International Journal of Engineering Trends and Technology (IJETT) – Volume23 Number 4- May 2015
A Pneumatic Muscle Driven Wearable Parallel
Robot for Ankle Joint Rehabilitation
Ms. S. Muthulakshmi #1, Mr. D. Sunderlin Shibu *2
#1PG
student, #2 Assistant Professor, Dept. of Biomedical Engineering, Anna University,
Udaya School of Engineering, Ammandivilai, Kanyakumari, Tamil Nadu, India.
Abstract— Ankle is the most common injuries part in human
body because the ankle joint is made up of three bones that are
tibia, fibula and talus. These three bones are joining together at
the ankle joint by ligaments that will allow normal ankle activity.
Tendons join muscles to the bones to do the work of making the
ankle and foot movement, along with help keep the joints stable.
A sprain which is defines as damage to ligaments when they are
stretched or twisted beyond their normal range of motion and
fracture is describes a breakage in one or more of the bones.
Rehabilitation after surgery involves time and attention to
restore strength and range of motion so peoples can return to
pre-injury function. This wearable parallel robot designed for
ankle rehabilitation process in step by step procedure. Some
important performance indices are identified to accomplish the
requirements of the ankle rehabilitation treatment and the
wearable robot design procedure. Robot design is adaptable to
subjects by varying physiological abilities and age groups. The
movements of pneumatic muscle actuators are treating the ankle
injuries for the rehabilitation aspects. This robot is improving
the mobility and flexibility, improving ankle strength, coordination and returning to full fitness.
Keywords— PIC microcontroller, pneumatic cylinder,
PWM (pulse width modulation), PMA (pneumatic muscle
actuators).
I. INTRODUCTION
The Ankle injuries are very common to all
people because ankle joints are very complicated
structure in human body and ankle joints are the
very important joint of the body. Ankle sprain is a
severe injury and its frequency be approximately inbetween 15 and 20% of all sports injury and is the
most common in emergency and more than 1
millions of peoples can visit emergency room
because of ankle injuries. Ankle sprain and ankle
fractures are the most common injuries in ankle
joints. Ankle injury is definite by the variety of
tissues, bone, ligament (bone to bone connection)
(or) tendon (muscle to bone connection) damaged.
Ankle sprain may occur when the ankle is turned or
warped unexpectedly into any direction then the
ligaments cannot able to tolerate the force so the
sprain can take place. Sprained ankle otherwise
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called as ankle scratch, warped ankle, rolled ankle,
ankle injuries (or) ankle ligament injury and floppy
ankle. If the ankle sprains occur, the blood vessels
are damaged so the body fluids are leakage to the
surrounding of the ankle joints after that the
swelling can occur. In earlier stage the treatment
process for ankle rehabilitation is usually simple,
comprising elastic bands, wobble boards, and foam
rollers. Such rehabilitation devices are typically
used in regimens that include exercises both in the
clinic and at home. Ankle robot has lightweight but
great pneumatic muscle actuators (PMA) which
increase skeletal muscles actuation. At the heart of
these injuries lies a lack of three important qualities:
strength, flexibility, and range of motion. Increasing
this quality, that will supports remedial and helps to
avoid further injuries. On the other hands the
patients should increase their flexibility and potency
beyond pre-injury levels. But they are must securely
come back to the normal actions and movement.
The general rehabilitation program for ankle sprains
is carried out in stages. The initial stage of
treatment right after injury is considered the acute
phase of rehabilitation and is focused on reducing
effusion and swelling at the affected to promote
healing of the injured tissues. A reduction in
effusion can be achieved with elevation, application
of ice, and compression. The injured ankle is also
often immobilized. However, as prolonged
immobilization of the ankle may lead to reduced
range of motion (ROM), compounding of
sensorimotor deficits and muscular atrophy, the
next phase of ankle rehabilitation typically involves
ROM and muscle strengthening exercises. The aim
of rehabilitation is get back to full function without
boundaries [19], [14], [5].
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International Journal of Engineering Trends and Technology (IJETT) – Volume23 Number 4- May 2015
II. METHODOLOGY
An Ankle robot has these essential
characteristics are Sensing is an initial steps that is
the robot should capable to sense its environment.
Here I used U-Slot sensor senses the position of the
ankle then it’s given to the robot awareness of its
environment. Second step is a movement that is the
robot requires being capable to be in motion around
its location. The ankle robot is moving on the
platform otherwise the robot requests to move. And
calculate the robot movements in the full robot
moves or half-done moves [13]. The movement of
robots are in x, y and z direction. Third one is
energy these ankle robot needs to be capable the
power itself (electrically powered). The method of
ankle robot gets its energy will depend on the
movement of actuators [16]. 5v, 12v power supply
is given to the ankle robot. A rehabilitation devices
needs to some kind of smarts input for activating
robot. A programmer gives the smart input in
LabVIEW. The robot will have some kind of
program for the data receiving.
The robot
movements are based on the received data.
A. Block Diagram and Description
LCD
PC( Lab
VIEW)
DRIVER
CIRCUIT
RS232
PIC 16F877
R E L AY C I R C U I T
SCU
SLOT
SENSOR
COMPRESSOR
A N K L E R E H A B I L I T AT I O N
ROBOT
P N E U M AT I C
VA LV E
P N E U M AT I C
CYLINDER
moderate medial ankle injuries (ETM2),
injuries (CNT FOOT) (or) fracture [6].
severe ankle
Fig. 1 Front Panel Selection in LabVIEW
Manually select the input that is what kind of injuries the
patient’s have and click the day for gradual rehabilitation
process. If the patient have mild ankle injuries means to click
the ETL1 and click the day. Based upon the day selection the
pneumatic cylinder movement controlled and that was fully
programmed in PIC 16F877A
2) RC232: The RS-232(X) is a communication cable,
commonly used for transferring and receiving the serial data
between two devices that is between pc (lab VIEW inputs)
and PIC16F877A microcontroller. In the serial port pin3 is
transmit (TXD) data from PC LabVIEW input to MAX232
converters and pin2 (RXD) is a receiving data.
The MAX232 is performing double action that is
transmitting or receives the data between PC to RC232. The
drivers give RS-232 voltage outputs (approx. + 7.5 V or -7.5V)
starting a single + 5 V supply by on-chip charge pumps and
external charging device. It makes a valuable for implement
RS-232 in devices or else it doesn’t require any voltages
outside from 0 V to + 5 V range [20].
Fig. 1 Block Diagram
1) LabVIEW: LabVIEW (Laboratory Virtual Instrument
Engineering Workbench) is a platform for system-designing
and development environment in visual programming
language from National Instrumentation. Lab VIEW ties the
creation of user interfaces (called front panels) into the
development cycle [25]. Set the inputs for ankle injuries type
that is mild lateral ankle injuries (ETL1), moderate lateral
ankle injuries (ETL2), mild medial ankle injuries (ETM1),
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International Journal of Engineering Trends and Technology (IJETT) – Volume23 Number 4- May 2015
preset to a stable voltage. The circuit is prepared for linear
voltage regulator 7805 beside with resistors and capacitor with
bridge rectifier and diodes. 7812 is widely used for 12V
regulator circuits. In this 7812 designed by using two
capacitors, one for input and another one for output so that it
will achieve fixed regulation. In these ankle robot should
reach 12V 1A current by a heat sink plate.
Fig. 3 RS232 connected to the PIC16F877
The RS7805 series can provide fixed voltage for ankle
rehabilitation robot. The main advantages of these RS7805 are
removing the distribution problem, local on card regulation.
Protect from overheating, shock and internal current limiting.
If enough temperature dropping is provide, it will deliver
more than 1A output current. Even though designed part of
robot the most part as fixed voltage regulators, these devices
can adjust voltages and currents by an external component.
3) PIC16F877: The PIC16F887 is recent advanced
products from Microcontroller. A microcontroller is the
combination of a microprocessor, memory, input and output
ports and some of the special functions like timer, analogue to
digital converter, mathematics processor and PWM generator
in one chip. A microcontroller will take an input from a device
it is controlling hence controls the ankle robot by sending
signals to different components in the robot. The PIC16F877
have the below features such as, High-Performance RISC
CPU, operating speed is 20 megahertz and 200 ns for
instruction cycle, the operating voltage is 4.0-5.5v, the
temperature ranges from -40° to +85°C , fifteen interrupt
source, and it’s have 35 single word instruction. Some special
features are 14.3 Kbytes flash memory, 368 bytes of data
SRAM and 256 bytes of data EEPROM, easy programmable
by using software. RC oscillator program for code production,
sleep mode is available for power save. In peripheral features
are 33 I/O (input and output) pins and 5 I/O (input and output)
ports that is port A, B, C, D, E. It has 3 timer circuits that are
Timer 0, 1, 2. In a Timer0 have 8- bit timer and counter with
8-bit prescaler, Time1 have 16- bit timer and counter with
prescaler, Timer2 have 8-bit timer and counter with period
register, prescaler, postscaler. And it has 10-bit PWM modules,
supports the Parallel Slave Port. The maximum resolution is
200 ns, 8 channel analogy to digital converters are inbuilt. .
A 16x2 LCD display is very basic component and is very
usually used in different devices and circuits. The reasons are
it’s have no limitation for displaying characters, very cheap,
easily accessible. 16x2 LCD means it can show 16 characters
in 2 rows. PortD of microcontroller was connected to the LCD
that is 7 to 14 pin of LCD was connected to the PIC16f877 for
reading and displaying the data. The fixed 5V was given to the
5th pin of LCD.
Fig. 4 5v, 12v voltage regulator circuit
4) SCU and SLOT sensor: signal conditioning unit is to
perform the filtering, amplifying, isolation process and uses in
the analogy to digital converters. The slot sensor is to detect
the vibration and oscillation in the ankle robot. The main
advantage is high resistance to vibration. Slot sensor is to
detect small parts in a short distance. The transmission and
receiving functions are in one conveyor.
A fixed voltage power supply is very much important for
electronic devices. In a designing part of 7805 the
semiconductor materials are used for regulating fixed voltage
and current. If any deviation in the fixed rate means the
devices get damaged. These circuits will convert AC to DC.
By using voltage regulator DC, the tolerant output will be
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before work could be done [3], [17]. The working principle
of the pneumatic cylinder as shown in the Fig. 6.
Fig. 6 PMA working principle
III. RESULTS
Fig. 5 LCD Module Interfacing With
Microcontroller
5) Relay and Driver Circuit: Relay is a device which
allows low power to switch a comparatively high current and
voltage on or low current voltage is off. In a driver circuits are
used to amplify signals from PIC microcontrollers in order to
control power switches in semiconductor devices and also
additional functions which include isolating the power circuit
and the control circuit, detecting malfunctions, reporting
failures and storing to the control system, precaution against
failure, analysing sensor signals, and creating auxiliary
voltages.
6) Pneumatic Valve and Pneumatic Cylinder: In
Controlling of valves is a basic element of any pneumatic
system. Selecting the right air valves to control system
pressure, direction of flow and rate of flow. Air compressor is
a device that converts power (from an electric motor) into
potential energy by forcing air into a smaller volume and thus
increasing its pressure. This pressurised air was entering into a
pneumatic valve.
Pneumatic Valve is important to regulate amount of the
compressed air to supply to actuator. The actuator is used to
convert pneumatic power (electrical) into mechanical power.
When the compressed air enters to the pneumatic cylinder
then the muscle is enlarged that is the actuator is moving
downward direction (x-direction actuators). Whereas when it
is being deflated, the muscle turns back to its upward
direction. [24], [22], [15]. Here the pneumatic valve have the
pressure 1.5-8kgf/cm2 and 4V210-08 model.
Pneumatic system is applying force to a gaseous fluid like
air and transmits pneumatic pressure all through the fluid and
converting the stored energy back into mechanical force,
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The main objective of this project is to regain
strength, flexibility and increasing ankle range of
movement. These ankle robots were focused on
regain strength and flexibility by taking an ankle
exercises. Give exercise to the sprained ankle so
that the range of motion will increase while the pain
and swelling is decreasing. Physiotherapist assigns
different types of ankle injuries exercises that deal
with ankle flexibility, strengthening, and balance.
The ankle injuries exercises are given by the
pneumatic control system development for the
Ankle joint rehabilitation. A PWM scheme for a set
of pneumatic valves will control pressures and flow
rate of the air. Rehabilitation was considers as
active setup for the selection of treatment
procedure. In this project active mode was desirable
since it includes the increase tendons strength and
muscles of the ankle, finally recovering pre-injury
position. The movement of the ankle joints was
pain free level because the ankle robot exercises are
step by step procedure.
In existing method the ankle flexibility and
strengthens are improve by giving the exercise to
the ankle and the movements are rotating the foot in
circular axis, up and down (planterflexion and
dorsiflexion), side to side (inversion and eversion).
I have a survey for 100 ankle injured peoples.
Based on my survey: more than 40% of peoples are
affected by mild lateral ankle sprain ( ETL1), 20%
of peoples are have moderate lateral ankle sprain
(ETL2), 10% for mild medial ankle sprain, 8% for
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moderate medial ankle sprain and more than 20%
of peoples are affected by fracture and severe ankle
sprain. The ankle sprain and ankle fractures are the
most common ankle injuries. So here I used five
injuries level settings in the LabVIEW that is ETL1
(Partial tear of a ligament in medial side), ETL2
(Incomplete tear of a ligament in medial side),
ETM1 (Partial tear of a ligament in lateral side),
ETM2 (Incomplete tear of a ligament in lateral side),
CNT FOOT (contusion in the ankle or Complete
tear of a ligament) & Fracture (break in one or more
bone).
If the patients have mild medial ankle injuries,
then to select the input ETL1 and click the day1
options in the LabVIEW. Then the movements of
pneumatic cylinders are 10counts in x-direction
(inversion and eversion), 5 sec gap, 10 counts in ydirection (planterflexion and dorsiflexion), 5sec gap,
and 5counts in z- direction these steps are repeated
2 times for first day of treatment. The next day click
the day2 option then the ankle robot movements are
15counts in x-direction, 3 sec gap, and 15counts in
y-direction, 3 sec gap, and 10counts in z- direction
this steps are repeated 3 times. And the 3rd day click
the day3 options then the ankle robot movements
are 20counts in x-direction, 1 sec gap, and 20counts
in y-direction, 1sec gap, and 15counts in zdirection these steps repeated 5 times. A pneumatic
cylinder movements (counts in x, y and z direction)
and time gap between the x, y, and z are varying
based on the injuries level which selected in
LabVIEW. In this method, the movements of robot
are regaining the strength and flexibility also
returns to the pre-injury functions. The robot has
successfully treated the ankle injuries for
rehabilitation aspect as well as exercise for lower
leg paralysed patient.
As shown in the below figure for ankle
rehabilitation robot. Put the patient ankle to the
moving platform and select the injuries type (in
LabVIEW). Then the pneumatic cylinders moves
based on the selection that will be treat the ankle
injuries.
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Fig. 7 Ankle rehabilitation robot
IV. CONCLUSIONS
In this project for the patient comfortable the
devices is keep with their patient home itself.
Because this devices interface with a computer and
rehabilitation robot. The ankle robot is ability to
perform three directions of the movements. The
pneumatic cylinder movements are called as
exercise of the injured ankle. These movements of
exercise are used to make more effective for relief
the ankle injuries, pain and increase the range of
motion. The main advantage of this project is
gradually increasing the strength, ROM, flexibility
and also to prevent further injury of the ankle. The
ankle robot control was an easy task by using
LabVIEW as a controlling device. Finally the
application of rehabilitative device of the robot is
required to intractable with the patient. In olden
techniques ankle strengthens exercise are more
difficult by using towel stretch, step ups, walking
on toes and the patient can’t able to balance their
ankle in wobble board. In my project I implement
this ankle rehabilitation robot methods was very
simple, more effective, patient can set the levels
easily (selecting the day in LabVIEW) and low risk.
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