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Application Case in Machinery Industry
Case I
Application of Senlan Inverter in Planer Type Miller
I
General
The planer type miller is a type of equipment machining large scale workpieces, and its
electrical control system includes the main drive of work bench and the logic control of
feed mechanism. Jiaozuo Maike Metallurgical Machinery Co., Ltd. has a set of planer
type miller, which has been used for many years since 1970s. The main drive for the
work bench of the planer type miller is with DC reversible speed control drive mode.
However, original DC speed control system has been obsolete, so it is impossible to
carry out replacement for the DC speed control system, and it is inevitable to carry out
technical transformation.
II
Transformation Solutions
In regard to transformation of DC speed control system, if the DC motor is remained, the
speed control system can be with digital silicon controlled DC speed control system such
as Eurotherm 590A, Siemens 6RA70, and ABB DCS400 etc. The advantages of this
solution lie in original DC motor is utilized for economy saving, but it also has obvious
weakness, which is the DC motor, compared with AC async squirrel cage motor, requires
more maintenance work. Especially for this DC motor used for many years, its
commutator wears a lot, so the maintaining cost is higher.
Another solution is to use AC speed control system, the main drive DC motor is changed
as AC async squirrel cage motor, and the speed control system is with inverters. The
weakness of this solution is high transformation cost because it not only requires to use
inverters, but requires to change DC motor as AC motor. However, AC motor has simple
structure and small amount of maintenance, and the inverter has good performance and is
easy for optimum control. By comparison between two solutions, the transformation
solution of AC speed control is selected.
III Frequency-conversion Transformation of Planer Type Miller
1.
Model Selection of Inverter and Capacity Calculation
The model selection of inverters shall be carried out depending on capacity of AC
motor, which shall be selected based on DC motor. The DC motor of original work
bench has following parameters: PN=18.5kW, nN=1000r/min; and the parameters of
appropriate AC motor: PN=18.5kW, nN=970r/min. The planer type miller often
works at low-speed machining status, so it is required the motor has a big torque at
low speed in order to ensure machining quality. Considering the mechanical
properties of AC motor, an appropriate bigger capacity shall be selected as selecting
AC motor. In this case, the AC motor shall be 22kW 6-phase squirrel cage motor.
The SB61G+ inverter produced by Hope SenLan Science & Technology Holding
Corp., Ltd. is selected. Considering the short return travel time and big inertia of the
work bench for miller, it is required to configure braking unit and resistor, and the
braking resistor is with standard configuration of 30Ω, 5kW based on 100% braking
torque; and considering frequent braking, the resistor capacity is appropriately
increased to 10kW.
2.
Setting of Inverter Functions
1
From the process flow of the planer type miller, we can know: the work bench
includes four stages of travel speeds, i.e. n1, n2, n3 and return travel speed. It is
assumed that the SB61G+22KW is with multi-stage speed control manner, and its
input terminals for multi-stage frequency control are X1, X2, X3, and X4; the
frequency value of multi-stage speed is determined by the workpiece machined, and
the time of speed increasing and decreasing is determined by F009, F010, and
F631-F636; and, its control signal is from contactless switch of the miller, so the
inverter will carry out speed-increasing, speed-decreasing, reverse, or
constant-speed traveling only if the work bench of the miller moves to
corresponding location and the output signals sent from contactless switch is
transmitted to corresponding input ports of the inverter.
3.
Application of PLC
Due to aging of control lines and low-voltage components, the work bench of
planner type miller is not only subject to frequency-conversion speed regulation
transformation for its main drive, but to transformation for its control lines. The
PLC can greatly reduce complexity of control circuit lines and can reduce cost. The
HOLLIAS-LEC G3 40-point PLC is selected, and the programming method is
ladder diagram. This is not complicate, no more descriptions.
Case II
Application of Senlan Inverter in Vertical Lathe
I
General
One unit has one set of C516A single-column vertical lathe. Through yield investigations,
the drive system of the original lathe is with one 30 KW motor as main drive, which runs
at constant speed and realizes speed regulation through reduction gearbox and hydraulic
system. The system cannot realize stepless speed regulation, so the maintaining work
amount of the hydraulic system is big.
II
Frequency-conversion Transformation Solution for Hydraulic System of Lathe
Due to it is very difficult to maintain original hydraulic system, we can remove it and
directly use inverters to drive the spindle motor, and then we can continuously regulate
speed by regulating motor frequency. However, the lifting-lowering of the beam and
moving of knives depend on original hydraulic system, so it cannot be removed
completely. If the hydraulic system is required to be removed completely, a drive async
motor shall be provided for the beam and knives. The following requirements shall be
met to ensure reliable operation of lathe in this transformation.
1.
Requirements for Motor
In general, it is required to use frequency conversion motor, or use ordinary motor
plus fan to meet heat dissipation requirements of the motor at low frequency, and
the motor shall be with a wide range of speed regulation.
2.
Technical Requirements for Inverter
1)
Big Torque at Low Frequency
When the lathe operates at low speed, strong overload capacity is required. The
inverter can provide 150% overload protection and can meet equipment
requirements. The vector inverter, able to reach 150% rate torque at low
frequency (1-10Hz), is selected.
2
2)
Fast Dynamic Response Speed of Torque and High Accuracy at Stable Speed
The vector inverter is selected because it can realize good dynamic response
effects and can make fast response through outputting changes of torque and
based on load changes so as to realize speed stability of rotating shaft.
3)
Fast Speed for Speeding Down for Stop
Usually the speeding up and down time of lathe is short, the speeding up time
is guaranteed by properties of inverters, while the speeding down time depends
on attached braking resistor or unit.
4)
Self-learning of Motor Parameters
After the vector inverter is used, in order to achieve good control performance,
usually self-learning of motor parameters is necessary so as to get accurate
motor internal parameters for vector control calculation. Self-learning of motor
parameters need know the following plate data: rated power, rated frequency,
rated speed, rated voltage, and rated current. The plate of some
frequency-conversion motor may not indicate rated speed, which can be
estimated based on experiences. Such self-learning has to be carried out as
no-load (no-load on the motor shaft) because motor parameters from
self-learning can be ensured their correctness only when it is no-load. If
no-load operation is not permitted by site conditions, it may be considered to
use motor parameters of ex-factory inverter for a trial run.
5)
Frequency and Run Commands
The frequency and run commands of inverters used in lathe all come from the
controller. Generally there are two categories of setting channels: one is analog
setting, and the other is multi-stage speed setting, or both, with multi-stage
speed as priority. Analog setting is mainly voltage-type analog, with current
type too. These two types of analogy can be collected by inverters.
3.
Disturbance Resistance
Good disturbance resisting tests have been done as ex-factory of inverters, so they
have strong anti-disturbance capability. But the inverter itself is a disturbing source,
so in use, it is difficult to avoid the disturbance from the inverter on other
equipment. Especially the frequency and run commands also may be disturbed, and
serious disturbance may result in instable frequency commands and thus faulty
actions of the inverter and so on. The method for resolving such problems is to add
magnet rings on output lines of the inverter so as to reduce high-frequency
radiation.
The Senlan SB70G series vector control inverter can meet above conditions
completely. The Senlan SB70G series vector control inverter is a new generation of
high-performance inverter that is self-developed by Hope SenLan Science &
Technology Holding Corp., with high reliability and strong functions. It can be
widely applied to industries such as metallurgy, petrochemistry, building materials,
coal, foods, paper-making, printing and dyeing, and water supply.
We select Senlan SB70G37KW inverter drive spindle 30kW motor. Considering the
motor requires fast braking, it is required to equip with braking unit and resistor.
The braking unit shall be model Senlan SZ20G30/45 (calculated based on 100%
braking torque), and the braking resistor shall be 6kW/15Ω.
III Energy-saving Analysis after Frequency-conversion Transformation for Hydraulic
System of Lathe
3
Due to complete protection functions for motor by inverter, the maintenance work is
greatly reduced, and some major components in hydraulic system such as solenoid valve
and oil pump are reduced too. When hydraulic system fails, troubleshooting is
complicate, while the operations of speed regulation for inverters are simple, convenient,
and highly reliable. The constant-speed running of original spindle motor
Case III
Application of Senlan Inverter in Transformation of B2151 Planer Miller
I
Electrical Transformation
1.
Remove two sets of machine units, DC main drive motor, and electrical cabinet.
2.
Make a new electrical cabinet (size: 2200×1000×650) with spray coating inside and
outside and two daylight lamps shall be installed on inner top to facilitate work of
repairmen. The temperature inside the cabinet shall be controlled by two
control-box temperature regulating machines to ensure reliable work of the
frequency-conversion speed regulating system and programmable controller.
3.
Frequency-conversion speed regulating system shall be the first domestic brand of
Senlan SB80G55KW inverter. This “high-performance inverter” is used to solve
problems of mechanical impact and vibration, and its true current vector control is
able to make the lathe operate under the state of high efficiency and accuracy. The
attached braking unit and resistor can let motor stop within 1.5s; satisfy frequent
start/stop and normal/reverse rotating; able to change speed automatically and
stably based on machining requirements during working process; as normal/reverse
rotating, the speeding up/down process can prevent from impact on mechanical
parts and current impact of the system; stepless speed regulating is available within
the range from zero to the rated speed, and operating is stable; and the system has
many protection functions such as motor overheat protection. In order to ensure
speed regulating accuracy and low-speed torque, a high-precision coder shall be
installed on the tail pat of the frequency-conversion motor to form a close-loop
vector control.
4.
Remove main drive DC motor and install a new 55kW frequency-conversion motor.
By calculating, the 55kW frequency-conversion motor absolutely can replace 60kW
DC motor to meet working requirements of planer. But the coupling between motor
and reduction gearbox and the motor base shall be redone.
5. The electrical part shall be with Siemens produced S7-200 programmable controller,
and the input/output modules shall be extended so as to reach quantity of 58
input/output interfaces and at least five interfaces for input and output respectively.
Meantime, increase two-way DAC (Digital-to-Analogue Conversion) modules so
that operators can set the speed through touch screen of HMI for
normal/reverse-direction working based on displayed speed value.
6.
Original limit switches that control the reciprocating movement of the work bench
shall be all replaced with import famous brand Schneider produced proximity
switches for control.
7.
Remove the old hanging button station and make a new, which shall include HMI,
emergency stop button, and signal lamp, and shall be with spray coating both inside
and outside.
8.
As normal/reverse rotating of the work bench, each shall be added with one-step
speeding-down function so as to avoid the damage on workpieces by knives, reduce
4
direction-switching noise greatly, reduce mechanical impact, and prolong service
life of mechanical part.
9.
Under the precondition of satisfying production requirements, other functions shall
meet requirements for lathe.
10. All electrical lines and the limit switch shall be replaced. The AC motor not
replaced shall be subject to testing and maintenance.
11. The hydraulic lubricating system shall be transformed to conform to mechanical
parts.
12. Connection lines between lathe and control box shall be laid with PVC lines
according to requirements of specifications.
II
Advantage Comparison for Transformation of B2151 Planer Type Miller
The advantages after transformation will be described from the following three aspects:
energy-saving, maintainability, and operating performance.
1.
Energy-saving
1.1 The original system uses a drive structure: AC motor drives co-axial DC generator,
which then generates power to drive DC motor. Speed regulation: change voltage of
magnetic field for the DC generator to regulate its DC output and further to regulate
the operating speed of the DC motor. The process of energy conversion of the
system: from AC electric energy to mechanical energy (AC motor), to AC electric
energy (DC generator), and finally to mechanical energy (DC motor). There are
three times of energy conversion, and each time has energy loss inevitably, so the
more the times of energy conversion, the more the loss of energy.
After transformation, the system uses AC inverter drive motor for working, which
converts electric energy to mechanical energy directly. Therefore, only the energy
loss during energy conversion process can save 2/3 compared with original system.
1.2 After start up, the AC motor and DC generator of original system are always in
operating position, so its no-load loss is big. Further, as the speed regulating mode
of AC units is in braking operation of DC motor, most of energy converts to heat
energy that is consumed in motors of the unit and directly results in a low utilization
ratio of energy.
After using frequency-conversion speed regulating system, no energy consumption
if the work bench does not operate, so the system standby loss reduces greatly.
2.
Maintenance
2.1 Original system units have DC motor and DC generator, the commutator and carbon
brush of both need maintenance, and the DC motor has a high failure rate, long
maintaining period, and high expenses.
After transformation, the system is provided with squirrel cage async motor, which
has a long use period and low maintaining expenses.
2.2 The original electrical control cabinet is controlled by separate relays, with many
nodes for control circuit and with complicate lines, so its failure is difficult for
positioning and troubleshooting.
After transformation, the system is controlled by PLC programmable controller,
with simple peripheral circuits, so system failures reduce greatly and maintaining
work amount is small.
The control system is provided with industrial touch screen as HMI to provide
5
graphical user interface in Chinese. On the touch screen, there are complete fault
displays, diagnosis, and records, and situations of each node in the whole system
can be recorded for reviewing at any time.
2.3 The travel switch used in original system has a low reliability, and easy aging and
mechanical wear of contact surfaces between nodes may result in inaccuracy of
node actions and faults of the system, so it is required to check node situations of
each travel switch usually.
After transformation, the system is provided with high-performance contactless
inductance approach switch, so there is no aging and wear of nodes and reliability
of the system is enhanced greatly. Besides, it needs no replacement.
3.
Performance
3.1 After transformation, the system is with special AC frequency-conversion speed
regulating motor and the high-performance vector control frequency converter for
speed regulation, and digitalized speed regulation is realized. Compared with the
analog DC speed regulating system of original system, the speed regulating
accuracy is higher, the torque output at the same frequency is bigger, operating of
the work bend is more stable, and the output planing (shaping) force is bigger.
3.2 The system control is with PLC (Programmable Logic Controller) combined with
digital inverter to realize speeding up/down intelligent control through elaborately
tailored software. It can set optimized speeding up/down time based on different
speeds so that direction switching is more stable and without impact and so as to
prolong service life of the mechanical drive system and to meet various process
requirements of workpieces.
III Instruction to Frequency-conversion Transformation of B2151 Planer Type Miller
The B2151 planer is a 6m planer produced by 305 factory in the early 1970s.
1.
Motor
The planer has seven motors in total. MG is the main work bench drive
frequency-conversion motor (55kW/6P); FL is main work bench
frequency-conversion motor fan motor (550W); MC is vertical knife-holder motor
(2.2kW); MY is side knife holder motor (2.2kW); MH is beam lifting-lowering
motor (5.5kW); MR is lubricating pump motor (250W); and MJ is beam
tightening-loosing motor (750W).
2.
Control of Main Work Bench
The main work bench carried out drive operation by the inverter driving frequency
conversion motor. The actions of work bench include: step forward, step backward,
advancing, and backing etc., which are controlled by the eight limit (4 for
advancing and 4 for backing) proximity switches installed on the side of lathe. Step
forward and step backward operate when press it down and stop when release it,
and they are not limited by oil pressure and each proximity switch (i.e. free setting
available). This work condition aims for inspecting and repair oil lines by users and
for other equipment under the work bench.
When press down the operating buttons for advancing and backing, the work bench
operates automatically based on set speed. When the limit post of the work bench
contacts the first limit proximity switch, the work bench speeds down based on the
preset speeding-down speed.
When it contacts the second, the work bench speeds down, and when contact the
third, PLC gives stop command, it switches direction to carry out reverse running.
6
During running, if the work bench is offside to contact the fourth limit proximity
switch for limit safety, PLC will enforce the work bench stop or switch direction
(setting through touch screen) to prevent the work bench from rushing out.
If it is required to stop the work bench, you can press stop button to cut off the
control circuit of the work bench, and then the work bench will stop. At this
moment, the voltage at DC bus for the inverter is to feed back energy to power grid
through braking unit.
During operation of the work bench, if the motor loop of lubricating oil pump or
that of work bench fails, the work bench in cutting process will complete this travel
and stop until to the end of advancing or backing. The setting of this protection aims
to prevent that emergency stop caused by faults during cutting process may result in
knife damage or influence surface quality of machined workpieces. Therefore, if
fails, the work bench will stop at the end of travel.
3.
Control of Lubricating Oil Pump
The operation of work bench requires lubrication, so the lubricating oil pump is
required to be started when the work bench is started. On electrical cabinet, the
control switch of lubricating pump has three working positions: left-forward
position of “Automatic Running”, middle position of “Zero Position”, and
right-forward position of “Continuous Running”. If work bench does not work
while lubricating pump is required to run, this switch shall be set at the position of
“Continuous Running”, and when work bench runs automatically, this switch shall
be set at the position of “Automatic Running”.
After running of oil pump motor, charge oil for lubricating pump. To certain
pressure, pressure switch is connected to prepare conditions for automatic work of
work bench.
4.
Beam Control Loop
Actions of the beam include lifting/lowering and releasing/clamping movements.
Beam actions are interlocked with movement of the work bench through PLC
programs, and the beam can be operated to move only when the work bench stops
working. On the contrary, the work bench can be operated to move only when the
beam stops moving and is clamped.
When it is required the beam moves by lifting-lowering, press down corresponding
operating buttons. At this moment, the beam clamps to release the motor for
operating, and then the beam releases gradually. When the beam runs into the
releasing travel switch, it releases and the clamped motor stops, and then the beam
moves by lifting-lowering. When the lifting-lowering movement reaches positions
or runs into lifting-limit travel switch or lowering-limit travel switch, the beam
stops moving. The beam clamps the actions of the motor so as to gradually clamp
the beam. The beam releases the clamped motor and uses inverters for driving.
When clamping torque reaches setting torque, the beam releases the clamped motor
and stops moving automatically. At this moment, the work bench can be operated.
When the beam is lowering, after releasing the lowering button, the beam motor
still has return-lifting action to eliminate the gap between lead screws and nuts. This
reverse lifting runs for a period and then it stops clamping. At this moment, users
can set on the touch screen freely.
5.
Tool-lifter Control Circuit
There are three tool-rest tool-lifter switches in the electrical cabinet. When it is
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required one tool-rest lifts, the corresponding tool-lifter switch can be located on
“Open” position. The planer is provided with DC electromagnet tool-lifter. When
the work bench is backing, PLC will power on the tool-lifter contactor and load DC
voltage to tool-lifter coils through full-bridge rectified modules, and the tool-lifter
takes actions. When the work bench is advancing, the coils of the tool-lifter power
off.
6.
Tool-rest Control Circuit
The control of the tool-rest includes two working statuses: rapid moving and
automatic feeding. When the rapid-moving and automatic-feeding change-over
handles installed on the feed box are put on the “Rapid Moving” position, operate
corresponding buttons on the hanging button station, and the tool-rest will move
rapidly based on required direction. The tool-rest motor only has one moving
direction, and the moving direction of the tool-rest is changed depending on
machines.
When working automatically, the handles shall be put on “Automatic Feeding”
position to ensure the work bench works automatically but not able to move rapidly.
After the work bench backs to the end, the tool-rest motor powers on to force the
tool-rest to feed. When advancing is changed to backing, the motor moves
adversely for a while to reset the feed mechanism for preparing for the next feed.
On the hanging button station, the buttons for the tool-rest and beam are pressed for
working and released for stopping.
7.
Operation and Display of Touch Screen
The touch screen can be operated by lightly touching the screen surface. The touch
screen can display and set various process parameters and operating statuses, and
users can carry out operating setting and query based on the display.
8
Case IV
Application of Senlan SB80B Inverter in Production Line of Cold Bend for
Goods-Shelf
1.
System Composition
9
1.1 The molding process flow of the cold bend for goods-shelf: uncoiling
leveling
cutting-head welding
on-line servo feeding and piercing rolling of molded cold
bend straightening
fixed-length cutting off (or servo tracking cutting-off)
packaging later-period painting and so on. The Senlan SB80B industrial vector
control inverter is mainly applied to the rolling process of the molded cold bend, and also
can be applied to the speed matching system for uncoiling and leveling machine units.
Figure 1 Sketch of Production Line for Goods-shelf Cold Bend Molding
1.2 According to the design and process requirements for piercing and molding for cold
bend of goods-shelf components (beam), the cold-bend machine unit for the goods-shelf
component (beam) is usually comprised of 12 archways, and the cold bend machine unit
for the goods-shelf (column) is generally comprised of 17 archways. Their working
principle is basically same, but the working loads and the powers of selected inverters
are different. The following will mainly take the application of the cold bend machine
unit for the beam as an example for discussion. The steel coiling materials are fed by the
guiding feed device in front of the first archway to pass the steel band into the cold-bend
machine unit for cold-bend molding processing, the main power of this cold-bend
machine unit consists of the 30kW Senlan SB80B industrial vector control inverter and
async motor drive system, and the power passing between archways can be achieved by
chain drives or gear banks; The main control system shall be MELSEC FX2N-32MR
programmable controller, the close loop control feedback signals is provided with signal
switching value and length measuring by 2000pulses/revolution revolving coder through
passive measuring. And then according to line quantity of selected coder and location
measure to be run, determine corresponding measuring pulses and set PLC to produce
corresponding actions as detecting corresponding pulse value to realize accurate control
for fixed-length cutting off for products, with basic length control accuracy to over
±0.5mm and distribution range of repeatable length control error by no more than 1mm.
1.3 Main Configuration of System Hardware Structure
(1) Select FX2N-32MR plus FX2N-232-BD communication modules, one piece for
each.
(2) Touch screen shall be GP37W2-BG41-24V model, or microcomputer controlled
upper computer system.
(3) KOYO revolving coder TRD-NH1200-RZ, measuring roller, and 24V switch
power supply, one for each.
(4) 30kW Senlan SB80B industrial vector control inverter, one set.
(5) Three-phase squirrel cage AC async motor: Y series, 4-poles, 22kW, and one set.
(6) Other electrical optional parts, for example, the PG speed control card to be
configured to receive speed feedback signals of the coder, and built-in DC reactor.
Normally, in actual application, the inverter also requires braking unit and resistor
10
for achieving sufficient braking torque at the state of regeneration.
2.
Principle of Electrical Close-Loop Stepless Control System
2.1 The realization of close-loop stepless control for cold bend machine unit of the
goods-shelf component (beam) shall be based on properties of inverters and inverter
motors, i.e. high-performance close-loop speed vector and torque vector control property;
The true close-loop (with speed-sensor or speed-sensorless device) speed and torque
vector control algorithm for rotor yield-oriented of accurate magnetic-flux observer shall
be used to complete work; Namely, carry out appropriate regulation according to ideal
speeding-up and speeding-down curves of the inverter under certain loads or to reference
data of properties of inverters of different brands and specifications, load properties of
machining piece of cold bend machine unit, and load properties of motors and so on. The
system uses PG v/f control mode, and its basic control principle is shown in Figure 2.
Figure 2 Principle Diagram of System Close-loop Stepless Control
2.2 The basic control idea: the Senlan SB80B industrial vector control inverter and the
frequency-conversion motor form internal close-loop control system, and the revolving
coder and PLC form external close-loop control system; Namely, 1) according
to
current feedback speed signals measured by the revolving coder, properly regulate output
drive frequency value for inverters so as to ensure the frequency-conversion motor
operates at required stable speed; concrete molding process requirements and load
fluctuating laws for cold-bend products shall also be referenced to select appropriate
speed control mode, including initial moving acceleration, accelerating control time,
stable operating speed and distance, decelerating moving acceleration and control time,
which shall be based to ensure stability of operation of the master machine and the
control-feedback operating process and to eliminate out-of-tolerance faults caused by
instability. 2) according to displacement feedback signals from pulse measuring value
by the revolving coder and the preset control programs, properly regulate the output
drive frequency of the inverter so that the frequency-conversion motor first operates at a
higher speed to approach the location for fixed-length cutting-off control of cold bend
products, then works stably at a lower speed and brakes accurately at such control place.
If necessary, a mechanical brake device can be used to help with rapid positioning, and
then the cutting-off control signal can be sent out through output control point to realize
hydraulic stop of cutting. PLC control system collects operating data in real time during
working process, and carries out continuous comparison with standard location
parameters stored in software control data block and makes control decisions so as to
achieve rapid and accurate positioning and improve working efficiency and to realize
overall dynamic management for production management system by exchanging
working information with monitoring system.
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2.3 In the control system for the production line of goods-shelf component (column), which
is imported by our company, the programmable controller is mainly used as lower
computer to check status of each status point and to directly control the start/stop of the
control system and cutting of other control units. It also sends the I/O statuses of each
point to upper computer through the control board card, and the computer combines data
from the programmable controller and other equipment to carry out corresponding
processing and display.
3
Model Selection and Capacity Determination for Inverter
3.1 The electrical drive of the goods-shelf cold bend molding equipment is mainly to drive
cold bend roller, with its resisting torque T L determined by multiplication of the friction
FL between cold bend roller and steel coiling materials by the cold-bend roller radius r,
i.e. TL  FL  r . Here, the radius of the cold bend roller is constant, and the friction FL
is related to the piercing design process level of relevant cold-bend products, drive
efficiency of machine unit, and the friction factor between relevant materials and the
roller and is not related to the revolving speed. This is a kind of typical constant torque
load mechanical property. As this kind of load torque is not related to revolving speed,
the resisting torque of the load remains same during speed regulating process. The
frequency-conversion speed regulation system is selected based on normal requirements
and also based on the speed regulating range for operating of machine unit,
characteristics of resisting torque T L , and requirements for mechanical properties: (1)
The inverter with relatively simple V/F control mode shall be selected to apply to:
matching of the individual frequency-conversion speed-regulating control such as
uncoiler, leveler, and pressure machine to the overall speed. (2) The
inverter
with
feedback vector control mode shall be applied in cold bend molding machine unit and
on-line hydraulic cutting-stop equipment to achieve accurate speed control and location
positioning and hydraulic cutting-stop functions that run repetitively nearby zero-speed
area, currently with achievable location control accuracy up to over ±0.1mm. The higher
the accuracy value, the lower the production efficiency, even taking place location
positioning vibration. According to the process characteristics of goods-shelf products,
the location accuracy is fit to be controlled at about ±0.5mm. The main power system of
the goods-shelf cold bend machine unit shall be mainly with feedback vector control
mode, with its control principle shown as Figure 2. The vector control, according to
motor general theory and coordinate shift theory, decomposes the stator current of AC
motor into the magnetic-yield current component for the oriented coordinate of the
magnetic yield and its normal-direction torque current component. After decoupling by
changing the fixed coordinate system to revolving coordinate system, the control for AC
amount is changed to that for DC amount. In this way, AC motor can be equivalent to
DC motor to achieve the same control functions as DC motor. At present, the AC
electrical drive can be completely comparable to DC electrical drive.
3.2 In regard to the calculation and determination about molding power for cold-bend
machine unit, the drive power of the machine unit is usually determined from actual
experiences by referencing to standard codes and empirical design parameters of part
machine units. It also can be calculated from the molding torque required for the roller
that revolves and loads molding counter-force (load), for example, the molding torque
T=P (molding load) ×L (between-roller contact length). The actually measuring value is
usually higher than the calculated value. Among, the empirical calculation formula for
electric resistance welded tube is also provided. In fact, different manufacturers have
different standards for the design of the power of machine unit and also have some
differences in the drive power of machine unit (e.g. chain drive and gear drive). For
example, the import production line of a company has molding width of 226mm,
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molding angle of 360 degree, thickness of coiling materials: 4.0mm, design quality of
selected coiling materials: SS490, and main power of the machine unit: 37kW; but for
the domestic cold-bend production line: molding width of 336mm, maximum molding
angle of 1080 degree and general molding angle of 720 degree, thickness of coiling
materials: 4.0mm, design quality of selected coiling materials: SS490, and main power
of the machine unit: 132kW. By comparison, the difference is big. Especially when the
error in the thickness of coiling materials is out of tolerance, the load of the machine unit
may change, the cold-bend molding force may attach to the rolling force on the thickness
of board materials, the system may take place overload stop phenomenon. Due to
working under vector control manner, it can provide sufficiently big start torque.
3.3 At last, the capacity selection of the inverter is decided by many factors such as motor
capacity, rated motor current, and motor accelerating/decelerating time. Among them,
the rated motor current is the key factor. In order to achieve perfect control functions for
inverters, generally the power of inverters shall meet: ≥K×1.732×Vm×Im
K: current wave-form correction coefficient, Vm: rated motor voltage, and Im: rated
motor current.
3.4 AC frequency-conversion speed regulating is achieved through inverters and is essential
to the capacity determination for inverters. Proper capacity selection itself is a kind of
energy-saving and consumption reduction measure. According to current data and
experiences, there are three simple methods:
(1) Determination of actual motor power: first measure actual power of the motor, and
based on this, select capacity of inverters.
(2) Formula method: if the safety factor is taken as 1.05, then the capacity of inverters:
Pb=1.05Pm/hm×cosy(kW).
In the formula, Pm: motor load, and hm: motor power. After calculating Pb, specific
specification can be selected according to product catalog.
(3) Motor rated current method: the selection process of inverter capacity is the
optimum matching process between the inverter and motor. The most common and
safe method is the inverter capacity is bigger than or equal to rated power of the
motor. But in actual matching, the difference between actual power and rated power
of the motor shall be considered. In general, the selected property is bigger than that
actually required. Therefore, it is proper to select inverter according to actual power
of the motor or according to concretely selected inverter brand and property. Main
power consumption of cold-bend machine unit for the goods-shelf component
(beam): that for bending power of goods-shelf component (beam), and that for
overcoming friction resisting force between roller and workpiece, friction resisting
force of roller bearing, machine unit drive resisting force and power consumption.
In general, empirical calculation method and simple formula are used to calculate
jointly with magnification method. Normally, successful cases for cold-bend
molding can be referenced to compare and calculate, and based on this, the actual
power of the specific model inverter can be determined. In this case, the actual
power of the selected inverter is about 22kW.
3.5 The Senlan SB80B industrial vector control inverter has multi-stage speed selection
function, including terminals such as normal start/stop, reverse start/stop, external fault,
fault reset, multi-stage speed command 1, multi-stage speed command 2, jog frequency
selection, external base-pole blockade command, multi-stage speed command 3,
multi-stage speed command 4, accelerating/decelerating time selection, abnormal stop,
and multi-function analog input. The PLC output points can be directly used to control
ON/OFF status of input terminals so as to realize speed increasing, speed decreasing and
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accurate stop of inverters. Each-stage speed value can be set through preset function of
inverters.
3.6 Selection of braking resistor: built-in DC reactor, power factor: ≥0.94, small harmonics
of power supply input, effective to defend electrical surge, voltage, and burr to prolong
service life of internal circuit components. Generally they shall be selected within the
recommended resisting power and resistance value range. If the motor of a machine unit
has a high speed, its speed can be appropriately reduced to get a big braking torque. If
the minimum value cannot meet braking torque, the inverter with a bigger stage power
shall be selected.
3.7 Integrating a variety of factors, we select Senlan SB80B industrial vector control inverter,
and especially its zero servo function (function for remaining the stop status of motor) is
very effective for positioning control for cold bend molding of goods-shelf component
(beam) and to meet production control requirements for hydraulic cutting-stop and can
further improve molding quality and production efficiency of goods-shelf components.
4.
Design of External Interface
4.1 Mitsubishi FX2N PLC includes many high-speed counters. Through measuring test, the
C251 counter with two-phase counting input and reply frequency of 30kHz is selected.
The A and B output terminals of the revolving coder are connected with X0 and X1 input
points of PLC to be able to stably catch close-loop control feedback signals required for
machining products on the cold bend machine unit for goods-shelf component (beam), to
realize program comparison and output of control signals after positioning for machining
length and location for cold bend products, and to realize fixed-length hydraulic
cutting-stop action for cold-bend products. Calculation of maximum operating speed of
the machine unit: the roller girth measured is multiplied by the reply frequency of 30kHz,
and then the result is divided by the pulse quantity per minute of the revolving coder. For
example, the diameter of the measuring roller selected by our company is Φ60mm, the
girth is 188.5mm, and then the maximum moving displacement per second is:
188.5mm×30000÷2000=2.827m. The maximum theoretical movement speed of the cold
bend machine unit for the goods-shelf component (beam) is required within
169m/minute, and general moving speed is designed at about 20m/minute. The
maximum for detecting the PG output pulse is 300kHz, and the PG output frequency
( fPG ) is calculated with the formula below.
fPG 
Motor speed as maximum frequency output (min 1 )
 PG( p / rev )
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4.2 The multi-stage output control for Senlan SB80B industrial vector control inverter by the
upper computer is carried out through controlling power-on/off signals at output
terminals to select multi-stage commands or output analog signals (0-±10V) to the input
end of multi-functional analog quantity to carry out adaptive normal/reverse running,
high/low speed, moving positioning and stop control etc. Details are shown in Figure 3.
fPG 
Motor speed as maximum frequency output (min 1 )
 PG( p / rev )
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Normal running PLC Y0
Fault output PLC X24
Reverse running PLC Y1
Multi-stage speed 1 PLC Y2
Normal inching PLC Y4
Normal inching PLC Y4
Reverse inching PLC Y5
2 Ω
2 Ω
Figure 3 PLC Control Sketch of Senlan SB80B Industrial Vector Control Inverter
4.3 The Senlan SB80B industrial vector control inverter has torque response of less than
10ms, torque control function, zero servo and location control functions; for cold-bend
machine unit, it follows with the control mode of “speeding up running speeding down
low-speed running and normal/reverse regulation stop” is regarded as one running
cycle, and the interval within each cycle is for cutting-off of cold-bend products and
action reset of the system. In particular, the “Stop” concept in the above running cycle
shall be understood as zero-servo function status, and it can realize and remain stop
status of the motor under external PLC or PC signals or analog commands. Proper
setting of these parameters can regulate cutting-off control accuracy for positioning
moving and productivity of the machine unit and adapt them to load requirements.
4.4 During a test run, if faults such as error-regulation and vibration are caused by control
performance, please refer to the mode regulating parameter with PG vector control, i.e.
proportional gain for speed control, integration time parameter, speed control gain for
corresponding frequency-conversion, once extending time for speed control, and
selective carrier frequency and so on. During actual running, the PID control module can
be used to realize speed control and positioning regulation so as to realize sync control.
Namely, the offset between speed commands and speed detected value is let approach
zero.
4.5 Main control error comes from mechanical making error, the measuring accuracy
feeding back from measuring roller, as well as the surface quality and molding process
of the selected cold-bend rolling materials, which are also the key to successful
application this time. The mechanical control accuracy of the system has some
influences on the control accuracy of electrical system. The on-line regulating time and
cycle for the system can be shortened by comprehensive controls such as electrical
power-on for maintaining torque balance with actual situations, proper mechanical
positioning and braking, and flatness of machining materials. In order to guarantee the
quality and production cost of cold-bend components, it shall be required to periodically
carry out calibration and correctness for wear of the measuring roller of the revolving
coder, re-regulation of parameter changes for relevant peripheral machine unit or the
machine unit during commissioning, and maintenance for the machine unit and so on so
as to reach high-accuracy location control in many cases as far as possible. Besides,
carry out parameter optimization and performance analysis for concrete products to
improve wide application for the system.
5.
Application Effects
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The Senlan SB80B industrial vector control inverter achieves multi-stage speed system
control, which ensures the automatic control requirements of the machine unit for
goods-shelf cold-bend and has characteristics such as stable and reliable operation and
high-accuracy positioning. Practices also prove the Senlan SB80B industrial vector
control inverter completely can meet the requirements for speed regulation and basic
positioning control of the machine unit for goods-shelf cold-bend and has improved
productivity. This inverter control manner also can be applied in other motor
frequency-conversion speed-regulation systems that require speed regulation and
positioning control.
Case V
Application of Senlan Inverter in Centrifugal Pipe Casting Machine
I
Production Process of Cast-iron Pipe
Chongzhou Pipe Casting Plant in Sichuan produces water-supply cast-iron pipes with
large caliber. In order to reduce thickness of pipe wall and ensure quality of cast-iron
pipes, the centrifugal casting method is used to produce large-caliber water supply pipes.
Namely, high-temperature melted iron is dumped into a die, and then the die is revolved
at high speed. Due to centrifugal force, the melted iron is fast molded in the die. After
remaining for several minutes, open the die and take out pipes when the iron-pipe
temperature reduces from about 700 C -800 C to zero. The die of the pipe casting
machine is put on front and back four driving wheels, and original driving mode is two
37kW electromagnetic speed regulating motors drive through bell wheel. It is shown as
Figure 4.
Die
Motor 1
Motor 2
Figure 4 Driving Diagram of Pipe Casting Machine
II
Load Mechanical Property of Pipe Casting Machine
The load of pipe casting machine features big-inertia load, and certain amount of melted
iron shall be added in before start for such heavy load start. Due to poor low-speed
torque of the electromagnetic speed regulator, a big capacity motor is used to ensure
normal production. As shown in Figure 4, the driving of the pipe casting machine is
commonly carried by two 37kW motors, and thus there are sync issue between the two
motors. It is difficult to achieve sync through regulation by electromagnetic speed
regulator, while original manual regulation for sync often cannot be ensured. If async,
there is only one motor for output, so this motor is in over-load state while the other is in
power generation state. This is bad for motor operation and may damage the motor
sometimes.
III Frequency-conversion Speed Regulation of Pipe Casting Machine
According to above mentioned situations, select Senlan SB61G+ series inverter. In case
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of two 37kW inverters, sync control shall be considered to achieve good sync effects, but
it is required and troublesome to connect synchronizer externally. One 75kW inverter is
used to control two motors, which have some differences in their properties and speeds,
so if the speed difference is not big, use requirements can be met. The pipe casting
machine has a low sync requirement for two motors. For simplicity, motors are
connected in parallel, and a SB61G+75KW inverter is used to drive two 37kW motors.
In order to protect motors, each shall be installed with thermal relay, as RJ1 and RJ2
shown in Figure 8-2. Assuming F01=3, speed regulation is controlled by X4 and X5
terminals, X4 for speeding up and X5 for speeding down. Assuming stop time is 120s,
start DC braking when the speed is decreased to the output frequency 5Hz of inverters.
By yield testing, one motor has line current of 57A, the other 38A, and regulate
characteristic curve of inverters so that the difference of line current between two motors
is reduced as far as possible. The control principle for frequency-conversion speed
regulation is shown as Figure 5.
RJ1
DZ
FU
UVW
M1
RST
K1
SA1
SA2
FWD
BT40S75KW
SB61G+75KW
X4
RJ2
M2
X5
CM
Figure 5 Control Principle for Frequency-conversion Speed Regulation for Pipe Casting
Machine
IV Effects after Transformation
After frequency conversion transformation is done for the pipe casting machine, the
speed regulating is easy, and balance load distribution sync between two motors can be
achieved not requiring sync regulation during operation. Revolving speed can be
regulated to above 1200r/min, and operation is stable. After inverters are used to replace
electromagnetic speed regulator, good energy-saving can be achieved. According to
measuring by electric meter in pipe casting plant, the energy saving can be 22% or so,
with obvious economic benefits.
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