| In our real life, particles can be found everywhere. Many kinds of products and materialsexist in the form of particles. Besides, the quality and properties of products and materials aredirectly affected by the distribution of the particle size. At present, the laser particle sizeanalyzer is one of the main means to measure the particle size, which has been widely used inmany areas such as industry, agriculture, medicine, etc. The laser particle size analyzertypically adopts the small-angle forward scattering theorem. Its multielement photodetectorconsists of several doroids, and a circle center is required to coincide with the incident light axis.The adjustment process is called laser particle size analyzer centering. The manual centeringmethod will not only increase the interference from human factors, but also the technicalrequirements of the operators. In order to avoid the situation mentioned above, automaticcentering method is adopted instead in this paper. The content of this paper concerns the designof the stepping motor driver which is based on SCM and automatic centering of the laserparticle size analyzer. The main work includes certain aspects described as follows:1. Design of stepping motor. C8051SCM produced by Cygnal is adopted in this system.There are2-way12-bit D/A converter,2-way voltage comparators and other components in theseries of SCM, which can be used for the design of the peripheral circuits. This highlyintegrated system of components not only provides a convenience for the design for low powerconsumption, small size, high reliability and high-performance drives, but also reduces the costof the driver. The system adopts Chopping Wave Constant Current Division driving controltechnology and uses C8051F SCM as the core control, looking up the internal currentbreakdown table and obtaining the corresponding value of the current ladder through thejudgment of the input signal and the current state, then outputing a corresponding controlvoltage through the internal D/A conversion. The electrical current detection circuit detects theelectrical current size of the motor winding and converts it into voltage, then compares thisvoltage with the output control voltage of the D/A conversion through the internalmicrocontroller of SCM, and generates the PWM signal. Subsequently the PWM signalcontrols the work of the H-bridge and makes the stepping motor winding current close to the reference value.2. Design of the three-dimensional mobile platform. The photoelectric detector is installedon a mobile stage which is adjustable in the three directions: up and down, left and right, frontand back. The three-dimensional precise moving table consists of3rings to achieve the aboveprinciple. In order to reduce the impact of errors, the base was designed as much as possible toensure the linear relationship of movement between the driving part and the driven one, and ittries to ensure that the rails have better movement of linearity in the design of the rail structureand technics.3. Stepping motor control of the mobile platform. The up and down, left and right, frontand back movements of the mobile platform is controlled by a stepping motor in order toachieve automatic centering of the laser particle size analyzer. System program consists of themain program, the straight program, the reverse program and speed control program, and themain program separately invoke other subroutines according to their state program. Thethree-dimensional mobile platform can be driven up, front, and right movements by setting thestepper motor to move in obverse, or just the reverse.4. C8051F20SCM controls the stepping motor to coincide. The control signal is generatedby the SCM. The basic control functions are described as follows: control the order ofcommutation, control the turning diversion of the stepping motor, control the speed of thestepping motor. If one control pulse is sent to the stepping motor, it will turn one step, and thenanother pulse, another step. The shorter the interval of the two pulses is, the faster the steppingmotor turns. Therefore, the pulse frequency determines the speed of the stepping motor. Thespeed of the stepping motor can be adjusted by changing the frequency of the pulse that thestepping motor emit. The system will use the C8051F SCM to control the two-phase hybridstepping motor, which drives the implementing mechanisms to move along the X direction, Ydirection and Z direction (left and right, up and down, front and back), meanwhile controllingthe rotation number of steps to achieve automatic centering. |
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