JPS6095987A - Laser unit - Google Patents

Abstract

PURPOSE:To obtain the circuit suitable for a laser beam printer at low cost by fixing a semiconductor laser element on a base metal plate of good thermal conductivity and arranging a heating device on a back surface of the metal plate to emitt the laser beam to the outside through a collimater lens while controlling laser driving current to make the laser beam output constant. CONSTITUTION:A semiconductor laser element 1 is fixed on a metal base 8 of good thermal conductivity such as of Al and a heating device 9 is arranged on a back surface of the base 8 and is covered with a heat insulating material 10, which is fixed to a printed board 11. Also, a collimater lens 5 for obtaining parallel beams is arranged oppositely to the element 1 and is fixed to a holder 6 by use of a nut 7. Further, a thermistor 4 and a pin photodiode 12 are arranged in a periphery of the element 1, thereby observing the laser beam output and keeping the output onstant. In this case, when the laser controlling temperature is T1 deg.C, environmental ultimate temperature is T2 deg.C, usable ultimate temperature is T3 deg.C, wavelength oscillation changing rate is alpha and allowable wavelength value beta, the values are selected so as to satisfy alpha(T2-T1)<=beta and T1<=T2.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser beam printer (hereinafter referred to as LBI) and a laser unit, and more particularly to a temperature control device for a laser unit using a semiconductor laser.

Recently, semiconductor lasers have been used as lasers used in LBP due to demands for smaller devices and lower costs.

However, as shown in Figure 1, the wavelength (λ) of the oscillated laser light of this semiconductor laser varies depending on the operating temperature (T), and the rate of change Δλ/ΔT is approximately 0.2 to 0.6. Furthermore, as shown in FIG. 2, the optical output (P) with respect to the drive current (I) changes depending on the temperature. On the other hand, the sensitivity of a photoreceptor that receives a laser beam and forms an electrostatic latent image changes with respect to the wavelength as shown in FIG. 6, and also depends on its output. Therefore, in order to obtain a constant sensitivity in this photoreceptor, it is necessary to control the laser wavelength and output to be constant.

For this reason, conventionally, as shown in FIG. 4, for example, a method has been adopted in which the semiconductor laser is kept at a constant temperature to avoid fluctuations in its wavelength and optical output. Therefore, the semiconductor laser 1 is
This method uses the Lucie effect, a phenomenon in which heat is generated or absorbed depending on the direction of the current when a weak current flows through the contact surfaces of dissimilar metals, and electrons can be switched between a cooling surface and a heating surface by changing the direction of the current. It is attached to the cooling device 2 (hereinafter referred to as the Lucier element). This Lutier element 2 is attached to the heat sink B. Also, a temperature detector 4 such as a thermistor that detects the temperature of the semiconductor laser 1
is attached to the semiconductor laser 1.

The laser beam emitted from the semiconductor laser 1 is configured to be collimated by a collimator lens 5 fixed to a holder 6 with a nut 7.

As a result, if the temperature of the semiconductor laser is kept constant, the oscillation wavelength will be constant, as can be seen from Figure 1, and if the laser drive current is kept constant, the laser light will inevitably change. The output is also kept constant, and the latent image obtained on the photoreceptor that receives this light is constant, resulting in stable image quality.

However, in this case, the drive circuit for the g-Lucie element becomes complicated, and two power supplies are required in order to obtain cooling and heat generation phenomena by changing the direction of the current flowing. Furthermore, the fourth
As shown in the figure, components are piled up in the direction of the optical axis of the laser, which makes the device complicated, such as the need to correct out-of-focus in the direction of the optical axis due to environmental changes, leading to increased costs.

Another method is to monitor the semiconductor laser light output using a pin photodiode or the like, and control the laser drive current to keep the laser light output constant.
There is also a method called the c (o) no ξ war control) method. However, in this case, although the laser light output is constant, the oscillation wavelength varies, so a constant latent image cannot be obtained on the photoreceptor, and therefore stable image quality cannot be obtained.

An object of the present invention is to provide a simple and inexpensive laser unit that solves the problems including the above-mentioned problems.

The structure and operation of the present invention will be described below with reference to FIG. 5, which shows a cross section of the structure of one embodiment of the laser unit according to the present invention.

The semiconductor laser 1 is attached to a base 8 made of a metal with good thermal conductivity such as aluminum, and on the opposite side, a heater 9 for heating the semiconductor laser 1 is connected to the base 8 via a heat insulating material 10. It is sandwiched and fixed to the substrate 11. Further, the collimator lens 5 for obtaining parallel light beams is fixed to the holder 6 with a nut 7, as in the conventional example.
is attached to the base 8. A pin photodiode 12 that monitors the laser light emitted to the side opposite to the side emitted to the photoconductor is built into the package that houses the semiconductor laser, and the temperature of the semiconductor laser 1 is detected on or near the package. A thermistor 4 is provided.

To describe the operation of the laser unit according to the present invention configured as described above, this unit is used in the APC (auto 7ξ power control) method described above, and the laser light output emitted by the pin photodiode 12 is is monitored, and the laser drive current is controlled so as to keep this laser light output constant, so that the required amount of constant light output is applied to the photoreceptor to receive light.

Next, a method for controlling the oscillation wavelength of the laser unit according to the present invention will be described.

The laser unit according to the present invention includes heating by a heater,
If the temperature of the laser unit is adjusted to a constant temperature by natural heat radiation, and the temperature of the laser unit exceeds the above-mentioned constant temperature adjustment temperature due to the atmosphere, etc., for example, T2,
The operation at this temperature T2 and the intermittent action of the current for temperature adjustment are linked to the main switch of a device such as a laser beam printer to which this laser unit is installed, and the main switch is turned on and off. It is characterized by constant temperature control. This will be explained in more detail below.

As shown in FIG. 1, the temperature-wavelength characteristic of a semiconductor laser is such that the oscillation wavelength increases by 0.2 to 0.3 nm for each degree of temperature. Let this rate of change be α.

On the other hand, the sensitivity of the photoreceptor is currently LB
The wavelength of the semiconductor laser light used in P is 780-80
There is a sudden change near 0 [nm], but under a constant laser light output, for laser light around 790 (nm), even if it changes by +2 (nm), it remains stable by about ζ1 on the photoreceptor. A latent image is obtained, and the image quality is not a problem.The wavelength tolerance value is set to ±β (β is a positive value).

Further, let the temperature control temperature of the laser be TI [C], and let T2 [°C] be the highest temperature reached by the laser unit at the ambient temperature T6 of the laser due to the ambient temperature or conductive heat from the laser unit mounting surface. By the way, T2 varies depending on the conditions inside the machine where the laser unit is installed, but it is 5 to 10 degrees (℃,
) high, about 40°C. Further, the maximum operating temperature T of the laser element 1 is approximately 80°C. Here, if the laser temperature control temperature T is selected to satisfy both the expressions α(T2-TI)≦β (1) and T,≦Ts (2), a stable latent image can be obtained on the photoreceptor. It is possible to obtain stable image quality.

For example, α=0.25 (nm/℃), β=τ(nm
) T2 = 40 (1::l +T3 = 80 [℃], then from formula (1), +2), T1 is 32C℃]≦T
, ≦80C°C).

At this time, the laser temperature T changes, as can be seen from Figure 6, when the laser environmental temperature T: changes, the laser temperature control temperature T,
T until it exceeds T, and when it exceeds this, it increases equally as the laser environment temperature T: increases, and changes to the maximum temperature T2.

In addition, as shown in the timing chart in Figure 7, this laser temperature control method is linked to the main switch of the device to which the laser unit, such as the LBP, is attached, and the laser temperature control starts as soon as the main switch is turned on. Since the temperature is constantly controlled until the printer is turned off, the laser can always emit light in a standby state, and when a print command signal is received, the laser can emit light immediately.

In addition, in the present invention, the heating heater is placed on the opposite side of the base 8 to which the laser 1 is attached, but a heater with less thermal deformation, such as a ceramic heater, is placed between the laser 1 and the base 8. In this case, since the load to be temperature regulated is small (a), the capacity of the heater can be reduced, and the responsiveness is also improved, so the accuracy of temperature control can be improved.

In addition, in the above explanation, the case where the temperature control temperature 1゛ of the laser is less than or equal to the maximum temperature T2, but if T1 is 1゛2 or more, the laser temperature is maintained at a constant temperature regardless of environmental changes.
A more stable image can be obtained.

As described above, the laser unit I+-+ according to the present invention
+Ina! Fi! /7-11m sex 1r)hWko*mshi,
4ζ；→−＾＾q, shiL, j−M operation circuit is also inexpensive,
Furthermore, since the configuration of the laser unit is simple, there is no need to perform focus correction in the optical axis direction. Furthermore, if the temperature control temperature TI of the laser unit is below the maximum temperature T2, and the environmental temperature T; exceeds 'l'1, the heater is turned off, so the overall power consumption is reduced. In addition, since the laser unit is always in a standby state, printing can be performed immediately, which provides extremely significant usability effects.

[Brief explanation of drawings]

Figure 1 is a wavelength/temperature characteristic diagram of a semiconductor laser, Figure 2 is a characteristic diagram of drive current/laser light output versus temperature of the semiconductor laser, and Figure 3 is a sensitivity/wavelength characteristic diagram of a photoreceptor. 4 is a partial cross-sectional view showing the structure of a conventional semiconductor laser unit, FIG. 5 is a cross-sectional view showing the structure of one embodiment of the semiconductor laser unit according to the present invention, and FIG. 6 is a partial cross-sectional view showing the structure of a semiconductor laser unit according to the present invention. FIG. 7, which is a diagram showing the laser temperature with respect to the laser environment temperature of the laser unit, is a timing chart of the temperature control method of the semiconductor laser unit according to the present invention. 1... Semiconductor laser 2... is a Lutier element 6...
Heat sink 4...Thermistor 5...Collimator lens 6...Holder 7...Nut 8...Base 9...Warmer 10...Insulating material 11...Flint plate 12... Pin photodiode Figure 11 Hill 1. mA Figure 2 Delay λ nm Figure 3 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. A semiconductor laser, a warmer for heating the semiconductor laser, a temperature detection means for detecting the temperature of the semiconductor laser, and a detector for monitoring the laser light output of the semiconductor laser. and the temperature of the semiconductor laser detected by the temperature detection means is maintained at a predetermined constant temperature maintenance control by intermittent energization control of the drive current of the warmer, and the temperature of the semiconductor laser detected by the temperature detection means is maintained at a predetermined constant temperature maintenance control), and the temperature of the semiconductor laser detected by the temperature detection means is In a laser unit in which the laser light output of the semiconductor laser is maintained at a predetermined constant value by controlling the driving current of the semiconductor laser, the maximum environmental temperature during use of the laser unit is 2 [° C.]
, the rate of change of the wavelength of the semiconductor laser light with respect to temperature is α
(nm/℃λ The permissible sensitivity fluctuation value of the semiconductor laser light to the laser light wavelength of the photoreceptor is β [nm] (β is a positive value)
, and the maximum operating temperature of the semiconductor laser, T, [°C]
A laser unit characterized in that the laser unit is configured to be controlled to a temperature T [:° C.] that satisfies the following relationships: α(TI-TI)≦β and T,≦T3. 28 The constant temperature maintenance control of the semiconductor laser unit is interlocked with the intermittent operation of the main switch of the target mounting device of the laser unit, and the temperature is always controlled when the main switch is in the "ON" state. Φ The unit described in the section.