JP2005223967A - Flexible actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator drivable at high speed with low voltage as the power supply of a home robot in which the drive source itself is small, lightweight, flexible and safe, problem of lifetime incident to evaporation of solvent is solved, and high reliability is ensured by suppressing degradation of performance incident to electrolysis. <P>SOLUTION: The flexible actuator 3 employs expansion/contraction deformation incident to electric stimulus of polymer gel containing ionic liquid or a polymer itself. A pair of electrodes 2a and 2b are provided in contact with the polymer gel or the polymer 1, and one end thereof is clamped by holding members 5a and 5b provided on the inside of lead-out electrodes 4a and 4b before being applied with a drive voltage from a drive power supply 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a flexible actuator that can be applied to a home robot or the like, can be deformed by electrical stimulation, and is flexible and lightweight.

  As a drive source for a joint drive mechanism of a conventional industrial robot, an electromagnetic motor, a hydraulic actuator, a pneumatic actuator, or the like is used. The joint drive mechanism using these drive sources is made of a hard and heavy material such as one using a metal-based electromagnetic motor and speed reduction mechanism, or one using a metal hydraulic / pneumatic cylinder. , Managed and used in a specific place in the factory.

  In contrast, robot drive sources that are expected to play an active role in households, offices, hospitals, etc. for housework support and work support, and nursing care support for the elderly and disabled, are small in size. Lightweight, flexible and safe.

  Among such pneumatic actuators, there is a flexible pneumatic pneumatic actuator, but auxiliary equipment such as compressors and control valves are required for driving, reducing the overall weight of the system. There is a limit.

  On the other hand, artificial muscle actuators using various polymer materials that are lightweight and flexible are proposed, and their practical application is eagerly desired.

  For polymer actuators that operate by electrical stimulation, see SG. Wax et al., Smart Structures And Materials 1999: Electroactive Polymer Actuators and Devices, Proc. SPIE, Vol. 3669, pp. 2-10, 1999. As a keynote lecture. Every year there is a conference on research in this field, and research is actively conducted. Research has been made on polymer actuators driven by electrical stimulation in polymer gels, metal composite ion polymers, conductive polymers, dielectric elastomers, and the like. Among these, the polymer gel has been expected as an actuator having a light and flexible property similar to a muscle of a living body.

  Conventionally proposed actuators using polymer gels include those using ionic polymer gels and nonionic polymer gels. As an example of an ionic polymer gel, Patent Document 1 discloses a method of deforming and expanding by applying a potential to an electrolyte, that is, a polymer containing ions.

  In particular, a method for dehydration or desolvation by applying a potential to a polymer electrolyte in a water-containing state or a state swollen in an appropriate organic solvent is disclosed. The polymer electrolyte undergoes weight loss and shrinkage change due to dehydration or desolvation by application of an electric potential, but in order to restore this, it is necessary to contact water or a solvent to absorb water or the solvent. Considering the ease of control as an actuator, it is desirable to change reversibly with the application of a potential. In addition, this actuator has the disadvantages that it takes time for solvent removal and swelling, and the deformation is slow. Also, this actuator requires water or a solvent in principle, and when used in the air, there is a problem of life due to solvent evaporation.

  As another example of the ionic polymer gel, Patent Document 2 discloses an actuator element using an ion exchange resin film as a driver. This is an actuator using a metal composite ion polymer (IPMC), which is also an actuator using an ionic polymer gel in a broad sense. The drive mechanism of this actuator is that the cation of the ion exchange resin membrane moves to the cathode side when voltage is applied, and moisture molecules move in the membrane accompanying this ion, so there is a difference in the amount of moisture between the anode side and the cathode side. The film body sandwiched between the electrodes is curved. The operable voltage application range is limited to a low voltage on the order of 1 V that does not cause water electrolysis. In addition, this actuator requires water in principle, and is suitable for application in water or in vivo, but when used in air, there is a problem of life due to water evaporation.

  Patent Document 3 discloses a method of deforming a gel by solvent pulling accompanying charge injection by applying an electric field to a gel material that has been swollen with a nonionic dielectric solvent. This driving method is disadvantageous in that, in the embodiment of the polyvinyl alcohol / dimethyl sulfoxide gel, the driving deformation requires about 500 V per 1 mm in thickness and requires a relatively high driving voltage. Further, in principle, this actuator requires the presence of an organic solvent, and as described above, there is a problem of life due to solvent evaporation.

JP-A-61-71683 Japanese Patent Publication No. 7-4075 JP 2000-253682 A

  As described above, in the case of using a flexible and lightweight polymer gel as an electrical stimulation actuator, there is a problem of a lifetime due to evaporation of the solvent. In addition, the polymer gel using an ionic solvent has a problem that the decomposition voltage is low and the performance is deteriorated due to electrolysis and the response is slow. Moreover, the polymer gel using a nonionic solvent has a problem of high driving voltage required for deformation.

  On the other hand, ionic liquids having various physical properties different from those of the conventional organic solvents as described above have recently been attracting attention.

  The present inventor pays attention to the excellent characteristics of this ionic liquid, examines whether a polymer gel containing the ionic liquid or a polymer obtained by polymerizing an ionic liquid structure functions as an actuator, and can be used as an actuator. I found out. The literatures of the conventional examples described above do not disclose an actuator that deforms a polymer gel containing an ionic liquid or a polymer obtained by polymerizing an ionic liquid structure.

  An object of the present invention is to solve these problems, and to provide a flexible actuator that is excellent in reliability, lightweight, flexible and safe.

  The flexible actuator of the present invention is a flexible actuator that expands and contracts by applying an electric field to a polymer, and the polymer is a polymer gel or polymer containing an ionic liquid. Achieved.

  Furthermore, the flexible actuator according to the present invention is a flexible actuator that expands and contracts by applying an electric field to a polymer. The polymer is a polymer gel obtained by polymerizing the ionic liquid, or the ionic liquid. In order to achieve the above-mentioned object, a polymer obtained by polymerizing the cation or anion structure constituting the compound is used.

  Furthermore, in the flexible actuator according to the present invention, in any one of the configurations described above, the polymer gel in which at least one pair of electrodes for applying the electric field contains the ionic liquid or the cation constituting the ionic liquid. Or it is good also as the bending rigidity of the said electrode being lower than the bending rigidity of the said polymer gel, provided in contact with the said polymer which superposed | polymerized the anion structure.

  According to the present invention, an electrically stimulated actuator using a flexible and lightweight polymer gel or polymer that uses expansion and contraction deformation associated with electrical stimulation of the polymer gel containing the ionic liquid or the polymer itself. As a driving source for housework support robots, etc., the driving source itself can be used as a small, lightweight, flexible, and safe actuator, solves the problem of life due to solvent evaporation, and performance accompanying electrolysis There is a remarkable effect that it is possible to provide a new actuator that is less deteriorated, highly reliable, and can be driven at high speed and at a low voltage.

  Embodiments according to the present invention will be described below in detail with reference to the drawings.

  A flexible actuator according to the present invention is a flexible actuator in which an electric field is applied to a polymer to expand and contract, and the polymer is a polymer gel or polymer containing an ionic liquid. .

  The ionic liquid has recently attracted attention as a solvent that exhibits various physical properties different from those of conventional organic solvents. Here, the ionic liquid refers to an organic salt which is composed of a cation (cation) and an anion (anion) and is liquid in a use temperature range near room temperature. The ionic liquid is sometimes called a room temperature molten salt, an ionic liquid, an ionic fluid, an ionic oil, or the like. General organic solvents are volatile and mostly flammable due to their vapor pressure, whereas ionic liquids have negligible vapor pressure and are excellent in thermal stability. It is also chemically and electrochemically stable.

  Examples of the cation (cation) used in the ionic liquid of the present invention include imidazolium cation (Chemical Formula 1), pyridinium cation (Chemical Formula 2), pyrrolidinium cation (Chemical Formula 3), ammonium cation (Chemical Formula 4), and the like. It can be illustrated.

However, in Chemical Formulas 1 to 4, R _{1 to} R ₁₁ represent H, an alkyl group, a vinyl group, and an alkoxy group, respectively.

On the other hand, examples of the anion (anion) of the ionic liquid used in the present invention include Br ⁻ , Cl ⁻ , I ⁻ , PF ₆ ⁻ , BF ₄ ⁻ , CF ₃ SO ₃ ⁻ , NO ₃ ⁻ , RCOO ⁻ and RSO. _{^{3 -, NH 2 CHRCOO -,}} SO 4 2-, and the like can be exemplified. The ionic liquid used in the present invention is obtained, for example, by a combination of the above anions and cations, and as an synthesis method thereof, a method such as an anion exchange method, an acid ester method, or a neutralization method can be used.

  As a first method for making these ionic liquids into a film or gel, for example, there is a method in which a monomer and a polymerization initiator are reacted in an ionic liquid to form a gel. The monomer molecule is not particularly limited as long as it gives a film-like or gel-like product, but is not limited to polyvinyl polymer, polyether polymer, polyamide polymer, polyester polymer, polycarbonate polymer, ionene. Polymers are preferably used for this purpose.

  As a second method for making these ionic liquids into a film or gel, there is a method of polymerizing an ionic liquid comprising a cation having an unsaturated substituent such as a vinyl group. Examples of cations used for such purposes include 1-vinyl imidazolium cation, 1-vinyl, 3-alkyl imidazolium cation, and the like. Of course, it is an effective method for the present invention to control such physical properties by further dissolving such an ionic liquid polymer with an appropriate polymer material.

  Further, polymerizing the anion portion of the ionic liquid is also an effective means for the purpose of the present invention. As anions used for such purposes, acid monomers such as carboxylic acid, sulfonic acid, acrylic acid, methacrylic acid, and vinyl sulfonic acid, and styrene are preferably used for this purpose. As such an ionic liquid type polymer, for example, a polymer composed of 1,3-diethylimidazolium cation and polymethacrylic acid can be exemplified.

  Japanese Patent Application Laid-Open No. 10-265673 discloses a polymer compound composite obtained by solidifying an ionic liquid and a method for producing the same. Furthermore, the above publication discloses a polymer compound complex (polymer gel) obtained by polymerizing an onium salt of cyclic amidine or pyridine with an alkyl group added as an ionic liquid.

  The inventor focused on the excellent characteristics of the ionic liquid, created a sample for the purpose of examining whether the polymer gel containing the ionic liquid functions as an actuator, and experimented on deformation driving by applying an electric field. It was found that it deformed reversibly in response to. This actuator is excellent in non-volatile properties and thermal stability, which are the inherent characteristics of ionic liquid gels, and is also very stable chemically and electrochemically, compared to gel actuators using conventional solvents. Met.

  FIG. 1 is a configuration diagram of a flexible actuator 3 and a measurement system 9 in which a driving experiment thereof is performed according to an embodiment of the present invention. The flexible actuator 3 in the above embodiment of the present invention is configured, for example, in a substantially rectangular parallelepiped shape, and is configured by providing a pair of plate electrodes 2a and 2b in contact with a polymer gel or polymer 1 containing an ionic liquid. Has been. One end of the flexible actuator 3 was sandwiched between insulating holding members 5a and 5b such as glass plates provided with extraction electrodes 4a and 4b on the inner side to form a fixed end. A pair of electrodes 2a and 2b are electrically connected to the extraction electrodes 4a and 4b, respectively. A drive power supply 6 having a function generator function is connected to the extraction electrodes 4a and 4b, and a drive voltage is applied to the extraction electrodes 4a and 4b by the drive power supply 6 and a waveform of the drive voltage is generated by an oscilloscope 7 having a waveform recording function. Record and observe. The other end side surface of the flexible actuator 3 is irradiated with a measuring laser beam 9a from the laser head 8b of the laser displacement meter 8a, and the displacement of the flexible actuator 3 is detected from the change in the position of the reflected light. Are simultaneously recorded and observed with an oscilloscope 7.

  FIGS. 2A and 2B show how the flexible actuator 3 bends when a voltage is applied. 6A shows a state in which the voltage applied from the drive power source 6 is open and no voltage is applied to the actuator 3. FIG. 5B shows a state where the voltage is applied from the drive power source 6 to the actuator 3. Shows a state of bending in the thickness direction.

  According to the above embodiment, in the flexible actuator 3 that applies an electric field to the polymer 1 to expand and contract by deformation, the polymer 1 is a polymer gel or polymer 1 containing an ionic liquid. As a drive source for a housework support robot or the like, the drive source itself can be used as an electrostimulation type flexible actuator 3 that is small, light, flexible, lightweight, and safe. It is particularly effective as a driving source for fingers of a housework support robot and a driving source for joints of the arm of the hand. Therefore, since the solvent contained in the polymer is non-volatile, it is possible to solve the problem of the lifetime due to the evaporation of the solvent, and the ionic liquid is chemically and electrochemically stable and has a high decomposition voltage and is accompanied by electrolysis. There is a remarkable effect that it is possible to provide a new actuator that can be driven with high reliability, high speed, and low voltage with little performance deterioration.

  More specific examples of the above embodiment of the present invention will be described in detail below.

(Example 1)
Dissolving methyl methacrylate (MMA) as a monomer in a molar ratio of 1: 1 in an ionic liquid consisting of 1 ethyl 3 methylimidazolium (EMI) as a cation and trifluoromethylsulfonylimide (TFSI) as an anion, Ethylene glycol dimethacrylate (EDGDMA) was added as a crosslinking agent in an amount of 2 mol% based on MMA, and benzoyl peroxide (BPO) as a polymerization initiator was dissolved in an amount of 2 mol% based on the total monomers. These solutions were poured into a glass plate through a Teflon (registered trademark) spacer and polymerized by heating at 80 ° C. for 12 hours to obtain a polymer gel sheet containing an ionic liquid.

  In order to test whether or not the polymer gel 1 containing the ionic liquid of the polymer gel sheet can be deformed by applying an electric field, the polymer gel sheet is cut into a strip shape, and a pair of means is used as means for applying an electric field. Electrodes 2a and 2b were provided to sandwich the polymer gel sheet 1. Specifically, a strip-shaped sample having a length of 13 mm, a width of 3 mm, and a thickness of 130 μm was cut out from the sheet, and a gold foil having a length of 13 mm, a width of 3 mm, and a thickness of 1 μm was bonded to both surfaces as a pair of electrodes 2a and 2b. The surface of the polymer gel sheet was sticky per se, and was adhered almost uniformly by simply placing a gold foil on the sheet.

  The sample of the strip-shaped polymer gel sheet with electrodes was subjected to displacement measurement accompanying application of an electric field by the measurement system 9 described in FIG. 3 mm from the longitudinal end of the sample of the strip-shaped polymer gel sheet with electrodes is sandwiched between slide glass plates which are holding members 5a and 5b provided inside with extraction electrodes 4a and 4b made of copper foil, and fixed. The end. Therefore, the above sample is a cantilever beam with a protruding length from the fixed end of 10 mm. The laser spot of the laser displacement meter 8 is irradiated to a position 9 mm from the fixed end, and the deflection displacement at this position is measured. It was measured. A sawtooth alternating voltage of ± 2 V and 0.25 Hz is applied to the extraction electrodes 4a and 4b from the drive power source 6, and the waveform of this drive voltage and the analog voltage output of the laser displacement meter 8 are output by an oscilloscope 7 having a waveform recording function. Simultaneous observation and recording.

  FIG. 3 shows changes over time in drive voltage and displacement. The upper part of FIG. 3 shows the change over time of the driving voltage, and the lower part shows the change over time of the relative displacement observed by the laser displacement meter 8. A deflection deformation with an amplitude of 4 μm was observed corresponding to the voltage application of ± 2V. This deformation is a substantially reversible change corresponding to the voltage value. Further, when + voltage was applied to the electrode 2b side on the laser irradiation side, it was bent and deformed toward the laser irradiation side.

  Although the mechanism of this mechanical deformation is not clear, it has been found for the first time that the polymer gel 1 containing an ionic liquid repeats reversible deformation by applying a voltage.

  The measurement sample has a large capacity equivalent to the μF order and also has properties as an electric double layer capacitor. It seems that the large electrostatic energy injected by the voltage application to the electrode was converted into mechanical energy. For example, an unbalance between the electrodes of the electrostatic repulsion between similar ions in the vicinity of the electric double layer formed at the electrode interface is considered as a deformation mechanism. In the EMI-TFSI ionic liquid contained in the prepared polymer gel, the cation transport number is larger than the anion transport number, and it is considered that the repulsive force of the cation collected on the negative electrode side is superior to the anion collected on the positive electrode side. In addition, it is considered that there is an interaction between a cross-linked polymer network and bulky cations and anions at a site localized in the vicinity of the electric double layer.

  Apart from actuators using polymer gels, the IEEJ Proceedings E, Vol. 122, No. 2, page 97 (2002) have electrodes that can be flexibly deformed on both sides of a thin sheet of dielectric elastomer. A method is disclosed in which the dielectric elastomer is deformed by an electrostatic force provided by applying a voltage between the electrodes. This method has a drawback that a high electric field of the order of 100 V per 1 μm thickness is required for deformation.

  On the other hand, although it is difficult for an ionic liquid to obtain a dielectric constant specific to a substance due to the influence of electric double layer capacity, it is also expected to have a large dielectric constant because of its large polarity. The magnitude of the electrostatic force acting between the electrodes is also expected to increase, and a deformation mechanism as a dielectric elastomer may also act. In this case, if a voltage is applied to a sample having the same thickness, it is expected that the sample can be driven at a lower voltage.

  The polymer-based actuator containing the ionic liquid of the present invention has a non-volatile solvent, and the polymer gel actuator containing a conventionally proposed solvent has a problem of an essential life due to solvent evaporation. Has a very remarkable effect.

  In addition, the ionic liquid is chemically and electrochemically stable and has a high decomposition voltage, and there is little performance deterioration due to electrolysis, which has been a problem in actuators using polymer gels using ionic solvents that have been proposed in the past. effective. This feature has a significant effect on improving the operating cycle life of the actuator as well as solving the lifetime associated with evaporation.

  Furthermore, the ionic liquid has high thermal stability, and the heat resistance of the EMI-TFSI ionic liquid used for sample preparation in this example is 400 ° C. or higher, and a polymer gel mainly composed of this is used. The actuator of the present invention is flame retardant and has the effect of being safe for use.

  Furthermore, the actuator of the present invention can be driven even at a low voltage of several volts as shown in the driving experiment results. In the actuators using a polymer gel using a nonionic solvent and the actuators using a dielectric elastomer that have been proposed in the past. The problem that the drive voltage that was the problem is high can be solved.

  As described above in the explanation of the verification experiment, the deformation response speed is confirmed to be at least in the order of seconds, and if the deformation mechanism corresponds to the rapid charge / discharge characteristics as an electric double layer capacitor, A faster response can be expected.

Since the elastic modulus of the sample prepared in this example was mainly intended to verify whether it could operate in principle, a sample having a relatively low elastic modulus was prepared by the above-described procedure, and the elastic modulus was 2.4 MN. / M ² . For operation as a dielectric polymer, it is not always necessary to apply an electric field even if the electrode is not in direct contact with the polymer gel, but other materials may be used, but in order to perform the operation associated with the formation of the electric double layer, A pair of electrodes may be provided in contact with the polymer gel. In this case, it is desirable that the bending rigidity of the electrode is lower than that of the polymer gel so that the rigidity of the electrode does not hinder the movement of the polymer gel. As a result, the reduction of the generated displacement can be suppressed to about 50% or less.

  The polymer gel constituting the actuator of the present invention is not limited to containing only an ionic liquid as the solvent. Other solvents may be included in order to improve various performances desired as an actuator, such as generated displacement, generated force, and deformation speed. Further, there is no restriction on adding a chemical modification or physical complexation to the cross-linked polymer chain that becomes the holding body of the ionic liquid by a usual method.

(Example 2)
An example in which the cation portion of the ionic liquid is polymerized will be described. 1.88 g of 1-vinyl-3-ethylimidazolium bromide obtained by reacting N-vinylimidazole and bromoethane and 1.42 g of propionic acid are added to 20 ml of acetonitrile and dissolved by stirring. Hydrochloric acid was distilled off under reduced pressure. Acetone was further added, and distillation was performed again to remove the solvent and the remaining hydrobromic acid.

Add 5 mol% of azobisisobutyronitrile as a radical polymerization initiator to the molten salt monomer as a radical polymerization initiator with respect to the vinyl monomer unit, add ethanol to react the monomer, and the resulting ionic liquid monomer has a radical polymerization initiator. After further adding ethanol, polymerization was performed at a temperature of 70 ° C. for 25 minutes, and the solvent was filtered under reduced pressure to obtain a molten salt polymer. The obtained reaction product is rubber-like and has a structure in which 3-ethylimidazolium cation is attached to the side chain of polyethylene and CH ₃ CH ₂ COO ⁻ is bonded as an anion.

  The product was formed into a film, and the operation as an actuator was confirmed by the same method as in Example 1. As a result, the same excellent characteristics could be confirmed.

(Example 3)
Next, an example in which the anion portion of the ionic liquid is polymerized will be described. 1,3-diethylimidazolium bromide (14.5 g) obtained by reacting 1-ethylimidazole and bromoethane and methacrylic acid (6.2 g) were dissolved in acetonitrile solvent (50 ml) at room temperature, and the same room temperature was obtained. The solvent and the resulting hydrobromic acid were distilled off under reduced pressure. Further, 20 ml of acetone was added to the reaction product, and distillation under reduced pressure was performed again to remove the solvent and the remaining hydrobromic acid.

  Add 5 mol% of azobisisobutyronitrile as a radical polymerization initiator to the molten salt monomer as a radical polymerization initiator with respect to the vinyl monomer unit, add ethanol to react the monomer, and the resulting ionic liquid monomer has a radical polymerization initiator. After adding ethanol, polymerization was performed at a temperature of 70 ° C. for 25 minutes, and the solvent was filtered under reduced pressure to obtain a product. The product was rubbery and was a polymer composed of polymethacrylate anion and 1,3-diethylimidazolium cation.

  The product was formed into a film and the operation as an actuator was confirmed by the same method as in Example 1. As a result, the same excellent characteristics could be confirmed.

  As described above, the physical properties of the actuator of the present invention can be adjusted more widely by using a polymer gel obtained by polymerizing an ionic liquid or a polymer obtained by polymerizing an ionic liquid structure. As in the sample prepared in Example 2, the cation portion of the ionic liquid may be polymerized, or as shown in Example 3, the anion portion may be polymerized.

  According to the technique of dissolving monomers and performing in-situ polymerization by the techniques shown in Examples 1, 2, and 3, various physical properties desirable as an actuator can be created. For example, in order to generate a force that moves a load as an actuator, moderate rigidity is required, but a desirable elastic modulus of the polymer gel can be obtained. Furthermore, it is possible to obtain various physical properties that are desirable for high-speed driving, large generating power, and high reliability.

  The flexible actuator of the present invention can be applied as a drive source that is required to be flexible, lightweight, and safe, such as a home robot. Further, it can be used as a substitute for the drive source of any drive mechanism to which an electromagnetic motor, a pneumatic cylinder, or the like has been applied, and has great industrial utility value.

It is a block diagram of the flexible actuator and drive and measurement system in one embodiment of the present invention. (A), (b) is sectional drawing showing the non-operation state and operation state of the flexible actuator in the said embodiment of this invention, respectively. It is a graph which shows the measurement result of the time change of the drive voltage in the said operation state of the flexible actuator in the said embodiment, and a displacement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Polymer gel or polymer 2a, 2b electrode 3 Flexible actuator 4a, 4b Lead electrode 5a, 5b Holding member 6 Drive power supply 7 Oscilloscope 8 Laser displacement meter 9 Measurement system

Claims (3)

In a flexible actuator that applies an electric field to the polymer (1) to expand and contract,
A flexible actuator, wherein the polymer is a polymer gel or polymer containing an ionic liquid.   The polymer (1) containing the ionic liquid is a polymer gel obtained by polymerizing the ionic liquid, or a polymer obtained by polymerizing a cation or an anion structure constituting the ionic liquid. The flexible actuator according to claim 1. The polymer (1) in which at least one pair of electrodes (2a, 2b) for applying the electric field polymerizes the polymer gel containing the ionic liquid or the cation or anion structure constituting the ionic liquid. The flexible actuator according to claim 1 or 2, wherein the flexible rigidity of the electrode is lower than the bending rigidity of the polymer.

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