THE INTERACTIVE ASSEMBLY AND COMPUTER ANIMATION
OF RECONFIGURABLE ROBOTIC SYSTEMS

by

RICHARD NELSON HOOPER, B.S.

THESIS

Presented to the Faculty of the Graduate School of
The University of Texas at Austin
in Partial Fulfillment
of the Requirements
for the Degree of

MASTER OF SCIENCE IN ENGINEERING

THE UNIVERSITY OF TEXAS AT AUSTIN

DECEMBER 1990

Chapter 1

Introduction

Computer animation provides a means of viewing robot motion to aid in human perception and decision making for both design and operation. Current applications of computer animation to robotics have focused on the simulation and programming of existing robots. The most common uses are workcell design, off-line programming and the promotion of research programs. Since robots are usually purchased in their final configuration, there has been little demand for computer applications that aid in the design of the robot itself. The development of a modular reconfigurable robotic architecture presents an excellent opportunity to apply computer animation to the early stages of the robot design. Interactive software packages that generate computer animations have found wide acceptance for programming and simulating industrial robots. Animated workcell design involves graphically placing the robot in its environment, also called the workcell. Machines, tools, parts and any other objects that the robot will interact with are also placed in the workcell.

Figure 1.1: Simulation of a common industrial robot performing a pick and place operation.

Off-line programming uses animation to replace the actual robot while programming the robot's motion and its interactions with its environment. This allows the actual robot to remain in service while programs are being developed and thus decreases costly downtime [24]. Research program promotion is also a very important application of computer animation. Computer animation can be used to effectively convey ideas while an impressive graphical simulation of a robot performing a complex maneuver will enhance a company's or research program's high-tech image. 

Current robots are purchased in their final configuration from the robot manufacturer. These robots are typically designed to perform a specific task, and if the application changes significantly the robot is rendered obsolete. The development of a generalized modular robotic architecture using a set of one, two and three degree of freedom joint modules and generic links greatly reduces the threat of obsolescence of the robotic system [ 46]. A modular architecture also represents an excellent opportunity to use interactive computer animation in the development of the robot itself, as well as in the development of robot technology through research enhanced by the use of three-dimensional computer animation as a visualization tool. 

Available graphics workstations can produce very smooth animations of a robot moving in a complex environment. Dedicated graphics hardware performs the calculations necessary to display solid-surface models on the computer screen. These images are able to be displayed in color, three­dimensions, perspective and with hidden surfaces removed, resulting in very realistic animations. The main drawback to using these graphics workstations is that writing the programs for computer animation is complex and quite time consuming, often requiring thousands of lines of code to produce a single animation. The difficulty and significant time investment in writing the computer animation code has led to the development of application programs that aid in the production of computer animations on graphics workstations [9][11][26][32]. 

1.1 Current Uses of Computer Animation in Robotics 
1.1.1 Workcell Design
Computer animation enjoys widespread application in the design and programming of robotic workcells [3]. In animated workcell design the robot is graphically placed in an environment with the tools, machines and other objects that it will interact with while performing its task. The arrangement of these objects and the robot path through the environment can be visually simulated. Potential problems often become illuminated during animation and the cycle times of the robot can be studied. 

 A robot workcell contains all of the physical objects that the robot will interact with while performing its task. The cell may include process machinery, inspection equipment and material handling devices as well as many other types of specialized tools. Cell layout involves graphically placing the robot among these objects such that the robot may perform its task as efficiently as possible. All of the objects must be placed within the robot's reach. The use of computer animation allows many different arrangements to be simulated and compared without requiring that the actual robot be taken off line. 

There is also an extremely large number of paths that the robot can take while performing its task. Interactive computer graphics has proven to be an effective method of visualizing the path planning process [51]. The workcell designer visually inspects the configuration of the cell and chooses the path for the robot to take while performing its task. The path is then communicated to the graphics program for animation. The cell designer then visually evaluates the path and makes iterations until acceptable results are achieved. 

The computer animation will highlight potential problems with the workcell design and path plan before the actual robot has a potentially disastrous problem. An excellent example of this is collision detection. The workcell designer can see collisions between graphical objects and modify the cell layout and path plan before any actual collisions occur. It is also possible to have the computer animation automatically check for collisions and visually highlight them, such as by changing surf ace colors. The consequences of a collision in the actual workcell could be extremely expensive as well as creating a tremendous safety hazard. 

Cycle times are another aspect of workcell design that can be studied using computer animation. The cycle time refers to the amount of time that it takes the robot to perform or cycle through its task. The cycle time can be predicted by incorporating a dynamic model with the computer animation. Cycle time is a very important consideration when integrating the robot into the entire production process. Computer animation helps the workcell designer envision the phase relationships between the operation of the robot and other processes involved in the production process. Accurate prediction of cycle times helps the production engineer determine what level of throughput can be expected from the robotic workcell.