On January 4, 2011, the digital displacement sensor of the displacement measuring system with high accuracy, high resolution and good stability characteristics, and system SPP RS 232 interface circuit to solve the problem of PC and position feedback link between the short distance transmission. One meter infrared solar telescope terminal platform in order to get the clear solar spectrum, the displacement measurement system. This paper introduces the structure of the system and the working principle of the displacement sensor, and expounds the hardware design and software design of the data acquisition part SPP RS 232 interface circuit. Experimental results show. The displacement measurement results can meet the accuracy and real-time requirements of the focusing of the infrared telescope. The system will be put into trial by the end of 2009.
Introduction
In many computer application systems, the parallel interface and RS 232 serial interface are the most commonly used two standard interfaces. The standard parallel interface uses 8 bit data parallel forward transmission, which is characterized by high transmission speed and short transmission distance. The RS 232 serial interface is often used in the connection between data terminal equipment and data communication equipment.
Tilt meter Solar Telescope (hereinafter referred to as YNST) of the primary mirror will focus the displacement measurement system based on digital displacement sensor, the scientific objectives proposed, requires focusing range M3 mirror mirror focusing in O ~ 20 mm, and the displacement measurement value will be displayed on the digital display or control software and the transmission rate is not high, but the transmission distance in 10 ~ 15 m. High precision digital displacement sensor system and choose only the standard parallel interface (standard Parallel, Port, SPP, SPP) data transmission line which is connected with the host computer is short, therefore in the system to ensure the data transmission rate of the feedback system prerequisite requirements, between the computer and digital displacement sensor access SPP RS the 232 interface circuit, solve the problem of short transmission distance.
The structure of the system and the working principle of the displacement sensor
1. System structure
The overall structure of the system is shown in Figure 1. The system is composed of upper computer, motion control and displacement feedback. The host computer is an industrial control computer with at least two COM ports. The motion control part mainly by the motion controller, drive, hybrid stepping motor and the level of mechanical motion device; displacement feedback is mainly composed of digital displacement sensor and SPP digital display meter RS 232 interface circuit. Digital displacement sensor model for 5CB ~ 10C, displacement measurement range of 0 ~ 20 mm, digital display meter reading range of O ~ 19.999 mm, resolution of 1 m, linearity of the full range of 0.05%, that is, the accuracy of up to 10μm.
2. Working principle of digital displacement sensor
The digital displacement sensor consists of a differential transformer (LVDT) and an electrical measuring instrument. LVDT is the displacement of the measured displacement into the electrical signal sensor, which has simple structure and easy to use, long life and other characteristics, can be directly used to measure the relative displacement between objects, the length of the object changes. The utility model not only can be used to measure the static displacement but also can measure the dynamic displacement, and the electronic measuring instrument is composed of an electronic measuring circuit, a digital panel table and a A / D conversion board. A / D conversion board has a single terminal 16 analog input, A / D conversion bit is 14, the conversion rate of up to 10 s. The basic structure of LVDT is composed of a coil and a movable iron core which is surrounded by a spiral original edge and two side windings on the cylindrical framework, and the principle is shown in figure 2.
When the primary side of the supply of an oscillation voltage, due to electromagnetic induction, the two sides on the side of the induced voltage V1 and V2. If the core is at the center position of the coil, two pairs of edge to the primary side of the transformer is exactly the same, and pay the edge of the two AC voltage respectively by the detection circuit after detection, the two DC voltage the output DC voltage difference, differential V is zero. When the displacement of the iron core, the upper side of the edge and the primary side of the mutual inductance increases, while the lower, that is, V1>V2, the differential DC output voltage V>O, and vice versa. LVDT two secondary side induction voltage of V1, see figure V2 and qualitative relationship between the differential DC output voltage V and the iron core coil position 3, visible differential DC voltage V and the core displacement is linear in a certain range. When measuring the LVDT casing is clamped in the frame of reference, and the core rod fastening connection at the point of measurement, when the measured object is driven by core displacement relative to the moving coil, which linearly change the output voltage LVDT. By measuring the output voltage of the LVDT, the displacement of the measured object can be measured.
3. The realization of hardware and software of data acquisition interface
he motion controller system is developed by Yunnan Optoelectronics Laboratory, it communicates with the host computer through the RS 232 or RS 485 serial interface, serial signal format: COMl port, baud rate 4800 B / s, no parity, 8 data bits, 1 stop bit. Digital displacement sensor displacement feedback only provide standard parallel connected with the peripheral device interface, the A / D card pin 2 ~ 9 occupancy as input port, pin 10 to 13 as the output port, the port input and output electric TTL in average level. AT89C51 microcontroller as the core of the SPP 232 RS interface circuit by writing the input port to the A / D into the operating state, read the output port to get A / D conversion data and other information. A / D conversion results for the 14 bit binary number, divided into two groups to read, read the first group 8, second groups of low read 6. Each group is divided into two small reading, each time 4, the last one is the 2.
3. Hardware design of data acquisition interface circuit
Figure 4 is AT89C51 as the core of the SPP switch to the RS interface circuit schematic of the. AT89C51 is a 4 KB flash programmable read-only memory, low power consumption, low price, high performance CMOS 8 bit microcontroller. Connected to the input port P1 port and digital displacement sensor chip, into the operating state to the sensor in A / D, four bit high connected with the sensor output port of the P2 port, for the 14 data information read A / D conversion.
4. System software design
Figure 5 is the program flow chart, which figure 5 (a) for the host computer mainly through the motion controller to control the stepper motor rotation program flow chart, figure 5 (b) for the system feedback link displacement feedback program flow chart. Figure 6 is prepared by VC host computer control software interface, the host computer control software called MSComm control to achieve the upper computer and the control of the movement and the link between the position feedback. The host computer receives the 14 bit data sent by the interface circuit, and carries on the shift and the data processing to the data.
5. Displacement measurement experiment
The SPP RS 232 interface simulation using Protel and KeiI software design of PCB interface circuit board processing device, good selection after welding, assembly language programming, debugging through the line to download the program to the microcontroller, assembly of the whole system, the displacement measurement experiment. The stepping motor is connected with a horizontal moving mechanical device with a high accuracy and a reading scale, and the upper machine controls the stepping motor to rotate through the motion controller, thereby driving the mechanical device to move.
For the displacement measurement experiment data, can be seen from table 1, the stable displacement measurement results, compared with the actual mechanical device error is small displacement, high measurement accuracy, and experiment, the system response time is short, high real-time performance, meet the main mirror focusing solar telescope scientific goals in M3 mirror focusing request;