Delta robots are becoming increasingly popular for many types of applications, because they’re fast, have small footprints and feature large work envelopes. In addition to assembly applications, such as adhesive dispensing and screwdriving, the machines feed, pick, place, stack and kit a wide variety of parts and components.
Over the last decade, engineers have developed smaller and smaller delta robots for tasks in limited workspaces. But, shrinking them further to the millimeter scale with conventional manufacturing techniques and components has proven fruitless.
A team of students at Harvard University’s Wyss Institute for Biologically Inspired Engineering has successfully tackled the challenge. By integrating microfabrication techniques with high-performance composite materials that can incorporate flexural joints and bending actuators, they recently created a robot that’s the size of a penny.
The milliDelta can operate with high speed, force and micron precision. It measures 15 by 15 by 20 millimeters and has a total mass of 430 milligrams.
“The milliDelta is a millimeter-scale version of a delta robot,” says Hayley McClintock, a staff researcher at the Wyss Institute. “We scaled the dimensions down using printed-circuit microelectromechanical systems, laminate manufacturing techniques and high-power density piezoelectric actuators that were developed at the Harvard Microrobotics Lab.
“[The piezoelectric actuators enable the milliDelta] to perform movements at frequencies 15 to 20 times higher than those of other currently available delta robots,” claims McClintock.
“We were impressed with the speed and precision of industrial-sized delta robots and thought that these qualities could be beneficial for applications at the millimeter scale,” explains McClintock. “In addition, we knew that desirable qualities, such as speed, would improve since the smaller size yields a lower inertia, enabling higher accelerations.
“The milliDelta design incorporates a composite laminate structure with embedded flexural joints that approximate the more complicated joints found in large-scale delta robots,” McClintock points out. “With the help of an assembly jig, this laminate can be precisely folded [like pop-up books and origami] into a millimeter-scale delta robot.”
The composite consists of a rigid carbon-fiber layer and a flexible polyimide layer. The layers are bonded together using a heat- and pressure-activated sheet adhesive. The actuators are also a composite laminate, made with a central conducting carbon-fiber layer sandwiched between oppositely charged piezoceramic sheets.
“To develop millimeter-scale robots, we replaced conventional parts, such as pin and universal joints, with combinations of revolute hinges,” explains McClintock. “Similarly, instead of using rotational actuation that is hampered by significant frictional losses, we designed a transmission linkage system to convert the linear output of piezo actuators to rotational input for the milliDelta.”
According to McClintock, the robot can operate in a workspace of 7 cubic millimeters. It has a payload capacity of 1.3 grams. The robot can achieve frequencies up to 75 hertz, with a velocity and acceleration of 0.45 meters per second and 22 g, respectively.
“The milliDelta can apply forces and exhibit trajectories that, together with its high frequencies, could make it ideal for micromanipulations in industrial pick-and-place processes,” says McClintock. “[Other potential applications include] microscopic surgeries, such as retinal microsurgeries performed on the human eye.
“Due to its high precision and speed, the milliDelta can be useful for tasks that require precision in small workspaces and fast movement,” claims McClintock. “Some examples we explored are tremor compensation for microsurgery.
“The milliDelta has the potential to reduce hand tremors by around 81 percent,” adds McClintock. “Combining this result with its compact form, we believe our robot could be used as an end effector for microsurgical devices or for assembly operations that require a steady hand.”
To see a video of the milliDelta robot in operation, click here.
