System and method for detecting surface perturbations

This disclosure provides systems, methods and apparatus for assessing a surface using a piezoelectric element. In one aspect, the method includes applying a device to the surface, wherein the device includes at least one piezoelectric element and at least one EMS device, wherein the EMS device includes a conductive first layer separated from a conductive second layer, and wherein the piezoelectric element is electrically coupled to the EMS device such that a force applied to the piezoelectric element results in a voltage applied across the first and second layers.

TECHNICAL FIELD

This disclosure relates to sensors configured to detect surface perturbations.

DESCRIPTION OF THE RELATED TECHNOLOGY

Electromechanical systems include devices having electrical and mechanical elements, actuators, transducers, sensors, optical components (e.g., mirrors) and electronics. Electromechanical systems can be manufactured at a variety of scales including, but not limited to, microscales and nanoscales. For example, microelectromechanical systems (MEMS) devices can include structures having sizes ranging from about a micron to hundreds of microns or more. Nanoelectromechanical systems (NEMS) devices can include structures having sizes smaller than a micron including, for example, sizes smaller than several hundred nanometers. Electromechanical elements may be created using deposition, etching, lithography, and/or other micromachining processes that etch away parts of substrates and/or deposited material layers, or that add layers to form electrical and electromechanical devices.

One type of electromechanical systems device is called an interferometric modulator (IMOD). As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In some implementations, an interferometric modulator may include a pair of conductive plates, one or both of which may be transparent and/or reflective, wholly or in part, and capable of relative motion upon application of an appropriate electrical signal. In an implementation, one plate may include a stationary layer deposited on a substrate and the other plate may include a metallic membrane separated from the stationary layer by an air gap. The position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Interferometric modulator devices have a wide range of applications, and are anticipated to be used in improving existing products and creating new products.

In many manufacturing and quality control processes, it can be desirable to assess the flatness and/or uniformity of a surface. Traditionally, such assessment was performed either by sight or touch of a craftsman or using expensive ultrasonic, optical, or capacitive sensors that use a processor to provide an analysis of the surface under examination. It would be desirable to have a reliable and reproducible method of detecting surface perturbations without the need for expensive equipment

SUMMARY

One innovative aspect of the subject matter described in this disclosure can be implemented in a device for assessing a surface. In some implementations, the device includes at least one piezoelectric element and at least one electromechanical system (EMS) device. The EMS device may include a conductive first layer separated from a conductive second layer. The piezoelectric element may be electrically coupled to the EMS device such that a force applied to the piezoelectric element results in an introduction of charge to both the first and second layers.

In some implementations, the at least one piezoelectric element includes a two-dimensional array of piezoelectric elements, the at least one EMS device comprises a two-dimensional array of EMS devices, and each of the piezoelectric elements is electrically coupled to an EMS device at a corresponding location.

In some implementations, the at least one EMS device comprises at least one interferometric modulator. In some implementations, the first layer is at least partially reflective and at least partially transmissive and wherein the second layer is at least partially reflective.

In some implementations, a method of assessing a surface comprises applying a device to the surface, the device comprising at least one piezoelectric element and at least one EMS device including a conductive first layer separated from a conductive second layer, wherein the piezoelectric element is electrically coupled to the EMS device such that a force applied to the piezoelectric element results in an introduction of charge to both the first and second layers.

In some implementations, the method further includes viewing the at least one EMS device and determining the presence of a perturbation on the surface based on the viewing. The viewing may be performed by an image capturing device and the determining may be performed by a processor.

In some implementations, determining the presence of a perturbation comprises determining that at least one EMS device at a specific location has changed appearance and determining the presence of a perturbation at a corresponding location of the specific location. In some implementations, the method further includes removing the perturbation from the surface. In some implementations, removing the perturbation comprises machining, sanding, or laser-removing the perturbation.

In some implementations, a device for assessing a surface comprises means for generating a voltage in response to an applied force and means for changing reflective properties in response to an applied voltage. The means for generating may be electrically coupled to the means for changing such that a force applied to the means for generating results in a voltage applied across means for changing.

In some implementations, the means for generating comprises at least one piezoelectric element. In some implementations, the means for changing comprises at least one EMS device.

DETAILED DESCRIPTION

The following detailed description is directed to certain implementations for the purposes of describing the innovative aspects. However, the teachings herein can be applied in a multitude of different ways. Thus, the teachings are not intended to be limited to the implementations depicted solely in the Figures, but instead have wide applicability as will be readily apparent to one having ordinary skill in the art.

One implementation described herein includes a sensor with at least one piezoelectric element coupled to at least one EMS device. When pressure is applied to the piezoelectric element, a voltage is generated and applied to opposing surfaces of the EMS device, thereby drawing the opposing surfaces together. Pressure can be applied to the piezoelectric element when the sensor is pressed against a surface. Perturbations or asperities in the surface can result in additional pressure that can result in additional voltage generated by the piezoelectric element. The additional voltage, in turn, can result in additional displacement of the surfaces of the EMS device.

Particular implementations of the subject matter described in this disclosure can be implemented to realize one or more of the following potential advantages. In some implementations, such a sensor can be incorporated into a device that transforms, without a battery or external power source, surface perturbations into a false color image that can be viewed by a user to determine locations and magnitudes of such perturbations. Thus, the device can be used to reliably and reproducibly detect surface perturbations without the need for expensive equipment such as a processor or a power source. Of course, in other implementations, the device may include these features, including, for example, a processor or a power source.

One example of a suitable EMS device, to which the described implementations may apply, is a reflective display device. Reflective display devices can incorporate interferometric modulators (IMODs) to selectively absorb and/or reflect light incident thereon using principles of optical interference. IMODs can include an absorber, a reflector that is movable with respect to the absorber, and an optical resonant cavity defined between the absorber and the reflector. The reflector can be moved to two or more different positions, which can change the size of the optical resonant cavity and thereby affect the reflectance of the interferometric modulator. The reflectance spectrums of IMODs can create fairly broad spectral bands which can be shifted across the visible wavelengths to generate different colors. The position of the spectral band can be adjusted by changing the thickness of the optical resonant cavity, i.e., by changing the position of the reflector.

FIGS. 1A and 1Bare example block diagrams of a system including a piezoelectric element110coupled to an EMS device130.

The piezoelectric element110generates a voltage across two points of the piezoelectric element110when a force F, such as a pressure, is applied to the piezoelectric element110. The piezoelectric element110can be a naturally occurring or man-made material. For example, the piezoelectric element110can be quartz, wood, gallium orthophosphate (GaPO4), langasite (La3Ga5SiO14), barium titanate (BaTiO3), lead titanate (PbTiO3), potassium niobate (KNbO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), sodium tungstate (Na2WO3), sodium potassium niobate (NaKNb), bismuth ferrite (BiFeO3), sodium niobate NaNbO3, or polyvinylidene fluoride (PVDF). In some implementations, the piezoelectric element110is lead zirconate titanate (Pb[ZrxTi1−x]O3, 0<x<1), also known as PZT.

Depending on how the piezoelectric element110is prepared, three main modes of operation can be distinguished: transverse, longitudinal, and shear. In transverse operation, a force applied along a first axis can generate a voltage across a second axis perpendicular to the first axis. The amount of voltage generated can be generally proportional to the applied force and also can depend on the geometric dimensions of the piezoelectric element110.

In longitudinal operation, a force applied along a first axis can generate a voltage across the same axis. The amount of voltage generated can be generally proportional to the applied force and may not strongly depend on the geometric dimensions of the piezoelectric element110. Thus, in some implementations, the piezoelectric element110can include many piezoelectric elements110mechanically in series and electrically in parallel to increase the resulting voltage.

In shear operation, as in longitudinal operation, a force applied along a first axis can generate a voltage across the same axis that can be generally proportional to the applied force and may not strongly depend on the geometric dimensions of the piezoelectric element110.

As described above, in response to a force applied to the piezoelectric element110, a voltage can be generated across the piezoelectric element110. The piezoelectric element110can be coupled via one or more conductors120to a EMS device130. Thus, a generated voltage can be applied to the EMS device130.

In some implementations, as illustrated inFIG. 1A, a first surface112of the piezoelectric element110can be coupled via a first conductor122to a first layer132of the EMS device130and a second surface114can be coupled via a second conductor124to a second layer134of the EMS device130. In some other implementations, as illustrated inFIG. 1B, a first surface112of the piezoelectric element110can be coupled via a first conductor122to both a first layer132and a second layer134of the EMS device130and a second surface114can be coupled via a second conductor124to a separate capacitive element126.

When a force is applied to a piezoelectric element, the element creates a field that moves positive charges in one direction and negative charges in another. In the implementation ofFIG. 1A, a first conductor122connects to a location where positive charges are transported and a second conductor124connects to a location where negative charges are transported. Thus, the first layer132and second layer134of the EMS device130are pulled towards one another as the opposite charges attract. However, in the implementation ofFIG. 1B, The first conductor132couples the first layer132and the second layer134of the EMS device to the same surface112of the piezoelectric element110. Thus, both the first layer132and second layer134acquire either negative or positive charges. Thus, the first layer132and second layer134are pushed apart from one another as the similar charges repel.

When positive or negative charge is introduced to the first layer132and charge of an opposite polarity is introduced to the second layer134of the EMS device130, the first layer132and second layer134can be attracted to one another. When positive or negative charge is introduced to the first layer132and charge of the same polarity is introduced to the second layer134of the EMS device130, the first layer132and second layer134can be repelled from one another

In some implementations, the EMS device130can be an interferometric modulator. Thus, the first layer132can be conductive, at least partially reflective, and at least partially transmissive and the second layer134can be conductive and at least partially reflective. Thus, the cavity between the two surfaces can function as an interferometric cavity. In some implementations, the EMS device130can inferometrically modulate at least one visible wavelength of light. In some implementations, the gap distance between the first layer132and second layer can be less than 5 μm, less than 4 μm, less than 3 μm, less than 2 μm, or less than 1 μm. The reflective properties of the EMS device130can depend, at least in part, on the gap distance between the first layer132and the second layer134. In some implementations, the EMS device130can reflect different wavelengths of light depending on the gap distance. Thus, the EMS device130can appear as a different color depending on the gap distance, which is a function of the voltage applied which is, in turn, a function of the force applied to the piezoelectric element110.

In other implementations, the EMS device can be a cantilevered device in which a first surface can bend towards a second surface when a voltage is applied across the surfaces. In other implementations, the EMS device can be a liquid crystal element that can change its absorptive properties when a voltage is applied across the surfaces. In some implementations, the EMS device can be a spatial light modulator. In some implementations, the EMS device can be a holographic spatial light modulator. Each of these EMS devices can change its reflective properties in response to an applied voltage.

The gap distance of the EMS device can be a static distance when no voltage is applied the device. However, as mentioned above, when a force is applied to the piezoelectric element110, the gap distance and reflective properties of the EMS device130can change. Thus, the gap distance of the EMS device can be a deflected distance whose amount of deflection is based on the force applied to the piezoelectric element110. When the force is removed, the piezoelectric element110may no longer generate a voltage and, therefore, a voltage may not be applied to the EMS device130. In some implementations, because of hysteresis in the materials of the EMS device130, the EMS device130can automatically return to the static distance.

Although the piezoelectric element110can be modeled as a voltage source when a force is applied, the piezoelectric element110may be dissimilar to a battery in that the piezoelectric element may not continuously generate a current. Particularly, in response to an amount of applied force, the piezoelectric element110can generate a proportional amount of charge. If this charge is removed by, for example, completing a circuit between the two sides of the piezoelectric element110or by coupling both sides of the piezoelectric element110to a ground potential, the piezoelectric element110may be rendered inert. Once the circuit is broken and the force removed, an opposite charge can be generated. This charge can also be removed by completing a circuit between the two sides or by coupling both sides to a ground potential. However, in the implementation illustrated inFIG. 1, no circuit is formed and a maintained force can generate a maintained voltage applied across the first layer132and second layer134of the EMS device130.

The system100and principles described above with respect toFIG. 1can be used in a device for detecting perturbations in a surface.FIG. 2is an example cross-sectional view of a device for detecting perturbations in a surface. The device200can include an array of piezoelectric elements210, each electrically coupled to at least one interferometric modulator230. The coupling of the piezoelectric elements210to the interferometric modulators230can be one-to-one, many-to-one, or one-to-many. In some implementations, the device can include a two-dimensional array of piezoelectric elements210and a two-dimensional array of interferometric modulators230and each piezoelectric element210can be coupled to an interferometric modulator230at a corresponding location.

In some implementations, such as the implementation illustrated inFIG. 2, each piezoelectric element210can be coupled to an interferometric modulator230by two conductors222,224. In particular, a first side of the piezoelectric element210can be coupled by a first conductor222to a first layer232of the interferometric modulator230and a second side of the piezoelectric element210can be coupled by a second conductor224to a second layer234of the interferometric modulator230. The first layer232of the interferometric modulator230can be conductive, at least partially reflective, and at least partially transmissive. The second layer234of the interferometric modulator230can be conductive and at least partially reflective. The first layer232and second layer234can be separated by support posts233.

The array of piezoelectric elements210can be supported and protected by a flexible membrane240that can be applied to the surface201to be tested. The flexible membrane240can be made of an elastomer or other suitable material. An elastomer can be an elastic polymer, such as rubber. The array of piezoelectric elements210can be sandwiched between the flexible membrane240and a substrate250. The piezoelectric elements210can be directly attached to the flexible membrane240or can be formed on or attached to the substrate250. Similarly, the interferometric modulators can be formed on the substrate250. The substrate250can be formed of glass, plastic, metal, ceramic, or any suitable material.

The degree of flexibility of the flexible membrane240can be made commensurate with a range of surface irregularity to be measured. An artisan or user might use multiple such devices200as a series of inspection tools of various sensitivity, just as the surface to be measured might have been created through the use of a series of progressively less coarse sand papers.

In some implementations, the device200can also include a housing260that protects the interferometric modulators. The housing260can be formed of glass, plastic, metal, ceramic, or any suitable material. In some implementations, the housing260can include a transparent window262through which the interferometric modulators230can be viewed by a user of the device200. In some implementations, the housing260can include a portion245between the flexible membrane240and the substrate250. In some implementations, the portion245can be elastic, allowing for pressure from a uniformly flat surface to be applied to all the piezoelectric elements210simultaneously. In other implementations, the portion245can be rigid such that only perturbations202in the surface201result in pressure applied to the piezoelectric elements210.

When the device200is pressed against the surface201, pressure from the surface can push against the flexible membrane240. The piezoelectric elements230can be squeezed between the flexible membrane240and the substrate250, thereby deforming the piezoelectric elements210and generating a voltage that can be applied to the interferometric modulator230via the conductors. The first layer232of each interferometric modulator230can be displaced with respect to the second layer234according to the amount of voltage applied via the conductors. In some implementations, the second layer234is rigidly attached to the substrate250and, therefore, may not be displaced. When the first layer232is displaced relative to the second layer234, the reflective properties and apparent color of the interferometric modulator230can change, revealing to a user the amount of force applied to the corresponding piezoelectric element210.

In some implementations, perfect surface flatness can be displayed as magenta, and increasing deviations from flatness can cause the interferometric modulator230to display red, orange, yellow, green, cyan and blue. In other implementations, the colors are reversed.

FIG. 3Ais an example cross-sectional view of the device ofFIG. 2applied to a surface. When the device200is pressed against the surface201, the perturbation202can press against the rightmost piezoelectric element210. The piezoelectric element210can deform and generate a voltage. The voltage can be applied to the interferometric modulator230in the corresponding location, resulting in the first layer232of the interferometric modulator moving closer the second layer234. Thus, the reflective properties and the apparent color of the interferometric modulator230can change and, in particular, differ from the apparent color of the other interferometric modulators230. Thus, a user of the device200can detect and locate the perturbation202.

FIG. 3Billustrates the cross-sectional view ofFIG. 3Awith the device in another position. If the device200is moved along the surface201, the relative position of the perturbation202with respect to the device200can change. Thus, the perturbation202can apply a force to a different piezoelectric element210resulting in a change of color of a different interferometric modulator230. Thus, a user of the device200can detect and locate the perturbation202by moving the device along the surface201.

In some implementations, the device200also can include an image capture device to image the interferometric modulators230. In some implementations, such imaging can include measuring the capacitance of each interferometric modulator230and saving this information into a memory.

As described above with respect toFIG. 1, if two surfaces of a piezoelectric element210are electrically coupled, or if both surfaces are coupled to ground, a current can flow removing charge accumulated by the piezoelectric element. In some implementations, the device200can include shunts that can, based on input from a user, selectively discharge the accumulated charge of the piezoelectric elements210by either electrically coupling both surfaces together or by electrically coupling both surfaces to a ground potential. Thus, if a user of the device200activates the shunts, the device can be zeroed to a particular pressure profile. This can be useful to reset the device before assessing a surface.

FIG. 4is another example cross-sectional view of a device for detecting perturbations in a surface. The device400ofFIG. 4can be the same as the device200ofFIG. 2except for the relative position of the interferometric modulators230with respect to the substrate250. Whereas, in some implementations, such as the device200illustrated inFIG. 2, the interferometric modulators230can be attached to substrate250against which the piezoelectric elements210can be pressed, in other implementations, such as the device400illustrated inFIG. 4, the interferometric modulators can be attached to a second substrate452that is not between the interferometric modulators and the piezoelectric elements. In some implementations, the second substrate452can also perform the function of the window, thereby reducing the number of parts and simplifying construction of the tool.

FIG. 5is an example flowchart illustrating a method of assessing a surface. The method500can begin in block510by applying a device to the surface such as the device200ofFIG. 2. In particular, the device can include at least one piezoelectric element and at least one EMS device including a conductive first layer separated from a conductive second layer. In some implementations, the piezoelectric element can be electrically coupled to the EMS device such that a force applied to the piezoelectric element results in a voltage applied across the first and second layers. Thus, a perturbation of a surface can be detected. In some implementations, the device can be applied by a user, such as a craftsman, a manufacturer, or a quality control inspector. In other implementations, the device can be applied automatically by a testing machine. In some implementations, applying the device to the surface can include moving the device along the surface.

In some implementations, the at least one piezoelectric element can include a two-dimensional array of piezoelectric elements. Likewise, in some implementations, the at least one EMS device can include a two-dimensional array of EMS devices. In some implementations, each of the piezoelectric elements can be electrically coupled to a EMS device at a corresponding location. The at least one EMS device can include, for example, an interferometric modulator or a two-dimensional array of interferometric modulators. In particular, in some implementations, the first layer can be at least partially reflective and at least partially transmissive and the second layer can be at least partially reflective.

In some implementations, the device can include a flexible membrane and a substrate and the at least one piezoelectric element can be sandwiched between the flexible membrane and the substrate. Thus, applying the device to the surface can include applying a flexible membrane of the device to the substrate. In some implementations, the device can include a housing. Thus, applying the device to the surface can include holding the device by the housing and moving the device along the surface.

The method500can continue to block520by viewing the at least one EMS device. In some implementations, the housing can include a transparent window through which a user can view the at least one EMS device. In some implementations, the viewing can be performed by a user. In other implementations, the viewing can be performed by a testing machine including a camera or other image capturing device.

The method500can continue to block530by determining the presence of a perturbation on the surface based on the viewing. Determining the presence can include, for example, determining that at least one MEMS device at a specific location has changed appearance and determining the presence of a perturbation at a corresponding location of the specific location. In some implementations, the determining can be performed by a user. In other implementations, the determining can be performed by a testing machine including a processor which determines the presence of a perturbation based on a captured image of the at least one EMS device. In some implementations, the changed appearance may be a changed color of the at least one MEMS device. In some other implementations, the changed appearance may be a change in brightness of the at least one MEMS device.

The method500can continue to block540by removing the perturbation from the surface. The perturbation can be removed by machining the perturbation, sanding the perturbation, laser-removing the perturbation, etc. In some implementations, the perturbation can be removed by a user, such as a craftsman or a quality control inspector. In other implementations, the perturbation can be removed automatically by a testing or finishing machine.

Once a perturbation is removed, the method500can end or repeat (in block540) to further assess the surface and remove other perturbations.

FIG. 6is an example flowchart illustrating a method of manufacturing a device for assessing a surface. The method600can begin in block610by electrically coupling at least one piezoelectric element to at least one EMS device including a conductive first layer separated from a conductive second layer. The piezoelectric element can be electrically coupled to the EMS device such that a force applied to the piezoelectric element results in a voltage applied across the first and second layers. The electrical coupling can be performed, for example, by positioning the piezoelectric element next to the EMS device or by connecting conductors between the piezoelectric element and the EMS device.

In some implementations, the coupling can include electrically coupling a two-dimensional array of piezoelectric elements to a two-dimensional array of EMS devices such that each of the piezoelectric elements is electrically coupled to a EMS device at a corresponding location. In some implementations, the at least one EMS device can include at least one interferometric modulator or a two-dimensional array of interferometric modulators.

In some implementations, the method600can include sandwiching the at least one EMS device between a flexible membrane and a substrate. In some implementations, the flexible membrane can be made of an elastomer and the substrate can be made of glass, plastic, metal, or ceramic. In some implementations, the method600also can include forming the at least one EMS device on the substrate. The at least one EMS element can be formed as an interferometric modulator, a cantilevered device, a liquid crystal element, a spatial light modulator, or a holographic spatial light modulator. In some implementations, the method600can include forming the at least one EMS device on a second substrate.

Various modifications to the implementations described in this disclosure may be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other implementations without departing from the spirit or scope of this disclosure. Thus, the disclosure is not intended to be limited to the implementations shown herein, but is to be accorded the widest scope consistent with the claims, the principles and the novel features disclosed herein. The word “exemplary” is used exclusively herein to mean “serving as an example, instance, or illustration.” Any implementation described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations. Additionally, a person having ordinary skill in the art will readily appreciate, the terms “upper” and “lower” are sometimes used for ease of describing the figures, and indicate relative positions corresponding to the orientation of the figure on a properly oriented page, and may not reflect the proper orientation of the IMOD as implemented.