Research And Development Of Crane Smart Overload Limiter

The application of electronic technology promotes that weighing technology is becoming more and more automatic,integrated,diversified and intellective.The overload limiter is initially used in hoisting machinery (such as bridge-type and gate-type),which is mechanical and has big volume and complex structure,so until now the overload limiter has been replaced by the electronic type.We require high precision and accuracy about measurement and control,besides we also require high performance and reliability about system.Firstly we must ensure the function of overload limiter,then in order to improve the product quality we have to improve the integration and the reliability of system.The signal collected by load cell is transmitted to the next level using shielded cable,and then the signal can be further processed (such as enlargement,A/D conversion and controller of single-chip).But in this way,the signal will be attenuated and the sensitivity of the whole system will be reduced.In the industrial field,the shielded cable which is damaged due to environmental factors and nature of work will lose the ability to transmit signals.Because the installation of shielded cable makes that it's difficult to detect the source of trouble,it is hard to inspect and maintain the system.This design replaces the shielded cable by short-range wireless transmission module nRF24L01 which can overcome the problems caused by the shielded cable.This paper illustrates the research background and significance of the design,analyzes the domestic and overseas status of overload limiter and summarizes the main contents of the study and works.According to the requirement,the main and auxiliary hook of overload limiter are designed,the installation of sensor is analyzed,so the accuracy of the collected signals can be ensured and the signals can be processed in the next level.In chapter 2,two design schemes are presented. After determining the program,the sending and receiving hardwares of the overload limiter are designed,the hardwares are separated into several modules.In sending end of the load cell,the amplifying circuit module,the A/D converted module,the single-chip (AT89S52) and the peripheral circuit module are integrated into one (that is functional integrated sensor).In the receiving end, AT89S52 is also used as a core control chip.The relay control module,the power module,the wireless module nRF24L01 and the acousto-optic alarm module are designed too.Based on the expansion of 8255A,the nixie tube display module is designed.The corresponding software is compiled according to the modularized design.The key to wireless communication is to prevent the interference of other devices of the same band.This design uses nRF24L01,so the work channel is optional and the switching time of channel is very short.Frequency-hopping spread spectrum can resolve the wireless interference introduced by other frequency 2.4G equipments such as a Bluetooth, Wi-Fi,Zig-Bee,etc.