Strojársky priemysel

Application of SLANVERT Inverter in Centrifugal Pipe Casting Machine

I  Production Process of Cast-iron Pipe
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 -800 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.

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 SLANVERT SB61G+ series inverter. In case 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.

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.


Application of SLANVERT SB80B Inverter in Production Line of Cold Bend for Goods-Shelf

1. System Composition
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 SLANVERT 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 SLANVERT 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 SLANVERT 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 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 SLANVERT 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.

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 TL 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 TL, 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, 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 SLANVERT 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 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 SLANVERT 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.


4.2 The multi-stage output control for SLANVERT 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.

Figure 3 PLC Control Sketch of SLANVERT SB80B Industrial Vector Control Inverter

4.3 The SLANVERT 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
The SLANVERT 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 SLANVERT 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.


Application of SLANVERT 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 SLANVERT 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 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 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. 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 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.


Application of SLANVERT 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) 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 SLANVERT SB70G series vector control inverter can meet above conditions completely. The SLANVERT 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 SLANVERT 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 SLANVERT 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
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


Frequency-conversion Energy-Saving Transformation for Plastic Film Blowing Machine

The plastic film blowing machine is a kind of equipment from making plastic films. The speed regulation of lots of old equipment is with electromagnet speed regulating. From principles of electromagnetic speed regulation, this is a kind of energy-consumed low-efficiency speed regulation manner, with efficiency of only 85% at the maximum speed, the lower the speed, the lower the efficiency. Further, the electromagnetic speed regulation has soft mechanical properties and poor load-carrying capacity, so it cannot permit operation at low speed. For energy-saving, frequency-conversion energy-saving transformation is carried out for the film blowing machine, and its method is as follows: 

One 37kW AC async squirrel cage motor is used to drive the extrusion machine and reeling traction. As extrusion and winding are both with mechanical property of constant torque load, the general inverter with constant torque property is selected. In this case, the SLANVERT SB70G37KW inverter is selected. The SLANVERT SB70G series inverter is a kind of high-performance vector control inverter, with overload capacity of 150% and rated load of one minute. It control modes can be through key board or terminals. The other requirements of film blowing machine for inverters are stable operation and easy regulation.

The transformation is simple for implementation only by connecting inverters into motor circuit. It is assumed the inverter is operated through external terminals, and its speed is regulated by potentiometer. The time for speeding up/down is set as 20s in order for stable speeding up/down. The transformation for motors has two methods: one is to use ordinary squirrel cage motor to replace electromagnetic speed regulating motor; another is to regulate the speed to maximum through speed regulator and still to use electromagnetic speed regulating motor for driving. The first method has obvious energy saving effects, and the later has 15% less energy saving than the first, so the later method is only an expedient measure.