Single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus-shaped oblique prism

Abstract

The present invention provides a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, which is composed of a plurality of deployable units with the same structure, wherein an upper rhombus-shaped oblique prism mechanism is connected to a lower rhombus-shaped oblique prism mechanism through a connecting rod to form a deployable unit. The first notch of the outer ring support seat in the first deployable unit is connected to the first end of the outer ring circumferential folding rod through the eighth rotation pair, the second end of the outer ring circumferential folding rod is connected to the first notch of the outer ring support seat in the second deployable unit through the eighth rotation pair, the second notch of the inner ring support seat in the first deployable unit is connected to the first end of the inner ring circumferential folding rod through the fifteenth rotation pair, the second end of the inner ring circumferential folding rod is connected to the second notch of the inner ring support seat in the second deployable unit through the fifteenth rotation pair, to form a multi-faceted double-ring truss. The present invention has the characteristics of high rigidity, flexible movement, and large folding ratio, and has a large folding rate and stability, and is widely used in communication satellites and space probes.

Description

Technical Field

[0001] The invention relates to the technical field of satellite-borne deployable antennas, and in particular to a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism. Background Art

[0002] Communication and data transmission between various types of spacecraft and the earth in space need to be achieved through antennas. With the rapid development of aerospace science and technology, the gain requirements of space antennas are getting higher and higher to meet the needs of different space missions. A simple and effective way to improve antenna gain is to increase the diameter of the antenna. Due to the limited space in the payload compartment of the launch vehicle, the deployable antenna mechanism that can be folded during storage and transportation and fully unfolded in orbit is widely used in spacecraft such as satellite platforms, space stations, and space telescopes. Due to its good application prospects, the deployable antenna has become one of the research hotspots in the field of aerospace. An important application of space deployable mechanisms in the field of aerospace is as a deployment and support mechanism for satellite-borne antennas. The mesh reflector deployable antenna is an important type of satellite-borne antenna. It is mainly composed of a deployable support mechanism and a reflector formed by tensioning a cable net structure. It has the characteristics of large caliber, high folding rate and light weight. It is widely used in the field of satellite-borne large-caliber antennas. The types of large-caliber satellite-borne space deployable antennas that have been successfully developed so far mainly include frame-type deployable antennas, ring-type truss-type deployable antennas, stretchable rib-type deployable antennas, and ring-type cylindrical deployable antennas. Among several types of deployable space mechanisms, the application range of the ring truss deployable antenna can completely cover the one-dimensional, two-dimensional and three-dimensional structural forms of space. Different from ordinary parallel mechanisms or hybrid mechanisms, it is a complex space multi-closed-loop coupling mechanism with multiple closed loops, few degrees of freedom and over-constrained. The ring truss deployable antenna mechanism is a truss structure when fully deployed, with high overall stiffness and easy control of surface accuracy. Therefore, the ring truss deployable antenna is widely used and is also the main development target of space deployable mechanisms at present and in the long term. Carrying out a series of innovative research work related to the ring truss deployable antenna as the main research line is of great significance to improving the level of my country's aerospace science research and accelerating the development of a strong aerospace country. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus oblique prism, and utilizes different notches on a first support seat, an outer ring support seat, an inner ring support seat and a central support seat to form an upper rhombus oblique prism mechanism and a lower rhombus oblique prism mechanism with a first folding rod, a second folding rod and a radial web rod. At the same time, the upper rhombus oblique prism mechanism is formed into an deployable unit through a connecting rod and a lower rhombus oblique prism mechanism. The deployable units with the same structure are modularly reorganized, and the folding rods are formed into a structural layout of the rhombus oblique prism mechanism in the deployable unit, and are connected through a rotating pair, so that the entire antenna mechanism has the characteristics of a large folding ratio, good manufacturing processability, high structural rigidity, a rapid deployment process, a reflecting surface with a high reflectivity curved surface, and a light weight of the driving parts of the entire mechanism.

[0004] The present invention provides a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, which includes a plurality of deployable units with the same structure, and two adjacent deployable units are respectively connected to each other through an outer ring circumferential folding rod and an inner ring circumferential folding rod. In two adjacent deployable units, the first notch of the outer ring support seat in the first deployable unit is connected to the first end of the outer ring circumferential folding rod, the second end of the outer ring circumferential folding rod is connected to the first notch of the outer ring support seat in the second deployable unit, the second notch of the inner ring support seat in the first deployable unit is connected to the first end of the inner ring circumferential folding rod, the second end of the inner ring circumferential folding rod is connected to the second notch of the inner ring support seat in the second deployable unit, the second notch of the first support seat in the first deployable unit is connected to the second notch of the first support seat in the second deployable unit, and the second notch of the second support seat in the first deployable unit is connected to the second notch of the second support seat in the second deployable unit. The expandable unit includes an upper rhombus-shaped oblique prism mechanism, a lower rhombus-shaped oblique prism mechanism and a connecting rod, wherein the upper rhombus-shaped oblique prism mechanism is connected to the lower rhombus-shaped oblique prism mechanism via the connecting rod; the upper rhombus-shaped oblique prism mechanism includes a first support seat, an outer ring support seat, an inner ring support seat, a central support seat, a first folding rod, a second folding rod and a radial web rod. The first support seat is provided with a first slot and a second slot at both ends of the left side, the angle between the middle planes of the first slot and the second slot is α (α<180°), the angle between the middle plane of the second slot and the symmetry plane is [45-(180 / N)]°, N is the number of expandable units, and a third slot is provided at the bottom of the first support seat; the first slot and the second slot are provided at both ends of the left side of the outer ring support seat, the angle between the middle planes of the first slot and the second slot is [45-(180 / N)]°, the angle between the middle plane of the second slot and the symmetry plane is [90-(α / 2)]°, and a third slot is provided at the bottom of the outer ring support seat, and the middle plane of the third slot coincides with the symmetry plane. The two ends of the left side of the inner ring support seat are respectively provided with a first slot and a second slot, the angle between the middle plane of the first slot and the symmetry plane is [90-(α / 2)]°, the angle between the middle plane of the first slot and the second slot is [45+(180 / N)]°, and the bottom of the inner ring support seat is provided with a third slot, the middle plane of the third slot coincides with the symmetry plane; the first end, the second end and the third end of the center support seat are respectively provided with a first slot, a second slot and a third slot, the angle between the middle planes of the first slot and the third slot is 180°, and the middle plane of the first slot coincides with the symmetry plane.The first slot of the first support seat is connected to the first end of the first folding rod, the second end of the first folding rod is connected to the second slot of the outer ring support seat, the second slot of the first support seat is connected to the first end of the second folding rod, the second end of the second folding rod is connected to the first slot of the inner ring support seat, the first slot, the second slot and the third slot of the center support seat are respectively connected to the first ends of the first radial web rod, the second radial web rod and the third radial web rod, the second ends of the first radial web rod, the second radial web rod and the third radial web rod are respectively connected to the outer ring support seat, the inner ring support seat and the third slot of the first support seat.

[0005] Preferably, in the first support seat, the first support seat is a left-right symmetrical structure, the number of the first slot, the second slot and the third slot are two, and the first slot, the second slot and the third slot are symmetrically distributed on both sides of the symmetry plane; in the outer ring support seat, the outer ring support seat is a left-right symmetrical structure, the number of the first slot, the second slot and the third slot are two, and the first slot, the second slot and the third slot are symmetrically distributed on both sides of the symmetry plane; in the inner ring support seat, the inner ring support seat is a left-right symmetrical structure, the number of the first slot and the second slot are two, and the first slot and the second slot are symmetrically distributed on both sides of the symmetry plane, and the number of the third slot is one; in the center support seat, the center support seat is a left-right symmetrical structure, the number of the second slot is two, and the second slot is symmetrically distributed on both sides of the symmetry plane.

[0006] Preferably, the first folding rod includes a first straight rod, a second straight rod and a third rotating pair, the first straight rod and the second straight rod are of equal length, and the first straight rod is connected to the second straight rod through the third rotating pair; the second folding rod includes a third straight rod, a fourth straight rod and a fourth rotating pair, the third straight rod and the fourth straight rod are of equal length, and the third straight rod is connected to the fourth straight rod through the fourth rotating pair; the outer ring circumferential folding rod includes a fifth straight rod, a sixth straight rod and a first rotating pair, the fifth straight rod and the sixth straight rod are of equal length, and the fifth straight rod is connected to the sixth straight rod through the first rotating pair; the inner ring circumferential folding rod includes a seventh straight rod, an eighth straight rod and a second rotating pair, the seventh straight rod and the eighth straight rod are of equal length, and the seventh straight rod is connected to the eighth straight rod through the second rotating pair, and the rotating pair on the folding rod allows it to rotate in only one direction, thereby ensuring the reliability and synchronization of the retraction and extension movement of the entire device under one drive input.

[0007] Preferably, in the lower rhombus oblique prism mechanism, it includes a second support seat, a first folding rod, a second folding rod, an outer ring support seat, a center support seat, an inner ring support seat and a radial web rod, the second support seat is a left-right symmetrical structure, the first end and the second end of the left side of the second support seat are respectively provided with a first slot and a second slot, the angle between the middle planes of the first slot and the second slot is α (α<180°), the angle between the middle plane of the second slot and the symmetry plane is [45-(180 / N)]°, N is the number of expandable units, a third slot is provided at the bottom of the second support seat, the number of the first slot, the second slot and the third slot are all two, and the first slot, the second slot and the third slot are symmetrically distributed on both sides of the symmetry plane.

[0008] Preferably, in the lower rhombus oblique prism mechanism, the first slot of the second support seat is connected to the first end of the second folding rod through a seventeenth rotation pair, the second end of the second folding rod is connected to the second slot of the outer ring support seat through a ninth rotation pair, the second slot of the second support seat is connected to the first end of the first folding rod through a nineteenth rotation pair, the second end of the first folding rod is connected to the first slot of the inner ring support seat through a fourteenth rotation pair, the first slot, the second slot and the third slot of the center support seat are connected to the first ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod through a twelfth rotation pair, an eleventh rotation pair and a thirteenth rotation pair, respectively, and the second ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod are connected to the third slot of the outer ring support seat, the third slot of the inner ring support seat and the third slot of the second support seat through a tenth rotation pair, a sixteenth rotation pair and an eighteenth rotation pair, respectively.

[0009] Preferably, in the upper rhombus oblique prism mechanism, the planes where the first support seat, the outer ring support seat, the center support seat and the inner ring support seat are located are parallel to each other, and in the lower rhombus oblique prism mechanism, the planes where the second support seat, the outer ring support seat, the center support seat and the inner ring support seat are located are parallel to each other; the outer ring support seat and the inner ring support seat are both on the circumscribed circle of an N-gon, and the line connecting the outer ring support seat and the inner ring support seat converges at the center of the N-gon.

[0010] Preferably, in the upper rhombus oblique prism mechanism, it includes two first support seats with identical structures, two first folding rods with identical structures, two second folding rods with identical structures, four radial web rods with identical structures, an outer ring support seat, an intermediate support seat and an inner ring support seat. The two first support seats with identical structures, an outer ring support seat and an inner ring support seat are arranged in a rhombus shape on the projection plane, the outer ring support seat and the two first folding rods with identical structures constitute the upper half of the rhombus, and the inner ring support seat and the two second folding rods with identical structures constitute the lower half of the rhombus.

[0011] Preferably, in the expanded state of the upper rhombus oblique prism mechanism, the two first support seats with identical structures are at the same height, the center support seat and the inner ring support seat are at the same height, the height of the outer ring support seat is greater than the height of the two first support seats with identical structures, and the height of the two first support seats with identical structures is greater than the height of the center support seat and the inner ring support seat.

[0012] Preferably, in the lower rhombus oblique prism mechanism, it includes two second support seats with identical structures, two first folding rods with identical structures, two second folding rods with identical structures, four radial web rods with identical structures, an outer ring support seat, an intermediate support seat and an inner ring support seat. The two second support seats with identical structures, an outer ring support seat and an inner ring support seat are arranged in a rhombus shape on the projection plane, and the outer ring support seat and the two second folding rods with identical structures constitute the upper half of the rhombus, and the inner ring support seat and the two first folding rods with identical structures constitute the lower half of the rhombus.

[0013] Preferably, in any state of the lower rhombus oblique prism mechanism, the two second support seats with the same structure are at the same height, the center support seat and the inner ring support seat are at the same height, the height of the outer ring support seat is greater than the height of the two second support seats with the same structure, and the height of the two second support seats with the same structure is greater than the height of the center support seat and the inner ring support seat.

[0014] Compared with the prior art, the present invention has the following advantages:

[0015] 1. The double-ring truss deployable antenna mechanism of the present invention is composed of deployable units consisting of an upper rhombus oblique prism mechanism and a lower rhombus oblique prism mechanism, which are combined at a certain angle. Compared with the single-layer ring truss deployable antenna mechanism, it has higher rigidity, rapid deployment and large folding ratio, and can be applied to ultra-large aperture space deployable antennas.

[0016] 2. When the present invention is unfolded, the arrangement position of the support base of the rhombus oblique prism mechanism in each deployable unit and the folding rods of different lengths enable the rhombus oblique prism mechanism to have a tetrahedral support mechanism, so that the entire device has higher structural rigidity and stronger bearing capacity, which can meet the rigidity requirements of large-caliber space deployable antenna mechanisms.

[0017] 3. The connection form of the rhombus oblique prism mechanism in the expandable unit of the present invention and the setting of the kinematic pair on the folding rod make the entire expandable unit divided into an upper rhombus oblique prism mechanism and a lower rhombus oblique prism mechanism. The upper rhombus oblique prism mechanism is a single-degree-of-freedom mechanism, and the lower rhombus oblique prism mechanism can be synchronously folded by folding the upper rhombus oblique prism mechanism. The movement of the entire rhombus oblique prism mechanism is synchronized, resulting in the entire expandable unit having only one degree of freedom, so that the entire device is a single-degree-of-freedom mechanism. Therefore, only one drive input is required during the folding and unfolding process of each expandable unit. The implementation method is simple, which can ensure the reliability and synchronization of the folding and unfolding movement of the entire device.

[0018] 4. The height of the outer ring support seat in each deployable unit of the present invention is higher than that of the inner ring support seat, so that the reflecting surface of the entire device is a parabola, which has high directivity and high surface accuracy.

[0019] 5. The present invention is a double-ring truss deployable antenna mechanism composed of N deployable units with the same structure. Each deployable unit contains exactly the same parts. The entire device has high continuity of movement, simple structure, and convenient processing. It can be applied to communication satellites, space stations and space probes. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a semi-expanded structural diagram of a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0021] Figure 2 This is a fully expanded structural diagram of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0022] Figure 3 This is a fully folded structural diagram of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0023] Figure 4 It is a fully expanded structural diagram of the deployable unit of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism of the present invention;

[0024] Figure 5 It is a semi-expanded structural diagram of the deployable unit of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism of the present invention;

[0025] Figure 6It is a structural diagram of a fully folded deployable unit of a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0026] Figure 7 It is a fully expanded structural diagram of two connected expandable units of a single-degree-of-freedom double-ring truss expandable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0027] Figure 8 It is a fully expanded structure diagram of the upper rhombus oblique prism mechanism of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on the rhombus oblique prism of the present invention;

[0028] Fig. 9 It is a fully expanded structural diagram of the lower rhombus oblique prism mechanism of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism of the present invention;

[0029] Fig.10 It is a semi-expanded structural diagram of an upper rhombus oblique prism mechanism of a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus oblique prism according to the present invention;

[0030] Fig.11 It is a top view of the upper rhombus oblique prism mechanism of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism of the present invention when it is completely folded;

[0031] Fig.12 It is a structural diagram of the first support seat of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism of the present invention;

[0032] Fig.13 It is a structural diagram of the second support base of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism according to the present invention;

[0033] Fig.14 It is a structural diagram of the outer ring support seat of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism of the present invention;

[0034] Fig.15 It is a structural diagram of the central support seat of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism of the present invention;

[0035] Fig.16 It is a structural diagram of the inner ring support seat of the single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prisms of the present invention.

[0036] Main reference numerals:

[0037] Expandable unit A, upper rhombus oblique prism mechanism B, lower rhombus oblique prism mechanism C, connecting rod 1, outer ring circumferential folding rod 2, inner ring circumferential folding rod 3, first support seat 4, radial web rod 5, first folding rod 6, second folding rod 7, outer ring support seat 8, center support seat 9, inner ring support seat 10, second support seat 11, first rotation pair C1, second rotation pair C2, third rotation pair C3, fourth rotation pair C4, fifth rotation pair C5, sixth rotation pair C6, seventh rotation pair C7, eighth rotation pair C8, ninth rotation pair C9, tenth rotation pair C10, eleventh rotation pair C11, twelfth rotation pair C12, thirteenth rotation pair C13, fourteenth rotation pair C14, fifteenth rotation pair C15, sixteenth rotation pair C16, seventeenth rotation pair C17, eighteenth rotation pair C18, nineteenth rotation pair C19. DETAILED DESCRIPTION

[0038] In order to fully describe the technical content, structural features, objectives and effects of the present invention, the following will be described in detail with reference to the accompanying drawings.

[0039] A single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, such as Figures 1 to 3 As shown, it includes a plurality of deployable units A with the same structure, and two adjacent deployable units A are connected to each other through a common first support seat 4, a second support seat 11, an outer ring circumferential folding rod 2 and an inner ring circumferential folding rod 3. The entire antenna mechanism is a multi-faceted double ring truss structure when deployed and folded.

[0040] Specifically, the expandable unit A includes an upper rhombus oblique prism mechanism B, a lower rhombus oblique prism mechanism C and two connecting rods 1 with the same structure. The outer ring support seat 8 and the inner ring support seat 10 of the upper rhombus oblique prism mechanism B are respectively connected to the outer ring support seat 8 and the inner ring support seat 10 of the lower rhombus oblique prism mechanism C through the connecting rod 1. The connecting rod 1 is used to fix the relative relationship between the two outer ring support seats 8 and the inner ring support seats 10 on the same side in the vertical direction.

[0041] like Figures 4 to 7As shown, the first notch of the outer ring support seat 8 in the first deployable unit A is connected to the first end of the outer ring circumferential folding rod 2 through the eighth rotation pair C8, and the second end of the outer ring circumferential folding rod 2 is connected to the first notch of the outer ring support seat 8 in the second deployable unit A through the eighth rotation pair C8, forming the outer ring of two deployable units A; the second notch of the inner ring support seat 10 in the first deployable unit A is connected to the first end of the inner ring circumferential folding rod 3 through the fifteenth rotation pair C15, and the second end of the inner ring circumferential folding rod 3 is connected to the second notch of the inner ring support seat 10 in the second deployable unit A through the fifteenth rotation pair C15, forming the inner ring of two deployable units A. The upper rhombus oblique prism mechanism B in two adjacent deployable units A is connected through the second notch of the first support seat 4, and the lower rhombus oblique prism mechanism C is connected through the second notch of the second support seat 11. Specifically, N deployable units A are connected through the outer ring circumferential folding rod 2 and the inner ring circumferential folding rod 3 to form the inner ring and outer ring of the double-ring truss deployable antenna mechanism.

[0042] like Figure 8 As shown, the upper rhombus oblique prism mechanism B includes a first support seat 4, a first folding rod 6, a second folding rod 7, an outer ring support seat 8, a center support seat 9, an inner ring support seat 10 and a radial web 5; the first support seat 4, the second support seat 11, the outer ring support seat 8, the center support seat 9 and the inner ring support seat 10 are respectively provided with notches with different distribution positions and the same structure, which are used to respectively connect the first folding rod 6 or the second folding rod 7 or the outer ring circumferential folding rod 2 or the inner ring circumferential folding rod 3, so as to facilitate the rapid assembly of the adjacent upper rhombus oblique prism mechanism B or the lower rhombus oblique prism mechanism C or the two expandable units A by rotating the pair, thereby forming a double-ring truss structure with rhombus oblique prisms.

[0043] like Fig.10 and Fig.11 As shown, the first slot of the first support seat 4 is connected to the first end of the first folding rod 6 through the fifth rotation pair C5, the second end of the first folding rod 6 is connected to the second slot of the outer ring support seat 8 through the ninth rotation pair C9, the second slot of the first support seat 4 is connected to the first end of the second folding rod 7 through the seventh rotation pair C7, the second end of the second folding rod 7 is connected to the first slot of the inner ring support seat 10 through the fourteenth rotation pair C14, the first slot, the second slot and the third slot of the center support seat 9 are respectively connected to the first ends of the first radial web rod, the second radial web rod and the third radial web rod through the twelfth rotation pair C12, the eleventh rotation pair C11 and the thirteenth rotation pair C13, the second ends of the first radial web rod, the second radial web rod and the third radial web rod are respectively connected to the third slot of the outer ring support seat 8, the third slot of the inner ring support seat 10 and the third slot of the first support seat 4 through the tenth rotation pair C10, the sixteenth rotation pair C16 and the sixth rotation pair C6.

[0044] like Fig.12 As shown, the first support seat 4 is a bilaterally symmetrical structure, the first end and the second end of the left side of the first support seat 4 are respectively provided with a first notch and a second notch, the angle between the middle plane of the first notch and the second notch is 90°, the angle between the middle plane of the second notch and the symmetry plane is [45-(180 / N)]°, N is the number of expandable units A, the bottom of the first support seat 4 is provided with a third notch, the angle between the middle plane of the third notch and the symmetry plane is 90°. The number of the first notch, the second notch and the third notch are all two, and the first notch, the second notch and the third notch are symmetrically distributed on both sides of the symmetry plane.

[0045] like Fig.14 As shown, the outer ring support seat 8 is a bilaterally symmetrical structure, the first end and the second end of the left side of the outer ring support seat 8 are respectively provided with a first notch and a second notch, the angle between the middle planes of the first notch and the second notch is [45-(180 / N)]°, N is the number of expandable units A, the angle between the middle plane of the second notch and the symmetry plane is 45°, and the bottom of the outer ring support seat 8 is provided with a third notch, the middle plane of the third notch coincides with the symmetry plane. The number of the first notch, the second notch and the third notch are all two, and the first notch, the second notch and the third notch are symmetrically distributed on both sides of the symmetry plane.

[0046] like Fig.15 As shown, the central support seat 9 is a bilaterally symmetrical structure, and the first end, second end and third end of the central support seat 9 are respectively provided with a first notch, a second notch and a third notch, the angle between the middle planes of the first notch and the second notch is 75°, the angle between the middle planes of the first notch and the third notch is 180°, and the middle plane of the first notch coincides with the symmetry plane. The number of the second notches is two, and the second notches are symmetrically distributed on both sides of the symmetry plane.

[0047] like Fig.16 As shown, the inner ring support seat 10 is a bilaterally symmetrical structure, the first end and the second end of the left side of the inner ring support seat 10 are respectively provided with a first notch and a second notch, the angle between the middle plane of the first notch and the symmetry plane is 45°, the angle between the middle plane of the first notch and the second notch is [45+(180 / N)]°, N is the number of expandable units A, the bottom of the inner ring support seat 10 is provided with a third notch, the middle plane of the third notch coincides with the symmetry plane. The number of the first notch and the second notch are both two, the first notch and the second notch are symmetrically distributed on both sides of the symmetry plane, and the number of the third notch is both one.

[0048] The first folding rod 6 includes a first straight rod, a second straight rod and a third rotation pair C3, the first straight rod and the second straight rod are of equal length, and the first straight rod is connected to the second straight rod through the third rotation pair C3; the second folding rod 7 includes a third straight rod, a fourth straight rod and a fourth rotation pair C4, the third straight rod and the fourth straight rod are of equal length, and the third straight rod is connected to the fourth straight rod through the fourth rotation pair C4; the outer ring circumferential folding rod 2 includes a fifth straight rod, a sixth straight rod and the first rotation pair C1, the fifth straight rod and the sixth straight rod are of equal length, and the fifth straight rod is connected to the sixth straight rod through the first rotation pair C1; the inner ring circumferential folding rod 3 includes a seventh straight rod, an eighth straight rod and the second rotation pair C2, the seventh straight rod and the eighth straight rod are of equal length, and the seventh straight rod is connected to the eighth straight rod through the second rotation pair C2.

[0049] like Fig. 9 As shown, in the lower rhombus oblique prism mechanism C, it includes a second support seat 11, a first folding rod 6, a second folding rod 7, an outer ring support seat 8, a central support seat 9, an inner ring support seat 10 and a radial web rod 5, as shown in FIG. Fig.13 As shown, the second support seat 11 is a bilaterally symmetrical structure, the first end and the second end of the left side of the second support seat 11 are respectively provided with a first notch and a second notch, the angle between the middle plane of the first notch and the second notch is 90°, the angle between the middle plane of the second notch and the symmetry plane is [45-180 / N]°, N is the number of expandable units A, the bottom of the second support seat 11 is provided with a third notch, the angle between the middle plane of the third notch and the symmetry plane is 60°. The number of the first notch, the second notch and the third notch are all two, and the first notch, the second notch and the third notch are symmetrically distributed on both sides of the symmetry plane.

[0050] The first slot of the second support seat 11 is connected to the first end of the second folding rod 7 through the seventeenth rotation pair C17, the second end of the second folding rod 7 is connected to the second slot of the outer ring support seat 8 through the ninth rotation pair C9, the second slot of the second support seat 11 is connected to the first end of the first folding rod 6 through the nineteenth rotation pair C19, the second end of the first folding rod 6 is connected to the first slot of the inner ring support seat 10 through the fourteenth rotation pair C14, the first slot, the second slot and the third slot of the center support seat 9 are respectively connected to the first ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod through the twelfth rotation pair C12, the eleventh rotation pair C11 and the thirteenth rotation pair C13, the second ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod are respectively connected to the third slot of the outer ring support seat 8, the third slot of the inner ring support seat 10 and the third slot of the second support seat 11 through the tenth rotation pair C10, the sixteenth rotation pair C16 and the eighteenth rotation pair C18.

[0051] In the upper rhombus oblique prism mechanism B, the planes where the first support seat 4, the outer ring support seat 8, the center support seat 9 and the inner ring support seat 10 are located are parallel to each other; in the lower rhombus oblique prism mechanism C, the planes where the second support seat 11, the outer ring support seat 8, the center support seat 9 and the inner ring support seat 10 are located are parallel to each other; the outer ring support seat 8 and the inner ring support seat 10 are both on the circumscribed circle of the N-gon, and the connecting line of the outer ring support seat 8 and the inner ring support seat 10 converges at the center of the N-gon to complete the synchronous folding and unfolding of the upper rhombus oblique prism mechanism B and the lower rhombus oblique prism mechanism C.

[0052] In a specific embodiment of the present invention, in the upper rhombus oblique prism mechanism B, it includes two first support seats 4 with identical structures, two first folding rods 6 with identical structures, two second folding rods 7 with identical structures, four radial web rods 5 with identical structures, an outer ring support seat 8, an intermediate support seat 9 and an inner ring support seat 10. The two first support seats 4 with identical structures, an outer ring support seat 8 and an inner ring support seat 10 are arranged in a rhombus shape on the projection plane. The outer ring support seat 8 and the two first folding rods 6 with identical structures form the upper half of the rhombus, and the inner ring support seat 10 and the two second folding rods 7 with identical structures form the lower half of the rhombus. The two ends of the upper half of the rhombus are respectively connected to the two ends of the lower half of the rhombus through two second support seats 11 with identical structures.

[0053] In the lower rhombus oblique prism mechanism C, it includes two second support seats 11 with identical structures, two first folding rods 6 with identical structures, two second folding rods 7 with identical structures, four radial web rods 5 with identical structures, an outer ring support seat 8, an intermediate support seat 9 and an inner ring support seat 10. The two second support seats 11 with identical structures, an outer ring support seat 8 and an inner ring support seat 10 are arranged in a rhombus shape on the projection plane. The outer ring support seat 8 and the two second folding rods 7 with identical structures form the upper half of the rhombus, and the inner ring support seat 10 and the two first folding rods 6 with identical structures form the lower half of the rhombus. The two ends of the upper half of the rhombus are respectively connected by the two second support seats 11 with identical structures and the two ends of the lower half of the rhombus.

[0054] Furthermore, in order to arrange the reflecting surface on the surface where the outer ring support seat 8 of the upper rhombus oblique prism mechanism B is located, the utilization rate of this double-ring truss deployable antenna is improved. In the deployed state of the upper rhombus oblique prism mechanism B, the two first support seats 4 with the same structure are at the same height, the central support seat 9 and the inner ring support seat 10 are at the same height, the height of the outer ring support seat 8 is greater than the height of the two first support seats 4 with the same structure, and the height of the two first support seats 4 with the same structure is greater than the height of the central support seat 9 and the inner ring support seat 10. In any state of the lower rhombus oblique prism mechanism C, the two second support seats 11 with the same structure are at the same height, the central support seat 9 and the inner ring support seat 10 are at the same height, the height of the outer ring support seat 8 is greater than the height of the two second support seats 11 with the same structure, and the height of the two second support seats 11 with the same structure is greater than the height of the central support seat 9 and the inner ring support seat 10.

[0055] The following is a further description of a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus oblique prism according to the present invention in conjunction with an embodiment:

[0056] The large-aperture satellite antennas used in space are mainly single-ring truss-type deployable antennas. When the antenna aperture exceeds the order of 20 meters, as the antenna aperture increases, the overall structural stiffness of the antenna decreases rapidly, and a contradiction between the antenna enlargement and the structural stiffness will arise. In view of the fact that the single-ring truss-type deployable antenna mechanism can no longer meet the requirements of the working stiffness of the ultra-large-aperture deployable antenna, the present invention proposes a single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, which is preferably used in the ultra-large-aperture space deployable antenna to improve the stiffness of the space ultra-large-aperture antenna after deployment. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism is a single-degree-of-freedom mechanism, and a drive is added to any of the third rotational pairs C3 or the fourteenth rotational pairs C4 in the upper rhombus-shaped oblique prism mechanism B or the lower rhombus-shaped oblique prism mechanism C. When the inner ring support seat 10 touches each other, the single-degree-of-freedom double-ring truss deployable antenna mechanism based on the rhombus-shaped oblique prism is folded.

[0057] In this specific embodiment, the single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus is composed of 12 deployable units A with exactly the same structure. The upper rhombus oblique prism mechanism B in two adjacent deployable units A is connected through the second notch of the first support seat 4, and the lower rhombus oblique prism mechanism C is connected through the second notch of the second support seat 11; the first notch of the outer ring support seat 8 in the first deployable unit A of the two adjacent deployable units A is connected to the first end of the outer ring circumferential folding rod 2 through the eighth rotation pair C8, and the second end of the outer ring circumferential folding rod 2 is connected through the eighth rotation pair C8. The movable pair C8 is connected to the first slot of the outer ring support seat 8 in the second expandable unit A of the two adjacent expandable units A to form the outer ring of the two adjacent expandable units A; the second slot of the inner ring support seat 10 in the first expandable unit A of the two adjacent expandable units A is connected to the first end of the inner ring circumferential folding rod 3 through the fifteenth rotating pair C15, and the second end of the inner ring circumferential folding rod 3 is connected to the second slot of the inner ring support seat 10 in the second expandable unit A of the two adjacent expandable units A through the fifteenth rotating pair C15 to form the inner ring of the two adjacent expandable units A.

[0058] In the 12 deployable units A with exactly the same structure in the single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, the first support seat 4 of the upper rhombus-shaped oblique prism mechanism B takes the middle plane of the left and right forks as the symmetry plane, and the first fork and the second fork on the left side of the first support seat 4 are respectively provided with a first slot and a second slot, and the angle between the middle plane of the first slot and the second slot is 90°, and the angle between the middle plane of the second slot and the symmetry plane is 30°, and the bottom fork of the first support seat 4 is provided with a third slot, and the angle between the middle plane of the third slot and the symmetry plane is 90°.

[0059] The second support seat 11 of the lower rhombus oblique prism mechanism C takes the middle plane of the left and right forks as the symmetry plane, and the first fork and the second fork on the left side of the second support seat 11 are respectively provided with a first slot and a second slot, and the angle between the middle planes of the first slot and the second slot is 90°, and the angle between the middle plane of the second slot and the symmetry plane is 30°. The bottom fork of the second support seat 11 is provided with a third slot, and the angle between the middle plane of the third slot and the symmetry plane is 60°.

[0060] The outer ring support seat 8 of the upper rhombus oblique prism mechanism B and the lower rhombus oblique prism mechanism C takes the middle plane of the left and right forks as the symmetry plane, and the first fork and the second fork on the left side of the outer ring support seat 8 are respectively provided with a first slot and a second slot, and the angle between the middle planes of the first slot and the second slot is 30°, and the angle between the middle plane of the second slot and the symmetry plane is 45°. The bottom fork of the outer ring support seat 8 is provided with a third slot, and the middle plane of the third slot coincides with the symmetry plane.

[0061] The central support seat 9 of the upper rhombus oblique prism mechanism B and the lower rhombus oblique prism mechanism C takes the middle plane of the left and right forks as the symmetry plane, and has four open forks on the upper, lower, left and right sides. The notches on the upper and lower side forks are in the same plane as the middle plane of the left and right forks, and the angle between the notches of the left and right forks and the middle plane of the left and right forks is 75°.

[0062] The inner ring support seat 10 of the upper rhombus oblique prism mechanism B and the lower rhombus oblique prism mechanism C takes the middle plane of the left and right forks as the symmetry plane, and the first fork and the second fork on the left side of the inner ring support seat 10 are respectively provided with a first slot and a second slot, and the angle between the middle plane of the first slot and the symmetry plane is 45°, and the angle between the middle plane of the first slot and the second slot is 60°. The bottom fork of the inner ring support seat 10 is provided with a third slot, and the middle plane of the third slot coincides with the symmetry plane.

[0063] In this specific embodiment, the single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism only requires one drive for the retracting or folding process, and the control method of the overall antenna mechanism is simple, ensuring the reliability and synchronization of the retracting or folding movement, while being able to improve the overall structural stiffness of the antenna and having a strong bearing capacity.

[0064] The embodiments described above are only descriptions of the preferred implementation modes of the present invention, and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A single-degree-of-freedom double-ring truss deployable antenna mechanism based on a rhombus-shaped oblique prism, comprising a plurality of deployable units with the same structure, wherein two adjacent deployable units are connected to each other through an outer ring circumferential folding rod and an inner ring circumferential folding rod, respectively, and characterized in that: The expandable unit comprises an upper rhombus-shaped oblique prism mechanism, a lower rhombus-shaped oblique prism mechanism and a connecting rod, wherein the upper rhombus-shaped oblique prism mechanism is connected to the lower rhombus-shaped oblique prism mechanism through the connecting rod; the upper rhombus-shaped oblique prism mechanism comprises a first support seat, an outer ring support seat, an inner ring support seat, a central support seat, a first folding rod, a second folding rod and a radial web rod; The first support seat is provided with a first slot and a second slot at both ends of the left side, the angle between the middle planes of the first slot and the second slot of the first support seat is set to α, and α<180°, the angle between the middle plane of the second slot of the first support seat and the symmetry plane is [45-(180 / N)]°, N is the number of expandable units, and the first support seat is provided with a third slot at the bottom; the first and second slots are provided with a first slot and a second slot at both ends of the left side of the outer ring support seat, the angle between the middle planes of the first slot and the second slot of the outer ring support seat is [45-(180 / N)]°, the angle between the middle plane of the second slot of the outer ring support seat and the symmetry plane is [90-(α / 2)]°, and the third slot is provided at the bottom of the outer ring support seat, and the middle plane of the third slot of the outer ring support seat coincides with the symmetry plane; The two ends of the left side of the inner ring support seat are respectively provided with a first notch and a second notch, the angle between the middle plane of the first notch of the inner ring support seat and the symmetry plane is [90-(α / 2)]°, the angle between the middle plane of the first notch of the inner ring support seat and the second notch of the inner ring support seat is [45+(180 / N)]°, the bottom of the inner ring support seat is provided with a third notch, the middle plane of the third notch of the inner ring support seat coincides with the symmetry plane; the first end, the second end and the third end of the center support seat are respectively provided with a first notch, a second notch and a third notch, the angle between the middle plane of the first notch and the third notch of the center support seat is 180°, and the middle plane of the first notch of the center support seat coincides with the symmetry plane; The first notch of the first support seat is connected to the first end of the first folding rod, the second end of the first folding rod is connected to the second notch of the outer ring support seat, the second notch of the first support seat is connected to the first end of the second folding rod, the second end of the second folding rod is connected to the first notch of the inner ring support seat, the first notch, the second notch and the third notch of the center support seat are respectively connected to the first ends of the first radial web rod, the second radial web rod and the third radial web rod, and the second ends of the first radial web rod, the second radial web rod and the third radial web rod are respectively connected to the outer ring support seat, the inner ring support seat and the third notch of the first support seat; In the lower rhombus oblique prism mechanism, it includes a second support seat, a first folding rod of the lower rhombus oblique prism mechanism, a second folding rod of the lower rhombus oblique prism mechanism, an outer ring support seat of the lower rhombus oblique prism mechanism, a central support seat of the lower rhombus oblique prism mechanism, an inner ring support seat of the lower rhombus oblique prism mechanism and a radial web rod of the lower rhombus oblique prism mechanism, the second support seat is a left-right symmetrical structure, the first end and the second end of the left side of the second support seat are respectively provided with a first notch and a second notch, the angle between the first notch of the second support seat and the middle plane of the second notch is α, α<180°, the angle between the middle plane of the second notch of the second support seat and the symmetry plane is [45-180 / N]°, N is the number of expandable units, the bottom of the second support seat is provided with a third notch, the number of the first notch, the second notch and the third notch of the second support seat are all two, and the first notch, the second notch and the third notch of the second support seat are symmetrically distributed on both sides of the symmetry plane; In two adjacent expandable units, the first notches of the outer ring support seat and the outer ring support seat of the lower rhombus oblique prism mechanism in the first expandable unit are respectively connected to the first end of the outer ring circumferential folding rod and the first end of the outer ring circumferential folding rod of the lower rhombus oblique prism mechanism, the second end of the outer ring circumferential folding rod and the second end of the outer ring circumferential folding rod of the lower rhombus oblique prism mechanism are respectively connected to the first notches of the outer ring support seat and the outer ring support seat of the lower rhombus oblique prism mechanism in the second expandable unit, the second notches of the inner ring support seat in the first expandable unit and the second notches of the inner ring support seat of the lower rhombus oblique prism mechanism are respectively connected to the first end of the inner ring circumferential folding rod The first and second expandable units are connected with each other, and the second notch of the first support seat in the first expandable unit is connected with the second notch of the first support seat in the second expandable unit, and the second notch of the second support seat in the second expandable unit is connected with the second notch of the second support seat in the second expandable unit.

2. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: In the first support seat, the first support seat is a left-right symmetrical structure, and the number of the first slot, the second slot and the third slot of the first support seat are both two, and the first slot, the second slot and the third slot of the first support seat are symmetrically distributed on both sides of the symmetry plane; in the outer ring support seat, the outer ring support seat is a left-right symmetrical structure, and the number of the first slot, the second slot and the third slot of the outer ring support seat are both two, and the first slot, the second slot and the third slot of the outer ring support seat are symmetrically distributed on both sides of the symmetry plane; in the inner ring support seat, the inner ring support seat is a left-right symmetrical structure, and the number of the first slot and the second slot of the inner ring support seat are both two, and the first slot and the second slot of the inner ring support seat are symmetrically distributed on both sides of the symmetry plane, and the number of the third slot of the inner ring support seat is one; in the center support seat, the center support seat is a left-right symmetrical structure, and the number of the second slot of the center support seat is both two, and the second slot of the center support seat is symmetrically distributed on both sides of the symmetry plane.

3. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: The first folding rod comprises a first straight rod, a second straight rod and a third rotating pair, the first straight rod and the second straight rod are of equal length, and the first straight rod is connected to the second straight rod through the third rotating pair; the second folding rod comprises a third straight rod, a fourth straight rod and a fourth rotating pair, the third straight rod and the fourth straight rod are of equal length, and the third straight rod is connected to the fourth straight rod through the fourth rotating pair; the outer ring circumferential folding rod comprises a fifth straight rod, a sixth straight rod and a first rotating pair, the fifth straight rod and the sixth straight rod are of equal length, and the fifth straight rod is connected to the sixth straight rod through the first rotating pair; the inner ring circumferential folding rod comprises a seventh straight rod, an eighth straight rod and a second rotating pair, the seventh straight rod and the eighth straight rod are of equal length, and the seventh straight rod is connected to the eighth straight rod through the second rotating pair, and the rotating pair on the folding rod enables it to rotate in only one direction, thereby ensuring the reliability and synchronization of the retracting and extending movement of the entire device under one drive input.

4. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: In the lower rhombus oblique prism mechanism, the first notch of the second support seat is connected to the first end of the second folding rod of the lower rhombus oblique prism mechanism through the seventeenth rotation pair, the second end of the second folding rod of the lower rhombus oblique prism mechanism is connected to the second notch of the outer ring support seat of the lower rhombus oblique prism mechanism through the ninth rotation pair, the second notch of the second support seat is connected to the first end of the first folding rod of the lower rhombus oblique prism mechanism through the nineteenth rotation pair, and the second end of the first folding rod of the lower rhombus oblique prism mechanism is connected to the inner ring support seat of the lower rhombus oblique prism mechanism through the fourteenth rotation pair. The first slot is connected, the first slot, the second slot and the third slot of the central support seat of the lower rhombus oblique prism mechanism are respectively connected to the first ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod through the twelfth rotation pair, the eleventh rotation pair and the thirteenth rotation pair, and the second ends of the fourth radial web rod, the fifth radial web rod and the sixth radial web rod are respectively connected to the third slot of the outer ring support seat of the lower rhombus oblique prism mechanism, the third slot of the inner ring support seat of the lower rhombus oblique prism mechanism and the third slot of the second support seat through the tenth rotation pair, the sixteenth rotation pair and the eighteenth rotation pair.

5. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: In the upper rhombus-shaped oblique prism mechanism, the planes where the first support seat, the outer ring support seat, the center support seat and the inner ring support seat are located are parallel to each other, the outer ring support seat and the inner ring support seat are both on the circumscribed circle of the N-gon, and the line connecting the outer ring support seat and the inner ring support seat converges at the center of the N-gon; in the lower rhombus-shaped oblique prism mechanism, the planes where the second support seat, the outer ring support seat of the lower rhombus-shaped oblique prism mechanism, the center support seat of the lower rhombus-shaped oblique prism mechanism and the inner ring support seat of the lower rhombus-shaped oblique prism mechanism are located are parallel to each other; the outer ring support seat of the lower rhombus-shaped oblique prism mechanism and the inner ring support seat of the lower rhombus-shaped oblique prism mechanism are both on the circumscribed circle of the N-gon, and the line connecting the outer ring support seat of the lower rhombus-shaped oblique prism mechanism and the inner ring support seat of the lower rhombus-shaped oblique prism mechanism converges at the center of the N-gon.

6. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: In the upper rhombus oblique prism mechanism, it includes two first support seats with identical structures, two first folding rods with identical structures, two second folding rods with identical structures, four radial web rods with identical structures, an outer ring support seat, an intermediate support seat and an inner ring support seat. The two first support seats with identical structures, an outer ring support seat and an inner ring support seat are arranged in a rhombus shape on the projection plane. The outer ring support seat and the two first folding rods with identical structures constitute the upper half of the rhombus, and the inner ring support seat and the two second folding rods with identical structures constitute the lower half of the rhombus.

7. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 5 or 6, characterized in that: In the expanded state of the upper rhombus oblique prism mechanism, the two first support seats with the same structure are at the same height, the center support seat and the inner ring support seat are at the same height, the height of the outer ring support seat is greater than the height of the two first support seats with the same structure, and the height of the two first support seats with the same structure is greater than the height of the center support seat and the inner ring support seat.

8. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1, characterized in that: In the lower rhombus oblique prism mechanism, it includes two second support seats with identical structures, two first folding rods of the lower rhombus oblique prism mechanism with identical structures, two second folding rods of the lower rhombus oblique prism mechanism with identical structures, four radial web rods of the lower rhombus oblique prism mechanism with identical structures, an outer ring support seat of the lower rhombus oblique prism mechanism, an intermediate support seat of the lower rhombus oblique prism mechanism and an inner ring support seat of the lower rhombus oblique prism mechanism. The two second support seats with identical structures, an outer ring support seat of the lower rhombus oblique prism mechanism and an inner ring support seat of the lower rhombus oblique prism mechanism are arranged in a rhombus shape on the projection plane. The outer ring support seat of the lower rhombus oblique prism mechanism and the two second folding rods of the lower rhombus oblique prism mechanism with identical structures constitute the upper half of the rhombus, and the inner ring support seat of the lower rhombus oblique prism mechanism and the two first folding rods of the lower rhombus oblique prism mechanism with identical structures constitute the lower half of the rhombus.

9. The single-degree-of-freedom double-ring truss deployable antenna mechanism based on rhombus oblique prism according to claim 1 or 8, characterized in that: In any state of the lower rhombus oblique prism mechanism, two second support seats with identical structures are at the same height, the central support seat of the lower rhombus oblique prism mechanism and the inner ring support seat of the lower rhombus oblique prism mechanism are at the same height, the height of the outer ring support seat of the lower rhombus oblique prism mechanism is greater than the height of the two second support seats with identical structures, and the height of the two second support seats with identical structures is greater than the height of the central support seat of the lower rhombus oblique prism mechanism and the inner ring support seat of the lower rhombus oblique prism mechanism.

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