REHABILITATION ENGINEERING

1. THE MARCUS
INTELLIGENT
HAND PROSTHESES
VADLAMUDI NAMRATHA
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2. MARCUS
Manipulative Automatic Reaction
Control and User Supervision
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3. WHY ?
 Many artificial hands are driven through direct
mechanical links to the operator.
 They are successful in use, but have only a
single motion and are visually unattractive.
 To some members of the limb deficient
population appearance is very important, and
these individuals therefore opt for hands that
are more natural in appearance but have little
or no function.
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4.  The active cosmetic hands have only one
degree of freedom, with all the digits (fingers)
opening and closing together, this limits their
functional range.
 To add more function necessitates the addition
of further independent degrees of freedom at
the gripper.
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5.  The application of mechatronics principles to
artificial hands has lagged a long way behind
other areas of medical technology.
 Current provision can only perform a limited
range of tasks.
 By adding sensors and a microprocessor it is
possible to control a more complex and
functional hand with simpler instructions.
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HOW?

6. INTRODUCTION
 The MARCUS hand is an example of advanced
prosthesis, which resulted from a project in INAIL
R&D Department, Budiro, Italy.
 MARCUS is a prosthetic hand controlled by the
user through myoelectric sensors.
 The hand consists of position, force and slippage
sensors through which a microcontroller
automatically controls the interaction of the
hand with the object.
 The control strategy automatically increment the
force on the grasped object if slippage conditions
occur.
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7.  Supervisory control exists in this design and the
brain is also involved in it.
 Based on the local, visual and sensory
feedbacks the signals are manipulated.
 There exist correlation functions between the
EMG signals and the feedback signals, which
define the task level, based on which the
decision is to be taken.
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8. Comparison of the Myoelectric
Hand Designs
Myoelectric Hand
Designs:
Different Feedbacks
Available:
Traditional
Myoelectric
Hand
Southampt
on Hand
MARCUS
Intelligent
Hand
Brain
Controlled
Hand
Visual Feedback Initially
available
Initially
available
Available Available
Local Feedback Not
Available
Available Available Not
Available
Sensory Feedback Not
Available
Available Available Available
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9. Control methods
 If the user interface and feedback loops are
poor or difficult to maintain, then the operator
will under-use or completely reject the device.
 The key issue in the control is that of the
appropriate form of the control input.
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10. The hierarchical control of human
central nervous system
 The basic form of the central nervous system (CNS)
of a human being is hierarchical, as the tasks of
controlling the hand and digits are broken up into
three layers.
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11.  At the lowest level the force and position of
individual fingers are managed.
 These reflexes are then commanded by an
intermediate level that coordinates the fingers to
create a hand shape and grip force in response to
the shape of the target object and the action that
is intended for it.
 Above this is the strategic control of the hand.
 This is the level of the consciousness of the
individual.
 The person simply desires to move an object, and
the system coordinates the action to achieve this
goal with very little conscious thought.
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12. The MARCUS hand - hierarchical
control scheme
 The hand has two degrees of freedom, these are:
finger flexion and thumb flexion.
 This hand consists of three fingers: a thumb, an
index finger and a middle finger; the last two are
connected at the base of the phalanxes.
 The hand consists of two separate motors, the first
one driving the thumb movement and the second
one driving the movement of the index and the
middle fingers which are mechanically coupled.
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13.  Both the fingers and the palm of the hand have
sensors, this enables, in suitable phases of the
hand’s functioning cycle, the recognition of
contact with an object and any possible slipping
of the same.
 The EMG signals picked up at the stump and the
signals of the sensors are used to control the
motors of the hand.
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14.  The motors operate in such a way as to ensure
an optimal contact and an increase in the
strength of grip sufficient to avoid slipping.
 This configuration allows differential flexion
speeds for the fingers and thumb, which shows
that the thumb does not move during grasping
but is held as a support onto which the fingers
close.
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15. MARCUS hand sensory system
 Force Sensors
 Palm sensors
 Kinaesthetic sensors
 Slip sensors
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16. Force Sensors
 The force sensors located at the fingertips of
three fingers.
 The force sensor is capable of withstanding the
maximum load of 120N.
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17. Palm sensors
 Palm sensors are used to detect the contact
occurring between the palmer regions of the
prosthetic hand and the grasped object.
 The information extracted from the palm
sensors are used to select one of the two
possible types of grasp configurations the hand
can perform.
 Due to its great sensitivity and small thickness,
the FSR sensor is used as palm sensor.
 The pressure sensors along the surface of the
fingers are used to determine the degree of
rotation of the fingers with respect to the palm.
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18. Kinaesthetic sensors
 The function of kinaesthetic sensors is that of
recording the joint rotation of the prosthetic
hand in order to provide to the control system
geometrical information about the grasping
configuration.
 Hall effect sensor is used. This sensor is fixed to
the metacarpus phalangeal joint.
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19. Slip sensors
 The slip sensors are integrated at the fingertip
level.
 A very small microphone detects vibrations
produced by the slippage of the object.
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20. Grip types
 The separated degrees of freedom also allow
the hand to adopt both of the standard grip
types that a human can employ;
 precision grip, where the thumb opposes the
tips of the other digits
 power grip, where the thumb wraps around
the rear of the fingers.
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21. 21

22. Automatic Touch
 An EMG signal impulse generated by the
contraction of a remaining muscle of the stump is
sufficient to obtain the automatic grip with certain
strength.
 On receiving this impulse, the prosthetic hand
begins a closing action and goes on closing until the
FSR sensors produce a signal that is greater or
equal to a certain value called “contact threshold.”
 Then it stops, since the object has been grasped
with the required strength of grip.
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23.  In brief, the patient only gives the “start” order of
the grip action, after which the later occurs
automatically without calling further on the
patient’s will.
 By the connection between the PC and the
microcontroller, the parameters on which the
function of automatic grip depends can be set in
order to optimize the behaviour of the prosthesis,
according to the patient’s requirements.
 Once contact with an object has been reached
automatically, the patient can further increase the
strength of the grip by activating the flexor
muscle again. The prosthetic hand goes in the
“squeeze” state and starts to work again.
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24. The advantages of the automatic
touch
 It frees the patient from the need for visual
control during the grip action.
 It lessens the risk of damaging delicate objects
(especially in patients new to prosthesis).
 It increases the speed of the grip: since the grip
is automatic, the actuator can be given
maximum power, thus maximum speed.
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25. Control diagram for the MARCUS artificial
hand
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26. • The degree of opening of the hand is
proportional to the muscular tension; therefore,
when the muscle relaxes the hand closes
naturally upon the object (POSITION).
• The shape of the object is detected by sensors
on the palmar surface of the hand while a
computer controller selects a grip posture from
a small repertoire to suit the most appropriate
general shape.
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27.  The controller then makes detailed corrections
of that shape to suit the exact shape of the
object. This maximizes the contact area while
minimizing the contact force. In this phase, a
light touch is maintained so the operator can
manoeuvre the object within the hand to
obtain the best attitude (TOUCH).
 Then the user can instruct the computer to hold
the object (HOLD).
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28.  If the grip tension is too low, the object slips
within the grasp, the slippage is detected by
sensors on the hand, and resulting in an
increase in the force in proportion to the time
that slippage occurs.
 At any time, the operator can either instruct
the hand to increase the grip force, overriding
the slip reflex (SQUEEZE) or to open (RELEASE).
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29.  The threshold when this occurs can be set
higher than for when the hand is opened
empty, so that holding or releasing objects
becomes a more deliberate act than opening
the hand when empty.
 Finally co-contraction of both muscles causes
the hand to be disabled and the system is then
shutdown to conserve power (PARK).
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30.  The computer system can thus be used to minimise the
power consumption so that the duration of the hand on
a single charge is over eight hours, which has been
identified as the average time individuals use the hand
in a day.
 In addition the computer can maintain a check on the
rest of the hand systems, it measures the rate of change
of the sensors' output so that any sensor failure is
detected and the hand is safely powered down.
 This procedure has been applied to a number of
mechanisms, first in the laboratory and more recently in
the field. Users have found it easy to learn and use.
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31. References
 http://www.scribd.com/doc/18651364/Myoele
ctric-Arm www.myoelectricprosthesis.com
 The MARCUS intelligent hand prosthesis by P
Kyberd, R Tregldgo, R Sachetti, H Schmidl -
Rehabilitation Technology: Strategies for the
European Union: Proceedings – By E. Ballabio
 The Mechanical Design of a MARCUS prosthetic
hand by M. Bergamasco & S. Sacattareggia, IEEE
International workshop on Robot and Human
Communication, Tokyo, 1995.
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32.  A Hall effect sensor is a transducer that varies its output
voltage in response to a magnetic field. Hall effect
sensors are used for proximity switching, positioning,
speed detection, and current sensing applications. In its
simplest form, the sensor operates as an analog
transducer, directly returning a voltage.
 A force-sensing resistor is a material
whose resistance changes when a force or pressure is
applied. They are also known as "force-sensitive resistor"
and "FSR". Force-sensing resistors are commonly used to
create pressure-sensing "buttons" and have applications in
many fields, including musical instruments, car occupancy
sensors, Foot pronation systems and portable electronics.
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Glossary

33.  Flexor-
muscle that when contracted acts to bend a joi
nt or limb in the body
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