PLC overhead crane

Main points of PLC control system design of overhead crane

First, the design process

Overhead crane PLC system design, mainly includes the following links:

1, fully understand the various types of overhead crane production process structure, principles, conditions and characteristics.

2, fully understand and determine the user’s functional control requirements. General users, especially the characteristics of the PLC is completely unfamiliar to the user, the early requirements of the functional requirements are incomplete, and some may also be difficult to achieve. In the understanding of the object on the basis of the initiative, for the sake of users, introduced PLC features, for those who do not need to add additional hardware overhead and can fully play the potential of PLC functions, such as automatic counting, equipment, running time records are active For the user to consider; for those who spend a lot of investment, and the effectiveness of the function is not explained to the user, in respect of user opinions on the basis of the coordination and handling.

3, to determine the device in addition to the PLC device outside the hardware structure: including to achieve all the necessary control functions of the sensor, switch button, the implementation of the alarm and other input and output devices.

4, draw the timing diagram and state diagram and other functional flow chart. Depth analysis of system functions, lay the foundation for programming.

5, PLC device selection:

1) Analysis of the requirements of the system itself:

① Determine the number and type of I / O ports required by the system.

② determine the CPU should have the main function.

③ determine the size and type of memory capacity.

④ According to the scene to determine whether the need for remote I / O.

⑤ consider the system work environment requirements.

2) Analysis of market products:

To see which models meet the requirements in the technical performance, which can basically meet the requirements, in these models, and then the price comparison and measurement, and consider the reliability of the product, the availability of timely and after-sales service reputation , From which to choose a more ideal product.

6, the application of the design and simulation debugging, because the PLC all the control functions are through its application (or user program) to achieve the implementation. Therefore, the program design is undoubtedly the PLC application system key link. Should make full use of PLC a variety of simple, efficient programming instruction function to prepare the program.

PLC programming technical points:

① List the PLC input / output channel assignment table.

② According to the functional flow chart to draw the program flow chart and program structure function module diagram.

③ register the elements of the program at any time, easy to check and avoid duplication.

④ use more internal relays, to avoid too complicated mixed logic.

⑤ pay attention to consider the system function requirements did not think of the problem, such as interlocking, interlocking and so on.

⑥ to modify and simplify the program.

⑦ enter the program into the PLC and use the analog I / O device in accordance with the control requirements for analog debugging.

7, the real field of joint debugging.

This is a system, complex, tedious and indispensable work, it requires overhead crane manufacturers, control equipment manufacturers, users and design commissioners in close cooperation.

① PLC control cabinet and overhead crane on a variety of electrical equipment, the implementation of components connected to determine the accuracy, you can carry out the real field of joint debugging.

② First of all, the control circuit of the various agencies to check, check the action of various relay contactors meet the logic requirements of the overhead crane agencies, a variety of fault display alarm is accurate, or modify the application in the field until the exact date.

③ close the main circuit switch, the agencies no-load test, methods and steps with the ②.

④ Finally, the load test of the whole machine, the load test must be carried out by the order of light load, half load and rated load step by step, until the whole operation of the whole equipment to meet the technical specifications of the requirements, in line with national lifting transport machinery Of the relevant norms and standards, and ultimately get the user’s approval.

Second, should pay attention to the problem

In order to improve the reliability of the system, in the design process, we should pay attention to the following aspects:

1, leaving the output module (port) the load left some room. The most vulnerable part of the PLC device itself is the output module. The easiest way to reduce the output port load is to add a power amplification link to convert it with a relatively small intermediate relay with both pull-in and hold-on power. In addition, the design and selection should pay special attention to the output characteristics of these output modules.

2, pay attention to the output module of the external circuit protection. In order to prevent the output circuit from being damaged due to the short circuit of the external circuit or the like, a short circuit protection device may be provided at its output port.

3, interlock, interlock function of the hardware and software settings. Simply in the PLC internal logic interlock and interlock, often in the external circuit failure when the loss of the role. Such as the motor is the positive and negative contactor interlock and AC and DC contactor interlock, etc., only in the application to achieve is not enough. Because the contactor will often appear the main point “burned” and the main circuit in the coil after the power is still uninterrupted failure, then give the opposite control command will cause a serious short circuit of the main circuit. The solution to this problem is to introduce the contact points of the two contactors into the PLC input port, and then in the software to them in a closed way into the other side of the output coil, you can play a more protective role. Coupled with the hardware on the interlock, even more perfect.

4, the requirements of the PLC power supply and system of pressure protection. In the overhead crane loading and unloading site, the power quality is generally poor, interference, fluctuations, low voltage operation and instantaneous high voltage often occur, will have an impact on the operation of the PLC device. Although most of the PLC system has a strong power to adapt, but the use of high-quality power supply will undoubtedly increase the reliability of the system. In the application development to pay special attention to the system of pressure protection, to consider the state of failure when the initial state of the system recovery and interlock.

5, using a certain anti-jamming measures.

6, retain the reserve control means.