Abstract:
There is provided a wireless-type power supply method that is applied to the case where an object to which energy is to be transmitted is relatively small, such as a micromachine, and that allows high-voltage electrical energy to be transmitted without using a wire. In this method, the optical energy from an light source is converted into high-voltage electrical energy by means of an energy transducer formed of either a piezoelectric element or a photovoltaic element on the above-described object, and the high-voltage electrical energy is supplied to an actuator, whereby the construction of the receiving side of the energy transmission is simplified.

Description:
TECHNICAL FIELD OF THE INVENTION  
         [0001]    The present invention relates to a method for wireless-type power supply by light from a distant location, and particularly, to a method for supplying a high-voltage power to an energy transducer such as a micromachine by irradiating the transducer with light.  
         DESCRIPTION OF THE RELATED ART  
         [0002]    With recent progress in semiconductor manufacturing techniques and the like, research-and-development as well as proposals of prototypes of various micromachines (also named as “Micro Electro Mechanical Systems (MEMS) or Micro System Technology (MST) have been actively performed. Such systems have numerous functions and elements which are each integrated despite of the miniaturization of the size thereof, and find complicated and high-technique applications. Under such circumstances, in order to put micromachines to practical use, an energy supply method and effective power supply means for an actuating portion (actuator) constitute important elements for development.  
           [0003]    In particular, when the dimension of a micromachine relative to that of a human operator becomes significantly small, conventional power supply methods using a wire become disadvantageous. Specifically, the dimension of the wire relative to that of the micromachine body becomes large, and thereby, not only the actuation for the micromachine causes a problem, but also the weight of peripheral portions and the friction occurring therebetween come to have an influence such as not to be neglected. In addition, there may be cases where directions of actions of the micromachine and the actuation range thereof are subjected to limitations, depending on the stiffness and the length of the wire.  
           [0004]    One method for wireless-type power supply for a micromachine from a distant location, is light-based one. In this supply method, as an energy source, an electromagnetic wave such as light beam, a microwave, a sound wave, or the like is used, while as a receiver, a solar cell constituted of amorphous silicon, a silicon single crystal, or the like is used. Proposals have been made not only of a stationary-type and a battery-equipped self-traveling type micromachines, but also of a battery-unequipped type micromachine.  
           [0005]    Wireless-type power supply systems comprise (1) solar light and a solar cell, (2) a microwave and a light-receiving element. On the other hand, as wire-type power supply methods, there have been numerous proposals of electrical methods, magnetic methods, and the like. FIGS. 5A and 5B are bock diagrams showing self-traveling (wireless type) power supply systems, and FIG. 5C is a block diagram showing a stationary (wire type) power supply system.  
           [0006]    The control system also serves as an energy source, and the micromachine body is not equipped with an energy source. This relation can be seen from FIGS. 5A and 5B. The micromachine body has an energy receiving function, an energy conversion function, and an energy output function. However, these functions are performed by a single functional element, but not by a device as a system. As an actuator, an actuating mechanism such as an electrostatic actuator is used.  
           [0007]    For example, Japanese Unexamined Patent application Publication No. 4-241004 proposes a concept that solar light and a solar cell are used as an energy source and a receiver, respectively, and Japanese Unexamined Patent application Publication No. 6-46539 discloses that light beams, a microwave, and a sound wave are used as an energy supply system, and that an amorphous solar cell as a photovoltaic element, a monolithic microwave IC, and a piezoelectric material are each employed as a receiver for energy source.  
           [0008]    The electric power generation by a solar battery has already been put into actual use for objects which have a large size, such as a space structure. However, since the solar cell as a unit only generates about  1  volt or below, and incapable of generating a high voltage, it is necessary to integrate solar cells by connecting them in series. However, this causes a cost rise and incurs the complication of a device system to be produced.  
           [0009]    Techniques of transmitting energy to an intra-pipe actuator by means of microwave transmission have already been devised. In these techniques, however, for the case of a microwave, the propagation mode suited to the energy transmission is limited to a predetermined mode (TEn), so that the frequency range is restricted corresponding to the intra-pipe dimensions. In addition, it has been pointed out that these techniques involve problems in that they cannot be applied to the spaces in open systems and pipes having locally different dimensions. A little more improvement would be required, in order to bring up these techniques to the practical application stage.  
         SUMMARY OF THE INVENTION  
         [0010]    Accordingly, it is an object of the present invention to provide a wireless-type power supply method that is fundamentally applied to the case where an object to which energy is to be transmitted, is relatively small, and that allows high-voltage electrical energy to be transmitted without using a wire.  
           [0011]    It is another specific object to provide a wireless-type power supply method effective in applying to the energy supply to portable electronic equipment, handy medical diagnosis systems, micromachines in open systems (including micromachines for use in the atmosphere, for use under water, and for use in a vacuum) , environmental monitoring micromachines, in-vivo diagnosis monitoring machines, and intra-pipe maintenance machines.  
           [0012]    It is still another object to provide a wireless-type power supply method which allows energy transmission from a remote location, and which has the overall system thereof simplified.  
           [0013]    It is a further object to provide a wireless-type power supply method allows a high-voltage and low-current output to be achieved, which is suited to the actuating source for an electrostatic actuator.  
           [0014]    In order to achieve the above-described objects, the present invention provides a method for wireless-type power supply, which is applied to the case where an object to which energy is to be transmitted, is relatively small. In this method, the optical energy from an light source is converted into high-voltage electrical energy by an energy transducer formed of either a piezoelectric element or a photovoltaic element on the above-described object, and the above-described high-voltage electrical energy is supplied to an actuator.  
           [0015]    In a preferred embodiment of the present invention, a thermal excitation light source emitting visible infrared region laser light is used as a light source, and a piezoelectric element generating a thermal strain due to optical absorption is used as an energy transducer. More specifically, for the above-described piezoelectric element, a piezoelectric material constituted of lead zirconate titanate, barium titanate, or lead titanate is used.  
           [0016]    In another preferred embodiment of the present invention, a photovoltaic light source laser or an ultraviolet irradiation lamp is used as a light source, and a photovoltaic element generating a photovoltaic effect is used as an energy transducer. More specifically, for the above-described photovoltaic element, a photovoltaic functional material constituted of lead lanthanum zirconate titanate, lithium niobate, or lithium tantalate is used.  
           [0017]    In the above-described method in accordance with the present invention, since the electric output is characterized by a high voltage and low current, the electric output is suited to an actuating source for an electrostatic actuator which performs actuation using a high voltage and low current.  
           [0018]    Also, by using the bimorph type as the energy transducer, it is possible to resonate the energy transducer to obtain a high-voltage output, and thereby to provide the control over the electrostatic actuator with superior responsivity.  
           [0019]    The objects to which relatively small energies are to be transmitted, and which are suited to being subjected to the application of the above-described method in accordance with the present invention, specifically include portable electronic equipment, handy medical diagnosis systems, micromachines in open systems (including micromachines for use in the atmosphere, for use under water, and for use in a vacuum), environmental monitoring micromachines, in-vivo diagnosis monitoring machines, and intra-pipe maintenance machines.  
           [0020]    The above-described method in accordance with the present invention is arranged to allow energy transmission from a remote location by using a piezoelectric element or a photovoltaic element, and thereby the overall system thereof is simplified by unifying the structure and function, resulting in a simplified manufacturing, Furthermore, the method in accordance with the present invention allows the application thereof in open systems, and enables the output to be increased by making use of the resonance between the thermo-electromotive force and the photovoltaic force due to light-receiving.  
           [0021]    Moreover, since the present invention does not use a device as a solar battery but constitutes a receiver using a ceramic-based single element, a simple system can be realized. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a conceptual block diagram explaining the outline of the present invention;  
         [0023]    [0023]FIG. 2 is a diagram showing an embodiment of the present invention;  
         [0024]    [0024]FIG. 3 is a diagram showing another embodiment of the present invention;  
         [0025]    [0025]FIGS. 4A and 4B are diagrams showing an embodiment applied to an micromachine, wherein FIG. 4A is an outline view of this embodiment and FIG. 4B is a view showing an energy transducer therein; and  
         [0026]    [0026]FIGS. 5A to  5 C are block diagrams explaining the outlines of a conventional energy supply method, wherein FIG. 5A shows a self-traveling type (energy source equipped and signal transmitting type), FIG. 5B shows a self-traveling type (energy source transmitting type), and  5 C illustrates a stationary type. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The energy supply method in accordance with the present invention is suited to an object to which energy is to be transmitted is relatively small, such as a micromachine. This method comprises converting the optical energy from an light source into high-voltage electrical energy by an energy transducer formed of either a piezoelectric element or a photovoltaic element on the above-described object; and supplying the above-described high-voltage electrical energy to an actuator. More specifically, in this method,  
         [0028]    (1) a thermal excitation light source such as the visible infrared region laser is used as a light source, and a piezoelectric element generating a thermal strain due to optical absorption is used as an energy transducer, or  
         [0029]    (2) a photovoltaic light source laser or an (ultraviolet irradiation) lamp is used as a light source, and a photovoltaic element generating a photovoltaic effect is used as an energy transducer.  
         [0030]    The output generated in the above-described energy transducer is taken out as a high-voltage output, and this output is supplied to the actuator.  
         [0031]    The piezoelectric element generating a thermal strain is an element formed of piezoelectric material such as lead zirconate titanate (PZT) , lead lanthanum zirconate titanate(PLZT), barium titanate, or lead titanate. By irradiating the surface of the piezoelectric element with a directional light which can generate the wavelength of the infrared or visible region, thermal expansion is induced in the piezoelectric element. As a result, the piezoelectric element is subjected to expansions and contractions due to the periodic thermal expansion, thereby generating electric power. By laminating two sheets of piezoelectric elements so that the directions of the spontaneous polarization thereof become opposite to each other in order to form a bimorph structure, by vibrating the bimorph piezoelectric element from the both sides thereof, and by irradiating the bimorph piezoelectric element with light having a period such as to correspond to the natural frequency of the bimorph piezoelectric element, the bimorph structure comes into a resonant state. This enhances the effect of inducing high-voltage and that of raising the voltage.  
         [0032]    The above-described photovoltaic element is an element formed of a photovoltaic functional material such as lead lanthanum zirconate titanate (PLZT), lithium niobate (LN), or lithium tantalate (LT). A lamp or a laser capable of generating the wavelength of the ultraviolet region is used as a light source, and after a photovoltaic force has been induced by the light irradiation, a high-voltage output is achieved. The use of this photovoltaic material allows the same output as that of the above-described piezoelectric elements to be achieved. It has been confirmed that the electric output obtained by this type of element amounts to several kilovolts. Therefore, it becomes possible to construct an efficient micromachine by connecting thereto an actuating mechanism suited to a high voltage and low current, such as an electrostatic actuator.  
         [0033]    [0033]FIG. 1 is a conceptual block diagram showing a system for executing the energy supply method in accordance with the present invention. The light/heat  2  emitted from a light source control system  1  which controllably supplies optical-and-thermal energies, is inputted, without using a wire, to an energy transducer  3 , which is constituted of a piezoelectric element or a photovoltaic element on an actuated device  5  to which energy is to be transmitted. Then, the high-voltage output which the energy transducer  3  outputs by a thermal strain effect or a photovoltaic effect is inputted to the actuator (actuating mechanism)  4 , which actuates the actuated device  5 . As the actuated device  5 , a battery-unequipped self-traveling type micromachine is desirable. The piezoelectric element or the photovoltaic element constituting the minute energy transducer  3  can constitute a receiving portion, a converting portion, and an output portion using a single element.  
         [0034]    [0034]FIG. 2 is an embodiment wherein a comb-type electrostatic actuator  9  is used as an actuating mechanism  4  which is provided with a high-voltage output from the energy transducer  3 .  
         [0035]    The fixed portion  10  and the movable portion  11  of the electrostatic actuator  9  is each connected to the electrode  6  of the energy transducer  3  via conducting wires  7  and  8 , and the movable portion  11  is supported on supporting portions  12  such as springs. Reference character Ps denotes the direction of spontaneous polarization and an induced electromotive force. Reference numeral  13  denotes a polarity switch for changing the polarity of an output voltage. This polarity switch  13  is adapted to be used only when a photovoltaic element is used as the energy transducer  3 .  
         [0036]    In this embodiment, once the surface of the transducer  3  has been irradiated with the light/heat  2 , an electromotive force in the Ps direction is induced, and a high-voltage power is applied across the fixed portion  10  and the movable portion  11  of the electrostatic actuator  9 . As a consequence, the movable portion  11  is actuated in the direction of, for example, the arrow indicated in the figure. The actuation duration of the movable portion  11  corresponds to the irradiation duration (number of pulses) of light, and the actuation direction is determined by the switching of the polarity switch  13 . The teeth of the movable portion  11  of the electrostatic actuator  9  is arranged to move between teeth of the fixed portion without contacting teeth of the fixed portion.  
         [0037]    [0037]FIG. 3 shows another embodiment of the present invention, wherein a piezoelectric element  14  having a bimorph structure is used, and wherein both sides of the piezoelectric element  14  is irradiated with light  2 A and  2 B which have a period such as to correspond to the natural frequency of the piezoelectric element  14 . The output voltage of the piezoelectric element  14  is outputted from a common electrode  15  via a conducting wire  7 . In this method, the piezoelectric element  14  quickly comes into a resonant state. Making a phase difference between the lights  2 A and  2 B with which both sides of the piezoelectric element is irradiated, provides advantages in quickly creating a resonant state.  
         [0038]    [0038]FIG. 4A is a schematic view showing an embodiment wherein the energy supply method in accordance with the present invention is applied to a micromachine, and FIG. 4B is a diagram explaining the energy transducer in the embodiment shown in FIG. 4A. Once the surface of a pair of conversion elements  17  in an energy transducer  14  with a bimorph structure on a micromachine  17  has been irradiated with the laser lights  2 A and  2 B from a pair of controllable light sources  16  such as lasers, the electromotive force in the Ps direction is induced in each of the pair of the conversion elements, and thereby a power is supplied to the actuating mechanism in the micromachine  17 . The actuating mechanism for micromachine is operated by controlling the light supply by light sources  16  such as lasers.