passing to the lower end 29 of the frame structure 25.

Each tether line 23 preferably includes a ent section 35 and a non- resilient section 37. In this respect. the resilient section 35 is preferably arranged end to end with the non-resilient section 37’ with the non-resilient section 37 passing around the upper end lower pulleys 32, 33‘ The non—resilient section 37 is preferably a cable, for example a wire cable. it the silient section 37' is in the form of a chain, for e a roller chain or the like, the lower'pulleys 33 and the upper pulleys 32 can be replaced with sprockets [0037} The ent n 35 of the tether line 23 preferably includes one or more elastic cords 39, as shown in Figure 6, which extend between opposing first and second mounting blocks 41, 42 of the resilient n 35. in this regard, the first mounting block 41 is preferably mounted to the support rm 5 with the second mounting block 42 being mounted to an end of the-nonaresilient section :37 of the tether line 23. The elastic cords 39 are held in tension with the second mounting block 42 being pulled away from the first mounting block 41 by the non.- resilient n 3? of the tether line 28. By changing the spring rate of the cords andfor adjusting the position of the tirst mounting block 41 on the support platform , allowances can be made that changes in payload or occupant mess. Although multiple elastic cords 39 are provided in the embodiment shown in Figure 6, a singular elastic cord which extends back and forth multiple times n the opposing first and second mounting blocks 41, 42 could instead he used, A tether line 23 such as that described above could also be used as a resilient member is for the first balance assembly ll, as shown in Figure 6. 2014/050252 The arrangement of the non-resilient section 35 of the tether line 23 over the upper and lower puileys 32, 33 ensures that the resilient section 35 of the tether line 23 s largely unaffecteoi during iongituoinal, lateral and vertical displacement of the support platform 5 and payload. [0039} in a particularly preferred embodiment, the support platform 5 includes an upper section 43 and a lower section 45, as illustrated in Figure 6. The payload is mounted. to the upper section 43. The lower section 45. is preterabiy in the form of a ring which is able to swivel with respect to the upper section 43 and is thereby isolated or decoupled from yaw rotation of the d. in this respect, the first mounting block 41 of the non-resilient section 37 is preferably secured to the lower section 45 of the support platform 5 such that yaw rotation of the payload does not significantly impact upon the second balance assembly 13. The upper n 43 of the support platform 5 is free to rotate about the vertical axis with respect to the lower section 45.

The combined effect of the strut 9 and first and second balance assemblies 11, 13 make it le for the payioao on the support platform 5 to remain substantially balanced in all positions and orientations. in other words, the d can be held in a state of neutral equilibrium or near neutral equilibrium and can stay stable and at rest in ail positions and orientations withDut imparting significant load on the actuators 7. Accordingly, the actuators 7 can be sized to merely move the payload rather than support the payload. The apparatus 1 can also be packaged entirely within the confines of an existing Stewart platform and can be y or y passive in its operation. [0041} As the present invention may be embodied in several forms without departing from the essentiai teristics of the invention, it should be understood that the.aboveoeseribed ments. should not be ered to limit the present invention but rather should be construed broadly. Various cations and equivalent arrangements are intended to be within the spirit and scope of the invention.

Claims (19)

Claims

1. An apparatus for maintaining a support platform and a payload mountable hereon in near neutral equilibrium relative to a base structure, the support platform being spaced from the base ure by a plurality of actuators which provide the support platform with six degrees of freedom relative to the base ure about longitudinal, lateral and al axes, the apparatus including: a substantially upright strut mountable between the base structure and support rm for supporting the weight of the support platform and payload, a first balance assembly for counteracting forces imparted on the strut when the payload is moved udinally and/or laterally with respect to the base structure, a second balance assembly for counteracting forces imparted on the support platform when the payload is pivoted about the longitudinal and/or lateral axes with respect to the base structure, wherein the forces counteracted by the first balance assembly and the second balance assembly reduce the load imparted on the actuators by the payload, wherein the first balance assembly includes three or more resilient members connected between the strut and the base structure, and wherein the second balance assembly includes three or more tether lines having a first end connected to the support platform or payload and a second end connected to the strut.

2. The apparatus as claimed in claim 1 wherein the ent members extend outwardly from the strut and are angularly spaced apart a substantially equal distance on the base ure.

3. The apparatus as claimed in claim 2 wherein the base structure includes a three or more outwardly and upwardly extending mounting arms which are rly spaced apart a substantially equal distance, each ent member having one end secured to a corresponding mounting arm.

4. The apparatus as d in claim 3 wherein each ent member includes one or more elastic cords which extend between the strut and the mounting arm.

5. The apparatus as claimed in any one of claims 1 - 4 wherein the strut es a main housing pivotally mounted to the base structure, and a cylinder vertically displaceable with respect to the main housing.

6. The apparatus as claimed in claim 5 wherein the strut further includes a frame structure positioned around the main housing and the cylinder.

7. The apparatus as claimed in claim 6 n the one or more elastic cords of the resilient members are secured to the frame structure of the strut.

8. The apparatus as claimed in claim 5 or 6 n the one or more elastic cords of the ent members are secured to the main g of the strut.

9. The tus as claimed in claim 1 wherein the tether lines are angularly spaced apart a substantially equal distance on the support platform or payload.

10. The apparatus as claimed in claim 9 wherein the frame structure includes an upper end secured to the cylinder and a lower end ing around the main housing.

11. The apparatus as claimed in claim 10 wherein the lower end includes a plurality of rollers for travelling along an outer surface of the main housing when the cylinder is vertically displaced with t to the main housing.

12. The apparatus as claimed in any one of claims 6 - 11 wherein the second end of each tether line is secured to the lower end of the frame structure.

13. The apparatus as claimed in claim 11 n the second balance assembly further includes a plurality of upper pulleys mounted on the outer surface of the main housing, and a plurality of lower pulleys mounted on the base structure, each tether line passing over an upper pulley and under a lower pulley.

14. The apparatus as claimed in any one of claims 1 - 13 wherein each tether line includes a resilient section arranged end to end with a silient section.

15. The apparatus as claimed in claim 14 wherein the non-resilient section of the tether line is a cable.

16. The apparatus as claimed in either claim 14 or 15 wherein the resilient section of the tether line includes one or more elastic cords which extend between opposing first and second mounting blocks of the resilient section.

17. The apparatus as claimed in any one of the preceding claims wherein the t platform includes an upper n and a lower n, the lower section being able to swivel with respect to the upper section.

18. The tus as claimed in claim 17 wherein the first mounting block is d to the lower section of the support platform.

19. A motion platform including: a base structure; a support platform for mounting a payload thereon; a plurality of actuators connected between the base structure and the support platform, the actuators providing the support platform with six degrees of freedom relative to the base structure about udinal, lateral and vertical axes, and an apparatus as claimed in any one of claims 1 - 18.