JP2013037998A - X-ray high voltage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray high voltage device which, even when power supply is cut off, can quickly decelerate the rotation of an X-ray tube anode.SOLUTION: The X-ray high voltage device in an embodiment includes: a rotary anode X-ray tube; a starter inverter which supplies current to the stator coil of the rotary anode; a smoothing capacitor which, by smoothing a pulsating current derived by rectification from an AC power source, supplies DC voltage to the starter inverter; a power source cutoff detection unit which detects a power source cutoff of the AC power source; and a starter control circuit which, when a power source cutoff is detected by the power source cutoff detection unit, extends the pulse width of an inverter drive signal, which is subjected to pulse width modulation at a prescribed duty cycle before being input to the starter inverter, according to reduction in the smoothing capacitor voltage, and also sets the rotational frequency of the inverter drive signal to a resonance rotational frequency of the rotary anode X-ray tube or less.

Description

  Embodiments described herein relate generally to an X-ray high voltage apparatus used in an X-ray diagnostic apparatus having a rotating anode X-ray tube.

  Conventionally, in an X-ray diagnostic apparatus using a rotary anode X-ray tube as an X-ray generation source, anode rotation is controlled by a starter control circuit incorporated in an X-ray high voltage apparatus. The anode rotation speed is controlled according to the X-ray output conditions, and is controlled so that the rotation speed is low (for example, 60 rotations per second) when the X-ray output is low, and the rotation speed is high (for example, 180 rotations per second) when the X-ray output is high. Here, the anode rotation has a resonance rotation frequency (resonance point) at which mechanical vibration increases (for example, 70 rotations per second), and rotating for a long time in the vicinity of this rotation frequency may damage the bearing bearing of the rotation shaft. (See Patent Document 1).

  When the bearing is worn out, rotation failure and noise increase are caused, so that the diagnosis using this apparatus is adversely affected. For this reason, it is necessary to start and stop from high-speed rotation that passes through the resonance rotation frequency in as short a time as possible. Normally, both the time from the start of rotation to the high-speed rotation of 180 rotations per second or the time from the high-speed rotation of 180 rotations per second to the rotation stop is about several seconds.

  Further, when the power of the X-ray diagnostic apparatus is turned off, the X-ray tube anode may still be rotated depending on the use state of the apparatus, for example, immediately after imaging. For this reason, there is also a device having a shutdown function that shuts off the power supply after stopping the anode rotation by performing a brake operation on the rotation of the anode instead of shutting off the power supply simultaneously with the operation of turning off the power supply.

  However, even in such a device, if a power failure occurs while the X-ray tube anode is rotating, the rotation of the X-ray tube anode cannot be braked. The X-ray tube anode continues inertial rotation for a while due to inertia, and the rotational speed is gradually reduced due to friction of the bearings. When rotating at a rotational speed higher than the resonant rotational frequency, the resonant rotational frequency is passed slowly, causing bearing bearing wear and noise problems.

  Even when the power is shut down due to a power failure or emergency situation, the state before the power is turned off is stored, so that when the power is turned on again, the rotor of the X-ray tube is braked to rapidly reduce the rotational speed. Some reduce the passage time of the resonance rotation frequency (see Patent Document 2). However, it corresponds only when the power is turned on again.

JP 62-69495 A JP 2000-173776 A

  The problem to be solved by the present invention is to solve the above-mentioned problems and to provide an X-ray high voltage apparatus capable of quickly decelerating the rotation of the X-ray tube anode even when the power is cut off. And

  In order to achieve the above object, an X-ray high-voltage apparatus according to an embodiment smoothes a pulsating flow obtained by rectifying an AC power source, a rotating anode X-ray tube, an inverter for a starter that supplies current to a stator coil of the rotating anode. A smoothing capacitor that supplies a DC voltage to the starter inverter, a power-off detection unit that detects power-off of the AC power supply, and a power-off detection unit that detects a power-off in the starter inverter. The pulse width of the inverter drive signal input after being pulse width modulated with the duty ratio is extended in accordance with the decrease in the smoothing capacitor voltage, and the rotational frequency of the inverter drive signal is set to the resonant rotation of the rotary anode X-ray tube. And a starter control circuit that is set to be equal to or lower than the frequency.

The block diagram of the X-ray high voltage apparatus in embodiment. The operation principle figure of the inverter for starters in the same embodiment. Explanatory drawing of the current waveform which flows into the stator coil in the embodiment. Explanatory drawing of the normal brake mode in the embodiment. Explanatory drawing of the brake mode at the time of the power interruption in the embodiment. The block diagram of the X-ray high voltage apparatus in other embodiment. Explanatory drawing of the brake mode at the time of the power interruption in the embodiment.

  Hereinafter, embodiments for carrying out the invention will be described in detail with reference to FIGS. 1 to 7.

  FIG. 1 is a block diagram of an X-ray high voltage apparatus according to this embodiment. A rotary anode X-ray tube 10 used in the X-ray high voltage apparatus of the present embodiment includes an X-ray tube 101 and a starter circuit for rotating the anode. The starter circuit includes a rotor 102 that rotates the X-ray tube anode and a stator coil 103 that generates a rotating magnetic field.

  Moreover, the X-ray high voltage apparatus of this embodiment is divided into two types: a high voltage circuit system for applying a high voltage and a starter control circuit system for rotating the anode.

  The high voltage circuit system includes a commercial AC power supply 11, a DC power supply 12, a high voltage inverter 13, and a high voltage transformer 14, and applies a high voltage to the anode and cathode of the X-ray tube 101.

  The DC power supply 12 includes a rectifier 121 that converts AC to DC and a smoothing capacitor 122 that smoothes the rectified pulsating flow.

  The starter control circuit system includes an AC power supply 11, a power interruption detection unit 15 that detects that the power supply of the AC power supply 11 is cut off, a starter control AC / DC converter 16 that converts AC to DC, and an X-ray tube anode It comprises a starter control circuit 17 for controlling the rotational speed and a starter inverter 18 for applying a current to the stator coil 103 of the starter circuit.

  The starter control AC / DC converter 16 that converts the alternating current output of the alternating current power supply 11 into direct current has a power storage unit 161 in order to provide the direct current power output even when the power supply is interrupted.

  The starter control circuit 17 includes a power supply unit 171 that distributes power in the circuit, a rotation frequency setting unit 172 that sets a frequency that is a rotation speed target according to the rotation operation mode of the X-ray tube anode, and a starter inverter 18. Pulse width modulation (PWM) is applied to the inverter drive signal input to the switching element, the pulse width is controlled and expanded according to the rotation operation mode, and the rotation frequency and pulse width are determined. The inverter driving unit 174 outputs an inverter driving signal.

  The starter inverter 18 includes switching elements A, B, C, and D such as four IGBTs (Insulated Gate Bipolar Transistors). The current flowing through the stator coil 103 is reversed between when switching elements A and D are turned on and switching elements B and C are turned off, and when switching elements A and D are turned off and switching elements B and C are turned on. AC current can flow. Therefore, the starter inverter 18 performs a switching operation so that an alternating current having a frequency targeted for the rotational speed flows through the stator coil 103 of the rotary anode X-ray tube 10. Further, a phase difference is generated between the currents of the two stator coils 103 by the phase advance capacitor 104. The high voltage inverter 13 and the starter inverter 18 share the DC power supply 12.

  Next, the operation principle of the starter control circuit 17 will be described with reference to FIG. Hereinafter, description will be made assuming an IGBT as a switching element. Although there are various inverter operation methods for generating alternating current, a simple single-phase inverter will be described here for explanation. 2A shows the voltage waveform of the inverter drive signal input to the switching elements A and D from the inverter drive unit 174, and FIG. 2B shows the inverter drive signal input to the switching elements B and C. A voltage waveform is shown. The switching elements A, B and C, D are pulse width modulated so as to be turned on / off at a time interval Tp sufficiently shorter than the rotation period of the X-ray tube anode set by the rotation frequency setting unit 172. As shown, it may be considered that a voltage that is a temporal average value is input and a current that is a temporal average value is output. The temporal average value of the output current can be changed by changing the ratio (duty ratio) of the on-time to the period Tp of the pulse modulation. This pulse width control can be performed by the pulse width expansion unit 173. The duty ratio is determined so that an excessive current does not flow through the stator coil 103.

  FIG. 3 shows the state of the current waveform flowing in the stator coil 103 by the voltage waveform of the inverter drive signal input to the starter inverter 18. A current when switching elements A and B are turned on and a current when switching elements C and D are turned on are applied to stator coil 103 in opposite directions. As shown by the double arrow in FIG. 3, one period of this current determines the rotation period of the X-ray tube anode.

  Next, the rotation operation mode of the starter control circuit 17 will be described. The rotation operation mode of the starter control circuit 17 is (1) a low-speed rotation mode of, for example, about 60 rotations per second, (2) a high-speed rotation mode of, for example, about 180 rotations per second, (3) There are brake modes. In the present embodiment, in addition to this normal brake mode, (4) a brake mode at power-off is provided.

  The low-speed rotation mode and the high-speed rotation mode are achieved by changing the rotation period of the X-ray tube anode shown in FIGS. 2 and 3, that is, the rotation frequency to 60 times per second and 180 times per second, respectively.

  Next, the normal brake mode will be described with reference to FIG. In the rotation of the X-ray tube anode, there is a resonance rotation frequency at which mechanical vibration increases, which exists between the rotation speed of the low rotation mode and the high rotation mode, for example, around 70 rotations per second. Rotating for a long time in the vicinity of this rotational speed may damage the bearing bearing of the rotating shaft, and if the bearing is worn out, it may cause rotation failure and increase in noise. Therefore, high-speed rotation start (high-speed rotation mode) that passes through the resonance rotation frequency and stop from high-speed rotation (normal brake mode) stabilize the rotation operation so that the time to pass through the resonance rotation frequency is as short as possible. Need to do. Usually, it takes about several seconds for the time from the start of rotation to high speed rotation of 180 rotations per second, or the time to stop rotation from high speed rotation of 180 rotations per second.

  As shown in FIG. 4A, in the normal brake mode, the inverter drive signal subjected to the above-described pulse width modulation is input to the switching elements A and D until the X-ray tube anode stops. On the other hand, nothing is input to the switching elements B and C as shown in FIG. That is, braking is applied by setting the rotation frequency to 0 in the rotation frequency setting unit 172 and stopping the rotating magnetic field. By applying such braking, the rotation time in the vicinity of the resonance rotation frequency can be shortened to prevent the bearing from being damaged.

  Next, a brake mode at the time of power shutoff that operates when the power is shut off due to a power failure or emergency situation, which is a feature of the present embodiment, will be described with reference to FIG. It is assumed that the X-ray tube anode is rotating in the high speed rotation mode.

  First, assume that the AC power supply is cut off due to a power failure or emergency situation. The DC power source 12 that is the main power source for the high-voltage inverter 13 and the starter inverter 18 has a smoothing capacitor 122, and electric charge remains in the smoothing capacitor 122 even after the AC power source 11 is turned off.

  Further, since the AC / DC converter 17 for starter control power supply has a power storage function by the power storage unit 161, a DC power output is possible for a certain period of time after the AC power supply is shut off. The storage method is not particularly limited, but simple methods such as a capacitor and a battery are conceivable. In addition, since the fixed time may be at least a short time (several seconds) that allows at least one brake mode when the power is shut off, a large storage capacity is not necessary.

  As a result, the starter control circuit 17 can operate normally for a certain period of time after the AC power supply 11 is shut off. When the power-off detector 15 detects the interruption of the AC power supply 11 (power-off detection), the starter control circuit 17 immediately performs control in the brake mode at the time of power interruption. The power supply voltage of the starter inverter 18 applies a current to the stator coil 103 using the electric charge remaining in the smoothing capacitor 122 to brake the rotation of the X-ray tube anode.

  As shown in FIG. 5B, the DC voltage output from the smoothing capacitor 122 decreases as the charge stored in the smoothing capacitor 122 is used when the AC power supply 11 is shut off. Therefore, when the power supply voltage supplied to the starter inverter 18 decreases, the output current also decreases. In order to ensure the braking effectiveness, it is necessary to pass a current of a certain value or more to the stator coil 103. Therefore, as shown in FIG. 5A, in accordance with the DC voltage drop of the smoothing capacitor 122, the pulse width expansion unit 173 performs control to extend the pulse width of the inverter drive signal input to the starter inverter 18, and the stator Control is performed so that the current flowing through the coil 103 is corrected to be constant (dotted line).

  Further, the rotation frequency of the inverter drive signal input to the switching elements A and B is set to a rotation frequency equal to or lower than the resonance rotation frequency by the rotation frequency setting unit 171. This is because it is sufficient if the rotation time near the resonance rotation frequency can be shortened to prevent the bearing from being damaged. The rotation frequency may be set to 0 as in the normal brake mode. The rotational frequency to be set below the resonance rotational frequency is determined by taking various measurements such as the time from the high speed rotation to the resonance rotational frequency or less in consideration of the capacity of the smoothing capacitor 122, the current value flowing through the stator coil 103, and the like. To do.

  Here, the DC voltage output from the smoothing capacitor 122 and the capacitance of the smoothing capacitor 122 when the power is shut off will be described.

  The inverter drive signal input to the starter inverter 18 is pulse width modulated. Therefore, the time-averaged output current of the starter inverter 18 decreases corresponding to the duty ratio of the pulse width. For example, if the duty ratio is 1/2, the time average output current of the starter inverter 18 is 1/2. If the duty ratio is set to 1, the time average output current of the starter inverter 18 can be doubled. Therefore, considering the case when the power is cut off, even if the DC current output from the starter inverter 18 is halved, if the duty of the pulse width is set to 1, the output DC current is normal before the power is shut off. Can be set to any value.

  In other words, the current flowing through the stator coil 103 can be made constant by extending the pulse width of the inverter drive signal as long as it falls within a range in which the current before multiplying the power is reduced to the current value multiplied by the duty ratio. It is possible to maintain the braking effect.

  With respect to the capacity of the smoothing capacitor 122, the time until the rotation of the X-ray tube anode becomes at least the resonance rotation frequency or less after the power-off detection is measured in a normal brake mode, and a constant duty ratio that does not extend the pulse width within this time When the pulse modulation is performed, the capacity is set so that the direct current output from the starter inverter can hold a current value equal to or greater than a value obtained by multiplying the direct current value before power-off by the duty ratio.

  In addition, the capacity of the smoothing capacitor 122 is best to satisfy the above-described conditions. However, even if not satisfied, the present embodiment quickly rotates the X-ray tube anode to a rotational speed equal to or lower than the resonance rotational frequency. A certain effect can be obtained because the purpose is to lower the value.

  Further, in the brake mode at the time of power-off, the method of extending the pulse width of the inverter drive signal is to measure the DC voltage output from the smoothing capacitor 122 and the output current of the starter inverter 18 after the power-off detection, A pulse width expansion rate that makes the current of the stator coil 103 constant may be set in advance in a ROM (Read Only Memory) or the like as a table, and the pulse width may be expanded in accordance with this table.

  Therefore, as shown in FIG. 5C, the inverter drive signal pulse waveform (solid line) input to the starter inverter 18 is expanded as the output voltage of the smoothing capacitor 122 decreases. The current (one-dot chain line) is constant.

  In the present embodiment, the current flowing through the stator coil 103 is assumed to be a single-phase current. However, even when a three-phase stator coil is used, the same idea can be applied.

  As described above, in this embodiment, even when the power is shut off, the brake can be effectively applied to the rotation of the X-ray tube anode, so that it is possible to solve the problems of bearing bearing wear and noise.

  Further, an embodiment will be described in which the brake mode when the power is shut off can be actively operated by actually observing the current flowing through the stator coil.

  FIG. 6 is a block diagram of the X-ray high voltage apparatus in this embodiment. In addition to the block diagram of FIG. 1, a peak detector 175 that detects the peak of the current flowing through the stator coil 203 and a current comparator 177 that outputs a signal corresponding to the difference compared with a predetermined current regulation value 176 are provided. doing.

  With reference to FIG. 7, the brake mode when the power is turned off according to this embodiment will be described. FIG. 7A shows a decrease in the output voltage of the smoothing capacitor 122 due to the occurrence of power interruption.

FIG. 7B shows an inverter drive signal pulse waveform (solid line) that is input to the starter inverter 18 as the output voltage of the smoothing capacitor 122 decreases, an inverter output current (dotted line) that flows through the stator coil 103, and Average current (one-dot chain line) is shown.

  As shown in FIG. 7A, after detecting the power interruption indicated by the arrow, the output voltage of the smoothing capacitor 122 decreases. Along with this, the output current of the starter inverter 18 also decreases. In order to prevent this, a peak detection circuit 175 is connected between the starter inverter 18 and the stator coil 103 to detect the peak current value of the inverter output current. The current to be passed through the stator coil 103 is set as the current regulation value 176, and the pulse width of the inverter drive signal is extended corresponding to the difference value between the current regulation value 176 output from the current comparison unit 177 and the peak current value.

  By extending the pulse width of the inverter drive signal, the current flowing through the stator coil 103 increases, and the peak current value of the peak detector 175 also increases. Then, when the peak current value becomes the same as the current preset value 176, the extension of the pulse width is stopped and the pulse of the inverter drive signal is turned off. The pulse off time is the same as the normal brake mode. While the pulse is off, the DC voltage of the smoothing capacitor 122 supplied to the starter inverter 18 and the inverter output current are also greatly reduced. Therefore, in the next pulse, until the peak current value reaches the current regulation value 176. Furthermore, it is necessary to extend the pulse width.

  In this way, by repeating the pulse modulation operation that extends the pulse width of the inverter drive signal with time, the average current flowing through the stator coil 103 becomes a waveform as shown by a one-dot chain line, and the decrease in the current flowing through the stator coil 103 is reduced. Is possible. In FIG. 7, the frequency set by the rotation frequency setting circuit 172 is set to 0 and only the control of the switching elements A and D has been described. However, as shown by the dotted line in FIG. 6, the switching element B of the starter inverter 18 , C is also detected, and the same control is performed, so that the rotation frequency setting circuit 172 can set an arbitrary rotation frequency equal to or lower than the resonance rotation frequency.

  The inverter output current peak detection control shown in the present embodiment can be operated not only when the power is shut off but also when it is normal. In that case, it becomes possible to flow a constant current to the stator coil 203 stably even with respect to voltage fluctuations of the AC power supply.

  Accordingly, active control can be performed on the pulse width of the inverter drive signal, and optimum pulse width control can be performed even when the power is not cut off.

  According to the embodiment described above, the power failure occurred in the state where the X-ray tube anode is rotating or the operation was mistaken in normal operation, and the power was forcibly turned off without performing the shutdown process of the apparatus. Even in this case, the rotation of the X-ray tube anode can be braked, and the wear and noise generation of the anode bearing can be suppressed.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 ... Rotating anode X-ray tube 11 ... AC power supply 12 ... DC power supply 13 ... High voltage inverter 14 ... High voltage transformer 15 ... Power-off detection part 16 ... Starter control AC / DC converter 17 ... Starter control circuit 18 ... For starter Inverter 101 ... X-ray tube 102 ... Rotor 103 ... Stator coil 161 ... Power storage unit 172 ... Rotation frequency setting unit 173 ... Pulse width extension unit 174 ... Inverter drive unit 175 ... Peak detection unit 176 ... Voltage predetermined value 177 ... Current comparison unit

Claims (5)

A rotating anode X-ray tube;
An inverter for a starter for supplying a current to a stator coil of the rotary anode X-ray tube;
A smoothing capacitor for smoothing a pulsating flow obtained by rectifying an AC power supply and supplying a DC voltage to the starter inverter;
A power-off detector that detects a power-off of the AC power supply;
When power-off detection is detected by the power-off detector, the pulse width of the inverter drive signal that is input to the starter inverter after being subjected to pulse width modulation at a predetermined duty ratio is extended in accordance with a decrease in the voltage of the smoothing capacitor. And a starter control circuit for setting a rotation frequency of the inverter drive signal to be equal to or lower than a resonance rotation frequency of the rotary anode X-ray tube;
An X-ray high voltage apparatus comprising: A rotating anode X-ray tube;
An inverter for a starter for supplying a current to a stator coil of the rotary anode X-ray tube;
A smoothing capacitor for smoothing a pulsating flow obtained by rectifying an AC power supply and supplying a DC voltage to the starter inverter;
A power-off detector that detects a power-off of the AC power supply;
A peak detector for detecting a peak current value of the stator coil;
A current comparison unit that compares the peak current value with a current regulation value to be passed through the stator coil;
Extending the pulse width of the inverter drive signal that is pulse-width-modulated and input to the starter inverter according to the output of the current comparator, and extending the rotation frequency of the inverter drive signal to the rotary anode A starter control circuit that is set to be equal to or lower than the resonance rotational frequency of the X-ray tube;
An X-ray high voltage apparatus comprising:   The smoothing capacitor outputs the output from the starter inverter when the rotation speed of the rotating anode is pulse-modulated with a constant pulse width of a predetermined duty ratio in a time from the power-off to at least the resonance rotation frequency or less. The X-ray high voltage apparatus according to claim 1 or 2, wherein the direct current to be applied has a capacity capable of holding a current value obtained by multiplying the direct current value before the power-off by the predetermined duty ratio.   3. The X-ray high voltage apparatus according to claim 1, wherein the rotational frequency of the rotary anode X-ray tube is set to 0 when the power is turned off.   4. The X-ray high voltage apparatus according to claim 3, wherein the starter control circuit is supplied with power from a backup power source that operates when the power is cut off.

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