JPS63126195A - Invertor type x-ray device - Google Patents

Abstract

PURPOSE:To decrease pulsation of a tube voltage wave form at inversion of an invertor as well as constrain an overshoot by applying changing of a standing start time and a standing time of a switch by the tube voltage, a tube current, and a length of a high voltage cable to two current paths of the invertor. CONSTITUTION:A signal selector 110 selects output signals aB-dB of a programable timer B109 and outputs a selected signal to drive circuits 102-105. The programable timer B109 outputs a signal which controls a standing start time tB and a standing time tS in the second half period of the invertor on. When transistors 23 and 24 are turned on with base currents c and d inputted to transistors 23 and 24 respectively, a current flows to a current path B of an invertor 20, and a voltage of a reversed polarity to a previous polarity is outputted from the invertor 20. And the transistor 23 is turned off temporarily during the time from t5 to t6, and the transistor 23 is again turned on at the time t6. This makes the current path B to make the same operation as of the current path A and constrains a vibration of an impressed voltage Vx to a X-ray tube 60.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an inverter type X-ray device, and in particular, an inverter-type
The present invention relates to a technique for suppressing tube voltage overshoot and reducing tube voltage pulsations.

[Conventional technology]

X-ray devices using inverters have been published in various documents in recent years. A typical schematic configuration of this inverter type X-ray apparatus is shown in FIG. The inverter type X-ray device includes a DC type g10 having an electromotive force E, a full bridge type inverter (hereinafter simply referred to as an inverter) 20 that converts the voltage manually applied from the DC power supply 10 into an AC voltage and outputs it, and an inverter. a high voltage transformer 30 that boosts the AC voltage from 20;
It includes an aftereffect rectifier circuit 40 that converts the AC voltage boosted by the high voltage transformer 30 into a DC voltage, a capacitor 50 that smoothes the output voltage of the aftereffect rectifier circuit 40, and an X-ray tube 60. The inverter 20 converts the output of the DC power supply 10 into AC power and supplies AC power to the primary winding of the high voltage transformer 30. The transistors 21 are turned on by flowing pace currents a, b, c, and d, respectively. ,22,23,24
and.

Transistor protection diodes 25 and 26 are connected in antiparallel to these transistors 21 to 24, respectively.
27.28 (referred to as a flywheel diode). Then, transistors 21 and 22 form one current path A, and transistors 23 and 24 form the other current path B, and transistors 21 and 22 are simultaneously turned on to cause current to flow through current path A. AC power is supplied to the primary winding of the high-voltage transformer 30 by alternately repeating the operation of turning on transistors 23 and 24 at the same time and causing current to flow through current path B. Note that a pause time is provided between the operations in which current path A and current path B are turned on alternately, and the transistors 21 and 22 of current path A and the transistors 23 and 24 of the other current path B are turned on at the same time. I try not to have anything to do.

[Problem that the invention seeks to solve]

If the current path A from the DC power source 10 in FIG. 4 to the X-ray tube 60 as a load is represented by an equivalent circuit as shown in FIG. From the DC power supply 10 to the transistor 2 in FIG.
1. Power is supplied to the parallel connection circuit of the capacitor 50 and the X-wire winding 60 via the inductance L of the high voltage transformer and the diode 41, and the diode 44. Returning to the DC power supply 10 via the transistor 22 means that in FIG.
This is equivalent to the case where the current flows in the circuit of resistance R→(capacitor 50//load 6)→DC power supply 1. Here, the first
The switch 2 is connected to the transistor 21 in FIG.
The switch 8 corresponds to the diode 28.

In the circuit shown in FIG. 5, when the first switch 2 is turned on, the voltage V applied to the load 6 is changed to, for example, the 61st switch (b).
As shown in , it often oscillates until it reaches a steady state. Particularly in the case of power supply circuits, in order to improve power transfer efficiency, the resistance from the power supply to the load, that is, R in Figure 5, is made as small as possible, so the damping effect against the increase in load current during the transient period is poor, and the Vibration occurs at r7 and C in the figure.

In the inverter, when current path A and current path B are turned on alternately as described above, the transient phenomenon shown in FIG. 6 is repeated as shown in FIG. 7 every time the polarity is reversed. This pulsation occurs when the peak value of the tube voltage is detected as the X-ray imaging condition, such as an X-ray device, and even if the peak value is the expected value, the actual Since the dose (X-ray rate) will be reduced, it is necessary to reduce the pulsation.

Therefore, in an inverter type X-ray apparatus, the present invention suppresses overshoot without delaying the rise time of tube voltage by controlling the inverter, and also reduces pulsation of the tube voltage waveform when the inverter polarity is reversed. The purpose is to provide technology to

[Means for solving the problems] The features of the present invention for achieving the above object are as follows:
A DC power source; to a fourth switching element and a first switching element connected in antiparallel to each of these switching elements.
a full-bridge inverter configured with a fourth diode, a high-voltage transformer connected to the output side of this full-bridge inverter, a rectifier circuit connected to the output side of this high-voltage transformer, and Inverter type Xa equipped with an X-ray tube connected to a rectifier circuit via a high-voltage cable
In the device, a first half period of the inverter in which the first switching element and the fourth switching element are turned on simultaneously, and a second half period of the inverter in which the second switching element and the third switching element are turned on simultaneously. and cycles are alternately repeated at a predetermined frequency, and within the first and subsequent on-cycle periods of the inverter.

The inverter is provided with means for providing a predetermined inverter stop period after each predetermined time has elapsed after turning on.

[Effect]

The effect of the inverter's rest (off) period within the on-period of the inverter's half cycle will be explained with reference to the circuit of FIG. In the operation of the circuit shown in FIG. 5, as shown in FIG.
When the first switch 2 is closed, the change from 1 to 2 in FIG.
→3→R→(50/6)→A current flows through the circuit 1, and power is supplied to the load 6. If the first switch 2 remains closed, the voltage V applied to the load 6 will rise as shown by the solid line 203 as shown in FIG. 8(c), and will overshoot and oscillate as shown by the broken line 204. Become.

Therefore, at time t1 when the voltage V applied to the load 6 becomes equal to a predetermined voltage, for example, the electromotive force E of the DC current 'g1,
The first switch 2 is opened and the second switch 8 is closed. At this time t1, the coils in FIG. 5: 3,
That is, the current i flowing through the inductance L rises as shown by the solid line 206 shown in FIG. 8(d), and becomes larger than the steady value i=E/R=EG after the transition period has passed. Due to this current change, the magnetic energy of the inductance L causes current i to flow through the circuit 3→R→(50//6)→8→3, but since the power supply from DC current g1 has stopped, The current i rapidly decreases as shown by a solid line 207. At this time, the voltage of the capacitor 5-0 does not change much because the amount of discharge to the load 6 and the amount of charging of the inductance L due to magnetic energy are approximately equal.

Then, the time t when the current i becomes equal to the steady-state value EG
2, the second switch 8 is opened and the first switch 2 is closed again. Then, the current i changes from 1 to 2 again
→3→R→(5◇//6)→Flows in the circuit of 1. At this time, as described above, the voltage of the capacitor 5 does not change much and is approximately equal to E shown in FIG. 8(c), and the current i flowing through the inductance L is a steady value EG.

There is no energy transfer between the coil 3 of inductance L and the capacitor 5 of capacitance C.

The voltage applied to the load 6 remains constant.

The present invention applies the above circuit to current path A and current path B of an inverter of an inverter type X-ray apparatus. However, the oscillation frequency J of the tube voltage waveform that occurs when the polarity of the inverter is reversed is as follows: Tube voltage C: Capacitance of high voltage cable and capacitor L: Leakage inductance of high voltage transformer R8 As shown by circuit resistance, tube voltage, When the tube current and high voltage cable length change, the oscillation period of the tube voltage waveform also changes. So 1
In the present invention, depending on the tube voltage, tube current, and length of the high-voltage cable, the pause (off) start time ta of the first switch shown in FIG.
, ~12) is applied to the two current paths A and iti flow path B of the inverter.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a main circuit configuration of an inverter type X-ray apparatus and a block configuration of an inverter control circuit.

The main circuit configuration is the same except that the DC power supply [variable DC power supply] 1 in FIG. 4 is replaced.

This variable DC type g11 includes, for example, a rectifier circuit that converts an AC voltage into a DC voltage, and a DC/D converter connected to this rectifier circuit.
It is composed of something like CC/lead C, and its output voltage is appropriately transformed and input to the inverter 20. Inverter 2
The input terminal to 0 is set by the voltage regulator 101 controlling the variable DC power supply 11 according to the set tube voltage value and tube current value.

106 is a central processing unit f! 1 (hereinafter referred to as CPU)
A read-only memory (hereinafter referred to as ROM) stores data for controlling the optimum pause start time TFS and pause time Ts during the half cycle after the inverter 20 starts turning on, corresponding to the tube voltage, tube current, and high voltage cable length. 10
From 7, pressurize the set tube.

The pause start time T depends on the tube current and high voltage cable length.
n and pause time Ts, and transfer the data to programmable timers 108 and 109. The programmable timers 108 and 109 actually control the transistors 21 to 2 of the inverter 20 based on the input data.
4 and outputs this signal to the signal selector 110. The signal selector 110 selects a programmable timer AlO3 and a programmable timer B1 according to the X-ray radiation signal and the operating frequency of the inverter 20.
The output signal of 09 is selectively outputted to drive circuits 102-105 of transistors 21-24, respectively. Drive circuit 10
2 to 105 drive the corresponding transistors 21 to 24 according to the output of the signal selector 110, respectively.

Next, the operation of the system shown in FIG. 1 will be explained using the time chart shown in FIG. 2.

Before starting X-ray radiation, the tube voltage and tube current are set to desired values, and the tube voltage signal and tube current signal corresponding to these values are input to the voltage regulator 101 and the CPU 106, and the voltage regulator 101 adjusts the variable DC power supply 11 according to the two input signals so that the set tube voltage is obtained. On the other hand, in addition to the above two signals, the CPU 106 also receives
Data corresponding to capacitance C that changes depending on the high voltage cable length is input as a high voltage cable length signal. In response to these three signals, the CPU 106 reads the control data from the ROM 07 that stores the control data for the inverter 20, and sets the programmable timer AlO3.
The control data is transferred to the programmable timer B109. Note that this control data includes the pause start time t, so and pause time tso during the first half cycle of the inverter on immediately after the inverter 20 starts operating, and the pause time tso during the inverter on half cycle after the second half cycle of the inverter on. In order to set the pause start time ts and the pause time ts, it is necessary to use different data. This is because the voltage of the capacitor 50 is zero before the inverter 20 starts operating, but once the inverter 20 starts operating, power is supplied to the X-ray tube 60, which is the load, and the voltage becomes close to the set tube voltage. This is because the time it takes for the capacitor 50 to reach the set tube voltage in subsequent operations is different.

The programmable timer AlO3 and the programmable timer B i O9 are signals a^ to d that operate the transistors 21 to 24 according to control data from the CPU 106.
It continues to output ^ and aB-dn.

Now, at time t-x, the X-ray emission start signal is sent to the signal selector 110.
, the signal selector 110 selects the signals a^ to d^ from the programmable timer AlO3 at time to and outputs them to the drive circuits 102 to 105. by this,
First, the first half cycle of turning on the inverter 20 starts. As shown in Fig. 2 (a) and (b),
By inputting base currents a and b to transistors 21 and 22, respectively, at time to, a current flows through one current path A of inverter 20, as in FIG.
The first switch 2 shown in the figure is in an on state.

As a result, 11 → 21 → L → 41 → (50//60) →
A current flows through the circuit 44→22→11 (hereinafter referred to as loop I), and power supply to the Xi tube 60 is started. At this time, the load current iL is as shown in FIG.
Due to the leakage inductance L of 0 and the capacitance C of the capacitor 50 and high voltage cable,
Further, the output voltage VT of the transformer 30 increases as shown in FIG. 2(f).

Next, the voltage VX applied to the X-ray tube 60 is a predetermined voltage.

For example, at time t1 when the electromotive force Ev of the variable DC power supply 11 becomes equal to the high voltage transformer secondary side conversion value EVZ, the second
As shown in Figure (a), the base current a is stopped and the transistor 21 is turned off. At this time, the diode 28 connected in antiparallel to the transistor 24 is forward biased and turned on, which is the same state as when the first switch 2 is turned off and the second switch 8 is turned on, as shown in FIG. . Then, the current that was flowing in loop ■ until now becomes L → 41 → (
50//60) → 44 → 22 → 28 → L circuit (hereinafter,
(referred to as loop IT). At this time, since the power supply from the variable DC power supply 11 is stopped, the power supply to the X-ray tube 60 is only from the magnetic energy of the inductance r and the discharge from the capacitor 50, as shown in FIG. 2(e).
As shown in , the load current i! flows through the leakage inductance L! , decreases rapidly.

Next, the load current i is the electromotive force E of the variable DC power supply 11.
At time tIL when the secondary conversion value Evz of v becomes equal to the value (EvzXG) divided by the resistance value of the X-ray tube 60, the base current a is inputted to the transistor 21 again and the transistor 2
Turn on 1. Then, the current that was flowing in loop (■) flows in loop I again. At this time, the load current i flowing through the leakage inductance L flows at a value that is the tube current multiplied by the step-up ratio of the transformer 30, that is, power is supplied to the X-ray tube 60 at a steady value after the transient phenomenon has ended. Also, capacitor 50
Between times t1 and t2, while supplying power to the X-ray tube 60, it is charged by the magnetic energy of the leakage inductance L, so its voltage hardly changes.
It is equal to the secondary side conversion value Evz of the high voltage transformer 30 of the electromotive force Ev of the variable DC power supply 11, and the voltage Vx applied to the X-ray tube 60 is also equal to that value. At time t2, all the voltages and currents in the loop (1) have steady values, and no transient phenomenon occurs.6 Therefore, next, the polarity of the inverter 20 is reversed, so the transistors 21.2
Power is constantly supplied to the X-ray tube 60 until time t8 when Vx2 is turned off, and the applied voltage Vx does not oscillate.

Next, from time t8 to ta, base currents a, b
, c, d are all stopped, and transistors 21, 22, 23
．． 24 are all turned off, and power supply to the X-ray tube 60 is stopped.

Next, at time t4, the signal selector 110 selects the output signals aB to dB of the programmable timer B109,
A six programmable timer B109 outputting to the drive circuits 102 to 105 outputs a signal for controlling the pause start time tn and the pause time ts in the second half period of inverter ON. Base currents C and d shown in FIGS. 2(Q) and (d) are respectively input to transistors 23.24 to turn on transistors 23.24. Then, a current flows through the current path B of the inverter 20 in the same manner as shown in FIG. 4, and the inverter 20 outputs a voltage with a polarity opposite to that described above, as shown in FIG. 2(f).

Then, the transistor 23 is temporarily turned off from time t♂ to ta, and the transistor 23 is turned on again at time t6. This causes the current path B to operate in the same manner as the above-described current path A, thereby suppressing vibrations in the voltage Vx applied to the X-ray tube 60.

Thereafter, every time the polarity of the inverter 20 is reversed, the signal selector 110
is the signal of the programmable timer B109 to the drive circuit 10.
2 to 105 are repeated.

The voltage Vx applied to the X-ray tube 60 has a waveform as shown in FIG. 2(g), and when the inverter 20 reverses the polarity, the power supply from the variable DC power supply 11 is stopped, so it temporarily decreases. However, the vibration is suppressed.

FIG. 3 shows the tube voltage waveform obtained by this example.
In the conventional device, as shown by the broken line 201, a large overshoot occurs when the tube voltage rises, and thereafter, vibration occurs every time the inverter polarity is reversed. However, according to this embodiment, when the tube voltage rises, without overshoot.

As shown in Fig. 1171202, even if the polarity of the inverter is reversed, the oscillation of the tube voltage can be suppressed.

Even if the tube voltage, tube current, and length of the high-voltage cable change, control can be performed according to these conditions.This vibration suppression effect is especially effective when the tube current is small, where the tube voltage tends to oscillate. There is something big.

The present invention is not limited to the above embodiments, but may be explained as follows.

[Second Embodiment] In the configuration shown in FIG. 1, it is possible to eliminate the human input signal regarding the high voltage cable length and also eliminate the need to store a large number of inverter control data regarding the high voltage cable length in the ROM 107. This is because the high voltage cable length is determined to be a certain length at the time when the line equipment is installed or installed.

This is because it is sufficient to store only the necessary inverter control data for the determined high voltage cable length in the ROM 107 in advance.

[Third Embodiment] As the next modification of the present invention, from the tube voltage signal and the tube current signal manually input to CP old 06 in FIG.
(Tube voltage) = G, ROM107
Control data for the inverter corresponding to this G may be stored in . As shown in equation (1) above, this is
One of the factors that determines the vibration period when the inverter's polarity is reversed is G. Therefore, even if the tube voltage and tube current are different, if G is the same, the vibration period will be the same, so the inverter control data can also be the same. .

Note that it is also possible to combine the second embodiment and the third embodiment.

According to the above second embodiment, third embodiment, or a combination of the second embodiment and the third embodiment, it is possible to reduce the control data of the inverter, and as a result, the ROM
memory capacity can be reduced.

〔effect〕

As described above, according to the present invention, in an inverter-type X-ray apparatus, by simply controlling the switching elements of the inverter, overshoot at the rise of tube voltage can be prevented and the polarity of the inverter can be controlled under various load conditions. The pulsation of the tube voltage during reversal can be suppressed, and as a result, the emitted X-ray dose rate can be improved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of an inverter-type A tube voltage waveform diagram, Fig. 4 is a circuit diagram showing the schematic configuration of an inverter-type xIs device, Fig. 5 is an equivalent circuit diagram during an on-half period of the inverter in the configuration of Fig. 4, and Fig. 6 shows the operation of Fig. 5. A time chart diagram, FIG. 7 is a tube voltage waveform diagram of a conventional device, and FIG. 8 is a diagram for explaining the present invention in detail using FIG. 5. 10... DC power supply, 11... Variable DC power supply, 20.
...Full bridge inverter, 21-24...Transistor, 25-28...Diode, 30...High-voltage transformer, 40...Full-wave rectifier circuit, 50...Capacitor, 60... X-ray tube, 101...Voltage regulator, 1
02-1, 05...Drive circuit, 106・CPU, L
O7--ROM, 108, 109--programmable timer, 110--signal selector.
1゛■゛:

Claims (1)

[Scope of Claims] 1. A DC power source, a high voltage transformer, and two current paths through which a reverse current flows from the DC power source to the primary winding of the high voltage transformer, each current path being a first current path and a second current path. an inverter having two switching elements and a diode connected in antiparallel to the second switching element; a rectifier circuit that converts the AC voltage output from the high voltage transformer into a DC voltage; and the rectifier circuit. X connected via high voltage cable to
In an inverter-type X-ray apparatus that includes a ray tube and an inverter control circuit that alternately operates two current paths of the inverter at a certain period, the inverter control circuit operates based on a set X-ray condition signal. a first control circuit that generates a signal for setting a timing and a stop time to start stopping the power supply from the DC power source to the high voltage transformer within each operating cycle period of the two current paths; An inverter-type X-ray apparatus comprising: a second control circuit that controls on/off the first switching elements in the two current paths accordingly. 2. In the inverter type X-ray apparatus, the first control circuit controls the first half cycle of the inverter on and the subsequent second half cycle when the inverter starts operating based on the X-ray emission start signal according to the X-ray conditions. 2. The inverter-type X-ray apparatus according to claim 1, wherein the start time and stop time of stopping the power supply from the DC power source to the high-voltage transformer are set to different values thereafter. 3. The X-ray conditions input to the first control circuit are signals corresponding to the tube voltage value, tube current value, and length of the high-voltage cable, or a signal corresponding to the ratio of the tube current and tube voltage. An inverter type X-ray apparatus according to claims 1 and 2.