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The need to create more viable soft sensors is increasing in tandem with the growing interest in soft robots. Several sensing methods, like capacitive stretch sensing and intrinsic capacitive self-sensing, have proven to be useful when controlling soft electro-hydraulic actuators, but are still problematic. This is due to challenges around high-voltage electronic interference or the inability to accurately sense the actuator at higher actuation frequencies. These issues are compounded when trying to sense and control the movement of a multiactuator system. To address these shortcomings, we describe a two-part magnetic sensing mechanism to measure the changes in displacement of an electro-hydraulic (HASEL) actuator. Our magnetic sensing mechanism can achieve high accuracy and precision for the HASEL actuator displacement range, and accurately tracks motion at actuation frequencies up to 30 Hz, while being robust to changes in ambient temperature and relative humidity. The high accuracy of the magnetic sensing mechanism is also further emphasized in the gripper demonstration. Using this sensing mechanism, we can detect submillimeter difference in the diameters of three tomatoes. Finally, we successfully perform closed-loop control of one folded HASEL actuator using the sensor, which is then scaled into a deformable tilting platform of six units (one HASEL actuator and one sensor) that control a desired end effector position in 3D space. This work demonstrates the first instance of sensing electro-hydraulic deformation using a magnetic sensing mechanism. The ability to more accurately and precisely sense and control HASEL actuators and similar soft actuators is necessary to improve the abilities of soft, robotic platforms.
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Reduction of Residual Vibration in Displacement-Amplified Micro-Electromagnetic Actuators with Non-linear Dynamics Using Input Shaping
Micro-electromagnetic actuators have been used in many fields and industries for systems such as microftuidic systems, positioning stages, and robotic manipulators. Small-scale electromagnetic actuators are able to provide rapid motion with high positioning accuracy. The actuator presented in this paper utilizes a displacement amplification mechanism to increase the maximum stroke length that can be achieved. The dynamics of this actuator are nonlinear due to the dependence of the applied force on gap distance between the coils and the amplification mechanism. This nonlinearity causes the performance of PID control to vary with respect to the displacement of the actuator. The control method proposed in this paper to limit the overshoot resulting from nonlinearity uses a combination of PID control and robust input shapers. Using robust input shapers to account for parameter variation across the workspace, the combined controller eliminates the overshoot while maintaining short settling times. Simulations are presented to demonstrate the performance of the proposed method.
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- Award ID(s):
- 1714043
- PAR ID:
- 10076427
- Date Published:
- Journal Name:
- 2018 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM)
- Page Range / eLocation ID:
- 574 to 579
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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null (Ed.)Dielectric elastomer (DE) materials, a category of electroactive polymers, can be used to design actuators that are flexible, resilient, lightweight, and durable. However, due to the uncertainties in its actuation dynamics, DE actuators always rely on feedback control to perform accurate and safe operations. In this paper, a tubular dielectric elastomer actuator (DEA) with self-sensing capability is developed. It does not require external devices to measure displacement for feedback control. The displacement of the actuator is controlled using a proportional-integral controller with the capacitance measured at high probing frequency as the self-sensing mechanism component of the actuator. By superimposing actuation and probing voltage and applying them to the DE tube, the actuation voltage activates the movement of the DE tube and the probing voltage is used for self-sensing. Fast Fourier Transform (FFT) is then used to filter a given frequency of the probing current and voltage and then calculate the capacitance from the probing current and voltage during each time window. With the relationship between capacitance and displacement of the DE tube, the displacement output is estimated online and self-sensing without an external sensor is achieved. The self-sensing signal is then used as a feedback signal in a closed-loop design to follow a reference signal for tracking. The experimental results validate the self-sensing of the DE actuator in feedback control.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/AIM.2018.8452238
