Non-contact information monitoring system

Abstract

The deformation monitoring system comprises a first camera configured to capture a first image of the object, a second camera configured to capture a second image of the object, and a controller configured to perform the steps of imaging the object with the first camera at a first time and imaging the object with the second camera, determining a first location of a first measurement point and a first location of a second measurement point on the object at the first time based on the imaging by the first and second cameras at the first time, imaging the object with the first camera and imaging the object with the second camera at a second time, determining locations of the first and second measurement points on the object at the second time based on the imaging by the first and second cameras at the second time, and determining a deformation of the object based on the locations of the first and second measurement points at the first and second times.

Description

[Technical field]

[0001] The present invention relates to a deformation monitoring system and a deformation monitoring method. [Background technology]

[0002] All physical objects constantly deform in shape as they undergo changes in temperature, relaxation of residual stresses, etc. For example, the suspension components of an automobile (e.g., push rods, wishbones, drive shafts, etc.) all bend, twist, compress, and stretch as the automobile travels along the road. During the design phase of these components, they may be placed into test rigs that deform the components by simulating the forces they will experience during use. Measuring these deformations allows engineers to optimize the component's design to reduce cost and weight while also ensuring that the components will not break during use.

[0003] As a further example, when a material (e.g., a carbon composite) is being manufactured, a sample of the manufactured material may be placed in a testing machine that deforms the sample by applying a force (often tension or compression). By measuring the resulting deformation, it is possible to measure a property of the material (e.g., elastic modulus) as part of a quality control or other testing process.

[0004] Whatever the object, there is frequently a need to accurately measure deformation of the object, whether the deformation is produced via a test apparatus or through actual use.

[0005] Traditionally, deformation measurements have been made using "contact" sensors such as digital test indicators, linear variable differential transformers, and strain gauges. Such devices are typically only capable of measuring a single location on an object, and can only measure deformation along a single axis. Thus, to obtain a detailed understanding of the deformation, it may be necessary to install multiple such sensors on the object. For this reason, the use of such sensors tends to be time consuming and expensive, and the associated wiring quickly becomes unwieldy and prone to failure. Furthermore, each sensor in contact with the object exerts a force on the object, and will therefore have some effect on the deformation being measured. In some cases, the force exerted by the sensor can dramatically affect the deformation of the object, making it difficult to obtain accurate deformation data. Summary of the Invention

[0006] According to a first aspect of the present invention, there is provided a deformation monitoring system for measuring deformation of an object, the system comprising: a first camera configured to capture a first image of the object; a second camera configured to capture a second image of the object and in a known orientation relative to the first camera; and a controller configured to cause the deformation monitoring system to perform the steps of imaging the object with the first camera at a first time, imaging the object with the second camera at the first time, determining a first location of a first measurement point on the object at the first time and a first location of a second measurement point on the object at the first time based on the imaging by the first camera and the second camera at the first time, imaging the object with the first camera at a second time different from the first time, imaging the object with the second camera at the second time, determining a location of a first measurement point on the object at the second time and a location of a second measurement point on the object at the second time based on the imaging by the first camera and the second camera at the second time, and determining a deformation of the object based on the locations of the first measurement point and the second measurement point at the first time and the second time.

[0007] Such a configuration allows the system to more easily and accurately measure deformation of the object. The system may also function with a single camera, but it may be difficult to detect or measure movement of the measurement point along the optical axis of the camera (also called out-of-plane movement). Determining the location of the measurement point on the object based on imaging by the first and second cameras may include a photogrammetry process or the like.

[0008] Additionally, the system can monitor more than two measurement points at a single time, allowing deeper analysis to be performed. Each camera may image at least two measurement points on the object, and optionally more than two measurement points. The measurement points may all be captured within a single image taken by each camera.

[0009] The measurement points may be features or symbols on the object. The measurement points may be corners, edges, or holes on the object. Alternatively, the measurement points may be symbols drawn on the object, such as circles or crosses. The measurement points may also be referred to as measurement locations. An image of the object captured by the camera may include the measurement points, and the controller may identify the measurement points in the image. In this manner, the locations of the measurement points may be determined.

[0010] Determining the locations of the measurement points may include identifying symbols or features on the object.

[0011] Determining the locations of the measurement points may include using a Hough transform, which allows the measurement points to be more easily located within the image, especially when the features or symbols defining the measurement points are distorted, such as by being imaged at an oblique corner.

[0012] The controller may be configured to determine locations of one or more holes, edges, and / or corners of the object, and the determination of the locations of the measurement points may be based at least in part on the determined locations of the one or more holes, edges, and / or corners, which may assist in locating the measurement points and may reduce the likelihood of misidentification of the measurement points.

[0013] Determining the locations of the measurement points may include determining locations in an object-based coordinate system or another non-native coordinate system. The system may use a coordinate system based on a measurement system having an origin at the camera, for example, but using a different coordinate system may allow the system to be used with low latency because the calculation of transformations is simpler. A non-native coordinate system may be more useful to a user because less downstream processing is required to obtain meaningful results.

[0014] The system may further comprise an artificial light source configured to illuminate the object. The light source may improve image quality. It may also improve the signal-to-noise ratio of the image data, allowing the measurement point to be more accurately positioned by the controller. Additionally, the light source may reduce the exposure time required for the image, improving the accuracy of the measurement and allowing the location of the measurement point to be determined with more precise timing.

[0015] The artificial light source may be configured to generate monochromatic light, and optionally the first camera and / or the second camera may include a bandpass filter configured to allow light of the wavelength of the artificial light source. This allows the image to be taken with less interference, such as radiation generated by the temperature of the object or other ambient light. This may particularly improve the measurement accuracy when there is some change in the spectrum of the light emitted by the test sample, such as due to ambient light or heating of the test piece. Such changes in light conditions may lead to measurement inaccuracies due to chromatic aberration of the lens, which may cause the measurement location in the image to move apparently, resulting in inaccurate measurement data.

[0016] The artificial light source may be configured to generate polarized light. Optionally, the first camera and / or the second camera may include a polarizing filter arranged orthogonal to the polarization direction of the artificial light source. This may reduce glare from the light source detected by the camera, as only non-specular reflections of light from the light source may be detected. Reducing glare increases the reliability of the measurement, as the controller is less likely to misidentify a measurement point.

[0017] The light source may be a strobe light. Optionally, the strobe light may be synchronized with the first and second cameras so that the object is illuminated during the imaging of the object by the first and second cameras. In this way, the strobe light may be "overlaid", which means that a high instantaneous power may be used for the light, providing a high level of illumination and allowing images to be generated with short exposure times. This may allow the time at which the object image should be determined to be more accurate, and therefore may allow for higher deformation measurement accuracy. The overall latency of the device may also be reduced, which may be particularly beneficial in closed-loop control of measurements and images. Motion blur is also reduced, improving measurement accuracy.

[0018] The first and second cameras may be arranged in a fixed orientation. In other words, the optical axes of the first and second cameras may be fixed relative to each other such that the position and orientation of the second camera relative to the first camera is known and constant. For example, the cameras may be mounted to each other or on a common platform. Alternatively, the second camera may be movable relative to the first camera and the orientation of the second camera relative to the first camera may be measured and transmitted to the controller via an encoder or the like.

[0019] The first and second cameras may each have a focal length, and the focal length may be the same at the first time and the second time, which may make it easier to calculate the position of the measurement location from the images.

[0020] The controller may be configured to attempt to determine the locations of the first and second measurement points (i.e., in the image acquired at the first time) at a first time, and may be configured to instruct the first camera and / or the second camera to acquire further images of the object based on a failure to do so. In other words, if the controller is unable to identify one or more of the measurement points in an image from the first or second camera at a first time, the controller may instruct the camera to acquire further images, which may then be analyzed to determine the locations of the measurement points. Thus, the controller may be configured to determine whether to instruct the first camera and / or the second camera to acquire at least one further image of the object at a first time based on a level of success in determining the locations of the measurement points.

[0021] The controller may be configured to attempt to determine locations of the measurement points in an image from the first camera and an image from the second camera, and to determine a level of success for each image separately.

[0022] Based on a failure to determine a location of the measurement point in images from only one of the first camera and the second camera at a first time, the controller may be configured to instruct only the corresponding one of the first camera and the second camera to acquire at least one further image.

[0023] The controller may attempt to determine locations of the measurement points in the further images, and may abort commands to acquire further images based on determining the locations of all of the measurement points in the further images. The controller may also begin measuring the object at this stage, such as measuring distances between the measurement points. This allows for a more automated system and reduces the burden on the user.

[0024] The controller may be configured to cause the deformation monitoring system to acquire images of the measurement points at further times following the second time until determining the location of at least one of the measurement locations fails, thereby allowing the system to act autonomously to continue making measurements until the experiment is terminated, such as by failure of the sample or removal of the sample by a user.

[0025] The system may further comprise an accelerometer or a magnetometer, and the controller may be configured to determine the orientation of the first camera and / or the second camera based on the output of the accelerometer or the magnetometer. The accelerometer may determine the orientation of the deformation monitoring system relative to the horizontal, and the magnetometer may determine the orientation of the deformation monitoring system relative to magnetic north. Thus, the deformation monitoring system may be used to measure objects in an environment and compare the deformations to a known reference frame.

[0026] The deformation monitoring system may further comprise an alignment system configured to project alignment markings proximate to the object. The alignment system may comprise a laser configured to project alignment markings proximate to the object, i.e. generally towards the object. The alignment markings may indicate the limits of the measurement volumes of the first camera and the second camera and / or the centres of the measurement volumes. The alignment system may be fixed to the cameras to move with the cameras, thus assisting a user in setting up the deformation monitoring system to ensure that the measurement points are within the measurement volumes and within the images acquired by the cameras.

[0027] The controller may be configured to perform a verification function, the verification function including the steps of recognizing a verification object, measuring a distance between measurement points on the verification object, and comparing the measured distance to a known value of the distance between the measurement points on the verification object. The controller may be configured to repeat the measurement and comparison steps of the verification function until determining at least one of the measurement locations fails. The verification function may improve the accuracy and reliability of the results, and may do so in an automated manner, reducing the burden on the user. Repeated measurements may further improve the verification function, as the user may be free to move the verification object and perform the verification process more completely.

[0028] The controller may be configured to record at least one of the images from the first and second cameras, the locations of the measurement points, and the determined deformation. The recording function may enable the system to be used as a stand-alone system, with the data being transferred to a separate system at a later time.

[0029] The controller is configured to identify an identifier from the images from the first camera and / or the second camera. The identifier may be unique. The identifier may be on or associated with the object. The identifier may be alphanumeric or a barcode or a QR code. Data from the identifier may be captured and recorded together with the measurement data and / or the images. This may assist a user in processing the data at a later time.

[0030] According to a second aspect of the present invention, there is provided a method for monitoring deformation of an object, the method comprising the steps of providing an object having first and second measurement points, imaging the first and second measurement points with a first camera, imaging the first and second measurement points with a second camera, determining locations of the first and second measurement points based on the imaging by the first and second cameras, deforming the object to generate a deformed object having deformed measurement points, imaging the first and second deformation measurement points with the first camera, imaging the first and second deformation measurement points with the second camera, determining locations of the first and second deformation measurement points based on the imaging by the first and second cameras, and determining the deformation of the object based on the locations of the first and second measurement points and the locations of the first and second deformation measurement points.

[0031] Such a method provides a non-contact method for measuring deformation of an object.

[0032] The method may further include drawing or attaching symbols on the object indicating the measurement points, which may enable the measurement points to be more easily determined by the controller.

[0033] The step of imaging the first measurement point and the second measurement point with the first camera may consist of taking a single image, and / or the step of imaging the first measurement point and the second measurement point with the second camera may consist of taking a single image. In general, the cameras may be configured to provide an image where each image includes all the measurement points. In particular, where there are two cameras, each of the two cameras may be configured such that each measurement point is visible in each image from the two cameras.

[0034] The method may include positioning the camera so that the side of the image sensor of the camera having the most pixels is aligned with a long axis of the test object.

[0035] The method may include positioning one of the cameras such that its optical axis is perpendicular to a plane that intersects the first measurement point and the second measurement point. [Brief description of the drawings]

[0036] [Figure 1] 1 shows a test rig incorporating a deformation monitoring system according to the present invention; [Figure 2a] 1 is a schematic diagram of a deformation monitoring system according to the present invention; [Figure 2b] 1 is a schematic diagram of a deformation monitoring system according to the present invention; [Figure 3a] 1 illustrates a test specimen for use with a deformation monitoring system according to the present invention. [Figure 3b] 1 illustrates a verification object for use with a deformation monitoring system according to the present invention; [Figure 4] Figures 4a-4g show different possible appearances of the measurement point. [Diagram 5] 4 is a flow chart illustrating a method for monitoring deformation according to the present invention. [Figure 6] 4 is a flow chart illustrating an alternative method of monitoring deformation in accordance with the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037] The device of the invention may measure the position, movement and deformation of an object at multiple instants of time. At each instant of time, the device measures the position of one or more measurement points on the object. The positions are measured in three dimensions in a coordinate system local to the device. This coordinate system is called the native coordinate system. From the measured positions of the measurement points, the device may calculate, at each instant of time, measurement data such as: - The location of each measurement point, the position of a measurement point relative to other measurement points, The distance between a pair of measurement points, The position and / or direction of a line passing through two or more measurement points, The position and / or orientation of a plane passing through three or more measurement points, the position and / or orientation of at least three measurement locations in a local coordinate system, if the positions in that local coordinate system are known. The local coordinate system may be the local coordinate system of the object; - any change in any of the above occurring from one moment to another, · The position, movement and / or deformation of an object may be readily inferred from one or more of the above.

[0038] FIG. 1 shows a testing apparatus 10 including a test specimen 12 that can be deformed by the movement of a crosshead 18 that can exert a compressive or tensile force on the test specimen 12. The test specimen 12 has two measurement points, a first measurement point 14 and a second measurement point 16. The measurement points 14, 16 are shown as circles drawn on the surface of the test specimen 12, but it will be understood that alternative measurement points such as edges, corners, or holes of the test specimen 12 can be used, or other symbols such as crosses and speckles can be drawn on the surface. In some cases, features of the test specimen 12, such as edges and corners, can be used during the determination of the locations of the measurement points, but are not themselves measurement points. Such features are sometimes referred to as indirect measurement points. A deformation monitoring system 100, which in the configuration of FIG. 1 can function as an extensometer, is configured to observe the test specimen 12 as it is deformed by the movement of the crosshead 18.

[0039] 2a and 2b are schematic diagrams showing parts of a deformation monitoring system 100. FIG.

[0040] The controller 102 is configured to control the functions of the deformation monitoring system and may take any suitable form, such as a general purpose computer, one or more data processors with appropriate memory and I / O devices, and / or an ASIC.

[0041] The deformation monitoring system 100 also includes at least two cameras 104a, 104b and may include one or more lights 104c. The lights and cameras together may be referred to as a camera and light assembly 104. As used herein, the term camera is intended to refer to any image capture device that generates an image that can be analyzed to find measurement points. Similarly, the term "light" is used for any device that can emit electromagnetic radiation to enhance the image captured by the camera.

[0042] One or both of the two cameras may utilize a monochrome sensor having 1440x1080 pixels. The camera may also, or alternatively, be configured to output a strobe output signal that is active during the exposure of the image and receive a trigger input signal that can be used to trigger the sensor to capture the image. The strobe output signal may be used to activate a strobe light and synchronize the camera exposure with the light activation. A suitable image sensor is a Sony IMX 273 sensor capable of capturing full frames at 276Hz. The sensor may be coupled with an 8mm focal length lens, a 470nm bandpass filter and / or a polarizing filter. An image sensor with a higher pixel resolution may be used to increase the measurement resolution of the device. A higher measurement data rate may be achieved using an image sensor capable of capturing at a higher frame rate. Lenses with different focal lengths may be used to achieve different sizes, shapes or positions of the measurement volume.

[0043] Additionally, the cameras may be coupled such that the strobe output of one camera can be received as a trigger input signal for the other cameras, and all cameras may synchronously capture images at the same time.

[0044] The light 104c is configured to illuminate the measurement points on the test specimen as shown in Figure 1. The cameras 104a, 104b are configured to observe the measurement points on the test specimen.

[0045] The light 104c may have an array of 32 LEDs that emit light that is primarily blue. A suitable LED is a Cree XP-E2 Blue LED. Each LED may be coupled with a lens to produce a beam angle that evenly illuminates the measurement volume of the device. The LEDs may be coupled with a polarizer element so that the emitted light is primarily polarized in a single orientation. The LEDs may be split into two or more banks, such as two banks of 16, so that the intensities of the banks may be different to achieve even illumination of all sides of the test specimen.

[0046] If the light may be a strobe light and may be synchronized with the camera, the strobe outputs of the cameras may be combined via a logical "or" function so that the light is active whenever either camera is capturing an image. The strobe signals may be connected such that the LED is on only if the combined strobe signal is active. This may have the effect of synchronizing the strobe of the light to the exposure period of the camera. The camera may be operated at a capture rate of greater than 80 Hz to avoid visible flickering of the light which may be harmful to people with photosensitivity to flickering lights.

[0047] The cameras 104a, 104b are mounted such that they are held in a fixed positional relationship relative to one another, such as via a mounting bracket, so that their external calibration parameters do not change after performing the calibration process. The focal length and focal distance of the camera lenses are fixed prior to performing the calibration procedure, so that the intrinsic camera parameters do not change after performing the calibration process. In other embodiments, the cameras may simply have a known orientation and / or position.

[0048] Each camera 104a, 104b has a field of view that is a frustum extending from the camera's lens. If the two frustums overlap, measurements can be made using both cameras. The overlap volume is sometimes called the measurement volume.

[0049] Some or all of the system's components may be mounted on or in a common housing, which may also contain a power source, such as a battery or a wired electrical input connector.

[0050] Each camera captures a sequence of two or more images that are sent to a controller. Image capture may be synchronized across all cameras so that all cameras capture images at the same instant in time. This ensures that three-dimensional measurements made from the images are not adversely affected by motion of the specimen relative to the cameras.

[0051] To keep the device's measurement latency as low as possible, each image can be made available to the controller as soon as possible after it is captured. To this end, if the image data needs to be transferred, for example, over a bus, the bus should be high bandwidth and low latency. In one example, the high bandwidth bus can be a MIPI-CSI bus with one or more lanes operating at over 1 Gbit / s.

[0052] A digital camera contains an image sensor consisting of a two-dimensional rectangular array of pixels, which typically has more pixels along one side than along the other. Because test pieces are typically long and thin, it is advantageous to position the camera so that the side of the image sensor that has the most pixels is aligned with the long axis of the test piece. This maximizes the number of pixels along the length of the sample, maximizing the measurement resolution of the device.

[0053] If the measurement location is contained substantially in a plane (including along a line) or in multiple parallel planes, it may be advantageous to position one of the cameras with its optical axis perpendicular to the plane. This may make it easier to automatically detect the measurement location in an image captured from that camera. Images captured from that camera may also be more easily interpreted by an operator.

[0054] The cameras may be fitted with optical bandpass filters so that the light detected by the image sensor in each camera is essentially monochromatic. Without such filters, any change to the wavelength of the light illuminating the test specimen may result in an apparent shift in the measurement location due to chromatic aberration of the lens, and thus inaccurate measurement data. Such changes in the wavelength of the light illuminating the test specimen typically occur when there is a change to the ambient lighting (e.g., artificial lights are turned on / off, curtains / blinds are opened / closed, clouds pass in front of the sun, etc.) or when the temperature of the test specimen changes such that the amount and / or wavelength of light emitted by the test specimen changes.

[0055] The light may be configured to produce essentially monochromatic light, which may be used instead of or in conjunction with matching an optical bandpass filter to the camera to reduce the effects of chromatic aberration in the camera lens. When used in conjunction with an optical bandpass filter, the nominal wavelength of the monochromatic light may match the nominal bandpass wavelength of the optical filter.

[0056] The light may be configured to produce polarized light, and the camera may be fitted with a polarizing filter, aligned to pass light polarized in a direction essentially orthogonal to the polarization direction of the light. This reduces glare in the image caused by specular reflection of light from shiny test specimens, windows, transparent safety screens, etc. Such glare may otherwise adversely affect the accuracy of the measurement data, as it interferes with the view of the measurement location in the image.

[0057] The lights may be strobed to be on while any camera is exposing an image, but off when no camera is exposing an image. Thus, the percentage of time the lights are on (also known as the "duty cycle") may be less than 100%. A duty cycle less than 100% reduces the power consumption of the device and / or allows the lights to be overdriven (operated at an intensity above their nominal rating). Overdriving the lights allows the exposure time of the cameras to be reduced, thereby reducing the measurement latency of the device and reducing measurement inaccuracies caused by motion blur.

[0058] In the illustrated embodiment, the controller 102 is configured to perform the following functions. Camera & light control and image capture function Automatic operation function Orientation detection function Measurement location detection function Measurement function Recording function Verification function -Test piece label reading function

[0059] It will be appreciated that the controller 102 may have any one or more of these functions in any suitable combination. For example, the controller may have the functions of camera and light control, automatic operation, orientation detection, measurement location detection and measurement. However, any of the other three functions may be performed by the controller, or any of the first five functions may be omitted from the controller.

[0060] To perform these functions, the controller 102 may include a processor, electronic storage, and input / output connections. Each of the controller's functions is described in detail in the following sections.

[0061] The camera & light control and image capture functions of the controller configure each camera to capture a sequence of two or more images. The captured images are grouped into image sets, with each image set including one image from each of at least two cameras. If the camera & light assembly has more than one camera, ideally an image set will include one image from each camera. In this way, the sequence of images captured by the cameras becomes a sequence of image sets. If image capture is synchronized across all cameras, all images in an image set are captured at the same instant in time.

[0062] Once the images have been captured and grouped into image sets, the image sets are then passed to other elements of the controller (e.g., parts that perform measurement functions). To keep the measurement latency of the device as short as possible, each image set is sent to other parts of the controller as soon as possible after the images are received from the camera.

[0063] The camera & light control and image capture functions of the controller also configure the camera & light with appropriate settings, including but not limited to camera exposure time, camera image gain, camera frame rate, and light intensity. The camera & light settings that affect image exposure (e.g., camera exposure time, camera image gain, and light intensity) may be automatically changed so that optimal image exposure is achieved even if the appearance of the measurement location changes over time or from specimen to specimen. Image exposure is optimal when the area of ​​the image corresponding to the measurement location is exposed such that contrast is maximized but there are no overexposed pixels (i.e., when the pixels within that area do not have an intensity value that corresponds to the maximum possible intensity value of the pixel). Achieving optimal image exposure improves the signal-to-noise ratio of the image, thus maximizing the precision and resolution of the measurement data.

[0064] The automatic operation features of the controller may automatically control all components of the device such that no interaction from an operator is required to perform measurements on a batch of one or more test strips. In summary, the device automatically determines when a test strip is placed within the measurement volume of the device by automatically identifying measurement locations on the test strip. The device then determines when to begin measuring the locations of these measurement locations and continues measuring until it automatically determines that testing of the test strip is complete, at which point the device stops the measurement process and prepares to detect the next test strip.

[0065] The automatic operation function can be controlled as shown in the flow chart 300 of FIG. 5. In step 302, the initial state performs the camera & light control and image capture functions. After receiving a set of captured images, the automatic operation function utilizes the measurement location detection function in step 304 to detect a measurement location (within the measurement volume of the device) that is visible in the captured images. Whether the measurement location is successfully detected is determined in step 306, and based on the determination, the controller may proceed to the measurement state in step 308, otherwise, capture the next available set of images and attempt to detect the measurement location again. In some cases, the controller may determine whether the measurement point is stationary and may acquire additional images until the measurement point is deemed stationary. The controller may transition to the measurement state in step 308 based on a determination that the measurement point is stationary in the images acquired in step 302.

[0066] Once in the measurement state 308, the controller repeatedly performs the measurement functions on one image set in steps 308 and 310 until the controller automatically determines that the measurement process is complete in step 312. The measurement process may be considered complete using criteria such as, but not limited to, the following: The measurement location is no longer within the measurement volume. It is no longer possible to measure the 3D position of a measurement location. This can happen, for example, if the measurement location is not visible from two or more cameras. The specimen has stopped deforming.

[0067] Once the measurement process is deemed complete, it returns to the initial state 302 where it performs camera & light control and image capture.

[0068] The orientation detection function determines a transformation that can be used within the measurement function of the controller to convert measurement data from the native coordinate system to a measurement coordinate system. The native coordinate system may be at the center of the device or may be the coordinate system in which the locations of the measurement points are first determined. The measurement coordinate system may be a coordinate system more relevant to the user, such as a coordinate system aligned with the features of the measurement sample and / or the north and / or vertical axis.

[0069] The transformation may be an identity transformation, in which case the measurement coordinate system is the same as the native coordinate system. Alternatively, one or more sensors may be used to detect the orientation of the device with respect to an external reference, such as vertical, horizontal, or magnetic north. Such sensors may include one or more accelerometers or magnetometers. Given the detected orientation of the device, a transformation that converts measurement data from the native coordinate system to a measurement coordinate system defined with respect to one or more external references (such as horizontal, vertical, or magnetic north) is easily determined.

[0070] The measurement location detection function of the controller is configured to automatically find all measurement locations that are visible in the images of the image set. For each measurement location found, its location is identified in every image in which it is visible. The locations in the images may be expressed as coordinates to the two-dimensional image sensor array of the camera.

[0071] If the measurement locations have a known appearance, or if marks with a known appearance have been applied to the measurement locations, they can be found and their image locations ascertained through techniques well known to those skilled in the art of image processing (edge ​​detection, template matching, generalized Hough transform, Harris corner detector, etc.). For example, if the measurement locations appear as circular shapes, a Hough transform may be used to find the circles and ascertain the image coordinates of the center of each circle. Using such techniques, measurement locations with a variety of appearances can be readily found, including, but not limited to, circular spots, circular rings, lines, crosshairs, bull's-eyes, checkers, and "speckle" patterns.

[0072] Alternatively or additionally, if there are identifiable features on the test piece away from the depicted measurement points, and the location of the measurement location relative to those identifiable features is known, the measurement location can be found by first finding the other identifiable features, and then inferring the location of the measurement location from the location of the identifiable features. Examples of such identifiable features include edges, corners, holes, etc. Such identifiable features can be readily found using techniques such as the Canny edge detector, Harris corner detector, generalized Hough transform, etc., which are well known to those skilled in the art of image processing.

[0073] FIG. 3a shows that the measurement points 202a and 202b are spaced apart by a distance D 1 2 shows a test specimen 200 that is known to lie along a centerline 208 that is equidistant from a center point 206, spaced at intervals of 100 mm. Since the centerline 208 and center point 206 can be readily calculated from the detected positions of corner features 204a-d on the test specimen, the locations of measurement points 202a, 202b can be inferred from the detected positions of corner features 204a-d.

[0074] In some test scenarios, it may be advantageous to check whether the measurement point has been stationary for a predefined amount of time before considering it to have been successfully found, for example, this can avoid the device unnecessarily entering a measurement state while a test strip is still loaded into the UTM prior to testing.

[0075] A variety of different shapes and symbols can be applied to the test specimen to indicate the measurement points. Such examples are shown in Figures 4a-4g. Figure 4a shows a filled circle, Figure 4b shows a white circle or ring, Figure 4c shows a dash, Figure 4d shows a cross, Figure 4e shows a ring with a filled circle inside, Figure 4f shows two touching squares diagonally touching at the corners, also known as checkers, and Figure 4g shows a speckle pattern. Any of these shapes may be used to indicate the measurement locations.

[0076] The measurement function of the controller receives the sequence of image sets and generates, for each image set, measurement data as described above. In addition to or instead of any of the above measurement data, other measurement data may be generated. Such other measurement data may include one or more of the following: Axial strain between two measurement locations located along the longitudinal axis of the specimen Transverse strain between two measurement locations located across the transverse axis of the specimen Distortion along any direction (e.g., 45 degrees from the longitudinal axis) Displacement of the test specimen Rotation of the specimen (around any axis) -Bending of test specimen The distance between the two measurement locations Displacement at one or more measurement locations

[0077] The following steps outline one method for generating the measurement data. 1) Ascertaining at least one three-dimensional position (in a native coordinate system) of each measurement location at an instant in time corresponding to the time an image in the image set was captured. 2) Calculating measurement data from the ascertained three-dimensional positions of the measurement locations, for example by comparing the relative positions of the measurement locations at different times. 3) Transforming the measurement data into the measurement coordinate system using the transformation determined by the orientation detection function. 4) outputting the measurement data via a measurement data output system. 5) If the controller includes a recording function, the image set and measurement data may be passed to the part of the controller that provides the recording function.

[0078] The recording facility comprises a storage element, such as a disk drive, on which various data is recorded. The recorded data may include one or more of the following: a sequence of one or more images from one or more of the cameras; a sequence of one or more image sets, and A sequence of one or more measurement data values. The storage device may be volatile or non-volatile.

[0079] The verification feature of the controller allows the operator to verify that the device is measuring accurately. To use this feature, the operator positions a verification object, such as the one shown in FIG. 3b, within the measurement volume of the device. The verification object 250 has two or more verification marks 252a, 252b in known positions relative to each other. For example, the verification object 250 may have two or more verification marks 252a, 252b at a known distance D 100.000 mm apart. 2 has two verification marks.

[0080] The verification element of the controller is the distance D between the two verification marks 252a, 252b. 2 Then, measure the measured distance D 2 to the known distance between the verification marks to calculate an error value. To determine if the device is measuring accurately, the error value is compared to a predefined range of acceptable error values. If the error is within the acceptable range, the device is considered to be measuring accurately.

[0081] In one method, a controller receives a sequence of image sets and performs the following steps for each image set. 1) Detecting the location of the verification mark. This may be accomplished using a verification object detection function that is essentially the same as the measurement location detection function of the controller. 2) Ascertaining the three-dimensional location of each verification mark, which may be accomplished using a verification function that is essentially the same as the measurement function of the controller. 3) Compare the measured relative positions of the verification marks to the known relative positions to calculate an error value. For example, if the verification marks are known to be 100.00 mm apart and are measured to be 100.010 mm apart, the error is calculated to be 0.010 mm. The error value may also be expressed as a relative error by dividing by the known distance. The relative error may also be expressed as a percentage. In this example, an error of 0.010 mm may be expressed as a relative error of 0.01%. 4) The error value is compared to a predefined range, such as + / - 0.1 mm or a relative error of + / - 0.1%. If the error value is within the acceptable range, the device is considered to be working correctly. 5) Report to the operator whether the device is working correctly or not. The error value and / or the relative error may also be reported to the operator.

[0082] The system may function with a high degree of autonomy utilizing the control scheme illustrated in Figure 6, detailed below. Once in the verification state, it repeatedly performs the verification functions for each image set, one after the other, until it automatically determines that the verification process is complete. The verification process may be considered complete using criteria such as, but not limited to: The verification mark is no longer within the measurement volume. The 3D position of the verification mark can no longer be measured. This can happen, for example, if the measurement location is not visible from two or more cameras. Once the verification process is deemed complete, it returns to the initial state where it performs camera & light control and image capture.

[0083] The controller may also include a test strip label reading function that may automatically read information encoded on a label associated with the test strip. The label may consist of a handwritten or machine printed alphanumeric sequence or other code (such as a barcode or QR code) that encodes information related to the test being performed, such as a unique serial, batch, or test identifier. The label may be attached to the test strip or elsewhere within the frustum of at least one of the cameras.

[0084] Any information read from the test strip label may be added to the measurement data.

[0085] In one embodiment, the label is read using readily available methods and tools for optical character recognition (OCR), barcode reading, or QR code reading.

[0086] The deformation monitoring system 100 also comprises a measurement data output system 110, which provides an interface for transmitting the measurement data to one or more external systems. The measurement data may also include information read from the test strip label. The measurement data may be transmitted in the form of an analog signal or a stream of digital data. The interface may consist of multiple channels so that multiple measurement data values ​​may be transmitted simultaneously. The interface may utilize a wired or wireless connection.

[0087] The deformation monitoring system 100 may include an alignment system 106 that assists the operator in positioning the specimen and / or device such that the measurement point is within the measurement volume of the device. This may be achieved by making aspects of the measurement volume visible to the operator, which may include: The extent of the measurement volume, such as the top, bottom or corner of the measurement volume · A point or line within the measurement volume, such as a center point or center line

[0088] In one embodiment, such sides are made visible to the operator by projecting a mark, such as a dot or line, that is visible to the operator and aligned with one or more sides of the measurement volume. Such marks may be projected via a laser line or laser dot projector.

[0089] The deformation monitoring system 100 may have a user interface 108 that may include buttons, controls, voice recognition, gesture recognition, indicators, a display screen, a touch screen, audio, voice output, etc. These elements interact with a controller to enable an operator to do one or more of the following: Monitoring the state of a device (e.g., on / off, measuring / not measuring, etc.) Check whether the device is calibrating correctly -Monitoring measurement data values Configuring or controlling aspects of the device

[0090] One or more elements of the user interface may be provided remotely by a separate device, such as a computer, tablet, or smartphone. In this case, the device may provide an interface that allows a connection between the controller and the remote elements of the user interface. The interface may be wired or wireless, such as Wi-Fi, Ethernet, Bluetooth, or a cellular or satellite data connection.

[0091] 6 illustrates a control method 350 for providing automatic functionality to the deformation monitoring system 100. The system may begin by operating the camera & light device to capture an image in step 352. The controller then detects measurement points in the image in step 354. It is determined by the controller in step 356 whether the measurement points are found. If the measurement points are identified, the controller may begin measuring parameters such as the distance between the measurement points in step 358. The system may then repeatedly take images and measure image properties in steps 360 and 358 until it is determined that the measurements are complete in step 362.

[0092] If the system is unable to detect the measurement point at step 354, the system may enter a verification routine and attempt to detect a verification object, such as object 250 shown in FIG. 3b, at step 364. If the system determines that the verification object is within the captured image, a decision is made at step 366 to initiate the verification function of the controller described above. The verification function is performed at step 368 and may involve multiple images being taken using the camera & light system at step 370. Once verification is complete, as may be determined at step 372, the system may return to the initial step or may be ready to accept a test specimen for testing.

[0093] Accordingly, a deformation monitoring system according to an embodiment of the present invention is provided with capabilities that can solve one or more, and in some embodiments all, of the following technical problems:

[0094] (Inaccurate measurement data) If the object is shiny (e.g. metal), reflections can be picked up by the camera and interfere with the measurement. If an object is hot (e.g. part of a jet engine), it may glow and become red, yellow or even white hot. This glow may interfere with measurements. If the object is behind a window (such as a safety screen), the camera may pick up reflections on the window that interfere with the measurement. Out-of-plane movement (movement of an object towards or away from the device) can cause inaccuracies in the measurement data. For example, consider a device that uses a single camera. If an object is closer to the camera, it will appear larger in the image (due to perspective). However, if the object remains the same distance from the camera but is heated so that it expands (due to thermal expansion), the object will also appear larger in the image. Such a device cannot determine if the object has actually deformed or if it has moved towards / away from the camera. Thus, the device cannot accurately measure deformation when there is movement towards or away from the camera. · It is not easy to check whether the device is measuring accurately.

[0095] (Complicated and slow to use) · Very specific marks (such as circular spot marks) must be applied to the object at the desired measurement locations. These marks are designed to define the measurement locations and be easily detectable in the camera image. Applying these marks can be a time-consuming and laborious process. User input is required to configure and operate the device (e.g., manual selection of measurement locations, manual starting and stopping of measurement functions, etc.). This can require an interactive user interface (e.g., a GUI on a touch screen), which adds complexity. For batch testing (i.e., sequential testing of multiple objects), the time to test each object can be significantly increased due to the required operator interaction. · Providing a device that does not need to be positioned at a precise distance (the "working distance") from or precisely aligned with a point on the object being measured. In most testing scenarios, it is advantageous for measurements to be in a coordinate system, such as a coordinate system local to the object being measured. However, many devices measure in a coordinate system local to the device. Further steps must be taken to transform the measurement data into the desired coordinate system. These steps add complexity and are time consuming, making the device more complex and slower to use. When multiple objects are tested (e.g., batch testing), records must be kept that describe which set of measurement data pertains to which object. This is often accomplished by labeling the objects with a unique number or code. That label must then be entered into the system that is capturing the measurement data. This task is often performed by an operator reading the label and then manually entering it via the device's user interface. This process is time consuming and prone to error.

[0096] (Not suitable for use in closed loop control) Some test scenarios require the device to form part of a closed-loop control system, where the load force applied by the test rig varies automatically according to the deformation currently being measured. For the control loop to operate correctly, the measurement data generated by the device must have a high enough data rate, a low enough measurement latency and be sufficiently constant. Some devices are not suitable for use in closed-loop control systems because they are unable to generate measurement data with a sufficient data rate or acceptable latency.

[0097] In some cases, the camera may acquire an image of only one measurement point, in which case the deformation can be measured using a known reference, such as a fixed point to which the test specimen can be fixed.

[0098] Furthermore, the deformation measurement system may have more than two cameras, which not only improves the reliability of the system but also increases the measurement volume and allows data to be obtained over a wider range.

[0099] A deformation measurement system having three or more cameras, or configured to operate at only one measurement point, may have substantially similar features to the deformation measurement system described above.

[0100] Further specific examples of the present disclosure are described in the following clauses. (Clause A) 1. A method for determining deformation of an object, comprising the steps of: Providing an object having a first measurement point and a second measurement point; capturing an image of the first measurement point and the second measurement point with a first camera; capturing an image of the first measurement point and the second measurement point with a second camera; determining locations of the first measurement point and the second measurement point based on imaging by the first camera and the second camera; deforming the object to generate a deformed object having deformation measurement points; capturing an image of a first deformation measurement point and a second deformation measurement point with the first camera; capturing an image of the first deformation measurement point and the second deformation measurement point with the second camera; determining the locations of the first deformation measurement point and the second deformation measurement point based on imaging by the first camera and the second camera; determining a deformation of the object based on the locations of the first measurement points and the second measurement points and the locations of the first deformation measurement points and the second deformation measurement points; A method comprising: (Clause B) The method of claim A, wherein the measurement points are symbols painted on the object. (Clause C) The method of claim A, wherein the measurement point is a hole, an edge, or a corner of the measurement object. (Clause D) The method of claim B, wherein determining the locations of the measurement points includes determining locations of one or more holes, edges, and / or corners of the object. (Clause E) The method of any one of clauses A to D, wherein determining the locations of the first measurement points and the second measurement points, and / or the first deformed measurement points and the second deformed measurement points includes using a Hough transform. (Clause F) The method of any one of clauses A to E, wherein determining the locations of the first measurement point and the second measurement point and / or the first and second deformation measurement points comprises determining the locations in an object-based coordinate system. (Clause G) The method of any one of clauses A-F, further comprising illuminating the object with an artificial light source. (Clause H) The method of claim G, wherein the artificial light source produces monochromatic light. (Clause I) The method of claim H, wherein the first camera and / or the second camera include a bandpass filter configured to allow light at a wavelength of the artificial light source. (Clause J) The method of clause G, H or I, wherein the artificial light source produces polarized light. (Clause K) The method of claim J, wherein the first camera and / or the second camera are equipped with a polarizing filter positioned orthogonal to a polarization direction of the artificial light source. (Clause L) The method of any one of clauses G-K, wherein the light source is a strobe light. (Clause M) The method of claim L, wherein the strobe light is synchronized with the first camera and the second camera so that the object is illuminated. (Clause N) and / or imaging the first measurement point and the second measurement point with the first camera comprises acquiring a single image; and / or and / or imaging the first measurement point and the second measurement point with the second camera comprises capturing a single image; and / or and / or imaging the first deformation measurement point and the second deformation measurement point with the first camera comprises capturing a single image; and / or The method of any one of clauses A to M, wherein capturing the first deformation measurement point and the second deformation measurement point with the second camera comprises capturing a single image. (Clause O) The method of any one of clauses A-N, wherein the first camera and the second camera are maintained at a fixed orientation. (Clause P) The first camera and the second camera each have a focal length, and the focal lengths are the same when capturing an image of the measurement point and the deformation measurement point. (Clause Q) the first camera and the second camera are synchronized such that the imaging of the first measurement point and the second measurement point by the first camera and the imaging of the first measurement point and the second measurement point by the second camera are simultaneous; and / or The method described in any one of clauses A to P, wherein the first camera and the second camera are synchronized so that imaging of the first deformation measurement point and the second deformation measurement point by the first camera and imaging of the first deformation measurement point and the second deformation measurement point by the second camera are simultaneous. (Clause R) The method of any one of clauses A-Q, wherein a controller attempts to determine the locations of the first measurement point and the second measurement point, and based on a level of success of the determination, commands the first camera and / or the second camera to acquire further images of the first measurement point and the second measurement point. (Clause S) The method of any one of clauses A-R, further comprising determining an orientation of the first camera and / or the second camera based on an output of an accelerometer or a magnetometer. (Clause T) A deformation monitoring system, comprising: a first image capture device configured to capture a first image of the object; a second image capture device configured to capture a second image of the object, the second image capture device being at a known orientation relative to the first image capture device; a controller configured to cause the deformation monitoring system to execute a method according to any one of clauses A to S; A deformation monitoring system comprising:

Claims

1. 1. A deformation monitoring system for measuring deformation of an object, comprising: a first camera configured to capture a first image of the object; a second camera configured to capture a second image of the object and at a fixed orientation relative to the first camera; A controller for the deformation monitoring system, imaging the object with the first camera at a first time; imaging the object with the second camera at the first time; determining a first location of a first measurement point on the object at the first time and a first location of a second measurement point on the object at the first time based on imaging by the first camera and the second camera at the first time; imaging the object with the first camera at a second time; imaging the object with the second camera at the second time; determining locations of the first measurement point on the object at the second time and a second measurement point on the object at the second time based on imaging by the first camera and the second camera at the second time; determining a deformation of the object based on the locations of the first measurement point and the second measurement point at the first time and the second time; A controller configured to run A deformation monitoring system comprising:

2. The deformation monitoring system of claim 1 , wherein determining the locations of the measurement points comprises identifying symbols or features on the object.

3. 3. The deformation monitoring system of claim 2, wherein the controller is configured to determine locations of one or more holes, edges, and / or corners of the object, and determining the locations of the measurement points is based at least in part on the determined locations of the one or more holes, edges, and / or corners.

4. The deformation monitoring system according to any one of claims 1 to 3, further comprising an artificial light source configured to illuminate the object.

5. The deformation monitoring system of claim 4 , wherein the artificial light source is configured to generate monochromatic light.

6. The deformation monitoring system of claim 5 , wherein the first camera and / or the second camera comprises a bandpass filter configured to allow light at a wavelength of the artificial light source.

7. The deformation monitoring system according to any one of claims 4 to 6, wherein the artificial light source is configured to generate polarized light.

8. The deformation monitoring system according to claim 7 , wherein the first camera and / or the second camera are provided with a polarizing filter arranged orthogonal to a polarization direction of the artificial light source.

9. The deformation monitoring system according to any one of claims 4 to 8, wherein the light source is a strobe light.

10. The deformation monitoring system of claim 9 , wherein the strobe light is synchronized with the first camera and the second camera such that the object is illuminated during imaging of the object by the first camera and the second camera.

11. The deformation monitoring system of any one of claims 1 to 10, wherein the first camera and the second camera each have a focal length, and the controller is configured so that the focal lengths are the same at the first time and the second time.

12. The deformation monitoring system of any one of claims 1 to 11, wherein the controller is configured to attempt to determine the location of the first measurement point and the second measurement point at the first time and, based on a level of success in determining the location of the measurement point, decide whether to instruct the first camera and / or the second camera to acquire at least one further image of the object.

13. The deformation monitoring system of claim 12, wherein based on failure to determine the location of the measurement point at the first time, the controller is configured to instruct the first camera and / or the second camera to acquire further images of the object before determining the location of the measurement point.

14. 14. The deformation monitoring system of claim 12 or 13, wherein the controller is configured to attempt to determine the location of the measurement point in the image from the first camera and the image from the second camera at the first time and to determine a level of success for each image individually.

15. 15. The deformation monitoring system of claim 14, wherein based on failure to determine the location of the measurement point in images from only one of the first camera and the second camera at the first time, the controller is configured to instruct only a corresponding one of the first camera and the second camera to acquire at least one further image before determining the location of the measurement point.

16. A deformation monitoring system according to any one of claims 12 to 15, wherein based on successful determination of the location of the measurement point at the first time, the controller is configured to stop instructing the first camera and / or the second camera to acquire further images of the object and to start determining the location of the measurement point.

17. The deformation monitoring system of any one of claims 1 to 16, wherein the controller is configured to cause the deformation monitoring system to acquire images of the measurement points at further times following the second time until determination of at least one of the measurement locations fails.

18. The deformation monitoring system of any one of claims 1 to 17, further comprising an accelerometer or a magnetometer, and the controller is configured to determine an orientation of the first camera and / or the second camera based on an output of the accelerometer or the magnetometer.

19. The deformation monitoring system of any one of claims 1 to 18, further comprising an alignment system configured to project alignment markings proximate to the object.

20. The deformation monitoring system of claim 19 , wherein the alignment system comprises a laser configured to project alignment markings proximate to the object.

21. The deformation monitoring system according to claim 19 or 20, wherein the alignment markings indicate limits of a measurement volume of the first camera and the second camera and / or a centre of the measurement volume.

22. The controller is configured to perform a verification function, the verification function comprising: recognizing a verification object; measuring distances between measurement points on the verification object; comparing the measured distance with a known value of the distance between the measurement points on the verification object; The deformation monitoring system according to any one of claims 1 to 21, comprising:

23. 23. The deformation monitoring system of claim 22, wherein the controller is configured to repeat the measuring and comparing steps of the verification feature until determination of at least one of the measurement locations fails.

24. The controller: the images from the first camera and the second camera; the location of the measurement point; and The determined deformation The deformation monitoring system according to any one of claims 1 to 23, configured to record at least one of:

25. A deformation monitoring system according to any preceding claim, wherein the controller is configured to identify an identifier from the images from the first camera and / or the second camera.

26. 1. A method for monitoring deformation of an object, comprising: Providing an object having a first measurement point and a second measurement point; capturing an image of the first measurement point and the second measurement point with a first camera; capturing an image of the first measurement point and the second measurement point with a second camera; determining locations of the first measurement point and the second measurement point based on imaging by the first camera and the second camera; deforming the object to generate a deformed object having deformation measurement points; capturing an image of a first deformation measurement point and a second deformation measurement point with the first camera; capturing an image of the first deformation measurement point and the second deformation measurement point with the second camera; determining the locations of the first deformation measurement point and the second deformation measurement point based on imaging by the first camera and the second camera; determining a deformation of the object based on the locations of the first measurement points and the second measurement points and the locations of the first deformation measurement points and the second deformation measurement points; A method for monitoring deformation of an object, comprising:

Images