Abstract: This article introduced realizes the nuclear magnetic resonance meter bed body examination system’s hardware and the software design by the AVR monolithic integrated circuit, analyzed and has studied the bed body transversal motion and the longitudinal motion accuracy control question thoroughly.
Key word: AVR monolithic integrated circuit; Examination system; Motor control;
1 Introduction
In recent years along with medicine technology fast development, nuclear magnetic resonance meter already in large and middle scale hospitals by widespread application. At present, in the nuclear magnetic resonance meter’s production process, the bed body part must moves into the electromagnetism screened room assembly together after the magnet be able to carry on the examination, this to the personnel and the commodity is the very big waste. In view of this kind of condition, this article designed a set of nuclear magnetic resonance meter bed body part motion control and the examination system, it could carry on the examination independently to the bed body part, but does not will certainly completely systematically after the screened room installment examined, thus reduced the nuclear magnetic resonance meter bed body part production and the examination cost, reduced the production cycle.
This design take the general medical group’s Ovation5 nuclear magnetic resonance meter’s bed body as an object, to actuates the bed body to make the transversal motion the cocurrent to step-by-step the electrical machinery and the actuation bed body makes the longitudinal motion the direct-current servo electrical machinery’s accuracy control question to carry on a more thorough analysis and the research. The system has mainly used ATMEL Corporation’s Atmega128 monolithic integrated circuit and ALTRA Corporation’s EPM240T100 the CPLD chip takes the master control part, has realized to the bed body longitudinal and the transversal motion accuracy control and the examination. The master control electric circuit has selected the entire numerical control method and the antijamming design, has the very high resistance to interference.
2 Examination system’s hardware design
2.1 system hardware structures
This examination system mainly by the master control board, demonstrates the part, the push-key switch, the sensor, the serial communication and the motor control part constitution. The bed body’s movement divides into the transversal motion and the longitudinal motion two conditions, step-by-steps separately by the cocurrent the electrical machinery and the direct-current servo electrical machinery realizes. This system’s hardware architecture as shown in Figure 1.
Figure 1 System hardware structure schematic drawing
May see from Figure 1, electrical machinery’s logical control realizes by the master control board. System after initialization, when the switch or the pressed key send out the make-and-break signal for the master control board, by monolithic integrated circuit judgment bed body current condition, if the bed body has not been in the limiting position, then the monolithic integrated circuit sends out the driving signal to the corresponding electrical machinery, actuates the bed body to the corresponding direction movement, otherwise bed body stop motion. The transversal motion uses the open-loop control, the traveling position the pulse integer decision which sends out by the monolithic integrated circuit. The longitudinal motion uses the closed-loop control, in directs current on the servo electrical machinery’s encoder by the connection to feed back the position signal to give the master control board.
2.2 master control board hardware design
Master control board mainly by the AVR monolithic integrated circuit, CPLD, filter circuit, constitutions and so on level switch electric circuit and serial port communication circuit. The AVR monolithic integrated circuit mainly realizes the control function, CPLD mainly realizes the I/O mouth expansion, the logical judgement and to inputs, the output signal code decoding function.
This system uses AVR the Atmega128 monolithic integrated circuit is one kind of high performance, the low power loss 8 microprocessors, uses the advanced RISC structure, 133 instructions majority might complete in a clock cycle, satisfy this system to carry out the speed request. It has the non-volatility procedure and the data-carrier storage, in the 128K byte system programmable Flash. As a result of this system to fore-and-aft distance’s fluctuation, lateral distance’s fluctuation, programmings and so on keyboard scanning needs to use the timer. But this monolithic integrated circuit provided two to have the independent pre-frequency divider and the comparator function 8 timer/counter separately, as well as two had the pre-frequency divider, the comparison function and the capture function 16 timer/counter. It has two group 8 PWM and 6 groups resolution programmable (2 to 16) PWM output comparison modulator. It has the independent internal oscillator’s programmable watch-dog timer, can prevent the procedure to run effectively flies.
Figure 2 master control board hardware diagram
Master control board hardware diagram as shown in Figure 2, after system initialization, when has movement pressed key signal input the monolithic integrated circuit, the monolithic integrated circuit will output corresponding longitudinal or the aileron control signal. Monolithic integrated circuit receive after filter’s longitudinal electrical machinery encoder’s signal, by internal procedure computation current crosswise and vertical position, and the current positional information will output CPLD, by the CPLD actuation demonstration part, demonstrates current crosswise and the vertical position. Under the life test pattern, the longitudinal demonstration part also at the same time may demonstrate the life test counting. This system has the serial communication function, can through the serial interface and PC machine or other equipment correspondence.
3 Control system’s software design
The master control board first receives from user’s operation signal, then acts according to these signals the condition, realizes through the AVR monolithic integrated circuit and the CPLD internal procedure to the electrical machinery the control and the demonstration function. In this examination system, because needs to control the information which and to demonstrate to be many, and the relatedness is very strong, therefore needs to carry on the complex programming to the monolithic integrated circuit to be able to realize each function. Speaking of this system, the AVR monolithic integrated circuit solidifies the procedure the quality, immediate influence overall system’s movement stability and control precision, therefore the AVR monolithic integrated circuit solidifies the procedure the programming technology to become the systems control the key, this simultaneously is also this system’s design key one. Through the analysis bed body’s design requirements and the actual operational aspect, the design develops a set of bed body movement test order, enables the test system to be able to the bed body actual movement in all state of motion, the movement precision and the movement life carries on the test.
3.1 motor control strategy
This system to step-by-stepped the electrical machinery to use the open-loop control, has used the closed-loop control to the direct-current servo electrical machinery.
3.1.1 step-by-step electrical machinery’s control
The cocurrent step-by-steps the electrical machinery to send out the pulse driving signal by the master control board to step-by-step the electrical machinery driver to the cocurrent, thus actuates to step-by-step the electrical machinery movement. Electrical machinery’s rotation angle and the position the pulse integer decision which sends out by the master control board. The monolithic integrated circuit is through the control to driver output pulse quantity, after undergoing the computation, judges the current bed body lateral attitude. Lateral attitude through nixietube demonstration on user interface. Because step-by-steps the electrical machinery to have the characteristic which the error does not accumulate, can therefore realize through this split-ring’s control mode step-by-steps electrical machinery’s accuracy control.
3.1.2 servo electrical machinery’s control
The direct-current servo electrical machinery is the PWM driving signal which sends out by the monolithic integrated circuit after the enlargement actuates the electrical machinery movement. Through meets on electrical machinery’s encoder’s feedback signal and around the limiting position sensor judgment bed body current vertical position, has realized the direct-current servo electrical machinery’s closed-loop control. The control motor-driven signal, may realize the electrical machinery/to stop, the/reverse and to add/the deceleration function, thus realizes the bed body’s simple motion, the compound movement and assigns the state of motion. The servo electrical machinery’s actuation is sends out the control signal by the master control board, actuates the direct-current servo electrical machinery movement by the driving circuit, matches (encoder) surveys electrical machinery’s corner by the pulse generator, after the filter feeds back gives the monolithic integrated circuit, thus constituted electrical machinery’s closed-loop control system, has realized to the direct-current servo electrical machinery’s accuracy control.
3.2 AVR monolithic integrated circuits solidify the procedure
The AVR monolithic integrated circuit solidifies the procedure to use the ICC language compilation, and uses modular the design method, divides into the master routine, the keyboard scanning module, the display module, the motion control module, the transversal motion test module, the longitudinal motion test module and the life test module. The modular design causes the software to be more flexible, is advantageous for the transfer and the transplant, and is occurring wrongly, might very quick find the mistake, enormous enhancement system’s reliability and stability.
3.2.1 master routines
The master routine must complete system’s initialization, the interrupt establishment, the global variable establishment and the watch-dog establishment and so on. After the initialization had ended, the system enters the main inquiry cyclic process, the operation which the judgment current carries on, and enters the corresponding functional module. In the system program has selected the status byte method, realizes the master routine and each functional module, as well as between each functional module’s state of motion’s correspondence, had guaranteed cuts when each functional module, system’s security and stability. System master routine’s flow chart as shown in Figure 3.
Figure 3 master routine flow chart
Figure 4 keyboard scanning module program flow diagram
3.2.2 keyboard scanning module
Because is not high to the system response speed request, therefore the keyboard scanning has selected the inquiry method. Keyboard scanning module program flow diagram as shown in Figure 4, longitudinal motion’s priority is bigger than the transversal motion the priority, when the longitudinal pressed key and the crosswise pressed key simultaneously press down, the bed body the longitudinal motion, the transversal motion pressed key will be shielded.
3.2.3 life test module
The life measurement component is in this system the structure is most complex, involves variable most functional modules, and simultaneously has the system status byte and the life test condition shift quantity, therefore between each functional module’s condition correspondence is also more complex than other functional module. In this module, mainly realized the bed body to carry on the compound movement automatically the function, and could establish in advance to each kind circulating motion counting, thus realized to the bed body’s life test.
Figure 5 life test module
3.3 CPLD solidification procedure
The CPLD solidification procedure uses the VHDL language compilation. The major function is:
① Actuation “vertical position” nixietube demonstration current vertical position or life test counting;
② After limiting position sensor’s difference signal decoding, the output gives MCU;
③ The receive lateral attitude signal, and actuates “the lateral attitude” the nixietube, the demonstration lateral attitude;
④ The actuation limiting position instructs LED;
4 Conclusion
Through practical application which carries in the nuclear magnetic resonance meter’s bed body, proves the Ming dynasty printed books system to be able to realize completely to the bed body’s control function, and satisfies to the bed body each kind of test request, has the high stable reliability. This system can the independence carry on the examination to the nuclear magnetic resonance meter’s bed body, reduced the production cost greatly, reduced has lived has not produced the cycle, had the high application value.
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