Discussion on the selection of control appliances

2022-10-15
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Discussion on the selection of control appliances in the electrical control of CNC machine tools

with the development of science and technology, social products also tend to diversify, the product renewal cycle continues to shrink, the proportion of mass production of products begins to increase, and the processing requirements for products are becoming higher and higher. Now the traditional processing equipment can no longer meet the complex and diverse needs of society for products, Therefore, high-precision and efficient automatic production equipment CNC machine tools were born. The electrical control performance of the data machine tool depends on the electrical control mode of the data machine tool, so the machine tool is essentially a device that converts the electromechanical capacity, and its main function is to convert the electrical energy into the mechanical energy required by the machine tool processing technology

this paper mainly focuses on the control electrical appliances of CNC machine tools, and interprets the electrical principles of CNC machine tools in the relevant analysis and discussion, so that it looks more clear

1. Brief description of the electrical control of CNC machine tools

CNC machine tools are equipment that need long-term continuous operation. Therefore, in practical application, the reliability requirements of CNC machine tools are relatively high, so in the selection of electrical control system design and components, we should fully use fault-tolerant technology and redundancy technology, as well as reliability technology as the basis and guarantee. At the same time, on this basis, it should also be required to have progressiveness characteristics, such as the new combined functions of some electrical components, the use of information electronic appliances, and the use of power electronic power devices. It is required that the selected components must be the most mature products that can meet the relevant national standards and have relevant authorization and certification. In addition, the electrical control system must also have certain maintainability, stability, safety, humanized operation, good control characteristics and other good performance

2. Selection of control appliances in the electrical control of CNC machine tools

2.1 selection of relays

relays are electrical components that need to be connected or disconnected through the change of input signals. The physical quantities input into relays are usually voltage, current, temperature and pressure, and the corresponding contact action is output. The general selection principle of relay requires that the type selection should be carried out according to the specific environment required, and then the relay should be determined according to the characteristics of the input signal. The types of various new extrusion products can be developed, and the corresponding parameters can also be input to select them. Mainly, different capacities and types of relays can be selected according to the load. Relays with different structural characteristics and principles of action require completely different input signals in nature. For example, thermal relays operate through thermal effects, while biological relays operate through sound effects. Therefore, users are required to select relay types according to the nature of input signals

2.2 selection of transformers

transformers are electrical appliances that convert a certain value of AC voltage into different values of AC voltage. The specific types of transformers are as follows: A. three-phase transformers. Generally, in three-phase AC systems, the change of three-phase voltage can be achieved by using three single transformers or one three-phase transformer, so it is necessary to optimize the selection of three-phase transformers, In CNC machine tools, the three-phase transformer is also mainly used to supply power to the drive service system; b. Machine tool control transformer, which is generally suitable for circuits with a frequency of 50 to 60 Hz, and the colloid must have a constant viscoelastic input voltage lower than 660 V. It is usually used as the power control and stepping motor driver of general electrical appliances in various machine tools and mechanical equipment, as well as the power supply of indicator lamp voltage and local lighting. The selection principles of transformers mainly include: a. the selection principles of standard transformers. This kind of transformer usually needs to select the primary rated voltage in combination with the actual situation, and then select the secondary rated voltage. Generally, it is necessary to determine the rated current of each winding with the domestic experimental machine manufacturer according to the load situation, and it is required to be greater than and equal to the load current, At the same time, the corresponding transformer shall be selected according to the voltage and current of the secondary and the rated capacity of the secondary. b. For non-standard transformers, the corresponding primary rated voltage, secondary winding voltage and current capacity, as well as power frequency shall be selected for non-standard transformers

2.3 selection of low voltage circuit breaker

low voltage circuit breaker is also known as automatic air switch, which is an electrical component that combines control and protection functions. Generally, the mortgage circuit breaker will not frequently connect and disconnect the main power switch of the circuit and the switch of local current. Once there are short-circuit, overload, undervoltage and other related faults, it will cut off the circuit by itself, so as to effectively protect the electrical equipment in series behind it. Moreover, after disconnecting the current causing the fault, it is generally not necessary to replace the parts. Therefore, low-voltage circuit breakers are more and more widely used in CNC machine tools. The selection principle of low-voltage circuit breaker is that the rated current and voltage of low-voltage circuit breaker should be greater than or equal to the normal working voltage and current of relevant lines and equipment. The withstand limit and making and breaking capacity of the mortgage circuit breaker should be greater than or equal to the maximum short-circuit current. At the same time, the rated voltage of the undervoltage release should be equal to the rated voltage of the line, and the rated current of the overcurrent release should be greater than or equal to the limit load current of the line

2.4 selection of contactors

contactors are mainly used to control the on or off circuit and load circuit. They are usually composed of electromagnetic mechanism arc extinguishing device and contact system, as well as other relevant parts. Their true working principle is that after the coil is energized, the electromagnetic attraction generated by the iron core effectively pulls the armature, The iron bit drives the contact system to act, so that the normally closed contacts are disconnected, and some normally open contacts are closed. When the related coil is powered off, the electromagnetic suction also disappears, the armature is usually fully released under the reactive spring force, and the contact system will also be reset. The selection principle of contactors is mainly to select the use category of relevant contactors in combination with the work task of controlling current load required by contactors. Generally, there are two kinds of rated voltage of contactors, which are 500V and 300V respectively. However, it is required that it is greater than or equal to the voltage of the load circuit, which is mainly determined by the power of the motor and relevant operation conditions to host the current top of the contact, The current type and voltage level of contactor coil are generally the same as that of control circuit, while the specific number and type of contacts should try to meet the needs of circuit and control circuit

to sum up, CNC machine tool is a kind of electromechanical integration equipment that integrates Electromechanical, hydraulic and pneumatic. The core of reliable operation of CNC machine tool lies in its electrical control system. Therefore, it is necessary to understand and master the functions and use principles of common control appliances of CNC machine tool, so as to effectively help the fault maintenance and transformation of electrical control of CNC machine tool, as well as the design, So as to ensure the availability of CNC machine tools 11 The oil pump plunger is rusted and operates stably

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