1. Field of Invention
The invention relates to a multi-beam emitting apparatus that is structured so that a semiconductor laser device and a support plate are surely electrically connected each other while improving their heat radiation, by press-fitting the semiconductor laser device into the support plate.
2. Description of Related Art
There is a light beam scanner that is used in a laser printer. In the light beam scanner, a light beam modulated based on an image signal is deflected by a polygon mirror so that a photosensitive body is moved in a sub-scanning direction such that the surface of the photosensitive body is scanned with the light beam as the surface of the photosensitive body is scanned with the light beam in a main scanning direction. By doing so, the surface of the photosensitive body is exposed and thus a latent image is formed thereon.
Recently, in the light beam scanner of this type, a multi-beam scanner has been proposed which simultaneously scans a plurality of scan lines with a plurality of light beams. This multi-beam scanner has a plurality of laser emitting portions, so that the multi-beam scanner can simultaneously scan the plurality of scan lines in the main scanning direction with the plurality of laser beams. Therefore, the surface of the photosensitive body can be exposed in a short time as compared with a case where the surface of the photosensitive body is scanned with one laser beam. Especially, if a laser diode, having a plurality of laser emitting portions, and a photodiode as a photoreceptor of the laser beam emitted from the laser emitting portions are provided in a same case of a semiconductor laser device, the structure of the laser-beam scanner can be simplified. Further, the pitch of two laser beams to be emitted from the laser emitting portions is maintained constant. Because the photodiode is provided inside the semiconductor laser device, no special structure for receiving light is needed in the laser-beam scanner. Therefore, the light emission from the laser emitting portions can be surely monitored by one photoreceptor. The laser-beam scanner having such a semiconductor laser device can be simplified in its structure and can be downsized.
In a conventional semiconductor laser device provided with a laser diode having one laser emitting portion (hereinafter referred to as a single LD), three connecting pins are provided. Two are provided to a case as a leg and are each connected to the laser diode and a photodiode. The other is also provided to the case as a leg and is connected to the laser diode and the photodiode as a common lead. Therefore, for example, a semiconductor laser device provided with a laser diode having two laser emitting portions (hereinafter referred to as a twin-LDs) needs four connecting pins to have the same structure as the semiconductor laser device having the single LD. Generally, soldering is an effective method to wire a fourth connecting pin for reliable connection with good conductivity. However, the laser diode cannot be soldered using an automatic soldering system because the laser diode is sensitive to heat and has a light emitting hole therein. Therefore, an expert has to manually solder the laser diode to respective portions using a loupe. In addition, the laser diode is sensitive to static electricity. Accordingly, stringent anti-static measures are required even when manually soldering, so that the operation becomes complicated. For these reasons, the production efficiency is greatly decreased even with an increase of only one soldering operation.
Further, for the semiconductor laser device with four connecting pins, a conveyance device, a testing device and the like used for handling or testing the semiconductor laser device having three connecting pins cannot be used. Therefore, devices need to be newly installed or modified to adapt for the specification of the semiconductor laser device with four connecting pins, and thus time is wasted and costs are increased.
Generally, the connecting pins are averagely arranged on the same circumference at positions where the circumference is divided into four or eight. For example, when the semiconductor laser device has three connecting pins, the pins are arranged to make an isosceles triangle. Accordingly, there is no chance that the semiconductor laser device is accidentally inserted in an incorrect direction. However, when the semiconductor laser device has four connecting pins, the pins are arranged to make a square. Therefore, it becomes easy to insert the semiconductor laser device in an incorrect direction. To prevent such a mistake, extra man-hours are needed to make the arrangement of the connecting pins irregular.
When the semiconductor laser device has the twin-LDs, there are two light emitting points, so that the amount of heat generated by the laser diodes is doubled. Accordingly, when the heat dissipating condition is the same as the semiconductor laser device having the single LD, the temperature inside of the case of the semiconductor laser device increases. As a result, the efficiency of the laser diode decreases and unevenness of exposure develops on the surface of the photosensitive body because power of the laser beams varies even though the drive current of the laser diode is constant.
The invention provides a multi-beam emitting apparatus that has high production efficiency, is easy to handle or test, and can perform stable exposure.
In order to achieve the above and other objects, the multi-beam emitting apparatus includes a plurality of laser emitting portions, a semiconductor laser device including a metal case covering the laser emitting portions therein, a support plate supporting the metal case and a drive circuit driving the laser emitting portions. One terminal of each laser emitting portion is electrically connected to the metal case inside the metal case, another terminal of each laser emitting portion is insulated from the metal case and is conducted to outside the metal case by respective connecting pins. The metal case is electrically connected to the support plate by press-fitting into the support plate, and the drive circuit is electrically connected to the support plate.
In the multi-beam emitting apparatus according to the invention, there is provided a plurality of laser emitting portions, a semiconductor laser device including a metal case covering the laser emitting portions therein, a support plate supporting the metal case, and a drive circuit driving the laser emitting portions. One terminal of each laser emitting portion is electrically connected to the metal case within the metal case. Accordingly, the number of connecting pins can be reduced as compared with a case where all electrical connections are provided using the connecting pins. Further, the metal case is electrically connected to the support plate by press-fitting into the support plate, so that high electrical conductivity can be maintained and the number of connecting pins can be reduced as compared with a case where all electrical connections are established by the connecting pins. Further, the metal case is electrically connected to the support plate by press-fitting. Therefore, excellent heat conductivity can be maintained, a reliable electrical connection can be maintained for a while without soldering, and heat generated by the laser emitting portions can be effectively dissipated.
According to one aspect of the invention, the semiconductor laser device includes a photoreceptor and the photoreceptor is electrically connected to the metal case in the inside of the metal case.
In the multi-beam emitting apparatus according to the structure, the semiconductor laser device includes a photoreceptor that is electrically connected to the metal case within the metal case. Therefore, the light amount of the laser beam can be detected with a compact structure.
According to another aspect of the invention, the connecting pins comprise four connecting pins including a connecting pin conducting electricity with the metal case. One of the connecting pins is cut off before the semiconductor laser device is press-fit into the support plate or before the connecting pins are connected to the drive circuit and then the multi-beam emitting apparatus is assembled.
In the multi-beam emitting apparatus according to the structure, four connecting pins are provided, including the connecting pin conducting to the metal case. At the time of inspection, the connecting pin conducting to the metal case is connected to the ground potential. Accordingly, the cathode of the semiconductor laser device can be easily maintained at the ground potential. Before the semiconductor laser device is press-fit into the support plate or the connecting pins are connected to the drive circuit, the connecting pin that conducts to the metal case is cut off. Therefore, the semiconductor laser device can be of the same structure, such as having three connecting pins, as the conventional semiconductor laser device having one laser emitting portion. Accordingly, the semiconductor laser device can be manufactured using a part, or all, of the conventional manufacturing equipment, such as a conveyance apparatus and a testing apparatus. Particularly, the mechanical parts of conventional manufacturing equipment have the advantage of being useable for manufacturing this structure of the semiconductor laser device.
According to another aspect of the invention, the support plate is electrically connected to a ground potential of the drive circuit.
In the multi-beam emitting apparatus according to the invention, the support plate is connected to the ground potential of the drive circuit. Therefore, when the metal frame of the multi-beam emitting apparatus is the ground potential, no special structure for conduction is needed.
According to another aspect of the invention, at least two leglike contact portions protrude through the support plate and the support plate is electrically connected to the drive circuit.
In the multi-beam emitting apparatus according to the invention, at least two leglike contact portions protrude through the support plate and the support plate is electrically connected to the drive circuit. Therefore, the occurrence of surge current can be prevented. Consequently, a malfunction of the laser drive circuit, laser emitting failure, and static damage of the laser diode can be prevented so that the laser diode can stably emit a laser beam.
According to another aspect of the invention, the support plate is provided with an engagement hole protruding from the contact portion, the drive circuit is provided with a perforation and a land covered with metal provided around the perforation, and the contact portion and the land are contact pressed to each other and are electrically connected by fixing using a screw that perforates the engagement hole of the contact portion and the perforation of the land.
In the multi-beam emitting apparatus according to the invention, the support plate and the drive circuit are fixed by a screw penetrating into an engagement hole formed in the contact portion of the support plate and the penetration hole formed in the drive circuit and the contact portion is electrically connected to a land that is a conductive portion covered with a metal provided around the penetration hole. Therefore, the drive circuit and the support plate can be easily separated from each other and a position of the drive circuit and the support plate can be relatively adjusted. Consequently, the support plate and the drive circuit can be surely electrically connected to each other and assembly, adjustment, and repair can be easily performed.
According to another aspect of the invention, the support plate is formed of a metal that is softer than the metal used for the metal case and has a penetration hole having an inside diameter 5 to 60 xcexcm that is smaller than an outside diameter of the metal case. The support plate and an outer wall of the metal case intimately contact an inner wall of the penetration hole by press-fitting the metal case into the penetration hole so that the semiconductor laser device are electrically connected.
In the multi-beam emitting apparatus according to the invention, the support plate has the penetration hole that has an inside diameter 5-60 xcexcm smaller than an outer diameter of the metal case and is formed of a metal that is softer then the metal case. Therefore, the metal case can be press-fit into the support plate without undue force and the metal case is intimately contacted to the support plate. Consequently, the electrical connection between the support plate and the metal case can be maintained for a while with stability, heat can be radiated from the support plate and the metal case with excellent heat conductivity, and the semiconductor laser device can be prevented from excessively increasing in temperature.