The Design and Control of a LowPower, UpperLimb Prosthesis Anthony M' Jarc, Meghan E' Pearson, and M

1
The Design and Control of a Low-Power,
Upper-Limb Prosthesis Anthony M. Jarc, Meghan
E. Pearson, and Mason A. Peck, Control Moment
Gyroscope (CMG) Research Team, Sibley School of
Mechanical Engineering, Cornell University,
Ithaca, New York

• INTRODUCTION
• The purpose of this study is to design and
  control a three degree-of-freedom prosthetic arm
  with reduced power consumption and high torque
  output in order to address power consumption
  issues that currently limit the design of
  prosthetic limbs. Control moment gyroscopes
  (CMGs) are a unique solution to this problem
  because they generate large output torques while
  requiring less power than conventional actuators
  3. In a CMG, a gimbal tilts a spinning rotor
  causing a gyroscopic torque perpendicular to the
  rotor spin axis and the gimbal axis. Scissored
  pairs of CMGs rotate with equal and opposite
  gimbal angles, which produces a net torque along
  the arm segments axis of rotation (Fig. 1). The
  arm accelerates when the CMGs are gimbaled at a
  constant velocity and retains a constant velocity
  when the CMGs are not moving and tilted away from
  their initial gimbal angles.
• Electromyographic (EMG) signals, which have been
  shown to correlate with arm output force 1,
  will be used to control the arms movements.
  These signals will be collected from the biceps
  brachii for the elbow joint, brachioradialis for
  the forearm, and the flexor carpi radialis and
  extensor digitorum cammunus for the wrist.
  

The EMG signals were band-pass filtered with a
second-order Butterworth filter (cut-off
frequency 20-1000 Hz) to remove movement
artifacts, full-wave rectified, and low-pass
filtered again with a second-order Butterworth
filter (cut-off frequency 1 Hz) 2. A sample,
filtered bicep EMG signal is shown for a series
of five bicep curls, lifting 30 pounds (Fig. 4).
Figure 2. A CAD model of the CMG design, which
includes the rotor (dark gray) and gimbal casing
(light gray).
Table 1. Joint specifications generated by the
CMG and physical arm design. All values
correspond to when the rotor is spinning at
13,000RPM.
Figure 4. Filtered EMG data from the biceps
that will be used as control inputs for the elbow
joint.
The arm allows 360 degrees of rotation about each
joint (Fig. 3). When functioning as a prosthetic
limb, the range of motion will be limited to
physiological standards. The arm will be
constructed of extruded acrylic tubes with
aluminum inserts. The elbow is 6 in diameter,
the forearm is 6 in diameter, and the wrist is
4.5 in diameter.
The filtered EMG signals will be torque inputs
for the feedback control system.

• SUMMARY CONCLUSIONS
• This project offers a novel approach to
  actuating prosthetic limbs that improves power
  efficiency without sacrificing its agility.
• A three degree-of-freedom prototype arm will be
  developed that demonstrates the unique advantages
  of the CMGs.
• Real-time, myoelectric control will be used to
  validate the use of the arm as a prosthesis.
• With more experimentation, improved methods to
  examine neural control and more efficient CMG
  designs will be used to include task oriented
  movements.

DESIGN METHODS The small-scale CMGs in this
project use a steel rotor and an aluminum gimbal
casing (Fig. 2). Each segment has two CMGs a
scissored pair. The scissored pairs of CMGs are
capable of outputting maximum torque when
gimbaled to 45 degrees (Table 1). The maximum,
estimated load that the arm can move with all
three segments is approximately 6 lbs, an
improvement over current prosthetics.
References 1 Bigland-Ritchie, B. EMG/force
relations and fatigue of human voluntary
contractions. Exerc Sport Sci Rev. Vol. 9, pp.
75-117. 2 Ferris, D.P., Gordon, K.E., Sawicki,
G.S., Peethambaran, A. An Improved powered
ankle-foot orthosis using proportional
myoelectric control. Gait and Posture. 2005 3
Peck, M. Low-Power, High Agility Space Robotics
AIAA Guidance, Navigation, and Control Conference
and Exhibit. 2005-6243, August 2005. Acknowledgem
ents Funding provided by Lockheed Martin
Corporation. Special thanks to Dr. Keenan and
Robert McNamara for their help with EMG signal
recording.
Figure 3. CAD model of the arms physical
structure. Note that each segment contains a
scissored pair of CMGs about its axis of rotation.
Figure 1. A model illustrating the angular
momentum exchange due to the gimbaling of the CMG
scissored pair 3.