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Device of magnetostrictive and piezoelectric materials for magnetic force control
Journal of Magnetism and Magnetic Materials 258–259 (2003) 490–492
Device of magnetostrictive and piezoelectric materials for magnetic force control Toshiyuki Ueno*, Jinhao Qiu, Junji Tani Institute of Fluid Science, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Japan
Abstract A new type of magnetic force control device composed of two functional materials, a giant magnetostrictive material and a piezoelectric material, is proposed for coil-less magnetic force control. The magnetic force control is based on the inverse magnetostrictive effect of Terfenol-D coupled via strain with the piezoelectric actuator and the variation of the voltage applied to the piezoelectric actuator is converted to the variation of magnetic force via a magnetic circuit in the device. Because the piezoelectric actuator is an electrically capacitive load, this magnetic force control method has the advantages of zero power consumption and zero heat generation in steady-state operation. In this paper, the principle of magnetic force controlling is described and the characteristics of the device are investigated with experiments. r 2002 Published by Elsevier Science B.V. Keywords: Inverse magnetostrictive effect; Giant magnetostrictive material; Piezoelectric material; Magnetic force control
1. Introduction Electromagnets have been essential devices for converting electric energy to mechanical energy via magnetic circuit and controlling magnetic force in various devices. Basically, electromagnets use an electric current to generate magnetic force. When the current flow through the coils, a part of the electric energy is converted to heat due to the resistance of the coils. The resistance of electromagnets does not only waste energy, but also causes the heat generation, which is harmful in many applications. To solve this problem, a coil-less magnetic force control method based on the inverse magnetostrictive effect of magnetostrictive materials is proposed by authors [1]. The new magnetic force control method converts the variation of the stress applied to the magnetostrictive materials to the variation of magnetization, and further to that of magnetic force via magnetic circuits. For the realization of the coil-less magnetic force control, a device composed of two functional materials: giant magnetostrictive material (GMM) [2] and piezoelectric material (PZT), and magnetic circuits including magnets are also proposed. *Corresponding author. Tel./fax: +81-22-217-5249. E-mail address: [email protected] (T. Ueno).
In the device, two materials are mechanically coupled via strain to control the strain of GMM by the voltage applied to PZT and the generated strain in GMM is converted to the variation of the magnetic force via magnetic circuits. Since PZTs are electrically capacitive, no current flows in steady state and therefore the device has advantages of zero power consumption the zero heat generation in maintaining the constant magnetic force. In this paper, the principle of the magnetic force control with the inverse magnetostrictive effect is described with the basic magnetic circuit and the device. To confirm the principle, the device, which consists of a Terfenol-D rod and a stack piezoelectric actuator, was fabricated and the characteristics of magnetic forces control were investigated by experiments. The power consumption and heat generation of the device and the conventional electromagnet were compared to verify the advantages of the device.
2. Devices with magnetic force control A new type of coil-less magnetic force control device is shown in Fig. 1. This device consists mainly of a stack piezoelectric (PZT) actuator, a Terfenol-D rod, a ring permanent magnet and two ferromagnetic and
0304-8853/03/$ - see front matter r 2002 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 1 0 6 5 - X
T. Ueno et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 490–492
nonmagnetic plates, and also has a mechanism to control the prestress in the rod inside. As shown in Fig. 1, the rod placed inside the ring magnet, the middle ferromagnetic plate and the PZT actuator are lined up and constrained between the left ferromagnetic and right nonmagnetic plates by four nonmagnetic bolts. A preload is applied to both the rod and to the actuator by tightening four bolts. The fabricated device is shown in Fig. 2. The principle of the magnetic force control with the device is explained with the magnetic circuits shown in Fig. 3. With the moving yoke connecting two ferromagnetic plates, two parallel flux loops, one consisting of the magnet, fixed yokes and rod (labeled with I), and the other consisting of the magnet, fixed yokes, gap and moving yoke (labeled with II), are constructed. The
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magnet is used in the loop I to magnetize the rod and to induce the magnetostriction and in loop II to provide the bias magnetic (attractive) force. When the voltage applied to the PZT actuator is increased under the constant gap, the actuator generates the compressive load and hence compressive strain in the rod is increased. Due to the inverse magnetostrictive effect, the increasing load decreases the magnetization inside the rod, which causes the decrease of the flux in loop I. Because the sum of fluxes in loops I and II is constant, the decrease of flux in loop I causes the increase of flux in loop II and also the increase of the magnetic force. When the voltage is decreased, the magnetic force is decreased in the opposite manner, therefore the magnetic force can be controlled with the voltage of the PZT actuator. Terfenol-D is suitable for this device, since the elastic modulus of Terfenol-D is relatively small compared with the conventional magnetostrictive materials.
3. Experiment
Fig. 1. Configuration of magnetic force control device (left) and its cross section (right).
Fig. 2. Fabricated device.
Fig. 3. Mechanism of magnetic force control with device.
The static and dynamic performance of the device was investigated by following measurements: (i) Under the constant gap, sinusoidal voltage (0–100 or 0–200 V) of 10 Hz was applied to the PZT actuator. The average strain of the rod was measured with four strain gages attached to the rod 901 apart, and the magnetic force acting on the moving yoke was measured with a load cell. To evaluate the power consumption, the input electrical energy to the PZT actuator was measured with a power meter connected between the actuator and the amplifier. (ii) Under the constant gap, the frequency response of magnetic force was measured by integrating the induced voltage of the pick-up coil placed in the gap when white noise was applied to the actuator. Fig. 4 shows the result of measurement (i): the relationships between applied voltage, strain and magnetic force under the constant gap of 0.2 and 1.0 mm. The principle described is verified by the curves in the figures. In the case of 0.2 mm gap, the absolute value of compressive strain increased by 650 ppm and the force decreased by 10 N as the voltage was increased from 0 to 200 V. The increment of force in the case of 1.0 mm gap is smaller than that in the case of 0.2 mm gap. Due to the hysteretic property of both piezoelectric and magnetostrictive materials, hysteresis is observed in all curves. Fig. 5 shows the frequency responses of the magnetic force to the applied voltage. The magnitude and phase delay of the force at 1 kHz compared with static response are 9 dB and 651. This performance is sufficient for the low frequency control (o100 Hz). The delay of the force to the applied voltage mainly depends on the delay between the voltage and strain due to the
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T. Ueno et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 490–492 Table 1 Comparison of power and temperature in electromagnet and device in steady and dynamic operation Coil
Device
Steady operation Max input voltage (V) Power consumption (W) Temperature increase (T)
2 3.0 9.0
200 0.0 0.0
Dynamic operation (100 Hz) Max input voltage (V) Power consumption (W) Temperature increase (T)
2 1.2 5.4
200 2.5 59
Fig. 4. Relationship between voltage, strain and force under constant gaps of 0.2 mm (left) and 1.0 mm (right).
Table 1. The electromagnet consumed 3 W to maintain the constant force because of the Joule loss, and the temperature of coil rose from 271 to 361. However, no power consumption and heat generation were observed for the device. In the dynamic operation where an alternating voltage was applied, the input current increased with the frequency and heat was generated mainly due to dielectric loss. This comparison indicates that the device is suitable for the control at the low frequency or maintaining constant magnetic force.
4. Conclusion
Fig. 5. Frequency response.
PZT property and in addition between the force and magnetic flux in the rod due to the eddy current inside the rod and yokes. The prime advantages of the device are low power consumption and heat generation in a steady-state operation. To verify these advantages, the power consumption and heat generation of the device were measured in both steady-state operation (maintaining the constant magnetic force of 3 N) and dynamic operation (oscillating the magnetic force with the amplitude of 3 N and frequency of 100 Hz) and compared with those of the electromagnet. The electromagnet used for comparison consists of a yoke of the same size with 150 turns of wire (diameter: 0.5 mm) wound around the magnet. The results are shown in
In this paper, the principle of the magnetic force control by inverse magnetostrictive effect of magnetostrictive material was described and the device, the composition of a giant magnetostrictive rod and a stack piezoelectric actuator, was fabricated to realize the principle practically. The relationship between voltage and force was also measured in specific cases and the device was confirmed to be suitable for the magnetic force control and in the low frequency range. The advantage of zero power consumption and heat generation of the device in a steady-state operation was also confirmed by the comparison of the device with the electromagnet.
References [1] T. Ueno, J. Qiu, T. Junji, JSME. Ser. C. 66 (2000) 110. [2] G. Engdahl, Handbook of Giant Magnetostrictive Materials, Academic Press, New York, 2000.
Device of magnetostrictive and piezoelectric materials for magnetic force control Toshiyuki Ueno*, Jinhao Qiu, Junji Tani Institute of Fluid Science, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai, Japan
Abstract A new type of magnetic force control device composed of two functional materials, a giant magnetostrictive material and a piezoelectric material, is proposed for coil-less magnetic force control. The magnetic force control is based on the inverse magnetostrictive effect of Terfenol-D coupled via strain with the piezoelectric actuator and the variation of the voltage applied to the piezoelectric actuator is converted to the variation of magnetic force via a magnetic circuit in the device. Because the piezoelectric actuator is an electrically capacitive load, this magnetic force control method has the advantages of zero power consumption and zero heat generation in steady-state operation. In this paper, the principle of magnetic force controlling is described and the characteristics of the device are investigated with experiments. r 2002 Published by Elsevier Science B.V. Keywords: Inverse magnetostrictive effect; Giant magnetostrictive material; Piezoelectric material; Magnetic force control
1. Introduction Electromagnets have been essential devices for converting electric energy to mechanical energy via magnetic circuit and controlling magnetic force in various devices. Basically, electromagnets use an electric current to generate magnetic force. When the current flow through the coils, a part of the electric energy is converted to heat due to the resistance of the coils. The resistance of electromagnets does not only waste energy, but also causes the heat generation, which is harmful in many applications. To solve this problem, a coil-less magnetic force control method based on the inverse magnetostrictive effect of magnetostrictive materials is proposed by authors [1]. The new magnetic force control method converts the variation of the stress applied to the magnetostrictive materials to the variation of magnetization, and further to that of magnetic force via magnetic circuits. For the realization of the coil-less magnetic force control, a device composed of two functional materials: giant magnetostrictive material (GMM) [2] and piezoelectric material (PZT), and magnetic circuits including magnets are also proposed. *Corresponding author. Tel./fax: +81-22-217-5249. E-mail address: [email protected] (T. Ueno).
In the device, two materials are mechanically coupled via strain to control the strain of GMM by the voltage applied to PZT and the generated strain in GMM is converted to the variation of the magnetic force via magnetic circuits. Since PZTs are electrically capacitive, no current flows in steady state and therefore the device has advantages of zero power consumption the zero heat generation in maintaining the constant magnetic force. In this paper, the principle of the magnetic force control with the inverse magnetostrictive effect is described with the basic magnetic circuit and the device. To confirm the principle, the device, which consists of a Terfenol-D rod and a stack piezoelectric actuator, was fabricated and the characteristics of magnetic forces control were investigated by experiments. The power consumption and heat generation of the device and the conventional electromagnet were compared to verify the advantages of the device.
2. Devices with magnetic force control A new type of coil-less magnetic force control device is shown in Fig. 1. This device consists mainly of a stack piezoelectric (PZT) actuator, a Terfenol-D rod, a ring permanent magnet and two ferromagnetic and
0304-8853/03/$ - see front matter r 2002 Published by Elsevier Science B.V. PII: S 0 3 0 4 - 8 8 5 3 ( 0 2 ) 0 1 0 6 5 - X
T. Ueno et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 490–492
nonmagnetic plates, and also has a mechanism to control the prestress in the rod inside. As shown in Fig. 1, the rod placed inside the ring magnet, the middle ferromagnetic plate and the PZT actuator are lined up and constrained between the left ferromagnetic and right nonmagnetic plates by four nonmagnetic bolts. A preload is applied to both the rod and to the actuator by tightening four bolts. The fabricated device is shown in Fig. 2. The principle of the magnetic force control with the device is explained with the magnetic circuits shown in Fig. 3. With the moving yoke connecting two ferromagnetic plates, two parallel flux loops, one consisting of the magnet, fixed yokes and rod (labeled with I), and the other consisting of the magnet, fixed yokes, gap and moving yoke (labeled with II), are constructed. The
491
magnet is used in the loop I to magnetize the rod and to induce the magnetostriction and in loop II to provide the bias magnetic (attractive) force. When the voltage applied to the PZT actuator is increased under the constant gap, the actuator generates the compressive load and hence compressive strain in the rod is increased. Due to the inverse magnetostrictive effect, the increasing load decreases the magnetization inside the rod, which causes the decrease of the flux in loop I. Because the sum of fluxes in loops I and II is constant, the decrease of flux in loop I causes the increase of flux in loop II and also the increase of the magnetic force. When the voltage is decreased, the magnetic force is decreased in the opposite manner, therefore the magnetic force can be controlled with the voltage of the PZT actuator. Terfenol-D is suitable for this device, since the elastic modulus of Terfenol-D is relatively small compared with the conventional magnetostrictive materials.
3. Experiment
Fig. 1. Configuration of magnetic force control device (left) and its cross section (right).
Fig. 2. Fabricated device.
Fig. 3. Mechanism of magnetic force control with device.
The static and dynamic performance of the device was investigated by following measurements: (i) Under the constant gap, sinusoidal voltage (0–100 or 0–200 V) of 10 Hz was applied to the PZT actuator. The average strain of the rod was measured with four strain gages attached to the rod 901 apart, and the magnetic force acting on the moving yoke was measured with a load cell. To evaluate the power consumption, the input electrical energy to the PZT actuator was measured with a power meter connected between the actuator and the amplifier. (ii) Under the constant gap, the frequency response of magnetic force was measured by integrating the induced voltage of the pick-up coil placed in the gap when white noise was applied to the actuator. Fig. 4 shows the result of measurement (i): the relationships between applied voltage, strain and magnetic force under the constant gap of 0.2 and 1.0 mm. The principle described is verified by the curves in the figures. In the case of 0.2 mm gap, the absolute value of compressive strain increased by 650 ppm and the force decreased by 10 N as the voltage was increased from 0 to 200 V. The increment of force in the case of 1.0 mm gap is smaller than that in the case of 0.2 mm gap. Due to the hysteretic property of both piezoelectric and magnetostrictive materials, hysteresis is observed in all curves. Fig. 5 shows the frequency responses of the magnetic force to the applied voltage. The magnitude and phase delay of the force at 1 kHz compared with static response are 9 dB and 651. This performance is sufficient for the low frequency control (o100 Hz). The delay of the force to the applied voltage mainly depends on the delay between the voltage and strain due to the
492
T. Ueno et al. / Journal of Magnetism and Magnetic Materials 258–259 (2003) 490–492 Table 1 Comparison of power and temperature in electromagnet and device in steady and dynamic operation Coil
Device
Steady operation Max input voltage (V) Power consumption (W) Temperature increase (T)
2 3.0 9.0
200 0.0 0.0
Dynamic operation (100 Hz) Max input voltage (V) Power consumption (W) Temperature increase (T)
2 1.2 5.4
200 2.5 59
Fig. 4. Relationship between voltage, strain and force under constant gaps of 0.2 mm (left) and 1.0 mm (right).
Table 1. The electromagnet consumed 3 W to maintain the constant force because of the Joule loss, and the temperature of coil rose from 271 to 361. However, no power consumption and heat generation were observed for the device. In the dynamic operation where an alternating voltage was applied, the input current increased with the frequency and heat was generated mainly due to dielectric loss. This comparison indicates that the device is suitable for the control at the low frequency or maintaining constant magnetic force.
4. Conclusion
Fig. 5. Frequency response.
PZT property and in addition between the force and magnetic flux in the rod due to the eddy current inside the rod and yokes. The prime advantages of the device are low power consumption and heat generation in a steady-state operation. To verify these advantages, the power consumption and heat generation of the device were measured in both steady-state operation (maintaining the constant magnetic force of 3 N) and dynamic operation (oscillating the magnetic force with the amplitude of 3 N and frequency of 100 Hz) and compared with those of the electromagnet. The electromagnet used for comparison consists of a yoke of the same size with 150 turns of wire (diameter: 0.5 mm) wound around the magnet. The results are shown in
In this paper, the principle of the magnetic force control by inverse magnetostrictive effect of magnetostrictive material was described and the device, the composition of a giant magnetostrictive rod and a stack piezoelectric actuator, was fabricated to realize the principle practically. The relationship between voltage and force was also measured in specific cases and the device was confirmed to be suitable for the magnetic force control and in the low frequency range. The advantage of zero power consumption and heat generation of the device in a steady-state operation was also confirmed by the comparison of the device with the electromagnet.
References [1] T. Ueno, J. Qiu, T. Junji, JSME. Ser. C. 66 (2000) 110. [2] G. Engdahl, Handbook of Giant Magnetostrictive Materials, Academic Press, New York, 2000.