Conference Paper

DEVELOPMENT OF A BISTABLE SMA ACTUATED INDUSTRIAL GRIPPER BASED ON A COMPLIANT DESIGN

Authors:
  • ZeMA - Zentrum für Mechatronik und Automatisierungstechnik gGmbH
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Abstract

Within industrial manufacturing, most processing steps are accompanied by transporting and positioning of workpieces. The active interfaces between handling system and workpiece are industrial grippers, which often are driven by pneumatics. On the way to better energy efficiency and digitalization, companies are looking for new actuation technologies with more sensor integration and higher efficiencies. Commonly used actuators like solenoids and electric engines are in many cases too heavy and large for direct integration into the gripping system. Shape memory alloy (SMA) actuators are suited to overcome those drawbacks of conventional actuation systems, because of their high energy density. Additionally, they feature self-sensing abilities that lead to sensor-less monitoring and control of the actuator element. Another drawback of conventional grippers is their design, which is based on moving parts with linear guides and bearings. These parts are prone to wear, especially in abrasive environments. This can be improved by a compliant gripper design that is based on flexure hinges and thus dispenses with joints, bearings and guides. In the presented work, the development process of a functional prototype for a compliant gripper driven by a bistable SMA actuator for industrial applications is outlined. The focus lies on the development of the compliant kinematics, where first results of FEM simulation are discussed. As a result, a working gripper-prototype which is manufactured with modern 3D-printing technologies is introduced.

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Chapter
Full-text available
The high energy density of shape memory alloy actuators in combination with their self-sensing ability and their unique form factors allow for the design of miniaturized and compact but yet powerful actuator-sensor-systems. These properties as well as their noise and emission free operation make them attractive actuator solutions for industrial applications. Specifically in the fields of material handling, soft robotics and continuum robotics, there have been several developments of SMA based grippers, end-effectors and robotic structures.
Patent
Full-text available
The invention relates to an actuator device (1) for providing at least two actuator positions, comprising an elastic bending element (2), which at at least one fastening point (31, 32, 34) is held such that by exerting a switching torque at the fastening point (31, 32, 34), an elastic deformation of the bending (2) leads to a change from a first actuator position into a second actuator position, and comprising at least one actuator element (41, 42) having a shape memory wire, wherein by heating, the shape memory wire generates a tractive force, and is thus coupled to a section of the bending element (2) at the fastening point (31, 32, 34), such that the tractive force causes the switching moment to be brought about at the fastening point (31, 32, 34) in order to move the bending element (2) from the first actuator position into the second actuator position.
Article
Full-text available
Thermal shape memory alloy (SMA) actuators are known for their superior energy density (force-volume-ratio) compared to other actuation principles, allowing the construction of lightweight and compact systems. Furthermore, SMA actuators can be used as sensors, as their electrical resistance changes during activation. Using this multifunctionality, this work aims at presenting the development, fabrication and validation of an SMA driven robotic end-effector. The end-effector prototype is designed in a modular concept and consists of four independent arms with two degrees of freedom (DOF). Each arm can rotate in-plane and also tilt out-of-plane to allow gripping of various workpiece geometries. Both DOF actuator components consist of an SMA wire working against a tension spring. The tilting joint has an additional mechanism that creates two energy-free rest positions to improve energy-efficiency. The end-effector is designed to carry a maximum load of 10 kg. In a test bench for the validation of the SMA driven end-effector joints, hall sensors are used to measure the gripping arm displacement. In addition, the resistance of the SMA wires is monitored during activation. The dynamic system performance is analyzed using different activation current levels. Finally, a PI control with Hall sensor feedback is implemented to position the first DOF at arbitrary angles within its 90° rotation radius.
Article
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Dielectric elastomers represent a relatively new technology with high potentials for actuators’ applications. Thanks to their lightweight, fast operations, energy efficiency, low power consumption, large deformations, and high scalability, dielectric elastomers permit to develop novel mechatronic systems capable of overperforming standard actuation technologies, such as solenoid valves, in several applications. This article presents a novel design for a dielectric elastomer– driven actuator system which enables closing and opening of a contactor. The design is based on a combination between circular out-of-plane dielectric elastomer membranes and a bi-stable biasing system which allows to increase the out-ofplane stroke. Characterization of the contactor is initially performed in order to establish the actuator requirements in terms of force and stroke. Then, systematic design and manufacturing are carried out for both dielectric elastomer membranes and biasing mechanism. Finally, the effectiveness of the actuator in closing and opening the contactor is validated experimentally. The results show comparable dynamic performance to a conventional electromagnetic drive, with the additional advantage of a significantly lower energy consumption.
Conference Paper
Full-text available
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Conference Paper
Full-text available
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Article
Full-text available
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Conference Paper
Full-text available
Shape Memory Alloy (SMA) actuators like SMA wires are already present in a few commercially available products, like valves or locking mechanisms. In these actuator systems, the SMA wires are always coupled with an additional biasing mechanism, such as a restoring coil spring. Other possible restoring forces are, for example, the gravitational force of a mass or the pulling force of a second SMA actuator. One drawback of an SMA actuator wire system, such as when coupled with a coil spring, is the continuous energy needed to remain in the contracted position. In this paper, a new SMA actuator design is presented that addresses and solves this drawback. In this actuator, a bi-stable snap mechanism is combined with a protagonist-antagonist SMA wire configuration. In this way, the actuator has two defined stable and energy-free positions. The SMA wires are only activated to switch between these two positions.
Article
Full-text available
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Article
This paper presents the design and development of a high precision microgripper for micromanipulation. The design is based on a hybrid flexure-based compliant mechanism and a bias spring structure which render high fidelity and inherent mechanical advantages. Finite element analysis (FEA) was conducted to evaluate responses of the model under specified load and displacement to investigate optimum design of the model. The prototype of the proposed microgripper was fabricated using electro-discharge machining (EDM) process. An experimental study of the performance was carried out and the results are presented. The experimental results are also compared with the computational analysis results. The results show that a high level of displacement amplification and a maximum stroke of 100 μm can be achieved.
Article
A microgripper system is presented, which consists of a monolithic shape memory alloy (SMA) device of mm size and an integrated optical position sensor. Gripper closing and opening is performed by two integrated actuators, which form an antagonistic pair. Investigations of temperature profiles by coupled finite-element simulations and infrared microscopy demonstrate a sufficient thermal insulation of the actuators for their selective control. The motion of gripping jaws is transmitted by an integrated gearing mechanism into a linear motion of an integrated optical slit, which is detected by change of optical transmission. The maximum stroke and force of the gripping jaws are 300 μm and 35 mN, respectively. In the range between 10 and 90% of the maximum stroke, positioning is achieved within 140 ms with an accuracy of about 2 μm.
Vacuum gripper system based on bistable SMA actuation
  • F Welsch
  • M Schmidt
  • S M Kirsch
  • S Seelecke
  • P Motzki
F. Welsch, M. Schmidt, S. M. Kirsch, S. Seelecke, and P. Motzki, "Vacuum gripper system based on bistable SMA actuation," ASME 2018 Conf. Smart Mater. Adapt. Struct. Intell. Syst. SMASIS 2018, vol. 1, no. September 2019, 2018.
Shape memory alloys in continuum and soft robotic applications
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Y. Goergen et al., "Shape memory alloys in continuum and soft robotic applications," ASME 2019 Conf. Smart Mater. Adapt. Struct. Intell. Syst. SMASIS 2019, no. December, 2019.
FFZ Glashuette -Greiftechnik
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F. Glashuette, "FFZ Glashuette -Greiftechnik," 2019. [Online].