[IEEE 2011 2nd International Conference on Instrumentation, Communications, Information Technology,...

2011 International Conference on Instrumentation, Communication, Information Technology and Biomedical Engineering

8-9 November 2011, Bandung, Indonesia

Development of Automatic Continuous Passive

Motion Therapeutic System

Michael Kharis Saputra

1 and Aulia Arif Iskandar

2

1Department of Biomedcial Engineering, Swiss German University, BSD, Indonesia

(E-mail: [email protected]) 2Department of Biomedical Engineering, Swiss German University, BSD, Indonesia

(E-mail: [email protected])

Abstract - After knee replacement surgery, a patient

immediately needs a therapeutic treatment. A therapist flexes and

extends the leg around the knee to eliminate the joint stiffness.

The research is to design and develop a system of automatic

Continuous Passive Motion (CPM) device so that patients no

longer have to control it. The system will stop and return to its

starting condition whenever there is patient pain. It is a force that

is released by the patient in an opposite direction and will be

represented as holding the DC motor shaft. A DC motor, H-

bridge, microcontroller, and ADC modules are needed to develop

this system. DC motor rotates clockwise with about 4V-5V as its

voltage. If the DC motor receives load, the voltage will decrease

and will be detected by ADC. The motor will stop if the voltage

reaches 3V or less. After around 1.5s, it will rotate again with an

opposite direction. The system is very sensitive to the patient pain,

and if it is applied to CPM, it can improve patient safety.

Keyword: CPM, microcontroller, h-bridge, ADC, DC motor

I. INTRODUCTION

Knee is a hinge joint between thigh and shank. Athletes and old people sometimes had a fractured or worn knee surface

because of their habit. These kinds of knee can be irritated. The

patients are firstly suggested to get nonsurgical treatment, such

as physiotherapy or exercise. If they are no longer effective to

improve mobility and reduce the pain, then the Knee

Replacement surgery is one of the recommended ways. There

are more than 1 million hip and knee replacements per year in

the United States [1]. This procedure replaces the damaged

knee surface with artificial surfaces. The materials of the

artificial knee surface have to be compatible and durable also

near frictionless.

After the surgical treatment, patients need to recover. In this condition, with help from therapist, patients usually do some

exercise to train their knee to move like a normal knee. Some

doctor may put the patient into a motion machine therapy. This

machine also called Continuous Passive Motion (CPM). The

device will flex and extend the knee continuously. Patient’s

muscle will not produce any force that is why the machine

named passive.

Over fifty years, since the knee surgery has been

implemented, joint stiffness is the major problem following the

knee surgery. A CPM was developed so that the patient can

start to move as soon as possible right after the surgery to

prevent the stiffness [2]. Nowadays, many manufactures are producing CPM devices

with a controller or remote. The patient can control whether he

wants a flexion or extension motion. For example, patient starts

the device with 90o of the angle between thigh and shank. He

pushes the button in the remote controller to extend his knee. If

he feels pain or wants to extend his knee no more, then he can

stop pressing the extension button, and start pressing the

flexion button.

II. METHODOLOGY

Fig. 1 – Block Diagram

In Fig. 1, the input is the direction of the motor rotation. Microcontroller set the H-Bridge so that it controls the motor to

rotate clockwise at the first condition. In microcontroller, the

DC motor voltage will be a feedback from ADC. Normally, the

DC motor voltage is 4V-5V. When the motor shaft is given an

extra load, the motor voltage will drop. If the voltage of the DC

motor reaches 3V or less, then the microcontroller will set an

output, so that the H-bridge will make the motor stops and turn

to rotate counter clockwise. Whenever the switch sensor is

triggered, the microcontroller will accept that as a feedback

also, and set an output to H-bridge that will let the motor stops

and rotate clockwise again. In order to develop the automatic therapeutic system of

CPM several modules were used, which are:

Microcontroller ATMEL AT89S52, 8K Bytes Flash

Memory

H-bridge MC33887

ADC0820, 8-bit resolution, 2.5µs conversion time

DC Motor

Data cable (10-pins socket)

978-1-4577-1166-4/11/$26.00 ©2011 IEEE



9V battery and socket

Jumpers

M-IDE Studio for MCS-51, Pinnacle, and ISP_PROG v1.3 (Software)

Fig. 2 – Flow Chart

The system was developed with assumption that the first or

start condition of the patient’s leg was flexed 90o. When the

system starts, the device begins to extend the leg (see Fig. 2).

While the leg is being extended, the sensor of the system is

also detecting the patient’s resistant movement. The resistant

movement is the motion of the patient that will resist the device

in extending the leg. It means the resistance is in form of knee flexion (opposite direction). When the patient releases the

motion that resists the device, the motor that is extending the

leg will have voltage drop. This condition is the detection that

is sensed by the sensor. If so, then the motor will stops and

begins to flex the leg.

If there is no detection of the patients’ resistance

movement, the device will continue to extend the leg until it

reach the maximum knee extension. When it reaches its

maximum, it gives big resistance to the motor (like the resistant

movement), and the motor will also have voltage drop. As

already explained above, it will trigger the motor to stop and

begin the leg flexion. The device will flex the leg until it reaches start condition.

The reaching of the start condition will trigger a sensor. When

the sensor is triggered, the system will stop the flexing and also

start in extending the leg again.

Fig. 3 – Schematic Diagram

In schematic diagram above, the pin 2.0 and 2.1 from the

microcontroller are used to control the motor rotation

indirectly. They are attached to MIN 1 and MIN 2 in the H-

Bridge module. If both MIN 1 and MIN 2 are low or high, then

the motor is in a freewheeling condition. When MIN 1 is set

high and MIN 2 is set low, then the motor will rotate

clockwise. Oppositely, if MIN 1 is low and MIN 2 is high, then

it will rotate counter clockwise. Pin 2.2 and 2.3 are connected

to MEN and MSLP in H-Bridge. If MEN is high or 5V, then

the module enables the output of MOUT1 and MOUT2, which will be attached to the motor. The H-Bridge will work in a full

operation if MSLP is high too.

Port 1 acts as input pins from Analogue Digital Converter.

There are 8 pins that are constructed as port 1, which represent

the 8 bit of the ADC. Pin 1.0 reflects the first bit from the ADC

and so on until pin 1.7 represent the eighth bit. Pin 2.4 is

connected to a sensor. It will receive a signal whenever the

switch sensor is closed. At the H-Bridge, MOUT 1 and MOUT

2 are attached to the motor at two poles. Pin is set to the

ground (low) in order for the to be recognized by the

converter. MODE is also set to low to enable the read mode.

Pin 3.5 from the microcontroller is connected to pin. This

is the control from microcontroller to the ADC, whenever pin

3.5 is low, ADC will start to convert analogue Vin, which is the analogue input to the ADC, to digital. After the conversion, pin

3.5 has to be high again to end the conversion time. Vref ( ) is

connected to the 5V and Vref ( ) is attached to ground to let

the Vref become 5V. This Vref specifies the range of analogue

input to be between 0V-5V.



Fig. 4– Inside a CPM [3]

There is the mechanical part inside a CPM. This part

actually consists of 4 parts (see Fig. 4b). They are DC motor,

coupling, and ball screw (ball and lead screw). The ball is

actually the red dot and the lead screw is the blue part in the

Fig. 4a. The coupling connects the motor and the ball screw.

Whenever the motor rotates, the lead screw will also rotate.

The direction of the motor rotation is proportional to the lead

screw rotation direction. This rotation direction will have an

effect to the ball motion.

Fig. 5 – Patient pain (a) and motor rotation direction (b) relationship [3]

When the DC motor rotates in clockwise direction, the lead

screw will also rotate in the same direction. In this condition,

the ball will move along the lead screw path to the left

direction. If the ball (red dot in Fig. 5a) is moving to the left

direction, the leg will be extended. Oppositely, when the DC motor rotates in counter clockwise direction, which means the

lead screw also rotates in the same direction, the ball will move

along the path to the right direction. This condition will lead to

the flexion of the leg (see Fig. 5b).

For example, if the CPM is in process of extending the

patient’s leg, and the patient feels pain, then the patient will

release a force that will hold the motion of the machine. This

force is in an opposite direction of the machine motion (Fig.

5a).

This force (Fpain) that is holding the motion of the ball, will

affect the rotation of the lead screw and so the DC motor. The rotation will be given an extra load. Since there is no patient

who is involved in this thesis work, this extra load will

represent the patient pain.

The DC motor characteristic says that if the motor shaft is

hold or given an extra load, the RPM will decrease, and will

lead to the drop of the motor voltage. This drop voltage is the

one that will be sensed as the patient pain. The sensor that is

used in this thesis work is an ADC0820.

The microcontroller program was also developed using

assembly language.

Fig. 6 – Microcontroller Program

III. RESULT AND DISCUSSION

When the system starts, the DC motor rotates in clockwise

direction. When the motor shaft is being given an extra load,

the DC motor voltage drops. Normally the voltage of DC

motor is 4V-5V. With threshold 3V, the motor stops rotating,

and begins to rotate in an opposite direction, which is counter clockwise.

3V threshold is just an assumption. It can be manipulated or

changed during the calibration. The manipulation of the

threshold lies in line 15 of the microcontroller program.

3V is 153 in the ADC. In case the ADC sends 153 to R1

through P1 (line 13), this number will be added to accumulator,

which contains a number, 102. In line 16, these both numbers

were summed. When it these two numbers reach 255 or less,

there will be no carry anymore. This carry will be sensed in

line 17. If there is no carry then the program will continue to

line 18. In case the ADC sense more than 3V, the output of the

ADC will send a number more than 153 to the P1, and thus the

R1 is also more than 153. If this number was added with 102, it

will result a number more than 255. If the accumulator contains

a number more than 255, then it will have a carry. If there is a

carry, then the program from line 17 will go back to line 9 to

recheck the DC motor voltage.

IV. CONCLUSION

From this work, several points can be concluded. The

automatic CPM therapeutic system can be made using a

microcontroller, H-bridge, ADC, and a DC motor. The

microcontroller gives signals to H-bridge, ADC, and also gets

signals from ADC and S1 switch sensor as feedbacks. In

normal condition, the DC motor voltage is about 4V-5V. The

DC motor shaft is hold to represent the patient pain. When the



DC motor is hold, its voltage goes down. With the 3V

threshold, the motor stops if its voltage reaches 3V or less and

starts to rotate in an opposite direction. The ADC, as the sensor, senses this decrease voltage. This system is very

sensitive to the patient pain. If it is applied to the CPM, it can

help reducing patient injuries, which means increase patient

safety.

ACKNOWLEDGEMENT

Firstly, the author is grateful to Jesus Christ because of His

love, guidance, helps, blessings, and mercies. This work can

only be done by helps and will from Him. In this opportunity

also, the author wants to thank Mr. Aulia Arif Iskandar, M.T.,

as the thesis advisor, for his concern and helps, for all the answers that have been given to all of the author’s questions,

his beloved family, especially his parents, for the prayers,

supports, and loves, Mr. Arko, Ph.D., for the time, helps, and

all of the answers of the author’s questions, Mr. Tabligh

Permana for assistance, supports, and ideas, Mr. Agung

Margiyanto for all helps and supports, Yonathan A.S. for the

prayers and supports, and Mechatronics students for all the

helps.

REFERENCES

[1] http://www.pjstar.com/features/x1925176074/Number-of-hip-and-knee-

replacements-climbs-as-technology-improves, accessed March 27, 2011

[2] http://orthopedics.about.com/cs/kneereplacement/i/cpm.htm, accessed

March 27, 2011

[3] http://www.continuouspassivemotion.org/Pages/Engineering%20CPM%20

by%20JS.html, accessed June 20, 2011

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