In order to adjust the product structure, it is necessary to transform the original double face grinding machine for constant speed grinding into differential speed grinding, so that the speed of the motor of the right wheel can be regulated by frequency conversion with the change of the product. Because the current use of frequency conversion speed regulation equipment, once the converter is damaged and needs to be repaired, the machine will not work. Therefore proposed to transformed right wheel motor frequency control of motor speed at the same time, it is best to keep the original star start operation namely Y the triangle structure, so that when the inverter after removed, has no the differential grinding machine tool, but after simple changes, using Y operation can still uniform grinding, reduce downtime.
The key technology of this transformation task is the least modified circuit and the least control ladder diagram, so that the transformed machine tool can conveniently and reliably realize the conversion between frequency conversion and speed control operation and Y operation.
1. Existing control circuit diagram and ladder diagram
The machine was originally used for constant speed grinding, and the motors of the left and right grinding wheels were started by Y and then switched to operation. Main control circuit diagram and ladder diagram of the existing right wheel Y operation of the machine tool.
-Q3 is the air switch (circuit breaker), the trip current is 80 A; -M2 is the motor for the right grinding wheel, with the power of 30 kW; -KM4, -KM5 and -KM6 are all AC contactors, among which -KM4 is used to control the main power supply of the motor of the right grinding wheel. When -KM4 and -KM6 are connected, the motor Y of the right grinding wheel starts. When -KM4 and -KM5 are connected, the motor of the right grinding wheel runs.
-KM5 and -KM6 require mechanical interlocking to ensure interphase short circuit during conversion.
The FANUC numerical control system is adopted as the control core. The logical action of the machine tool and the operation of the grinding wheel motor are controlled by the PWC of the numerical control system. The output point Y1.5 of the PMC controls an intermediate relay, and the normally open contact of the relay is used to control the AC contact-KM4. The output point Y1.5 can be used to control the main power supply AC contactor KM4 of the right grinding wheel motor. Similarly, the output point Y1.4 is used to control the motor of the right grinding wheel to run the AC contactor -KM5, and the output point Y1.3 is used to control the motor of the right grinding wheel to start the AC contactor -KM6.
The PMC input point X12.4 of the CNC system is the start signal of the right grinding wheel, the input point X12.5 is the stop signal of the right grinding wheel, the input point X14.7 is the closure signal of the protective cover, the input point X11.5 is the emergency return signal, and the internal signal G8.4 is connected under normal conditions (high level). When the signal is disconnected (becomes low), the CNC system enters the emergency stop state. The grinding wheel motor is not allowed to run under the condition of open shield, so as to avoid accidents. In other words, the closure of the protective cover is one of the necessary conditions for the grinding wheel motor to operate. When the protective cover is closed, there is no emergency return signal and the internal signal G8.4 is switched on, press the start button of the right grinding wheel on the button plate of the operating table, and the start signal X12.4 of the right grinding wheel will be displayed. At this time, the output signal Y1.5 will be output, and the main power supply of the motor of the right grinding wheel will be drawn and connected to the main power supply. After a delay, Y1.3 will be output, and the motor Y of the right grinding wheel will start the AC contactor -KM6 suction. At this time, -KM4 and -KM6 are all connected, and the motor Y of the right grinding wheel will start and reach the rated speed
After that, stop the output of Y1.3 and disconnect the motor Y of the right grinding wheel to start the AC contactor -KM6. After a delay (to ensure that the motor of the right grinding wheel does not start and run at the same time, so as to avoid short circuit of the motor of the right grinding wheel), output Y1.4 to make the motor of the right grinding wheel run the AC contactor -KM5. At this time, because -KM4 and -KM5 are connected at the same time, the motor of the right grinding wheel runs. Thus, the conversion from starting to running of motor Y of the right grinding wheel is completed.
After that, when the stop button of the right grinding wheel is pressed and the stop signal of the right grinding wheel is X12.5, or when the emergency return button is pressed and the emergency return signal is X11.5, the CNC system will stop output Y1.5 and Y1.4. The AC contactor KM4 of the main power supply of the motor of the right grinding wheel and the AC contactor KM5 of the motor of the right grinding wheel are disconnected, so that the motor of the right grinding wheel stops running; Or when the internal signal G8.4 is disconnected, the numerical control system will stop output Y1.5 and Y1.4 while entering the emergency stop state, so that the AC contactor KM4 of the main power supply of the motor of the right grinding wheel and the AC contactor KM5 of the motor of the right grinding wheel are both disconnected and the motor of the right grinding wheel stops.
2. Control of conventional frequency conversion speed regulation
Usually, when frequency conversion is used for speed regulation, the output U, V and W of the frequency converter are directly connected to the motor. By controlling the frequency converter,
The output U, V and W are changed to control the motor speed. Frequency conversion speed control circuit diagram and control ladder diagram.
-Q3 is the air switch (circuit breaker), the trip current is 80 A; -M2 is the motor for the right grinding wheel, with the power of 30 kW; -K19 is an intermediate relay, which is used to control the start and stop of the frequency converter. The operating frequency can be set by the button on the frequency converter. The output point Y2.2 of PMC is used to control the intermediate relay-K19, and the normally open contact of -K19 is used to control the on-off state of SF and CW of frequency converter, so as to control the operation of frequency converter :-K19 is energized, its normally open contact is connected, then the frequency converter runs; -K19 power off, its normally open contact is disconnected, then the frequency converter stops.
When the protective cover is closed, there is no emergency return signal and the internal signal G8.4 is connected, press the start button of the right grinding wheel, then the start signal X12.4 of the right grinding wheel will be displayed. At this time, Y2.2 will be output, the intermediate relay-K19 will be powered on, its normally open contact will be connected, and the motor of the right grinding wheel will run. When the stop button of the right grinding wheel is pressed, there will be a stop signal X12.5 of the right grinding wheel, the CNC system will stop output Y2.2, the intermediate relay-K19 is powered off, its normally open contact is disconnected, the frequency converter stops output, and the motor of the right grinding wheel stops running.
3. Control circuit diagram and ladder diagram after transformation
In the conventional frequency conversion speed regulation circuit, the motor is only connected with 3 power cables, while Y operation needs to be connected with 6 power cables to realize the conversion from Y connection to connection. Therefore, when controlling the motor according to the conventional frequency conversion speed regulation circuit, the circuit changes greatly when switching from frequency conversion operation to Y operation. The machine tool because of the original Y running circuit, so, in the transformation of the full use of the original circuit, the motor is still connected to 6 power lines, but when the machine tool frequency conversion operation, the machine tool power, through the PMC control will be connected to the motor operation mode. The specific implementation method is as follows.
(1) When the CNC system is powered on normally,
Contact R9091.1 is connected and R9091.0 is disconnected. Therefore, the output signal controlled by contact R9091.1 is output after the NC system is normally energized; The output signal controlled by contact R9091.0 has no output after the NC system is powered on normally.
(2) When the motor of the right grinding wheel runs with frequency conversion, the output point Y2.5 is used on the hardware line to control the AC contactor KM4 of the main power supply of the motor of the right grinding wheel, and the output point Y2.4 is used to control the motor of the right grinding wheel to run the AC contactor KM5. The output point Y2.3 is used to control the motor Y of the right grinding wheel to start the AC contactor -KM6, while the output points Y1.5, Y1.4 and Y1.3 are suspended without connection. In the control ladder diagram, contact R9091.1 is directly used to control the output signals Y2.5 and Y2.4, so that after the NC system is powered on normally, Y2.5 and Y2.4 will be directly output; At the same time, contact R9091.0 is used to control the output signal Y2.3, so that Y2.3 has no output after the NC system is normally energized. In this way, -KM 4 and -KM 5 are simultaneously engaged after the NC system is normally energized, so that the motor of the right grinding wheel is in running connection. However, since the frequency converter has no output at this time, the motor of the right grinding wheel will not run until the U, V, and W output of the frequency converter have voltage, the motor of the right grinding wheel will run according to the frequency controller of the frequency converter.
(3) When Y is running, the output point Y1.5 is used to control -KM4, the output point Y1.4 is used to control -KM5, and the output point Y1.3 is used to control -KM6 on the hardware line, while the output points Y2.5, Y2.4 and Y2.3 are suspended. Therefore, After the NC system is powered on normally, although Y2.5 and Y2.4 have output and Y2.3 has no output, because the output points Y2.5, Y2.4 and Y2.3 are suspended, no action will be performed in fact and the motor of the right grinding wheel will not be in running connection. After the transformation of the machine tool, the output of the frequency converter is taken as the input of the operation structure of Y, and its control circuit diagram and ladder diagram are shown in Figure 3.
Its control flow.
It is not difficult to find that when the frequency converter is not used, the three-phase input and output of the frequency converter are respectively short-circuited, then FIG. 3 is exactly the same as the control circuit diagram during operation. When the motor of the right grinding wheel runs with frequency conversion, as mentioned above, Y2.5 is used to control -KM4 on the hardware line, Y2.4 is used to control -KM5, and Y 2.3 is used to control -KM6, while the output points Y1.5, Y1.4 and Y1.3 are not connected. After the NC system is powered on normally, The right wheel motor is in the running connection. When the start button of the right grinding wheel is pressed under the condition that the protective cover is closed, there is no emergency return signal and the internal signal G8.4 is connected, the start signal X12.4 of the right grinding wheel will be displayed, and Y2.2 will be output. The normally open contact of the intermediate relay-K19 will be connected, the frequency converter will run and output, and the motor of the right grinding wheel will run. At the same time, the output points Y1.5, Y1.4 and Y1.3 in the ladder diagram will also carry out the conversion from Y startup to operation as described in the right grinding wheel motor Y running before, but because the actual circuit is connected to the output points Y2.5, Y2.4 and Y2.3, However, the output points Y1.5, Y1.4 and Y1.3 are not connected, so although Y1.5, Y1.4 and Y1.3 have output, no action will be performed. When the stop button of the right grinding wheel is pressed, there will be a stop signal X12.5 of the right grinding wheel, and the CNC system will stop output Y2.2. The intermediate relay-K19 is powered off, its normally open contact is disconnected, and the frequency converter stops, making the motor of the right grinding wheel stop. At the same time, output Y1.5, Y1.4 also stops.
When the motor Y of the right grinding wheel is running, the output point Y1.5 is used to control -KM4 on the hardware line, and the output point Y1.4 is used to control it
-KM5, with the output point Y1.3 control -KM6, and the output point Y2.5, Y2.4, Y2.3 are not connected, so after the normal power of the CNC system, although Y2.5, Y2.4 have output, but because they are not connected to the hardware line, will not perform any action. When the right grinding wheel start button is pressed under the condition that the protective cover is closed, there is no emergency return signal and the internal signal G8.4 is connected, the right grinding wheel will start
Signal X12.4, Y1.5 output at this time, make -KM4 pull in and switch on the main power supply, Y1.3 output after delay, make -KM6 pull in and start the motor Y of the right grinding wheel. After delay, stop Y1.3 output first and disconnect -KM6. After delay, Y1.4 is output to make -KM5 snap and the motor of right grinding wheel runs.
4.4 Structural characteristics analysis of three examples of aerostatic motorized spindles
As shown in Figure 6 ~ Figure 8, the spindle is different in the configuration position of the slave motor, the position of the thrust bearing, the number of journal bearings used, and the structure type of the bearing. Silicon cutting electric spindle (referred to as cutting shaft) used before and after the journal bearings are two sets, the other two kinds of electric spindle used a single set of bearings. Cutting and grinding spindle thrust bearings are provided at the front end, while PCB drilling and milling spindle thrust bearings are provided at the back end. Because the rear end of the bearing does not need to have a rotating shaft through, the use of rear thrust bearing can increase the rear thrust surface of the bearing, to meet the need for larger axial force when drilling larger holes.
As shown in Figure 6 and Figure 7, the motor of the motorized spindle is configured in the rear of the front and rear journal bearings, because its speed is relatively not too high, and the rear overhanging structure has no great influence on the rotation performance, which makes the disassembly, assembly and maintenance more convenient. More importantly, it avoids the threat of the bearing inlet caused by the corrosion of the silicon steel sheet of the motor rotor. Due to the high speed of PCB shaft and structural reasons, its motor is configured in the middle. Its motor shaft adopts welded copper squirrel cage rotor, which increases the available space in the center of the shaft and facilitates the arrangement of the loose broaching tool system in the middle of the shaft. The copper squirrel cage rotor also prevents the impact of corrosion of silicon steel rotor on bearings.
The intake holes of the journal bearing of the motorized spindle in FIG. 6 ~ 8 are double rows of holes, and the intake holes are simple orifice throttling type. The structure is that an air cavity with countersunk hole shape is made at the outlet of the intake hole, as shown in FIG. 4a. This type of technology is good, easy to manufacture, under the premise of meeting the performance requirements of the support, the use of this structure is feasible. Annular air intakes are used in thrust bearings, and the air cavity used in cutting shaft and grinding shaft is as shown in FIG. 5c. Countersunk air cavity is added at the outlet of the air intakes, which is also a simple orifice throttling type. In order to improve bearing performance and make it run smoothly at very high speed, PCB shaft adopts annular air cavity as shown in FIG. 5a. When designing electric spindle of aerostatic bearing, reasonable design of aerostatic bearing should be carried out according to the application occasions of electric spindle and its requirements for accuracy, bearing capacity and stiffness. Flexible application of the number and configuration of bearings, taking into account the use, processing, assembly, maintenance and other factors, to achieve the best overall performance of pneumatic bearing electric spindle products.
5 conclusion
In terms of technology, the material, structure type of aerostatic bearing, the rotor structure type and process method of high-speed motorized spindle, the overall design of aerostatic bearing motorized spindle product, manufacturing technology and other aspects still need to be carried out
