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#436414 Japanese Researchers Teaching Robots to ...
When mobile manipulators eventually make it into our homes, self-repair is going to be a very important function. Hopefully, these robots will be durable enough that they won’t need to be repaired very often, but from time to time they’ll almost certainly need minor maintenance. At Humanoids 2019 in Toronto, researchers from the University of Tokyo showed how they taught a PR2 to perform simple repairs on itself by tightening its own screws. And using that skill, the robot was also able to augment itself, adding accessories like hooks to help it carry more stuff. Clever robot!
To keep things simple, the researchers provided the robot with CAD data that tells it exactly where all of its screws are.
At the moment, the robot can’t directly detect on its own whether a particular screw needs tightening, although it can tell if its physical pose doesn’t match its digital model, which suggests that something has gone wonky. It can also check its screws autonomously from time to time, or rely on a human physically pointing out that it has a screw loose, using the human’s finger location to identify which screw it is. Another challenge is that most robots, like most humans, are limited in the areas on themselves that they can comfortably reach. So to tighten up everything, they might have to find themselves a robot friend to help, just like humans help each other put on sunblock.
The actual tightening is either super easy or quite complicated, depending on the location and orientation of the screw. If the robot is lucky, it can just use its continuous wrist rotation for tightening, but if a screw is located in a tight position that requires an Allen wrench, the robot has to regrasp the tool over and over as it incrementally tightens the screw.
Image: University of Tokyo
In one experiment, the researchers taught a PR2 robot to attach a hook to one of its shoulders. The robot uses one hand to grasp the hook and another hand to grasp a screwdriver. The researchers tested the hook by hanging a tote bag on it.
The other neat trick that a robot can do once it can tighten screws on its own body is to add new bits of hardware to itself. PR2 was thoughtfully designed with mounting points on its shoulders (or maybe technically its neck) and head, and it turns out that it can reach these points with its manipulators, allowing to modify itself, as the researchers explain:
When PR2 wants to have a lot of things, the only two hands are not enough to realize that. So we let PR2 to use a bag the same as we put it on our shoulder. PR2 started attaching the hook whose pose is calculated with self CAD data with a driver on his shoulder in order to put a bag on his shoulder. PR2 finished attaching the hook, and the people put a lot of cans in a tote bag and put it on PR2’s shoulder.
“Self-Repair and Self-Extension by Tightening Screws based on Precise Calculation of Screw Pose of Self-Body with CAD Data and Graph Search with Regrasping a Driver,” by Takayuki Murooka, Kei Okada, and Masayuki Inaba from the University of Tokyo, was presented at Humanoids 2019 in Toronto, Canada. Continue reading
#436180 Bipedal Robot Cassie Cal Learns to ...
There’s no particular reason why knowing how to juggle would be a useful skill for a robot. Despite this, robots are frequently taught how to juggle things. Blind robots can juggle, humanoid robots can juggle, and even drones can juggle. Why? Because juggling is hard, man! You have to think about a bunch of different things at once, and also do a bunch of different things at once, which this particular human at least finds to be overly stressful. While juggling may not stress robots out, it does require carefully coordinated sensing and computing and actuation, which means that it’s as good a task as any (and a more entertaining task than most) for testing the capabilities of your system.
UC Berkeley’s Cassie Cal robot, which consists of two legs and what could be called a torso if you were feeling charitable, has just learned to juggle by bouncing a ball on what would be her head if she had one of those. The idea is that if Cassie can juggle while balancing at the same time, she’ll be better able to do other things that require dynamic multitasking, too. And if that doesn’t work out, she’ll still be able to join the circus.
Cassie’s juggling is assisted by an external motion capture system that tracks the location of the ball, but otherwise everything is autonomous. Cassie is able to juggle the ball by leaning forwards and backwards, left and right, and moving up and down. She does this while maintaining her own balance, which is the whole point of this research—successfully executing two dynamic behaviors that may sometimes be at odds with one another. The end goal here is not to make a better juggling robot, but rather to explore dynamic multitasking, a skill that robots will need in order to be successful in human environments.
This work is from the Hybrid Robotics Lab at UC Berkeley, led by Koushil Sreenath, and is being done by Katherine Poggensee, Albert Li, Daniel Sotsaikich, Bike Zhang, and Prasanth Kotaru.
For a bit more detail, we spoke with Albert Li via email.
Image: UC Berkeley
UC Berkeley’s Cassie Cal getting ready to juggle.
IEEE Spectrum: What would be involved in getting Cassie to juggle without relying on motion capture?
Albert Li: Our motivation for starting off with motion capture was to first address the control challenge of juggling on a biped without worrying about implementing the perception. We actually do have a ball detector working on a camera, which would mean we wouldn’t have to rely on the motion capture system. However, we need to mount the camera in a way that it would provide the best upwards field of view, and we also have develop a reliable estimator. The estimator is particularly important because when the ball gets close enough to the camera, we actually can’t track the ball and have to assume our dynamic models describe its motion accurately enough until it bounces back up.
What keeps Cassie from juggling indefinitely?
There are a few factors that affect how long Cassie can sustain a juggle. While in simulation the paddle exhibits homogeneous properties like its stiffness and damping, in reality every surface has anisotropic contact properties. So, there are parts of the paddle which may be better for juggling than others (and importantly, react differently than modeled). These differences in contact are also exacerbated due to how the paddle is cantilevered when mounted on Cassie. When the ball hits these areas, it leads to a larger than expected error in a juggle. Due to the small size of the paddle, the ball may then just hit the paddle’s edge and end the juggling run. Over a very long run, this is a likely occurrence. Additionally, some large juggling errors could cause Cassie’s feet to slip slightly, which ends up changing the stable standing position over time. Since this version of the controller assumes Cassie is stationary, this change in position eventually leads to poor juggles and failure.
Would Cassie be able to juggle while walking (or hovershoe-ing)?
Walking (and hovershoe-ing) while juggling is a far more challenging problem and is certainly a goal for future research. Some of these challenges include getting the paddle to precise poses to juggle the ball while also moving to avoid any destabilizing effects of stepping incorrectly. The number of juggles per step of walking could also vary and make the mathematics of the problem more challenging. The controller goal is also more involved. While the current goal of the juggling controller is to juggle the ball to a static apex position, with a walking juggling controller, we may instead want to hit the ball forwards and also walk forwards to bounce it, juggle the ball along a particular path, etc. Solving such challenges would be the main thrusts of the follow-up research.
Can you give an example of a practical task that would be made possible by using a controller like this?
Studying juggling means studying contact behavior and leveraging our models of it to achieve a known objective. Juggling could also be used to study predictable post-contact flight behavior. Consider the scenario where a robot is attempting to make a catch, but fails, letting the ball to bounce off of its hand, and then recovering the catch. This behavior could also be intentional: It is often easier to first execute a bounce to direct the target and then perform a subsequent action. For example, volleyball players could in principle directly hit a spiked ball back, but almost always bump the ball back up and then return it.
Even beyond this motivating example, the kinds of models we employ to get juggling working are more generally applicable to any task that involves contact, which could include tasks besides bouncing like sliding and rolling. For example, clearing space on a desk by pushing objects to the side may be preferable than individually manipulating each and every object on it.
You mention collaborative juggling or juggling multiple balls—is that something you’ve tried yet? Can you talk a bit more about what you’re working on next?
We haven’t yet started working on collaborative or multi-ball juggling, but that’s also a goal for future work. Juggling multiple balls statically is probably the most reasonable next goal, but presents additional challenges. For instance, you have to encode a notion of juggling urgency (if the second ball isn’t hit hard enough, you have less time to get the first ball up before you get back to the second one).
On the other hand, collaborative human-robot juggling requires a more advanced decision-making framework. To get robust multi-agent juggling, the robot will need to employ some sort of probabilistic model of the expected human behavior (are they likely to move somewhere? Are they trying to catch the ball high or low? Is it safe to hit the ball back?). In general, developing such human models is difficult since humans are fairly unpredictable and often don’t exhibit rational behavior. This will be a focus of future work.
[ Hybrid Robotics Lab ] Continue reading