Sewing machine shops in chennai - VS Sewing Machines
The whole system mainly include the power supply module, PMSM, magnetic encoder, central control unit, detection and
protection circuit and a few other auxiliary control parts. The
hardware block diagram is shown as the figure 1. In order to
enhance the control accuracy and processing speed, two 32-bit
microcontrollers uPD70F3184 produced by NEC Corporation of
Japan are used as the core-controller of the control board and the
signals processor of the magnetic encoder, respectively. After
digital difference and error correction the absolute magnetic
encoder has a very high precision[5]. The core-controller realizes
input-output function and motor control function. In the corecontroller, a full-digital design method is adopted to implement
the close-loop control of PMSM, including current loop, speed
loop and position loop[7]. Most of the control function can be
achieved by software instead of hardware, so can reduce the cost
of industrial sewing machines driving control system.
Switching
Power Supply
Driver Circuit
Rectifier
Protection
U nits
I P M M o d u le P M S M
Magnetic
Encoder
Power
G r id
C o re -controller
Current
D ecetion
S C I
A D I/O
Fig. 1 Hardware block diagram
CONTROL SYSTEM STRUCTURE
A. Mathematic model of PMSM
Sine-wave PMSM most commonly used method of analysis is
the rotating d-q coordinate mathematical model. The model not
only can be used for analyzing the motor’s steady performance,
can also be used to analysis the dynamic performance of the
motor. In the drive control system it is used to estimate the
motor’s speed and the position of the magnetic pole. The stator
voltage and flux equations of PMSM in the rotating d-q
coordinate are given by:
⎪
⎪
⎩
⎪
⎪
⎨
⎧
+ Ψ +
Ψ
=
− Ψ +
Ψ
=
e d s q
q
q
e q s d
d
d
R i
dt
d
u
R i
dt
d
u
ω
ω
(1)
Position Control of PM Synchronous Motors Used
for Sewing Machines Based on High Accuracy Magnetic Encoder
Hongqin Xie
1
, Kai Yang2
, Dadai Lu3
State Key Laboratory of Advanced Electromagnetic Engineering and Technology
Huazhong University of Science and Technology
Wuhan, 430074, R.P.China
E-mail: hongqin125@126.com
⎩
⎨
⎧
Ψ = Ψ = + Ψ
d q q
d d d f
L i
L i
(2)
where ud, uq, id and iq are the stator voltages and currents,
respectively, Rs is the stator resistance, Ld and Lq are the d-q axis
stator inductances, respectively, Ψd and Ψq are the d-q axis stator
magnetic flux, respectively, ωe is the electrical angular velocity,
Ψf is the rotor flux.
For the surface-mounted PMSM studied by the paper, the Ld
equals to the Lq. So the electromagnetic torque equation is
e n f q 2
3 T = P Ψ i Sewing machine shops in chennai
(3)
where Pn is the pole pairs.
The mechanical equation of the PMSM is described as:
e
e
e ω
ω
− = + RΩ dt
d T T J
L
(4)
where J and RΩ are the inertia and the friction coefficient of the
motor, respectively, Te and TL are the electromagnetic torque and
the load torque, respectively.
B. Structure of the control system
Fig.2 shows the various components of the control system,
including PI, Park, IPark, Clark module and so on. The udc comes
from the single-phase rectifier bridge[8]. In the position loop, a
negative feedback and a proportional regulator is used in order to
get a rigidity position control without overshoot. In the speed
loop, a negative feedback of the motor’s speed and a PI regulator
is used. The output of the speed regulator is the reference current
value. The classical PI control strategy is used in the current
loop[9]. Before entering PI module the calculated actual speed and
the currents should go through low-pass filter, reducing highfrequency interference. For a PMSM there are several strategies
to calculate the d-axes and q-axes currents. In the article a vector
control method on the basis of zero d-axes current is adopted to
get a maximum torque current ratio.
Inverter SVPW
M
P I
d/d t Park
P M S M Magnetic
Encoder
IPark
iqre f
idre f =0
ud c
iq
id
ia
ib
ic
iα
iβ
θ ωe θ
*
udre f uαre f ━ ━ ━ uβre f ━
θ
P P I
P I
Clark
ω uqre f *
e
Fig. 2 Structure of the Control System
C. Magnetic encoder module
The structure of the improved magnetic encoder is shown as
the figure 3. It mainly includes the alnico, the soft magnetic
ferrite and the Hall elements, etc. A pair of permanent magnets, which are placed in the alnico symmetrically and rotate
following the motor, are the sources of the angle signals. The
soft magnetic ferrite is used to reduce the flux leakage, makes
sure the internal magnetic field is more uniform and
concentration. The six channels voltage produced by the Hall
elements are divided into three groups as shown in the figure.
After digital difference, the value scope of the samples is
expanded and the system error by installation is reduced.
N
S
x
y
Hallelement
A ir G ap
So ft
Magnetic
Fe rrite
Aln ic o
A+
A- B+ BC+
CFig. 3 Structure of the Magnetic Encoder
The signal processing part of the magnetic encoder is given in
figure 4. The core-controller communicates with the processor of
the magnetic encoder for the motor’s real-time speed signal. After getting the order of the core-controller, the processor starts
AD converter to sampling the voltages, which are from the Hall
elements. https://vssewingmachine.in/ Then it matches the samples values with the standard
table, prepared in its storage, to gain the speed signal and
feedback the result to the core-controller.
Hallelements
Computing
U nit
A D
Converter S C I Co r e -controller
Signal Processor
Six
Channels
Voltage
Sta rt-u p
A D
Digital
Voltage
Signal
Results Ord e rs
Re a l-time
Sp e e d
Signal
So u rce Control
Board
Fig. 4 Signal Processing Part of the Magnetic Encoder
Fig.5 shows the program flow chart of the magnetic encoder, which is compiled according to the working process above. As
can be seen from the chart, the basic idea of the program is that
the signal processor makes different responses depending on the
various instructions given by the core-controller.
Initialization
Receive the
Instructions ?
Static AD
Sampling
Sampling Voltages and
Calculating Sp e ed
Case 1: Sta rt-u p
A D ?
Case 2: Req u ire the
Re a l-time Sp e e d ?
Send Real-time
Sp eed
Default: Send Error
Y e s
N o
Start
Fig. 5 Program Flow Chart of the Magnetic Encoder
Fig.6 shows the photo of the drive control system. With this
system several experiments are carried out to test the control
performance of the system.
Fig. 6 Photo of the Drive Control System
A. Angle detection of the magnetic encoder
Angle calculation module, one the most important part of the
magnetic encoder, is used to gain the position and speed signals
of the motor serving the drive control system. The main idea of
the computational procedure is that the divide the whole interval
into six parts and set an Angle as the base value in each small
interval. These Angles are 0 degrees, 60 degrees, 120 degrees, 180 degrees, 240 degrees, 300 and degrees. Look up the standard
table to get an offset angle value using the AD samples values as
the offset address. The actual machinery angle is the sum the
offset angle value and the base value of this small interval. In
accordance with the method above, getting the actual angle
waveform from the magnetic encoder is shown in figure 7.
Fig. 7 Actual Angle Waveform
The horizontal ordinate is the value of angle changing from 0
to 65535. The vertical coordinate is the digital samples values of
the voltages outputted by the three groups Hall elements. As
shown in the figure, the results are very good sine curves. But
distortion of the shape is still existent in some points. It will have
an unfavorable effect on the control performance of the system.
B. Performance of starting current
The control system adopts PM+ of NEC Company as the
software design platform. This design platform can not store data
online, also can not generate dynamic diagram. So to watch the
motor’s dynamic speed waveform directly becomes troublesome.
This experiment studies the motor’s start procedure with the
starting current waveform. Reference speed is 4000 rpm, starting
with the rated load (1.2 N·m). The observation of the starting
current curve on the oscillograph is given in Fig.8.
Fig.8 Starting Current Curve Fig.8 shows that the current transition process holds about
0.134s. In this period, its magnitude is almost 1.5 times the value
of the following steady-state current. When the motor runs stable,
the cycle and amplitude of the current keep constant primary. The current curve above indirectly reflects the starting process of
the motor and speed control performance of the system.
C. Performance of steady-state current
Fig.9 gives the waveform of a steady-state phase current
observed by an oscilloscope.
Fig.9 Steady-state Phase Current Curve The figure above shows that the current’s amplitude and
frequency are constant. The waveform is of a better sinusoidal
property. The motor could go with a steady operation and the
speed fluctuation is small. The control system basically achieves
the expected control performance. At the same time the current
waveform still contains much burr, because the signals of the
magnetic encoder are not precise enough and the influence of the
disturbance is inevitable in the current detection scene. Therefore,
it is very important to enhance the filtering on feedback signals
and improve the precision of the magnetic encoder for the future
work.
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