Patent Publication Number: US-2022238786-A1

Title: Optical actuator

Description:
GOVERNMENT RIGHTS 
     This invention was made with government support under NCI Grant# ROI CA166379 awarded by the National Institute for Health. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     An optical actuator is described and, more particularly, an optical actuator which creates a mechanical movement to do direct work. 
     Design of an actuator varies by intended use. For example, MRI machines have strong magnetic fields, and MRI-compatible robotics is a growing field. Conventional nonferrous piezoelectric motors can be made MRI compatible, but not MRI Safe. The non-ferrous metals in conventional piezoelectric actuators effects the BO field homogeneity of the MRI leading to distortions and reduced image quality. Pneumatic and hydraulic actuators can be made with no metal components, but this can lead to reduced precision and increased size. 
     In vacuum environments, traditional motors can be teleoperated and powered by onboard batteries; however, operation time is limited to the life of the batteries. Special seals can be created such that motor cables traverse the vacuum seal, but this adds complexity to the design of the vacuum chamber and poses a source of failure. 
     For explosive environments, such as fuel tanks in airplanes, motors can be shielded or operate with low voltages that have reduced sparking risk. For example, piezoelectric motors do not arc. 
     For the foregoing reasons, there is a need for a new actuator with no requirement for electronics or metallic components at or near the point of actuation. The actuator should be MRI Safe and usable as well in vacuum and explosive environments. Ideally, the actuator should be injection moldable or 3D printed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more complete understanding of the optical actuator, reference should now be had to the embodiments shown in the accompanying drawings and described below. In the drawings: 
         FIG. 1  is a perspective view of an embodiment of an optically actuated photostrictive actuator. 
         FIG. 2  is a perspective view of another embodiment of a photostrictive actuator. 
         FIG. 3  is a schematic side elevation view of an optical source for use with a photostrictive actuator as shown in  FIGS. 1 and 2 . 
         FIG. 4  is a perspective view of an embodiment of a piezoelectric actuator. 
         FIG. 5  is a schematic view of a plurality of optical sources for use with a photostrictive actuator as shown in  FIGS. 1 and 2 . 
         FIG. 6  is a schematic side elevation view of a plurality of movable optical sources for use with a photostrictive actuator as shown in  FIGS. 1 and 2 . 
         FIG. 7  is an embodiment of a photostrictive actuator for delivering vibration or sound. 
         FIG. 8  is a schematic view of another embodiment of a photorestrictive actuator. 
         FIG. 9  is a graph showing two patterns of pulsed light output delivered to light generators of the actuator shown in  FIG. 8 . 
         FIG. 10  shows Azobenzene LCPs deforming when exposed to 450 nm wavelength UV light and returning to its undeformed state when exposed to 365 nm wavelength UV light. 
         FIG. 11  is a schematic view of another embodiment of a photorestrictive actuator. 
         FIG. 12  is a graph showing two patterns of pulsed light output delivered to light generators of the actuator shown in  FIG. 11 . 
         FIG. 13  is a schematic view of an embodiment of a rotary motor. 
         FIG. 14  is a schematic view of an embodiment of a dual surface drive linear motor. 
         FIGS. 15 a  and 15 b    are schematic views of an embodiment of a multi-directional stack motor in a relaxation status and an excited status, respectively. 
         FIG. 16  is a schematic view of light output on an illumination surface of the multi-directional stack motor shown in  FIGS. 15 a    and  15   b.    
         FIG. 17  is a graph showing four patterns of pulsed light output delivered to the multi-directional stack motor shown in  FIGS. 15 a    and  15   b.    
         FIG. 18  is a schematic view of an embodiment of an apparatus for use in an underwater environment. 
         FIG. 19  is a schematic view of an embodiment of an apparatus for use in a vacuum environment. 
     
    
    
     DESCRIPTION 
     Certain terminology is used herein for convenience only and is not to be taken as a limiting. For example, words such as “upper,” “lower,” “left,” “right,” “horizontal,” “vertical,” “upward,” “downward,” “top” and “bottom” merely describe the configurations shown in the FIGs. Indeed, the components may be oriented in any direction and the terminology, therefore, should be understood as encompassing such variations unless specified otherwise. The words “interior” and “exterior” refer to directions toward and away from, respectively, the geometric center of the core and designated parts thereof. The terminology includes the words specifically mentioned above, derivatives thereof and words of similar import. 
     A photostrictive, or photomechanical, actuator comprises a material which deforms when exposed to light, or other electromagnetic radiation, and partially returns substantially to a first undeformed state when the light is removed under a hysteresis effect. The deformable material could be a layer of lanthanum doped lead zirconium titanate (PLZT). In alternative embodiments, the deformable material may be another material with a light activated strain, including but not limited to lead magnesium niobate-lead titanate (PMN-PT), BiFeO 3 , and azobenzene-containing liquid-crystalline polymers (LCP&#39;s). A single ultraviolet (UV) light source will deform PLZT, PMN-PT and BiFeO 3 . Controlling the duration of delivery of the light for exposing the material causes desired deformation. Various types of light sources may be used, including across a spectrum (including center wavelength and associated FWHM). Light sources used to control the actuator, or portions thereof, may be pulsed on and off or may be controlled with variable intensity. 
     In one configuration, (Pb 0.97 La 0.03) (Zr 0.52 Ti 0.48) 1-0.03/4O 3 , [PLZT (3/52/48)] doped with 0.5% WO 3  performs with a photostrictive effect under 366 nm wavelength and 10 mW/cm 2  power density UV light source. For example, the response time of PLZT (3/52/48) is typically slow, several seconds up to one minute. As an alternative, PMN-PT-32% has a larger piezoelectric constant and faster response time, about 1 second. BiFeO 3  performs with less photostrictive efficiency as compare to optimized PLZT ceramic; however, the BiFeO 3  single crystal will be more suitable for certain applications due to a much faster response time, below about 100 μs. Azobenzene LCPs deform when exposed to 450 nm wavelength UV light and returns to the undeformed state when exposed to 365 nm wavelength UV light ( FIG. 10 ). A phase-changing, pulsed light system may be applied to any of the materials. The different materials have different timescales for the contraction and extension, and the appropriate dynamic parameters may be tuned by material selection and preparation, as well as the light source configuration and control. Different materials with different time responses or spectral responses may be combined into a single actuator for control over the motion, and in some embodiments, completely or partially decouple the motion of different portions of the actuator. 
     Light from a light source may be controlled and the light patterns designed and customized for application to the photostrictive material. In one configuration, a light guide is comprised of one or more optical fiber cables and may output the desired pattern. In one embodiment, light output will be converted to pulsed light output via pulsed light generators with a predetermined pattern. A laser will generate a light output in the spectrum between 300 nm and 10,000 nm. A suitable laser may be selected from lasers including, but not limited, to Ar-ion laser; Nd: YAG lasers; Ti: sapphire lasers; tunable solid state and dye lasers; semiconductor laser; and carbon dioxide lasers. As described above, a control system can be applied to generate variable intensity light output. The desired light output can be spread by an optical system, which is comprising to apparatus generating a light output in the visible or infrared spectrum, and other guides via a lens or another coupler. 
     Referring now to the drawings, an embodiment of an embodiment of a photostrictive, or photomechanical, actuator is shown in  FIG. 1  and generally designated at  100 . The actuator comprises a material  101  which deforms when exposed to light, or other electromagnetic radiation, and partially returns substantially to its first undeformed state when the light is removed under hysteresis effect. In one embodiment, the material  101  may be a discrete component bonded to other layers of the actuator  100 , or the material  101  may be directly applied to another material. 
     The embodiment of the actuator as seen in  FIG. 1  further comprises a stator  102 . The optically actuated material  101  is bonded to the stator  102 , which functions to transmit the deformation of the material  101 . 
     Deformation of the material  101  is induced by one or more optical sources  103 ,  104  comprising light sources that illuminate the material  101 . The light sources  103 ,  104  may be fully integrated into a fixture such as, but not limited to, LEDs or lasers. The light sources can be disposed in a motor enclosure with the actuator  100 . Alternatively, light generators may be remote from the actuator  100  or the site of actuation and optically coupled to the light sources  103 ,  104 , such as through optical fibers or other light guides. In this configuration, one or more lens may be disposed in the body of the motor enclosure. 
     The stator  102  is frictionally coupled to a moving element  105 . Deformation is transmitted by the stator  102  to the moving element  105  which converts deformation transmitted by the stator  102  into motion of the moving element  105 . In one embodiment, the stator  102  has a predetermined periodic pattern of deformation. 
     In one embodiment, the actuator  100  is a rotary motor. The light-actuated material  101  bonded to the stator  102  deforms when exposed to the light sources  103 ,  104 , resulting in rotation of the moving element  105 . The moving element  105  thus functions as a rotor. in this rotary motor embodiment, a form of attachment, such as a rotational shaft  106  or a mounting hole pattern, mechanically couples the motor such that the motion can be used by an external device. 
     In one application, the material  101  and the stator  102  are fixed in space and the rotor  105  moves relative to the material  101  and the stator  102 . This arrangement has the advantage of enabling the light sources  103 ,  104  to also remain fixed. However, it is understood that the material  101  and the stator  102  may move with respect to rotor  105  which remain as a fixed element. 
     Another embodiment of a photostrictive actuator is shown in  FIG. 2 . This embodiment of the actuator comprises a material  201  which deforms when exposed to light or other electromagnetic radiation and returns substantially to its undeformed state when the light is removed. The material  201  is disposed on a stator  202 . The stator  202  can be used to generate translational motion along one or more degrees of freedom to an adjacent planar or spherical moving body  205 . The moving body  205  may be loaded against the stator  202  via a spring or massive object  207  against gravity. The moving body  205  can be attached via a protrusion, a mounting hole pattern  206 , or may be used directly to push or pull another object. It is understood this arrangement does not exclude the scenario wherein the moving body  205  can be part of another object that is being actuated. The arrangement also does not exclude a configuration wherein the moving body  205  can be rotated in addition to, or instead of, translated. 
     Referring to  FIG. 3 , an optical source  301  can be used to produce light or other electromagnetic radiation. The optical source  301  can be coupled to an optical de-multiplexer  303 . The de-multiplexer may comprise a beam splitter and acoustic shutters to time or direct produced light or other electromagnetic radiation into a fiber  304  or other guide to the material  101 ,  201  that deforms when exposed to light. It is understood, however, that the output from the acoustic de-multiplexer  303  may be directly coupled onto a target part. In another embodiment, shown in  FIG. 5 , multiple optical sources  501  are each coupled  504  via fibers or other guides to a lens  503  or another coupler. 
     A regular piezoelectric actuator  400  ( FIG. 4 ), or equivalent, can be converted into an optical actuator via the addition of photoelectric converters  403 . The photoelectric converters  403  can be attached directly to piezoelectric material  401  or another material that has electrically dependent strain characteristics. 
     As shown in  FIG. 6 , the optical termination  602  can be coupled to or spaced from a material  603  which deforms when exposed to light or other electromagnetic radiation and returns substantially to its undeformed state when the light is removed. It is understood that the optical termination  602  may be movable relative to the material  603 . 
     An embodiment of an actuator shown in  FIG. 7  can be used to create varying pressures in a medium, such as required to produce sound. This embodiment of the actuator comprises a material  701  which deforms when exposed to light or other electromagnetic radiation. This material is bonded to a layer  702  that transfers, couples or amplifies the vibrations onto an element  703  which, in turn, couples or moves the medium. The element  703  can be cone shaped, flat, circular, or other design that is meant to displace the medium within which the element  703  resides. However, it is understood that the actuator may also create pressures in a medium in which the actuator does not completely, or at all, reside. 
     Another embodiment of an actuator is shown in  FIG. 8  and generally designated at  800 . In this embodiment, the actuator  800  comprises a light-actuated material  801 , which may be a discrete component bonded to other layers, or may be directly applied to another material acting as stator. A rotor  802  is paired with the surface of the material with high pressure in a direction toward the stator as indicted by an arrow  809  in  FIG. 8 . A light source  805  generates light output that passes through a light guide  808 . In one embodiment, the light guide  808  comprises of one or more optical fibers. In one configuration, the light guide  808  is a multi-mode fiber optic cable. The light output is transferred through via the fiber optic cable  808  to one configuration of the optical system  803 ,  804  which direct the light output upon the illumination surface of the material  801  and excited the illuminated area. In one embodiment, the light output will be converted to pulsed light output via pulsed light generators  806 ,  807 . As shown in  FIG. 9 , first pulsed light generators  806  deliver a pattern  901  while second pulsed light generators  807  deliver another pattern  902 . With these patterns, the shape of the excited area deforms and generates a traveling wave in a direction indicated by an arrow  810 . The traveling wave engages the surface of the rotor  802  at each individual wave peak of the elliptical trajectory  811  where the rotor is frictionally coupled to the material  801  for output generating motion. The direction of movement  812  of the rotor  802  as indicated by an arrow  812  is a direction opposite to the direction  810  which a traveling wave follows. 
     In another embodiment shown in  FIG. 11 , the light actuating material  1101  comprises Azobenzene LCPs. The light actuating material  1101  may be a discrete component bonded to other layers, of the light actuating material  1101  may be directly applied to another material acting as a stator. A rotor  1102  is paired with the surface of stator with high pressure in a direction toward the stator as indicted by an arrow  1110  in  FIG. 10 . Light sources  905 ,  906  generate various light output that passes through a light guide  1109 . In one embodiment, the light guide  1109  comprises one or more optical fibers. In this configuration, 365 nm wavelength and 450 nm wavelength UV light, respectively, go into multi-mode fiber optic cable  1109 . In one embodiment, each light output will be converted to pulsed light output via pulsed light generators  1107 ,  1108 . The pulsed light will follow the patterns shown in  FIG. 12 . In one configuration, one light output  1107  will have two pulse patterns  1001 ,  1003  and the other light output  1108  will have another two pulse patterns  1202 ,  1204 . 
     Light output is transferred via fiber optic cable to two configurations of optical systems  1103 ,  1104 , each designed to direct the light output upon the illumination surface of the material  1101  and excited the illuminated area. The shape of the excited area deforms and generates a traveling wave in a direction indicated by an arrow  1112 . The traveling wave engages the surface of the rotor  1102  at each individual wave peak of the elliptical trajectory where the rotor is frictionally coupled to the material  1101  for output generating motion. The direction of movement of the rotor  1102  as indicated by an arrow  1113  is a direction opposite to the direction  1112  which a traveling wave follows. The rotor rotates in a direction indicated by an arrow  1113  opposite to the direction of the traveling wave  1112 . 
     An embodiment of a rotary motor is shown in  FIG. 13  and generally designated at  1300 . The rotary motor  1300  comprises a photostrictive material  1301  which functions as a stator. A rotor  1302  is paired with the surface of the stator under high pressure in a direction indicated by an arrow  1306 . In one configuration, light output is transferred via optic cables  1305  to one configuration of an optical system  1303 ,  1304  designed to direct the light output upon the illumination surface of the material  1301 . As described above, the light delivered may following an excited pattern. The shape of the excited area of the material deforms and generates a traveling wave in a direction indicated by an arrow  1308 . The rotor  1302  engages the stator only at each individual wave peak of the elliptical trajectory where the rotor is frictionally coupled to the material  1301  for output generating motion. The direction of movement  1309  of the rotor  1302  is a direction opposite to the direction which a traveling wave follows as indicated by an arrow  1308 . The rotor  1302  rotates in the direction  1309  opposite to the direction of the traveling wave  1308 . 
     Referring to  FIG. 14 , an embodiment of a dual surface drive linear motor is shown and generally designated at  1400 . The linear motor  1400  comprises a pair of layers of photostrictive material  1401  are acting as stators. A slider  1402  is sandwiched between a top layer and a bottom layer of stators. High pressure is applied across the layers in a direction indicated by an arrow  1405 . In one configuration, light output is transferred via optic cables  1404  to an optical array system  1403  designed to direct the light output upon an illumination surface of the material  1401 . The light is delivered in a pattern as described above. T shape of the excited area of the material  1401  deforms and generates a traveling wave  1407 . The slider  1402  touches the stator only at each wave peak on both top and bottom surfaces. The peaks of the wave carry out orbital of surface particle, for example ellipse trajectory, movement  1407 . The direction of movement of this orbital of surface particle  1406  is a direction contrary to the direction of the traveling wave  1407 . The slider moves in a direction  1408  opposite to the traveling wave  1407 . 
     Referring to  FIGS. 15 a  and 15 b   , show an embodiment of a multi-directional stack motor generally designated at  1500 . In one embodiment, the stack motor  1500  comprises a bimorphic polymeric photostrictive materials stacked together to a desired array structure. In one configuration, a 2×2×5 array of bimorphic material is stacked. An output element  1502  is centrally located on a top surface of the array  1501 . A light source  1503  generates light output that passes through a light guide. In one embodiment, light output will be converted to pulsed light output via pulsed light generators  1504  following the example phase shifting patterns  1701 - 1704  shown in  FIG. 17 . One light source will follow one pulse pattern  1701 . Two light sources will follow a second pulse pattern  1702 . Three light sources will follow a third pulse pattern  1703 . Four light sources will follow a fourth pulse pattern  1704 . Light output is transferred into multi-mode fiber optic cable  1505  and then reflects and spreads upon the illumination surface of the material ( FIG. 16 ). Another embodiment can be fiber sensor connector or fiber terminal connecting and spread method. The output light transfers from fiber optic cable  1603  to one configuration of optical the system  1602 . In one embodiment, two layers array of 45° reflecting micro mirrors  1607 ,  1608  are disposed between the two layers of bimorphic polymeric photostrictive material  1601 . When the light output  1606  is illuminating, the light is reflected by the micro-mirror array and illuminates the surface of the material  1601 . In one configuration, the light output may be passed through the front mirrors to reach the end mirrors. Light power loss and reflecting ratio need to be considered. Under the arrangement shown in  FIG. 17 , the whole stack array twists around and the output element rotates on a surface parallel to the ground. In another embodiment, the patterns can be different phase shifting setup, for example, 30° phase shifting with overlap causing the output element to rotate on a surface parallel to the ground but in a smaller circle. Alternate switchable working pulse patterns, for example only 1 and 3 output pulse while 2 and 4 output none, the output element rotates on a surface vertical to the ground. 
       FIG. 18  shows an embodiment of an apparatus under water environment application and is generally designated at  1800 . In one embodiment, the apparatus  1800  includes a motor  1801  located in a water tank  1803  and below the water  1804  surface. In one configuration, pulsed light output is transferred via optic cable  1806  to an optical system  1805  designed to direct the light output. The light output  1807  illuminates the water  1808 , which light output reflects and, primarily, refracts  1809  a certain angle through water and illuminates upon the surface of the photostrictive material  1802  to excite and deform the material. The light output power loss needs to be carefully considered due to reflection, refraction and passing through water. The location of the actuator  1800  and light output also need to be aligned to transfer the maximum light power density. It is understood that different liquid, as well as multiple layers of liquid, with different refractive indices can be used. The refractive angle needs to be accurate. 
       FIG. 19  shows an embodiment of an apparatus for use in a vacuum chamber environment and is generally designated at  1900 . In one embodiment, the apparatus  1900  comprises an actuator  1901  located inside a vacuum chamber  1903 . In one configuration, the chamber  1903  has an upper surface including a glass window  1904  or other transparent material with sufficient light absorbance index. An external pump  1905  maintains the vacuum state  1911  within the chamber  1903 . In use, pulsed light output is transferred via an optic cable  1907  to an optical system  1906  designed to direct the light output. The light output  1908  illuminates upon the glass at  1909 . The light output reflects and mainly passes  1910  through the glass and illuminates the surface of the photostrictive material  1902  to excite and deform. In a configuration, the light output power loss needs to be considered due to transparent material absorbance index. The location of the actuator  1901  and the light output also need to be aligned to transfer the maximum light power density. In another embodiment, a nested vacuum chamber configuration can be also applied. In this configuration the dual transparent material absorbance needs to be considered. In another embodiment, superconducting environment with super low temperature and super high pressure may also applied to this configuration. 
     The photostrictive actuator as described herein has many advantages, including providing a type of optical motor that is compatible in unique environments, such as MRI machines, vacuum environments, explosive environments, and the like. The actuator can safely operate in the strong magnetic fields of the MRI machine, magnetoencephalogram, or other NMR devices. The actuator can thus achieve the highest interoperability classification of “MRI Safe”. In a vacuum environment, the drive signal to the actuator can be passed through a clear window, which is typically available in vacuum chambers. An optical coupling allows the motor to be actuated without a wire breaching the vacuum seal. This may also apply to underwater applications. The actuator can operate without battery life restrictions. The actuator operates without any electronics in an explosive environment, which removes the risk associated with sparking of the motor. 
     The actuator will also work in other highly sensitive environments, such as for instrumentation, where electronics must be removed from the actuator to minimize chances for interference. This could be applicable to scientific instrumentation for terrestrial labs as well as space applications. Moreover, the optical “back end” of the motor may be a large, intricate device. However, at the point of actuation, the optical back end could be coupled to a very low cost piezo crystal (essentially just a ceramic disc) without necessarily needing physical contact (i.e. across a sterile boundary). This arrangement could be ideal for actuated modules in a single-use sterilized surgical kit. Micro-actuation techniques may be possible by placing an optical unit remotely and a highly focused small optical fiber or light guide at the actuator. 
     If made into a vibration device or a speaker, the resonant motor may operate as an underwater ultrasonic module when made from parts that do not corrode and as there are no wires losing their conductivity in ionic environments. in an aerospace application, an optical coupling allows the motor to be actuated without a wire control setup, for example, for use as rolling a reaction wheel in Hubble Space Telescope turning angles. Other more direct solutions are possible without the need for tangential solutions, such as battery, shielding, etc., as in the aforementioned industries. 
     Although the optical actuator has been shown and described in considerable detail with respect to only a few exemplary embodiments thereof, it should be understood by those skilled in the art that we do not intend to limit ourselves to the embodiments since various modifications, omissions and additions may be made to the disclosed embodiments without materially departing from the novel teachings and advantages of the apparatus, particularly in light of the foregoing teachings. Accordingly, we intend to cover all such modifications, omission, additions and equivalents as may be included within the spirit and scope of the apparatus, system and method as defined by the following claims. In the claims, means-plus-function clauses are intended to sticker the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures. Thus, although a nail and a screw may not be structural equivalents in that a nail employs a cylindrical surface to secure wooden parts together, whereas a screw employs a helical surface, in the environment of fastening wooden parts, a nail and a screw may be equivalent structures.