Space Robotic

The Design, Planning and Control of Robotic Systems in Space

Sponsor

NASA Langley Research Center

Investigators

Dubowsky, S., Moore, C., Corrigan, T., Torres, M., Meller, U., Antonella, S., Mavroidis, C. and Yoshida, K.

Introduction

In the future, robotic systems will be expected to perform important tasks in space, in orbit and in planetary exploration. However, such applications introduce a number of technical problems not found in conventional earth-bound industrial robots. To design useful and practical systems to meet the needs of future space missions, substantial technical development is required, including in the areas of the design, control and planning. The objective of this three-year research program is to develop such design paradigms and control and planning algorithms to enable future space robotic systems to meet their proposed mission objectives. The underlying intellectual focus of the program is to construct a set of integrated design, planning and control techniques based on an understanding of the fundamental mechanics of space robotic systems.

Free-Floating and Free-Flying Systems

These systems consist of a rigid manipulator that is supported from a spacecraft. Dynamic coupling between the manipulator and the spacecraft causes unwanted motion of the system. This motion which can be compensated by reaction jets in the case of free-flying systems or can be uncontrollable in the case of free-foating systems, creates problems in the control of the manipulator and degrades seriously its performance [3-5]. The main contributions from this laboratory, in the study of these systems are:

The Virtual Manipulator Method [6, 7]

This method simplifies the system's dynamics by transforming a free-floating or free-flying system into an equivalent "virtual" fixed base manipulator.

Dynamic Singularities [8, 9]:

These are singular configurations of free-floating and free flying systems that depend on the system's dynamic parameters and not only on its kinematic parameters. Control and planning algorithms that do not take into account this important mechanical property can present occasional problems.

Endpoint Control of Free-Floating Systems [10, 11]

Taking into account the special kinematic and dynamic properties of these systems such as the dynamic singularities, fixed based manipulator control algorithms were modified and shown to achieve good performance in the case of free-floating and free-flying systems.

Coordinated Manipulator/Spacecraft Motion Control [12]

This is a method to control the position and attitude of a system's spacecraft in a coordinated way by using the inherent redundancy in space robotic systems.

Failure Recovery Control [13]

This method controls a space manipulator system after failure of one of its joints by maintaining the system's inertial matrix invariant with respect to the failed joint.

Enhanced Disturbance Map [14,-17]

A graphical tool that can be used to find manipulator paths that result in minimum dynamic disturbances to the spacecraft.

Compliant Base -- Long Reach Manipulators

The hazardous and inaccessible task locations in space applications has given rise to a new class of space robotic systems: compliant base space manipulator systems. These systems include long reach manipulator systems and exploratory vehicle mounted manipulators. They consist of a small fast rigid manipulator mounted on either a long reach flexible deployable structure or a suspension vehicle. As in free floating and free-flying systems the dynamic coupling between the manipulator and its supporting structure results in residual vibrations of the supporting structure which degrade the system's performance [18, 19]. The methods, algorithms and theories developed in this area are:

Coupling Map [20-22]:

A method that finds manipulator paths that transfer minimum energy to the manipulator compliant base. Three path-planning algorithms were derived based on the Coupling Map: Base Relocation, Hot Spot Method and the Redundancy Resolver Algorithm.

Mobile Manipulator Jacobian Transpose Control [23-29]:

This is an extended jacobian transpose control algorithm developed for exploratory vehicle mounted systems. It compensates for the vehicle motions caused by the manipulator motion by measuring the vehicle position and orientation in inertial space using inclinometers and ultrasonic sensors.

Pseudo-Passive Energy Dissipation [19]:

A closed-loop manipulator controller for compliant based systems that enables the manipulator to damp out the lightly damped residual vibrations of its supporting structure after the manipulator reaches the final point of its path.

Inferred Endpoint Control [30-34]:

A closed-loop manipulator controller for long reach space manipulator systems that permits controlling the manipulator end-effector position in spite of the presence of some base vibrations using easily obtained strain meausrements on the deployable structure.

Emulation of Micro-Gravity Conditions [35-39]:

Using a six degree of freedom Stewart Platform (see section 3) two methods were developed to achieve microgravity emulation of the motion of space manipulator systems. These methods are: the Learning Micro-Gravity Compensation Method and the Model Micro-Gravity Compensation Method.

Impact Dynamics [40]:
Experiments were performed to study the dynamic behavior of spaceborne manipulator systems under impact. A method called Extended Inverse Inertia Tensor that can predict impact forces in fixed base manipulator systems was extended in the case of long reach space manipulator systems. Based on this method configurations of the system that result in minimum impact forces were found.