Yoshihiko Koseki

Design and accuracy evaluation of high-speed and high precision parallel mechanism

We have developed a precise and high-speed arm applied to assembly processes in electrical product and machine industries. The arm is designed based on the requirement from Japanese major industries. The paper addresses the background of the development, the required specification for the robot arm, and the brief introduction of the prototype arm and evaluations of accuracy. We test the repeatability of parallel mechanism. Then we calibrate the kinematic model of parallel mechanism to improve its absolute accuracy using laser tracking coordinate measuring system.

The first measurement of a three-dimensional coordinate by use of a laser tracking interferometer system based on trilateration

A three-dimensional coordinate of a target position was measured using a laser tracking interferometer system based on laser trilateration. Laser interferometers, which are mounted on two-directional rotating stages, track the motion of the target retroreflector. By applying the principle of trilateration, the position of the retroreflector is estimated using the optical path difference caused by the motion of the target. Four laser interferometers were used, which produced redundancy in the measurement. By taking advantage of the redundancy, the position of the interferometers and the initial position of the target is self-calibrated and consequently the target position was calculated. The measurement error of a preliminary experiment was about m for a 1 m measurement.

Kinematic analysis of translational 3-DOF micro parallel mechanism using matrix method

We apply the matrix method to kinematic analysis of our translational 3-DOF micro parallel mechanism for an instance of general flexure mechanisms. The matrix method has been well developed in architecture to analyze a frame structure. We found that this method is well applicable to such a flexure mechanism with circular notched hinges as our micro parallel mechanism because it is approximate to the Rahmen structure. Our matrix method can calculate a compliance matrix with less nodes of matrix than conventional finite element method. First, the compliance matrices of a circular notched hinge and some other beams are defined and the coordinate transformations of compliance matrix are introduced. Next, an analysis of our micro parallel mechanism is demonstrated.

Kinematic analysis of a translational 3-d.o.f. micro-parallel mechanism using the matrix method

In this paper, we applied the matrix method to kinematic analysis of our translational 3-d.o.f. micro-parallel mechanism for an instance of general flexure mechanisms. The matrix method has been well developed in architecture to analyze frame structures. We found that this method is well suited to such a flexure mechanism with circular notched hinges as our micro-parallel mechanism because it can be approximated to a Rahmen structure. Our matrix method can calculate a compliance matrix with less matrix nodes than the conventional finite element method. First, the compliance matrices of a circular notched hinge and some other beams are defined, and the coordinate transformations of the compliance matrix are introduced. Secondly, an analysis of our micro-parallel mechanism is demonstrated.

Endoscope Manipulator for Trans-nasal Neurosurgery, Optimized for and Compatible to Vertical Field Open MRI

This paper preliminarily reports the robotic system working inside the gantry of vertical field Open MRI. This manipulator is new in terms of the application to vertical field Open MRI, cost effectiveness, accuracy and stiffness sufficient for endoscope manipulation. The endoscope manipulation for trans-nasal neurosurgery under MR-guidance was selected as the sample task. The endoscope operation in MR-gantry might provide the surgeon(s) with real-time feedback of MR image to endoscopic image and the reverse. This facilitates the comprehensive understanding, because MRI compensates the vision lost through narrow opening of keyhole surgery with global view. So this surgery is a good motivation for combination of MRI and robotic systems. In this paper, the design and implementation are presented and preliminary test shows good MR-compatibility, accuracy and stiffness.

Design of 3-DOF parallel mechanism with thin plate for micro finger module in micro manipulation

A dexterous micro manipulation system was developed for applications such as assembling micro machines, manipulating cells, and micro surgery. We (1996, 1999) have proposed a concept of a two fingered micro hand, and designed and built a prototype. We succeeded in performing basic micro manipulations, including the grasp, release, and rotation of a microscopic object. The two-fingered micro hand prototype needs to be more miniaturized for higher accuracy and use in the small chamber of SEM. In this paper, we propose a new 3-DOF parallel mechanism for the micromanipulator in order to achieve low cost and small size. The new mechanism is only used for punching holes and bending a thin plate. The two-fingered micro hand with the mechanism was designed and a prototype developed. An experiment shows the excellent micro capability of the mechanism.

Robotic Assist for MR-Guided Surgery Using Leverage and Parallelepiped Mechanism

In this paper, we would propose a novel mechanism of surgical manipulator, which assists the surgeon in precise positioning and handling of surgical devices, like biopsy needle, endscope, in MR-guided surgery. This mechanism can transmit 3 translational and 3 rotational motion from the outside to the inside of MR imaging area using leverage and parallelepiped mechanism. Such a remote actuation is significantly helpful for robotic assist under MR-guided surgery because the strong magnet of MR denies the existence of magnetic and electric devices around imaging area. This mechanism also has merits of the mechanical safety and simple shape. The combination of stereotactic imaging and precise positioning would enable a less invasive surgery in brain and spine surgery.

Restriction on the arrangement of laser trackers in laser trilateration

Laser trilateration is an effective technique for measuring three-dimensional coordinates. Taking advantage of a fourth laser tracker, the positions of all four laser trackers can be determined by a self-calibration algorithm. We show a restriction on the arrangement of laser trackers, namely, no tracker must exist on the plane defined by the other three trackers. A method of evaluating the measurement results is also discussed.

Coaxial Needle Insertion Assistant With Enhanced Force Feedback

Many medical procedures involving needle insertion into soft tissues, such as anesthesia, biopsy, brachytherapy, and placement of electrodes, are performed without image guidance. In such procedures, haptic detection of changing tissue properties at different depths during needle insertion is important for needle localization and detection of subsurface structures. However, changes in tissue mechanical properties deep inside the tissue are difficult for human operators to sense, because the relatively large friction force between the needle shaft and the surrounding tissue masks the smaller tip forces. A novel robotic coaxial needle insertion assistant, which enhances operator force perception, is presented. This one-degree-of-freedom cable-driven robot provides to the operator a scaled version of the force applied by the needle tip to the tissue, using a novel design and sensors that separate the needle tip force from the shaft friction force. The ability of human operators to use the robot to detect membranes embedded in artificial soft tissue was tested under the conditions of 1) tip force and shaft force feedback, and 2) tip force only feedback. The ratio of successful to unsuccessful membrane detections was significantly higher (up to 50%) when only the needle tip force was provided to the user.

Remote actuation mechanism for MR-compatible manipulator using leverage and parallelogram - workspace analysis, workspace control, and stiffness evaluation

In this paper, a novel mechanism of remote actuation was proposed and its mechanical problems were discussed. This mechanism consists of leverage and parallelogram mechanism and transmits 3 d.o.f translational and 3 d.o.f rotational motions from the input to output. Such a remote actuation is significantly useful for robotic assist around MRI where the strong and precise magnet is used for imaging, because mutual effect between MRI and robot are inverse proportional to the distance. In this paper, the basic ideas of mechanism were introduced firstly. The discussions of its stiffness and workspace conclude their trade-off. Our new idea of workspace control for mechanical safety is preliminary discussed.