Sensors are used in the cutting-edge imaging system design of tactile research

Have you ever played a racing game on a TV where the controller vibrates to warn you when you go off the track? If so, you have already had a sense of what a haptic interface is. The word haptic comes from the Greek word haptikos, which means to grasp or sense. With haptic robotics, users can feel a distant or virtual environment. Haptic interfaces give users real tactile feedback, allowing users to feel things that they are not directly touching. For example, a haptic interface allows you to feel the resistance of a simulated flight steering wheel, and the tactile feedback allows the pilot to know how much force to apply.

One of the most cutting-edge areas of tactile research is called "passive tactile." General tactile interfaces are active, meaning that the system uses power devices such as motors and wind to increase the system force perceived by the user. The risk of active tactile systems is that the power devices may increase the force too much and injure the user. Passive tactile interface designs have safety options, using passive power devices such as magnetorheological brakes to eliminate system forces instead of adding forces to the system. Passive tactile interfaces are not only safe, but also more energy-efficient.

Researchers at the Intelligent Machine Dynamics Laboratory (IMDL) at Georgia Institute of Technology are investigating the use of passive haptic systems. Dr. Wayne Book and graduate student Benjamin Black are investigating whether passive haptic systems can provide the same benefits as active haptic systems for remote device operation, with the added benefit of additional safety features. A major limitation of passive haptic systems is that the devices cannot be fixed in place. Also, in contrast to active haptic systems, passive powered devices must guide the operator to the desired location. Dr. Book and Black are attempting to overcome this difficulty by developing advanced passive powered device control schemes.

Using a graphical system design approach

Using the graphical system design approach, system design was divided into several steps. Graphical system design introduces graphical development software tools and off-the-shelf hardware to speed up the design, modeling and configuration of embedded control devices. The researchers used the National Instruments LabVIEW graphical software development platform to design and simulate tactile control systems and remote operation communications. The designed products were configured to a real-time PXI control and data acquisition system to test the solutions. The advantage of this testing method is that Dr. Book and Black can avoid spending energy on low-end embedded software development and customized hardware design when configuring the product, and instead devote themselves to repeated trials and designs.

Researchers can quickly import their master-slave controller algorithms into LabVIEW and then use high-level programming interfaces to load dynamic devices and sensors. By loading the algorithms with actual hardware, they can verify the correctness of the theory with real data. Figure 1 shows the graphical source code of the researcher operating the slave controller position. In addition, the software tool provides high-level acquisition interfaces, such as the timed-loop function. The timed-loop is a LabVIEW program structure that can collect priority and multithreading details. Through these different types of acquisition methods, engineers and scientists can easily apply multithreading functions to their software. This gives researchers more time to perfect the designed product instead of spending time on low-level code development.

Hardware design and configuration

The researchers configured software algorithms to PXI modular hardware systems. These systems include deterministic, real-time controllers and appropriate I/O modules that can contact the sensors of the experimental tactile devices. Using the LabVIEW Real-Time Module, the researchers configured their algorithms to the PXI controllers for headless operation. They used plug-and-play motion control modules to handle linear slave motors and multifunction data acquisition devices to handle fixed-point sensors.

The test instrumentation for this study used a 2-DOF manipulator as the master to control a 1-DOF linear motor as the slave. There was no physical connection between the master and slave; instead, a PIX real-time control system was connected to the master and another system was connected to the slave, as shown in Figure 2. PIX system 1 used a deterministic application on NI LabVIEW to read out the gamma sensor and the optical encoder on the master manipulator. The researchers used this data to determine the master's position and communicated the position to PXI system 2.

PXI system 2 uses the master position as a fixed point to output signals to a 4KHz PD (proportional differential) controller designed in LabVIEW to run the linear motor and read position data on the optical encoder. The slave is constrained by the physical structure and its movement is blocked. The slave position is transmitted back to the master via UDP to PXI system 1, which loads the data into the control algorithm that determines the tactile force that should be applied to the user to make them feel the presence of the physical constraint. The force is driven by the magnetorheological actuator. The purpose of the system is to have the slave position track the master position.

Dr. Book and Black are now conducting simulation experiments and further research using dynamic systems based on LabVIEW. Using system identification techniques, the researchers can use the actual data collected in simulation and feedback experiments to build a digital simulation structure of the dynamics between the master and slave devices. They use the result inequality combined with the LabVIEW simulation module to calculate the real-time formula that simulates the feedback between different control laws. This simulation process helps them to verify the laws more quickly and repeatedly before actually applying them to the production of tactile devices.

Summarize

This research story once again illustrates how current technological advances can pave the way for future technologies. Using a graphical systems design approach, Dr. Book and Black took advantage of the democratization of embedded development to achieve groundbreaking research.