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
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) 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
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 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.