| Grating scale is a kind of precise detecting sensor and is widely used in modern precision measurement fields. For example, it is always used in angular measurement and linear measurement on CNC machine system. For its excellent characteristics of high precision, wide scale and fast response, it has been commonly used in the detection of closed-loop control of CNC machine system, especially in high-speed and high-precision processing activities. However, the test device for grating scale data available in the market requires so much professional knowledge to operate that the industrial workers cannot handle it cleaver and skillfully. Besides, the existing equipment is much more expensive, not suitable for small and medium enterprises. According to the above reasons, designing a low-cost, easy-to-operate grating scale test platform is becoming more and more practically significant.First, current situation of main scale acquisition device is investigated, as well as the trend of industry bus transmission protocols. By comparing characteristics of different kinds of bus protocols, strengthens of Biss is shown, such as its outstanding performance in speed, costs and open liscence/standard, etc. Considering the characteristics of the host and industrial current environment, RS485 is selected as the transmission method between the acquisition device and the storage system.According the design requirements, Altera’s Cyclone II FPGA chip is selected as the main CPU of the acquisition board. Command pulse receiving part, encoder data receiving part, FPGA peripheral circuit design and power are completed. Power supply ripple is analyzed and optimizated. While designing the storage system, TI’s high performance, low-cost chip AM335 x is chosen as the CPU, USB circuit which is responsible for the hard disk is finished. Besides, during this process, full consideration is given to the priciples of electromagnetic compatibility and signal integrity on the PCB layout for a reasonable design.Using VHDL programming language, Biss protocol, RS485 protocol, encoder and pulse counter module are designed. And the solution to USB hard disk storaging which involved ring buffer is promoted. Each module’s function is tested seperately, and the results shows that this platform could finish the acquisition and storage process successfully.In last part of the thesis, the final test is conducted. Grating scale is fixed on the axis of the machine, command pulse and encouder pulse came from the motion controller, when the process of acquisition and storage finished. The software Offline Data Analysis helps to plot and analyze the data in the hard disk. Additionally, stability and real-time performance is analyzed. The final results shows that this platform could finish the acquisition and storage job successfully. |
