Thursday, March 15, 2012
Saturday, July 30, 2011
Inverse Kinematics
I recently signed up for an IEEE membership, which got me access to a few select journals, namely the IEEE Transactions on Robotics. Every now and then I go back and check out what new articles have been posted, and I thought I'd share one.
Sugihara, T. "Solvability-Unconcerned Inverse Kinematics by the Levenberg--Marquardt Method"
This is a very practical paper that compares a number of IK algorithms, providing a brief overview of each. For robot systems such as humanoids, we are always concerned with two problems: resolving redundancy and overcoming numerical instability due to singular matrices. This paper addresses the problem of numerical stability and speed. I highly recommend it to anyone studying such problems.
Sugihara, T. "Solvability-Unconcerned Inverse Kinematics by the Levenberg--Marquardt Method"
This is a very practical paper that compares a number of IK algorithms, providing a brief overview of each. For robot systems such as humanoids, we are always concerned with two problems: resolving redundancy and overcoming numerical instability due to singular matrices. This paper addresses the problem of numerical stability and speed. I highly recommend it to anyone studying such problems.
Saturday, June 18, 2011
Tuesday, April 19, 2011
Push Recovery While Walking in Place Experiments
Today I took some video of my current work on push recovery while walking in place. In this experiment, the humanoid robot is walking in place using a model predictive controller (MPC) that continuously optimizes footsteps and center of mass (COM) motion. The MPC outputs desired footstep locations and center of pressure location (COP) which are converted to desired torques for the full body using multi-objective inverse dynamics.
Friday, February 11, 2011
Hip Strategy Experiments
I took some video yesterday demonstrating new robot balance control that can perform a "hip strategy". Basically there are multiple objectives, one to keep the center of mass (COM) over the feet and another to keep the torso upright. Keeping the COM over the feet is more important, so after a large push the robot will decide to swing its torso forward to achieve that objective. Once it is stabilized, it can return to an upright posture. The video demonstrates pushing from both directions in the sagittal plane which is the more unstable direction.
The basic controller is similar to the one used in [1], which uses optimization to trade off between several objectives related to balance. In this case, there are objectives related to regulating the COM, regulating posture, regulating angular momentum, and minimizing joint torques and contact forces. Inequality constraints are imposed to keep the feet flat on the ground and avoid joint torque limits. This is a very generalizable and easy to implement approach to full body balance control.
The basic controller is similar to the one used in [1], which uses optimization to trade off between several objectives related to balance. In this case, there are objectives related to regulating the COM, regulating posture, regulating angular momentum, and minimizing joint torques and contact forces. Inequality constraints are imposed to keep the feet flat on the ground and avoid joint torque limits. This is a very generalizable and easy to implement approach to full body balance control.
[1] Y. Abe, M. da Silva, and J. Popovic, “Multiobjective control with frictional contacts,” Proceedings of the 2007 ACM SIGGRAPH/Eurographics symposium on Computer animation, 2007, pp. 249-258.
Thursday, December 30, 2010
Interview with Hometown Newspaper
ROBOTS HELP STUDY BALANCE
Edition: Wednesday, December 29, 2010
By KAREN BRADY
Staff Writer
In the 1950s, robots were predicted to be the wave of the future.
Well, the future is here.
Today, robots are routinely used in a number of applications in industry, medicine, and the military. One type will even vacuum your floors.
And, like Robby the Robot, who appeared in the 1956 sci-fi classic, Forbidden Planet, robots remain ever popular on the silver screen. From the terrifying cyborg assassin T-800 Terminator, portrayed by Arnold Schwarzenegger in the 1984 movie The Terminator, to the endearing Number 5 from the 1986 movie, Short Circuit, robots are as popular today as they were in the 1950s.
To former Chickasha High School student Benjamin Stephens, robots are a passion.
Currently working toward his Doctorate Degree in robotics at Carnegie Mellon University in Pittsburg, Pa., Stephens spends his days with a life-sized somewhat humanoid robot, that has eyes and can move like a human.
"Its very much like a person," Stephens says.
His focus of study is understanding human balance.
"My research is on balance and my goal is for the robot to walk and get around without falling down," Stephens said. "Most of my work is programming the controls, reading sensors and outputting forces at each of the joints."
Stephens describes himself as being multi-disciplined, or good at a lot of things.
"Programming computers, building things and complex math - you need knowledge of all those things," Stephens said. "When you''re good at a lot of things, it makes you more valuable. Its just fun to me and I get to work on some really cool stuff."
Stephens came to Chickasha with his family when he was 3 years old. He attended Chickasha schools, taking as many high school science and math classes as he could while still in junior high.
"There wasn''t much left as far as science and math classes," he said.
It was then that Stephens applied for entrance into the Oklahoma School of Science and Math in Oklahoma City. He was accepted and spent his junior and senior years of high school as a student at OSSM.
"There''s a lot of science and math classes and its all about going to college," Stephens said. "Its pretty intense and its pretty strict. You''re there to go to school and learn. It was great and I learned a lot and made a lot of friends. Its a good starting point for a good college."
The 32-acre OSSM campus, which is located south of the state capitol near the Oklahoma Health Center''s medical and research facilities, houses 144 junior and senior students. Listed as a state agency, the school is funded by the Oklahoma Legislature and is open to all students across the state. Students pay no tuition and room and board are provided by the state. Applications to OSSM are due in March of a student''s sophomore year.
After graduating from OSSM in 2002, Stephens attended Northwestern University in Evanston, Ill., in the Chicago area, earning his Bachelor''s of Science Degree in mechanical engineering. He then entered graduate school at Carnegie Mellon University in Pittsburg, where he is in his final year of his Ph. D. program.
Stephens says the study of human balance poses some unique problems.
"We''re trying to figure out how intuitive knowledge, like balance in humans, works," he said. "As people get older, they fall and sustain injuries. How can we help them? Teach them new exercises? Studying a humanoid robot, we have to recreate that control system artificially since we can''t go in and extract the information from the brain. Its really complex."
Stephens plans to graduate in the summer of 2011, and is still trying to decide what he wants to do next.
"I''d like to continue the same work; we''re just getting started in this area," he said.
His options include working for a robotics company or in an academic position. In fact, Stephens has applied for some postdocs (post doctoral programs of study) in order to continue his research and to develop contacts in the field.
"I figure its the best thing for my future," he said.
Stephens says health care and the growing number of senior citizens in the U. S. are areas where robotics may come into play.
"As the average age increases and a larger percentage of the population becomes elderly, they are limited in their mobility, they have no job and they are not as independent as they would like to be," Stephens said. "Now, we send someone to help, but there are so many who need help and so few to help, we have to do something else. Robotics is one approach."
Stephens said personal robots will become popular in coming decades, such as the aforementioned small, simple robots that vacuum floors automatically and require no interaction.
"It''s hard. People might not want a robot to come in and take over," Stephens said. "They feel independent when they can do things on their own, so they want the robot as invisible as possible, but they want it to do enough to let them have a more independent life."
Stephens said robot sensors could monitor people in the kitchen, for example, to detect abnormalities such as a fall or a fire and then notify healthcare workers when there is a problem.
"Helping the elderly is becoming a common theme," Stephens said. "We have to do something about it regardless of whether robotics is the answer."
Advice to students
"Surround yourself with motivated smart people," says Stephens. "My friends were maybe more motivated and smarter than I was. Education is an investment. You''ve got to do it; you''ve got to focus on this. What you do right now is going to set you up later in life. It''s hard for young people to understand."
Stephens says making big money is not a priority for him.
"Work hard on the problem and maybe help people along the way," he advises. "If you want to do exciting things in the future, you''ve got to work for it, not just settle or get by.
"The ones who stand out are successful. Do what you like and put a lot into that or be pretty good at a lot of things.
"Math and physics came in handy for me, all I do is math, not hard math, I don''t do fancy quantum physics. Have a good, fundamental understanding of math. Like sports, its all about the fundamentals."
To see Stephen''s robot in action, visit http://www.cs.cmu.edu/bstephe1/.
[via chickashaleader.com]
Edition: Wednesday, December 29, 2010
By KAREN BRADY
Staff Writer
In the 1950s, robots were predicted to be the wave of the future.
Well, the future is here.
Today, robots are routinely used in a number of applications in industry, medicine, and the military. One type will even vacuum your floors.
And, like Robby the Robot, who appeared in the 1956 sci-fi classic, Forbidden Planet, robots remain ever popular on the silver screen. From the terrifying cyborg assassin T-800 Terminator, portrayed by Arnold Schwarzenegger in the 1984 movie The Terminator, to the endearing Number 5 from the 1986 movie, Short Circuit, robots are as popular today as they were in the 1950s.
To former Chickasha High School student Benjamin Stephens, robots are a passion.
Currently working toward his Doctorate Degree in robotics at Carnegie Mellon University in Pittsburg, Pa., Stephens spends his days with a life-sized somewhat humanoid robot, that has eyes and can move like a human.
"Its very much like a person," Stephens says.
His focus of study is understanding human balance.
"My research is on balance and my goal is for the robot to walk and get around without falling down," Stephens said. "Most of my work is programming the controls, reading sensors and outputting forces at each of the joints."
Stephens describes himself as being multi-disciplined, or good at a lot of things.
"Programming computers, building things and complex math - you need knowledge of all those things," Stephens said. "When you''re good at a lot of things, it makes you more valuable. Its just fun to me and I get to work on some really cool stuff."
Stephens came to Chickasha with his family when he was 3 years old. He attended Chickasha schools, taking as many high school science and math classes as he could while still in junior high.
"There wasn''t much left as far as science and math classes," he said.
It was then that Stephens applied for entrance into the Oklahoma School of Science and Math in Oklahoma City. He was accepted and spent his junior and senior years of high school as a student at OSSM.
"There''s a lot of science and math classes and its all about going to college," Stephens said. "Its pretty intense and its pretty strict. You''re there to go to school and learn. It was great and I learned a lot and made a lot of friends. Its a good starting point for a good college."
The 32-acre OSSM campus, which is located south of the state capitol near the Oklahoma Health Center''s medical and research facilities, houses 144 junior and senior students. Listed as a state agency, the school is funded by the Oklahoma Legislature and is open to all students across the state. Students pay no tuition and room and board are provided by the state. Applications to OSSM are due in March of a student''s sophomore year.
After graduating from OSSM in 2002, Stephens attended Northwestern University in Evanston, Ill., in the Chicago area, earning his Bachelor''s of Science Degree in mechanical engineering. He then entered graduate school at Carnegie Mellon University in Pittsburg, where he is in his final year of his Ph. D. program.
Stephens says the study of human balance poses some unique problems.
"We''re trying to figure out how intuitive knowledge, like balance in humans, works," he said. "As people get older, they fall and sustain injuries. How can we help them? Teach them new exercises? Studying a humanoid robot, we have to recreate that control system artificially since we can''t go in and extract the information from the brain. Its really complex."
Stephens plans to graduate in the summer of 2011, and is still trying to decide what he wants to do next.
"I''d like to continue the same work; we''re just getting started in this area," he said.
His options include working for a robotics company or in an academic position. In fact, Stephens has applied for some postdocs (post doctoral programs of study) in order to continue his research and to develop contacts in the field.
"I figure its the best thing for my future," he said.
Stephens says health care and the growing number of senior citizens in the U. S. are areas where robotics may come into play.
"As the average age increases and a larger percentage of the population becomes elderly, they are limited in their mobility, they have no job and they are not as independent as they would like to be," Stephens said. "Now, we send someone to help, but there are so many who need help and so few to help, we have to do something else. Robotics is one approach."
Stephens said personal robots will become popular in coming decades, such as the aforementioned small, simple robots that vacuum floors automatically and require no interaction.
"It''s hard. People might not want a robot to come in and take over," Stephens said. "They feel independent when they can do things on their own, so they want the robot as invisible as possible, but they want it to do enough to let them have a more independent life."
Stephens said robot sensors could monitor people in the kitchen, for example, to detect abnormalities such as a fall or a fire and then notify healthcare workers when there is a problem.
"Helping the elderly is becoming a common theme," Stephens said. "We have to do something about it regardless of whether robotics is the answer."
Advice to students
"Surround yourself with motivated smart people," says Stephens. "My friends were maybe more motivated and smarter than I was. Education is an investment. You''ve got to do it; you''ve got to focus on this. What you do right now is going to set you up later in life. It''s hard for young people to understand."
Stephens says making big money is not a priority for him.
"Work hard on the problem and maybe help people along the way," he advises. "If you want to do exciting things in the future, you''ve got to work for it, not just settle or get by.
"The ones who stand out are successful. Do what you like and put a lot into that or be pretty good at a lot of things.
"Math and physics came in handy for me, all I do is math, not hard math, I don''t do fancy quantum physics. Have a good, fundamental understanding of math. Like sports, its all about the fundamentals."
To see Stephen''s robot in action, visit http://www.cs.cmu.edu/bstephe1/.
[via chickashaleader.com]
Monday, November 15, 2010
Push Recovery Experiments
I have taken some video of push recovery experiments on the Sarcos Primus humanoid robot. The controller is based on the "Push Recovery Model Predictive Control" that will be presented at Humanoids 2010 (download my paper). The basic idea is to use a very simplified model of the robot to continuously determine optimal center of mass (COM) motion and footstep locations to prevent the robot from falling over.
This video highlights some improvements over the experimental results in the paper that include: continuously resolving the optimization (Receding Horizon Control) at 50 Hz, automatically taking multiple steps to recover, and automatically deciding which foot to step first with.
This video highlights some improvements over the experimental results in the paper that include: continuously resolving the optimization (Receding Horizon Control) at 50 Hz, automatically taking multiple steps to recover, and automatically deciding which foot to step first with.
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