Emilio J. González-Galván

An efficient multi-camera, multi-target scheme for the three-dimensional control of robots using uncalibrated vision

Abstract A vision-based control methodology is presented in this paper that can perform accurate, three-dimensional (3D), positioning and path-tracking tasks. Tested with the challenging manufacturing task of welding in an unstructured environment, the proposed methodology has proven to be highly reliable, consistently achieving terminal precision of 1 mm . A key limiting factor for this high precision is camera–space resolution per unit physical space. This paper also presents a means of preserving and even increasing this ratio over a large region of the robots workspace by using data from multiple vision sensors. In the experiments reported in this paper, a laser is used to facilitate the image processing aspect of the vision-based control strategy. The laser projects “laser spots” over the workpiece in order to gather information about the workpiece geometry. Previous applications of the control method were limited to considering only local, geometric information of the workpiece, close to the region where the robots tool is going to be placed. This paper presents a methodology to consider all available information about the geometry of the workpiece. This data is represented in a compact matrix format that is used within the algorithm to evaluate an optimal robot configuration. The proposed strategy processes and stores the information that comes from various vision sensors in an efficient manner. An important goal of the proposed methodology is to facilitate the use of industrial robots in unstructured environments. A graphical-user-interface (GUI) has been developed that simplifies the use of the robot/vision system. With this GUI, complex tasks such as welding can be successfully performed by users with limited experience in the control of robots and welding techniques.

Workspace and Payload-Capacity of a New Reconfigurable Delta Parallel Robot

In this paper the workspace and payload capacity of a new design of reconfigurable Delta-type parallel robot is analysed. The reconfiguration is achieved by adjusting the length of the kinematic chains of a given robot link simultaneously and symmetrically during the operation of the robot. This would produce a dynamic workspace in shape and volume. A numerical analysis of the variation of shape and volume of the workspace and payload capacity of the robot is presented. Based both on the results of this analysis and on practical requirements, a proposal for the design of a reconfiguring mechanism is presented.

Towards a robotic plasma spraying operation using vision

An uncalibrated, vision-guided robotic system, based on the method of camera-space manipulation, has been developed to reduce the time and cost associated with teaching a robot a suitable trajectory for plasma coating. The system achieves a high level of precision in both position and orientation control of a 6-DOF robotic arm.

Optimization of Industrial, Vision-Based, Intuitively Generated Robot Point-Allocating Tasks Using Genetic Algorithms

Current industrial robot-programming methods require, depending on the task to be developed, an elevated degree of technical ability and time from a human operator, in order to obtain a precise, nonoptimal result. This correspondence paper presents a methodology used to generate an optimal sequence of robot configurations that enable a precise point-allocating task applicable, for instance, to spot-welding, drilling, or electronic component placement maneuvers. The optimization process starts from a nonoptimal, initial sequence designated intuitively by a human operator using an easy-to-use interface. In this correspondence paper, intuitive programming is considered as the process of defining, in a computer graphics environment and with a limited user knowledge of robotics or the industrial task, the sequence of motions that enable the execution of a complex industrial robotic maneuver. Such an initial sequence is later followed by a robot, very precisely, using a vision-based, calibration-free, robot control method. Further robot path optimization is performed with a genetic algorithm approach. An industrial robot, which is part of the experimental setup, was used in order to validate the proposed procedure.

A Dynamic-compensation Approach to Impedance Control of Robot Manipulators

This paper presents an impedance–control strategy with dynamic compensation for interaction control of robot manipulators. The proposed impedance controller has been developed considering that the equilibrium point of the closed-loop system, composed by the combination of the controller and the full nonlinear robot dynamics is, locally, asymptotically stable in agreement with Lyapunov’s direct method. The performance of the proposed controller is verified through simulation and experimental results obtained from the implementation of an interaction task involving a two degree-of-freedom, direct-drive robot.

The differential calculus of screws: Theory, geometrical interpretation, and applications

Abstract This article presents a novel and original formula for the higher-order time derivatives, and also for the partial derivatives of screws, which are successively computed in terms of Lie products, thus leading to the automation of the differentiation process. Through the process and, due to the pure geometric nature of the derivation approach, an enlightening physical interpretation of several screw derivatives is accomplished. Important applications for the proposed formula include higher-order kinematic analysis of open and closed kinematic chains and also the kinematic synthesis of serial and parallel manipulators. More specifically, the existence of a natural relationship is shown between the differential calculus of screws and the Lie subalgebras associated with the expected finite displacements of the end effector of an open kinematic chain. In this regard, a simple and comprehensible methodology is obtained, which considerably reduces the abstraction level frequently required when one resorts to more abstract concepts, such as Lie groups or Lie subalgebras; thus keeping the required mathematical background to the extent that is strictly necessary for kinematic purposes. Furthermore, by following the approach proposed in this article, the elements of Lie subalgebra arise in a natural way — due to the corresponding changes in screws through time — and they also have the typical shape of the so-called ordered Lie products that characterize those screws that are compatible with the feasible joint displacements of an arbitrary serial manipulator. Finally, several application examples — involving typical, serial manipulators — are presented in order to prove the feasibility and validity of the proposed method.

Camera pan/tilt to eliminate the workspace-size/pixel-resolution tradeoff with camera–space manipulation

Abstract The successful implementation of close-tolerance, three-dimensional rigid body assembly has been robustly achieved using camera-space manipulation in a limited region of the manipulators workspace. The extension of this capability to a broader region can in general be achieved by mounting the cameras on computer-controlled platforms or “pan/tilt” units. The use of this type of platform enables the encompassing of a large physical region within the fields of view of the cameras, while preserving an approximately constant image-plane resolution per unit physical space. The paper describes the derivations involved in the determination of view parameters when the information of the angles of pan/tilt rotation of the cameras is available. Such procedure enables adequate parameter observability with a greatly reduced sampling in terms of number and breadth. Practical considerations for the implementation of this capability for a high-precision, three-dimensional task across a large workspace region are also presented.

Efficient Camera-Space Target Disposition in a Matrix of Moments Structure Using Camera-Space Manipulation

This paper introduces a newestimation approach for determining the sequence of internal manipulator configurations which are required to perform a task on an arbitrarily positioned and oriented workpiece, in the context of the method of camera-space manipulation— a robust and precise means of controlling three-dimensional robot maneuvers using vision. Despite a nonlinear estimation model, a recursive scheme is developed. This approach reduces the computational and memory burden that is required by the “batch” estimation approach while retaining identical results. The same formalism that permits this result is used to condense to a minimum the visual information required to create “camera-space objectives.” The discussion includes actual experimental results wherein robust, millimeter six-axis positioning precision with a three-dimensional, rigid-body task is achieved using a very large GMF S-400 robot.

Path-Tracking Maneuvers With Industrial Robot Manipulators Using Uncalibrated Vision and Impedance Control

This paper presents an interaction control strategy for industrial robot manipulators which consists of the combination of a calibration-free, vision-based control method with an impedance-control approach. The vision-based, robot control method known as camera-space manipulation is used to generate a given, previously defined trajectory over an arbitrary surface. Then, a kinematic impedance controller is implemented in order to regulate the interaction forces generated by the contact between the robot end-effector and the work surface where the trajectory is traced. The paper presents experimental evidence on how the vision-force sensory fusion is applied to a path-tracking task, using a Fanuc M16-iB industrial robot equipped with a force/torque sensor at the wrist. In this task, several levels of interaction force between the robot end-effector and the surface were defined. As discussed in the paper, such a synergy between the control schemes is seen as a viable alternative for performing industrial maneuvers that require force modulation between the tool held by the robot and the working surface.

Robot Positioning Using Camera-Space Manipulation With a Linear Camera Model

This paper presents a new version of the camera-space-manipulation method (CSM). The set of nonlinear view parameters of the classic CSM is replaced with a linear model. Simulations and experiments show a similar precision error for the two methods. However, the new approach is simpler to implement and is faster.