Digital Twinning of Miniature Industrial Robotic Arm (MIRA)

A digital twin is defined, fundamentally, as an evolving digital profile of the historical and current behavior of a physical object or process that helps optimize business performance. The digital twin is based on massive, cumulative, real-time, real-world data measurements across an array of dimensions. These measurements can create an evolving profile of the object or process in the digital world that may provide important insights on system performance, leading to actions in the physical world such as a change in product design or manufacturing process. Nowadays, conventional design and operation methods are often neglected, as it is not feasible to store real time data. By using digital models, it becomes possible to interpret measurements, operational and fleet data in a different way rather than just detecting deviations from the norm. Several modes of failure can be simulated for the current situation trying to reproduce the actual measurement signals. The comparison of the simulated signals with measured ones can help to identify the failure mode. Overall the Digital Twin is a practical technology, which yields better results.

a. About MIRA and its digital twin

• Miniature Version of Industrial Robotic Arm is intended for demonstrating working principle of industrial robot.
• It is a wireless model having five Degree of Freedom and working on a Bluetooth system doing functions of pick and place an object.
• Different attachments can be used to define various purposes of the Robotic Arm. The project work was interfacing of physical model of Miniature Industrial Robotic Arm (MIRA) with 3DEXPERIENCE platform to create the digital twin of the model.

The whole project was done in two phases – Virtual to Real Digital Twin and Real to Virtual Digital Twin. In the first phase, the physical model of MIRA is controlled by its virtual model and in the second phase, its digital model behaves exactly the same as its physical model.

b. Modifying electronic architecture of servo motors

To get the feedback from the robotic arm, all the servo motors were modified. There is one potentiometer present inside one servo motor which rotates with the shaft and sends feedback signal to the circuit board. Feedback is nothing but the analog values of that potentiometer which it is sending to the circuit board. Therefore, one extra single pin was solder to the port of servo motors. This made servos to give feedback signal to external processing system. After then the pin needs to connect to the controller to send it to the software platform.

c. Creating software interface

Digital Twin of MIRA comes with the software controlling part. In this project 3D EXPERIRNCE Platform was used to create the virtual world of MIRA. Here, functions were described and logics were built to get the desired outputs from the process. This was done in RFLP and Dymola Behavior Modeling apps. These apps carry ability to build physical world process in logical manner.

d. Virtual to Real Digital Twin

In order to execute this process, we added one predefined set of angle values in the table format. This logic will execute and process in the FMI model of Arduino, which will send the output to the physical Arduino connected externally to the system via USB port. In order to validate the logic, connections of the FMI Arduino block were made with the virtual model block and then it was simulated. After, it can be seen that both models – the virtual model present in the system and actual physical model of the arm will behave similar. Since signals are going from the virtual system to the actual arm, a loop is created, which is continuously going on by sending the signal to the physical model from the system. Thus the process is called as Virtual to Real Digital Twin.

e. Real to Virtual Digital Twin

In this process, the virtual world MIRA follows the real world MIRA. This process also starts similarly as the previous process. Here, when the physical MIRA moves, the real servo motors generates the signal. This signal goes to the Arduino board. The signal coming from all servo motors are collected here, and get transmitted to the CPU, as Arduino is connected to it via USB cable. These signals then enter in logical file of MIRA present in the software. Here, the signals get processed and converted to degree values from analog values. The logical file sends these signals to virtual servo motors of digital world MIRA. This makes the digital world MIRA to replicate the movement of real world. So this process is called as Real to Virtual Digital Twin process.