MCU core, ultrasonic tooth machine software and hardware design solutions (1)

This article on a single chip at the core of ultrasonic tooth machine software and hardware design, the scaler with current sampling feedback automatically scan search resonance point, resonant frequency and vibration strength digital lock, minimal resonance point drift, solved using Analog oscillator circuit design of ultrasonic scaler of some inherent defect,

First, the hardware design

Hardware circuit diagrams shown in Figure 1.

The scaler of basic works as follows: as the core of the oscillation circuit TL494 in MPU control under the duty cycle of push-pull output pulse controlled by MPU serial send data to the oscillation frequency control circuit, control of the oscillation circuit, the oscillation frequency oscillator produces oscillations signal duty cycle and frequency is controlled by MPU oscillation signal power amplifier circuit amplification, high-frequency transformer boost after driving Piezoelectric ceramic plate, the ultrasonic oscillation signal to ultrasonic machinery vibration signal, the mechanical vibration to be good and clear irritate and dental calculus, etc, so as to achieve the appearance of the teeth.

　

1, power supply design

Ultrasonic scaler in typical power for 10 ~ 20 W, and require 180 ~ 250 v wide voltage range of work, in order to meet the requirements, reduced the power part of the heating, this circuit power partly by switching power supply.

The whole circuit schematic diagram shown in Figure 2.

　　

The switching power supply with Motorola MC34063 of DC-DC controller chip, the circuit has a line of simple, low cost, high efficiency, low temperature rise.

Core component MC34063 is a single-chip bipolar linear integrated circuit, the chip contains a temperature compensated bandgap, a duty cycle control oscillator drive and high current output switch. Output voltage U = (1 + R2/RI) · 1.25 V, current limiting resistors 1 Ω and therefore lose people current is limited to 0.3 V/1 A Ω = 0.3.

2. oscillation circuit

Oscillation signal generation there are a variety of ways.

The easiest way is by direct PWM output PIC16F73, the method is simple and convenient, but there are two drawbacks: first, does not have push-pull oscillation signal. Therefore power amplifier can only work in just half a week, low efficiency, heat more serious, is not conducive to circuit stable jobs. Second, Piezoelectric ceramic plate of resonant points (30 ± 5) kHz, harmonic frequency band width ≤ 80 Hz. The PWM output PIC16F73 in 25 to 35 kHz frequencies, Hz step frequency ≥ lOO, the PWM output PICl6F73 could not find the Piezoelectric ceramic plate of best resonance point. I design oscillation circuit resolved the problem.

Oscillation circuit control chip, the chip used TLt94 internal block diagram shown in Figure 3, the specific circuit shown in Figure 2.

Push-pull oscillation signal 9 feet of by TL494 and 10 feet output, this signal frequency from T1. 494 of 5 feet and 6 feet external capacitor and resistor Rt decision Ct, Rt and Ct should use low temperature drift of resistors and capacitors. The oscillation frequency is calculated as: fosc = 1.1/2Rt · Ct; the signal duty cycle consists of 1 foot TL494 and 2 feet add decided signal voltage.

3, frequency control

To meet the Piezoelectric ceramic plate oscillation frequency is 25 to 35 kHz, step frequency ≤ 80 Hz, Figure 2 circuit Rw is resistance of 20 k Ω rough adjustment potentiometers, Digital Potentiometers IC4 is PICl6F73 control of fine adjustment potentiometer.

Calculate Rw coarse (to 5 k 1C4 Ω), make the changes, the fosc 24.5 to 35.7kHz, meet the requirements. Refine selection of digital potentiometer IC4 k total resistance 10 Ω, 256-level adjustable MCP41010, communication with PIcl6F73 MCP41010 using convenient SPI, stepping resistance is 39.0625 Ω. Oscillator frequency of stepping into:

Oscillation frequency is 35 kHz time step frequency 30.4 Hz, the oscillation frequency is 25 kHz frequency when stepping 15.6 Hz.

From the above data, using digital potentiometer control TL494 works can meet the Piezoelectric ceramic resonator bandwidth requirements.

4, the intensity control