A multiple-shape memory polymer-metal composite actuator capable of programmable control, creating complex 3D motion of bending, twisting, and oscillation

Abstract

Development of biomimetic actuators has been an essential motivation in the study of smart materials. However, few materials are capable of controlling complex twisting and bending deformations simultaneously or separately using a dynamic control system. Here, we report an ionic polymer-metal composite actuator having multiple-shape memory effect, and is able to perform complex motion by two external inputs, electrical and thermal. Prior to the development of this type of actuator, this capability only could be realized with existing actuator technologies by using multiple actuators or another robotic system. This paper introduces a soft multiple-shape-memory polymer-metal composite (MSMPMC) actuator having multiple degrees-of-freedom that demonstrates high maneuverability when controlled by two external inputs, electrical and thermal. These multiple inputs allow for complex motions that are routine in nature, but that would be otherwise difficult to obtain with a single actuator. To the best of the authors' knowledge, this MSMPMC actuator is the first solitary actuator capable of multiple-input control and the resulting deformability and maneuverability.

Figure 1. Properties of an IPMC made with Nafion™ membrane.

(a) An IPMC sample in the evaporating pan. (b) A scanning electron microscopy (SEM) image of a cross-section of IPMC. The IPMC consists of the electrode on both sides and the polymer membrane between them. (c) An illustration of the IPMC operating principle. Deformation will occur if an electric field is applied across the IPMC, which causes the ions to redistribute along with the water molecule. The size of the IPMC is 50.78 mm in length, 9.82 mm in width and 0.53 mm in thickness. (d) Continuous deformation of IPMC in one cycle under the voltage of 2.6 V amplitude and 1 Hz frequency. (e) Input voltage, output current, and displacement of IPMC versus time under the above voltage input.

Figure 2. Nafion™ fiber demonstrating quadruple shape memory cycles with a 1-g weight on the tip.

Triple shapes of the Nafion™ fiber, 99.87 mm in length and 0.95 mm in diameter, were programmed with loops having different shapes wrapping around a metal rod in the water. The fiber with original shape, S0, was wrapped and programmed at 85 °C and fixed at 75 °C to achieve the first programmed shape, S1. The second shape, S2, and third shape, S3, was programmed at 70 °C, 55 °C and fixed at 60 °C and 21 °C, respectively by wrapping around the rod with different cycles. Then, the Nafion™ fiber was reheated. The Nafion™ fiber recovered to S2′, S1′, and S0′ upon reheating to 55 °C, 70 °C, and 85 °C, respectively.

Figure 3. Programming of MSMPMC.

(a) The original shape of MSMPMC. The length, width, and thickness of the MSMPMC were 51.81 mm, 10.49 mm, and 0.60 mm, respectively. The tip of the MSMPMC was painted white to facilitate image analysis. A side line was painted on the MSMPMC to distinguish the deformation. (b) The first shape of the MSMPMC was programmed by heating at 85 °C and cooling at 70 °C. The MSMPMC was wrapped around a rod during the programming. (c) The second shape of the MSMPMC was programmed by heating at 60 °C and cooling at 22 °C.

Figure 4. A MSMPMC actuator with multiple degree-of-freedom deformation.

The sample was under a sinusoid AC voltage of 3.7 V initial amplitude and 1 Hz frequency. The water was heated from 22 °C (room temperature) to 90 °C.

Figure 5. MSMPMC 3D motion trajectory.

(a) 3D position track of MSMPMC actuator. The applied sinusoid AC voltage has 3.7 V initial amplitude and 1 Hz frequency. The measured temperature increased from 34.9 °C to 84.3 °C. (b) 3D motion of the MSMPMC tip line.

Figure 6. Deformation of MSMPMC.

(a) Bending displacement and temperature of MSMPMC versus time under an external electrical input of 3.7 V initial amplitude and 1 Hz frequency and thermal input from 34.9 °C to 84.3 °C. (b) Twisting angle and temperature of MSMPMC versus time under external electrical and thermal input.

Figure 7. Impedance response of MSMPMC.

(a) Measured voltage response of MSMPMC versus time. The initial amplitude of sinusoid voltage input was 3.7 V and the frequency was 1 Hz. (b) Measured current response of MSMPMC versus time. (c) Electrical impedance of MSMPMC versus temperature.

Figure 8. Experimental setup.

The experimental setup used for measuring thermal and electromechanical responses of the MSMPMC actuator.