Motion system

Abstract: Our visual system can solve the difficult problem of representing multiple motions in the same part of the visual space, the motion transparency problem. We investigated the conditions under which transparent motion perception occurs through psychophysical observations, using a series of visual displays composed of two simple patterns moving in opposite directions. We found that whenever a display has finely balanced opposing motion signals in all local regions, it is perceptually nontransparent. The displays that appeared transparent always contain locally unbalanced motion signals, with some local regions having net motion signals in one direction and some other regions in the opposite direction. These interdigitating net motion signals in both directions appear to be integrated separately to form two overlapping transparent surfaces. Displays that were spatially balanced could be made perceptually transparent if the two components moving in opposite directions were at different stereo depth planes or had different spatial frequency contents. Our results can be explained by proposing a disparity- and spatial frequency-specific suppression stage in the motion pathway, at which motion signals of different directions, but of the same disparity and spatial frequency contents, locally inhibit each other. Such a mechanism would suppress noise input to the motion system, which generally activates several direction channels simultaneously, and would still not eliminate activity evoked by transparent surfaces that are at different depths or have different textures.

Abstract: An XY stage for precision movement for use in aligning a wafer in a microlithography system. A main stage supporting the wafer straddles a movable beam that is magnetically driven in a first linear direction in the XY plane. A follower stage, mechanically independent of the main stage, also moves in the first linear (X) direction and its motion is electronically synchronized by a control system with the main stage motion in the X direction. Electromagnetic drive motors include magnetic tracks mounted on the follower stage which cooperate with motor coils mounted on the edges of the main stage to move the main stage in a second linear (Y) direction normal to the X direction. Thus the main stage is isolated from mechanical disturbances in the XY plane since there is no mechanical connections and is lightened by removing the weight of the magnetic tracks from the beam. A cable follower stage moves in the Y direction on the follower stage and supports the cables connecting to the main stage, thereby reducing cable drag. An air circulation system is provided in the magnetic tracks on the follower stage to remove heat from operation of the electromagnetic motors. Air is removed from a central region of each track by a vacuum duct enhanced by air plugs fitting at the two ends of the motor coil assembly on the main stage to contain the air therein.

Abstract: To make a robot track a given desired motion trajectory, a learning control scheme is proposed which is based on the repeatability of robot motion. In this scheme the robot obtains a desired motion by repeating trials (test motion). A merit of this control scheme is that the input torque pattern that generates the desired motion can be formed without estimating the physical parameters of robot dynamics. In practice, to allow the robot motion to approach the desired one in each trial, the input torque given to the robot at the present trial is modified only by the velocity signal of the real robot motion at the previous trial and the desired one. The convergence to the desired motion is theoretically proved for a linear time-varying mechanical system, which is an approximate representation of nonlinear robot dynamics in the vicinity of the desired motion. The effectiveness of this control scheme is demonstrated through actual experiments in which a revolute-type manipulator with three degrees of freedom is used, and the desired motion trajectory is given not only in terms of joint-angle coordinates but also in terms of task-oriented coordinates. >

Abstract: In biaxial motion systems, applying the cross-coupled control (CCC) significantly improves contouring accuracy for linear and circular contours. As geometrical and parametric curves become more popular in modern manufacturing, machining processes with multiaxis motion systems are required, however, the available biaxial CCC cannot be directly applied to arbitrary contours with multiaxis machining systems. In this paper, we propose a novel approach for arbitrary contours by estimating the contouring error vector to efficiently determine the variable gains for CCC. Experimental results for a biaxial motion system indicate that the proposed approach efficiently yields variable gains similar to those in traditional CCC. Furthermore, results on a three-axis CNC machining center show that the present approach significantly improves motion accuracy in multiaxis motion systems.