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Research and application of three servo manipulators in injection molding machine

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Research and application of three servo manipulators in injection molding machine

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With the rapid development of the injection molding industry, the existing full pneumatic manipulators and single servo manipulators for injection molding machines have not been able to meet the needs of users. This paper takes the three-axis servo manipulator for injection molding machine as the research object. For the manipulator model, the finite element method is used for analysis and optimization to find the best structure. The control system of the three servo manipulators was developed by combining the touch screen and the motion controller. The method of selecting the capacity of the servo motor was given by calculation. The performance of the motor is optimized through experiments.
Introduction


The robot is an automatic device that can imitate the functions of the human hand and the arm, and grasps, transports, or manipulates the tool according to a fixed procedure. It is a new technology emerging in the field of modern automatic control and has become an important part of modern mechanical manufacturing production systems. The part of the composition. The rapid development of the manipulator is increasingly recognized by its positive effects: first, it can partially replace manual operation; second, it can follow the requirements of the production process, follow a certain procedure, time and position to complete the workpiece. Transfer and handling; third, it can operate the necessary tools for welding and assembly. Modern injection molding machines are equipped with robots, which are part of the function of the human arm. The injection molded products can be automatically removed to stack, arrange and place the products according to the predetermined requirements. When producing similar products, the injection molding machine is basically fixed in injection and molding time. Therefore, the efficiency of the injection molding machine depends on the removal time of the product. The time from the completion of the mold opening to the completion of the next mold clamping determines the working efficiency of the injection molding machine. The shorter the time the robot takes out the product, the more efficient the injection molding machine.

This paper mainly analyzes and discusses the mechanical structure analysis and control system design of the three servo manipulators. Starting from the existing manipulators, the three-servo robotic body is designed and processed by the three-dimensional software Pro/Engineer, and the multi-axis motion controller is combined with the touch screen. Development of servo robot controllers.
(1) Design and assemble a three-dimensional model of the three servo manipulator through the three-dimensional design software Pro/Engineer. The numerical simulation analysis of the designed three-servo injection manipulator was carried out by using finite element numerical analysis software PAIRAN.
(2) The method of selecting the capacity of the servo motor is given by calculation. The hardware connection mode of the three servo manipulators in the position control mode and the method of adjusting the parameters of the servo motor are determined.
(3) Using the step servo to develop the motion control system of the three servo manipulators, analyze the flow of the robot automatic operation, and introduce the functions of some main programs of the motion control system.


1 Finite element analysis of three servo manipulators
Injection molding machine manipulators are required to be stable and reliable in mechanical design and control system design. The three-servo robot model was designed by using 3D software Pro/Engineer, and the static analysis, modal analysis and harmonic response analysis of the three servo manipulator model were carried out by using the finite element method. Based on the finite element calculation results, the three servo manipulator structure model is optimized.
1.1 Introduction of three servo manipulator mechanical model

According to the existing all-pneumatic, single-servo robot, the model of the three-dimensional manipulator is established by Pro/Engineer as shown in the figure:
1.2 Manipulator vibration modal analysis calculation

Vibration modal analysis of the designed prototype to determine the natural frequency and mode shape to avoid resonance of the machine during operation, and to provide a theoretical basis for analyzing structural dynamic response and other dynamic characteristics. The manipulator generally works at low-order frequencies. Therefore, when modal analysis is performed on the structure, all natural frequencies and modes are not obtained. The low-order frequencies of the manipulator system are considered, and the first four-order modes are given:
1.3 Manipulator vibration modal analysis calculation
The modal analysis of the optimized manipulator is performed using PATRAN software, and the first 4th order node amplitude cloud map is listed.


2 Robot servo motor selection and application
The selection and commissioning of the servo motor directly affects the overall performance of the robot. The servo motor has insufficient capacity, and the robot will be overloaded for a long time; the servo motor capacity is too large, which affects the performance of the manipulator; the servo debugging is not good, the robot movement is uncoordinated and unstable, and the ideal control effect is not achieved.
2.1 Overview of Capacity Selection Calculation
The selection of servo motor is selected by the selection software, but each brand of servo motor corresponds to a servo selection software, which restricts the reasonable selection of the servo motor model. The user must select the servo motor selection software completely. Understand, at the same time with the actual experience of servo motor can be correctly selected, therefore, it is meaningful to give a general calculation method to select the capacity of the servo motor to increase the flexibility of servo motor selection.
Calculation of servo motor capacity
W, Wl: movable part weight; W2 weight; household: friction coefficient; GL: reduction ratio; BP screw; pitch (mm)
1, the maximum moving speed of the servo V
The maximum speed of robot movement is affected by two factors.
(1) The number of teeth and the pitch of the timing pulley. The larger the value, the faster the robot moves.
(2), reducer reduction ratio, the smaller the reduction ratio, the faster the robot speed. The rated speed of the small inertia servo motor is generally 2500-300Or/min, and the rated speed above the medium inertia is about 1500-2000r/min.
The parameters of the selected cross-section reducer and pulley are as follows:
Selecting the precision wide-purpose reducer, the reduction ratio is 1:10, and the number of synchronous gears is 20. Since the robot developed this time is a medium-sized manipulator, the main installation object is a medium-sized injection molding machine. The speed requirement is not high. According to the above calculation, 1:10 is selected. The reduction ratio reducer is fully compliant.


2.2 Application of servo motor
Through the installation and debugging of the electrical part of the manipulator, it is found that the stability of the servo motor determines the overall performance of the servo motor. This development selects the position control method of the servo motor to drive the servo motor, which has the advantages of accurate positioning and strong anti-interference ability.


 2.2.1 Servo hardware connection in position mode
The three-servo robot uses the position control method of the servo to drive the motor to the servo motor of the step I000w.
For example, ED430-0100-LA-K-000, the driver power supply wiring is as follows:

In order to operate the motor, the following components are required:
1. Logic voltage 24VDC (low voltage, safe isolation from 230VAC) is provided to the logic power supply of the driver control circuit.
2. Power supply (24VDC ~ 70VDC) single-phase or three-phase 220VAC is provided to ED430 series servo drive
3.ED430 driver + terminal block
4. Motor and related cables (motor cable, encoder cable, RS232 programming communication cable)
5. A mechanical structure (such as a guide rail) with an origin and a limit switch
2.2.2 Provide logic power to the drive (controller's power supply X4)
The logic supply voltage is valid from 18V to 30VDC and is connected to +24VGND of X4.
Please refer to the following figure for the external wiring diagram of ED servo drive.

3 Robotic man-machine interface development and design
3.1 The basic principle of the touch screen
The basic principle of the touch screen is that when a touch screen mounted on the front end of the display is touched with a finger or other object, the touched position (in the form of coordinates) is detected by the touch screen controller and passed through an interface (such as RS-2 to make a serial port). It is sent to the CPU to determine the information entered. Touch screen systems typically include a touch screen controller (card) and a touch detection device.
Touch screen parameter settings

The development of the touch screen is more flexible and can meet the development needs of the robot system. It is suitable for industrial development and use. By writing macro programs, it can realize complex manipulator human-computer interaction interface form, suitable for robot users, and choose the touch screen of step MT8403T. The picture is as follows:
3.2 Manipulator man-machine interface needs to display the function
Since the injection molding machine manipulators determine the specific action flow according to the relevant molds used in the injection molding machine, the action parameters of the manipulator must be carried out through the man-machine interface, and the satisfactory manipulator action effect is obtained through teaching and manual means. Therefore, the development of the man-machine interface of the robot must be developed around the robot's first-off action. The human-machine interface should also contain the following information:
1. Display of teaching program and teaching program action, mainly related to the movement of each motion axis, the action of each solenoid valve, delay, jump, judgment and other action instructions and modification of related parameters
2. Software stroke security protection interface
3. Product stacking procedures, additional equipment (such as conveyor belt, fuel injection equipment control)
4.FO signal display, real-time monitoring of the action of the robot through this interface
5. Robot alarm information
4 Analysis and design of three servo manipulator control system
The digital motion controller is a high-performance digital motion controller based on micro-processing technology. It can easily realize various motion forms such as linear, circular arc, spiral interpolation, electronic gear, electronic cam, synchronous tracking control, virtual axis control, etc. Wide interface with the driver: RS232, 485, Ethernet, Medbus, DevieeNET, Profibus, Sercos and general servo interface (pulse + direction).
Motion controllers are mostly divided into stepping axis control and servo axis control, and the two generally share the same port. The step control axis generally drives the stepping motor by means of PWM (pulse width modulation), and different pulse waves are generated through parameter adjustment; and the stepping motor is controlled by subdivision; the servo control axis is mainly It is used to drive the servo motor or encoder. Most of them use analog quantity or voltage control mode. The control voltage can be adjusted arbitrarily. The speed and direction of the servo motor can be changed by adjusting the magnitude and positive and negative voltage. In the robot industry, the servo motor is controlled by the position control mode of the servo motor (ie, the pulse control mode), and the normal motion of the servo motor is controlled by the AB phase pulse and the positive and negative of the pulse.
4.1 Three servo manipulator main action flow
The speciality of the manipulators used in the injection molding industry is basically the same as that of the robot. The only purpose is to safely and reliably remove the products produced in the most reasonable and quick way.

Robot control flow
The main working process of the robot is concentrated in the automatic running program. • During the automatic running process, the robot moves according to the predetermined program and monitors the robot's motion process in real time. Once the system is unstable, the program runs abnormally. The detection signal is incomplete; the servo motor alarms, etc., immediately shut down the entire program to achieve the purpose of safety protection.
4.2 Analysis and discussion of robot motion control system
The action of the manipulator often requires the relationship between the control pulse and the speed to be converted into a relationship between the pulse and the distance, which makes it easier to control the servo motor, is conducive to the preparation of the program, and is more conducive to the expression of the teaching mode. The relevant parameters are as follows:
The pulley size of each axle and the deceleration of the reducer are as follows:
Horizontal axis: 23 teeth, pitch IOmm, reduction ratio 1:9
UNTIS=(131072*9)/(23*10)=10257
Pulling shaft: 15 teeth, pitch IOmm, reduction ratio 1:5
UNTIS=(131072*5)/(15*10)=8738
Up and down: smart tooth, tooth distance IOmm, reduction ratio l:5
UNTIS=(131072*5)/(15*10)=8378
The meaning of the above parameters is that the above number of pulses are transmitted, and the corresponding axis motion distance is 1 mm. During the teaching process, the motion controller calls the input value by calling the internal package to obtain the number of pulses to be sent, and then controls the servo motor operation.
4.3 Robot program development

During the development process, we strictly distinguish the main program of the robot motion control from the subroutine, so that the whole control process is clear and rationalized.
5 Summary
Multi-axis servo manipulators are a development trend for injection molding machine-specific manipulators. Based on the existing full pneumatic manipulator and single-axis servo manipulator, the actual model of the three servo manipulator was designed and developed, and the mechanical structure of the manipulator was analyzed and optimized to improve the mechanical performance of the manipulator.
The control system of the three servo manipulators was developed using a hardware development platform combining Step servo and human machine interface. The commonly used manipulator origin return method has been improved to improve the performance of the manipulator in the process of returning to the origin.

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