REAL-TIME VIDEO EXTENSOMETER

Abstract

Extensometer (10) for measuring strain / stress on a test specimen (200) in a material testing device (190), comprising: - an imaging device (16) for producing an image of a test sample (200) which is subjected to a stress-inducing load; - a calculating device (30, 22, 24) for receiving the image of a test sample (200), for determining the movement of targets (202) on a test sample (200) and for determining the strain / stress from the determined movement of the targets (202); and - an output device (400) for outputting the specified strain / stress in real time, characterized by that the imaging device (16) and the calculating device (22, 24) are located on a single printed circuit board (15), wherein the computing device (30, 22, 24) comprises a field-programmable gate array (22) and a microprocessor (24), and wherein the entire data path from image data input to output takes place in hardware, and that the extensometer (10) has an input for receiving a trigger or synchronization signal to initiate operation or time stamping and, upon receipt of the signal, to generate a time-stamped image of the test sample (200), and that the output device (400) is designed to output the specified strain / stress along with the image with the timestamp.

Description

Background of the Revelation

[0001] This application claims priority under 35 USC 119(e) to U.S. Provisional Patent Application Serial No. 62 / 029,650, filed July 28, 2014. Area of ​​Revelation

[0002] This disclosure relates to a method of real-time measurement of voltage and associated data using video techniques. Description of the state of the art

[0003] Video strain measurement is well known in the art and well-developed for its intended purpose. However, a significant limiting aspect of strain measurement using a video device is collecting images at a considerable speed, delivering the images to an image processing device, processing the images to obtain a displacement or strain value, outputting the strain value in a software-processable format, and synchronizing the value with other data collected via conventional real-time methods (e.g., force transducers with electrically tuned bridges).

[0004] There are many manufacturers of video processing extensometers. Some of the main companies that supply them are Shimadzo, Zwick, and Imetrum. Generally, they all use the methodology of using a visual camera as an external device, inputting it to a PC or video processing hardware, and using hardware to convert the data into an electrical signal, or having a software interface compatible with the materials testing system.

[0005] The state of the art includes the IPVE and AVE 1, manufactured by Instron, which are well-developed for their intended purposes. These devices use an external camera, a PC, and analog outputs to capture images and process stress values ​​from these images. This stress data is calculated by software in the PC and is output via analog outputs. This is in Fig. 1 shown.

[0006] There are many algorithms for calculating voltage from video images, and each has advantages and disadvantages. The main disadvantage of most systems is that they use a standard high-speed visual camera, transmit the images to a processing system via a high-speed bus, process the images using a standard or suitable processing system, such as a PC or microcontroller, and then output the data internally to software on the processing system or via converters as electrical signals. These systems typically take an entire image and operate on the arrangement of pixels to produce a voltage or displacement value. Calculating voltage or displacement in this way is computationally intensive and requires a large microprocessor system.In addition, to guarantee real-time performance to meet many materials testing requirements, a real-time operating system is used in the processing system. After calculating the stress or displacement data, they are output to the software on a PC, which requires a specialized interface and is not very portable, or they are output via an analog or encoder device. These systems have problems with latency, integration, and required computing power.

[0007] The document US 4 690 001 A relates to an extensometer having the features of the preamble of independent patent claim 1.

[0008] The publication Image processing: Open source system wins vision award (https: / / www.vision-systems.com / factory / consumer-packaqed-qoods / article / 16738217 / imaqge-processing-opensource-system-wins-vision-award) describes a video camera in which a camera chip and a computing device are combined on a printed circuit board.

[0009] The document US 2004 / 0 145 724 A1 discloses a device for testing samples and in particular for mechanical testing of materials or components.

[0010] The publication by Lucero, J., and Arbel, Y.: Designing High-Performance Video Systems with the Zynq-7000 AII Programmable SoC, Application Note: Zynq-7000 All Programmable SoC. XAPP792(v1.0.1) describes the programming of video system control.

[0011] The publication Blackfin FPGA EZ-Extender Manual Revision 1.0, October 2005. Analog Devices, Inc. Analog Devices Inc. Norwood, USA, 2005 describes an FPGA EZ Extender for the camera chip of a video camera. Objectives and Summary of Revelation

[0012] The object underlying the invention is achieved by an extensometer according to independent claim 1, wherein advantageous developments of the extensometer according to the invention are specified in the dependent claims.

[0013] It is therefore an object of the present disclosure to develop further improvements in a real-time video extensometer.

[0014] Embodiments of this disclosure address the above-mentioned deficiencies by combining the image source, data processing, and electrical output on a single processing card to obtain high-frequency images and low latency in the data flow. Furthermore, the data processing device or FPGA (field-programmable gate array) processes the image on a pixel-by-pixel basis and updates the output of the intermediate strain result so that upon receipt of the final image pixel, a final strain / stress value is obtained and immediately output for evaluation. This hardware and method makes the real-time video extensometer similar to conventional electromechanical devices (such as plug-in devices) and allows them to be connected and used with materials testing systems in the same manner.The end result of high-speed real-time video processing is significantly improved accuracy, much faster tracking of sample strain, and very low latency data, allowing the user to perform and meet a full range of test standards.

[0015] The real-time video extensometer combines image inputs, data processing, and strain / stress data output on a single video processing card to minimize input and output data latency and maximize processing speed. The video processing card also eliminates external latency and processing time issues related to operating systems. The main reason for the improvement with regard to the processing system is the implementation of the entire algorithm on the FPGA (field-programmable gate array) portion of the data processing system. This design and implementation allows the entire data path from the input to the input to be handled in hardware, making the entire system deterministic and highly sensitive. Short description of the drawings

[0016] Further objects and advantages of the disclosure will become apparent from the following description and from the accompanying drawings in which Fig. 1 is a perspective view of the prior art, Fig. 2 is a perspective view of components of the device of the present disclosure, Fig. 3 is a schematic representation of the device of the present disclosure, Fig. 4 is a block diagram of the video processing card of the apparatus of the present disclosure. Detailed description of the preferred embodiment

[0017] With reference to the detailed drawings, in which like numbers refer to like elements in the different views, it can be seen that Fig. 1 is a prior art extensometer 1000. This extensometer 1000 uses an external camera, PC, and data communication to capture images and generate strain / strain values. The strain / strain data is calculated by software both in the PC and via analog outputs. Specifically, the electronics housing 1010 contains a printed circuit board, a camera (usually with a polarizing and light filter), and lenses for different fields of view. The image obtained by the camera is captured through a constant density air tube (CDAT) 1020. An integral illumination unit 1030 is attached to the side of the constant density air tube (CDAT) 1020. A two-dimensional calibration device 1040 is also provided.

[0018] Fig. Figure 2 shows the external appearance of an embodiment of the real-time video extensometer 10 of the present disclosure. The real-time video extensometer 10 has an integral illumination unit 12, which is implemented as an LED array for illuminating the sample to be tested (see Fig. 3, element 200, as well as video targets 202 which are painted or otherwise attached to the sample 200) as shown by the test frame 190 of Fig. 3. The real-time video extensometer 10 further comprises an electronics housing 14 which houses a printed circuit board or video processing card 15 (see also Fig. 3 and Fig. 4) and a camera or image sensor 16 (see also Fig. 3) with a polarizing filter 17 (see Fig. 3). The camera or image sensor 16 includes various lenses for a range of fields of view. The electronics housing 14 further includes a lens access 18 to allow access to the various lenses and a plate for calibrating the real-time video extensometer 10. Furthermore, the extensometer 10 includes a constant density air tube (CDAT) 20 with 90 degrees of light polarization to the integral illumination unit 12 (implemented as an LED array) and the lens of the camera 16. A two-dimensional calibration device 21, similar to that of the prior art, is additionally used.

[0019] As in Fig. As shown in Figure 3, the video processing card 15 includes a field-programmable gate array (FPGA) 22 (to increase processing speed) and a microprocessor 24. The video processing card also includes a line 19 to control the fans 20' of the constant density air tube (CDAT) 20 to create a virtual air tube. The real-time video extensometer 10 is connected to the materials testing fixture (test frame 190) and software using standard interfaces, including Ethernet, analog, encoder, or SPI interfaces. This allows the device to be plugged into and used by existing systems without the need for specialized integration software or hardware. The real-time video extensometer 10 provides axial and transverse encoder or analog information to the material testing device 190 through lines 302 and 304, respectively.The materials testing device 190 provides trigger / synchronization information to the real-time video extensometer 10 through line 306. The real-time video extensometer 10 and the materials testing device 190 exchange real-time test data, including strain / stress data, with the external computer 400 (illustrated as a laptop, although it is conceivable that other computing or processing devices could be implemented) via lines 308, 310. Typically, the real-time video extensometer 10 provides strain / stress data to the materials testing device 190, which in turn provides strain and strain / stress data to the external computer 400.

[0020] Fig. Figure 4 is a block diagram showing an overview of a typical embodiment of the real-time video extensometer 10 of the present disclosure. The video image is input to the system using an on-board image sensor 16 or auxiliary camera connection port input 40 (also shown in Fig. 3). The collected image data is processed by the processing system entirely in the programmable logic (see FPGA 22 of Fig. 3) the processing system 30 (such as, but not limited to, a Zync XC7020 SoC) where specialized logic is used to calculate multiple axes of strain / strain values ​​(i.e., the change or percentage change in the distance between the targets, as determined by video monitoring of the video targets 202 mounted on the sample 200, as in Fig. 3 shown, calculated) and send the data to the material testing device 190 ( Fig. 3) via the on-board axial or cross digital-to-analog converter (DAC) 32 or 34, the encoder 36 or the SPI interface 38, which finally through the lines 302, 304 of Fig. 3. In particular, the digital-to-analog converters (DACs) 32, 34 provide axial and transverse strain or displacement signals, respectively (typically in the range of negative 10 volts to positive 10 volts), which enable two separate (typically axial and transverse or otherwise perpendicular to each other) strain or displacement signals to be output in real time to the materials testing device 190.

[0021] The encoder 36 may have two quadrature encoder outputs, allowing two separate strain or displacement signals to be output in real time to the materials testing controller. The SPI interface 38 communicates digitized signals to any number of PCs and further outputs in real time to the materials testing device 190.

[0022] Further functions of the real-time video extensometer 10 are typically implemented by the main board, which is implemented as the video processing card 15.

[0023] The onboard imager and lens (camera) 16 implements a device view image sensor to provide high-speed images to the processing system 30.

[0024] The auxiliary camera connection port input 40 uses standard connections to enable the use of a standard visual camera device. This can be used instead of or in conjunction with the onboard imager and lens (camera) 16. An accelerometer 42 is mounted on the lens 16 to sense acceleration (usually in all three dimensions) for use in the algorithm and / or event detector.

[0025] The synchronization device 44 allows an external device, such as a material testing machine 190 (see Fig. 3), a synchronization pulse via line 306 (see Fig. 3) to send images to the external computer or PC 400 (see Fig. 3) for later alignment. This time stamping allows the additional calculation of a time-dependent stress / strain test result from the images (which may be a post-processing result). Similarly, the trigger 46 allows an external device, such as a materials testing machine 190, to trigger an event over line 306 (see Fig. 3) in the data processing device and perform functions such as high-speed image buffering and transfer to the external computer or PC 400 (see Fig. 3). This enables the real-time calculation of a time-dependent stress / strain test result.

[0026] Fan control 19 is the speed control for the fans 20' of the CDAT 20 to optimize the CDATs 20 in distance. LED control 48 has two rows of LED / projector array controls for use with the two different cameras.

[0027] Video GigE block 50 provides an Ethernet connection suitable for high-speed image transmission. Similarly, user GigE block 52 and controller GigE block 54 provide Ethernet connections to enable processing system 30 and the controller of materials testing device 190 to communicate with an external computer or PC 400 via an Ethernet switch 56.

[0028] USB port 58 provides error corrections and notifications to the image processing device.

[0029] DDR3 RAM 60 provides internal memory to enable storage of images and other data as captured by high-speed sensor 16. Further, some embodiments may include a SODIMM interconnect (not shown) to provide an onboard memory interconnect to enable storage of high-speed and long-duration images from high-speed image sensor 16.

[0030] Embodiments of the present disclosure typically have many of the following advantages: 1. High-speed data input, processing and output. 2. Hardware (FPGA)-based algorithm implementation for deterministic real-time behavior without side effects of microprocessor or PC systems. 3. Single circuit board instead of many integrated hardware parts. 4. Significant cost reductions for the camera, processing system, and output device. This offers price flexibility while still meeting very high specifications. 5. Standalone video device directly outputs strain or tension and can be used with many existing systems. 6. Ease of use due to its self-contained design. The device is similar to standard attachable extensometers. 7. The device can provide data at a rate that can be used for control. 8. The device can be used in higher-speed applications due to the increased data rate. This can be used, for example, to collect data and perform control on a dynamic system operating with a sinusoidal waveform.

[0031] Significant advantages of typical embodiments of this disclosure are greatly improved accuracy, much faster sample tracking, and very low latency data, which allow the user to perform and meet a full range of testing standards.

[0032] A typical test procedure is in Fig.3. The sample 200 with video targets 202 is mounted in the materials testing machine 190. Immediately after the sample 200 is subjected to a stress-inducing load by the materials testing device 190, a command signal is sent to the video processing card 15 and the materials testing device 190 and to the external computer 400. The real-time video extensometer 10 then records the absolute distance between the video targets 202 and monitors the relative movement of the video targets 202 to calculate the strain / strain in real time. The stress data and strain data, which are exchanged and typically organized among the real-time video extensometer 10, the materials testing device 190, and the external computer 400, are displayed on the screen of the external computer 400.

[0033] Thus, several of the aforementioned objects and advantages are most effectively achieved. While preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no way limited thereby.

Claims

[1] Extensometer (10) for measuring a strain / stress on a test sample (200) in a material testing device (190), comprising: - an imaging device (16) for generating an image of a test sample (200) which is subjected to a stress-inducing load; - a computing device (30, 22, 24) for receiving the image of a test sample (200), for determining the movement of targets (202) on a test sample (200), and for determining the strain / stress from the determined movement of the targets (202); and - an output device (400) for outputting the determined strain / stress in real time, characterized by , that the imaging device (16) and the computing device (22, 24) are located on a single circuit board (15), wherein the computing device (30, 22, 24) comprises a field-programmable gate array (22) and a microprocessor (24), and wherein the entire data path from the image data input to the output takes place in the hardware, and that the extensometer (10) has an input for receiving a trigger or synchronization signal to initiate operation or time stamping and, upon receipt of the signal, to generate an image of the test sample (200) with a time stamp, and that the output device (400) is designed to output the determined strain / tension together with the image with the time stamp. [2] Extensometer (10) according to claim 1, wherein the strain / stress is determined in two perpendicular directions. [3] Extensometer (10) according to claim 1, wherein the strain / stress is determined in the axial direction and in the transverse direction. [4] The extensometer (10) of claim 1, further comprising a constant density air tube (20) through which the imaging device (16) views the test sample (200). [5] Extensometer (10) according to claim 4, wherein the constant density air tube (20) comprises at least one fan (20'), thereby creating a virtual air tube (20). [6] Extensometer (10) according to claim 5, wherein the at least one fan (20') of the constant density air tube (20) is at least partially controlled by the single circuit board (15). [7] The extensometer (10) of claim 1, further comprising an Ethernet connection. [8] The extensometer (10) of claim 1, further comprising an illumination device (12) for illuminating the test sample (200). [9] Extensometer (10) according to claim 8, wherein the illumination device (12) emits polarized light. [10] The extensometer (10) of claim 1, further comprising an auxiliary camera connection port input (40) for receiving an image of a test sample (200) subjected to a stress-induced load.

Images