JPH0453012Y2 - - Google Patents

Description

[Detailed explanation of the idea]

B. Purpose of the invention [Field of industrial application] The present invention relates to a laser device used as a laser beam oscillation source in, for example, a laser beam printer or a laser disk device. [Prior Art] For example, a semiconductor laser has a characteristic that the wavelength of the laser changes due to temperature changes.
Generally, depending on the temperature, the laser wavelength is approximately 0.2 ~
It changes at a rate of 0.3 nm/°C. Therefore, when the temperature of the laser chip changes from standard room temperature (25°C) to 35°C, the wavelength shifts by approximately 2 to 3 nm towards longer wavelengths. Conversely, the temperature of the laser chip is
℃, the wavelength of the laser decreases from 4 to
6nm shift. Such temperature dependence of lasers is a phenomenon that is observed not only in semiconductor lasers but also in, for example, dye lasers, gas lasers, and the like. For convenience, the laser will be described below as a semiconductor laser. Therefore, in the laser device, measures are taken to control the temperature of the laser and its surroundings to a predetermined, substantially constant temperature. One of them is one that uses a Peltier element. This uses a Peltier device to maintain and control the laser chip and ambient temperature at approximately 20 to 25°C. However, in order to maintain the laser chip at 20 to 25°C, the Peltier element requires a large current, and therefore a large and large-capacity power supply is required. Further, the Peltier element itself is large, and the Peltier element itself is not necessarily stable. In addition, the temperature of the laser chip and its surroundings is managed by controlling the supply of electricity to the heater using a heat-generating heater such as a nichrome wire. FIG. 1 is a schematic diagram of an example of a semiconductor laser unit 20 whose temperature is controlled using a heat generating heater. That is, the unit 20 includes a substrate 21 and this substrate 2.
1, a semiconductor laser 1 (chip) fixed to this support 22, a cap 2 that covers and seals the support 22 and the laser 1.
3. The cap 23 has a glass window 24 through which the laser beam 2 passes. 21,
The members 22 and 23 (excluding the window 24) may be made of a metal material with good thermal conductivity, such as aluminum, brass, or stainless steel. Reference numeral 25 denotes a heat generating heater made of nichrome or the like, which is thermally coupled to the laser 1 via a good heat conductor such as the support 22. 26 is a temperature sensing element such as a thermistor or thermocouple placed near the laser 1. The signal from the element 26 is transmitted to a well-known temperature control circuit 27, and the circuit 27 cuts off and on the power applied to the heater 25 from the power source 28 in accordance with the signal, thereby maintaining the temperature of the laser 1 at a predetermined temperature. This predetermined temperature T is 5 to 10 degrees higher than the upper limit temperature of the usage environment of the device, for example, 35℃.
The temperature may be as high as 40°C to 45°C.
Driving the laser at too high a temperature, approximately 50° C. or higher, is undesirable because it accelerates the deterioration of the laser. [Problems to be solved by the invention] This temperature control method is rough in terms of accuracy, and the control temperature fluctuation range (ripple) is relatively large, making it difficult to control temperature within the ideal control fluctuation amount of ±0.2℃. . In other words, the center temperature of the laser temperature adjustment should be set to 40 to 45
℃, the detection delay due to the heat conduction time of temperature detection means such as a thermistor, and the delay due to the start-up time of the heat generating heater increase temperature fluctuations. When this amount of variation exceeds ±0.2° C., for example, in a laser beam printer, image variation occurs due to the wavelength variation of the laser. For example, problems arise such as variations in line thickness or uneven density. Furthermore, continuing to periodically apply temperature fluctuations of 1° C. or more has the disadvantage of adversely affecting the stability of the semiconductor laser crystal and shortening the life of the laser. This invention utilizes a heat-generating heater to control the power supply to the heater to manage the temperature adjustment of the laser, and it is possible to keep the controlled temperature variation within ±0.2℃, thereby making it possible to always An object of the present invention is to provide a laser device capable of stable laser oscillation. B. Structure of the invention [Means for solving the problem] The invention includes a laser light source, a heater that heats the laser light source, a power source that supplies power to the heater, and a means for detecting the temperature of the laser light source. When the temperature detected by the detection means is less than a predetermined temperature, the power supply supplies power to the heater, and when the temperature detected by the detection means reaches a predetermined temperature or higher, the power supply to the heater is stopped. In a laser device comprising a temperature adjustment circuit that adjusts the temperature of the laser light source by repeating the above operation, during the period when the heater is energized, a pulse current is applied from the power source to the heater, and the temperature is adjusted. means for measuring the output voltage of the power supply during a period in which the temperature detected by the detection means is equal to or higher than a predetermined temperature and the power supply from the power supply to the heater is stopped; and a period in which the power supply to the heater is stopped. The heater is characterized by comprising means for changing the ratio of on time and off time in pulse energization to the heater in accordance with the voltage measured by the voltage measuring means during the period in which the heater is energized subsequent to . It is a laser device. [Function] Pulse energization makes it possible to reduce the amount of heat generated by the heater per unit time, which reduces the possibility of detection delays in the temperature detection means, which reduces the temperature ripple of the heater and improves temperature accuracy. In addition, by changing the heater's on time and off time during pulse energization to the heater according to the output voltage of the power supply measured during the period when the energization is stopped, high accuracy can be achieved when the power supply voltage changes. It is possible to adjust the temperature, and it is also possible to accurately measure the power supply voltage without being affected by voltage drops due to specific load resistance or fluctuations in voltage due to pulsed energization, and laser control temperature fluctuations can be kept within ±0.2 degrees. It is now possible to control the temperature with high precision. [Embodiment] Fig. 2 shows an embodiment of a semiconductor laser unit that is temperature-controlled according to the present invention. Components common to the unit shown in Fig. 1 are given common reference numerals. The explanation will be omitted. Reference numeral 29 denotes a voltage detection circuit of the power supply 28 that supplies power to the heater 25. A signal from the temperature sensing element 26 is transmitted to a temperature adjustment circuit 27. On the other hand, the output voltage of the power supply 28 is measured by a voltage detection circuit 29 and transmitted to the temperature adjustment circuit 27. The temperature adjustment circuit 27 intermittents the power that the power supply 28 applies to the heater 25 based on the above two signals. In that case, pulse energization is performed when power is supplied to the heater 25, and pulse energization is completely cut off when power is not supplied. That is, the temperature detection means 26 detects the temperature control temperature To.
When it is detected that the above temperature has been reached, the temperature adjustment circuit 2
7 cuts off the pulse current input from the power source 28 to the heater 25 . When the temperature detection means 26 detects that the temperature has become lower than the temperature control temperature To, the temperature adjustment circuit connects the heater 25 and the pulse power supply 28 and restarts the supply of electric power. By performing pulse energization in this manner, it is possible to suppress the amount of heat generated by the heater per unit time, and the temperature detection means 26
Since a detection delay is less likely to occur, the temperature ripple of the heater 25 is reduced. Therefore, highly accurate temperature control is possible. Furthermore, by installing a temperature adjustment circuit that switches the ratio of pulse on time and pulse off time during pulse energization based on the power supply voltage that supplies power to the heater, the laser management temperature fluctuation can be reduced by ±0.2
It has become possible to control the temperature with high precision within ℃. The intermittent procedure will be explained below. When the temperature detection means 26 detects that the temperature control temperature To has reached or higher, the temperature adjustment circuit 27 turns on the power supply 28.
The power input to the heater 25 is cut off. In this state, the voltage detection means 29 detects the voltage V of the power supply 28 and inputs it to the temperature adjustment circuit 27. When the temperature detection means 26 detects that the temperature has become lower than the temperature control temperature To, the temperature adjustment circuit 27 switches the heater 2
5 and the power supply 28 to resume power supply.
At this time, power is supplied by pulse input, and the ratio of the on time and off time of this pulse is calculated and determined within the temperature adjustment circuit 27 based on the above-mentioned power supply voltage V. This energization causes the temperature detection means 26 to reach the temperature To again.
It will be stopped if it detects that it has exceeded the limit. The pattern of this temperature adjustment is shown in FIG. That is, heater 2
If it is detected that the power supply voltage is Vb when the heater 25 is turned off, the temperature adjustment circuit 27 determines that the voltage is high and widens the pulse gap as indicated by symbol B when the heater 25 is energized next time. Conversely, if it detects that the power supply voltage is Vc, the temperature adjustment circuit 27 determines that the voltage is low, and narrows the pulse interval when energizing the heater 25 next time as shown by symbol C ( In the figure, it is fully energized). In this way, the reason why the power supply voltage is measured when the power supply to the heater 25 is cut off is because an unregulated power supply is used as the power supply, and while the heater 25 is being supplied with power, the voltage drop due to the load resistance of the heater and the pulse This is because the voltage fluctuates drastically due to energization, making accurate voltage detection impossible. In the experiment, the heat capacity of the laser unit 20
In contrast to the heater 25 of 26.5 J/deg, a heater 25 with an output of 12 watt was used. At this time, the output voltage of the power supply 28 and the ratio of the on-level time to the off-level time during pulse energization were as shown in the table below.

[Table] Figure 4 shows a flowchart for this temperature adjustment. The chart starts when the laser unit 20 begins to heat up after the power of the laser printer is turned on and the temperature exceeds the set temperature To for the first time. The process will be explained below according to the flow. At the start, the laser unit temperature T is
is exceeded, so the heater 25 is turned off (step 1). After that, gradually the laser unit 2
0 cools and eventually reaches a temperature below To (step 2). Then, the power supply voltage V is measured (step 3), and the power supply voltage is input to the temperature adjustment circuit 27. Based on the above measured voltage V, the microcomputer determines the pulse interval for energizing the heater (step 4), and starts energizing the heater 25 in pulses (step 5). The temperature detection means 26 detects that the temperature T of the unit 20 is
This energization continues until it detects that the voltage has exceeded To. When T>To (step 6), the process returns to step 1 immediately after the start of the flowchart. With the control flow described above, temperature fluctuations in the laser unit can be minimized. The above flow continues until the device is powered down and is reset at either time or upon power up. Note that when a constant voltage power source is used as a power source for the heater, it is not necessary to perform pulse energization as described above. However, using a constant voltage power supply increases the cost of the circuit and increases the size of the power supply, which is not preferable for producing a small, low-cost printer. Furthermore, the amount of heat generated from the constant voltage power source is large, causing a problem of temperature rise of the device. In addition, it wastes a lot of electricity, so it is not suitable for energy saving. C. Effects of the Invention As described above, according to the present invention, the temperature of the laser can be controlled with high precision within a small fluctuation range of ±0.2°C, thereby suppressing changes in the laser wavelength due to temperature changes, which was a problem in the past. For example, in the case of laser beam printers, it has become possible to eliminate uneven image density and line width variations caused by changes in laser temperature. Furthermore, it is possible to use a small and inexpensive semiconductor laser as a light source for a laser beam printer, etc., and it is possible to significantly reduce costs and make the device smaller and lighter. Furthermore, since the power supply does not require a constant voltage power supply, a small and inexpensive power supply can be used, and the space required for parts and the power supply is also small, which has the advantage of making the device smaller and cheaper, as well as reducing power consumption. Not only is it suitable for energy saving, it also prevents the temperature of the device from rising due to unnecessary heat radiation. The above explanation was given using a semiconductor laser device as an example, but
The phenomenon that the laser oscillation wavelength depends on temperature is also observed in other laser devices such as dye lasers and gas lasers. Therefore, the present invention can be effectively applied to such a laser device as well.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of the laser unit, FIG. 2 is a longitudinal sectional view of the laser unit according to the present invention, FIG. 3 is a timing chart for temperature adjustment of the laser unit according to the present invention, and FIG. 4 is a temperature chart according to the present invention. Flowchart showing adjustments. 1 is a laser, 25 is a heater, 26 is a temperature detection means, 27 is a temperature adjustment circuit, 28 is a power supply, and 29 is a voltage detection means.

Claims (1)

[Claims for Utility Model Registration] A laser light source, a heater that heats the laser light source, a power source that supplies power to the heater, a means for detecting the temperature of the laser light source, and a temperature detected by the detecting means. By repeating the operation of energizing the heater from the power supply when the temperature is lower than a predetermined temperature, and stopping the power supply from the power supply to the heater when the temperature detected by the detection means reaches the predetermined temperature or higher, In a laser device comprising a temperature adjustment circuit that adjusts the temperature of a laser light source, during a period in which the heater is energized, a pulse current is applied to the heater from a power source, and the temperature adjustment circuit is detected by the detection means. means for measuring the output voltage of the power source during a period in which the power supply from the power source to the heater is stopped when the temperature at which the heater is turned is equal to or higher than a predetermined temperature; A laser device comprising: means for changing the ratio of on time to off time in pulse energization to the heater according to the voltage measured by the measuring means.