JP7594433B2 - Laser diode power supply unit - Google Patents

Description

This invention relates to a power supply device for driving a high-output, high-speed laser oscillator that is applied to metal processing processes such as welding and cutting. For example, it relates to a power supply device for driving a laser diode processing system that uses a laser diode as a laser oscillator and irradiates a target object with a laser beam (hereinafter, LD driving power supply device).

The LD drive power supply unit drives the laser diode used as a pulsed laser oscillator at high speed. This requires a steep rise in the drive current, and the rise time is set, for example, in the range of 60 μs to 600 μs. In addition, the target value of the drive current and the pulse characteristics (DC output to 2 kHz) are also set to various values depending on the application.

The power supply device for driving LDs is equipped with a power conversion unit including a switching element, and a control unit including PWM control with a feedback circuit, etc., so that the driving current can have any desired characteristics. The control unit controls the pulse width of the PWM signal according to the target value of the driving current set by the user (Patent Document 1).

JP 2013-240801 A

In a power supply device for driving an LD, information indicating the target value of the drive current and the slope of the rise of the drive current is input to set the pulse characteristics of the drive current output to the laser diode. For example, 100% or 50% of the rated value is input as the target value of the drive current, and a STEP signal corresponding to the step response characteristics of the rise of the drive current is input as information indicating the slope of the rise of the drive current (hereinafter sometimes simply referred to as information indicating the slope). In such a power supply device, the target value of the drive current is constantly changing, and the information indicating the slope of the rise of the drive current is a constant value.

On the other hand, LD driving power supplies require various drive current specifications depending on the characteristics of the laser diode. However, since the information indicating the above slope is a fixed value, there is a problem that if the target value of the drive current fluctuates, the rise time also fluctuates.

This issue will be explained with reference to Figure 1.

Figure 1 shows the target value (hereinafter, "target value") of the laser diode drive current input from the outside to the LD drive power supply device, and the trajectory (dotted line) of the current command value generated inside the LD drive power supply device to control the drive current.

When the LD driving power supply device is started, the control unit within the LD driving power supply device receives information indicating the slope of the driving current from the outside, and calculates the slope di/dt of the current command value based on that information. The control unit then sets the current command value using di/dt, and controls the driving current so that it becomes the current command value. The LD driving power supply device also continuously receives a target value from the outside as a higher-level command value.

In the example shown in FIG. 1, when the target value is set to 0% at startup and 100% of the rated value when starting up as shown in FIG. 1(A), the slope di/dt of the current command value is calculated based on the above information, and the current command value is controlled with this slope di/dt. Also, as shown in FIG. 1(B), if the previous target value is 0% of the rated value and the current target value is changed to 50% of the rated value, the current command value is controlled with the above slope di/dt. Also, as shown in FIG. 1(C), if the previous target value is 50% of the rated value and the current target value is changed to 100% of the rated value, the current command value is controlled with the above slope di/dt. In either case, the slope di/dt of the current command value is the same. The time when the trajectory of the current command value (dotted line) is 10% to 90% of the target value is defined as the rise time. In FIG. 1(A), the rise time T1 is the time from 10% to 90% of the target value of 100%, in FIG. 1(B), the rise time T1' is the time from 5% to 45% of the target value of 50%, and in FIG. 1(C), the rise time T1'' is the time from 55% to 95% of the target value of 100%.

In the above control, the rise times T1' and T1'' in Figures 1(B) and (C) are half the rise time T1 in Figure 1(A). This is because the slope di/dt of the current command value is the same regardless of the target value.

In this way, if the slope of the current command value di/dt is constant, the rise time will change every time the target value changes. On the other hand, one way to solve this problem is to use a readjustment method in which information indicating the slope of the current command value is changed and resent from the outside to the LD drive power supply device every time the target value changes.

However, in the case of control that requires readjustment every time the target value changes as described above, if the target value changes frequently, it is necessary to constantly input/output signals or communicate between the outside and the LD drive power supply device. This causes problems such as control delays and poor response performance of the LD drive power supply device.

The object of this invention is to provide a power supply device for driving an LD that can keep the rise time of the current command value constant even if the target value changes. Another object of this invention is to provide a power supply device for driving an LD that does not need to change and resend information indicating the slope of the current command value from the outside when the target value changes.

The LD driving power supply device of the present invention comprises:
A power supply device for driving a laser diode that outputs a driving current to the laser diode,
a control unit that continuously receives an upper command value indicating a target value of the drive current from an external device and also receives information indicating a rising slope of the current command value from an external device, and generates a current command value based on the information;
a power conversion unit that generates the drive current based on the current command value,
The control unit is
The slope of the rise of the current command value is corrected based on the difference between a previous target value previously received and set and a current target value currently received and set.

When the target value received from outside fluctuates, the control unit corrects the slope of the rise of the current command value that had been used for control up until that point, based on the difference (amount of change) between the previous target value received last time and the current target value received this time.

This will be explained with reference to Figure 2.

For example, as shown in FIG. 1A, if the target value is set to 0% at startup and 100% of the rated value when the motor starts up after startup, the slope di/dt of the current command value is calculated based on the information indicating the slope, and the current command value is controlled with this slope di/dt. On the other hand, as shown in FIG. 1B, if the previous target value is 0% of the rated value and the current target value is changed to 50% of the rated value, the difference (amount of change) is 50%. Therefore, the slope di/dt is corrected to 50%/100%. Therefore, the slope di/dt is corrected to 1/2. Also, as shown in FIG. 1C, if the previous target value is 50% of the rated value and the current target value is changed to 100% of the rated value, the difference (amount of change) is 50%. Therefore, the slope di/dt is corrected to 50%/100%. Therefore, in the case of FIG. 1C, the slope di/dt is also corrected to 1/2.

By making this correction, the rise time T1 shown in FIG. 2(A) becomes equal to the rise time T1' shown in FIG. 2(B). Also, the time T1 shown in FIG. 2(A) becomes equal to the rise time T1'' shown in FIG. 2(C). By making this correction every time the target value changes, it is possible to always guarantee that T1 = T1' = T1'', and the LD driving power supply device does not need to receive information indicating the rise slope from an external device every time the target value changes. In other words, once the LD driving power supply device receives information indicating the rise slope, it does not need to receive it again even if the target value changes thereafter.

When the control unit receives the upper command value continuously, it sets the upper command value when the inclination (hereinafter, this inclination may be referred to as a slope) disappears to the current target value.

Because higher-level command values are sent continuously, it is necessary to determine which command value will be the target value, but when the higher-level command value no longer has a slope, the control unit sets that value as the current target value. This allows the current target value to be set correctly. Also, the difference (amount of change) between the previous target value and the current target value is updated only when, for example, the previous higher-level command value received had a slope and the current higher-level command value received does not have a slope. By controlling in this way, the difference (amount of change) can be correctly determined, and the slope di/dt of the current command value can also be correctly corrected.

The control unit calculates the current command value based on the information until the value reaches a preset switching point. The switching point is the timing at which the control unit switches the slope control of the current command value. In the period until the current command value reaches the switching point, the current command value is generated based on the information. When the current command value passes the switching point, the current command value is controlled so that it reaches the current target value with an appropriate rising curve.

The switching point is changed depending on the size of the current target value.

When the current target value falls below 100% of the rated value, the current difference between the current target value and the switching point becomes smaller. If this current difference becomes smaller than a certain level, it becomes difficult to control the current command value after the switching point. Therefore, it is desirable to change the switching point when the current target value falls below 100% of the rated value by a certain level. For example, it is possible to change the switching point at a predetermined ratio to the current target value.

In addition, the information and the higher-level command values can be received from a higher-level system controller.

For example, a STEP signal that indirectly indicates the information is received from a higher-level system controller. The setting unit has a table that indicates the correspondence between STEP signals and parameters that indicate the slope, and obtains the parameter that corresponds to the STEP number received from the higher-level system from the table. This parameter becomes the slope information for controlling the current command value.

According to this invention, even if the current target value fluctuates, the slope of the rise of the current command value is automatically corrected, and the rise time does not change and is always constant. In addition, there is no need to resend information indicating the slope of the current command value from the outside to the LD drive power supply device every time the target value changes.

1 shows a target value of a drive current (hereinafter, referred to as a target value) and a locus of a current command value (dotted line) in a conventional laser diode processing device. 1 shows a target value of the drive current (hereinafter, referred to as the target value) and a locus (dotted line) of the current command value in a laser diode processing device according to an embodiment of the present invention. 1 is a configuration diagram of a laser diode processing apparatus according to an embodiment of the present invention. 1 is a configuration diagram of a laser diode system including a power supply device 2 for driving an LD. Table T is shown. FIG. 2 is a block diagram of a control unit 21. 4 shows the step response characteristic of the current command value D. 4 is a flowchart showing the operation of a control unit 21. FIG. 13 is a diagram showing a higher-level command value and a change amount.

Figure 3 is a diagram showing the configuration of a laser diode processing device according to an embodiment of the present invention.

The laser diode processing device is composed of a host system controller 1, a power supply device for driving a laser diode (hereinafter referred to as a LD driving power supply device) 2, a laser diode (hereinafter referred to as an LD) 3, and a processing head 4 that is fiber-connected to the LD 3. The LD 3 includes multiple laser diodes. The LD driving power supply device 2 and the LD 3 constitute a laser oscillator.

The upper system controller 1 outputs a start signal to the LD driving power supply device 2, and outputs a STEP signal that indirectly indicates the slope of the current command value D before starting up the LD 3. In addition, the upper system controller 1 continuously outputs upper command values including the current target value P of the driving current as an analog signal before and after starting up the LD 3. Note that in the following explanation, n may be added to indicate the time of calculation in the calculation period (sampling period). For example, the current command value D(n) indicates the current command value at the time of the current calculation, and the current command value D(n-1) indicates the current command value at the time of the previous calculation.

The control unit 21 in the LD driving power supply device 2 acquires a parameter C corresponding to the STEP signal by referring to table T. Parameter C is a value for obtaining the slope of the current command value D (di/dt: current change rate for each sampling) when the target value is 100% of the rated value. The control unit 21 controls the slope of the current command value D for each sampling by calculation using the parameter C described below. In addition, as described below, when the current target value P(n) changes from the previous target value P(n-1), the control unit 21 corrects the parameter C to parameter C' based on the amount of change.

Note that the current target value P(n) is the target value P that is newly set after the target value P has changed, and the previous target value P(n-1) is the target value P before the current target value P(n) was set.

In addition, the control unit 21 in the LD driving power supply device 2 acquires the upper command value received from the upper system controller 1 for each sampling.

After receiving the start-up signal, the LD driving power supply unit 2 is driven by a PWM signal using a three-phase AC power supply as a power source, and outputs a driving current for the LD 3. The LD 3 is composed of a combination of multiple laser diode elements. The LD 3 irradiates a high-power laser beam 5 onto the workpiece 6 via the processing head 4. The LD driving power supply unit 2 has a large capacity of over 20 kW and generates a large current, so the laser beam 5 has the power to melt the beam spot on the workpiece 6.

Figure 4 is a diagram showing the configuration of a laser diode system including a power supply unit 2 for driving an LD.

The LD driving power supply device 2 includes a power conversion unit 20 that rectifies the three-phase AC voltage, controls the switching element SW with a PWM signal, and outputs the signal via a reactor L and a capacitor C. The LD driving power supply device 2 also includes a control unit 21 that generates a PWM signal, and a Hall CT 22 that detects the output current and feeds it back to the control unit 21.

The control unit 21 includes a setting unit 21a that sets information for controlling the rising slope of the current command value D (this information is parameter C, as described below) and the current target value P(n) of the current command value D, and a PWM generating unit 21b that generates a PWM signal and outputs it to the power conversion unit 20.

The upper system controller 1 outputs a start signal to start the LD driving power supply device 2 via the signal line 7. It also sends a STEP signal once to the control unit 21, and further continuously outputs an upper command value in analog quantity. The STEP signal is information that indicates the slope of the rise of the driving current.

When the control unit 21 receives a STEP signal, it refers to table T in the setting unit 21a to obtain parameter C. Parameter C is a value for controlling the slope of the rise of the current command value D. As described later, in this embodiment, the STEP signal sent from the upper system controller 1 is set to 16 stages between 60 μs and 600 μs in rise time. The rise time of the current command value D is determined by the user in the upper system controller 1 with reference to the rated current and rated voltage of LD3. In addition, when the current target value P(n) changes from the previous target value P(n-1), the control unit 21 corrects parameter C based on the difference (amount of change) and sets parameter C'.

Figure 5 shows table T.

Table T shows the correspondence between STEP signals and parameter C. Parameter C is a value for determining the slope (di/dt: current change rate for each sampling) of the current command value D when the target value is 100% of the rated value. In this example, there are 16 types of STEP signals, from 1 to 16, and the smaller the value, the larger the value of parameter C (the steeper the slope). For example, when STEP signal = 1, parameter C is 100, and parameter C = 100 indicates that the slope of the current command value D is maximum, i.e., the rise time of the current command value D is shortest. Also, for example, when STEP signal = 16, parameter C is 50, and parameter C = 50 indicates that the slope of the current command value D is minimum, i.e., the rise time of the current command value D is longest.

Note that the parameter C shown in Table T is an example value.

The control unit 21 sets the parameter C obtained by referring to table T in the setting unit 21a as a value for controlling the rising slope of the current command value D. The control unit 21 also receives the upper command value continuously sent as an analog amount from the upper system controller 1. The value at which the slope of this upper command value disappears becomes the current target value P(n). The control unit 21 further corrects the parameter C based on the difference (hereinafter, the amount of change) between the previous target value P(n-1) and the current target value P(n), and calculates the parameter C' using the following formula.

Parameter C' = Parameter C × Change (%) ------- (1)
where change amount (%) = current target value P(n) (%) - previous target value P(n-1) (%)
For example, immediately after the start of operation of the LD driving power supply device 2, the operation starts from zero and gradually increases, so the previous target value P(n-1) is zero, and the amount of change is equal to the current target value P(n). Therefore, parameter C'=parameter C, and there is no change in the parameter value. Also, if the previous target value P(n-1) is 50% and the current target value P(n) changes to 100%, the amount of change is 50%. Therefore, parameter C'=parameter C×(50%). At this time, the gradient di/dt of the rise of the current command value D is 1/2 of the previous value. Note that if the previous target value P(n-1) is 100% and the current target value P(n) drops to 50%, the current target value P(n) falls, and the amount of change is −50%. However, in the software calculation process, the amount of change is treated as an absolute value. Therefore, parameter C' at the time of the fall is parameter C'=parameter C×(50%), just like at the time of the rise. At this time, the falling gradient di/dt of the current command value D becomes 1/2 of the previous gradient. In this embodiment, the above formula (1) can be applied even when the current target value P(n) decreases in this manner.

When the control unit 21 receives a STEP signal from the upper system controller 1, it extracts the parameter C stored (set) in the setting unit 21a. It also receives the upper command value continuously sent from the upper system controller 1, and determines the upper command value when the slope of the command value stops changing as the current target value P(n). When there is a difference between the acquired current target value P(n) and the previous target value P(n-1), the control unit 21 obtains the difference as the amount of change, and based on the amount of change, corrects the parameter C as described above to obtain the parameter C'. The control unit 21 obtains the above-mentioned slope di/dt based on this parameter C', and controls the slope of the rise of the current command value D using this di/dt. The PWM generation unit 21b and the error amplifier 21e described later generate a PWM signal based on the current command value D, and output it to the power conversion unit 20.

The magnitude of the drive current output from the power conversion unit 20 is detected by the Hall CT 22 and fed back to the control unit 21. The PWM generation unit 21b controls the pulse width of the PWM signal so that the fed back detection value becomes the current command value D.

Figure 6 is a block diagram of the control unit 21.

The STEP signal sent from the upper system controller 1 is received by the setting unit 21a. A parameter C is extracted from the STEP signal by referring to table T, and the parameter C is set in the setting unit 21a. The setting unit 21a determines the current target value P(n) from the upper command value continuously sent from the upper system controller 1, and sets this current target value P(n) in the setting unit 21a. The previous target value P(n-1) is also set in the setting unit 21a. As described later, the setting unit 21a determines the current target value P(n) by slope determination, which detects the slope of the upper command value. The slope determination is based on the results of two calculations, a normal moving average (signed) and an absolute value moving average (unsigned) for the amount of change in the target value. This is to prevent erroneous detection of the slope determination for noise that causes the amount of change in the target value to fluctuate up and down in a short period of time.

The slope control unit 21c reads out the parameter C set in the setting unit 21a as a digital value. The slope control unit 21c also acquires the current target value P(n) and previous target value P(n-1) set in the setting unit 21a. The parameter correction unit 21d in the slope control unit 21c corrects the parameter C based on the difference (amount of change) between the current target value P(n) and the previous target value P(n-1) to obtain a parameter C'. The slope control unit 21c controls the slope of the rise of the current command value D using di/dt based on the parameter C' obtained in this way.

The output of the gradient control unit 21c is output to the error amplifier 21e as a current command value D. The output of the Hall CT 22 is also input to the error amplifier 21e. The error amplifier 21e outputs the error between the current command value D and the Hall CT 22 to the PWM generation unit 21b. The PWM generation unit 21b and the error amplifier 21e control the pulse width of the PWM signal so that the error becomes zero.

The tilt control unit 21c has its functions realized by a CPU and software. The calculation period (CPU timer interrupt period) of the tilt control and correction control in the CPU is set to a high speed (for example, about 10 μs).

Next, we will explain the tilt control.

Figure 7 shows the step response characteristics of the current command value D. Figure 7 (A) shows the rise of the trajectory of the current command value D when the current target value P is commanded to 100% of the rated value after startup. Figure 7 (B) shows the rise of the trajectory of the current command value D when the previous target value P was 0% of the rated value and the current target value P is commanded to 50% of the rated value, and Figure 7 (C) shows the rise of the trajectory of the current command value D when the previous target value P was 50% of the rated value and the current target value P is commanded to 100% of the rated value. In Figures 7 (A), (B), and (C), the setting unit 21a continuously receives the current target value P, so the trajectory of the current target value P is as shown by the dotted arrow line in the figure.

In FIG. 7(A), time T1 indicates the rise time of the current command value D. Time T1 is the time from time t1, when the current command value D becomes 10% of the rated value, to time t2, when the change amount to the current target value P (100% of the rated value) becomes 90%.

In FIG. 7(B), time T1' is the time from time t1' when the current command value D is 10% (5% of the rated value) of the change to the current target value P to time t2' when it is 90% (45% of the rated value) of the change to the current target value P. In FIG. 7(C), time T1'' is the time from time t1'' when the current command value D is 10% (55% of the rated value) of the change to the current target value P to time t2'' when it is 90% (95% of the rated value) of the change to the current target value P.

The parameter correction unit 21d in the gradient control unit 21c calculates the parameter C' using the above formula (1) before controlling the gradient of the current command value D. Then, the gradient control unit 21c controls the gradient of the current command value D using di/dt based on the parameter C'.

For example, as shown in FIG. 7A, when the current target value P is commanded to be 100% of the rated value after startup, the parameter C′ is calculated by the above formula (1) as follows:
C' = C x change ((100% - 0%)/100%) = C
It becomes.

Also, as shown in FIG. 7B, when the current target value P changes from 0% to 50% of the rated value, the parameter C′ is calculated by the above formula (1) as follows:
C' = C x change ((50% - 0%)/100%) = 1/2 x C
In this case, since parameter C' is 1/2 of parameter C, the gradient di/dt of the rise of current command value D is also 1/2. As a result, the rise time of current command value D becomes T1' in FIG. 7B. In this case, rise time T1' is the same as rise time T1 shown in FIG. 7A.

Also, as shown in FIG. 7C, when the current target value P changes from 50% to 100% of the rated value, the parameter C′ is calculated by the above formula (1) as follows:
C' = C x change ((100% - 50%) / 100%) = 1/2 x C
In this case, since parameter C' is 1/2 of parameter C, the gradient di/dt of the rise of current command value D is also 1/2. As a result, the rise time of current command value D becomes T1" in FIG. 7C. In this case, rise time T1" is the same as rise time T1 shown in FIG. 7A and rise time T1' shown in FIG. 7B.

In this way, when the current target value P fluctuates, the parameter C' also changes proportionally, and the rise time (T1, T1', T1'') of the current command value D always remains the same. Moreover, the calculation of the parameter C' is simple, as shown in the above formula (1).

In the above explanation, the case where the current target value P has changed to a value larger than the previous one has been shown, but even if the current target value P has changed to a value smaller than the previous one, the calculation result will be the same because the amount of change is treated as an absolute value in the software calculation process. For example, when the current target value P in FIG. 7(A) changes from 100% of the rated value to 50% of the rated value in FIG. 7(B), the parameter C' at the time of falling can be calculated using the above formula (1) in the same way as the time of rising. In other words, the fall time of the current command value D is equal to T1' in FIG. 7(B). Therefore, even if the current target value P has changed to a value smaller than the previous one, the rise time of the current command value D is kept constant.

The slope control unit 21c calculates the above di/dt from the parameter C' and controls the slope of the current command value D using this di/dt.

In this embodiment, a switching point d for switching the slope control of the current command value D is set in the slope control unit 21c. The switching point d is shown in Figures 7(A), (B), and (C). In the figure, the rising start time of the current command value D is t3, t3', and t3'', the time of the switching point d is t4, t4', and t4'', and the time when the current command value D reaches the current target value P and stabilizes is t5, t5', and t5''. The switching point d is the position where the current value is 80% of the current target value P when the load is not light. This switching point d can be arbitrarily determined by the designer in the control unit 21, and is automatically adjusted in the control unit 21 based on the magnitude of the change in the current target value P (the deviation of the current). Switching point d is referred to as the timing at which the slope control is switched from control between t3 and t4, between t3' and t4', or between t3" and t4" (processing 1) to control between t4 and t5, between t4' and t5', or between t4" and t5" (processing 2).

The current target value P is read from the setting unit 21a at the sampling period by the slope control unit 21c.

Process 1 is a process that controls the slope of the current command value D between t3 and t4, between t3' and t4', or between t3" and t4". In process 1, the current command value D is linearly controlled based on the above slope di/dt.

Process 2 is a process that controls the slope of the current command value D between t4 and t5, between t4' and t5', or between t4" and t5". In process 2, the current command value D is controlled so that it gradually reaches the current target value P without overshooting.

7B and 7C, when the current target value P is changed, the current command value D is similarly controlled by the process 1 and the process 2.
FIG. 8 is a flowchart showing the operation of the control unit 21.

The operation period (sampling period) shown in this flowchart is 10 μs in this example, and this operation period is the calculation period (CPU timer interrupt period) during which the slope control unit 21c controls the slope of the current command value D. In this flowchart, the calculation time is indicated by n, and for example, the current command value D controlled in the current calculation time is the current current command value D(n), and the current command value D controlled in the previous calculation time is the previous current command value D(n-1). In addition, the current target value P used in the current calculation time is the current target value P(n), and the previous target value P used in the previous calculation time is the previous target value P(n-1).

In ST1, the setting unit 21a acquires the command value of the current target value P(n) from the upper system controller 1. This command value is continuously sent from the upper system controller 1. Figure 9 shows the sampling time (indicated by a circle) at which the command value of the current target value P(n) is acquired. To avoid sudden changes and improve accuracy, this value is averaged with the acquired values from a predetermined number of samplings and converted into a digital value.

In ST2, the slope of the command value is detected. As shown in FIG. 9, the slope is detected by checking whether there is a difference (slope) between the command value previously acquired (after moving average) and the command value currently acquired (after moving average). If there is a slope, the command value has not reached the target value, so the target value is not updated and the process proceeds to ST4. If there is no slope, the slope of the command value has disappeared, so in ST3, the command value acquired in ST1 is determined to be the current target value P(n) and set in the setting unit 21a. The previous target value P(n-1) is also set in the setting unit 21a.

In ST4, the deviation DF between the current target value P(n) and the previous current command value D(n-1) is calculated.

The deviation amount DF is used in ST8.

In ST5, it is determined whether there was a slope last time (No in ST2 last time) and whether there is no slope this time (Yes in ST2 this time). Only if this determination is Yes does the process proceed to ST6 and the amount of change is updated. If the determination is No, the process proceeds to ST7 and the amount of change is not updated. By controlling in this way, the amount of change can be correctly determined, and therefore the slope di/dt of the current command value can also be correctly corrected.

In ST6, the amount of change V from the previous target value P(n-1) to the current target value P(n) is calculated in percentage. For example, if the previous target value P(n-1) is 50% and the current target value P(n) is 100%, the amount of change V is calculated as follows:
V (%) = 100% - 50%
That is 50%.

In ST7, parameter C is obtained by referring to table T in setting unit 21a, and switching point d (see FIG. 7) is set. As described above, switching point d is the position where the current value is 80% of the current target value P(n) when the load is not light. If the current target value P(n) becomes low and the current change amount is 2% or less of the rated ratio, it is fixed at 50% of the current target value P(n). Specifically, it is appropriately set in advance by experiments, etc. The setting position of switching point d is changed because if the current change amount is low, the current difference between switching point d and target value P becomes small, and process 2 cannot be controlled well.

In ST8, the parameter C' is calculated based on the amount of change V using the following formula.

Parameter C' (%) = Parameter C × Change V (%)
By determining the slope di/dt from the parameter C' and controlling the slope of the current command value D based on this, the rise time of the current command value D can be controlled to be constant even if the current target value P(n) fluctuates.

In ST9, the deviation amount DF is compared with the switching point d. In order to compare the switching point d in ST7 with the deviation amount DF, the current target value P(n) is set to 100% and the switching point d is shown as the difference from this. In other words, when the switching point d is at 80% of the current target value P(n), the switching point d in ST7 is expressed as 100%-80%=20%. If the deviation amount DF is less than the switching point d, the period is t3-t4, t3'-t4', or t3"-t4" in FIG. 7, so proceed to process 1 (ST10). If the deviation amount DF is equal to or greater than the switching point d, the period is t4-t5, t4'-t5', or t4"-t5" in FIG. 7, so proceed to process 2 (ST11).

Process 1 in ST10 is a process for calculating the current current command value D(n) at the rise time corresponding to the step signal between t3 and t4 in FIG. 7(A), between t3' and t4' in FIG. 7(B), or between t3" and t4" in FIG. 7(C). The current current command value D(n) is calculated using the following formula.

D(n)=f(C', D(n-1), DF)
Here, C' is the parameter corrected in ST8, D(n-1) is the current command value obtained in the previous calculation, DF is the current target value P(n ) and the previous current command value D(n-1).

Processing 2 in ST11 is processing to calculate the current current command value D(n) that reaches the target value most quickly while suppressing overshooting between t4 and t5 in FIG. 7(A), between t4' and t5' in FIG. 7(B), or between t4" and t5" in FIG. 7(C). In processing 1, the current current command value D(n) is controlled to have a linear slope, and in processing 2, the current current command value D(n) is controlled to reach the current target value P(n) along an appropriate curve. In processing 2, the current current command value D(n) is calculated using the following formula.

D(n)=f'(D(n-1))
In the above formula, the function f represents a straight line, but the function f' is a logarithmic function that reaches the target value P with an appropriate curve.

ST12 is a process for updating the current current command value D(n) obtained by the calculation in ST10 or ST11 as the current current command value. The current current command value D(n) updated in ST11 is used as the previous current command value D(n-1) in the process for the next calculation.

By using the above control, when the current target value P(n) changes, parameter C' is found by simple calculation, and the slope of the current current command value D(n) is controlled based on this parameter C'. Therefore, the rise time can be kept constant even if the current target value P(n) fluctuates. Also, it is sufficient to prepare only one table T, and there is no need to prepare multiple tables according to the target values.

1--Higher system controller 2--Power supply device for driving laser diode 3--Laser oscillator 21--Control unit 21c--Inclination control unit 21d--Parameter C correction unit

Claims (5)

1. A power supply device for driving a laser diode, the power supply device setting a target value of a driving current every time a pulsed driving current is output to a laser diode,
a control unit that receives information indicating a rising slope of a current command value from an external device, sets the received information , receives a target value of the drive current from an external device for each of the pulsed drive currents, sets the received target value , and generates a current command value based on the information;
a power conversion unit that generates the drive current based on the current command value,
The control unit is
A power supply device for driving a laser diode, which corrects the slope of the rise of the current command value based on the set information based on the difference between a previous target value, which is the target value of the pulsed drive current received and set last time, and a current target value, which is the target value of the pulsed drive current received and set this time, so that the rise time of the pulsed drive current is always the same . The power supply device for driving a laser diode according to claim 1, wherein the control unit continuously receives a higher-level command value indicating a target value of the driving current from an external source, and sets the higher-level command value when the slope disappears as the target value. The power supply device for driving a laser diode according to claim 1, wherein the control unit calculates the current command value based on the information until the current command value reaches a preset switching point. 4. The power supply device for driving a laser diode according to claim 3 , wherein the switching point is changed in accordance with the magnitude of the current target value. 5. The power supply device for driving a laser diode according to claim 1, wherein said information and said target value are received from a host system controller.

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