JPS6126276A - Laser unit - Google Patents

Abstract

PURPOSE:To obtain a unit of surely low cost and short wait-time by a method wherein a thermistor of positive temperature characteristic is used for controlling the oscillation wavelength of the titled unit, and the temperature for temperature regulation of the semiconductor laser and the Curie temperature of the thermistor are brought into a specific relation. CONSTITUTION:A laser package 1 made of Al or Cu containing a semiconductor laser and filled with dry N2 gas is fixed on a base 2, and this package is surrounded with a holder 7 having a collimator lens 6 that makes laser output beams parallel. The thermistor 3 of positive temperature characteristic which is a heating means is provided on the back of the base 2 and pressed with a printed board 4, which is then secured with machine screws 5. The package 1 is provided with a temperature-detecting means 8 such as a thermocouple or a thermistor arranged along this, and the output of this means is given to the thermistor 3 via control circuit 10 that impresses the first and second reference signals 10a and 10b and drive circuit 11, thus controlling the conduction to the laser. Here, the temperature characteristics of the laser and the thermistor are set at T1<T2 (T1: temperature for temperature regulation of laser, T2: Curie temperature of thermistor).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a laser unit using a semiconductor laser.

[Background of the invention]

Semiconductor lasers have the characteristic that their oscillation wavelength and output change depending on the temperature. On the other hand, when such semiconductor lasers are used in, for example, a laser beam printer, a photoconductor that receives laser light and forms a latent image. Also, the surface potential changes depending on the oscillation wavelength and output of the laser beam, which affects image quality. Fluctuations in wavelength and output are also undesirable in other devices that use semiconductor lasers (information reading devices, communication devices, etc.), so in laser units that use semiconductor lasers, it is necessary to control the laser output and wavelength. There is a need.

One of these methods is the method disclosed in Japanese Patent Application Laid-open No. 81695/1983. In this method, the laser is cooled using a thermoelectric cooling element to control the oscillation wavelength, and on the other hand, the laser is emitted to the outside using a photodetecting element built into the laser arm or cage to control the output. Monitor the laser beam emitted from the opposite side of the laser beam,
The laser output and wavelength are stabilized using a method called APC, which controls the laser drive voltage so that the output of the monitor is constant.

This method uses a thermoelectric cooling element, but the thermoelectric cooling element has a complicated structure, and various measures are required to prevent dew condensation from forming on the semiconductor laser/9 cage during cooling.

As described above, a thermoelectric cooling element has conventionally been used to control the wavelength of the laser unit, but in order to eliminate this drawback, the present invention controls the oscillation wavelength by heating the laser unit.

When this laser unit is used in a laser beam printer, etc., as mentioned above, the photoreceptor that receives the laser beam and forms a latent image has a characteristic that the surface potential changes depending on the oscillation wavelength of the laser beam. It is necessary to suppress the oscillation wavelength of the laser to within a few nanometers. Here, there is generally a rate of change of 0 between the laser oscillation wavelength and the temperature.
．． Since the relationship is 2 to 0.3 nm/'C, it is necessary to control the temperature to about 10C or less during laser temperature fluctuations.

On the other hand, considering the atmospheric temperature within the laser beam blink in which this laser unit is used, it may reach a maximum of about 45°C. Therefore, if this laser unit is controlled at around 35°C, the temperature will be controlled at 35°C during most of the use, and until the ambient temperature exceeds this and reaches the maximum temperature of 45°C, the laser unit temperature will be kept at 35°C. The control is turned off, and the temperature fluctuation of the laser unit and the laser unit increases with the ambient temperature from 35℃ to 4℃.
It can be suppressed at 5°C or 10°C.

In addition, in order to keep the laser output constant, the laser beam is monitored by a bin photodiode installed inside the laser cage, and the current value that drives the laser is controlled so that the output is constant. The output of can be kept constant. Such an output control means is disclosed in the above-mentioned Japanese Patent Application Laid-open No. 50-8.
Those described in Japanese Patent No. 1695 can be used.

Although good image quality can be obtained by controlling the temperature and output in this way, such a laser unit also has the following problems.

For example, the shorter the wait time, the time it takes for the semiconductor laser to reach a predetermined temperature and become ready for output after the main power is turned on, the better. In order to reduce this wait time to 1 minute or less at the lowest environmental temperature, the capacity of the heater must be approximately 20 watts or more. If this capacity is increased, the rate of increase in temperature of the laser unit will increase, but even after reaching the temperature control temperature, the temperature of the laser unit will not exceed the predetermined temperature control temperature. Wait time actually becomes longer due to natural cooling. In addition, even with a capacity of about 20 watts, if the temperature detection thermistor is defective or the temperature control circuit is defective, temperature control may not be possible, and if the heater is energized and then disconnected, the unit will
Problems such as fires may occur when the temperature rises to over 30°F (°C) and components become deformed. Therefore, it is necessary to install a large temperature heater or to provide a mechanism that automatically stops the power supply to the heater when the temperature exceeds a certain level, but this is not reliable due to poor contact with the mounting surface. It is difficult to explain, and the configuration becomes complicated and the cost increases.

[Purpose of the invention]

The purpose of the present invention is to use a heating method to control the oscillation wavelength of a laser unit, and to ensure safety, which is a problem with heating type laser units,
Another object of the present invention is to provide a laser unit that is inexpensive and has a short curing time.

[Summary of the invention]

As described above, conventionally, the oscillation wavelength of a laser unit was controlled by cooling the unit, but the present invention controls the oscillation wavelength by heating the unit. However, when heating the laser unit with a normal nichrome heater, etc., there will be a large overshoot when the temperature is changed from the temperature control after heating starts, and therefore the wait time will be long and the speed at the time of temperature control will be large. , 76 is large, and therefore the wavelength fluctuation is large (4) - To prevent such a disadvantage, the present invention uses a positive temperature thermistor as the heating means.

That is, the laser unit according to the present invention includes a semiconductor laser, a means for heating the semiconductor laser, and a means for controlling the temperature of the semiconductor laser by detecting the temperature of the semiconductor laser, and heats the semiconductor laser. As a means, a positive temperature characteristic thermistor is provided, and when the temperature control temperature of the semiconductor laser is TI and the Curie temperature of the positive temperature characteristic thermistor is T2, 'rt (T!) is obtained. It is characterized by:

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a laser unit according to the present invention. In the figure, 1 is a dry-chip semiconductor laser.

Lasano sealed with raw gas! This laser cage 1 is attached to a base 2 made of a material with good thermal conductivity, such as aluminum or copper, by adhesive or screws. On the opposite surface of the base 2, a positive temperature thermistor 3 is fixed with a thermally conductive adhesive or the like as a means for heating the semiconductor laser.

The terminals of the positive temperature thermistor 3 and the laser are soldered to a printed board 4, and the cylinder board 4 is fixed to the base 2 with screws 5 through spacers 9. On the other hand, the collimator lens 6 that collimates the emitted light of the laser is adjusted in the optical axis direction and the direction perpendicular to the optical axis, and then fixed to the holder 7 with adhesive or screws. It is fixed to the base 2 with screws.

In addition, in order to detect the temperature of the semiconductor laser and control the temperature of the semiconductor laser, a temperature sensor such as a thermocouple or thermistor is installed near the top surface of the laser beam or package 1 or the side surface of the laser package 1 to detect the temperature of the laser. Means 8 is fixed by adhesive or a leaf spring.

The temperature detection means 8 is connected to the positive temperature thermistor 3 via a control circuit 10 and a drive circuit 11, and a first reference signal 1 corresponding to 35° C., for example, is supplied to the control circuit 10.
0a and a second reference signal 10b corresponding to, for example, 33 to 34°C. The detection means 8 activates the drive circuit 11 when the detected temperature exceeds the Curie temperature of the positive temperature thermistor 3.
deenergizes and stops energizing the positive temperature thermistor 3,
When the detected temperature reaches a temperature slightly lower than the temperature control temperature, the drive circuit 11 is energized to start energizing the positive temperature thermistor 3. This temperature control state will be explained later with reference to FIG.

A bin photodiode that receives laser light emitted from the opposite side that does not reach the photoreceptor is installed in the laser package, and controls the output of the laser.

Next, the above positive temperature characteristic thermistor 3 will be described.

The positive temperature characteristic thermistor is made of an oxide semiconductor whose main component is barium titanate.
The Curie temperature, that is, the temperature at which the electrical resistance suddenly changes, can be arbitrarily set in the range of .degree. C. to +330.degree. For example, as shown in FIG. 2, a positive temperature characteristic thermistor has a resistance value of about 1.00 at room temperature, but changes to 10 to 10'Ω at the Curie temperature T3. Therefore, when a constant voltage is applied, a large current flows and generates heat because the resistance value is low at low temperatures, but when the temperature reaches the Curie temperature T, the resistance value suddenly increases, making it difficult for the current to flow and generating heat. decreases. Therefore, the positive temperature characteristic thermistor is able to self-regulate its temperature at a substantially constant temperature T8 without the need for a temperature regulating circuit, even though the temperature is in an equilibrium state near the Curie temperature T2.

As mentioned above, the temperature of the laser unit is controlled by detecting the temperature of the semiconductor laser using a thermistor installed on the laser plane, on the top surface of the cage 1, or in the vicinity. T1, about 35
The positive temperature characteristic thermistor is turned on and off at ℃ to perform heating and natural cooling to control the temperature.For this reason, the temperature T of the positive temperature characteristic thermistor is set higher than the temperature control temperature Tl. For example, the operation of the laser unit of the present invention when using a positive temperature characteristic thermistor as shown in FIG. 2 will be explained with reference to FIG. First, the initial startup state of temperature control will be described. The normal operating condition of the laser unit is about 10 DEG C. to 30 DEG C., and the resistance value of the positive temperature characteristic thermistor is about 200 at this time. If the main power is turned on and 24V is applied to the positive temperature coefficient thermistor, the positive temperature coefficient thermistor generates heat of 28.8 watts, and the semiconductor laser is heated. At this time 28
．． Since the semiconductor laser has a large capacity of 8 volts, the temperature of the semiconductor laser increases rapidly. However, as the temperature control temperature T1 approaches approximately 35°C, the temperature approaches the Curie temperature Tz of the PTC thermistor, so the resistance value of the PTC thermistor increases, and it becomes difficult for current to flow.The capacitance of the PTC thermistor naturally decreases. As the size of the semiconductor laser decreases, the rate of temperature rise slows down. Therefore, the temperature control temperature T1 can be reached smoothly, and a start-up can be achieved with less oversheeting and a short start-up time.

Next, the temperature control state at the controlled temperature T1 will be described. Temperature is detected by a thermistor near the semiconductor laser, and when the temperature of the semiconductor laser reaches 35°C, the positive temperature characteristic thermistor stops energizing and when the temperature T1' is slightly lower than 35°C (for example, 1 to 2°C lower than 35°C). Turn on electricity. In other words, in a temperature control method that uses heating and natural cooling by turning the heater energized on and off, it is better to set the necessary minimum heater capacity for heating, for example, about 5 to 15 watts, to reduce the temperature during temperature control. However, the resistance value of the positive temperature coefficient thermistor of the present invention is about 400 at 35°C, so it works as a small-capacity heater of 14.4 watts, so the temperature , temperature control can be performed with less effort. (For example, in a laser beam printer, if the temperature ripple is large, density unevenness will become noticeable on the image height.) As mentioned above, at startup, 20 to 3
It is possible to have a high heater capacity of 0 watts and a high temperature rise rate, and a low heater capacity of about 5 to 15 watts and a low temperature rise rate at the temperature control temperature T1, so the start-up time is shortened. , and smoothly adjust the temperature T
1, and has good temperature control accuracy with little temperature linnor.
You can get a laser unit.

Furthermore, the Curie temperature T2 of a positive temperature characteristic thermistor with such temperature control temperature characteristics is higher than the temperature control temperature T1;
Since the temperature is approximately 100℃, if the thermistor attached to the semiconductor laser that detects the temperature control circuit is disconnected or damaged, or the temperature control circuit is damaged, the positive temperature characteristic thermistor will Even in the rare worst case where the laser unit is energized and then left unenergized, the temperature of this laser unit will not exceed the Curie temperature T2, and therefore will not exceed the thermal deformation temperature of the parts that make up the laser unit, so any damage must be repaired. If so, the laser unit can be reused. Further, since T2 is about 100° C., temperature hinnies and a protection circuit for detecting runaway temperature are not required. An example of a laser beam printer to which the laser unit according to the present invention can be applied is schematically shown in FIG. In Figure 4,
2o is an electrophotographic photoreceptor, 21 is a charger, 22 is a developer,
23 is a transfer paper, and 24 is a transfer charger. Recorded signal 2
5 is sent to the drive circuit 26, which causes the semiconductor laser 2
Drive 7.

The semiconductor laser 27 generates a laser beam modulated in accordance with the recorded signal, and the laser beam is rotated by the rotating polygon mirror 2.
8 to scan the electrophotographic photoreceptor 20. As a result, an electrostatic latent image is formed on the photoconductor 2o, this latent image is developed by the developing device 22, and the obtained toner image is transferred to the transfer paper 23 and fixed by the fixing device (not shown). Ru.

In the above embodiment, the positive temperature coefficient thermistor is mounted on the opposite side of the base from the semiconductor laser, but if it is mounted near the semiconductor laser, the capacitance or size can be further reduced. In addition, if the laser unit is covered with a heat insulating material such as rubber or plastic to insulate the positive temperature coefficient thermistor from the outside environment, fluctuations in the temperature characteristics of the positive temperature coefficient thermistor will be reduced, and temperature control accuracy will be further improved. Furthermore, the capacity of the positive temperature characteristic thermistor can be reduced.

〔Effect of the invention〕

As described above, the present invention provides a heater for a laser unit that has a temperature control temperature T of a semiconductor laser and a higher Curie temperature T.
By using a positive temperature characteristic thermistor with 2,
Since the wait time can be shortened and temperature control accuracy can be improved, when applied to a laser beam printer, a laser beam printer with high performance and good image quality can be obtained. In addition, since safety can be improved, there is no need for temperature fuses or countermeasures when temperature control is not possible, and the device can be made smaller, the configuration can be simplified, and the cost can be reduced. The present invention is not limited to laser beam printers, but can also be applied to laser units for communication devices such as information reading devices and optical communication devices. In addition, at that time, the temperature control temperature is also determined as appropriate depending on the equipment used.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an embodiment of a laser unit according to the present invention, FIG. 2 is a diagram showing an example of the characteristics of a positive temperature characteristic thermistor used in the laser unit of the present invention, and FIG. 3 is a cross-sectional view showing an example of a laser unit according to the present invention. FIG. 4 is a diagram illustrating the operation of the unit, and is a diagram schematically showing a laser beam series using the laser unit of the present invention. 1... Laser package 2... Base 3... Positive temperature characteristic thermistor 4... Printed circuit board 5... Screw 6... Collimator lens 7... Holder 8... Temperature detection means 9 ... Spacer 10 ... Control circuit 11 ... Drive circuit
20... Electrophotographic photoreceptor 21... Charger
22...Developer 23...Transfer paper 24
...Transfer charger 25...Recorded signal 26...
・Drive circuit 27...Semiconductor laser 28...Rotating polygon mirror Fig.

Claims (1)

[Claims] A semiconductor laser, a means for heating the semiconductor laser, and a means for detecting the temperature of the semiconductor laser to control the temperature of the semiconductor laser. A laser unit characterized in that a characteristic thermistor is provided, and the positive temperature characteristic thermistor satisfies T_1<T_2 when the temperature control temperature of the semiconductor laser is T_1 and the Curie temperature of the positive temperature characteristic thermistor is T_2.