Blow molding machine is an automatic equipment.
According to the technical parameters and design requirements of the high-speed rotary blow molding machine, the key issues to be discussed are determined by analyzing the main action process, structural composition and control system software and hardware.
Two key issues of counting program and synchronization control are studied.
By analyzing the characteristics of the parison counting and the positions of the revolution group and the screw group, the counting program flow is designed, and the trajectory of the synchronous control is discussed.
Design requirements for high speed rotary blow molding machine
High-speed rotary blow molding machine is a fully electric continuous reciprocating linear bi-directional stretch blow molding machine with a capacity of The capacity is 18,000 bottles per hour, with an average of 10 PET bottles per 2 seconds, which is the leading speed in Asia. Adopting The machine is equipped with a fully electric servo control system, high automation, and a high pressure gas recovery system, which can recover about 25% of the high pressure gas per unit time, saving cost and energy, and the mouth opening remains unchanged, so when changing different types of blanks, only the mold needs to be changed. The scope of application can blow water bottles, tea bottles, carbonated beverage bottles, oil bottles and other PET packaging bottles. High speed The main technical parameters of high speed rotary blow molding machine are shown in Table 2-1.
Technical items of blow molding machine
|Tie rod stroke||mm||228.8|
|Stroke of bottom die||mm||30|
|Number of cavities||Unit||10|
|Max. bottle capacity||Itr||0.6|
|Max. tooth size||mm||38|
|Max. bottle diameter||mm||68|
|Max. bottle height||mm||260|
|Low pressure air consumption||ltr/min||2500|
|High pressure air consumption||ltr/min||10000|
Table 2-1 The main technical parameters of high-speed rotary blowing machine
Overview of high speed rotary blow molding machine
Blowing machine action flow
The overall structure of the high-speed rotary blow molding machine mainly consists of the following parts, respectively, the preforms rectification machine and conveyor, rotary heating device (metric group), variable pitch conveying device (screw group), into the preforms out of the bottle device (into the mold group) and stretch blow molding device (tie rod group and molding group). The action flow of high-speed rotary blow molding is shown in Figure 2-1.
|Preform sorting and entry||→||Rotary heating||→||Preform pitch widening|
|Forming group||Screw group|
|Finished product discharge||←||Blowing and forming||←||Preform feeding into forming group|
|Tie rod group||Mold feeding group|
The above table is the action flow of high speed rotary PET bottle blowing machine
The action flow of the high-speed rotary blow molding machine is shown in Figure 2-1. The preforms are transported from the hopper to the lineup machine, where the preforms are arranged neatly on the lead rail with the opening upwards. Two sensors are installed on the lead rail, one to detect the presence of preforms and the other to detect if there are too many preforms on the lead rail. The preforms are transported through the lead rail to the star paddle and then pressed into the billet holder and into the stator.
The male group is a gyratory heater that rotates in a clockwise direction, and the preforms move on the conveyor chain in both self and male rotation. At this point, the spacing between the preforms is small, while in the blow molding mechanism the spacing between the molds is large, so after crossing the heater, the preforms pass through a pitch changer to make the preforms larger. The screw set uses a variable pitch screw configuration.
The jaws of the variable pitch screw are first synchronized with the Then the pitch of the billet is widened from 40 mm to 80 mm and finally the billet with a pitch of 80 mm is fed into the blowing unit. The billet with a pitch of 80mm is fed into the blow molding mechanism. The billet completes the stretching and blowing process in the blow molding mechanism. The blow molded PET bottle is taken out of the molding mechanism by the jaws of the bottle outlet.
Control system composition of blowing machine
The control system of high-speed rotary blowing machine can be divided into the following two parts.
One is the motion control part, covering to motors, servo amplifiers and controllers.
The second is the logic control part, covering to the output relays of switching quantity, various sensors of switching signals and proximity signals.
The system adopts the structure of IPC PC + motion controller, and the control system structure is as shown in Figure 2-2. The control system structure is shown in Figure 2-2.
|Human-computer interaction||→||Industrial Computers|
|D/A Modules||Motion Controller||Digital input modules||Digital output modules|
|6-channel SCR||Amplifier||Sensor output||Relay Outputs|
The above table is the control system structure diagram
During the operation of the blowing machine, all logic control is done by I/O expansion module and IPC communication, while all motion control is done by motion controller.
The high-speed rotary blowing machine adopts Advantech industrial-grade integrated workstation TPC-1259H as the IPC, the motion controller adopts Galil’s 6-axis motion controller DMC-4163/PICM-20105*2/DIN, and the I/O expansion module adopts Galil’s PLC module, which is a RIO-47200-(1LSN) with 16 I/Os and 8 12-bit DACs, respectively. The RIO-47200-(1LSNK-8AO_10V12bit) and three RIO-47200-(1LSNK, 2LSNK) equipped with 16 I/Os are used for I/O expansion.
The control system of high-speed rotary blowing machine mainly consists of motion control part and logic control part.
(1) Motion control part of the control system
The motion control part mainly refers to the linkage control of the five-axis AC servo motors, which include the forming group motor, the mold feeding group motor, the screw group motor, the male rotation group motor and the tie rod group motor, as shown in Table 2-2.
Below table 2-2 is Servo motor parameters
|Serial number/name||Performance index/model||Power (W)||Maximum speed (rpm)||With or without brake||Electronic gear ratio|
|Forming group||ECMA-E11320||2000||2000||without brake||1280/4|
|Into the mold group||ECMA-E11320||2000||2000||without brake||2560/5|
|Screw group||ECMA-E11820||2000||2000||without brake||48695/125|
|Male rotation group||ECMA-E11830||3000||2000||without brake||1280/10|
|Tie rod group||ECMA-E11830||3000||2000||without brake||1280/5|
(2) Logic control part of the control system
The logic control section includes 48 digital outputs, 41 general digital inputs, 15 special digital inputs and 6 D / A output module. The general digital output is used to control the cylinder solenoid valve and pre-blowing, high-pressure blowing, exhaust, recycling and other blow molding The general-purpose digital outputs are used to control cylinder solenoid valves and blow molding actions such as pre-blow, high-pressure blow, exhaust, and recovery.
The general purpose digital inputs include calculation sensors, sensors on the infeed chute, tie rod limit and screw clamping The sensors on the jaws or cylinders such as inlet and outlet jaws, sealing cylinders, etc. Dedicated digital inputs are mainly the positive and negative limits of the five-axis The sensors on the positive and negative limits of the servo motor and the proximity sensor of the home position.
Control system software design
The control system software is divided into a four-layer structure.
The first layer structure is the driver library provided by each equipment supplier.
The second layer is the monitoring and communication program, which is used for real-time communication and monitoring during the operation of the control system modules.
The third layer is the control program, which is the core of the whole control system and consists of three parts: motion control program, logic control program and human-machine interface program.
The fourth layer is the main control program, which is mainly responsible for the main control part and data management.
The first, second and third layers are real-time control modules, while the fourth layer is the coordination program, which is a non-real-time control program .
The software structure of the high-speed rotary blowing machine is illustrated in Figure 2-3.
Figure 2-3 Software Structure of PET Bottle Blowing Machine
|Master Control Module||File and data management modules|
|Motion Control Module||Human Machine Interface Module||Logic Control Module|
|Monitoring Module||Communication Module||Fault diagnosis and alarm module|
|Underlying Driver Library|
Key issues of high speed rotary blow molding machine
Counting of preforms and synchronization program flow
The control system of high speed rotary blow molding machine consists of three threads, and the three threads accomplish the following three tasks simultaneously.
ROTARY GROUP RUN, COUNTING & SYNCHRONIZATION and BLOW MOLDING ACTION.
Each task of the three threads must be completed within the time required to ensure capacity.
Among them, counting and synchronization is the focus of the study of high-speed rotary blow molding machine, counting is to calculate the number of preforms in the revolution group and detect the presence of each preformseat, synchronization means that the jaws on the screw needs to complete the synchronization with the preformseat in the revolution group and clamping the preformseat on the preformaction before the pitch change, the action flow and data flow as shown in Figure 2-4 below.
The two counting sensors are placed in a staggered position in order to detect the falling edge signal of the blank holder sensor and read the signal of the preformsensor.
The roles of the two counting sensors are as follows.
(1) When the preformsensor detects a set of 10 falling edge signals, the screw servo motor starts and enters synchronous mode.
(2) The main function of the preformsensor is to detect whether there is a preformon the preformholder, and the molding module corresponding to the preformholder without a preformdoes not start the blowing cylinder.
Below table is the counting and synchronizing action flow and data flow
However, due to the installation conditions, the preformsensor is installed in a position that is several billets away from the screw jaws, so the signal detected from the preformsensor is saved in the array InSen and then processed by the intermediate variable InMed and saved in the array InMld of the blow molding information.
Assuming that the preformsensor is installed in a position 3 billets away from the screw gripper, the program flow is as follows.
The two counting sensors are used to obtain the signals of a group of 10 blanks to the array InSen to InSen; the intermediate variable InMed has 13 elements, and the counting variables InSen to InSen are copied to the intermediate variables InMed to InMed, where the remaining intermediate variables InMed to InMed are the information of the last group of blanks 8, 9 and 10 recorded in the previous program loop.
Finally, the intermediate variables InMed to InMed are stored in the blow variables InMld to InMld, while the intermediate variables InMed to InMed are assigned to InMed to InMed as intermediate variables for the next cycle.
Synchronous trajectory control method for screw group and metric group
The synchronous motion control of the screw group and the metric group of the high-speed rotary blow molding machine is a group of 10 jaws of the screw group to synchronize with the metric group of blanks in speed and position before the pitch change after the completion of the billet counting.
It is assumed that the motor of the stator group is the main shaft and the motor of the screw group is the slave shaft. The main shaft blank holder is moving at a certain speed and the slave shaft drives the jaws to start at a certain point and finally synchronize the speed and position at the synchronization point.
By analyzing the change of the trajectory of the slave axis, the expressions of the speed and position of the slave axis starting at different positions are deduced, and then the planning of the trajectory of the slave axis is derived.
Since the high-speed rotary blowing machine adopts the control system structure of IPC PC + motion controller, the synchronous motion control of the screw group and the metric group is suitable for the control strategy based on the synchronous motion trajectory. The synchronous motion trajectory is related to the position and spacing of the count completion points of the master and slave axes.
According to the requirements of the installation position of the screw group, it is assumed that the distance from the spindle count completion point to the synchronous point is Sx, the displacement from the starting point of the slave axis to the synchronous point is Sy, the distance between the spindle count completion point and the starting position of the slave axis is ∆S, the speed of the spindle is vx, and the speed of the slave axis is vy. There are four main cases.
(1) The starting point of the slave axis overtakes the completion point of the spindle count, and ∆S ≤ Sx/ 2. As shown in Figure 2-5.
The relationship between the master and slave axis positions is as follows.
Sy = Sx – ∆S
Assuming that the time required to reach synchronization is t , the displacement of the master and slave axes during synchronization can be calculated as follows.
If the slave velocity vy is uniformly accelerated from zero initial velocity to vx with minimum acceleration aa , then the acceleration of A can be calculated from equation (2-2) as follows.
It is also known that the displacement when the slave axis is synchronized is ∆S and the main axis is 2∆S .
Below is the first type of simultaneous motion planning
(2) Overtake the spindle count completion point from the axis starting point and ∆ S > Sx / 2. as shown in Figure 2-6.
Below is the Second synchronous motion planning
This case is similar to the case (1).
However, in order to ensure the synchronization of the position, the spindle is started at t0 time and then the slave axis is synchronized with uniform acceleration from the starting point, at this time, the slave axis needs to advance Sy to achieve synchronization, and the acceleration aa is calculated by the following formula.
The time t0 can then be calculated by the following equation.
(3) The starting point of the slave axis is behind the completion point of the spindle count, as shown in Figure 2-7. The relationship between the master and slave axis positions is as follows.
From the velocity variation of the slave axis shown in Figure 2-7, a velocity plan is used to first accelerate to the maximum velocity vym and then decelerate. Assuming an acceleration of aa and a deceleration of ad, the displacement Sy for the slave axis to reach synchronization is calculated as follows.
The collation leads to the following.
The equation about the maximum velocity vym can be obtained by combining the relationship equations (2-6) and (2-8).
Below is the third type of synchronized motion planning
Solving the equation yields an expression for the transcendental velocity vym from the axis.
The acceleration and deceleration can be made equal, i.e., a a = ad = a , so that the expression for vym can be reduced as follows.
Thus the theoretical minimum value of vym can be calculated as follows.
(4) The starting point of the slave axis and the completion point of the spindle count are at the same position, or the starting point of the slave axis is slightly ahead of the completion point of the spindle count. However, due to the limitation of servo motor acceleration, the synchronous motion planning of (1) cannot be adopted.
In this case The same method as the synchronous motion planning in (3) is used.
If the starting point of the slave axis is at the same position as the starting point of the spindle, the expression of the overrun speed vym is as follows.
Similarly, the theoretical minimum value of vym can be calculated.
The synchronous motion control of the screw group is realized by electronic gear and electronic cam.
The synchronous motion of the high-speed gyratory blowing unit uses the electronic gear and electronic cam mode of Galil’s DMC-4163, and the two-axis synchronous motion experimental platform uses the FOLLOW mode of Goodco’s GTS-400 series.
The electronic gear provides an electronic gear ratio that allows the control commands of the slave and spindle to mesh as a set of gears at a certain ratio.
The e-gear provides two modes, instantaneous e-gear engagement and ramped e-gear engagement, as shown in Figure 2-8 and Figure 2-9 for the speed comparison of the master and slave axes under the two e-gears .
Below is the transient electronic gear engagement
Ramped electronic gear engagement
Under low speed conditions, the use of instantaneous electronic gears can be considered as the speed instantaneously reaching the synchronous speed value, thus planning the synchronous motion. When the synchronous motion is planned, the slave axis only needs to wait at the synchronous point and the electronic gear engages when the spindle moves to the synchronous point.
However, in some cases However, in some cases, the spindle needs to move at a high speed, and using instantaneous electronic gear engagement will immediately produce The synchronization tracking error is extremely large and the current input from the axis motor is extremely high, causing a very large shock.
Using ramp electronic gearing allows the acceleration to increase slowly, thus reducing the shock to the slave axis.
The electronic cam of the DMC-4163 motion controller is similar to the FOLLOW mode of the GTS series motion controller in that it uses a virtual cam CAM to plan the position relationship between the master and slave axes, either linearly or periodically. The electronic cam function is shown in Figure 2-10.
The electronic cam function is shown in Figure 2-10. (3) and (4).
Deviation of synchronization control
In synchronization, the clamping jaws of the screw group are synchronized in position and velocity with the blank holders of the stator group, when Define the position deviation and speed deviation between the screw group (slave axis) and the stator group (spindle) as follows, respectively.
Among them, according to the actual commissioning, it is known that the deviation of master and slave axis position at the synchronization point e p (t ) is ±1mm and the mean value of speed deviation e v(t ) is 0, the blowing machine can complete the clamping operation.
Combined with the basic mechanism and control system of the high-speed rotary blowing machine, by analyzing its key issues, the following was mainly accomplished.
(1) For the technical parameters and design requirements of the high-speed rotary blowing machine, the action flow of the blowing machine is analyzed, and the motion control part and software control part of the control system are constructed by using multi-axis servo technology.
(2) In order to solve the problem of counting and synchronization of the blanks of the high-speed rotary blowing machine, the staggered structure of double counting sensors is proposed, the synchronization action flow of the blowing machine and the blowing action flow are analyzed, and the counting procedure based on intermediate variables is proposed.
(3) To solve the key synchronization control problem of high-speed rotary blowing machine, the synchronization starting position of the metric group mechanism and the screw group mechanism are studied, and four cases of synchronization motion trajectory are obtained. For different synchronous motion trajectories, the displacement and velocity relationship equations of the male rotating group and the screw group are studied, and finally the implementation method of synchronous motion control is proposed, and the foundation for the next step of control system identification and servo controller design is laid.