Sensor/actuator feedback systems

Some of the EAP materials can be used as a sensor and an actuator in same devices. IPMC is a typical example of such materials. In this section, the sensor function of the IPMC and its application to the sensor/actuator feedback systems are explained. 

Hunt, A., Chen, Z., Tan, X. and Kruusmaa, M. (2009). Feedback control of a coupled IPMC (ionic polymer-metal composite) sensor-actuator, in Proceedings of the ASME 2009 Dynamic Systems and Control Conference (Hollywood, CA). 

It was reported that the IPMC has a function of not only an actuator but also a sensor, like a piezo-material [17]. Yamakita et al. [18] studied the sensor property of Nafion/Au and developed the IPMC sensor/actuator system. The response of the IPMC actuator was controlled by the feedback of the same IPMC sensor signal. 

In order to confirm the validity of the sensor system, we demonstrate an experiment of feedback control using IPMC sensor/actuator. In the experiments, a pair of IPMC strips is conneeted in parallel. One of the IPMC strips is used as an actuator, and... 

In addition to a thermostatically operated home heating system, identify two other feedback control systems that can be found in most residences. Describe briefiy how each of them works include sensor, actuator, and controller information. 

We use a simple liquid level controller to illustrate the concept of a classic feedback control system.1 In this example (Fig. 5.1), we monitor the liquid level in a vessel and use the information to adjust the opening of an effluent valve to keep the liquid level at some user-specified value (the set point or reference). In this case, the liquid level is both the measured variable and the controlled variable—they are the same in a single-input single-output (SISO) system. In this respect, the controlled variable is also the output variable of the SISO system. A system refers to the process which we need to control plus the controller and accompanying accessories such as sensors and actuators.2... 

Combustion instability that leads to performance deterioration and excessive mechanical loads, which could result in reduced life and premature failure, is an important issue with modern gas turbine engines and ramjet and scramjet combustors. Various techniques of passive and active control to reduce combustion instabilities and improve performance are addressed. Since extensive, promising research is being carried out to develop sensors and actuators, these techniques can be used in practical combustors in the near future. The topics covered in Section 3 provide the required chemical, kinetic, and fluid dynamic understanding to help the designer who is involved in active feedback control for combustion systems. 

Unlike the open-loop control, which basically provides a transfer function for the input signals to actuators, the feedback control systems receive feedback signals from sensors then compare the signals with the set point. The controller can then control the plant to the desired set point according to the feedback signal. There are five basic feedback control models (Morriss 1995) ... 

As an example, consider the design of a simple conveyor mechanism, depicted in Fig. 5.3, built from multiple DEAs that will push a small cylindrical object forward. One solution is to use a central controller to coordinate the behavior of each actuator. Without feedback, the timing of actuation of each DEA would need to follow a predetermined pattern. However, as the object accelerates, or if objects with different masses or rotational inertias are transported, it would be difficult to ensure synchronized actuation in such an inflexible system. To improve flexibility, feedback from each actuator is required. Typically this would involve conventional external sensors, e.g., laser displacement sensors, LVDTs, optical encoders, or motion sensors, and the use of a centralized controller to coordinate the overall... 

The basic principle of feedback control is shown schematically below. A system is observed by sensors that produce measurements (y) at each time these measurements are compared to the desired performance of the system (r) and the difference between the desired (r) and actual state (y) is used to create an error (c = r — y) a controller, usually implemented on a computer or via analog circuitry, operates on this error to decide which actuation actions (m) should be applied to the system to change its state from where it is to where it should be. 

Based on the PW modulator, the PID controller is designed to control the multi-stacked actuator. The control system is illustrated in Fig. 7.24. The PID controller transforms the error between the command and the feedback signals from the sensor to the command for the PW modulator. The PW modulator transforms the output of the PID controller into a pulse sequence, which is applied to the multi-stacked actuator. 

The feedforward algorithms utilize the setpoint information, either by itself or coupled with sensor data from the system, along with a map generated from models or empirical data. The map transforms the system-level setpoint targets and any feedback signals into a setpoint that is recognizable by the individual actuators such as speed, valve position, and so on. 

---