Autonomous Mechanical Assembly on the Space Shuttle: An Overview

The space shuttle will be equipped with a pair of 50 ft. manipulators used to handle payloads and to perform mechanical assembly operations. Although current plans call for these manipulators to be operated by a human teleoperator. The possibility of using results from robotics and machine intelligence to automate this shuttle assembly system was investigated. The major components of an autonomous mechanical assembly system are examined, along with the technology base upon which they depend. The state of the art in advanced automation is also assessed

Simplifying Tool Usage in Teleoperative Tasks

Modern robotic research has presented the opportunity for enhanced teleoperative systems. Teleprogramming has been developed for teleoperation in time-delayed environments, but can also lead to increased productivity in non-delayed teleoperation. Powered tools are used to increase the abilities of the remote manipulator. However, tools add to the complexity of the system, both in terms of control and sensing. Teleprogramming can be used to simplify the operators interaction with the manipulator/tool system. Further, the adaptive sensing algorithm of the remote site system (using an instrumented compliant wrist for feedback) simplifies the sensory requirements of the system. Current remote-site implementation of a teleprogramming tool-usage strategy that simplifies tool use is described in this document. The use of powered tools in teleoperation tasks is illustrated by two examples, one using an air-powered impact wrench, and the other using an electric winch. Both of these tools are implemented at our remote site workcell, consisting of a Puma 560 robot working on the task of removing the top of a large box

Sensors: A Key to Successful Robot-Based Assembly

Computer controlled robots offer a number of significant advantages in manufacturing and assembly tasks. These include consistent product reliability and the ability to work in harsh environments. The programmable nature of robotic automation allows the possibility of applying them to a number of tasks. In particular, significant savings can be expected in batch production, if robots can be applied to produce numbers of products successfully without plant re-tooling. Unfortunately, despite considerable progress made in robot programming [Lozano-Perez 83] [Paul 81] ;Ahmad 84] [Graver et al. 84] [Bonner & Shin 82] and in sensing [Gonzalez & Safabakhsh 82] [Fu 82] [Hall et al. 82], [Goto et al. 80], [Hirzinger & Dietrich 86], [Harmon 84], kinematics and control strategies [Whitney 85] [Luh S3] [Lee 82], a number of problems still remain unsolved before en-mass applications take place. In fact, in current applications, the specialized tooling for manufacturing a particular product may make up as much as 80% of the production line cost. In such a production line the robot is often used only as a programmable parts transfer device. Improving robots ability to sense and adapt to different products or environments so as to handle a larger variety of products without retooling is essential. It is just as important to be able to program them easily and quickly, without requiring the user to have a detailed understanding of complex robot programming languages and control schemes such as RCCL [Hayward & Paul 84], VAL-II [Shimano et al., 84], AML [Taylor et al., 83], SR3L-90 [Ahmad 84] or AL [Mujtaba & Goldman 79]. Currently there are a number of Computer Aided Design (CAD) packages available which simplify the robot programming problem. Such packages allow the automation system designer to simulate the assembly workcell which may consist of various machines and robots. The designer can then pick the motion sequences the robot has to execute in order to achieve the desired assembly task. This is done by viewing the motions on a graphical screen from different viewing angles to check for collisions and to ensure the relative positioning is correct, much the same way1 as it is done in on-line teach playback methods (see Figure 1). Off-line robot programming on CAD stations does not always lead to successful results due to two reasons: (i) The robot mechanism is inherently inaccurate due to incorrect kinematic models programmed in their control system [Wu 83] [Hayati 83] [Ahmad 87] [Whitney et ■ al. 84]. (ii) The assembly workcell model represented in the controller is not accurate. As a result parts and tools are not exactly located and their exact position may vary. This causes a predefined kinematic motion sequence program to fail, as it cannot deal with positional uncertainties. Sensors to detect real-time errors in the part and tool positions are obviously required with tailored sensor-based motion strategies to ensure assembly accomplishment. In this chapter we deal with how sensors are used to successfully ensure assembly task accomplishment. We illustrate the use of various sensors by going through an actual assembly of an oil pump. Additionally we illustrate a number of motion strategies which have been developed to deal with assembly errors. Initially, we discuss a number of sensors found in typical robotic assembly systems in Section 1. In Section 2 we discuss how and when sensors are to be used during an assembly operation. Issues relating to sensing and robust assembly systems are discussed very briefly in Section 3. Section 4 details a sensor-based robot assembly to illustrate practical applications

Robot Manipulator Control and Computational Cost

In this paper robot control algorithms are considered from the point of view of computational complexity. All the algorithms provide for hybrid position and force control which is appropriate to unstructured environments. Both joint coordinate and generalized coordinate motion schemes are considered. The findings are interesting in that the peripheral processing involved in all methods, sometimes, swamps the orders of magnitude differences in computation involved in the inner loops. It is also interesting to note the similarity in complexity between direct methods and differential. Between joint coordinate methods and generalized coordinate methods there is a general two to one ratio in complexity. In general a 0.75 M Flop, 1.25 Mip machine is required to provide for a control rate of 250 hz

Planificación automática y supervisión de operaciones de montaje mediante robots

One of the main topics to be solved in order to fully automate a robotized assembly task is the automatic determination of the movements to be done by the robot to properly perform the tasks when the existing uncertainty is not negligible. This problem is of particular theoretical and practical interest when rotational degrees of freedom and friction forces are taken into account. In this thesis, an automatic movement planner that considers these aspects is proposed, including the description of how to execute the plan and supervise the evolution of the task. In order to generate the plan, the task is represented by a finite number of states, which are associated to the nodes of a graph with the links connecting contiguous states. Then, using uncertainty models developed in the thesis, the domains of the possible configurations and reaction forces that can be measured by the corresponding sensors in each task state are determined. From the existing initial conditions of the task and the desired final conditions, an initial and a goal state are determined, and, using the state graph, a sequence of contiguous states joining them is searched. At the same time, state transition operators (movement directions of the robot) that may allow the transition from one state to the next in the sequence are also determined.The execution of the task according to the plan basically consist in the estimation of the current state by matching the sensorial information obtained on-line with the domains of configuration and force of each state, and then, the application of the proper state transition operator to proceed in the state sequence towards the goal state.The main contributions of the thesis are the following: on one side, as a general contribution, the proposed planning procedure that allows the simultaneous consideration of friction forces, rotational degrees of freedom, and the different uncertainty sources that affect a robotized task; on the other side, as more specific contributions, the proposal of task states as the occurrence of a set of basic contacts, and, for movements on a plane, the fusion of the uncertainty models and the determination of the reaction forces possible in any contact situation by using the dual representation of the force lines. The thesis includes the application of the developed concepts to a simple assembly task (the block in the corner problem) considering movements on a plane. Although the implementation is not a general application prototype, it contributes to the validation of the theoretical results of the work.Uno de los principales problemas a resolver en la automatización total de una tarea de montaje robotizada, es la determinación automática de los movimientos que debe realizar el robot para llevar a cabo la tarea cuando la incertidumbre que le afecta es significativa. Este problema es de especial interés teórico y práctico cuando se consideran grados de libertad de rotación y fuerzas de fricción. En la tesis se propone un planificador automático de movimientos que tiene en cuenta estos aspectos. Se describe también cómo llevar a cabo la ejecución del plan y supervisar la evolución de la tarea.Para llevar a cabo la planificación, la tarea se representa mediante un conjunto finito de estados. Considerando la incertidumbre mediante modelos desarrollados en la tesis, se determinan los dominios de observación de configuraciones y de fuerzas de reacción que pueden ser indicadas por los sensores cuando tiene lugar cada estado de la tarea. Los estados de la tarea se representan como nodos de un grafo en el que los arcos unen los estados contiguos.A partir de las condiciones iniciales de la tarea y condiciones finales deseadas se establecen sendos estados inicial y final, y, utilizando el grafo de estados, se determina una secuencia de estados contiguos que los ligue. Paralelamente, se determinan operadores de cambio de estado (direcciones de movimiento del robot) que pueden permitir la transición de un estado a otro de la secuencia.La ejecución de la tarea acorde al plan consiste básicamente en estimar el estado en curso contrastando la información sensorial obtenida en-línea con los dominios de observación de configuración y fuerza, para aplicar entonces el operador de cambio de estado que corresponda, y así sucesivamente hasta alcanzar el estado final.Las principales aportaciones de la tesis son las siguientes. Por un lado, desde un punto de vista general, cabe destacar el procedimiento de planificación propuesto, que permite considerar simultáneamente fuerzas de fricción, grados de libertad de rotación y las incertidumbres que afectan a una tarea de montaje robotizada. Por otra parte, pueden mencionarse como aportaciones particulares, la introducción del concepto de estados de la tarea como ocurrencia de un determinado conjunto de contactos básicos y, para el caso de movimientos en un plano, el modelado y fusión de incertidumbre de una forma más precisa que las descritas en trabajos previos, así como la determinación de las fuerzas de reacción que pueden tener lugar en cualquier contacto mediante el uso de la representación dual de sus rectas de acción. La tesis incluye la aplicación de los conceptos teóricos desarrollados a una tarea de montaje (bloque en la esquina) considerando movimientos de los objetos en un plano. Aunque la implementación no pretende ser un prototipo de aplicación general, contribuye a la validación de los resultados del trabajo