Application of a Precision-Enhancing Measure in 3D Rigid-Body Positioning Using Camera-Space Manipulation

Abstract

This article presents an iterative procedure for improving the precision obtainable with camera-space manipulation. It also reports on extensive experimental results using this procedure with a task of some historical note in the area of vision-guided robotics, a task that involves close-tolerance, 3D, rigid-body assembly. The procedure was devised to achieve higher pre cision by introducing to parameter estimates the accuracy of the "perspective" camera model, while retaining the numerical advantage of the orthographic model. The camera-space coor dinates of each of several visually detected cues on the grasped object are multiplied by an iteratively improved correction fac tor, so that the modified image-plane appearances of the cues more closely approach the ideal of an orthographic projection. The correction factor is normalized near the point of maneuver termination so that camera-space maneuver objectives may stay unchanged. A similar strategy may be used to determine the camera-space objectives themselves. Results of experimental and simulation studies are presented and discussed.

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

“…In the first step, the method uses an orthographic camera model [31] and the nominal forward kinematics model of the robot arm. In the second step, which is known as flattening, the effect of perspective projection is included in order to increase the precision of the orthographic model [30].…”

“…It is important to distinguish between the new method and a previous pinhole-based method discarded in former works [20], [30]. That proposal used the nonlinear equations associated with the pinhole model.…”

Automatic visual guidance of a forklift engaging a pallet

“…2, and camera reference frames, Fig. 2, to obtain identical results as would have been achieved by using the more accurate 'pin-hole' camera model (see [7] for more detail).…”

“…MCSM is an extension of standard Camera-Space Manipulation (CSM), a control strategy that has proven through years of testing to provide highly accurate control of holonomic systems using fixed cameras [5][6][7]. Standard CSM has even been used to control a mobile manipulator, a miniature 'simulated' forklift [8,9].…”

<title>Nonholonomic camera-space manipulation using cameras mounted on a mobile base</title>

“…The alternative of "Camera-Space Manipulation," introduced in 1986 and subsequently developed, [1][2][3]7,14,[24][25][26][27][28][29] is highly effective in situations where, during maneuver execution, the participating, uncalibrated, wall-or tripodmounted cameras can reliably be counted upon to remain stationary between the time of visual access to the workpiece (prior to any blockage) and the time of maneuver culmination, and where the workpiece also remains stationary. CSM is especially useful where maneuver closure itself can cause significant obscuration to cameras of the visual error prior to maneuver culmination.…”