Research On The Stability Control Of The Visual Axis For The Optoelectronic Stabilized Platform With A Spherical Mechanism

As an imaging device placed on a vehicle carrier,the avionics stabilisation platform is capable of identifying,capturing,tracking,positioning and measuring targets in a specific area,and has a wide range of applications in ground imaging.In recent years,with the development of modern avionics technology,the need for high-precision and long-endurance earth observation has become increasingly prominent.The avionics stabilisation platform needs to overcome complex multi-source non-linear perturbations during flight,achieve high-precision visual axis stability control,and at the same time needs to carry more effective imaging loads within the volume and weight constraints.Therefore,it is of great engineering value to study the control methods of high precision and high load ratio optoelectronic stabilised platforms.This dissertation takes the tandem spherical mechanism as the research object,thoroughly investigates the kinematic and dynamic characteristics of the spherical mechanism,based on theoretical analysis and combined with experimental verification,and conducts a more in-depth research on the control technology of the optical stabilised platform with spherical mechanism for visual axis stabilisation.The main research contents of this paper are as follows.1.In order to realise the control of a spherical mechanism optoelectronic stabilised platform,its mathematical model is first analysed.By means of the D-H parameter method in the field of robotics the D-H parameter table of the mechanism is obtained and a coordinate system is established for the mechanism.The forward and inverse kinematic model of the mechanism can be deduced from the coordinate transformation relations.Based on the principle of virtual work,the dynamics of the mechanism is derived using the Lagrangian method.Simulations and experiments are carried out to verify the forward and inverse kinematic models as well as the kinetic model.2.Aiming at the problem of unbalanced moments in the photoelectric stabilised platform of the spherical mechanism,a gravity compensation algorithm based on the dynamics model of the mechanism is studied,and a gravity compensation controller is designed to compensate for the effects of the unbalanced moments and inertia forces of the spherical mechanism itself,so as to improve the response speed and control accuracy of the system.3.For the problem of joint coupling of spherical mechanism and the existence of multi-source disturbance in the system,the research is conducted for the intra-joint space loop compensation technique and the apparent axis stability control method.Due to the coupling between the joints of the tandem spherical mechanism and the multisource disturbances such as friction,model uncertainty,wind resistance and carrier motion during operation,an internal loop compensation technique based on an adaptive sliding-mode-assisted disturbance observer is proposed to decouple the joint coupling of the tandem spherical mechanism and to compensate for the model uncertainty and external disturbances of the system on the basis of the gravity compensation algorithm.The velocity loop feedback controller is also designed to achieve the apparent axis stability control of the inertially stabilised platform.Finally,experimental validation is carried out and the results show that the method is able to decouple the joint space of the spherical mechanism,and that the performance of the method is significantly improved in terms of immunity to disturbances.4.In the process of implementing the joint space control method,the position,velocity and acceleration mapping relationship between the joint space and the working space is established through the forward and inverse kinematic model,which requires several kinematic transformations,which inadvertently reduces the control accuracy of the system and increases the computational complexity.In order to further simplify the complexity and intuitiveness of the tandem spherical mechanism control method,the tandem spherical mechanism work space control method is investigated.A twostage adaptive sliding-mode-assisted disturbance observer method based on joint space and work space is designed for direct control of the end load of the tandem spherical mechanism,and a feedback controller combined with a force compensation controller and a velocity loop is used to achieve high accuracy control of the tandem spherical structure.Finally,the effectiveness of the method is verified experimentally and the control effect is superior to that of the joint space.In summary,this paper addresses the study of the apparent axis stability control of an optoelectronic stabilised platform with a spherical mechanism,applies the new mechanism to an avionics system,and combines control algorithms such as the adaptive sliding-mode-assisted interference observer to improve the load ratio and apparent axis stability accuracy of the optoelectronic system,providing theoretical support and design reference for research and application in related fields.