Control of conducting polymer actuators without physical feedback: simulated feedback control approach with particle swarm optimization

Abstract

Conducting polymer actuators have shown significant potential in articulating micro instruments, manipulation devices, and robotics. However, implementing a feedback control strategy to enhance their positioning ability and accuracy in any application requires a feedback sensor, which is extremely large in size compared to the size of the actuators. Therefore, this paper proposes a new sensorless control scheme without the use of a position feedback sensor. With the help of the system identification technique and particle swarm optimization, the control scheme, which we call the simulated feedback control system, showed a satisfactory command tracking performance for the conducting polymer actuator's step and dynamic displacement responses, especially under a disturbance, without needing a physical feedback loop, but using a simulated feedback loop. The primary contribution of this study is to propose and experimentally evaluate the simulated feedback control scheme for a class of the conducting polymer actuators known as tri-layer polymer actuators, which can operate both in dry and wet media. This control approach can also be extended to other smart actuators or systems, for which the feedback control based on external sensing is impractical.

How the type of input function affects the dynamic response of conducting polymer actuators

“…We have found that the four smooth inputs consume less electrical power than sharp inputs such as a step input with discontinuous higher order derivatives. We also obtained an improved transient response performance from the smooth inputs, especially under the simulated feedback control strategy, which we have proposed previously [13]. The idea of using a smooth input command, which results in lower power consumption and better control performance, can be extended to other smart actuators.…”

“…The structure of a PPy actuator [13] As shown in Figure 2, when a potential difference is applied to the actuator via platinum contacts, the PPy on positive electrode is oxidized and on the other hand, the negatively charged PPy layer is reduced. The TFSI -anions in the electrolyte will move into the positively charged PPy layer and cause a volume expansion.…”

“…The displacement of the CPA is measured and recorded by a laser-based displacement sensor. Figure 3 Schematic representation of the experimental setup [13] …”

“…These methods have focused on i) establishing a feedback control system using position data provided by an external sensor or sensors and ii) establishing inversion-based feedforward control approaches without using externally provided feedback data [7][8][9][10][11][12][13][14][15]. Compared to a conducting polymer actuator, the sensor used in the first approach is extremely large, which limits the CPAs' application and brings extra complexity and cost.…”

“…With reference to the experimental results presented in this study, one obvious effect is the minimum electrical power consumed under smooth inputs, which is expected to extend the operational life of the actuators. We have used a step input, a harmonic input, a cycloidal input, an exponential input and a ramp input to evaluate the command tracking ability of the actuators under open loop control and a simulated feedback control approach, on which we have reported recently [13]. In the simulated feedback control method, we employed a PID controller whose gains are determined by a particle swarm algorithm in order to optimize the control system performance.…”