Hiromasa Oku

Variable-focus lens with 1-kHz bandwidth

This paper proposes a variable-focus lens with 1-kHz bandwidth. The lens transforms its shape rapidly using the liquid pressure generated by a piezo stack actuator. This mechanism also includes a built-in motion amplifier with high bandwidth to compensate for the short working range of the piezo stack actuator. Prototypes have been developed to validate the proposed design. A 1-kHz bandwidth of the lenses was confirmed by measuring the frequency responses. Refractive power ranging from -1/167 to 1/129 mm(-1) and a maximum resolution of 12.3 cycles/mm were attained.

Two-dimensional tracking of a motile micro-organism allowing high-resolution observation with various imaging techniques

In this article, a micro-organism tracking system using a high-speed vision system is reported. This system two dimensionally tracks a freely swimming micro-organism within the field of an optical microscope by moving a chamber of target micro-organisms based on high-speed visual feedback. The system we developed could track a paramecium using various imaging techniques, including bright-field illumination, dark-field illumination, and differential interference contrast, at magnifications of 5 times and 20 times. A maximum tracking duration of 300s was demonstrated. Also, the system could track an object with a velocity of up to 35 000μm∕s (175diameters∕s), which is significantly faster than swimming micro-organisms.

Robust high-speed tracking against illumination changes for dynamic projection mapping

Dynamic Projection Mapping, projection-based AR for a moving object without misalignment by a high-speed optical axis controller by rotational mirrors, has a trade-off between stability of highspeed tracking and high visibility for a variety of projection content. In this paper, a system that will provide robust high-speed tracking without any markers on objects against illumination changes, including projected images, is realized by introducing a retroreflective background with the optical axis controller for Dynamic Projection Mapping. Low-intensity episcopic light is projected with Projection Mapping content, and the light reflected from the background is sufficient for high-speed cameras but is nearly invisible to observers. In addition, we introduce adaptive windows and peripheral weighted erosion to maintain accurate high-speed tracking. Under low light conditions, we examined the visual performance of diffuse reflection and retroreflection from both camera and observer viewpoints. We evaluated stability relative to illumination and disturbance caused by non-target objects. Dynamic Projection Mapping with partially well-lit content in a low-intensity light environment is realized by our proposed system.

1 ms Auto Pan-Tilt – video shooting technology for objects in motion based on Saccade Mirror with background subtraction

In this paper, the authors propose a state-of-the-art video shooting system for some randomly and quickly moving objects, which is based on our precise centering technology ‘1 ms Auto Pan-Tilt.’ It can capture the certain moving target as if it stopped and were fixed at the center of the image. In a previous study, we proposed and developed a handmade special device to control a camera gaze promptly, yet, it was not applicable for a real situation. This time, we remodeled the device as a unit with plural camera ports, which realized obtaining high-resolution movies. Moreover, with quantifying the system mathematically, we proposed a robust algorithm for a real use. Videos obtained by the new system help us grasp the detail movement of the target object more clearly, which is highly demanded in the realms of the measurement, astronomy, broadcasting service, and so on. Graphical Abstract

An improved low-optical-power variable focus lens with a large aperture

We report an improved method of fabricating a variable focus lens in which an in-plane pretension force is applied to a membrane. This method realized a lens with a large optical aperture and high performance in a low-optical-power region. The method was verified by comparing membranes in a simulation using the finite element method. A prototype with a 26 mm-diameter aperture was fabricated, and the wavefront behavior was measured by using a Shack-Hartmann sensor. Thanks to the in-plane pretension force, the lens achieved an infinite focal length with a wavefront error of 105.1 nm root mean square.

Saccade Mirror 3: High-speed gaze controller with ultra wide gaze control range using triple rotational mirrors

This paper reports the prototype of a new optical high-speed gaze controller, named Saccade Mirror 3, that overcomes the limited gaze control range (~60 deg) of our previously proposed high-speed gaze controller, called Saccade Mirror. Saccade Mirror 3 is based on three automated rotational mirrors, and this gaze control mechanism can achieve an ultrawide gaze control range of 360 deg in theory. A prototype was developed based on this mechanism. A gaze control range of over 260 degrees in the pan direction and a high-speed response of about 10 ms were confirmed. Furthermore, the prototype was applied to high-speed visual tracking coupled with a 1000 fps high-speed vision system. A visual tracking algorithm was developed for this mechanism, and high-speed tracking of a table tennis ball in play and a flying drone was successfully demonstrated.

A pair of diopter-adjustable eyeglasses for presbyopia correction

We describe and demonstrate a pair of diopter-adjustable eyeglasses aimed to correct presbyopia; the glasses provide a tunable optical power in the whole surface of the lens cell, eliminating the optical distortion typical of bifocal/trifocal or progressive glasses. The wearer can actively control the optical power by a simple sliding gesture on the bridge of the glasses, so that presbyopic vision can be interactively corrected. Results from a preliminary experiment showed that a presbyopia sufferer could clearly observe near and far objects under the assistant accommodation of the glasses. Designing a truly wearable system poses some challenges – none of them theoretical – so the system should be feasible in the near future.

Design Principles of a High-Speed Omni-Scannable Gaze Controller

We propose design principles of a high-speed omni-scannable gaze controller that is advantageous over previously proposed omni-scannable controllers in terms of response time. This is achieved by overcoming the narrow scanning range of the high-speed Saccade Mirror, a gaze controller that employs single-axis rotating mirrors, while maintaining its short response time. It is first shown that in order to achieve an omni-scan with single-axis rotating mirrors, the gaze controller must follow certain conditions. We then give design principles, and determine the positions and shapes through an optimization under evaluation functions and constraints. The response time is estimated by the inertia of the mirrors, and is shown to be superior to conventional commercial omni-scannable gaze controllers.

Mirror-based high-speed gaze controller calibration with optics and illumination control

A precise calibration method for optical high-speed gaze controllers using rotational mirrors is proposed. The mirror-based pan/tilt camera can change gaze direction more quickly than a conventional pan-tilt-zoom camera, which actuates the camera itself. The high-speed gaze controller can track moving objects at high magnification and can utilize new applications of three-dimensional measurement. However, the controller is difficult to calibrate owing to shallow depth of field (DOF) at close focus positions and mechanical differences. We propose to control optics and illumination to detect calibration pattern control points precisely against shallow DOF; we deepen the DOF using a small aperture, coaxial episcopic illumination, and a retroreflective checkerboard pattern. We introduce mirror thickness for an exact gaze control model and bundle adjustment for large center-of-projection translation. We confirm that wide gaze range calibration is achieved more accurately than when mirror thickness is not considered.

An adaptive achromatic doublet design by double variable focus lenses

An adaptive chromatic doublet that designed by doublet variable focus lenses was proposed. Two lenses were in filled with different liquids, so that the lenses could perform low and high dispersion proprieties. The proposed doublet could performance a tunable focal length, and meanwhile its chromatic aberration could be corrected. Four available liquids candidates were proposed to fabricate two variable focus lenses that would be designed with liquid-membrane-liquid structure, so that they could realize a large aperture adaptive achromatic doublet. The improvement of the achromatic behaviors was confirmed that the chromatic focal shift range was 2.5% for the adaptive singlet and 0.05% for the adaptive doublet.