JP3507967B2 - Ultrasonic oscillator oscillation control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent frequency skipping which can occur by oscillation conditions when a power source is turned on by a relatively simple constitution of a circuit and to obtain effective oscillation by constantly oscillating at a specified frequency. SOLUTION: A judgment means 1 which judges whether oscillation is abnormal or not by detecting the oscillation frequency and comparing it with a standard oscillation frequency and a correction means 8 which returns the oscillation frequency to the standard oscillation frequency when the oscillation is judged to be abnormal are provided.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation control device for maintaining an oscillation frequency of an oscillation circuit using an ultrasonic transducer at a predetermined frequency. 2. Description of the Related Art In an apparatus using ultrasonic waves, it is necessary to oscillate an oscillation circuit combined with an ultrasonic vibrator at a predetermined frequency. As a general control method for this purpose, a method of detecting an optimum frequency of a vibrator and feeding it back to an oscillation circuit to maintain the oscillation frequency at a predetermined value is known. A voltage or phase indicating the state is detected, and a feedback loop is configured so that these are in an optimum state (for example, Japanese Patent Application Laid-Open Nos. Sho 62-114550 and Sho 63-114550).
127709). [0003] In the case of a dental ultrasonic scaler which is one of the ultrasonic devices, if the above control oscillates around the optimum resonance frequency, the temperature, the type and shape of the chip, the load applied to the chip, etc. Oscillation continues at that frequency irrespective of the fluctuation, and dental treatment using ultrasonic vibration can be performed without any trouble. FIG. 3 illustrates the relationship between the frequency and the admittance of the ultrasonic vibrator used in the ultrasonic scaler. There are two resonance peaks at 27 kHz and 35 kHz. In this case, if the oscillator oscillates at 27 kHz, the oscillator generates effective oscillation as a scaler. However, since effective oscillation cannot be generated at 35 kHz, conventionally, the reference oscillation frequency of the oscillation circuit is forcibly set to 27 kHz. It oscillates at this frequency. [0004] However, in such a conventional system, a strong load is applied to the chip at the start of oscillation immediately after the power is turned on, or the vibration characteristics of the vibrator are deteriorated. In some cases, oscillation may start at around 35 kHz depending on the oscillation conditions. This phenomenon is known as so-called frequency jump. The cause is that the resonance state is indirectly detected not by the frequency itself but by a voltage or a phase. That is, since the voltage in this case only shows a peak at the resonance frequency and the actual frequency is unknown, and the phase does not indicate the actual frequency, it is indirectly detected by the voltage or the phase. It can only detect whether it is approaching the resonance frequency. Also, even if the frequency is not the predetermined resonance frequency, once oscillation starts at a frequency other than the predetermined frequency, this is fed back and continued as it is, and it is possible to return to the normal frequency where effective vibration can be obtained. In particular, this frequency jump is likely to occur in a vibrator having poor vibration characteristics or a deteriorated vibrator. Therefore, in order to prevent this phenomenon, it is necessary to provide a complicated prevention circuit, and there has been a problem that the apparatus becomes expensive. The present invention has been made in view of this point, and aims to always obtain an effective vibration by directly detecting the oscillation frequency and returning to a predetermined oscillation frequency in the case of abnormal oscillation. It is. [0007] In order to achieve the above-mentioned object, the present invention sets in advance depending on oscillation conditions.
Abnormal frequency greatly deviated from the specified reference oscillation frequency
Oscillation circuit that may start self-excited oscillation
In the oscillation control device for an ultrasonic transducer, an oscillation frequency detecting means for directly detecting the frequency or period of the voltage generated in the oscillation circuit, and the detected oscillation frequency is increased from a preset reference oscillation frequency. A determining means for determining whether or not the abnormal oscillation has a shifted abnormal frequency, and forcing the actual oscillation frequency different from the reference oscillation frequency to the reference oscillation frequency when the abnormal oscillation is determined. Correction means for pulling back the target. This correction means converts a resonance circuit having a time constant corresponding to the reference oscillation frequency into a circuit having a time constant corresponding to a frequency lower than the reference oscillation frequency, or a circuit having a time constant corresponding to a frequency higher than the reference oscillation frequency. A means is provided for temporarily changing and restoring after a set waiting time. Next, an embodiment of the present invention will be described with reference to an example shown in the drawings. In the circuit diagram of FIG. 1, 1 is a CPU, 2 is an oscillation circuit, 3 is an ultrasonic vibrator, 4 is a drive circuit, 5 is an operation unit having various switches, 6 is a display unit, 7 is a power supply circuit, Reference numeral 8 denotes a correction circuit, which is connected to the CPU 1 with a circuit configuration as shown. The oscillating circuit 2 is a circuit for causing oscillation in combination with the vibrator 3, and includes a matching transformer 2
1, a oscillating transistor 22, a series resonance circuit 23 including a coil L1 and a capacitor C1, and the like. The time constant of the series resonance circuit 23 is selected to a value that oscillates at a predetermined frequency in combination with the vibrator 3, and the vibrator 3 is driven by the transistor 22 at a frequency determined by feedback of the vibration. You. One end of the series resonance circuit 23 is connected through a feedback line 24 to C
It is connected to the counter / timer input port C / T of PU1 so that the oscillation voltage is always input to CPU1. The correction circuit 8 is provided in the series resonance circuit 23, and includes a capacitor C2 connected in parallel to the capacitor C1, a switch SW1 inserted in series with the capacitor C2, and a capacitor C1 connected in series with the capacitor C1. And a switch SW2 connected in parallel with the capacitor C3. Switch SW1 is CP
The switch SW2 is opened and closed by a control signal from the output port P1 of U1 and by a control signal from the output port P2. The circuit shown in FIG. 1 is configured as described above. The operation is started in response to the operation of the operation unit 5, and is controlled by the CPU 1 and performed according to the procedure shown in the flowchart of FIG. First, at the time of startup, as shown in FIG.
Is turned off and the switch SW2 is turned on, a start signal is sent to the drive circuit 4, and oscillation is started. The oscillation frequency is detected by measuring the cycle of the input voltage to the port C / T by the CPU 1, and it is determined whether or not the frequency is a preset normal frequency, that is, the reference oscillation frequency. Continued as it is. On the other hand, when the oscillation frequency is not normal,
Proceeding to the next step, it is determined whether it is higher or lower than normal. If it is higher, a control signal is output from the output port P1 of the CPU 1 and the switch SW1 is turned on. For this reason, the capacitor C2 is connected in parallel to the capacitor C1, and the capacitance of the series resonance circuit 23 increases, and the time constant becomes a value corresponding to a frequency lower than the reference oscillation frequency. Therefore, the oscillation frequency is forcibly reduced. To the reference oscillation frequency. In the example shown in FIG. 3, this corresponds to the case where oscillation occurs at 35 kHz higher than the original frequency. When abnormal oscillation at this frequency is detected, the oscillation is forcibly returned to 27 kHz. If the oscillation frequency is lower than normal, C
A control signal is output from the output port P2 of PU1, and the switch SW2 is turned off. For this reason, the capacitor C3 is connected in series with the capacitor C1, and the capacitance of the series resonance circuit 23 is reduced, and the time constant becomes a value corresponding to a frequency higher than the reference oscillation frequency, so that the oscillation frequency is forcibly increased. To the reference oscillation frequency. That is, by temporarily changing the time constant of the series resonance circuit 23, the feedback of the vibration of the vibrator 3 is overcome and the oscillation is returned to the normal frequency. Since the return to the reference oscillation frequency is performed in a relatively short time, the ON state of the switch SW1 or the OFF state of the switch SW2 only needs to be continued for, for example, 100 ms. The switch SW1 is turned off and the switch SW2 is turned on again, and the normal operation at the reference oscillation frequency is continued thereafter. As described above, in this example, the oscillation frequency is not detected indirectly by the voltage or the phase.
Since the period of the oscillation frequency is directly measured by the CPU 1, it is possible to reliably detect whether or not the oscillation is abnormal. Moreover, by temporarily changing the time constant of the series resonance circuit 23, it is possible to return the oscillation frequency to a predetermined oscillation frequency and to vibrate the vibrator 3 at an effective frequency during abnormal oscillation. Therefore, if the present invention is applied to, for example, the ultrasonic scaler for dental use as described above, a frequency load may occur if a strong load is applied to the chip or the vibration characteristics of the vibrator are deteriorated. However, since this is automatically detected and immediately returns to the normal frequency, effective vibration can always be obtained and the device can be used easily. In particular, a light emitting section is provided at the tip of the handpiece,
In the ultrasonic scaler, which guides the light for illumination through the light guide, the ultrasonic vibrator and the horn that guides the vibration to the chip are surrounded by the light guide, and the member attached to the light guide is provided. Because of these factors, the oscillation condition tends to be suitable for oscillation at a frequency at which effective vibration cannot be generated. Therefore, by implementing the present invention on an ultrasonic scaler with a light guide,
It is possible to oscillate at a regular frequency by removing the influence of the light guide, which is extremely effective for practical use. The oscillation frequency is most easily measured by measuring the period as described above. However, the frequency may be directly counted in combination with a frequency divider or the like. Further, it is also possible to perform analog processing of converting the voltage signal into a voltage signal corresponding to the frequency using an appropriate FV converter and discriminating the voltage signal with a comparator or the like. Does not indicate a peak, but changes unambiguously in response to the frequency, so that the actual oscillation frequency can be reliably detected. As is apparent from the above description, the present invention provides a reference oscillation which is set in advance depending on the oscillation conditions.
Self-oscillation occurs at an abnormal frequency
Ultrasonic vibrator with oscillation circuit that may be started
In the oscillation control device, an oscillation frequency detecting means for directly detecting a frequency or a period of a voltage generated in an oscillation circuit, and an abnormal frequency in which the detected oscillation frequency largely deviates from a preset reference oscillation frequency. Determining means for determining whether or not abnormal oscillation occurs, and correcting means for forcibly pulling back the actual oscillation frequency different from the reference oscillation frequency to the reference oscillation frequency when it is determined that the oscillation is abnormal. It is provided with. Therefore, even if an abnormal oscillation such as a frequency jump occurs, the oscillator can be automatically returned to the predetermined oscillation frequency and the oscillator can be vibrated at an effective frequency.
There is no need to use a complicated circuit for the feedback from the vibrator or provide a frequency jump prevention circuit, making it easy to obtain an ultrasonic device with stable operation, and a vibrator with poor vibration characteristics. But it can be used. The oscillation frequency is directly detected based on the frequency or cycle of the voltage generated in the oscillation circuit .
In addition, since the oscillation frequency is not indirectly detected by the voltage or the phase, it is possible to reliably detect whether or not the oscillation is abnormal. Further, a resonance circuit having a time constant corresponding to the reference oscillation frequency is replaced with a circuit having a time constant corresponding to a frequency lower than the reference oscillation frequency or a circuit having a time constant corresponding to a frequency higher than the reference oscillation frequency. Temporarily change and restore after a set waiting time
Therefore, abnormal oscillation can be returned to normal oscillation with a simple circuit configuration. In particular, the present invention is effective in improving the usability of the apparatus by applying to an ultrasonic scaler which is likely to cause a frequency jump under the use conditions, and according to the present invention, it is possible to obtain an effective vibration. The disadvantage of the ultrasonic scaler with a light guide, which easily oscillates at a frequency that cannot be obtained, is solved, and there is a great effect on its practical use.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram of an example of an oscillation control device for an ultrasonic transducer according to the present invention. FIG. 2 is a flowchart showing a control procedure of the apparatus. FIG. 3 is a graph illustrating the relationship between the frequency and admittance of an ultrasonic transducer. [Description of Signs] 1 CPU 2 Oscillation circuit 3 Ultrasonic transducer 8 Correction circuit 23 Series resonance circuit C / T Counter / timer input port L1 Coil C1, C2, C3 Capacitor SW1, SW2 Switch P1, P2 Output port

Claims (1)

(57) [Claims] [Claim 1] It is set in advance depending on oscillation conditions.
At an abnormal frequency greatly deviated from the reference oscillation frequency
Supersonic with oscillation circuit where excitation oscillation may start
In the oscillation control device of the wave oscillator, the oscillation frequency detecting means for directly detecting the frequency or period of the voltage generated in the oscillation circuit, and the detected oscillation frequency greatly deviates from a preset reference oscillation frequency . Determining means for determining whether or not an abnormal oscillation that results in an abnormal frequency; and forcing the actual oscillation frequency different from the reference oscillation frequency to the reference oscillation frequency when the abnormal oscillation is determined. Correction means, and the correction means converts the resonance circuit having a time constant corresponding to the reference oscillation frequency to a circuit having a time constant corresponding to a frequency lower than the reference oscillation frequency, or a circuit having a time constant higher than the reference oscillation frequency. It is characterized by being provided with a means for temporarily changing to a circuit having a time constant corresponding to the frequency and returning to the original state after a set waiting time. That oscillation control device of the ultrasonic vibrator.