Application of the hottest mscl210 in micro displa

Application of mscl210 in micro displacement sensor system

0 introduction

micro manipulation has been applied in many application fields, especially in nano micron positioning system, the sensor is required to detect micro force and displacement information. At present, there are many principles for micro displacement detection, such as optical, magnetic and inductive, capacitive and piezoelectric, but these are mostly inconvenient for robots to obtain micro multi-dimensional force and displacement information. In order to use the multi-dimensional force sensor with mature technology for the acquisition of micro force and micro displacement information, the robot sensor laboratory of Hefei Institute of intelligence, Chinese Academy of Sciences, while transforming the structural parameters of the multi-dimensional force sensor, makes full use of many new features of mscl210 single chip microcomputer of Texas Instruments (Ti), such as its own 8-way 24 bit high-precision - △ A/D converter, programmable gain amplification (PGA) and filter, and realizes the high-precision measurement of force and displacement. This paper mainly discusses the application of microcomputer, hoping to help improve the integration degree, resolution, stability and human-computer interaction ability of the sensor

1 characteristics of multi-dimensional force sensor and introduction to mscl210

the structure of micro displacement sensor mainly draws lessons from the structural characteristics of robot six dimensional wrist force sensor in the laboratory, and the double E-shaped diaphragm structure is also used in the design. Firstly, the improved two-dimensional force sensor is used to detect the force information on the X and Y dimensions acting on the object, and then it is converted into the displacement information of the plane. At the same time, based on the robot six dimensional force sensor, it changes the relevant structural parameters, such as range and sensitivity, in order to achieve the acquisition of small force and displacement information

Texas Instruments has newly introduced a powerful microprocessor mscl210 with 24 bit a/D converter. Mscl210 has some enhancement characteristics, and is especially suitable for measuring weak signals output by high-precision temperature and pressure sensors. Mscl210 mainly includes enhanced 8052 microcontroller core, flash memory, high-performance simulation functions and high-performance peripherals. The core of the enhanced 8052 microcontroller includes dual data indicators, and the speed of executing instructions is three times faster than that of the standard 8052 core. This MIPS function enables users to optimize speed, power and noise according to special needs. Figure 1 is a block diagram of mscl210 ADC

msc1210 input multiplexer is more flexible than general ADG, and each input pin of it can be configured as positive input or negative input for specific measurement. Compared with the input pair usually defined by the startup ADC component, MSC1210 can define one pin as a negative input and the other as a positive input, making the design convenient and free. A group of bridge outputs of the micro displacement sensor are respectively connected to ain0 and ain1 of MSC1210 ADC as a differential input; The other group of bridge outputs are respectively connected to ain2 and ain3 of MSC1210 ADC as the second differential input. The initialization value of admux register is: admux=ox01

according to the data of TI's MSC1210, the input buffer can reduce the possibility of offset in ADC measurement. As long as the characteristics of the input signal allow, it should be used. The only case where the input buffer is not used is that the maximum voltage on one of the analog inputs is higher than 1.5 V below the normal rail voltage. Without buffer, the input impedance of MSC1210 is 5 m/PGA. When the buffer is enabled to actively meet the growing safety requirements, the impedance is generally 10 G. The input voltage range is reduced and the analog power supply current increases. In the above-mentioned only case, the buffer was not used in the experiment, but the buf bit in the ADC control register (adcono.3) was cleared, that is, the buffer was turned off, but the effect was ideal, and the zero output deviation of the sensor changed little. The gain of programmable gain amplifier (PGA) can be set to 1,2, 4, 8, 16, 32, 64 or 128. Using PGA can greatly improve the effective resolution of ADC. Of course, the gain setting should be reasonable, otherwise the noise will also be amplified. In the experiment, the gain of micro displacement sensor is set to 64 (to be exact, it should be the gain of PGA of cl210 ADC after the MS warranty period)

msc1210 digital filter has three types: fast build, sinc2 or sinc3, and there is also an automatic mode. After the input channel or PGA is changed, the automatic mode can modify the sinc filter to the best available option. After switching to the new channel, it can use the fast establishment filter for the next two conversions, and the first conversion should be discarded. Then, sinc2 and then sinc3 filters are used to improve the noise performance. This operation can combine the low noise advantage of sinc3 filter and the fast response of fast recovery time filter at the same time. Sinc in digital filter is a kind of FIR filter in digital filter, which is often used in ADC of △ 1. When the input channel changes suddenly, the output takes some time to correctly represent the new input. The time required depends on the type 1 material surface treatment of the filter used. Sinc2 usually represents the data output time requiring 2 cycles, sinc3 represents the data output time requiring 3 cycles, and others require 1 cycle. Generally speaking, if sinc3 filter is used, when the input channel is changed, the first three sampled output data cannot be used and should be discarded; Only the fourth output data is available. This is crucial

msc1210 can use either internal reference voltage or external reference voltage. The starting configuration of the reference voltage is internal 2.5 v. The reference voltage can be selected through the adcon0 register. The internal reference voltage was enabled in the experiment, and was selected as 1.25 V by setting adcon0.4 (vrefh). It should be noted that enabling internal VREF does not eliminate the need for external connections. The refout pin must still be connected to vref+, and vref- must still be connected to agnd, so that the internal VREF can operate normally. Due to space limitations, other functions of MSC1210 ADC are not introduced here

2 hardware composition of sensor

due to the high integration of MSC1210 ADC, the hardware system composition is very simple. Because of this importance, the function of the experimental machine is clear. Figure 2 is a partial rendering of the micro displacement sensor. The strain resistor is pasted on the surface of the E-type diaphragm in a specific direction through a special process, and connected to form two groups of automatically decoupled Wheatstone full bridge circuits as the analog output of the original force information. The compact circuit board is placed in a circular aperture

Figure 3 is the circuit structure diagram of the experimental system. The experimental system is mainly composed of sensor body (output original analog signal), MSC1210 core, serial communication circuit and PC. As mentioned above, a group of bridge outputs of the micro displacement sensor are respectively connected to ain0 and ain1 of MSC1210 ADC as a differential input; The other group of bridge outputs are respectively connected to ain2 and ain3 of MSC1210 ADC as the second differential input. MSC1210 communicates with PC through RS 232 to display information and control MSC1210

3 software design of MSC1210 data acquisition system

the setting of each control word of MSC1210 ADC will greatly affect the final resolution and stability of the sensor. For example, whether the input buffer is used or not, the selection of programmable amplifier gain, the selection of modulator clock speed (which determines the analog sampling rate and the selection of filter model), and so on, these parameters are not set at one time. Some of them need to be combined and tried repeatedly, and finally get satisfactory results. In order to avoid having to download to the flash program memory after modifying the program every time, the initialization of ADC of MSC1210 before operation is fully controlled by PC. First, the PC transmits various necessary control information to MSC1210 through the serial port, and MSC1210 initializes the ADC according to these information. Specifically, the PC sends six bytes to MSC1210, including the filter model, the sampling value in aclk, adcon2 and adcon3 registers, the delay value after modifying the analog input channel, the number of data output cycles that must be discarded, and the gain of the programmable amplifier. Then, MSC1210 starts the initialization of ADC. After entering the normal working state, if it is found that the current data output cycle number has been greater than the preset data output cycle number that must be discarded, MSC1210 considers this output data and its subsequent output data to be valid, but it does not immediately send the data to the PC, but immediately modify the analog input channel, and then make the output of the previous input channel invalid, and then enter the next data output cycle. The workflow of mscl210 can be simply shown in Figure 4. In addition to the initialization control of MSC1210 ADC, PC is mainly responsible for displaying the data sent by mscl210 through RS 232 serial port in the appropriate position of the window in real time with visual graphics. MSC1210 sends 4 bytes to PC each time. These four bytes are defined as follows: the first byte represents the channel number of the sensor, and 0 represents the differential input between ain0 and ain1, that is, x-dimensional information; 1 refers to the differential input of ain2 and ain3, that is, the information of Y dimension. The last three bytes are the 24 bit binary representation of the output data and the conversion result of MSC1210 ADC. When the PC processing process detects that the input buffer is full of 4 bytes, it reads the data of the buffer and empties the input buffer at the same time. After identifying the channel according to the first byte, convert the data into voltage value and display it to the corresponding position (unit: MV), and open up two graphic display areas in the window to display the signal changes of x-axis and y-axis in real time respectively. In order to better observe the small changes of the signal, the process provides the function of graphic amplification and display. For convenience, the magnification can be 12.5 times and 125 times

4 experimental results

after repeated tests, combined with the actual requirements, the data output rate of the micro displacement sensor is finally positioned at 10 Hz, with a resolution of 15 bits, which has high stability and achieved good results. The selection of relevant parameters is as follows: the filter model of MSC1210 is sinc3, aclk is 1, the sampling value in adcon2 and adcon3 registers is set to 1080, the analog input buffer is turned off, the analog input channel is changed, 3 data output cycles are discarded, and internal self correction of offset and gain is adopted. Figure 5 is the graphic display of the data output of the micro displacement sensor during operation. The two curves represent the force on the x-axis and y-axis respectively. According to the force information, the displacement information can be easily calculated

based on the multi-dimensional force sensor technology of the robot sensor laboratory of Hefei Institute of intelligence, Chinese Academy of Sciences, the micro displacement sensor is successfully developed by using the advantages of MSC1210, which has the advantages of small size, high resolution, good stability and so on. MSC1210 Single chip microcomputer is a powerful data acquisition chip, which can be widely used in instrumentation, measurement and control, navigation and other fields