Synthesis features

of the space manipulator control system

A.P.Alpatov, P.A.Byelonozhko, P.P.Byelonozhko, S.V.Tarasov, A.A.Fokov

Institute of Technical Mechanics of National Sciences Academy of Ukraine and

National Space Agency of Ukraine,

Ukraine

 

While there appeared essentially new technical devices in a space robotics, expansion of orbital application area of manipulators is proceeding. Functional requirements both to devices, and to control systems become stricter. Perspective projects of orbital complexes, bases on the Moon and planets of Solar system, assume in addition to the traditional problems solved with use of manipulators (particularly moving of the loads, the special equipment, astronauts, etc. in a vicinity of orbital stations and the reusable transport spaceships), occurrence of new problems, for example, installation of space techniques on special robotized orbital platforms.

The offered synthesis technique of an executive control system has been developed during research of final rigidity influence of reusable spaceship manipulator design elements on dynamics of manipulation.

Control object is a system from orbital spaceship (OSS) and payload (PL) connected by six-linked anthropomorphous handling device (manipulator), formed by rotary kinematics pairs of the fifth class. In the assumption of an opportunity to neglect disturbing  exposure (aerodynamic, gravitational, etc.) and at the switched - off stabilization system of angular position OSS, and the set entry conditions, mutual position of elements of system OSS-manipulator-PL is determined by action of the torques created in joints of the manipulator by mobility degrees drives. An input of an executive control system is programs of an angle change in joints as functions of time, an output is changes in time of joint angles.

The basic features of control object are:

- Mobility OSS (the basis of the manipulator) in inertial space;

- Small mass of the handling device in comparison with OSS and PL mass;

- Final rigidity of links and reducing unit;

- Low engine power of mobility degree drives.

At the initial stage the simplified design model of the handling device - two rigid bodies connected by the manipulator with rigid massless links was considered.

Thus, at a initial synthesis stage of an executive control system:

-         the simplified design model of control object (the handling device and drive mobility degrees) is offered and the assumptions are accepted, allowing to lower the order of the dynamic equation system;

-         the concept of the basic configuration is formulated, allowing to use a method of the "frozen" parameters without the aprioristic definition of a basic trajectory;

-         the structure of an executive control system as set of servosystems on each joint is determined;

-         on the basis of the allocated system concept the feedback parameters are chosen;

-         an executive system stability with consideration of channel interrelation through the control object is confirmed by frequency methods and numerical integration.

It was confirmed serviceability of the suggested executive system providing comprehensible quality of controlled movement dynamics.

The received results have formed a basis of the further researches of influence of the handling device final link rigidity and mobility degrees of reducer on dynamics of controlled manipulator movement. Problems have been formulated:

-         more full account of link and reducer elastic properties getting importance first of all for control object features of dynamics;

-         the program movement synthesis providing the solution of manipulation problems and preferable from the requirements to controlled movement parameters (position accuracy, to transient characteristics);

-         the analysis of an executive control system, synthesis of adjusting devices.

The solution of these problems according to the suggested methodical approach was expedient for carrying out stage by stage.

As a result of all research complex hierarchical mathematical model set of the manipulating device having a various complexity level has been developed. In addition to described design model in which the link mass (not deformable and deformable) is taken into account were examined above. Combinations of system parameters at which use of the simplified design models is fair have been determined. On the basis of the developed methodical approaches the structure is offered and parameters of control algorithms providing comprehensible quality of controlled movement dynamics (including the indemnification of dynamic mistakes) are determined. Formation ways of program movements for angles in joints as functions of time are offered and realized in settlement variants. Estimations of influence on controlled movement dynamics of system  element  final rigidity (links of the handling device and drive reducers of mobility degrees) are made, recommendations on an expedient choice of design parameters are formulated.

The suggested approach to the an executive control system synthesis problem solution of the space manipulator, based on use of dynamic model set, can be recommended as practically effective analysis tool of the modern complex spatially advanced space objects. At dynamic research of their controlled  movement there is an necessity of elastic properties account of design elements.

Particularly let's note, that at a choice stage of the design model it’s reasonable to take into account opportunities of modern computer modelling means of rigid bodies system dynamics of the considerably simplifying bulky procedure of an equation conclusion and equipped with well advanced means of visualization and the complex analysis of researched dynamic features process. For their effective use at the similar problems solution the original approach to representation is offered for elastic deformable elements by finite-dimensional design model.