Vibration analysis and topology optimization of the header of full-feeding
rice combine harvester
Han Tang1, Changsu Xu1, Jianhua Zhu1, Rui Guan2, Jinwu Wang1*
(1. College of Engineering, Northeast Agricultural University, Harbin 150030, China;
2. School of Water Conservancy and Civil Engineering, Northeast Agricultural University, Harbin 150030, China)
Abstract: The header frame of full-feeding rice combine harvester was characterized by severe vibration due to the excitation
force generated by the movement of each working part. In order to solve the problem, the parametric model of the header frame
was established, and the accuracy of the finite element model was verified by comparison of the results of the free modal
analysis and free vibration modal test based on Eigensystem Realization Algorithm (ERA). Then the constrained modal
frequencies were calculated and compared with the external excitation source frequencies, the results showed that the first and
eighth order modal natural frequencies were coupled with the excitation frequencies of the threshing cylinder and the engine
respectively, which were apt to resonate. To avoid resonance and achieve lightweight design, topology optimization, and finite
element analysis were carried out. The optimization results showed that the strength and rigidity meet the requirements and the
weight was 14.17% lower than before. The first and eighth order modal natural frequencies were far away from the excitation
frequencies range of the threshing cylinder and engine, and the frequencies were far away from the range of each excitation
frequency, which effectively avoided the occurrence of resonance. Field experiments showed that the peak value of the
vibration acceleration in the three directions of the 8 measuring points of the optimized header frame was significantly reduced,
which effectively reduced the vibration of the header frame during harvest. This study provides a method for obtaining the
vibration characteristics of key components of agricultural machinery and provides a reference for the weight and vibration
reduction of header frames of rice, wheat, rape, and other crop combine harvesters.
Keywords: eigensystem realization algorithm, modal analysis, free modal test, topology optimization, lightweight, field
experiment
DOI: 10.25165/j.ijabe.20231604.7096
Citation: Tang H, Xu C S, Zhu J H, Guan R, Wang J W. Vibration analysis and topology optimization of the header of full-
feeding rice combine harvester. Int J Agric & Biol Eng, 2023; 16(4): 96–108.
1 Introduction
Rice is one of the most important food crops in the world, and
its production plays a vital role in ensuring global food security and
economic stability. China's rice cultivation area reaches 30 million
hm2, and its output accounts for about 40% of the country's total
grain output. In 2020, the comprehensive mechanization level of
rice reached 85.0%. As the key link in the entire mechanization of
rice production, harvest has reached 93.1%[1]. Mechanized
harvesting mainly has two methods: segmented harvesting and
combined harvesting[2], and the segmented harvesting method is
gradually replaced by the combined harvesting method which saves
labor and time. The full-feeding combine harvester is widely used in
China because of its high production efficiency and strong
adaptability. As one of the most critical working parts, the header
has the function of picking, cutting, and conveying. Its reliability
directly affects the level of subsequent threshing, cleaning, and
other processes. The header frame is the main bearing cavity of reel,
auger, cutter, and other working parts, which plays the role of
fixation, support, and protection. Because the frame is subject to
vibrated by multi-source excitation, which directly affects the
reliability of the whole machine and the harvesting effect[3].
The application of vibration response characteristics in the field
of agricultural machinery provided a reference for the development
of some fruit harvesters[4-8], but the vibration was harmful to
mechanical components in most cases. Aiming at the problems of
violent vibration, low reliability, and bad comfort in the operation
of agricultural machinery, many scholars have made a lot of
research on mechanical theory, simulation analysis, vibration
detection, optimization design, etc. Zou et al.[9] found that there was
a correlation between structural mode and vibration. With the
application of computer technology, finite element analysis
software is widely used in structural modal analysis. Bajoria et al.[10]
conducted a free modal analysis on the cold-bent frame using
ANSYS and its vibration characteristics were obtained. Kumar et
al.[11] built the parametric model of vehicle gearbox components and
conducted modal analysis to obtain the natural frequency and mode.
An effective method for studying the vibration of key components
of agricultural machinery was provided by the modal analysis, but
the vibration characteristics of the mechanical structure cannot be
accurately obtained by software simulation alone. Jin et al.[12]
obtained the vibration characteristics of vehicle-mounted spray
based on modal test, and verified the excitation characteristics of
different combined modal shapes. The research of the above
scholars only explored the vibration characteristics of mechanical
Received date: 2021-12-09 Accepted date: 2022-12-31
Biographies: Han Tang, PhD, Associate Professor, research interest: related
mechanism of seed metering device, Email: [email protected]; Changsu Xu,
PhD, research interest: loss reduction method of combined harvest, Email:
[email protected]; Jianhua Zhu, Master, research interest: key tech-
nology and equipment for rice combined harvesting, Email: huazai423@126.
com; Rui Guan, Master, Laboratory assistant, interest: reliability engineering of
agricultural machinery, Email: [email protected]
*Corresponding author: Jinwu Wang, PhD, Professor, research interest:
reliability engineering of agricultural machinery. College of Engineering,
Northeast Agricultural University, Harbin 150030, China. Tel: +86-451-
55190950, Email: [email protected]
96 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4
structures by means of single software simulation or single free
mode test, and did not organically combine the two, which cannot
verify the accuracy of finite element model establishment, and
cannot provide accurate data reference for later optimization design.
The free modal test results are the vibration characteristics of
mechanical structure without additional constraints, some scholars
have found that the modal test with constraints on the structure
according to the actual situation can better match the modal
results[13]. However, there will be significant dynamic coupling
between the structure and the working parts that need to be solved
in the process of constrained modal test, and the application of
vibration isolation device between them will destroy the actual
constrained state, so the accurate structural vibration characteristics
cannot be obtained[14].
The purpose of obtaining the vibration characteristics of
structure was to reduce the occurrence of vibration. Most of the
studies aimed at reducing the vibration of tractors to improve
driving comfort. Deboli et al.[15] conducted experimental research on
agricultural tractor seats with different surfaces and configurations
to obtain the transfer rate of the seats in three orthogonal directions,
providing reference for reducing cab vibration and improving
comfort. Deprezk et al.[16] and Cheng et al.[17] reduced the impact of
vibration by changing the structural parameters of the suspension,
and effectively improved the driving comfort of the tractor. In view
of the multi-excitation sources and complex vibration of the
combine harvester, the research focused on the vibration reduction
of key components. Jiang et al.[18] effectively reduced the resonance
of rape mower frame by increasing the arch structure of the frame.
Li et al.[19] optimized the parameters of combine harvester header
frame and increased the counterweight of cutter crankshaft to
effectively reduce the vibration amplitude. Most of the above
researches were designed to reduce vibration by adding vibration-
isolating plates, reinforcing beams, and other weight-increasing
forms, which can effectively reduce the vibration of the structure
while increasing the quality of the structure, but cannot achieve the
purpose of reducing the weight of the structure while ensuring
mechanical performance.
The optimization methods of key components are mostly
focused on shape optimization and size optimization, but topology
optimization with larger design space and higher efficiency than
that is gaining more and more attention[20]. Topology optimization
uses the given design domain, constraints, and load conditions to
determine whether there are cavities in the structure, the number
and location of cavities, and other topological forms. It divides the
region into enough sub-regions and analyzes the structure. At the
same time, according to some optimization strategies and criteria, it
deletes some elements from the sub-regions, describes the optimal
topology of the structure with the remaining elements, and the
modal frequency can be changed to avoid resonance by changing
the mass and stiffness distribution of the structure. Xu et al.[21]
reduced the quality of stamping die for high-strength steel of
automobiles through topology optimization, and ensured the
forming performance of stamping parts by using the die. Kim et
al.[22] carried out topology optimization on the rear suspension of the
vehicle to improve the ride comfort and handling stability of the
vehicle. Qin et al.[23] proposed a topology optimization design
method for metamaterials, the vibration reduction performance of
the new metamaterials was 12% higher than that of the traditional
honeycomb materials. Stanford et al.[24] carried out topology
optimization on the structural parameters of the aircraft blades to
solve the aeroelastic flutter problem of the aircraft blades. Topology
optimization has become a hot topic in optimization methods.
In view of that, this paper made an in-depth analysis of the
vibration characteristics of the header frame of a full-feeding rice
combine harvester. The accuracy of the model was verified by
establishing the parameterized model of the header frame, combined
with free modal analysis and modal test. The vibration
characteristics of the header frame were obtained by constrained
modal analysis, and the excitation sources that affect the resonance
were explored. The solution was based on the topological
optimization method from the perspective of lightweight to solve
the resonance problem caused by the vibration coupling between the
header frame and the excitation sources.
2 Materials and methods
2.1 Structure and working process of full-feeding rice combine
A certain model of full-feeding rice combine harvester is
widely used in many cultivation areas in China. The structure of the
machine is shown in Figure 1. It is mainly composed of header
assembly, tilt conveyor, threshing device, cleaning device,
unloading auger, grain tank, and other working parts as well as
relevant accessories such as hydraulic system. The wide track wheel
and deep mud feet paddy field power chassis can ensure sufficient
touchdown area and good trafficability in the complex paddy field
environment. The width of the header is 2000 mm, which can meet
the requirements of efficient harvest in the field. Stepless adjustable
reel and angle adjustable reel spring teeth can effectively reduce
header loss and improve the adaptability of harvesting lodging
crops. The combined configuration of the axial threshing cylinder
and sieve has the advantages of clean threshing and small cleaning
loss. The specific technical parameters are listed in Table 1.
1 2 3 45
8
1234
56
a. Schematic
b. Machine
7891011
1. Reel 2. Divider 3. Auger 4. Header frame 5. Tilt conveyor 6. Cab 7.Grain tank
8. Unloading auger 9. Threshing device 10. Cleaning device 11. Power chassis
Figure 1 Structure of full-feeding rice combine harvester
April, 2023 Tang H, et al. Vibration analysis and topology optimization of the header of full-feeding rice combine harvesterVol. 16 No. 4 97
Table 1 Technical parameters of full-feeding rice combine
harvester
Parameters Value
Overall dimension/mm×mm×mm 5130×2470×2750
Rated power/kW 75
Track width/mm 450
Header width/mm 2000
Ground clearance of chassis/mm 672
Threshing cylinder/mm×mm Φ620×1960
Sieve/m2 1.24
Reel diameter/mm Φ900
Feed rate/t·h–1 16.2
Operation speed /km·h–1 0-4.8
During the harvesting, the divider separates the rice to be cut
from the uncut rice, and the reel guides the rice to be cut to the
cutter so that the cut rice is laid on the header frame, and the tilted
conveyor transports it that is concentrated by the anger to the
threshing device. The threshed grains and chaff are sent to the
cleaning device composed of the sieve and the cleaning fan for
cleaning. And then, the clean grains enter into the grain tank and are
unloaded by the unloading auger, and the stalks and sundries are
discharged out of the machine, so as to complete the whole harvesting
process of rice cutting, conveying, threshing, and cleaning.
2.2 Modal analysis and test of header frame
To find out whether the natural frequencies of header frame
were coupled with the frequencies of the excitation source to cause
resonance, modal simulation analysis and related research were
carried out and their modal characteristics were solved. The
accuracy of the finite element model was verified by the
combination of the finite element free modal analysis and the free
vibration modal test. Constrained modal analysis was used instead
of constrained modal test to avoid the dynamic coupling between
the working parts and the solution was obtained. The vibration
characteristics of the header frame were more accurate and reliable,
which provided a reference for the optimization and improvement
of the header frame.
2.2.1 Header frame model
The header of a full-feeding rice combine harvester, widely
used in China, was taken as the research object. Its frame was 690 mm
long and 2000 mm wide along the forward direction. It was mainly
composed of square steel, angle steel, and steel plate formed by
Q235A structural steel and rigidly connected by welding. In order to
reduce the simulation time and ensure the integrity of the structure,
we simplified it. 1) Bolt holes fillets far smaller than the grid size,
and stamping bars which have less impact on mechanical properties
were not considered. 2) Welding flanging which has less impact on
the structure and the change of material properties due to welding
was ignored. Using 3D software CATIA parameterized the model,
as shown in Figure 2.
1 2 3 4 5 6 7 8
1. Side members 2. Stiffeners 3. Side walls 4. Floor 5. Rear walls 6. Tilt conveyor
inlet 7. Vertical members 8. Beams
Figure 2 Header frame model
2.2.2 Free modal analysis of finite element
The normally basic differential equation of vibration is[25]M¨x+C˙x+Kx P=0 (1)
where, M is the mass matrix of the vibration system; C is the
damping matrix; K is the stiffness matrix; P is the external
excitation; x is the vibration displacement vector.
For the header frame, the natural frequency is obtained by
analyzing the dynamic response of the structure when there is no
load, i.e. P=0, and the damping of the header frame is very small,
which approximately meets C=0. The differential equation of
undamped elastic vibration is obtained as follows:M˙x+Kx=0 (2)
The general form of the solution of the equation isx=φe
jwt
(3)
where, φ is the corresponding eigenvector; j is the imaginary unit; w
is the natural frequency, Hz; t is the time, s.
Substitute the solution of the equation to get:Kφ=2Mφ (4)
where, λ is the eigenvalue of the system. The eigenvalues in modal
analysis can be obtained if λ=w2 is satisfied.
The free modal analysis of finite element mainly studied the
natural vibration characteristics of the frame in the free state. The
structure was discretized by the finite element method and the
mathematical model of its eigenvalues was established. Then the
eigenvalues and eigenvectors of the system were calculated by the
approximate principle analysis to reflect its vibration frequencies
and corresponding modal shapes[26].
The 3D model of header frame was imported into ANSYS
Workbench 18.0 in .STP format for free modal analysis. The header
frame can be regarded as a thin-walled structure, which was defined
as a shell, and the material was defined as a structural steel
(Q235A), whose yield strength was 235 MPa, elastic modulus was
210 GPa, density was 7850 kg/m3, Poisson's ratio was 0.3. In order
to make the analysis results more accurate, the cell size set by grid
division was 10 mm, and the final total number of cells was 242 896,
and the total number of nodes was 479 761. The free mode analysis
of finite element does not need to impose constraints, and the first
six order rigid body modes with zero frequency will appear[27]. The
low-order vibration had a great influence on the header frame
structure, so the non-zero first 8-order modal characteristics were
analyzed.
2.2.3 Free modal test
The key of free modal test was modal parameter identification,
which was the process of establishing state space expression from
test data. The Eigensystem Realization Algorithm (ERA) is to use
the multipoint excitation multipoint response method, take the
impulse response function as the time domain identification method
of the basic model, realize the singular value decomposition of
Hankel matrix, and obtain the minimum order system matrix. The
following equation is the basic principle of ERA.
Let n-dimensional discrete system state equation:¨
x(k+1)=Ax(k)+Bu(k)
y(k)=Cx(k)
(5)
where, x(k) is the state vector; y(k) is the observation vector; u(k) is
the control vector; K is the sample indicator factor; A is the n×n
dimension state coefficient matrix; B is the n×m dimension control
98 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4
coefficient matrix; C is the p×n dimension observation coefficient
matrix.
The system state equation described by Markov parameter (free
pulse response function) is as follows:Y(k)=CA
k 1
B (6)
Using the measured free response data Y(k) to construct the
normalized Hankel block matrixH
r s(k 1)=
2
6
6
6
6
4
Y(k) :::Y(k+t
s 1)
Y(j
1+k):::Y(j
1+k+t
s 1)
::: ::: :::
Y(j
r 1+k):::Y(j
r 1+k+t
s 1)
3
7
7
7
7
5
psm
(7)
The singular value decomposition of Hrs (0) is carried out:H
r s(0)=PDQ
T
(8)
where, P and Q are r·p×n dimension left singular vector matrix and
s·m×n dimension right singular vector matrix respectively; D is
diag[d1, d2, d3, ..., dn] n×n dimension singular value diagonal matrix.
Define:¨
E
T
p=[I
p;O
p;:::;O
p];E
T
m=[I
m;O
m;:::;O
m]
P
d=PD;P
n
d=D
1
P
T
(9)
where, Ip and Im are p and m-order unit matrices respectively; Op
and Om are p and m-order zero matrices respectively.
Derived:Y(k 1)=E
T
pH
r s(k)E
m=E
T
pPD
1=2
[D
1=2
P
T
H
r s(1)QD
1=2
]
k
D
1=2
Q
T
E
m
(10)
Through comparison, it can be got that8
>
<
>
:
A=D
1=2
P
T
H
r s(1)QD
1=2
B=D
1=2
Q
T
E
m
C=E
T
pPD
1=2
(11)
Solve the eigenvalue Z and eigenvector φ of the system state
coefficient matrix A,ϕ
1
Aϕ=Z;Z=diag[z
1;z
2;:::;z
n] (12)
The relationship between complex parameters considering
Laplace transforms and Z transform:S
i=
1
∆9
ln(z
i) (13) ∆
where, i=1, 2, 3, … , n, is the sample sampling interval.
Obtain modal parameters:8
>
<
>
:
w
i=Im(s
i)
5
i= Re(s
i)=js
ij
E
T
pPD
1=2
ϕ=Cϕ
(14) ϕ
where, wi is the i order natural frequency; ξi is the i order damping
ratio; is the mode matrix.
Through the ERA, the excitation and response of header frame
obtained from modal test can be effectively processed, and the
natural frequencies, damping ratio, and corresponding modal shapes
can be obtained.
The free modal test was to verify the accuracy of header frame
parametric modeling by comparing the results of free mode
calculation. In order to identify the modal parameters of the system,
the force hammer was used to excite the header frame, and the
acceleration sensor was used to pick up the response, which
provided the basis for the analysis of vibration characteristics of
structural system and the optimization design of structural dynamic
characteristics. There is a relationship between the excitation point
and the response point[28], i.e.:H
i j(!)=
N
∑
i=1
ϕ
riϕ
r j
m
r[(!
2
r !
2
)+j25
r!
r!]
(15) ϕ
riϕ
r j
where, Hij(ω) is the transfer function of the system; N is the total
order of the identified modes; is the r order mode shape at
points i and j; mr is the modal mass; ξr is the modal damping ratio;
ωr is the modal frequency.
In the test, in order to ensure that the rigid body modal of the
frame was less than 1/3 of the first elastic body modal, the header
frame was hoisted with soft rubber rope by means of three-point
suspension[29]. The test equipment consisted of computer, INV3018C
8-channel 24 bit high-precision data acquisition instrument (Beijing
Dongfang Institute, Beijing, China), LC-2D force hammer (Beijing
Dongfang Institute, Beijing, China), AY100I piezoelectric
acceleration sensor (Beijing Dongfang Institute, Beijing, China) and
DASP-10 modal analysis system (Beijing Dongfang Institute,
Beijing, China). The equipment connection is shown in Figure 3.
1
2
3 4 5 6
7
8
1. Header frame 2. Soft rubber rope 3. Lifting ring 4. Acceleration sensor
5. Signal transmission wire 6. Computer 7. Data acquisition instrument 8. Force
hammer
Figure 3 Equipment connection diagram
In order to avoid the additional mass effect and to decompose
the repetitive modes easily, the multi-input and multi-output
(MIMO) method was adopted in this test. LC-2D force hammer was
used to excite all measuring points of the whole structure. In order
to ensure high signal-to-noise ratio of the hammering signal, the
measuring points were arranged to reflect the overall shape of the
entity and reflect the external force acting point, structural
intersection point, and important response point. Finally, a
hammering model with 65 measuring points was established, as
shown in Figure 4.
15
21
35
36
49
48
37
34
22
23
33
38
47
46
39
32
24
25
52
31
40
45
26
27
2
60
61
62
63
64
44
4
41
165
5030
16
17
18
53
19
51
20
3
28
29
42
43
5
6
7
8
9
10
11
12
13
59
58
57
56
55
14
54
Figure 4 Measuring point model of header frame
The excitation signal of the force sensor on the hammer and the
response signal of the piezoelectric acceleration sensor were
April, 2023 Tang H, et al. Vibration analysis and topology optimization of the header of full-feeding rice combine harvesterVol. 16 No. 4 99
transmitted to the data acquisition instrument at the same time. The
time-domain signal was decomposed by the singular value of
Hankel matrix through the ERA, and the system matrix of the
minimum order was obtained, so as to identify the natural
frequencies and modal shapes of the structure. The test principle is
shown in Figure 5. Among them, the response point should not only
avoid the node but also be placed in a position easy to excite.
Finally, the piezoelectric acceleration sensors were arranged at 16,
24, and 38 points on the measurement point model of the rack as the
response point to receive signals.
Header frame
LC-2D force hammer
Performance index
Measuring range
Sensitivity
Linearity
AY100I piezoelectric accelerometer sensor
Performance index
Sensitivity
Maximum frequency
Resolution
100 mV/g
10000 Hz
0.0002
0-2 kN
INV3018C data acquisition instrument
Performance index Value
8
102.4 kHz
24A/D resolution
ComputerSignal analysis systemParameter identification system
Sampling frequency
Parallel channel
4 pC/N
<1%
Response signal
Value
Value
Excitation signal
Figure 5 Test schematic diagram
The first eight modal frequencies and modes of the collected
signals were extracted by Frequency Response Function (FRF)
calculation, impulse response function solution and ERA. In order
to verify the mode correlation of the test mode, the Modal
Assurance Criterion (MAC) was used for evaluation, and the mode
correlation matrix verification is shown in Figure 6. The first mock
exam is the correlation coefficient between two vectors. The MAC
value of the two vectors of the same physical mode is close to 1,
while the MAC value between the two vectors of the different
modes is relatively small, which indicates that the two modal
vectors are similar to the same mode[30]. It can be seen from the
figure that the correlation coefficient between the diagonal element
and its own mode was always 1, and the peak value of the non-
diagonal element was less than 0.3 of the threshold value of the
discriminant correlation degree, which indicated that the
orthogonality between the two vectors was good, the first eight
modes of the header frame were independent modes, the test
coherence was good, and the results of the modal test parameters
were reliable.
The j
th
of column of MAC
The i
th
of column of MAC
MAC%
100
30
Figure 6 Confidence matrix of modal test analysis
In order to compare the errors of frequency between finite
element free modal analysis and modal test, Equation (16) was
used.e=
jF
1 F
2j
F
2
100% (16) F
1 F
2
where, e is the error, %; is the frequency of finite element free
modal analysis, Hz; is the frequency of modal test, Hz.
2.2.4 Constrained modal analysis of finite element
Based on the accurate model of the header frame, it was
imported into ANSYS Workbench. According to the actual
constraint state of the header, the fixed boundary conditions were
set at the entrance of the tilt conveyor for finite element constrained
modal analysis.
2.3 Frequency of excitation source
When the external excitation frequency is close to or equal to
the restrained modal frequency of header frame, resonance will
occur[31]. Resonance leads to the transmission, expansion, and
radiation of vibration and noise on the machine, which seriously
affects the reliability and driving comfort. Under the action of local
mode or coupling vibration, it led to the deformation of the weak
part, stress concentration, and fatigue damage[32]. In addition, severe
vibration and grain contact led to a large area of header loss, which
affected the harvest effect. The engine, threshing cylinder, sieve,
and other working parts were installed on the main frame of the
combine harvester, whose vibration can be transmitted to the header
frame through the main frame. Exploring the factors that affected
the vibration of the header frame and analyzed its excitation
frequency, and the modal frequencies of each order of the header
frame avoided the external excitation frequency, so as to effectively
avoid the occurrence of resonance.
100 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4
1) The engine is the main vibration source of the combine
harvester. The vibration comes from the periodic gas pressure in the
cylinder and the inertia force produced by the reciprocating motion
of the crank. The calculation formula of the excitation frequency isf
1=
2nz
609
(17) n
where, f1 is the excitation frequency of engine, Hz; is the engine
speed, and its working speed is 2200-2400 r/min; z is the number of
engine cylinders; τ is the number of engine strokes. This machine
adopts an in-line four cylinder four stroke engine, so z is 4 and τ is 4.
2) The rotary motion of the working parts on the header can
also produce violent vibration, such as the rotation of the reel, the
rotation of the auger, the reciprocating motion of the cutter, etc., in
which the vibration of the cutter mainly comes from the rotary
motion of the spatial crank connecting rod slider structure[33], and the
excitation frequency is obtained by converting the crank speed of
the cutter. In addition, the rotating working parts that are in contact
with the combine frame can also transmit the vibration on the
frame, such as the threshing cylinder and the crankshaft of the sieve.
The rotating speed was measured by RM-1000 photoelectric
tachometer (Shanghai TES Electronics Co., Ltd., Shanghai, China).
The formula for calculating the excitation frequency of rotating
working parts isf
2=
n
60
(18)
where, f2 is the excitation frequency of rotating working parts, Hz; n
is the rotation speed, r/min. The rotation speed of reel is 40-55 r/min,
the rotation speed of the cutter crank is 400-450 r/min, the rotation
speed of the anger is 145-180 r/min, the rotation speed of the
threshing cylinder is 700-800 r/min, the excitation frequency of the
sieve is caused by the reciprocating motion, and the rotation speed
of the crank driving shaft of the sieve is 350-400 r/min.
3) The road conditions of the harvester are mostly rural roads
and paddy fields after drying, and the combine harvester has a good
vibration isolation effect by contacting the ground through the track
with small rigidity. Its excitation frequency is generally 0-3 Hz[34].
According to the resonance theory, resonance occurs when the
natural frequency of the structure has the following relationship
with the external excitation frequency[35], that is0:8f
c⩽f⩽1:2f
c (19) f
c f
where, is the natural frequency of the structure, Hz; is the
external excitation frequency, Hz.
2.4 Topology optimization of header frame
Taking the first-order and eighth-order frequencies as the
optimization objective and different mass fraction as the constraint
condition in ANSYS Workbench 18.0, topology optimization was
carried out. In the process of rice harvest, the pressure of screw
conveyor on rice was all acting on the floor. In topology
optimization, the material of floor was reserved, and the remaining
parts such as side walls, stiffeners and rear walls were taken as
optimization areas to explore the influence on the modal frequency
of header. In order to obtain a reasonable and reliable topology of
header frame, and to control the checkerboard phenomenon, avoid
small force transfer path and material accumulation, which makes
the complexity of the optimized configuration larger, three times of
the size when dividing the grid was taken as the minimum member
size, and six times of the size was taken as the maximum size. That
was, the minimum member size was 30 mm and the maximum
member size was 60 mm. The topology optimization model with
10%-90% mass fraction constraints is shown in Figure 7.
a. 10% b. 20% c. 30%
d. 40% e. 50% f. 60%
g. 70% h. 80% i. 90%
Figure 7 Topology optimization with different mass fraction constraints
If the density exceeds the set threshold value after optimization
iteration, no material will be displayed. Through the gradual
iteration of different mass constraints, it can reflect the influence of
specific structural position on the frequencies of header frame.
Figure 7 shows that the side walls of header frame first have a large
area of material deletion, which indicates that the side wall material
has a great influence on improving the frame frequency during the
optimization process. Some materials of the rear walls have also
been deleted, and then the rear wall material has a second effect on
the frame frequency after the side wall. In the mold reconstruction,
the addition and deletion of the side wall material and the change of
the rear wall material need to be considered.
In order to explore the change rule of strength and rigidity of
header frame after topology optimization under different mass
constraints, the static analysis and average frequency analysis were
carried out. Among them, the static analysis mainly checked the
strength and rigidity of the frame under different mass constraints.
The frame had its own gravity, and at the same time received the
gravity load of the components installed on it. There are still some
hydraulic pipelines and other auxiliary parts on the header, but the
mass of auxiliary parts can be ignored compared with that of other
parts. The volume of each part of header was obtained by Creo 2.0
software, and the mass of each part was obtained by material
density and converted into weight. The external load on the frame
was simplified as equivalent load and loaded to the corresponding
part of the frame, and the static simulation analysis was carried out.
The load on the frame and the loading mode are listed in Table 2.
2.5 Field experiment
In October 2019, a comparative field experiment of rice harvest
was conducted in the rice experimental area of Qing'an County,
April, 2023 Tang H, et al. Vibration analysis and topology optimization of the header of full-feeding rice combine harvesterVol. 16 No. 4 101
Suihua City, Heilongjiang Province. The experiment mainly
included two parts: one was to compare whether the vibration of
header frame decreases before and after optimization, and the other
was to determine whether the header frame increases the header loss
after optimization. The two experiments can be carried out at the
same time without mutual influence. The experimental area had flat
ground and upright rice without lodging. Longjing 29 was a rice
variety. Its natural properties were as follows: height was 73.3 cm,
1000 grain weight was 37.7 g, the ratio of grain to grass was 1.06,
moisture content of stem was 27.6%-32.4%, moisture content of
grain was 13.5%-16.6%, and there was no natural seed dropping.
The advance distance of each experiment was 200 m, and 10 m of
crops were reserved in front of the experiment area to ensure that
the harvester can work stably before entering the experiment area.
The height of header was 30 cm, and the engine speed was
2300 r/min to ensure that the operating parameters of all working
parts such as driving speed and reel speed were unchanged.
The field experiment is shown in Figure 8. Place the measuring
point near the excitation source of header frame prone to vibration
radiation, and use INV9832-50 acceleration sensor (Beijing
Dongfang Institute, Beijing, China) to collect the vibration
characteristics in X (forward direction), Y (left and right direction)
and Z (vertical direction)[36,37], and the position of the measuring
point is shown in Figure 9.
a. Working condition b. Regionalization
Figure 8 Field experiment
During the experiment, the sampling method was set as
continuous sampling, the sampling frequency was 2 kHz, the
analysis frequency was 625 Hz, the number of time-domain points
was 4096, the number of frequency-domain lines was 1600 and the
average number was 10.
The vibration signal of each measuring point was collected
three times, and a group of data with the best effect was taken for
analysis. The total vibration amount of each measuring point can be
expressed by the root mean square value of vibration acceleration[38].a=
É
a
2
x+a
2
y+a
2
z
3
(20)
where, a is the Root Mean Square (RMS) value of vibration
acceleration of each measuring point, m/s2; ax, ay, and az are the
peak values of vibration acceleration in X, Y, and Z directions of
each measuring point, m/s2.
In order to further verify whether the optimized header frame
increases header loss due to the sealing problem, two nylon mesh
bags were fixed on the rice stalk outlet and the tail of the cleaning
screen with bolts to collect the residue after straw crushing, so as to
eliminate the interference of threshing loss and cleaning loss and
ensure the accuracy of header loss measurement. By manually
picking up the grain weight and header loss of header frame before
and after optimization in an area of 20 m2[39], repeat the experiment
three times to get the average value.
3 Results and discussion
3.1 Vibration characteristics of header frame
Table 3 shows the comparison between the results of finite
element free modal analysis and free vibration modal test. The
results showed that the eighth-order modal shapes were consistent
and the natural frequency error was small. The main causes of the
errors were as follows: 1) the dynamic stiffness of the system was
increased to a certain extent by some welding spots on the header
frame, which was the main reason for the larger frequency error of
modal calculation; 2) In the initial stage of the model, the weight of
the pores had little influence on the model, and some accessories
such as bolts and damping materials were ignored; 3) The structure
discretization, iterative calculation, signal acquisition, and
processing all produced inevitable errors; 4) The header frame was
hoisted with soft rubber rope to ensure that the rigid body mode of
the frame was less than 1/3 of the first elastic body mode, which
was approximate to the free state but not the absolutely free state.
5) The header frame was large in volume, the impact force of the
Table 2 Load of header frame
Load Type Load level/NApplication position
Reel Concentrated force652 Side member left and right
Auger Concentrated force430 Stiffener left and right
Cutter Uniform force 284 Front end of floor
Transmission partsConcentrated force230 Side wall left
Table 3 Comparison between free modal analysis of finite element and free modal test
Order
Free modal analysis of finite element Free modal test
Error/%
Calculated frequency/Hz Vibration mode Test frequency/HzVibration mode
1 15.58 Local bending deformation of the floor 15.52 Consistent 0.39
2 27.23 Overall bending, vertical members deformation 26.44 Consistent 2.99
3 33.69 Overall bending, beams deformation 34.37 Consistent 1.98
4 37.77 Local bending of the floor, rear walls deformation 38.78 Consistent 2.60
5 42.37 Local torsional bending deformation of the floor 42.51 Consistent 0.33
6 56.63 Overall bending, Torsional Deformation of the floor and vertical members54.05 Consistent 4.78
7 58.79 Local bending deformation of the floor 60.26 Consistent 2.89
8 69.24 Local torsional bending deformation of the floor 71.37 Consistent 2.98
Left
view
Right
view
Bottom
view
7
5
1
3
6 42
8
Note: Measuring point 1 is 1/3 of the side wall left; Point 2 is 1/3 of the side wall
right; Point 3 is 1/2 of the stiffener left; Point 4 is 1/2 of the stiffener right; Point
5 is 1/2 of the rear wall; Point 6 is 1/3 of the rear wall; Point 7 is 1/2 of the floor;
Point 8 is 1/3 of the floor.
Figure 9 Measuring point position of header frame in
field experiment
102 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4
force hammer generating the excitation was relatively small, and
part of the energy transmitted from the excitation point to the
response point was seriously attenuated. However, within the
allowable error range, the established finite element parametric
model was accurate and reliable, which laid a foundation for further
finite element constrained modal analysis.
It can be seen from Figure 10, the frequency range of the eighth-
order constrained modal is 13.20-79.64 Hz, and the modal
frequencies of each stage are significantly different from those of
the free modal. Refer to the data in comparison Table 4 and Figure 9
for the difference. The constrained modal frequency can more
accurately reflect the vibration characteristics of the structure,
which was consistent with the research results of Chen et al.[40]
Because of the large size and small rigidity of the header of the
combine harvester, the constrained modal vibration mode mainly
showed the local torsion and deformation of the floor and side
walls. Since the outer edge of the header floor needed to be
connected with the cutter device, the failure to install the stiffener
leads to large deformation in the third, sixth, and seventh modal
shapes. While the side walls are in the weak link that crosses the
divider installation, resulting in local deformation. The fifth and
eighth modal shapes were the overall modal of the header frame.
Therefore, the side walls were the main part of the structural
vibration and radiated noise of the header, which should be
considered in the optimization and improvement.
In this study, the accuracy of the finite element model of the
header frame was verified by free modal analysis and free vibration
modal test, and the modal shapes and frequencies of the constraint
modal are solved at the same time. This method can provide a
beneficial reference for accurately obtaining the natural frequency
of the constraint state when solving structural vibration
characteristics.
16.079 Max
14.293
12.506
10.720
8.933
7.1464
5.3598
3.5732
1.7866
0.00
250.00 750.00
a. First-order modal shapes
(13.20 Hz)
b. Second-order modal shapes
(36.07 Hz)
c. Third-order modal shapes
(41.12 Hz)
d. Fourth-order modal shapes
(51.59 Hz)
e. Fifth-order modal shapes
(59.15 Hz)
f. Sixth-order modal shapes
(65.17 Hz)
g. Seventh-order modal shapes
(68.21 Hz)
h. Eighth-order modal shapes
(79.64 Hz)
Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00 Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00 Y
X
Z
Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00
500.00 1000.00 (mm)
0 Min
20.739 Max
18.435
16.130
13.826
11.522
9.2173
6.913
4.6087
2.3043
0 Min
21.174 Max
18.821
16.469
14.116
11.763
9.4106
7.0579
2.3526
4.7053
0 Min
12.575 Max
11.178
9.7804
8.3832
6.9860
5.5888
4.1916
1.3972
2.7944
0 Min
6.7526Max
6.0023
5.2520
4.5017
3.7514
3.0012
2.2509
1.5006
0.75029
0.00
250.00 750.00
Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00
Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00
Y
X
Z
Y
X
Z
500.00 1000.00 (mm) 0.00
250.00 750.00
500.00 1000.00 (mm)
0 Min
22.298 Max
19.821
17.343
14.866
12.388
9.9103
7.4328
4.9552
2.4776
0 Min
23.546 Max
20.930
18.313
15.697
13.081
10.465
7.8486
2.6162
5.2324
0 Min
5.3678 Max
4.7713
4.1749
3.5785
2.9821
2.3857
1.7893
0.59642
1.1928
0 Min
Figure 10 Constrained modal shapes and corresponding frequencies
Table 4 Frequency excitation source
Excitation source Frequency/Hz
Engine 73.33-80
Reel 0.67-7.50
Cutter 6.67-7.50
Auger 2.42-3
Threshing cylinder 11.67-13.33
Sieve 5.83-6.67
Ground 0-3
3.2 Resonance analysis with multi-source excitation
The frequency of each excitation source is listed in Table 4.
When the frequency of the excitation source was close to the natural
frequency of each stage of the header frame, resonance occurred.
According to the analysis of the excitation source of the header,
the first-order modal frequency was 13.20 Hz, which was in the
range of 11.67-13.33 Hz of the threshing cylinder, and they are
prone to resonance. The eighth-order modal frequency was 79.64 Hz
in the range of 73.33-80.00 Hz of the engine, and they were prone
to resonance. Therefore, it was necessary to optimize the header
frame, improve its first and eighth order modal frequencies to avoid
the excitation frequency of the threshing cylinder and engine, and
ensure that other modals do not have frequency exchange
phenomenon to avoid resonance effectively.
Due to the different materials used in the working parts and the
non-circular rotation caused by the wear between the contact
surfaces of the rotating parts, the vibration will increase. When the
excitation sources work at the same time, some non-rotating parts
will vibrate. These vibrations have a certain frequency. When the
vibration frequency is coupled with the natural frequency of the
header frame, they will also become the excitation sources of the
header frame. The interaction of the excitation sources is complex,
and cannot be directly obtained by calculation or test, and the
contribution of vibration is different. In the later stage, we will carry
out the blind source identification and analysis of the excitation
force by using the principal component analysis method, and focus
on the influence of the signal-to-noise ratio, the distribution of
measuring points, and the number of measuring points on the
principal component power spectrum, contribution rate, cumulative
contribution rate and the number of excitation sources, in order to
get the primary and secondary relationship between the coupling
effects of various excitation sources.
3.3 Analysis of topology optimization results
3.3.1 Static analysis of different mass fraction constraint
The maximum stress under different mass fraction constraints
is shown in Figure 11, and its maximum stress directly reflects the
strength of header frame. The regression equation in Figure 10 is
used to analyze and predict the relationship between maximum
April, 2023 Tang H, et al. Vibration analysis and topology optimization of the header of full-feeding rice combine harvesterVol. 16 No. 4 103
stress and removal. R2 represents the overall fit of the regression
equation. The maximum value of R2 is 1. The greater R2, the better
the fitting degree of the regression equation. With the increase of
the mass fraction constraint in the process of topology optimization,
the maximum stress tended to stabilize first and then increase.
Because the various reinforcement beams of the header frame
played a skeleton and load-bearing role, the side walls and the rear
walls were not effective areas for carrying working parts. When the
mass fraction constraint was from 10% to 50%, only the side walls
and the destruction of some materials from the rear walls do not
cause damage to various skeleton beams, resulting in a steady trend
in the maximum stress and a small increase, which did not affect the
overall strength of the structure. When the mass fraction constraint
was greater than 50%, the maximum stress growth trend increased
obviously. When the mass fraction constraint was 60%, the
maximum stress was 240.9 MPa, which exceeded the allowable
stress 235 MPa of the frame. The side members and beams of the
header frame were damaged one after another and sharp openings
appeared, resulting in stress concentration. The larger reel load and
anger were respectively loaded on the side members and stiffeners,
the header frame as a whole cannot bear its pressure, and the
strength cannot meet the requirements.
600
500
400
300
Maximal stress/MPa
200
100
0
10 20
74.378.1 80.697.2
135.0
240.9
324.0
403.1
506.7y=8.606x
2
−30.475+95.395
R
2
=0.9919
30 40
Reduce the mass fraction of materials/%
50 60 70 80 90
Figure 11 Maximum stress under different mass
fraction constraint
The maximum deformation under different mass fraction
constraints is shown in Figure 12, and its maximum deformation
directly reflects the rigidity of header frame. With the increase of
the mass fraction constraint in the process of topology optimization,
the maximum deformation tends to stabilize first and then increase.
The maximum deformation occurs in the large area of the floor
when the fraction constraint was in the range of 10%-50%, mainly
because the width of the header floor was large and the skeleton
beam was small, the frame structure of the header damaged in this
stage does not involve the header floor, and its deformation tended
to small and steady rise. When the fraction constraint was more than
50%, the deformation began to increase significantly. The
maximum deformation was transferred from the header floor to the
side walls, mainly because the side members and other supporting
frame beams were damaged one after another. Because the reel was
mainly loaded on the left and right sides of the side members, the
side walls installed at the lower part of the side members with less
rigidity were deformed greatly, while the anger installed at the left
and right sides of the stiffeners is deformed greatly. As the mass
fraction constraints continue to increase, the removal of materials
increased, and its side members, beams, and vertical members were
damaged more seriously. The whole header frame can no longer
bear the load of reel, anger, and other working parts without the
support of framework beam, resulting in the deformation increased
to the header frame loss of bearing and protection capacity, and the
rigidity can no longer meet the requirements. So when the mass
fraction constraint was more than 50%, it was not the best reference
for topology optimization. 14
12
10
6
8
Maximal deformation/mm
4
2
0
10 20
0.29
0.430.61.04
1.48
2.72
5.07
9.81
11.86y=0.2955x
2
−1.5372+2.03
R
2
=0.9783
30 40
Reduce the mass fraction of materials/%
50 60 70 80 90
Figure 12 Maximum deformation under different mass
fraction constraint
3.3.2 Frequency analysis of different mass fraction constraint
The first and eighth order frequencies under different mass
fraction constraints are shown in Figure 13. With the increased mass
fraction constraint in the process of topology optimization, the first
and eighth order frequencies tended to increase. In this stage, the
material of the side walls and the rear walls were mainly removed.
Because the side walls and the rear walls were the non-structural
concentrated mass that can protect the rice from leakage. With the
decrease of the non-structural concentrated mass, the modal
frequencies increased gradually.
200
180
160
140
120
Frequency/Hz
100
80
60
40
20
0
10 20
13.7514.2216.73 17.1018.3221.4426.05
33.73
42.68
173.7
157.59
133.49
116.14
103.62
93.06
y=0.5973x
2
−2.6855x+17.183
y=1.5415x
2
−3.6574x+83.983
R
2
=0.9823
R
2
=0.9968
87.87
First order frequencyEighth order frequency
84.11
81.02
30 40
Reduce the mass fraction of materials/%
50 60 70 80 90
Figure 13 First and eighth order frequencies under different mass
fraction constraint
According to the excitation frequencies of threshing drum and
engine, the first and eighth natural frequencies of header frame need
to be greater than 16.66 Hz and 100 Hz, respectively. It can be seen
from Figure 12 that the first-order natural frequency of the header
frame need to meet 40% of the mass of the removal optimization
area, and the eighth-order natural frequency needs to meet 50% of
the mass of the removal optimization area to avoid resonance.
Considering synthetically the strength, rigidity, average
frequency, and other indexes of header frame after topology
optimization, processing and manufacturing factors, and the
closeness of the working state of header floor, the topological
configuration was geometrically repaired by analyzing its density
distribution nephogram, and the topological structure was restored
in the working environment of CATIA_V5_R20. Based on 50% of
the mass fraction constraint, A trapezoidal hole with an upper
bottom of 250 mm, a lower bottom of 400 mm, and a height of
250 mm shall be opened on the side walls. In order to prevent the
rice after harvesting from leaking out, a stiffener with a width of
10 mm shall be installed inside the opening. A hexagon groove with
a length of 35 mm and a width of 10 mm shall be opened on the two
rear walls, In order to avoid the fatigue damage caused by stress
concentration, the edges of the opening are all rounded. The
reconstructed header frame is shown in Figure 14.
3.4 Comparison of results before and after optimization
In order to verify the optimization effect of the reconstructed
header frame model, ANSYS Workbench 18.0 was used to carry
out static and modal analysis of the header frame before and after
the optimization, as listed in Table 5.
104 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4
Table 5 Performance comparison of header frame before and
after topology optimization
Optimization
situation
Mass/
kg
Maximum
stress/MPa
Maximum
deformation/mm
Before optimization96.16 70.6 0.37
After optimization82.53 128.6 0.42
Topology optimization aims at increasing the average
frequency and taking into account the lightweight design. Its quality
was reduced by 14.17%. Because the maximum stress and
maximum deformation of header frame will inevitably increase
after material removal, the maximum stress of 128.6 MPa was far
lower than the fatigue failure stress of 235 MPa, which met the
strength requirements. The maximum deformation of 0.42 mm still
belonged to the small deformation category and meets certain
rigidity requirements. The modal analysis was carried out. The
eighth-order restrained modal frequencies and modes are shown in
Figure 15.
The range of the 8-order constrained modal frequencies were
17.83-101.59 Hz after optimization, and the main vibration modal
shapes were the local torsion and deformation at the installation of
the header floor cutter. Because of the hole structure in the rear
walls, the mass and stiffness distribution change, which led to the
whole rear walls and had no vibration displacement. Before
optimization, the side walls with large vibration displacement also
have obvious improvement. The first three modal shapes had a great
influence on the overall structure and did not have vibration, and the
maximum displacement of the fourth modal shape was only 0.11 mm.
The eighth-order modal shapes behaved as the overall mode before
optimization, while the overall mode changed to the local mode
after optimization, and the overall performance was better than that
before optimization.
0.50841 Max
0.45192
0.39543
0.33894
0.28245
0.22596
0.16947
0.11298 0.000 0.500
0.250
a. First-order modal shapes
(17.83 Hz)
e. Fifth-order modal shapes
(61.36 Hz)
f. Sixth-order modal shapes
(67.97 Hz)
b. Second-order modal shapes
(36.51 Hz)
g. Seventh order modal shapes
(72.38 Hz)
c. Third-order modal shapes
(43.05 Hz)
h. Eighth-order modal shapes
(101.59 Hz)
d. Fourth-order modal shapes
(54.08 Hz)
0.750
1.000 (m) 0.000 0.500
0.250 0.750
1.000 (m)X
Z
Y
X
Z
Y
0.056491
0 Min
0.66612 Max
0.59211
0.51810
0.44408
0.37007
0.29605
0.22204
0.14803
0.074014
0 Min
0.000 0.500
0.250 0.750
1.000 (m) X
Z
Y
0.66895 Max
0.59463
0.52030
0.44597
0.37164
0.29731
0.22298
0.14866
0.074328
0 Min
0.000 0.500
0.250 0.750
1.000 (m) X
Z
Y
0.48604 Max
0.43204
0.37803
0.32403
0.27002
0.21602
0.16201
0.10801
0.054005
0 Min
0.65297 Max
0.58041
0.50786
0.43531
0.36276
0.29021
0.21766
0.14510 0.000 0.500
0.250 0.750
1.000 (m) 0.000 0.500
0.250 0.750
1.000 (m)X
Z
Y
X
Z
Y
0.072552
0 Min
0.74613 Max
0.66322
0.58032
0.49742
0.41451
0.33161
0.24871
0.16581
0.082903
0 Min
0.000 0.500
0.250 0.750
1.000 (m) X
Z
Y
0.34083 Max
0.30296
0.26509
0.22722
0.18935
0.15148
0.11361
0.07574
0.03787
0 Min
0.000 0.500
0.250 0.750
1.000 (m) X
Z
Y
0.74632 Max
0.66340
0.58047
0.49755
0.41462
0.33170
0.24877
0.16585
0.082925
0 Min
Figure 15 Constrained modal shapes and corresponding frequencies after optimization
It can be seen from Table 6 that after optimization, the
frequencies of each order were improved to different degrees,
among which the first and eighth order modal frequencies were
obviously improved, from 13.75 Hz and 81.02 Hz to 17.83 Hz and
101.59 Hz, respectively, increasing by 35.08% and 27.56%. The
results indicated that the topology optimization effect was
significant. The first and eighth order natural frequencies before
optimization were within the excitation frequency range of
threshing cylinder and engine respectively, which were easy to
resonate. The first and eighth natural frequencies were far away
from the excitation frequency range of threshing cylinder and
engine, other modal frequencies did not exchange and were far
away from the range of excitation frequencies, which showed that
the resonance was effectively avoided after topology optimization.
In this study, the vibration characteristics of the header frame
were studied and the excitation frequencies were far away from the
threshing cylinder and the engine to reduce the resonance. By
analyzing the vibration characteristics of the excitation source,
blocking the vibration transmission or optimizing the structure of
the excitation source to keep its frequencies far away from the
natural frequencies of the research object, the resonance can also be
avoided. For example, the engine was the main source of excitation
that affects the vibration of the tractor[41], and the transmission of the
unbalanced inertia force of the engine on the tractor can be
effectively reduced by installing a vibration isolator between the
tractor engine and the chassis[42,43]. In addition, the topology
optimization method is used to optimize the header frame to reduce
resonance and realize lightweight design, which provided
lightweight design basis for reducing the vibration of header frame,
and provide reference for other types of machinery in the field of
agricultural machinery to reduce weight and vibration. Some
scholars got the optimal structure through the combination of multi-
objective topology optimization such as stiffness and frequency, and
Table 6 Natural frequencies comparison before and after
optimization
Order
Before
optimization/Hz
After
optimization/Hz
Variation/Hz
Variation
ratio/%
1 13.20 17.83 4.63 35.08
2 36.07 36.51 0.44 10.22
3 41.12 43.05 2.39 5.81
4 51.59 54.08 2.49 4.83
5 59.15 61.36 2.21 3.74
6 65.17 67.97 2.80 4.30
7 68.21 72.38 4.17 6.11
8 79.64 101.59 21.95 27.56
Figure 14 Reconstructed header frame model
April, 2023 Tang H, et al. Vibration analysis and topology optimization of the header of full-feeding rice combine harvesterVol. 16 No. 4 105
the combination of topology optimization and shape optimization,
and other optimization methods had also achieved good
optimization results[44-47]. In the later stage, based on the multi-
objective topology optimization, combined with a variety of
optimization methods, we will focus on the research of weight
reduction and vibration reduction of key components of combine
harvester, in order to broaden new optimization channels and
methods for key components of agricultural machinery.
3.5 Results of field experiment
The peak value and RMS value of vibration acceleration in
three directions of each measuring point are listed in Table 7.
Table 7 Peak acceleration comparison of field experiment
before and after optimization
Measuring
point
Before optimization After optimization
Peak vibration
acceleration/m s–2
RMS/
m·s–2
Peak vibration
acceleration/m·s–2
RMS/
m·s–2
X Y Z X Y Z
1 12.3219.1210.8614.559.3213.727.7510.57
2 12.7718.5510.9114.459.6214.438.1311.06
3 9.6213.299.4910.944.325.775.165.12
4 9.4112.809.6710.744.485.684.985.07
5 26.4523.8721.9924.176.008.836.307.16
6 23.1418.7620.4720.875.548.745.916.88
7 4.425.868.676.563.443.566.624.77
8 4.015.497.575.873.513.275.234.10
In the field experiment, because of the good soft damping
effect of paddy field and the good vibration isolation effect of wide
track wheel, the random excitation of the ground had little effect on
the header frame, which can be ignored. It can be seen from Table 7
that the peak value of vibration acceleration before optimization
was relatively large in all directions, and the RMS value of
vibration acceleration at measuring point 5 was 24.17 m/s2. Mainly
due to the resonance phenomenon caused by the vibration coupling
between the excitation frequency of the engine and the threshing
cylinder with large load and the natural frequency of the header
frame. The header frame was an axisymmetric mechanism, and
measuring points 1 and 2 showed that there was little difference in
the peak value and the RMS value of vibration acceleration in the
three directions of X, Y, and Z when measuring points are arranged
symmetrically on the left and right side walls. The peak value in Y
direction was significantly higher than that in X and Z directions,
which indicated that the inertia force of the cutter still affect the
vibration in Y direction close to the cutter even if the reciprocating
motion of the cutter does not cause resonance of the header frame. It
cannot be avoided after optimization, which was a common
problem of the reciprocating cutter. The effect of Y direction
vibration can be reduced by adding appropriate control parameter
balance block on the crankshaft[48]. Measuring points 3 and 4 were
placed at the stiffeners on the left and right sides. Since the
stiffeners were fixed on the side walls of header frame, they were
equivalent to the thickened side walls, and their overall vibration
acceleration peaks were smaller than the side walls. The rear walls
were obviously affected by resonance. Since 1/2 of the rear walls
were longer than 1/3 of the rear walls from the fixed position of the
framework, the overall vibration of measuring point 5 was greater
than that of measuring point 6. Measuring points 7 and 8
respectively measured the vibration acceleration of the floor of the
header frame, and the peak value was smaller than that of other
measuring points. The reason was that in the experiment, the
feeding rate was uniform at the normal harvesting speed, the load
fluctuation was small, and the rice was filled with the gap between
the screw pusher and the bottom plate, resulting in the rice
absorbing part of the vibration. After topology optimization, the
peak value of vibration acceleration and the RMS value of vibration
acceleration of each measuring point were reduced to different
degrees. The RMS values of vibration acceleration of measuring
points 5 and 6 with obvious vibration are reduced by 70.38% and
67.03% respectively, and no violent vibration occurred in the
harvesting process. Field experiment showed that topology
optimization can effectively reduce the amplitude of header frame
and avoid resonance.
Before optimization, the grain yield was 36.28 kg, the header
loss was 303.64 g, and the header loss rate was 0.83%. After
optimization, the grain yield was 34.60 kg, the header loss rate was
268.49 g, and the header loss rate was 0.77%. The results showed
that the optimized header frame does not increase the header loss. It
was possible that because the rated engine speed of combine
harvester is forward and its feeding amount was uniform, a large
amount of straw after harvesting by cutter was intertwined with
each other under the action of screw conveyor and telescopic finger,
which can form a certain protection for rice panicle head and do not
thresh at the header. The small-scale hole digging design of header
side wall and rear mounting plate do not cause grain leakage and
increase header loss.
When the natural properties of crops are the same, header loss
is mainly related to cutter speed, reel speed, travel speed, etc. The
fully-feeding rice combine harvester adopts the reciprocating cutter.
The cutting speed of this kind of cutter is small, which will cause
the rice straw with small rigidity to be pushed down or missed and
the straw to tilt and shake, resulting in a large header loss[49], and the
cutting distance is generally controlled at 60-80 mm during the
working. When the speed of the reel is high, the impact on the ear
of the crop will be intensified, resulting in a sharp increase in header
loss, and the speed ratio of the reel is generally 1.5-1.6[50]. Therefore,
in the design of header loss verification experiment, it is necessary
to ensure that the engines of each group of tests work at rated speed
and keep consistent so that the cutter speed, reel speed, and
traveling speed reach the best, the inconsistency of working
parameters of working parts shall be avoided to interfere with the
verification of header frame sealing and affect the experiment
results.
4 Conclusions
Based on the analysis and optimization of the vibration
characteristics of the header frame, the research conclusions were as
follows:
1) The natural frequency and external excitation frequency of
the header were analyzed. The first-order modal frequency of the
header frame was 13.20 Hz within the range of 11.67-13.33 Hz of
the excitation frequency of the threshing drum, and the eighth order
modal frequency was 79.64 Hz within the range of 73.33-80 Hz of
the engine excitation frequency, which was prone to resonance.
2) The optimized header frame met the strength and stiffness
requirements, and the first and eighth modal frequencies were
increased by 35% and 22.5% respectively, avoiding resonance.
3) After optimization, the mass of header frame was reduced by
14.17%, and the root mean square values of vibration accelerations
at measuring points 5 and 6 were reduced by 70.38% and 67.03%
respectively. This study provides an effective reference for weight
reduction and vibration reduction of the header frame of rice, wheat,
106 April, 2023 Int J Agric & Biol Eng Open Access at https://www.ijabe.org Vol. 16 No. 4