JP6673149B2 - Rotating anode type X-ray tube apparatus and its rotating anode driving device - Google Patents

Description

  The present invention relates to a rotary anode X-ray tube device used for medical X-ray diagnostic devices such as general X-ray devices or X-ray CT devices, and an anode rotation driving device for the rotary anode X-ray tube device.

  A rotating anode type X-ray tube (hereinafter sometimes simply referred to as an X-ray tube) is an anode rotating drive using the principle of an induction motor in order to increase an allowable load of the anode by moving an electron impact surface. Rotate on device. The X-ray tube is provided with a rotor coil on the rotation axis of an anode rotatably supported by a rotation axis in the X-ray tube, and a stator coil outside the X-ray tube, and a current is applied to the stator coil. By generating a rotating magnetic field, the anode is rotated via the rotor coil.

  The anode rotation drive device is divided into a two-phase type and a three-phase type according to the number of phases of the stator coil (see Patent Document 1). Each of the anode rotation driving devices converts a DC voltage from a DC voltage power supply into an AC voltage by an inverter circuit, applies a two-phase AC signal having a phase difference of 90 degrees to a stator coil in a two-phase system, and outputs a three-phase system. Then, a three-phase AC signal having a phase difference of 120 degrees is applied to the stator coil. The two-phase type has an advantage that the stator coil can be manufactured simply and at low cost, and the three-phase type has an advantage that it is advantageous for high-speed response.

Japanese Patent No. 4262810 JP-A-60-198099

  A factor that determines the upper limit of the AC voltage from the inverter circuit applied to the stator coil of the anode rotation drive device is a maximum voltage output from a DC power supply connected to the inverter circuit.

  The anode rotation drive devices of any number of phases have operation modes such as high-speed operation, low-speed operation, rotation maintenance, start, braking, and stop. Each operation mode defines the magnitude of the AC voltage sent from the inverter circuit to the stator coil, and the magnitude of the AC voltage is controlled by pulse width modulation (PWM) of the inverter circuit. Usually, the highest AC voltage is required in the high-speed operation mode. Therefore, the DC power supply has a structure sufficient to output the highest AC voltage.

  Further, for example, a two-phase anode rotation drive device includes a main coil and an auxiliary coil as stator coils, and the auxiliary coil has a larger number of turns than the main coil. The important factor that generates the torque for rotating the anode is not the voltage applied to the stator coil, but the current flowing through the stator coil, and more specifically, the rotating magnetic field generated by the current. When the number of turns of the coil is large, the impedance generally increases in proportion to the square of the number of turns. If an attempt is made to make the amplitude of the magnetic flux generated by the current equal between the main coil and the auxiliary coil, it is necessary to apply a higher voltage to the auxiliary coil than to the main coil. Also in this case, it is necessary to provide a DC power supply capable of outputting a voltage capable of flowing a current required by the auxiliary coil.

  Further, when the inverter circuit converts the DC voltage into a two-phase AC voltage supplied to the main coil and the auxiliary coil, the more the phase difference between the two-phase AC voltages deviates from the ideal phase difference, that is, 90 °, the more the AC voltage becomes. A large voltage is hardly obtained as a peak value, and a high DC voltage is required before conversion by an inverter circuit in order to obtain a required peak voltage.

  The required amplitude of the AC voltage applied to the stator coil changes depending on the type of X-ray tube as well as the operation mode.

  As described above, the DC power supply connected to the inverter circuit must be capable of outputting a high voltage that satisfies the requirement of the maximum value of the AC voltage applied to the stator coil from the inverter circuit. There are problems that the cost ratio of the DC power supply in the driving device is increased, the breakdown voltage of the switching element included in the inverter circuit is increased, and the size of the anode rotation driving device is increased.

  An object of the present invention is to solve the above-described problem by enabling the maximum value of an AC voltage applied from an inverter circuit to a stator coil to be constituted by a DC power supply connected to a low-voltage inverter circuit. Is what you do.

  The anode rotary drive of the present invention is intended for both the two-phase type and the three-phase type.

  An anode rotation driving device according to the present invention includes a DC power source and a plurality of switching elements, the stator being connected to the DC power source, generating an AC voltage from the DC voltage of the DC power source, and generating a rotating magnetic field of the X-ray tube. An inverter circuit that outputs to a coil; a PWM waveform generator that performs pulse width modulation (PWM) control on the switching element of the inverter circuit to generate a two-phase or three-phase AC voltage from the DC voltage as the AC voltage; A capacitor is connected in series with the input side of at least one phase stator coil of the stator coil, and the capacitor has a capacitance forming a series resonance circuit with the stator coil to which it is connected.

  In the present invention, by forming a series resonance circuit by connecting a capacitor in series to the input side of the stator coil, the amplitude of the AC voltage applied to the stator coil is larger than that applied directly from the inverter circuit. The phase becomes larger than the phase of the AC voltage applied directly from the inverter circuit. This will be described with reference to FIGS.

  As shown in FIG. 2, consider a series LCR circuit in which a capacitor is connected in series with a stator coil. Let the impedance of the LCR circuit be Z and its power factor angle be θ. In the LCR circuit, when the impedance of the LR series unit as the stator unit is Zs and the power factor angle is φ, the following relationship is established.

ＬＣＲの印加電圧をｖ₁＝Ｖ₀ｓｉｎ ωｔ、ステータの印加電圧ｖ_s（振幅Ｖ_s、進み位相α）とすると、

共振条件

のとき、ｖｓの振幅Ｖｓは、

となる。

共振条件

のとき、

となり、位相が進む。

Assuming that the applied voltage of the LCR is v ₁ = V ₀ sin ωt, and the applied voltage v _{s of the} stator (amplitude V _s , leading phase α),

Resonance condition

When, the amplitude Vs of vs is

Becomes

Resonance condition

When,

And the phase advances.

  This is represented by a vector diagram as shown in FIG.

  Here, the term "constituting a series resonance circuit" includes not only a condition that strictly satisfies the resonance condition expressed by the above equation, but also includes a case where the resonance condition deviates somewhat. For example, even if the capacitance of the capacitor is set in advance so as to strictly satisfy the resonance condition, the difference between the rotational frequency of the rotor coil of the X-ray tube and the drive frequency of the AC voltage supplied to the stator coil from the inverter circuit is obtained. When the impedance (including the inductance) of the input circuit from the inverter circuit to the stator coil changes depending on the ratio (= slip), the resonance condition is not strict. The present invention includes such a case, and does not require a strict resonance condition. In short, "Constituting a series resonance circuit" means that the amplitude of the AC voltage applied to the stator coil becomes larger due to resonance than when no capacitor is connected by connecting a capacitor in series to the stator coil. Covers the case.

  The present invention is characterized in that a capacitor is connected in series to the input side of the stator coil to form a series resonance circuit. However, connecting a capacitor in series to the input side of the stator coil itself is a conventional two-phase anode rotation. This is also done in the mechanism.

  For example, in FIG. 13A of Patent Document 1, two outputs of a single-phase full-bridge inverter circuit 21 are supplied as Vmain to a main coil, Vcom to a common end of both coils, and Vsub to an auxiliary coil. At this time, a capacitor 50 is inserted in series with the auxiliary coil to shift the phase of Vsub by 90 ° from Vmain. However, as is apparent from the fact that the capacitor 50 is named “phase shift capacitor 50”, the capacitor 50 is inserted to shift the phase by 90 °, and a series resonance circuit is formed by the capacitor 50 and the auxiliary coil. Is not described or suggested.

  FIGS. 1 and 3 of Patent Document 2 also describe that a capacitor 3C is connected in series to an auxiliary coil of a stator coil of a two-phase anode rotating mechanism, but the capacitor 3C is provided for what purpose. Nothing is described as to whether or not it is done. Since the two-phase anode rotating mechanism has the same configuration as that of Patent Document 1, and the capacitor 3C is connected in series to the auxiliary coil of the stator coil, this capacitor 3C is also considered as a phase shift capacitor for shifting the phase by 90 °. Is equivalent. Patent Document 2 neither describes nor suggests that a series resonance circuit is formed by the capacitor 3C and the auxiliary coil.

  A rotary anode type X-ray tube apparatus according to the present invention includes an X-ray tube, an anode provided in the X-ray tube, and a target rotatably supported by a rotating shaft; A rotor attached to the rotating shaft, a cathode disposed in the X-ray tube so as to face the target, and irradiating the target with an electron beam, and the rotor disposed outside the X-ray tube. A rotating anode drive device for applying an AC voltage to the stator coil, and a rotating anode type X-ray tube device of the present invention as the rotating anode drive device. is there.

  The rotary anode driving device of the present invention is required to connect a capacitor in series to at least one phase stator coil and to use a series resonance phenomenon to flow a current from the inverter circuit to the impedance of the stator coil. A low-voltage DC power supply that can generate only an AC voltage smaller than the AC voltage can be used. As a result, the cost and size of the rotary anode driving device itself can be reduced.

FIG. 2 is a circuit diagram showing a first embodiment of the rotary anode driving device. It is a series LCR circuit diagram. It is a vector diagram which shows the change of the amplitude and phase by series resonance. It is a schematic structure figure showing an example of an X-ray tube device. (A), (B) is an example of a schematic diagram of a PWM voltage waveform applied to each of a main coil and an auxiliary coil from an inverter circuit without resonance. (A) and (B) are examples of schematic diagrams of PWM voltage waveforms respectively applied to a main coil and an auxiliary coil from an inverter circuit, and a resonance capacitor is connected only to the auxiliary coil. The Vx-z voltage waveform in (A) is the same as that in FIG. 6B, and the Vx-z 'in (B) is a voltage waveform when the peak of the voltage applied to the stator coil is reduced. FIG. 3 is a circuit diagram showing an embodiment in which a resonance capacitor having a different capacitance is connected to a main coil and an auxiliary coil in a two-phase X-ray tube. This is an embodiment in the case where the X-ray tube has three-phase stator coils.

  A stator coil connected in series with a capacitor can utilize series resonance in a state where the capacitor is connected in all operation modes such as high-speed operation, low-speed operation, and rotation maintaining. However, it may not be necessary to apply an AC voltage having an amplitude equal to or larger than the DC power supply voltage to the stator coil, for example, during a low-speed operation.

  In one embodiment, it is possible to select whether or not to connect a capacitor to the stator coil according to an operation mode, and a bypass circuit connected in parallel to the capacitor and an input side of the capacitor are provided. And a switching mechanism for selectively connecting the output of the inverter circuit to either the capacitor or the bypass circuit.

  When such a switching mechanism is provided, the switching operation according to the operation mode can be instructed from outside each time, or can be automatically instructed according to a predetermined program. Embodiments for performing such automation further include a control unit that controls the switching operation of the switching mechanism. The control unit selects the capacitor in an operation mode in which a voltage higher than the output voltage of the DC power supply is required, and selects the bypass circuit in an operation mode in which the voltage may be lower than the output voltage of the DC power supply. The switching operation of the switching mechanism is controlled.

  X-ray tubes targeted by the present invention include a two-phase type and a three-phase type. An example of the two-phase X-ray tube includes one having a two-phase stator coil including a first stator coil and a second stator coil having a larger number of turns than the first stator coil. In this case, since the second stator coil requires an AC voltage having a larger amplitude than the first stator coil, that is, a drive voltage having a larger amplitude, a capacitor for resonance is connected in series with at least the second stator coil. Connected.

  Specifically, an X-ray tube device having a two-phase stator coil has a main coil and an auxiliary coil having different impedances due to the number of turns of the stator coil. The auxiliary coil has more turns and an impedance than the main coil. The main coil corresponds to the first stator coil, and the auxiliary coil corresponds to the second stator coil. Also in this case, since the drive voltage supplied to the auxiliary coil is increased by resonance, an output voltage that satisfies the drive voltage necessary to supply a current for applying a rotational torque to the auxiliary coil as a DC power supply connected to the inverter circuit is used. Without a DC power supply, it is possible to use a DC power supply having an output voltage that can be increased to its drive voltage by resonance.

  In the two-phase X-ray tube of this example, a capacitor having a capacitance forming a series resonance circuit with the first stator coil is also connected in series to the input side of the first stator coil. The capacitor connected to the first stator coil may be configured to be connected to a capacitor having a larger capacitance than the capacitor connected to the first stator coil. In this case, even if there is no DC power supply having an output voltage that satisfies a drive voltage required to supply a current for applying a rotating torque to the first stator coil, an output that can be increased to the drive voltage by resonance is provided. A DC power supply having a voltage can be used, and a DC power supply having a lower voltage can be used.

  The X-ray tube targeted by the present invention is not necessarily limited to one provided with stator coils having different numbers of turns. That is, the present invention also covers a case where a stator coil is provided with two or three phases and all the stator coils have the same number of turns. In that case, the capacitors constituting the resonance circuit are connected to all the stator coils. In addition, a bypass circuit is provided in parallel with each capacitor, and a switching mechanism for selectively connecting the output of the inverter circuit to each of the capacitors or each of the bypass circuits is provided on the input side of each capacitor, so that a high-speed operation is provided. The capacitor may be selected to use the resonance phenomenon only when a drive voltage having such a large amplitude is required.

  When a capacitor constituting a resonance circuit is connected only to some phases of the stator coil, the phase of the current flowing through the stator coil that has caused resonance by connecting the capacitor is increased. Usually, in a two-phase X-ray tube, the current phase difference between the two-phase stator coils is set to 90 °, and in a three-phase X-ray tube, the current phase difference between the three-phase stator coils is set to 120 °. In each case, the rotational torque generated between the stator coil and the rotor is maximized. However, when the anode rotation speed changes, the phase difference between the current flowing through the stator coil connected to the capacitor and the current flowing through the stator coil not connected to the capacitor deviates from a preset current phase difference. The rotation torque is reduced. Therefore, it is preferable to adjust the PWM control of the inverter circuit so that the current phase difference between the stator coils is maintained at a predetermined phase difference. The predetermined phase difference is approximately 90 ° for a two-phase X-ray tube and approximately 120 ° for a three-phase X-ray tube.

  In the present invention, it is preferable to further include a phase difference adjusting unit configured to maintain a current phase difference between the stator coils at a predetermined phase difference.

  One example of such a phase difference adjustment unit is a current detection unit that detects a phase of a current flowing through each stator coil, a PWM waveform generation unit, and a phase detection unit that detects a phase of a current flowing through each stator coil detected by the current detection unit. And a waveform calculator for controlling an inverter circuit via a PWM waveform generator so as to suppress or eliminate a deviation of a phase difference between the stator coils from a predetermined phase difference.

According to the present invention, a resonance circuit is formed by connecting a capacitor to at least one phase stator coil, and a driving voltage applied to the stator coil is increased by a DC voltage of a DC power supply connected to an inverter circuit. Therefore, it is preferable to assume that a situation in which the increased drive voltage exceeds the withstand voltage of the stator coil may occur. In the embodiment for that purpose, the peak voltage of the driving voltage is suppressed by devising the PWM voltage waveform input to the stator coil connected to the capacitor, and the risk of dielectric breakdown of the stator coil is reduced. For example, for a stator coil having a capacitor connected in series, the PWM voltage output from the inverter circuit is not a sine wave (v = v ₀ sin (ωt)), but ωt is 0 to 90 ° and 180 ° to 270 °. Zero out part of the range. Thus, the peak voltage applied to the stator coil can be reduced in a time region in which the voltage applied to the stator coil is dominant by the voltage between the series capacitors.

  Specifically, in one embodiment, the average value of the PWM voltage (rectangular wave) for the AC voltage output from the inverter circuit to the stator coil connected to the capacitor is represented by a sine wave indicated by a broken line in FIG. When the polarity of the voltage between the capacitors is equal to or less than a predetermined ratio (for example, 5%) of the average value of the applied voltage indicated by, the duty ratio becomes zero in the region through the PWM waveform generator. And a waveform calculator for controlling the inverter circuit.

  FIG. 4 shows an embodiment of the X-ray tube apparatus to which the present invention is applied. Here, the two-phase type is shown, but the three-phase type is basically the same.

  In the X-ray tube 2, an anode 8 having an umbrella-shaped target 6 fixed to the tip of the rotating shaft 4 is arranged. The rotating shaft 4 has a base end rotatably supported by a support 10. A rotor 12 is attached to the rotating shaft 4 in the X-ray tube 2. Further, a cathode 14 is disposed in the X-ray tube 2 so as to face the umbrella-shaped portion of the target 6 and to irradiate the target 6 with an electron beam 16 to generate an X-ray 18.

  Stator coils 20A and 20B for generating a rotating magnetic field with respect to the rotor 12 are arranged outside the X-ray tube 2 in order to rotate the anode 8. A rotating anode driving device 22 is provided for applying an AC driving voltage for generating a rotating magnetic field to the stator coils 20A and 20B. The rotary anode driving device 22 will be described later in detail.

  In such an X-ray tube device, when a driving voltage is applied from the rotating anode driving device 22 to the stator coils 20A and 20B, a rotating magnetic field is generated, and the target 6 rotates via the rotor 12. The rotation of the target 6 increases the electron impact area of the target 6 and extends the life of the anode. In addition, the current of the electron beam 16 can be increased to increase the amount of X-rays generated.

  Several embodiments of the rotary anode driving device 22 will be described. The rotary anode driving device 22 can be basically configured independently of the X-ray tube, and can be applied to different types of X-ray tubes.

  FIG. 1 shows a first embodiment of the rotary anode driving device 22. Here, an example in which the present invention is applied to a two-phase X-ray tube will be described, but the application of the rotary anode driving device of the present invention is not limited to the two-phase X-ray tube. The three-phase method will be described later in another embodiment.

  A DC power supply 26 is connected in parallel to the inverter circuit 24. The inverter circuit 24 generates an AC voltage from the DC voltage of the DC power supply 26 to generate two-phase stator coils 30 and 32 that generate a rotating magnetic field of the X-ray tube 28. Output.

  The inverter circuit 24 is a three-phase full-bridge inverter circuit having six switching elements Qx1 to Qz2. In the inverter circuit 24, a series circuit of three sets of switching elements including (Qx1, Qx2), (Qy1, Qy2), and (Qz1, Qz2) is connected to the DC power supply 26 in parallel. The connection points between the switching elements of each set are the output terminals 38x, 38y, 38z. The output terminals 38x and 38y are connected between both ends of the stator coil 30, and the output terminals 38x and 38z are connected between both ends of the stator coil 32.

  The switching elements Qx1 to Qz2 are shown by connecting a diode 36 to an IGBT (insulated gate bipolar transistor) 34 in parallel. MOSFETs (field effect transistors) may be used as the switching elements Qx1 to Qz2. Since the MOSFET has a diode function, the diode 36 need not be separately provided. However, the switching elements Qx1 to Qz2 are not limited to these.

  Although the DC power supply 26 is not particularly limited, a boost chopper circuit is used in this embodiment. The DC voltage control unit 40 performs PWM control on the boost chopper circuit to increase the voltage to a predetermined voltage. The voltage of the DC power supply 26 is detected by a DC voltage detection unit 42. The DC voltage detection unit 42 may perform a detection method insulated using, for example, a photocoupler.

  One of the two-phase stator coils 30 and 32 is a main coil, and the other stator coil 32 is an auxiliary coil. The number of turns of the main coil 30 and the auxiliary coil 32 is larger in the auxiliary coil 32 than in the main coil 30. If the inductance of the main coil 30 is Lx-y, the resistance is Rx-y, the inductance of the auxiliary coil 32 is Lx-z, and the resistance is Rx-z, Lx-y <Lx-z, Rxy-Rx-z Becomes

  In this embodiment, since the impedance of the auxiliary coil 32 is larger than the impedance of the main coil 30, if the amplitude of the magnetic flux generated by the auxiliary coil 32 is made to be substantially the same as the magnetic flux generated by the main coil 30, An AC voltage higher than that of the main coil 30 needs to be applied to 32. To make the amplitude of the AC voltage larger than the DC voltage of the DC power supply 26, a capacitor 46 is connected in series to the input side of the auxiliary coil 32. The capacitor 46 has a capacitance that forms a series resonance circuit with the auxiliary coil 32.

  The magnitude of the capacitance is set in advance so as to form a series resonance circuit with the auxiliary coil 32 by calculation or experiment. However, the magnitude of the capacitance does not need to strictly satisfy the resonance condition, and the impedance of the input circuit from the inverter circuit to the auxiliary coil 32 changes due to slippage. What is necessary is just to maintain a situation in which the amplitude of the AC voltage applied to the auxiliary coil 32 is always larger by connecting the capacitor 46 in series than when the capacitor 46 is not connected.

  The capacitor 46 may be always connected to the auxiliary coil 32. However, in this embodiment, the configuration is such that whether or not the capacitor 46 is connected to the auxiliary coil 32 can be selected. Therefore, a bypass circuit 48 is connected in parallel with the capacitor 46, and a switching mechanism 50 for selectively connecting the output of the inverter circuit 24 to either the capacitor 46 or the bypass circuit 48 is arranged on the input side of the capacitor 46. . The switching mechanism 50 can be configured by a power relay or the like.

  A PWM waveform generator 44 is provided for performing PWM control on the switching elements Qx1 to Qz2 of the inverter circuit 24 and generating a two-phase AC voltage from the DC voltage of the DC power supply 26.

  A current detector 45 is provided in a circuit from the inverter circuit 24 to the stator coils 30 and 32 in order to detect a current amount and a current phase by an AC voltage applied to the stator coils 30 and 32 from the inverter circuit 24. As the current detector 45, for example, a current transformer connected in series to a circuit from the inverter circuit 24 to the stator coils 30 and 32 can be used.

  A condition storage unit 52 is provided for storing DC voltage information according to the X-ray tube to be selected, as well as waveform conditions according to the operation mode.

  A waveform calculation unit 54 is provided. The waveform calculation unit 54 reads the waveform condition according to at least one of the type and the operation mode of the X-ray tube from the condition storage unit 52, and reads the information of the current amount and the current phase detected by the current detection unit 45, and selects the information. A voltage waveform (voltage amplitude and phase difference of each phase) output from the PWM waveform generation unit 44 to the inverter circuit 24 is calculated according to the type and operation mode of the X-ray tube to be performed.

  An X-ray high voltage generator 56 is connected to input a signal indicating the type of X-ray tube to be selected and the operation mode.

  A signal for controlling whether to connect the capacitor 46 to the auxiliary coil 32 via the switching element 50 according to the type of X-ray tube to be selected and the operation mode input from the X-ray high voltage generator 56 is issued. For this purpose, a main control unit 58 is provided. The main control unit 58 also inputs information on the type of X-ray tube to be selected or a signal indicating an operation mode to the waveform calculation unit 54, reads DC voltage information corresponding to the selected X-ray tube from the condition storage unit 52, Output to DC voltage control unit 40.

  The DC voltage control unit 40, the PWM waveform generation unit 44, the condition storage unit 52, the waveform calculation unit 54, and the main control unit 58 are realized by a dedicated computer, a general-purpose personal computer, or a CPU and a memory device. The generator 56 is realized by the computer or CPU and the input device.

  In the rotary anode driving device having such a configuration, when a signal representing the type and operation mode of the selected X-ray tube is input from the X-ray high voltage generator 56 to the main control unit 58, the main control unit 58 selects. A switching signal is output to the switching element 50 as to whether or not the capacitor 46 is connected to the auxiliary coil 32 in accordance with the type and operation mode of the X-ray tube, and the type and operation mode signal of the selected X-ray tube are output. The signal is output to the waveform calculator 54. Further, the main control unit 58 reads DC voltage information corresponding to the type of the selected X-ray tube from the condition storage unit 52 and outputs the DC voltage information to the DC voltage control unit 40. The waveform calculation unit 54 reads the waveform condition corresponding to the type of the X-ray tube and the operation mode signal from the condition storage unit 52, and, together with the information of the DC voltage, the current amount and the current phase detected by the current detection unit 45, the PWM waveform generation unit The voltage waveform conditions (voltage amplitude and phase difference of each phase) to be output to 44 are calculated. The PWM waveform generator 44 converts the voltage waveform condition input from the waveform calculator 54 into a PWM waveform, and outputs the PWM waveform to the inverter circuit 24.

  Subsequently, the voltage applied to the main coil 30 and the auxiliary 32 will be described with reference to FIGS.

  FIGS. 5A and 5B show that the switching circuit 50 is connected to the bypass circuit 48 side, and when the capacitor 46 is not connected, the inverter circuit 24 is PWM-controlled so that the main coil 30 and the auxiliary coil 32 is an example of a PWM voltage waveform applied to each of 32. The PWM voltage waveform becomes an AC voltage waveform when averaged over time.

  Vx-y is the voltage applied to the main coil 30, Vx-z is the voltage applied to the auxiliary coil 32, Vc is the DC voltage of the bus of the inverter circuit 24, that is, the output voltage of the DC power supply 26, Tc is the PWM carrier frequency period, Tdv is the phase difference between the PWM voltages, and Ti is the period of the PWM voltage signal output from the inverter circuit 24.

  In the range of the phase difference Tdv, it is necessary to apply a negative voltage to Vxy and a positive voltage to Vxz. At this time, the operation of the switching elements Qx1 to Qz2 of the inverter circuit 24 in FIG. 1 will be considered.

To apply a negative voltage to Vx-y Qx1: OFF; Qx2: ON
Qy1: ON; Qy2: OFF
Becomes On the other hand, to apply a positive voltage to Vx-z Qx1: ON; Qx2: OFF
Qz1: OFF; Qz2: ON
Becomes

  That is, both a period during which the X phase of the inverter circuit 24 is turned on and a period during which the X phase of the inverter circuit 24 is turned off are required during the PWM carrier frequency period Tc. The combination of the average voltage condition and the phase difference is not output, which limits the input voltage.

  On the other hand, a PWM voltage waveform when the capacitor 46 is connected will be described with reference to FIG. FIGS. 6A and 6B show that when the switching element 50 is connected to the capacitor 46 side and the capacitor 46 is connected to the auxiliary coil 32, the inverter circuit 24 is PWM-controlled, and the inverter circuit 24 It is an example of a PWM voltage waveform applied to each of the auxiliary coils 32. No capacitor is connected to the main coil 30. The switching mechanism 50 is connected to the capacitor 46 at the time of starting rotation or in the high-speed rotation mode, and when a voltage higher than that of the main coil 30 needs to be applied to the auxiliary coil 32.

  In order to apply a voltage higher than that of the main coil 30 to the auxiliary coil 32, the duty ratio of the PWM voltage waveform needs to be higher than that of the auxiliary coil.

  The output from the inverter circuit 24 is directly applied to the main coil 30, and the output from the inverter circuit 24 is applied to the auxiliary coil 32 through a capacitor 46. The voltages applied to the main coil 30 and the auxiliary coil 32 are Vxy and Vxz, respectively. The solid line represents the actual voltage under PWM control, and the dashed line represents the average. Further, it is assumed that the voltage output from the inverter circuit 24 is a sine wave when the average value of each period of the carrier frequency Tc is taken.

  As indicated by the solid line, Vx-z has a waveform in which a PWM waveform is superimposed on a sine wave which is a voltage between capacitors. Due to the resonance, the voltage amplitude becomes larger than that applied directly from the inverter circuit 24. The phase is advanced from the phase of the PWM voltage. That is, the phase difference between the PWM voltages Vx-y and Vx-z becomes smaller, and the upper limit of the output voltage becomes larger.

  Due to the change in the anode rotation speed, the phase difference between the current flowing through the stator coil to which the capacitor is connected and the current flowing through the stator coil to which the capacitor is not connected deviates from a preset current phase difference. The inverter circuit 24 can be subjected to PWM control so that the current phase difference between the stator coils is maintained at a predetermined phase difference so that the rotation torque does not decrease. Thereby, the rotation torque can be maintained.

  As another embodiment, a phase difference adjustment for suppressing or eliminating a deviation of a phase difference between the stator coils from a predetermined phase difference (90 ° for two phases, 120 ° for three phases) by feedback control. A part can be provided. The phase difference adjustment unit is configured by the current detection unit 45, the PWM waveform generation unit 44, and the waveform calculation unit 54 in FIG. The current detector 45 detects the phase of the current flowing through the auxiliary coil 32 to which the main coil 30 and the capacitor 46 are connected. The waveform calculator 54 detects the phase of the current flowing through the main coil 30 and the auxiliary coil 32 detected by the current detector 45. Based on the phase, the inverter circuit 24 is feedback-controlled via the PWM waveform generator 44 so as to maintain the phase difference between the main coil 30 and the auxiliary coil 32 at a predetermined phase difference, that is, approximately 90 °. Here, the phase difference of approximately 90 ° includes a phase difference that is not exactly 90 ° but does not lead to a decrease in the anode rotation speed.

  Further, the voltage waveform when the voltage applied to the stator coil is reduced without significantly deteriorating the PWM voltage without significantly deteriorating the performance is shown as Vx-z 'in FIG. 7B. The Vx-z voltage waveform in FIG. 7A is the same as that in FIG. This is a case where a pulse of a small width that does not contribute much to the PWM voltage is not output in a time region in which the pulse voltage of the capacitor voltage and the pulse voltage of the PWM voltage are applied with the same positive or negative polarity. As a result, the peak value Vp of the voltage applied to the stator coil becomes smaller as Vp '. Further, the average voltage waveform shown by the broken line is not significantly affected.

  Specifically, for example, in FIG. 1, with respect to the AC voltage output from the inverter circuit 24 to the auxiliary coil 32 to which the capacitor 46 is connected, the average value of the PWM voltage (rectangular wave) is indicated by a sine wave. When the polarity is the same as the voltage between the capacitors 46 in a region of 5% or less of the voltage average value, the waveform calculation unit 54 operates the inverter circuit 24 via the PWM waveform generation unit 44 so that the duty ratio becomes zero in that region. Can be realized by controlling

  FIG. 8 shows a two-phase X-ray tube taken up in FIG. 1, in which an input side of the main coil 30 is also connected in series with a capacitor C1 having a capacitance forming a series resonance circuit with the main coil 30. In this embodiment, the capacitor (C2 + C2) connected to the auxiliary coil 32 has a capacitance different from that of the capacitor C1 connected to the auxiliary coil 32.

  In this embodiment, it is possible to select whether to connect a capacitor to the main coil 30 by a bypass circuit and a switching mechanism or to connect a single capacitor. Two capacitors are connected in series to the auxiliary coil 32. Depending on the bypass circuit and the switching mechanism of each capacitor, no capacitor is connected, only one capacitor is connected, or two capacitors are connected. Can be connected in series. The capacitances of the capacitors C1 and C2 may be the same or different, but the capacitance of (C2 + C2) is larger than the capacitance of C1.

  Also in this embodiment, the DC voltage control unit 40, DC voltage detection unit 42, current detection unit 45, PWM waveform generation unit 44, condition storage unit 52, waveform calculation unit 54, X-ray high voltage generation shown in FIG. Although a unit 56 and a main control unit 58 are provided, illustration is omitted.

  As still another embodiment, the X-ray tube 28 includes two-phase or three-phase stator coils, all of the stator coils have the same number of turns, and the input side of all of the stator coils is connected to the respective stator coils. In the figure, capacitors connected to form a resonance circuit are connected. FIG. 9 shows an embodiment in which the X-ray tube 28 has three-phase stator coils. The same applies to a case in which two-phase stator coils are provided.

  Here, the number of turns of the three-phase stator coils 60-1, 60-2, and 60-3 is equal to each other. The capacitors 62-1, 62-2, and 62-3 constituting the resonance circuit also have the same capacitance C for all the stator coils 60-1, 60-2, and 60-3. Bypass circuits 64-1, 64-2, and 64-3 are provided in parallel with the capacitors 62-1, 62-2, and 62-3, and are provided on the input sides of the capacitors 62-1, 62-2, and 62-3. A switching mechanism 66-1, which selectively connects the output of the inverter circuit 24 to each of the capacitors 62-1, 62-2, 62-3 or each of the bypass circuits 64-1, 64-2, 64-3; 66-2 and 66-3 are provided. Also in this embodiment, the DC voltage control unit 40, the DC voltage detection unit 42, the PWM waveform generation unit 44, the condition storage unit 52, the waveform calculation unit 54, the X-ray high voltage generation unit 56, and the main control shown in FIG. A portion 58 is provided, but is not shown.

The capacitors 62-1, 62-2, and 62-3 may be selected to utilize the resonance phenomenon only when a high-amplitude drive voltage is required, such as during high-speed operation.
In this embodiment, the bypass circuits 64-1, 64-2, 64-3 and the switching mechanisms 66-1, 66-2, 66-3 can be omitted. In this case, the capacitor is connected in all operation modes such as high-speed operation, low-speed operation, rotation maintenance, and braking. Even in such an embodiment, it is possible to use a DC power supply having a DC voltage lower than a power supply voltage required to supply a drive voltage having an amplitude required at the time of starting the stator coil or operating at a high speed. it can.

  In this embodiment, since the amount of phase advance generated in all the stator coils 60-1, 60-2, 60-3 is equal, the phase difference between the stator coils 60-1, 60-2, 60-3 is reduced. There is no need for adjustment, and the current detector 45 shown in FIG. 1 is not always necessary.

Reference Signs List 24 Inverter circuit 26 DC power supply 28 X-ray tube 30, 32, 60-1, 60-2, 60-3 Stator coil 40 DC voltage control unit 42 DC voltage detection unit 46, 62-1, 62-2, 62-3 Capacitors 48, 64-1, 64-2, 64-3 Bypass circuit 50, 66-1, 66-2, 66-3 Switching mechanism for resonance circuit 52 Condition storage unit 45 Current detection unit 54 Waveform calculation unit 56 X-ray High voltage generator Qx1-Qz2 Switching element of inverter circuit

Claims (11)

A rotating anode driving device for driving the rotating anode X-ray tube by applying an AC voltage to a stator coil that generates a rotating magnetic field of the rotating anode X-ray tube,
DC power supply,
Connected to the DC power supply comprises a plurality of switching elements, and an inverter circuit for outputting to said stator coil to generate an AC voltage from the DC voltage of the DC power supply,
A PWM waveform generator that performs PWM control on the switching element of the inverter circuit and generates a two-phase or three-phase AC voltage from the DC voltage as the AC voltage;
A capacitor connected in series to an input side of at least one phase stator coil of the stator coil, the capacitor having a capacitance forming a series resonance circuit with the stator coil to which the capacitor is connected. And a rotary anode drive device comprising:   An output of the DC power supply is smaller than a maximum value of an AC voltage necessary to drive the rotary anode type X-ray tube, and an AC voltage applied to the stator coil due to a resonance phenomenon between the stator coil and the capacitor. 2. The rotating anode drive according to claim 1, wherein the rotating anode driving device is configured to reach the maximum value. A bypass circuit connected in parallel to the capacitor;
A switching mechanism disposed on the input side of the capacitor, for selectively connecting the output of the inverter circuit to either the capacitor or the bypass circuit;
The rotary anode driving device according to claim 1, further comprising: The type of the rotary anode type X-ray tube or the operation mode in which a voltage higher than the output voltage of the DC power source is required, the capacitor is selected, and the voltage of the rotary anode type may be lower than the output voltage of the DC power source. 4. The rotary anode driving device according to claim 3 , further comprising a control unit that controls a switching operation of the switching mechanism so as to select the bypass circuit when the type of the X-ray tube, the operation mode, or the activation mode is selected. The rotary anode type X-ray tube includes a two-phase stator coil including a first stator coil and a second stator coil having a larger number of turns than the first stator coil,
The capacitor rotating anode drive apparatus as claimed in claim 1 which is adapted to be connected to at least the second stator coil in any one of four. A capacitor having a capacitance constituting a series resonance circuit with the first stator coil is also connected in series to an input side of the first stator coil,
The rotating anode according to claim 5 , wherein the capacitor connected to the second stator coil is configured to be connected to a capacitor having a larger capacitance than a capacitor connected to the first stator coil. Drive. The rotary anode type X-ray tube includes a two-phase or three-phase stator coil, and all stator coils have the same number of turns.
The rotary anode driving device according to any one of claims 1 to 4 , wherein the capacitor is configured to be connected to all the stator coils. For the current flowing through the stator coil in which the capacitor is connected, any one of claims 1 to 7, further comprising a phase difference adjusting section configured to adjust the phase difference to a predetermined phase difference between the stator coils The rotating anode drive device according to claim 1. The phase difference adjustment unit, a current detection unit that detects the phase of the current flowing through each stator coil,
The PWM waveform generator;
The inverter through the PWM waveform generator so as to suppress or eliminate a deviation of a phase difference between the stator coils from a predetermined phase difference based on a phase of a current flowing through each stator coil detected by the current detector. A waveform calculation unit for controlling the circuit,
The rotating anode driving device according to claim 8 , further comprising: A region where the average value of the PWM voltage (rectangular wave) of the AC voltage output from the inverter circuit to the stator coil connected to the capacitor is equal to or less than a predetermined ratio of the average value of the applied voltage indicated by the sine wave. 2. The apparatus according to claim 1, further comprising a waveform calculation unit that controls the inverter circuit via the PWM waveform generation unit so that a duty ratio becomes zero in the region when the polarity is the same as the voltage between the capacitors. 10. The rotary anode driving device according to any one of claims 9 to 9 . An X-ray tube,
An anode wherein arranged in the X-ray tube bulb, comprising a target which is rotatably supported together with the rotating shaft is mounted on the rotary shaft,
A rotor coil attached to the rotating shaft in the X-ray tube;
A cathode disposed in the X-ray tube so as to face the target, and irradiating the target with an electron beam;
A stator coil that is arranged outside the X-ray tube and generates a rotating magnetic field with respect to the rotor coil;
Rotating anode X-ray tube apparatus provided with a rotating anode drive apparatus according to any one of claims 1 to 10 for applying an AC voltage to the stator coil.

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