The Hosaka Laboratory of the University of Tokyo is developing a high-power vibration power generator.
By vibrating the rotating body and using the gyro effect, it generates 1W or more from low frequency vibration of about 1Hz.

What is a gyro generator?

Conventional vibration power generation

Generators that use environmental vibration have been commercialized for a long time. The representative is a generator developed by a British venture company that uses bearing vibration of railway vehicles. It produces 20mW with a fist size.

For those that use the vibration of the human body, there is Seiko Kinetic built into the wristwatch. The average power generation is 10 μW. Since the power of the arm in daily activities is about 10W, the power generation efficiency is 10-6.

Output comparison of electromagnetic induction generator

The problem with conventional vibration power generation is that the output at low frequency vibration is small. To solve this problem, vibration power generators using the gyro effect are being researched. This figure shows the theoretical values ​​of conventional and gyro power generation. The conventional type uses simple vibration in which the weight vibrates at the same frequency as the input vibration. It’s the same as a pendulum. In that case, the amount of power generation is maximum at the resonance frequency, and the power generation power is proportional to the cube of the frequency. On the other hand, in the gyro type, the weight rotates at high speed and tilt vibration is applied to the weight. The generated power is proportional to the square of the frequency and the rotation speed. Even if the vibration frequency is low, if the rotation speed is increased, the amount of power generation will increase as much as possible. The ratio of the amount of power generated by the simple vibration type and the gyro type is vibration frequency / rotation angular velocity / 2. The frequency is about 1Hz for vibrations of the human body and ocean waves. The rotation of the weight can be about 3000 rpm = 50 Hz even if a model motor is used. In that case, the ratio of power generation will be 25 times. In other words, in low-frequency vibration, the gyro type can obtain several tens of times the output of the simple vibration type.

Types of gyro generators

Gyro generators have two types of flywheel rotation, one is by motor and the other is by friction. Both have the property that the rotation speed naturally increases when vibration is applied. We are studying both in our laboratory.

Motor rotation type generator

Motor rotation type acceleration principle

This figure shows the motor rotation type acceleration principle. ① Give the initial speed of rotation. This is a rotation around the x-axis. (2) Tilt vibration is applied to the entire generator from the outside. This is a rotation around the y-axis. (3) Then, precession vibration occurs due to the gyro effect. This is a rotation around the z axis. ④ Speed up with gears. ⑤ The permanent magnet is rotated and electromagnetic induction is used to generate electricity in the coil. ⑥ Rectify. ⑦ Boosts. ⑧ Power is returned to the rotation motor. Then, the rotation speed increases, the precession vibration increases, and the induced voltage increases, which is a positive feedback, and the rotation speed increases exponentially. ⑨ When the rotation speed is sufficiently high, output to the outside.

Power feedback issues

Feeding back power does not mean that the rotation will increase indefinitely. As the rotation speed increases, the counter electromotive voltage of the rotation motor increases. When it becomes equal to the generated voltage, no current flows. Therefore, boost the FB voltage. Since the booster is a transformer, it does not consume energy. However, there is an upper limit to the rotation speed even if the pressure is increased. In the booster circuit, the input current increases in proportion to the booster ratio, so the voltage drop due to the resistance of the generator coil increases, and the input voltage of the booster circuit drops, causing him to end up. Therefore, the upper limit of the boost ratio is about 5 times. This determines the upper limit of the rotation speed.

Motor rotation type 1.8W experimental machine

This is the first experimental motor-rotating gyro generator that we developed. This generator produces 1.8W. The diameter of the flywheel is 100mm, the material is Tungsten alloy, and the size is desktop size. The gyro has a dead center, and the gyro effect disappears when the rotation axis and the input axis become parallel. Also, when both are at right angles, Ja’s Iro effect is maximized. When the flywheel is free, the parallel position becomes the stable equilibrium point and the right-angled position becomes the unstable equilibrium point, the rotation axis gradually approaches the dead center, and the precession swing stops. Therefore, a torsion spring is attached to the precession shaft so that the right-angled position is the stable equilibrium point. This causes the flywheel to always vibrate at the maximum gyro effect.

Power generation at constant speed rotation

Power generation characteristics during constant speed rotation. The flywheel is rotated at a constant speed by an external power supply. The rotation speed is 500 rpm, the input tilt amplitude is 17.7 deg, and the vibration frequency is 2.5 Hz. The average generated 1.8 W in the calculation and 1.87 W in the experiment. For the calculation, we have developed a simulator that includes the gyro effect and the characteristics of the power generation motor. The vibration amplitude fluctuates in the experiment because it was manually vibrated. The power consumption required to drive the rotation motor was 84.6 mW. The net power generation after deducting this is 1.8W.

Rotation speed increase due to the return of generated power

It is a rotation speed increase by the return of generated power. You can see that the rotation speed increases over time. Increasing the boost ratio from 1.0 to 1.6 also increases the speed of acceleration. However, it is stalling at a boost ratio of 5.0. This is because the boost ratio was too high, the current of the rotation motor decreased, and the drive torque of the rotation motor became less than the friction torque. Variable boosting is when the boosting ratio is optimally changed according to the number of revolutions. In this case, the rotation speed is the maximum. In this experiment, the flywheel is made of aluminum. In the calculation, we are developing a simulator that includes the characteristics of the feedback circuit.

Boost ratio and kinetic energy in variable boost

The boost ratio and the kinetic energy of rotation in variable boosting. Kinetic energy is increasing over time. Since this energy is the integrated value of power generation, the amount of power generation can be estimated from the slope, which is about 0.1W. The reason why the amount of power generation is smaller than that of constant speed rotation is that aluminum is used for the flywheel and the speed increase ratio of the gears is lowered. Also, the boost ratio increases over time. This is because the higher the rotation speed, the higher the counter electromotive voltage, which requires a higher input voltage. In the experiment, there is a part where the boost ratio is lowered. This is because the vibration amplitude temporarily decreased because the input vibration was applied manually.

Miniaturization of generator

A generator that is a palm-sized miniaturized motor rotation type. The rotation motor is built into the flywheel and integrated. In addition, the gimbal and stator are integrated. As a result, the occupied volume of the rotation motor has been effectively reduced to zero. The flywheel diameter is 70mm.

Experiment, calculation result

It is an experiment and calculation result of a small generator. It rotates at a constant speed with an external power supply. Experiments and calculations are in good agreement for both power generation voltage and power. The reason why the voltage stops at 0V is that when the amplitude of the inner gimbal becomes large, it hits the outer gimbal and the precession stops. The average power is 0.4 W in calculation and 0.393 W in experiment. The net output is 0.104 W, which is obtained by subtracting the power consumption of the rotating motor from 0.289 W from the power generation of 0.393 W.

Large generator for buoys

A large generator for buoys. A flywheel with a diameter of 300 mm and vibration of 0.5 Hz generates 4 W. The flywheel is lightened to reduce weight. A total of four power generation motors are installed, two on the top and two on the bottom.

Friction rotation type generator

Friction rotation type

I will explain the rotation principle of the friction rotation type. The basic principle is the same as the exercise equipment called Dynabee. Dynabee is an old technology patented by Mishler in 1973. It performs three-dimensional rotation that combines rotation synchronized with the hand and high-speed rotation.

For the operation of Dynabee, please refer to the video of Mr. yamagasusumu, for example.
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Dynabee type generator (development of other organizations)

Generates 0.1W. Input vibration needs to be synchronized with precession rotation

Friction rotation type acceleration principle

Our friction-rotating generator generates electricity with arbitrary vibration. The speed-up principle is as follows. ① Give the flywheel the initial speed of rotation. Rotation around the x-axis. (2) Gives tilting vibration to the whole body. It is a rotation around the y-axis. This is the source of energy. ③ Precession rotation occurs due to the gyro effect. Rotation around the z-axis. ④ The rotation axis rolls on the track due to friction. The tracks are donut-shaped rings, one above the other, and the ends of the shaft are separate tracks. The frictional force is in the same direction as the rotation, and the rotation is accelerated. Unlike Dynabee, the flywheel is supported by gimbals and ball bearings, and the precession and rotation friction are very small. In addition, there is a spring on the precession axis, which causes the flywheel to vibrate and precess.

Friction rotation generator that rotates with arbitrary vibration

I will explain in detail the mechanism of speeding up with arbitrary vibration.。

As shown in Fig. 1, let the tracks be A, B, C, D. The track can be straight or arcuate. The flywheel is rotating clockwise (CW) when viewed from the right.

Figure 2 (a) shows the track rotating counterclockwise (CCW). At this time, track A touches the left side of the rotation axis and track D touches the right side, and CCW torque is applied to the flywheel. Then, due to the gyro effect, the flywheel rotates by precession as shown in the figure. Then, as shown in Fig. 2 (b), the axis of rotation moves to the right on track D. Then, a leftward frictional force acts from the track to the rotation axis, and the rotation axis rotates to CW. This orientation is the same as the original rotation, so the rotation speeds up. The torque that rotates the rotation axis to CW also works from track A.

Figure 3 (a) shows the track rotating to CW. At this time, track B touches the left side of the rotation axis and track C touches the right side, and the torque of CW is added to the flywheel. Then, due to the gyro effect, the flywheel rotates by precession in the opposite direction to that shown in Fig. 2. Then, as shown in Fig. 3 (b), the rotation axis advances to the left on the lower surface of track A. Then, a rightward frictional force acts from the track to the rotation axis, and the rotation axis rotates to CW. Since this direction is the same as the original rotation, the rotation speeds up, and the rotation axis is also CW from track B. The torque that rotates on the axis works. From the above, the speed-increasing torque works on the rotation axis regardless of the tilt rotation of the track.

This kind of operation was temporarily possible even with conventional Dynabee. However, in the past, it stalled after several tilt reversals. The cause was the loss of moving energy due to friction. When the precession reverses, slippage occurs between the track and the axis of rotation, slowing the rate of rotation. If there is no acceleration more than the decrease before the next reversal, it will stall. In the past, the rotation friction between rotation and precession was large, and the speed increase was slow. We disassembled the three-dimensional rotating shaft into three parts and used ball bearings for each to reduce friction. As a result, the speed is increased faster, and it can be accelerated by any vibration.

Friction rotation / straight track type

This is a straight track type prototype. Straight tracks are easy to make. This prototype rotates at 2000 rpm and generates 1.6 W due to irregular vibration of 4 Hz and 20 deg on average. A generator is built into the flywheel for miniaturization.

Friction rotation / arc track type

This is an arc track type prototype. Since the precession angle can be large, it can generate electricity even with low-frequency vibration. For human body mounting, flywheel φ70, vibration 1.7Hz, power generation 1.5W. We are also making a miniaturized generator by modifying the gimbal. For large size buoys, it generates 3W at φ300, 0.5Hz.

The Spin acceleration mechanism is shown in a CG video

Application of gyro power generation

Application of gyro power generation (concept) ①

The application of gyro power generation is assumed to be in two fields. The first is an observation buoy. The energy that can be used on the surface of the sea includes sunlight, wind power, and wave power, and the wave power is the largest in terms of energy density. However, since the frequency of ocean waves is as low as 0.2 to 0.5 Hz, conventional vibration power generation cannot be used. Therefore, the application of gyro power generation began. In Europe, generators with a length of 10 m or more used as power plants are being researched. We are aiming for a smaller generator. It is mounted on a buoy with a diameter of about 60 cm. We are considering two generators.

The first is the mooring observation buoy. Monitor coastal cages and set nets. The generator is a motor rotation type, and generates 10W at 0.5Hz with an outer diameter of φ600. Ocean Waves D. He converts electricity into electricity, monitors the sea with fishfinders, sensors (water temperature, salt), and sends data via terrestrial communications. The second is the drift observation buoy. It is used in the open sea, for the movement of fish schools in the EEZ boundary, and for meteorological observation in the high seas. The generator is a motor rotation type, 2 degrees of freedom, outer diameter φ800, and generates 0.2Hz, 10W. In addition to sensors, it performs satellite communication.

Application of gyro type generator (concept) ②

The second application of gyro power generation is air conditioning wear. A generator fixed to the human body or backpack turns the fan to vaporize sweat and exchange air. The latter is an air-conditioned face shield for infectious diseases. Since these can be driven by 1W, a friction rotation type generator that is advantageous for miniaturization is used.

Major research presentations on gyro power generation

【Motor rotation type】

  • 1) Hiroshi Hosaka, Yuki Tajima: Analytical and Experimental Study on Gyroscopic Power Generator with Power Feedback, Sens. Mater., 32, 7 (2020) 2551–2567
  • 2) Hiroshi Hosaka, Yoshinori Oonish, Yuki Tajima: High-power Vibration Generator Using Gyroscopic Effect, Sens. Mater., 31,11, (2019)
  • 3) Yuki Tajima, Hiroshi Hosaka: Research on motor rotation type gyro generators-speeding up rotation by returning generated power-, Journal of Precision Engineering, 85, 7, (2019)
  • 4) Akio Toyoshima, Hiroshi Hosaka, Akira Yamashita: Development of Small-Sized Motor-Driven Gyroscopic Power Generator Works Under Low-Frequency Vibration, Proc. ASME 2019 Int. Mech. Eng. Congr. And Exp. IMECE2019, November 11-14 , 2019, Salt Lake City, UT, USA, IMECE2019-11115
  • 5) Yoshinori Onishi, Hiroshi Hosaka, Yuki Tajima: Research on motor rotation type gyro generator, power generation characteristics at constant rotation, Journal of Precision Engineering, 84, 10, (2018)

Friction rotation type

  • 1) 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, IMECE 2019-10474
  • 2) Japanese Patent Application Laid-Open No. 2019-146477, Hiroshi Hosaka, Yasuhisa Ikeda, Precession Rotation Mechanism and Power Generation Device, The University of Tokyo

Dynabee type

  • 1) Tomoyuki Takahashi, Atsushi Iwasaki, Hiroshi Hosaka: Passive control of gyro type generator, Journal of Robotics Society of Japan 29, 8, p.661-666, (2011)
  • 2) 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.
  • 3) 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)
  • 4) 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)