JP2018068003A - Power supply for laser, switching converter - Google Patents

Abstract

A laser power source capable of stabilizing output energy with high accuracy is provided. A high-frequency power source has an input connected to a bank capacitor and intermittently supplies an alternating voltage to a laser light source. The charging circuit 102 includes a first switching converter 120 that charges the bank capacitor 104 during an idle period of the high-frequency power source. The controller 124 acquires the inductance of the reactor L1 based on the temperature of the reactor L1 detected by the temperature sensor 122, and calculates the ON time of the switching transistor M1 using the inductance. [Selection] Figure 5

Description

  The present invention relates to a switching converter.

Laser processing apparatuses are widely used as industrial processing tools. FIG. 1 is a block diagram of the laser processing apparatus 1r. The laser processing apparatus 1r includes a laser light source 2 such as a CO ₂ laser, and a laser power source 4r that supplies AC power to the laser light source 2 and excites it. The laser power source 4 r includes a DC power source 6 and a high frequency power source 8. The DC power supply 6 stabilizes the output DC voltage _VDC at a target value by feedback control using PID (Proportional-Integral-Differential) control or PI control. The high frequency power supply 8 receives the direct current voltage _VDC , converts it into an alternating voltage, and supplies it to the laser light source 2 that is a load.

In the laser processing apparatus 1r for drilling, the laser light source 2 operates discontinuously. That is, a relatively short light emission period of several microseconds to 10 microseconds and a pause period that is the same, short, or long are alternately repeated. In order to stabilize the output energy of the laser light source 2, the DC voltage _VDC must be within a predetermined allowable fluctuation range.

  FIG. 2 is an operation waveform diagram of the laser processing apparatus 1r of FIG. The vertical and horizontal axes of the waveform diagrams and time charts referred to in this specification are enlarged or reduced as appropriate for easy understanding, and each waveform shown is also simplified for easy understanding. Or exaggerated or emphasized.

The high frequency power supply 8 repeats an operation period and a rest period in accordance with the turning on and off of the laser light source 2. When the high-frequency power supply 8 shifts from the rest period to the operation period, a feedback response delay occurs in the direct-current power supply 6, and the direct-current voltage _VDC may decrease and deviate from the allowable variation range. When the operation period of the high-frequency power supply 8 shifts from the operation period to the idle period, the direct-current voltage _VDC increases due to a feedback delay, and may deviate from the allowable variation range.

In addition, when switching to a different processing, the target value of the DC voltage _VDC may be switched. Again, if the response speed of the DC power supply 6 is slow, the transition time until the DC voltage _VDC reaches the next target value becomes long. Since the laser light source 2 cannot emit light during the period in which the DC voltage _VDC deviates from the allowable voltage range, it causes a reduction in operating rate (repetition frequency).

When the allowable voltage range is widened, the output energy of the laser varies widely from shot to shot, and when the allowable voltage range is narrowed, the operating rate decreases. In order to achieve both uniform output energy and high repetition frequency, the laser power source 1r is required to bring the DC voltage _VDC close to the target voltage in a short time.

Japanese Patent Laid-Open No. 2006-59932

As a result of studying a laser power source, the present inventors have recognized the following problems. A switching converter is used for the laser power source. The switching converter includes a switching element, a reactor, and the like. Since a large current flows through the reactor, the temperature rises. When the reactor generates heat, its inductance value changes. When the controller of the switching converter uses the inductance value of the reactor for the control calculation of the switching element, the fluctuation of the inductance value causes the fluctuation of the DC voltage _VDC .

  Laser drilling machines for drills are required to increase in speed year by year, and both processing speed and processing accuracy are required. Improvements that contribute to this are also required for laser power supplies.

  SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and one of exemplary purposes of an embodiment thereof is to provide a laser power source that can stabilize output energy with high accuracy even at a high repetition frequency.

  One embodiment of the present invention relates to a laser power source. The laser power supply includes a bank capacitor, a high-frequency power source whose input is connected to the bank capacitor, and intermittently supplies an alternating voltage to the laser light source, and a charge that includes a first switching converter that charges the bank capacitor during a high-frequency power supply idle period. A circuit. The first switching converter acquires a reactor inductance based on a reactor, a switching transistor, a temperature sensor that measures the temperature of the reactor, and a reactor temperature detected by the temperature sensor, and uses the inductance to switch the switching transistor. And a controller for calculating the on-time of.

  The inductance of the reactor depends on the magnetic permeability of the core (iron core), and the magnetic permeability of the core varies depending on the temperature. Therefore, if the inductance of the reactor is constant in the controller and the on-time of the switching transistor is calculated, when the inductance fluctuates, the error in the charging current supplied from the reactor to the bank capacitor increases by one switching of the switching transistor. End up. Therefore, by monitoring the temperature of the reactor and reflecting it in the calculation of the on-time, it becomes possible to control the charging current to the bank capacitor with high accuracy, and as a result, the output energy of the laser can be stabilized with high accuracy.

The controller may calculate the on-time of the switching transistor based on the difference between the detected value of the voltage of the bank capacitor and the target voltage.
When the difference between the detected value of the bank capacitor voltage and the target voltage is ΔV, the charge amount Q to be supplied to the bank capacitor can be calculated by Q = C × ΔV. Therefore, the on-time of the switching transistor may be calculated so that the charge amount Q is supplied to the bank capacitor.

  The temperature sensor may be configured to measure the temperature of the core of the reactor. The temperature sensor may be attached to the surface of the core or embedded in the core.

The charging circuit may further include a second switching converter that charges the bank capacitor with high accuracy after the rough charging operation of the bank capacitor by the first switching converter. The second switching converter acquires a reactor inductance based on a reactor, a switching transistor, a temperature sensor that measures the temperature of the reactor, and a reactor temperature detected by the temperature sensor, and uses the inductance to switch the switching transistor. And a controller for calculating the on-time of the.
By making the inductance of the reactor of the second switching converter smaller than the inductance of the reactor of the first switching converter, the amount of charge per switching by the second switching converter can be reduced, and highly accurate charging is possible. .

  The second switching converter may be a synchronous rectification type (buck-boost type) capable of charging and discharging the bank capacitor. As a result, when the bank capacitor is overcharged and the voltage of the bank capacitor exceeds the target voltage, the voltage can be lowered to approach the target voltage.

  Note that any combination of the above-described constituent elements and the constituent elements and expressions of the present invention replaced with each other among methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, the output energy of a laser can be stabilized regardless of temperature fluctuations even at a high repetition frequency.

It is a block diagram of a laser processing apparatus. It is an operation | movement waveform diagram of the laser processing apparatus of FIG. It is a block diagram of the laser processing apparatus which concerns on embodiment. It is an operation | movement waveform diagram of the laser processing apparatus of FIG. FIG. 5 is a block diagram of a laser power supply charging circuit according to the embodiment. It is a perspective view which shows a reactor. It is a figure which shows an example of the temperature dependence of an inductance. It is an operation | movement waveform diagram of a 1st switching converter. It is a circuit diagram of the charging circuit which concerns on a modification. FIG. 10 is an operation waveform diagram of the charging power supply of FIG. 9.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

FIG. 3 is a block diagram of the laser processing apparatus 1 according to the embodiment. The laser processing apparatus 1 includes a laser light source 2 and a laser power source 100. The laser light source 2 is, for example, a CO ₂ laser. The laser power source 100 supplies AC power to the laser light source 2 to excite it.

The laser power source 100 includes a charging circuit 102, a bank capacitor 104, and a high frequency power source 106. The high frequency power supply 106 has an input 108 connected to the bank capacitor 104 and an output connected to the laser light source 2. The high-frequency power source 106 receives the DC voltage _VDC generated in the bank capacitor 104 and intermittently supplies an alternating voltage (drive voltage) V _DRV to the laser light source 2. That is, the high frequency power supply 106 performs a switching operation during the light emission period of the laser light source 2, and the switching of the high frequency power supply 106 is stopped during the light extinction period of the laser light source 2. A period during which the high-frequency power source 106 is switched is referred to as an operation period, and a period during which the switching is stopped is referred to as a pause period. The configuration of the high-frequency power source 106 is not particularly limited, and a known technique may be used.

The bank capacitor 104 can be grasped as a direct current power source such as an electric storage device that supplies power to the high frequency power source 106 by itself. The charging circuit 102 charges the bank capacitor 104 to the target voltage V _REF during the pause period of the high-frequency power source 106. During the operation period of the high-frequency power source 106, the charging of the bank capacitor 104 is stopped, so that the voltage _VDC of the bank capacitor 104 decreases due to discharge by the high-frequency power source 106. Therefore, the capacity of the bank capacitor 104 is designed so that the direct-current voltage V _DC does not fall below the lower limit of the allowable range even in the discharge process by the high-frequency power source 106.

The above is the overall configuration of the laser processing apparatus 1. Next, the operation will be described. FIG. 4 is an operation waveform diagram of the laser processing apparatus 1 of FIG. The high frequency power supply 106 operates intermittently at a repetition frequency of about 5 kHz and a duty ratio of about 5%. During the operation period of the high frequency power source 106, the bank capacitor 104 behaves as a power source for supplying power to the high frequency power source 106. During this time, the charging power supply 102 is stopped, and the DC voltage _VDC of the bank capacitor 104 is lowered by discharging. However, since the capacity of the bank capacitor 104 is sufficiently large, the direct voltage _VDC does not fall below the lower limit of the allowable voltage range.

When the operation of the high-frequency power supply 106 is stopped and the suspension period starts, the charging of the bank capacitor 104 by the charging power supply 102 starts, and the bank capacitor 104 is charged to the target voltage _VREF . The laser processing apparatus 1 repeats this operation.

  Next, the configuration of the laser power source 100 will be described. FIG. 5 is a block diagram of the charging circuit 102 of the laser power source 100 according to the embodiment.

The charging circuit 102 includes a rectifying / smoothing circuit 110 and a first switching converter 120. Rectifier smoothing circuit 110 receives a commercial AC voltage _{V AC,} rectifies it, and smoothed to produce a DC voltage _{V IN.} For example the commercial AC voltage _{V AC} is a three-phase 200V, DC voltage _{V IN} is 280 V. As shown in FIG. 4, the rectifying / smoothing circuit 110 may be a combination of the rectifying circuit 112 and the smoothing capacitor 114. Alternatively, the rectifying / smoothing circuit 110 may be an AC / DC converter. The commercial AC voltage V _AC may be a single phase.

The target voltage V _REF of the voltage V _DC of the bank capacitor 104 is, for example, 500V. The first switching converter 120 receives the DC voltage _VIN and supplies a charging current I _CHG1 to the bank capacitor 104. The first switching converter 120 is a diode rectification type boost converter including a reactor L ₁ , a switching transistor M ₁ , and a rectifier diode D ₁ . The charging current I _CHG1 generated by the first switching converter 120 flows only in the direction in which the bank capacitor 104 is charged.

Temperature sensor 122 measures the temperature of the reactor _{L 1.} Temperature sensor 122 is a thermocouple or a thermistor, a posistor or the like, for generating an electrical signals S ₁ corresponding to the measured temperature. This electrical signal S ₁ is input to the controller 124.

FIG. 6 is a perspective view showing the reactor. Here shows the annular solenoid as a reactor L _1. The inductance L is expressed by the following equation using the magnetic permeability μ of the core (iron core), the number N of coil windings, the radius r of the coil winding, and the radius R of the annular core, and is proportional to the magnetic permeability μ of the core. .
L = μN ² r ² / (2R) (1)
Note that an air gap exists inside the core 200, and the magnetic permeability μ ₀ of the air gap also affects the inductance L. However, since the thickness of the air gap is sufficiently smaller than the thickness of the core, the equation (1) Omitted.

The magnetic permeability μ of the core has temperature dependence and can be expressed as a function f (T) of temperature.
μ = f (T) (2)
Substituting equation (2) into equation (1) yields equation (3).
L = f (T) · N ² r ² / (2R) (3)
Since N ² r ² / (2R) is a constant A,
L = A · f (T) (4)
It becomes. FIG. 7 is a diagram illustrating an example of temperature dependence of inductance.

As described above, the actual inductance includes terms of the core permeability μ and the air gap permeability μ ₀ , but the air gap term is sufficiently smaller than the core term, and the air permeability μ _0. The temperature dependency of can be regarded as substantially zero. Further, the heat of the coil winding 202 that is a heating element is transmitted to the core 200 through the air gap 204. Therefore, the temperatures of the coil winding 202 and the core 200 do not necessarily match. If the temperature sensor 122 is attached to the coil winding 202, the temperature of the core 200 cannot be accurately measured.

  For these reasons, the temperature sensor 122 is configured to directly measure the temperature T of the core of the reactor L. For example, the temperature sensor 122 may be directly attached to the surface of the core, or may be embedded in the core. Thereby, the temperature fluctuation of the inductance L can be detected accurately.

Returning to FIG. The controller 124 acquires the inductance L of the reactor L ₁ based on the temperature T of the reactor L ₁ detected by the temperature sensor 122. For example, a function f (T) representing the relationship between the magnetic permeability μ and the temperature T measured in advance may be stored in the controller 124. Then, the controller 124 may calculate the inductance L according to the equation (4). Of course, when the controller 124 calculates the inductance L, the air gap term may be taken into account.

  Alternatively, the controller 124 may store the relationship between the temperature T and the magnetic permeability μ as a lookup table, obtain the magnetic permeability μ by referring to the table, and calculate the inductance L. Alternatively, the relationship between the temperature T and the inductance L may be held as a lookup table.

The controller 124 calculates the _ON time T _ON of the switching transistor M ₁ using the inductance L acquired in this way. The controller 124 can calculate the _ON time T _ON of the switching transistor M ₁ based on the difference ΔV between the detected value V _DET of the voltage V _DC of the bank capacitor 104 and the target voltage V _REF . More specifically, the charge amount Q to be supplied to the bank capacitor 104 is calculated based on the difference ΔV between the detected value V _DET of the voltage _VDC of the bank capacitor 104 and the target voltage V _REF so that the charge amount Q can be obtained. the on-time _{T oN} the switching transistor _{M 1} may be calculated on.

The detection value V _DET is preferably measured in a state where the operation of the high-frequency power source 106 is stopped and the current I _OUT flowing from the bank capacitor 104 to the high-frequency power source 106 becomes zero. Therefore, the controller 124 may monitor the current I _OUT from the bank capacitor 104 and measure the voltage V _DC of the bank capacitor 104 after the current I _OUT becomes zero.

_{Assume that} the difference between the measured value V _DET of the voltage V _DC of the bank capacitor 104 and the target voltage V _REF is ΔV. At this time, the charge amount Q that the first switching converter 120 should supply to the bank capacitor 104 is:
Q = C × ΔV = C × (V _REF −V _DET )
It is. C is the capacity of the bank capacitor 104.

The first switching converter 120 supplies this charge Q to the bank capacitor 104 by one switching of the switching transistor M ₁ .

FIG. 8 is an operation waveform diagram of the first switching converter 120. During the laser emission period, the output current I _OUT is supplied from the bank capacitor 104 to the high frequency power source 106. During this time, the laser power source 100 is in a rest state, the bank capacitor 104 is discharged by the output current I _OUT , and the voltage V _DC decreases. When the output current I _OUT eventually becomes zero, the voltage V _DC becomes stable. The detected value V _DET of the stabilized voltage V _DC is taken into the controller 124.

Then, the controller 124 calculates the _ON time T _ON of the switching transistor M ₁ based on the difference between the detection value V _DET and the target value V _REF .

In the on-period _{T ON} switching transistors _{M 1,} to one end of the reactor _{L 1} input voltage _{V IN} is, the other end a ground voltage (0V) is applied. Therefore, when the switching transistor M ₁ is turned on, the current I _L flowing through the reactor L ₁ increases from zero with a slope V _IN / L. The amount of current I _L at the end of the on period T _ON (peak value) is given by the following equation.
I _PEAK = V _IN / L × T _ON
Reactor current I _L during the ON period of the switching transistor M ₁ is not supplied to the bank capacitor 104.

Following the switching transistor M ₁ and is turned off. When the switching transistor _{M 1} is turned off, the end of a reactor _{L 1} input voltage _{V IN} is, _V DC + _{V F} is applied to the other end. V _F is the forward voltage of the rectifier diode D ₁ . In the off period _{T CHG} switching _{M 1,} the reactor current _{I L} is the peak value _{I PEAK} as an initial value, decreases with a slope _{(V IN -V DC -V F)} / L.
I _L = I _PEAK −∫ (V _DC + V _F −V _IN ) / Ldt
When V _F << V _DC and V _F << V _IN , the reactor current I _L is I _L = I _PEAK −∫ (V _DC −V _IN ) / Ldt
It becomes. Reactor current _{I L} which hatched, the charging current _{I CHG} to the bank capacitor 104. The charge amount Q supplied to the bank capacitor 104 corresponds to a hatched area.
Q = ∫ {I _PEAK −∫ (V _DC −V _IN ) / Ldt} dt
= ∫ {V _IN / L × T _ON −∫ (V _DC −V _IN ) / Ldt} dt

Therefore,
C × (V _REF −V _DET ) = ∫ {V _IN / L × T _ON −∫ (V _DC −V _IN ) / Ldt} dt
To meet, it can be seen that may be calculated on-time T _ON.

When the fluctuation of the input voltage _VIN is large, it is desirable to detect the voltage level together with the DC voltage V _DC . On the other hand, when the input voltage _VIN is stabilized to a predetermined voltage level with high accuracy, a specified value can be used instead of the detected value.

The above is the operation of the first switching converter 120. According to the first switching converter 120, taking into account the temperature variation of the inductance L of the reactor L _1, the on-time T _ON can be accurately calculated. Thereby, even if temperature fluctuation occurs, the voltage V _DC of the bank capacitor 104 can be brought close to the target voltage V _REF by switching once. Thereby, shot defects can be reduced. Further, since the charging time is shortened, it is possible to suppress a decrease in the repetition frequency of laser light emission, and a high repetition rate can be realized.

  FIG. 9 is a circuit diagram of a charging circuit 102A according to a modification. The charging circuit 102 includes a second switching converter 140 in addition to the first switching converter 120. The second switching converter 140 charges the bank capacitor 104 with high accuracy after the first switching converter 120 performs a rough charging operation of the bank capacitor 104.

The second switching converter 140 is a synchronous rectification boost converter including a reactor L ₂ , a switching transistor M ₂ , and a synchronous rectification transistor M ₃ . Similar to the first switching converter 120, the second switching converter 140 is provided with a temperature sensor 142 that measures the temperature of the reactor L ₂ . The controller 144, based on the temperature of the reactor L ₂ in which the temperature sensor 142 has detected, obtains the inductance of the reactor L _2, by utilizing the inductance switching transistor M ₂ on-time T _ON and the off time (synchronous rectification transistor M ₃ of on-time to calculate the _{T oN).}

The charging current I _CHG2 generated by the second switching converter 140 can flow not only in the direction of charging the bank capacitor 104 but also in the direction of discharging it. As a result of charging by the first switching converter 120, when the voltage V _DC is insufficient to the target value V _REF , the second switching converter 140 can finely adjust the voltage _DC to increase. When the voltage V _DC exceeds the target value V _REF as a result of charging by the above, the second switching converter 140 can finely adjust the voltage _DC to decrease.

Here, the first switching converter 120 needs to rapidly charge the bank capacitor 104 and is required to supply as much current I _CHG1 as possible to the bank capacitor 104 in one switching operation. Therefore the inductance L of the reactor L ₁ is greater value is selected.

The charge amount is a time integration amount of the charge current. Therefore, when charging a certain amount of charge, the higher the current peak value, the shorter the charging pulse time width. In other words, the smaller the inductance, the faster the charging speed. The second switching converter 140 is required to quickly and finely adjust the charge of the bank capacitor 104 by several switching operations. Thus the inductance of the reactor L ₂ is smaller than that of the reactor L ₁ is preferred.

The calculation of the on-time by the controller 144 of the second switching converter 140 can be the same as that of the controller 124. Alternatively the controller 144, the PI control or PID control may be calculated on-time _{T ON.}

Next, the operation of the charging circuit 102A will be described.
FIG. 10 is an operation waveform diagram of the charging power source 102A of FIG. When the high-frequency power source 106 enters a rest period, first, the bank capacitor 104 is quickly charged by the first switching converter 120. Subsequently, switching of the transistors M ₂ and M ₃ of the second switching converter 140 starts, and the voltage V _DC of the bank capacitor 104 is further brought closer to the target voltage V _REF .

By the combined use of the first switching converter 120 and the second switching converter 140, the voltage V _DC of the bank capacitor 104 is brought close to the target voltage V _REF in a short time by the first switching converter 120, and the voltage is increased with high accuracy by the second switching converter 140. V _DC can be brought closer to the target voltage V _REF and stabilized.

  In the embodiment, the description has been given of the improvement in accuracy of the switching converter used for the laser power supply. However, the present invention is not limited to this. can do. The present invention discloses the following invention.

  One embodiment of the present invention relates to a switching converter. The switching converter acquires a reactor inductance based on a reactor, a switching transistor, a temperature sensor that measures the temperature of the reactor, and a reactor temperature detected by the temperature sensor, and uses the inductance to switch the switching transistor. A controller for calculating an on-time.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments merely show one aspect of the principle and application of the present invention. Many variations and modifications of the arrangement are allowed without departing from the spirit of the present invention defined in the scope.

DESCRIPTION OF SYMBOLS 1r ... Laser processing apparatus, 2 ... Laser light source, 4r ... Laser power source, 6 ... DC power source, 8 ... High frequency power source, 100 ... Laser power source, 102 ... Charging circuit, 104 ... Bank capacitor, 106 ... High frequency power source, 110 ... Rectifier / smoothing circuit 112 ... rectifier circuit 114 ... smoothing capacitor 120 ... first switching converter 122 ... temperature sensor 124 ... controller 140 ... second switching converter 142 ... temperature sensor 144 ... controller 200 ... core , 202 ... coil winding, 204 ... air gap, L ₁ , L ₂ ... reactor, M ₁ ... switching transistor, D ₁ ... rectifier diode, M ₂ ... switching transistor, M ₃ ... synchronous rectifier transistor.

Claims (5)

A bank capacitor;
A high-frequency power source whose input is connected to the bank capacitor and intermittently supplies an alternating voltage to the laser light source;
A charging circuit including a first switching converter for charging the bank capacitor during an idle period of the high-frequency power source;
With
The first switching converter includes:
Reactor,
A switching transistor;
A temperature sensor for measuring the temperature of the reactor;
Based on the temperature of the reactor detected by the temperature sensor, acquiring the inductance of the reactor, and calculating the on-time of the switching transistor using the inductance;
A laser power supply comprising:   2. The laser power source according to claim 1, wherein the controller calculates an ON time of the switching transistor based on a difference between a detected value of the voltage of the bank capacitor and a target voltage.   The laser power supply according to claim 1, wherein the temperature sensor is configured to measure a temperature of a core of the reactor. The charging circuit further includes a second switching converter that charges the bank capacitor with high accuracy after a rough charging operation of the bank capacitor by the first switching converter;
The second switching converter includes:
Reactor,
A switching transistor;
A temperature sensor for measuring the temperature of the reactor;
Based on the temperature of the reactor detected by the temperature sensor, acquiring the inductance of the reactor, and calculating the on-time of the switching transistor using the inductance;
The laser power supply according to claim 1, comprising: A reactor, a switching transistor,
A temperature sensor for measuring the temperature of the reactor;
Based on the temperature of the reactor detected by the temperature sensor, acquiring the inductance of the reactor, and calculating the on-time of the switching transistor using the inductance;
A switching converter comprising:

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