Method for orienting a hexapod turret

• US 7,081,866 B2
• Filed: 05/30/2002
• Issued: 07/25/2006
• Est. Priority Date: 05/31/2001
• Status: Expired due to Term

• Current Assignee: Safran Data Systems
• Original Assignee: In-Snec
• Inventors: Gaechter, Jean Pierre
• Primary Examiner(s): CHEN, SHIH CHAO
• Application Number:
  US10/479,648
• Publication Number:
  US 20040244525A1
• Time in Patent Office: 1,517 Days
• Field of Search: 343/832, 343/878, 343/880, 343/882, 343/912
• US Class Current: 343/880
• CPC Class Codes: H01Q 1/125 Means for positioning
• CPC Class Codes: H01Q 3/08 for varying two co-ordinates of the orientation
• CPC Class Codes: Y10T 74/20305 Robotic arm
• CPC Class Codes: Y10T 74/20329 Joint between elements

Abstract

The invention relates to a method for displacing a moving plate (20) of a hexapod (100) whose legs (1, 2, 3, 4, 5, 6) are provided with a length adjusting device from an orientation V_i which is defined by the azimuth-elevation coordinates thereof (α_i, β_i) towards an orientation V_i+1 which is defined by the azimuth-elevation coordinates thereof (α_i+1, β_i+1), characterized in that it comprises stages wherein: a law is defined which defines an offset distance d according to the orientation of the plate (20); the offset distance corresponding to the orientation V_i+1 is determined; the adjustment devices are controlled in order to modify the lengths L₁–L₆ of the legs (1, 2, 3, 4, 5, 6) in order to displace the moving plate (20) from orientation V₁ to orientation V_i+1 and to offset it in relation to the normal on the fixed base (10) of the hexapode (100) via the centre OA of said base (10) on the azimuth plane of V_i+1 of the distance d.

Claims

1. A process for moving a moving plate (20) of a hexapod (100) whose legs (1, 2, 3, 4, 5, 6) are fitted with a length-adjusting device, from an orientation V₁ defined by its azimuth-elevation (α

_i, β

_i) coordinates towards an orientation V_i+1 defined by its azimuth-elevation ((α

_I+1, β

_I+1) coordinates, characterised in that it comprises stages wherein;

a law is defined which defines an offset distance d according to the orientation of the plate (20),

the offset distance corresponding to the orientation V_i+1 is determined,

the length adjustment device is controlled in order to modify lengths L₁ to L₆ of the legs (1, 2, 3, 4, 5, 6) in order to displace the moving plate (20) from orientation V_i to orientation V_i+1 and to offset it in relation to the perpendicular on a fixed base (10) of the hexapod (100) passing through a centre OA of said base (10), in the azimuth plane of V_i+1 of the distance d.

2. The process as claimed in claim 1, characterised in that an offset law is defined giving a unique position of a centre OB of the plate in space as a function of its orientation.

3. The process as claimed in claim 2, characterised in that the offset law defines a continuous geometric surface.

4. The process as claimed in claim 3, characterised in that the offset surface is a plane.

5. The process as claimed in claim 3, characterised in that the offset surface is a portion of a sphere.

6. The process as claimed claim 1, wherein the moving plate (20) is moved by controlling rotation of the moving plate (20) around an axis perpendicular to a plane containing the pointing vectors V_i and V_i+1.

7. The process as claimed in claim 2, wherein a variation in length of the legs (1, 2, 3, 4, 5, 6) of the hexapod (100) is determined according to the following stages:

a reference position of the hexapod (100) is defined according to which all the legs (1, 2, 3, 4, 5, 6) are adjusted to a length L₀,

the variation in length of each leg (1, 2, 3, 4, 5, 6) is determined so that the moving plate (20) of the hexapod (100) moves from the reference position to the pointing direction V_i+1 by virtual rotation in the plane of azimuth _i+1, and by virtual translation of the centre OB of the plate (20) towards an offset surface defined by the offset law,

a variation in total length is deduced therefrom for each leg (1, 2, 3, 4, 5, 6) to switch from direction V_i to direction V_i+1.

8. The process as claimed in claim 1, wherein the overall orientation movement of the moving plate (20) is organised in a succession of unit displacements of azimuth Δ

α and

elevation Δ

β

of the moving plate (20).

9. The process as claimed in claim 1, wherein the adjustment devices are controlled as a function of the lengths L_i of the legs (1, 2, 3, 4, 5, 6) to be obtained and in that this calculation takes into consideration relative angles between the elements making up links joining the legs (1, 2, 3, 4, 5, 6) to the plate (20) and to the fixed base (10).

10. The process as claimed in claim 9, characterised in that the relative angles between the elements making up the links connecting the legs (1, 2, 3, 4, 5, 6) to the plate (20) and to the base (10) are determined from positions of linking points calculated between the legs (1, 2, 3, 4, 5, 6) and the plate (20), and from this relative rotations between the sliding assemblies of the jacks is deduced.

11. The process as claimed in claim 10, characterised in that each leg (1, 2, 3, 4, 5, 6) of the hexapod (100) comprises a jack constituted by two assemblies sliding relative to one another and an actuator (61) whose exit axis (62) drives in rotation a screw (65) making up a helicoidal link between the sliding assemblies, in that an additional elongation of each jack is deduced due to the relative rotations between its sliding assemblies (L_A, L_B) as a function of the geometric characteristic of the helicoidal link, and in that this additional elongation is taken into account for establishing a set-point for controlling the actuator (61).

12. The process as claimed in claim 1, wherein angles formed by the axes of the legs (1, 2, 3, 4, 5, 6) and the perpendicular to the plane of the fixed base (10) and the angles formed by the axes of the legs (1, 2, 3, 4, 5, 6) and the perpendicular to the plane of the moving plate (20) are always less than a maximum angle defined between 40 and 80 degrees.

13. The process as claimed in claim 1, wherein there is continuous verification that the overall rotation of the moving plate (20) relative to the vertical to the fixed base (10) is zero.

14. The process as claimed in claim 13, characterised in that when it is detected that the overall rotation of the moving plate (20) relative to the vertical to the fixed base (10) is no longer zero a command is generated to stop the movement of the hexapod (100).

15. A device for displacing the moving plate (20) of a hexapod (100), characterised in that it comprises control means for implementing the process as claimed in any one of the preceding claims.

16. The device as claimed in claim 15, characterised in that each leg (1, 2, 3, 4, 5, 6) of the hexapod (100) comprises a jack comprising a first and a second assembly (L_A, L_B) capable of sliding relative to one another, an actuator (61) whose output axis (62) drives in rotation a screw (65) placed perpendicularly in the axis (62) of a motor (61), said screw (65) extending over the length of the first assembly (L_A) and capable of pivoting inside a nut (66) mounted solid with the second assembly (L_B), rotation of the screw (65) in the nut (66) driving translation of the second assembly (L_B) relative to the first assembly (L_A).

17. The device as claimed in claim 16, characterised in that the control means are intended to determine any additional elongation of each jack due to the relative rotations between its sliding assemblies (L_A, L_B) as a function of the geometric characteristics of the helicoidal link, and to take into account this additional elongation to establish a set-point to control the actuator (61).

18. The device as claimed in claim 16, characterised in that it comprises means for measuring the position of the axis (62) of the actuator (61).

19. The device as claimed in claim 15, wherein links are arranged on the fixed base (10) according to a first circle of radius RA and links are arranged on the moving plate (20) according to a second circle of radius RB, the RA/RB ratio being substantially equal to 1.5.

20. The device as claimed in claim 15, wherein the links are arranged in pairs on the moving plate (20) or on the fixed base (10) in accordance with a circle of radius R, the distance between two links of the same pair being substantially equal to R/10.

21. The device as claimed in claim 15, wherein the maximum elongation of a leg is less than or equal to 2.

22. The device as claimed in claim 15, wherein the maximum elongation of a leg is greater than or equal to 1.7.

23. The device as claimed in claim 15, further comprising means for verifying that the overall rotation of the moving plate (20) relative to a vertical to the fixed base (10) is zero.

24. The device as claimed in claim 23, characterised in that it comprises an element rigid in torsion connected at a first end, to the moving plate (20) via a rigid link and at a second end, to the fixed base (10) via a pivoting link, as well as means for detecting rotation of the second end of the element relative to the base (20).

25. The device as claimed in claim 24, characterised in that the rotation detecting means comprise an indicator element fixed at the second end of the cable as well as a detection circuit, and in that when the second end of the cable is fixed relative to the base (10) the indicator element makes contact with the detection circuit and when the second end of the cable turns relative to the fixed base (10), the indicator element breaks this contact.