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- Publisher
- Hindawi Publishing Corporation
- Copyright
- Copyright © 2019 Homar Lopez-Hawa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
- ISSN
- 1687-9600
- eISSN
- 1687-9619
- DOI
- 10.1155/2019/5304267
- Publisher site
- See Article on Publisher Site
Abstract
Hindawi Journal of Robotics Volume 2019, Article ID 5304267, 8 pages https://doi.org/10.1155/2019/5304267 Research Article 1 2 2 2 Homar Lopez-Hawa, Alexander VanPelt, Suveen Emmanuel, and Yimesker Yihun Department of Industrial, Systems and Manufacturing Engineering, Wichita State University, Wichita, KS, USA Department of Mechanical Engineering, Wichita State University, Wichita, KS, USA Correspondence should be addressed to Yimesker Yihun; yimesker.yihun@wichita.edu Received 14 August 2018; Accepted 22 November 2018; Published 3 February 2019 Academic Editor: Raffaele Di Gregorio Copyright © 2019 Homar Lopez-Hawa et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. This study seeks to advance technologies pertaining to integratio n of low-cost collaborative robots to perform scanning operations where moderate accuracy is needed. Part inspection is an almost universal aspect of manufacturing which traditionally requires human observation. Advanced metrology techniques, such as scanning, allow greater inspection capabilities but still require a human operator and require significant capital investment. Using off-the-shelf line scanners in conjunction with small collaborative robots can completely automate the inspection process while minimizing cost. This project seeks to investigate the feasibility of utilizing a UR5 robot with a Keyence line scanner for scanning inspection in an industrial setting. Data from the line scanner is gathered, along with the position and orientation of the end-effector of the robot. The data are collected, combined, and analyzed in MATLAB to generate surface geometry. A user interface will allow viewing of the specific points gathered, expedite product inspection during manufacturing, and involve humans in higher skill-based decision-making tasks. A professional grade scan of the test part is used for comparison of experimentally gathered data. Feasibility is assessed on cost, effectiveness, ease of programming and operation, and development difficulty. In the preliminary result, it was found that the UR5 and line scanner provide a cheap and easily programmable and automated solution to line inspection. However, effectiveness and difficulty of development may pose challenges that require future research. 1. Introduction been particularly given to automated laser line scanning [2, 5] to mitigate errors caused by manual scanning and to increase Robotic line scanners are used today in a wide variety the efficiency of scanned data. of applications and industries. One such area is in the Studies have been further done to enhance robotic scan- manufacturing industry in which certain inspection systems ning technologies in Nondestructive Testing (NDT) applica- are required to inspect surfaces of components as manufac- tions to examine microdefects in manufactured parts. NDT tured parts become more complex and high quality of such uses a 6-degree-of-freedom industrial robot and positions parts are required. Coordinate Measuring Machines (CMM) the probe normal to the test surface. There are two types of are normally used for such inspection purposes where the NDT robotic scanning methods, which are Ultrasonic Probe machine makes physical contact with each point on the Grabbed by Robot (UPGR), similar to Figure 1(d), and Test surface (Figure 1(a)) [1]. The major problem with such contact Object GrabbedbyRobot(TOGR).Therfi stmethodhowever type method is its slow acquiring of data from a surface. had drawbacks due to challenges posed in positioning the As a solution, laser line scanning technology was proposed probe around complex shapes and for this reason the TOGR (Figure 1(c)). The main advantage of laser line scanners over method was tested. Unlike the UPGR method, where the the CMM is that it is a non-contact-based scanning method end effector grabs the NDT probe, the TOGR method grabs that can obtain large amounts of data in a shorter time using the test specimen and manipulates it around the stationary a technique known as “high resolution of digitization and probe. The key advantage of this method is that, unlike other inspection” [2]. For this reason, visually scanned technologies methods, which require several joint motions, this method have been growing in the recent years [3, 4]. Attention has may only need one joint motion, the end eeff ctor’s motion, 2 Journal of Robotics (a) (c) (d) (b) Figure 1: (a) Manual inspection. (b) Manual probing. (c) 2D automated scanning. (d) 3D automated scanning. to manipulate the specimen around the probe [5]. TOGR has of a material surface in many spectral bands within the enabled the robot to perform high-speed automatic inspec- visible light and near infrared spectrum and this reflective tion of complex structures, particularly ones that have curved information is useful in determining the materials the surface surface profiles such as turbine blades and milling tools. is made from [9, 10]. Ultrasonic Sensors are another type of sensors used in robotic scanning. Ultrasonic testing is Another novel area where laser line scanning has gain attention is in underwater 3D reconstruction of objects [6]. used to detect microdefects in parts. Ultrasonic time-domain The conventional method of detecting objects underwater reflectometry (UDTR) technique is employed in NDT in which the UT probe scans the sample and detects a flaw echo is using acoustic technology; however, this method has relatively low precision in reconstructing objects underwater. wave if there is a microdefect in the material. In a sample To overcome this, laser line scanning has been given attention with no defects, the material will give only a surface echo due to its high precision and antijamming capabilities. Com- wave and a backwall echo wave [5]. Thermographic imaging pared to traditional light sources, laser light has the capability is a sensing technology used in the automotive final assembly to reduce backscatter and forward scatter underwater in an line to reduce the cost factor due to manual labor [11]. In environment of low light and high turbidity. Experiments for the final assembly line, a water-leak test is conducted on the this purpose have been conducted, one particular case using vehicle to investigate any moisture leaks in the interior of the vehicle. The thermographic images can detect the moisture a laser line scanner to scan a keyboard first on land, and then in a sink lled fi with water [7]. The experiment revealed some content inside the interior of a vehicle for a water drop decent results but still had issues with accuracy of calibration diameter as low as 1 mm [12]. Due to its relative high accuracy, thermographic imaging is a good sensing technology that can and laser extraction and therefore is in an experimental stage. An experiment of this magnitude could be integrated into be utilized. Line laser scanners have become more popular as our project and the results could be compared. Another they provide faster output than regular CMM [13]. This type area where line scanning is used is in space applications, of sensor are made of a laser source and an optical sensor. particularly in continuous scanning of low earth orbit (LEO). Complementary metal oxide semiconductor- (CMOS-) CMOS-TDI line sensors, a sensor type used in space applica- based and coupled-charge device (CCD) are the most popular tions, convert an incident light signal into an electrical signal imaging sensors. Thanks to its characteristics, such as small [8]. Concisely, the scanner has several pixels where each pixel size, low cost, and performance, CMOS technology is widely accepted as the preferred one [14]. However, this type of collects photons from the same region but at different times and the time difference is considered to produce a better sensor has its drawbacks. Systematic error occurs due to scan of low earth orbit images [8]. The efi ld of archeology reflection of the surface, defects of the lenses, laser source, and uses scanning technologies to study artefacts [7, 9]. The the nonuniform environmental illumination, which causes an most common technique used is hyperspectral line scanning. increment in uncertainty [13]. In order to reduce or correct This method takes advantage of the spectral reflectance of the systematic error obtained from Laser scanning, a global the different artefacts and as each material has its own model of error is being studied and developed [15]. This spectral signature, data from hyperspectral scans will reveal global error takes in consideration error that influences the what material the artefacts are made from and many other mechanical parts involved in the system. Due to this, the material properties. From industrial applications on land, to systematic error has been reduced by half when compared to underwater, as well as outer space applications, line scanning references values. In many different areas, the need for having a digital has many benefits as evident from the above examples. In robotic scanning of objects, proper sensing of the reproduction of a real-world object in order to analyze said object is another important feature that should not be object is a topic of interest. In the medical world, having the ignored. As discussed earlier in the paper, hyperspectral line correct shape of the residual shape and volume of amputees’ scanning is one sensing technology used in studying artefacts limb poses a better product when a prosthesis needs to be in archeology. Hyperspectral imaging uses the reflectiveness designed [16]. Even for anthropologist, this is an appealing Journal of Robotics 3 2D Scanning Scanner- Using the line Controller Box Scanner GUI in Matlab Result 3D to recreate the Validation object Calibration 3D object Robot position UR5 Controller Box Orientation Figure 2: Flowchart for scanning process. technology due to its capability of digitalizing cultural her- scanner need to be converted to the global reference frame to itage artifacts [17]. Even with the impressive technological generate the cloud point data for the scanned object. evolution that has been in motion in the last years, 3D scanning remains as a rather expensive process and not so 3. Data Generation and Communication commonly implemented. The fact that regular 3D scanning 3.1. Scanning Operation. To conduct this experiment, a line operations require a significant human intervention and that thesetting upcan betimeconsuming has anegative impact in scanner is mounted onto a UR5 robot. A converter plate is designed to allow the scanner to remain rfi mly in place during the appeal of this technology [18]. The emergence of Industry the scanning process. Two plates were designed in a CAD 4.0 promises high work productivity through a successful implementation of human-robot cooperative systems, where software and 3D-printed to allow the line scanner to easily be attached to the UR5 as shown in Figure 3. An object that a human interacts and collaborates with robots. However, needs to be scanned will be located in the production line such a human-robot work environment at industrial scale presents some unique challenges that require human workers and in the workspace of the robot. A path then will be pro- grammed for therobot to follow,in order for itto beableto to adapt to the changes and the evolving technologies easily with minimal retraining and new skill efforts. Also, moving access the features of the reference piece. This will also allow predicting the outcome of the process to some degree. Due to from traditional industrial robots to collaborative robots typi- this, it is then easier to troubleshoot the process if something cally limits the spindle speed to 250 mm/s to prevent a human from being injured before the collision is detected [19]. This is going wrong and if the information is not as expected. poses a huge limitation in the production rate, as cycle times 3.2. Data Transmission/Communication. After the UR5 pro- are extremely important in manufacturing processes, because it impacts efficiency, quality, and overall productivity. For ceeds to follow the predetermined path and the line scanner gathers the data, the information from both the robot and the some industrial tasks, such as lifting and tt fi ing in an assembly scanner needs to be put together. To have the data in such operation, and quality inspection tasks, a human can make important decisions through a simplified GUI-Based HRI form, a communication has to be established between the UR5 and the line scanner. The UR5 has Ethernet capabilities platform while running the robot at higher speed and maintaining a higher production rate. This study investigates and it can send either joint angle data or𝑍𝑋𝑌 position of thejoints. Allowing communication between thelinescanner the feasibility of utilizing a UR5 robot with a Keyence line and the computer was a challenging task. The scanner must scanner for scanning inspection in an industrial setting. The idealgoalis to be ableto develop a fullyautomated low-cost be connected to a controller box, which provides power to the scanner. Communication between this controller and the 3D scanner that can be able to scan objects in a small interval computer utilizes a USB connection, as it is shown in Figure 2. of time and that needs little or no human assistance at all. Specific toolboxes are provided by Keyence to allow data acquisition from various programming languages. MATLAB 2. Methodology is not one of those languages, so another language, such as In this study, an ao ff rdable and easily operated robotic system, Visual Basic, must be utilized. The easiest solution will be to which can perform moderately accurate scanning inspection, alter a preexisting example program provided by Keyence in is developed using a UR5 and a line scanner. The UR5 position order to capture the data and save it as a data lfi e. This data lfi e sensors (the end-eeff ctor, 𝑥,𝑦,𝑧 position data and roll, pitch, can be then imported into the Matlab to automate the process. and yaw orientations) are integrated with a line scanner data, and an inverse kinematics is employed to construct the point 3.3. Data Processing. For the development of this work, a cloud of the scanned object. The data from the UR5 has been Matlab graphical user interface (GUI) has been created. An overview of the GUI can be seen in Figure 4. The GUI can be sent to the computer via an Ethernet socket communication. At the same time, the line scanner sends the scanned raw used to model any type of robot with up to seven revolute data to the scanner controller box and process it (Figure 2). A joints; it takes the Denavit-Hartenberg parameters (DH USB cable is used to send the processed scanned data to the Parameters) as an input and accordingly generates the sketch computer interface. These inputs from both the UR5 and the of the robot. This feature provides flexibility and provides 4 Journal of Robotics Keyence Line Scanner Figure 3: Assembly of the plate, line scanner, and UR5 end-effector with the object. Figure 4: Overview of the graphical user interface. the opportunity to adapt the scanning system with the given where𝑎 is the link length (distance between frames along𝑥 ), 𝑖 𝑖 robot geometry. Section 3.3.1 provides the calculation and 𝛼 is the link twist (rotation about𝑥 axis),𝑑 is the link offset 𝑖 𝑖 𝑖 structure of the robot behind the Matlab GUI code. (distance along𝑧 between frames), and𝜃 is the link angle 𝑖−1 𝑖 (rotation about𝑧 axis). 𝑖−1 3.3.1. DH Table Creation. For the creation of the robot When the user provides the number of joints of the robot, skeleton, the DH parameters are used to generate the the specific number of rows becomes available in the DH homogeneous transformation matrices 𝐴 . This is done in table on the GUI. With the information filled in the table, the the MATLAB code following symbolic operations included homogeneous transformation matrices will be calculated. For in the software and with the help of a for-loop that will the calculation of the transformation matrices, the forward repeat depending on the number of joints selected, and these kinematic equations with joint variables(𝜃 ,𝑑 ),and the link 𝑖 𝑖 matrices will be saved in a structure type of variable that will dimensions(𝛼 ,𝑎 ), will be used as shown in (2), and each𝑇 𝑖 𝑖 𝑖 contain all the information regarding the robot. The general matrix is stored in another location following the structure structure of these matrices is as follows: type variable: 𝑇 =𝐴 ⋅𝐴 ...𝐴 . (2) 𝑛 1 2 𝑛 cos𝜃 − sin𝜃 cos𝛼 sin𝜃 sin𝛼 𝑎 cos𝜃 𝑖 𝑖 𝑖 𝑖 𝑖 𝑖 𝑖 [ ] (1) sin𝜃 cos𝜃 cos𝛼 − cos𝜃 sin𝛼 𝑎 sin𝜃 𝑖 𝑖 𝑖 𝑖 𝑖 𝑖 𝑖 [ ] After each matrix is calculated in symbolic notation = , [ ] 0 sin𝛼 cos𝛼 𝑑 𝑖 𝑖 𝑖 and the “Generate Robot” button is pressed, the code then 00 0 1 [ ] proceeds to generate the schematic of the robot in an Journal of Robotics 5 DH Table Input Robot Plot Area Joint Selection Manual Manipulation of Robot Joint Data Simulation from Robot Start Laser Scan Data Figure 5: Example of the GUI aeft r sketching the UR5. initial position based on the DH table. In order for the operator to visualize the scanning process. The code takes the position information of the robot (end-effector position and plot to be effective, generating the points of a cylinder is required, and this is done through the embedded Matlab orientation) and combines it with the line scanner to get the function “cylinder.” The transformation matrix is applied to cloud points of the scanned object and to simulate the scan the original cylinder and then each cylinder is plotted to operation, as shown in Figure 7. A zoom-in of the result of represent each link and each joint as it is shown in Figure 5. the scan is shown in Figure 8. To obtain a clear image and find to show the details of the object, more cloud points need to be taken. However, if the overall size is required, only few 4. Data Validation cloud points are needed, and hence the scanning process will The cloud points obtained from the line scanner are trans- be expedite. formed using the joint information from the UR5, and the The accuracy of the scan is verified based on the overall resulting data are plotted in the GUI. To test the system inte- dimension, as it is shown in Figure 9, and only few cloud gration, a Professional Quality Tool Hardened and Precision points are used; looking at two reference cloud points, and Ground1 ×2 ×3 Block [20] is used, and the dimensions their value along the𝑧− direction, the height of the scanned of the block are known for comparison with its scand output. block is 25.3𝑚𝑚 ,for the 25.4𝑚𝑚 height of the original For more robustness, the RMS value are calculated. object. For example, by increasing few more scanned cloud points on the top surface, the object shown in Figure 8 is somewhat recreated with the shape and holes in the middle. 5. Results and Discussions However, still more cloud points and calibrations are required The main objective of this project was to identify the com- for the full construction of the object. The system can be calibrated for accuracy and repeatability based on the munication capabilities between the robot, line scanner, and computer to automate scanning process in industrial setting. trends of the successive scans of the same object. Another This communication was identiefi d and established, utilizing factor, which is not necessarily a problem but a suggestion a combination of Ethernet socket communication and USB for improvement, is the communication channel. In this connections so that all scanning data and robot position data study, communication between computer and the UR5 and between computer and the scanner was achieved by Ethernet can be automatically acquired (Figure 6). Another key objective is to generate a MATLAB user socket communication and USB cable, respectively. As cables interface to simulate the process and to apply the correct create clutter, using wireless communication may help in reducing clutter while transmitting a higher range of data transformation to the data gathered from the line scanner. This interface was successfully created, allowing a human [21]. 6 Journal of Robotics 9 pin USB Cable Computer Interface Scanner Controller Box Ethernet Socket Internal Communication Connection Robot Position UR Controller Box MATLAB GUI Figure 6: Communication setup and data flow. Figure 7: Simulation of the scan process. 6. Conclusion to reach around and even inside of parts needing to be scanned. This is a clear advantage over stationary mounted The solution for automated part inspection provides a variety line scanners located above the part to be scanned. The UR5 of benefits. The UR5 and line scanner cost approximately also allows operators to be quickly trained, as paths can $35,000 that is significantly cheaper than other metrology easily be retaught for a new part using the free drive mode hardware, which is upwards of $100,000. The collaborative of the robot. This scanning method has also shown to be nature of the robot allows humans to work in the area of accurate. This is acceptable for areas that do not require the robot without risk of injury. This is a large advantage the high accuracy of professional metrology equipment. The code generated for use on this robot can be generalized to compared to conventional industrial robots, which require a large footprint for safety guarding. This UR5 allows a be used with other robotsaswell, as anyDHtable canbe huge amount of efl xibility in positioning of the line scanner used as an input to the program. In the future, various areas Journal of Robotics 7 Cloud Points of the Scanned Object −20 −0.4 −0.6 −0.8 −1 −1.2 −30 −20 −10 Y in [mm] −1.4 Y in [mm] Figure 8: Isometric view of points from scanned object. Cloud Points of the Scanned Object X: -0.7176 Y: -5.802 Z: 25.22 X: -0.7176 Y: -5.805 Z: 25.22 −5 −30 −20 −10 0 10 20 Y in [mm] Figure 9: Front view of the scanned object. must be investigated to create an improved, competitive part reflectivity of the laser beam depending on the surface being inspection tool in the manufacturing sector. scanned. 7. Future Works Data Availability This project lacks an automatic pass/fail feature. The program The research data related to the graphical user interface (GUI) can be written in manner where if the scanned object is an development, equipment, and experimental setups used to accurate scan, a message such as “Object Passed Scan” will support the findings of this study are included within the appear. If the generated scan is a poor representation of the article. scanned object, “Failed Scan” or a similar message can appear and discard the scan. Another problem we encountered Conflicts of Interest during the scan was an error in the generated data due to reflection of the laser beam. This gave some inaccurate The authors declare that they have no conflicts of interest. data for the scan at certain cloud points of the scan. This error increases with an increase in reflectivity of the object References being used and therefore methods to eradicate or minimize this issue further research is required. More specifically, a [1] H. Kunzmann, F. Wald ¨ ele, and E. 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Journal of Robotics – Hindawi Publishing Corporation
Published: Feb 3, 2019