JPH0487298A - Resonant inverter type x-ray device - Google Patents

Abstract

PURPOSE:To miniaturize an X-ray device and improve efficiency by controlling the tube voltage with two parameters: operating frequency and phase difference of an inverter, gradually increasing the frequency from the start, and gradually decreasing the phase difference. CONSTITUTION:A phase difference signal generating means 9 generates the phase difference signal setting the operating phase difference of the switching element of an inverter 2 based on the tube voltage rising signal and the frequency signal. The phase difference of this phase difference signal is decreased as time elapses in response to the time change of the tube voltage rising signal and the frequency signal. The frequency signal and the phase difference signal are inputted to the drive signal generating means 10 of the switching element of the inverter 2, and the drive pulse of the switching element is outputted from the generating means 10. The frequency of the drive pulse is increased and its phase difference is decreased as time elapses. An X-ray device is miniaturized and made lightweight, its efficiency is improved, and the cost can be reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an inverter type X-ray high voltage device that applies high voltage to an X-ray tube using an inverter, and in particular, relates to an inverter type X-ray high voltage device that uses an inverter to apply high voltage to an The present invention relates to a method for starting up a tube voltage of a resonant inverter type X-ray high voltage device that applies a high voltage to an X-ray tube.

[Conventional technology]

A conventional resonant inverter type X-ray high voltage device includes a resonant inverter that converts DC power supply voltage to high frequency AC, a high voltage transformer that boosts the output voltage of this resonant inverter,
It consisted of a rectifier circuit that rectified the output voltage of this high voltage transformer, and an X-ray tube to which the output voltage of this rectifier circuit was applied. In order to reduce the size and weight of such an X-ray high voltage device, it is most effective to make the above-mentioned high voltage transformer small and lightweight. The high voltage transformer can be made smaller and lighter by increasing the frequency of the input voltage thereto.

As a means for increasing the frequency of the input voltage to such a high voltage transformer, there is a conventional method using a series resonant inverter disclosed in US Pat. No. 4,225,788. This utilizes the resonance between the leakage inductance of the high-voltage transformer and the resonance capacitor connected in series with the inverter, and controls the frequency of the inverter to control the voltage supplied to the X-ray tube as a load. It is supposed to be done.

Furthermore, as described in Japanese Patent Application Laid-Open No. 63-1.90556, the inverter current is cut off by shifting the on/off phases of two sets of opposing switching elements of a resonant inverter, and the output voltage is reduced. Some are designed to be controlled.

[Problem to be solved by the invention]

An X-ray apparatus using a frequency control type resonant inverter described in the above-mentioned US Pat. No. 4,225,788,
In the X-ray apparatus using a phase difference control type resonant inverter described in JP-A No. 63-190556,
There were points that needed to be improved in order to start up the tube voltage as follows.

(1) In the frequency control system, when starting up the tube voltage, the operating frequency of the inverter is increased from a low frequency to a high frequency in a region below the resonant frequency of the resonant circuit, for example. However, where the operating frequency of the inverter is low, the time integral value of the voltage applied to the high voltage transformer (applied voltage time product) becomes large. Therefore, it became necessary to increase the cross-sectional area of the transformer's iron core, and as a result, there was a problem that miniaturization of the transformer was restricted.

(2) In the phase difference control type, in order to downsize the transformer, the operating frequency of the inverter is set to a predetermined high frequency, and the phase difference is changed from a large phase difference to a small phase difference. However, when two switching elements facing each other with a large phase difference are turned on and off, the switching elements are turned on and off in a region where the inverter current is large. For this reason, switching loss increases,
Problems arise in that efficiency deteriorates and expensive switching elements with large ratings must be used.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems, reduce the size and weight of a high-voltage transformer, and provide an efficient and low-cost resonant inverter type xi device.

[Means to solve the problem]

To achieve the above object, the present invention provides a direct current power source, a resonant inverter that converts the output voltage of the direct current power source into high frequency alternating current, a high voltage transformer that boosts the output voltage of the resonant inverter, and a high voltage transformer that boosts the output voltage of the resonant inverter. In a resonant inverter-type X-ray apparatus that is equipped with a rectifier circuit that rectifies the output voltage of the rectifier and an X-ray tube to which the output voltage of the rectifier circuit is applied, the resonant inverter corresponds to the set tube voltage when the resonant inverter starts operating. means for generating a tube voltage start-up signal that increases with the passage of time, and a frequency signal that increases the operating frequency of the resonant inverter with the passage of time in response to the tube voltage rise signal. means for generating a phase difference signal that reduces the operating phase difference of the switching elements of the resonant inverter over time in response to the tube voltage rise signal and the frequency signal; and means for generating an inverter drive signal corresponding to the phase difference signal.

[Effect]

Prior to X-ray emission, the tube voltage is set in the X-ray device. When the tube voltage is set, the signal is input to the tube voltage rise signal generating means. The tube voltage rise signal generating means generates a tube voltage rise signal that gradually increases over time in order to gradually raise the tube voltage to a set value in accordance with the set tube voltage. This tube voltage rising signal is output to both the frequency signal generating means and the phase difference signal generating means.

The frequency signal generating means generates a frequency signal for setting the operating frequency of the inverter to gradually increase based on the gradually increasing tube voltage rise signal. On the other hand, the 5 phase difference signal generating means generates a phase difference signal for setting the operating phase difference of the switching elements of the inverter based on the tube voltage rising signal and the frequency signal. This phase difference signal corresponds to the time change between the tube voltage rise signal and the frequency signal, and the phase difference becomes smaller as time passes.

Then, the frequency signal and the phase difference signal are inputted to a driving signal generating means for a switching element of the inverter, and a driving pulse for the switching element is outputted from the driving signal generating means. As time passes, the frequency of this drive pulse increases and at the same time the phase difference decreases.

When the switching elements of the inverter are driven by this drive pulse, the tube voltage is gradually increased to the set value over time.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 8. FIG. 1 shows the main circuit configuration of a resonant inverter type X-ray apparatus according to the present invention.

In FIG. 1, reference numeral 1 consists of a DC power source, for example, one that rectifies a commercial power source and outputs a DC voltage, or a battery. 2 is an inverter that converts the output of the DC power supply 1 into high-frequency AC, and transistors T rl+ Tr2 .
Tr3+ Tri and their transistors Trl~T
diodes D1 . D
zs Da and D constitute a full bridge type inverter, 3 is a high voltage transformer that boosts the output voltage of inverter 2, 4 is a rectifier circuit that performs full wave rectification of the output voltage of high voltage transformer 3, 5 is an X-ray tube that emits X-rays to which the output voltage of the rectifier circuit 4 is applied via a high-voltage cable (not shown) having a capacitance C2. In addition, high voltage transformer 3
has a primary winding and a secondary winding, a resonant capacitor C1 is connected in series to the -order winding, and the connection body between these -order windings and the resonance capacitor C1 is the output side of the inverter 2. It is connected to the. Reference numeral 6 designates the operation console of this device, 7 designates a tube voltage start-up signal generation circuit, 8 designates a frequency signal generation circuit, 9 designates a phase difference signal generation circuit, 10 designates a pulse distribution circuit, and 11 designates base drives of transistors T r 1 to Tri. It is a circuit.

As shown in FIG. 1, the present invention inputs a tube voltage setting signal V set from an operation console 6 to a tube voltage start-up signal generation circuit 7, and increases the tube voltage in steps as time passes. The signal ■1 is inputted to the frequency signal generation circuit 8 and the phase difference signal generation circuit 9, and the frequency signal generation circuit 8 generates a pulse Pt that gradually increases the operating frequency of the inverter 2. , in the phase difference signal generation circuit 9, the output signal ■1 of the tube voltage rise signal generation circuit 7
and the output pulse Pi of the frequency signal generation circuit 8, a pulse Pφ whose phase difference gradually decreases in accordance with the tube voltage setting value is created, and from these pulses Pt and Pφ, the transistors T r 1 to T r of the inverter 2 are generated. This is to create a pulse to drive Tra.

Hereinafter, a method of generating a frequency signal and a method of generating a phase difference signal will be explained with reference to FIGS. 2 and 4, and FIGS. 5 and 7.

FIG. 2 is a diagram showing an example of the configuration of the frequency signal generation circuit 8, and FIG. 4 is an operational waveform diagram thereof. Note that FIG. 3 shows the relationship between the inverter operating frequency and tube voltage of the resonance type inverter X-ray apparatus. In FIG. 2, 81 is a sawtooth wave generating circuit, 82 is an operational amplifier, 83 is a comparator, and 84 is a frequency divider. This frequency signal generation circuit 8 has an input voltage V+,
That is, the tube voltage setting signal V s e output from the console 6
The signal (d) outputted by the tube voltage rise signal generation circuit 7 in response to time t is inputted, and the frequency signal Pz is outputted in the relationship shown in FIG. 3 with respect to this input signal (d)1. The operational amplifier 82 generates a difference signal (Vc Vl
), and on the other hand, the sawtooth wave generating circuit 81 outputs a signal ■ having the waveform shown in FIG. Output.

These signals (VC-Vl) and vn are input to the comparator 83. Comparator 83 compares (VC-Vl) and Vn and outputs signal Pc. The signal Pc becomes 0" when (VC-Vl) and Vn match, and becomes 411+1 otherwise.The sawtooth wave generating circuit 81 is reset by this "○" force. The output signal Pc of the comparator 83 is input to the frequency divider 84, frequency-divided, becomes a frequency signal P, and is output to the pulse distribution circuit 10.The signal Pc is also input to the tube voltage rise signal generation It is output to the circuit 7.The tube voltage rise signal generation circuit 7
Outputs vI which increases sequentially for each pulse.

Next, the phase difference signal generation circuit 9 will be explained.

The phase difference signal generation circuit 9 is, for example, as shown in FIG. 5, a sawtooth wave generation circuit (2) 91 which inputs the frequency signal P and outputs a sawtooth wave signal VS shown in FIG. and an inverter 92 that inverts the tube voltage rising signal, and compares this sawtooth wave signal Vs with the output signal V 1' of the inverter 92, and generates a phase difference signal P between V s > V t '.
The comparator (2) 93 outputs φ.

As shown in FIG. 7, when the phase difference φ is defined as the rise of P'z and the rise of Pφ, the phase difference φ becomes smaller as time passes. This phase difference signal Pφ is supplied to the pulse distribution circuit 10
Output to.

Next, the tube voltage startup operation of the inverter type X-ray apparatus shown in FIG. 1 will be explained with reference to FIG.

When the operator sets the tube voltage on the console 6 (of course, since this is an X-ray device, the tube current and X-ray emission time are also set) and inputs an X-ray emission command, the tube voltage setting signal V s e +
is output from the console 6 to the tube voltage start-up signal generation circuit 7. Then, the tube voltage rise signal generation circuit 7 is as shown in FIG. 8(c).
It outputs a tube voltage rise signal V1 that increases stepwise with time as shown in FIG. This tube voltage rising signal v
1 is input to the frequency signal generation circuit 8 and the phase difference signal generation circuit 9. As shown in FIG. 4, the frequency signal generating circuit 8 generates a signal V that increases stepwise with time.

Based on, the difference between the constant voltage signals Vc and vl (vc-vl
) and sawtooth signal■. and a pulsed frequency signal P
Create t. The frequency of this P increases with time, corresponding to vl which increases stepwise with time. This Pt is then input to the pulse distribution circuit 10 and the phase difference signal generation circuit 9. Phase difference signal generation circuit 9
A phase difference signal Pφ is created by comparing vi′, which is the inversion of V, with a sawtooth wave signal Vs created based on Pi. This phase difference signal Pφ is output to the pulse distribution circuit 10. The pulse distribution circuit 10 receives the frequency signal P1 and the phase difference signal Pφ as shown in FIG. 8(f).

Create and output pulse signals (g), (h), and (i). Of the pulse signals (f) to (i), (f) and (h) and (g) and (j) are outputted in the on and off states in reverse order, and the pulse distribution circuit 10 (f
), (g), (h), and (i) are output to the base drive circuits 11a-1] and d, respectively. The base drive circuits 11a to lld amplify each of the output signals of the pulse distribution circuit 10 and supply the amplified signals to the bases of the transistors Tr1 to Tr4 of the inverter 2, thereby driving the transistors Trx to Tr4.

Next, the operation of inverter 2 will be explained. Frequency signal Pt
At time t1 when the voltage becomes 111 I+, the base drive circuit 1
1 outputs (f) which turns on the transistor Trl, and the transistor T r 1 turns on. Next, at time t2 when the phase difference signal Pφ becomes 111 I+, the base drive circuit 11 outputs (g) which turns on the transistor Tr4. This turns on both transistors Tri and Tr4, and a current (resonant current) with an oscillation period determined by the capacitor and inductance flows through the resonant circuit formed including Trx and Tr4.

Of the capacitors and inductances that determine this oscillation period, the capacitors include a resonance capacitor C1 connected in series to the primary winding of the high voltage transformer 3, and a stray capacitance existing between the layers of the secondary winding of the high voltage transformer 3. , and the stray capacitance C2 of the high voltage cable from the rectifier circuit 4 to the xi tube 5, and the inductance is the leakage inductance (not shown) of the high voltage transformer 3 and the inductance of the wiring.

The frequency signal Pf becomes (lOI+) at time t3, which turns off the transistor T r 1, and the resonance flowing through the circuit of the transistor T r z → resonant capacitor C high-voltage transformer primary winding → transistor T. The current is cut off, and on the other hand, the transistor Tr2 is turned on.Then, after time t8, the T-th transistor and Trz are turned on at the same time, but since the transistors Trs and Trx are turned off, there is no current from the DC power supply 1. No current flows.

At time t4, the base drive circuit 11 turns off the transistor Tr4 and turns on the transistor Tr3 in response to a signal from the pulse distribution circuit 10. Then, the transistor T
A resonant current flows through a resonant circuit formed including rz and T r 3.

At time t5, the first operation cycle of the inverter ends, and the frequency signal Pt becomes tL I IT again. At this time, the transistor Tr2 is turned off, and the transistor Tr1 is turned on, and then the inverter enters the second operation cycle. Time t when the inverter enters the second operation cycle.

, the phase difference signal Pφ becomes 111 IT. At this time, transistor Tr2 is turned off, and transistor Tri
turns on. Below, at time t7, P□ is 11 CL
IT, Pφ becomes trO''', Trs is turned off, and Tr2 is turned on. At time t8, Tr4 is turned off, and Tr3 is turned on, and the second operation cycle of the inverter ends at time t8. .

Thereafter, the inverter operates in the third operation cycle, . . . , the n-th operation cycle. Then, at time tN when the n-th operation cycle ends, the tube voltage rise signal Vi
becomes a steady value, and from then on the inverter has a tube voltage of Vse.
It operates repeatedly at a frequency and a phase difference of t (in FIG. 8, the phase difference is assumed to be zero).

The operating cycles of the inverter at the time of starting up the tube voltage are as follows:
T□, Tel T31..., Tn, these become T1>Tz>T3>->Tn, and the phase difference is sequentially φ, φ2... φ3. ...,φ. Then, they become φ1>φ2>φ3>...>φ.

By controlling the frequency and phase difference of the resonant inverter as described above, the resonance current generated in the primary winding of the high voltage transformer 3 is converted into the exciting current of the high voltage transformer 3 and the stray capacitance of the secondary winding. The high-voltage current that is obtained by subtracting the current flowing through the rectifier circuit 4
The X-rays are smoothed by the stray capacitance of the high-voltage cable rectified by and applied to the X-ray tube 5, and the X-rays are emitted from the X-ray tube 5. By controlling the inverter as described above, the voltage applied to the X-ray tube is controlled to gradually increase.

As explained above, according to this embodiment, the operating frequency of the resonant inverter is gradually increased with respect to the set tube voltage, and the 1 phase difference is gradually decreased to raise the tube voltage. As with conventional double-stroke control, the iron core becomes larger due to an increase in the applied voltage time product of the high-voltage transformer at low frequencies in the control method that uses only the operating frequency, and the inverter current (resonant current) increases in the control method that uses only the phase difference. By the way, both problems of increased loss due to on/off of the inverter switching element can be avoided.

Next, a second embodiment of the present invention will be described with reference to FIG.

This second embodiment detects the actual tube voltage, compares the detected value with the tube voltage rise signal, and adds the difference to the tube voltage rise signal to be output next. The tube voltage start-up signal is outputted to the frequency signal generation circuit and the phase difference signal generation circuit, thereby making it possible to accurately set up and set the tube voltage.

In the configuration shown in FIG. 9, reference numeral 12 detects the voltage actually applied to the X-ray tube 5. In the configuration shown in FIG. For example, a tube voltage detector 13 consisting of a voltage divider converts the output signal of the tube voltage detector 12 into an inverter 2.
14 is an error amplifier that converts the error between the output signal of the tube voltage rise signal generation circuit 7 at a certain time and the resulting output signal of the signal conversion circuit 13. This is calculated, added to the next tube voltage rise signal, and output. The rest of the configuration is the same as that in FIG. 1, so the explanation will be omitted. Next, the operation of the configuration device in FIG. 9 will be explained.

In the first operation cycle of the inverter 2, when Vlk is output as a tube voltage rise signal to the frequency signal generation circuit 8 and the phase difference signal generation circuit 9, the frequency signal generation circuit 8 outputs the frequency signal P1k and then the phase difference signal. Pφ3 is output from the generating circuit 9. The inverter 2 has the above-mentioned Pxk and P
The T-th transistors to Tr4 are driven by a drive pulse group output from the pulse distribution circuit based on φk.

A tube voltage is applied to the X-ray tube 5 by the resonance current generated thereby. This tube voltage is detected by a tube voltage detector 12 and output to a signal conversion circuit 13. The signal conversion circuit 13 converts the input signal to correspond to the signal in the inverter control system and outputs it to the error amplifier 14. The error amplifier 14 receives the tube voltage rise signal VIk and this V
Detection signal V of the tube voltage applied to the X-ray tube 5 by Ik
Calculate the difference α from Xk.

At the next operating cycle of the inverter 2, that is, the (k+1)th operating cycle, the tube voltage rise signal generation circuit 7 outputs Vl(k+1).
Outputs 11. This V t(m+t+ is the error amplifier 1
4, the error amplifier 14 outputs vIk and V x
The difference α from b is added to VI(h+s+) and output. This sets the operating frequency and phase difference of the inverter 2 in the (k+1)th operating cycle.Hereinafter, this newly set frequency and phase will be The inverter 2 operates based on the phase difference, and tube voltage is applied to the X-ray tube 5.

According to this second embodiment, the actual tube voltage is fed back every operating cycle of the inverter to set the next operating frequency and phase difference. Can be set accurately.

Further, even if there is a fluctuation in the DC power supply voltage, the tube voltage can always be kept at the set value without being affected by the fluctuation.

Although the present invention has been described above with reference to two preferred embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. For example, the inverter system may be a half-bridge system instead of a full-bridge system, and the resonance system may be replaced with a system that adds a resonant capacitor, which eliminates the leakage inductance and stray capacitance of the high-voltage transformer itself. A method using a resonant element or another resonant method may be used.

Also, regarding the switching elements of the inverter,
In place of the bipolar transistor, a self-blocking element such as GT◯ or IGBT may be used.

Furthermore, although the above embodiment has been explained using analog control, the tube voltage start-up signal generation circuit 2 frequency signal generation circuit 9
Of course, the control system may be constructed by digitizing the signals from the phase difference signal generation circuit, pulse distribution circuit, etc., and using a microprocessor unit (MPU), memory such as RAM, ROM, etc.

〔Effect of the invention〕

As described above, according to the present invention, the tube voltage is determined using two parameters, the operating frequency of the inverter and the phase difference, and the frequency is gradually increased from the start of startup, and the phase difference is gradually decreased. Therefore, it is possible to eliminate the drawbacks of the conventional system in which the tube voltage is started up only by frequency control or only by phase difference control. That is, in the present invention, since the phase difference is not zero even in the operating cycle where the frequency of the inverter is low, the applied voltage time product of the high voltage transformer can be reduced. Therefore, the iron core of the high voltage transformer can be made smaller.

Furthermore, since the two parameters of phase difference and frequency are controlled together, it is possible to avoid turning on/off the switching element in a phase where the resonance current is large by using the frequency parameter. Therefore, switching loss in the inverter can be reduced.

As described above, according to the present invention, it is possible to reduce the size and weight of a high-voltage transformer, and to improve the efficiency and reduce the cost of an inverter-type X-ray apparatus.

[Brief explanation of the drawing]

FIG. 1 shows a resonant inverter type X according to an embodiment of the present invention.
2 is a diagram showing a configuration example of the frequency signal generation circuit shown in FIG. 1, FIG. 3 is a diagram showing the correspondence between tube voltage and inverter frequency, and FIG. FIG. 2 is an operational waveform diagram of the frequency signal generation circuit, FIG. 5 is a diagram showing an example of the configuration of the phase difference signal generation circuit, FIG. 6 is a diagram showing the correspondence between tube voltage and phase difference of the inverter, and FIG. The figure is an operational waveform diagram of the phase difference signal generation circuit shown in Figure S, Figure 8 is an operational waveform diagram of each part of the resonant inverter type X-ray apparatus shown in Figure 1, and Figure 9 is a diagram of the second embodiment of the present invention. FIG. 2 is a main circuit configuration diagram of a resonant inverter type X-ray apparatus according to an example. 1. DC power supply, 2. Inverter, 3. High voltage transformer,
5... X-ray tube, 6... Operation console, 7... Tube voltage start-up signal generation circuit, 8... Frequency signal generation circuit, 9... Phase difference signal generation circuit, 10... Pulse distribution circuit, 11...Base drive circuit, 12.Tube voltage detector, 13...Signal conversion circuit, 14...Error amplifier, Tri to Tr4...Transistor, vs et...Tube voltage setting signal, ■,
・・Tube voltage rise signal, Pr・・Frequency signal, Pφ・
・・Phase difference Ge Biwei Sen 82 樗塵 Spring Ge ward calculation Etsu Zu Wei 7 Diagram Bizu - 吋用

Claims (1)

[Claims] 1. A DC power supply, a resonant inverter that converts the output voltage of this DC power supply into high-frequency AC, a high voltage transformer that boosts the output voltage of this resonant inverter, and a rectifier circuit that rectifies the output voltage of this high voltage transformer. and an X-ray tube to which the output voltage of this rectifier circuit is applied.
In the line device, means for generating a tube voltage start-up signal that corresponds to a set tube voltage at the start of operation of the resonant inverter and increases over time; means for generating a frequency signal that increases the operating frequency of the resonant type inverter over time; and means for generating a frequency signal that increases the operating frequency of the resonant type inverter over time; 1. A resonant inverter type X-ray apparatus, comprising: means for generating a phase difference signal that decreases at the same time; and means for generating an inverter drive signal corresponding to the frequency signal and the phase difference signal.