Posts Tagged ‘model’

Best Robotic Legs Ever?

Friday, July 6th, 2012

A very interesting development has been reported by the Daily Disruption News Desk regarding robotic legs that are claimed to “fully model walking in a biologically accurate manner.” This will come as good news for spinal cord injury patients. Those of us who follow developments in artificial intelligence and robotics will likely take note as well.

I read this account with fascination, and immediately wanted to sketch out my understanding in model form. Extending the colloquialism, to a hammer, everything is a nail – to a systems engineer, everything must be modeled. As conveyed in the article, human walking is controlled by a neural network called the central pattern generator (CPG), which is anatomically located in the lumbar region. It’s purpose is to generate rhythmic muscle signals. The researchers said in its simplest form the CPG can be modeled by a neuron pair that each fire signals in alternating fashion.

To complete this model in addition to the neural architecture, the robot needs muscle-skeleton and sensory feedback components. Roughly, this system can be modeled as shown:

I could be wrong, but this is how I understand the Robotic Leg System!

Co-author of the study Dr Theresa Klein was quoted as saying “…we were able to produce a walking gait, without balance, which mimicked human walking with only a simple half-centre controlling the hips and a set of reflex responses controlling the lower limb.”

So, did you catch that? That was quite a surprising statement. Two things are totally counter intuitive to me. First, she said the robot works “without balance.” Does that mean that this robot does not need an “inner ear” to balance? Second, the CPG apparently apparently converts coarse motor commands into forces applied at the hip joint only. The “dangling part of the leg, the lower limb, just follows reflexively, implementing easily programmable commands that simple follow what is happening up stream at the hip.

Another implication of this analysis is that the brain proper plays less of a role in controlling gait that I would have guessed.

This would be a good time to confess that I could be totally wrong in my interpretation of this research and its result; I am learning as I go.

Speaking of which, the CPG model of this study is apparently a good facsimile of how gait is refined from early childhood steps through later improvement during the maturing process. The CPG in humans gets better over time as it learns the best walk to walk by repetition.

This is exciting as I can see similarities between this system and what I am learning in my artificial intelligence class. The evolving understanding of complex bio-mechanical systems as well as advances in AI make this a great time to be a student of such things.

Math as Model

Sunday, July 1st, 2012

My elementary math education in must have been effective – to this day there are specific, although arguably obscure, things that I remember. Specific useful items such as multiplication tables – check. Addition, subtraction, division – check. A little on the obscure, but still useful side, the concepts of additive and multiplicative identity. Respectively, those two identities are, zero plus anything equals that same anything, unchanged, and one times anything equals that same anything, again, unchanged . So identities – check. Rote facts and concepts dutifully absorbed. But one key idea was missing. Why does math matter? What’s it good for? Just a little bit of mathematical philosophy would have gone a long way.

That key missing idea is actually pretty simple – it is that math serves as a model; a method to simplify and understand the world. Once modeled we have a means to comprehend, deal with and predict behaviors in the future.

These things are essential to problem solving – this is the basis for so much of our industry as humans.

This concept might seem obscure at first, but throughout my many years of practice as an aerospace engineer, I’ve learned that the concept serves as the foundation of understanding – models are key to our understanding of the world.

If someone had explained this to me as a child, in terms I could comprehend, which I think it easily realizable, I could have avoided substantial frustrations while learning math – years of math classes that took me all the way through five semester of college math.

Even though I survived my journey could have been much easier.

As a young boy growing up, I was surrounded by models as plaything. Building blocks, Legos, Lincoln Logs, Tinkertoys and even model airplanes. All of these things let me build models. Along the way I was asking , and answering questions that were important to me at the time. What would happen if I stacked the pieces this way, or that? Do I need attach wheels here to make it my creation balanced? What would my model look like if I changed this aspect or that?.

If I would have known that learning math was all about modeling the world, my understanding and ease in class would have been greatly facilitated. After all, for me, modeling was fun.

How much easier would my education have gone? Rather than just survive, I believe I would have thrived.