Sebastian Reitelshöfer

Aerosol jet printing and lightweight power electronics for dielectric elastomer actuators

Dielectric elastomer actuators have been subject of researches in materials science since almost two decades. The synonymous denotation “artificial muscles” emphasizes the potential capability of those actuators, whereat the skeletal muscles of mammals, which are the biological archetypes, even are exceeded pertaining energy density and efficiency. These new kind of actuators depicts promising actuators for the development of a new generation of robotic solutions, such as inherently safe systems for human robot cooperation, highly dynamical, mobile and energy autarkic kinematics or even prosthetics. Since there are several challenges to be handled, like the high supply voltage, no automated manufacturing process for multilayered dielectric elastomer actuators is available and thus no actuators systems based on dielectric elastomer actuators for complex robot kinematics or commercial products. Now the Aerosol Jet Printing process seems suitable for an automated manufacturing process by printing such actuators and is investigated within the framework of the Bavarian biomimetic initiative “bionicum-forschung”. With this additive process stacked actuators are printed, where insulating and conducting layers are alternating and the automated manufacturing of stacked actuators with thousands of layers seems possible in the long term. With the new built actuators, new mobile and autarkic platforms in the range of a capuchin will be designed. Therefore lightweight power electronics are necessary, which investigation represents the second main research task within the project. Here only one high-mass central power supply is able to individually operate each of the artificial muscles on the platform with a pulse width modulated high voltage signal. Thus each actuator does not need its own supply. The presented project aims with the development of a mobile and autarkic platform the improvement of actual robot platforms regarding to dynamical interactions with the environment, like jumping, and the progress of the actual state of the art of robotics.

A robot motion planner for 6-DOF industrial robots based on the cell decomposition of the workspace

This paper describes an autonomous robot motion planner for 6-DOF industrial robots based on the approximate cell decomposition of the workspace. Known obstacles lead to a hierarchical decomposition up to a predefined degree of the start cell which contains the whole robot workspace. A connectivity tree is searched for the shortest path from the start to the goal position for the Tool Center Point (TCP) of the robot. Center points and points between adjacent cells are used as interpolation points for the robots path. All possible configurations are calculated for these points and checked for absence of collisions and compliance with kinematic constraints. Subsequently paths between possible configurations of interpolation points are checked for feasibility. If points cannot be reached artificial obstacles are constructed and the work space model is updated.

Aerosol-Jet-Printing silicone layers and electrodes for stacked dielectric elastomer actuators in one processing device

In this contribution we present recent findings of our efforts to qualify the so called Aerosol-Jet-Printing process as an additive manufacturing approach for stacked dielectric elastomer actuators (DEA). With the presented system we are able to print the two essential structural elements dielectric layer and electrode in one machine. The system is capable of generating RTV-2 silicone layers made of Wacker Elastosil P 7670. Therefore, two aerosol streams of both precursor components A and B are generated in parallel and mixed in one printing nozzle that is attached to a 4-axis kinematic. At maximum speed the printing of one circular Elastosil layer with a calculated thickness of 10 μm and a diameter of 1 cm takes 12 seconds while the process keeps stable for 4.5 hours allowing a quite high overall material output and the generation of numerous silicone layers. By adding a second printing nozzle and the infrastructure to generate a third aerosol, the system is also capable of printing inks with conductive particles in parallel to the silicone. We have printed a reduced graphene oxide (rGO) ink prepared in our lab to generate electrodes on VHB 4905, Elastosil foils and finally on Aerosol-Jet-Printed Elastosil layers. With rGO ink printed on Elastosil foil, layers with a 4-point measured sheet resistance as low as 4 kΩ can be realized leaving room for improving the electrode printing time, which at the moment is not as good as the quite good time-frame for printing the silicone layers. Up to now we have used the system to print a fully functional two-layer stacked DEA to demonstrate the principle of continuously 3D printing actuators.

Dielectric elastomer actuators — On the way to new actuation-systems driving future assistive, compliant and safe robots and prostheses

For almost 20 years, dielectric elastomer actuators (DEAs) have been the subject of intense research in material science. A large number of publications describe artificial muscles based on DEAs as a promising alternative for an energy efficient, lightweight and flexible actuation architecture. DEAs could improve and extend the capabilities of robotic and prosthetic devices in terms of their dynamical performance and their eligibility for energy autarkic operation. However, up to now DEAs are not available on a large scale with reproducible characteristics nor are they yet usable on a system integration level. In this paper we present recent findings of our ongoing five-year project to qualify DEAs as feasible artificial muscles for usage in compliant robot kinematics and soft prosthetic devices. The focus of this contribution lies on a new automated production process using Aerosol Jet Printing for stacked DEAs with very thin layers for reduced driving voltages and improved mechanical characteristics resulting from the additive manufacturing. Secondly, a new set of lightweight power electronics based on pulse width modulation (PWM) is presented which aims at the improvement of the overall specific power of DEA driven kinematic systems.

Sensor-guided jogging for visually impaired

This paper introduces an approach for enabling visually impaired and blind people to practice jogging activities by 3D environment perception for course detection and collision avoidance, as well as feedback generation in an intuitive manner. Besides a system concept, first prototypic realizations, that confirm the general feasibility, are presented for this domain, which has not been addressed by research until now.

Dielectric elastomer actuators as self-sensing devices: a new method of superimposing actuating and sensing signals

Dielectric elastomer actuators (DEAs) have a lot of advantages such as high energy efficiency, unrivaled power-toweight ratio and soft structure. Furthermore this new kind of actuator is capable of sensing its deformation and status without additional sensing devices. Therefore, DEAs are acknowledged as self-sensing actuators. In this contribution a new self-sensing technique for DEAs is presented, in which the capacitance of DEAs under deformation is measured using high voltage signals. For this purpose, simple signal processing algorithms and a novel method of superimposing actuating and sensing signals are implemented. By connecting the ground potential electrode of the DEA to a sinusoidal sensing signal, the DEA is used as a passive first order high-pass filter. The other electrode of the DEA is connected to the actuation voltage, which is superimposed with the sinusoidal signal. The amplitude of this signal is basically dependent on the capacitance of the actuator. Therefore, the change of the capacitance induced by contraction of the actuator alters the amplitude of the sinusoidal signal. The amplitude change can then be interpreted as capacity change and can be used to estimate the mechanical deformation of the DEA. In comparison to existing methods, this approach is promising for a miniaturized circuit and therefore for later use in mobile systems. In this paper, the new concept of superimposing actuating and sensing signals for self-sensing DEAs is validated with an experimental setup and several known capacities. The first results are presented and discussed in detail.

A new production process for soft actuators and sensors based on dielectric elastomers intended for safe human robot interaction

Dielectric elastomers are the subject of intense research in material science. A large number of publications describe artificial muscles based on dielectric elastomer actuators as a promising alternative for an energy efficient, lightweight and flexible actuation architecture. Dielectric elastomer actuators could improve and extend the capabilities of robots in terms of soft kinematics for the direct physical interaction between humans and robots. They could also improve the dynamical performance and the eligibility for energy autarkic operation of robotic systems. Another field of application are dielectric elastomer sensors that can bear and detect large deformation. However, up to now dielectric elastomer actuators and sensors are not available on a large scale with reproducible characteristics. The focus of this contribution lies on a new automated production process using Aerosol-Jet-Printing for dielectric elastomer actuators and sensors with very favorable characteristics resulting from the additive manufacturing aiming at an improved availability of such sensors and actuators.

Self-calibration method for a robotic based 3D scanning system

This paper describes a method for extrinsic sensor calibration for a 2D laser profile sensor on a robot arm used as a robot based 3D scanning system. In order to establish a relationship between the sensor measurements and the robot positions, the transformation between the robot flange and the sensor reference frame are determined. The developed calibration method is implemented as an automated self-calibration. It is based on the use of a pin as a fixed reference. The robot is aligned to the tip of the pin automatically with certain orientations. The sensor transformation is calculated based on six recorded robot positions. Finally, the accuracy of the calibration is determined with an additional robot position.

Combining a collaborative robot and a lightweight Jamming-Gripper to realize an intuitively to use and flexible co-worker

By using collaborative robotic systems, new approaches like programming by demonstration can effectively be realized. As (re)programming of robots thereby gets fast and easy, such systems can facilitate the transition of industrial robots to flexible automation solutions suitable for small companies and small batch sizes. One reason that is preventing the usage of those robots on a broader scale is the fact that for nearly every different work piece a new gripping system has to be designed or at least mechanically adapted. The presented integration of a collaborative robot with a universal Jamming-Gripper broadens the spectrum of parts that can be handled by one robotic system without any mechanical modification.

Accuracy Analysis and Improvement for Cooperative Industrial Robots.

The cooperative working of multiple robots on a common task often requires a high geometric accuracy. If such a system is modeled, many sources of error are present, which can quickly lead to inadequate process results. In order to avoid this, it is important to carry out a calibration in which deviations are determined. Subsequently, the model can be adapted to the actual conditions. In the scope of this work a kinematic calibration method for multi-robot systems is developed and realized with a robot setup consisting of two industrial robot arms. The accuracy of the robot system is significantly improved by the developed approach, which has been proven by experimental investigations.