## Research history

We have been studying gyro power generation since 2005. The start is JST’s subsidy business. “Strategic Creative Research Promotion Project CREST, Research Area” Advanced Integrated Sensing Technology “, Research Project” Mobile Sensing Technology for Safety and Security “, 2005-2011, Principal Investigator Tomomasa Sato” So, in 2008, we developed a vibration power generator that generates electric power from the vibration of a moving object (1). This is the first gyro generator. This is a Dynabee with a coil and magnet mounted, and the output is 0.1W or more. However, it has the disadvantage that it generates electricity only with specific vibrations determined by the rotation speed. Specifically, the frequency ratio of input vibration to rotation speed must match the ratio of track diameter to rotation axis diameter. Also, the initial speed of rotation had to be given by hand, and it did not work unattended. After that, similar generators were commercialized by several Western ventures, but all had similar problems and were at the toy level.

In 2009, we conducted a transient response analysis of Dynabee in order to expand the vibration frequency band that can generate electricity (2). As a result, it was found that the vibration frequency that can generate electricity has a slight range with respect to the rotation speed. When the frequency ratio of vibration and rotation is close to the above diameter ratio, the rotation speed changes arbitrarily and matches the diameter ratio. It was also found that the width of this stable region increases as the electromagnetic damping decreases.

(2)

In 2011, based on this principle, we announced a method to change the electromagnetic damping according to the input vibration (3). The smaller the electromagnetic damping, the more stable it is, but the smaller the amount of power generation. Therefore, when the frequency ratio of vibration and rotation is far from the target value, the electromagnetic damping is lowered, and when it is close, it is raised. Electromagnetic damping is controlled by winding multiple coils and changing the number of coils connected to the load. This increased the stability range, but the effect was small.

In 2011, the stable range will be greatly expanded, and the start of rotation will be resolved. Announced self-starting method (4). This is a way to have a small battery and let the generator act as a motor. At the start of rotation, the motor is started by the electric power from the storage battery. In addition, the rotation speed is changed by the motor according to the input vibration. Previously it was passive control, but this is active control that uses generated power. With this, it is possible to rotate and generate electricity at any rotation speed and any input vibration. However, this method also had its drawbacks. The problem was that the power required to change the rotation speed was large. When the vibration changes drastically, the power consumption of the motor becomes larger than the amount of power generated, and it no longer functions effectively as a generator.

In 2018, we announced a motor-rotating generator that develops self-starting and separates the motor for rotation and power generation (5). It generates electricity even with random vibration and generates 1.8W. The reason why Dynabee generates electricity only with specific vibrations is that rotation and precession are combined by rolling. When the direction of the input vibration is reversed, the precession is reversed, the rotation torque is reversed, and the torque that slows down the rotation works. If a ratchet can be inserted between the precession and the rotation to make the rotation torque unidirectional, this problem will be solved. However, the ratchet cannot be used due to its large friction and dimensions. Therefore, we devised a method to electrically make the torque unidirectional. The basis is self-starting. Since gyro torque is generated in the precession direction, a generator is attached to the precession shaft to generate electricity, rectified in one direction by a diode bridge, and input to another motor attached to the rotation shaft. I immediately came up with this method, but when I actually made it, the amount of power generated was small and I couldn’t rotate it.

I can’t rotate. After several years of trial and error, it was found that a small-diameter gear should be used to accelerate precession rotation, and a small-diameter coreless motor should be used to generate electricity. The Dynabee type generates electricity by rotation, so the speed of the magnet is high, while the motor rotation type generates electricity by precession, so the speed of the magnet is reduced to about 1/50. Speed-up gears can solve this problem, but speed-up gears are greatly affected by inertia and backlash, so a gear train with a small diameter and high precision is required. In addition, the precession is a vibrational rotation, so the motor also had to have a small moment of inertia. I tried all kinds of motors and found that the motor with 100x gear head attached to Adamand Namiki Precision SCL18 has sufficient performance. I was able to drive air-conditioned clothes with the generator I made.

In 2019, we improved the feedback method of the generated power of the motor rotation type generator (6). The rotating motor is rotated by the generated power, but the generated voltage is low and the counter electromotive force of the rotating motor is the limit, so the rotation speed does not increase. As a result of examining the FB circuit in detail, it was found that the number of revolutions increased by inserting a step-up or step-down circuit, and that the boost ratio had an optimum value determined by the rotation speed. We have manufactured a control circuit that measures the speed of rotation and precession by the generated voltage and controls the duty ratio of the chopper type booster circuit with a microcomputer.

(6)

In 2019, we announced an improved Dynabee-type friction-rotating generator that generates electricity with arbitrary vibration (7). A ball bearing is used to receive the part where sliding friction occurs in Dynabee. When the input vibration is reversed, the precession is reversed, but at the same time, the rolling surface of the rotation axis is also reversed so that the rotation torque due to friction is in the same direction. Even with Dynabee, such a reversal occurs momentarily, but if the reversal is repeated, the rotation will stall. It was found that the reason for this is that the slip friction during reversal is larger than the gyro torque, and that if the friction is made extremely small, the vehicle will not stall no matter how much it is reversed. Currently, it is palm-sized and generates more than 1W.

In 2020, we manufactured a friction-rotating and motor-rotating generator using a flywheel with a diameter of 300 mm, which is used for observation buoys. Currently, we are looking for a company that can cooperate with commercialization.

### Papers

- (1) Tomohiro Ishii, Yuji Goto, Tatsuya Ogawa, Hiroshi Hosaka: Research on Gyro-type Vibration Power Generators, Journal of Precision Engineering, 74, 7, p.764-768, (2008)
- (2) Satoru Yoshikawa, Atsushi Iwasaki, Mikifumi Kishimoto, Hiroshi Hosaka, Ken Sasaki: Transient response analysis of gyro type vibration power generator, Journal of Precision Engineering, 76, 2, p.238-242, (2010)
- (3) Tomoyuki Takahashi, Atsushi Iwasaki, Hiroshi Hosaka: Passive control of gyro type generator, Journal of Robotics Society of Japan 29, 8, p.661-666, (2011)
- (4) Yohei Kamiya, Hiroshi Hosaka: Self Activation of the Gyroscopic Power Generator, Proc. ASME 2011 Int. Mech. Eng. Congr. And Exp., IMECE2011 November 11-17, 2011, Denver, Colorado, USA, IMECE2011-63057 .
- (5) Hiroshi Hosaka, Yoshinori Oonish, Yuki Tajima: High-power Vibration Generator Using Gyroscopic Effect, Sens. Mater., 31,11, p.3655–3668 (2019).

※Click here to download (SAM2019_2296.pdf) - (6) Hiroshi Hosaka, Yuki Tajima : Analytical and Experimental Study on Gyroscopic Power Generator with Power Feedback, Sens. Mater., 32, 7 (2020) 2551–2567.

※Click here to download (SAM2020_2846.pdf) - (7) Aya Watanabe, Ryousuke Yuyama, Hiroshi Hosaka, Akira Yamashita: Fundamental Study on Friction-Driven Gyroscopic Power Generator Works Under Arbitrary Vibration, Proc. ASME 2019 Int. Mech. Eng. Congr. And Exp. IMECE2019, November 11-14 , 2019, Salt Lake City, UT, USA, IMECE2019-10474

### About affiliated companies

The gyro generators listed here are manufactured by Siki Mold Co., Ltd.