Abstract:
A hex-axis horizontal movement dynamic simulator is aimed at Modular Design without hydraulic or pneumatic system but which were conventionally used in the so called Stewart Platform; this dynamic simulator comprises three sets of movement control unit with symmetrical structure located at the positions relative to each other forming three sides of an equilateral triangle, and a load-carrying platform which connected to the three movement control by means of three sets of universal-joint yoke mechanism each relative position located on the load-carrying platform are each other arranged to form as three sides of an equilateral triangle too; with this type of arrangement, this dynamic simulator have a 6-degree of freedom motion when a sets of movement control unit makes different rectilinear motion, the load-carrying platform will generate a combination of spatial translation motion and angular motion.

Description:
FIELD OF THE INVENTION 
   The invention relates to a hex-axis horizontal movement dynamic simulator and more particularly to 6-degrees-of-freedom motion simulating equipment used in modular design. 
   BACKGROUND OF THE RELATED ART 
   An early structure of a 6-degrees-of-freedom motion simulating platform was proposed by the Englishman Steward and is customarily called the Stewart Platform. For a long time, there was no significant improvement in the design of the Stewart Platform, which employed a hydraulic or pneumatic system to achieve the effect of changing the length of an actuating rod by varying the stroke of a cylinder rod to enable 6-degrees-of-freedom spatial motion. Moreover, since the parts and components comprising the conventional Stewart Platform were not modular in design and oil and air leakage problems occasionally occurred with the hydraulic and pneumatic systems, the Stewart Platform was inconvenient and required substantial maintenance. 
   SUMMARY OF THE INVENTION 
   A goal of the present invention is to provide a solution to the above-described problems of the conventional Stewart Platform by employing a modular design instead of the hydraulic or pneumatic system used by the conventional Stewart Platform. 
   Another goal of the present invention is to provide a hex-axis horizontal movement dynamic simulator that can simulate the motion of 6 degrees of freedom without employing a hydraulic or pneumatic system. 
   A further goal of the invention is to provide a hex-axis horizontal movement dynamic simulator having a modular structure that comprises three modular movement control units of the same structure. The modular movement control units are located at positions relative to each other forming three sides of an equilateral triangle and are pivoted to a load-carrying platform by a universal-joint yoke mechanism corresponding to each of the three movement control units. 
   A further goal of the invention is to provide a specific structure of a modular movement control unit that can precisely control the movement of the load-carrying platform and provide a motion simulation platform having 6 degrees of freedom. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates a first embodiment of the hex-axis horizontal movement dynamic simulator of the invention that has three sets of movement control units of the same structure located separately at the positions forming three sides of an equilateral triangle. 
       FIG. 2  illustrates the hex-axis horizontal movement dynamic simulator of  FIG. 1  showing the variation of translation and angular motion of the load-carrying platform. 
       FIG. 3  is a schematic drawing of the invention shown in  FIG. 2  as viewed from another direction. 
       FIG. 4  is a disassembly drawing showing the parts of the movement control unit illustrated in  FIG. 1 . 
       FIG. 5  illustrates a second embodiment of the hex-axis horizontal movement dynamic simulator having three sets of movement control units of the same structure located separately at the positions forming three sides of an equilateral triangle. 
       FIG. 6  is a disassembly drawing showing parts of the movement control unit illustrated in  FIG. 5 . 
       FIG. 7  illustrates a third type of embodiment of the hex-axis horizontal movement dynamic simulator having three sets of movement control units of the same structure located separately at the positions forming three sides of an equilateral triangle. 
       FIG. 8  is a disassembly drawing showing the parts of the movement control unit illustrated in  FIG. 7 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to  FIG. 1  and  FIG. 2 , a key point of the invention is that no hydraulic or pneumatic system is used in a hex-axis motion simulator  10 . For each universal-joint yoke mechanism  27 , one end of each of two fixed-length connecting rods  26  are pivoted to the universal-joint yoke mechanism  27  and the other ends of the connecting rods  26  are separately connected to a transmission-joint yoke mechanism  25 . Further, each transmission-joint yoke mechanism  25  is pivoted to a sliding seat  24  and the rectilinear translation motion and position of each transmission-joint yoke mechanism  25  is controlled by controlling the rectilinear translation and position of the corresponding sliding seat  24  so as to generate a motion of 6 degrees of freedom that controls the spatial motion and position of the load-carrying platform. 
   Hex-axis horizontal movement dynamic simulator  10  comprises three movement control units  20 , of the same structure, that are fixed on a foundation  50  at the locations relative to each other forming three sides of an equilateral triangle. Each of the three movement control units  20  is pivoted to the load carrying platform  60  by a universal-joint yoke mechanism  27 . Thus the locations at which the three universal-joint yoke mechanisms  27  are pivoted to the load-carrying platform  60  form an equilateral triangle. 
   Each movement control unit  20  is symmetrically structured to comprise a universal-joint yoke mechanism  27 , two connecting rods of fixed length  26 , two transmission-joint yoke mechanisms  25 , two sliding seats  24 , two lead screws  23 , two servo-driving mechanisms  22 , and a rectilinear translation guide  21 . Since universal-joint yoke mechanism  27  is pivotally connected to load-carrying platform  60 , it can generate a motion of 1 degree of freedom relative to load-carrying platform  60 . Since one end of each of the two connecting rods  26  is pivotally connected to the same universal-joint yoke mechanism  27 , the connecting rod can generate a motion of 2 degrees of freedom. 
   Therefore, the end of the connecting rod pivoted to the universal-joint yoke mechanism  27  has 3 degrees of freedom for generating a spatial motion relative to the load-carrying platform. Further, the other ends of the two connecting rods are symmetrically pivoted to separate driving joint yoke mechanisms  25  that can generate a spatial motion of 2 degrees of freedom. Since the transmission-joint yoke mechanism  25  of each connecting rod  26  is pivoted to a sliding seat  24 , the transmission-joint yoke mechanism  25  has 1 degree of freedom for generating a spatial motion relative to the sliding seat  24 . Therefore, the end of the connecting rod  26  pivoted to the transmission-joint yoke mechanism  25  has 3 degrees of freedom relative to the sliding seat  24  for spatial motion. 
   Based on the above-mentioned arrangement, both ends of each connecting rod  26  of each movement control unit  20  have 3 degrees of freedom for generating a spatial motion. Since all connecting rods are fixed-length rigid bodies, when the sliding seat  24  is displaced rectilinearly, the transmission-joint yoke mechanism  25  on one end of the connecting rod  26  is restricted to rectilinear translation together with the sliding seat  24 , which enables the connecting rod  26  to generate a spatial displacement of 6 degrees of freedom. Through the variation of spatial position of every connecting rod  26 , the universal-joint yoke mechanism  27  on the other end of the connecting rod  26  will generate a relative spatial-displacement following the rectilinear displacement of the transmission-joint yoke mechanism  25 . 
   Therefore, when the sliding seat  24  makes a rectilinear translation to another place together with the transmission joint yoke mechanism  25  to which it is pivoted, the spatial position of the connecting rod  26  on the transmission-joint yoke mechanism  25  associated with 6 degrees of freedom will vary. That is, the universal-joint yoke mechanism  27  on one end of each connecting rod  26  will change its spatial position relative to the transmission-joint yoke mechanism  25  and actuate the load-carrying platform  60  to vary its spatial position. 
   Each of  FIGS. 1–3  corresponds to the rectilinear displacement of different sliding seats  24 , which slide on different movement control units  20  that are respectively located at the positions forming three sides of an equilateral triangle. The sliding seats  24  may have relative displacements for the load-carrying platform  60 . Therefore, through the synchronous and precise control of the rectilinear movement of each sliding seat  24  of each movement control unit  20 , such as may be provided by a computer system, the spatial movement of each universal-joint yoke mechanism  27  relative to the others can be precisely controlled to achieve a precise control of the motion of load-carrying platform  60  and to generate linear and angular displacement spatially. 
   The mechanism that enables each sliding seat  24  of each movement control unit  20  to generate a rectilinear motion comprises two lead screws  23 , two servo-driving mechanisms  22  having servo-motors  221 , a rectilinear translation guide  21  having two guide seats  212  and two straight sliding rails  211 . Each sliding seat  24  has a female screw thread that engages with the lead screw  23 . The servo-motor  221  of the servo-driving mechanism  22  is employed to drive the lead screw  23  to rotate, which enables the sliding seat  24  on one of the guide seats  212  of the rectilinear translation guide  21  to be guided by the straight sliding rail  211  and to generate rectilinear displacement. Therefore, the rectilinear movement of each sliding seat  24  can be precisely controlled by the precise control of the rotating speed and angular displacement of the servo-motor  221  of each servo-driving mechanism  22 , through which a precise control of the variation of linear and angular displacement of the load-carrying platform  60  can be achieved. 
   The first embodiment of the movement control unit is shown in  FIGS. 1–4  and comprises a base seat  40 , a universal joint yoke mechanism  27 , two connecting rods of fixed length  26 , two transmission-joint yoke mechanisms  25 , two sliding seats  24 , two lead screws  23 , two servo-driving mechanisms  22 , and a rectilinear translation guide  21 . The base seat  40  is a longitudinal plate fastened to the foundation  50  by bolt. The rectilinear translation guide  21  has two linear sliding rails  211  parallel to each other and two identical guide seats  212 . The two linear sliding rails  211  are installed on the surface of the base seat  40  along the longitudinal direction of the base seat and parallel to each other, and the bottom side of each guide seat  212  has two parallel guide slots that match the shape and gauge of the two straight sliding rails  211 . Thus, each guide seat  212  can be installed on and match the two straight sliding rails  211  and slide on the two straight sliding rails along the guiding direction. 
   Each servo-driving mechanism  22  comprises a servo-motor  221  assembled with a driving pulley  222 , a driving belt  223 , a driven pulley  224  and a bearing plate  225  that drives a lead screw  23 . The bearing plate  225  of each servo-driving mechanism  22  is installed at a position near a different end of the base seat  40  so as to form a bracket for mounting the two lead screws  23  with bearings and to have the two lead screws  23  parallel to the two straight sliding rails  211 . The driving pulley  222  is mounted on the driving shaft of the servo-motor  221 , and the driven pulley  224  is mounted on the lead screw  23 . The driving pulley  222  and the driven pulley  224  are connected by the driving belt  223 . 
   The sliding seat  24  is rectangular shaped and fastened to the guide seat  212  of the rectilinear translation guide  21 . On the sliding seat  24 , two penetrating holes  241 ,  242  are prepared. Hole  241  has a female screw thread and engages with the lead screw  23 . The other hole  242  is a passage for another lead screw  23  to pass through. Further, on the top surface of each sliding seat  24 , is a mounting recess  243  for pivotally mounting the transmission joint yoke mechanism  25 . 
   The transmission-joint yoke mechanism  25  comprises a U-shaped yoke  251  and a T-shaped pivot axis. The horizontal stub shaft formed on both sides of the T-shaped pivot axis is pivoted to the two vertical portions of the U-shaped yoke  251  by a bearing and nut that enable the perpendicular stub shaft of the T-shaped pivot axis to have 1 degree of freedom of rotational motion relative to the U-shaped yoke  251 . On the bottom side of the U-shaped yoke  251 , is a mounting shaft  253  that is pivotally mounted to the mounting recess  243  by a bearing and nut that provide the transmission joint yoke mechanism  25  with 1 degree of freedom of rotational motion relative to the sliding seat  24 . The perpendicular stub shaft of the T-shaped pivot axis  252  of each transmission-joint yoke mechanism  25  has 2 degrees of freedom of rotational motion relative to the sliding seat  24  to which it is mounted. 
   The universal-joint yoke mechanism  27  comprises an inverse U-shaped yoke  271 , a cardan shaft  272 , a neck-ring seat  274 , and a cover plate  275 . The left and right horizontal stub shafts formed on both sides of the cardan shaft  272  are pivoted to the two vertical portions of the inverse U-shaped yoke  271  by a bearing and nut that enable the perpendicular stub shaft formed on the front and rear side of the cardan shaft ( 272 ) to have 1 degree of freedom of rotational motion relative to the inverse U-shaped yoke  271 . On the top side of the inverse U-shaped yoke  271 , is a mounting shaft  273  that is pivoted to the neck-ring seat  274  by a bearing. A cover plate  275  is mounted on the upper side of the neck-ring seat  274 , through which the whole assembly of the universal-joint yoke mechanism  27  is mounted on the load-carrying platform  60 . Thus, the inverse U-shaped yoke  271  has 1 degree of freedom of rotational motion relative to the neck-ring seat  274  or the cover plate  275 . The perpendicular stub shaft on the front and rear side of the cardan shaft  272  of the inverse U-shaped yoke  271  has 2 degrees of freedom of rotational motion relative to the neck-ring seat  274  or cover-plate  275 . 
   Every connecting rod  26  has a fixed length. On both ends of the connecting rod  26 , are pivoting holes through which the front end of the connecting rod is pivotally connected to the front perpendicular stub shaft or rear perpendicular stub shaft of the cardan shaft  272  of the universal-joint  27 . Thus, the pivoting hole on the front end of the connecting rod  26  has 1 degree of freedom of rotational motion relative to the perpendicular stub shaft of the cardan shaft  272 . The pivoting hole on the front end of every connecting rod  26  has 3 degrees of freedom of rotational motion relative to the neck-ring seat  274  or cover plate  275 . The pivoting hole on the rear end of every connecting rod  26  is pivotally connected to the perpendicular stub shaft of the T-shaped pivot axis  252  by a bearing and nut that provide the pivoting hole on the rear end of every connecting rod  26  with 1 degree of freedom of rotational motion relative to the perpendicular stub shaft of the T-shaped pivot axis  252 . The pivoting hole on the rear end of every connecting rod  26  has 3 degrees of freedom of rotational motion relative to the sliding seat  24 . 
   Since each end of the connecting rod  26  has 3 degrees of freedom of rotational motion, the whole connecting rod  26  has 6 degrees of freedom for generating a spatial motion. The above-mentioned mechanism, as verified by the equation of mobility in Spatial Mechanism, generates a spatial motion of 6 degrees of freedom, according to Gruebler&#39;s formula for a spatial mechanism: 
                 F   =       6   ⁢     (     L   -   j   -   1     )       +       ∑     i   =   1     j     ⁢     f   i                       L   =   32     ,     j   =   36     ,           ∑     i   =   1     j     ⁢     f   i       =   36     ;     F   =   6                   
Where
 
   F: Number of degrees of freedom of the whole mechanism 
   L: Total number of members in the mechanism 
   J: Total number of joints in the mechanism 
   f i : The number of degree of freedom of the i th  joint. 
   Therefore, the relative rotating angle and rotating speed of the servo-motor  221  of the servo-driving mechanism  22  of each movement control unit  20 , based on the required data or condition of the relative motion of the load-carrying platform  60  in space and by applying the precise calculation and control of the computer system (not shown in drawings), can be synchronously controlled. The sliding seat  24  and transmission-joint yoke mechanism  25  on each of the three movement control units can synchronously generate different rectilinear movements to drive the connecting rods  26  to generate relative spatial-displacements and control the relative spatial-movement of each universal-joint yoke mechanism  27 , thus enabling the load-carrying platform  60  to vary its posture and angular position so as to simulate the state of a carrier (such as vehicle, ship, airplane and roller coaster etc.) making a spatial motion of 6 degrees of freedom. 
   In the following, is another embodiment of the movement control unit  20  that has the same mechanical structure and the same effect as that of the first embodiment of the control unit  20 . This second embodiment applies the same technical and actuating principle to enable the load-carrying platform  60  to simulate a spatial motion of 6 degrees of freedom. The construction members and the inter-actuating relationship can be obtained by reference to the detailed description of the first embodiment mentioned above, which shall not be repeated here. The following description describes the second embodiment of the movement control unit  20 . 
   The second embodiment of the movement control unit  20  is shown in  FIGS. 5 and 6  and comprises a machine bed  41 , one universal-joint yoke mechanism  27 , two fixed-length connecting rods, two transmission-joint yoke mechanisms  25 , two sliding seats  24 , two lead screws  23 , two servo-driving mechanisms  22 , and a rectilinear translation guide  21 . The components of the universal-joint yoke mechanism  27 , the connecting rod  26 , the transmission-joint yoke mechanism  25 , the lead screw  23 , the servo-driving mechanism  22 , and the rectilinear translation guide  21  are the same as those in the first embodiment of the invention. 
   But, the machine bed  41  of the second embodiment of the invention is a rectangular stand made of a metal plate having an inverse U-shaped cross-section that is fastened on the foundation  50 . A cover plate  411  is mounted on both the left and right ends of the machine bed  41  with holes and an opening prepared at appropriate positions. The servo-motor  221  of the servo-driving mechanism  22  is installed inside the machine bed  41 . The driving shaft of the servo-motor  221  extends outside the machine bed  41 . Through the opening of the cover plate  411  of the machine bed  41 , a driving pulley  222  is mounted and fastened on the driving shaft of the driving-servo motor  221 . Two support plates  227  of the servo-driving mechanism  22  are installed at places closed to both ends of the machine bed  41  to form the support for pivotally mounting the two lead screws  23  by bearings in a position parallel to the two straight sliding rails  211  of the rectilinear translation guide  21 . The driven pulley  224  is mounted and fastened on the lead screw  23  with a transmission belt installed on and passing through the driving pulley  222  and driven pulley  224 . Therefore, the driving power of the servo-motor  221  is transmitted to the lead screw  23  through the driving pulley  222 , the transmission belt  223 , and the driven pulley  224 . 
   The sliding seat  24  employed in the second embodiment of the invention comprises a sliding block  244  and a neck ring seat  246 . The sliding block  244  is fastened on the guide seat  212  of the rectilinear translation guide mechanism  21 . On the sliding block  244 , two holes are provided, one of which has a female screw thread and engages with a lead screw  23 . The other hole serves as the passage for another lead screw to pass through. The neck-ring seat  246  is fastened on the top side of the sliding block  244  or a fastening plate  245  is installed on the top side of the sliding block  244 , first, and then the neck-ring  246  is fastened on the fastening plate  245 . The mounting shaft  253  of the U-shaped yoke  251  of the transmission-joint yoke mechanism  25  is pivoted to the circular access on the tope side of the neck-ring seat  246  by a bearing and related parts. 
   The sliding seat  24  employed in the second embodiment and the first embodiment can be exchanged and used in either of the two embodiments or in other embodiments of the invention. 
   The third embodiment of the movement control unit  20  is shown in  FIGS. 7 and 8  and comprises a base seat  40 , a universal-joint yoke mechanism  29 , two fixed-length connecting rods  26 , two sliding yoke mechanisms  28 , two leading screws  23 , two servo-driving mechanisms  22 , and a rectilinear translation guide  21 . The connecting rod  26 , lead screw  23 , servo-driving mechanism  22 , and rectilinear translation guide  21  are the same as those employed in the first embodiment. The structure of the universal-joint yoke mechanism  29  is similar to the sliding yoke mechanism  28 . 
   The universal-joint yoke mechanism  29  of the third embodiment comprises an inverse U-shaped yoke assembly  291 , a pivoting plate  293 , a pivoting shaft  295 , two fixing blocks  296 , an L-shaped yoke plate  297 , a fastening yoke plate  298 , and two cover plates  299 . The L-shaped yoke plate is formed by a horizontal portion and a vertical portion. The horizontal portion is fastened on the load-carrying platform  60 . A vertical portion hole is provided for mounting a shaft. The fastening yoke plate  298  is a plate-shaped member with appropriate thickness having an appearance symmetric to that of the vertical portion of the L-shaped yoke plate  297 . A shaft mounting hole is also provided on the fastening yoke plate  298 , which is to be assembled with the L-shaped yoke plate  297  to form a yoke assembly. The pivoting plate  293  is rectangular shape with a pivoting access in its center position and horizontal stub shafts  294  extended symmetrically from both sides opposite to each other that pivotally mount in the hole on the L-shaped yoke plate  297  and the fastening yoke plate  298  by bearings and related parts. The two cover plates are fastened on one side of the vertical portion of the L-shaped yoke plate  297  and the fastening yoke plate  298  to fix the whole assembly and provide the pivoting plate  293  with 1 degree of freedom of rotational motion relative to the L-shaped yoke plate  297  and the fastening yoke plate  298 . The yoke assembly  291  has a mounting shaft  292  extended upwardly from its top side and is mounted in the pivoting access in the center position of the pivoting plate  293  by a bearing, and a cover is fastened on the mounting surface of the pivoting plate to fix the assembly. Therefore, the yoke assembly has 1 degree of freedom of rotational motion relative to the pivoting plate  293  and has 2 degrees of freedom of motion relative to the L-shaped yoke plate  297  and the fastening yoke plate  298 . The bottom side of the two flanks of the yoke assembly  291  has a semicircular recess, and the fixing block  296  also has a corresponding semicircular recess on the top side. A shaft  295  is pivotally installed by fixing the two fixing blocks on the bottom side of the two flanks of the yoke assembly  291 , and both ends of the pivoting shaft  295  can be pivotally connected to the connecting rod  26  so as to provide the pivot hole on the front end of each connecting rod with 1 degree of freedom of rotational motion relative to the yoke assembly  291  and 3 degrees of freedom of rotational motion relative to the L-shaped yoke plate  297  and the fastening yoke plate  298 . 
   The sliding yoke mechanism  28  employed in the third embodiment comprises a U-shaped yoke assembly  281 , a pivoting plate  283 , a shaft  285 , two fixing blocks  286 , an L-shaped sliding yoke plate  287 , a sliding fastening plate  288 , and two cover plates  289 . The L-shaped sliding yoke plate  287  has a horizontal portion and a vertical portion and is fastened on the guide seat  212  of the rectilinear translation guide  21  through its horizontal portion. The L-shaped sliding yoke plate  287  has two penetrating holes, one of which has a female screw thread and engages with the lead screw  23 . The other hole serves as a passage for another lead screw  23  to pass through. In addition, the vertical portion of the L-shaped sliding yoke plate  287  has a pivoting hole. The sliding fastening plate  288  is a plate-shaped member of appropriate thickness and has an appearance symmetric to that of the vertical portion of the L-shaped sliding yoke plate. Two penetrating holes and a pivoting hole are provided on the sliding fastening plate  288 . The two penetrating holes are for the two lead screws  23  to pass through. A yoke assembly is formed by assembling the sliding fastening plate  288  and the L-shaped sliding yoke plate  287 . The pivoting plate  283  is rectangular shaped with a pivoting access in a center position and horizontal stub shafts  284  extended symmetrically from both sides opposite to each other that pivotally mount in the hole on the L-shaped sliding yoke plate  287  and the sliding fastening yoke plate  288  by a bearing and related parts. Two cover plates are fastened on one side of the vertical portion of the L-shaped sliding yoke plate  287  and the sliding fastening plate  288  to fix the whole assembly so that the pivoting plate  283  has 1 degree of freedom of rotational motion relative to the L-shaped sliding yoke plate  287  and the sliding fastening plate  288 . The yoke assembly  281  has a mounting shaft  282  extended downwardly from its bottom side that is pivotally mounted in the pivoting access in the center position of the pivoting plate  283  by a bearing and related parts. A cover is fastened on the pivoting plate  283  to fix the assembly. Thus, the U-shaped yoke assembly  281  has 1 degree of freedom of rotational motion relative to the pivoting plate  283  and has 2 degrees of freedom of rotational motion relative to the L-shaped sliding yoke plate  287  and the sliding fastening plate  288 . The top side of the two vertical portions of the U-shaped yoke assembly has a semicircular recess, and a corresponding semicircular recess is provided on the fixing block  286  on the bottom side. A shaft  285  is pivotally installed by fixing the two fixing blocks  286  on the top side of the U-shaped yoke assembly, and both ends of the pivoting shaft  285  can be pivotally connected to the connecting rod  26  so as to provide the pivot hole on the rear end of the connecting rod  26  with 1 degree of freedom of rotational motion relative to the U-shaped yoke assembly  281  and 3 degrees of freedom of rotational motion relative to the L-shaped sliding yoke plate  287  and the sliding fastening plate  288 . Since both ends of the connecting rod  26  have 3 degrees of freedom of rotational motion, each connecting rod  26  has 6 degrees of freedom of rotational motion in space.