JPS614198A - X-ray device - Google Patents

Abstract

PURPOSE:To enable restraint of overshoot of pipe voltage wave shape and oscillation when high tension cable length is different by controlling resistance value and operating time of a variable resistance means provided between a DC transforming means and a DC-AC converting means. CONSTITUTION:A pipe voltage signal Ekv, a pipe current signal EmA and a signal Ec corresponding to high tension cable length are input into a control condition calculating circuit 34. The circuit 34 computes the optimum damping resistance value to restrain oscillation of pipe voltage and insertion time there of by signals Ekv, EmA and Ec and outputs corresponding signals ER, ET to monomultiplexors 35, 36 respectively. The output of the monomultiplexor 35 shows a time ratio giving optimum damping resistance value to a variable resistance means 62 and the output of the monomultiplexor 36 is synchronized with output AC voltage of a DC-AC converting means 63 to determine optimum time width when damping resistance value is inserted.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an inverter-type X-ray high voltage device, and particularly to an X-ray device suitable for a stationary, large-capacity device.

[Background of the invention]

Conventional inverter-based X-ray equipment uses a switching element to convert a DC voltage set to a constant voltage into an AC voltage, boosts the voltage using a high-voltage transformer, and then outputs the DC voltage again via a high-voltage rectifier circuit. was applied to the wire tube.

These circuit systems include stray capacitance and leakage reactance of the high-voltage transformer, stray capacitance of the high-voltage cable connecting the high-voltage rectifier and the X-ray tube, and the circuits are prone to vibration. For this reason, the voltage applied to the X-ray tube (hereinafter referred to as tube voltage) may overshoot when voltage application starts, or even when the switching element for DC-AC conversion turns on and off even in a steady state. It was causing vibrations. The overshoot of the tube voltage waveform deteriorates the withstand voltage characteristics of the X-ray tube and becomes a cause of poor tube voltage setting accuracy.

Moreover, the vibration of the tube voltage waveform reduced the generated X-ray dose.

In addition, in recent years, with the reduction of equipment installation space and cost savings in hospitals, examples of so-called satellite equipment, in which a single high-voltage X-ray device drives X-ray tube equipment installed in many rooms, have become available. is increasing. In this case, since the length of the high-voltage cable that supplies power to the X-ray tube is different for each tube, the value of the stray capacitance located on the high-voltage side is different, resulting in a difference in the tube voltage waveform. Therefore, even under the same X-ray generation conditions, each X-ray tube has a different X-ray view.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray apparatus that suppresses overshoot and vibration of a tube voltage waveform, uses a flat tube voltage waveform, and can generate the same regardless of the length of a high-voltage cable.

[Summary of the invention]

To suppress the oscillation of the tube voltage, the oscillating current flowing through the inverter circuit can be damped using a resistor for the necessary time.
However, at this time, since the tube voltage and tube current period are different,
The time required for braking and the resistance value vary. Therefore, a variable resistance means that can have any resistance value for any time is inserted in a place where the oscillating current can be limited in the inverter circuit, and the optimum braking condition (braking resistance value) calculated from each condition of tube voltage, tube current, high voltage cable length, etc. R, d, braking time Td)
By setting the variable resistance means at , it is possible to dampen the imaging current in the inverter circuit and suppress vibrations in the tube voltage.

[Embodiments of the invention]

An embodiment of the present invention will be explained below with reference to FIG. The DC voltage source 60Vc is the output of a full-wave rectifier 7 connected to an AC power source 50, and a filter including a reactor 8 and a capacitor 9 is provided to obtain a smoothed DC voltage. The DC transformation means 61 transforms and adjusts the output voltage of the DC voltage source 60 to a voltage that satisfies the set XS* radiation conditions, and includes the chopper 1, flywheel diode 10. It consists of a reactor 11% capacitor 12 and a voltage detection resistor 17.

The voltage adjusted to the set voltage is inputted to the DC-AC conversion means 63 via the variable resistance means 62. The DC-AC conversion means 63 is constituted by a full bridge circuit consisting of switching elements 3, 4, 5.6, such as transistors, and flywheel diodes 13, 14, 15.16, respectively.

Here, it is generally converted into a high frequency AC voltage of several hundred Hz,
It is applied to the high voltage generator 64. High frequency AC voltage is
The voltage is stepped up by the high voltage transformer 20 and converted to direct current by the high voltage rectifier 21, and then applied to the X-ray tube 22.

The operation of this circuit will be explained using FIGS. 2 and 3.

When the desired tube voltage and tube current are selected before X-ray irradiation, input terminals 51 and 52 receive the IT tube voltage equivalent signal EK.
v and tube current equivalent signal E□^ are input. - The optimum primary voltage equivalent signal E is calculated from the primary voltage calculation circuit 31 Egv and EIIIA. The monomulti 32 generates a pulse with a duty ratio corresponding to E at the frequency of the oscillator 30, and is driven by the chopper I via the drive circuit 33. capacitor 12
The primary voltage generated across the zero terminals is monitored by the voltage detection resistor 17, and the detected voltage is negatively fed back to the negative voltage calculation circuit.
Keep the generated primary voltage stable. The variable resistance means 62 is
By short-circuiting the resistor 18' inserted into the circuit between the DC transformation means 62 and the DC-AC transformation means 63 at an arbitrary time ratio using the switching element 2, the resistance value is reduced isometrically. If the operating frequency of the switching element 2 is sufficiently large compared to the natural frequency of the circuit and the resistance value of the resistor 18 is R1, then the braking resistance value R' formed in the circuit is R'=( 1-D)R...(1) According to equation (1), F), D=0, that is, if switching element 2 is left off, R' becomes the maximum value R, ])=
In other words, if the switching element 2 is left on, R' is the minimum value r. becomes. Here, "am" is the on-resistance of the switching element 2, and its value is smaller than R.

Therefore, by changing the time ratio, the resistance value can be changed up to rp. The switching element 2 is driven by a braking condition setting means 65. First, tube voltage signal EK
v, the tube current signal E□A, and the signal 1']C corresponding to the length of the high-voltage cable to be used in the braking condition subtraction circuit 34.
Enter. The circuit 34 calculates the optimum braking resistance value 1 to 1 to suppress the vibration of the tube voltage based on the signals Exv g EmAI Ec, and outputs a signal ER11 corresponding to this to the 'mono multi 35. Similarly, the circuit 34 also calculates the time during which the braking resistor is inserted (braking time), and outputs a corresponding signal ET11 to the monomulti 36. In general, the optimal braking resistance and braking time for suppressing tube voltage vibration,
The relationship between tube voltage and tube current is shown in FIG. 2(a), and the relationship with high voltage cable length is shown in FIG. 2(b). In addition,
In FIG. 2(a), the X-ray tube equivalent resistance Rx is the tube voltage divided by the tube current.

Although the trigger input A of the monomulti 35 is synchronized with the operation of the chopper 1 at 8 shown in FIG. 3A, there is no particular need for synchronization. A is divided into a frequency of about 1/10 by the frequency divider 39, and becomes a synchronizing signal for the DC-AC conversion means 63 (FIG. 3B), and also serves as a trigger input for the monomulti 36. The output of the multi 35 (FIG. 3 C) is the duty ratio that makes the variable resistance means the optimum braking resistance value, and the output of the mono multi 36 (FIG. 3 D) is synchronized with the output AC voltage of the means 63. The optimum time width for inserting the braking resistance value is determined.The switching element 2 is driven via the drive circuit 38 by the signal E, which is the NAND condition of C and D.The DC-AC conversion means 63 In this case, the pair of switching elements 3 and 5 and the pair of switching elements 4 and 5 are turned on and off alternately by the flip-flop 40 via the drive circuit 44.
Or KONL 5 and 6 at the same time, mono multi 41 so that there is no
A rest period for the switching element is provided. During this rest period, the electromagnetic energy of the high voltage transformer 20 is regenerated to the power supply side as a current flowing through the flywheel diodes 14 and 16 or 13 and 15. At this time, a diode 19 is provided to prevent the switching element 2 from being destroyed by the high voltage generated across the resistor 18. Most of the current energy regenerated to the power supply side is spent charging the capacitor 12, but in order to limit the voltage rise of the capacitor, the position of the diode 19 is changed as shown in FIG. , it is also possible to limit the current flowing toward the power supply side using the resistor 18.

・In addition, 37 in the figure is a NANDAND circuit Fi drive circuit,
42 and 43 are AND circuits.

〔Effect of the invention〕

゛According to the present invention, it is possible to suppress overshoot and vibration of the tube voltage waveform and generate a flat tube voltage waveform even when a plurality of X-ray tubes with different cable lengths are provided.
line equipment can be provided.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of one embodiment of the present invention, Fig. 2 is a graph showing the operation of the circuit in the embodiment, Fig. 3 is a timing chart showing the operation of the embodiment, and Fig. 4 is another embodiment. FIG. 30... Generator, 31... -Nth voltage calculation circuit, 32
゜41...Mono multi, 33.44...Drive circuit,
34... Braking condition calculation circuit, 39... Frequency divider, 40
...Flip-flop, 42.43...A N,
D circuit. Mo2 evil (α) (-e)

Claims (1)

[Claims] 1. A DC transformer that transforms the voltage of a DC voltage source into a set voltage, a DC-AC converter that converts the set voltage into an AC voltage, and a high-voltage transformer that steps up the AC voltage. Prepare,
In an inverter-type X-ray apparatus that applies the output of the high-voltage transformer to the X-ray tube via a high-voltage rectifier, variable resistance means for suppressing oscillating current is provided between the DC transformation means and the DC-AC conversion means. , X-ray tube voltage, and
An X-ray apparatus comprising: a braking condition setting means for controlling the resistance value of the variable resistance means and the time during which it operates as a resistor according to the tube current and the length of the high voltage cable used. 2. The X-ray apparatus according to claim 1, wherein the variable resistance means chops the resistance using a switching element.