Manufacturing Bits: Nov. 12

There’s a knife-wielding robot in the supermarket; a new way to construct photovoltaic cells leads to a major breakthrough.


Knife-Wielding Robot
Cornell University has taught a knife-wielding robot to work in a mock-supermarket checkout line.

In doing so, researchers have modified a Baxter robot from Rethink Robotics. In the experiment, the robot coactively learns and makes adjustments while an action is in progress. But when performing tasks at a checkout line, the robot’s problem is to identify the appropriate trajectories.

For example, a robot checking out a kitchen knife at a grocery store should move it at a safe distance away from nearby humans. In one experiment, the robot wielded a knife at the checkout line. A video can be seen here.

“In this work we propose an algorithm for learning user preferences over trajectories through interactive feedback from the user in a co-active learning setting,” according to a paper from Ashesh Jain, Brian Wojcik, Thorsten Joachims and Ashutosh Saxena from the Department of Computer Science at Cornell.

“Unlike in other learning settings, where a human first demonstrates optimal trajectories for a task to the robot, our learning model does not rely on the user’s ability to demonstrate optimal trajectories a priori,” according to the paper. “Instead, our learning algorithm explicitly guides the learning process and merely requires the user to incrementally improve the robot’s trajectories. From these interactive improvements the robot learns a general model of the user’s preferences in an online fashion. We show empirically that a small number of such interactions is sufficient to adapt a robot to a changed task. Since the user does not have to demonstrate a (near) optimal trajectory to the robot, we argue that our feedback is easier to provide and more widely applicable.”

Photovoltaic Breakthrough
The University of Pennsylvania and Drexel University have devised a new way to construct solar cells.

Researchers from the universities have made use of perovskite oxides for visible-light-absorbing ferroelectric and photovoltaic materials. Perovskite is a calcium titanium oxide mineral species.

Researchers have developed a family of single-phase solid oxide solutions using conventional solid-state methods. The oxides exhibit both ferroelectricity and a variation of direct bandgaps in the range 1.1 to 3.8 electronvolts.

The x=0.1 composition is polar at room temperature. It has a direct bandgap of 1.39 electronvolts and has a photocurrent density approximately 50 times larger than that of the classic ferroelectric materials, according to researchers. They also have the ability to absorb three to six times more solar energy than the current ferroelectric materials.

The unique molecular structure of peroviskite oxides allow these materials to more efficiently absorb energy from the sun. Source: Drexel University.

The unique molecular structure of peroviskite oxides allow these materials to more efficiently absorb energy from the sun. Source: Drexel University.

“There’s a small category of materials, however, that when you shine light on them, the electron takes off in one particular direction without having to cross from one material to another,” said Andrew Rappe of Penn State, on Drexel University’s Web site. “We call this the ‘bulk’ photovoltaic effect, rather than the ‘interface’ effect that happens in existing solar cells. This phenomenon has been known since the 1970s, but we don’t make solar cells this way because they have only been demonstrated with ultraviolet light, and most of the energy from the sun is in the visible and infrared spectrum.”

Finding a material that exhibits the bulk photovoltaic would simplify solar cell construction. “Think of photons coming from the sun as coins raining down on you, with the different frequencies of light being like pennies, nickels, dimes and so on,” Rappe said. “A quality of your light-absorbing material called its ‘bandgap’ determines the denominations you can catch. The Shockley-Queisser limit says that whatever you catch is only as valuable as the lowest denomination your bandgap allows. If you pick a material with a bandgap that can catch dimes, you can catch dimes, quarters and silver dollars, but they’ll all only be worth the energy equivalent of 10 cents when you catch them.”