Abstract
Aiming at the problem that it is difficult to generate the dynamic decoupling equation of the parallel six-dimensional acceleration sensing mechanism, two typical parallel six-dimensional acceleration sensing mechanisms are taken as examples. By analyzing the scale constraint relationship between the hinge points on the mass block and the hinge points on the base of the sensing mechanism, a new method for establishing the dynamic equation of the sensing mechanism is proposed. Firstly, based on the scale constraint relationship between the hinge points on the mass block and the hinge points on the base of the sensing mechanism, the expression of the branch rod length is obtained. The inherent constraint relationship between the branches is excavated and the branch coordination closed chain of the “12-6” configuration is constructed. The output coordination equation of the sensing mechanism is successfully derived. Secondly, the dynamic equations of “12-4” and “12-6” configurations are constructed by the Newton-Euler method, and the forward decoupling equations of the two configurations are solved by combining the dynamic equations and the output coordination equations. Finally, the virtual prototype experiment is carried out, and the maximum reference errors of the forward decoupling equations of the two configuration sensing mechanisms are 4.23% and 6.53%, respectively. The results show that the proposed method is effective and feasible, and meets the real-time requirements.
With the development of science and technology and the improvement of people’s understanding of the objective world, it is more and more important to detect the six-dimensional motion of objects in three-dimensional space. For example, in order to realize the dynamic control of the end effector of the space robot, the complete motion information of the robot body must be obtained in real time. In addition, the space rigid motion of the carrier is involved in inertial navigation, artificial intelligence, space docking and other field
The measurement performance of the six-axis accelerometer is mainly determined by the operating performance of its sensing mechanis
In general, the research methods of mechanism dynamics include the general equation of dynamics, Hamilton canonical equation, Newton-Euler method, Lagrange equation, Kane method and so on. You et al
When the Newton-Euler method is used to analyze the dynamics of redundant mechanisms, it is difficult to establish supplementary equations. To this end, taking two typical six-axis acceleration sensing mechanisms as the research object, this paper derives the two-configuration complementary equation (that is, the output coordination equation), and solves the forward decoupling equation of the two configurations. The research content of this paper lays a theoretical foundation for fault handling and configuration synthesis of sensing mechanisms.
The prototype of the parallel six-axis acceleration sensing mechanism is shown in

Fig.1 Principle prototype of parallel six-dimensional acceleration sensing mechanism
The composite ball hinge in the sensing mechanism is generally located at the midpoint and vertex of the edge line of the mass block. Therefore, two typical sensing mechanisms are selected in this paper, which are the “12-4” configuration of the composite spherical hinge at the vertex of the mass block (
The Newton-Euler method is used to analyze the forward dynamics of redundant mechanisms. The difficulty lies in generating the output coordination equation of the mechanism. The research ideas of this section are as follows: Firstly, the scale constraint relationship between the hinge points on the mass block and the hinge points on the base of the sensing mechanism is analyzed. Secondly, the expression of the rod length of the branch chain is deduced theoretically, and the inherent constraint relationship between the rod lengths is excavated. Finally, Hooke’s law is used to derive the output coordination equation.
The fixed coordinate systems {Q1} and {Q2} are established on the mass block and the base, respectively, as shown in

Fig.2 Two coordinate systems in the system
The quaternion is selected to represent the attitude of the mass block of the sensing mechanism. In Ref.[
(1) |
As shown in
(2) |
As shown in
(3) |
The branch vector in {Q2} is expressed as
(4) |
(5) |
where is the coordinate of the mass center of mass in {Q2}.
Substituting Eqs.(1─3) into
(6) |
According to
(7) |
Using Hooke’s law, the output coordination equation is derived as
(8) |
where ki is the axial stiffness of the i branch chain, and fi the axial force of the i branch chain.
Assuming that the stiffness of each branch is consistent,
(9) |
where ;;;;;.
Using the method of the previous section, the branch chain expression of the “12⁃6” configuration is derived as
(10) |
The analytical expression of the branch chain length shown in the
(11) |
Further, the output coordination equation is derived according to
(12) |
where ;;;;;.
Differently, after studying the output coordination equation of “12-6” type, it is found that

Fig.3 Regular hexagon coordinated closed chain of “12-6” configuration
The decoupling of the forward dynamics of the parallel six-dimensional acceleration sensing mechanism belongs to the second-order statically indeterminate problem, so it is necessary to find a supplementary equation to transform the statically indeterminate problem into a statically indeterminate problem. The output coordination equation of the two configurations has been derived above, that is, the supplementary equation. The research ideas of this section are as follows: Firstly, based on the Newton-Euler method, the dynamic equations of the two configurations are constructed; then, the dynamic solution of the two configurations is completed by combining the dynamic equation and the coordination equation.
Since the quality of the mass block of the sensing mechanism is far greater than that of the branch chain, the 12 branches of the sensing mechanism can be regarded as two-force rods. In this section, we also use the quaternion Φ=φ0+φ1i+φ2j+φ3k to represent the rotation matrix of the base relative to the inertial frame, and its expression is
(13) |
where
where E3 is a third-order unit matrix.
The dynamic equations of the “12-4” configuration are constructed by Newton-Euler method, we have
(14) |
(15) |
where , are the three-dimensional linear acceleration vector and the three-dimensional angular acceleration vector in the basic excitation are represented, respectively; ; m represents the mass of the mass block and g the acceleration of gravity; ; .
The configurational kinetic equations of “12-6” are constructed as follows
(16) |
(17) |
where ,.
Combining the coordination
(18) |
where , , represents the kth element of the vector, 0 the sixth-order zero column vector, and C a 12×12 matrix with -1, 0, and 1 as elements.
According to the theory of the basic solution system of and linear equations, F must have a definite and unique solution, that is
(19) |
The solution of the forward decoupling equation of the “12-6” configuration is exactly the same as the above process, and the calculation results also show that the branched chain force of the configuration also has a definite and unique solution.
The virtual prototype of the “12-4” sensing mechanism is established in the software package ADAMS, as shown in

Fig.4 Regular hexagon coordinated closed chain of “12-4” configuration
Item | Simulation parameter |
---|---|
X direction translation /mm | 1×cos(10πt)-1 |
Y direction translation /mm | 0.3×cos(10πt)-0.3 |
Z direction translation /mm | 3×cos(10πt)-3 |
Rotate around X /rad | 0.3×cos(10πt)-0.3 |
Rotate around Y/rad | 0.3×cos(10πt)-0.3 |
Rotate around Z/rad | 3×cos(10πt)-3 |
n/mm | 50 |
m/kg | 62.408 |
L/mm | 50 |
k/(N·m |
5.02×1 |
Simulation time /s | 5 |
Simulation step size /s | 0.002 |
Configuration | 12⁃4 | 12⁃6 |
---|---|---|
Maximum reference error/% | 4.23 | 6.53 |
Taking two typical six-dimensional acceleration sensing mechanisms as examples, by analyzing the scale constraint relationship between the hinge points on the mass block and the hinge points on the base of the sensing mechanism, the analytical formula of the branch length is derived theoretically. Based on this, the inherent constraint relationship between all branches of the sensing mechanism is explored, and the output coordination equation of the sensing mechanism is established. The forward dynamic equation of the mechanism is established by Newton-Euler method, and the forward decoupling equation of the sensing mechanism is solved by combining the output coordination equations. This method lays a theoretical foundation for improving the dynamic decoupling accuracy of multi-dimensional sensing system.
Contributions Statement
Dr. YOU Jingjing proposed the model, designed the research program for analysis. Mr. ZHANG Xianzhu explained the results and wrote the manuscript. Ms. ZHANG Yuanwei contributed to the discussion and background of the study. All authors commented on the manuscript draft and approved the submission.
Acknowledgements
This work was supported in part by the National Natural Science Foundation of China (No.51405237).
Conflict of Interest
The authors declare no competing interests.
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