[edu]Harmonic drive

[edu]Harmonic drive

What is a harmonic drive?

A cool kind of gear.  It was invented in 1957 by C.W. Musser.

220px-Harmonic_drive_animationThe advantages include: no backlash, compactness and light weight, high gear ratios, reconfigurable ratios within a standard housing, good resolution and excellent repeatability (linear representation) when repositioning inertial loads, high torque capability, and coaxial input and output shafts.High gear reduction ratios are possible in a small volume (a ratio from 30:1 up to 320:1 is possible in the same space in which planetary gears typically only produce a 10:1 ratio).

Disadvantages include a tendency for ‘wind-up’ (a torsional spring rate) and potential degradation over time from mechanical shocks and environment.

 

 

Cross-section of a strain wave gearing mechanism.220px-Harmonic-drive-explanationA: circular spline (fixed)
B: flex spline (attached to output shaft, not shown)
C: wave generator (attached to input shaft, not shown)

 

For a strain wave gearing mechanism, the gearing reduction ratio can be calculated from the number of teeth on each gear:

\text{reduction ratio} = \frac {\text{flex spline teeth} - \text{circular spline teeth}} {\text{flex spline teeth}}

For example, if there are 202 teeth on the circular spline and 200 on the flex spline, the reduction ratio is (200 − 202)/200 = −0.01

Thus the flex spline spins at 1/100 the speed of the wave generator plug and in the opposite direction. This allows different reduction ratios to be set without changing the mechanism’s shape, increasing its weight, or adding stages.

Look Mom! I shrink the Arduino!

olimex

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We love to play with Arduino and like it very much but one thing have always bothered us – it’s HUGE.

What you do when you want to make small data logger, RF/Zigbee baecon, sensor network, something wearable etc? use this BRICK? No way.

This is how the idea for OLIMEXINO-NANO came.

We made complete Arduino replacement with size of only 30x30x8 mm

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What you see on the pictures above is TOP and BOTTOM view of the OLIMEXINO-NANO.

It have these features:

  • ATMega32U4 processor (Leonardo compatible)
  • micro USB connector for programming and power supply when debugging
  • RESET button
  • USER button
  • microSD card connector for data logging on SD-card
  • UEXT connector for RF, Zigbee, Ethernet, RELAY, RGB LED, etc UEXT modules
  • two status LEDs
  • Connector 14 pin 0.05″
  • Connector 20 pin 0.05″

the connectors allow other boards to stackup like normal Arduino shields.

The first shield we made is with Battery…

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Robot control part 1: Forward transformation matrices

studywolf

I’m doing a tour of learning down at the Brains in Silicon lab run by Dr. Kwabena Boahen for the next month or so working on learning a bunch about building and controlling robots and some other things, and one of the super interesting things that I’m reading about is effective methods for force control of robots. I’ve mentioned operational space (or task space) control of robotic systems before, in the context of learning the inverse kinematic transformation, but down here the approach is to analytically derive the dynamics of the system (as opposed to learning them) and use these to explicitly calculate control signals to move in task space that take advantage of the passive dynamics of the system.

In case you don’t remember what those words mean, operational (or task) space refers to a different configuration space than the basic / default robot configuration space. FOR EXAMPLE:…

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[examples]3D Printed exoskeleton arms help a little girl move it’s arms first time

[examples]3D Printed exoskeleton arms help a little girl move it's arms first time

a leading manufacturer of 3D printers and production systems for prototyping and manufacturing, says that the “magic arms” WREX exoskeleton, designed by Nemours/Alfred l. duPont Hospital for Children, has been nominated for the Designs of the Year 2013 awards by London’s Design Museum.

Using a Stratasys Dimension 3D Printer, researchers at the Alfred I. duPont Hospital for Children in Philadelphia were able to help four-year-old Emma Lavelle overcome the limitations of a congenital disorder, allowing her to use her arms for the first time. The “magic arms” device is a custom-designed robotic exoskeleton that enables her to conquer greatly limited joint mobility and underdeveloped muscles.

The Designs of the Year is an international awards program, showcasing the most innovative and imaginative designs from the past year. It spans seven categories: Architecture, Digital, Fashion, Furniture, Graphics, Transport and Product. Category winners and the overall winner will be decided by a jury and announced to the public on 17th April 2013. The nominated entries will also be available to view in an exhibition at the Design Museum, running from March 20th 2013.

“This is an exciting time for 3D printing, as more people become aware of its potential and its impact,” said Stratasys Executive VP of Global Marketing, Jon Cobb. “We are honored to have been involved in such a worthwhile project and pleased to see it recognized by the design community.”

Besides its customer being an award finalist, Stratasys itself has been named a finalist for three Golden Mousetrap Awards from U.S. industry magazine, Design News. It was recognized in the Materials and Assembly category for its Mojo 3D Printer, its Objet30 3D Printer, and its Objet line of digital materials. Award subcategories are engineering plastics and rapid prototyping machines.

[examples]Wild car

WildCat is a four-legged robot being developed to run fast on all types of terrain. So far WildCat has run at about 16 mph on flat terrain using bounding and galloping gaits. The video shows WildCat’s best performance so far. WildCat is being developed by Boston Dynamics with funding from DARPA’s M3 program. For more information about WIldCat visit our website at http://www.BostonDynamics.com.

PS: Ok, we love Boston dynamics.

[examples] Latest updates on Atlas

Atlas is an anthropomorphic robot designed to operate on rough terrain. The video shows Atlas balancing as it walks on rocky terrain and when pushed from the side. The balance and control system places the feet and swings the arms and upper body to stay upright. The controller uses inertial, kinematic and load data from Atlas’s sensors. Atlas is being developed by Boston Dynamics with funding from DARPA’s M3 program. For more information visit http://www.BostonDynamics.com

[news] First mind-controlled bionic leg

After losing his lower right leg in a motorcycle accident four-and-a-half years ago, 32-year-old Zac Vawter has been fitted with an artificial limb that uses neurosignals from his upper leg muscles to control the prosthetic knee and ankle. The motorized limb is the first thought-controlled bionic leg, scientists at the Rehabilitation Institute of Chicago reported Wednesday in The New England Journal of Medicine.

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When Vawter thinks he wants to move his leg, the brain signal travels down his spinal cord and through peripheral nerves and is picked up by electrodes in the bionic leg. Unlike robotic models currently on the market, the prosthesis allows a normal, smooth gait no matter the incline.

“It makes a phenomenal difference,” says Vawter, a software engineer from Yelm, Wash., whose right leg was amputated through the knee in 2009 after he crashed his motorcycle. Aware of the institute’s work on bionic arms, Vawter and his surgeon contacted Hargrove and the team developing the pioneering prosthesis. For nearly three years ending in October, 2012, Vawter would travel to the institute periodically.

Vawter would remove his mechanical leg, slip into the bionic one, and run through a set of experiments the scientists devised, suggesting improvements and providing feedback on what was working and what was not.

Two electrodes pick up signals from the hamstring muscle, where the nerves that had run through Vawter’s lower leg were redirected during the amputation. “So when Zac is thinking about moving his ankle, his hamstring contracts,” says Hargrove.

More electrodes pick up signals from other muscles in the residual limb. The complex pattern recognition software contained in the on-board computer interprets these electrical signals from the upper leg as well as mechanical signals from the bionic leg and “figures out what Zac is trying to do,” says Hargrove.

The U.S. Army’s Telemedicine and Advanced Technology Research Center funded the Chicago study with an $8 million grant to add neural information to the control systems of advanced robotic leg prostheses. Devising a thought-controlled bionic leg has been more challenging than a thought-controlled bionic arm, says Hargrove.

That’s because the motors must be powerful enough to provide the energy to allow someone to stand and push along — and they must be small. Also, the computer control system must be safe.

“If there is a mistake or error that could cause someone to fall, that could be potentially catastrophic, and we want to avoid that at all costs,” says Hargrove.

 

source: NBC News Channel

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