Design and Analysis of Learning Case based on Knee Rehabilitation

Training Device

Ying Chang

Jilin Agricultural Science and Technology University, Jilin, China

Keywords: Case Analysis, Knee Joint Rehabilitation Training Device, Structural Design.

Abstract: With the aging of population, the increase of physical diseases such as stroke and transportation, the number

of patients with limb dyskinesia, especially knee dyskinesia, increases sharply. This paper introduces the

structural design and analysis of knee joint rehabilitation training device, which can maximize the recovery

of patients' motor function, provide the basis for rehabilitation doctors to evaluate the effect of rehabilitation

training and formulate rehabilitation plan, reduce the labor intensity of rehabilitation doctors, and improve

the rehabilitation efficiency. Through the case design and analysis of knee rehabilitation training device,

students' mechanical design calculation ability can be cultivated, and students' understanding and

application of basic knowledge can be enhanced.

1 INTRODUCTION

In order to change the situation of relying solely on

rehabilitation physicians to assist patients with knee

joint to carry out rehabilitation training, further

improve the efficiency of rehabilitation training, and

improve the rehabilitation effect, the rehabilitation

robot technology combining robotics and

rehabilitation medicine has increasingly become a

research hotspot of scholars at home and abroad

(Wang, Chang, Zhu 2019). So far, many scholars at

home and abroad have done a lot of research work

on the rehabilitation robot, especially the lower limb

knee joint rehabilitation robot, and have made many

achievements (Weber-Spickschen, Colcuc, Hanke, et

al. 2017, Mavroidis, Bonato 2007, Koller-Hodac,

Leonardo, Walpen, et al. 2011, Koller-Hodac,

Leonardo, Walpen, et al. 2010, Smart portable

rehabilitation devices 2005, Adnan, Karamat,

Kamal, et al. 2014).

According to the rehabilitation training posture

of patients, lower limb rehabilitation institutions can

be divided into two categories: horizontal CPM

machine and vertical lower limb auxiliary

rehabilitation device (Hu 2009). At present, the most

commonly used lower limb rehabilitation device is

the horizontal CPM machine, and the lower limb fit

adopts the lap type. Patients can use the lying

position after operation, and put the lower limb

directly on the CPM mechanism for training. The

concept of CPM was put forward by Salter, a

Canadian Orthopaedic expert, after a lot of

experiments in the 1970s. It is the use of special

equipment by mechanical or electronic devices to

drive or maintain part of the limb movement, so that

the joint for a long time of slow passive movement,

so that the combination of treatment and

rehabilitation, can relieve pain, improve joint range

of motion, prevent joint contracture and adhesion. It

can promote the regeneration and repair of intra-

articular cartilage, and is conducive to the recovery

of limb function (Li, Li 2007). CPM machine

training is a mature method for postoperative limb

continuous exercise training (Morris 1995). The

development of CPM has gone through three

historical stages. Salter first put forward the concept

of CPM in 1975 after trial and clinical research. In

1982, Coutts et al. Applied CPM device to human

rehabilitation training. In 1992, McInnes et al.

Started a prospective study to explore the application

effect of CPM in different situations (Ning, Xu, Li

2007). At present, CPM technology has been widely

accepted in orthopedic rehabilitation field in China,

and its application scope is becoming wider and

wider.

This device can be worn on the lower limbs of

patients, and can fit closely with the legs. The parts

of the mechanism that fit the lower limbs are

generally made of light and soft materials, which are

Chang, Y.

Design and Analysis of Learning Case based on Knee Rehabilitation Training Device.

DOI: 10.5220/0011370900003438

In Proceedings of the 1st International Conference on Health Big Data and Intelligent Healthcare (ICHIH 2022), pages 391-395

ISBN: 978-989-758-596-8

391

closely combined with the legs, so it can achieve

more accurate angle control. The wearable structure

makes the training flexible, and rehabilitation

training can be carried out in standing, sitting and

lying positions. In this kind of research, pneumatic

artificial muscle and cylinder are more selected as

actuators, which can provide certain flexibility and

relatively high safety. However, due to the short

stroke of pneumatic artificial muscle and cylinder,

the rehabilitation angle of this kind of rehabilitation

mechanism is relatively small, which can not meet

the requirements of large angle rehabilitation, so it is

often used in gait training and disability assistance.

This kind of device is complicated and inconvenient

to wear. Because the vertical lower limb auxiliary

rehabilitation mechanism is mostly wearable, it fits

closely with the human body, and the bending angle

of the mechanism is equal to the bending angle of

the human joint, which can achieve accurate control.

Moreover, it uses pneumatic artificial muscle or air

cylinder as the driver, which has good flexibility and

can meet the safety when contacting with people.

Due to the limitation of rehabilitation posture, the

vertical lower limb auxiliary rehabilitation

mechanism can not be used for postoperative

rehabilitation, and the rehabilitation angle is very

small, so it is mostly used for auxiliary rehabilitation

training. But the wearable mechanism is generally

more complex, and to distinguish between the left

and right legs, wearing trouble, not very practical.

Through such analysis and data searching, students

can understand the cutting-edge technology, master

the specific application and implementation process

of mechanical design, design the corresponding

design scheme, reasonably analyze the design

calculation, and cooperate with the team to complete

the design and rationality analysis. In this process,

design calculation will be checked repeatedly, which

can cultivate one's design calculation ability and

craftsmanship spirit.

Mechanical structure design is the basis of

rehabilitation training for rehabilitation robot. This

paper mainly analyzes the structure design of knee

rehabilitation robot, and designs a reasonable

structure of rehabilitation robot. Through the

introduction of this case, students' craftsmanship

spirit can be cultivated in the process of design and

calculation.

2 DESIGN AND CALCULATION

OF KNEE REHABILITATION

TRAINING DEVICE

2.1 Weight and Height Data

The relationship between weight and height is as

follows

Normal weight

=H-110(kg) (1)

Ideal weight

=H-100(kg) (2)

If a person's weight is often lower than or higher

than 10% of the normal weight, it is an abnormal

state.

2.2 Calculation of Body Volume and

Surface Area

When the body weight is 50-100kg, the body

volume and surface area can be calculated according

to the following formula.

Calculation of human body volume

V = 1.015W-4.937 (3)

Where V is the volume of human body (m

); W

is the body weight (kg).

Through the design and calculation of human

body data, students' learning ability and application

ability of interdisciplinary knowledge can be

cultivated.

2.3 Weight and Height Data

According to ergonomics, the knee joint is rotated to

achieve the effect of rehabilitation treatment. The

weight of the human body accounts for about 35%

of the total weight of the human body. The average

person's weight is generally between 50kg-100kg,

and the m

leg

is 17.5kg-35kg. The rotation times of

knee rehabilitation treatment cycle is n

= 6 r/min,

the transmission ratio is I = 3. The stepping motor

with rated voltage of 220 V and rated power of 20 W

is selected.

2.4 Structural Design of Belt Drive

（1）Determination of calculated power P

=Ka·P=1.0 X 20W=20W (4)

ICHIH 2022 - International Conference on Health Big Data and Intelligent Healthcare

392

Among them, the rehabilitation robot works 4-6

hours a day, so the working condition coefficient Ka

= 1.0.

（2）Determination of V-belt pattern

Check the mechanical engineering manual and

select a-belt by P

and n

（3）Determine the reference diameter of the

pulley and check the belt speed

The datum diameter d

of the primary pulley is

75mm.

Check the belt speed according to the formula:









 ×

××

×

m/s=0.07m/s

Where n

= I = 18r / min.

Because the belt wheel speed is required to be

suitable for human knee rehabilitation treatment, the

belt speed of 0.07m/s can ensure human safety and

the stability of the machine.

Calculate the reference diameter of large pulley

=i·d

(5)

Select standard diameter d

= 150 mm.

2.5 Determine the Center Sistance and

Reference Length of V-pulley

(1) Primary selection with formula a

0.7（d

-d

）≤a

≤2（d

） (6)

Therefore, primary a

= 400mm.

(2) Calculate the required base length of the tape

a≈2 a













（







）







(7)

a =[2 × 400+ 2π × （ 75+150 ） + ×

1100 1156

−

]mm

≈1156mm

Look up the table and select the datum diameter

1100mm.

(3) Checking the wrap angle on the small pulley

≈180 º﹣（d

-d

）

.º



=180 º-（150-75）

.º



≈168 º＞120 º

(4) The number Z of design bands

A single V-belt is used, and the number of V-

belts is 1.

From d

= 75mm, n

= 18r / min, P

= 0.26kw is

obtained. According to n

= 18r / min, I = 2, ∆P

0.05kw is obtained. Look up the table to get K α=

0.98，K

=0.91。

The initial tension F of a single belt is obtained

from the formula

=500

（.



）









+qv



=67N

According to the table, the mass per unit length

of type a belt q = 0.105kg/m.

(5) Calculate the axial force F

=2zF

sin







=2×1×67×sin

º



=134N

(6) Design conclusion

The common V-belt of type A is selected, the

datum length of the selected belt is 1100mm, the

datum diameter of the pulley d

= 75mm, d

150mm, the center distance is controlled at about a =

400mm, and the initial tension of a single belt F

134 N. The final CATIA design is shown in Fig.1.

Figure 1: Belt drive structure.

3 DESIGN AND CALCULATION

OF KNEE REHABILITATION

TRAINING DEVICE

3.1 Design and Calculation of Thigh

Bar

The average thigh width of healthy adult men is 150

mm-170 mm, and the calf width is 100 mm-120 mm.

Therefore, according to the ergonomic structure

design, the modeling sketch in CATIA software is

shown in Fig.2.

Model design of main parts of lower limb

rehabilitation robot.

Figure 2: Thigh bar.

Design and Analysis of Learning Case based on Knee Rehabilitation Training Device

393

3.2 Design and Calculation of Spindle

The function of the main shaft is to connect the

pulley and the leg bar. Under the support of the leg

bar and the bearing, the main shaft can rotate and

transmit the motion of the motor to the leg bar, so as

to drive the rotation of the leg bar and realize the

purpose of circular rotation. The sketch of the

spindle is shown in Fig.3.

Figure 3: The spindle.

Bearing, end cover and large pulley are installed

at 60mm part of left end. In order to save materials

and simplify the design, the shank part is directly

welded to the spindle part to achieve better human-

computer interaction.

3.3 Design and the Design of Leg Bar

of Spindle

The shank rod is connected with the main shaft by

welding, so that it can be better stressed and

manufactured. According to the weight and size of

the human body, the shank rod adopts a cylinder

with a diameter of 10 mm and can be made of

aluminum alloy with a length of 400 mm. The back

end is connected by plate and welded, so that the

human body can step on or tie on the leg during

training. The leg bar is shown in Fig.4.

Figure 4: The design of leg bar.

3.4 Design of Bearing End Cover

The function of the bearing end cover is to prevent

the axial movement of the bearing, so the end cover

is used for axial positioning. Bearing end cover is

divided into two kinds, front cover and rear cover, so

it needs to be designed and processed separately.

According to the maximum outer diameter 40mm

and inner diameter 32mm of the thigh bar, the

design is carried out. The two end caps are shown in

Fig.5.

Figure 5: Bearing end cover.

3.5 Selection of Bearings

The above analysis shows that the axial force F =

134N, the pressure exerted by human legs is about F

= 116N, through the working state of the bearing,

the radial force F

= 250N, the axial force F

= 60N.

And use deep groove ball bearing.

(1) To find the ratio of F

and F

, there is a

formula:





250

=0.24

According to the bearing manual, when e = 0.24,

X= 0.56, Y= 1.8.

(2) Preliminary calculation of the equivalent

dynamic load P, where the working factor f

= 1.0

P= f

（XF

+YF

）=1.0×（

0.56×250+1.8×60）N =248N

(3) According to the formula, the basic rated

dynamic load of the bearing is calculated

C=P











= 248 ×



××







N =870N

ICHIH 2022 - International Conference on Health Big Data and Intelligent Healthcare

394

It is assumed that the use time of the lower limb

rehabilitation robot is 4000 hours. According to the

bearing manual, 6200 bearing is used. Deep groove

ball bearing with inner diameter d = 10 mm, outer

diameter D = 32 mm and width B = 10 mm.

3.6 Force Analysis

According to the analysis of the operation of the

lower limb rehabilitation machine, the motor applies

torque on the small pulley, and the small pulley

drives the belt to rotate, so as to drive the large

pulley to rotate. The movement and force are

transmitted through the key and act on the main

shaft to realize the rotation of the main shaft.

Therefore, the rigid constraint is set through the part

connected by the key, and is applied to the face

corresponding to the key. There are many ways of

modal extraction, and block Lanczos method is used

in this paper.

The natural frequency of the assembly body is

determined by its structure. After modal analysis, the

vibration of the shaft is mainly concentrated in the

middle, which will swing left and right. The

maximum frequency of the sixth mode is 73.442Hz.

The vibration mainly includes the rotation of the

spindle, left and right swing, and the swing of the

spindle base along the Z axis. The minimum

frequency is 25.111Hz. The mechanism can work

normally.

4 CONCLUSIONS

When introducing these ideological and political

breakthroughs, try not to express the teachers' own

views directly, and use more cases, facts and

phenomena to inspire students to think, the effect

will be better. After practice, students are easy to

accept the actual case and video. Through practice, it

is found that in the process of design, calculation

and analysis of knee joint rehabilitation training

device, students have cultivated the ability of

independent thinking, analysis, problem-solving and

interdisciplinary learning, and cultivated their

craftsmanship spirit. Therefore, the actual design

and calculation of cases to explain knowledge points

can better help students understand and apply

knowledge.

ACKNOWLEDGEMENTS

This research was supported by Jilin Agricultural

Science and Technology University 's 2020 school-

level "Curriculum Ideological and Political" teaching

reform curriculum project-mechanical design basis.

REFERENCES

Wang L , Chang Y , Zhu H . Internal Model Control and

Experimental Study of Ankle Rehabilitation Robot[J].

Robotica, 2019:1-17.

Weber-Spickschen T S , Colcuc C , Hanke A , et al. Fun

During Knee Rehabilitation: Feasibility and

Acceptability Testing of a New Android-Based

Training Device[J]. The Open Medical Informatics

Journal, 2017, 11(1):29-36.

Mavroidis P , Bonato I . Design, Control and Human

Testing of an Active Knee Rehabilitation Orthotic

Device[C]// Proceedings 2007 IEEE International

Conference on Robotics and Automation. IEEE, 2007.

Koller-Hodac A , Leonardo D , Walpen S , et al. Knee

orthopaedic device how robotic technology can

improve outcome in knee rehabilitation[J]. IEEE

International Conference on Rehabilitation Robotics :

proceedings, 2011, 2011:5975347.

Koller-Hodac A , D Leonardo, Walpen S , et al. A novel

robotic device for knee rehabilitation improved

physical therapy through automated process[C]// IEEE

Ras & Embs International Conference on Biomedical

Robotics & Biomechatronics. IEEE, 2010.

Smart portable rehabilitation devices[J]. Journal of

NeuroEngineering and Rehabilitation, 2005, 2(1):1-15.

Adnan M , Karamat A , Kamal N , et al. Design of Gear

Bearing Drive (GBD) Based Active Knee

Rehabilitation Orthotic Device (AKROD)[C]// First

International Young Engineerings Convention (IYEC-

2014). 2014.

Hu Haiyan. Research on structure and control technology

of compliant knee joint rehabilitation device. Nanjing

University of technology, 2009

Li Yi, Li Ziqing. Research progress of CPM on

rehabilitation after total knee arthroplasty. Journal of

Yangtze University (self SCIENCE EDITION),

science and engineering volume, 2007,04:157-160 +

178

Morris J. The Value of Continuous Passive Motion in

Rehabilitation Following Total Knee Replacement.

Physiotherapy, 1995, 81(9):557-562.

Ning Lixin, Xu Yan, Li Dongwen. Application progress of

continuous passive motion after total knee arthroplasty

[J]. Chinese Journal of rehabilitation medicine,

2007,03:286-288

Design and Analysis of Learning Case based on Knee Rehabilitation Training Device

395