Spacesuit hip joint plays an important role on astronaut activities, such as planetary walking and surveying. This paper proposes a conceptual design of hard hip joint in consideration of the coupling effect of spacesuit hip joint and astronaut thigh. Firstly, lower extremity activities are introduced to illustrate the mobility of hard hip joint, such as walking, kneeing, and abduction. A conceptual design of hard hip joint is explained in detail, including geometric structure, components, design parameters, and mechanism models. Secondly, a 3-linkage coupling mechanism model is built up by synthesizing that conceptual design of hard hip joint. An equiangular dual-perpendicular representation method is brought out to parameterize that mechanism model of hard hip joint. Particularly, four geometric constraints are, respectively, given out to avoid impact between the hip joint and the thigh and to ensure the continuity of thigh motion. Finally, motion equations of hip joint parts are established by using coordinate transformation and vector representation. A case study is conducted to verify the correctness of the proposed representation method and that coupling mechanism model.
Hip joint is an important component in spacesuit, which enables mobility of astronauts wearing pressurized spacesuits to complete missions, including walking and surveying. Hip joint is briefly classified into soft hip joint and hard hip joint. Generally, hard hip joint is made of some rigid materials, such as aluminum alloy and stiffness composite. Soft hip joint is made of soft materials, such as nylon and fabric. General spacesuit is pressurized with gas to a certain pressure level making it stiff in the vacuum of space [
Spacesuit field involves many topics widely, such as mobility and agility [
Spacesuit is different from other classical spacecraft, which is characterized as the human-suit interactive spacecraft. As for spacesuit hip joint, there exists a strong coupling effect between hip joint and astronaut thigh. The coupling effect is embodied by impact, rubbing, etc. Therefore, the conceptual design of hip joint should pay attention to above coupling effect. To solve above problem, this paper brings forward an equiangular dual-perpendicular representation method and two related geometric constraints. Moreover, a 3-linkage coupling mechanism model is constructed based on a conceptual model of the hip joint. That coupling mechanism model is helpful for parametric design and motion analysis. To ensure the motion continuity of the joint and thigh, two additional geometric constraints are brought out and discussed in detail. Furthermore, motion equations of hip joint part are established using coordinate transformation and vector representation. Finally, a case study is conducted to verify the correctness of the proposed representation method and coupling mechanism model of the hip joint.
Four basic lower extremity activities of designed spacesuit are illustrated in Figure
Four basic lower extremity activities of designed spacesuit.
Conceptual models of the hip joint and its components are constructed, as shown in Figure
Conceptual models of the (a) hip joint and (b) its components.
To reduce manufacturing cost, a similar geometric structure is used to design upper part and lower part, as shown in Figure
Geometric structure and parameters of (a) joint part and (b) link.
Due to large stiffness, hip joint part is treated as a rigid body theoretically. Thus, the geometric structure can be synthesized to be one link from point
By combining the thigh with the hip joint, a hip joint assembly is constructed, as shown in Figure
Models of (a) hip joint assembly (b) 3-linkage coupling mechanism.
By assembling above links, a 3-linkage coupling mechanism model of hip joint assembly can be built up, as shown in Figure
Generally, there are many requirements on spacesuit, such as motion, safety, strength, and weight. This paper is mainly aimed at impacting and motioning continuity. To solve above two problems, an equiangular dual-perpendicular method is firstly brought out to parameterize a conceptual model of hard hip joint, as illustrated in Figure
An equiangular dual-perpendicular method.
To avoid impact between the hip joint and the thigh, two geometric constraints must be satisfied. The first constraint is that both segment lines
In order to ensure continuous motion of the thigh, two geometric constraints are proposed in addition. The first constraint is that segment line
Above all, those problems can be solved by introducing four geometric constraints, including two perpendicular constraints, one symmetric constraint and one coincident constraint.
Based on above four constraints, structure parameters of hip joint and briefs part can be obtained. Next, we derive the structure parameters of hip joint. In Figure
Intuitively, the geometric structure of briefs part is a spherical shell. Neglecting its shell thickness, it consists of three tangent circles, as shown in Figure
Model and parameters of briefs part.
Among above three parameters, parameters
In global coordinate frame
By combining equations (
Furthermore, radius
From equations (
Firstly, we try to construct the coupling mechanism model of hip joint assembly in global coordinate frame
Mechanism models of (a) thigh and (b) hip joint assembly.
Next, we will derive motion equations of upper part (link 1) and lower part (link 2) in coordinate frame
From circle
Because of
Secondly, we will derive thigh motion equation in coordinate frame
By coordinate transformation, unit vector
By substituting equations (
From Figure
According to
Based on the relationship between planar rotation and fixed axis rotation, parameters
Above all, motion equations (equation (
For convenience of programming, computation procedure is given to solve design parameters and motion equations based on known conditions, as shown in Figure
Computation procedure.
Based on above computation procedure, related program was developed to carry out a case study, where design parameters are set to
Motion curves of upper part (green solid curve) and lower part (blue solid curve) and thigh (red solid curve).
Around a coupling effect of hip joint and thigh, this paper proposes an equiangular dual-perpendicular method to design a conceptual model of hip joint. Geometric structure and coupling constraints are discussed in detail. Specifically speaking, two perpendicular constraints are given out to avoid impact between hip joint and thigh. Symmetric and coincident constraints are brought out to realize thigh continuous motion. Based on above constraints, a 3-linkage coupling mechanism model is built up. Motion equations of hip joint are derived by using coordinate transformation and vector representation. Meanwhile, related computation procedure is formed to solve structural parameters and motion parameters, respectively. Finally, a case study is conducted to verify the proposed representation method and motion equations. Results show that the conceptual design of hip joint is correct and feasible.
No data were used to support this study.
The authors declare that they have no conflicts of interest.
The National Natural Science Foundation of China under the grant No. 51675087 supports this research.