Patent Application
20140339391
1. Technical Field
The present disclosure relates to a movement device having a Stewart platform, in particular, to a movement device having a Stewart platform with four extensible links.
2. Description of Related Art
Stewart platform has been used in many applications, for example flight simulators, machine tools, biped locomotion system and surgery manipulators. The geometry of conventional Stewart platform is composed of a fixed base, a movable platform, and six linear actuators connecting the fixed base and the movable platform. This is a six degree of freedom universal-prismatic-spherical mechanism, including heave, surge, sway, yaw, pitch, and roll. No additional structural members are needed in Stewart platform because the actuators also function as structural members. The drawbacks of the Stewart platform are small workspace and complexity in control. In addition to controlling six linear actuators simultaneously in a nonlinear manner, the existence of singular positions creates more complexity in controlling the mechanism.
An exemplary embodiment of the present disclosure provides movement device having a Stewart platform.
According to one exemplary embodiment of the present disclosure, the movement device having a Stewart platform has a supporting body disposed on a horizontal plane, a movable platform, a first extensible link, a second extensible link, a third extensible link and a fourth extensible link. The first extensible link and the second extensible link are each rotatably connected to and having one DOF with respect to the supporting body, and respectively rotating about two rotation axes. The first extensible link and the second extensible link are each rotatably connected to and having two DOFs with respect to the movable platform. The extension directions of the first extensible link and the second extensible link are parallel to each another. The third extensible link and the fourth extensible link are each rotatably connected to and having two DOFs with respect to the supporting body, and the third extensible link and the fourth extensible link are each rotatably connected to and having two DOFs with respect to the movable platform.
When the movement device is in an equilibrium condition, the extension directions of the first and the second extensible links lie in a first common plane, and the rotation axes are perpendicular to the first common plane. The vertical projections of the extension directions of the extensible links on a normal plane perpendicular to the horizontal plane slant toward the horizontal plane. The vertical projection of the extension direction of the third extensible link slants toward a first direction whereas the vertical projections of the extension directions of the other three extensible links slant toward a second direction opposite to the first direction.
To sum up, the present disclosure illustrates the movement device having a Stewart platform which can reduce the control complexity. The extensible links are arranged in such a way that they can be controlled to provide a steady and smooth adjustment process to users or to maintain the horizontal orientation of the platform when changing elevation or moving sideways.
In order to further understand the techniques, means and effects of the present disclosure, the following detailed descriptions and appended drawings are hereby referred, such that, through which, the purposes, features and aspects of the present disclosure can be thoroughly and concretely appreciated; however, the appended drawings are merely provided for reference and illustration, without any intention to be used for limiting the present disclosure.
The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
Reference will now be made in detail to the exemplary embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts.
A movement device having a Stewart platform 100 comprises a supporting body 110, a movable platform 120, a first upper extensible link 130, a second upper extensible link 140, a first bottom extensible link 150, and a second bottom extensible link 160. The supporting body 110 is disposed on a horizontal plane P0. The upper extensible links 130, 140 are each rotatably connected to and having one DOF with respect to the supporting body 110, and respectively rotating about two rotation axes X. Meanwhile, the upper extensible links 130, 140 are each rotatably connected to and having two DOFs with respect to the movable platform 120. The bottom extensible links 150, 160 are each rotatably connected to and having two DOFs with respect to the supporting body 110. Also, the bottom extensible links 150, 160 are each rotatably connected to and having two DOFs with respect to the movable platform 120.
In the instant embodiment, the horizontal normal plane P0 is the x-y plane. The upper extensible links 130, 140 are rotatably connected between an upper portion of the supporting body 110 and the movable platform 120. The bottom extensible links 150, 160 are rotatably connected between a bottom portion of the supporting body 110 and the movable platform 120. The extension directions of the upper extensible links 130, 140 are in parallel with one another. The movement device having a Stewart platform 100 is capable of motion of the moveable platform 120 in heaving, pitching, and swaying.
For example, the movement device 100 is converted into a wheelchair with seat adjustment mechanism, as shown in
Referring to
In particular, referring to
The first end 131 of the first upper extensible link 130 is rotatably connected to a left portion of the platform 120 and is distant from a left edge E3 of the platform 120 by a first distance d1. The first end 141 of the second upper extensible link 140 is rotatably connected to a right portion of the platform 120 and is distant from a right edge E4 of the platform 120, which is in parallel with the left edge E3, by a second distance d2. The first distance d1 is longer than the second distance d2.
Similarly, the first end 151 of the first bottom extensible link 150 is rotatably connected to the left portion of the platform 120 and is distant from the left edge E3 by a third distance d3. The first end 161 of the second bottom extensible link 160 is rotatably connected to the right portion of the platform 120 and is distant from the right edge E4 by a fourth distance d4. The third distance d3 is longer than the fourth distance d4. Moreover, a distance D1 between the first end 131 of the first upper extensible link 130 and the first end 141 of the second upper extensible link 140 is substantially equal to a distance D2 between the first end 151 of the first bottom extensible link 150 and the first end 161 of the second bottom extensible link 160.
Referring again to
The bottom base 112 of the chassis 110a has a crossbar 1121 arranged parallel with the horizontal plane P0. The second end 152,162 of each bottom extensible link 150,160 is respectively rotatably connected to the crossbar 1121. In other words, a vertical distance h3 between the second end 152 of the first bottom extensible link 150 and the horizontal plane P0 is substantially equal to a vertical distance h4 between the second end 162 of the second bottom extensible link 160 and the horizontal plane P0.
The movement device 100 can be in an equilibrium condition, wherein the equilibrium condition is defined to be a condition, in which the movable platform 120 stays still and the gravity center of movable platform 120 is in the middle point of the moving path of each motion. When the movement device 100 is in the equilibrium condition, the extension directions of the upper extensible links 130,140 may lie in a first common plane P1, and the extension directions of the bottom extensible links 150,160 may lie in a second common plane P2. The rotation axes X are perpendicular to the first common plane P1.
To put it concretely, as referring to
More particular, the first common plane P1 and the second common plane P2 tilt backward, that is, to −x direction. However, the present disclosure is not limited thereby as those skilled in the art may choose any appropriate angle of tilt for the better seat pressure management and comfortable sitting postures adjustment. Consequently, the upper extensible links 130,140 respectively provide a component of a force F1 directed in a third direction D3, whereas the bottom extensible links 150,160 respectively provide a component of a force F2 directed in a fourth direction D4. The third direction D3 and the fourth direction D4 are in parallel with the horizontal plane P0 and are opposite to one another. In the instant embodiment, the third direction D3 is +x direction and the fourth direction D4 is −x direction.
Moreover, referring again to
In the instant embodiment, the first direction D1 is −y direction and the second direction D2 is +y direction. Consequently, the first bottom extensible link 150 provides a component of a force F3 directed in the first direction D1, whereas the other three extensible links 130,140,160 respectively provides a component of a force F4 directed in the second direction D2. So that the upper extensible links 130,140 can extend and retract in the same speed to provide a steady and smooth moving process to users. To put it concretely, the vertical projections on the normal plane Pn of the extension directions of the upper extensible links 130,140 and the first bottom extensible link 150 slant toward the horizontal plane P0 at an angle. The vertical projection on the normal plane Pn of the extension direction of the second bottom extensible link 160 slants toward the horizontal plane P0 at an angle.
In the instant embodiment, the vertical projection on the normal plane Pn of the extension direction of the first upper extensible link 130 slants towards the horizontal plane P0 at a first angle G1. The vertical projection on the normal plane Pn of the extension direction of the second upper extensible link 140 slants towards the horizontal plane P0 at a second angle G2. The vertical projection on the normal plane Pn of the extension direction of the first bottom extensible link 150 slants towards the horizontal plane P0 at a third angle G3. The vertical projection on the normal plane Pn of the extension direction of the second bottom extensible link 160 slants towards the horizontal plane P0 at a fourth angle G4. The third angle G3 is not equal to the other three angles G1, G2, G4. In particular, the first angle G1, the second angle G2, and the fourth angle G4 can be all equal to one other.
Furthermore, when the movement device 100 is in the equilibrium condition, the front edge E1 and the back edge E2 of the platform 120 lie in the first direction D1 (−y) or the second direction D2 (+y). More specifically, when the movement device 100 is in the equilibrium condition, the first ends 131,141 of the upper extensible links 130,140 point toward a first common axis L1, while the first ends 151,161 of the bottom extensible links 150,160 point toward a second common axis L2. It is worth to note that the first common axis L1 and the second common axis L2 are in parallel with the first direction D1 or the second direction D2.
Moreover, referring to
The operation of the movement device having a Stewart platform 100 is next described. Referring to
Referring to
Referring to
The upper extensible links 130,140 and the second bottom extensible link 160 are arranged in such a way that the movement device having a Stewart platform 100 can be controlled in a linear manner. That is, when the user pushes a button to perform tilt-in-space, changes elevation or moves sideways, the upper extensible links 130,140 and the second bottom extensible link 160 extend or retract at the same speed. The first bottom extensible link 150 is the only one that has to be controlled in a nonlinear manner. Thereby, the movable platform 120 may maintain the horizontal orientation when changing elevation or moving sideways.
Simulation of the Movement Device Having a Stewart Platform
The motion of the movable platform 120 with respect to the length variation of each extensible link 130,140,150,160 is tested. The work space of the movement device having a Stewart platform 100 described in Table 2 is realized in the instant embodiment.
In all three tests, the speed of the upper extensible links 130,140 and the second bottom extensible link 160 are the same in the adjustment of platform 120 elevation, tilt-in-space, and sideways movement, which is important in the practical operation of the movement device 100. When the user simply pushes a button coupled to the operation device 180 to adjust the platform 120, the user can control the upper extensible links 130,140 and the second bottom extensible link 160 extend or retract at a preset constant speed. In other words, the speed of the first bottom extensible link 150 is the only parameter to be determined, which greatly reduces the complexity of the control scheme. The speed of the first bottom extensible link 150 can be determined from the position of the platform 120 and speed of other three extensible links 130,140,150.
In other instant embodiment, on the wheelchair with the movement device 100, the user can adjust the platform 120 by pushing three buttons located on the armrest of the wheelchair 100. When the wheelchair user pushes a button for tilt-in-space, a button for seat elevation adjustment, or a button for moving sideways, the upper extensible links 130,140 and the second bottom 160 extend or retract at a preset constant speed at all time. The extension or retraction speed of the first bottom extensible link 150 can be calculated by an Arduino microcontroller from the current position of the platform 120 to the expected position after a given interval of time.
In summary, the wheelchair with the movement device 100 is capable of motion in heaving, pitching, and swaying to provide a comfortable seat adjustment function. The movement device 100 with above described arrangement of the extensible links 130,140,150,160 can reduce the control complexity of the parallel mechanism, so that the wheelchair user can make the seat adjustment by simply pressing a button. When the user pushes a button to perform tilt-in-space, changes elevation or moves sideways, the upper extensible links 130,140 and the second bottom extensible link 160 can be controlled in a linear manner, while the first bottom extensible link 150 is the only one that has to be controlled in a nonlinear manner. Moreover, the upper extensible links 130,140 and the second bottom extensible link 160 can extend or retract at the same speed. The extensible links 130,140,150,160 are arranged in such a way that they can be controlled to provide a steady and smooth adjustment process to users or to maintain the horizontal orientation of the platform 120 when changing elevation or moving sideways.
The above-mentioned descriptions represent merely the exemplary embodiment of the present disclosure, without any intention to limit the scope of the present disclosure thereto. Various equivalent changes, alternations or modifications based on the claims of present disclosure are all consequently viewed as being embraced by the scope of the present disclosure.
