Masaaki Omoto

Basic performance of a desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance controllability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots with high position resolution. A tool attached to the tip of the z-axis has a small ball-end shape. Also, the control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feedforward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Further, the position feedforward loop leads the tool tip along cutter location data. It is expected that the NC machine tool delicately removes surface cusps with under about 0.3 mm height on a mold, and finishes the surface with high quality. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash that causes the position inaccuracy at the tip of the abrasive tool, through a simple position/force measurement. Through a similar position/force measurement and a surface following control experiment along a lens mold, the basic position/force controllability of the proposed NC machine tool is demonstrated.

High precision polishing robot using a learning-based surface following controller

In this paper, a high precision polishing robot with a learning-based surface following controller is proposed for polishing PET (poly ethylene terephthalate) bottle molds with curve surface. The shape of a mounted abrasive tool, attached to the tip of the robot arm, is a ball-end type. When a PET bottle mold with a large curvature is polished, not only the orientation of the mounted abrasive tool is fixed but also its revolution is locked. The motion of the mounted abrasive tool is feedforwardly controlled based on initial trajectory calculated in advance. The trajectory is generated by cutter location data constituted from a CAM system. The trajectory is modified through the process of actual polishing. The surface is polished by a polishing force acting between the mold and the abrasive tool. The polishing force is assumed to be considered as a composite force of the contact and kinematic friction forces, in which the friction consists of Coulomb and viscous frictions. Velocities in the normal and tangent directions are delicately controlled so that the proposed system is effective for obtaining a polishing surface as achieved by skilled workers.

Intelligent desktop NC machine tool with compliant motion capability

In this paper, a new desktop NC machine tool with compliance control capability is presented for finishing metallic molds with small curved surface. The NC machine tool consists of three single-axis robots. Tools attached to the tip of the z-axis are ball-end abrasive tools. The control system of the NC machine tool is composed of a force feedback loop, position feedback loop and position feed-forward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction force. The position feedback loop controls the position in pick feed direction. Further, the position feed-forward loop leads the tool tip along cutter location data. In order to first confirm the application limit of a conventional industrial robot to a finishing task, we evaluate the backlash that causes the position inaccuracy at the tip of an abrasive tool, through a simple position/force measurement. Through a similar measurement and a surface following control experiment along a lens mold, the basic position/force controllability with high resolutions is demonstrated.

Generation of normalized tool vector from 3-axis CL data and its application to a mold polishing robot

Cutter location (CL) data with normal vectors can be used for not only a desired trajectory of tools translational motions but also a desired force direction for molds. In this paper, such normalized tool vectors from 3-axis CL data are generated for a polishing robot. The resultant CL data allow the polishing robot based on an industrial robot to realize a teaching-less operation of position and force. The present robot can also control the polishing force consisting of the contact and kinetic friction forces. During the polishing of a mold, a position feedback loop has a delicate contribution to the force feedback loop in Cartesian space so as not to make the tool deviate from the desired trajectory. The effectiveness and validity of the proposed robot have been proved by actual polishing experiments using an aluminum mold with curved surface.

Orthogonal-type robot with a CAD/CAM-based position/force controller

In this paper, a new desktop orthogonal-type robot with a CAD/CAM-based position/force controller is presented for finishing small metallic molds with curved surface. The robot consists of a three-axis robot whose single one has a high position accuracy of 1 µm, which means that it can perform higher resolutions of position and force, compared to general industrial robots. A thin wood stick tool with a ball-end tip is attached to the z-axis through a force sensor. The control system of the robot is comprised of a force feedback loop, position feedback loop and position feedforward loop. The force feedback loop controls the polishing force consisting of tool contact force and kinetic friction forces. The position feedback loop controls the position in pick feed direction. Further, the position feedforward loop leads the tool tip along a spiral path. We first evaluate the backlash that causes inaccuracy in position at the tip of the abrasive tool, by simply measuring the position and force. Next, a surface following control experiment along a lens mold is conducted, in which the mold has axis-symmetric concave areas. Finally, a LED lens mold is further finished by using the proposed system in order to demonstrate the performance and promise.

An open-architecture-based hybrid control method with a weak coupling between position feedback-loop and force feedback-loop (application to a mold polishing robot)

Cutter location (CL) data with normal vectors can be used for not only a desired trajectory of tools translational motion but also desired force directions for a mold polishing robot. In this paper, such normalized tool vectors are systematically generated from 3-axis CL data. The resultant CL data allow the polishing robot with an abrasive tool to realize a teaching-less operation of position and force. The present robot can also control the polishing force consisting of the contact and kinetic friction forces. During the polishing of a mold, a position feedback loop has a delicate contribution to the force feedback loop in Cartesian space so that a stable force control and an accurate pick feed control can be simultaneously achieved. The effectiveness and validity of the proposed robot have been proved by actual polishing experiments using a duralumin mold with curved surface.