Data processing: generic control systems or specific application – Specific application – apparatus or process – Robot control
Reexamination Certificate
1998-12-15
2001-09-11
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Robot control
C700S251000, C700S255000, C700S262000, C700S263000, C074S490030, C074S490050, C074S490060, C901S023000, C901S029000, C464S062100
Reexamination Certificate
active
06289263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to mobile robots and, more particularly, to a robot having a spherical exo-skeleton and an internal propulsion mechanism.
2. Discussion
Mobile robots have been studied for decades. Researchers have investigated robot applications ranging from material transportation in factory environments to space exploration. A particularly extensive area of mobile robot application is found in the automobile industry where robots transport components from manufacturing work stations to the assembly lines. These automated guided vehicles (AGVs) follow a track on the ground and have the ability to avoid collisions with obstacles in their path. Autonomous mobile robots designed for planetary exploration and sample collection during space missions have also received significant attention in recent years. This attention has resulted in advancement of mobile robot technology and a corresponding increase in the effectiveness of mobile robots in a wide range of applications.
Mobile robot technology has primarily focused on robot designs having a body with wheels for mobility. This has led to advancements in motion planning and control of the rolling wheel. Notwithstanding these developments, wheeled mobile robots have significant deficiencies that have not been adequately overcome. For example, wheeled robots often times have difficulty traversing rough terrain. While this problem may be reduced by increasing the size of the wheels of the robot, increases in wheel size cause various undesirable consequences including an increase in the overall size and weight of the robot. Unfortunately, increases in wheel sizes do not necessarily result in corresponding increases in operational features such as payload capacity. Also, wheeled robots are adversely effected by harsh operating environments such as heat, chemicals, and the like.
The present invention relates to a spherical mobile robot that moves by rolling over terrain The control of a rolling sphere involves reconfiguration of its position and orientation coordinates. Control strategies developed for wheeled mobile robots do not directly relate to precise control of the reconfiguration of the rolling sphere.
Wheeled mobile robots belong to a class of systems known as nonholonomic systems. Feedback control strategies developed for nonholonomic systems are typically smooth and time varying, piecewise non-smooth and time-invariant, or a hybrid combination of the two. Such strategies, however, are applicable to nonholonomic systems that can be converted into a special form, known as chained form. It has not been possible to convert the kinematic model of the sphere into chained form. Therefore, the above strategies do not lend themselves directly to the reconfiguration problem of the rolling sphere.
Typically, among control strategies for nonholonomic systems, time-varying controllers suffer from slow rates of convergence. Faster convergence rates can be achieved through the design of piecewise non-smooth time-invariant controllers. However, piecewise non-smooth time-invariant controllers may involve multiple switchings and may lead to undesirable chattering. Hybrid controllers are based on switchings at discrete-time instants between various low level smooth controllers. Such controllers tend to combine the advantages of both the time-varying and time-invariant controllers.
While non-smooth control is generally sufficient to provide operational capability to a spherical robot of the type described herein, a non-smooth technique has undesirable characteristics including intermittent motion and chattering. A non-smooth controller is particularly undesirable in the present invention in view of the spherical robot's internal drive mechanism. More particularly, the internal drive mechanism may be limited in its ability to generate the large accelerations necessary for non-smooth control of the system.
SUMMARY OF THE INVENTION
In view of the above, a need exists for a mobile robot that effectively traverses rough terrain. Accordingly, the present invention includes a spherical exo-skeleton and an internal mechanism for propulsion. The spherical exo-skeleton of the present invention may be increased or decreased in size as necessary to satisfy various design and operational parameters including payload capacity and mobility in rough terrain. Specifically, as the spherical diameter of the mobile robot increases, its ability to traverse rough terrain and its payload capacity also increase. The drive mechanism of the present invention described and claimed herein provides mobility by continuously distributing or spinning masses within the spherical cavity that creates a moment about the center of the sphere thereby enabling the sphere to accelerate or decelerate, move with constant velocity, or servo at a point as and when necessary. The motion of the sphere is controlled through sensing and feedback.
The spherical robot has a high degree of stability and the capability for rapid maneuvers and movement over rough terrain. With an internal power source, sensors for feedback, a microprocessor for motion control, and other hardware, the robot achieves autonomy and functions as a mobile robot. The spherical robot has superior mobility compared to wheeled robots because a sphere can roll in two directions. Additionally, the radius of the sphere will be relatively large since the sphere represents the outer perimeter of the robot.
Other advantages of the present invention include the ability to fabricate the exo-skeleton of the spherical robot from materials that protect the operating components of the robot during use in harsh environments. For example, the exo-skeleton may be formed of an armor-type material to provide a robotic soldier, fire and heat resistant material for fire prevention/fighting applications, and other condition resistant material for robotic applications in other harsh environments.
A simple control strategy known in the art is contemplated for use with the present invention when precise control of the position or the orientation of the sphere, but not both, is required. The present invention further includes a feedback control strategy for the control of both position and orientation coordinates of the spherical robot. This control strategy asymptotically converges the spherical robot from any Cartesian coordinates x,y, to any other, and at the same time reorients the sphere such that a given point on the surface of the sphere always appears at the top upright position.
The present invention includes a spherical robot having a spherical body and a drive mechanism. The spherical body defines a cavity and a center. The drive mechanism is disposed within the cavity and coupled to the spherical body and has a plurality of masses that can be positioned or spun within the cavity to create a moment about the center of the body that selectively cause the body to rotate. The present invention also includes a method for moving a spherical robot from a starting position to a target that includes the steps of providing a robot having a spherical body defining a cavity with a drive mechanism disposed in the cavity and coupled to the body, sensing the position of the body relative to the target, calculating target angular velocities for rotating the body to position the body at the target in a selected orientation, and actuating the drive mechanism to rotate the body at the target angular velocities.
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Li, Z., and Canny, J., 1990, “Motion of Two Rigid Bodies with Rolling Constraint”, IEEE Transactions on Roboti
Board of Trustees operating Michigan State University
Cuchlinski Jr. William A.
Harness & Dickey & Pierce P.L.C.
Marc McDieunel
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