JPH02148780A - Stabilizing method for temperature of semiconductor laser element - Google Patents

Abstract

PURPOSE:To accurately control a laser element (LD) stably at a high speed by setting suitable proportional constant in a state that the temperatures of the LD and a heat sink are equilibrated, and operating a proportional integration differentiator. CONSTITUTION:A predetermined time in which LD 1 and a heat sink 2 arrive at equilibrated temperature is set to a MPU 10. The injection of a light emitting current to the LD 1 is started under the control of the MPU 10, a switch SW 9 is simultaneously switched to apply temperature data Z detected by a temperature sensor 4 to a Peltier element driver 5 to proportionally control it. When the time count of the MPU 10 becomes a predetermined time, a proportional constant is set from the MPU 10 to a proportional integration differentiator (PID) circuit 8, the SW 9 is switched to input temperature data Z thereto to operate the circuit 8. Since the temperatures of the sink 2 and the LD 1 are already equilibrated, the following fine temperature control can be accurately conducted at a high speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for stabilizing the temperature of a 11-conductor laser diode (LD). This relates to a procedure for controlling using a PID control force type.

[Prior Art] In a laser length measuring device that uses an interferometer that uses laser light to precisely measure the distance traveled by an object, it is necessary for the oscillation wavelength of the LD to be stable in order to achieve good measurement accuracy. be. Since the oscillation wavelength of an LD is greatly influenced by its operating temperature, the temperature is stabilized.

Figures 2 (a) and (b) show the conventional temperature stabilization method for the LD of the light source used in a laser length measuring device.
In a), LD! is fixed to a metal heat sink 2 having high thermal conductivity, and a Peltier element 3 and a temperature sensor 4, whose temperature increases or decreases depending on the direction of supplied current, are attached to the heat sink. A heat radiation Z3a is attached to the Peltier element. The temperature data of the heat sink detected by the temperature sensor is given to the Peltier element-r driver 5 to control the supply current to the Peltier element Y. On the other hand, a light emitting current is injected into L D t from the LD power supply 4, the temperature is stabilized by the heat sink, and a constant wavelength is generated. Figure (b) shows the temperature curve of a controlled heat sink.If the initial temperature is Zo and the first temperature measurement is Zs, normally the current in the Peltier element initially flows excessively as shown by curve V. The temperature exceeds Zs, and after some time passes, it becomes under due to a reverse current, and such oscillatory changes continue until it finally settles to Zs. Note that there are cases where the curve is not oscillatory but asymptotically approaches Zs like the curve e. Whether the temperature change is oscillatory or not depends not only on the control method, but also on the resistance to heat conduction, inertia, and capacity of the controlled object.

Now, in the case of an α1 long instrument using an LD, the temperature stability of the LD is very strict due to the precise measurement, and the
100 to I/th 000 (°C) is required, and l-
When using the control described above, the vibration becomes somewhat complicated due to temperature changes in the external environment including heat generation at the heat sink temperature Ll). Furthermore, even once the target temperature is reached, the environmental temperature constantly changes, so a time lag is unavoidable in order to always maintain stability. In order to overcome these drawbacks, a proportional-integral-derivative (PID) control method based on automatic control theory is used.

The PID control method is well known, but to explain its concept, generally when controlling a controlled object to a constant state Zs, a change mz indicating a change in the state of the controlled object is taken, and Z is Adding a force proportional to the integral (I) of Z and a force proportional to the differential value (I) to the proportional external force (P), we get P+I+
The object to be controlled is controlled by an external force D. now,
When the state of the controlled object is Y, the following equation holds.

Y=KP z+KI f zdt+KDdz/dt ・
”(1) Here, KP is the constant of proportionality to 2, Kl,
KD are proportionality constants for the time integral and derivative of 2, respectively. PID control is performed by setting each of these proportionality constants. The method for determining each constant will be omitted. In addition,
Recently, dedicated IC devices have been manufactured that calculate the (+) equation by simply adding 5 to each proportionality constant.

In the above, the conventional method of controlling the supply current of the Peltier element T in proportion to the temperature data 2 explained in FIG. According to this method, changes in state Z can be accurately captured, and temperature stabilization can be expected with high precision in a short time.

A conventional configuration and operation in which the PID control method is applied to LD temperature control will be explained with reference to FIGS. 3(a) and 3(b). figure(
In a), the time-varying temperature data 2 of the heat sink detected by the temperature sensor 4 is compared with an appropriate reference voltage E by the comparator 7, and inputted to the PID control circuit 8, where its integral value and differential value are calculated. , are multiplied by each of the above proportionality constants set in advance, and Y in equation (1) is calculated.

The obtained Y data is sent to the Peltier element driver 5 by 1 degree.
The current of the Peltier element 3 is controlled by this loop, and the temperature of the heat sink is kept constant by constantly controlling the current to z 75 (Oh).The vibration curve V in Figure (b)
shows the controlled temperature change of the heat sink. Please note that the heat sink temperature always fluctuates depending on the environmental temperature.
Even with the PID control method, it is impossible to always match the temperature Zs exactly, and as shown in Figure (b), the temperature difference δ
2 remains, and this is controlled within the permissible value.

[Problem to be Solved] A conventional procedure when the PID control method is applied to temperature stabilization of an LD will be explained with reference to the flowchart shown in FIG. First, start with the LD current and temperature control OFF.■
, [16 Set temperature Zs and PID constant in PID circuit■. Next, the PID circuit is turned on and operated (2), and it is detected that the temperature of the heat sink has reached almost Zs (2), and at this point, the current is turned on (Ll), that is, the current is turned on (2). Hereafter P
I I) The circuit continues to operate ■, and the temperature is stabilized to perform measurement ■. However, when using such a procedure, if the initial temperature Zo of the heat sink is significantly different from the target value Zs, control may not be performed smoothly because the PID constant is not appropriate, and furthermore, the target value ZS may not be reached. After that, L! ] Current is injected, so
The temperature of the heat sink will rise by tlT and the control will become unstable, or it will take a long time to stabilize.
Stable and quick temperature control is not possible. According to the basics of automatic control, in PID control, it is appropriate to first set a constant for a temperature slightly lower than the target value, and then change the constant three times when this temperature is approximately reached. However, in this case, since there is an effect of heat generation due to Lt) current, it is not necessarily possible to follow the basic procedure, and the problem is the timing to turn on the LD current. is necessary.

This invention has been made in view of the above 4-, and aims to provide a procedure that enables stable, quick, and highly accurate control in stabilizing the temperature of an LD using the PID control method. .

[One step to solve the problem] This invention attaches a Peltier element and a temperature sensor to a heat sink to which an LD is fixed, and calculates proportional integral differential (
PID) A method of stabilizing the temperature of the LD by controlling the supply current of the Peltier element using a control method, in which the temperature of the LD is stabilized by time control of a microprocessor. At the point when the temperatures of both are almost at β equilibrium, the microprocessor sets the proportionality constants for the proportional (P), integral (I), and differential (D) of the PID control method to the PTD control circuit, and operates the PID circuit. .

[] During a certain period of time during which the light emitting current is injected into the memory I), the supply current of the Peltier element is controlled by P control proportional to the temperature data, and thereafter the PID control is performed.

[Operation] When following the procedure described in L, first, the temperature of the heat sink in contact with the LD current is 1-9? However, due to the time control of the microprocessor, the temperatures of both are balanced after a certain period of time. At this point of equilibrium, the PID proportionality constant appropriate for that temperature state is set in the circuit and operated, so that PID control operates smoothly and quickly in accordance with subsequent changes in heat sink temperature due to minute fluctuations in the LD current, etc. As a result, the temperature of the LD is stabilized with high precision.

Next, during a certain period of time until the temperatures of G and G are balanced, the supply current of the Peltier element is controlled by P control proportional to the temperature data, so the equilibrium is maintained in the natural state without relying on this. It is possible to reach an equilibrium state in a shorter time than in the case of

[Embodiment] FIG. 1(a) is a block system diagram in an embodiment of the method for temperature stabilizing an 11-conductor laser element according to the present invention. In the figure, % L D t is fixed to a heat sink 2, and a Peltier element J'3 and a temperature sensor 4 are attached to the heat sink. Under the time control of the microprocessor 10, the LD power source 6 starts injecting current into the LD, and the temperature data Z detected by the temperature sensor is directly sent to the Peltier element driver 5 by 9° via the changeover switch 9. P control proportional to 2 is performed. The switch 9 is switched after a certain period of time according to the time measurement of the microprocessor, the temperature data is inputted to the PID control circuit 8, the calculation of the above formula <1) is performed, and the control data Y is sent to the Peltier element driver 5. The temperature of the Peltier element 3 is controlled to be constant.

In the above, a dedicated device is used for the PID control circuit 8. In addition, the PID proportionality constant for the target or equilibrium temperature is stored in the microprocessor in advance, and the PID
It is transferred and set at any time before the control circuit starts operating.

In 1- below, P control is performed as necessary, and can be omitted in cases where the length of time to reach equilibrium in a natural state is not a problem, and in that case, the changeover switch 9 is unnecessary. .

FIG. 1(b) shows a flowchart for FIG. 1(a), and the procedure will be explained using FIG. 1(a) together.

■ Set a certain time to reach equilibrium temperature for the mass and microprocessor lO. This fixed time is rme, L1
] The photothermal I/O of the element 1, the heat capacity 11 of the heat sink, the operating characteristics of the Peltier element with respect to the supplied current, etc. are experimentally determined as reference. Next, injection of light emitting current to the LD is started under the time control of the microprocessor (1), and at the same time, the temperature data Z detected by the temperature sensor is transferred to the Peltier element driver 5 by switching the switch 9 to operate the P control [phase]. When the time count of the microprocessor reaches a certain time, the microprocessor sets a proportional constant to the PID control circuit 8 [phase], and manually inputs the temperature data 2 by switching the switch to operate the PID control circuit [ phase]. Since the temperatures of the heat sink and LD have already reached an equilibrium state at the time of ■, subsequent minute temperature control is performed quickly and accurately, allowing measurement work to be carried out immediately.■
can be started. Note that, depending on the case, the P control in (2) may be omitted.

[Effects of the Invention As is clear from the explanation below-1-, in the method for stabilizing the temperature of a μ conductor laser element according to the present invention, a light emitting current is first injected into Ll) before the measurement operation, and the temperature is maintained constant. After a period of time, when the temperatures of both the LD and the heat sink are balanced, set an appropriate proportionality constant for this state and perform PI.
Since the D circuit is operated, the control instability caused by injecting the LD light emitting current in the middle of the PID control operation as in the conventional case is eliminated, and the PID control effect is exerted. In addition, if necessary, P control is performed until the temperature of the LD and heat sink reach equilibrium to shorten the time required, which greatly contributes to the technology of stabilizing the temperature of the LD. .

[Brief explanation of the drawing]

1(a) and 1(b) are block diagrams and flowcharts for side control procedures in an embodiment of the method for stabilizing conductor laser priming according to the present invention, and FIG.
a) and (b) are explanatory diagrams of the temperature stabilization method using conventional P control for LD, and Figures 3 (a) and (b) are for L
Explanatory diagram of conventional PII) control method for D, 4th
The figure is a flowchart for FIGS. 3(a) and 3(b). DESCRIPTION OF SYMBOLS 1...P1'' conductor laser element (LD), 2...Heat sink, 3...Peltier element 13a...Radiator, 4...Temperature sensor, 5...Peltier element driver, 6... - LD power supply, 7... Comparator, 8... PID control circuit, 9... Selector switch, 10... Microprocessor ■~■... Step number of flowchart. Figure 1 (b) ■

Claims (2)

[Claims] (1) A Peltier element and a temperature sensor are attached to a heat sink to which a semiconductor laser element (hereinafter simply referred to as LD) is fixed, and a proportional-integral-derivative (PID) control method is used to control the time-varying temperature data detected by the temperature sensor. In the method of stabilizing the temperature of the LD by controlling the supply current of the Peltier element, the temperature of both the LD and the heat sink is maintained by injecting a light emitting current into the LD for a certain period of time under time control by a microprocessor. At the time of equilibrium, the microprocessor sets proportional constants for proportionality (P), integral (I), and differential (D) of the PID control method to the PID control circuit, and operates the PID control circuit. A method for stabilizing the temperature of a semiconductor μ laser device. (2) A method for stabilizing the temperature of a semiconductor laser device according to claim 1, wherein the supply current of the Peltier device is controlled by P control proportional to the temperature data during a certain period of time during which the light emitting current is injected into the LD.