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3-D Printing Devised for Sensors in Soft Robotics

3-D printed soft gripper

3-D printed soft gripper (Ryan Truby, Harvard University)

1 March 2018. Engineering researchers developed techniques using three-dimensional printing that enables robotic devices made with soft materials, like those in health care, to sense more properties of objects they encounter. A team from bioengineering labs at Harvard University describes these techniques in the 27 February issue of the journal Advanced Materials (paid subscription required).

Robotic devices made with soft materials are desirable features for systems coming in close contact with people and animals, particularly in health care, such as surgical robots, where their actions can have life and death consequences. Embedding sensors for properties like shape and pressure can help substantially in improving the capabilities of these systems, but up to now building in sensors to soft robots was a challenging task. A key problem is the rigid nature of of most electronic sensors, which reduces the friendliness of these devices to their environment.

Researchers from the Harvard University labs of Jennifer Lewis and Robert Wood designed a solution to this problem, which they outline in the paper. Both Lewis and Wood study soft robotics, with Lewis’s lab specializing in materials, while Wood’s group focuses more on the electronics. The team led by recent graduate student and first author Ryan Truby uses advances in 3-D printing to integrate working sensors in soft materials, and still keep the robotic devices friendly to the living beings they contact.

The researchers’ designed a way of 3-D printing soft robotic actuators — components that move and control machines — with sensing capabilities already mixed into the printing materials. Their solution is a gel that conducts electrical signals, formulated into an ink that can be combined with the flexible materials laid down by the 3-D printer. The sensor circuits then are designed into the printing instructions, and produced in a single process known as embedded 3-D printing, a technique devised in Lewis’s lab.

“The function and design flexibility of this method is unparalleled,” says Truby in a university statement. “This new ink combined with our embedded 3-D printing process allows us to combine both soft sensing and actuation in one integrated soft robotic system.”

The team tested their process with a 3-D printed soft robotic gripper. Embedded in the 3-fingered gripper are sensors for shape, pressure, and temperature. Tests of the device show the gripper can accurately sense inflation pressure and curvature, as well as temperature. In addition, multiple contact sensors in the gripper makes it possible for the device to sense both light and firm touches of objects.

The authors say this embedded process can be readily integrated into current 3-D systems for soft robotics, but they plan to add in machine learning capabilities that train the devices to better interact with various object shapes, leading to more closed-loop control of soft robots.

The following video demonstrates the sensors and soft gripper.

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