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Design of a Multipurpose Hybrid Leg Extension Machine Stephen Watkins, Jordan Streussnig, Dan Rogers Advisor: Dr. Nitin Sharma Project Goal Component Design Calibration Future Work Acknowledgments − Dr. Nitin Sharma − Naji Alibeji − Nick Kirsch − University of Pittsburgh Swanson School of Engineering − Mechanical Engineering Department − Dr. Anne Robertson − Heather Manns − Swanson School machine shop. References 1. Understanding DC Motor Characteristics http://lancet.mit.edu/motors/motors3.html 2. Leeson Motors: http://www.leeson.com/ 3. Grove Gear: http://www.grovegear.com/ 4. Minarik Drives: http://www.minarikdrives.com/ 5. Understanding Induction Motor Nameplate Information, May 1, 2004 Ed Cowern, P.E. 6. Peak Torque and IEMG Activity of Quadriceps Femoris Muscle at Three Different Knee Angles in a Collegiate Population, Shenoy 7. Isokinetic Dynamometry Applications and Limitations, V. Baltzopoulos 1989 8. Biodex: http://www.biodex.com/ 9. Experimental Demonstration of RISE-Based NMES of Human Quadriceps Muscle, N. Sharma 2008 Design a machine capable of automatically performing the following functions: Generate a co-operative leg extension torque through an electric motor along with leg extension torque produced by quadriceps muscle via Functional Electrical Stimulation (FES) Work as an inexpensive dynamometer to measure leg extension torque as an indication of quadriceps muscle strength Above: Leg extension machine and assembly Right: Pulley and motor assembly Motor Control System • In the future, possibility of testing automatic control algorithms designed to control hybrid exoskeletons that combine electric motors and FES devices The controller used is a Minarik variable frequency drive capable of controlling position, speed and torque output of the motor using dynamic controls from MATLAB Simulink. MATLAB Simulink program using Robust Integral of the Sine of the Error [8] Stroke victims with a weakened connection to their muscles can re-strengthen the connections via rehabilitation. Limbs affected by spinal cord injuries require exercise assistance to reduce atrophy and increase bone density. Existing dynamometers can cost over $35,000 [7] Overall goal is to restore walking in persons with paralysis or mobility disorders 2 technologies exist FES: Low level electrical currents that cause contraction of muscles Exo-skeletal: powered orthosis Both technologies have technical challenges but they compensate for one another if combined. FES has been prescribed for this but fatigues muscles, so motor assist is required Motivation Problem statement: Design an electric motor and gear drive that can sustain a maximal stimulated knee torque in an able-bodied person, 1133 in*lbf [5] Maximum speed 60 leg extensions per minute (30 RPM) Voltage vs Motor Speed line fit (left) can be used to control speed through voltage. Above: FES-assisted leg extension Motor 1 hp 90VDC 1750 RPM 54 in*lb Gear Box 0.933 hp 7.5 Ratio 233 RPM 378 in*lb Pulley1 2.86 in Pulley2 9.54 in FINAL 69.9 RPM 1260.9 in*lb u = input to motor; e1 = joint position error; e2 = filtered position error; qd = desired angle; q = actual angle; ks, α1, α2, and β = constant positive control gains; sgn = signum function
