Inkjet Printing of Complex Soft Machines with Densely Integrated Electrostatic Actuators

Abstract

Soft machines consist of distributed and interconnected actuators, sensors, logic elements, and ideally a power supply, integrated in a stretchable body. Their intrinsic compliance makes them interesting for a wide array of applications, from soft robotics [1] to organs on a chip. [2] The field has seen rapid growth, in view of the versatility of soft machines, [3] their ability to replicate animal-like motion, [4-7] their intrinsic safety for human interactions, [1] resilience, [8-10] and the ability to use material compliance and elasticity as a means to both simplify control and add function. [11] Given the highly integrated nature of complex soft machines, and the need for many different materials for functional and structural elements, additive manufacturing is an appealing method both to create soft machines with multiple independent actuators and to rapidly tailor dimensions, material properties, and device functions to different tasks. [12,13] As a fully printed soft machine requires no assembly, circuits and systems too complex for manual fabrication and assembly become possible. Printing has allowed complex soft structures with advanced materials, [14] but the focus to date has been mostly on pneumatic structures (i.e., printed chambers) and strain sensors for soft robot end effectors. [12,15] With a few exceptions such as the Octobot, [16] liquid-crystal artificial cilia, [17] or ionic electroactive polymers, [18-20] nearly all printed actuators are pneumatically driven fluidic elastomer actuator (FEAs) devices requiring external air pressure connections to inflate or deflate the bladders. [1,21] Fluidic actuation requires elastomers with well-defined channels but needs no electrical elements. In contrast, including electrically operated actuators embeds the electromechanical conversion into the device and reduces the number of external components. However, it adds important requirements, such as printing magnetic materials or metal coils for electromagnetic actuation, resistive tracks for Joule heating, or dielectrics with a high electrical breakdown, absence of pin holes, and the need for high thickness uniformity if electrostatic actuation is used. Actuators with embedded electrical actuation have been realized using printing processes, either partially printed in combination with additional fabrication methods or fully printed. The first category includes ionic electroactive polymers actuators, with printed polymer layers, but metallic electrodes deposited by other methods. [18,20] The second category includes hybrid pneumatic and shape memory polymer actuators with integrated Joule heating [22] or fully printed ionic microactuators. [19] In this work, we use inkjet printing to produce complex soft machines with integrated electrostatic zipping actuators in a single process. We use a three-material printing process which

Printable Smart Materials and Devices: Strategies and Applications

“…A multimaterial inkjet printing method for integrated soft actuators is developed, combining dense arrays of electrostatic actuators, multilayer electrical routing, and complex networks of microfluidic channels in one printing process. 121 These soft actuators demonstrate that inkjet printing produces densely packed high-voltage actuators (Figure 4b). Logic actuators are expected to be printed in the future for integrated autonomous soft machines.…”

“…As for the smart actuators, inkjet printing strategies are suitable for layer-by-layer patterning electrodes and actuating materials. A multimaterial inkjet printing method for integrated soft actuators is developed, combining dense arrays of electrostatic actuators, multilayer electrical routing, and complex networks of microfluidic channels in one printing process . These soft actuators demonstrate that inkjet printing produces densely packed high-voltage actuators (Figure b).…”

Control Strategies for Soft Robot Systems

“…Dielectric elastomer actuators (DEAs) use the attractive force between positive and negative charges on opposite electrodes to deform a soft elastomer dielectric (Figure 1b). [32][33][34][35][36][37] DEAs can be prepared from low-cost materials using manual [38] or automated fabrication approaches [39][40][41][42] and possess advantages of large strains and fast actuation speeds.…”

Processing of Self‐Healing Polymers for Soft Robotics

“…In contrast to SLA and DLP, this technique allows to print multi‐material objects by having multiple nozzles. [ 152,289–291 ] This was demonstrated by Hughes et al., [ 51 ] who printed a piano‐playing soft robotic hand with passive intelligence in a single inkjet printing procedure with three distinct materials, of which one was used as soluble support. By depositing a ratio of two different photo‐resins on a single location, prior to UV exposure, gradients of mechanical properties can be printed in soft robotics as well, as demonstrated by Bartlett et al.…”