**2.2. Verification experiment and discussion**

### *2.2.1. Float magnetic particle*

In order to realize the above-mentioned principle of operation, magnetic particles with a specific gravity smaller than the liquid are required. Fig.3 shows a photograph and schematic diagram of the particles. The diameter of each particle is 1-2 mm. The particles are composed of magnetic iron oxide 4.5%, Kerosene 95.2% and Additives 0.3%.

### *2.2.2. Verification models*

Fig.4 shows the photograph of two types of the model used for the verification of the above-mentioned principle. Fig.4(a) is a hard model for multi-directional drive on a solid surface, and Fig.4(b) is a soft model for crawling on uneven ground.

(d) Magnetic particles return to the upper part slowly

**Figure 1.** Magnetic drive principle with simple magnetic field

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This section describes the development of a unique magnetic fluid and the proposal of a

The explanation shows the magnetic drive principle by use of floating magnetic fluid and a

Fig.1 shows the schematic diagram of the rolling object that is driven by the proposed magnetic drive principle. The functional section(1) and the liquid(2) are sealed in the interior

The inner wall(4) and outer wall(5) of the outer cover are covered with the small projections or a textured material. The projections play the role of creating friction. Floating magnetic particles(6) are employed in a magnetic field. The specific gravity of these magnetic particles is smaller than the liquid, so they gather in the upper part of the rolling object when no magnetic

When a magnetic field is applied, the magnetic particles move in the direction of the magnetic field quickly. The path they take is just inside the outer cover, because both the magnetism and buoyancy are working on the magnetic particles. The particles collide with the projections on

The external side of the outer cover does not slip on the ground, because there is friction between the ground and the outer wall. Consequently, the rolling object moves in the direction of the magnetic field (Fig. 1(c)). After the magnetic field is removed, the magnetic particles will return to the upper part of the rolling objet slowly (Fig. 1(d)), the rolling object stayed at the same position. By repeating the above, the rolling object can move a long distance.

If the specific gravity of a magnetic particle is larger than the liquid, the object rotates in the opposite direction (Fig.2). The movement becomes unstable because it may move in the

In order to realize the above-mentioned principle of operation, magnetic particles with a specific gravity smaller than the liquid are required. Fig.3 shows a photograph and schematic diagram of the particles. The diameter of each particle is 1-2 mm. The particles are composed

Fig.4 shows the photograph of two types of the model used for the verification of the above-mentioned principle. Fig.4(a) is a hard model for multi-directional drive on a solid

**2. A unique magnetic fluid and driving principle**

driving principle by use of the magnetic fluid.

the inner wall of the outer cover (Fig. 1(b)).

opposite direction to the magnetic field.

*2.2.1. Float magnetic particle*

*2.2.2. Verification models*

**2.2. Verification experiment and discussion**

of magnetic iron oxide 4.5%, Kerosene 95.2% and Additives 0.3%.

surface, and Fig.4(b) is a soft model for crawling on uneven ground.

**2.1. Principle of magnetic drive**

simple magnetic field.

by the outer cover(3).

field is applied.

**Figure 2.** Reverse drive. If the specific gravity of a magnetic particle is larger than a liquid, the rolling object rotates conversely.

(a)Hard model for omni directional drive (b)Soft model for crawling on an uneven surface

**Figure 4.** Two types of the model for the verification of the above-mentioned principle

#### *2.2.3. Generator of magnetic field*

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**Figure 2.** Reverse drive. If the specific gravity of a magnetic particle is larger than a liquid, the rolling

**Figure 3.** Photograph and schematic diagram of a magnetic particle with specific gravity smaller than a

(a)Hard model for omni directional drive (b)Soft model for crawling on an uneven surface

**Figure 4.** Two types of the model for the verification of the above-mentioned principle

object rotates conversely.

liquid

Fig.5 shows the system that generates the magnetic field necessary to move the model, it consists of a solenoid (outer diameter: 100 mm, inner diameter: 50 mm, length: 100 mm, cross-sectional dimension of coil line: 2 × 5mm, 163 turns); a power supply (applied voltage: 50 - 900 V, capacitance of capacitor: 10 mF, maximum permissible current: 10000 A); and a sensor probe that measures the flux density of three axes. The charging time of the power supply is 0 - 5 s, the solenoid generates a magnetic field with a peak because the stored charge is discharged all at once. Fig.6 shows a graph of the magnetic field generated by the system; about 2 T can be generated. Fig.7 shows the wave shape of the magnetic flux density at a point on the center axis that is 7 cm from the edge of the solenoid.

### *2.2.4. Results and discussions*

In order to verify the drive principle, an experiment to drive a solid model as shown in Fig.4 (a) was conducted. At first, The magnetic flux density:150 mT was generated horizontally. The model motions captured by camera are shown in Fig.8. The monitor in the captured image shows the value of the flux density. The magnetic particles were shifted to the upper part of the solid model by magnetic force, contacting the inside of the outer cover. All the particles were moved a distance of 2 cm by one 150 mT magnetic field impulse. As a result, this experiment demonstrated the practicality of the magnetic drive principle using a simple magnetic field. Next, a magnetic flux density of 150 mT was generated obliquely downward. The magnetic particles were shifted obliquely downward and didn't contact the inside the outer cover, so the model didn't move.

Fig.9 and Fig.11 show the model motions captured by camera, when the magnetic flux density was generated horizontally. Magnetic particles clumped together and adhered to the inside wall. The form of the clump did not disintegrate when shaken and the center of gravity of the clump was maintained (Fig.9(1)). When a magnetic field was applied, the model began to rotate and roll in the direction of rotation, with the clump maintaining its form (Fig.9(2)(3)). When the inclination of the clump in the model became large, each particle began to move

**Figure 5.** Total system of generating the impulse to the magnetic field for driving the models, it consists of a solenoid, a power supply, and a sensor probe that measures the flux density of three axes.

**Figure 6.** Graph of the magnetic field produced by the system, about 2 Tesla (T) can be generated.

**Figure 7.** Wave shape of the magnetic flux density at the point of 12 cm on a center axis from the edge of the solenoid.

**Figure 8.** Captured motions of the rolling model. The magnetic flux density:150[mT] was generated horizontally. The monitor in back shows the value of flux density.

430 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges New Magnetic Translation/Rotation Drive by Use of Magnetic Particles with Specific Gravity Smaller than a Liquid <sup>7</sup> 431 New Magnetic Translation/Rotation Drive by Use of Magnetic Particles with Speci c Gravity Smaller than a Liquid

**Figure 9.** Captured motion which there is slide in the particle

**Figure 10.** Move Path of each particle

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**Figure 6.** Graph of the magnetic field produced by the system, about 2 Tesla (T) can be generated.

**Figure 7.** Wave shape of the magnetic flux density at the point of 12 cm on a center axis from the edge of

**Figure 8.** Captured motions of the rolling model. The magnetic flux density:150[mT] was generated

horizontally. The monitor in back shows the value of flux density.

the solenoid.

8 Will-be-set-by-IN-TECH 432 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges

separately due to its buoyancy, and the shape of the clump changed (Fig.9(4)(5)). The position of the center of gravity became stable, so the rotation stopped (Fig.9(6)). If the form did not change, the model turned back to its original position (Fig.11, left-side figures).

**Figure 11.** Captured motion which there is slide in the particle and the inner wall.

Fig.10 shows the path of each particle. The particles were circulated by convection, that is, a sequential convection current can cause sequential rolling. This result says that there is another magnetic wave pattern in addition to the impulse one shown in Fig.7. As a result, it became clear that our proposed driving principle results from not only collision of the magnetic particles with the outer cover but also the flow resistance between the particles and the cover. Equation 1 shows the force *F* produced on the magnetic particles by the external magnetic field.

$$F = M \frac{dH}{dr} = \frac{[wbm][\text{N}/wb]}{[m]} = [\text{N}] \tag{1}$$

432 Smart Actuation and Sensing Systems – Recent Advances and Future Challenges New Magnetic Translation/Rotation Drive by Use of Magnetic Particles with Specific Gravity Smaller than a Liquid <sup>9</sup> 433 New Magnetic Translation/Rotation Drive by Use of Magnetic Particles with Speci c Gravity Smaller than a Liquid

**Figure 12.** The graph of the measured magnetic field produced by the equipment of Fig.5. The values are measured by the gauss meter for every mass of a magnetic particle.

*M* is the magnetic moment, *H* is the magnetic field strength and *r* is position of the magnetic particle. Fig.12 shows the graph of the measured magnetic field produced by the equipment in Fig.5. The mass, of each magnetic particle is measured using the gauss meter.

### **2.3. Applications**

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separately due to its buoyancy, and the shape of the clump changed (Fig.9(4)(5)). The position of the center of gravity became stable, so the rotation stopped (Fig.9(6)). If the form did not

change, the model turned back to its original position (Fig.11, left-side figures).

**Figure 11.** Captured motion which there is slide in the particle and the inner wall.

*<sup>F</sup>* <sup>=</sup> *<sup>M</sup> dH*

magnetic field.

Fig.10 shows the path of each particle. The particles were circulated by convection, that is, a sequential convection current can cause sequential rolling. This result says that there is another magnetic wave pattern in addition to the impulse one shown in Fig.7. As a result, it became clear that our proposed driving principle results from not only collision of the magnetic particles with the outer cover but also the flow resistance between the particles and the cover. Equation 1 shows the force *F* produced on the magnetic particles by the external

*dr* <sup>=</sup> [*wbm*][*N*/*wb*]

[*m*] = [*N*] (1)

This chapter introduces some mechanisms that make use of the magnetic drive principle.

(1)Ring type (Fig.13(a)) This mechanism consists of an outer cover in ring form and an axis of rotation. The torque can be taken from the main axis.

(2) Propeller type (Fig.13(b)) After a magnetic field is applied and the magnetic particles flow downward, the particles then float back up due to buoyancy. When a particle contacts a propeller, torque is generated.

**Figure 13.** Mechanisms which applied the magnetic drive principle

Fig.14 shows the prototype of Ring type (Fig.13(a)), Fig.15 explains the principle of driving. In order to verify the drive principle, an experiment to drive a simple model was developed. Fig.16 shows the model motions captured by camera, when the magnetic flux density was

**Figure 14.** Prototype of ring type (cross wheel)

**Figure 15.** Driving Principle of cross wheel

generated horizontally. Magnetic particles pushed the inside wall of the cross wheel, rotated the wheel, then the model drove itself forward.

This driving principle could be applied to medical robots shown in Fig.17. One impulse of magnetic force produces 90 degree rotation of cross wheel. This mechanism is able to control the travel distance, little influenced by friction and viscosity of organs[9]. In addition, No actuator and no battery are required for devices inserted in the body. The external magnetic field is suitable for supplying the rotating or driving force to the device. This application has the advantage over a capsule robot that has a permanent magnet mounted in its interior.

**Figure 16.** Motions of cross wheel captured by camera

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generated horizontally. Magnetic particles pushed the inside wall of the cross wheel, rotated

**Figure 14.** Prototype of ring type (cross wheel)

**Figure 15.** Driving Principle of cross wheel

the wheel, then the model drove itself forward.

(a)Design of cross wheel

(b)Prototype fabricated by 3D printer

**Figure 17.** Schematic diagram of internal medical robot in bowel
