JPH0527959B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to Regarding equipment.

[Technical background of the invention and its problems] As a conventional X-ray device, for example, US Pat.
As disclosed in No. 4225788, there is a so-called series resonant bridge inverter system.

Conventional X-ray equipment using this series resonant bridge inverter method rectifies and smoothes an AC voltage supplied from a power source (generally a commercial power source) to obtain a DC voltage, and then converts this DC voltage into The first and second thyristors alternately switch, and this switching voltage is applied to one of the transformers.
A damped vibration is induced by applying the voltage to a resonant circuit consisting of a resonant capacitor connected in series to the secondary winding, and the X-ray tube voltage is obtained based on the voltage induced in the secondary winding of the transformer. .

Incidentally, the X-ray tube voltage in such an X-ray apparatus is conventionally set to a predetermined value by varying the firing cycles of the first and second thyristors or by varying the input voltage.

However, if an attempt is made to vary the X-ray tube voltage by changing the firing periods of the first and second thyristors, the following problems arise.

Figures 4a and 4b are waveform diagrams showing the relationship between the current flowing in the primary winding of the transformer due to switching of the first and second thyristors and the gate pulse of the thyristor. b indicates the current flowing when the thyristor is turned on, and b indicates the current flowing when the second thyristor is turned on. Note that the shaded area is a current that can flow in the opposite direction due to damped vibration of the resonant circuit.

As shown in Figure 4a, gate pulses GP1 and GP2 are applied to the gates of the first and second thyristors.
When the repetition period is short (maximum ignition frequency), the current flowing through the transformer is continuous, so the X-ray tube voltage becomes high, and the pulsating current component (ripple) included in this X-back tube voltage is small. .

On the other hand, as shown in FIG. 4b, the gate pulse applied to the gates of the first and second thyristors
If the repetition period of GP1 and GP2 is long (low firing frequency), more ripples will flow to the transformer.

Therefore, when the X-ray tube voltage is varied over a wide range by changing the firing period of the first and second thyristors,
The lower the X-ray tube voltage, the more ripples occur. In this way, if there are many ripples included in the X-ray tube voltage, the amount of X-rays generated by the X-ray tube will decrease, making it impossible to obtain good X-ray pictures (particularly in breast cancer that is performed in the low X-ray tube voltage region). (This will be disadvantageous when photographing)
In addition to the above, there was a further drawback that the variable range of the X-ray tube voltage was narrow. Therefore, a method of varying the X-ray tube voltage by adding a circuit for controlling the input voltage to the transformer may be considered, but in this case, the problem arises that the entire circuit becomes complicated and expensive.

[Object of the Invention] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an X-ray apparatus in which the X-ray tube voltage can be varied without increasing ripple.

[Summary of the Invention] The outline of the present invention for achieving the above object is to rectify and smooth an input AC voltage to obtain a DC voltage, and to apply this DC voltage to the primary winding of a transformer at a predetermined period. In the
A resonant circuit consisting of a secondary winding and a plurality of resonant capacitors each connected to the primary winding via a switch, and a full bridge or A bridge part that can be selected as one of the circuit configurations of the half bridge, and a control means that controls the opening and closing of a switch of the resonant circuit and a switch of the bridge part, respectively, and controls the cycle of the DC voltage applied from the bridge part to the resonant circuit. The present invention is characterized in that the resonance conditions of the resonance circuit and the circuit configuration of the bridge section can be arbitrarily selected to obtain a desired X-ray tube voltage.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing the configuration of the X-ray device,
1 is a power supply that supplies alternating voltage to this device. Further, 2 is a rectifying means for rectifying the alternating current voltage supplied from the power source 1, in which rectifiers 2a, 2b, 2c, and 2d are bridge-connected; and 3 is a capacitor 3a and 3d connected in series with each other; This is a smoothing means for smoothing the voltage rectified by the rectifying means 2.

Incidentally, the rectifying means 2 and the smoothing means 3 are referred to as a rectifying/smoothing means 22.

A transformer 6 has a primary winding 6a and a secondary winding 6b, and a resonance capacitor group 5 is connected in series to the primary winding 6a of the transformer 6 to form a resonant circuit. This resonance capacitor group 5 includes a plurality of capacitors 5a ₁ , 5a ₂ , ... 5a _o and a plurality of switches 5b ₁ , 5b ₂ , ..., 5b _o (n≧2), and the capacitor 5a ₁ and the switch 5b ₁ , capacitor 5a ₂ and switch 5b ₂ ,..., capacitor 5a _o and switch 5
b _o are connected in series, and these are connected in parallel to each other.

The switches 5b ₁ , 5b ₂ , . . . , _5bo are controlled to open and close by a control means 19, which will be described later.

20 is a bridge part, and this bridge part 20
are diodes 13A, 15A and thyristor 12
An intermediate connection point between a first half bridge section 20A in which A and 14A are connected in antiparallel, a second half bridge section 20B in which diodes 13B and 15B and thyristors 12B and 14B are connected in antiparallel, and a second half bridge section 20B. and the intermediate connection point of the capacitors 3a and 3b of the rectifying means ₃ , the intermediate connection point of the second half bridge section 20B, the diode 13B, the thyristor 12B, the diode 15B, and the thyristor 1.
4B and the switches SW ₂ and 4B respectively,
SW ₃ . Each of the switches 12A, 14A, 12B, and 14B is controlled by a gate pulse from a control means 19, which will be described later.

In addition, switches SW ₁ , SW ₂ , and SW ₃ are also used as control means 1.
The opening/closing is controlled by 9.

16 is a first detection means for detecting a primary current (for example, includes a current transformer);
17 is an I/V (current/voltage) that converts the output (current signal) of the first detection means 16 into a voltage signal;
The converting means 7 is a rectifying means for rectifying the voltage induced in the secondary winding 6b, and 8 is a capacitor connected in parallel to the rectifying means 7 and smoothing the output of the rectifying means 7. The voltage smoothed by the capacitor 8 is applied between the anode 9a and the filament 9b of the X-ray tube 9 via the high-voltage cables 10a and 10b.
11b are connected in series.
detected by.

19 is each thyristor 1 of the bridge section 20;
2A, 14A, 12B, and 14B at a predetermined period to control the timing of DC voltage application to the resonant circuit;
Feedforward control and feedback control (described in detail later) are performed based on the detection signals of the second detection means 16 and 11, and each switch SW ₁ , SW ₂ , SW of the second half bridge section 20B is controlled. ₃
This is a control means that sends an opening/closing control signal to the

Next, the operation of the device configured as described above will be explained.

The AC voltage supplied from the power source 1 is applied to the rectification/smoothing means 22, rectified by the rectification means 2, smoothed by the smoothing means 3, and supplied to the bridge section 20 as a DC voltage. Bridge part 20
An opening/closing control signal is sent from the control means 19 to the switches SW ₁ , SW ₂ , SW ₃ constituting the second half bridge section 20B, and the switch SW ₁ is opened.
Assuming that SW ₂ and SW ₃ are in the closed state, in this state a full bridge is formed by the diodes 13A and 15A of the first half bridge section 20A and the diodes 13A and 15A of the second half bridge section 20B.

In this state, gate pulses are alternately supplied from the control means 19 to the thyristors 12A and 14B and the thyristors 14A and 12B at a predetermined period, and these perform switching operations alternately.

When the thyristors 12A, 14B are turned on, the current due to the DC voltage of the capacitor 3a flows through the thyristors 12A, 14B to the primary winding 6a.
flows for half a period (forward direction), then the resonant capacitor 5 and the primary winding 6a (strictly speaking, the secondary side of the transformer 6)
Due to the damped oscillation determined by
Thyristor 12A, 1 that had been in the on state until then
4B is turned off, and the current for the next half cycle (in the opposite direction) flows through diodes 13A and 15B.
Therefore, once the thyristors 12A and 14B are turned on, one period of primary current flows through the primary winding 6a.

Similarly, when the thyristors 14A and 12B are turned on, one period of primary current flows through the primary winding 6a, but the current direction is
The direction is opposite to that when A and 14B turn on.

In this way, when the primary current flows through the primary winding 6a, a voltage is induced in the secondary winding 6b. This induced voltage is rectified by the rectifier 7 and smoothed by the capacitor 8, and then applied as an X-ray tube voltage between the anode 9a and filament 9b of the X-ray tube 9.

When the switch SW ₁ is controlled to be closed and the switches SW ₂ and SW ₃ are controlled to be opened by the next opening/closing control signal from the control means 19, the bridge section 20 becomes a half-bridge state consisting of only diodes 13A and 15A. . In this case, the diodes 13B, 15B and the thyristors 12B, 14B of the second half-bridge section 20B are no longer involved in the operation of this device, and the primary current determined by the switching period of the thyristors 12A, 14A of the first half-bridge section 20A is The current flows to the primary winding 6a.

However, when the bridge section 20 is a full bridge, a DC voltage approximately equal to the DC voltage supplied from the rectifying/smoothing means 22 is applied to the primary winding 6a, whereas when the bridge section 20 is a half bridge, the DC voltage is applied to the primary winding 6a. The value will be halved.

An opening/closing control signal is sent from the control means 10 to each switch 5b ₁ , 5b ₂ , ..., 5b _o of the resonance capacitor group 5 connected between the second half bridge 20B and the primary winding 6a. A capacitor capacity that forms a resonant circuit with the next winding 6a is selected.

Next, variable X-ray tube voltage will be explained. X
When attempting to vary the line tube voltage, each switch SW ₁ , SW 2 , SW ₂ of the second half bridge section 20B
SW ₃ and each switch 5 of resonance capacitor group 5
b ₁ , 5b ₂ , ..., 5b _o , and change the timing of the opening/closing control signal of each thyristor 12A, 14.
This is done by changing the repetition period of gate pulses for A, 12B, and 14B.

That is, before the X-ray tube 9 emits X-rays, each switch SW ₁ ,
SW ₂ and SW ₃ are switched by opening/closing control signals to set the bridge section 20 to either a full bridge or a half bridge. Thereby, the voltage applied to the primary winding 6a can be selected as either the output voltage of the rectifying/smoothing means 22 or half thereof.

In addition, the capacitor capacity of the resonance capacitor group 5 is arbitrarily selected by opening/closing control of the switches 5b ₁ , 5b ₂ , ..., 5b _o , thereby changing the series resonance condition of the resonance circuit and applying the voltage to the primary winding 6a. Vary the voltage.

Furthermore, the voltage applied to the primary winding 6a can be adjusted by changing the repetition period of gate pulses for each thyristor 12A, 14A, 12B, 14B of the bridge section 20 from the control means.

In this way, the circuit configuration of the bridge section 20 and the resonance conditions of the resonance circuit are controlled by the control means 19, and the voltage applied to the primary winding 6a is set in advance (for example, set to a low voltage), so that the gate pulse It is possible to reduce the X-ray tube voltage to a desired value without setting the ignition frequency to a low value as shown in FIG. Therefore, ripples included at low X-ray tube voltages are extremely small compared to conventional devices, which is advantageous in mammography, for example, performed in a low X-ray tube voltage region.

Incidentally, the opening/closing control signal and gate pulse from the control means 19 described above can also be automatically generated by using the μ-CPU.

Next, feedback control and feedback control in the control means 19 will be explained using a half bridge state as an example.

The primary current flowing through the primary winding 6a is detected by the first detection means 16, and the detection signal is converted into a voltage signal via the I/V conversion means 17 and then input to the control means 19. .

Here, the control means 19 controls the thyristor 1 based on the detection signal output from the first detection means 16.
The next timing signal will not be output unless the turn-off of 2A and 14A is confirmed (confirmation that the current direction is reversed from one cycle of primary current due to damped oscillation). That is, feed forward control is performed so that unless one thyristor, for example 12A, which is in an on state is turned off, the other thyristor, for example 14A, is not turned on.

In this way, by performing feedforward control based on the detection signal of the first detection means 16, it is possible to avoid the worst situation in which both the thyristors 12A and 14A are turned on. Therefore, the device operates stably.

Further, the X-ray tube voltage is detected by the second detection means 11, and the detection signal is inputted to the control means 19.

Here, the control means 19 performs feedback control to stabilize the X-ray tube voltage based on the detection signal of the second detection means 11. For example, when the X-ray tube voltage becomes lower than a predetermined value, the repetition period of the gate pulse is shortened to increase the X-ray tube voltage.

In this way, by performing feedback control based on the detection signal of the second detection means 11, damping can be suppressed and a stable X-ray tube voltage can be obtained.

It goes without saying that the present invention is not limited to the embodiments described above, and that modifications can be made as appropriate within the scope of the gist of the present invention.

For example, although three types of means are shown as means for varying the X-ray tube voltage, these means can be arbitrarily combined.

Further, the capacitances of the capacitors 5a ₁ , 5a ₂ , ..., 5a _o in the resonance capacitor group 5 may be the same or different, and the combination and selection can be made arbitrarily, and the capacitances shown in FIG. It can also be implemented by configuring the capacitors 5a ₁ , 5a ₂ , . . . , _{5a o} to be connected in series and short-circuited by the switches 5b ₁ , 5b ₂ , . . . , 5bo.

Furthermore, the switches SW ₂ and SW ₃ of the second half bridge section 20B can be connected only to the diodes 13B and 15B, respectively, as shown in FIG.

In this case, it is necessary not to apply gate pulses to the thyristors 12B and 14B.

[Effects of the Invention] According to the present invention described in detail above, by not only controlling the timing of DC voltage application to the resonant circuit but also varying the voltage applied to the primary winding, ripples can be reduced and applied over a wide range. X that can be varied over
An X-ray device capable of obtaining a ray tube voltage can be provided.

[Brief explanation of the drawing]

1 is a circuit diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a modification of the resonance capacitor group in the device shown in FIG. 1, and FIG. 3 is a circuit diagram showing a modification of the resonance capacitor group in the device shown in FIG. FIGS. 4a and 4b are waveform diagrams showing gate pulse states in the respective conventional X-ray apparatuses. 1... Power supply (AC), 2... Rectifying means, 3...
Smoothing means, 5...Resonance capacitor group, 5a ₁ to 5
a _o ...Resonance capacitor, 5b ₁ to 5b _o ... Switch, 6... Transformer, 6a... Primary winding, 6b...
Secondary winding, 9... X-ray tube, 11... Second detection means, 16... First detection means, 19... Control means, 20... Bridge section, 20A... First half bridge section , 20B... second half bridge section, 22... rectification/smoothing means.

Claims (1)

[Claims] 1. A DC voltage is obtained by rectifying and smoothing an input AC voltage, and this DC voltage is applied to the primary winding of a transformer at a predetermined period to In an X-ray device, the voltage of the X-ray tube is obtained based on the current induced in the secondary winding of the transformer by applying a current to the primary winding of the transformer. a resonant circuit consisting of a plurality of connected resonant capacitors; a bridge section that applies the DC voltage to the resonant circuit at a predetermined period and can select either a full bridge or a half bridge circuit configuration via a switch; control means for controlling the opening and closing of the switch of the resonant circuit and the switch of the bridge section, respectively, and controlling the cycle of the DC voltage applied from the bridge section to the resonant circuit, and the control means controls the resonance conditions of the resonant circuit and the circuit configuration of the bridge section. An X-ray apparatus characterized in that a desired X-ray tube voltage is obtained by arbitrarily selecting the voltage. 2. The control means is configured to control the opening and closing of the switch of the resonant circuit and the switch of the bridge section, and control the cycle of the DC voltage applied to the resonant circuit simultaneously or in conjunction with each other. X-ray equipment.