First, the design idea of mechatronics system development
The advantage of mechatronics lies in absorbing the strengths of related disciplines and comprehensively applying them to achieve the overall optimization effect. Therefore, in the development process of mechatronics system, the role of technology integration and interdisciplinary should be emphasized. The development of mechatronics system is a multi-level and multi-unit system engineering. After all the units of the system are combined into a system, the functions of each unit overlap each other, and assist, promote and improve each other, so that the overall function is greater than the simple sum of the functions of each unit, that is, "the whole is greater than the sum of its parts." Of course, if the design is not proper, the system will lead to contradictions and frictions between units and internal friction due to the differences between units. If the internal friction is too large, the whole may be less than the sum of its parts, thus losing the advantage of integration. Therefore, in the development process, on the one hand, it is required to select the mechanical system parameters that match the electrical parameters of the control system when designing the mechanical system; At the same time, it is also required that the electrical parameters should be selected and determined according to the inherent structural parameters of the mechanical system when designing the control system. The comprehensive application of mechanical technology and microelectronics technology makes them closely combined, coordinated and complementary, which fully embodies the advantages of mechatronics.
Second, the design method of mechatronics system
There are substitution method, overall design method and combination method for the design scheme of electromechanical integration system.
1, substitution method
This method replaces the traditional mechanical control mechanism with electrical control. This method is often used to transform traditional mechanical products and develop new products. If the mechanical transmission mechanism is replaced by electric speed regulation system, and the mechanical cam control mechanism, latch plate, step switch and relay are replaced by programmable controller or microcomputer to make up for the shortcomings of mechanical technology, this method can not only greatly simplify the mechanical structure, but also improve the performance and quality of the system. The disadvantage of this method is that it can't jump out of the framework of the original system, which is not conducive to development ideas, especially when developing brand-new products.
2. Overall design method
This method is mainly used for the development of brand-new products and systems. In the design, the design of each subsystem is completely considered from the overall goal of the system, so the interface is simple and may even be integrated with each other. For example, the rotating shaft of the laser scanning mirror of some laser printers is the rotor shaft of the motor, which is an example of the combination of executive mechanism and motion mechanism. Today, with the popularization of large-scale integrated circuits and microcomputers, with the development of precision machinery technology, it is entirely possible to design a new mechatronics product that organically integrates elements such as actuators, motion mechanisms, detection sensors, controls and car bodies.
3. Combination method
This method is to select various standard modules and combine them into various electromechanical integration systems like building blocks. For example, when designing CNC machine tools, we can choose industrial series products from the perspective of the whole system, such as CNC units, servo drive units, position sensing detection units, spindle speed control units and various mechanical standard parts or units, and then design interfaces to organically combine all units. When developing mechatronics system, this method can shorten the design and development cycle, save the cost of tooling and equipment, and be beneficial to production management, use and maintenance.
Third, the content of mechatronics system design
The main contents of control system design in mechatronics system (product) can be summarized as: determining the overall control scheme of the system, determining the control algorithm, selecting a microcomputer, designing the hardware and software of the system, and coordinating the system.
1. Determine the overall control scheme of the system.
(1) Determine the control task
Before designing the system, the working process of the controlled object must be thoroughly investigated, analyzed and familiar with, and the specific requirements in practical application must be made clear. The tasks to be completed by the system should be determined according to the mechanical and electronic function division scheme, and then the control process and tasks should be described by control flow chart or other appropriate forms, and the design task specification should be written as the basis of the whole control system design.
(2) Design the overall scheme of the control system.
1) determines whether the control structure of the system is open loop or closed loop.
2) When adopting closed-loop control, we should consider the selection of detection sensors, the required accuracy level, and the installation and use environment of the mechanism.
3) Choose whether the actuator is electric, pneumatic, hydraulic or other, compare the advantages and disadvantages of the schemes according to the specific requirements of the controlled object, and choose the best one to use.
4) Clarify the role of microcomputer in the system: whether it is fixed value calculation, direct control or data processing and its functions, which input/output channels are needed and which peripheral devices are configured. Finally, the principle block diagram and supplementary explanation of the system composition are drawn as the basis for further design, and the cost is preliminarily estimated.
2. Establish a mathematical model and determine the control method.
Establishing the mathematical model of the system is a complex process and a tentative process, which needs to be weighed repeatedly.
1) according to the physical structure of the control system that has been preliminarily determined, the mathematical model expressions of each link and the whole system are established and composed by using appropriate control theory and methods. By calculating static and dynamic characteristics, it provides a basis for computer operation.
2) Choose different control algorithms according to different control objects and different control performance requirements. PID control algorithm is often used in the direct digital control system of process control equipment. Minimum beat control is a common control algorithm in position digital servo system. Control algorithms such as point-by-point comparison method, digital integration method and data sampling method are often used in machine tool numerical control. In addition, there are many control algorithms for optimal control, stochastic control and adaptive control.
3) When the control system is complex, the control algorithm is also complex. In order to facilitate the design and debugging, we can ignore the influence of small nonlinearity, small delay and other factors and simplify the control algorithm reasonably. Using computer system simulation technology, the control algorithm is gradually improved until the best control effect is obtained.
In a word, the determination of control algorithm is a gradual process of repeated revision and experiment.
Step 3 choose a microcomputer
Given the task undertaken by a microcomputer, there are many microcomputer schemes to accomplish the same task. Generally speaking, the selection is based on the principle that the given task (including the determined control algorithm) can be completed, the function of the selected microcomputer can be fully exerted, and a certain functional margin is left.
Starting from the requirements of controlling production machinery or production process, the microcomputer shall meet the following requirements:
(1) has a perfect interrupt system.
For the control computer, the real-time control function is a major feature. It includes the real-time control ability when the system is in normal operation and the emergency handling ability when a fault occurs. This kind of processing and control generally adopts interrupt control mode, that is, the CPU receives the terminal request in time, suspends the original execution program, then executes the corresponding interrupt service program, and then returns to continue executing the original program after the interrupt processing is completed.
When selecting the interface chip corresponding to CPU, there should also be an interrupt mode to ensure that the control system can meet various requirements put forward in production. For more complex control, we should consider using real-time operating system.
(2) Sufficient storage capacity
Because the memory capacity of microcomputer is limited, when the memory capacity is not enough to store programs and data, the memory should be expanded or equipped with appropriate external memory (such as hard disk, etc.). ).
(3) Complete input/output channels
I/O channel is a channel for exchanging information between the external process of the system and the microcomputer. According to the actual needs, there are switch input/output channels, analog input/output channels, digital input/output channels and direct data channels to realize the rapid and batch exchange of information. The working modes of channels are serial, parallel, random selection and working in a predetermined order.
(4) Selection of microprocessor chip
The essence of this choice is to determine the word length, speed and instruction system of the microprocessor that can meet the requirements of control function. These three are interdependent. General selection:
1) ordinary sequence control and program control, and 1 bit microprocessor can be selected;
2) 4-bit microprocessor can be used for systems with small calculation amount and low requirements on calculation accuracy and speed, such as calculator, household appliance control, simple control, etc.
3) For systems with high calculation accuracy and fast processing speed, such as economical WEDM, common machine tool control and temperature control, 8-bit microprocessor can be selected.
4) 16-bit or 32-bit microprocessor can be used in systems that require high calculation accuracy and fast processing speed, even RIRC or multi-CPU with reduced instruction set operations, such as production process control and high-speed machine tool control with complex control algorithms, especially for large amount of data processing.
(5) Selection of system bus
Microcomputer is mainly composed of several printed circuit boards (designed and manufactured according to functional modules). Of course, the connection between boards is realized by the connection between sockets of printed boards. Usually, in order to bring convenience to use and maintenance, it is hoped that the wiring between sockets is universal-every printed board in a system can be plugged into any socket. At the same time, it is necessary to establish a standard for sockets and connections for the universality and interchangeability of circuit boards produced by various manufacturers. This is the origin of system bus selection.
At present, the buses supporting microcomputer systems and mechanisms are: STD bus supports 8-bit and 16-bit word length; The multi-bus type can support the word length of 16, and the type II can support the word length of 32. S- 100 bus can support 16 bit word length; VERSA bus can support 32-bit word length, VME bus can support 32-bit word length. Manufacturers provide OEM products of various models and specifications for this kind of bus, including master module and slave module, which users can choose at will.
4. Overall design of the system
The system design is mainly based on the above control scheme, design requirements, the type of microcomputer selected and the specific design of the system. Its design can be divided into two types: hardware interface design and software design.
In the overall design of the system, one of the most important problems is how to solve the reliable and timely information exchange channel between microcomputer, controlled object and operator and the timing arrangement of time-sharing control. That is, the hardware configuration and software measures are comprehensively considered to solve the sequence arrangement of system operation and ensure the orderly operation of the system.
(1) interface design
For a product (or system), it is often necessary to transfer power, motion, commands or information between its components and subsystems, which are realized through various interfaces. There are usually mechanical interfaces between components of a mechanical body, between actuators and between detection sensors and actuators. The signal transmission interface between electronic circuit modules, the conversion interface between controller and detection sensor, and the conversion interface between controller and actuator are usually electrical interfaces.
The internal and external interface of mechatronics products is actually an interface for exchanging materials, energy and information, which has the functions of storage, conversion and service. According to the function, interfaces can be divided into the following three types:
1) zero interface. Without any conversion, directly connecting two parts with combined relationship is called zero interface, such as connecting pipe, cable, terminal post, rigid coupling and so on.
2) Universal conversion interface. There is energy or information conversion between two parts with combined relationship, but the interface without microprocessor is a universal conversion interface. Such as reducer, transformer, electromagnetic clutch, amplifier, photoelectric coupler, A/D converter, D/A converter, etc.
3) Intelligent conversion interface. It is a conversion interface with microprocessor, which is programmable, so it can automatically change the interface conditions, such as 8255A, 8279, PIO, etc.
At present, most hardware interfaces and software interfaces have been standardized or are gradually being standardized. For the hardware interface, you can choose the appropriate interface according to your own needs when designing, and then write the corresponding program with the interface.
(2) the design of the console
Microcomputer control system must be convenient for man-machine contact, and usually a console is designed for field operators. Generally, this kind of console can't be replaced by a microcomputer's own keyboard. The reason is that the field operator needs a simple, clear and safe operation panel to operate the machine. Therefore, the operation console is required to have the following functions:
1) has one or several groups of data input keys (numeric keys or dip switches, etc.). ) is used to input or update given values, modify controller parameters or other necessary data.
2) There are one or more groups of function keys or changeover switches, which are used to change the working mode, start and stop the system or complete a specific function.
3) There is a display device or screen that displays various operation states, parameters and fault indications. There should be an "emergency stop" button on the console, which is used to stop the system running in an emergency and switch to fault handling.
It should be clearly pointed out that every signal on the console is closely related to the running state of the system. When designing, the functions and significance of these switches, buttons, keyboards, monitors and fault indicators must be made clear, and the hardware of the console and its corresponding management program should be carefully designed to make the designed operation console convenient and safe, and even if it makes mistakes, it will not cause serious consequences.
(3) Power supply design of microcomputer control system.
The power supply in microcomputer control system can have different types (DC and AC) and specifications (voltage and power) according to needs. According to the usage, the performance requirements are different. In the design process, reasonable debugging should be selected according to the actual requirements to control the voltage change. The power supply itself should have overvoltage, short circuit, overload protection and thermal protection, otherwise it will cause irreparable losses.
(4) Installation and connection design of the whole machine
This is a complete structural design. The installation of microcomputer control system includes not only the connection arrangement with the controlled object, but also the installation and connection of the host itself. Its design principles should be the reliability of installation and connection and the convenience of use, assembly and maintenance.
1) The installation connection structure is shockproof, that is, the printed circuit board, connectors and components, including cables, must be firmly installed on the same shell and will not be loosened due to vibration.
2) Adopt standard or special locking connectors with good manufacturing quality to ensure reliable contact and convenient use and maintenance.
3) The wiring structure should be reasonable to prevent mutual electromagnetic coupling interference. Be sure to separate the signal line from the power line and run the lines separately. For analog signals, more attention should be paid to the length of wiring and shielding. If the wiring is too long, measures such as signal enhancement should be considered.
4) Install safety ground wire, signal ground wire, shielding ground wire, power ground wire and strong current ground wire correctly, and finally connect the ground wire. The grounding wire should be of one-point grounding type, that is, the signal grounding wire, the power grounding wire and the controlled object grounding wire (safely) should be connected to the common grounding point. General public grounding point must be in good contact with the earth, and general grounding resistance should be less than (4 ~ 7) Ω.
(5) Software design
For the selected microcomputer control system, the microcomputer itself has certain software support. Generally, these softwares require users to understand its usage and basic principles. If the microcomputer is designed as a special control computer in a certain control field, users need to use the computer instruction system and the corresponding development system to design system software, that is, control software, management software, diagnosis software and so on. The design requirements of these system software are more specific and targeted.
In microcomputer control, its software tasks can be divided into two basic types: data processing and process control. Data processing mainly includes data acquisition, digital filtering, scale transformation, numerical calculation and so on. Process control is mainly to let the microcomputer calculate according to a certain control algorithm, and then output it to control production.
5. System calibration
After the design of microcomputer control system is completed, the hardware circuit should be made, installed and tested, and the continuous baking machine should be operated. Each module of the software should be debugged on a microcomputer to make it correct and then saved. After the above work is completed, the simulation test of system debugging can be carried out by combining software and hardware. After it is correct, the field experiment will be carried out until it is officially put into operation. At this stage, the most important thing is to carefully design the methods and steps of simulation debugging and the testing means used.
In addition, before the field test, the wiring should be carefully checked before the field debugging. The steps of field debugging should be carefully considered according to different objects. First of all, the automatic protection projects involved should be tested, and the tests can only be carried out after the functions, parameters and other projects are confirmed to be effective.