JP6954733B2 - Laser power supply - Google Patents

Description

The present invention relates to a switching converter.

Laser processing equipment is widely used as an industrial processing tool. 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 supply 4r that supplies AC power to the laser light source 2 to excite it. The laser power supply 4r includes a DC power supply 6 and a high frequency power supply 8. _{The DC power supply 6 stabilizes its output DC voltage VDC} to a target value by feedback control using PID (Proportional-Integral-Differential) control or PI control. The high-frequency power supply 8 receives a DC voltage _VDC , converts it into an alternating voltage, and supplies it to the laser light source 2 which is a load.

In the laser processing apparatus 1r for a drill, the laser light source 2 operates discontinuously. That is, a relatively short light emission period of several microseconds to 10 microseconds and a similar, short, or long rest period 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 charts and time charts referred to in the present specification are appropriately enlarged or reduced for ease of understanding, and each waveform shown is also simplified for ease of understanding. Or exaggerated or emphasized.

The high-frequency power supply 8 repeats an operation period and a rest period according to whether the laser light source 2 is turned on or off. When the high-frequency power supply 8 shifts from the hibernation period to the operation period, the feedback response delay occurs in the DC power supply 6, the DC voltage _VDC may decrease, and the DC power supply 8 may deviate from the permissible fluctuation range. When the high-frequency power supply 8 shifts from the operating period to the rest period, the DC voltage _VDC may rise due to the feedback delay and deviate from the permissible fluctuation range.

Further, when switching to a different process, _{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. During the period when the DC voltage _VDC deviates from the permissible voltage range, the laser light source 2 cannot emit light, which causes a decrease in the operating rate (repetition frequency).

When the permissible voltage range is widened, the variation in the output energy of the laser for each shot becomes large, and when the permissible voltage range is narrowed, the operating rate decreases. In order to achieve both uniform output energy and high repetition frequency, the laser power supply 1r _{is required to bring the DC voltage VDC} closer to the target voltage in a short time.

Japanese Unexamined Patent Publication No. 2016-59932

As a result of examining the power supply for the laser, the present inventors have come to recognize the following problems. A switching converter is used as the power supply for the laser. 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 fluctuates. 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 machining equipment for drills is required to be faster year by year, and both machining speed and machining accuracy are required. Improvements that contribute to this are also required for laser power supplies.

The present invention has been made in view of the above problems, and one of the exemplary purposes of the embodiment is to provide a power source for a laser capable of stabilizing output energy with high accuracy even at a high repetition frequency.

One aspect of the present invention relates to a laser power supply. The laser power supply includes a bank capacitor, a high-frequency power supply whose input is connected to the bank capacitor and intermittently supplies an alternating voltage to the laser light source, and a first switching converter that charges the bank capacitor during the pause period of the high-frequency power supply. It is equipped with a circuit. The first switching converter acquires the inductance of the reactor based on the reactor, the switching transistor, the temperature sensor that measures the temperature of the reactor, and the temperature of the reactor detected by the temperature sensor, and uses the inductance to obtain the switching transistor. Includes a controller that calculates the on-time of the.

The inductance of the reactor depends on the magnetic permeability of the core (iron core), but the magnetic permeability of the core fluctuates with temperature. Therefore, if the on-time of the switching transistor is calculated with the inductance of the reactor constant in the controller, the error of the charging current supplied from the reactor to the bank capacitor by one switching of the switching transistor becomes large when the inductance fluctuates. It ends up. Therefore, by monitoring the temperature of the reactor and reflecting it in the calculation of the on-time, it is possible to control the charging current to the bank capacitor with high accuracy, and by extension, 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 voltage of the bank capacitor and the target voltage is ΔV, the amount of charge 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 this amount of charge Q is supplied to the bank capacitor.

The temperature sensor may be configured to measure the temperature of the reactor core. The temperature sensor may be mounted on 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 the inductance of the reactor based on the reactor, the switching transistor, the temperature sensor that measures the temperature of the reactor, and the temperature of the reactor detected by the temperature sensor, and uses the inductance to obtain the switching transistor. It may include a controller that calculates 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 charged per switching by the second switching converter can be reduced, and highly accurate charging becomes possible. ..

The second switching converter may be a synchronous rectification type (boost-boost type) capable of charging and discharging a 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.

It should be noted that any combination of the above components or components and expressions of the present invention that are mutually replaced between methods, devices, systems, and the like are also effective as aspects of the present invention.

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

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

Hereinafter, the present invention will be described with reference to the drawings based on preferred embodiments. The same or equivalent components, members, and processes shown in the drawings shall be designated by the same reference numerals, and redundant description will be omitted as appropriate. Further, the embodiment is not limited to the invention, but is an example, and all the features and combinations thereof described in the embodiment 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 supply 100. The laser light source 2 is, for example, a CO ₂ laser. The laser power supply 100 supplies AC power to the laser light source 2 to excite it.

The laser power supply 100 includes a charging circuit 102, a bank capacitor 104, and a high frequency power supply 106. The input 108 of the high-frequency power supply 106 is connected to the bank capacitor 104, and the output of the high-frequency power supply 106 is connected to the laser light source 2. The high-frequency power supply 106 receives the DC voltage _VDC generated in the bank capacitor 104, and intermittently supplies the alternating voltage (driving voltage) V _{DRV to the laser light source 2.} That is, the high-frequency power supply 106 switches during the light emitting period of the laser light source 2, and the switching of the high-frequency power supply 106 stops during the light-off period of the laser light source 2. The period during which the high-frequency power supply 106 switches is referred to as an operating period, and the period during which switching stops is referred to as a pause period. The configuration of the high frequency power supply 106 is not particularly limited, and a known technique may be used.

The bank capacitor 104 can be grasped as a DC power source such as a power storage device that supplies electric 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 supply 106. Since charging of the bank capacitor 104 is stopped during the operation period of the high frequency power supply 106, the voltage _VDC of the bank capacitor 104 is lowered by the discharge by the high frequency power supply 106. _{Therefore, the capacity of the bank capacitor 104 is designed so that the DC voltage VDC} does not fall below the lower limit of the allowable range even in the process of discharging by the high frequency power supply 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 repeating frequency of about 5 kHz and a duty ratio of about 5%. During the operating period of the high frequency power supply 106, the bank capacitor 104 behaves as a power source for supplying power to the high frequency power supply 106. During this time, the charging power supply 102 is stopped, and the DC voltage _VDC of the bank capacitor 104 drops due to the discharge. However, since the capacity of the bank capacitor 104 is sufficiently large, the DC 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 pause period is entered, the charging power supply 102 starts charging the bank capacitor 104, and the bank capacitor 104 is charged to the _{target voltage V REF.} The laser processing device 1 repeats this operation.

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

The charging circuit 102 includes a rectifying smoothing circuit 110 and a first switching converter 120. The rectifying and smoothing circuit 110 receives a commercial AC voltage V _AC , rectifies and smoothes it, and generates a _{DC voltage V IN.} For example, the commercial AC voltage V _AC is a three-phase 200 V, and the DC voltage V _IN is 280 V. As shown in FIG. 4, the rectifying and smoothing circuit 110 may be a combination of the rectifying circuit 112 and the smoothing capacitor 114. Alternatively, the rectification 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, 500 V. The first switching converter 120 receives the DC voltage _VIN and supplies the _{charging current ICHG1} to the bank capacitor 104. The first switching converter 120 is a diode rectifying type boost converter including _{a reactor L 1} , a switching transistor M ₁ , and a rectifying diode D _{1. The charging current ICHG1} generated by the first switching converter 120 flows only in the direction of charging the bank capacitor 104.

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. The electric 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 of turns N of the coil winding, 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)
There is an air gap inside the core 200, and the magnetic permeability μ ₀ of the air gap also affects the inductance L, but the thickness of the air gap is sufficiently smaller than the thickness of the core, so in equation (1) It is omitted.

The magnetic permeability μ of the core has temperature dependence and can be expressed by a function f (T) of temperature.
μ = f (T)… (2)
Substituting Eq. (2) into Eq. (1) gives Eq. (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)
Will be. FIG. 7 is a diagram showing an example of the temperature dependence of inductance.

As mentioned above, the actual inductance includes _{the terms of core permeability μ and 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 dependence of is virtually zero. Further, the heat of the coil winding 202, which is a heating element, is transferred to the core 200 through the air gap 204. Therefore, the temperatures of the coil winding 202 and the core 200 do not always match, and when the temperature sensor 122 is attached to the coil winding 202, the temperature of the core 200 cannot be measured accurately.

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 attached directly to the surface of the core or may be embedded in the core. As a result, the temperature fluctuation of the inductance L can be accurately detected.

Return to FIG. The controller 124, based on the temperature T of the reactor _{L 1} of the temperature sensor 122 has detected, to obtain the inductance L of the reactor _{L 1.} For example, the 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 term of the air gap may be taken into consideration.

Alternatively, the controller 124 may keep the relationship between the temperature T and the magnetic permeability μ as a look-up table, acquire 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 maintained as a look-up table.

The controller 124 utilizes the inductance L obtained this way to calculate the on-time T _ON the switching transistor M _1. The controller 124 may be based on the difference ΔV of the detection value _{V DET} and the target voltage _{V REF} of the voltage _{V DC} of the bank capacitor 104, to calculate the on-time _{T ON} the switching transistor _{M 1.} More specifically, the amount of charge 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 V DC} of the bank capacitor 104 and the target voltage V _{REF, so that the amount of charge Q can be obtained.} the on-time _{T oN} the switching transistor _{M 1} may be calculated on.

The detected value V _DET is preferably measured in a state where the operation of the high frequency power supply 106 is stopped and the current I _{OUT flowing from the bank capacitor 104 to the high frequency power supply 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.}

It is assumed 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 amount of charge Q that the first switching converter 120 should supply to the bank capacitor 104 is
Q = C × ΔV = C × (V _REF −V _DET )
Is. C is the capacitance of the bank capacitor 104.

First switching converter 120, a single switching of the switching transistor _{M 1,} and supplies the electric charge Q in the bank capacitor 104.

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 to the high frequency power supply 106 from the bank capacitor 104. During this period, the laser power supply 100 is in a dormant state, the bank capacitor 104 is _{discharged by the output current I OUT} , and the voltage _VDC decreases. When the output current I _OUT becomes zero, the voltage _VDC stabilizes. The detected value V _DET of the voltage V _DC after stabilization 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 detected 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 with a slope _{V IN} / L from zero. 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.

Subsequently, the switching transistor M ₁ turns 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, it decreases with a slope _{(V IN -V DC -V F)} / L.
_{I L = I PEAK -∫ (V} DC + V F -V IN) / Ldt
V _F «V _DC, When _V F _{«V IN,} reactor current _{I L I L = I PEAK -∫ (V} DC -V IN) / Ldt
Will be. Reactor current _{I L} which hatched, the charging current _{I CHG} to the bank capacitor 104. The amount of charge Q supplied to the bank capacitor 104 corresponds to the 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 VDC.} 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. As a result, even if the temperature fluctuates, the voltage V _DC of the bank capacitor 104 can be brought close to the target voltage V _{REF by switching once.} As a result, 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 emission, and a high repetition rate can be realized.

FIG. 9 is a circuit diagram of the charging circuit 102A according to the modified example. 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 rough charging operation of the bank capacitor 104 by the first switching converter 120.

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. Like the first switching converter 120, the second switching converter 140, a temperature sensor 142 for measuring the temperature of the reactor _{L 2} is provided. 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. _{When the voltage V DC} is insufficient for the target value V _{REF as} a result of charging by the first switching converter 120, the second switching converter 140 can be finely adjusted in the direction of increasing _{the voltage DC, and the first switching converter 120 When the voltage V DC} exceeds the target value V _REF as a result of charging by the second switching converter 140, the voltage _DC can be finely adjusted in a direction of lowering the voltage DC.

Here, the first switching converter 120 needs to quickly charge the bank capacitor 104, and is required to supply as _{much current IC HG1 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 charge amount is the time integral amount of the charge current. Therefore, when charging a constant 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 fine-tune the charge of the bank capacitor 104 by several switching operations. Therefore, the inductance of the _{reactor L 2} is preferably smaller than that _{of the reactor L 1.}

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.}

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

By using the first switching converter 120 and the second switching converter 140 together, the first switching converter 120 brings the voltage _VDC of the bank capacitor 104 closer to the target voltage V _REF in a short time, and the second switching converter 140 brings the voltage with higher accuracy. The _VDC can be further brought closer to the target voltage V _{REF and stabilized.}

In the embodiment, the improvement of the accuracy of the switching converter used for the power supply for the laser has been described, but the present invention is not limited to this, and the combination of the first switching converter 120 and the second switching converter 140, or each of them, is used for various purposes. can do. The following inventions are disclosed herein.

One aspect of the present invention relates to a switching converter. This switching converter acquires the inductance of the reactor based on the reactor, the switching transistor, the temperature sensor that measures the temperature of the reactor, and the temperature of the reactor detected by the temperature sensor, and uses the inductance to obtain the inductance of the switching transistor. It is equipped with a controller that calculates the on-time.

Although the present invention has been described using specific terms and phrases based on the embodiments, the embodiments show only one aspect of the principles and applications of the present invention, and the embodiments are claimed. Many modifications and arrangement changes are permitted within the range not departing from the idea of the present invention defined in the scope.

1r ... Laser processing device, 2 ... Laser light source, 4r ... Laser power supply, 6 ... DC power supply, 8 ... High frequency power supply, 100 ... Laser power supply, 102 ... Charging circuit, 104 ... Bank capacitor, 106 ... High frequency power supply, 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 (3)

With a bank capacitor
A high-frequency power supply 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 that charges the bank capacitor during the pause period of the high frequency power supply.
With
The first switching converter is
The first reactor and
The first switching transistor and
Attached to the surface of the core of the first reactor, or embedded in the core, a first temperature sensor for measuring the temperature of the core,
Based on the temperature of the core of the first reactor detected by the first temperature sensor, the inductance of the first reactor is acquired, and the on-time of the first switching transistor is calculated using the inductance. With the controller
A power supply for a laser, characterized by including. The laser power supply according to claim 1, wherein the first controller calculates an on-time of the first switching transistor based on a difference between a detected value of a voltage of the bank capacitor and a target voltage. 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 is
With the second reactor,
The second switching transistor and
Attached to the surface of the core of the second reactor. Alternatively, a second temperature sensor embedded in the core and measuring the temperature of the core,
Based on the temperature of the core of the second reactor detected by the second temperature sensor, the inductance of the second reactor is acquired, and the on-time of the second switching transistor is calculated using the inductance. With the controller
The laser power supply according to claim 1 or 2, wherein the laser power supply comprises.

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