JP3955072B2 - Multi-beam scanning device and multi-beam detection method for multi-beam scanning device - Google Patents

Description

The present invention relates to a multi-beam scanning device and a multi-beam detection method for the multi-beam scanning device.

  An optical scanning device that deflects a light beam whose intensity is modulated by an image signal and scans a surface to be scanned for image formation is widely known in connection with a digital copying machine, various optical printers, and the like. Recently, a multi-beam scanning device that simultaneously scans a plurality of scanning lines at a time has been proposed with the aim of increasing the scanning speed, and among them, the practical application of the two-beam scanning device is actively intended.

  In the two-beam scanning device, the surface to be scanned is simultaneously scanned with two light spots, but the two light spots are not accurately aligned in the sub-scanning direction (even if they are aligned correctly, The positional relationship between the light spots may be shifted due to mechanical vibration or the like, and the two light spots may be intentionally shifted in the main scanning direction), so that the image writing positions on the two scanning lines scanned simultaneously are aligned. In order to achieve this, it is necessary to separately detect two light beams to be scanned simultaneously and to synchronize the start of image writing for each light beam. Various methods for performing two-beam detection for this purpose are known (for example, Patent Documents 1 and 2).

  Incidentally, the two light sources used in the two-beam scanning device are generally semiconductor lasers, and the emitted light beam is in a linearly polarized state. When such a light beam in a linearly polarized state is deflected by a general polygon mirror as an optical deflector, the reflectivity varies according to the variation of the reflection angle by the deflecting reflection surface, and the light spot is caused by the image height of the light spot. In order to correct such shading, a light beam from a semiconductor laser is often passed through a quarter wavelength plate to be in a circularly polarized state for the purpose of correcting such shading.

  In the invention disclosed in Patent Document 1, the shading correction is not taken into consideration, and in consideration of the shading correction, the present invention cannot separately detect the two light beams.

  Patent Document 2 discloses detection of two light beams in consideration of shading correction. However, in order to detect two light beams separately, only one light source is turned on and two light sources are turned on simultaneously. 2 beam detection is complicated.

  Individual detection of light beams is also necessary in a multi-beam scanning apparatus that simultaneously scans the surface to be scanned with three or more light spots.

Japanese Patent Laid-Open No. 6-344592 JP-A-7-72399

An object of the present invention is to realize a novel multi-beam detection method capable of separately detecting a plurality of light beams directed to a scanning region in a multi-beam scanning device in a state where a plurality of light sources are simultaneously turned on.

Another object of the present invention is to realize a novel multi-beam scanning apparatus that implements the novel multi-beam detection method.

Prior to the description of the present invention, a two-beam detection method for a two-beam scanning device will be described.
A two-beam detection method for a two-beam scanning device is “a light beam from two independent light sources is reflected and deflected by a deflecting reflection surface of a common optical deflector, and each deflected deflected light beam is a common scanning imaging optical. In a two-beam scanning device that collects two light spots on the surface to be scanned by the system and simultaneously scans the two scanning lines, the two light beams traveling toward the scanning region are separated from each other and detected. Has characteristics.

That is, the light intensities of the two light beams traveling toward the scanning region are made different from each other and are incident on the common light receiving element in a condensed manner, and the “lighting time of each light beam passing through the light receiving surface of the light receiving element” is different. Set the shape of the light-receiving surface, convert the output from the light-receiving element to a rectangular signal at a plurality of different threshold levels, and use the signal converted to a rectangular signal by one of the threshold levels as a detection signal for one light flux. Then, a predetermined calculation is performed on the plurality of signals converted into rectangular signals in order to obtain detection signals for the other light flux.
“Condensately incident” the two light beams traveling toward the scanning region on the common light receiving element means that each light beam incident on the light receiving surface of the light receiving element is condensed near the light receiving surface.

As a method for making the light intensities of the two light beams toward the scanning region different from each other, a “method of making the light emission intensities of the respective light sources different” may be used. The circularly polarized light beams are rotated in the opposite directions (for shading correction) by the four-wavelength plate, and the two light beams traveling toward the scanning region are returned to “linearly polarized light whose polarization directions are orthogonal to each other” by the second quarter-wave plate. A method may be used in which two light beams having different light intensities are obtained by passing the light beams through a common polarizer. In this case, the azimuth of the polarizer (the azimuth that transmits all the polarized light beams) is “non-perpendicular, non-parallel and non-45 degrees” with respect to the polarization direction of the one light beam that has become the linearly polarized light.

As understood from the above description, the light source in the case of the latter is using linear polarization of the emitted light beam by a semiconductor laser, since in the former case does not use the polarization characteristics of the two beams, The light source in the former invention is not limited to a semiconductor laser, and for example, a light emitting diode can be used as the light source.

  The output from the common light receiving element is converted into a rectangular signal at a plurality of threshold levels. When the rectangular signal is converted into a rectangular signal at two different threshold levels, the signal converted into a rectangular signal at the higher threshold level is represented by T2, When the signal converted into a rectangular signal at the lower threshold level is T1, and the inverted signal of the above signal: T2 (signal: the signal obtained by inverting the high and low of T2) is T2 ', the signal: T2 is one light beam. And the result of calculation: T1 · T2 ′ can be used as the other detection signal. The present invention is effective when the two light spots are separated in the main scanning direction so that the signal converted into a rectangular signal at the lower threshold level becomes a signal separated for each light beam.

  When the output from the light receiving element is converted into a rectangular signal at three threshold levels, the signal converted into a rectangular signal at the higher threshold level is T3, and the signal converted into a rectangular signal at the lower threshold level is T1, When the signal converted to a rectangular signal at an intermediate threshold level is T2, and the inverted signal of the above signal: T2 is T2 ′, the signal: T2 is set as a detection signal of one light beam, and the result of calculation: T1 · T2 ′ + T3 is obtained. The other detection signal can be used. This method is effective whether the two light spots are close to or apart from each other in the main scanning direction.

The two-beam detection method for a two-beam scanning device is “reflecting the light beams from two independent semiconductor lasers on the deflection reflection surface of a common optical deflector after making the circularly polarized light reverse to each other by a common quarter-wave plate. In the two-beam scanning apparatus that scans two scanning lines simultaneously by condensing each deflected light beam deflected and deflected as two light spots on the surface to be scanned by a common scanning imaging optical system. This is a method for separating and detecting two light beams heading toward each other, and has the following characteristics.

  That is, two light beams traveling toward the scanning region are incident on the polarization beam splitter through another common quarter-wave plate to spatially separate each light beam, and each separated light beam is applied to a corresponding light receiving element. Detect by entering.

  Another two-beam scanning device states, “After making the light beams from two independent semiconductor lasers be circularly polarized in the opposite directions by a common quarter-wave plate, they are reflected by the deflecting reflecting surface of the optical deflector and deflected. A two-beam scanning device that condenses each deflected light beam deflected as two light spots on a surface to be scanned by a common scanning imaging optical system, and simultaneously scans two scanning lines. In order to detect the light beam independently, the light receiving element, the light beam condensing means, the light intensity differentiating means, the signal converting means, and the calculating means are provided.

  The “light receiving element” is provided in common for the two light beams so as to receive the two light beams traveling toward the scanning region, and the light receiving surface shape of the light receiving surface is linearly increased in the scanning orthogonal direction. Have The “scanning direction” is a direction in which the deflected light beam crosses the surface along with the deflection of the deflected light beam when considering a surface orthogonal to the principal light beam of the ideal deflected light beam at the position of the light receiving surface of the light receiving element. The direction perpendicular to the scanning direction is the “scanning orthogonal direction”.

The “light beam condensing means” is a means for condensing two light beams on a common light receiving element, and a dedicated optical system (such as a lens or a concave mirror) may be used, or a part of the scanning imaging optical system is also used. You may let them.
“Light intensity differentiating means” is means for differentiating the light intensities of two light beams incident on the light receiving element.
The “signaling means” is means for converting the output of the light receiving element into a rectangular signal at a plurality of different threshold levels, and various comparators can be used.
The “calculation means” is means for performing a predetermined calculation on each signal obtained from the signal converting means, and for example, a microcomputer can be used.

  In the other two-beam scanning device, the “light intensity differentiating means” is a light source control means for controlling the semiconductor lasers so that the emission intensities of the semiconductor lasers are different from each other when the two light beams are directed to the scanning region. Can be configured.

  Alternatively, the above-mentioned “light intensity differentiating means” is provided in common for the two light beams traveling toward the scanning region, and makes the two light beams linearly polarized light orthogonal to each other, and this quarter-wave plate and the light receiving element. And a polarizer arranged in such a state that the transmission intensity of each light beam is different.

  In the above-described two-beam scanning device, “the calculating means has a function of calculating the pitch of the two light spots in the scanning orthogonal direction based on the signal obtained from the signal converting means”.

The two-beam scanning device states that “the light beams from two independent semiconductor lasers are made to be circularly polarized in the opposite directions by a common quarter-wave plate, then reflected and deflected by a deflecting reflecting surface of a common optical deflector, and deflected. Each of the deflected light beams is condensed as two light spots on the surface to be scanned by a common scanning imaging optical system, and the two light beams traveling toward the scanning region are transmitted in a two-beam scanning device that simultaneously scans two scanning lines. , Another common quarter wave plate for spatial separation, a polarization beam splitter for spatial separation of two light fluxes transmitted through the quarter wave plate, and each spatially separated light flux It has two light receiving elements that receive light correspondingly and output an output for a detection signal ”.

  As the “scanning imaging optical system”, any known optical system can be used in connection with a single beam scanning apparatus, including an fθ lens.

The above is the case of two-beam scanning.
The case of “multi-beam scanning” will be described below.
The n optical beams of the multi-beam detection method for a multi-beam scanning device from the "Independent n (≧ 2) pieces of the light source, is deflected by reflection at the deflection reflecting surface of the common optical deflector, the deflected In a multi-beam scanning device that condenses deflected light beams as n light spots on a surface to be scanned by a common scanning imaging optical system, and simultaneously scans n scanning lines, the n light beams traveling toward the scanning region are separated from each other. ”And has the following characteristics.

  That is, the light receiving surfaces of the light receiving elements are configured such that the light intensity of the n light beams traveling toward the scanning region are made different from each other and are incident on the common light receiving element in a concentrated manner, and the time required for each light beam to pass through the light receiving surface of the light receiving element is different A shape is set, and the output from the light receiving element is converted into a rectangular signal at a plurality of different threshold levels, and a signal converted into a rectangular signal by one of the threshold levels is used as a detection signal for one light flux, and is rectangular at each threshold level. Predetermined calculations are performed on the plurality of signal signals to obtain detection signals for other light beams.

  In order to make the light intensities of the n light fluxes toward the scanning region different from each other, the light emission intensities of the n light sources may be made different, or the light fluxes from the respective light sources are combined by a semi-transparent mirror and transmitted for each light flux. You may carry out by changing the number of the mirrors.

  n light spots are separated in the main scanning direction so as to be received one by one by the common light receiving element, and the outputs from the common light receiving elements are converted into rectangular signals at n different threshold levels, When the signal converted into a rectangular signal by the i-th threshold level counted from the higher threshold level is τi (i = 1 to n) and the inverted signal of τi is τi ′, the signal τ1 is the highest light. An intensity light flux detection signal can be used as the detection signal for the i-th light intensity light beam with calculation: τi · τj ′ (i = 2 to n, j = i−1).

  As n independent light sources in multi-beam scanning, when n is 2, a light source similar to the above-described invention can be used. When n is 3 or more, n LEDs, n semiconductor lasers, or a combination of a semiconductor laser and an LED can be used as n light sources, and a semiconductor laser array and an LED are combined. You can also.

  Furthermore, “two independent semiconductor laser light sources, at least one of which is a semiconductor laser array” can be used as the light source of the multi-beam scanning device. As is well known, the semiconductor laser array is a light source having a plurality of semiconductor laser light sources in a monolithic manner, and can emit a light beam independently from each semiconductor laser light source. Such a semiconductor laser array and a normal semiconductor laser having a single light emitting portion are collectively referred to as a “semiconductor laser light source”.

  When two independent semiconductor laser light sources, at least one of which is a semiconductor laser array, are used, the number of light beams radiated from the light source is the smallest when the semiconductor laser light source has a normal single light emitting unit. In this case, the other semiconductor laser light source is a semiconductor laser array having two independent light emitting portions. In this case, the total number of luminous fluxes is 3.

The multi-beam detection method for a multi-beam scanning device according to the present invention is such that “ n (≧ 3) light beams from a plurality of independent semiconductor laser light sources are divided into two groups opposite to each other by a common quarter-wave plate . After making circularly polarized light, it is reflected and deflected by the deflecting / reflecting surface of the common optical deflector, and each deflected light beam is condensed as n light spots on the surface to be scanned by the common scanning imaging optical system. In a multi-beam scanning device that simultaneously scans n scanning lines, the light beam traveling toward the scanning region is detected separately and has the following characteristics.

That is, each light beam traveling toward the scanning region is incident on the polarization beam splitter through another common quarter-wave plate, and is spatially separated as two groups of light beams whose polarization directions are orthogonal to each other. The groups are made incident on the corresponding light receiving elements. In this case, one of the separated luminous flux groups has one or more luminous fluxes, and the other has two or more luminous fluxes.

  The shape of the light receiving surface of the light receiving element that receives two or more light beams is set so that the time required for the light beams incident on the light receiving elements to pass through the light receiving surface is different. The output from the light receiving element that receives two or more light beams is converted into a rectangular signal at a plurality of different threshold levels, and a signal converted into a rectangular signal at one of the threshold levels is used as a detection signal for one light beam, A predetermined calculation is performed on a plurality of signals converted into rectangular signals at the threshold level to obtain detection signals for other light beams.

  That is, each light beam is distinguished depending on which of the two light receiving elements receives the light, and further, when the light receiving element receives two or more light beams, they are distinguished from each other by the method as described above. When the total number of deflected light beams is three and one light receiving element receives only one light beam, the light beam can be detected only by detecting the output of the light receiving element. When each light receiving element receives two or more light beams, each light beam can be distinguished for each light receiving element by the method as described above.

Another multi-beam scanning device states that “at least one is a semiconductor laser array, and three or more light beams from two independent semiconductor laser light sources are reflected and deflected by a deflecting reflection surface of a common optical deflector. A multi-beam scanning device for condensing each deflected light beam as three or more light spots on a surface to be scanned by a common scanning imaging optical system, and simultaneously scanning three or more scanning lines. It has a light beam condensing means, a light intensity differentiating means, a signal converting means, and a computing means.

The “light receiving element” has a light receiving surface shape in which each light beam traveling toward the scanning region is received in common and the width of the light receiving surface in the scanning direction linearly increases in the scanning orthogonal direction.
The “light beam condensing means” condenses three or more light beams on a common light receiving element.
The “light intensity differentiating means” makes the light intensities of the light beams incident on the light receiving elements different from each other.
The “signaling means” converts the output of the light receiving element into a rectangular signal at a plurality of different threshold levels.
The “signaling means” performs a predetermined operation on each signal obtained from the signalizing means.

The multi-beam scanning device according to the present invention is described as follows: “3 or more light beams from a plurality of independent semiconductor laser light sources are converted into two groups of circularly polarized light beams that are opposite to each other by a common quarter wavelength plate, and then a common light deflection is performed. The deflected light beams are reflected and deflected by the deflecting reflecting surface of the detector, and the deflected deflected light beams are condensed as three or more light spots on the surface to be scanned by a common scanning imaging optical system, and three or more scanning lines are simultaneously scanned. The multi-beam scanning device ”includes a second quarter-wave plate, a polarizing beam splitter, and two light receiving elements.

The “second quarter-wave plate” is common to each light flux so as to transmit each light flux toward the scanning region. By passing through the second quarter-wave plate , each light beam is separated into two groups of light beams whose polarization planes are orthogonal to each other.
The “polarizing beam splitter” spatially separates three or more light beams that have passed through the second quarter-wave plate into two light beam groups having orthogonal polarization planes.
The “two light receiving elements” receive the corresponding light beam groups spatially separated and output detection signal outputs. The shape of the light receiving surface of the light receiving element that receives two or more light beams is set so that the time required for the light beam incident on the light receiving elements to pass through the light receiving surface is different.

  The "light intensity differentiating means" makes the light intensities of the light beams emitted from the semiconductor laser light sources emitting two or more light beams different from each other, and the "signaling means" outputs the light receiving element that receives two or more light beams. Can be converted into rectangular signals at a plurality of different threshold levels, and a predetermined calculation can be performed on each signal obtained from the signal conversion means by the "calculation means".

  In the above multi-beam scanning device, both of the two semiconductor laser light sources can be a semiconductor laser array. In this case, the number of scanning lines simultaneously scanned is four or more.

  Further, in these multi-beam scanning devices, the “light intensity differentiating means” controls each semiconductor laser light source so that the light emission intensity of the light emitting portion of each semiconductor laser light source is different from each other when each light flux goes to the scanning region. It can be a light source control means to control.

  In the above-described two-beam scanning device, the calculating means can have a function of calculating the pitch in the scanning orthogonal direction of three or more light spots by a signal obtained from the signal converting means.

As described above, according to the present invention and according to the present invention, a novel multi-beam scanning device and multi-beam detection method can be realized.

According to the multi-beam detection method of the present invention, it is possible to reliably detect two or more light beams in a state where a plurality of light emitting units are turned on.

First, a basic configuration will be described by taking a two-beam scanning device as an example.
From the light source unit denoted by reference numeral 10 in FIG. 1A, two light beams for two-beam scanning are emitted as parallel light beams, respectively. The two emitted light beams pass through the opening of the aperture plate 20 for shaping the light spot and enter the cylinder lens 30. The cylinder lens 30 refers to a sub-scanning corresponding direction (a direction corresponding to a sub-scanning direction parallel to a virtual optical path obtained by linearly developing an optical path from a light source to a surface to be scanned. A direction corresponding to the direction parallel to the main scanning direction is referred to as a main scanning corresponding direction). As a line image that is long in the main scanning corresponding direction in the vicinity of the deflection reflection surface 41 of the polygon mirror 40 that is an optical deflector. Form an image.

  When the polygon mirror 40 rotates at a constant speed in the direction of the arrow, the two light beams reflected by the deflecting and reflecting surface become deflected light beams, and two fθ lenses 32 that are “scanning imaging optical systems” act on the surface to be scanned 50. The light is condensed as a light spot and the surface to be scanned 50 is scanned. Since a photoconductive photoconductor is usually provided at the scanning surface position, the light spot substantially scans the photoconductor.

  The light source unit 10 includes two semiconductor lasers 11 and 12, two collimating lenses 13 and 14 in a casing 18, a half-wave plate 15 that rotates a polarization plane of a light beam from the semiconductor laser 11 by 90 degrees, It has a beam combining prism 16 for combining the light beams from the semiconductor lasers 11 and 12, and a quarter wavelength plate 17 for changing the polarization state of the two combined light beams into a circularly polarized state.

  The light beams emitted from the semiconductor lasers 11 and 12 are converted into parallel light beams by the corresponding collimator lenses 13 and 14 and then enter the beam combining prism 16. The light beam from the semiconductor laser 11 passes through the polarization beam splitter film 162 in the beam combining prism 16 and is emitted from the beam combining prism 16. The light beam from the semiconductor laser 12 is internally reflected by the inclined surface 161 of the beam combining prism 16, reflected by the polarization beam splitter film 162, and emitted from the beam combining prism 16.

In the state of FIG. 1A, both the collimating lenses 13 and 14 are “in the same plane parallel to the main scanning corresponding direction”. At least one of the semiconductor lasers 11 and 12 is deviated from the optical axis of the corresponding collimator lens by a minute distance in the main / sub-scanning corresponding direction. In FIG. 1A, the deviation of the semiconductor laser 12 from the optical axis of the collimating lens 14 in the sub-scanning corresponding direction is “exaggerated”. That is, the straight line connecting the light emitting portions of the semiconductor lasers 11 and 12 forms a minute angle: θ _A with the main scanning corresponding direction, and the two light beams emitted from the beam combining prism 16 correspond to the sub-scanning due to the inclination of the angle: θ _A. Slightly inclined in the direction. With this small angle, the interval P _{S in} the sub-scanning direction between the two light spots condensed on the surface to be scanned 50 is determined.

Further, due to a slight deviation in the main scanning corresponding direction from the optical axis of the corresponding collimating lens of the semiconductor lasers 11 and 12, the light beams emitted from the beam combining prism 16 are very small as shown in the figure in the main scanning direction. corner: make the θ _B. The angle: θ _B determines the interval P _{M in} the main scanning direction between the two light spots condensed on the surface to be scanned 50.

In the state of FIG. 1A, the light source unit 10 is rotated around the optical axis of the collimating lens 13 to connect these spots while keeping the distance between the two light spots on the scanned surface 50 constant. The direction can be rotated, and this can be used to adjust the spacings: P _M , P _S.

  The two light beams emitted from the beam combining prism 16 have linearly polarized light planes orthogonal to each other, and the above-described “shading” occurs. Set the surrounding circular polarization state. In this way, the two light beams that have been combined and subjected to shading correction are emitted from the light source unit 10.

  The two light beams emitted from the light source unit 10 and deflected by the polygon mirror 40 are deflected toward the scanning region, but enter the mirror 61 through the fθ lens 32 and are reflected by the mirror 61 on the way to the scanning region. Then, the light enters the light receiving element 64 through the quarter-wave plate 62 and the polarizer 63. The light receiving element 64 is arranged on the optical path through the mirror 61 at a position equivalent to the scanned surface 50 (the drawing is not drawn as such for the purpose of drawing), and both light beams are on the light receiving surface of the light receiving element 64. Condensed as a light spot. Therefore, the fθ lens 32 constitutes “light beam condensing means” for condensing two light beams on a common light receiving element 64.

  When the two light beams reflected by the mirror 61 are incident on the quarter-wave plate 62, they are “circularly polarized in opposite directions” as shown in FIG. 1B and pass through the quarter-wave plate 62. By this, as shown in the figure, it is converted into “linear polarization states orthogonal to each other”. The two light beams that are in the polarization state orthogonal to each other as described above are transmitted through the polarizer 63.

As shown in FIG. 1B, the orientation of the polarizer 63 (direction in which the linearly polarized light beam is transmitted to the maximum) is inclined by an angle: θ with respect to the polarization direction of the light beam B1 (light beam from the semiconductor laser 11). The ratio of the light beams B1 and B2 that pass through the polarizer 63 is cos ² θ: sin ² θ. Therefore, by appropriately selecting the angle θ, the light intensity of the light beams B1 and B2 is varied on the light receiving surface 64 of the light receiving element 64 as shown in FIG. .

  That is, in the embodiment of FIG. 1, a quarter-wave plate 62 that is provided in common for the two light beams traveling toward the scanning region and converts the two light beams into linearly polarized light that is orthogonal to each other, 64 is different from the polarizer 63 arranged in such a manner that the transmission intensity of each light beam is different from that of the polarizer 63, which makes the light intensity of the two light beams incident on the light receiving element 64 different from each other. Means ".

Thus, before the two deflected light beams reach the scanning region, the light intensities are made different from each other and incident on the common light receiving element 64 in a condensed manner.
As shown in FIG. 1C, the light receiving surface of the light receiving element 64 has a right triangle shape, and one of the two sides sandwiching the right angle is “parallel to the scanning direction (left-right direction in the figure)”. The other is “parallel to the scanning orthogonal direction (vertical direction in the figure)”.
Accordingly, the light receiving element 64 has a shape in which the width of the light receiving surface 64A in the scanning direction “linearly increases in the direction orthogonal to the scanning”, and thus each light beam B1, B2 passes through the light receiving surface 64A (in the scanning direction). F) Time to pass is different.
In FIG. 1C, symbols SP1 and SP2 indicate light spots obtained by collecting the light beams B1 and B2.

  When the light beams B1 and B2 pass through the light receiving surface 64A, a light receiving signal is emitted from the light receiving element 64, and this light receiving signal is converted into a rectangular signal by the signal converting / calculating means 65 and further subjected to necessary calculations. The signal converting / calculating means 65 is a combination of the signal converting means and the calculating means according to the seventh aspect of the invention, and is, for example, a microcomputer. When the signal from the light receiving element 64 is input to the signal converting / calculating means 65, it is digitized and then converted into a rectangular signal using two or three threshold levels.

First, as shown in FIG. 1 (c), the light spot SP1, SP2 forming a light beam B1, B2 are sufficiently separated in the scanning direction (distance in FIG. 1 (a): is sufficiently large _{P M)} I will explain the case.

  As described above, the light intensity of the light spot SP1 of the light beam B1 is made larger than that of the light spot SP2, and the time for crossing the light receiving surface 64A is shorter for the light spot SP1 than for the light spot SP2. The signal obtained from the light receiving element 64 is as shown in FIG.

  Therefore, when this signal is converted into a rectangular signal at the two threshold levels TH1 and TH2, the signal is rectangularized according to the lower threshold level TH1, and the signal is converted into a rectangle according to the higher threshold level TH2. : T2 is obtained (FIG. 2B). Of these signals: T1 and T2, the signal: T2 corresponds only to the light beam B1 having a high light intensity, so that the signal: T2 can be used as the detection signal: Beam1 for the light beam B1 (FIG. 2 (c)). .

  Further, when the inverted signal of the signal T2 is T2 ′, and the product T1 · T2 ′ of the signal T2 ′ and the signal T1 is calculated, a rectangular signal corresponding only to the light beam B2 having a low light intensity is obtained. Therefore, this can be used as a detection signal Beam2 for the light beam B2. The signal: inverted signal T2: T2 'and the operation: T1 · T2' are of course performed in the signalizing / calculating means 65.

  The synchronization of the image writing position with respect to the light beams B1 and B2 may be controlled based on the rise of the detection signal: Beam1 for the light beam B1 and the rise of the detection signal: Beam2 for the light beam B2.

The speed when the deflected light beams B1 and B2 cross the light receiving surface 64A of the light receiving element 64: v is uniquely determined according to the rotational speed of the polygon mirror 40.
Therefore, as shown in FIG. 2C, the durations of the detection signals: Beam1 and Beam2 are set to t ₁ and t ₂ as shown in the figure, and the hypotenuse of the light receiving surface 64 as shown in FIG. 1C. If the angle formed by the base portion is α: α, “v · (t ₂ −t ₁ ) tan α” is the distance between the light spots SP1 and SP2 in the sub-scanning direction (interval in FIG. 1A: P _S ). equal. Therefore, if the signalizing / calculating means 65 has the time counting function of the time: t ₁ and t _{2 and} the function of performing the calculation: v · (t ₂ -t ₁ ) tan α, the two light spots It is possible to measure the pitch P _{S in the} direction orthogonal to the scanning.

As shown in FIG. 3, when the distance between the two light spots SP1 and SP2 in the scanning direction (interval in FIG. 1A: P _M ) becomes small, the detection signal separated for each light beam is obtained by the method described above. It is not possible. In this case, the output of the light receiving element 64 is converted into a rectangular signal at three threshold levels.

  This case is shown in FIG. As shown in FIG. 4 (a), the three threshold levels are TH1, TH2, TH3 in order from the lowest, and the signals converted into rectangular signals by these are rectangularized at T1, T2, T3, respectively, and the intermediate threshold level: TH2. Assuming that the inverted signal of the signal: T2 is T2 ′, the result of these and the calculation: T1 · T2 ′ is as shown in FIG. 4B.

  Among these signals, the signal: T2 corresponds only to the light beam B1 having a high light intensity, and therefore the signal: T2 can be used as the detection signal: Beam1 for the light beam B1 (FIG. 4C).

  Further, as shown in FIG. 4C, the result of the calculation: T1 · T2 ′ + T3 corresponds only to the light beam B2 having a low light intensity, so that this can be used as the detection signal: Beam2 for the light beam B2. . Of course, the necessary calculation is performed in the signalization / calculation means 65.

  In this way, when the light spot SP2 slightly precedes the light spot SP1 (FIG. 4 (4-1)), when the light spots SP1 and SP2 are completely aligned in the scanning orthogonal direction (FIG. 4 ( 4-2)), when the light spot SP1 slightly precedes the light spot SP2 (FIG. 4 (4-3)), and when the light spots SP1 and SP2 are sufficiently separated in the scanning direction (FIG. 4 (FIG. 4)). 4-4)), the light beams B1 and B2 can be reliably separated and detected.

Incidentally, in the FIG. 1 (a), the quarter-wave plate 17 in the case of not performing the shading correction is not required, quarter wave plate 62 is in this case be necessary, only the polarizer 63 Thus, the light intensities of the light beams B1 and B2 can be differentiated, and the detection signal of each light beam can be obtained in the same manner as described above.

Further, in the FIG. 1 (a), the 1/4-wave plate 62 the polarization state of the two beams, after the linear polarization state orthogonal to each other, in succession to the two light receiving elements arranged them in the scanning direction of incidence It is also conceivable to provide polarizers on the light receiving surfaces of the respective light receiving elements so that the polarization directions of these polarizers are orthogonal to each other.

FIG. 5 shows another example . The same parts as those in FIG. 1 are denoted by the same reference numerals as in FIG. The light receiving element 64 has a light receiving surface shape as shown in FIG.

In this embodiment , the light intensity differentiating means is a “light source control means” (not shown), and when two light beams (two light beams B1 and B2 described with reference to FIG. 1) are directed to the scanning region, the semiconductor lasers 11 and 12 are used. The semiconductor lasers are controlled so that the emission intensities of the semiconductor lasers differ from each other.

At this time, if the control is performed so that the emission intensity of the semiconductor laser 11 is larger than the emission intensity of the semiconductor laser 12, the light beams B1 and B2 are respectively transmitted in the same manner as described with reference to FIGS. Corresponding detection signals: Beam 1 and Beam 2 can be obtained.
Also in this case, it is possible to measure the pitch P _S in the scanning orthogonal direction of the two light spots by the calculation: v · (t ₂ −t ₁ ) tan α.

In the form of FIG. 5, the quarter wavelength plate 62 and the polarizer 63 are unnecessary as compared with the form example of FIG. 1, and thus the cost can be reduced.

In the embodiment shown in FIGS. 1 and 5, the light receiving surface of the light receiving element 64 may have the oblique side of the shape shown in FIG. Also good. The light receiving surface may have various shapes such as an isosceles triangle with the apex in the scanning orthogonal direction.

FIG. 6 is a diagram showing another example .

The same parts as those in the embodiment of FIG. 1 are denoted by the same reference numerals as in FIG.

Unlike the embodiment shown in FIG. 1A, the two light beams that have passed through the quarter-wave plate 62 enter the polarization beam splitter 70. As described with reference to FIG. 1B, the two light beams transmitted through the quarter-wave plate 62 are in a linear polarization state in which the polarization states are orthogonal to each other. The light beam B1 is transmitted through the polarization beam splitter 70 and incident on the light receiving element 71 in a focused manner. Therefore, the detection signal of the light beam B1 can be obtained from the output of the light receiving element 71.

  A light beam (referred to as a light beam B2) from the semiconductor laser 12 is spatially separated from the light beam B1 by being reflected by the polarization beam splitter 70, and enters the light receiving element 72 to generate a corresponding detection signal.

FIG. 7 shows an example of the multi-beam scanning device, following FIG. In order to avoid complications, the same reference numerals as in FIG. 1A are used for those which are not likely to be confused.

The light source unit 100 is the same as that described with reference to FIG. 1A, but semiconductor laser arrays 110 and 120 are used as semiconductor laser light sources. The semiconductor laser arrays 110 and 120 are both semiconductor laser light sources having two light emitting portions monolithically. The arrangement directions of the light emitting portions of the semiconductor laser arrays 110 and 120 are parallel to each other. Four parallel light beams (only two are shown in order to avoid confusion) are radiated in which the direction between the light beams to be emitted is different by an angle: θ _B.

  These four light beams are radiated from the light source unit 100 as circularly polarized light by the quarter-wave plate 17 as a countermeasure against shading, and enter the cylinder lens 30 through the opening of the aperture plate 200 for light spot shaping. Then, the light is condensed only in the sub-scanning corresponding direction by the cylinder lens 30 and is formed as a long line image in the main scanning corresponding direction in the vicinity of the deflection reflection surface 41 of the polygon mirror 40 which is a “common optical deflector”. The deflected light beam deflected by the rotation of the polygon mirror 40 is condensed as four light spots on the surface to be scanned 50 by the action of the fθ lens 32 which is a “common scanning imaging optical system”. The surface to be scanned 50 which is the photosensitive surface is scanned.

Based on the positional relationship between the semiconductor laser arrays 110 and 120 and the collimating lenses 13 and 14 corresponding thereto, and the angles: θ _A and θ _{B in} the drawing, the sub-scanning direction of the _{interval: P} M, P _S is determined. Further, P _M and P _S can be adjusted by rotating and adjusting the light source unit 10 around the optical axis of the collimating lens 13.

That is, in FIG. 7, four light beams from the semiconductor laser arrays 110 and 120, which are two “semiconductor laser light sources”, are reflected and deflected by the deflection reflection surface of a common optical deflector, and each deflected light beam is deflected. An example of a multi-beam scanning device is shown in which a common scanning imaging optical system collects four light spots on the surface to be scanned 50 and simultaneously scans four scanning lines.

  This apparatus has a common light receiving element 640 that receives four light beams that pass through the fθ lens 32 and travel toward the scanning region, and a mirror 61 that reflects the four light beams toward the light receiving element 640. All of the four light beams incident on the light receiving surface of the light receiving element 640 are condensed near the light receiving surface as a light spot by the fθ lens 32 which is a “light beam condensing unit”.

  In this embodiment, when the “light source control means” that is the driving means (not shown in FIG. 7) of the semiconductor lasers 110 and 120 constitutes “light intensity differentiation means” and performs multi-beam detection. The light emission intensities of the four light emitting units are made different, and the light intensities of the four light beams incident on the light receiving element 640 are made different from each other.

  FIG. 8D illustrates the relationship between the shape of the light receiving surface 640A of the light receiving element 640 common to the four light beams and the four light spots that sequentially pass through the light receiving surface 640A. In FIG. 8 (d), the distance between the light spots S1 to S4 in the scanning direction (left and right direction in the figure) is drawn smaller than the actual one. The light-receiving surface 640A receives only one light spot at a time.

  When the light beams B1 to B4 forming the respective light spots SP1 to SP4 pass through the light receiving surface 640A as indicated by the arrows in the figure, the light beams have different light intensities, and the light receiving surface 640A is in the scanning direction (left and right direction in the figure). Since the width linearly changes in the scanning orthogonal direction (vertical direction in the figure), an output as shown in FIG. 8A is obtained from the light receiving element 640.

  When this output is “rectangularized” at four different threshold levels: TH1 ′ to TH4 ′ as shown in FIG. 8A, the output is shown in FIG. 8B according to the threshold levels: TH1 ′ to TH4 ′. Rectangular signals τ1 to τ4 as shown are obtained. The rectangular signal generation by the threshold levels TH1 'to TH4' is performed by the signalizing / calculating means 650, which is a microcomputer or the like forming the "rectangular signal generating means".

  The signal conversion / calculation means 650 also functions as “calculation means” and performs the following calculation on the rectangular signals: τ1 to τ4. That is, among the rectangular signals: τi, an inversion signal: τi ′ for i = 1 to 3 is generated, and operations between the rectangular signals: τ2 to τ4: τ2 · τ1 ′, τ3 · τ2 ′, τ4 · τ3 'I do. FIG. 8C shows the calculation result and the rectangular signal τ1.

  The results of calculation: τ 2 · τ 1 ′, τ 3 τ 2 ′, τ 4 τ 3 ′ are separated from each other by a rectangular signal, and are also separated from the rectangular signal τ 1. Since these rectangular signals: τ1, τ2, τ1 ′, τ3, τ2 ′, τ4, τ3 ′ correspond to the light spots SP1 to SP4 of the light beams B1 to B4, respectively, detection signals of the light beams B1 to B4: Beam1 to Beam4 Can be used.

That is, in the embodiment described with reference to FIG. 7 and FIG. 8, the multi-beam scanning device converts the light beams from four independent light sources (light emitting portions of the semiconductor laser array) into a deflecting reflection surface of a common optical deflector. A multi-beam scanning device for condensing and deflecting each deflected light beam as a light beam on a scanned surface by a common scanning imaging optical system and simultaneously scanning four scanning lines The light intensity of the four light beams traveling toward the scanning region is made different from each other so as to be incident on the common light receiving element 640 in a condensed manner, and light is received so that the time for each light beam to pass through the light receiving surface 640A of the light receiving element 640 is different. The shape of the light receiving surface 640A of the element 640 is set, and the output from the light receiving element 640 is converted into a rectangular signal at a plurality of different threshold levels: TH1 ′ to TH4 ′, and one of the threshold levels is selected. The signal τ1 converted into a rectangular signal by τ1 is used as a detection signal for one light beam B1, and a predetermined calculation is performed on a plurality of signals converted into rectangular signals at each threshold level to detect signals for the other light beams B2 to B4. Thus, the four light beams are detected separately from each other.

In the above embodiment , the light intensity of each light source is made different so that the light intensities of the four light fluxes toward the scanning region are made different from each other, and the signal converted into the rectangular signal at the four threshold levels is inverted with respect to τi. Using τi ′, calculation: τi · τj ′ is performed to obtain a light flux detection signal. Further, it is “two independent semiconductor laser arrays” that constitute the light emitting part of the light source part.

The signalizing / calculating means 650 shown in FIG. 7 also has a passing speed: v and each passing time: t ₁ when the light spots S1 to S4 corresponding to each of the four light beams B1 to B4 pass through the light receiving surface 640A. To t ₄ (see FIG. 8C) and the base angle 留 of the light receiving surface 640A:
P _S1 = v · (t ₂ −t ₁ ) · tan α, P _S2 = v · (t ₃ −t ₂ ) · tan α,
P _S3 = v · (t ₄ −t ₃ ) · tan α
And has a function of calculating the pitches P _{S1 to} P _S3 (see FIG. 8C) in the scanning orthogonal direction of the light spots SP1 to SP4.

In the embodiment described with reference to FIGS. 7 and 8, if one of the semiconductor laser light sources 110 and 120 in the light source unit 10 is a “semiconductor laser having a normal single light emitting unit”, three scanning lines with three light beams are used. The multi-beam scanning device scans four or more scanning lines at a time by providing both of the semiconductor laser light sources 110 and 120 with two or more light emitting sections. In any case, in the same manner as described above, each beam can be separated to perform multi-beam detection, and the pitch in the scanning orthogonal direction can also be calculated.

FIG. 9A shows an embodiment of the multi-beam scanning device of the present invention . In order to avoid confusion, the same reference numerals as in FIG. 7 are used for those that are not likely to be confused. Since parts other than the quarter-wave plate 62, the polarizing beam splitter 70, and the light receiving elements 710 and 720 from FIG. 9A are the same as those in the embodiment of FIG. 7, only the characteristic parts will be described in FIG.

  The four light beams transmitted through the quarter wavelength plate 62 are incident on the polarization beam splitter 70.

  The four light beams transmitted through the quarter-wave plate 62 return to the linearly polarized state in which the polarization states are orthogonal to each other. Therefore, the light beams from the semiconductor laser array 110 (referred to as light beams B1 and B2) are transmitted through the polarization beam splitter 70. Then, the light is incident on the light receiving element 710 in a condensed manner. On the other hand, a light beam (referred to as light beams B 3 and B 4) from the semiconductor laser 120 is spatially separated from the light beams B 1 and B 2 by being reflected by the polarization beam splitter 70 and enters the light receiving element 720.

  That is, in the embodiment shown in FIG. 9A, the light beams from the two semiconductor laser light sources 110 and 120, which are semiconductor laser arrays, are “reversely rotated for each semiconductor laser light source by the common quarter wavelength plate 17”. The circularly polarized light is reflected and deflected by the deflecting / reflecting surface of the common optical deflector 40, and each deflected light beam is deflected into four light spots on the surface to be scanned 50 by the common scanning imaging optical system 32. And the four scanning lines are scanned simultaneously.

  Each light beam traveling toward the scanning region passes through another common quarter-wave plate 62 and is spatially separated by the polarization beam splitter 70 according to the semiconductor laser light sources 110 and 120. The spatially separated light flux groups are received by the two light receiving elements 710 and 720, and output for detection signals is generated. As in the embodiment of FIG. 7, a “light source control unit” (not shown) that is a driving unit for the semiconductor lasers 110 and 120 constitutes a “light intensity differentiating unit” and performs four beam emission when performing multi-beam detection. The light emission intensities of the four light beams incident on the light receiving element 640 are made different from each other.

  As shown in FIG. 9B, the light receiving surface shape of the light receiving elements 710 and 720 is a right triangle shape having a base angle of right angle and angle α, and the light receiving surface 710A is a light spot SP1 by the light beams B1 and B2. , SP2 is received, and the light receiving surface 720A receives the light spots SP3, SP4 by the light beams B3, B4.

  Therefore, when the light spots SP1 and SP2 and the light spots SP3 and SP4 are sufficiently separated in the scanning direction and each of the light receiving surfaces 710A and 720A "receives one light spot at a time", the above-described FIG. By performing the same method as described with respect to the outputs of the light receiving elements 710 and 720 (performed by signal / calculation means not shown), the light spots SP1 and SP2 and the light spot SP3 are also obtained. 4 and SP4 are close to each other in the scanning direction, the same method as described with reference to FIG. 4 is performed on the outputs of the light receiving elements 710 and 720 (by signal / calculation means not shown). The four light beams can be detected separately from each other.

  That is, the multi-beam scanning apparatus of the embodiment of FIG. 9 performs the multi-beam detection method.

Further, the light spot S1~S4 corresponding to each of the four light beams B1~B4, respectively receiving surface 710A, passing speed as it passes through 720A: and the transit _time: and t 1 ~t _4, the light receiving surface 710A , 720A base angle: α is used to calculate:
P _S1 = v · (t ₂ −t ₁ ) · tan α,
P _S3 = v · (t ₄ −t ₃ ) · tan α
It is apparent that the scanning orthogonal pitch P _S1 of the light spots SP1 and SP2 and the scanning orthogonal pitch P _S3 of the light spots SP1 and SP2 can be calculated. The pitch P _{S3 in} the scanning orthogonal direction of the light spots SP2 and SP3 is calculated by using the distance D in the scanning orthogonal direction shown in FIG. 9B:
P _S3 = (D + v · t ₃ · tan α) -v · t ₂ · tan α
= D + (t ₃ −t ₂ ) · v · tan α
You can know by doing.

  The means for combining the light beams from the plurality of light sources is not limited to the example described above, and a prism 16A having a reflecting surface 16A1 and semi-mirror surfaces 16A2, 16A3 and 16A4 as shown in FIG. Alternatively, as shown in (b), a prism 16B having a reflecting surface 16B1 and semi-transparent surfaces 16B2, 16B3, and 16B4 may be used. When such a prism is used as “light intensity differentiating means”, it is possible to “different the intensity of each light beam” by simply combining light beams having the same light intensity.

It is a figure for demonstrating the embodiment of a 2 beam scanning system . It is a figure for demonstrating formation of the detection signal in the example of a form of FIG. It is a figure which shows the example of the positional relationship of the two light spots in the example of FIG. 1, and the relationship with the light-receiving surface of a light receiving element. It is a figure for demonstrating the said example of a form . It is a figure for demonstrating another example of a form. It is a figure for demonstrating another example of a form . It is a figure for demonstrating another example of a form . It is a figure for demonstrating formation of the detection signal in the example of a form of FIG. It is a figure for demonstrating one Embodiment of invention. It is a figure which shows two examples of another example which synthesize | combines a several light beam.

Explanation of symbols

10 Light source section 11, 12 Light source (semiconductor laser)
30 Cylinder lens 32 Scanning imaging optical system (fθ lens)
DESCRIPTION OF SYMBOLS 40 Optical deflector 41 Deflection reflective surface 50 Scanned surface 62 1/4 wavelength plate 63 Polarizer 64 Light receiving element 64A Light receiving surface 100 Light source part 110,120 Semiconductor laser light source which is a semiconductor laser array 640 Light receiving element 640A Light receiving surface

Claims (2)

The n (≧ 3) light beams from a plurality of independent semiconductor lasers are converted into two groups of circularly polarized light opposite to each other by a common quarter-wave plate, and then reflected by the deflecting / reflecting surface of a common optical deflector. was deflected by the deflected beam a common scanning image forming optical system is deflected on the surface to be scanned is condensed as n optical spot, in the multibeam scanning equipment to scan n scan lines simultaneously,
A method of detecting n light beams traveling toward a scanning region separately from each other,
The n light beams traveling toward the scanning region are incident on the polarization beam splitter via another common quarter-wave plate, and are spatially separated as two groups of light beams whose polarization directions are orthogonal to each other. The two groups of light beams are incident on the corresponding light receiving elements,
The shape of the light receiving surface of the light receiving element that receives a plurality of light fluxes is different from each other in the time that each of the plurality of light fluxes passes through the light receiving surface, and the n light fluxes are detected by each of the light receiving elements. beam detecting how for multi-beam scanning device. The n (≧ 3) light beams from a plurality of independent semiconductor lasers are converted into two groups of circularly polarized light opposite to each other by a common quarter-wave plate, and then reflected by the deflecting / reflecting surface of a common optical deflector. In a multi-beam scanning apparatus that deflects and deflects each deflected light beam as n light spots on a surface to be scanned by a common scanning imaging optical system, and simultaneously scans n scanning lines.
Another common quarter-wave plate that transmits the n light fluxes toward the scanning region;
A polarizing beam splitter that spatially separates the n light beams transmitted through the other quarter-wave plate as two groups of light beams whose polarization directions are orthogonal to each other ;
Two light receiving elements that receive each spatially separated light beam correspondingly and output an output for a detection signal ;
At least one of the one light receiving elements receives a plurality of light beams, and has a light receiving surface shape in which the width of the light receiving surface in the scanning direction increases linearly in the scanning orthogonal direction .

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